JP5082627B2 - Image forming apparatus and program - Google Patents

Description

  The present invention relates to an image forming apparatus, a control apparatus, and a program.

In an image forming apparatus using an electrophotographic system such as a copying machine or a printer, an electrostatic latent image formed on an image holding member such as a photosensitive drum is converted into a developing device holding a developer composed of toner and a carrier, for example. Developing. Then, for example, by maintaining the mixing ratio (toner concentration) of the developer toner and the carrier in the developing device within a predetermined range, control is performed so that a stable image density is always obtained.
As a conventional technique for suppressing fluctuations in image density, for example, in Patent Document 1, a toner image of a pattern image having a predetermined area ratio is formed on the surface of an intermediate transfer member, and the toner adhesion amount of the toner image is detected. A technique for appropriately controlling the toner density of the developer based on the detection result is described.

JP 2006-220846 A (page 10-11)

  SUMMARY OF THE INVENTION An object of the present invention is to provide a technique that is not easily affected by temperature and humidity inside and outside the apparatus when the toner density in the developing apparatus is controlled in accordance with the toner adhesion amount on the image carrier.

According to a first aspect of the present invention, there is provided developing means for developing an electrostatic latent image formed on an image carrier with a developer containing a carrier and toner, and a toner image developed on the image carrier by the developing means. Or density detecting means for detecting the density of the toner image comprising a first pattern composed of predetermined isolated lines or dots in the toner image transferred from the image carrier onto the transfer medium; A toner amount adjusting unit that adjusts the toner amount supplied to the developing unit based on the density of the toner image having the first pattern detected by the density detecting unit , and developed on the image carrier. For the density detection means relating to the toner image comprising the second pattern having a higher image area ratio than the first pattern in the toner image or the toner image transferred onto the transfer medium. Based on the detected the density, a is the image forming apparatus characterized by comprising a control means for controlling the developing contrast potential.
Here, “isolated line” and “isolated dot” are lines and dots that constitute a pixel, and are formed in an independent state that does not intersect with other lines or dots.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the image forming apparatus further includes a latent image forming unit that forms an electrostatic latent image on the image holding member, and the control unit includes the latent image forming unit. One or both of the latent image forming conditions set by the developing unit and the developing conditions set by the developing unit are controlled.
According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the toner amount adjusting means is the first pattern configured by the isolated lines whose line width is set to 20 μm or more and 130 μm or less. The toner amount is adjusted based on the density of the toner image.
According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect, the toner amount adjusting means includes the first pattern including the isolated lines whose mutual interval is set to 170 μm or more. The toner amount is adjusted based on the density of the toner image.

According to a fifth aspect of the present invention, in the image forming apparatus according to the first aspect, the toner amount adjusting means is the first pattern including the isolated dots having a dot diameter set to 30 μm or more and 200 μm or less. The toner amount is adjusted based on the density of the toner image.
According to a sixth aspect of the present invention, in the image forming apparatus according to the fifth aspect, the toner amount adjusting means includes the first pattern configured by the isolated dots whose mutual interval is set to 160 μm or more. The toner amount is adjusted based on the density of the toner image.
According to a seventh aspect of the present invention, in the image forming apparatus according to the first aspect, a toner supply unit that supplies toner to the developing unit, and the density detection unit after the toner amount adjustment unit adjusts the toner amount And a determination unit that determines that the remaining amount of toner in the toner supply unit is low when the density detected in step 1 is equal to or less than a predetermined value.
According to an eighth aspect of the present invention, in the image forming apparatus according to the first aspect, the development contrast potential is controlled based on the density of the toner image composed of the first pattern detected by the density detection unit. It is further characterized by further comprising a control means.
According to a ninth aspect of the present invention, in the image forming apparatus according to the eighth aspect, the control unit is configured such that the density of the toner image including the first pattern detected by the density detection unit is a first level. The developing contrast potential is set to be large when the density is smaller than a predetermined value, and the developing contrast potential is set to be small when the density is larger than a second predetermined value.

According to a tenth aspect of the present invention, there is provided a latent image forming unit that forms an electrostatic latent image on an image carrier by charging and exposure, and an electrostatic latent image formed on the image carrier by the latent image forming unit. A developing unit that develops with a developer including a carrier and a toner; a toner image developed on the image holding member by the developing unit or a predetermined toner image transferred from the image holding member onto a transfer medium; Density detecting means for detecting the density of the toner image consisting of a first pattern composed of isolated lines or dots, and the density of the toner image consisting of the first pattern detected by the density detecting means. Based on the toner amount adjusting means for adjusting the toner amount supplied to the developing means, and the toner image developed on the image carrier or the front of the toner image transferred on the transfer medium. A charging potential and exposure set by the latent image forming unit based on the density detected by the density detecting unit with respect to the toner image having the second pattern having a higher image area ratio than the first pattern. An image forming apparatus comprising: a control unit that controls any one of a light amount or a developing potential set by the developing unit or a combination thereof.

According to an eleventh aspect of the present invention, in the image forming apparatus according to the tenth aspect, the toner amount adjusting means is based on the first pattern constituted by the isolated lines whose line width is set to 20 μm or more and 130 μm or less. The toner amount is adjusted based on the density of the toner image .
According to a twelfth aspect of the present invention, in the image forming apparatus according to the eleventh aspect, the toner amount adjusting unit includes the first pattern including the isolated lines whose mutual interval is set to 170 μm or more. The toner amount is adjusted based on the density of the toner image.

According to a thirteenth aspect of the present invention, in the image forming apparatus according to the tenth aspect, the toner amount adjusting unit is configured to use the first pattern including the isolated dots having a dot diameter set to 30 μm to 200 μm. The toner amount is adjusted based on the density of the toner image.
According to a fourteenth aspect of the present invention, in the image forming apparatus according to the thirteenth aspect, the toner amount adjusting unit includes the first pattern configured by the isolated dots whose mutual interval is set to 160 μm or more. The toner amount is adjusted based on the density of the toner image.
According to a fifteenth aspect of the present invention, in the image forming apparatus according to the tenth aspect, a toner supply unit that supplies toner to the developing unit, and the density detection unit after the toner amount adjustment unit adjusts the toner amount And a determination unit that determines that the remaining amount of toner in the toner supply unit is low when the density detected in step 1 is equal to or less than a predetermined value.
According to a sixteenth aspect of the present invention, in the image forming apparatus according to the tenth aspect, the development contrast potential is controlled based on the density of the toner image composed of the first pattern detected by the density detecting means. It is further characterized by further comprising a control means.
According to a seventeenth aspect of the present invention, in the image forming apparatus according to the sixteenth aspect, the control unit is configured such that the density of the toner image including the first pattern detected by the density detection unit is a first level. The developing contrast potential is set to be large when the density is smaller than a predetermined value, and the developing contrast potential is set to be small when the density is larger than a second predetermined value.

According to an eighteenth aspect of the present invention, a predetermined isolated line or dot in the toner image developed on the image carrier by the developing unit or the toner image transferred from the image carrier onto the transfer medium is stored in a computer. And adjusting the amount of toner supplied to the developing unit based on the density information regarding the toner image including the first pattern and the density information regarding the toner image including the first pattern. And a second pattern having a higher image area ratio than the first pattern in the toner image developed on the image carrier or the toner image transferred on the transfer medium. A program for realizing a function of controlling a development contrast potential based on the density information relating to a toner image.

According to a nineteenth aspect of the present invention, in the program according to the eighteenth aspect, the toner supply for supplying toner to the developing means when the density information acquired after adjusting the toner amount indicates a density equal to or lower than a predetermined value. A function of determining that the remaining amount of toner in the means is small is further realized.
According to a twentieth aspect of the present invention, the program according to the eighteenth aspect further realizes a function of controlling a development contrast potential based on the acquired density information regarding the toner image including the first pattern. Features.

According to the twenty-first aspect of the present invention, the toner image formed on the image carrier by developing the electrostatic latent image formed on the image carrier by the charging and exposure by the latent image forming unit by the developing unit. Or a function of acquiring density information relating to the toner image composed of a first pattern composed of a predetermined isolated line or dot in the toner image transferred from the image carrier onto the transfer medium; A function of adjusting the amount of toner supplied to the developing means based on the density information relating to the toner image comprising one pattern, and the toner image developed on the image carrier or the transfer image transferred onto the transfer medium. The latent image forming hand is based on the density information relating to the toner image composed of the second pattern having a higher image area ratio than the first pattern in the toner image. Charging potential is set at a program for causing and a function of controlling any one or a combination of these developing potential set by the exposure amount or the developing means.

According to a twenty-second aspect of the present invention, in the program according to the twenty-first aspect, the toner supply for supplying toner to the developing unit when the density information acquired after adjusting the toner amount indicates a density equal to or lower than a predetermined value. A function of determining that the remaining amount of toner in the means is small is further realized.
According to a twenty-third aspect of the present invention , the program according to the twenty- first aspect further realizes a function of controlling a development contrast potential based on the acquired density information regarding the toner image having the first pattern. Features.

  This program may be executed by loading a program stored in a reserved area such as a hard disk or a DVD-ROM into the RAM, for example. In addition, there is a form that is executed by the CPU in a state stored in the ROM in advance. Further, when a rewritable ROM such as an EEPROM is provided, only a program may be provided and installed in the ROM after the apparatus is assembled. In providing this program, it is also conceivable that the program is transmitted to the apparatus via a network such as the Internet and installed in the ROM of the apparatus.

According to the first aspect of the present invention, it is possible to control the toner density in a state that is less susceptible to the influence of temperature and humidity than in the case where the present invention is not adopted.
According to the second aspect of the present invention, the image density can be stabilized even when the toner charge amount of the developer is different due to the fluctuation of the temperature and humidity environment as compared with the case where the present invention is not adopted.
According to the third aspect of the present invention, compared to the case where the present invention is not adopted, the density detection of the toner image can be performed more stably regardless of the temperature and humidity conditions.
According to the fourth aspect of the present invention, compared to the case where the present invention is not adopted, the density detection of the toner image can be performed more stably regardless of the temperature and humidity conditions.

According to the fifth aspect of the present invention, compared to the case where the present invention is not adopted, the density detection of the toner image can be performed more stably regardless of the temperature and humidity conditions.
According to the sixth aspect of the present invention, compared to the case where the present invention is not adopted, the density detection of the toner image can be performed more stably regardless of the temperature and humidity conditions.
According to the seventh aspect of the present invention, the remaining amount of toner in the toner supply means can be estimated.
According to the eighth aspect of the present invention, it is possible to stabilize the density in an image composed of isolated lines and isolated dots as compared with the case where the present invention is not adopted.
According to the ninth aspect of the present invention, when the toner supply amount control is performed, a time delay until the toner density of the developer is controlled to the target value is compensated, and the present invention is not employed. In comparison, it is possible to stabilize the density in an image composed of isolated lines and isolated dots.

