JPH07183991A - Image forming device - Google Patents

Abstract

(57) [Summary] [Object] To provide an image forming apparatus capable of preventing positional deviation of superimposed images. An image reading unit 1 having a driving unit 107 for scanning an original, and writing for writing an image signal read by the image reading unit 1 on a photoconductor 9 line by line to form an electrostatic latent image. In the image forming apparatus having the means 8, the control means for setting the cycle of the write synchronization signal of the writing means 8 as the optical signal accumulation time of the light receiving element and for performing the drive start timing of the driving means 107 in synchronization with the write synchronization signal. Equipped with 101.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a digital color copying machine or a facsimile capable of forming a superposed image, and more particularly to a technique for preventing misalignment of reading position in the sub-scanning direction during superposed image formation. An image forming apparatus.

[0002]

2. Description of the Related Art In an image forming apparatus, when a document driving motor is a DC motor, the scanning speed is changed by zooming by calculating the number of pulses of a speed control encoder from the motor start to the document leading edge position, and the document leading edge is changed. Even if the rise time up to is changed, the leading edge position of image writing can be determined almost accurately. However, during continuous scanning, the torque of the motor fluctuated due to the temperature rise, and the stop position varied, resulting in registration deviation. In order to reduce this variation, a sensor is attached to the leading edge of the document, and the timing when the carriage crosses the sensor is used as the document reading timing, so that the reading leading edge position can be obtained regardless of the magnification and delay in the rise time. It was When the document scanning motor is a pulse motor, it is determined by the number of excitation pulses up to the document leading edge.
In the case of the pulse motor, there is no problem because the position error does not vary due to the rising of the motor or the like.

[0003]

However, when a color copying machine, a color image forming apparatus, etc. are repeatedly scanned, R
In the image forming apparatus that forms YMCK for each color from the GB signal, the position at which the document leading edge sensor is cut off and the line synchronization signal are generated asynchronously, so the reading position during repeated scanning during image formation is the same. Different from each other, an image reading misalignment occurred within 1 line.

The present invention has been made based on such a background, and it is an object of the present invention to provide an image forming apparatus capable of preventing positional deviation of superimposed images.

[0005]

SUMMARY OF THE INVENTION The above object is to provide an image reading unit having a driving unit for scanning an original and an image signal read by the image reading unit on a photosensitive member line by line to electrostatically discharge. In an image forming apparatus having a writing unit that forms a latent image, the period of the writing synchronization signal of the writing unit is set to the optical signal accumulation time of the light receiving element, and the drive start timing of the driving unit is synchronized with the writing synchronization signal. This is achieved by the first means with the controlling means performing.

The above object can also be achieved by the second means for controlling the control means so that the generation of the image reading start signal is performed by the counting of the writing synchronizing signal counting means. In this case, the counting means can be composed of a counter outside the CPU.

Further, the above-mentioned object is that the driving means is constituted by a pulse motor, and the control means controls the image reading means so as to change the sub-scanning magnification by changing the scanning speed, and at the same time, to control the pulse motor speed. It is also achieved by a third means that controls the counting means to generate a image reading start signal by causing the counting means to count a count value according to the magnification change from a standing constant position.

[0008]

In the first means, the drive start timing is synchronized with the writing timing of the image signal,
Eliminates misalignment during repeated scanning.

In the second means, by counting the write synchronization signal (PMSYNC), from the drive start to the generation of the read start signal (FGATE),
The synchronization with the write timing is guaranteed. In addition, CP
When PMSYNC is counted and FGATE is generated by a counting means external to the U, it is possible to prevent a decrease in processing capability when an interrupt is input directly to the CPU.

In the third means, the registration setting for correcting mechanical variations between the home position sensor of the image reading means and the document image leading edge becomes easy in the entire magnification range.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a color copying machine as an image forming apparatus according to the present invention, and FIG. 2 is an enlarged block diagram of the photosensitive member and an intermediate transfer belt. In FIG. 1, 1 is a color image reading device (color scanner), 2 is a color image recording device (color printer), 3 is a document, 4 is an illumination lamp, 5-1, 5-2, 5-3 are mirror groups, 6 is a lens
7 is a photoelectric conversion element (CCD), 8 is a writing optical unit, 8-1 is a laser, 8-2 is a polygon mirror, 8-3.
Is a polygon motor, 8-4 is an f / θ lens, 8-5 is a reflection mirror, 9 is a photoconductor drum, 10 is a photoconductor cleaning unit, 11 is a discharge lamp, 12 is a charger, 13 is a potential sensor, and 14 is Bk developing device, 15 is a C developing device, 16
Is an M developing device, 17 is a Y developing device, 18 is a developing density pattern detector, 19 is an intermediate transfer belt, 20 is a belt transfer bias roller, 21 is a belt driving roller, 22 is a belt cleaning unit, 23 is a paper transfer unit, 24 is a transfer paper, 25 is a paper feed roller, 26 is a registration roller, 27
Is a paper transport unit, 28 is a fixing device, 28-1 is a fixing roller, 28-2 is a pressure roller, 29 is a copy tray, 3
Reference numerals 0, 31, 32, and 33 denote transfer sheet cassettes, and 34 denotes a manual feed tray.

