JPH08146783A - Image forming device - Google Patents

Abstract

(57) [Summary] [Object] To prevent slippage due to insufficient driving force between an intermediate transfer belt of an image forming apparatus and its driving roller at low cost without generating discharge products. [Structure] When the frictional force between the driving roller 21 and the intermediate transfer belt 19 is insufficient, the driving roller 21 and the intermediate transfer belt 19 are
Since a slip occurs between the drive roller 21 and the core metal of the drive roller 21, the drive roller 21 is charged and an electrostatic attraction force is applied between the drive roller 21 and the intermediate transfer belt 19 to prevent the slip. To prevent. If the drive roller 21 is always charged, it becomes easy to adsorb toner and dust floating in the machine. Therefore, the drive roller 21 is charged in synchronization with the timing of a high load at which the intermediate transfer belt 19 tends to slip. The drive roller 21 is not charged when unnecessary.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a copying machine, a printer,
Regarding an image forming apparatus using an electrophotographic system such as FAX,
In particular, the present invention relates to an image forming apparatus having a carrier that carries toner and conveys an object to be carried to the next step.

[0002]

2. Description of the Related Art A conventional carrier used in this type of image forming apparatus is an endless belt which is stretched around a plurality of rollers and driven to rotate, and is called an intermediate transfer belt or the like.
The toner image transferred from the latent image bearing member is rotatably driven until it is transferred to a transfer material such as transfer paper to become an intermediate transfer member that conveys the toner image.

In the image forming apparatus using such an intermediate transfer member, the driving force between the intermediate transfer member and the driving roller is insufficient,
There is the problem of slipping. In particular, there is a high probability that a problem will occur when a high load is applied to the intermediate transfer member. That is, when the toner image is transferred to the transfer material by contacting the transfer material, a large load is applied to the intermediate transfer member due to the contact with the transfer material. Further, even if the cleaning means comes into contact with the intermediate transfer member to clean the toner image, a large load is applied to the intermediate transfer member, causing slippage. To solve this problem, Japanese Patent Laid-Open No. 1-235
In the technique disclosed in Japanese Patent No. 968, an intermediate transfer member is charged by an attraction charger, and an electrostatic attraction force is applied between the intermediate transfer member and a grounded driving roller to assist the driving force and solve the problem.

[0004]

However, if an adsorption charger is provided as a means for compensating the driving force, the cost will increase accordingly, and the discharge products such as ozone generated from the adsorption charger will reduce the discharge product concentration in the machine. High,
There is also a problem that it causes a problem that the photosensitive member, the intermediate transfer member, or the like suffers a bad image.

The present invention has been made in view of such conventional problems, and an object thereof is to provide an image forming apparatus which is inexpensive, does not generate discharge products, and prevents slipping due to insufficient driving force.

[0006]

In order to achieve the above object, an image forming apparatus according to the present invention has an intermediate transfer member which is formed into an endless belt shape and is stretched around a plurality of rollers and driven to rotate. In an image forming apparatus that transfers a toner image formed on a latent image carrier to the intermediate transfer body and transfers the toner image to a transfer material, the drive is performed when a high load is applied to the intermediate transfer body. The roller is electrically charged.

The image forming apparatus according to the present invention may be configured so that the driving roller is charged when the toner on the intermediate transfer member is transferred to the transfer material.

The image forming apparatus according to the present invention can be configured to charge the drive roller when cleaning the toner on the intermediate transfer member.

An image forming apparatus according to the present invention is the image forming apparatus according to any one of claims 1 to 3, further comprising means for determining a driving force shortage for driving the intermediate transfer member. The driving roller may be charged when it is determined that the driving force is insufficient.

