A Proposal for Torque Reference Control of a Stepping Motor in Soft Actuation

Abstract

A torque reference control scheme for stepping motor is proposed in conjunction with the soft actuation where passive softness due to step failure and inherent position/velocity controllability can be achieved selectively. It is easily expected that the motor torque will be adjusted by the motor current, when the torque angle, the rotor angle with respect to load free stable position, is well stabilized by the innermost control loop of the soft actuation. In regular full step operation, however, the step angle is somewhat bigger to provide sufficient resolution in the torque angle. To improve torque angle controllability, a micro-step driving method is introduced into the soft actuation scheme. Performances of proposed torque reference operation regime is demonstrated by contact force measurements and constant torque indicial responses with a direct drive manipulator.