JP2003241470A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect a situation that pattern density becomes abnormal because of the fault of a sensor or the like in the case of changing the density of a pattern image so as not to be influenced by damage and soiling on a transfer belt in a printer performing the registration of respective colors by writing the pattern image on the transfer belt or the like. <P>SOLUTION: The image forming apparatus is equipped with a plurality of image forming means, an endless belt, a pattern detection sensor constituted of a light emitting element and a light receiving element for reading the specified pattern image formed on the endless belt by a plurality of image forming means, the sensor constituted to output a pattern detection signal when an output value in accordance with reflected light quantity received by the light receiving element of the pattern detection sensor is equal to or above a threshold and a density changing means for varying the output density of the specified pattern image, and a registration correction means for electrically or mechanically correcting the registration of the respective image forming means based on the pattern detection signal and a display means for displaying an error message. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus adopting an electrophotographic system or an electrostatic recording system, and more particularly to an endless belt used as a transfer material carrier or an intermediate transfer member (an endless belt as a transfer material carrier). A belt and an endless belt as an intermediate transfer member are collectively referred to as a transfer belt) and are related to an image forming apparatus having a function of automatically correcting an image shift during multiple image formation.

[0002]

2. Description of the Related Art Conventionally, an electrostatic latent image on a photosensitive member is developed by irradiating a photosensitive drum with laser beam light which is light-modulated according to recording information or light from a light emitting element such as an LED, and an electrophotographic process. Has a plurality of recording devices for transferring an image to a transfer paper or an intermediate transfer belt, and the transfer material conveying belt sequentially conveys the transfer paper to each recording device to perform multiple transfer of each image on the transfer paper, or an intermediate transfer belt. There has been proposed an image forming apparatus capable of forming a color image by a method in which each image is multiply transferred and then collectively transferred to a transfer paper.

In this type of image forming apparatus, the image is formed on each photosensitive drum due to a mechanical mounting error between the photosensitive drums, an optical path length error of each laser beam, an optical path change, a warp due to an environmental temperature of the LED, and the like. Further, the registration of each color image becomes inconsistent on the transfer material finally subjected to multiple transfer. For this reason, a photosensor reads the registration correction pattern image formed on the transfer belt from each photosensitive drum, detects the registration deviation on the photosensitive drum corresponding to each color, and outputs the image signal to be recorded as an electrical signal. Correction, and a folding mirror provided in the optical path of the laser beam is driven to correct the change in the optical path length or the change in the optical path.

Various patterns have been proposed for the registration correction pattern image.
In the '98810 publication, a first line segment arranged at a predetermined angle with a process direction, which is a moving direction of a transfer belt, and a second line segment symmetrically arranged with an imaginary line orthogonal to the first line segment intersecting the process direction. A pattern consisting of line segments has been proposed. Such a registration correction pattern image is read by a photosensor including an LED and a light emitting element such as a phototransistor and a light receiving element. Two of these photosensors are arranged at a predetermined distance in the direction orthogonal to the process direction, and the registration correction pattern image is also formed so as to pass over the photosensor. FIG. 8 shows how the photosensors 60 and 61 detect the registration correction pattern 203 on the transfer belt 31. It should be noted that the transfer belt 31 is made of a material whose reflectance of light (eg infrared light) emitted by the LED 201 in the photosensors 60 and 61 is higher than that of the pattern 203. Enables pattern detection.

