A mobile manipulator is a robotic system consisting of a robotic manipulator mounted
onto a mobile base. This greatly extends the workspace of the robotic manipulator
and allows it to perform more tasks. However, combining both systems increases the
complexity of the control task as well as introducing additional controller tasks such
as coordination of motion, where executing the task can involve using both the mobile
base and manipulator, and cooperation of task, where many tasks can be executed at
once.
In this thesis a controller for a mobile manipulator is developed from smaller,
simple controller blocks, allowing the controller to be flexible, easy to understand,
and straightforward to implement using well-known embedded software implementation
approaches. A behaviour-based approach was used to build the individual controllers,
and a hierarchical structure was used to organise the individual controllers to provide
cooperation between them and coordinated motion.
The task assigned to the controller was to reach a series of waypoints in a large
workspace, while satisfying performance metrics of manipulability and tip-over sta-
bility. The operation of the controller was tested in simulation using 100 randomly
generated scenarios consisting of five randomly generated waypoints in each. Using
default thresholds for manipulability and tip-over stability, the controller was success-
fully able to complete all scenarios. Further simulations were then performed testing
the effects of varying the thresholds of the performance metrics to explore the tradeoffs
involved in different parameter choices. The controller was successful in a majority of
these scenarios, with only a few failing due to extreme threshold choices. The reasons
for these failures, and the corresponding lessons for robot designers are discussed.
Finally, to demonstrate the modularity of the controller, an obstacle avoidance con-
troller was added and simulation results showed the controller was capable of avoiding
obstacles while still performing the same tasks that were used in previous tests.
Successful simulation results of the controller across a range of performance metrics
shows that the combination of a behaviour based and hierarchical approach to mobile
manipulator control is not only capable of producing a functional controller, but also
one that is more modular and easier to understand than the monolithic controllers
developed by other researchers.
| Identifer | oai:union.ndltd.org:canterbury.ac.nz/oai:ir.canterbury.ac.nz:10092/8375 |
| Date | January 2013 |
| Creators | Gong, Kelvin |
| Publisher | University of Canterbury. Electrical and Computer Engineering |
| Source Sets | University of Canterbury |
| Language | English |
| Detected Language | English |
| Type | Electronic thesis or dissertation, Text |
| Rights | Copyright Kelvin Gong, http://library.canterbury.ac.nz/thesis/etheses_copyright.shtml |
| Relation | NZCU |
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