US3747886A - Load balancer with safety control - Google Patents

Abstract

A load balancer having a load support arm with a power cylinder having a piston operably connected to the arm with a control circuit including a pilot operated valve for directing pressure fluid to the cylinder to maintain a constant pressure on the cylinder piston in all positions of the load support arm with means for limiting the rate of movement of said load support arm in the event that either the load is lost or there is a loss of fluid pressure acting on said piston when there is a load on the load support arm.

Description

United States Patent "[191 Carlson et al.

[ 1 July 24, 1973 LOAD BALANCER WITH SAFETY CONTROL [51] Int. Cl 366d 1/00 [58] Field 01 Search 248/325; 91/433;

[56] References Cited 7 UNITED STATES PATENTS 3,402,911 9/1968 O'Neill 248/325 3,635,442 l/l972 Ulbing 254/168 2,939,431 6/1960 Bottje 91/433 2,901,219 8/1959 Bottje 254/168 3,307,819 3/1967 Cocito. 248/363 3,561,471 2/1971 Sands 137/460 3,434,493 3/1969 Owens 137/460 3,675,899 7/1972 McKendrick 254/168 3,259,352 7/1966 Olsen 248/325 FOREIGN PATENTS OR APPLICATIONS 1,012,460 12/1965 Great Britain 92/8 Primary Examiner-J. Franklin Foss Attorney-Hofgren, Wegner, Allen, Stellman & McCord [57] ABSTRACT A load balancer having a load support arm with a power cylinder having a piston operably connected to the arm with a control circuit including a pilot operated valve for directing pressure fluid to the cylinder to maintain a constant pressure on the cylinder piston in all positions of the load support arm with means for limiting the rate of movement of said load support arm in the event that .either the load is lost or there is a loss of fluid pressure acting on said piston when there is a load on the load support arm.

5 Claims, 4 Drawing Figures PATENTEnJumma i Z J/ I LOAD BALANCER WITH SAFETY CONTROL BACKGROUND OF THE INVENTION This invention relates to a load balancer wherein a parallelogram arm system includes a load support arm and a piston and cylinder device connected to the parallelogram arm system. A control circuit applies fluid pressure to the cylinder in an amount sufficient to balance the weight of the load in all positions of the para]- lelogram arm system, and safety controls make certain that there is no rapid rate of movement of the load sup port arm in the event that either the load is lost from the load support arm, which would result in rapid upward movement of the load support arm or there is a loss of fluid pressure acting on the cylinder which would result in a rapid rate of descent of the load support arm when carrying a load.

Load balancers are disclosed in prior patents owned by the assignee of this application. Olsen US. Pat. N 0. 3,259,351 discloses a load balancer having the basic configuration of a parallelogram arm system. A control circuit includes a pilot valve responsive to a control pressure and pressure in the cylinder acting on the parallelogram arm system for balancing a load in all positions of the parallelogram arm system. This patent does not disclose any safety control for limiting movement of the parallelogram arm system when there is a loss of load nor a safety control which becomes operative when there is a loss of pressure fluid to limit the rate of descent of the load support arm of the parallelogram arm system.

Olsen US. Pat. No. 3,259,352 discloses a load balancer with a control circuit therefor, a safety control for controlling the rate of ascent of the load support arm thereof. This safety control requires the use of a pressure piloted variable orifice valve. There is a dis closure of a control for the rate of descent of the load support arm in the event there is a loss of pressure fluid, however, this circuit requires a fixed orifice and a bypass therefor including a fluid operated valve shown particularly in FIG. 3 of the patent and adds to the complexities of the circuit. The disclosures of the aforesaid Olsen patents in their disclosure of the parallelogram arm system and the connection of a piston and cylinder thereto are incorporated herein by reference.

SUMMARY This disclosure relates to an improved load balancer having safety controls limiting the rate of movement of the parallelogram arm system and the load support arm thereof in the event of possible, but improbable, conditions arising.

