JP2534706B2 - Image forming device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus such as a digital color image forming apparatus having a plurality of photoconductors.

(Prior Art) In an image forming apparatus that forms a color image using a plurality of photoconductors, factors of positional deviation in the transfer paper feed direction (vertical registration) are as follows. There is a position, the linear velocity of the transfer belt, etc., and each of them is guaranteed with parts accuracy and assembly accuracy.
Readjustment is required due to variations due to component replacement.

As a method for solving this problem, there has been proposed a method (Japanese Patent Application Laid-Open No. 59-155870) in which a transfer paper is detected by a sensor provided in front of each transfer position to obtain a write timing of each color. It is difficult to guarantee the positional deviation limit (about 0.15 mm) of a color image due to variations in mounting positions and variations in detection positions of each sensor.

It should be noted that the same applicant as the present invention has already filed a device for transferring the measurement pattern of each color to the transfer belt, measuring the pitch thereof, and detecting the positional deviation. However, there was a problem that the pitch of the measurement pattern could not be accurately measured because the seam was detected.

(Object) The present invention has been made on the basis of such a background, and a color image is obtained by superposing a plurality of color images on a transfer paper sent by a conveyor belt. An object of the present invention is to provide an image forming apparatus such as a digital color image forming apparatus capable of reducing the color misregistration in the transfer paper conveyance direction of each color with a simple structure.

In particular, it is an object of the present invention to accurately measure color misregistration without being affected by the joint of the endless conveying means having the joint.

(Structure) Therefore, the present invention relates to a photoconductor, a charging unit that uniformly charges the surface of the photoconductor, an exposure unit that projects image light according to recording information onto the photoconductor, and an electrostatic latent image of the photoconductor. A plurality of recording devices each having a developing means for developing a toner image and a transfer means for transferring the visible image of the photoconductor onto the transfer paper are arranged along the conveyance direction of the transfer paper. It is intended for an image forming apparatus that has an endless conveying means for conveying a transfer paper, and sequentially conveys the transfer paper to each recording device by the endless conveying means, and superimposes and transfers an image on the transfer paper. is there.

And is arranged near the surface of the endless conveying means,
Detecting means for optically detecting the measurement pattern image for each color formed on the endless conveying means by each recording device, and the seam of the endless conveying means is detected by the detecting means, and when the apparatus is stopped An endless conveyance means stop position control means (for example, a main unit described later) that controls the stop position of the endless conveyance means so that the joint position of the endless conveyance means does not overlap the transfer position of the toner image for measurement at the time of the next image formation. Control unit and
And a erasing means for erasing the measurement pattern image detected by the detecting means from the endless conveying means.

Hereinafter, the configuration and operation of the present invention will be described in detail based on the embodiments shown in the drawings.

First, FIG. 1 is a schematic diagram of a digital color image forming apparatus to which the present invention is applied.

FIG. 1 shows a color copying machine as an example of the image forming apparatus. The copying machine includes a scanner unit 1 for reading an original, an image processing unit 2 for electrically processing an image signal output as a digital signal from the scanner unit 1, and image recording information of each color from the image processing unit 2. And a printer section 3 for forming an image on a copy sheet based on the above. The scanner unit 1 has a lamp 5 for scanning and illuminating the original document on the original document table 4, for example, a fluorescent lamp. The reflected light from the document when illuminated by the fluorescent lamp 5 is reflected by the mirrors 6, 7, 8 and enters the imaging lens 9. By the imaging lens 9,
The image light is imaged on the dichroic prism 10 and is split into, for example, light of three kinds of wavelengths of red R, green G, and blue B, and a light receiver 11, for example, CCD 11 for red, for each wavelength light.
It is incident on R, CCD 11G for green, and CCD 11B for blue. Each C
The CDs 11R, 11G, and 11B convert incident light into digital signals and output the digital signals. The outputs are subjected to necessary processing in the image processing unit 2 and recorded color information of each color, for example, black (hereinafter Bk).
, Yellow (Y), magenta (M), and cyan (C) for recording.

Figure 1 shows an example of forming four colors of Bk, Y, M and C.
It is also possible to form a color image using only colors. In that case, the number of recording devices can be reduced by one from the example of FIG.

The signal from the image processing unit 2 is input to the printer unit 3 and the laser light emitting devices 12Bk, 12C, 12M and 12Y of the respective colors are input.
Sent to

In the printer section, four sets of recording devices 13Y, 13M,
13C and 13Bk are arranged side by side. Since each recording device 13 is composed of the same constituent member, the recording device for C will be described and the other colors will be omitted for simplification of description. For each color, the same parts are denoted by the same reference numerals, and in order to distinguish the configuration of each color, the reference numerals are added to indicate the respective colors.

