JP5124390B2 - Image forming apparatus - Google Patents

Description

 The present invention relates to an image forming apparatus such as a copier, a printer, or a multifunction peripheral.

In recent years, as one of image forming methods in an image forming apparatus using electrophotography represented by a copying machine or a printer, four colors of black (BK), yellow (Y), magenta (M), and cyan (C) are used. The color tandem system that realizes high-speed full-color printing by arranging the photosensitive drums in a row and sequentially transferring the toner images of each color formed (developed) on each photosensitive drum to paper or an intermediate transfer member is known. It has been. For example, in Patent Documents 1 and 2 listed below, in an image forming apparatus employing such a color tandem method, in order to prevent color misregistration caused by dimensional errors or mounting errors of mechanical parts such as a photosensitive drum. A technique related to the correction processing is disclosed.
JP-A-10-278338 JP 2007-30207 A

  By the way, in the image forming apparatus adopting the color tandem method, the cause of the color misregistration is not limited to the dimensional error and the mounting error of the machine parts. For example, in recent image forming apparatuses, in order to increase the speed, a configuration in which a plurality of arithmetic circuits that execute predetermined arithmetic processing based on output signals of various sensors and output various control signals is installed is adopted. Yes. These arithmetic circuits are arranged on individual boards in order to reduce the board scale, and furthermore, an oscillation circuit as a clock signal source for operating each arithmetic circuit is individually provided on each board. It is common to have. The reason for adopting a configuration in which an oscillation circuit is individually provided for each substrate (for each arithmetic circuit) in this way is that if a configuration in which a clock signal generated by an oscillation circuit on a certain substrate is supplied to another substrate is employed, This is because a high frequency causes a problem in clock transmission quality and unnecessary electromagnetic radiation increases.

  However, even when a configuration in which an oscillation circuit is provided for each substrate is employed, each oscillation circuit has a tolerance with respect to an ideal oscillation frequency, so that the oscillation frequencies of all the oscillation circuits are kept exactly the same. There is no. There is a possibility that the tolerance deviation of the oscillation frequency existing between the oscillation circuits causes the color deviation described above. Here, in order to specifically explain the color shift caused by the tolerance shift of the oscillation frequency, for example, a laser scanning unit (hereinafter referred to as a laser scanning unit) that performs exposure by irradiating the photosensitive drum with a laser by a polygon mirror. The toner image of each color formed (developed) on the photosensitive drum of each color is sequentially transferred (primary transfer) to the transfer belt, which is an intermediate transfer body, and then formed on the transfer belt. Assume an image forming apparatus that employs a color tandem method in which an image is collectively transferred (secondary transfer) onto a sheet by a secondary transfer roller.

  In such an image forming apparatus, an arithmetic circuit that generates a control clock signal of a polygon motor (motor that drives a polygon mirror) that determines the laser scanning speed of the LSU and a control clock signal of a rotating bell motor that drives the transfer belt are generated. If the oscillation circuit that supplies the clock signal is provided separately from the arithmetic circuit that performs the operation, there is a tolerance deviation in the oscillation frequency between the oscillation circuits. A speed difference is generated with respect to the moving speed of the belt, and as a result, color misregistration occurs in the sub-scanning direction of the image primarily transferred onto the transfer belt.

 The present applicant has applied for an invention that can prevent color misregistration caused by tolerance deviation of oscillation frequency existing in each oscillation circuit as described above as Japanese Patent Application No. 2007-300240. Hereinafter, regarding the invention described in Japanese Patent Application No. 2007-300240, as shown in FIG. 6, a first arithmetic circuit 33 that supplies a first control clock signal to a polygon motor and a second control clock signal to a bell motor are provided. A motor control circuit including the second arithmetic circuit 37 to be supplied will be described as an example.

  In FIG. 6, the reference oscillation circuit 30 generates a reference clock signal having a frequency fo and outputs the reference clock signal to the first frequency counter 32 and the second frequency counter 36. Here, the frequency fo of the reference clock signal is set to a sufficiently low value (for example, 1/1000) as compared with the frequency fa of the first clock signal and the frequency fb of the second clock signal described below. The first oscillation circuit 31 generates a first clock signal having the frequency fa and outputs the first clock signal to the first frequency counter 32 and the first arithmetic circuit 33.

