MultiBody Dynamics Analysis Software on Real Time ...

MultiBody Dynamics MultiBody Dynamics Analysis Software on Analysis Software on Real Time Distributed Real Time Distributed SystemsSystems

Pierangelo MasaratiPierangelo MasaratiMarco MorandiniMarco Morandini

Dipartimento di Ingegneria AerospazialeDipartimento di Ingegneria AerospazialePolitecnico di Milano (Italy)Politecnico di Milano (Italy)

One-day meeting on:One-day meeting on:RTAI, present and futureRTAI, present and future

July 8July 8thth, 2004, 2004

OutlineOutline

● Objectives and approach:Objectives and approach:● problem description & requirementsproblem description & requirements● software requirementssoftware requirements

● Key results:Key results:● software developmentsoftware development● model rationalizationmodel rationalization● software performances improvementsoftware performances improvement

● Concluding remarksConcluding remarks

ObjectiveObjective● Develop a Develop a General Purpose Real-General Purpose Real-

TimeTime experiment simulator: experiment simulator:● hard real-time capabilitieshard real-time capabilities● minimal modeling limitationsminimal modeling limitations● commonality of modelingcommonality of modeling

● Develop real-time models and Develop real-time models and controls for a wide spectrum of controls for a wide spectrum of applicationsapplications● model accuracymodel accuracy● analysis accuracyanalysis accuracy● distributed controldistributed control

Real-Time SimulationReal-Time Simulation

● Requirements:Requirements:● exploit OS multitask/memory protection exploit OS multitask/memory protection

paradigmsparadigms● use generic libraries (algebra, use generic libraries (algebra,

communication, ...)communication, ...)● use general purpose simulation softwareuse general purpose simulation software● use/develop Open-Source softwareuse/develop Open-Source software● run on ''low'' cost platforms (dual Athlon)run on ''low'' cost platforms (dual Athlon)

Real-Time SimulationReal-Time Simulation● Proposed solution:Proposed solution:

● RTAI (Real-Time Application Interface) for RTAI (Real-Time Application Interface) for LinuxLinuxhttp://www.rtai.org/ http://www.rtai.org/

● RTnet (Hard Real-Time Networking for RTnet (Hard Real-Time Networking for Linux/RTAI)Linux/RTAI)http://www.rts.uni-hannover.de/rtnet/http://www.rts.uni-hannover.de/rtnet/

● MBDyn (MultiBody Dynamics)MBDyn (MultiBody Dynamics)http://www.mbdyn.org/http://www.mbdyn.org/

● RTAILab data acquisition/control code RTAILab data acquisition/control code generationgenerationhttp://www.rtai.org/http://www.rtai.org/

Real-Time Sim.: StatusReal-Time Sim.: Status● Real-time software:Real-time software:

● Linux/RTAI mature (industry level applications)Linux/RTAI mature (industry level applications)● simulation software real-time enabledsimulation software real-time enabled

● Multibody software development:Multibody software development:● MBDyn multibody mature, multidisciplinaryMBDyn multibody mature, multidisciplinary● development lines drawn, partially investigateddevelopment lines drawn, partially investigated

● Multibody model of COMAU SMART robot:Multibody model of COMAU SMART robot:● redundant coordinate set model (>100 redundant coordinate set model (>100

unknowns)unknowns)● dynamic friction modelsdynamic friction models● timings estimates available (up to 2KHz on timings estimates available (up to 2KHz on

Athlon 2.4 Ghz equivalent)Athlon 2.4 Ghz equivalent)● distributed control via RTAILab/RTnetdistributed control via RTAILab/RTnet

Real-Time SimulationReal-Time Simulation

Traditional real-time Traditional real-time simulations:simulations:

● minimal set (ODE)minimal set (ODE)● explicit integrationexplicit integration● specialized topologyspecialized topology● bound to OS internalsbound to OS internals

Proposed real-time Proposed real-time solution:solution:

● redundant set (DAE)redundant set (DAE)● implicit integrationimplicit integration● general topologygeneral topology● POSIX compliantPOSIX compliant

● fast, fast, fast!fast, fast, fast!● difficult to extenddifficult to extend● code/tool code/tool

duplicationduplication

● performance performance limitationslimitations

● code/tool code/tool commonalitycommonality

● modeling flexibilitymodeling flexibility

Real-Time Enabled SoftwareReal-Time Enabled Software

ConventionalConventionalsimulation simulation softwaresoftware

Real-time enabledReal-time enabledsimulation softwaresimulation software

● Avoid / wrap system callsAvoid / wrap system calls● Statically preserve stack / initialize resourcesStatically preserve stack / initialize resources● STL containers: memory poolsSTL containers: memory pools● Insert few task execution / control statementsInsert few task execution / control statements● Add real-time I/O communication provisionsAdd real-time I/O communication provisions

~180,000 LOC

Real-Time Enabled SoftwareReal-Time Enabled Software

● Distributed Real-Distributed Real-time software:time software:● hard RTnet for hard RTnet for

control loopcontrol loop● soft RTnet for soft RTnet for

monitoringmonitoring

MBDyn: FeaturesMBDyn: Features

● Dynamic analysis of deformable multibody Dynamic analysis of deformable multibody mechanical systemsmechanical systems

● Integrated analysis of hydraulic, electric and Integrated analysis of hydraulic, electric and generic, control related componentsgeneric, control related components

● Aeroelastic, rotorcraft-oriented analysisAeroelastic, rotorcraft-oriented analysis● Open-Source http://www.mbdyn.org/Open-Source http://www.mbdyn.org/

