DC Shift error correction for electro-optical measuring system
AssigneeKeuffel & Esser Company
InventorStefan Orsen
Life of this patent
Estimating the term…
Abstract
In an electro-optical measuring system which utilizes a sin/cos signal pair to determine the extent and direction of physical displacement, measurement errors often occurring as a result of extraneous DC level shifts in generated signals are corrected in a procedure which regularly samples the maxima and minima of the signals, derives from those values the median DC levels of the signals, compares the median levels to a reference DC level in the system to determine any differences, and applies any detected differences as corrective factors to position measurement signal values.
Claims9
A method of correcting errors resulting from the DC level shift, with respect to a preselected reference voltage, of a sinusoidal electrical signal generated in an electro-optical measuring system in response to displacement to be measured, said method comprising:
- (a) generating a second signal in phase quadrature with said sinusoidal signal;
- (b) gating a sampling amplitude value of said sinusoidal signal whenever the amplitude of said second signal equals said preselected reference voltage, thereby to obtain an indication of the amplitude values of said sinusoidal signal at substantially the maximum and minimum of a given cycle of said sinusoidal signal;
- (c) averaging said sampled values to obtain an indication of the median amplitude of said sinusoidal signal cycle;
- and
- (d) shifting the amplitude values of the sinusoidal signal half-cycle adjacent said median toward the value of said reference voltage by an amount equal to the difference between said median and said reference voltage.
In an electro-optical measuring system which comprises generating a sinuosidal electrical signal in response to displacement to be measured and relating the amplitude of said signal to a preselected reference voltage to provide an indication of the extent of said displacement, an improvement which compensates for extraneous shifts in the level of said signal, said improvement comprising:
- (a) generating a second signal in phase quadrature with said sinusoidal signal;
- (b) gating a sample amplitude value of said sinusoidal signal whenever the amplitude of said second signal equals said preselected reference voltage, thereby to obtain an indication of the amplitude values of said sinusoidal signal at substantially the maximum and minimum of a given cycle of said sinusoidal signal;
- (c) averaging said sampled values to obtain an indication of the median amplitude of said sinusoidal signal cycle;
- and
- (d) shifting the amplitude values of the sinusoidal signal half-cycle adjacent said median toward the value of said reference voltage by an amount equal to the difference between said median and said reference voltage.
Means for correcting errors resulting from the DC level shift, with respect to a preselected reference voltage, of a sinusoidal electrical signal generated in an electro-optical measuring system in response to displacement to be measured, said correcting means comprising:
- (a) means for generating a second signal in phase quadrature with said sinusoidal signal;
- (b) means for comparing said second signal to said preselected reference voltage and generating a sampling trigger pulse whenever the amplitude of said second signal equals said reference voltage;
- (c) means responsive to said trigger pulses for providing an indication of the amplitude of said sinusoidal signal at the time of occurrence of each such pulse, thereby to obtain an indication of the amplitude values of said sinusoidal signal at substantially the maximum and minimum of a given cycle of said sinusoidal signal;
- (d) means for averaging said maximum and minimum values to thereby obtain an indication of the median amplitude of said sinusoidal signal cycle;
- and
- (e) means for utilizing the value of said median amplitude to shift the amplitude values of the sinusoidal signal half-cycle adjacent said median toward the value of said reference voltage by an amount equal to the difference between said median and said reference voltage.
Dependencies are inferred from the claim text.