JP2006208847A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device which can prevent the misalignment of the relative position of an image carrier and a position detection means. <P>SOLUTION: The position detection means 202 and 203 detect the position of a sheet before it is transported to a transfer unit where an image on an image carrier 12 is transferred. The position of an image formed on the image carrier 12 is controlled according to the position of the sheet, based on the signal from the position detection means 202 and 203. The position detection means 202 and 203 are disposed in an image forming unit 311 integrally in which the image carrier 12 is disposed, and which is disposed in the image forming device body in a manner that it can be taken out. By this arrangement, the misalignment of the relative position of the image carrier 12 and the position detection means 202 and 203 can be prevented. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus, and more particularly to an apparatus that controls the position of an image formed on an image carrier in accordance with the position of a sheet.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine, a printer, a facsimile, or a complex machine thereof, an image forming unit that forms an image on a sheet, a sheet feeding unit that feeds a sheet to the image forming unit, and an image forming unit In order to form an image on both sides of the sheet, the sheet formed by the image forming unit is reversed. There is known a type having a sheet reversal conveyance path and the like for feeding again to the image forming unit.

  FIG. 11 is a schematic sectional view of an electrophotographic copying machine which is an example of such a conventional image forming apparatus. This electrophotographic copying machine (hereinafter referred to as a copying machine) is a copying machine which is the main body of the image forming apparatus. Built into the main body 1, a document reading unit 4 that reads a document image, an image forming unit 10 that forms an image on a sheet based on image information read by the document reading unit 4, and a copying machine body 1 Deck feeding units 34 and 35 and cassette feeding units 36 and 37 for feeding the sheets S stacked on the decks 30 and 31 and the sheet cassettes 32 and 33 to the image forming unit 10 are provided. A plurality of sheets S can be continuously fed to the image forming unit 10 from the sheet feeding units 34 to 37.

  Here, the document reading unit 4 includes a document feeding device 3 that transports a document to a predetermined position on a document table 2 made of a transparent glass plate fixedly provided on the upper portion of the copying machine main body 1. Further, the image forming unit 10 is formed on the surface of the photosensitive drum 12 charged by the charger 13, the charger 13 for uniformly charging the surface of the photosensitive drum 12 as the image bearing member, and the surface of the photosensitive drum 12. The developed electrostatic latent image is developed to form a toner image to be transferred to the sheet S, and a transfer unit for transferring the developed toner image on the surface of the photosensitive drum 12 to the sheet S. A transfer charger 19 configured with the photosensitive drum 12, a separation charger 20 for separating the sheet S on which the toner image is transferred from the photosensitive drum 12, and a toner remaining on the photosensitive drum 12 after the toner image is transferred. And a cleaner 26 for removing water.

  In the copying machine having such a configuration, the image of the document on the document table 2 is read by the document reading unit 4, and based on the data, the writing laser unit 5 emits a laser beam and uniformly By scanning the charged photosensitive drum 12, an electrostatic latent image is formed on the photosensitive drum 12.

  In addition, on the downstream side of the image forming unit 10, a conveyance unit 21 for conveying the sheet S to which the toner image is transferred, and a toner image on the sheet S conveyed by the conveyance unit 21 are fixed as a permanent image. The fixing device 22 is provided. Further, on the downstream side of the fixing device 22, a discharge roller 24 for discharging the sheet S on which the toner image is fixed by the fixing device 22 from the copying machine main body 1 is provided. Is provided with a discharge tray 25 for receiving the sheet S discharged by the discharge roller 24.

  By the way, in such a copying machine, the conveyance rollers 105, 107, 108, 109, 110, 111, 112, 123 are disposed on the conveyance path for conveying the sheet S from the sheet feeding units 34 to 37 to the image forming unit 10. In addition, sheet path sensors 104, 116, 117, and 118 for detecting the leading edge and the trailing edge of the sheet S are disposed. The sheet S fed by each conveyance roller is sent to the image forming unit 10 by a registration roller 106. A registration sensor 120 for detecting the leading edge of the sheet is disposed near the upstream side of the registration roller 106 in the sheet conveyance direction.

  Here, the conveyance roller 107 is a pre-registration roller for feeding the sheet S sent from each of the sheet feeding units 34 to 37 to the registration roller 106, and this conveyance roller (hereinafter referred to as pre-registration roller) 107. The first conveyance roller 105, the sheet path sensor 104, the second conveyance roller 108, the third conveyance roller 109, the sheet path sensor 116, the fourth conveyance roller 110, and the sheet path sensor 117 are disposed in the upstream sheet conveyance path. Arranged in order.

  In addition, a sheet conveyance path connected to the deck feeding unit 35 is branched from the conveyance path between the pre-registration roller 107 and the first conveyance roller 105, and the fifth conveyance from the downstream side to this sheet conveyance path. A roller 111, a sixth conveyance roller 112, a sheet path sensor 118, and a seventh conveyance roller 123 are arranged in this order.

