Patent Publication Number: US-9421656-B2

Title: Workpiece-positioning device and workpiece manufacturing method

Description:
TECHNICAL FIELD 
     The present invention relates to a workpiece-positioning device and a workpiece manufacturing method which utilizes the device. 
     BACKGROUND ART 
     A lithium ion secondary battery package includes a specific number of stacked battery cell packs each incorporating a battery cell (single cell) that are accommodated in a housing. Inside the housing, the battery cell packs are electrically connected in series or in parallel with one another. Specifically, the battery cell packs are connected in series or in parallel by spot-welding electrode tabs of the individual battery cell packs. Desired power performance is obtained by connecting the battery cell packs in this way. 
     As the electrode tabs are connected as mentioned above, there exist electrode tabs which should be spot-welded as well as electrode tabs which should not be spot-welded. Thus, according to Japanese Patent No. 4462386-B2, electrode tabs of battery cell packs are initially formed in a large size and subsequently cut into specific shapes so that only particular ones of the electrode tabs can be connected. 
     SUMMARY OF INVENTION 
     Meanwhile, individual battery cell packs are so soft that poor productivity will result if the battery cell packs are grasped in each successive manufacturing process. Thus, in a battery manufacturing factory, each battery cell pack is placed on a pallet and transferred to each successive process. One of such processes is a process for cutting electrode tabs. This process requires high cutting accuracy because the electrode tabs must be cut to an exact shape. To achieve the high cutting accuracy of the electrode tabs, it is necessary to position the battery cell pack with high precision relative to the pallet and further position the pallet with high precision relative to factory facilities. Moreover, since the battery cell pack is so soft as mentioned above, it has been difficult to exactly position the battery cell pack relative to the pallet. Furthermore, taking into consideration large-scale production to be undertaken, it is necessary to accomplish such positioning in a short time. 
     Japanese Patent No. 4462386-B2 is not meant to be applied to large-scale production, and there has been a need for a technique suitable for large-scale production. 
     The present invention has been made in light of the aforementioned problems of the prior art. Accordingly, it is an object of the present invention to provide a workpiece-positioning device and a workpiece manufacturing method that utilizes the device which can position a workpiece (battery cell pack) and a pallet at exact relative positions without the need to waste cycle time. 
     According to one mode of the present invention, a workpiece-positioning device including a workpiece holder of holding a workpiece and a workpiece holder up/down mechanism of moving the workpiece holder up and down is provided, the workpiece-positioning device further including a free pallet movement mechanism of freely moving a pallet parallel to a reference plane to shift the pallet to a position where the workpiece held by the workpiece holder is lowered so that a positioning pin of the pallet is inserted into a positioning hole made in the workpiece. 
     An embodiment of the invention and advantages thereof will be described in detail hereinbelow in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIGS. 1A and 1B  are explanatory representations of the internal structure of a lithium ion secondary battery cell pack. 
         FIGS. 2A and 2B  are representations of the external appearance of the lithium ion secondary battery cell pack. 
         FIGS. 3A-3C  are representations of a pallet on which the battery cell pack is placed. 
         FIGS. 4A and 4B  are representations of a platform used in one embodiment of a workpiece-positioning device according to the present invention. 
         FIG. 5  is a plan view of a production line using the workpiece-positioning device according to the invention. 
         FIG. 6  is a side view for explaining operation of the workpiece-positioning device according to the present invention. 
         FIGS. 7A, 7B-1 and 7B-2  are explanatory representations of an electrode tab cutting process. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiment 
       FIGS. 1A and 1B  are explanatory representations of the internal structure of a lithium ion secondary battery cell pack, wherein  FIG. 1A  is a perspective view and  FIG. 1B  is a cross-sectional view taken along lines B-B of  FIG. 1A . Note that each part is deformed. 
     To facilitate understanding of the present invention, the lithium ion secondary battery cell pack is first described. 
