JP2001337547A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent faulty transfer by preventing the surface charge density of transfer material from getting uneven due to charge supplied from a transfer electrifying means at a transfer part even when speed variation is caused by the fluctuation of the thickness in the peripheral direction of a recording material carrying belt. SOLUTION: In a transfer electrifier, the transfer current ITr of a power source is constant-current controlled, and the variation ΔVL of carrying belt speed (recording material carrying speed) V is changed as shown by ΔVL=ΔhL.ω (ΔhL: the fluctuation amount of the thickness and ω: the angular velocity of a driving roll), and the surface charge density Δσ of the recording material is changed as shown by Δσ=ITr/(V+ΔVL).G-ITr/V.G (G: the thrust length of the electrifier), and the faulty transfer due to too much or too little surface charge density is caused. Then, the thickness of the carrying belt is measured all over the periphery so as to obtain the profile of the thickness distribution all over the periphery. At the time of forming an image, the transfer current ITr is controlled by a control means corresponding to ΔVL (according to the profile of the thickness distribution) so as to restrain the change width of Δσ to the minimum.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to a full-color or mono-color image forming method in which a visible image is formed on an image carrier by an electrophotographic recording method or an electrostatic recording method, and the visible image is transferred to a recording material to obtain an image. The present invention relates to an image forming apparatus such as a color copying machine or a printer.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus employing an electrophotographic recording method forms a latent image on a photosensitive drum as an image carrier using light, magnetism, electric charge, and the like, and develops the latent image. The image forming apparatus includes an image forming unit that obtains a visible image, a recording material conveying unit that conveys the recording material to a transfer position of the image forming unit, and a fixing unit that fixes the visible image transferred to the recording material.

[0003] As a recording material conveying means, a belt-shaped conveying member (conveying belt) is frequently used in terms of conveying property, and the recording material is carried and conveyed to a transfer position and further to a fixing device. At this time, the recording material is held and carried on the transport belt by electrostatic attraction.

The transport belt is stretched and supported by one driving roller and at least one driven roller, and is driven to rotate by the driving roller. The conveyance belt is stretched with a constant force between the driving roller and the driven roller, and the conveyance belt is not slackened between these rollers, and is conveyed from the most upstream image forming portion at a constant speed. It moves to the image forming unit on the downstream side.

As described above, the recording material is electrostatically attracted to the transport belt, transported to each image forming section while being held by the transport belt, and the toner of each color formed in each image forming section. The image is transferred, and the toner image is fixed by the fixing device, so that a full-color image is obtained on the recording material.

[0006] The recording material transport belt shifts due to a long rotation or an external force during the recording material jam processing (the belt moves on the roller axis in a direction perpendicular to the driving direction).
Is provided to prevent the belt from falling off the roller.

A conventional image forming apparatus will be described with reference to FIG. FIG. 7 is a schematic diagram of a conventional full-color image forming apparatus.

The present image forming apparatus includes first, second, third and fourth four image forming units Pa and P in a main body CP of the apparatus.
b, Pc and Pd are juxtaposed. From the cassettes 7a and 7b storing the recording material in the apparatus main body CP, the fixing device 11 is moved.
A recording material transport belt (belt-like recording material transport member) 8 for transporting a recording material through these image forming portions is provided below the first to fourth image forming portions Pa to Pd. . The transport belt 8 is stretched and supported by a driven roller 9 and a driving roller 10, and is
It is driven to rotate in the direction. The driven roller 9 is provided with an application unit 9 a for applying tension to the transport belt 8 and a belt deviation regulating unit (not shown).

The transport belt 8 is a belt made of a thin dielectric material and carries a recording material which is fed out of the cassettes 7a and 7b and fed synchronously by the registration roller pair 100. The paper is sequentially transported to Pb, Pc, and Pd. The fixing device 11 receives the recording material discharged from the drive roller 10 side, and collectively fixes the toner images of the respective colors, which are transferred on the recording material in the respective image forming units Pa to Pd, in a full-color manner. To form a permanent image.

