JPS63280273A - Image forming device - Google Patents

Abstract

PURPOSE:To reduce the color deviation of respective colors in a transfer paper carrying direction with simple constitution by forming a measuring pattern image in each color on a transfer belt, detecting the passage of the image and correcting the timing. CONSTITUTION:The titled device is provided with a pattern image signal generating mean for forming a measuring pattern image 28 in each color on the transfer belt 21, a detecting means for detecting the passage of each color pattern image 28 and detecting timing counting means CNT1-4 for counting up the detecting timing based upon the means 27, a comparing operation means 60 for comparing the count value with a set value and calculation a deviation in accordance with necessity respective color writing timing signal generating means to be changed at their setting in accordance with an output value from the means 60, and a detecting means 29 for detecting the state of a belt 21 before forming the pattern image 28 on the upstream of a transfer means. Consequently, color deviations can be accurately measured and compensated without being influenced by the dirt of the carrying belt 21, the dirt of the sensor, the dispersion of sensitivity, or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an image forming apparatus, and particularly to a digital color image forming apparatus having a plurality of photoreceptors.

(Prior art) In an image forming apparatus that forms color images using multiple photoreceptors, the factors that cause misalignment in the transfer paper feeding direction (vertical registration) include the installation position and circumferential speed of each photoreceptor, and the exposure to the photoreceptor. The position, linear speed of the transfer belt, etc. were configured to guarantee each component accuracy and assembly accuracy, but this resulted in high component costs and assembly costs, and due to changes in each factor over time and variations due to component replacement. Readjustment is required.

As a method to solve this problem, a method has been proposed (Japanese Patent Laid-Open No. 59-155870) that detects the transfer paper using a sensor installed in front of each transfer position and obtains the prediction timing for each color. Due to variations in the mounting positions of the sensors and variations in the detection positions of each sensor, it has been difficult to guarantee the positional shift limit (about 0.15 m) for color images.

In addition, an application has already been filed by the same applicant as the present invention for detecting measurement patterns of each color on the transfer belt and measuring their pitch to detect positional deviation. It may not be possible to reliably read the measurement pattern due to scratches on the sensor, dirt on the detection sensor, variations in sensitivity of the detection sensor, etc.

(Objective) The present invention has been made based on such a background, and provides a color image forming apparatus that obtains one color image by superimposing a plurality of color images on a transfer sheet fed by a conveyor belt. The present invention provides a digital color image forming apparatus that can reduce color misregistration in the transport direction of transfer paper for each color with a simple configuration. The purpose is to measure color shift with high precision without being affected.

(Structure) For this purpose, the present invention includes a pattern image signal generation means for forming a measurement pattern image for each color on a transfer belt, a detection means for detecting passage of each color pattern image, and a detection timing count by the detection means. means, a comparison calculation means for comparing the count value by the detection timing counting means with a set value and calculating a deviation amount as necessary, and generation of a writing timing signal for each color whose setting can be changed according to the output value from the calculation means. The apparatus is characterized in that it has a detection means upstream of the transfer means and detects the state of the belt before forming a pattern image.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure and operation of the present invention will be explained in detail below based on 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.

In FIG. 1, a color copying machine is shown as an example of an image recording device.The copying machine includes a scanner part 1 for reading a document and an image signal outputted as a digital signal from the scanner part l electrically. It has an image processing section 2 and a printer section 3 that forms an image on copy paper based on image recording information of each color from the image processing section 2. The scanner part 1 has a lamp 5, such as a fluorescent lamp, for scanning and illuminating the document on the document table 4. The reflected light from the document when illuminated by the fluorescent lamp 5 is reflected by the mirror 6.7.8 and enters the imaging lens 9. The image light is focused on the guichroic prism 1θ by the imaging lens 9,
For example, the light is separated into three wavelengths of red R, green G, and blue B, and each wavelength of light is incident on the light receiver 11, for example, the CCD 11R for red, the CCD IIG for green, and the CCD 1 IB for blue. Each CCDIIR, II
G.

11B converts the incident light into a digital signal and outputs it, and the output is subjected to necessary processing in the image processing unit 2 to record color information of each color, such as black (hereinafter abbreviated as Bk), yellow (Y), etc. (abbreviation).