 The first frequency counter 32 is a frequency counter that uses the reference clock signal as the clock to be measured and the first clock signal as the measurement clock, and has a first count value Ca that represents the result of measuring the period of the reference clock signal with the first clock signal. (= Fa / fo) is output to the first arithmetic circuit 33. The first sensor group 34 is a sensor for detecting information necessary for generating the first control clock signal, such as the drive start timing and drive stop timing of the polygon motor, and outputs an output signal representing this information to the first arithmetic circuit. To 33.

 The first arithmetic circuit 33 divides the first clock signal (frequency division ratio Na) based on the first count value Ca and the information acquired from the first sensor group 34 to control the polygon motor. A control clock signal is generated. Here, the first arithmetic circuit 33 has a function of generating the first control clock signal by correcting the frequency shift between the reference clock signal and the first clock signal based on the first count value Ca. Specifically, the first arithmetic circuit 33 stores in advance a first count value Cao in an ideal case where there is no tolerance deviation between the oscillation frequencies of the reference oscillation circuit 30 and the first oscillation circuit 31. The frequency deviation rate Za (= Ca / Cao) is calculated by dividing the first count value Ca output from the counter 32 by the ideal first count value Cao.

 Then, the first arithmetic circuit 33 corrects the frequency division ratio Na using the frequency deviation rate Za calculated as described above (specifically, the frequency division ratio Na is multiplied by the frequency deviation rate Za), and the correction is performed. A first control clock signal is generated using the subsequent frequency division ratio Na ′. At this time, the frequency fa1 of the first control clock signal is represented by fa1 = fa / Na ′ = fa / (Na · Za). That is, the first control clock signal is generated in a state where the frequency deviation between the reference clock signal and the first clock signal is corrected.

  The second oscillation circuit 35 generates a second clock signal having the frequency fb and outputs it to the second frequency counter 36 and the second arithmetic circuit 37. The second frequency counter 36 is a frequency counter that uses the reference clock signal as the clock to be measured and the second clock signal as the measurement clock, and a second count value Cb that represents the result of measuring the period of the reference clock signal with the second clock signal. (= Fb / fo) is output to the second arithmetic circuit 37. The second sensor group 38 is a sensor for detecting information necessary for generating the second control clock signal, such as the drive start timing and drive stop timing of the rotary bell motor, and outputs an output signal representing this information to the second arithmetic circuit. To 37.

 The second arithmetic circuit 37 divides the second clock signal (frequency division ratio Nb) based on the second count value Cb and the information acquired from the second sensor group 38 to control the second bell motor. A control clock signal is generated. Here, the second arithmetic circuit 37 has a function of correcting the frequency shift between the reference clock signal and the second clock signal based on the second count value Cb and generating a second control clock signal. Specifically, the second arithmetic circuit 37 stores in advance a second count value Cbo in an ideal case where there is no tolerance deviation between the oscillation frequencies of the reference oscillation circuit 30 and the second oscillation circuit 35, and the second frequency The frequency deviation rate Zb (= Cb / Cbo) is calculated by dividing the second count value Cb output from the counter 36 by the ideal second count value Cbo.

 Then, the second arithmetic circuit 37 corrects the frequency division ratio Nb using the frequency deviation rate Zb calculated as described above (specifically, the frequency division rate Nb is multiplied by the frequency deviation rate Zb), and the correction is performed. A second control clock signal is generated using the subsequent frequency division ratio Nb ′. At this time, the frequency fb1 of the second control clock signal is represented by fb1 = fb / Nb ′ = fb / (Nb · Zb). That is, the second control clock signal is generated in a state where the frequency deviation between the reference clock signal and the second clock signal is corrected.

 By adopting such a configuration, even if there is a tolerance deviation in the oscillation frequencies fa and fb of the first oscillation circuit 31 and the second oscillation circuit 35, the first arithmetic circuit 33 generates the first Since the 1 control clock signal and the second control clock signal generated by the second arithmetic circuit 37 are maintained in a synchronous relationship with the reference clock signal, the laser scanning speed (exposure processing speed) and the transfer belt It is possible to prevent a speed difference from occurring with respect to the moving speed, and as a result, it is possible to prevent color misregistration from occurring in the sub-scanning direction of the image primarily transferred onto the transfer belt.