Next, each part will be described in detail. Each of the image forming units Pa, Pb, Pc, and Pd has substantially the same configuration, and includes photosensitive drums 1a, 1b, 1c, and 1d as image carriers that are driven to rotate in the direction of arrow B. Around the drum, primary chargers 2a, 2
b, 2c, 2d, developing units 3a, 3b, 3c, 3d for developing the electrostatic latent image formed on the photosensitive drum, and transfer chargers 4a, 4 for transferring the developed toner images of each color to a recording material.
b, 4c, 4d and cleaning devices 5a, 5b, 5c, 5d for removing the toner remaining on the photosensitive drum are sequentially arranged in the drum rotation direction (B direction). Exposure optical systems 6a, 6b, 6c and 6d are provided above the photosensitive drums 1a, 1b, 1c and 1d, respectively.

The developing device 3a contains yellow toner, and the developing device 3b contains magenta toner.
c contains cyan toner, and the developing device 3d contains black toner.

As the transfer chargers 4a to 4d, a non-contact charger such as a corona discharge or a contact charger using a transfer charger such as a blade, a roller, or a brush is used. Non-contact chargers generate ozone,
Since it is charged via air, it is vulnerable to fluctuations in the temperature and humidity environment of the atmosphere, and there are problems that images are not stably formed.
On the other hand, the contact charger has advantages such as ozonelessness, resistance to environmental changes in temperature and humidity, and high image quality.

The transfer charger sets the current contributing to the transfer at a constant current (constant current control) to stabilize the image, and the transfer voltage at the time of transfer to a constant voltage (constant voltage control). It is known that transfer defects that occur when a small-sized recording material or an image with a low image ratio is formed can be reduced.

In the above-described full-color image forming apparatus,
When the recording material is placed on the transport belt 8, the transport belt 8
Of the photosensitive drums 1a,
Image formation is sequentially started for 1b, 1c, and 1d. By the steps of charging, image exposure and development, a yellow toner image is formed on the photosensitive drum 1a of the first image forming unit Pa, a magenta toner image is formed on the photosensitive drum 1b of the second image forming unit Pb, and a third image is formed. A cyan toner image is formed on the photosensitive drum 1c of the forming unit Pc, and a black toner image is formed on the photosensitive drum 1d of the fourth image forming unit Pd.

By the movement of the conveyor belt 8, the recording material is changed to the photosensitive drums 1a to 1d of the first to fourth image forming units Pa to Pd.
Sequentially pass through the transfer section under the photosensitive drum 1a, and
1d is transferred to each transfer charger 4
The images are sequentially transferred in a superimposed manner by a to 4d to form a full-color image on the recording material.

After passing through the final fourth image forming portion Pd, the recording material is separated from the conveyor belt 8 and sent to the fixing device 11, where the toner images of the respective colors superimposed and transferred in the fixing device 11 are transferred. After being fused and fixed, the sheet is discharged to the sheet discharge tray 12.

[0017]

However, a desired color image should be formed on the above-described recording material on the assumption that the recording material is conveyed at a constant speed. Due to the thickness variation over time, the drive roller 9
A change occurs in the recording material conveyance speed defined by the formula (1), whereby the amount of charge per unit area supplied to the recording material or the like from the transfer charger 4 (4a to 4d) in the transfer section is uneven,
There is a problem that an image becomes defective.

Further, a change in the thickness of the transfer belt 8 over the entire circumferential length causes a large change in the transfer impedance at the transfer portion, and similarly, the charge per unit area supplied to the recording material or the like at the transfer portion. There is a problem in that the amount becomes uneven and an image becomes defective.

The above-mentioned problem is caused by the primary transfer of the toner image on the photosensitive drum to an intermediate transfer member such as an intermediate transfer belt, and the secondary transfer from the intermediate transfer member to a recording material. Occurs during the primary transfer and the secondary transfer.

