JP5941819B2 - Medium feeding control method, medium feeding apparatus, and image forming apparatus - Google Patents

Description

  The present invention relates to a medium feeding control method, a medium feeding apparatus, and an image forming apparatus for feeding a medium one by one from a medium accommodating unit that loads and accommodates a plurality of media to a conveyance path.

  Conventionally, when a plurality of media (paper) are sequentially sent out one by one from a paper cassette or the like, the rear end of the medium sent out first is detected by a transport sensor, and the next medium is sent out based on the detection timing. (For example, refer to Patent Document 1).

JP 2012-53390 A (see paragraphs 0041-0044)

  However, there is a case where the medium sent out from the paper cassette or the like cannot be separated one by one by the separation mechanism, and so-called “double feeding” occurs in which the next medium is pushed out from the paper cassette or the like by the previous medium. When such double feeding occurs, the trailing edge of the previous medium cannot be detected by the transport sensor, and the timing for feeding the next medium cannot be determined.

  As a countermeasure, it is conceivable to detect the trailing edge of the previous medium with another sensor provided further downstream than the transport sensor. In this case, the timing of sending the next medium is delayed (the medium interval is reduced). For this reason, there is a problem in that in the transfer portion that transfers the image to the medium, the leading edge of the image cannot coincide with the leading edge of the medium, resulting in printing failure.

  SUMMARY An advantage of some aspects of the invention is that it provides a medium feeding control method, a medium feeding apparatus, and an image forming apparatus capable of feeding a medium at a substantially constant interval. To do.

The medium feeding control method according to the present invention includes a primary transfer unit that primarily transfers a developer image to an intermediate transfer member, and a secondary transfer unit that secondarily transfers the developer image from the intermediate transfer member to a medium. This is a medium feeding control method in the apparatus. In the medium feeding control method, a medium accommodating unit capable of accommodating a plurality of media, a feeding unit that feeds a medium from the medium accommodating unit to a conveyance path, and a medium fed by the feeding unit one by one Separating means for separating, conveying means for conveying the medium fed by the feeding means to the secondary transfer unit at a first speed, a first conveying sensor for detecting the medium in the conveying path, and a first conveying sensor in the conveying path. A second transport sensor that detects the medium downstream of the first transport sensor, a third transport sensor that is disposed upstream of the secondary transfer unit along the transport path, and that detects the medium; And a fourth transport sensor that is disposed downstream of the third transport sensor and detects the medium . In order to make the leading edge of the medium coincide with the leading edge of the developer image on the intermediate transfer member at the secondary transfer portion, the medium conveying speed by the conveying means is based on the timing when the third conveying sensor detects the medium leading edge. Is decelerated to a second speed that is lower than the first speed, and then the medium conveying speed by the conveying means is accelerated to the first speed based on the timing at which the fourth conveying sensor detects the leading edge of the medium. Let Based on the timing at which the first transport sensor detects the trailing edge of the previously fed medium, the next medium is fed by the feeding means. If the first transport sensor cannot detect the trailing edge of the previously fed medium, the following timing is determined based on the timing at which the second conveying sensor detects the trailing edge of the previously fed medium. Feed the media. The feeding speed of the next medium is the third speed higher than the first speed when the previously fed medium is transported at the first speed, and the first fed medium is the first speed. When transported at a speed of 2, the fourth speed is set to be higher than the second speed and lower than the third speed.

The medium feeding device of the present invention is an image forming apparatus having a primary transfer portion that primarily transfers a developer image to an intermediate transfer member, and a secondary transfer portion that secondarily transfers the developer image from the intermediate transfer member to a medium. This is a medium feeding device to be used. The medium feeding device separates a medium accommodating section capable of accommodating a plurality of media, a feeding means for feeding the medium from the medium accommodating section to the transport path, and a medium fed by the feeding means one by one. Separating means, conveying means for conveying the medium fed by the feeding means to the secondary transfer section at a first speed, a first conveying sensor for detecting the medium in the conveying path, and a first in the conveying path. A second conveyance sensor that detects the medium downstream of the conveyance sensor, a third conveyance sensor that is disposed upstream of the secondary transfer unit along the conveyance path, and that detects the medium, along the conveyance path And a fourth transport sensor that detects the medium, a feeding unit, and a medium feeding control unit that controls the feeding unit. The medium feeding control unit matches the leading edge of the medium and the leading edge of the developer image on the intermediate transfer body in the secondary transfer unit, so that the third transport sensor detects the leading edge of the medium, The medium conveying speed by the conveying means is reduced based on the timing at which the fourth conveying sensor detects the leading edge of the medium after the medium conveying speed by the conveying means is decelerated to a second speed lower than the first speed. Is accelerated to a first speed. Based on the timing at which the first transport sensor detects the trailing edge of the previously fed medium, the next medium is fed by the feeding means. If the first transport sensor cannot detect the trailing edge of the previously fed medium, the following timing is determined based on the timing at which the second conveying sensor detects the trailing edge of the previously fed medium. Feed the media. The feeding speed of the next medium is the third speed higher than the first speed when the previously fed medium is transported at the first speed, and the first fed medium is the first speed. When transported at a speed of 2, the fourth speed is set to be higher than the second speed and lower than the third speed.

An image forming apparatus of the present invention includes the medium feeding device described above .

  According to the present invention, it is possible to feed the medium at regular intervals, thereby reducing printing defects.

1 is a diagram illustrating a basic configuration of an image forming apparatus according to a first embodiment of the present invention. 2 is a block diagram illustrating a control system of the image forming apparatus according to the first embodiment. FIG. It is a block diagram which shows the control system regarding the medium feeding control in 1st Embodiment. FIG. 5A is a schematic diagram for explaining the write start position adjustment at the secondary transfer unit in the first embodiment, and FIG. 8B is a diagram for explaining deceleration / acceleration of the carry motor. 6 is a timing chart illustrating the operation timing of medium feeding control during normal operation according to the first embodiment. FIG. 6 is a schematic diagram illustrating a state in which a medium protrudes from a feed roller and a separation roller by double feed. 6 is a timing chart showing operation timing when a printing error due to double feeding occurs. 3 is a timing chart showing the operation timing of medium feeding control in the first embodiment of the present invention. FIG. 6 is a block diagram illustrating a control system of an image forming apparatus according to a second embodiment of the present invention. 10 is a timing chart illustrating operation timing of medium feeding control in the second embodiment of the present invention.

First embodiment.
<Configuration of image forming apparatus>
FIG. 1 is a diagram showing a basic configuration of an image forming apparatus 100 according to the first embodiment of the present invention. The image forming apparatus 100 includes image forming units 102Y, 102M, 102C, and 102K that form yellow (Y), magenta (M), cyan (C), and black (K) toner images.

  The image forming units 102Y, 102M, 102C, and 102K are arranged in a line along the movement path of the intermediate transfer belt 112 described later, from left to right in the drawing. Since the image forming units 102Y, 102M, 102C, and 102K have the same configuration except for the toner (developer) to be used, they are collectively referred to as the image forming unit 102 here.

  The image forming unit 102 has a photosensitive drum 109 as a latent image carrier. The photosensitive drum 109 is a substantially cylindrical member having a photosensitive layer on the surface, and rotates counterclockwise in the drawing.

  A charging roller 105 as a charging member for uniformly charging the surface of the photosensitive drum 109 along the rotation direction of the photosensitive drum 109 and the surface of the photosensitive drum 109 uniformly charged by the charging roller 105 are exposed. The LED head 103 as an exposure device for forming an electrostatic latent image, the developing roller 107 as a developer carrying member for developing the electrostatic latent image on the surface of the photosensitive drum 109, and the surface of the photosensitive drum 109. A cleaning blade 110 as a cleaning member for removing residual toner is disposed.

