A torque motor is an electrical motor that is used for applications at low rotary speed quite often in direct drive without gear.
Moreover, the torque motors are very often used in cyclic machines with acceleration, constant speed, deceleration and return and also in applications of machines with constant operation delivering a power at constant speed. Torque motors are therefore more often qualified in torque and related speed than in power and the maximum torque is equal to 3 to 4 times the rated torque for allowing high dynamics.
Traditionnally the applications of motion control in factory automation and in particular machine-tools used electrical motors with high rotary speed coupled through a gear to the load for reducing the motor speed and increasing the motor torque to the ones needed by the axis of the machine. However, the gears create problems of maintenance, reliability, accuracy, plays and loss of efficiency that penalize technically and economically the servomechanisms. That is the reason why the machine builders have initiated since several years to eliminate the gears by using motors rotating at low speed and consequently with high torque capability for achieving a direct drive of the automated axis.
Currently, the applications of torque motors and high torque motors are not only regarding motion control in processes and cyclic machines of factory automation but also motion control outside factories as stage technologies, amusement parks, electrical ground and subsea vehicles. There are DC and AC multiphase torque motors. Nowadays, the applications of AC three- phase synchronous permanent magnets Torque motors and High Torque motors, as ALXION ST and STK, are increasing more and more.
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