JP2007003704A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus carrying out a process for controlling stabilization of variation in speed in a belt occurring due to eccentricity of a disc of an encoder in position control by a low cost method. <P>SOLUTION: The image forming apparatus includes: a transfer transportation belt 60, a transfer driving motor 302, an entrance roller 66, the encoder 301 with two sensors detecting the state of circulation movement of the transfer transportation belt 60, a composition circuit 501, a multiplier circuit 502, a counter 503 carrying out counting, a sampling circuit 504 and a data storing means storing data for signal generating timing for the two sensors when the belt performs circulation movement. When feed back control is carried out by a count value of the sampling circuit 504, the data storing means is referred to and when the signal generating timing for the two sensors vary at the same time, one of the output signals is delayed and signal processing is carried out thereafter. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine or a laser printer.

  Conventionally, in feedback control, it is desired to improve the response to load fluctuations by increasing the control gain. However, increasing the control gain increases the one-rotation component of the disk, resulting in increased color misregistration. In this case, the feedback control was unavoidable with a low control gain. For this reason, other fluctuation components that are originally desired to be controlled have not been sufficiently removed. A method of controlling the speed fluctuation of the transfer belt generated by the eccentricity of the disk attached to the driven roller is known (for example, see Patent Document 1). This is because the driving roller is rotated at a constant speed, the angular velocity information obtained from the output of the encoder is acquired over at least one period of the driving roller, and the first half part and the latter half part are added by dividing the driving roller by 1/2 period. The eccentric speed fluctuation component due to the driving roller is canceled out, and only the speed fluctuation due to the driven roller is extracted. Further, at the time of image formation, the speed running of the belt is made constant by taking the difference between the angular velocity information detected from the driven roller and the speed fluctuation.

  By the way, a typical method for forming a color image includes a direct transfer method in which toner images of different colors formed on a plurality of photoconductors are transferred while being directly superimposed on a recording sheet, and a color image formed on a plurality of photoconductors. There is an intermediate transfer method in which different toner images are transferred while being superimposed on an intermediate transfer member, and then transferred onto a recording sheet at once. Since the plurality of photoconductors are arranged to face the recording paper or the intermediate transfer member, it is called a tandem system, and yellow (Y), magenta (M), cyan (C), and black (K) for each photoconductor. An electrophotographic process such as formation of an electrostatic latent image and development is executed for each of the colors, and the image is transferred onto a running recording sheet in the direct transfer method, and onto a running intermediate transfer member in the intermediate transfer method.

  In the tandem color image forming apparatus using each of these methods, the direct transfer method receives an endless belt that runs while supporting the recording paper, and the intermediate transfer method receives an image from a photoconductor. Generally, an endless belt to be carried is employed. Then, an image forming unit including four photoconductors is installed side by side on one running side of the belt.

  In the tandem color image forming apparatus, it is important to prevent the occurrence of color misregistration in order to accurately superimpose toner images (dot images) of each color of YMCK in order. Therefore, in any transfer system, in order to avoid color misregistration due to transfer belt speed fluctuation, an encoder is attached to one of the driven shafts composed of a plurality of transfer units, and the transfer speed is changed according to the rotation speed fluctuation of the encoder. Feedback control of the rotational speed of the drive roller is an effective means.

  The most common method for realizing this feedback control is proportional control (PI control). This calculates the position deviation e (n) from the difference between the target angular displacement Ref (n) of the encoder and the detected angular displacement P (n-1) of the encoder, and applies a low-pass filter to the calculation result to remove high frequency noise. In addition, the output of the encoder is always driven at the target angular displacement by applying a control gain and adding a constant standard drive pulse frequency to control the drive pulse frequency of the drive motor connected to the drive roller. It is a method to control.

  As actual control, a counter that counts the rising edge of the output of the encoder pulse and a counter that counts every control cycle (for example, 1 ms) are used, and the calculation result of the target angular displacement that moves during the control cycle (1 ms). The position deviation can be acquired from the difference from the detected angular displacement obtained by acquiring the encoder count value for each control cycle. A specific calculation is as follows when the roller diameter of the driven shaft to which the encoder is attached is φ15.615.

e (n) = θ0 × q−θ1 × ne Unit: rad
e (n) [rad]: Position deviation (calculated in this sampling) θ0 [rad]: Movement angle per control cycle (= 2π × V × E-3 / 15.615π [rad])
θ1 [rad]: Movement angle per encoder pulse (= 2π / p [rad])
q: Count value of control cycle timer V: Belt linear velocity [mm / s]

Here, for example, assuming that the control resolution is 300 ms and the encoder resolution is 300 pulses per revolution, and the feedback control is performed so that the transfer belt operates at 162 mm / s, the following is assumed.
θ0 = 2π × 162 × E-3 / 15.615π = 0.0207487 [rad]
θ1 = 2π / p = 2π / 300 = 0.0209439 [rad]
A position deviation is acquired by performing the above calculation for every control period, and feedback control is performed.

  A general encoder configuration is such that a disk having a slit that transmits light with a resolution of several hundred units in the circumferential direction is press-fitted into the driven roller shaft and rotates simultaneously with the driven roller. By detecting at this point, a pulsed ON / OFF signal is obtained according to the amount of rotation of the driven roller. The rotational speed of the driving roller is controlled by detecting the moving angle of the driven roller using this pulse-like ON / OFF signal.

JP 2000-47547 A

  However, in the conventional technology as shown above, due to the processing accuracy of the concentricity of the disc, when the disc is attached to the driven roller, it may be attached in a state shifted from each other. When rotated in a state, the disk is rotated in an eccentric state even though the driven roller rotates at a constant speed. When this is read by the sensor, one rotation component of the disk is output to the sensor output.

