Abstract:
A paper pickup mechanism located on one side of a feeding paper tray consists of a pickup roller, a plurality of gears and a plurality of linkage bars to form a highly free mechanism that drives the pickup roller rotating in the paper feeding direction and generating a torque to enable the pickup roller exerting a force on the top paper of the paper tray and provide an automatic compensating paper pickup force. By rearranging the structural locations of the elements, fewer gears are required to transmit the driving power, and energy loss and noise generation are reduced.

Description:
FIELD OF THE INVENTION 
   The invention relates to a paper pickup mechanism and particularly to a paper pickup mechanism that employs fewer gears to transmit power to achieve lower energy loss and noise and compensate paper pickup force automatically. 
   BACKGROUND OF THE INVENTION 
   In general, the paper conveying mechanisms used in copiers, printers or facsimile machines have two rubber rollers that have a greater friction coefficient. One serves as a pickup roller and the other serves as a feed roller. The paper located on the top layer is firstly separated by the pickup roller, and is transferred by the feed roller to the printing module for printing. The driving power source usually is located between the two rubber rollers. A drive element, such as a gear set or belt, is used to transmit the driving power to the two rollers. 
   Nowadays, miniaturization and integration is a prevailing trend. Either single function machines such as printers, copiers, FAX machines, or Multi-Function Peripheral (MFP) that integrates the functions of copying, printing, facsimile or scanning have to rearrange and reconfigure the structure to catch up with this trend. Hence to simplify the existing paper pickup or feeding mechanism has become unavoidable. 
   Using the paper pickup mechanism that has gear sets to transmit driving power to the pickup roller, there&#39;s friction between gears. As a result, energy is lost and noise is generated when the gears transmit the driving power. Therefore, it is preferable to have as few gears as possible. However, this is not always attainable in a practical mechanism. In a conventional power transmission design, it is not uncommon to find more than ten gears of different sizes. There are several reasons why. One is the constraint of a gear transmission path in the structural design, and the other is to enable the pickup roller to have automatic compensating capability. 
   Take U.S. Pat. No. 5,527,026 assigned to LEXMARK Co. of U.S.A. for instance. Its drive roller 13 is pivotally engaged with a gear located on the bottom of a gear train 1. A drive gear 3 located at the front end of the gear train is stationary. The entire gear train 1 and the drive roller 13 are rotatable according to the amount of paper so that the drive roller 13 is always located on the surface of the paper on the top. When all the gears in the gear train 1 rotate and drive the drive roller 13, a torque is generated to enable the driver gear to exert a normal force to the paper on the top. The normal force is alterable depending on the properties of the paper, such as variety of weight, density and stiffness. Thus an automatic compensation pickup force is generated according to different properties of the paper, therefore multi-feeds or feeding failure of paper may be avoided. 
   In other words, if the drive roller is pivoted on a “swing arm” such as the gear train mentioned above, the pickup roller is constantly in contact with the paper on the top. Then no matter how much paper is in the paper tray, the normal fore alters according to the properties of the paper. 
   As the driving power source is located between the pickup roller and the feed roller, as indicated in U.S. Pat. No. 5,527,026 to LEXMARK Co., the driving power source must be located on the paper feeding direction 17. Hence the shortest driving power transmission path should have a drive gear 3 of a gear chain 1 to be located between the drive roller 13 and the driving power source. On the contrary, in the cited reference, the driving power must be transmitted to the drive gear 3 located at the remote location. Thus it needs more gears. As a result, power loss and noise generation are more severe. 
   SUMMARY OF THE INVENTION 
   The primary object of the invention is to overcome the aforesaid problems of conventional paper pickup mechanisms that use too many gears and incur severe power loss and noise generation. 
   The paper pickup mechanism of the invention mainly includes driver gear, idler gear, a swing arm, pickup gear and a pickup roller. The driver gear receives rotation power transmitted from a driving power source and has a still spindle. The idler gear engages with the driver gear and has a spindle connecting to the spindle of the driver gear through a first linkage bar. The swing arm has a pivoted end and a swing end and rotates around the pivoted end. The pickup gear is located on the swing end of the swing arm and is engaged with the idler gear, and a second linkage bar links rotation axes of these two gears. The pickup roller is coaxial with the pickup gear and is driven by the driver gear to rotate in paper feeding direction, to generate a torque to allow the pickup roller to exert a force on the paper on the top of the feeding paper tray. 
   The pickup mechanism of the invention can provide an automatic compensating pickup force for a pickup roller. In addition, by adjusting the arrangement of the position of the elements, fewer gears are required for transmitting the driving power. Thus energy loss and noise generation also are reduced. 
   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 
       FIG. 1  is a perspective view of the first preferred embodiment of the invention; 
       FIG. 2  is another perspective view of the first preferred embodiment of the invention, with the feeding paper tray indicated by broken lines; 
       FIG. 3  is a schematic side view of the first preferred embodiment of the invention in an operating condition, showing the pickup mechanism, picking up paper; 
       FIG. 4  is a schematic side view of the first preferred embodiment of the invention in an operating condition, showing the pickup mechanism condition when the feeding paper tray is depleted of paper; 
       FIG. 5  is a perspective view of the second preferred embodiment of the invention; 
       FIG. 6  is another perspective view of the second preferred embodiment of the invention, with the feeding paper tray indicated by broken lines; 
       FIG. 7  is a schematic side view of the second preferred embodiment of the invention in an operating condition; and 
       FIG. 8  is a schematic side view of a third preferred embodiment of the invention in an operating condition. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Refer to  FIGS. 1 through 4  for a first preferred embodiment of the invention. The paper pickup mechanism  100  according to the invention is located on an inner side of a feeding paper tray  400 . It mainly includes driver gear  110 , idler gear  120 , a swing arm  130 , pickup gear  140  and pickup roller  150 . Their structural and operational configurations are described as follows. Referring to  FIGS. 1 and 2 , the driver gear  110  is mounted on an axle strut  410  located on an inner side of the feeding paper tray  400 . The axle strut is pivoted and engaged with a gear set  500  located on the outer side of the feeding paper tray  400  and is driven to rotate. The gear set  500  transmits rotational power from a driving power source (not shown in the drawings) to the driver gear  110 . 
