Using tilt-control in non-contact manipulation systems: Development of 2-DOF tilting actuator with remote center of rotation

Abstract

Levitation systems allow delicate objects to be handled without contact by actively controlling a levitation force that suspends the object. A drawback of levitation systems for thin objects is that the lateral force can not be controlled actively and is much weaker than the levitation force. This is a problem for non-contact manipulation systems as the object may loose its alignment with the levitator (and drop) because of the inertial forces coming from the lateral accelerations. In earlier work, a solution was proposed using Tilt Control in which lateral accelerations are compensated by the levitation force by tilting both the object and the levitator. This concept has been verified in an experimental setup that was capable of tilting around only one axis. In this paper, a new and unique design is presented of a tilting actuator that is capable of rotating around two axis, so that full 3D-space manipulation is possible. A key aspect of the Tilt Control strategy is that the center of rotation is at the center of mass of the levitated object and, for the tilting actuator, this means that it should have a remote center of rotation. A spherical cap or dome-shaped structure supported by three ball bearings, is used as the fundamental principle for the tilting actuator design as it has a natural remote center. The design and realization of this tilting actuator are described in this paper and a pilot experiment was carried out in which the tilting actuator, with a magnetic levitator installed, was attached to a linear motor. The results showed successful tilting action as relative lateral motion of the levitated object were significantly reduced on two axis.