  Further, around the developing roller 107, a supply roller 106 as a supply member for supplying toner to the developing roller 107, and a developer regulating member for regulating the thickness of the developer layer formed on the surface of the developing roller 107. The developing blade 108 is disposed. A toner storage box 104 as a developer supply unit is detachably attached to the upper portion of the image forming unit 102.

  Transfer rollers 111Y, 111M, 111C, and 111K as primary transfer members are arranged to face the lower sides of the respective photosensitive drums 109 of the image forming units 102Y, 102M, 102C, and 102K.

  An intermediate transfer belt 112 as an intermediate transfer member is provided so as to pass between each photosensitive drum 109 and the transfer rollers 111Y, 111M, 111C, and 111K. A primary transfer bias voltage is applied to the transfer rollers 111Y, 111M, 111C, and 111K, and a toner image (developer image) formed on the surface of each photosensitive drum 109 is transferred to the intermediate transfer belt 112. Transfer to the surface.

  The intermediate transfer belt 112 is an endless belt, and includes transfer rollers 111Y, 111M, 111C, and 111K, an intermediate transfer belt drive roller 113, intermediate transfer belt driven rollers 114, 115, and 116, and a secondary transfer backup roller 117. It is stretched around.

  Further, a secondary transfer roller 133 as a secondary transfer member is disposed at a position facing the secondary transfer backup roller 117 via the intermediate transfer belt 112. A secondary transfer bias voltage is applied to the secondary transfer roller 133, and the toner image on the surface of the intermediate transfer belt 112 is transferred to the medium P as described later. A secondary transfer portion is formed by the secondary transfer roller 133 and the secondary transfer backup roller 117.

  An intermediate transfer belt cleaning blade 118 is in contact with the surface of the intermediate transfer belt 112. The intermediate transfer belt cleaning blade 118 scrapes off the toner adhering to the intermediate transfer belt 112 and cleans it. In addition, a waste toner box 119 is provided to store the waste toner scraped off by the intermediate transfer belt cleaning blade 118.

  A medium tray 120 as a medium storage unit is detachably attached to the lower part of the image forming apparatus 100. In the medium tray 120, a plurality of media P such as printing paper are stored in a stacked state.

  A pickup roller 121 serving as a feeding unit is disposed at a position in contact with the uppermost medium P stacked on the medium tray 120. The pickup roller 121 feeds the medium P from the medium tray 120.

  Adjacent to the pickup roller 121, a feed roller 122 as a feeding unit and a separation roller 123 as a separating unit are arranged. The feed roller 122 feeds the medium P fed by the pickup roller 121 from the medium tray 120 to the first transport path 125. The separation roller 123 applies a force in the direction opposite to the conveyance direction from the back side of the feed roller 122 to the medium P to separate the medium P one by one.

  A first transport sensor 124 that detects the presence or absence of the medium P and a second transport sensor 126 are arranged along the first transport path 125. For example, the first transport sensor 124 outputs an ON signal when the medium P is at the position of the first transport sensor 124, and outputs an OFF signal when there is no medium P. When the output changes from the OFF signal to the ON signal, it can be seen that the leading edge of the medium P has passed through the first transport sensor 124. Conversely, when the output changes from the ON signal to the OFF signal, it can be seen that the rear end of the medium P has passed through the first conveyance sensor 124. The same applies to the second transport sensor 126. However, the conveyance sensors 124 and 126 are not limited to such a configuration, and various sensors and detection methods can be used.

  A registration roller pair 127 as a roller pair is disposed on the downstream side of the second conveyance sensor 126 along the conveyance direction of the medium P. The registration roller pair 127 starts rotating at a predetermined timing after the medium P passes through the second transport sensor 126. While the registration roller pair 127 is stopped, the medium P is pressed against the nip portion to correct the skew, and then the registration roller pair 127 rotates to convey the medium P to the second conveyance path 129.

  Along the second conveyance path 129, conveyance roller pairs 128 and 131 are arranged as conveyance means for conveying the medium P to the secondary transfer portion (secondary transfer roller 133 and secondary transfer backup roller 117). The transport roller pair 128 is disposed on the upstream side in the transport direction of the medium P, and the transport roller pair 131 is disposed on the downstream side in the transport direction of the medium P.

  A third transport sensor 130 is disposed upstream of the transport roller pair 131, and a fourth transport sensor 132 is disposed downstream. The third conveyance sensor 130 and the fourth conveyance sensor 132 can detect the passage of the leading edge and the trailing edge of the medium P, similarly to the first conveyance sensor 124 and the second conveyance sensor 126. The third conveyance sensor 130 and the fourth conveyance sensor 132 are used to determine the timing of writing the medium P (described later) and applying the secondary transfer bias voltage.

  A fixing unit 135 as a fixing unit is disposed on the downstream side of the secondary transfer portion (secondary transfer roller 133 and secondary transfer backup roller 117) along the conveyance direction of the medium P. The fixing unit 135 has a pair of upper and lower fixing rollers 136 and 137 as heat fixing members, and heats and pressurizes the medium P on which the toner image is transferred, thereby fixing the toner image on the medium P.

  Discharge roller pairs 139 and 140 are disposed further downstream of the fixing unit 135. The pair of discharge rollers 139 and 140 conveys the medium P that has passed through the fixing unit 135 along the third conveyance path 138 and discharges the medium P to the outside of the image forming apparatus 100. A discharge tray 141 for stacking the discharged medium P is provided on the upper part of the image forming apparatus 100, and the medium P is placed on the discharge tray 141 face down.

  FIG. 1 schematically shows motors (M) 142, 143, 144, 145, 146, and 147 as drive sources, and clutches (CL) 148 and 149 that connect and disconnect driving force transmission from each motor. It is shown. The motors 142 to 147 and the clutches 148 and 149 can be arranged at desired positions in consideration of the arrangement of the components of the image forming apparatus 100.

  The feed motor 142 generates a driving force that rotates the pickup roller 121, the feed roller 122, and the registration roller pair 127. Driving force transmission from the feed motor 142 to the pickup roller 121 and the feed roller 122 is connected / disconnected by the feed clutch 148. Driving force transmission to the registration roller pair 127 is connected / disconnected by the registration clutch 149.

  The transport motor 143 generates a driving force that rotates the transport roller pair 128 and 131. The fixing / discharging motor 144 generates a driving force for rotating the fixing roller 137 and the discharge roller pair 139 and 140 below the fixing unit 135. The intermediate transfer belt motor 145 is a drive source that generates a driving force of an intermediate transfer belt drive roller 113 that causes the intermediate transfer belt 112 to travel.

  The photosensitive drum driving motor 146 generates a driving force for rotating the photosensitive drum 109 of the black (K) image forming unit 102K. The photosensitive drum driving motor 147 generates a driving force for rotating the photosensitive drum 109 of the yellow (Y), magenta (M), and cyan (C) image forming units 102Y, 102M, and 102C.

<Control system of image forming apparatus>
FIG. 2 is a block diagram illustrating a control system of the image forming apparatus 100 according to the first embodiment. In FIG. 2, the parts having the same configuration included in the image forming units 102Y, 102M, 102C, and 102K are shown as four-tiered blocks.

  The control unit of the image forming apparatus 100 includes a host interface unit 201, a command / image processing unit 202, an LED head interface unit 203, and a printer engine control unit 204. The printer engine control unit 204 includes a feeding / conveying control unit (medium feeding control unit) 205, an LED head control unit 206, a motor control unit 207, a process bias control unit 208, and a fixing control unit 217. .

  The host interface unit 201 receives commands and image data transmitted from an external computer or the like and transmits them to the command / image processing unit 202. The command / image processing unit 202 outputs image data to the LED head interface unit 203 and outputs a command to the printer engine control unit 204.

