JP4818022B2 - Image forming apparatus and control method thereof - Google Patents

Description

  The present invention relates to an image forming apparatus and a control method thereof, and more particularly to an image forming apparatus such as a color copying machine and a color laser printer and a control method thereof.

  Conventionally, yellow (Y), magenta (M), cyan (C), and black (Bk) process cartridges (hereinafter referred to as “cartridges”) are arranged in tandem to transfer a color image to a recording material. A tandem type image forming apparatus is known.

  As shown in FIG. 18, a conventional tandem type image forming apparatus 201 includes a transfer belt 205 which is a recording material carrier for carrying and conveying a recording material P in a paper cassette 202, and a tandem along the recording material carrying surface. Cartridges 214 to 217 arranged in a shape. Further, the image forming apparatus 201 includes optical units 218 to 221 provided above the cartridges 214 to 217 and photosensitive drums 206 to 209 as image carriers of the cartridges 214 to 217. . Further, the image forming apparatus 201 includes transfer rollers 210 to 213 that are arranged with the transfer belt 205 interposed therebetween corresponding to the photosensitive drums 206 to 209.

  In the above configuration, the image forming apparatus 201 feeds the recording material P in the paper cassette 202 to the inside by the backup roller 203 and the paper feed / conveyance roller 229. Next, yellow, magenta, cyan, and black toner images obtained through a known electrophotographic process are transferred onto the fed recording material P in an overlapping manner. Thereafter, the transferred toner image is fixed on the recording material P by the fixing unit 222, and then the recording material P is discharged out of the apparatus via the paper discharge sensor 224 and the paper path 223.

  When a toner image is also formed on the back surface of the recording material P, the image forming apparatus 201 conveys the recording material P exiting the fixing unit 222 to the transfer belt 205 again via the paper path 225, and the same process is performed. Then, an image is also formed on the back surface.

  During such an image forming operation on the recording material P, the transfer belt 205 is rotationally driven by the transfer belt driving roller 204. Further, the optical units 218 to 221 for the respective colors form latent images by exposing and scanning the surfaces of the respective photosensitive drums 206 to 209 with the laser beams L1 to L4. Further, regarding these series of image forming operations, the image forming apparatus 201 performs synchronous control so that an image is transferred from a predetermined position on the recording material P being conveyed.

  The image forming apparatus 201 includes a paper feed / conveyance motor (not shown) that drives the paper feed / conveyance roller 229 and a transfer belt drive motor (not shown) that drives the transfer belt drive roller 204. The image forming apparatus 201 includes a photosensitive drum driving motor (not shown) that drives the photosensitive drums 206 to 209 of each color, and a fixing driving motor (not shown) that drives the fixing roller 222 a of the fixing unit 222. In order to obtain a good image, these motors are controlled at a constant rotational speed.

  On the other hand, as the temperature inside the apparatus increases due to the temperature control of the heater built in the fixing unit 222 and the heat generated by each drive motor, the transfer belt drive roller 204 undergoes thermal expansion, and the diameter of the transfer belt drive roller 204 increases. There is. At this time, even if the transfer belt drive roller 204 itself rotates at a constant rotational speed as described above, the peripheral speed of the transfer belt 205 increases as the roller diameter changes. As a result, when a toner image of each color is transferred onto the recording material P, a so-called color misregistration occurs, resulting in a problem that the image quality is remarkably deteriorated. Such a problem also occurs in the case of an image forming apparatus provided with an intermediate transfer member.

  In addition, as the temperature inside the image forming apparatus 202 rises, the difference between the recording material conveyance force by the paper feed / conveyance roller 229 and the recording material conveyance force by the transfer belt 205 increases, thereby causing color misregistration and image blurring. There are things to do. Specifically, when the recording material conveying force by the paper feeding / conveying roller 229 is larger than the recording material conveying force by the transfer belt 205, the recording material P, in particular, the recording material P is relatively stiff, such as thick paper. When a certain material is used, image blurring occurs at the rear end portion of the recording material P. Conversely, when the recording material conveyance force by the transfer belt 205 is larger than the recording material conveyance force by the paper feed / conveyance roller 229, there is a problem that image blurring or color misregistration occurs at the leading end portion of the recording material P. .

  As one means for solving such a problem, first, the surface image is sampled at a constant rate by a sensor that reads the surface image formed on either the recording material or the transfer belt (or intermediate transfer member). Next, based on the sampled surface image, the moving speed (hereinafter simply referred to as “moving speed”) of either the recording material or the transfer belt (or the intermediate transfer member) is calculated, and a plurality of drives included in the image forming apparatus is calculated. There is one that variably controls the rotation speed of a motor (for example, see Patent Document 1).

There is also a sensor that detects the end of the transfer belt, and changes the alignment amount of the steering roller using a driving means such as a stepping motor in accordance with the output of the sensor (see, for example, Patent Document 2).
JP 2002-202705 A JP 2004-35200 A

  However, in the surface image sampling method using the conventional sensor, the belt surface area (= number of frame pixels) that can be detected by one sample is limited, and the rotational speed of the plurality of drive motors is variably controlled. I couldn't do it well.

  Hereinafter, a conventional sampling method will be specifically described with reference to FIG. Here, the sampling sensor is an area sensor 100 having m pixels in the moving direction and n pixels in the vertical direction, and the sampling target is an image transferred onto the surface of the intermediate transfer belt 101 driven in the moving direction 102.

  First, the area sensor 100 determines a characteristic image pattern from the surface image 103 acquired at time t, and sets the center of gravity as the target 104. Thereafter, the above processing is performed at regular time intervals (sample rate Δt), and the moving speed of the intermediate transfer belt 101 is calculated from the obtained displacement amount of the position of the target 104 and the value of Δt.

  Further, the moving speed of the intermediate transfer belt 101 is set according to the material of the recording material, whereby the image forming speed (process speed) is controlled. For example, when the recording material is cardboard, the process speed is controlled to be lower than that of ordinary paper in order to improve fixability. The problem here is the relationship between the detection area of the area sensor 100 and the image processing time (hereinafter simply referred to as “image processing time”) for the image data input to each pixel in the detection area. . The following describes three cases: (1) when the process speed is slow (thick paper mode), (2) when the process speed is fast (normal paper mode), and (3) when the processing time is increased in the general paper mode.

  20 to 22 are diagrams showing image patterns in the detection area 100 detected every time Δt has elapsed from when the sample time (t) is t1 in the above three cases.

  In FIG. 20, the area sensor 100 has m pixels in the moving direction of the intermediate transfer belt 101 (hereinafter referred to as “Y coordinate”) and n pixels in the moving direction and the vertical direction (hereinafter referred to as “X coordinate”). A case where a detection area is provided and the set speed of the intermediate transfer belt 101 is Va is shown. At this time, the Y coordinate of the target 104 acquired when the sample time is t1 (FIG. 20A) is 2, and the Y coordinate of the target 104 acquired when the sample time is t1 + Δt (FIG. 20B) is 6. It is. That is, at any sample time, the Y coordinate of the target 104 exists in the detection area (region indicated by Y).

  Accordingly, the moving speed of the intermediate transfer belt 101 can be calculated by {Y (t1 + Δt) −Y (t1)} / Δt = (6-2) / Δt.

