JP6607834B2 - Medium conveying apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a medium conveying apparatus that conveys a medium such as recording paper and an image forming apparatus using the medium conveying apparatus.

  Conventionally, as a device of this type, the peripheral surface is disposed so as to contact the medium, the rotation of a follower roller that rotates as the medium moves is detected, the amount of movement of the medium is detected, and the movement of the medium is driven. There was something to control (see, for example, Patent Document 1). Further, a method for detecting the rotation of the encoder provided on the transmitted rotation shaft by transmitting the rotation of the rotation roller to another rotation shaft with a belt stretched between the shafts when detecting the rotation of the rotation roller is disclosed. (For example, refer to Patent Document 2).

JP 2001-294337 A (page 3, FIG. 1) JP 2007-331887 (page 9, FIG. 11)

  In the above-described conventional medium conveying apparatus, the follower roller is disposed at a position away from the drive roller that conveys and drives the medium in the medium conveying direction, so that the medium is affected by expansion and contraction of the medium itself. Therefore, it is difficult to accurately grasp the deviation amount of the medium, and it is difficult to perform accurate conveyance control including the moving position of the medium. For this reason, in the image forming apparatus, the accuracy of the printing position is lowered, and it is difficult to suppress the expansion and contraction of the printed image.

A medium conveying apparatus according to the present invention includes a first rotating shaft that rotates by receiving a driving force, a fixed roller that is fixedly disposed on the first rotating shaft, a coaxial roller that is disposed on the fixed roller, A universal roller rotatably held; a first rotation detection device that detects first rotation information of the fixed roller; and a second rotation detection device that detects second rotation information of the universal roller. It is characterized by having.

  An image forming apparatus according to the present invention includes the above-described medium transport device, a developer image transfer unit that transfers a developer image onto a recording medium transported by the medium transport device, the first rotation information, and the second rotation information. And a control unit that calculates a slip amount of the recording medium based on the rotation information and rotationally controls a drive motor that rotationally drives the first rotation shaft based on the slip amount.

  According to the medium conveyance device of the present invention, since the amount of deviation of the medium to be conveyed can be accurately grasped, accurate conveyance control including the moving position of the medium can be performed. According to the image forming apparatus of the present invention, The printing position accuracy can be improved and the expansion and contraction of the printed image can be suppressed.

1 is a main part configuration diagram schematically showing a main part configuration of a printer according to a first embodiment of the present invention; It is an external appearance perspective view which shows the principal part structure of a registration roller pair. In FIG. 1, it is the elements on larger scale which expanded between the registration roller and the secondary transfer part. 2 is a block diagram illustrating a circuit configuration of a main control system of the printer. FIG. 6 is a flowchart illustrating a flow of detection of conveyance slip that occurs when a recording sheet is conveyed by a registration roller pair and correction processing for the conveyance slip performed by a printer control unit. 6 is a flowchart showing a process of adjusting the speed of the registration motor in step S108 of the flowchart of FIG. It is a figure where it uses for description of a registration motor speed adjustment limit point. It is a figure where it uses for description of the structure of the registration roller pair by this invention, and the characteristic of the drive method. It is a schematic block diagram which shows the arrangement | positioning relationship of a registration roller pair and a follower roller in a comparative example. It is a top view which shows the arrangement | positioning relationship of the accompanying roller in a comparative example, the encoder for detecting rotation of this accompanying roller, and a sensor. It is a schematic block diagram which shows another arrangement | positioning relationship example of the accompanying roller and the encoder and sensor for detecting rotation of this accompanying roller in a comparative example. It is a figure where it uses for description of the structure of a drive roller and a follower roller in the comparative example, and the characteristic of the drive method.

Embodiment 1 FIG.
FIG. 1 is a main part configuration diagram schematically showing a main part configuration of a printer 1 as an image forming apparatus according to a first embodiment of the present invention.

  As shown in the figure, the printer 1 has a movement path of an intermediate transfer belt 54 as an intermediate transfer member. The intermediate transfer belt 54 is a high-resistance semiconductive plastic film and is formed in a seamless endless shape. The intermediate transfer belt 54 is spanned between the driving roller 51, the belt driven roller 52, and the backup roller 53, and is rotationally driven by the driving roller 51. And moves in the direction of arrow A. The drive roller 51 is rotationally driven by a belt motor 114 (FIG. 4) described later.

  Between the belt driven roller 52 and the driving roller 51, an image drum unit (hereinafter abbreviated as an ID unit) 11 for forming a yellow (Y) toner image in order from the upstream side in the moving direction of the intermediate transfer belt 54, magenta ( An ID unit 12 that forms a toner image of M), an ID unit 13 that forms a toner image of cyan (C), and an ID unit 14 that forms a toner image of black (K) are aligned along the intermediate transfer belt 54. The toner images of the corresponding colors are formed on the respective photosensitive drums 11a, 12a, 13a, and 14a.

