Abstract:
A pick mechanism located on one side of a paper tray includes a plurality of gears, linkage bars and a pickup roller to form a mechanism with a high degree of freedom. The pickup roller may be driven to rotate in the direction of paper feeding to generate a torque to apply a force on the top sheet of the paper tray and provide an automatic compensation for the pickup force. Furthermore, the mechanism is simply structured to save cost and space.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates to a pick mechanism for paper and particularly to a pick mechanism that has a simple structure and saves space.  
         BACKGROUND OF THE INVENTION  
         [0002]    With ever changing of digital technologies, many electronic products have become very popular. The advance of technologies also makes these electronic products more compact and miniaturized. In addition, functional integration also has become a trend and an appeal in the market place.  
           [0003]    In the office environments, it is very common to integrate business machines such as a printer, copier, and FAX machine to become a Multi-Function Peripheral (MFP) that combines the functions of copying, printing, facsimile and scanning. Whether single function or multiple functions, the process of miniaturization has to rearrange and reorganize the physical structure. In these products, a paper conveying mechanism, including a paper picking and transfer mechanism, has to be simplified.  
           [0004]    In general, the paper conveying mechanism used in the copiers, printers or FAX machines usually has two rubber rollers with a greater friction coefficient. One is a pickup roller and the other is a feed roller. The top sheet of a paper is first separated by the pickup roller, and then is transported by the feed roller to the printing module for printing. The driving power source usually is located between the two rubber rollers. A transmission element such as a gear set or belt is used to transmit the driving power to the two rollers.  
           [0005]    For the pick mechanism that uses the pickup roller to fetch paper, the gear to transmit power will generate friction and result in energy loss and noise. Thus, it is preferable to use as few gears as possible. Another requirement for the pick mechanism is to prevent multi-feeds or failed feeds caused by varying of paper properties such as weight, density or stiffness.  
           [0006]    In order to equip the pickup roller with automatic compensating capability, the pickup roller usually is movable. Such a design makes the pick mechanism more complicated. It also takes more space. For instance, LEXMARK Co. of U.S.A, has disclosed U.S. Pat. No. 5,527,026 which has a drive roller ( 13 ) pivotally engaged on a bottom gear of a gear train ( 1 ). The drive gear ( 3 ) at the front end of the gear train is stationary. The entire gear train ( 1 ) and the drive roller ( 13 ) are movable depending on the amount of paper. The drive roller ( 13 ) is in contact with the surface of the top sheet. When all the gears in the gear train ( 1 ) rotate to drive the drive roller ( 13 ), a torque is generated to enable the drive roller to apply a normal force to the top sheet. The normal force alters according to the characteristics of paper, thus can automatically compensate the pickup force, depending on the characteristics of paper, to avoid the problems of multi-feeds or failed feeds.  
           [0007]    In other words, if the drive roller is mounted on a movable end of a swinging arm (such as the gear train), the drive roller may be in contact with the top sheet all the time regardless the amount of paper in the paper tray. Meanwhile, it can increase or decrease a normal pick-up force according to the characteristics of paper.  
           [0008]    However, the pick mechanism that adopts the swinging arm still is not perfect. For instance, in the U.S. Pat. No. 5,527,026 assigned to LEXMARK Co., every gear in the gear train ( 1 ) is fixed relative to another. When the entire gear train ( 1 ) is swung for paper picking, it does not have much space to move. Moreover, when the quantity of paper changes (or the depth of paper tray alters), the moving path is not extended directly from the drive gear to the paper, but moves sideward in the swinging direction. Hence, a greater space must be reserved to accommodate the swinging of the entire gear train ( 1 ). It does not meet the miniaturization requirement.  
         SUMMARY OF THE INVENTION  
         [0009]    Therefore, the primary object of the invention is to resolve the previously mentioned disadvantages occurred to the conventional pick mechanisms such as bulky size, complicated structure, higher cost and a spatial design problem.  
           [0010]    The invention provides a pick mechanism that mainly includes a transmission gear, an idling gear, a swinging arm, a pickup gear and a pickup roller. The transmission gear is connected to a power input shaft. The idling gear is engaged with the transmission gear, and the axis of the idling gear is coupled with the power input shaft through a first linkage bar. The pickup gear is engaged with the idling gear, and the axis of the pickup gear is coupled with the axis of the idling gear through a second linkage bar. The pickup roller is located on one side of the pickup gear and is coupled on a same pivot shaft with the pickup gear. When the power output shaft drives the transmission gear, the power is transmitted through the idling gear and the pickup gear to drive the pickup roller to rotate in the direction of paper feeding. The pickup roller applies a force on the top sheet of paper contained in the paper tray to move the top sheet.  
