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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Algorithmica 13 (1995), S. 266-282 
    ISSN: 1432-0541
    Keywords: Graph minors ; NP-completeness ; Planar graphs ; Matching problems ; Treewidth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract The computational complexity of a number of problems concerning induced structures in graphs is studied, and compared with the complexity of corresponding problems concerning non-induced structures. The effect on these problems of restricting the input to planar graphs is also considered. The principal results include: (1) Induced Maximum Matching and Induced Directed Path are NP-complete for planar graphs, (2) for every fixed graphH, InducedH-Minor Testing can be accomplished for planar graphs in time0(n), and (3) there are graphsH for which InducedH-Minor Testing is NP-complete for unrestricted input. Some useful structural theorems concerning induced minors are presented, including a bound on the treewidth of planar graphs that exclude a planar induced minor.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Naturwissenschaften 21 (1933), S. 268-275 
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    The international journal of advanced manufacturing technology 9 (1994), S. 49-55 
    ISSN: 1433-3015
    Keywords: Dynamics ; Industrial robots ; Joint elasticity ; Optimal trajectories ; Path planning ; Simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A procedure is presented for planning optimal trajectories for application to industrial robots. First, trajectories are optimised by considering the nominal dynamics of a robot with rigid links and joints and with constraints on joint torque and speed. The minimum-time optimisation criterion is complemented by a miminal dynamic energy criterion that leads to smoother actuator inputs that do not excite joint vibrations. Weighting factors for these cost functions are then determined by trial simulations. By these means the effect of controller characteristics and elasticity, friction and backlash in the joints may be taken into account. A minimum-time movement for the real-world robot is obtained which displays the dynamical behaviour predicted in the planning procedure. Results from measurements and simulations for a PUMA 562 robot illustrate the approach. Further improvements may be achieved by a custom controller with the feedforward torques as shown in a comparison of trajectories executed with a VAL2 controller and a custom controller.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 81 (1990), S. 397-407 
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The anisotropyA-B of the double force tensor of O atoms on octahedral interstitial sites in V was determined in a neutron diffraction study. The applied experimental method bases on the fact that elastic stresses change, depending on the value ofA-B the O populations on octahedral sites with different spatial orientations The population changes were determined from the variations in the Bragg intensities. The anisotropy of the dobule-force tensor was found to beA-B=(7.5±1.5)eV.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Archive of applied mechanics 41 (1972), S. 329-341 
    ISSN: 1432-0681
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Summary The problem of coupling between the nutational oscillation of a gyro containing liquid and the natural oscillation of the rotating liquid itself is investigated for a rotationally symmetric gyro with arbitrarily many rotationally symmetric liquid containers. The linearized equations are treated numerically using the method of Bubnow-Galerkin. The stability of the motion is investigated using the method of residues and the envelopemethod.
    Notes: Übersicht Für einen drehsymmetrischen Kreisel mit beliebig vielen rotationssymmetrischeu Flüssigkeitsbehältern wird das Problem der gekoppelten Nutationsschwingungen des Kreisels und der Eigenschwingungen der rotierenden Flüssigkeiten untersucht. Die zugrunde gelegte linearisierte Theorie wird numerisch mit Hilfe des Verfahrens von Bubnow-Galerkin behandelt. Stabilitätsuntersuchungen werden nach der Residuenmethode und dem Einhüllenden-Verfahren durchgeführt.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Archive of applied mechanics 69 (1999), S. 265-285 
    ISSN: 1432-0681
    Keywords: Key words Multibody system ; contact ; unilateral constraint ; Coulomb friction ; stick-slip ; variational inequality.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary Couplings in machines and mechanisms exhibiting backlash and friction phenomena can be modeled as multibody systems with unilateral constraints and Coulomb friction. The structure of the differential-algebraic equations describing the system depends on the state of the constraints. The contact forces occurring at active constraints are taken into account in the equations of motion as Lagrange multipliers. Additionally, the kinematic conditions of all active constraints are formulated on the acceleration level. Contact and friction laws are sufficient conditions for state transitions of active constraints, and are represented by nonsmooth characteristics. Several formulations, like the linear complementarity problem, and two different nonlinear systems of equations are presented together with their solution method. The theory is applied to a mechanical system containing three-dimensional and coupled unilateral constraints with friction.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Archive of applied mechanics 54 (1984), S. 232-240 
    ISSN: 1432-0681
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Summary Impulsive motion of dynamical systems may be caused by external impulsive forces or by impulsive constraints. The second case will be investigated more thoroughly with reference to some practical problems, where impulsive contraints may lead to a reduction of the number of degress of freedom thus modifying the structure of the system considered. An example of a non-linear oscillator illustrates the theory.