According to the tenth aspect of the present invention, it is possible to control the toner density in a state that is less susceptible to the influence of temperature and humidity than in the case where the present invention is not adopted.
According to the eleventh aspect of the present invention, compared to the case where the present invention is not adopted, the density detection of the toner image can be performed more stably regardless of the temperature and humidity conditions.
According to the twelfth aspect of the present invention, compared to the case where the present invention is not adopted, the density detection of the toner image can be performed more stably regardless of the temperature and humidity conditions.

According to the thirteenth aspect of the present invention, compared to the case where the present invention is not adopted, the density detection of the toner image can be performed more stably regardless of the temperature and humidity conditions.
According to the fourteenth aspect of the present invention, compared to the case where the present invention is not adopted, the density detection of the toner image can be performed more stably regardless of the temperature and humidity conditions.
According to the fifteenth aspect of the present invention, the remaining amount of toner in the toner supply means can be estimated.
According to the sixteenth aspect of the present invention, it is possible to stabilize the density of an image composed of isolated lines and isolated dots, compared to a case where the present invention is not adopted.
According to the seventeenth aspect of the present invention, when the toner supply amount control is performed, a time delay until the toner density of the developer is controlled to the target value is complemented, and the present invention is not adopted. In comparison, it is possible to stabilize the density in an image composed of isolated lines and isolated dots.

According to the eighteenth aspect of the present invention, it is possible to control the toner concentration in a state that is less susceptible to the influence of temperature and humidity than in the case where the present invention is not adopted.
According to the nineteenth aspect of the present invention, the remaining amount of toner in the toner supply means can be estimated.
According to claim 20 of the present invention, isolated lines and isolated dots are compared to the case where the present invention is not adopted.
It is possible to stabilize the density of an image consisting of

According to the twenty-first aspect of the present invention, it is possible to control the toner concentration in a state that is less susceptible to the influence of temperature and humidity than in the case where the present invention is not adopted.
According to the twenty-second aspect of the present invention, the remaining amount of toner in the toner supply means can be estimated.
According to the twenty-third aspect of the present invention, it is possible to stabilize the density of an image composed of isolated lines and isolated dots as compared with the case where the present invention is not adopted.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
[Embodiment 1]
FIG. 1 is a diagram illustrating an example of a configuration of an image forming apparatus 1 to which the exemplary embodiment is applied. An image forming apparatus 1 shown in FIG. 1 is a so-called tandem type digital color printer using an electrophotographic method, and an image forming process unit 20 that forms an image corresponding to image data of each color, and the entire image forming apparatus 1. A control unit 60 that controls the operation of the image processing unit, for example, an image processing unit 69 that performs predetermined image processing such as screen processing on image data received from an image reading device 4 such as a personal computer (PC) 3 or a scanner, a processing program, etc. For example, a main storage unit 90 realized by a hard disk (Hard Disk Drive).
Further, the image forming apparatus 1 includes a reference density detection sensor 55 as an example of a density detection unit that detects the density of a reference density pattern image formed of each color toner image formed on an intermediate transfer belt 41 described later.

The image forming process unit 20 forms four image forming units that respectively form yellow (Y), magenta (M), cyan (C), and black (K) toner images that are arranged in parallel at regular intervals. Units 30Y, 30M, 30C, and 30K (hereinafter, these are also collectively referred to as “image forming unit 30”).
Here, FIG. 2 is a diagram illustrating an example of the configuration of the image forming unit 30. As shown in FIG. 2, the image forming unit 30 charges the surface of the photosensitive drum 31 as an example of an image carrier on which an electrostatic latent image is formed while rotating in the direction of arrow A, and the surface of the photosensitive drum 31. A charging roller 32 as an example of a latent image forming unit, a developing unit 33 as an example of a developing unit for developing an electrostatic latent image formed on the photosensitive drum 31, and the surface of the photosensitive drum 31 after primary transfer are cleaned. A photoreceptor cleaner 36 is provided.

  The charging roll 32 is composed of a roll member in which a conductive elastic layer and a conductive surface layer are sequentially laminated on a conductive core bar such as aluminum or stainless steel. Then, a charging bias is supplied from a charging power source (not shown), and the surface of the photosensitive drum 31 is uniformly charged at a predetermined potential while being driven to rotate relative to the photosensitive drum 31. Here, the charging bias value supplied from the charging power source is set based on a control signal from the control unit 60.

The developing units 33 are configured as developing units 33Y, 33M, 33C, and 33K that develop yellow (Y), magenta (M), cyan (C), and black (K) toners in the image forming units 30, respectively. The
Each developing device 33 includes a support container 331 for containing the developer, a developing roll 332 for holding and transporting the developer, a developing magnet 333 for adsorbing the developer to the developing roll 332, and a layer thickness (application amount) of the developer. A regulating blade 334 that regulates the developer), developer conveying screws 335, 336 that circulate and move the developer in the longitudinal direction of the developing device 33, and toner containers 35Y, 35M, which are examples of toner supply means for storing each color toner. A toner supply path 337 for supplying toner from 35C and 35K (hereinafter also collectively referred to as “toner container 35”) to the support container 331 is provided.

The support container 331 has an opening toward the photosensitive drum 31, and a developer containing portion that contains a developer in which toner and a carrier that is magnetic particles are mixed is provided inside. The developer accommodating portion is divided into a first developer accommodating portion 331 b and a second developer accommodating portion 331 c by an accommodating portion wall 331 a provided in the longitudinal direction of the developing device 33.
A developer conveying screw 335 is disposed in the first developer accommodating portion 331b, and a developer conveying screw 336 is disposed in the second developer accommodating portion 331c. The accommodating portion walls 331a are not provided at both ends in the longitudinal direction of the developing device 33, and the first developer accommodating portion 331b and the second developer accommodating portion 331c are connected at the both end portions so that the developer It is comprised so that it may distribute mutually.

The developing roll 332 is made of a nonmagnetic material such as aluminum or SUS, and is rotated in the direction of arrow C by a driving unit (not shown). The developing roll 332 is supplied with a developing bias consisting of a DC voltage from a developing power source (not shown) or a developing bias in which a DC voltage is superimposed on an AC voltage, and forms a developing electric field between the developing roller 332 and the photosensitive drum 31. Yes. Here, the developing bias value supplied from the developing power source is set based on a control signal from the control unit 60.
A developing magnet 333 is disposed inside the developing roll 332. The developing magnet 333 is provided with a developing pole N1 provided facing the photosensitive drum 31, a trimming pole S1 provided facing the regulating blade 334, and regulating the amount of developer applied, and supports the developed developer. In order to form a repulsive magnetic field in order to release the developer held on the developing roller 332 and the conveying pole S2 that is transported into the container 331, the same polarity (adjacently arranged from the upstream side in the rotation direction of the developing roller 332) Magnetic poles N2 (first repulsive magnetic poles) and magnetic poles N3 (second repulsive magnetic poles) having the same repulsive pole are arranged along the circumferential direction.
The regulating blade 334 is made of a nonmagnetic material or a magnetic material, and regulates the layer thickness of the developer held on the developing roll 332 together with the trimming pole S1 of the developing magnet 333 to a certain amount. As a result, a predetermined amount of developer is uniformly supplied to the photosensitive drum 31 along the axial direction of the developing roll 332, and an electrostatic latent image formed on the photosensitive drum 31 under the action of the developing electric field is generated. develop.

  In the developing roll 332 including the developing magnet 333, after the developer held in the first developer accommodating portion 331b is attracted to the developing roll 332 by the second repulsive magnetic pole N3 on the downstream side of the same-polar repulsive pole, The developer amount (application amount) on the developing roll 332 is regulated to a predetermined amount by the trimming pole S1 and the regulating blade 334. Then, the developer roll 332 is rotated to convey the developer to the photosensitive drum 31, and under the developing electric field, the developer is spiked by the developing pole N <b> 1 and brought into contact with the photosensitive drum 31, so that the photosensitive drum 31 is brought into contact. Develop the electrostatic latent image above. The developer that has been developed is transported into the support container 331 by the transport pole S2, and is separated from the developing roll 332 by the repulsive magnetic fields of the first repulsive magnetic pole N2 and the second repelling magnetic pole N3. Further, the developer separated from the developing roll 332 is collected in the first developer accommodating portion 331b.

  On the other hand, the developer conveying screw 335 of the first developer accommodating portion 331b and the developer conveying screw 336 of the second developer accommodating portion 331c are each provided with a helical screw around the shaft. The developer conveying screw 335 and the developer conveying screw 336 are rotated in opposite directions by driving means (not shown) to convey the toner and the carrier in opposite directions while stirring. Since the first developer accommodating portion 331b and the second developer accommodating portion 331c are connected at both ends of the developing device 33, the developer flows into each other, and the developer conveying screw 335 and the developer conveying screw 336 cause the first developer accommodating portion 331b and the second developer accommodating portion 331c to be connected to each other. The first developer container 331b and the second developer container 331c are configured to circulate between the first developer container 331b and the second developer container 331c. Therefore, the developer separated from the developing roll 332 and collected in the first developer accommodating portion 331b is conveyed to the second developer accommodating portion 331c by the developer conveying screw 335 and the developer conveying screw 336.

In addition, a toner supply path 337 for supplying toner to the second developer accommodating portion 331c is formed in the support container 331 at the upper portion of the longitudinal center portion of the second developer accommodating portion 331c. The toner supply path 337 is connected to each toner container 35 by a toner conveyance path 37, and is configured such that toner is replenished by a replenishment screw (not shown) provided in the toner conveyance path 37.
When the toner is supplied from the toner containers 35 to the developer in the second developer container 331c, the mixing ratio (toner density) of the toner and the carrier in the developer is controlled under the control of the controller 60 described later. ) Is controlled to be controlled within a predetermined range. The developer to which toner is newly supplied is sufficiently agitated and mixed with the toner by the developer conveying screw 336, and the first developer accommodating portion 331b by the developer conveying screw 335 and the developer conveying screw 336 is obtained. And the second developer accommodating portion 331c are conveyed again to the first developer accommodating portion 331b. Then, the developer in which the toner concentration is adjusted to a predetermined range and the toner is sufficiently charged is supplied to the developing roll 332 from the first developer accommodating portion 331b. In this way, the developer is circulated.

Next, the photoconductor cleaner 36 brings a plate-like member formed of a rubber material such as urethane rubber into contact with the surface of the photoconductor drum 31 to remove toner, paper powder, and the like attached on the photoconductor drum 31.
Further, the image forming unit 30 includes a potential sensor 68 that detects the surface potential of the photosensitive drum 31 on the downstream side of the charging roller 32 in the rotation direction of the photosensitive drum 31. The potential sensor 68 detects the surface potential of the photosensitive drum 31 and sends the detection value (surface potential detection value) to the control unit 60. The control unit 60 controls the surface potential of the photosensitive drum 31 by adjusting the charging bias value supplied to the charging roll 32 based on the acquired surface potential detection value.

