Toward event-based haptics: rendering contact using open-loop force pulses

An event-based method is proposed to improve realism in haptic displays. Many interesting interactions, for example tapping on a stiff environment, are characterized by ringing and high-frequency force signals. Traditional closed loop controllers, however, do not generate much information between 300 Hz and 1 kHz, to which human users are very sensitive. We propose brief open-loop playback at these frequencies, triggered by appropriate events. As a first step in rendering contact with stiff virtual surfaces, we apply short force pulses that neutralize momentum as quickly as possible and bring the haptic device to rest. Experiments verify shorter penetration depths and higher effective stiffness compared to those of traditional displays. The pulses also provide high-frequency signals and improve the user's sense of touch. Event-based playback presents a substantial departure from traditional approaches, as high frequency forces are generated separately from low-frequency feedback. These forces are computed as functions of the contact event and conditions instead of the user's instantaneous state.