The development of a prototype two degree-of-freedom parallel mechanism for application to unmanned ground vehicle target tracking is presented. The mechanism is extremely simple, decoupling the two end-effector degrees-of- freedom (DOFs) with an easily fabricated and inexpensive connection of passive joints. A summary of the parallel mechanism's kinematic design and singularity analysis is provided. A 2-DOF tracking system using a digital camera with a large time delay is presented. A command feedforward controller is designed to extend the tracking bandwidth by approximately two octaves beyond that of the feedback controller without violating causality. Experimental data is presented that shows improvement in the tracking performance by a factor of 2.4 over the feedback system alone.
Parkins, Jeffrey A. and O'Brien, John F. (2012). "A Modified Command Feedforward Tracking Control System Applied to the PRRR-RR Parallel Mechanism." Active and Passive Smart Structures and Integrated Systems 8341, 83410N-1-83410N-15.