JP2003263034A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small and inexpensive image forming apparatus in which paper is highly accurately carried without using a paper carrying belt, color slippage is reduced, and the reliability is high and the maintenance is easy. <P>SOLUTION: The outside diameter of a photoreceptor is set equal to or smaller that such a value that the stiffness energy of the paper is made larger than the sucking energy of the paper, so that the paper can naturally be separated and the apparatus can be miniaturized. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying machine, a facsimile and a printer, and more particularly to an image forming apparatus using an electrophotographic system.

[0002]

2. Description of the Related Art In recent years, with the improvement of personal computer capabilities in offices, a large number of documents are handled, and printers and copiers with high processing capability are becoming popular due to the progress of network technology. On the other hand, due to the rapid spread of inkjet printers,
Documents are also on the rise. However, an engine capable of outputting a satisfactory black-and-white and color document including speed is under development and its appearance is awaited.

In one of the conventional image forming apparatuses, a plurality of image forming units are arranged on a sheet conveying path extending in the horizontal direction, and the sheets moving along the sheet conveying path are sequentially arranged from the image forming units. Transfer the toner image and color it on the paper.
A so-called tandem type that forms an image is known. As the paper conveyance method, a transfer roller conveyance method is provided in which a transfer roller that comes into contact with the image carrier (photoreceptor) of each image forming unit is provided, and the paper is conveyed by the photoreceptor and the transfer roller. Alternatively, there has already been proposed a belt conveyance system in which a sheet conveyance belt that circulates along a sheet conveyance path is provided, and the sheet conveyance belt holds the sheet by, for example, electrostatic attraction.

Regarding the arrangement structure of each image forming unit, a horizontal type in which a plurality of image forming units are arranged side by side with respect to a sheet conveying path along the horizontal direction, or a sheet conveying path along the vertical direction. On the other hand, a vertical installation type in which a plurality of image forming units are arranged in the vertical direction has already been proposed. In the case of the horizontal type, it is said that the stability of sheet conveyance during transfer is excellent. On the other hand, in the case of the vertical type,
With respect to the arrangement of the plurality of image forming units, the space can be effectively used, so that the unit interval can be shortened.

For example, the image forming apparatus disclosed in Japanese Unexamined Patent Publication No. 9-325560 proposes an apparatus for vertically conveying a sheet. In this application, the paper transport roll is
The distance between the registration roller and the fixing device is shorter than the paper length to improve the paper feeding accuracy, and the registration roller can be used without using the paper conveyance belt or the intermediate transfer belt.
There is disclosed a method in which a sheet is conveyed at a nip portion between a roller and a fixing device or a transfer roller and a photoconductor. The sheet conveying belt is expensive, and the belt unit requires measures to prevent the belt from meandering, resulting in an increase in size of the apparatus and an increase in cost. On the other hand, this method is suitable for downsizing and cost reduction of the device.

[0006]

However, the above-mentioned image forming apparatus has the following problems.

When the toner image is transferred onto the paper, the semi-insulating paper is brought into close contact with the charged photoconductor, and a voltage opposite to the polarity of the photoconductor is applied from the back surface of the paper. Therefore, the force of adhering to the photoconductor acts on the paper. The paper separating means is effective for preventing the paper from sticking to the photoconductor, but since the separating claw disturbs the image, it is attached only to the edge of the paper that does not disturb the image, and its effect is very unsatisfactory. It is stable. It has been conventionally known to dispose a charger for separation and a light source for removing charges of the photoconductor,
Both of them not only increase the cost, but also cannot be incorporated in a small device. If the separation becomes unstable, an error occurs in the paper traveling path, which causes misregistration in the paper feeding direction and deteriorates the image quality.

Further, when the paper is conveyed at the nip between the transfer roller and the photoconductor, the paper will meander unless the parallelism of the photoconductor is ensured with high precision, which causes plate misalignment in a direction perpendicular to the paper feeding direction. . The same applies to the parallelism between the paper feed roller and the photoconductor.

If the paper gripping force between the transfer roller and the photoconductor is weak, the paper will slip when the leading edge of the paper collides with the paper guide, the transfer roller, the photoconductor, or the fixing device, and the paper will slip. Speed fluctuations can occur. At this time, if four transfer rollers are used, the sheet is sent from the registration roller and passes through four transfer parts until the image formation is completed by the four image forming parts. Occurs four times and at the same timing, even a small speed fluctuation can cause color misregistration. Further, since the paper is sent out on the surfaces of the four photoconductors, the surface speeds of the four photoconductors must be synchronized. A large error factor in the surface speed of the four photoconductors is the diameter variation of the photoconductors. Accurately aligning four diameters increases the manufacturing cost. Therefore, a method has been proposed in which a drive belt is wound around the outer periphery of the photoconductor to frictionally drive the photoconductors so that the speeds of the four photoconductors are equalized (JP-A-10-177311 and JP-A-10-186778).
However, even in that case, the paper feed speed fluctuates in one cycle of the photoconductor due to the shake of the photoconductor in the axial direction (straightness error), and the phase of the magnitude of the shake is four photoconductors. Do not match. If the speeds do not match, the paper will slip between the image forming units or the paper will bend, resulting in misregistration of print registration.

