Patent Publication Number: US-6712351-B2

Title: Sheet feeding apparatus

Description:
This application incorporates by reference Taiwan application Serial No. 090110666, filed May 3, 2001. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates in general to a sheet feeding apparatus, and in particular, to a sheet feeding apparatus using an elastic device. 
     2. Description of the Related Art 
     The performance of the conventional image forming apparatus, such as a printer, copy machine, facsimile machine, or the like, is greatly affected by the quality of sheet feeding. A sheet feeding apparatus capable of separating and feeding sheets one-by-one smoothly and continuously is therefore in great demand. 
     Taking the printer as an example of the image forming apparatus, a conventional sheet feeding apparatus is illustrated in FIG.  1 A. The printer is typically equipped with an automatic sheet feeding apparatus, wherein sheets of papers are first positioned at a rest plate and driven one-by-one by the sheet feeding apparatus to the image forming apparatus. In FIG. 1A, a base  101  for supporting the sheets is at the bottom of the automatic sheet feeding apparatus. A roller  150  is installed above the base  101  to drive the sheets forward. The base  101  has a sheet-separating pad  103 , for separating sheets one-by-one, and a number of smooth ribs  102 . 
     The front view shown in FIG. 1B illustrates the movement of the sheets. The sheet separating pad  103  and the smooth ribs  102  are located on the base  101  of the automatic sheet feeding apparatus and are parallel to each other. The ribs  102  act to elevate the sheets in order to facilitate the smooth movement of the individual sheets. Materials with low friction coefficient are ideal for the manufacture of the ribs  102 ; thus a smooth rubber or plastic is frequently used because of the additional advantage of low cost. The side view shown in FIG. 1C illustrates the movement of the sheets. The sheet  105  is driven by the roller  150  (not shown), and is moved along the direction A. The front edge  107  of the sheet  105  touches the surfaces of the ribs  102  and slides along the direction A. 
     Then referring to FIG. 1D, the friction force to the sheet is illustrated. While the sheet  105  is forwarded along the direction A, the ribs  102  generate a friction force against the movement of the sheet  105 . If the thickness of the sheet  105  reaches to a certain level, the friction force will not have much influence on the movement of the sheet. However, if the sheet  105  is thin, the lower edge  107  can bend around, instead of moving forward smoothly, as shown in FIG.  1 E. 
     In FIG. 1E, the lower edge  107  of sheet  105  is in contact with the ribs  102 . The roller (not shown) drives the sheet  105  forward along the direction A, but the friction force pushes the sheet backward along the direction B. As the roller continues to drive the sheet  105 , the sheet  105  can potentially roll up and cause a paper jam. 
     In addition to the ribs  102 , the sheet-separating pad  103  is also a key element of the conventional base  101 . FIG. 2 shows the side view of the sheet-separating pad  103  and the sheets  105 . The sheet-separating pad  103  is shaped similarly to a saw in that it has a number of sawtooth-like protrusions  106 . Each protrusion  106  rises up at an angle α. The friction force generated by the sheet-separating pad  103  against the sheets is large enough to separate each sheet. The sheet-separating pad  103  is typically positioned along the sheet moving direction A. Thus, as the sheet  105  moves and rises along the sawtooth-like protrusions  106 , it is separated from the other sheets. The movement of the sheet  105  depends on the angle α and the friction coefficient, which is affected by the material and thickness of the sheet  105 . 
     The type of printing sheet can vary greatly, with the material and thickness being just two factors. The thickness, usually defined by g/m 2 , can vary within a wide range, for example, from thick postcards, envelopes, and plastic plates to thin plain papers. The conventional sheet-separating pad is designed to satisfy a certain range of printing materials. The incline angle α and the material type (which affects the coefficient of friction) of the sheet separating pad  103  are determined factors, thus only printing materials within the designated range are suitable. Printing materials outside the designated range may cause paper jams or reduce the sheet feeding accuracy. Furthermore, the high precision requirement in the manufacturing of the sheet-separating pad causes difficulties in fabrication and results in higher cost. To summarize, the disadvantages of the conventional sheet feeding apparatus comprise the following: 
     1. paper jams; 
     2. limited printing materials; 
     3. less accuracy in sheet separation; and 
     4. higher cost in fabrication of the sheet-separating pad. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide a sheet feeding apparatus that enhances the stability of sheet separation and reduces the potential for paper jams. 