An object of the present invention is to supply a recording material or the like from a transfer charging unit to a recording material in a transfer unit even if there is a thickness variation in a circumferential direction of a recording material conveying belt or an intermediate transfer body and a speed variation accompanying the thickness variation. It is an object of the present invention to provide an image forming apparatus capable of preventing unevenness in charge amount per unit area and obtaining a high-quality image free from image defects due to transfer failure.

[0021]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
An image bearing member on which a toner image is formed, a rotating recording material transport belt that carries a recording material and transports the image material to the image bearing member, and a toner image on the image bearing member on a recording material on the transport belt. In the image forming apparatus having a transfer charging unit for transferring, the thickness of the recording material conveying belt is measured over the entire circumference, a profile of a thickness distribution over the entire circumference of the conveying belt is obtained, and the thickness distribution of the thickness distribution is measured. Depending on the profile,
An image forming apparatus, wherein the transfer charging unit is controlled.

According to the present invention, the transfer charging means controls the transfer current at a constant current by the control means, and the control means of the transfer charging means controls the transfer current in accordance with the thickness distribution profile. Control. The transfer voltage of the transfer charging unit is controlled at a constant voltage, and the control unit of the transfer charging unit controls the transfer voltage according to the profile of the thickness distribution. The entire circumference of the recording material conveying belt is N
Divided into a plurality of areas, the average thickness in each of the N areas is obtained from the measured values of the thickness of the conveyor belt over the entire circumference, and the entire circumference of the transport belt divided into the N areas is determined. In the profile of the average thickness distribution, representing the profile of the thickness distribution over the entire circumference of the conveyor belt,
The transfer charging means is controlled. The average thickness in each of the N areas is written or affixed to the recording material transport belt as a numerical table. A plurality of the image carriers are provided, and a plurality of color toner images are formed on the plurality of the image carriers.

The present invention also provides an image carrier on which a toner image is formed, a rotating intermediate transfer member, and a first transfer charging means for transferring the toner image on the image carrier to the intermediate transfer member. And an image forming apparatus having a second charging means for transferring the toner image on the intermediate transfer member to a recording material conveyed to the intermediate transfer member, wherein the thickness of the intermediate transfer member is measured over the entire circumference. A profile of a thickness distribution over the entire circumference of the intermediate transfer body, and controlling the first transfer charging unit and the second transfer charging unit according to the profile of the thickness distribution. An image forming apparatus.

Further, the present invention comprises a rotating belt-shaped image carrier on which a toner image is formed, and a transfer charging means for transferring the toner image on the image carrier to a recording material or an intermediate transfer member. In the image forming apparatus, the thickness of the belt-shaped image carrier is measured over the entire circumference to obtain a profile of a thickness distribution over the entire circumference of the belt-shaped image carrier, and according to the profile of the thickness distribution, An image forming apparatus, wherein the transfer charging unit is controlled.

[0025]

Embodiments of the present invention will be described below in more detail with reference to the drawings.

Embodiment 1 The present invention is embodied in a full-color image forming apparatus in which a plurality of photosensitive drums as image carriers and a transport belt as a recording material transport member are arranged as shown in FIG. Can be. The basic configuration of the image forming apparatus of the present invention is the same as that of the image forming apparatus of FIG.
Hereinafter, description will be made with reference to FIG. 7 as necessary.

FIG. 1 shows a recording material conveying means in an embodiment of the image forming apparatus of the present invention.

The recording material conveying means includes a conveying belt 8 of a recording material conveying member, a driven roller 9 and a driving roller 10 which are stretched and supported by being wrapped around the conveying belt 8, and a driving source (not shown).

In the present invention, the recording material conveying belt 8 is
For example, after being formed by centrifugal molding or the like, the thickness of the transport belt is measured over the entire circumference by an appropriate thickness measuring means, and the thickness distribution over the entire circumference, that is, the thickness profile is obtained.

