Patent Publication Number: US-2010119345-A1

Title: Position-returning mechanism for a pick-and-place apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a position-returning mechanism and, more particularly, to a position-returning mechanism for a pick-and-place apparatus. 
     2. Description of Related Art 
     In the conventional art, all machines or equipments involving an operation of moving or positioning require a position-returning mechanism to proceed with buffering and to assist positioning. Such a requirement is particularly required in the industry of semiconductor, package test and precise machine, which needs high precision. 
     The position-returning mechanism commonly seen in the conventional art is shown in  FIG. 5 . The conventional position-returning mechanism includes a screw spring  93 , a steel ball  92  and a positioning base  91 . One end of the screw spring  93  connects against a fixing surface (not shown in the drawing), and the other end is configured to dispose the steel ball  92 . A circular recess  911  is concavely provided on an upper surface of the positioning base  91  and a part of the steel ball  92  is received in the circular recess  911 . The operating principle is as follows. As the screw spring  93  generate a radial displacement due to a radial force, a part of the steel ball  92  moves out of the circular recess  911 . As the force causing the displacement is removed, the spring force of the screw spring  93  urges the steel ball  92  to fall back into the circular recess  911 , thereby producing position-returning mechanism. 
     Base on this, though the conventional position-returning mechanism achieves the effect of position-returning, it is uneasy to assemble and maintain, and further, the cost is higher. In addition, the circular recess  911  on the upper surface of the positioning base  91 , or the steel ball  92  is easily subject to serious wearing out due to long time usage, such that the normal effect cannot be shown. On the other hand, the screw spring  93  is also an important factor to affect the ability of position-returning. If an improper screw spring  93  is adopted, it is easy to produce insufficient returning force, or no effect can be produced, if the spring force is too big, which even causes damage to the machinery parts. 
     Therefore, it is desirable to provide an improved position-returning mechanism for a pick-and-place apparatus, capable of providing simple structure, low cost, ease of assembling and maintaining, and long time use. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a position-returning mechanism for a pick-and-place apparatus, comprising a fixing shaft base, a fixing base, a movable base, at least two ring sprig pillars and a shaft rod. The fixing shaft base includes a fixing portion. The fixing base is installed beneath the fixing shaft base and provides a centering through hole, in which at least two first circular recesses are respectively concavely provided in an equal angle along an outer periphery of the centering through hole on a lower surface of the fixing base. In addition, at least two fixing blocks are respectively convexly provided in an equal angle on the lower surface of the fixing base, respectively each of the at least two fixing blocks is disposed and inserted between two adjacent first circular recesses, an axial buffer unit is provided and received in an internal part of each of the at least two fixing blocks, and the axial buffer unit is convexly extending downward to an external part of each of the fixing blocks. 
     Further, the movable base is installed with a centering shaft hole, in which at least two second circular recesses are concavely provided on an upper surface of the movable base corresponding to the at least two first circular recesses of the fixing base. In which at least two recessing portions are hollowed out and concavely provided at the movable base corresponding to the at least two fixing blocks of the fixing base, and the at least two recessing portions are respectively bigger than the corresponding at least two fixing blocks. Further, the at least two ring sprig pillars are provided and received respectively in the at least two first circular recesses and in the at least two second circular recesses. 
     Still further, the shaft rod includes a head portion and a tail portion. The head portion is hooked against a lower surface of the movable base, and the trail portion is pierced through the centering shaft hole and the centering through hole and is fixed and installed on the fixing portion of the fixing shaft base, such that the fixing base and the movable base are interposed between the head portion and the fixing shaft base and maintained to space apart an axial gap each other for slight movement in an axial direction. In addition, the diameter of the tail portion of the shaft rod is smaller than the centering shaft hole of the movable base and maintains to space apart a radial gap each other, such that the movable base can make slight radial movement laterally or slight coaxial rotation. Therefore, the invention is capable of providing position-returning functions of radial displacement, axial displacement and axial rotation. 
