| 摘要 |
PURPOSE:To obtain a unitized and smaller structure by a method wherein a photo receiving disk is rotated on a moving body, and a laser beam from a fixed light source is hit upon a photo detector through a slit and lens to determine the position of the irradiation point in the form of polar coordinates. CONSTITUTION:A slit 2 is formed in a photo receiving disk 1 to extend from the center O near to the circumference thereof, the disk being arranged in a proper position of a tunnel excavating shield, for example. A laser beam L having passed a slit 2 is defracted by a lens 3 to be hit upon a photo detector 4 which is arranged on a center axis of the photo receiving disk 1. A distance (r) from the center O to an irradiation point P is determined based on a photo receiving time of the photo detector 4. Then, an angle of rotation (theta) of the photo receiving disk 1 from the base line OX at the time when the photo detector 4 has received the laser beam is detected using, e.g., such means as a rotary encoder 6 mounted over a rotary shaft 5. As a result, the position of the irradiation point P is determined in the form of polar coordinates (r, theta) with the center O as the origin of coordinates. |
