High-Precision FBG 3-D Force Sensor Based on Spatial Hierarchical Sensing Structure

A 3-D force sensor based on fiber Bragg grating (FBG) is proposed in this article. A spatially layered elastomer structure is designed, and a single-mode fiber inscribed with four FBGs is laid at each place of the structure to realize the 3-D force sensing of the robot and compensate for temperature interference. The principle of FBG sensing and force measurement is investigated to reveal the mapping relationship between the wavelength drift and force of this 3-D force sensor. Based on the finite-element simulation analysis, the FBG package position is optimized, and the sensor prototype is tested. Experimental results show that the linearity of the 3-D force sensor force sensing is good, and its sensitivity is 3.104, 3.077, and 1.890 pm/N. Based on sparrow search algorithm optimization extreme learning machine (SSA-ELM), a nonlinear decoupling algorithm is used to construct the neural network model, and the SSA is used to optimize the model and obtain the best initial weights and thresholds of the network. The maximum I error after decoupling is 1.58%, the maximum II error is 0.93%, and the decoupling training time is 1.44 s. The algorithm can construct the interdimensional coupling relationship of 3-D force more effectively and improve the sensor measurement accuracy. In addition, the sensor has strong resistance to electromagnetic interference and noise, fewer sensitive components, a simple lineup, a small structure and lightweight, and easy processing, and meets the requirements of miniaturization, lightweight, and refinement of multidimensional force sensors for collaborative robots.