     According to the invention, the shaft rod may be a screw rod, the fixing portion of the fixing shaft base is an inner screw hole and the screw rod is correspondingly screwed and fixed in the inner screw hole, whereby the screw rod can link and be configured to install the fixing base and the movable base. The invention further comprises at least a bearing, which is installed between the fixing base and the movable base, for reducing wearing away and friction force between the fixing base and the movable base when in movement or rotation. 
     Besides, each of the at least two ring spring pillars is a hollow spring pillar surrounded and joined together by two ends of a steel strip, a hollow spring pillar surrounded and sealed tightly by two ends of a steel strip, a hollow spring pillar surrounded openly but not connected by two ends of a steel strip, a screw spring pillar screwed and surrounded from a center by a steel strip, or an equivalent spring pillar appearing in other forms. 
     In the invention, a mechanical arm is further installed on an upper surface of the fixing base and the fixing shaft base is installed on a lower part of the mechanical arm, thereby providing the functions of movement and rising and descending of the entire position-returning mechanism. In addition, the lower surface of the movable base is further installed with a guiding base and the guiding base includes at least a guiding hole. Through the guiding hole of the guiding base incorporated with a guiding pillar of a test base, precise positioning can be made. Furthermore, a lower surface of the guiding base further provides a vacuum sucking head for proceeding with sucking and placing a chip or other objects. 
     Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of the entire equipment according to a preferred embodiment of the invention; 
         FIG. 2  is an exploded view of a position-returning mechanism according to a preferred embodiment of the invention; 
         FIG. 3  is a cross-sectional view of a position-returning mechanism according to a preferred embodiment of the invention; 
         FIG. 4A to 4D  are each a schematic diagram of a ring sprig pillar according to a preferred embodiment of the invention; 
         FIG. 5  is a schematic diagram of a conventional position-returning mechanism. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The detail of the invention will be explained with a pick-and-place apparatus for carrying a chip in a semiconductor package test industry. However, the invention should not be limited to such an equipment or industry, but may be applied to any machine or equipment requiring precise positioning, position-returning or buffering. 
     With reference to  FIG. 1 , there is shown a schematic diagram of the entire equipment according to a position-returning mechanism for a pick-and-place apparatus of a preferred embodiment of the invention. The drawing shows an apparatus for carrying a chip in a chip package test process, in which it is illustrated a test base  84 , and a chip inserting slot  842  is provided in the center of the test base. The apparatus is mainly used to test whether the chip is in a normal operation, or to test related parameters of the chip. Each of two ends of the test base  84  provides convexly a guiding pillar  841 . 
     Further, on an upper side of the test base  84 , it shows a vacuum sucking head  82 , mainly used for sucking and placing a chip  83 . A guiding base  8  is provided on an upper surface of the vacuum sucking head  82  and used for installing the vacuum sucking head  82 . Each of two ends of the guiding base  8  is provided with a guiding hole  81 , which corresponds to a guiding pillar  841 . As the vacuum sucking head  82  reaches a position to be ready for descending and placing the chip  83  to the chip inserting slot  842 , the chip  83  will be placed precisely in the chip inserting slot  842  via insertion matching of the guiding pillar  841  and the guiding hole  81 . 
     In addition, the drawing shows a mechanical arm  7 , providing the functions of movement and rising and descending of the entire equipment. The mechanical arm  7  is connected with a position-returning mechanism  1  and a lower part of the mechanical arm  7  is connected to the guiding base  8 . However, as the vacuum sucking head  82  is descending and ready for sucking and placing the chip  83 , it inevitably produces displacement deviation resulting from error of machine parts or long time use, rendering incapableness of precise positioning. The position-returning mechanism  1  is able to absorb error and produce buffer, i.e. providing displacement tolerance in a radial direction and an axial direction, and providing tolerance of rotational tolerance, thereby allowing the guiding hole  81  to be smoothly inserted into the guiding pillar  841 . As the guiding base  8  rises, the guiding hole  81  is departed from the guiding pillar  841  and then the position-returning mechanism  1  provides position returning, i.e. returning to the position of the original shaft center so as to be adapted to deviation error of different test bases  84 . 
