The core technology of torque sensors has undergone significant breakthroughs from traditional strain gauges to modern fiber optic sensing, driving fundamental changes in measurement accuracy and applicable environments.
Maturity and limitations of strain gauge technology
Traditional strain gauge torque sensors are based on the strain effect of metal or semiconductor materials. When the elastic shaft experiences shear strain due to torque, the resistance value of the strain gauge attached to the shaft surface changes accordingly, which is converted into an electrical signal through a Wheatstone bridge. This technology is mature and reliable, but it is susceptible to electromagnetic interference, temperature drift, and has limited long-term stability, making it difficult to meet high-precision requirements in the environment.
Breakthrough in the principle of fiber optic sensing
The emergence of fiber optic torque sensors marks a breakthrough in the principle level. It mainly uses fiber Bragg grating (FBG) technology: a periodic refractive index modulation grating region is made inside the fiber core. When torque is applied to the axis with the grating attached, strain causes a change in the grating period or effective refractive index, resulting in a shift in the center wavelength of reflection/transmission. By demodulating the wavelength displacement, the torque value can be accurately inverted.
Technological advantages and breakthroughs
Compared to strain gauges, fiber optic sensing has achieved multiple breakthroughs: firstly, its anti-interference ability has increased significantly. Fiber optic itself is an insulating medium, immune to electromagnetic interference, and suitable for strong electromagnetic environments (such as inside motors and generators); Secondly, breakthroughs in accuracy and stability have been made, with wavelength encoded signals not affected by fluctuations in the light source, and temperature and strain can be measured separately, significantly reducing drift; Thirdly, there is structural innovation, with sensors that are small in size and lightweight, enabling distributed measurement or embedding within composite materials, opening up new avenues for monitoring the state of rotating machinery and intelligent structural design.
The core technology of torque sensing, from measuring electrical signals from strain gauges to wavelength modulation of optical fibers, has moved from the analog electronics era to the photonics era. This principle breakthrough not only improves measurement performance, but also promotes the development of sensors towards miniaturization, integration, and networking, becoming a key link in equipment intelligence.