Author(s): Jan Holterman, Theo J.A. de Vries
Active damping can be realised robustly through the use of a position actuator, a
collocated force sensor, and control based on ‘Integral Force Feedback’ (IFF). Instead
of a pure integrator, it is also possible to use a first-order lowpass-filter in the
feedback loop (‘leaking IFF’). For both cases, the maximum achievable relative
damping for a certain vibration mode can easily be predicted. If the achievable
damping is too low, it is possible to improve this by means of ‘crosstalk-compensation’.
A close look at these strategies reveals that there is a one-to-one relation
between ‘leaking IFF’ and ‘crosstalk-compensation’. The presented theory is verified
by means of active damping experiments within the lens support of a wafer stepper.