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  • 1.
    Edlund, Jeanette
    et al.
    Sveriges lantbruksuniversitet.
    Servin, Martin
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Keramati, Ehsan
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    A long-tracked bogie design for forestry machines on soft and rough terrain2013In: Journal of terramechanics, ISSN 0022-4898, E-ISSN 1879-1204, Vol. 50, no 2, p. 73-83Article in journal (Refereed)
    Abstract [en]

    A new design for a tracked forestry machine bogie (long track bogie; LTB) on soft and rough terrain is investigated using nonsmooth multibody dynamics simulation. The new bogie has a big wheel that is connected to and aligned with the chassis main axis. A bogie frame is mounted on the wheel axis but left to rotate freely up to a maximum angle and smaller wheels that also rotate freely are mounted on the frame legs with axes plane parallel to the driving wheel. The wheels are covered by a single conventional forestry machine metal track. The new bogie is shown to have higher mobility and cause less ground damage than a conventional tracked bogie but requires larger torque to create the same traction force as a conventional bogie. The new bogie also gives less acceleration when passing obstacles than the conventional bogie. Additionally, due to the shape and size of the new bogie concept, it can pass wider ditches.

  • 2.
    Ringdahl, Ola
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Hellström, Thomas
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Wästerlund, Iwan
    Dept. of Forest Resource Management, Swedish University of Agricultural Sciences.
    Lindroos, Ola
    Dept. of Forest Resource Management, Swedish University of Agricultural Sciences.
    Estimating wheel slip for a forest machine using RTK-DGPS2012In: Journal of terramechanics, ISSN 0022-4898, E-ISSN 1879-1204, Vol. 49, no 5, p. 271-279Article in journal (Refereed)
    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.

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  • 3.
    Wallin, Erik
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wiberg, Viktor
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Vesterlund, Folke
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Holmgren, Johan
    Swedish University of Agricultural Sciences, Sweden.
    Persson, Henrik
    Swedish University of Agricultural Sciences, Sweden.
    Servin, Martin
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Learning multiobjective rough terrain traversability2022In: Journal of terramechanics, ISSN 0022-4898, E-ISSN 1879-1204, Vol. 102, p. 17-26Article in journal (Refereed)
    Abstract [en]

    We present a method that uses high-resolution topography data of rough terrain, and ground vehicle simulation, to predict traversability. Traversability is expressed as three independent measures: the ability to traverse the terrain at a target speed, energy consumption, and acceleration. The measures are continuous and reflect different objectives for planning that go beyond binary classification. A deep neural network is trained to predict the traversability measures from the local heightmap and target speed. To produce training data, we use an articulated vehicle with wheeled bogie suspensions and procedurally generated terrains. We evaluate the model on laser-scanned forest terrains, previously unseen by the model. The model predicts traversability with an accuracy of 90%. Predictions rely on features from the high-dimensional terrain data that surpass local roughness and slope relative to the heading. Correlations show that the three traversability measures are complementary to each other. With an inference speed 3000 times faster than the ground truth simulation and trivially parallelizable, the model is well suited for traversability analysis and optimal path planning over large areas.

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  • 4.
    Wiberg, Viktor
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Servin, Martin
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Nordfjell, Tomas
    Swedish University of Agricultural Sciences, Umeå, Sweden.
    Discrete element modelling of large soil deformations under heavy vehicles2021In: Journal of terramechanics, ISSN 0022-4898, E-ISSN 1879-1204, Vol. 93, p. 11-21Article in journal (Refereed)
    Abstract [en]

    This paper addresses the challenges of creating realistic models of soil for simulations of heavy vehicles on weak terrain. We modelled dense soils using the discrete element method with variable parameters for surface friction, normal cohesion, and rolling resistance. To find out what type of soils can be represented, we measured the internal friction and bulk cohesion of over 100 different virtual samples. To test the model, we simulated rut formation from a heavy vehicle with different loads and soil strengths. We conclude that the relevant space of dense frictional and frictional-cohesive soils can be represented and that the model is applicable for simulation of large deformations induced by heavy vehicles on weak terrain.

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