  On the other hand, recent image forming apparatuses are operated by supplying respective control clock signals to a plurality of mechatronic components. Therefore, using the invention of the above-mentioned Japanese Patent Application No. 2007-300240, if it is attempted to completely correct the tolerance shift between the oscillation circuits in the entire system inside the image forming apparatus, all the circuits generating the respective control clock signals It is necessary to perform a correction operation (including hardware and software), and resources such as a CPU and an arithmetic circuit are consumed for the correction operation.

  As described above, when resources such as a CPU and an arithmetic circuit are used for the calculation of the clock correction process, the processing capability of the entire system is lowered. In addition, in order to suppress a decrease in the processing capacity of the entire system, a high-performance CPU and arithmetic circuit capable of performing high-speed and complicated processing are required, resulting in an increase in apparatus cost.

 The present invention has been made in view of the above-described circumstances, and an object thereof is to provide an image forming apparatus capable of preventing color misregistration with high accuracy while minimizing resource consumption.

  In order to achieve the above object, the present invention provides, as a first solving means related to an image forming apparatus, an oscillation circuit that supplies a clock signal to an arithmetic circuit that generates a control clock signal for controlling a drive unit, An image forming apparatus provided separately for each arithmetic circuit, and adopting a configuration capable of maintaining a synchronous relationship between a control clock signal that causes at least color misregistration in the sub-scanning direction and a predetermined reference clock signal In addition, a control unit that forms patches of each color corresponding to each developing device at predetermined intervals along the sub-scanning direction, and a patch detection signal that is installed at a predetermined position and becomes a predetermined level every time the color patch passes. A patch detection sensor that outputs, and a counter that uses a horizontal synchronization signal that defines one line period as a measurement clock and the patch detection signal as a clock to be measured. Grasp the color misregistration amount count value based on the serial counter, the color shift amount and performs feedback control so is corrected.

 Further, as a second solving means relating to the image forming apparatus, in the first solving means, the synchronization relationship between the control clock signal that causes the color shift in the sub-scanning direction and a predetermined reference clock signal is maintained. A reference clock generation circuit for generating a reference clock signal having a frequency lower than that of the clock signal, and a circuit provided separately for each of the arithmetic circuits, the reference clock signal as a clock to be measured, and the oscillation circuit Each of the arithmetic circuits, based on the count value of the frequency counter corresponding to itself, based on the count value of the frequency counter corresponding to itself, A configuration is adopted in which the control clock signal is generated by correcting a frequency shift with respect to the reference clock signal. To.

 Further, as a third solving means relating to the image forming apparatus, in the second solving means, each of the arithmetic circuits has a count value of a frequency counter corresponding to the arithmetic circuit, and an oscillation frequency of the oscillation circuit corresponding to the arithmetic circuit. The frequency deviation rate is calculated by dividing by the count value in the ideal case, the frequency deviation rate is multiplied by the division ratio used to generate the control clock signal, and the frequency division ratio after the multiplication is self-determined. The control clock signal is generated by dividing the clock signal supplied from the oscillation circuit corresponding to the above.

 Further, as a fourth solving means relating to the image forming apparatus, in any of the above first to third solving means, when a laser scanning unit is used as an exposure device, a dot clock for defining the dot size A reference clock signal generated by dividing the signal, a control clock signal that defines the speed of the motor that scans the laser, a control clock signal that defines the speed of the transport system motor, and a motor that rotationally drives the photosensitive drum It is characterized by adopting a configuration that maintains a synchronous relationship with a control clock signal that defines the speed of the signal.

 Further, as a fifth solving means relating to the image forming apparatus, in any one of the first to third solving means, when an LED print head is used as an exposure device, it is generated by dividing the horizontal synchronizing signal. A configuration is employed in which a synchronization relationship is maintained between a reference clock signal, a control clock signal that defines the speed of the transport system motor, and a control clock signal that defines the speed of the motor that rotationally drives the photosensitive drum. .

