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Kinematic control of redundant knuckle booms
KTH, Superseded Departments, Machine Design. (Mechatronics Lab)
2004 (English)Licentiate 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

Place, publisher, year, edition, pages
Stockholm: Maskinkonstruktion , 2004. , 75 p.
Trita-MMK, ISSN 1400-1179 ; 2004:1
Keyword [en]
manipulator, kinematic control. Redundant
URN: urn:nbn:se:kth:diva-1731OAI: diva2:7696
Available from: 2004-06-23 Created: 2004-06-23 Last updated: 2012-03-22
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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