Feedback Control of Macro/Micro Manipulators
Two link joint flexible macro manipulator carrying a
two-armed micro manipulator with a "satellite".
Macro/Micro Manipulators
Long reach space manipulators, such as the Space Shuttle Remote
Manipulator System (RMS), must be made as lightweight as possible.
A lightweight manipulator will have flexibility both in the drive
system and in the structure of the manipulator. This flexibility
limits the speed and dexterity that can be achieved at the end-point
of a manipulator. A much smaller manipulator can be faster and more
rigid, at the expense of workspace. Thus the combination of a small
"micro" manipulator carried by a large "macro" manipulator creates a
robot that can be dextrous over a large area. A planned space
macro/micro system is the Space Station manipulator, the SSRMS/SPDM.
Another example of a macro/micro manipulator is the human arm/hand.
Experimental System
The experimental system in the lab consists of a planar manipulator
operating in a two dimensional space-like environment. The end-point
of the macro arm floats on an air bearing over a large, flat granite
table. The macro part of the manipulator features two 1.5m long
links, each with built in joint flexibility. The two micro arms are
similar to the ones on the
free-flying space robots. Also shown is a small free floating
object that the robot can catch and manipulate. An overhead vision
system senses the end-point position of the arms as well as the
position of the object.
Research
The goal of the research is to remove the human from the low-level
control of moving each arm. Instead, the human should give
tasks for the robot to complete autonomously. It is desired to
have a low-level control loop that can accurately control the
end-point of each micro arm. While much research has been done on
controlling redundant robotic systems, many of these techniques break
down when there is flexibility between the motor and the
robot. Current research is on using techniques such as backstepping to
account for the joint flexibility in combination with rigid robot
redundancy management schemes.
Micro manipulator grabbing the object
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For questions or comments contact: heidi@arl.stanford.edu
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