           [0011]    The invention aims at achieving effects such as enabling the pickup roller to compensate the pickup force automatically, simplifying the structure, adjusting the operation mechanism and reducing the space needed.  
           [0012]    The foregoing, as well as additional objects, features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a perspective view of a first embodiment of the invention, with the paper tray indicated by broken lines.  
         [0014]    [0014]FIG. 2 is a perspective view of the first embodiment of the invention, with the paper tray and the outer frame indicated by broken lines.  
         [0015]    [0015]FIG. 3 is a perspective view of the first embodiment of the invention from another side.  
         [0016]    [0016]FIG. 4 is a side view of the first embodiment of the invention, with the side-wall of the paper tray removed.  
         [0017]    [0017]FIG. 5 is a schematic view of the first embodiment of the invention showing the pick mechanism in a paper pickup condition.  
         [0018]    [0018]FIG. 6 is a schematic view of the first embodiment of the invention showing the pick mechanism in a paper feeding condition.  
         [0019]    [0019]FIG. 7 is a schematic view of the second embodiment of the invention showing the pick mechanism in a paper pickup condition.  
         [0020]    [0020]FIG. 8 is a schematic view of the second embodiment of the invention showing the pick mechanism in a paper feeding condition. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]    Refer to FIGS. 1 through 6 for a first preferred embodiment of the invention. The pick mechanism  100  of the invention is located in a paper tray  200 . It includes an outer frame  110 , and a transmission gear  120 , an idling gear  130 , a pickup gear  140  and a pickup roller  150  located in the outer frame  110 . Details of the structural and operational relationship of the elements will be elaborated as follows.  
         [0022]    Referring to FIGS. 1 through 4, the outer frame  110  is formed in an U-shape. It has one side fastening to a rectangular linkage block  111 . The linkage block  111  is fastened to an inner side of a side-wall  210  of the paper tray  200 . Namely, the outer frame  110  is stationary. The outer frame  110  has straight retaining slots  112  (referring to FIG. 1) and  113  (referring to FIG. 3) closed to one end, and is run through by a power input shaft  121 . The power input shaft  121  runs through two side-walls  210  (only one sidewall is shown) of the paper tray  200 . In this embodiment, the power-input shaft  121  provides rotation power in one direction (clockwise direction, as shown in FIGS. 5 and 6).  
         [0023]    The transmission gear  120  is mounted on the power input shaft  121  inside the outer frame  110  and may be driven by the power input shaft  121  to rotate. As the axis of the power input shaft  121  is fixed, the axis of the transmission gear also is fixed.  
         [0024]    The idling gear  130  is engaged with the transmission gear  120 . Its axis is coupled with the power input shaft  121  through a first linkage bar  160 . The first linkage bar  160  is formed in a plate.  
         [0025]    The pickup gear  140  is engaged with the idling gear  130 . Its axis is coupled with the axis of the idling gear  130  through a second linkage bar  170 .  
         [0026]    The pickup roller  150  and the pickup gear  140  are coupled on the same pivot shaft  180  and may rotate synchronously. The pivot shaft  180  has one end running through the second linkage bar  170  and the retaining slot  112  of the outer frame  110  (referring to FIG. 1) and other end running through the retaining slot  113  (referring to FIG. 3). The pickup roller  150  is a composite structure different from the conventional pickup roller, which has a roller surface made of a single material. Instead, the roller surface of the invention is divided into two sections. One section is a high friction surface  151 , which has a greater friction coefficient, and other section is a low friction surface  152 , which has a lower friction coefficient (referring to FIGS. 3 and 4). The low friction surface  152  has two feed wheels  153 . In practice, the lower friction surface  152  and the feed wheels  153  may be made from hard plastics that have a smooth surface.  
         [0027]    The structural elements and their relationship with the pick mechanism  100  are depicted as above. Referring to FIGS. 5 and 6, also FIGS. 1 through 4, during paper pickup process, the power input shaft  121  provides rotational power (clockwise direction) to drive the transmission gear  120 , idling gear  130 , pickup gear  140  and pickup roller  150  in this order. Moreover, the pickup roller  150  rotates clockwise in the direction of the paper feeding direction  220 .  
