Plastic article or earthenware shaping or treating: apparatus – Control means responsive to or actuated by means sensing or... – Molding pressure control means responsive to pressure at...
Reexamination Certificate
1999-02-01
2001-02-13
Davis, Robert (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Control means responsive to or actuated by means sensing or...
Molding pressure control means responsive to pressure at...
C425S150000, C425S170000, C425S171000, C425S529000, C425S540000
Reexamination Certificate
active
06186760
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to blow mold machines, and more particularly to a system for monitoring and controlling workstation parameters.
BACKGROUND OF THE INVENTION
Hollow, plastic containers are typically manufactured using a blow mold machine. In general, there are two types of machines: a two-stage, reheat, stretch blow mold machine and a one-stage blow mold machine. Typically a stretch blow mold machine consumes a plastic preform created utilizing an extruder, in an injection-molding operation. Alternatively, a one-stage blow mold machine uses a parison formed by an extruder in a more continuous process. That is to say the preform is injection molded and can be warehoused, whereas the parison is formed just before it is blown.
Functionally, the one-stage blow mold machine differs from the following discussion of two-stage machines in that the parison is typically formed just before it is transformed into the container and there is no stretch rod. On two-stage or reheat-stretch machines, the preforms are conveyed to the stretch blow mold machine and often times inspected by automated visual scanners to detect irregularities. Any preforms failing to meet preprogrammed criterion are rejected before being loaded into the stretch blow mold machine. In general, the first step of the stretch blow mold process is to reheat the preform in an oven upstream from the stretch blow mold machine rotary table. The preforms are heated as they are conveyed through the oven. Typically, the heated preform is transferred to the rotary stretch blow mold machine at the load station. The load station includes rotating arms that grasp the preform and place the preform in the two-piece mold cavity. The load station is synchronized with the stretch blow mold machine wheel and the mold closes around the preform after the preform is loaded.
As the wheel continues to rotate, the stretch rod is driven down through the neck of the preform. When the stretch rod is moving down, low-pressure air (typically 150 psi) is introduced into the preform via the hollow stretch rod to prevent the preform from collapsing on the stretch rod. Some time after the stretch rod reaches its maximum extension or stroke, high pressure blow air (typically 600 psi) is applied to the inside of the preform to force the heated plastic against the mold surrounding the preform. It is understood that the container may be formed by any fluid, not only air. The mold is typically cooled by chilled process water circulated in the jacketed mold. The high-pressure blow air is applied to the now formed container for a portion of the wheel's revolution to allow the container to cool.
After the cooling interval, the center rod retracts and the blow air is exhausted. The stretch rod retracts to the fully retracted position before the mold opens to expose the container for extraction. The extraction or unload station is synchronized to the stretch blow mold machine wheel and transfers the container from the wheel to the exit conveyor. The exit conveyor transports the container to an approval inspection station and then on to a palletizer.
Stretch blow mold machines are available in many configurations ranging from two stations to 40 or more stations. Previously, there has been no way to monitor specific process parameters at the individual stations used to produce a container. Previous systems were only able to monitor process parameters as they related to all stations on a wheel. Blow air pressure and water values could only be determined at the manifold level. There was no method to monitor the displacement of the stretch rod. Station molds, stretch rods, valves, seals, cams, ports, orifices, and other unique components wear at different rates, are subject to different alignment errors during normal operation, mold changes and routine maintenance activities. These differences affect the quality of containers produced. Significant station-to-station differences are difficult or impossible to detect during continuous production. Quality problems are detected only during random quality control samples. If a bad container is found during this quality check, it is impossible to determine how many out of specification containers have been produced.
A stretch blow mold machine may produce as many as 40,000 or more containers per hour. The wheel is totally enclosed by safety walls and doors. The high angular velocities make it difficult to visually observe station actions without the use of a strobe light. Very small process changes negatively affect the quality of the container. Most of these process changes are not detectable external to the machine. Even if slip rings were employed to provide power to the wheel, communicating across these rings severely limits the data throughput due to the high noise margin induced by slip ring brushes.
Rotating platforms for container formations create an unusually difficult environment to monitor and control the process. This environment not only challenges existing control methods; but, makes it impossible to communicate large volumes of high-resolution data necessary to visualize and control the process.
A need has thus arisen for a system for monitoring and controlling workstation parameters of a blow mold machine.
SUMMARY OF THE INVENTION
The present invention allows for the monitoring of critical blow mold parameters to determine in real time, during continuous process operations which workstations are producing out of specification containers and effect closed loop controls used to fabricate the container. Transducers continuously monitor the process parameters. The controller senses the speed of the stretch blow mold machine and dynamically changes the interrupt interval to ensure the transducer sampling is synchronized to the angular velocity of the wheel. Closed-loop feedback control is made possible by modifying outputs used to control servovalves, servocylinders, servomotors, and other continuous control devices. The controller is able to process the data and detect an out of tolerance condition. Such out of tolerance product is either rejected from the machine by wheel mounted devices or a coded signal is transmitted to the machine controller to reject the product from the discharge stream. A profile of the process control parameters is transmitted to a computer to create graphs and selected indices for detailed analysis. Key data is also trended in graphical and tabular form for historical and statistical analysis purposes.
REFERENCES:
patent: 3097398 (1963-07-01), Iglesby
patent: 3737275 (1973-06-01), Kontz
patent: 3752627 (1973-08-01), Bourgeois et al.
patent: 4021517 (1977-05-01), Schmidt et al.
patent: 4325897 (1982-04-01), Zerle et al.
patent: 4372735 (1983-02-01), Collette
patent: 4826418 (1989-05-01), Kamiguchi
patent: 5169705 (1992-12-01), Coxhead et al.
patent: 5244610 (1993-09-01), Kitzmiller
patent: 5269672 (1993-12-01), DiGangi, Jr.
patent: 5322651 (1994-06-01), Emmer
patent: 5470218 (1995-11-01), Hillman et al.
patent: 5572816 (1996-11-01), Anderson, Jr. et al.
patent: 5626804 (1997-05-01), Benkowski et al.
patent: 5866175 (1999-02-01), Latham
Davis Robert
Locke Liddell & Sapp LLP
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