Further, the sheet conveying speed at the transfer portion on the most upstream side in the sheet conveying direction is determined by the sheet conveying resistance of the registration roller,
It is affected by fluctuations in the paper feed speed. This tends to be remarkable when thick paper is used, and the influence becomes large when the apparatus is downsized and the distance between the registration roller and the transfer roller is narrowed. This is because the sheet conveyance speed at the registration roller causes microslip of the sheet between the transfer roller and the photoconductor due to the rigidity of the sheet.
Therefore, in order to miniaturize the apparatus and to cope with a wide variety of paper types, it is necessary to synchronize and match the paper conveyance speed of the registration roller with the speed of the photoconductor.

The present invention solves the above-mentioned problems, and conveys a sheet with high accuracy without using a sheet conveying belt, has a small color shift, is small in size, low in price, highly reliable, and easy in maintenance. The purpose is to provide.

[0012]

To achieve the above object, in an image forming apparatus of the present invention, a plurality of image forming units having an image carrier and arranged along a transfer material conveying path, And a transfer unit that is arranged to face the image carrier of each of the image forming units and that transfers a toner image on the image carrier onto a transfer material, and that moves along the transfer material transport path. In an image forming apparatus that sequentially transfers a toner image from the image carrier of each of the plurality of image forming units to a transfer material, the transfer material shown in (Equation 1) is electrostatically attracted to the image carrier. Energy (Ua)
And the elastic deformation energy (Ub) of the transfer material in the state where the transfer material is wound around the image carrier as shown in (Equation 2), Ua <Ub. To do.

According to the image forming apparatus of the present invention, the elastic energy is larger than the adsorption energy of the transfer material, so that stable separation can be realized without requiring any special separating means. Furthermore, when the separation means such as a separating claw or a charger is used for separation, the transfer material is adsorbed up to the point where those separation means operate, so that the separation may vary due to variations in the separation means. Although there are variations in points, which causes misregistration in the transfer material conveying direction, since the transfer material does not wrap around the photoconductor in the first place, stable plate registration can be realized.

Further, it is preferable that the transfer material and the image carrier are separated by the rigidity of the transfer material. As a result, the transfer material can be separated with a simple structure.

Further, it is preferable to have a transfer material adsorbing means for adsorbing the transfer material immediately before the transfer position of the transfer means on the transfer material conveying path. This allows the car
It is possible to reduce the error in the transport path even with a transfer material having internal distortion such as a transfer material that has been printed or a transfer material that prints on both sides.

Further, the image forming apparatus of the present invention has a plurality of image forming units each having an image carrier and arranged along the transfer material conveying path, and the image carrier of each of the plurality of image forming units. A transfer unit that is arranged to face each other and transfers a toner image on the image carrier onto a transfer material; and a transfer unit that is arranged upstream of the plurality of image forming units in the transfer material transport direction and is directed toward the plurality of image forming units. An upstream transfer material conveying means for conveying the transfer material, and a downstream side for conveying the transfer material sent from the plurality of image forming units to the outside of the apparatus, which is arranged on the downstream side in the transfer material conveying direction of the plurality of image forming units. And an image forming apparatus for sequentially transferring a toner image from the image carrier of each of the plurality of image forming units to the transfer material that moves along the transfer material conveying path. A drive motor for driving the upstream side transfer material conveying means and the downstream side transfer so that the transfer material conveying speed by the upstream side transfer material conveying means and the transfer material conveying speed by the downstream side transfer material conveying means always match. At least one of the drive motors for driving the material conveying means is servo-controlled.

As a result, the transfer material conveying speed of the upstream side transfer material conveying means and the transfer material conveying speed of the downstream side transfer material conveying means can be made to coincide with each other, and the transfer material conveying speeds of the both transfer material conveying means deviate from each other. It is possible to suppress the color shift due to.

Further, the upstream side transfer material conveying means or the downstream side transfer material conveying means driven by the servo-controlled drive motor is driven by a gear from the servo-controlled drive motor. It is preferable that the driving force is transmitted and the reduction ratio by the gear is 1: n (n is an integer).

As a result, the cycle of servo control can be shortened and the memory for servo control can be reduced. Furthermore, origin detection becomes simple.

The upstream side transfer material conveying means or the downstream side transfer material conveying means driven by the servo-controlled drive motor comprises a pair of rollers which abut each other to form a nip. The ratio of the outer diameter of the roller driven by the servo-controlled drive motor to the outer diameter of the other roller of the pair of rollers is preferably m: 1 (m is an integer).

As a result, the cycle of servo control can be shortened and the memory for servo control can be reduced. Furthermore, origin detection becomes simple.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below in detail based on the embodiments shown in the accompanying drawings.

(First Embodiment) FIG. 1 shows a first embodiment of a color image forming apparatus to which the present invention is applied. In FIG. 1, the color image forming apparatus has image forming units 1a to 1d of four colors (yellow, magenta, cyan, and black in the present embodiment) arranged vertically in the apparatus, and supply units below the image forming units 1a to 1d. Sheet cassette 10 for storing sheets for printing
No. 0 is provided, and a paper transport path serving as a transport path for the paper from the paper feed cassette 100 is vertically disposed at a position corresponding to each of the image forming units 1a to 1d.

