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  • 1
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    Global and local current sheet thickness estimates during the late growth phase (1992)
    In:  CASI
    Details
    Publikationsdatum: 2004-12-03
    Beschreibung: The thinning and intensification of the cross tail current sheet during the substorm growth phase are analyzed during the CDAW 6 substorm (22 Mar. 1979) using two complementary methods. The magnetic field and current sheet development are determined using data from two spacecraft and a global magnetic field model with several free parameters. These results are compared with the local calculation of the current sheet location and structure previously done by McPherron et al. Both methods lead to the conclusion that an extremely thin current sheet existed prior to the substorm onset, and the thicknesses estimated by the two methods at substorm onset agree relatively well. The plasma data from the ISEE 1 spacecraft at 13 R(sub E) show an anisotropy in the low energy electrons during the growth phase which disappears just before the substorm onset. The global magnetic model results suggest that the field is sufficiently stretched to scatter such low energy electrons. The strong stretching may improve the conditions for the growth of the ion tearing instability in the near Earth tail at substorm onset.
    Schlagwort(e): GEOPHYSICS
    Materialart: ESA, Substorms 1; p 131-135
    Format: text
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  • 2
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    Magnetic cloud passage at Earth and associated substorm activity (1992)
    In:  CASI
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    Publikationsdatum: 2004-12-03
    Beschreibung: An approach to the study of the solar wind-magnetosphere interaction by signal type, that is, by examining the effect in the magnetosphere of well defined interplanetary structures, is presented. Focus is on the response of the magnetosphere to interplanetary magnetic clouds. Among their properties are: the slow and smooth variation of the magnetic field vector, with fluctuation level well below common interplanetary values; the similarly well behaved bulk flow; the wide range of field and flow parameters; and the longevity of passage (1 to 2 days). If the magnetic cloud is oriented such that a long period of uninterruptedly northward pointing field is followed by a long interval of continuously southward pointing field, then the transition of the magnetosphere from a quiescent state (the 'ground state') to a very active state can be studied, the latter being sustained by continued forcing from the magnetic cloud. A synopsis of the main findings of a recent study in such an interaction is given, concentrating on the substorm activity attending the second part of cloud passage.
    Schlagwort(e): GEOPHYSICS
    Materialart: ESA, Substorms 1; p 371-376
    Format: text
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  • 3
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    Control and applications of cooperating disparate robotic manipulators relevant to nuclear waste management (1991)
    In:  CASI
    Details
    Publikationsdatum: 2004-12-03
    Beschreibung: Remote handling in nuclear waste management requires a robotic system with precise motion as well as a large workspace. The concept of a small arm mounted on the end of a large arm may satisfy such needs. However, the performance of such a serial configuration lacks payload capacity which is a crucial factor for handling a massive object. Also, this configuration induces more flexibility on the structure. To overcome these problems, the topology of bracing the tip of the small arm (not the large arm) and having an end effector in the middle of the chain is proposed in this paper. Also, control of these cooperating disparate manipulators is accomplished in computer simulations. Thus, this robotic system can have the accuracy of the small arm, and at the same time, it can have the payload capacity and large workspace of the large arm.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: Manipulation Strategies for Massive Space Payloads; 8 p
    Format: text
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  • 4
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    Robot vibration control using inertial damping forces (1991)
    In:  CASI
    Details
    Publikationsdatum: 2004-12-03
    Beschreibung: This paper concerns the suppression of the vibration of a large flexible robot by inertial forces of a small robot which is located at the tip of the large robot. A controller for generating damping forces to a large robot is designed based on the two time scale model. The controller does not need to calculate the quasi-steady variables and is efficient in computation. Simulation results show the effectiveness of the inertial forces and the controller designed.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: Manipulation Strategies for Massive Space Payloads; 8 p
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  • 5
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    A time domain inverse dynamic method for the end point tracking control of a flexible manipulator (1991)
    In:  CASI
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    Publikationsdatum: 2004-12-03
    Beschreibung: The inverse dynamic equation of a flexible manipulator was solved in the time domain. By dividing the inverse system equation into the causal part and the anticausal part, we calculated the torque and the trajectories of all state variables for a given end point trajectory. The interpretation of this method in the frequency domain was explained in detail using the two-sided Laplace transform and the convolution integral. The open loop control of the inverse dynamic method shows an excellent result in simulation. For real applications, a practical control strategy is proposed by adding a feedback tracking control loop to the inverse dynamic feedforward control, and its good experimental performance is presented.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: Manipulation Strategies for Massive Space Payloads; 28 p
