JP2003098795A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent erroneous detection of a color slurring correction pattern detection sensor constituted by using a light emitting element and a light receiving element caused by scratch and staining on a transfer belt. SOLUTION: This image forming apparatus having a plurality of image forming parts is provided with a plurality of thresholds in the detection sensor constituted by using the light emitting element and the light receiving element in order to detect color slurring, and is equipped with a step for operating the detection means without writing a correction pattern, a means for deciding whether or not erroneous detection output caused by the scratch and the staining on the transfer belt is found as the result of the step, a means for selecting and switching the threshold at which the erroneous detection is prevented when the erroneous detection is found, and a means for controlling timing to operate the above-mentioned means.

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 electrostatic system, an electrophotographic recording system, or the like, and more particularly to detecting registration deviation between four colors occurring in an image forming apparatus having a plurality of image forming units. The present invention relates to an image forming apparatus having a sensor that has a function to automatically correct registration deviation.

[0002]

2. Description of the Related Art Conventionally, a photosensitive drum is irradiated with laser beam light modulated according to recorded information or light emitted from a light emitting element such as an LED to develop an electrostatic latent image on a photosensitive member by 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 such as multiple transfer of each image and then batch transfer 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, and a warp due to the ambient temperature of the LED. Further, the registration of each color image becomes inconsistent on the transfer material finally subjected to multiple transfer. For this reason, conventionally, a registration correction pattern image formed on the transfer belt from each photosensitive drum is read by a CCD sensor or the like, a registration deviation corresponding to each color is detected, and automatic correction is performed.

As described above, in the conventional image forming apparatus, an expensive CCD sensor is used to detect the registration deviation, and the correction pattern is read as an image. Therefore, it was possible to distinguish the pattern from the scratches or stains on the transfer belt.

[0005]

However, in the case of detecting a registration deviation as in the image forming apparatus of the present invention using an inexpensive sensor composed of an infrared emitting LED and a PD (photodiode), it is necessary to correct it. One line of the pattern image will be read. The sensor discriminates between the pattern surface and the belt surface based on the difference in the detected voltage due to the difference in the reflectance between the correction pattern (toner) surface and the transfer belt surface with the sensitivity level as the boundary. To generate. Therefore, when there are scratches or dirt on the transfer belt, the sensor generates a detection signal when the detection voltage exceeds the sensitivity level and reaches the pattern detection level area due to the decrease in reflectance due to scratches or dirt. I will end up. The problem is to eliminate the false detection output due to such belt scratches and stains.

[0006]

In the present invention, a plurality of sensitivity levels (threshold values) are provided in the detection means for detecting the deviation of the registration of each color image, and the predetermined level is set before the detection operation step of the detection means. A false detection countermeasure operation step of operating the detection means without forming a correction pattern, a false detection determination means for determining the presence or absence of a false detection output, and a case where there is a false detection output by the false detection determination means In addition, the sensitivity level selection switching control unit can prevent erroneous detection output due to scratches or stains on the transfer belt by the color misregistration correction pattern detection operation by the detection unit.

Further, the timing of performing the erroneous detection countermeasure operation step is switched to a control means for turning on the power of the apparatus, at a predetermined time interval or every predetermined number of times of image formation, and a direction for decreasing the sensitivity above the sensitivity level. Even if it becomes impossible, by providing the means for permitting the image formation in the BK single color, it is possible to provide the apparatus for forming the high quality image without lowering the productivity.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION [First Embodiment] The present invention will be described below based on the embodiments shown in the drawings.

FIG. 1 is a sectional view of an essential part of an image forming apparatus embodying the present invention. The image forming apparatus of the present embodiment is an electrophotographic system, and further, a plurality of image forming units considered to be particularly effective for the present invention are arranged in parallel, and a color image output apparatus adopting an intermediate transfer system is described. Go.

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 (not shown). To be done.

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 surfaces of the photosensitive drums 11a to 11d are given a uniform amount of charge. Then, by the optical systems 13a to 13d, the light beam such as a laser beam modulated according to the recording image signal is passed through the folding mirrors 16a to 16d to the photosensitive drum 11a.
An electrostatic latent image is formed there by exposing it to ~ 11d.

