Abstract:
An injection molding machine includes various devices for reducing injection cycle time. A molded article detection apparatus and method are disclosed. The detection system and method determines if an article, or a portion thereof, remains on a machine core pin after the article ejection cycle has occurred, and, if so, communicates this condition to both the machine controller and the take-out controller. This prevents the machine from starting a new cycle and damaging the injection mold. Also, by communicating the extraction status to both the take-out controller and machine controller, if no articles or portions remain, injection cycle time is reduced. Additionally, a variable vacuum pressure apparatus and method are described. The apparatus and method allows early removal of molded articles from the molds into a take-out plate while the parts are still warm.

Description:
This application claims the benefit of U.S. Provisional Application No. 60/085,730, filed May 15, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a system and method for reducing the cycle time of an injection molding machine. More particularly, the invention relates to an improved device and method for detecting the presence of an article on a mold of an injection molding machine, and controlling the operation of the device on the basis of this detection. The invention further relates to a device and method for removing molded articles from a mold of an injection molding machine before the articles are fully cooled. Both of these devices and methods, when used individually or together in an injection molding machine, reduce the machine&#39;s injection cycle time. 
     2. Description of Related Art 
     Containers are commonly made by blow molding a parison or preform that is made from polyethylene terephthalate (PET) material. The PET preheat and blow parisons are commonly manufactured by injection molding equipment. Containers may be injection molded in high-volume, multi-cavity molds. 
     It is important to reduce the overall cycle time for several reasons: (1) greater efficiency and cost-competitiveness; (2) reduced resin degradation due to prolonged residence time in the mold (specifically, acetaldehyde in PET parts); and (3) improved visual part quality (crystallization, seen as cloudy regions in the molded parts, may occur if cycle times are excessive). 
     Problems may also occur if articles or portions of articles are left on the mold core pins after the ejection cycle. Portions of articles may remain on the core pins due to (1) failure of the ejection system, (2) breakage of the parison during stripping from the cores, or (3) a “short shot” due to insufficient plasticized material being supplied to the mold cavities. If any molded portions remain on the core pins when the injection mold halves close, the injection mold may be damaged or the next successive part may be defective. To prevent this from happening, a conventional injection molding machine is set-up such that the device (e.g., a take-out plate) used to remove the molded parts from the core pins does not leave the molding area until it receives a signal from the injection molding machine controller that all the molded articles (or portions) have been removed from the core. This conservative approach lengthens the total molding injection cycle time. It also does not confirm that all of the molded articles are on the take-out plate and off the mold core pins. Thus, it would be desirable to reduce the injection cycle time by removing this conservatism from the injection molding process. 
     To further reduce cycle time, it would be desirable to remove the molded articles from the mold core before they are fully cooled. However, in this state, the parts are soft and malleable and susceptible to surface damage and mechanical deformation. Thus, there is also a need to develop a way to extract molded parts while they are still warm to reduce total cycle time. 
     SUMMARY OF THE PRESENT INVENTION 
     It is therefore a principal object of the present invention to provide apparatuses and methods for reducing the total injection cycle time needed to mold and safely eject parisons in a multi-cavity mold. The invention is, however, not restricted to parisons, and may apply to any molded article that shrinks onto the core halves of a mold after injection and cooling. 
     In one aspect of the present invention, an apparatus for controlling a machine controller and a take-out controller of an injection molding machine includes a radiation source, a radiation detector, a machine controller, and a take-out controller. The radiation source projects radiation to a mold plate. The radiation detector receives the projected radiation from the mold plate. The machine controller receives a signal from the radiation detector, determines whether any molded parts or portions of molded parts remain at a predetermined position on the mold plate, and provides a command signal to stop injection operations when it is determined that molded parts or portions of molded parts remain at the predetermined position. The take-out controller substantially simultaneously receives a signal from the radiation detector, determines whether any molded parts or portions of molded parts remain at a predetermined position on the mold plate, and provides a command signal to stop take-out operations when it is determined that molded parts or portions of molded parts remain at the predetermined position. 
