Abstract:
A clamping frame for a plastic sheet thermoforming apparatus and which is designed for gripping and retaining the peripheral edge of the plastic sheet. The frame includes a pair of pivotally interconnected jaws which are pivoted between open and closed positions by an air cylinder actuator. The actuator is mounted to one of the jaws, and the operative pressurized air is fed to and removed from the actuator via fluid delivery lines which are located within the interior of the jaw to which the actuator is mounted. External air hoses are thereby avoided, and the air streams which flow through the jaw have a cooling effect.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims the benefit of U.S. Provisional Application Serial No. 60/261,663 filed Jan. 16, 2001. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates to an improved clamping frame for supporting the peripheral edges of a sheet of thermoplastic material in a thermoforming apparatus.  
           [0003]    Thermoforming apparatus for forming plastic sheets typically comprise a heating station and a molding station, and several carrier clamping frames are provided for gripping the edges of the plastic sheets so as to support the sheets at the heating station and moving them to the molding station. The clamping frames presently comprise a pair of pivotally connected gripping jaws and a pneumatic cylinder for opening and closing the jaws to grip the sheet. External hoses are provided for actuating each of the cylinders.  
           [0004]    Thermoforming apparatus of the described type usually include a large number of such clamping frames, and the presence of the associated large number of hoses can interfere with the operation and movement of the clamping frames, and they are subject to leakage.  
           [0005]    It is an object of the present invention to provide a clamping frame of the described type which has a reduced potential for air leaks, and thereby reduces maintenance. It is also an object to provide means for efficiently cooling the frame. Other objects include increasing the capacity and reliability of thermoforming machines of the described type.  
         SUMMARY OF THE INVENTION  
         [0006]    The above and other objects and advantages of the invention are achieved by the provision of a clamping frame which comprises a pair of pivotally interconnected gripping jaws which are pivoted between open and closed positions by at least one actuator. The actuator comprises a fluid operated cylinder, and a fluid delivery system is provided for operating the actuator, which includes first and second fluid passages located within the jaw to which the actuator is attached.  
           [0007]    In one preferred embodiment the actuator takes the form of an air cylinder which is mounted to one of the jaws and which includes a slideable piston. Fluid pressure ports are located at the opposite ends of the cylinder so that the piston can be biased and moved in either direction. The jaw to which the cylinder is mounted includes a mounting surface which includes outlets which communicate with respective ones of the fluid passages, and the cylinder is fixedly mounted to the jaw so as to overlie the mounting surface and so that the pressure ports communicate directly with respective ones of the outlets.  
           [0008]    Thus with the present invention, leakage prone couplings between air hoses and the air cylinders are eliminated, and the problems of interference caused by the external hoses of the prior art are significantly alleviated. Also, the flow of the fluid (e.g. air) through the internal passages in the jaw tends to cool the jaws.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    Some of the objects and advantages of the present invention having been stated, others will appear as the description proceeds, when considered in association with the accompanying drawings, in which:  
         [0010]    [0010]FIG. 1 is a fragmentary perspective view of a clamping frame of the prior art;  
         [0011]    [0011]FIG. 2 is a sectional view of the clamping frame shown in FIG. 1;  
         [0012]    [0012]FIG. 3 is a fragmentary perspective view of one embodiment of the clamping frame of the present invention;  
         [0013]    [0013]FIG. 4 is a sectional view of the clamping frame shown in FIG. 3;  
         [0014]    [0014]FIGS. 5 and 6 are views corresponding to FIGS. 3 and 4, and showing a further embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]    Referring more particularly to the drawings, FIGS. 1 and 2 show a prior art clamping frame  10  of the described type, and which includes a pair of clamping jaws  12 ,  14  which are mounted for pivotal movement about the axis of a longitudinal pin  15 . Depending upon the length of the clamping frame  10  there may be provided a plurality of air cylinders  16 . An air cylinder  16  is pivotally mounted to a bracket  18  which is joined to the lower jaw  12 , and the air cylinder has an internal piston  19  which is connected to an output shaft  20 . The output shaft  20  is pivotally joined to the upper jaw  14 . A pair of flexible hoses  22 ,  23  are connected via a coupling to one opposite end of the cylinder  16 , and a suitable air valve (not shown) is connected to the hoses  22 ,  23  and leads to a source of pressurized air or to an adjacent air cylinder. A second pair of flexible hoses  24 ,  25  are connected via a coupling to the other end of the cylinder  16  and serve to function in combination with the first pair of hoses. In operation, the pressurized air enters through one of the hoses into one end of the cylinder and the other hose is vented. Thus the jaws may be pivoted between the open and closed positions as seen in FIG. 2. Also, the cylinder  16  pivots about its mounting axis on the bracket  18  between the solid line and dashed line positions, and the hoses  22 ,  23  necessarily flex.  