In the present embodiment, the image forming units 1a to 1d are arranged in the order of yellow,
The toner images of magenta, cyan, and black are formed on the photoconductor. The toner images of the respective colors formed on the photoconductor are sequentially transferred to a sheet (not shown). An optical unit 3 irradiates the photoconductor with laser light to write an electrostatic latent image on the photoconductor. In this embodiment, the optical unit 3 is composed of a semiconductor laser (not shown), a polygon mirror, and an imaging lens, and the light from the semiconductor laser (not shown) is deflected by the polygon mirror. It is configured such that scanning is performed and an optical image is guided to an exposure point on the photoconductor through an imaging lens.

FIG. 2 is a diagram showing details of the image forming units 1a to 1d used in the present embodiment. Here, the image forming unit refers to one set of the divided photosensitive member portion 18 and developing portion 19. The photosensitive member portion 18 includes a drum-shaped photosensitive member 10, a charging roller 13 that charges the photosensitive member 10 in advance, and a cleaner 12 that is an elastic sponge roller that removes residual toner on the photosensitive member 10. Integrated car
It is a tridge. It is considered that the diameter of the photoconductor 10 is preferably 30 mm to 16 mm from the viewpoints of shortening the distance between the image forming units, paper transportability, and transferability. Details will be described later.

On the other hand, the cleaner 12 is disposed on the upper side of the photosensitive member and has a roller shape of a conductive urethane foam, and is provided with a voltage having a polarity opposite to that of the toner while being applied to the photosensitive member. While having a peripheral speed difference with 10, the photosensitive drum 10 is rotated in contact with the photosensitive member 10 in the same rotation direction to scrape off the residual toner on the photosensitive member.

The developing section 19 has a developing case 14, which contains a developer containing a predetermined color toner, and the developing case 14 has a pair of developing cases. A developer agitator 15 as a developer stirring member, and a developing roller 16 at an opening portion of the developing case 14 facing the photoconductor 10 and developing on the developing roller 16 A developer layer thickness regulating blade 17 for regulating the layer thickness of the developer is provided. Then, a developing bias (not shown) is applied to the developing roller 16, so that the developer (toner) on the developing roller 16 flies toward the photoconductor. This time, since the two-component developing method that can extend the life of the developing section is adopted, the developer consisting of toner and carrier is stored. However, due to the structure, the developing unit of the one-component developing method is adopted to non-magnetic developing. A one-component developer composed of a developer or a magnetic developer may be contained. The gap between the photoconductor and the developing roller is adjusted by a cap roller which is rotatable coaxially with both ends of the developing roller. In particular, in this embodiment, the developer containing space is secured by extending the developing case 14 containing the developer in the depth direction, so that the vertical dimension of the image forming unit is short. It is set to the size.

Further, as shown in FIG. 3, in order to make the peripheral speeds of the photoconductors of the respective photoconductor parts the same, a ball bearing for fixing the outer circumference, a temperature change, and sliding of the photoconductor on aluminum. The outer peripheral surface of the photoconductor 10 is rotatably supported by a sliding bearing made of a resin material in which nylon is mixed with polyethylene, which is excellent in kinematics, so that rotational shake of each photoconductor 10 is suppressed and a single photoconductor drive belt is provided. The same surface of 102 is brought into pressure contact with the outer peripheral surface of the non-printing area of each photoconductor 10 and frictionally driven by the driving means, so that the peripheral speed of each photoconductor 10 is made the same. Belt drive pulley 1 of photoconductor drive belt 102
A shake of 03 causes uneven speed of the photoconductor 10,
The interval length between the image forming units on the paper transport path is approximately an integral multiple of the outer peripheral length of the belt drive pulley 103 of the photoconductor drive belt 102. In the case of this embodiment, the distance between the image forming units is set to 25.1 mm, and the outer diameter of the belt driving pulley of the photoconductor driving belt is φ8 (8 × 3.14 = 2).
5.12 mm). The photosensitive member drive belt 102
When the diameter of the belt driving pulley 103 is small, in order to obtain a sufficient frictional force, a urethane rubber coating on the surface of the belt driving pulley 103 is about 50 to 200 μm, or a ceramic coating is about 50 to 200 μm. When applied, the belt drive pulley 103 and the photoconductor drive belt 1
It is possible to prevent the slip between the two. On the other hand, if the coating is excessively thick, the coating unevenness causes a shake. Therefore, in the present embodiment, the coating of the urethane rubber is set to 100 μm. The photosensitive member drive belt 102 is made of urethane rubber or chloroprene rubber with aramid as the core wire, has a thickness of 0.8 mm and a width of 10 mm. By applying an appropriate tension, a drive without slip can be obtained by the above combination. Was given. Here, in the present embodiment, if the length of the belt is about 250 mm, it is possible to sufficiently drive the photoconductor having the layout under the above conditions, but here, the length is set to 350 mm. This is because it is easy to correct the misregistration due to the thickness variation of the belt,
This is because the sheet misalignment at the time of continuous printing, the sum of the sheet lengths, and the belt length are matched so that the plate misalignment is always at the same place on the sheet. It is advisable to attach a home position mark to the belt so that the misregistration is constant even during intermittent printing, and to synchronize with the start of the printing operation.
When the layout of the photoconductor drive belt 102 is designed so that the same surface as the surface that contacts the surface of the belt drive pulley 103 contacts the photoconductor 10, the photoconductor drive belt 102 alone is inspected and a cleaning mechanism for preventing foreign matter from adhering. It is desirable because it can simplify things such as

Further, in the present embodiment, as shown in FIG. 4, the main body of the image forming apparatus has an opening / closing door 2 on the left side in FIG. 4, and an image is formed through the opening when the opening / closing door 2 is opened. The forming units 1a to 1d can be taken in and out. In the closed state, the opening / closing door 2 presses and contacts the photoconductor 10 to transfer the toner image on the photoconductor to a sheet.
a to d are attached.

