JP2006298515A - Paper feeding device and image forming device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a paper feeding device capable of increasing printing speed, while maintaining reliability at low paper feeding speed, without losing merits in design of an FRR type such as position accuracy tolerance. <P>SOLUTION: A means 10 for detecting the leading end of a paper sheet is provided at a position between the leading end of the paper sheets P stacked on a bottom plate 9 to a nip part of a feed roller 2. In the case wherein detection cycle of the leading end detecting means 10 is set at, for example, 10 mm per a second in the normal control, in order to instantaneously detect existence of paper sheet P with the leading end detecting means 10 when the trailing end of the fed paper sheet P passes through a separately feeding part, detection cycle of the leading end detecting means 10 is set at about half of the described one, for example, at 5 mm per a second or less to hasten start of the following paper feeding operation, and accuracy in the case of stopping the leading end of the following paper with the leading end detecting means 10 is improved to restrict variations of interval between the paper sheets. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a paper feeding device such as a copying machine, a printer, and a facsimile, and an image forming apparatus using the same.

  FIG. 3 is a sectional view conceptually showing an image forming apparatus such as an electrophotographic copying machine or printer. The image forming apparatus mainly includes a reading unit 11 that reads a document, an image forming unit 12 that forms an image, an automatic document feeder (ADF) 13, and a document discharge tray that stacks documents sent from the ADF 13. 14, a paper feed unit 19 including paper feed cassettes 15 to 18, and a paper discharge unit (discharge tray 20) for stacking recording paper.

  Then, when the document D is set on the document table 21 of the ADF 13 and an operation on an operation unit (not shown), for example, a press operation of a print key is performed, the uppermost document D is sent out in the direction of the arrow B1 by the rotation of the pickup roller 22. Then, by the rotation of the document conveying belt 23, the paper is fed onto the contact glass 24 fixed to the image reading unit 11, and stops there. The image of the document D placed on the contact glass 24 is read by a reading device 25 located between the image forming unit 12 and the contact glass 24. The reading device 25 includes a light source 26 that illuminates the document D on the contact glass 24, an optical system 27 that forms an image of the document, a photoelectric conversion element 28 that includes a CCD that forms an image of the document, and the like. After the image reading is completed, the document D is transported in the direction of arrow B2 by the rotation of the transport belt 23 and discharged onto the paper discharge tray 14. In this way, the document D is fed one by one onto the contact glass 24 and the document image is read by the image reading unit 11.

  On the other hand, inside the image forming unit 12, a photoconductor 30 as an image carrier is disposed. The photosensitive member 30 is driven to rotate clockwise in the drawing, and the surface is charged to a predetermined potential by the charging device 31. Further, the writing unit 32 emits a laser beam L that is light-modulated in accordance with image information read by the reading device 25, and the surface of the charged photoreceptor 30 is exposed with the laser beam L. An electrostatic latent image is formed on the surface of the body 30. When the electrostatic latent image passes through the developing device 33, the electrostatic latent image is transferred onto a sheet P, which is a recording medium fed between the photosensitive member 30 and the transfer device 34 by the opposing transfer device 34. The surface of the photoconductor 30 after the toner image is transferred is cleaned by a cleaning device 35.

  A plurality of paper feed cassettes 15 to 18 arranged at the lower part of the image forming unit 12 contain paper P, and the paper P is sent out from any one of the paper feed cassettes 15 to 18 in the direction of arrow B3. The toner image formed on the surface of the photoreceptor 30 as described above is transferred onto the surface. Next, the sheet P is passed through the fixing device 36 in the image forming unit 12 as indicated by an arrow B4, and the toner image transferred to the surface of the sheet P by the action of heat and pressure is fixed. The sheet P that has passed through the fixing device 36 is conveyed by the discharge roller pair 37, discharged to the discharge tray 20 as indicated by an arrow B5, and stacked.

