Frequency domain stability observer and active damping control for stable haptic interaction

Stable haptic interaction has been studied extensively using an energy-based approach, because energy is an indirect index reflecting unstable haptic behaviour. When a haptic system generates energy, the system becomes unstable. Therefore the energy-based approach should provide a point of reference for defining generated energy. However, in some practical cases, such as a multi-layered virtual wall, it is difficult to determine the point of reference. As a result, unstable behaviour cannot be detected promptly. To resolve this problem, a new observer, working in the frequency domain, was tested in this research. The observer directly examined unstable behaviour vibration, rather than analysing the indirect index reflecting the behaviour. The observer quantified the degree of instability of a haptic system, and a newly developed controller generated variable damping in proportion to this quantitative instability. In the case of a multi-layered virtual wall, the proposed methods were much faster in detecting haptic instability than other schemes, and successfully eliminated unstable behaviour.