Torque motors are a special class of brushless permanent-magnet synchronous motors. Since the payload is directly connected to the rotor without the use of transmission elements, torque motors are classified as direct drives.
Depending on your perspective, a torque motor is either a rolled-up linear motor or a classic servodrive with a large number of poles. It is the large number of poles that enables conventional torque motors to attain high torque at moderate speeds. Another attractive feature is their compact design which includes a narrow lamination stack and a large hollow shaft or bore.
As with linear motors, torque motors are a type of “frameless” motor. This means that the motor does not include a housing, bearings, or feedback device. These components can be selected by the machine builder and optimized according to the required performance, or purchased as part of an assembly.
Torque motors produce high torque at moderate speeds and even when stationary or “stalled”. Contrary to traditional drives, the sizing and selection of a torque motor is purely based on torque, not power. Fundamentally, the peak torque determines the maximum torque that the motor physically produces and the continuous torque defines the amount of torque the motor can continuously supply. The duty cycle of the application will define the dependency on peak or continuous torque.