Abstract: A power tool has a flywheel for driving a working member such as the driver of a fastener tool. A motor mounted at a rear end of a tool handle drives the flywheel mounted in a tool housing at the forward end of the handle. A cable is secured to a drum and to the working member. A clutch selectively couples the flywheel to the drum to wind up the cable and drive the working member forcefully. A return cable is wound on the driver drum against a spring bias to rewind the drum, unwind the cable and return the working member to its prior status when the clutch decouples the flywheel from the drum. When coupled to the drum, the motor speed and flywheel speed is reduced. An electronic control operates the motor to recapture the initial speed within 500 milliseconds of the speed reduction. The electronic control includes a phase-locked loop velocity control.

Abstract: A series universal AC/DC motor is controlled by switching the phase angle of an AC signal with a triac power switch in response to a motor control providing a phase-locked loop velocity control. A speed command circuit provides a reference frequency corresponding to a selected motor speed. The reference frequency is compared to a feedback frequency representing actual motor speed. An error signal representing the phase difference between the reference and feedback frequencies is compared to a ramp signal produced by the AC power source, and a resulting trigger pulse is used to control the triac power switch, thereby regulating the speed of the motor.