  On the other hand, as shown in FIG. 21, when the size of the detection area is m × n pixels and the set speed of the intermediate transfer belt 101 is Vb (> Va), the Y coordinate of the target 104 has a sample time of t1. Sometimes it is in the detection area (region indicated by Y) (FIG. 21A). However, after the lapse of Δt (FIG. 21B), the Y coordinate of the target 104 is outside the detection area (a region indicated by U). Accordingly, the moving speed of the intermediate transfer belt 101 cannot be calculated.

  At this time, as shown in FIG. 22, when the size of the detection area is expanded to (m + 5) × n pixels, the Y coordinate of the target 104 acquired when the sample time is t1 (FIG. 22A) is Even at time t1 + Δt (FIG. 22B), it exists in the detection area. However, the image processing time of the area sensor 100 increases in proportion to the size of the detection area (number of pixels). Therefore, for example, if the detection area is expanded to such an extent that the Y coordinate of the target 104 exists even at the sample time t1 + 2Δt (FIG. 22C), the next image pattern is read before the reading of the image pattern in the detection area is completed. Will be generated in the detection area. Therefore, since the position of the target 104 cannot be determined accurately, the moving speed of the intermediate transfer belt 101 cannot be calculated.

  That is, in order to calculate the moving speed of the intermediate transfer belt 101, the image processing time is shorter than the sample time, and the Y coordinate of the target 104 is within the detection area at both the sample time t and t + Δt. It can be seen that there are two constraints. Conventionally, it has been difficult to satisfy these two constraints at the same time. Specifically, it has been difficult to achieve both “widening the detection area” and “higher processing speed”.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of performing high-quality image output free from color shift and image blur due to temperature rise in the apparatus, and a control method thereof.

In order to achieve the above object, an image forming apparatus according to claim 1 is an image forming apparatus for transferring an image formed on an image carrier onto a recording material via a belt, and the belt is set in advance. A belt moving means for moving at a moving speed v, a sensor for reading the surface image of the belt at a predetermined sampling rate Δt, and the belt moving means based on the surface image read by the sensor. Detecting means for detecting a belt shift amount, and limiting means for limiting the detection area of the sensor to the number of pixels m in the Y direction, which is the moving direction of the belt, and the number n of pixels in the X direction, which is the belt moving direction, wherein the limiting means, the moving velocity v of the belt the Y-direction number of pixels m of the detection area of the previous SL sensor by the sampling rate Δt A first setting means for setting a value equal to or greater than a multiplied value _mmin; and when the shift amount is smaller than a predetermined size, the sensor determines the number of pixels n in the X direction of the detection area of the sensor. The minimum value n _min that can be set as the size in the X direction is set, and when the shift amount is equal to or larger than the predetermined size, the number n of pixels in the X direction in the detection area of the sensor is determined from the minimum value n _min . And a second setting means for setting the number m of pixels in the Y direction to a maximum value m _max or less that the sensor can set as the size of the detection area in the Y direction. And

In order to achieve the above object, a control method according to claim 5 is a control method of an image forming apparatus for transferring an image formed on an image carrier onto a recording material via a belt, wherein the belt is preliminarily mounted. A belt moving step of moving at a set moving speed v ; a reading step of reading a surface image of the belt by a sensor at a predetermined sampling rate Δt; and the belt movement based on the surface image read by the reading step A detecting step for detecting a shift amount of the belt moved in the step; and a detection area of the sensor, the number of pixels in the Y direction which is the moving direction of the belt and the number of pixels in the X direction which is the shifting direction of the belt. a limitation step of limiting the said limitation means, the bell of the Y-direction number of pixels m of the detection area of the previous SL sensors The X-direction of the pixels of the movement and the first setting step of the speed v is set to a value m _min or more values multiplied by the sampling rate Delta] t, the detection area of the sensor when the near amount is smaller than the predetermined size The number n is set to the minimum value n _min that the sensor can set as the size of the detection area in the X direction, and when the shift amount is greater than or equal to the predetermined size, the detection area of the sensor in the X direction The number of pixels n is set to a value larger than the minimum value n _min , and the number m of pixels in the Y direction is set to a maximum value m _max or less that the sensor can set as the size in the Y direction of the detection area . And a setting step.

  According to the present invention, it is possible to reliably calculate the shift amount of the moving belt, and it is possible to perform high-quality image output free from color shift and image blur due to temperature rise in the apparatus.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a cross-sectional view of a main part of a color printer as an image forming apparatus according to an embodiment of the present invention.

  In FIG. 1, the color printer 1 includes an image output unit 1P and an image reading unit 1R.

  The image output unit 1P includes an image forming unit 10 in which four stations a to d having the same configuration are arranged side by side, a feeding unit 20, an intermediate transfer unit 30, and a fixing unit 40. Further, the image output unit 1P includes a control board 70 and an image sensor unit 60 as image reading means.

  In the image forming unit 10, photosensitive drums 11a to 11d as image carriers that are rotationally driven in the direction of the arrow shown in the drawing are pivotally supported at the center. Further, primary chargers 12a to 12d, optical systems 13a to 13d, and developing devices 14a to 14d are arranged in the rotation direction facing the outer peripheral surfaces of the respective photosensitive drums 11a to 11d.

  With the above configuration, the image forming unit 10 sequentially performs image formation with each toner through the following process.

  First, in the primary chargers 12a to 12d, a uniform charge amount of charge is applied to the surfaces of the photosensitive drums 11a to 11d. Next, laser beams modulated by the optical systems 13a to 13d according to the recording image signal are exposed on the photosensitive drums 11a to 11d to form electrostatic latent images on the photosensitive drums 11a to 11d. Then, each electrostatic latent image is visualized as a toner image by developing devices 14a to 14d each containing developer (toner) of four colors of yellow, cyan, magenta, and black. Incidentally, on the downstream side of the image primary transfer areas Ta to Td where the visualized toner image is transferred to the belt 31 as an intermediate transfer member, the toner image remains on the photosensitive drums 11a to 11d without being transferred to the recording material P. The toner that has been removed is scraped off by the cleaning devices 15a to 15d. Thereby, the surfaces of the photosensitive drums 11a to 11d are cleaned.

  The feeding unit 20 includes cassettes 21a and 21b and a manual feed tray 27 for storing the recording material P, and pickup rollers 22a and 22b for feeding the recording material P one by one in the cassettes 21a and 21b or from the manual feed tray 27. 26. The feeding unit 20 includes a feeding roller pair 23 and a feeding guide 24 for conveying the recording material P fed from the pickup rollers 22a, 22b, and 26 to the secondary transfer region Te. Further, the feeding unit 20 includes registration rollers 25 a and 25 b for feeding the recording material P to the secondary transfer region Te in accordance with the image forming timing in the image forming unit 10.

  The intermediate transfer unit 30 applies an appropriate tension to the belt 31 by a biasing force of a belt 31, a metal driving roller (downstream roller) 32 that transmits a driving force to the belt 31, and a spring (elastic member) (not shown). Tension roller (upstream roller) 33. Further, the intermediate transfer unit 30 includes a secondary transfer inner roller 34 facing the secondary transfer region Te with the belt 31 interposed therebetween, and a secondary transfer region Te from the secondary transfer region Te in the transport direction (the direction of arrow B in the drawing). An outer roller 80 provided outside the belt 31 is provided in a wound state.

  In addition, as a material of the belt 31, for example, PET (polyethylene terephthalate), PVdF (polyvinylidene fluoride), or the like is used.

  The drive roller 32 is rotationally driven by a belt motor (not shown), and coats the surface of the roller with rubber (urethane or chloroprene) having a thickness of several millimeters. Thereby, it is possible to prevent a slip between the belt 31 and the primary transfer plane A formed between the driving roller 32 and the tension roller 33.

