JPH02304465A - Color image forming device - Google Patents

Abstract

PURPOSE:To decrease color deviation in the transferring paper along the carrying direction with a simple constitution by having a pattern image for detection formed responding to each color on a transferring belt when the temperature inside the device is changed and the changed value exceeds a certain value. CONSTITUTION:Temperature detecting means 76 and 77 which detect the temperature at a specified position in the device, an image pattern forming means for detecting 27 which form detecting pattern images 28C, 28M, 28Y, and 28BK responding to each color on the transferring belt 21 when temperature change over a certain level is detected by the beforementioned temperature detecting means 76 and 77, and a compensation processing means which detects the image patterns for detecting 28C, 28M, 28Y, and 28BK formed on the transferring belt 21 by the means 27 which compensates the amount of deviation in the direction the paper is carried for each color judged based on the detected content are provided. Then by this compensating signal, the starting of the writing timing of the writing unit is changed and the position alignment for images of each color can be carried out. Thus deviation of each color due to temperature change, etc., can be eliminated.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention comprises a plurality of development and transfer units corresponding to a plurality of colors that are arranged continuously along a transfer belt, and the transfer belt transfers images to each transfer position. The present invention relates to a color image forming apparatus that conveys paper and sequentially forms color images.

[Prior Art] Color image forming apparatuses include various image forming methods.
One of these methods is to arrange photoreceptors corresponding to multiple different colors at regular intervals on the same plane, and transfer paper to each transfer position in order to transfer each color of toner one after another, thereby creating a color image. There are some that record.

The problem with a color image forming apparatus with such a configuration is that the transfer paper is conveyed to the transfer position of the responding photoconductor in accordance with the transfer timing of each photoconductor so that each color is accurately superimposed. be.

If this timing deviates, color shift will occur and the image quality will be significantly degraded.

The main causes of this color shift include deviations in the mounting positions and circumferential speeds of each photoreceptor, deviations in the exposure position for each photoreceptor, and deviations in the linear velocity of the transfer belt. Furthermore, there are misalignments due to expansion and contraction of various parts of the device due to temperature changes. In particular, in the case of a digital color image forming apparatus that performs writing using a laser, the optical path changes as various parts of the apparatus expand and contract due to temperature changes, and the exposure position with respect to the photoreceptor changes.

In order to prevent this, a conventional method has been to perform positional deviation correction processing at regular intervals or for each copying operation.

[Problems to be Solved by the Invention] However, in the conventional color image forming apparatus described above, if there is a large temperature change from the current correction to the next correction, the positional deviation on the image is kept within a predetermined range. It was difficult to keep it in check.

Further, even when the temperature of the apparatus is stable and fluctuations in positional deviation are small, performing positional deviation correction processing requires operations such as reducing the copying speed, resulting in a decrease in operability.

The present invention has been made in view of the actual state of the prior art described above, and an object of the present invention is to provide a color image forming apparatus that can reduce color misregistration in the transfer paper transport direction with a simple configuration.

[Means for Solving the Problems] In order to achieve the above object, the present invention arranges photoreceptors corresponding to a plurality of different colors at regular intervals and on the same plane, and A latent image is formed by an electrophotographic means, this latent image is turned into a toner image by a developing device, and a transfer sheet is sequentially conveyed by a transfer belt to the transfer position of each photoreceptor, and the toner images of each color are sequentially superimposed and transferred. In a color image forming apparatus that records a color image,
a temperature detection means for detecting the temperature of a specific part within the apparatus; and a detection means for forming a detection pattern image corresponding to each color on the transfer belt when the temperature detection means detects a temperature change of a certain level or more. A pattern image forming means, and a positional deviation correction processing means for detecting a detection pattern image formed by the means on the transfer belt and correcting the amount of deviation in the paper conveyance direction of each color determined based on the detected content. It is set up.

