JP2003295539A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a high quality image excellent in reproducibility with simple control without complicated control such as correction of image writing speed, when speed difference between a moving speed on a surface of a transfer member and that of a surface of an image carrier is controlled. <P>SOLUTION: When an image formation signal is inputted (s11), a control part 70 discriminates whether a predetermined image formation mode is a letter image mode (s12). When the letter image mode is set, a circumferential speed of photosensitive drums 3a-3d is controlled so that a prescribed speed difference is formed between the circumferential speed of a transfer carrier belt 7 and that of the drums 3a-3d (s13), and completion of image forming processing is stood by (s14). When a photo image mode is set, completion of the image forming processing is stood by (s16), without changing the circumferential speed of the photosensitive drums 3a-3d keeping the same speed with the circumferential speed of the transfer carrier belt 7. When the image forming processing is completed, it is returned to the stand-by state (s14, s16→s11). <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic copying machine, a printer and a printer for forming an image by transferring a toner image from the surface of an image carrier onto a recording medium such as a sheet of paper which is held and conveyed by a transfer member. The present invention relates to an image forming apparatus such as a facsimile.

[0002]

2. Description of the Related Art Conventionally, as a method for forming an image on a recording medium, an electrostatic latent image formed on an image carrier by an exposure process based on image information is visualized as a toner image in a developing process, and the image carrier is visualized. In an electrophotographic image forming apparatus that transfers a toner image formed above onto a recording medium using a transfer member, generally, the recording medium held on the transfer member surface is placed between the image carrier surface and the transfer member surface. I'm trying to pinch it and let it pass. In such an image forming apparatus,
Moving speed of image carrier surface (for example, peripheral speed of photosensitive drum)
If a large speed difference occurs between the moving speed of the transfer member surface and the moving speed of the transfer member surface (for example, the peripheral speed of the transfer belt or the transfer roller), the moving direction of the image carrier surface and the transfer member surface is more than Also causes a transfer deviation or the like in which the toner image is transferred in a wide range, and uneven density occurs in the toner image transferred to the recording medium. In order to prevent uneven density of the toner image on the recording medium, the moving speed of the image carrier surface and the moving speed of the transfer member surface should be substantially the same.

However, a toner image formed on the basis of binary image information such as a line image made up of characters or a dot image is formed relatively thick on the surface of the image carrier, and is transferred to the recording medium at the central portion. It is easy to cause a phenomenon in which the toner is not transferred and is lost (generally called a hollow phenomenon). In order to prevent this hollowing-out phenomenon, there is a control in which a slight speed difference is provided between the moving speed of the image carrier surface and the moving speed of the transfer member surface during image formation based on binary image information. .

For example, Japanese Unexamined Patent Publication No. H5-273873 discloses a structure in which the moving speed of the transfer member surface is controlled to be slower than the moving speed of the photosensitive member surface. According to this configuration, the transfer is performed in a state where the recording medium is slightly slipped on the surface of the photoconductor, and it is possible to prevent the occurrence of the image dropout phenomenon during the transfer.

Further, Japanese Patent Application Laid-Open No. 7-319302 discloses a structure in which the moving speed of the transfer member surface is controlled to be higher than the moving speed of the image carrier surface. It is said that also with this configuration, it is possible to prevent the occurrence of the image dropout phenomenon during transfer.

On the other hand, in a multi-color image forming apparatus that transfers toner images of different colors from a plurality of image carriers on a single recording medium, another problem of poor image quality is that the image carrier has sudden fluctuations in rotation. The image may have color unevenness. JP-A-11-
According to Japanese Patent Laid-Open No. 65222, the moving speed of the surface of the image carrier is transferred in order to prevent the fluctuation of the rotation of the photosensitive drum, which is the image carrier, due to the speed fluctuation of the surface of the transfer belt, which is the transfer member, and prevent the occurrence of color unevenness. A configuration is disclosed in which the drive speed of a drive motor that drives each image carrier is set so as to be higher than the moving speed of the member surface. According to this configuration,
It is said that each image carrier is apparently driven by the transfer member, the inertia torque of each image carrier is added to the transfer member, and the speed fluctuation of the surface of the transfer member can be suppressed.

However, if a speed difference is provided between the peripheral speed of the photoconductor drum, which is the image carrier, and the peripheral speed of the transfer belt, which is the transfer member, the peripheral speed of the photoconductor drum is affected and uneven density occurs. On the contrary, in a solid image in the intermediate density region or the low density region, image unevenness is conspicuous on the contrary and the image quality is deteriorated. In particular, in a multicolor image formed by a multicolor image forming apparatus, image density unevenness appears as color unevenness, and even density unevenness that does not pose a problem when forming a black and white image is conspicuous, resulting in a significant decrease in image quality. .

In order to solve these problems, Japanese Patent Laid-Open No. 9-
In Japanese Patent Laid-Open No. 297473, a drive unit for a transfer roller (transfer member) is separately provided, or a unit for cutting drive transmission to the transfer roller (transfer member) is provided if necessary, and the photosensitive drum is selected according to image characteristics. There is disclosed a configuration in which the peripheral speed of the transfer roller is switched manually or automatically. According to this structure, the peripheral speed of the transfer roller (moving speed of the transfer member surface) is made faster than the peripheral speed of the photosensitive drum (moving speed of the image carrier surface) to prevent image dropout in the character image. It is said that it is possible to prevent the occurrence of density unevenness in an image having many halftones such as photographs in the device.

[0009]

However, when the moving speed of the surface of the transfer member is controlled with respect to the moving speed of the surface of the image carrier to give a speed difference between them, a toner image is transferred from the image carrier to the recording medium. When the image is transferred, the magnification of the image changes,
There is a problem that the image information cannot be accurately reproduced. That is, when the moving speed of the transfer member surface is higher than the moving speed of the image carrier surface, the image is enlarged, and when it is slow, the image is reduced.

In order to solve this problem, when the moving speed of the surface of the transfer member is controlled with respect to the moving speed of the surface of the image carrier to give a speed difference therebetween, the image in the exposure process for the image carrier is By performing complicated control such as correcting the writing speed of information according to the speed difference between the surface of the transfer member and the surface of the image carrier, the image finally transferred to the recording medium becomes equivalent to the image information. You have to make it a magnification.

An object of the present invention is to prevent the hollow portion of a character image and the uneven density of a photographic image and always obtain a good image quality regardless of the attribute of the image information, so that the moving speed of the transfer member surface and the surface of the image carrier can be improved. When controlling the speed difference from the moving speed, it is not necessary to perform complicated control such as correction of the image writing speed,
An object of the present invention is to provide an image forming apparatus capable of obtaining a high-quality image excellent in reproducibility with simple control.

[0012]

The present invention has the following structure as means for solving the above problems.

(1) A transfer which exposes the surface of the image bearing member based on image information to form an electrostatic latent image, visualizes the electrostatic latent image as a toner image, and moves in the same direction as the surface of the image bearing member. In an image forming apparatus that transfers a toner image from the surface of an image carrier to a recording medium that is held and conveyed on the surface of a member, the surface of the image carrier is changed by changing the moving speed of the surface of the image carrier according to the attribute of image information. A control means for controlling the speed difference between the moving speed of the transfer member and the moving speed of the facing surface of the transfer member is provided.

