JPH10240097A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a toner image of plural colors from deviation in a position by providing means detecting a rotary position of latent image carrying means, and the means detecting the rotary position of the image carrier provided in connecting with the image carrying means. SOLUTION: In this device, the photoreceptor rotation position detecting means 5 detects a mark formed on the photoreceptor belt 1 rear side. The time point counting a necessary numbers from a falling edge of the photoreceptor belt rotary position detecting signal becomes the time pint when a seam of the photoreceptor belt 1 just passes through the exposure point, therefore the image is formed by evading the seam of the photoreceptor belt 1. While, the intermediate transfer material rotary position detecting signal, detects the rotary position of the intermediate transfer material 8 by the intermediate rotary position detecting means 10 by forming the slits of the specific numbers on the periphery of the intermediate transfer material encoder plate 9. Since the position counted the necessary numbers from the rising edge of the intermediate transfer rotary position detecting signal becomes as an exposure starting reference of the respective color, the toner of four colors are laid over the other without position shifting on the intermediate transfer material 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image forming apparatus such as a page printer for printing image data.

[0002]

2. Description of the Related Art Conventionally, printers based on various principles have been proposed as output terminals of personal computers, workstations and the like. In particular, a laser beam printer (hereinafter abbreviated as LBP) using an electrophotographic process and laser technology. ) Is superior in terms of recording speed and print quality and is rapidly spreading.

[0003] In the market, there is an increasing demand for color conversion of LBP. In the case of color LBP, it is necessary to superimpose and print four color toners of cyan, magenta, yellow and black, which are the three primary colors of printing. . Since it is impossible to write image data for four colors at a time on a latent image carrier (hereinafter, referred to as a photoreceptor belt) used for LBP, writing of image data for one color is completed, and development with toner is performed. At this point, an image is once transferred onto an image carrier (hereinafter referred to as an intermediate transfer member), image data of the next color is written on the photoreceptor belt, and when development with the next color toner is completed, the intermediate transfer is performed. It is transcribed onto the body over the previous color.

When this cycle is completed for four colors, finally, images for four colors are collectively transferred from the intermediate transfer body onto a recording medium, and the recording medium undergoes a fixing process in which the toner is melted and fixed on the recording medium. After that, I have obtained a color image. Hereinafter, the exposure start timing in the operation of the image forming apparatus according to the related art will be described with reference to FIGS.

In FIG. 5, reference numeral 1 denotes a closed loop Ni.
This is a photosensitive belt as a latent image holding means in which a photosensitive layer such as an organic photoconductor (OPC) is applied in a thin film form on an outer peripheral surface of a (nickel) belt base material. This photoreceptor belt 1
Is technically difficult to manufacture seamlessly,
A rectangular sheet-shaped photoreceptor belt is attached at both ends and has a physical joint. Photoreceptor belt 1
Is supported by three photoconductor transport rollers 2, 3, and 4, and is rotated in the direction of arrow A by a drive motor (not shown). Reference numeral 5 denotes a photoreceptor belt rotation position detecting means for detecting a mark formed on the back surface of the photoreceptor belt 1, which prevents an image from being formed on a joint of the photoreceptor belt 1.

Reference numeral 6 denotes an exposure optical system (hereinafter abbreviated as LSU) comprising a laser driving device, a polygon mirror, a lens system, a motor for rotating the polygon mirror, etc. (not shown).
Thus, an electrostatic latent image is formed on the charged photosensitive belt 1. Reference numeral 7 denotes an exposure light beam emitted from the LSU 6. The exposure light beam 7 is obtained by subjecting an image signal from a gradation converter (not shown) to light intensity modulation or pulse width modulation by a laser driving circuit (not shown), and corresponding to a specific color on the photoreceptor belt 1. An electrostatic latent image is formed.

