Control Moment Gyros as Space-Robotics Actuators

摘要

Control moment gyros (CMGs) are an energy-efficient means of reactionless actuation. CMGs operate by gimbaling a high-speed rotor to change the momentum of a base body. We investigate a robotic linkage actuated by scissored-pair CMGs. Scissored pairs constrain the output torque from the CMGs to act along the joint axis, eliminating undesirable gyroscopic reaction torques. This work compares the energy required to actuate a robotic linkage with either CMGs or direct drive motors. We show that the CMG power is equal to the direct-drive power for a large range of gimbal inertias and peak gimbal angles. The transverse rate does not independently affect this result. We find that the scissored pair’s peak gimbal rate is a ratio of body acceleration to body rate. The equations of motion for an n-link robot with CMGs are presented in a recursive form for easy implementation in software. The results for a one-link robot extend easily to two-link robots with orthogonal joint axes when the peak body rate and peak gimbal angle are adjusted to account for the influence of neighboring links. CMGs surprisingly outperform direct drive for a two-link robot with parallel joint axes when the joints rotate with opposite sign, as in reaching tasks; although the reverse is true when the joints act in unison. These differences arise because CMGs produce body torques with a zero-torque boundary condition at the joint, whereas direct drive produces joint torques. I.