  In such an image forming apparatus such as a copying machine, a sheet feeding device as shown in FIG. 4 is well known as a sheet feeding device for feeding sheets one by one from the sheet tray 1. That is, a feed roller 2 that rotates in the feeding direction of the paper P, and a separate roller 3 that is pressed against the feed roller 2 to make a pair and a driving force is applied in a direction opposite to the feeding direction via a torque limiter. Friction separation roller type (hereinafter referred to as FRR type) paper feeding devices having the above are well known.

  In the FRR type paper feeding device, the paper P is normally called by the calling roller 4 geared to the feed roller 2, and the paper P fed by the feed roller 2 reaches the grip roller 5 provided downstream in the paper conveying direction. If so, the calling roller 4 is separated from the paper surface of the paper P, and the drive of the feed roller 2 is stopped before the trailing edge of the paper P exceeds the nip of the feed roller 2. This is because if the feed roller 2 is always driven, the next sheet is also fed continuously, which hinders image formation. The feed roller 2 is provided with a one-way clutch. Even if the drive is stopped and the shaft of the feed roller 2 does not rotate, the feed roller 2 is also conveyed in the conveyance direction of the sheet P along with the conveyance of the sheet P by the grip roller 5. It is designed to follow and rotate.

  In such a sheet feeding device, the timing of the start of feeding the next sheet P is the sheet P1 forwardly fed by the sheet detecting means 6 provided downstream of the grip roller 5 where the behavior of the sheet P is stable (slip rate is reduced). Using the leading edge detection as a trigger, the driving of the calling roller 4 and the feed roller 2 is started at a predetermined timing that does not collide with the rear end of the forward-feed paper P1 and satisfies a predetermined printing speed.

  By the way, in recent years, copying machines, printers, and the like tend to keep the paper speed at the time of image formation low, aiming at high image quality. In addition, since higher printing speed is required at the same time, it is becoming possible to increase the printing speed at a low paper feeding speed by narrowing the gap between papers in the paper feeding unit.

  In the above FRR system, the separation performance of the paper P is high, and even if the positional relationship between the leading edge position of the paper P and the feed roller 2 is rough, the separation performance is not affected. It is a suitable paper feeding method for a front loading type paper feeding tray which has become mainstream in recent years.

  On the other hand, in the FRR system, however, the distance from the leading edge of the paper P stacked on the paper feeding tray 1 to the feed roller 2 is such that the leading edge is retracted due to the raising of the paper feeding tray side wall 7 and the paper guide 8 and the bottom plate 9 when the paper is small. Therefore, the leading edge of the next paper P2 taken out by friction with the pre-feed paper P1 may reach the feed roller 2 at the start of the paper feed. There were variations in the starting position.

  The timing of starting the next paper feed must be set so that the paper P starting from the position of the feed roller 2 does not collide with the rear end of the forward paper P1, and the actual paper gap is 30 mm at the maximum. In some cases, the printing speed may become larger than the interval, which hinders the increase in the printing speed.

  On the other hand, the leading edge detection means 10 is provided downstream of the feed roller 2 in the sheet conveyance direction, the sheet is conveyed to the leading edge detection means 10 at an increased speed, and the conveyance is stopped when the leading edge of the sheet is detected to determine the sheet start position. Some use this means. This compensates for the time loss that temporarily stops the conveyance, and requires a considerable speed increase. Accordingly, both the feed roller 2 and the grip roller 5 require a considerably large stepping motor, which increases the cost.

  When the feed roller 2 and the grip roller 5 are also used for driving, an electromagnetic clutch is required for the feed roller section. However, since the clutch is turned off and on more than usual, the life of the clutch is reduced and reliability is increased. It was missing.

  In view of the above-described problems, the present invention provides a sheet feeding device capable of increasing the printing speed at a low sheet feeding speed while maintaining reliability without destroying the design advantages such as the FRR position accuracy tolerance. For the purpose.