Returning to FIG. 1, the image forming process unit 20 includes a laser exposure unit 26 as an example of a latent image forming unit that exposes each photosensitive drum 31 provided in each image forming unit 30, and each photosensitive member of each image forming unit 30. The intermediate transfer belt 41 as an example of a transfer medium on which the color toner images formed on the body drum 31 are transferred in a multiple manner, and the color toner images of the image forming units 30 are sequentially transferred to the intermediate transfer belt 41 at the primary transfer portion T1. The primary transfer roll 42 (primary transfer) and the superimposed toner image transferred onto the intermediate transfer belt 41 are collectively transferred (secondary transfer) onto the paper P, which is a recording material (recording paper), at the secondary transfer portion T2. A secondary transfer roll 40 and a fixing device 80 for fixing the secondary transferred image on the paper P are provided.
Here, the laser exposure unit 26 is a semiconductor laser 27 as a light source, a scanning optical system (not shown) that scans and exposes a laser beam to the photosensitive drum 31, for example, a rotating polygon mirror (polygon mirror) formed of a regular hexagonal body. 28, a laser driver 29 for controlling the driving of the semiconductor laser 27 is provided. The laser driver 29 receives image data from the image processing unit 69, a light amount control signal from the control unit 60, and the like, and performs lighting control of the semiconductor laser 27, output light amount control, and the like.
In the present embodiment, the configuration using the laser exposure unit 26 is shown. However, as another example of the latent image forming unit, a light emitting element array in which a large number of light emitting elements such as LEDs are arranged in a line may be used. .

  In the image forming apparatus 1 of the present embodiment, the image forming process unit 20 performs an image forming operation under the control of the control unit 60. That is, the image data input from the PC 3 or the image reading device 4 is subjected to predetermined image processing such as screen processing by the image processing unit 69 and supplied to the laser exposure unit 26. For example, in the yellow (Y) image forming unit 30 </ b> Y, the surface of the photosensitive drum 31 that is uniformly charged at a predetermined potential by the charging roll 32 is based on the image data from the image processing unit 69 by the laser exposure unit 26. Then, scanning exposure is performed with the laser light whose lighting is controlled, and an electrostatic latent image is formed on the photosensitive drum 31. The formed electrostatic latent image is developed by the developing device 33Y, and a yellow (Y) toner image is formed on the photosensitive drum 31. In the image forming units 30M, 30C, and 30K, magenta (M), cyan (C), and black (K) toner images are similarly formed.

Each color toner image formed by each image forming unit 30 is a primary transfer roll to which a predetermined primary transfer bias is applied from a transfer power source (not shown) on an intermediate transfer belt 41 that circulates and moves in the direction of arrow B in FIG. The toner images are electrostatically transferred sequentially by 42 and superimposed on the intermediate transfer belt 41. As the intermediate transfer belt 41 moves, the superimposed toner image is conveyed toward the secondary transfer portion T2 where the secondary transfer roll 40 and the backup roll 49 are disposed.
On the other hand, the sheet P as an example of the transfer medium is taken out from the sheet holding unit 71 by a pickup roll 72 for sending out, and is transported to the position of a registration roll 74 for regulating the position of the sheet P along the transport path R1. The Then, the sheet P is conveyed from the registration roll 74 toward the secondary transfer portion T2 in synchronization with the timing at which the superimposed toner image is conveyed to the secondary transfer portion T2. In the secondary transfer portion T2, the superimposed toner images are collectively and statically formed on the paper P by the action of the transfer electric field formed between the secondary transfer roll 40 and the backup roll 49 to which the secondary transfer bias voltage is applied. Electrotransfer (secondary transfer) is performed.
Note that the sheet P is also transported to the secondary transfer portion T2 from the duplex transport path R2 and the transport path R3 from the manual sheet storage section 75.

Thereafter, the sheet P on which the superimposed toner image is electrostatically transferred is peeled from the intermediate transfer belt 41 and conveyed to the fixing device 80. The unfixed toner image on the paper P conveyed to the fixing device 80 is fixed on the paper P by being subjected to fixing processing by heat and pressure by the fixing device 80. The paper P on which the fixed image is formed is conveyed to a paper stacking unit 91 provided in the discharge unit of the image forming apparatus 1. On the other hand, the toner (transfer residual toner) adhering to the intermediate transfer belt 41 after the secondary transfer is removed by a belt cleaner 45 disposed so as to come into contact with the intermediate transfer belt 41 to prepare for the next image forming cycle. .
In this manner, image formation in the image forming apparatus 1 is repeatedly executed for the designated number of sheets.

Subsequently, an image density adjustment process performed in the image forming apparatus 1 of the present embodiment will be described.
In the image forming apparatus 1 of the present embodiment, in order to suppress fluctuations in the density of an image to be formed, for example, at a predetermined interval such as at the start of image formation or every predetermined number of prints during an image forming operation. “Image density adjustment processing” is performed. In the image density adjustment process of the present embodiment, the mixing ratio of the toner in the developer and the carrier in each developer 33 based on the density of a predetermined reference density pattern image formed in each image forming unit 30. The amount of toner supplied from each toner container 35 is adjusted so that (toner density) is controlled within a predetermined range. Further, if necessary, development such as a latent image forming condition such as an output light amount value of the semiconductor laser 27 in the laser exposure unit 26 or a charging bias value supplied to the charging roll 32, a developing bias supplied to the developing roll 332, or the like. Conditions (hereinafter collectively referred to as “image forming conditions”) are adjusted. Such image density adjustment processing is performed under the control of the control unit 60 functioning as control means, toner amount adjustment means, and determination means in the present embodiment.

An image density adjustment process performed in the image forming apparatus 1 of the present embodiment will be described.
First, the control unit 60 sets the surface potential of the photoconductive drum 31 in each image forming unit 30 to a predetermined potential level. At that time, various image forming conditions such as an output light amount value of the semiconductor laser 27, a developing bias value, and a primary transfer bias value of the primary transfer roll 42 are set to predetermined predetermined values. Each image forming unit 30 forms two different types of reference density pattern images.
Here, FIG. 3 is a diagram illustrating an example of a state in which two different types of reference density pattern images formed by the image forming units 30 are primarily transferred onto the intermediate transfer belt 41. As shown in FIG. 3, in the black (K) image forming unit 30K, as a reference density pattern image, for example, an isolation as an example of a first pattern in which isolated lines having a predetermined line width are formed at predetermined intervals. A high area ratio reference density as an example of a second pattern formed with a line reference density pattern image K-1 and an image area ratio (ratio of the area occupied by the image) higher than that of the isolated line reference density pattern image K-1. A pattern image K-2 is formed.
Similarly, the isolated line reference density pattern image Y-1 and the high area ratio reference density pattern image Y-2 in the yellow (Y) image forming unit 30Y, and the isolated line reference density pattern in the magenta (M) image forming unit 30M. The isolated line reference density pattern image C-1 and the high area ratio reference density pattern image C-2 are respectively formed in the image M-1, the high area ratio reference density pattern image M-2, and the cyan (C) image forming unit 30C. The
It should be noted that, instead of the isolated line reference density pattern image, isolated dot reference density pattern images Y-1 ′, M-1 ′, as an example of a first pattern in which isolated dots of a predetermined diameter are formed at predetermined intervals. C-1 ′ and K-1 ′ (not shown) can also be used.
The “isolated lines” and “isolated dots” here are lines and dots that constitute pixels formed by screen processing in the image processing unit 69, for example, and are independent without having intersections with other lines or dots. The one formed in the state.

The density of the reference density pattern image formed on the intermediate transfer belt 41 is detected for each color by the reference density detection sensor 55 arranged on the downstream side in the conveyance direction of the intermediate transfer belt 41 of the image forming unit 30K. . The detected density detection value of each color reference density pattern image is sent to the control unit 60 as density information. Therefore, the control unit 60 also functions as density information acquisition means.
The control unit 60 that has acquired the density detection value of each color reference density pattern image from the reference density detection sensor 55 sets the toner supply amount corresponding to the density detection value of each color reference density pattern image. Then, the toner supply amount from each toner container 35 to each developing device 33 is controlled. Furthermore, various image forming conditions such as latent image forming conditions and development conditions are set as necessary. Thereby, fluctuations in image density on the paper P are suppressed and the image quality is maintained at a high level.

  FIG. 4 is a block diagram illustrating a functional configuration for performing image density adjustment processing in the control unit 60 of the present embodiment. As shown in FIG. 4, the control unit 60 includes a toner supply amount control unit 61 as an example of a toner amount adjustment unit and a development bias control unit as an example of a control unit as an example of a functional unit that performs image density adjustment processing. 62, a charging bias control unit 63 as an example of a control unit, and a laser light amount control unit 64 as an example of a control unit. The density detection value of each color reference density pattern image by the reference density detection sensor 55 is sent to the toner supply amount control unit 61, the developing bias control unit 62, the charging bias control unit 63, and the laser light quantity control unit 64, respectively.

  FIG. 5 is a block diagram showing an internal configuration of the control unit 60 of the present embodiment. As shown in FIG. 5, when performing the image density adjustment process, the control unit 60 is executed by the CPU 601 that executes digital arithmetic processing according to a predetermined processing program, the RAM 602 that is used as a work memory of the CPU 601, and the CPU 601. ROM 603 for storing processing programs to be rewritten, EEPROM 604 as an example of a storage means capable of storing data even when power supply is interrupted, image forming process unit 20 connected to control unit 60 and main storage unit 90 and an interface unit 605 for controlling input / output of signals to / from each unit such as the reference density detection sensor 55.

Then, the CPU 601 of the control unit 60 stores programs for realizing the functions of the toner supply amount control unit 61, the development bias control unit 62, the charging bias control unit 63, and the laser light amount control unit 64 from the main storage unit 90 to the RAM 602 and the like. Read and perform various processes. A table (for example, a toner supply amount table) provided in various function units described later is stored in advance in the EEPROM 604 of the control unit 60.
The main storage unit 90 stores a processing program executed by the control unit 60, and the control unit 60 reads the processing program when the image forming apparatus 1 is started up. Image density adjustment processing in the unit 60 is executed.

  Here, the toner supply amount control unit 61 is provided with a toner supply amount table that defines the correspondence between the detected density value and the toner supply amount. Based on the toner supply amount table, each toner container 35 to each developing device. The toner supply amount to 33 is controlled. The development bias controller 62 includes a development bias voltage table that defines the correspondence between the density detection value and the development bias value, and controls the development bias value applied to the development roll 332 based on the development bias voltage table. . The charging bias control unit 63 includes a charging bias voltage table that defines a correspondence relationship between the density detection value and the charging bias voltage value. Based on the charging bias voltage table, each charging roll 32 of each image forming unit 30 is provided. To control the charging bias value supplied to The laser light quantity control unit 64 includes an output light quantity table that defines the correspondence between the density detection value and the output light quantity. Based on this output light quantity table, the semiconductor laser irradiated to the photosensitive drum 31 from the laser exposure unit 26. The output light quantity value of 27 is controlled.

