DETECTION CIRCUIT FOR THE MAXIMA AND MINIMA OF A LOW FREQUENCY VARIABLE AMPLITUDE ELECTRIC SIGNAL AND THE APPLICATION OF THIS CIRCUIT TO APPARATUS FOR DETECTING THE RELATIVE POSITION AND THE DIRECTION OF RELATIVE MOVEMENT OF TWO OBJECTS

摘要

An optical position sensing apparatus utilizing a grating having two sets of opaque and transparent lines thereon, one of the sets being off-set from the other is associated with a source-detector assembly, the source and detector assembly including pairs of light sources and detection devices with at least one of the devices of one of the pairs being aligned with one set of light interrupting opaque lines and the other device of the pair being aligned with the other set of light interrupting opaque lines so that the image of the area illuminated by the opposing source is projected back upon the area of the grating in front of its respective detector as by an imaging reflect surface, preferably a concave mirror. Because the signal from the detectors varies in time and magnitude, and there is DC leakage from the detectors, it is necessary to establish a threshold detection voltage to insure a proper signal output wave form for both position and direction of relative motion sensing. This is accomplished by generating first and second voltage references to follow the peak and valley of the signal and generating the threshold level detection voltage which may then be compared to the input signal to create a predetermined wave form having a predetermined frequency relationship to the input signal.