JP3372881B2 - Image forming device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine or a printer.

[0002]

2. Description of the Related Art Recently, an image forming apparatus as a digital data information transmission by a data communication network and a hard output device of the information has been actively proposed. An image forming apparatus of this type includes a digital printer or a digital copying machine.

FIG. 19 shows a schematic structure of a digital printer. The photoconductor (photosensitive drum) 1 has a photoconductive layer provided on a cylindrical conductive substrate, and is rotatably supported in the direction of arrow R1 in the figure. Then, around the photosensitive drum 1, a scoro-tocon charger (primary charger) that evenly charges the surface of the photosensitive drum 1 substantially in order along the rotation direction.
2. An original is read, the photosensitive drum 1 is exposed based on an image signal proportional to the density of an image, and an exposure device 3 that forms an electrostatic latent image, toner is attached to the electrostatic latent image and developed as a toner image. The developing device 7, the corona transfer charger (transfer charger) 8 that transfers the toner image formed on the photosensitive drum 1 onto the transfer paper P that is a transfer material, and the transfer paper P on which the toner image is transferred to the photosensitive drum 1 An electrostatic separation charging device (separation charging device) 9, a cleaning device 13 that removes residual toner on the photosensitive drum 1 after transferring a toner image, a pre-exposure lamp 30 that removes residual charge on the photosensitive drum 1, and the like. Are arranged. The transfer paper P on which the toner image is transferred is
After being separated from the photosensitive drum 1, it is conveyed to the fixing device 12, where the toner image on the surface is fixed, and a desired print image is formed and discharged to the outside of the image forming apparatus main body.

The reader section 18 irradiates the original 15 placed on the original glass table 14 with an illumination lamp 16 and reflects the reflected light into a photoelectric conversion element (1-line CCD) 19.
By forming an image on the top, it is converted into an electric signal corresponding to the image information. Here, the reflected light from the document 15 illuminated by the illumination lamp 16 is reflected by the mirrors 17a, 17b, 1
The photoelectric conversion element 19 is guided by the lens 17d after being guided to 7c.
Imaged above. The electric signal output from the photoelectric conversion element 19 is A / D converted by the A / D converter 21 to be 8-bit digital image data, and then the black signal generation circuit 22 uses the luminance information as density information. Is converted into image density data by the binarization circuit 23.

The 8-bit digital image data signal generated as described above is input to the laser drive circuit 24. The laser drive circuit 24 is a well-known PWM circuit, and according to the magnitude of the input image density signal, Semiconductor laser 20
Modulates the light emission time for n / off.

For example, when image data for each pixel is input in the laser scanning direction as shown in FIG. 4A, the drive signal for turning the laser on / off is as shown in FIG. 4B. ing. That is, the on-duty of the laser drive signal when the image data is 00 hex is 5% of the 1-pixel scan time, the on-duty of the laser drive signal when the image data is FF hex is 85% of the 1-pixel scan time, and so on. In this way, shading is realized by making the area gradation within one pixel.

Further, FIG. 6 shows a general IL characteristic (driving current-light quantity characteristic) of the laser.
The drive currents used when off are Ion / Io, respectively.
Since it is ff, the laser drive current for the image signal of FIG. 4 is as shown in (c), and this is the current that the PWM circuit drives the laser.

This laser drive system is roughly classified into the above-mentioned PWM circuit and binary laser drive circuit. PW
The M circuit modulates the pulse width signal corresponding to the time during which the semiconductor laser emits light according to the magnitude of the input image density signal as described above, while the binarization circuit changes the pulse width signal according to the pixel size. The signal is converted into a two-stage signal of a specific on-light emission signal and an off signal, which is input to the laser drive circuit 24 to turn on / off the laser (semiconductor laser element) 20. As a typical binarization method, there is a method of generating a binarized signal by a method such as an error diffusion method or a dither method based on image data. It is constant regardless of. The difference is that a pixel having a low density emits a laser with a low probability, and a pixel having a high density emits a laser with a high probability.

As described above, the laser light emitted according to the image signal is raster-scanned and written on the photosensitive drum 1 via the polygon mirror scanner 28 and the mirror 17f which rotate at high speed, and a digital electrostatic latent image is stored as image information. Form.

Conventionally, as an electrophotographic method, US Pat. No. 2,297,961 and JP-B-42-23910 are known.
A large number of methods are known, as described in Japanese Patent Publication No. 43-24748 and Japanese Patent Publication No. 43-24748. In general,
An electric latent image is formed on a photosensitive drum, which is a recording medium using a photoelectric substance, by various means, and then the latent image is developed with a toner (developer), and the obtained toner image is formed as necessary. The toner image is transferred onto a transfer material such as paper, and the toner image is fixed on the transfer material by heating or solvent vapor to obtain a copied image.

Various developing methods are also known for visualizing an electric latent image by using a developer. For example,
The magnetic brush developing method described in U.S. Pat. No. 2,874,063, the powder cloud method described in U.S. Pat. No. 2,21,776, a fur brush developing method, a liquid developing method, etc. There is a way. Among these developing methods, a magnetic brush developing method using a two-component developer mainly composed of a toner and a carrier has been widely put into practical use. Of the two-component developer, that is, deterioration of the toner and fluctuation of the mixing ratio of the toner and the carrier.

In order to avoid such drawbacks, various developing methods using a one-component developer consisting of only toner have been proposed. According to this developing method, it is not necessary to control the mixing ratio of the toner to the carrier, which has the advantage of simplifying the apparatus.

In the above-mentioned one-component developing method, it is difficult to apply a charge to the toner because no carrier is used. Therefore, various methods for charging the toner have been studied.

For example, Japanese Patent Laid-Open Publication No. 50-4539 discloses that
A method of imparting an electrostatic charge by frictional charging with a toner carrier, and JP-A-54-2100 describe a method of providing a friction member and imparting an electrostatic charge by frictional charging with the friction member. ing. Further, a method of applying a voltage to the friction member, a method of charging the toner by a charging member such as corona charging, and the like have been devised.

Further, as a transfer material conveying path, conventionally,
A desired print image is formed on the transfer material, and the transfer material is discharged to the outside of the image forming apparatus main body. However, the transfer material only has a conveyance path to a discharge tray, a sorting device, a double-sided conveyance device, or a conveyance device for multiplex printing.

[0016]

According to the above-mentioned conventional example, a system having a means (hereinafter referred to as "through-pass double-sided transport system") for transporting the transfer material without retaining a plurality of transfer materials after fixing is provided. , The transfer material heated up to about 200 ° C. in the fixing process reaches the sheet feeding step again within a short time so that the heat radiation is not completely completed, and reaches the transfer position (transfer portion) via the transfer / transport member. Becomes That is, the re-feeding in the through-pass double-sided conveyance has more heat diffusion and influence than the case where the transfer material is fed from the transfer material feeder. Particularly in an apparatus capable of high-speed image formation with a long service life, the transfer material comes into contact with the transport roller while still having a high heat of about 50 to 100 ° C., so that the transfer roller is configured to feed and transport the transfer material. Precipitated substances from the rubber material may be offset to the paper and carried to the photoconductor and re-attached to the photoconductor surface, and after long-term use, the substances are gradually laminated to form a film on the photoconductor. However, if the film absorbs moisture in the air and absorbs moisture, the surface resistance of the photoconductor decreases, and the charge of the electrostatic latent image after exposure including image information data cannot be retained and the surface direction of the surface cannot be maintained. The image is disturbed and disturbs a part of the image information (a part corresponding to the paper feed roller or the transport roller) or the whole, and as a phenomenon on the image, the image flows as if the water-based ink flows into water.

When the corona charging method is used as a method for primary charging the photoreceptor, ozone generated by corona discharge or a nitrate substance as a discharge product forms a film on the photoreceptor, and Image deletion occurs in the same manner as the adhered substance, but when mixed with the above-mentioned adhered substances and laminated, the image deterioration is further deteriorated. The same applies to the post charger, the transfer charger, and the separation charger.

In order to solve the above-mentioned problems, a method has been conventionally used in which a developer is adhered onto a photosensitive member and supplied to a cleaning device to enhance the polishing effect on the surface of the photosensitive member. Regarding the timing of supply, it is necessary to supply in a state other than image formation, and it is also necessary to maximize the time for polishing after the supply. However, in order to take a sufficient polishing time, there is a problem that the preparation time for starting up the image forming apparatus becomes very long. Also,
Although ozone gas is sucked and discharged by sucking air from inside the shield case of each charger with a fan, it is not possible to completely discharge the gas, and it is not possible to expose the ozone gas due to substances adhering to the surface of the photoconductor. It was not possible to prevent adverse effects on the body, and image deletion could not be completely suppressed.