Next, the toner supply amount control performed by the toner supply amount control unit 61 of this embodiment will be described.
The toner supply amount control unit 61 is the isolated line reference density pattern image Y-1, M-1, C-1, K-1, or isolated dot reference density pattern formed by each image forming unit 30 shown in FIG. Toner from each toner container 35 to each developing device 33 based on the density detection value detected by the reference density detection sensor 55 for the images Y-1 ′, M-1 ′, C-1 ′, and K-1 ′. Control the supply amount.

FIG. 6 shows a 20 mm × 20 mm square pattern image of 1 on 4 off (vertical line) at 600 dpi (dot per inch) as an isolated line reference density pattern image, and the developer toner density (%) and the reference in the image forming unit 30K. It is the figure which compared the relationship with the density | concentration index | exponent which is a density | concentration detection value in the density | concentration detection sensor 55, changing temperature / humidity conditions.
Note that the 1on4off isolated line reference density pattern image at 600 dpi in FIG. 6 is 1 dot lighting 4 dots in the main scanning direction by a 1-bit pixel (also referred to as “1 dot”) having a diameter of about 42.3 μm and 600 dpi. Non-lighting is repeated to form an isolated line reference density pattern image composed of vertical lines in the sub-scanning direction. The data value when the density detection value of the reference density detection sensor 55 is detected as 8-bit data (0 to 255) is defined as “density index”. As temperature and humidity conditions to be compared, a temperature of 28 ° C. and a relative humidity of 80% RH and a temperature of 10 ° C. and a relative humidity of 30% RH are set.

As shown in FIG. 6, the density detection value (density index) regarding the isolated line reference density pattern image shows a unique correlation with the toner density even under different temperature and humidity conditions. Therefore, if the detected density value is detected by the reference density detection sensor 55 for the isolated line reference density pattern images Y-1, M-1, C-1, and K-1, the toner density can be set regardless of the temperature and humidity conditions. It can be detected with high accuracy.
6 shows the correlation between the detected density value and the toner density for the isolated line reference density pattern image as the reference density pattern image, the isolated dot reference density pattern images Y-1 ′, M-1 ′, Even when C-1 ′ and K-1 ′ are used, the density detection value and the toner density show a unique correlation that does not depend on the temperature and humidity conditions, like the isolated line reference density pattern image.

FIG. 7 is a graph showing the relationship between the charge amount (μC / g) of the toner that forms the isolated line reference density pattern image in FIG. 6 and the density index that is the density detection value of the reference density detection sensor 55. It is. As shown in FIG. 7, when attention is paid to the toner that forms the isolated line reference density pattern image having the same density index, the toner charge amount in the environment of the temperature 28 ° C. and the relative humidity 80% RH is 10 ° C. relative humidity 30 The value is lower than the toner charge amount in the% RH environment. The result of FIG. 7 supports the phenomenon that the toner charge amount decreases as the temperature and humidity become higher. However, the result of FIG. 6 means that the density detection value relating to the isolated line reference density pattern image uniquely corresponds to the toner density even when the toner charge amount varies depending on the temperature and humidity conditions as shown in FIG. ing.
Therefore, the toner supply amount control unit 61 according to the present embodiment uses the isolated line reference density pattern images Y−1, M−1, C−1, K−1 or isolated dot reference formed in each image forming unit 30. Based on the density detection values detected by the reference density detection sensor 55 for the density pattern images Y-1 ′, M-1 ′, C-1 ′, and K-1 ′, the toner containers 35Y, 35M, 35C, and 35K. The toner supply amount to each developing device 33 is adjusted. Accordingly, high-precision control of the toner density in each developing device 33 is realized regardless of the toner charge amount.

Subsequently, FIG. 8 shows the line width of the isolated line when the isolated line reference density pattern images Y-1, M-1, C-1, and K-1 are formed as the reference density pattern image, and the reference density detection sensor 55. It is the figure which showed the relationship with the dispersion | variation (density fluctuation rate) of the density detection value of the detected isolated line reference | standard density pattern image. In FIG. 8, the developing device 33 in which the toner density is adjusted to 5.2% under both temperature and humidity conditions of a temperature of 28 ° C. and a relative humidity of 80% RH and a temperature of 10 ° C. and a relative humidity of 30% RH. The density fluctuation rate in each developing device 33 in which the toner density was adjusted to 8.1% was calculated. Also, the density fluctuation rate is calculated at a rate of once per 100 sheets when the image forming apparatus 1 in the state set to the same image forming condition performs 1000 image forming operations. It is. Further, the density variation rate here is defined as n for each density detection value detected multiple times for each line width, and I for the average value of the density detection values for each line width, according to the following equation (1). The fluctuation rate regarding the detected value is obtained, and the average is obtained as the density fluctuation rate at each line width.
Fluctuation rate for each concentration detection value = ((n−I) / I) × 100 (%) (1)
As shown in FIG. 8, the concentration fluctuation rate is such that a stable concentration detection value is obtained including the temperature and humidity conditions of both the temperature 28 ° C. relative humidity 80% RH environment and the temperature 10 ° C. relative humidity 30% RH environment. In order to keep the value within 10% or less, it is necessary to form the isolated line with a line width of 20 μm or more for the isolated line reference density pattern image.

Similarly, FIG. 9 shows the dot diameter of the isolated dots when the isolated dot reference density pattern images Y-1 ′, M-1 ′, C-1 ′, and K-1 ′ are formed as the reference density pattern images, and the reference 6 is a diagram showing a relationship with variation (density variation rate) in density detection values of an isolated dot reference density pattern image detected by a density detection sensor 55. FIG. Also in FIG. 9, the concentration fluctuation rate was obtained under the same conditions as in FIG.
As shown in FIG. 9, in order to suppress the density variation rate within a range of 10% or less at which a stable density detection value is obtained, the isolated dot reference density pattern image is formed so that the dot diameter of the isolated dot is 30 μm or more. It will be necessary.

By the way, the line width of the isolated line in the isolated line reference density pattern image for obtaining a stable density detection value by the reference density detection sensor 55 is 20 μm or more, and the dot diameter of the isolated dot in the isolated dot reference density pattern image is 30 μm or more. This condition is considered to be based on the following reasons.
First, the surface potential (VH: charged potential) of the photosensitive drum 31 charged by the charging roll 32, the latent image potential (V: exposed portion potential) of the area exposed by the laser exposure device 26, and the developing device (development). The relationship with the direct current component (VDC) of the developing bias applied to the rolls 332) 33 will be described. FIG. 10 is a diagram showing the relationship among the charging potential VH, the exposure portion potential V, and the development bias direct current component VDC. In the image forming apparatus 1 of the present embodiment, the so-called reversal development method in which the photosensitive drum 31 is charged with a negative charge by the charging roll 32 and the development in the developing unit 33 is performed with a negatively charged toner. Is used. Accordingly, the region of the charging potential VH in FIG. 10 is a white background (background). Further, the potential VL becomes the latent image potential in the highest density region formed on the photosensitive drum 31.

The development contrast potential which is the difference (| V−VDC |) between the exposure portion potential V and the development bias voltage VDC shown in FIG. 10 is a factor that determines the image density of the image portion. When the development contrast potential is small, a sufficient image density cannot be obtained. For example, the development contrast potential V1 is small in a latent image in which the line width of the isolated line and the dot diameter of the isolated dot are small. For this reason, if the exposure portion potential V fluctuates even slightly in a latent image having a small line width or dot diameter, the variation rate of the development contrast potential V1 becomes large. Thereby, the density detection value by the density detection sensor 55 becomes unstable. On the other hand, the development contrast potential V2 is large in a latent image in which the line width of the isolated line and the dot diameter of the isolated dot are large. For this reason, even if the exposure portion potential V fluctuates in a latent image having a large line width or dot diameter, the variation rate of the development contrast potential V2 is small, so that the density detection value by the density detection sensor 55 becomes stable.
Therefore, as described above, in the isolated line reference density pattern image, the line width of the isolated line is set to 20 μm or more, and in the isolated dot reference density pattern image, the dot diameter of the isolated dot is set to 30 μm or more. A stable density detection value is obtained by the detection sensor 55.

Next, the condition regarding the distance between isolated lines in the isolated line reference density pattern image for obtaining a stable density detection value by the reference density detection sensor 55 regardless of the temperature and humidity conditions, and the isolation in the isolated dot reference density pattern image The conditions regarding the dot interval will be described.
FIG. 11 shows the relationship between the toner density (%) of the developer and the density detection value (density index) in the reference density detection sensor 55 when an isolated line reference density pattern image is formed as the reference density pattern image. It is the figure which changed and changed the mutual space | interval. That is, in FIG. 11, 1 on 1 off which repeats 1 dot lighting 1 dot non lighting in the main scanning direction, 1 on 3 off which repeats 1 dot lighting 3 dots non lighting in the main scanning direction by a 1 bit pixel (1 dot) having a diameter of about 42.3 μm of 600 dpi. A 1 on 6 off repetition of 1 dot lighting and 4 dot non lighting, and a 1 on 6 off isolated line reference density pattern image repeating 1 dot lighting and 6 dot non lighting were formed and compared. The temperature and humidity conditions to be compared are a temperature 28 ° C. relative humidity 80% RH environment and a temperature 10 ° C. relative humidity 30% RH environment.

From the result of FIG. 11, when an isolated line reference density pattern image with 4 or more non-lighting dots is formed in a state where 1 dot lighting is set, the temperature is 28 ° C. relative humidity 80% RH environment and the temperature is 10 ° C. relative. The density detection value by the reference density detection sensor 55 with respect to the humidity 30% RH environment is hardly different. Therefore, in order to obtain a stable density detection value by the reference density detection sensor 55 regardless of the temperature and humidity conditions, the isolated line reference density pattern image has an isolated line when the line width is about 42.3 μm, which is 600 dpi. If the distance between the isolated lines is 127 μm for three lines, it is not sufficient, and if it is about 170 μm or more for four lines, it is sufficient.
Therefore, when the image density adjustment processing is performed in the control unit 60 of the present embodiment, when the isolated line reference density pattern image is formed as the reference density pattern image, the isolated density is obtained in order to obtain the above-described stable density detection value. The distance between the line and the isolated line is set to 170 μm or more.

  FIG. 12 shows the relationship between the toner density (%) of the developer and the density detection value (density index) of the reference density detection sensor 55 when an isolated dot reference density pattern image is formed as the reference density pattern image. It is the figure which changed and changed the space | interval of isolated dots. That is, in FIG. 12, an isolated dot reference density pattern image having a resolution of 100 dpi with an image area ratio of 25%, 20%, 15%, and 10% was formed and compared. Similarly, the temperature and humidity conditions to be compared are a temperature 28 ° C. relative humidity 80% RH environment and a temperature 10 ° C. relative humidity 30% RH environment.