         [0016]    [0016]FIGS. 3 and 4 show one embodiment of the novel clamping frame  30  of the present invention. As illustrated, the clamping frame  30  comprises upper and lower gripping jaws  31 ,  32  which extend in a longitudinal direction, i.e. perpendicular to the plane of FIG. 4. The jaws  31 ,  32  are pivotally interconnected by means of a longitudinally extending pivot pin  34  which is secured to a mounting bracket  35  which is in turn bolted to the lower jaw  32 . The jaws  31 ,  32  have opposing clamping faces, and they may be pivoted between a closed position as seen in solid lines in FIG. 4 and wherein the clamping faces directly overlie each other to grip and retain the peripheral edge of the plastic sheet (not shown) therebetween, and an open position as seen in dashed lines in FIG. 4.  
         [0017]    At least one actuator  36  is provided for pivoting the jaws between the open and closed positions, it being understood that in the case of clamping frames which have a relatively long longitudinal length, several actuators  36  may be provided which are longitudinally spaced apart. The actuator  36  comprises an air cylinder  38  having a piston  39  slideably mounted therein, and the piston  39  is connected to an output shaft  40 . The output shaft  40  is connected via a linkage  42  to the upper jaw  31 , and the linkage  42  is pivotally connected to both the output shaft  40  and the upper jaw  31 . Thus when the piston  39  is in its lower position, the jaws are closed, and when the piston is raised the jaws are opened.  
         [0018]    The air cylinder  38  includes air pressure ports  44 ,  45  in the respective opposite ends of the cylinder, so that when pressurized air enters the upper port  44  the piston  39  is lowered and when the air enters the lower port  45  the piston  39  is raised.  
         [0019]    In the embodiment of FIGS. 3 and 4, the lower jaw  32  has a generally T-shaped cross section and it is composed of a generally horizontal upper leg  46  and a depending leg  48 . The upper jaw  31  is generally flat, and the upper jaw and the pivot pin  34  are positioned on the side of the upper leg opposite the depending leg  48 . The depending leg  48  includes a mounting surface  50  on the right side thereof as seen in FIG. 4, and the cylinder  38  of the actuator is mounted to the depending leg  48  so as to overlie the mounting surface  50  in a contiguous relationship. Also, the cylinder  38  is oriented such that the output shaft  40  is disposed in a generally vertical orientation.  
         [0020]    An air delivery system is provided for selectively delivering pressurized air to the fluid pressure ports  44 ,  45  to cause the piston  39  to move in either direction within the cylinder  38  and thereby cause the jaws  31 ,  32  to open and close. The air delivery system includes first and second air delivery lines  51 ,  52  which extend longitudinally within the depending leg  48  of the lower jaw  32 . Also, the mounting surface  50  includes outlets  51   a,    52   a  which communicate with respective ones of the air delivery lines  51 ,  52 . The outlets  51   a,    52   a  are positioned so that when the cylinder  38  is assembled to the depending leg as seen in FIG. 4, the pressure ports  44 ,  45  communicate directly with respective ones of the outlets  51   a,    52   a,  thereby establishing communication between the ports and air delivery lines. A suitable O-ring seal or the like may be positioned at the interface between the ports and outlets to assure an air tight interconnection.  
         [0021]    The air delivery lines  51   a,    52   a  are connected via conventional valves, to a source of pressurized air (not shown) so as to permit air to flow in either direction through the lines and thereby permit control of the movement of the piston  39  and thus the jaws  31 ,  32 .  
         [0022]    As illustrated, the upper jaw  31  includes an internal, longitudinally extending air line  54  which permits a cooling air stream to be passed through the upper jaw.  
         [0023]    [0023]FIGS. 5 and 6 illustrate a second embodiment of a clamping frame  60  which embodies the invention, wherein the actuator  62  is mounted to the upper jaw  64 . More particularly, the upper jaw  64  has a mounting surface  65  which is located on the side of the upper jaw opposite the lower jaw  66 . The upper jaw  64  includes two air delivery lines  68 ,  69 , which communicate with outlets on the mounting surface  65  and which in turn communicate with the air delivery lines  68 ,  69 .  
         [0024]    The actuator  62  is mounted to the mounting surface  65  so as to be oriented so that the piston  70  and output shaft  71  move in a generally horizontal direction, and the output shaft  71  is connected to a mounting bracket  72  via a pivotable linkage  74 . The mounting bracket  72  is in turn connected to the lower jaw  66  by bolts.  
         [0025]    The air delivery lines  68 ,  69  are connected to a suitable pressurized air source as described above, so that the movement of the piston causes the upper arm  64  to move between the closed position as seen in solid lines and the open position as seen in dashed lines in FIG. 6.  
         [0026]    The upper jaw  64  also includes an internal air line  76  which permits a cooling air flow as described above.  
         [0027]    Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.