Mechatronic design and control of low-velocity, high-precision positioning systems in the presence of friction

The significance of high-precision positioning systems is ever increasing. As industrial competition becomes fierce, precision industries such as semiconductor, machine tool, measurement equipment, and robotics are being pushed towards the limit of technology for better performance.; A positioning system is a controlled electromechanical motion system consisting of a controller, an actuator, a transmission and an end-effector, of which the position has to be controlled. The complete high-precision positioning system design includes design concept generation, mechanical/electromechanical dynamic analysis, simulation of system dynamics, component selection and fabrication, electronic hardware and transducer selection and interfacing, circuit design and wiring, software design, system parameter identification and verification, and finally, controller design and implementation. These tasks involve many specialized engineers from different engineering disciplines. Because of the sheer amount of people involved, development of such systems is quite difficult. The mechatronic system design integrates all those tasks and realizes more features than any of the technologies alone. A complete mechatronic system design methodology is introduced in this research.; This research used the rotational and the translational positioning test-beds to which most mechanical driving systems can be simplified. Complete mechatronic design process of modeling, parameter identification, dynamic system investigation, control design, and hardware build-up and implementation was demonstrated on the test-beds.; Parasitic system nonlinearities, such as friction, backlash, compliance, and motor torque ripple, render it difficult to achieve accurate modeling, identification, and compensation. Among the parasitic system nonlinearities, friction is most difficult to deal with and is the main error source in precision positioning. Frictional effects at moderate velocities are somewhat predictable, however the effects of friction at low velocities, especially with velocity reversals, are difficult to model. High precision tracking requires excellent control of slow motion and positioning. Extensive survey of friction dynamics, models, and compensation methods were surveyed.; To compensate the friction, the adaptive controller and the nonlinear reduced-order observer were investigated and incorporated to the conventional linear feedback controllers. It was proved experimentally that adding those friction compensators to the conventional linear feedback controllers, especially cascade controller, could hugely reduce position errors.