   The idler gear  120  is engaged with the driver gear  110 . Its rotation axis is connected to a first linkage bar  160  formed in an elongated plate. 
   The swing arm  130  also is formed in an elongated plate. It has a pivoted upper end  131 , located upstream relative to the direction of paper feeding  440  from the rotation axis of the idler gear  120 , and coupling with a hollow and transverse connecting strut  132  to engage pivotally with an axle  420  extending from the inner wall of the feeding paper tray  400 . So the entire swing arm  130  can swing around the connecting strut  132  at the pivoted end  131 . The swing arm  130  has a bottom to serve as a swing end  133 . The swing end  133  has two sides extending downwards to form respectively a first connection plate  134  and a second connection plate  135 . 
   The pickup gear  140  is mounted on an outer side of the first connection plate  134  of the swing arm  130 . It is engaged with the idler gear  120  and its rotation axis is connected to the rotation axis of the idler gear  120  through a second linkage bar  170 . 
   The surface of the pickup roller  150  has a greater friction coefficient and is generally made from rubber. It is located between the first connection plate  134  and the second connection plate  135  of the swing end  133  of the swing arm  130 , and is coaxial with the pickup gear  140 . 
   Refer to  FIGS. 3 and 4  for the configuration of the elements of the paper pickup mechanism  100 . The paper pickup mechanism  100  is substantially a “four bar linkage mechanism”. In addition to the first linkage bar  160 , second linkage bar  170  and the swing arm  130 , the distance between the pivoted end  131  of the swing arm  130  and the axle of the driver gear  110  serves as the fourth linkage bar. Because of the property of the “four bar linkage mechanism”, the idler gear  120  and the pickup roller  150  have a lot of degree of freedom. Adding the torque generated by rotation, depending on whether there is paper (as shown in  FIG. 3 ) or not (as shown in  FIG. 4 ), the pickup roller  150  can always exert a force in the direction of the feeding paper tray  400 . 
   During the paper pickup process, the driver gear  110 , whose rotation axis is located downstream of the rotation axis of the idler gear  120  in the direction of paper feeding  440 , receives driving power from the gear set  500  and rotates in clockwise direction, and drives sequentially the idler gear  120 , pickup gear  140  and pickup roller  150 . The pickup roller  150  rotates clockwise in the direction of paper feeding  440 . As the pickup roller  150  is movable and serves as an joint of the “four bar linkage mechanism” that has a lot of degree of freedom, its rotation generates a torque that forms a normal force applying on the paper  430  located on the top of the feeding paper tray  400 . The normal force gradually increases until the paper  430  on the top starts moving in the paper feeding direction  440 . Namely, the normal force varies depending on the properties of the paper such as weight, density or stiffness. Thus it can automatically compensate the paper pickup force according to different paper properties, without the problems of multi-feeds or feeding failure. 
   Moreover, prior techniques generally have the driving source locating between the pickup roller and the feed roller, i.e. with the driving source located on the paper feeding direction. But in terms of the embodiment of the invention, the gear set transmits the driving power to the axle rod  420  as shown in  FIGS. 1 and 2 , i.e. with the pickup roller located between the driving source (on the paper feeding direction  440 ) and the driver gear. As a result, the whole gear set has to use more gears and causes greater energy loss and noise generation. In contrast, the embodiment has driver gear  110  responsible for the driving located between the driving source and the pickup roller  150 . Thus the distance of driving power transmission is shorter, and the number of gears required in the gear set  500  is lower. As a result, noise is lower and energy loss in the power transmission also is less. 
   Furthermore, in the embodiment, the second linkage bar  170  could be omitted in a practical environment. This is because the driver gear  110  rotates clockwise during the pickup operation (as shown in  FIG. 3 , with the second linkage bar  170  omitted), and the first linkage bar  160  is driven by friction forces and generates inactivity in clockwise rotation. Consequently, the idler gear  120  also moves toward the paper  430 . Thus, the idler gear  120  maintains an engaging condition with the pickup gear  140  during paper pickup and provides a normal force pressing the paper  430 . Hence even without the second linkage bar  170 , the paper pickup function still is provided. 
   Refer to  FIGS. 5 ,  6  and  7  for a second preferred embodiment of the invention. The main difference between the paper pickup mechanism  200  in this embodiment and the first embodiment is that the first linkage bar  230  has additional gear  240  between the idler gear  220  and the driver gear  210 . And the additional gear  240  is engaged respectively with the idler gear  220  and the driver gear  210 . Such a design increases the capacity of the feeding paper tray  600 . This is because the length of the first linkage bars  230  increases. As a result, the moving range of the pickup roller  250  increases and covers the entire feeding paper tray  600 . Of course, a similar approach may also be applied to the second linkage bar between the idler gear and the pickup gear. 
   While the two embodiments set forth above are adopted on an upright feeding paper tray, in fact, the invention may also be adapted on a horizontal feeding paper tray as shown in  FIG. 8 . As the invention essentially employs a “four bar linkage mechanism” during the paper pickup process, the gravity force of the paper pickup mechanism  300  is not an important factor that affects the operation; hence a similar mechanism can also be adapted on a horizontal feeding paper tray  700 . 
   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 not departing from the spirit and scope of the invention.