From the results shown in FIG. 12, when an isolated dot reference density pattern image having an image area ratio of 15% or less is formed, between a temperature of 28 ° C. relative humidity of 80% RH environment and a temperature of 10 ° C. relative humidity of 30% RH environment. The density detection values obtained by the reference density detection sensor 55 hardly differ. In a square area of 254 μm × 254 μm, which is a unit pixel area of 100 dpi, when the image area ratio is 15%, the dot diameter is 98 μm (here, the isolated dots are assumed to be square), and adjacent dots Is 156 μm. When the image area ratio is 20%, the dot diameter is 114 μm, and the distance between adjacent dots is 140 μm. Therefore, in order to obtain a stable density detection value by the reference density detection sensor 55 regardless of the temperature and humidity conditions, the interval between adjacent dots may be set to 156 μm or more at which the image area ratio is 15% or less.
Therefore, when performing the image density adjustment process in the control unit 60 of the present embodiment, in order to obtain the above-described stable density detection value when the isolated dot reference density pattern image is formed as the reference density pattern image, The interval between adjacent dots is set to 160 μm or more.
In the present embodiment, the line width and the dot diameter are calculated when the length obtained by dividing 1 inch by the number of dpi is one pixel (1 bit), and regarding the isolated dot, the isolated dot is regarded as a square. The length of one side was defined as the dot diameter.

Next, when the above-mentioned conditions regarding the distance between isolated lines in the isolated line reference density pattern image and the distance between isolated dots in the isolated dot reference density pattern image are satisfied, the reference density detection sensor 55 stabilizes it regardless of the temperature and humidity conditions. A condition regarding the line width of the isolated line and a condition regarding the diameter of the isolated dot for obtaining the detected density value will be described.
FIG. 13 shows the relationship between the toner density (%) of the developer and the density detection value (density index) in the reference density detection sensor 55 when an isolated line reference density pattern image is formed as the reference density pattern image. It is the figure which changed and changed the line | wire width of the isolated line in the state where the space | interval of lines met said conditions. That is, in FIG. 13, 1 on 4 off, which repeats 1 dot lighting 4 dots non-lighting in the main scanning direction, 2 on 4 off, 2 dots lighting 4 dots non-lighting in the main scanning direction by a 1-bit pixel (1 dot) having a diameter of about 42.3 μm of 600 dpi 3 on 4 off repeating 3 dot lighting 4 dot non lighting 4 on 4 off repeating 4 dot lighting 4 on 4 off 5 on 4 off isolated line reference density pattern images repeating 5 dot lighting 4 dot non lighting were formed and compared. The temperature and humidity conditions to be compared are a temperature 28 ° C. relative humidity 80% RH environment and a temperature 10 ° C. relative humidity 30% RH environment.

From the results shown in FIG. 13, when an isolated line reference density pattern image with 3 dots or less is set in a state where 4 dots are not lit, the temperature is 28 ° C. relative humidity 80% RH environment and the temperature is 10 ° C. relative humidity. The density detection value by the reference density detection sensor 55 with respect to the 30% RH environment is hardly different. Therefore, in order to obtain a stable density detection value by the reference density detection sensor 55 regardless of the temperature and humidity conditions, in the isolated line reference density pattern image, the line width of the isolated line is approximately 42.3 μm, which is 600 dpi. The width is within the allowable range up to approximately 130 μm for the three line segments, and is outside the allowable range at 170 μm or more for the four line segments.
Therefore, when the image density adjustment processing is performed in the control unit 60 of the present embodiment, when the isolated line reference density pattern image is formed as the reference density pattern image, the isolated line for obtaining the above-described stable density detection value is obtained. In consideration of the condition of the line width of 20 μm or more (see FIG. 8), the line width of the isolated line is set to 20 μm or more and 130 μm or less.

  FIG. 14 shows the relationship between the toner density (%) of the developer and the density detection value (density index) of the reference density detection sensor 55 when an isolated dot reference density pattern image is formed as the reference density pattern image. FIG. 5 is a diagram comparing the diameters of isolated dots while the distance between the isolated dots satisfies the above condition. That is, in FIG. 14, an isolated dot reference density pattern image having a resolution of 50 dpi with an image area ratio of 25%, 20%, 15%, and 10% is formed and compared. Similarly, the temperature and humidity conditions to be compared are a temperature 28 ° C. relative humidity 80% RH environment and a temperature 10 ° C. relative humidity 30% RH environment.

From the results shown in FIG. 14, when an isolated dot reference density pattern image having an image area ratio of 15% or less is formed, between a temperature of 28 ° C. relative humidity of 80% RH environment and a temperature of 10 ° C. relative humidity of 30% RH environment. The density detection values obtained by the reference density detection sensor 55 hardly differ. In a square area of 508 μm × 508 μm, which is a unit pixel area of 50 dpi, when the image area ratio is 15%, the dot diameter is 197 μm, and the interval between adjacent dots is 311 μm. When the image area ratio is 20%, the dot diameter is 227 μm, and the distance between adjacent dots is 281 μm. Therefore, in order to obtain a stable density detection value by the reference density detection sensor 55 regardless of the temperature and humidity conditions, the dot diameter may be set to 200 μm or less at which the image area ratio is approximately 15% or less.
Therefore, when performing the image density adjustment processing in the control unit 60 of the present embodiment, the isolated dot for obtaining the above-described stable density detection value when the isolated dot reference density pattern image is formed as the reference density pattern image. The dot diameter of the isolated dots is set to 30 μm or more and 200 μm or less in consideration of the condition (see FIG. 9) of the dot diameter of 30 μm or more.

  Incidentally, as described above, the toner density of the developer can be detected with high accuracy by using an isolated pattern image such as an isolated line reference density pattern image or an isolated dot reference density pattern image based on the following principle. it is conceivable that. 15A shows an electric field formed between the electrostatic latent image of the isolated pattern image and the developing roll 332 of the developing device 33, and FIG. 15B shows an image (high density image) formed at a high density. 6 is a diagram illustrating an electric field formed between the electrostatic latent image and a developing roll 332 of the developing device 33. FIG. As shown in FIG. 15B, since the electrostatic latent image of the high density image is superimposed on the surrounding electrostatic latent image, the developing roll to which the electrostatic latent image of the high density image and the developing bias are applied. The electric field formed by 332 has a substantially uniform gradient in the gap between the photosensitive drum 31 and the developing roll 332. Therefore, the lines of electric force from the electrostatic latent image of the high density image are directed toward the surface of the developing roll 332 and reach from the surface of the photosensitive drum 31 to a deep portion of the developer layer. On the other hand, as shown in FIG. 15A, the electric field formed by the electrostatic latent image of the isolated pattern image by the isolated line or the isolated dot and the developing roll 332 generates the electrostatic latent image of the isolated pattern image. It has a curved slope as the center. Thereby, the electric lines of force from the isolated pattern image diffuse. Furthermore, the electric field strength in this case is small. For this reason, the range in which the effective electric field force reaches the toner is limited to the vicinity of the electrostatic latent image, and the electric lines of force from the isolated pattern image only reach the vicinity of the surface of the first layer of the developer layer. .

As a result, in the electrostatic latent image of the high density image in FIG. 15B, the development proceeds until the charge of the electrostatic latent image is neutralized by the toner charge adhered to the development. The (toner adhesion amount) depends on the toner charge amount. On the other hand, in the case of an electrostatic latent image of an isolated pattern image such as an isolated line or an isolated dot, only the toner present on the surface of the first layer of the developer layer contributes to the development, and the charge amount of the electrostatic latent image Development does not proceed until the solution is sufficiently neutralized. In other words, the amount of toner developed in isolated lines and dots is determined by the amount of toner present on the surface of the developer layer first layer. Since the toner amount on the surface of the first layer of the developer layer is proportional to the toner concentration of the developer, the density (toner adhesion amount) of the isolated pattern image in the electrostatic latent image represents the toner concentration of the developer. It becomes.
However, in the state where the distance between isolated lines and dots is reduced and the line width and isolated dot diameter of the isolated lines are increased, the electric field similar to that of a high-density image is obtained by superimposing the electric fields of adjacent electrostatic latent images. Is formed. As a result, the range covered by the electric field is widened, and the dependency on the toner charge amount is increased as in the case of the high density image. For this reason, it is considered that the unambiguous correlation between the developed toner amount (toner adhesion amount) and the toner concentration of the developer does not match due to fluctuations in the temperature and humidity conditions.

As described above, in the toner supply amount control unit 61 of the present embodiment, the isolated line reference density pattern images Y−1, M−1, C−1, K−1 formed by the respective image forming units 30, or Each development from each toner container 35 is performed based on the density detection value detected by the reference density detection sensor 55 for the isolated dot reference density pattern images Y-1 ′, M-1 ′, C-1 ′, and K-1 ′. The toner supply amount to the device 33 is controlled. At that time, the isolated line reference density pattern images Y-1, M-1, C-1, and K-1 were used to obtain a stable density detection value by the reference density detection sensor 55 regardless of the temperature and humidity conditions. In this case, the line width of the isolated line is set to 20 μm or more and 130 μm or less, and the distance between the isolated line and the isolated line is set to 170 μm or more. When the isolated dot reference density pattern images Y-1 ′, M-1 ′, C-1 ′, and K-1 ′ are used, the dot diameter of the isolated dots is set to 30 μm or more and 200 μm or less, and the adjacent dots Is set to 160 μm or more.
FIG. 16 shows the toner density (%) of the developer and the reference density detection sensor 55 when the isolated line reference density pattern images Y-1, M-1, C-1, and K-1 are formed by 1 on 4 off of 600 dpi. It is the figure which showed the relationship with a density | concentration detection value (density index). Each image forming unit 30 of the present embodiment forms isolated line reference density pattern images Y-1, M-1, C-1, and K-1 by 1 on 4 off of 600 dpi, and controls the toner supply amount of the present embodiment. In the unit 61, the density index of the isolated line reference density pattern images Y-1, M-1, C-1, and K-1 is set using the relationship shown in FIG. The toner supply amount from each toner container 35 to each developing device 33 is controlled so as to be set to a target density index range that is, for example, 7 to 9%.

Subsequently, image density adjustment performed by functional components in the control unit 60 other than the toner supply amount control unit 61 of the present embodiment, that is, the developing bias control unit 62, the charging bias control unit 63, and the laser light quantity control unit 64. Processing will be described.
As shown in FIG. 3 above, in the image forming apparatus 1 of the present embodiment, in each image forming unit 30, in addition to the isolated line reference density pattern image and the isolated dot reference density pattern image, the isolated line reference density pattern High area ratio reference density pattern images Y-2, M-2, C-2, and K-2 formed at a higher image area ratio than the image and the isolated dot reference density pattern image are formed. If necessary, the developing bias controller 62 is based on the density detection values of the reference density detection sensor 55 for the high area ratio reference density pattern images Y-2, M-2, C-2, and K-2. Is a developing bias value applied to the developing roll 332, a charging bias control unit 63 is a charging bias value supplied to the charging roll 32, and a laser light quantity control unit 64 is a semiconductor laser 27 that irradiates the photosensitive drum 31 from the laser exposure unit 26. The output light quantity value of each is controlled.