● Dynamics analysis: solution of Initial Dynamics analysis: solution of Initial Value problems (IVP)Value problems (IVP)

● Static/kinematic analysis modeled as Static/kinematic analysis modeled as downgraded dynamics analysisdowngraded dynamics analysis

● Eigenanalysis by Proper Orthogonal Eigenanalysis by Proper Orthogonal Decomposition of time seriesDecomposition of time series

● Typical analysis procedure consists in Typical analysis procedure consists in performing ''virtual experiments''performing ''virtual experiments''

MBDyn: Analysis DescriptionMBDyn: Analysis Description

MBDyn: Analysis DescriptionMBDyn: Analysis Description● BodiesBodies● JointsJoints

● RigidRigid● DeformableDeformable

● LumpedLumped● BeamsBeams● ModalModalLibraries:Libraries:

● MechanicalMechanical

●AerodynamicAerodynamic

● HydraulicHydraulic

●ControlsControls

● Absolute/relative position, orientation, vel., acc.Absolute/relative position, orientation, vel., acc.● Nonlinearities: geometry, contacts, tires, frictionNonlinearities: geometry, contacts, tires, friction● Interaction with deformable bodiesInteraction with deformable bodies

● Rigid/deformable blade elementRigid/deformable blade element● Rotor inflowRotor inflow● State-space on modal bodiesState-space on modal bodies

● Pipes, actuators, valves, sources, sinksPipes, actuators, valves, sources, sinks

● Electric motorsElectric motors● Strain, displacement, acceleration sensorsStrain, displacement, acceleration sensors● System modeling/signal processing elementsSystem modeling/signal processing elements● Programmable elementsProgrammable elements

● CFD couplingCFD coupling

Real-Time ExperimentReal-Time Experiment

LaboratoryLaboratory

RobotRobot

ControlControl

A/DA/D D/AD/A

HardwareHardwarein the Loopin the LoopSimulationSimulation

SimulationSimulation

ControlControl

RTnetRTnet

Virtual ExperimentVirtual Experimentas a cheap and safe as a cheap and safe replacementreplacementof experiment setupof experiment setup

Real-Time Virtual Real-Time Virtual ExperimentExperiment

RTnetRTnet

Simulation ImprovementsSimulation ImprovementsSoftware:Software:● sparse matrix/vector sparse matrix/vector

handling during handling during assemblyassembly

● sparse solution sparse solution handlinghandling

● assembly assembly parallelizationparallelization

● solution parallelizationsolution parallelization● hardware hardware

improvementsimprovements

Model:Model:● topology rationalizationtopology rationalization● constraints idealizationconstraints idealization● deformability reduction deformability reduction

(and elimination)(and elimination)

Software ImprovementsSoftware ImprovementsGuidelines:Guidelines:● beneficial for standard solution as wellbeneficial for standard solution as well● assembly/solution: ~ 70-80 vs. 25-15 % CPU timeassembly/solution: ~ 70-80 vs. 25-15 % CPU time

Results:Results: speed-upspeed-up● assembly in compressed matrix form:assembly in compressed matrix form: -10/-20 %-10/-20 %● multi-threaded assembly:multi-threaded assembly: -0/15 %-0/15 %● dense solver:dense solver: +50/-40 %+50/-40 %● iterative solver (worst case limitation)iterative solver (worst case limitation)● multi-threaded solution (n.a. yet)multi-threaded solution (n.a. yet)

Overall:Overall: -20/-45 %-20/-45 %

Comau robot modelComau robot model

Model description:Model description:● rigid bodies, plane rotation jointsrigid bodies, plane rotation joints● frictionfriction● 6 DOFs, 120 unknowns6 DOFs, 120 unknowns● from 500 Hz to 2kHz from 500 Hz to 2kHz

(Athlon XP 2400+)(Athlon XP 2400+)

Comau control and monitorComau control and monitor

Concluding RemarksConcluding Remarks● General purpose real-time multibody General purpose real-time multibody

simulation is feasiblesimulation is feasible● Performances on robot simulations Performances on robot simulations

meet requirementsmeet requirements● There is room for software/model There is room for software/model

improvements:improvements:• electric motorselectric motors• feed-forwardfeed-forward• parallel solutionparallel solution

● Real-time software optimization Real-time software optimization beneficial for conventional GP beneficial for conventional GP simulations as wellsimulations as well

Previous worksPrevious works

● M. Attolico, P. Masarati, M. W. Nixon and P. M. Attolico, P. Masarati, M. W. Nixon and P. Mantegazza, “Real-Time Multibody Analysis of Mantegazza, “Real-Time Multibody Analysis of Wind-Tunnel Rotorcraft Models for Virtual Wind-Tunnel Rotorcraft Models for Virtual Experiment Purposes”, AHS 4Experiment Purposes”, AHS 4thth Decennial Decennial Specialists' Conference on Aeromechanics, Specialists' Conference on Aeromechanics, Fisherman's Wharf, San Francisco, CA, January Fisherman's Wharf, San Francisco, CA, January 21-23, 2004.21-23, 2004.

● M. Attolico and P. Masarati, “A Multibody User-M. Attolico and P. Masarati, “A Multibody User-Space Hard Real-Time Environment for the Space Hard Real-Time Environment for the Simulation of Space Robots”, Fifth Real-Time Simulation of Space Robots”, Fifth Real-Time Linux Workshop, November 9-11, 2003, Linux Workshop, November 9-11, 2003, Valencia, Spain.Valencia, Spain.

● Acknowledgements to Matteo Martegani, Acknowledgements to Matteo Martegani, Michele Attolico and Giuseppe Quaranta.Michele Attolico and Giuseppe Quaranta.