The recording device 13C includes a photoconductor 14 in addition to the laser light emitting device 12C.
C, eg having a photoconductor drum.

The photoconductor 14C includes a charging charger 15C, an exposure device using a laser light emitting device 12C, a developing device 16C, and a transfer charger 17.
C and the like are attached similarly to known copying machines.

Photoconductor 14C uniformly charged by charging charger 15C
Forms a latent image of a cyan light image by exposure with the laser beam emitting device 12C, and develops it with the developing device 16C to form a visible image. The copy paper supplied from the paper feed unit 19, for example, one of the two paper feed cassettes, by the paper feed roller 18 is fed to the transfer belt 21 with the leading ends aligned by the registration rollers 20 and at the same timing. The copy papers conveyed by the transfer belt 21 are the photoconductors 14Bk and 14B having the visible images, respectively.
The images are sequentially sent to C, 14M and 14Y, and a visible image is transferred under the action of the transfer charger 17. The transferred copy paper is fixed on the fixing roller 22.
The sheet is fixed by the sheet, and is discharged by the sheet discharge roller 23.

By being electrostatically attracted to the transfer belt 21, the copy paper can be accurately conveyed at the speed of the transfer belt.

FIG. 2 is a front view of the transfer belt portion. Transfer belt 21
Is supported by a belt driving roller 24 and a driven roller 25,
And transfer the transfer paper. Further, the cleaning unit 26 removes the toner adhering to the belt. A reflection type sensor 27 is provided as a pattern image detecting means on the downstream side of the photoconductor 14 in the belt moving direction.

The detection means is provided on the drive roller portion of the transfer belt to prevent the influence of the transfer belt fluttering and to keep the distance between the transfer belt and the transfer belt constant.

 FIG. 3 is a system block diagram according to the embodiment.

The system controller 30 controls each module of the scanner 1, the image processing unit 2, and the printer 3. The contents of the control include display control of the operation panel 31, key input processing, start signal to the scanner 1 and printer 3, transmission of a scaling factor designating signal, image processing unit 2 according to the mode set on the operation panel 31. Controlling the entire system by sending image processing mode specification signals (color conversion, masking, trimming, mirroring, etc.) to each, abnormal signals from each module, and operating status signals (Wait, Ready, Busy, Stop, etc.) To do.

The scanner 1 scans a document at a scanning speed that matches a scaling ratio designated by a start signal from the system controller 30 and reads a document image with a reading element such as a CCD.
As R, G, and B 8-bit image data, the image processing unit is synchronized with S-LSYNC (horizontal synchronization signal), S-STROBE (image clock), and FGATE (vertical synchronization signal) from the image processing unit 2. Send to 2.

The image processing unit 2 is 8 bits for each of R, G and B sent from the scan analyzer 1.
Is subjected to image processing such as γ correction, UCR (removal of undercolor) and color correction, converted into image data of 3 bits for each of Y, M, C and Bk and sent to the printer 3. Also, in response to commands from the system controller 30, scaling processing, masking, trimming,
Edit processing such as color conversion and mirroring is performed. Also, Y, M,
It has a buffer memory for outputting the image data of C and Bk while shifting them by the distance between the photosensitive drums of the printer 3.

The printer 3 outputs laser light in accordance with 3-bit image data of Y, M, C, and Bk transmitted from the image processing unit 2 in synchronization with P-LSYNC (horizontal synchronization signal) and P-STROBE (image clock). The emitting device is modulated, and a copy image is obtained on a transfer paper by an electrophotographic process.

 FIG. 4 shows an example of the detection pattern of the present invention.

In each recording device, the pattern image visualized by the signal from the pattern image signal generating means outside the transfer paper area is transferred to the transfer belt 21 and a (a) as shown in FIG. mm) spacing. The pattern images 28Bk, C, M, and Y sequentially pass through the sensor 27 according to the movement of the belt, and are detected by the sensor 27. The image interval a is a numerical value that can be arbitrarily selected by setting the exposure timing for each recording device in advance.

In the color copying machine shown in FIG. 1, the image processing unit 2
It is necessary to shift the transmission of the image data of each color from the photosensitive drums of the respective colors by the distance.

FIG. 5 is a block diagram showing the structure of the buffer memory for that purpose and the structure of the pattern image signal generating means.

