Abstract:
A method and apparatus for handling preforms from an injection molding machine whereby an array of molded articles received from the mold is reconfigured into a single row to assist in downstream auxiliary processing.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation-in-part of an application entitled “System and Apparatus for Injection Molding Articles with Reduced Crystallization”, U.S. patent application Ser. No. 09/877,680, filed Jun. 8, 2001, which claims the benefit of priority from U.S. Provisional Application No. 60/267,859, filed Feb. 9, 2001. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates generally to the handling of injection molded articles. More particularly, the invention relates to a method and apparatus for handling injection molded articles of substantially amorphous polyethylene terephthalate and similar materials, whereby an array of molded articles is reconfigured into a single row.  
           [0004]    2. Summary of the Prior Art  
           [0005]    The use of polyethylene terephthalate (hereinafter referred to as “PET”) and similar materials as the materials of choice in the formation of numerous injection molded articles is well known in the art. For example, in the bottle and container industry, the blow molding of injection molded PET preforms has gained wide acceptance, and is experiencing strong growth. Among the reasons for this is the fact that PET and similar materials offer a wide range of desirable properties. Specifically, PET materials generally evidence high strength, good clarity, and low gas permeation characteristics. Further, PET materials are comparatively easy to recycle. Accordingly, they are desirable for use in retail packaging applications.  
           [0006]    In systems and apparatus for the injection molding of articles/preforms of the type alluded to above, a mold and a molten material transport means are commonly provided. The mold typically includes a first cavity extending inwardly from an outer surface of the mold to an inner end, an article formation cavity, and a gate connecting the first cavity to the article formation cavity. The gate defines an inlet orifice in the inner end of the first cavity, and an outlet orifice which opens into the article formation cavity.  
         SUMMARY OF THE INVENTION  
         [0007]    The primary aspect of the invention is to provide a product handling device having a serpentine channel having a first end and an outlet end in which sections thereof correspond to an arrangement of an array of molding cores of an injection mold, the serpentine channel defined within a plate and arranged to receive, in use, preforms presented thereto in a pattern of said array. The device further includes a drive mechanism positioned relative to the channel, the drive mechanism including drive means arranged to advance preforms, located in use within the serpentine channel, towards the outlet end, whereby preforms egress from outlet end of the channel as a single row of preforms.  
           [0008]    Another aspect of the present invention relates to a method of converting a two-dimensional array of preforms into a one dimensional row of preforms in a singulator having a serpentine channel, the method comprising the steps of placing the two-dimensional array of preforms into corresponding sections of the serpentine channel, engaging the preforms with a mechanically driven drive member to urge the preforms through the serpentine channel, and from an outlet of the serpentine channel egressing the preforms from the singulator as a row of preforms.  
           [0009]    The foregoing is achieved by providing an injection molding machine which comprises a plurality of preform mold cavities for the formation of molded articles therein. Following the molding process, the preforms are placed in the singulator so that each preform may be passed inline, and alternatively subjected to further processing by such devices as laser cutting of an elongated gate vestige, or automated preform inspection, etc. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1A is a simplified isometric view of an injection molding machine base in accordance with the present invention;  
         [0011]    [0011]FIG. 1B is a simplified operator side view of an injection molding machine in accordance with the present invention;  
         [0012]    [0012]FIG. 2 is an isometric view of the underside of the shuttle table in accordance with the present invention;  
         [0013]    [0013]FIG. 3 is an enlarged isometric view of the laser cutting station with an array of preforms;  
         [0014]    [0014]FIG. 4 is a partial detail view of the laser cutting station;  
         [0015]    [0015]FIG. 5 is a detailed cross-sectional view of a typical preform  
         [0016]    [0016]FIG. 6 is a top plan view of the laser system layout.  