  The X, Y, and Z axes in FIG. 1 take the X axis in the direction of movement of the intermediate transfer belt 54 between the belt driven roller 52 and the drive roller 51 (in the direction of arrow A). The Y axis is taken in the rotation axis direction of 11a to 14a, and the Z axis is taken in a direction perpendicular to both the axes. Here, it is assumed that the Z-axis is arranged in a substantially vertical direction.

  Since each ID unit has the same configuration, the internal configuration thereof will be described by taking the black (K) ID unit 14 as an example. In the ID unit 14, a photoconductive drum 14a as an image carrier is rotatably arranged in the direction of the arrow. Around the photoconductive drum 14a, the surface of the photoconductive drum 14a is sequentially arranged from the upstream side in the rotation direction. An electrostatic latent image is formed by selectively irradiating light from a light source such as an LED onto the surface of the charging roller 14b for uniformly charging the surface by contacting with a constant pressure and supplying the charge uniformly. An exposure head 24 for forming is provided. Here, the exposure heads 21 to 24 are configured to be detachable from the corresponding ID units 11 to 14, respectively, and the ID units 11 to 14 and the exposure heads 21 to 24 correspond to a developer image forming unit.

  Further, a toner of a predetermined color (here, black) is attached to the surface of the surface of the photosensitive drum 14a where the electrostatic latent image is formed and developed to generate a toner image, and on the photosensitive drum 14a. A cleaning blade 14e for removing residual toner remaining when the toner image is transferred to the intermediate transfer belt 54 is provided. For this reason, the cleaning blade 14e is formed of an elastic body, and the edge portion thereof is arranged so as to contact the surface of the photosensitive drum 14a with a constant pressure.

  The developing roller 14c is disposed in contact with a supply roller 14d that supplies toner to the developing roller 14c and frictionally charges the toner, and a toner cartridge 14f that stores toner to be supplied to the supply roller 14d is disposed above them. ing. The toner cartridge 14f stores black (K) toner and is detachably attached to the ID unit 14 body. Note that the rotating body used in each of these devices rotates by receiving power from an ID motor 115 (FIG. 4) described later via a gear or the like.

  Primary transfer rollers 31 to 34 as primary transfer members are arranged to face the respective photosensitive drums 11 a to 14 a of the ID units 11 to 14 with an intermediate transfer belt 54 interposed therebetween. The primary transfer rollers 31 to 34 move the intermediate transfer belt 54 sandwiched in the direction of arrow A while the photosensitive drums 11a to 14a are in contact with the intermediate transfer belt 54 at the primary transfer positions. The toner images of the respective colors formed on the surfaces 14a to 14a are sequentially superimposed on the intermediate transfer belt 54 for primary transfer. During the primary transfer, as will be described later, a predetermined transfer voltage is applied to each of the primary transfer rollers 31 to 34 by the transfer bias generator 107 (FIG. 4).

  The cleaning blade 55 is disposed in contact with the intermediate transfer belt 54 at a position facing the belt driven roller 52 and scrapes off adhering substances such as toner adhering to the surface of the intermediate transfer belt 54. The deposits scraped off here fall into the cleaner container 56 and are accommodated.

  As described above, the intermediate transfer belt 54 transports the toner images (color images) of the respective colors formed by the developer image forming unit in a superimposed manner to the secondary transfer unit 63. In the secondary transfer unit 63 as a developer image transfer unit, the toner image primarily transferred to the intermediate transfer belt 54 is carried out from a registration roller pair 75 described later by a secondary transfer roller 61 to which a predetermined voltage is applied. Secondary transfer is performed on the recording paper 2 to be printed.

  The recording medium accommodating cassette 71 is detachably attached to the lower part of the printer 1 and stacks recording paper 2 as a recording medium. The recording sheets 2 loaded in the recording medium accommodating cassette 71 are taken out one by one by a discriminating means (not shown) and a hopping roller 72 at a predetermined timing, and the intermediate transfer belt 54 is conveyed by a pair of conveying rollers 73 and 74 and a pair of registration rollers 75. Are conveyed to a secondary transfer portion 63 which is a nip portion of the secondary transfer roller 61. During this time, skew is corrected by the registration roller pair 75.

  As will be described later, the hopping roller 72 is rotationally driven by the hopping motor 111 (FIG. 4), the registration roller pair 75 is rotationally driven by the registration motor 112 (FIG. 4), and the conveyance roller pairs 73, 74, and 76 are the conveyance motor 113. (FIG. 4). In FIG. 1, the conveyance path of the recording paper 2 is indicated by a dotted line. The hopping roller 72, the conveyance roller pairs 73, 74, and 76, and the registration roller pair 75 correspond to the medium conveyance unit.