FIG. 6 is a timing chart showing the operation of the block diagram of FIG. 5 (the timing chart of the waveform of the portion indicated by).

In the color copying machine of this embodiment, since the recording devices are arranged in the order of Bk, C, M and Y, the image data of Bk processed by the image processing unit 2 is output as it is, C, M,
The image data of Y is different from the image data of Bk.
Output with a delay of t _DC , T _DM , T _DY .

FIG. 7 is an explanatory diagram for setting the delay times t _DC , T _DM , and T _DY of image data.

The length from the exposure position to the transfer position for each photoconductor 14 is l ₁ (mm), the photoconductor linear velocity is v ₁ (mm / sec), the photoconductor distance is l ₂ (mm), and the transfer belt linear velocity is v ₂ (mm / sec)
Duration t ₁ to the transfer from the exposure when the respective photosensitive body with the same value _{t 1 = l 1 / v 1} (sec) Time to move between each photoconductor and _{t 2, t 2 = l 2} / v 2 (Sec) That is, t _DC = l ₂ / v ₂ (sec) T _DM = 2l ₂ / v ₂ (sec) T _DY = 3l ₂ / v in order to form each color image on the transfer paper at the same position. ₂ (sec).

As shown in FIG. 5, the circuit configurations of C, M and Y are the same, so Bk and C will be described. The rising edge of the vertical synchronizing signal FGATE sent from the scanner 1 is detected by the rising edge detection circuit 40. Since each input of Bk, C, M, and Y and FGATE are input at the same time, the output of the rise detection circuit 40 is a signal indicating the start of image writing of Bk. The output of the rising edge detection circuit 40 is input to the Bk pattern signal generation means 41 and outputs a detection pattern. That is, in the case of Bk,
The leading edge of the image and the pattern position are the same in the moving direction of the belt 21 (FIG. 4).

The output of the rising edge detection circuit 40 is input to the reset terminal of the address counter C42a via the OR gate.
Address counter: C42a is reset. According to the count value of the address counter 42a, the input image data of C is stored in a buffer memory: C43a.

On the other hand, the output of the address counter 42a is compared with the set value of the address setter C45a by the comparator C44a, and when the output of the address counter 42a matches the set value of the address setter 45a, the comparator 44a outputs a match signal. Output. This coincidence signal is input to the reset terminal of the buffer memory 43a through the OR gate, resets the output of the address counter 42a to "0", and accesses the address 0 of the buffer memory 43a again. The buffer memory 43a reads the already stored image data and then writes the newly input image data at the same address.

Here, if the set value of the address setter 45a is set to the drum interval (t _DC ) between Bk and C, the images of Bk and C can be aligned and formed on the transfer paper. Comparator: C
The coincidence signal of 44a is also input to the delay device: C46a, which triggers the delay device 46a, and outputs a detection pattern by the pattern signal generation means: C47a after a predetermined time from the coincidence signal of the comparator 44a.

Since the coincidence signal of the comparator C44a is output simultaneously with the leading edge of the image of C, the detection pattern of C is output with a delay of the delay time (t _PC ) by the delay device C46a from the leading edge of the image.

Here, delay device: The delay time of C46a is a (mm)
If the time required for the movement is set, a C detection pattern can be created with a delay of a (mm) from the leading end of the image as shown in FIG.

The same applies to M and Y. Address setter: M45b set value = t _DM Address setter: Y45c set value = t _DY Delay device: M46b set time = t _PM = 2a / v ₂ Delay device: Y46c If the set time = t _PY = 3a / v ₂ is set, the leading edge of the image can be matched for each color, and at the same time, the detection pattern can be output with a (mm) pitch as shown in FIG.

Here, if each image position of Bk, C, M, Y is deviated on the transfer paper due to the variation of the position of each photoconductor, the variation of the exposure position with respect to the photoconductor, the variation of the linear velocity of the photoconductor and the transfer belt, it is detected. The work pattern also shifts correspondingly, and the position shift amount of the image can be detected by measuring the interval between the detection patterns.

FIG. 8 shows an embodiment of the pattern detection circuit according to the present invention. The output current of the phototransistor Ph of the reflection type sensor 27 is converted into a voltage by the resistor R ₂ [waveform of the part shown in FIG. 10 (a)], and the capacitor C2 cuts the D component to extract only the AC component [ Waveform of the portion shown in FIG. 10 (b)]. This signal is input to the inverting amplifier AMP2 via the voltage follower AMP1, and is amplified to an appropriate voltage level (the waveform shown in FIG. 10 (c)). The output of AMP2 is compared with the threshold voltage V _TH which is determined by the comparator COMP1 in resistor R8 and R9, to obtain a square wave output [waveform of the portion shown in FIG. 10 (d)]. By measuring the pitch of the rectangular wave output, the interval between the detection patterns transferred to the transfer belt 21 can be known.

