SAMCEF for Machine Tools resulting from the EU MECOMAT ...

SAMCEF for Machine Tools resulting from the EU MECOMAT* project

Patrick Morelle (1), Didier Granville (2), Michel Goffart (2)

(1) SAMTECH Deutschland (2) SAMTECH Oskar-Kalbfell-Platz 8 Rue des Chasseurs-Ardennais 8, D-72764 Reutlingen, GERMANY B-4031 ANGLEUR (LIEGE), BELGIUM Phone : +49 7121 92 20 0 Phone: +32 43616969 Fax : +49 7121 92 20 90 Fax: +32 43616980

[email protected] [email protected] [email protected]

* MEchatronic COmpiler for Machine Tools design - EU GROWTH project

Abstract: The main objective of the MECOMAT FP5 project (January 2001 - January 2004) was to develop a methodology and a Computer-Aided Engineering tool for the mechatronic design of Machine Tools, which supports both the conceptual design and detailed verifications. The project resulted in an integrated software system for the synthesis, the analysis and the optimization of Machine Tools following a mechatronic approach, where the design of mechanisms, structures and control systems can be performed concurrently. From the results of this project, SAMTECH developed and industrialized a new professional software solution dedicated to Machine Tool manufacturers: SAMCEF for Machine Tools. The idea of SAMCEF for Machine Tools is to propose to the Machine Tool Designers an integrated advanced CAE tool based on CAD geometry and giving access to different levels of Machine-Tool models and to different analysis types, without having to switch from one user environment to another one. The solution, driven by the CAD/CAE User environment SAMCEF Field, is based on the general capabilities of linear analysis modules of SAMCEF (SAMCEF Linear), the advanced non-linear FE solver SAMCEF Mecano, coupling efficiently non-linear Finite Element Analysis, rigid/flexible Multi-Body Simulation and Controller Simulation in the same analysis module and the optimization/task management platform BOSS quattro. Keywords: Computer Aided Engineering, Machine Tool Design, Mechanism, Structure, Mechatronics, Control system, linear and non-linear Finite Element Analysis, Multi-Body Simulation, Optimization, Graphical User Interface, Tasks Manager, SAMCEF, BOSS quattro.

1 Introduction The MECOMAT consortium has developed a Computer Aided Engineering system as outlined in Figure 1. Figure 1 shows the basic functional modules, as specific objectives of the MECOMAT project, and their interrelationship. The vertical arrows indicate the main course of the design process starting with the design specifications, and ending with an optimal design solution. Basically the design process can be divided into two phases: - (I) The conceptual design, where the space of possible design alternatives are explored,

preliminarily analyzed and optimized; - (II) The detailed mechatronic design phase, where the detailed coupled structural and control

models are generated, and precisely analyzed and optimized.

1NAFEMS Seminar: „Mechatronics in Structural Analysis“

May 5 - 6, 2004 Wiesbaden, Germany

Seven main functional modules were developed and the integration of theses modules was performed during the last part of the project: layout design; design of motion units; servomechanism design; mechanical modeling; mechatronic compiler; graphical user interface; and analysis/optimization tools.

5

1 Design specifications

6 Detailed mechanicaldesign

8 Mechatronic compiler

Optimal machine tool design

I. Conceptual Design

II. Detailed mechatronic design

2 Layout Design

Preliminary analysis optimization concept

7 Det n

ailed control desig

4 Servomechanism design

3 Design of motion units

Figure 1: Functional modules of the design system There was a lack of appropriate methods and tools for this kind of design support. This project is the answer to a demand for extra support during the early stages of the design process where the major decisions on the commitment of resources are made, and during the detailed design where precise modeling, analysis and optimization techniques are necessary for combined structures, mechanisms and controller analysis (figure 2). The MECOMAT consortium has been established by nine partners from five European countries with the representation of three industrial machine tools designer (COMAU, HOLROYD, CESI), two research institutes (CETIM, CNR-ITIA), three universities (KU Leuven, University of LANCASTER, University of BUDAPEST) and the Finite Element Software company SAMTECH, acting as coordinator.

