Compliant admittance-coupled DMP with Type II singularity evader

This video shows the execution of a trajectory generated by Dynamic Movement Primitives (DMP) to simultaneously provide an admittance behavior and avoid Type II singular configurations for the 4-DOF parallel robot. The trajectory is modified by one coupling action defined for the human-robot admittance interaction and another for the singularity avoidance.

The original reference trajectory is static and initially close to a singularity in the axis of rotation around Z (ψ). In this experiment, the human tries to push the robot toward the singularity by exerting a torque on Z (bottom-right chart), which provokes its rotation thanks to the admittance behavior (bottom-left chart). However, as soon as the minΩ_c singularity indicator falls below the limit, the evader is activated through a coupling action and keeps the robot out of the singularity, also ceasing the admittance behavior gradually. This results in a struggle between the human and the robot with smooth movements to ensure their safety. In the charts, “ref” is the reference of the rotation around Z, “meas” is the measurement of the signals, and “lim” is the limit for minΩ_c.

The core controller is a PD+G, used to track the trajectory generated by the DMP, affected by both coupling actions.