Novel method of A/D conversion for incremental position sensors

Modern servosystems use digital measurement of speed as well as position. One of the most used type of sensor is the two-phase incremental optical encoder. Normally the analogue signals of this encoder are converted to logical pulses which enable position measurement by a bi-directional counter. However, the analogue signals contain much more accurate information about position than the logical signals. That is why the analogue signals of incremental sensors are used for measuring position and speed with high resolution. Existing methods consider the linear or sine dependence of the signals on the measured position and use two fast D/A converters for converting these signals. The proposed method has no special requirements on the shape of the measured signals and is based on the use of two A/D converters for imitating the measured signals and a comparator for transforming the phase error as a feedback signal to a bit stream for digital processing. However, this method can be improved by replacing the comparator with an A/D converter. The resulting measured speed and position in a digital form is generated internally by a microcontroller used for speed and position control. The external output of the measured speed or position in analogue form is used only for verification of the correct conversion