Probe having passive means transmitting an output signal by reactive coupling

Claim 1

A machine tool comprising: a head, a probe detachably secured to said head, said head being movable relative to a workpiece to bring said probe into a predetermined position relative thereto for the purpose of taking a measurement of said workpiece, a first electric circuit provided on said probe, said first electric circuit having no source of operative power, a second electric circuit provided on said head, a reactive coupling having adjacent electric coupling parts which are not wired together and which are respectively provided on opposing portions of said head and said probe and spaced apart by an air gap separating said opposing portions, said electrical coupling parts being respectively arranged in said first and second electric circuits, the coupling part arranged in the first circuit being separable from the coupling part arranged in the second circuit upon detachment of said probe from said head, an oscillator connected to the second circuit to produce therein oscillations transmittable to the first circuit by virtue of said coupling when the probe is secured to the head, the first and second circuits cooperating to determine the impedance offered to said oscillations in said second circuit, means provided on the probe for stepwise changing the state of the first circuit responsive to the probe attaining said predetermined position to thereby stepwise change said impedance, and sensing means connected to the second circuit for sensing changes in the oscillations in said second circuit produced by a change in said impedance.