SHEET FEEDING APPARATUS IN A PRINTER

Abstract: A sheet feeding apparatus in a printer is provided with: feeding rollers (112,126) for holding and feeding a sheet of paper therebetween; and an operation lever for changing the contact pressure of the feeding rollers (112) by attaching or detaching the feeding roller to or from the opposite feeding roller (114) depending on a type of sheet, e.g., a continuous form transferred by pin tractors or a manually inserted cut sheet. The operation lever also connects or disconnects a clutch mechanism provided between a drive motor (121) and the pin tractors (148) simultaneously with the attaching/detaching operation for the feeding rollers. A single operation of the operation lever can achieve a precise transfer of a selected type of sheet while suspending another type of sheet in the printer. The sheet feeding apparatus is also provided with a transmission mechanism (132,138) for transmitting a torque between the platen (107) and the feeding rollers by a friction driving force. The transmission mechanism prevents the inertia force of the platen from rotating the feeding rollers uselessly.

Description: BACKGROUND OF THE INVENTION The present invention relates to a sheet feeding apparatus in a printer, and more particularly to a sheet feeding apparatus which can properly feed both a continuous form and cut sheets. Many conventional printers are provided with paper feeding rollers, which are driven by a drive motor, at upstream and downstream sides of the platen in a paper feed direction. In order to prevent friction on the platen, the platen and these paper feeding rollers are engaged with each other by way of a series of gears, toothed belts and pulleys, and the like, so that the platen is rotated synchronously with and at the same speed as the paper feeding rollers driven by the drive motor. Some sheet feeding apparatuses in these printers can selectively feed a continuous form and cut sheets. More specifically, a continuous form having feed holes at both side edges thereof is fed to the printing position on the platen by way of a first paper path including pin tractors, while cut sheets are fed to the printing position by way of a second paper path located between the printing position and the first paper path. In these sheet feeding apparatuses, the feeding speed of the paper feeding rollers occasionally becomes higher than that of the pin tractors due to a small dimensional error, even though they are designed to feed a sheet at the same speed. Thus, a provision has been made to feed a continuous form positively by the pin tractors and to cause the continuous form to slip over the paper feeding rollers in case the feeding speed of the paper feeding rollers becomes higher than that of the pin tractors. To elaborate, when a continuous form is selected for printing, the paper feeding rollers on the first paper path are set apart from the sheet and the other paper feeding rollers are set to contact the sheet with weaker pressure. When cut sheets are selected for printing, on the other hand, the paper feeding rollers at both sides of the printing position must contact the sheet with pressure necessary to feed the cut sheets of a variety of thickness only by the friction between the paper feeding rollers and the sheets. If the paper feeding rollers and the pin tractors are structured to be driven by a single driving source like a motor, cut sheets are not to be printed until the continuous form is removed from the pin tractors or the pin tractors are disconnected from the driving source so as not to feed the continuous form together with the cut sheets. Therefore, these conventional printers have a problem that it requires two different operations, namely: to attach or detach the feeding rollers to or from their opposite ones; and to connect or disconnect the pin tractors with the driving source. If the continuous form is undesirably pressed by the paper feeding rollers at the front and rear of the printing position because of failure in adjusting the contact pressure of the paper feeding rollers, the pin feed holes at the both side edges of the continuous form will be torn by the pins of the pin tractors which move slower than the paper feeding rollers, or the cut sheets selected for printing can not be fed properly because they are not supported firmly between the paper feeding rollers at the front and rear of the printing position. EP-A-0235633 on the other hand discloses a paper feeder having a common channel for single and endless sheets, but the single sheets are friction roller driven upstream from the common channel such that endless sheets are fed to the common channel downstream of friction rollers. It is accordingly an object of the present invention to provide a sheet feeding apparatus in a printer which can automatically connect or