Counterbalance actuator

Abstract: A counterbalance actuator is disclosed for reducing the energy required in weight lifting operations. The counterbalance actuator includes a piston (20) and a flexible bellows (32) attached to the piston. A bellows extension (40) is attached to the top of the bellows with a gas impervious seal. The bellows extension (40) permits the counterbalance actuator to achieve an extended stroke while allowing the counterbalance actuator to be collapsed to a reduced size.

Description: This invention relates to gas actuated air springs. Counterbalance devices are used in weight lifting operations to oppose the load due to gravity. For example, U.S. patent no. 4,600,095 of July 15, 1986, the teachings of which are incorporated herein by reference, shows a mechanical press which has an elevated welding station. A lift mechanism is disposed below a conveyor passing beneath the welding station. The lift mechanism is designed to elevate a platen with a straight line vertical motion to place a workpiece carried to the station on the conveyor into contact with the welding guns in the welding station. In such operation, the lift mechanism used to move the platen to place the workpiece in contact with the welding guns must accelerate to a relatively high velocity and then decrease to a near zero velocity at the end of each multiple stage stroke so that the workpiece is gently engaged against the welding guns, and thereafter gently deposited back on the conveyor. The workpiece may be raised and lowered through a distance of approximately 60.96 cm (24 inches) at a relatively rapid rate of one to two seconds. A counterbalance is used to reduce, usually by 85 percent or more, the power required to rapidly move the load which, without a counterbalance, would require substantially increased energy. One form of counterbalance frequently utilized is an air spring, which comprises a flexible rubber-fabric bellows having a column of compressed air within the bellows. The air spring provides a source of potential energy which may be utilized to counteract gravity acting on the platen. The platen may be moved toward and away form the work station, for example toward and away from the welding guns, by a lift mechanism such as that described in the aforementioned U.S. Patent No. 4,600,095. Air springs which have found use in such applications are manufactured, for example, by Firestone Industrial Products Co., of Noblesville, Indiana. Typical commercially available air springs have a useful stroke of approximately three to eighteen inches. When an extended stroke is required, the air springs must be stacked on top of one another to increase the stroke without degrading their weight carrying ability. However, the foregoing arrangement requires that the stacked air springs be joined together by a canter plate, for example, in the manner shown on page sixteen of the Firestone catalog number DAM-a or in U.S. Patent No. 4,825,681. Additionally, the plates connecting the air springs may be required to be guided by the use of vertical bars or rails, to insure accurate vertical motion of the plates connecting the air springs together. While the guidance rods used in stacked air spring applications help maintain stability, they require additional components and accurate alignment to insure that the stroke provided by the stacked air springs operate in a vertical column. Additionally, in some application's it is impractical to use vertical guide bars due to space limitations. Finally, stacked air springs may simply not provide a relatively constant force over an extended travel distance required for some industrial applications. Another possible way of increasing the stroke of an air spring is to increase the vertical height of the rubber-fabric bellows. However, bellows having substantially larger vertical dimensions can become slender and unstable with respect to its diameter, thereby risking catastrophic failure due to buckling. Also, increasing the vertical height of the rubber-fabric bellows often exceeds the capacities of existing forming equipment. New equipment to extend capacities is prohibitively expensive for all but the highest volume applications. Consequently, there is a need to increase the stroke of an air spring or counterbalance actuator while not adversely affecting the costs or mechanical stability. US-A-1414635 also shows a lift mechanism in the form of a pneumatic ram using as its drive means a pneumatically pressurized space defined by a flexible tube having its lower end region sealingly connected to the upper end region of a cylindrical tube. The flexible tube can fold into and be extended from the cylindrical tube as the pressure is reduced and increased, respectively. Telescopic aligning and guiding means are provided to support the drive means. According to the present invention there is provided a lift mechanism comprising a base, a moveable platen drive means coupled between