Free Kinematic Singularity Controller for a Planetary Gear Based Cobot

Cobots are devices that interact with human operators to execute tasks in non deterministic and unstructured environments. Controlling a cobot can be seen as a path following problem, such that the controller restricts the motion of the device to the desired trajectory, impeding motion in orthogonal directions. Velocity control is a common strategy for path following, in the particular case of cobots, it allows the user to modulate the speed of the device while the controller changes the direction of motion as required. However, velocity controls are not suitable when the controller works or crosses through kinematic singularities, where bad conditioning of the velocity arises. In this paper a velocity control for cobots is presented, that is free of Jacobian singularities. The performance of the proposed controller is shown by experimental results in a two degree of freedom cobot with differential gear trains in serial configuration. Experimental results show that by using the proposed controller, cobotic systems performance is not affected by kinematic singularities, so, cobots can properly work in their whole workspace.