         [0017]    [0017]FIG. 7 is an isometric view of the topside of the singulator in accordance with the present invention;  
         [0018]    [0018]FIG. 8 is an isometric view of the topside of the singulator in accordance with an alternative embodiment of the present invention; 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]    Referring first to FIG. 5 which shows a blank  108 , also termed preform, of a substantially amorphous thermoplastic material, preferably PET, having a mouth portion  122 , a substantially conical portion  124  extending from the mouth portion, a substantially cylindrical portion  126 , and a region of material  128  which, when forming the blank  108  into a container, forms the bottom of the container. The blank  108  has a central cavity  130  with a substantially cylindrical upper portion  132  and a substantially cylindrical lower portion  134 , whose circumference is smaller than that of the upper portion  132 . The transition between the upper and lower portions  132 ,  134  of the central cavity is a substantially conical transition portion  136 . The cylindrical lower portion  134  is closed at its bottom, which is bulging outwards and comprises an elongated vestige or sprue  109 . It is this elongated vestige  109  that will be severed from the preform  108  because it exhibits high crystallinity.  
         [0020]    The preform  108  thus serves as starting material in the making of a blow-molded container for example a reusable bottle for beverages.  
         [0021]    The mouth portion  122  has a threaded portion  138  and an annular gripping portion  140 . The material forming the mouth portion  122  is designated A in FIG. 5. The conical portion  124  encloses the substantially cylindrical upper portion  132  of the central cavity of the blank  108 . The cone of the conical portion  124  results from an increase of the thickness of this portion towards the bottom of the blank  108 . The material of the blank  108  forming the conical portion  124  is designated B in FIG. 5.  
         [0022]    The proximal part, with respect to the bottom of the blank  108 , of the substantially cylindrical upper portion  132  of the cavity  130  is defined by a wall having a substantially uniform wall thickness in all parts of the cylindrical portion  126 . The region of the substantially cylindrical portion is marked C in FIG. 5.  
         [0023]    The region of material  128 , which after reshaping of the blank  108  is intended to constitute the bottom of the container, has an increased wall thickness in the region of the transition portion  136  of the cavity of the blank  108 , and maintains this wall thickness substantially throughout the entire region of the substantially cylindrical lower portion  134  of the cavity. The wall thickness of the blank  108  thereafter decreases in the closed bottom of the blank to have its minimum thickness in a central region of material  142  in the bottom of the blank  108 . Reference D indicates the material of the blank  108  which in the resulting container is reshaped to form part of the bottom of the container, while reference E indicates the material of the blank  108  which substantially retains its shape when forming the container.  
         [0024]    Referring now to FIGS. 1A and 1B, an injection molding system  10  according to the present invention is generally shown. The injection molding system  10  is comprised of an injection molding machine  12 , a transport subsystem  14 , a pick and place robot  16 , a laser cutting station  18  and an inspection station (not shown). All of these subsystems work together to form a high speed manufacturing process for the production of injection molded articles, for example PET preforms  108 .  
         [0025]    In the preferred embodiment, the injection molding machine  12  is an index type machine with a rotary turret  36  for the production of PET preforms  108 . As one skilled in the art will recognize however, any type injection molding machine may easily be adapted for use with the present invention.  
         [0026]    Injection molding machine  10  generally includes a rotary turret  36  with a plurality of movable mold halves  37   a - 37   d,  a stationary mold half and platen  34  and injection unit  32 , all positioned on base  30 .  
         [0027]    Injection molding system  10  may be used for molding a variety of different types of articles and accordingly, is not limited for use with any particular type of article. Preforms are referred to throughout this description by way of example only.  
         [0028]    While the rotary turret  36  is shown throughout this description as rotatable on a horizontal axis, and this is the preferred embodiment, it is feasible that a similar design of a movable turret block providing the clamping action may be provided which is rotatable on a vertical axis. Accordingly, this invention is not considered limited to the horizontal axis feature.  
