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Automation in forestry: development of unmanned forwarders
Umeå University, Faculty of Science and Technology, Department of Computing Science.
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: urn:nbn:se:umu:diva-43265ISBN: 978-91-7459-213-9OAI: oai:DiVA.org:umu-43265DiVA: diva2:412664
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
List of papers
1. Autonomous forest vehicles: historic, envisioned, and state-of-the-art
Open this publication in new window or tab >>Autonomous forest vehicles: historic, envisioned, and state-of-the-art
2009 (English)In: International Journal of Forest Engineering, ISSN 1494-2119, Vol. 20, no 1, 33-38 p.Article in journal (Refereed) Published
Abstract [en]

The feasibility of using autonomous forest vehicles (which can be regarded as logical developments in the ongoing automation of forest machines), the systems that could be applied in them, their potential advantages and their limitations (in the foreseeable future) are considered here. The aims were to analyse: (1) the factors influencing the degree of automation in logging; (2) the technical principles that can be applied to autonomous forest machines, and (3) the feasibility of developing an autonomous path-tracking forest vehicle. A type of vehicle that is believed to have considerable commercial potential is an autonomous forwarder. The degree of automation is influenced by increased productivity, the machine operator as a bottle-neck, cost reduction, and environmental aspects. Technical principles that can be applied to autonomous forest vehicles are satellite navigation, wheel odometry, laser scanner and radar. A new path-tracking algorithm has been developed to reduce deviations from the desired path by utilizing the driver’s steering commands. The presented system has demonstrated both possibilities and difficulties associated with autonomous forest machines. It is in a field study shown that it is quite possible for them to learn and track a path previously demonstrated by an operator with an accuracy of 0.1m on flat ground and also to detect and avoid unexpected obstacles. Although the forest machine safely avoids obstacles, the study shows that further research in the field of obstacle avoidance is needed to optimize performance and ensure safe operation in a real forest environment.

Keyword
obstacle detection, path-tracking, robotic, system architecture
National Category
Computer Science Forest Science
Research subject
Computer Science; Social Pharmacy
Identifiers
urn:nbn:se:umu:diva-19866 (URN)
Available from: 2009-12-22 Created: 2009-03-12 Last updated: 2011-05-09Bibliographically approved
2. Potentials of possible machine systems for directly loading logs in cut-to-length harvesting
Open this publication in new window or tab >>Potentials of possible machine systems for directly loading logs in cut-to-length harvesting
2012 (English)In: Canadian Journal of Forest Research, ISSN 0045-5067, Vol. 42, no 5, 970-985 p.Article in journal (Refereed) Published
Abstract [en]

In conventional mechanized cut-to-length systems, a harvester fells and cuts trees into logs that are stored on the ground until a forwarder picks them up and carries them to landing sites. A proposed improvement is to place logs directly into the load spaces of transporting machines as they are cut. Such integrated loading could result in cost reductions, shorter lead times from stump to landing, and lower fuel consumption. However, it might also create waiting times for the machines involved, whereas multifunctional machines are likely to be expensive. Thus, it is important to analyze whether or not the advantages of any changes outweigh the disadvantages. The conventional system was compared with four potential systems, including two with autonomous forwarders, using discrete-event simulation with stochastic elements in which harvests of more than 1000 final felling stands (containing in total 1.6 million m3) were simulated 35 times per system. The results indicate that harwarders have substantial potential (less expensive on ≥80% of the volume and fuel consumption decreased by ≥18%) and may become competitive if key innovations are developed. Systems with cooperating machines have considerably less potential, limited to very specific stand conditions. The results conform with expected difficulties in integrating processing and transporting machines’ work in variable environments.

Place, publisher, year, edition, pages
Canadian Science Publishing, 2012
National Category
Computer and Information Science Forest Science
Research subject
Computer and Information Science
Identifiers
urn:nbn:se:umu:diva-54619 (URN)10.1139/x2012-036 (DOI)
Note

Included in thesis in manuscript form.

Available from: 2012-11-20 Created: 2012-05-02 Last updated: 2012-11-20Bibliographically approved
3. Follow the Past: a Path Tracking Algorithm for Autonomous Vehicles
Open this publication in new window or tab >>Follow the Past: a Path Tracking Algorithm for Autonomous Vehicles
2006 (English)In: International Journal of Vehicle Autonomous Systems, ISSN 1741-5306, Vol. 4, no 2/3/4, 216-224 p.Article in journal (Refereed) Published
Abstract [en]

A number of algorithms for path tracking are described in the robotics literature. Traditional algorithms, like Pure Pursuit and Follow the Carrot, use position information to compute steering commands that make a vehicle follow a pre-defined path approximately. These algorithms are well known to cut corners, since they do not explicitly take into account the actual curvature of the path. In this paper we present a novel algorithm that uses recorded steering commands to overcome this problem. The algorithm is constructed within the behavioural paradigm common in intelligent robotics and is divided into three separate behaviours, each responsible for one aspect of the path-tracking task. The algorithm is implemented both on a simulator for autonomous forest machines and a physical small-scale robot. The results are compared with the Pure Pursuit and the Follow the Carrot algorithms and show a significant improvement in performance.

