JPH01269958A - Image forming device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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 causes of misalignment in the transfer paper feeding direction (vertical registration) include the mounting position and circumferential speed of each photoreceptor, the exposure position relative to the photoreceptor, and the transfer belt. linear speed, etc., and each was configured to guarantee component accuracy and assembly accuracy, but this resulted in high component costs and assembly costs, and readjustment was required due to changes in each factor over time and variations due to component replacement. becomes.

As a method to solve this problem, a method has been proposed in which the writing timing of each color is obtained by detecting the transfer paper using a sensor installed in front of each transfer position (Japanese Patent Application Laid-open No. 155870/1983). 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 mm) for color images.

Furthermore, in order to reduce the effects of noise and scratches on the belt in this method, a method has also been proposed in which a large number of data are collected for each color and processing such as averaging is performed. In this case, in order to obtain a large amount of data, you can make the device larger and create measurement patterns outside the transfer area, or if you keep the device small, increase the image interval and output more measurement patterns between them. It turns out.

However, increasing the size of the device may increase costs, create new problems, and increase the image spacing (which would reduce the actual image forming speed).

〔the purpose〕

The present invention was made based on such a background, and eliminates the drawbacks of the above-mentioned conventional techniques, and by superimposing a plurality of color images on a transfer sheet fed by a conveyor belt, a single color image is created. An object of the present invention is to provide a (digital color) image forming apparatus that can reduce color misregistration of each color in the transfer paper conveyance direction with a simple configuration.

〔composition〕

In order to achieve this object, the present invention includes a photoreceptor, a charger that uniformly charges the surface of the photoreceptor, an exposure means that projects image light on the photoreceptor according to recorded information, and an electrostatic potential of the photoreceptor. A plurality of recording devices each having a developing means for developing an image and a transfer means for transferring a developed image on a photoreceptor onto a transfer paper are arranged, and the transfer paper is sequentially conveyed to each recording device by a transfer belt to overlap and transfer the images. The image forming apparatus 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 counting means for the detection means. , a comparison calculating means for comparing the count value by the detection timing counting means with a set value and calculating a deviation amount as necessary, and a writing start timing signal generating means whose setting can be changed according to the output value from the calculating means. and a first one for measuring the amount of deviation. A second measurement mode is prepared, and the first measurement mode is performed during normal image formation.
It is characterized by having a control means for performing the second measurement mode when a predetermined condition is reached in the measurement mode.

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.

FIG. 1 shows a color copying machine as an example of an image recording device. The copying machine includes a scanner part 1 for reading originals, image processing parts 2 and 1 that electrically process image signals output as digital signals from the scanner part 1, and images of each color from the image processing part 2. It has a printer section 3 that forms an image on copy paper based on recorded information. 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 imaged onto the guichroic prism 10 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 input to a light receiver 1), for example, a red CCD 1) R, a green CCD IIG, and a blue CCD 1 IB. Each CCDIIR, II
G.

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

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 number of recording devices can be reduced by one compared to the example shown in FIG.

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 unit 3 includes four sets of recording devices 13Y,
13M, 13C, and 138k are arranged side by side. Since each recording device 13 is made of the same constituent members, in order to simplify the explanation, the recording device for C will be explained, and the explanations for other colors will be omitted. Furthermore, for each color layer,
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 13c includes a photoreceptor 14c, for example, a photoreceptor drum, in addition to the laser beam emitting device 12G.

A charger 15c, an exposure position by a laser beam emitting device W12C, a developing device 16C, a transfer charger 17C, and the like are attached to the photoreceptor 14C in the same manner as in a known copying apparatus.

The photoconductor 14C, which is uniformly charged by the charger 15-C, is exposed to light by the laser beam emitting device 12C.
A latent cyan light image is formed and developed by the developing device 16C to form a developed image. Paper feed section 19 by paper feed roller 18,
For example, a transfer sheet supplied from either of two paper feed cassettes is sent to a transfer belt 21 with its leading edge aligned by registration rollers 20 and at the same timing. Transfer bell 1
The transfer paper conveyed by -21 is sequentially sent to photoreceptors 148 14C, 14M, 14, and Y on which a developed image is formed, and the developed image is transferred under the action of the transfer charger 17. The transferred 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 transfer 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 the A direction 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.