     According to the object of the invention, a sheet-separating pad for use in a sheet feeding apparatus is disclosed. The sheet-separating pad comprises a pad base having a top surface and a groove. Numerous inclined protrusions are formed at one or two sides of the groove on the top surface of the base to guide the sheet(s) in a certain direction. An elastic device, such as a spiral spring or a series of connected spring leaves, is situated in the groove. The spiral spring or series of spring leaves protrudes above the top surface of the base in order to separate the sheets. Driven by rollers, the sheets rise gradually along the protrusions so that the sheets can be separated one-by-one. Moreover, the radial arrangement of the ribs and the sheet-separating pad allows the lower edge of each sheet to move forward smoothly such that a paper jam can be prevented. 
    
    
     Other objects, features, and advantages of the invention will become apparent from the following detailed description of the preferred but non-limiting embodiments. The following description of the preferred embodiments of the present invention is made with reference to the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A shows a conventional automatic sheet feeding apparatus. 
     FIG. 1B shows the front view of the movement of the sheets, according to conventional sheet feeding apparatus of FIG.  1 A. 
     FIG. 1C shows the side view of the movement of the sheets, according to conventional sheet feeding apparatus of FIG.  1 A. 
     FIG. 1D illustrates the friction to the sheet. 
     FIG. 1E shows the sheet bending at the lower edge. 
     FIG. 2 shows the side view of the sheet-separating pad and the sheets, according to conventional sheet feeding apparatus of FIG.  1 A. 
     FIGS. 3A and 3B show the sheet-separating pads according to a preferred embodiment of the invention. 
     FIG. 3C shows the side view of the pad base and the spiral spring according to a preferred embodiment of the invention. 
     FIG. 4A shows a portion of the sheet-separation pad according to a preferred embodiment of the invention. 
     FIG. 4B to FIG. 4D show the process of sheet separation using a sheet feeding apparatus of the present invention. 
     FIG. 5 shows another sheet feeding apparatus of the invention, using a series of connected spring leaves to facilitate sheet separation. 
     FIG. 6 shows the radial arrangement of the ribs and the sheet-separating pad of the pad base. 
     FIG. 7A shows the top view of the ribs and the sheet-separating pad according to a preferred embodiment of the invention. 
     FIG. 7B shows another top view of the ribs and the sheet-separating pad according to a preferred embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 3A and 3B show the sheet separating pad according a preferred embodiment of the invention. The sheet separating pad  300  comprises the pad base  301 , the groove  310 , and the spiral spring  311 . The spiral spring  311  is positioned within the groove  310 . The groove  310  is formed along the central line of the pad base  301  and the longitudinal axis of the groove  310  is parallel to the direction of the sheet movement. The spiral spring  311  and the groove  310  are designed so that the top of the spiral spring  311  is higher than the top surface of the pad base  301 . While the paper sheet (not shown) is positioned above the sheet-separating pad  300 , the lower edge  107  of the sheet is in contact with a spring ring  317  of the spiral spring  311 . As the sheet  105  is driven forward to the paper exit, the spring ring  317 , which is in contact with the sheet  105 , also is driven forward. Referring to FIG. 3C, numerous inclined protrusions  312  are formed at either one or both sides of the groove  310  for guiding the paper sheet  105 . When the paper sheet  105  is driven forward, the lower edge  107  of the sheet  105  slides on the top surface of the inclined protrusion  312  and guided by the protrusion  312  to move upward gradually. When the lower edge  107  is driven onto the highest point  312   a  of the inclined protrusion  312 , the lower edge  107  will easily move over the first spring ring which was firstly in contact with the sheet  105 , and then the lower edge  107  will move to contact the next spring ring  317 . After the lower edge  107  moves over the first spring ring, the first spring ring once pushed forward will return to its original position. By repeating the above-mentioned steps, these paper sheets can be separated accurately one-by-one. 
     In FIG. 3C, the side view of the base and the spiral spring  311  is shown. The top of each spring ring  317  is higher than the top surface of the base  301 , and is approximately as high as the highest point  312   a  of the inclined protrusion  312 . As a result, after the sheet  105  is driven to move over the first spring ring  317  and the protrusion  312 , the sheet  105  will move from the first spring ring until it reaches the next ring. The protrusions  312  can be either (a) separated structures fixed onto the base  301  one-by-one, or (b) structures integrally formed with the base  301  through a single molding process. 
