Ultrathin Three-Axis FBG Wrist Force Sensor for Collaborative Robots

Collaborative robots equipped with multicomponent force-sensing systems at the human-robot-environment interaction interface provides competitive advantages, such as collaboration, flexibility, and reliability. Most wrist force sensors use the cross-beam structures with electrical strain gauge measurement technologies. This article proposes an approach to develop a new ultrathin three-axis fiber Bragg grating (FBG) force sensor. First, an appropriate elastomer with embedded floating beams in ultrathin dimensions to measure three-axis force is designed using a finite-element method (FEM). A temperature-compensated extreme learning machine (TC-ELM) network is proposed to achieve the characteristics of low coupling and temperature compensation (TC). Calibration and experiment on the UR5 robot are conducted, and results illustrate that the highest sensitivity of the sensor can reach 34.07 pm/N, the repetition error is less than 5%, and the maximum coupling error is less than 0.21%. The maximum temperature drift after compensation is less than 20 pm. The proposed sensor has identical output as a commercial sensor and performs well in dynamic loading and unloading operations. Finally, comparison results from commercial and academic alternatives demonstrate the interest of the proposed approach to develop high-performance and integrated force-sensing solutions.

I. Introduction

With the current increasing demands for automation in the industry, robot sensing technology has become one of the most active technologies in the field of robotics, such as robot vision [1]–[3], tactile [4], [5], and robot force sensors [6]–[8]. Since 1970, robotic multiaxis force-sensing research has attracted significant attention [9], and it can promote the development of robot intelligence. The multiaxis wrist force sensor is most commonly used in robot operations and is installed on the wrist of the robot in such a way that the manipulator can perform fine operations. The application of robots in aerospace, deep-sea exploration, medical surgery, and other fields poses a larger challenge to the performance of robot wrist force sensors.