 According to the present invention, a configuration is employed that enables the synchronization relationship between a control clock signal that causes at least color misregistration in the sub-scanning direction and a predetermined reference clock signal to be maintained, as well as individual variations, environmental fluctuations, and the like. Because of the color deviation caused by changes in roller diameter, belt extension, and paper slip due to the It is possible to prevent color misregistration with high accuracy while suppressing.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. As an image forming apparatus according to this embodiment, a laser color printer adopting a color tandem method will be described as an example. FIG. 1 is a schematic configuration diagram of an image forming apparatus 100 according to the present embodiment. As shown in FIG. 1, an image forming apparatus 100 according to the present embodiment includes image forming units 10Y, 10M, 10C, and 10B, a transfer belt 20, conveying rollers 21 and 22, primary transfer rollers 23Y and 23M, 23C, 23B, a secondary transfer roller 24, a paper cassette 25, a paper feed roller 26, a fixing device 27, and a paper discharge roller 28.

  The image forming units 10Y, 10M, 10C, and 10B are provided corresponding to four colors of yellow (Y), magenta (M), cyan (C), and black (BK), and Y in the figure. They are arranged in a line along the axial direction (sub-scanning direction), and toner images of four colors of yellow, magenta, cyan, and black are sequentially transferred to the transfer belt 20 by respective processes of charging, exposure, development, and transfer. (Primary transfer). In the following, detailed configurations of the image forming units 10Y, 10M, 10C, and 10B will be described. However, each unit is different in color of developer (toner) to be used, and the main configuration is the same. This will be described using the image forming unit 10Y.

  The image forming unit 10Y includes a photosensitive drum 11Y, a charger 12Y, an exposure device 13Y, and a developing device 14Y. The photosensitive drum 11Y is a cylindrical electrostatic latent image carrier having a rotation axis in the X-axis direction (main scanning direction) in the figure, and faces the primary transfer roller 23Y with the transfer belt 20 sandwiched therebetween. As shown in FIG. The rotational speed of the photosensitive drum 11Y is determined by the rotational speed of a photosensitive drum motor (not shown), and this photosensitive drum motor is controlled by a third control clock signal supplied from a third arithmetic circuit 42 described later. It is what is done.

 The charger 12Y extends along the rotation axis direction (that is, the X-axis direction) of the photoconductor drum 11Y, and discharges negatively charged electric charges toward the surface of the photoconductor drum 11Y. The surface of the drum 11Y is uniformly charged (charging process).

 The exposure unit 13Y is composed of a laser scanning unit (LSU) including a laser light source (not shown), a polygon motor, and the like, and a photosensitive member by rotating the polygon motor with laser light emitted from the laser light source. By scanning along the main scanning direction of the drum 11Y, negative charges at predetermined positions on the surface of the photosensitive drum 11Y are erased, and an electrostatic latent image corresponding to a yellow image is formed (exposure processing). That is, the laser scanning speed (exposure processing speed) is determined by the rotational speed of the polygon motor, and this polygon motor is controlled by a first control clock signal supplied from a first arithmetic circuit 33 described later. is there.

 The developing device 14Y extends along the rotational axis direction of the photosensitive drum 11Y, receives toner supplied from a yellow toner cartridge (not shown), and discharges the toner toward the surface of the photosensitive drum 11Y. Thus, a toner image corresponding to the electrostatic latent image formed by the exposure process is formed on the surface of the photosensitive drum 11Y (development process). The toner image thus formed on the surface of the photosensitive drum 11Y is transferred onto the transfer belt 20 that moves in the Y-axis direction between the photosensitive drum 11Y and the primary transfer roller 23Y (primary transfer processing). ). Specifically, a predetermined transfer voltage is applied to the primary transfer roller 23Y, and the transfer belt 20 is positively charged, whereby the toner image formed on the surface of the photosensitive drum 11Y is transferred onto the transfer belt 20. .

  The image forming units 10M, 10C, and 10B have the same configuration as the image forming unit 10Y described above. In other words, the image forming unit 10M includes a photosensitive drum 11M, a charger 12M, an exposure device 13M, and a developing device 14M. A toner image corresponding to a magenta image formed on the surface of the photosensitive drum 11M is photosensitive. The image is transferred onto the transfer belt 20 that moves in the Y-axis direction between the body drum 11M and the primary transfer roller 23M.

 The image forming unit 10C includes a photosensitive drum 11C, a charger 12C, an exposure device 13C, and a developing device 14C. A toner image corresponding to a cyan image formed on the surface of the photosensitive drum 11C is photosensitive. The toner image is transferred onto the transfer belt 20 that moves in the Y-axis direction between the body drum 11C and the primary transfer roller 23C. The image forming unit 10B includes a photosensitive drum 11B, a charger 12B, an exposure device 13B, and a developing device 14B. A toner image corresponding to a black image formed on the surface of the photosensitive drum 11B is a photosensitive member. The toner image is transferred onto the transfer belt 20 that moves in the Y-axis direction between the body drum 11B and the primary transfer roller 23B.

