Abstract:
A staking apparatus is provided for use in assembling two or more workpieces, wherein one of the workpieces is made from a thermally softenable and pressure deformable material. The staking apparatus includes a first end plate, an intermediate plate aligned with and spaced apart from the first end plate and a first extensible member disposed therebetween. A second end plate is provided that is extensible in relation to the intermediate plate by the first extensible member. A vent tube, which supplies a flow of air unto the workpiece, and a second extensible member are secured for movement with the second end plate. A staking tool is mounted to the second extensible member and is extensible between a working position, wherein a portion of the thermally softenable workpiece is deformed, and a storage position. A method of operating the staking apparatus is also disclosed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a heat staking apparatus for joining two or more workpieces and, more particularly, to a compact, self-controlled staking apparatus for joining two or more workpieces. 
     2. Description of the Related Art 
     Heat staking is a well-known process for permanently joining two or more of parts at one or more discrete locations. In the heat staking process, one of the joined parts includes a short thermoplastic post or stud that is inserted through a hole or aperture in the mating part. The stud is heated until it is plastically deformable and then shaped or otherwise deformed by a suitable staking tool to form a rivet-like end on the stud that secures the mating parts together. 
     Known heat staking machines, such as the machine disclosed in U.S. Pat. No. 6,093,277, are configured to repetitively assemble a single article or a family of articles. Known heat staking machines are relatively large and typically employ one or more staking tools assembled on a support structure and a separate control system to facilitate heating of the staking tool prior to deforming the stud. To reconfigure or “retool” these machines, each individual staking tool must be disassembled from the control system and rearranged or removed from the heat staking machine. Additionally, known staking machines typically employ a single control system for several heat staking tools, which idles all the staking tools when the control system is rendered inoperable. Accordingly, there exists a need for a compact, self-controlled staking apparatus that can be readily configurable, either alone or in combination with several similar staking apparatus, to assemble a single article or a family of articles. 
     SUMMARY OF THE INVENTION 
     A staking apparatus is provided for use in assembling two or more workpieces, wherein one of the workpieces is made from a thermally softenable and pressure deformable material. The staking apparatus includes a first end plate, an intermediate plate aligned with and spaced apart from the first end plate and a first extensible member disposed therebetween. A second end plate is provided that is extensible in relation to the intermediate plate by the first extensible member. A vent tube, which supplies a flow of air unto the workpiece, and a second extensible member are secured for movement with the second end plate. A staking tool is mounted to the second extensible member and is extensible between a working position, wherein a portion of the thermally softenable workpiece is deformed, and a storage position. A control system, for controlling operation of the staking apparatus, is preferably provided substantially between the first end plate and intermediate plate, giving the staking apparatus a compact package. A method of operating the staking apparatus is also disclosed. 
     Among other advantages, the inventive staking apparatus is compact and readily configurable with similarly designed staking apparatus to repetitively assemble a single article or family of articles. Another advantage is that the staking apparatus includes its own control system, allowing it to remain operable when cooperating staking apparatus are rendered inoperable. 
     Various additional aspects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features and inventive aspects of the present invention will become more apparent upon reading the following detailed description, claims, and drawings, of which the following is a brief description: 
         FIG. 1  is a partial cross-sectional view showing a pair of workpieces and a vent tube prior to being secured together. 
         FIG. 2  is a partial cross-sectional view showing the two workpieces of  FIG. 1  being secured together by deforming a stud on one workpiece with a staking tool. 
         FIG. 3  is a partial cross-sectional view showing the two workpieces of  FIG. 1  secured together. 
         FIG. 4  is a plan view of a staking apparatus, according to a preferred embodiment of the present invention, with a cover removed for clarity. 
         FIG. 5  is a side view of the staking apparatus of FIG.  4 . 
         FIG. 6  is a first end view of the staking apparatus of FIG.  4 . 
         FIG. 7  is a second end view of the staking apparatus of FIG.  4 . 
         FIG. 8  is a plan view of the staking apparatus of  FIG. 4  showing a first extensible member fully extended. 
         FIG. 9  is a plan view of the staking apparatus of  FIG. 4  showing the first extensible member fully extended and a second extensible member fully extended. 
