Patent Publication Number: US-2004041329-A1

Title: Sheet feeder

Description:
BACKGROUND OF THE INVENTION  
       [0001] The present invention relates to a sheet feeder for holding a plurality of paper sheets and feeding individual sheets one by one to an image reading device, printer or the like. Specifically, it relates to a sheet feeder provided with a sheet sensor for detecting the absence/existence of a sheet and the width of a sheet by sensing a change of a swing angle of a sensor lever.  
       [0002] Particularly in image reading devices or printers, separating a paper sheet from a pile of sheets loaded in a sheet feeding portion and feeding it to a next process is a very important technique which therefore has been implemented by using a various well-known structures and arrangements of printers etc.  
       [0003] There are various kinds of methods for separating a paper sheet from a plurality of sheets, e.g., by using a combination of a feeding roller and a reverse rotating roller or a combination of a feeding roller and a separating nail or a combination of a feeding roller and a separating plate or vacuum suckers.  
       [0004] A method using a rotary (swinging) lever for discriminating the size of a paper sheet and the existence/absence of a paper sheet is also known. Specifically, this conventional method has been implemented in such a manner that the swinging lever can take refuge in an opening made on a sheet supporting table to widen the swinging range of the swinging lever in order to increase the detection ability of the swinging lever.  
       [0005] In recent years, there has been seen the tendency of miniaturization of image forming apparatuses such as image reading devices and printers which in turn have a tendency that a number of loaded paper sheets increases, then the capability of loading a larger number of paper sheets in a smaller space becomes an important designing element ensuring separation and transportation of an individual paper sheet. Consequently, saving in the physical space for mounting a sheet sensor has become an important problem to be solved.  
       SUMMARY OF THE INVENTION  
       [0006] An object of the present invention is to provide a sheet feeder capable of causing a conventional sensor lever to swing in accordance with an amount of sheets loaded in a sheet cassette and detecting the amount of the sheets based on a change in a swing angle of the sensor lever, wherein a bottom board for supporting a pile of sheets has a notch for receiving the sensor lever so that the sensor lever can surely detect the existence/absence of the paper by increasing a changing amount of the swing angle of the sensor lever before and after the last sheet is fed. In this instance, it is difficult to achieve a sufficient sheet holding capacity since the maximum amount of sheets loaded on the bottom board may be restricted by a distance between a surface of the bottom board and the supporting axis of the sensor lever.  
       [0007] Therefore, the sheet feeder according to the present invention can load an increased amount of sheets by enabling the sensor lever to swing for loading a larger number of sheets in the sheet cassette and, when an amount of sheets increases, retracting the sensor lever from the pile of sheets. On the contrary, with a small amount of remaining sheets, the sensor lever is prevented from retracting never to fail in detecting the state of no remaining sheet in the sheet cassette.  
       [0008] Another object of the present invention is to provide a sheet feeder separating a sheet from a pile of sheets loaded in a sheet cassette and feeding it to a next process, wherein a sensor lever abuts against a top of a pile of sheets in the sheet cassette and swings with a swinging axis and changes its angle in accordance with an amount of sheets loaded in the sheet cassette, and when a large number of sheets are loaded in the sheet cassette the swinging axis can move upward together with the sensor lever in the direction of separating the sensor lever from the pile of sheets. This makes it possible to increase the maximum number of sheets to be loaded by using space efficiently when designing a compact image reading device or printer which needs to ensure separation and transportation of a sheet.  
       [0009] Another object of the present invention is to provide a sheet feeder as described above, wherein a sensor lever is supported at its swinging axis in an elliptic hole made in a supporting member and has an abutting member which may abut against the receiving portion of the supporting member to prevent the swinging axis of the sensor lever from moving with a small amount or no amount of sheets. This simple means enables the sheet feeder to surely prevent the movement of the swinging axis of the sensor lever, ensuring the reliable operation of the sensor lever with a small amount of remaining sheets to be fed.  