[Operation] According to the above means, when the temperature inside the device changes and the amount of change exceeds a certain value, a command is issued to form a detection pattern image, and a detection pattern image corresponding to each color is printed on the transfer belt. A pattern image is formed. This pattern image is detected, the amount of deviation of each color is calculated from the amount of change in the interval between the images, and a correction signal is generated to correct this amount of deviation.

By changing the writing timing of the writing unit using this correction signal, the images of each color are aligned. Therefore, it is possible to eliminate misalignment of each color due to temperature changes or the like.

[Example] Hereinafter, a color image forming apparatus according to the present invention will be described in detail based on the drawings.

FIG. 1 is a block diagram showing a schematic configuration of the present invention, FIG. 2 is a schematic front view showing the configuration of a digital color image forming apparatus to which the present invention is applied, and FIG. 3 is a color image forming apparatus shown in FIG. FIG. 3 is a front view showing the transfer belt section of FIG.

FIG. 2 shows a color copying machine as a color image forming apparatus, and this color copying machine includes a scanner section 1 for reading images. It consists of an image processing section 2 that electrically processes the image signal output as a digital signal from the scanner section 1, and a printer section 3 that forms an image on transfer paper based on the image recording information of each color from the image processing section 2. There is.

The scanner section 1 includes a lamp 5 (for example, a fluorescent lamp) that scans and illuminates the document on the document table 4.

The reflected light from the document when illuminated by the lamp 5 is reflected by the mirror 6 , 7 , 8 and enters the imaging lens 9 . The imaging lens 9 converts one image light into a dichroic prism 1
image on 0. The dichroic prism 10 converts the incident image light into, for example, red (R), green (G), and blue (B).
The light is divided into three types of wavelengths, and each is divided into red CCD (charge coupled device) 11R1 green CCD IIG and blue CCD
Inject it into IIB. These CCDI IR, 11G,
11B 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, and recorded color information of each color, such as black (hereinafter referred to as BK) and yellow (hereinafter referred to as Y), magenta (hereinafter referred to as M),
The signals are converted into signals for recording each color of cyan (hereinafter referred to as C).

In addition, in FIG. 2, it is assumed that a color image is formed using four colors, BK, Y, M, and C.

It is also possible to use three colors excluding BK.

The output signal of the image processing section 2 is applied to the printer section 3,
12BK laser beams with each color information.

12G, 12M, and 12Y are output to the writing unit 12. The printer section 3 includes four recording devices (representatively indicated by reference numeral 13) 138K.

13C, 13M, and 13Y are installed on the same plane at regular intervals. Each recording device 13 has the same configuration.

Next, the detailed configuration of the recording bag W13 will be explained using the one for cyan (recording device 13c) as an example.

The recording device 13c includes a charger 1 that charges the surface of the photoreceptor drum 14C1 before exposure.
5C1 Cyan laser beam for exposing to form a latent image on the charged photoconductor surface 12C1 Developing device for developing the latent image on the photoconductor surface with toner 16C1 Transfer charger for transferring the toner image on the photoconductor surface to transfer paper It has an electrophotographic configuration equipped with 17C and the like.

To explain the image forming method, first, the photoconductor drum 14C, which is uniformly charged by the charger 15G, is irradiated with modulated light according to image information by the cyan laser beam 12C, and the photoconductor drum 14C is exposed to light. The developing device 16C is applied to the latent cyan image formed on the drum 14C.
to form a visible image. At the same time that the developed toner image reaches the transfer position.

The transfer paper is sent out from the paper feed section 19 by the paper feed rollers 18.

For example, the leading edge of the transfer paper supplied from either of the two paper feed cassettes is aligned by the registration rollers 20, and the paper is sent to the transfer belt 21 at the same timing. The transfer paper conveyed by the transfer belt 21 is placed on the photoreceptor drums 148 on which developed images are formed, respectively.
4Y, transferred to transfer charger 178, 17C,
17M.

A developed image is transferred under the action of 17Y. The transferred paper is fixed by a fixing roller 22 and then discharged by a paper discharge roller 23.

