Overview and working principle of torque sensor

1、 Overview of Torque Sensor

A torque sensor is a detection device that can sense the measured torque information. Its function is to convert the natural signals related to torque into electrical signals or other required forms of information output to meet the requirements of information transmission, processing, storage, display, recording, and control< a>

2. Working principle of torque sensor

1. Principle of automotive steering system

When the car turns, the torque sensor will feel the torque and intended direction of rotation of the steering wheel, and these signals will be sent to the electronic control unit through the data bus. The electronic control unit will send action commands to the motor controller based on the transmission torque, intended direction, and other data signals. The motor will output corresponding rotational torque according to specific needs< a>

2. Principle of static torque sensor (resistance strain principle)

Static torque sensor converts the strain generated by torsional torque into an electrical signal that is linearly related to it based on the resistance strain principle. Static refers to the measurement of elastic bodies by sensors that do not participate in relative motion. From the perspective of force, this type of test is to test the relative reaction force of an elastic body. Static torque sensors should not rotate more than 360 degrees and are generally used to test situations where torque changes slowly. The sampling speed is generally less than 50 times per second, such as testing manual torque wrenches, static load torque of transmissions, etc< a>

3. Principle of dynamic torque sensor (strain electrical measurement technology)

The dynamic torque sensor can measure the electrical signal of the elastic shaft being twisted. It uses strain electrical measurement technology to form a strain bridge on the elastic shaft, thereby providing power to the strain bridge. After amplifying the signal, it undergoes frequency conversion to become a frequency signal proportional to the strain. Generally used to test situations with drastic torque changes, it is necessary to implement torque capture or peak torque, such as tightening machines, electric wrenches, motor output torque, engine output torque, drill pipe torque, etc< a>

4. Principle of non-contact torque sensor

The input shaft and output shaft of non-contact torque sensor are connected by a torsion bar, and the input shaft has a keyway and the output shaft has a keyway.

. When the torsion bar is twisted by the rotational torque of the steering wheel, the relative position between the keyway on the input shaft and the keyway on the output shaft is changed. The relative displacement change between the spline and keyway is equal to the twisting amount of the torsion rod, causing the magnetic induction intensity on the spline to change. The change in magnetic induction intensity is converted into a voltage signal through the coil. Due to its non-contact working mode, it has a long lifespan, high reliability, is less susceptible to wear, has less delay, and is less affected by shaft deflection and axial offset. It has been widely used in the field of sedans< a>

5. Principle of strain gauge torque sensor (strain electrical measurement technology)

Strain gauge sensor torque measurement adopts strain electrical measurement technology. Attach strain gauges to the elastic shaft to form a measuring bridge. When the elastic shaft undergoes slight deformation due to torque, it causes a change in the resistance value of the bridge. The change in resistance of the strain bridge is converted into a change in electrical signal to achieve torque measurement. The sensor consists of an elastic shaft, a measuring bridge, an instrument amplifier, and an interface circuit. Its characteristics are high resolution, small error, large measurement range, low price, easy to choose and use in large quantities< a>

6. Principle of Phase Difference Torque and Speed Sensor (Magnetoelectric Phase Difference Torque Measurement Technology)

When there is a phase difference, the torsion sensor is a torsion angle phase difference sensor. Its principle is to install two sets of gears with exactly the same number of teeth, shape, and installation angle on both ends of the elastic shaft according to the magneto electric phase difference torque measurement technology, and install a proximity sensor on the outside of the gear.

. When the elastic shaft rotates, the waveforms of the two sets of sensors produce a phase difference, thereby calculating the torque. Its main feature is the non-contact transmission of torque signals, the detected signal is a digital signal, and the speed is relatively high. However, this type of torque sensor has a large volume and poor performance at low speeds, so its application is not very widespread< a>

3. Classification of torque sensors

1. Classification by measurement state

Static torque sensors: As mentioned above, they are suitable for situations with slow torque changes, rotation not exceeding 360 degrees, low sampling speed, and work according to the principle of resistance strain< a>
Dynamic torque sensor: can be used in situations with severe torque changes, can capture torque or torque peaks, and uses working principles such as strain electrical measurement technology< a>

2. Classified by working mode

Non contact torque sensor: The input and output shafts are connected by a torsion bar, and the change in magnetic induction intensity caused by the relative position of the spline and keyway is converted into a voltage signal to measure torque, which has the advantages of long service life.

< a> Strain gauge torque sensor: A measuring bridge is composed of strain gauges attached to an elastic shaft, and torque measurement is achieved using strain electrical measurement technology. It has the characteristics of high resolution and small error< a> Phase difference torque speed sensor: Based on magneto electric phase difference torque measurement technology, the torque is calculated by the waveform phase difference generated by the gears at both ends of the elastic shaft and the proximity sensor. The signal is a digital signal, but it has problems such as large volume and poor low-speed performance< a>

4. Application areas of torque sensors

1. Detection of rotating power equipment

Used for detecting the output torque and power of rotating power equipment such as electric motors, engines, and internal combustion engines.< a>

2. Mechanical device testing

It can detect the torque and power of fans, water pumps, gearboxes, and torque wrenches, and is also used for torque and power testing in railway locomotives, automobiles, tractors, airplanes, ships, and mining machinery.

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3. Other fields

It can be used for torque and power detection in sewage treatment systems, for manufacturing viscometers, and also has applications in process and industrial processes. It can also be used in laboratories, testing departments, production monitoring, and quality control.

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Fifth, the selection guide for torque sensors

1. According to the torque type of the measured object

If the measured object is dynamic torque, such as measuring the starting curve, stopping curve, and various working conditions of the motor, a measuring instrument with an analog output port that can output analog signals should be selected.< a>

2. According to the working conditions of the application,

When using in the laboratory, try to choose a torque meter with higher accuracy, and the accuracy level should not be lower than 0.5 or 1;

; If the application is in an industrial field, a torque meter with high reliability and simple structure must be selected, and the accuracy is not required to be too high. The accuracy level is generally 1, 2, or 3< a>

3. According to the structural characteristics of the tested object and the testing location

Try to use non-invasive sensors, and the shaft system can be continuously opened in the measurement situation.

. If an interventional sensor is used, the shaft system must be disconnected, and the elastic shaft, as a component of the machine, intervenes in the entire transmission system, which is inconvenient to use< a>

4. Use non-contact signal transmission methods as much as possible based on the speed and rated torque value of the tested object.

. Contact transmission commonly uses slip ring type, which is prone to wear, requires frequent cleaning, is difficult to install, has low signal measurement accuracy, and the allowable measurement speed for measuring rotational torque is greatly limited. When measuring the high rotational speed of the object, a non-contact torque meter must be used. In addition, in terms of selecting the range of the torque sensor, considering that the accuracy of the sensor is calculated based on the full range, the range of the sensor should not be too large for the rated torque being measured, in order to avoid measurement errors during actual measurement; On the other hand, the range of the sensor must have sufficient margin for the measured object. If there is string vibration phenomenon in the measured torque, that is, the amplitude of string vibration torque is superimposed on the steady-state torque, the range of the sensor shall not be greater than 1.5 times the measured torque; If measuring dynamic torque, the selected sensor range should generally be more than twice the rated torque< a>