  Further, a sheet reversing path is joined to the conveying path between the sixth conveying roller 112 and the seventh conveying roller 123. From the downstream side, the sheet reversing path includes a sheet path sensor 119, a double-sided right roller 113, The double-sided left roller 114, the reverse roller 115 rotating in the forward and reverse directions, and the sheet reverser 121 are arranged in this order.

  In this copying machine, in order to form an image on both sides of the sheet S, the sheet S on which the image is formed by the image forming unit 10 is reversed by the sheet reversing unit 121 and the reversing roller 115 and sent to the sheet reversing path. The left roller 114, the double-sided right roller 113, the sixth transport roller 112, the fifth transport roller 111, the pre-registration roller 107, and the registration roller 106 are fed again to the image forming unit 10.

  Each of these rollers is rotationally driven by transmitting a driving force of a driving motor (not shown). The rotation operation of each roller is controlled by a control unit (not shown) based on the detection result of each sheet path sensor.

  Next, as an example of the sheet feeding operation in such a conventional copying machine, see the diagram shown in FIG. 12 showing the positional relationship between the leading and trailing edges of the sheet when the deck feeding unit 34 feeds the sheet. To explain.

  At the start of sheet feeding, the pickup motor 101, the feeding roller 102, the separation roller 103, the first conveying roller 105, and the pre-registration roller 107 are rotationally driven by a driving motor. At this time, the registration roller 106 is still in a stopped state.

  At the time of sheet feeding, first, the pickup roller 101 sends the sheet S set on the deck 30 to the feeding roller 102. Here, the sheet S is separated into only the uppermost sheet by a separation roller 103 provided opposite to the feeding roller 102 and applied with a force that rotates in a direction opposite to the conveying direction with a constant torque.

  The uppermost sheet is detected by the sheet path sensor 104 and conveyed by the first conveying roller 105. Here, in the deck feeding unit 34, not only the sheet S whose leading end is at the normal stacking position of the deck 30 but also the next sheet may be sent, and the next sheet is fed to the deck 30 side by the separation roller 103. However, the leading edge position at the start of feeding the next sheet varies between the normal position and the position of the separation roller 103. For this reason, it is necessary to eliminate this variation before the sheet reaches the registration roller 106.

  In view of this, the copying machine performs a so-called pre-registration operation for adjusting the interval between sheets (paper interval). For this reason, when the sheet leading edge is detected by the sheet path sensor 104, first, based on the detection timing. Thus, the rotation of the first conveying roller 105 is temporarily stopped, the sheet S is stopped at a predetermined position on the conveying path, and the control for starting the rotation of the first conveying roller 105 again after a predetermined time has elapsed.

  Specifically, after the leading edge of the sheet is detected by the sheet path sensor 104, the first conveyance roller 105 is temporarily stopped at a timing when it reaches a predetermined position (pre-registration position) A (see FIG. 11) on the conveyance path. Confirm the stop position of the tip. The time B at which the leading edge of the sheet is expected to arrive at the registration roller 106 [B = (distance C to the registration roller 106) / (sheet conveyance speed β of the first conveyance roller 105 until reaching the registration roller 106)] Assuming that, the first transport roller 105 is controlled to restart.

  As a result, the sheet S reaches the stopped registration roller 106 via the pre-registration roller 107. After that, the sheet S is fed by a predetermined amount by the pre-registration roller 107 with the leading end abutted against the stopped registration roller 106, and the entire sheet is looped to correct the skew of the sheet S. Is done.

  Next, when the registration roller 106 starts rotating at a constant speed (process speed) α, the sheet S is transferred to the image forming unit 10, specifically, a transfer unit configured by the photosensitive drum 12 and the transfer charger 19. The toner image that has been formed on the photosensitive drum 12 until then is transferred onto the upper surface.

  The sheet S on which the toner image has been transferred in this manner is then sent to the fixing device 22 by the transport unit 21 to fix the toner image. In the case of single-sided copying, the discharge tray 25 passes through the discharge roller 24. In the case of double-sided copying, after the reversing operation is performed by the sheet reversing unit 121, the sheet reversing path is sequentially conveyed by the reversing roller 115, the double-sided left roller 114, and the double-sided right roller 113, and the image is again printed. It is sent to the forming unit 10.

  Here, as the timing for starting the feeding of the second and subsequent sheets S at the time of continuous feeding, a certain time has elapsed since the previous sheet restarted the first conveying roller 105 as shown in FIG. The feeding control is performed in the same manner as described above.

  Even when the sheets S are continuously fed from the other deck feeding unit 35 and cassette feeding units 36 and 37, the same pre-registration operation as described above is performed. Further, in the case of performing double-sided copying by continuously feeding the sheet S from any of the sheet feeding units, the double-sided right roller 113 is rotated based on the detection timing of the sheet leading edge by the sheet path sensor 119 on the double-sided conveyance path. Is temporarily stopped between the sheet sensor 119, the deck feeding unit 35, and the junction part of the double-sided conveyance path, and a pre-registration operation is performed in which rotation is started again after a predetermined time has elapsed.

