| Thermal control and uniformity of temperature in machine tools and metrology instruments is a fundamental limitation to precision engineering. The problem scales unfavorably with larger devices. It is well established that oil showering provides the best means of thermal control by at least an order of magnitude. At Stanford, we have been developing actuation and sensing techniques based on quiet hydraulics to take advantage of the improved thermal control possible with hydraulic technology. The devices are designed at low Reynolds number to avoid turbulence, which could disturb the machine function. This dissertation describes a new method of non-contacting straightedge detection and the basis for design and calibration by reversal.;Since no slideway is perfectly straight, there must be provision for measuring and correcting error motion. We have developed a novel hydraulic sensor for measuring non-straightness and yaw called a "differential oil gage". This technology has the potential of being both more robust and less expensive than using LVDT's, capacitive gages, magnetic eddy current sensors, or optical devices as straightedge sensors. A differential oil gage measurement has no probe contact: There is neither lift off nor sensitivity to surface contamination. Furthermore, since the oil gage measurement averages over the straightedge surface, sensitivity to errors with short correlation distance is reduced.;While the sensor uses the same technology as an externally pressurized bearing, its function and requirements are much different. The oil gage should have low stiffness and force levels in order to minimize the disturbances on the rest of the system. Evaluations of the prototype oil gage sensor are very promising. It has demonstrated a good signal to noise ratio, good linearity and repeatability at the 50 nm level, but has an undesired stiffness. We have developed five approaches to minimize or remove the effect of stiffness while still retaining the signal sensitivity. |
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