  As described above, the image forming units 10Y, 10M, 10C, and 10B sequentially transfer the toner images corresponding to the yellow, magenta, cyan, and black images onto the transfer belt 20 that is an intermediate transfer member, and thereby form one toner. It is superimposed on the image. The transfer belt 20 reciprocates in the Y-axis direction (sub-scanning direction) by the rotation of the conveying rollers 21 and 22, and the moving speed and the image forming speed (development) by the image forming units 10Y, 10M, 10C, and 10B. The speed until the processing is completed is synchronously controlled so that no color misregistration occurs when the toner images are sequentially transferred and superimposed on the transfer belt 20. The moving speed of the transfer belt 20 is determined by a rotation bell motor (not shown) for rotationally driving the conveying rollers 21 and 22, and this rotation bell motor is supplied from a second operation circuit 37 described later. It is controlled by a signal.

  The secondary transfer roller 24 is installed so as to face the transport roller 21 with the transfer belt 20 sandwiched therebetween, and the paper P is fed from the paper cassette 25 to the secondary transfer roller 24 and the transfer belt 20 by the paper feed roller 26. , The toner image formed on the transfer belt 20 is collectively transferred onto the paper P (secondary transfer process). The paper P on which the toner image is formed by such secondary transfer processing is conveyed to the fixing device 27.

  The fixing device 27 is composed of a heating roller 27a and a pressure roller 27b arranged to face each other, and heats and presses the paper P conveyed between the heating roller 27a and the pressure roller 27b. The toner image is fixed on the paper P (fixing process). As a result, a desired full-color image is formed on the paper P. The paper P on which the full-color image is formed is discharged outside the apparatus main body by the paper discharge roller 28.

  On the other hand, FIG. 2 is a block diagram of a main part of the image forming apparatus 100 described above. In FIG. 2, a video clock (dot clock that defines the dot size), a polygon clock (first control clock signal that defines the speed of the polygon motor), and a carrier clock (which defines the speed of the transfer bell motor of the carrier system). Block configuration of a motor control circuit for preventing the occurrence of color misregistration while maintaining a synchronous relationship between the second control clock signal) and the drum drive clock (third control clock signal defining the speed of the photosensitive drum motor) An example is shown. In FIG. 2, the same components as those in FIG. 6 are denoted by the same reference numerals, and description thereof will be omitted.

  As shown in FIG. 2, a video clock generation circuit 30A and a frequency dividing circuit 30B are provided as a reference clock generation circuit instead of the reference oscillation circuit 30, and a third control clock signal for the photosensitive drum motor is further provided. Are provided with a third oscillation circuit 40, a third frequency counter 41, a third arithmetic circuit 42, and a third sensor group 43.

  The video clock generation circuit 30A generates a video clock signal and outputs it to the frequency dividing circuit 30B. The frequency dividing circuit 30B generates a reference clock signal by dividing the Video clock signal by a predetermined dividing ratio, and the reference clock signal is generated by the first frequency counter 32, the second frequency counter 35, and the third frequency counter 41. Output to.

 The third oscillation circuit 40 generates a third clock signal and outputs it to the third frequency counter 41 and the third arithmetic circuit 42. The third frequency counter 41 is a frequency counter that uses the reference clock signal as the clock to be measured and the third clock signal as the measurement clock, and has a third count value that represents the result of measuring the period of the reference clock signal with the third clock signal. Output to the third arithmetic circuit 42.

  Similarly to the first arithmetic circuit 33 and the second arithmetic circuit 37, the third arithmetic circuit 42 drives the photosensitive drum motor based on the third clock signal, the third count value, and the output signal of the third sensor group 43. A third control clock signal is generated, and the third control clock signal is supplied to the photosensitive drum motor. The third sensor group 43 is a sensor for detecting information necessary for generating the third control clock signal, such as the drive start timing and the drive stop timing of the photosensitive drum motor, and outputs an output signal representing this information to the third sensor signal. The result is output to the arithmetic circuit 42.

