Abstract:
The feeding of plastic sheet material to a trim press is carried out utilizing an endless belt conveyor which supports and drives the plastic sheet in a manner which is coordinated with the cycle of drawing of the sheet material into the trim press dies. The surface of the conveyor belt supports the plastic sheet for upward movement with little or no dragging of the sheet material, and the position of the plastic sheet being engaged with the conveyor can be set by an operator utilizing guide plates and guide wheels located at a position near the intake end of the conveyor. The conveyor belt may be driven continuously at a rate corresponding to the rate at which plastic sheet is drawn into the trim press, or in intermittent motion by a motor in a manner that is coordinated with the intermittent feeding of the sheet material into the trim press.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention pertains generally to the field of plastic thermoforming equipment and to feeding of thermoformed plastic sheet material.  
         BACKGROUND OF THE INVENTION  
         [0002]    In the thermoforming or vacuum forming process for producing plastic articles, a continuous sheet or web of thermoplastic is advanced in a step-wise fashion through a thermoforming machine wherein a section of the web is heated to soften it and then drawn into a mold. The plastic sheet assumes the form of the mold, cools and hardens. Generally, the multiple individual plastic parts formed in this manner, such as the common “clamshell” plastic containers, must be cut from the surrounding plastic web material. The formed plastic parts are typically cut from the surrounding sheet in a separate trim press in which the plastic sheet is advanced, section by section, to be engaged by a cutting die which cuts the formed parts out of the surrounding sheet. The trim press typically has an advancement mechanism which engages the plastic sheet to pull each formed section in a step-by-step fashion to the position of the cutting dies.  
           [0003]    In one common arrangement for feeding the formed plastic sheet into the trim press, the continuous plastic sheet is drawn upwardly onto a curved canopy formed of guide rods and then vertically downwardly into the trim press. The typical stationary canopy is formed of guide rods which laterally orient the position of the plastic sheet so that it is in proper position to be engaged by the driving mechanism within the trim press. The plastic sheet may be driven up the stationary guide rods by rollers driven by a motor controlled by a limit switch. The limit switch is tripped to turn off the motor driven rollers when a section of sheet is discharged from the canopy that corresponds to the length of sheet that will be drawn into the trim press.  
           [0004]    Because the width of the formed plastic sheet and the position of the formed parts in the sheet may vary from one production run to another, the position of the guide rods must be manually adjusted for each production run. The manual adjustment of the positions of the guide rods is relatively time consuming, commonly requiring 45 minutes to an hour and a half depending on whether guide rods need to be added or removed. The adjustment of the guide rods also requires the operator to climb to the top of the trim press to reach all of the guide rods, a physical requirement that although necessary with conventional equipment would preferably be avoided. Other functional disadvantages of conventional stationary guide rods have been observed, including the formation of scratches on the plastic sheet as it is dragged along the stationary guide rods, the presence of plastic dust generated from the sliding plastic, and the potential buckling of thin gauge plastic sheet as it is pulled and then released by the driving mechanism within the trim press. Various designs have been proposed for assisting the feeding of the sheet into the trim press using an oscillating or reciprocating type canopy, for example, as shown in U.S. Pat. Nos. 4,306,474, 4,360,139, and 4,380,183. However, canopy arrangements with stationary guide rods continue to be utilized with standard commercial trim presses.  
         SUMMARY OF THE INVENTION  
         [0005]    In accordance with the invention, feeding of plastic sheet material to a trim press is carried out utilizing an endless belt conveyor which supports and drives the plastic sheet material being fed to the trim press in a manner which is coordinated with the cycle of drawing of the sheet material into the trim press dies. The surface of the conveyor belt supports the plastic sheet material for upward movement with little or no dragging of the sheet material across the conveyor surface, thereby minimizing scratching of the plastic material and the generation of plastic dust. The conveyor also serves to drive the plastic sheet material up to a discharge position above the trim press rather than requiring that the plastic sheet be pulled by the force of the trim press drive mechanism, reducing stretching of the plastic sheet as compared with conventional stationary canopy guides, and reducing the load imposed on the drive mechanism within the trim press. Adjustment of the position of the plastic sheet being engaged with the conveyor can be easily set by an operator at a position near the bottom or intake end in a quick and convenient manner, minimizing the labor involved in setup and reducing setup time to a few minutes. The apparatus of the invention may be constructed to be set up by an operator without requiring any tools.  
