| 摘要 |
<p>A power tool (10) such as an electric drill typically contains a gear train (20) that couples the output spindle of the motor (16) to the tool bit-receiving chuck (22) and has associated therewith a degree of looseness which must be taken up before torque from the motor is applied to the tool bit. A control circuit (12) for the power tool increases the effective torque output of the tool by alternately turning the motor on and off, with the duration of the off-time sufficient to permit the gear train to relax, thus giving the motor a "running start" when power is reapplied. Various alternative schemes for transitioning to this ratcheting mode of operation are disclosed including the sensing of a predetermined threshold current, a predetermined increase in motor current, and a predetermined rate of deceleration in motor speed. The control circuit preferably provides the operator with means (14,15) for adjusting the transition point as well as for varying the duration of the on-time in the ratcheting mode. A corresponding method for controlling the operation of the electric motor of a power tool is also disclosed. <IMAGE></p> |
