Self-adjusting load balancing pneumatic hoist

Abstract

The present invention is directed to a pneumatic hoist incorporating a load balancing system whereby a load supported by the hoist may be vertically repositioned by applying a relatively small force against the load in the direction of desired movement. The load balancing system utilizes a pressure regulator which is capable of continuously maintaining the pressure in the hoist to equal a reference pressure automatically established as required to balance the load and sealed in a pilot chamber of the regulator to provide for the vertical displacement of the load in response to a relatively small force applied in the direction of the desired movement.

Government Interests

The present invention relates generally to a pneumatic hoist, and more particularly to a load balancing system for such a pneumatic hoist wherein the load supported by the hoist may be vertically displaced by applying a relatively light force to the load. This invention was made in the course of, or under, a contract with the United States Atomic Energy Commission.

Description

In the fabrication of relatively heavy and complex equipment such as nuclear reactors or in the loading of heavy workpieces in precision metal working machines, there is often a need to follow meticulous handling procedures to effect the desired assembly without damage. The weight of many of these components or workpieces necessitates the use of lifting mechanisms for setting them into their desired position. However, due to inaccurate control of lifting mechanisms, the components are often damaged during the assembly. Efforts to obviate or minimize structural damage to components include the use of pneumatic hoists which substantially overcome many of the problems attendant with the use of other types of hoists. However, it was found that the commercially available pneumatic hoists did not accurately respond to the light force desired for moving a workpiece small distances and lacked the means of being easily and readily adjusted to the precise weight of each load handled. In fact, most of the commercially available pneumatic hoists required that in order to move a load from a fixed position to a new position, the volume of air in the hoist must be increased or decreased by manually operating a valve separate from the hoist. With the load balanced against the pressure on the piston in a fixed position in order to move the piston and the load attached thereon, the operator must operate suitable valving to overcome the pressure acting upon the piston. In some of the more advanced pneumatic hoists, the air pressure applied to the piston is controlled by throttling an orifice or bleeding an aperture, or by manually adjusting a regulator. These previously available hoists were not found to supply satisfactory solutions for providing the required ease of handling and resisting the forces of impact upon the components or workpieces being assembled.

Accordingly, it is the primary aim or goal of the present invention to provide a pneumatic hoist with a control system wherein the lifting force of the hoist is automatically adjusted to the load and by applying a relatively small force on the load in the desired direction to move the load to the desired location without impact. In other words, with the present invention, a heavy load supported by the hoist may be vertically displaced by a single operator in much the same manner as if the load was of a weight easily supported by the operator. To achieve this objective the pneumatic hoist employs a load balancing system in which the hoist is coupled to a pressure regulator through suitable valving wherein the regulator utilizes a reference pressure automatically set to that corresponding to the pressure required to freely support the load in an initial position and is capable of continuously maintaining the pressure in the hoist to this reference pressure when externally applied forces upon the load change the pressure in the hoist. This capability for automatically setting and maintaining the pressure in the hoist to maintain a continuous balance of the load is especially useful for significantly reducing forces of impact encountered during handling operations and for providing exact alignment of mating parts.

Other and further objects of the invention will be obvious upon an understanding of the illustrative embodiment about to be described, or will be indicated in the appended claims, and various advantages not referred to herein will occur to one skilled in the art upon employment of the invention in practice.

In the accompanying drawing, the figure is a schematic diagram of the pneumatic hoist and control system of the present invention.

A preferred embodiment of the invention has been chosen for the purpose of illustration and description. The preferred embodiment illustrated is not intended to be exhaustive or to limit the invention to the precise form disclosed. It is chosen and described in order to best explain the principles of the invention and their application in practical use to thereby enable others skilled in the art to best utilize the invention in various embodiments and modifications as are best adapted to the particular use contemplated.

Described generally, the present invention is an improved pneumatic hoist of the type using air in a compression chamber formed by a piston in a cylinder for supporting a load attached to the piston, wherein the improvement comprises a pressure regulator containing a reference pressure chamber and a regulator chamber separated from one another by a movable diaphragm-like structure. This structure is interlinked with an atmospheric vent and a compressed air supply for changing the pressure in the regulator chamber in response to movement of the structure until the pressure in all three chambers is balanced. Valve means are used for selectively interconnecting the reference pressure chamber and the regulator chamber with the compression chamber in the hoist so as to first equalize the loadsupporting pressure in the compression chamber with the pressure in the reference pressure chamber and thereafter isolate the pressure in the reference chamber and connecting the compression chamber with the regulator chamber. Pressure changes in the compression chamber, resulting from the application of an external force on the load, move the diaphragm-mounted piston to either vent air from or receive air into the regulator chamber until the pressure in the compression chamber is equal to the pressure in the reference pressure chamber. This capability of maintaining the proper continuous pressure in the compression chamber provides the desired continuous balanced support of the load.