An object of this invention is to provide a new and improved load balancer with safety controls limiting the rate of rise of the load support arm thereof in the event that there is either a loss of load or the control circuit therefor is rendered operative when a load is not on the load support arm and for limiting the rate of descent of the load support arm whena load is carried thereon and there is a loss of pressure fluid for the load balancer.

Another object of the invention is to provide a load balancer as defined in the preceding paragraph wherein the structure for limiting the rate of rise of the load support arm in the event a load is lost from or not present on the load support arm includes a second fluid circuit connected to the power cylinder for the load balancer with the second fluid circuit having a reservoir, a fluid line extending between the reservoir and the power cylinder, and a velocity control valve in the line permitting free fluid flow from the reservoir to the power cylinder and restricting the flow from the power cylinder to the reservoir when the flow is above a predetermined rate.

Still another object of the invention is to provide a load balancer having a parallelogram arm system including a load support arm with a power cylinder having a piston connected thereto, a control circuit for maintaining a fluid pressure acting on the piston in the cylinder, and means for limiting the rate of descent of the load support arm in the event there is a loss of fluid pressure including a velocity control valve in a fluid exhaust passage of the control circuit with the velocity control valve having a normal position to permit normal fluid flow therethrough and movable to an airflow restricting position in response to a predetermined rate of flow therethrough whereby the rate of flow from the power cylinder is limited to a value sufficient to prevent rapid downward movement of the load support arm but still permit movement thereof at a normal rate during normal operation of the load balancer.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation of the load balancer;

FIG. 2 is a schematic illustration of a fluid actuated balancer control circuit with the safety controls incorporated therein;

FIG. 3 is a vertical central section of a velocity control valve incorporated in a fluid line; and

FIG. 4 is a fragmentary section of the pilot operated valve of the primary control circuit and showing a velocity control valve mounted therein and as a central section therethrough.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT The load balancer is shown generally in FIG. 1 and includes a base member 10 which can be either a floor mounted pedestal or can be suspended from an overhead mount. The base member 10 mounts a parallelogram arm system with a first arm 15 pivotally mounted to the base member 10 by a pivot-mounting 16. A sec ond arm 20 is a load support arm and is pivoted to the first arm at a pivot pin mounting 21. A third arm of the parallelogram system 22 is pivoted to load support arm 20 by a pivot connection 23 and a fourth arm 25 is pivotally connected at 26 and 27, respectively, to the first arm 15 and the third arm 22 to complete the parallelogram arm system.

The lower end of the load support arm 20 has means for supporting a load which in the form shown is a simple hook 30. A counterweight 31 connected to an end of the first arm 15 balances the weight of the arms when not supporting a load and a power cylinder structure indicated generally at 35 is provided for balancing a load supported on the load support arm by means such as the hook 30. l

The power cylinder 35 has a piston 36 (FIG. 2) with a piston rod 37 which connects to a plate 38 which is guided for up and down movement on the base member 10 by a pair of rollers 40 and 41 secured to the base member 10 and movable within a guide slot 42 in the plate 38. The piston rod 37 is connected to the plate 38 by a pin 45. The lower end of the cylinder is connected to a bracket 46 extending from the base member at a mounting 47.

The plate 38 has a generally horizontal slot 50 which receives a roller 51 connected to and defining the pivot 27 for interconnecting the third arm 22 and fourth arm 25 of the parallelogram system whereby the power cylinder acting on the plate 38 is operatively connected to the parallelogram system. As fluid under pressure is directed to the underside of the piston 36 to exert upward force on the piston rod 37, this force acts on the roller 51 to correspondingly change the relation of the parallelogram arm system with pivoting of the first arm about the pivot 16 to lift the load support arm 20. The construction of the load balancer parallelogram arm system is shown more particularly in ONeill US. Pat. No. 3,402,911 owned by the assignee of this application. in the ONeill patent, the parallelogram arm structure is shown in more detail and it will be noted that there are a pair of the plates as plate 38 in this application in spaced apart relation with the connection of the piston rod 37 being intermediate the spaced apart plates. The ONeill patent shows the power cylinder disposed above the parallelogram arm system with the load balancer depending from an overhead support. However, the function is the same in either arrangement of the power cylinder, that is, either above or below the parallelogram arm system. Reference may be made to the ONeill patent for a more detailed disclosure of the specifics of the parallelogram arms and mounting thereof to a supporting base member 10. 1