         FIG. 10  is a schematic illustration of a valve arrangement contained within the staking apparatus of FIG.  1 . 
         FIG. 11  is a schematic illustration of an electrical system contained within the staking apparatus of FIG.  1 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, the preferred embodiments of the present invention are shown in detail. Referring to  FIG. 1 , a staking apparatus  20  according to a preferred embodiment of the present invention is shown positioned above first and second workpieces  22  and  24 , respectively, which are to be joined together. As is well known in the art, a stud  26  made from a thermally softenable and pressure deformable material, such as ABS plastic, projects upwardly from first workpiece  22  and passes through a hole  18  formed in second workpiece  24 . As illustrated in  FIGS. 2 and 3 , stud  26  is deformed by a staking tool  28  to fasten first and second workpieces  22 ,  24  together, as will be described in further detail below. 
     A plan view of staking apparatus  20  is illustrated in  FIG. 4  with a cover  29  removed to view a control system  30  for controlling operation of staking apparatus  20 . Staking apparatus  20  includes a first end plate  32  and an intermediate plate  34  substantially aligned with and spaced apart from first end plate  32 . A first extensible member  36 , such as a pneumatic cylinder, is supported between first end plate  32  and intermediate plate  34 . First extensible member  36  is supported in a hole  38  in first end plate  32 . Intermediate plate  34  includes a hole  40  therethrough that allows passage of a rod  42  that extends from and retracts into first extensible member  36 , as will be describe in detail below. A side plate  44  is attached to first end plate  32  and intermediate plate  34  by fasteners  46 , such as a bolt or the like. At least one support shaft  48  is also attached to first end plate  32  and intermediate plate  34  by fasteners  46 . 
     A second end plate  50  is provided adjacent intermediate plate  34  and is extensible in relation to intermediate plate  34  by first extensible member  36 . A support arm  52  having at least one bearing member  54  is slidably received over support shaft  48 . Bearing member  54  is preferably an oil-impregnated sleeve bearing that is press-fit into support arm  52 . A second extensible member  56  is supported between support arm  52  and second end plate  50  and is fixed for travel therewith. At least one tie rod  58  extends freely through intermediate plate  34  and is fixedly attached to support arm  52  and second end plate  50 . An axially adjustable collar  60  is attached to tie rod  58  and abuts intermediate plate  34  as support arm  52  slides toward intermediate plate  34  to limit the travel of second end plate  50 . 
     An adapter  62  is attached to second extensible member  56  and is used to secure a tube  64 , which is shown in cross section in  FIG. 4 , to second extensible member  56 . A rod  68  extends from second extensible member  56  and is configured to receive a coupler  70 . Coupler  70  is preferably threaded onto the end of rod  68  and is attached with a fastener (not illustrated), such as a set-screw or the like. A push rod  72  is secured on one end to coupler  70  and on the other end to staking tool  28 . Push rod  72  may be adjusted axially within coupler  70  to increase or decrease the length of push rod  72  if desired. 
     A generally cylindrical sleeve  74  is secured within tube  64  by at least one fastener  76 , such as a set-screw or the like. Second end plate  50  is secured to tube  64  by at least one fastener  77 , as best shown in  FIG. 6. A  vent tube  78 , which is shown in cross section in  FIG. 4 , is preferably secured to sleeve  74  by a press fit connection. Staking tool  28  is extensible between a stored position, wherein tool  28  resides substantially within sleeve  74 , and a working position (FIG.  9 ), wherein tool  28  extends at least partially outward of vent tube  78 . A sealing member  66  is preferably provided on coupler  70  and abuts sleeve  74  when tool  28  is in the working position to substantially prevent airflow in a direction toward second extensible member  56 . 
     When second extensible member  56  functions as a pneumatic cylinder, a pair of flexible conduits  80  and  82 , such as a hose, are provided between intermediate plate  34  and first and second ports  84  and  86 , respectively, of second extensible member  56 . Although not illustrated in  FIG. 4 , each conduit  80  and  82  is provided in sealed communication with control system  30 . 