  Primary transfer devices 35a to 35d as primary transfer means are disposed in the primary transfer regions Ta to Td where the photosensitive drums 11a to 11d and the belt 31 face each other, and behind the belt 31. The secondary transfer region Te is formed by disposing the secondary transfer device 36 at a position facing the secondary transfer inner roller 34.

  A cleaning device 50 for cleaning the image forming surface of the belt 31 is disposed downstream of the secondary transfer region Te on the belt 31. The cleaning device 50 includes a cleaner blade 51 and a waste toner box 52 that stores waste toner. Here, as the material of the cleaner blade 51, polyurethane rubber or the like is used.

  The fixing unit 40 records in a fixing roller 41a having a heat source such as a halogen heater therein, a pressure roller 41b that applies pressure to the fixing roller 41a, and a nip portion between the fixing roller 41a and the pressure roller 41b. And a guide 43 for guiding the material P. The fixing unit 40 further includes an inner discharge roller 44 and an outer discharge roller 45 for guiding the recording material P discharged through the fixing roller 41a and the pressure roller 41b to the outside of the apparatus. In the present embodiment, only the fixing roller 41a has a heat source, but the pressure roller 41b may also have a heat source.

  The control board 70 includes a control board and a motor drive board for controlling operations in the image output unit 1P.

  Next, the operation of the color printer 1 will be specifically described.

  First, when an image forming operation start signal is issued, the recording material P is sent out one by one from the cassette 21a by the pickup roller 22a. The recording material P is guided between the feeding guides 24 by the feeding roller pair 23 and conveyed to the registration rollers 25a and 25b. At this time, the registration rollers 25a and 25b are stopped, and the leading edge of the recording material P comes into contact with the nip portion. Thereafter, the registration rollers 25a and 25b start rotating in accordance with the timing at which the image forming unit 10 starts image formation. The rotation timings of the registration rollers 25a and 25b are set so that the recording material P and the toner image primarily transferred from the image forming unit 10 onto the belt 31 are exactly the same in the secondary transfer region Te.

  On the other hand, when an image forming operation start signal is issued, the image forming unit 10 forms a toner image on the photosensitive drum 11d that is the most upstream in the rotation direction of the belt 31 through the process described above. Thereafter, primary transfer is performed on the belt 31 in the primary transfer region Td by the primary transfer device 35d to which a high voltage is applied. Next, the toner image primarily transferred onto the belt 31 is conveyed to the next primary transfer region Tc. Thereafter, the transfer of the toner image in the primary transfer region Tc is performed with a delay by the time during which the toner image is conveyed. As a result, the next toner image is transferred by aligning the resist on the previous image. Thereafter, the same processing is performed for the transfer of the toner image in the primary transfer regions Tb and Ta, and the four color toner images are primarily transferred onto the belt 31.

  Thereafter, when the recording material P enters the secondary transfer region Te and contacts the belt 31, a high voltage is applied to the secondary transfer device 36 in accordance with the passing timing of the recording material P. Then, the four color toner images formed on the belt 31 by the process described above are transferred onto the surface of the recording material P. Thereafter, the recording material P on which the four color toner images have been transferred is accurately guided by the conveyance guide 43 to the nip portion between the fixing roller 41a of the fixing unit 40 and the pressure roller 41b.

  The toner image is then fixed on the surface of the recording material P by the heat of the roller pair 41a and 41b of the fixing unit 40 and the pressure of the nip. After the image fixing is completed, the recording material P is discharged to the inner discharge roller 44 and the outer discharge. It is conveyed by the roller 45 and discharged outside the apparatus.

  FIG. 2 is a block diagram showing a schematic configuration of the intermediate transfer unit 30 in FIG.

  In FIG. 2, the intermediate transfer unit 30 has a driving roller 32, a secondary transfer inner roller 34 as a secondary transfer means, and a tension roller 33, and the belt 31 is suspended from these by these. Further, the intermediate transfer unit 30 has an outer roller 80, which suspends the belt 31 from the outside.

  The tension roller 33 is urged leftward in the figure by a spring member (not shown), and applies an appropriate tension to the belt 31. Further, the outer roller 80 is configured such that the rear side end in the figure is pivotally supported by a bearing (not shown), and the alignment can be adjusted by moving the front side end in the direction of arrow C in the figure.

  FIG. 3 is a perspective view showing only the front half side of the outer roller 80 in FIG. Hereinafter, a mechanism for adjusting the alignment of the outer roller 80 will be described with reference to FIG.

  In FIG. 3, the shaft 80a of the outer roller 80 is rotatably supported by a long bearing 83 fixed to a side plate (not shown). The long bearing 83 is fitted into only the V direction in the figure with respect to the shaft 80a, and the long hole 83a allows movement only in the directions of arrows R1 and R2 perpendicular to the V direction (direction parallel to the arrow C in FIG. 2). Is provided. Further, on the opposite side of the long bearing 83 as seen from the outer roller 80, a bearing 82 is engaged with the shaft 80a. On the other hand, a steering motor 81 is fixed to a side plate (not shown). An output shaft 81 a provided with a lead is attached to the distal end portion of the steering motor 81, and the distal end portion of the output shaft 81 a is in contact with the bearing 82. A spring member (not shown) is in contact with the bearing 82 on the opposite side of the bearing 82 when viewed from the tip of the shaft 81a, and presses the bearing 82 against the output shaft 81a.

  The steering motor 81 is a stepping motor. When the steering motor 81 rotates in the arrow M1 direction, the output shaft 81a moves in the arrow L1 direction. Further, when rotating in the arrow M2 direction, the output shaft 81a moves in the arrow L2 direction. Accordingly, when the steering motor 81 rotates in the arrow M1 direction by a predetermined number of steps, the tip end portion of the output shaft 81a moves in the arrow L1 direction by a predetermined amount. At the same time, the bearing 82 moves in the direction of the arrow L1 by a predetermined amount. Conversely, when the steering motor 81 rotates in the direction of the arrow M2 by a predetermined number of steps, the tip of the output shaft 81a moves in the direction of the arrow L2 by a predetermined amount, and at the same time, the bearing 82 also moves in the direction of the arrow L2 by a predetermined amount. To do. That is, the front side of the outer roller 80 can be moved in the direction of the arrow R1 or R2 by the steering motor 81, and as a result, the alignment of the outer roller 80 can be adjusted.

  The amount of deviation of the belt 31 can be controlled by aligning the outer roller 80 by the above-described method. That is, when the front side of the outer roller 80 is moved in the direction of the arrow R1, a shift force in the direction of the arrow S1 is generated with respect to the belt 31, and when the front side of the outer roller 80 is moved in the direction of the arrow R2, the direction of the arrow S2 with respect to the belt 31 is increased. Creates a deviating force in the direction.

  If the alignment of the outer roller 80 is adjusted using this characteristic, a shifting force is positively generated in a direction to cancel the shifting force generated in the belt 31 due to distortion of the main body of the apparatus. The vehicle can be driven without deviating from the predetermined position.

  As shown in FIG. 1, the image sensor unit 60 is disposed in the vicinity of the photosensitive drum 11a and the belt 31, irradiates the surface of the belt 31 with light, collects the reflected light, and forms an image. The surface image of a certain area on the belt 31 is detected.

  FIG. 4 is a block diagram schematically showing a circuit configuration of the image output unit 1P in FIG.

