JP5640755B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, a plotter, and a multi-function machine provided with at least one of these, and more specifically, by developing a latent image formed on an image carrier. The present invention relates to an image forming apparatus that makes a visible image and obtains a multi-color image by superimposing a plurality of visible images.

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, an image forming apparatus using an endless belt as an intermediate transfer member that is a transfer medium or a recording sheet that is a transfer medium is known.
The belt is stretched between a plurality of rollers and driven to circulate. At this time, the belt position moves in a direction perpendicular to the belt conveyance direction (hereinafter referred to as “main scanning direction”), and belt conveyance. A “belt skew” in which the direction is inclined in the main scanning direction may occur.
When the belt skew occurs, the image forming position on the transfer medium such as the intermediate transfer member or the recording paper is displaced, which causes image distortion.

Also, monochrome images of black (hereinafter referred to as “K”), yellow (hereinafter abbreviated as “Y”), magenta (hereinafter abbreviated as “M”), and cyan (hereinafter abbreviated as “C”). In a color image forming apparatus that forms each image and superimposes them on a transfer medium to obtain a color image, a shift in image forming position appears as a color shift between the color toner images.
All of these lead to degradation of image quality, and it is necessary to take some measures for the belt skew in order to obtain a high-quality image.

  In order to cope with the above problem, various methods have been proposed, and one of them is a method of providing a guide member near the endless belt. However, the force in the main scanning direction generated on the endless belt is regulated by abutting a guide member provided on the belt surface against the end surface of the belt conveying roller to suppress the deviation of the endless belt. Belt skew due to the main scanning direction shake of the guide member and the end face of the conveying roller cannot be suppressed, and there is a defect that image distortion and color misregistration occur due to positional deviation in the main scanning direction.

On the other hand, in Patent Document 1, in a system in which the deviation of the belt is regulated by a deviation guide member provided on the belt, the latent image formed on the image carrier is based on a meandering component for one period of the belt measured in advance. A configuration for controlling the position is described.
Further, as a method other than providing a guide member near the endless belt, the method described in Patent Document 2 is known. In this document, a skew detection means for detecting that the endless belt is conveyed in a state inclined with respect to the conveyance direction, and a skew detection when the skew detection of the endless belt is detected by the skew detection means. A configuration is described in which image distortion is corrected by the image forming means based on the skew amount of the endless belt detected by the means.
In Patent Document 3, a plurality of belt position detecting means and belt main scanning direction displacement detecting means are arranged in a plane for transferring a visible image on an image carrier, and main scanning detected by each belt position detecting means. Based on each direction position information and each main scanning direction displacement information detected by each belt main scanning direction displacement detecting means, the latent image forming position correcting means corrects the main scanning direction latent image forming position on the image carrier. The configuration is marked.

By providing a guide member near the endless belt as described above, belt slippage is suppressed and the influence of belt meandering that cannot be suppressed by the guide member is suppressed by controlling the latent image forming position on the image carrier. The method has the following problems.
In Patent Document 1, since the meandering component for one belt period including the belt conveyance roller end face runout and the main scanning direction runout of the shift guide member is measured in advance, belt meandering due to runout of both the roller end face and the guide member is suppressed. However, in order to cope with the deformation of the endless belt and the side guide member over time and the deformation due to environmental changes such as temperature and humidity, it is necessary to frequently measure the meandering component, and frequently perform the image forming operation. Therefore, the image output speed is greatly hindered. There is also a problem that it is difficult to cope with dynamic deformation due to the influence of vibration or the like.

Further, in the method of suppressing the belt deviation by providing the deviation guide member on the endless belt, when the belt is driven at a high speed, a large external force is applied to the deviation guide member, and the belt and the deviation guide member are buckled or damaged. It is easy to invite and it is difficult to speed up image output.
On the other hand, in Patent Document 3, in which a latent image forming position on an image carrier is controlled by detecting a belt skew without providing a guide member on the endless belt, a belt position detecting unit and a belt main scanning direction are disclosed. Since it is necessary to arrange a plurality of displacement detection means and to provide a signal processing unit for estimating the belt movement trajectory based on the detection signal of each detection means, an increase in apparatus cost is avoided due to these factors. I can't.

Further, the method described in Patent Document 2 has the following problems.
As a first method for detecting the skew of the belt, a method using a control signal of the steering roller is shown, but the steering roller adjusts the inclination so that each part on the belt always passes through the same position after one round. Thus, the belt deviation is corrected, and what kind of skew occurs between the rollers during one round is determined by the inclined state of each roller. For this reason, the skew of the belt on the image transfer surface from the image carrier that affects image distortion and color misregistration is not determined only by the inclination of the steering roller. If a roller other than the steering roller is tilted due to temperature fluctuations, temporal fluctuations, etc., the belt skew cannot be accurately detected by the steering roller control signal, and accurate correction is impossible.

