Sheet feeding apparatus and sheet processing apparatus

Abstract: A sheet feeding apparatus has a pair of feeding roller (4) and separating roller (5,6) an inter-shaft distance changing mechanism (19,20a,20,21) for the pair of rollers, and sheet detecting means (14,15), and a sheet fed is rammed against the surface on which the feeding roller and the separating roller overlap each other to thereby correct skew feeding, and the feeding roller and the separating roller are moved away from each other to thereby feed the sheet. When the passage of the fed sheet between the feeding roller and the separating roller is detected the feeding roller and the separating roller assume a state in which sheet feeding is impossible. By the above-described operation being performed for each sheet, the correction of skew feeding and the separation of a sheet are effected by the feeding roller and the separating roller.

Description: BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a sheet feeding apparatus and a sheet processing apparatus comprising the same. In particular, this invention relates to a sheet feeding apparatus for feeding and conveying sheets (paper leaves such as originals, transfer paper, photosensitive paper, electrostatic recording paper, thermosensitive paper, printing paper, OHP sheets, envelopes and postcards) such as cards and thin paper leaves piled in various sheet-using apparatuses such as image forming apparatuses including rotary type cameras, facsimile apparatuses, printing machines, copying machines, printers, word processors, etc. and other apparatuses such as automatic original feeding apparatuses, punching machines and paper binding machines one by one to a sheet processing portion such as an image forming portion, an exposure portion and a processing portion. Related Background Art As one of the sheet separating mechanisms of sheet feeding apparatus for separating and conveying piled sheets one by one, there is known a mechanism using a pair of comb-toothed rollers. This mechanism is such that two comb-toothed rollers formed with comb-tooth-like grooves in the outer peripheral portion thereof are disposed in opposed relationship with each other substantially in parallelism to each other with the concave surfaces and convex surfaces of their grooves axially overlapping each other in non-contact with each other, and one of the two rollers is used as a feeding roller and the frictional force thereof with respect to a sheet is made great and the other roller is used as a separating roller and the frictional force thereof with respect to the sheet is made smaller than that of the feeding roller. The feeding roller is rotated in a forward feeding direction and the separating roller is rotated in a reverse feeding direction, and the sheet is fed to the nip portion between this pair of rollers. Thereby, even if a plurality of sheets are fed in overlapping relationship with one another, only the sheet which is in contact with the feeding roller is passed through the nip portion by the feeding force of the feeding roller rotated in the forward feeding direction, irrespective of the separating roller rotated in the reverse feeding direction, and the other sheets are reversely conveyed by the separating roller rotated in the reverse feeding direction and is prevented from coming into or being passed through the nip portion, whereby only that sheet which is in contact with the feeding roller is separated and conveyed. There is also known a mechanism in which when sheets are separated and conveyed one by one, a movable guide plate provided at one side or both sides of the sheet to prevent skew feeding is moved and the side portion of a skew-fed sheet is pushed against the guide plate to thereby correct skew feeding, or a mechanism in which the skew feeding of a sheet being fed is detected by the use of a sensor and as required, a conveying roller is rotatively driven by an amount corresponding to the skew feeding to thereby forcibly effect correction. Fig. 9A schematically shows the construction of a sheet feeding apparatus using a pair of comb-toothed rollers as a sheet separating mechanism. Sheets 200 are piled and set in a predetermined manner on a sheet supply tray 1. This sheet supply tray 1 is vertically controlled to a sheet supply position indicated by solid line and a standby position indicated by dots-and-dash line. An upper guide plate 2 and a lower guide plate 3 together constitute a sheet conveying path. The sheet supply tray side of the lower guide plate 3 is downwardly bent forwardly of the fore end of the sheet supply tray 1 to provide a sheet leading end ramming plate portion 3a for uniformizing the position of the leading end surface of the sheets piled on the sheet supply tray 1. A sheet feeding roller 4 picks up and feeds the sheets 200 piled and set on the sheet supply tray 1. A pair of