disconnect a clutch mechanism between a driving source and pin tractors synchronously with a selecting operation for attaching or detaching the feeding rollers to or from the opposite ones in accordance with a type of sheet to be printed. It is another object of the present invention to provide a sheet feeding apparatus in a printer which can support both a first type of sheet and a second type of sheet and can selectively feed either of the two types. The objects are achieved by a sheet feeding apparatus in a printer comprising: a first paper feeding means and a second paper feeding means located at a first position before a printing position and at a second position after the printing position, respectively, for holding and feeding a sheet of paper toward the printing position, the first paper feeding means comprising a first roller and an opposite second roller and the second paper feeding means comprising a third roller and an opposite fourth roller; a first paper path including pin tractors for feeding a first type of sheet, which is provided with pin feed holes on both side edges thereof, by means of the pin tractors whose pins fit in the pin feed holes on the first type of sheet; a second paper path for guiding a second type of sheet toward the first paper feeding means; a torque transmission means for connecting the pin tractors with a driving source of the first and second paper feeding means by way of a clutch means that can be selectively connected and disconnected; characterised by the pin tractors being for feeding the first type of sheet into the first paper feeding means; an operation means for shifting at least the first roller so as to selectively attach and detach the first roller to and from the second roller; and an interlocking means for connecting the clutch means when the operation means detaches the first roller from the second roller, and for disconnecting the clutch means when the operation means attaches the first roller to the second roller. The present invention will be described in more detail with examples and reference to the accompanying drawings. A first embodiment of the present invention is illustrated in Figs. 1 through 12 wherein: Fig. 1 is a longitudinal sectional view of a main portion of a printer as the first embodiment; Fig. 2 is a partial sectional view illustrating in detail an operation lever for selectively pressing feeding rollers against a sheet and setting them apart from the sheet; Fig. 3 is a partial sectional side elevation illustrating an interlock mechanism for connecting and disconnecting a tractor unit with a driving source in response to the selecting operation for attaching or detaching the feeding rollers to or from the opposite ones; Fig. 4 is a partial transverse sectional view enlarging a structure supporting the tractor unit including the interlock mechanism; Fig. 5 is a side view illustrating a gear mechanism; Fig. 6 is a partial sectional view illustrating in detail a connecting structure of support levers on the feeding rollers; Fig. 7 is a partial sectional view taken along a section line VII-VII in Fig. 3; Fig. 8 is another partial sectional view illustrating an alternate operational state for that of Fig. 7; Figs. 9, 10 and 11 are enlarged sectional views illustrating three states when the operation lever is at its first, second and third positions; and Fig. 12 is an enlarged side view illustrating cams which are connected with the support levers. DETAILED DESCRIPTION OF THE EMBODIMENTS Hereinafter, a printer as a first embodiment of the present invention will be described in detail referring to Figs. 1 though 12. Referring first to Fig. 1, a print mechanical unit 4 is located in one side area of a printer case 1 while a tractor unit 5 is in the other side area thereof. A unit frame 6 of the print mechanical unit 4 consists of a hollow horizontal bar 8 supported between a pair of side frames 7, and two round guide bars 9 and 10. A cylindrical platen 11 is rotatably supported between the side frames 7 and above the guide bars 9 and 10. As shown in Fig. 5, a toothed pulley 30 is attached to one end of a platen shaft 11a of the platen 11. A carriage 12 is supported between the guide bars 9 and 10 movably along the width of the printer, and on the upper portion of the carriage 12 a printhead 13 is located so as to slant upward and face the platen 11 above it. A sheet of paper is printed at a printing position on the platen 11 by means of the printhead 13 via an ink ribbon 15. A pair of feeding rollers 16 and 17 and another pair of feeding rollers 18 and 19 are located before and after the printing position on the platen 11, respectively, along the paper feed direction and substantially on the tangent line of the printing position. As shown in Fig. 5, the feeding roller 16 has a shaft 16a attached with a pair of gears 31 and 32 