  On the other hand, as a second method for detecting the belt skew, a method for forming a mark for image position detection in a non-image area located between the image areas of the intermediate transfer belt and detecting it by the mark detection means is shown. However, in order to form the image position detection mark, it is necessary to develop the mark latent image formed on the image carrier with toner and transfer it onto the intermediate transfer belt. There is a problem that the toner is consumed and the image forming cost increases. Further, while a normal image is transferred from the intermediate transfer belt to a recording material such as paper, the image position detection mark needs to be removed by a cleaning member without being transferred, and the load of cleaning the intermediate transfer belt is increased. Increases and causes cleaning failure.

Further, as a third method for detecting the belt skew, a method for detecting belt edges at a plurality of positions in the belt conveyance direction of the image transfer surface from the image carrier is shown. In order to detect the belt edge, it is necessary to arrange a plurality of belt edge sensors which only need to be arranged, which increases the cost.
In addition, it is difficult to arrange a plurality of belt edge sensors in the belt conveyance direction of the image transfer surface on which a plurality of image carriers are arranged for creating a full-color image. And increase costs. Further, in order to detect the skew of the belt from the signals of the two edge sensors, a signal processing circuit for processing each signal is required. Due to these factors, an increase in apparatus cost is inevitable.

  The present invention has been made in view of the above problems, and can greatly increase the speed of image output without using a configuration that obstructs high-speed belt driving, such as a shift guide member, and is simple and low-cost. With this simple structure, the movement (shift) of the endless belt in the main scanning direction can be accurately detected and corrected, and the skew of the endless belt can be accurately detected to reliably correct the image forming position of the image carrier. Accordingly, it is an object of the present invention to realize an image forming apparatus that can prevent image distortion and color misregistration due to positional deviation in the main scanning direction and can greatly improve the image quality of an output image.

  In order to achieve the above object, the invention described in claim 1 makes an image carrier, latent image forming means for forming a latent image on the image carrier, and visualizing the formed latent image. A developing unit; an intermediate transfer member that primarily transfers a visible image formed on the image carrier; and a secondary transfer unit that transfers a transfer image on the intermediate transfer member to a recording material. The body is an intermediate transfer belt composed of an endless belt member stretched between a plurality of substantially parallel rollers, and visible images formed on a plurality of image carriers are sequentially placed on the intermediate transfer belt. An image forming apparatus for forming a multi-color image by transferring to a belt, belt misalignment correcting means for correcting a positional deviation of the intermediate transfer belt in the main scanning direction, and image formation in the main scanning direction on the intermediate transfer belt. An image forming position correcting means for correcting a positional shift; Belt deviation detecting means for detecting a positional deviation in the main scanning direction of the intermediate transfer belt, and based on the positional deviation information detected by the belt deviation detecting means, the belt deviation correcting means uses the belt deviation correcting means. In the image forming apparatus that corrects the positional deviation in the scanning direction, the belt deviation detecting unit emits a parallel light beam parallel to the belt sub-scanning direction on the belt surface on which the visible image is transferred on the intermediate transfer belt. And at two positions in the belt sub-scanning direction, abut against the end of the belt surface, respectively, and move in the same direction according to the movement of the intermediate transfer belt in the main scanning direction. A light-shielding portion having a different light-shielding direction for the parallel light flux, and a light-receiving portion for receiving the parallel light flux after the light shielding by the two light-shielding portions. Detecting a belt shift by detecting a change in the light receiving position of the parallel light beam caused by shielding the parallel light beam, and detecting a belt inclination on the belt surface by a change in the received light amount of the parallel light beam, The image forming position in the main scanning direction on the intermediate transfer belt is corrected based on the detected belt inclination.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the light receiving unit is configured by a solid-state image sensor, and a change in a light receiving position and a received light amount are determined by an output signal of the solid-state image sensor. According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the light receiving unit is configured by an optical position detection element, and an output of the optical position detection element. A change in the light receiving position and a change in the amount of received light are detected by the signal.
According to a fourth aspect of the present invention, in the image forming apparatus according to the first aspect, the light receiving unit includes a light receiving element that divides the light receiving region into two in the moving direction of the light blocking unit, and includes two light receiving regions. A change in the amount of received light is detected by the sum of the detection signals, and a change in the light reception position is detected by a difference in the detection signals.

According to a fifth aspect of the present invention, in the image forming apparatus according to the first aspect, the two light shielding portions have a configuration of a slit grating composed of a light shielding region and a transmission region having a constant interval. And
According to a sixth aspect of the present invention, in the image forming apparatus according to the fifth aspect, the slit width of the slit grating is at least four times the necessary detection range of the movement of the intermediate transfer belt in the main scanning direction due to belt inclination. It is characterized by that.
According to a seventh aspect of the present invention, in the image forming apparatus according to the first aspect, each of the two light shielding portions includes a light shielding member that shields the parallel light flux, and a detection member that contacts an end portion of the belt surface. The light shielding member and the detection member have a rotation support member for rotating in accordance with the movement of the intermediate transfer belt in the main scanning direction, and the rotation radius with respect to the rotation support member is greater than the detection member. The light-shielding member is larger.

