JP6432799B2 - Paper feeding device, image forming device, and image reading device - Google Patents

Description

  The present invention relates to a sheet feeding device, an image forming apparatus, and an image reading apparatus.

  2. Description of the Related Art Image forming apparatuses such as copying machines, printers, and facsimiles are equipped with a paper feeding device that feeds paper one by one from a paper tray that stores a bundle of paper. As a paper feeding method of such a paper feeding device, an FRR paper feeding method and an RF paper feeding method are known. The FRR method (Feed and Reverse Roller method) applies reverse torque to a separation roller as a separating member in order to feed sheets one by one. The RF method (Roller Friction method) does not apply reverse torque to the separate roller. FIG. 9 shows an example of an FRR type paper feed mechanism. In the figure, 51 is a paper feed tray, 52 is a paper guide, 53 is a bottom plate, 54 is a calling roller, 55 is a feed roller, 56 is a separation roller, 58 is a grip roller, K1 is a front end detection means, K2 is a paper detection means, P is a sheet bundle, P1 is a preceding sheet, and P2 is a next sheet.

  The FRR system has a feed roller 55 and a separation roller 56 that is in pressure contact with the feed roller 55. The feed roller 55 rotates in the paper feeding direction, but the separation roller 56 is reverse to the feeding direction via a torque limiter. Is given a driving force (reverse torque). Since the FRR method applies reverse torque, the separation performance is higher than that of the RF method. Both types have the advantage that the paper separation performance is not affected even if the positional relationship between the front end position of the paper and the pressure contact portion (feed nip) between the feed roller 55 and the separation roller 56 is rough. For this reason, an extra cost for increasing the position accuracy is not required, and the sheet feeding method is suitable for a front loading type sheet feeding tray which has become mainstream in recent years.

  In the FRR type and RF type paper feeders, the paper is normally called from the paper bundle by the rotation of the call roller 54 geared to the feed roller 55. The calling roller 54 contacts the uppermost sheet of the sheet bundle P, and feeds the sheet (preceding sheet P1) downstream in the transport direction. Then, the fed-out preceding paper P1 is fed downstream in the transport direction by a feed roller 55 positioned on the downstream side of the paper feed tray 51. Even before the trailing edge of the preceding paper P1 passes the grounding point of the calling roller 54, when the leading edge of the preceding paper P1 reaches the grip roller 58 provided further downstream, the calling roller 54 is separated from the paper surface of the preceding paper (or not). To drive). When the front end of the preceding paper P1 is detected by the paper detection means K2 located further downstream of the grip roller 58, the calling roller 54 is moved to the top of the paper feed tray 51 to feed out the next paper P2 using this paper detection as a trigger. The upper sheet (next sheet P2) is brought into contact (or re-driven) with the surface of the sheet.

  On the other hand, the feed roller 55 is stopped before the trailing edge of the preceding paper P1 exceeds the feed nip in order to prevent paper jam. A one-way clutch is connected to the rotation shaft of the feed roller 55. Even if the drive of the feed roller 55 is stopped, the feed roller 55 itself rotates in the conveyance direction of the paper conveyed by the grip roller 58 (driven rotation). ) By stopping the driving of the feed roller 55 and rotating the separation roller 56 in the reverse direction, even if the front end of the next paper P2 reaches the feed nip in a form following the rear end of the preceding paper P1, paper separation is reliably performed. No paper jam occurs due to the inability to control the gap between the preceding paper P1 and the next paper P2.

  The start timing of the next paper P2 is triggered by the detection of the leading edge of the preceding paper P1 by the paper detection means K2 provided downstream of the grip roller 58 where the behavior of the paper is stable (slip rate is reduced). With this trigger, the driving of the calling roller 54 and the feed roller 55 is started at a predetermined timing that does not collide with the rear end of the preceding paper P1 and satisfies a predetermined print productivity.

  By the way, in recent copiers and printers, it is necessary to keep the paper speed at the time of image formation low with the aim of high image quality and low power consumption, while high printing speed (high print productivity) is also required. Yes. For this reason, the paper speed is kept low, but the gap between the papers in the paper feeding unit is set narrow to achieve both high image quality and high print productivity.

  As described above, the FRR method and the RF method are advantageous in terms of cost and suitable for the front loading type. However, in the conventional FRR method and RF method, as described above, the next paper P2 of the paper feed tray 51 is fed out using the front edge detection of the preceding paper P1 by the front edge detection means as a trigger, so that the preceding paper P1 and the next paper P2 are fed out. The space between the papers was relatively wide.

  On the other hand, the distance from the front end position of the paper stacking section of the paper feed tray 51 to the feed nip of the feed roller 55 is such that the front wall 1a of the paper feed tray 51, the paper guide 52, and the paper cassette bottom plate 53 when the paper is fewly stacked. It changes between 15 and 30 mm due to the retreat of the front end of the sheet bundle due to the rise. For this reason, a large variation occurs in the start position depending on whether or not the preceding paper P1 and the next paper P2 are taken out by friction. That is, when there is a take-out due to friction, the next paper P2 taken out by friction with the preceding paper P1 may have already reached the feed roller 55 when the next paper P2 starts.

  The start timing of the next sheet P2 must be determined at a later timing when the sheet taken up to the position of the earliest feed roller 55 does not collide with the rear end of the preceding sheet P1. As a result, the actual paper gap between the next paper P2 and the preceding paper P1 started from the rearmost paper feed tray 51 is about 30 mm larger than the target paper gap, and the printing speed is increased. It became a factor to inhibit.

  Accordingly, in view of such a problem, as shown in FIG. 9, a paper front end detection unit K1 is provided on the downstream side of the feed roller 55, and the next paper P2 is conveyed to the front end detection unit K1 at an increased conveyance speed. A paper device has been proposed (see FIG. 5 of Japanese Patent Laid-Open No. 2005-213039 of Patent Document 1).

In this paper feeding device, after the trailing edge of the preceding paper P1 exceeds the leading edge detection means K1, when the leading edge detection means K1 detects the leading edge of the next paper P2, the paper detection is performed between the preceding paper P1 and the next paper P2. It is determined whether or not the minimum sheet interval δ that can be detected by means K2 is secured. That is, the sheet interval δ is calculated from the time when the front edge of the preceding paper P1 is detected by the paper detection means K2, the length of the paper, and the time when the front edge of the next paper P2 is detected by the front edge detection means K1. Then, the conveyance state of the feed roller 55 is controlled so that the minimum sheet interval δ is formed when the front end of the next sheet P2 reaches the sheet detection means K2 downstream of the grip roller 58. When the front edge of the next paper P2 is detected by the front edge detection means K1, if the front edge of the preceding paper P1 has not reached the paper detection means K2, the transport of the next paper P2 is temporarily stopped and the start position of the next paper P2 is determined. It was like that.

  However, once the feeding of the next sheet P2 is stopped, a time loss due to this stop occurs. In order to compensate for this time loss, a considerable increase in speed is required when resuming feeding thereafter, and a considerably large stepping motor is required for both the feed roller 55 and the grip roller 58 in order to cope with this increase in speed. It was.

  Further, when the feed roller 55 does not have its own drive source and the drive force is obtained from the grip roller 58, an electromagnetic clutch is required for the shaft portion of the feed roller 55. However, since the number of times the clutch is turned on / off increases more than usual, there is a problem in that the life of the clutch is reduced and reliability is lost.

  Therefore, in Japanese Patent Application Laid-Open No. 2005-213039 (FIG. 1) of Patent Document 1, as shown in FIG. 10, between the front end position of the paper stacking portion (paper bundle P) and the separation feeding portion (feed roller 55). An improved paper feeder provided with a paper detection means K3 is disclosed. That is, in order to shorten the interval between sheets, a sheet detecting unit K3 is provided in place of the front end detecting unit K1 disposed on the downstream side of the feed roller 55. If the paper detection means K3 detects “no paper” when the trailing edge of the preceding paper P1 passes through the separation feeding unit, the next paper P2 is preliminarily fed without stopping the driving of the calling roller 54. I have to.

  However, even in this improved paper feeding device, the calling roller 54 must be temporarily separated from the paper surface of the preceding paper P1 or not driven before the trailing edge of the preceding paper P1 passes through the calling roller 54 in order to prevent paper jam. . And the moment (predetermined time T4 of FIG. 2 of cited reference 1) when the trailing edge of the preceding paper P1 passes through the separation feeding unit (feed roller 55) after the separation or non-driving is captured by the control timer. At the same time, it is necessary to detect the presence / absence of the paper in the paper detection means at the moment in a short time, and to determine in a short time whether or not the calling roller 54 is brought into contact or redriven based on the detection result.

  For this reason, high detection accuracy and high timer accuracy for setting the detection timing are required. This increases the load on the control system, thereby causing a control delay, and paper jam is likely to occur due to the control delay. Instability of the control system becomes a problem. In addition, due to a delay in the response of the solenoid that abuts and separates the calling roller 54, the variation between the papers and the frequency of the paper jam that accompanies it increase, or the pressing and separation of the calling roller 54 are repeated in a short time. The operation sound generated by this has hindered silence.

  Accordingly, in view of the above-described problems, the present invention provides a sheet feeding device capable of obtaining a stable sheet feeding operation with a long service life and low noise without losing design advantages such as tolerance of positional accuracy of the FRR method and the RF method. The purpose is to do.

  In order to solve the above-described problems, the present invention is disposed upstream of the front end position of the paper stacking unit by a predetermined distance and contacts the uppermost paper of the paper stacking unit, and transports the contacted paper one by one. A calling roller that feeds downstream, a feed roller that feeds the fed paper to the downstream side, and a plurality of feed papers partially overlapping each other through the pressure contact portion in pressure contact with the feed roller In the sheet feeding device having a separation feeding unit having a separation member that prevents the second and subsequent sheets of the overlapped sheets from being conveyed when being fed out in a state, the front end position of the sheet stacking unit and the separation A double feed detecting means for detecting the overlap of the fed paper is provided between the feed section and the feed roller and the feed roller based on a predetermined feed start signal. If the double feed detecting means detects that there is an overlap of paper before the trailing edge of the preceding paper being fed in reaches the call roller, the paper feeding by the call roller is stopped and the next paper feed is stopped. Resuming the feeding of the next sheet at the feeding timing, and detecting the double feed in a state where the trailing edge of the preceding sheet fed by the feed roller is moving between the calling roller and the front end position of the sheet stacking unit. When the means detects that there is no overlap of sheets, it starts the preliminary feeding of the next sheet by the calling roller, and based on the detection result of the overlap of the sheets of the double feed detection means by the front end of the preliminary feeding sheet. When the front edge of the preliminary feeding paper stops between the double feed detecting means and the separation feeding unit, the feeding by the calling roller is temporarily stopped and the next paper is fed. A sheet feeding apparatus which is characterized in that so as to resume the feeding of the following sheet at the timing.

  Further, in order to solve the above-described problem, the present invention is arranged on the upstream side of conveyance by a predetermined distance from the front end position of the sheet stacking unit and abuts on the uppermost sheet of the sheet stacking unit. A call roller that feeds the transported downstream sheet to the downstream side, a feed roller that feeds the fed paper sheet to the transport downstream side, and a plurality of the fed sheets partially overlap each other through the pressure contact portion in pressure contact with the feed roller In a sheet feeding device including a separation feeding unit having a separation member that prevents conveyance of the second and subsequent sheets of the overlapped sheets when the paper is about to be fed out in a state of being fed, the operation state of the separation member is detected Separation operation detection means is provided to drive the calling roller and the feed roller based on a predetermined feeding start signal, and the trailing edge of the preceding paper fed by the feed roller is the calling When the separating operation detecting means detects the operation of the separating member before reaching the roller, the feeding of the sheet by the calling roller is stopped and the feeding of the next sheet is resumed at the next sheet feeding timing, The separation operation detecting means detects the non-operation of the separation member in a state where the rear end of the preceding paper fed by the feed roller is moving between the calling roller and the front end position of the paper stacking unit. In this case, preliminary feeding of the next sheet by the calling roller is started, and when the separating operation detecting means detects that the separating member is operated by the front end of the preliminary feeding sheet, the feeding by the calling roller is temporarily stopped and the next feeding is stopped. According to another aspect of the invention, there is provided a paper feeding device that resumes feeding the next paper at a paper feeding timing.

  The present invention provides a double feed detecting means for detecting the overlap of the fed paper between the front end position of the paper stacking portion and the separation feeding portion, and the trailing edge of the preceding paper fed by the feed roller is the calling roller and the paper When the multi-feed detection means detects that there is no overlap of sheets while moving between the front end positions of the stacking unit, the pre-feeding of the next sheet by the calling roller starts and the front end of the pre-feed sheet Based on the detection result of the overlap of the sheet by the double feed detection means by the timing, the feeding by the calling roller is temporarily stopped at the timing when the front edge of the preliminary feeding paper stops between the double feed detection means and the separation feeding section. Since the feeding of the next sheet is resumed at the timing of feeding the next sheet, it has a long service life and low noise without compromising the design advantages such as the positional accuracy tolerance of the sheet feeding method such as the FRR method and the RF method. Stable sheet feeding operation is obtained.

  The present invention also provides a separating operation detecting means for detecting the operating state of the separating member, and the separating operation detecting means until the trailing edge of the preceding paper fed by the feed roller reaches the calling roller. When an operation is detected, the paper feeding by the calling roller is stopped and the next paper feeding is resumed at the next paper feeding timing, and the trailing edge of the preceding paper fed by the feed roller is located between the calling roller and the paper stacking unit. When the separation operation detecting means detects the non-operation of the separation member while moving between the front end position, the next roller starts pre-feeding by the calling roller and is separated by the front end of the pre-feed sheet. When the separation operation detecting means detects that the member has moved, the feeding by the calling roller is temporarily stopped and the next paper feeding is resumed at the next paper feeding timing. Because, without disturbing the position design advantages of precision tolerance or the like of the paper feeding system provided with a separating member, stable sheet feeding operation is obtained with an inexpensive construction in a long life and low noise.