FIG. 9 shows an embodiment of the pattern interval measuring circuit. First
Figure 11 shows the timing chart.

Before starting the measurement of the pattern interval, the CPU 60 issues a CLEAR signal to clear the counters CNT1 to CNT4. The output of the detection circuit is input to the clock terminal of the counter CNT1, and the outputs A and B of CNT1 output the signals shown in FIG.

A signal representing the pattern interval between Bk and C can be obtained by ANDing the signal obtained by inverting the A output and the B output of CNT1 (AND1). Also, by taking the exclusive OR of the A output and the B output (EOR1), a signal representing the pattern interval of Bk and M can be obtained. Further, by ORing the A output and the B output (OR1), a signal representing the pattern interval between Bk and Y is obtained.

The signals indicating the pattern intervals of Bk and C, Bk and M, Bk and Y are connected to the enable inputs of the counters CNT2, CNT3, and CNT4, respectively, and the counters CNT2, CNT3, and CNT4 have the enable inputs between “H”. Count the reference clock, Bk and C, Bk and M,
Binary data is output in proportion to the pattern interval between Bk and Y.

When the counting operation of CNT2, CNT3, and CNT4 ends, CPU60
The SEL0 and SEL1 outputs control the data selector 61 to sequentially fetch the binary data of CNT2, CNT3, and CNT4 into the CPU 60. FIG. 12 (a) shows a flowchart of the above operation.

The CPU 60 compares the fetched output value of the counter with a reference value, calculates the difference between the reference value and the measured value, and outputs correction signals C, M, Y for correcting the difference. By sending this correction signal to the address setting units: C, M, and Y45 shown in FIG. 5 and changing the writing start timing of the image with respect to Bk, the alignment of the image of each color can be realized.

Now, assuming that the frequency of the reference clock is F (Hz), the pattern intervals L _C , L _M , L _Y of _C , _M , and _Y are L _C = (K _C / F) × v ₂ (mm) L with respect to Bk. _M = (K _M / F) × v ₂ (mm) L _Y = (K _Y / F) × v ₂ (mm) (where K _C , K _M , and K _Y are the measured clock numbers). Therefore, the deviation from the set value of each pattern interval is D _C , D _M , D _Y is D _C = L _C −a (mm) D _M = L _M −2a (mm) D _Y = L _Y −3a (mm) Becomes

The correction signals H _C , H _M , and H _Y are obtained by multiplying D _C , D _M , and D _Y by a count for converting the shift amount on the belt into a memory address, and H _C = C × D _C H _M = C × D _M H _Y = C × D _Y FIG. 12 (b) shows the progress of the above calculation.

In the present invention, the detection patterns are formed in the order of Bk, C, M, and Y at the interval of a (mm) with reference to the image front end of each color. The a (mm) means that the belt speed becomes a (mm) when the speed is in accordance with the set value, and when the belt speed is deviated from the set value due to variations in parts or the like, the pattern interval a ' (Mm) is a ′ = (v ₂ ′ / v ₂ ) × av ₂ : designed value of belt speed v ₂ ′: actual value of belt speed.

However time is detected by the detection sensor t is _{t = a '/ v 2'} = a / v 2 , and the the actual belt speed can be measured independently accurately pattern interval.

By the way, the transfer belt 2 used in the image forming apparatus of the present invention is formed of an endless polyester film and has a seam. The reflectance of the seam portion is lower than that of the other portions, and when the seam is detected by the reflective sensor, the output signal is the same as when the measurement pattern 28 is detected.

Therefore, the measurement pattern 28 is formed on the seam of the transfer belt 21.
When is transferred, the pitch of the measurement pattern 28 cannot be accurately measured.

In order to prevent this problem, it is necessary to prevent the transfer position of the measurement pattern 28 onto the transfer belt 21 from overlapping the seam of the transfer belt 21.

The measurement of the measurement pattern 28 in the present invention does not have to be performed every time an image is formed, and when forming a plurality of repeat images, it is sufficient to perform the measurement only once at the beginning. Therefore, by controlling the stop position of the seam of the transfer belt 21 at the end of image formation, it is possible not to overlap the transfer position of the measurement pattern 28 on the transfer belt 21 at the next image formation.