The thickness of an arbitrary portion in the circumferential direction of the transport belt 8 is determined at any position in the width direction orthogonal to the belt moving direction (the direction of arrow A), such as the front portion, the center portion, and the back portion of the belt. It is the same. When a plurality of conveyor belts 8 are picked up and the conveyor belts are manufactured in the same manufacturing process, the thickness of the same number of the conveyor belts in the circumferential direction is the same. It is empirically known that the distribution of the belt thickness in the circumferential direction, that is, the profile of the belt thickness in the entire circumferential direction is substantially the same.
FIG. 2 shows a measurement example of a thickness profile over the entire circumference (length L) of a typical belt.

As described in the section of the prior art, a desired color image should be formed on the recording material on the assumption that the recording material is conveyed at a constant speed. 7 causes a change in the recording material conveyance speed defined by the driving roller 9, whereby the unit supplied from the transfer charger 4 (4 a to 4 d) of FIG. The charge amount per area may be uneven, resulting in an image defect.

According to the present invention, even when the thickness of a recording material conveying belt or the like fluctuates in the circumferential direction, the amount of charge per unit area supplied from the transfer charger to the recording material or the like at the transfer portion is uneven. Is to prevent The phenomenon of uneven charge is
In particular, in the present embodiment, a method of preventing the transfer charging device 4 when the constant current control is performed will be described in detail.

If there is a variation in the thickness of the transport belt 8, a speed variation (also a variation in the recording material transport speed) occurs in the transport belt, and the variation in the speed variation of the transport belt causes the thickness of the transport belt to be h. , The thickness variation at the entire circumference L of the belt is Δ
Assuming that h _L , r is the radius of the drive roller 9 around which the belt is wound, and ω is its angular velocity, the speed fluctuation of the transport belt speed (linear speed) V defined by the drive roller is represented by ΔV _L, as follows: You.

ΔV _L = Δh _L · ω (1) Due to the speed variation of the transport belt, and thus the transport speed variation of the recording material, on the recording material by the transfer current supplied from the transfer charger 4 to the recording material. A change occurs in the amount of charge per unit area, that is, the surface charge density σ [C / cm ² ].

FIG. 3 shows the amount of change Δσ in the surface charge density described above, together with the conveyance belt speed fluctuation ΔV _L and the transfer current Itr. In FIG. 3, t on the horizontal axis is time. The transfer current Itr is a transfer current of constant current control.

The surface charge density σ is given by the following equation: σ [C / cm ² ] = Itr / V · G (2) where Itr: transfer current, V: conveyor belt speed, G: transfer charger thrust length It is represented by

Therefore, Δσ is as follows: Δσ = Itr / (V + ΔV _L ) · G−Itr / V · G (3)

Looking at each of the graphs shown in FIG.
Since the transfer current Itr is a constant current control, Itr always shows a constant value with respect to time t. The conveyance belt speed variation (recording material conveyance speed) ΔV _L indicates a change according to the equation (1), and the surface charge density Δσ indicates a change according to the equation (3).

Attention is paid to point A in FIG.
Is negative. This indicates that the surface charge density given to the recording material by the transfer charger around point A is smaller than the appropriate value Δσ = 0, and in some cases, a transfer failure due to insufficient surface charge density is caused. . The vicinity of the point B is opposite to the point A, indicating that the surface charge density is larger than an appropriate value.
In some cases, transfer failure due to excessive surface charge density is caused.

Therefore, in this embodiment, the transfer current Itr is controlled in accordance with ΔV _L by the control means for controlling the transfer power supply for applying the transfer voltage to the transfer charger at a constant current, and the variation width of Δσ is minimized. This suppresses the occurrence of transfer failure due to the shortage or excessive surface charge density as described above.

FIG. 4 shows an example of the surface charge density change Δσ when the transfer current control according to the present embodiment is performed. It can be seen that the surface charge density change Δσ is almost zero by changing the transfer current Itr with respect to the time t according to the conveyance belt speed fluctuation ΔV _L.

The details of the control of the transfer current Itr according to the conveyance belt speed variation ΔV _L will be described below.

