| 摘要 |
A speed control device for portable power tools having particular applicability to electric drills. The speed control device is adapted to automatically adjust the speed of the motor (15) in accordance with changes in the diameter of the tool bit used. The device includes a sensor that senses the opening and closing of the jaws of the chuck. The sensor is mechanically coupled to a potentiometer circuit (30) whose output signal is varied in accordance with movement of the sensor. The output signal of the potentiometer circuit (30) controls the firing angle of a thyristor (34), which in turn controls the current supplied to the motor. In addition, the preferred embodiment includes a speed select switch (SW1) which is connected to the potentiometer circuit (30) to set the appropriate speed range for the motor, given the particular type of work material. |
