Resistance plate in a sheet feed device

Abstract: An auto sheet feed device (20) for a printer is described. The device includes a pivoting paper loading plate (22) and a pick up device (26) for picking up sheets (P) loaded onto the paper loading plate (22). A knock-up spring (24) presses the paper loading plate (22) and hence the uppermost sheet loaded onto it into contact with the pick up device (26). A resistance plate (251), for separating the sheets of paper (P) loaded onto the paper loading plate (22) is provided and this resistance plate (251) is pivoted by a gear mechanism (253) in accordance with movement of the paper loading plate (22) to maintain the angle between the two substantially invariant. The gear mechanism includes a rack gear (255) on the paper loading plate, an idler gear (254) and a fan-shaped driven gear (253) on the resistance plate (251).

Description: BACKGROUND TO THE INVENTION The present invention relates to an auto sheet feed device for use in an office automation system that uses a resistance plate to separate sheets of paper to be fed. Generally, many devices, such as printers, copier and facsimiles are included in office automation systems. However, the present invention will be explained with reference to an ink-jet printer, which prints by forming letters on printing paper by ejecting droplets of ink through a nozzle. The numbers of nozzles used in an ink-jet printer is generally about 64 and the picture resolution is usually about 300-1200 DPI (Dots Per Inch). Colour printing is possible with some kinds of cartridge. Such a printer 10, as illustrated in FIGs. 1 and 2, comprises an auto paper feeder 20 which feeds papers P for printing, a paper transporter 30 for transporting papers fed from the auto paper feeder 20, a printing device 40 that prints on the papers transported by the paper transporter 30 and a paper discharger 50 that discharges the papers printed by the printing device 40. All theses are contained within the body of the apparatus 10. When papers are loaded on the knock-up plate of the auto paper feeder 20, it adjusts to the size of the loaded papers by movement to the right or the left. When the user gives a print command to print data from a computer, the papers are acted on by the elastic force of a knock-up spring 24 and a pick up roller 28 picks up the papers from the knock-up plate 22 and transports papers, one by one, to the paper transporter 30. The papers transported to the paper transporter 30 are transported to the printing device 40 by the rotation of a feed roller 31 and a friction roller 32. Once the papers are fed from the paper transporter 30, a carriage driving motor 45 is driven and an associated pulley 46 is also driven. Then, as the belt 44 drives to the left or the right, papers are printed by ejection of ink onto the paper from the transporter 30 through a nozzle 42a on the cartridge 42 which slides to the left and the right along a carriage shaft 43 that is fixed to a guide rail. The printed paper moves, while being printed upon, and once it reaches the paper discharger 60, a discharge operation is performed by its passing between a discharge roller 61 and a star wheel 62. Conventional paper feeding systems use, for paper separation, CLAW separation methods, resistance plate separation methods, friction pad separation methods and roller reverse rotation separation methods. Which auto separation method is chosen depends on the price of the paper or suchlike, reliability, area, properties of the paper, etc. In office automation system such as a printer, various special papers, such as general copy paper (e.g. A4), OHP paper, postcards, envelopes, are used, and so CLAW and resistance place separation methods are mixed and used. Making use of the differences in friction with the resistance plate according to the entering angle of the paper is a characteristic of the resistance plate separation method, and thus the entering angle of the paper loaded on the uppermost edge and the angle of the resistance plate are very important factors involved in the reliability of paper feed. EP-A-0734875 shows the structure of the auto paper feeder 20 which uses the resistance plate separation method. That method will now be described with reference to FIG. 3. Since the separation resistance place 25 is fixed in a body of the printer, e.g. as show fixed to the left upper edge of the main frame 21, the variability of paper entering angle due to differences in quantity of paper loaded cannot easily be absorbed. Thus, with the knock-up plate 22 pushed downward, the entering angle of the papers fully loaded on the uppermost edge tends toward the direction D, such as when new papers are loaded. As the papers are consumed, the amount of paper remaining gets lower and the knock-up plate 22 rises as a result of the elastic force of the knock-up spring 23 and so the entering angle of the papers tends towards the direction C. Accordingly, the entering angle of papers changes by an angle a=1-2, changing the separation of the papers for the fixed resistance plate, and as a result the reliability of the paper feed in feeding the papers deteriorates. In addition, problems such as multiple sheet feeding, jamming and non-feeding can occur. SUMMARY OF THE INVENTION Accordingly, it is therefore an object of the present invention to provide an improved separation structure using a resistance plate. Accordingly, the present invention provides an auto sheet feed device comprising: a pivoting paper loading plate; a pick up device for picking up sheets loaded onto the paper loading plate; means for biasing the paper loading plate towards a position at which the uppermost sheet loaded onto it is offered up to the pick up device; a resistance plate for separating the sheets of paper loaded onto the paper loading plate and picked up by the pick up device; and means for pivoting the resistance plate in accordance with movement of the paper loading plate to maintain the angle between the two substantially invariant. The paper loading plate may pivot upwards and downwards about an axis adjacent the end of the plate remote from the pick up device. The means for biasing the paper loading plate may be adapted to press the said uppermost sheet against the pick up device. Preferably, the means for pivoting the resistance plate comprises: a rack gear formed on the paper loading plate; an idler gear in driving engagement with the rack gear; and a driven gear on the resistance plate and centred on the axis about which the resistance plate pivots in driving engagement with the idler gear. The driven gear may be fan-shaped. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The present invention will now be described by way of example with reference to the accompanying drawings in which: FIG. 1 is a perspective view illustrating the construction of a conventional ink-jet printer; FIG. 2 is an operational side view of the printer of FIG. 1; FIG. 3 is a side view illustrating problems occurring in paper feed with a resistance plate separation method; FIG. 4 is a side view of a printer according to the present invention, showing papers loaded in the auto sheet feeder; and FIGs. 5 and 6 illustrate a driving process of the auto sheet feeder. BRIEF DESCRIPTION OF THE INVENTION As shown in FIG. 4, to one side of the auto sheet feeder 20 is attached a resistance plate variable device 250 comprising a variable resistance plate 251, a fan shaped gear 253 rotating around a hinge shaft 252 in one side of the variable resistance plate 251, a rack gear 255 formed on the knock-up plate 22 and an idler gear 254 turning the fan shaped gear 253 according to the driving of the rack gear 255. The gearing is such that the paper entering angle relative to the resistance plate is invariant, irrespective of the quantity of paper loaded. The variable resistance plate 251 rotates according to movement of the fan shaped gear 253. As is known, the auto sheet feed device comprises a knock-up plate 22 which moves upward and downward according to the amount of paper loaded and consumed and pivoted on a hinge 29. A semicircular pick up roller 26 picks up papers loaded on the knock-up plate 22 according to print signals and a knock-up spring 24 in the other side of the main frame 21 pushes smoothly, to raise the knock-up plate 22 and to prevent contact noise with the knock-up plate 22, when the pick up roller 26 is picking up the paper sheet. The rack gear 255 formed on the knock-up plate 22 is attached to the left of the knock-up spring 24, and the rack gear 255 moves together with upward and downward movement of the knock-up plate 22, rotating anticlockwise or clockwise as the case may be. Then, the idler gear 254 is driven according to the driving of the rack gear 255 and then turns the fan shaped gear 253, and so to rotate the variable resistance plate 251 to the appropriate degree. The operation of such a structure can be considered in conjunction with the accompanying FIGs. 5 and 6 as follows. If the maximum number of papers are loaded in the auto sheet feeder 20, then the knock-up plate 22 is pushed downward and so the knock-up spring 24 is compressed. Furthermore, when the knock-up plate 22 is pushed downward, the rack gear 255 moves downward and the idler gear 254 rotates clockwise. As the idler gear 254 is rotated clockwise by the rack gear 255, the fan shaped gear 253 and the variable resistance plate 251 rotate too. Accordingly, as in FIG. 5, an angle B is formed between the paper and the variable resistance plate 251. Thereafter, the printer receives a print command from the computer. The printer is commanded to print and causes the pick up roller 26 continuously to pick up the sheets of papers and so the quantity of paper loaded reduces and the knock-up plate 22 carrying the papers rises gradually because of the force of restitution of the knock-up spring 24. As the knock-up plate 22 rises little by little, the rack gear 255 attached to the knock-up plate H 22 also rises. This turns the idler gear 254 anticlockwise and the fan shaped gear 253 is rotated clockwise. Consequently, as in FIG. 6, an angle A is formed because the variable resistance plate 251 is rotated. As A and B preserve a certain angle and the angle of the variable resistance plate 251 is corrected according to the quantity of paper loaded, the entering angle of the papers and the friction angle of the resistance plate is preserved invariant irrespective of the quantity of paper loaded and the reliability of the paper feed separation is improved. Furthermore, as the number of times the paper is refilled is reduced by allowing more paper to be carried, the device is greatly more convenient.