  The LED head interface unit 203 receives an input such as a head drive pulse generated by an LED head control unit 206 (described later) in the printer engine control unit 204 and causes the LED head 103 to emit light.

  The LED head control unit 206 of the printer engine control unit 204 generates a head drive pulse for causing the LED head 103 to emit light based on the image data output from the command / image processing unit 202, and outputs it to the LED head interface unit 203. To do. The LED head control unit 206 also synchronizes the timing of light emission of the LED head 103 based on the transport distance and speed of the toner image formed on the exposed portion by the light emission of the LED head 103 and the transport of the medium P. An output synchronization signal is also generated.

  The motor control unit 207 generates drive pulses for driving the feed motor 142, the conveyance motor 143, the fixing / discharging motor 144, the intermediate transfer belt motor 145, and the photosensitive drum driving motors 146 and 147.

  The feeding / conveyance control unit 205 is generated by the first conveyance sensor 124, the second conveyance sensor 126, the detection signals from the third conveyance sensor 130 and the fourth conveyance sensor 132, and the LED head control unit 206. On the basis of the image output synchronization signal, control is performed to feed the medium P from the medium tray 120 and to convey the medium P along the conveying paths 125, 129, and 138 by the drive pulse generated by the motor control unit 207.

  The fixing control unit 217 causes the heater 210 incorporated in the fixing rollers 136 and 137 to generate heat based on the temperature detection value by the thermistor 209 provided in the fixing unit 135 to bring the fixing unit 135 to a predetermined temperature. Control.

The process bias control unit 208 supplies a target output value of each bias voltage to the charging bias generation unit 212, the development / supply bias generation unit 213, the primary transfer bias generation unit 214, the secondary transfer bias generation unit 215, and the backup bias generation unit 216. A control signal based on is output.

  The charging bias generator 212 applies a charging bias voltage to the charging roller 105 of the image forming unit 102. The development / supply bias generation unit 213 applies a development bias voltage and a supply bias voltage to the development roller 107 and the supply roller 106 of the image forming unit 102, respectively.

  The primary transfer bias generator 214 applies a primary transfer bias voltage to the primary transfer roller 111 (111Y, 111M, 111C, 111K). The secondary transfer bias generator 215 applies a secondary transfer bias voltage to the secondary transfer roller 133. The backup bias generator 216 applies a backup bias voltage to the secondary transfer backup roller 117.

  Each of the bias generation units 212, 213, 213, 214, and 216 described above constitutes a process bias unit 211.

  FIG. 3 illustrates a part of the control system of the image forming apparatus 100 according to the first embodiment that performs control (feed / transport control) for feeding the medium P to the transport path 129 and transporting it to the secondary transfer unit. FIG. In FIG. 3, portions not directly related to the feeding / conveying control (for example, driving control portions of the fixing / discharging motor 144 and the photosensitive drum driving motors 146, 147) are omitted.

The motor control unit 207 of the printer engine control unit 204 controls the feed motor control unit 301 that controls the drive of the feed motor 142, the transport motor control unit 302 that controls the drive of the transport motor 143, and the drive of the intermediate transfer belt motor 145. And an intermediate transfer belt motor control unit 303 for controlling.

  The motor control unit 207 further includes a control unit that controls the driving of the fixing / discharging motor 144 and a control unit that controls the driving of the photosensitive drum driving motors 146 and 147. These are illustrated and described. Omitted.

  The feeding / conveying control unit 205 receives conveyance signals S401, S402, S403, and S404 from the first conveyance sensor 124, the second conveyance sensor 126, the third conveyance sensor 130, and the fourth conveyance sensor 132, respectively. Entered. The conveyance signals S401, S402, S403, and S404 indicate the presence / absence of the medium P at each of the first conveyance sensor 124, the second conveyance sensor 126, the third conveyance sensor 130, and the fourth conveyance sensor 132. Signal.

  The feeding / conveying control unit 205 outputs an ON / OFF signal S405 and an acceleration / deceleration signal S406 to the feed motor control unit 301, and outputs an ON / OFF signal S408 and an acceleration / deceleration signal S409 to the conveyance motor control unit 302. Then, an ON / OFF signal S411 and an acceleration / deceleration signal S412 are output to the intermediate transfer belt motor control unit 303.

  The feed motor control unit 301 outputs a feed motor drive pulse S407 based on the ON / OFF signal S405 and the acceleration / deceleration signal S406. The feed motor drive pulse S407 is output to the feed motor drive pulse counter 304 and also to the drive circuit 142D of the feed motor 142. The feed motor drive pulse counter 304 counts the number of feed motor drive pulses S407 and uses it to generate various timings in feed / conveyance control. The drive circuit 142D outputs a drive output S417 to the feed motor 142 to drive the feed motor 142.

  The transport motor control unit 302 outputs a transport motor drive pulse S410 based on the ON / OFF signal S408 and the acceleration / deceleration signal S409. The carry motor drive pulse S410 is output to the carry motor drive pulse counter 305 and also to the drive circuit 143D of the carry motor 143. The transport motor drive pulse counter 305 counts the number of transport motor drive pulses S410 and uses it to generate various timings in feed / transport control. The drive circuit 143D outputs a drive output S418 to the carry motor 143 to drive the carry motor 143.

The intermediate transfer belt motor control unit 303 outputs an intermediate transfer belt motor drive pulse S413 based on the ON / OFF signal S411 and the acceleration / deceleration signal S412. The intermediate transfer belt motor drive pulse S413 is output to the intermediate transfer belt motor drive pulse counter 306 and also to the drive circuit 145D of the intermediate transfer belt motor 145. The intermediate transfer belt motor drive pulse counter 306 counts the number of intermediate transfer belt motor drive pulses S413 and uses it to generate various timings in feed / feed control. The drive circuit 145D outputs a drive output S419 to the intermediate transfer belt motor 145 to drive the intermediate transfer belt motor 145.

  The feeding / conveying control unit 205 also outputs an ON / OFF signal S414 to the feed clutch 148, and outputs an ON / OFF signal S415 to the registration clutch 149. The feed clutch 148 operates in response to the ON / OFF signal S414 and switches connection / disconnection of driving force transmission to the pickup roller 121 and the feed roller 122. The registration clutch 149 operates in response to the ON / OFF signal S415 and switches transmission / disconnection of the driving force to the registration roller pair 127.

  The image synchronization signal S416 is also input from the LED head controller 206 to the feeding / conveyance controller 205. This image synchronization signal S416 is used for driving (lighting) control of the LED head 103. In order to align the position of the toner image and the medium P, the LED head control unit 206 sends it to the feeding / conveyance control unit 205. Is also output. The size information S420 of the medium P is input from the command / image processing unit 202 to the feeding / conveying control unit 205.

  In the image forming apparatus 100 described above, the components for feeding the medium P on the medium tray 120 to the conveyance path 125, that is, the pickup roller 121, the feed roller 122, the separation roller 123, the first conveyance sensor 124, the registration roller A component including the pair 127, the second conveyance sensor 126, the feed motor 142, and the feeding / conveying control unit 205 is referred to as a “medium feeding device”.

<Operation of Image Forming Apparatus>
Next, the basic operation of the image forming apparatus 100 according to the first embodiment will be described with reference to FIGS. When the power of the image forming apparatus 100 is turned on, the fixing control unit 217 of the printer engine control unit 204 supplies a current to the heater 210 based on the temperature detection value output from the thermistor 209 of the fixing unit 135, and the fixing roller 136. , 137 is set to a predetermined temperature.

  Further, print data described in a page description language (PDL) or the like is input to the image forming apparatus 100 from an external device (not shown) such as a computer via the host interface unit 201 (FIG. 2). . The input print data is converted into bitmap data by the command / image processing unit 202 and output to the printer engine control unit 204. Thereby, a printing operation is started.