           [0006]    A canopy feed apparatus in accordance with the invention includes frame members forming a frame, an endless belt conveyor mounted to the frame having a conveyor belt with a top facing side extending from an intake end to a discharge end, and a motor connected to the belt to drive the belt. When the apparatus is mounted to feed a trim press, the conveyor extends upwardly from its intake end to its discharge end with a plastic sheet exiting from the discharge end guided by guide rods downwardly into the trim press. The conveyor belt may be driven continuously to discharge plastic sheet continuously at a rate corresponding to the average rate at which the plastic sheet is drawn into the trim press. The conveyor belt may also be driven in intermittent motion by the motor in a manner that is coordinated with the intermittent feeding of the sheet material into the trim press. The coordination of the conveyor belt motion with the trim press feeding may be carried out utilizing means for detecting a plastic sheet extending outwardly from the discharge end of the conveyor belt a selected distance and for controlling the motor of the conveyor to shut off power to the motor when a section of plastic sheet exiting from the conveyor extends more than the selected distance from the discharge end. The means for detecting can include a limit switch with a trip rod extending therefrom that is mounted such that the trip rod is positioned to be contacted by a section of plastic sheet discharged from the conveyor. The excess plastic sheet exiting from the discharge end of the conveyor bulges out until it reaches the selected distance from the discharge end, at which time the power to the motor for the conveyor is cut off, stopping the conveyor. When the trim press then operates to draw a section of plastic sheet downwardly into the trim press, the excess plastic sheet material is drawn away from the trip rod, resulting in the conveyor motor being turned on and the conveyor belt being driven to feed additional plastic sheet material until the excess material again reaches the trip rod to turn off the conveyor. A blower may be mounted under the conveyor at the discharge end to blow air outwardly to drive the excess plastic sheet outwardly into contact with the trip rod of the limit switch. The feeding of the plastic sheet from the conveyor in this manner is fully coordinated with the drawing of the plastic sheet into the trim press, so that substantially no strain is imposed on the plastic sheet being fed into the trim press, while at the same time avoiding over-feed of plastic sheet from the conveyor which might interfere with the sheet feeding process.  
           [0007]    Setup of the feed apparatus may be carried out quickly and conveniently utilizing a pair of guide plates and guide wheels mounted for lateral adjustment over the top surface of the conveyor belt at a position near the intake end of the conveyor. Preferably, a pair of mounting bars extend laterally between frame members above the top facing side of the conveyor belt, and the guide plates and guide wheels are mounted for sliding movement on the mounting bars while restraining the guide plates and guide wheels from movement in other directions. A hand operated clamp and a locking mechanism for each guide plate and guide wheel may be utilized by the operator to lock the guide plates and guide wheels at selected lateral positions at which the guide plates are spaced apart a distance equal to the width of the sheet being fed, and such that the sheet being fed will reach the trim press at the proper lateral position. The guide wheels may be mounted for movement toward and away from the top surface of the conveyor, with an air cylinder at each guide wheel being utilized to selectively press the guide wheel into engagement with the plastic sheet supported on the surface of the conveyor.  
           [0008]    Curved guide rods are preferably mounted at the discharge end of the conveyor and extend above and below the position of plastic sheet exiting from the discharge end of the conveyor to guide the plastic sheet downwardly to a proper position for feeding into the trim press.  
           [0009]    Further objects, features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    In the drawings:  
         [0011]    [0011]FIG. 1 is a partially cut away perspective view of a canopy feed apparatus in accordance with the invention mounted in a position to feed plastic sheet material to a trim press.  
         [0012]    [0012]FIG. 2 is a side view of the canopy feed apparatus of the invention.  
         [0013]    [0013]FIG. 3 is a partial view of the intake end of the canopy feed apparatus of the invention.  
         [0014]    [0014]FIG. 4 is a partial detailed view of the intake end of the feed apparatus showing the mounting of guide plates and guide wheels above the top surface of the conveyor.  
         [0015]    [0015]FIG. 5 is a partial perspective view of the discharge end of the feed apparatus of the invention.  