Claims: An auto sheet feed device (20) comprising: a pivoting paper loading plate (22), a pick up device (26) for picking up sheets (P) loaded onto the paper loading plate (22); means (24) for biasing the paper loading plate (22) towards a position at which the uppermost sheet loaded onto it is offered up to the pick up device (26); a resistance plate (251) for separating the sheets of paper (P) loaded onto the paper loading plate (22) and picked up by the pick up device (26); characterised by means (250) for pivoting the resistance plate (251) in accordance with movement of the paper loading plate (22) to maintain the angle (A,B) between the two substantially invariant. A device according to claim 1 in which the paper loading plate (22) pivots upwards and downwards about an axis (29) adjacent the end of the plate remote from the pick up device. A device according to claim 1 or claim 2 in which the means (24) for biasing the paper loading plate (22) is adapted to press the said uppermost sheet against the pick up device (26). A device according to any preceding claim in which the means (250) for pivoting the resistance plate comprises: a rack (255) gear formed on the paper loading plate (22); an idler gear (254) in driving engagement with the rack gear (255), and a driven gear (253) on the resistance plate (251) and centred on the axis (252) about which the resistance plate (251) pivots in driving engagement with the idler gear (254). A device according to claim 4 in which the driven gear (253) is fan-shaped.

Inventors: JANG HEUNG-KYU, JANG, HEUNG-KYU
Applicants: SAMSUNG ELECTRONICS CO LTD, SAMSUNG ELECTRONICS CO. LTD.
Application year: 1998
Main classification: B65H3
IPC codes: B65H3, G03G15