     Please refer to  FIG. 2  together with  FIG. 3 .  FIG. 2  is an exploded view of a position-returning mechanism  1  according to a preferred embodiment of the invention and  FIG. 3  is a cross-sectional view of the position-returning mechanism  1  according to the preferred embodiment of the invention. As shown, a fixing shaft base  54  includes a fixing portion  541 , which is an inner screw hole. A fixing base  2  is installed beneath the fixing shaft base  54  and provides a centering through hole  21 , in which three first circular recesses  22  are respectively concavely provided in an equal angle along an outer periphery of the centering through hole  21  on a lower surface  24  of the fixing base  2 . In addition, three fixing blocks  230  are respectively convexly provided in an equal angle on the lower surface  24  of the fixing base, in which each of the three fixing blocks  230  is disposed and inserted between two adjacent first circular recesses  22 . 
     A shaft buffer unit  23  is provided and received in an internal part of each of the three fixing blocks  230 , and the shaft buffer unit  23  is convexly extending downward to an external part of each of the fixing blocks  230 . According to the embodiment, the shaft buffer unit  23  includes an air pressure guiding pillar  231  and a sliding sleeve  232 . The air pressure guiding pillar  231  is filled with high pressure gas and the sliding sleeve  232  is slid and provided in the air pressure guiding pillar  231  and protruded from the lower surface  24  of the fixing base  2 . The high pressure gas in the air pressure guiding pillar  231  is capable of supporting the sliding sleeve  232 , thereby producing buffer force in a axial direction. 
     Further, as shown, a movable base  3  is installed with a movable shaft base  36 , and a centering shaft hole  31  is provided in the center of the movable shaft base  36 . Three second circular recesses  32  are concavely provided on an upper surface  33  of the movable base  3  corresponding to the three first circular recesses  22  of the fixing base  2 . Three recessing portions  34  are hollowed out and concavely provided at the movable base  3  corresponding to the three fixing blocks  230  of the fixing base  2 , and the three recessing portions  34  are respectively bigger than the corresponding one of the fixing blocks  230 . The recessing portions  34  are to receive the fixing blocks  230  so as to allow the shaft buffer unit  23  of each of the fixing blocks  230  to support the guiding base  8  beneath thereof. 
     Further, three ring sprig pillars  4  are provided and received in the corresponding three first circular recesses  22  and in the three second circular recesses  32 . According to the embodiment, each of the ring spring pillars  4  is a hollow spring pillar  41  surrounded and joined together by two ends of a steel strip, as shown in  FIG. 4A . Of course, each of the ring spring pillars  4  may be a hollow open spring pillar  42  surrounded openly but not connected by two ends of a steel strip, as shown in  FIG. 4B , a hollow sealing spring pillar  43  surrounded and sealed tightly by two ends of a steel strip, as shown in  FIG. 4C , or a screw spring pillar  44  screwed and surrounded from a center by a steel strip, as shown in  FIG. 4D . 
     Please refer to  FIGS. 2 and 3  continuously. As shown, according to the embodiment, a shaft rod  5  is a screw rod  53  and includes a head portion  51  and a tail portion  52 . The head portion  51  is hooked against a lower surface  35  of the movable shaft base  36  to prevent the movable base  3  from being fallen off. The tail portion  52  of the screw rod  53  is pierced through the centering shaft hole  31  and the centering through hole  21 , and is screwed and fixed in the inner screw hole of the fixing portion  541  of the fixing shaft base  54 , such that the fixing base  2  and the movable base  3  are interposed between the head portion  51  and the fixing shaft base  54  and maintained to space apart an axial gap Ta each other for slight movement in an axial direction. The diameter of the tail portion  52  of the shaft rod  5  is smaller than the diameter of the centering shaft hole  31  of the movable base  3  and maintains to space apart a radial gap Tr each other, such that the movable base  3  can make slight radial movement laterally or slight coaxial rotation. Further, a bearing  6  is installed between the fixing base  2  and the movable base  3  to reduce wearing away and friction force between the fixing base  2  and the movable base  3  when in movement or rotation. 
     Although the present invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the scope of the invention as hereinafter claimed.