Pneumatic surface-following control system

摘要

An apparatus for maintaining the end of a probe carrying a sensor, such as an eddy current probe, a predetermined distance from a workpiece includes a housing in which a piston is permitted to move. Air under pressure, introduced into a first chamber formed within the housing, acts on a first surface of the piston to urge it toward the workpiece. An air bearing is used to permit the almost friction free axial movement of the piston within the housing. Some of the air passes from the first chamber through a restricted opening in the piston into a second chamber and is vented toward the workpiece. The pressure in the second chamber will vary as a function of the distance of the end of the probe to the workpiece surface. The piston is provided with a second, larger, surface area exposed to the variable pressure in the second chamber, and as a result, the piston is urged away from the workpiece. The pressures acting in the two surfaces work together to maintain the piston, and the sensor, a constant distance from the workpiece.