Particularly, when an a-Si photoconductor is used as a photoconductor in a high humidity environment, ozone is often generated due to discharge over a long period of time, and if left for a long period of time later, the ozone product or discharge product thereof is generated. An object adheres to the surface of the photoconductor and absorbs moisture to cause an image-like image in the initial image after the power of the image forming apparatus is turned on.

Further, when the laser or LED spot exposure writing is performed on the photosensitive member by digital data, the phenomenon of the image deletion becomes remarkable. Laser spot size of 600 dpi, spot diameter 50-70
In the case of μm, it becomes a minute dot, and even a slight disturbance of electric charge is visually integrated as an aggregate and recognized as a difference from a normal portion, which is more noticeable and manifests as a violent image flow phenomenon. It will turn.

Further, as the developing system, in the electric field flight developing method using a one-component magnetic developer mainly utilizing the electric field developing phenomenon, and the jumping developing method, the disturbance of the electrostatic latent image on the photoreceptor is faithfully reproduced as the image. The surface resistance of the developer particles decreases when the image forming apparatus is started up in a high-humidity environment and the developer adsorbs moisture while being left alone.
Since the amount of electric charge to be held by the developer cannot be maintained and the developing efficiency is slightly decreased, there is a problem that the density decrease and the image deletion phenomenon are more easily visible. This obstacle is aggravated as the reproducibility of the fine dots is lowered depending on the moisture adsorbed to the developer particles, that is, the defect occurs as a decrease in density or deterioration of image flow depending on humidity or the amount of moisture in the air.

The present invention has been made in view of the above circumstances, and even when the amount of water in the surrounding environment changes,
An object of the present invention is to provide an image forming apparatus that prevents image deletion.

[0023]

The present invention according to claim 1
Is a charging means for uniformly charging the surface of the image bearing member, an exposing means for exposing the charged surface of the image bearing member according to image data to form an electrostatic latent image, and a toner for the electrostatic latent image. Developing means for adhering and developing as a toner image, transfer means for transferring the toner image formed on the image carrier to a transfer material, fixing means for fixing the toner image on the transfer material , and after the toner image transfer A cleaning means for cleaning the surface of the image carrier , and a detection means for detecting the amount of water in the surrounding environment.
That in the image forming apparatus, in a state where the moisture content of the ambient environment is detected to be the specific amount of water or by said detecting means
The number of normal image forming operations performed by
And then, the charging means and the toner image for polishing on the image bearing member is formed by operating said exposure means and said developing means, the this <br/> and supplies it to the cleaning unit Characterize.

The present invention according to claim 2 is as described in claim 1 .
In the image forming apparatus, it can enter the specific number der of
It is characterized by

[0025]

[0026]

[0027]

[0028]

[0029]

[0030]

[0031]

[0032]

[0033]

[0034]

[0035]

[0036]

[0037]

[0038]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

<First Embodiment> FIG. 1 shows an example of an image forming apparatus according to the present invention. The image forming apparatus shown in FIG.
FIG. 1 is a laser beam printer (hereinafter referred to as “image forming apparatus”), and FIG. 1 is a vertical cross-sectional view showing its schematic configuration.

The image forming apparatus shown in the figure includes a drum type electrophotographic photosensitive member (hereinafter referred to as "photosensitive drum") 1 as an image bearing member. The photosensitive drum 1 is provided with a photoconductive layer (electrostatic latent image forming photoconductor) on a cylindrical conductive substrate, and is rotatably supported in the direction of arrow R1 in the figure. Then, around the photosensitive drum 1, a scoro-tocon charger (primary charger) 2 for uniformly charging the surface of the photosensitive drum 1 in order along the rotation direction, a document is read, and an image signal proportional to the image density is obtained. The photosensitive drum 1 is exposed to light to form an electrostatic latent image (micropoint exposure means) 3, a developing device 7 for adhering toner to the electrostatic latent image to develop it as a toner image, and a photosensitive material after development. A developer charge amount control charging device (hereinafter referred to as “post charging device”) 62 for adjusting the charge amount of the toner image of the toner image on the drum 1 so as to increase the transfer efficiency is arranged. Further, a transport system for transporting the transfer paper (transfer material) P to the transfer portion is arranged. Then, a corona transfer charger (transfer charger) 8 as a transfer device that transfers the toner image formed on the photosensitive drum 1 onto the transfer paper P, and the transfer paper P on which the toner image is transferred is separated from the photosensitive drum 1. Electrostatic separation charger (separation charger)
9. A cleaning device 13 for removing the residual toner remaining on the photosensitive drum 1 after the transfer of the toner image, a pre-exposure lamp 30 for removing the residual charge of the photosensitive drum 1, and the like are arranged. The transfer paper P on which the toner image is transferred is
After being separated from the photosensitive drum 1, it is conveyed to a fixing device 12, where the toner image on the surface is fixed, a desired print image is formed, and the toner image is discharged to the outside of the image forming apparatus main body 101.

The reader section 18 irradiates the original 15 placed on the original glass table 14 with light from the illumination lamp 16 and reflects the reflected light into a photoelectric conversion element (1 line CCD) 19.
By forming an image on the top, it is converted into an electric signal corresponding to the image information. Here, the reflected light from the document 15 illuminated by the illumination lamp 16 is reflected by the mirrors 17a, 17b, 1
The photoelectric conversion element 19 is guided by the lens 17d after being guided to 7c.
Imaged above. The electric signal output by the photoelectric conversion element 19 is A / D converted by the A / D converter 21 to obtain 8-bit digital image data, and thereafter,
The black signal generation circuit 22 performs log conversion to convert the luminance information into the density information and obtains the image density data.

The image density data (8
(bit digital image data signal) is converted into a two-stage signal of an on emission time of a specific on time according to the pixel size and an off signal via the binarization circuit 23, input to the laser drive circuit 24, and converted into a drive current. After the dot reproducibility correction is added, the semiconductor laser is turned on / off at the drive signal timing binarized by the error diffusion method according to the magnitude of the input image density signal.

In the present embodiment, the binarization circuit 23 is realized by the error diffusion method, but of course, the dither method may be used, or another method may be used. Alternatively, the semiconductor laser on / off light emission time may be modulated according to the magnitude of the image density signal input after the laser drive circuit 24 is subjected to dot reproducibility correction to the drive current by a well-known PWM circuit.

For example, the laser lighting of binary image data will be briefly described as shown in FIG. 5. When the image data of each pixel is input in the laser scanning direction as shown in (a), the laser is turned on. The drive current for turning off / off is as shown in (b), and the light is turned on for a certain time with a constant drive current regardless of the image data. And the exposure density in the plurality of pixel regions is modulated. That is, the number of times the laser drive signal is turned on when the image data is 00 hex is set to 0% of the lighting pixel ratio in the total number of pixels in a specific plural pixel area, and the number of times the laser drive signal is turned on when FF hex is For example, the lighting pixel ratio to the total number of pixels in a specific plural pixel area is 100%. However, even if the lighting pixel ratio is 0%, a constant drive current is flowing as a bias current, and slight light emission is performed. In this way, shading is realized by making area gradation within a specific plural pixel region.

Further, it is of course possible to adopt the PWM system as shown in FIG. When the image data for each pixel is input in the laser scanning direction as shown in (a), the drive signal for turning the laser on / off is as shown in (b). That is, the on-duty of the laser drive signal when the image data is 00 hex is set to 5 for one pixel scan time.
%, And the on-duty of the laser drive signal at the time of FFhex is 85% of one pixel scan time. In this way, shading is realized by making area gradation within one pixel.

Further, FIG. 6 shows a general IL characteristic (driving current-light quantity characteristic) of the laser.
The drive currents used when off are Ion / Io, respectively.
Since it is ff, the laser drive currents for the image signals in FIGS. 5 and 4 are as shown in (b) and (c), respectively, which are the binarization circuit 23 and the PWM circuit (not shown) and the laser shown in FIG. It is a current for driving the laser 20 via the drive circuit 24. At this time, Ioff is not 0 mA,
By setting it to be slightly smaller than Threshold,
It is known that the rise of the light amount when the laser is on is improved.

Here, as the laser, a visible light laser of 680 nm is used.

As described above, the laser light driven and emitted according to the image signal is raster-scanned and written on the photosensitive drum 1 through the polygon mirror scanner 28 and the mirror 17f that rotate at high speed, and a digital electrostatic latent image is recorded as image information. Form.