In FIG. 2, 10-1 is a static eliminator before cleaning, 10-2 is a brush roller, 10-3 is a rubber blade, 14-1 is a Bk developing sleeve, and 15-1.
Is a developing sleeve for C, 16-1 is a developing sleeve for M, 1
7-1 is a Y developing sleeve, 14-2 is a Bk developing paddle, 15-2 is a C developing paddle, 16-2 is an M developing paddle, 17-2 is a Y developing paddle, and 14-3 is Bk. Toner concentration detection sensor, 15-3 for C toner concentration detection sensor, 16-3 for M toner concentration detection sensor, 17-3
Is a toner concentration detection sensor for Y, 22-1 is a brush roller, 22-2 is a rubber blade, 22-3 is a contact / separation mechanism, 2
3-1 is a paper transfer bias roller, 23-2 is a roller cleaning blade, and 23-3 is a contact / separation mechanism.

The color scanner 1 forms an image of the original 3 on the color sensor 7 through the illumination lamp 4, the mirror group 5, and the lens 6, and outputs the color image information of the original, for example, blue (B), Each color separation light of green (G) and red (R) is read and converted into an electric image signal. In this example, the color sensor 7 is composed of B, G, and R color separation means and a photoelectric conversion element such as a CCD, and simultaneously reads three colors. 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 (Bk), cyan (C), Color image data of magenta (M) and yellow (Y) is obtained. Then, the color printer 2 described below visualizes Bk, C, M, and Y to obtain a final color copy.

The operation method of the color scanner 1 for obtaining Bk, C, M, and Y image data is as shown in FIG. The mirror optical system scans the document in the direction of the left arrow to obtain image data of one color for each scan. By repeating this operation four times in total, sequential four-color image data is obtained. Then, each time it is visualized by the color printer 2, these are superposed to form a four-color full-color image.

Next, the outline of the color printer 2 will be described.

The writing optical unit 8 converts the color image data from the color scanner 1 into an optical signal, performs optical writing corresponding to the original image, and forms an electrostatic latent image on the photosensitive drum 9. The unit 8 includes a laser 8-1, a light emission drive control unit (not shown), a polygon mirror 8-2.
And its rotation motor 8-3, an f / θ lens 8-4, a reflection mirror 8-5, and the like.

The photoconductor drum 9 rotates counterclockwise as indicated by an arrow, and around the photoconductor drum 9, a photoconductor cleaning unit (including a pre-cleaning static eliminator) 10, a static elimination lamp 11, a charger 12, and a potential sensor 13 are provided. , 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.

In order to develop the electrostatic latent image, each developing device is
Developing sleeves (14-1, 15-1, 16-1, 17 that rotate by bringing the ears of the developer into contact with the surface of the photosensitive drum 9)
-1) and the developing paddles (14-2, 15-2, 16-2, 17-) that rotate to pump up and stir the developer.
2) and a toner concentration detection sensor for the developer (14-
3, 15-3, 16-3, 17-3) and the like.

In the standby state, all the four developing devices are in a state in which the developer on the developing sleeves is in the state of cutting off (development inoperative), but the order of the developing operation (color image forming order) is as follows.
An example of Bk, C, M, and Y will be described below (however, the image forming order is not limited to this).

When the copy operation is started, the color scanner 1 starts reading Bk image data from a predetermined timing, and optical writing / latent image formation by laser light is started based on the image data (hereinafter referred to as Bk image data). The electrostatic latent image by Bk is referred to as 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, the developing sleeve 14-1 is started to rotate to raise the agent before the latent image tip reaches the developing position of the Bk developing device 14. The Bk latent image is developed with Bk toner.

Thereafter, the developing operation of the Bk latent image area is continued, but when the trailing edge of the latent image passes the Bk developing position,
The agent on the Bk developing sleeve 14-1 is promptly cut off, and 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. It should be noted that the brush cutting is performed by switching the rotation direction of the developing sleeve 14-1 to the opposite direction to that during the developing operation.