  As described above, in the conventional copying machine, the variation in the sheet leading end position in the sheet feeding unit is removed by the above-described pre-registration operation, thereby determining the sheet leading end position and stably feeding the registration roller 106. I am doing so. Further, even when the sheet S is temporarily stopped in the conveyance path by the pre-registration operation, in order to catch up with the previous sheet, the sheet conveyance speed (process speed α of the registration roller 106) in the image forming unit 10 is used. Also, the conveyance speed β in the conveyance path from the sheet feeding unit to the registration roller 106 is set to be faster (see, for example, Patent Document 1).

JP 2002-029649 A

  By the way, in such a conventional copying machine (image forming apparatus), there is an increasing need to write an image in a frame on a sheet on which a frame has been printed in advance. In this case, the image is written on the sheet. Misalignment is becoming a problem.

  Here, such misregistration is composed of three elements: “leading edge misregistration”, “side edge registration misalignment”, and “skew”. Among these, “leading edge misregistration” is the entry of the sheet into the registration roller 106. This is due to a difference in condition (thick paper does not enter the back, thin paper does not enter the back) or variations in the connection of the electromagnetic clutch that starts the rotation of the registration roller 106.

  Further, the “lateral edge registration misalignment” is caused by variations in the positions of the decks 30 and 31 and the sheet cassettes 32 and 33 themselves, and variations due to insufficient pressing force of a pressing member (not shown) that holds the sheets in those units. For example, as described above, “skew” is a method in which a loop is formed by abutting against the registration roller 106 as described above, and in the case where the skew is taken, the skew cannot be removed when the skew amount is large. It is because of that.

  Therefore, for example, as shown in FIGS. 13 and 14, the skew correction device 200 </ b> A that is a skew correction unit in the copying machine main body 1 and a position detection unit that detects the position of the sheet before being conveyed to the transfer unit. It is conceivable to provide a sheet position detection device 200B for shifting the image writing position. Here, the skew correction device 200A is coaxial and corrects skew using the difference in speed between the skew correction rollers 200a and 200b, which can independently control the speed, and is provided with two correction sensors. The speed difference is obtained from the information of 201a and 201b and controlled.

  Further, the sheet position detecting device 200B is arranged so that the position of the sheet can be detected before the timing when the laser unit 5 starts writing on the photosensitive drum 12, and the leading edge detection sensor 202 (202a, 202b) that detects the leading edge in the conveyance direction. ) And a CIS sensor 203 that detects the side edge position of the sheet S, and a control unit (not shown) moves the laser writing position with respect to the photosensitive drum 12 based on information of these two sensors 202 and 203. Yes. By providing such a skew correction device 200A and the sheet position detection device 200B, highly accurate writing position control can be performed.

  Incidentally, as shown in FIG. 15, a unit F in which a pre-registration roller 107, conveying rollers 105, 108, 109, and 110 and sheet path sensors 104, 116, and 117 are arranged on the side wall surface 1A of the copying machine main body 1 is provided. It can be opened and closed. Further, as shown in FIG. 16, the copying machine main body 1 includes a unit G provided with a skew feeding correction device 200A, a sheet position detection device 200B, a conveyance unit 21, a fixing device 22, a discharge roller 24, and the like, and image formation. A sheet reversing unit 121, a double-sided left roller 114, a double-sided right roller 113, a sixth transporting roller 112, and a fifth transporting roller 111 for reversing and feeding the sheet on which the image has been formed by the unit 10 are arranged. The unit H is provided so that it can be pulled out in the front side, that is, in a direction orthogonal to the sheet feeding direction.

  When a sheet jam occurs, the unit F is opened to open the right side of the copier body 1 in order to take out the jam sheet. If necessary, the unit G and the unit H are pulled out from the copier body 1 to the front. The sheet inside the machine is removed.

  However, since the unit G is heavy with a mass of several tens of kg, it is difficult to always set it at a predetermined position when it is set in the copying machine main body 1 after the jam processing is finished. Some degree of misalignment may occur.

  When the unit G cannot be set at a predetermined position as described above, the relative positions of the photosensitive drum 12, the skew feeding correction device 200A, and the sheet position detection device 200B are shifted, and as described above, the skew is not corrected. Even if high-precision writing position control is performed by the line correction device 200A and the sheet position detection device 200B, the accuracy of the writing position does not increase as it is, and paper feeding for adjustment is required every time the unit G is put in and out. .

  Therefore, the present invention has been made in view of such a current situation, and provides an image forming apparatus in which the relative position between the photosensitive drum 12 (image carrier) and the sheet position detection device 200B is not shifted. It is the purpose.