In this embodiment, an amorphous silicon drum is used as the photosensitive drum 1. Amorphous silicon drum has high stability of characteristics and high durability on the conductive substrate.
It has a long life. The a-Si photoconductor, which has a long life, high speed output, and is surface-curing SiC-curing type, and has a high photosensitivity in the photosensitive layer, has a high charge retention ability and there is almost no scattering of irradiation light by the surface layer. Since the minute electrostatic latent image in the minute spot exposed portion is held without electric charge diffusion, a minute latent image such as 600 dpi or 1200 dpi is faithfully formed and a high definition latent image is formed.

FIGS. 2A to 2C show steps for explaining the image forming process of this embodiment, and schematically show the relationship between the surface potential of the photosensitive member and the developing bias in each figure. There is.

In (a), the photoconductor is charged with a corona charger +
It is uniformly charged to 420V.

In (b), the image information is exposed and the surface potential of the image information exposed portion is attenuated to +50 V to form an electrostatic latent image. Since the image exposure is a pulse-width-modulated light amount as described above, the actual photosensitive drum potential after exposure is, in principle, only the potential of the laser off portion and the potential of the laser on portion. In a general non-contact surface electrometer, which measures the integrated potential in a sufficiently wide area with respect to the spot diameter of, the potential is apparently measured as a halftone potential. That is, even in the non-image portion (image data 00hex) of the image area, since the slight exposure is performed as described above, the surface potential is attenuated to +400 V, and the image portion of one image area (image data FFhex) At, the surface potential is attenuated to +50 V to form an electrostatic latent image.

Next, in (c), a developing bias voltage (for example, alternating current AC to direct current DC +2 is applied to the sleeve of the developing device).
80V superimposed etc. The DC component is shown by a broken line. )
Is applied to reversely develop the exposed portion. Here, the developing device uses a known one-component magnetic toner to perform the development without contacting the photoconductor.

An image streak preventing sequence by detecting a high humidity environment, which is a feature of the present invention, will be shown below. The following is a summary of each condition of the sequence for each purpose.

Example 1. Post-rotation toner black band due to high humidity detection ・ Purpose: Elimination of flow substances (shaving off) as a measure for image flow ・ Overview: Environmental sensor detects a certain amount of moisture or more and judges that it is a high humidity environment, forming a specific number of images After the counting, the drum rotation, the developing device and the cleaner system rotation are performed in the subsequent rotation, and the primary charging, the laser exposure and the development are performed on the drum during the rotation to form a toner black band.・ Conditions: 1) High humidity judgment: Water content of 9 g or more. (As a guide, NN23
Water content is 10.5 g at 60 ° C.) 2) Idle rotation time: Assuming that a copy / print is taken after a solid black color, this is used as a substitute for idle rotation. That is,
It has no special idle rotation time. However, the time required for the solid black to reach the cleaning blade should be the lower limit, and the rotation time should be as long as possible within the design range. 3) Primary charging: Output with the same control value as the image area (default output when there is no data). The output time is equivalent to the black band width. 4) Laser: Output with the same power control value as the image area (default output when there is no data). FF hex solid image area. The output time is equivalent to the black band width. 5) Development: Output with the same DC control value as the image area. AC + D
C (default output when there is no data). The output time is equivalent to the black band width. DC value can be entered. The black belt density can be changed. The developing AC is also used as the separating claw AC, and is on until the black band passes through the separating claw. 6) Black band: Sub scanning direction length: 40 mm on drum surface. Input is possible. Length in the main scanning direction: A3 width, which is the nominal width when the image area is centered. Lateral registration tolerance (longitudinal direction transfer paper edge misalignment correction intersection)
Does not include. Timing: Post-rotation at the end of a job after reaching a specific number of copy and print counts or pre-rotation of the next job (in the case of pre-rotation, the distance from the image area is more than the sheet interval). Interval specific number of sheets: every default 200 sheets. Input is possible. (In the experiment, we confirmed the streak prevention and elimination effect with a 20 mm width of post-rotation black belt for every 200 sheets.)

Example 2. HH, JJ, NL morning one toner black belt + idle rotation and a combination system of HH specific number of post-rotation black belt.・ Purpose: Elimination of flow substances (shaving off) by image flow countermeasures ・ Overview: Morning judgment and when the environment is in the following moisture content area,
At the preparation stage of image formation, the drum rotation, the developing device, and the cleaner system are also rotated under the following conditions, and during the rotation, primary charging, laser exposure, and development are performed on the drum to form a toner black belt, and the environment. When the sensor detects more than a specific amount of water and determines that the environment is high humidity, the drum is rotated, the developing device and the cleaner system are rotated by the post-rotation after counting the specific number of image formations, and the primary charging is performed on the drum. Then, laser exposure and development are performed to form a toner black band. a) Asahi toner black band + idle rotation and post-rotation black band after each specific number of sheets counting: water content W ≧ 9g b) Morning Ichi rotation: water content 9g> W ≧ 5g c) Normal multi-rotation only: water content 5g Less than less than that, the drum idle rotation, the developing device, and the cleaner system also idle idle, and at the same time as the idle rotation starts, primary charging, laser exposure, and development are performed on the drum to form a toner black band. . -Conditions: 1) Judgment in the morning: The fixing thermistor temperature is 100 ° C or less when the main switch is on. 2) Environmental Judgment: a) Morning toner black belt + idle rotation and post-rotation black belt after counting a specific number of sheets: Water content W ≧ 9 g (NN23 ° C., 60 as a guide)
% Is water content 10.5 g) b) Morning dry rotation: Water content 9 g> W ≧ 5 g c) Normal multi-rotation only: Water content is less than 5 g 3) Empty rotation time: a) ・ Masaichi toner black belt + idle rotation : Immediately after HH judgment in the morning until the fixing thermistor temperature is 195 ° C. About 4.5 minutes (rotation time varies depending on the temperature of the fixing thermistor at the start of idle rotation). -Post-rotation black belt: Assuming that a copy / print is taken after solid black, substitute it for idle rotation. That is, it has no special idle rotation time. However, the time required for the solid black to reach the cleaning blade should be the lower limit, and the rotation time should be as long as possible within the design range. 4) Primary charging: Output with the same control value as the image area (default output when there is no data). The output time is equivalent to the black band width. 5) Laser: Output with the same power control value as the image area (default output when there is no data). FF hex solid image area. The output time is equivalent to the black band width. 6) Development: Output with the same DC control value as the image area. AC + D
C (default output when there is no data). The output time is equivalent to the black band width. DC value can be input and the black band density can be changed. 7) Black belt: Sub scanning direction length: Asaichi black belt 40 on the drum surface
0mm, black belt after rotation 20mm. The black band width can be entered. Length in main scanning direction: Nominal width of A3 width in the center of the image area (horizontal registration tolerance is not included) Timing: Asaichi Black belt is in front of multiple rotation The post-rotation black band indicates post-rotation at the end of a job after the specific number of copies and prints reaches a specific number, or during pre-rotation of the next job (in the case of pre-rotation, it is moved away from the image area by more than the sheet interval). Post-rotation black band interval Specific number of sheets: Every default 200 sheets. Input is possible.・ Effect: The flow and streak flow is 400 mm in the morning, 4.5 minutes in idling, and about 20 mm after the black swirl after every 200 sheets.

Now, the operation of the above-described example 1 of the present embodiment will be described step by step with reference to FIG.

When the environment is a specific water content region, the water content W ≧ 9
When g is detected, it is determined to be a high humidity environment (a). When the default number of the specific number of integrated counts for copying and printing (the specific number of intervals) is set to 200, the 200th sheet is set as the copy start. It detects that the specific number has been reached, and operates to perform the post-rotation black belt during the post-rotation at the end of this job. Even after the laser exposure of the image area is completed, the drum drive motor continues to operate, the drum idle rotation is performed, and at the same time, the developing device drive motor is operated to rotate the developing device sleeve, and at the same time, the cleaner system drive motor (main motor) is operated. Then, the cleaner system also idles. Further, the polygon mirror rotation drive of the laser scanning system continues to operate.

The primary charging is also continuously performed, and the control value similar to that in the image area, that is, the potential control value at the closest timing is used as the charge amount for output. If there is no previous data, the program default value is output. The output extension time is equal to or longer than the black band width time, and there is a slight extra charging area before and after the black band. The total time is 20 mm or more in the circumferential direction on the drum. The length in the main scanning direction is distributed to the center of the image area, and charging is performed to a width not smaller than the nominal width of A3 width.

