Patent Document

BACKGROUND 
   The present invention relates to method and apparatus for trimming flashing which forms when plastic members are fused together. More particularly, the present invention relates to method and apparatus for trimming flashing without the need for removing the joined members from the joining equipment and transporting the members to a remote trimming/polishing station. 
   High speed automatic equipment for joining frame components which have been cut to size and supplied to the equipment for fabricating a frame or a frame-like structure, are well known in the art. 
   The typical operation is to provide plastic frame members which have been processed preparatory to the joining operation to form a frame, for example. Although machines of this nature are capable of simultaneously joining substantially all four corners of a frame structure, a description will be given herein of the manner in which two frame members forming one corner of the frame structure are joined, it being understood that the other three corners are formed in a substantially identical manner and are also performed substantially simultaneously with the corner joining operation described hereunder. 
   The frame members, which have previously been precision mitred to form a corner, are placed in the machine, typically referred to as a conventional 4-point welder structure, are positioned within clamping devices and are moved towards one another so that the surfaces to be joined engage a locator plate which typically provides a gap of the order of one quarter inch (0.25″) between the surfaces to be joined. The clamping assemblies clamp the frame members in place so that the surfaces to be joined extend a given distance beyond their clamping devices in a direction toward the opposite clamping device. 
   The clamping devices are then moved apart by an amount sufficient to enable the locator plate to be withdrawn. After the locator plate is withdrawn, a heated plate is placed in the gap region between the surfaces to be joined. The clamping devices then move the frame members towards one another causing the surfaces to be joined to engage opposing surfaces of the heated plate which heats the surfaces to be joined to a level sufficient to heat a marginal end portion of each frame member to a softened or molten state. This is accomplished by adjusting/controlling the temperature of the heated plate and the time interval during which the engaging surfaces of the frame member are in contact with the heated plate to achieve the desired molten state. 
   Thereafter, the clamping assemblies are moved to separate the frame members to enable the heated plate to be withdrawn. After the heated plate has been removed from the region between the heated, molten surfaces, the clamping members are moved to bring the heated molten, surfaces of the cooperating frame members into intimate engagement. This action causes the molten surfaces to fuse together as they undergo cooling. In addition, the bringing together of the frame members causes some of the molten material to be squeezed out from the region between the joined ends of the engaged frame members, whereby the molten material squeezed out from between the joined surfaces, forms an undesirable flashing. 
   After the frame members have cooled sufficiently, the frame is removed from the clamping assemblies. 
   The frame assembly is removed to a separate location from the four 4-point welding equipment to undergo trimming and polishing, necessitating: removal of the completed frame; transportation to a trimming/polishing station; clamping of the frame at the trimming/polishing station; and performing the trimming/polishing operations. In addition, the techniques presently used for trimming/polishing the flashing typically requires a large amount of manual labor to obtain frames having the desired clean, aesthetic appearance in the regions of the joined corners. 
   SUMMARY 
   The present invention is characterized by comprising method and apparatus for performing a trimming operation which takes place at the welding station and immediately following the welding operations, thereby significantly reducing the amount of handling required in the employment of conventional techniques while totally eliminating the need to transport frame assemblies requiring trimming operations to a second location for performance thereof. In addition the present invention is characterized by comprising method and apparatus for performing a trimming operation which provides a frame having a clean, aesthetically pleasing appearance in the regions of the mitred corners while eliminating the need for the labor intensive activities necessary when employing conventional techniques. 
   The present invention is characterized by comprising method and apparatus for mounting the trimming assembly directly upon an automated welder system, which may be a single point, two (2) point or four (4) point welder for joining frame members whose center line are perpendicular as well as joining members whose longitudinal center lines are parallel or form any angle therebetween, enabling the trimming operation to be performed while the joined members of the frame are still mounted in the automated welder, thereby totally eliminating the need for removal of the frame from the automated welder and transporting and mounting the frame upon appropriate trimming/polishing equipment. 
   More specifically, the apparatus of the present invention comprises guide blocks joined to the clamping assemblies of the welder equipment. The trimming apparatus comprises a pair of guide members which serve to guide reciprocally mounted trimming blades. Actuators are provided for each of the trimming blades for selective extension and retraction thereof. In addition thereto, a latching assembly is provided for selectively latching the guide blocks to one another to prevent their movement during the operation of the trimming blade(s),thereby assuring clean, effective trimming of the flashing which avoids the need for additional finishing/polishing. Latching activators are provided separately and independently of the trimming blade activators for selectively latching and delatching the guide block. 