FIG. 8 shows how the phototransistor 202 receives the light emitted by the LED 201 and reflected by the pattern 203 or the transfer belt 31, and FIG. 7 shows the phototransistor 202 receiving the reflected light and converting it into an electric signal. The following shows a light receiving circuit. First, when the transfer belt 31 is detected, the amount of reflected light is large, so a large amount of photocurrent flows through the phototransistor 202, and current-voltage conversion is performed by the resistor 407 and amplification is performed by the resistors 402 to 404 and the operational amplifier 401. When the pattern 203 is detected, the amount of reflected light is small, so that a photocurrent smaller than that in the transfer belt portion flows through the phototransistor 202, and is similarly current-voltage converted by the resistor 407 and amplified by the resistors 402 to 404 and the operational amplifier 401. . A state in which the light receiving circuit detects the reflected light in the order of the transfer belt portion → the pattern portion → the transfer belt portion 301 in FIG.
Is. By setting the threshold value level to a predetermined level between the transfer belt detection level and the pattern detection level by the electronic volume 406 capable of changing the threshold level, that is, by comparing the current-voltage converted value with this threshold level by the comparator 405, the pattern is obtained. The sensing output 302 can be produced. This pattern detection output 302 that is sequentially sent is read, registration deviation is detected from the pattern interval, etc., the image signal to be recorded is electrically corrected, and the folding mirror provided in the laser beam optical path is driven. Then, the optical path length change or the optical path change is corrected.
Further, the threshold value set in the electronic volume 406 is changed according to the minimum value of the reflected light amount for one rotation of the transfer belt 31, and at the same time, the density (laser light amount) for forming the pattern is also changed to form the pattern with an appropriate density. Doing so consumes toner other than for image formation, which increases the running cost, and the reflection-type optical sensor used for pattern detection is sensitive to stains and the like. It prevented the detection from deteriorating due to toner stains.

[0006]

However, in the prior art example, even if the sensor is in an abnormal state due to deterioration of the sensor due to adhesion of toner, decrease in light amount due to sensor failure / deterioration deterioration, etc., the light amount of the laser is increased rapidly. It may be possible to control by increasing the density of the pattern image, and it is considered that remarkable toner consumption and in-machine contamination may occur.

The present invention has been made by paying attention to the above-mentioned problems, and when the density of a pattern image is changed so as not to be affected by scratches or stains on the belt, the sensor may be damaged. An object of the present invention is to provide an image forming apparatus capable of detecting that the pattern density is abnormal.

[0008]

In order to solve the above-mentioned problems, the present invention has the following constitutions (1) to (4).

(1) A plurality of image forming means for forming a visible image (toner image) on a photosensitive member by an electrophotographic method or an electrostatic recording method, and a drive which is close to the image forming means and transmits rotational drive. A pattern detection including an endless belt stretched and driven by a roller and at least one driven roller, and a light emitting element and a light receiving element for reading a predetermined pattern image formed on the endless belt by the plurality of image forming means. A sensor, a sensor configured to output a pattern detection signal when the output value corresponding to the amount of reflected light received by the light receiving element of the pattern detection sensor is equal to or more than a threshold value, and a density change for varying the output density of the predetermined pattern image. Means and a register for electrically or mechanically correcting the registration of each image forming means based on the pattern detection signal. A rotation of the endless belt as an initial operation for detecting the amount of reflected light including scratches and stains on the endless belt before performing the registration correction. Then, the amount of reflected light of the endless belt is read by the pattern detection sensor, and the output density of the predetermined pattern image is changed according to the output signal of the pattern detection signal at that time or the amount of reflected light received by the light receiving element of the pattern detection sensor. In the image forming apparatus, it is determined whether the output of the reflected light amount of the pattern image is within a predetermined range, and an error message is displayed when a pattern image exceeding the predetermined range is detected a predetermined number of times. An image forming apparatus comprising:

(2) It has the threshold value changing means, and performs a scratch detection operation for detecting scratches or stains on the endless belt before performing the registration correction, and rotates the endless belt once to perform the pattern. The image forming apparatus according to (1), wherein the detection sensor reads the amount of reflected light from the endless belt, and the threshold value is changed according to the output signal of the pattern detection signal at that time.

(3) The image forming apparatus according to (1), wherein the endless belt is used as a transfer material conveying means.

(4) The image forming apparatus according to (1), wherein the endless belt is used as an intermediate transfer belt.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below based on examples with reference to the drawings.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of an image forming apparatus embodying the present invention. The image forming apparatus of this embodiment is an electrophotographic system, and a color image output apparatus will be described in which a plurality of image forming units in which the present invention is considered to be particularly effective are arranged in parallel.

The color image forming apparatus comprises an image reading section 1R and an image output section 1P. The image reading unit 1R optically reads a document image, converts it into an electric signal, and sends it to the image output unit 1P, but a detailed description thereof will be omitted.