       [0010] A further object of the present invention is to provide a sheet feeder as described above, wherein a sensor lever is supported at its swinging axis with a noncircular cross-section inserted in an elliptic hole with an enlarged round portion made in the supporting member to prevent the movement of the swinging axis in the elliptic hole of the supporting member with a small amount or no amount of sheets, thereby ensuring the reliable operation of the sensor lever with a small amount of remaining sheets in the cassettes.  
       [0011] A still further object of the present invention is to provide a sheet feeder as described above, wherein a lower tip of the sensor lever can fall into a concave formed in a sheet piling portion to increase the rotation angle of the sensor lever before and after the last sheet is fed, thereby ensuring the reliable detection of the existence/absence of the sheets. 
     
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
     [0012]FIG. 1 is a schematic sectional view of a laser facsimile apparatus using a sheet feeder according to the present invention.  
     [0013]FIG. 2 is a perspective view of a sheet cassette used in the laser facsimile apparatus.  
     [0014]FIGS. 3A, 3B and  3 C are sectional side views for explaining the operation of the sheet cassette.  
     [0015]FIG. 4 is a side view of the first example of a sheet sensor used in a sheet feeder according to the present invention.  
     [0016]FIG. 5 is a side view of the second example of a sheet sensor used in a sheet feeder according to the present invention.  
    
    
     PREFERRED EMBODIMENTS OF THE INVENTION  
     [0017] A sheet feeder according to the present invention is to separate a sheet from a sheet pile and feed it to a next processing portion and is applied for an image reading device in which document sheets piled are picked up one by one, scanned by a document reading device and then delivered out, or an image forming device, for example, a printer wherein cut-sheets are picked up one by one, printed by a printing portion and then delivered out. The following example is the case of using a sheet feeder according to the present invention in a laser facsimile apparatus using the Carlson process.  
     [0018]FIG. 1 schematically illustrates in cross section a laser facsimile apparatus using a sheet feeder according to the present invention, where electronic circuits etc. which do not directly relate to the present invention are omitted for simplicity. In the laser facsimile apparatus, a control portion  1  is a man-machine interface portion having various kinds of key buttons for inputting information by a user and a display for presenting information to a user.  
     [0019] A plurality of documents to be read are loaded on a document feeding portion  2  and separated one by one by a separating rubber plate  4  disposed opposite to a separator roller  3  and fed to a document reading unit  5  by which it is read and then delivered by a document delivering rollers  6  to a document discharging portion  7  where a document stacker (not shown in FIG. 1) is provided for receiving documents delivered.  
     [0020] A pile of sheets (recording paper) S are loaded in a sheet cassette  11  wherefrom one sheet is separated and fed by a pickup roller  12  (to be described later) to an image transferring portion  19  where toner from a light-sensitive drum  14  is transferred on the sheet S and forms a visible image on the sheet S. The sheet carrying a toner-developed image is then heated by a fixing roller  21  for fusing and fixing toner which forms the image on the sheet S. The sheet S is transported along a document transporting route  20  through the fixing roller  21  to a delivery stacker  22 . For simplicity, some of the sheet guides disposed along the document transporting route  20  for transporting a sheet S are not shown in FIG. 1.  
     [0021] Printing the sheet S is carried out as follows:  
     [0022] Laser beam L from a laser unit  16  transfers image on the light-sensitive drum  14  previously electrically charged by a charging portion  15 . Laser beam L is modulated with information to be printed and converted by a polygon mirror (not shown) to a scanning beam which beam is then reflected from a reflecting mirror  17  and scan the electrically charged surface of the light-sensitive drum  14  to form a latent electrostatic image thereon to be transferred later on a recording paper sheet. Namely, the scanning laser beam L carries thereon an on-off imaging pattern necessary for forming an image to be printed and the drum electrically charged in advance by the charging portion  15  is scanned by the laser beam L becomes to have decreased potentials of exposed parts on its surface in accordance with the scanning pattern, resulting in forming a latent electrostatic image to be printed on the light-sensitive drum  14 . The latent electrostatic image formed on the light-sensitive drum  14  is developed with toner picked up from a developing bath  18  to present a visible image which is then transferred onto a sheet S by an image transfer portion  19 . A sensor lever according to the present invention is applied as a sheet sensor for a pile of sheets S loaded in a sheet cassette  11  of the shown laser facsimile apparatus.  