   The activators may be electrically operated solenoids or hydraulic or pneumatic devices. In one preferred embodiment, the activators are pneumatically controlled activators forming a part of a pneumatic system for operating the latches at a first pressure level known as “shop psi” for operating the latches and moving the trimming blades in the retraction direction and being provided with a booster regulator for extending the trimming blades at a higher pressure level hereinafter referred to as a high psi. 
   The trimming system is preferably operated under control of a programmed logic controller (PLC) for automatically controlling the trimming system through a preprogrammed sequence and further automatically initiating operation responsive to control signals from the automated welder system, enabling operation of the trimming system in proper synchronizing and time relationship with the automated, welder equipment. 
   The guide blocks and cutting blades may be designed to accommodate a variety of different frame structures so as to provide trimming for frames of complex cross-section configurations as well as cross-sections of simple shapes having substantially flat external surfaces at the same time without interfering with the or complicating the design and operation of the welder equipment, enabling operation of the welder equipment without any design modifications to accommodate the trimming system. 
   The cooperating cutting blades may be operated to perform a variety of different combinations of cutting/shearing steps to perform a trimming operation which removes flashing from the joined ends of frames and the like to a degree sufficient to eliminate the need for any further trimming/polishing operations. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described in detail hereinbelow making reference to the drawings, in which: 
       FIG. 1  is a simplified diagram showing the actuators for the trimming and locking operations and the programmed logic controller for operating the actuators in accordance with a pre-programmed sequence. 
       FIG. 2  is a plan view showing the fixtures for holding frame members to be joined and the pressure lines comprised thereof. 
       FIGS. 3   a  and  3   b  are perspective views showing the fixtures of  FIG. 2  in greater detail. 
       FIG. 4  is a perspective view of the fixtures of  FIGS. 2 ,  3   a  and  3   b  with portions thereof removed to facilitate an understanding of the operations of the various actuators employed in the trimming system. 
       FIG. 5  is a top plan view showing the locking system in greater detail. 
       FIGS. 6   a  and  6   b  respectively show a top plan view and an end view of a shoe holding four (4) trimming blades. 
       FIGS. 7   a ,  7   b  and  7   c  are front, side and top views of blade “ 1 ” in  FIG. 6   b.    
       FIGS. 8   a ,  8   b  and  8   c  are front, side and top views of blade “ 2 ” in  FIG. 6   b.    
       FIGS. 9   a ,  9   b  and  9   c  are front, side and top views of blade “ 3 ” in  FIG. 6   b.    
       FIGS. 10 ,  10   b  and  10   c  are front, side and top views of blade “ 4 ” in  FIG. 6   b.    
       FIGS. 11   a  and  11   b  are tables showing two possible programmed sequences of the trimming operations obtainable through the programmed logic controller of FIG.  1 . 
       FIGS. 12   a - 12   d  are cross sections of the different profiles of frame members capable of being joined and trimmed employing the system of the present invention. 
       FIGS. 13   a - 13   c  are cross sections of other profiles of frame members capable of being trimmed by the system of the present invention, and respectively showing trimming apparatus adapted for use in trimming a single stack, a double stack and a four-high stack of profiles. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  is a simplified block diagram showing an actuator system  10  for selectively operating the reciprocating trimming knives and the locking mechanism. A programmable logic controller (PLC)  12  is programmed to operate the trimming and locking actuators in a predetermined sequence which can be modified according to the type of profile being trimmed. 
   A source  14  provides the desired “shop” pressure, typically of the order of 90 psi, which is coupled through line  16  to a booster regulator  18 , and line  16   a  to  16   b  and  16   c  which are respectively coupled to solenoid-operated control valves  18  and  20  for respectively operating the fixture locking cylinder  22  and trimming blade cylinder  24 . 
   The output of booster  18 , which is of the order of 170 psi, is coupled to a safety valve  28  through reservoir  26 . A pair of one-way valves provided in valve structure  30  prevent the pressure in high pressure line  16   d  from entering into low pressure line  16   b , and vice versa. 