of different sizes at one end of the shaft 16a on the opposite side to the toothed pulley 30 on the platen shaft 11a. Similarly, shafts 17a, 18a and 19a of the other feeding rollers 17, 18 and 19 are attached with their respective gears 33, 34 and 35 at their ends. A motor 36 is attached on one of the side frames 7 and its drive shaft 36a is attached with a gear 37. Another pair of gears 38 and 39 of different sizes are attached to a shaft 40 in such a manner that the larger gear 38 is engaged with the gear 37 on the drive shaft 36a while the smaller gear 39 is engaged with an intermediate gear 42 on a shaft 41 which is engaged with the gear 31 on the roller shaft 16a, thereby connecting the gears 37 and 31 with each other. The gear 32 on the shaft 16a of the feeding roller 16 is engaged with the gear 33 on the shaft 17a of the feeding roller 17, and the gear 34 on the shaft 18a of the feeding roller 18 is engaged with the gear 35 on the shaft 19a of the feeding roller 19. Toothed pulleys 43 and 44 are attached to the shafts 16a and 18a, respectively, on the same side as the toothed pulley 30 on the platen shaft 11a and on the opposite side to the gears 31, 32, and 34. A transmission belt 45 encircles these toothed pulleys 30, 43 and 44. Upon rotation of the motor 36, the feeding rollers 16, 17, 18, and 19 are rotated in the paper feed direction together with the platen 11 via this transmission mechanism consisting of the gears and the belt, thereby holding and advancing a sheet of paper. As shown in Fig. 1, a paper path member 20 and a guide member 27 are disposed opposite to each other substantially on the lower side and the upper side, respectively, of the tangent line of the printing position on the platen 11. The paper path member 20, the guide member 27 and the feeding rollers 16 through 19 altogether form a paper guide path 21 passing through the printing position. The paper guide path 21 is substantially flat and slants upward to the paper feed direction so that the paper inlet is located lower than the paper outlet. As shown in Figs. 1 and 4, the tractor unit 5 includes a guide shaft 22 and a transmission shaft 23 which extend in parallel to each other across the width of the printer. The tractor unit 5 also includes a pair of left and right pin tractors 24 supported movably on the shafts 22 and 23 for adjustment across the width of the paper. The upper surface of each pin tractor 24 is disposed on the upstream of the paper guide path 21 substantially in the same plane as the paper guide path 21 so that it slants upward in the paper feed direction. Like an ordinary printer of a similar kind, each pin tractor 24 comprises a pair of pulleys supported on the shafts 22 and 23, and a belt with pins which is wound around the pulleys. The pins on the pin tractors 24 fit in pin feed holes spaced along the outer edges of a continuous form. The upper surface of the pin tractors 24 forms a first paper path for feeding the continuous form onto the paper guide path 21. As shown in Fig. 5, a gear 47 attached on the transmission shaft 23 is engaged with the gear 39. As a result, when the motor 36 rotates the transmission shaft 23, the pin tractor 24 is accordingly rotated so that the continuous form is fed into the paper guide path 21. A manual guide plate 25 is supported between both side frames 7 of the printing unit frame 6 in the upper position relative to the tractor unit 5. On the upper surface of the manual guide plate 25, a guide plane 26 extends substantially horizontally so as to intersect with the paper guide path 21 at a particular angle. The guide plane 26 of the manual guide plate 25 forms a second paper path along which an individual cut sheet of paper manually inserted is fed into the paper guide path 21. As for an operation mechanism 61, it is provided for attaching or detaching the feeding rollers 17 and 18 to or from a sheet, the feeding rollers 17 and 18 being opposite to each other below and above a sheet and also before and after the printing position. Referring to Fig. 6, a pair of first support levers 62, one of them being shown in the drawing, are rotatably supported on the side frames 7 by a shaft 63 attached at the center of each support lever 62. A press strip 62a is provided at one end portion of the support lever 62. A pair of second support levers 66, one of them being shown in the drawing, are rotatably supported on each end of the platen shaft 11a of the platen 11, each having a press strip 66a at one end portion. On the other end portions of the first and second support levers 62 and 66, both ends of the shafts 17a and 18a of the feeding rollers 17 and 18 are rotatably attached. The other feeding rollers 16 and 19 are rotatably supported on their specific positions on the side frames 7. The operation mechanism 61 also comprises an operation shaft 64 rotatably