The Bk toner image formed on the photoconductor 9 is transferred onto the surface of the intermediate transfer belt 19 which is driven at the same speed as the photoconductor drum 9 (hereinafter, the toner image is transferred from the photoconductor to the intermediate transfer belt). Is called the belt transfer). The belt transfer is performed by applying a predetermined bias voltage to the transfer bias roller 20 while the photosensitive drum 9 and the intermediate transfer belt 19 are in contact with each other. It should be noted that, on the intermediate transfer belt 19, the Bk, C, M, and Y toner images sequentially formed on the photosensitive drum 9 are sequentially aligned on the same surface to form a belt transfer image of four-color superimposition. , Perform batch transfer to transfer paper. The structure and operation of this intermediate transfer belt unit will be described later.

On the side of the photoconductor drum 9, the Bk process is followed by the C process, but the C image data reading by the color scanner 1 starts at a predetermined timing, and the C latent image is written by the laser light writing by the image data. Form. The C developing device 15 has the same Bk
After the trailing edge of the latent image has passed and before the leading edge of the C latent image has arrived, the developing sleeve 15-1 is started to rotate so that the agent is spiked to develop the C latent image 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 C developing sleeve 1 is developed as in the case of the Bk developing device.
The agent on 5-1 is cut off. This is also completed before the leading edge of the next M latent image arrives. The operations of image data reading / latent image formation / development for the steps M and Y are the same as the steps Bk and C described above, 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 as described below by a drive motor (not shown). Belt cleaning unit 22
Is composed of a brush roller 22-1, a rubber blade 22-2, a contact / separation mechanism 22-3 from the belt, and the like.
While the fourth color is being transferred on the belt, it is separated from the belt surface by the contact / separation mechanism 22-3.

The paper transfer unit 23 includes a paper transfer bias roller 23-1, a roller cleaning blade 23-2,
And a belt contact / separation mechanism 23-3 and the like. The bias roller 23-1 is normally the belt 1
Although separated from the 9th surface, the four-color superimposed image formed on the surface of the intermediate transfer belt 19 is pressed by the contact / separation mechanism 23-3 at a timing when the transferred images are collectively transferred onto the transfer paper. A predetermined bias voltage is applied to 1 to perform transfer to paper. The transfer paper 24 is fed by the paper feed roller 25 and the registration roller 26 at the timing when the leading edge of the four-color superimposed image on the intermediate transfer belt surface reaches the paper transfer position.

The movement of the intermediate transfer belt 19 is 1
As the operation method after the belt transfer of the Bk toner image of the color is completed up to the rear end portion, there are three types of a constant speed forward movement method, a skip forward movement method, and a quick return method.
One of these methods is used, or a combination of efficient methods (in terms of copy speed, etc.) is used according to the copy size.

1) Constant-speed forward movement method (a) Even after the Bk toner image is transferred onto the belt, the forward movement is continued at a constant speed.

(B) When the front end position of the Bk image on the surface of the belt 19 again reaches the belt transfer position of the contact portion with the photosensitive drum 9, the photosensitive drum 9 side advances the end of the next C toner image. The image is formed with a timing so that the copy is exactly at that position. As a result, the C image is accurately aligned with the Bk image, and is superimposed on the intermediate transfer belt 19,
The belt is transferred.

(C) After that, by the same operation, M, Y
Proceeding to the image process, a belt transfer image of four colors is obtained.

(D) Subsequent to the step of transferring the Y toner image belt of the fourth color, the four color superimposed toner images on the belt surface are collectively transferred onto the transfer paper 24 as described above while moving forward. 2) Skip forward movement method (a) After the belt transfer of the Bk toner image is completed, the belt 19 is separated from the surface of the photosensitive drum 9 and is skipped at a high speed in the forward movement direction as it is. Return to dynamic speed. After that, the belt 19 is brought into contact with the photosensitive drum 9 again.

(B) Then, when the front end position of the Bk image on the surface of the belt 19 reaches the belt transfer position again, the front end portion of the next C toner image on the side of the photosensitive drum 9 is just at that position. , Form an image at the right time. As a result, the C image is accurately aligned with the Bk image and transferred onto the belt in a superimposed manner.

(C) After that, by the same operation, M, Y
Proceeding to the image process, a belt transfer image of four colors is obtained.

(D) Subsequent to 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.

3) Reciprocating motion (quick return) system (a) After the transfer of the Bk image on the belt 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 is applied in the reverse direction. To return. 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 by a preset distance, it is stopped and brought into a standby state.

(B) 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. In this case as well, the C image is transferred under the condition that the C image is accurately overlapped with the Bk image on the surface of the belt 19.