The feeding / feeding control unit 205 of the printer engine control unit 204 drives the intermediate transfer belt motor 145 and the photosensitive drum driving motors 146 and 147 via the motor control unit 207. As a result, the intermediate transfer belt 112 and the photosensitive drum 109, the charging roller 105, the developing roller 107, and the supply roller 106 in each image forming unit 102 rotate. The feeding / feeding control unit 205 further drives the fixing / discharging motor 144, whereby the fixing rollers 136, 137 and the discharging roller pair 139, 140 rotate.

  Further, toner images are formed by an electrophotographic process in each of the image forming units 102Y, 102M, 102C, and 102K. That is, the process bias control unit 208 applies a charging bias voltage from the charging voltage bias generation unit 212 to the charging roller 105, and uniformly charges the surface of the photosensitive drum 109 by the charging roller 105. Next, the LED head control unit 206 generates a head drive pulse based on the above bitmap data to drive the LED head 103, and exposes the surface of the photosensitive drum 109 to form an electrostatic latent image.

  Further, the process bias control unit 208 applies a bias voltage from the development / supply bias generation unit 213 to the development roller 107 and the supply roller 106 and is supplied with toner on the surface of the development roller 107. The electrostatic latent image is developed. That is, a toner image is formed on the photosensitive drum 109.

  The process bias controller 208 further applies a primary transfer bias voltage from the primary transfer bias generator 214 to the primary transfer roller 111, and transfers the toner image on the photosensitive drum 109 to the intermediate transfer belt 112. As a result, the toner images of the respective colors formed on the photosensitive drums 109 of the image forming units 102Y, 102M, 102C, and 102K are transferred to the intermediate transfer belt 112.

  The feeding / conveying control unit 205 starts driving the feed motor 142 and the conveying motor 143 at the same time as the driving of the intermediate transfer belt motor 145 and the photosensitive drum driving motors 146 and 147 described above. 148 and the registration clutch 149 are OFF (disconnected). The feeding / conveying control unit 205 turns on (connects) the feed clutch 148 at a predetermined timing after the light emission (toner image formation) of the LED head 103 is started in each image forming unit 102.

  As the feed clutch 148 is turned on, the pickup roller 121 and the feed roller 122 are rotated by the driving force of the feed motor 142. The medium P is fed from the medium tray 120 by the rotation of the pickup roller 121 and further fed to the first transport path 125 by the feed roller 122. The medium P fed to the first transport path 125 is abutted against the nip portion of the registration roller pair 127.

  The feeding / conveying control unit 205 counts the feed motor driving pulse S407 by the feed motor driving pulse counter 304 based on the timing at which the second conveying sensor 126 detects the leading edge of the medium P, and sets the predetermined count number C2. At this point, the feed clutch 148 is turned off and the registration clutch 149 is turned on. As a result, the feed motor 142 stops rotating, and the registration roller pair 127 starts rotating.

  The count number C2 is the distance (mm) from the second conveyance sensor 126 to the registration roller pair 127, the amount of contact of the medium P against the registration roller pair 127 (mm), and the feed amount of the feed roller 122 per pulse. (Mm / pulse). As a result, the medium P is pressed against the nip portion of the registration roller pair 127, and thereafter, the medium P is conveyed by the registration roller pair 127 with the skew corrected.

  Further, the feeding / conveyance control unit 205 counts the conveyance motor drive pulse S410 by the conveyance motor drive pulse counter 305 based on the timing at which the second conveyance sensor 126 detects the trailing edge of the medium P, and performs a predetermined count. When the number C2 ′ is reached, the registration clutch 149 is turned off.

  The count number C2 'is determined by the distance (mm) from the second conveyance sensor 126 to the registration roller pair 127 and the feed amount (mm / pulse) of the feed roller 122 per pulse. That is, after the rear end of the medium P passes through the registration roller pair 127, the rotation of the registration roller pair 127 is stopped to correct the skew of the next medium P.

  Further, since the transport motor 143 has already been rotated as described above, the medium P that has passed through the registration roller pair 127 is transported along the second transport path 129 by the transport roller pairs 128 and 131.

  In the process so far, the drive speeds of the feed motor 142, the transport motor 143, the intermediate transfer belt motor 145, and the photosensitive drum drive motors 146 and 147 are set to the “process speed Vp” for transporting the medium P at a predetermined speed. Is set. The process speed Vp is a speed at which the medium P is conveyed when the toner image is transferred to the medium P, and is also a speed at which the intermediate transfer belt 112 is moved. On the other hand, an adjustment speed Vc, which will be described later, is a speed that decelerates from the process speed Vp in order to adjust the writing position in the secondary transfer portion.

  In the present specification, the motor driving speed (number of rotations) will be described in terms of the transport speed (mm / s) of the medium P.

  While the medium P is being transported along the second transport path 129, the feeding / transport control unit 205 detects when the third transport sensor 130 and the fourth transport sensor 132 detect the leading edge of the medium P. Is used as a reference to adjust the writing position (writing position of the toner image on the medium P) in the secondary transfer portion.

Hereinafter, the adjustment of the writing start position in the secondary transfer unit will be described.
FIG. 4A is a schematic diagram for explaining the adjustment of the writing position in the secondary transfer unit. The toner image formed on the surface of the photosensitive drum 109 is transferred to the intermediate transfer belt 112 and travels to the secondary transfer unit. When the medium P reaches the third conveyance sensor 130, the medium P is already conveyed to some extent ahead of the toner image. The distance that the medium P is advanced with respect to the toner image may be adjusted at the ON timing of the feed clutch 148 or may be adjusted at the ON timing of the registration clutch 149 after the abutting process.

  If the distance for causing the medium P to precede the toner image is too short, the adjustment distance (described later) becomes short. On the other hand, if the distance is too long, the alignment accuracy between the medium P and the toner image may be lowered. The distance for leading P is preferably about 20 to 30 mm.

  The feeding / conveying control unit 205 counts the conveyance motor drive pulse S410 by the conveyance motor drive pulse counter 305 after the third conveyance sensor 130 detects the leading edge of the medium P, and reaches a predetermined count number C3. At this point, the transport motor 143 is decelerated from the process speed Vp to the adjustment speed Vc.

  Thereafter, after the fourth transport sensor 132 detects the leading edge of the medium P, the transport motor drive pulse counter 305 counts the transport motor drive pulse S410, and when the count number C4 is reached, the transport motor 143 is adjusted. Accelerate from Vc and return to process speed Vp. The change in speed of the transport motor 143 at this time is shown in FIG.

  When the transport motor 143 decelerates / accelerates, the feed motor 142 also decelerates / accelerates in synchronization with this. On the other hand, the intermediate transfer belt motor 145 and the photosensitive drum drive motors 146 and 147 are driven at a constant process speed Vp without being decelerated or accelerated.

  The count number C3 for determining the timing for starting the deceleration of the transport motor 143 and the count number C4 for determining the timing for starting the acceleration are respectively determined as follows.

  First, as shown in FIG. 4A, the distance (mm) from the exposure position on the photosensitive drum 109 of the most upstream image forming unit 102Y to the secondary transfer roller 133 is defined as Limg. Further, when the third transport sensor 130 detects the leading edge of the medium P, the distance (mm) that the toner image has traveled from the exposure position on the photosensitive drum 109 is represented as Dimg. When the fourth transport sensor 132 detects the leading edge of the medium P, the distance (mm) that the toner image has traveled from the exposure position on the photosensitive drum 109 is Dimg2.