     [0023]FIG. 2 is a perspective view of a sheet cassette used in a laser facsimile apparatus. Sheets are piled on a bottom board  23  of the sheet cassette  11 , which board is supported at one end by a supporting shaft  25  and can be lifted by a force of a spring  26  (see FIGS. 3A, 3B and  3 C). The front edge of the top of the sheet pile is prevented from being lifted by a pair of sheet limiting fingers  27 . Namely, the top of the sheet pile is always pressed by the sheet limiting fingers  27 .  
     [0024] When a pickup roller  12  starts rotation and pushes the top sheet by the friction force produced there between, then only the top sheet is fed forward (to right in FIG. 2) overcoming the preventing force of the sheet limiting fingers  27 . Namely, owing to the fact that a friction force produced between the pickup roller  12  and a top sheet is greater than a total of a preventive force of the sheet limiting fingers  27  and a friction force produced between a top sheet and the next sheet, only the top sheet can be separated and fed from the cassette to a next process.  
     [0025] When the last sheet S was fed from the sheet cassette  11  shown in FIG. 2, i.e., no paper exist on the bottom board  23  of the sheet cassette  11 , a (front) lower tip  34 a of a sensor lever  34  falls into a concave (i.e., “sensor lever receiving port”)  24  formed on the bottom board  23  with a large change in swing angle, which is detected to indicate the absence of the sheet S in the sheet cassette  11 . The provision of the sensor lever receiving port  24  can produce a greater change in swing angle of the sensor lever  34  before and after the last sheet S disappears from the sheet cassette  11 , thereby making it possible to surely detect the state of no paper existing in the sheet cassette  11 . A change in a swing angle of the sensor lever  34  can be detected by using a suitable sensor element such as a micro-switch, reed switch, electromagnetic sensor, photo coupler and so on. A linear arrangement of plural micro-switches for detecting an angle of the sensor lever  34  is effective to indicate an approximate amount of recording sheets remaining in the sheet cassette  11 .  
     [0026]FIGS. 3A, 3B and  3 C are sectional side elevations for explaining the operation of the sheet cassette. FIG. 3A shows the sheet cassette loaded with a sufficient amount of sheets, FIG. 3B shows the sheet cassette with a small amount of sheets therein and FIG. 3C shows the sheet cassette with no paper therein.  
     [0027] In FIG. 3A, the sheet cassette  11  is full loaded with paper sheets S on the top of which a sensor lever  34  lies taking an approximate horizontal angular position. In this state, a whole sensor lever  34  with its swinging axis (sensor lever axis)  35  is lifted upward by the effect of technical means (to be described later) to increase the number of sheets to be loaded in the sheet cassette  11 .  
     [0028]FIG. 3B illustrates the state of the sheet cassette  11  containing a small amount of paper sheets S in which the bottom board  23  supported by the supporting shaft  25  is tilted with its front end lifted on the side of the pickup roller  12 . In this state, the top of paper sheets abuts against the sheet limiting fingers  27  and the function of separating a top sheet and feeding it by the pickup roller  12  still remains in ready to operate. The lower tip  34 a of the sensor lever  34  moved downward from the position shown in FIG. 3A. However, a detection signal “no paper” cannot be generated in this state of the sensor lever  34 .  
     [0029] When the last sheet was fed from the sheet cassette  11 , the sensor lever  34  falls into the sensor lever receiving port  24  formed on the bottom board as shown in FIG. 3C. In this state, the lower tip  34 a of the sensor lever  34  dropped by a considerable angle, which can be easily detected to indicate the absence of paper in the sheet cassette  11 .  