In this embodiment, the transfer means 20a to 20d employ a rotatable transfer roller coated with a foamed conductive member. The transfer roller is attached by a guide groove (not shown) formed on both sides of the opening / closing door 2 at both ends of the transfer roller.
A transfer pressing spring is provided so as to come into contact with the photoconductor 10 from the backside with a predetermined pressing force by the transfer positioning means formed on the main body side of the image forming apparatus.
The photoconductor 10 is rotated by the photoconductor 10. The outer diameter of the transfer roller was 16 and the hardness was 30 degrees (Asker-C). Then, a predetermined transfer electric field is applied to the transfer roller so as to give a transfer force to the transfer roller side with respect to the toner image on the photoconductor.
Further, as shown in FIG. 5, paper guides 21a to 21d for restricting the movement path of the paper are provided on the front side of each photoconductor 10. The paper guides 21a to 21d are used for the transfer rollers 20.
(A to d) are integrally supported by each transfer roller 2
According to the positioning of 0 (a to d), they are arranged so that the plunging angle and the position of the sheet into each of the photoconductors 10a to 10d are the same,
The guides 21a to 21d extend toward the direction in which the back surface including the leading end of the sheet to be transferred and conveyed always contacts the sheet and toward the nip region between the photoconductors 10a to 10d and the transfer roller 20 (a to d). Are moved in contact with each other, and the leading end of the sheet is adjusted to abut the photoconductors 10a to 10d side before the nip area. The angle of the paper guide is important for stabilizing the paper traveling direction. Also, even if the paper angle is strictly adjusted, due to the curl of the paper itself,
The paper guide may not work. Especially when using a paper whose back side has already been printed with a high printing rate,
The curl is remarkable. In such a case, it is particularly effective to attract the paper to the paper guide. Specifically, the paper to which a voltage is applied at the transfer unit is charged, so if the paper guide is made of a conductive material and the paper guide is set to an appropriate potential, the paper is attracted to the guide and the paper runs. The trajectory is stable. As another method, it is effective to provide a fan that sucks the paper on the paper guide. In a high humidity environment where the electric resistance of the paper decreases and the electrostatic adsorption force decreases, it is preferable to use aerodynamic force like a fan.

Next, the operation of the color image forming apparatus according to this embodiment will be described. In response to an output signal from a personal computer (not shown) or the like, the paper in the paper feed cassette 100 is sent out by the feed roller, and then the leading end of the paper reaches the nip portion of the entrance side registration roller 4. Then,
The sheet is nip-transported by the registration roller 4 on the inlet side, and sequentially rushes into the transfer portion of each of the image forming units 1a to 1d on the sheet transport path. At this time, if a relationship of V1 ≧ V2 is established between the sheet conveying speed V1 at the entrance side registration roller and the sheet speed V2 at the photoconductor, the most upstream image forming unit 1a and the entrance side registration roller are formed. A deflection of the sheet is formed between the sheet 4 and the sheet. If the paper friction force at the transfer position is sufficiently high as the reaction force due to the slack of the paper, the nip conveyance force of the entrance-side registration roller 4 is applied to the paper that has entered the transfer site of the most upstream image forming unit and the transfer roller. The impact can be ignored. However, when a strong sheet such as thick paper is used, the bending force of the sheet between the most upstream image forming unit 1a and the entrance side registration roller 4 causes the sheet to slip at the transfer position,
The paper conveyance speed becomes unstable. In order to minimize the size of the apparatus, it is preferable that the distance between the registration roller 4 and the most upstream transfer unit is shorter, but the bending force of the paper is further increased, and the slip of the paper at the transfer position is more likely to occur. On the other hand, it is well known that if the pressure of the transfer rollers 20a to 20d is excessively increased in order to prevent slippage, a partial transfer failure is likely to occur particularly in the case of characters and the like. However, when the transfer roller pressure is lowered, the sheet conveying force at the transfer portion is reduced, and the sheet is easily affected by the sheet conveying speed of the registration rollers and the sheet bending force. Therefore, in consideration of image quality and stability for a wide range of sheets, it is desired that the speed difference between the registration roller and the image forming unit is small.

The speed ratio between the registration roller and the photosensitive member is 1:
Even with No. 1, the sheet feeding speed at the registration roller includes unevenness due to eccentric runout of the registration roller, the photoconductor, or their drive gears. This unevenness causes a variation in the time when the sheet reaches each of the image forming units 1a to 1d, and causes a periodically varying plate misregistration. However, even if there is unevenness in time for the paper to reach each image forming unit, if the cycle of the unevenness coincides with the cycle in which the paper is sent between the image forming units, unevenness in speed may occur, but misregistration of colors may occur. Don't Therefore, it is desirable to match the distance between the image forming units with the outer peripheral length of the registration roller. This is the same when thick paper is used even when V1 ≧ V2.

