LAUSR

A two-degrees-of-freedom spherical parallel link mechanism (2-DOF SPM) was designed to ensure that it only has rotational degrees of freedom in two directions around a fixed center. In general, 2-DOF SPM includes passive rotating pairs, and at least two actuators are needed to change the end-effector posture. The arrangement of the links and pairs determines the characteristics and performance of SPM, so 2-DOF SPMs were designed considering various requirements, such as output torque, accuracy, and space constraints for applications. To satisfy these requirements, arc prismatic pairs can be used in SPMs. In order to use in SPMs, as for arc prismatic pairs, the concrete configuration and design methods for arc prismatic pairs have been studied. Furthermore, in order to compensate for the influence of friction on the positioning error, the control model considering the friction has been proposed by constructing a feedback loop containing experimentally found parameters. However, the conventional model is not a mechanical model of friction. Therefore, it is not suitable for calculating the friction force and understanding how the limit of the workspace changes due to the influence of friction. In this study, we construct a mechanical friction model considering the intersection angle change between the input and the rail slide direction. In addition, using the friction model, we clarify the influences of friction on the workspace and driving the SPM to realize high-performance 2-DOF SPM. First, we theoretically clarified the influence of friction on the workspace by considering the case of a slider-type differential-drive 2-DOF SPM. Second, the driving torque was experimentally measured, and the influence of friction on driving was examined.