Development of the active spatial rolling contact pair to generate the specified trajectory

Linkage mechanisms with 1 DOF composed of only lower pairs cannot generate the specified motion completely because of severe kinematic limitation of lower pairs. In order to relax the kinematic limitation and to generate the specified spatial trajectory completely, the authors have proposed the spatial rolling contact pair (SRCP), where two links in contact at a line roll relatively with generating the specified relative spatial trajectory completely, as a novel kinematic pair used for a spatial-path generator with 1 DOF. However, since it is a passive kinematic pair, it must be used in a closed-loop mechanism. Thus, the spatial-path generator with the SRCP cannot be simplified enough. In this paper, the ”active” spatial rolling contact pair (ASRCP), which is driven by several active elastic elements such as flexible linear actuators, is developed to achieve a simple spatial-path generator. Firstly, a design method to optimally arrange active elastic elements between two links of the SRCP based on a transmission index is proposed. Here, a method to use more than the minimum number of active elastic elements which are required to constitute force-closure state is described to design the ASRCP in order to achieve sufficient motion range. Besides, a control method of the ASRCP to generate the ideal rolling motion is proposed, where actuation forces of active elastic elements to get high stability between the links are calculated with the use of the actuation redundancy. As examples, the ASRCP driven with reeled-wires and the ASRCP driven with fluid-driven artificial muscles are designed and prototyped. Then, they are controlled with the proposed method, and their performances are investigated through motion capture experiments.