Automatic paper feed apparatus

Abstract: An apparatus (50) comprising, sheet stacking means (55) for stacking and storing a plurality of sheets (54), rotary paper feed means (53A,53B) brought into contact with the sheet to feed it, biasing means (56) for biasing the sheets stacked toward the rotary paper feed means (53A,53B), separating means, having an inclined surface (57) for bringing the sheet fed into contact with the inclined surface (57) to separate only one sheet and supply the separated one sheet to the downstream side, and maintaining means (64), brought into contact with the uppermost surface for maintaining the uppermost sheet at a position corresponding to the inclined surface (57) against a biasing force of the biasing means (56).

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an automatic sheet feeding apparatus and an image recording apparatus comprising the automatic sheet feeding apparatus. Related Background Art An image recording apparatus such as a printer, a copying machine, or a facsimile machine is arranged to record an image on a recording sheet (recording medium) such as a paper sheet or a plastic thin sheet by selectively driving energy generation elements of a recording head. Recording apparatuses can be classified into ink-jet, wire-dot, thermal, laser beam recording systems in accordance with recording schemes. Recording sheets used in these recording apparatuses are classified into normal paper, thick paper such as a postcard or envelope, and a special sheet such as a plastic thin sheet. Sheets can be manually fed or automatically fed by an automatic sheet feeding apparatus. An automatic sheet feeding apparatus usually comprises a drive unit for rotating a sheet feeding roller to feed out a recording sheet and a sheet stacking means for stacking the recording sheets. The drive unit is driven in synchronism with a convey system in the recording apparatus, thereby feeding the recording sheets one by one. The automatic sheet feeding apparatuses are also classified into a built-in sheet feeding apparatus and a detachable sheet feeding apparatus. An automatic sheet feeding apparatus comprises sheet feeding rollers rotated together with a drive shaft, a sheet stacking plate on which a plurality of recording sheets can be stacked, a spring biasing means for biasing the sheet stacking plate toward the sheet feeding rollers to urge the recording sheet to the sheet feeding rollers, and a separating means consisting of an ascending surface formed in front of the paper feed direction of the sheet feeding rollers. In an automatic sheet feeding apparatus using the above separating means, the stacked sheets must always be kept in tight contact with the sheet feeding rollers unlike an apparatus using separation grippers due to the following reason. When a contact force is short or becomes absent, the second and subsequent sheets float and ride on the ascending surface, and it is difficult to separate the sheets one by one. In addition, the second and subsequent sheets tend to be moved together with the sheet fed by the convey means in the recording apparatus, thereby causing multiple or double sheet feeding. On the other hand, in order to properly feed each recording sheet by a convey roller in the recording apparatus, a frictional resistance (brake) must be eliminatedor reduced upon stopping of the sheet feeding rollers. In a conventional automatic sheet feeding apparatus of this type, in order to satisfy the above conditions, a one-way clutch is arranged in a driving force transmission mechanism (transmission mechanism) for the sheet feeding rollers. Prior arts which disclose this technique are exemplified by JP-A-54138714 and JP-A-6697877. In an arrangement including this one-way clutch, the structure becomes complicated and bulky at high cost. An automatic sheet feeding apparatus comprising the features of the preamble of claim 1 is known from document Patent Abstracts of Japan, vol. 12, no 251 (M-718) (3098) 15 July 1988 & JP-A-63 037 044. This known automatic sheet feeding apparatus comprises a maintaining means for maintaining the uppermost sheet at a position separated from the rotary sheet feeding means when said rotary sheet feeding means does not feed the sheet, wherein the maintaining means comprises a free roller. The free roller of the maintaining means of the known automatic sheet feeding apparatus is rotatably mounted on the drive shaft of the rotary sheet feeding means. The biasing means biases the sheets stacked on the sheet stacking means towards said rotary sheet feeding means so that the biasing force generates a load acting on the at least one free roller while said rotary sheet feeding means does not feed the sheet. This load is transferred to the drive shaft of the rotary sheet feeding means and results in a certain resistance against rotation of the drive shaft, said resistance being greatest when the drive shaft is started to rotate. This resistance requires a comparatively powerful driving source and associated elements such as a motor and a spring clutch. SUMMARY OF THE INVENTION It is an object of the invention to improve the automatic sheet feeding apparatus according to the preamble of claim 1 such that the drive system of the rotary sheet feeding means can be made compact and simple by reducing the load on the drive shaft. Further, an image recording apparatus comprising the improved automatic sheet feeding apparatus shall be provided. This object is achieved by the automatic sheet feeding apparatus according to claim 1 and by the image-recording apparatus according to claim 10. According to the invention, the free roller of the automatic sheet feeding apparatus is rotatably mounted on a shaft which is disposed parallel to and upstream in the sheet feeding direction of the drive shaft of the rotary sheet feeding means. This results in that the shaft of the rotary sheet feeding means is not loaded by the biasing force of the biasing means as long as the rotary sheet feeding means does not feed the sheet. Therefore, the resistance against rotation of the shaft is smaller and the drive system can be made compact and simple with low power consumption. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a partially cutaway front view of an automatic sheet feeding apparatus according to the first embodiment of the present invention; Fig. 2 is a sectional view of the automatic sheet feeding apparatus in Fig. 1 along the line II - II thereof; Fig. 3 is a sectional view showing a state wherein the automatic sheet feeding apparatus shown in Fig. 1 is incorporated into an image recording apparatus; Fig. 4 is a plan view of the state of Fig. 3; Fig. 5 is a longitudinal sectional view showing a detailed structure of a sheet feeding roller and a free roller shown in Fig. 1; Fig. 6 is a sectional view of the structure along the line VI - VI in Fig. 5; Fig. 7 is a sectional view of the structure along the line VII - VII in Fig. 5; Fig. 8 is a perspective view illustrating a state wherein the recording apparatus shown in Fig. 3 is laterally located; Fig. 9 is a longitudinal sectional view showing a detailed structure of a one-rotation spring clutch shown in Fig. 1; Fig. 10 is a front view of a control ring and a control lever in Fig. 9; Fig. 11 is a side view of the structure when viewed from the line XI in Fig. 10; Fig. 12 is a side view of the control ring when viewed from the line XII in Fig. 10; Fig. 13 is a side view of the control ring when viewed from the line XIII in Fig. 10; Fig. 14 is a rear view showing the automatic sheet feeding apparatus on the recording apparatus in Fig. 3; Fig. 15 is a perspective view of the automatic sheet feeding apparatus of Fig. 1 when viewed from the mounting surface of the recording apparatus; Fig. 16 is a sectional view showing the main part of a locked state of a connecting portion between the recording apparatus and the automatic sheet feeding apparatus shown in Fig. 3; Fig. 17 is a sectional view showing the main part of a lock release state in Fig. 16; Fig. 18 is a plan view of a sheet stacking plate and a sheet guide in the automatic sheet feeding apparatus shown in Fig. 1; Fig. 19 is a sectional view of the structure along the line XIX - XIX in Fig. 18; Fig. 20 is a partially cutaway front view of an automatic sheet feeding apparatus according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the accompaying drawings. The first embodiment will be described with reference to Figs. 1 to 19. Fig. 1 is a front view of an automatic sheet feeding apparatus according to the first embodiment of the present invention when viewed from the line I - I of Fig. 2. Fig. 2 is a sectional view of the apparatus along the line II - II in Fig. 1, Fig. 3 is a sectional view comprising the automatic sheet feeding apparatus shown in Fig. 1 of an image recording apparatus, and Fig. 4 is a plan view of the image recording apparatus shown in Fig. 3. Referring to Figs. 1 to 4, a frame 51 of an automatic sheet feeding apparatus 50 is a single unit. A gear box portion 51A is formed in the left portion of the frame 51, a stacking plate support portion 51B is formed at the central portion of the frame 51, and a cover portion 51C is formed in the right portion of the frame 51. A drive shaft 52 passes above the sheet stacking plate support portion 51b, and both end portions of the drive shaft 52 are rotatably supported by the gear box portion 51A and the cover portion 51C. Two sheet feeding rollers 53A and 53B are mounted on the drive shaft 52 so as to be rotated together with. In the illustrated structure, the sheet feeding roller 53A is mounted to be movable along the shaft 52 in a direction of sheet width, while the roller 53B is fixed on the shaft 52. A sheet stacking plate 55 capable of stacking a plurality of recording sheets (cut sheets) 54 can be vertically movably held on the sheet stacking plate support portion 51B. The sheet stacking plate 55 is biased by an urging spring 56 (Fig. 2) mounted between the frame 51 and the sheet stacking plate 55, so that the sheet stacking plate 55 is urged toward the sheet feeding rollers 53A and 53B. Therefore, the recording sheets 54 stacked on the sheet stacking plate 55 are always biased by the spring 56 toward the sheet feeding rollers 53A and 53B. When sheets having different sizes are used as the recording sheets 54, or when sheets having the same size are fed in a widthwise or longitudinal direction, the position of the sheet feeding roller 53A is adjusted together with a sheet guide 65 (to be described later). A separating means 57 consisting of an ascending surface on which the uppermost recording sheet 54 can ride is formed downstream of the sheet feeding rollers 53A and 53B in the sheet feeding direction, or at a position adjacent to the front end of the sheet stacking plate 55. In this embodiment, the separating means 57 is formed in part of the frame 51. Each of the sheet feeding rollers 53A and 53B comprises a semi-circular roller having a semi-circular shape (or D shape) having equi- and nonequi-radial surfaces. The equi-radial sectional surface is a circumferential surface brought into contact with the recording sheet 54 to feed it, while the nonequi-radial sectional surface is a circumferential surface kept separated from the recording sheet 54 within a predetermined angular interval of a paper feed wait position (reference or initial position) as the central position. A support shaft 301 parallel to the drive shaft 52 is arranged upstream in the paper feed direction of the drive shaft 52. Both end portions of the support shaft 301 are held by the gear box portion 51A and the cover portion 51C. The support shaft 301 is mounted to be normally stationary. Free rollers 302A and 302B adjacent to the sheet feeding rollers 53A and 53B are rotatably supported on the support shaft 301 at positions respectively corresponding to the rollers 53A and 53B. The free roller 302A is mounted to be moved together with the corresponding sheet feeding rollers 53A along the shaft 301 in the sheet widthwise