     In another aspect of the present invention, an injection molding machine includes a platen, a mold attached to the platen, a radiation emitting element, a radiation receiving element, a take-out controller and a machine controller. The mold includes at least one core pin extending perpendicular to a surface of the mold and has a longitudinal axis. The radiation emitting element is adjacent the mold and positioned to emit a radiation beam proximate the core pin and perpendicular to the longitudinal axis of the core pin. The radiation receiving element is adjacent the mold and positioned to receive the radiation beam emitted from the radiation emitting element. The take-out controller is connected to the radiation receiving element and receives signals from the radiation receiving element. The machine controller, which is connected to the radiation emitting and receiving elements, provides power and control signals to the elements, and receives signals from the radiation receiving element. 
     In a further aspect of the invention, an apparatus for detecting the presence of an article on a mold core pin of an injection molding machine includes at least one radiation emitting element, at least one radiation receiving, a take-out controller, and a machine controller. The radiation emitting element is adjacent the mold and positioned to emit a radiation beam proximate the core pin and perpendicular to the longitudinal axis of the core pin. The radiation receiving element is spaced apart from the radiation emitting element and positioned to receive the emitted radiation. The take-out controller is connected to the radiation receiving element and provides a signal to stop a take-out device when the radiation receiving element indicates that the article has not been removed from a predetermined portion of the mold core pin. The machine controller, which is connected to the radiation emitting and receiving elements, provides power and control signals to the elements, and provides a signal to stop injection operations when the radiation receiving element indicates that the article has not been removed from the predetermined position. 
     In yet another aspect of the present invention, a method of detecting the presence of an article on a mold core pin of an injection molding machine includes positioning a radiation transmitting element to transmit radiation proximate the mold core pin and perpendicular to a longitudinal axis thereof, positioning a radiation receiving element at a position spaced apart from the radiation transmitting element, and determining that an article is still present on the mold core pin when the transmitted radiation is not received by the radiation receiving element. A signal is transmitted substantially simultaneously to both a machine controller and a take-out controller when it is determined that an article is present on the mold core pin. 
     In still another aspect of the present invention, an apparatus for controlling a vacuum device which removes molded parts from a a mold plate of an injection molding machine includes a controller which controls the vacuum device so as to apply a higher vacuum pressure to the molded parts to begin their removal from the mold plate, and to apply a lower vacuum pressure to the molded parts after they begin moving from the mold plate. This is because partially cooled parts are soft and can be deformed if exposed to a sustained high vacuum pressure. 
     In still a further aspect of the present invention, an apparatus for removing a molded article from a mold of an injection molding machine includes a plate, at least one vacuum passage, at least one hollow receiving member, a vacuum pressure source, and a vacuum relief valve. The plate has at least first and second surfaces, and at least one vacuum passage extending between the first and second surfaces, wherein each passage includes a port on the first and second surfaces. The at least one hollow receiving member is attached to the second surface of the plate, and each hollow member has two openings wherein one opening surrounds a vacuum passage port. The vacuum pressure source is in fluid communication with each port on the first surface of plate, and the vacuum relief valve is in fluid communication with each port on the first surface of the plate, and varies the vacuum pressure applied to the molded part. 
     In an additional aspect of the present invention, an apparatus for removing an article from the mold of an injection molding machine includes a plate, a hollow tube, vacuum pressure generating means, vacuum pressure sensing means, and a relief valve. The hollow tube is attached to a first surface of the plate, and has a hollow central portion for receiving the article from the mold. The vacuum generating means generates a vacuum within the hollow tube, such that the vacuum pressure develops a force urging the article from the mold toward the hollow central portion. The vacuum pressure sensing means senses the magnitude of the vacuum pressure within the hollow tube and generates a control signal if the vacuum pressure reaches a first predetermined magnitude. The relief valve means receives the control signal from the sensing means and reduces the magnitude of the vacuum pressure to a second predetermined magnitude. 
     In yet an additional aspect of the present invention, a method of removing a molded article from a mold of an injection molding machine includes connecting a vacuum pressure source to a receiving means that receives the molded article, wherein the vacuum pressure source generates a vacuum pressure magnitude within the receiving means; moving the receiving means adjacent the molded article, such that the vacuum pressure within said receiving means draws said molded article into said receiving means; sensing the vacuum pressure magnitude within the receiving means; and reducing the vacuum pressure magnitude within the receiving means to a predetermined magnitude. 