Described in greater detail and with reference to the accompanying drawing, the pneumatic hoist is generally shown at 10 supporting a load 12 with the primary lifting support provided by a crane 14 attached to the hoist. The pneumatic hoist is shown comprising a cylinder 16 containing a movable piston 18 therein with a piston rod 20 affixed to the piston 18 and the load 12 whereby vertical displacement of the piston 18 moves the load. The support of the load is provided by air pressure acting upon the piston from within a compression chamber 21 defined by the piston and cylinder. To assure minimal air leakage from chamber 21, seals 22 and 24 are provided about the piston rod and the piston, respectively. A vent 26 is provided through the cylinder wall on the side of the piston opposite chamber 21 to equalize the pressure in the upper part of the cylinder with the surrounding ambient pressure as the volume of the cylinder changes with relocation of the piston. Of course, if desired, by merely inverting the arrangement shown, the piston rod may be coupled to the crane and the cylinder may be coupled to the load.

The control system for automatically setting and maintaining the air pressure for supporting the load 12 and for maintaining that pressure as the load 12 moves in response to the application of an externally applied force by a human operator or human controlled mechanism is shown comprising a regulator 28 and attendant valves and conduits which will be discussed below. The regulator 28 comprises a housing 30 containing a diaphragm-like piston 32 therein which divides the housing 30 into chambers 34 and 36. The piston 32 is provided with a passageway 38 which communicates with the chamber 34 and atmosphere. The chambers in housing 30 are placed in registry with chamber 21 of the hoist by a conduit 40, a two-way selector valve 42, and conduits 44 and 46 which communicate with chambers 34 and 36 of housing 30, respectively. The chamber 34 is also connected to a compressed air supply 48 through a conduit 50. Chamber 34 contains a valve means 52 which adjusts the pressure therein by either bleeding air from the chamber through passageway 38 or by allowing pressurized fluid from air source 48 to enter chamber 34 through conduit 50. This valve means 52 is shown comprising a ball 54 in contact with the opening of passageway 38 in piston 32 and a ball 56 in valve 57 that is in contact with and seals the opening of conduit 50 in chamber 34. The balls 54 and 56 are interconnected by a rod 58 and are normally held by bias spring 60 in positions which close passageway 38 and conduit 50, as shown, so that both passageways are sealed when the pressures on both sides of piston 32 are equalized or are discreetly opened as these pressures differ. In order to provide the hoist 10 with the mass of pressurized air necessary to initially support the load 12, a conduit 62 is connected between the compressed air supply 48 and compression chamber 21 in the hoist 10 which contains a valve 64 for controlling the flow of air to chamber 21. With piston 18 at its low position valve 64 is held in the open position, the compressed air passes through conduit 62 into chamber 21 until the piston 18 moves in an upward direction to suspend the load 12. When the load is in the desired vertical position, that is with piston 18 out of contact with valve 64, the valve 64 is closed to terminate the flow of air into chamber 21. During this flow of air into chamber 21, the valve 42 is in a position which blocks communication between chambers 34 and 21 and simultaneously places chamber 36 in registry with chamber 21 so as to equalize or balance the pressure of the air in chamber 36 with that in chamber 21. Also, as the air flows into chamber 36 via conduits 40 and 46, the piston 32 is displaced or flexed downwardly to move ball 56 off its seat so as to allow compressed air to flow into chamber 34 until the pressures in chambers 34 and 36 are balanced. With the load supported by the air pressure against piston 18, the valve 42 is repositioned so as to place chamber 34 in registry with the chamber 21 of the hoist via conduits 40 and 44. This movement of the valve isolates chamber 36 so as to maintain the pressure therein as a reference pressure corresponding to the pressure of air necessary for the hoist to support the load.

In operation, with valve 42 placing the chambers 21 and 34 in registry, application of a force against the load 12 in a vertical upward direction by a human operator will slightly move the piston 18 upwardly so as to decrease the air pressure in both chamber 21 of the hoist 10 and chamber 34 of regulator 28. This decrease in air pressure will cause the piston 32 to be flexed downwardly due to the greater pressure of the air in chamber 36. This downward movement of the piston moves ball 56 off its seat so as to place the chamber 34 in communication with the air supply 48. With this communication established, pressurized air enters chambers 34 and 21 until the load change is removed and the pressure in chamber 34 is again balanced with chamber 36 so as to return piston 32 to its initial position where ball 56 again seals conduit 50. The admittance of the pressurized fluid to chamber 21 during this vertical movement of the load allows piston 18 and the load to be placed in a new position indicative of the forces applied by the operator against the load. Alternatively, a downwardly directed force applied by the operator against the load 12 causes the air pressure in chambers 21 and 34 to be increased to a pressure greater than the reference pressure in chamber 36 so as to move the piston 32 in an upward direction and thereby pulling the piston 32 away from the ball 54 for opening passageway 38 to atmosphere. With this opening established, the air pressure in chambers 21 and 34 is decreased until the load change is removed and with the pressures in chambers 34 and 36 again in balance, the piston 32 is returned to its initial position by the action of the pressure in chamber 36. The weight of the supported load may be easily determined by monitoring the pressure in the chamber 21 by employing a simple air pressure gage calibrated in the desired weight units as shown at 66 in conduit 40.