feeding roller and separating roller 5 and 6 are disposed downstream of the sheet feeding roller 4 with respect to the direction of sheet conveyance. The feeding roller 5 is an upper roller and the separating roller 6 is a lower roller. The feeding roller 5 and the separating roller 6, as shown in the perspective view of Fig. 9B, are such that comb-toothed rollers formed with comb-tooth-like grooves in the outer peripheral portions thereof are disposed in opposed relationship with each other substantially in parallelism to each other with the concave surfaces and convex surfaces of the grooves thereof axially overlapping each other in non-contact with each other. The frictional force of the feeding roller 5 with respect to the sheet is made greater than the frictional force of the separating roller 6 with respect to the sheet. Registration rollers 16 and conveying rollers 17 are successively disposed downstream of the pair of feeding roller and separating roller 5 and 6 with respect to the direction of sheet conveyance. The sheet feeding roller 4 receives the transmission of motive power from a first motor M1 through a pulley 12, a belt 11, a two-step pulley 10, a belt 8 and a pulley 4a, and is rotatively driven in the clockwise direction of arrow which is a forward feeding direction. Of the feeding roller 5 and the separating roller 6, the feeding roller 5 receives the transmission of motive power from the first motor M1 through the pulley 12, the belt 11, the two-step pulley 10, a belt 9 and a pulley 5a, and is rotatively driven in the clockwise direction of arrow A which is the forward feeding direction. Also, the separating roller 6 receives the transmission of motive power from a second motor M2 through a pulley 13, a belt 7 and a pulley 6a, and is rotatively driven at the nip portion with the feeding roller 5 in the clockwise direction of arrow B which is a reverse feeding direction. Of the feeding roller 5 and the separating roller 6, the feeding roller 5 is disposed on a movable chassis 21 pivotally movable about the support shaft of the two-step pulley 10. The reference numeral 20 designates a shaft provided on the upper side of the movable chassis 21, and the reference character 20a denotes a cam follower provided on one end side of this shaft 20. The reference numeral 19 designates an eccentric cam, and the movable chassis 21 is counter-clockwisely biased about the support shaft of the two-step pulley 10 by a biasing spring member, not shown, so that the cam follower 20a may be normally in contact with the lower surface portion of the eccentric cam 19. The reference numeral 27 denotes an adjusting knob for rotatively operating the eccentric cam 19. The above-described adjusting knob 27, eccentric cam 19, can follower 20a, shaft 20, movable chassis 21, etc. together constitute a mechanism for changing the distance between the shafts of the feeding roller 5 and the separating roller 6. That is, by the adjusting knob 27 being turned, the cam 19 is rotated and the motion of the cam is transmitted to the feeding roller 5 through the cam follower 20a, the shaft 20 and the movable chassis 21, and the vertical position of the feeding roller 5 is displaced, and the distance between the shafts of the feeding roller 5 and the separating roller 6 can be changed more or less to thereby adjust the amount of entry or the amount of gap of the feeding roller 5 relative to the separating roller 6 in accordance with the thickness of the sheet. Thus, during non-sheet feeding, the sheet supply tray 1 is lowered to its standby position indicated by dots-and-dash line, and is downwardly spaced apart from the sheet feeding roller 4. In this state, the sheets 200 are piled and set on the sheet supply tray 1. The sheets 200 are sufficiently inserted until the leading end thereof strikes against the ramming plate portion 3a, whereby the position of the leading end surface of the sheets piled on the sheet supply tray 1 is uniformized. On the basis of a sheet feed starting signal, the sheet supply tray 1 is moved upwardly and as indicated by solid lines, the upper surface of the leading end side of the sheets 200 piled on the sheet supply tray 1 is held in contact with the lower surface of the sheet feeding roller 4. Thereupon, the uppermost sheet 22 of the piled sheets 200 is fed out (picked up) by the rotating sheet feeding roller 4, and arrives at the nip portion between the feeding roller 5 and the separating roller 6 while being guided by the upper guide plate 2 and the lower guide plate 3 and enters the nip portion. The uppermost sheet 22 which has entered the nip portion is conveyed through the nip portion by the feeding force of the feeding roller 5 rotated in the forward feeding direction, irrespective of the separating roller 6 rotated in the reverse feeding direction, because the frictional force of the feeding roller 5 