     The lithium ion secondary battery cell pack  200  includes a specific number of stacked unit batteries  210  which are electrically connected in parallel and an outer pack  220 . Although not illustrated, a prescribed number of lithium ion secondary battery cell packs  200  are stacked and accommodated in a box (housing) made of aluminum, for example, to form a lithium ion secondary battery package. 
     Each of the unit batteries  210  includes a separator  211 , a positive electrode  212  and a negative electrode  213 . 
     The separator  211  is an electrolytic layer. 
     The positive electrode  212  includes a thin, sheet-like positive electrode collector  212   a  and positive electrode layers  212   b  which are formed on both sides of the positive electrode collector  212   a . Meanwhile, in the positive electrode  212  located in an outermost layer, the positive electrode layer  212   b  is formed on only one side of the positive electrode collector  212   a . Individual positive electrode collectors  212   a  are joined together and electrically connected in parallel, as if forming a single assembly. In  FIG. 1B , the individual positive electrode collectors  212   a  are joined on a left side, forming a single assembly. This portion where the individual positive electrode collectors  212   a  are collected constitutes a positive electrode collector portion. 
     The negative electrode  213  includes a thin, sheet-like negative electrode collector  213   a  and negative electrode layers  213   b  which are formed on both sides of the negative electrode collector  213   a . Meanwhile, in the negative electrode  213  located in an outermost layer, the negative electrode layer  213   b  is formed on only one side of the negative electrode collector  213   a . Individual negative electrode collectors  213   a  are joined together and electrically connected in parallel, as if forming a single assembly. In  FIG. 1B , the individual negative electrode collectors  213   a  are joined on a right side, forming a single assembly. This portion where the individual negative electrode collectors  213   a  are collected constitutes a negative electrode collector portion. 
     The outer pack  220  accommodates the stacked unit batteries  210 . While various materials are available for making the outer pack  220 , one candidate would be a sheet material made of a polymer-metal composite laminate film produced by coating aluminum with a polypropylene film, for example. The outer pack  220  is formed by first heat-sealing three sides thereof with one side left open under conditions where the stacked unit batteries  210  are accommodated in the outer pack  220 . Then, after filling the outer pack  220  with an electrolytic solution, the one open side is heat-sealed. The outer pack  220  is provided with a positive electrode tab  222  and a negative electrode tab  223  from which electric power is taken out to the exterior of the unit batteries  210 . 
     One end of the positive electrode tab  222  is connected to the positive electrode collector portion inside the outer pack  220  while the other end of the positive electrode tab  222  extends to the outside of the outer pack  220 . 
     One end of the negative electrode tab  223  is connected to the negative electrode collector portion inside the outer pack  220  while the other end of the negative electrode tab  223  extends to the outside of the outer pack  220 . 
       FIGS. 2A and 2B  are representations of the external appearance of the lithium ion secondary battery cell pack, wherein  FIG. 2A  is a plan view and  FIG. 2B  is a side view. 
     The positive electrode tab  222  and the negative electrode tab  223  stick out from one side (left side as illustrated in  FIG. 2A ) of the outer pack  220  of the battery cell pack  200 . In a heat-sealed portion of the outer pack  220 , there are formed positioning holes  225  outside the positive electrode tab  222  and the negative electrode tab  223  (above the positive electrode tab  222  and below the negative electrode tab  223  as illustrated in  FIG. 2A ). 
       FIGS. 3A-3C  are representations of a pallet on which the battery cell pack is placed, wherein  FIG. 3A  is a plan view,  FIG. 3B  is a side view and  FIG. 3C  is an enlarged side view of the vicinity of a positioning pin. 
     The pallet  300  has a generally quadrilateral shape. The pallet  300  is made of resin. Two positioning pins  301  are provided on the pallet  300  at one side thereof (left side as illustrated in  FIG. 3A ). As can be seen from  FIG. 3C , these positioning pins  301  have pointed ends. The diameter of a basal part of each positioning pin  301  coincides with the diameter of each positioning hole  225  made in the battery cell pack  200 . Therefore, the battery cell pack  200  can be positioned on the pallet  300  without creating any misalignment of relative positions therebetween when the positioning holes  225  of the battery cell pack  200  are fitted on the positioning pins  301 . 
