Spherical actuators with multiple degrees-of-freedom

There is a growing need for programmable servo-controlled high-speed actuation in multiple axes, for applications as diverse as robotic manipulators, infrared and laser tracking systems, and automated manufacturing. At present, multi-degree-of-freedom motions are realised almost exclusively by using a separate motor/actuator for each axis, which results in relatively complicated and heavy transmission systems. This inevitably compromises the dynamic performance and servo-tracking accuracy, due to the combined effects of inertia backlash, nonlinear friction, and elastic deformation of gears. Actuators with multiple degrees-of-freedom should alleviate these problems, whilst being lighter and more efficient. However, although they have been the subject of research for several decades, and numerous concepts have been proposed, their application potential has not been realised, probably due to the complexity of their structure and related difficulties in modelling their electromagnetic behaviour and optimising their design. This paper describes two new forms of spherical actuator, and highlights the key design and operational issues.