In this embodiment, the registration roller 4 and
The diameter of the belt driving pulley 103 of the photoconductor driving belt 102 is φ8, and the distance between the image forming units 1a to 1d is 25.
1 mm (φ8 × 3.14), driven by one motor (not shown), the registration roller 4 and the photosensitive member driving belt 1
No. 02 belt drive pulley 103 was driven by a 1: 1 gear. If the gear ratio between the registration roller 4 and the belt driving pulley 103 of the photosensitive member driving belt 102 is not an integral multiple, the phase of meshing of the gears shifts with rotation, and harmonic components are added to the speed unevenness, which is not desirable. Desirably, the registration roller 4 is laid out so that the registration roller 4 also serves as the belt driving pulley 103 of the photoconductor driving belt 102 from the viewpoint of reducing color misregistration.

Further, the passing speed of the paper at the transfer position of each of the image forming units 1a to 1d is sent by the surface speed of each of the photoconductors 10a to 10d. The surface velocities of the four photoconductors are synchronized with each other by the configuration described above. Moreover, since the transfer position interval of each of the image forming units 1a to 1d is set sufficiently short (25.1 mm) with respect to the paper, the vicinity of the leading end of the paper that enters the transfer position of each of the image forming units 1a to 1d. Is held at the entrance side registration roller or the transfer nip portion (nip portion between the photoconductor and the transfer roller) of the image forming units 1a to 1c on the front side.
Even with thin paper, the free end length is sufficient to allow the paper to be stiff, so the position of the leading edge of the paper that enters the transfer position of each image forming unit a-d is stable. For this reason, since the timings of the sheets entering the transfer positions of the image forming units 1a to 1d are kept constant, the transfer position deviations of the toner images of the respective colors are eliminated, and the color deviations and the color unevenness of the color images are eliminated. .

When the leading end of the sheet reaches the fixing unit 5 and is nipped, the conveying speed V3 of the fixing unit 5 and the photosensitive member 10 are reached.
When the peripheral velocities of a to d are V2, there is a relationship of V2 ≧ V3, so that the slack occurs in the sheet between the fixing device 5 and the most downstream image forming unit 1d, and the sheet conveying force by the fixing device is increased by each image forming unit 1a. There is no influence on the paper at the transfer positions of ~ d. However, also in this case, the paper gripping force at the transfer position is weakened, and when thick paper is used, the reaction force of the slack of the paper between the fixing device and the most downstream image forming unit 1d affects the paper transport speed. Therefore, V2 = V3
However, in the present embodiment, V3 = 0.994 × V2 is set in consideration of the fluctuation of the fixing roller of the fixing device and the speed unevenness (about 0.5%) due to the fluctuation of the drive gear. , Optimized by experimentally obtaining the distance between the most downstream image forming unit 1d and the fixing device and the shape of the paper guide in which the paper of the maximum thickness used in this image forming apparatus does not slip at the transfer position. did. Therefore, the passing speed of the paper at the transfer position of each of the image forming units 1a to 1d is always kept constant, and the occurrence of color misregistration is reduced.

In particular, in this embodiment, since the cycle of the unevenness of the feed of the registration roller and the interval of the image forming unit are matched, the unevenness of the feed of the registration roller does not affect the unevenness of the paper feed at the transfer position. , Color misregistration
It is possible to reduce the speed variation at the transfer position due to the shake of the spot, and it is possible to reduce the color shift.

Ua is given by the following equation, where Ua is the energy with which the paper is attracted to the photoconductor by the transfer electric field.

[0038]

[Equation 3]

On the other hand, the bending energy of paper is

[0040]

[Equation 4]

The condition that the paper is not wound around the photoconductor is Ua <
Ub, so

[0042]

[Equation 5]

Here, the surface potential Vs of the photoconductor is Vs = -100.
0V, surface potential of transfer means Vt = + 1000V, longitudinal elastic modulus of paper E = 2.1 × 10 ⁹ N / m ² , paper thickness d ₄ =
50 × 10 ^-6 m, the gap between the photoconductor and the paper is d ₂ = 1
Substituting 0 ⁻⁶ m gives R <20 mm.

In order to confirm the above results, high temperature and high humidity (3
3 ℃, relative humidity 80%), low temperature and low humidity (6 ℃, relative humidity 2)
Under the condition of 0%), a continuous paper feed test of 10 sheets was performed using thin paper (thickness 50 μm) and thick paper (thickness 120 μm). In the test, the surface potential of the photoconductor was −1000V and the voltage of the transfer roller was + 1000V. The diameter of the photoconductor is φ16 mm, φ24 mm, φ40 mm, and φ60 m for the test.
m was selected to evaluate paper separation. The results are shown in (Table 1).