  The present invention includes an image carrier on which an image is formed, a transfer unit that transfers an image on the image carrier to a sheet, and a position detection unit that detects the position of the sheet before being conveyed to the transfer unit. In the image forming apparatus that controls the position of the image formed on the image carrier based on the detection signal of the sheet position from the position detector, the image forming apparatus main body and the image carrier are attached, And an image forming unit that can be pulled out from the main body of the image forming apparatus, and the position detecting means is provided integrally with the image forming unit.

  As in the present invention, the position detection means is integrally provided in the image forming unit that is attached to the image carrier and is detachable from the main body of the image forming apparatus. The relative position can be prevented from shifting.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic sectional view of an electrophotographic copying machine as an example of an image forming apparatus according to an embodiment of the present invention. In FIG. 1, the same reference numerals as those in FIGS. 11, 13, and 14 indicate the same or corresponding parts, and thus detailed description thereof is omitted.

  In FIG. 1, reference numeral 311 denotes a photosensitive drum 12, which is an image carrier, a charger 13, a developing device 14, a transfer charger 19, skew correction rollers 200a and 200b of a skew feeding correction device 200A, and a correction sensor 201a of a sheet position detection device 200B. , 201b, an image forming unit including a leading edge detection sensor 202 for detecting the leading edge position of the sheet, a CIS sensor 203 serving as a side edge detecting sensor for detecting the side edge position of the sheet, and the image forming unit 311 is a copying machine. The main body 1 can be pulled out by slide rails 311a and 311b.

  Thus, the image forming unit 311 integrally including the photosensitive drum 12 and the leading edge detection sensor 202 and the CIS sensor 203 as position detection means for detecting the position of the sheet S can be pulled out from the copying machine main body 1. By providing, for example, during maintenance, the developer 14 can be replaced, and the skew correction rollers 200a and 200b, the correction sensors 201a and 201b, the tip detection sensor 202, the CIS sensor 203, the pre-transfer drive roller 309, and the like can be easily accessed. ing.

  Further, by providing the photosensitive drum 12, the leading edge detection sensor 202, and the CIS sensor 203 integrally with the image forming unit 311 as described above, the image forming unit 311 is pulled out and pushed into the copying machine main body 1 during maintenance, for example. Even when this is performed, the relative positions of the photosensitive drum 12 and the tip detection sensor 202 and the CIS sensor 203 are not shifted.

  The image forming unit 311 includes an image forming unit front plate 301 and an image forming unit rear plate 302 that support the photosensitive drum 12, the charger 13, the developing unit 14, and the cleaner 26, as shown in FIGS. A right frame 303 connecting the image forming unit front side plate 301 and the image forming unit rear side plate 302; a right lower frame 304 below the developing unit 14 and connecting the image forming unit front side plate 301 and the image forming unit rear side plate 302; In addition to the left frame 305 that is above and connects the image forming unit front plate 301 and the image forming unit rear plate 302 and the frame that connects the image forming unit front plate 301 and the image forming unit rear plate 302, it also serves as the upper sheet guide in the register unit. A cash register upper guide 306 is provided.

  The registration upper guide 306 supports correction sensors 201a and 201b, a tip detection sensor 202, and a CIS sensor 203, and the registration upper guide 306 is provided with positioning holes 306a and 306b.

  Reference numerals 307a and 307b denote drive motors for driving the skew correction rollers 200a and 200b, and are attached to the lower right frame 304. Reference numerals 308a and 308b denote drive belts that connect the drive motors 307a and 307b and the skew correction rollers 200a and 200b. Reference numeral 309 is provided upstream of the transfer portion constituted by the photosensitive drum 12 and the transfer charger 19 and downstream of the skew correction rollers 200a and 200b, and the position is detected by the tip detection sensor 202 and the CIS sensor 203. This is a pre-transfer driving roller that is one roller of a conveying roller pair that conveys the subsequent sheet to the transfer unit, and the shaft 310 of the skew correction rollers 200a and 200b is similar to the shaft 309a of the pre-transfer driving roller 309. End portions are supported by the front side plate 301 and the image forming unit rear side plate 302.

  In FIG. 1, G1 can be pulled forward by slide rails G1a and G1b, and as shown in FIG. 4, a transfer charger 19, a separation charger 20, a transport unit 21, a fixing device 22, and a discharge roller. 24 is a first unit, and the other unit, the first unit G1, is provided with a register lower guide unit 312.

  Here, the skew correction that comes in contact with the pre-transfer driven roller 309 and the pre-transfer driven roller 314 and the skew correction rollers 200a and 200b, which are the other rollers in contact with the pre-transfer driving roller 309, is in contact with the lower registration unit 312. A lower registration guide 313 provided with driven rollers 315a and 315b is provided opposite to the upper registration guide 306 (see FIG. 2), and lower registration protrusions 313a and 313b are provided on the upper surface of the lower registration guide 313. Is formed. A registration guide 306 serving as a conveyance guide member and a registration lower guide 313 serving as another conveyance guide member constitute a conveyance guide unit that guides the sheet to the transfer unit.

