Practical control of non-friction mechanism for precision positioning

This paper describes the practical control of non-friction mechanism for precision positioning. Non-friction mechanism is often used for precision positioning. Even though it has a simple structure, still, plant identification is compulsory needed during designing a conventional controller. This makes the controller non-user-friendly and non-practical-used in industry. For overcoming this problem, practical controller design procedure based on NCTF (nominal characteristic trajectory following) controller is proposed. NCTF controller consists of a nominal characteristic trajectory (NCT) and a PI compensator, which is free from exact modeling and parameter identification. The NCT is determined using an open-loop time responses of the mechanism. The PI compensator is used to make the mechanism motion to follow the NCT and it is tuned without given model parameters. Non-friction mechanism has non-damping a characteristic and often has a short-working range. A suitable current input to stop the non-damping mechanism within a short working range in open-loop condition and to be able to improve the damping characteristic of the mechanism is necessary. The positioning performances of two different current inputs are examined and discussed. The positioning performance of NCTF control system is evaluated based on simulation and experimental results.