Press-actuation system

Abstract

A press has upper and lower dies, an actuating element spaced vertically from one of the dies, and a platen carrying the one die and between the element and the one die. A membrane defines a closed chamber having one side operatively bearing vertically on the platen and an opposite side bearing vertically on the element. A fluid supply pressurizes the chamber and maintains in the chamber a predetermined pressure. An actuator connected to the element vertically displaces the element, platen, and one die.

Description

FIELD OF THE INVENTION

The present invention relates to pres. More particularly this invention concerns an actuation system for a press.

BACKGROUND OF THE INVENTION

A typical press used, for example, in a packing machine to laminate together two plastic foils has an upper die and a lower die, normally heated. Typically the upper die has a planar lower face and the lower die has a planar upper face formed with an array of upwardly open pockets. A planar upper foil and a lower foil formed with an array of upwardly open product-containing blisters are passed horizontally through the press. The two dies are pressed together between advance steps of the foils when the blisters are aligned with the pockets in the lower die to laminate the two foils together between the blisters. Such systems are described in German patent documents 197 40 988 and 74 05 441 and in U.S. Pat. No. 5,105,603.

The two dies are relatively large and quite massive, and the foils are quite thin and are formed of a moderately fragile plastic. It is therefore essential that the dies be moved together with enormous precision so as to press the foils together with just enough force that they bond together, but not so much that they extrude out or are damaged.

Obviously the problem here is that any slight misalignment can result in a spoiled workpiece. If the two foils are not solidly bonded together, the resultant package is unusable. Similarly if the two foils are pinched excessively, there will be weak spots or holes that also result in an unusable finished product.

OBJECTS OF THE INVENTION

It is therefore an object of the present invention to provide an improved press-actuation system.

Another object is the provision of such an improved press-actuation system that overcomes the above-given disadvantages, in particular that ensures that the pressure exerted on the foils will be uniform and accurately controlled.

SUMMARY OF THE INVENTION

A press has according to the invention upper and lower dies, an actuating element spaced vertically from one of the dies, and a platen carrying the one die and between the element and the one die. A membrane defines a closed chamber having one side operatively bearing vertically on the platen and an opposite side bearing vertically on the element. A fluid supply pressurizes the chamber and maintains in the chamber a predetermined pressure. An actuator connected to the element vertically displaces the element, platen, and one die.

Thus with this system the pressurizable chamber provided between the actuator and the one die limits the maximum pressure the one die can apply to the workpiece. If the actuator, which is typically a powerful hydraulic cylinder or motor, moves the element somewhat too far, the chamber will simply deform and the pressure transmitted to the workpiece will be that in the chamber. In addition if one of the dies is slightly canted, that is nonparallel, to the other die, the chamber will deform to allow them to move parallel without pinching or overly compressing the workpiece. What is more, the actuator can be set to perform a simple lifting stroke and any adjustment or fine-tuning of the closing pressure is handled by the supply system connected to the force-transmitting chamber.

What is more, the chamber ensures that the force of the press actuator, which typically is applied at one or more separate locations to the actuating element, is distributed over the entire platen. Thus even if the element deforms, the platen will be applied smoothly and flatly.

According to the invention the platen and element together form a compartment holding the membrane. The platen is provided with guide bars in which the element is vertically slidable, and/or the platen is formed with a cavity open toward the element and holding the membrane and in which the actuating element is slidable. The cavity receives the membrane with some play, that is lateral spacing, so it can spread and deform as needed.

The supply system pressurizes the chamber with a gas, normally air. This makes it possible to control the workpiece-clamping pressure accurately and very easily. What is more, such a pneumatic system is environmentally friendly as compared, for example, to a oil-filled hydraulic system, as any leakage does not create a problem and, if minor, does not even require shutting down the press.

The membrane according to the invention forms a bladder. It can have several compartments for local control of pressure, or be formed as a stack of compartments. The bladder can easily be exchanged or replaced. When multiple bladders are used, they can be switched out to achieve different pressures in different areas, and generally provide local pressure control.

The press further has according to the invention a source of fluid under pressure, a valve between the source and the chamber, and a controller connected to the valve and including a sensor connected to the chamber for determining a pressure therein for operating the valve according to a sensed pressure for maintaining the predetermined pressure in the chamber. The valve includes a pressure-reducing valve and/or a proportional valve. The sensor can be associated with a comparator to establish upper and lower pressure limits for the valve and operate in a feedback system to maintain the pressure in the chamber substantially constant. A pressure-reducing valve limits the maximum pressure to prevent damage to the workpiece no matter what else occurs.

