Abstract: An apparatus for positioning a work piece along a Z-axis includes a base having a depression with an open top in it forming a chamber. A cover member has a rigid central portion and a rigid outer portion coupled with the central portion by an intermediate flexure. The cover member overlies and is secured to the base member at the outer portion of the cover member to close the chamber. Fluid under pressure applied to the chamber is used to move the central portion of the cover member along the Z-axis proportionally to the pressure of fluid applied to the chamber by flexing of the flexure.