     The process of separating the sheets by using the sheet feeding apparatus of the present invention is further explained as follows. In FIG. 4A, to illustrate the example below, a portion of the sheet separation pad  300  is magnified. A number of protrusions  312  and the spiral spring  311  are positioned on the base  101  of the sheet-separation pad  300 . The spiral spring  311  includes a number of spring rings  317 . Three adjacent spring rings  317  are labeled as spring ring i, spring ring j, and spring ring k, respectively. Two sheets, sheet  105   a  and sheet  105   b , are placed on the sheet-separation pad  300 . The sheet  105   a  is placed between the spring ring i and the spring ring j. As shown in FIG. 4B, the original distance between the spring ring i and spring ring j is approximately equal to the distance between spring ring j and spring ring k. As shown in FIG. 4C, when the sheet  105   a  is driven by the roller (not shown) and contacts the spring ring j, the spring ring j is indirectly driven forward. The roller has no direct contact with other sheets, so the other sheets below sheet  105   a  will not advance forward. Therefore, the sheet  105   a  is separated from the other sheets. In FIG. 4C, the sheet  105   a  is elevated to the highest point  312   a  of the inclined protrusion  312 . As the roller (not shown) continues to drive the sheet  105   a  forward, the sheet  105   a  will move over the top of the spring ring j and fall into the gap between the spring ring j and the spring ring k, and then the spring ring j will return to its original position. 
     Through the aforementioned sheet separation process, even if there are two or more sheets fall into the same gap between two spring rings, these sheets will be separated gradually. Moreover, the spiral spring  317  can be replaced by other elastic devices such as spring leaves. 
     Referring to FIG. 5, it shows a sheet feeding apparatus according to another embodiment of the present invention, wherein a series of connected spring leaves facilitates the sheet-separation process. Similarly to the sheet-separating pad  300  and the base  101  shown in FIG. 3A, the inclined protrusions  312  are formed along both sides of the groove  310 . In FIG. 5, the bottoms of the leaf springs  501  are fixed at the bottom of groove  310 . The top of the leaf springs  501  is approximately as high as the highest point  312   a  of the protrusions  312 . 
     The sheet-separating pad of the present invention can separate sheets of various materials and thickness by the forward and backward motion of an elastic device, such as the spring leaves. In comparison, the conventional sheet-separating pad of FIGS. 1A and 2 can separate a less variety of sheets because the protrusions on the pad have a fixed incline angle α. Furthermore, the sheet feeding apparatus with the sheet-separating pads of the invention is simple in structure and thus simple to manufacture. Because the precision requirement in manufacturing is not as strict as that of the conventional one. Hence, the sheet feeding apparatus of the present invention is a cost-effective solution. 
     A further improvement of the sheet feeding apparatus, which prevents sheets from rolling up and the consequential paper jam, is disclosed. It is achieved by the radial arrangement of the ribs  102  and the sheet-separating pad  103  shown in FIG.  6 . The surfaces of the ribs  102  are smooth. While the sheet  105  moves, friction force C pushes the sheet  105  toward two sides of the sheet separating apparatus but does not hinder the movement of the sheet  105  toward the direction A. The sheet  105  moves forward smoothly and is prevented from rolling up, therefore eliminating a potential paper jam. 
     FIG. 7A shows the top view of the ribs and the sheet-separating pad according to another embodiment of the invention. The longitudinal axis of the inner rib and the sheet-separating pad are relative to the paper sheet movement direction A with an angle â. The outer ribs are positioned at the same angle â to the inner rib and sheet-separating pad ▪ so the longitudinal axis of the ribs and the sheet-separating pad are relative to each other with an angle â. The angle â is not limited as long as the radial arrangement generates a friction force in a direction perpendicular to the direction of sheet movement, which pushes the sheet  105  smoothly and thus prevents the sheet from bending but allows the sheet  105  to move smoothly. 
     FIG. 7B shows another top view of the ribs and the sheet-separating pad according to further embodiment of the invention. The longitudinal axis of the inner rib and the sheet-separating pad are both parallel to the paper sheet movement direction A, while the longitudinal axis of the two outer ribs are relative to the direction A with an angle γ so that the friction force in a direction perpendicular to the direction of sheet movement generated pushes the sheet  105  smoothly and thus prevents the sheet from bending but allows the sheet  105  to move smoothly. 
     The sheet feeding apparatus of the invention disclosed herein offers the following advantages: 
     1. wider range of suitable printing materials; 
     2. high accuracy in sheet separation; 
     3. prevention of paper jams; and 
     4. reduction in cost. 
     While the invention has been described by way of examples and in terms of the preferred embodiments, it is to be understood that the invention is not limited hereto. On the contrary, it is intended to cover various modifications and similar arrangements and procedures, and therefore the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.