Abstract: A magnetic encoder is disclosed that provides a uniform magnetic field which is time modulated at a carrier frequency and space modulated by a repetitive pattern of eddy-current conducting lands that move with variable motion. The time modulation is provided by driving an electrical coil in a resonant tank circuit. The space modulation provides areas of higher and lower magnetic field intensity which change in correspondence with the motion of the conducting lands. The intensity of the varying magnetic field is detected by a series connected pair of stationary coils that are positioned orthogonal to both the direction of the changing magnetic field and the direction of the motion of the conducting lands. The pair of stationary coils yield a differential electrical signal that is representative of the motion of the conducting lands.

Abstract: A light beam encoder for measuring absolute distance over a linear path with an accuracy of at least that provided by incremental optical encoders, but over longer ranges than can readily be achieved with optical linear encoders due to the difficulty of providing a sufficiently long optical scale with the requisite accuracy and resolution. The resolution provided by the light beam encoder can be approximately 1-10 microns. A high frequency amplitude modulated light beam is reflected by a reflector disposed at the distance to be measured, and the phase lag of the reflected light beam is determined to provide an absolute measure of the distance. The encoder mixes a local oscillator signal generated by a phase locked loop with both a reference oscillator signal and the distance signal. Thus, the heterodyne mixers provide two low frequency signals preserving the phase lag between the two optical signals.

Abstract: A digital resolver is provided that accepts an analog representation of an angular or linear displacement within a reticle modulation cycle of a rotatable or translatable member, and provides a highly accurate output digital representation of the displacement within the cycle, even during rapid movement of the member. An encoder cooperative with the interpolator receives an analog signal that represents the displacement, and yields a pair of quadrature-phased sine wave signals accordingly. These signals are provided to the interpolator, wherein each is multiplied by a stored digital representation of a trigonometric function of the output digital signal. The resulting products are then added so as to provide an error signal which is used to drive a digital control loop, such that a digital output signal is provided that represents displacement within a reticle cycle.