Observing Pose and Motion through Contact

Abstract

This paper investigates how to "observe" a planar object being pushed by a finger. The pushing is governed by a nonlinear system that relates through contact the object pose and motion to the finger motion. Nonlinear observability theory is employed to show that the contact information is often sufficient for the finger to determine not only the pose but also the motion of the object. Therefore a sensing strategy can be realized as an observer of the nonlinear dynamical system. Two observers are subsequently discussed. The first observer, based on the result of Gauthier, Hammouri, and Othman (1992), has its "gain" determined by the solution of a Lyapunov-like equation. The second observer, introduced in our earlier work, solves for the initial (motionless) object pose from a few intermediate contact points. Simulations have been done to demonstrate the feasibility of the two observers. A sensor has been implemented using strain gauges and mounted on an Adept robot with which preliminary experiments have been conducted. From a general perspective, this work presents an approach for acquiring geometric and dynamical information about a task from a small amount of tactile data, with the application of nonlinear observability theory.