    Format: text
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  • 6
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    Control for two cooperating disparate manipulators (1991)
    In:  CASI
    Details
    Publikationsdatum: 2004-12-03
    Beschreibung: This research seeks to provide an advanced force control strategy for a flexible manipulator. Two main issues with force control of flexible arms are discussed: non-collocation and robustness.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: Manipulation Strategies for Massive Space Payloads; 2 p
    Format: text
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  • 7
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    Contact control for advanced applications of light weight arms (1991)
    In:  CASI
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    Publikationsdatum: 2004-12-03
    Beschreibung: Many applications of robotic and teleoperated manipulator arms require operation in contact and non-contact regimes. This paper deals with both regimes and the transition between them with special attention given to problems of flexibility in the links and drives. This is referred to as contact control. Inverse dynamics is used to plan the tip motion of the flexible link so that the free motion can stop very near the contact surface without collision due to overshoot. Contact must occur at a very low speed since the high frequency impact forces are too sudden to be affected by any feedback generated torques applied to a joint at the other end of the link. The effect of approach velocity and surface properties are discussed. Force tracking is implemented by commands to the deflection states of the link and the contact force. This enables a natural transition between tip position and tip force control that is not possible when the arm is treated as rigid. The effect of feedback gain, force trajectory, and desired final force are of particular interest and are studied. Experimental results are presented on a one link arm and the system performance in the overall contact task is analyzed. Extension to multi-link cases with potential applications are discussed.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: Manipulation Strategies for Massive Space Payloads; 8 p
    Format: text
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  • 8
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    Control of a flexible bracing manipulator (1991)
    In:  CASI
    Details
    Publikationsdatum: 2004-12-03
    Beschreibung: Many applications of robotic manipulator arms require operation in contact and noncontact regimes. Control of impact between the arm's tip and the environment has been largely ignored in prior research. The impact phenomena was investigated through simulation and experiment for the realization of the bracing strategy, and the key factors of the behavior were understood well. The approaching velocity is dominant parameter for the magnitude of the impact force. The impact is also affected by the compliance of the environmental surface.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: Manipulation Strategies for Massive Space Payloads; 2 p
    Format: text
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  • 9
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    Control of a small working robot on a large flexible manipulator for suppressing vibrations (1991)
    In:  CASI
    Details
    Publikationsdatum: 2004-12-03
    Beschreibung: The short term objective of this research is the completion of experimental configuration of the Small Articulated Robot (SAM) and the derivations of the actuator dynamics of the Robotic Arm, Large and Flexible (RALF). In order to control vibrations SAM should have larger bandwidth than that of the vibrations. The bandwidth of SAM consist of 3 parts; structural rigidity, processing speed of controller, and motor speed. The structural rigidity was increased to a reasonably high value by attaching aluminum angles at weak points and replacing thin side plates by thicker ones. The high processing speed of the controller was achieved by using parallel processors (three 68000 process, three interface board, and one main processor (IBM-XT)). Maximum joint speed and acceleration of SAM is known as about 4 rad/s and 15 rad/sq s. Hence SAM can move only .04 rad at 3 Hz which is the natural frequency of RALF. This will be checked by experiment.
    Schlagwort(e): MECHANICAL ENGINEERING
    Materialart: Manipulation Strategies for Massive Space Payloads; 2 p
    Format: text
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  • 10
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    Magnetotail instability (1992)
    In:  CASI
    Details
    Publikationsdatum: 2004-12-03
    Beschreibung: The stability of the geomagnetic tail is investigated on the basis of three dimensional resistive magnetohydrodynamic simulations, using different dynamic constraints and different initial equilibria. Different forms of the energy equation for isotropic pressure are found to have no significant effect on the dynamic growth of a resistive tearing instability, which is responsible for near Earth reconnection, plasmoid formation and ejection, and the generation of fast plasma flows. The constraints of a modified double adiabatic approach, however, can quench the tearing instability through the development of large, mirror type, anisotropies in the boundary regions of the plasma sheet, unless isotropization occurs on fast, nearly Alfvenic, time scales. The presence of a net cross tail magnetic field component B(sub yN) can reduce the growth of the instability without complete stabilization. An increase of B(sub z) from midnight toward the tail flanks, however, by more than a factor of about 3, apparently completely stabilizes the tearing mode. Stabilization and destabilization thus may depend on properties and constraints (and their release) in regions other than the neutral sheet where reconnection is initiated.
    Schlagwort(e): GEOPHYSICS
    Materialart: ESA, Substorms 1; p 225-230
    Format: text
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