  4, the image output unit 1P includes a DSP (digital signal processor) 50, a CPU 51, and drum drive motors 52a to 52d for driving the photosensitive drums 11a to 11d (FIG. 1) of the respective colors. In addition, the image output unit 1P includes a belt motor 56 that drives a driving roller 32 that transmits driving force to the belt 31, a fixing motor 57 that drives a fixing roller 41a of the fixing unit 40, an image sensor unit 60, and a feeding A paper feed motor 62 for driving the roller pair 23. Further, the image output unit 1P controls the amount of deviation of the belt 31 and the paper feed motor driver 61 for controlling the paper feed motor 62, the drum drive motor units 63a to 63d for controlling the drum drive motors 52a to 52d for the respective colors. And a steering motor 81. The image output unit 1 </ b> P includes a fixing unit 40, a high voltage unit 59, and a steering motor driver 67 that controls the steering motor 81.

  The drum drive motors 52a to 52d, the belt motor 56, the paper feed motor 62, the steering motor 81, and the image sensor unit 60 are controlled by the DSP 50. The drum drive motor units 63a to 63d, the high voltage unit 59, and the fixing unit 40 are controlled by the CPU 51.

  FIG. 5 is a block diagram schematically showing a circuit configuration of the belt motor 56 controlled by the DSP 50 in FIG.

  Here, the circuit configuration of the drum drive motors 52 a to 52 d controlled by the DSP 50 has the same configuration as that of the belt motor 56. Therefore, only the circuit configuration of the belt motor 56 will be described below, and redundant description of the circuit configuration of the drum drive motors 52a to 52d will be omitted.

  The belt motor 56 is a three-phase DC motor and is built in the DC motor unit 601.

  The DC motor unit 601 includes a control IC 602 and a driver 603 in addition to the belt motor 56. The control IC 602 includes a pre-driver 605 and a logic circuit 606. Furthermore, it is connected to the control IC 602 and is arranged in the vicinity of the belt motor 56, and includes three Hall sensors 607 to 609 for detecting the rotational speed of the belt motor 56 and a speed detecting MR sensor 610.

  The DSP 50 transmits a motor activation signal 611 for controlling the activation of the belt motor 56. The DSP 50 calculates the motor rotation speed based on the speed detection signal 613 from the speed detection MR sensor 610, and generates a PWM signal 612 for controlling the motor rotation speed of the belt motor 56 based on the calculated speed. Send.

  On the other hand, the control IC 602 controls switching and amplification of the direction of the current supplied by the driver 603 to the coil of the belt motor 56 based on the rotation speed detected by the Hall sensors 607 to 609 and the PWM signal 612 from the DSP 50.

  FIG. 6 is a diagram used for explaining an image acquisition method on the surface of the belt 31 by the image sensor unit 60 in FIG.

  In FIG. 6, the image sensor unit 60 is disposed so as to face the belt 31, and includes an LED 33 that is an illumination member, a CMOS sensor 304 that is an image detection member, a lens 35, and an imaging lens 36.

  Light having the LED 33 as a light source is irradiated obliquely onto the surface of the belt 31 through the lens 35. At this time, when the recording material P has been conveyed to the irradiation position, light is irradiated onto the surface of the recording material P.

  Thereafter, the reflected light is collected through the imaging lens 36 and imaged on the CMOS sensor 304. In this way, the surface image of the belt 31 or the recording material P can be read.

  In the present embodiment, the LED 33 is used as the illumination member. However, the present invention is not limited to this, and it goes without saying that a light source such as a laser may be used.

  FIG. 7 shows a surface image of the belt 31 acquired by the image sensor unit 60.

  In FIG. 7, the image sensor unit 60 (not shown) obtains the enlarged image 71 after enlarging the surface image of the belt 31 with the imaging lens 36.

  After that, the image sensor unit 60 divides the image 71a in the detection area of the size of m × n pixels out of the obtained enlarged image 71 out of pixels evenly arranged in the CMOS sensor 304 into segments. Detect. Further, the CMOS sensor 304 performs gradation detection on the image 71a in the detection area with 8 × 8 pixels as one pixel, and acquires this as an image image 72. That is, the CMOS sensor 304 has a resolution of 8 bits per pixel. Needless to say, the resolution of one pixel is not limited to that according to the present embodiment.

  Here, the size of the image 71a in the detection area in the Y direction is a speed set in advance according to the type of the recording material P to be conveyed (hereinafter referred to as “set speed”). It is set to be larger than the value multiplied by. Thereby, even if the set speed is high, the displacement amount of the belt 31 in the Y direction can be reliably detected in the detection area.

  Moreover, it is preferable to irradiate the light which uses LED33 as a light source from the diagonal as mentioned above. As a result, it is possible to reliably detect the image of the uneven shadow formed on the surface of the belt 31. This unevenness is preferably formed in advance in a range that does not affect the transfer control on the belt 31. Thereby, the read surface image pattern can be characterized. Furthermore, the surface layer of the belt 31 is preferably made of a transparent material. As a result, even if the above unevenness is applied to the surface of the belt 31 in advance, the influence on the transfer control can be reduced.

  FIG. 8 is a block diagram schematically showing the configuration of the image sensor unit 60.

  8, the image sensor unit 60 includes a CMOS sensor 304 having a resolution of 8 × 8 pixels, a control circuit 93, an A / D converter 94, a filter circuit 95, an output circuit 96, and a PLL circuit 97.

  The control circuit 93 receives various signals transmitted from the DSP 50 (not shown), and sets control parameters such as filter constants based on these signals.

  Specifically, as shown in FIG. 9, when the / CS signal S5 (value L) is transmitted from the DSP 50, the control circuit 93 sets its own control mode to the control parameter transfer mode, and the DATA from the DSP 50 Waiting for signal reception. At this time, the DATA signal transmitted from the DSP 50 is transmitted at a frequency synchronized with the clock signal S2.

  Thereafter, when receiving a DATA signal from the DSP 50, the control circuit 93 generates an LED lighting instruction command, a detection area setting command, a gain adjustment command, and the like based on the DATA signal.

  The CMOS sensor 304 sets the size of the detection area according to the detection area setting command. On the other hand, the filter circuit 95 determines the gain of the CMOS sensor 304 in accordance with the generated gain adjustment command. Thereby, the gain can be adjusted according to the material of the belt 31, that is, the reflectance of the belt 31, and the calculation of the position of the center of gravity, which will be described later, can be realized accurately and reliably. This gain adjustment is performed until a certain degree of contrast is generated for each pixel data of the image 71a in the detection area.

  As shown in FIG. 9, when the / CS signal S1 (value H) is transmitted from the DSP 50, the control circuit 93 sets its own control mode to the image data transfer mode and receives the DATA signal from the DSP 50. Interrupt. At this time, the clock transmitted from the DSP 50 has a frequency synchronized with an interrupt signal generated at the sampling rate in a sampling control unit 510 (FIG. 11) described later.

  Thereafter, when the control circuit 93 receives the clock signal S2 transmitted from the DSP 50 via the PLL circuit 97, the control circuit 93 generates a trigger signal based on the received clock signal S2.

  The CMOS sensor 304 generates pixel data constituting the detection area image 71 a at the reception timing of the trigger signal, and transmits the pixel data to the output circuit 96 via the ADC 94 and the filter circuit 95. As a result, the pixel data of the detection area image 71 a subjected to gain adjustment or the like is sequentially transmitted to the output circuit 96. At this time, the filter circuit 95 converts the surface image into pixel data from which, for example, 8-bit 256 gradation data is reduced to 16 gradations and components due to noise are removed by filtering.

