Research Papers

A Novel Wire-Driven Variable-Stiffness Joint Based on a Permanent Magnetic Mechanism

[+] Author and Article Information
Ming Zhang

School of Mechanical Engineering and Automation,
Northeastern University,
Shenyang 110819, China
e-mail: zhangming@stumail.neu.edu.cn

Lijin Fang

Faculty of Robot Science and Engineering,
Northeastern University,
Shenyang 110169, China
e-mail: ljfang@mail.neu.edu.cn

Feng Sun

School of Mechanical Engineering,
Shenyang University of Technology,
Shenyang 110870, China
e-mail: sunfeng@sut.edu.cn

Koichi Oka

Department of Intelligent Mechanical Systems Engineering,
Kochi University of Technology,
Kami-city, Kochi 782-8502, Japan
e-mail: oka.koichi@kochi-tech.ac.jp

1Corresponding author.

Contributed by the Mechanisms and Robotics Committee of ASME for publication in the Journal of Mechanisms and Robotics. Manuscript received July 2, 2018; final manuscript received April 22, 2019; published online July 8, 2019. Assoc. Editor: K. H. Low.

J. Mechanisms Robotics 11(5), 051001 (Jul 08, 2019) (9 pages) Paper No: JMR-18-1194; doi: 10.1115/1.4043684 History: Received July 02, 2018; Accepted April 25, 2019

The variable-stiffness joint (VSJ) plays an important role in creating compliant and powerful motions. This paper presents a novel wire-driven VSJ based on a permanent magnetic mechanism (PMM). The proposed joint regulates the joint stiffness with lower energy consumption through a wide range via the permanent magnetic mechanism. This effect possibly depends on the novel nonlinear combination of a permanent magnet-spring and wire-driven system that achieves the same stiffness with lower wire tension. A trapezoidal layout of the joint is proposed. Because of the relationship among the stiffness, the position of the joint and the stiffness of the PMM, the stiffness model is also been established. Based on this model, the decoupling controller is built to independently control the position and stiffness of the joint. Experiments show that the VSJPMM achieves position and stiffness independently and also reduces energy and power required to regulate the stiffness compared with the traditional approach. In addition, the proposed mechanism displays a powerful motion and short stiffness adjustment time.

Copyright © 2019 by ASME
Topics: Stiffness , Wire
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Fig. 1

Prototype of the VSJPMM. (a) CAD design of VSJPMM. (b) The internal structure of the prototype. 1, wire; 2, pulley with V-groove; 3, permanent magnet mechanism; 4, pulley with V-groove; 5, wire winch; 6, harmonic reducer and DC servo motor with encoder; 7, base; 8, shaft and thin-walled ball bearings; 9, operating arm; 10, encoder; and 11, fixed seat.

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Fig. 2

Structure of the PMM. (a) Cutaway view of PMM. (b) Photo of PMM. 1, fixed pulley; 2, wire; 3, movable pulley; 4, slideway; 5, fixed annular permanent magnet; and 6, movable annular permanent magnet.

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Fig. 3

Mechanistic model of the VSJPMM

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Fig. 4

Wire-driven system. d means the half-horizontal distance between the two fixed pulleys, r′ means the pulley radius, and h means the vertical distance between the fixed pulley and the movable pulley

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Fig. 5

Schematic diagram of the control system

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Fig. 6

VSJPMM prototype system

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Fig. 7

Changing axial displacement between the magnets (Color version online.)

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Fig. 8

VSJPMM stiffness regulation

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Fig. 9

Stiffness and position decoupling test

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Fig. 10

Response of the position step at different stiffness

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Fig. 11

Response of the position step at different stiffness

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Fig. 12

Sine trajectory tracking

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Fig. 13

Playing darts with VSJPMM



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