  Further, since one rotation component is amplified by feedback control to rotate the drive roller, the transfer belt speed fluctuates every time the disk rotates, and color misregistration occurs.

  The control method disclosed in Patent Document 1 measures the pulse interval of the encoder with a constant clock, and subtracts the encoder speed fluctuation when the drive roller is rotated at a constant speed from the encoder speed when feedback control is performed. Therefore, the speed control is performed so as to cancel the speed fluctuation caused by the disk eccentricity and to keep the encoder speed constant. This requires a clock rate that can sample the effect sufficiently, high-speed hardware that can process it, and measurement means such as a high-resolution counter and timer, which are disadvantageous in terms of cost.

  Further, as described above, the position deviation e (n) is calculated from the difference between the target angular displacement Ref (ni) of the encoder and the detected angular displacement P (n−1) of the encoder, and the drive pulse frequency of the drive motor is calculated from the calculation result. In the case of position control for controlling the control method, the control method disclosed in Patent Document 1 cannot be applied.

  The present invention has been made in view of the above, and provides an image forming apparatus that performs control by a low-cost method for stabilizing the speed fluctuation of a belt caused by eccentricity of an encoder disk in position control. The purpose is to do.

  In order to solve the above-described problems and achieve the object, the invention according to claim 1 is driven by a recording member carrier, a driving means for driving the recording member carrier, and driving of the recording member carrier. At least one driven part, and a plurality of marks arranged at a fixed interval and disposed at at least one position of the driving means or the driven part, respectively, are attached at positions shifted by 180 degrees, for detecting the marks An encoder that has two sensors and detects the circumferential movement state of the recording member carrier, a combining unit that combines the outputs of the two sensors, and a multiplying unit that multiplies the combined signal of the combining unit by half. A counter that counts the signal multiplied by ½, sampling means that samples the count value output from the counter at a fixed timing, Data storage means for storing in advance the signal generation timing data of the two sensors output when the recording member carrier rotates, and the control target is determined by the count value obtained by the sampling means. When performing feedback control on the value, referring to the data stored in the data storage means, if the signal generation timing of the two sensors changes at the same time, after delaying one of the output signals, The signal processing is performed.

  According to the first aspect of the present invention, when performing feedback control on the control target value based on the count value obtained by the sampling means, the data stored in the data storage means is referred to and the signals of the two sensors If the generation timing changes at the same time, delay the output signal of one of the signals and perform subsequent signal processing to control the belt speed fluctuation caused by the eccentricity of the encoder disk in position control. It becomes possible to do.

  According to a second aspect of the present invention, the data input to the data storage means is performed by checking the signal generation timings of the outputs of the two sensors before the encoder is incorporated in the image forming apparatus. Is performed by an input from an external input means.

  According to the second aspect of the present invention, in the first aspect, the data input to the data storage means is performed by checking the signal generation timing of the outputs of the two sensors before the encoder is incorporated in the image forming apparatus. By inputting an appropriate delay amount from an external input means, it becomes possible for a service person in the market to respond, for example, and even if the encoder part is replaced, the input of the signal with the optimum delay amount is input from the outside. By correcting, a target frequency signal without error can be obtained.

  According to a third aspect of the present invention, there is provided a detecting means for detecting a signal generation timing of the two sensor outputs, the detection by the detecting means is performed when the encoder is incorporated in the image forming apparatus, and the necessary The delay amount is calculated by the image forming apparatus itself.

  According to the third aspect of the present invention, in the first aspect, when the encoder is incorporated in the image forming apparatus, detection is performed by the detection means, and the necessary delay amount is calculated by the image forming apparatus itself. Only the sensor output on one side is delayed so that the sensor output does not change at the same time, and then input to the synthesizing means, and a target frequency signal without error is obtained.

  Further, the invention according to claim 4 is characterized in that the detecting means detects the generation timing at every certain time and calculates a necessary delay amount.

  According to the fourth aspect of the present invention, in the third aspect, the detection means detects the occurrence timing at every predetermined time and calculates a necessary delay amount, thereby avoiding an error-free aim in consideration of changes with time. The frequency signal is obtained.

  The invention according to claim 5 is characterized in that an encoder whose relative position is adjusted in advance is used so that the output signals of the two sensors do not change simultaneously when the encoder is driven.

  According to the fifth aspect of the invention, in the first aspect, when the encoder is driven, the encoders of the two sensors are adjusted by using the encoders whose relative positions are adjusted in advance so that the output signals of the two sensors do not change simultaneously. The output does not change at the same time, and a target frequency signal without error can be obtained.

  The image forming apparatus according to the present invention (Claim 1) refers to the data stored in the data storage means when performing feedback control with respect to the control target value based on the count value obtained by the sampling means. When the signal generation timing of two sensors changes at the same time, the output speed of one of the sensors is delayed before the subsequent signal processing is performed, so that the belt speed fluctuation caused by the eccentricity of the encoder disk in position control is stabilized. There is an effect that the control to be performed can be performed with an inexpensive configuration.

  The image forming apparatus according to the second aspect of the present invention is the image forming apparatus according to the first aspect, wherein the data input to the data storage means is the signal generation timing of the outputs of the two sensors before the encoder is incorporated into the image forming apparatus. If the necessary delay amount is input from the external input means, for example, it becomes possible for a service person in the market to respond, and even if the encoder part is replaced, the signal with the optimum delay amount By re-inputting the input from the outside, there is an effect that a target frequency signal without error can be obtained.

  According to a third aspect of the present invention, the image forming apparatus according to the first aspect performs detection by a detecting unit when the encoder is incorporated in the image forming apparatus, and the image forming apparatus itself calculates a necessary delay amount. By doing so, it is possible to obtain a target frequency signal with no error by delaying only one sensor output so that the two sensor outputs do not change at the same time and then inputting to the combining means. Play.