The balancing of a load supported on the load support arm is controlled by the pressure of fluid supplied to the cylinder 35 and to the space therein beneath the piston 36. This fluid can either be hydraulic or pneumatic with the circuit being disclosed herein as a pressure air circuit. The basics of the pressure regulating circuit for the cylinder 35 are generally similar to those shown in FIG. 11 of Olsen U.S. Pat. No. 3,259,351, previously referred to. As shown particularly in FIG. 2 of this application, a line 60 is connectable to a source of fluid under pressure such as a factory air line, and extends to a pilot operated valve indicated generally at 61 having two operating positions and a center closed position. The valve is shown in the center closed position wherein the air supply line 60 is blocked and also an air exhaust line 62 leading from the valve is blocked. A third line 63 interconnecting the valve 61 and the lower side of the cylinder 35 is also blocked. When a load is engaged by the hook 30 of the load support arm 20, an operator can operate control devices located in a control box 65 at the lower end of the load support arm and which is shown in FIG. 2.

This control box includes a pair of load, no- load toggle switches 66 and 67 and a pair of load adjustment regulators 68 and 69 in the form of pressure regulating valves. These components are in parallel between a line 70 branching from the air supply line 60 and a line 71 leading to an air pilot 72 for the pilot operated valve 61. With this construction, the pressure regulating valves 68 and 69 can be set to two different air pressures when the same two different weight loads are being handled repeatedly, and then the appropriate toggle switch 66 or 67 can be operated. When there are a variety of loads of different weights then either of the pressure regulating valves 68 or 69 can be suitably adjusted. This adjustment is done visually since the in-- crease in pressure can be directed into the line 71 and pilot 7 2. It can be visually detected when the load starts to rise and this indicates the proper pressure is being supplied to the pilot 72 to balance the load. This balanced condition has resulted from supplying air to the pilot 72 to shift the pilot valve 61 upwardly from the position shown wherein a passage in the valve connects the supply line 60 to line 63 leading to the lower side of the cylinder 35 which builds up pressure and resultingly creates a force acting on the piston rod 37 to act through the parallelogram ann system. The pressure existing in line 63 is also directed to a pilot section 81 of the pilot operated valve 61 and when the pressure from cylinder 35 reaches a value equal to the pressure acting on pilot 72 there will be the same pressure on pilot 81 which will bring the pilot operated valve 61 back to the center closed position to maintain the parallelogram arm system in a desired position.

If an operator manually raises or lowers the load, this is detected by a variation in the pressure of the air on the underside of piston 36 because of a change in the size of the chamber. If the operator raises the load, piston 36 rises to lower the pressure in the lower side of the cylinder 35 which is detected by pilot 81 with a greater pressure in pilot 72 shifting the pilot operated valve 61 upwardly to direct pressure air to the cylinder 35 and bring the pilot operated valves back into balance. If the operator lowers the load, the piston 36 lowers to increase the pressure in the lower side of the cylinder which causes pilot 81 to be at a higher pressure than pilot 72 of the pilot operated valve 61 which lowers the latter valve from the position shown in FIG. 2 whereby the passage 85 in the valve connects the line 63 to the exhaust line 62 to resultingly lower the pressure in the lower side of the cylinder 35 until the air in pilots 72 and 81 is again in balance with the result that the pilot operated valve 61 returns to the center closed position.

The foregoing control circuit, although differing in detail is generally similar to that shown in the Olsen patents previously referred to herein.