  On the other hand, when receiving the clock signal S2 from the DSP, the PLL circuit 97 generates a transmission synchronous clock (TXC) S4 in response thereto. The output circuit 96 transmits the sequentially transmitted pixel data to the DSP 50 at the reception timing of the generated TXC signal.

  With the above processing, the DSP 50 can reliably receive the detection area image 71a transmitted from the image sensor unit 60 as pixel data for each sampling rate in the image data transfer mode.

  FIG. 11 is a block diagram showing a schematic configuration of the DSP 50 in FIG.

  11, the DSP 50 includes an I / O control unit 508 that exchanges signals with external devices such as the image sensor unit 60 and the CPU 51, and a sampling control unit 510 that generates an interrupt signal at a constant sampling rate.

  The DSP 50 also includes a read image buffer 501 that holds pixel data transmitted in synchronization with the TXC signal. Each pixel data held is associated with an address in the Y direction, which is the moving direction of the belt 31, designated by the I / O control unit 508, and an address in the X direction, which is the direction in which the belt 31 is shifted. ing.

  The read image buffer 501 samples the held pixel data based on the interrupt signal from the sampling control unit 510 and transmits it to the image memory 502. The image memory 502 sequentially stores data from the read image buffer 501 as a reference image.

  The DSP 50 binarizes the reference image stored in the image memory 502 for each pixel based on a predetermined threshold value, and the x direction and the binarization processing unit 503 based on the reference image after the binarization processing. and a center of gravity calculation processing unit 504 that calculates the center of gravity in the y direction. Further, the DSP 50 includes a barycentric position coordinate detecting unit 505 that detects an address (coordinate) of pixel data located at the calculated barycentric position as barycentric position coordinates.

  The DSP 50 also includes a speed calculation processing unit 506 that calculates the moving speed and the shift amount of the belt 31, and a motor control unit 507 that controls the belt motor 56 and the steering motor 81.

  The speed calculation processing unit 506 first detects the shift amount of the center of gravity of the belt 31 from the detection result of the center of gravity position coordinates sequentially transmitted from the center of gravity position coordinate detection unit 505. Thereafter, the moving speed of the belt 31 is calculated based on the detected Y-direction component of the deviation amount and the sampling rate. The same process is performed for the X direction to calculate the amount of deviation of the belt 31.

  For example, as shown in FIG. 10A, as a result of calculating the centroid position at sampling times t1, t2 (= t1 + Δt) and t3 (= t2 ++ t), the centroid position is displaced only in the Y direction. At this time, the shift amount calculated by the speed calculation processing unit 506 is zero. In this case, the DSP 50 determines that there is no deviation in the belt 31, and the steering motor 58 is not controlled by the motor control unit 507 described later. On the other hand, as shown in FIG. 10B, as a result of calculating the centroid position at the sampling times t1, t2, and t3, the centroid position may be displaced in both the X and Y directions. In this case, the DSP 50 controls the motor speed of the belt motor 56 by the motor control unit 507 so that the moving speed calculated by the speed calculation processing unit 506 is not the set speed. In this case, the DSP 50 determines that the belt 31 is deviated, and the motor control unit 507 controls the steering motor 81 via the motor driver 67 so as to eliminate the deviation amount calculated by the speed calculation processing unit 506. To control.

  The motor control unit 507 controls the belt motor 56 and the steering motor 81 by a method to be described later based on the moving speed and the shift amount of the belt 31 calculated by the speed calculation processing unit 506. More specifically, the shift control of the belt 31 is performed by sending a drive pulse having the number of steps corresponding to the calculated shift amount to the steering motor driver 67.

  The speed calculation processing unit 506 includes a filter processing unit 506a that performs filter processing. As a result, the detection noise and calculation error included in the calculated moving speed and shift amount of the belt 31 can be removed, and the control of the belt motor 56 and the steering motor 81 can be optimized. Specifically, even when the calculated moving speed value suddenly changes due to detection noise or the like, the motor speed of the belt motor 56 is not suddenly changed, thereby preventing image deterioration. In the shift control, even if the calculated shift amount suddenly changes due to detection noise or the like, the number of drive pulses transmitted to the steering motor driver 67 is not changed suddenly, and the step-out of the steering motor 81 is prevented. Is preventing.

  The illumination light amount of the LED 33 in the CMOS sensor 304 is controlled by illumination logic 511 as illumination light amount control means provided in the DSP 50. In the DSP 50, the illumination logic 511, the sampling control unit 510, the image memory 502, the speed calculation processing unit 506 including the filter processing unit 506a, and the motor control unit 507 can be controlled in a programmable manner.

  Further, as described above, the detection area has a size m in the Y direction larger than a value obtained by multiplying the set speed by the sampling rate. However, in order to set the size of the detection area so that the displacement amount in the X and Y directions of the belt 31 can be reliably acquired within the time of the sampling rate, it is limited as follows according to the shift amount of the belt 31. To do.

  Specifically, as shown in FIG. 10A, when the belt 31 is not deviated at all or only a small amount is deviated, the size n of the detection area in the X direction is set as follows. To do.

n = n ₂ <n ₁
n ₂ : Minimum value that the CMOS sensor 304 can set as the size of the detection area in the X direction n ₁ : Size of the CMOS sensor 304 in the X direction On the other hand, as shown in FIG. If there is a deviation, the size m in the Y direction of the detection area is set as follows.

m ≦ m ₁
n> n ₂
m ₁ : Size of the CMOS sensor 304 in the Y direction As described above, by limiting the size of the detection area, the shift amount and the moving speed of the rotating belt 31 can be reliably calculated even if the set speed is high. Therefore, it is possible to perform high-quality image output without color shift and image blur due to temperature rise in the apparatus.

  Furthermore, the amount of displacement per unit time of the belt 31 is generally very small compared to the Y direction compared to the Y direction. For this reason, the detection area is controlled such that the size in the Y direction is larger than the size in the X direction.

  Next, a method for calculating the center of gravity by the center of gravity calculation processing unit 504 and a method for calculating the relative speed and the deviation amount of the intermediate transfer belt by the speed calculation processing unit 506 will be described.

  FIG. 12 is a diagram used for explaining the centroid calculation process executed by the centroid calculation processing unit 504 in FIG. Specifically, FIGS. 12A and 12C show an image (binarized image) after binarizing the image 71a in the detection area at the sample times t1 and t2, and FIG. 12B and FIG. (D) shows a table of the centroid calculation results.

  In FIG. 12, the binarized images 161 and 162 are obtained by the binarization processing unit 503 using the detection area image 71a sampled when the center of gravity of the surface image 71 of the belt 31 is displaced only in the Y direction. It is the image binarized based on the threshold value.

  Hereinafter, the center of gravity calculation processing method will be described in detail by taking the center of gravity calculation processing unit 504 as an example of processing for the binarized image 161.

  First, the center-of-gravity calculation processing unit 504 sets a coefficient for each of the detection areas in the X and Y directions. In the present embodiment, as shown in Table 163, the coefficient is 15 in the upper left row of the detection area, the coefficient 7 in the upper left column, the coefficient 8 in the lower right row, and the coefficient 0 in the lower right column. Is set.

