A torque motor is a specialized form of
DC electric motor
An electric motor is a machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a electromagnetic coil, wire winding to gene ...
which can operate indefinitely while
stalled, without incurring damage. In this mode of operation, the motor will apply a steady
torque
In physics and mechanics, torque is the rotational analogue of linear force. It is also referred to as the moment of force (also abbreviated to moment). The symbol for torque is typically \boldsymbol\tau, the lowercase Greek letter ''tau''. Wh ...
to the load (hence the name). A torque motor that cannot perform a complete rotation is known as a limited angle torque motor.
Brushless torque motors are available; elimination of commutators and brushes allows higher speed operation.
Construction
Torque motors normally use
toroid
In mathematics, a toroid is a surface of revolution with a hole in the middle. The axis of revolution passes through the hole and so does not intersect the surface. For example, when a rectangle is rotated around an axis parallel to one of its ...
al 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.
Linear versions
An analogous device, moving linearly rather than rotating, is described as a ''. These are widely used for
refrigeration
Refrigeration is any of various types of cooling of a space, substance, or system to lower and/or maintain its temperature below the ambient one (while the removed heat is ejected to a place of higher temperature).IIR International Dictionary of ...
compressor
A compressor is a mechanical device that increases the pressure of a gas by reducing its volume. An air compressor is a specific type of gas compressor.
Many compressors can be staged, that is, the gas is compressed several times in steps o ...
s and ultra-quiet
air compressor
An air compressor is a machine that takes ambient air from the surroundings and discharges it at a higher pressure. It is an application of a gas compressor and a Pneumatics, pneumatic device that energy conversion, converts mechanical power (from ...
s, where the force motor produces
simple harmonic motion
In mechanics and physics, simple harmonic motion (sometimes abbreviated as ) is a special type of periodic motion an object experiences by means of a restoring force whose magnitude is directly proportional to the distance of the object from ...
in conjunction with a restoring spring.
Applications
Tape recorders
A common application of a torque motor would be the supply- and take-up reel motors in a
tape drive
A tape drive is a data storage device that reads and writes data on a magnetic tape. Magnetic-tape data storage is typically used for offline, archival data storage. Tape media generally has a favorable unit cost and long archival stability.
...
. 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.
Computer games
In the computer gaming world, torque motors are used in force feedback steering wheels.
Throttle control
Another common application is the control of the
throttle
A throttle is a mechanism by which fluid flow is managed by construction or obstruction.
An engine's power can be increased or decreased by the restriction of inlet gases (by the use of a throttle), but usually decreased. The term ''throttle'' ha ...
of an
internal combustion engine
An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal comb ...
in conjunction with an
electronic 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.
Actuators
Torque motors can be used as
actuator
An actuator is a machine element, component of a machine that produces force, torque, or Displacement (geometry), displacement, when an electrical, Pneumatics, pneumatic or Hydraulic fluid, hydraulic input is supplied to it in a system (called an ...
s for
direct-drive mechanism
A direct-drive mechanism is a mechanism design where the force or torque from a prime mover is transmitted directly to the effector device (such as the drive wheels of a vehicle) without involving any intermediate couplings such as a gear train ...
s in some situations where otherwise geared electric motors would be used; for example, in
motion control systems or
servomechanism
In mechanical and control engineering, a servomechanism (also called servo system, or simply servo) is a control system for the position and its time derivatives, such as velocity, of a mechanical system. It often includes a servomotor, and ...
s. Actuators are hardware devices that converts the controller command signal into a change in a physical parameters.
References
External links
*https://www.machinedesign.com/motors-drives/article/21832523/torque-motors-do-the-trick overview article in trade journal
*https://www.kollmorgen.com/sites/default/files/public_downloads/Kollmorgen%20Inland%20Motor%20Direct%20Drive%20DC%20Motors%20Catalog%20EN.pdf
Electric motors
Actuators
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