Place, publisher, year, edition, pages
Inderscience, 2006
Keyword
behavioural robotics; outdoor navigation; path tracking; vehicle autonomous systems; autonomous vehicles; intelligent robotics; robot navigation; autonomous forest machines; mobile robots.
National Category
Computer Science
Research subject
Computer Science
Identifiers
urn:nbn:se:umu:diva-30390 (URN)10.1504/IJVAS.2006.012208 (DOI)
Available from: 2009-12-21 Created: 2009-12-21 Last updated: 2011-05-04Bibliographically approved
4. A Java-based middleware for control and sensing in mobile robotics
Open this publication in new window or tab >>A Java-based middleware for control and sensing in mobile robotics
2008 (English)In: International Conference on Intelligent Automation and Robotics 2008, 2008, 649-654 p.Conference paper (Refereed)
Abstract [en]

Many of the existing mobile-robot software packages do not include handling of sensors and actuators in a sufficiently systematic and uniform way, as described later in this section. The software framework proposed in this paper, denoted NAV2000, addresses the specific need for interchangeability of components in robotics. At the lowest level, sensors, and sometimes also actuators, often have to be replaced by similar, yet not identical, components. At a higher level, the target vehicle often changes during the work process. The presented software provides a framework that supports these replacements and allows configurations of sensors, actuators, and target machines to be specified and manipulated in an efficient manner. The system can be distributed over a network of computers if some software modules require more computing power, i.e. more hardware can be added to the system without any software changes. To accomplish sufficient monitoring of the system's health, a dedicated system keeps track of all software modules. The system uses logfiles to enable convenient debugging and performance analysis of hardware and software modules. The software has been developed as part of, and is currently in use in, a R&D-project for an autonomous path-tracking forest machine.

Keyword
Software engineering, Mobile-robot software, Autonomous vehicles
National Category
Computer Science
Research subject
Computer Science
Identifiers
urn:nbn:se:umu:diva-19886 (URN)978-988-98671-0-2 (ISBN)
Available from: 2009-12-10 Created: 2009-03-12 Last updated: 2011-05-10Bibliographically approved
5. Path tracking in forest terrain by an autonomous forwarder
Open this publication in new window or tab >>Path tracking in forest terrain by an autonomous forwarder
Show others...
2011 (English)In: Scandinavian Journal of Forest Research, ISSN 0282-7581, 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
Keyword
Forestry, Robotics, automation, autonomous vehicles
National Category
Computer Science Agricultural Sciences
Research subject
Computer and Information Science
Identifiers
urn:nbn:se:umu:diva-41796 (URN)10.1080/02827581.2011.566889 (DOI)
Available from: 2012-11-20 Created: 2011-04-01 Last updated: 2012-11-20Bibliographically approved
6. Real-time path planning using a simulator-in-the-loop
Open this publication in new window or tab >>Real-time path planning using a simulator-in-the-loop
2009 (English)In: International Journal Vehicle Autonomous Systems, ISSN 1471-0226, Vol. 7, no 1/2, 56-72 p.Article in journal (Refereed) Published
Abstract [en]

This paper describes the development of a real-time path planner for off-road vehicles using a simulator. The general idea with the presented system is to extend a standard path-tracking algorithm with a simulator that, in real-time, tries to predict collisions in a window forward in time. If a collision is predicted, the vehicle is stopped and a path-search phase is initiated. Variants of the original path are generated and simulated until a feasible path is found. The real vehicle then continues, now tracking the replanned path.

Place, publisher, year, edition, pages
Inderscience, 2009
Keyword
path planning; simulator in the loop; obstacle avoidance; off-road vehicles; simulation; collision avoidance; path tracking.
National Category
Computer Science
Research subject
Computer Science
Identifiers
urn:nbn:se:umu:diva-30271 (URN)10.1504/IJVAS.2009.027967 (DOI)
Available from: 2009-12-17 Created: 2009-12-15 Last updated: 2011-05-10Bibliographically approved
7. Estimating wheel slip for a forest machine using RTK-DGPS
Open this publication in new window or tab >>Estimating wheel slip for a forest machine using RTK-DGPS
2012 (English)In: Journal of terramechanics, ISSN 0022-4898, E-ISSN 1879-1204, Vol. 49, no 5, 271-279 p.Article in journal (Refereed) Published
Abstract [en]

Wheel slip may increase the risk for wheel rutting and tear up ground vegetation and superficial roots and thereby decreasing the bearing capacity of the ground, but also reducing the growth of nearby standing forest trees. With increased slip, more energy is consumed for making wheel ruts in the ground, with increased fuel consumption as a result. This paper proposes a novel method for measuring slip in an uneven forest terrain with an 8WD forestry machine. This is done by comparing the wheel velocity reported by the machine and velocity measured with an accurate DGPS system. Field tests with a forestry machine showed that slip could be calculated accurately with the suggested method. The tests showed that there was almost no slip on asphalt or gravel surfaces. In a forest environment, 10–15% slip was common. A future extension of the method enabling estimation of the slip of each wheel pair in the bogies is also suggested.

National Category
Forest Science Computer Science
Research subject
Computer and Information Science
Identifiers
urn:nbn:se:umu:diva-43264 (URN)10.1016/j.jterra.2012.08.003 (DOI)
Available from: 2012-11-20 Created: 2011-04-26 Last updated: 2013-01-28Bibliographically approved

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