The image output section 1P is roughly classified into the image forming section 1
0 (four stations a, b, c, and d are arranged in parallel and have the same configuration), a sheet feeding unit 20, an intermediate transfer unit 30, a fixing unit 40, and a control unit 70.

Further, each unit will be described in detail. The image forming unit 10 has the following configuration. Photosensitive drums 11a and 11b as image carriers,
11c and 11d are pivotally supported at their centers, and are rotationally driven in the direction of the arrow. The primary chargers 12a, 12b, 12 face the outer peripheral surfaces of the photosensitive drums 11a to 11d in the rotation direction thereof.
c, 12d, optical systems 13a, 13b, 13c, 13d,
The folding mirrors 16a, 16b, 16c, 16d and the developing devices 14a, 14b, 14c, 14d are arranged. In the primary chargers 12a to 12d, the photosensitive drum 11
A uniform amount of charge is applied to the surface of a to 11d. Then, by the optical systems 13a to 13d, a light beam such as a laser beam modulated according to the recording image signal is applied to the photosensitive drum 1.
An electrostatic latent image is formed there by exposing on 1a-11d. Further, developing devices 14a to 14d that respectively store four color developers of yellow, cyan, magenta, and black (hereinafter, referred to as toners) are stored.
To visualize the electrostatic latent image. Image transfer regions Ta, Tb for transferring the visualized visible image to the intermediate transfer member,
On the downstream side of Tc and Td, the cleaning devices 15a, 1
Toner left on the photosensitive drums 11a to 11d without being transferred to the transfer material by 5b, 15c, and 15d is scraped off to clean the drum surface. By the process described above, image formation with each toner is sequentially performed.

The paper feeding unit 20 includes cassettes 21a and 21b for storing the recording material P and a manual feed tray 2.
7. Pickup rollers 22a, 22 for feeding the recording materials P one by one from the cassette or the manual feed tray
b and 26, a paper feed roller pair 23 and a paper feed guide 24 for conveying the recording material P sent from each pickup roller to the registration rollers, and the recording material P is secondarily arranged in accordance with the image forming timing of the image forming unit. Transfer area Te
It is composed of registration rollers 25a and 25b for sending out to.

The intermediate transfer unit 30 will be described in detail. The intermediate transfer belt 31 (the material thereof is, for example, P
ET [polyethylene terephthalate] and PVdF [polyvinylidene fluoride] are used) to apply an appropriate tension to the intermediate transfer belt 31 by a driving roller 32 for transmitting drive to the intermediate transfer belt 31 and a spring (not shown). The applied tension roller 33 and the driven roller 34 which faces the secondary transfer area Te with the belt interposed therebetween are wound around. Of these, the primary transfer plane A is formed between the drive roller 32 and the tension roller 33. The drive roller 32 is a metal roller whose surface is coated with rubber (urethane or chloroprene) having a thickness of several mm to prevent slippage with the belt. The drive roller 32 is rotationally driven by a pulse motor (not shown). In the primary transfer areas Ta to Td where the photosensitive drums 11a to 11d and the intermediate transfer belt 31 face each other, a primary transfer charger 35a is provided on the back side of the intermediate transfer belt 31.
~ 35d are arranged. A secondary transfer roller 36 is arranged so as to face the driven roller 34, and forms a secondary transfer area Te by a nip with the intermediate transfer belt 31. The secondary transfer roller 36 is pressed against the intermediate transfer body with an appropriate pressure. Further, on the intermediate transfer belt 31, downstream of the secondary transfer area Te, a cleaning unit 50 (a blade 51 and a waste toner box 5 for storing waste toner) for cleaning the image forming surface of the intermediate transfer belt 31.
2) is provided.

The fixing unit 40 includes a fixing roller 41a having a heat source such as a halogen heater therein, a roller 41b (which may also have a heat source) pressed by the roller, and a nip between the roller pair. Guide 43 for guiding the transfer material P to the sheet, fixing heat insulating covers 46 and 47 for confining heat of the fixing unit 40 inside, and further guiding the transfer material P discharged from the roller pair to the outside of the apparatus. It includes an internal paper discharge roller 44, an external paper discharge roller 45, a paper discharge tray 48 on which the transfer material P is stacked, and the like.

