Abstract:
A method and apparatus is disclosed for inspection of molded closures that would measure specific parameters of the closure on an on-line basis as they are ejected from an associated compression molding apparatus. Measuring specific parameters of the closure on an on-line basis identifies problems with specific tool sets, sub-systems, and process settings of the molding apparatus, thus substantially reducing the amount of scrap that is produced.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention generally relates to process monitoring of molded closures. In particular, the invention relates to an apparatus and method for monitoring molded closures after manufacture of the closures.  
       BACKGROUND OF THE INVENTION  
       [0002]     A rotary compression molding apparatus is typically employed for the manufacture of molded plastic closures. A rotary turret carries multiple, vertically oriented tool assemblies which are rotated by the turret relative to upper and lower fixed cams. Rotary motion of the tooling relatively moves respective sets of upper and lower or, male and female, mold assemblies. As the turret rotates, a metered charge of molten plastic is placed into each open female mold, and the male and female molds relatively move to compress the molten plastic therebetween to form the closure. Liquid cooling within the tooling promotes rapid plastic solidification. The molding cycle is completed by relative movement of the tooling to open the mold cavity, and eject the molded closure.  
         [0003]     Quality monitoring or inspection techniques employed after compression molding have necessarily resulted in a lag time between identification of molding problems and their correction. By one inspection technique, molded closures are sampled, and carefully measured. As a result of the time lag between identification of a problem and its correction, many unacceptable closures may be produced. It is also possible that poor quality closures can be manufactured between the times at which samples are taken. Additionally, the detection of a poor quality closure does not necessarily identify the specific problem that resulted in its formation, thus requiring secondary measurements and process experiments to determine the cause of the faults. Examples of secondary measurements and process experiments would be dimensional measurements obtained from a coordinate measuring machine or a caliper.  
         [0004]     Another technique for inspecting molded closure parts employs a vision-based inspection system, which visually inspect either periodic closure samples, or 100% of the closures being molded. However, these systems have proven to be expensive to implement in connection with high speed production, which may entail hundreds of closures per minute. Such vision-based systems are sensitive to the background lighting of the room that the apparatus is in and process lighting angles. While the time lag between manufacturing and inspection is minimal, detection of poor quality closures does not give specific information regarding the cause of the problem.  
         [0005]     An inspection or monitoring system is needed wherein measurement of molded closures can be effected on an on-line basis as they are ejected from an associated compression molding apparatus. The testing would be conducted in a fashion such that each individual closure can be associated with a particular one of the mold tooling sets of the molding apparatus. Problems associated with the specific tool set can thus be readily identified. Furthermore, by monitoring specific parameters, specific sub-systems and process settings of the molding apparatus could be modified. For example, temperature measurement of each closure correlates to dimensional shifts, quality shifts, and cooling system performance. Measurement of top panel thickness correlates directly to closure weight and final dimensions. Warpage indicators or the concavity of the closure top surface, correlate directly to cooling flow and plastic melt temperature.  
         [0006]     Combinations of measurements&#39; behavior would allow technicians to quickly diagnose a problem and point to a sub-system of the molder, or individual tool that would require maintenance or adjustment. Because the measurements would be variables, rather than attributes, they would lend themselves to control charting, and would indicate processes that were changing, thus giving early warning of changing processes and allowing maintenance and adjustment to be performed before scrap is produced. This would be in direct distinction from the previous methods, which are only triggered when scrap is produced.  