Here, in FIG. 17, a 20 mm × 20 mm square pattern image of a 200-line line with an image area ratio of 60% is formed as the high area ratio reference density pattern images Y-2, M-2, C-2, and K-2. 6 is a diagram comparing the relationship between the toner density (%) of the developer and the density detection value (density index) of the reference density detection sensor 55 while changing the temperature and humidity conditions. FIG. 18 shows the relationship between the charge amount (μC / g) of the toner forming the high area ratio reference density pattern image in FIG. 17 and the density detection value (density index) in the reference density detection sensor 55. FIG. As the temperature and humidity conditions to be compared in FIGS. 17 and 18, a temperature of 28 ° C. and a relative humidity of 80% RH and a temperature of 10 ° C. and a relative humidity of 30% RH were set as described above.
As shown in FIG. 17, the density detection value for the high area ratio reference density pattern image shows a different correlation with the toner density under different temperature and humidity conditions. Therefore, if the toner supply amount from each toner container 35 to each developing device 33 is adjusted based on the density detection value related to the high area ratio reference density pattern image, it is difficult to accurately control the toner density. However, on the other hand, as shown in FIG. 18, when the high area ratio reference density pattern image is used, the temperature is 28 ° C. relative humidity 80% RH environment and the temperature 10 ° C. relative humidity 30% RH environment. The density detection value (density index) has a unique correlation with the toner charge amount. When the toner charge amount is high, the density index decreases. When the toner charge amount is low, the density index increases.

By the way, the toner supply amount control unit 61 according to the present embodiment is configured to use the isolated line reference density pattern images Y-1, M-1, C-1, K-1, and the isolated dot reference formed in each image forming unit 30. Based on the density detection values detected by the reference density detection sensor 55 for the density pattern images Y-1 ′, M-1 ′, C-1 ′, and K-1 ′, the toner containers 35Y, 35M, 35C, and 35K. The toner supply amount to each developing device 33 is controlled. However, even if the toner density of the developer is controlled with high accuracy using the isolated line reference density pattern image or the isolated dot reference density pattern image, the toner charge amount varies depending on, for example, the temperature and humidity conditions, and is formed on the paper P. In some cases, the image density is higher or lower than the predetermined density.
Therefore, the control unit 60 according to the present embodiment provides a reference for the high area ratio reference density pattern images Y-2, M-2, C-2, and K-2 that have a unique correlation with the toner charge amount. Based on the density detection value of the density detection sensor 55, the developing bias value applied to the developing roll 332, the charging bias value supplied to the charging roll 32, and the output light quantity value of the semiconductor laser 27 are controlled as necessary. Thus, the image density formed on the paper P is adjusted.

  The control unit 60 of the present embodiment controls the development bias value, the charging bias value, and the output light amount value of the semiconductor laser 27 as follows. That is, as shown in FIG. 18 described above, the toner charge amount has a unique correlation with the density index in both the temperature 28 ° C. relative humidity 80% RH environment and the temperature 10 ° C. relative humidity 30% RH environment. Show the relationship. When the toner charge amount is high, the density index decreases. When the toner charge amount is low, the density index increases. Therefore, when the toner supply amount control unit 61 controls the toner supply amount to each developing device 33, the high area ratio reference density pattern images Y-2, M-2, C-2, K by the reference density detection sensor 55 are used. If the density detection value for -2 exceeds a predetermined density level, it can be determined that the toner density of the developer is appropriate, but the toner charge amount in the developing device 33 is low. If the density detection value is lower than the predetermined density level, it can be determined that the toner density of the developer is appropriate, but the toner charge amount in the developing device 33 is high.

  Therefore, the control unit 60 according to the present embodiment sets the density detection values for the high area ratio reference density pattern images Y-2, M-2, C-2, and K-2 by the reference density detection sensor 55 to a predetermined density level. In the above case, the paper is made to correspond to a low toner charge amount in any one or more of the developing bias value applied to the developing roll 332, the charging bias value supplied to the charging roll 32, and the output light amount value of the semiconductor laser 27 Settings are made to lower the density of the image formed on P. Further, when the density detection values for the high area ratio reference density pattern images Y-2, M-2, C-2, and K-2 are equal to or lower than a predetermined density level, the paper is made to correspond to a high toner charge amount. Settings are made to increase the density of the image formed on P.

  Here, FIG. 19 is a diagram for explaining a density detection value region in which image density adjustment processing is performed by the developing bias control unit 62, the charging bias control unit 63, and the laser light quantity control unit 64. As shown in FIG. 19, the density detection value (density index) for the isolated line reference density pattern image or the isolated dot reference density pattern image is in an area (density setting range) where the toner density of the developer is set within a predetermined range. When the density detection value for the high area ratio reference density pattern images Y-2, M-2, C-2, and K-2 is a region (density region 1) having a predetermined density level 1 or higher when controlled. In addition, any one or more of the developing bias control unit 62, the charging bias control unit 63, and the laser light amount control unit 64 perform setting so as to reduce the density of the image formed on the paper P. Further, when the density detection value for the high area ratio reference density pattern images Y-2, M-2, C-2, and K-2 is an area (density area 2) that is equal to or lower than a predetermined density level 2, development bias is applied. Any one or more of the control unit 62, the charging bias control unit 63, and the laser light amount control unit 64 performs setting to increase the image density formed on the paper P.

As an example, when the density detection values for the high area ratio reference density pattern images Y-2, M-2, C-2, and K-2 are density level 1 or higher (density area 1 in FIG. 19). Is the difference between the potential VL which is the latent image potential in the highest density area formed on the photosensitive drum 31 and the developing bias voltage VDC applied to the developing roll 332 without supplying toner to the developing device 33 ( The development bias control unit 62 controls the development bias voltage VDC so that | VDC-VL |) becomes small, and the laser light quantity control unit 64 outputs the semiconductor laser 27 irradiated to the photosensitive drum 31 from the laser exposure unit 26. Control the light intensity value. As a result, the development contrast potential which is the difference (| V−VDC |) between the exposure portion potential V and the development bias voltage VDC is reduced, and the image density formed on the paper P is set low.
In this case, the development bias control is performed so that the difference between the development bias voltage VDC and the charging potential VH (| VH−VDC |) or the ratio between | VH−VDC | and | VDC−VL | does not fluctuate. The unit 62 controls the developing bias voltage VDC, and the laser light amount control unit 64 controls the output light amount value of the semiconductor laser 27. This is to suppress the so-called “ground fog” in the white background (background).

Further, when the density detection values for the high area ratio reference density pattern images Y-2, M-2, C-2, and K-2 are equal to or lower than the density level 2 (density area 2 in FIG. 19), the developing device. The developing bias control unit 62 controls the developing bias voltage VDC so that the difference between the potential VL and the developing bias voltage VDC (| VDC−VL |) becomes large without supplying toner to 33, and the laser light quantity The control unit 64 controls the output light amount value of the semiconductor laser 27. As a result, the development contrast potential which is the difference (| V−VDC |) between the exposure portion potential V and the development bias voltage VDC is increased, and the image density formed on the paper P is set high.
In this case, the development bias control is performed so that the difference between the development bias voltage VDC and the charging potential VH (| VH−VDC |) or the ratio between | VH−VDC | and | VDC−VL | does not fluctuate. The unit 62 controls the developing bias voltage VDC, and the laser light amount control unit 64 controls the output light amount value of the semiconductor laser 27. Similarly, this is to suppress so-called “ground fogging” in the white background (background).
In this way, in the control unit 60 of the present embodiment, the image density formed on the paper P is stably maintained in accordance with the change in the toner charge amount.

  Further, FIG. 20 shows the toner density of the developer when forming a high area ratio reference density pattern image Y-2, M-2, C-2, K-2 of 200 lines with an image area ratio of 60% ( %) And a density detection value (density index) in the reference density detection sensor 55. FIG. In each image forming unit 30 of the present embodiment, a high area ratio reference density pattern image Y-2, M-2, C-2, K-2 of 200 lines and a line area of 60% is formed and controlled. Based on the density index when the toner density of the developer is set to, for example, 7 to 9%, which is an appropriate toner density range, for example, the developing unit 60 and the charging bias control unit 63, the density level 1 and the density level 2 of FIG. In the developing bias control unit 62, the charging bias control unit 63, and the laser light amount control unit 64 of the present embodiment, the high area ratio reference density pattern images Y-2, M-2, and C-2 by the reference density detection sensor 55 are used. , K-2 are compared with the set density level 1 and density level 2, and the above-described control is performed.

The image density adjustment processing by the developing bias control unit 62, the charging bias control unit 63, and the laser light amount control unit 64 is performed by any one of the developing bias control unit 62, the charging bias control unit 63, and the laser light amount control unit 64 or It is possible to adopt a mode in which a plurality of modes are used, or a mode in which all of the development bias control unit 62, the charging bias control unit 63, and the laser light quantity control unit 64 are used.
In addition to the output light quantity value of the semiconductor laser 27 as a latent image forming condition and the charging bias value supplied to the charging roll 32 and the developing bias supplied to the developing roll 332 as a developing condition, the temperature of the fixing device 80 Alternatively, image density adjustment processing using the primary transfer bias value of the primary transfer roll 42, the secondary transfer bias value of the secondary transfer roll 40, or the like can be performed.
Furthermore, in FIG. 20, the case where the high area ratio reference density pattern images Y-2, M-2, C-2, and K-2 of 200 lines with an image area ratio of 60% are formed is shown as an example. However, from the results of experiments conducted separately from this, the development contrast potential using the high area ratio reference density pattern images Y-2, M-2, C-2, and K-2 having an image area ratio of 50% or more is described. If the above control is performed, the image density is stably maintained.

Subsequently, toner empty detection in each toner container 35 performed by the control unit 60 of the present embodiment will be described.
The toner supply amount control unit 61 of the present embodiment uses the density index of the isolated line reference density pattern images Y-1, M-1, C-1, and K-1 as the target density based on the relationship shown in FIG. The toner supply amount from each toner container 35 to each developing device 33 is controlled so as to be set in the index range. At this time, the control unit 60 of the present embodiment transmits a control signal instructing to replenish toner to each toner container 35 from the toner supply amount control unit 61, but the isolated line reference density When the density detection value (density index) detected by the reference density detection sensor 55 for the pattern image or the isolated dot reference density pattern image does not exceed a predetermined value, the isolated line reference density pattern image or density line image that does not exceed the predetermined value It is determined that the amount of toner in the toner container 35 for supplying toner to the image forming unit 30 on which the isolated dot reference density pattern image is formed is “0” (so-called “empty”). For example, the density index of the isolated line reference density pattern image Y-1 formed by the image forming unit 30Y has transmitted a control signal instructing to supply toner from the toner supply amount control unit 61 to the toner container 35Y. However, if the predetermined value is not exceeded, the toner amount in the toner container 35Y is determined to be “0”. The control unit 60 here functions as a determination unit.
When the control unit 60 determines that the toner amount in the toner container 35 is “0”, the corresponding toner container 35, for example, the toner container 35Y, is displayed on the operation display panel (not shown) of the image forming apparatus 1. A warning is displayed to warn the user that the toner inside is “empty”. At that time, a warning can be given by voice. Furthermore, the operation of the image forming apparatus 1 can be stopped.

