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  • 1.
    Löfgren, Björn
    KTH, Superseded Departments, Machine Design.
    Kinematic control of redundant knuckle booms2004Licentiate thesis, monograph (Other scientific)
    Abstract [en]

    A kinematically redundant four degrees of freedommanipulator arm, a knuckle boom, is studied. Three joints arerevolute and one linear. Since only three degrees of freedomare needed for positioning, we have one redundant degree offreedom. Three different kinematic control strategies arestudied. One is based on the maximization of velocity (localoptimisation). This strategy is non-repeatable and cansometimes lead to kinematically unfavourable positions. In thesecond strategy, which is based on the maximization of staticlifting capacity (local optimisation), one of the degrees offreedom (the linear joint) is made a function of the toolcentre point position. The third strategy, which is based ondynamic programming (global optimization), calculates theshortest time that is possible for the tool centre point to gofrom one point to another point in the working area. The threestrategies are compared in a simulation study. The simulationsshow the necessary speed requirements for all joints whenperforming straight paths in the manipulator work area. Thesimulations also show the difference in time consumptionsbetween the three control algorithms and also what happens whenthe joints reach their maximum velocity limits.

    KeywordsManipulator, Kinematic Control, RedundantLanguage

  • 2.
    Löfgren, Björn
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Kinematic Control of Redundant Knuckle Booms with Automatic Path Following Functions2009Doctoral 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.

  • 3.
    Löfgren, Björn
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Ohlsson, K.
    Wikander, Jan
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Egermark, T.
    An evaluation of boom tip control for forest machines in a real-time forest machine simulator2007In: Human Factors: The Journal of the Human Factors and Ergonomics Society, ISSN 0018-7208Article in journal (Other academic)
  • 4.
    Löfgren, Björn
    et al.
    Forestry Research Institute of Sweden, Sweden.
    Ohlsson, Kjell
    Wikander, Jan
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    The fidelity of a real time forest machine simulator2007In: Fall Simulation Interoperability Workshop 2007, 2007, p. 377-398Conference 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.

  • 5.
    Löfgren, Björn
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Wikander, Jan
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Kinematic control of redundant knuckle Booms with Path Tracking under Geometric, Velocity and Acceleration Constraints2009In: International Journal of Forest Engineering, ISSN 1494-2119, E-ISSN 1913-2220Article in journal (Other academic)
  • 6.
    Pirnazarov, Abdurasul
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Palaniappan, Revathi
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Sellgren, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Löfgren, Björn
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Predicting the mobility of tracked forestry machines operating on Nordic forest soil2013In: 7th Americas Regional Conference of the ISTVS, 2013Conference paper (Refereed)
  • 7.
    Pirnazarov, Abdurasul
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Wijekoon, Madura
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Sellgren, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Löfgren, Björn
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Andersson, Kjell
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Modeling of the bearing capacity of Nordic forest soil2012In: 12th European Conference of the ISTVS, 2012Conference paper (Other academic)
  • 8.
    Sellgren, Ulf
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Pirnazarov, Abdurasul
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Andersson, Kjell
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Löfgren, Björn
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Model-Based Development of machines for sustainable forestry2012In: 12th European Conference of the ISTVS, 2012Conference paper (Other academic)
  • 9.
    Sellgren, Ulf
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Pirnazarov, Abdurasul
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Löfgren, Björn
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Development of a methodology for predicting the bearing capacity of rooted soft soil2013In: 7th Americas Regional Conference of the ISTVS, 2013Conference paper (Refereed)
  • 10.
    Wikander, Jan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Löfgren, Björn
    The Forest Research Institute of Sweden, Skogforsk, Uppsala, Sweden.
    Kinematic Control of Redundant Knuckle Booms2009In: International Journal of Forest Engineering, ISSN 1913-2220, Vol. 20, no 1, p. 22-30Article in journal (Refereed)
    Abstract [en]

    The Swedish forestry industry competes on an international market; because raw material is more expensive than in other parts of the world, the chain from the stump to the industry needs to be very effective. One part in this chain is cutting and transporting trees from the forest to the landing area for further transportation with trucks to the paper or saw mill. When cutting and transporting trees, forestry machines equipped with booms are used to handle the trees. If boom handling time can be reduced thereby increasing productivity by 10 percent, the Swedish forestry industry can earn up to 250 million Swedish crowns (US$35 million) per year.One way to decrease boom handling time is to introduce automatization. This paper describes how to solve the kinematic control of knuckle booms used on forestry machines when automatization is introduced. The objective was to develop a kinematic control strategy for maximum lifting capacity, which is suited for computer-controlled knuckle booms that are redundant. This strategy was analyzed with respect to time consumption when the manipulator tip moves along a predetermined path. The analysis was conducted on a knuckle boom used on a forwarder in a forestry application. The knuckle boom had one redundant degree of freedom. The analysis showed the necessary joint speed requirements and time consumption for certain motion cycles and also what happens when the joints reach their maximum velocity limits.

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