  Further, the lower register guide 313 can be moved up and down by an elevating device 316, and when it is in the raised position, the lower register protrusions 313a and 313b are engaged with the positioning holes 306a and 306b of the upper register 306. As a result, the first unit G1 is positioned with respect to the image forming unit 311 via the registration lower guide protrusions 313a and 313b and the positioning holes 306a and 306b of the registration upper guide 306.

  When the first unit G1 is positioned in this way, the pre-transfer driving roller 309, the pre-transfer driven roller 314, the skew correction rollers 200a and 200b, and the skew correction driven rollers 315a and 315b come into contact with each other to sandwich and convey the sheet. Will be able to.

  When in the lowered position, the registration lower guide projections 313a and 313b are disengaged from the positioning holes 306a and 306b of the registration upper guide 306, and the pre-transfer driving roller 309 and the pre-transfer driven roller 314 are skewed. The correction rollers 200a and 200b and the skew correction driven rollers 315a and 315b are also separated from each other.

  In other words, the lower registration guide 313 is configured such that the pre-transfer driving roller 309 and the pre-transfer driven roller 314, the skew correction rollers 200a and 200b, and the skew correction driven rollers 315a and 315b are in contact with each other, and the pre-transfer driving roller 309 and the pre-transfer driving roller 309. The driven roller 314, the skew correction rollers 200a and 200b, and the skew correction driven rollers 315a and 315b can be moved to positions separated from each other. Reference numeral 317 denotes a paper gap control sensor for controlling the paper gap.

  In FIG. 1, H1 is a second unit that can be pulled out forward by slide rails H1a and H1b. The second unit H1 includes a sheet reversing section 121, a double-sided left roller 114, a double-sided right side as shown in FIG. A roller 113, a sixth conveyance roller 112, and a fifth conveyance roller 111 are arranged.

  In FIG. 1, reference numeral 130 denotes a control unit that controls the sheet conveyance speed of each roller provided in the sheet conveyance path and the double-sided conveyance path, and the control unit 130 controls the sheet conveyance speed of each roller. It has become. As will be described later, the control unit 130 controls the writing position by the laser unit 5 based on the leading edge position and side edge position information from the leading edge detection sensor 202 and the CIS sensor 203.

  Here, in the present embodiment, the second pre-registration roller 204 in FIG. 1, the pre-registration roller 107, the first conveyance roller 105 as a pre-registration conveyance unit on the upstream side in the sheet conveyance direction of the pre-registration roller 107, The second conveyance roller 108 on the upstream side in the sheet conveyance direction of the first conveyance roller 105 can be switched between a process speed α that is the sheet conveyance speed of the photosensitive drum 12 and a first speed β that is faster than the process speed α. Yes.

  Each of these rollers is paired with another roller, and each of the rollers is a release solenoid 204a, 107a, 105a, 108a for releasing the pressure between the rollers and a release arm 204b, 107b, 105b, 108b. The pressure between the rollers can be released by turning on the release solenoids 204a, 107a, 105a, and 108a.

  Further, the third conveying roller 109 upstream of the second conveying roller 108 in the sheet conveying direction, the fourth conveying roller 110 upstream of the third conveying roller 109 in the sheet conveying direction, the fifth conveying roller 111, and the fifth conveying roller. The sixth conveyance roller 112 on the upstream side in the sheet conveyance direction of the roller 111 and the seventh conveyance roller 123 on the upstream side in the sheet conveyance direction of the sixth conveyance roller 112 are rotationally driven at the first speed β. Yes.

  In addition, the fifth transport roller 111 and the sixth transport roller 112 are each a pair of other rollers, and each includes release solenoids 111a and 112a and release arms 111b and 112b for releasing the pressure between the rollers. The pressure between the rollers can be released by turning on the release solenoids 111a and 112a.

  Further, the double-sided right roller 113, double-sided left roller 114, and reverse roller 115 arranged in the sheet reverse path can be switched between the first speed β described above and the second speed γ for sheet reverse. It has become.

  The control unit 130 receives sheet detection signals from the respective sheet path sensors 104, 116, 117, 118, and 119, and the control unit 130 receives the sheet path sensors 104, 116, The rotation of each transport roller is controlled based on the detection timings 117, 118, and 119. The controller 130 corrects the pre-registration conveyance when continuously feeding sheets, and details thereof will be described later.

  Next, the feeding operation in the present embodiment will be described with reference to the diagram shown in FIG. 5 showing the positional relationship between the leading edge and the trailing edge of the sheet when the sheet is fed from the deck feeding unit 34, for example. .

  At the start of sheet feeding, the pickup roller 101, the feeding roller 102, the separation roller 103, the first conveying roller 105, and the pre-registration roller 107 are rotationally driven. At this time, the registration roller 106 is still in a stopped state.

  When the sheet feeding is started, the pickup roller 101 first feeds the sheet S set on the deck 30 to the feeding roller 102. Here, the sheet S is separated into only the uppermost sheet by a separation roller 103 provided opposite to the feeding roller 102 and applied with a force that rotates in a direction opposite to the conveying direction with a constant torque.