[0045]

[Table 1]

In Table 1, ∘ indicates that there was no separation failure during the test, Δ indicates that separation was carried out but peeled off while partly winding around the photoreceptor, and x indicates that separation failure occurred and the photosensitive material was exposed. It indicates that the paper is wrapped around the body. When this result is compared with the above R <20 mm, it shows that the formula can be quantitatively evaluated.

From these results, when the diameter of the photosensitive member was set to φ16 and the image forming apparatus of FIG. 1 was experimentally manufactured and tested, not only the separation failure of the paper but also the plate misalignment due to the delay of the separation point of the paper did not occur. It was

(Second Embodiment) FIG. 6 shows another embodiment of the image forming apparatus to which the present invention is applied. In the present embodiment, detailed description of the same components as in the first embodiment will be omitted. In FIG. 6, a transfer roller is used at the most downstream transfer position, but a film-shaped transfer means is used as the other transfer means. This film is a resin filled with a conductive filler, and has a thickness of 80 μm, which is made by adding carbon to a polyolefin resin to make it conductive.
The film is processed and used. The material is not limited to this, and a fibrous brush made by adding carbon to nylon or rayon may be used. The film-shaped transfer means is fixed to the fixing bracket with a conductive adhesive,
It is attached diagonally to the photoconductor. In this case, the traveling direction of the leading edge of the sheet is particularly important. As shown in FIG. 7, the sheet guide is attached with a slight inclination so that the leading edge of the sheet faces the photoconductor, and the leading edge of the sheet is transferred onto the film. The film-like transfer means is prevented from being damaged by directly hitting the means. The operation of the apparatus in this case will be described.

The sheet sent by the registration roller 4 is transferred to the film-like transfer means 22 after the leading edge of the sheet collides with the photoconductor.
The toner image on the photoconductor is transferred to a sheet by being sandwiched between a to c and the photoconductor 10 and applied to the film. From the transfer position of the most upstream image forming unit, the paper passes through the second and third color image forming units, reaches the most downstream image forming unit, and the leading edge of the paper is transferred to the most downstream photosensitive member. The paper is gripped between the rollers and the paper is conveyed by both the registration roller and the transfer unit. At this time, between the registration roller and the transfer section,
If there is an error, misregistration will occur and the image quality will deteriorate. In this case, the registration roller and the most downstream photoconductor were driven by the photoconductor drive belt to ensure speed synchronization (FIG. 8). Compared to the first embodiment in which the speeds of four photoconductors are synchronized by the photoconductor drive belt, the number of photoconductors to be driven is small, so that the driving load can be reduced. In addition, since the winding angle of the belt can be made large, the slip between the belt and the photosensitive member and between the belt and the driving roller can be reduced. At the transfer portions of the photoconductors 10a to 10c other than the most downstream side, the paper slips on the photoconductor and is conveyed. In this case, even if there is eccentricity of the photoconductor, the transfer position is corrected by slipping when the image is transferred to the paper, so if the speed of the paper and the writing speed to the photoconductor match, color misregistration occurs. It doesn't. Similarly, the photoconductors 10a to 10c
Even if there are variations in the diameter of the sheet, it does not affect the sheet conveying speed, and therefore, color shift does not occur.

Here, in this embodiment, the photoconductor 10d of the image forming unit located on the most downstream side and the registration roller 4 are arranged.
Is driven by the photoconductor drive belt 102 to synchronize the speeds. However, the registration roller 4 and the sensor for measuring the speed of the most downstream photoconductor 10d or the fixing device 5 are installed, and the respective speeds are set. The speed may be synchronized by feedback control. So-called servo control is performed. FIG. 9 shows a speed measurement mode. In FIG. 9, a strip-shaped bar code reading marker 105 is attached to the surface of a rotating roller. The reading marker 105 is a black and white pattern with a pitch of 200 μm and is printed with high accuracy. An LED sensor (a light emitting portion and a light receiving portion) for detecting the reflected light of this marker is arranged, and the average value of the tangential velocity of the roller rotation and the uneven profile are measured. The part of the joint is the data of the other part.
Correction of the joint part by supplementing from the data. Since the joint portion involves a sharp frequency change, it is preferable to provide a filter for canceling high frequency components in the signal processing unit of the LED sensor. By feeding back the speed and the unevenness of the rotating roller thus obtained to the pulse for determining the feed speed of the drive motor, it is possible to realize the paper feed at a constant speed. Even if the diameter of the roller varies within the design value range and the average speed also varies, LE
It can be determined from the frequency of the D sensor. Such a feedback control system is an accurate marker,
Since the high-sensitivity LED sensor, signal processing, motor speed control, etc. are expensive, it is more advantageous in terms of cost to reduce the number of speed control objects as in the present embodiment. In this embodiment, it is most appropriate that the resist roller is incorporated in the main body and the photoconductor (consumable) is exchanged for use.
The control system shown in FIG. 9 is applied to the most downstream photosensitive member, and the registration roller and fixing roller are improved in mechanical accuracy, and the runout and diameter tolerance are measured at the time of factory shipment (using a laser Doppler device etc. ), It is also a good method to reduce the cost to embed the data for determining the rotational speed of the resist roller in the machine based on the data.

