Wave Haptics: Providing Stiff Coupling to Virtual Environments

Traditional haptic rendering creates virtual springs using DC motors with current amplifiers and encoder-based position feedback. In these schemes, quantization, discretization, and amplifier bandwidth all impose performance limits. Meanwhile the amplifiers try to cancel the motor’s electrical dynamics, though they are actually beneficial to the haptic display. We present an alternate approach that fully embraces and utilizes all electrical dynamics, following two insights. First, the electrical inductance L can serve as a stiffness, providing a natural sensor-less elastic coupling between the virtual environment and the user. Second, we take advantage of the electrical resistance R to compute, by means of analog circuitry, a wave transform. Implementing virtual objects in a wave domain provides robustness to servo delays or discretization. The resulting system requires only a simple voltage drive circuit. Built upon the motor’s physical behavior, it can outperform traditional approaches, achieving higher virtual stiffness. Encoder feedback is only required for absolute position information, with damping and velocity information inherently available from back-EMF effects. A prototype 1-DOF system has been implemented and confirms the promise of this novel paradigm.