A position measurement apparatus

摘要

A precision measurement apparatus detects the point at which a measurement probe contacts the surface of an object 37 to be measured by detecting the formation of a magnetic circuit as the probe approaches the object. This is achieved by making the probe of an electroconductive material and locating the probe and the object (which must also be metal or similar electroconductive material) as part of a magnetic circuit. The circuit includes an inductive sensor 1 responsive to ambient or externally induced electromagnetic fields and which produces an output signal which changes in response to the circuit being formed. Because the circuit is formed before actual contact is made the apparatus can sense when the probe approaches the object and adjust its speed accordingly. In a preferred arrangement the probe may in fact be the cutting tool 36 of a CNC machine tool, in which case the apparatus may also be used to detect breakage of the cutting tool.