The previously known control circuit has been subject to safety problems. One safety problem has arisen when a load is lost from the load support arm 20 as by falling off the hook 30. This causes a raising of the load support arm and of the piston 36 for a reduction of pressure in the lower part of the cylinder 35 which is a detection that the control valve 61 or pilot operated valve 61 should move upwardly with the result that additional air is supplied to the lower side of the cylinder which could cause a runaway condition.

The safety control provided under this condition also takes into account the possibility that the controls in control box 65 might be operated to supply pressure to the underside of the cylinder 35 when there is no load present on the load support arm 20. This would result in the same fast rate of ascent of the load support arm as when a load is lost from the arm. The safety control includes a second fluid circuit including an oil reservoir provided with a removable cover 91 having an air vent 92 and a pair of baffle plates 93 extending into the reservoir and downwardly from the underside of the cover 91. The reservoir is connected to the top side of the cylinder 35 and above the piston 36 by a line 94 which has a velocity control valve therein. This velocity control valve is located within the reservoir 90 and is shown in detail in FIG. 3. The valve includes a spool locked to a land 101 within a section of the line 92 by an annular shoulder 102 and a snap-ring 103. This valve spool has a central transverse wall 105 provided with a small opening 106 and with the wall of the valve spool having two circumferentially disposed rows of flow passage openings 107 and 108.

A movable sleeve 110 has a left-hand part thereof, as viewed in FIG. 3, surrounding a part of the spool 100 and is limited in its movement to the right by a snapring 111 positioned in a groove in a wall of the section of the line 94. The sleeve 110 is urged to a normal position shown in FIG. 3 by a spring 112 acting between a spring retainer 115 abutted against the right-hand end of the spool 100 and an aperture effectively secured to the sleeve 110 by a snapring 117 fitted into a groove in the sleeve 110. With the parts of the velocity control valve positioned as shown in FIG. 3, and with flow toward the right side of the valve being from the top of the cylinder 35, there is free flow through the internal openings of the disc 116 and snap- rings 111 and 117 with the flow being toward the left as viewed in FIG. 3. Flow is through the small opening 106 as .well as through the circumferential rows of openings 107 and 108. The disc 116 senses the rate of flow from right to left through the velocity control valve and when the force resulting from pressure drop thereacross exceeds the force of the spring 112 the sleeve 110 moves toward the left to a position indicated by a broken line 120 wherein the sleeve blocks the circumferential rows of openings108 whereby the only flow-through the valve is through the small opening 106 which limits the rate at which oil can be displaced from the upper side of the cylinder 35 and therefore limits the rate of movement of the piston 36 and the parallelogram arm system including the load support arm 20.

As the flow from right to left stops or decreases below the predetermined value set by the selection of the spring 112 the valve spring 112 will shift the sleeve 110 to the normal position shown in FIG. 3 whereby there can again be uncontrolled flow in either direction through the velocity control valve. With this velocity control valve there can be normal operation without any restriction caused by the velocity control valve, but the valve does limit the rate of flow of oil from the top of the cylinder to the reservoir to make certain that there is not a runaway rate of rise of the load balancer.

An improved control is provided for safety in the event of a pressure air loss. This safety control incorporates a velocity control valve, indicated in the schematic illustration of FIG. 2 at 130, mounted within the body of the pilot-operated valve 61. This is particularly shown in FIG. 4 wherein the body of thepilot-operated valve 61 has an air passage 131 and a chamber 132. A multi-apertured disc 133 is mounted in the chamber and is urged against a retention snap ring 134 by a spring 135 in the chamber and surrounding a part of the air passage .131. Flow from the pilot-operated valve 61 to exhaust is from right to left as viewed inFIG. 4 and in normal operation, the rate of flow is sufficiently small that the disc 133 remains in the position shown in FIG. 4 under the urging of the spring 135. As the flow increases above a predetermined rate, as set by the value of the spring 135, the pressure drop across the disc creates a force to move the disc against the urging of the spring and cause the disc to move against an end of the air passage 131. This results in blocking some of the apertures in the disc 133 andleaving only a single aperture 136 in communication with the air passage 131 whereby substantial restriction to airflow is created and air can flow from the underside of the cylinder 35 at a slow controlled flow rate. This limits the rate at which the load support arm 20 can move downwardly and prevents damage or injury from a lowering of the load balancer because of the loss of air supply. As soon as the air flow drops below the predetermined value, the spring returns thedisc 133 to position shown in FIG. 4, where it is held against the snap ring 134 and there is substantially free flow of air through the velocity control valve to permit normal adjustment movement of the load balancer under the urging of an opera- 101'.

