Identifying Position-Dependent Mechanical Systems: A Modal Approach Applied to a Flexible Wafer Stage

Increasingly stringent performance requirements for motion control necessitate the use of increasingly detailed models of the system behavior. Motion systems inherently move, therefore, spatio-temporal models of the flexible dynamics are essential. In this paper, a two-step approach for the identification of the spatio-temporal behavior of mechanical systems is developed and applied to a lightweight prototype industrial wafer stage. The proposed approach exploits a modal modeling framework and combines recently developed powerful linear time invariant (LTI) identification tools with a spline-based mode-shape interpolation approach to estimate the spatial system behavior. The experimental results for the wafer stage application confirm the suitability of the proposed approach for the identification of complex position-dependent mechanical systems, and its potential for motion control performance improvements

Nonlinear Control of a Linear Motion System, in

Abstract: It is well-known that Bode’s gain/phase relation imposes limitations on the performance of a linear system. To circumvent these limitations, two examples from literature on nonlinear controllers, more precisely, a PID with nonlinear gain and a SPAN (split-path nonlinear) filter, are implemented on a motion system in order to improve the step response in comparison with a conventional linear PID controller. Simulations and experiments are presented and it is shown that these nonlinear control strategies can outperform a linear PID controller

Global feedforward control of spatio-temporal mechanical systems: with application to a prototype wafer stage

High throughput requirements on high-precision manufacturing systems lead to a situation where the flexible dynamics hamper the performance at the positions of interest. Since these points are typically not measured directly, high performance local control of measured positions may lead to deteriorated performance due to internal deformations. A possible solution is to employ a control strategy which ensures that the desired rigid body motion is achieved, without exciting the parasitic flexible dynamics. In this paper, a feedforward controller design procedure is developed that achieves this type of global performance, which in turn leads to increased performance at the unmeasured positions of interest. The proposed method is applied to an experimental wafer stage showing that the proposed approach indeed leads to superior results with respect to the traditional local control approach

Identification of position-dependent mechanical systems

abstract onl

Global feedforward control of spatio-temporal mechanical systems:with application to a prototype wafer stage

\u3cp\u3eHigh throughput requirements on high-precision manufacturing systems lead to a situation where the flexible dynamics hamper the performance at the positions of interest. Since these points are typically not measured directly, high performance local control of measured positions may lead to deteriorated performance due to internal deformations. A possible solution is to employ a control strategy which ensures that the desired rigid body motion is achieved, without exciting the parasitic flexible dynamics. In this paper, a feedforward controller design procedure is developed that achieves this type of global performance, which in turn leads to increased performance at the unmeasured positions of interest. The proposed method is applied to an experimental wafer stage showing that the proposed approach indeed leads to superior results with respect to the traditional local control approach.\u3c/p\u3

Estimating structural deformations for inferential control: a disturbance observer approach

Increasingly stringent requirements for motion systems lead to a situation where the positioning performance can often not be measured directly and therefore has to be estimated. A typical example is a wafer stage, where the performance is desired at the point-of-exposure on the wafer but the sensors are located at the edge of the wafer stage. Increasingly stringent performance requirements necessitate taking structural deformations, caused by actuation or disturbance forces, into account. The aim of this paper is to develop a disturbance observer approach including an observer relevant model identification approach and to experimentally validate this approach on a prototype motion system. The experimental results confirm that the proposed disturbance observer approach leads to an improved estimation of the unmeasured performance variables