A balanced positioning apparatus comprises a balance mass which is supported so as to be moveable in the three degrees of freedom, such as X and Y translation and rotation about the Z-axis. Drive forces in these degrees of freedom act directly between the positioning body and the balance mass. Reaction...http://www.google.de/patents/US7034920?utm_source=gb-gplus-sharePatent US7034920 - Balanced positioning system for use in lithographic apparatus