  Next, the uppermost sheet is detected by the sheet path sensor 104 and conveyed by the first conveying roller 105. Here, in the deck feeding unit 34, not only the sheet whose leading end is at the regular stacking position of the deck 30 but also the next sheet may be sent out, and the next sheet is fed to the deck 30 side by the separation roller 103. However, there is a possibility that a large variation may occur between the regular position and the position of the separation roller 103 at the leading edge position at the start of feeding of the next sheet. It is necessary to reduce the level to a level that can be controlled.

  Therefore, in the copying machine, in order to perform a pre-registration operation for adjusting the interval between sheets (paper interval), the rotation of the first conveying roller 105 is temporarily stopped based on the detection timing of the leading edge of the sheet by the sheet path sensor 104. Then, the leading edge of the sheet being nipped and conveyed by the first conveying roller 105 is stopped at a predetermined position on the conveying path, and the control to start the rotation of the first conveying roller 105 again after a predetermined time has elapsed.

  Specifically, as shown in FIG. 5, the first transport roller 105 at a timing when the leading edge of the sheet comes to a predetermined position (pre-registration position) A (see FIG. 1) on the transport path after the sheet path sensor 104 detects it. Is temporarily stopped, and the stop position of the leading edge of the sheet is determined. Then, the time B [B = (distance C to the sheet spacing control sensor 317) / (time until the sheet spacing control sensor 317 is reached) / the time when the leading edge of the sheet is expected to arrive at the sheet spacing control sensor 317 is estimated. Assuming the sheet conveyance speed β)], the first conveyance roller 105 is controlled to be restarted. For example, the restart is performed so that the paper trailing edge control sensor 317 is reached at a time J after the trailing edge of the previous sheet passes through the paper spacing control sensor 317.

  Here, as shown in FIG. 6, a predetermined sheet length K, a time L for decelerating from the speed β to α, a distance M during which the decelerated sheet moves during the time L, and a sheet from the position A as planned. When the distance between the point N at which deceleration starts and the sheet spacing control sensor 317 when the distance B reaches the spacing control sensor 317 is P, the restarted sheet has a trailing edge at the trailing edge of the previous sheet. The time J that reaches the paper gap control sensor 317 after passing through 317 is represented by (K + M + P) / α−LP / β.

  However, the time B varies somewhat due to the relationship of passing through the bending path. Therefore, the deviation time Q between the actual arrival time at the paper gap control sensor 317 and the time B is corrected by moving the deceleration position within the range of the area R. For example, when the time Q is early, the deceleration position N is set to a position where the distance from the paper spacing control sensor 317 is PQ × β as shown in FIG. 7, and when the time Q is late, FIG. As shown in FIG. 4, the sheet spacing is controlled by setting the deceleration position N to a position where the distance from the sheet spacing control sensor 317 is P + Q × β.

  Next, as shown in FIG. 9, the leading edge of the sheet is sandwiched between skew correction rollers 200a and 200b (and skew correction driven rollers 315a and 315b), and the skew amount is detected by the correction sensors 201a and 201b. Thereafter, the release solenoids 204a and 107a (also release solenoids 105a and 108a depending on the size) are operated, and the pressure of each transport roller is released.

  Next, when the leading edge of the sheet S is in the skew correction area T, the skew correction roller that holds the preceding side of the sheet S is temporarily decelerated by the correction amount. As a result, the skew is corrected. At this time, as described above, since the pressure on the upstream conveying roller is released, the skew of the sheet S is corrected without resistance.

  Next, when the leading edge of the sheet S reaches the leading edge detection sensor 202 and the CIS sensor 203, the leading edge detection sensor 202 and the CIS sensor 203 determine the leading edge position and the side edge position of the sheet S, and this information is sent to the control unit 130. send. Then, the control unit 130 controls the laser unit 5 to shift the writing position based on this information, and forms an image on the photosensitive drum 12. Thereby, an image can be accurately formed on the sheet S.

  By the way, in the copying machine having such a configuration, when a sheet is jammed and, for example, a signal is not input even after a predetermined time elapses from the correction sensors 201a and 201b, the control unit 130 determines that a jam has occurred. First, the register lower guide 313 is lowered by the lifting device 316. As a result, the registration lower guide projections 313a and 313b are disengaged from the positioning holes 306a and 306b of the registration upper guide 306, and the pre-transfer driving roller 309 and the pre-transfer driven roller 314, the skew correction rollers 200a and 200b, and the skew correction driven The rollers 315a and 315b are also separated.

  Next, the unit F1 is opened on the right side, the remaining sheets are removed, and when there are other sheets, the first unit G1 is pulled out to open each paper path, and the jammed sheet is processed. If necessary, the jammed sheet is processed after the second unit H1 is pulled out.