Next, the laser exposure is turned off for a specific time once the image area is completed, and then the black band is turned on. When the laser is turned on, output is performed with the same power control value as in the image area.
If there is no such data, the program default value is output. The image area is FF as the image data level
hex It is a solid hit. The length in the main scanning direction is a nominal width of A3 width when the image area is centered. That is, the laser beam scanning is performed with a width that does not include the adjustment tolerance of registration (lateral registration) in the main scanning direction. Here, the image area FFhe of 297 mm
x output is being performed. The output time is the time corresponding to the black band width, here the time corresponding to 20 mm in the circumferential direction on the drum. Further, before outputting FFhex, a bias current is flown to slightly illuminate in order to speed up the rise of the laser output. The output data is not limited to FFhex but may be 80hex or 40he depending on the state of the image forming apparatus.
x or the like is also acceptable.

Next, in the development, the AC voltage + DC voltage is output. The AC voltage is output at the standard voltage, and the DC voltage is output at the DC control value similar to that in the image area. In the present embodiment, the DC control value of the black band width is 280V, but the DC control value of 300V for the non-image area is output so as to completely cover the area where the primary charging before and after the black band width is output. It is set to suppress reversal development in the area of primary charging only. Although only the DC voltage is shown in FIG. 21, the AC voltage is DC.
On in the area that further covers the voltage (for non-image) tilt area
is doing. If there is no previous data, the DC control value is output with the program default value. The output time is the time corresponding to the black band width, and here it is 20 in the circumferential direction on the drum.
The time is equivalent to mm. The DC value is set on the scanning panel so that the black band density can be changed.

After the toner band is formed on the drum, the black toner band is conveyed to the drum cleaning device and blocked by the edge of the cleaning blade, and the accumulated toner scrapes off the laminated substance on the drum surface. Since this scraping effect is proportional to the rubbing time, the time should be secured as much as possible in order to secure the longest possible time.

Further, in the above-described black band formation, as shown in FIG. 22, the black band data of the post-rotation black band is controlled (the black band width is fixed) according to the detected water content, and the black band width control is performed. By fixing (black band image data is fixed), it is possible to supply the black band toner to the most suitable cleaning blade according to the environmental humidity, and the influence of the moisture absorbing substance on the drum on the image depending on the environmental moisture content. Since it is possible to supply the toner according to the degree, it is possible to avoid wasteful toner consumption due to an excessive toner black band even in a high humidity environment when the water content is relatively low. On the contrary, when the water content is extremely high, it is possible to control so as to sufficiently scrape off the moisture absorbing portion of the surface layer of the adsorbed moisture absorbing substance by supplying more toner. The selection of control contents is variable depending on the usage status of the image forming apparatus. In particular, as the number of sheets used during a specific period increases, it is desirable to increase the black band width and select a large amount of the hygroscopic substance to be scraped off. This makes it possible to properly handle all environmental humidity regions and always provide good images.

As described above, the high humidity environment (the water content per cubic meter unit volume is 9
Even in an environment of g / m ³ or more), the image forming apparatus can obtain a good image for a long period of time regardless of the environment.

The method of correcting unevenness in the main scanning direction when the developing device 7 or other uneven density occurs will be described in detail below.

FIG. 7 is a schematic diagram of a factor analysis of the cause of uneven density in the main scanning direction. The vertical axis represents the surface potential on the photosensitive drum, and the horizontal axis represents an arbitrary position in the main scanning direction.

(A) shows the potential at the place where the charging potential is normally obtained at the target potential of 400 V and at the place where it is smaller than the target potential. This is because the charging ability characteristic of the photosensitive drum 1 is different from the characteristic of the surface potential obtained on the photosensitive drum 1 with respect to the current applied to the corona wire of the primary charger 2 as shown by the three types of characteristic curves in FIG. It is the surface potential unevenness that occurs. Even if the charging ability characteristics of the photosensitive drum 1 are uniform, if the charging ability of the primary charger 2 is not uniform depending on the position in the main scanning direction, uneven surface potential occurs.

FIG. 7B shows the potentials at the place where the target potential of the exposed portion is normally 50V and the place where the surface potential is higher than the target potential, although the surface potential is formed uniformly by charging. There is. This is the surface potential unevenness that occurs due to the different photosensitivity characteristics of the photosensitive drum 1 as shown by the three types of characteristic curves in FIG. In addition, the photosensitive drum 1
Even if the photosensitivity characteristic is uniform, the surface potential unevenness occurs when the light irradiation amount is nonuniform depending on the position in the main scanning direction.

In FIG. 7C, although the surface potential formation by charging and the surface potential formation by the potential decay by exposure were performed uniformly, the potential and the potential of the exposed portion are normally 50 V. Also shows a small place. This is Figure 1
As shown in three characteristic curves of 0, the surface potential of the photosensitive drum 1 and the application D to the developing sleeve carrying and carrying the developer D
This is density unevenness that occurs because the developing ability with respect to the developing contrast, which is the difference in C voltage, is different. This density unevenness occurs when the charging characteristic is non-uniform in the main scanning direction, or when the gap between the photosensitive drum 1 and the developing sleeve is non-uniform depending on the position in the main scanning direction.

Further, there is density unevenness due to non-uniformity of transfer efficiency at the time of transfer or separation (not shown) in the main scanning direction.

Here, all the above-mentioned factors causing unevenness are comprehensively detected from the output printout image and corrected.

FIG. 12 is a flow chart showing the outline of the flow of the correction operation.

Step (S1) The image forming apparatus of the present embodiment has an "improving image mode" as an image unevenness improving mode in the input interface, and first starts that mode.

Step (S2) Next, an axial non-uniformity (main scanning direction non-uniformity) correction mode is selected.

Step (S3) The key for starting the axial unevenness correction mode is pressed to start.

Step (S4) The image forming apparatus outputs a test image sample as shown in FIG. The conditions for forming this sample are:
In order to form an image of completely solid black, halftone halftone, solid white, etc., three kinds of image exposure conditions are obtained by the primary charging conditions for forming the surface potential as described above (F0, 80 in FIG. 11 with an 8-bit signal). , 00 hex), develop, transfer, and fix under the above-mentioned developing conditions, output a sample, and detect the tone density reproduction characteristic by the density characteristic detecting means (not shown).

Step (S5) The output sample is placed by the mode executor on the document table at a specific position such that the leading end and the front or rear side of the sample in the sheet passing direction are completed by the document recognizing means (not shown). Judge whether or not is detected.

Step (S6) When the completion of the placement is judged, the document is read by the reader as described above. 400-60 reading by this reader
It is desirable to read at a resolution of about 0 dpi.

Step (S7) Whether or not this original is a test image sample is determined by whether or not the density gradation is an equivalent pattern. If it is determined that it is not the test image sample, an error is notified in step S11, and this processing ends. In this case, step S
You may return to 5 processing.

Step (S8) When it is determined that the image is a test image sample, the axial density distribution is calculated as shown in FIG. 13 (b). When the test image sample is formed at the PWM level of F0, 80, 00 hex, the read density distribution of the halftone part of 80 hex where the unevenness is most easily detected is calculated (F0, 8
The density distribution may be calculated at 0:00 hex. ).

Step (S9) When the target density is set to 0.5 in FIG. 13B, the increase / decrease of 0.5 in the read density distribution of the halftone portion is made to correspond to each pixel in the main scanning direction. Calculate to. If the negative correction is represented by a negative value and the positive correction is represented by a positive sign, the required correction density is as shown in FIG.
It is a diagram of the required correction density as if the polarity was reversed.

Step (S10) The correction light amount (correction level) for each pixel of the dot exposure laser is obtained from the diagram of the required correction density with reference to FIG. As an example, in FIG. 14, when the required correction density is +0.8, the surface potential is −200 V, and the photosensitive drum surface light amount is +0.25 μJ.
This indicates that the image data needs to be corrected by +80 hex. A correction amount level corresponding to each pixel in the main scanning direction is assigned by this capacity, and a correction table is created. Here, this mode ends, and the operation panel, which is the input interface unit of the image forming apparatus, returns to the normal copy or print mode.

Thus, when the correction amount corresponding to each pixel position in the main scanning direction is determined, it is stored in the correction table in the main scanning unevenness correction circuit 50 (see FIG. 1) as the correction value creating means. .

FIG. 20 shows a concrete circuit configuration of the main scanning unevenness correction circuit 50 in the present embodiment.

The illustrated correction table 101 and adder 10
4, the selector 102, and the address generation circuit 103 form a main scanning unevenness correction circuit 50. CPU100
Is a control unit that controls the entire apparatus, and includes a control program as a copying machine, a ROM that stores the program according to the flowchart of FIG. 12 described above, and a work area. It has a RAM to use.