Figure 2: Structures, Mechanisms and Controller aspects embedded in the MECOMAT Mechatronic Compiler



Typical applications of the MECOMAT project can be found in all the companies active in the field of Machine Tool design, even if they don’t use any numerical simulation tools yet. However, other categories of potential applications of MECOMAT can be found in several industrial sectors where the interest of mechatronic numerical simulation is increasing, such as space industry (active control of vibrations of large flexible space structures like reflectors, solar arrays, optical mirrors), aeronautical industry (damping device of landing gears, actuation of flaps, slats...), car industry (active control of suspension), railway industry (active control of pendulum trains, control of pantograph contact on catenaries), textile industry (weaving machines)…

2 Description of MECOMAT modules

2.1 Layout design (Budapest University of Technology and Economics)

The Layout Design Module of MECOMAT supports the designers in the synthesis, the analysis and the optimization of the preliminary mechanical structure of 3-axis Machine Tools. The Machine Tool layouts are described by some layouts parameters by which the different variants of Machine Tool models are synthesized from a parametric component library (Figure 3). Figure 4 shows some components of the main classes of the component library. The synthesized Machine Tool models (assemblies), as a result, have parametric geometry. For the evaluation of the generated machine variants, several analyses were developed, e.g., a geometric analysis; a volume analysis; a static analysis; a modal analysis; or a clearance analysis. The optimizations of the configuration and/or of the geometric parameters can then be carried out by the optimization module of the MECOMAT system, where the multi-criteria optimization objectives can be composed from the following sub-objectives (that are derived from the analyses presented above): e.g., minimize the total volume, minimize the static deformations, minimize the geometric interferences, and maximize the lowest natural frequency.

Figure 3: Examples of 3-axis machine tool layouts

Base with GuideFixed Headstock Cross SlideFixed Table Moving Table

Figure 4: Examples of components



2.2 Design of motion units (CESI)

This module of MECOMAT allows to define and to populate a standard library of motion units, such as slideways, kinematical chains, motors, from which the designer can build a parametric structural model. A general method was developed, which is able to overcome the information-exchange problem between different 3D CAD systems. The realization of components by means of a particular CAD system and then its translation into a neutral exchange format (e.g. IGES, STEP) is not always an optimal solution: the increasing size of such files and their non-parametric format make dimension modifications difficult.

Mot ore

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Giunto

Ghiera Cuscinet t i

Cuscinet t i

Support oSlave

Support oMast er

Tampone

Modular AssemblyLibrary Management

EnvironmentCalculation Sw

Figure 5: Motion units database

This aspect is definitely a major drawback, because the dimensions of components change very frequently during the course of the iterative design. The MECOMAT method is based on a “part family” approach, which is suitable to create a large number of parts that are “geometrically similar” but different in dimensions. This method (data base) is SW-independent, which means that the library could be implemented in different CAD systems. The main result of this method is a database giving the possibility to exchange the library among the different modules of the design software.

2.3 Design of servomechanisms/controllers (University of Lancaster)

The design of servomechanisms/controllers of the MECOMAT system is taken in charge by Schemebuilder. Schemebuilder is a conceptual design environment, which was developed at the University of Lancaster and has been successfully applied to industrial problems. Within MECOMAT, Schemebuilder was extended to the design of servomechanism/controllers for Machine Tools. Schemebuilder provides an integrated environment to handle designs at the conceptual stage right through to testing using computer simulations [8, 9]. Technical solutions and design principles [10, 11] are retrieved from the knowledge base and pieced together in a fully interactive and dynamic process. A Control Advisor [12] and a Hydraulic Advisor [13] are also available. Schemebuilder has a knowledge base for multiple-axis control problems where interaction between axis drives could be significant. Specific design requirements regarding sensor selection, position accuracy, repeatability and dynamic response performance were customized for the envisaged Machine Tool applications. The output of Schemebuilder is a MATLAB Simulink model that can be embedded within SAMCEF.

Figure 6: Schemebuilder



2.4 Mechanical modeling (ITIA-CNR)

The mechanical model of a Machine Tool can be very simple or very sophisticated depending on the objectives of the designer. Typical simple objectives can be a simple linear static analysis including gravity field and tool forces or a simple modal analysis predicting the eigen frequencies or the mode shapes of a given configuration of the machine. However, the designer may be also interested in describing the true physical non-linear dynamic behavior of its Machine Tool in working conditions, interacting (and vibrating) dynamically with its controllers. With the software tools developed in MECOMAT, it is now possible to achieve these objectives with a generic CAD based model. The model has to contain a consistent description of all the parts and the connection devices of the Machine Tool. The User environment of the MECOMAT system is SAMCEF Field, the CAD Based CAE pre-/post-processor of SAMCEF. In addition to linear capabilities, it gives also access to the component library and the solver of SAMCEF Mecano [17] with different detail levels for the bodies (simple rigid bodies or refined models with detailed meshed structures or super-elements to reduce the computational time) and for the kinematical connection devices (rigid or flexible kinematical joints), depending on the choices made by the designers (Figure 7). The introduction of control boxes in the mechanical model is done through the definition of some inputs (“sensors”) and outputs (“actuators”) of the digital control device.