Note that Dimg is determined by the intermediate transfer belt motor drive pulse counter 306 from the start of light emission of the LED head 103 (that is, output of the image synchronization signal S416) until the third conveyance sensor 130 detects the leading edge of the medium P. It is obtained from the intermediate transfer belt motor drive pulse S413 to be counted and the feed amount (mm / pulse) of the intermediate transfer belt 112 per pulse. Dimg2 is an intermediate transfer belt motor drive pulse S413 counted by the intermediate transfer belt motor drive pulse counter 306 from the start of light emission of the LED head 103 to when the fourth transport sensor 132 detects the leading edge of the medium P. It is obtained from the feed amount (mm / pulse) of the intermediate transfer belt 112 per pulse.

  The distance (mm) from the third transport sensor 130 to the leading edge position (acceleration start position) of the medium P when acceleration is started is D1, and the distance (mm) from the acceleration start position to the secondary transfer roller 133 ) To D2. The distance (mm) from the fourth conveyance sensor 132 to the secondary transfer roller 133 is D3, and the distance (mm) from the third conveyance sensor 130 to the fourth conveyance sensor 132 is D4.

  Further, as shown in FIG. 4B, the deceleration distance (mm) of the transport motor 143 is Ddec, and the deceleration time (s) is Tdec. Further, the conveyance motor 143 acceleration distance (mm) is Dacc and the acceleration time (s) is Tacc. A feed amount (mm / pulse) per pulse of the transport motor 143 is set to Pf.

  Further, let X be the distance (mm) that the medium P travels after the third transport sensor 130 detects the leading edge of the medium P and before the transport motor 143 starts to decelerate. The distance (mm) traveled by the medium P between the time when the fourth transport sensor 132 detects the leading edge of the medium P and the start of acceleration of the transport motor 143 is Y.

  The time from when the third transport sensor 130 detects the leading edge of the medium P until the toner image reaches the secondary transfer roller 133 is the same as the time until the medium P reaches the secondary transfer roller 133. From the relationship, the following equation (1) is obtained.

  The left side of the expression (1) is the time from when the leading edge of the medium P passes through the third conveyance sensor 130 until the toner image on the intermediate transfer belt 112 reaches the secondary transfer roller 133. That is, the distance traveled by the toner image (Limg-Dimg) is divided by the process speed Vp.

  The right side of the expression (1) is the time from when the leading edge of the medium P passes through the third conveyance sensor 130 to when the medium P reaches the secondary transfer roller 133. More specifically, the first term on the right side is the time that the medium P travels from the end of the medium P passing through the third transport sensor 130 to the deceleration start position where the transport motor 143 starts to decelerate. The second term on the right side is the time required for deceleration from the process speed Vp to the adjustment speed Vc. The third term on the right side is the time for the medium P to travel to the acceleration start position at which acceleration of the transport motor 143 starts after decelerating to the adjustment speed Vc. The fourth term on the right side is the time required for acceleration from the adjustment speed Vc to the process speed Vp. The fifth term on the right side is the time from the return to the process speed Vp until the leading edge of the medium P reaches the secondary transfer roller 133.

  Also, the time from when the fourth transport sensor 132 detects the leading edge of the medium P until the toner image reaches the secondary transfer roller 133, and the time until the medium P reaches the secondary transfer roller 133. Therefore, the following equation (2) is obtained.

  The left side of equation (2) is the time from when the leading edge of the medium P passes through the fourth conveyance sensor 132 until the toner image on the intermediate transfer belt 112 reaches the secondary transfer roller 133. That is, the distance (Limg−Dimg2) that the toner image travels is divided by the process speed Vp.

  The right side of the expression (2) is the time from when the medium P passes through the fourth conveyance sensor 132 until the medium P reaches the secondary transfer roller 133. That is, the first term on the right side is the time that the medium P travels from the leading end of the medium P to the deceleration start position at which the conveyance motor 143 starts decelerating after passing through the fourth conveyance sensor 132. The second term on the right side is the time required for deceleration from the process speed Vp to the adjustment speed Vc. The third term on the right side is the time for the medium P to travel to the position where acceleration of the transport motor 143 starts after the speed is reduced to the adjustment speed Vc. The fourth term on the right side is the time required for acceleration from the adjustment speed Vc to the process speed Vp. The fifth term on the right side is the time for the leading edge of the medium P to reach the secondary transfer roller 133 after returning to the process speed Vp.

  When the equations (1) and (2) are solved for X and Y, the following equations (3) and (4) are obtained. Note that the int function is a function that rounds down the decimal point to an integer.

Here, A1, A2, and A3 are as follows.

  The feeding / conveying control unit 205 controls the driving speed of the conveying motor 143 as shown in FIG. 4B based on the count numbers C3 and C4 obtained from the equations (3) and (4). That is, when the count number of the transport motor drive pulse S410 reaches C3 after the third transport sensor 130 detects the leading edge of the medium P, the transport motor 143 is decelerated from the process speed Vp to the adjustment speed Vc. Thereafter, when the count number of the transport motor drive pulse S410 reaches C4 after the fourth transport sensor 132 detects the leading edge of the medium P, the transport motor 143 is accelerated from the adjustment speed Vc to the process speed Vp.

  Accordingly, the leading edge of the conveyed medium P and the leading edge of the toner image on the intermediate transfer belt 112 can be aligned at the secondary transfer portion (secondary transfer roller 133 and secondary transfer backup roller 117). . It should be noted that the distance traveled by the medium P in the course of deceleration of the transport motor 143 from the process speed Vp to the adjustment speed Vc, operation at the adjustment speed Vc, and acceleration from the adjustment speed Vc to the process speed Vp is the adjustment distance (FIG. 4). (B) is a portion indicated by hatching. This adjustment distance is a distance necessary for positioning (that is, writing position adjustment) between the leading edge of the medium P and the leading edge of the toner image on the intermediate transfer belt 112.

  The process bias control unit 208 applies the secondary transfer bias voltage from the secondary transfer bias generation unit 215 to the secondary transfer roller 133 at a predetermined timing based on the detection of the leading edge of the medium P by the fourth transport sensor 132. . When the medium P passes through the secondary transfer roller 133, the toner image is transferred from the surface of the intermediate transfer belt 112 to the surface of the medium P by the secondary transfer bias voltage. Note that when there is no medium P on the secondary transfer roller 133, a small amount of toner (so-called fog toner) leaked from the image forming unit 102 is applied by applying a backup bias voltage to the secondary transfer backup roller 117. It is attracted to the intermediate transfer belt 112 side so as not to adhere to the secondary transfer roller 133.

  The process bias control unit 208 stops the application of the secondary transfer bias voltage at a predetermined timing after the fourth transport sensor 132 detects the trailing edge of the medium P.

  The medium P that has passed through the secondary transfer portion (the secondary transfer roller 133 and the secondary transfer backup roller 117) reaches the fixing unit 135. As described above, the heater 210 of the fixing unit 135 is heated to a predetermined temperature, and the fixing rollers 136 and 137 are rotating. The medium P passes through the nip portions of the fixing rollers 136 and 137 and is heated and pressurized to fix the toner image on the surface of the medium P. The medium P that has passed through the fixing unit 135 is conveyed by a pair of discharge rollers 139 and 140 that have already been rotated, and is discharged to a discharge tray 141.

  The feeding of the next medium P is started based on the timing at which the first transport sensor 124 detects the rear end of the previous medium P (the medium fed earlier). Here, the next medium P is fed at a timing such that the interval (medium interval) between the trailing edge of the previous medium P and the leading edge of the next medium P is shorter than the toner image formation interval. (Specifically, the feed clutch 148 is connected). As a result, the leading edge of the medium P precedes the leading edge of the toner image, and the adjustment distance (FIG. 4B) of the writing position at the secondary transfer portion is ensured.