     In still an additional aspect of the present invention, an injection molding machine includes a platen, a mold attached to the platen, clamping means for applying a clamping load to the mold, and injection means for injecting molten material into the mold. Radiation emitting means, positioned adjacent the mold, emits radiation proximate the mold. Radiation receiving means, positioned adjacent the mold, receives the radiation emitted from the radiation emitting means. Machine controller means controls the operation of the clamping means and the injection means, provides power and control signals to the radiation emitting and receiving means, and receives signals from the radiation receiving means. The machine also includes a movable take-out plate having a first surface adjacent the surface of the mold, and a hollow tube attached to the first surface of the take-out plate. The hollow tube includes a hollow central portion for receiving an article from the mold. Means for moving the take-out plate. Take-out controller means controls the take-out plate moving means, and receives signals from the radiation receiving means. Means for generating a vacuum pressure within the hollow tube, wherein the vacuum pressure develops a force urging the article from the mold toward the hollow central portion. Vacuum pressure sensing means senses a magnitude of the vacuum pressure within the hollow tube and generates a control signal if the vacuum pressure reaches a first predetermined magnitude. Relief valve means receives the control signal from the sensing means and reduces the magnitude of the vacuum pressure to a second predetermined magnitude. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an article detection device according to a first embodiment of the present invention. 
     FIG. 2 is a section view of showing two possible core pin conditions following completion of an injection mold cycle. 
     FIG. 3 is a plan view of an article detection device according to a second embodiment of the present invention. 
     FIGS.  4 ( a )- 4 ( d ) illustrate various removal states of an injection molded article by a takeout plate according to the present invention. 
     FIG. 5 is a schematic showing a vacuum pressure removal device according to the present invention according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1,  2 , and  3  depict systems for detecting the presence of an article, or portion of an article, on the core pin of an injection mold after an ejection step of the injection mold cycle has occurred. The depicted systems are capable of scanning a plurality of aligned core pins and detecting the presence of articles that fail to eject. Referring now to FIGS. 1 and 2, a detailed description of a first embodiment of the present invention will be provided. 
     In the first embodiment, the detection system includes a plurality of radiation emitting elements  33  and radiation receiving elements  34 . These elements  33 ,  34  are attached to a mold  32  that is mounted on a platen  31 , and are arranged such that each receiving element  34  is directly opposite a transmitting element  33 . The radiation emitters and detectors  33 ,  34  could be any device known to the ordinarily skilled artisan. For example, emitting elements  33  could be, but are not limited to, infrared light sources, white light sources, or light emitting diodes (LEDs). Examples of receiving elements  34  include, but are not limited to, photoresistors, photodiodes, phototransistors, or photovoltaic cells. These devices can also include appropriate lenses to reduce ambient light sensitivity. In the preferred embodiment, the radiation emitting and receiving elements are laser emitters and detectors. 
     The radiation emitting elements  33  are electrically connected to a machine controller  35 . The radiation receiving elements  34  are electrically connected to both machine controller  35  and a take-out controller  36 . Connections  33 ′ connect emitting elements  33  to machine controller  35 , and connections  34 ′ connect receiving elements  34  to machine controller  35  and take-out controller  36 . Connections  33 ′ and  34 ′ could be any connecting device known to the ordinarily skilled artisan, such as electrical cords, wiring, or cables, or fiber optic cables. However, in the preferred embodiment these connections are electrical cords. Machine controller  35  provides power and control signals, via connections  33 ′,  34 ′, to emitting and receiving elements  33 ,  34 . Receiving elements  34  provide signals to both machine controller  35  and take-out controller  36 , as will be described further below. 
