A Novel Compact High-Sensitivity Fiber Bragg Grating Sensor for Microvibration Measurement of Robot Joints

Microvibration measurement is crucial for fault diagnosis of robot joints. An increasing number of fiber Bragg grating (FBG) vibration sensors have been developed based on different sensing principles. However, these FBG vibration sensors cannot be applied to high-frequency vibration measurement or embedded into robot joints due to their low resonant frequency, narrow working frequency band, and large size. In this article, a novel compact high-sensitivity FBG sensor is proposed to measure dynamic strain variations induced by microvibrations of robot joints. In the FBG sensor, a sensitization structure is designed, and an FBG is pasted on the sensitization structure by the two-point encapsulation method. When installing the FBG sensor onto an object, thin silicone rubbers are used to reduce the effect of the dynamic strain variation on two support components of the sensitization structure. To improve its measurement performance, the sensitization structure is optimized by response surface methodology and nondominated sorting genetic algorithm. A vibration response experiment is executed by establishing a vibration test rig, which demonstrates that the FBG sensor has a resonant frequency of 10 kHz, a working frequency band of 50 Hz–9 kHz, and a great linear response characteristic. Furthermore, after establishing a condition monitoring system of robot joints, the practicability and effectiveness of the FBG sensor for microvibration measurement of robot joints are demonstrated. The FBG sensor has the following advantages: compact structure, uniform stress distribution, high resonant frequency, wide working frequency band, strong embeddability, and great dynamic strain amplification capability.