Towards a Framework for Changing-Contact Robot Manipulation
This addresses the challenge of controlling robots in tasks with changing contacts, which is incremental as it builds on existing variable impedance controllers.
The paper tackles the problem of robot manipulation tasks involving making and breaking contact, which have discontinuous dynamics, by presenting a framework that smooths motion trajectories to predict contact times and achieve desired impact forces. It experimentally demonstrates this in sliding tasks with multiple contact changes, showing improved control.
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.