   The PLC  12  receives a signal from the 4-point welder, as will be more fully described, to initiate the operation of the trimming apparatus. 
   The cooperating fixtures are shown in  FIGS. 3   a  and  3   b  separated from one another while  FIG. 4  shows the fixtures in the trimming-ready position locked together in readiness for operation of the trimming blades. The upper and lower fixtures  32  and  34  embrace one of the frame members F 1  therebetween and are each provided with diagonally aligned faces  32   a  and  34   a  which are arranged to be directly opposite the diagonally aligned faces  36   a  and  38   a  of the upper and lower fixture members  36  and  38 , respectively, which receive a cooperating frame member F 2 . The fixtures  32 - 34  and  36 - 38  are arranged in the manner shown in  FIGS. 2 and 4  and clamp the frame members F 1  and F 2  in the manner shown so that their cooperating surfaces to be joined are arranged in spaced, parallel fashion and are maintained in this alignment throughout the welding and trimming operation. The end surfaces of frame members F 1  and F 2  protrude of the order of 0.25 inches beyond the end surfaces of their associated fixtures. Each upper and lower fixture  32  and  34  is provided with an elongated slot  32   b ,  34   b  for slideably receiving and guiding a locking actuator  22  as shown in  FIG. 1 , as well as a swingably mounted locking plate  40  and  42 . Each locking plate is mounted to pivot about a pivot pin  44 , only one of which is shown in FIG.  4  and in FIG.  5  and is swingable between a retracted position  40 ′ shown in dotted fashion and a locking position  40  shown in solid line fashion in FIG.  5 . Other locking techniques may be used to restrain the fixture from moving during operation of the trimming blades. For example, making reference to  FIG. 5 , the plate  40  of  FIG. 5 , may enter into slot  50  in upper fixture  36  and containing pin  54 . Plate  40  may have an opening for receiving pin  54  in the slot of fixture  32 . As the two fixtures  32  and  36  move together, the locking plate  40  may move over pin  54 . Cylinder  22  operates by extending piston rod  22   a  causing the end portion of the piston rod to press locking plate  40  downwardly causing pin  54  to enter the opening in plate  40  and thereby lock fixtures  32  and  36  against movement during the trimming operation. 
   Locking plate  40  of  FIGS. 4 and 5 , for example, is swung about pivot  44  by means of a pin  46  on piston arm  22   a  which is received within a slot  40   a  provided in locking plate  40 . The fixture locking actuator cylinder  22  shown in  FIGS. 1 ,  3   a ,  4  and  5 , drives piston arm  22   a  in the direction of arrow A to move locking plate  40 , by pin  46 , in a counter clockwise direction about pivot pin  44 , as shown in  FIG. 5  so as to reach the locking position. As was mentioned hereinabove, the shop pressure (typically 90 psi) enters into cylinder  22  through line  16   e  under control of the solenoid operated valve  18  when in a first state. Piston  22   a  is retracted by operating solenoid controlled valve to move to a second state to apply shop pressure to cylinder  22  through line  16   f  causing the blocking plate  40  to occupy the dotted line position  40 ′ shown in FIG.  5 . 
   The upper and lower fixtures  36  and  38  shown in  FIG. 3   b  are each provided with elongated slots  50  and  52  which slidably receive the free ends of the pistons  22   a  and also receive at least a portion of the locking plate  40 . Each of the slots  50  and  52  is provided with a locking pin  54 ,  56  which cooperates with locking slot  40   b  in each locking plate  40 .  FIG. 4  shows a portion of the upper fixture  32  removed to expose the locking mechanism actuator cylinder  22  and showing the piston  22   a  in the extended state, causing the locking plate  40  to be pivoted into the position where its slot  40   b  captures the pin  5 A shown in  FIG. 3   b , the locking position being shown best in  FIGS. 4 and 5 . 
   It should be understood that the upper fixtures  32  and  36  are locked to one another and that the lower fixtures  34  and  38  are locked to one another, the lower locking fixture assembly being substantially identical in design and function to the upper locking fixture description described hereinabove. The locking mechanism prevents the fixtures from moving relative to one another when the trimming blades are operated to prevent the frames being joined from experiencing any movement during trimming of the flashing and also to prevent the cooperating fixture members from moving during the trimming operation, thereby providing a trimming operation which completely removes the flashing, thus avoiding the need for any further trimming and/or polishing operations. 