direction. The free roller 302B is rotatable with respect to the shaft 301, but is stationary on the shaft 301 along the sheet widthwise direction. Fig. 5 is a horizontal sectional view of the sheet feeding roller 53A on the drive shaft 52 and the free roller 302A on the support shaft 301, Fig. 6 is a sectional view of the above structure along the line VI-VI of Fig. 5, and Fig. 7 is an end view of the structure along the line VII-VII of Fig. 5. Referring to Figs. 5 to 7, the sheet feeding roller 53A comprises a boss portion 58 made of a hard plastic material or the like and fitted on the drive shaft 52, and a rubber layer 59 fixed on the outer surface of the boss portion 58 by an adhesive or the like. The circumferential surface of the sheet feeding roller which includes the rubber layer 59 constitutes the equi-radial sectional surface for generating a feeding force and the nonequi-radial sectional surface which is kept separated from the recording sheet 54, as described above. The sectional shape of the rubber layer 59 is a semi-circular or D shape obtained by partially cutting an arc by a chord. Axial projections 60 formed on the inner circumferential surface of the boss portion 58 are engaged with and fitted in axial grooves 61 formed in the drive shaft 52, so that the boss portion 58 can be rotated together with the drive shaft 52 and can be slid within a predetermined axial range. A cylindrical portion 62 having a smaller diameter than that of the sheet feeding roller and coaxially extending with the drive shaft 52 is formed in the boss portion 58. A circumferential groove 63 with which the sheet guide 65 is vertically engaged is formed integrally in the cylindrical portion 62. The free roller 302A is adjacent to the sheet feeding roller 53A and is rotatably supported on the support shaft 301 which is parallel to the drive shaft 52. An axially extending boss portion 303 is formed on the free roller 302A. A circumferential removal preventive groove 305 slidably engaged with a vertical notch 304 of the sheet guide 65 is formed on the boss portion 303. The sheet guide 65 is arranged to guide the side edges of a recording sheet 54 on a sheet stacking plate 55 and is mounted to be adjusted with respect to the sheet stacking plate 55 in the sheet widthwise direction. The sheet feeding roller 53A and the free rotation roller 302A are mounted to be simultaneously moved in the sheet widthwise direction through the sheet guide 65 so as to maintain a predetermined positional relationship. The positions and outer diameters of the free rotation rollers 302A and 302B are determined so that the rollers 302A and 302B are slightly separated from the recording sheet 54 farther than the sheet feeding surfaces (equi-radial sectional surfaces) of the sheet feeding rollers 53A and 53B, i.e., the surfaces of the rollers 302A and 302B are slightly retracted from the sheet surfaces, but are closer to the recording sheet 54 than the notches (nonequi-radial sectional surfaces) of the sheet feeding rollers, i.e., the surfaces of the rollers 302A and 302B slightly extend from the sheet surfaces. The free rollers 302A and 302B are made of a material such as a hard plastic material having a relatively small frictional coefficient. The sheet guide 65 is mounted to be slidable within a predetermined range of the sheet width with respect to the sheet stacking plate 55. A distal end portion 113 of the sheet guide 65 is engaged with the circumferential groove 63 (Fig. 23) of the sheet feeding roller 53A, and the almost vertical notch 304 formed in the sheet guide 65 is slidably engaged with the circumferential groove 305 of the free rotation roller 302A. For this reason, when the sheet guide 65 is moved so as to adjust the paper width, the sheet feeding roller 53A and the free roller 302A adjacent thereto are simultaneously moved to predetermined positions, respectively. The right sheet feeding roller 53B and the right free rotation roller 302B in Fig. 4 are mounted on the drive shaft 52 and on the support shaft 301 at predetermined positions, so that they constitute an almost symmetrical arrangement with the sheet feeding roller 53A and the free rotation roller 302A. Since the sheet feeding roller 53B is fixed on the drive shaft 52 and the free roller 302B is rotatable on the support shaft 301 but is stationary along the axial direction, the circumferential grooves 63 and 305 are omitted, and portions corresponding to the boss portions 58 and 303 are removed. A function corresponding to the sheet guide 65 can be replaced with the inner wall surface of the cover portion 51C of the frame 51. The right sheet feeding roller 53B and the right free roler 302B may be moved, and a corresponding right sheet guide 65 or an equivalent member is arranged to obtain a symmetrical arrangement. As will be described with reference to Figs. 18 and 19, the sheet guide 65 is slidable along the sheet stacking plate 55 within a predetermined range of the sheet width. Since the sheet guide 65 can be moved along directions (i.e., vertical direction in the illustration) to come close to or to be separated from the sheet feeding roller 53 together with the sheet stacking plate 55, the distal end portion 113 engaged with the groove 63 is vertically formed to be optimally engaged with the groove 63 regardless of the vertical position (i.e., the stacking height of the recording sheets 54) of the sheet stacking plate 55. The automatic sheet feeding apparatus 50 of this embodiment is detachably mounted as a unit on an image recording unit 10 to form the image recording apparatus of Fig. 3. The automatic sheet feeding apparatus 50 is synchronously driven by a sheet convey roller by using a drive source (e.g., a motor for the sheet convey means drive source) of the recording unit 10. The recording unit 10 is vertically set, as shown in Fig. 3, when the automatic sheet fedding apparatus 50 is mounted thereon. When the recording unit is singly used, as the image recording apparatus, i.e., when the automatic sheet feeding