Specification of force-controlled actions in the "task frame formalism"-a synthesis

Autonomous robot tasks involving contacts with the environment must be performed under active force control if the geometric uncertainties in the task models are too large to cope with by means of passive compliance only. In practice, task specification of force-controlled actions is closely linked to the task frame formalism (TFF), also known as the compliance frame formalism. The TFF is a very intuitive and controller-independent approach to model a motion constraint, and to specify the desired forces and motions compatible with this constraint. However, it has never been defined clearly and unambiguously, and it cannot cope with all possible constrained motion tasks. This paper provides, for the first time, a formal definition of what makes up a TFF task specification. It gives also a synthesis of which tasks the TFF can cope with, and proposes a generic textual task specification formalism. Finally, it describes an example constrained motion task that the TFF cannot handle.