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The fidelity of a real time forest machine simulator
Forestry Research Institute of Sweden, Sweden.
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.ORCID iD: 0000-0002-7550-3134
2007 (English)In: Fall Simulation Interoperability Workshop 2007, 2007, 377-398 p.Conference paper (Refereed)
Abstract [en]

It is essential to reduce the mental and physical stress on forest machine operators. The operator in a harvester cuts down one tree each 47 second, makes 12 decisions per tree and uses on average 24 functions per tree. In Sweden, we are using the Cut To Length (CTL) method, which means that the tree is cut in pieces out in the stand. This is done 1000 times a day. The solutions that come into our mind, to help the operators, are full or semi automation and other ways to improve the Human Machine Interaction (HMI). It is not practical or cost effective to initially develop automation or HMI ideas on real machines. Instead, a better solution is to use simulators. Normally, the existing forest machine simulators are used in teaching future forest machine operators. In our case, we use the simulator as a research tool. To rely on the result coming from tests with the simulator we performed a fidelity test. We conducted a time study, where a harvester operator have cut down approximately 500 trees and we have also measured data from the stand such as tree diameter, height, position, height to first live branch and tree type. We have also measured the terrain. The same stand and terrain data was implemented into the simulator and the same operator performed the same work again. The results demonstrated that there is a good fidelity between a real forest machine and the simulator. The time difference between the reality and the simulator is just ± 5 % for different work operations. Qualitatively, the results were on par. Several aspects on simulator fidelity will be discussed in the paper.

Place, publisher, year, edition, pages
2007. 377-398 p.
Keyword [en]
Fidelity, Forestry machine simulator, Real time simulator
National Category
Reliability and Maintenance
URN: urn:nbn:se:kth:diva-14282ScopusID: 2-s2.0-84867817857ISBN: 978-162276144-9OAI: diva2:332006
Fall Simulation Interoperability Workshop 2007; Orlando, FL; United States; 16 September 2007 through 21 September 2007

QC 20100729

Available from: 2010-07-29 Created: 2010-07-29 Last updated: 2014-10-27Bibliographically approved
In thesis
1. Kinematic Control of Redundant Knuckle Booms with Automatic Path Following Functions
Open this publication in new window or tab >>Kinematic Control of Redundant Knuckle Booms with Automatic Path Following Functions
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

To stay competitive internationally, the Swedish forestry sector must increase its productivity by 2 to 3% annually. There are a variety of ways in which productivity can be increased. One option is to develop remote-controlled or unmanned machines, thus reducing the need for operator intervention. Another option—and one that could be achieved sooner than full automation—would be to make some functions semi-automatic. Semi-automatic operation of the knuckle boom and felling head in particular would create “mini-breaks” for the operators, thereby reducing mental and physiological stress. It would also reduce training time and increase the productivity of a large proportion of operators.

The objective of this thesis work has been to develop and evaluate algorithms for simplified boom control on forest machines. Algorithms for so called boom tip control, as well as automatic boom functions have been introduced. The algorithms solve the inverse kinematics of kinematically redundant knuckle booms while maximizing lifting capacity. The boom tip control was evaluated – first by means of a kinematic simulation and then in a dynamic forest machine simulator. The results show that boom tip control is an easier system to learn in comparison to conventional control, leading to savings in production due to shorter learning times and operators being able to reach full production sooner. Boom tip control also creates less mental strain than conventional control, which in the long run will reduce mental stress on operators of forest machines. The maximum lifting capacity algorithm was then developed further to enable TCP path-tracking, which was also implemented and evaluated in the simulator.

An evaluation of the fidelity of the dynamic forest machine simulator was performed to ensure validity of the results achieved with the simplified boom control. The results from the study show that there is good fidelity between the forest machine simulator and a real forest machine, and that the results from simulations are reliable. It is also concluded that the simulator was a useful research tool for the studies performed in the context of this thesis work.

The thesis had two overall objectives. The first was to provide the industry and forestry sector with usable and verified ideas and results in the area of automation. This has been accomplished with the implementation of a simplified boom control and semi-automation on a forwarder in a recently started joint venture between a hydraulic manufacturer, a forest machine manufacturer and a forest enterprise. The second objective was to strengthen the research and development links between the forestry sector and technical university research. This has been accomplished through the thesis work itself and by a number of courses, projects and Masters theses over the last three years. About 150 students in total have been studying forest machine technology in one way or the other.

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. 78 p.
Trita-MMK, ISSN 1400-1179 ; 2009:24
Hydraulic manipulator, redundancy, kinematic control, local optimization, knuckle boom, forest machine, forwarder, boom tip control, joystick control, simulations, path following
National Category
Reliability and Maintenance
urn:nbn:se:kth:diva-11495 (URN)978-91-7415-513-6 (ISBN)
Public defence
2009-12-04, Sal M3, Brinellvägen 64, KTH, Stockholm, 13:00 (English)
QC 20100729Available from: 2009-11-17 Created: 2009-11-17 Last updated: 2010-07-29Bibliographically approved

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