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Zhou Di
Department of Control Science
and Engineering,
Harbin Institute of Technology,
Harbin 150001, China
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H¥SYNCHRONIZATION
CONTROL
OF LINEAR SYSTEMS AND ITS
APPLICATION TO WAFER-
RETICAL
STAGE*
Abstract: For the outputs of two nth-order linear control systems to work in synchronization and meanwhile to track their commands, a H¥ synchronization control scheme is presented. In terms of two uncoupled single variable linear systems, a multivariable coupled system is established by choosing one output and the difference of the two outputs as a new output vector, so that both command tracking and synchronization properties can be demonstrated by a H¥ performance index. To improve the synchronization and tracking performance and to guarantee the system robust stability, the mixed sensitivity H¥ design methodology is adopted. The presented synchronization scheme is then extended to the case where one of the two systems include two input variables, and then applied to the position synchronization control of a wafer-retical stage. The wafer-reticle stage consists of a wafer stage, a reticle coarse stage, and a reticle fine stage. The reticle coarse stage picks up the reticle fine stage. The three stages ought to tack their commands, but synchronization between the wafer stage and the reticle
fine stage must be stressed in the tracking process. In the
application, by appropriately determining the weighting matrices
for the sensitivity function and the complementary sensitivity
function, a satisfactory H¥ synchronization controller is obtained to realize highly accurate position synchronization, and to guarantee tracking performance. The above results are verified by simulation experiments.
Key words:
H¥ control Mixed sensitivity Synchronization control Wafer-reticle stage |