         [0029]    As shown in FIG. 1, rotary turret  36  is preferably longitudinally movable on base  30  via a set of bearings blocks  43  attached to the bottom of a pair of turret fittings (not shown). Base  30  includes linear bearings  44  which engage bearing blocks  43  and counteract upward forces and tipping forces that may act on the turret block assembly. Rotary turret  36  is rotatable preferably by a rotational drive (not shown) in communication with belts and pulleys, preferably an electric servo drive motor and preferably on a horizontal axis H through arcuate sectors preferably of substantially 90 degrees. Preferably, the rotational drive is connected via a belt drive (not shown) to axis (not shown) for rotating the rotary turret  36 , as shown in FIG. 1, while the electric servo drive motor is preferably mounted on one of turret fittings (not shown) extending from base  30 .  
         [0030]    As shown in FIG. 1, rotary turret  36  includes a plurality of movable mold halves, i.e. movable mold halves  37   a - 37   d  each of which includes a plurality of mold cores  45   a - 45   d,  respectively, each set having at least one mold core, adapted for engagement with a set of mold cavities  40 , each set including at least one mold cavity and located in stationary mold half and platen  34 . Preferably, four movable mold halves or faces  37   a - 37   d  are provided on rotary turret  36 , although any number supportable by the size of the rotary turret  36  can be used. Sets of mold cores  45   a - 45   d  are adapted to be rotated into horizontal and vertical alignment with sets of mold cavities  40 .  
         [0031]    Referring still to FIG. 1, rotary turret  36  includes sets of ejector pistons or stripper rings (not shown), and a system for the operation thereof, which operate on sets of mold cores  45   a - 45   d  and strippers positioned on movable mold halves  37   a - 37   d,  respectively. Accordingly, sets of ejector pistons or stripper rings (not shown) are positioned within rotary turret  36  and parallel to sets of mold cores  45   a - 45   d  and perform the function of stripping the mold cores of finished molded articles, for example, preforms, such as those shown in FIGS. 4 and 5. Each movable mold half  37   a - 37   d  and platen  34  includes at least one ejector piston in each set (not shown) for stripping finished articles from sets of mold cores  45   a - 45   d.  For the detailed design of the ejector piston or stripper ring system for use with sets (not shown), reference is made to U.S. Pat. No. 5,383,780, issued Jun. 24, 1995, to the assignee of the present invention, for incorporation by reference of a design of the ejector piston or stripper ring system, particularly column 4, line 29, to column 7, line 6, and FIGS.  1 - 8 . Preferably, the ejector piston or stripper ring system is actuated via the hydraulic services supplied to the rotary turret  36 , as discussed below. The hydraulically actuated ejector piston or stripper ring system actuated by on board hydraulic services is the preferred design, however, other designs may be used.  
         [0032]    Rotary turret  36  is movable backward and forward along linear bearings  44  on base  30  via piston/cylinder assemblies  38  positioned in stationary mold half and platen  34 , as shown in FIG. 1. Preferably four piston/cylinder assemblies  38 , as shown in FIG. 1 are used which are positioned in the corners of stationary mold half or platen  34 . Each piston/cylinder assembly  38  is attached to tie bars  47 , respectively, which tie bar  47  acts as the piston shaft. Accordingly, tie bars  47  extend from the piston/cylinder assemblies  38  and are connected at an opposite end to rotary turret  36 . In order to move rotary turret  36  backward and forward relative stationary mold half and platen  34 , pressurized fluid is forced into cylinders assemblies  38 . The side of the cylinder assemblies  38  in which pressurized fluid is forced against, determines the direction in which rotary turret  36  moves relative stationary mold half and platen  34 , that is, either into an open or closed position. Tie bars  47  pass through the turret fittings  46  and are attached thereto via retaining nuts.  