  In the secondary transfer unit 63, the toner image transferred to the intermediate transfer belt 54 by the secondary transfer roller 61 is secondarily (re) transferred to the recording paper 2 conveyed to the nip portion, and transferred. 2 is discharged in the direction of arrow C along the transport path. During the secondary transfer, as will be described later, a predetermined transfer voltage is applied to the secondary transfer roller 61 by the transfer bias generator 107 (FIG. 4).

  The fixing unit 68 includes a heat roller 66 having a heat source therein, and a pressure roller 67 urged against the heat roller 66 by an urging means (not shown), and the recording paper 2 is heated with the heat roller 66 and the pressure roller 67. During the passage, the toner image transferred onto the recording paper 2 is fixed by heat and pressure. The conveyance roller pair 76 discharges the recording sheet 2 on which the toner is fixed to a stacker unit 69 formed outside the printer 1.

  FIG. 2 is an external perspective view showing the main configuration of the registration roller pair 75. As shown in the figure, the registration roller pair 75 is disposed on the lower side and is coaxial with the drive roller 81 and the drive roller 81 that are rotationally driven by a registration motor 112 (FIG. 4) to be described later. A rotation roller 89 is disposed so as to be rotatable, and an idle roller (roller not having its own driving means) 82 is disposed on the upper side.

  The drive roller 81 includes a rotation shaft 81a as a first rotation shaft, six divided rollers 83 to 88 as fixed rollers, and a first encoder 80a. The six divided rollers 83 to 88 are fixedly arranged at substantially equal intervals, with a rotation shaft 81a being coaxial, three from the both end sides, with a space for disposing the rotation roller 89 at the center. The first encoder 80a is fixedly arranged coaxially with the divided rollers 83 to 88 on the end side of the divided roller 83 fixedly arranged on the outer side.

  In the central portion of the drive roller 81, a follower roller 89 as a free roller is arranged coaxially with the six divided rollers 83 to 88. The follower roller 89 is arranged with respect to the rotation shaft 81a. The directional movement is restricted and is rotatably arranged. Further, a second encoder 89 a is coaxially fixedly disposed on the follow roller 89. The outer diameters of the split rollers 83 to 88 and the follower roller 89 are the same.

  The first sensor 91 is disposed at a position where a plurality of slits formed radially at equal angular intervals can be individually detected in the first encoder 80a. For example, the first sensor 91 is obtained by detecting light transmitted through the slit. The first rotation information of the encoder 80a is transmitted to the printer control unit 101 (FIG. 4) described later. The first encoder 80a and the first sensor 91 correspond to the first rotation detection device.

  The second sensor 92 is disposed at a position where the plurality of slits radially formed at equal angular intervals can be individually detected by the second encoder 89a, and is obtained by detecting light transmitted through the slit, for example. The second rotation information of the 2-encoder 89a is transmitted to the printer control unit 101 (FIG. 4) described later. The second encoder 89a and the second sensor 92 correspond to a second rotation detection device.

  The idle roller 82 is disposed such that the rotation shaft 82a as the second rotation shaft is parallel to the rotation shaft 81a of the drive roller 81 and the peripheral surface thereof is in contact with the peripheral surface of each roller of the drive roller 81. Yes. Therefore, the idle roller 82 rotates with the rotation of the drive roller 81 when the recording paper 2 is not sandwiched, and rotates with the conveyance movement of the recording paper 2 when the recording paper 2 is sandwiched.

  Further, when the recording paper 2 is not sandwiched, the follower roller 89 is rotated by the rotation operation of the idle roller 82, and when the recording paper 2 is sandwiched, the follower roller 89 rotates as the recording paper 2 is transported. . Accordingly, even if the follow roller 89 is in a state where the drive roller 81 is rotated, the recording paper 2 is not moved for some reason, for example, slipping, or the moving speed thereof is divided by the dividing rollers 83 to 83. If it does not match the rotation of 88, the rotation is stopped or the rotation speed of the split rollers 83 to 88 is lowered. That is, the follow roller 89 rotates at a rotation speed according to the actual moving speed of the recording paper 2.

  FIG. 3 is a partially enlarged view in which the space between the registration roller pair 75 and the secondary transfer unit 63 in FIG. 1 is enlarged. As shown in the drawing, a recording sheet sensor 77 is disposed downstream of the registration roller pair 75 in the medium conveyance direction (arrow C direction). The recording paper sensor 77 may be a combination of a lever that is displaced in contact with the passing paper and a displacement sensor that detects the displacement of the lever, and, as shown in FIG. It may be a transmission type sensor arranged above and below (shown), and has an arrangement and configuration capable of detecting the leading edge and the trailing edge of the recording paper 2 being conveyed.

