Hall-Effect Incremental Angle Encoder

Abstract

This paper describes a magnetic angle-encoder development utilizing two microminiature Hall-effect probes and a single-track magnetic drum. This approach to angle encoding and measurement offers possibilities for developing compact and higher-resolution angle encoders for inertial guidance and space platform applications. The Hall-effect probes allow measurement of the magnetic drum's recorded field directly instead of the usual time derivative of flux, thus readout can be accomplished at zero angular rate. The probe consists of a semiconductor crystal, mounted in a plane parallel to the drum, in order to sense the vertical component of the recorded signal. Both indium arsenide (InAs) and indium antimonide (InSb) crystals measuring 0.030×0.005×0.0003 inch in length, width and thickness, respectively, have been used. The width of the crystal has been the determining angular resolution factor for the encoder. Analyses of probes sensing the vertical and horizontal components of the magnetic field, respectively, are included. The crystal is ac excited with 10 mw of power at 40 kc. The resulting signal readout can be amplitude or phase modulated as determined by the balancing resistor connected between the input and output of the crystal. The signal is amplified, detected and shaped so that the resulting square waves are available to a digital computer or a bi-directional counter. The maximum modulating frequency has been set at 1000 cps. This upper limit is determined by drum size, maximum rpm of the drum, and the recorded bit packing density. The probe resolves bit densities of 180 bits per inch. Using a 1.