1 is a schematic configuration diagram of a printer (image forming apparatus) according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram of an image forming unit for yellow included in the printer. It is explanatory drawing of the side frame vicinity of the state which open | released the side frame of the said printer. FIG. 2 is a schematic side view of a paper feeding device (type 1) provided in the printer. FIG. 2 is a schematic side view of a paper feeding device (type 2) provided in the printer. It is a principal part enlarged view of the said paper feeder (type 1). It is a principal part enlarged view which concerns on the 1st modification of the said paper feeder (type 1). It is a principal part enlarged view which concerns on the 2nd modification of the said paper feeder (type 1). It is a principal part enlarged view which concerns on the 3rd modification of the said paper feeder (type 1). It is a principal part enlarged view of the said paper feeder (type 2), Comprising: (A) is a side view, (B) is a BB line arrow front view of (A). It is a principal part enlarged view of the said paper feeder (type 2). It is a flowchart which shows the action | operation of the paper feeder (type 1) of FIG. 5A. It is a flowchart which shows the action | operation of the paper feeder (type 1) of FIG. 5B. It is a flowchart which shows the action | operation of the paper feeder (type 1) of FIG. 5C. It is a flowchart which shows the action | operation of the paper feeder (type 2) of FIG. 5E. 4B is a time chart showing the operation of the calling roller 54 and the separation feeding unit of the paper feeding device (type 1) of FIG. 4A. 5B is a time chart showing the operation of the calling roller 54, the separation feeding unit, and the grip roller of the paper feeding device (type 1) of FIG. 5D. It is a time chart which shows the operation | movement of the calling roller 54 of the paper feeding apparatus (type 2) of FIG. 5E, and a separation feeding part. It is a time chart which shows the operation | movement of the calling roller 54 of the paper feeder (type 2) of FIG. 5F, a separation feeding part, and a grip roller. 1 is a schematic configuration diagram of an embodiment in which the present invention is applied to a sheet feeding device of an image reading apparatus. It is a schematic side view of the conventional paper feeder. It is a schematic side view of another conventional paper feeder.

(Image forming device)
Hereinafter, an embodiment of a tandem type color laser printer (hereinafter simply referred to as “printer 500”) in which a plurality of photoconductors are arranged in parallel as an image forming apparatus provided with a sheet feeding device of the present invention will be described with reference to FIGS. 3 will be described. Thereafter, details of the sheet feeding device used for the printer 500 will be described with reference to FIGS. 4A to 7D.
The present invention is also applicable to an image forming apparatus such as a copying machine other than a color laser printer, a facsimile machine, or a multifunction machine having two or three functions of a copying machine, a facsimile machine, and a printer. Furthermore, the present invention can be applied to an image reading apparatus that does not have an image forming apparatus.

FIG. 1 is a schematic configuration diagram of a printer 500 according to the present embodiment. The printer 500 includes an image forming unit 200 and a paper feeding unit 300 on which the image forming unit 200 is placed.
The printer 500 includes four image forming units 1 (Y) as image forming units for forming images of each color of yellow (Y), cyan (C), magenta (M), and black (Bk). , M, C, Bk). Each of the image forming units 1 (Y, M, C, Bk) includes drum-shaped photoconductors 2 (Y, M, C, Bk), and four photoconductors 2 (Y, M, C, Bk) The image forming units 200 are arranged in parallel at equal intervals in the left-right direction in the drawing. Each photoconductor 2 (Y, M, C, Bk) is rotated in the direction of the arrow when driving is transmitted from a drive source (not shown) during operation of the printer 500.

  Around each photosensitive member 2 (Y, M, C, Bk), members and devices necessary for electrophotographic image formation, such as a developing device, are provided, and four image forming units 1 (Y, M, C) are provided. , Bk). In the description of the present embodiment, Y (yellow), C (cyan), and M representing the color are displayed after the number indicating the constituent member of each image forming unit 1 for convenience so as to correspond to the toner color of the image to be formed. (Magenta) and Bk (black) are added as subscripts. In particular, in the general description, these subscripts may be omitted.

  In the printer 500, the four image forming units 1 (Y, M, C, and Bk) have almost the same configuration except that the toner color to be used is different.

FIG. 2 is a schematic explanatory diagram of the yellow image forming unit 1Y among the four image forming units 1 (Y, M, C, Bk).
As shown in FIG. 2, in the image forming unit 1Y, image forming members such as a charging device 4Y, a developing device 5Y, and a cleaning device 3Y are sequentially arranged around the photoreceptor 2Y according to an electrophotographic process. The charging device 4Y includes a charging roller 4aY facing the photoreceptor 2Y, and the developing device 5Y includes a developing roller 5aY, a developing blade 5bY, a screw 5cY, and the like. The cleaning device 3Y includes a cleaning brush 3aY, a cleaning blade 3bY, a recovery screw 3cY, and the like.

  As the photoreceptor 2Y, for example, a photoconductor 2Y having a layer structure in which an organic semiconductor layer that is a photoconductive substance is provided on the surface of an aluminum cylinder having a diameter of about 30 to 120 [mm] can be used. It is possible to use a belt-like photoconductor.

  As shown in FIG. 1, below each photoconductor 2 (Y, C, M, Bk), each photoconductor 2 that has been uniformly charged by each charging device 4 with laser light 8 corresponding to image data for each color. An exposure device 80 is provided as a latent image forming means for scanning the surface of the surface and forming an electrostatic latent image. Between each charging device 4 and each developing device 5, an elongated space is secured in the direction of the rotation axis of the photoconductor 2 so that the laser light 8 irradiated by the exposure device 80 enters the photoconductor 2. ing.

  An exposure apparatus 80 shown in FIG. 1 is a laser scan type exposure apparatus using a laser light source, a polygon mirror, and the like, and laser light 8 (modulated in accordance with image data to be formed from four semiconductor lasers (not shown). Y, C, M, Bk). The exposure apparatus 80 accommodates optical parts and control parts by a metal or resin casing, and is provided with a light-transmitting dustproof member at the upper exit. Although the printer 500 shown in FIG. 1 is composed of a single housing, a plurality of exposure apparatuses can be individually provided in each image forming unit. In addition to an exposure apparatus that employs laser light, an exposure apparatus that combines a known LED array and an imaging means can be employed.

  When the yellow (Y), cyan (C), magenta (M), and black (Bk) toners are consumed by the developing devices 5 (Y, C, M, and Bk) that handle the respective colors, toner detection (not shown) is performed. Detected by means. Then, the toner is supplied from the four toner cartridges 40 (Y, C, M, Bk), which are provided in the upper part of the printer 500, to the respective developing devices 5 by toner supply means (not shown).

  The outer shell of each toner cartridge 40 is a container made of resin, paper, or the like, and is provided with a discharge port in part and can be easily attached to and detached from the mounting portion 400 of the printer 500. When mounted, this discharge port is combined with individual toner replenishing means provided in the printer 500 main body. In addition, in the printer 500, the mounting unit 400 and the toner cartridge 40 are paired so that the toner cartridge 40 of each color is erroneously mounted and toner is not replenished to a developing device that handles different colors. Wear prevention means are provided.

  The developing device 5 includes two screws 5cY for stirring and conveying the toner and the carrier, as representatively shown in the yellow image forming unit 1Y of FIG. When the developing device 5Y is mounted on the printer 500, one end of the toner replenishing means is connected to the upper part of the left screw 5cY in FIG. The toner is supplied to the developing roller 5aY rotating in the direction of the arrow by the screw 5cY, but the thickness of the toner layer on the surface of the developing roller 5aY is regulated to a predetermined thickness by the developing blade 5bY.

  The developing roller 5aY is a cylinder made of stainless steel or aluminum, and is supported by the frame of the developing device 5Y so as to be rotatable and a distance from the photoreceptor 2Y is properly secured. A magnet is provided. The electrostatic latent image for each color formed on the surface of each photoconductor 2 by the laser light 8 is developed by the developing device 5 that handles toner of a predetermined color, and becomes a visible image.

  An intermediate transfer unit 6 is provided above the photosensitive member 2 (Y, C, M, Bk). The intermediate transfer belt 6a is provided with an intermediate transfer belt 6a serving as an image carrier that is stretched over a plurality of rollers 6b, 6c, 6d, and 6e. Drive in the direction of the arrow. The intermediate transfer belt 6a is endless and is stretched so that the surface of each photoconductor 2 after contacting the developing device 5 is in contact therewith. Four primary transfer rollers 7 (Y, C, M, K) are provided on the inner peripheral portion of the belt so as to face the respective photoreceptors 2.

  A belt cleaning device 6h is provided on the outer peripheral portion of the intermediate transfer belt 6a at a position facing the cleaning counter roller 6e. The belt cleaning device 6h wipes off unnecessary toner remaining on the surface of the intermediate transfer belt 6a and foreign matters such as paper dust. The cleaning facing roller 6e facing the belt cleaning device 6h includes a mechanism for applying tension to the intermediate transfer belt 6a. The belt cleaning device 6h is always moved to ensure an appropriate belt tension, but the belt cleaning device 6h facing the intermediate transfer belt 6a of the cleaning facing roller 6e can also move in conjunction.

  As the intermediate transfer belt 6a, for example, a belt having a base of a resin film or rubber having a base thickness of 50 to 600 [μm] is preferable. The belt has a resistance value that enables the toner image carried by each photoconductor 2 to be electrostatically transferred to the belt surface by a bias applied to each primary transfer roller 7. Each member related to the intermediate transfer belt 6 a included in the printer 500 is supported integrally with the intermediate transfer belt 6 a and is configured as an intermediate transfer unit 6, and can be attached to and detached from the printer 500.

  As an example of the intermediate transfer belt, the intermediate transfer belt 6a is obtained by dispersing carbon in polyamide and adjusting the volume resistance of about 10 6 to 10 12 [Ωcm]. Further, the intermediate transfer belt 6a is provided with a belt detent rib (not shown) for stabilizing the running of the belt on one side or both ends of the belt.

  As an example of the primary transfer roller, the primary transfer roller 7 of the printer 500 is obtained by coating the surface of a metal roller serving as a core metal with a conductive rubber material, and a bias is applied to the core metal portion from a power source (not shown). In the conductive rubber material, carbon is dispersed in urethane rubber, and the resistance is adjusted to a volume resistance of about 10 5 [Ωcm]. As the primary transfer roller, a metal roller having no rubber layer can be used.

  On the outer periphery of the intermediate transfer belt 6a, a secondary transfer roller 14a is provided at a position facing the secondary transfer counter roller 6b as a support roller with the intermediate transfer belt 6a interposed therebetween. The secondary transfer roller 14a is formed by coating the surface of a metal roller serving as a metal core with a conductive rubber, and a bias is applied to the metal core part from the power supply 14b. Carbon is dispersed in the conductive rubber, and the volume resistance is adjusted to about 10 7 [Ωcm].

  The secondary transfer roller 14a is in contact with the intermediate transfer belt 6a at a position facing the secondary transfer counter roller 6b to form a secondary transfer nip as a secondary transfer portion. In the secondary transfer nip, a toner image carried by the intermediate transfer belt 6a is applied by applying a bias while passing the transfer sheet S (paper) as a recording medium between the intermediate transfer belt 6a and the secondary transfer roller 14a. It is electrostatically transferred to the transfer paper S.

  A plurality of, e.g., two-stage sheet cassettes 9 </ b> A and 9 </ b> B are arranged in the sheet feeder 300 below the exposure device 80 so as to be drawable. The transfer paper S stored in these paper feed cassettes is selectively sent out by the rotation of the corresponding calling rollers 5410A and 10B, and is fed to the paper feed path P1 by the separation rollers 11A and 11B and the transport roller pairs 12A and 12B. Sent.

  In the paper feed path P1, a timing roller pair 13 including a pair of rollers is provided in order to take a feeding timing for feeding the transfer paper S to the secondary transfer unit. The transfer sheet S is conveyed from the timing roller pair 13 toward the secondary transfer nip formed by the intermediate transfer belt 6a and the secondary transfer roller 14a.

The printer 500 includes a manual tray 25 as a manual paper feed unit on the right side in FIG. 1, and the manual tray 25 is rotated when not in use and is a side frame F that is a part of the printer 500 main body. Can be stored.
The uppermost transfer sheet S stored in the manual feed tray 25 is fed by the manual feed roller 26. Then, the sheet is separated by a reverse roller 27 as a separating unit so that only one sheet is reliably conveyed, and is sent to the timing roller pair 13 through the sheet feeding path P1 by the conveying roller pairs 22 and 24.

  A fixing device 15 having a heating unit is provided above the secondary transfer nip. The fixing device 15 provided in the printer 500 includes a fixing roller 15a having a built-in heater and a pressure roller 15b that contacts the fixing roller 15a while applying pressure. The fixing device is not limited to such a configuration, and a type employing a belt and a heating method employing IH can be appropriately employed.

  The switching guide 63 can be rotated, and when the state shown in the figure is established, the transfer sheet S that has been fixed is guided to a guide member 61a that forms a paper discharge path. The transfer sheet S guided by the guide member 61 a is discharged as indicated by an arrow D in FIG. 1 by the rotation of the discharge roller 62 and is stacked on the discharge tray 60 at the top of the image printer 500.

  The printer 500 shown in FIG. 1 has a duplex unit including a refeed path and a roller for reversing and refeeding the transfer sheet S so that images can be automatically formed on both sides of the transfer sheet S. doing. More specifically, the switching guide 63 includes a switchback path P5 and a refeed path P6 inside the side frame F, and transfers the transfer sheet S on which image formation has been completed on one side to the feed path P1. A second switching guide G2 and a third switching guide G3 are provided.

  In addition, a reversing roller 18a and a reversing roller 22 that are connected to a driving source (not shown) and can be reversed by controlling the driving source are provided. Rollers 23 and 24 are in contact with the reverse roller 22. When the reverse roller 22 rotates in the clockwise direction, the paper is conveyed from the manual feed tray 25 in cooperation with the roller 24. Further, when rotating counterclockwise, the transfer sheet S in the refeed path P6 is fed again in the direction of the timing roller pair 13 in cooperation with the roller 23.

  When the switching guide 63 rotates in the clockwise direction from the state shown in the figure, the transfer sheet S that has been fixed is guided to the reverse conveyance path P4 by the roller pair 17 and conveyed to the reverse roller pair 18 via the second switching guide G2. And once sent to the switchback path P5. After the transfer paper S is sent to the switchback path P5, the reverse roller 18a of the reverse roller pair 18 rotates counterclockwise, and the second switching guide G2 rotates counterclockwise. Is sent from the switchback path P5 to the refeed path P6. The transfer sheet S conveyed by the roller pairs 15c, 20 and 14c, 21 in the refeed path P6 is further conveyed to the roller pairs 22, 23 and reaches the timing roller pair 13.

  The printer 500 shown in FIG. 1 includes a paper feeding device 50 that is an additional paper feeding unit below the paper feeding unit 300. The paper feeding device 50 shown in FIG. 1 includes two paper feeding cassettes 9C and 9D. However, a type with a larger number of paper feeding cassettes can be adopted, and a type with a built-in paper feeding cassette with a larger number of papers can be used. Good.

  In the printer 500, a third switching guide G3 located above the fixing device 15 and downstream in the conveying direction of the roller pair 17 rotates counterclockwise from the state of FIG. 1, and guides the transfer sheet S after fixing. The paper can be conveyed to the paper discharge path P8 and discharged to another paper discharge device (not shown). Another example of the paper discharge device is a bin tray having several stages of paper discharge trays.