   The locking mechanism actuating cylinders  22  are operated to retract the pistons  22   a  upon completion of the trimming operation to enable separation of the fixtures preparatory to removal of the joined frame members. 
   Each of the fixtures  32 ,  34 ,  36  and  38  is provided with a reciprocating trimming blade assembly  58 ,  60  shown in  FIG. 3   a  and  62 ,  64 , shown in  FIG. 3   b . Each trimming blade assembly has its blades joined to a boot B, each boot having a projection which is driven by an associated trimming cylinder  24 .  FIGS. 6   a  and  6   b  are top and front end views of a boot holding four ( 4 ) trimming blades  1 ,  2 ,  3 , and  4 , which are secured to the boot B by suitable fastening screws (not shown).  FIGS. 7   a - 10   c  show front, side and top views of blades  1 - 4 . Openings O in the blades  1 - 4  receive the aforementioned fasteners for securement to boot B. The cutting edges  1   a - 4   a  are arranged along the edges of the boot B. A plurality of blades are employed to trim flashing in the embodiment of  FIGS. 6   a ,  6   b . Blades may be provided to trim flashing from outside corners. Surfaces S 1 , S 2 , etc. of the more complex frames of  FIGS. 12   a  to  12   c  are the surfaces trimmed by the trimming blades. It should be understood that the number, sizes and configurations of the blades are a function of the surfaces of the frames to be trimmed and may be easily designed/modified to accommodate different profiles whether simple or complex. 
     FIG. 2  shows a simplified plan view of one corner trimming assembly showing the pneumatic lines coupled thereto for activating the latching and trimming assemblies. 
     FIG. 3   a  is a perspective view showing a portion of the trimming assembly of  FIG. 2  which incorporates the latching hook and the pneumatic activators therefor. 
     FIG. 3   b  is a perspective view showing the latching assembly portion which cooperates with that shown in  FIG. 3   a  and having the latch receiving slot for receiving the latching hook which is latched to the pin provided in the slot. 
     FIG. 4  shows portions of the upper fixtures  32  and  36  removed, exposing the trimming actuator cylinders  24  the boots  58   a ,  62   a  and the boot projections  56   b  and  62   b . Each of the trimming actuator cylinders  24  is provided with a piston  24   a , each piston having its free end coupled to the associated boot projection  58   b ,  62   b . Making reference to  FIGS. 1 and 2 , solenoid operated valve  20 , in a first position, couples the high pressure line  60   d  to line  16   g  causing the piston  24   a  to be extended, driving the associated trimming blade toward the trimming/cutting position. When the solenoid operated valve  20  is moved to a second state, compressed air at shop psi (typically 90 psi) is coupled to cylinder  24  through line  16   h  retracting the associated trimming blade at the lower pressure level. 
   Although  FIG. 1  shows only a single trimming actuator cylinder  24  and locking actuator cylinder  22 , it should be understood that two locking activating cylinders  22  are provided at each corner assembly comprised of upper and lower fixtures as shown in  FIGS. 3   a  and  3   b  and that four trimming actuating cylinders are provided at each corner for selective operation of the trimming knives  58 ,  60 ,  62  and  64 . 
   A typical operating sequence will now be described. Initially, the welding operation takes place prior to the trimming operation. It should be understood that the welding operation may comprise equipment for fusing all four corners of a frame or alternatively for fusing only one corner, it being understood that the present invention may be utilized with equal success and efficiency in either single corner or four corner fusing equipment as well as 2 or 3 corner point welding units. 
   The operation of the joining of two frame members at one corner will be described herein for purposes of simplicity, it being understood that the welding and trimming operations that are not shown are substantially identical in design and function. 
   The frame members F 1  and F 2  to be joined are respectively placed between the fixture pairs  32 - 34  and  36 - 38 . Although not shown for purposes of simplicity, it should be understood that suitable clamping means that such as hydraulically or pneumatically operated clamping pistons or electrically operated solenoids urge the cooperating fixtures  32 - 34  and  36 - 38  toward one another to suitably clamp the frame member F 1  and F 2  therebetween. 