In this structure, the speed difference between the moving speed of the surface of the image carrier and the moving speed of the facing surface of the transfer member is changed depending on the attribute of the image information to be imaged. Controlled by. Therefore, the appropriate value for achieving good image quality varies depending on the attribute of the image information. The difference in speed between the moving speed of the image carrier surface and the moving speed of the transfer member surface changes the moving speed of the image carrier surface. As long as the moving speed of the transfer member surface is maintained at an appropriate speed with respect to the writing speed for the image carrier, even if the moving speed of the image carrier surface changes with the attribute of the image information, An image having the same magnification as the image information is formed on the recording medium that moves at the same moving speed as the surface of the transfer member. Even when the speed difference between the moving speed of the image carrier surface and the moving speed of the transfer member surface is changed to obtain a good image quality regardless of the attribute of the image information, the writing speed of the image to the image carrier is changed. You don't have to.

(2) The control means moves the surface of the image carrier according to the attribute of the image information, that is, whether the image information is mainly a binary image or the image information has an intermediate density image. It is characterized by changing.

In this configuration, the moving speed of the surface of the image carrier is changed between the time of image formation for image information mainly consisting of binary images and the time of image formation for image information having an intermediate density image. The speed difference between the moving speed of the surface of the image carrier and the moving speed of the surface of the transfer member is controlled. Therefore, an image having a good image quality for both image information such as a character image mainly including a binary image and image information such as a photographic image having an intermediate density image is corrected for the writing speed to the image carrier. The recording medium is formed on the recording medium in a highly reproducible state without any complicated control.

(3) The control means determines the attribute of the image information based on the image forming mode set from the outside.

In this structure, the moving speed of the surface of the image carrier and the transfer member are changed by changing the moving speed of the surface of the image carrier according to the image forming mode set outside the control means such as the external terminal or the operation panel. The speed difference from the moving speed of the surface is controlled. When the image forming mode such as the character image forming mode or the photographic image forming mode changes, the attribute of the image information targeted for image formation may change, and the control means sets the setting contents of the image forming mode desired by the operator. The attribute of the image information is judged from the above, and the speed difference between the moving speed of the image carrier surface and the moving speed of the transfer member surface corresponding to the judged attribute is realized by changing the moving speed of the image carrier surface. Therefore, a speed difference between the moving speed of the image carrier surface and the moving speed of the transfer member surface, which is suitable for the attribute of the image information to be image-formed, is realized by changing the moving speed of the image carrier surface. An image of good image quality can be easily and accurately formed on a recording medium in a highly reproducible state regardless of attributes.

(4) When the image information is mainly a binary image, the control means sets the moving speed of the surface of the image carrier different from the moving speed of the surface of the transfer member to form an intermediate density image. When the image information has the image information, it is characterized in that the moving speed of the surface of the image carrier is substantially matched with the moving speed of the surface of the transfer member.

In this structure, the moving speed of the surface of the image carrier moves during the image formation of the image information mainly composed of the binary image whose image quality remarkably deteriorates due to the occurrence of the hollow image phenomenon. The speed of movement of the surface of the image carrier substantially matches the speed of movement of the surface of the transfer member during image formation for image information having an intermediate density image, which is controlled to a speed different from the speed and causes a significant deterioration in image quality due to uneven density. Controlled by speed. Therefore, for image information mainly composed of binary images, image formation is performed by giving a speed difference between the moving speed of the image carrier surface and the moving speed of the transfer member surface in order to prevent the hollow image phenomenon. For image information having an intermediate density image, image formation is performed by making the moving speed of the image carrier surface and the moving speed of the transfer member surface substantially equal to each other in order to prevent uneven density. For both the image information to be recorded and the image information having the intermediate density image, an image with good image quality is formed on the recording medium with high reproducibility by controlling only the moving speed of the surface of the image carrier.

(5) The control means makes the moving speed of the surface of the image carrier different from the moving speed of the surface of the transfer member when the character image mode mainly including the character image is set as the image forming mode, It is characterized in that the moving speed of the surface of the image carrier is made to substantially match the moving speed of the surface of the transfer member when the photographic image mode mainly for photographic images is set.

In this structure, when the character image mode is set for the image information mainly composed of the character image whose image quality is remarkably deteriorated due to the occurrence of the hollow image phenomenon, the moving speed of the surface of the image carrier is set. Is controlled to a speed different from the moving speed of the transfer member surface, and the image quality is significantly deteriorated due to the occurrence of density unevenness. The moving speed of the body surface is controlled to a speed substantially matching the moving speed of the transfer member surface. Therefore, for image information that is mainly composed of character images, an image is formed by providing a speed difference between the moving speed of the image carrier surface and the moving speed of the transfer member surface in order to prevent the hollow image phenomenon. Regarding the image information of the main body, image formation is performed by making the moving speed of the image carrier surface and the moving speed of the transfer member surface substantially equal to each other in order to prevent density unevenness. For any of the above image information, an image of good image quality is formed on the recording medium with high reproducibility by controlling only the moving speed of the surface of the image carrier.

(6) The control means makes the moving speed of the surface of the image carrier faster than the moving speed of the surface of the transfer member, so that the speed difference between the moving speed of the surface of the image carrier and the moving speed of the surface of the transfer member. Is provided.

In this structure, when a speed difference is given between the moving speed of the image carrier surface and the moving speed of the transfer member surface, the moving speed of the image carrier surface is made faster than the moving speed of the transfer member surface. . Therefore, when the toner image is transferred from the surface of the image carrier to the recording medium, a force in the direction of contracting the conveying direction of the recording medium acts on the toner image, and the adhesive force of the toner image to the surface of the image carrier decreases. Image dropouts are prevented. Further, by matching the writing speed in the exposure process to the surface of the image carrier with the moving speed of the surface of the transfer member, the surface of the image carrier moves faster than the writing speed so that the image carrier is expanded. The toner image formed on the surface is reduced and transferred to the recording medium moving at a relatively low speed with respect to the surface of the image carrier at the same magnification as that at the time of expansion, and the image information is accurately reproduced.

(7) The control means makes the moving speed of the surface of the image bearing member slower than the moving speed of the surface of the transfer member, so that a velocity difference between the moving speed of the surface of the image bearing member and the moving speed of the surface of the transfer member. Is provided.

In this structure, when a speed difference is given between the moving speed of the image carrier surface and the moving speed of the transfer member surface, the moving speed of the image carrier surface is made slower than the moving speed of the transfer member surface. It Therefore, at the time of transferring the toner image from the surface of the image carrier to the recording medium, a force in the direction of extending the recording medium in the conveying direction acts on the toner image, and the adhesive force of the toner image to the surface of the image carrier decreases. Image dropouts are prevented. Further, by matching the writing speed in the exposure step for the surface of the image carrier with the moving speed of the surface of the transfer member, the surface of the image carrier moves slower than the writing speed and the image carrier is reduced in size. The toner image formed on the surface is expanded and transferred to a recording medium that moves at a relatively low speed with respect to the surface of the image carrier at the same magnification as that at the time of reduction, and the image information is accurately reproduced.