Next, an operation during single-sided printing in which the printer 500 forms an image on one side of the transfer paper S will be described.
First, an electrostatic latent image is obtained by irradiating the surface of the photoreceptor 2Y uniformly charged by the charging roller 4aY with laser light 8Y corresponding to image data for yellow emitted from the semiconductor laser by the operation of the exposure device 80. Is formed.
This electrostatic latent image is subjected to development processing by the developing roller 5aY and is developed with yellow toner, becomes a visible image, and receives a transfer action by the primary transfer roller 7Y on the surface of the intermediate transfer belt 6a that moves in synchronization with the photoreceptor 2Y. The primary transfer. Such latent image formation, development, and primary transfer operations are sequentially performed in the same manner on the other photoreceptors 2 (C, M, and Bk) at the same timing.

  As a result, yellow Y, cyan C, magenta M, and black Bk toner images are carried on the surface of the intermediate transfer belt 6a as overlapping four-color toner images, and the surface moves in the direction of the arrow. It is conveyed together with the transfer belt 6a. On the other hand, the remaining toner and foreign matter are cleaned by the cleaning device 3 on the surface of the photoreceptor 2 that has passed the position facing the primary transfer roller 7 with the intermediate transfer belt 6a interposed therebetween.

  The four-color toner image formed on the intermediate transfer belt 6a is transferred onto the transfer sheet S conveyed in synchronization with the intermediate transfer belt 6a by receiving a transfer action by the secondary transfer roller 14a. The surface of the intermediate transfer belt 6a is cleaned by a belt cleaning device 6h to prepare for the next image formation / transfer process. The transfer sheet S on which the image has been transferred is subjected to a fixing action by the fixing device 15 and is discharged onto the sheet discharge tray 60 by the sheet discharge roller 62 with the image surface facing downward (face down).

Next, an operation at the time of duplex printing in which the printer 500 forms images on both sides of the transfer paper S will be described.
The transfer sheet S having the image transferred from the intermediate transfer belt 6a on one side thereof and passing through the fixing device 15 is guided toward the roller pair 17 by the switching guide 63 by the same operation as in the above-described single-side printing. The transfer sheet S that travels above the second switching guide G2 at the rotational position in FIG. 1 through the third switching guide G3 and the reverse conveying path P4 provided on the downstream side of the roller pair 17 in the conveying direction is the reverse roller pair. 18 to the switchback path P5.

  At this time, the reverse roller 18a is driven to rotate clockwise. The roller pair 19 in the switchback path P5 is also a roller pair capable of forward and reverse rotation, and once the transfer paper S is received in the switchback path P5, it is reversely rotated to reversely transfer the transfer paper S. When the rotation directions of the roller pair 19 and the reverse roller pair 18 are reversed, the second switching guide G2 rotates counterclockwise from the posture shown in FIG.

  The pair of rollers 15c, 20, 14c, and 21 is transported in the refeed path P6 with the rear end until the transfer sheet S enters the switchback path P5, and transported toward the feed path P1. The timing roller pair 13 is reached. Thereafter, the transfer sheet S having an image on one side is conveyed again toward the secondary transfer nip where the secondary transfer roller 14a and the intermediate transfer belt 6a face each other at the timing of the timing roller pair 13. The toner image on the intermediate transfer belt 6a is transferred to the other side of the transfer paper S.

  Images to be formed on the second surface of the transfer paper S are sequentially formed by an image forming process that is started when the transfer paper S is conveyed to a predetermined position. The image forming process in this case is also the same as the above-described full-color toner image formation during single-sided printing, and this full-color toner image is carried on the intermediate transfer belt 6a. However, since the front and rear of the transfer sheet S are reversed in the conveyance path, the image data emitted from the exposure device 80 is generated so that the image is formed in the reverse direction in the sheet conveyance direction compared to the first image formation. Is controlled and executed.

  The transfer sheet S having the full-color toner image transferred on both sides in this way is again discharged onto the discharge tray 60 by the discharge roller 62 after undergoing fixing processing by the fixing device 15. In the printer 500, several transfer sheets S can be simultaneously transported to the transport path in order to increase the efficiency of double-sided image formation. In addition, the formation timing of the images to be formed on the front and back sides of the transfer sheet S is executed by a control unit (not shown).

  In the printer 500, the polarity of the toner image formed on the photoreceptor 2 is negative, and the toner image on the photoreceptor 2 is transferred to the surface of the intermediate transfer belt 6a by applying a positive charge to the primary transfer roller 7. Is done. Further, the toner image on the surface of the intermediate transfer belt 6a is transferred onto the transfer sheet S by applying a positive charge to the secondary transfer roller 14a.

  The single-sided printing operation and the double-sided printing operation have been described with reference to an example in which full-color printing is performed. However, there are photosensitive members that are not used during black-and-white monochrome printing. Not only do not operate the unused photoreceptor 2 (Y, M, C) and the developing device 5 (Y, M, C), but these unused photoreceptor 2 (Y, M, C), the intermediate transfer belt 6a, Is provided with a mechanism for keeping them in a non-contact state. In the printer 500, an internal frame 6f that supports the roller 6d and the primary transfer rollers 7Y, 7C, and 7M is supported so as to be rotatable about a frame shaft 6g.

  At the time of monochrome printing, the inner frame 6f is rotated in the direction away from the photosensitive member 2 (Y, M, C) (clockwise in FIG. 1), so that only the photosensitive member 2K comes into contact with the intermediate transfer belt 6a. By executing the image process, a monochrome image with black toner is created. In this way, the photoreceptor 2 (Y, M, C) of the image forming unit 1 (Y, M, C) that is not used during monochrome printing is separated from the intermediate transfer belt 6a, and the photoreceptor 2 (Y, M, C). Further, stopping the developing device 5 (Y, M, C) is advantageous in terms of improving the life of the image forming unit 1 (Y, M, C).

  In the printer 500, when the necessity for maintenance, part replacement, or the like occurs, the maintenance is performed by opening an exterior cover (not shown). At the time of this maintenance, the operability can be improved by exchanging the process cartridge as a unit by integrally supporting the members constituting the image forming unit 1 shown in FIG.

  Further, when the image forming unit 1 shown in FIG. 1 is configured as a process cartridge, a guide unit and a handle for mounting on the printer 500 are provided to facilitate attachment and detachment. In addition, providing a storage device (for example, an IC tag) that stores the characteristics and operation status of the process cartridge provides a guideline for maintenance, and increases convenience in maintenance management of the process cartridge.

  Further, when maintenance or replacement is performed with respect to the intermediate transfer unit 6, the intermediate transfer belt 6 a and each photoconductor 2 may be separated from each other, and the intermediate transfer unit 6 may be pulled out from the printer 500 main body.

  FIG. 3 is an explanatory view of the vicinity of the side frame F in a state where the side frame F is opened from the printer 500 in the state of FIG. The side frame F includes a duplex unit 30 and a secondary transfer unit 14, and is rotatable with respect to the printer 500 about a lower rotation axis Fa as a rotation center. When the frame F is rotated, the upper part can be opened as shown in FIG.

  Further, on the upper surface of the side frame F, an engagement protrusion 71 as an engaged member is provided. The engaging protrusion 71 is an engaging portion of the pull-in device 70 provided on the upper portion of the printer 500 when the side frame F is moved in the closing direction so that the secondary transfer unit 14 and the duplex unit 30 can be attached to the printer 500. Engage with. When the engaging protrusion 71 as the engaged member of the side frame F is engaged with the engaging portion of the drawing device 70, the drawing device 70 draws the side frame F toward the printer 500.

  When the frame is retracted by the retracting device 70, the guide portion 31 a of the stopper member 31 comes into contact with the blocking member 32. Then, the stopper member 31 is rotated by the pulling force of the pulling device 70 to get over the blocking member 32, the side frame F is closed, and the secondary transfer unit 14 and the duplex unit 30 are mounted at the mounting position.

  Prior to opening the side frame F, the stopper member 31 provided on the side frame F is rotated by operating a lock lever (not shown) to remove the stopper member 31 from the blocking member 32 provided on the printer 500 side. Release the stopper function and release it. As shown in FIG. 3, since the plurality of transport paths (P1, P2, P6) can be opened by opening the side frame F, it is easy to treat the jammed transfer paper S generated in these transport paths. it can.

  The secondary transfer unit 14 in which the post-transfer conveyance path P2 and the switchback path P5 are formed on both sides of the casing has the center of the roller 23 as the rotation center, and when the side frame F is opened as shown in FIG. The secondary transfer roller 14a is separated from the intermediate transfer belt 6a. Further, the secondary transfer unit 14 is given a turning habit so that the roller 14 c is separated from the roller 21. The secondary transfer unit 14 includes a power source 14b inside, and a unit having a transfer function of the transfer paper S outside the case.

  The fixing device 15 also has a conveyance roller 15c and a conveyance guide surface, and a part thereof constitutes a refeed path P6. The fixing device 15 is supported in the state shown in FIG. 3 so that it can be pulled out to the right in the drawing. Therefore, it is possible to easily handle a paper jam that has occurred inside the fixing device 15.

  The conveying roller 15c is urged toward the roller 20 by a spring (not shown), and the conveying roller 14c is urged toward the roller 21 by a spring (not shown). The rollers on the printer 500 side of the conveying roller pairs 12A and 12B are urged toward the rollers 12Aa and 12Ba on the side frame F side of the conveying roller pairs 12A and 12B by a spring (not shown).

  As a result, when the side frame F is in the closed position in FIG. 1, the side frame F is opened in a direction to be opened by the rollers on the printer 500 side of the conveyance roller 15c, the conveyance roller 14c, and the conveyance roller pair 12A and 12B. Be energized. As a result, the stopper surface 31b of the stopper member 31 and the blocking member 32 come into contact with each other, and the side frame F is positioned.

(Paper Feeder-Type 1)
The printer 500 as the image forming apparatus has been described above. Next, a paper feeding device (type 1 and type 2) used in the printer 500 will be described in more detail with reference to FIGS. 4A to 7D. The sheet feeding device (type 1) in FIG. 4A and the sheet feeding device (type 2) in FIG. 4B are shown as the additional sheet feeding device 50 in FIG. 1, but the same applies to the sheet feeding unit 300 provided thereon. It is applicable to.

  As described above, the sheet feeding device 50 can obtain a stable sheet feeding operation with a long service life and low noise without destroying the design advantages such as the FRR and RF position accuracy tolerances. Also, even for paper types with large paper-to-paper friction variation, the paper-to-paper friction variation is reduced by maintaining a minimum distance between the papers at the start of paper feeding without burdening the paper. Can be achieved.

  In addition, the paper feeding device 50 can avoid the trouble of transportation caused by a thick paper and can realize high print productivity with stable paper feeding. The sheet feeding device 50 is provided between the front end position of the sheet stacking portion (sheet bundle P) and the feed nip of the feed roller 55 of the conventional sheet feeding device shown in FIGS. A double feed detecting means K4 is disposed (including the position of the feed nip) as shown in FIG. 4A. Examples of three paper feeders 50 are shown in FIG. 5A to FIG. 5C depending on the arrangement position of the double feed detecting means K4.

  Further, FIG. 5D shows an example of the paper feeding device 50 in which the feeding speeds of the feed roller 55 and the grip roller 58 are different. 5D is the same as FIG. 5A except for the difference between the conveying speeds V1 and V2 (V2 <V1). Note that the difference between the transport speeds V1 and V2 can be applied to the paper feeding device 50 shown in FIGS. 5B and 5C. Details of the sheet feeding device 50 will be described below.

(Configuration of paper feeder-Type 1)
As shown in FIG. 4A, the paper feeding device 50 has a box-shaped paper feeding tray 51 having an open top, and a flat bottom plate 53 is disposed inside the paper feeding tray 51. The bottom plate 53 can swing up and down around a support shaft 53a at one end thereof, and is urged to rotate upward by an urging means (not shown). A calling roller 54 is disposed above the paper feed tray 51 on the side opposite to the support shaft 53 a, and this calling roller 54 contacts the uppermost sheet of the sheet bundle P stacked on the bottom plate 53. By rotating in contact with each other, paper is fed out one by one.

  As shown in FIG. 5A, the calling roller 54 is arranged upstream from the front end position of the sheet bundle P by a distance γ. As a result, when the calling roller 54 is continuously driven, the rear end of the preceding paper P1 and the front end of the next paper P2 can be fed out with the distance γ overlapped. Although the calling roller 54 can be driven by a unique drive source, in this embodiment, the call roller 54 is driven by a drive source of a feed roller 55 described below via a clutch.

  In front of the calling roller 54, a feed roller 55 and a separation roller 56 as a separate feeding unit are arranged in a vertically opposed state. The position of the rotation shaft of the feed roller 55 is fixed, but the rotation shaft of the separation roller 56 as a separating member is supported so as to be movable toward the feed roller 55 and is urged toward the feed roller 55 by a spring 56a. A so-called “feed nip” is formed at a contact portion between the feed roller 55 and the separation roller 56, and the sheets are fed into the feed nip one by one in the direction of the arrow.

  The feed roller 55 is driven to rotate in the paper feeding direction via a one-way clutch, while the separation roller 56 can be driven in a direction opposite to the feeding direction via a torque limiter. The separate roller 56 is driven to rotate by contacting the feed roller 55 by sliding the torque limiter when one sheet is held at the feed nip. However, when two or more sheets are held, reverse feeding prevents the double feeding of sheets. It has become so. That is, when two or more sheets are sandwiched in the feed nip, only one uppermost sheet is fed by the feed roller 55, and the remaining sheets are stopped with the front end of the sheet in contact with the separation roller 56. It has become.

  As shown in FIG. 5A, double feed detecting means K4 is disposed between the front end position of the paper stacking section (paper bundle P) and the feed nip of the feed roller 55. As this double feed detecting means K4, an optical type or an ultrasonic type is known. The optical type has a light emitting element and a light receiving element as described in, for example, Japanese Patent Application Laid-Open No. 2006-321215, and double feeding based on the amount of light received by the light receiving element when two or more sheets enter between them. Detect the presence or absence.

  The ultrasonic type has, for example, an oscillator that oscillates ultrasonic waves and a geophone that receives ultrasonic waves as described in Japanese Patent Application Laid-Open No. 2004-284806, and performs multiple feeding based on the waveform of the ultrasonic waves received by the geophone. The presence or absence of is detected. In this embodiment, a light emitting element K4a is disposed on the upper side as the optical double feed detecting means K4, and a light receiving element K4b is disposed on the lower side. The presence or absence of double feeding is detected based on the amount of light received by the light receiving element K4b when two or more sheets enter between them.

