Linear magnetic clutch to automatically control torque output

A novel eddy-current Magnetic Clutch (MC) unit with its torque-adjustable mechanism is proposed by this research. As to mechanical structure, the MC unit is mainly constituted by a squirrel-cage inner rotor and a magnet-embedded outer rotor. The transmitted output torque can be adjusted by either the Overlapped Length (OL) or the relative angular velocity between outer rotor and inner rotor. Firstly, the mathematical model of the MC system is developed. Secondly, the features and characterization of the MC unit are explored by intensive experiments under various overlapped length and relative rotational speed between inner rotor and outer rotor. The major novelties of the MC system unit include: (i). being very handy to operate even for non-professional users, (ii). the output torque of the proposed MC can be adjusted automatically, and (iii). the proposed MC can be easily incorporated to any torque control system. To examine the validity of the MC unit, two control strategies, i.e., PID action and pole-placement method are presented and compared for the performance of the closed-loop feedback systems. In addition, the locations of system roots are found to ensure the stability of the torque control loops. At last, several experiments are undertaken, including constant torque control and variable torque control. Particularly, an experiment of screw-driven into a wooden board is conducted to illustrate the drilling quality much upgraded by the proposed torque control device. Besides, a couple of torque-tracking experiments realistically manifest the quick response and high precision of the MC unit. In summary, either for stability or performance, the proposed MC feedback system is eligible to execute superior torque tracking or torque regulation.