Wave haptics: Building stiff controllers from the natural motor dynamics

Haptics, like the fields of robotics and motion control, relies on high stiffness position control of electric motors. Traditionally, DC motors arc driven by current amplifiers designed to hide their electrical dynamics. Meanwhile encoder-based position feedback creates virtual springs. Unfortunately this cancellation-replacement approach experiences performance limits due to sensor quantization, discretization, and amplifier bandwidths. An alternate approach is presented, noting the inherent inductor-resistor dynamics of the motor arc beneficial to the haptic task. Two main insights are followed, which may be utilized independently or preferably in combination. First, the electrical inductance L can serve as a stiffness, providing a natural sensorless coupling between the virtual environment and the user. Second, the electrical resistance R can create a natural wave transformation, providing a robust computer interface between the discrete and continuous time domains. The resulting analog circuit implements a simple voltage drive and can achieve higher stiffiness than traditional approaches, especially in the frequency range where human users are most sensitive. A prototype 1-DOF system has been implemented and confirms the promise of this novel paradigm.