According to the invention the press further has a second actuating element spaced vertically from the other of the dies, a second platen carrying the other die and between the second element and the other die, a second membrane defining a closed chamber having one side operatively bearing vertically on the second platen and an opposite side bearing vertically on the second element. The supply means also pressurizes the second membrane.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1 is a partly diagrammatic vertical section through part of a press according to the invention; and

FIG. 2 is a partly diagrammatic vertical section through a press in accordance with the invention.

SPECIFIC DESCRIPTION

As seen in FIG. 1 a press 1 according to the invention has a lower die 2 typically formed with an array of upwardly open pockets and carried on a massive cast platen 3. An actuating plate or element 5 underneath the plate 3 is vertically reciprocal by an actuator, e.g. a motor or hydraulic cylinder, shown schematically at 4 to open and close the press 1. The platen 3 is formed with a downwardly open cavity 13 in which the plate 5 can slide limitedly vertically and bars 11 surrounding the cavity 13 also guide the plate 5 and prevent it from becoming disconnected in a lowermost position from the platen 3.

According to the invention a flexible and even somewhat elastomeric membrane 7 forming a bladder 10 defining a closed chamber 19 is carried with some lateral clearance in the cavity 13. It is connected via a feed line or passage 13 in the platen 3 with a supply conduit 9 connected via a pressure-limiting valve 12 and a proportional valve 15 with a supply 17 of fluid, here air, under relatively high pressure.

FIG. 2, where reference numerals identical to those of FIG. 1 but with primes are used for structurally and/or functionally identical parts, shows how an upper die 2′ can be carried on a plate 5′ that is fixed as indicated at 18, or that can also be movable by its own actuator.

Both of the supply lines 9 and 9′, in which the fluid pressure is identical to that in the respective bladders 10 and 10′, are connected to respective pressure sensors 14 and 14′ in turn connected to a controller 16 that also operates the valves 12, 12′, 15, and 15′. This controller 16 therefore maintains a perfectly uniform and relatively low pressure in both of the bladders 10 and 10′, which can be subdivided into individually pressurizable compartments as indicated at 19 in FIG. 1.

Thus even through the actuator 4 is dimensioned to shift the relatively massive structure constituted by the die 2, platen 3, and actuating element 5 with considerable force, the actual pressure that the dies 2 and 2′ will bring to bear on a pair of foils F₁ and F₂ passing horizontally in steps in a direction D through the press 1 is determined by the pressure in the bladders 10 and/or 10′. As a result it is not necessary to provide an extraordinarily sensitive and complex control system for the actuator 4, and it is also not essential to perfectly align the dies 2 and 2′ so they close in perfect parallelism. Instead a simple pneumatic pressure-control system limits the pressure the dies 1 and 2′ will apply to the workpiece formed by the foils F₁ and F₂.

Claims

1. A press comprising:

upper and lower dies;

an actuating element spaced vertically from one of the dies;

a platen carrying the one die and between the element and the one die;

a membrane defining a closed chamber having one side operatively bearing vertically on the platen and an opposite side bearing vertically on the element;

supply means for pressurizing the chamber and maintaining in the chamber a predetermined pressure; and

drive means including an actuator connected to the element for vertically displacing the element, platen, and one die.

2. The press defined in claim 1 wherein the platen and element together form a compartment holding the membrane.

3. The press defined in claim 2 wherein the platen is provided with guide bars in which the element is vertically slidable.

4. The press defined in claim 2 wherein the platen is formed with a cavity open toward the element and holding the membrane.

5. The press defined in claim 1 wherein the supply means pressurizes the chamber with a gas.

6. The press defined in claim 5 wherein the membrane forms a bladder.

7. The press defined in claim 1, further comprising:

a source of fluid under pressure;

a valve between the source and the chamber; and

control means connected to the valve and including a sensor connected to the chamber for determining a pressure therein for operating the valve according to a sensed pressure for maintaining the predetermined pressure in the chamber.

8. The press defined in claim 7 wherein the valve includes a pressure-reducing valve.

9. The press defined in claim 7 wherein the valve includes a proportional valve.

10. The press defined in claim 1 wherein the chamber is subdivided into a plurality of individually controllable compartments.

11. The press defined in claim 1, further comprising

a second actuating element spaced vertically from the other of the dies;

a second platen carrying the other die and between the second element and the other die; and

a second membrane defining a closed chamber having one side operatively bearing vertically on the second platen and an opposite side bearing vertically on the second element, the supply means also pressurizing the second membrane.

12. The press defined in claim 1 wherein the supply means maintains in the chamber a substantially constant pressure regardless of a vertical position of the one die and element.