FIG. 10 shows an example of a method for measuring the runout and diameter tolerance of the rotating roller. In FIG. 10A, 51 is a heat roller used in the fixing device 5, and 107 is a surface velocity measuring device of the heat roller. For 107, a non-contact measurement method using a laser Doppler device, a bar code-shaped reading pattern used in FIG. 9 is attached for measurement, or a contact-type speed measuring device or the like is used. You can Reference numeral 108 is an origin detection plate having an origin mark attached at one place.
It is fixed coaxially with the tracker 51. Reference numeral 109 is an optical sensor for detecting the mark on the origin detecting plate. The heater roller 51 is connected to a motor (not shown) as shown in FIG. 10 (b). When the motor is rotated, the surface speed of the heat roller and the output of the origin sensor with respect to the motor rotation angle are observed as shown in FIG. The rotation speed of the heat roller varies due to eccentricity of the heat roller, misalignment of the rotating shaft, accuracy of the entire drive gear train, and the like. This fluctuation is a value peculiar to the entire system that drives the heater and has some periodicity. From the relationship between the periodicity and the origin sensor, it is possible to open control the drive frequency of the motor by obtaining an inverse function that keeps the surface velocity of the heater roller constant. What is important here is the cycle of the surface velocity of the heat roller and the output of the origin sensor. Assuming that the reduction gear ratio of the heat roller is 1: n (n is an integer), the longest variation cycle can be the rotation cycle of the heat roller. On the other hand, if the reduction gear ratio is not set to 1: n, the least common multiple of the gear ratio becomes the longest cycle. FIG. 11 shows the case where the gear reduction ratio is not set to 1: n. In this example,
The speed fluctuation is observed as the sum of the speed fluctuation of one rotation cycle and the speed fluctuation of five rotation cycles. In this case, it becomes impossible to uniquely determine the speed unevenness from the output of the origin sensor and the rotation angle of the motor. Therefore,
The reduction gear ratio of the trolley gear is preferably 1: n. At that time, to embed data in the machine, EP-RO
It is more desirable to provide data for each part in a form such as M, because the registration roller and the fixing roller can be replaced at a local repair shop due to a trouble such as a failure. Since the paper is conveyed while being sandwiched between two pairs of rotating rollers, it is affected by the speed fluctuation of each roller and the coefficient of friction. Therefore, FIGS.
At 0, the rotation speed of the rotating roller was measured to control the rotation speed of the motor. However, it is preferable to combine two rollers to measure the speed unevenness when the paper is conveyed. In particular, when the control object is a large load torque such as a fixing roller and a multi-stage reduction gear train, it is necessary to pay attention to each speed fluctuation due to accumulation of gear accuracy. In that case, it is desirable to measure the speed fluctuations of the roller and the paper while being incorporated in the apparatus.

Regarding the diameters of the two rollers constituting the fixing device, the ratio of the diameter of the heat roller driven by the servo-controlled drive motor and the diameter of the driven pressure roller is m: 1 (where m is It is preferably an integer). In this example, the ratio is 1: 1. By configuring in this way,
Similar to the reduction ratio of the drive motor described above, the longest variation cycle can be set as the rotation cycle of the heat roller.

FIG. 12 shows an outline of the printing apparatus in which the unevenness of the sheet conveying speed in the fixing device is previously measured and the data is incorporated in this way. In FIG. 12, the film-like transfer means is
I am using one. In this device, the unevenness of the sheet conveyance speed at the registration roller and the unevenness of the sheet conveyance speed at the fixing device are measured by the laser Doppler device, inverse function data is created, and the motor for driving the registration roller and the fixing roller are driven. Generates pulse signal data for the motor. The image forming units are laid out at a pitch of 25 mm.
The distance from the registration roller to the fixing roller was 145 mm. Since the distance from the registration roller to the fixing roller is short, the paper fed by the registration roller is supported by the paper guide and the photoconductor roller provided between the paper and the rigidity of the paper, and the leading edge of the paper is fed. The leading edge of the paper passes through the transfer means 22a to 22d, reaches the fixing device 5, and is conveyed by the fixing roller and the registration roller. The speed of the fixing roller is adjusted by the aforementioned servo control to adjust the average speed,
Since the uneven speed is canceled out, the speed is adjusted to match the speed of the registration roller. Therefore, color shift can be suppressed.

In the above-described embodiment, the heat roller among the fixing rollers is driven by the servo-controlled drive motor. However, the present invention is not limited to this, and the pressure roller may be driven by the servo-controlled drive motor. Of course, the same effect can be obtained.

The same effect can be obtained by using the servo control described above not only for the fixing device but also for other transfer material conveying means.

[0056]

As described above, according to the present invention, it is possible to secure the stability of sheet conveyance without using expensive means such as a conveyor belt, and to provide a color image forming apparatus without color misregistration or color unevenness. It becomes possible to obtain.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an outline of an image forming apparatus according to a first embodiment.

FIG. 2 is an explanatory diagram showing details of an image forming unit used in the first embodiment.

FIG. 3 is an explanatory diagram showing details of a photoconductor driving device used in the first embodiment.

FIG. 4 is a detailed explanatory diagram showing attachment / detachment of the image forming unit used in the first embodiment.

FIG. 5 is an explanatory diagram showing details of a sheet conveyance path used in the first embodiment.

FIG. 6A is an explanatory view showing the outline of the image forming apparatus according to the second embodiment, and FIG. 6B is an explanatory view showing the details of the film-like transfer means.