with respect to the sheet is greater than that of the separating roller 6. Also, even if a plurality of sheets 22, 22', ... are overlapping fed to the nip portion by the sheet feeding roller 4, only the sheet 22 of the double-fed sheets which is in contact with the feeding roller 5 passes through the nip portion by the feeding force of the feeding roller 5 rotated in the forward feeding direction, irrespective of the separating roller 6 rotated in the reverse feeding direction. The other sheets 22', ... are reversely conveyed by the separating roller 6 rotated in the reverse feeding direction and is prevented from entering or passing through the nip portion and double feeding is thus prevented, whereby only the sheet 22 which is in contact with the feeding roller 5 is separated and conveyed. The sheet 22 separated and conveyed by the pair of feeding roller and separating roller 5 and 6 passes the registration rollers 16 and the conveying rollers 17 and is fed to a sheet processing portion such as a reading portion, not shown. The registration rollers 16 determine the conveyance timing at which the sheet 22 is conveyed to the sheet processing portion, in conformity with the instructions from a control portion (CPU), not shown, and effect the conveyance of the sheet. When sheets of different thicknesses are to be fed, the adjusting knob 27 is rotatively operated to thereby change the amount of entry or the amount of gap of the feeding roller 5 relative to the separating roller 6 at the nip portion between the feeding roller 5 and the separating roller 6, and set it to a predetermined sheet thickness. That is, the rotated position of the cam 19 connected to the adjusting knob 27 is changed, whereby the shaft 20 in contact with the cam 19 and the movable chassis 21 connected to the shaft 20 are moved to change the distance between the shafts of the feeding roller 5 and the separating roller 6, whereby said setting is effected and even sheets of different thicknesses can be conveyed while avoiding double feeding. In the case of the above-described sheet separating mechanism, the distance between the shafts of the pair of comb-toothed rollers which are the feeding roller and the separating roller is adjustable so that normal separation may be done even if the thickness of the sheet changes. However, there has been the problem that the above-mentioned adjustment must be manually effected to a proper position for each thickness of the sheets being fed and sheets of different thicknesses cannot be mixedly piled and processed. Also, movable guide plates (not shown) provided at one side or both sides of the sheets are moved to prevent the skew feeding when the sheets are separated and conveyed one by one, and correction is effected with the side portions of the sheets rammed against the guide plates to prevent skew feeding. Such a skew feeding correcting mechanism has been very cumbersome in that the positions of the guide plates must be changed when sheets of different widths are to be conveyed. Also, a mechanism for detecting the skew feeding of a sheet being conveyed by the use of a sensor, and effecting rotative driving by an amount corresponding to the skew feeding by the use of a conveying roller as required to thereby forcibly correct the skew feeding has suffered from the disadvantage that the construction is complicated and sheets become wrinkled. A sheet feeding apparatus comprising the features summarized in the pre-characterizing clause of claim 1 is known from document US-A-5 678 817. In this known sheet feeding apparatus, the control means controls the operation of the inter-shaft distance changing means such that, with the start of feeding, the inter-shaft distance is reduced or is maintained constant, such that the operation of spacing the inter-shaft distance stops when a load applied by the fed sheet to the feeding rotatable member is substantially equal to a frictional force exerted by a frictional mechanism, and such that, when the feeding of the sheet is completed, the inter-shaft distance remains as it is. Document US-A-5 443 359 discloses a sheet feeding apparatus in which a separating rotatable member is biased against the sheet and a feeding rotatable member by means of a compression device. This known sheet feeding apparatus does not comprise an inter-shaft distance changing means. Document EP-A-0 591 526 discloses a sheet feeding apparatus having a sheet separating rotatable member which can be moved in a direction vertical to the sheet feeding path. When a sheet is inserted under the sheet separating rotatable member, the sheet lifts the rotatable member by a distance corresponding to the thickness of the sheet. This known sheet feeding apparatus does not comprise an inter-shaft distance changing means. SUMMARY OF THE INVENTION It is also an object of the present invention to provide a sheet processing