In the configuration shown, the correction table 101
Has a capacity of at least the number of pixels in the main scanning direction (9 bits per pixel, 1 bit of which is plus or minus sign bit). Then, the correction data of each pixel generated based on the image data obtained by reading the test image sample as described above is written in the corresponding address position of this correction table (which is configured by the RAM). Therefore, the CPU 100 outputs a signal for supplying the address from the CPU 100 to the correction table 101 to the selector 102, and outputs the address, the data to be written, and the write signal to the correction table 101. When the writing of the correction data for all the pixel positions in the main scanning direction is completed in this way, a signal for selecting an address from the address generation circuit 103 is output to the selector 102, and a read signal is output.

The address generation circuit 103 includes the photosensitive drum 1
A beam detect signal provided in the vicinity of is used as a trigger, and when a predetermined time comes, the correction table 1 is synchronized with the carrier clock of the image data from the black signal generation circuit 22.
Address signals are sequentially output to 01. As a result, the correction table 101 outputs the correction signal in synchronization with the image data (pixel data) from the black signal generation circuit 22. The adder 104 adds the data from the correction table 101 to the image data from the black signal generation circuit 22, and outputs the result to the binarization circuit 23. Since the correction table stores the positive and negative correction data as described above, the adder 104 binarizes the image data obtained by correcting the characteristics of the image data according to the characteristics of the printer engine. It will be output to the circuit 23.

Before and after the description, the test image sample is formed by the CPU 100 by setting 00 for each predetermined number of main scanning lines.
The data of hex, 80 hex, and f0 hex are output instead of the black signal generation circuit 22. However, since it is a test image formation for knowing the characteristics of the printer engine, no data is output from the correction table 101, or 0 data is always output. In some cases, when forming a test image sample, the correction table 101 may include 00, 80 hex, and f0he.
It is also possible to write x at an appropriate timing and output it. At this time, if the image reading is not performed, the data of 0 is output from the black signal generation circuit 22, so that the test image sample shown above can be formed as a result. The advantage in this case is that a test image sample can be formed only with the configuration of FIG.

Since the correction table 101 described above is used to correct data such as image unevenness at the 8-bit multi-valued signal stage, uniform data is formed at the time of binarization and at the time of laser writing. In this case, the density unevenness is completely corrected, and it is possible to always provide a high-quality image having no density unevenness in the longitudinal direction (main scanning direction). In particular, according to the present embodiment, it becomes possible to suppress uneven density in a relatively low density portion (highlight portion).

When applied to a device for forming an image by the PWM system, the output of the adder 104 is D / A converted and compared with the triangular wave from the triangular wave generating circuit, as shown in FIG. , A signal having a pulse width depending on the concentration may be generated and supplied to the laser drive circuit 24. The reason why the pulse width signal is generated even when the density is 0 is as described above. The laser drive circuit 24 is driven so as to generate laser light for a time period depending on the pulse width of the pulse width modulation signal.

As described above, when the temperature of the fixing thermistor when the main switch is on is below the specific temperature and the environment is within the specific moisture content region (below), it is judged to be the morning and high humidity environment (and each environment), According to the water content area, the drum is idled (developing device and cleaner system are idled), and at the same time as the idle rotation is started, primary charging, laser exposure and development are performed on the drum to form a black toner band. By combining them, and by further correcting the density unevenness at the laser writing level using the correction table, the density is sufficiently increased and the developability is increased to the point where the reproducibility of isolated dots can be sufficiently secured. Thus, even in the first copy image in the morning in a high humidity environment, a high-quality image with no image deletion, high density and no density unevenness in the longitudinal direction (main scanning direction) can always be obtained.

<Second Embodiment> FIG. 15 shows a second embodiment of the image forming apparatus according to the present invention. The figure is a vertical cross-sectional view showing a schematic configuration of the image forming apparatus.

The photosensitive drum 1 is formed by providing a photoconductive layer on a cylindrical conductive substrate, and is rotatably supported in the direction of arrow R1 in the figure. Then, around the photosensitive drum 1, a primary charging device (first scorotocon charging device) that charges the surface of the photosensitive drum 1 uniformly along the rotation direction thereof.
2. A first exposure device 3, which reads a document, exposes the photosensitive drum 1 based on a first image signal proportional to the density of one color image separated into two colors, and forms a first electrostatic latent image, A first developing device 4 for forming a first image by attaching toner to the first electrostatic latent image, and a recharging device (second scorotron charger) for charging the photosensitive drum 1 after carrying the first image. )
5. Second exposure for forming a second electrostatic latent image by performing exposure of an amount obtained by adding a certain exposure amount to the exposure amount based on the second image signal proportional to the density of the separated other color image Device 6,
A second developing device 7 for forming a second image by attaching toner to the second electrostatic latent image, a pre-transfer charger 62 for charging the color superposed image formed on the photosensitive drum 1 before transfer, a transfer Corona transfer charger (transfer charger) 8 for transferring onto the transfer paper P, which is a material, and the transfer paper P on which the color superposed image is transferred, on the photosensitive drum 1.
From the electrostatic separation charger (separation charger) 9, a cleaning device 13 for removing the residual toner remaining on the photosensitive drum 1 after transferring the color superposed image, a pre-exposure lamp for removing the residual charge on the photosensitive drum 1. 30 and the like are arranged.
Further, the transfer paper P on which the color superposed image is transferred is the photosensitive drum 1
After being separated from the sheet, it is conveyed to the fixing device 12, where the toner image on the surface is fixed, a desired print image is formed, and the sheet is discharged to the outside of the image forming apparatus main body.

Here, the connecting duct 61 is directly connected to the pre-transfer charger 62, and the blowing fan 60 is further connected thereto.

Further, the image scanner section 18 illuminates the original 15 placed on the original glass table 14 with the illumination lamp 1.
6 scans and reads, and the photoelectric conversion element 19 converts image information into an electric signal.
The reflected light from the document 15 scanned by the
The light is guided to a, 17b, and 17c, and is imaged by the lens 17d on the photoelectric conversion element 19 including the red, green, and blue filters. The electric signals from which the red, green, and blue components have been output by the photoelectric conversion element 19 are digitized by the A / D converter 21, and then sent to the signal processing unit 22 as a color separation unit to red and black. Is converted into an image signal proportional to the image density of each component.

Here, the axial direction (main scanning direction) unevenness correction table 50 corrects the image data for each pixel (see 50 in FIG. 17).

The red image signal (first image signal) and the black image signal (second image signal) are sent to the laser drivers 24b and 24a as a signal generator, and the red image signal and the black image signal are received. Lasers 20b, 20
The light emission of a is turned on / off. The laser light emitted in response to the red signal is the polygon mirror 2 as the first image information.
8. Write the first electrostatic latent image on the photosensitive drum 1 via the mirror 17e. The laser light emitted in an amount corresponding to the black signal writes the second electrostatic latent image on the photosensitive drum 1 as the second image information via the polygon mirror 28 and the mirrors 17f and 17g.

In this embodiment, an amorphous silicon drum is used as the photosensitive drum 1. Amorphous silicon drums have the characteristics of high durability and long life.

FIG. 16 illustrates the image forming process in the two-color image forming mode of the present embodiment.
(F) shows each process, and the surface potential of the photosensitive drum 1 is schematically shown in each figure.

In (a), the photosensitive drum 1 is charged by the corona charger 2 to, for example, + 400V, and then in (b) the first exposure of the image information is performed, and the surface potential of the exposed portion is set to + 50V, for example. Attenuate to form a first electrostatic latent image.

Next, in (c), a developing bias voltage (for example, +300 V: shown by a broken line) is applied to the developing sleeve of the first developing device 4 to reversely develop the exposed portion.

After the first development, recharging is carried out in (d), but 600 V larger than the desired second development position potential 400 V is applied to the grid of the recharger 5, and the first development non-image area is, for example, It is controlled to be charged to 600V. At that time, the first developing section is charged to, for example, 500V.

Next, when the exposure according to the second image information is performed in (e), a constant exposure amount is applied to the entire surface (for example, the first development non-image area is attenuated by 200 V compared to the second development single color). Large exposure is performed. At this time, in the first developing section, the exposure by the constant exposure amount does not attenuate as much as the potential in the first developing non-image area, but only 100 V, for example. This is because the first developer does not transmit light but scatters it, and the transmittance was 50%. The target potential after recharging at the first developing non-image area is such that the surface potential after exposure with the second exposure constant addition exposure amount of 0.25 μJ becomes the second developing position target potential 400 V by the known straight line of drum sensitivity 800 V / μJ. Assuming it was 600V. Next, the amount of light reaching the first image developing unit on the drum is 0.125 μJ from the known toner layer transmittance of 50%. First as in the method described above
After recharging the developed image portion, the target potential may be set to 500V.

