With the rapid development of sensor technology, torque sensors have become an important research direction. Torque measurement, as a key parameter reflecting the operating status and detection of various mechanical rotation systems, is related to the performance of the entire rotation system, manifested in its output power, energy consumption, service life, safety, and stability.
Torque measurement has been applied in various fields such as petroleum, automotive, shipbuilding, aerospace, construction machinery, transportation, dentistry, medical devices, motors, robotics, and bionic machinery. With the depletion of global resources and the demands of national strategies, the drawbacks of traditional contact-based torque measurement, such as easy wear and tear and susceptibility to environmental factors, have become increasingly apparent. To improve the measurement accuracy of torque sensors, reduce operating costs, and enhance anti-interference capabilities, non-contact electromagnetic torque measurement has emerged.
(Torque sensor)
Since the 1980s, after developed countries such as the United States and Japan developed electromagnetic torque sensors, the scientific community has conducted in-depth research on them. Various new types of electromagnetic torque sensors have emerged. The main sensors listed below represent innovations and improvements in structure, manufacturing processes, and measurement methods, making significant contributions to this field.
1. Vertical electromagnetic torque sensor
This type of sensor uses a master stage for measurement and a slave stage for calibration. Electromagnetic simulations were performed using Maxwell software to analyze parameters such as output voltage, number of excitation coil turns, and rotor thickness. The sensor's structural parameters were optimized using a combination of linear reduced-inertia-weighted particle swarm optimization and the finite element method. Groups with large voltage fluctuations and poor structural parameters were removed, and a set of design parameters was identified that caused errors in the sensor's nonlinearity. This set of parameters guided the sensor's manufacturing process, specifically for the electromagnetic torque of the vertical structure.
2. Hall effect torque sensor
This sensor uses a low-cost permanent magnet (N35 neodymium iron boron) as the excitation to generate a magnetic field. Its shape is designed as a sheet, with adjacent sheets having their N and S poles arranged in opposite polarities radially around the rotating shaft, forming a magnetic ring around the shaft. When the shaft rotates, the magnetic rings at both ends generate a periodic alternating magnetic field. Within this magnetic field, a Hall element generates a Hall voltage. Due to the phase difference between the two ends of the rotating shaft, the relative torsional angle between the two voltage signals can be calculated.
3. Differential electromagnetic induction torque sensor
One end of the output iron core of the sensor shaft is concentrically fixed to the rotating shaft, while the other end is connected to the sensor shaft via a bearing and can rotate. The output winding is arranged in the slot of the output iron core. The excitation core is fixed to the excitation bushing, and the excitation winding is mounted on the excitation core. The working principle of this sensor is to convert the torque angle signal into a closed magnetic circuit flux of the sensor, where the flux is generated by the magnetic circuit formed by the excitation core, the air gap, and the output iron core. Due to the load torque, the two magnetic fluxes of the output winding are no longer the same, and the generated electromotive forces are no longer equal. After differential output, the output winding will generate an electromotive force linearly related to the angle, and then through electromagnetic coupling, the electromotive force is proportional to the load torque T. This design achieves structural innovation while simultaneously enabling the measurement of both dynamic and static torque.
4. Annular ball grid electromagnetic torque sensor
By combining the measurement principle of optical grating torque sensors with electromagnetic methods, a novel electromagnetic torque sensor, named the ring-shaped spherical grating torque sensor, has been developed. Its principle still utilizes the phenomenon of electromagnetic induction, filling a gap in the field of combining optical gratings and electromagnetic methods.
The sensor consists of a ring-shaped magnetic steel ball and an electromagnetic detector array. Its main innovation lies in incorporating a ring-shaped ball grid while retaining the electromagnetic measuring head, thus perfectly combining the two. Since the ball grid ring is fixed, when the drive shaft rotates, the metal balls within the ring grid experience different magnetic reluctance compared to air. This change in magnetic reluctance translates into relative displacement between the reading head and the ball grid, allowing for the measurement of torque. This sensor boasts advantages such as stable physical properties and reliable structure.
In industry, electromagnetic torque sensors have been applied in power steering systems of traditional automobiles, transmissions and drive shafts, as well as in the transmission systems of ships and aircraft engines, test benches and motors, where torque measurement and power calculation are required.
Since the beginning of the 21st century, with the advancement of technology and the development of materials, this type of sensor has broken through the limitations of traditional industry applications and has begun to emerge in robotics and biomedicine.
