Abstract:
A feeding mechanism. The feeding mechanism includes a shaft, an arm and a resilient element. The arm rotates on the shaft and has a second contact surface. The resilient element has a first contact surface contacting the second contact surface at a first contact point and exerts a first torque on the shaft when the arm is in a first position, and the first contact surface contacts the second contact surface at a second contact point, exerting a second torque on the shaft when the arm is in a second position, the first torque being substantially equal to the second torque.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates in general to a feeding mechanism, and more particularly, to a feeding mechanism capable of feeding media sheets of various thickness precisely.  
         [0003]     2. Description of the Related Art  
         [0004]     Referring to  FIG. 1 , the feeding mechanism  10  of a conventional business machine has a roller  12 , a plurality of detachable separators  14 , a shaft  16 , an arm  18  and a resilient element  26  such as a torsion spring. The arm  18  is rotatable on the shaft  16 , and the resilient element  26  exerts a spring force on the arm  18  such that the media sheets in the tray  22  can be driven by the roller  12 .  
         [0005]     The included angle between the arm  18  and the tray  22  dominates the deformation of resilient element  26 . As shown in  FIGS. 2   a  and  3   a,  when the tray  22  is empty, the deformation of resilient element  26  exceeds that when the tray  20  filled with sheets S. Referring to  FIGS. 2   b  and  3   b,  the resilient element  26  has a deforming angle α when the tray  22  is empty and a larger deforming angle β when filled. As the resilient element  26  has a larger deforming angle when filled, a larger normal force is exerted on the sheets S. When only a few sheets S are in the tray  22 , the resilient element  26  merely exerts minimal force on the arm  18 , and improper feeding may occur because the arm  18  does not exert adequate normal driving force on the sheets S. On the contrary, when a large number of sheets S are loaded in the tray  22 , as shown in  FIG. 3   a,  accidental feeding of multiple sheets may occur as the arm  18  exerts excess normal diving force thereon.  
         [0006]      FIG. 4  illustrates sheets of various thicknesses applied in the conventional feeding mechanism  10 . With respect to the thickest sheet  202 , the roller  12  must apply a proper driving force, between 12˜70 g, to feed a single sheet. Misfeed (no sheet is loaded) occurs when the normal driving force is less than 12 g, and multiple feed (multiple sheets are driven at the same time) occurs when the normal driving force is over 70 g.  
         [0007]     If the roller  12  provides a normal driving force between 10˜30 g with respect to loading a number of the sheets  202  as shown by the hatched region R in  FIG. 4 , the sheets  202  may be misfed when force is less than 10 g from the overlap between the hatched region A and R shown in  FIG. 4 . Moreover, when the thinnest sheets  210  receive normal driving force over 25 g, multiple feed may occur from the overlap between the hatched region B and R shown in  FIG. 4 .  
         [0008]     As mentioned above, due to the excessively broad range of normal driving force, only sheets  204 ,  206 ,  208  can be assumed of precise delivery by the conventional feeding mechanism  10 . It is therefore not convenient to apply media sheets of various thicknesses.  
       SUMMARY OF THE INVENTION  
       [0009]     Accordingly, an object of the present invention is to provide a feeding mechanism applicable with sheets of various thickness. The feeding mechanism includes a shaft, an arm and a resilient element. The arm rotates on the shaft and has a second contact surface. The resilient element has a first contact surface contacting the second contact surface at a first contact point and exerts a first torque on the shaft when the arm is in a first position, and the first contact surface contacts the second contact surface at a second contact point, exerting a second torque on the shaft when the arm is in a second position, the first torque being substantially equal to the second torque. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0010]     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings, given by way of illustration only and thus not intended to be limitative of the present invention.  
         [0011]      FIG. 1  is a perspective diagram of a conventional feeding mechanism.  
         [0012]      FIG. 2   a  is a lateral view of the feeding mechanism when the tray is empty, based on  FIG. 1 .  
         [0013]      FIG. 2   b  is a perspective diagrams of the resilient element when the tray is empty, based on  FIG. 2   a.    
         [0014]      FIG. 3   a  is a lateral view of the feeding mechanism when the tray is filled, based on  FIG. 1 .  
         [0015]      FIG. 3   b  is a perspective diagram of the resilient element when the tray is filled, based on  FIG. 3   a.    
         [0016]      FIG. 4  is a diagram of a conventional feeding mechanism applying a normal driving force with respect to sheets of various thicknesses.  