the base and the platent for raising the platen with respect to the base, and, in addition to the drive means, a counterbalance actuator to counteract the weight of the platen, the counterbalance actuator comprising means defining an enclosed, expandable, space and means for introducing gas under pressure into the space, the lift mechanism being characterised in that the defining means of an enclosed expandable space of the counterbalance actuator comprises an upper and a lower hollow member, having substantially rigid sidewalls, joined by a flexible tube with the lower end region of the tube being sealingly connected to the upper end region of the lower member and with the upper end region of the tube being sealingly connected to the lower end region of the upper member, such that, in going to a retracted condition of the actuator, one of the members surrounds the other with the flexible tube folded therebetween. It will be appreciated that, without the upper member or bellows extension, in a retracted condition the flexible tube would be folded approximately in half and the maximum extension would thus be approximately one half of the axial length of the tube. By virtue of the upper member or bellows extension a lower fully retracted condition is achievable thus allowing the actuator to be designed to have an extension equal to a major portion of the axial length of the tube. As the axial length of the flexible tube is thus shorter than it would otherwise be to achieve a given extension, it is possible to avoid guides that have heretofore been required to provide support in the case of larger extensions. Thus, embodiments of the invention may provide a counterbalance actuator having an extended stroke while being able to provide sufficient potential energy for use in industrial manufacturing applications and, in particular, in automotive or truck assembly applications. Embodiments of the invention may provide a counterbalance actuator having an extended stroke capability which can be easily manufactured using existing bellows forming equipment. Embodiments of the invention may also provide a counterbalance actuator having an extended stroke capability which can fit in the space occupied by an air spring with a smaller overall vertical stroke. In an embodiment of the invention, the lower end of the tube or flexible bellows is fastened with an airtight seal to the lower member to allow air to be trapped under pressure within the lower member and bellows combination and retained therein. The upper end of the flexible bellows is fastened to the upper member which is a bellows extension which comprises a rigid tube having a stiff side wall and an end plate. The lower end of the bellows extension is open and is sealingly attached to the top end of the flexible bellows to provide an airtight seal between the bellows extension and the bellows. The diameter of the bellows extension is made sufficiently greater than the diameter of the lower member to permit the bellows extension to fit around the lower member when air is bled out of the bellows and to allow the flexible wall of the bellows to reside between the lower member and the wall of the bellows extension. The lower member, bellows extension and flexible bellows thereby exhibit a "telescoping effect" when air is removed from the bellows to allow the bellows extension to collapse onto the lower member. For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, wherein: Fig. 1 is a side view of a lift mechanism having a platen; Fig. 2 is a side view in section showing a counterbalance actuator; and Fig. 3 is a side view of a lift mechanism similar to that show in Fig. 1 showing the counterbalance actuator positioned beneath a platen and the lift mechanism used to move the platen from a lowered position to a raised position. Fig. 1 shows a welding press 10 to which embodiments of the disclosed invention may be advantageously applied. The welding press 10 includes a lifting table 12 having a platen 14 (shown in raised and lowered positions) for supporting a workpiece. Welding guns and tooling (not shown) may be secured on and above the platen 14 to perform welding operations on a workpiece (not shown) that is moved onto the platen 14 in a manner well known in the field of assembling automobiles or other large components. A lifting mechanism (partially shown in Fig. 3) such as that disclosed in U.S. Patent No. 4,600,095 may be disposed beneath the lifting table 12 to move the platen 14 in a vertical motion toward and away from the welding guns supported above the table. As those skilled in the art of manufacturing equipment for the assembly of large, complex, objects (for example, automobiles) will appreciate, the platen and load carried by it (including any tooling used to accurately locate the load on the platen with respect to the welding guns) can be of substantial weight, for example, it is not unusual for such a mechanism together with the load