  As shown in FIG. 5A, the double feed detecting means K4 is disposed such that its optical axis is spaced upstream from the feed nip by a distance β. Even if the distance β is set to the minimum (the maximum overlap length between the rear end of the preceding paper P1 and the front end of the next paper P2) between the papers when being fed by the calling roller 54, two sheets in the feed nip. The distance is set such that the above paper is not caught. That is, the distance is set so as not to reach the feed nip when the front edge of the next paper P2 is overlapped with the rear edge of the preceding paper P1.

  5B, the optical axis of the double feed detecting means K4 is arranged at a distance η upstream from the feed nip, and in FIG. 5C, the optical axis of the double feed detecting means K4 is arranged to coincide with the position of the feed nip. It is installed. As described above, the position of the optical axis of the double feed detecting means K4 can be arranged by changing the distance away from the upstream side of the feed nip.

  Corresponding to the fact that the distance to be separated to the upstream side is different as described above, the control flowcharts of the respective sheet feeding apparatuses are different as shown in FIGS. 6A to 6C. The sheet feeding device of FIG. 5A is controlled by the flowchart of FIG. 6A, and the sheet feeding devices of FIGS. 5B and 5C are controlled by the flowcharts of FIGS. 6B and 6C, respectively. These flowcharts will be described later.

  On the downstream side of the feed roller 55, a grip roller 58 is disposed at a distance L from the feed nip of the feed roller 55. The grip roller 58 grips the front end of the paper fed by the feed roller 55 and conveys it further downstream. On the downstream side of the grip roller 58, paper detection means K2 is disposed. When the leading edge of the preceding sheet P1 is detected by the sheet detecting means K2, the calling roller 54 is moved to the uppermost sheet (the next sheet P2) of the sheet bundle P in the sheet feeding tray 51 in order to feed out the next sheet P2 by using the sheet detection as a trigger. ) Is brought into contact with (or re-driven).

(Paper Feeder Operation-Type 1)
(Operation of the paper feeder in FIG. 5A)
The sheet feeding device 50 is configured as described above, and is fed by driving the grip roller 58, the calling roller 54, and the feed roller 55 in a state where the calling roller 54 is in contact with the uppermost portion of the sheet bundle P. Is started. When the calling roller 54 rotates in the direction of the arrow in FIG. 4A, the uppermost sheet of the sheet bundle P is fed out, and the front end of the fed sheet is pinched by the feed nip of the feed roller 55. Thereafter, the sheet is conveyed downstream by the feed roller 55, and when the front end of the sheet is gripped by the grip roller 58 and the front end of the sheet is detected by the sheet detecting means K2, the driving of the feed roller 55 is stopped and the feed roller is stopped. 55 is driven rotation.

  The calling roller 54 is continuously fed as long as the double feed detecting means K4 detects that there is no sheet overlap, and the next sheet P2 is overlapped with the next sheet P2 at the distance γ as shown in FIG. 5A. It is drawn out continuously. The feeding operation of the calling roller 54 may be continuously performed without interruption except for the sheet overlap “existence” detection of the double feed detection means K4 from the start of sheet feeding. Further, when a sufficient conveying force for feeding can be obtained only by the feed roller 55, the feeding operation by the calling roller 54 may be appropriately interrupted.

  The next paper P2 fed out in the state of being overlapped with the preceding paper P1 as shown in FIG. 5A is detected by the double feed detecting means K4 as having the front end of the distance γ overlapping and “present”. Thus, when the double feed detecting means K4 detects that there is an overlap, the driving of the calling roller 54 is stopped at a “predetermined timing” from the detection time point. The “predetermined timing” is a timing at which the front end of the next sheet P2 can be stopped between the optical axis of the double feed detecting means K4 and the feed nip. For example, as shown in FIG. 5A, when the distance of the sheet conveyed at “predetermined timing” is α, the distance α is set to an arbitrary distance within a range not exceeding the distance β to the feed nip.

  In order to stop the driving of the calling roller 54, the clutch connected to the drive source of the feed roller 55 is disconnected. However, even if the clutch is disconnected simultaneously with the detection of the overlap “existence”, some driving stop distance due to the response of the clutch coming out. Although this driving stop distance varies depending on the paper feeding device, it can be measured and confirmed in advance, and the “predetermined timing” includes this driving stop distance. Thus, by stopping the calling roller 54 at a predetermined timing, the start position of the next sheet P2 can be stably set at a predetermined position immediately upstream of the feed nip.

  The start timing of the next paper P2 is the same as in the prior art, and the detection of the leading edge of the preceding paper P1 by the paper detection means K2 provided downstream of the grip roller 58 where the behavior of the paper is stable (slip rate is reduced) is used as a trigger. Then, the driving of the calling roller 54 and the feed roller 55 is repeated at a predetermined timing at which the front end of the next paper P2 does not collide with the rear end of the preceding paper P1 and the predetermined print productivity is satisfied. This “predetermined timing” will be described in relation to the distance η in the operation description of the sheet feeding device in FIG. 5B described later.

  In the paper feeding device 50 according to the embodiment of the present invention, it is not necessary to make a paper gap for detecting the presence or absence of paper between the calling roller 54 and the feed roller 55 as described above. In this respect, the print productivity of the paper feeding device 50 can be improved as compared with the conventional paper feeding device shown in FIGS. Further, since it is not necessary to increase the speed of paper feeding as in the conventional model of FIG. 9, the power consumption of the driving source of the feed roller 55 can be suppressed, and further, the conveyance speed of the whole paper feeding device can be reduced by shortening the paper interval. Overall energy saving can be achieved.

  When there is no double feed, it is not necessary to temporarily stop the feeding operation of the calling roller 54 before the trailing edge of the preceding paper P1 exceeds the grounding point of the calling roller 54. Therefore, even when a common drive source is used for the calling roller 54 and the feed roller 55, an operation for separating the calling roller 54 from the paper surface is not necessary. In addition, when the feeding by the calling roller 54 is stopped due to the occurrence of double feed, the feeding load including the feed roller 55 can be stopped, and the control load can be reduced. It becomes possible.

  Compared to the detection of the next paper P2 by the paper detection means K3 by detecting the moment when the trailing edge of the preceding paper P1 passes through the feed nip as shown in FIG. There is enough time for detection. For this reason, it is not necessary to count the moment when the trailing edge of the preceding paper P1 passes through the feed nip with a highly accurate control timer, and the control load on the CPU that controls the control means can be reduced. By reducing the load on the CPU, it is possible to suppress the occurrence of a jam due to a control delay or the like, and to realize a stable paper feed conveyance.

(Operation of the paper feeder in FIG. 5B)
In the paper feeding device of FIG. 5B, the optical axis of the double feed detecting means K4 is disposed away from the feed nip by a distance η upstream. The distance η is the driving stop distance of the calling roller 54 described above. 5B is the same as the paper feeding device of FIG. 5A except for the timing at which the feeding operation of the calling roller 54 is stopped. In the paper feeder of FIG. 5B, when the leading edge of the overlap distance γ between the preceding paper P1 and the next paper P2 is detected by the double feed detecting means K4, the driving of the calling roller 54 is stopped simultaneously with the detection time. Thereby, the start position of the next sheet P2 becomes the feed nip position.

  The start timing of the next paper P2 is the same as in the prior art, and the detection of the leading edge of the preceding paper P1 by the paper detection means K2 provided downstream of the grip roller 58 where the behavior of the paper is stable (slip rate is reduced) is used as a trigger. Then, the driving of the calling roller 54 and the feed roller 55 is repeated at a predetermined timing at which the front end of the next paper P2 does not collide with the rear end of the preceding paper P1 and the predetermined print productivity is satisfied.

  Here, the “predetermined timing” that does not collide with the trailing edge of the preceding paper P1 will be described below. Whether or not to “reject” depends on the interval between the preceding paper P1 and the next paper P2, and it is assumed that the paper detection means K2 can detect this interval (paper interval). The minimum paper interval that can be detected by the reflective sensor is about δ = 8 mm.

  Further, the timing roller applies the front end of the sheet to the roller while correcting the sheet and corrects the skew. For this reason, when the trailing edge of the sheet comes out of the conveying roller immediately before the timing roller, the trailing edge of the sheet extends backward by the amount of slack, and the gap between the leading edge of the next sheet is shortened. The amount of sag is usually about 2 to 6 mm. Further, since the front end of the sheet at the start of feeding does not exceed the feed nip, the feed nip is the most downstream position at the start of feeding.

  Accordingly, the timing at which the rear edge of the preceding paper P1 does not collide is the time when the trailing edge of the preceding paper P1 has passed through the feed nip and the paper interval δ and the amount of sag are conveyed for paper detection. Actually, in addition to these, it is necessary to consider the difference in slip between the preceding paper P1 and the next paper, so a slight margin (for example, 1 mm) is added. As described above, the basis of the “predetermined timing” is that the feeding of the next sheet P2 by the feed roller 55 after the trailing edge of the preceding sheet P1 passes through the feed nip and after transporting δ = 15 mm (= 8 mm + 6 mm + 1 mm).

  Furthermore, when the next sheet P2 is started at the above timing, the sheet start position varies from 0 to 30 mm in the conventional model that is not the sheet interval shortening type (see the above [0009] stage). For this reason, as print productivity, 45 mm obtained by adding δ = 15 mm to the maximum variation of 30 mm at the paper start position corresponds to the paper interval.

Also, in the conventional model (Patent Document 1: Japanese Patent Application Laid-Open No. 2005-213039) of the paper interval shortening type as shown in FIG. 9, the presence or absence of paper is generally detected by a reflective sensor. However, the position of the reflection type sensor needs to be disposed 12 mm before the feed nip in order to satisfy the sheet interval of 8 mm for detecting the sheet and the drive stop distance κ of the feed roller 55 (assuming it is 4 mm conveyance). is there. For this reason, the variation in the paper start position is 0 to 12 mm, so that the print productivity corresponding to the maximum paper interval of 27 mm (15 mm + 12 mm) is obtained.

  On the other hand, in the embodiment of the present invention, the detection position of the double feed detection means K4 is arranged upstream of the feed nip by the drive stop distance η when the driving of the calling roller 54 is stopped, and the sheet interval for paper detection is set. It is unnecessary. For this reason, the start position variation of the next sheet P2 is 0 to η (≈κ = 4 mm), and the print productivity corresponding to the maximum sheet interval of 19 mm (15 mm + 4 mm) can be increased even at the same conveyance speed.

  When the double feed detection means K4 detects that there is an overlap, the pre-feeding conveyance of the calling roller 54 is immediately stopped, so that the front edge of the next paper P2 exceeds the distance η to the feed nip separated from the detection position by the drive stop distance. It will not be transported. Therefore, the sheet does not bend between the calling roller 54 and the feed roller 55, and the sheet is not burdened. In addition, since it is not necessary to set the detection timing in the double feed detection means K4, there is no need for a control timer for capturing the moment when the preceding paper P1 passes through the feed nip in the conventional model as shown in FIGS. It is possible to reduce the control load of the CPU that controls the control means.

  Further, the next paper P2 is conveyed so as to overlap the preceding paper P1 by a distance γ between the front end position of the paper stacking unit (paper bundle P) and the grounding position of the calling roller 54. For this reason, it is possible to detect the overlap of the sheet before the conveyance distance (η + γ) from the detection of the leading edge of the next sheet P2 until the trailing edge of the preceding sheet P1 passes through the feed nip, and the preliminary feeding and conveyance of the calling roller 54 can be stopped. Accordingly, even when the driving of the calling roller 54 and the feed roller 55 is combined, the drive of the feed roller 55 is surely stopped at the latest when the trailing edge of the preceding paper P1 passes through the feed nip. Therefore, there is no fear of protruding from the feed nip of the front end of the next sheet P2, and stable sheet spacing control is possible.

  In particular, in the case of a sheet having a large variation in sheet-to-sheet friction, the next sheet P2 is often taken out by the conveyance of the preceding sheet P1. In such a case, even if the leading edge of the next paper P2 exceeds the overlap detection position when the double feed detection means K4 starts detection, the double feed detection means K4 is disposed at a position sufficiently close to the feed nip. The gap can be kept within a minimum variation. Accordingly, it is possible to achieve higher print productivity than the conventional model. Further, if the drive stop distance is minimized by incorporating brake control into the drive stop of the calling roller 54 and the feed roller 55, the detection position of the double feed detection means K4 can be further arranged closer to the feed nip. . Therefore, the print productivity can be further improved.

(Operation of the paper feeder in FIG. 5C)
5C is arranged such that the optical axis of the double feed detecting means K4 coincides with the position of the feed nip, and the calling roller 54 performs the feeding operation simultaneously with the detection of the overlap “existence” of the double feed detecting means K4. In order to be able to stop, the sheet bundle P is disposed so as to be separated from the uppermost part.

  When the calling roller 54 and the feed roller 55 are gear-coupled, the driving stop distance of the calling roller 54 is smaller than the driving stop distance of the feed roller 55 that is pressed against the separate roller 56 and has a large load. Longer by rush. For this reason, when the driving of the calling roller 54 and the feed roller 55 is stopped based on the detection of “over” of the overlap of the double feed detecting means K4, the sheet may bend as shown by the broken line in FIG. 5C. That is, the sheet may be bent between the calling roller 54 and the feed roller 55 due to the difference in the driving stop distance. In the case of thick paper, slip marks may occur due to the difference in the driving stop distance.

  Therefore, the calling roller 54 is arranged to be separated from the paper surface as described above. As a result, it is possible to eliminate the problem of the occurrence of sheet bending and slip traces, and it is possible to obtain stable conveyance without buckling even for a sheet having low rigidity, thereby satisfying sheet compatibility.

(Operation of the paper feeder in FIG. 5D)
As described above, the sheet feeding device 50 in FIG. 5D has a difference in the conveyance speed between the feed roller 55 and the grip roller 58. That is, when the conveyance speed of the grip roller 58 is V1, and the conveyance speed of the feed roller 55 is V2, the magnitude relationship of V2 <V1 is set. Others are the same as those of the sheet feeder 50 of FIG. 5A.

  By making a difference in the conveyance speed in this way, the space between the trailing edge of the preceding sheet and the leading edge of the next sheet is enlarged between the feed roller 55 and the grip roller 58. In the paper feeding device 50 of FIG. 5D, the paper gap is expanded in this way, but the target final paper gap is about the minimum paper gap δ = 8 mm that can be detected by the paper detection sensor K2 as described above (see above). [Ref. [0099] stage). The details of the enlargement between the sheets due to the speed difference (V2 <V1) will be described after the operation of the sheet feeding device 50 of FIGS. 5A to 5C described above.

  Next, the operation of the sheet feeding device 50 of FIGS. 5A to 5C will be described with reference to the flowcharts of FIGS. 6A to 6C. Since the flowchart of FIG. 6A is a basic form, in the following description, FIG. 6A will be mainly described, and FIG. 6B and FIG.

