Abstract: A robotic height sensor employs the defocussing of a spot of light to detect the motion of a probe contacting a reference object. The defocussing changes the electrical output of a photodetector which output is used to control a height drive mechanism. In a preferred embodiment of the invention, an intentional weakened portion of a shaft is provided for permitting limited lateral freedom of the shaft to accommodate minor irregularities in a workpiece.

Abstract: Air bearing pads for supporting a one-axis table in a granite bridge positioning apparatus on a thin film of air include machine-thinned sections for providing resilience to the pads in order to permit flexing sufficient to accommodate surface irregularities on the supporting surface. A single air pressure regulator provides a source of pressurized air to flow-control devices of a plurality of air bearing pads supporting a one-axis table. The individual flow-control devices adjust the flow of air to their respective air bearing pads to individually adjust the lift of the pads.