         [0017]      FIG. 5  is a perspective diagram of the feeding mechanism in accordance with the present invention.  
         [0018]      FIGS. 6   a,    6   b,    6   c  are perspective diagrams of a resilient element exerting different spring forces on the contact portion in accordance with the present invention.  
         [0019]      FIG. 6   d  is a perspective diagram of the resilient element exerting a constant torque T on the shaft in accordance with the present invention.  
         [0020]      FIG. 7  is a diagram illustrating the feeding mechanism applying a normal driving force with respect to sheets of various thicknesses in accordance with the present invention.  
         [0021]      FIGS. 8   a,    8   b,    8   c  are perspective diagrams of the second embodiment in accordance with the present invention.  
         [0022]      FIGS. 9   a,    9   b,    9   c  are perspective diagrams of the third embodiment in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
     FIRST EMBODIMENT  
       [0023]     An object of the present invention is to provide a feeding mechanism preventing misfeed and multiple feed. The feeding mechanism is applied to business machines, such as printers or scanners. Referring to  FIG. 5 , the feeding mechanism has a shaft  33 , an arm  18  and a resilient element  26 . The arm  18  is rotatable on the shaft  33  and has a contact portion  66 . The resilient element  26  is a tension spring rotating on a pivot  51 , having a fixed end  31  and an extended portion  32 . The extended portion  32  has a first contact surface Ca contacting and sliding on the second contact surface Cb of the contact portion  66  at a contact point C in 3-D space.  
         [0024]     In this embodiment, the resilient element  26  exerts a contacting force F at the contact point C and applies a torque T to the shaft  33 . The torque T is determined by the contacting force F and the distance from the shaft  33  to the contact point C. To exert a constant normal driving force P on the sheets, the contact surfaces Ca and Cb are predetermined such that the resilient element  26  can apply a constant torque T to the shaft  33 . As the distance from the shaft  33  to the roller  12  is fixed, a constant driving force P can be therefore applied to the sheets.  
         [0025]     Referring to  FIGS. 6   a,    6   b  and  6   c,  when the resilient element  26  has different deforming angles αl, α 2  and α 3  respectively, it exerts forces F 1 , F 2  and F 3  on the contact portion  66 , wherein the arm  18  is correspondingly in the first, second and third positions. Particularly, the relationships between the resilient element  26  deforming angles and the driving forces are α 1 &gt;α 2 &gt;α 3  and F 1 &lt;F 2 &lt;F 3 .  
         [0026]     In  FIG. 6   a,  the fixed end  31  and the pivot  51  are fixed to the tray  22  as shown in  FIG. 1 , wherein the first contact surface Ca contacts the second contact surface Cb at a contact point C 1  in 3-D space. When the sheets in the tray  22  elevate the arm  18 , forming an inclined angle β 1 , the resilient element  26  is compressed at a deforming angle α 1  and exerts a force F 1  on the contact portion  66 . As shown in  FIG. 6   a,  the force F 1  applies a torque T 1  to the shaft  33 , wherein T 1 =F 1 ·d 1  (d 1  is the distance from the shaft  33  to the contact point C 1 ).  
         [0027]     When thicker or more sheets are loaded, as shown in  FIG. 6   b,  the arm  18  is elevated forming an inclined angle β 2 , and the resilient element  26  is compressed at a deforming angle α 2  and exerts a force F 2  on the contact portion  66 , wherein α 1 &gt;α 2 . The force F 2  applies a torque T 2  to the shaft  33 , wherein T 2 =F 2  d 2  (d 2  is the distance from the shaft  33  to the contact point C 2 ).  
         [0028]     In  FIG. 6   c,  when the loaded sheets are thicker or more than  FIG. 6   b,  the arm  18  is elevated forming an inclined angle β 3 , and the resilient element  26  is compressed at a deforming angle α 3  and exerts a force F 3  on the contact portion  66 , wherein α 1 &gt;α 2 &gt;α 3 . As shown in  FIG. 6   c,  the force F 3  applies a torque T 3  to the shaft  33 , wherein T 3 =F 3  d 3  (d 3  is the distance from the shaft  33  to the contact point C 3 ).  
