The issues researched in this thesis work relate to the theoretical and practical problems
in analysis, design and implementation of mobile, tracked, semi-autonomous machines in out-of-
door environments (particularly the work sites of small to medium size, 100x100m). A
complete navigation system is analyzed and proposed while the focus has been placed on
developing an efficient path planning subsystem. Mechanisms of ensuring that the paths are
safe are also proposed.
The path planner is based on searching an elevation map of the work space. The search
algorithm is based upon the A* search with a novel cost function. The cost function optimizes
the path with regard to the cost map that reflects length of the path and relative altitude change
along the path. These objectives contribute toward improving path efficiency and satisfying
environmental standards which are general objectives for heavy mobile machines in off-road
environments. Multiple versions of the cost function are used to provide multiple paths which
allow an operator to have final control over the choice. Having multiple paths increases the
chances that the operator (or supervisor) will be able to find a path that fits a variety of other
objectives that have to be considered in real world conditions (for example moving obstacles,
soil type etc.).
One special case of terrain is studied in great detail. When travelling slopes it is necessary to
enforce switchbacking (climbing in a zig-zag fashion) to account for mechanical limitations of
the vehicle and to reduce the soil disturbance on these specially sensitive areas. The additional
features for the search algorithm are developed to produce such paths when travelling slopes.
This has been achieved by choosing suitable cost functions and placing additional constraints
on the number and nature of turns along the path generated by the search algorithm. This is
the area that no other existing grid search path planner covers. The path planner was implemented and tested on grids representing different terrain types
that range from flat to severely hilly. The 30x30 grid required an average of 1.55 sec CPU
time to perform which is suitable for the intended usage.
The off-line implementation of the path planner is accompanied by a custom graphical
interface for path presentation. This GUI is also a prototype of the operator's interface planned
for the final version of the navigation system.
A partial integration of the navigation system was achieved and evaluated on a mini-excavator.
An already existing control system was adjusted for use in leading the mini-excavator
along the path determined by the path planner. The control strategy was very simple, yet we
demonstrated good precision of path following (position error was less then 3% on an 8x8m
field), based on the fact that a path is made up of links between neighbouring nodes in a regular
grid. Ways of reducing potentially accrued errors on bigger fields are proposed.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:BVAU.2429/7928 |
| Date | 05 1900 |
| Creators | Kusalovic, Dejan |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Relation | UBC Retrospective Theses Digitization Project [http://www.library.ubc.ca/archives/retro_theses/] |
Page generated in 0.0019 seconds