     Also, there are formed positioning holes  302  in the pallet  300 . These positioning holes  302  are fitted on positioning pins provided in each process facility. With this arrangement, the pallet  300  is positioned without creating any positional misalignment with respect to each process facility. Further, there are formed holes  303  in side surfaces of the pallet  300 . As depicted in  FIG. 3A , four holes  303  are formed. The pallet  300  is moved with claws of a robot arm inserted into these four holes  303 . 
     As mentioned above, the battery cell pack  200  is positioned on the pallet  300  without creating any misalignment of relative positions therebetween when the positioning holes  225  of the battery cell pack  200  are fitted on the positioning pins  301 . By the way, the positioning holes  225  of the battery cell pack  200  are formed in the outer pack  220  which is formed with a sheet material made of a polymer-metal composite laminate film. The outer pack  220  thus produced is so soft that there is a risk that the positioning holes  225  may become enlarged, deformed or ripped if an excessive external force is applied unnecessarily. Also, pins projecting from an insulative spacer for preventing a short circuit between the electrode tabs of the individual battery cell packs that are stacked are inserted into the positioning holes  225  formed in the battery cell pack  200  in a succeeding process. This means that the positioning holes  225  are also used for mutual positioning of the insulative spacer and the battery cell pack  200 . Therefore, it is necessary to prevent deformation or the like of the positioning holes  225  (refer to Japanese Patent No. 4379467-B2). 
     The inventors of the present application have found through strenuous studies that it is possible to position a workpiece (battery cell pack  200 ) and a pallet at exact relative positions without enlarging, deforming or ripping the outer pack  220  (the positioning holes  225 ) and without the need to waste cycle time if the battery cell pack  200  is lowered so that the positioning holes  225  fit on the positioning pins  301  of the pallet  300  under conditions where the pallet  300  is freely movable parallel to a reference plane, or under conditions where the pallet  300  is lifted, for example. A specific structure for realizing such an idea of the inventors is described hereunder. 
       FIGS. 4A and 4B  are representations of a platform used in one embodiment of a workpiece-positioning device according to the present invention, wherein  FIG. 4A  is a plan view and  FIG. 4B  is a vertical cross-sectional view. 
     Such a workpiece-positioning device is now described hereunder. 
     Air feeding channels  101  and air ejecting channels  102  are formed in a platform  100  of the workpiece-positioning device for placing the pallet  300 . 
     The air feeding channels  101  have openings in side surfaces and air supplied from an air supply facility flows through the air feeding channels  101 . As depicted in  FIGS. 4A and 4B , six air feeding channels  101  are formed. 
     The air ejecting channels  102  connect to the air feeding channels  101  and have openings in an upper surface  100   a . The air which has flowed from the air feeding channels  101  flows into the air ejecting channels  102  and is forced out upward therefrom. As depicted in  FIGS. 4A and 4B , there are provided two air ejecting channels  102  for each air feeding channel  101 . Meanwhile, the air ejecting channels  102  have a smaller diameter than that of the air feeding channels  101 . Therefore, the air flows at a higher speed through the air ejecting channels  102  than through the air feeding channels  101 . 
       FIG. 5  is a plan view of a production line using the workpiece-positioning device of the present invention. A right side and left side (as illustrated) of this production line are upstream and downstream sides thereof, respectively. 
     The battery cell pack  200  manufactured in an upstream process flows along a production line upstream of a robot arm  110  and is held by suction by the robot arm  110  (holding process # 101 ). The robot arm  110  turns along its own moving path to transfer the battery cell pack  200  onto a left-side production line. The pallet  300  is placed on the platform  100  on this left-side production line. 
       FIG. 6  is a side view for explaining operation of the workpiece-positioning device according to the present invention. 
     The robot arm  110  includes a workpiece holder  111  for suction-holding the battery cell pack  200  and a workpiece holder up/down mechanism  112  for moving the workpiece holder  111  up and down. 
