Stable haptic display with energy-compensating control

Sampled-data system nature is the main factor for a haptic system to exhibit non-passive behaviors or instabilities through "energy leaks", particularly for stiff objects rendering. An energy-compensating method is presented aiming to improve the haptic system's performance based on the concept of doing work. Using ideal continuous-time haptic system as a reference, we define an energy-compensating controller (ECC controller) which compensates the energy leaks caused by zero-order-hold and asynchronous switching during entering and leaving contacts. The ECC controller not only removes the unwanted over-work from the virtual environment during leaving contacts to eliminate the system's potential non-passive behaviors, but also enlarges the work that should be done by the operator according to the reference system's value when new contacts arise. The proposed method was tested and verified with the implementation of a "virtual stiff-wall" via Delta 6-DOF haptic device.