The transfer sheet is conveyed by the transfer belt 21, and since it is conveyed while being attracted to the transfer belt 21 by electrostatic force, there is no misalignment between the transfer sheet and the transfer belt 21. Therefore, the transfer paper is transferred to the transfer belt 2.
It will be conveyed with high precision at a speed of 1.

As shown in FIG. 3, in the transfer belt section, both ends of the transfer belt 21 are supported by a belt drive roller 24 and a driven roller 25, and as the transfer belt 21 moves in six directions, the rolling and special paper is integrally moved. transported. Further, toner that adheres to the transfer belt 21 during transfer is removed by a cleaning unit 26. Note that the reference numeral 27 is a reflective sensor for detecting a pattern image, and the photosensitive drum 14
It is installed at a location located on the downstream side in the direction of belt movement. The configuration of the embodiment shown in FIG. 1 will be explained.

The system controller 40 that centrally controls various controls for image formation includes a scanner unit 1. Image processing section 2 that processes the read image information
, a printer unit 3° for recording image information processed by the image processing unit 2 onto transfer paper, and an operation panel 41 for setting copy conditions and displaying setting contents.

Here, the system controller 40 includes an operation panel 41
Display control, key manual processing, movement control of the scanner unit 1 and printer unit 3, signal transmission according to the specified magnification ratio, image processing mode designation signal to the image processing unit 2 (color conversion, masking, trimming, mirroring, etc.) sending, abnormal signals from each module, operating status status signals (standby, reading).

Controls the entire system (ready, busy, stop, etc.).

The scanner unit 1 scans a document at a scanning speed that matches the magnification specified by a start signal from the system controller 40, reads the document image with a reading element such as a CCD, and generates an 8-bit R2O, 8 image. Output as data. For this output, the horizontal synchronization signal (S-Lync) output from the image processing section 2, the image clock (S-Lync),
-Strobe), and vertical synchronization signal (FGATE)
The images are sent to the image processing section 2 in synchronization with each of the images.

The image processing unit 2 receives RlG, 8 sent from the scanner unit 1.
The image data is subjected to image processing such as γ correction, UCR, and color correction, and is further converted into 3-bit image data of BK, C, M, and Y, and then sent to the printer section 3. Also 1
The image processing unit 2 performs scaling processing, masking, trimming, color conversion, etc. according to instructions from the system controller 40.
Perform editing processing such as mirroring. Further, the image processing section 2 has a buffer memory for outputting BK, C, M, and Y image data shifted by the distance between the photosensitive drums of the printer section 3.

The printer unit 3 receives a horizontal synchronization signal (P-L 5ync)
, the laser beam is modulated according to 3-bit image data of each of BK, C, M, and Y sent from the image processing section 2 in synchronization with the image clock (P-S probe), and the modulated light is transmitted to the photoreceptor drum 14. The surface of the paper is exposed to light, and a copy image is formed on the transfer paper by an electrophotographic process.

FIG. 4 is a plan view showing an example of a detection pattern formed on the transfer belt 21. FIG. By detecting this pattern, it is possible to know the amount of transfer position shift of each image.

Pattern images for detection 28BK, 28C, 28M, 28
Y is the photosensitive drums 14BK, 14C, and 14M generated by a pattern image generation circuit to be described later.

Six pattern images 28BK and 2 are visualized outside the transfer area of the transfer paper 14Y and are transferred to the transfer belt 21, respectively.
8G, 28M, and 28Y, as shown in FIG.
The light reaches the reflective sensor 27 according to the movement of the light, and is sequentially detected. Note that the interval a can be arbitrarily selected by setting the exposure timing for each recording device 14 in advance.

FIG. 5 is a circuit diagram showing the details of the image data delay output circuit and the pattern image generation circuit, and FIG. 6 is a timing chart showing the operation of each part of the circuit in FIG.
corresponds to the operating point in FIG.

The circuit in Figure 5 consists of four blocks for black BK, cyan C, magenta M, and yellow Y, but each has the same circuit configuration, so redundant explanation will be omitted. I will only explain about.