The image forming apparatus according to the present invention counts the cumulative operation time of the intermediate transfer body since the last maintenance of the intermediate transfer unit as the determination means of the driving force shortage of the intermediate transfer body, and the cumulative operation time is calculated. It can be configured to determine that the driving force is insufficient when a certain reference value is exceeded.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of a color copying apparatus which is an example of an image forming apparatus according to the present invention, and FIG. 2 is an enlarged view around a photoconductor and an intermediate transfer belt. The structure and operation of the present apparatus will be described below. A color image reading apparatus (hereinafter referred to as a color scanner) 1 converts an image of a document 3 through a lighting lamp 4, a mirror group 5 and a lens 6 into a photoelectric device such as a CCD. An image is formed on the color sensor 7 using a conversion element, and color image information of the original 3 is read for each color separation light of, for example, Blue (hereinafter referred to as B), Green (the same G), and Red (the same R), Convert to electrical image signal. Then, based on the B, G, and R color-separated image signal intensity levels obtained by the color scanner 1, color conversion processing is performed by an image processing unit (not shown), and Black (same BK), C
yan (the same C), Magenta (the same M), Yello
Color image data of w (same Y) is obtained. This is visualized with BK, C, M, and Y by a color image recording device (hereinafter, referred to as a color printer) described below,
These are superimposed to form a four-color full-color image.

Next, the color printer 2 will be described. Laser 8-1, polygon mirror 8-2, polygon motor 8
-3, an f / θ lens 8-4, a reflection mirror 8-5, and the like, the writing optical unit 8 converts the color image data from the color scanner 1 into an optical signal and performs optical writing corresponding to the original image. , An electrostatic latent image is formed on the photosensitive drum 9.

The photoconductor drum 9 rotates counterclockwise as indicated by the arrow, around which the photoconductor cleaning unit 10 (pre-cleaning static eliminator 10-1, brush roller 10-2, rubber blade 10-3) is provided. ), Static elimination lamp 11, charging device 12, potential sensor 13, BK developing device 1
4, a C developing device 15, an M developing device 16, a Y developing device 17, a development density pattern detector 18, an intermediate transfer belt 19 and the like are arranged. Each developing device is a developing sleeve (14-1, 15-1, 16-1, 17-1) that rotates so that the developer faces the photoconductor drum 9 in order to develop the electrostatic latent image.
And a developer paddle (14-2, 15-2, 16-2, 17-2) that rotates to pump up and stir the developer, and a toner concentration detection sensor (14-3, 15-) of the developer.
3, 16-3, 17-3) and the like.

Development operation sequence (color image formation sequence)
Will be described below with the examples of BK, C, M and Y. However, the image forming order is not limited to this. When the copying operation is started, the color scanner 1 starts reading BK image data at a predetermined timing, and optical writing by a laser beam and latent image formation are started based on the image data (hereinafter, BK image data is used. The electrostatic latent image is called a BK latent image. The same applies to C, M, and Y).
In order to enable development from the tip of the BK latent image, rotation of the developing sleeve 14-1 is started before the tip of the latent image reaches the developing position of the BK developing device 14, and the BK latent image is developed with BK toner. To do. After that, the developing operation of the BK latent image area is continued, but when the rear end portion of the BK latent image passes the BK developing position, the developing operation is disabled. This is completed at least before the leading edge of the C latent image by the next C image data arrives.

The BK toner image formed on the photosensitive drum 9 is transferred onto the surface of the intermediate transfer belt 19 which is driven at the same speed as the photosensitive drum 9. Hereinafter, the toner image transfer from the photosensitive drum 9 to the intermediate transfer belt 19 is referred to as belt transfer. The belt transfer is performed by the photosensitive drum 9 and the intermediate transfer belt 1.
This is performed by applying a predetermined bias voltage to the transfer bias roller 20 when 9 is in contact. It should be noted that BK sequentially formed on the photoconductor drum 9 on the intermediate transfer belt 19,
The toner images of C, M, and Y are sequentially aligned on the same surface to form a belt transfer image of four-color overlapping, and then they are collectively transferred to a transfer paper.

On the side of the photosensitive drum 9, the BK process is followed by the C process, but the color scanner 1 starts from a predetermined timing.
C image data reading is started by C, and a C latent image is formed by writing laser light by the image data. The C developing device 15 starts the rotation of the developing sleeve 15-1 with respect to the developing position after the trailing edge of the previous BK latent image has passed and before the leading edge of the C latent image has reached the C latent image. Is developed with C toner. After that, the development of the C latent image area is continued, but when the trailing edge of the latent image passes, the development is inoperative as in the case of the previous BK developing device. This is also completed before the leading edge of the next M latent image arrives. The steps of M and Y are the same as the steps of BK and C, respectively, in the operations of image data reading, latent image formation, and development, and therefore the description thereof is omitted.

