| 摘要 |
PURPOSE: To simplify an optical adjustment and to prevent the erroneous detection of a focal position caused by the influence of a geometrical pattern on an object surface. CONSTITUTION: A rotation is imparted to an index luminous flux emitted through an index plate and an index image formed on the object surface 42 is rotated at the specified speed of the rotation on the object surface at an image rotator 18. When a luminous flux reflected by the object surface 42 by the irradiation of the index image is incident again from an opposite direction while rotating the index image, a reverse rotation is imparted to the luminous flux reflected at the image rotator 18 and the index image which is reformed and a light receiving surface are relatively rotated so as to always make the direction of the index image which is reformed definite with respect to the light receiving surface of a light receiving element 48. Therefore, the luminous flux reflected by the different area of the object surface is incident on the light receiving surface of the light receiving element 48 while rotating the index image, and the index image of the same direction is always image- reformed. |