  The sheet feeding device according to claim 1 of the present invention includes a calling roller that feeds out a sheet from a stack of stacked sheets, a feed roller that feeds the fed-out sheet, and 2 when a plurality of sheets are fed out. A friction separation roller type paper feeding device having a separation feeding unit comprising a separation roller pressed against the feed roller in order to prevent conveyance of the second and subsequent sheets, wherein the separation feeding from the leading edge of the stacked paper When detecting means for detecting paper is provided between the paper and the continuous paper feeding, the detecting means detects the absence of paper when the trailing edge of the fed paper exits the separation feeding section. In the sheet feeding device that feeds out the next sheet feeding without stopping the driving of the calling roller, the detection period of the detection unit is set to about half the time during normal control.

  According to a second aspect of the present invention, in the paper feeding device of the first aspect, the detection period of the detection means is 5 milliseconds or less.

  According to a third aspect of the present invention, in the paper feeding device according to the first or second aspect, it is possible to set an expected time for the trailing edge of the paper to pass through the separation feeding unit.

  According to the fourth aspect of the present invention, in the paper feeding device according to any one of the first to third aspects, the estimated time for the trailing edge of the paper to exit the separation feeding unit can be set as a default value for each paper feeding mode. It is characterized by that.

  An image forming apparatus according to a fifth aspect of the present invention includes the paper feeding device according to any one of the first to fourth aspects.

  According to a sixth aspect of the present invention, the paper feeding device according to the first or second aspect is provided, and an operation unit capable of setting an expected time for the rear end of the paper to leave the separation feeding unit is provided.

  According to the seventh aspect of the present invention, the paper feeding device according to any one of the first to third aspects is provided, and the expected time for the trailing edge of the sheet to exit the separation feeding unit can be set as a default value for each sheet feeding mode. It has an operation part.

  The paper feeding device according to the present invention is a friction separation roller type, and when continuous feeding is performed, the detection means detects the absence of paper when the trailing edge of the paper to be fed leaves the separation feeding unit. Since the next paper feed is carried out without stopping the driving of the calling roller, and the detection means has a detection cycle of 5 milliseconds or less, the next paper feed operation is speeded up and the next paper leading edge detection accuracy is more than doubled. Further, variation between papers can be reduced.

  The best mode for carrying out the present invention will be described below with reference to the embodiments shown in the drawings.

A first embodiment of the present invention will be described.
A detection means for detecting paper is provided between the leading edge of the stacked paper and the separation feeding section, and the detection means is configured to detect when the trailing edge of the paper to be fed during continuous feeding passes through the separation feeding section. FIG. 1 shows the configuration of a sheet feeding device that feeds out the next sheet feeding without stopping the driving of the calling roller when the absence is detected. In FIG. 1, the overall configuration is the same as the conventional example of FIG. The present invention is used in an image forming apparatus such as an electrophotographic copying machine or a printer as shown in FIG.

  In the paper feeding device of FIG. 1, the leading edge detecting means 10 provided between the feed roller 2 and the grip roller 5 in the conventional example of FIG. 4 is moved from the leading edge of the paper P stacked on the bottom plate 9 to the feed roller 2. It is provided at a position between the nip part.

  The operation will be described below. The sheet P called by the calling roller 4 is in contact with the feed roller 2 rotating in the feeding direction of the sheet P and is paired with the feed roller 2 and driven in the direction opposite to the feeding direction via the torque limiter. It is sent to a separation feeding unit formed by a separation roller (separation member) 3 to which a force is applied, and only one uppermost sheet is conveyed.

  The paper P fed from the separation feeding unit passes through the grip roller 5 provided downstream in the transport direction, and the leading edge is detected by the paper detection means 6. The control means (not shown) stops the driving of the feed roller 2 before the time T1 when the trailing edge of the paper P exceeds the nip of the feed roller 2 based on the paper leading edge detection information by the paper detection means 6 and preset paper size information. . Further, the calling roller 4 is separated from the paper surface during a time T2 when the leading end of the sheet passes through the nip portion of the grip roller 5 and the trailing end of the sheet passes through the grounding portion of the calling roller 4.

