Research Papers: Design of Mechanisms and Robotic Systems

Dynamics and Trajectory Planning for Reconfigurable Space Multibody Robots

[+] Author and Article Information
Quan Hu

School of Aerospace Engineering,
Beijing Institute of Technology,
Beijing 100081, China
e-mail: huquan2690@bit.edu.cn

Jingrui Zhang

School of Aerospace Engineering,
Beijing Institute of Technology,
Beijing 100081, China
e-mail: zhangjingrui@bit.edu.cn

Contributed by the Mechanisms and Robotics Committee of ASME for publication in the JOURNAL OF MECHANICAL DESIGN. Manuscript received September 15, 2014; final manuscript received June 30, 2015; published online July 30, 2015. Assoc. Editor: Ettore Pennestri.

J. Mech. Des 137(9), 092304 (Jul 30, 2015) (12 pages) Paper No: MD-14-1588; doi: 10.1115/1.4031055 History: Received September 15, 2014

A free-floating space robot equipped with multiple reconfigurable manipulators is designed and investigated in this paper. Lockable passive cylindrical joints (PCJs) are utilized to make the manipulator have the ability of changing its length and twisted angle. Each cylindrical joint, connecting two adjacent rigid links, has no embedded actuators but a brake mechanism. Normally, the mechanism is locked during the operation. When in the reconfiguration stage, two manipulators grasp each other to form a closed loop. Then one PCJ is unlocked, whose relative rotation and translation can be changed by the active torques at other joints. This system is a typical space multibody system. The dynamics of the space robot with unlocked cylindrical joints and a closed structural loop is investigated. The equations of motion are derived through Maggi–Kane's method. The obtained mathematical model is free of multipliers, which makes it suitable for controller design. A trajectory planning algorithm capable of avoiding the configuration singularity of the manipulators is proposed. A slide mode controller embedded with an extended state observer (ESO) is designed for the trajectory tracking control. Numerical simulations demonstrate the effectiveness of the trajectory planning and control strategy for the reconfiguration process.

Copyright © 2015 by ASME
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Fig. 1

A space platform with three reconfigurable manipulators

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Fig. 2

(a) Reference frames and sizes of the manipulators, and (b) the length of the links is changeable

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Fig. 3

(a) Expand manipulators 1 and 2 from their initial position; (b) the EEs grasp each other to form a loop; (c) unlock PCJ 1 to change the length of the first long link of manipulator 1; (d) lock PCJ 1 and unlock PCJ 2 to change the length of the second long link of manipulator 1; (e) the EEs release each other after the length changing of manipulators 1 and 2; and (f) the configuration of the manipulator 3 can also be changed by the same approach

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Fig. 4

Sketch of a reconfigurable space robot at the reconfiguration stage

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Fig. 5

(a) Revolute joint and (b) cylindrical joint

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Fig. 6

Equivalent system for the robot in reconfiguration stage

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Fig. 7

Block diagram of the controller

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Fig. 8

Disturbing force and torque at the PCJ of B12

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Fig. 9

Desired relative rotational speeds: (a) links 11–13 and (b) links 14–16

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Fig. 10

Errors of the relative rotational angles: (a) links 11–13 and (b) links 14–16

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Fig. 11

Motion at the released PCJ

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Fig. 12

Joint torques of (a) links 11–13 and (b) links 14–16

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Fig. 13

Singularity measurement of M2′

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Fig. 14

Attitude response of B1

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Fig. 15

(a) Momentum balance and (b) energy balance




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