Linear scale measuring device and position detection method using the same
AssigneeMitutoyo Corporation
InventorToshiharu Miyata
Life of this patent
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Abstract
A linear scale type measuring device capable of canceling an error caused by inclination of an encoder, a moire error, is disclosed. A linear encoder disposed relative to a scale includes two sensors A and B which are arranged such that they are inclined at a predetermined angle θ with regard to the scale. At the time of measurement, a detection value corresponding to that with no inclination can be obtained by an operation based on detection values from the sensors A and B, and the known angle θ, even when the encoder is further inclined by any angle δ.
Claims3
A linear scale measuring device comprising:
- a pair of scales;
- a linear encoder disposed relative to said pair of scales;
- and
- an operation unit for detecting the position of said linear encoder relative to said pair of scales based on an output from said linear encoder,
- wherein said linear encoder includes two sensors with regard to each of said pair of scales, the sensors being previously arranged such that they are inclined at a known angle with respect to the measuring direction of said scales, and
- wherein said operation unit detects the position of said linear encoder resulting from the inclination of the sensors with regard to the measuring direction of the scales, based on detection signals from the sensors and said known angle which is previously set, by calculating a detection phase of said linear encoder relative to a scale according to
- ΦO=(ΦAδ+ΦBδ)/2−2π/λ·L{sinθ+(ΦAO−ΦBO−ΦAδ+ΦBδ)/4πsinθ·cosθ}, and
- wherein the phases detected by said two sensors are ΦAδ, and ΦBδ, respectively, the initial phases of the two sensors are ΦAO, and ΦBO, respectively, said predetermined angle is θ, a wavelength of said scale is λ, and a distance between the rotation center of the sensors and the center point between the two sensors when the sensors are inclined relative to the scale by the predetermined angle θ is L.
A method of detecting a position using a linear scale type measuring device comprising a pair of scales and a linear encoder, the method comprising the steps of:
- (a) inclining two sensors arranged collinearly within said linear encoder at a predetermined angle with respect to each of said pair of scales;
- (b) detecting a phase of each of said sensors using said sensors relative to a scale;
- and
- (c) calculating a detection phase of said linear encoder relative to a scale based on the detected phases, said predetermined angle, and initial phases of said sensors, the detection phase of said linear encoder relative to a scale being calculated by
- ΦO=(ΦAδ+ΦBδ)/2−2π/λ·L {sinθ+(ΦAO−ΦBO−ΦAδ+ΦBδ)/4πsinθ·cosθ},
- wherein the phases detected by said two sensors are ΦAδ and ΦBδ, respectively, the initial phases of the two sensors are ΦAO, and ΦBO, respectively, said predetermined angle is θ, a wavelength of said scale is λ, and a distance between the rotation center of the sensors and the center point between the two sensors when the sensors are inclined relative to the scale by the predetermined angle θ is L.
Dependencies are inferred from the claim text.