The control unit 70 comprises a CPU 801 for controlling the operation of the mechanism in each unit, a motor driver section 802, a laser driver 808 for driving a laser for recording an image on a photosensitive member, and the like ( Figure 5
(A)).

Next, a description will be added according to the operation of the apparatus.

When the image forming operation start signal is issued from the CPU 801, the paper feeding operation is started from the paper feeding stage selected according to the selected paper size and the like. For example, when the paper is fed from the upper paper feed stage, first, the transfer material P is sent out one by one from the cassette 21a by the pickup roller 22a. Then, the transfer material P is guided between the paper feed guides 24 by the paper feed roller pair 23 and conveyed to the registration rollers 25a and 25b. At that time, the registration rollers 25a and 25b are stopped, and the leading end of the paper hits the nip portion. After that, the registration rollers 25a and 25b start rotating at the timing when the image forming unit 10 starts forming an image. The timing of this rotation is set so that the transfer material P and the toner image primarily transferred from the image forming unit 10 onto the intermediate transfer belt 31 coincide with each other in the secondary transfer area Te.

On the other hand, in the image forming section 10, when the image forming operation start signal is issued, the toner image formed on the photosensitive drum 11d, which is the most upstream in the rotation direction of the intermediate transfer belt 31, by the above-described process becomes high. By the primary transfer charger 35d to which a voltage is applied, the primary transfer area T
At d, the image is primarily transferred to the intermediate transfer belt 31. The primary-transferred toner image is conveyed to the next primary transfer area Tc. There, the image formation is performed with a delay between the image forming units by the time when the toner image is conveyed, and the next toner image is transferred by aligning the resist on the previous image. The same steps are repeated below, and eventually the four color toner images are primarily transferred onto the intermediate transfer belt 31.

After that, when the recording material P enters the secondary transfer area Te and comes into contact with the intermediate transfer belt 31, a high voltage is applied to the secondary transfer roller 36 in synchronization with the passage timing of the recording material P. Then, the four color toner images formed on the intermediate transfer belt 31 by the above-described process are transferred to the surface of the recording material P. After that, the recording material P is accurately guided to the fixing roller nip portion by the conveyance guide 43. Then, the toner image is fixed on the paper surface by the heat of the roller pair 41a and 41b and the pressure of the nip. Thereafter, the paper is conveyed by the inner and outer paper discharge rollers 44 and 45, the paper is discharged to the outside of the machine, and is stacked on the paper discharge tray 48.

Next, the registration correction operation will be described with reference to the control unit block diagram of FIG. 5A and the light receiving circuit of FIG. Control unit 70 of FIG. 5 (a)
Is a CPU 801 that controls the image output unit 1P, a ROM 806 that stores a control program and data, a RAM 803,
The pattern width is shaped by receiving the output from the motor driver unit 802 that drives various motors and the photosensors 60 and 61, and receiving the output from the light receiving circuit 807 and the light receiving circuit 807 that converts it into a waveform that can be processed by the pattern width shaping unit. A pattern width shaping unit 804, a pattern width & position storage unit (registers D to S) 805 for storing the pattern width and position,
The CPU 801 includes a laser driver 808 that controls the amount of laser light and performs lighting control according to image data. CP
When the registration correction operation is started by the instruction from U801 and the registration pattern is detected, the photo sensor 60,
61 and the light receiving circuit 807 convert the signals into electric signals, which are input to the pattern width shaping unit 804 and the CPU 801. The light receiving portion analog signal input to the CPU 801 is converted into a voltage by the phototransistor 202 as shown in FIG.
01 is a signal amplified by a predetermined gain, and the pattern detection signal input to the pattern forming unit 804 and the CPU 801 is the light receiving unit analog signal of the comparator 40.
Electronic volume 4 set from CPU 801 by 5
The pattern detection output signal is waveform-shaped by using the output of 06 as a threshold. In the pattern width shaping unit 804, the CPU
Only when the pattern detection output for a predetermined width T or more set by 801 continues, it is determined that the pattern is a pattern, and the pattern width and pattern position are stored in the pattern width & position storage unit (register) 805. Based on the stored data, the registration deviation on the photosensitive drum corresponding to each color is calculated using the table stored in the CPU 801 and the ROM 806, and the image signal to be recorded is electrically corrected and the laser beam is corrected. The folding mirror 16a provided in the optical path is driven (the motor is driven by the motor driver 802 to control the mirror) to correct the optical path length change or the optical path change. As the detection means for detecting the registration correction pattern image, the same photosensors 60 and 61 as in the conventional example of FIG. 8 are used.