         [0029]     With respect to the three states and diagrams mentioned, the resilient element  26  undergoes different compressing forces and has the deforming angles α 1 , α 2  and α 3  respectively, wherein α 1 &gt;α 2 &gt;α 3 . Moreover, the corresponding contacting forces F 1 , F 2  and F 3  are exerted on the contact points C 1 , C 2  and C 3  between the resilient element  26  and the contact portion  66 , wherein F 1 &lt;F 2 &lt;F 3 . As the angles α 1 , α 2 , α 3  and the forces F 1 , F 2  and F 3  can be detected, the first contact surface Ca and the second contact surface Cb are practically designed with respect to the corresponding distances d 1 , d 2  and d 3  to meet the condition of T=T 1 =F 1  d 1 =T 2 =F 2  d 2 =T 3 =F 3  d 3 =Tn, wherein Tn is a constant.  
         [0030]     Referring to  FIG. 6   d,  the resilient element  26  contacts the contact portion  66  and applies a constant torque T to the shaft  33 . The constant torque T is transferred to the arm  18  such that the roller  12  applies a constant driving force to the sheets. As mentioned, the first and second contact surface Ca and Cb are predetermined to meet the condition of T=T 1 =F 1  d 1 =T 2 =F 2  d 2 =T 3 =F 3  d 3 =Tn, wherein Tn is a constant.  
         [0031]     Regardless of the contact point between the contact portion  66  and the resilient element  26 , the feeding mechanism of the present invention can always apply a constant and stable torque to the arm  18  to feed smoothly without misfeed and multiple feed. It is therefore more suitable for use with sheets of various thicknesses.  
         [0032]     FIG,  7  illustrates sheets  302 ,  304 ,  306 ,  308 ,  310  of various thicknesses applied to the feeding mechanism of the present invention. With respect to the thickest sheet  302  according to  FIG. 7 , when the roller  12  applies a normal driving force between 12˜70 g, the sheets are properly fed one by one. With respect to the thinnest sheet  302 , when the roller  12  applies a force between 3˜25 g, the sheets are properly fed one by one. Referring to  FIG. 7 , the roller  12  of the present invention is capable of applying a maximum normal driving force of 20 g to the sheets when the tray  20  is filled and a minimum normal driving force of 15 g when the tray  20  is empty. Therefore, sheets  302 ,  304 ,  306 ,  308 ,  310  are all deliverable, with no threat of misfeed and multiple feed, due to the stable driving force according to the present invention.  
       SECOND EMBODIMENT  
       [0033]     Referring to  FIGS. 8   a,    8   b  and  8   c,  the resilient element  26  is connected to a contacting member  7  with the extended portion  32  fixed thereon, wherein the contacting member  7  and the extended portion  32  are rotatable on the pivot  71  fixed to the tray  22  as shown in  FIG. 1 . The contacting member  7  has a slot  70  with a first contact surface Ca′, wherein the second contact surface Cb is movable in the slot  70  and contacts the first contact surface Ca′. As shown in  FIGS. 8   a,    8   b  and  8   c,  the resilient element  26  takes deforming angles α 1 , α 2  and α 3  respectively when the arm  18  is elevated when loading sheets of different thicknesses.  
       THIRD EMBODIMENT  
       [0034]     Referring to  FIGS. 9   a,    9   b  and  9   c,  the contacting member  7  is rotatable on the pivot  71  fixed to the tray  22  as shown in  FIG. 1 , and a spring  8  connects the contacting member  7  and the tray  22 . The contacting member  7  has a slot  70  with a first contact surface Ca′, wherein the second contact surface Cb is movable in the slot  70  and contacts the first contact surface Ca′. As shown in  FIGS. 9   a,    9   b  and  9   c,  the spring  8  extended when the arm  18  is propped up when loading different thicknesses of sheets. As mentioned, the contact surfaces Ca′ and Cb are predetermined according to the constant torque condition such that the tension spring  8  exerts a constant torque on the shaft  33  to feed the media sheets smoothly.  
         [0035]     In summary, the present invention provides a feeding mechanism exerting a stable and constant driving force on media sheets to prevent misfeed and multiple feed. The profiles of the resilient element  26  and the arm  18  are appropriately designed to compensate for variations in spring force, and constant torque minimizes instability of the driving force applied to the sheets. That is, considering the variation of spring force from the resilient element  26 , the first contact surface Ca and second contact surface Cb are therefore calculated and predetermined to exert a constant torque on the shaft  33 . For arrangement in a restricted space, one contact surface (such as the first contact surface Ca) can be determined first, and the other corresponding contact surface (such as the second contact surface Cb) is determined according to the constant torque conditions mentioned, wherein the first contact surface Ca or the second contact surface Cb can be flat or curved.  
         [0036]     While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation to encompass all such modifications and similar arrangements.