The increasing use of parallel cable-driven mechanisms calls for a better understanding of their behavior and highly efficient algorithms to attenuate their drawbacks at the design stage. One of these drawbacks is the high probability of mechanical interferences between the moving parts of the mechanism. In this paper, the phenomenon is described under the assumption that a cable is a line segment in space. When a mechanical contact occurs between two cables or between a cable and an edge of the end effector, these entities necessarily lie in the same plane, and then the three-dimensional problem becomes two-dimensional. This fact is used to simplify the equations, and leads to exhaustive descriptions of the associated interference loci in the constant-orientation workspace of a cable-driven mechanism. These results provide a fast method to graphically represent all interference regions in the manipulator workspace, given its geometry and the orientation of its end effector.

This paper presents a cable-driven parallel mechanism as a haptic interface and its underlying control method. This human-sized, three-degree-of-freedom mechanism has a tetrahedral architecture, four cables and evolves in three-dimensional space. A brief review of the kinematics of the mechanism is presented. Also, an admittance control law coupled with a closed-loop velocity controller is proposed. The control method is then refined by introducing adaptations for smooth surfaces and sharp edges. This control method is then validated by experimental results. Furthermore, the geometry of the mechanism is identified by a method that does not require any other sensor than the motor encoders.