  Here, when the first unit G1 is pulled out, the registration lower guide 313 is lowered, the pre-transfer driven roller 314 is the pre-transfer driving roller 309, and the skew correction driven rollers 315a and 315b are the skew correction rollers 200a and 200b, respectively. Even if there is a sheet between the pre-transfer driven roller 314 and the pre-transfer driving roller 309 or between the skew correction driven rollers 315a and 315b and the skew correction rollers 200a and 200b, the first unit is separated. G1 can be easily pulled out without damaging the sheet.

  That is, the pre-transfer driven roller 314 and the skew correction driven rollers 315a and 315b are provided in the first unit G1 so as to be able to come into contact with and separate from the pre-transfer driving roller 309 and the skew correction rollers 200a and 200b. Even when there is a sheet between the front drive roller 309 or between the skew correction driven rollers 315a and 315b and the skew correction rollers 200a and 200b, the sheet is not left and the photosensitive drum 12 is not damaged. The sheet can be processed, and it is possible to prevent the sheet processing from having a significant influence on the subsequent image formation.

  Next, after the jammed sheet is removed and jammed, the first unit G1 is pushed in. When the first unit G1 is pushed in this way, the lower registration guide 313 is first lifted by the lifting device 316. As a result, the lower registration guide 306a and 306b of the registration upper guide 306 of the image forming unit 311 is obtained. The protrusions 313a and 313b are engaged with each other, and the pre-transfer driving roller 309 and the pre-transfer driven roller 314, the skew correction rollers 200a and 200b, and the skew correction driven rollers 315a and 315b are in contact with each other.

  That is, when the first unit G1 is pushed in in this way, the image forming unit 311 and the first unit G1 are positioned with the positioning holes 306a and 306b of the image forming unit 311 and the registration lower guide protrusions 313a and 313b of the first unit G1. Positioning is performed by the engagement.

  Here, as described above, since the photosensitive drum 12, the leading edge detection sensor 202, and the CIS sensor 203 are integrally provided in the image forming unit 311, for example, the image forming unit 311 is attached to the copying machine main body 1 during maintenance. Even when the drawer / push-in operation is performed, the relative positions of the photosensitive drum 12, the tip detection sensor 202, and the CIS sensor 203 are not shifted.

  Accordingly, when the first unit G1 is pulled out and pushed in without pulling out the image forming unit 311 as described above, the correction sensors 201a and 201b, the leading edge detection sensor 202, the CIS sensor 203, Since the skew correction rollers 200a and 200b and the pre-transfer driving roller 314 have a desired positional relationship, the writing position control on the sheet can be performed with high accuracy. In addition, since the position of the registration upper guide 306 whose positional relationship with each of these sensors and rollers is important does not change, it is possible to ensure the conveyance stability.

  As described above, the front end detection sensor 202 and the CIS sensor 203 are integrally provided in the image forming unit 311 to which the photosensitive drum 12 is attached and which can be pulled out to the copying machine main body 1. The relative positions of the detection sensor 202 and the CIS sensor 203 can be prevented from shifting. This also enables highly accurate writing position control.

  In the present embodiment, as described above, the pre-transfer driven roller 314 and the skew correction driven rollers 315a and 315b are provided in the first unit G1, and the registration lower guide 313 is usually lifted by the lifting device 316, The pre-transfer driving roller 309, the pre-transfer driven roller 314, the skew correction rollers 200a and 200b, and the skew correction driven rollers 315a and 315b are brought into contact with each other. That is, the pre-transfer driven roller 314 and the skew correction driven rollers 315a and 315b related to the conveyance stability are not provided in the image forming unit 311.

  However, the pre-transfer driven roller 314 and the skew correction driven rollers 315a and 315b have a friction coefficient much smaller than that of the pre-transfer driving roller 309 and the skew correction rollers 200a and 200b. Even if it is not provided, there is little influence on the conveyance stability.

  For example, the pre-transfer driving roller 309 (made of rubber) has a dynamic friction coefficient of 2.0, the pre-transfer driven roller 314 (made of resin) has a dynamic friction coefficient of 0.2, and the pre-transfer driven roller 314 is 0 with respect to the normal direction. Suppose that it is tilted 1 °.

  Here, when the pre-transfer driving roller 309 is similarly inclined by 0.1 °, it is shifted by 0.0017 mm (= sin 0.1 °) per 1 mm conveyance with respect to the normal direction. If this is considered by A3 (420 mm), it will shift | displace 0.73 mm (= 0.0017 * 420), and will become a problem.

  However, since the pre-transfer driving roller 309 is provided integrally with the image forming unit 311 and faces the normal direction, in this case, the transfer force by the pre-transfer driving roller 309 is U as shown in FIG. The conveyance force by the front driven roller 314 is expressed as 0.1 U, and if it proceeds in the direction of the resultant force, the displacement is 0.00017 mm (= 0.1 × sin 0.1 °) per 1 mm conveyance, and even A3 (420 mm) is 0. .073mm and only a minute amount. Therefore, even if the pre-transfer driven roller 314 and the skew correction driven rollers 315a and 315b are provided in the first unit G1 as in the present embodiment, the conveyance stability can be ensured.