In the present embodiment, the semiconductor laser is used as the second exposure means, but complicated processing and the like are not required in the second developing monochromatic mode and the two-color mode. Since the light amount of the laser is determined by the laser drive current, a constant offset current is added to the drive current in the second developing monochromatic mode in the two-color mode. That is, weak exposure is also applied to the part where the second image signal is off, and exposure is also applied to the on part with an exposure amount almost equal to that, and the potential of the first developed image part is 400 V The potential of the non-image area is also 400
V, and when the second image signal is on, the first developing non-image portion is exposed to 50V. After this, in the developing process, the second
By applying a bias of 300V to the developing sleeve,
It is possible to obtain a sufficient second image density without the second developer being mixed in the first developing portion or being developed in the first and second image non-image portions.

The image deletion prevention sequence by the high humidity environment detection, which is a feature of this embodiment, is shown below.
The operation is the same as that in the first embodiment described above, and will not be repeated.

The operation of this embodiment will be described step by step with reference to FIG.

When the environment is a specific water content area, the water content W ≧ 9
When g is detected, it is determined to be a high humidity environment (a). When the default number of the specific number of integrated counts for copying and printing (the specific number of intervals) is set to 200, the 200th sheet is set as the copy start. It detects that the specific number has been reached, and operates to perform the post-rotation black belt during the post-rotation at the end of this job. Even after the laser exposure of the image area is completed, the drum drive motor continues to operate to idle the drum, and at the same time the developer drive motor operates to rotate the sleeve of the developer, and at the same time the cleaner drive motor (main motor) operates. Then, the cleaner system also idles. Further, the polygon mirror rotation drive of the laser scanning system continues to operate.

The primary charging is also continuously performed, and the control value similar to that in the image area, that is, the potential control value at the closest timing is used as the charge amount for output. If there is no previous data, the program default value is output. The output extension time is equal to or longer than the black band width time, and there is a slight extra charging area before and after the black band. The total time is 20 mm or more in the circumferential direction on the drum. The length in the main scanning direction is distributed to the center of the image area, and charging is performed to a width not smaller than the nominal width of A3 width.

Next, the laser exposure is turned off for a specific time once the image area is completed, and then the black band is turned on. When the laser is turned on, output is performed with the same power control value as in the image area.
If there is no such data, the program default value is output. The image area is FF as the image data level
hex It is a solid hit. The length in the main scanning direction is a nominal width of A3 width when the image area is centered. That is, the laser beam scanning is performed with a width that does not include the adjustment tolerance of registration (lateral registration) in the main scanning direction. Here, the image area FFhe of 297 mm
x output is being performed. The output time is the time corresponding to the black band width, here the time corresponding to 20 mm in the circumferential direction on the drum. Further, before outputting FFhex, a bias current is flown to slightly illuminate in order to speed up the rise of the laser output. The output data is not limited to FFhex but may be 80hex or 40he depending on the state of the image forming apparatus.
x or the like is also acceptable.

Next, in the development, the AC voltage + DC voltage is output. The AC voltage is output as a standard voltage, and the DC voltage is output as a DC control value similar to that in the image area. In the present embodiment, the DC control value of the black band width is 280V, but the DC control value of 300V for the non-image area is output so as to completely cover the area where the primary charging before and after the black band width is output. It is set to suppress reversal development in the area of primary charging only. Although only the DC voltage is shown in FIG. 21, the AC voltage is DC.
On in the area that further covers the voltage (for non-image) tilt area
is doing. If there is no previous data, the DC control value is output with the program default value. The output time is the time corresponding to the black band width, and here it is 20 in the circumferential direction on the drum.
The time is equivalent to mm. The DC value is set on the scanning panel so that the black band density can be changed.

After the toner band is formed on the drum, the black toner band is conveyed to the drum cleaning device and blocked by the edge of the cleaning blade, and the accumulated toner scrapes off the laminated substance on the drum surface. Since this scraping effect is proportional to the rubbing time, the time should be secured as much as possible in order to secure the longest possible time.

Further, in the above black band formation, as shown in FIG. 22, the black band data of the post-rotation black band is controlled (the black band width is fixed) and the black band width control is performed in accordance with the detected water content. By fixing (black band image data is fixed), it is possible to supply the black band toner to the most suitable cleaning blade according to the environmental humidity, and the influence of the moisture absorbing substance on the drum on the image depending on the environmental moisture content. Since it is possible to supply the toner according to the degree, it is possible to avoid wasteful toner consumption due to an excessive toner black band even in a high humidity environment when the water content is relatively low. On the contrary, when the water content is extremely high, it is possible to control so as to sufficiently scrape off the moisture absorbing portion of the surface layer of the adsorbed moisture absorbing substance by supplying more toner. The selection of control contents is variable depending on the usage status of the image forming apparatus. In particular, as the number of sheets used during a specific period increases, it is desirable to increase the black band width and select a large amount of the hygroscopic substance to be scraped off. This makes it possible to properly handle all environmental humidity regions and always provide good images.

As described above, the most humid environment (the water content per cubic meter unit volume is 9
Even in an environment of g / m ³ or more), the image forming apparatus can obtain a good image for a long period of time regardless of the environment.

The method of correcting unevenness in the main scanning direction when density unevenness occurs in the developing device and other devices will be described in detail below.

Similar to the first embodiment, description will be made using the operation flow for creating the correction table 50 in FIG.

(1) The image forming apparatus according to the present embodiment has an "improving image mode" as an image unevenness improving mode in the input interface, and the mode is started first.

(2) Next, the axial nonuniformity (main scanning nonuniformity) correction mode is selected.

(3) Start the axial unevenness correction mode. Press the key to start.

(4) The image forming apparatus outputs a test image sample as shown in FIG. As the forming conditions of this sample, in order to form an image of completely solid black, halftone halftone, solid white, etc., three kinds of image exposure conditions were obtained by the primary charging condition for forming the surface potential as described above (Fig. 11 PWM level F0, 80, 00 hex), and the sample is output after developing, transferring and fixing under the above-mentioned developing conditions.

Here, as a feature of this embodiment, test image sample output is performed for each of the two colors (for example, red and black). After this, perform the following steps (5) to (10) for each red and black color.

(5) The output sample is placed on the document table by the mode executor at the specified position such that the leading end and the front side or the back side of the sample in the sheet passing direction, and the completion of placement by the document recognizing means (not shown). Judge whether it is detected.

(6) When the completion of placing is judged, the document is read by the reader as described above. It is desirable that reading by this reader is performed at a resolution of about 400 to 600 dpi.

(7) Whether or not this original is a test image sample is determined by whether or not the patterns have the same density gradation.

(8) When it is determined that the image is a test image sample, the axial density distribution is calculated as shown in FIG. 13 (b). When the test image sample is formed at the PWM level of F0, 80, and 00hex, the read density distribution of the halftone portion of 80hex where the unevenness is most easily detected is calculated (the density distribution is calculated at F0, 80, and 00hex, respectively). May be.).

(9) As shown in FIG.
In the case of 5, the increase / decrease of the read density distribution of the halftone portion with respect to 0.5 is calculated so as to correspond to each pixel in the main scanning direction. If the negative correction is represented by a negative sign and the positive correction is represented by a positive sign, the required correction density is a diagram of the necessary correction density as shown in FIG.

(10) The correction light amount (correction level) for each pixel of the dot exposure laser is obtained from the diagram of the required correction density with reference to FIG. As an example, the required correction density is +0.8 in FIG.
In the case of, the surface potential is -200 V, and the drum surface light quantity is +
This indicates that it is necessary to correct 0.25 μJ and +80 hex for image data. A correction amount level corresponding to each pixel in the main scanning direction is assigned by this capacity, and a correction table is created. Here, this mode ends, and the operation panel, which is the input interface unit of the image forming apparatus, returns to the normal copy or print mode.

As described above, when the temperature of the fixing thermistor when the main switch is on is below the specific temperature and the environment is within the specific moisture content area (below), it is judged to be the morning and high humidity environment (and each environment), The drum idle rotation (developing device, cleaner system idle rotation) is performed according to the water content area, and primary charging, laser exposure, and development are performed on the drum at almost the same time as idle rotation is started to form a black toner band. Noto
Furthermore, by using the correction table to correct the density unevenness at the laser writing level, the developability has risen to the point where sufficient density can be obtained and the reproducibility of isolated dots can be sufficiently secured. Even in the first copy image in the environment in the morning, a high-density two-color image with no image deletion and high density and no density unevenness in the longitudinal direction (main scanning direction) can be obtained.