supported between the side frames 7. A pair of cams 65 are provided on each end of the operation shaft 64 so that the cams 65 are connected with the press strips 62a and 66a on the support levers 62 and 66 as will be described in detail later. A spring 67 is provided between a portion 62b of the first support lever 62 and a pin 68 on the side frame 7 so that the first support lever 62 is forced counterclockwise in Fig. 6. As a result, the feeding roller 17 is pressed into contact with the opposite feeding roller 16, and the press strip 62a comes into contact with the cam 65. Another spring 74 is provided between a portion 66b of the second support lever 66 and a pin 75 on the side frame 7 so that the second support lever 66 is forced counterclockwise in Fig. 6. As a consequence, the feeding roller 18 is pressed against the opposite feeding roller 19 and the press strip 66a comes into contact with the cam 65. In this embodiment, the spring 67 has greater resilience than the spring 74 so that the feeding roller 17 located upstream in the paper feed direction presses the sheet more effectively than the feeding roller 18 located downstream. As shown in Fig. 2, an operation lever 69 is rotatably attached around a support cylinder 70 on one of the side frames 7. At the center of the support cylinder 70, the operation lever 69 is joined with one end of the operation shaft 64. The body portion of the operation lever 69 includes a resilient connecting pin 71 which is selectively engaged with one of three connecting recesses 72 provided around the peripheral surface of the support cylinder 70. Thus, the operation lever 69 can be kept in one of three positions shown by the symbols I, II, and III in Figs. 1, 2, and 6. As shown in Figs. 9 through 12, the cams 65 are structured as a pair of cams 65A and 65B which are connected with the support levers 62 and 66, respectively. The cam 65A has a higher cam plane 65Aa which lowers the press strip 62a of the first support lever 62 against the force of the spring 67 when the operation lever 69 is moved to either the second position II or the third position III. The cam 65A also has a lower cam plane so that the press strip 62a springs back to its upper position when the operation lever 69 is moved to the first position I. Similarly, the other cam 65B has a higher cam plane 65Ba which lowers the press strip 66a of the second support lever 66 against the force of the spring 74 when the operation lever 69 is moved to the third position III. The cam 65B also has a lower cam plane so that the press strip 66a springs back to its upper position when the operation lever 69 is moved to either the first position I or the second position II. When the operation lever 69 is moved to the position I, as shown in Fig. 9, the lower cam planes of both cams 65A and 65B come into contact with the press strips 62a and 66a of the support levers 62 and 66. The springs 67 and 74 press the feeding rollers 17 and 18 made of rubber against the opposite feeding rollers 16 and 19, thereby holding the sheet with pressure before and after the printing position. When the operation lever 69 is moved to the position II, as shown in Fig. 10, the higher cam plane 65Aa of the cam 65A comes into contact with the press strip 62a. Accordingly, the feeding rollers 17 before the printing position is set apart from the opposite feeding roller 16 against the force of the spring 67. When the operation lever 69 is moved to the position III, the higher cam planes 65Aa and 65Ba of both cams 65A and 65B come into contact with the press strips 62a and 66a, respectively. As a result, the feeding rollers 17 and 18 are set apart from the opposite feeding rollers 16 and 19, thereby releasing the sheet from the pressure. In case of printing on an individual cut sheet of paper which is manually inserted from the second paper path on the manual guide plate 25 into the paper guide path 21, the operation lever 69 is moved to the position I so as to press the feeding rollers 17 and 18 against the opposite feeding rollers 16 and 19. As a consequence, even if the inserted sheet is so stiff that it is curved against its resiliency through the guide plane 26 and the paper guide path 21, the sheet is held firmly between the feeding rollers 16 and 17 and advanced in the line feed direction by the rotation of the feeding rollers 16 through 19. In case of printing on a continuous form which is fed through the first paper path on the tractor unit 5, the operation lever 69 is moved to the position II so as to set the feeding roller 17 apart from the opposite feeding roller 16 before the printing position. As a consequence, the continuous form is fed smoothly by the rotation of the pin tractor 24 and the feeding rollers 18 and 19 after the printing position. The spring 74 is provided for pressing the feeding rollers 18 and 19 