Next, the intermediate transfer belt unit will be described. The intermediate transfer belt 19 is stretched around a drive roller 21, a belt transfer bias roller 20, and a group of driven rollers, and is drive-controlled by a drive motor (not shown). The belt cleaning unit 22 includes a brush roller 22-
1. Rubber blade 22-2 and belt contact / separation mechanism 2
It is composed of 2-3 or the like, and is separated from the belt surface by the contact / separation mechanism 22-3 during the belt transfer of the second, third and fourth colors after the belt transfer of the first color BK image. .

The paper transfer unit 23 is composed of a paper transfer bias roller 23-1, a roller cleaning blade 23-2 and a belt contact / separation mechanism 23-3.
The paper transfer bias roller 23-1 is normally separated from the surface of the belt 19, but when transferring the four-color child images formed on the surface of the intermediate transfer belt 19 to the transfer paper all at once, the paper transfer bias roller 23-1 comes into contact with the transfer paper at a timing. It is pressed by the separating mechanism 23-3 and a predetermined bias voltage is applied to transfer it to the paper. The transfer paper 24
The paper is fed by the paper feed roller 25 and the registration roller 26 at the timing when the leading end of the four-color superimposed image on the surface of the intermediate transfer belt 19 reaches the paper transfer position.

The operation of the intermediate transfer belt 19 is the first color B
As the operation method after the belt transfer of the K toner image is completed up to the rear end, there are three types of a constant speed forward movement method, a skip forward movement method, and a reciprocating movement method. According to copy size (copy speed etc.)
Operate by a combination of efficient methods.

The constant speed forward movement method (1) continues the forward movement at a constant speed even after the BK toner image is transferred onto the belt. (2) When the leading edge position of the BK image on the surface of the belt 19 reaches the belt transfer position of the contact portion with the photosensitive drum 9 again,
An image is formed on the side of the photoconductor drum 9 with a timing so that the front end of the next C toner image is exactly at that position.
As a result, the C image is accurately aligned with the BK image and is transferred onto the intermediate transfer belt 19 in a superimposed manner. (3) Thereafter, the same operation is performed to proceed to the M and Y image process, and a belt transfer image of four colors is obtained. (4) The four-color Y toner image belt transfer process is continued, and the four-color superposed toner image on the belt surface is moved as it is.
As described above, they are collectively transferred to the transfer paper 24.

The skip forward method is as follows: (1) When the belt transfer of the BK toner image is completed, the belt 19 is separated from the surface of the photosensitive drum 9, and the high speed skip is performed in the same forward direction to move a predetermined amount. Return to the forward speed. Further, thereafter, the belt 19 is brought into contact with the photosensitive drum 9 again. (2) When the leading edge position of the BK image on the surface of the belt 19 reaches the repeat belt transfer position, the photosensitive drum 9 side takes timing so that the leading edge portion of the next C toner image is exactly at that position. An image is formed. As a result, the C image is accurately aligned with the BK image and transferred onto the belt in a superimposed manner. (3) After that, the same operation is performed to proceed to the M and Y image processes, and a belt transfer image of four colors is obtained. (4) Following the step of transferring the Y toner image belt of the fourth color, the four-color superimposed toner image on the surface of the belt 19 is collectively transferred onto the transfer paper 24 at the same forward speed.