  The image forming apparatus according to the present invention (Claim 4) is the image forming apparatus according to Claim 3, in which the detecting means detects the occurrence timing at every certain time and calculates a necessary delay amount, so that the change with time is detected. There is an effect that it is possible to obtain a target frequency signal with no error in consideration.

  The image forming apparatus according to the present invention (Claim 5) uses the encoder according to Claim 1 in which the relative position is adjusted in advance so that the output signals of the two sensors do not change simultaneously when the encoder is driven. As a result, the outputs of the two sensors do not change at the same time, and there is an effect that a target frequency signal without error can be obtained.

  Exemplary embodiments of an image forming apparatus according to the present invention will be explained below in detail with reference to the accompanying drawings.

(Embodiment)
One embodiment in which the present invention is applied to an electrophotographic color laser printer (hereinafter referred to as “laser printer”) as an image forming apparatus will be described with reference to FIGS.

  FIG. 1 is an explanatory diagram showing a schematic configuration of a laser printer according to an embodiment of the present invention. This laser printer includes four toner image forming units 1Y, 1M, 1C, 1K (hereinafter referred to as “yellow” (Y), magenta (M), cyan (C), and black (K)). The subscripts Y, M, C, and K of the reference numerals indicate yellow, magenta, cyan, and black members, respectively, and the transfer direction of the recording paper 100 (along arrow A in the drawing). 60 in the traveling direction) are arranged in order from the upstream side. Each of the toner image forming units 1Y, 1M, 1C, and 1K includes photosensitive drums 11Y, 11M, 11C, and 11K as image carriers and a developing unit. The arrangement of the toner image forming units 1Y, 1M, 1C, and 1K is set so that the rotation axes of the photosensitive drums are parallel to each other and arranged at a predetermined pitch in the recording paper moving direction. Yes.

  In addition to the toner image forming units 1Y, 1M, 1C, and 1K, the laser printer carries the optical writing unit 2, the paper feed cassettes 3 and 4, the registration roller pair 5, and the recording paper 100, and each toner image forming unit. A transfer unit 6 as a belt driving device having a transfer conveyance belt 60 as a transfer conveyance member that conveys the sheet so as to pass through the transfer position, a belt fixing type fixing unit 7, a paper discharge tray 8, and the like. In addition, a manual feed tray MF and a toner supply container TC are provided, and a waste toner bottle, a duplex / reversing unit, a power supply unit, and the like (not shown) are also provided in a space S indicated by a two-dot chain line.

  The optical writing unit 2 includes a light source, a polygon mirror, an fθ lens, a reflection mirror, and the like, and irradiates the surface of each of the photosensitive drums 11Y, 11M, 11C, and 11K while scanning with laser light based on image data.

  FIG. 2 is an enlarged view showing a schematic configuration of the transfer unit 6. The transfer conveyance belt 60 used in the transfer unit 6 is a high-resistance endless single-layer belt having a volume resistivity of 109 to 1011 Ωcm, and the material thereof is PVDF (polyvinylidene fluoride). The transfer conveyance belt 60 is wound around support rollers 61 to 68 so as to pass through the transfer positions that are in contact with and face the photosensitive drums 11Y, 11M, 11C, and 11K of the toner image forming units. Of these rollers, reference numeral 61 is appropriately described as an entrance roller, reference numeral 63 is a transfer driving roller, reference numeral 66 is a lower right roller, and reference numeral 68 is a backup roller.

  Out of these supporting rollers, the outer peripheral surface of the transfer / conveying belt 60 is opposed to the supporting roller (entrance roller) 61 on the upstream side in the recording sheet moving direction so that the electrostatic adsorption roller 80 to which a predetermined voltage is applied from the power source 65a is opposed. Is arranged. The recording paper 100 that has passed between the two support rollers 61 and 62 is electrostatically adsorbed onto the transfer conveyance belt 60.

  Reference numeral 63 denotes a transfer driving roller for frictionally driving the transfer conveyance belt 60, which is connected to a driving source (not shown) and rotates in the direction of the arrow.

  As a transfer electric field forming means for forming a transfer electric field at each transfer position, transfer bias applying members 67Y, 67M, 67M, 67M, 67C and 67K are provided. These are bias rollers provided with a sponge or the like on the outer periphery, and a transfer bias is applied to the roller core from each transfer bias power source 9Y, 9M, 9C, 9K. Due to the action of the applied transfer bias, a transfer charge is applied to the transfer conveyance belt 60, and a transfer electric field having a predetermined strength is formed between the transfer conveyance belt 60 and the surface of the photosensitive drum at each transfer position. Further, a backup roller 68 is provided in order to keep the contact between the recording paper 100 and the photosensitive drums 11Y, 11M, and 11C in the transfer area and to obtain the best transfer nip.

  The transfer bias applying members 67Y, 67M, and 67C and the backup roller 68 disposed in the vicinity thereof are integrally held by the swing bracket 93 so as to be rotatable, and can be rotated around a rotation shaft 94. This rotation is clockwise when the cam 96 fixed to the cam shaft 97 is rotated in the direction of the arrow.

  The entrance roller 61 and the suction roller 80 are integrally supported by the entrance roller bracket 90, and can be rotated clockwise from the state shown in FIG. A hole 95 provided in the swing bracket 93 and a pin 92 fixed to the entrance roller bracket 90 are engaged with each other, and rotate in conjunction with the rotation of the swing bracket 93. By the clockwise rotation of the entrance roller bracket 90 and the swinging bracket 93, the bias applying members 67Y, 67M, and 67C and the backup roller 68 disposed in the vicinity thereof are separated from the photosensitive drums 11Y, 11M, and 11C. The entrance roller 61 and the suction roller 80 also move downward. It is possible to avoid contact between the photosensitive drums 11Y, 11M, and 11C and the transfer / conveying belt 60 when forming a black-only image.