     A heater  92  is indirectly connected to second end plate  50  by at least one support member  93  and is placed in communication with vent tube  78  through a hole in sleeve  74 . Heater  92  is also place in communication with a tube  94  that is attached to second end plate  50  via a duct  96  in second end plate  50  and a duct  97  in support member  93 . Tube  94  extends through a larger diameter tube  96  that is attached on one end to intermediate plate  34  and on the other end to a flow control valve  98 . Tube  94  extends through a sealing plate  100  that is secured to intermediate plate  34 . Sealing plate  100  generally includes a sealing member (not illustrated), such as an o-ring, which seals against tube  94  and allows tube  94  to extend into and out of tube  96 . Heater  92  is also provided with an electrical coupling  99  that extends through second end plate  50 . An electrical conduit, such as a wire (not illustrated), extends between electrical coupling  99  and control system  30  to supply electricity to heater  92  during operation. 
     Referring to  FIG. 5 , a bottom cover  102  and top cover  29  are secured to first end plate  32 , intermediate plate  34  and side plate  44 , such that control system  30  is contained substantially therebetween. In a preferred embodiment, control system  30  includes a relay  106 , a current transformer  108  and a terminal strip  110  that cooperatively control operation of heater  92 . As illustrated in  FIG. 11 , a switch  112 , which is preferably pneumatically actuated, is provided in a circuit that includes a power source, current transformer  108  and heater  92 . Current transformer  108  is provided in electrical communication with relay  106 , which is positioned in a second circuit that includes at least one signaling device  114 , such as an indicator light or audible indicator. 
     In a preferred embodiment of the present invention, first and second extensible cylinders  36 ,  56  are pneumatically operated. Therefore, control system  30 , as described herein, includes a means of distributing fluid power between a source of compressed air and first and second extensible cylinders  36 ,  56 . However, it will be appreciated that other extensible devices, such as a motor driven screw mechanism, may be used in place of first and second extensible cylinders  36 ,  56  without departing from the scope of the present invention. In such a configuration, control system  30  may include specific devices, such as a programmable logic controller (PLC), for controlling operation of the extensible members. 
     Referring to  FIG. 10 , staking apparatus  20  is provided with a main port  116  to which the source of compressed air is connected. Main port  116  is provided in direct communication with a pair of four-way valves  118 ,  120  and a two-way valve  122 , which are preferably, but not necessarily, pneumatically operated to simplify operation of staking apparatus  20 . For clarity, the conduits provided between port  116  and valves  118 ,  120  and  122  are not illustrated in  FIGS. 4 ,  8  and  9 , but are illustrated schematically in FIG.  10 . Similarly, conduits provided between all pneumatically operated elements, as described herein, are not illustrated in  FIGS. 4 ,  8  and  9 , but are illustrated schematically in FIG.  10 . 
     First four-way valve  118  is provided in communication with a first pulse valve  124  and a third four-way valve  126 , both of which also being pneumatically operated. When actuated to a first position, third four-way valve  126  supplies air to a first timer  130 , which is preferably pneumatically operated, and switch  112 . First timer  130  is configured to supply air to a first volume chamber  132  until a first predetermined pressure in first volume chamber  132  is achieved, at which point timer  130  actuates or “shifts” to supply a signal or pulse of air to third four-way valve  126 . The predetermined pressure that causes timer  130  to shift is selectively adjustable by an operator of staking apparatus  20  through an adjustment member  134 , such as a screw, that extends through side plate  44  (FIGS.  4  and  5 ). 
     Referring still to  FIG. 10 , third four-way valve  126  can be actuated to a second position that supplies air to a second pulse valve  135 , which in turn provides a signal to second four-way valve  120 . When actuated to a first position, second four-way valve  120  supplies air to second extensible cylinder  56  causing it to extend. When shifted to a second position, second four-way valve  120  supplies air to a second timer  136  that is configured to supply air to a second volume chamber  138 . Second timer  136  and second volume chamber  138  are preferably substantially similar to first timer  130  and first volume chamber  132 . However, the predetermined pressure in second volume chamber  138  that causes timer  136  to shift is selectively adjustable by an operator of staking apparatus through an adjustment member  140 , such as a screw, that extends through side plate  44  (FIGS.  4  and  5 ). Although the above described control system  30  is configured with pneumatically operated valves to distribute compressed air through control system  30 , it is not necessarily limited thereto. Alternatively, other suitable air distribution devices, such as electromechanically operated valves, are also within the scope of this invention. 