According to an eighth aspect of the present invention, in the image forming apparatus according to the seventh aspect, the rotational force about the rotation support member generated by gravity is in a direction in which the detection member abuts against an end of the belt surface. It is characterized by being.
The invention according to claim 9 is the image forming apparatus according to any one of claims 1 to 8, wherein the parallel light beam emitted from the light source unit is shielded by the two light shielding units. The optical axis is folded 180 degrees by the reflecting means, and is incident on the light receiving unit installed integrally with the light source unit.
According to a tenth aspect of the present invention, in the image forming apparatus according to the ninth aspect, the reflecting means is a corner cube prism.

According to the present invention, it is possible to significantly increase the image output speed without using a configuration that obstructs high-speed belt driving such as a shift guide member, and it is possible to accurately detect the endless belt with a configuration with a large degree of layout freedom. Since the shift and skew can be detected, the apparatus can be reduced in size and cost.
In addition, the belt deviation is surely corrected based on the detected deviation information, and the image formation position of the intermediate transfer belt is reliably corrected based on the detected skew information, so that image distortion and color deviation due to misregistration in the main scanning direction are achieved. Therefore, the output image can be greatly improved in image quality.

According to the second aspect of the present invention, it is possible to accurately detect the shift and skew of the endless belt with a simple configuration, so that the apparatus can be downsized.
According to the third aspect of the present invention, since it is possible to detect the endless belt shift and skewing at high speed and high accuracy, high image quality can be achieved.
According to the fourth aspect of the present invention, the endless belt shift and skew can be detected with high accuracy with a low-cost configuration, so that the cost of the apparatus can be reduced and the image quality can be improved.
According to the fifth aspect of the present invention, since it is possible to detect the deviation and skew of the endless belt with high accuracy, it is possible to improve the image quality.
According to the sixth aspect of the invention, since the endless belt shift and skew can be detected with high accuracy and reliability, high image quality and improved reliability can be achieved.
According to the invention described in claim 7, 8, 9 or 10, since it is possible to detect the deviation of the endless belt and skewing with high accuracy with a simple, space-saving and high-strength configuration, the apparatus can be reduced in size and cost. Image quality and reliability can be improved.

1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention. FIG. 4 is a perspective view illustrating a driving configuration and a supporting configuration of an intermediate transfer belt. It is a perspective view for demonstrating belt skew feeding and the problem by it. It is a block diagram of an image formation position correction means. It is a perspective view of a belt deviation detection means. It is a figure which shows the change of the position of the light beam which light-receiving part injects, and the change of received light quantity. It is a figure which shows the change of the position of the light beam which the light-receiving part injects in 2nd Embodiment, and the change of received light quantity. It is a perspective view of the belt deviation detection means in the third embodiment.

Embodiments of the present invention will be described below with reference to the drawings. First, a first embodiment will be described with reference to FIGS.
FIG. 1 shows the configuration of an image forming apparatus according to this embodiment. FIG. 1 is a schematic configuration diagram showing a main part of a so-called tandem type image forming apparatus that uses four photosensitive drums provided with developing devices in parallel and forms a full-color image on an intermediate transfer belt.
In this image forming apparatus, at the time of image formation, four image carriers (hereinafter referred to as “photosensitive drums”) 101, 102, 103, 104 are rotationally driven in an arrow direction (counterclockwise direction), and the surface thereof is charged. After being uniformly charged by 111, 112, 113, and 114, exposure is performed in accordance with input image information by exposure devices 121, 122, 123, and 124 as latent image forming means to form an electrostatic latent image. . The latent image forming means may be formed integrally without forming each color individually.
The yellow developing unit 131 attaches toner to the electrostatic latent image on the photosensitive drum 101 and develops it as a yellow toner image, and the magenta developing unit 132 attaches toner to the electrostatic latent image on the photosensitive drum 102. The toner is developed as a magenta toner image, the toner is attached to the electrostatic latent image on the photosensitive drum 103 by the cyan developing device 133 and developed as a cyan toner image, and the electrostatic image on the photosensitive drum 104 is developed by the black developing device 134. Toner is attached to the latent image and developed as a black toner image.

The yellow toner image, magenta toner image, cyan toner image, and black toner image are in contact with the photosensitive drums 101, 102, 103, and 104 on the intermediate transfer belt 200 as an intermediate transfer member that rotates in the direction of the arrow. The toner image is primarily transferred to the toner image and superimposed as a four-color toner image. The primary transfer is performed by a primary transfer roller (no numbering) facing the photosensitive drum with the intermediate transfer belt 200 interposed therebetween.
These four color toner images are secondarily transferred by the secondary transfer roller 222 to the recording material P conveyed from a paper feed cassette (not shown), whereby a full color image can be obtained.
In FIG. 1, reference numeral 220 denotes a registration roller pair, 221 and 224 denote paper conveyance guides, 223 denotes a belt conveyance device, 225 denotes fixing means, and 226 denotes a paper discharge roller pair.