  On the other hand, the transfer bias applying member 67K and the backup roller 68 adjacent to the transfer bias applying member 67K are rotatably supported by the outlet bracket 98, and are rotatable about a shaft 99 coaxial with the outlet roller 62. When the transfer unit 6 is attached to or detached from the main body, the transfer unit 6 is rotated clockwise by an operation of a handle (not shown) to transfer the transfer bias applying member 67K and the backup roller 68 adjacent thereto from the photosensitive drum 11K for black image formation. Are separated from each other.

  A cleaning device 85 including a brush roller and a cleaning blade is disposed on the outer peripheral surface of the transfer conveyance belt 60 wound around the transfer driving roller 63. The cleaning device 85 removes foreign matters such as toner adhering to the transfer conveyance belt 60.

  A roller 64 is provided downstream of the driving roller 63 in the traveling direction of the transfer conveyance belt 60 in a direction to push the outer peripheral surface of the transfer conveyance belt, and a winding angle around the drive roller 83 is ensured. A tension roller 65 that applies tension to the belt with a pressing member (spring) 69 is provided in a loop of the transfer conveyance belt 60 further downstream from the roller 64.

  The one-dot chain line in FIG. 1 shown above indicates the conveyance path of the recording paper 100. The recording paper 100 fed from the paper feed cassettes 3 and 4 or the manual feed tray MF is transported by a transport roller while being guided by a transport guide (not shown), and is transported to a temporary stop position where the registration roller pair 5 is provided. The recording paper 100 delivered by the registration roller pair 5 at a predetermined timing is carried on the transfer conveyance belt 60, conveyed toward the toner image forming units 1Y, 1M, 1C, and 1K, and passes through the transfer nips. .

  The toner images developed on the toner drums 11Y, 11M, 11C, and 11K of the toner image forming units 1Y, 1M, 1C, and 1K are superimposed on the recording paper 100 at the respective transfer nips, and the transfer electric field and nip It is transferred onto the recording paper 100 under the action of pressure. By this superposition transfer, a full color toner image is formed on the recording paper 100.

  The surfaces of the photosensitive drums 11Y, 11M, 11C, and 11K after the toner image transfer are cleaned by a cleaning device, and are further neutralized to prepare for the formation of the next electrostatic latent image.

  On the other hand, after the full color toner image is fixed by the fixing unit 7, the recording paper 100 on which the full color toner image is formed corresponds to the rotation direction of the switching guide G in the first paper discharge direction B or the second paper discharge direction B. In the paper discharge direction C. When the paper is discharged from the first paper discharge direction B onto the paper discharge tray 8, it is stacked in a so-called face-down state with the image surface down. On the other hand, when the paper is discharged in the second paper discharge direction C, it is conveyed toward another post-processing device (not shown) (such as a sorter or a binding device) or again for double-sided printing via a switchback unit. It is conveyed to the registration roller pair 5.

  With the above configuration, a full color image is formed on the recording paper 100. In the tandem color image forming apparatus, it is important to prevent the occurrence of color misregistration by accurately superimposing the toner images of the respective colors. However, the drive roller 63, the entrance roller 61, the exit roller 99, and the transfer / conveying belt 60 used in the transfer unit 6 are subject to a manufacturing error of several tens of μm when the parts are manufactured. Due to this error, a fluctuation component generated when each part makes one rotation is transmitted to the transfer conveyance belt 60, and the conveyance speed of the paper fluctuates, so that the toner on each of the photosensitive drums 11Y, 11M, 11C, and 11K is transferred. A slight shift occurs in the timing of transfer to the recording paper 100, and a color shift occurs in the sub-scanning direction. In particular, in an apparatus that forms an image with minute dots such as 1200 × 1200 DPI as in this embodiment, a timing shift of several μm is conspicuous as a color shift. In this embodiment, an encoder is provided on the shaft of the lower right roller 66, the rotation speed of the encoder is detected, and the rotation of the drive roller 63 is feedback-controlled so that the transfer belt 60 travels constantly.

  FIG. 3 shows a configuration of main parts of the transfer unit 6 and a block diagram of a control system. The transfer drive roller 63 is connected to the drive gear of the transfer drive motor 302 by a timing belt 303, and is rotated in proportion to the drive speed of the transfer drive motor 302 by rotating the drive transfer motor 302. When the transfer driving roller 63 rotates, the transfer conveyance belt 60 is driven, and when the transfer conveyance belt 60 is driven, the lower right roller 66 rotates. In this embodiment, the encoder 301 is arranged on the axis of the lower right roller 66, and the rotational speed of the lower right roller 66 is detected by the encoder 301 to control the speed of the transfer drive motor 302. This is performed in order to minimize the speed fluctuation because the color shift occurs due to the speed fluctuation of the transfer conveyance belt 60 as described above.

  That is, light from the light emitting elements 402 and 406 is received by the light receiving elements 403 and 407 through the disc 401 (see FIGS. 4 and 5), respectively, and these two outputs are input to the combining circuit 501 to be combined. Further, the output synthesized by the synthesis circuit 501 is multiplied by ½ by the multiplication circuit 502, the signal multiplied by ½ is counted by the counter 503, and the count value of the counter is sampled at a constant timing by the sampling circuit 504. The signals of the two sensors (light emitting elements 402 and 406) that are output when the transfer conveyance belt 60 rotates when performing feedback control with respect to the control target value based on the count value obtained by the sampling circuit 504. The generation timing (generation timing data 800) is checked in advance, and if both change simultaneously, the output signal of one side is delayed and the subsequent signal processing is performed. Details of this control will be described later.