  The feed roller 2 is provided with a one-way clutch. Even if the drive is stopped and the shaft of the feed roller 2 does not rotate, the feed roller 2 moves in the paper transport direction along with the paper transported by the grip roller 5. It is designed to follow and rotate. The sheet P conveyed by the grip roller 5 is aligned with a registration roller (not shown), and is discharged out of the image forming apparatus through an image forming / fixing unit.

  Next, a case where two or more sheets are printed will be described. The conveyance of the first sheet P1 is the same as described above. The timing of starting the next paper feed is triggered by the detection of the leading edge of the forward feed P1 by the paper detection means 6 provided downstream of the grip roller 5 where the behavior of the paper is stable (slip rate is reduced). Thus, the idea of starting the driving of the calling roller 4 and the feed roller 2 at a predetermined timing that does not collide with the rear end of the front sheet P1 and satisfies a predetermined printing speed is the same as that of the conventional image forming apparatus.

  Although the timing at which the next paper feed P2 does not collide with the rear end of the previous paper feed P1, if the paper detection means 6 on the transport path cannot detect the paper interval, the paper collision cannot be confirmed. Become. In the reflective sensor, it is about 8 mm. In the registration roller, the sheet is bent and the leading edge of the sheet is applied to the roller to correct the skew. Accordingly, when the trailing edge of the sheet comes off from the conveyance roller immediately before the registration roller, the trailing edge of the sheet remains by the amount of the slack, and the gap between the sheets is shortened. The amount of slack is about 2 to 6 mm.

  Further, since the leading edge of the sheet at the start of feeding does not exceed the nip portion of the feed roller 2, this is the most downstream position at the start of feeding. Therefore, the timing at which the rear end of the front paper P1 does not collide is the time when the rear end of the front paper passes through the nip portion of the feed roller 2 and the paper is transported by the amount of slack for detecting the paper. Actually, in addition to these, since a difference in slip between the previous paper P1 and the next paper P2 is taken into consideration, a slight margin is added. In the present embodiment, it is assumed that the rear end of the forward feeding has passed 15 mm after passing through the nip portion of the feed roller 2 (T3).

  When the next paper feed is started at this timing, the paper start position varies from 0 to 30 mm in the configuration of the conventional machine. Therefore, the printing unit stops at the registration portion at a paper interval of 45 mm including the 15 mm conveyance (T3). It corresponds to the interval between the papers with the time t added. On the other hand, the position of the leading edge detection means 10 is provided between the leading edge of the stacked sheets and the nip portion of the feed roller 2.

  Specifically, it is 12 mm before the nip portion of the feed roller 2. As an operation, when the leading edge detecting means 10 detects the presence of a sheet due to the leading edge of the next sheet P2 being brought out due to friction immediately before the trailing edge of the preceding sheet P1 passes through the nip portion of the feed roller 2, Then, the driving of the feed roller 2 is stopped before passing the rear end of the preceding sheet P1, and the next sheet feeding is started at the predetermined time T3 described above. Conversely, if the leading edge detection means 10 detects the absence of paper immediately before the trailing edge of the forward paper P1 passes through the nip portion of the feed roller 2, the feed roller 2 is not stopped and the calling roller 4 is postfed. The paper P2 is brought into contact with the paper surface.

  FIG. 2 is a flowchart for explaining the operation flow of the above-described sheet feeding device. As described above, driving is started (step 1), and driving of the feed roller 2 is turned on (step 2). The sheet that has been brought into contact with the calling roller 4 (step 3) and is fed from the separating and feeding sections 2 and 3 passes through the grip roller 5 provided downstream, and the leading edge of the sheet is detected by the sheet detecting means 6. When the leading edge of the sheet is detected by the sheet detecting means 6 (step 4), it is determined whether or not a predetermined time T2 has elapsed (step 5), and when the predetermined time has elapsed, the calling roller 4 is separated (step 6).