The signals are converted into signals for recording each color of magenta (abbreviated as M) and cyan (abbreviated as C).

Although FIG. 1 shows an example of forming four colors, Bk, Y, M, and C, it is also possible to form a color image using only three colors. In that case, the recording device should be 1# for the example in Figure 1! You can also reduce i.

The signal from the image processing section 2 is input to the printer section 3,
Laser light emitting device of each color W 12 Bk, 12C
, 12M, and 12Y.

In the illustrated example, the printer section includes four sets of recording devices 13Y, 1
3M, 13G, and 138k are arranged side by side. Each record! ! Attire! 13 are made up of the same components, so in order to focus on the front vehicle, the recording device for C will be explained, and the description of the other colors will be omitted. In addition, for each color,
The same parts are given the same reference numerals, and in order to distinguish the composition of each color, a subscript indicating each color is added to the reference numbers.

The recording device 13G includes a photoreceptor 14G, for example, a photoreceptor drum, in addition to the laser beam emitting device 12G.

A charger 15C, an exposure device using a laser beam emitting device 12C, a developing device 16G, a transfer charger 17C, and the like are attached to the photoconductor 14C in the same manner as in a known copying apparatus.

Photoreceptor 1 uniformly charged by charger 15G
4C forms a cyan latent image through exposure by the laser beam emitting device 12G, and develops it by the developing device 16C to form a developed image. Copy paper is fed by a paper feed roller 18 from a paper feed unit 19, for example, one of two paper feed cassettes, and the leading edge of the copy paper is aligned by a registration roller 20 and sent to a transfer belt 21 at the same timing. Transfer belt 2
The copy sheets conveyed by 1 are sequentially sent to photoreceptors 148, 14C, 14M, and 14Y, each having a developed image formed thereon, and the developed image is transferred under the action of the transfer charger 17. The transferred copy paper is fixed by a fixing roller 22 and discharged by a paper discharge roller 23.

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

FIG. 2 is a front view of the transfer belt section. Transfer belt 21
is supported by a belt drive roller 24 and a driven roller 25, and moves in six directions to convey the transfer paper. Further, the cleaning unit 26 removes toner adhering to the belt. A reflective sensor 27 is provided as a pattern image detection means on the downstream side of the photoreceptor 14 in the belt movement direction.

Furthermore, a reflective sensor 29 is provided as a detection means for detecting the state of the belt before forming a pattern image upstream of the transfer means.
is provided.

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

The system controller 30 controls each module of the scanner 1, image processing section 2, and printer 3. The control contents include display control on the operation panel 31, manual key processing, and according to the mode set on the operation panel 31.
Sending start signals and scaling ratio designation signals to the scanner 1 and printer 3; image processing mode designation signals to the image processing unit 2 (color conversion, masking, trimming, mirroring, etc.)
transmission, abnormal signals from each module, operating status status signals (Wait, Ready, Busy, 5
top, etc.) to control the entire system.

The scanner 1 scans the original at a scanning speed that matches the magnification specified by the start signal from the system controller 30, reads the original image with a reading element such as a COD, and converts it into image data of 8 bits each for R, G, and B. , 5-LSYNC (horizontal synchronization signal) from image processing section 2, S-8T
It is sent to the image processing section 2 in synchronization with R6BE (image clock) and FGATE (vertical synchronization signal).

The image processing unit 2 receives the R and G signals sent from the scanner 1.

Image processing such as T correction, UCRC under color removal), and color correction is performed on each 5-bit B image data, and Y, M, and C are obtained.

Bk is converted into 3-bit image data for each and sent to the printer 3. It also performs editing processes such as scaling, masking, trimming, color conversion, and mirroring according to commands from the system controller 30.
, Bk image data is shifted by the distance between the photosensitive drums of the printer 3 and outputted.

The printer 3 operates a laser beam emitting device according to image data of 3 bits each of Y, M, C, and Bk sent from the image processing unit 2 in synchronization with P-LSYNC (horizontal synchronization signal) and P-3TROBE (image clock). is modulated, and a copy image is obtained on transfer paper using an electrophotographic process.