apparatus 50 is not mounted on the recording unit, the recording apparatus can be horizontally set, as shown in Fig. 8. A schematic arrangement of the recording unit 10 will be described with reference to Figs. 3 and 8. Referring to Figs. 3 and 8, a sheet insertion port 11 and a sheet discharge port 12 are formed in the upper surface (i.e., the front surface in a upright state) of the recording unit 10. A recording sheet inserted into the sheet insertion port 11 is brought into tight contact with the circumferential surface of a platen roller 14 which also serves as a sheet convey roller and is fed in a direction of an arrow A along a substantially U-shaped recording sheet convey path. An image is recorded on the recording sheet while the recording sheet passes through a recording unit facing a recording head 15. The recording sheet is then discharged upward (the front surface in the upright state) from the sheet discharge port 12. A paper feed tray 16 is pivotally supported on the upper surface of the recording unit 10 so as to be closed or opened. When the recording apparatus is used (i.e., in the recording mode), the paper feed tray 16 is open and serves as a paper feed tray. However, when the recording apparatus is not used (storage state), the paper feed tray 16 is set in the closed position, as indicated by the solid line in Fig. 3. In this case, the paper feed tray 16 serves as a cover 16 for protecting the sheet insertion port 11, the sheet discharge port 12, and the upper surface of the recording apparatus which has switches and display elements. Refering to Fig. 3, the recording head 15 is mounted on a carriage 22 reciprocated along the platen roller 14 and parallel guide shafts 21. The illustrated recording head 15 is an ink-jet head incorporating an ink tank. A sheet press member 23 for pressing the recording sheet on the platen roller 14 is arranged in the upstream of the recording head 15 along the feed direction. The sheet press member 23 is brought into tight contact with the outer surface of the platen roller 14 by a spring (not shown). An urging force of the sheet press member 23 can be released upon operation of a lever. Spur gears 26 and paper discharge rollers 27 which assist discharge of the recording sheet are disposed at the sheet discharge port 12. Fig. 14 is a view showing a bottom surface (i.e., the rear surface to which the automatic sheet feeding apparatus 50 is mounted when the recording apparatus 10 is set in the upright state). A second sheet insertion port 28 is formed in the rear surface of the recording apparatus 10. A second recording sheet convey path almost linearly extending from the insertion port 28 to the sheet discharge port 12 through the recording unit located between the recording head 15 and the convey roller (platen roller) 14 extends in an almost horizontal direction. The second recording sheet convey path is used when the recording unit 10 is set in the upright state. Since the second recording sheet convey path is not curved, a rigid recording sheet such as a thick sheet (e.g., a postcard or envelope) or a special sheet (e.g., a plastic sheet) can be easily fed. In the upright state, as shown in Figs. 3 and 14, the automatic sheet feeding apparatus 50 is detachably mounted on the recording unit 10, and the recording sheets 54 are fed from the sheet insertion port 28 of the rear surface (upright state) one by one. The automatic sheet feeding apparatus 50 is positioned to feed the recording sheet form the inlet (sheet insertion port) 28 to the linear convey path and is detachably mounted on the rear surface (i.e., the opening surface of the inlet 28) of the recording unit 10. When the automatic sheet feeding apparatus 50 is mounted on the recording unit 10, the paper feed tray 16 is set at an open position, as indicated by the alternate long and two short dashed line in Fig. 3, and is used as a paper discharge tray. The recording sheet 54 fed from the automatic sheet feeding apparatus 50 through the sheet insertion port 28 is fed and gripped between the convey roller 14 and the sheet press member 23 and is fed to the paper feed position (normally, a regist position) by the convey roller 14 and the sheet feeding roller 53 synchronously rotated with the convey roller 14. When the semi-circular sheet feeding roller 53 returns to the initial position and the sheet feed force is released, a recording operation is started. An image is recorded on the recording sheet 54 while the recording sheet 54 is being fed by the convey roller 14. The recording sheet 54 fed by the convey roller 14 is fed between the paper discharge rollers 27 and the spur gears 26. Thereafter, the recording sheet is fed by the convey roller 14 and the paper discharge rollers 27 synchronously driven with the convey roller 14. The discharge rollers 27 is synchronously driven at almost the same peripheral speed as that of the convey roller 14. In the subsequent recording operation, the recording sheet 54 is conveyed by the convey roller 14 and the paper discharge rollers 27. The recorded sheet 54 is discharged onto the paper feed tray 16 which also serves as the paper discharge tray. When the recording sheet 54 is discharged or fed by the convey roller 14 or both the convey roller and paper discharge rollers 27, the recording sheet 54 is kept in tight contact with only the free rotation roller 302 even in the presence of the recording sheet 54 in the automatic sheet feeding apparatus 50. In this state, since the recording sheet 54 is kept separated from the sheet feeding roller 53, the recording sheet 54 can almost be freely pulled without any resistance, thereby eliminating the brake function at the time of recording sheet feeding. Multiple sheet feed (double feed) can also be prevented. In the state wherein the automatic sheet feeding apparatus 50 is mounted on the recording unit 10, a gear (i.e., an output gear from the recording unit 10) fixed on the shaft of the sheet convey roller 14 is meshed with an input gear 72 arranged in the gear