A Novel Torque Sensing Approach to Eliminate Stiction in Haptic Devices with Hybrid Motor/Brake Actuation

Hybrid haptic devices combining brakes and motors enable precise force rendering in applications spanning teleoperation to virtual reality simulation. Brakes can provide a strong resistance to motion, while motors can simulate interactions with elastic or animated elements. However, a common issue arises when the user pushes against an elastic element and reverses motion. Upon reversal, the actuator must apply a force in the direction of the user’s motion. Since brakes can only oppose a force, they instead resist the user, creating an unwanted resistance known as stiction. Solutions to this problem often involve bulky rotary torque sensors or imprecise strain gauges to detect the user-applied force and deactivate the brake accordingly. However, these solutions introduce substantial inertia and friction to the actuator, are expensive, and not suitable for portable devices.This paper introduces a novel torque sensing approach that embeds a miniature 1-DOF force sensor in a rotary hybrid actuator without adding any inertia or friction. A new control algorithm is proposed to determine an optimal partition of a virtual environment torque between the brake and motor, and disengage the brake before stiction occurs. The proposed approach is validated through a series of experimental testing on a 1-DOF hybrid actuator prototype. The results show that proposed approach successfully eliminates stiction while preventing oscillations around zero velocity. Compared to conventional instrumentation methods, this implementation offers a more costeffective, compact, and reliable alternative to the design and control of hybrid actuators.