At least three detectors disposed on a line perpendicular to a straight line fringe pattern and on centers at one-fourth the fringe period provide signals indicative of the intensities of the pattern incident on them. The signals are manipulated to render equal the fringe intensity terms of the expressions from the sinusoidally varying signals as part of the procedure for deriving the phase value. Derivation of the phase value is a step in derivation of displacement. The fringes are created in an interferometric device or from a sinusoidally varying grating.
In incremental detectors, measurement signals thereof are first corrected in graduation-specific fashion with respect to amplitude offsets, and phase displacement, and a rough angle is determined. The residual error of the rough angle is fine-corrected via rough-angle-specific, graduation-independent rough angle correction values and a position signal is determined in this way. The correction values for amplitudes offsets, and phase displacement are determined using regression, and the rough angle correction values are determined using high-precision reference angle measurements.
A stable single-frequency laser interferometer comprises a Michelson interferometer having a power stabilized single-frequency laser and a dual light sensor comprising two closely spaced very small sensor surfaces mounted in substantially the same plane. Devices rotate the plane of the dual light sensor and/or elements of the interferometer to adjust the effective convergent angle of the recombining beams to have a sufficiently large effective convergent angle to promote stability and so that the output signals of the two sensors are in phase quadrature.
A detector is described, intended for use in metrology systems of the type which produce interference fringe patterns which contain a phase which is characteristic of the parameter under measurement, particularly displacement or position. The detector is in the form of an array of elements whose outputs are electrically interconnected so as to form three or more signals displaced from one another in phase by a fixed amount. The detector is provided on a single monolithic, silicon substrate using microelectronics techniques.
A metrology system includes means for generating an interference fringe pattern as a function of a parameter to be measured, transducer apparatus for simultaneously generating three intensity-modulated optical signals, I.sub.R, I.sub.S and I.sub.T, that are related to the interference fringe pattern; signal processing apparatus for accurately determining an aspect of the interference fringe pattern from the three signals; means for accumulating phase information proportional to the aspect of the interference fringe pattern; and means for converting the accumulated phase and aspect information to desired outputs indicative of the parameter to be measured.
A portable extended life metrology system is disclosed. The system is of the kind which includes means for generating an interference fringe pattern as a function of a parameter to be measured, transducer apparatus for simultaneously generating three intensity-modulated optical signals, I.sub.R, I.sub.S and I.sub.T that are related to the interference fringe pattern; signal processing apparatus for accurately determining an aspect of the interference fringe pattern form the three signals; means for accumulating phase information proportional to the aspect of the interference fringe pattern; and means for converting the accumulated phase and aspect information to desired outputs indicative of the parameter to be measured. The system includes a pulsed drive circuit designed to minimize its power drain without affecting its measurement accuracy and an energy source connected by the pulsed drive circuit to a radiation source to power the same in two operative states: a low, standby mode and a higher operational mode, with incremental and self-adaptive switching therebetween. The pulsed drive circuit controls the energy per pulse, the pulse repetition rate, and returns residual energy to the energy source of the system.