(C) After that, by the same operation, M, Y
Proceeding to the image process, a belt transfer image of four colors is obtained.

(D) Subsequent to the belt transfer process of the Y toner image of the fourth color, the toner is moved forward at the same speed without returning, and the four color superposed toner images on the surface of the belt 19 are collectively transferred onto the transfer paper 24. .

The transfer paper 24 to which the four-color superposed toner images have been collectively transferred from the surface of the intermediate transfer belt 19 is conveyed to the fixing device 28 by the paper conveying unit 27 and the fixing roller 28-1 controlled to a predetermined temperature. The toner image is melted and fixed by the pressure roller 28-2 and is carried out to the copy tray 29 to obtain a full color copy.

The photosensitive drum 9 after the belt transfer is
Photoconductor cleaning unit 10 (pre-cleaning static eliminator 10-1, brush roller 10-2, rubber blade 10)
-3) The surface is cleaned and the static elimination lamp 1
With 1, the charge is uniformly removed.

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.

For repeat copying, the color scanner 1
The operation of the above step and the image formation on the photosensitive drum 9 proceed to the second Bk (first color) image step at a predetermined timing after the first Y (fourth color) image step. Further, in the intermediate transfer belt 19, after the batch transfer process of the first four-color superimposed image onto the transfer paper 24, the surface of the intermediate transfer belt 19 is cleaned by the cleaning unit 22 and the second B
k The toner image is transferred on the belt. After that,
The operation is similar to that of the first sheet.

The transfer paper cassettes 30, 31, 32,
The transfer paper 24 of various sizes is stored in the storage unit 33, and is fed and conveyed in the direction of the registration roller 26 at a timing from a storage cassette of the size of paper designated by the operation panel (not shown).

Up to this point, the description has been given of the copy mode in which four full colors are obtained. However, in the case of the three-color copy mode and the two-color copy mode, the designated color and the number of times are changed.
The same operation as above is performed. In the case of the single-color copy mode, until the predetermined number of sheets are finished, only the developing device of that color is in the developing operation (agent standing) state, and the intermediate transfer belt 19 remains in contact with the surface of the photosensitive drum 9. The copying operation is performed while the belt cleaner 22 is driven at a constant speed in the forward direction and the belt cleaner 22 is still in contact with the belt 19.

FIG. 3 is a block diagram of the image reading section of the image forming apparatus according to the embodiment.

The scanner CPU 101 executes a program stored in the ROM 102 and reads / writes data and the like from / to the RAM 103 to control the entire scanner unit. Further, it is connected to the system control unit 104 by serial communication, and performs an operation instructed by transmitting and receiving commands and data. The CPU 101 is the I / O 10
A document detection sensor, an HP sensor, a pressure plate opening / closing sensor, a cooling fan, etc. are connected via 5 to control detection and ON / OFF. The motor driver 106 receives the excitation pulse sequence from the port output, and drives the document scanning drive pulse motor 107.

The original image is formed on the CCD 7 by passing a light signal through a plurality of mirrors and lenses by the lamp light amount output driven by the lamp regulator 108. CCD7
Are supplied with various drive clocks by the timing generation gate array 109, and an analog image signal is input from the CCD 7 to the amplifier 110. This timing gate array 109 is an FGA that counts PMSYNC.
It has a TE start counter and starts counting by the output port signal from the CPU 101.
GATE can be generated.

A feedback voltage for dark current correction is applied to the amplifier 110. This is the CPU
Parallel-to-serial converter 1 bus-connected to 101
11 to D / A converter 11 by serial data
2 is driven. With this feedback voltage, the black level adjustment (D
The A1, DA2) analog image data is input to the A / D converter 113. A / D converter 113
Vref is adjusted (DA3) by the voltage from the D / A converter 112 so as to correspond to the gain of the analog image data.

The A / D converter 113 converts this reference voltage into a digital signal and inputs it to the shading gate array 114. Shading gate array 114
Has a function of correcting uneven light amount of the illumination system and variation of pixel output of the CCD 7. When the lamp is off, black correction is performed to set the output data in the black memory, and white correction is performed to set the white memory by turning on the lamp on the white reference plate. The image read data is arithmetically processed from the data in the black memory and the white memory, and the data after shading correction is output. This is the line correction memory 115.
Image data of the number of lines of B and G and B and R of the three-line CCD is delayed in the memory to align the read image of BGR and output to the IPU 116. The setting of the interline correction memory 115 is controlled by the timing gate array 114 according to the magnification.