In the event a predetermined constant force is desired to be applied by the hoist, the mass of air necessary to provide this force may be admitted into chamber 21 through a conduit 68 coupling this chamber with the air supply 48 while valve 42 is maintained in position to connect chambers 21 and 36. A valve 70 in conduit 68 is selectively operable for providing this load lifting force against the piston 18.

When the load 12 is placed in its desired position and the hoist is no longer required for supporting the load, the pressure within chamber 21 of the hoist is released by the action of regulator 28 when the pressure in chamber 36 is reduced to that of the atmosphere by the operation of valve 72 in conduit 74 which is connected to chamber 36 via conduit 46.

It will be seen that the present invention provides a unique control over the movement and control of relatively heavy loads by continuously supporting the load and allowing its position and speed of movement to be in response to a low effort command of the operator. The only contact force between the load and its support is the applied force used by the operator to move the load. The air pressure required for the operation of the subject invention may be about 100 psig with the consumption of air being dependent upon the weight of the load being lifted. For example, air consumption has been measured at less than 10 standard cubic feet per hour (scfh) while holding a 1500 pound load in a balanced position. The instantaneous demand for a few seconds required to establish a balanced condition is about 125 scfh. The air requirements for balancing the load and for lifting a load are higher than that required for maintaining the system in a balanced condition. The amount of air required is also dependent upon weight of the load being lifted. Of course, as described above, no air flow from the compressed air supply is employed during load descent. As an example of the relatively light forces required of the human operator for vertically displacing a supported load, a load of 760 pounds requires an externally applied force of only about 0.75 pounds to effect movement. The velocity of travel is roughly proportional to the force applied. The externally applied force may be held for a relatively long duration to effect a substantial vertical displacement of the load or for a relatively short duration to effect a vertical displacement in the order of a fraction of an inch. The capability of this system for minimizing the forces of impact has been dramatically demonstrated by manually setting the 760-pound weight on a styrofoam cup with the cup actually limiting (without rupturing) the downward movement of the load. The lifting capabilities of the hoist of the subject invention are limited by the particular size of the hoist and attendant components so as to provide a system which may be utilized to handle loads of several tons or as low as a few pounds.

As various changes may be made in the form, construction, and arrangement of the parts herein without departing from the spirit and scope of the invention and without sacrificing any of its advantages, it is to be understood that all matter herein is to be interpreted as illustrative and not in a limiting sense.

Claims

What is claimed is:

1. A pneumatic hoist positionable between a load and load lifting mechanism for automatically maintaining the load in a selected vertical position provided upon displacing the load by exerting an externally applied force thereon and for significantly reducing the force required to effect the displacement of the load, comprising a cylinder and piston assembly with said cylinder connectable to one of said load and said lifting mechanism and said piston connectable to the other of said one of said load and said lifting mechanism, a housing, movable piston means disposed in said housing for dividing the latter into first and second chambers, a passageway in said piston means communicating with said first chamber and atmosphere, conduit means in registry with both of said chambers and further chamber on one side of said piston in said cylinder, valve means in said conduit means for selectively placing either the first or second chamber in communication with said cylinder, a further conduit means in registry with said first chamber for introducing a flow of pressurized air thereinto from a compressed air supply, and further valve means in said first chamber for regulating the flow of said air through said passageway to atmosphere and into said first chamber from said further conduit means in response to the direction of movement of said piston means with said movement being responsive to the pressure differential in said first chamber and said second chamber.

2. The pneumatic hoist claimed in claim 1, wherein an additional conduit means connects said further chamber and said compressed air supply, additional valve means are in said additional conduit means for placing said further chamber in registry with said compressed air supply for introducing compressed air into said further chamber, and wherein the first mentioned valve means places said second chamber in registry with said compressed air supply through said additional conduit means simultaneously with said further chamber.

3. The pneumatic hoist claimed in claim 2 wherein a still further conduit means connects said further chamber and said compressed air supply, and wherein valve means are disposed in said still further conduit means contiguous to said further chamber and contactable by said piston for effecting flow of compressed air through said still further conduit means into said further chamber.

4. The pneumatic hoist claimed in claim 1 wherein valve means are in registry with said second chamber for discharging compressed air therein to atmosphere.

5. The pneumatic hoist claimed in claim 1 wherein said further valve means comprises a first ball engageable with the passageway in said piston means, a second ball engageable with said further conduit means, a rod interconnecting said balls, and bias means urging both of said first ball and said second ball into an air flow inhibiting engagement with said passageway and said further conduit means, and wherein said piston operates said further valve means to selectively establish communication between said first chamber and atmosphere and said first chamber and said compressed air supply when the pressure in said first chamber is respectively greater and less than the pressure in said second chamber.