<Third Embodiment> FIG. 18 is a schematic structural view of an image forming apparatus according to a third embodiment of the present invention.

The photosensitive drum 11 has a photoconductive layer provided on a cylindrical conductive substrate, and is rotatably supported in the direction of arrow R1 in the figure. Then, around the photosensitive drum 1, a scoro-tocon charger (primary charger) for uniformly charging the surface of the photosensitive drum 1 in order along the rotation direction thereof.
2. An original reading device, an exposure device 3 that exposes the photosensitive drum 1 based on an image signal proportional to the image density to form an electrostatic latent image, and toner is attached to the electrostatic latent image to develop it as a toner image. Developing device 7, post-charger (pre-transfer charger) 62 for charging the toner image before transfer, corona transfer charging for transferring the toner image formed on the photosensitive drum 1 onto a transfer paper P which is a transfer material. Device (transfer charger) 8, electrostatic separation charger (separation charger) 9 that separates the transfer paper P on which the toner image has been transferred from the photosensitive drum 1, and after the toner image has been transferred, remains on the photosensitive drum 1. A cleaning device 13 for removing residual toner, a pre-exposure lamp 30 for removing residual charges on the photosensitive drum 1, and the like are arranged. The transfer paper P on which the toner image is transferred is separated from the photosensitive drum 1 and then conveyed to the fixing device 12, where the toner image on the surface is fixed, and a desired print image is formed, and the image forming apparatus main body is formed. Is discharged to the outside.

The reader section 18 irradiates the original 15 placed on the original glass table 14 with light from the illumination lamp 16 and reflects the reflected light into a photoelectric conversion element (1-line CCD) 19.
By forming an image on the top, it is converted into an electric signal corresponding to the image information. Here, the reflected light from the document 15 illuminated by the illumination lamp 16 is reflected by the mirrors 17a, 17b, 1
The photoelectric conversion element 19 is guided by the lens 17d after being guided to 7c.
Imaged above. The electric signal output from the photoelectric conversion element 19 is A / D converted by the A / D converter 21 to obtain 8-bit digital image data, and then the black signal generation circuit 22 converts the luminance information into the density information. The image is subjected to log conversion to obtain image density data.

Here, as shown in FIG. 1 or 3, the main scanning unevenness correction circuit 50 of the present invention corrects the image density data for each pixel in the main scanning direction. A correction method in the main scanning unevenness correction circuit will be described in detail later.

The 8-bit digital image data signal generated as described above is applied to the LED drive circuit 2 which is a feature of the present invention.
4c (see FIG. 18), and LED drive circuit 24c
Is a well-known PWM circuit, and turns on the LED as the light emitting element 20c according to the magnitude of the input image density signal.
Modulates the light emission time for n / off. Light emitting element 20c
Are arranged in the main scanning direction.

As described above, the LED light driven and emitted according to the image signal is written on the photosensitive drum 1 to form a digital electrostatic latent image as image information.

In this embodiment, an amorphous silicon drum is used as the photosensitive drum 1. Amorphous silicon drums have the characteristics of a conductive substrate with high stability and high durability and long life.

Each step for explaining the image forming process of this embodiment is the same as that of the first embodiment.

The image deletion prevention sequence by the high humidity environment detection, which is a feature of this embodiment, is shown below. The following is a summary of each condition of the sequence for each purpose.

Here, the operation of the above-described example 1 of the present embodiment will be described step by step with reference to FIG.

When the environment is a specific water content area, the water content W ≧ 9
When g is detected, it is determined to be a high humidity environment (a). When the default number of the specific number of integrated counts for copying and printing (the specific number of intervals) is set to 200, the 200th sheet is set as the copy start. It detects that the specific number has been reached, and operates to perform the post-rotation black belt during the post-rotation at the end of this job. Even after the laser exposure of the image area is completed, the drum drive motor continues to operate, the drum idle rotation is performed, and at the same time, the developing device drive motor is operated to rotate the developing device sleeve, and at the same time, the cleaner system drive motor (main motor) is operated. Then, the cleaner system also idles. Further, the polygon mirror rotation drive of the laser scanning system continues to operate.

The primary charging is also continuously carried out, and as the charging amount, the same control value as in the image area, that is, the potential control value at the closest time is used for output. If there is no previous data, the program default value is output. The output extension time is equal to or longer than the black band width time, and there is a slight extra charging area before and after the black band. The total time is 20 mm or more in the circumferential direction on the drum. The length in the main scanning direction is distributed to the center of the image area, and charging is performed to a width not smaller than the nominal width of A3 width.

Next, the laser exposure is turned off for a specific time once the image area is completed, and then the black band is turned on. When the laser is turned on, output is performed with the same power control value as in the image area.
If there is no such data, the program default value is output. The image area is FF as the image data level
hex It is a solid hit. The length in the main scanning direction is a nominal width of A3 width when the image area is centered. That is, the laser beam scanning is performed with a width that does not include the adjustment tolerance of registration (lateral registration) in the main scanning direction. Here, the image area FFhe of 297 mm
x output is being performed. The output time is the time corresponding to the black band width, here the time corresponding to 20 mm in the circumferential direction on the drum. Further, before outputting FFhex, a bias current is flown to slightly illuminate in order to speed up the rise of the laser output. The output data is not limited to FFhex but may be 80hex or 40he depending on the state of the image forming apparatus.
x or the like is also acceptable.

Next, in the development, the AC voltage + DC voltage is output. The AC voltage is output as a standard voltage, and the DC voltage is output as a DC control value similar to that in the image area. In the present embodiment, the DC control value of the black band width is 280V, but the DC control value of 300V for the non-image area is output so as to completely cover the area where the primary charging before and after the black band width is output. It is set to suppress reversal development in the area of primary charging only. Although only the DC voltage is shown in FIG. 21, the AC voltage is DC.
On in the area that further covers the voltage (for non-image) tilt area
is doing. If there is no previous data, the DC control value is output with the program default value. The output time is the time corresponding to the black band width, and here it is 20 in the circumferential direction on the drum.
The time is equivalent to mm. The DC value is set on the scanning panel so that the black band density can be changed.

After the toner band is formed on the drum, the black toner band is conveyed to the drum cleaning device and is blocked by the edge of the cleaning blade, and the accumulated toner scrapes off the laminated substance on the drum surface. Since this scraping effect is proportional to the rubbing time, the time should be secured as much as possible in order to secure the longest possible time.

Further, in the above black band formation, as shown in FIG. 22, the black band data of the post-rotation black band is controlled (the black band width is fixed) and the black band width control is performed in accordance with the detected water content. By fixing (black band image data is fixed), it is possible to supply the black band toner to the most suitable cleaning blade according to the environmental humidity, and the influence of the moisture absorbing substance on the drum on the image depending on the environmental moisture content. Since it is possible to supply the toner according to the degree, it is possible to avoid wasteful toner consumption due to an excessive toner black band even in a high humidity environment when the water content is relatively low. On the contrary, when the water content is extremely high, it is possible to control so as to sufficiently scrape off the moisture absorbing portion of the surface layer of the adsorbed moisture absorbing substance by supplying more toner. The selection of control contents is variable depending on the usage status of the image forming apparatus. In particular, as the number of sheets used during a specific period increases, it is desirable to increase the black band width and select a large amount of the hygroscopic substance to be scraped off. This makes it possible to properly handle all environmental humidity regions and always provide good images.

As described above, the most humid environment (the water content per cubic meter unit volume is 9
Even in an environment of g / m ³ or more), the image forming apparatus can obtain a good image for a long period of time regardless of the environment.

A method of correcting unevenness in the main scanning direction when unevenness in density occurs in the developing device and other devices will be described in detail below.

As in the case of the first embodiment, the operation of creating the correction table 50 shown in FIG. 12 will be described.

(1) The image forming apparatus of the present embodiment has an "improving image mode" as an image unevenness improving mode in the input interface, and first starts that mode.

(2) Next, the axial nonuniformity (main scanning nonuniformity) correction mode is selected.

(3) Start the axial unevenness correction mode. Press the key to start.

(4) The image forming apparatus outputs a test image sample as shown in FIG. 13 (a). As the forming conditions of this sample, in order to form an image of completely solid black, halftone halftone, solid white, etc., three kinds of image exposure conditions were obtained by the primary charging condition for forming the surface potential as described above (Fig. 11 PWM level F0, 80, 00 hex), and the sample is output after developing, transferring and fixing under the above-mentioned developing conditions.