apparatus having such a sheet feeding apparatus is an object of the present invention to provide a sheet feeding apparatus which can automatically separate and convey sheets of different thicknesses by a simple construction and can also automatically correct the skew feeding of the sheets. According to the invention, these objects are achieved by the sheet feeding apparatus according to Claim 1 and the sheet processing apparatus according to claim 10. In the invention, the fed sheet is rammed against the opposed portion of the sheet feeding rotatable member and the sheet separating rotatable member to thereby correct skew feeding, and the sheet is fed by the operation of spacing the inter-shaft distance of said two rotatable members being performed. When the passage of the fed sheet between said two rotatable members is detected, said two rotatable members become incapable of feeding a sheet by the inter-shaft distance thereof being narrowed. The above-described operation is performed for each sheet, whereby the correction of skew feeding and the separation of a sheet are effected by the feeding roller and the separating roller. Advantageous developments of the invention are defined in the dependent claims. Thus, the sheet feeding apparatus according to the present invention can feed sheets independently of the thicknesses of the sheets, and yet can avoid double feeding even if sheets of different thicknesses are mixed, and can feed the sheets accurately one by one. Also, the end surface of a skew-fed sheet is rammed against the sheet feeding rotatable member and the sheet separating rotatable member overlapping axially thereof in non-contact with each other, whereby the correction of skew feeding can be effected. Thus, it becomes unnecessary to manually adjust thickness for each thickness of sheets, and it also becomes unnecessary to detect the posture of the sheet being conveyed and correct the skew feeding thereof in the conveyance path. As described above, the automatic separation of sheets and the correction of the skew feeding thereof can be effected by only the mechanism of the sheet feeding rotatable member and the sheet separating rotatable member and therefore, the apparatus itself becomes very compact and simple. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 schematically shows the construction of a sheet feeding apparatus according to a first embodiment of the present invention. Fig. 2 is a block diagram of a control system. Fig. 3 is a flow chart of operation. Fig. 4 is a perspective view showing the manner in which a skew-fed sheet is rammed against a feeding roller and a separating roller to thereby correct the skew feeding. Fig. 5 is a perspective view showing the vertical movement of the feeding roller. Fig. 6 schematically shows the construction of a sheet feeding apparatus according to a second embodiment of the present invention. Fig. 7 is a flow chart of operation. Fig. 8 schematically shows the construction of a sheet feeding apparatus according to a third embodiment of the present invention. Figs. 9A and 9B schematically show the construction of a sheet feeding apparatus according to the prior art. DESCRIPTION OF THE PREFERRED EMBODIMENTS <First Embodiment> (Figs. 1 to 5) Fig. 1 schematically shows the construction of a sheet feeding apparatus according to a first embodiment of the present invention. Constituent members and portions common to those of the aforedescribed sheet feeding apparatus of Figs. 9A and 9B are given common reference characters and need not be described again. In the sheet feeding apparatus according to the present embodiment, first and second sheet sensors 15 and 14 as sheet detecting means are disposed at the sheet entrance side and the sheet exit side, respectively, of the nip portion between a pair of feeding roller and separating roller 5 and 6. The second sheet sensor 14 serves to detect a sheet fed to the nip portion between the pair of feeding roller and separating roller 5 and 6 by a sheet feeding roller 4, and this sensor will hereinafter be referred to as the pre-sheet feeding sensor. The first sheet sensor 15 serves to detect a sheet which has passed through the nip portion between the pair of feeding roller and separating roller 5 and 6, and this sensor will hereinafter be referred to as the post-sheet feeding sensor. Also, in the sheet feeding apparatus according to the present embodiment, the rotation of the eccentric cam 19 of the inter-shaft distance changing mechanism 19, 20a, 20, 21 of the pair of feeding roller and separating roller 5 and 6 may be automatically effected by a stepping motor M3 instead of a manually operated adjusting knob 27. That is, the sheet detection signals of the pre-sheet feeding sensor 14 and the post-sheet feeding sensor are inputted to a control portion (hereinafter referred to as the CPU) 26. The CPU 26 controls