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  • 1
    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.
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  • 2
    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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  • 3
    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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  • 4
    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
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Archive of applied mechanics 58 (1988), S. 113-125 
    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 Clattering vibrations in gear-boxes may be described as a sequence of impulsive processes [3, 5]. The motion between two impacts during teeth-meshing can be represented analytically. This leads to discrete and invertible mappings for the motion in phase-space. As a result one gets strange attractors or periodical behaviour according to the set of parameters under consideration. Transitions from periodic to chaotic states (and vice versa) are indicated by Ljapunov's exponents. Some parameter influences become visible by applying estimates of the phasespace boundaries. The examples of a one-stage and a two-stage gearing show advantages of the method as compared to usual numerical simulations.
    Notes: Übersicht Rassel- und Klapperschwingungen in Zahnradgetrieben lassen sich als Folgen von Stoßprozessen beschreiben [3, 5]. Dabei kann man die Bewegung von einem Stoß zum nächsten im allgemeinen analytisch darstellen. Dies ermöglicht die Herleitung diskreter und invertierbarer Abbildungsfunktionen und damit eine Darstellung der Bewegung im Phasenraum als eine Art Poincaré-Abbildung. Als Ergebnis erhält man je nach Parametersituation seltsame Attraktoren oder Fixpunkte, die sich verzweigen. Die Übergänge von periodischen zu chaotischen Zuständen und umgekehrt werden vom Verlauf der Ljapunov-Exponenten angezeigt, strukturelle Aussagen werden mit Hilfe von Abschätzungen der Phasenraumgrenzen möglich. Die Anwendungsbeispiele des einstufigen und zweistufigen Stirnradgetriebes zeigen die Vorteile des Verfahrens, insbesondere gegenüber gewöhnlichen numerischen Simulationen.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Archive of applied mechanics 64 (1994), S. 395-407 
    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: Übersicht Präzisionswaagen mit einem Auflösevermögen bis 107 sind extrem empfindlich gegenüber Fehlertoleranzen ihrer Bauteile. Insbesondere setzt der Reglerentwurf für solche Waagen die Kenntnis solcher Fehlereinflüsse voraus. Da das Modell einen Frequenzbereich bis 4 kHz abbilden muß, werden bis zu 200 Freiheitsgrade mit einer Vielzahl elastischer Eigenformen berücksichtigt. Das System ist dynamisch zwar linear, enthält die Bauparameter jedoch in nichtlinearer Form. Die für die Reglerauslegung wichtigen Abweichungen von der mittleren Amplitudenfrequenzfunktion werden in folgender Weise bestimt: Gegeben sind ein nominaler Parametersatz und alle Fehlertoleranzen aus Konstruktion und Fertigung. Gesucht ist diejenige Kombination von Bauparametern und ihrer Toleranzen, die bei jeder Frequenz die maximale Abweichung von der nominalen Frequenzfunktion ergibt. Das daraus folgende nichtlineare Optimierungsproblem liefert zusammen mit einem großen Satz von Ungleichungsnebenbedingungen die Lösung. Von nahezu 500 Bauparametern haben nur etwa 20 Parameter eine wesentlichen Einfluß, insgesamt etwa 95%, auf die Streuung der Amplitudenfrequenzfunktion.