Figure 7: Mechanical components library

A possibility was also foreseen to output linearized mechanical models to represent correctly the instantaneous dynamic behavior of mechanical system during the control design.



2.5 Mechatronic design and optimization (KU LEUVEN)

In order to optimize the Machine Tools, the designer must be able to estimate precisely the machine performance. This performance can for instance depend on structural deformations [22,23] as well as on control tracking error [21]. For this purpose, an integrated machine model (which describes the dynamic behavior of the mechanical structure and that of the control system) was considered. A specific infrastructure was developed to merge the output of control design (C or FORTRAN code) with the mechanical module SAMCEF Mecano. The graphical interface SAMCEF Field allows to define the control boxes (inputs and outputs) inside the mechatronic compiler and to connect it to the mechanical part of the model. In order to obtain models that are suitable for both conceptual and detailed design, several levels of modeling aspect can be used successively, as explained before. The mechanical structure can for instance be described as lumped parameter model with compliant guideways or as a more complex Finite Element model (with or without reduction in a Super-Element). Research work at K.U. LEUVEN showed that an indirect strategy is well suited and efficient for the simultaneous optimization of structural and controller design variables in mechatronic systems [20]. This strategy is being extended in MECOMAT and generalized for a broader class of mechatronic systems. Figure 8 demonstrates a typical example for a mechatronic optimization of a 3-axis machine tool. An approximate structural design model (ADM) is generated. Based on this approximation, an optimization of the structural and control parameters is done. With these optimal parameters the FE-model is updated and the performance is checked. This loop is repeated until convergence. This strategy was implemented into the MECOMAT system.

Designimprovements

Exactresults

Approximateresults

New designvariables

Initialapproximations

Yes

No

Convergence ?Yes Optimised

mechatronicdesign

ConstraintsOK ?

NoController

optimalisation

Numericaloptimisation

ADM+control

Updated approximations

Initial design

FE+control FE+control

Figure 8: Mechatronic design process

2.6 Graphical user interface (SAMTECH) SAMCEF Field ([18]) is the Graphical User Interface that is developed by SAMTECH and was used to build the MECOMAT environment for the mechatronic design of Machine Tools. The modeling is defined directly on the geometry. It allows easy modifications of the modeling refinement (for example to go from a simple rigid body modeling to a detailed meshed one or the opposite). It also allows an easy switch from an analysis type to another one (for example, from a non-linear mechanism analysis using SAMCEF Mecano to a linear modal analysis using SAMCEF Dynam or a linear static analysis using SAMCEF Asef). Controllers coming from MATLAB Simulink (through Schemebuilder) were also included in the environment.

Figure 9: SAMCEF Field



2.7 Task management and optimization platform (SAMTECH)

In order to connect all the modules of the MECOMAT system and to automate the MECOMAT optimization processes, specific scripts and drivers were developed inside the environment of BOSS quattro. BOSS quattro ([19]) is dedicated to analyzing and optimizing the influence of parameters on responses yielded by external software through the use of specialized drivers. On one hand, the analysis leads to display the response curves with respect to the parameters. On the other hand, BOSS quattro can also perform a sensitivity analysis and searches for the optimal parameter values in order to satisfy some criteria on the responses. Zero order methods (genetic algorithms) are also available. As an application manager, BOSS quattro controls the execution of external applications and interacts with their environment. Fully menu driven, this user-friendly tool makes the definition of process loops and task chaining easy. The simultaneous use of models (CAD, FE or any other type) is then straightforward since applications are considered as “black boxes”, which receives parameters and gives responses back.

Figure 10: BOSS quattro



3 Presentation of SAMCEF for Machine Tools SAMCEF for Machine Tools is currently industrialized by SAMTECH from the results of MECOMAT. It offers now a new environment for the global design and the detailed mechatronic verification of Machine Tools. It is a Computer Aided Engineering tool completely based on geometries defined locally or imported from well-known CAD systems. It offers a complete toolbox of components giving for the first time to the designer the possibility to use the same modeling environment during the whole design process from A to Z, i.e. from simple rigid body simulation to check the global kinematics of the Machine Tool to very detailed verification using Finite Element technique of the dynamic behavior of the machine tool interacting with its controllers. In the past, the mechanical design of Machine Tools was mainly based on rigid body mechanism simulation and separate local and usually linear structure analysis using Finite Element Method. SAMCEF for Machine Tools proposes now the integration of these complementary disciplines into the same modeling environment with, in addition, the management of behavior laws of servomechanisms. As illustrated on figure 11, SAMCEF for Machine Tools is based on the following software tools developed by SAMTECH:

SAMCEF Field, the associative object oriented modeling environment of SAMCEF; SAMCEF Linear, the complete set of linear modules of SAMCEF for structure FE analysis:

o Linear static FE analysis (SAMCEF Asef); o Modal FE analysis and Super-Element creation/restitution (SAMCEF Dynam).