box 51A of the automatic sheet feeding apparatus 50 (see Figs. 1 and 3). Therefore, the input gear 72 is driven in synchronism with sheet feeding of the recording unit 10. Rotation of the input gear 72 is transmitted to a gear (cluth gear) 74 on the drive shaft 52 through a gear 73. A one-rotation spring clutch 75 is arranged between the gear 74 and the drive shaft 52. This one-rotation spring clutch 75 is operated as follows. Upon slight reverse rotation (i.e., rotation in a direction opposite to the feed direction) of the sheet convey roller (platen roller) 14 performed on the basis of a paper feed signal, the one-rotation spring clutch 75 is rotated in the reverse direction at the reference or initial position where the sheet feeding roller 53 is kept separated from the recording sheet 54. By this reverse rotation, engagement with a control means such as a control lever (hook) for preventing recording rotation is released, so that the spring clutch 75 is switched from an OFF state to an ON state. Even if the sheet feeding roller 53 is kept separated from the recording sheet 54, the free roller 302 having a shape of a true circle is kept in contact with the recording sheet 54. In a clutch ON state, upon rotation of the sheet feeding roller (D-shaped or semi-circular roller) 53 in synchronism with rotation of the convey roller (platen roller) 14 by a predetermined amount in the recording direction, only one recording sheet 54 is separated from the remaining sheets and is fed to the position exceeding a sheet receiving portion of the platen roller 14. When the roller 53 returns to the initial position (i.e., a position where a gap is formed between the sheet feeding roller 53 and the recording sheet 54), the control means is locked at a position for preventing rotation in the recording direction, and the spring clutch 75 is turned off. The platen roller 14 is disconnected from the sheet feeding roller 53, thereby stopping the sheet feeding roller 53. Therefore, only one recording sheet 54 is separated and fed during one revolution of the sheet feeding roller 53 (drive shaft 52). Fig. 9 is a longitudinal sectional view showing a structure of the one-rotation spring clutch 75. Figs. 10 to 13 are views for explaining a control lever (control means) and a control ring shown in Fig. 9. The one-rotation spring clutch 75 mounted on the drive shaft 52 comprises a boss portion (winding body) 76 integrally formed with the clutch gear (input gear) 74, a clutch coil spring 77, a clutch drum 78, and a control ring 79. As shown in Figs. 10 to 13, a control means (control lever) 80 for controlling a clutch operation is axially and radially inwardly urged by a control spring 81. The clutch drum 78 is fixed on the drive shaft 52 and is rotated together therewith. The clutch gear 74 having the boss portion 76 is rotatably fitted on the drive shaft 52. Clutch spring seat portions are formed on the circumferential surface portions of the boss portion 76 and the clutch drum 78. The clutch coil spring 77 is bridged between the boss portion 76 and the clutch drum 78. One end of the clutch coil spring 77 is engaged with a hole 82 formed in the clutch drum 78 and is always connected to the clutch drum 78. The other end of the clutch coil spring 77 is hooked by a notch 83 formed in the control ring 79 rotatably fitted on the outer surface of the clutch coil spring 77. The control ring 79 has a shape. as shown in Figs. 10 to 13, and counterclockwise rotation in the plan view of Fig. 10 corresponds to the paper feed direction of the sheet feeding roller 53. The control lever 80 is pivotally fitted on a shaft 84 arranged in the gear box portion 51 A of the frame 51. As shown in Figs. 10 and 11, the control lever 80 is biased axially (right direction in Fig. 11) and radially inward with respect to the control ring 79 by the control spring 81. In a paper feed wait state (i.e., the reference noncontact position of the sheet feeding roller 53), the control lever 80 is hooked by a notch 85 of the control ring 79. In this state, the recording sheet 54 is kept in contact with the free rollers 302 (302A, 302B). When a paper feed command is output from a control unit, the convey roller 14 is rotated by a predetermined amount in the reverse direction. In synchronism with this rotation, the control ring 79 is rotated by a predetermined number of steps in the reverse direction (i.e., clockwise rotation) through the transmitting means (clutch gear) 74 and the clutch coil spring 77. This rotation causes reverse rotation of the convey roller 14, and the clutch coil spring 77 wound around the boss portion (winding body) 76 tends to be loosened. However, in practice, since a load such as a contact force with the recording sheet 54 is small, an initial tightening torque of the clutch coil spring 77 acts to transmit rotation of the clutch gear (transmitting means) 74. The control ring 79 hooked at the spring end of the clutch coil spring 77 is rotated by a predetermined number of steps in the reverse direction. Upon reverse rotation of the control ring 79, the control lever 80 is moved radially outward along an inclined surface portion 86 of the notch 85 of the control ring 79. When the control lever 80 rides on a surface 88, it is urged against a surface 87 by the control spring 81. Therefore, the control lever 80 slides along the surfaces 87 and 88. The control ring 79 is rotated by about one revolution in the forward direction. More specifically, when the clutch gear 74 is rotated in the forward direction in synchronism with rotation of the convey roller 14, the clutch coil spring 77 wound around the boss portion 76 is rotated in a tightening direction, so that the boss portion 76, the clutch coil spring 77, and the clutch drum 78 are rotated together. The torque is transmitted to the drive shaft 52 and the sheet feeding roller 53. At the same time, the control ring 79 engaged with one end of the clutch coil spring 77 is rotated in the same direction. By this rotation and a biasing force of the