| 摘要 |
PCT No. PCT/FI90/00229 Sec. 371 Date Mar. 17, 1992 Sec. 102(e) Date Mar. 17, 1992 PCT Filed Sep. 27, 1990 PCT Pub. No. WO91/05140 PCT Pub. Date Apr. 18, 1991.A drilling apparatus and a method for its control maintains the alignment of a drill head while driving a tunnel. The control is achieved by manipulating the center of gravity of a drill bit unit with respect to a line determined by two supporting points of a protecting tube which are the sole points of the protecting tube supported against the tunnel bottom.
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