| 摘要 |
PURPOSE:To realize a method for preventing the bending of laser beam when measurement is performed by utilizing the laser beam by sending air having a constant temperature into a straight pipe wherein the laser beam passes, and maintaining the uniform temperature along the entire length and the entire space in the straight pipe. CONSTITUTION:A laser beam is projected on a photodetector 11 in a shield excavator 2 from a laser transmitter 10 which is provided in a starting vertical shaft 8 through the inside of an underground pipe 1. Whether the shield excavator 2 is directed toward the specified advancing direction or not is measured from the light receiving position. Thus, the excavation is performed. At this time, the temperature of the air in the buried pipe is high at the upper part and low at the lower part. The straight advance of the laser beam is impeded by the difference in temperatures. To eliminate the impedance, the air at the constant temperature is supplied to the underground pipe 1 from a blower 16 which is arranged in the starting vertical shaft 8. The temperature distribution in the buried pipe 1 is kept uniform by the air. Therefore, the laser beam from the laser transmitter 10 is uniformly projected on the photodetector 11 without bending in the buried pipe 1, and the survey and the measurement characterized by excellent accuracy can be performed. |