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

In each recording device, the pattern image visualized outside the transfer paper area by the signal from the pattern image signal generating means is transferred to the transfer belt 21, and as shown in FIG. They are located at intervals of . And C, M in the pattern image 288.

Y passes through the sensor 27 sequentially as the belt moves, and the zero image interval a detected by the sensor 27 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 transmission of image data of each color from the image processing section 2 must be shifted by the distance between the photosensitive drums of the respective colors.

Figure 5 shows 1. FIG. 2 is a block diagram showing the configuration of a buffer memory for this purpose and the configuration of a pattern image signal generation means.

FIG. 6 is a timing chart showing the operation of the block diagram in FIG. 5 (timing chart of the waveforms of the portions indicated by Φ to [phase]).

In the color copying machine of this embodiment, Bk and C.

Since the recording devices are arranged in the order of M and Y, the Bk image data is processed by the image processing unit 2 and output as is, and the C, M, and Y image data are , toe and 'r6MIT□, respectively.

Figure 7 shows the image data delay time tsc, TDNI T
! FIG. 3 is an explanatory diagram for setting lv.

The length from the exposure position to the transfer position for each photoreceptor 14 is 11 (ms), and the linear velocity of the photoreceptor is Vl (fin/sec).
), the distance between photoconductors is 1! , (Tsuru), If the linear speed of the transfer belt is Vg (ms/sec), the time required from exposure to transfer is 1. is the same value for each photoconductor, and t
+ -1+ /vI (sec) If the time to move between each photoreceptor is 1t, tz = j
! t /vt (see) That is, in order to form images of each color at the same position on the transfer paper, toc-Jz/Vz (sec) Tsg=2 It t / vt (see)T
oy” 31x / Vz (see).

As shown in FIG. 5, the circuit configurations of C, M, and Y are the same, so Bk and C will be explained. A rise detection circuit 40 detects the rise of the vertical synchronization signal FGATE sent from the scanner l. Since the Bk, C, M, and Y inputs and FGATE are input at the same time, the output of the rise detection circuit 40 is a signal representing the start of Bk image writing. The output of the rising edge detection circuit 40 is input to a Bk pattern signal generation means 41, which 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 bell 21 (FIG. 4).

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

On the other hand, the output of the address counter 42a is the comparator: C44.
a, the address setter: C45a is compared with the set value, and the output of the address counter 42a is sent to the address setter 4.
When the value matches the set value of 5a, the comparator 44a outputs a match signal. This -ffi&(fr number is buffer memory 4
It is input to the reset terminal of 3a via an OR gate, resets the output of address counter 42a to #0#, and accesses address 0 of buffer memory 43a again.

After reading the already stored image data, the buffer memory 43a writes newly input image data to the same address.

Here, if the setting value of the address setting device 45a is set to the drum interval (tea) of Bk and C,
An image can be created by aligning the k and C images.

The coincidence signal of the comparator: C44a is also input to the delay device: C46a, triggering the delay device 46a, and the matching signal of the comparator: C44a.
After a certain period of time from the matching signal, pattern signal generating means: C
47a outputs a detection pattern.

Since the coincidence signal of the comparator C44a is output at the same time as the leading edge of the image C, the detection pattern of C is outputted with a delay of the delay time (t*c) by the delay device C46a from the leading edge of the image.

Here, the delay device: C46a's delay time is set to a(+
+n) If you set it to the time required to move, the fourth
As shown in the figure, the detection pattern C can be created with a delay of a (fl) from the leading edge of the image.

The same goes for M and Y, address setter: M45b setting value - tDM address setter: Y45c setting value t6V delay device t: M46b
Setting time of -t PN-'l a / V 1 delay device: Setting time of Y46c - tpv-3a/vH,
It is possible to set the leading edge of the image once for each color, and at the same time, it is possible to output the detection pattern at a (crane) pitch as shown in FIG.

Here, if the Bk, C, M, and Y image positions shift on the transfer paper due to variations in the position of each photoconductor, variations in the exposure position with respect to the photoconductor, and variations in the linear speed of the photoconductor and transfer belt, the detection The detection pattern also shifts accordingly, and by measuring the interval between the detection patterns, the amount of positional shift of the image can be detected.

