| 摘要 |
PROBLEM TO BE SOLVED: To provide a ground excavator which prevents bits from interfering with each other and eliminates an unexcavated portion in the ground. SOLUTION: The ground excavator is provided with a cutter head 16 which is rotatably supported at the front end of an excavator body, and the cutter head 16 has a plurality of center bits 20 arranged at the center thereof, and a plurality of peripheral bits 22 arranged on the external peripheral side of the center bits 20. The bits are formed like an almost conical shapes, and circumferentially arranged at predetermined angular intervals so that an axis of each of the bits 20, 22 is oriented in a center axis direction. The peripheral bits 22 are formed so as to be expandable and contractible in diameter. The bits 20, 22 are reduced and shortened in diameter in order to avoid interference therebetween at the time of the diameter contraction of the peripheral bits 22, and at least one of the center bits 20 is shifted outward in order to be located between the remaining center bits and the peripheral bits at the time of the diameter expansion of the peripheral bits 22. COPYRIGHT: (C)2008,JPO&INPIT
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