  Next, by multiplying the address of each pixel data of the binarized image 161 transmitted from the binarization processing unit 503 by the set coefficient, which row has the binarized data, and Find the number (existence number) indicating how many exist in the column. As shown in Table 163, regarding the binarized image 161, the number of existence is 1 in the column of coefficient 6, the number of existence is 2 in the column of coefficient 5, the number of existence is 3 in the row of coefficient 11, and the number of existence is in the row of coefficient 13. 2 is required.

  Thereafter, based on the existence number, partial sums are obtained for all the rows and columns. Specifically, the calculation of the partial sum is 6 × 1 = 6 because the existence number is 1 in the column of coefficient 6, 5 × 2 = 10 in the column of coefficient 5, and 11 × 3 = 33 in the row of coefficient 11. In the row of the coefficient 13, it is calculated as 13 × 2 = 26.

  Further, the sum of the partial sums calculated for each row and each column is calculated. As shown in Table 163, for the binarized image 161, the row partial sum is calculated as 105 and the column partial sum is calculated as 37.

  Finally, the partial sum is divided by the existence number to calculate the center of gravity in the X and Y directions. Here, the center of gravity in the X direction is calculated as 105 ÷ 9 = 11.7, and the center of gravity in the Y direction is calculated as 37 ÷ 9 = 4.11. This result is transmitted to the barycentric position coordinate detecting unit 505, and it is detected that the address of the pixel data at the barycentric position is (11, 4).

  Similar processing is performed on the binarized image 162. As a result, as shown in Table 164, the center of gravity in the X direction is calculated as 11.7, the center of gravity in the Y direction is calculated as 20.11, and the address of the pixel data at the center of gravity is (11, 20). Is detected.

  Next, the speed calculation processing unit 506 calculates the displacement amount of the address of the pixel data at the detected gravity center position, and calculates the movement amount of the belt 31 between the sample times t1 and t2. Here, the calculated displacement amount is 0 pixel in the X direction and 16 pixels in the Y direction, and the size of one pixel according to the present embodiment is 10 μm in the Y direction. Therefore, the movement amount of the belt 31 is calculated to be 160 μm in the Y direction.

  Further, the speed calculation processing unit 506 calculates the moving speed of the belt 31 based on the values of the sample times t1 and t2 and the calculated moving amount of the belt 31. Here, since the sample time t2 is a time elapsed by the sampling rate Δt (1 ms) from the sample time t1, a value of 0.16 mm ÷ 1 ms = 160 mm / sec is calculated as the moving speed of the belt 31.

  FIG. 13 is a diagram illustrating a modified example of the binarized image in FIG. 12 and the table of centroid calculation results thereof.

  13A and 13C, binarized images 165 and 166 are images of the detection area sampled when the center of gravity position of the surface image 71 of the belt 31 is displaced in both the X and Y directions. 71a is an image binarized by the binarization processing unit 503.

  First, the barycentric position of the binarized image 165 is calculated by the same method as the process shown in FIG. As a result, as shown in Table 167 (FIG. 13B), the center of gravity in the X direction is calculated as 11.7, the center of gravity in the Y direction is calculated as 4.11, and the address of the pixel data at the center of gravity is (11, 4) is detected.

  Similarly, when the position of the center of gravity of the binarized image 166 is calculated, the center of gravity in the X direction is calculated as 3.7 and the center of gravity in the Y direction is calculated as 20.11 as shown in Table 168 (FIG. 13 (d)). Furthermore, it is detected that the address of the pixel data at the center of gravity position is (3, 20).

  Next, the speed calculation processing unit 506 calculates the displacement amount of the address of the pixel data at the detected gravity center position, and calculates the movement amount of the belt 31 between the sample times t1 and t2. Here, the calculated displacement amount is −8 pixels in the X direction and 16 pixels in the Y direction, and the size of one pixel according to the present embodiment is also 10 μm in the X direction. Therefore, the movement amount of the belt 31 is calculated to be 160 μm in the Y direction and −80 μm in the X direction.

  Further, the speed calculation processing unit 506 calculates the moving speed of the belt 31 based on the values of the sample times t1 and t2 and the calculated moving amount of the belt 31. The value of 0.16 mm ÷ 1 ms = 160 mm / sec is calculated as the moving speed of the belt 31, and the value of 0.08 mm ÷ 1 ms = 80 mm / sec is calculated as the deviation amount of the belt 31.

  FIG. 14 is a flowchart illustrating a procedure of control processing of the moving speed and the shift amount of the belt 31 executed by the DSP 50.

  In FIG. 14, first, the I / O control unit 508 transmits a / CS signal having a value L to the image sensor unit 60, and sets the control mode of the image sensor unit 60 (control circuit 93) to the control parameter transfer mode (step). S1401).

  Next, the I / O control unit 508 transmits a DATA signal for address designation and LED lighting instruction to the image sensor unit 60 (step S1402). When this signal is received, the image sensor unit 60 starts irradiating the LED light on the surface of the belt 31 with the LED 33, and detects an image in the detection area where the address is specified among the surface images.

  Subsequently, the I / O control unit 508 transmits a gain adjustment instruction DATA signal to the image sensor unit 60 (step S1403). When this signal is received, the image sensor unit 60 adjusts the gain by the filter circuit 95 so that the detection of the acquired surface image is in an optimum state.

  Next, the / CS signal of value H is transmitted to the image sensor unit 60 by the I / O control unit 508, the control mode is switched to the image data transfer mode (step S1404), and the processing count n is set to 1 (step S1404). S1405).

  Next, every time the detection sampling time (the sampling rate of the present embodiment is 1 ms) has elapsed (YES in step S1406), the sampling control unit 510 issues an interrupt signal (step S1407). The transmitted interrupt signal is transmitted to the I / O control unit 508, the read image buffer 501, and the image memory 502.

  When the I / O control unit 508 receives the interrupt signal from the sampling control unit 510 (YES in step S1408), the I / O control unit 508 transmits a CLOCK signal synchronized with the interrupt signal to the image sensor unit 60 (step S1409). Upon receiving this signal, the image sensor unit 60 generates a transmission synchronization clock (TXC) by the PLL circuit 97 based on the CLOCK signal. Thereafter, the pixel data in the detection area 71a is transmitted to the DSP 50 (read image buffer 501) at a timing synchronized with the generated transmission synchronization clock. The transmitted pixel data is sequentially held in the read image buffer 501.

  When the read image buffer 501 receives an interrupt signal from the sampling control unit 510 (YES in step S1410), the read image buffer 501 transmits pixel data currently held to the image memory 502 as sampling data (step S1411). The image memory 502 sequentially holds the transmitted sampling data and transmits it to the binarization processing unit 503 at a timing synchronized with the interrupt signal from the sampling control unit 510.

  Next, when the binarization processing unit 503 receives the sampling data from the image memory 502, the binarization processing unit 503 binarizes each pixel data to generate a binarized image (step S1412). Then, the generated binary image is transmitted to the center-of-gravity calculation processing unit 506. Based on the binarized image, a center-of-gravity calculation process of FIG. 16 described later is performed (step S1413). By this processing, the address of the pixel data at the center of gravity is accurately detected, and the detected address value is sequentially transmitted to the speed calculation processing unit 506 in a state where the detected address value is associated with the processing count n.

  The processing from step S1406 to S1413 is repeated while incrementing the value of n by 1 (step S1414) until the value of n becomes m (NO in step S1415).

