Identification and Monitoring of Critical Slip Point for Flexible Finger Based on FBG

As an important performance indicator in perception, slip sensation determines the intelligence level of soft manipulators. Both excessive and insufficient forces can affect the quality of nondestructive grasping. There are few existing sensors with small volumes and the ability to predict slip. Fiber Bragg grating (FBG) is a flexible sensor with the advantages of small size, lightweight, and high sensitivity. This article proposes a slip criterion identifying the critical slip point of the flexible finger based on FBG. The equivalent model of the friction pair between the flexible finger and the rigid plane determines the criterion parameters. Besides, the relationships between the FBG wavelength and contact forces are obtained. The algorithm detecting the mutation point in the FBG signal can monitor and predict the critical slip point from rest to relative motion. The experimental results show that the predicted time is 0.8 s ahead of the critical slip point, which provides the adjustment time for the control system to prevent overall slip. This study offers new ideas for slip monitoring and prediction of objects and has broad application prospects in the nondestructive grasping of soft manipulators.