| 摘要 |
A ripping tool (60) positioned below the earth's surface is driven by the output of a vibrating, preferably resonant force transmitting beam (64) which has lateral dimensions smaller than those of the ripping tool and is positioned below the earth's surface. The beam is configured to have a single resonant node when restrained from vibrating at such node and is supported (66) so that the single node is above the earth's surface and restrained from vibrating. The output of the beam is enlarged in thickness to form a hammer. A protective gap is maintained by a tool stop (62) between the tool and the output of the force transmitting beam. The width of the tool stop is precisely controlled by shimming (63) the tool stop and/or the supports for the force transmitting beam. |
