Co-actuation: Achieve High Stiffness and Low Inertia in Force Feedback Device

Achieving high stiffness, low inertia and friction is a big challenge in the design of a haptic device. Admittance display is a common solution to obtain high stiffness but is difficult to achieve low inertia and friction. We describe a new concept of co-actuation to overcome this difficulty. The co-actuation approach disconnects the actuators and joints of a haptic device, making the two components work cooperatively according to characteristics of simulated environment. In free space, the joints are tracked and followed by the actuators. Users can move the joints freely without feeling resistance from the actuators. In constraint space, physical constraints driven by the actuators apply impedance to the joints. By producing a direct physical contact between the joints and the physical constraints, users can feel a hard virtual surface. The paper describes the mechanical and control design and implementation of a one degree-of-freedom DOF co-actuation module. Stiffness of 40i?źN/mm and friction force of less than 0.3i?źN was achieved on the module. By effectively reducing inertia and friction, the proposed approach demonstrates its potential advantage over conventional admittance displays. The co-actuation approach can be applied to multi-DOF haptic devices to achieve high stiffness, low inertia and friction.