Next, a method of controlling the detection threshold value of the light receiving circuit 807 at the time of performing registration correction pattern image density control and pattern detection in this embodiment will be described. In FIG. 3A, as an initial operation, the intermediate transfer belt 31
FIG. 3B shows the change in the reflected light amount detected by the CPU 801 during one rotation of the image when the detection threshold value and the pattern output density are properly corrected by the detected value of the reflected light amount of the intermediate transfer belt 31 in the initial operation. It shows how the phototransistor 202 receives the light emitted by the LED 201 and reflected by the pattern 203 or the transfer belt 31.

Registration correction pattern 203
Before the output, the intermediate transfer belt 31 is rotated once to receive the reflected light amount signal of the intermediate transfer belt 31 from the photosensors 60 and 61 by the light receiving unit 807, and after the predetermined amplification by the operational amplifier 401, the light receiving unit analog signal. As CPU8
01 AD input terminal. The CPU 801 samples the reflected light amount value of the intermediate transfer belt 31 input to the AD input terminal to detect the peak value. As a result, the minimum value of the amount of reflected light including stains and scratches on the intermediate transfer belt 31 can be obtained. Next, the CPU 801 determines that the intermediate transfer belt 31 obtained previously for the electronic volume 406.
A value offset by a predetermined level from the minimum value of the reflected light amount is set as a threshold value (0.5 V in this embodiment). Further, the CPU 801 emits laser light when outputting the registration correction pattern 203 of the laser so that the reflected light amount value is offset (0.5 V in this embodiment) by a predetermined level lower than the threshold value obtained earlier to the laser driver 808. The light amount is set to control the density of the registration correction pattern 203 (see FIG. 3B). At this time, by using a lookup table corresponding to the amount of laser light and the amount of reflected light of the registration correction pattern 203 as shown in the graph of FIG. 6, the CPU determines whether the controlled pattern density and the amount of laser light are in proper ranges.
801 detects.

In FIG. 6, the relationship between the ideal laser light amount and the pattern density is shown by a thick line and the upper and lower limits of the pattern density with respect to the laser light amount are shown by a thin line. The lower limit of the pattern density is determined in consideration of the actual transfer belt condition, but in this embodiment, it is set to ± 0.2 V with respect to the ideal solid line.

The sensor output is an analog output of 0-5V, but linearity cannot be obtained near 0 and 5V, so the concentration adjustment range is set to 1.5V to 3.5V. Further, the light amount of the laser is controlled by the CPU 801 to the laser driver unit 808 by 8-bit data.

Here, the CPU 801 determines whether or not the pattern density and the laser light amount are in appropriate ranges as follows. As an example, the proper pattern density is set to 3V, and the laser light amount setting when the pattern density is properly controlled is set to 140.
And When a proper laser light amount range when the laser light amount is 140 is obtained by using a look-up table like the graph of FIG. 6, it becomes a range of 2V ± 0.2V as shown in FIG. In this case, even if the light amount is increased, the reflected light amount does not follow and fall, so an error is displayed as an abnormality of the sensor.

