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Path tracking in forest terrain by an autonomous forwarder
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Dept. of Forest Resource Management, Swedish University of Agricultural Sciences.
Umeå University, Faculty of Science and Technology, Department of Computing Science.
(Dept. of Forest Resource Management, Swedish University of Agricultural Sciences)
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2011 (English)In: Scandinavian Journal of Forest Research, ISSN 0282-7581, E-ISSN 1651-1891, Vol. 26, no 4, 350-359 p.Article in journal (Refereed) Published
Abstract [en]

Autonomous navigation in forest terrain, where operation paths are rarely straight or flat and obstacles are common, is challenging. This paper evaluates a system designed to autonomously follow previously demonstrated paths in a forest environment without loading/unloading timber, a pre-step in the development of fully autonomous forwarders. The system consisted of a forwarder equipped with a high-precision global positioning system to measure the vehicle’s heading and position. A gyro was used to compensate for the influence of the vehicle’s roll and pitch. On an ordinary clear-cut forest area with numerous stumps, the vehicle was able to follow two different tracks, three times each at a speed of 1 m s-1, with a mean path tracking error of 6 and 7 cm, respectively. The error never exceeded 35 cm, and in 90% of the observations it was less than 14 and 15 cm, respectively. This accuracy is well within the necessary tolerance for forestry operations. In fact, a human operator would probably have a hard time following the track more accurately. Hence, the developed systems function satisfactorily when using previously demonstrated paths. However, further research on planning new paths in unknown unstructured terrain and on loading/unloading is required before timber transports can be fully automated.

Place, publisher, year, edition, pages
Taylor & Francis , 2011. Vol. 26, no 4, 350-359 p.
Keyword [en]
Forestry, Robotics, automation, autonomous vehicles
National Category
Computer Science Agricultural Sciences
Research subject
Computer and Information Science
Identifiers
URN: urn:nbn:se:umu:diva-41796DOI: 10.1080/02827581.2011.566889OAI: oai:DiVA.org:umu-41796DiVA: diva2:407822
Available from: 2012-11-20 Created: 2011-04-01 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Automation in forestry: development of unmanned forwarders
Open this publication in new window or tab >>Automation in forestry: development of unmanned forwarders
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

For the last 50 year, forestry operations have become more and more mechanized. In modern forestry in Europe two machines are typically used; a harvester that fells, debranches and cross-cuts the trees into logs and a forwarder that transports them to the nearest road. These machines are technically advanced and quite expensive, but have a very high production rate. In fact, the productivity is so high that the human operator risks becoming a bottleneck if the machines become even more efficient. One way of solving this is to change working methods such that some work tasks are not needed anymore. In this way, efficiency is improved without increasing the workload. Another way to solve the problem is to develop (semi-)autonomous vehicles. One part of the work described in this thesis is an analysis of the economical performance of four potential systems based on the concept of integrated loading. Two of these systems use autonomous forest machines. Results from simulations with large amounts of real forest data show that a promising system is an autonomous forwarder switching loads with a manned harwarder, a combination of harvester and forwarder. Autonomous forwarders able to do the same work as conventional forwarders would be even more profitable than any of the other systems analyzed in this study.The development of techniques and algorithms for autonomous navigation of forwarders that transport logs from the harvesting site to the nearest transportation road is a major part of the thesis. A novel path-tracking algorithm is introduced that is able to accurately guide a forest machine along a previously demonstrated path with high accuracy. To avoid obstacles, the VFH+ algorithm was modified to work on forest machines. However, tests with a forwarder showed that this algorithm performs unsatisfactory when there are narrow passages to negotiate with obstacles close to both sides of the vehicle. This led us to develop a real-time path-planner for off-road vehicles using a simulator to predict collisions in a window forward in time. The path-planner is able to safely navigate a forest machine around obstacles on and close to the path in a way that is hard or impossible to achieve with regular obstacle-avoidance algorithms that do not take the shape of the vehicle into account. To handle a multitude of sensors, actuators, and other hardware in a systematic and uniform way and to enable communication between software modules, a software framework (often called robotics middleware) was developed. The system can be distributed over a network of computers if some software modules require more computing power. The framework has shown to be a powerful tool for research and development of autonomous vehicles.A problem in forestry operations is wheel slip causing ground damage and reducing trafficability of forest machines. Using data collected during experiments with the autonomous forest machine, a method for measuring slip was developed. It can be used to detect excessive wheel slip and may ultimately be used to control the machine transmission to reduce the amount of slip.