Vertical synchronization signal (FGATE) sent from scanner section 1
) is detected by the rising edge detection circuit 51. At the same time, the rising edge of BK, C, M.

The image information of Y is output from the OR circuit 52. Buffer memory 53.
54.55. Each image information and vertical synchronization signal (
FGATE) are input at the same time, the output of the rising edge detection circuit 51 becomes a one-image writing start signal. This image writing start signal is input to each of the OR circuit 56 and the pattern signal generation circuit 57. Furthermore, OR circuit 5
6 is connected to the buffer memory 5 via the address counter 58.
Connected to 3.

In the pattern signal generation circuit 57, the rise detection circuit 5
BK pattern data is generated in synchronization with the output of 1. The OR circuit 52 outputs the logical sum of the BK pattern data and the BK image data. In this way, in the case of BK, the leading edge of the image and the pattern position are the same with respect to the belt movement direction.

The image writing start signal is applied to the address counters 58 via the OR circuit 56 and resets each of the address counters 58. Further, the address counter 58 counts the signal given from the OR circuit 56 and stores the C image data in the buffer memory 53 according to the count value. A comparator 59 is connected to the address counter 58, and an address setter 60 is connected to the comparator 59.

Comparator 59 compares the output signal of address counter 58 and the set value of address setter 60, and outputs a match signal when the two match. This match signal is output from the OR circuit 5.
2 to the reset terminal of the buffer memory 53, the output of the address counter 58 is reset to 0''', and address 0 of the buffer memory 53 is accessed again. After reading the image data, write the newly inputted image data at the same address. Here, set the address setter 60 to the distance (toc) between the BK and C photoconductor drums 14.
By setting , BK and C images can be aligned and formed on the transfer paper.

A delay device 61 is connected to the comparator 59, and a pattern signal generation circuit 62 is connected to this delay device 61. Further, a two-man OR circuit 63 is connected to the output terminals of the buffer memory 53 and the pattern signal generation circuit 62, and C image data is output from the output terminal.

The delay device 61 is triggered by the coincidence signal of the comparator 59 and generates an output signal after a certain period of time from the trigger time, and this signal is applied to the pattern signal generation circuit 62.

The pattern signal generation circuit 62 generates a detection pattern, which is output via the OR circuit 63. Comparator 59
Since the coincidence signal of is output at the same time as the leading edge of the image of C,
The detection pattern C is output with a delay of a delay time (tpc) caused by the delay device 61 from the leading edge of the image. here.

If the delay time is set to the time required for the transfer belt 21 to move by a (mm), the detection pattern C can be created with a delay of a (mm) from the leading edge of the image, as shown in FIG. can.

Here, the setting of the delay time of image data will be explained with reference to FIG.

The length from the exposure position to the transfer position for each photoreceptor drum 14 is Q, (mm), and the linear velocity of the photoreceptor is v, (+
m/sec), the distance between the photoconductors is Ω, (ffi, *), and the linear speed of the transfer belt is v2 (17 seconds), then the time t1 required from exposure to transfer is the same for each photoconductor, and t = Q x / v min (seconds) If the time taken to move between each photoreceptor is expressed as linear.

j2=02/Vx (seconds) That is, in order to form images of each color at the same position on the transfer paper, t oc= Q z/V, (seconds) j DM= 2 Q 2 / V z (seconds) t ov
” 39 Z / V 2 (seconds).

Similarly to the case of cyan C, the delay times of the address setter and the delay device can be set as follows for magenta M and yellow Y.

Address setter: M setting value: joM n: Y#: tDy delay
Setting time of device-M tpM=2a/vz:Yt+=j,y=3a/v.

If you do this, you can match the tip of the image with each color,
At the same time, a detection pattern is created as shown in Figure 4.
m) It can be output in pitch.

Here, the variations in each of the photoreceptor drums 14.

