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authors Makkonen, Petri
year 1999
title On multi body systems simulation in product design
source KTH Stockholm
summary The aim of this thesis is to provide a basis for efficient modelling and software use in simulation driven product development. The capabilities of modern commercial computer software for design are analysed experimentally and qualitatively. An integrated simulation model for design of mechanical systems, based on four different "simulation views" is proposed: An integrated CAE (Computer Aided Engineering) model using Solid Geometry (CAD), Finite Element Modelling (FEM), Multi Body Systems Modelling (MBS) and Dynamic System Simulation utilising Block System Modelling tools is presented. A theoretical design process model for simulation driven design based on the theory of product chromosome is introduced. This thesis comprises a summary and six papers. Paper A presents the general framework and a distributed model for simulation based on CAD, FEM, MBS and Block Systems modelling. Paper B outlines a framework to integrate all these models into MBS simulation for performance prediction and optimisation of mechanical systems, using a modular approach. This methodology has been applied to design of industrial robots of parallel robot type. During the development process, from concept design to detail design, models have been refined from kinematic to dynamic and to elastodynamic models, finally including joint backlash. A method for analysing the kinematic Jacobian by using MBS simulation is presented. Motor torque requirements are studied by varying major robot geometry parameters, in dimensionless form for generality. The robot TCP (Tool Center Point) path in time space, predicted from elastodynamic model simulations, has been transformed to the frequency space by Fourier analysis. By comparison of this result with linear (modal) eigen frequency analysis from the elastodynamic MBS model, internal model validation is obtained. Paper C presents a study of joint backlash. An impact model for joint clearance, utilised in paper B, has been developed and compared to a simplified spring-damper model. The impact model was found to predict contact loss over a wider range of rotational speed than the spring-damper model. Increased joint bearing stiffness was found to widen the speed region of chaotic behaviour, due to loss of contact, while increased damping will reduce the chaotic range. The impact model was found to have stable under- and overcritical speed ranges, around the loss of contact region. The undercritical limit depends on the gravitational load on the clearance joint. Papers D and E give examples of the distributed simulation model approach proposed in paper A. Paper D presents simulation and optimisation of linear servo drives for a 3-axis gantry robot, using block systems modelling. The specified kinematic behaviour is simulated with multi body modelling, while drive systems and control system are modelled using a block system model for each drive. The block system model has been used for optimisation of the transmission and motor selection. Paper E presents an approach for re-using CAD geometry for multi body modelling of a rock drilling rig boom. Paper F presents synthesis methods for mechanical systems. Joint and part number synthesis is performed using the Grübler and Euler equations. The synthesis is continued by applying the theory of generative grammar, from which the grammatical rules of planar mechanisms have been formulated. An example of topological synthesis of mechanisms utilising this grammar is presented. Finally, dimensional synthesis of the mechanism is carried out by utilising non-linear programming with addition of a penalty function to avoid singularities.
keywords Simulation; Optimisation; Control Systems; Computer Aided Engineering; Multi Body Systems; Finite Element Method; Backslash; Clearance; Industrial Robots; Parallel Robots
series thesis:PhD
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