Abstract:
Adjustable clamping frames for rotary thermoforming machine have movable sets of clamp supporting members which are driven by selectively engageable drive units to carry out a size adjustment at a station in the thermoforming machine.

Description:
BACKGROUND OF THE INVENTION 
     This invention concerns thermoforming machines of the type in which sheets of plastic from which a part is to formed are clamped in a frame at a loading station, and the frame with the sheet clamped therein is transferred through successive stations in the machine for heating, forming, cooling, unloading, etc. 
     In a common design for such machines, transfer of the clamping frames through the various stations is carried out by means of a rotary wheel carrier. 
     The plastic sheet is supported along its edges by a series of clamps arranged along the length of clamping frame members arranged in a rectangular shape. 
     Thermoforming machines often can be used for producing different parts, requiring different sheet sizes, and for this reason the clamping frame size must usually be changed to match the sheet size required. Heretofore, adjustable size frames have been used, usually requiring carrying out mechanical adjustments of the frame members manually while the frames are in the machine. This is a tedious, slow task, prone to error as the mechanic typically must enter spaces within the machine at locations where making adjustments is awkward. 
     Alternatively, the frames must be removed from the machine to be replaced with different size frames, or to be reassembled in a different size configuration. 
     It is the object of the present invention to provide a quicker, easier and less error prone method for adjusting the clamping frame size and a clamping frame used in such method. 
     SUMMARY OF THE INVENTION 
     The above object and others which will become apparent upon a reading of the following specification and claims are achieved by use of a pair of selectively engageable drive units, each drive unit used to adjust the spacing of a respective one of an adjustment mechanism associated with each pair of sets of parallel movable members included in the clamping frame. The pairs of movable members together form a rectangular space which receives the sheet to be clamped, and a series of clamp mechanisms on each of the movable members is used to clamp each side edge of the sheet. 
     The drive units are located at one of the machine stations, and each frame is adjustable upon being transferred therein by the drive units being moved into engagement with a respective adjustment mechanism. Each selectively engageable drive unit includes an output gear, and each unit is slidable to cause the output gear of the drive unit to move into and out of meshing engagement with a respective one of a gear included in each adjustment mechanism carried by each clamping frame. Each of the gears drives to pairs of parallel screw shafts received onto the ends of a respective pair of movable frame members. 
     The screw shafts are cause to be rotated in synchronism with each other by a cross shaft and pairs of meshing gears fixed to the cross shaft and screw shafts respectively. 
     The screw shafts have oppositely threaded segments which when rotated drive each engaged end of the movable frame members closer or further apart to carry out a size adjustments. 
     The selectively engageable drive units is being located in the thermoforming machine at a particular station allows a succession of clamping frames to be adjusted in turn by engagement of the drive units after each clamping frame is transferred to that station. 
     The powered adjustment may be carried out by an operator observing fixed scales on each frame as the drive motor is activated to shift the movable frame members to verify when a desired size adjustment has been reached. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a simplified plan view of a rotary transfer thermoforming machine utilizing powered adjustment clamping frames. 
     FIG. 2 is a plan view of a powered adjustment clamping frame according to the present invention. 
     FIG. 2A is an enlarged fragmentary plan view of a portion of the powered adjustment clamping frame shown in FIG.  2 . 
     FIG. 2B is an enlarged fragmentary plan view of a portion of the powered adjustment clamping frame shown in FIG.  2 . 
     FIG. 3 is a side elevational view of the powered adjustment clamping frame shown in FIG.  2 . 
     FIG. 3A is a side elevational enlarged view of one of the clamping mechanisms installed on the X-axis movable rails. 
     FIG. 4 is a front elevational view of the powered adjustment clamping frame shown in FIG. 2, showing engagement of drive units for the respective adjustment mechanisms for each rail set of the clamping frame. 
     FIG. 5 is a view of the section  5 — 5  taken in FIG.  2 . 
     FIG. 6 is a view of the section  6 — 6  taken in FIG.  2 . 
     FIG. 7 is a view of the section  7 — 7  taken in FIG.  2 . 