         [0033]    Services S, shown in FIG. 1, are provided to rotary turret  36  via a rotary union  31 . Accordingly, as rotary turret  36  rotates, services S are continuously supplied to the movable mold halves  37   a - 37   d.  Such services S include the supply of electricity, pressurized fluid, cooling fluids, and hydraulic fluids, etc. For using these services, rotary turret  36  also includes the required circuitry and control valves (not shown) on board and movable and rotatable with the turret block.  
         [0034]    Injection unit  32 , preferably in the form of a reciprocating screw injection unit, is connected with stationary mold half and platen  34  positioned on base  30  for providing melt to the mold cores for molding. Injection unit  32  is preferably movable into and out of engagement with stationary mold half and platen  34  by means of carriage cylinders (not shown) on rollers and hardened ways, similar to as described above for use with rotary turret  36 .  
         [0035]    Still referring to FIG. 1, the transport subsystem  14  comprises an inside and outside track  48   a  and  48   b  mounted to the base  30  and running from under the rotary turret  36  to a position of easy access by the pick and place robot  16 . A motor  50  is attached to one end of the inside track  48   a  which is in communication with a shaft  54  which runs between the inside and outside track  48   a  and  48   b.  Attached at each end of the shaft  54  is a pair of belts  52  which run the entire length of the tracks  48   a  and  48   b.  Attached to the inside surface of each track  48   a  and  48   b  is a second pair of linear bearings  56  which interface with a plurality of bearing blocks  60  (FIG. 2) rigidly affixed to a shuttle table  58 . Each belt  52  is attached to the shuttle table  58  such that the shuttle table  58  is operatively positioned (back and forth) through the use of the motor  50  along tracks  48   a  and  48   b.  In this arrangement, the shuttle table is controllably positioned beneath the rotary turret  36  to accept the molded preform  108 . Once the shuttle table  58  is filled with preforms  108 , it is operatively positioned at a far end of the tracks  48   a  and  48   b  for easy access by the pick and place robot  16 .  
         [0036]    Referring now to FIG. 2, the shuttle table  58  comprises a horizontal surface  62  with a plurality of holes  64  arranged to interface with the movable mold halves  37   a - 37   d  of the rotary turret  36 . Inserted in each hole  64  is a spacer  66  sized to accept the molded preform  108 . In the preferred embodiment, the spacers are made from a soft plastic material to minimize the scratching of the preform  108  that may occur during the handoffs from the shuttle table  58 .  
         [0037]    In the preferred embodiment, the shuttle table  58  must translate upwardly to interface with and catch the plurality of molded preforms  108  when they are released by the rotary turret  36 . To accomplish this motion, a servo-motor  68  is mounted beneath the horizontal surface  62  and in communication with a pair of ball screws  70 . Each ball screw  70  is attached to opposite ends of the horizontal surface  62  and grounded to an inside and outside support  74   a  and  74   b.  A second belt  72  runs between the ball screws  70  such that the servo-motor  68  controls both ball screws  70  for raising and lowering the horizontal surface  62  of the shuttle table  58 .  
         [0038]    Once the shuttle table  58  has received a plurality of preforms  108 , the table  58  moves away from the injection molding machine  12  and aligns with the robot  16 . The robot  16  comprises a frame  80  which carries a pick-up table  84  along a trackway  82 . The pickup table  84  interfaces with the shuttle table  58  with a plurality of air operated fingers  86  which are inserted into each preform  108 . The pick up table  84  is moved under precise control in a manner similar to the way the shuttle table  58  is moved and therefore won&#39;t be further described herein. In the preferred embodiment, once the air operated fingers  86  are positioned inside the preforms  108 , air is communicated to the fingers  86 , causing them to expand and grab on the inside surface of the preforms  108 . There are myriad methods for picking up the preforms  108 , and the forgoing is just an example of one of these methods and should not be read to limit the scope of the invention.  
