| 摘要 |
A power tool (1) has a percussive driving means for driving an impact tool (8). The driving means, which may be hydraulic or pneumatic, retracts the impact tool (8) on its return stroke, against the force developed by heavy-duty elastic ropes (24). During the impact stroke the impact tool (8) is urged downwardly by the elastic ropes and, if the tool is upright, by gravity. At the start of the impact stroke the ram (10) is uncoupled by means of a ball clutch. At the beginning of the return stroke the ball clutch acts to couple the ram once again to the weight (20) and impact tool (8), in order to lift these to the retracted position. It will be appreciated that the uncoupling of the ram for the impact stroke reduces the loss arising from the resistance of the ram.
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