1. A NEW PATH-TRACKING ALGORITHM:
Autonomous Navigation in Forest Environment
THE VISION OF FORESTRY 2015?
GOALS FOR THE PILOT PROJECT:
A prototype for a forest vehicle, capable of:
Learning a path run by a human operator
Autonomously tracking the path while accounting for
Unplanned deviations from the path
Obstacles such as trees, human beings and animals
Why unmanned?
Lower labor costs
Lower weight  Less ground damages Less emissions
Manned Harvester
Hard to make autonomous
The driver supervises one or several autonomous wood shuttles
Unmanned Wood shuttle
Takes the trees out of the forest
The work has been conducted on three different target machines, each with increased complexity. This approach greatly simplifies the research and development of both hardware and software.
TESTS WITH VALMET 830:
A NEW PATH-TRACKING ALGORITHM:
Follow-the-Past
The resulting set steering angle is the sum of Φα, Φβ and Φγ. When the distance to the path has been reduced close to zero, the set steering angle essentially equals Φγ, i.e. the forest machine tries to mimic the recorded steering commands of the human driver.
The forest machine initially started 15 meters away from the recorded path:
Well known problem of cutting the corners with traditional algorithms
Follow the Past consists of three reactive behaviors, which are then fused into a single steering command:
Φα : Move towards path Φβ : Turn towards the recorded orientation Φγ : Mimic the recorded steering
(a) Follow the Past
(b) Follow the Carrot
(c) Pure Pursuit
SYSTEM ARCHITECTURE:
SENSOR FUSION:
Since the GPS position may be incorrect when the vehicle tilts, the fused position is corrected with respect to vehicle roll and pitch.
Overview of the architecture of the developed system. The high- and low-level parts are split between two computers. The forest machine shown is a vision of what a future autonomous shuttle could look like.
Position from Laser odometry is fused with other sensors to get a better estimate of the position when the GPS does not work. The position error from the laser is less than 0.5 m in this example.
Department of Computing Science
Umeå University
Sweden
Project sponsored by Carl Tryggers Stiftelse, Kempe Foundations, Komatsu, Land Systems Hägglunds, LKAB, Umeå University, VINNOVA
Thomas Hellström
Ola Ringdahl