SAMCEF Mecano, the powerful non-linear module of SAMCEF for both mechanism simulation and non-linear structure FE analysis in static, kinematical or dynamic conditions;

BOSS quattro, the open object oriented task management and optimization platform, allowing also parametric studies, sensitivity analyses, statistical analyses, model updating with experiments, design of experiments and response surfaces.

Users can define simple control boxes directly in SAMCEF. In addition, direct interfaces allow to import digital control boxes from external functional simulation tools (MATLAB Simulink for example) into SAMCEF Mecano, but also to export the output of a linearized configuration, giving it back to the functional simulation tool that can serve for the design of controllers or servomechanisms (MATLAB Simulink for example). Using SAMCEF for Machine Tools, designers can chose the appropriate mechanical modeling of the Machine Tool depending on the progress of the design. The mechanical model can contain a description of all the parts (bodies) and the connection devices (joints) of the Machine Tool. Different modeling levels may be chosen, depending on the objectives of the analysis, not only for bodies (rigid bodies, beam, shell, volume FE models, Super-Elements…) but also for joints (ideal kinematical joints with or without friction laws, flexible sliders, ball screw element, linear motor, contact/friction conditions…). In order to connect the controllers to the mechanical model, “sensors” can be defined to measure inputs of controllers and “actuators” sending back the outputs of the controllers to the mechanical model. Finally, different types of mechanical analyses are accessible from the same modeling environment (transient non-linear analysis, static analysis, modal analysis and soon harmonic response on linear or linearized configurations…).

Figure 11: Structure of SAMCEF for Machine Tools



4 Applications

4.1 Detailed Box-in-Box example

Several kinds of Machines Tools were used during the MECOMAT project to test the developed software tools. The following test case was used during the whole project: Starting from the CAD description of an existing COMAU machine layout, a first SAMCEF Mecano modeling was built including rigid bodies and rigid kinematical joints. In a second step, flexible behavior and super-elements were introduced for the parts and flexible sliders for the joints of the machine. As illustrated hereafter, the first goal was to validate the mechanical behavior using simple linear analyses and then, to introduce of the controllers in the model to perform a mechatronic simulation.

Figure 12: Structure of COMAU machine analysis scheme The assembly of these parts including controllers has been used for different kinds of analysis: linear static, modal, non-linear, transient, ... without re-encoding of the model.



4.2 Other examples

Numerous other examples of applications can also be shown purely rigid or mixing rigid and flexible components, without any limitation of complexity.

Figure 13: Other applications

The results of the different analyses were validated regarding experiments, for example a high performance machine studied by CETIM using linear motors and guided by rails with rolls. The modeling was also realized using SAMCEF Mecano. The goal of the computation wass the prediction of the speed and the precision of the Machine Tool motions. A flexible multi-body modeling was made. The Super-Element technique was also used to reduce the analysis CPU consumption. Prismatic flexible sliders were used to represent the guiding rails. Linear motors were implemented in the generic non-linear force element. Digital controller acting on axes were modeled in MATLAB Simulink and integrated in SAMCEF Mecano. A comparison was made between numerical results and experiments. The conclusion was that the model was able to predict the speed and the precision of execution of the module with less than 8 % of error.



5 Conclusions The MECOMAT project objective was to develop a methodology and a Computer-Aided Engineering tool for the mechatronic design of Machine Tools, which supports both the conceptual and detailed design processes. The project developed an integrated software system for the synthesis, analysis and optimization of machine tools following a mechatronic approach where the design of the mechanisms, the structures and of the control systems is performed currently. Several functional modules were developed and integrated: layout design, design of motion units, servomechanism design, mechanical model, mechatronic compiler, graphical user interface, analysis and optimization tools. An industrialization of some results leads now to SAMCEF for Machine Tools, a very interesting software solution giving for the first time to the Machine Tool Manufacturer the access to all the state-of-the-art of Computer Aided Engineering techniques from the same CAD based environment.

Acknowledgement SAMTECH thanks the MECOMAT consortium for its fruitful collaboration during three years. The MECOMAT consortium thanks the European Commission for having supported the MECOMAT project. References [1] French, M.J. “Conceptual design for engineers”, The Design Council London, Springer-Verlag, second edition, 1985 [2] Sharpe, J. E. E., “Integrated Platform for AI Support of Complex Design - (Part I): Rapid Development Of Schemes From First

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