         [0007]     The primary object of the present invention is to provide a method and apparatus for monitoring molded closures that would measure specific parameters of the closure so that problems with specific tool sets, sub-systems, and process settings of the molding apparatus could be identified, thus substantially reducing the amount of scrap that is produced.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention is directed to an apparatus and method for monitoring molded plastic closures after manufacture of the closures. The method comprises passing the closures above an infrared sensor and measuring the temperature of the top panel of the closures, passing the closure above a first laser and measuring the concavity of the top panel, passing the closure under a second laser and measuring the location of the inside surface of the top panel, obtaining the thickness of the top panel by subtracting the concavity of the top panel from the location of the inside surface of the top panel, and approving or rejecting the closure. The infrared sensor measures the temperature of the top panel by emitting an infrared beam, preferably having a wavelength between about 8 to about 14 microns, onto the top panel surface and collecting the intensity of the beam reflectance from it. The first and second lasers measure the concavity and the location of the inside surface of the top panel by emitting a laser beam, preferably having a wavelength that is about 670 nanometers, onto the outside and inside surface of the top panel and collecting the distance between these surfaces and the laser face. The closures are approved or rejected by analyzing the measurements of the infrared sensor and the first and second lasers with a data acquisition control system that is connected to the infrared sensor and the first and second lasers. The measurements are then presented on a graphical user interface.  
         [0009]     The apparatus comprises an aluminum coated platform having an aluminum-coated supporting structure and a pocketwheel having pockets, a closure feeding means for feeding the closure to the pocketwheel, and a closure receiving means for receiving the closure after the closure is discharged from the pocketwheel. The closure feeding means and closure receiving means are preferably also pocketwheels having pockets for holding the closures. The pockets for the closure feeding pocketwheel, pocketwheel, and closure receiving pocketwheel are preferably 30 mm in diameter. The pocketwheel is radially oriented from the closure feeding pocketwheel and the closure receiving pocketwheel is radially oriented from the pocketwheel and across from the closure feeding pocketwheel. The pocketwheel, closure feeding pocketwheel, and closure receiving pocketwheel are connected to the platform via coupling means, preferably gears that have a motor coupled to them and allow the gears to transfer motion to the pocketwheels. The closure feeding pocketwheel and the closure receiving pocketwheel move in a direction opposite the pocketwheel. In addition, the infrared sensor is coupled to the platform and the first and second lasers, respectively positioned below and above the platform, are coupled to the supporting structure.  
         [0010]     In operation, the closure feeding pocketwheel accepts the closure from a molding apparatus and passes the closure to the pocketwheel. The pocketwheel passes the closure above the infrared sensor and the first laser and below the second laser, with the sensors and the lasers each measuring a parameter of the closure for approval or rejection. The pocketwheel passes the approved closures to the closure receiving pocketwheel, which clears these closures from the platform. The rejected closures are cleared from the platform by an airway situated on the side of the platform. The platform includes an aperture to receive the infrared beam from the infrared sensor and a slot to receive the laser beam from the first laser. The aperture is about a quarter inch in diameter and the slot is about an eighth inch in width and one inch in length. The closure feeding pocketwheel, preferably made of high density polyethylene, and the closure receiving pocketwheel, preferably made of coated aluminum, are about four and one-half inches in diameter. The pocketwheel, preferably made of coated aluminum, is about seven inches in diameter. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a perspective view of the closure monitor apparatus.  
         [0012]      FIG. 2  is a top view of the closure monitor apparatus.  
         [0013]      FIG. 3  is a bottom view of the closure monitor apparatus.  