         [0016]    [0016]FIG. 6 is a schematic diagram of the control and drive circuit for the feed apparatus for the invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]    With reference to the drawings, a canopy feed apparatus for a trim press in accordance with the invention is shown generally at  10  in FIG. 1, mounted adjacent to and in position to feed a continuous sheet or web  11  of thermoformed plastic material into a trim press  12 . The plastic sheet  11  typically has a series of parts  14  formed therein which are surrounded by the original sheet material and from which the parts  14  are to be cut in the trim press  12 . The parts  14 , which are formed in a conventional thermoforming apparatus (not shown), extend outwardly from a side of the sheet  11  opposite a flat side  15  as illustrated in FIG. 1. The trim press  12  may be any of the various conventional trim presses that are utilized for trimming formed plastic parts and will not be described further herein.  
         [0018]    The feed apparatus  10  includes a rigid frame  18  formed of frame members (e.g., of conventional structural steel) to which an endless belt conveyor  20  is mounted. The frame  18  serves to provide a structural support for the various parts of the apparatus and may be formed in any desired shape or construction to serve that purpose. For purposes of exemplifying the invention, the frame  18  as shown in the drawings includes two parallel main beams  21 , two main vertical beams  22  which extend downwardly from one end of the main beams  21 , and two lateral descending beams  24  which extend downwardly and outwardly from the other ends of the main beams  21  opposite that to which the vertical beams  22  are joined. A cross beam  25  extends between and is secured to the two main beams  21  and, as best shown in FIG. 2, braces  27  extend downwardly from the main beams  21  to bases  28  which are fixed to the bottoms of the main vertical beams  22 . The beams  21 ,  22 ,  24 ,  25 ,  27  and  28  are rigidly joined together by, for example, welding, to form a rigid structure. The conveyor  20  is mounted to the frame  18  at a lower end  30  of the lateral descending beams  24  and to the braces  27  at an upper position  31  of the conveyor  20 . The conveyor  20  is an endless belt conveyor having rigid stationary side rails  32  which are connected to the frame members at the positions  30  and  31  by, for example, being secured thereto with bolts (not shown).  
         [0019]    The conveyor  20  has an endless conveyor belt  33  that extends from a roller  34  at an intake end  35  of the conveyor to a roller  36  at a discharge end  37 , with the endless belt  33  having a top facing side  39  and a bottom side  40 . The conveyor belt  33  may be formed of a flexible material, e.g., various synthetic plastics, that is strong and durable and has a desired fairly high coefficient of friction with respect to the plastic material of the bottom surface  15  of the plastic sheet  11 . An example of a suitable commercial conveyor is the 3100 Series conveyor from Dorner Manufacturing Co. (Hartland, Wis.), preferably with a high coefficient of friction belt approved by the FDA for use with packaging for foods (e.g., /O3 Soft Top FDA with urethane surface and polyester body). Crossbars  42 , as shown in FIG. 1, may extend between the side rails  32  and be secured thereto to rigidify the conveyor structure. As shown in FIG. 2, an electric motor  44  (preferably including a speed reducing gearbox) is connected by a belt  45  to the upper end roller  36  to drive the belt  33  when the motor  44  is supplied with electrical power. For example, a DC motor may be used with a gear reducer (e.g., Tigear 60 to 1 gear ratio from Dodge Gearbox). The conveyor extends upwardly at an angle to horizontal (e.g., about 30° and preferably 28°) from the intake end to the discharge end.  
