On multi body systems simulation in product design

Abstract: The aim of this thesis is to provide a basis for efficientmodelling and software use in simulation driven productdevelopment. The capabilities of modern commercial computersoftware for design are analysed experimentally andqualitatively. An integrated simulation model for design ofmechanical 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 SystemSimulation utilising Block System Modelling tools is presented.A theoretical design process model for simulation driven designbased on the theory of product chromosome is introduced.This thesis comprises a summary and six papers. Paper Apresents the general framework and a distributed model forsimulation based on CAD, FEM, MBS and Block Systemsmodelling.Paper B outlines a framework to integrate all these modelsinto MBS simulation for performance prediction and optimisationof mechanical systems, using a modular approach. Thismethodology has been applied to design of industrial robots ofparallel robot type. During the development process, fromconcept design to detail design, models have been refined fromkinematic to dynamic and to elastodynamic models, finallyincluding joint backlash. A method for analysing the kinematicJacobian by using MBS simulation is presented. Motor torquerequirements are studied by varying major robot geometryparameters, in dimensionless form for generality. The robot TCP(Tool Center Point) path in time space, predicted fromelastodynamic model simulations, has been transformed to thefrequency space by Fourier analysis. By comparison of thisresult with linear (modal) eigen frequency analysis from theelastodynamic MBS model, internal model validation isobtained.Paper C presents a study of joint backlash. An impact modelfor joint clearance, utilised in paper B, has been developedand compared to a simplified spring-damper model. The impactmodel was found to predict contact loss over a wider range ofrotational speed than the spring-damper model. Increased jointbearing stiffness was found to widen the speed region ofchaotic behaviour, due to loss of contact, while increaseddamping will reduce the chaotic range. The impact model wasfound to have stable under- and overcritical speed ranges,around the loss of contact region. The undercritical limitdepends on the gravitational load on the clearance joint.Papers D and E give examples of the distributed simulationmodel approach proposed in paper A. Paper D presents simulationand optimisation of linear servo drives for a 3-axis gantryrobot, using block systems modelling. The specified kinematicbehaviour is simulated with multi body modelling, while drivesystems and control system are modelled using a block systemmodel for each drive. The block system model has been used foroptimisation of the transmission and motor selection. Paper Epresents an approach for re-using CAD geometry for multi bodymodelling of a rock drilling rig boom.Paper F presents synthesis methods for mechanical systems.Joint and part number synthesis is performed using theGrübler and Euler equations. The synthesis is continued byapplying the theory of generative grammar, from which thegrammatical rules of planar mechanisms have been formulated. Anexample of topological synthesis of mechanisms utilising thisgrammar is presented. Finally, dimensional synthesis of themechanism is carried out by utilising non-linear programmingwith addition of a penalty function to avoid singularities.Keywords:Design, Simulation, Optimisation, ControlSystems, Modelling, Computer Aided Design, Computer AidedEngineering, Multi Body Systems, Finite Element Method,Backslash, Clearance, Industrial Robots, Parallel Robots.