We claim:

1. In a load balancer, a frame, a load support arm movably mounted on said frame, a power cylinder having a piston movably connected to said arm to act against a load connected to said arm, means connectable to a source of fluid under pressure for applying fluid to said cylinder, a control circuit interposed be tween said means and said cylinder, said control circuit including a pilot operated valve for directing fluid to and from said cylinder, said valve being responsive to a control fluid pressure and cylinder fluid pressure whereby an imbalance in said fluid pressures causes said valve to restore 'a balance in said pressures, and safety control means for limiting the rate of movement of said load support arm in one direction in the event the load is removed from the load support arm and in the opposite direction in the event there is a loss of fluid under pressure, including a second fluid circuit connected to said cylinder and having a reservoir with a restricted rate of fluid flow from the cylinder to the reservoir.

2. A load balancer as defined in claim 1 wherein a line connects said cylinder and reservoir and a velocity control valve in said line permitting free fluid flow from the reservoir to said power cylinder and restricting the flow from the power cylinder to said reservoir when the flow is above a predetermined rate.

3. A load balancer as defined in claim 1 wherein said last mentioned means includes an exhaust line from said pilot operated valve which receives fluid from the power cylinder, and a velocity control valve in said exhaust line for restricting said fluid flow when the flow is above a predetermined rate.

4. A load balancer comprising a base member, a generally horizontal first arm pivotally mounted to said base member for rotation about a horizontal axis; a generally vertical second arm adapted to receive a load to be hoisted and balanced by said assembly, said second arm being pivotally connected to one end of said first arm; a third arm pivotally connected to said second arm; and a fourth arm pivotally connected at one end to the other end of said first arm and at its other end to said third arm, said arms between said pivotal connections forming a parallelogram; and means for applying a generally vertical force to said third arm, said means comprising an air-actuated piston, a cylinder in which said piston is reciprocable, a pressure regulating circuit connected to said cylinder to maintain a constant pressure on the piston in all positions of said assembly, and means for limiting the rate of movement of said second arm in the event that either the load is lost or there is a loss of air pressure acting on said piston, including a fluid line connecting said reservoir to said cylinder to communicate'with the side of the piston opposite the air-actuated side, and a velocity control valve in said line permitting free fluid flow from the reservoir to said cylinder and restricting the flow from the cylinder to said reservoir when the flow is above a predetermined rate. v

5. In a load balancer, a frame, a load support arm movably mounted on said frame, a power cylinder having a piston movably connected to said arm to act against a load connected to said arm, means connectable to a source of air under pressure for applying air to said cylinder, a control circuit interposed between said means and said cylinder, said control circuit including a pilot operated valve for directing air to and from said cylinder, said valve being responsive to a control air pressure and cylinder air pressure whereby an imbalance in said air pressure causes said valve to restore a balance in said pressures, an air exhaust passage from said pilot operated valve, and a velocity control valve in said exhaust passage having a normal position to permit normal air flow and movable to an air flow restricting position in response to a predetermined rate of flow therethrough, said velocity control valve including a body with an air passage and a chamber, a multiapertured disc movable in said chamber and having a diameter greater than the air passage, spring means urging said disc away from an end of said air passage and in a direction opposite to the direction of air flow through the exhaust passage and said air passage whereby air flow above a predetermined rate will move the disc against the spring action and into engagement with the air passage to reduce the number of apertures in the disc through which air can flow.