[0027]

1 is a diagram showing a schematic configuration of a multicolor image forming apparatus according to a first embodiment of the present invention. The multicolor image forming apparatus forms a multicolor or single color image on a predetermined sheet (recording medium) according to image data (image information) transmitted from the outside. The image data handled by this multicolor image forming apparatus corresponds to a color image using each color of black (K), cyan (C), magenta (M), and yellow (Y),
Four image stations S for forming images of these respective colors
a to Sd are provided. Each image forming station S
a to Sd have the same configuration, and as an example, the image forming station Sa includes an exposure unit 1a and a developing device 2.
a, a photosensitive drum 3a, a charger 5a, and a cleaner unit 4a are provided. Each image forming station Sa to
Toners of black (K), cyan (C), magenta (M), and yellow (Y) are stored in each of the Sd developing devices 2a to 2d.

The photosensitive drums 3a to 3d are the image bearing members of the present invention, and are rotatably arranged at the substantial center of the multicolor image forming apparatus. The chargers 5a to 5d are charging means for uniformly charging the surfaces of the photoconductor drums 3a to 3d to a predetermined potential in the charging step. In addition to contact type charging rollers and charging brushes, as shown in FIG. A non-contact charging charger is used. Each of the exposure units 1a to 1d is a laser scanning unit (LSU) including a laser irradiation unit and a reflection mirror, but a writing head in which light emitting elements such as EL or LED are arranged in an array can also be used.

The exposure units 1a to 1d irradiate the surface of the photoconductor drums 3a to 3d after the charging process with the laser light modulated by the image data of the corresponding color, and the surface of the photoconductor drums 3a to 3d is subjected to the image data. To form an electrostatic latent image. The developing devices 2a to 2d develop the electrostatic latent images formed on the surfaces of the photoconductor drums 3a to 3d into toner images with toner of corresponding colors. Cleaner unit 4
Are the photosensitive drums 3a to 3a after the toner image transfer step.
The toner remaining on the surface of 3d is removed and collected.

The transfer / conveying belt unit 8 arranged below the photosensitive drums 3a to 3d includes a transfer / conveying belt 7, a driving roller 57, a driven roller 58, a tension roller 59, transfer rollers 6a to 6d, a cleaning unit 9 and the like. Is equipped with. The transfer / transport belt 7 is stretched around the transfer rollers 6a to 6d, the transfer / transport belt driving roller 57, the transfer / transport belt driven roller 58, and the tension roller 59, and is rotated in the direction of arrow B to be electrostatically attracted to the upper surface. The sheet is placed on each of the photosensitive drums 3a to 3d and each of the transfer rollers 6.
The sheets a to 6d are sequentially passed to be conveyed. The transfer rollers 6a to 6d and the transfer / transport belt 7 correspond to the transfer member of the present invention.

The transfer / conveyance belt 7 is composed of the respective photosensitive drums 3a.
It is provided so as to contact a part of the surface of 3d.
Then, it has a function of forming a color toner image (multicolor toner image) by sequentially superposing and transferring the toner images of the respective colors formed on the photoconductor drums 3a to 3d onto the sheet. The material of the transfer / transport belt 7 is PC (polycarbonate), PVDF (polyvinylidene fluoride), P
TFE (Polytetrafluoroethylene polymer), ETF
E (ethylene tetralfluoroethylene polymer), polyimide, polyamide and the like are generally used. The transfer / transport belt 7 is formed in an endless shape using a film having a thickness of 80 to 150 μm and a volume resistivity of 10 ⁹ Ω · cm to 10 ¹³ Ω · cm. In this embodiment, the thickness is 100 μm
I am using a PC.

The transfer rollers 6a to 6d are arranged at positions facing the photoconductor drums 3a to 3d with the upper side surface of the transfer conveyance belt 7 interposed therebetween. Each transfer roller 6a
6d to 6d transfer the toner images carried on the respective surfaces of the photoconductor drums 3a to 3d to the sheet which is attracted to the upper side surface of the transfer and transport belt 7 and is transported. Each transfer roller 6
a to 6d are conductive elastic members such as urethane rubber or EPDM in which carbon or the like is dispersed around the core metal (having a resistance value of 10
^The outer diameter is about 14 to 20 mm and the hardness is 30 to 50 degrees (Asker C). A high voltage of +2 KV to +3 KV (high voltage of a polarity (+) opposite to the charging polarity (1) of the toner) is applied to each of the transfer rollers 6a to 6d from a high voltage power source for transfer in order to transfer the toner image. A high voltage is uniformly applied to the sheet from the conductive elastic member.

The cleaning unit 9 is provided with a cleaning blade type contact type cleaning member made of polyurethane or the like. The cleaning unit 9 removes the toner adhering to the transfer belt 7 by contact with the photosensitive drums 3a to 3d in order to prevent the back surface of the sheet from being soiled.

The paper feed tray 10 provided on the lower inside of the multicolor image forming apparatus accommodates sheets used for image formation. A paper discharge tray 15 provided at the top of the multicolor image forming apparatus stores printed sheets in a face-down state. The paper discharge tray 33 provided on the side of the multicolor image forming apparatus stores the image-formed sheets in a face-up state.

Inside the multicolor image forming apparatus, an S-shape for sending the sheets stored in the paper feed tray 10 to the paper discharge tray 15 via the transfer / conveying belt unit 8 and the fixing unit 12. A paper transport path having a shape is formed. Further, a pickup roller 16, a registration roller 14, a fixing unit 12, a conveyance direction switching gate 34, a conveyance roller 25, and the like are arranged near the paper conveyance path from the paper feed tray 10 to the paper ejection tray 15 and the paper ejection tray 33. Has been done.

The carrying roller 25 promotes the carrying of the sheet.
It is a small roller for assisting, and a plurality of rollers are provided along the paper transport path. The pickup roller 16 is
It is a feed-in roller that is provided at the end of the paper feed tray 10 and that feeds the sheets from the paper feed tray 10 one by one to the paper transport path.

The conveyance direction switching gate 34 is rotatably provided on the side cover 35, and the sheet passing through the fixing unit 12 is discharged to the discharge tray 15 or the discharge tray 3.
Leads selectively in three directions.

The registration roller 14 is the photosensitive drum 3a.
The sheet fed from the sheet feeding tray 10 is temporarily stopped on the upstream side of the transfer / conveyance belt unit 8 before the rotation of the transfer / conveyance belt unit 8 to 3d, and the transfer / conveyance belt unit 8 is synchronized with the rotation of the photosensitive drums 3a to 3d. Lead to. That is, the registration roller 14 determines whether each of the photoconductor drums 3a ...
The sheet is conveyed to the upper side surface of the transfer / conveyance belt 7 so that the front end portion of the toner image on the sheet 3d coincides with the front end portion of the image forming range on the sheet at a position facing the transfer rollers 6a to 6d.