  In FIG. 6A, first, the driving of the grip roller 58 is started in step S1. Next, in step S2, paper feed driving (for the preceding paper P1) is started. This paper feed drive is performed by driving the calling roller 54 and the feed roller 55. When the call roller 54 and the feed roller 55 are shared, the call roller 54 is intermittently driven by connecting and separating the clutch while the feed roller 55 is continuously driven. Accordingly, the calling roller 54 is driven by the clutch connection to “start feeding paper”, and the driving of the calling roller 54 is stopped by “separating the clutch” to “stop feeding paper”. The sheet called by the calling roller 54 is sent to the separation feeding unit by the feed roller 55 and the separation roller 56, and only the uppermost sheet is conveyed.

  The sheet fed downstream from the separation feeding unit passes through the grip roller 58 provided on the downstream side, and it is determined in step S3 whether the preceding sheet P1 (front end) is detected by the sheet detection unit K2. The The grip roller 58, the calling roller 54, and the feed roller 55 are driven until the front sheet P1 (front edge) is detected. The paper that has passed through the paper detection means K2 is then aligned with a timing roller (not shown), and is discharged out of the apparatus through an image forming / fixing section.

  Paper front edge detection information by the paper detection means K2 is sent to a control means (not shown), and the drive of the feed roller 55 is stopped by the control means based on the information. The stop timing is such that the driving of the feed roller 55 is stopped before the timing at which the trailing edge of the sheet crosses the feed nip, based on the sheet leading edge detection information and preset sheet size information.

  A one-way clutch is connected to the rotation shaft of the feed roller 55. Even if the drive of the feed roller 55 is stopped, the feed roller 55 itself rotates in the conveyance direction of the paper conveyed by the grip roller 58 (driven rotation). ) Due to such a drive stop of the feed roller 55, even if the front end of the next paper P2 reaches the feed nip following the rear end of the preceding paper P1, the separation roller 56 is rotationally driven in the direction opposite to the feeding direction. Therefore, separation from the preceding paper P1 is reliably performed. At this time, since only the front end portion of the next paper P2 is rubbed by these rollers 55 and 56, even the paper which is weak against friction and easily damaged is hardly damaged.

  When the paper detection means K2 detects the preceding paper P1 (the front edge thereof), it is determined in step S4 whether a predetermined time Ta has elapsed. The predetermined time Ta is a time until the trailing edge of the preceding paper P1 passes through the position of the calling roller 54, and it is determined from this timing whether or not the calling out is necessary.

  If it is determined in step S4 that the predetermined time Ta has elapsed, x = 0 is set in step S5. Next, the presence / absence of double feed is determined in step S6. If double feed is “not present”, the operation of incrementing the parameter “x” by 1 is repeated in step S7 until double feed “present” is detected.

  The “x” is a parameter necessary for determining whether or not the double feed detection unit has detected double feed at the next sheet start timing in the subsequent step S8. The apparatus of FIG. 5A controls the distance α that the leading edge of the next sheet P2 travels during Tc in step S9 starting from the optical axis position of the double feed detection means K4. Therefore, in “x> 1” in step S8, the Tc timer Determine the starting point.

  If it is determined in step S6 that the double feed is “present”, it is determined in step S8 whether the parameter x is “0” or more. If x = 0, it means that the front end of the next paper P2 has already exceeded the double feed detection means K4 at the next paper start timing, and the driving of the calling roller 54 is stopped in step S10.

  If it is determined in step S8 that the parameter x is 1 or more (x> 1), the leading edge of the next sheet P2 has been detected by the double feed detecting means K4, and thus the predetermined time Tc has elapsed in step S9. It is determined whether or not. If the predetermined time Tc has not elapsed, this determination is repeated until the predetermined time Tc has elapsed, and when the predetermined time Tc has elapsed, the driving of the calling roller 54 is stopped in step S10.

This predetermined time Tc determines the distance α that the leading edge of the next sheet P2 advances toward the feed nip after the leading edge of the next sheet P2 exceeds the double feed detecting means K4 as shown in FIG. 5A. Do not enter the nip.
In step S11, it is determined whether or not the number of jobs has been completed. If the number of jobs has been completed, the driving of the grip roller 58 is stopped in step S13.

  If the number of jobs has not ended, it is determined in step S12 whether or not the predetermined time Te has elapsed. If not, the circulation determination loop is repeated until the predetermined time Te has elapsed. This predetermined time Te determines the start timing of the next sheet P2, and when the predetermined time Te elapses, the process returns to step S2 and the driving of the calling roller 54 is resumed.

  The flowchart of FIG. 6B omits Steps S5 and S7 to Step 9 in the flowchart of FIG. 6A, and immediately stops the driving of the calling roller 54 in Step S10 in the case of double feed detection. Others are the same as the flowchart of FIG. 6A.

  The flowchart of FIG. 6C is obtained by omitting Steps S5 and S7 to Step 9 and adding Step S10a to the flowchart of FIG. 6A. In the case of double feed detection, the calling roller 54 is immediately separated from the sheet in Step S10a. I have to. Others are the same as the flowchart of FIG. 6A.

  FIG. 7A is a time chart showing the operation of the calling roller 54, the feed roller 55, and the separation roller 56 of the paper feeding device 50 of FIGS. 4A and 5A in relation to the overlap of the preceding paper P1 and the next paper P2. As for the arrow indicating the rotation direction of each roller, a solid line arrow indicates driving rotation, and a broken line arrow indicates driven rotation. The absence of an arrow indicates rotation stop. For convenience, the calling roller 54 indicates both ON / OFF of the drive and contact / separation with respect to the paper. However, the call roller 54 corresponds to the paper feeding / stopping of either the ON / OFF or the contact / separation. Can do. However, it may be configured to be capable of both ON / OFF and contact / separation as required.

The numbers from 1 to 6 in the time chart correspond to the six figures below the time chart. The following descriptions (1) to (6) correspond to numbers 1 to 6 in the time chart.
(1) The feed roller 55 is driven and the preceding paper P1 is being fed out. When this state is reached, a sufficient feeding and conveying force can be obtained only by the feed roller 55, so that the calling roller 54 is driven and rotated.

  As a result, the preceding paper P <b> 1 is fed out from the uppermost portion of the paper bundle P and fed by the feed roller 55. Since the trailing edge of the preceding paper P1 is close to the calling roller 54 to a predetermined distance, the driving of the calling roller 54 is started immediately after (1).

(2) When the trailing edge of the preceding paper P1 passes the grounding point of the calling roller 54 with the calling roller 54 being driven, the next paper P2 is called the calling roller with the calling roller 54 partially overlapping the preceding paper P1. 54 is paid out in contact with 54. At this time, since the double feed detection means K4 detects the overlap “none”, the feeding roller 54 does not stop, and the feeding of the next paper P2 is continued as it is after the feeding of the preceding paper P1.

(3) (4) When the overlap between the trailing edge of the preceding sheet P1 and the leading edge of the next sheet P2 is detected by the double feed detecting means K4, the driving roller 54 is stopped or separated. Although it is difficult to stop the driving of the calling roller 54 instantly, the separation does not take much time, and the bending of the paper can be eliminated instantly. Between (3) and (4) corresponds to step S9 (Tc) in FIG. 6A.

As a result, the front end of the next sheet P2 stops at a predetermined position immediately before the feed nip that has passed the double feed detecting means K4 by a distance α as shown in FIG. 5A. Further, the separation roller 56 prevents the front end of the next sheet P2 from entering the feed nip by the action of the torque limiter.
When the trailing edge of the preceding paper P1 passes through the double feed detecting means K4 as in (4) (during the predetermined time Te in step S12 in FIG. 6A), the next paper P2 can be started (step S2 in FIG. 6A). become.

(5) (6) This is a state in which the feed roller 55 is driven and the preceding paper P1 is fed out. When this state is reached, a sufficient feeding and conveying force can be obtained only by the feed roller 55, so that the calling roller 54 is driven and rotated. As a result, the preceding paper P <b> 1 is fed out from the uppermost portion of the paper bundle P and fed by the feed roller 55.

  In this state, the next sheet P2 (and the second sheet below it) is taken out by friction with the preceding sheet P1. Since the front end of the next paper P2 exceeds the double feed detecting means K4 before the rear end of the preceding paper P1 exceeds the calling roller 54, the overlap with the preceding paper P1 is detected by the double feed detecting means K4 and immediately the calling roller. 54 are spaced apart.

  This operation corresponds to step S8 → step S10 when x = 0 in the flowchart of FIG. 6A. As a result, the frictional force in the feeding direction with respect to the next paper P2 is eliminated, and the front end of the next paper P2 is prevented from entering the feed nip, so that double feed or jam can be prevented.

  FIG. 7A (6) illustrates a state in which the calling roller 54 is separated so as to correspond to S10a (calling roller separation) in the flowchart of FIG. 6C. However, when the sheet deflection is allowed between the calling roller 54 and the feed roller 55, the calling roller 54 may be simply stopped without separating the calling roller 54. As a result, even if the next paper P2 advances due to the frictional force in the feeding direction with respect to the next paper P2, the next paper P2 can be bent so as not to buckle, and the next paper P2 does not exceed the feed nip, and double feeding or jamming can be prevented. The sheet feeding device 50 shown in FIGS. 5A to 5C operates as described above.

  Next, the operation of the paper feeding device 50 in FIG. 5D has a difference (V2 <V1) between the conveyance speeds V1 and V2 of the feed roller 55 and the grip roller 58, which simplifies the drive control of the feed roller 55 and loads the control system. The purpose is to mitigate.

  That is, as described above, the front end of the preceding paper P1 is detected by the paper detection means K2 on the downstream side of the grip roller 58. With this paper detection as a trigger, the calling roller 54 is brought into contact with (or re-driven) the uppermost sheet (next sheet P2) of the sheet feed tray 51 to feed out the next sheet P2. In order to detect the front edge of the preceding paper P1 by the paper detection means K2, a minimum gap δ is required between the preceding paper and the rear edge of the preceding paper. This minimum gap δ is set between the rear end of the preceding sheet and the front end of the next sheet fed from the feed roller 55 in the conventional apparatus as shown in FIGS. 9 and 10, and the feed roller 55 and the grip roller 58 are The gap between the sheets is kept constant by driving at the same speed.

  However, in order to maintain a constant sheet spacing between the upstream and downstream rollers in this way, the upstream feed roller 55 is transported depending on the transport state of the preceding sheet transported by the downstream grip roller 58. It is necessary to always control the state. That is, every time the preceding paper transported by the grip roller 58 is delayed, the transport of the next paper by the feed roller 55 must be delayed correspondingly. Thus, if the drive of the feed roller 55 is finely controlled ON / OFF, a load is applied to the control system and stable paper conveyance becomes difficult.

  Therefore, it is necessary to stop the ON / OFF control of the driving of the upstream feed roller 55 according to the transport state of the downstream preceding paper as in the prior art, and it is necessary due to the difference in transport speed between the feed roller 55 and the downstream grip roller 58. The minimum gap between papers was ensured. That is, the minimum required paper interval is surely obtained until the leading edge of the next sheet reaches the sheet detecting means K2 due to the speed difference.

  In the paper feeding device 50 of FIG. 5D, when the double feed detection means K4 does not detect double feed, when the trailing edge of the preceding paper passes through the feed roller 55, the calling roller 54 and the feed roller 55 continue to be driven as before. If the double feed detection means K4 detects double feed, the call roller 54 temporarily stops driving (or separates from the sheet bundle P), and the call roller 54 resumes driving at the same time that the trailing edge of the preceding paper passes through the feed roller 55 ( Or, the sheet bundle P is grounded).

  When the front end of the preceding paper reaches the grip roller 58, the preceding paper is conveyed further downstream at the speed V1. Since the speed V1 is relatively faster than the feed roller 55 of the separation feeding unit, the feed roller 55 is rotated by the grip roller 58 along the sheet conveyed at the speed V1. The one-way clutch of the feed roller 55 and the torque limiter of the separate roller 56 enable this rotation.

  When the one-way clutch is not applied, the calling roller 54 that is driven via the clutch by the drive source of the feed roller 55 moves the calling roller 54 at the top of the sheet bundle P when the front end of the sheet reaches the grip roller 58. It is preferable to provide a separation mechanism that separates from the space. The trailing edge of the sheet conveyed by the grip roller 58 passes under the calling roller 54 in a state where the calling roller 54 is lifted from the sheet bundle P by the separation mechanism. At the moment when the trailing edge of the sheet passes through the separation feeding unit (feed roller 55), both the calling roller 54 and the feed roller 55 are driven. Then, at the same time as the trailing edge of the preceding paper P1 conveyed at the speed V1 by the grip roller 58, the next paper P2 is fed out from the feed roller 55 at the speed V2.

Here, if the minimum paper interval detectable by the paper detection means K2 is δ and the distance from the separation feeding unit (feed roller 55) to the grip roller 58 is L, the speed V1 so that the following relational expression is satisfied. , V2 is set.
V2 = V1 × {L− (δ−β + α)} / L (Formula 1)
V1: Conveying speed of the grip roller 58 V2: Conveying speed of the feed roller 55 α: Distance that the front edge of the sheet moves toward the feed nip after exceeding the double feed detecting means K4 β: Optical axis and feed nip of the double feed detecting means K4 Distance between

The (Expression 1) can be obtained by defining the time T1 and the time T2 as follows, and T1 = T2.
T1: Time from the trailing edge of the preceding paper P1 passing through the feed roller 55 until reaching the grip roller 58 at the speed V1 T2: When the driving of the calling roller 54 is resumed (or grounded to the sheet bundle P), the leading edge of the next paper P2 Time to reach the position of the nearest δ of the grip roller 58 at the speed V2

  When the paper has a slack amount (slack length) ε between the grip roller 58 and the downstream roller, even after the trailing edge of the paper passes through the grip roller 58, the slack amount ε corresponds to the slack amount ε. It stays at the exit of the grip roller 58 until it is conveyed. As a result, the gap between the trailing edge of the preceding paper P1 and the leading edge of the next paper P2 is clogged (shortened). Therefore, even if the paper stagnation occurs due to the sag amount ε, an extra paper space may be secured in advance by the sag amount ε so as to ensure the necessary paper space δ.

That is, when considering the sagging amount ε, the relational expression is expressed as follows.
V2 = V1 × {L− (δ−β + α + ε)} / L (Expression 2)
ε: Amount of slack in the paper between the grip roller 58 and the downstream roller

  Assuming that the speed V1 is determined by the conveyance speed of the timing roller pair matched to the downstream image forming linear speed, the speed V2 of the separation feeding unit is lower than the speed V1 from the above equation. By reducing the speed of the separating / feeding unit, it is possible to increase the separation time by the separation roller 56 and to suppress the slip of the feed roller 55, and to improve the stability of the sheet separating action.

