| 摘要 |
PROBLEM TO BE SOLVED: To accurately detect the beam position of reflection light and to accurately measure a height by allowing an optical filter to pass only reflection light within a horizontal surface including a light axis out of reflection light being distributed in a direction at right angle to the light axis. SOLUTION: Laser beam 8 becomes only circular polarization beam by a polarization plate 3 and further circular polarization beam by a λ/4 plate 5 and irradiates a linear object 50. Then, only irradiating beam from the normal direction of a sectional circle is reflected in a normal direction, returns coaxially along a plane including a light axis and becomes straight line polarization beam by the λ/4 plate 5, and is reflected at right angle by a polarization beam splitter 4. A light-shielding plate 7 passes only reflection beam in a normal direction and a photo detector 6 output a light-quantity signal S1 that is proportional to the quantity of received light. A calculator 40 calculates a position X1 of an optical head 10 when the quantity-of-light signal S1 is at its peak based on the quantity-of-light signal S1 and a position signal P1 of the optical head 10 from a scanning mechanism 30. Then, the height of the linear object 50 is measured from a gap to a position X2 that is calculated by rotating the optical head 10 by 180 degrees. |