The detection means is provided at the drive roller portion of the transfer belt to prevent the influence of flapping of the transfer belt and to maintain a constant distance from the transfer belt at all times.

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

The system controller 3o controls each module of the scanner 1, image processing unit 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 signals (Wait, Ready+Busy, 5to
p, etc.) to control the entire system.

The scanner 1 scans an original at a scanning speed that matches the magnification specified by a start signal from the system controller 30, reads the original image with a reading element such as a CCD, and generates image data of 8 bits each for R, G, and B. As, 5-LSYNC (horizontal synchronization signal) from image processing unit 2, S-3
It is sent to the image processing section 2 in synchronization with TROBE (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, UCR (undercolor removal), and color correction is performed on each 8-bit B image data, and Y and M are processed.

Convert to image data of 3 bits each for C and Bk and send to printer 3.
send to Further, according to commands from the system controller 30, editing processing such as scaling processing, masking, trimming, color conversion, and mirroring is performed.

It also includes a buffer memory for outputting Y, M, C, and Bk image data shifted by the distance between the photoreceptor drums of the printer 3.

The printer 3 emits laser light according to 3-bit Y, M, C, and Bk image data sent from the image processing unit 2 in synchronization with P-LSYNC (horizontal synchronization signal) and P-STROBE (image clock). The device is modulated to obtain a copy image on the 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 images visualized by the signals from the pattern image signal generating means at paper intervals are transferred to the transfer belt 21, and as shown in FIG.
mm). 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.

FIG. 5 is a block diagram showing the configuration of a buffer memory for this purpose and the configuration of a pattern image signal ordering means.

FIG. 6 is a timing chart showing the operation of the block diagram in FIG. 5 (timing chart of waveforms of portions indicated by ■, ■', ■~[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 , respectively t De, t DM+, toy
output with a delay.

FIG. 7 shows the delay time t of image data. C+ tDM+
“It is an explanatory diagram for setting Or.

The length from the exposure position to the transfer position for each photoreceptor 14 is 1. (mm), photoreceptor linear velocity is V, (mm/5e
c) If the distance between the photoreceptors is 122 (mm) and the linear speed of the transfer belt is v (mm/5ec), then the time required from exposure to transfer will be the same for each photoreceptor.
t l-1)+ / vl (sec) If the time to move between each photoreceptor is t2, then t z -1t / v
t (sec) That is, in order to form images of each color at the same position on the transfer paper, t oc-1z / v t (sec) t oN=
21 z / v z (see) L ov= 3
12 z / V z (sec).

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 1. Bk, C
, M, and Y and FGATE are input at the same time, the output of the rising edge detection circuit 40- is a signal representing the start of Bk image writing. Further, the falling edge of FGATE is detected by the falling edge detection circuit 48, and the signal is taken into the delay circuit Q49, which outputs a signal delayed by a certain period of time from the rear end of the image. Delay circuit: The output of Q49 is sent to Bk pattern signal generating means 4 via an OR gate.
1 and outputs a detection pattern. In other words, in the case of Bk, the leading edge of the image and the pattern position are on 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 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.

The output of the delay circuit Q49 is also input to the reset terminal of the address counter C42a via two OR gates. Further, a pattern output start signal is similarly inputted to the reset terminal of the address counter C42a.

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.
5a, the comparator 44a outputs a match signal. This match signal is input to the reset terminal of the buffer memory 4.33 via an OR gate, and the output of the address counter 42a is reset to #0# to access address O of the 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 (t nc) of Bk and C, the B
An image can be created by aligning the k and C images.

The match signal of the comparator: C44a is also input to the delay device: C46a, triggering the delay device 46a 7, and the comparator 44
Pattern signal generating means after a certain period of time from the matching signal of a:
Comparator C47a outputs a detection pattern: The coincidence signal of C44a is output twice, at the top of the C image and at the output of the Bk pattern signal.