I STATES PATENT OFFICE v CERTIFICATE OF CORRECTION- Patent No. .3 747, 886 Dated Q July 24, 1973 Itiventofls) Arthur B. Carlson and Robert W, Watson It is certified that error appears in the above-identified patent v and that said Letters Patent are hereby corrected as shown below:

in claim l, before the period, insert -when the rate of fluid flow the second fluid circuit exceeds a predetermined value-m Signed ahd sealed this 14th day of January 1975.

(SEAL) Attest= McCOY M. GIBSON JR. v c. MARSHALL DANN Attesting Officer Commissioner of Patents

Claims (5)

1. In a load balancer, a frame, a load support arm movably mounted on said frame, a power cylinder having a piston movably connected to said arm to act against a load connected to said arm, means connectable to a source of fluid under pressure for applying fluid to said cylinder, a control circuit interposed between said means and said cylinder, said control circuit including a pilot operated valve for directing fluid to and from said cylinder, said valve being responsive to a control fluid pressure and cylinder fluid pressure whereby an imbalance in said fluid pressures causes said valve to restore a balance in said pressures, and safety control means for limiting the rate of movement of said load support arm in one direction in the event the load is removed from the load support arm and in the opposite direction in the event there is a loss of fluid under pressure, including a second fluid circuit connected to said cylinder and having a reservoir with a restricted rate of fluid flow from the cylinder to the reservoir.

2. A load balancer as defined in claim 1 wherein a line connects said cylinder and reservoir and a velocity control valve in said line permitting free fluid flow from the reservoir to said power cylinder and restricting the flow from the power cylinder to said reservoir when the flow is above a predetermined rate.

3. A load balancer as defined in claim 1 wherein said last mentioned means includes an exhaust line from said pilot operated valve which receives fluid from the power cylinder, and a velocity control valve in said exhaust line for restricting said fluid flow when the flow is above a predetermined rate.

4. A load balancer comprising a base member, a generally horizontal first arm pivotally mounted to said base member for rotation about a horizontal axis; a generally vertical second arm adapted to receive a load to be hoisted and balanced by said assembly, said second arm being pivotally connected to one end of said first arm; a third arm pivotally connected to said second arm; and a fourth arm pivotally connected at one end to the other end of said first arm and at its other end to said third arm, said arms between said pivotal connections forming a parallelogram; and means for applying a generally vertical force to said third arm, said means comprising an air-actuated piston, a cylinder in which said piston is reciprocable, a pressure regulating circuit connected to said cylinder to maintain a constant pressure on the piston in all positions of said assembly, and means for limiting the rate of movement of said second arm in the event that either the load is lost or there is a loss of air pressure acting on said piston, including a fluid line connecting said reservoir to said cylinder to communicate with the side of the piston opposite the air-actuated side, and a velocity control valve in said line permitting free fluid flow from the reservoir to said cylinder and restricting the flow from the cylinder to said reservoir when the flow is above a predetermined rate.

5. In a load balancer, a frame, a load support arm movably mounted on said frame, a power cylinder having a piston movably connected to said arm to act against a load connected to said arm, means connectable to a source of air under pressure for applying air to said cylinder, a control circuit interposed between said means and said cylinder, said control circuit including a pilot operated valve for directing air to and from said cylinder, said valve being responsive to a control air pressure and cylinder air pressure whereby an imbalance in said air pressure causes said valve to restore a balance in said pressures, an air exhaust passage from said pilot operated valve, and a velocity control valve in said exhaust passage having a normal position to permit normal air flow and movable to an air flow restricting position in response to a predetermined rate of flow therethrough, said velocity control valve including a body with an air passage and a chamber, a multiapertured disc movable in said chamber and having a diameter greater than the air passage, spring means urging said disc away from an end of said air passage and in a direction opposite to the direction of air flow through the exhaust passage and said air passage whereby air flow above a predetermined rate will move the disc against the spring action and into engagement with the air passage to reduce the number of apertures in the disc through which air can flow.

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