Nonlinear compensation for pneumatic actuators with hysteresis - precision control for microlithography

The article describes a hysteresis compensation method developed to meet stringent specifications imposed by the precision positioning of optical elements in microlithography tools. Novel and effective implementation techniques are introduced for systems possessing hysteretic behavior. The real-time implementation of the algorithm was simplified by fixing the order of the curve fit for the nonlinear component of the actuator response, limiting the number of operators used to estimate the hysteresis loop, and varying only the slope /spl alpha/. Using LabView, a controller capable of accurately positioning up to 36 actuators within a fraction of a second is developed.