The detection pattern C is a delay device from the leading edge of the image: C46
The output delayed by the delay time (t pc) due to a and Bk
The output will be delayed by the delay time (tpc) from the pattern signal output of C47a, but since the output of pattern signal generating means C47a is ANDed with the inverted signal of I''GATE, The output is image 7 &
It is output only to 4.

Here, the delay device: C46a's delay time is a<m
m) If you set the time required to move, you can move from the Bk pattern to a at the paper interval as shown in Figure 4.
The detection pattern for C can be created with a delay of (mm).

The same goes for M and Y, address setter: M45b setting value = tDll address setter: Y45C setting value - toy delay device: M46b
Setting time of -t knee 2 a/v delay device 2 Y4
By setting the setting time of 6c to -Lrv=3a/v, it is possible to match the leading edge of the image for each color, and at the same time, it is possible to output the detection pattern at a pitch of a (mm) 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 a pattern detection circuit according to the present invention.

In the figure, the phototransistor P of the reflective sensor 27,
The output current of h is converted into voltage by resistor R2 [10th
Figure (0 part waveform shown in al), DC component is cut by capacitor C2 and only AC component is taken out [first
0 waveform of the 0 portion shown in Figure (b)].

This signal becomes the input of the inverting amplifier AMP2 via the voltage follower AMP1, and is amplified to an appropriate voltage L novel [the waveform of the 0 part shown in Figure 1O (C)].
The output of P2 is compared with the threshold voltage VT determined by the resistors R8 and R9 by the comparator COMPl, and a rectangular wave output is obtained [Figure 10 (waveform of the 0 part shown in d+)].The pitch of this rectangular wave output is measured. Then, 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, and the first
) The timing chart is shown in the figure.

Before starting measurement of pattern intervals, a clear signal is issued from the CPU 60 to clear the counters CNT1 to CNT4. The output of the detection circuit is input to the clock terminal of the counter CNTl, and the outputs A and B of the counter CNTl are the first
) Outputs the signal shown in the figure.

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 human output and the B output (OR1), a signal representing the Bk and Y pattern intervals is obtained.

Bk and C, Bk, l! : The signals representing the pattern intervals of M, Bk and Y are respectively sent to counters CNT2. CNT3, CN
Connected to the enable input of T4 and counter CN
T2. CNT3. CNT4 counts the reference clock while the enable input is “H” and calculates Bk and C, Bk and M
, outputs binary data proportional to the pattern interval of Bk and Y.

CNT2. CNT3. When the counting operation of CNT4 is completed, the data selector 61 is controlled by the 5ELO and 5ELL outputs of the CPU 60 to sequentially count CNT2. C
NT3. The binary data of CNT4 is taken into CPU60. FIG. 12 shows a flowchart of the above operation.

In the figure, first, a clear signal is output (S1--Step 1, the same applies hereafter), and the check timing for pattern interval measurement is determined (S2). If yes, CPU6
Set both 5ELO and 5ELI outputs of 0 to “L” (S
3) Read the output “KC” of counter CNT 2 (
S4). Next, leave 5ELO at "H" and 5ELL at L" (S5), read the output "KM" of CNT3 (S6), and set 5ELO to "L" and 5ELL to H (S7), and read the output "KM" of CNT3 (S6). Read the output “KY” (S
8).

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. By sending this correction signal to address setters: C, M, Y 45 shown in FIG. 5 and changing the timing at which the image is written for Bk, alignment of images of each color can be realized.

Now, if the frequency of the reference clock is F (Hz), then Bk
C, M, Y pattern spacing Lc, Ls, L based on
v is Lc = (Kc /F)XV, (mm)L, = (K
, /F)XV2 (mm)Lv = (Ky /F)x
Vt (mm) (where Kc, Ks r Kv are the measured clock numbers). Therefore, the deviations Dc, D, and Dv from the set values of each pattern interval are DC=Lc-a (mm) DH=LM-2a (mm) Dv=L, -3a (mm>).

The correction signals Hc, Hs*Hv are Dc, DH, D
By multiplying v by a count for converting the amount of deviation on the belt into a memory address, Hc=CXDc HM =CXDH HV =CXDv.

