Cut sheet feeding mechanism

Abstract: The cut sheet feeding mechanism comprises a transmitting means for transmitting a rotary force of a platen roller (12) to a pick-up roller (11) such that the pick-up roller (11) rotates in the same direction as the platen roller (12), and means for disenabling the transmitting operation after the pick-up roller (11) feeds the cut sheet by a predetermined length. In this improved cut sheet feeding mechanism the platen roller (12) and the pressure roller do not give the reverse feeding force to the leading edge of a cut sheet when a pick-up roller (11) feeds the leading portion of the cut sheet to the contact portion between the platen roller (12) and the pressure roller. The pick-up roller (11) is rotated to pick up a cut sheet by the rotation of the platen roller (12) in the direction for feeding the cut sheet to a printing position.

Description: The present invention relates to a cut sheet feeding mechanism for use in a printer, typewriter or the like, and more particularly to a cut sheet feeding mechanism for separating a cut sheet from stacked cut sheets in a sheet hopper and for feeding it to a printing position of a printing apparatus. Such a conventional sheet feeding mechanism is disclosed in U.S. Pat. No. 4,248,415 patented to Steinhilber on Feb. 3, 1981. This mechanism includes a pick-up roller for picking up a cut sheet from a sheet hopper and for feeding it to a platen roller on which the printing operation is carried out. The platen roller is connected to a drive motor and rotated by the drive motor in a first direction to feed the cut sheet in cooperation with a pressure roller urged to a surface of the platen roller during the printing operation. The pick-up roller also obtains its rotary force from the drive motor via transmission means which includes gears, a belt and an one-way clutch. In operation, first, the drive motor enables the platen roller to rotate in a second direction reverse to the first direction in order to pick up a cut sheet from the sheet hopper. The transmission means transmits the rotary force to the pick-up roller so as to rotate the pick-up roller in the first direction. Thus, the pick-up roller picks up the uppermost sheet in the sheet hopper and feeds it to a contact portion between the platen roller and the pressure roller. After the leading edge of the cut sheet has been fed to and pressed against the contact portion, the drive motor then rotates in the reverse direction, i.e., enable the platen roller to rotate in the first rotary direction to feed the cut sheet to the printing position. The transmission means does not transmit the rotary force of this direction to the pick-up roller by means of the one-way clutch. Accordingly, the rotation of the pick-up roller is stopped so as not to interrupt the feeding of the cut sheet by the platen roller and the pressure roller. In the conventional mechanism, the leading edge of the cut sheet is pressed by the pick-up roller against the contact portion where the pressure roller is urged to the platen roller which rotates in the second direction before the platen roller feeds the cut sheet to the printing position. Accordingly, the leading edge of the cut sheet is apt to be bent by the reverse feeding force of the platen roller, and moreover, gets out of the contact portion. EP-A-0 104 337 discloses a cut sheet feeding mechanism including a gear wheel provided with a gear portion at a part of circumference of the wheel for rotating a pick-up roller. The gear wheel is continuously rotated by a platen roller when the platen roller feeds a sheet. Therefore, the pick-up roller periodically comes in contact with the gear portion This means that the pick-up roller periodically rotates to pick up a cut sheet from a hopper and, therefore, the cut sheet is required to have the same length. Thus, the feeding mechanism cannot feed various kinds of cut sheets having various lengths. Therefore, an object of the present invention is to provide an improved cut sheet feeding mechanism in which a platen roller and a pressure roller do not give the reverse feeding force to the leading edge of a cut sheet when a pick-up roller feeds the leading portion of the cut sheet to the contact portion between the platen roller and the pressure roller. Another object of the present invention is to provide a cut sheet feeding mechanism in which a pick-up roller is rotated to pick up a cut sheet by the rotation of the platen roller in the direction for feeding the cut sheet to a printing position. The above objects are achieved by a cut sheet feeding mechanism having the features of claim 1. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a cut sheet feeding mechanism according to an embodiment of the present invention; Fig. 2 shows notched gears used in the cut sheet feeding mechanism shown in Fig. 1; Fig. 3 shows a planet gear used in the cut sheet feeding mechanism shown in Fig. 1; Fig. 4 is a cross-sectional view showing a sheet feeding path of a cut sheet feeding unit and a printer unit shown in Fig. 1; and Figs. 5 and 6 illustrate the operation of the cut sheet feeding mechanism shown in Fig. 1. DESCRIPTION OF THE PREFERRED EMBODIMENT Fig. 1 shows an embodiment of the present invention which comprises a print unit 100 and a cut sheet feeding unit 200. The cut sheet feeding unit 200 includes a sheet hopper 201 supported by a pair of shafts 202 to a frame 203. The sheet hopper 201 stores a plurality of cut sheets 204 stacked therein. Pick-up rollers 11 are rotatably provided above the sheet hopper 201 by a shaft 11a to be contacted with the uppermost sheet of the cut sheets 204 in the sheet hopper 201. One end of the shaft 11a is provided with a pick-up roller gear 6 which engages an idler gear 5. The idler gear 5 is rotatably supported on the frame 203 via a shaft 5a and engageable with a notched gear 4. The notched gear 4 is integrally formed with another notched gear 3 which has smaller diameter than the notched gear 4, as also shown in Figs. 2A and 2B. The notched gears 3 and 4 are coaxial with each other and rotatably provided on the frame 203 via a shaft 3a. Sectorial angles ϑ₃ and ϑ₄ of notch portions of the notched gears 3 and 4 are 31° and 49°, respectively. When the notch portion of the gear 4 is opposite to the idler gear 5, the gears 4 and 5 does not engage with each other. An idler gear 1 is rotatably provided on the frame 203 via a shaft 1a and engageable with the notched gear 3. As also shown in Fig. 3, an arm 9 is rotatably supported around the shaft 1a at its one end. The other end of the arm 9 has a shaft 2a around which a planet gear 2 is rotatably provided such that the planet gear 2 engages the idler gear 1. Frictional material such as rubber 2b is attached between the planet gear 2 and the shaft 2a so that the rotational friction between the planet gear 2 and the shaft 2a is greater than that between the one end of the arm 9 and the shaft 1a. Accordingly, the planet gear 2 can be rotated around the shaft 2a by the idle gear 1 only when the arm 9 is prevented from the rotation around the shaft 1a. The planet gear 2 can also engage with one of the notched gear 3 and an eject roller gear 7 by the rotation of the arm 9 around the shaft 1a. The eject roller gear 7 is connected to a roller shaft 10a which is rotatably supported by the frame 203. Eject rollers 10 are provided around the shaft 10a for ejecting a printed sheet from the printer unit 100 in cooperation with pressure rollers 13. A shaft 13a of the pressure rollers 13 is rotatably supported at both ends by levels 14 (only one is illustrated) which is biased by a spring 15 so that the pressure rollers 13 are urged to the eject rollers 10. The printer unit 100 includes a thermal head 24 and an inked ribbon cartridge 25 both are slidably supported by guide shafts 101 and 102. A platen roller 12 is rotatably supported at both ends on a frame 103 so as to opposite the thermal head 24. Under the platen roller 12, pressure rollers 26 and 27 are rotatably provided such that they are urged to the surface of the platen 12 by a known manner as described in U.S. Pat. Appln. Ser. No. 748,643 filed June 25, 1985 now issued as US-A-4 655 626. Additionally, a sheet guide 104 is provided for guiding the cut sheet supplied from the sheet feeding unit 200 to the portion between the platen roller 12 and the pressure rollers 26. A sensor 28 is also provided under the platen roller 12 for detecting a leading edge of the supplied cut sheet. One end of a shaft 12a of the platen roller 12 is provided with a platen gear 8 to which a rotary force is supplied by a drive motor 21 via a gear 22 connected to the drive motor 21 and an idler gear 23. When the drive motor 21 rotates in the counterclockwise direction, the platen roller 12 is rotated in the same direction to feed the cut sheet to the printing position where the thermal head 24 is located. The cut sheet feeding unit 200 is attached on the printer unit 100 by engaging a connector 205 with the platen shaft 12a and another connector 206 with a acceptor 105. When the cut sheet feeding unit 200 is attached, the idler gear 1 engages the platen gear 8, and then the rotary force of the drive motor 21 is transmitted to the idler gear 1. A sheet feeding path from the cut sheet feeding unit 200 to the printer unit 100 will be described in reference to Fig. 4. The uppermost sheet 204a is separated from the stacked sheet 204 and fed downward to a sheet guide 207 by the rotation of the pick-up roller 11 in the counterclockwise direction. The sheet 204a is further fed to the sheet guide 104 of the printer unit 100 by the guidance of a sheet guide 208. Then, the loading edge of the cut sheet 204a reaches at the portion where the pressure roller 26 is contacted to the platen roller 12 and is inserted therebetween. As the platen roller 12 is rotated in the counterclockwise direction, the cut sheet 204a is further fed by the platen roller 12 and the pressure roller 26. At this time, the feeding force of the pick-up roller 11 is not necessary. Moreover, it should be noted that the pick-up roller 11 must be stopped after the trailing edge of the sheet 204a has passed through the pick-up roller 11 to prevent the pick-up roller 11 from feeding the next uppermost