  By adopting such a configuration, even if a tolerance deviation of the oscillation frequency exists between the first oscillation circuit 31, the second oscillation circuit 35, and the third oscillation circuit 40, the Video The synchronous relationship among the clock (dot clock), the polygon clock (first control clock signal), the carrier clock (second control clock signal), and the drum drive clock (third control clock signal) is maintained, and the accuracy is high. It is possible to prevent color misregistration in the sub-scanning direction and equal magnification misregistration in the main scanning direction.

  1 illustrates the image forming apparatus 100 using a laser scanning unit (LSU) including a laser light source and a polygon motor as the exposure devices 13Y, 13M, 13C, and 13K. However, the LED print head is exposed. It may be used as a container. In this case, a horizontal synchronization signal (line clock that defines one line cycle), a carrier clock (second control clock signal for a rotating bell motor), and a drum drive clock (third control clock signal for a photosensitive drum motor) If the synchronous relationship is maintained, color misregistration in the sub-scanning direction can be prevented.

  As described above, in order to maintain the synchronous relationship among the horizontal synchronization signal, the carrier clock (second control clock signal), and the drum drive clock (third control clock signal), the video clock generation circuit 30A in FIG. Is replaced with a horizontal synchronizing signal generation circuit, and it is not necessary to use a polygon motor. Therefore, the first oscillation circuit 31, the first frequency counter 32, the first arithmetic circuit 33, and the first sensor group 34 may be deleted.

  On the other hand, in the image forming apparatus 100, the roller diameter, the belt extension amount, the paper slip amount, and the like change due to individual variation, environmental variation, and the like. Conventionally, a method of correcting color misregistration by feedback control based on the above has been employed. In this case, as a method of measuring the color misregistration amount, as shown in FIG. 3, each color (yellow (Y), magenta (M), cyan (C) corresponding to each of the developing devices 14Y, 14M, 14M, and 14B). , Black (BK) patches are formed at predetermined intervals along the sub-scanning direction, and the time taken for the patches of each color to pass over the fixedly mounted sensor surface is measured. In general, the distance between patches is calculated from the relationship with the (conveying speed), and the difference between this calculation result and the target value of the distance between patches is used as the amount of color misregistration.

  For example, if a patch is formed by setting the target value of the inter-patch distance as 50 lines, and the calculation result of the inter-patch distance obtained from the time when the patch passes on the sensor surface is 52 lines, it is equivalent to 2 lines. It can be seen that color misregistration occurs. Therefore, the speed of the transfer bell motor, the photosensitive drum motor, etc. of the conveying system may be feedback controlled so as to correct the color misregistration amount for these two lines.

  However, when calculating the inter-patch distance using the time measuring method in this way, a time measuring means such as a timer is used. Originally, the operation clock of this timer is also synchronized with the above-described reference clock signal. Need to be maintained. That is, separately, a counter circuit and an arithmetic circuit having a frequency deviation correction function for maintaining the synchronous relationship between the timer operation clock and the reference clock signal are required (increasing resource consumption).

  For this reason, in this embodiment, in order to prevent color misregistration with high accuracy while minimizing resource consumption, at least a control clock signal that causes color misregistration in the sub-scanning direction and a predetermined reference clock A configuration is employed that allows the synchronization relationship with the signal to be maintained. That is, as shown in FIG. 2, when a laser scanning unit is used as the exposure unit, the reference clock signal generated by dividing the video clock signal (dot clock) and the speed of the polygon motor are defined. A structure that maintains a synchronous relationship between one control clock signal, a second control clock signal that defines the speed of the rotating bell motor, and a third control clock signal that defines the speed of the photosensitive drum motor is employed as an exposure device. When the print head is used, a configuration is adopted in which the synchronization relationship among the reference clock signal generated by dividing the horizontal synchronization signal, the second control clock signal, and the third control clock signal is maintained.

  In the present embodiment, the configuration shown in FIG. 4 is employed for color misregistration caused by changes in roller diameter, belt extension amount, and paper slip amount due to individual variations and environmental variations. In FIG. 4, reference numeral 50 denotes a patch detection sensor, reference numeral 51 denotes a counter, and reference numeral 52 denotes a control unit. The patch detection sensor 50 is an optical sensor, for example. The patch detection sensor 50 is installed at a predetermined location in the vicinity of the transfer belt 20 or in the sheet conveyance path, and a patch detection signal that becomes high every time a patch of each color passes to the counter 51. Output.

