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Research Papers

A Novel Continuum Robot Using Twin-Pivot Compliant Joints: Design, Modeling, and Validation

[+] Author and Article Information
Xin Dong

Department of Mechanical,
Materials and Manufacturing Engineering,
University of Nottingham,
C31 Coates Building,
University Park,
Nottingham NG7 2RD, UK

Mark Raffles

Department of Mechanical,
Materials and Manufacturing Engineering,
University of Nottingham,
Manufacturing Building,
University Park,
Nottingham NG7 2RD, UK

Salvador Cobos-Guzman

Department of Mechanical,
Materials and Manufacturing Engineering,
University of Nottingham,
Manufacturing Building,
University Park,
Nottingham NG7 2RD, UK

Dragos Axinte

Department of Mechanical,
Materials and Manufacturing Engineering,
University of Nottingham,
A63 Coates Building,
University Park,
Nottingham NG7 2RD, UK
e-mail: Dragos.Axinte@nottingham.ac.uk

James Kell

Repair Technology,
Rolls-Royce plc,
Derby DE24 8BJ, UK

1Corresponding author.

Manuscript received February 16, 2015; final manuscript received July 14, 2015; published online November 24, 2015. Assoc. Editor: Byung-Ju Yi.

J. Mechanisms Robotics 8(2), 021010 (Nov 24, 2015) (14 pages) Paper No: JMR-15-1035; doi: 10.1115/1.4031340 History: Received February 16, 2015; Revised July 14, 2015; Accepted July 24, 2015

A twisting problem is identified from the central located flexible backbone continuum robot. Regarding this problem, a design solution is required to mechanically minimize this twisting angle along the backbone. Further, the error caused by the kinematic assumption of previous works is identified as well, which requires a kinematic solution to minimize. The scope of this paper is to introduce, describe and teste a novel design of continuum robot which has a twin-pivot compliant joint construction that minimizes the twisting around its axis. A kinematics model is introduced which can be applied to a wide range of twin-pivot construction with two pairs of cables per section design. And according to this model, the approach for minimising the kinematic error is developed. Furthermore, based on the geometry and material property of compliant joint, the work volumes for single/three-section continuum robot are presented, respectively. The kinematic analysis has been verified by a three-section prototype of continuum robot and adequate accuracy and repeatability tests carried out. And in the test, the system generates relatively small twisting angles when a range of end loads is applied at the end of the arm. Utilising the concept presented in this paper, it is possible to develop a continuum robot which can minimize the twisting angle and be accurately controlled. In this paper, a novel design of continuum robot which has a twin-pivot compliant joint construction that minimizes the twisting around its axis is introduced, described and tested. A kinematics model is introduced which can be applied to a wide range of twin-pivot construction with two pairs of cables per section design. Furthermore, based on the geometry and material property of compliant joint, the work volumes for single/three-section continuum robot are presented, respectively. Finally, the kinematic analysis has been verified by a three-section prototype of continuum and adequate accuracy and repeatability tests carried out.

Copyright © 2016 by ASME
Topics: Kinematics , Robots , Cables , Design , Disks
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Figures

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Fig. 1

A schematic representation of the parasitic twist of the continuum robot utilizing the central located flexible backbone design: (a) original configuration (affected by gravity); (b) twisting configuration (affected by gravity + end load); (c) the twisting problem identified from a physical demonstrator (each section is 100 mm in length and 15 mm in diameter; the diameter of the NiTi backbone is 1 mm; the end load is 20 g and the twisting angle is 30 deg)

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Fig. 2

Schematic showing the difference between section and tip disk bending angles: (a) continuous backbone (represented without the platforms) [25] (b) flexible backbone [6]

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Fig. 3

A plot of the difference between bending angle of section and orientation angle of tip disk (as shown in Fig. 2(b), flexible backbone length and disk thickness are 15 mm and 5 mm, respectively); at 0 deg section bending, the difference is 0 deg. And the max angle difference is 8 deg at section bending angle 90 deg, direction angle 0 deg.

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Fig. 4

Continuum robot construction using twin-pivot compliant joints concept: (a) general view of twin-pivot compliant joints robot, (b) one segment of twin-rod concept one, and (c)one segment of twin-sheet concept

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Fig. 5

(a) General view of continuum robot system and (b) one segment construction

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Fig. 6

conceptual schematic of Twin actuation design

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Fig. 8

Schematic for kinematic model of single segment of twin-pivot continuum robot

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Fig. 9

(a) Joint 1 bending section view (b) Top view of disk B

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Fig. 10

DH frames for one single segment (Coordinate 0 and 3 locate at the center of the top surface of the disks A and C; Coordinate 1 locates at the intersection point of central axes of disks A and B; Coordinate 2 locates at the intersection point of central axes of disks B and C; bending plane β1 is vertical with bending plane β2)

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Fig. 11

Difference between section bending angle and tip disk orientation (twin-pivot backbone continuum robot)

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Fig. 12

Configuration of single section

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Fig. 13

Iteration method for inverse kinematics

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Fig. 14

An example of cable tension plot in work volume of single section (stiffness k = 37.5 N/mm of a 0.75 mm diameter steel cable of 400 mm length: 200 mm in continuum unit and 200 mm in actuation system); in the work volume, the original tension is 100 N at 0 deg bending; the min tension is 95 N at bending angle 131.8 deg, direction angle ± 46.4 deg and ±133.5 deg

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Fig. 15

Strain model of single compliant joint

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Fig. 16

Max bending of one joint

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Fig. 17

Work volume (a) 3D single section work volume and (b) 2D section view of three sections work volume (XZ)

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Fig. 18

Three-section continuum demonstrator performing controlled motions

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Fig. 19

The setup of the measurement system (IMETRUM video gauge system)

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Fig. 20

Operation approach for the system

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Fig. 21

Repeatability of three-section demonstrator: (a): TCP position repeatability test with respect to 30 deg bend (b):TCP position repeatability test with respect to 60 deg bend (c):TCP position repeatability test with respect to 90 deg bend (Note: One bend and return is called one loop)

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Fig. 22

Twisting measurement of three-section demonstrator: configuration for twisting measurement (a) original configuration without end load (b) twisting configuration

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Fig. 23

Three-section demonstrator performing load carrying capability: (a) 200 g end load and (b) 450 g end load

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