eTaSL/eTC: A constraint-based task specification language and robot controller using expression graphs

This paper presents a new framework for constraint-based task specification of robot controllers. A task specification language (eTaSL) is defined as well as a corresponding implementation of a controller (eTC). This new framework is based on feature variables and a new concept referred to as expression graphs. It avoids some of the common pitfalls in previous frameworks, and provides a flexible and composable way to define robot control tasks. An architecture for a robot controller is proposed, as well as an implementation that can execute tasks described in the new specification language. Typical usage patterns for the new framework are explained on an example consisting of a kinematically redundant, bi-manual task on a PR2 robot. A comparison with existing frameworks shows the advantages of the new approach.