Towards a Framework for Changing-Contact Robot Manipulation

TL;DR

This paper introduces a framework that enables smooth, continuous control of robot manipulation tasks involving changing contact states by predicting contact events and adjusting motion trajectories accordingly.

Contribution

The authors develop a novel framework that predicts contact timings and modifies robot trajectories to ensure smooth dynamics in changing-contact manipulation tasks.

Findings

Framework effectively predicts contact events.

Achieves smooth, impact-controlled trajectories.

Validated on sliding tasks with multiple contact changes.

Abstract

Many robot manipulation tasks require the robot to make and break contact with objects and surfaces. The dynamics of such changing-contact robot manipulation tasks are discontinuous when contact is made or broken, and continuous elsewhere. These discontinuities make it difficult to construct and use a single dynamics model or control strategy for any such task. We present a framework for smooth dynamics and control of such changing-contact manipulation tasks. For any given target motion trajectory, the framework incrementally improves its prediction of when contacts will occur. This prediction and a model relating approach velocity to impact force modify the velocity profile of the motion sequence such that it is $C^\infty$ smooth, and help achieve a desired force on impact. We implement this framework by building on our hybrid force-motion variable impedance controller for continuous contact tasks. We experimentally evaluate our framework in the illustrative context of sliding tasks involving multiple contact changes with transitions between surfaces of different properties.