control spring 81, the control lever 80 is moved onto the surface 88 and is then urged toward the surface 87. Therefore, the control lever 80 can be smoothly slid along the surfaces 87 and 88. By this rotation in the forward direction, the sheet feeding roller 53 is driven to start feeding the recording sheet 54. When the control ring 79 is rotated through a predetermined angle in the forward direction, the control lever 80 descends to a surface 89 along a descending surface 93 and is guided to contact the surface 89 by a surface 94. Further forward rotation causes the distal end of the control lever 80 to hook with the notch 85 of the control ring 79, thereby stopping the control ring 79. That is, when forward rotation through a predetermined angle is completed, the control lever 80 is descended to the surface 89 by the surface 93 and is slid by a predetermined angle along the surfaces 87 and 89. Further forward rotation allows ascending of the control lever 80 along the surface 94, and the control lever 80 is slid along the surfaces 89 and 90. Further forward rotation by one revolution causes the control lever 80 to drop from the surfaces 89 and 90, and the control lever 80 is fitted in the notch 85 formed in the dropping position. The control lever 80 is locked in the notch 85, so that rotation of the control ring 79 is stopped. When rotation of the control ring 79 is stopped, the one-rotation spring clutch 75 is set in the clutch OFF state again. The above operations are summarized below. Upon initial reverse rotation of the control ring 79 (a predetermined number of pulses), a paper feed trigger signal is generated or rotating the sheet feeding roller 53 by one revolution. The sheet feeding roller 53 is driven during one forward revolution of the control ring 79. When the sheet feeding roller 53 and the control ring 79 are rotated by one revolution and return to the initial positions, the control lever 80 is fitted in the notch 85 again to turn off the clutch. The sheet feeding roller 53 is stopped at the reference position. The number of pulses of the reverse trigger signal is determined so that the control lever 80 is moved along the surface 86 of the control ring 79 and is removed from the notch 85 and moved onto the surfaces 87 and 88 when sheet feeding roller 53 is rotated in the reverse direction upon rotation of the convey roller drive motor of the recording apparatus 10. The number of pulses is determined so as not to cause the sheet feeding roller 53 to interface with other portions such as the recording sheet 54, i.e., so as not to cause operation errors such as misregistration of the sheet. According to the one-ration spring clutch 75 described above, since the sheet feeding roller 53 is controlled to perform rotation by one revolution, the recording sheet 54 is located at a position shifted more than a predetermined initial position of the recording sheet 54 in the paper feed direction, i.e., a position passing through the separating means 57. Therefore, a decrease in necessary paper feed amount in the recording unit 10 can be prevented. By the range of the equi-radial sectional surface which is brought into contact with the recording sheet 54, even if paper feeding is completed unless the sheet feeding roller 53 is rotated by one revolution, the control ring 79 can return to the initial position. Even after rotation of the sheet feeding roller 53 is stopped, the drive source is kept rotated to pick up the recording sheet 54. Incomplete engagement of the control lever 80 due to a shortage of rotation of the control ring 79 can be perfectly prevented. Therefore, the control ring 79 is controlled to always return to the initial position (i.e., the position where the semi-circular or D-shaped notch opposes the recording sheet 54 without contact, and only each free roller 302 is kept in contact with the recording sheet 54). For this reason, even if a paper feed error is about to occur due to misregistration of the recording sheet or ist slippage, the recording sheet can be properly fed. A connecting structure between the recording unit 10 and the automatic sheet feeding apparatus 50 detachable therefrom will be described below. Fig. 14 is a rear view showing an automatic sheet feeding apparatus mounting surface of the recording apparatus 10, Fig. 15 is a perspective view showing the mounting surface (front surface) of the automatic paper feed apparatus 50. Fig. 16 is a horizontal sectional view showing a connecting state between the recording unit 10 and the automatic sheet feeding apparatus 50, and Fig. 17 shows an unlocked state from the state shown in Fig. 16. As shown in Figs. 14, 16, and 17, the output gear 71 which synchronously rotates with the platen roller 14 is axially supported on the rear surface side of the recording apparatus 10. The input 72 capable of transmitting a rotational force to the sheet feeding roller 53 (drive shaft 52) is axially supported on the mounting surface of the automatic sheet feeding apparatus 50, as shown in Figs. 15 to 17. At the time of connection between the recording unit 10 and the automatic sheet feeding apparatus 50, the gears 71 and 72 are meshed with each other, so that a driving force for the sheet feeding roller 53 is transmitted to the automatic sheet feeding apparatus. A frame member 35 for supporting bearing portions of the platen roller 14 and a sheet convey motor 34 is arranged om the recording unit 10, and a case portion is mounted on the frame member 35. A hook member 103 having a lever 101 and a hook member 103 having a distal end hook 102 are swingable and movable back and forth by a predetermined amount in the automatic sheet feeding apparatus 50. The hook member 103 is biased inward by a tension spring 104. An opening 201 for receiving the hook 102 through a case opening is formed at a position corresponding to the hook 102 in the frame member 35 of the recording apparatus 10. The hook 102 is engaged with the peripheral portion of the opening 201. As shown in Figs. 16 and 17, a rounded