<Media spacing control>
Here, control of the interval of the media P sequentially fed from the media tray 120 will be described.
FIG. 5 is a timing chart showing the operation timing of medium feeding control during normal operation. During normal operation (that is, when “multiple feeding” described later has not occurred), the feeding / feeding control unit 205 causes the first transport sensor 124 to move to the previous medium P (N−1). When the rear end is detected, the feed motor drive pulse counter 304 starts counting the feed motor drive pulse S407. When the count reaches C1, the feed clutch 148 is connected (ON), and the feed roller 122 is rotated to continue. Medium P (N) is fed. That is, an interval corresponding to the count number C1 is secured between the rear end of the previous medium P (N) and the front end of the next medium P (N-1).

  As described above, when the second transport sensor 126 detects the leading edge of the medium P (N−1), the feed motor drive pulse counter 304 starts counting the feed motor drive pulse S407 and reaches the count number C2. Then, the feed clutch 148 is turned off to stop the rotation of the feed roller 122, and at the same time, the registration clutch 149 is connected (ON) to start the rotation of the registration roller pair 127 (this causes the medium P (N) to become the registration roller). Conveyed by pair 127).

  When the second conveyance sensor 126 detects the trailing edge of the medium P (N), the conveyance motor drive pulse counter 305 starts counting the conveyance motor drive pulse S410. When the count number C2 ′ is reached, the registration clutch 149 is reached. Is turned off and the rotation of the registration roller pair 127 is stopped. As a result, the medium P (N) is transported by the transport roller pairs 128 and 131.

  When the third conveyance sensor 130 detects the leading edge of the medium P (N), the feeding / conveyance control unit 205 counts the conveyance motor drive pulse S410 by the conveyance motor drive pulse counter 305, and when the count reaches C3. The speed of the transport motor 143 is reduced from the process speed Vp to the adjustment speed Vc. Further, when the fourth transport sensor 132 detects the leading edge of the medium P (N), the transport motor drive pulse counter 305 counts the transport motor drive pulse S410. When the count reaches C4, the speed of the transport motor 143 is increased. Accelerate to process speed Vp. Subsequent processing is as described above.

  Here, as schematically shown in FIG. 6, the medium P on the medium tray 120 may be fed in an overlapping manner by the feed roller 122 and the separation roller 123.

  When only one medium P is fed from the feed roller 122 (or when there is no medium P), the separation roller 123 follows the feed roller 122 and rotates in the transport direction. Are fed in an overlapping state, a force is applied to the lower medium P of the two overlapping sheets in a direction opposite to the conveying direction. Therefore, normally, the medium P is fed one by one.

  However, in some cases, such as when a strong electrostatic force is generated between the media P loaded on the media tray 120, the two media P may not be separated by the separation roller 123. In such a case, the next medium P (N) may protrude from the separation roller 123 while the medium P (N-1) is being fed. This phenomenon is called “multiple feeding”.

  When the next medium P (N) protrudes from the separation roller 123 in this way, the first transport sensor 124 remains ON, and the rear end of the previous medium P (N-1) cannot be detected. Therefore, the feeding of the next medium P (N) is started based on the timing when the first transport sensor 124 detects the trailing edge of the medium P (N-1) as in the normal operation (FIG. 5). (That is, the feed clutch 148 cannot be turned on).

  Therefore, in such a case, the feed clutch 148 is turned on based on the timing at which the second transport sensor 126 detects the trailing edge of the medium P (N−1) (feed of the next medium P (N)). Start sending). FIG. 7 is a timing chart showing the operation timing when such medium feeding control is performed.

  However, when the medium feeding control shown in FIG. 7 is performed, the time during which the second transport sensor 126 detects the trailing edge of the medium P (N-1) is the first transport during normal operation (FIG. 5). Since the sensor 124 is later than the time for detecting the trailing edge of the medium P (N−1), the start of feeding the medium P (N) is delayed accordingly.

  As described above, the medium P (N) is conveyed so as to precede the leading edge of the toner image. However, if the feeding of the medium P (N) is delayed, the preceding distance becomes shorter (may be 0). Or the leading edge of the medium P (N) is conveyed later than the leading edge of the toner image. Therefore, the above-described adjustment distance (FIG. 4B) cannot be ensured, and processing (writing position adjustment) for matching the leading edge of the medium P (N) with the leading edge of the toner image cannot be performed. As a result, a positional error occurs between the medium P and the toner image, resulting in a printing error, toner printed on the page is wasted, and if there is a subsequent page, toner printed on the page is wasted. .

  Therefore, in the first embodiment of the present invention, when the first transport sensor 124 cannot detect the trailing edge of the medium P (N−1), the second transport sensor 126 detects the medium P (N -1) The feed motor is fed for a predetermined period in order to feed the next medium P (N) based on the timing at which the rear end is detected and to shorten the interval with the previous medium P (N-1). The drive speed of 142 is accelerated from the process speed Vp to the first recovery speed vr1. When the transport motor 143 has already been decelerated for adjusting the writing position, the drive speed of the feed motor 142 is accelerated from the adjustment speed Vc to the second recovery speed Vr2 (= process speed Vp).

  FIG. 8 is a timing chart showing the operation timing when double feeding of the medium P occurs in the first embodiment.

The feeding / feeding control unit 205 detects the medium P by the length A + a obtained by adding the desired margin a to the medium size A after the second transport sensor 126 detects the leading edge of the medium P (N−1). If the first conveyance sensor 124 cannot detect the trailing edge of the medium P even if it is conveyed, it is determined that a double feed has occurred (that is, the next medium P (N) has protruded from the separation roller 123). The medium size A is included in the medium size information S420 (FIG. 3) input from the command / image processing unit 202.

That is, the feed / feed control unit 205 determines the number of pulses of the feed motor drive pulse S407 by the feed motor drive pulse counter 304 after the second transport sensor 126 detects the leading edge of the medium P (N-1). If the first conveyance sensor 124 remains ON when the count number corresponding to the length A + a is reached, it is determined that double feeding has occurred.

  When the second transport sensor 126 detects the trailing edge of the medium P (N−1), the drive speed of the feed motor 142 is accelerated from the process speed vp to the first recovery speed Vr1. The feeding / conveying control unit 205 further counts the feed motor driving pulse S407 by the feed motor driving pulse counter 304 after the second conveying sensor 126 detects the trailing edge of the medium P (N), and the count number When C1 is reached, the feed clutch 148 is connected (ON). That is, the pickup roller 121 and the feed roller 122 feed the next medium P (N) at a higher speed (Vr1) than during normal operation (Vp).

The feeding / feeding control unit 205 further counts the feed motor driving pulse S407 after the second conveyance sensor 126 detects the leading edge of the next medium P (N), and reaches the count number C2. Then, the feed clutch 148 is disconnected (OFF), and the registration clutch 149 is connected (ON).

  After turning on the registration clutch 149, the feed motor 142 is decelerated from the recovery speed Vr1 to the process speed Vp. Here, in the case where the transport motor 143 has shifted to the deceleration process to the adjustment speed Vc in order to adjust the writing position of the previous medium P (N−1), the feed motor 142 starts from the first recovery speed Vr1. Decelerate to adjustment speed Vc.

  As described above, since the pickup roller 121 and the feed roller 122 feed the next medium P (N) at a higher speed (Vr1) than during normal operation (Vp), the feeding start of the medium P (N) is started. The delay can be recovered to some extent (or completely). Thereby, the relationship that the leading edge of the medium P (N) precedes the leading edge of the toner image can be maintained, and an adjustment distance (indicated by reference numeral L2 in FIG. 8) can be secured. Therefore, the operation of matching the leading edge of the medium P (N) with the leading edge of the toner image by the deceleration and acceleration of the conveyance speed of the medium P (N) (that is, the operation of adjusting the writing position in the secondary transfer unit) is performed reliably. be able to. Note that a distance traveled by the medium P by the acceleration of the feed motor 142 as compared with the normal operation is a recovery distance (reference numeral L3 in FIG. 8).