against each other to such a degree that if the feeding rollers 18 and 19 feed the form faster than the pin tractor 24, the feeding rollers 18 and 19 slip over the form. In case the sheet gets stuck in the paper guide path 21, the operation lever 69 is moved to the position III so as to set the feeding rollers 17 and 18 apart from the opposite feeding rollers 16 and 19. As a result, the stuck paper is easily removed out of the paper guide path 21. Hereinafter a description will be given for a mechanism for connecting or disconnecting the pin tractors 24 with the motor 36 synchronously with the alternation of the holding pressure of the feeding rollers 17 and 18 by the operation lever 69. Referring to Fig. 4, the tractor unit 5 has a frame structure with a pair of tractor unit frames 73 which support both ends of the guide shaft 22. The transmission shaft 23 is supported between the tractor unit frames 73 rotatably and movably in the direction of the shaft line thereof. The gear 47 on the transmission shaft 23 is connected and disconnected with the gear 39 based on the axial movement of the transmission shaft 23. Including these gears 47 and 39, a torque transmission mechanism 76 consists of plural gears provided between the transmission shaft 23 and the motor 36. In the present embodiment, a clutch 77 is provided for connecting and disconnecting a torque transmission course by means of the gears 47 and 39 which are removably engaged with each other. Normally a spring 78 forces the transmission shaft 23 to the left in Fig. 4 so that the gear 47 is engaged with the gear 39 to maintain the clutch 77 in the connected state. Referring to Figs. 3 and 4, an interlocking member 79 is provided between the operation shaft 64 of the operation mechanism 61 and the transmission shaft 23 of the tractor unit 5. The interlocking member 79 connects and disconnects the clutch 77 synchronously with the operation mechanism 61. More specifically, a side cam 80 of the interlocking member 79 has a slot 80a in the center thereof which receives a pin 81 provided on one of the side frames 7, so that the side cam 80 is supported on the side frame 7 movably up and down. The side cam 80 also has an aperture 80b at the upper end and another slot 80c at the lower end. A rotating medium 82 is attached to the operation shaft 64 at its end opposite to the operation lever 69. The end portion of the rotating medium 82 has a pin 82a which is received in the aperture 80b of the side cam 80. As shown in Figs. 3, 4 and 7, the side cam 80 comprises a higher cam plane 80d and a lower cam plane 80e on the outer face of the lower end of the side cam 80, thereby providing the side cam 80 with a ledge jutting vertically to the movable direction of the side cam 80. The transmission shaft 23 is provided with a thinner portion 23a and a connecting head 23b at the opposite end to the gear 39 and 47. The thinner portion 23a extends through the slot 80c of the side cam 80, and the connecting head 23b is connected with either the higher cam plane 80d or the lower cam plane 80e of the side cam 80. When the operation lever 69 is moved to either the position II or the position III, the lower cam plane 80e of the side cam 80 is connected with the connecting head 23b of the transmission shaft 23, as shown in Figs. 3, 4, and 7, and the clutch 77 is maintained in the connected state by means of the spring 78. Alternatively, when the operation lever 69 is moved to the position I, the rotating medium 82 raises the side cam 80 and the higher cam plane 80d of the side cam 80 is connected with the connecting head 23b of the transmission shaft 23, as shown in Fig. 8. As a consequence, the transmission shaft 23 is moved to the right in Fig. 4, and the gear 47 is moved across the shaft line apart from the opposite gear 39 so as to put the clutch 77 into the disconnected state. Therefore, only a single operation makes it possible to attach or detach the feeding rollers 17 and 18 to or from their respective opposite feeding rollers 16 and 19 and simultaneously to connect or disconnect the clutch 77, and one of the two states can be easily selected. In the present embodiment, a paper edge sensor 85 is provided between the platen 11 and the upper feeding roller 16 at the upstream side in the paper feed direction so as to detect a leading edge of a continuous form. In case an additional switch (not shown) is operated for putting back the continuous form from the printing position before setting the operation lever 69 into the position I, the motor 36 rotates backward the platen 11, the feeding rollers 16 through 19, and the pin tractor 24 so as to put back the continuous form away from the printing position on the platen 11 until the paper edge sensor 85 detects the leading edge of the continuous form. Thereafter, the motor 36 is stopped after a rotation for a