Thereafter, when the value of n becomes m (YES in step S1415), the speed calculation processing unit 506 moves the belt 31 at n (= 2 to m) based on the address value transmitted from the barycentric position coordinate detection unit 505. The speed and the shift amount are calculated (step S1416). Here, the moving speed V ₁ (n) and the shift amount V ₂ (n) when the number of processes is n are calculated as follows.

V ₁ (n) = {Y (n) −Y (n−1)} / Δt
V ₂ (n) = {X (n) −X (n−1)} / Δt
Y (n): Y-direction address value X (n) when the processing count is n: X-direction address value when the processing count is n Δt: Sampling rate Next, the average processing of the calculated moving speed and shift amount (Step S1417), and the result of the average processing is stored in the memory as data (step S1418).

  When the processing in step S1418 is completed, the I / O control unit 508 transmits a / CS signal having a value L to the image sensor unit 60, and switches the control mode to the control parameter transfer mode again (step S1419). At this time, the I / O control unit 508 returns the frequency of the CLOCK signal transmitted to the image sensor unit 60 to the normal frequency.

  Next, the I / O control unit 508 transmits an LED turn-off instruction DATA signal to the image sensor unit 60 (step S1420). When this signal is received, the image sensor unit 60 ends the irradiation of the LED light on the surface of the belt 31 by the LED 33.

  Further, the speed calculation processing unit 506 sets the target speed of the belt 31 based on the data stored in the memory in step S1418, and transmits this to the motor control unit 507 (step S1421).

  The motor control unit 507 controls the belt motor 56 and the steering motor based on the target speed (step S1422), and ends this process.

  According to the processing of FIG. 14, the moving speed of the belt 31 can be made constant, and the deviation generated in the belt 31 can be eliminated.

  FIG. 15 is a flowchart showing the procedure of the motor control process in step S1422 of FIG.

  In FIG. 15, first, the motor control unit 507 transmits a motor start signal 611 (FIG. 5) to the belt motor 56 (step S110). Thereafter, a flag indicating the state of the belt motor 56 is set to NOT-READY (step S111), and a pulse of the speed detection signal 613 transmitted from the speed detection MR sensor 610 installed in the belt motor 56 is detected (step S111). Step S112).

  Next, based on the speed detection signal 613, the motor rotation speed of the belt motor 56 is calculated (step S113). Here, for example, when a speed signal of 30 pulses is output for one rotation of the motor and the pulse interval is tsec, the motor rotational speed ω of the belt motor 56 is ω = 2π / 30 / t (rad / sec). Is calculated.

  Next, it is determined whether or not the motor rotation speed ω is 50% or more of the target speed set in step S1422 of FIG. 14 (step S114). As a result, if it is less than 50%, the PWM on-duty is set to 80% (step S115), a PWM pulse is output (step S121), and this process is terminated.

  On the other hand, if the result of determination in step S114 is 50% or more, it is further determined whether or not the motor rotation speed ω is within ± 5% of the target speed (step S116). If the result is within ± 5%, a flag indicating the state of the belt motor 56 is set to the READY flag (step S117).

  Next, the difference between the target speed and the motor rotational speed ω is calculated (step S118), PI calculation (control) is performed (step S119), the PWM pulse width after the control is calculated (step S120), and the PWM pulse is calculated. This is output (step S121), and this process is terminated.

  According to this processing, the power of the belt motor 56 corresponding to the PWM pulse is controlled by the circuit of the DC motor unit 601 shown in FIG. 5, and the belt motor 56 is servo controlled so as to always follow the target speed. Is done.

  FIG. 16 is a flowchart showing the procedure of the center-of-gravity calculation process in step S1413 of FIG.

  In FIG. 16, first, when the center-of-gravity calculation processing unit 506 receives a binarized image from the binarization processing unit 503 (YES in step S1601), the received binarized image is processed by the method of FIGS. The center of gravity position is calculated (step S1602). Next, the barycentric position coordinate detection unit 505 detects the address of the pixel data at the calculated barycentric position (step S1603). As described above with reference to FIG. 14, the detected address value is transmitted to the speed calculation processing unit 506.

  Thereafter, when the current value of n is 1 (YES in step S1604), the process is terminated as it is, and the process proceeds to step S1414 and subsequent steps in FIG. On the other hand, when the current value of n is 2 (NO in step S1604, YES in step S1605), the speed calculation processing unit 506 causes the shift amount of the belt 31 (= {X (2) −X (1)} / Δt)) is calculated (step S1606).

  Next, it is determined whether or not the calculated shift amount is equal to or less than a predetermined value (step S1607). As a result of the determination, if it is equal to or smaller than the predetermined value, the present process is terminated as it is, and the process proceeds to step S1414 and subsequent steps in FIG. On the other hand, if the result of determination in step S1607 is greater than the predetermined value, the DSP 50 transmits a / CS signal of value L to the image sensor unit 60 by the I / O control unit 508, and sets the control mode to the control parameter transfer mode. (Step S1608). At this time, the I / O control unit 508 returns the frequency of the CLOCK signal transmitted to the image sensor unit 60 to the normal frequency.

  Next, after the I / O control unit 508 transmits an address-designated DATA signal that increases the width of the detection area in the X direction and decreases the width in the Y direction to the image sensor unit 60 (step S1609), FIG. The process proceeds to step S1404. When the image sensor unit 60 receives the DATA signal transmitted in step S1609, the image sensor unit 60 changes the detection area to the addressed area.

  On the other hand, if n ≧ 3 as a result of the determination in step S1605, the process is terminated as it is, and the process proceeds to step S1414.

  According to this process, when the deviation amount of the belt 31 is greater than the predetermined value (NO in step S1607), the DSP 50 issues a detection area change instruction (step S1609). Accordingly, even if the moving speed of the belt 31 is high, the center of gravity is detected with high accuracy without losing sight, and even if the shifting amount is a predetermined value or more, the moving speed of the belt 31 is kept constant and the shifting is performed. Control can be performed.

  In the present embodiment, as shown in FIG. 1, the image sensor unit 60 is disposed in the vicinity of the photosensitive drum 11a. However, the present invention is not limited to this, and any place where the surface image of the belt 31 can be obtained may be used. Needless to say.

  The belt motor 56 is incorporated in the DC motor 602 (FIG. 5). However, the belt motor 56 is not limited to this as long as the belt motor 56 can drive the belt 31 with high accuracy. For example, it goes without saying that the belt motor 56 may be incorporated in the stepping motor, for example.

  FIG. 17 is a cross-sectional view showing a modification of the image output unit 1P.

  In FIG. 17, the image output unit 1 </ b> P ′ is different from the image output unit 1 </ b> P in that four stations a, b, c, and d directly form an image on the recording material P without intermediate transfer to the belt 31. The image sensor unit 60 is different from the image output unit 1P in that the position of the image sensor unit 60 is not in the vicinity of the photosensitive drum 11a and the belt 31 but in the vicinity of the photosensitive drum 11d and the belt 31. Hereinafter, the same components are denoted by the same reference numerals, and redundant description is omitted.

  In FIG. 17, the image output unit 1P ′ includes a belt 31 that is a recording material carrier for carrying and conveying the recording material P. Yellow Y, magenta M, cyan C, Stations a ′ to d ′ for black Bk are arranged in tandem. Further, transfer rollers 35a 'to 35d' are arranged so as to correspond to the photosensitive drums 11a to 11d of the stations a 'to d' with the belt 31 interposed therebetween. Each of the stations a 'to d' includes charging rollers 12a 'to 12d', developing devices 14a to 14d, and cleaning devices 15a to 15d around the photosensitive drums 11a to 11d.

