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Atorque motor is a specialized form ofDCelectric motor which can operate indefinitely whilestalled, without incurring damage. In this mode of operation, the motor will apply a steadytorque to the load (hence the name). A torque motor that cannot perform a complete rotation is known as alimited angle torque motor.Brushless torque motors are available; elimination of commutators and brushes allows higher speed operation.[citation needed]
Torque motors normally usetoroidal construction, allowing them to have wider diameter, more torque, and better dissipation of heat. They differ from other motors in their higher torque, thermal performance, and ability to operate while drawing high current in a stalled state.
An analogous device, moving linearly rather than rotating, is described as a 'force motor'. These are widely used forrefrigerationcompressors and ultra-quietair compressors, where the force motor producessimple harmonic motion in conjunction with a restoring spring.
A common application of a torque motor would be the supply- and take-up reel motors in atape drive. In this application, driven from a low voltage, the characteristics of these motors allow a relatively constant light tension to be applied to the tape whether or not the capstan is feeding tape past the tape heads. Driven from a higher voltage (and so delivering a higher torque), the torque motors can also achieve fast-forward and rewind operation without requiring any additional mechanics such as gears or clutches.
In the computer gaming world, torque motors are used in force feedback steering wheels.
Another common application is the control of thethrottle of aninternal combustion engine in conjunction with anelectronic governor. In this usage, the motor works against a return spring to move the throttle in accordance with the output of the governor. The latter monitors engine speed by counting electrical pulses from the ignition system or from a magnetic pickup and, depending on the speed, makes small adjustments to the amount of current applied to the motor. If the engine starts to slow down relative to the desired speed, the current will be increased, the motor will develop more torque, pulling against the return spring and opening the throttle. Should the engine run too fast, the governor will reduce the current being applied to the motor, causing the return spring to pull back and close the throttle.
Torque motors can be used asactuators fordirect-drive mechanisms in some situations where otherwise geared electric motors would be used; for example, inmotion control systems orservomechanisms. Actuators are hardware devices that converts the controller command signal into a change in a physical parameters.
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