Further, the electrostatic latent images are visualized by the developing devices 14a to 14d which respectively contain four color developers (hereinafter, referred to as toners) of yellow, cyan, magenta and black. Image transfer areas Ta, Tb, Tc for transferring the visualized visible image to the intermediate transfer member,
On the downstream side of Td, the cleaning devices 15a, 15b,
Toner left on the photosensitive drums 11a to 11d without being transferred to the transfer material by 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 27, and pickup rollers 22a and 22b for feeding the recording material P one by one in the cassette or from the manual feed tray.
6, 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 a secondary transfer area of the recording material P in accordance with the image forming timing of the image forming unit. It consists of registration rollers 25a and 25b for feeding to Te.

The intermediate transfer unit 30 will be described in detail. The intermediate transfer belt 31 includes a driving roller 32 that transmits driving force to the intermediate transfer belt 31, a driven roller 33 that follows the rotation of the medium-sized transfer belt 31, and a secondary transfer counter roller that faces the secondary transfer area Te with the belt interposed therebetween. Let it wind around 34. Of these, a primary transfer plane A is formed between the drive roller 32 and the driven 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, primary transfer chargers 35a to 35d are provided on the back of the intermediate transfer belt 31.
Are arranged. A secondary transfer roller 36 is arranged so as to face the secondary transfer counter 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. In addition, on the intermediate transfer belt, the secondary transfer area Te
A cleaning blade 51 for cleaning the image forming surface of the intermediate transfer belt 31 and a waste toner box 52 for storing waste toner are provided downstream of the above.

The fixing unit 40 includes a fixing roller 41a having a heat source such as a halogen heater therein, a pressure roller 41b (which may also have a heat source), and a nip portion of the roller pair. The guide 43 includes a guide 43 for guiding the transfer material P to, and an inner paper discharge roller 44 and an outer paper discharge roller 45 for further guiding the transfer material P discharged from the roller pair to the outside of the apparatus.

The control unit comprises a control board 50 for controlling the operation of the mechanism in each unit, a motor drive board (not shown), and the like.

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

When the image forming operation start signal is issued, first, the transfer material P is sent out from the cassette 21a one by one 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 roller is stopped, and the leading edge of the paper hits the nip portion. After that, the registration rollers start rotating at the timing when the image forming unit starts forming an image. The timing of this rotation timing is set so that the transfer material P and the toner image primarily transferred from the image forming unit onto the intermediate transfer belt coincide with each other in the secondary transfer area Te.

On the other hand, in the image forming portion, 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, has a high voltage. Is applied to the intermediate transfer belt 31 in the primary transfer area Td by the primary transfer charger 35d. 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 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 pairs 41A and 41B and the pressure of the nip. After that, the paper is conveyed by the inner and outer paper ejection rollers 44 and 45, and the paper is ejected to the outside of the machine.

FIG. 2 is a schematic view of the vicinity of the pattern image detecting means 60 for detecting the registration correcting pattern image of the image forming apparatus according to the embodiment of the present invention. The detection unit 60 is configured to include an LED and a PD, is located on the downstream side of the most downstream photosensitive drum 11a in the belt traveling direction among the plurality of photosensitive drums, and is located at the position Sa on the intermediate transfer belt 31. The registration correction pattern image formed on the intermediate transfer belt is read.

Further, as shown in FIG. 3, they are arranged at both ends of the intermediate transfer belt. The correction is performed based on the registration deviation amount detected by the detection unit 60.

FIG. 4 shows the flow until the detection data is generated by the detection means 60. The PD receives the reflected light of infrared light (which may be transmitted light, but will be described as a reflective type below) emitted from the LED to the intermediate transfer belt 31, and the current flowing in accordance with the received light amount is converted into a voltage. Convert.

