Abstract: A shaft angle encoder comprises a code disc (21) mountable coaxially upon a rotary shaft (20) whose angular position is to be continuously measured. Coarse-bit angular position data are encoded digitally in Gray code by a pattern of opaque and transparent sectors provided on a plurality of inner annular tracks on the code disc (21). Fine-bit angular position data are encoded in analog triangular waveforms generated by the outermost annular track on the code disc (21). The analog position data are converted to fine-bit digital values, which are combined with coarse-bit digital values to obtain an angular position measurement. Alignment of the fine-bit digital values with the coarse-bit digital values obtained from the Gray code position data is accomplished by using information provided by overlapping the least significant bit of the coarse-bit digital values with the most significant bit of the fine-code digital values.

Abstract: A shaft angle encoder comprises a code disc (21) mountable coaxially upon a rotary shaft (20) whose angular position is to be continuously measured. Coarse-bit angular position data are encoded digitally in Gray code by a pattern of opaque and transparent sectors provided on a plurality of inner annular tracks on the code disc (21). Fine-bit angular position data are encoded in analog triangular waveforms generated by the outermost annular track on the code disc (21). The analog position data are converted to fine-bit digital values, which are combined with coarse-bit digital values to obtain an angular position measurement. Alignment of the fine-bit digital values with the coarse-bit digital values obtained from the Gray code position data is accomplished by using information provided by overlapping the least significant bit of the coarse-bit digital values with the most significant bit of the fine-code digital values.