  Further, by setting the speeds V1 and V2 as described above, the feed roller 55 can be set to simple continuous drive control at the speed V2, for example. As a result, the load on the control system is reduced, and by reducing the load, the occurrence of a jam due to a control delay or the like can be suppressed, and stable paper feeding and conveyance can be realized.

  Further, while the feed roller 55 is in contact with the paper being conveyed by the grip roller 58, the feed roller 55 can be non-driven / drivenly rotated, so that the control of the feed roller 55 during that time becomes unnecessary. Similarly, the load on the control system is reduced.

  In addition, the paper feeding device 50 in FIG. 5D secures the minimum necessary paper gap in the same manner as the paper feeding devices in FIGS. 5A to 5C, so that high print productivity can be realized. The conveyance speed V2 of the feed roller 55 is lower than the conventional speed, but this is the result of averaging the conventional paper interval stop time (OFF time of driving ON / OFF control) and the normal speed (speed V1 when ON). To do. Therefore, there is almost no influence on the print productivity due to the decrease in the conveyance speed V2 of the feed roller 55.

  7B is a time chart showing the operation of the calling roller 54, the feed roller 55, the separation roller 56, and the grip roller 58 of the paper feeding device 50 of FIGS. 4B and 5F in relation to the overlap of the preceding paper P1 and the next paper P2. It is a chart. It is the same as FIG. 7A except that the drive of the grip roller 58 is added compared to FIG. 7A and the drive of the feed roller 55 is slightly different.

  That is, the driving of the feed roller 55 in FIG. 7B can be arbitrarily performed from the start of conveyance of the preceding paper P1 by the grip roller 58 to immediately before the trailing edge of the preceding paper P1 passes through the separation feeding unit. For example, the feed roller 55 may be continuously driven at the speed V2 so that the drive portion A indicated by the broken line in the time chart is continuous in the horizontal direction, or the drive of the feed roller 55 may be thinned out appropriately in order to reduce power consumption. (For example, the solid line part below the drive part A).

  Further, as indicated by a drive portion B indicated by a broken line in the time chart, it is possible to drive the feed roller 55 gently with a margin earlier than the next paper start timing by a predetermined time. Thus, by gently raising the feed roller 55, it is possible to reduce the load on the drive system, and it is also possible to reduce an increase in control load such as higher accuracy of the timer. In this respect, since the conventional paper feeder forms a predetermined sheet gap at the position of the feed roller, the feed roller must be suddenly started at the next paper feed start timing, and a load is applied to the drive system and the control system. It was.

  As described above, the paper gap formation by the speed difference (V2 <V1) of the paper feeding device 50 in FIG. 5D can also be applied to the paper feeding device 50 in FIG. 5B. In the paper feeding device 50 in FIG. 5B, β in FIG. 5A is shortened to coincide with α (β = α). In this way, at the moment when the trailing edge of the preceding paper P1 in FIG. 5B comes out of the feed roller 55, it is possible to start transporting the leading edge of the next paper P2 by the feed roller 55 so as to follow the trailing edge of the preceding paper P1 without a gap. .

  Further, since the feed roller 55 may be in an arbitrary driving state until the conveyance of the next paper P2 is started, the feed roller 55 is already at the speed V2 at the time when the conveyance of the next paper P2 is started using the driving portion B of FIG. 7B. Can be in a standing state. As a result, the time delay of starting the next sheet can be minimized. In such an embodiment, the paper gap between the feed roller 55 and the grip roller 58 starts from substantially zero and then gradually increases to form a minimum paper gap δ at the position of the grip roller 58. Therefore, it is possible to maximize the print productivity and at the same time to save energy of the entire apparatus by reducing the conveying speed of the entire sheet feeding apparatus.

(Paper Feeder-Type 2)
4B is provided with a photo interrupter 151 in place of the double feed detecting means K4 in FIG. 4A. As will be described later, the photo interrupter 151 is a separation operation detection unit that detects a separation operation of the separation roller 56 as a separation member, that is, an operation state of whether or not the separation roller 56 is rotating. The other configuration is the same as that of the sheet feeding device 50 of FIG. 4A. The paper feeding device 50 is also shown as the additional paper feeding device 50 in FIG. 1, but is similarly applicable to the paper feeding unit 300 provided thereon.

  The paper feeding method in this embodiment is an RF (Roller Friction) paper feeding method in which the separation roller 56 that is a separation member is not reversely driven. This method also has design advantages such as tolerance for positional accuracy similar to the FRR method. When the above-described FRR paper feeding method is adopted, the operation state of the separate roller 56 or its torque limiter (the rotation direction, that is, whether it is feed rotation or reverse rotation) is detected by the detection means.

  The sheet feeding device 50 is configured to provide a stable sheet feeding operation with a long service life, low noise, and low cost without losing design advantages such as positional accuracy tolerance of the RF system. Also, even for paper types with large paper-to-paper friction variation, the paper-to-paper friction variation is reduced by maintaining a minimum distance between the papers at the start of paper feeding without burdening the paper. Can be achieved.

  In addition, the paper feeding device 50 can avoid the trouble of transportation caused by a thick paper and can realize high print productivity with stable paper feeding. In order to obtain the above-described effects, the sheet feeding device 50 is provided with separation operation detecting means for detecting the operation state of the separation member as shown in FIG. 5E in the conventional sheet feeding device shown in FIGS. ing.

(Configuration of paper feeder-Type 2)
The feed roller 55 is rotationally driven in the paper feeding direction via a one-way clutch, similarly to the paper feeding device of FIG. 4A. On the other hand, the separate roller 56 is pivotally supported by a non-rotatable separate roller shaft 154 via a torque limiter 152 as shown in FIGS. 5E (A) and (B). When one sheet is held at the feed nip, the separate roller 56 abuts on the feed roller 55 by the torque limiter 152 slipping between the separate roller shaft 154 and is driven to rotate. However, when two or more sheets are held in the feed nip, the separate roller 56 is supported by the separate roller shaft 154 in a state where the rotation is stopped via the torque limiter 152, thereby preventing the double feeding of the sheets. ing. That is, when two or more sheets are sandwiched in the feed nip, only one uppermost sheet is fed by the feed roller 55, and the remaining sheets have their front end abutted against the rotation-separated separation roller 56. It will be stopped in the state.

  That is, when the separation roller 56 rotates in the transport direction, there is no sheet, or there is only one sheet sandwiched between the feed nips, so no separation operation is performed. On the other hand, when the separation roller 56 is stopped, two or more sheets are sandwiched in the feed nip, so that the separation operation is performed or the driving is stopped. The sheet feeding device in FIG. 5E is controlled by the flowchart in FIG. 6D. The flowchart will be described later.

  An encoder 150 serving as a separation operation detection unit is provided on the outer shell 153 of the torque limiter 152 that rotates integrally with the separation roller 56. When the torque limiter 152 is not used, the encoder 150 can be attached to the shaft portion of the separate roller 56.

  A photo interrupter 151 serving as a separation operation detecting unit is disposed so as to sandwich the outer periphery of the encoder 150. The photo interrupter 151 detects whether or not the separation roller 56 is rotating.

  The photo interrupter 151 itself is inexpensive and saves space because it may be disposed at one location on one side of the paper. Further, there is an advantage that high accuracy is not required with respect to the mounting position as in the reflective sensor K4.

  The separate roller shaft 154 is movably supported on the feed roller 55 side and is urged toward the feed roller 55 side by a spring 56a. A so-called “feed nip” is formed at a contact portion between the feed roller 55 and the separation roller 56, and the sheets are fed into the feed nip one by one in the direction of the arrow. The photo interrupter 151 is disposed so as to follow the movement of the separate roller shaft 154 toward the feed roller 55. The positional relationship between the photo interrupter 151 and the encoder 150 is always maintained regardless of the movement of the separate roller shaft 154.

  A grip roller 58 is disposed on the downstream side of the feed roller 55 as shown in FIG. 5F. The configuration around the grip roller 58 is the same as that shown in FIG. 4A.

(Paper Feeder Operation-Type 2)
(Operation of the paper feeder in FIG. 5E)
The sheet feeding device 50 is configured as described above, and is fed by driving the grip roller 58, the calling roller 54, and the feed roller 55 in a state where the calling roller 54 is in contact with the uppermost portion of the sheet bundle P. Is started. When the calling roller 54 rotates in the direction of the arrow in FIG. 4B, the uppermost sheet of the sheet bundle P is fed out, and the front end of the fed sheet is pinched by the feed nip of the feed roller 55. Thereafter, the sheet is conveyed downstream by the feed roller 55, and when the front end of the sheet is gripped by the grip roller 58 and the front end of the sheet is detected by the sheet detecting means K2, the driving of the feed roller 55 is stopped and the feed roller is stopped. 55 is driven rotation.

  If the separation operation detecting means detects “no separation operation” before the trailing edge of the preceding paper P1 exceeds the contact position of the calling roller 54, the calling roller 54 continues or operates the feeding of the preceding paper P1. Then, following the preceding paper P1, the next paper P2 is continuously fed out in a state of being overlapped at a distance γ as shown in FIGS. 5E (A) and (B). The feeding operation of the calling roller 54 may be continuously performed without interruption from the start of paper feed, except when the “separation operation is detected” is detected by the separation operation detection unit. However, when a sufficient conveying force for feeding can be obtained with only the feed roller 55, the feeding operation by the calling roller 54 may be interrupted as appropriate.

  When the leading edge of the next paper P2 fed out in a state of overlapping the preceding paper P1 as shown in FIG. 5E (A) reaches the feed nip, the photo interrupter 151 serving as the separation operation detecting means “has a separation operation”. Detected as Thus, when the photo interrupter 151 detects “separation operation is present”, the driving of the calling roller 54 is stopped.

  Once “separation operation is detected” is detected, the calling roller 54 is not driven until the next paper feed timing. Even when “with separation operation” is not detected, a safety control for temporarily stopping the pre-feeding is performed at the timing when the trailing edge of the preceding paper P1 passes through the vicinity of the feed nip, and a control for waiting for the next paper feeding timing is performed. Also good.

  To stop the driving of the calling roller 54, the clutch that connects the feed roller 55 to the driving source is disconnected. However, even if the clutch is disengaged at the same time as the detection of “separation operation is present”, some drive stop distance is obtained due to the response of the clutch. As a result, as shown by the broken line in FIG. 5E (A), the sheet may be bent between the calling roller 54 and the feed roller 55, or slip marks may be generated in the case of a thick sheet.

  Therefore, the calling roller 54 is arranged to be separated from the paper surface as described above. As a result, it is possible to eliminate the problem of the occurrence of sheet bending and slip traces, and it is possible to obtain stable conveyance without buckling even for a sheet having low rigidity, thereby satisfying sheet compatibility.

  The start timing of the next paper P2 is the same as in the prior art, and the detection of the leading edge of the preceding paper P1 by the paper detection means K2 provided downstream of the grip roller 58 where the behavior of the paper is stable (slip rate is reduced) is used as a trigger. Then, the driving of the calling roller 54 and the feed roller 55 is repeated at a predetermined timing at which the front end of the next paper P2 does not collide with the rear end of the preceding paper P1 and the predetermined print productivity is satisfied.

  Even in this type 2 paper feeding device 50, it is not necessary to make a paper gap for detecting the presence or absence of paper between the calling roller 54 and the feed roller 55 as described above. Therefore, the print productivity of the paper feeding device 50 can be increased as compared with the conventional paper feeding device shown in FIGS. Further, since it is not necessary to increase the speed of paper feeding as in the conventional model of FIG. 9, the power consumption of the driving source of the feed roller 55 can be suppressed, and further, the conveyance speed of the whole paper feeding device can be reduced by shortening the paper interval. Overall energy saving can be achieved.

  When there is no separation operation, it is not necessary to temporarily stop the feeding operation of the calling roller 54 before the trailing edge of the preceding paper P1 exceeds the grounding point of the calling roller 54. Therefore, even when a common drive source is used for the calling roller 54 and the feed roller 55, an operation for separating the calling roller 54 from the paper surface is not necessary. In addition, when the feeding operation by the calling roller 54 is stopped due to the separation operation, it is possible to stop the feeding drive including the feed roller 55 and to reduce the control load. It becomes possible.

  Further, the detection of the presence or absence of the separation operation by the separation operation detection unit is more significant than the detection of the next sheet P2 by the detection of the sheet detection unit K3 by capturing the moment when the trailing edge of the preceding sheet P1 passes through the feed nip as shown in FIG. Has time to spare. For this reason, it is not necessary to count the moment when the trailing edge of the preceding paper P1 passes through the feed nip with a highly accurate control timer, and the control load on the CPU that controls the control means can be reduced. By reducing the load on the CPU, it is possible to suppress the occurrence of a jam due to a control delay or the like, and to realize a stable paper feed conveyance. Since the separation operation detecting means detects the rotation of the separation roller 56, it can be constituted by a low-precision encoder 150 and a photo interrupter 151. Therefore, the above-mentioned performance can be obtained with a conventional and inexpensive configuration without using an expensive sensor such as an ultrasonic sensor.

  Next, the operation of the sheet feeding device (type 2) 50 in FIG. 5E will be described with reference to the flowchart in FIG. 6D. A step different from the flowchart of FIG. 6C is that the presence or absence of “separation operation” is determined in step 6 instead of “double feed detection”. Others are the same as the flowchart of FIG. 6C.

  In FIG. 6D, first, driving of the grip roller 58 is started in step S1. Next, in step S2, paper feed driving (for the preceding paper P1) is started. This paper feed drive is performed by driving the calling roller 54 and the feed roller 55. When the call roller 54 and the feed roller 55 are shared, the call roller 54 is intermittently driven by connecting and separating the clutch while the feed roller 55 is continuously driven. Accordingly, the calling roller 54 is driven by the clutch connection to “start feeding paper”, and the driving of the calling roller 54 is stopped by “separating the clutch” to “stop feeding paper”. The sheet called by the calling roller 54 is sent to the separation feeding unit by the feed roller 55 and the separation roller 56, and only the uppermost sheet is conveyed.

  The sheet fed downstream from the separation feeding unit passes through the grip roller 58 provided on the downstream side, and it is determined in step S3 whether the preceding sheet P1 (front end) is detected by the sheet detection unit K2. The The grip roller 58, the calling roller 54, and the feed roller 55 are driven until the front sheet P1 (front edge) is detected. The paper that has passed through the paper detection means K2 is then aligned with a timing roller (not shown), and is discharged out of the apparatus through an image forming / fixing section.

  Paper front edge detection information by the paper detection means K2 is sent to a control means (not shown), and the drive of the feed roller 55 is stopped by the control means based on the information. The stop timing is such that the driving of the feed roller 55 is stopped before the timing at which the trailing edge of the sheet crosses the feed nip, based on the sheet leading edge detection information and preset sheet size information.