If the BK, C, M, and Y image positions shift on the transfer paper due to variations in the exposure position with respect to the photoconductor drum 14, fluctuations in the linear speed of the photoconductor drum 14 and the transfer belt 21, etc., The detection pattern also shifts accordingly, so by measuring the distance between these detection turns,
It becomes possible to detect the amount of positional displacement jr of the image. Next, a circuit for detecting turns will be described.

FIG. 8 is a circuit diagram showing an example of a pattern detection circuit.

The reflective sensor 27 is one light emitting diode (hereinafter referred to as "light emitting diode").

A phototransistor (hereinafter referred to as PH) that receives reflected light when the transfer belt 21 is irradiated with optical power from the LED (hereinafter referred to as PH). LED
A series circuit of a resistor R1 and a variable resistor VR1 is inserted into Ph, and a resistor R2 is inserted into Ph. variable resistance VRI
By varying the amount of light emitted, the amount of light emitted can be adjusted. ph outputs an output current according to the amount of received light, and a voltage corresponding to the current value is generated in the resistor R2.

A filter circuit 81 is connected to the reflective sensor 27 using capacitors C1 and C2 and a resistor R3, and is configured so that only the alternating current component is extracted by cutting the direct current component. A voltage follower 82 featuring high input impedance is connected to the filter circuit 81, and an amplifier 83 is provided to amplify its output signal.

The amplifier 83 includes an operational amplifier OPI and input resistors R4 and R5.
, a circuit configuration having an inverting amplification function using feedback resistors R6 and VH2 is adopted, and the output signal of the voltage follower 82 is amplified to a predetermined level. The amplifier 83 has a comparator 8
4 is connected, and this comparator 84 is composed of an operational amplifier OP2, an input resistor R7, threshold voltage setting resistors R8 and R9, and a load resistor R10.

FIGS. 10(a) to 10(d) show operation waveform diagrams at points ① to ② in the pattern detection circuit of FIG. 8.

In the pattern 288 shown in FIG. 4, 28C, 28M, 2
8Y is detected by the 1 reflection type sensor 27 as shown in FIG. 10(a). This detection signal is in a state where it is added to a certain level of DC voltage, and moreover, the level of the DC component is higher than that of the AC component. Therefore, as shown in FIG. 10(b), the filter circuit 81 cuts the DC component and extracts only the AC component. This signal is amplified by an amplifier 83 to a required level as shown in FIG. 10(c). The amplified signal by this amplification If Ha 83 is compared with a threshold voltage (threshold voltage V-N) by a comparator 84, and a rectangular wave voltage shown in FIG. 10(d) is output. Threshold voltage V T in this case
n is given by the following equation.

V, N=R9/(R8+R9)x5 (V) By measuring the pitch of this rectangular wave voltage, the transfer belt 21
It is possible to know the interval between the detection patterns transferred to the image.

FIG. 9 is a circuit diagram showing an example of a pattern interval measuring circuit, and FIG. 11 is an operation waveform diagram of each part of the circuit of FIG. 10.

A data selector 92 is connected to a CPU 91 forming the core of the system controller 40, and counters 93, 94, and 95 are connected to each of three inputs of this data selector 92. Further, each enable (EN) terminal of the counters 93, 94, 95 is connected to an AND circuit (AND) 9.
6, the respective output terminals of an exclusive OR circuit (EOR) 97 and an OR circuit 98 are connected. AND circuit 9
6. Exclusive OR circuit 97 and OR circuit 98
The input terminals of the counter 100 are connected in parallel to the output terminals A and B of the counter 100. However, AND circuit 9
An inverter 99 is inserted between one input terminal of the counter 6 and the output terminal 8 of the counter 100. counter 100
has a clock terminal GK and a clear terminal CLR, the output signal of the detection circuit is applied to the clock terminal, and the clear signal of CP-U91 is applied to the clear terminal.

Next, the operation of the circuit in FIG. 9 will be explained with reference to the flowchart in FIG. 12.

Before starting the pattern interval measurement, the CPU 91 outputs a clear signal in 8 steps 101, and the counters 93, 9
The output of the detection circuit shown in FIG.
The output signals CNTl-A and CNTI-B shown in FIG. 11 are outputted from the outputs A and B thereof.