Next, the registration correction operation sequence will be described with reference to the flowchart of FIG. CPU
801 performs the registration correction operation at the timing when image formation can be performed, for example, when the power of the image forming apparatus is turned on or after a predetermined time has passed since the power was turned on. When the registration correction operation starts, the CPU 801 determines in f701 whether or not to perform the initial operation. The initial operation may be performed every time the registration correction operation is performed, or may be performed only at a predetermined timing such as only the registration correction operation performed after the power is turned on and the door is opened and closed. When performing the initial operation, the intermediate transfer belt 31 is rotationally driven at f709, and the sensor LED 201 is turned on at f710. After that, the reflected light amount when the intermediate transfer belt 31 is driven to rotate once at f711 is sampled at the AD input port of the CPU 801, and the minimum reflected light amount is obtained. Then f71
The LED 201 is turned off at 2, and at f713, the CPU 801 obtains the set value of the electronic volume so that the threshold becomes 0.5V lower than the minimum reflected light amount of the intermediate transfer belt 31 obtained at f711, and further 0.5V from the threshold. The laser driver 808 obtains the set value of the emitted light amount of the laser so that the reflected light amount is low. After that, the registration correction operation from f703 is sequentially performed. When the initial operation is not performed, the intermediate transfer belt 31 is rotationally driven at f702, and then the registration correction operation from f703 is sequentially performed.

Next, the registration correction operation from f703 will be described. After the laser light amount and the threshold value obtained in the initial operation are set in f703, the registration pattern image writing is started in f704. The registration pattern image written on the transfer belt is the photosensors 60 and 6.
LED 201 is turned on before passing 1 (f70
5) At f706, the pattern detection operation is started.

At f706, as described above, the signals from the photosensors 60 and 61 are passed through the light receiving circuit 807 and the pattern width shaping section 804 for shaping the pattern width, thereby eliminating false detection signals due to scratches or stains. The pattern width and position are sequentially stored in the registers D to S shown in the pattern width & position storage unit (register) 805. At f707, the LED 201 is turned off, the rotational driving of the intermediate transfer belt 31 is stopped, and the pattern interval detection operation ends. Next, in f714, the CPU 801 determines whether or not the sequentially sampled pattern densities are within the proper range with respect to the set laser light amount, and if there are three or more that exceed the proper range, the CPU 801 proceeds to f715. Display an error message. If the number is two or less, the operation proceeds to f708, where the image signal to be recorded is electrically corrected based on the data stored in the register, the table stored in the ROM 806, etc., and is provided in the laser beam optical path. The folding mirror 16a is driven to correct the optical path length change or the optical path change, and the registration correction operation is completed.

For example, when the cashier pattern image as shown in FIG. 2 is read, the cashier pattern is stored. The photosensor 60 reads the pattern 501 based on the registration pattern output obtained by reading the pattern 501.
Position data and width data of registers D, E, F, G
To store. Similarly, based on the registration pattern output obtained by reading the patterns 502-504, the pattern 50
The position data and width data of 2 to 504 are stored in H to S.

Although the registration correction method in the intermediate transfer method (collective transfer method) using the intermediate transfer belt has been described in this embodiment, it is needless to say that the method is also effective in the multiple transfer method using the transfer material conveying belt. Nor.

[0038]

[Embodiment 2] In Embodiment 1, the means for changing the light emission amount of the laser in order to change the density of the registration detection pattern is taken as an example. However, in the system in which the recording density can be changed by PWM driving of the laser, the density is changed. The same effect can be obtained by a method of changing the light emission duty of the laser.

[0039]

As described above, before the registration correction is performed, the intermediate transfer belt is rotated once to detect the reflected light amount of the intermediate transfer belt, and the density of the registration correction detection pattern is optimized. The abnormal toner consumption and the contamination of the sensor due to the toner can be reduced by adjusting the laser light amount and the pattern density output within the proper range.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a color image forming apparatus.

FIG. 2 is a diagram showing a registration correction pattern image.

3A and 3B are diagrams showing an output when a pattern of the photo sensor of the present embodiment is read.

FIG. 4 is a flowchart of registration correction operation according to this embodiment.

5A is a diagram showing a control unit in the present embodiment, and FIG. 5B is a diagram showing a pattern width & position storage unit.

FIG. 6 is a diagram showing a relationship between a laser light amount and a pattern reflected light amount in this embodiment.

FIG. 7 is a diagram illustrating a light receiving circuit that receives an output of a photo sensor.

FIG. 8 is a diagram showing how a photo sensor reads a pattern on a transfer belt.

FIG. 9 is a diagram showing an output when a pattern of a photo sensor is read.

