Implementation of a revolute-joint-based asymmetric Schönflies motion haptic device with redundant actuation

In this work, a revolute joint-based asymmetric Schönflies motion (SM) haptic device with 4-Degree-of-Freedom (DOF) force feedback capability is developed. The SM haptic device is composed of a redundantly actuated parallel sub-module which has translational 3-DOF output motion, a pantograph limb which takes the role of providing 1-DOF rotational output motion, and a revolute joint allowing the relative motion between them. All five DC motors without gearhead are placed on the ground by employing proper parallel transmission linkages for power transmission. The large singularity-free workspace and the improved kinematic characteristics are secured by redundantly actuating the 3-DOF sub-module. Thus, the SM haptic device has excellent features such as the unlimited 1-DOF rotational output motion, minimal friction, minimal inertia, and large dexterous workspace. Mobility analysis, kinematic modeling, singularity analysis, optimal design, and linear inertia modeling of the SM haptic device are conducted. Then a prototype with two operational modes such as gravity compensation and linear inertia compensation modes is implemented. Through friction measurements, motion tests for gravity and/or linear inertia compensation modes, and virtual wall experiments, it is confirmed that the prototype possesses minimal friction as well as good gravity and linear inertia compensation performances sufficient for the high-quality haptic device applications such as medical training, robot-assisted surgery, etc.