Bow spring/tendon actuation for low cost haptic interfaces

This paper describes a novel bow spring and tendon actuator design for a haptic interface that provides high-bandwidth force transmission to the fingers, with a large range of motion. This is combined with a low-cost stepper motor and a low-cost optical encoder, along with self-calibration and control compensation to produce a smooth force source with excellent hard virtual wall rendering capabilities. Four techniques are discussed to compensate for bow spring, friction, and ripple torques in the actuator. Experimental results quantify the achieved force rendering quality of each technique, and provide a measure of hard virtual surface rendering quality in one degree of freedom.