 Hereinafter, description will be given with reference to examples.

FIG. 13 is a control block diagram of the printer unit 3. The main control unit 70 is composed of a ROM, a RAM, an I / O interface, etc., with a CPU at the center. On the input side, a paper discharge sensor 71 for detecting the discharge of the transfer paper to the outside of the machine, and a paper end sensor for detecting the presence or absence of the transfer paper in the cassette
72, a registration sensor 73 for controlling the sheet feeding to the registration rollers, a cassette size sensor 74 for detecting the size of the cassette, and a toner sensor for detecting the concentration of each developer of Bk, C, M and Y There is a thermistor 76 for detecting the temperatures of Bk, C, M, Y75 and the fixing heater 79.

On the other hand, on the output side, a high-voltage power supply 77 for supplying high voltage to various types of chargers and developing units, a heater control unit 78 for controlling the temperature of the fixing heater 79, and a toner replenishing clutch 80 for replenishing toner to the developing device. There is a motor driver 81 for controlling various motors.

Further, there are a polygon motor driver 82 for controlling the polygon motor, a video controller 84 for receiving the image data from the image processing device and controlling the LD driver 83 for each color, and an interface with the system controller.

The output of the pattern detection circuit is input to the main control unit 70, and by the output signal of this pattern detection circuit,
Performs machine stop control.

FIG. 14 is a flow chart of machine stop control. The discharge sensor 71 checks the discharge of the last sheet of the repeat to the outside of the machine, and after the discharge is completed, the first input of the pattern detection circuit 71 is determined as the belt seam. When the belt seam is detected, the timer is started, and when the timer counts the set time, the transfer belt is stopped.

FIG. 15 is a time chart showing the above operation. By appropriately selecting the set time of the timer, it is possible to prevent the transfer position of the measurement pattern on the transfer belt from overlapping the seam position of the transfer belt at the start of the next image formation.

(Effect) The present invention is as described above, and the color misregistration can be accurately measured without being affected by the joint of the endless conveying means having the joint.

[Brief description of drawings]

1 is a schematic view of a digital color image forming apparatus to which the present invention is applied, FIG. 2 is a front view of a transfer belt unit, FIG. 3 is a system block diagram according to an embodiment of the present invention, and FIG. FIG. 5 shows an example of a detection pattern, FIG. 5 is a block diagram of the image data transmission control, FIG. 6 is a timing chart of each part thereof, and FIG. 7 is an explanatory diagram for setting a delay time of the image data. FIG. 8 is a diagram showing an embodiment of a pattern detecting circuit according to the present invention, FIG. 9 is a diagram showing an embodiment of a pattern interval measuring circuit, and FIGS. 10 (a), (b), and
(C) and (d) are waveform charts of respective parts in FIG. 8, FIG. 11 is a timing chart in FIG. 9, FIGS. 12 (a) and (b) are control flow charts according to the present invention, and FIG. FIG. 14 is a control block diagram of the printer section, FIG. 14 is a flow chart of machine stop control, and FIG. 15 is a time chart showing the operation. 27 ... Detecting means, 41,47 ... Pattern image signal generating means, CNT1,2,3,4 ... Detecting timing counting means, 60 ...
… Comparison means, 21 …… Transfer belt.

Claims (1)

(57) [Claims] 1. A photoconductor, a charging means for uniformly charging the surface of the photoconductor, an exposing means for projecting image light according to recording information onto the photoconductor, and an electrostatic latent image on the photoconductor is developed. A plurality of recording devices each having a developing means and a transfer means for transferring the visible image of the photoconductor onto the transfer paper are arranged along the transporting direction of the transfer paper,
It has an endless conveying means for conveying the transfer paper between the photoconductor of each recording device and the transfer means, and the transfer paper is successively conveyed to each recording device by the endless conveying means, and the image is superposed on the transfer paper. In the image forming apparatus for transferring, a detecting unit arranged near the surface of the endless conveying unit and optically detecting the measurement pattern image for each color formed on the endless conveying unit by each recording device, and , The detection means detects the seam of the endless conveyance means, and the endless conveyance means does not overlap the transfer position of the measurement toner image at the time of the next image formation when the seam position of the endless conveyance means when the apparatus is stopped. Endless conveying means stop position control means for controlling the stop position of the means, and erasing means for erasing the measurement pattern image detected by the detecting means from the endless conveying means. An image forming apparatus comprising.