On the improvement of tracking performance of positioning tables

In this paper, a new robust adaptive control scheme for nonlinear motorized 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 on-line implementation because it simplifies the conventional modeling in n states parameters to only one time parameter. Therefore, system dynamics can be obtained on-line 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.