  4 and 5 show detailed configurations of the lower right roller 66 and the encoder 301. FIG. The encoder 301 includes a disk 401, light emitting elements 402 and 406, light receiving elements 403 and 407, and press-fitting bushes 404 and 405. The disc 401 is fixed by press-fitting press-fitting bushes 404 and 405 on the shaft of the lower right roller 66, and is rotated simultaneously with the rotation of the lower right roller 66. The disc 401 has slits that transmit light with a resolution of several hundred units in the circumferential direction, and the light emitting elements 402 and 406 and the light receiving elements 403 and 407 are arranged at positions shifted by 180 degrees on both sides thereof. A pulsed ON / OFF signal is obtained according to the rotation amount of the lower right roller 66. The driving amount of the transfer driving motor 302 is controlled by detecting the moving angle of the lower right roller 66 (hereinafter referred to as angular displacement) using this pulse-like ON / OFF signal.

  An error of several μm occurs in the machining of the coaxial hole when the disc 401 is press-fitted into the lower right roller 66, and it is practically impossible to reduce this to zero in consideration of component accuracy (machining accuracy). is there. Therefore, when the disc 401 is attached to the lower right roller 66, it may be attached in a state of being shifted from each other. When the disc 401 is rotated in this state, the disc 401 is rotated even though the lower right roller 66 is rotating at a constant speed. Is rotated in an eccentric state. When this is read by a sensor, angular displacement fluctuations occur every cycle of the disk.

  The sampling results of the two light receiving elements 403 and 407 when the drive motor 302 is driven at a constant speed and the count value of the encoder 301 is sampled by the sampling circuit 504 (see FIG. 3) at a constant timing are shown in FIGS. Show. FIG. 6A is a sampling result when the disk 401 is not eccentric, and FIG. 6B is a sampling result when the disk 401 is eccentric. Normally, when the disc 401 is not decentered, the sampling result rises to the right, but when there is decentration, the sampling result is a sine wave. Since the two light receiving elements 403 and 407 are arranged at positions shifted by 180 degrees, the phase of the sine wave of the sampling result is shifted by 180 degrees.

  In other words, the two sampling results can be combined to cancel the angular displacement fluctuation caused by the eccentricity of the disk 401. The present invention is characterized in that the two sampling results are synthesized by the synthesis circuit 501, thereby performing proportional control calculation that is not affected by the eccentricity of the disk 401 and making the speed of the transfer conveyance belt 60 constant.

  A specific method for combining the outputs of the two light receiving elements 403 and 407 will be described below. FIG. 9 is a block diagram for implementing the output synthesis of the present invention. The output signals of the light receiving elements 403 and 407 are input to the synthesizing circuit 501, and after synthesizing, the signals further pass through the multiplier circuit 502. In the multiplier circuit 502, the frequency is halved by synchronizing with the prepared reference clock. Multiply to output. Then, drive control is performed using this output signal.

  Note that a delay circuit 505 is also provided before the synthesis circuit 501. In general, OR synthesis is simple, but if two sensor outputs overlap, the clock is simply reduced by one, resulting in an error in the resulting frequency. The delay circuit 505 is for suppressing this error, and a control unit such as the CPU 901 can intentionally delay the timing of one output signal. As a result, the input timing of the two sensor outputs to the synthesis circuit 501 can be shifted, and the frequency remains unchanged. Therefore, the signals after the synthesis circuit 501 and the multiplication circuit 502 are accurately synthesized. Become.

  The subsequent control processing will be specifically described below. FIG. 7 is a block diagram of a drive control apparatus for carrying out the drive control method according to the embodiment of the present invention. Hereinafter, the case where the drive control apparatus of this embodiment is applied to the rotating body drive apparatus of the above embodiment will be described.

  In FIG. 7, the difference e (n) between the target angular displacement Ref (n) of the encoder 301 and the detected angular displacement P (n−1) of the encoder 301 is input to the control controller unit 801. The control controller unit 801 includes a low-pass filter 802 for removing high frequency noise and a proportional element (gain Kp) 803. In the control controller unit 801, a correction amount for the standard drive pulse frequency used for driving the transfer drive motor 302 is obtained and provided to the calculation unit 804. In the calculation unit 804, the correction amount is added to the constant standard drive pulse frequency Refp_c to determine the drive pulse frequency f (n).

  Also, the detected angular displacement error of the encoder 301 due to the eccentricity of the disk 401 of the encoder 301 measured in advance when the drive motor 302 is driven at a constant speed is added to the target angular displacement Ref (n). The difference displacement amount is calculated by taking the difference e (n) from P (n−1). The detection angular displacement error due to the eccentricity of the disk 401 is added so as to be repeated periodically according to the output timing of the mark sensor detected by the rotation of the disk 401.

  FIG. 8 is a block diagram showing a control system of the transfer drive motor 302 and a hardware configuration to be controlled in this embodiment. This control system digitally controls the drive pulse of the transfer drive motor 302 based on the output signal of the encoder 301. This control system includes a CPU 901, a RAM 902, a ROM 903, an IO control unit 904, a transfer motor drive I / F unit 906, a driver 907, a detection IO unit 908, a bus 909, and an external device 910.

  The CPU 901 controls the entire image forming apparatus including the reception of image data input from the external apparatus 910 and the transmission / reception control of control commands. A RAM 901 used for work, a ROM 903 for storing a program, and an IO control unit 904 are connected to each other via a bus 909, and a motor and a clutch that drive data load / read processing and loads 905 according to instructions from the CPU 901. Various operations such as solenoids and sensors are executed.

  The transfer motor drive motor IF 906 outputs a drive pulse signal to the transfer drive motor 302 via the driver 907 in response to a drive command from the CPU 901. Since the transfer drive motor 302 is driven to rotate according to the frequency of the drive pulse signal, the drive speed control can be varied.