  A one-way clutch is connected to the rotation shaft of the feed roller 55. Even if the drive of the feed roller 55 is stopped, the feed roller 55 itself rotates in the conveyance direction of the paper conveyed by the grip roller 58 (driven rotation). ) By stopping the driving of the feed roller 55, the separation roller 56 is supported by a non-rotatable shaft via the torque limiter even if the front end of the next paper P2 reaches just before the feed nip in a form following the rear end of the preceding paper P1. Therefore, separation from the preceding paper P1 is performed reliably. At this time, since only the front end portion of the next paper P2 is rubbed by these rollers 55 and 56, even the paper which is weak against friction and easily damaged is hardly damaged.

  When the paper detection means K2 detects the preceding paper P1 (the front edge thereof), it is determined in step S4 whether a predetermined time Ta has elapsed. The predetermined time Ta is a time until the trailing edge of the preceding paper P1 passes through the position of the calling roller 54, and it is determined from this timing whether or not preliminary feeding is necessary.

  If it is determined in step S4 that the predetermined time Ta has elapsed, it is determined in step S6 whether or not a separation operation by the photo interrupter 151 has occurred. If “no separation operation”, the driving of the calling roller 54 is continued until “separation operation” is detected.

  If it is determined in step S6 that “separation operation is present”, it means that the front edge of the next sheet P2 has reached just before the feed nip. In this case, the calling roller 54 is immediately separated from the sheet in step S10a, and the driving of the calling roller 54 is stopped in step S10.

  Next, in step S11, it is determined whether or not the number of jobs has been completed. If the number of jobs has been completed, the driving of the grip roller 58 is stopped in step S13, and the process ends.

  If the number of jobs has not ended, it is determined in step S12 whether or not a predetermined time Te has elapsed. If the predetermined time Te has not elapsed, the circulation determination loop is repeated until the predetermined time Te has elapsed. This predetermined time Te determines the start timing of the next sheet P2, and when the predetermined time Te elapses, the process returns to step S2 and the driving of the calling roller 54 is resumed.

  FIG. 7C is a time chart showing the operation of the calling roller 54, the feed roller 55, and the separation roller 56 of the paper feeding device (type 2) 50 of FIGS. 4B and 5E in relation to the overlap of the preceding paper P1 and the next paper P2. It is a chart. As for the arrow indicating the rotation direction of each roller, a solid line arrow indicates driving rotation, and a broken line arrow indicates driven rotation. The absence of an arrow indicates rotation stop. For convenience, the calling roller 54 indicates both ON / OFF of the drive and contact / separation with respect to the paper. However, the call roller 54 corresponds to the paper feeding / stopping of either the ON / OFF or the contact / separation. Can do. However, it may be configured to be capable of both ON / OFF and contact / separation as required.

  The numbers from 1 to 6 in the time chart correspond to the six figures below the time chart. The following descriptions (1) to (6) correspond to numbers 1 to 6 in the time chart. (1) The feed roller 55 is driven and the preceding paper P1 is being fed out. When this state is reached, a sufficient feeding and conveying force can be obtained only by the feed roller 55, so that the calling roller 54 is driven and rotated.

  As a result, the preceding paper P <b> 1 is fed out from the uppermost portion of the paper bundle P and fed by the feed roller 55. However, the next paper P2 remains in the paper stacking position. Since the trailing edge of the preceding paper P1 is approaching a predetermined distance behind the calling roller 54, the driving of the calling roller 54 is started immediately after (1).

(2) When the trailing edge of the preceding paper P1 passes the grounding point of the calling roller 54 with the calling roller 54 being driven, the next paper P2 is called the calling roller with the calling roller 54 partially overlapping the preceding paper P1. 54 is paid out in contact with 54. At this time, since the separation operation detecting means detects “no separation operation”, the calling roller 54 does not stop, and the feeding of the next paper P2 is continued as it is after the feeding of the preceding paper P1.

(3) Since the front end of the next paper P2 that has been fed over the preceding paper P1 reaches just before the feed nip and “separation operation is present” is detected, the calling roller 54 is stopped or separated from the next paper P2. . Although it is difficult to instantaneously complete the drive stop of the calling roller 54, the separation does not take much time, and the deflection of the paper is also eliminated instantly. The separation roller 56 prevents the front end of the next sheet P2 from entering the feed nip by the action of the torque limiter 152.

(4) When the trailing edge of the preceding sheet P1 passes through the leading edge of the trailing sheet P2, the overlapping of the sheets disappears and the separation roller 56 starts to rotate, and the separation operation detecting means detects “no separation operation”. This driven rotation is performed until the preceding paper P1 passes through the feed nip, and the front end of the succeeding paper P2 that has come to just before the feed nip enters the feed nip and stops. When the trailing edge of the preceding paper P1 passes through the feed nip in this way (during the predetermined time Te in step S12 in FIG. 6D), the next paper P2 can be started (step S2 in FIG. 6D).

(5) (6) This is a state in which the feed roller 55 is driven and the preceding paper P1 is fed out. When this state is reached, a sufficient conveying force can be obtained only by the feed roller 55, so that the calling roller 54 is driven to rotate. As a result, the preceding sheet P1 is fed from the top of the sheet bundle P.

  Also, due to friction with the preceding paper P1, the next paper P2 and the second secondary paper below it are taken out, and the front edge of the next paper P2 immediately before the feed nip before the trailing edge of the preceding paper P1 exceeds the calling roller 54. Has reached. In this state, the “separation operation is present” is detected by the separation operation detection means, and the calling roller 54 is immediately separated.

  The separation operation of the calling roller 54 corresponds to step S10a in the flowchart of FIG. 6D. Thereby, the frictional force in the feeding direction with respect to the next paper P2 is eliminated, and the front end of the next paper P2 is prevented from entering the feed nip. Therefore, it is possible to prevent double feeding or jamming.

  FIG. 7C (6) illustrates a state in which the calling roller 54 is separated so as to correspond to S10a (calling roller separation) in the flowchart of FIG. 6D. However, if the sheet is allowed to be bent between the calling roller 54 and the feed roller 55, the calling roller 54 may be simply stopped without separating the calling roller 54. As a result, even if the next paper P2 advances due to the frictional force in the feeding direction with respect to the next paper P2, the next paper P2 can be bent so as not to buckle, and the front edge of the next paper P2 does not exceed the feed nip, and double feed or jamming is performed. Can be prevented.

  The sheet feeder 50 of FIG. 5E operates as described above. As described above, the RF paper feeding method in which the separation roller 56 is not reversely driven has been described as an example. However, by using the separation operation detecting unit that can determine the rotation direction of the separate roller 56, the FRR supply that applies the reverse drive to the separation roller 56 is used. A paper method may be used.

  Next, the operation of the paper feeding device 50 in FIG. 5F has a difference (V2 <V1) between the conveyance speeds V1 and V2 of the feed roller 55 and the grip roller 58, which simplifies the drive control of the feed roller 55 and loads the control system. The purpose is to mitigate.

  That is, as described above, when the front end of the preceding paper P1 is detected by the paper detection means K2 on the downstream side of the grip roller 58, the call roller 54 feeds the next paper P2 using this paper detection as a trigger. It is brought into contact with the paper surface of the uppermost sheet (next sheet P2). The calling roller 54 stands by in the contact state. In order to detect the front end of the preceding paper P1 by the paper detection means K2, a minimum gap (inter-paper) δ is required between the front end of the preceding paper P1 and the rear end of the paper. In the conventional apparatus as shown in FIGS. 9 and 10, the minimum gap δ is set between the rear end of the preceding sheet fed from the feed roller 55 and the front end of the next sheet. Then, by driving the feed roller 55 and the grip roller 58 at the same speed, the gap between the sheets is kept constant.

  However, in order to maintain a constant sheet spacing between the upstream and downstream rollers in this way, the upstream feed roller 55 is transported depending on the transport state of the preceding sheet transported by the downstream grip roller 58. It is necessary to always control the state. That is, every time the preceding paper transported by the grip roller 58 is delayed, the transport of the next paper by the feed roller 55 must be delayed correspondingly. Thus, if the drive of the feed roller 55 is finely controlled ON / OFF, a load is applied to the control system and stable paper conveyance becomes difficult.

  Therefore, it is necessary to stop the ON / OFF control of the driving of the upstream feed roller 55 according to the transport state of the downstream preceding paper as in the prior art, and it is necessary due to the difference in transport speed between the feed roller 55 and the downstream grip roller 58. The minimum gap between papers was ensured. That is, the minimum required paper interval is surely obtained until the leading edge of the next sheet reaches the sheet detecting means K2 due to the speed difference.

  When the above-described safety control is not performed in the sheet feeding device 50 of FIG. The roller 55 continues to be driven as before. When the separation operation detecting means detects “separation operation is present”, the calling roller 54 temporarily stops driving (or separates from the sheet bundle P). At this time, since the leading edge of the succeeding paper P2 has already entered the feed nip, if the feed roller 55 is driven slightly before the trailing edge of the preceding paper passes through the feed roller 55, the trailing edge of the preceding paper becomes the feed roller 55. At the same time, the feeding of the succeeding paper P2 can be started. The calling roller 54 may be resumed (or grounded to the sheet bundle P) in an auxiliary manner after the trailing edge of the preceding sheet passes through the feed roller 55.

  When the front end of the preceding sheet reaches the grip roller 58, the preceding sheet is conveyed further downstream at the speed V1. Since the speed V1 is relatively faster than the feed roller 55 of the separation feeding unit, the feed roller 55 is rotated by the grip roller 58 along the sheet conveyed at the speed V1. The one-way clutch of the feed roller 55 and the torque limiter 152 of the separate roller 56 enable this rotation.

  When the one-way clutch is not applied, the calling roller 54 that is driven via the clutch by the drive source of the feed roller 55 moves the calling roller 54 at the top of the sheet bundle P when the front end of the sheet reaches the grip roller 58. It is preferable to provide a separation mechanism that separates from the space. The trailing edge of the sheet conveyed by the grip roller 58 passes under the calling roller 54 in a state where the calling roller 54 is lifted from the sheet bundle P by the separation mechanism. At the moment when the trailing edge of the sheet passes through the separation feeding unit (feed roller 55), both the calling roller 54 and the feed roller 55 are driven. Accordingly, the next paper P2 is fed out from the feed roller 55 at the speed V2 simultaneously with the trailing end omission in the separating and feeding unit of the preceding paper P1 conveyed at the speed V1 by the grip roller 58.

The speeds V1 and V2 are set so that the following relational expression is established.
V2 = V1 × {L− (δ + ε)} / L (Formula 3)
V1: Conveying speed of the grip roller 58 V2: Conveying speed of the feed roller 55 δ: Minimum paper interval detectable by the paper detection means K2 L: Distance from the separation feeding unit (feed roller 55) to the grip roller 58 ε : Amount of paper slack between the grip roller 58 and the downstream roller

  When the paper has a sag amount (sag length) ε between the grip roller 58 and the downstream roller, the paper is conveyed by the downstream roller by the sag amount ε even after the rear end of the paper passes through the grip roller 58. Until the grip roller 58 exits. As a result, the gap between the trailing edge of the preceding paper P1 and the leading edge of the next paper P2 is clogged (shortened). In view of this, even when the paper amount is clogged by the sag amount ε, an extra paper space is secured in advance by the sag amount ε so as to ensure the necessary paper space δ. Compared with the above (Equation 2), it can be seen that the start position of the next sheet P2 by the resumption of driving of the calling roller 54 (or the sheet bundle P grounding) has moved to the downstream side by β-α.

  Assuming that the speed V1 is determined by the conveyance speed of the pair of timing rollers matched to the downstream image forming linear speed, the speed V2 of the separation feeding unit (feed roller 55) is lower than the speed V1 from the above equation. By reducing the speed of the separating / feeding unit, it is possible to increase the separation time by the separation roller 56 and to suppress the slip of the feed roller 55, and to improve the stability of the sheet separating action.

  Further, by setting the speeds V1 and V2 as described above, the feed roller 55 can be set to simple continuous drive control at the speed V2, for example. As a result, the load on the control system is reduced, and by reducing the load, the occurrence of a jam due to a control delay or the like can be suppressed, and stable paper feeding and conveyance can be realized.

  Further, while the feed roller 55 is in contact with the paper being conveyed by the grip roller 58, the feed roller 55 can be non-driven / drivenly rotated, so that the control of the feed roller 55 during that time becomes unnecessary. Similarly, the load on the control system is reduced.

  In addition, the paper feeding device 50 shown in FIG. 5F can secure the minimum necessary gap between the papers as in the paper feeding device shown in FIG. 5E, so that high print productivity can be realized. The conveyance speed V2 of the feed roller 55 is lower than the conventional speed, but this is the result of averaging the conventional paper interval stop time (OFF time of driving ON / OFF control) and the normal speed (speed V1 when ON). Just do it. Therefore, there is almost no influence on the print productivity due to the decrease in the conveyance speed V2 of the feed roller 55.

  7D is a time chart showing the operation of the calling roller 54, the feed roller 55, the separation roller 56, and the grip roller 58 of the paper feeding device 50 shown in FIGS. 4B and 5F in relation to the overlap of the preceding paper P1 and the next paper P2. It is a chart. It is the same as FIG. 7C except that the drive of the grip roller 58 is added compared to FIG. 7C and the drive of the feed roller 55 is slightly different.

  That is, the feed roller 55 in FIG. 7D is driven from the start of conveyance of the preceding paper P1 by the grip roller 58 until just before the rear end of the preceding paper P1 passes through the separation feeding unit (feed roller 55). Driving may be arbitrary. For example, the feed roller 55 may be continuously driven at the speed V2 so that the drive portion A indicated by the broken line in the time chart is continuous in the horizontal direction, or the drive of the feed roller 55 may be thinned out appropriately in order to reduce power consumption. Good (for example, the solid line part below the drive part A).

  Further, as shown in the drive portion B indicated by the broken line in the time chart, it is possible to drive the feed roller 55 gently with a margin earlier than the next paper start timing. Thus, by gently raising the feed roller 55, it is possible to reduce the load on the drive system, and it is also possible to reduce an increase in control load such as higher accuracy of the timer. In this respect, since the conventional paper feeding apparatus needs to form a predetermined sheet gap at the position of the feed roller 55, the feed roller 55 must be sharply raised at the next paper feed start timing, and the drive system and the control are controlled. The system was overloaded.

  As described above, the above-described paper gap formation by the speed difference (V2 <V1) of the paper feeding device 50 in FIG. 5F can also be applied to the paper feeding device 50 (type 2) in FIG. 5E. 5E can start transporting the front end of the next paper P2 by the feed roller 55 at the moment when the rear end of the preceding paper P1 comes out of the feed roller 55 without chasing the rear end of the preceding paper P1. it can.