  Next, it is determined whether or not a predetermined time T4 has been reached (step 7). If so, the leading edge detection means 10 determines whether or not there is a sheet (step 8). If there is no sheet, it is determined whether or not the number of jobs has been completed (step 9), and if it has been completed, the drive is stopped (step 14). If there is a sheet in step (step 8), it is determined whether it is a predetermined time T1 (step 10). If so, the drive of the feed roller 2 is turned off (step 11). Next, it is determined whether or not the number of jobs has been completed (step 12). If the number of jobs has been completed, the driving is stopped (step 14). If not, it is determined whether or not the predetermined time T3 is reached (step 13). If the predetermined time T3 is reached, the driving of the feed roller 2 is turned on (step 2). By doing this, when the leading edge detection means 10 detects the presence of a sheet, the printing speed corresponds to the sheet interval obtained by adding the registration unit stop time t to the maximum sheet interval of 27 mm (15 mm + 12 mm).

  In the case of paper absence detection, the print speed corresponds to the paper interval obtained by adding the response time T of the calling roller 4 and the registration unit stop time t to the paper interval of 12 mm at the minimum. Further, the printing speed corresponds to the sheet interval obtained by adding the response time T of the calling roller 4 and the registration unit stop time t to the sheet interval of 30 mm between the sheet loading position and the nip portion of the feed roller 2 at the maximum.

  If the response time T of the calling roller 4 is set to a time corresponding to 3 mm conveyance, the setting of the minimum interval of 15 mm is not divided, and the printing speed at this time is between the sheets obtained by adding the registration unit stop time t to the sheet interval of 33 mm. It will be corresponding. Therefore, the paper interval is shortened by 12 mm compared with the configuration of the conventional apparatus. In this embodiment, since it is not necessary to increase the sheet feeding speed, a normal constant speed motor is sufficient as the drive motor. Further, since the next sheet is frequently taken out with a bad sheet bundle having a large variation in the inter-sheet friction coefficient, the occurrence with a normal sheet bundle is rare. Therefore, the number of driving off / on times of the feed roller 2 is reduced. For this reason, when the feed roller 2 and the grip roller 5 are also used for driving and an electromagnetic clutch is used for the feed roller portion, the life of the clutch can be reduced, so that the reliability of the system is improved.

  In the above and the following description, only the FRR sheet feeding method is described as an example, but the present invention is also effective in a friction separation roller method in which the separation roller is not reversely driven and only the second and subsequent sheets are blocked. In the above configuration, when the leading edge detecting means 10 detects the absence of paper immediately before the trailing edge of the transported paper passes through the nip portion of the feed roller 2, a predetermined time T5 has elapsed since the calling roller 4 was brought into contact with the paper surface. If the leading edge detecting means 10 does not detect the paper, the driving is stopped, the calling roller 4 is separated from the paper surface, and a paper end (paper out) display is performed on a display unit (not shown).

  In the normal control described above, if the detection cycle of the leading edge detection means 10 is, for example, every 10 milliseconds, the leading edge detection means 10 determines whether or not the paper P is present when the trailing edge of the paper P to be fed leaves the separation feeding section. The detection cycle of the leading edge detection means 10 is set to half or less, that is, 5 milliseconds or less so that it can be detected instantaneously, the start of the next sheet feeding operation is accelerated, and the accuracy when the leading edge of the next sheet is stopped by the leading edge detection means 10 is also improved. , Suppress the variation between paper.

  In addition, although it is preferable that the detection period of the front-end | tip detection means 10 is half or less than normal time, it does not have to be so. Therefore, the detection period in this specification is about half of the normal time, which may be longer or shorter than half of the normal time, as long as the desired paper conveyance control is possible. .

  That is, a calling roller for feeding out the paper from the stacked paper bundle, a feed roller for feeding the fed paper, and a feed roller for preventing the second and subsequent sheets from being fed when a plurality of papers are fed out. A friction separation roller type paper feed device having a separation feeding unit composed of a pressure-separated separate roller, and provided with detection means for detecting paper between the leading edge of the stacked paper and the separation feeding unit, and continuously feeding When the trailing edge of the paper to be fed when the paper is fed passes through the separation feeding section and the detection means detects the absence of paper, the next paper feeding is performed without stopping the driving of the calling roller. In the characteristic paper feeding device, the detection means, for example, has a detection period of about half of the normal time of 5 milliseconds or less, thereby speeding up the next paper feeding operation and doubles the detection accuracy of the leading edge of the next paper. It can reduce variations in the sheet interval. Further, since only the detection cycle of the detection means is increased, the increase in control load can be minimized.