The reciprocating motion (quick return) system is as follows: (1) When the belt transfer of the BK toner image is completed, the belt 19 is separated from the surface of the photosensitive drum 9, and the forward motion is stopped, and at the same time, the high speed return is performed in the opposite direction. Let In the return, the front end position of the BK image on the surface of the belt 19 passes through the position corresponding to the belt transfer in the opposite direction, and after moving for a preset distance, it is stopped and put in the standby state. (2) Next, when the front end portion of the C toner image on the photosensitive drum 9 side reaches a predetermined position before the belt transfer position, the intermediate transfer belt 19 is restarted in the forward direction. Further, the belt 19 is brought into contact with the surface of the photosensitive drum 9 again. Also in this case, the belt C is transferred under the condition that the C image accurately overlaps the BK image on the surface of the belt 19. (3) After that, the same operation is performed to proceed to the M and Y image processes, and a belt transfer image of four colors is obtained. (4) Subsequent to the belt transfer process of the Y toner image of the fourth color, the four-color superimposed toner image on the surface of the belt 19 is collectively transferred onto the transfer paper 24 without returning and moving at the same speed.

The transfer paper 24 on which the four-color superimposed toner images are collectively transferred from the surface of the intermediate transfer belt 19 is a paper transport unit 27.
Then, the toner image is conveyed to the fixing device 28, and the toner image is melted and fixed by the fixing roller 28-1 and the pressure roller 28-2, which are controlled to a predetermined temperature, and is carried out to the copy tray 29 to obtain a full-color copy. The photosensitive drum 9 after the belt transfer
Is subjected to surface cleaning by the photoconductor cleaning unit 10 and is uniformly discharged by the discharging lamp 11.

After the toner image is transferred onto the transfer paper 24, the surface of the intermediate transfer belt 19 is cleaned by pressing the cleaning unit 22 again by the contact / separation mechanism 22-3. At the time of repeat copy, the operation of the color scanner 1 and the image formation on the photosensitive drum 9 are performed at the predetermined timing at the second BK (first color) image process after the first Y (fourth color) image process. move on. Further, in the case of the intermediate transfer belt 19, the second BK toner image is belt-transferred to the area whose surface is cleaned by the cleaning unit 22, following the batch transfer process of the first four-color superimposed image onto the transfer paper. To be done. After that, the same operation as the first sheet is performed. The transfer paper cassettes 30, 31, 32, and 33 store transfer paper of various sizes, and an operation panel (not shown)
The paper is fed and conveyed in the direction of the registration roller 26 at a timing from the storage cassette for the size paper designated by. Three
Reference numeral 4 is a manual paper feed tray for OHP paper, thick paper, and the like.

The above is the description of the copy mode for obtaining four full colors, but in the case of the three-color copy mode and the two-color copy mode, the same operation as described above is performed for the designated number of colors and the number of times. In the single-color copy mode, only the developing device for the color is kept in the developing operation state until the predetermined number of sheets are finished, and the intermediate transfer belt 19 is kept in contact with the surface of the photosensitive drum 9 at a constant speed in the forward direction. The belt cleaner 22 is driven and the copy operation is performed while the belt cleaner 22 is still in contact with the belt 19.

In the intermediate transfer belt system as described above, when the driving force for driving the intermediate transfer belt 19 (specifically, the frictional force between the driving roller 21 and the intermediate transfer belt 19) is insufficient, Intermediate transfer belt 1
Slip occurs between 9 and. Therefore drive roller 2
Drive roller 2 by applying a bias to core metal 1
1 is electrified, and electrostatic attraction is applied between the drive roller 21 and the intermediate transfer belt 19 to prevent slip. However,
When the drive roller 21 is charged, the electrostatic attraction force with the intermediate transfer belt 19 increases, and at the same time, toner or dust floating in the machine is easily attracted. Therefore, the side effects can be minimized by not charging the drive roller 21 when it is unnecessary and charging it only when it is necessary. In particular, since the slip of the intermediate transfer belt 19 is highly likely to occur at the timing when a high load is applied, the drive roller 21 is synchronized with the timing.
It is advisable to charge the to prevent slippage at that time.

When the toner image on the intermediate transfer belt 19 is transferred onto the transfer material, a high load is applied to the belt and slipping easily occurs. Therefore, the drive roller 21 is charged in synchronization with the timing at which the toner image on the intermediate transfer belt 19 is transferred onto the transfer material, so that the slip at the time of transfer can be prevented. Further, even when the toner on the intermediate transfer belt 19 is cleaned, a high load is applied to the belt and slipping easily occurs. In this case, the drive roller 21 may be charged in synchronization with the timing of cleaning the toner on the intermediate transfer belt 19 to prevent slippage during cleaning.