         [0039]    Once the plurality of preforms  108  in the form of an array are retrieved by the pick up table  84 , the table translates to a distal location so that the preforms are aligned with a singulator  88 . The singulator  88  of FIG. 1 is shown in more detail in FIG. 7, as having a flat plate  200  with a continuous serpentine groove  89  machined therein, the plate  200  is preferably made from Derlin™. The pitch between straight parallel sections of the serpentine channel corresponds to a pitch between columns in a mold plate. The serpentine groove  89  is designed to accept a plurality of different preform sizes. Once the preforms  108  are properly seated in the groove  89  by the pick up table  84  (FIG. 1), the air in the fingers  86  (FIG. 1) is removed and the plurality of preforms  108  are released into the groove  89 . The array of preforms may also be delivered thereto by other equivalent device to the pickup table  84  such as an end-of-arm-tool on a robot. The serpentine channel  850  is dimensioned such that a annular gripping portion  140 , formed in the molded article, is too large to slip into the serpentine channel, i.e. the annular gripping portion of the preform rests on an upper surface  200  of the singulator. The singulator  88  further includes a drive chain  202  driven by a drive motor  204 . The drive chain can, for example, be either of a rubber construction or a linked construction. The drive chain  202  is a continuous drive chain that is linked to the drive motor  204  through at least one sprocket  208  or the like. The drive chain therefore follows the serpentine channel  89  along a substantial proportion (if not the entire length of) its path through the plate  200 . Guides  210  and free-rotating sprockets  206  define a path of the drive chain adjacent to the serpentine channel. In order to advance preforms located in the serpentine channel  89 , drive members (such as paddles)  212  are coupled to the drive chain  202 , such drive paddles preferably being of an plastic material with some limited elastic properties. The drive paddles  212  extend across the surface of the serpentine channel  89 . The drive paddles therefore engage against a neck or upper surface of the preform to urge, under the control of the motor drive  204 , the array of preforms along the serpentine channel  89  and into a linear row of preforms that egress from the singulator  88  and into the conveyor  90  (FIG. 1) and are moved onwards for further handling or processing. The drive chain can include one or more drive paddles  212 . In operation, the drive motor is preferably intermittent stop-start mode and is controlled using feedback from proximity sensors  216  mounted to the plate  200  and proximity targets mounted to the driven sprocket  208 .  
         [0040]    Reference is now made to FIG. 8 in which an alternative embodiment of the singulator  88  of FIG. 1 is shown. The singulator  88 , previously described as a flat plate  840  containing a continuous serpentine channel  850 , may be made from a machined plate of steel or aluminum or, alternatively, it can be constructed in a box-like fashion. The serpentine channel is configured to receive an array of preforms delivered thereto by the pick-up table  84  or other equivalent device, such as an end-of-arm-tool on a robot. In other words, a pitch between straight parallel sections of the serpentine channel corresponds to a pitch between columns in a mold plate. The serpentine channel  850  is dimensioned such that a annular gripping portion  140 , formed in the molded article, is too large to slip into the serpentine channel, i.e. the annular gripping portion of the preform rests on an upper surface  864  of the singulator. It is preferably that the majority of the body portion of the preform is contained within the channel. The singulator  88  further includes a drive chain  866  driven by a drive motor  868 . The drive chain can, for example, be either of a rubber construction or a linked construction. The drive chain  868  is a continuous drive chain that is linked to the drive motor  868  through at least one sprocket  870  or the like. The drive chain therefore follows the serpentine channel  850  along a substantial proportion (if not the entire length of) its path through the plate  840 . Rollers, small free-rotating sprockets  872  define a path of the drive chain adjacent to the serpentine channel. In order to advance preforms located in the serpentine channel  850 , drive members (such as paddles)  874  are coupled to the drive chain  866 , such drive paddles preferably being of an plastic material with some limited elastic properties. The drive paddles  874  extend across the surface of the serpentine channel  850 . The drive paddles therefore engage against a neck or upper surface of the preform to urge, under the control of the motor drive  868 , the array of preforms along the serpentine channel  850  and into a linear row of preforms that egress from the singulator  88  and are moved onwards for further handling or processing, preferably, by a conveyor system (not shown) coupled to an outlet  876  of the singulator  88 . The drive chain can include one or more drive paddles  874 . The singulator  88  may include a heat sink or other cooling system  880  (e.g. a water-cooled system including channels or piping  882  located through the singulator  88 ).  
