ABSTRACT
In the previous chapter, the motion control of parallel robots has been analyzed through a variety of different control topologies and control schemes. These controllers are suitable when the moving platform of the robot accurately tracks a desired motion trajectory, while no interacting forces are needed to be applied. However, in many applications, it may occur that the robot moving platform is in contact with a stiff environment and specific interacting wrench is required. Parallel robots used in precision machining, grinding, or microassembly may be seen as representatives of such applications. In such applications, the contact wrench describes the state of interaction more effectively than the position and orientation of the moving platform. The problem of force control can be described as to derive the actuator forces required to generate a prescribed desired wrench (force/torque) at the manipulator moving platform, when the manipulator is carrying out its desired motion. In such a situation, the robot is interacting with a stiff environment, and a considerable interacting wrench is applied to the robot moving platform. This problem and its extents are treated in the force control algorithms described in this chapter. A force control strategy is one that modifies position trajectories based on the sensed wrench, or force-motion relations.