sheet. After the leading edge of the cut sheet 204a is detected by the sensor 28, the platen roller 12 is further rotated in the counterclockwise direction by a predetermined feeding amount to locate the first print line of the sheet 204a in front of the head 24. The head 24 carries out a printing operation line by line on the sheet 204a, as the platen roller 12 intermittently feed the sheet 204a. Then, the leading edge of the sheet 204a is inserted between the eject roller 10 and the pressure roller 13 and fed thereby out of the printer unit 100. The printed sheet 204a is stacked in a sheet stacker 209 by the eject roller 10. Incidentally, the sheet guides 207 and 208 and the sheet stacker 209 are provided on the cut sheet feeding unit 200, however, they are omitted in Fig. 1 for the purpose of illustration. The operation of the cut sheet feeding mechanism will be now described in reference to Figs. 5 and 6. Initially, the planet gear 2 engages the eject roller gear 7 while the idler gears 1 and 5 disengage the notched gears 3 and 4, respectively, as shown in Fig. 5. The numbers of teeth of the gears 1, 2, 3, 4, 5, 6, and 8 are "55", "30", "58" (but "5" is lacked by the notched portion), "58" (but "8" is lacked by the notched portion), "30", "35" and "76", respectively. First, the drive motor 21 enables the platen gear 8 to rotate in the direction of arrow b₈ by an angle of 21°. Then, the idle roller 1 is rotated in the direction of arrow b₁ by an angle of 29° (= 76/55 x 21°) so that the arm 9 is rotated around the shaft 1a in the counterclockwise direction by the angle of 29° as illustrated by one-dot and dashed line in Fig. 5. Thus, the planet gear 2 engages the notched gear 3. The platen gear 8 is further rotated in the direction of arrow b₈ by an angle of 15°. Then, the planet gear 2 is rotated in the direction of arrow b₂ via the idler gear 1 since the arm 9 cannot further be rotated in the counterclockwise direction. Due to the rotation of the planet gear 2, the notched gears 3 and 4 are rotated in the direction of arrow b₃ by an angle of about 18°. Thus, the notched gear 3 comes to engage with the idler gear 1 as shown in Fig. 6. Until the above operation, the pick-up roller gear 6 is not rotated, and therefore the pick-up roller 11 does not feed the cut sheet 204a. Next, the drive motor 21 rotates the platen gear 8 in the reverse direction, i.e., the direction of arrow a₈. This causes the idler roller 1 to rotate in the direction of arrow a₁ and the arm 9 to rotate in the clockwise direction as illustrated in the one-dot and dashed line in Fig. 6. Thus, the planet gear 2 disengages the notched gear 3 but engages the eject roller gear 7. The platen gear 8 is further rotated in the direction of arrow a₈ to rotate the idler gear 1 in the direction of arrow a₁. Thus, the rotation is transmitted to the notched gear 3, and the gears 3 and 4 are rotated in the direction of arrow a₃. Then, the notched gear 4 engages the idler gear 5 to rotate it in the direction of arrow a₅, and therefore, the pick-up gear 6 is rotated in the direction of arrow a₆. Accordingly, the pick-up roller 11 is rotated to pick up the uppermost cut sheet 204a from the sheet hopper 201 and to feed it to the printer unit 100. It should be noted that the rotation of the platen gear 8 is transmitted to the pick-up roller gear 6 in the same direction. When the notched gear 3 is rotated by one rotation, the notched portions of the gears 3 and 4 come to be opposite to the idler gears 1 and 5, respectively, and return to the initial states (Fig. 5). In other words, the notched gears 3 and 4 disengage the idler gears 1 and 5, respectively. By the one rotation of the notched gear 4, the pick-up roller 11 feeds the cut sheet 204a to the portion where the leading edge of the sheet 204a is inserted between the platen roller 12 and the pressure rollers 26 and the trailing portion of the sheet 204a is still in contact to the pick-up roller 11. Since the platen roller 12 is rotated in the direction of arrow a₈, which is the direction to feed the sheet to the printing position, the leading edge of the sheet 204a when reaching the portion between the platen roller 12 and the pressure rollers 26 is not subject to the reverse feeding force. After that, the cut sheet 204a is fed by the platen roller 12 and the pressure rollers 26 and 27. The drive motor 21 further rotates the platen gear 8 in the direction a₈ under the state shown in Fig. 5, in order to rotate the platen roller 12 for the printing operation. The rotation of the idler gear 1 enables the planet gear 2 to rotate in the direction of arrow a₂, and then enables the eject roller gear 7 to rotate in the direction of arrow a₇. Incidentally, the pick-up roller 11 is rotated following the feeding operation of the platen roller 12 since it contacts the trailing portion of the sheet 204a, however, the rotation of the idler gear 5 is not transmitted to the notched gear 4 owing to the notch portion. As described above, the cut sheet feeding mechanism according to the present invention can feed the cut sheet from the sheet hopper to the print unit with high reliability.

