Practical controller design for precision positioning, independent of friction characteristic

In this contribution, a practical controller design for non-contact mechanism and contact mechanism is discussed. The design procedure is applicable and totally independent of friction characteristic. Thus, designer does not need to consider the friction characteristic of a mechanism and it is a valuable controller approach in industry. The practical controller design procedure which based on current Nominal Characteristic Trajectory Following (NCTF) controller is proposed and improved. The NCTF controller is comprehensive, comprising of a Nominal Characteristic Trajectory (NCT) and a PI compensator, which is free from exact modeling and parameter identification. In NCTF controller design, the NCT is constructed from the open-loop responses of the mechanism. The designed input signal for open-loop experiment is needed to satisfy the following two conditions: (1) the displacement by the input signal must be smaller than the working range of the mechanism to avoid any damage to the mechanism; (2) the suitable input signal needs to produce sufficient rapid and smooth response during deceleration to satisfy the desired specifications because the response significantly influences the reference following characteristic of the control system. So far, the NCTF controllers had been implemented to the mechanisms which have sufficient large damping characteristics and it was natural to satisfy the condition (1). However, non-contact and low damping mechanisms do not have sufficient damping characteristics. Since the high damping characteristics of the mechanism have been used before, the condition (2) is still not yet been considered. Therefore, the design procedure of the input signal satisfying the two conditions is proposed and verified by experiments in this paper. The common conditions of the input signal which is independent of friction characteristic of the mechanisms are discussed. Then, the experimental verifications are performed using non-contact mechanism and contact mechanism. In this paper, the performance evaluation is discussed separately in two parts. In part 1, by using the non-contact mechanism, the positioning results of two different NCTs are compared in order to show the usefulness of the modified suitable input. In part 2, the contact mechanism is used to show the effectiveness of the NCTF controller with its simple and practical design procedure, which is independent of friction characteristic. The effectiveness of the Continuous Motion NCTF controller is verified with the PID controller experimentally in positioning control and tracking control. The experimental results prove that the displacements of the open-loop responses for NCTs are always smaller than the working range and the design procedure of the input signal is successfully independent of the friction characteristic of the mechanism. Overall, the Continuous Motion NCTF controller which has simple and practical design procedure exhibits the high performance in positioning and tracking control with contact mechanism and non-contact mechanism, as compared to the PID controller. The PID controller shows the low adaptability in motion control performances for both conditions of mechanism. (C) 2009 Elsevier Inc. All rights reserved.