     When the robot arm  110  moves down, air is spewed out of the platform  100 . This causes the pallet  300  to rise slightly so that the pallet  300  can be freely moved parallel to the reference plane (i.e., the upper surface  100   a  of the platform  100 ) (free pallet movement process # 102 ). Then, under conditions where the pallet  300  is slightly lifted, the robot arm  110  descends to place the battery cell pack  200  down on the pallet  300 . At this time, the positioning holes  225  of the battery cell pack  200  fit on the positioning pins  301  of the pallet  300  (lowering process # 103 ). Since the pallet  300  is lifted above the platform  100  at this time, the pallet  300  moves to a position where the battery cell pack  200  is located. Therefore, the outer pack  220  (the positioning holes  225 ) is neither ripped nor deformed in any occasions. 
       FIGS. 7A, 7B-1 and 7B-2  are explanatory representations of an electrode tab cutting process, wherein  FIG. 7A  illustrates a situation before cutting,  FIG. 7B-1  illustrates one shape of the electrode tabs after cutting, and  FIG. 7B-2  illustrates another shape of the electrode tabs after cutting. 
     On the left-side production line of  FIG. 5 , the pallet  300  is moved by a robot arm other than the robot arm  110  used for moving the battery cell pack  200  while holding the same by suction. Specifically, the pallet  300  is moved with claws of the robot arm inserted into the holes  303  in the pallet  300 . The pallet  300  is placed on a platform of each process facility, wherein the pallet  300  is positioned with the aid of the positioning holes  302 . The electrode tabs are cut to a desired shape in this condition as depicted in  FIG. 7B-1  or  FIG. 7B-2 . Incidentally, the shapes of the electrode tabs after the cutting that are depicted in the Figures are simply illustrative and are not limited to these shapes. Also, although only two kinds of shapes are illustrated in  FIGS. 7A, 7B-1 and 7B-2 , the electrode tabs are cut to more than the two kinds of shapes in accordance with specifications of each battery package. 
     In a process further downstream, the pins projecting from the insulative spacer are inserted into the positioning holes  225  formed in the battery cell pack  200  to fixedly determine relative positions of the insulative spacer and the battery cell pack  200 . 
     According to the present embodiment, the workpiece (battery cell pack  200 ) is set in place under conditions where the pallet  300  is lifted by the air forced out of the platform  100 . With this arrangement adopted, the pallet  300  moves to a position where the battery cell pack  200  is located when the positioning holes  225  of the battery cell pack  200  fit on the positioning pins  301  of the pallet  300 . Therefore, it is possible to keep the battery cell pack  200  from being acted upon by an undesired force, and the outer pack  220  (the positioning holes  225 ) is neither ripped nor deformed in any occasions. Moreover, there is no need to waste cycle time as the positioning requires a minimal period of time. 
     It is evident that the present invention is not limited to the above-described embodiment but various modifications and alterations are possible within the scope of the technological concept of the invention and such modifications and alterations are contained in the technical scope thereof. 
     For example, while the foregoing discussion has presented an illustrative example in which the pallet  300  is lifted from the platform  100  by forcing out the air as a free pallet movement mechanism for freely moving the pallet  300  parallel to the reference plane, the invention is not limited thereto. The pallet  300  may be lifted by utilizing a magnetic repelling force. It is also possible to employ a mechanism in which bearing balls are arranged on the upper surface of the platform  100 . Furthermore, it is possible to employ a mechanism in which a film of oil is formed on the upper surface of the platform  100 . Moreover, it is possible to employ a mechanism using a water tank containing water to float the pallet  300 , instead of using the platform. 
     Also, while the foregoing discussion has presented an illustrative example in which the battery cell pack  200  is handled as a workpiece, the workpiece may be other than the battery cell pack  200 . 
     The present application claims priority to Japanese Patent Application No. 2010-138052 filed in Japan Patent Office on Jun. 17, 2010. The contents of this application are incorporated herein by reference in their entirety.