the driving of the stepping motor M3 in conformity with the thickness of a fed sheet on the basis of the detection signal of one of the pre-sheet feeding sensor 14 and the post-sheet feeding sensor 15 and rotates the eccentric cam 19 of the inter-shaft distance changing mechanism of the pair of feeding roller and separating roller 5 and 6 to thereby change the inter-shaft distance between the feeding roller 5 and the separating roller 6 and appropriately automatically adjust the amount of entry or the amount of gap of the feeding roller 5 with respect to the separating roller 6 in accordance with the thickness of the sheet. Fig. 2 is a block diagram of the control system of the apparatus, and Fig. 3 is a flow chart of the operation of the apparatus. The signals from the pre-sheet feeding sensor 14 and the post-sheet feeding sensor 15 are controlled and calculated by the CPU 26, and an operating signal is sent to the first motor M1, the second motor M2 and the stepping motor M3, thereby giving driving to the mechanism allotted to each of them. In the operation flow of Fig. 3, the manner of piling and setting sheets 200 on the sheet supply tray 1, the upward movement of the sheet supply tray 1 and the start of the sheet feeding (pick-up) by the rotation of the sheet feeding roller 4 are the same as those in the aforedescribed sheet feeding apparatus of Figs. 13A and 13B (steps S1 and S2). A sheet 22 which has arrived at the nip portion between the feeding roller 5 and the separating roller 6 is detected by the pre-sheet feeding sensor 14 (step S3), and strikes against the nip portion between the feeding roller 5 and the separating roller 6 which are in a state in which they are in non-contact with each other and overlap each other axially thereof to thereby hamper the feeding of the sheet (set position) (step S4). Here, for example, when the sheet 22 is not aligned and is fed with the end surface of the piled sheets 200 being not uniformized, or when the sheet 22 is skew-fed or conveyed by the sheet feeding roller 4, the leading end portion of the fed sheet 22 strikes against the surface of nip between the feeding roller 5 and the separating roller 6, and this sheet 22 is pushed in feeding by the sheet feeding roller 4, whereby the end surface of the skew-fed sheet 22 is aligned on the surface of nip between the feeding roller 5 and the separating roller 6 and the posture thereof is corrected. Fig. 4 shows a state in which the end surface of this sheet 22 is aligned and the posture thereof is corrected. Thereafter, the sheet 22 corrected in skew feeding is conveyed as follows. When the sheet 22 fed to the nip portion between the pair of feeding roller and separating roller 5 and 6 by the sheet feeding roller 4 is detected by the pre-sheet feeding sensor, the CPU 26 drives the stepping motor M3 of the inter-shaft distance changing mechanism M3, 19, 20a, 20, 21 and controls the movement of the feeding roller 5 in a direction away from the separating roller 6, i.e., an upward direction U as indicated in Fig. 5 (step S6). From the set position of a state in which the feeding roller 5 and the separating roller 6 formed with comb-tooth like grooves on the outer peripheral portions thereof are opposed to each other and the concave surfaces and convex surface of the grooves overlap each other axially thereof in non-contact with each other to thereby hamper sheet feeding, the feeding roller 5 is moved upwardly to widen the spacing thereof with respect to the separating roller 6 in the inter-shaft direction thereof, and by the driving rotation of the sheet feeding roller 4 and the driving rotation of the feeding roller 5, there is provided a spacing enough to be capable of feeding a sheet 22 striking against the nip portion between the feeding roller 5 and the separating roller 6. Here, when sheets 22, 22', ... are double-fed, the uppermost sheet 22 directly contacting with the feeding roller 5 is fed by the feeding roller 5 being rotated in the forward feeding direction, and the other double-fed sheets 22', ... are reversely conveyed by the separating roller 6 being rotated in the reverse feeding direction and are prevented from entering or passing through the nip portion, whereby double feeding is prevented. Thereby, only the sheet 22 which is in contact with the feeding roller 5 is separated and conveyed. When the uppermost sheet 22 has passed through the spacing between the feeding roller 5 and the separating roller 6, the post-sheet feeding sensor 15 detects the passage of the sheet 22 (step S7), and transmits a detection signal to the CPU 26. In response to the detection signal, the CPU 26 feeds back the signal to the stepping motor M3 to thereby stop the driving of the stepping motor M3. At this time, the feeding roller 5 provides a spacing corresponding to the thickness of the sheet 22 with respect to the separating