  In this embodiment, as an example, the relationship between the process speed Vp, the adjustment speed Vc, the first recovery speed Vr1, and the second recovery speed Vr2 is expressed as Vp−Vc = Vr1−Vr2 = Vr1−Vp (Vr2 = Vp). However, the present invention is not limited to this.

  As described above, according to the first embodiment of the present invention, when the first transport sensor 124 cannot detect the trailing edge of the previous medium P (N-1) due to double feeding. The feeding of the next medium P (N) is started and the feeding speed is accelerated based on the timing when the second transport sensor 126 detects the trailing edge of the previous medium P (N-1). Thus, the interval with the previous medium P (N-1) is shortened. Therefore, the medium interval does not spread more than necessary, and the writing position adjustment at the secondary transfer portion can be performed reliably. Accordingly, it is possible to prevent the occurrence of a printing error due to the positional deviation between the medium P and the toner image and to eliminate waste of toner.

Second embodiment.
Next, a second embodiment of the present invention will be described. Constituent elements similar to those of the first embodiment are denoted by the same reference numerals.

  FIG. 9 is a block diagram showing a control system in the second embodiment of the present invention. The difference from the control system (FIG. 3) of the first embodiment is that a medium interval control unit 901 is added to the feeding / conveying control unit 205. The medium interval control unit 901 receives a signal S402 indicating the presence / absence of the medium P output from the second transport sensor 126 and the count number output from the feed motor drive pulse counter 304. Other configurations are the same as those of the first embodiment.

  Next, the operation of the second embodiment will be described with a focus on differences from the operation similar to the first embodiment.

  As described in the first embodiment, when the next medium P (N) protrudes from the separation roller 123 when feeding the medium P (N-1), the first transport sensor 124 The rear end of the medium P (N-1) cannot be detected. Therefore, also in the second embodiment, the feeding of the medium P (N) is started based on the timing at which the second transport sensor 126 detects the trailing edge of the medium P (N-1). That is, after the second conveyance sensor 126 detects the trailing edge of the medium P (N−1), the feed motor drive pulse counter 304 counts the feed motor drive pulse S407 and feeds when the count reaches C1. The clutch 148 is turned on.

  At this time, after the second transport sensor 126 detects the rear end of the medium P (N−1), the second transport sensor 126 detects the front end of the medium P (N). The feed motor drive pulse S407 is counted by the feed motor drive pulse counter 304, and the interval between the medium P (N-1) and the medium P (N) is obtained based on the counted number.

Then, based on the determined medium interval (referred to as a medium interval value), a period for driving the feed motor 142 at the recovery speed Vr is determined. Here, it is assumed that the feed motor 142 is accelerated after the second transport sensor 126 detects the leading edge of the medium P (N). The medium interval control unit 901 calculates a feed motor drive pulse count number C5 corresponding to a period during which the feed motor 142 is driven at the recovery speed Vr based on the medium interval value described above.

  In the example shown in FIG. 10, when the feed motor 142 starts to accelerate, the transport motor 143 is driven at the adjustment speed Vc for adjusting the writing position of the previous medium P (N−1). Therefore, here, the feed motor 142 is accelerated from the adjustment speed Vc to the second recovery speed Vr2. Further, if the writing position adjustment is not performed at the start of acceleration of the feed motor 142, the feed motor 142 is accelerated from the process speed Vp to the first recovery speed Vr1.

Specifically, the medium interval value GS (mm) is as follows.
GS = Ph · Cg
Ph is a feed amount (mm / pulse) of the feed roller 122 / registration roller pair 127 per pulse. Cg is a feed motor counted by the feed motor drive pulse counter 304 between the time when the second transport sensor 126 detects the trailing edge of the medium P (N-1) and the leading edge of the medium P (N). This is the number of pulses of the drive pulse S407.

When the target medium interval (mm) is Gp, the distance Gr (mm) shortened by accelerating the feed motor 142 from the process speed Vp to the recovery speed Vr is:
Gr = Gp-GS = Gp-Ph.Cg
It becomes.
Thus, the acceleration time Tr (S) to the recovery speed Vr is
Tr = Gr / (Vr−Vp) = (Gp−Ph · Cg) / (Vr−Vp)
It becomes.

  Here, for the sake of simplicity of explanation, the calculation is performed by excluding the acceleration / deceleration period of the feed motor 142 and the amount of abutment of the medium P against the registration roller pair 127. However, by taking these into account, higher accuracy can be obtained. With this, the medium interval can be controlled.

  In this embodiment, Vr−Vp = Vr1−Vp = Vr2−Vc is taken as an example, but when Vr1−Vp ≠ Vr2−Vc, the process speed Vp is accelerated to the first recovery speed Vr1. The calculation may be performed separately for the case of accelerating from the adjustment speed Vc to the second recovery speed Vr2.

When the drive pulse rate when the drive speed of the feed motor 142 is the recovery speed Vr is Rr (pulse / s), the feed motor drive pulse count number C5 for maintaining the recovery speed Vr is:
C5 = Rr.Tr = Rr. (Gp-Ph.Cg + B) / (Vr-Vp)
It becomes.

  By driving the feed motor 142 at the recovery speed Vr until the number of drive pulses counted by the feed motor drive pulse counter 304 reaches C5, the medium P (N) is fed at a higher speed (Vr) than during normal operation. The distance from the previous medium P (N-1) can be set to a predetermined medium distance (mm). A distance traveled by the medium P by the acceleration of the feed motor 142 as compared with the normal operation is a recovery distance (reference numeral L3 in FIG. 10).

  FIG. 10 is a timing chart illustrating the operation timing of the medium feeding control according to the second embodiment.

In the same manner as in the first embodiment (FIG. 8), the feed / feed control unit 205 detects the feed motor drive pulse S407 after the second transport sensor 126 detects the leading edge of the medium P (N-1). When the first conveyance sensor 124 remains ON when the count number corresponding to the length A + a is reached, it is determined that double feeding has occurred.

The feeding / feeding control unit 205 further detects the trailing edge of the medium P (N−1) after the second conveying sensor 126 detects the trailing edge of the medium P (N−1). The feed motor drive pulse S407 is counted until it is detected, and the feed motor drive pulse count number C5 is determined based on the count number. Then, the drive speed of the feed motor 142 is accelerated from the process speed Vp to the first recovery speed Vr1.

The feed / feed control unit 205 counts the feed motor drive pulse S407 by the feed motor drive pulse counter 304, and when the feed motor drive pulse count number C5 is reached, the drive speed of the feed motor 142 is changed from the first recovery speed Vr1. Decrease to process speed Vp.

  In the example of FIG. 10, while the feed motor 142 is accelerated, the feed clutch 148 is disconnected (OFF) and the registration clutch 149 is connected (ON), and the medium P (N) is fed. Is switched from the feed roller 122 to the registration roller pair 127. In this example, the medium P (N) is fed at high speed mainly by the registration roller pair 127.

In the medium feeding control (FIG. 8) in the first embodiment described above, the feed motor 142 is changed from the recovery speed Vr to the process speed Vp regardless of the amount of the medium P (N−1) protruding from the separation roller 123. The return timing is fixed, but when the amount of the medium P (N-1) is large, the recovery distance is insufficient to completely recover the delay in the conveyance start of the medium P (N), and the secondary transfer is performed. There is a possibility that the adjustment distance L2 at the portion is shorter than the adjustment distance L1 during normal operation.

  On the other hand, in the medium feeding control (FIG. 10) in the second embodiment, the interval between the previous medium P (N-1) and the next medium P (N) is measured, and a predetermined medium interval is set. In order to accelerate the feed motor 142 only for a period necessary for obtaining, the adjustment distance L2 at the secondary transfer portion is made substantially the same as the adjustment distance L1 at the time of normal operation regardless of the amount of protrusion of the medium P. Can do.

