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# Counter Balancing System For Revolute Joint

IP.com Disclosure Number: IPCOM000048469D
Original Publication Date: 1982-Feb-01
Included in the Prior Art Database: 2005-Feb-08
Document File: 3 page(s) / 60K

IBM

## Related People

Brennemann, AE: AUTHOR [+2]

## Abstract

The off-axis loading of a rotary axis, namely, the pitch axis of a hydraulic manipulator, causes many difficulties. The geometry of the system is shown in Fig. 1A where a mass of weight "W" is attached, by an arm "R", to a shaft that is the power-driven pitch axis of the manipulator. When no torque is applied to the shaft, the weight is down; thus, the static position of R is vertical. When the shaft is rotated from the zero position. W produces a restoring torque according to the relation T(RES) equals W.R. sin phi, which is graphed in Fig. 1B. It is desirable in some instances to be able to have W remain at any position of Phi when no power is applied to the shaft from a servo system.

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Counter Balancing System For Revolute Joint

The off-axis loading of a rotary axis, namely, the pitch axis of a hydraulic manipulator, causes many difficulties. The geometry of the system is shown in Fig. 1A where a mass of weight "W" is attached, by an arm "R", to a shaft that is the power-driven pitch axis of the manipulator. When no torque is applied to the shaft, the weight is down; thus, the static position of R is vertical. When the shaft is rotated from the zero position. W produces a restoring torque according to the relation T(RES) equals W.R. sin phi, which is graphed in Fig. 1B. It is desirable in some instances to be able to have W remain at any position of Phi when no power is applied to the shaft from a servo system.

Several approaches or systems for achieving static stability will now be described. To have static stability the counter-balancing system should produce the opposite polarity torque that follows the sin Phi relation. Fig. 2 shows one approach.

In Fig. 2, a cylinder and piston produce a constant force on the horizontal bar. The bar, in turn, pushes up on the pinion, producing a torque opposite that of the weight W. By proper design of the physical parameters and air pressure, the torque can exactly counter the torque of the weight W. However, the physical implementation of this scheme is cumbersome in that the horizontal bar will tend to rotate and would have to be guided at its ends. Also, the air-pressure cylinder would need a supply hose and would add complexity to the system. It would be possible to replace the air-piston arrangement with a spring and also to prevent the bar from rotating. Fig. 3 shows a development along this line.

In Fig. 3, G1 is connected to the shaft with the off-center load and it is geared to G2 and G3, which are the same diameter. Force is applied to the bottom of the bar, and now the two pinions or rollers prevent the bar from rotating. This system can be made to exactly balance the weight W for any angle Phi if the...