     Operation of the inventive staking apparatus  20  will be described herein with reference to  FIGS. 8 and 9 . Provided a source of air and electricity are connected to staking apparatus  20 , the operating sequence is initiated by an operator selectively supplying a signal or pulse of air to first four-way valve  118 . The operator may initiate this pulse of air by simultaneously depressing a pair of pneumatically operated safety switches, or by any other suitable means known in the art. 
     Upon receipt of a signal or pulse of air, first four-way valve  118  shifts and supplies air to first extensible member  36 , pulse valve  124 , and third four-way valve  126 . Regarding first extensible member  36 , the receipt of air causes it to extended second end plate  50  away from intermediate plate  34 , as illustrated in FIG.  8 . As described above, the distance first extensible member  36  extends second end plate  50  is selectively variable by adjusting the position of collar  60  along tie rod  58 . As shown in  FIG. 8 , extension of second extensible member  36  and second end plate  50  stops when collar  60  abuts intermediate plate  34 . 
     Regarding third four-way valve  126 , the receipt of air from first four-way valve  118  causes it to supply air to timer  130  and switch  112  virtually simultaneously. Upon receipt of air pressure, switch  112  shifts and supplies electricity to operate heater  92 . Transformer  108  draws a small amount of current from a live wire between switch  112  and heater  92 , which opens the normally closed relay  106 . If a malfunction occurs in heater  92 , such as a break in the internal heating coil, transformer  108  will not be able to draw current from the live wire. In his situation, relay  106  will not open, thereby completing the circuit that activates signaling device(s)  114  to warn the operator that beater  92  has malfunctioned. 
     Regarding pulse valve  124 , the receipt of air from first four-way valve  118  causes it to send a pulse of air to two-way valve  122 . This application of air pressure causes two-way valve  122  to shift and supply air through control valve  98 , tubes  97  and  94 , duct  96  in second end plate  50  and heater  92 . The heated air that exits heater  92  is redirected through vent tube  78  and is expelled from vent tube  78  over stud  26 , as shown in FIG.  1 . Heated air is continuously expelled from vent tube  78  until timer  130  senses the predetermined air pressure in first volume chamber  132  and shifts. 
     Once shifted, timer  130  sends a pulse of air to third four-way valve  126  causing third four-way valve  126  to shift and turn off the air supply to switch  112  and timer  130 . The shifting of third four-way valve  126  also causes it to supply air to actuate pulse valve  135 . When actuated, pulse valve  135  sends a pulse of air to second four-way valve  120 , causing it to shift and supply air to second extensible member  56  and timer  136 . Receipt of air into second extensible member  56  causes it to extend staking tool  28  against stud  26  to form stud  26  over second workpeice  24 , as shown in FIG.  2 . The distance staking tool  28  extends into vent tube  78  is selectively adjustable to accommodate various studs  26  and workpieces  22 ,  24 . 
     After termination of electricity to heater  92 , non-heated air is continuously passing through heater  92  and is directed through duct  79  in staking tool  28  to cool staking tool  28  and the newly formed stud  26 . The non-heated air passes through staking tool  28  until timer  136  senses the predetermined air pressure in second volume chamber  138  and shifts. Once shifted, timer  136  supplies a pulse of air to shift first and second four-way valves  118 ,  120  and two-way valve  122 . Once sifted, first four-way valve  118  supplies air to first extensible member  52  causing it to retract second end plate  50  toward intermediate plate  34 . Virtually simultaneously, the shifted second four-way valve  120  supplies air to second extensible member  56  causing it to retract staking tool  28  into vent tube  78 . Once shifted, two-way valve  122  terminates the flow of air through heater  92 . In this configuration, all items are returned to their home positions, as shown in  FIG. 4 , and the operating cycle is deemed complete. 
     Although certain preferred embodiments of the present invention have been described, the invention is not limited to the illustrations described and shown herein, which are deemed to be merely illustrative of the best modes of carrying out the invention. A person of ordinary skill in the art will realize that certain modifications and variations will come within the teachings of this invention and that such variations and modifications arc within its spirit and the scope as defined by the claims.