portion is formed at the edge of the opening 201 to facilitate smooth engagement with the hook 102. When the hook 102 shown in Fig. 16 is engaged with the opening 201, the tension spring 104 is extended (e.g., by 1 to 2 mm), and the automatic sheet feeding apparatus 50 can be connected to the recording unit 10 by this spring force. Upon pivotal movement of the lever 101, a hook member 103 is released, as shown in Fig. 17, so that the automatic sheet feeding apparatus 50 can be detached from the recording unit 10. A connecting urging force is received at three abutment surfaces. As shown in Fig. 14 to 16, the automatic sheet feeding apparatus 50 has a first abutment surface 105 serving as a reference abutment surface, and second and third abutment surfaces 106 and 107. The reference abutment surface 105 is formed near the input gear 72, as shown in Figs. 14 to 16. A mating reference abutment surface 202 for the reference abutment surface 105 is formed on the frame member 35 having a higher rigidity and is located near a meshing portion between the gears 71 and 72. The line of action of the hook portion 103 for applying a contact force to the connecting portion is selected to obtain a stable connection state in consideration of the three abutment surfaces 105, 106, and 107. The second and third abutment surfaces 106 and 107 can be brought into direct contact with the rear surface of the recording unit 10. Positioning pins 203 and 204 are formed on the mounting surface of the automatic sheet feeding apparatus 50. When these pins 203 and 204 are fitted into positioning holes 205 and 206 formed in the rear surface of the recording unit 10, the automatic sheet feeding apparatus 50 can be positioned on the recording unit 10. The hole 205 as one of the holes 205 and 206 comprises an elongated hole, as shown in Fig. 14. Fig. 18 is a plan view of the sheet stacking plate 55 and the sheet guide 65, and Fig. 19 is a sectional view of the structure along the line XIX - XIX of Fig. 18. Referring to Figs. 18 and 19, a guide groove 111 is formed in a predetermined range along the sheet widthwise direction of the sheet stacking plate 55, and an engaging portion 112 slidable along the guide groove 111 is formed in the lower portion of the sheet guide 65. As shown in Fig. 19, the upper surface of the engaging portion 112 has the same level as that of the upper surface of the sheet stacking plate 55, and the recording sheets 54 can be stacked on the identical surfaces. The distal end portion 113 of the sheet guide 65 is engaged with the groove 63 (Figs. 5 and 7). When the sheet guide 65 is moved to adjust the sheet width, the sheet feeding roller 53A and the free roller 302 are simultaneously adjusted for this positioning. In the embodiment decribed above, contact between the sheet feeding rollers 53 and the recording sheet 54 is released at the reference position, and the free rollers 302 for holding the recording sheets at the reference position are arranged on another supporting shaft 301 independently of the drive shaft 52. For this reason, a load (contact force) of the drive shaft 52 at the reference position can be eliminated. Driving efficiency for driving the sheet feeding roller 52 through a spring clutch or the like can be improved. In addition, a motor as a driving source can be made compact and simple with low power consumption, thereby achieving a lightweight, compact arrangement at low cost. Fig. 20 shows a second embodiment of the present invention. In this embodiment, in place of the semi-circular roller in the embodiment described above, a sheet feeding roller is swingably arranged to be brought into contact or separated from an upper surface of a stacked sheet. More specifically, a sheet feeding roller 53C is rotatably supported on a drive shaft 52A, and the shaft 52A is supported to be pivotal about a shaft 52B by a lever 52C. The sheet feeding roller 53C receives a rotational force from a drive transmitting means (not shown). With this arrangement, when the sheet feeding roller 53C feeds a recording sheet 54 and is rotated by one revolution, the sheet feeding roller 53C is swung to a position to be separated from the upper surface of the recording sheet 54, as indicated by the dotted line in Fig. 20. At this time, a free roller 302A is brought into contact with the upper surface of the recording sheet 54 and holds the uppermost recording sheet to a position corresponding to the inclined surface 57, thereby properly separating the recording sheets 54 one by one. The automatic sheet feeding apparatus 50 of each embodiment described above is suitable for feeding of a thick recording sheet or a rigid recording sheet. An ink-jet recording system suitable for the recording unit 10 will be described below. The ink-jet recording system comprises liquid injection ports for injecting a liquid recording ink as flying droplets, fluid flow paths communicating with the injection ports, and injection energy generating means, arranged midway along the liquid flow paths, for generating injection energies for forming flying droplets of the liquid ink in the paths. The injection energy generating means are selectively driven in accordance with an image signal, and ink droplets are injected to form an image. A method of generating the injection energy is a method using a pressure energy generating means such as electromechanical conversion elements (e.g., piezoelectric elements), a method using an electromagnetic energy generating means for irradiating a liquid ink with an electromagnetic wave such as a laser to inject the ink upon heating, or a method using a heat energy generating means for heating the liquid ink with electrothermal conversion elements to inject an ink. Of these methods, a system for injecting the ink by using the heat energy generating means such as electrothermal conversion elements is suitable because it allows high-resolution recording because the liquid injection ports can be arranged at a high density and a compact recording head can be arranged.