  The secondary transfer unit 63 receives the recording paper 2 conveyed by the registration roller pair 75, and the recording paper 2 passes through the intermediate transfer belt 54 and the secondary transfer roller 61 in the process of passing through the intermediate transfer belt 54. The primary transferred toner image is secondarily transferred onto the recording surface of the recording paper 2.

  FIG. 4 is a block diagram illustrating a circuit configuration of a main control system of the printer 1.

  In the figure, the host interface unit 102 transmits / receives data to / from a command / image processing unit 103, and the command / image processing unit 103 outputs image data to the exposure head interface unit 104. The exposure head interface unit 104 controls head drive pulses and the like by the printer control unit 101, and causes the exposure heads 21 to 24 for each color to emit light.

  The printer control unit 101 as a control unit includes a microprocessor, a ROM, a RAM, an input / output port, a timer, and the like, and sends voltage setting signals to the charging bias generation unit 105, the development bias generation unit 106, and the transfer bias generation unit 107. send. The charging bias generator 105 is individually provided for each of the charging rollers 11b to 14b (only 14b is shown in FIG. 1) of the ID units 11 to 14 for yellow (Y), magenta (M), cyan (C), and black (K). Similarly, the developing bias generator 106 individually applies the bias voltage to the developing rollers 11c to 14c (only 14c is shown in FIG. 1) of the ID units 11 to 14 for the respective colors.

  The transfer bias generator 107 is for each color arranged to face the photosensitive drums 11a to 14a of the ID units 11 to 14 for yellow (Y), magenta (M), cyan (C), and black (K). A bias voltage is individually applied to the primary transfer rollers 31 to 34 and the secondary transfer roller 61.

  The printer control unit 101 includes a hopping motor 111 that drives the hopping roller 72, a registration motor 112 as a drive motor that drives the registration roller pair 75, a conveyance motor 113 that drives the conveyance roller pairs 73, 74, and 76, and a drive roller 51. Four drum motors (Y, M, C, K) 115 for individually driving each rotating body such as a belt motor 114 to be driven, each photosensitive drum 11a to 14a of the ID units 11 to 14 for each ID unit, and a fixing unit The fixing unit motor 116 that drives the 68 heat rollers 66 and the pressure roller 67 is driven at a predetermined timing. The fixing heater 109 provided in the heat roller 66 of the fixing unit 68 is temperature-controlled by the printer control unit 101 in accordance with the detection value of the thermistor 108 that detects the temperature of the heat roller 66.

  The first sensor 91 detects the slit of the first encoder 80a, so that the first rotation information of the drive roller 81, that is, the divided rollers 83 to 88 (FIG. 2) of the registration roller pair 75 is rotationally driven from the registration motor 112. Drive rotation information when rotating by receiving the force is transmitted to the printer control unit 101, and the second sensor 92 detects the slit of the second encoder 89a, thereby detecting the second of the follower roller 89 (FIG. 2). Rotation information, that is, actual movement rotation information in which the accompanying roller 89 rotates in accordance with the actual movement amount of the recording paper 2 is transmitted to the printer control unit 101. The recording paper sensor 77 detects the recording paper 2 carried out from the registration roller pair 75 and transmits the paper detection information to the printer control unit 101.

  In the above configuration, the outline of the printing operation of the printer 1 will be described first with reference mainly to FIGS.

  The printer 1 inputs print data described in PDL (Page Description Language) or the like from an external device via the host interface unit 102. The input data is converted into bitmap data by the command / image processing unit 103. The printer 1 starts the printing operation after setting the fixing heater 109 of the fixing unit 68 (FIG. 1) to a predetermined temperature by controlling the temperature according to the temperature detection value of the thermistor 108.

  The recording paper 2 set in the recording medium accommodating cassette 71 is fed by the hopping roller 72 and the conveying roller pair 73 and 74, and after the skew is corrected by the registration roller pair 75, the timing is synchronized with the electrophotographic process. It is conveyed to the next transfer unit 63.

  On the other hand, the four ID units 11 to 14 form toner images on the internal photosensitive drums 11a to 14a by an electrophotographic process. In this electrophotographic process, each of the four photosensitive drums 11a to 14a is arranged in correspondence with each other, and individual electrostatic latent images are generated by exposure heads 21 to 24 (FIG. 1) which are turned on according to bitmap data. It is formed. The electrostatic latent images are developed by correspondingly arranged developing rollers 11c to 14c, whereby toner images of corresponding colors are formed on the four photosensitive drums 11a to 14a, respectively.