Next, the present invention will be specifically described.
When the scanner start code transmitted to start the scanner image reading operation is received from the system control unit, a reception interrupt occurs. Within the receive interrupt, processing branches depending on the instruction code. When the scanner start code is received, the acknowledge signal transmission request flag is set, the PMSYNC external interrupt is enabled, and the processing is ended.

On the main body side, the polygon motor 8-3 rotates, the laser beam is reflected by the polygon mirror 8-2, is input to the synchronization detection plate, generates the synchronization signal PMSYNC, and outputs it to the scanner section. There is. Therefore, PMSYN
C External interrupt occurs. In this external interrupt, the excitation pulse generation timer of the pulse motor 107 is started. When the excitation pulse is generated, the slow-up and down-timer set values are set in advance in the ROM 102 as a table. Therefore, a pulse is generated when the excitation pulse generation timer count value coincides with the motor 10
Drive 7 This enables the motor start in synchronization with PMSYNC. The scanner scanning speed is calculated by the magnification data command before the scanner start is received, and the timer value of the speed corresponding to each magnification is calculated.
The count setting value of the down table is determined.

Since the time to the image front end position is constant depending on the pulse time and the number of pulses, the generation of the reading start signal FGATE after the motor start generates a table of the number of PMSYNC counts for this time for each magnification. By setting this in the timing gate array 109 and starting the FGATE start counter, when the motor is started and FGATE is generated,
By synchronizing with PMSYNC, it is possible to prevent the occurrence of an image reading shift for each reading scan.

When the slow-up table is linear acceleration, the counter value of PMSYNC depending on the magnification can be easily calculated, but when it is non-linear, it is difficult to calculate, and further, the mechanical variation between the leading edge of the document and the HP sensor is corrected. Registration setting is required. In the above embodiment, this correction becomes difficult, and an example in which the resist setting can be easily performed will be shown below.

PMS from the standing position in the entire magnification range
Start the YNC counter and output FGATE. That is, counting is started from the position where the constant speed is equal to or more than the number of slow-up pulses at the time of minimum reduction.

The rising position can be understood by generating an interrupt by counting the motor driving pulse by an external interrupt for counting the motor driving pulse. The generation of this interrupt starts the FGATE start counter of the timing gate array 109. If the PMSYNC counter value at the same magnification is set (registration setting value), the setting value at each magnification can be calculated as the PMSYNC counter value at the same magnification × magnification, so that the mechanical range in the entire magnification range is set. It is possible to deal with variations.

[0055]

According to the first aspect of the present invention, by synchronizing the drive start timing with the writing timing of the image signal, it is possible to eliminate the reading deviation during repeated scanning and reduce the color deviation of the output image. .

According to the second aspect of the present invention, by counting the write synchronization signal (PMSYNC), the synchronization with the write timing is guaranteed from the drive start to the generation of the read start signal (FGATE), and the accuracy is improved. Can be planned.

According to the third aspect of the present invention, the count means outside the CPU counts PMSYNC,
By generating GATE, it is possible to prevent a decrease in processing capability when an interrupt is directly input to the CPU, eliminate the need to use a high-speed CPU, and reduce costs.

According to the fourth aspect of the present invention, the registration setting for correcting the mechanical variation between the home position sensor of the image reading means and the document image leading edge can be facilitated in the entire magnification range, and the registration deviation can be prevented. It can be reduced.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a color copying apparatus as an image forming apparatus according to the present invention.

FIG. 2 is an enlarged configuration diagram around a photoconductor and an intermediate transfer belt of the color copying apparatus shown in FIG.

FIG. 3 is a block diagram of an image reading unit of the image forming apparatus according to the exemplary embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 color scanner (image reading means) 2 color printer 8 writing optical unit (writing means) 9 photoconductor drum (photoconductor) 101 CPU (control means) 107 pulse motor (driving means)

Claims (4)

[Claims] 1. An image reading means having a driving means for scanning an original, and a writing means for writing an image signal read by the image reading means line by line on a photoconductor to form an electrostatic latent image. In the image forming apparatus having the above-mentioned, a control means for setting the cycle of the write synchronization signal of the writing means as the optical signal accumulation time of the light receiving element and for performing the drive start timing of the drive means in synchronization with the write synchronization signal is provided. Image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the control unit controls the generation of the image reading start signal to be performed by the counting of the writing synchronization signal counting unit. 3. The image forming apparatus according to claim 2, wherein the counting unit is a counter external to the CPU. 4. The pulse motor according to claim 1, wherein the driving means is composed of a pulse motor, and the control means controls the image reading means so as to change the sub-scanning magnification by changing the scanning speed. An image forming apparatus, characterized in that the counting means is controlled to generate a image reading start signal by counting the count value according to the magnification change from a constant position where the speed has risen.