Patent ID: 6864494

Claim:
Semiconductor processing apparatus having a base and a movable member, said movable member having a mass and being mounted for reciprocation relative to the base over a displacement range having a vertical component, and a force compensator for applying a substantially constant compensation force to said movable member over said displacement range to compensate at least partially for the force of gravity on said mass of said member, said force compensator comprising, a vacuum cylinder having a closed end and an open end, a piston movable in said cylinder over a stroke, said piston defining an enclosed region between said piston and said closed end, said open end being open to ambient atmosphere, a source of vacuum connected to said enclosed region, said source being arranged to provide in said enclosed region a vacuum pressure which remains not above about 10% of normal ambient pressure, a first connecting point associated with said cylinder, and a second connection point associated with said piston, one of said first and second connecting points being connected to said movable member and the other of said connecting points being connected to said base, whereby movement of said movable member relative to said base over said displacement range causes movement of said piston in said cylinder over said stroke.