    Notes: übersicht Sto\vorgänge in dynamischen Systemen können durch äu\ere Einwirkung oder durch sto\artig auftretende Zwangsbedingungen zustande kommen. Insbesondere der zweite Fall wird im folgenden betrachtet, wobei für technisch wichtige Probleme das Verschwinden von Freiheitsgraden und damit eine änderung der Systemstruktur von Interesse ist. Das Beispiel eines nichtlinearen Schwingers verdeutlicht die Theorie.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Archive of applied mechanics 69 (1999), S. 429-442 
    ISSN: 1432-0681
    Keywords: Key words statics ; two-member linkage ; Coulomb friction ; robotics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary The static interaction of a two-member linkage with a given surface is investigated. Dry friction acts at the point of contact of the linkage with the surface. The linkage has two drives generating torques at its joints. The optimal distribution of the joint torques is determined to maximize the friction force at the point of contact. The dependence of this maximal force on the lengths of the links and on the linkage configuration is investigated. The results obtained can be applied to the analysis and optimization of various robotic systems, in particular, manipulators interacting with rough surfaces and walking machines, especially tube-crawling robots.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Archive of applied mechanics 56 (1986), S. 25-37 
    ISSN: 1432-0681
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Summary In gearboxes of motor vehicles all components not being shifted to transmit torque may be excited to perform clattering vibrations. This type of oscillations can be resolved in a more or less stochastic sequence of impacts taking place at the edges of the gear or bearing tolerances. The energy for this impulsive process comes from motor-engine vibrations in connection with a nonlinear behaviour of the clutch. Based on an impulsive theory for multibody systems a method is presented to analyse these clattering vibrations. For optimizing the essential parameters of the system, i.e. excitation form, tolerances, damping, friction, a simulation program is developed. Clattering noise is assumed to be proportional to the energy losses due to impacts at the edges of the plays. Results compare well with practical experiences.
    Notes: Übersicht In Schaltgetrieben für Kraftfahrzeuge führen in allen Gängen diejenigen Schalträder und im Leerlauf oder im direkten Gang auch die Vorgelegewelle innerhalb ihrer Spiele Rasselschwingungen aus, die an der Momentenübertragung nicht beteiligt sind und damit wegen fehlender Verspannung klappern können. Als Erregung für diese durch Stöße verursachten Rasselschwingungen wirkt im wesentlichen die Drehungleichförmigkeit des Antriebsritzels und damit letztlich die zeitliche Schwankung des Motormoments in Verbindung mit der nichtlinearen Kupplungskennlinie. In der vorliegenden Arbeit wird, ausgehend von einer Theorie mechanischer Systeme mit unstetigen Übergängen, ein Verfahren zur praxisnahen Berechnung dieser Rasselschwingungen vorgestellt. In einem Simulationsprogramm lassen Variationen der wesentlichen Parameter, wie etwa der Erregercharakteristik, der Zahn- und Lagerspiele, der Zahn- und Lagerdämpfung sowie der Schleppmomente, Rückschlüsse auf optimale Parameterkombinationen zu. Die leicht zu ermittelnden Energieverluste bei Stößen liefern einen groben Anhaltspunkt für die Rasselgeräusche. Das gewählte Modell entspricht den beobachteten physikalischen Phänomenen.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Archive of applied mechanics 62 (1992), S. 361-362 
    ISSN: 1432-0681
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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