  The toner images formed on the four photosensitive drums 11a to 14a are transferred to the intermediate transfer belt by the transfer bias voltages applied to the primary transfer rollers 31 to 34 disposed to face the respective photosensitive drums. The primary transfer is carried out sequentially on 54. The toner image (color image) primarily transferred onto the intermediate transfer belt 54 is conveyed to the secondary transfer unit 63 in synchronization with the electrophotographic process by the secondary transfer roller 61 to which a predetermined voltage is applied. Secondary transfer is performed on the recording surface of the sheet 2. Therefore, the printer control unit 101 adjusts the electrophotographic process by the developer image forming unit, the conveyance timing of the recording paper 2 and the like based on the paper detection from a paper detector (not shown).

  The recording sheet 2 on which the toner image has been secondarily transferred to the recording surface is fixed by the fixing unit 68, further transported by the transport roller pair 76, and discharged to the stacker unit 69 outside the apparatus.

  Next, detection of conveyance slip that occurs when the recording paper 2 is conveyed by the registration roller pair 75 and correction processing for conveyance slip performed by the printer control unit 101 will be described with reference to the flowchart of FIG. For convenience of explanation, the description starts from the state where the leading end of the recording paper 2 has reached the registration roller pair 75.

  It is monitored whether or not the recording paper sensor 77 has detected the leading edge of the recording paper 2 conveyed by the registration roller pair 75 (step S101). If it is detected (step S101, Yes), a sampling timer is set. Turns on (step S102). The sampling timer generates timing at regular intervals (hereinafter referred to as sampling timing) for comparing the rotation information of the first sensor 91 and the second sensor 92. As will be described later, the speed of the registration motor 112 is also adjusted at this sampling timing.

  The first rotation information (drive rotation information) of the first sensor 91 here is generated by detecting a plurality of slits formed radially at equal angular intervals in the first encoder 80a. The second rotation information (actual movement rotation information) of the second sensor 92 is a plurality of pulses formed radially at equiangular intervals in the second sensor 92. This is a pulse that is generated by detecting the slit and whose cycle is shortened in proportion to the rotational speed of the follower roller 89. Further, the slits of the first encoder 80a and the second encoder 89a are formed at the same angular interval and the same number.

  Next, each counter value of the first counter that counts the first rotation information pulse and the second counter that counts the second rotation information pulse is initialized to 0 (step S103), and is stored in a predetermined memory. Each variable of the previous value (Cn-1) and current value (Cn) of the difference between the counter values is also initialized (step 104).

  Thereafter, the first counter starts counting the rising and falling edges of the pulse waveform of the first rotation information and the second counter starts counting the rising and falling edges of the pulse waveform of the second rotation information (step S105). ). Hereinafter, the cumulative count number of the rising and falling edges of each pulse waveform of the first and second rotation information may be simply referred to as a count number.

Next, when the time elapses by the sampling timing (a predetermined fixed time) (Yes in step S106), the current value (Cn) of the difference between the accumulated counter values of the first counter and the second counter.
(Cn) = “cumulative count value of the first counter”
-"Cumulative count value of second counter" (1)
Is stored as a variable (Cn) in a predetermined memory (step S7).

  Therefore, the current value (Cn) is a numerical value proportional to the amount of slip that has occurred since the start of measurement.

  The current value (Cn) is passed to the registration motor speed adjustment algorithm in the next step S108 together with the previous value (Cn-1) (however, the first time is set to zero) to adjust the speed of the registration motor 112. Used for. Here, the contents of the registration motor speed adjustment algorithm in step S108 will be described.

  FIG. 6 is a flowchart showing the process of adjusting the speed of the registration motor 112 in step S108. For this speed adjustment, as shown in the figure, the four speed adjustments from the first to the fourth are alternatively selected and applied according to the determinations in steps S201 to S203.

First, the current value (Cn) according to the above equation (1) is expressed by the following equation (Cn) ≦ 1 (2)
Is satisfied (step S201). If the current value (Cn) is 1 or less (step S201, Yes), the first speed adjustment is executed (step S204).

  That is, in this case, the difference between the “first cumulative count value” of the first encoder 80a on the drive roller 81 side and the “second cumulative count value” of the second encoder 89a on the follower roller 89 side is 1 count (edge) Therefore, it can be determined that the recording paper 2 can be conveyed (no slippage) according to the control theoretical value. Therefore, in this first speed adjustment, the registration motor speed is set to the reference printing speed at which the peripheral speed of the drive roller 81 becomes the desired transport speed of the recording paper 2 and the medium transport is continued.

  Note that the conveyance position of the recording paper 2 when the recording paper 2 is conveyed without sliding at the reference printing speed may be hereinafter referred to as a target conveyance position of the recording paper 2.