         [0041]    Although the drive chain  866  is shown to be on the surface  864  of the singulator  88 , it may also be included beneath the surface should a box-like construction be employed. Indeed, internal mounting may be preferably from a safety handling perspective.  
         [0042]    Referring to FIGS. 3 and 4, the preforms  108  travel down the conveyor  90  to the laser cutting station  18 . The laser cutting station  18  comprises a rotary track  92  which accepts the preforms from the conveyor  90  and spins them in a circular fashion past a plurality of laser beams  103 . The rotary track  92  comprises a circular holder  96  with a plurality of pockets to accept the preforms  108  from the conveyor  90 . The rotational speed of the rotary track  92  is matched with the linear speed of the conveyor  90  so that preforms  108  are quickly and easily transferred into the pockets of the circular holder  96 . As the rotary track  92  rotates (and before the preform aligns with the first laser beam  103 ), a segmented top plate  94  is lowered into contact with the top surface of the preform  108  and forces the bottom of the preform  108  to interface with a lower shield  98 . In this arrangement, the elongated vestige  109  is now properly aligned with the plurality of laser beams  103  as they travel around with the rotary track  92 . The elongated vestige  109  travels past each laser beam  103  in rapid succession, thereby severing the vestige  109  from the preform  108 . The now severed vestige  109  drops into a reclamation bin  112 , where the vestige  109  will be later re-melted and recycled.  
         [0043]    The shield  98  is specifically designed to both protect the main body of the preform  108  from damage by the laser and also maintain a given length of remaining vestige. Testing has shown that without the shield  98 , energy from the laser  102  can cause inadvertent damage to the body of the preform  108 . In addition, international quality inspection criteria dictate the required length of any remaining vestige. Using the shield  98  insures the laser cuts the elongated vestige  109  at the proper location.  
         [0044]    Referring to FIG. 6, the various optical components which comprise the laser cutting setup are generally shown. Two lasers  102  are each aligned such that the laser beam passes first through a splitter  106   a  and  106   b  respectively. The splitters  106   a  and  106   b  are designed to reflect half of the laser beam power at 90 degrees from the entering beam, and allow the other half of the laser beam power to continue on to a mirror  118   a  and  118   b  where the remaining laser beam power is also reflected at 90 degrees from the entering beam. In the preferred embodiment, the optimum laser cutting set up was found to be two 500 W CO 2  lasers focused inline with the elongated vestige  109 . In this arrangement, four laser beams, each with approximately 250 watts of power are transmitted to a bank of focusing lenses  104   a - 104   d.  Positioners  120   a - 120   d  are attached to each lens  104  and allow for minute adjustments to the focused laser beam for machine set.  
         [0045]    A by-product of the laser cut is a very fine dust which tends to accumulate on the outside surface of the preform. To remove this dust, a brush  115  is mounted in the path of the preforms  108  as it passes to an unload conveyor  116 . Alternatively, or in combination, forced air could be blown over the preforms as the cut is made, or an electrical charge could be placed on the preforms to repel the flying plastic dust.  
         [0046]    The unload conveyor  116  accepts the preforms  108  in a linear fashion after they have been cut and transfers them to an inspection station (not shown) where each preform is inspected for compliance with quality control standards.  
         [0047]    It is to be understood that the invention is not limited to the illustrations described and shown herein, which are deemed to be merely illustrative of the best modes of carrying out the invention, and which are susceptible of modification of form, size, arrangement of parts and details of operation. The invention rather is intended to encompass all such modifications which are within its spirit and scope as defined by the claims.