Design of a novel spherical actuator using a VCM principle

Abstract

Many industrial applications require multi-DOF (degree-of-freedom) rotational motions to achieve various tar-gets. As of now, multi-DOF spherical motion are realized almost exclusively by using a separate 1-DOF motor for each axis. Each 1-DOF motor is connected by gears and links. While 1-DOF motor can provide accurate motions on a single axis, the combinations of these single-axis motors as multi-DOF devices are rather bulky and incapable. Be-cause friction and backlash exists in motion transmission mechanisms, the combined multi-DOF actuator has poor accuracy. In addition, this type of combined multi-DOF actuator system has kinematic singularities in the operation range. In order to solve these problems, several spherical actuators have been developed. Spherical actuators are capable of multi-DOF rotational motion within a single joint. For these last few decades, spherical actuator has been a popular research topic around the world because it has the advantages of compact size, high motion precision, fast response, direct driven, non-singularity in workspace and high efficiency. In addition the spherical actuator has a wide potential application: robotic wrist, elbow, and shoulder actuators; camera actuators for surveillance; manufacturing machine actuators; head ramp and side-view mirror actuators for automobile Most spherical actuators are based on the principle of electromagnetism. The three dimensional nature of the electromagnetic field distribution in almost all previous spherical actuators make their electromagnetic and dynamic behavior difficult to analyze and this has been a significant obstacle to their design optimization and servo application. Closed-loop control systems for nonlinear electromagnetic spherical actuators especially have difficulties due to a number of uncertainties involving system identification and force/torque computation. As a result, the potential advantages of employing spherical actuators have not been realized. Ther...