 The counter 51 is a counter that uses a horizontal synchronization signal that defines one line cycle as a measurement clock and a patch detection signal as a clock to be measured, and controls a count value that represents the result of measuring the cycle of the patch detection signal using the horizontal synchronization signal. To 52. Here, when the LED print head is used as the exposure device, the horizontal synchronization signal used for driving the LED print head can be used as it is. When a laser scanning unit is used as the exposure unit, a timing signal that defines the laser scanning timing for each line or a theoretical value calculated from the rotation speed of the polygon motor may be used as the horizontal synchronization signal. it can.

 As shown in FIG. 3, the control unit 52 controls each driving unit in the image forming apparatus 100 to form patches of each color corresponding to each developing device at predetermined intervals along the sub-scanning direction, and a counter. The color misregistration amount is grasped based on the count value 51, and feedback control is performed so that the color misregistration amount is corrected.

 FIG. 5 is a timing chart showing the temporal correspondence between the patch detection signal output from the patch detection sensor 50 and the horizontal synchronization signal. As shown in FIG. 5, the patch detection signal transitions to a high level at the timing when each color patch passes. On the other hand, since the horizontal synchronization signal is a signal that defines one line period, it has a higher frequency than the patch detection signal. The counter 51 counts the number of pulses of the horizontal synchronization signal existing within one period (between adjacent patches) of the patch detection signal. In other words, the count value of the counter 51 represents the number of lines existing between adjacent patches (that is, the distance between patches).

  The control unit 52 grasps the difference between the count value (inter-patch distance) obtained from the counter 51 as described above and the target value of the inter-patch distance as a color misregistration amount, and corrects the color misregistration amount. Perform feedback control. For example, if a patch is formed by setting the target value of the inter-patch distance as 50 lines, and the count value (inter-patch distance) obtained from the counter 51 is 52 lines, a color misalignment of 2 lines occurs. You can see that Therefore, the speed of the transfer bell motor, the photosensitive drum motor, etc. of the conveying system may be feedback controlled so as to correct the color misregistration amount for these two lines.

  As described above, according to the configuration of FIG. 4, it is not necessary to calculate the distance between patches using a time measuring means such as a timer, and the distance between patches can be obtained directly. There is no need for a counter circuit or an arithmetic circuit having a frequency shift correction function for maintaining a synchronous relationship with the signal.

  As described above, the present embodiment employs a configuration that can maintain a synchronous relationship between a control clock signal that causes at least color misregistration in the sub-scanning direction and a predetermined reference clock signal, and individual variations. With regard to color misregistration caused by changes in roller diameter, belt extension, and paper slip due to environmental fluctuations, etc., the resource consumption can be minimized by adopting the configuration shown in FIG. Therefore, it is possible to provide the image forming apparatus 100 capable of preventing color misregistration with high accuracy.

  In the above-described embodiment, when a laser scanning unit is used as a configuration capable of maintaining a synchronous relationship between a control clock signal and a reference clock signal that cause at least color misregistration in the sub-scanning direction, A reference clock signal generated by dividing the clock signal (dot clock), a first control clock signal that defines the speed of the polygon motor, a second control clock signal that defines the speed of the rotating bell motor, and the photosensitive drum When a configuration that maintains a synchronous relationship with a third control clock signal that defines the speed of the motor is employed and an LED print head is used, a reference clock signal generated by dividing the horizontal synchronous signal, and a second control Although the case where the configuration for maintaining the synchronous relationship between the clock signal and the third control clock signal is employed has been illustrated, Not limited thereto, the other may be provided which can maintain configuration synchronization relationship with a reference clock signal in the same manner when the control clock signal which causes color shift occurred in the sub-scanning direction is present.

  In the above-described embodiment, the counter 51 is hardware. However, the function of the counter 51 may be provided in the control unit 52 to be a software counter. Further, although the laser color printer has been described as an example of the image forming apparatus 100, the present invention is not limited to this, and the present invention is not limited to this. It can also be applied to those having a function.