roller 6, and in addition, such a constant surplus value that in sheet feeding, no load is applied to the sheet 22 and the sheet can smoothly pass between the feeding roller 5 and the separating roller 6 (step S8). That is, the stepping motor M3 is stopped when a predetermined inter-shaft distance suited for the thickness of the sheet is provided, and the feeding roller 5 and the separating roller 6 are stopped in a predetermined position wherein only one sheet is appropriately separated and fed. That is, the eccentric cam 19 connected to the stepping motor M3, which is now stopped, stops its driving rotation (step S9), whereby the operation of the inter-shaft distance changing mechanism of the feeding roller 5 and the separating roller 6 is stopped (step S10). When the sheet 22 detected by the post-sheet feeding sensor 15 has its arrival at and conveyance by the registration rollers 16 detected by the CPU 26 provided with calculating means for detecting the timing at which the sheet 22 is fed to the registration rollers 16, from the conveyance speed of the sheet 22 and the distance between the post-sheet feeding sensor 15 and the registration rollers 16 on the basis of the time until the sheet 22 arrives at the registration rollers 16 or the preset pulse number of the motor, the driving rotation of the sheet feeding roller 4 and the feeding roller 5 is stopped to avoid the succeeding feeding of the next sheets 22', ... (step S13). Thereafter, the fed sheet 22 has its conveyance timing determined by the registration rollers 16, and is conveyed to the conveying rollers 17. Since the sheet 22 is now conveyed by the registration rollers 16, the sheet feeding roller 4 and the feeding roller 5 have their driving released and become idly rotated (step S14). Thereafter, when the post-sheet feeding sensor 15 detects that the fed sheet 22 has passed between the feeding roller 5 and the separating roller 6 (step S16), the driving of the stepping motor M3 of the inter-shaft distance changing mechanism is resumed. The driving of the stepping motor M3 at this time is in a direction to move the feeding roller 5 downwardly as shown in Fig. 5 (step S17). Thereby, the feeding roller 5 and the separating roller 6 approach each other radially thereof in non-contact with each other, and return to the state before feeding in which they overlap each other and hamper sheet feeding, i.e., the set position (step S18). Then, on the basis of the driving of the stepping motor M3 being stopped and the operation of the inter-shaft distance changing mechanism being stopped, the operation of the feeding roller 5 and the separating roller 6 approaching each other radially thereof in non-contact with each other is also stopped, and the state before sheet feeding is brought about (step S20). Even if at this time, sheets of different thicknesses are mixed and fed, the feeding roller 5 and the separating roller 6 are moved as described above and the passage of each sheet 22 is detected by the sheet detecting sensor and therefore, the sheet can be automatically separated and fed independently of the thickness thereof. Next, when it is detected by the pre-sheet feeding sensor 14 that the second sheet 22' has been fed (step S21), the sheet feeding roller 4 and the feeding roller 5 start their driving rotation (step S22), and start the feeding of the second sheet 22' (steps S1 and S3). The above-described series of operations are performed for each sheet 22. <Second Embodiment> (Figs. 6 and 7) Fig. 6 schematically shows the construction of a sheet feeding apparatus according to a second embodiment of the present invention. The difference of the second embodiment from the first embodiment is that in the first embodiment, sheet feeding is effected by the sheet feeding roller 4, whereas in the present embodiment, the surface direction of the sheets 200 is supported by a sliding type sheet guide 29 slidable in the directions of arrows E and F and the upper guide plate 2, and the fed side end surface of the sheet is supported by a sheet leading end ramming plate portion 3a which is the extension of the lower guide plate 3, and sheet feeding is effected by the aforementioned sliding type sheet guide 29. Also, the sheets 200 ram against the feeding roller 5 and the separating roller 6 from above and therefore, the pre-sheet feeding sensor 14 becomes unnecessary, and an operation similar to that of the first embodiment becomes possible by only the post-sheet feeding sensor 15. Describing the operation of the present embodiment, the sheets 200 set at a predetermined position during sheet feeding are fed in the direction of arrow E to the sheet feeding portion (nip portion) in which the feeding roller 5 and the separating roller 6 overlap each other by the sliding type sheet guide 29 while ramming their end surface against the sheet leading end ramming plate portion 