         [0014]      FIG. 4  is a back view of the closure monitor apparatus. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0015]      FIG. 1  shows a perspective view of the closure monitor apparatus  10  of the invention. The apparatus  10  comprises a platform  11  having a supporting structure  12  and a pocketwheel  14 , a closure feeding means  13  for feeding the closure to the pocketwheel  14 , and a closure receiving means  15  for receiving the closure after the closure is discharged from the pocketwheel  14 , each of which are coupled to the platform  11 . For the purposes of this preferred embodiment, the closure feeding means  13  and closure receiving means  15  each comprise a pocketwheel. However, other means that would properly feed and receive the closures to and from the pocketwheel  14 , such as conveyor belts, could be used. The platform  11  and the supporting structure  12  are both made from metal, preferably coated aluminum. Together, the platform and supporting structure are about fifteen inches wide and ten inches high. The pocketwheels  13 ,  14 ,  15  each have pockets  23  for housing a closure during the monitoring process and are situated so that the pocketwheel  14  is radially oriented from the closure feeding pocketwheel  13  and the closure receiving pocketwheel  15  is radially oriented from the pocketwheel  14  and across from the closure feeding pocketwheel  13 . The closure feeding pocketwheel and closure receiving pocketwheel  13 , 15  are about four and a half inches in diameter and the pocketwheel  14  is about seven inches in diameter. The pockets  23  for the pocketwheels  13 ,  14 ,  15  are about thirty millimeters in diameter. In addition, the closure feeding pocketwheel  13  comprises plastic, preferably high definition polyethylene, and the pocketwheel and closure receiving pocketwheel  14 , 15  comprise metal, preferably coated aluminum. Pocketwheels comprised of aluminum leave marks on the closure and therefore contaminate the closure. Therefore, the pocketwheel and closure receiving pocketwheel  14 ,  15  are comprised of coated aluminum to substantially reduce the number of marks left on the closure. As will be described below, during the monitoring process, the closure feeding pocketwheel  13  accepts a closure from a molding apparatus. During this time, the possibility exists for the closure feeding pocketwheel  13  and the molding apparatus to collide and cause damage to the tooling for the molding apparatus. If the closure feeding pocketwheel  13  is comprised of plastic, which is softer than other materials such as coated aluminum, then damage to the tooling will be substantially reduced.  
         [0016]     The apparatus  10  also comprises an infrared sensor ( FIG. 3, 16 ) that is coupled to the platform  11 , a first laser ( FIG. 3, 18 ) that is coupled to the supporting structure  12  and situated below the platform  11  and under the pocketwheel  14 , and a second laser  17  that is also coupled to the supporting structure  12  and situated above the pocketwheel  14 . For the purposes of this invention, the infrared sensor ( FIG. 3, 16 ) is preferably a high speed infrared sensor and the lasers ( FIG. 3, 18 ),  17  are preferably visible red semiconductor lasers. The infrared sensor used in this invention was manufactured by Everest Interscience Incorporated and the lasers, each being Part No. LK031, were manufactured by Keyence Inc. The infrared sensor ( FIG. 3, 16 ) and the lasers ( FIG. 3, 18 ),  17  are coupled to the platform  11  and the supporting structure  12  via a coupling means  24  such as clamps, screws, fasteners, or a nut and bolt combination. The coupling means  24  preferably are constructed from aluminum or steel material, however the coupling means  24  may be constructed from any metal, metal alloy, or nonmetal that would provide rigid structural support . The closure feeding pocketwheel, pocketwheel, and closure receiving pocketwheel  13 , 14 , 15  are coupled to the platform  11  via coupling means, preferably gears ( FIGS. 3 and 4 ,  26 ), that are mounted on the closure feeding pocketwheel, pocketwheel, and closure receiving pocketwheel  13 , 14 , 15  and are housed below the platform  11 . The gears ( FIGS. 3 and 4 ,  26 ) transfer motion to the pocketwheels  13 , 14 , 15  from a motor  19  that is coupled to the gears ( FIGS. 3 and 4 ,  26 ) and the supporting structure  12 . The motor ( FIG. 4, 19 ) is coupled to the gears ( FIGS. 3 and 4 ,  26 ) and the supporting structure  12  via a coupling means  24  such as clamps, screws, fasteners, or a nut and bolt combination. The coupling means  24  preferably are constructed from aluminum or steel material, however the coupling means  24  may be constructed from any metal, metal alloy, or nonmetal that would provide rigid structural support. For the purposes of this invention, common spur gears were used and the motor  19  is a servomotor. The closure feeding pocketwheel and closure receiving pocketwheel  13 , 15  move in a direction opposite to the direction the pocketwheel  14  moves. Specifically, the closure feeding pocketwheel and closure receiving pocketwheel  13 , 15  move in a clockwise direction and the pocketwheel  14  moves in a counterclockwise direction.  
