Abstract: To permit reliable turn-OFF of the motor when the torque of the motor is sufficient to provide for reliable seating of a screw or nut being driven thereby, start conditions of the motor are sensed, either in form of low-current condition or high power factor; high-torque conditions are sensed by low power factor, or high-current, in dependence on the desired torque level which results, respectively, in a comparatively steep phase angle-torque or current level-torque curve. A switch control is energized to turn-OFF the motor current if the phase angles, or the motor current, respectively, are beyond predetermined levels. To prevent in-rush current, or high power factors from affecting the operation of the turn-OFF system, timing circuits are provided to disable the turn-OFF system when the motor is first turned-ON or if the phase angle difference, as determined by time-comparator networks, between current and voltage, is below a predetermined value.

Abstract: A helical spring couples a drive shaft geared to the motor with the work spindle. With this arrangement hard screwdriving operations can be extended in time so that time is added for the drive motor to come a stop after it is switched off. Transducers are provided for measuring the torque at which motor switch-off occurs, and also the cumulative angle of rotation, the latter for detecting defective screws. No switchdown of the drive speed is necessary before the screw is driven home.

Abstract: To reduce operating noise, and particularly the impact of sound pressure waves on the internal structure of the planing machine, the edges defining separating walls against which sound waves may impinge are inclined with respect to the axis of rotation of the cutter (16) or a theoretical line (46) parallel thereto, thereby extending the time of impact of individual pressure waves emanating from the cutter of incremental surface areas of the respective edges (26, 48, 50; 42, 52, 54; 30) to simultaneously attenuate the impact of the pressure waves and the timing of the impact.

Abstract: A power screwdriver that is equipped with a spring coupling between the motor drive and the tool spindle, a signal that indicates that a certain value of torque has been overstepped, at which the screwdriver must be sopped, first causes reversal of the motor, but before the motor appreciably turns in the reverse direction, powers shut-off, allowing the motor to coast. After another brief interval, power is reapplied to the motor in the original direction, again briefly. In this way it is possible for the final shut-off to occur when the motor is stopped and the spring is unstressed, avoiding oscillations of the motor-spring system. A triac bridge circuit makes possible quick reversals and brief applications of power. In such a bridge circuit, precautions must be taken to be sure one pair of triacs is extinguished before the other pair is ignited.