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Research Papers

An Underactuated Robotic Arm Based on Differential Gears for Capturing Moving Targets: Analysis and Design

[+] Author and Article Information
Qingchuan Wang

State Key Laboratory of Robotics and System,
Harbin Institute of Technology,
Harbin 150001, China

Qiquan Quan

Associate Professor
State Key Laboratory of Robotics and System,
Harbin Institute of Technology,
Harbin 150001, China
e-mail: quanqiquan@hit.edu.cn

Zongquan Deng

Professor
State Key Laboratory of Robotics and System,
Harbin Institute of Technology,
Harbin 150001, China

Xuyan Hou

Associate Professor
State Key Laboratory of Robotics and System,
Harbin Institute of Technology,
Harbin 150001, China

1Corresponding author.

Manuscript received May 14, 2015; final manuscript received February 13, 2016; published online March 16, 2016. Assoc. Editor: Aaron M. Dollar.

J. Mechanisms Robotics 8(4), 041012 (Mar 16, 2016) (13 pages) Paper No: JMR-15-1114; doi: 10.1115/1.4032811 History: Received May 14, 2015; Revised February 13, 2016

This paper presents the design of an underactuated robotic arm for capturing moving targets with an impact-absorbing capability. The arm consists of three joints (a base joint (BJ), a medial joint (MJ), and a distal joint (DJ)) that are driven by two actuators. A one-input dual-output planetary gear (PG) system, in which neither the ring gear nor the planetary carrier is fixed, is employed to distribute the driving torque between the MJ and DJ. As is well known, an underactuated arm may exhibit unstable grasping performance such that the arm loses contact with the target in certain grasping postures. Therefore, a method is presented for analyzing the equilibrium contact force and the relative movement trend between the target and the arm to determine the work space in which stable grasping is possible. The structural configuration parameters, such as the length ratios among the three beams and the reduction ratio of the PG system, were optimized to maximize the grasp stability work space. Subsequently, a prototype was designed and fabricated based on these optimized parameters. Experiments indicate that this arm design can effectively reduce the peak torque on the joints when grasping a moving target.

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References

Figures

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Fig. 1

Schematic diagram of the proposed arm

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Fig. 2

Grasping movements for a moving object and a stationary object

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Fig. 3

Transmission scheme for the proposed robotic arm

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Fig. 4

Static equilibrium analysis of the robotic arm

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Fig. 5

Static equilibrium analyses with different centers of balance: (a) DJ, (b) MJ and DJ, and (c) BJ, MJ, and DJ

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Fig. 6

Experimental results of normal contact force on three joint beams: (a) DJ beam, (b) MJ beam, and (c) BJ beam

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Fig. 7

Normal contact force on the MJ beam in the work space (h3/l3 = 0.3)

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Fig. 8

Movement of the underactuated part: (a) case 1: Ft2 > 0, θ3 > 0, (b) case 2: Ft2 > 0, θ3 < 0, (c) case 3: Ft2 < 0, θ3 > 0, and (d) case 4: Ft2 < 0, θ3 < 0

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Fig. 9

(a) Stable and (b) unstable grasping movements for the same robotic arm

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Fig. 10

One-beam contact configuration of the underactuated part [33]

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Fig. 11

Distribution of the stable and unstable grasping positions for a test parameter set

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Fig. 12

Movement of the proposed arm when capturing a moving target

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Fig. 13

Distribution of the stable and unstable grasping positions after optimization

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Fig. 14

Force distribution diagrams

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Fig. 15

Mechanical model of the proposed arm

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Fig. 16

The prototype of the proposed arm

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Fig. 17

Grip experiments using the prototype

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Fig. 18

Two working modes used to compare the effects of impact

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Fig. 19

Movement of the arm in a collision: (a) mode I and (b) mode II

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Fig. 20

Impact experiment results: (a) speed of the motor in the MJ and (b) impact torque on the BJ

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Fig. 21

Capturing experiment for a moving target

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Fig. 22

Various capturing experiments

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