The output signals CNT1-A and CNTI-B are connected to the inverter 9.
An AND circuit 96 performs a logical product with the signal inverted at step 9 to generate a signal representing the BK and C pattern spacing. Further, the exclusive OR circuit 97 calculates the exclusive OR of the two outputs of the counter 100, and outputs BK and M.
A signal representing the pattern interval is obtained. Similarly, counter 1
The two outputs of 00 are ORed by an OR circuit 98 to obtain a signal representing the BK and Y pattern spacing.

Signals representing the pattern intervals of BK and C, BK and M, and BK and Y are applied to each enable (EN) terminal of the counters 93, 94.95, and the counters 93 to 9
5 counts the reference clock while the EN terminal input is at L (H) level and outputs binary data proportional to each pattern interval. When the counters 93 to 95 complete the counting operation, the CPU 91 outputs the reference clock. select signal (
SELO, 5ELL) controls the data selector 92, and the binary data output from the counters 93 to 95 is taken into the CPU 91.

At this time, the CPU 91 determines the check timing,
(Step 102), then 5ELO.

Step 103): 5ELL is once set to "L" level.

Read the binary data output from the counter 93 (step 104), then set 5ELO to “H” level and set 5EL
Set L to "L3 level" (105) and read the binary data output from the counter 94 (step 106)
, Furthermore, 5ELO is set to “L pz level,” and 5ELL is set to “L pz level.”
H'' level and reads the binary data output from the counter 95 (step 108).

The CPU 91 compares the captured output data of the counters 93 to 95 with a reference value, calculates the difference between the reference value and the measured value, and generates a correction signal CM HCl2 for correcting the difference.
, Mll H, 11, y II HYIt are applied to the address setter 60 shown in FIG. 5, and the image writing timing for BK is changed to align the images of each color.

Now, if the frequency of the reference clock is F (Hz),
C, M, Y pattern spacing Lc=L with BK as reference
n-LY becomes as follows.

L c = K c / F X 2 (+a+a)L
H= KM/F X 2 (ff1m)Ly=Kv/
F X 2 (ms) (However, K (!, KM-KY is the measured number of clocks) Therefore, the deviation Dc from the set value of each pattern interval,
D, , D'r are as follows.

Dc=Lc-a (n+■) DM=LM-2a (ms+) Dv=LY-3a (+sm) Correction signals Ha, HN, HY are used to input the amount of deviation on the transfer belt 21 to memory address in Dc-DH, Dr. Multiplying by the coefficient for conversion, it is shown as follows.

Hc” CX Dc HM = CX D n Hy = CX Dy In the present invention, the detection patterns are set at intervals of a (am) for BK, C, and M, with the image tip of each color as a reference.

It is assumed that they are created in the order of Y. This a (-m) is.

This means that the speed of the transfer belt 21 reaches that value when it matches the design value.If the speed of the transfer belt 21 deviates from the design value due to variations in one part, the pattern interval a1 (mm) is as follows. It is expressed by the formula.
, a□=V,. / vz

t=at/Vz. = a / V.

Therefore, the pattern spacing can be accurately measured regardless of the actual belt speed.

Next, the mechanism of occurrence of positional deviation due to temperature will be explained.

FIG. 13 is a front view showing the detailed configuration of the writing unit 12 shown in FIG. 2. FIG.

In the figure, 31 is a housing, 128, 12C, 12M.

12Y is a laser beam of each color, 34 is a polygon mirror for scanning the laser beam 12 in the length direction of the photosensitive drum 14, 35BK, 35C, 35M, 35Y
36 is an fO lens for performing focusing correction of the light emitted from the polygon mirror 34, and a mirror for sending the light emitted from the polygon mirror 34 to each exposure point of the four photoreceptor drums 14. Further, 37 is a temperature detection element. The reflective surface of the polygon mirror 34 has two stages, the upper stage is used for C and M, and the lower stage is used for BK and Y.