Reference numeral 8 denotes a metal such as aluminum (for example, having a diameter of 20).
0 mm) An intermediate transfer member as an image carrying means in which a belt-shaped sheet made of a conductive resin or the like is wound around a base tube, and is rotated in the direction of arrow B by a drive motor (not shown). 9
Is an intermediate transfer member encoder plate for detecting the rotational position of the intermediate transfer member 8, which is attached to the side surface of the intermediate transfer member 8 and rotates in conjunction with the intermediate transfer member 8. For example, 400 slits are formed around the intermediate transfer body encoder plate 9, and the rotation position of the intermediate transfer body is detected by the intermediate transfer body rotation position detection unit 10. The circumference of the photosensitive belt 1 and the circumference of the intermediate transfer body 8 are designed to be the same.

In FIG. 6, a signal NOPCHP is a photoreceptor belt rotation position detection signal, which is normally at a high level when the photoreceptor belt rotation position detection means 5 detects a marker formed on the back surface of the photoreceptor belt 1. Low level. The signal TRMENC is an intermediate transfer member rotational position detection signal, and goes low when the slit of the intermediate transfer member encoder plate passes through the intermediate transfer member rotational position detecting means, and goes high when the slit passes therethrough. Signal NTRMH
P is an exposure start reference signal, and exposure of each color is started based on the falling edge of this signal.

When printing is started, first, the photosensitive belt 1
Then, the intermediate transfer member 8 starts rotating, and the photosensitive belt rotation position detecting means 5 detects a mark formed on the back surface of the photosensitive belt 1. Conventionally, in order to prevent the seam of the photoreceptor belt 1 from entering an image, exposure of each color is started based on the falling edge of the photoreceptor belt rotation position detection signal NOPCHP.

However, there is always a difference in the circumferential length between the photosensitive belt 1 and the intermediate transfer member 8, and the rotational speed difference between the photosensitive belt 1 and the intermediate transfer member 8 causes a difference in the rotation length between the photosensitive belt 1 and the intermediate transfer member 8. The color toner image was misaligned, causing poor image quality. Therefore, as a countermeasure, the following exposure start timing control has been proposed.

When the photoreceptor belt 1 and the intermediate transfer member 8 start rotating and the photoreceptor belt rotation position detecting means 5 detects a mark formed on the back surface of the photoreceptor belt 1, as shown in FIG. Belt rotation position detection signal NOPCHP
The number of rising edges of the intermediate transfer body rotation position detection signal TRMENUC counted from the falling edge of, for example, five counts is set as the exposure start reference for the first color.

The photosensitive belt rotational position detection signal NOP
The point in time when five points have been counted from the falling edge of CHP is the point in time when the joint of the photosensitive belt 1 has just passed the exposure point, and an image is formed avoiding the joint of the photosensitive belt 1. The count from the falling of the photosensitive belt rotational position detection signal NOPCHP is arbitrarily set according to the positional relationship between the photosensitive belt rotational position detection means 5 and the exposure point. The exposure start criterion for the second and subsequent colors is assumed to be a value obtained by counting 400 rising edges of the intermediate transfer body rotation position detection signal TRMENUC from the exposure start criterion for the first color. In the case of continuous printing, the intermediate transfer member rotational position detection signal TRMENC is used for all colors of the second and subsequent sheets.
Are counted as 400 when the rising edge is counted as an exposure start reference.

[0013]

However, in the above-described conventional configuration, although the four color toner images overlap on the intermediate transfer member 8 without displacement, a circumferential difference between the photosensitive belt 1 and the intermediate transfer member 8 occurs. Therefore, at the time of continuous printing, a seam of the photoreceptor belt 1 is formed in an image area, causing a serious image quality defect. For example, since the photoreceptor belt 1 has an A3 vertical size of 420 mm for 628 mm,
The margin for avoiding the seam is about 208 mm, but if the circumferential length difference between the photoreceptor belt 1 and the intermediate transfer body 8 is about 1 mm, the seam enters the image at about the 200th continuous printing.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus in which a seam of a photoreceptor belt does not always enter an image even during continuous printing, and there is no displacement of a toner image of a plurality of colors.

