US 3428298 A
Description (OCR text may contain errors)
Feb.'l8, 1969. a. R. POWELL 3,428,298
' TOQL BALANCER Filed Jan. 3/1966 INVENTOR. I [064? A? Pan/51.4
Feb. 18, 1969 f E. R. POWELL TOOL BALANCER Sheet of. 3
Filed Jan. 5. 1966 Y INVENTORY 5064A 2 flan/44 mm ww Ar TOAA/EVS United States Patent Claims ABSTRACT OF THE DISCLOSURE A pneumatically-operated tool balancer substantially offsets the weight of heavy tools so that they can be manipulated by an operator for extended periods without fatigue. Air pressure is used to offset the tool weight and has the principal advantage that the same amount of weight of the tool is offset regardless of the vertical position of the tool, so that the effective weight of the tool remains constant.
This invention relates to a tool 'balancer and specifically to a pneumatically-operated tool balancer.
Tool balancers are in common use for partially supporting larger tools which cannot conveniently be carried and manipulated by hand, at least for any extended period of time. Tool balancers now known employ springs to suspend the tools and partially offset the weight thereof. Even though long springs are employed in such balancers, when a tool is used in a low position, the resistance of the springs increases so that the effective weight of the tool for the operator is less. On the other hand, when the tool is raised to a higher position, the resistance afforded by the springs decreases and the effective weight of the tool is thereby more. Consequently, depending on the position, the weight of the tool constantly varies for the operator, rendering the operation more difficult and causing fatigue earlier. The long springs of the balancers also require considerable head room and maintenance. In addition, if the balancers were to be used with tools of different weights, the springs had to be replaced or changed.
The present invention provides a tool balancer which employs air or other suitable gas under pressure rather than springs. The air acts on a piston which in turn acts on a drum on which is wound a cable which supports the tool. The force resulting from the air pressure remains constant whether the tool is in a low position or a higher position so that the effective weight of the tool remains the same under all conditions. Further, if the balancer is to be used with a tool of a different weight, the air pressure employed can be easily changed to accommodate the second tool as easily as the first with the effective weight of both tools being the same. In addition, the balancer is constructed so that repairs can be made quickly with the balancer capable of being readily disassembled. The new balancer also is compact and requires little maintenance.
It is, therefore, a principal object of the invention to provide an improved tool balancer which maintains effective weight of the tool constant under all conditions.
Another object of the invention is to provide a tool balancer which consumes relatively little space.
A further object of the invention is to provide a tool balancer which can be easily regulated to accommodate tools of different weights.
Other objects and advantages of the invention will be apparent from the following detailed description of a preferred embodiment thereof, reference being made to the accompanying drawings, in which:
FIG. 1 is a view in perspective of a tool balancer according to the invention partially supporting a hand manipulated tool in an operating position;
FIG. 2 is an enlarged view in longitudinal cross section of the tool balancer shown in FIG. 1 with a cable drum and piston in one position;
FIG. 3 is a view somewhat similar to FIG. 2 with the cable drum and the piston in another position; and
FIG. 4 is a somwhat schematic view in cross section of a controller to regulate the pressure of air supplied to the balancer.
Referring more particularly to FIG. 1, a pneumaticallyoperated tool balancer according to the invention is indicated at 10 and, as shown, is suspended from an overhead support or beam 12 by a trolley 14. A large tool 16 is suspended by a hanger cable 18 from a ring 20 attached to a balancer cable 22. The tool 16 can be of various types which are too heavy for an operator to handle, at least for any extended period of time. Tools of this nature may be in the form of riveters, spot Welders, grinding machines, large drills, and buffers. Such tools frequently are used in a wide variety of positions from points down near the floor, for example, to points up around shoulder level or above.
With tool balancers of the usual spring-loaded type heretofore known, the effective weight of the tool, meaning that weight felt by the operator, is less near the floor and more at higher levels. The change in the effective weight is reduced by using a sufficiently long spring or spring design but the change nevertheless will not be completely eliminated. Even though the weight change is reduced, the longer spring design requires: much more overhead space. Further, if the tool is to be replaced by one of a different weight, considerable adjustment has heretofore been necessary to enable the balancer to accommodate the new tool.
Referring to FIGS. 2 and 3, the balancer 10 has a housing 24 which includes a central cylindrical wall or cover 26, a left end cover 28, and a right end cover 30. The cylindrical wall 26 has a large rectangular central opening 32 (FIG. 1) through which the cable 22 can pass with guide bars 34 located on the wall 26 on each side of the cable.
