Non-contact torsion sensor using fibre Bragg gratings

Abstract

Non-contact measurement of torsion on a rotating shaft was done with fibre Bragg gratings and involved the use of graded index lenses for transmitting optical information between the light source and the gratings, and back to a spectrum analyser. Special Böhler steel with high yield strength was used for the shaft. For the experimental measurements, one end of the shaft was clamped in a lathe chuck, and the other end was fixed to a brake system, allowing the application of torque on the rotating shaft. Up to 97 N m of torque was applied to the shaft rotating at 190 rpm, and the results were very close to the expected values. Whereas torsion changes the differential-mode wavelength of the gratings in the proposed configuration, this wavelength difference is insensitive to temperature. For the particular system investigated experimentally, the differential wavelength change was 7.4 pm N −1 m −1 , and the corresponding temperature sensitivity was −0.547 pm • C −1 .

Fiber-Optic Sensors for Measurements of Torsion, Twist and Rotation: A Review

“…In these configurations, conventional fiber-optic strain sensors (mostly FBGs) are applied to measure directly the shear stress at the surface of the measurement body, while this measured stress is then correlated to twist/rotation or torque. Differential configurations of FBGs or other fiber-optic strain sensors, at a 45° angle relative to the shaft axis (Figure 26) are, thus, commonly employed to enhance the sensitivity and achieve efficient temperature compensation as, for example, shown in [106,107,108,109,110,111]. Similar results can be achieved by specially designed measurements bodies as, for example, reported in [112].…”

A Two Fiber Bragg Gratings Sensing System to Monitor the Torque of Rotating Shaft

“…The reflection spectra of two FBGs undergoing dynamic uniform strain are symmetrical about their central wavelengths, and the dependence relationship of the wavelength on the strain and temperature change can be written as [ 3 , 4 , 5 , 6 ]: where and are respectively the strains at the midpoints of two FBGs pasted along the direction of 45° on the surface of circular shaft as shown in Figure 3 , so , . Δ T is the temperature change, λ 10 and λ 20 are the initial wavelengths of two FBGs without the strain, p e = 0.22 is the effective elastooptic parameter of optical fiber.…”

“…Compared with electrical sensors, fiber Bragg grating (FBG) sensors have unique advantages such as immunity to electromagnetic fields, compatibility with harsh environmental conditions, multiplexing capabilities, high sensitivity, small volume, light weight and low noise. Therefore, FBGs are becoming widely used in health monitoring, vibration measurement, and other areas and are attracting more and more attention in diverse application [ 3 , 4 , 5 , 6 ]. Antunes proposed an L-shaped beam-based FBG sensor to monitor structure vibration [ 7 ], Weng constructed a diaphragm-based acceleration sensor for structure health monitoring [ 8 ], Liu presented a flat diaphragm-based FBG sensor to determine the vibration acceleration of a measured body [ 9 ], Wang proposed a non-contact magnetic coupling FBG sensor to achieve non-contact measurements of object displacement [ 10 ] and Tan presented a non-contact vibration FBG sensor to monitor the vibration of rotating shafts [ 11 ].…”

Field Demonstration of Real-Time Wind Turbine Foundation Strain Monitoring

“…Indeed, both Higuera et al and Ciang et al [ 9 ] highlight the value of FBG sensors for fatigue and damage-detection in wind turbine components. Previous research in this area has included FBG strain gauges in blades [ 10 ], wind turbine towers [ 11 ], foundation piles [ 12 ], gearboxes [ 13 , 14 ], accelerometers [ 15 ], and for temperature and generator current measurements [ 16 , 17 , 18 ]. Higuera specifically notes that the instrumentation of onshore, concrete wind turbine foundations with optical fibre sensors could provide valuable structural health monitoring data during construction and operation [ 8 ].…”