Design, Perceptual Modeling, and Grasping Performance Evaluation of Multibranch Flexible Grippers

Abstract

Adaptive grasping (AG) of objects with unknown shapes and contact force sensing during grasping are two critical issues in object grasping. However, most of the current grippers that rely on passive grasping mechanisms do not consider both of these functions at the same time. In this article, we design a multibranch compliant flexible gripper (MBCFG), propose a method for intrinsic force perception and extrinsic deformation measurement without tactile sensor measurement, and finally achieve stable grasping of irregular objects and “force–deformation” sensing in real time. Furthermore, based on the above perceptual model, the envelope degree of grasping and the grasping force constraint model are established, which in turn indicates the evaluation method of grasping quality (GQ). Experimental results show that the flexible gripper (FG) has high sensing accuracy (i.e., its average error is less than 0.78 mm) for the external force applied at the two end nodes, but the error occurs much more when the external force is applied at its middle node (i.e., its average error is about 2.76 mm). In addition, the FG assembled at the end-effector of the robot successfully grasped a variety of objects with different shapes. Besides, the experiments of pick-and-place operation showed that the grasping performance based on “force–deformation” perception was good. Moreover, the fitted envelope curve and the shape curve of the FG also matched very well, which further proved the AG and contact force perception capability of the FG for objects with unknown shapes.