[0015]

According to the present invention, there is provided an image forming apparatus comprising: means for detecting a rotational position of a latent image carrier; and means for detecting a rotational position of an image carrier provided in connection with the image carrier. It has.

[0016]

DETAILED DESCRIPTION OF THE INVENTION An image forming apparatus according to the first aspect of the present invention has the following features.
There are provided means for detecting the rotational position of the latent image carrier, and means for detecting the rotational position of the image carrier provided in connection with the image carrier.

Therefore, by detecting the rotational positions of the latent image carrying means and the image carrier, it is possible to always prevent the seam of the photosensitive belt from entering the image, and there is no misalignment of the toner images of a plurality of colors. Images can be obtained.

Hereinafter, the operation of the image forming apparatus according to the embodiment of the present invention will be described with reference to the drawings. First, the configuration around the photosensitive belt will be described. In FIG. 1, reference numeral 1 denotes a photosensitive belt in which a photosensitive layer such as an organic photoconductor (OPC) is applied in a thin film shape on an outer peripheral surface of a closed loop Ni (nickel) belt base material. The photoreceptor belt 1 is technically difficult to manufacture seamlessly, and has a seam formed by bonding both ends of a rectangular sheet-shaped photoreceptor belt. The photosensitive belt 1 is 3
It is supported by the photoconductor transport rollers 2, 3, and 4 and is rotated in the direction of arrow A by a drive motor (not shown).

On the peripheral surface of the photoreceptor belt 1, a charger 11, an exposure optical system (hereinafter abbreviated as LSU) 6, a black (K), a yellow (Y),
Magenta (M) and cyan (C) color developing units 12, 1
3, 14, 15; an intermediate transfer member 8; a photosensitive member cleaning means 35;

The charger 11 includes a charging line made of a tungsten wire or the like, a shield plate made of a metal plate, and a grid plate (not shown). When a high negative voltage is applied to the charging line, the charging line performs corona discharge. When a voltage of, for example, -700 V is applied to the grid plate, the photosensitive belt 1
Is uniformly charged to a negative potential of about -700V.

The LSU 6 includes a laser driving device, a polygon mirror, a lens system, a motor for rotating a polygon mirror (not shown), etc., and forms an electrostatic latent image on the charged photosensitive belt 1. Reference numeral 7 denotes an exposure light beam emitted from the LSU 6. The exposure light beam 7 is obtained by subjecting an image signal from a gradation converter (not shown) to light intensity modulation or pulse width modulation by a laser driving circuit (not shown), and corresponding to a specific color on the photoreceptor belt 1. An electrostatic latent image is formed.

Each of the developing devices 12, 13, 14, and 15 stores toner corresponding to each color, and a developing device separating / contacting drive motor (not shown) corresponding to each color of the developing device control means (not shown). (Not shown), the developing device separation / contact cams 12-a, 13-
The photosensitive drum 1 is brought into contact with and separated from the photosensitive belt 1 at timings corresponding to the respective colors via -a, 14-a, and 15-a, and the electrostatic latent image formed on the photosensitive belt 1 is developed with toner. At this time,
The operation of contacting and separating each developing unit from the photoreceptor belt 1 is managed by developing unit position detecting means (not shown).

The photoreceptor belt rotation position detecting means 5 detects a mark formed on the back surface of the photoreceptor belt 1 and serves to prevent an image from being formed on a joint of the photoreceptor belt 1. Things.