Abstract [sv]

De senaste 50 åren har skogsbruket blivit alltmer mekaniserat. I det moderna skogsbruket i Europa används normalt två olika maskiner; en skördare som fäller, kvistar och kapar träden till stockar samt en skotare som transporterar dem till närmsta väg. Dessa maskiner är tekniskt avancerade och ganska dyra, men har samtidigt en mycket hög produktivitet. De är så effektiva att föraren riskerar att bli en flaskhals om produktiviteten ökar ännu mer. Ett sätt att lösa detta är att ändra arbetssätt så att ett eller flera arbetsmoment inte behövs längre. Därmed ökar effektiviteten utan att arbetsbördan ökar. Ett annat sätt att lösa problemet är att utveckla (halv-)autonoma fordon. En del av denna avhandling är en analys av ekonomisk prestanda för fyra tänkbara system som alla bygger på konceptet integrerad lastning, varav två använder autonoma skotare. Resultaten visar att ett lovande system är ett lastväxlingssystem där en autonom skotare byter lastutrymme med en bemannad drivare, en kombination av skotare och skördare. Autonoma skotare som kan utföra samma arbete som konventionella skotare visade sig ha störst potential av de analyserade systemen.Tekniker och algoritmer för autonom navigering av skotare för transport av stockar till närmaste väg är en viktig del i avhandlingen. En ny algoritm för att följa en tidigare demonstrerad väg med hög noggrannhet introduceras. För att undvika hinder modifierades algoritmen VFH+ så att den fungerar med skogsmaskiner. Tester med en skotare visade emellertid att algoritmen presterar otillfredsställande i trånga passager med näraliggande hinder på båda sidor av fordonet. Detta ledde till utvecklingen av en algoritm för ruttplanering för terränggående fordon som med hjälp av en simulator kan förutsäga kollisioner i ett fönster framåt i tiden. Ruttplaneraren klarar att navigera en skogsmaskin förbi hinder som finns på eller nära rutten på ett sätt som är svårt eller omöjligt att uppnå med standardalgoritmer för att undvika hinder, eftersom de inte beaktar formen på fordonet.För att kunna hantera en mångfald av sensorer, styrdon och annan hårdvara på ett systematiskt och enhetligt sätt, och för att möjliggöra för kommunikation mellan mjukvarumoduler, implementerades ett programvarusystem (ofta kallat middleware). Systemet kan distribueras över ett nätverk av datorer om några programmoduler kräver mer datorkraft. Detta ramverk har visat sig vara ett kraftfullt verktyg för forskning och utveckling av autonoma fordon. Ett vanligt problem i skogsbruket är hjulslirning som orsakar markskador och minskar framkomligheten för skogsmaskiner. Med hjälp av data som samlats in under experimenten med den autonoma skogsmaskinen utvecklades en metod för att mäta hjulslirning. Denna metod kan användas för att upptäcka slirning mellan hjul och mark och skulle kunna användas för att styra maskinens transmission för att minska slirning.

Place, publisher, year, edition, pages
Umeå: Institutionen för datavetenskap, Umeå Universitet, 2011. 26 p.
Series
Report / UMINF, ISSN 0348-0542 ; 11.03
National Category
Computer Science Forest Science
Research subject
Computer and Information Science
Identifiers
urn:nbn:se:umu:diva-43265 (URN)978-91-7459-213-9 (ISBN)
Public defence
2011-05-26, MIT-huset, MA121, Umeå universitet, Umeå, 13:15 (English)
Opponent
Supervisors
Available from: 2011-05-05 Created: 2011-04-26 Last updated: 2012-11-20Bibliographically approved

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