1 is a schematic cross-sectional view of an electrophotographic copying machine that is an example of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a diagram illustrating a configuration of an image forming unit provided in the electrophotographic copying machine. FIG. 3 is a side view of the image forming unit. FIG. 3 is a diagram illustrating the configuration of a first unit G1 and a second unit H1 provided in the electrophotographic copying machine. The figure showing the positional relationship between the leading edge and the trailing edge of the sheet when the sheet is fed by the deck feeding section of the electrophotographic copying machine. FIG. 6 is a diagram for explaining calculation of a time for restarting after the trailing edge of the previous sheet has passed through the paper gap control sensor in FIG. 5. The 1st figure explaining correction | amendment of the time which performs the said restart. The 2nd figure explaining correction | amendment of the time which performs the said restart. FIG. 2 is a diagram illustrating a skew feeding correction device and an image writing position shift device provided in the electrophotographic copying machine. FIG. 4 is a diagram for explaining sheet misalignment due to a tilt of a pre-transfer driven roller provided in the electrophotographic copying machine. FIG. 10 is a schematic cross-sectional view of an electrophotographic copying machine that is an example of a conventional image forming apparatus. FIG. 5 is a diagram illustrating a positional relationship between the leading edge and the trailing edge of a sheet when a sheet is fed by a deck feeding unit of the conventional electrophotographic copying machine. FIG. 6 is a schematic cross-sectional view of an electrophotographic copying machine that is another example of a conventional image forming apparatus. FIG. 3 is a diagram showing a skew feeding correction device and an image writing position shift device provided in the conventional electrophotographic copying machine. The figure which shows the unit structure of the said conventional electrophotographic copying machine. The figure which shows the structure of the unit G and the unit H of the said conventional electrophotographic copying machine.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Copier main body 10 Image formation part 12 Photosensitive drum 19 Transfer charger 130 Control part 200A Skew correction apparatus 200B Sheet position detection apparatus 200a, 200b Skew correction roller 202 Tip detection sensor 203 CIS sensor 301 Image formation part front plate 302 Image formation Rear plate 306 Registration upper guide 306a, 306b Positioning hole 309 Pre-transfer driving roller 311 Image forming unit 312 Registration lower guide unit 313 Registration lower guide 313a, 313b Registration lower guide protrusion 314 Pre-transfer driven roller 315a, 315b Skew correction driven roller 316 Lifting device G1 1st unit S seat

Claims (8)

An image carrier on which an image is formed; a transfer unit that transfers an image on the image carrier to a sheet; and a position detection unit that detects a position of the sheet before being conveyed to the transfer unit. In the image forming apparatus configured to control the position of the image formed on the image carrier based on the detection signal of the sheet position from the means,
An image forming apparatus main body;
An image forming unit to which the image carrier is attached and provided so as to be able to be pulled out to the image forming apparatus main body;
With
An image forming apparatus, wherein the image forming unit is provided with the position detecting unit.   The image forming apparatus according to claim 1, wherein the position detection unit includes a leading edge detection sensor that detects a leading edge of the sheet and a side edge detection sensor that detects a side edge of the sheet.   3. The image forming apparatus according to claim 1, wherein the image forming unit is provided with skew feeding correcting means for correcting skew feeding of the sheet before the position is detected by the position detecting means. .   The image forming apparatus according to claim 1, wherein a conveyance guide member that constitutes a conveyance guide unit that guides a sheet to the transfer unit is attached to the image forming unit. .   Another unit is provided adjacent to the image forming unit, and one roller of a pair of transport rollers that transports the sheet whose position is detected by the position detecting unit to the transfer unit is attached to the image forming unit, The image forming apparatus according to claim 1, wherein the other roller of the pair of conveying rollers is attached to the other unit.   6. The other roller of the conveyance roller pair provided in the other unit can be brought into contact with and separated from one roller of the conveyance roller pair provided in the image forming unit. Image forming apparatus.   The other unit is provided in the image forming apparatus main body so that it can be pulled out, and the other unit is positioned by the image forming unit, and when the other unit is positioned, the other unit becomes the image. The image forming apparatus according to claim 6, wherein the other roller of the pair of transport rollers spaced apart when pulled out from the main body of the forming apparatus comes into contact with one roller of the pair of transport rollers. The other unit is provided with another conveyance guide member that constitutes the conveyance guide portion together with the conveyance guide member provided in the image forming unit, and the other roller of the conveyance roller pair is disposed on the other conveyance guide member. And the other conveyance guide member is positioned so that the other roller of the conveyance roller pair contacts one roller of the conveyance roller pair, and the other roller of the conveyance roller pair is one of the conveyance roller pairs. The image forming apparatus according to claim 7, wherein the image forming apparatus is movable to a position separated from the roller.

Images