Next, the configuration around the intermediate transfer member will be described. The intermediate transfer body 8 is formed by winding a belt-shaped sheet made of a conductive resin or the like around a base tube made of metal such as aluminum (for example, having a diameter of 200 mm), and is rotated in the direction of arrow B by a drive motor (not shown). Move. Reference numeral 16 denotes an intermediate transfer member cleaning unit formed of rubber or the like in a blade shape. The intermediate transfer member cleaning unit 16 is separated from the intermediate transfer member 8 while a synthetic image is formed on the intermediate transfer member 8. , Contact only during cleaning, and the intermediate transfer member 8
The remaining toner not transferred to the recording medium 17 is removed. Reference numeral 9 denotes an intermediate transfer body encoder plate for detecting the rotational position of the intermediate transfer body 8, which is attached to a side surface of the intermediate transfer body 8 and rotates in conjunction with the intermediate transfer body 8. For example, 400 slits are formed around the intermediate transfer body encoder plate 9, and the rotation position of the intermediate transfer body is detected by the intermediate transfer body rotation position detection unit 10.

A signal from the intermediate transfer member rotational position detecting means 10 may be used as a speed signal necessary for rotating the intermediate transfer member 8 at a constant speed. The circumference of the photosensitive belt 1 and the circumference of the intermediate transfer body 8 are designed to be the same.

Next, the configurations of the paper feeding system and the fixing system will be described. The recording medium 17 is sent out one sheet at a time from a recording medium cassette 18 to a sheet transport path 20 by a paper feed roller 19. A transfer unit 21 transfers the composite image on the intermediate transfer body 8 to the recording medium 17. The transfer unit 21 includes a transfer belt 22 formed of conductive rubber or the like in a belt shape, and
A transfer unit 23 for applying a transfer bias for transferring the composite image on the intermediate transfer body 8 to the recording medium 17;
And a separator 24 for applying a bias to prevent electrostatic adhesion to the intermediate transfer body 8 after the composite image is transferred. Reference numeral 25 denotes a fixing device including a heat roller 26 having a heat source therein and a pressure roller 27. The fixing device 25 presses the composite image transferred on the recording medium 17 with the rotation of the heat roller 26 and the pressure roller 27 while being held therebetween. Then, the toner is fixed to the recording medium 17 by the heat and the heat to form a color image.

The image forming operation of the image forming apparatus configured as described above will be described below. Here, description will be made on the assumption that image development is performed in the order of black, cyan, magenta, and yellow.

The photoreceptor belt 1 and the intermediate transfer member 8 are driven by a driving source (not shown) in the directions of arrows A and B, and are controlled so that their peripheral speeds become the same constant speed. You. In this state, first, a negative high voltage is applied to the charger 11 to uniformly charge the surface of the photoreceptor belt 1 to about -700V. Next, the photoreceptor belt 1 is rotated in the direction of arrow A, and corresponds to data of a predetermined color, for example, black (K), of a plurality of color components on the uniformly charged surface of the photoreceptor belt 1. When the exposure light beam 7 of the laser beam is applied, the irradiated portion of the surface of the photoreceptor belt 1 loses its charge, and an electrostatic latent image is formed.

On the other hand, the black developing device 12 comes into contact with the photosensitive belt 1 at a predetermined timing. The toner in the developing device 12 is given a negative charge in advance, is irradiated with the exposure light beam 7 on the photoreceptor belt 1, and the toner adheres only to a portion where the charge has been lost (electrostatic latent image portion). Development by a so-called negative-positive process is performed. The developing device 12 transfers the toner image formed on the surface of the photoreceptor belt 1 to the intermediate transfer member 8 for each color. Residual toner not transferred from the photoreceptor belt 1 to the intermediate transfer member 8 is removed by the photoreceptor cleaning unit 13, and the residual toner is scraped off by the charge remover 14.
The upper charge is removed.

Thereafter, similar development is performed in the order of cyan, magenta, and yellow, and toner images of four colors are superimposed on the intermediate transfer member 8 to form a composite image. The composite image formed in this manner is transferred from the recording medium cassette 18 to the transfer unit 23 by applying a high voltage of approximately +1 kV to the transfer unit 23 by the transfer unit 21 that has been separated so far. The images are collectively transferred to the recording medium 17 sent along the transport path 20. Further, a voltage is applied to the separator 24 such that an electrostatic force acts to attract the recording medium 17, and the recording medium 17 on which the transfer of the composite image has been completed is separated from the intermediate transfer body 8.

