Experimental Calibration of the Constraining Linkage of a 4 Degrees of Freedom Parallel Manipulator

In this article, an experimental calibration of the constraining linkage of a wire-actuated parallel robot is discussed. The experimental test bed includes a prototyped 4 degrees of freedom wire-actuated parallel manipulator and an optical tracking system. The parallel manipulator employs hybrid actuation ofjoints and wires and includes a rigid branch to constrain the motion of its mobile platform in roll and yaw rotations. The kinematic calibration of the rigid branch is performed. A point-to-point path is designed for the manipulator and an optical tracking system is used as an external measuring device to track a tool attaqhed to the mobile platform and to register the manipulator poses. The deviation between the actual (measured) pose of t~e mobile platform and the calculated pose (via direct kinematics using the joint encoders), which could be due to errors in the kinematic parameters, actuators and sensors, is used as the error function.