With such a configuration, when the ambient temperature rises, the resin or aluminum alloy body 31 expands and contracts.
As a result, the beam 11 irradiation position on the photoreceptor drum 14 changes. When the beam irradiation position changes, the distance from the irradiation position to the transfer point changes, so that when the transfer point intervals are the same, each image of each unit is shifted in the transfer paper conveyance direction. Furthermore, although the transfer point interval naturally changes due to temperature changes, color shift occurs because the change in the beam irradiation position and the change in the transfer point interval do not match.

FIG. 14 is a block diagram showing details of the control section of the printer section 3. As shown in FIG.

This control unit is positioned as a slave to the system controller 40 in FIG. 1, and is controlled by the CPU.

It is mainly composed of a main control section 70 that includes ROM, RAM, input/output interface circuits, and the like. It also has a function of sending a pattern generation permission signal to the pattern signal generation means 62 shown in FIG.

On the input side of the main control unit 70, there is a paper discharge sensor 71 that detects the discharge of transfer paper to the outside of the machine, a paper end sensor 72 that detects the presence or absence of transfer paper in the cassette, and a paper end sensor 72 that controls paper feeding to the registration rollers. a registration sensor 73 for detecting the size of the cassette, and a cassette size sensor 74 for detecting the size of the cassette.
, toner sensors 75a to 75a for detecting the density of toner of each color.
75d.

A thermistor 76 for detecting the temperature of the fixing heater and a thermistor 77 for detecting the temperature of the writing unit 12 are connected.

Further, on the output side, a charging high-voltage power supply 78 for charging the photosensitive drum 14, a transfer high-voltage power supply 79 for transferring the toner image onto the transfer paper, and a belt static elimination high-voltage power supply 101 for removing the charge on the transfer belt 21. , a developing bias high-voltage power supply 111, a replenishment bias high-voltage power supply 112, a heater control unit 115 that controls energization to the heaters 113 and 114 of the fixing device, a toner replenishment clutch 116 that replenishes toner to the developing device, a paper feed motor 117, and a resistor. A pulse motor driver 119 that drives the motor 118, various motors (motor 121 for the photosensitive drum 14, transfer belt 2
1 motor 121, developing roller motor 122, and fixing roller motor 123). A laser driver 125 for generating laser beams for each color, a polygon motor driver 126 that immediately operates a motor 127 that is a rotational drive source for the polygon mirror 34, a laser driver 125 that receives image data from the image processing unit 2, and a polygon Each video control section 128 that controls the motor driver 126 is connected.

FIG. 15 is a flowchart showing a process for detecting a positional shift of an image based on temperature detection of the writing unit 12.

When the power is turned on, it is determined whether or not the power-on flag is set (step 151), and if the power-on flag is "1", it is set to "0" (step 152), and the temperature of the writing unit 12 is determined. The detection signal of the thermistor 77 that is detecting is taken in (step 153), and in order to use that temperature value as a reference value,
H (step 154), while step 15
If the power-on flag '0'' is determined in step 1, the detection signal of the thermistor 77 is immediately fetched (step 155).
), it is determined whether or not there has been an increase in α from the TMEM in which the detected temperature is stored (step 156). If no rise is observed, the process is terminated, and if there is a rise, a pattern generation permission signal is sent (step 157), and the detected temperature in step 15.5 is stored in the temperature memory T.
Store in MEM and update memory contents.

As described above, every time the temperature of the writing unit 12 increases by α, the positional deviation detection operation is performed to correct the writing timing of each color. In this way, by correcting the positional deviation of each color in relation to the temperature change of the writing unit 12, it is possible to always suppress the positional deviation of each color within an allowable range.