By the way, according to the pattern output method described so far,
With paper spacing, it may be possible to measure only two of each photoreceptor. If erroneous detection occurs due to noise, belt seams, etc., the image may deteriorate.

Therefore, in the present invention, only the amount of deviation is measured at paper intervals, and the amount of deviation is stored in the RAM. At that time, the setting value of the write timing signal generating means is not changed. However, if the amount of deviation exceeds a certain amount, it is calculated whether the amount of deviation measured in the past also exceeds the certain amount, and whether the amount of deviation exceeds the certain amount consecutively for a predetermined number of times. Alternatively, it is checked whether a predetermined number of times exceeds a certain amount. If this condition is exceeded, the copying process is interrupted once for the next transfer sheet. Then, the amount of deviation is measured again, and the setting value of the writing timing signal generating means is changed based on the amount of deviation at that time. Then, the interrupted copying process is resumed and continued.

When measuring the amount of deviation again, take more data and
Processing such as averaging is performed for each photoreceptor to calculate the amount of deviation with the influence of errors due to noise, belt seams, etc. reduced as much as possible.

FIG. 13 shows a flowchart when calculating the deviation amount. X
is the predetermined amount of deviation among the deviations stored in RAM:
It shows the number of deviations exceeding A, N is the number of data to be calculated, B is a predetermined quantity, and B<N.

In this flow, first, the amount of deviation is calculated (SL
), and after storing the deviation amount in the RAM (S2), the above-mentioned X is set to 0 (S3). Next, if the amount of deviation exceeds a predetermined value A (S4), add 1 to that number (S5), R
The AM data address address is incremented by one (S6). Decrease the number of calculation data by one (S7) and determine whether N<O (
S8).

If YES, determine whether there is a predetermined number or more of data exceeding a predetermined amount of deviation (S9); if YES, interrupt the copying process (510); measure and calculate the average amount of deviation (Sil); The correction amount is calculated (S12), the write timing setting value is changed (S13), and finally the copying process return operation is performed (S14).

FIG. 14 shows a RAM area for storing misalignment data. In this figure, the latest data is X(0).

〔effect〕

The present invention has been described above, and according to the present invention, it is possible to provide an image forming apparatus that is capable of always performing highly accurate positioning with an apparatus of the minimum necessary size.

[Brief explanation of the drawing]

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 the detection pattern, FIG. 6 is a block diagram for controlling the transmission of image data, and FIG. 6 is a timing chart 1-1 of each part. Explanatory drawings, 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, and FIG. 10 (al, (bl. c) and (d) are waveform diagrams of each part of the 8th part, Figure 1) is a timing chart in Figure 9, Figure 12 is a pattern interval measurement control flowchart according to the present invention, and Figure 13 is a deviation in the image writing position. Flowchart for quantity calculation,
FIG. 14 is a diagram showing a RAM area for storing deviation amount data. 27...Detection means, 30...System controller, 41.47...Pattern image signal generation means, CN
Tl, 2, 3.4... detection timing counting means,
60... Comparison calculation means, 21... Transfer belt. Figure 3 Figure 7 Figure 4 Factor θ Mi

Claims (3)

[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 forming 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. Comparison calculation means for comparing the value with a set value and calculating the amount of deviation as necessary, and means for generating a writing timing signal for each color whose setting can be changed according to the output value from the calculation means, and measuring the amount of deviation mentioned above. 1st for,
A second measurement mode is provided, and a first measurement mode is provided during normal image formation.
An image forming apparatus characterized by having a control unit that performs a measurement mode and performs a second measurement mode when a predetermined condition is reached in the first measurement mode. (2) The first measurement mode is a mode in which the amount of deviation is measured at image intervals, and at that time, the setting value of the writing timing signal generation means is not changed. Forming device. (3) The above-mentioned second measurement mode is to output the measurement pattern image continuously, average a large number of deviation measurement values, and generate a writing timing signal for each color based on the averaged deviation amount of each color. The image forming apparatus according to claim 1, wherein the image forming apparatus is in a mode for changing the set value of the generating means.