   A locator plate, not shown for purposes of simplicity, is extended into the region between the fixture pairs  32 - 34  and  36 - 38  and the fixtures are closed into the locator plate. The members being joined are inserted into the fixtures and the clamping actuators clamp the frame members in place. As is conventional, the processed ends F 1   a  and F 2   a  of the frame members of F 1  and F 2  are arranged by the locator plate so as to extend slightly beyond the end faces of the fixtures. For example, the mitred end of frame member F 1  is arranged to extended preferably about ⅛ th  of an inch beyond faces  32   a  and  34   a  for fixtures  32  and  34 . Frame member F 2  has its processed surface F 2   a  extending a similar distance beyond the faces  36   a  and  38   a  of fixtures  36  and  38 . These distances may be modified according to the materials being joined, as well as other factors. 
   With the frame members in this position and locked in place, the fixtures are moved apart and the locator plate is retracted. The heating plate is then extended into the gap between the mitred end surfaces and the fixtures are moved towards one another causing the end surfaces to make contact with the heated plate in order to melt the end portion of each frame member for a period sufficient to render the plastic material softened or molten. The ends of the frame members F 1  and F 2  are typically maintained in contact with the heat plate for approximately 20 seconds. The heat plate is typically maintained at a temperature of 450° F. when joining frames formed of PVC, for example, which is used for storm windows and the like. Other materials may require different temperatures and different dwell times according to the material being used. For example, resilient gaskets used in refrigerators for sealing a refrigerator door, require less heat to soften the material sufficient for fusing two joined pieces. 
   Thereafter, the fixtures are moved apart and the heat plate is retracted from the region between the fixtures. The fixtures are then moved into an engaged position joining the heated, molten ends of the frame members. The members are maintained in this fusion position for about 20 to 25 seconds, allowing the frame members to be fused together and cooled. 
   In the present invention, the PLC  12  takes the signal from the welder assembly which may be signals provided to 24 volt dc solenoids employed in conventional welder machines. 
   The trim cycle begins whereby PLC  12 , upon receipt of the appropriate signal from the welder, operates the solenoid controlled valves  18  causing the valves to couple the “shop” psi to the line  16   e  of the locking mechanism actuator cylinder  22  whereupon the piston arms  22   a  are extended causing the latching plates  40  and  42  to enter into the cooperating slots  50  and  52  in fixtures  36  and  38  (see  FIG. 3   a  and  3   b ) whereby the slot  40   b  in the upper latching plate  40  and  42   b  in the lower latching plate  42  move into the locking position with the associated locking pins  54  and  56 , the manner in which the cooperating locking pin  54  is received within slot  40   b  of locking plate  40  being shown best in FIG.  5 . Once the locking plates are in the locking position, the trimming operation can now be initiated.  FIG. 11   a  shows a table of one trimming sequence comprised of 25 steps. The headings of the five columns reading from left to right are the step numbers; relationship of each step to the prior step (i.e. is it before or after); the timing of each step; the activity of each step and the total time elapsed. 
   Making reference to the table shown in  FIG. 11   a , initially the heads lock (step  1 ) and thereafter actuating cylinders  24  are activated whereby the higher psi is applied to the lines  16   g  causing both pairs of trimming blades, i.e. the upper pair of assemblies  58 - 62  and, simultaneously therewith the cooperating lower pair of trimming knife assemblies  60 - 64  provided in the lower fixtures  34 - 38 , to be extended (step  2 ). 
   At step  3  the left trimming knife of each trimming pair, i.e., the trimming knives of assemblies  58  and  60  of fixtures  32  and  34 , are retracted at the lower psi. At step  4  the left trimming knives of assemblies  58  and  60  are then extended. At step  5 , the right trimming knives i.e. the trimming knives of assemblies  62  and  64  of the upper and lower fixtures  36  and  38  are retracted at the lower psi and then at step  6  they are extended at the higher psi. By retracting and extending the trimming blade assemblies  58 - 64  through a number of different steps, this assures the complete removal of the flashing. The number of steps typically may vary in accordance with the nature of the members and/or materials being fused. For example, when making gasket frames formed of a resilient compressible material, it has been found that such materials require a lesser number of steps to perform a trimming operation. Thus, according to the material, the program is selected which removes the flashing without the need for further removal by cutting by hand and/or polishing. 