FIG. 2 shows a support structure of the intermediate transfer belt 200 and a belt deviation correction unit.
The intermediate transfer belt 200 is stretched by a plurality of substantially parallel rollers, and is driven in the belt conveyance direction by one drive roller 211 among them. While the driving roller 211 and the driven rollers 212 and 213 are fixed at predetermined positions, both ends of the rotation shaft of the tension roller 214 are urged in the direction of the arrow, and the belt is stretched with a substantially constant tension.
The correction roller 215 corrects a shift generated in the intermediate transfer belt 200, that is, a movement (positional deviation) in the main scanning direction. One end of the rotation shaft of the correction roller 215 is a pivot bearing or the like in a direction perpendicular to the roller rotation axis. The other end side is supported so as to be able to reciprocate in the direction of the arrow by an actuator 216 serving as a belt shift correction means.

By driving the actuator 216 based on information from the belt deviation detection means described later, and swinging the correction roller 215 so that the belt moves in a direction opposite to the generated movement (position shift) in the belt main scanning direction, The belt shift is controlled within a certain range, and the belt shift can be suppressed without providing a shift guide member or the like. In FIG. 2, reference numeral 227 denotes a belt drive motor.
Here, the belt conveyance state corrected to the state where there is no belt deviation is shown by a one-dot chain line in FIG.
In FIG. 3, due to the influence of the inclination of each roller that conveys the belt, the intermediate transfer belt 200 is conveyed in a direction inclined at an oblique angle θ as indicated by a solid line on the image transfer surface.
Therefore, the image formed on the image transfer surface is inclined at the skew angle θ, and the transfer position on the intermediate transfer belt of the image formed by each image carrier is displaced in the main scanning direction. That is, image distortion and color misregistration in a color image occur.

As image forming position correcting means for correcting the image forming position in the main scanning direction on the intermediate transfer belt in accordance with the change in the belt skew angle, rollers other than the steering roller are inclined by the same configuration operation as the steering roller. And a method for changing the latent image forming position on the image carrier by providing an optical axis angle changing means in the optical path of the optical writing means for forming a latent image on the image carrier.
Here, when correcting the belt skew by inclining a roller other than the steering roller, the belt skew changes by correcting the belt skew, and the belt skew changes by correcting the belt skew. There is a problem that a high-function control system that performs accurate control is required and the cost increases.
Also, in the case where the optical axis angle changing means is provided in the optical path of the optical writing means, it is necessary to add highly accurate and reliable optical means, and there is a problem that the cost increases.

FIG. 4 shows a latent image forming position correcting unit which is an image forming position correcting unit in the present embodiment.
In FIG. 4, the image signal transferred from the printer driver unit is input to an image signal generation unit that constitutes an image writing control unit. Engine control information from the engine control unit is also input to the image writing control unit.
In the image signal generation unit, the input image signal is subjected to image processing by processing according to engine control information. At this time, in order to actually develop the image on the recording paper, the image signal generation unit performs processing with a pixel clock signal (wclk) that defines the minimum pixel used for image formation.
This pixel clock signal generates a clock signal (wclk) having a predetermined frequency based on information such as the resolution from the engine control unit and the photosensitive drum linear velocity in the pixel clock generation unit, and outputs the clock signal (wclk) to the image signal generation unit and the multiplication circuit unit. Entered. The actual image signal subjected to the image processing by the image signal generation unit is input to the writing position control unit. In addition, the write position control unit includes a synchronization detection signal (DETP) from the synchronization detection unit of the laser writing device, a belt displacement signal (Δa) created by the intermediate transfer belt skew feed information, and engine control information from the engine control unit. Entered.

  The synchronization detection signal (DETP) is a signal for keeping the writing start position in the main scanning direction constant when the laser beam is exposed on the photosensitive drum. This signal is an output signal from the synchronization detection plate arranged outside the scanning region on the photosensitive drum of the laser beam reflected and deflected by the polygon mirror 230 in the laser writing device. And the like, and the synchronization detection sensor photoelectrically converts the incident laser beam and outputs a synchronization detection signal (DETP).