A ball screw 36 with a helical groove 38 extends longitudinally through the housing 24 and is afiixed to the end covers 28 and 30 by machine screws 40 and 42. The screw 42 also supports an end sleeve 44 having a recess or chamber 46 receiving a substantial right end portion of the ball screw 36. The end of the sleeve 44, in turn, is received in a shallow recess 48 of the end cover 30 to aid in positioning the sleeve in the housing.
A ball nut 50 is mounted on the ball screw 36 and is of a type known in the art. Such ball nuts are available commercially from Saginaw Steering Gear Division of General Motors Corporation, for example. The ball nut 50 contains a plurality of bearing balls which extend into the groove 38 and move along the groove as the ball nut moves in a helical path along and around the ball screw 36. The ball nut 50 has .a recess 51 at the right end thereof to be received over the sleeve 44 when the ball nut 50 is in a right hand position as shown in FIG. 3. A drum 52 is mounted on the ball nut 50 by means of a key 54 located in a drum hub 56 so that the drum rotates with the ball nut 50. An inner sleeve 58 extends beyond the hub 56 toward the right end cover 30 and receives a thrust bearing 60. The hoist drum 52 has a shallow helical groove 62 therearound for the balancer cable 22 which is affixed to the drum at the end of the helical groove.
The ball nut 50 and the drum 52 rotate as a unit around the stationary ball screw 36. When a force is applied on the cable 22, the drum 52 and the ball nut 50 move toward the right along the groove 38. On the other hand, when a thrust force is applied against the thrust bearing 60, which force is greater than the force on the cable 22, the ball nut 50 and the drum 52 move toward the left along the groove 38, rotating in the opposite direction and winding the cable on the drum. The pitch of the helical groove 38 of the ball screw 36 and the pitch of the shallow groove 62 of the drum 52 preferably are equal so that the cable, at the point at which it is wound onto or unwound from the drum, always remains stationary relative to the longitudinal extent of the balancer 10.
A pneumatic chamber 64 is formed in the right end of the housing 24 by means of a thin wall portion 66 of the cylindrical wall 26, the right end cover 30, and a power piston 68. An annular shoulder stop 70 is formed at the end of the thin wall portion 66 in the cylindrical cover 26.
The power piston 68 includes a hub 72 and an integral circular flange 74. The hub 72 has a recess 76 containing an inner O-ring 78 which provides a seal with the sleeve 44 to enable the hub 72 to move slidably along the sleeve in sealing relationship therewith. An annular mounting plate 80 is located on the side of the flange 74 opposite the power chamber 64 and is affixed to the flange 74 by a plurality of screws or fasteners 82. A flexible sealing ring 84 has an inner annular portion 86 mounted between the flange 74 and the ring 80, and a outer peripheral portion 88 located adjacent the inner surface of the chamber 64 and extends toward the right end cover 30. The mounting plate 80 extends close to the surface of the chamber 64 to back up the flexible ring 84 while the flange 74 stops short of the chamber wall to provide clearance for the leg portion 88 of the sealing ring. In this manner, an effective piston is provided for the balancer which achieves an effective seal due to the fact that air pressure in the chamber 64 urges the leg 88 against the inner surface of the chamber 64 to improve the sealing arrangement. At the same time, however, the wear on the sealing ring 84 is minimal.
In the operation of the basic balancer, when power fluid such as air is supplied through an inlet 90 of the chamber 64, it bears against the piston 68 and, when the resulting force is sufficient, the piston pushes the drum 52 to the left through the thrust bearing 60. This action tends to raise the cable and reduce the effective weight of the tool. For example, a tool having an actual weight of fifty pounds can be made to have an effective weight of four poundsby suitable adjustment of the pressure of the fluid or air in the chamber 64. Regardless of how high the tool is raised or how far it is lowered, the force of the fluid in the chamber 64 acting on the piston 68 remains constant so that the effective weight of the tool does not vary whatsoever regardless of its position.
The pressure of the fluid in the chamber 64 is regulated by a controller 92 located adjacent the inlet 90. Air is supplied from a suitable source to the controller 92 through a fitting 94 and supplied to the inlet 90 through a fitting 96. The pressure of the air is easily regulated to accommodate a tool of a particular weight by a hand knob 98. Hence, if the tool to be balanced is changed, the balancer can be readily adjusted to accommodate the new tool in a matter of a few seconds.