and fixturing to weigh between 11 and 55 thousand kilograms (five and twenty-five thousand pounds). The energy required to move the platen and its load may be substantially decreased by utilizing one or more counterbalance actuators placed between the platen 14 and the floor 16 to counteract the force of gravity and reduce the energy required to move the platen 14 and its associated load. Fig. 2 shows a preferred embodiment of a counterbalance actuator 18 constructed in accordance with the teachings of the invention. Counterbalance actuator 18 includes piston 20 which, in the preferred embodiment shown, includes a circular piston wall 22. Piston wall 22 is connected to a base plate 24 which contains an orifice 26. Base plate 24 has fastened thereto a manifold 28 which permits air to be pumped into the counterbalance actuator 18 from a pipe 30. The counterbalance actuator 18 also includes a flexible bellows 32 constructed of a flexible material which will retain air under pressure, for example constructed from a rubber-fabric combination. The bellows fabric preferably comprises internal cords which prevent the bellows from stretching radially or longitudinally to any significant extent. For example it may be made up of four layers, an inner liner of calendered rubber, a ply of fabric reinforced rubber with its cords at an angle to the longitudinal and circumferential directions, a second ply of fabric reinforced rubber (with the cords at a specific bias angle to the other ply), and an outer cover of calendered rubber. Bellows 32 has a lower end 33 which is circular in shape and which contains a circular wire spring 34 to permit the wall 36 of the bellows to be retained to wall 22 of the piston with an air-tight seal having the wall 36 forced against a mating bead 38 on the upper extremity of cylinder wall 22 in a manner similar to that in which a tubeless tire is retained to a tire rim. The counterbalance actuator also includes a bellows extension or second, upper, rigid chamber 40 which is comprised of a side wall 42 and an end closure plate 44. The diameter "d" of the bellows extension is made sufficiently large so that it can easily slip over the piston 20 and accommodate the wall 36 of the collapsed bellows 32 when the bellows extension is collapsed around the piston 20. Side wall 42 of bellows extension 40 also includes a bead 46 at the lower extremity of the side wall 42 to receive and retain an end 47 of the wall 36 of the bellows 32. Preferably a circular wire spring 48 is embedded in the end 47 of the side wall 32 of the bellows 36 to engage the bead 46 of side wall 42 and to be retained against the side wall 42 in the same manner as the lower extremity of side wall 36 of the bellows is retained against the upper extremity of wall 22 of the piston 20. The piston 20, bellows 32 and bellows extension 40 form an air tight chamber which, when pressurized with air or another gas, for example, at pressure of up to 0.689 MPa (100 psi), causes an extension of the counterbalance actuator 18 from the collapsed condition shown in Fig. 2 to a condition shown in Fig. 3 where the fully extended bellows permits the bellows extension 40 to be fully extended above the piston 20. Each counterbalance actuator 18 used to counterbalance the weight or effect of gravity on the moveable platen 14 is connected via a pipe 28 and manifold 30 to one or more pressurized air accumulators or surge tanks 51 having a fixed volume. The accumulators have sufficient volume so that as the platen 14 is moved up and down, thereby causing a cyclical change in the air pressure in the counterbalance actuator 18, the pressure of the air contained in the system does not change dramatically due to variations in the effective volume of the combination of the accumulators and the counterbalance actuators connected thereto. For example, the volume of the accumulators should be ten or more times the volume of the counterbalance actuator connected to it. In addition, a source of makeup air may also be connected to the accumulators and counterbalance actuators through an air pressure regulating device to provide a source of additional air to replace any air which may leak from the system, for example from the seals between the bellows extension 36 and the bellows 28 or the seal between the piston 20 and the bellows 28 or from pipe joints in the system. Fig. 3 shows a lift mechanism to which the teachings of the invention may be applied. Platen 14 may be moved from its lower position, for example position 14a, to its raised position, for example 14b, by the use of a cycloidal motion to a pair of cycloidal linkages 74. The cycloidal mechanism controls motions of the cycloidal linkages 74 as taught by U.S. patent no. 4,075,911 which is owned by the owner of the present invention, and the teachings of which are incorporated herein by reference. Counterbalance actuator 76 includes a piston 78 which is connected to an air accumulator (not