Admittance control with Type II Singularity evader testing with a humans knee

A compliant-admittance controller complemented with a Type II evader module is implemented on a 4-DOF parallel robot and tested with a patient. The Type II singularity evader provides complete user control over the robot because the evader modifies online the actuators’ trajectory if a singularity is close. The proximity to a singularity is measured by the minimum angle Ω. The location of the actuator corresponding to limb 3 is presented to verify the activation of the evader module, while the moment around the z_m axis, measured by a force sensor, demonstrates the non-dangerous effort performed by the patient. In the figures, the subindex “a” represents the admittance reference, the subindex “d” stands for evader modifications, the subindex “c” stands for measurements, and the “lim” represents the experimental limits.