3a. Near the sheet feeding portion, the sheets 200 slide to the sheet feeding portion along the sheet leading end ramming plate portion 3a of a tapered shape from gravity, and strike against the overlapping portion of the feeding roller 5 and the separating roller 6 and are corrected in skew-feeding. At this time, the sliding type sheet guide 29 holds the posture of the sheets 200 by the upper guide plate 2, and the feeding roller 5 and the separating roller 6 against which the sheets 200 strike are in a state in which their driving rotation has been stopped. Next, the feeding roller 5 and the separating roller 6 start their driving rotation after a sufficient time has passed from after the sheets 200 have been set at a predetermined position and the sliding type sheet guide 29 has been moved. Thereafter, the feeding roller 5 is moved in a direction to space its inter-shaft distance from the separating roller 6. By the above-described operation, an operation similar to that of the first embodiment is performed after the feeding of the sheets 200 has been started. The flow chart of the above-described operation is shown in Fig. 7. <Third Embodiment> (Fig. 8) Fig. 8 schematically shows the construction of a sheet feeding apparatus according to a third embodiment of the present invention. The difference of the present embodiment from the first embodiment is that in the first embodiment, the feeding roller 5 is vertically movable, whereas in the present embodiment, the separating roller 6 is vertically movable and the feeding roller 5 is in a fixed position. The separating roller 6 is held on a movable chassis 23 coaxial with the support shaft 24 of the pulley 13 rotatively driven by the second motor M2 (not shown) and pivotally movable. The separating roller 6 receives a driving force through the pulley 13, the belt 7 and the pulley 6a and is rotated thereby. The reference numeral 25 designates a gear coaxial with the shaft 24 and provided integrally with the movable chassis 23. The reference numeral 26 denotes a worm gear meshing with this gear 25. This worm gear 26 is rotation-controlled by the stepping motor M3. By the stepping motor M3 being rotated forwardly and reversely, the gear 25, i.e., the movable chassis 23, is pivotally moved in a clockwise direction C or a counter-clockwise direction D about the shaft 24 by the worm gear 26. By the movable chassis 23 being pivotally moved in the clockwise direction C, the separating roller 6 is moved in a direction to space the distance from the feeding roller 5, i.e., downwardly. When the post-sheet feeding sensor 15 detects that a sheet 22 has passed between the feeding roller 5 and the separating roller 6 spaced apart from each other, the movable chassis 23 is pivotally moved in the counter-clockwise direction D. Thereby, the separating roller 6 is moved in an upward direction which is a direction in which it overlaps the feeding roller 5 axially thereof in non-contact with the latter, and stops its upward movement at a position before sheet feeding. In the meantime, the separating roller 6 receives a driving force through the pulley 13, the belt 7 and the pulley 6a and is rotated thereby. These operations, as in the first embodiment, are performed for each sheet being fed. 1) The feeding roller and the separating roller need not be comb-toothed rollers. Also, one or both of them may be a rotatable belt. 2) The inter-shaft distance changing mechanism of the feeding roller and the separating roller can be made into a construction in which both of the feeding roller and the separating roller are moved in a direction to widen the inter-shaft distance and a direction to narrow the inter-shaft distance. 3) The present invention is not restricted to an apparatus of the upper side separating and feeding type in which feeding is effected in succession from the upper one of the piled sheets, but can also be applied to an apparatus of the lower side separating and feeding type in which feeding is effected in succession from the lower one of the piled sheets. 4) The sheet feeding apparatus of the present invention can be widely used as an apparatus for conveying sheets such as cards and thin paper leaves piled in an image forming apparatus such as a rotary type camera, a facsimile apparatus, a printing machine, a copying machine, a printer or a word processor, or other various sheet-using apparatuses such as an automatic original feeding apparatus, a punching machine and a paper binding machine one by one to a sheet processing portion such as an image forming portion, an exposure portion or a processing portion. As described above, according to the present invention, there can be provided a sheet feeding apparatus which can automatically separate and convey sheets of different thicknesses by a simple construction and can also automatically correct the skew feeding of the sheets.