The fixing unit 12 includes a heat roller 31,
The pressure roller 32 and the like are provided. The heat roller 31 and the pressure roller 32 rotate while sandwiching the sheet. The heat roller 31 is set so as to have a predetermined fixing temperature based on a temperature detection value (not shown), and the sheet is thermocompression bonded together with the pressure roller 32 to melt and press the toner image transferred to the sheet. Then, the sheet is firmly heat-fixed.

2 and 3 are views for explaining the operation of the transfer / conveying belt unit of the multicolor image forming apparatus shown in FIG. In the above multicolor image forming apparatus, the transfer / conveying belt unit 8 is displaced to a different state during color image formation and during monochrome image formation. The transfer / transport belt unit 8 includes a support base 51 and a support base 52. The support base 51 axially supports the transfer rollers 6b to 6d and the drive roller 57, and includes a long hole 51a. An eccentric shaft 56 that constitutes the separation / contact drive unit 53 together with the motor M2 is fitted into the long hole 51a.
The support base 51 is centered on the rotation axis of the holding roller 54,
It is swingably supported by the support base 52 between the upper position shown in FIG. 2 and the lower position shown in FIG. The support base 52 is
The transfer roller 6a, the driven roller 58, and the holding roller 54 are pivotally supported, and the separation / contact drive unit 53 is held. Drive roller 5
7 is driven by a motor M1, and the photosensitive drums 3a ...
3d is driven by motors M3 to M6, respectively.
The motors M1 to M6 are controlled by the control unit 70.

When a color image is formed in which a toner image may be transferred from all of the photosensitive drums 3a to 3d onto a sheet that is adsorbed on the upper side surface of the transfer / conveyance belt 7 and conveyed, the support base 51 is set to the position shown in FIG. It is located at the upper position shown in FIG. In this state, the upper side surface of the transfer / transport belt 7 is in contact with the surface of each of the photoconductor drums 3a to 3d, and is sandwiched between each of the photoconductor drums 3a to 3d and each of the transfer rollers 6a to 6d.

When a black-and-white image is formed in which a toner image is transferred from only the photosensitive drum 3a to a sheet that is adsorbed on the upper side surface of the transfer / conveyance belt 7 and conveyed, the support base 51 is arranged as shown in FIG.
It is located at the lower position shown in. In this state, the transfer rollers 6b to 6d axially supported by the support base 51 are separated from the photoconductor drums 3b to 3d, and the upper side surface of the transfer / conveying belt 7 comes into contact with the surface of the photoconductor drum 3a only. 3a
And the transfer roller 6a.

When a large difference occurs between the peripheral speed (Vt) of the transfer / transport belt 7 which is the moving speed of the transfer member surface and the peripheral speed (Vd) of the photosensitive drums 3a to 3d which is the moving speed of the image carrier surface. Then, transfer deviation or the like occurs, and uneven density occurs in the toner image transferred to the sheet. Therefore, the transfer conveyance belt 7
Peripheral speed (Vt) of the photosensitive drums 3a to 3d (Vt)
motors M1, M3 to M6 so that they are substantially the same as
The rotation speed of is controlled by the control unit 70.

However, the toner image formed on the photosensitive drums 3a to 3d is relatively thick due to the image information mainly consisting of a binary image such as a line image consisting of characters or a dot image, and is relatively thick. Due to the pressure of the rollers 6a to 6d, the toner easily sticks to the surfaces of the photoconductor drums 3a to 3d, and when the toner image is transferred onto the sheet, the central portion of the toner image is not transferred but comes out.

Therefore, in the above-mentioned multicolor image forming apparatus, in order to prevent the occurrence of the hollow defect, the peripheral speed (Vt) of the transfer / conveying belt 7 and the peripheral speed (Vd) of the photosensitive drums 3a to 3d are set.
And gives a slight speed difference. This speed difference is obtained by setting the peripheral speed (Vt) of the transfer / conveying belt 7 to be constant, and the photosensitive drum 3
It is realized by changing the peripheral speed (Vd) of a to 3d.

This is because the peripheral speed (Vd) of the photosensitive drums 3a to 3d is constant and the peripheral speed (Vt) of the transfer / conveying belt 7 is set.
Is changed, the peripheral speed of the photosensitive drums 3a to 3d (V
d) is matched with the writing speed of the exposure units 1a to 1d, which are image writing means, and the images are written from the exposure units 1a to 1d to the photosensitive drums 3a to 3d at an appropriate magnification. Since the peripheral speed (Vt) of the transfer / conveyance belt 7 is different from the peripheral speed (Vd) of the photosensitive drums 3a to 3d, the transfer is performed from the photosensitive drums 3a to 3d onto the sheet conveyed on the transfer / conveyor belt 7. The magnification of the toner image varies from the proper magnification. That is, the photosensitive drums 3a to 3
With respect to the peripheral speed (Vd) of d, the peripheral speed (V
When t) is slow, the toner image is transferred to the sheet in a state in which the image written by the exposure units 1a to 1d is contracted in the sheet conveyance direction, and the optical drums 3a to 3d are transferred.
Relative to the peripheral speed (Vd) of the transfer / conveying belt 7.
When t) is fast, the toner image is transferred to the sheet in a state where the image written by the exposure units 1a to 1d is expanded in the sheet conveying direction, and the image information cannot be accurately reproduced on the sheet.

In order to solve this problem, the exposure unit 1 is adjusted according to the change in the peripheral speed (Vt) of the transfer / conveyance belt 7.
It is necessary to correct the writing speed by writing and to write the image in consideration of the change in the magnification when the image is transferred from the photoconductor drums 3a to 3d, and the drive motor M1 for driving the transfer / conveying belt 7. In addition to the control board for controlling the rotation speed of the photosensitive drums 3a to 3d, a control board for controlling the image writing speed by the exposure unit 1 is provided.
Image data must be written at different writing speeds depending on whether or not a speed difference is provided between d) and the peripheral speed (Vt) of the transfer / conveying belt 7. When the LSU is used as the exposure unit 1 as in the multicolor image forming apparatus, the rotation speed of the polygon mirror has to be controlled in order to change the writing speed, which complicates the control.

In the multicolor image forming apparatus according to this embodiment, as described above, the peripheral speed (Vt) of the transfer / conveying belt 7 is kept constant to control the peripheral speed (Vd) of the photosensitive drums 3a to 3d. The peripheral speed (Vt) of the transfer / conveying belt 7 and the peripheral speed (Vd) of the photosensitive drums 3a to 3d are made different from each other. In this case, since the peripheral speed (Vd) of the photoconductor drums 3a to 3d does not match the writing speed of the exposure unit 1, the exposure units 1a to 1d move to the photoconductor drums 3a to 3d.
However, since the peripheral speed (Vt) of the transfer / conveyance belt 7 matches the writing speed of the exposure unit 1, the magnification of the image written on the transfer / conveyor belt 7 is increased from the photosensitive drums 3a to 3d onto the transfer / conveyor belt 7. When the toner image is transferred to the sheet, the toner image is reduced or expanded so as to have an appropriate magnification, and an image is formed on the sheet at a magnification that matches the magnification at the time of writing by the exposure units 1a to 1d.

