Singularity Analysis of a Hybrid Serial-Cable Driven Planar Robot

In this study, we address the problem of singularities of a hybrid serial-cable driven planar robot. Based on an analytical kinetostatic analysis three types of singularities are determined, i.e., serial, parallel, and combined singularities. In addition, cable tensions should be positive, otherwise, the robot will be uncontrollable. The serial singularity corresponds to positions where the serial port of the robot is fully extended or fully folded. The parallel singularity corresponds to aligned cables and combined singularities correspond to both cases. Cable tensions distribution, within the workspace, is determined, which allowed the identification of regions where the cable tensions exceed an allowable value. The influence of physical parameters on the workspace of the robot and its singular configurations is also studied. An example of a gait rehabilitation system using this type of robot is shown. Based on the kinetostatic analysis, multi-objective optimization of the dexterity and the cable tensions is performed, which yielded solutions represented by a Pareto front. The results have been extended to the case of 3 degrees of freedom hybrid robot.