Subsequently, the recording medium 1 onto which the toner image has been transferred
7 is sent to a fixing device 25, where it is fixed by the heat of the heat roller 26 and the holding pressure of the pressure roller 27, and is output as a color image. Residual toner on the intermediate transfer member 8 that has not been completely transferred onto the recording medium 17 by the transfer unit 21 is removed by the intermediate transfer member cleaning unit 16. The intermediate transfer body cleaning unit 16 is in a separated position until a single composite image is obtained. After the composite image is transferred to the recording medium 17, the intermediate transfer body cleaning unit 16 comes into contact with the intermediate transfer body cleaning unit 16 and removes residual toner. The recording of one image is completed by the above series of operations.

Next, the timing control of the exposure start will be described in detail with reference to FIGS. In FIG. 2, 2
Reference numeral 8 denotes a CPU for performing various controls of the image forming apparatus; 29, an exposure start reference signal generating circuit; and 30, an image data processing circuit.

In FIG. 3, 31 and 32 are gate circuits,
Reference numeral 33 denotes a circuit which normally outputs a high level and outputs a low level for one cycle of the signal TRMEMC when the falling edge of the signal MODE1 is detected when the signal CNTEN is at a high level and five rising edges of the signal TRMEMC are counted. Normally outputs a high level signal C
When the falling edge of the signal NTRMHP is detected when NTEN is at a high level, the signal TRMENC is counted when 400 rising edges of the signal TRMEMC are counted.
Is a circuit that outputs a low level for one cycle.

The signal NOPCHP is a photoreceptor belt rotation position detection signal. When the photoreceptor belt rotation position detection means 5 detects a marker formed on the back surface of the photoreceptor belt 1 at a normally high level, the signal NOPCHP changes to a low level. Become. Signal TR
MENC is an intermediate transfer member rotation position detection signal, which goes low when the slit of the intermediate transfer member encoder plate 9 passes through the intermediate transfer member rotation position detection means, and goes high when the slit passes therethrough. The signal NTRMHP is an exposure start reference signal, and after being sent to the image data processing circuit,
Exposure of each color is started based on the falling edge of this signal.

The signal THSEL is an exposure start reference signal NT
A signal for switching the mode of RMHP generation, and a signal NOP
When the signal THSEL is at the low level at the falling edge of the CHP, the photosensitive belt rotation position detection signal NOP
An exposure start reference signal NTRMHP is generated from the CHP and the intermediate transfer member rotational position detection signal TRMENUC, and at other times, an exposure start reference signal NTRMHP is generated from only the intermediate transfer member rotational position detection signal TRMENC. Signal CNT
EN is a signal for enabling / disabling the circuits 33 and 34 to count the signal TRMEMC, and is in a permitted state when it is at a high level.

When printing is started, the CPU 28
Sets the signal CNTEN to a high level and the signal THSEL to a low level to rotate the photoreceptor belt 1 and the intermediate transfer member 8. The photoreceptor belt rotation position detecting means 5 detects a mark formed on the back surface of the photoreceptor belt 1. Signal NO
Since the signal THSEL is at the low level at the falling edge of the PCHP, the exposure start reference signal generation circuit 29
Is the signal TR from the falling edge of the signal NOPCHP.
For example, a point at which five rising edges of the MENC are counted is used as an exposure start reference for the first color (for example, black), and the signal NTRMHP is set to a low level for one cycle of the signal TRMENC.

This photoreceptor belt rotation position detection signal NOP
The point in time when five points have been counted from the falling edge of CHP is the point in time when the joint of the photosensitive belt 1 has just passed the exposure point, and an image is formed avoiding the joint of the photosensitive belt 1. The count number from the falling edge of the photoconductor belt rotation position detection signal NOPCHP is
It is arbitrarily set according to the positional relationship between the photoreceptor belt rotational position detecting means NOPCHP and the exposure point (mode 1).