     Radiation emitting and receiving elements  33 ,  34  are arranged such that the emitted radiation  37  scans across a series of core pins  38 . Thus, if the radiation  37  emitted from an emitting element  33  is not received by its concomitant receiving element  34 , this indicates that an article  39 , or portion of an article, remains on a core pin  38 . This situation is depicted in FIG.  2 . When this situation occurs, both machine controller  35  and take-out controller  36  are alerted virtually simultaneously via connections  34 ′. As a result, machine controller  36  will issue a command to stop the next clamping and injection operation, and take-out controller  36  will prevent movement of the take-out plate  41 . If, however, the radiation  37  emitted from the emitting elements  33  is received by the concomitant receiving elements  34 , then, once again, both controllers  35 ,  36  are simultaneously alerted to this situation. Machine controller  35  will not prohibit the next clamping and injection operations, and take-out controller  36  will command take-out plate  41  to move out of the mold area. 
     In a second embodiment of the present invention, as depicted in FIG. 3, a single emitting element  33  and single receiving element  34  can be used for detection. This is made possible by the use of radiation redirecting devices  42 . In this embodiment, an emitting element  33  is placed adjacent a series of core pins  38  of a mold  32 . The emitted radiation beam  37  scans across the plurality of core pins  38 , and a device  42  is placed directly opposite emitting element  33  to receive the emitted radiation beam  37 . Radiation beam  37 , if not blocked, is then redirected toward an adjacent device  42 , which in turn redirects beam  37  toward another device  42  on the opposite side of mold  32  along another series of core pins  38 . This redirection of beam  37  is continued for as many series of core pins  38  as are present on mold  32 . For the last series, beam  37  is received by receiving element  34 . Devices  42  may be any device known in the art for redirecting radiation. For example, devices  42  could be, but are not limited to, mirror-type reflectors, refracting lenses, or optical fibers, but in the preferred embodiment are prisms. 
     Operation of the second embodiment is similar to the first. Thus, if receiving element  34  does not receive beam  37 , then machine controller  35  and take-out controller  36  are simultaneously alerted. Controller  35  then issues a command to stop the next clamping and injection operation, and controller  36  prevents movement of the take-out plate  41 . If, however, the radiation beam  37  emitted from the emitting element  33  is received by receiving element  34 , then the next clamping and injection operations are not prohibited by machine controller  35 , and take-out controller  36  commands take-out plate  41  to leave the mold area. 
     Because machine controller  35  and take-out controller  36  are both directly connected to receiving element(s)  34 , both controllers are simultaneously alerted to whether an article  39 , or portion thereof, remains on a core pin  38 . Therefore, if no article  39 , or portion thereof, remains on a core pin  38 , then take-out controller  36  need not wait for a command from machine controller  35  to initiate movement of take-out plate  41 . As a result, significant injection molding cycle time savings can be realized. For example, for a 4×12 (48 cavity) mold, a cycle time saving between 100 and 150 milliseconds can be realized. Similar cycle time savings can be realized for other mold sizes. 
     Injection molding cycle time can also be improved by reducing the time it takes to transfer an article  39  from a core pin  38  to a take-out plate  41 . Accomplishing this time reduction using a high pressure vacuum, while avoiding the problems of the prior art, will now be discussed with reference to FIGS.  4 ( a )- 4 ( e ) and FIG.  5 . 
     FIGS.  4 ( a )- 4 ( d ) depict various removal states of an article  39  by a take-out plate  41 . Each of these Figures shows a portion of a take-out plate  41 , which includes passages  44  extending therethrough. Attached to take-out plate  41 , and surrounding each passage  44 , are tubes  43 . Tubes  43  include a cavity  45  for receiving an article  39 , and passages  46  extending between the cavity  45  and a port  47  in an end of the tube  43 . Each port  47  is collocated with a passage  44  of take-out plate  41 . A vacuum pressure is communicated to each passage  44 , and thus to each cavity  45 , to urge the article  39  toward the tube  43 . This general operation will now be described. 
     FIG.  4 ( a ) depicts article  39  positioned on core pin  38  following the molding process, and just prior to the removal process. Vacuum pressure is communicated to cavity  45 , via passages  44  and  46 , but article  39  has not been fully released. FIG.  4 ( b ) depicts the start of release of article  39  from core pin  38  by movement of neck splits  100  and  101 . FIGS.  4 ( c ) and  4 ( d ) depict further disengagement of article  39  from core pin  38 , and FIG.  4 ( e ) depicts full receipt of article  39  into cavity  45 . Referring now to FIG. 5, the improved system for effecting article extraction from the core pins according to the present invention will now be described in detail. 