         [0028]    In the pick mechanism  100 , the idling gear  130 , pickup gear  140  and pickup roller  150  are movable, and the first linkage bar  160  and the second linkage bar  170  are swingable. Thus during operation there are frictions between the rotating gears and the linkage bars. As a result, the first linkage bar  160  is subject to a clockwise torque  221  while the second linkage bar  170  is subject to a counterclockwise torque  222 . Overall, the pick mechanism  100 , except the stationary portions, has a tendency of moving in the direction of paper  230  in the paper tray  200 . In addition, the pivot shaft  180  of the pickup roller  150  and pickup gear  140  is confined in the retaining slots  112  and  113  (with the retaining slot  113  not shown in the drawings). The pickup roller  150  finally will be moved downwards in a biased manner. However, it is largely moved towards the paper  230 .  
         [0029]    When the high friction surface  151  of the pickup roller  150  touches the paper  230 , due to the constraints of the torque  221  and  222 , and the retaining slots  112  and  113 , a normal force  223  will be exerted on the paper  230 . And the normal force  223  will increase gradually until the paper  230  is moved in the direction of the paper feeding direction  240 . Namely, the amount of normal force  223  varies depending on the properties of paper such as weight, density or stiffness. Therefore, it can automatically compensate pickup force according to the properties of paper without the problems of multi-feeds or failed feeds. This is the so-called automatic compensation capability.  
         [0030]    Referring to FIG. 6, when the paper  230  is moved in the paper feeding direction for a distance D, and reaches the feed roller  300 , the pickup roller  150  is also turned from the high friction surface  151  to the lower friction surface  152  with the feed wheels  153  in contact with the paper  230 . The feed roller  300  picks up the paper  230  and moves the paper in the paper feeding direction  240 . The paper feed wheels  153  merely rotate with the paper  230  without affecting the movement of the paper  230 . When the paper  230  is separated from the paper feed wheels  153 , the pickup roller  150  rotates to make the high friction surface  151  touching the next sheet.  
         [0031]    It is obvious that the length of the high friction surface  151  of the pickup roller  150  and the distance D of the paper  230  being moved to the feed roller  300  are closely related. The length of the low friction surface  152  and the time for the pickup roller  150  to touch the next sheet also are related. These factors must be adjusted during implementation to match the automatic control operation. Moreover, while not affecting the movement of the paper  230 , the paper feed wheels  153  may be removed. In addition, the low friction surface  152  may be formed in an arched fashion to couple with the high friction surface  151  to form a complete circular surface.  
         [0032]    In addition, the roller surface of the pickup roller may also be an entirely high friction surface. Refer to FIGS. 7 and 8 for a second embodiment of a pick mechanism  400  of the invention. The main difference from the first embodiment is that the pickup roller  410  has only a high friction surface  411 . A fine-tuning adjustment must be made for the automatic control mechanism. During paper pickup, the power input shaft  420  turns in clockwise direction to drive the pickup roller  410 , moving in the paper feeding direction  510 , to contact and pickup paper by rotating. Once the paper  510  arrives in the feed roller  500 , the power input shaft  420  rotates counterclockwise to move the pickup roller  410  away from the paper  510  without impeding the continuous movement of the paper  520 . Next, in this embodiment, the power-input shaft  420  may provide bi-directional rotations clockwise and counterclockwise, while the first embodiment provides only single direction rotation.  
         [0033]    It is to be noted that the outer frame of the invention can provide stability for the entire mechanism during operation and provide a moving path for the retaining slots to confine the pickup roller. However, it is not mandatory in practice. When the outer frame is removed, slots may be formed on the paper tray to replace the retaining slots on the outer frame to enable the coaxial pivot shaft of the pickup gear and pickup roller to couple and move to confine the moving path of the pickup roller.  
         [0034]    In short, the invention is different from the conventional pickup mechanism that employs a swinging arm (such as U.S. Pat. No. 5,527,026 to LEXMARK Co.). It provides a pick mechanism that has a lot of space to move in. The total length may be directly extended according to variation of paper content. It does not need a large space like a swinging arm mechanism, and has a simpler structure and a smaller size. It can provide an automatic compensating capability. The invention also provides a novel composite pickup roller, which rotates only in one single direction in the paper feeding direction. Thus, driving of the pick mechanism is simpler and the complexity of automatic control is reduced.  
         [0035]    While the preferred embodiments of the invention have been set forth for the purpose of disclosure, modifications of the disclosed embodiments of the invention as well as other embodiments thereof may occur to those skilled in the art. Accordingly, the appended claims are intended to cover all embodiments, which do not depart from the spirit and scope of the invention.