The present invention relates to a position sensor and, in particular, to a position sensor which operates according to the principles described in U.S. Pat. No. 3,898,555 to Tellerman. In general, such devices incorporate a sonic waveguide cooperating with a magnet. The waveguide and magnet are mounted for movement with respect to each other. The device operates according to the principles of the Wiedemann effect. An electrical pulse is generated resulting in a magnetic field concentrated in the waveguide. The magnetic field of the cooperating magnet causes a sonic torsional pulse to be generated and travel along the waveguide. This sonic torsional pulse is converted to an electrical signal. The time interval between the current pulse and the reception of the sonic torsional pulse is representative of the location or position of the magnet along the waveguide. Such devices therefore provide an accurate indication of linear displacement, for example, in machine tool applications where the location of a machine element must be determined for the control of machine functions.
The prior art also includes variable potentiometer devices which have been a primary absolute displacement measuring sensor because of the simplicity of their operation, low cost, accuracy, and the ease with which they interface with electronics. On the other hand, this type of prior art sensor has several disadvantages. The potentiometer has a sliding contact and resistance element, both of which tend to wear with extensive use. The wiper contact is sensitive to contamination that in many machine applications is difficult to control or eliminate. The cost of such devices is also increased if it is necessary to convert the analog signal output of the potentiometer for use with digital controls.
Balluff of Germany has introduced a non-contact magnetostrictive displacement sensor which eliminates the disadvantages of potentiometer-type devices. However, the Balluff device appears to have relatively limited application wherein the magnet is mounted externally on the device housing for movement relative thereto. Also, the Balluff device does not achieve the cost benefits associated with potentiometer-type devices.
The present invention is directed toward providing a low cost magnetostrictive displacement sensor of modular design whereby it is adaptable to a wide range of machine requirements and applications and which incorporates other advantages of variable potentiometer devices without their disadvantages.