     The vacuum pressure part removal system is in fluid communication with take-out plate  41  via passages  51 . Passages  51  communicate with concomitant passages  44  on take-out plate  41  (see FIGS.  4 ( a )- 4 ( d )). Connected to each passage  51  is a vacuum device  49 . Each vacuum device includes a valve  52 , which could be any type known to an ordinarily skilled artisan that allows automatic, remote control. For example, valve  52  could be either a globe valve or a gate valve, and could be air-operated, solenoid-operated, or hydraulically operated. In the preferred embodiment, however, valve  52  is an air-operated globe valve. In fluid communication with each valve  52  is vacuum passage  53 . Vacuum passage  53  provides fluid communication between a vacuum source  54  and each valve  52 . Vacuum source  54  may be any device known in the art for developing a vacuum pressure, but in the preferred embodiment is a vacuum pump. Vacuum passage  53  can also include a filter  55  and a vacuum gauge  56 , both of which may be any type known in the art. As previously noted, in the preferred embodiment valves  52  are air-operated. Thus, in the preferred embodiment, each vacuum device  49  includes a solenoid-operated positioning valve  57  connected to each operator of valves  52 . Each positioning valve  57  directs the flow of the operating media (e.g., air) to and from each valve  52  operator to position each valve  52  to the open or close position. Although FIG. 5 shows only three passages  51  and concomitant vacuum devices  49 , this is only for exemplary purposes and any number may be used to meet the required size of the take-out plate  41 . 
     Also in fluid communication with each valve  52 , via vacuum passage  53 , is a vacuum relief device  58 . Vacuum relief device  58  includes valves  59  and  61 , which may be any type known in the art, as previously noted for valves  52  and  57 , but in the preferred embodiment are the same design as valves  52  and  57 , respectively. Connected to valve  59  is vacuum relief passage  62 , which can include a vacuum gauge  63  and an adjustable flow control device  64 . Vacuum gauge  63  and flow control device  64  can be any device known in the art for carrying out each individual function. Vacuum relief device  58  is controlled based upon the vacuum pressure sensed in vacuum passage  53 . When the magnitude of the vacuum pressure in vacuum passage  53  reaches a predetermined setpoint, valve  59  is opened thus reducing the vacuum pressure magnitude within each cavity  45  of each tube  43  connected to take-out plate  41 . Vacuum relief device  58  can be controlled by any device known in the art, but in the preferred embodiment is controlled by a variable setpoint vacuum switch  65 . 
     With the removal system just described, articles  39  can be extracted from core pins  38  early in the injection molding cycle, while the articles  39  are still warm. This is because as the articles  39  begin to seal within cavities  45  of tubes  43 , the magnitude of the vacuum in passage  53  is lowered by vacuum relief device  58 . Initially, a very high vacuum pressure is used to draw molded articles  39  toward cavities  45  while the articles  39  are still warm. As articles  39  begin entering cavities  45 , the magnitude of the vacuum begins increasing in vacuum passage  53 . When this magnitude reaches a predetermined, variable setpoint of more than 40 inches of water, positioning valve  61  is positioned to direct operating air to open valve  59 . Vacuum pressure in passage  53  is then reduced or maintained via flow control device  64 . Flow control device  64  is set to maintain the vacuum pressure magnitude to a level just above that necessary to hold articles  39  within cavities  45 . 
     If not reduced, the vacuum pressure would reach 130 inches of water and deform the preforms. (There is no time saving by using vacuum pressure relief, only protection of part quality.) If articles  39  are removed while still warm and a variable vacuum pressure is not used, articles  39  become elongated and contain surface marks. Thus, the variable vacuum system of the present invention reduces the overall injection molding cycle time while improving article  39  quality. 
     While preferred embodiments of the present invention have been illustrated in detail, it is apparent that modifications and adaptations of the preferred embodiments will occur to those skilled in the art. However, it will be expressly understood that such modifications and adaptations are within the spirit and scope of the present invention as set forth in the following claims.