IEEE Robotics & Automation Magazine - December 2018 - 86

Coordinated
Control of a
Dual-Arm
Space Robot
Novel Models and Simulations for
Robotic Control Methods

©iStockphoto/Romanokopny

By Lingling Shi, Hiranya Jayakoby, Jayantha Katupitiya, and Xin Jin

S

pace robots have attracted increasing attention for
performing, autonomously or telerobotically,
on-orbit servicing missions such as repairing, refueling, and upgrading spacecraft; reusing space
assets; and on-orbit assembly. The extension of
robot application to space can release astronauts from risky,
time-consuming, and expensive extravehicular activities [1].
However, in the microgravity environment, the floating base
of a space robot will be disturbed by the robot's arm
motion when it approaches or manipulates a target. The
motion of the spacecraft base resulting from this disturbance
will, conversely, affect the motion of end effectors (known as
coupling dynamics), making control of space robots more
complicated than that of fixed-base robots. In addition, such
a disturbance of spacecraft attitude may result in a
communication interruption between the spacecraft and the
ground station or a failure of energy accumulation caused by
disorientation of solar panels [2].
To extend the dexterity and flexibility of space robots, a
dual-arm or multiarm space robot can be employed to complete more complex tasks. This article addresses coordinated
motion control of the spacecraft and the manipulators for a

Digital Object Identifier 10.1109/MRA.2018.2864717
Date of publication: 25 September 2018

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IEEE ROBOTICS & AUTOMATION MAGAZINE

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december 2018

dual-arm space robot. Two types of robust controllers are
developed and applied to the robot. Through numerical simulation, the novel adaptive variable structure control (AVSC)
controller is demonstrated to deliver better performance for
the space robot approaching a target in terms of tracking
accuracy and energy consumption.
The operation of a space robot generally includes four
phases [3] as shown in Figure 1, of which the approaching
and postcapture phases require coordinated motion control of
the spacecraft base and the space manipulator. In terms of the
control of the spacecraft base, space robots can be classified as
free-flying, where the base is actively controlled, and freefloating, where the base is left free.
For a free-flying space robotic system with an attitudecontrolled base, strong system nonlinearities, multiple input
torques, practical uncertainties, and space disturbances make
the design of its motion controller a complicated problem.
Potential solutions for this problem can be classified into two
types: 1) base disturbance minimization dependent on path
planning and 2) active base control. The first control strategy
is constrained by the robot structure and will require redundancy to realize sophisticated path tracking. On the other
hand, active base control has higher flexibility, allowing space
robots with much simpler structures to engage in a range of
space tasks. Further, with an attitude-controlled base, a
1070-9932/18©2018IEEE
IEEE Robotics & Automation Magazine - December 2018

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