A transport belt 8 having a similar thickness profile in the belt circumferential direction at each of the front, middle, and back portions in the belt width direction.
In contrast, as shown in FIG. 1, a mark M serving as a home position is attached to a position indicating the reference. Further, a sensor S for detecting the mark M is provided in the apparatus. By detecting the mark M by the sensor S, the reference position with respect to the entire circumference of the conveyor belt 8 is determined, and the base point of one round of the conveyor belt is determined, so that the thickness profile in the entire circumference measured in advance is managed. be able to.

By installing a conveyor belt unit incorporating the conveyor belt 8 in the apparatus in a state where the thickness profile of the entire circumference is controlled, the position detected by the home position mark M is used as a reference. ,
The speed fluctuation amount ΔV _L caused by the thickness profile over the entire circumference of the conveyor belt can be predicted and calculated in advance.

Assuming that the transfer current Itr to be controlled is a function Itr (t) of the time t, Δσ = Itr (t) / (V + ΔV _L ) G−Itr / V · G (4) From = 0, Itr (t) = (V + ΔV _L ) · Itr / V (5) Itr (t) can be predicted and calculated.

Here, regarding the thickness profile over the entire circumference of the conveyor belt, it is complicated to perform the calculation of the expression (5) in all parts in the circumferential direction of the belt, and an enormous amount of calculation is required. In order to realize the above control, the control device may be complicated and expensive.

Therefore, preferably, the entire circumference of the transport belt is divided into N sections (areas), and the measured values of the thickness of the transport belt over the entire circumference, which have already been obtained, are used to determine the number of sections in each of the N sections. The average thickness is determined, and the profile of the average thickness distribution over the entire circumference of the transport belt divided into N sections represents the thickness profile over the entire circumference of the transport belt. There is no problem with handling such a simple belt thickness profile, and complicated calculations can be omitted, and control can be performed with simpler handling, which is industrially useful.

The thickness profile represented by N pieces is stored in the main body of the apparatus before the product is shipped, or is written on the belt itself or affixed with numerical data, so that the service can be provided when the product is installed. A human or user may input the information into the device. Further, a device for reading the written and affixed data may be provided and input to the device.

As described above, in this embodiment, the profile of the thickness of the recording material conveying belt in the circumferential direction is obtained, and the transfer current of the transfer charging means is controlled according to the thickness unevenness in the circumferential direction. Even if the recording material transport speed fluctuates due to unevenness, it is possible to prevent insufficient or insufficient surface charge density applied to the recording material, prevent transfer failure due to insufficient or excessive surface charge density, and perform good transfer. And high quality images.

Embodiment 2 As described in the section of the prior art, the variation in the thickness of the recording material conveying belt 8 over the entire circumferential length causes a large change in the transfer impedance at the transfer portion, and accordingly, the recording at the transfer portion. The charge amount per unit area (surface charge density) supplied to a material or the like may become uneven, which may result in an image defect.

This is because the phenomenon of the uneven charge amount becomes remarkable when the transfer charger 4 shown in FIG. 7 is particularly subjected to the constant-voltage control. The prevention method will be described in detail.

FIG. 5 shows the above-mentioned surface charge density variation Δσ together with the transport belt thickness variation Δh _L and the transfer voltage Vtr. The transfer voltage Vtr is a constant voltage control transfer voltage.

Focusing on point A in FIG. 5, since the belt thickness variation Δh _L is positive, the impedance applied to the transfer charger 4 in FIG. The change Δσ has decreased. At this time, in some cases, transfer failure occurs due to insufficient surface charge density. In the vicinity of the point B, which is opposite to the point A, the belt thickness variation Δh _L is negative, and the surface charge density variation Δσ is larger than an appropriate value (= 0). Also at this time, in some cases, transfer failure due to excessive surface charge density is caused.