FIG. 8 shows an embodiment of the pattern detection circuit according to the present invention, in which the output current of the phototransistor ph of the zero-reflection sensor 27 is converted into a voltage by the resistor Rm [FIG. 10(a)
waveform at the 0 portion shown in Figure 10 (b)], the DC component is cut by capacitor C2 and only the AC component is extracted
waveform of the 0 part shown in Figure 1 (C)], this signal becomes the input of the inverting amplifier AMP2 via the voltage follower AMP1, and is amplified to an appropriate voltage level [waveform of the 0 part shown in Figure 1 (C)], AMP2 The output of comparator CO
Threshold voltage V determined by resistors R8 and R9 by MPI?
M is compared to obtain a rectangular wave output [the waveform of the 0 portion shown in FIG. I can do it.

FIG. 9 shows an embodiment of the pattern interval measuring circuit. 1st
Figure 1 shows a timing chart.

Figure 13 shows an example where there is a scratch between the pattern images, and Figure 14 shows the sensor 27 under the conditions shown in Figure 13.
A timing chart is shown when the pattern passes through.

First, scratches as shown in FIG. 13 are quickly detected by a sensor 29 that detects the state before transfer.

The detection signal of the sensor 29 is detected by the detection circuit 62 in FIG. 9, and input to the exclusive OR EOR2 by the delay circuit 63 after being delayed by the time required for the belt to move from the sensor 29 to the sensor 27.

Then, only the pattern image is output to the output of the detection circuit 64 of the sensor 27 and the output of the exclusive OR EOR2 of the delay circuit 63. Then, when the number of patterns in the pattern image is detected, a signal indicating that the detection is valid (in this embodiment, since there are four pattern images, the output C of CNT1 is used) is output.

FIG. 15 shows an example where the pattern image overlaps with a scratch, and FIG. 16 shows a timing chart under the conditions as shown in FIG. 15.

As shown in FIG. 16, since the pattern C overlaps with the scratch, the exclusive OR EOR of the delayed output detected by the sensor 29 and the output of the detection circuit 64 of the sensor 27 is performed.
Only 3 pieces are output for output 2, in that case CNT
The output of the IG does not output a signal indicating that it is valid.

To measure the pattern spacing, before measuring the pattern spacing, send a clear signal from the CPU to counters CNT1 to CNT1.
Clear N↑4. The output of the exclusive OR EOR2 that detected the pattern image is input to the clock terminal of the counter CN T 1, and the outputs A, B,
C outputs the signal shown in FIG.

By ANDing (ANDI) the A output of CNT1 and a signal obtained by inverting the B output, a signal representing the pattern interval between Bk and C can be obtained.

Also, by taking the exclusive OR of A output and B output (
EORI), a signal representing the Bk and M pattern intervals can be obtained. Further, by ORing the A output and the B output (ORI), a signal representing the Bk and Y pattern intervals is obtained.

Signals representing the pattern intervals of Bk and C, Bk and M, and I3 and Y are respectively sent to counters CNT2. CNT3, CNT4
is connected to the enable input of the counter CN'r
2. CNT3. CNT4 counts the reference clock while the enable input is “H#” and outputs Bk and C, Bk and M,
Binary data proportional to the Bk and Y pattern spacing is output.

CN T 2 , CN 'r 3 , CN T 4
(7) When the counting operation is finished, the CPU 60
The data selector 61 is controlled by the LO and 5ELI outputs to sequentially select CNT2. CNT3. FIG. 12 shows a flowchart of the above operation in which the binary data of the CNT4 is taken into the CPU 60.

The check timing in FIG. 12 is sufficient time to read the number of output pattern images. If the patterns and scratches overlap as shown in FIG. 15 and four lines cannot be detected, the C output of the CNTl remains #L#, so erroneous data cannot be taken into the CPU.

The CPU 60 compares the captured 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, and Y for correcting the difference. This correction signal is sent to the address setter: C, M, Y45 shown in FIG.
By changing the timing at which images are written for Bk, alignment of images of each color can be realized.

Incidentally, in the present invention, if the belt is used in conditions where it is prone to scratches, it is not preferable to perform detection at the exact same position on the belt each time, so when using the belt under such conditions, it is not preferable to perform detection at the exact same position on the belt each time. It is preferable to detect at different positions.