     FIG. 8 is a fragmentary bottom plan view of the clamping frame in a direction looking up at the bottom of the clamping frame showing attached scales for each movable rail set. 
     FIG. 9 is a fragmentary plan view of the Y axis rail set of the clamping frame. 
     FIG. 10 is a fragmentary plan view of the X axis rail set of the clamping frame. 
     FIG. 11 is a fragmentary plan view of portions of the thermoforming machine and the disengageable drive for each of the respective clamping frame movable rail sets. 
     FIG. 12 is a side elevational view of one of the drive units shown in FIG.  11 . 
     FIG. 13 is an elevational view of meshing spur gears used to engage the rail set drive. 
     FIG. 14 is a fragmentary elevational view of a portion of a clamping frame with a diagrammatic representation of a servo drive for the adjustment drive. 
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, certain specific terminology will be employed for the sake of clarity and a particular embodiment described in accordance with the requirements of 35 USC 112, but it is to be understood that the same is not intended to be limiting and should not be so construed inasmuch as the invention is capable of taking many forms and variations within the scope of the appended claims. 
     Referring to FIG. 1, a rotary transfer machine  10  includes a rotary transfer carrier wheel  12  rotatably driven on a machine frame  14 , adapted to carry each of four clamping frames  16  successively through a load/unload station  18 , a heating station  20 , a forming station  22 , and a cooling station  24 . 
     Since such machines are well known in the art, details thereof will not be set forth herein. 
     This type of machine forms molded parts from thin sheets of plastic by heating the same in the heating station  20  prior to being formed in the forming station  22 . The formed part is cooled in the cooling station  24  and then unloaded in the load/unload station  18 . 
     The clamping frames  16  are mounted on seats  26  carried by carrier wheel  12  so as successively position each clamped sheet in each station. 
     Since thin sheets of plastic oriented in a horizontal position are used, it is necessary to support each sheet about its periphery as it is advanced through the stations by rotation of the carrier wheel  12 . This done by a series of clamps arranged around the rectangular space defined within each of the clamping frames  16 . 
     As shown in FIG. 2, the clamping frames  16  each include an outer rectangular fixed frame  28  constructed of rectangular tubing sections  30  welded together and mounted to frame members  32  of the carrier wheel  12  (some of which are shown in phantom lines). 
     Movably supported within the outer fixed frame  28  are two sets of parallel movable rails, i.e., a pair of spaced apart parallel “X” rails  34 , and a pair of movable “Y” rails  36 . The movable rails  34 ,  36  are disposed within the space within the fixed frame tubing members  30 , and supported therein by respective pairs of screw shafts  38 ,  40  rotatably supported on the outer fixed frame  28 . 
     Each of the pairs of screw shafts  38 ,  40  comprise oppositely threaded segments  38 A,  38 B;  38 C,  38 D;  40 A,  40 B; and  40 C,  40 D, which are each threadably received through a respective internally threaded carrier nut  46 ,  48 , each of which in turn is attached to a respective end of each of the movable rails  34 ,  36 . 
     As seen in FIG. 2A, screw shaft  38 A is driven by a spur gear  50  located outside the fixed frame  28  by an extension shaft  52  fixed to a bevel gear  54  and also to one end of the screw shaft  38 A. A support bearing block  56  fixed to fixed frame  28  rotatably supports the shaft  52 . 
     A pair of extension shafts  58 A, B and  58 C, D coupled together with universal joints  50 A,  60 B, interconnect screw shaft segments  38 A,  38 C with screw shaft segments  38 B,  38 D to cause them to rotate together. Support brackets  62  are also attached to fixed frame  28 . 
     Bevel gear  54  mates with a second bevel gear  64  fixed to a cross shaft  66  which extends across frame  28 , support  68  at the center, and supports  68  at each end cross shaft  66  has a bevel gear  70  attached to its opposite end meshing with a bevel gear attached to one end to the screw shaft  38 D. Thus, drive spur gear  50  drives all of the screw shaft segments  38 A- 38 D, in synchronism with each other, to move rails  36  together or apart while maintaining parallelism. 