(5) The output sample is placed on the document table by the mode executor at the front end and the front side or the back side of the sample at a specific position, and the document recognizing means (not shown) is used to complete the placement. Judge whether it is detected.

(6) When it is determined that the placement is completed, the document is read by the reader as described above. It is desirable that reading by this reader is performed at a resolution of about 400 to 600 dpi.

(7) Whether or not this original is a test image sample is determined by whether or not the patterns have the same density gradation.

(8) When the image is judged to be a test image sample, the axial density distribution is calculated as shown in FIG. 13 (b). When the test image sample is formed at the PWM level of F0, 80, and 00hex, the read density distribution of the halftone portion of 80hex where the unevenness is most easily detected is calculated (the density distribution is calculated at F0, 80, and 00hex, respectively). May be.).

(9) As shown in FIG.
In the case of 5, the increase / decrease of the read density distribution of the halftone portion with respect to 0.5 is calculated so as to correspond to each pixel in the main scanning direction. If the negative correction is represented by a negative sign and the positive correction is represented by a positive sign, the required correction density is a diagram of the necessary correction density as shown in FIG.

(10) The correction light amount (correction level) for each pixel of the dot exposure laser is obtained from the diagram of the required correction density with reference to FIG. As an example, the required correction density is +0.8 in FIG.
In the case of, the surface potential is -200 V, and the drum surface light quantity is +
This indicates that it is necessary to correct 0.25 μJ and +80 hex for image data. A correction amount level corresponding to each pixel in the main scanning direction is assigned by this capacity, and a correction table is created. Here, this mode ends, and the operation panel, which is the input interface unit of the image forming apparatus, returns to the normal copy or print mode.

As described above, the main switch on
When the fixing thermistor temperature at that time is below the specific temperature and the environment is within the specific water content area (below), it is judged as the first morning and high humidity environment (and each environment), and the drum idle rotation ( The developing device and the cleaner system are also idled), and at the same time as the idle rotation starts, primary charging, laser exposure, and development are performed on the drum to form a black toner band. By correcting the uneven density at the writing level, the developability has risen to the point where the density can be obtained sufficiently and the reproducibility of isolated dots can be sufficiently ensured. The first copy image in the morning in a high humidity environment Also in this case, it is possible to obtain a high-quality image having no image deletion, high density, and no density unevenness in the longitudinal direction (main scanning direction) with a small image forming apparatus.

In each of the above-described first to third embodiments, an example in which an image is formed by the binarization processing by the error diffusion method or the like (or the dither method or the like) has been described, but the image is formed by the PWM method. Of course, it can be applied to cases. In addition, when an image is formed by the PWM method, basically, a pixel having a difference in lightness and darkness for each pixel (actually, it is a pixel of a different size due to area modulation. Can be perceived as
The density distribution can be corrected by simply reading the density distribution with the reader unit according to the embodiment. However,
In order to read even one pixel without deviation, it is necessary to read with a very high accuracy, and as a practical matter, it is difficult to determine the characteristics of each pixel formed on the printer engine side from the read image. Printer resolution is 600d
This is because if it is pi, it is necessary to read an image with a deviation of less than 1/600 inch, which is very difficult as a practical problem. Therefore, as described above, the PW
Even in the case of forming by the M method, it is desirable to detect the density unevenness in the main scanning direction by the average value of a plurality of pixels read in the main scanning direction and correct it.

Although the present invention has been described by taking the printer as an example, it can be applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.).

In this case, since the above processing can be performed by the portion corresponding to the host computer, the present invention uses a storage medium having a program code of software for realizing the functions of the above-described embodiments as a system or a storage medium. It can also be achieved by supplying the program to the device and causing the computer (or the CPU or MPU) of the system or the device to read and execute the program code stored in the storage medium.

In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention.

As a storage medium for supplying the program code, for example, a floppy disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM,
CD-R, magnetic tape, non-volatile memory card, RO
M or the like can be used.

Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also the OS (operating system) running on the computer is executed based on the instruction of the program code. It goes without saying that it also includes the case where the system) performs a part or all of the actual processing and the processing realizes the functions of the above-described embodiments.

Further, after the program code read from the storage medium is written in the memory provided in the function expansion board inserted into the computer or the function expansion unit connected to the computer, based on the instruction of the program code, A CPU provided in the function expansion board or function expansion unit performs a part or all of the actual processing,
It goes without saying that the processing includes the case where the functions of the above-described embodiments are realized.

[0165]

As described above, according to the present invention,
It has been detected that the amount of water in the surrounding environment is above a certain amount.
And while this condition continues to be detected
Toner for polishing cannot be used until the number of image formation reaches a certain number.
-Since an image is formed, the shape of the toner image for polishing is
The amount of toner required for formation can be extremely reduced.
That is, the toner amount can be minimized.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing a schematic configuration of an image forming apparatus according to a first embodiment.

2A to 2C are diagrams schematically showing a relationship between a surface potential of a photosensitive drum and a developing bias.

FIG. 3 is a block diagram showing image processing according to the first embodiment.

FIGS. 4A to 4C are diagrams showing the relationship between image data for each pixel, a laser drive signal, and a drive current.

5 (a) and 5 (b) are diagrams for explaining laser lighting of binary image data.

FIG. 6 is a diagram showing general IL characteristics (driving current-light quantity characteristics) of a laser.

7A to 7C are schematic diagrams in which the cause of density unevenness in the main scanning direction is factor-analyzed.

FIG. 8 is a diagram showing a relationship between a charging wire current and a drum surface potential.

FIG. 9 is a diagram showing a relationship between an image exposure amount and a drum surface potential.

FIG. 10 is a diagram showing a relationship between development contrast potential and development density.

FIG. 11 is a diagram showing a relationship between image data and a wide area integrated image exposure amount.

FIG. 12 is a flowchart showing an outline of the flow of a correction operation.

13A to 13C are diagrams showing a test image sample, a read density, and a correction required density.

FIG. 14 is a diagram illustrating a correction amount.

FIG. 15 is a vertical sectional view showing a schematic configuration of the image forming apparatus according to the second embodiment.

16A to 16F are schematic diagrams for explaining an image forming process in a two-color image forming mode according to the second embodiment.

FIG. 17 is a block diagram showing image processing according to the second embodiment.

FIG. 18 is a vertical sectional view showing a schematic configuration of an image forming apparatus according to a third embodiment.

FIG. 19 is a vertical sectional view showing a schematic configuration of a conventional image forming apparatus.

FIG. 20 is a diagram showing a specific circuit configuration of a main scanning unevenness correction circuit.

FIG. 21 is a diagram showing a sequence according to the first embodiment.

FIG. 22 is a diagram showing the control of the water content of the black band width and the data for writing the black band.

[Explanation of symbols]

1 Image carrier (photosensitive drum) 2 Primary charger (scorotron charger) 3 Exposure means (exposure device) 7 Developing device 8 Transfer device (transfer charger) 20, 20a, 20b Exposure means (laser) 20c Exposure means (light emitting element, LED) 50 Correction value creating means (main scanning unevenness correction circuit) 62 Developer Charge Control Charger (Post Charger)

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-8-194364 (JP, A) JP-A-3-107957 (JP, A) JP-A 63-192074 (JP, A) JP-A 61- 4092 (JP, A) JP 8-115030 (JP, A) JP 2-44388 (JP, A) JP 4-317076 (JP, A) JP 4-352174 (JP, A) JP-A-7-20726 (JP, A) JP-A-7-287495 (JP, A) JP-A-4-234066 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G03G 15/00 G03G 15/04 G03G 21/00 G03G 21/10-21/14 G03G 21/20 B41J 2/44-2/46

Claims (2)

(57) [Claims] 1. A charging unit for uniformly charging the surface of an image carrier, an exposing unit for exposing the surface of the image carrier after charging according to image data to form an electrostatic latent image, and the electrostatic latent image. Developing means for developing toner image by attaching toner to the
Transfer means for transferring the toner image formed on the image carrier to a transfer material, fixing means for fixing the toner image on the transfer material , and cleaning means for cleaning the surface of the image carrier after the toner image transfer. , Detection means for detecting the amount of water in the surrounding environment
If, in an image forming apparatus having a normal image forming amount of water surrounding environment is performed by sensed state to be the specific amount of water or by said detecting means
After the number of operations has reached the specific number, to form a toner image for abrasive to the charging means and the exposure means and the said <br/> image bearing member by operating the developing means, the click this
An image forming apparatus characterized by supplying to a leaning means . 2. A feature that the specific number of times can be input
The image forming apparatus according to claim 1, which is a characteristic.