| 摘要 |
PROBLEM TO BE SOLVED: To secure safety and to perform initial measurement immediately after excavation. SOLUTION: A control part 14 is electrically connected to sensor heads 10a, 10b, and 10c. A laser beam L is emitted to each of corresponding reflecting sheet 12a, 12b, and 12c from each of the sensor heads 10a, 10b and 10c. By individually receiving the reflected laser beam, the distances between the sensor heads 10a, 10b, and 10c and the reflecting sheets 12a, 12b, and 12c are each computed on the basis of the phase differences between the emitted and received laser beams, etc. The distances are automatically and continuously measured at all times during sampling time. By continuously obtaining distances between three points in an excavation cross section with time, it is possible to obtain the convergence of the excavation cross section from the principle of triangulation.
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