FIG. 7 is an explanatory diagram showing details of a sheet conveyance path used in the second embodiment.

FIG. 8 is an explanatory diagram showing details of a photosensitive member driving device used in the second embodiment.

FIG. 9 is an explanatory view showing details of a roller speed measuring device used in the second embodiment.

10A is an explanatory view showing details of another roller speed measuring device used in the second embodiment, FIG. 10B is an explanatory view showing a gear configuration, and FIG. 10C is a relationship between a roller speed and an origin sensor. Illustration

FIG. 11 is an explanatory diagram showing the relationship between the roller speed and the origin sensor when the roller drive gear ratio is not an integral multiple.

FIG. 12A is an explanatory diagram showing an outline of the image forming apparatus according to the second embodiment, and FIG. 12B is an explanatory diagram showing details of a film-shaped transfer unit.

[Explanation of symbols]

1 (1a-1d) image forming unit 2 Transfer unit 3 Optical unit 4 Registration Roller 5 fixing device 10 photoconductor 11 Photoconductor unit housing 12 Cleaning Roller 13 Charging roller 14 Developer 20 (20a to 20d) Transfer roller 21 (21a-21d) Paper guide 22 (22a-22C) transfer film 23 Transfer film holding bracket 24 Opening hinge 25 Transfer film cleaning pad 26 Transfer film protection cover 27 Transfer film pressing plate 28 Transfer film fixed shaft 30 polygon mirror 31 Imaging lens 32 Reflective mirror 51 Pressure Roller 52 Heat Roller 100 paper cassette 102 photoconductor drive belt 103 belt belt drive pulley 104 Belt tension roller 105 Read Marker 106 LED sensor

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 21/14 G03G 21/00 372 (72) Inventor Akira Kumon 1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric Sangyo Co., Ltd. (72) Inventor Junichi Tanizaki 1006, Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. F term (reference) 2H027 DA16 DA17 DE02 DE07 DE10 EB04 ED02 ED16 ED24 ED25 EE03 EE04 EF09 2H030 AA01 AB02 AD04 AD05 AD05 AD05 AD05 AD05 BB44 BB53 BB71 2H033 AA14 BA11 BB17 BB37 CA13 CA40 2H200 FA06 FA16 FA20 GA12 GA23 GA29 GA30 GA34 GA45 GA47 GB15 GB25 GB30 HA02 HB12 HB14 HB22 JA02 JB10 JB12 JB17 JB20 KA12 PA10 PA11 PB14

Claims (6)

[Claims] 1. A plurality of image forming units having an image carrier and arranged along a transfer material conveying path, and the image carrier arranged so as to face the image carrier of each of the plurality of image forming units. A transfer means for transferring the toner image on the body onto a transfer material, and a toner image is sequentially transferred from the image carrier of each of the plurality of image forming units to the transfer material moving along the transfer material conveying path. In the image forming apparatus that transfers the
Energy (Ua) of electrostatically adsorbing the transfer material to the image carrier shown in (Equation 1) and the energy in the state in which the transfer material is wound around the image carrier shown in (Equation 2). Between the elastic deformation energy (Ub) of the transfer material, Ua <U
An image forming apparatus having a relationship of b. [Equation 1] [Equation 2] 2. The image forming apparatus according to claim 1, wherein the transfer material and the image carrier are separated by the rigidity of the transfer material. 3. The image forming apparatus according to claim 1, further comprising a transfer material adsorbing means for adsorbing the transfer material immediately before a transfer position of the transfer means on the transfer material conveying path. 4. A plurality of image forming units having an image carrier and arranged along a transfer material conveying path, and the image carrier arranged so as to face the image carrier of each of the plurality of image forming units. A transfer unit that transfers the toner image on the body onto a transfer material, and an upstream transfer unit that is arranged upstream of the plurality of image forming units in the transfer material conveying direction and conveys the transfer material toward the plurality of image forming units. A material conveying means and a downstream transfer material conveying means arranged downstream of the plurality of image forming units in the transfer material conveying direction and conveying the transfer material sent from the plurality of image forming units to the outside of the apparatus. In the image forming apparatus for sequentially transferring the toner image from the image carrier of each of the plurality of image forming units to the transfer material moving along the transfer material conveying path, the upstream side transfer material conveying means is provided. Drive motor for driving the upstream side transfer material transporting means and drive for driving the downstream side transfer material transporting means so that the transfer material transporting speed by the downstream side transfer material transporting means always coincides with each other. An image forming apparatus characterized in that at least one of the motors is servo-controlled. 5. The upstream side transfer material carrying means or the downstream side transfer material carrying means driven by the servo-controlled drive motor is driven by a gear from the servo-controlled drive motor. The image forming apparatus according to claim 4, wherein the driving force is transmitted, and the reduction ratio by the gear is 1: n (n is an integer). 6. The upstream-side transfer material transporting means or the downstream-side transfer material transporting means driven by the servo-controlled drive motor comprises a pair of rollers that abut each other to form a nip. 5. The ratio of the outer diameter of the roller driven by the servo-controlled drive motor to the outer diameter of the other roller is m: 1 (m is an integer). The image forming apparatus described.