In this page you will find some videos related with the treatment of Type II singularities

Real-time singularity avoidance for rehabilitation parallel robots

This video shows the problem related to Type II singularities in a patient-passive knee exercise assisted by a parallel robot and the solution provided by the real-time singularity avoidance algorithm proposed by the authors. The control over the mobile platform (end-effector) is lost in a Type II singularity. To solve this problem, the authors proposed a real-time Tye II singularity avoidance algorithm to complement the trajectory control law. The proposed singularity avoidance algorithm modifies the trajectory of two actuators identified by the minimum angle Ω between two instantaneous axes from the Output Twist Screws. Based on 3D tracking system, the loss of control over the end-effector is verified by measuring the rotation of the mobile platform around the Zm axis. Moreover, the position tracking in the actuators in limb 3 (q33) and 4 (q42) are plotted to verify the minimum deviation calculated by the proposed singularity avoidance algorithm.

Admittance control without Type II Singularity evader

A raw compliant-admittance controller implemented on a 4-DOF parallel robot. The video shows how the user drives the robot to a Type II singularity and loses control with a final fall of the robot. The proximity to a singularity is measured by the determinant of the forward Jacobian (‖J_D ‖) and the minimum angle Ω. The robot’s location on z_m, measured by a 3D tracking system, verifies the robot’s fall. In the figures, the subindex “a” represents the admittance reference, the subindex “c” stands for measurements, and the “lim” represents the experimental limits.

Admittance control with Type II Singularity evader

A compliant-admittance controller complemented with a Type II evader module is implemented on a 4-DOF parallel robot. 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 on limb 3 is presented to verify the activation of the evader module, while the robot’s location on z_m measured by a 3D tracking system demonstrates the complete control over the robot. 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.

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.