Claims: A sheet feeding apparatus comprising a sheet feeding rotatable member (5) rotated in a forward feeding direction and a sheet separating rotatable member (6) rotated in a reverse feeding direction, said sheet feeding rotatable member (5) and said sheet separating rotatable member (6) being disposed in opposed relationship with each other and rotated at the opposed portion, and separating and conveying sheets (200) one by one between both said rotatable members (5, 6); inter-shaft distance changing means (19 to 21, 20a, M3; 23 to 26, M3) for at least one of both said rotatable members (5, 6) to change the inter-shaft distance thereof relative to the other rotatable member; first sheet detecting means (15) provided near both said rotatable members (5, 6) for detecting the passage of the sheets (200); and control means (26) for controlling the operation of said inter-shaft distance changing means (19 to 21, 20a, M3; 23 to 26, M3) characterized in that said control means (26) controls so with the start of feeding, at least one of both said rotatable members (5, 6) may start the operation of spacing its inter-shaft distance relative to the other rotatable member so as to increase the inter-shaft distance, and so that the operation of spacing said inter-shaft distance may be stopped, when a sheet (22) is detected by said first sheet detecting means (15) or after the operation of spacing said inter-shaft distance by a predetermined amount has been performed form the point of time at which a sheet (22) has been detected by said first sheet detecting means (15), and so that when the feeding of said sheet (22) is completed, at least on of both said rotatable members (5, 6) may bring the inter-shaft distance thereof relative to the other rotatable member close to a position in which feeding is impossible. A sheet feeding apparatus according to claim 1, wherein said sheet feeding rotatable member (5) and said sheet separating rotatable member (6) are rollers, and the rotary shafts of said rollers are substantially parallel to each other and said rollers are formed with comb-tooth-like grooves on the outer peripheral portions thereof, and have a shape in which the concave surfaces and convex surfaces of the grooves are in non-contact with each other and can overlap each other axially thereof. A sheet feeding apparatus according to claim 1 or 2, wherein said sheet feeding rotatable member (5) and said sheet separating rotatable member (6) are in a state in which they hamper the feeding of the sheets (200) before the feeding of the sheets (200) is started or after the inter-shaft distance has been brought close. A sheet feeding apparatus according to any one of claims 1 to 3 wherein said first detecting means (15) is provided downstream of the most proximate portions of both said rotatable members (5, 6) with respect to the direction of sheet conveyance and wherein said sheet detecting means (15) detects the passage of a sheet (22) through the most proximate portions of both said rotatable members (5, 6). A sheet feeding apparatus according to claim 1, wherein a second sheet detecting means (14) is disposed near the sheet entrance of both said rotatable members (5, 6); wherein said first sheet detecting means (15) is disposed near the sheet exit of both said rotatable members (5, 6); wherein said inter-shaft distance changing means (19 to 21, 20a, M3; 23 to 26, M3) moves the rotary shafts of both said rotatable members (5, 6) toward and away from each other to thereby change the distance between both said rotatable members (5, 6); and wherein said control means (26) controls said inter-shaft distance changing means so that the rotary shafts of said rotatable members (5, 6) may be moved in a direction to widen the spacing therebetween by the sheet detection of said second sheet detecting means (14), and then the movement of the rotary shafts of both said rotatable members (5, 6) may be stopped at a predetermined position by the sheet detection of said first sheet detecting means (15). A sheet feeding apparatus according to claim 5, wherein said control means (26) controls so that when said first sheet detecting means (15) has come to detect no sheet (22) after it has detected the sheet, the rotary shafts of both said rotatable members (5, 6) may be moved in a direction to narrow the spacing therebetween, and when the spacing has reached a set spacing, the movement my be stopped. A sheet feeding apparatus according to claim 5 or 6, wherein said control means (26) performs the operation of controlling said spacing each time a sheet (22) is fed. A sheet feeding apparatus according to any one of claims 5 to 7, wherein said feeding rotatable member (5) has large-diametered portions and small-diametered portions alternately in the axial direction of the rotary shaft thereof, said separating rotatable member (6) has large-diametered portions and small-diametered portions alternately in the axial direction of the rotary shaft thereof, and both said rotatable members (5, 6) are disposed so that the large-diametered portions and the small-diametered portions thereof may be opposed to each other. A sheet feeding apparatus according to claim 8, wherein both said rotatable members (5, 6) are disposed with the large-diametered portions thereof overlapping each other so that the large-diametered portions of one of both said rotatable members (5, 6) may come into the small-diametered portions of the other rotatable member. A sheet processing apparatus comprising the sheet feeding apparatus according to any one of claims 1 to 9 and image forming means for imaging an image on the sheet fed by said sheet feeding apparatus.

Inventors: KOMURO HIROSHI, OKITSU KATSUHIKO, SASHIDA MINORU, SUGIYAMA KAZUHIDE, KOMURO, HIROSHI, OKITSU, KATSUHIKO, SASHIDA, MINORU, SUGIYAMA, KAZUHIDE, Komuro, Hiroshi c/o Canon Denshi K. K., Okitsu, Katsuhiko c/o Canon Denshi K. K., Sashida, Minoru c/o Canon Denshi K. K., Sugiyama, Kazuhide c/o Canon Denshi K. K.
Applicants: CANON DENSHI KK, CANON DENSHI KABUSHIKI KAISHA
Application year: 1999
Main classification: B65H3
IPC codes: B65H3, B65H9