On the improvement of tracking performance of positioning tables

In this paper, a new robust adaptive control scheme for nonlinear positioning tables is presented. The proposed scheme can effectively handle the nonlinearities and time-varying uncertainties. By using the proposed controller to deal with the flexibility in the coupler and nonlinearity in the ball-screw system, a completely closed-loop system for a positioning table can be achieved with the signal from the linear encoder in the mounting plate instead of from the rotatory encoder, as in conventional control approaches. As a result, a good tracking performance can be achieved. Unlike the traditional robust adaptive schemes, the proposed scheme is based on a new direct dynamics identification approach. This new approach facilitates the online implementation because it simplifies the conventional modeling in n states parameters to only one time parameter. Therefore, system dynamics can be obtained online with respect to time from the past known control activities. The dynamics identification procedure, adaptive scheme design and controller synthesis are presented in this paper. The experimental results for a positioning table are included to illustrate of the effectiveness of the proposed control scheme.