The driving force for driving the intermediate transfer belt 19 is the cleaning of the driving roller 21 and the intermediate transfer belt 19
It is highest immediately after maintenance such as replacement of the machine, and there is no problem for a while after that, but when the machine is used, that is, image formation is repeated, scattering of toner, paper dust, dust inside the machine, shavings of the intermediate transfer belt 19, driving roller 21 wear,
It decreases due to dirt and the like, and eventually slips occur between the drive roller 21 and the belt 19. Therefore, when the driving force shortage determination unit determines that the driving force is insufficient, the drive roller 21 is charged, so that the slip can be prevented.

Intermediate transfer belt 19 and its driving roller 21
The driving force shortage determination means measures the slip amount between the drive roller 21 and the belt 19 and compares the measured slip amount with a certain reference value to determine whether the level is a problem. An example of a method for measuring slip is shown in FIG. This means is provided with a positional deviation mark 37 on the intermediate transfer belt 19.
Is pasted, the intermediate transfer belt 19 is rotated, the mark 37 is read by the mark detection sensor 38, the output pulse of the encoder 36 attached to the drive roller 21 is counted by the counter 36, and the signal output from the mark detection sensor 38. Trigger by the intermediate transfer belt 1
The number of rotations (number of pulses) of the drive roller 21 when one rotation of 9 is performed is read. And the intermediate transfer belt 19
The pulse number of the drive roller 21 is read in a state in which nothing comes into contact with, the paper transfer unit or the belt cleaner is then brought into contact with the intermediate transfer belt 19, and the pulse number at that time is measured. Then, the number of pulses is compared with the number of pulses at the time of free, which will be described below, and
Find the slip amount of.

FIG. 4 shows an example measured by this method. In this figure, the drive roller 21 of the intermediate transfer belt 19 is 5000
The relationship between the driving linear velocity ratio of the intermediate transfer belt 19 and the result of measurement of how many pulses it takes for the intermediate transfer belt 19 to make one rotation assuming that one rotation is made by a pulse is shown. The belt drive linear velocity ratio is obtained by dividing the intermediate transfer belt linear velocity by the photosensitive drum linear velocity. A curve A in FIG. 4 shows a change in the number of pulses when the photosensitive drum 9, the belt cleaner, and the paper transfer unit are separated from the intermediate transfer belt 19 (referred to as a free state), and a curve B shows when the belt cleaner is in contact. A change in the number of pulses, curve C shows a change in the number of pulses when the drive roller 21 is charged while the belt cleaner is in contact. The number of pulses when the belt cleaner is pressed is larger than the number of pulses when the intermediate transfer belt 19 of the curve A is rotating freely, and the belt drive roller 21
It is considered that the driving force for the sheet is insufficient and the sheet is slipping with the intermediate transfer belt 19. On the other hand, the drive roller 21
It can be seen that by charging C, the number of pulses becomes close to the number of pulses in the free state as shown by the curve C, and the slip is reduced.

The slip measuring operation between the intermediate transfer belt 19 and the intermediate transfer belt driving roller as described above is preferably performed at the time of warming up after the power of the image forming apparatus main body is turned on. As a result, the image forming operation is not interrupted for the main measurement operation, the measurement can be performed at an appropriate frequency, and the occurrence of insufficient driving force can be reliably detected.

As described above, the driving force between the intermediate transfer belt 19 and the driving roller 21 gradually decreases as the image forming operation is repeated.
The operating time corresponding to the limit value of the driving force can be determined by previously obtaining the relationship between the operating time from the maintenance of 9 and the driving force (slip amount) by an experiment. That is, the cumulative operation time of the intermediate transfer belt 19 since the last maintenance of the intermediate transfer belt unit is counted, and when this operation time reaches the previously obtained time, it is determined that the driving force is insufficient, and the next maintenance is performed. Clear the counter at. Of course, other characteristics such as the number of copies and the operating time of the photoconductor can be adopted as the criterion.

