Massive Parallelization of Multibody System Simulation

This paper deals with the decrease in CPU time necessary for simulating multibody systems by massive parallelization. The direct dynamics of multibody systems has to be solved by a system of linear algebraic equations. This is a bottleneck for the efficient usage of multiple processors. Simultaneous solution of this task means that the excitation is immediately spread into all components of the multibody system. The bottleneck can be avoided by introducing additional dynamics, and this leads to the possibility of massive parallelization. Two approaches are described. One is a heterogeneousmultiscale method, and the other involves solving a system of linear algebraic equations by artificial dynamics

Design Tool for Kinematics of Multibody Systems

This research provides a methodology and a tool for selection of appropriate robotic system based on the singularities in the workspace of the machines, suitable for both, designers and users. The kinematic problem solutions are managed through design methodology and represented with function modelling language, IDEF0. This novel approach specifies step by step activities on how to model robotic systems with math and programming tools, like Maple 17 and Matlab 2010. Symbolical and numerical solutions of kinematics, Jacobian matrix, singularities and workspace are successfully obtained for three types of multibody systems; general CNC machine, Mitsubishi MELFA RV-3SDB robot and Yaskawa Motoman DA-20, dual arm collaborative robot. CNC-R Global Reconfigurable Kinematic Model is developed for analyses of different types of manipulators. The main purpose of this design tool for kinematics of multibody systems is to help in kinematics problem solving, by providing visual representation of the workspace with the singularity locus of the same. It represents a set of iterative methods for kinematic design of manipulators, and so at the end, visual presentation of the effective work region, including singular configurations. The methodology is appropriate for any n-DOF multibody system, even for dual arm collaborativ

Dynamics Of Reconfigurable Multibody Space Systems Connected By Magnetic Flux Pinning

Many future space systems, from solar power collection satellites to sparseaperture telescopes, will involve large-scale space structures which must be launched in a modular fashion. Currently, assembling modular structures in orbit is a challenging problem in multi-vehicle control or human-vehicle interaction. Some novel approaches to assembling modular space structures or formation-flying space systems involve augmenting the system dynamics with non-contacting force fields such as electromagnetic interactions. However, familiar divergenceless forces are subject to Earnshaw's Theorem and require active control in 6 DOF for stability. This study proposes an approach to modular spacecraft assembly based on the passively stable physics of magnetic flux pinning, an interaction between superconductors and magnetic fields which is not limited by Earnshaw's Theorem. Spacecraft modules linked by flux pinning passively fall into stable, many-degree-of-freedom basins of attraction in which flux pinning holds the modules together with stiffness and damping but no mechanical contact. This dissertation reports several system identification experiments that characterize the physical properties of flux pinning for spacecraft applications and identify avenues for design of flux-pinning space hardware. Once assembled in orbit, altering a spacecraft to effect repairs or adapt to new missions presents significant control challenges as well. Flux-pinning technology also offers exciting possibilities for new spacecraft-reconfiguration techniques, in which a spacecraft changes structure and function at the system level. Flux-pinned modular spacecraft can reconfigure in such a way that the passive physics of flux pinning and the space environment govern the low-level dynamics of a reconfiguration maneuver, instead of full-state feedback control. These reconfiguration maneuvers take the form of sequences of passively stable evolutions to equilibrium states, with joint kinematics between modules preventing collisions. This dissertation develops a theory for multibody spacecraft reconfiguration controllers that take a high-level, hybrid-systems approach in which a pre-computed graph structure stores all the reachable configurations that meet certain design-specified criteria. Edges of the graph carry mission-related weights so that a space system can optimize power consumption, robustness measures, or other performance metrics during a maneuver. These technologies and control strategies may provide opportunities for versatile space systems that can accomplish a wide variety of future missions

Development of Mobile Machining Cell

This report covers some initial aspects of development of the mobile InnoMill machining cell. The new machining paradigm where the machine is mounted on the workpiece is compared to the old paradigm where the workpiece is mounted inside the machine, and differences are discussed. Parametric studies of the workpiece case study of the InnoMill project, the Vestas V112-3.0MW wind turbine hub, are performed to supply insight regarding load capacity etc. for the machine designers. The hub finite element model is validated using experimental results from Operational Modal Analysis performed on the hub. Furthermore, the InnoMill concept is described, and work regarding the 6 degree of freedom parallel kinematic manipulator which is present in the concept is performed. A numerical procedure accounting for base deflections due to static loading is proposed and implemented. Additionally, a six degree of freedom spring-mass model vibrational response is compared to vibrational response obtained from experiments on the 6 degree of freedom parallel kinematic manipulator at Aarhus University. The model, which is based on assumptions commonly found in literature, is rejected. Finally, an outlook for the remaining part of the PhD project is presented

Proceedings of the 3rd Annual Conference on Aerospace Computational Control, volume 1

Conference topics included definition of tool requirements, advanced multibody component representation descriptions, model reduction, parallel computation, real time simulation, control design and analysis software, user interface issues, testing and verification, and applications to spacecraft, robotics, and aircraft

High-Accuracy Orbital Dynamics Simulation through Keplerian and Equinoctial Parameters

none2In the last few years a Modelica library for spacecraft modelling and simulation has been developed, on the basis of the Modelica Multibody Library. The aim of this paper is to demonstrate improvements in terms of simulation accuracy and efficiency which can be obtained by using Keplerian or Equinoctial parameters instead of Cartesian coordinates as state variables in the spacecraft model. The rigid body model of the standard MultiBody library is extended by adding the equations defining a transformation of the body center-of-mass coodinates from Keplerian and Equinoctial parameters to Cartesian coordinates, and by setting the former as preferred states, instead of the latter. The remaining parts of the model, including the model of the gravitational field, are left untouched, thus ensuring maximum re-usability of third-party code. The results shown in the paper demonstrate the superior accuracy and speed of computation in the reference case of a point-mass gravity field.F. Casella; M. LoveraCasella, Francesco; Lovera, Marc

Parallel Manipulators

In recent years, parallel kinematics mechanisms have attracted a lot of attention from the academic and industrial communities due to potential applications not only as robot manipulators but also as machine tools. Generally, the criteria used to compare the performance of traditional serial robots and parallel robots are the workspace, the ratio between the payload and the robot mass, accuracy, and dynamic behaviour. In addition to the reduced coupling effect between joints, parallel robots bring the benefits of much higher payload-robot mass ratios, superior accuracy and greater stiffness; qualities which lead to better dynamic performance. The main drawback with parallel robots is the relatively small workspace. A great deal of research on parallel robots has been carried out worldwide, and a large number of parallel mechanism systems have been built for various applications, such as remote handling, machine tools, medical robots, simulators, micro-robots, and humanoid robots. This book opens a window to exceptional research and development work on parallel mechanisms contributed by authors from around the world. Through this window the reader can get a good view of current parallel robot research and applications