  Note that the next medium P (N) is detected based on the timing at which the second transport sensor 126 detects the trailing edge of the previous medium P (N-1) each time regardless of whether double feeding has occurred. It is also possible to perform the medium feeding control of this embodiment. However, it is not preferable to increase the feeding speed more than necessary from the viewpoints of an increase in device operation noise, wear of the feed roller 122, and the like.

  As described above, according to the second embodiment of the present invention, the drive speed of the feed motor 142 is accelerated to increase the previous medium P (N -1) and the next medium P (N) can be shortened, and the writing position at the secondary transfer portion can be adjusted reliably. Therefore, it is possible to reduce a printing error due to a positional deviation between the medium P and the toner image, and to suppress waste of toner. In addition, since the medium interval can be managed more accurately than in the first embodiment, a more stable medium feeding operation can be realized.

  The present invention can be applied to an electrophotographic color image forming apparatus, such as a color printer, a color copying machine, a facsimile, or a color complex machine having a plurality of functions of these. The present invention may also be applied to a monochrome image forming apparatus.

DESCRIPTION OF SYMBOLS 100 Image forming apparatus, 102, 102Y, 102M, 102C, 102K Image forming unit, 109 Photosensitive drum (image carrier), 111, 111Y, 111M, 111C, 111K Primary transfer roller (primary transfer member), 112 Intermediate transfer belt (Intermediate transfer member), 117 secondary transfer backup roller, 120 medium tray (medium container), 121 pickup roller, 122 feed roller (feeding means), 123 separation roller (separation means), 124 first transport sensor, 125 First transport path, 126 Second transport sensor, 127 Registration roller pair (roller pair), 128, 131 Transport roller pair (transport means), 130 Third transport sensor, 132 Fourth transport sensor, 133 Second Secondary transfer roller (secondary transfer part), 135 Fixing unit (fixing means) 139, 140 Discharge roller pair, 142 Feed motor (motor), 143 Conveyance motor, 144 Fixing / discharge motor, 145 Intermediate transfer belt motor, 146, 147 Photosensitive drum drive motor, 148 Feed clutch, 149 Registration clutch, 204 Printer engine control unit, 205 feeding / conveying control unit (medium feeding control unit), 304 feed motor driving pulse counter, 305 conveying motor driving pulse counter, 306 intermediate transfer belt motor driving pulse counter, 314 feed clutch, 315 registration clutch 901 Medium interval control unit, P medium.

Claims (9)

A medium feeding control method in an image forming apparatus, comprising: a primary transfer portion that primarily transfers a developer image to an intermediate transfer member; and a secondary transfer portion that secondarily transfers a developer image from the intermediate transfer member to a medium. ,
A medium accommodating section capable of accommodating a plurality of media;
A feeding means for feeding a medium from the medium accommodating unit to a conveyance path;
Separating means for separating the medium fed by the feeding means one by one;
Conveying means for conveying the medium fed by the feeding means to the secondary transfer section at a first speed;
A first transport sensor for detecting a medium in the transport path;
A second transport sensor for detecting a medium on the downstream side of the first transport sensor in the transport path ;
A third transport sensor that is disposed upstream of the secondary transfer unit along the transport path and detects a medium;
A fourth transport sensor that is disposed on the downstream side of the third transport sensor along the transport path and detects the medium , and
In order to make the leading edge of the medium coincide with the leading edge of the developer image on the intermediate transfer member in the secondary transfer portion, the conveying means determines whether the leading edge of the medium is detected by the third conveying sensor. The medium conveying speed is decelerated to a second speed lower than the first speed, and then the medium conveying speed by the conveying means based on the timing at which the fourth conveying sensor detects the leading edge of the medium. Accelerating to the first speed,
Based on the timing at which the first transport sensor detects the trailing edge of the previously fed medium, the next medium is fed by the feeding means,
When the first transport sensor cannot detect the rear end of the previously fed medium, based on the timing at which the second transport sensor detects the rear end of the previously fed medium. , Feed the following media,
The feeding speed of the next medium is set to a third speed higher than the first speed when the previously fed medium is being transported at the first speed, and is fed to the first medium. When the medium thus conveyed is transported at the second speed, a fourth speed that is higher than the second speed and lower than the third speed is set . The feeding means is a feed roller rotated by a motor,
The medium feeding control method according to claim 1 , wherein the first speed or the second speed is accelerated by accelerating a driving speed of the motor. Using a roller pair that conveys the medium fed by the feed roller,
With the rotation of the roller pair stopped, the medium is applied to the nip portion of the roller pair, and then the rotation of the roller pair is started to correct the skew of the medium.
3. The medium according to claim 2, wherein the drive speed of the motor is accelerated after the second conveyance sensor detects the trailing edge of the medium and before the rotation of the feed roller is started. Feed control method. Using a clutch that switches connection and disconnection of driving force transmission from the motor to the roller pair,
4. The medium feeding control according to claim 3, wherein the driving speed of the motor is accelerated after the second conveyance sensor detects the trailing edge of the medium and before the clutch is connected. 5. Method. A medium feeding device used in an image forming apparatus having a primary transfer portion for primary transfer of a developer image to an intermediate transfer member and a secondary transfer portion for secondary transfer of a developer image from the intermediate transfer member to a medium. And
A medium accommodating section capable of accommodating a plurality of media;
A feeding means for feeding a medium from the medium accommodating unit to a conveyance path;
Separating means for separating the medium fed by the feeding means one by one;
Conveying means for conveying the medium fed by the feeding means to the secondary transfer section at a first speed;
A first transport sensor for detecting a medium in the transport path;
A second transport sensor for detecting a medium on the downstream side of the first transport sensor in the transport path;
A third transport sensor that is disposed upstream of the secondary transfer unit along the transport path and detects a medium;
A fourth transport sensor that is disposed downstream of the third transport sensor along the transport path and detects a medium;
A medium feeding control unit for controlling the feeding means and the conveying means ,
The medium feeding control unit is
In order to make the leading edge of the medium coincide with the leading edge of the developer image on the intermediate transfer member in the secondary transfer portion, the conveying means determines whether the leading edge of the medium is detected by the third conveying sensor. The medium conveying speed is decelerated to a second speed lower than the first speed, and then the medium conveying speed by the conveying means based on the timing at which the fourth conveying sensor detects the leading edge of the medium. Accelerating to the first speed,
Based on the timing at which the first transport sensor detects the trailing edge of the previously fed medium, the next medium is fed by the feeding means,
When the first transport sensor cannot detect the rear end of the previously fed medium, based on the timing at which the second transport sensor detects the rear end of the previously fed medium. , Feed the following media,
The feeding speed of the next medium is set to a third speed higher than the first speed when the previously fed medium is being transported at the first speed, and is fed to the first medium. When the medium thus conveyed is conveyed at the second speed, the fourth speed is set to be a fourth speed that is higher than the second speed and lower than the third speed . The feeding means is a feed roller rotated by a motor,
The medium feeding device according to claim 5 , wherein the medium feeding control unit accelerates the first speed or the second speed by accelerating a driving speed of the motor. A roller pair for conveying the medium fed by the feed roller;
The medium feeding control unit is
With the rotation of the roller pair stopped, the medium is applied to the nip portion of the roller pair, and then the rotation of the roller pair is started to correct the skew of the medium.
The medium according to claim 6 , wherein the drive speed of the motor is accelerated after the second conveyance sensor detects the trailing edge of the medium and before the rotation of the feed roller is started. Feeding device. A clutch that switches connection and disconnection of driving force transmission from the motor to the roller pair;
The medium feeding control unit is
The medium feeding device according to claim 7 , wherein the driving speed of the motor is accelerated after the second conveyance sensor detects the trailing edge of the medium and before the clutch is connected. . An image forming apparatus comprising the medium feeding device according to claim 5 .

Images