Therefore, in the present embodiment, the transfer voltage Vtr is controlled in accordance with the belt thickness variation Δh _L by the control means for controlling the transfer power supply for applying the transfer voltage to the transfer charger at a constant voltage, thereby obtaining the surface charge. By minimizing the density change Δσ, the occurrence of transfer failure due to the shortage or excessive surface charge density as described above was prevented.

FIG. 6 shows an example of the surface charge density change Δσ when the transfer voltage control according to the present embodiment is performed. It can be seen that the surface charge density change Δσ is almost zero by changing the transfer voltage Vtr with respect to the time t according to the conveyance belt thickness fluctuation Δh _L.

The control amount of the transfer voltage Vtr is determined in advance by predicting how much the transfer impedance changes in accordance with the belt thickness unevenness Δh _L , and based on the result, Vtr
Is desirable.

In the present embodiment, the profile of the thickness of the recording material conveying belt in the circumferential direction is obtained, and the transfer voltage of the transfer means is controlled in accordance with the thickness unevenness in the circumferential direction. Even if the impedance fluctuates, the insufficient and excessive surface charge density applied to the recording material can be eliminated to prevent poor transfer due to the insufficient or excessive surface charge density, and good quality images can be obtained by performing good transfer. I got it.

In each of the above embodiments, the case of the image forming apparatus for transferring the toner image on the image carrier to the recording material conveyed by the conveyor belt has been described. The present invention can also be applied to an image forming apparatus in which a toner image is primarily transferred onto a rotating intermediate transfer body such as an intermediate transfer belt, and then secondary transferred onto a recording material conveyed to the intermediate transfer body. It is possible to eliminate the excess and deficiency of the surface charge density at the time of the primary transfer and the secondary transfer due to the speed variation due to the thickness variation of the intermediate transfer body in the circumferential direction, and to achieve a good primary transfer and
The next transfer can be performed.

Further, the present invention provides an image forming apparatus or an intermediate transfer member for forming a toner image on a photosensitive belt which is a belt-shaped image carrier and transferring the toner image to a recording material conveyed by a conveyance belt. If is installed,
The present invention can also be applied to an image forming apparatus in which primary transfer is performed on an intermediate transfer member and then secondary transfer is performed on a recording material conveyed to the intermediate transfer member. At the time of transfer due to the speed fluctuation, it is possible to eliminate the excess and deficiency of the surface charge density and perform good transfer.

[0060]

As described above, according to the present invention,
Since the circumferential profile of the thickness of the recording material conveyance belt or the intermediate transfer body is determined in advance, and the transfer current or the transfer voltage of the transfer charging unit is controlled in accordance with the thickness unevenness in the circumferential direction, the recording material conveyance belt or the intermediate transfer member is controlled. Even if the recording material transport speed fluctuates due to fluctuations in the thickness of the transfer body in the circumferential direction, there is no shortage or excess of surface charge density applied to the recording material, preventing transfer failure due to insufficient or excessive surface charge density And high quality images can be obtained by performing good transfer.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a recording material conveying unit in an embodiment of an image forming apparatus of the present invention.

FIG. 2 is a diagram illustrating an example of measuring a thickness profile over the entire circumference of a conveyance belt of the recording material conveyance unit in FIG. 1;

FIG. 3 is a diagram illustrating a change amount Δσ of a surface charge density in a conveyance belt together with a conveyance belt speed variation ΔV _L and a transfer current Itr.

FIG. 4 shows an example of a surface charge density change Δσ when the transfer current control according to the embodiment of FIG. 1 is performed;
FIG. 6 is a diagram showing the state together with _L and transfer current Itr.

FIG. 5 is a diagram showing a surface charge density change amount Δσ in the transport belt together with a transport belt thickness variation Δh _L and a transfer voltage Vtr.

FIG. 6 is a diagram illustrating an example of a surface charge density change Δσ when a transfer voltage control is performed according to another embodiment of the present invention, together with a conveyance belt thickness change Δh _L and a transfer voltage Vtr.

FIG. 7 is a schematic diagram showing a conventional image forming apparatus.