  Further, since the feed roller 55 may be in an arbitrary driving state until the conveyance of the next paper P2 is started, the feed roller 55 is already at the speed V2 at the time when the conveyance of the next paper P2 is started by using the driving portion B of FIG. 7D. Can be in a standing state. As a result, the time delay of starting the next sheet can be minimized.

  In such an embodiment, the paper gap between the feed roller 55 and the grip roller 58 starts from substantially zero and then gradually increases to form a minimum paper gap δ at the position of the grip roller 58. Therefore, it is possible to maximize the print productivity and at the same time to save energy of the entire apparatus by reducing the conveying speed of the entire sheet feeding apparatus.

(Feeding device of image reading device)
The paper feeding device of the present invention can be applied to the paper feeding device of the image forming apparatus, and also can be applied to the paper feeding device of the image reading device to save energy as in the case of the image forming device described above. FIG. 8 shows an embodiment in which the present invention is applied to an automatic sheet feeder (ADF) 90 of an automatic image reading apparatus.

  As shown in FIG. 8, the ADF 90 includes a paper feed tray 91, and the paper bundle P is placed on the paper feed tray 91 so that the document surface faces upward.

Further, although not shown, a set filler is provided near the front end of the paper feed tray 91 in the paper feed direction, which rotates when the paper is placed. Further, a paper set sensor 92 that detects that a paper is placed on the paper feed tray 91 is provided at the lowermost part on the movement locus of the leading end of the set filler. That is, the paper set sensor 92 detects the placement of the paper when the paper is set on the paper feed tray 91 and the set filler rotates and the leading end of the set filler comes off the paper set sensor. It has become.

  In addition, a stopper claw 93 is provided on the downstream side of the sheet feeding direction with respect to the sheet feeding tray 91. The stopper claw 93 is moved between an abutting position (solid line position) where the front end of the sheet bundle P is abutted by a sheet feeding solenoid (not shown) and a retreating position (broken line position) for retreating downward from the position. It has become.

  Therefore, when the front end of the sheet bundle P is abutted when the stopper claw 93 is in the abutting position, the front end of the sheet bundle P is aligned. Further, the width direction of the sheet bundle P is abutted against a side fence (not shown) provided on the sheet feed tray 91, whereby positioning in a direction orthogonal to the sheet conveyance direction is performed.

  The transport unit 97 of the ADF 90 includes a calling roller 94, a separation feeding unit 95, a pull-out unit 98, a turn unit 99, a reading transport unit 100, a paper discharge unit 101, and a switchback unit 102. Yes.

  The calling roller 94 is moved up and down between a position where it is retracted from the sheet bundle P by a sheet feeding solenoid (not shown) and a position where it is in contact with the upper surface of the sheet bundle P. The separating and feeding unit 95 includes a pair of left and right feed rollers 95a and 95b, a paper feed belt 95c stretched between the pair of feed rollers 95a and 95b, and a separator facing the paper feed belt 95c across the conveyance path. A roller 96 is used.

  On the front side of the feed nip where the separation roller 96 is in pressure contact with the paper feed belt 95c, double feed detection means K4 is disposed as shown in an enlarged manner. This double feed detecting means K4 can be configured by an optical type, an ultrasonic type or the like as in the previous embodiment. In this embodiment, the optical double feed detecting means K4 is used, and the light emitting element K4a is arranged on the upper side. The light receiving element K4b is disposed on the lower side. The presence or absence of double feeding is detected based on the amount of light received by the light receiving element K4b when two or more sheets enter between them.

  The arrangement position of the double feed detection means K4, that is, the distance to the feed nip, can be at least three embodiments as in FIGS. 5A to 5C. In FIG. 8, as shown in an enlarged view, the double feed detecting means K4 is disposed away from the feed nip by a distance β to the upstream side of the conveyance (arrangement position corresponding to FIG. 5A). Even when the paper interval when the feeding roller 94 is fed out is set to the minimum, two or more sheets are prevented from being caught in the feed nip. The operation of the double feed detecting means K4 at this time is the same as the operation described in the paper feeding device of the image forming apparatus.

  The sheet feeding belt 95c rotates in the sheet feeding direction (clockwise rotation direction), and the separation roller 96 rotates in the direction opposite to the sheet feeding direction. Further, the separate roller 96 rotates in the reverse direction with respect to the paper feed belt 95c when the paper is double fed. However, when the separation roller 96 is in contact with the paper feed belt 95c or when only one sheet is conveyed, the torque limiter (not shown) acts to follow the paper feed belt 95c. Yes.

  In the separation feeding unit 95, the calling roller 94 is brought into contact with the uppermost sheet (preceding sheet P 1) of the sheet bundle P placed on the sheet feeding tray 91 with the stopper claw 93 retracted to the broken line position. As a result, the fed paper is sent to the downstream side, and when the paper is double fed, the second and subsequent sheets are separated by the paper feed belt 95c and the separation roller 96 and sent to the downstream side. .

  The pull-out unit 98 includes a grip roller pair 98a composed of a pair of rollers arranged so as to sandwich the conveyance path, and a sheet detection unit K2 disposed on the downstream side of the grip roller pair 98a. The pull-out unit 98 performs primary abutting alignment of the fed paper according to the drive timing of the grip roller pair 98a and the separation feeding unit 95, and transports the aligned paper downstream in the transport direction. Further, the paper detection means K2 detects the front end of the paper conveyed from the separation feeding unit 95.

  The turn part 99 is composed of a conveyance path that curves from the top to the bottom of the conveyance path, and includes a registration sensor 104 as a detection unit according to the present invention and a reading entrance roller pair 105. The turn unit 99 turns the sheet conveyed from the pull-out unit 98 by conveying the curved conveyance path, and conveys the surface of the sheet downward by the reading entrance roller pair 105 to the vicinity of the slit glass 106. It has become. Further, the registration sensor 104 detects the front end and the rear end of the sheet conveyed from the pull-out unit 98 to the reading conveyance unit 100.

  The reading conveyance unit 100 includes a reading guide disposed at a position facing the slit glass 106 across the conveyance path, and a reading exit roller pair 108 including a pair of rollers disposed so as to sandwich the conveyance path after completion of reading. have. The reading conveyance unit 100 conveys the sheet conveyed to the vicinity of the slit glass 106 while bringing the surface of the document into contact with the slit glass 106 while being guided by a reading guide. The original image conveyed at the image reading position 109 is read by an optical system of a scanner unit (not shown), and the paper after the reading is further conveyed downstream in the conveying direction by the reading exit roller pair 108.

  The paper discharge unit 101 includes a paper discharge roller pair 110 including a pair of rollers and a paper discharge sensor 111 in the vicinity of the paper discharge port. The paper discharge roller pair 110 discharges the paper conveyed by the reading exit roller pair 108 to the paper discharge tray 112. Further, the paper discharge sensor 111 detects the trailing edge of the paper that is conveyed by the reading exit roller pair 108 and discharged from the paper discharge port to the paper discharge tray 112.

  The switchback unit 102 includes a switching claw 113 provided in the vicinity of the paper discharge port and a reverse roller pair 114. The switching claw 113 moves up and down by driving a reverse switching solenoid (not shown). The lower position of the vertical movement is a position (a position indicated by a broken line) for switching to a conveyance path for conveying the sheet conveyed from the discharge roller pair 110 to the reverse roller pair 114. Further, the upper position is a position (a position indicated by a solid line) for switching to the switchback path 102a for transporting the paper switched back by the reverse roller pair 114 to the grip roller pair 98a. The reversing roller pair 114 is configured to reversely convey the paper to be switched back for reading both sides of the paper to the switchback path 102a.

  Accordingly, the switchback unit 102 is configured to switch back the sheet to be read on both sides via the switching claw 113, the reverse roller pair 114, and the switchback path 102a to the grip roller pair 98a.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, A various deformation | transformation is possible. For example, in the above-described embodiment, the FRR paper feeding method or the RF paper feeding method is taken as an example of the separation feeding unit. However, other types of separation feeding units may be used.

51: Paper feed tray 52: Paper guide 53: Bottom plate 54: Call roller 55: Feed roller 56: Separating roller 58: Grip roller 150: Encoder 151: Photo interrupter 151: Separation operation detecting means 152: Torque limiter 153: Outer 154: Separate roller shaft P: paper bundle P1: preceding paper P2: next paper K2: paper detection means K4: double feed detection means

JP 2005-213039 A

Claims (12)

A calling roller disposed upstream of the sheet stacking unit from the front end position of the sheet stacking unit and contacting the uppermost sheet of the sheet stacking unit and feeding the sheet downstream in the transporting direction; and downstream of the calling roller in the transporting direction In a paper feeding device having a feed roller disposed on the side and a separating member that presses against the feed roller to form a pressure contact portion,
A double feed detecting means for detecting overlap of paper between the front end position of the paper stacking portion and the pressure contact portion;
Driving the calling roller and the feed roller;
When the multi-feed detection means detects that there is no overlap between the preceding paper and the next paper, the paper feeding by the calling roller is continuously operated,
When the double feed detection means detects that there is an overlap between the preceding paper and the next paper, the feeding roller stops the feeding so that the front edge of the next paper stops between the double feed detection means and the press contact portion. And the feeding of the next sheet by the calling roller is resumed so that the leading edge of the next sheet does not collide with the trailing edge of the preceding sheet. A calling roller disposed upstream of the sheet stacking unit from the front end position of the sheet stacking unit and contacting the uppermost sheet of the sheet stacking unit and feeding the sheet downstream in the transporting direction; and downstream of the calling roller in the transporting direction In a paper feeding device having a feed roller disposed on the side and a separating member that presses against the feed roller to form a pressure contact portion,
A double feed detecting means for detecting overlap of paper between the front end position of the paper stacking portion and the pressure contact portion;
Driving the calling roller and the feed roller;
When the multi-feed detection means detects that there is no overlap between the preceding paper and the next paper, the paper feeding by the calling roller is continuously operated,
When the multi-feed detection means detects that there is an overlap between the preceding paper and the next paper, the feeding roller stops feeding so that the front edge of the next paper can start from the press contact portion, and the front edge of the next paper is advanced. A paper feeding device which resumes feeding of the next paper by the calling roller so as not to collide with the trailing edge of the paper. A calling roller disposed upstream of the sheet stacking unit from the front end position of the sheet stacking unit and contacting the uppermost sheet of the sheet stacking unit and feeding the sheet downstream in the transporting direction; and downstream of the calling roller in the transporting direction In a paper feeding device having a feed roller disposed on the side and a separating member that presses against the feed roller to form a pressure contact portion,
Provided in the press contact portion is a double feed detection means for detecting the overlap of paper,
Driving the calling roller and the feed roller;
When the multi-feed detection means detects that there is no overlap between the preceding paper and the next paper, the paper feeding by the calling roller is continuously operated,
When the multi-feed detection means detects that there is overlap between the preceding paper and the next paper, the front edge of the next paper is separated from the paper contacting the calling roller so that it can start from the press contact portion, and the next paper The sheet feeding device restarts feeding of the next sheet by the calling roller so that the leading edge of the sheet does not collide with the trailing edge of the preceding sheet.   A grip roller that feeds the paper fed from the feed roller further downstream is provided at a position spaced apart from the pressure contact portion on the downstream side in the transport direction by a predetermined distance, and the feed roller is transported more than the grip roller. The speed is set to a low speed, and the difference between the conveyance speeds of the grip roller and the feed roller causes a gap between the trailing edge of the preceding sheet fed by the grip roller and the leading edge of the next sheet fed by the feed roller. 4. The sheet feeding device according to claim 1, wherein a minimum sheet interval that can be detected by a sheet detecting unit provided on the conveyance downstream side of the grip roller is formed. The sheet feeding device according to claim 4, wherein V2 = V1 × {L− (δ−β + α)} / L, where V1 is a conveyance speed of the grip roller and V2 is a conveyance speed of the feed roller.
Here, L is the distance from the pressure contact portion to the grip roller, δ is the minimum paper interval detectable by the paper detection means, and α is the pressure contact portion after the front edge of the paper has passed the double feed detection means. A distance advancing, β, is a distance between the double feed detecting means and the pressure contact portion.   The sheet feeding device according to claim 1, wherein the pressure contact portion is an FRR type separation member or an RF type separation member.   The paper feeding device according to any one of claims 1 to 6, wherein the double feed detection means is an optical double feed detection means or an ultrasonic double feed detection means.   An image forming apparatus comprising the sheet feeding device according to claim 1.   An image reading apparatus comprising the sheet feeding device according to claim 1. A calling roller disposed upstream of the sheet stacking unit from the front end position of the sheet stacking unit and contacting the uppermost sheet of the sheet stacking unit and feeding the sheet downstream in the transporting direction; and downstream of the calling roller in the transporting direction In a paper feeding device having a feed roller disposed on the side and a separating member that presses against the feed roller to form a pressure contact portion,
Separation operation detection means for detecting the overlap of sheets is provided in the separation member,
A grip roller for feeding the paper fed from the feed roller to the downstream side of the transport is provided at a position spaced apart from the pressure contact portion by a predetermined distance on the downstream side in the transport direction,
The conveyance speed of the feed roller is set to be lower than that of the grip roller, and the trailing edge of the preceding paper fed by the grip roller is fed by the difference between the conveyance speeds of the grip roller and the feed roller. A minimum paper interval that can be detected by the paper detection means provided on the conveyance downstream side of the grip roller is formed between the front end of the next paper and
Driving the calling roller and the feed roller;
When the separation operation detecting means detects that there is no overlap between the preceding sheet and the next sheet, the sheet feeding operation by the calling roller is continuously operated,
When the separation operation detection means detects that there is overlap between the preceding sheet and the next sheet, the front end of the next sheet is separated from the sheet contacting the calling roller so that it can start from the press contact portion, and the next sheet Resuming the feeding of the next paper by the calling roller so that the front edge of the paper does not collide with the rear edge of the preceding paper ,
A sheet feeding device characterized in that V2 = V1 × {L− (δ + ε)} / L, where V1 is a conveying speed of the grip roller and V2 is a conveying speed of the feed roller.
Here, L is the distance from the pressure contact portion to the grip roller, δ is the minimum gap between sheets that can be detected by the sheet detection means, and ε is the amount of sheet sag between the grip roller and the downstream roller.   The pressure contact portion includes a separation roller as a separation member that is in contact with the feed roller and is driven to rotate at a predetermined torque or more, and the separation operation detection unit detects a rotation state of the separation roller. Item 10. The sheet feeding device according to item 10.   12. The sheet feeding device according to claim 10, wherein the feeding roller stops feeding by separating the calling roller from the uppermost sheet of the sheet stacking unit.

Images