Multi-DOF Counterbalancing and Applications to Robots

Most robot arms use expensive motors and speed reducers to provide torques sufficient to support the robot mass and payload. If the gravitational torques due to the robot mass and/or payload can be compensated by some means, the robot would need much smaller torques for its operation, which can save energy and enables the use of cheaper actuator modules. To this end, counterbalance mechanisms (CBMs) or passive gravity compensators, which can fully or nearly compensate for the gravitational torques due to the robot mass and/or payload, have been developed so far. CBMs can be implemented by various mechanisms, such as wire-type, gear-type, and link-type mechanisms. Since most robot arms have 2 or 3 pitch joints, which are subjected to gravity, multi-DOF counterbalancing techniques are also required to fully compensate for the gravitational torques regardless of the robot’s configuration. In this chapter, the principle of CBM and multi-DOF counterbalancing are discussed in detail. In addition, some counterbalance robot arms are presented to demonstrate their performance of gravity compensation. Simulation and experimental results show that the CBMs effectively decrease the torque required to support the robot mass and payload, thus allowing the prospective use of low-cost motors and speed reducers for high performance robot arms.