What Is a Torque Limiter?
A Torque Limiter is a device that shuts off or limits power transmission in the event of overload of rotating equipment.
They are mainly used to protect human bodies and mechanical equipment. Since there are various types of power shutdown structures, it is necessary to select one depending on the intended use.
Uses of Torque Limiters
Torque Limiters are used in a wide range of applications, from everyday commodities to large industrial equipment.
Specific applications are as follows:
- Swiveling functions of household fans
- Impact wrenches
- Automatic doors of department stores and elevators
- Lid opening and closing of toilet seats with automatic opening/closing functions
- Robot vacuum cleaners and cooperative robots
- Giant dampers for exhaust gas treatment equipment
Protect equipment and prevent personal injury by preventing the application of external, unexpected forces.
Torque Limiters can also be used to limit torque and equalize work, as in the case of impact wrenches. In power tools, they are used in many cases.
Principle of Torque Limiter
Torque Limiters are classified into two types based on their principle of operation. The powered disconnect type and the slip type.
1. Power Disconnect Type
This type of torque limiter cuts off the edge between the drive and driven shafts when the torque exceeds the set torque. Since no heat is generated due to slip, this type can be applied to large equipment.
2. Slip Type
The slip type limits torque by slipping between the drive and driven shafts when the set torque is exceeded. It is compact and inexpensive, but not suitable for high torque.
Types of Torque Limiters
There are various types of Torque Limiters. The following descriptions are some of them:
1. Friction Type
This type connects the drive and driven shafts via a multi-disc clutch or torsional recoil. The transmission force is limited by the slippage of the multi-disc clutch or torsional coil. In the multi-disc clutch type, the slip force can be adjusted by the clutch’s applied pressure. Since frictional force is used, frequent operation causes wear and reduces the transmission force.
2. Magnet Type
This is a method in which magnets are provided on the drive and driven shafts, and power is transmitted by the attractive force of the magnets. The shafts slip when the torque is overloaded, but there is no wear and no heat generation. Since the magnets are kept in contact with each other, the system is also quiet.
3. Clutch Type
The clutch operates to shut off the power when a torque greater than the set value is applied. By interlocking the clutch actuation with an electrical contact, it is possible to output a contact point.
4. Shear Pin Type
This method uses a material break called a shear pin. The specified torque is set by the shear pin material and notch diameter. The torque is limited by stopping when the installed shear pin breaks. This method is used for large equipment because of its simple structure and relatively low cost. However, periodic replacement of parts is required, and the shear pin must be replaced after operation.
5. Electric Type
All of the above are mechanical Torque Limiters, but it is also possible to limit torque with an electrical interlock. A shock relay or inverter shuts off the power supply in the event of an overload.
When an inverter is used, it is also possible to limit torque by controlling the current value. Cooperative robots, for example, may limit torque using a torque sensor.
Other Information on Torque Limiters
Motor With Torque Limiter
Torque Limiters for industrial equipment are applied to motors with reduction gears. In the past, they were generally mounted on the sprocket section of the driven side. In recent years, reduction gear motors with Torque Limiters have been developed with the goal of downsizing.
Torque Limiters using a coil spring or load cell as a sensor is installed in the motor to enable highly accurate torque management. In addition, by incorporating different types of Torque Limiters not only in the motor but also in the sprocket section, double safety measures can be taken.
Torque Limiters with reduction gear motors are also available with adjustable bolts that allow the torque limit to be set as desired. The torque limit can be adjusted after installation on site.