  An output signal of the encoder 305 is input to the detection IO unit 908. The detection IO unit 908 processes the output pulses of the light receiving elements (encoder sensors) 403 and 407 and converts them into digital numerical values. The detection IO unit 908 includes a counter that counts output pulses of the light receiving elements (encoder sensors) 403 and 407. Then, the numerical value counted by this counter is multiplied by a predetermined conversion constant of the pulse number diagonal displacement to convert it into a digital numerical value corresponding to the angular displacement of the lower right roller 66. A digital numerical value signal corresponding to the angular displacement of the disk 401 is sent to the CPU 901 via the bus 909.

  The transfer motor drive IF unit 906 generates a pulsed control signal having the drive frequency based on the drive frequency command signal sent from the CPU 901.

  The driver 907 is composed of a power semiconductor element (for example, a transistor). The driver 907 operates based on the pulsed control signal output from the transfer motor drive IF unit 906 and applies a pulsed drive voltage to the transfer drive motor 302. As a result, the transfer drive motor 302 is driven and controlled at a predetermined drive frequency output from the CPU 901. As a result, the additional value is controlled so that the angular displacement of the disk 401 follows the target angular displacement, and the lower right roller 66 rotates at a predetermined angular displacement. The angular displacement of the disk 401 is detected by the light receiving elements (encoder sensors) 403 and 407 and the detection IO unit 908, and is taken into the CPU 901 and the control is repeated.

  FIG. 12 shows a timing chart for realizing this control. First, the count value of the encoder pulse counter 1 measured by the detection IO unit 908 is incremented by the rising edge of the encoder pulse output. Further, the control cycle of this control is 1 ms, and the count value of the control cycle timer counter is incremented every time the CPU 901 is interrupted by the control cycle timer. The timer is started when the rising edge of the encoder pulse is detected for the first time after the through-up and settling of the transfer drive motor 302 is completed, and the count value of the control cycle timer counter is reset. Also, every time the CPU 901 is interrupted by the control cycle timer, the count value: ne of the encoder pulse counter 1 is acquired and the count value: q of the control cycle timer counter is acquired and incremented.

Based on each count value, the position deviation is calculated as follows.
P (n-1) = θ1 × ne
Ref (n) = θ0 × q
e (n) = Ref (n) -P (n-1) Unit: rad
Here, the symbols in the above are as follows.
e (n) [rad]: Position deviation (calculated in this sampling) θ0 [rad]: Movement angle per control period 1 [ms] (= 2π × V × E-3 / In [rad])
θ1 [rad]: Movement angle per encoder pulse (= 2π / p [rad])
q: Count value of control cycle timer V: Belt linear velocity [mm / s]
l: Lower right roller diameter [mm]
f: Period of disk rotation [Hz]

  In this embodiment, the outer diameter of the lower right roller 66 to which the encoder 301 is attached is φ15.515 [mm]. In this embodiment, the encoder resolution p is assumed to be 300 pulses per revolution.

  Next, in order to avoid responding to a sudden position change, a filter operation with the following specifications is performed on the calculated deviation.

Filter type: Butterworth IIR low-pass filter Sampling frequency: 1 KHz (= equal to control period)
Passband ripple (Rp): 0.01 dB
Stop band end attenuation (Rs): 2 dB
Passband edge frequency (Fp): 50 Hz
Stopband edge frequency (Fs): 100Hz

FIG. 15 shows a block diagram of this filter calculation, and FIG. 16 shows a list of filter coefficients. Two-stage cascade connection is used, and the intermediate nodes in each stage are u1 (n), u1 (n-1), u1 (n-2) and u2 (n), u2 (n-1), u2 (n-2), respectively. It is determined. Here, the meaning of the index is as follows.
(N): Current sampling
(N-1): Previous sampling
(N-2): Two previous samplings

The following program operation is performed each time a control timer interrupt occurs during feedback execution.
u1 (n) = a11 * u1 (n-1) + a21 * u1 (n-2) + e (n) * ISF
e1 (n) = b01 * u1 (n) + b11 * u1 (n-1) + b21 * u1 (n-2)
u1 (n-2) = × u1 (n-1)
u1 (n-1) = u1 (n)
u2 (n) = a12 * u2 (n-1) + a22 * u2 (n-2) + e2 (n)
e '(n) = b02 * u2 (n) + b12 * u2 (n-1) + b22 * u2 (n-2)
u2 (n-2) = * u2 (n-1)
u2 (n-1) = u2 (n)

  FIG. 13 shows the amplitude characteristics of this filter, and FIG. 14 shows the phase characteristics.

Next, a control amount (pulse frequency f ′ (n)) for the controlled object is obtained. In the control block diagram, first, PID (P; Proportional, I; Integral, D; Differential) control is considered as a position controller.
F (S) = G (S) × E ′ (S) = Kp × E ′ (S) + Ki × E ′ (S) / S + Kd × S × E ′ (S)
However, Kp: proportional gain, Ki: integral gain, Kd: differential gain G (S) = F (S) / E ′ (S) = Kp + Ki / S + Kd × S (1)
Here, when the bilinear transformation (S = (2 / T) × (1−Z−1) / (1 + Z−1)) is performed on the equation [1], the following equation is obtained.
G (Z) = (b0 + b1 * Z-1 + b2 * Z-2 / (1-a1 * Z-1-a2 * Z-2) [2]
However, a11 = 0
a2 = 1
b0 = Kp + T × Ki / 2 + 2 × Kd / T
b1 = T × Ki−4 × Kd / T
b2 = Kp + T × Ki / 2 + 2 × Kd / T

The above equation [2] is represented as a block diagram as shown in FIG. Here, e ′ (n) and f (n) indicate that E ′ (S) and F (S) are treated as discrete data, respectively. In FIG. 17, when w (n), w (n-1), and w (n-2) are defined as intermediate nodes, the difference equation is as follows (general expression for PID control). Here, the meaning of the index is as follows.
(n): Current sampling
(n-1): Previous sampling
(n-2): previous sampling w (n) = a1 * w (n-1) + a2 * w (n-2) + e '(n) (3)
f (n) = b0 * w (n) + b1 * w (n-1) + b2 * w (n-2) ... [4]
Considering proportional control as a position controller, the integral gain and derivative gain are zero.