  The paper fed from the separation feeding unit passes through the grip roller 5 provided downstream, and the paper detection means 6 detects the leading edge of the paper. The control means (not shown) predicts the time for the trailing edge of the transported paper to pass through the leading edge detecting means 10 from the leading edge detection information, the preset paper size information and the conveying speed, and reads the leading edge detecting means 10. Actually, the passage time varies depending on the slip inherent to the sheet. In some cases, the leading end of the next sheet may erroneously detect the trailing end of the advance sheet P1. In view of this, it is possible to adjust the predicted trailing edge passage time of the advance sheet P1 from an operation unit (not shown), and to make an optimum setting for the sheet to be used. That is, by making it possible to set the expected time for the trailing edge of the sheet to pass through the separation feeding unit from the operation unit, it is possible to cope with slip inherent to the sheet and to improve sheet compatibility. In addition, since the reading time of the detection means with a fine detection cycle can be set short according to the paper type, the control load is further reduced.

  Depending on the printer, a paper passing mode in which the paper type is limited to some extent may be provided. Examples of the paper passing mode include thick paper, thin paper, OHP, envelope, postcard, and label paper. For such a mode, the estimated rear end passage time may be set to a dedicated default value. By setting the default value for each paper passing mode for the expected time for the trailing edge of the paper to pass through the separation feeding unit, the troublesome setting for each paper passing mode can be eliminated.

1 is a conceptual cross-sectional view of a sheet feeding device according to a first embodiment of the present invention. 1 is a flowchart for explaining the operation flow of the sheet feeding device of FIG. Sectional view conceptually showing an image forming apparatus such as an electrophotographic copying machine or printer Conceptual sectional view of a conventional paper feeder

Explanation of symbols

1: Paper tray 2: Feed roller 3: Separation roller 4: Calling roller 5: Grip roller 6: Paper detection means 7: Paper feed tray side wall 8: Paper guide 9: Bottom plate 10: Lead detection means P, P1, P2: Paper 15-18: Paper feed cassette

Claims (7)

A call roller for feeding out the paper from the stacked paper stack, a feed roller for feeding the fed paper, and the feed roller for preventing the second and subsequent sheets from being fed when a plurality of sheets are fed out. Friction separation roller type paper feeding device having a separation feeding unit composed of a separate roller brought into pressure contact with the paper, and provided with a detecting means for detecting paper between the front end of the stacked paper and the separation feeding unit When continuously feeding, when the trailing edge of the fed paper exits the separation feeding unit and the detecting means detects the absence of paper, the next paper feeding is performed without stopping the driving of the calling roller. In the sheet feeding device that performs the feeding operation, the detection cycle of the detection unit is set to a time that is approximately half of that during normal control. 2. The paper feeding apparatus according to claim 1, wherein the detection period of the detection means is 5 milliseconds or less. 3. The paper feeding device according to claim 1, wherein an expected time for the trailing edge of the paper to leave the separation feeding unit can be set. 4. The paper feeding device according to claim 1, wherein the estimated time for the trailing edge of the paper to leave the separation feeding unit can be set as a default value for each paper passing mode. An image forming apparatus comprising the sheet feeding device according to claim 1. An image forming apparatus comprising the sheet feeding device according to claim 1, further comprising an operation unit capable of setting an expected time for the trailing edge of the sheet to leave the separation feeding unit. 4. An operation unit comprising the sheet feeding device according to claim 1, wherein an expected time for the trailing edge of the sheet to exit the separation feeding unit can be set as a default value for each sheet passing mode. Image forming apparatus.