That is, when the peripheral speed (Vt) of the transfer / conveying belt 7 is kept constant and the peripheral speed (Vd) of the photosensitive drums 3a to 3d is increased, the peripheral speed (Vd) of the photosensitive drums 3a to 3d is changed to the exposure unit. An image in which the magnification is increased from the exposure units 1a to 1d due to the writing speed higher than that of the exposure units 1a to 1d is written on the photoconductor drums 3a to 3d. ~ 1
Peripheral speed (Vd) of the photosensitive drum 3 matched to the writing speed of d
Since the speed is slower, the toner image is reduced and transferred to the sheet so that the magnification is appropriate during the transfer process.

When the peripheral speed (Vt) of the transfer / conveying belt 7 is kept constant and the peripheral speed (Vd) of the photosensitive drums 3a to 3d is slowed, the peripheral speed (Vd) of the photosensitive drums 3a to 3d is changed to the exposure unit. An image in a state in which the magnification is reduced from the exposure units 1a to 1d due to being slower than the writing speed of 1a to 1d is written on the photoconductor drums 3a to 3d, but the sheet conveyance speed by the transfer conveyance belt 7 is set to the exposure unit 1a. ~ 1
Since the speed is higher than the peripheral speed (Vd) of the photoconductor drums 3a to 3d matched to the writing speed of d, the toner image is expanded and transferred to the sheet so as to have an appropriate magnification during the transfer process.

Therefore, the peripheral speed (V
By changing the peripheral speed (Vd) of the photosensitive drums 3a to 3d while keeping t) constant to give a speed difference to both, regardless of the change of the peripheral speed (Vd) of the photosensitive drums 3a to 3d. , The image writing speed by the exposure unit 1 can be kept constant, and the peripheral speed (V) of the photosensitive drums 3a to 3d can be maintained.
It suffices to provide a control means for controlling d), and an image of good image quality can be accurately reproduced by a simple control of changing the peripheral speeds of the photoconductor drums 3a to 3d according to the attribute of the image. .

Here, the image whose image quality remarkably deteriorates when the dropout phenomenon occurs is mainly a binary image such as a character image. For an image mainly composed of binary images, the peripheral speed of the photosensitive drums 3a to 3d is set to the transfer / conveyance belt 7.
The speed is controlled to be faster or slower than the peripheral speed of. On the other hand, an image whose image quality remarkably deteriorates when density unevenness occurs is an image including an image of intermediate density such as a photographic image. For images including intermediate density images, the peripheral speeds of the photosensitive drums 3a to 3d are controlled so as to match the peripheral speed of the transfer / conveying belt 7.

In the multicolor image forming apparatus according to this embodiment, the control section 70 sets the image mode to the image mode data input together with the image data from the external device, the image mode set and input on the operation panel, and the external device. The attribute of the image information to be image-formed is determined by determining the content of the image data thus generated or the file format of the image data input from the external device, and the photosensitive drums 3a to 3d are driven based on the determination result. Motor M3-M
6 to control the rotation speed. As a result, the photosensitive drum 3
By controlling only the peripheral speed (Vd) of a to 3d, the peripheral speed (Vt) of the transfer conveyance belt 7 that is the moving speed of the transfer member surface and the photosensitive drums 3a to 3d that is the moving speed of the image carrier surface. By adjusting the speed difference from the peripheral speed (Vd) and performing simple control regardless of the image attribute, it is possible to form a high-quality image with excellent reproducibility without changing the magnification.

For example, when the character image mode is set on the operation panel, the peripheral speed (Vt) of the transfer / conveying belt 7 and the peripheral speeds of the photosensitive drums 3a to 3d (without changing the rotation speed of the motor M1). The rotation speeds of the motors M3 to M6 are controlled so as to give a speed difference to Vd). Here, the peripheral speed (Vd) of the photosensitive drums 3a to 3d may be slower or faster than the peripheral speed (Vt) of the transfer / conveying belt 7.

On the other hand, when the photographic image mode is set on the operation panel, the peripheral speed (Vt) of the transfer / conveying belt 7 and the peripheral speeds of the photosensitive drums 3a to 3d (without changing the rotation speed of the motor M1). The rotation speeds of the motors M3 to M6 are controlled so that Vd) becomes substantially the same.

Specifically, the peripheral speed (V
When lowering the peripheral speed (Vd) of the photosensitive drums 3a to 3d with respect to t), the peripheral speed (Vd) of the photosensitive drums 3a to 3d is set to be 1% ± more than the peripheral speed (Vt) of the transfer / conveying belt 7. 0.5
Delay in the range of%. Further, the peripheral speed (V
The same applies to the case where the peripheral speed (Vd) of the photoconductor drums 3a to 3d is made faster than t), and the peripheral speed (Vd) of the photoconductor drums 3a to 3d is larger than the peripheral speed (Vt) of the transfer / conveying belt 7. In the range of 1% ± 0.5%. These ranges are ranges that can prevent the hollow defect that is experimentally determined in the multicolor image forming apparatus according to this embodiment. If the range is exceeded, not only density unevenness becomes noticeable but also In color image formation, color unevenness and color misregistration also occur.

On the other hand, when the peripheral speed (Vt) of the transfer / conveyance belt 7 and the peripheral speed (Vd) of the photosensitive drum 3 are made substantially the same, the peripheral speed (Vt) of the transfer / conveyor belt 7 and the photosensitive drum 3 are set. Three
The peripheral speed (Vd) and the speed fluctuation are controlled to be ± 0.5% or less.

However, in these speed setting ranges, the image forming speed is 120 mm / sec and the transfer / conveying belt is set to 1 mm.
This is a value when a PC sheet of 00 μm is used and plain paper is used as a sheet, and is not limited to this value when the material of the transfer / transport belt 7, the material of the recording member, or the image forming speed is different. It may also vary depending on the type and characteristics of the developer.

Since the speed of the transfer / conveyance belt 7 is controlled at a constant speed as a reference speed, the conveyance speed of the sheet does not change, and the conveyance roller 25 for conveying the sheet and the heat roller 31 as a fixing roller are used. It is not necessary to change the speed of members such as the pressure roller 32.

FIG. 4 is a flow chart for explaining a part of the processing procedure of the control unit of the multicolor image forming apparatus. When the multicolor image forming apparatus is powered on and the initial setting is completed, the control unit 70 determines whether an image forming signal is input (s11). When the image forming signal is not input, the control unit 70 stands by without performing the image forming operation. When the image forming signal is input, the control unit 70
Determines whether the image forming mode designated by the external device or the image forming mode set on the operation panel is the character image mode (s12).

The determination of the image forming mode in s12 is performed by determining whether the image data to be image-formed is character image data, or whether the image data file format is a binary image or character image data. The determination may be whether or not the data format is based on them.

When the character image mode is set, the control section 70 forms a predetermined speed difference between the peripheral speed of the photosensitive drums 3a to 3d and the peripheral speed of the transfer / conveying belt 7. (S13) and waits for the completion of the image forming process (s14). When the image forming process is completed, the control unit 7
0 controls the peripheral speed of the photosensitive drums 3a to 3d to the same speed as the peripheral speed of the transfer / conveying belt 7 and returns to the standby state (s1.
5 → s11).