Claims: A cut sheet feeding mechanism (200) for feeding a cut sheet (204a) from a sheet hopper (201) to a platen roller (12) provided on a platen roller shaft (12a) connected to a drive motor (21), said platen roller (12) being rotated by said drive motor (21) in a forward rotary direction to further feed said cut sheet (204a) to a printing position of a printer (100), said cut sheet feeding mechanism (200) comprising: a pick-up roller (11), provided on a pick-up roller shaft (11a), which rotates in said forward rotary direction to pick-up said cut sheet (204a) from stacked cut sheets (204) in said sheet hopper (201); a platen gear (8) connected to said platen roller shaft(12a); a first idler gear (1) provided on an idler gear shaft (1a) and engaged with said platen gear (8); a first notched gear (3) including a first gear portion and a first notched portion, said first notched gear (3) being engaged with said first idler gear (1) at said first gear portion and being disengaged with said first idler gear (1) at said first notched potion; and a pick-up roller gear (6) connected to said pick-up roller shaft (11a), said pick-up roller gear (6) being associated with said first notched gear (3); CHARACTERIZED IN THAT said cut sheet feeding mechanism further comprises: a planet gear (2) rotatably supported by an arm (9) such that said planet gear (2) is engaged with said first idler gear (1), said arm (9) being rotatably supported by said idler gear shaft (1a); said drive motor (21) driving said platen gear (8) to rotate in a reverse rotary direction (b8), reverse to said forward rotary direction, when said first notched portion of said first notched gear (3) is opposed to said first idler gear (1) so as to rotate said arm (9) around said idler gear shaft (1a) to engage said planet gear (2) with said first gear portion of said first notched gear (3), so that said first notched gear (3) is rotated in said forward rotary direction (b3) by said platen gear (8) through said first idler gear (1) and said planet gear (2), whereby said first gear portion of said first notched gear (3) is engaged with said first idler gear (1); said drive motor (21) subsequently driving said platen gear (8) to rotate in said forward rotary direction (a8) so as to rotate said arm (9) around said idler gear shaft (1a) to separate said planet gear (2) from said first notched gear (3) so that said first notched gear (3) is further rotated in said forward rotary direction (a3,a3=b3) by said platen gear (8) through said first idler gear (1), and said pick-up roller gear (6) is rotated in said forward rotary direction (a6) by said first notched gear (3) until said first notched portion of said first notched gear (3) is opposed to said first idler gear (1), whereby a rotary force of said platen roller (12) in said forward direction is transmitted to said pick-up roller (6) in a manner that said pick-up roller (6) also rotates in said forward direction until said pick-up roller (6) has fed said cut sheet (204a) from said sheet hopper (201) by a predetermined length. The cut sheet feeding mechanism as claimed in claim 1, further comprising a second notched gear (4) coaxial with said first notched gear (3) and rotating together with said first notched gear, said second notched gear (4) including a second gear portion and a second notched portion, and a second idler gear (5) engaged with said pick-up roller gear (6), said second idler gear (5) being engaged with said second gear portion of said second notched gear (4) when said first idler gear (1) is engaged with said first gear portion of said first notched gear (3) and being opposed to said second notched portion of said second notched gear when said first idler gear (1) is opposed to said first notched portion of said first notched gear (3). The cut sheet feeding mechanism as claimed in claim 1 or 2, further comprising an eject roller shaft (10a), an eject roller (10), provided on said eject roller shaft, for feeding said cut sheet out of said printer, and further comprising an eject roller gear (7) provided on said eject roller shaft, said eject roller gear being engaged with said planet gear (2) when said planet gear (2) is separated from said first idler gear (3) so that said rotary force of said platen gear (8) is also transmitted to said eject roller (10). The cut sheet feeding mechanism as claimed in any of claims 1 to 3, wherein said planet gear (2) is attached to said arm (9) via a planet gear shaft (2a), and a frictional material (2b) is attached between said planet gear (2) and said planet gear shaft (2a) so that the rotational friction between said planet gear (2) and said planet gear shaft (2a) is greater than that between said arm (9) and said idler gear shaft (1a).

Inventors: NAKAMURA HIRONORI, SHIMOGAWARA JUN, NAKAMURA, HIRONORI, SHIMOGAWARA, JUN
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1987
Main classification: B41J13
IPC codes: B41J13, B65H3