Frank Bernhard Sperling

Multivariable feedback control design for high-precision wafer stage motion

Abstract Conventional PID-like SISO controllers are still the most common in industry, but with performance requirements becoming tighter there is a growing need for advanced controllers. For the positioning devices in IC-manufacturing, plant interaction is a major performance-limiting factor. MIMO control can be invoked to attack this problem. A practically feasible procedure is presented to design MIMO feedback controllers for electromechanical positioning devices, using H ∞ /μ techniques. Weighting filters are proposed to straightforwardly and effectively impose performance and uncertainty specifications. Experiments show that MIMO control can considerably improve upon the performance with multiloop SISO control. Some problems are highlighted that are important for industrial practice, but that lack a workable solution.

Point-to-point control of a high accuracy positioning mechanism

Compares three open-loop command generating methods for the point-to-point control of a wafer stage. Whereas the theoretical time-optimal bang-bang force command results in excessive residual vibration due to excitation of resonant modes, shaped force profiles have the property not to excite these modes while still allowing for fast movements. The most successful shaping method turned out to be the one which was best able to handle uncertainty in our knowledge of the resonant mode dynamics, and the way this knowledge is used to shape the spectral content of the force command. Besides comparing three shaping methods, it was also investigated how the feedback and feedforward compensators affect the point-to-point motion.

Point-to-point control of a MIMO servomechanism

Many modern mechanical servomechanisms require high precision point-to-point motion of a mass without residual vibration. In our previous paper (1997) we showed how residual-free motion could be accomplished for one linear motor of a high-precision servo. In this paper, we show how the theory of command shaping for residual free motions can be extended for systems with multiple inputs and outputs.

Experimentally validated multivariable /spl mu/ feedback controller design for a high-precision wafer stage

Conventional PID-like SISO controllers are still common in industrial servo systems, but the ever increasing performance requirements call for advanced MIMO control. This paper presents /spl mu/ feedback controller design for high-precision wafer stage motion. Weighting filters-are proposed to straightforwardly and effectively impose performance and uncertainty specifications. The performance has been experimentally verified and compared with conventional multiloop SISO control.

A nonlinear dynamic filter to improve disturbance rejection in optical storage drives

To improve the low-frequency disturbance rejection properties of a DVD drive subjected to harmonic shocks, a variable gain control design in combination with an additional notch filter is suggested. A nonlinear control design is applied to overcome the trade-off between disturbance rejection and measurement noise sensitivity. Hereto the loop gain is increased beyond a threshold value for the radial error signal. To extend the current variable gain limitation, an additional notch filter is introduced. By tuning the notch filter parameters, stability is guaranteed way beyond the gain values obtained in the filters absence. Stability is studied globally on the basis of absolute stability theory and locally via numerical computation. The resulting performance is studied numerically on the basis of a nonlinear sensitivity analysis.

Computing periodic solutions for a CD-player with impact using piecewise linear shooting

This paper consists of two contributions in the field of nonlinear systems: (1) the introduction of a piecewise linear shooting algorithm, and (2) an analysis of the periodic behavior of a CD-player under harmonic excitation. Compared to a single shooting algorithm, which does not explicitly account for the piecewise linear nature of the CD-player model, the piecewise linear shooting algorithm can provide a significant decrease in computational effort. Namely, the transition times are efficiently solved by Henons method after detecting a regime crossing. Consequently, the integration-step refinement, typically encountered when using ODE routines, is avoided as much as possible. With piecewise linear shooting, the periodic behavior of a CD-player with impact is studied as a function of both the excitation frequency and amplitude. It is shown that the rich dynamic behavior such as encountered in experiments largely justifies the usage of a single degree-of-freedom piecewise linear model.