| 摘要 |
A drill head assembly includes a shaft having a shaft axis, an oscillator assembly operatively associated with the shaft, the oscillator assembly having at least one eccentrically weighted rotor configured to rotate about a pivot point to generate an oscillating vibratory force, wherein an oscillation centerline is defined transverse to the shaft axis and including the pivot point. The drill head assembly also includes a lower bearing coupled to the shaft on a first side of the oscillation centerline and an upper bearing coupled to the shaft on a second side of the oscillation centerline, the second side being opposite the first side.
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