Patent ID: 7328125

Claim:
A measuring method of a shape of a cross-sectional circle, which is orthogonal to an axis of a cylinder to be measured, by the following steps (i) to (vi) using measuring means constructed of (a) a cylinder support jig, and (b) a mount having first, second and third sensors for detecting displacements, which are located on a cross section including the cross-sectional circle, are aimed at a measurement reference point (O 0 ) which is an intersecting point of the axis with the cross-sectional circle, and are arranged and fixed so that an angle formed between lines connecting the O 0 with the first sensor and the second sensor and an angle formed between lines connecting the O 0 with the second sensor and the third sensor are θ°, comprising: (i) a step of measuring each of distances ΔL 1 , ΔL 2 and ΔL 3 between each of the first, second and third sensors and intersecting points of lines connecting the respective sensors and the O 0 with a circumference of the cross-sectional circle of the cylinder to be measured, (ii) a step of calculating each of distances L 1 , L 2 and L 3 between the respective intersecting points of lines connecting the respective first, second and third sensors and the O 0 with a circumference of a cross-sectional circle of the cylinder to be measured and the O 0 according to the following equations: L 1 = LS 1 −ΔL 1 , L 2 = LS 2 −ΔL 2 , L 3 = LS 3 −ΔL 3 , wherein LS 1 , LS 2 and LS 3 are distances between each of the first, second and third sensors and the O 0 , (iii) a step of rotating the cylinder to be measured by θ° in a direction toward the second sensor from the first sensor, and repeating the steps (i) and (ii), (iv) a step of calculating a distance Δ 01 between a floating point 0 ′, which is a point on the cross-sectional circle of the cylinder to be measured corresponding to the O 0 before the rotation in the step (iii), and a line passing through the O 0 and intersecting at a right-angle with the line connecting the first sensor and the O 0 , from L 1 and L 2 obtained in the step (ii) and L 2 and L 3 obtained in the step (iii), (v) a step of calculating a distance between the 0′ and a line intersecting at a right-angle with a line connecting the first sensor and the O 0 at an intersecting point of the line connecting the first sensor and the O 0 with a circumference of a cross-sectional circle of the cylinder to be measured after the rotation, from L 1 obtained in the step (iii) and Δ 01 obtained in the step (iv), and (vi) a step of obtaining the shape of the cross-sectional circle based on the distance calculated in the step (v).