1 is a schematic configuration diagram of an image forming apparatus 100 according to an embodiment of the present invention. 1 is a block configuration diagram of a motor control circuit in an image forming apparatus 100 according to an embodiment of the present invention. FIG. 6 is an explanatory diagram relating to measurement of a color misregistration amount caused by individual variation, environmental variation, and the like in the image forming apparatus 100 according to an embodiment of the present invention. 3 is a circuit block diagram for correcting a color misregistration amount caused by individual variation, environmental variation, and the like in the image forming apparatus 100 according to an embodiment of the present invention. FIG. FIG. 6 is a supplementary explanatory diagram regarding correction of a color misregistration amount caused by individual variation, environmental variation, and the like in the image forming apparatus 100 according to an embodiment of the present invention. It is explanatory drawing regarding the circuit structure for color shift prevention of the image forming apparatus applied previously.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 ... Image forming apparatus, 10Y, 10M, 10C, 10B ... Image forming unit, 20 ... Transfer belt, 21, 22 ... Conveyance roller, 23Y, 23M, 23C, 23B ... Primary transfer roller, 24 ... Secondary transfer roller, 25 ... paper cassette, 26 ... feed roller, 27 ... fixer, 28 ... discharge roller, 30A ... Video clock generation circuit, 30B ... frequency divider circuit, 31 ... first oscillation circuit, 32 ... first frequency counter, 33 ... 1st arithmetic circuit, 34 ... 1st sensor group, 35 ... 2nd oscillation circuit, 36 ... 2nd frequency counter, 37 ... 2nd arithmetic circuit, 38 ... 2nd sensor group, 40 ... 3rd oscillation circuit, 41 ... 3rd frequency counter, 42 ... 3rd arithmetic circuit, 43 ... 3rd sensor group, 50 ... Patch detection sensor, 51 ... Counter, 52 ... Control part

Claims (5)

An image forming apparatus including an oscillation circuit for supplying a clock signal to an arithmetic circuit that generates a control clock signal for controlling a driving unit, for each arithmetic circuit,
Adopting a configuration capable of maintaining a synchronous relationship between a control clock signal that causes at least color misregistration in the sub-scanning direction and a predetermined reference clock signal,
A control unit that forms patches of each color corresponding to each developer at predetermined intervals along the sub-scanning direction;
A patch detection sensor that is installed at a predetermined location and outputs a patch detection signal having a predetermined level each time the patch of each color passes;
A counter that uses a horizontal synchronization signal defining one line cycle as a measurement clock and the patch detection signal as a clock to be measured,
The image forming apparatus, wherein the control unit grasps a color misregistration amount based on a count value of the counter and performs feedback control so that the color misregistration amount is corrected. As a configuration capable of maintaining a synchronous relationship between a control clock signal that causes color misregistration in the sub-scanning direction and a predetermined reference clock signal,
A reference clock generation circuit for generating a reference clock signal having a lower frequency than the clock signal;
A frequency counter provided individually for each arithmetic circuit, the reference clock signal as a clock to be measured, and a clock signal supplied from the oscillation circuit as a measurement clock,
Each of the arithmetic circuits generates the control clock signal by correcting a frequency shift of the clock signal supplied from the oscillation circuit corresponding to the reference clock signal based on the count value of the frequency counter corresponding to the arithmetic circuit. The image forming apparatus according to claim 1, wherein a configuration is adopted.  Each of the arithmetic circuits calculates the frequency deviation rate by dividing the count value of the frequency counter corresponding to itself by the count value when the oscillation frequency of the oscillation circuit corresponding to itself is ideal. The control clock signal is generated by multiplying the division ratio used to generate the control clock signal by the frequency, and dividing the clock signal supplied from the oscillation circuit corresponding to itself by the division ratio after the multiplication. The image forming apparatus according to claim 2, wherein: When using a laser scanning unit as an exposure unit,
A reference clock signal generated by dividing the dot clock signal that defines the size of the dot, a control clock signal that defines the speed of the motor that scans the laser, and a control clock signal that defines the speed of the transport system motor The image forming apparatus according to claim 1, wherein a configuration is employed in which a synchronous relationship with a control clock signal that defines a speed of a motor that rotationally drives the photosensitive drum is maintained. In the case of using an LED print head as an exposure device,
The synchronization relationship between the reference clock signal generated by dividing the horizontal synchronization signal, the control clock signal that defines the speed of the transport system motor, and the control clock signal that defines the speed of the motor that rotates and drives the photosensitive drum. The image forming apparatus according to claim 1, wherein a configuration to maintain is adopted.

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