In the determination of s12, if the photographic image mode is set, the control unit 70 changes the peripheral speed of the photosensitive drums 3a to 3d at the same speed as the peripheral speed of the transfer / conveying belt 7. Without waiting for the completion of the image forming processing (s16), when the image forming processing is completed, it returns to the waiting state (s16 → s11).

By the above processing, in the multicolor image forming apparatus according to this embodiment, the photosensitive drum 3 is initially set.
The peripheral speeds of a to 3d and the peripheral speed of the transfer / conveying belt 7 are set to the same speed, and the state corresponding to the photographic image mode is set. If the peripheral speeds of the photoconductor drums 3a to 3d are the same as the peripheral speed of the transfer / transport belt 7, the occurrence of wear due to the surfaces of the photoconductor drums 3a to 3d and the surface of the transfer / transport belt 7 rubbing against each other. This is preferable because it can be prevented and the life can be extended. However, the photosensitive drums 3a-3
A state corresponding to the character image mode in which a predetermined speed difference is provided between the peripheral speed of d and the peripheral speed of the transfer / conveying belt 7 is defined as an initial state, and when the photographic image mode is set, the photosensitive belt 3
The peripheral speeds of a to 3d are changed so as to be the same as the peripheral speed of the transfer / conveyance belt 7, and the peripheral speeds of the photoconductor belts 3a to 3d are changed after the completion of the image forming process in the photographic image mode. The control may be performed so as to be slower or faster than the peripheral speed by a predetermined amount.

FIG. 5 is a view showing the schematic arrangement of a digital copying machine which is a monochromatic image forming apparatus according to the second embodiment of the present invention. An automatic document feeder 112 is provided on a document table 111 made of transparent glass on the upper surface of the digital copying machine 100. The automatic document feeder 112 is
This is a device for feeding the originals set on the original set tray one by one onto the original table 111.

The document reading unit 110 is arranged below the document table 111 and scans and reads an image of a document placed on the document table 111. The first scanning unit 113,
It has a second scanning unit 114, an optical lens 115, and a photoelectric conversion element (CCD line sensor) 116.
The first scanning unit 113 is equipped with an exposure lamp unit that exposes the document image surface and a first mirror that reflects a reflected light image from the document image surface in a predetermined direction. The second scanning unit 114 has a second mirror and a third mirror that guide the reflected light from the document reflected from the first mirror to the CCD line sensor 116. Optical lens 115
Forms an image of the reflected light from the document on the CCD line sensor 116.

The document reading section 110 is the automatic document feeder 1
Due to the operation related to 12, the automatic document feeder 112
The image of the document automatically conveyed by is read at a predetermined exposure position.

The original image read by the original reading unit 110 is sent as image data to an image data input unit (not shown) and subjected to predetermined image processing, and then temporarily stored in the memory of the image processing unit to output an output instruction. Is read out and transferred to the laser writing unit 227 of the image forming unit 210.

The laser writing unit 227 emits a laser beam modulated by image data read from the memory or image data input from an external device, a semiconductor laser light source, a polygon mirror for deflecting the laser beam at an equal angular velocity, and , And an f-θ lens for correcting the laser light deflected at a constant angular velocity so as to be deflected at a constant angular velocity on the photosensitive drum (image carrier) 222.
In the digital copying machine 100 according to this embodiment, the laser writing unit is used as a means for writing an image on the surface of the photosensitive drum 222 which is an image carrier.
A solid-state scanning writing unit using a light emitting element such as D or EL may be used.

In addition, in the image forming section 210, a charger 223 for charging the surface of the photoconductor drum 222 to a predetermined potential around the photoconductor drum 222, and an electrostatic latent image formed on the surface of the photoconductor drum 222. A developing device 224 that supplies toner to the toner to visualize the toner image, a transfer roller 225 that is a transfer member that transfers the toner image carried on the surface of the photosensitive drum 222 to a sheet that is a recording medium, and the photosensitive drum 22.
Cleaning device 2 for collecting the toner remaining on the surface of 2
26, and a static eliminator 229 such as a static eliminator for removing charges remaining on the surface of the photoconductor drum 222. The sheet onto which the toner image has been transferred by the image forming unit 210 is sent to the fixing unit 217 and is heated and pressed to firmly fix the toner image on the sheet.

The transfer roller 225 is composed of a conductive elastic member (having a resistance value of about 10 ⁴ Ω) in which carbon or the like is dispersed in a core metal such as urethane rubber or EPDM, and has an outer diameter of 14 to 2
About 0 mm and hardness of 30 to 50 degrees (Asker C) are used, and a high voltage of +2 KV to 3 KV is applied as a transfer bias from a high voltage power source for transfer.

As the cleaning device 226, a contact blade type cleaning member made of polyurethane or the like is generally used.

On the discharge side of the image forming section 210, in addition to the fixing unit 217, a switchback path 221 for reversing the front and rear ends of the sheet in the conveying direction in order to form an image again on the back surface of the sheet is formed. There is. In addition, a post-processing device that includes a post-processing mechanism that performs a stapling process or the like on a sheet on which an image is formed and an elevating tray 261 that stores the sheet on one side surface that is the discharge side of the digital copying machine 100. 260 is installed. The sheet on which the toner image has been fixed by the fixing unit 217 passes through the switchback path 221 as necessary, and the sheet discharge roller 219.
At, the sheet is guided to the post-processing device 260, subjected to a predetermined post-processing by the post-processing mechanism, and then discharged onto the elevating tray 261.

The paper feeding unit is disposed below the image forming unit 210, and a manual tray 254 provided on the other side surface of the digital copying machine 100 and a double-sided unit mounted inside the digital copying machine 100. 255 and paper tray 2
51, and paper feed trays 252 and 253 provided in the multi-stage paper feed unit 270. Further, the sheets fed from these trays 251 to 254 are used to transfer the sheets fed from the trays 251 to 254 to the photosensitive drum 222 and the transfer roller 225 in the image forming unit 210.
The transfer means 250 is provided to transfer to a transfer position between and. The double-sided unit 255 communicates with a switchback path 221 that reverses the front and rear ends of the sheet, and temporarily stores the sheet having an image formed on one side when forming an image on both sides of the sheet. The duplex unit 255 has a configuration that can be replaced with a normal paper tray.
Can be replaced with a normal paper cassette.

Digital copier 10 according to this embodiment
An image forming apparatus 0 performs a direct transfer type image forming process in which a toner image is directly transferred from the surface of the photosensitive drum 222 to the sheet. However, it is an image forming apparatus that performs an image forming process of an intermediate transfer system in which a toner image formed on a photosensitive drum is primarily transferred to an intermediate transfer member, and then the toner image is secondarily transferred from the intermediate transfer member to a sheet. However, the following configurations can be similarly applied.

FIG. 6 is a diagram showing a structure of a main part including a transfer roller and a photosensitive drum of the digital copying machine.
The transfer roller 225 is driven by the motor M11, and the photosensitive drum 222 is driven by the motor M13.
The rotations of the motors M11 and M13 are controlled by the control unit 170.