Now, if the frequency of the reference clock is F(H2), then Bk
C, M, Y pattern spacing Lc, L, , L with reference to
, is Lc e= (Kc /F) Kv2 (wm)LH
= (Ks /F)XV2 (w)LY - (Kv
/F) XV wealth (+n) (However, Kc * KM *
Kv is the measured clock number). Therefore, the deviation from the set value of each pattern interval Dc i D, 4. Dv is Dc = Lc - a (al) Ds' = 1. +-2a (a) Dy -Lv -3a (n).

Correction No. 48 Hc, H, 4, Hv is Dc, DH*
The above calculation process is shown in FIG. 12), in which Dv is multiplied by a count for converting the amount of deviation on the belt into a memory address to obtain Hc-CXDc HM -CXDM Hy -CxD.

In the present invention, the detection patterns are arranged at intervals of a(m) using the leading edge of the image of each color as a reference for Bk and C.

Created in the order of M and Y. a (o) means a (wi) when the belt speed is as designed.
Therefore, if the belt speed deviates from the design value due to component variations, the pattern interval a'
(w) is a'wa (Vz'/Vg)xa v2: Design value of belt speed v tI = Actual value of belt speed.

However, the time t detected by the detection sensor is t
/ / v, / case a / V 2, and the pattern interval can be accurately measured regardless of the actual belt speed.

(Effects) The present invention is as described above, and is not affected by dirt on the conveyor belt, dirt on the sensor, variation in sensitivity, etc., and can compensate for this by accurately measuring color shift.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a digital color image forming apparatus to which the present invention is applied, FIG. 2 is a front view of a transfer belt section, FIG. 3 is a system block diagram according to an embodiment of the present invention, and FIG. 4 is a schematic diagram of a digital color image forming apparatus to which the present invention is applied. 5 is a block diagram showing an example of a detection pattern, FIG. 5 is a block diagram for controlling the transmission of image data, FIG. 6 is a timing chart of each part, and FIG. 7 is an explanatory diagram for setting the delay time of image data. , FIG. 8 is a diagram showing an embodiment of the pattern detection circuit according to the present invention, FIG. 9 is a diagram showing an embodiment of the pattern interval measuring circuit according to the present invention, and FIG. 10 (al, (bl. (C ), (d) is a waveform diagram of the numbered part in Figure 8, Figure 11 is a timing chart in Figure 9, Figure 12 is a control flowchart according to the present invention, and Figure 13 is a case where there is a flaw between detection patterns. FIG. 14 is a sensor detection waveform diagram under these conditions, FIG. 15 is a belt plan view when the detection pattern and flaw overlap, and FIG. 16 is a sensor detection waveform diagram under those conditions. 21...Transfer belt, 27.29...Detection means, 4
1゜47...Pattern image signal generation means, CNTl
. 2.3.4...Detection timing counting means, 6°・
... Comparison calculation means. Figure 7 - + J X Mi 0 (a) BK CM Y Figure 10 (b)! IL translation ``1'' Figure 12 Figure 13 Figure 14 NTJC

Claims (2)

[Claims] (1) a photoconductor, a charger that uniformly charges the surface of the photoconductor, an exposure device that projects image light on the photoconductor according to recorded information, and a developing device that develops an electrostatic latent image on the photoconductor; In an image recording apparatus in which a plurality of recording devices each having a transfer means for transferring a developed image of a photoreceptor onto a transfer paper are arranged, and the transfer paper is sequentially conveyed to each recording device by a transfer belt to transfer images in an overlapping manner, the transfer belt A pattern image signal generation means for forming a measurement pattern image for each color on the top, a detection means for detecting passage of each color pattern image, a detection timing counting means by the detection means, and a count by the detection timing counting means. It has a comparison calculation means that compares the value with a set value and calculates the deviation amount as necessary, and a writing start timing signal generation means for each color whose setting can be changed according to the output value from the calculation means. An image forming apparatus characterized by having, upstream, a detection means for detecting a state of a belt before forming a pattern image. (2) A patent claim characterized in that if the number of patterns measured within a specified time is smaller than the actually generated pattern image signal, the count value measured within the specified time is canceled. The image forming apparatus according to the range (1).