System and apparatus to determine the angular position, and speed of a

Abstract

To positively allocate output signals from a transducer scanning marker elements arranged at a uniform distance from the center of a rotating disk, the markers are located around the circumference of the disk in accordance with a predetermined pattern, for example, uniformly distributed 30.degree. apart, or distributed with uniformly increasing relative distances, and an additional market element (33) and forming a reference marker is located in the zones between adjacent markers spaced from a neighboring marker element (21) of the plurality of marker elements by a distance which is substantially larger than the angular distance with respect to the marker element at the other side of the reference marker. The outputs from a pick-up sensor are evaluated by applying the outputs to two counters, counting a different clock rate, the count output of one of the counters being stored and compared with a subsequent count state of the other counter operating at a higher clock rate. If the second counter has not reached the previously stored count, a positive indication that the sense marker as the reference marker is obtained, permitting a comparator to switch over a transfer switch to route the sensor output to a line indicating that the marker was the reference marker; if the faster-counting counter has, however, reached the count state of a slower counter in the prior cycle, an indication is obtained that the marker is a regularly recurring one, thus permitting control of the transfer of the output from the sensor to a routing line indicating that the marker is a regularly recurring one. The count rates are preferably sufficiently different to accomodate expected variations in speed of rotation of the disk within the recurrence time between adjacent markers.