If there is a large difference between the peripheral speed (Vr) of the transfer roller 225, which is the moving speed of the surface of the transfer member, and the peripheral speed (Vd) of the photosensitive drum 222, which is the moving speed of the surface of the image carrier, transfer deviation or the like occurs. Occurs, and uneven density occurs in the toner image transferred to the sheet passing between the photoconductor drum 222 and the transfer roller 225. Therefore, the rotation speeds of the motors M11 and M13 are controlled by the control unit 170 so that the peripheral speed (Vr) of the transfer roller 225 and the peripheral speed (Vd) of the photoconductor drum 222 become substantially the same.

However, the toner image for a binary image formed by a line image such as characters or a dot image is formed relatively thick on the surface of the photosensitive drum 222, and is the center of the image when transferred to a sheet. A hollow phenomenon occurs in which a part is not transferred and comes out. Therefore, the peripheral speed (Vr) of the transfer roller 225
And a peripheral speed (Vd) of the photosensitive drum 222 need to be slightly different from each other to control so as not to cause the void phenomenon.

The image information that causes a remarkable deterioration of the image quality when the hollow defect occurs is mainly the binary image such as a character image formed in the character image mode, and the image quality when the density unevenness occurs. The image information that causes a remarkable decrease in the image information is an image information having an intermediate density image such as a photographic image.

Therefore, in the digital copying machine according to this embodiment, in the control section 170, the image mode data input together with the image data from the external device, the image mode set and input on the operation panel, the image input from the external device. The content of the data or the attribute of the image information to be imaged is determined by determining the file format of the image data input from the external device, and the rotation speed of the motor M13 that drives the photosensitive drum 222 based on the determination result. To control. As a result, by controlling only the peripheral speed (Vd) of the photosensitive drum 222, the peripheral speed (Vr) of the transfer roller 225, which is the moving speed of the transfer member surface, and the photosensitive drum 222, which is the moving speed of the image carrier surface. Peripheral speed (V
The speed difference with d) is adjusted so that a high-quality image can be formed with excellent reproducibility without changing the magnification by simple control regardless of the image attribute.

For example, when the character image mode is set on the operation panel, the peripheral speed (Vr) of the transfer roller 225 and the peripheral speed (Vd) of the photosensitive drum 222 are changed without changing the rotational speed of the motor M11. The rotation speed of the motor M13 is controlled so as to give a speed difference between the two. here,
The peripheral speed (Vd) of the photosensitive drum 222 is set to the transfer roller 225.
It may be slower or faster than the peripheral speed (Vr).

On the other hand, when the photographic image mode is set on the operation panel, the peripheral speed (Vr) of the transfer roller 225 and the peripheral speed (Vd) of the photosensitive drum 222 are changed without changing the rotational speed of the motor M11. So that
The rotation speed of the motor M13 is controlled.

Specifically, the peripheral speed of the transfer roller 225 (V
When lowering the peripheral speed (Vd) of the photosensitive drum 222 with respect to r), the peripheral speed (Vd) of the photosensitive drum 222 is set to 1% ± 0.5% than the peripheral speed (Vr) of the transfer roller 225. Delay in range. The same applies to the case where the peripheral speed (Vd) of the photosensitive drum 222 is set higher than the peripheral speed (Vr) of the transfer roller 225, and the peripheral speed (Vr) of the transfer roller 225 is higher than that of the photosensitive drum 222. Peripheral speed (Vd) is 1% ± 0.5%
In the range of. These ranges are ranges that can prevent the hollow defect that is obtained by experiments in the multicolor image forming apparatus according to this embodiment, and if this range is exceeded,
Not only density unevenness becomes noticeable, but also color unevenness and color misregistration occur in multicolor image formation.

On the other hand, when the peripheral speed (Vr) of the transfer roller 225 and the peripheral speed (Vd) of the photosensitive drum 222 are made substantially the same, the peripheral speed (Vr) of the transfer roller 225 and the peripheral speed of the photosensitive drum 222 are set. The speed fluctuation with the peripheral speed (Vd) is controlled to be ± 0.5% or less.

However, these speed setting ranges are values when the image forming speed is 120 mm / sec and plain paper is used as the sheet, and are limited to these values when the sheet quality and the image forming speed are different. is not. Further, the speed setting range may vary depending on the type and characteristics of the developer.

Although only the speed control of the photosensitive drum 222 and the transfer roller 225 is described here, the peripheral speed of the transfer roller 225 is constant regardless of the peripheral speed of the photosensitive drum 222, and therefore the sheet is conveyed. The speed does not change, and the speed of the carrying roller of the carrying unit 250 for carrying the sheet, the fixing roller of the fixing unit 217, and the like may be set to a constant carrying speed.

The processing procedure of the control section 170 is the same as the processing procedure shown in the flowchart of FIG.

In the above embodiment, the speed difference between the surface speed of the image carrier (the peripheral speed of the photosensitive drum) and the surface speed of the transfer member (the peripheral speed of the transfer / transport belt and the peripheral speed of the transfer roller). Regarding, regarding only whether or not to give a speed difference according to the attributes of two types of image information, it is not limited to this. For example, two different speed differences may be set, or different speed differences may be set according to the attributes of three or more types of images.

[0089]

EFFECTS OF THE INVENTION (1) The moving speed of the surface of the image carrier is changed by the speed difference between the moving speed of the surface of the image carrier and the moving speed of the facing surface of the transfer member according to the attribute of the image information to be imaged. The optimum value for realizing good image quality varies depending on the attribute of the image information by controlling by the control by the difference in speed between the moving speed of the image carrier surface and the moving speed of the transfer member surface. This is achieved by changing the moving speed, and as long as the moving speed of the transfer member surface is maintained at an appropriate speed with respect to the writing speed for the image carrier, the moving speed of the image carrier surface changes with the attribute of the image information. Even in this case, it is possible to form an image having the same magnification as the image information on the recording medium that moves at the same moving speed as the transfer member surface. Even when the speed difference between the moving speed of the surface of the image carrier and the moving speed of the surface of the transfer member is changed to obtain good image quality regardless of the attribute of the image information, the speed of writing the image on the image carrier is also changed. Need not be changed.

Therefore, the moving speed of the surface of the transfer member and the moving speed of the surface of the image bearing member are kept in order to obtain a good image quality irrespective of the attribute of the image information by preventing hollowing of the character image and uneven density of the photographic image. Even when controlling the speed difference, it is possible to obtain a high-quality image having excellent reproducibility with simple control, without the need for complicated control such as correction of the image writing speed.

(2) The speed of movement of the surface of the image carrier is changed between the time of image formation for image information having a binary image as a main component and the time of image formation for image information having an intermediate density image. By controlling the speed difference between the moving speed of the body surface and the moving speed of the transfer member surface, image information such as a character image mainly composed of a binary image and image information such as a photographic image having an intermediate density image can be obtained. It is possible to form an image of good image quality for both of the above conditions on the recording medium in a highly reproducible state without complicated control for correcting the writing speed for the image carrier.

