Low velocity compensation for first order periodic error caused by beam shear

This paper describes low velocity first order periodic error compensation caused by beam shear. It is shown that the error compensation is possible using the first order error signal magnitude obtained at high velocity and the interference signal magnitude identified at arbitrarily low velocities. The approach is based on the inverse-proportional relationship between the interference signal and first order periodic error signal magnitudes with variable shear. An experimental setup is described where beam shear is intentionally modified and the first order periodic error is monitored to validate this relationship. A simple compensation algorithm is presented and demonstrated.