         [0017]     During the monitoring process, the closure feeding pocketwheel  13  accepts a plastic closure, with the plastic closure being upside down, from a molding apparatus that is situated above the monitoring apparatus  10  and beside the closure feeding pocketwheel  13 . The closure is then passed from the closure feeding pocketwhel  13  to the pocketwheel  14 . The pocketwheel  14  passes the closure above the infrared sensor ( FIG. 3, 16 ) and the first laser ( FIG. 3, 18 ) and below the second laser  17 . The infrared sensor ( FIG. 3, 16 ) measures the temperature of the top panel of the closure by emitting an infrared beam onto the top panel and collecting the intensity of the beam reflectance from it. The infrared beam is emitted through an aperture ( FIG. 2, 20 ) on the platform  11  and has a wavelength that is between about  8  to about  14  microns. The aperture ( FIG. 2, 20 ) is about a quarter inch in diameter. The first and second lasers ( FIG. 3 ,  18 ,),  17  measure the concavity and the location of the inside surface of the top panel respectively by emitting a laser beam onto the outside and inside surfaces of the top panel and collecting the distance from these surfaces to the laser face. For the purposes of this invention, concavity means the maximum depth of the top panel curvature that is observed in the center of the closure top panel. The distance from the outside and inside surfaces of the top panel is measured using the triangulation measurement system. The lasers use a Charged Coupled Device (CCD) array as a light receiving element. The light reflected by the outside and inside surfaces passes through a receiver lens that focuses the light on the CCD. The CCD detects the peak value, or the brightest point, of the light quantity distribution of the laser beam spot and identifies this as the target position on the inside and outside surfaces of the top panel. The thickness of the top panel is then obtained by subtracting the concavity of the top panel from the location of the inside surface of the top panel.  
         [0018]     The laser beam from the first laser ( FIG. 3, 18 ) is emitted through a slot ( FIG. 2, 21 ) in the platform  11 . Each of the laser beams from the first and second lasers ( FIG. 3, 18 ),  17  have a wavelength that is about 670 nanometers. The slot ( FIG. 2, 21 ) has a width of about one eighth inch and a length of about one inch. The calculation of the measurements can be performed either manually or electronically, but for the purposes of this invention the calculations were performed electronically by a data acquisition control system that is coupled to the infrared sensor ( FIG. 3, 16 ) and lasers ( FIG. 3, 18 ),  17  via electrical wires  25 . The control system, which drives the servomotor and synchronizes it to the molding machine rotation, is manufactured from Alan Bradley Programmable Logic Control (PLC) components and proprietary software. After the measurements are performed, the closure is passed from the pocketwheel  14  to the closure receiving pocketwheel  15 . Based on the measurements, the closures are either approved or rejected. The closure receiving pocketwheel  15  passes approved closures to a passageway  22  made for collecting the closures. The passageway  22  is coupled to the platform  11 , is situated next to the closure receiving pocketwheel  15 , and comprises stainless steel. Rejected closures are cleared from the closure receiving pocketwheel  15  and platform  11  by an airway  27  on the side of the platform  11  below the closure receiving pocketwheel  15 . The airway  27  comprises an aperture that is about 0.03 inches in diameter and blows the rejected closure into a chute (not shown) that leads the rejected closure into a scrap box (not shown).  
         [0019]     Temperature measurement of each closure, by the infrared sensor ( FIG. 3, 16 ), correlates to dimensional shifts, quality shifts, and cooling system performance. Measurement of top panel thickness, by a combination of the measurements of the first and second lasers ( FIG. 3,18 ),  17  correlates directly to closure weight and final dimensions. Warpage indicators or the concavity of the closure top surface, as measured by the first laser ( FIG. 3,18 ), correlates directly to cooling flow and plastic melt temperature. Combinations of measurements&#39; behavior allow technicians to quickly diagnose a problem and point to a sub-system of the molder, or individual tool that requires maintenance or adjustment. Because the measurements are variables, rather than attributes, they lend themselves to control charting, and indicate processes that are changing, thus giving early warning of changing processes and allowing maintenance and adjustment to be performed before scrap is produced. For the purposes of this invention, the process moves at a speed that is equal to the speed of the production flow, which is about 500-600 with the capacity of 1200 parts/minute.  
         [0020]     Having described the presently preferred embodiments, it is to be understood that the invention may be otherwise embodied within the scope of the appended claims.