| 摘要 |
<p>Disclosed is an electric tool equipped with a speed-changing device that automatically changes speeds in response to an increase in external torque added to a spindle, wherein the screw-tightening operation can be performed faster than with the prior art. In the high-speed, low-torque mode prior to an automatic speed change, an extremely high output rotational frequency is set to a degree such that an output torque is insufficient to perform screw tightening to the end. The output rotational frequency prior to the speed change is set in a range of approximately 4.5-6.0 times that of the output rotational frequency after the speed change. Thus, with the initial screw tightening the work can be performed quickly with a higher rotational speed than with the prior art, and after the automatic speed change the screw tightening can be completed with a large output torque.</p> |