[Explanation of symbols]

 1a to 1d Photosensitive Drum 4a to 4d Transfer Charger 8 Recording Material Conveying Belt 10 Drive Roller M Mark S Sensor

Claims (12)

[Claims] An image bearing member on which a toner image is formed; a rotating recording material transport belt that carries a recording material and transports the image material to the image bearing member; and a transport belt that transports the toner image on the image bearing member. In the image forming apparatus provided with a transfer charging means for transferring to the above recording material, by measuring the thickness of the recording material transport belt over the entire circumference, to obtain a profile of the thickness distribution over the entire circumference of the transport belt, An image forming apparatus, wherein the transfer charging unit is controlled in accordance with the thickness distribution profile. 2. An image carrier on which a toner image is formed, a rotating intermediate transfer member, first transfer charging means for transferring a toner image on the image carrier to the intermediate transfer member, In an image forming apparatus provided with a second transfer charging unit for transferring a toner image on a transfer body to a recording material conveyed to an intermediate transfer body, the thickness of the intermediate transfer body is measured over the entire circumference, An image forming apparatus comprising: obtaining a profile of a thickness distribution over the entire circumference of a transfer body; and controlling the first transfer charging unit and the second transfer charging unit in accordance with the profile of the thickness distribution. 3. An image forming apparatus comprising: a rotating belt-shaped image carrier on which a toner image is formed; and transfer charging means for transferring the toner image on the image carrier to a recording material or an intermediate transfer member. Measuring the thickness of the belt-shaped image carrier over the entire circumference to obtain a profile of the thickness distribution over the entire circumference of the belt-shaped image carrier, and according to the thickness distribution profile, the transfer charging unit An image forming apparatus comprising: 4. The transfer charging device according to claim 1, wherein a transfer current is controlled at a constant current, and a control device of the transfer charging device controls the transfer current in accordance with the profile of the thickness distribution. An image forming apparatus according to any one of the above items. 5. The transfer charging device according to claim 1, wherein a transfer voltage is controlled at a constant voltage, and a control device of the transfer charging device controls the transfer voltage in accordance with the profile of the thickness distribution. An image forming apparatus according to any one of the above items. 6. A method for dividing an entire circumference of the recording material transport belt into N areas, and calculating an average thickness in each of the N areas from a measured value of the transport belt thickness over the entire circumference. The transfer charging unit is controlled by representing a profile of a thickness distribution over the entire circumference of the transport belt with a profile of an average thickness distribution over the entire circumference of the transport belt divided into the N areas. The image forming apparatus according to any one of items 1, 4, and 5. 7. An entire thickness of the intermediate transfer body is divided into N areas, and an average thickness in each of the N areas is determined from a measured value of the thickness of the intermediate transfer body over the entire circumference. The transfer charging unit is controlled by representing the profile of the average thickness distribution over the entire circumference of the intermediate transfer body divided into the N areas as a profile of the thickness distribution over the entire circumference of the intermediate transfer body. The image forming apparatus according to claim 2. 8. An entire thickness of the belt-shaped image carrier is divided into N areas, and an average thickness in each of the N areas is measured from a measured value of the belt-shaped image carrier thickness over the entire circumference. The profile of the average thickness distribution over the entire circumference of the belt-shaped image carrier divided into the N areas is represented by the profile of the thickness distribution over the entire circumference of the belt-shaped image carrier. And controlling the transfer charging means.
The image forming apparatus according to any one of the above items. 9. The image forming apparatus according to claim 6, wherein the average thickness in each of the N areas is written or stuck on the recording material conveying belt as a numerical value table. 10. The image forming apparatus according to claim 7, wherein the average thickness in each of the N areas is written or affixed to the intermediate transfer body as a numerical value table. 11. The image forming apparatus according to claim 8, wherein an average thickness in each of the N areas is written or affixed to the belt-shaped image carrier as a numerical value table. 12. The image forming apparatus according to claim 1, wherein a plurality of said image carriers are provided, and a plurality of color toner images are formed on said plurality of image carriers.