[Explanation of symbols]

A Primary transfer plane P Recording material Ta to Td Image transfer area (Primary transfer area) Te Secondary transfer area 1P Image output section 1R Image reading section 10 Image forming section 11a to 11d Photosensitive drum 12a to 12d Primary charger 13a to 13d Optical Units (optical system) 14a to 14d Developing devices 15a to 15d Cleaning devices 16a to 16d Folding mirror 20 Paper feeding units 21a and 21b Cassettes 22a and 22b Pickup rollers 23 Paper feeding roller pairs 24 Paper feeding guides 25a and 25b Registration rollers 26 Pickup rollers 27 Manual Feed Tray 30 Intermediate Transfer Unit 31 Intermediate Transfer Belt (Transfer Belt) 32 Drive Roller 33 Tension Roller 34 Driven Rollers 35a to 35d Primary Transfer Charger 36 Secondary Transfer Roller 40 Fixing Unit 41a Fixing Roller 41b Fixing Roller Roller 43 pressed by 41a Guide 44 Inner sheet discharge roller 45 Outer sheet discharge rollers 46, 47 Fixing heat insulating cover 48 Sheet discharge tray 50 Cleaning unit 51 Blade 52 Waste toner box 60, 61 Photo sensor 70 Control unit 201 LED 202 Photo Transistor 203 Registration correction pattern (pattern) 401 Operational amplifier 402, 403, 404, 407 Resistor 405 Comparator 406 Electronic volume 501, 502, 503, 504 Pattern 801 CPU 802 Motor driver 803 RAM 804 Pattern width shaping section (pattern forming section) ) 805 Pattern width & position storage section (register) 806 ROM 807 Light receiving circuit (light receiving section) 808 Laser driver

Continued front page    F term (reference) 2H027 DE02 DE07 EB06 EC03 EC06                       ED04 EE07 EK03 GA30 HA01                       HA12 ZA07                 2H030 AA01 AB02 AD16 BB02 BB16                       BB42 BB44 BB56                 2H200 FA04 GA12 GA23 GA34 GA44                       GA47 GB22 HB12 HB14 HB22                       JA02 JB06 JB10 JC03 JC07                       JC12 JC15 JC20 MA04 PB16                       PB39

Claims (4)

[Claims] 1. A plurality of image forming means for forming a visible image (toner image) on a photoconductor by an electrophotographic method or an electrostatic recording method, and a drive roller which is close to the image forming means and transmits rotational drive. And a pattern detection sensor including an endless belt stretched and driven by at least one driven roller, and a light emitting element and a light receiving element for reading a predetermined pattern image formed on the endless belt by the plurality of image forming means. And a sensor configured to output a pattern detection signal when an output value corresponding to the amount of reflected light received by the light receiving element of the pattern detection sensor is equal to or more than a threshold value, and a density changing means for varying the output density of the predetermined pattern image. And a resist for electrically or mechanically correcting the registration of each image forming means based on the pattern detection signal. A rotation correction means and a display means for displaying an error message, and the endless belt is rotated once as an initial operation for detecting the amount of reflected light including scratches and dirt on the endless belt before performing the registration correction. The amount of reflected light of the endless belt is read by the pattern detection sensor, and the output density of the predetermined pattern image is changed according to the output signal of the pattern detection signal at that time or the amount of reflected light received by the light receiving element of the pattern detection sensor. In the image forming apparatus, it is determined whether or not the output of the reflected light amount of the pattern image is within a predetermined range, and an error message is displayed when the pattern image exceeding the predetermined range is detected a predetermined number of times. An image forming apparatus characterized by the above. 2. The endless belt having a threshold value changing means and performing a scratch detection operation for detecting scratches or stains on the endless belt before performing the registration correction.
The image forming apparatus according to claim 1, wherein the pattern detection sensor is rotated to read the reflected light amount of the endless belt, and the threshold value is changed according to an output signal of the pattern detection signal at that time. 3. The image forming apparatus according to claim 1, wherein the endless belt is used as a transfer material conveying unit. 4. The image forming apparatus according to claim 1, wherein the endless belt is used as an intermediate transfer belt.