     FIG. 2B shown that a second drive spur gear  72  and shaft  74  projects from the opposite end of the fixed frame  28 , supported on a bearing block  76  attached to a frame member  30 . Shaft  74  has a bevel gear  78  attached thereto mating with another bevel gear  80  which in turn is fixed to one end of screw shaft segment  40 C to drive the same. 
     Shaft  74  is also attached to a two piece cross shaft  82  (best seen in FIGS. 7 and 9) supported on brackets  84 . A bevel gear  86  is attached to the opposite end of cross shaft  82  meshing with a mating bevel gear  88  attached to screw shaft segment  40 A. 
     Screw shaft segments  40 A,  40 B are connected together with U-joints  90  and screw shaft segments  40 C and  40 D are connected together with U-joints  92 . 
     The drive spur gear  72  rotates all of the screw shaft segments  40 A-D in synchronism to cause movement of movable rails  34  together or apart while maintaining parallelism. 
     Rails  36  are located above the rails  34  to allow the change in spacing of both set of rails  34 ,  36 . 
     Rails  36  have a series of pneumatically operated conventional clamping mechanisms  94  mounted thereto, by a corresponding series of hanger brackets  96  attached to the rails  36  which locate clamping pins  98  and pin rails  100  in the same plane as clamping pins  102  and pin rails  104  of clamping mechanisms  106  mounted to movable rails  34 . 
     The pin rails  100  and  104  lie in the same plane, as the bottom sides thereof define the surface against which the sheet material is clamped. Thus, the pin rails  100 ,  104  cannot move into each others space in the same fashion as can be done by the stacked sets of movable rails  34 ,  36 . Thus, the “short” pin rails  104  may be cut to the shortest width to which an adjustment is contemplated. For this reason, the movable rails  36  have a series of holes  108  to allow easy removal and/or changes in spacing of the clamping mechanisms  94  for different widths of sheet. 
     The full array of clamping mechanisms  106  on rails  34  are usually operated no matter the length of a particular sheet size. 
     FIGS. 4,  11  and  12  show the respective disengageable drive units  110 ,  112  for powering the adjustment of the movable rail sets  34 ,  36 . 
     The drive units  110 ,  112  are shown located at the forming station  22  to allow each separate clamping frame  16  to be adjusted successively by the same common drive units  110 ,  112 , but could also be located elsewhere in the machine. 
     Drive unit  110  is movable vertically on a guide structure  114  supported by a square tube post  116  held on a member  118  of the machine frame  119 . 
     A power cylinder  120 , also mounted to post  116  has an operating rod  122  connected to a slide bed  124  holding the drive unit  110 , allows powered movement up and down of the drive unit  110  to engage or disengage an output gear  126  with gear  50  on each clamping frame  16 . 
     Drive unit  112  similarly is movable vertically on a guide structure  128  mounted to a post  130  attached to a frame member  132 . 
     A power cylinder  134  has an operating rod  136  coupled to a slide bed  138  on which is mounted the drive unit  112  so as to power movement up and down to disengage or engage an output spur gear  140  with gear  72  on the clamping frame  16 . The spur gear sets  126 ,  50  and  140 ,  72  are offset as shown in FIG. 13 to insure that meshing engagement of the gears is achieved as the respective drive units  110 ,  112  are driven down. 
     Preferably, detectors  140 ,  142  are used to provide a signal to the operator that the gears are engaged, and/or to provide a safety interlock preventing attempted rotation of the carrier wheel  12  when the drive units  110  or  112  are engaged. 
     The drive units  110 ,  112  are preferably combinations of an electric motor and a gearbox  162 . 
     FIG. 8 shows respective scales  146 ,  148  connected to the fixed frame  28 , with suitable pointers  150 ,  152  provided on the carrier nuts  46 ,  48 , allowing the operator to determine when a desired champing frame size adjustment has been reached. 
     FIG. 14 shows an alternative arrangement in which a transducer  154  provides a signal to a controller  156  controlling the drive motor  160  to automatically drive the rail sets  34 ,  36  to a desired adjustment.