  The belt 31 is wound around a tension roller 33 and a driving roller 32, and moves in the direction of arrow X in the figure as the driving roller 32 rotates.

  In the above configuration, yellow, magenta, cyan, and black toner images obtained through a known electrophotographic process on the recording material P fed from the cassette 21a to the belt 31 by the pickup roller 22b and the feeding roller pair 23. Transcribe and transfer. Thereafter, the toner image is fixed by the fixing unit 40 and is discharged out of the apparatus by the inner discharge roller 44 and the outer discharge roller 45 through the paper discharge sensor 24.

  The image sensor unit 60 according to the present embodiment is disposed in the vicinity of the station d ′ and the belt 31 that are located on the most downstream side. Thereby, the influence of heat is the largest in the apparatus, more specifically, it is possible to quickly detect the change of the driving roller 32 in which the expansion of the roller diameter due to heat is significant and the change in the peripheral speed of the belt 31 accompanying this. it can.

  According to this process, even if the belt 31 does not have a function as an intermediate transfer member, the moving speed of the belt 31 can be detected with high accuracy. Even if the deviation amount is equal to or greater than a predetermined value, the deviation control can be performed while keeping the moving speed of the belt 31 constant.

  Another object of the present invention is to supply a storage medium storing software program codes for realizing the functions of the above-described embodiments to a system or apparatus, and the computer of the system or apparatus (or CPU, MPU, or the like). Is also achieved by reading and executing the program code stored in the storage medium.

  In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the program code and the storage medium storing the program code constitute the present invention. .

  Examples of the storage medium for supplying the program code include a floppy (registered trademark) disk, a hard disk, a magneto-optical disk, a CD-ROM, a CD-R, a CD-RW, a DVD-ROM, a DVD-RAM, and a DVD. An optical disc such as RW or DVD + RW, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used. Alternatively, the program code may be downloaded via a network.

  Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an OS (Operating System) running on the computer based on the instruction of the program code Includes a case where the functions of the above-described embodiments are realized by performing part or all of the actual processing.

  Furthermore, after the program code read from the storage medium is written to a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the expanded function is based on the instruction of the program code. This includes a case where a CPU or the like provided on the expansion board or the expansion unit performs part or all of the actual processing and the functions of the above-described embodiments are realized by the processing.

1 is a cross-sectional view of a main part of a color printer as an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating a schematic configuration of an intermediate transfer unit in FIG. 1. It is a perspective view which shows only the front half side of the outer roller in FIG. FIG. 2 is a block diagram schematically showing a circuit configuration of an image output unit in FIG. 1. FIG. 5 is a block diagram schematically showing a circuit configuration of a belt motor controlled by the DSP in FIG. 4. It is a figure used for demonstrating the image acquisition method on the surface of the belt by the image sensor unit in FIG. The surface image of the belt acquired by the image sensor unit is shown. It is a block diagram which shows the structure of an image sensor unit roughly. It is a figure used for demonstrating the signal transmitted to DSP in FIG. 8 from DSP. It is a figure which shows the gravity center position of a detection area, (a) shows the state which the gravity center position has displaced only to the Y direction, (b) has the state where the gravity center position has displaced in both X and Y directions Indicates. It is a block diagram which shows the schematic structure of DSP in FIG. It is a figure used for demonstrating the gravity center calculation process performed by the gravity center calculation process part of FIG. 11, (a) is the image (binarization) after binarizing the image of the detection area in sample time t1 (B) shows a table of the center of gravity calculation results, (c) shows a binarized image at the sample time t2, and (d) shows a table of the center of gravity calculation results. It is a figure which shows the modification of the table | surface of the binarized image in FIG. 12, and the gravity center calculation result based on the binarized image. It is a flowchart which shows the procedure of the control processing of the moving speed and deviation | shift amount of a belt performed by DSP. It is a flowchart which shows the procedure of the motor control process of step S1422 of FIG. It is a flowchart which shows the procedure of the gravity center calculation process of step S1413 of FIG. It is sectional drawing which shows the modification of an image output part. It is a block diagram which shows roughly the structure of the conventional tandem type image forming apparatus. It is a figure used for demonstrating the conventional sampling method. It is a figure which shows the 1st image pattern in the conventional detection area. It is a figure which shows the 2nd image pattern in the conventional detection area. It is a figure which shows the 3rd image pattern in the conventional detection area.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Color printer 1P Image output part 1R Image reading part ad Station 10 Image forming part 20 Feed unit 60 Image sensor unit 31 Belt 32 Drive roller 50 DSP
56 Belt motor 67 Motor driver 81 Motor 304 CMOS sensor

Claims (5)

An image forming apparatus for transferring an image formed on an image carrier via a belt to a recording material,
Belt moving means for moving the belt at a preset moving speed v ;
A sensor that reads a surface image of the belt at a predetermined sampling rate Δt ;
Detecting means for detecting a shift amount of the belt moved by the belt moving means based on the surface image read by the sensor;
Limiting means for limiting the detection area of the sensor to the number of pixels m in the Y direction which is the moving direction of the belt and the number n of pixels in the X direction which is the direction of the belt,
The limiting means is
A first setting means for setting prior Symbol the Y-direction value m _min or more values obtained by multiplying the moving velocity v in the sampling rate Δt of the pixel number m the belt detection area of the sensor,
When the shift amount is smaller than a predetermined size, the number n of pixels in the X direction of the detection area of the sensor is set to a minimum value n _min that the sensor can set as the size of the detection area in the X direction. When the amount is equal to or larger than the predetermined size, the sensor sets the number n of pixels in the X direction of the detection area to a value larger than the minimum value n _min and the sensor sets the number of pixels m in the Y direction. An image forming apparatus comprising: a second setting unit that sets the detection area to a maximum value m _{max that} can be set as a size in the Y direction .   2. The image forming apparatus according to claim 1, wherein the belt primarily transfers an image formed on the image carrier on a surface thereof, and secondarily transfers the primary transferred image onto the recording material. apparatus. The belt, the image forming apparatus according to claim 1 or 2, wherein the conveying the recording material. The sensor image forming apparatus according to any one of claims 1 to 3, characterized in that it comprises a plurality of photoelectric conversion elements. A control method of an image forming apparatus for transferring an image formed on an image carrier onto a recording material via a belt,
A belt moving step for moving the belt at a preset moving speed v ;
A reading step of reading a surface image of the belt by a sensor at a predetermined sampling rate Δt ;
A detecting step for detecting a shift amount of the belt moved in the belt moving step based on the surface image read in the reading step;
A limiting step of limiting the detection area of the sensor to the number of pixels m in the Y direction, which is the moving direction of the belt, and the number n of pixels in the X direction, which is a direction of the belt
The limiting means is
A first setting step of setting before Symbol the Y-direction value m _min or more values obtained by multiplying the moving velocity v in the sampling rate Δt of the pixel number m the belt detection area of the sensor,
When the shift amount is smaller than a predetermined size, the number n of pixels in the X direction of the detection area of the sensor is set to a minimum value n _min that the sensor can set as the size of the detection area in the X direction. When the amount is equal to or larger than the predetermined size, the sensor sets the number n of pixels in the X direction of the detection area to a value larger than the minimum value n _min and the sensor sets the number of pixels m in the Y direction. And a second setting step for setting the detection area to a maximum value m _{max that} can be set as a size in the Y direction .

Images