   In addition to operating the trimming blades so as to open and close simultaneously or so as to hold one blade closed while the other is repeatedly opened and closed, a shearing operation may be performed by holding one of the cooperating blades of each blade pair in a retracted position and repeatedly extending and retracting the other blade of the blade pairs. For example, the right hand blades  62  and  64  ( FIG. 3   b ) may be held in the retracted position while blades  58  and  60  are repeatedly retracted and extended, causing a shearing action whereby the blades  58  and  60  move to a position to shear and cut through the flashing formed at the jointure of the two joined frame members. 
   The shearing sequence may be alternated whereby the left-hand blades of assemblies  58 ,  60  perform shearing while the right-hand blades of assemblies  62  and  64  are retracted and the blade assemblies then reverse their operations so that the left-hand blades of assemblies  58  and  60  are retracted while the right-hand blades  62  and  64  perform the shearing operation. 
   The program of  FIG. 11   b  provides for repeated shearing operations where one blade assembly is retracted while the cooperating blade assembly is extended. See steps  3 - 5 ;  21 - 23  and  27 - 29 , for example, in addition to both extending and retracting at the same time. A variety of different combinations of cutting and shearing operations may be performed depending typically upon the nature of the material being trimmed. 
   In the example given, the frame members have a fairly regular shape. It should be understood that the fixture and blades of the present invention may be provided with any desired configuration so as to conform to the profile of the frame members being joined and trimmed. For example, the frame profiles may be quite simple such as a gasket having substantially flat surfaces or maybe a frame for a window such as a storm window and have a much more complicated frame profile, as shown by the different profiles of  FIGS. 12   a  to  12   d.    
   It can be seen that the present invention provides a novel apparatus and method for trimming plastic frame members and the like, and which is utilized in conjunction with conventional welding apparatus enabling the trimming operation to be performed while the frame members are retained at the welding apparatus thus eliminating the need for removing the fused frame members and relocating them to a separate independent apparatus. Although the preferred embodiment is directed to joining frame members, it should be understood that the trimming apparatus of the present invention may be used to trim any joined plastic members, regardless of their orientation and may be used to trim members whose center lines are arranged to be parallel, perpendicular or any angle there between. 
   In addition to the trimming apparatus embodiment described hereinabove, the present invention may be adapted for use in trimming joining members, such as, but not limited to, frame members and utilized with heating/fusing/joining apparatus capable of performing heating/fusing/joining operations on a single stack or frame or on multiple stacks of frames, simultaneously. 
   For example, the embodiment shown in  FIG. 13   a , as well as the embodiment of  FIGS. 3 and 3   a  are utilized for trimming a single stack of profiles. 
     FIG. 13   a  shows a somewhat complex “right-hand” profile P arranged in a suitable clamping fixture F to be joined to a “left-hand” profile, not shown for purposes of simplicity. For example, the fixture  32 ,  34  of  FIG. 2  is assumed to hold the “left-hand” profile and the fixture  36 ,  38  is assumed to hold the “right-hand” profile when viewing  FIG. 2  from the left-hand side of FIG.  2 . The surfaces to be trimmed are S 1 -S 7 . 
   Heating/fusing/joining structures are also available which are capable of simultaneously operating on a stack of two (2) or more members. For example,  FIG. 13   b  shows two identical “right-hand” profiles P arranged in a suitable clamping fixture F′ in which the profiles P, similar to that shown in  FIG. 13   a , to be joined to “left-hand” profiles are arranged stacked one upon the other. Thus, for example, a single point or multiple point welder capable of joining frame members of two frames stacked one upon the other, may be utilized with the present invention to thereby simultaneously trim two stacked frame members which have been joined. 
   Single or multiple point welders are not limited to joining double stacks and may be utilized to join multiple stacks greater in number than two. For example,  FIG. 13   c  shows a “quad” stack in which four (4) “right-hand” profiles P 1  are arranged stacked one upon another in a frame assembly F″ for joining with four(4) cooperating “left-hand” profiles. The trimmer arrangement of the present invention may trim surfaces S 1 -S 3  of the “quad” stack of profiles P 1 , the actual number of stacked profiles to be trimmed being a function of the single or multiple point welding apparatus as to whether it is capable of handling a single stack or multiple stacks of profiles. 
   It should be understood that the “right profiles” for single, double or quad stacks are held by clamping fixtures similar to those respectively shown in  FIGS. 13   a - 13   c.

Technology Category: b