In this embodiment, when the amount of received light is large, IV
The converted voltage becomes high, and when the reflected light decreases due to the correction pattern (toner) and the received light amount decreases, the IV change voltage becomes low. After the IV conversion, the peak hold circuit on the high voltage side and the low voltage side holds the highest voltage (detects the highest reflectance on the belt surface) and the lowest voltage (detects the lowest reflectance on the correction pattern surface). Then, the held voltage is divided by a resistor to set a slice level (sensitivity level). This set slice level and PD
A voltage value after the & IV conversion circuit is compared by a comparator, and a detection signal pulse is generated when the PD output is lower than the slice level.

FIG. 5 shows the waveform after IV conversion when the sensor detects the correction pattern. The relationship between the output level and the slice level when the sensor detects the belt surface and the correction pattern surface must be as shown in the figure. The area from the belt detection level to the slice level is called a belt detection area, and the area from the slice level to the correction pattern detection level is called a pattern detection area.

FIG. 6 shows a slice level adjusting circuit diagram according to the first embodiment of the present invention. It is assumed that this slice level adjusting circuit is outside the sensor unit. In this example, five slice levels are provided, and the slice level changes depending on the voltage division ratio by the resistance. A method for determining whether or not there is an erroneous detection due to a belt scratch or stain and controlling the switching of a plurality of slice levels will be described below.

First, the detection means is operated without forming the registration correction pattern in the erroneous detection countermeasure mode. That is, the intermediate transfer belt is idled without forming a correction pattern, and whether or not there is an erroneous detection output due to uneven reflectance on the belt surface is detected by the registration deviation detection sensor. Further, the low voltage side peak hold value and the slice level SHD during the normal detection operation are stored in the memory d4.
Memorized in. This is updated every time and the latest value is stored.

Whether or not there is a previous false detection output is determined by comparing the slice level SHDM stored in the memory d4 with the low voltage side peak hold value LV in the false detection countermeasure mode by the comparator d3. When the peak hold value LV is lower than the slice level SHDM, the pulse output VC is generated by the comparator d3. At this time, the arithmetic control unit d6 determines that erroneous detection due to belt scratches or stains will occur at this slice level. If the pulse output VC is not generated, the arithmetic control unit d6 determines that there is no false detection, and does not change the slice level,
Perform normal detection operation. When it is determined that there is an erroneous detection, the calculation control unit performs the following calculation and selects the slice level.

First, the ratio of the maximum fluctuation amount of the belt detection level is calculated.

[0032]

[Equation 1]

Next, although it is possible to set five slice levels by the resistors R1 to R6 in FIG. 6, the ratio of the belt detection area shown in FIG. 5 which is determined by these slice levels will be described below.

When S1 is ON,

[0035]

[Equation 2]

When S2 is ON,

[0037]

[Equation 3]

When S3 is ON,

[0039]

[Equation 4]

When S4 is ON,

[0041]

[Equation 5]

When S1 to S4 are OFF,

[0043]

[Equation 6]

The ratio of the belt detection area of SH1 to SH5 and the ratio of the maximum fluctuation amount of the belt detection level of (1) are compared, and the smallest one of the ratios of the belt detection areas larger than (1). And a new slice level is set by switching the switches from S1 to S4 by the decoder d5. The above is the operation in the false positive countermeasure mode,
FIG. 7 shows the flow of the false detection countermeasure mode described above.
It is a flowchart of.

[0045]

As described above, according to the present invention, the sensor for detecting the color misregistration is provided with a plurality of sensitivity levels (thresholds) serving as a boundary between the belt detection area and the pattern detection area, and these levels are selectively switched. As a result, it is possible to perform a color misregistration detection operation with high accuracy and without false detection output.

As a countermeasure against erroneous detection, control is performed such that it is performed only when the power is turned on, or every time a predetermined number of times of image formation has been performed for a certain predetermined time interval, or the sensitivity level cannot be switched. If this happens, the color misregistration correction accuracy of the color image will no longer be guaranteed, so the color image forming function will stop, but enabling high-quality images without reducing productivity by allowing image formation in BK single color A device for forming can be provided.

[Brief description of drawings]

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

FIG. 2 is a schematic view of the vicinity of a sensor 60 that detects a registration correction pattern in the present embodiment.

FIG. 3 is a top view of the vicinity shown in FIG.

