Control Considerations in the Design of a Parallel Kinematic Machine with Separate Actuation and Metrology Mechanisms

Abstract- Machines based on parallel kinematics typically utilize connector geometry to establish the kinematic state of the moving platform. Most active applications require the connectors to be both prime movers and sensors. In some applications, the connectors are passive, with a metrology function of determining moving platform position and orientation. A methodology is developed that generates optimized parallel kinematic mechanism geometry based on design criteria. This methodology is applied to two parallel kinematic mechanisms to develop a high payload machine that has direct manual input for motion command. The deign criteria utilized for objective function development are directly related to control issues. The actuation frame is developed with load leveling between actuators in mind, and the metrology frame is designed with accuracy of determination of position and orientation in mind. An overview of the machine’s control architecture is presented. Several control behaviors are detailed. A control behavior in which the operator provides the motion command directly is developed, and concerns with respect to command determination and sensitivity are discussed