When detecting the rising edge of the exposure start reference signal NTRMHP for the first color, the CPU 28 sets the signal THSEL to high level. Since the signal THSEL is at the high level as the exposure start reference for the second and subsequent colors, 400 rising edges of the intermediate transfer member rotational position detection signal are counted from the exposure start reference for the first color (mode 2). That is, since the exposure is started on the same position reference of the intermediate transfer member for all four colors, an image in which the toners of the four colors overlap on the intermediate transfer member 8 without displacement is obtained.

In the case of continuous printing, the signal THSEL is set to a low level when the CPU 28 detects the rising edge of the signal NTRMHP of the fourth color of the preceding sheet. By switching the mode of generating the exposure start reference signal to mode 1 every time the page to be printed changes, even if the circumferential length difference between the photosensitive belt 1 and the intermediate transfer member 8 occurs, the photosensitive belt 1 Can be obtained, and an image without misalignment of the toner images of a plurality of colors can be obtained. The timing of switching the mode of the exposure start reference signal generation to mode 1 is every page in the present embodiment, but may be any page.

When printing is completed, C is set at the rising edge of the exposure start reference signal NTRMHP immediately before the last color of the last page.
The PU 28 sets the signal CNTEN to a low level. In addition,
The signal TRMENUC can also be used as a speed signal for rotating the intermediate transfer body 8 at a constant speed.

[0041]

According to the present invention, exposure is started from two signals, a signal from the rotational position detecting means of the latent image carrying means and a signal from the image carrier rotational position detecting means provided in connection with the image carrying means. And the mode for controlling the timing of the start of exposure only from a signal from the image carrier rotational position detecting means provided in connection with the image carrier means. Can be prevented from entering the image, and misalignment of the toner images of a plurality of colors can be prevented.

[Brief description of the drawings]

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

FIG. 2 is a block diagram of exposure start timing control according to the embodiment of the present invention;

FIG. 3 is a detailed view of an exposure start reference generating circuit according to the embodiment of the present invention;

FIG. 4 is a timing chart of an exposure start of the image forming apparatus according to the embodiment of the present invention;

FIG. 5 is a configuration diagram around a photosensitive belt and an intermediate transfer member of a conventional image forming apparatus.

FIG. 6 is a timing chart of an exposure start of the conventional image forming apparatus.

[Description of Signs] 1 Photoconductor belt 5 Photoconductor belt rotation position detecting means 6 Exposure optical system 8 Intermediate transfer body 9 Intermediate transfer body encoder plate 10 Intermediate transfer body rotation position detection means 12, 13, 14, 15 Developing device

Claims (3)

[Claims] A latent image is formed by exposing the latent image on a latent image carrier;
The latent image formed on the latent image carrier is developed with one of the developing units having a plurality of different toners, and the formed toner image is transferred onto the image carrier.
An image forming apparatus for obtaining an image in which a plurality of different toner images are superimposed by repeating this multiple times, comprising: means for detecting a rotational position of the latent image holding means; and an image provided in connection with the image holding means. Means for detecting the rotational position of the carrier. 2. The exposure start timing is controlled by a signal from a means for detecting a rotational position of the latent image carrying means and a means for detecting a rotational position of an image carrier provided in connection with the image carrying means. The image forming apparatus according to claim 1, wherein: 3. The timing of the start of exposure is determined by the signal from the means for detecting the rotational position of the latent image carrier and the signal from the means for detecting the rotational position of the image carrier provided in connection with the image carrier. 2. The image forming apparatus according to claim 1, wherein said control means has two modes: a control mode based on two signals, and a control mode based on only a signal from a means for detecting a rotational position of the image carrier provided in connection with said image carrier means. Image forming apparatus.