Increasing the impedance range of admittance-type haptic interfaces by using Time Domain Passivity Approach

This paper proposes a method to increase the impedance range of admittance-type haptic interfaces. Admittance-type haptic interfaces are used in various applications that typically require interaction with high impedance virtual environments. However, the performance of admittance haptic interfaces is often judged by the lower boundary of the impedance that can be achieved without stability problem; in particular, minimum displayable inertia. It is well known that rendering the low value of inertia makes the admittance-type haptic interfaces unstable easily. This paper extends Time Domain Passivity Approach (TDPA) to lower down the minimum achievable inertia in an Admittance-type haptic interface. To use the well-developed TDPA framework, an admittance haptic interface should be represented in network domain with clear energy flows, which was not straightforward due to unclear causality. Therefore by introducing dependent effort and flow source concept, the admittance type haptic interface is represented in electrical network domain. This network representation allows us to have clear causality, and consequently allowing to implement TDPA. The proposed idea was experimentally verified, and found successful in bringing down the minimum inertia 10 times lower than without TDPA case.