(3) The moving speed of the image carrier surface and the transfer member surface by changing the moving speed of the image carrier surface according to the image forming mode set outside the control means such as an external terminal or an operation panel. By controlling the speed difference from the moving speed, the speed difference between the moving speed of the image carrier surface and the moving speed of the transfer member surface, which is suitable for the attribute of the image information to be image-formed, can be calculated. This can be realized by changing the moving speed, and an image of good image quality can be easily and accurately formed on the recording medium in a highly reproducible state regardless of the attribute of the image information.

(4) The moving speed of the surface of the image carrier is defined as the moving speed of the surface of the transfer member at the time of image formation for image information mainly composed of a binary image whose image quality is remarkably deteriorated due to the occurrence of the hollow image phenomenon. By controlling to different speeds, the moving speed of the image carrier surface is set to a speed that substantially matches the moving speed of the transfer member surface during image formation for image information having an intermediate density image in which the image quality is significantly deteriorated due to occurrence of uneven density. By controlling the image information, which mainly consists of binary images, a speed difference is given between the moving speed of the surface of the image carrier and the moving speed of the surface of the transfer member in order to prevent the hollow image. On the other hand, in the case of image information having an intermediate density image, in order to prevent uneven density, the image forming member surface and the transfer member surface should be made to substantially match in moving speed to form an image. It is possible to record an image of good image quality with high reproducibility by controlling only the moving speed of the surface of the image carrier for both the image information mainly consisting of binary images and the image information having an intermediate density image. It can be formed on a medium.

(5) When the character image mode is set, the moving speed of the image carrier surface is controlled to be different from the moving speed of the transfer member surface, and when the photographic image mode is set, the image is moved. By controlling the moving speed of the surface of the carrier substantially at the same as the moving speed of the surface of the transfer member, the moving speed of the surface of the image carrier and the transfer member can be prevented in order to prevent the hollowing-out phenomenon for image information mainly composed of character images. While image formation can be performed by giving a speed difference to the moving speed of the surface, for image information mainly composed of photographic images, the moving speed of the image carrier surface and the transfer member surface are moved to prevent density unevenness. It is possible to form an image at a speed that is substantially the same, and for both image information mainly composed of character images and image information mainly composed of photographic images, an image of good image quality can be obtained by controlling only the moving speed of the image carrier surface. Re It can be formed on the recording medium at a high sexual state.

(6) By making the moving speed of the image carrier surface faster than the moving speed of the transfer member surface when a speed difference is given between the moving speed of the image carrier surface and the moving speed of the transfer member surface. During transfer of the toner image from the surface of the image carrier to the recording medium, a force is applied to the toner image in a direction of contracting the conveying direction of the recording medium to reduce the adhesive force of the toner image to the surface of the image carrier to reduce the image. It is possible to prevent hollowing out. Further, by matching the writing speed in the exposure process to the surface of the image carrier with the moving speed of the surface of the transfer member, the surface of the image carrier moves faster than the writing speed so that the image carrier is expanded. The toner image formed on the surface can be reduced and transferred to a recording medium that moves at a relatively low speed with respect to the surface of the image carrier at the same magnification as when it is expanded, and image information can be accurately reproduced. .

(7) By making the moving speed of the image carrier surface slower than the moving speed of the transfer member surface when a speed difference is given between the moving speed of the image carrier surface and the moving speed of the transfer member surface. During transfer of the toner image from the surface of the image carrier to the recording medium, a force is applied to the toner image in a direction that extends in the conveying direction of the recording medium to reduce the adhesive force with the toner image on the surface of the image carrier to form an image. It is possible to prevent hollowing out. Further, by matching the writing speed in the exposure step for the surface of the image carrier with the moving speed of the surface of the transfer member, the surface of the image carrier moves slower than the writing speed and the image carrier is reduced in size. The toner image formed on the surface can be expanded and transferred to a recording medium that moves at a relatively low speed with respect to the surface of the image carrier at the same magnification as that at the time of reduction, and image information can be accurately reproduced. .

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a multicolor image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a state of a transfer / conveyance belt unit during color image formation by the multicolor image forming apparatus.

FIG. 3 is a diagram illustrating a state of a transfer / conveying belt unit at the time of forming a monochrome image in the multicolor image forming apparatus.

FIG. 4 is a flowchart illustrating a part of a processing procedure of a control unit of the multicolor image forming apparatus.

FIG. 5 is a diagram showing a schematic configuration of a digital copying machine which is a monochromatic image forming apparatus according to a second embodiment of the present invention.

FIG. 6 is a diagram showing a configuration of a main part including a transfer roller and a photoconductor drum of the digital copying machine.

[Explanation of symbols]

3a to 3d, 222-photosensitive drum (image bearing member) 6a to 6d, 225-transfer roller (transfer member) 7-transfer conveyor belt (transfer member) 70, 170-control unit (control means)

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masanobu Yamamoto             22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka             Inside the company (72) Inventor Takayuki Ohno             22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka             Inside the company F-term (reference) 2H027 DE07 EB02 EB04 EC20 ED02                       ED24 EE03 EE07 EF07 EF12                       EF13 EH08 EH10 FA35 FB19                       ZA07                 5C074 AA02 BB17 DD01 DD12 EE08                       EE11 FF03 FF06 FF13

Claims (7)

[Claims] 1. A transfer member which forms an electrostatic latent image by exposing the surface of the image carrier based on image information to visualize the electrostatic latent image as a toner image and moves in the same direction as the surface of the image carrier. In an image forming apparatus that transfers a toner image from the surface of an image carrier to a recording medium that is held and conveyed on the surface, the moving speed of the surface of the image carrier is changed by changing the moving speed of the surface of the image carrier according to the attribute of image information. An image forming apparatus comprising: a control unit that controls a speed difference between a moving speed and a moving speed of a facing surface of a transfer member. 2. The control means controls the moving speed of the surface of the image carrier according to the attribute of the image information indicating whether the image information is mainly a binary image or the image information having an intermediate density image. The image forming apparatus according to claim 1, wherein the image forming apparatus is changed. 3. The image forming apparatus according to claim 1, wherein the control means determines the attribute of the image information based on an image forming mode set from the outside. 4. The control means, when the image information is mainly a binary image, sets the moving speed of the surface of the image carrier different from the moving speed of the surface of the transfer member, and has an intermediate density image. 4. The image forming apparatus according to claim 1, wherein when the image information is image information, the moving speed of the surface of the image carrier is made substantially equal to the moving speed of the surface of the transfer member. 5. The control means sets the moving speed of the surface of the image carrier different from the moving speed of the transfer member when the character mode mainly including the character image is set as the image forming mode, and the photographic image is obtained. 4. The moving speed of the surface of the image carrier is made to substantially match the moving speed of the surface of the transfer member when the photographic mode mainly including is set.
The image forming apparatus according to item 1. 6. The control means sets a speed difference between the moving speed of the image carrier surface and the moving speed of the transfer member surface by making the moving speed of the image carrier surface faster than the moving speed of the transfer member surface. The image forming apparatus according to claim 1, wherein the image forming apparatus is provided. 7. The control means sets a speed difference between the moving speed of the surface of the image carrier and the moving speed of the surface of the transfer member by making the moving speed of the surface of the image carrier slower than the moving speed of the surface of the transfer member. The image forming apparatus according to claim 1, wherein the image forming apparatus is provided.