The belt displacement signal (Δa) is a signal indicating the displacement of the intermediate transfer belt in the main scanning direction, and is generated during the belt shift correction by the belt shift correction means in the main transfer direction of the intermediate transfer belt within the image transfer surface. Is a signal calculated from the belt skew information.
The writing position control unit synthesizes the real image signal from the image signal generation unit with the synchronization detection signal (DETP) at a predetermined timing, and generates a signal for driving the semiconductor laser as the light source. At this time, the start timing of writing the actual image signal from the synchronization detection signal is controlled according to the belt displacement signal (Δa). The writing position control unit receives a skew correction clock signal (dclk) obtained by multiplying the pixel clock signal (wclk) generated by the pixel clock generation unit. The skew correction clock signal (dclk) is a signal having a frequency higher than that of the pixel clock signal obtained by multiplying the pixel clock signal (wclk) that defines the minimum pixel capable of forming an image.
The skew correction clock signal (dclk) is a clock signal having a frequency corresponding to the detection resolution of the transfer slit position sensor, and one clock of the skew correction clock signal (dclk) corresponds to one resolution of the belt skew information. doing. A belt displacement signal (Δa) calculated from the belt skew information is detected, and a synchronization detection signal (DETP) and a belt displacement signal (Δa) are input to the writing position control unit.

Assuming that A (= N × wclk) from the synchronization detection signal when the belt displacement signal (Δa) is 0 to the start position of the actual image signal in the main scanning direction, if Δa> 0 is detected, synchronization detection is performed. The delay time from the signal to the actual image writing timing is changed to A + Δa × dclk, and the actual image writing start position is delayed with respect to the case where there is no belt skew. On the other hand, when Δa <0, the delay time is set to A−Δa × dclk, and the actual image writing start timing is relatively accelerated. The laser driving signal synthesized by the writing position control unit is input to the laser driving unit. The semiconductor laser mounted on the laser drive unit is repeatedly driven to turn on / off by turning on / off the laser drive signal.
A laser beam emitted by driving a semiconductor laser is incident on a laser writing device, passes through and reflects a plurality of lenses, mirrors, etc., and travels in the optical path. It is rotationally deflected by a polygon mirror 230 arranged in the middle of the optical path, and a laser beam is exposed on the photosensitive drum in the main scanning direction. The process from this exposure until an output image is obtained is as described above.

In the image forming apparatus as described above, the method for detecting the belt shift and belt skew according to the present invention will be described below.
In FIG. 5, on the outer side in the main scanning direction of the image transfer surface of the intermediate transfer belt 200, a light source unit 301 including a light source 302 such as a semiconductor laser and a collimator lens 303 for converting divergent light emitted from the light source 302 into parallel light. The parallel light beam 304 emitted from the light source unit 301 has an optical axis parallel to the belt sub-scanning direction.
In the belt sub-scanning direction, the two abutting portions are respectively in contact with the end 200a of the belt surface to which the image on the intermediate transfer belt 200 is transferred, and the same according to the movement of the intermediate transfer belt 200 in the main scanning direction. The light shielding portions 311 and 312 are arranged that move in the direction and differ in the light shielding direction of the parallel light flux 304 in the movement direction.

The light shielding portion 311 includes a detection member 311a that contacts the end portion 200a of the intermediate transfer belt 200 on the image transfer surface, a light shielding member 311b that shields the upper side of the parallel light flux 304 in the drawing, and a rotation support portion that rotatably supports these members. 311c.
The light shielding portion 312 includes a detection member 312a that contacts the end portion 200a of the intermediate transfer belt 200 on the image transfer surface, a light shielding member 312b that shields the lower side of the parallel light flux 304 in the drawing, and a rotational support that rotatably supports these members. Part 312c.
The rotation support portion 311c and the rotation support portion 312c are supported by a rotation shaft 313 parallel to the belt sub-scanning direction. Accordingly, the light shielding portions 311 and 312 are supported so as to be rotatable about the rotation shaft 313.
In this embodiment, the detection member 311a, the light shielding member 311b, and the rotation support portion 311c of the light shielding portion 311 are formed as an integral “light shielding detection member”. However, the detection member 311a and the light shielding member 311b are separately formed and synchronized. It is good also as a structure to rotate. The same applies to the light shielding unit 312.
The parallel light beam 304 emitted from the light source unit 301 enters the light receiving unit 305 after being sequentially shielded by the light shielding member 311 b of the light shielding unit 311 and the light shielding member 312 b of the light shielding unit 312.
The light source unit 301, the light shielding units 311 and 312, and the light receiving unit 305 constitute a belt deviation detection unit 300.

Details of the parallel light beam 304 incident on the light receiving unit 305 are shown in FIG.
The cross-sectional shape 304a of the parallel light flux emitted from the light source unit 301 is circular. However, in the light receiving unit 305 that is sequentially shielded by the light shielding units 311 and 312, the light shielding unit 311 causes the light to be shielded by the light shielding unit 311 as illustrated in FIG. The oval shape has an upper side shielded from light and a lower side shielded by the light shielding part 312.
Here, when the intermediate transfer belt 200 is deviated leftward in the drawing in FIG. 5, both the light shielding portions 311 and 312 rotate in the clockwise direction as the belt end moves in the main scanning direction.
Thereby, since both the light shielding members 311b and 312b move upward, the cross-sectional shape of the parallel light flux incident on the light receiving unit 305 moves upward as shown in FIG. 6B. Further, when a belt shift in the right direction in the drawing occurs in the intermediate transfer belt 200, the belt moves downward as shown in FIG.

