HFSM-Based Software Implementation of Haptic Interactions

We present a novel method to encapsulate and formalize haptic interaction in a compact systematic format using hierarchical finite state machines (HFSMs). HFSMs capture both reality-based and synthesized haptic interactions. The lowest level states in the hierarchy are impedances implemented by the haptic device. Transitions between states are governed by inequalities defining geometric and dynamic constraints. This model is compatible with other haptic rendering techniques and can be used as a low level application programming interface. We will describe the format and implementation and illustrate the approach with an example. Experimental results with a three-degree-of-freedom planar haptic interface are also presented.