GB1197085A - Shaft Angle Encoding - Google Patents

Abstract

1,197,085. Selective signalling. ITEK CORP. 14 July, 1967, No. 32468/67. Heading G4H. In a shaft position encoding system interpolation between scale divisions of the least significant track of a conventional coded scale is effected by quadrature sensing of the track, by combining the resulting signals, which will vary sinusoidally with position, in a plurality of resistance networks to produce a plurality of further signals (which will also vary sinusoidally with position) whose phases, with respect to one of the original sensed signals, will all be different and will cover uniformly a complete cycle of positional variation of the original signals, and then by examining these further signals sequentially, and counting those examined, until their polarity changes. The count attained then effects the desired interpolation. Thus if the sensed signals are sin # and cos #, where # represents position within one cycle of the divisions of the least significant track, then for an interpolation factor of eight, for example, these two signals are combined linearly in four resistance networks to produce the four signals sin (#-r#/4), r = 0, 1, 2, 3. As # increases from 0 to 360 degrees the following eight different combinations of polarities occur: and the particular quadrant in which 0 lies can be determined either by counting the number of plus signs, or, if the first sign is a minus, by inverting the signs and then again counting the plus signs, this count being increased by 4. A block diagram of a suitable circuit is given using a magnetic core counter and conventional transistor gates and amplifiers. The preferred method of sensing the scale is photo-electric but other methods, namely brish, capacitative, and inductive, are mentioned.