FBG-Embedded Robotic Manipulator Tool for Structural Integrity Monitoring From Critical Strain-Stress Pair Estimation

Abstract

This paper proposes an optical fiber sensor system based on the strain rosette strategy to monitor the stress-strain state on the surface of a robotic manipulator tool. Three Fiber Bragg Grating (FBG) sensors are positioned according to a deformation rosette configuration within a slot in two 3D printed claws. The equations based on elasticity theory to obtain the stress-strain state from the sensors data are developed and a methodology using an auxiliary temperature sensor to prevent cross-sensitivity and to avoid measurement errors is proposed. The characterization tests show a highly linear behavior in terms of sensitivity to strain (R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> = 0.996 for the linear regression of the means) and to temperature variation (lower R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> between FBGs equal to 0.9868). From the compression tests, it is possible to conclude that the dynamic range of the sensors is adequate to the load capacity of the claws. Grip tests with different objects were performed on the manipulator to verify the system’s feasibility in real-time applications. Finally, from the data processing of the experiments on the robot, it is possible to apply failure criteria and shows that the grip structure is not at risk during the tests.