Accordingly, the coefficients in FIG. 17 are as follows, and the above equations [3] and [4] are simplified as the following equation [5].
a1 = 0
a2 = 1
b0 = Kp
b1 = 0
b2 = −Kp
w (n) = a2 × w (n−2) + e ′ (n)
f (n) = Kp × w (n) −Kp × (n−2)
Ｆ f (n) = Kp × e ′ (n) (5)
In addition, the discrete data corresponding to F0 (S): f0 (n) is constant in this embodiment,
f0 (n) = 6105 [Hz]
It is. Therefore, the pulse frequency f ′ (n) set in the transfer drive motor 302 is finally calculated by the following equation.
f ′ (n) = f (n) + f0 (n) = Kp + e ′ (n) +6105 [Hz] (6)

  FIG. 18 shows an operation flowchart of the encoder pulse counter 1. First, it is determined whether or not it is the first pulse input after through-up and settling (step S1). If YES here, the encoder pulse counter 1 is cleared to zero (step S2), and the control cycle counter is cleared to zero (step S3). Then, the interrupt by the control cycle timer is permitted (step S4), the control cycle timer is started (step S5), and the process returns. If NO in step S1, the encoder pulse counter is incremented (step S6) and the process returns.

  FIG. 19 shows an operation flowchart of the encoder pulse counter 2. First, when an encoder pulse is input, the state of the disk mark sensor is determined (step S11). If YES here, the encoder pulse counter 2 is cleared to zero (step S12). If NO in step S11, the encoder pulse counter 2 is incremented (step S13) and the process returns.

  FIG. 20 shows a flowchart of interrupt processing by the control cycle timer. First, the control cycle timer counter is incremented (step S21), and then the encoder pulse count value: ne is acquired (step S22). Further, the value of Δθ is acquired with reference to the table data (step S23), and the table reference address is incremented (step S24). Using these values, position deviation calculation is performed (step S25), filter calculation is performed on the obtained position deviation (step S26), and control amount calculation (proportional calculation) is performed based on the result of the filter calculation. (Step S27), the frequency of the stepping motor drive pulse is actually changed (step S28), and the process returns.

  With the above control, the control for stabilizing the speed fluctuation of the transfer conveyance belt 60 caused by the eccentricity of the disk of the encoder 301 in the position control can be processed by an inexpensive method.

  In the above embodiment, the present invention is applied to the transfer unit 6 in the tandem printer in which a plurality of the photosensitive drums 11Y, 11M, 11C, and 11K are arranged on the transfer conveyance belt 60. The printer and the belt driving device to which can be applied are not limited to this configuration. In a printer having a belt driving device that rotationally drives an endless belt stretched around a plurality of rollers by at least one of the rollers, any belt driving device can be applied. is there.

  In this embodiment, the exposure light source is laser light. However, the present invention is not limited to this. For example, an LED array may be used.

  Next, the operation timing of the delay circuit in FIG. 9 will be described. Variations in the generation timings of the outputs of the two sensors (light receiving elements 403 and 407) are largely due to manufacturing variations of the encoder 301, particularly variations in sensor mounting within the encoder, and it can be said that most of them are related to the components of the encoder 301. Therefore, once it is decided to use the encoder, it can be said that the generation timings of the outputs of the two sensors (light receiving elements 403 and 407) are almost the same. In view of this feature, the present invention first checks the generation timing of the outputs of the two sensors (light receiving elements 403 and 407) as a single component before being incorporated into the machine. The necessary delay amount is calculated from that, and the relationship between one component and one characteristic value (delay amount) is clarified. After that, when the encoder 301 is assembled to the machine main body at the factory, the corresponding delay amount is stored in the memory through the machine operation unit interface or the like so that the delay amount is always applied when the encoder 301 operates. As a result, a signal with an optimum delay amount is input, and as a result, a target frequency signal without error is obtained. Note that this method can be used not only at the time of assembly in a manufacturing factory but also in the market through an external device 910 (see FIG. 8) such as an operation unit interface. Therefore, even if the encoder parts are replaced, there is a delay. Re-entering the amount will not cause a problem.

  Next, an example using the block diagram of FIG. 10 instead of FIG. 9 will be described. Although it has been described above that there is almost no component variation in the encoder 301, there are actually factors other than the encoder such as differences in signal paths and changes over time. Therefore, in the present invention, the delay amount as the mechanical system is calculated so that a more accurate frequency can be obtained. Specifically, as shown in FIG. 20, the CPU 901 directly detects two sensor outputs in a state of being incorporated as a mechanical system, examines the generation timing thereof, and the CPU 901 calculates an optimal delay amount. Thus, only the sensor output on one side is delayed and input to the synthesis circuit so that the two sensor outputs do not change simultaneously. As a result, an optimum delay as a mechanical system is applied, and as a result, a target frequency signal with less error is obtained.

