In previous introductory columns, we've introduced topics such as "Why measure sound and vibration?" and "Equipment for measuring sound."
This time, I'll be talking about "why we measure torque" and "the equipment used to measure torque."
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Torque is
Torque refers to "the force that causes a rotation around a certain axis."
For example, when you ride a bicycle, you have to pedal, and the force you exert to pedal is equivalent to torque. Other examples include the force you use to turn a doorknob when opening or closing a door, or the force you apply when opening and closing a bottle cap.
The unit of torque is expressed as N·m according to international standards and is read as "Newton-meter".
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Why measure torque?
Torque is defined as "the force that causes something to rotate." In the bicycle example mentioned earlier, strong torque means that you are pedaling with strong force, and the harder you pedal, the faster the bicycle will accelerate. In this case, "strong torque = strong acceleration." Strong acceleration means that the number of times the wheels rotate (rotational speed) in a given time increases, so the bicycle will go faster and be able to travel a longer distance in a given time.
The bicycle mentioned above is just one example, but rotating machinery and components are used in many fields, both industrial and consumer. Torque measurement is one of the important indicators for evaluating their performance.
About torque sensors (torque detectors)
Torque can be detected using two methods: one that measures torque from the twist angle (phase angle) of the shaft (phase difference method), and another that measures torque from the torsional strain of the shaft (torsional strain measurement method). Each of these methods has two detection techniques.
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Phase difference method
①Electromagnetic gear phase difference method
②Electromagnetic induction phase difference method
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Torsional strain measurement method
③ Distortion type
④ Magnetostrictive type
The torque detectors we manufacture use detection methods ①, ②, and ③.
In this column, we will explain items ① and ②, which have been the best-selling items to date.
Electromagnetic gear phase difference method
As shown in Figure 1, the torque sensor has gear A on the drive side and gear B on the load side of the torque transmission shaft. The twist angle between gears A and B is measured as a phase difference. The movement of each gear is captured by electromagnetic sensors C and D, and their output signals are fed into a torque calculation display, where the torque value is calculated from the phase difference of the signals.
Furthermore, torque is generated not only when the axis of the object is rotating, but also when it is stationary. Therefore, this detection method constantly generates a phase difference signal by continuously rotating a rotating hollow cylinder inside the torque detector at a constant rotational speed using a motor attached to the detector, allowing torque to be detected even when the axis of the object is stationary.
Electromagnetic induction phase difference method
In this system, phase difference plates are attached to both the drive and load sides of the torque transmission shaft. The phase difference plate has a structure in which slit-shaped holes are made of a thin metal plate. As shown in Figure 2, the drive coil and detection coil are arranged so as to sandwich the phase difference plate, and when the torque shaft twists, the magnetic field passing through the phase difference plate changes. This is extracted as a signal by the detection coil. This signal is input to a dedicated torque calculation display unit to calculate the torque value.
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This time, I gave a brief explanation of torque measurement, but each detection method has its own characteristics, and it is necessary to choose the optimal torque detector that suits your purpose and application.
I'd like to discuss these topics on another occasion.
The torque meters we handle are as follows:
Please take a look if you are interested.
Torque meters / related products
(Excerpt from the email newsletter issued on November 17, 2021)
