Torque sensors are primarily used to measure various torques, speeds, and machine compliance. They can convert changes in torque into electrical signals, and their accuracy is related to the accuracy of the testing system. Therefore, the accuracy of torque sensors is crucial. Their main feature is the ability to measure not only steady-state torque but also dynamic and static torque; moreover, they have high detection accuracy, good stability, and strong anti-interference capability. They can continuously measure forward and reverse torque without repeated zeroing, lack wearing parts such as conductive rings, and can operate at high speeds for extended periods. They output high-level frequency signals that can be directly sent to a computer for processing.
Development History of Torque Sensors
Although the technology of instruments has become increasingly mature, its development history has only gone through three stages.
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The Emergence of Measurement Technology In 1678, Robert Hooke published Hooke's Law, which established the proportional relationship between extension and the tension of related materials. Moreover, the emergence of bridge circuits enabled the measurement of very small voltage variations.
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The Birth of Torsional Sensors In 1945, a torsion sensor was introduced to the market. It operated on the principle that if the axial torque of the shaft loaded below rotates by one angle, the torque will also change proportionally, and this rotation angle can be measured by a measurement system.
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The Invention of Contemporary Torque Sensors Contemporary torque sensors have analog signal outputs, and adjacent drivers may experience disturbances in these interfaces. The emergence of digital electronic sensors in the future has strengthened their anti-interference ability.
Detailed Explanation of Torque Sensor
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Measurement Principle of Torque Sensor Attach a special torsional strain gauge to the tested elastic shaft to form a strain bridge. Measure the electrical signal of the elastic shaft by supplying power to the strain bridge. After the strain signal is amplified, it is converted into a frequency signal proportional to the distortion by voltage/frequency conversion.
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Structure of Torque Sensor The dedicated torque measurement board is a basic torque sensor installed on a dedicated elastic shaft to form a variable bridge. The shaft is fixed with: (1) the secondary coil of the energy ring transformer, (2) the primary coil of the signal ring transformer, and (3) a printed circuit board on the shaft, including a rectifier and voltage regulator power supply, instrumentation amplifier circuit, voltage conversion circuit, and signal output circuit.
Installation Steps for a Torque Sensor
Based on the connection of the length of the shaft and torque sensor, determine the distance between the prime mover and the load capacity, and adjust the distance between the axis of the prime mover and the load system relative to some reference data planes, so that the coaxiality of their axes is less than 0.03mm. Install the coupling on each respective shaft. Adjust the distance between the torque sensor and the reference plane to ensure that the coaxiality and load between the shaft and the prime mover shaft are less than 0.03mm, and fix the torque sensor on the reference plane. Fix a coupling and have the installation personnel complete it.
Characteristics of Torque Sensor
- Sensitive Signal Output: The waveform square wave or pulse wave can be freely selected.
- Quality Assurance: High detection accuracy, good stability, and strong anti-interference capability.
- Ease of Use: No need to repeatedly reset to zero; continuously measure positive and negative torque.
- Simple Device: Small in size, light in weight, and can be used independently without the need for secondary instruments.
- Power Supply Requirements: According to the number of pin connections in the information socket, only +15V and -15V (200mA) power supply can be provided, and the output impedance and torque are directly proportional to the square wave or pulse frequency signal.
Types of Torque Sensors
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Non-Contact Torque Sensor Non-contact torque sensors are also a type of dynamic torque sensor, known as torque sensors, torque speed sensors, rotational torque sensors, etc. The input shaft and output shaft are connected by torsion bars, with the input shaft being a keyway and the output shaft being a keyway. When the torsion bar twists under the action of rotational torque, the relative position of the spline and keyway changes, and the change in their relative displacement is the torsion of the torsion bar. This process changes the magnetic induction intensity on the spline and converts it into a voltage signal through the coil. Characteristics include a long service life, high reliability, minimal wear, small delay, minimal influence from the shaft, and a wide application range.
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