Next, when the current value (Cn) is larger than 1 (No in step S201), the next inequality is the current value (Cn) −the previous value (Cn−1) ≧ 1 (3)
Is satisfied (step S202), and when the inequality (3) is satisfied (step S202, Yes), the second speed adjustment is executed (step S205).

  That is, in this case, the slip amount is increased at the current measurement than at the previous measurement. Therefore, in order to recover the conveyance delay of the recording paper 2, in this second speed adjustment, the registration motor speed is increased by a speed corresponding to the difference of “current value (Cn) −previous value (Cn−1)” ( Set). Here, the speed setting of the registration motor 112 is performed based on a speed table prepared in advance, and a speed change suitable for eliminating the 1-count difference is set as one step, and several steps above and below the target printing speed. Are set in advance.

Next, when the above inequality (3) is not satisfied (step S202, No),
Current value (Cn) −Previous value (Cn−1) = 0 (4)
Is satisfied (step S203). If the above equation (4) is satisfied (step S203, Yes), the third speed adjustment is executed (step S206).

  That is, in this case, the slip amount does not change, but the transport delay (relative to the target transport position) of the recording paper 2 due to the slip still occurs (because equation (2) is not satisfied), and this transport delay is recovered. In the third speed adjustment, the registration motor speed is set to “speed increased by one step speed”. As a result, even if slipping still occurs, the conveyance delay of the recording paper 2 is eliminated by increasing the speed of the registration motor.

Next, when the above inequality (4) is not satisfied (step S203, No),
Current value (Cn) −Previous value (Cn−1) <0 (5)
And the fourth speed adjustment is executed (step S207).

  That is, in this case, it is indicated that the recording sheet 2 is approaching the target transport position due to the increase in the registration motor speed due to the previous speed adjustment or the decrease in the slip amount due to some factor. Accordingly, since it is necessary to gradually return the registration motor speed, in this fourth speed adjustment, the registration motor speed is set to the difference of “previous value (Cn−1) −current value (Cn) −1”. Execute (set) the speed reduction.

  At this time, in the case of “previous value (Cn−1) −current value (Cn) = 1”, the speed does not decrease and the current speed remains unchanged, but this is because the recording sheet 2 is delayed as the current conveyance status. This is because the target transport position is approached while canceling the minute, but there is still a transport delay of one counter value, so it is desired to further approach the current high speed.

  As described above, in the registration motor speed adjustment algorithm described above, the registration motor speed is adjusted (speed UP) based on the detected delay of the follower roller 89 (corresponding to the delay of the recording paper 2 slipping), The conveyance position of the recording paper 2 is brought close to or coincident with the target conveyance position.

  As described above, when the current speed adjustment of the registration motor 112 is completed in step S108 shown in FIG. 5, the current value (Cn) is stored as the previous value (Cn-1) (step S109).

  Next, it is monitored whether or not the leading end of the recording paper 2 has reached a “registration motor speed adjustment limit point” to be described later, and until it reaches, registration motor speed adjustment processing from step S106 to step S109 is performed. (Step S110, No). When the leading end of the recording paper 2 reaches the “registration motor speed adjustment limit point” (Yes in step S110), the registration motor speed is returned to the reference printing speed described above, and the series of processes is terminated.

  FIG. 7 is a diagram for explaining the registration motor speed adjustment limit point. This figure shows a state in which the recording paper 2 is conveyed by the registration roller pair 75 and detected by the recording paper sensor 77, and then the registration motor speed is adjusted at a predetermined sampling timing by the method described above. . Here, as shown in the figure, the registration motor speed is adjusted by one step up or two steps up from the reference printing speed by slipping during the conveyance of the recording paper 2.

  Eventually, the leading edge of the recording paper 2 reaches the secondary transfer portion 63. At this stage, the registration motor speed needs to be returned to the reference printing speed in order to perform the subsequent transfer process smoothly. The registration motor speed adjustment limit point corresponds to the minimum necessary distance between the secondary transfer portion 63 and the leading edge of the recording paper 2 necessary for this purpose, and is used to return the current registration motor speed to the reference printing speed. The required deceleration distance is calculated by the firmware and converted into the distance from the registration roller pair 75.

  In this embodiment, the registration motor speed is adjusted according to the flow shown in FIG. 6, but the present invention is not limited to this, and the registration motor speed may be adjusted by other methods. In short, it is only necessary to control the registration motor speed so as to compensate for the detected deviation amount until the leading edge of the recording paper 2 reaches the registration motor speed adjustment limit point.

  FIG. 8 is a diagram for explaining the configuration of the registration roller pair 75 according to the present invention and the characteristics of the driving method thereof.

