SHEET FEEDER

Abstract: A sheet feeder for printer; wherein a feeding roller (6) rotates in reverse direction to feeding-out direction for a very short time, and thus a rear end of sheet (7) in a sheet cartridge (5) is made contact a sheet stopper (14) provided at the rear end of the sheet cartridge (5) for separating sticking sheets.

Description: The invention relates to a sheet feeder for a printer, according to the pre-characterizing part of claim 1. In particular, the present invention relates to a sheet feeder for preventing undesirable plural sheet feeding. DE-A-2 407 098 - from which the present invention starts out - shows a sheet feeder for feeding a topmost sheet of stacked sheets being contained in a sheet case by means of a feeding roller from said sheet case into a portion of a printer, where characters or the like are printed onto said sheet. In order to have a separation of the topmost sheet from the remaining stacked sheets prior to feeding the topmost sheet from the sheet case, the feeding roller first carries out a reverse rotation, so that the topmost sheet is fed into the sheet case causing creation of a bow or curve in said topmost sheet, as the rear end of the sheet abuts against the inner rear surface of the sheet case. Said bow or curve then should separate the topmost sheet from the remaining stacked sheets, so that upon rotation of the feeding roller into feeding direction the topmost sheet is fed out of the sheet case. However, due to the fact that the rear edge of the topmost sheet is pressed against the inner rear surface of the sheet case upon separating the topmost sheet from the sheet stack for forming the bow or curve, there is the danger that the rear edge of the topmost sheet slips over the upper rear rim of the sheet case, this leading to misalignments of the topmost sheet with respect to the feeding roller and/or no sufficient separation of the topmost sheet from the sheet stack. It is therefore an object of the present invention to provide a sheet feeder ensuring a reliable separation of a topmost sheet to be feeded from the sheet case from the remaining sheet stack. Solution of the object is achieved by the characterizing features of claim 1. Subclaim 2 contains an advantageous modification of the invention. The following is an explanation of the invention, taken in conjunction with the accompanying drawings, in which: FIG.1 is a sectional view of a color printer having a sheet feeder embodying the present invention; FIG.2 is a sectional view of the paper cartridge in FIG.1; FIG.3 is a circuit diagram of a control circuit of the paper cartridge of FIG.1; FIGs. 4A and 4B are time charts for showing an operation of the control circuit of FIG.3; and FIG.5 is a flow chart for showing a feeding operation of the control circuit. FIG.1 shows a sectional view of sheet feeder of an embodiment of the present invention. An ink sheet 8 is conveyed to a take-up reel 10 from a feeding reel 9. A feeding roller 6 is moved so as to touch a top paper 7 (or other kind of sheet) of stacked papers in a paper cartridge 5. Then, the feeding roller 6 is rotated in reverse direction for a small angle as shown in FIG.1, so that the rear end of the paper touches a sheet stopper 14 provided at the rear end of the cartridge 5. Because the end part of the paper 7 is pushed to the sheet stopper, the top sheet is bent as shown in FIG.1. Therefore, the sheets are separated, even in case of close sticking of two or more sheet papers 7. Then, the feeding roller 6 rotates in the forward direction for taking out the separated top paper 7 from the paper cartridge 5. The paper 7, thus taken from the paper cartridge 5, is transferred to a platen roller 2. Further, the paper 7 is transferred to a position which is between the platen roller 2 and a thermal head 1 by means of pinch rollers 3, 4, and is printed with e.g. yellow ribbon. When the yellow print operation is completed, the paper 7 is transferred to a first paper passage 12. Next, the paper 7 is transferred to a second paper passage 13 by reversely rotating the platen roller 2. Then, the paper 7 is printed with e.g. magenta ribbon with rotation of the platen roller 2. Than, e.g. cyan print operation is carried out in the same manner as yellow or magenta print operation. FIG.2 shows a sectional view of the cartridge 5. At the rear end of the cartridge 5, the paper stopper 14 is provided. On a face of the stopper to be touched by the paper, a member 14a having elasticity and large friction in a direct ion of its surface, such as any one member of known hook and loop fastener, is provided. FIG.3 is a block diagram of control circuit 15. The control circuit 15 has a driver 22, a controller 20, an output port 38, ROM 32, CPU 34, RAM 36 and an input port 30. The driver 22 is provided for driving a motor 24 for rotating the feeding roller 6. CPU 34 detects the status of the printer by inputting status signals from the input port 30 and controls the controller 20 and the positioning circuit 3 for feeding roller 6 by outputting control signals from the output port 38. CPU 34 controls the printer in accordance with a computer program stored in ROM 32. FIG.5 shows a flow chart of this program. CPU 34 controls the positioning circuit 40 through the output port 38 to issue a command signal to contact the feeding roller 6 to the top sheet (step S1). Then, in step S2, CPU 34 outputs control pulses to the input terminal CU of the controller 20. When the control pulses are inputted to the input terminal CU of the controller 20, the controller 20 outputs pulse signals as shown in FIG.4A from output terminals ϑ₁ , ϑ₂ , ϑ₃ and ϑ₄. The driver 22 outputs signals corresponding to the pulse signals as shown in FIG.4A for driving the stepping motor 24. Therefore, the stepping motor 24 rotates in reverse direction. Next, in step S3, CPU 34 outputs control pulses to the input terminal CD of the controller 20. When the control pulses are inputted to the input terminal CD of the controller 20, the controller 20 outputs pulse signals as shown in FIG.4B from output terminals ϑ₁ , ϑ₂ , ϑ₃ and ϑ₄. Therefore, the stepping motor 24 rotates in forward direction. Although in the embodiment of the invention the sheet feeder is applied for a color thermal printer , in other modified embodiments of the invention the sheet feeder is applied for mono-color thermal printers or dot-matrix printers (mechanical impact printer). Although the invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been changed in the details of construction and the combination and arrangement of parts may be resorted to without departing from the invention as claimed.

Claims: A sheet feeder comprising: a sheet case (5); a sheet stopper (14); a feeding roller (6) which, in feeding operation, touches a topmost sheet (7) of stacked sheets in said sheet case (5); a feeding roller motor (24) for driving said feeding roller (6) and motor driving means (22) for feeding forward rotation current to said feeding roller motor (24) for issuing said topmost sheet (7) from said sheet case (5) and a reverse rotation current to said feeding roller motor (24) for a short time prior to feeding of said forward rotation current, characterized in that said sheet stopper (14) is provided at the rear end of said sheet case (5) wherein a touching surface (14a) of said sheet stopper (14) is of a material having friction against the topmost sheet (7) and elasticity, wherein upon feeding of said reverse rotation current to said feeding roller motor (24) the rear end of said topmost sheet (7) touches and pushes said sheet stopper (14), thereby causing separation of said topmost sheet (7). A sheet feeder according to claim 1, characterized in that said sheet stopper (14) is a loop-shaped member of a hook and loop fastener.

Inventors: NAKAMURA, HISASHI, SUGETA, SHIGERU, YAMAUCHI, NOBUHARU
Applicants: MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1988
Main classification: B41J13
IPC codes: B65H1, B41J13, B65H3