Note that it is also possible to determine whether or not the toner amount in the toner container 35 is “0” using the density detection value for the high area ratio reference density pattern image.
The determination that the toner amount in the toner container 35 is “0” is made by controlling the toner supply amount from each toner container 35 to each developing device 33 by the toner supply amount control unit 61, and the isolated line reference thereafter. When the density pattern image or the isolated dot reference density pattern image is repeatedly detected by the reference density detection sensor 55 a plurality of times and the density detection value detected by the reference density detection sensor 55 nevertheless does not exceed a predetermined value. It can also be determined that the toner amount in the corresponding toner container 35 is “0”.

  As described above, in the image forming apparatus 1 of the present embodiment, the density detection value (density index) for the isolated line reference density pattern image or the isolated dot reference density pattern image, the high area ratio reference density pattern image, and the toner supply Whether or not the specific toner container 35 is empty is determined based on a control signal for instructing the toner container 35 to replenish toner from the amount control unit 61. When it is determined that the specific toner container 35 is empty, the user is notified that the specific toner container 35 is empty.

  Note that in the image forming apparatus 1 of the present embodiment, the density detection unit detects the density of the isolated line reference density pattern image or the isolated dot reference density pattern image formed on the intermediate transfer belt 41 or the high area ratio reference density pattern image. The configuration for detection by the reference concentration detection sensor 55 as an example has been described. However, the reference density detection sensor 55 detects the density of the isolated line reference density pattern image or isolated dot reference density pattern image formed on the photosensitive drum 31 or the paper P, or the high area ratio reference density pattern image. It can also be adopted.

  As described above, in the control unit 60 of the present embodiment, the isolated line reference density pattern images Y-1, M-1, C-1, K-1, or isolated dots formed in each image forming unit 30. Based on the density detection values detected by the reference density detection sensor 55 for the reference density pattern images Y-1 ′, M-1 ′, C-1 ′, and K-1 ′, each developing device 33 is supplied from each toner container 35. Control the amount of toner supplied to At this time, when the isolated line reference density pattern images Y-1, M-1, C-1, and K-1 are used, the line width of the isolated line is set to 20 μm or more and 130 μm or less, and the isolated line and the isolated line are isolated. The line spacing is set to 170 μm or more. When the isolated dot reference density pattern images Y-1 ′, M-1 ′, C-1 ′, and K-1 ′ are used, the dot diameter of the isolated dots is set to 30 μm or more and 200 μm or less, and the adjacent dots Is set to 160 μm or more. Thereby, the toner density of the developer held in each developing device 33 is controlled with high accuracy regardless of the temperature and humidity conditions. Therefore, it is possible to form a high quality image with stable image density and little color unevenness.

Further, the control unit 60 of the present embodiment controls the density detection values for the high area ratio reference density pattern images Y-2, M-2, C-2, and K-2 when the toner density of the developer is controlled. The image density formed on the paper P is stabilized by adjusting various image forming conditions based on the above. Accordingly, the density of the image formed on the paper P is stabilized in accordance with the fluctuation of the toner charge amount.
Furthermore, when the control unit 60 of the present embodiment controls the toner supply amount, the reference density detection sensor 55 for the isolated line reference density pattern image, the isolated dot reference density pattern image, and the high area ratio reference density pattern image. Whether the specific toner container 35 is empty is determined based on the detected density value and the control signal instructing the toner supply amount control unit 61 to replenish the toner to the toner container 35. . Thereby, it is possible to notify the user that the specific toner container 35 is empty. Further, the formation of an image having a low density is suppressed.

[Embodiment 2]
In the first embodiment, each toner container is based on the detected density value detected by the reference density detection sensor 55 for the isolated line reference density pattern image or the isolated dot reference density pattern image formed by each image forming unit 30. The configuration for controlling the toner supply amount from each of the developing devices 33 to the developing device 33 has been described. In the present embodiment, when the toner supply amount control shown in the first embodiment is performed, a mechanism for supplementing a time delay until the toner density of the developer is controlled to the target value is further provided. The configuration will be described. In addition, the same code | symbol is used about the structure similar to Embodiment 1, and the detailed description is abbreviate | omitted here.

As described in the first exemplary embodiment, the control unit 60 is configured so that the toner supply amount control unit 61 uses the isolated line reference density pattern images Y−1, M−1, and C− formed by the image forming units 30. 1, K-1 or isolated dot reference density pattern images Y-1 ′, M-1 ′, C-1 ′, and K-1 ′ based on the density detection values detected by the reference density detection sensor 55. The amount of toner supplied from the toner containers 35Y, 35M, 35C, and 35K to each developing device 33 is controlled.
Further, the control unit 60 of the present embodiment controls the isolated line reference density pattern images Y-1, M-1, and C- formed by the image forming units 30 in accordance with the control of the toner supply amount. The development contrast based on the density detection value detected by the reference density detection sensor 55 for 1, K-1 or isolated dot reference density pattern images Y-1 ′, M-1 ′, C-1 ′, K-1 ′. Control V1.

  In the toner supply amount control unit 61 of the present embodiment, for example, the isolated line reference density pattern images Y-1, M-1, C-1, K-1, and the isolated dot reference density using the relationship shown in FIG. The density index of the pattern images Y-1 ′, M-1 ′, C-1 ′, and K-1 ′ is, for example, 7 to 9%, which is an appropriate range of toner density (appropriate toner density range) of the developer. Thus, the toner supply amount from each toner container 35 to each developing device 33 is controlled. However, when the density detection value detected by the reference density detection sensor 55 is lower than the appropriate range, toner supply from each toner container 35 to each developer 33 is started based on the control of the toner supply amount control unit 61. Even so, there is a time delay until the toner density of the developer in each developing device 33 reaches the appropriate range. The same applies when the density detection value is higher than the appropriate range. Therefore, the toner concentration of the developer in the developing device 33 varies between the start of toner supply to each developing device 33 and the time when the toner concentration reaches an appropriate range. That is, for example, in the width direction in the developing device 33, a state where a region where the toner density of the developer is high and a region where the toner concentration is low occurs. Further, in the developer circulation path in the developing device 33, a state where a region where the toner concentration of the developer is high and a region where the toner concentration is low occurs.

  On the other hand, as shown in FIG. 10 described above, the development contrast potential V1 is small in a latent image in which the line width of the isolated line and the dot diameter of the isolated dot are small. As a result, if the exposure portion potential V fluctuates even slightly in a latent image with a small line width or dot diameter, the variation rate of the development contrast potential V1 becomes large. For this reason, if there is a variation in the toner density of the developer, the area that is developed with the developer having a high toner density is developed thicker, whereas the area that is developed with the developer having a low toner density is not developed at all. Sometimes it happens. As described above, in a latent image having a small line width of isolated lines and a dot diameter of isolated dots, the variation in the toner density of the developer greatly affects the line width of the isolated lines and the size of the dot diameter of the isolated dots. .

Therefore, in the control unit 60 according to the present embodiment, when the toner supply to each developing device 33 is controlled in a situation where the density detection value detected by the reference density detection sensor 55 is lower than the appropriate range, the developing device The toner is supplied to 33, and the development contrast potential V1 is set to be large.
Here, FIG. 21 is a diagram illustrating an example of the control of the development contrast V1 performed by the control unit 60 when the density detection value detected by the reference density detection sensor 55 is lower than the appropriate range. FIG. 21A shows a potential state before controlling the development contrast V1, and FIG. 21B shows a potential state after controlling the development contrast V1. As shown in FIG. 21, when the density detection value of the reference density detection sensor 55 is lower than the appropriate range, the development bias controller 62 applies the development bias applied to each development roll 332 of the image forming unit 30. The voltage VDC is controlled so that the difference (| VH−VDC |) from the charging potential VH becomes small. As a result, the development contrast potential V1 that is the difference (| V−VDC |) between the exposure portion potential V and the development bias voltage VDC is set large.
In this case, the amount of laser light is not changed so that the difference (| VDC−VL |) between the potential VL, which is the latent image potential in the highest density region formed on the photosensitive drum 31, and the developing bias voltage VDC does not fluctuate. The control unit 64 reduces the output light amount value of the semiconductor laser 27 irradiated to the photosensitive drum 31 from the laser exposure unit 26. The reason why | VDC-VL | is controlled so as not to fluctuate is to suppress fluctuations in image density in the high density region.
In this way, when the developer toner concentration in each developing device 33 is unstable in a state where it is lower than the appropriate range, the developing capability for a latent image with a small line width of isolated lines and a small dot diameter of isolated dots is improved. The line width of the isolated line and the dot diameter of the isolated dot are stabilized.

In the control unit 60 of the present embodiment, when the toner supply to each developing device 33 is controlled in a situation where the density detection value detected by the reference density detection sensor 55 is higher than the appropriate range, the developing device The toner is not supplied to 33, and the development contrast potential V1 is set to be small.
Here, FIG. 22 is a diagram illustrating an example of the control of the development contrast V1 performed by the control unit 60 when the density detection value detected by the reference density detection sensor 55 is higher than the appropriate range. FIG. 22A shows the potential state before controlling the development contrast V1, and FIG. 22B shows the potential state after controlling the development contrast V1. As shown in FIG. 22, when the density detection value of the reference density detection sensor 55 is higher than the appropriate range, the development bias controller 62 applies the development bias applied to each development roll 332 of the image forming unit 30. The voltage VDC is controlled so that the difference (| VH−VDC |) from the charging potential VH becomes large. As a result, the development contrast potential V1 that is the difference (| V−VDC |) between the exposure portion potential V and the development bias voltage VDC is set to be small.
In this case, the amount of laser light is not changed so that the difference (| VDC−VL |) between the potential VL, which is the latent image potential in the highest density region formed on the photosensitive drum 31, and the developing bias voltage VDC does not change. The control unit 64 increases the output light amount value of the semiconductor laser 27 irradiated from the laser exposure unit 26 to the photosensitive drum 31. The reason why | VDC-VL | is controlled so as not to fluctuate is to suppress the fluctuation of the image density in the high density region, as in the above case.
As a result, when the toner density of the developer in each developing device 33 is unstable in a state where it is higher than the appropriate range, the developing ability for a latent image having a small line width of isolated lines or a small dot diameter of isolated dots is lowered, and The line width of the line and the dot diameter of the isolated dot are stabilized.

Here, FIG. 23 is a diagram comparing the case where the development contrast potential V1 is controlled and the case where it is not controlled when the toner supply to each developing device 33 is controlled. In FIG. 23, the horizontal axis represents the number of prints, and the vertical axis represents the image density. The image density on the vertical axis is a 1 on 1 off isolated line reference density pattern image. Furthermore, during printing, the temperature and humidity environment is changed between a 22 ° C. relative humidity 55% RH environment, a 28 ° C. relative humidity 80% RH environment, and a 10 ° C. relative humidity 30% RH environment to evaluate density. Went.
As shown in FIG. 23, by controlling the development contrast potential V1, the density of the 1 on 1 off isolated line reference density pattern image is higher than the target image density (target value) regardless of changes in the temperature and humidity environment. It was proved to be stable at the concentration value. As described above, by stabilizing at a density value higher than the target image density, it is possible to suppress the occurrence of a situation in which an image with a small line width of isolated lines or a dot diameter of isolated dots is not developed at all.