         [0020]    As best shown with reference to the views of FIGS. 3 and 4, a pair of mounting bars  47  extend laterally above the top surface  39  of the conveyor belt and are mounted at their ends to brackets  50  which are secured (e.g., by welding) to the lateral descending beams  24 . A ruler  48  is preferably mounted in front of the lower bar  47 . A pair of slide bearings  51  slide on the uppermost one of the mounting bars  47  and are connected to brackets  52  which support one end each of a pair of guide plates  54 . Another pair of slide bearings  51  are also mounted to slide on the second mounting bar  47  and support slide clamps  55  which each have a hand operated locking mechanism  56  by which the operator can lock the slide clamps  55  in place on the lower mounting bar  47 . The slide clamps  55  have brackets  58  connected thereto which are each connected to the forward end of one of the guide plates  54 . A pair of guide wheels  60  are mounted for rotation to brackets  62  which are themselves pivotally connected to the brackets  52 . Air pressure driven air cylinders  64  are connected at one end to the brackets  52  and at the other end to the pivoting brackets  62 . When supplied with air under pressure, the air cylinders  64  extend to drive the guide wheels  60  downwardly into contact with a plastic sheet supported on the top surface  39  of the conveyor. The lateral guide plates  54  serve to properly position the incoming plastic sheet as it reaches the intake end  35  of the conveyor so that when the sheet exits the conveyor it will be properly positioned laterally to be fed appropriately into the trim press. To adjust the lateral position of the guide plates  54 , the operator turns the handles of the locking mechanisms  56  on the clamps  55  to release the engagement of the clamps with the lower mounting bar  47  and then moves the guide plate  54  to a desired lateral position, at which the operator turns the handle on the locking mechanism  56  to clamp the guide plate  54  and the guide wheel  60  carried with it in the proper lateral position. The spacing between the two lateral guide plates  54  is selected to match the width of the plastic sheet being fed. To aid the operator in properly positioning the lateral guide plates, the ruler  48  preferably includes indicia  66  marked on a front face thereof which represent a distance scale (e.g., inches or centimeters, preferably as a half scale for convenience) which can be correlated by the operator with the clamp  55  to determine the lateral position of the clamp from one edge of the conveyor as well as the lateral distance between the two clamps and, therefore, the lateral distance between the two guide plates  54 . To aid in the proper support and positioning of the plastic sheet as it is being fed in, the lateral guide plates  54  preferably have lower inwardly extending sections  67  which can engage and support the outer edges of the incoming sheet, and the guide plates may be formed as full channels, each with upper inwardly extending section  68 . To further help guide the sheet into place between the guide plates  54 , downwardly curved metal tongue extensions  70  may be fixed to the incoming end of the extending section  67  of each guide plate, and extend over the curvature of the conveyor belt at the intake end  35 .  
         [0021]    After the operator has adjusted the lateral positions of the guide plates  54  during setup, a new plastic sheet to be fed is inserted between the guide plates  54  and pushed up under the guide wheels  60 . Air pressure is then supplied to the air cylinders  64  to drive the guide wheels  60  into contact with the plastic sheet. The guide wheels  60  are preferably positioned at the lateral edges of the plastic sheet, approximately at those portions of the plastic sheet that will ride on the inward extensions  67  of the lateral guide plates  54 . The guide wheels  60  press the plastic sheet against the top surface  39  of the conveyor to hold the plastic sheet in position so that it will not tend to wander laterally as it is being fed up the conveyor and to help stabilize the plastic sheet against bunching or wrinkling while it is on the conveyor.  
         [0022]    With reference to FIG. 5, the plastic sheet exiting from the discharge end  37  of the conveyor comes into engagement with and may be supported initially by a set of curved inner guide rods  74  which curve from a horizontal section  75  to a vertical section  76  that extends downwardly toward the trim press. A second, outer set of curved guide rods  78  extend from a generally horizontal section  79  spaced above the position at which the plastic sheet exits the discharge end of the conveyor and curve outwardly and then downwardly to a vertical section  80 , with the vertical sections  80  of the guide rods  78  spaced slightly outwardly of the vertical section  76  of the guide rods  74  to hold the plastic sheet  11  between them as it is fed downwardly into proper position in the trim press. The guide rods  78  are preferably set at lateral positions at which they will ride between the formed parts  14  on the sheet  11  or at the edges of the sheet to thereby provide some lateral guiding of the sheet into the trim press  12 . The guide rods  74  and  78  function similarly to and may be formed similarly to the conventional guide rods used at the top end of conventional canopy feed systems.  
         [0023]    As best shown in FIGS. 2 and 5, a limit switch  84  is mounted to a cross rod  85  which is itself mounted by brackets  86  and  87  to the frame. The limit switch  84  has a downwardly extending trip rod  88  which extends between the outer guide rods  78  at the curved section of the guide rods. The trip rod  88  is outwardly movable to trip the limit switch  84  from a normally closed to an open position. A power line  90  extends from the limit switch  84  to a control box  92  to supply power to and from the limit switch, as explained further below. The trip rod  88  is mounted at a position spaced outwardly a selected distance from the discharge end  37  of the conveyor at a position where it may be contacted by the plastic sheet material  11 , as illustrated in FIG. 2. During feeding operation, the conveyor belt  33  is driven by the motor  44  at a constant speed until the plastic sheet that exits from the discharge end of the conveyor bulges outwardly a sufficient distance to contact the trip rod  88  and displace it outwardly to switch the limit switch  84 , turning off the power to the motor  44  and stopping the conveyor. As the plastic sheet material  11  is then drawn downwardly into the trim press, the bulging section  94  of the plastic is drawn away from the trip rod  88 , allowing the trip rod to return by spring action to its normal position, at which the switch  84  is closed, supplying power to the motor  44  again to drive the conveyor belt  33 . A blower  95  may be mounted to the frame beneath the discharge end  37  of the conveyor and is positioned such that the outlet  96  of the blower is directed outwardly from the discharge end of the conveyor to blow the plastic sheet material exiting from the conveyor toward the outer guide rods  78  and toward the trip rod  88 , helping to ensure that the maximum extent of the bulge  94  caused by the excess of plastic sheet driven off of the conveyor is directed toward the trip rod  88 . It is understood that any other means for detecting that the plastic sheet exiting from the conveyor has reached the selected position may be utilized in place of the trip rod  88  and limit switch  84 . Examples include light beam detectors and sonic and other types of proximity sensors.  