FIG. 4 is a block diagram of a circuit near a correction pattern detection unit.

FIG. 5 is a diagram showing an output waveform when a pattern is detected by a correction pattern detection unit.

FIG. 6 is a block diagram of a slice level adjustment circuit unit of a correction pattern detection unit.

FIG. 7 is a diagram showing a flow of operations in the false detection countermeasure mode.

[Explanation of symbols]

11a, 11b, 11c, 11d Photosensitive drum 12a, 12b, 12c, 12d Primary charger 13a, 13b, 13c, 13d Optical system 14a, 14b, 14c, 14d Developing device 16a, 16b, 16c, 16d folding mirror

Continuation of front page (51) Int.Cl. ⁷ Identification symbol FI theme code (reference) G03G 21/00 510 G03G 21/00 510 F term (reference) 2H027 DA38 DA45 DE02 DE07 DE09 EB06 EC03 EC06 EC18 ED06 ED17 EE01 EF01 EF12 EK11 GB07 HA14 ZA07 2H030 AB02 AD16 BB02 BB16 BB42 BB56 BB63 2H200 FA04 FA13 GA12 GA23 GA34 GA47 GB11 GB22 GB25 HA02 HB12 HB14 JA02 JA23 JA25 JC03 JC07 JC12 JC19 JC20 LB02 LB09 LB13 PA13 PA20 PA13 PA20 PA20 PA20

Claims (8)

[Claims] 1. A plurality of image forming portions for forming a visible image (toner image) on a photoconductor by an electrophotographic method or an electrostatic recording method, and a driving roller which is close to the image forming portions and transmits rotational drive. And an endless belt that is stretched and driven by at least one driven roller, and a correction that forms a predetermined pattern image on the endless belt that faces the endless belt and that detects registration deviation on the endless belt. A pattern forming unit, a detecting unit that detects the correction pattern image by a sensor unit that includes a light emitting element and a light receiving element, and a registration deviation of each image forming unit is calculated based on the result of the detecting unit. In an image forming apparatus having a correction unit that electrically or mechanically corrects, scratches or stains on the endless belt, the The detection means is provided with a plurality of sensitivity levels (thresholds) in order to prevent the detection means from making an erroneous detection due to a decrease in the light emission amount of the light emitting element in the unit An image forming apparatus comprising a sensitivity level selection control means for selecting one of the above. 2. The image forming apparatus according to claim 1, wherein the set values of the plurality of sensitivity levels are the detection voltage 1 when the detection unit detects a predetermined correction pattern image and the endless belt. The detection voltage 2 is determined by a ratio obtained by dividing the detection voltage 2 by a plurality of resistors, and the sensitivity level is selected by switching the resistors. 3. The image forming apparatus according to claim 1, further comprising an erroneous detection countermeasure operation step of operating the detection unit without forming the predetermined correction pattern before the detection operation step of the detection unit, It is characterized by including erroneous detection determining means for determining the presence or absence of a detection output, and sensitivity level selection control means for selectively controlling another sensitivity level when the erroneous detection determining means determines that there is an erroneous detection output. Image forming apparatus. 4. The image forming apparatus according to claim 3, wherein the operation in the false detection countermeasure operation step is performed only when the power of the image forming apparatus is turned on. 5. The image forming apparatus according to claim 3, wherein the erroneous detection countermeasure operation step is performed every predetermined time. 6. The image forming apparatus according to claim 3, wherein the timing of performing the operation step is every time image formation is performed a predetermined number of times. 7. The image forming apparatus according to claim 3, wherein sensitivity is lowered when sensitivity level selection control is performed,
An image forming apparatus comprising: means for displaying some abnormality information when the sensitivity cannot be lowered below the sensitivity level in the situation where the determination means determines that there is an erroneous detection output. 8. The image forming apparatus according to claim 3, wherein the sensitivity is lowered when the sensitivity level is selectively controlled.
In a situation in which it is determined that there is a false detection output by the determination means, if the sensitivity cannot be reduced below the sensitivity level in the situation,
An image forming apparatus, which displays some abnormal information, but does not stop the apparatus, and is capable of forming an image in a single black color.