    Notes: Summary High precision balances with resolutions up to 107 are extremely sensitive to tolerances of the design parameters. The influence of these tolerances with respect to the dynamical behavior of the balance must be known for lay-out purposes of the balance control unit. The balance is modeled within a range of 4 kHz which results in about 200 degrees of freedom including a large number of elastic modes of all components. The system is linear with respect to dynamics but parameter influences are nonlinearly contained in the amplitude-frequency-function. Of central importance for control design is the following problem: Given a nominal set of design parameters and their relevant tolerances as foreseen by design and realized by manufacturing. Given further on the nominal amplitude-frequency-function for that set. Search for that combination of parameters and their tolerances which generate maximum deviations from the nominal amplitude-frequency-function at each frequency. This optimization problem is solved with a series of constraints applying sensitivity analysis for a pre-selection and then maximizing the deviations. Out of nearly 500 parameters of the balance only about 20 parameters have 95% of the influence on the deviations.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Archive of applied mechanics 63 (1993), S. 452-463 
    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: Übersicht In der Dynamik werden Strukturvarianzen dadurch verursacht, daß anfänglich räumlich getrennte Körper miteinander in Kontakt kommen und reibungsbehaftet aufeinander abgleiten oder abrollen können. Bei der Untersuchung solcher strukturvarianter Systeme, die dadurch ausgezeichnet sind, daß sich während ihrer zeitlichen Evolution die Zahl der Systemfreiheitsgrade durch das Aktiv-bzw. Passivwerden von latenten Bindungen ändert, bedingt und gesteuert durch die Systemdynamik selbst, wird folgendes Vorgehen gewählt: Ausgehend von einer Systembeschreibung in Minimalkoordinaten ohne Aufnahme der latenten Bindungen werden diejenigen als algebraische Nebenbedingungen und durch Einführen von Lagrange-Multiplikatoren in der Bewegungsgleichung berücksichtigt, die durch die Auswertung von kinematischen Indikatoren, hier Relativgeschwindigkeit und-abstand, als potentiell aktiv angezeigt werden. Eine hinreichende Bedingung für das Aktivbleiben oder Passivwerden aller potentiell aktiven Bindungen liefert die Lösung eines im ebenen Fall linearen Komplementaritätsproblems, das auf Beschleunigungsebene mit sich gegenseitig ausschließenden kinetischen Indikatoren argumentiert.
    Notes: Summary In multibody dynamics, topology variations are caused by the fact that bodies, that are initially separated from one another, get into contact and slide or roll along each other under the influence of friction. These topology variant systems are characterized by the fact that, during the evolution in time, their number of degrees of freedom changes by latent constraints becoming active or passive due to and controlled by the system dynamics itself. In studying such systems, the following procedure is selected: With a system description in minimal coordinates without use of latent constraints, the constraints that are indicated as being potentially active by the evaluation of kinematic indicators, in this case being relative velocity and distance, are considered as algebraic secondary conditions and are taken into account by including Lagrange multipliers in the equation of motion. A sufficient condition for all potentially active constraints to remain active or become passive is provided by the solution of a complementarity problem that, in a planar case, is linear and argues at acceleration level by self-excluding kinetic indicators.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Journal of intelligent and robotic systems 3 (1990), S. 251-258 
    ISSN: 1573-0409
    Keywords: Robot path planning ; time-optimization ; force control
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract In recent years, a topological method has been established by several authors for the evaluation of time-optimal trajectories for manipulators with tree-like structures and without forces at the gripper, i.e. for free trajectories. In the following, we extend this method to the case of an arbitrary force vector at the robot's hand, which corresponds to some path in contact with a surface. Optimizing the actuator torques in such a way might be seen as a first step to controlling trajectories with regard to position, orientation, and forces in the presence of elasticity. Results of the method confirm the basic ideas of the topological solution.
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  • 9
    ISSN: 1573-5028
    Keywords: mRNA regulation ; phytochrome ; ribulose-1,5-bisphosphate carboxylase ; rye ; transcription
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effect of red light and far-red light on the appearance of mRNA for the small and large subunit of ribulose-1,5-bisphosphate carboxylase in rye seedlings has been analysed. Irradiation of etiolated seedlings with a pulse of red light increased the mRNA level of the small subunit by a factor of 7–10 and that of the large subunit by a factor of 3. A pulse of far-red light resulted in a much lower, but measurable increase. The effect of red light is reverted by an immediate far-red pulse, demonstrating the classical phytochrome response.In vitro transcription experiments with nuclei isolated from red light-treated seedlings showed that the transcription rate of the small subunit mRNA was increased only by a factor of 1.5–2.5, indicating posttranscriptional as wells as transcriptional regulations of the small subunit of ribulose-1,5-bisphosphate carboxylase.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Nonlinear dynamics 1 (1990), S. 63-74 
    ISSN: 1573-269X
    Keywords: backlash ; impacts ; discrete mappings ; Fokker-Planck equation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Rattling in gears is a consequence of backlashes. It can be generated in those gear-wheels of a car transmission system, which are not under load. Models of rattling are established in three stages. from a straightforward patching method we proceed to a discrete mapping description and to a stochastic model applying the well-known Fokker-Planck equation. All three model stages are consistent and, moreover, they represent a good picture of the real world, which has been proven by tests.
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