[0033]

EFFECTS OF THE INVENTION Since the present invention has been described above, the driving force can be supplemented at a low cost without generating discharge products such as ozone as in the case of using an adsorption charger, and slip can be prevented. The effect is that you will be able to.

Further, the image forming apparatus according to the eighth aspect of the present invention can be easily performed without providing a special mechanism by determining the cumulative operating time of the intermediate transfer unit from the last maintenance of the intermediate transfer unit as the driving force determining means. In addition, there is an effect that it becomes possible to know when the driving force decreases.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a color copying apparatus.

FIG. 2 is a detailed view of the periphery of a photoconductor and an intermediate transfer belt.

FIG. 3 is a schematic diagram of an intermediate transfer belt slip measurement.

FIG. 4 is a diagram showing a relationship between a belt drive linear velocity ratio and a belt drive roller pulse number when a belt cleaner contacts an intermediate transfer belt.

[Explanation of symbols]

 1 Color Image Reading Device (Color Scanner) 2 Color Image Recording Device (Color Printer) 3 Original Document 4 Illumination Lamp 5 Mira Group 6 Lens 7 Color Sensor 8 Writing Optical Unit 8-1 Laser 8-2 Polygon Mirror 8-3 Polygon Motor 8 -4 f / θ lens 8-5 reflection mirror 9 photoconductor drum 10 photoconductor cleaning unit 10-1 static eliminator before cleaning 10-2 brush roller 10-3 rubber blade 11 static eliminator lamp 12 charger 13 potential sensor 14 Black (BK ) Developing device 14-1 BK developing sleeve 14-2 BK developing paddle 14-3 BK toner density detection sensor 15 Cyan (C) developing device 15-1 C developing sleeve 15-2 C developing paddle 15-3 C toner concentration detection sensor 16 Mag nta (M) developing device 16-1 M developing sleeve 16-2 M developing paddle 16-3 M toner concentration detection sensor 17 Yellow (Y) developing device 17-1 Y developing sleeve 17-2 Y developing paddle 17-3 Y toner density detection sensor 18 Development density pattern detector 19 Intermediate transfer belt 20 Belt transfer bias roller 21 Belt drive roller 22 Belt cleaning unit 22-1 Brush roller 22-2 Rubber blade 22-3 Contact / separation mechanism 23 Paper Transfer unit 23-1 Paper transfer bias roller 23-2 Roller cleaning blade 23-3 Contact / separation mechanism 24 Transfer paper 25 Paper feed roller 26 Registration roller 27 Paper transport unit 28 Fixer 28-1 Fixing roller 28-2 Pressure roller 29 Copy tray 30, 31, 32, 33 Transfer Cassette 34 hand feed tray 35 encoder 36 counter 37 positions Zuremaku 38 mark detecting sensor

Claims (5)

[Claims] 1. An intermediate transfer member, which is formed into an endless belt shape, is stretched around a plurality of rollers and driven to rotate, and a toner image formed on a latent image carrier is transferred to the intermediate transfer member. An image forming apparatus for transferring the toner image onto a transfer material is characterized in that the drive roller is charged when a high load is applied to the intermediate transfer member. 2. The image forming apparatus according to claim 1, wherein the driving roller is charged when the toner on the intermediate transfer member is transferred to a transfer material. 3. The image forming apparatus according to claim 1, wherein the drive roller is charged when the toner on the intermediate transfer member is cleaned. 4. The image forming apparatus according to any one of claims 1 to 3, further comprising means for determining whether the driving force for driving the intermediate transfer member is insufficient, and the means determines that the driving force is insufficient. An image forming apparatus characterized in that the drive roller is electrically charged. 5. The image forming apparatus according to claim 4, wherein the cumulative operation time of the intermediate transfer member since the last maintenance of the intermediate transfer unit is counted as the determination means of the driving force shortage of the intermediate transfer member, and the cumulative operation is performed. An image forming apparatus characterized in that when the time exceeds a certain reference value, it is determined that the driving force is insufficient.