Next, in FIG. 5, when the intermediate transfer belt 200 is tilted (skewed) in the counterclockwise direction in the drawing, the light shielding portion 311 moves in the counterclockwise direction in accordance with the position change of the belt end in the main scanning direction. , 312 rotate in the clockwise direction. Thereby, since the light shielding member 311b moves downward and 312b moves upward, the cross-sectional shape of the parallel light beam incident on the light receiving unit 305 is reduced in area as shown in FIG.
When the intermediate transfer belt 200 is inclined in the clockwise direction in the drawing (skew), the area increases as shown in FIG.

  As described above, in the configuration of the present invention, the belt shift on the intermediate belt transfer surface can be detected by the change in the position of the parallel beam incident on the light receiving unit 305, and the intermediate can be detected by the change in the amount of received parallel beam incident on the light receiving unit 305. Belt skew on the belt transfer surface can be detected.

In the above configuration, a plurality of light shielding portions 311 and 312 for detecting the main scanning direction of the belt end portion must be arranged in the sub scanning direction of the belt transfer surface, but the movement of the light shielding portions 311 and 312 is converted into an electric signal. Only one set of the light source unit 301 and the light receiving unit 305 as sensor means is required.
Conventionally, when detecting the position in the main scanning direction at two belt end portions, it has been necessary to arrange two detection members and sensor means in the vicinity of the belt transfer surface, whereas in the present invention, the sensor means is arranged on the belt transfer surface. Because it is possible to detect belt skew and skew only by installing one set at a position away from the machine, the flexibility of the device layout is greatly improved, and it is possible to reduce the size and cost of the device by reducing the belt circumference. Become.
Further, since there is only one set of the light source unit 301 and the light receiving unit 305 which are sensor means for converting the movement of the light shielding units 311 and 312 into electric signals, the signal processing circuit for processing signals can be reduced, and the cost of the apparatus can be reduced Is possible.

In the following, modes that can be adopted as the light receiving section are shown.
As shown in FIG. 6, the light receiving unit 305 is a CCD image sensor or the like as means for detecting the position and the amount of received light of the parallel light beam 304a incident on the light receiving unit 305 in the direction corresponding to the movement in the belt main scanning direction. You may comprise by a solid-state image sensor. In this case, by calculating the barycentric position and area of the light receiving region in the light receiving area of the solid-state imaging device at an arbitrary timing, it is possible to detect the position and the amount of received light of the parallel light beam 304a in the belt main scanning movement detection direction. .

The light receiving unit 305 may be configured by a light position detection element (PSD). In this case, unlike solid-state image sensors such as CCD, it is a non-divided type, so it has a feature that it can obtain continuous electric signals and has excellent position resolution and responsiveness. The incident position of the parallel light beam 304a can be detected by setting the direction, and the amount of received light can be detected by detecting the light intensity incident on the PSD.
Further, the light receiving unit 305 may be configured by a light receiving element (PD) in which the light receiving region is divided into two. In this case, the cost is lower than that of a solid-state imaging device or PSD, and as shown in FIG. 6, the light receiving area is divided into two light receiving areas 305a and 305b in the belt main scanning movement detection direction of the parallel light beam 304a by the dividing line 305c. By detecting the incident position of the parallel light beam 304a from the division and the difference between the received light amounts of the respective light receiving areas, differential detection can be performed and highly sensitive position detection is possible.
Here, the received light amount of the parallel light beam 304a can be detected from the sum of the received light amounts of the respective light receiving regions.

A second embodiment will be described with reference to FIG. Note that the same parts as those in the above embodiment are denoted by the same reference numerals, and unless otherwise specified, description of the configuration and functions already described is omitted, and only the main part will be described (the same applies to other embodiments below).
The light shielding members 311b and 312b of the light shielding parts 311 and 312 shown in FIG. 5 are formed into slit gratings 311d and 312d made up of light shielding parts and transmission parts having a constant interval (L) as shown in FIGS. Thus, the following functions and effects can be obtained.
The parallel light beam 304 emitted from the light source unit 301 enters the grating slit 311d formed in the light shielding member 311b of the light shielding unit 311 (see FIG. 7a), and the light beam is transmitted only through the transmission unit.
The light beam transmitted through the grating slit 311d is incident on the grating slit 312d formed in the light shielding member 312b of the light shielding portion 312 (see FIG. 7b). Here, at the center of the belt shift detection range, the lattice slits 312d and 311d in the belt main scanning movement detection direction are adjusted to positions shifted by L / 2. The light beam transmitted through the grating slit 312d enters the light receiving unit 305 (see FIG. 7c), and the width of the transmitted light beam in the belt main scanning movement detection direction is L / 2 at the center of the belt skew detection range.

