Research On Fiber Bragg Grating Torque Sensor Based On Magnetic Field Measurement

Torque is one of the most important parameters to characterize the performance of rotating mechanical systems.Therefore,the measurement technology for torque has become a critical section in research and development,quality verification,control optimization,condition monitoring and faults' diagnosis of various products.Fiber Bragg Grating(FBG)has been applied to vibration measurement of rotating machinery due to advantages of multi-points,strong ability of anti-electromagnetic interference,and easy to do distributed measurement until now.However,the measurement technology by FBG for the torque is complicated relatively at present,which means the FBG must be directly affixed to the shaft in order to obtain torque through sensing strain.For the intrusive technology,On the one hand,it is necessary to polish the smooth region on the shaft,and it is difficult to maintain.In addition,some auxiliary components like collimators must be used to transmit signal during rotation.For the mentioned disadvantages,we try to pick up the torque signal through magnetic circuit and then convert it into strain signal of the FBG in this article.The main research contents include:Firstly,a magnetic field measurement system was constructed based on the magnetic sensitivity of the magnetostrictive materials and the strain sensitivity of FBG,and a simple magnetic field generator was designed to test and analyze.Based on the experimental results we could acquire the linear interval of magnetic induction intensity for the design of magnetic circuit.Secondly,a design about static and dynamic torque sensor was proposed,and a specific structural design and an equivalent magnetic circuit model for the static torque sensor were established.It was theoretically shown that there was a linear relationship between the loading torque and the magnetic induction intensity in the working air gap.Thirdly,simulated the designed magnetic circuit structure by means of the finite element method and analyzed the overall magnetic field distribution and magnetic leakage.Afterwards,the geometric path was constructed in the post processing,which focused on the relationship between the magnetic induction intensity and the loading torsion in the working air gap.Simultaneously,the torsional deformation distribution of the elastic shaft was verified by simulation,and the safety check was performed.The simulation results show that the designed magnetic circuit structure could meet the requirements for picking up torque signals.Fourth,the FBG torque sensor experimental prototype was obtained based on magnetic field measurement.First of all,the magnetic field measurement and calibration experiments were designed.Here gauss meter was used to measure the magnetic induction intensity in the working air gap under torque loading.Then the FBG was embedded in the working air gap to acquire the relationship between center wavelength and loading torque,which verifies the feasibility of this new torque sensor.All in all,a new concept of FBG torque sensor based on magnetic field measurement was presented for the existing challenges of FBG intrusive torque measurement in this paper.To pick up the torque signal the magnetic circuit was constructed,and then the signal of magnetic field in the gap was detected and transmitted to FBG.By the relationship between the magnetic field and center wavelength of the FBG,the torque was obtained.The proposed research method makes full use of the convenience of constructing the magnetic circuit in the air gap by the magnetic field,the passive multi-field of the fiber grating,and the facilitation of the sensor network's constructing,providing new research ideas for the torque detection of FBG.