Plastic article or earthenware shaping or treating: apparatus – Control means responsive to or actuated by means sensing or... – Means responsive to abnormal condition completely stop...
Reexamination Certificate
1999-08-03
2001-03-13
Pyon, Harold (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Control means responsive to or actuated by means sensing or...
Means responsive to abnormal condition completely stop...
C425S398000, C425S408000, C425S451600, C100S286000
Reexamination Certificate
active
06200122
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention concerns thermoforming apparatus, and more particularly presses used in thermoforming parts from preheated plastic sheet material. Thermoforming is in wide spread use as a manufacturing method, and involves preheating of thin plastic sheet material in an oven and then advancing the same into a thermoforming press having a mold located between the press platens.
The plastic sheet is drawn against the mold surfaces during the forming operation carried out by the application of a vacuum or air pressure causing the sheet material to be drawn against the mold surfaces. Relatively large articles are often manufactured this way and considerable press loads are generated by the fluid pressure forces acting over large areas, which must be resisted by the press platens and their supporting structure.
The forces required also may be increased by the use of plug assist tools in which complementary tooling is carried by one of the platens and driven into the forming surfaces on the other tooling piece. The weight of the tooling supported by the platens thus can become considerable. A large servo motor has sometimes been used, the size of the motor in turn resulting in a relatively slow response time of the platen drive mechanism. The relatively thin wall thickness of the part makes accuracy in the forming process more critical.
Presses used in thermoforming typically involve a pair of columns supporting the platens in their up and down motion and plain bearings are used in the linkages used to drive the platens up and down and to guide the platens on the machine frame. This construction has limitations in that the deflections of the platens under heavy loading is not sufficient to prevent inaccuracies in the thin walled parts formed due to slight tilting and bending of the platens and the structure supporting the platens under the heavy press loads described. In addition, a single large servo motor has considerable inertia increasing the cycle time required. This construction also absorbs a significant portion of the motor power to overcome the frictional losses. Where the apparatus is taxed to its utmost capability, these losses become critical, and the press may not be able to execute the operation required.
Accordingly, it is an object of the present invention to provide a thermoforming apparatus having an improved thermoforming press in which the stability and precision movement of the platens is substantially improved over the prior art thermoforming presses.
It is a further object of the present invention to provide a press for use in thermoforming operations in which the frictional losses are significantly reduced.
It is yet another object of the present invention to provide a servo motor operated platen mechanism in which the response capability of the servo motor drive is improved over the prior art designs for heavier duty presses.
SUMMARY OF THE INVENTION
These objects and others which will become apparent upon a reading of the following specification and claims are achieved by a thermoforming press in which the platens are guided on precision antifriction bearings located at each of four corners of each of upper and lower press platens, the bearings mounted on each of four posts forming a part of the press frame. Both the upper and lower platens are thereby guided on each of their four corners with minimal friction losses, highly precision guided movement of the platens is obtained, and the platen is very stably supported by the linear antifriction bearings at each corner post.
Actuation of each platen is carried out by a set of four separate linkages connected to each plate at a location adjacent the four corners of the plated, such as to evenly distribute the forces imposed on the platen by the press forces.
Two separate servo motors are provided for each platen drive, each servo motor driving a transmission having an output shaft having a pair of crank arms affixed thereto, in turn driving two of the four toggle linkages provided for each platen.
Both the upper and lower platen are mounted and driven in the same manner, such that a total of four servo motors driving two sets of four toggle linkages is employed for operation of the platens.
The pivotal connections of the links making up the toggle linkages are provided with antifriction bearings at the pivotal connections such as to further reduce the frictional losses in the system.
The dual servo motor drive for each platen provides a rapid response press operation. A very stable support of the platens, even under heavy loading is achieved, and an only minimal frictional losses are experienced such as to maximize the capacity of the press for conducting thermoforming operations.
REFERENCES:
patent: 4088432 (1978-05-01), Farrell
patent: 4377377 (1983-03-01), Arends et al.
patent: 5002479 (1991-03-01), Brown et al.
patent: 5814185 (1998-09-01), Chun et al.
patent: 5925162 (1999-07-01), Nitschke et al.
Arends Albert W.
Chun Victor L.
Richard Andrew
Benefiel John R.
Brown Machine LLC.
Heckenberg Donald
Pyon Harold
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