Envelope Morphology of an Elephant Trunk-like Robot Based on Differential Cable–SMA Spring Actuation

Abstract

Most trunk-like robots are designed with distributed actuators to mimic the envelope-grasping behavior of elephant trunks in nature, leading to a complex actuation system. In this paper, a modular underactuated elephant trunk-imitating robot based on the combined drive of the cable and shape memory alloy (SMA) springs is designed. Unlike the traditional underactuated structure that can only passively adapt to the envelope of the object contour, the proposed elephant trunk robot can control the cable tension and the equivalent stiffness of the SMA springs to achieve active control of the envelope morphology for different target objects. The overall structure of the elephant trunk robot is designed and the principle of deformation envelope is elucidated. Based on the static model of the robot under load, the mapping relationship between the tension force and the tension angle between modules is derived. The positive kinematic model of the elephant trunk robot is established based on the Debavit–Hartenberg (D–H) method, the spatial position of the elephant trunk robot is obtained, and the Monte Carlo method is used to derive the robot’s working space. The active bending envelope grasping performance is further verified by building the prototype to perform grasping experiments on objects of various shapes.