Apparatus for controlling nut runner

An apparatus for controlling a nut runner for tightening a fastener, comprising:

• a motor operatively connected to an output shaft of the nut runner for rotating said output shaft;
• speed reducer means for reducing a rotational speed of said output shaft, said speed reducer means comprising a switching clutch shiftable selectively in higher and lower speed positions for rotating said output shaft in respective higher and lower speed ranges;
• torque sensor means for detecting a tightening torque of said output shaft;
• means for presetting torque and speed values corresponding to a switching torque, a snug torque, a final torque, a higher motor speed, a medium motor speed, and a lower motor speed;
• comparator means for comparing the detected tightening torque of said output shaft with each of said preset torque values corresponding to said switching, snug and final torques, said comparator means outputting a signal when said detected tightening torque reaches each of said preset torque values;
• switching means responsive to the signal output from said comparator means, said switching means outputting a switching signal for switching a rotational speed and torque of said output shaft;
• motor driver means responsive to switching signal for controlling said motor and said output shaft through said speed reducer, thereby rotating said output shaft at said higher, medium and lower motor speeds, respectively;
• wherein when the switching clutch is shifted into said higher speed position said output shaft is rotated with a lower torque at said higher speed;
• when the detected tightening torque reaches the preset switching torque the rotation of said output shaft is interrupted, the switching clutch is shifted into said lower speed position and thereafter said output shaft is rotated with a medium torque at said medium speed;
• when the detected tightening torque reaches said preset snug torque the rotation of said output shaft is interrupted and thereafter said output shaft is rotated with a higher torque at said lower speed;
• and when the detected tightening torque reaches said preset final torque the rotation of said output shaft is stopped.