TOK Torque Limiter web site

A torque limiter is an overload protection device that immediately blocks the input and output to protect the application when the load exceeds the setting.
For example, if a machine is no torque limiter and something trouble is occurred cause of something jam at the output side, a drive source such a motor may break down due to overload.
On the other hand, if the torque on the input side of a motor or other device is too high, the output side may break down.
By installing a torque limiter between the input and output sides, such component damage can be prevented.
As soon as the torque on the output side is back to the set torque or less, it returns from the protect condition to the transmission condition.

Power transmission is cut off

Power is being transmitted

Torque limiters are used in a wide range of applications, but TOK’s torque limiters are mainly used for paper separation to prevent overfeeding of bills and papers.

TOK torque limiter lineup and features

TOK is the only manufacturer in Japan to offer both spring and magnetic torque limiters in its product catalog.
The magnet type can handle high-speed rotation and has a long durability since the limited torque is not made by a friction but a non- contact magnet coupling.
On the other hand, the coil spring type is suitable for medium and low-speed applications because the torque source of the coil spring type is made by friction.
You can select the product that best suits your application and conditions of use.

Spring friction type toruqe limiters

Parts configurations of the spring friction type

The coil spring type consists of a housing, slider, sleeve, coil spring, lubricant, and cap.
Coil spring torque limiters have a sleeve press-fitted into the coil spring, and hooks at both ends of the spring contact the inside of the housing to prevent it from rotating in relative rotation with the housing.
When the sleeve rotates in this condition, the housing rotates through the hook of the spring.
However, when trying to transmit a torque higher than the set torque, the coil spring that is tightening the sleeve loosens and only the sleeve rotates with friction.
This friction is the principle of torque generation for coil spring type torque limiters.

The friction type of torque limiter how it works

Power is transmitted if within the rated torque.

State of a torque limiter

Power is cut off if the rated torque is exceeded due to overload.

State of a torque limiter

Magnetic hysteresis type torque limiters

Parts configurations of the magnetic hysteresis type

Magnetic torque limiters consist of the following parts: sleeve, magnet, semi-hard magnet, housing, bushing, slider, O-ring, and stopper.
The O-ring is used to prevent rattling between the sleeve and magnet, and the stopper functions as a detent between the sleeve and magnet, so that the sleeve and magnet are integrated without using any adhesive.
The housing and bushing are integrated with a semi-hard magnet and can rotate relative to the magnet.
Permanent magnets are pole-anisotropic ally magnetized with alternating N and S poles.
The semi-hard magnet is magnetized by a permanent magnet inserted in a non-contacting state, so that the part of the magnet that opposes the N-pole of the permanent magnet becomes the S-pole and the part that opposes the S-pole of the permanent magnet becomes the N-pole.
When the permanent magnet is rotated in this state, the permanent magnet and the semi-hard magnetic material are in a state where the magnetic forces repulsion each other around the entire circumference, and power is transmitted at a torque lower than this repulsive force.
However, as the transmission torque increases, the repulsive force of the magnet is defeated and the permanent magnet rotates while changing the magnetic poles of the semi-rigid magnetic material, thus shutting off the power.

The magnetic hysteresis type of torque limiter how it works

Power is transmitted if within the rated torque.

State of a torque limiter

Power is cut off if the rated torque is exceeded due to overload.

State of a torque limiter

Applications for torque limiter

〇For use as a safety mechanism
Electric shutters, conveyor belts, conveyor systems
For example, if something gets caught in a conveyor belt, a torque limiter can be used to stop the conveyor belt instantly, while the motor continues to run.

〇For use as paper feed or overfeed prevention
multi-function printer, card readers, OCR (high-speed scanners), printers, copiers
When using a multifunction printer or printer, the torque limiter prevents duplicate sheets of paper from being sent.

〇Tensioning and winding-up device
Windup device, label printers
Label printers can maintain tension on the roll of paper by using a torque limiter when printing and feeding labels.