     [0030]FIG. 4 illustrates a side view of the first example of a sheet sensor used in the sheet feeder according to the present invention. A sensor lever  34  has a sensor lever axis (swinging axis)  35  fitted in an elliptic hole  32  made in a sensor lever holding member  31  for the sensor lever and can freely swing. A sensor lever holding member  31  corresponds to a supporting member defined in claims. The sensor lever  34  locates at the lowest part of the elliptic hole  32  by its weight. The sensor lever  34  has a sensor lever abutting member  36  and the sensor lever holding member  31  has a sensor lever receiving member  33 . With a small amount of sheets in the cassette as shown FIG. 4, the sensor lever  34  swings and the sensor lever abutting member  36  abuts against the sensor lever receiving member  33  of the sensor lever holding member  31 . In this state, the sensor lever axis  35  cannot move upward in the elliptic hole  32 . As described above, when the number of sheets in the sheet cassette is small, the sensor lever axis  35  is prevented from moving upward in the elliptic hole  32  by abutting the sensor lever abutting member  36  against the sensor lever receiving member  33 . A change in angular position of the sensor lever  34  is correctly detected to indicate the existence/absence of a paper sheet in the cassette.  
     [0031]FIG. 5 illustrates a side view of the second example of a sheet sensor usable in a sheet feeder according to the present invention.  
     [0032] The sensor lever  43  has a sensor lever axis  44  movably fitted in an elliptic hole  42  made in a sensor lever holding member  41  for the sensor lever. The sensor lever axis  44  has a noncircular section of different sizes in radial directions. In the shown instance, the sensor lever axis  44  with an elliptic cross-section can or cannot move in the elliptic hole in the holding member depending on an angle of the sensor lever  43 . On the other hand, the elliptic hole  42  made in the holding member  41  has a larger diameter round hole  42   a  in its lower end of the elliptic hole  42 . Therefore, the sensor lever axis  44  can freely rotate in the larger round hole  42   a  at any angle of the sensor lever  43 . When the sensor lever  43  takes a near horizontal position in FIG. 5, the sensor lever axis  44  can move upward in the upper portion of the elliptic hole  42  since the direction of the longest diameter of the sensor lever axis  44  is identical to the longitudinal direction of the elliptic hole  42  of the sensor lever holding member  41 .  
     [0033] This sheet sensor can retract the sensor lever  43  upward by moving the sensor lever axis upward in the elliptic hole  42  when the sheet cassette is loaded with a large number of paper sheets. On the other hand, the sheet sensor keeps the sensor lever axis  44  in the large round hole  42   a  when the sensor lever  43  works with a reduced amount of sheets in the sheet cassette, reliably sensing the existence/absence of paper sheets to be fed.  
     [0034] While the present invention has been described by way of examples with the case that a sheet cassette is provided with a sheet sensor for sensing the existence/absence of paper sheets and an approximate amount of sheets remaining in the sheet cassette, it is also possible to discriminate the sizes of paper sheets to be used by arranging a plurality of sensors in width direction of the sheet cassette in accordance with different format sizes of paper sheets to be accommodated therein.  
     [0035] While the invention has been described with the application of the sheet feeder to a facsimile apparatus, image reading device, and printer, the sheet feeder can be also applied to any of other devices requiring feeding paper sheets from a pile of sheets and, therefore, the scope of the claims is not limited to the described applications and embodiments.  
     [0036] A sheet feeder according to the present invention is a compact structure and capable of accommodating a large number of paper sheets in the sheet cassette by swinging the sensor lever and retracting the sensor lever upward with its swinging axis moved in the direction parting from the top of sheets when a large amount of sheets are loaded in the sheet cassette, and making the movement of sensor lever reliable which detects the existence/absence of a paper sheet by the sensor lever.  
     [0037] With a small amount or no amount of sheets remaining in the sheet cassette, the abutting member is formed on the sensor lever and abuts against a receiving member of the supporting member, thereby preventing the movement of the swinging axis in a simple structure and enabling the movement of the sensor lever to be reliable.  
     [0038] The sensor lever has a swinging axis of a noncircular profile, which axis is fitted in an elliptic hole with an enlarged round hole formed in the supporting member. With a small amount or no amount of paper sheets remaining in the sheet cassette, the swinging axis is kept in the enlarged round hole in order to ensure the reliable action of the sensor lever with decreasing amount of the remaining sheets.  
     [0039] When the last sheet was fed from the sheet cassette, a lower tip of the sensor lever falls into a concave formed in the bottom board of the sheet cassette. This can provide a considerable change in swinging angle of the sensor lever before and after the last sheet is fed, which can be surely detected to indicate whether the last paper remains or not.