  As described above, in the control unit 60 according to the present embodiment, when toner supply to each developing device 33 is controlled, the toner concentration is increased until the toner concentration of the developer reaches the target value (appropriate range). The development contrast potential V1 is controlled under an unstable condition. This compensates for a time delay until the toner density of the developer is controlled to the target value, and stabilizes the line width of the isolated line and the dot diameter of the isolated dot.

1 is a diagram illustrating an example of a configuration of an image forming apparatus of the present invention. 2 is a diagram illustrating an example of a configuration of an image forming unit. FIG. FIG. 4 is a diagram illustrating an example of a state in which two different types of reference density pattern images formed by each image forming unit are primarily transferred onto an intermediate transfer belt. It is a block diagram explaining the functional structure which performs the image density adjustment process in a control part. It is a block diagram which shows the internal structure of a control part. FIG. 6 is a diagram comparing the relationship between the developer toner density and the density index for isolated line reference density pattern images while changing the temperature and humidity conditions. FIG. 6 is a diagram illustrating a relationship between a charge amount of a toner that forms an isolated line reference density pattern image and a density index. It is a figure which showed the relationship between the line width of the isolated line of an isolated line reference density pattern image, and the dispersion | variation (density fluctuation rate) of the density detection value of an isolated line reference density pattern image. FIG. 6 is a diagram showing a relationship between a dot diameter of an isolated dot of a reference density pattern image and a variation (density variation rate) of a density detection value of the isolated dot reference density pattern image. FIG. 5 is a diagram showing a relationship among a charging potential VH, an exposure portion potential V, and a developing bias direct current component VDC. FIG. 6 is a diagram comparing the relationship between the toner density (%) of a developer and a density index when an isolated line reference density pattern image is formed by changing the interval between isolated lines. FIG. 5 is a diagram comparing the relationship between the toner density (%) of a developer and a density index when an isolated dot reference density pattern image is formed while changing the interval between isolated dots. FIG. 5 is a diagram comparing the relationship between the developer toner density (%) and the density index when an isolated line reference density pattern image is formed, by changing the line width of the isolated line. FIG. 6 is a diagram comparing the relationship between the toner density (%) of a developer and a density index when an isolated dot reference density pattern image is formed by changing the diameter of an isolated dot. (A) illustrates the electric field formed between the electrostatic latent image of the isolated pattern image and the developing roll, and (b) illustrates the electric field formed between the electrostatic latent image of the high density image and the developing roll. FIG. FIG. 6 is a diagram showing a relationship between a toner density of a developer and a density index when an isolated line reference density pattern image is formed by 1 on 4 off of 600 dpi. FIG. 6 is a diagram illustrating a relationship between a toner density of a developer and a density index when a high area ratio reference density pattern image is formed. FIG. 6 is a diagram showing the relationship between the charge amount of a toner forming a high area ratio reference density pattern image and a density index while changing the temperature and humidity conditions. It is a figure explaining the density | concentration detection value area | region where an image density adjustment process is performed in a developing bias control part, a charging bias control part, and a laser light quantity control part. FIG. 5 is a diagram illustrating a relationship between a toner density of a developer and a density index when a high area ratio reference density pattern image having a line area of 200 lines and an image area ratio of 60% is formed. It is a figure explaining an example of control of development contrast V1 which a control part performs when a density detection value detected by a standard density detection sensor is lower than an appropriate range. It is a figure explaining an example of control of development contrast V1 which a control part performs when a density detection value detected by a standard density detection sensor is higher than an appropriate range. FIG. 6 is a diagram comparing the case where the development contrast potential V1 is controlled and the case where it is not controlled when controlling the toner supply to each developing device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 20 ... Image forming process part, 30 (30Y, 30M, 30C, 30K) ... Image forming unit, 31 ... Photosensitive drum, 32 ... Charging roll, 33 (33Y, 33M, 33C, 33K) ... Developing unit, 35Y, 35M, 35C, 35K ... toner container, 41 ... intermediate transfer belt, 55 ... reference density detection sensor, 60 ... control unit, 61 ... toner supply amount control unit, 62 ... development bias control unit, 63 ... charging Bias control unit, 64... Laser light amount control unit

Claims (23)

Developing means for developing the electrostatic latent image formed on the image carrier with a developer containing a carrier and toner;
From the toner pattern developed on the image carrier by the developing means or the first pattern composed of predetermined isolated lines or dots in the toner image transferred from the image carrier onto the transfer medium. Density detecting means for detecting the density of the toner image,
A toner amount adjusting means for adjusting the amount of toner supplied to the developing means based on the density of the toner image comprising the first pattern detected by the density detecting means ;
The toner image comprising the second pattern having a higher image area ratio than the first pattern in the toner image developed on the image carrier or the toner image transferred on the transfer medium. An image forming apparatus comprising: control means for controlling a development contrast potential based on the density detected by the density detection means . Further comprising latent image forming means for forming an electrostatic latent image on the image carrier,
2. The image according to claim 1 , wherein the control unit controls one or both of a latent image forming condition set by the latent image forming unit and a developing condition set by the developing unit. Forming equipment.   The toner amount adjusting unit adjusts the toner amount based on a density of the toner image including the first pattern composed of the isolated lines whose line width is set to 20 μm or more and 130 μm or less. The image forming apparatus according to claim 1. The toner amount adjusting means adjusts the toner amount based on the density of the toner image composed of the first pattern composed of the isolated lines whose mutual interval is set to 170 μm or more. The image forming apparatus according to claim 3 .   The toner amount adjusting unit adjusts the toner amount based on a density of the toner image including the first pattern including the isolated dots having a dot diameter set to 30 μm or more and 200 μm or less. The image forming apparatus according to claim 1. The toner amount adjusting means adjusts the toner amount based on the density of the toner image composed of the first pattern composed of the isolated dots whose mutual interval is set to 160 μm or more. The image forming apparatus according to claim 5 . Toner supply means for supplying toner to the developing means;
Determination means for determining that the remaining amount of toner in the toner supply means is low when the density detected by the density detection means after the toner amount adjustment means has adjusted the toner amount is below a predetermined value. The image forming apparatus according to claim 1, further comprising:   The image forming apparatus according to claim 1, further comprising a control unit that controls a development contrast potential based on the density of the toner image including the first pattern detected by the density detection unit. apparatus. The control unit sets the development contrast potential to be large when the density of the toner image having the first pattern detected by the density detection unit is smaller than a first predetermined value, and the density 9. The image forming apparatus according to claim 8 , wherein the development contrast potential is set to be small when the value is larger than the second predetermined value. A latent image forming means for forming an electrostatic latent image on the image carrier by charging and exposure;
Developing means for developing the electrostatic latent image formed on the image carrier by the latent image forming means with a developer containing a carrier and toner;
From the toner pattern developed on the image carrier by the developing means or the first pattern composed of predetermined isolated lines or dots in the toner image transferred from the image carrier onto the transfer medium. Density detecting means for detecting the density of the toner image,
A toner amount adjusting means for adjusting the amount of toner supplied to the developing means based on the density of the toner image comprising the first pattern detected by the density detecting means ;
The toner image comprising the second pattern having a higher image area ratio than the first pattern in the toner image developed on the image carrier or the toner image transferred on the transfer medium. Based on the density detected by the density detecting means, one of the charging potential set by the latent image forming means, the exposure light quantity, the developing potential set by the developing means, or a combination thereof is controlled. An image forming apparatus, comprising: The toner amount adjusting unit adjusts the toner amount based on a density of the toner image including the first pattern composed of the isolated lines whose line width is set to 20 μm or more and 130 μm or less. The image forming apparatus according to claim 10 . The toner amount adjusting means adjusts the toner amount based on the density of the toner image composed of the first pattern composed of the isolated lines whose mutual interval is set to 170 μm or more. The image forming apparatus according to claim 11 . The toner amount adjusting unit adjusts the toner amount based on a density of the toner image including the first pattern including the isolated dots having a dot diameter set to 30 μm or more and 200 μm or less. The image forming apparatus according to claim 10 . The toner amount adjusting means adjusts the toner amount based on the density of the toner image composed of the first pattern composed of the isolated dots whose mutual interval is set to 160 μm or more. The image forming apparatus according to claim 13 . Toner supply means for supplying toner to the developing means;
Determination means for determining that the remaining amount of toner in the toner supply means is low when the density detected by the density detection means after the toner amount adjustment means has adjusted the toner amount is below a predetermined value. The image forming apparatus according to claim 10 , further comprising: The image forming apparatus according to claim 10 , further comprising a control unit that controls a development contrast potential based on the density of the toner image including the first pattern detected by the density detection unit. apparatus. The control unit sets the development contrast potential to be large when the density of the toner image having the first pattern detected by the density detection unit is smaller than a first predetermined value, and the density The image forming apparatus according to claim 16 , wherein the development contrast potential is set to be small when the value is larger than a second predetermined value. On the computer,
The toner image developed on the image carrier by the developing means or the first pattern composed of a predetermined isolated line or dot in the toner image transferred from the image carrier onto the transfer medium. A function for acquiring density information about a toner image;
A function of adjusting the amount of toner supplied to the developing means based on the density information relating to the toner image comprising the first pattern ;
The toner image comprising the second pattern having a higher image area ratio than the first pattern in the toner image developed on the image carrier or the toner image transferred on the transfer medium. A program for realizing a function of controlling a development contrast potential based on density information . Further realizing a function of determining that the remaining amount of toner in the toner supply means for supplying toner to the developing means is low when the density information acquired after adjusting the toner amount indicates a density equal to or lower than a predetermined value. The program according to claim 18 . 19. The program according to claim 18 , further comprising a function of controlling a development contrast potential based on the acquired density information regarding the toner image including the acquired first pattern. On the computer,
The electrostatic latent image formed on the image carrier by charging and exposure by the latent image forming unit is developed by the developing unit and transferred from the toner image formed on the image carrier to the transfer medium. A function of acquiring density information relating to the toner image composed of a first pattern composed of predetermined isolated lines or dots in the toner image,
A function of adjusting the amount of toner supplied to the developing means based on the density information relating to the toner image comprising the first pattern ;
The toner image comprising the second pattern having a higher image area ratio than the first pattern in the toner image developed on the image carrier or the toner image transferred on the transfer medium. A function of controlling any one of a charging potential set by the latent image forming unit, an exposure light amount or a developing potential set by the developing unit, or a combination thereof based on density information ; A program characterized by being realized. Further realizing a function of determining that the remaining amount of toner in the toner supply means for supplying toner to the developing means is low when the density information acquired after adjusting the toner amount indicates a density equal to or lower than a predetermined value. The program according to claim 21, wherein: The program according to claim 21 , further comprising a function of controlling a development contrast potential based on the acquired density information regarding the toner image including the first pattern.

Images