Dynamic modeling and control of voice-coil actuators for high-fidelity display of haptic vibrations

Researchers have demonstrated haptic interfaces that display high-frequency vibrations by applying an oscillating waveform to a linear voice-coil actuator (also referred to as a linear resonant or recoil-type actuator). Seeking to optimize the performance of this class of haptic devices, this paper analyzes the electrical and mechanical dynamics of this haptic display approach. Experimental evaluation of the most common commercial voice-coil actuator, the Tactile Labs Haptuator, reveals how the drive circuitry, the actuator's suspension, and the user's hand impedance affect the system's frequency response and thus distort the desired vibration output. Compared to current-drive, voltage-drive circuitry beneficially increases the effective damping of this underdamped system. Previously assumed to be linear, the system's dynamic response is found to depend highly on the material used for the actuator's suspension; the nonlinearity of the standard Haptuator suspension undesirably causes the resonant frequency to shift based on the amplitude of the input signal. We reduce the output distortion by installing a more linear suspension material, and we use a feedforward controller to compensate for the remaining dynamics, instead of the standard constant-gain controller. Considering the metrics of unity frequency response and spectral dissimilarity, our approach considerably reduces the distortion presented to the user.