Enhancing rate-hardness of energy-bounding algorithm by considering Coulomb friction of haptic interface

In haptics, both transparency and stability are major requirements for providing realistic feeling of virtual objects. The crisp contact feeling at the instant of touch with high impedance walls is necessary especially for proper identification and manipulation of virtual objects. This paper presents a new passivity condition that explicitly includes Coulomb friction effects. Moreover, the energy bounding algorithm incorporating Coulomb friction effects shows that the viscous damping of the haptic device affects the maximum displayable stiffness in steady-state and that the Coulomb friction of the device contributes to temporarily enhance rate-hardness in initial transient responses. Experimental results are presented for showing effectiveness of the proposed derivation and control law.