         [0024]    In accordance with the invention, the conveyor belt  33  may also be driven at a constant speed that discharges plastic sheet from the discharge end at a rate that corresponds to the average rate at which plastic sheet is drawn into the trim press. In this mode of operation, utilization of the limit switch  84  is not necessary.  
         [0025]    The positions of the inner guide rods  74  and the outer guide rods  78  are preferably adjustable laterally to suit the size of the plastic sheet being fed and the positions of the formed parts  14  on the plastic sheets. As illustrated in FIG. 5, the inner guide rods  74  may be mounted to manually lockable clamps  97  which are laterally adjustable on a cross rod  98 . The outer guide rods  78  are also preferably mounted for lateral adjustment to manually lockable clamps  99  mounted for sliding movement on the cross rod  85  and at the bottom ends of the guide rods to manually lockable clamps  101  which are mounted for sliding movement on a cross rod  102  that is itself mounted to the frame.  
         [0026]    If desired, a set of support wheels  105  may be mounted to the frame in a position to be rotated downwardly to support the apparatus  10  when it is not in use and to be rotated out of the way (to the position shown in FIG. 1) when the feeding apparatus is set up in position to feed plastic sheet material to the trim press.  
         [0027]    The feeding arrangement of the present invention allows an efficient control system to be used for coordinating the feeding of the plastic sheet by the feeding apparatus  10  with the drawing of a plastic sheet into the trim press  12 . As illustrated in the simplified schematic diagram of FIG. 6, electrical power from power mains  106  is supplied to the control box  92  that encloses a main on/off switch  108  and a variable speed motor controller  109 . The control box  92  is connected by the lines  90  to the limit switch  84  and by power lines  111  to the DC motor  44 . A suitable commercial controller is a Model KBMG-212D variable speed SCR Control from KB Electronics, Inc. The limit switch  84  is connected to a relay coil  115  which when energized closes relay contacts  116  to provide power through the controller  109  to the motor. Several push button switches  118  may be connected in series with the limit switch  84  and are located at various positions to allow an operator to manually stop the conveyor. An adjustable potentiometer  120  connected to the controller  109  allows the output voltage from the controller to be adjusted. A switch  121  may be connected to the controller to allow reversal of the output voltage to reverse the direction of the conveyor. As also shown in FIG. 6, the motor  124  for the blower  96  may be connected to the main switch  108  through an on-off switch  126 . Fuses  128  and  129  are connected in the power lines for overload protection. When sheet feeding is to take place, the operator closes the main switch  108 , which supplies power to the normally closed limit switch  84 . As long as the limit switch  84  remains closed, the variable speed drive  109  is activated. The output power provided from the drive  109  to the motor  44  is adjusted by the operator so that the speed of the conveyor belt  33  is such as to advance an appropriate length of plastic sheet material before the limit switch  84  is tripped as the sheet material engages the trip rod  88 . The appropriate length of plastic sheet material that is to be advanced by the conveyor corresponds to the length of plastic sheet material that is drawn into the trim press during each advancement step of a section of plastic sheet material into the trim press cutting dies. The operator can simply adjust the speed of the drive  109  during operation to advance or retard the speed of the conveyor until the right amount of plastic sheet is advanced during each cycle of the trim press.  
         [0028]    It is understood that the invention is not confined to the particular embodiments set forth herein as illustrative, but embraces all such forms thereof as come within the scope of the following claims.