Claims: An automatic sheet feeding apparatus (50), comprising: sheet stacking means (55) for supporting a plurality of sheets (54); rotary sheet feeding means (52, 52A, 53, 53A, 53B, 53C), arranged to be brought into contact with or separated from an uppermost surface of the sheets stacked on said sheet stacking means (55), and actually brought into contact with the sheet to feed it, said rotary sheet feeding means comprising a drive shaft (52, 52A); biasing means (56) for biasing the sheets stacked on said sheet stacking means (55) toward said rotary sheet feeding means (52, 52A, 53, 53A, 53B, 53C); separating means (57) for separating sheets fed from said sheet stacking means (55) by said rotary sheet feeding means (52, 52A, 53, 53A, 53B, 53C) one by one; and maintaining means (301, 302, 302A, 302B) for maintaining the uppermost sheet at a position separated from said rotary sheet feeding means (52, 52A, 53, 53A, 53B, 53C) when said rotary sheet feeding means does not feed the sheet, said maintaining means (301, 302, 302A, 302B) comprising a free roller (302, 302A, 302B); characterized in that said free roller (302, 302A, 302B) is rotatably mounted on a shaft (301) which is disposed parallel to and upstream in the sheet feeding direction of said drive shaft (52, 52A) of said rotary sheet feeding means (52, 52A, 53, 53A, 53B, 53C). An apparatus according to claim 1, wherein said separating means (57) comprises an inclined surface formed downstream of said rotary sheet feeding means (52, 52A, 53, 53A, 53B, 53C) in the feeding direction, said rotary sheet feeding means bringing the sheet into contact with said inclined surface to separate only one sheet. An apparatus according to claim 1 or 2, wherein said rotary sheet feeding means (52, 53, 53A, 53B) comprises a sheet feeding roller (53, 53A, 53B) having a cut surface at part of a circumferential surface thereof. An apparatus according to claims 2 and 3, wherein said free roller (302, 302A, 302B) is arranged not to be brought into contact with the sheet when the circumferential surface of said sheet feeding roller (53, 53A, 53B, 53C) opposes the sheets stacked on said sheet stacking means (55) and to be brought into contact with the uppermost surface to maintain the uppermost sheet to a position corresponding to said inclined surface when said cut surface opposes the uppermost sheet. An apparatus according to one of claims 1 to 4, wherein said free roller (302, 302A, 302B) is arranged integrally with said shaft (301) for supporting said free roller. An apparatus according to claim 3, wherein said sheet feeding roller comprises a plurality of rollers (53A, 53B) mounted on said drive shaft (52), at least one roller (53A) of said plurality of rollers being movable on said drive shaft (52) along an axial direction thereof. An apparatus according to claim 6, further comprising a sheet guide (65), arranged in said sheet stacking means (55) to be movable in accordance with a sheet size, for regulating the position of the sheets in the widthwise direction, said sheet guide being interlocked with said movable sheet feeding roller (53A). An apparatus according to claim 3, wherein said sheet feeding roller (53) is mounted integrally with said drive shaft (52). An apparatus according to claim 8, wherein said sheet feeding roller comprises three rollers (53) located at predetermined intervals, two of said three rollers being used to feed a sheet having a small size, and said three rollers (53) being used to feed a sheet having a large size. An image recording apparatus, comprising an automatic sheet feeding apparatus (50) according to any of claims 1 to 9; and image recording means for recording an image on the sheet separated by said separating means (57). An apparatus according to claim 10, further comprising a horizontal linear convey path for discharging said one sheet separated by said separating means (57) and fed in a horizontal direction upon recording of an image on said one sheet by said image recording means in a horizontal state. An apparatus according to claim 10, wherein said image recording means constitutes an image recording unit (10), said automatic sheet feeding apparatus (50) constituting a unit being detachably mounted on said image recording unit (10). An apparatus according to claim 12, wherein said image recording unit (10) is located such that a longitudinal direction thereof is perpendicular to a horizontal plane, so that said sheet feeding apparatus (50) is detached from said image recording unit (10) from the horizontal direction. An apparatus according to claim 13, further comprising means (72, 73) for transmitting a driving force from a driving source of said image recording unit (10) to said rotary sheet feeding means (52, 52A, 53, 53A, 53B, 53C) of said sheet feeding apparatus (50) when said sheet feeding apparatus (50) is mounted on said image recording unit (10). An apparatus according to claim 12, wherein said image recording unit (10) comprises a linear convey path for recording an image on the sheet fed from said sheet feeding apparatus (50) and a U-shaped convey path for recording an image on a sheet inserted into a sheet insertion port (11) formed in said image recording unit (10). An apparatus according to claim 15, wherein said linear convey path has a sheet discharge port which serves as a sheet discharge port (12) of said U-shaped convey path. An apparatus according to claim 16, wherein said sheet insertion port (11) and said sheet discharge port (12) are formed so that sheet insertion and sheet discharge are performed on the same side with respect to said image recording unit (10). An apparatus according to claim 10, wherein said image recording apparatus is ink-jet recording means for recording an image upon injection of an ink. An apparatus according to claim 18, wherein said ink-jet recording means comprises an electrothermal conversion element, causing growth of a bubble upon heating of an ink to a temperature exceeding a film boiling temperature by said electrothermal conversion element, and wherein the ink is injected from an injection port and forms an image.

Inventors: KIYOHARA TAKEHIKO, KIYOHARA, TAKEHIKO, KIYOHARA, TAKEHIKO, C/O CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1991
Main classification: B65H3
IPC codes: B65H1, B65H3