[Effects of the Invention] As explained above, the present invention arranges photoreceptors corresponding to a plurality of different colors at regular intervals on the same plane, and forms a latent image on the surface of each photoreceptor by electrophotographic means. Then, this latent image is converted into a toner image by a developing device, and a transfer sheet is sequentially conveyed by a transfer belt to the transfer position of each photoreceptor, and a color image is recorded by sequentially overlapping and transferring the toner images of each color. In a color image forming apparatus, a temperature detection means detects the temperature of a specific part within the apparatus, and a detection pattern corresponding to each color is placed on the transfer belt when the temperature detection means detects a temperature change of a certain level or more. A detection pattern image forming means for forming an image, and a position for detecting the detection pattern image formed by the means on the transfer belt and correcting the amount of deviation in the paper conveyance direction of each color determined based on the detected content. Since a shift correction processing means is provided, it is possible to eliminate shifts in each color due to temperature changes or the like. Furthermore, since this correction is performed only when necessary, it does not cause a decrease in copy speed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a schematic configuration of the present invention. FIG. 2 is a schematic front view showing the configuration of a digital color image forming apparatus to which the present invention is applied, FIG. 3 is a front view showing a transfer belt section of the color image forming apparatus shown in FIG. 2, and FIG. 4 is a transfer FIG. 5 is a plan view showing an example of a detection pattern formed on the belt 21, FIG. 5 is a circuit diagram showing details of an image data delay output circuit and a pattern image generation circuit, and FIG. 6 is a circuit diagram showing details of an image data delay output circuit and a pattern image generation circuit. A timing chart showing the operation of each part of the
FIG. 7 is an explanatory diagram explaining the setting of the delay time of image data, FIG. 8 is a circuit diagram showing an example of a pattern detection circuit, and FIG.
The figure is a circuit diagram showing an example of a pattern interval measuring circuit, No. 10.
Figures (a) to (d) show the pattern detection circuit in Figure 8.
■An operating waveform diagram of each point, Figure 11 is an operating waveform diagram of each part of the circuit in Figure 10, Figure 12 is a flowchart showing the operation of the circuit in Figure 9, and Figure 13 is a diagram showing the operation of the circuit in Figure 2. A front view showing the detailed configuration of the printer unit 12, FIG.
FIG. 15 is a block diagram showing details of the control section of FIG. 1... Scanner section, 2... Image processing section, 3... Printer section, 12... Writing unit, 13G, 13M, 13Y, 13BK.・・・・・・
・Recording device, 14C, 14M, 14Y, 14BK...
... Photosensitive drum, 16C216M, 16Y, 16B
K...Developing device, 21...Transfer belt, 27...Reflection type sensor, 28C228M, 2
8Y, 28BK...Detection pattern image, 31
...Housing, 34...Polygon mirror,
40...System controller, 51...
... Rise detection circuit, 53-55 ... Buffer memory, 57゜62 ... Pattern signal generation means, 59 ... Comparator, 60 ... Address setting device, 61...Delay device, 70...
・Main control section, 76.77...Thermistor,
81...Filter circuit, 82...Voltage follower, 83...Amplifier, 84...
... Comparator, 91 ... CPU, 92 ...
...Data selector, 93~95°100...
Counter, 96...AND circuit, 97...
...Exclusive OR circuit, 98...OR circuit. Figure 3 Figure 4 Figure 7 Figure 1O (a) (C)
(d) Figure 12 Figure 13

Claims (1)

[Claims] A plurality of photoreceptors corresponding to different colors are arranged at regular intervals on the same plane, a latent image is formed on the surface of each photoreceptor by electrophotographic means, and this latent image is transferred to toner by a developing device. In a color image forming apparatus that records a color image by sequentially conveying the transfer paper to the transfer position of each photoreceptor using a transfer belt and sequentially overlapping and transferring the toner images of each color, temperature detection means for detecting the temperature of a region; and detection pattern image forming means for forming a detection pattern image corresponding to each color on the transfer belt when the temperature detection means detects a temperature change of a certain level or more. and detecting the detection pattern image on the transfer belt formed by the detection pattern image forming means,
A color image forming apparatus comprising: a positional deviation correction processing means for correcting the amount of deviation in the paper conveyance direction of each color determined based on the detected content.