Here, when the intermediate transfer belt 200 is deviated leftward in the drawing in FIG. 5, both the light shielding portions 311 and 312 rotate in the clockwise direction as the belt end moves in the main scanning direction. Thereby, since both the grating slits 311d and 312d move upward, each transmitted light beam incident on the light receiving unit 305 moves upward as shown in FIG. 7D. Further, when a belt shift in the right direction in the drawing occurs in the intermediate transfer belt 200, the belt moves downward as shown in FIG.
Next, in FIG. 5, when the intermediate transfer belt 200 is tilted (skewed) in the counterclockwise direction in the drawing, the light shielding portion 311 moves in the counterclockwise direction in accordance with the position change of the belt end in the main scanning direction. , 312 rotate in the clockwise direction. As a result, the grating slit 311d moves downward and the 312d moves upward, so that each transmitted light beam incident on the light receiving unit 305 has a reduced area as shown in FIG.
Further, when a belt tilt (skew) in the clockwise direction in the drawing occurs in the intermediate transfer belt 200, the area increases as shown in FIG. A belt shift on the intermediate belt transfer surface can be detected by a change in the position of each transmitted light beam incident on the light receiving unit 305, and a belt skew on the intermediate belt transfer surface can be detected by a change in the amount of received light of each transmitted light beam incident on the light receiving unit 305. it can.

As is apparent from FIG. 6, the change in the amount of light received (light receiving area) of the light receiving unit 305 caused by the change in the belt skew is not linear. On the other hand, in the configuration shown in FIG. 7, the light-shielding members 311b and 312b are lattice slits 311d and 312d, so that the change in the amount of light received (light-receiving area) of the light-receiving unit 305 caused by the change in the belt skew is made closer to linear. This makes it possible to detect skew accurately.
Further, in the method of detecting the light receiving position described above as a differential detection, the belt shift can be detected with high sensitivity, but the belt skew detection sensitivity cannot be improved. In the configuration, the light-shielding members 311b and 312b are lattice slits 311d and 312d, so that a change in the amount of received light due to the belt inclination can be increased, and belt skew can be detected with high sensitivity.

Here, as shown in FIGS. 7D and 7E, when the grating slits 311d and 312d move by L / 4 or more according to the belt, the transmitted light beam at the center exceeds the dividing line 305c. The difference signal between the light receiving areas 305a and 305b does not change.
However, this problem does not pose a problem when the light receiving unit 305 is a CCD or PSD instead of a two-part PD. On the other hand, as shown in FIGS. 7F and 7G, when each of the lattice slits 311d and 312d moves L / 4 according to the belt skew, the direction of the belt main scanning movement detection direction of each transmitted light flux Since the width is 0 or L, the detection range is limited. For this reason, the slit width of the slit gratings 311d and 312d needs to be at least four times the necessary detection range corresponding to the belt main scanning direction movement due to the belt inclination.

As shown in FIG. 5, the detection members 311a and 312a that contact the end of the intermediate transfer belt 200 and the light shielding portions 311 and 312 having the light shielding members 311b and 312b that shield the parallel light flux are rotated by the rotation support members 311c and 312c. It is supported so as to be rotatable about a rotation shaft 313 parallel to the belt sub-scanning direction.
A mechanism that supports the light shielding portions 311 and 312 so as to be movable in accordance with the movement of the belt end is not a parallel movement support mechanism, but a rotation movement support mechanism, thereby simplifying space saving and increasing strength and accuracy. It becomes possible.

In the light shielding portions 311 and 312, the light shielding members 311 b and 312 b that shield the parallel light flux are located at positions where the radial positions from the rotation centers of the rotation support portions 311 c and 312 c are larger than the detection members 311 a and 312 a contacting the belt end. Is formed.
As a result, the movement amounts of the light shielding member 311b and the light shielding portion 312b are larger than the movement amount of the belt end portion, and detection with high sensitivity becomes possible.
Further, in order to always contact the detection members 311a and 312a with the belt end portion 200a, it is usually necessary to add a contact force for bringing the detection members 311a and 312a into contact with the belt end portion by providing a spring mechanism or the like. However, as described above, the light shielding portions 311 and 312 are used as rotational support, and the rotational force about the rotational support portion caused by gravity is set in the direction in which the detection member comes into contact with the belt. The detection members 311a and 312a can be always brought into contact with the belt end portion without being provided.

FIG. 8 shows a third embodiment. In the present embodiment, the parallel light beam emitted from the light source unit 301 is sequentially shielded by the light shielding members 311 b and 312 b, and then the optical axis is turned back 180 degrees by the reflecting unit 306, and the light receiving unit 305 disposed in the vicinity of the light source unit 301. Is incident on.
With the configuration as described above, the light source unit 301 and the light receiving unit 305 can be disposed on an integrated support member, which enables high-precision and high-strength support, simplification of the adjustment mechanism, and space saving. It becomes possible.
In addition, since the electrical wiring to the light source 301 and the light receiving unit 305 can be simplified and the space can be saved, the cost of the apparatus can be reduced.
Here, since the reflecting means 306 is a corner cube prism, it is possible to accurately return the parallel light beam by 180 degrees regardless of the deviation or fluctuation of the reflecting means installation position, thereby improving detection accuracy and reducing adjustment work. The cost can be reduced.