  Next, an example will be described in which a change over time is reconsidered not only at the time of incorporation into a machine but also at certain time intervals, assuming a change with time. The value of “certain fixed time” varies depending on the mechanical system to be assembled. For example, in a system having a characteristic in which the generation timing changes in a long cycle, there is no problem if it is performed “every time the power is turned on”, which is always performed once a day, as long as the copying machine / printer is used. Also, if the occurrence timing changes in a short cycle, which changes in the daily use situation, such as changes due to the temperature in the machine, etc., detect the temperature in the machine and re-detect it due to the temperature change. Is the best. In any case, the “certain fixed time” varies depending on the system to be assembled. However, according to this embodiment, it is possible to cope with the mechanical system.

  Finally, the block diagram shown in FIG. 11 will be described. The two sensors (light receiving elements 403 and 407) in the encoder 301 are attached at positions that are 180 degrees out of phase, but the attachment accuracy is further defined. The encoder 301 has a plurality of marks arranged at regular intervals. The marks are arranged on a disk and sandwiched between two sensors. This mark is optically detected, but at the same time, the mark is accurately placed at a position where the polarity is reversed, such that the sensor on one side is H (high) and the sensor on one side is L (low). As a result, the two sensor outputs do not change at the same time, and the conventional delay circuit and the detection circuit associated therewith are not required, so that the configuration shown in FIG. 11 is obtained.

  Although the cost of the encoder 301 itself increases, the real-time processing of the CPU 901 is not necessary, and there is an advantage that the load on the microcomputer performance can be reduced.

  Therefore, according to the embodiment of the present invention described above, when the endless belt is controlled by the encoder attached to the driven roller, the control for stabilizing the speed fluctuation of the belt caused by the disk eccentricity can be performed with an inexpensive method. Thus, it is possible to perform processing, and good feedback control can be performed.

  As described above, the image forming apparatus according to the present invention is useful for an image forming apparatus such as a tandem type color copying machine or a color printer. In particular, in the tandem type full color image forming apparatus, the dot position of each color is determined. It is suitable for a device for performing high precision on a transfer belt or a device for driving an endless belt with high precision.

It is explanatory drawing which shows schematic structure of the laser printer concerning embodiment of this invention. FIG. 2 is an enlarged view showing a schematic configuration of a transfer unit in FIG. 1. FIG. 2 is a block diagram illustrating a configuration and a control system of main parts of a transfer unit in FIG. 1. It is explanatory drawing which shows the detailed structure of a lower right roller and an encoder in a transfer unit. It is explanatory drawing which shows the structure of the disc of an encoder, a light emitting element, and a light receiving element. It is a graph which shows the sampling result of two light receiving elements when the count value of an encoder (when there is no eccentricity in a disk) is sampled at a fixed timing. It is a graph which shows the sampling result of two light receiving elements when the count value of an encoder (when a disk has eccentricity) is sampled at a fixed timing. It is a block diagram which shows the structural example of the drive control concerning embodiment of this invention. FIG. 2 is a block diagram illustrating a control system of a transfer driving motor and a hardware configuration to be controlled according to an embodiment of the present invention. It is a block diagram which shows the structural example (1) of the drive control system concerning embodiment of this invention. It is a block diagram which shows the structural example (2) of the drive control system concerning embodiment of this invention. It is a block diagram which shows the structural example (3) of the drive control system concerning embodiment of this invention. It is a timing chart which shows the operation | movement of the drive control concerning embodiment of this invention. It is a graph which shows the amplitude characteristic of the filter concerning embodiment of this invention. It is a graph which shows the phase characteristic concerning embodiment of this invention. It is a block diagram which shows the filter calculation concerning embodiment of this invention. It is a graph which shows the filter coefficient concerning embodiment of this invention. It is a block diagram showing [2] Formula concerning embodiment of this invention. 3 is a flowchart showing the operation of the encoder pulse counter 1. 4 is a flowchart showing the operation of the encoder pulse counter 2. It is a flowchart which shows the interruption process by a control period timer.

Explanation of symbols

60 Transfer conveyor belt 66 Lower right roller 301 Encoder 302 Transfer drive motor 401 Disk 402, 406 Light emitting element 403, 407 Light receiving element 501 Synthesis circuit 502 Multiplication circuit 503 Counter 504 Sampling circuit 800 Generation timing data 901 CPU
902 RAM
907 Driver 910 External device

Claims (5)

A recording member carrier;
Driving means for driving the recording member carrier;
At least one driven portion driven by driving the recording member carrier;
A plurality of marks arranged at at least one location of the driving means or the driven portion, and arranged at regular intervals, and attached at positions shifted by 180 degrees, and having two sensors for detecting the marks; An encoder for detecting a circumferential movement state of the recording member carrier;
Combining means for combining the outputs of the two sensors;
A multiplier for multiplying the combined signal of the combiner by 1/2;
A counter for counting the signal multiplied by 1/2,
Sampling means for sampling the count value output from the counter at a fixed timing;
Data storage means for storing in advance signal generation timing data of the two sensors output when the recording member carrier rotates;
With
When the feedback control for the control target value is performed based on the count value obtained by the sampling means, referring to the data stored in the data storage means, and the signal generation timings of the two sensors change simultaneously Is an image forming apparatus that performs subsequent signal processing after delaying one output signal.   Data input to the data storage means is performed by checking the signal generation timing of the outputs of the two sensors before the encoder is incorporated in the image forming apparatus and inputting the necessary delay amount from the external input means. The image forming apparatus according to claim 1.   Detection means for detecting signal generation timings of the two sensor outputs is provided, and detection is performed by the detection means when the encoder is incorporated in the image forming apparatus, and the image forming apparatus itself calculates a necessary delay amount. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 3, wherein the detection unit detects a generation timing at every predetermined time and calculates a necessary delay amount.   The image forming apparatus according to claim 1, wherein an encoder whose relative position is adjusted in advance is used so that output signals of the two sensors do not change simultaneously when the encoder is driven.

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