Research Papers

Elephant’s Trunk Robot: An Extremely Versatile Under-Actuated Continuum Robot Driven by a Single Motor

[+] Author and Article Information
Yuwang Liu

State Key Laboratory of Robotics,
Shenyang Institute of Automation,
Chinese Academy of Sciences;
Institutes for Robotics and Intelligent Manufacturing,
Chinese Academy of Sciences,
114 Nanta Street,
Shenyang 110016, China
e-mail: liuyuwang@sia.cn

Zhuang Ge

Department of Mechanical Engineering and Automation,
Northeastern University,
3 Wenhua Street,
Shenyang 110819, China
e-mail: gezhuang@sia.cn

Shangkui Yang

Department of Mechanical Engineering and Automation,
Northeastern University,
3 Wenhua Street,
Shenyang 110819, China
e-mail: yangshangkui@sia.cn

Ian D. Walker

Department of Electrical and Computer Engineering,
Clemson University,
Clemson, SC 29634
e-mail: iwalker@clemson.edu

Zhaojie Ju

Department of Computing,
University of Portsmouth,
Buckingham Building, Lion Terrace,
Portsmouth PO1 3HE, UK
e-mail: zhaojie.ju@port.ac.uk

1Corresponding author.

Contributed by the Mechanisms and Robotics Committee of ASME for publication in the Journal of Mechanisms and Robotics. Manuscript received May 26, 2018; final manuscript received May 20, 2019; published online July 12, 2019. Assoc. Editor: Nabil Simaan.

J. Mechanisms Robotics 11(5), 051008 (Jul 12, 2019) (17 pages) Paper No: JMR-18-1154; doi: 10.1115/1.4043923 History: Received May 26, 2018; Accepted May 22, 2019

Continuous-bodied “trunk and tentacle” robots have increased self-adaptability and obstacle avoidance capabilities, compared with traditional, discrete-jointed, robots with large rigid links. In particular, continuous-bodied robots have obvious advantages in grasping objects across a wide range of external dimensions. Not only can they grasp objects using end effectors like traditional robots, but their bodies can also be regarded as a gripping device, and large objects with respect to the robot’s scale can be captured by the entire structure of the robots themselves. Existing trunk-like robots have distributed multidrive actuation and are often manufactured using soft materials, which leads to a complex actuator system that also limits their potential applications in dangerous and extreme environments. This paper introduces a new type of elephant’s trunk robot with very few driving constraints. The robot consists of a series of novel underactuated linkage units. With a single-motor drive, the robot can achieve stable grasping of objects of different shapes and sizes. The proposed robot simplifies the requirements of the sensing and control systems during the operation process and has the advantage of accomplishing the capture task without determining the exact shape and position of the target object. It is especially suitable for operations such as non-cooperative target capture in extremely dangerous environments, including those in outer space. Based on theoretical analysis and model design, a trunk robot prototype was developed, and a comprehensive experimental study of the bending/extension and grasping operation functions was conducted to verify the validity of the proposed robot design.

Copyright © 2019 by ASME
Topics: Robots , Motors , Engines
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Fig. 1

Elephant’s trunk robot: (a) dimensions, (b) hard shell, and (c) soft shell

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Fig. 2

Driving principle: all units are driven by the same motor

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Fig. 3

Robot grasps objects of different shapes and sizes: (a) holding irregularly shaped objects and (b) holding polygonal objects

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Fig. 4

Robot grasps objects at different positions: (a) holding a proximal target and (b) holding a closer target

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Fig. 5

Robot used in space extreme environments: (a) holding a satellite body that rotates around an isometric axis and (b) holding a satellite solar windsurfer that rotates around a central axis (size parameters can be designed according to the specific needs of the space application)

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Fig. 6

Mechanical design of the core robot units

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Fig. 7

Mechanical design of the base unit and unit 1

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Fig. 8

Schematics of the kinematic unit and motion pair–screw coordinate system: (a) two-unit schematic, (b) scissors mechanism, (c) left part of the scissors mechanism, and (d) right part of the scissors mechanism

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Fig. 9

Elephant’s trunk robot flowchart

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Fig. 10

(a) Initial angle of unit K and unit (K + 1) with different positions of the spring and (b) trajectory of the robot with different positions of spring

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Fig. 11

F–k curve: relationship between the force and the stiffness coefficient of the spring

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Fig. 12

Control system diagram of the robot: (a) system composition and (b) control system model

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Fig. 13

DH coordinate system of elephant’s trunk robot

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Fig. 14

Workspace of elephant’s trunk robot: (a) 3D view of workspace and (b) main section view of the workspace

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Fig. 15

Free bending experiments: (a) initial robot pose, (b) intermediate bending process, (c) bending final pose, and (d) curve of each unit rotation angle during bending

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Fig. 16

Holding a nonfixed sphere experiment: (a) initial robot pose, (b) contact with sphere, (c) lifting sphere, and (d) angle curve: rotating each unit during holding

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Fig. 17

Tubular holding experiments at fixed positions: (a) initial robot pose, (b) final posture after hold, and (c) curve of each unit rotation angle during hold

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Fig. 18

Grasping experiment with soft shell cover: (a) trash can, (b) packing box, and (c) elastic ball

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Fig. 19

Maximum adaptive load experiment



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