On the modeling of robots in contact with a dynamic environment

A new modeling approach for describing motion of robots in contact with a possibly dynamic environment is presented. The proposed technique allows to model all those cases in which purely kinematic constraints imposed on the robot end-effector live together with dynamic interactions. Suitable parametrizations are introduced for the environment configurations and constrained end-effector poses and for the exchanged forces. The generalized directions of 'static' environment reaction forces (orthogonal to the directions of admissible end-effector motion) and those of 'active' forces (responsible for energy transfer between robot and environment) are formally characterized. The overall dynamics of the robot-environment system is then derived in a unique framework. The obtained model structure is shown to be suitable for the design of hybrid control laws. Simple but significative examples are reported to illustrate the modeling procedure.