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

FIELD OF THE INVENTION AND RELATED ART STATEMENT

1. FIELD OF THE INVENTION

[0001] This invention relates to a sheet feeder for printer, particularly to that wherein undesirable plural sheets feeding is prevented.

2. DESCRIPTION OF THE RELATED ART

[0002] FIG.1 is a sectional view of sheet feeder of prior art. In FIG.1, an ink sheet 8 is conveyed to a take-up reel 10 from a feeding reel 9. The feeding roller 6 is moved in a direction shown by an arrow A in FIG.1 and is made touch to a top paper 7 of stacked papers in a paper cartridge 5. Then, by rotation of the feeding roller 6, the paper 7 is taken out from the paper cartridge 5 and is transferred to a platen roller 2. Further, the paper 7 is transferred between the platen roller 2 and a thermal head 1 by pinch rollers 3, 4, and printing is made with yellow ribbon 8 (see FIG.2) by a thermal head. When the yellow print operation is completed, the paper 7 is transferred to a first paper passage 12.

[0003] Next, the paper 7 is transferred to a second paper passage 13 by reversely rotating the platen roller 2 as shown in FIG.3. Then, the paper 7 is printed with magenta ribbon by forward rotation of the platen roller 2 as shown in FIG.4. Cyan print operation is carried out in the same manner as the operation of yellow or magenta print.

[0004] The structure of the above-mentioned conven­tional device suffers the problem that two or more papers are often taken out from the paper cartridge 5, thereby resulting in defect of printing. Therefore, it is necessary to prevent the problem of plural sheet taking-­out.

OBJECT AND SUMMARY OF THE INVENTION

[0005] It is an object of the present invention to solve the above-mentioned problem, by providing a sheet feeder wherein it is prevented that two or more sheets are taken out from the paper cartridge 5.

[0006] A sheet feeder in accordance with the present invention comprises:
    a sheet case,
    a sheet stopper provided at rear end of the sheet case,
    a feeding roller which, in feeding operation, touches top sheet of stacked sheets in the sheet case,
    a feeding roller motor for driving the feeding roller, and
    motor driving means for feeding forward rotation current to the feeding roller motor for issuing the top sheet from the sheet case and a reverse rotation current to the feeding roller motor for a short time prior to feeding of the forward rotation current, thereby making rear end of the top sheet touch and push the sheet stopper, thereby making separation of the top sheet.

[0007] In the present invention, the feeding roller rotates in reverse direction to feeding-out direction for a very short time, and thus the rear end of sheet in the sheet cartridge is made contact the sheet stopper provided at the rear end of the sheet cartridge. Therefore, even when two or more sheets are sticking each other, the sheets are separated by such reverse direction rotation of the feeding roller.

[0008] While the novel features of the invention are set forth particularly in the appended claims, the invention, both as to organization and content, will be better understood and appreciated, along with other objects and features thereof, from the following detailed description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] 

FIG.1 is the sectional view of the color printer having the sheet feeder of prior art.

FIGs. 2 to 4 are the sectional views of the color printer having sheet feeder of the prior art for showing operation thereof.

FIG.5 is a sectional view of a color printer having a sheet feeder embodying the present invention.

FIG.6 is a sectional view of the paper cartridge in FIG.5.

FIG.7 is a circuit diagram of a control circuit of the paper cartridge of FIG.5.

FIGs. 8A and 8B are time charts for showing an operation of the control circuit of FIG.7.

FIG.9 is a flow chart for showing feeding operation of the control circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] FIG.5 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 in direction shown by an arrow A in FIG.1 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.5, so that the rear end of paper is made touch 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.5. 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 yellow-ribbon (see FIG.2). When the yellow print operation is completed, the paper 7 is transferred to a first paper passage 12.

[0011] Next, the paper 7 is transferred to a second paper passage 13 by reversely rotating the platen roller 2 as shown in FIG.3. Then, the paper 7 is printed with magenta ribbon with rotation of the platen roller 2 as shown in FIG.4. Cyan print operation is carried out in the same manner as yellow or magenta print operation.

[0012] FIG.6 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 direction of its surface, such as any one member of known hook and loop fastener, is provided.

[0013] FIG.7 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 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.

[0014] FIG.9 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.8A from output terminals φ₁ , φ₂ , φ₃ and φ₄. The driver 22 outputs signals corresponding to the pulse signals as shown in FIG.8A for driving the stepping motor 24. Therefore, the stepping motor 24 rotates in reverse direction.

[0015] 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.8B from output terminals φ₁ , φ₂ , φ₃ and φ₄. Therefore, the stepping motor 24 rotates in forward direction.

[0016] Although in the embodiment of the invention the sheet feeder is applied for color thermal printer , in other modified embodiments of the invention the sheet feeder is applied for mono-color thermal printer or dot-­matrix printer (mechanical impact printer).

[0017] 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 spirit and the scope of the invention as hereinafter claimed.

Claims

1. A sheet feeder comprising:
      a sheet case,
      a sheet stopper provided at rear end of said sheet case,
      a feeding roller which, in feeding operation, touches top sheet of stacked sheets in said sheet case,
      a feeding roller motor for driving said feeding roller, and
      motor driving means for feeding forward rotation current to said feeding roller motor for issuing said top sheet from said sheet case and a reverse rotation current to said feeding roller motor for a short time prior to feeding of said forward rotation current, thereby making rear end of said top sheet touch and push said sheet stopper, thereby making separation of said top sheet.

2. A sheet feeder in accordance with claim 1, wherein
      touching surface of said sheet stopper is of a material having friction against the sheet and elasticity.

Drawing