  As described with reference to FIG. 2, the drive roller 81 and the follower roller 89 are arranged with the rotation shaft 81a to which the rotational force is transmitted from the registration motor 112 through a transmission mechanism such as a gear as the same axis (the divided rollers 83 to 83). 88) is fixedly arranged, and the other (rotating roller 89) is rotatably arranged.

  Accordingly, the rotation amount (first rotation information) transmitted by the drive roller 81 to the recording paper 2 can be detected without including the error of the transmission mechanism, and the actual rotation of the recording paper 2 by the follower roller 89 on the same axis. Can be detected without including the error of the transmission mechanism and the amount of expansion / contraction of the recording paper 2. Therefore, by comparing the first rotation information (drive rotation information) and the second rotation information (actual movement rotation information), the conveyance status of the recording paper 2 (sliding of the medium) with respect to the rotation operation of the drive roller 81 is compared. ) Can be detected accurately.

  Here, a comparative example will be described. FIG. 9 is a schematic configuration diagram showing an arrangement relationship between the registration roller pair 201 and the follower roller 205 in the comparative example.

  As shown in the figure, in this comparative example, the registration roller pair 201 is composed of a drive roller 203 to which a driving force is transmitted by a driving means (not shown) and an idle roller 204 that rotates with the driving roller 203, and the recording sandwiched between them. The paper 2 is conveyed in the direction of the arrow. The follow roller 205 is provided separately from the registration roller pair 201, has a rotation shaft 205 a (FIG. 10) parallel to the drive roller 203, and the recording paper so that the circumferential surface thereof is in contact with the recording paper 2. 2 are spaced apart upstream of the registration roller pair 201 in the conveyance direction.

  FIG. 10 is a plan view showing the positional relationship between the follower roller 205 and the encoder 205b and the sensor 206 for detecting the rotation of the follower roller 205. FIG.

  As shown in the figure, the encoder 205b is fixedly disposed outside the conveyance area on the rotation shaft 205a of the follower roller 205 extending outside the conveyance area of the recording paper 2 conveyed in the direction of the arrow. In order to detect a slit (not shown) formed in the encoder 205b and output rotation information to the printer control unit, the encoder 205b is arranged so as to sandwich the encoder 205b.

  FIG. 11 is a schematic configuration diagram illustrating another arrangement relationship example of the accompanying roller 205 and the encoder 205b and the sensor 206 for detecting the rotation of the accompanying roller 205. Here, the rotation of the follow roller 205 is transmitted to another rotating shaft by the belt 210 spanned between the shafts, and the encoder 205b is fixed on the transmitted rotating shaft. The sensor 206 is arranged so as to sandwich the encoder 205b so as to detect a slit formed in the encoder 205b and output rotation information to the printer control unit.

  FIG. 12 is a diagram for explaining the configuration of the drive roller 203 and the follower roller 205 and the characteristics of the driving method in the comparative example.

  The control theoretical value of the registration motor 212 that is a drive source for rotating the drive roller 203 that conveys the recording paper 2 and the rotation information of the follow roller 205 that rotates in synchronization with only the actual movement of the recording paper 2 are obtained. In comparison, the current recording paper conveyance status (medium slip) is confirmed. In this case, if there is a difference in the rotation detection cycle of the follower roller 205 with respect to the control theoretical cycle of the registration motor 212, it can be determined that the conveyance of the recording paper is delayed or slipping.

However, in this method, first, a rotation error occurs between the registration motor 212 and the drive roller 203 due to an error caused by the transmission mechanism on the drive roller 203 side. The error by the transmission mechanism here is an error generated when the rotation of the drive roller 203 is transmitted to the recording paper 2.
(1) An amount that is not transmitted to the recording paper 2 due to a backlash of a gear disposed between the registration motor 212 and the drive roller 203,
(2) An amount in which the recording paper slips due to the strength of the pressing force (roller tension) between the drive roller 203 and the idle roller 204 that rotates with the drive roller 203 and is not transmitted.
(3) There may be an error from the theoretical value generated due to the size (manufacturing variation) of the roller diameter of the drive roller 203. Due to these factors, there is an error not recognized by the control side.

  Further, an error between the follower roller 205 and the rotation detection mechanism (encoder 205b, sensor 206) also occurs due to the error caused by the transmission mechanism on the follower roller 205 side. The error due to the transmission mechanism here is the same as in (1) to (3) above, such as gear backlash, slippage, manufacturing variation in roller diameter of the follower roller 205, and expansion and contraction of the recording paper 2 itself. Can be considered.

  The slip detection of the recording paper (medium) 2 in this comparative example is calculated by the difference between the motor control theoretical value (the motor behavior recognized by the firmware) and the output value of the sensor 206 including all the error information described above. Therefore, this method cannot accurately detect the slip of the medium.

