| 摘要 |
PROBLEM TO BE SOLVED: To dig with the self-weight of an excavating device and a digging tool by automatically adapting the descending speed of the excavating device to the biting speed of the digging tool, in a pile driver for raining and lowering the excavating device using a rack method or an endless chain method. SOLUTION: A lifting device 3 and the excavating 8 are interconnected in such a way that the interval between them is variable, and a limit switch 10 for detecting the interval between the lifting device 3 and the excavating 8 is provided between them. The descending side circuit 17 of the drive circuit 12 of the lifting device 3 is provided with a solenoid valve 18 for stopping or lowering the lifting device 3 and is connected to the limit switch 10 by an electric circuit 20.
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