Tracking digital angle encoder

Abstract

A tracking digital angle encoder utilizing a translator, for providing the difference between an analog angle input and a digital angle input, a counter, which feeds the digital angle input to the translator, a detector, which controls the counter and is connected to the output of the translator to be activated by the output of the translator exceeding a predetermined trigger value, all of which are connected to cause the counter to count to a position where the output of the translator is less than the predetermined trigger level. When the output of the translator is less than the predetermined trigger value, the output of the counter provides a digital signal which closely approximates the analog angle input to the translator. A balanced demodulator which is connected to the output of the translator and receives a signal from a reference oscillator, which is equal to the carrier frequency, provides a pure sine function output representing the difference between the analog and digital inputs to the translator. An adjustment is provided between the counter and the threshold detector which permits the level at which the threshold detector activates the counter to be varied and thus the angle, to which each bit of the counter is equivalent, can be varied. This adjustment allows easy compensation for errors due to mechanical tolerances or mechanical wear in the system being controlled. The translator also provides an output which is equivalent to the cosine of the analog angle input. This cosine output is utilized for switching the counter to its midpoint when the power is first applied if the cosine value is negative, indicating the angular position of the analog signal is in the second or third quadrant.