What Is a Torque Transducer?
A torque transducer is a transducer that converts the torque of a rotating or stationary device, such as an engine, into an electrical quantity for measurement.
Torque is the moment of force around a rotating shaft acting around a fixed rotating shaft. In a rotating body, the amount of torsion of the rotating shaft is converted into an electrical quantity using a strain gage, etc., and is taken out to a stationary part using a slip ring or radio to measure the transmitted torque and torque fluctuation. Stable measurement is possible from stationary conditions to the high-speed rotation range.
Torque transducers are used for research, testing, and inspection of rotating equipment. In selecting a transducer, it is necessary to consider rotating or non-rotating, rotational speed, environmental conditions, and mounting conditions.
Uses of Torque Transducers
In the development of automobiles, torque is measured over a wide range of components, including the engine, transmission, drive shaft, axle, motor, and auxiliary equipment. We examine the strength of each axis in bench-top and driving tests, analyze torsional vibration by frequency analysis of torque fluctuations, and resolve noise and vibration caused by engine torque fluctuations.
Motor testers can test motor performance by installing a torque transducer between the test motor and the load device. Powder brakes and hysteresis brakes are used for the load to measure output torque relative to rotational speed.
It is also used to measure the rotational load of the roller. The torque transducer between the drive motor and the roller makes it possible to measure the torque when feeding paper or foil to determine the optimum conditions.
Principle of Torque Transducers
Torque transducers are available in a variety of conversion methods: strain gage type for non-rotating types, and magnetostrictive, strain gage type, or phase difference type for rotating types. The strain gage type is widely used because of its superiority in terms of accuracy and stability. Contact-type slip rings, non-contact FM transmitter transmissions, optical devices, and rotary transformer transmissions can be used for signal extraction from rotating bodies.
In addition to strain gage, magnetostrictive, and phase difference methods, torque can also be measured by capacitive, spring, optical, and piezoelectric methods. In any of these methods, the transmitted data is converted from the amount of strain to torque using the elastic modulus of the material used.
1. Strain Gage Type
The strain gage type consists of four gages assembled in a bridge, and accuracy is improved by zero-point compensation and temperature compensation. Strain gages are attached to the surface of the shaft to be measured in two orthogonal directions at a 45-degree angle to the axis of rotation, and the amount of strain is measured and converted to torque.
2. Magnetostrictive Type
The magnetostrictive type uses magnetostrictive material on the shaft and excites it with a coil on the fixed side to measure changes in magnetic permeability for non-contact torque detection.
3. Phase Difference Type
The phase difference type is a method of non-contact data transmission by electromagnetic pickup of the phase difference between two magnetic gears. The disadvantage of this method is its large size.
4. Capacitance Type
The principle is the same as that of the variable capacitor, and torque can be detected by changes in capacitance.
5. Spring Type
Simple structure, and can be calculated by displacement using a torsion spring.
6. Optical Type
Detects polarization of optical material attached to the surface of the rotating shaft.
7. Piezoelectric Type
This method uses a piezoelectric element.
Types of Torque Transducers
1. Strain Gage Type
When measuring rotational torque with the strain gage method, the torque signal from the rotating shaft is extracted to the fixed side. In the telemeter type, an electronic circuit including an amplifier and strain gages is fixed on the rotating shaft, and measurement is possible with the electronic circuit on the rotating shaft. In the rotary transformer type, a strain gage is attached to the rotating shaft, and an AC signal is measured by the rotary transformer. In the slip-ring type, a strain gage is attached to the rotating shaft, and measurement is made by power supply and signal transmission through a slip-ring.
2. Spring Type
When measuring rotational torque with the spring type, there are several methods to detect the displacement before and after the torsion spring from the fixed side in a non-contact manner. In the electromagnetic gear phasing method, a gear is attached to the front and rear of the torsion spring, and the phase difference at the location of the gear teeth can be measured by an electromagnetic detector. In the electromagnetic induction phasing method, a phasing plate is fixed in front of and behind the torsion spring, and a differential coil and a drive coil are installed in two pieces in front of and behind the phasing plate to measure the output of the differential coil.