shown) through an air inlet 80 to provide a constant pressurized supply of air for piston 78. The piston end 78 of the counterbalance actuator is rigidly fastened to the base of the lift mechanism while the bellows extension 82 is fastened to the platen 14. The counterbalance actuator 76 may have a stroke of approximately 60.96 cm (24 inches) to support motion of the platen through a travel distance of 60.96 cm (24 inches) from its lowered to its raised position. As shown in position 82a the bellows extension 82 may assume a collapsed position roughly enclosing the piston 78 when the platen 14 is lowered by the cycloidal drive mechanism. The counterbalance actuator will assume the extended telescoped position 82b when the drive mechanism moves the platen 14 to the position 14b. Construction of the counterbalance actuator with a bellows extension 82 as shown in Fig. 3 permits an extended stroke without requiring an excessively long bellows, while still permitting the counterbalance actuator to augment the vertical motion imparted into the platen by the drive mechanism. While a preferred embodiment of the invention has been shown, other variations in the invention may become evident to those skilled in the art as a result of the disclosure contained herein. For example, more than one counterbalance actuator could be used to counteract the force of gravity or inertial forces in applications where a heavy load must be supported or moved rapidly. Furthermore, while the invention has been shown as applied to a lift mechanism for use in a welding operation, it could also have advantages for other uses, for example in stamping presses.

Claims: A lift mechanism comprising a base (16), a moveable platen (14), drive means (74) coupled between the base and the platen for raising the platen with respect to the base, and, in addition to the drive means, a counterbalance actuator to counteract the weight of the platen (14), the counterbalance actuator comprising means defining an enclosed, expandable, space and means (28, 30) for introducing gas under pressure into the space, the lift mechanism being characterised in that the defining means of an enclosed expandable space of the counterbalance actuator comprises an upper and a lower hollow member (40, 20), having substantially rigid sidewalls (22, 42), joined by a flexible tube (32) with the lower end region of the tube being sealingly connected to the upper end region of the lower member and with the upper end region of the tube being sealingly connected to the lower end region of the upper member, such that, in going to a retracted condition of the actuator, one of the members surrounds the other with the flexible tube folded therebetween. A lift mechanism according to claim 1, wherein there is no axial aligning or guiding means provided within said space. A lift mechanism according to claim 2, wherein the counterbalance actuator is not laterally restrained other than by virtue of the connection of the upper and lower hollow members (20, 40) to the platen and base respectively. A lift mechanism according to any one of the preceding claims, wherein said upper hollow member (40) has a closure plate (44) forming a gas-impervious seal with the sidewall thereof and defining an end wall of said enclosed space. A lift mechanism according to claim 4, wherein the side wall and the closure plate of the upper hollow member comprise a single piece of material. A lift mechanism according to any one of the preceding claims, wherein, in said retracted condition, the upper hollow member (40) surrounds the lower hollow member (20). A lift mechanism according to any one of the preceding claims, wherein the upper and lower hollow members (40, 20) are cylindrical in shape. A lift mechanism according to any one of the preceding claims, wherein said flexible tube (32) is manufactured from a fabric-reinforced rubber material. A lift mechanism according to any one of the preceding claims, wherein the length of the flexible tube (36) is less than the length of the lower hollow tube (20). A lift mechanism according to any one of the preceding claims, wherein the length of the upper hollow member (40) is less than the length of the lower hollow member (20). A lift mechanism according to any one of the preceding claims, wherein the lower hollow member (20) is connected to a gas reservoir (51) having an accumulator tank approximately ten times greater than the volume of gas contained in the combination of the upper and lower hollow members and the flexible tube (36) when the flexible tube is fully extended above the lower hollow member. A lift mechanism according to any one of the preceding claims, wherein the flexible tube (36) comprises internal cords arranged substantially to prevent radial expansion of the tube.

Inventors: VAPHIADIS JOHN L, VAPHIADIS, JOHN L.
Applicants: WESTERN ATLAS INT INC, WESTERN ATLAS INC.
Application year: 1992
Main classification: B30B15
IPC codes: F16J3, B30B15