Unilateral and Bilateral Virtual Springs: Contact Transitions Unmask Device Dynamics

The study of haptic perception often makes use of haptic rendering to display the variety of impedances needed to run an experiment. Unacknowledged in many cases is the influence of the selected device hardware on what the user will feel, particularly in interactions featuring frequencies above the control bandwidth. While human motion is generally limited to 10 Hz, virtual environments with unilateral constraints are subject to excitation of a wider frequency spectrum through contact transitions. We employ the effective impedance decomposition to discuss the effects of parasitics outside the rendering bandwidth. We also introduce an analysis of the admittance and impedance controllers with respect to sensitivity to load cell noise. We explore these effects using a single degree-of-freedom device that can be configured for either a low or high mechanical advantage in a perceptual experiment, with experimental conditions designed through application of the effective impedance decomposition. We find that the excitation of high frequencies through contact transitions negatively impacts humans' ability to distinguish between stiffnesses.