101, 102, 103, 104 Photosensitive drums 121, 122, 123, 124 as image bearing members Exposure devices 131, 132, 133, 134 as latent image forming means Developing means 200 Intermediate transfer belt 216 as an intermediate transfer member Deviation correction unit 222 Secondary transfer unit 300 Belt deviation detection unit 301 Light source unit 305 Light receiving unit 311, 312 Light blocking unit

JP 2005-148127 A JP 2006-276427 A JP 2009-186495 A

Claims (10)

An image carrier, a latent image forming unit that forms a latent image on the image carrier, a developing unit that visualizes the formed latent image, and a visible image formed on the image carrier. An intermediate transfer member for primary transfer; and a secondary transfer unit for transferring a transfer image on the intermediate transfer member to a recording material. The intermediate transfer member is endlessly stretched between a plurality of substantially parallel rollers. An image forming apparatus that forms a multi-color image by sequentially transferring visible images formed on a plurality of image carriers onto the intermediate transfer belt. A belt shift correcting unit that corrects a positional deviation of the intermediate transfer belt in the main scanning direction; an image forming position correcting unit that corrects a positional shift of the image forming position in the main scanning direction on the intermediate transfer belt; and the intermediate transfer. Detects belt misalignment in the main scanning direction Includes a belt close detection means, and based on the positional displacement information detected by the belt deviation detecting means, the image forming apparatus to correct the positional deviation in the main scanning direction of the intermediate transfer belt by the belt deviation correcting means,
The belt deviation detecting means includes
A light source unit that emits a parallel light beam parallel to the belt sub-scanning direction on the belt surface on which the visible image is transferred on the intermediate transfer belt;
Arranged at two positions in the belt sub-scanning direction, abut against the end of the belt surface, respectively, move in the same direction according to the movement of the intermediate transfer belt in the main scanning direction, and the parallel light flux in the moving direction Light-shielding parts with different light-shielding directions,
A light receiving portion for receiving a parallel light flux after being shielded by the two light shielding portions;
And detecting a belt shift by detecting a change in a light receiving position of the parallel light flux by the two light shielding portions shielding the parallel light flux,
By detecting the amount of received light of the parallel light flux, the belt inclination on the belt surface is detected,
An image forming apparatus, wherein an image forming position in a main scanning direction on the intermediate transfer belt is corrected based on the detected belt inclination. The image forming apparatus according to claim 1.
An image forming apparatus comprising: a light receiving unit configured by a solid-state image sensor; and detecting a change in a light-receiving position and a change in a received light amount based on an output signal of the solid-state image sensor. The image forming apparatus according to claim 1.
2. The image forming apparatus according to claim 1, wherein the light receiving unit includes an optical position detecting element, and detects a change in the light receiving position and a change in the amount of received light based on an output signal of the optical position detecting element. The image forming apparatus according to claim 1.
The light receiving unit is composed of a light receiving element that divides the light receiving region into two in the moving direction of the light blocking unit, detects a change in the amount of received light by the sum of detection signals of the two light receiving regions, and receives light by a difference between detection signals. An image forming apparatus that detects a change in position. The image forming apparatus according to claim 1.
2. The image forming apparatus according to claim 2, wherein the two light shielding portions have a slit lattice configuration including a light shielding region and a transmission region having a constant interval. The image forming apparatus according to claim 5.
The image forming apparatus according to claim 1, wherein a slit width of the slit grating is at least four times a necessary detection range of movement of the intermediate transfer belt in the main scanning direction due to belt inclination. The image forming apparatus according to claim 1.
Each of the two light shielding portions includes a light shielding member that shields the parallel light flux, a detection member that abuts against an end of the belt surface, and the light shielding member and the detection member that move the intermediate transfer belt in the main scanning direction. An image forming apparatus, wherein the light shielding member is larger in radius of rotation with respect to the rotation support member than the detection member. The image forming apparatus according to claim 7.
The image forming apparatus according to claim 1, wherein a rotational force centered on the rotation support member caused by gravity is a direction in which the detection member abuts against an end of the belt surface. The image forming apparatus according to any one of claims 1 to 8,
The parallel light beam emitted from the light source part is shielded by the two light shielding parts, and then the optical axis is folded back by 180 degrees by the reflecting means and is incident on the light receiving part installed integrally with the light source part. An image forming apparatus. The image forming apparatus according to claim 9.
The image forming apparatus, wherein the reflecting means is a corner cube prism.

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