certain number of pulses, so that the leading edge of the continuous form is held at a determined position between the pin tractor 24 and the opposing feeding rollers 16 and 17 at the paper inlet side. In case of printing on an individual cut sheet with the continuous form being suspended in this state, the operation lever 69 is set into the position I so as to disconnect the clutch 77 and to interrupt the torque transmission to the pin tractor 24. Therefore, the continuous form is never fed with the individual cut sheet which is fed by the rotation of the feeding rollers 16 through 19. Furthermore, when the operation lever 69 is set into the position II and then an additional switch (not shown) is operated for advancing a sheet, the motor 36 rotates forward the platen 11, the feeding rollers 16 through 19 and the pin tractors 24 so as to advance the continuous form until the paper edge sensor 85 detects the leading edge of the continuous form. Thereafter, the motor 36 is stopped after a rotation for a certain number of pulses, so that an initial printing line on the continuous form is disposed opposite to the printing position on the platen 11 where the printhead 13 executes printing. The present embodiment may be applied to an ordinary printer that feeds a sheet of paper approximately halfway around a cylindrical platen, and that has press rollers pressing the sheet against the platen. As many apparently widely different embodiments of this invention may be made without departing from the scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.

Claims: A sheet feeding apparatus in a printer comprising: a first paper feeding means and a second paper feeding means located at a first position before a printing position and at a second position after the printing position, respectively, for holding and feeding a sheet of paper toward said printing position, said first paper feeding means comprising a first roller (17) and an opposite second roller (16) and said second paper feeding means comprising a third roller (18) and an opposite fourth roller (19); a first paper path including pin tractors (24) for feeding a first type of sheet, which is provided with pin feed holes on both side edges thereof, by means of said pin tractors (24) whose pins fit in the pin feed holes on said first type of sheet; a second paper path for guiding a second type of sheet toward said first paper feeding means; a torque transmission means (76) for connecting said pin tractors (24) with a driving source of said first and second paper feeding means by way of a clutch means (77) that can be selectively connected and disconnected; characterised by said pin tractors being for feeding said first type of sheet into said first paper feeding means; an operation means (61) for shifting at least said first roller (17) so as to selectively attach and detach said first roller (17) to and from said second roller (16); and an interlocking means (79) for connecting said clutch means (77) when said operation means (61) detaches said first roller (17) from said second roller (16), and for disconnecting said clutch means (77) when said operation means (61) attaches said first roller (17) to said second roller (16). The sheet feeding apparatus according to claim 1 wherein said operation means (61) shifts said second paper feeding means so as to selectively attach and detach said third roller (18) to and from said fourth roller (19), and said operation means (61) is selectively set in: a first position for attaching said first roller (17) to said opposite second roller (16), and for attaching said third roller (18) to said opposite fourth roller (19); a second position for detaching said first roller (17) from said second roller (16), and for attaching said third roller (18) to said fourth roller (19); and a third position for detaching said first roller (17) from said second roller (16), and for detaching said third roller (18) from said fourth roller (19). The sheet feeding apparatus according to claim 1 or 2 wherein: said operation means (61) comprises a pair of manually operable cams (65), and a first lever (62) and a second lever (66) each individually moved by its respective cam (65); and said first roller (17) is rotatably attached to said first lever (62), and said third roller (18) is rotatably attached to said second lever (66). The sheet feeding apparatus according to claim 1, 2 or 3 wherein: a first spring (67) forces said first and second rollers (17, 16) into contact with each other, and a second spring (74) forces said third and fourth rollers (18, 19) into contact with each other; and said first spring (67) has stronger resiliency than said second spring (74).

Inventors: YOKOI, TAKESHI BROTHER KOGYO K.K.
Applicants: BROTHER KOGYO KABUSHIKI KAISHA
Application year: 1988
Main classification: B41J11
IPC codes: B41J11