The controller 92 can be obtained from Lexington Controls, Inc. of Burlington, Mass, under the name Type Pressure Regulator. The controller 92, as shown more specifically in FIG. 4, includes a supply valve 100 and a relief valve 102 for controlling the pressure of the outlet gas or air. The outlet pressure applies force against a main loading diaphragm 104 with excess pressure enabling the air to escape past the valve 102 through exhaust vents 106 located in a spacer 108. The downstream air pressure also is transmitted to a control chamber 110 surrounding a capsule member 112, the interior of which communicates with the atmosphere through an adjusting stem 114. The capsule member 112 is of stainless steel and is stable under a wide variety of ambient conditions. A small movement of the capsule member 112 controls flow of air past a pilot valve 116 into a pilot chamber 118 and through a pilot restrictive vent 120. The resulting change in pressure in the pilot chamber 118, with the opening of the pilot valve 116, causes movement of a pilot diaphragm 122 which cooperates with the diaphragm 104 through the spacer 108 to operate the supply valve and the relief valve 102 to correct small errors in downstream pressure.
Various modifications of the above-described embodiment of the invention will be apparent to those skilled in the art, and its to be understood that such modifications can be made without departing from the scope of the invention, if they are within the spirit and the tenor of the accompanying claims.
1. In combination, a hand-manipulated tool which is too heavy for an operator to manipulate for long periods of time without help, a flexible cable connected to said tool so that the tool is at least partially balanced from end-to-end when supported by said cable, an overhead support, a housing supported. by said overhead support, a first and a second end cover on the ends of said housing, ball screw means extending centrally through said housing and aflixed at the ends to said end covers, a ball nut carried on said ball screw means, a cable drum mounted on said ball nut and. having a helical groove to receive the cable when wound thereon, an upper end of said cable being aflixed to said drum at an end of said groove, said ball screw means having a smooth cylindrical surface at the one end affixed to said first end cover, a piston mounted on said one end with an inner ring between said piston and said cylindrical surface, said piston comprising a central hub retaining said inner ring, an annular flange integral with said hub, an annular plate fastened to said flange, and a sealing ring held between said flange and said plate and having a peripheral portion beyond said flange and in contact with the inner surface of said housing, said peripheral portion extending toward said first end cover, said housing, said first end cover, and said piston forming a chamber of variable volume, a thrust bearing carried by said drum and located between said drum and said piston, an air controller mounted on said housing to supply air at a predetermined pressure to said chamber, said housing being free of any depending vent lines, and to vent air from the chamber to the atmosphere when the pressure exceeds the predetermined pressure, said controller having manually adjustable means for varying the pressure in the chamber to substantially offset a constant proportion of the weight of said tool for any vertical position thereof relative to said housing to provide a constant effective tool weight for the operator.
2. In combination, a hand-manipulated tool, a flexible cable connected to said tool, an overhead support, a housing supported by said overhead support, said housing being free of any depending vent lines, ball screw means extending centrally through said housing and having a smooth cylindrical surface on an end portion of said screw, a ball nut mounted on said screw, a cable drum mounted on said nut to receive the cable when wound thereon, an upper end of said cable being aflixed to said drum, a piston in said housing in sealing and slidable engagement with said cylindrical surface and. with a portion of the inner surface of said housing, bearing means located between said drum and said piston to enable relative rotation therebetween, means for supplying air to said housing on the side of said piston opposite said drum to urge said piston in the direction of said drum and for maintaining the air pressure substantially constant, and manually adjustable means for controlling the pressure to substantially offset a constant proportion of the weight of said tool for any vertical position of said tool relative to said housing,
3. The combination according to claim 2 characterized by said cylindrical end of said screw means being a sleeve and said housing having stop means at the interior surface to prevent movement of saidpiston beyond the end of said sleeve.
4. The combination according to claim 2 wherein said piston comprises a hub, an integral annular flange extending toward the inner surface of said housing, an annular flexible sealing ring mounted on said flange and having a portion extending between said flange and said housing surface in a direction away from the cable drum.
5. A tool balancer comprising a housing, a ball screw extending centrally through said housing, a ball nut mounted on said screw, a cable drum mounted on said not to receive a cable when wound thereon, piston means in said housing, bearing means between said drum and said piston to enable relative rotation therebetween, and a regulator for supplying air under substantially constant pressure to said housing on the side of said piston opposite said drum, said regulator having supply means for controlling air supplied to said chamber, a vent for venting air from said chamber to the atmosphere, means for controlling venting of the air from said chamber to said vent, means for controlling said supply means, and manually adjustable means extending externally of said regulator and said housing to regulate the: output pressure of said regulator to enable the pressure within said chamber to substantially offset, for any position, the weight of a tool to be carried by said tool balancer.
References Cited EVON C. BLUNK, Primary Examiner.
HARVEY C. HORNSBY, Assistant Examiner.
U.S. Cl. X.R.