In the present embodiment, improvement in accuracy is required only at the leading edge writing position. However, in the case of a long medium, the speed of the registration motor may be adjusted for the entire area.
Furthermore, in the present embodiment, an example in which one follower roller is arranged is shown. However, a pair of follower rollers are arranged at the left and right ends in the width direction of the recording sheet, and the skew amount of the recording sheet is detected and corrected. It is possible to adopt various modes, such as being configured to serve as both.

  As described above, according to the printer 1 of the present embodiment, the delay (slip) of the recording paper 2 can be accurately detected. Therefore, the conveyance delay of the recording paper 2 can be reduced by adjusting the motor speed. It is possible to correct accurately, and thus high-quality printing is possible.

  In the above-described embodiment, the example in which the present invention is applied to an image forming apparatus as a color electrophotographic printer has been described. However, the present invention is not limited thereto, and includes a copying machine, a facsimile machine, and an MFP. It can also be used for an image processing apparatus such as the above. Although a color printer has been described, a monochrome printer may be used.

DESCRIPTION OF SYMBOLS 1 Printer, 2 Recording paper, 11 ID unit, 11a Photosensitive drum, 12 ID unit, 12a Photosensitive drum, 13 ID unit, 13a Photosensitive drum, 14 ID unit, 14a Photosensitive drum, 14b Charging roller, 14c Developing roller , 14d supply roller, 14e cleaning blade, 14f toner cartridge, 21 exposure head, 22 exposure head, 23 exposure head, 24 exposure head, 31 primary transfer roller, 32 primary transfer roller, 33 primary transfer roller, 34 primary transfer roller Transfer roller, 51 Drive roller, 52 Belt driven roller, 53 Backup roller, 54 Intermediate transfer belt, 55 Cleaning blade, 56 Cleaner container, 61 Secondary transfer roller, 63 Secondary transfer section, 66 Heat roller, 67 Pressure roller 68 fixing unit, 69 stacker unit, 71 recording medium accommodating cassette, 72 hopping roller, 73 transport roller pair, 74 transport roller pair, 75 registration roller pair, 76 transport roller pair, 77 recording paper sensor, 81 drive roller, 80a first Encoder, 81a Rotating shaft, 82 Idle roller, 82a Rotating shaft, 83-88 Split roller, 89 Follow roller, 89a Second encoder, 91 First sensor, 92 Second sensor, 101 Printer control unit, 102 Host interface unit, DESCRIPTION OF SYMBOLS 103 Command / image processing part, 104 Exposure head interface part, 105 Charging bias generation part, 106 Development bias generation part, 107 Transfer bias generation part, 108 Thermistor, 109 Fixing heater, 111 Hopping motor, 112 Registration motor, 113 transport motor, 114 belt motor, 115 drum motor (T, Y, M, C, K), 116 fixing unit motor.

Claims (8)

A first rotating shaft that rotates upon receiving a driving force;
A fixed roller fixedly disposed on the first rotating shaft;
A free roller disposed coaxially with the fixed roller and rotatably held by the rotary shaft;
A first rotation detection device for detecting first rotation information of the fixed roller;
And a second rotation detection device for detecting second rotation information of the universal roller.   An idler having a second rotating shaft, wherein the second rotating shaft is arranged in parallel with the first rotating shaft so that the peripheral surface is in contact with the peripheral surface of the fixed roller and the peripheral surface of the universal roller The medium conveying apparatus according to claim 1, further comprising a roller.   3. The medium conveying apparatus according to claim 1, wherein a plurality of the fixed rollers are arranged in the first rotation axis direction via the universal roller. 4.   The first rotation detection device includes a first encoder that rotates integrally with the first rotation shaft, and a first sensor that detects a detected portion formed in the first encoder. The medium conveying apparatus according to claim 1, wherein the medium conveying apparatus is a medium conveying apparatus.   The medium conveying apparatus according to claim 4, wherein the detected part is a plurality of slits formed at equal angular intervals.   The second rotation detection device includes a second encoder that rotates integrally with the universal roller, and a second sensor that detects a detected portion formed in the second encoder. The medium carrying device according to any one of claims 1 to 5.   The medium conveying apparatus according to claim 6, wherein the detected part is a plurality of slits formed at equal angular intervals. A medium conveying device according to any one of claims 1 to 7,
A developer image transfer unit for transferring a developer image to a recording medium conveyed by the medium conveying device;
Control for calculating a slip amount of the recording medium based on the first rotation information and the second rotation information, and controlling rotation of a drive motor that rotationally drives the first rotation shaft based on the slip amount. And an image forming apparatus.

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