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  • 1.
    Carlsson, Henric
    et al.
    University West, Department of Engineering Science, Division of Automation and Computer Engineering.
    Danielsson, Fredrik
    University West, Department of Engineering Science, Division of Production Engineering.
    Lennartson, Bengt
    University West, Department of Engineering Science, Division of Production Engineering.
    General Time Synchronisation Method for PLC Programs Aiming at Virtual Verification and Development2008In: 17th IFAC World: Congress Proceedings of the 17th World Congress. The International Federation of Automatic Control. Soel, July 6-11, 2008, p. 4440-4445Conference paper (Other academic)
    Abstract [en]

    The latest state-of-the-art Computer Aided Production Engineering (CAPE) simulation technology offers OPC integration for PLC verification. A critical drawback with this technology has been identified and described within this paper. A new time synchronisation method and a simulation architecture are therefore presented and proposed. The time synchronisation method together with the architecture can be used when verifying and developing real-time dependent control logic for industrial control system, e.g. PLC with CAPE tools. The method described in this paper is general and should work on any PLCs that are compatible with the IEC 61131-3 standard. A test case was also carried out, showing that by disregarding time synchronisation it is impossible to verify real-time dependent PLC functions together with CAPE tools in a reliable way. However, the test case also shows that by applying the proposed time synchronisation method together with the described simulation architecture a successful industrial verification method is achieved

  • 2.
    Carlsson, Henrik
    et al.
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Svensson, Bo
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Danielsson, Fredrik
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    A General Virtual Manufacturing Concept for Programming, Verification and Optimisation of Complex Control Functions2008In: Proceedings of the 18th International Conference on Flexible Automation and Intelligent Manufacturing, FAIM 2008: June 30th - July 2nd, 2008, University of Skövde, Sweden / [ed] Leo J. de Vin, Skövde, 2008, p. 668-675Conference paper (Refereed)
    Abstract [en]

    This paper describes a general virtual manufacturing concept for industrial control systems. Our virtual manufacturing concept provides a distinct advantage; programming, verification and optimisation of complex real-time dependent control functions described by real control code, which can be directly transferred to the real manufacturing system. To achieve this distinct advantage, a time synchronised virtual manufacturing system is a necessity. The aim of this paper is thus to present and to describe in detail, our proposed virtual manufacturing concept. To the authors’ knowledge no such general virtual manufacturing concept, i.e. one that can correctly handle complex real-time dependent control functions, currently exists. To summarise previous work related to virtual manufacturing and industrial control systems, several critical issues have been identified. The virtual manufacturing concept proposed in this paper addresses these issues. To verify that our concept can manage these critical issues found and further is suitable in industrial applications a virtual manufacturing test case is also presented. The test case, that includes motion control (i.e. servo), complex control functions, real control systems etc., was carried out with success.

  • 3.
    Christiansson, Anna-Karin
    University West, Department of Technology.
    A unified framework for mixed continuous/discrete-time H_infinity -control2003Doctoral thesis, monograph (Other academic)
  • 4.
    Christiansson, Anna-Karin
    et al.
    University West, Department of Engineering Science, Division of Production Engineering.
    Danielsson, Fredrik
    University West, Department of Engineering Science, Division of Production Engineering.
    Heralic, Almir
    University West, Department of Engineering Science, Division of Production Engineering.
    Ottosson, Mattias
    University West, Department of Engineering Science, Division of Production Engineering.
    Hurtig, Kjell
    University West, Department of Engineering Science, Division of Production Engineering.
    Automation of a robotised metal deposition system using laser melting of wire2008In: 18th International Conference on Flexible Automation and Intelligent Manufacturing (FAIM 2008): Skövde, 30 June-2 July, 2008, p. 122-129Conference paper (Other academic)
    Abstract [en]

    This paper presents a system for full automation of free-form-fabrication of fully dense metal structures using robotized laser melting of wire. The structure is built of beads of melted wire laid side by side and layer upon layer governed by synchronized robot motion. By full automation is here meant that the process starts with a product specification of a component, and ends in a geometrically validated dense metal component fulfilling industrial material requirements. Due to the complexity of this flexible manufacturing system, a number of different disciplines are involved. This paper discusses mainly the system design, which includes how off-line programming is used for automatic generation of code and how feedback control is used for on-line adjustment of parameters based on desired building properties. To meet industrial needs, the project is carried out in a close cooperation between research and development activities in academy and industry.

  • 5.
    Christiansson, Anna-Karin
    et al.
    University West, Department of Engineering Science, Division of Automation and Computer Engineering.
    Lennartson, B.
    Chalmers University of Technology, Control Engineering Lab, Göteborg, Sweden .
    Toivonen, H.
    Åbo Akademi University, Department of Chemical Engineering, Åbo, Finland.
    Mixed continuous/discrete-time output feedback H∞ control: A unified approach1999In: European Control Conference, ECC 1999 - Conference Proceedings, 1999, p. 4077-4082Conference paper (Refereed)
    Abstract [en]

    A Riccati equation (RE) based solution to the H∞ optimal control problem for mixed continuous/discrete-time systems is presented. The results unify a number of recently penetrated H∞ control problems. In the infinite-horizon case a periodic behaviour is assumed, and it is shown how the related continuous RE with jumps can be replaced by an equivalent discrete periodic RE. A related algebraic RE, which involves the system behaviour during one period, then can be formulated and solved by standard methods. Typical applications are control of continuous-time or discrete-time periodic systems, as well as multirate and sampled-data control, including mixed continuous and sampled-data measurements. © 1999 EUCA.

  • 6.
    Christiansson, Anna-Karin
    et al.
    University West, Department of Engineering Science, Division of Automation and Computer Engineering.
    Lennartson, Bengt
    Chalmers University of Technology, Control Engineering Lab, Göteborg, Sweden.
    Low order sampled-data H∞ control2003In: Decision and Control, 2003. Proceedings. 42nd IEEE Conference on, 2003, Vol. 3, p. 2308-2313 Vol.3Conference paper (Refereed)
    Abstract [en]

    A method for obtaining low order sampled-data H∞ controllers is presented. The method is mainly based on a parametric static feedback controller for a plant that is augmented with the controller dynamics. The design of a full-order controller is a convex problem, while the optimisation problem for lower order controllers is non convex. The proposed method starts with design of a full-order sampled-data controller using Riccati equations. Then this controller is reduced by an ordinary model reduction technique, and the reduced controller is used as an initial value for an iterative procedure using linear matrix inequalities (LMIs) in the search for an optimal controller. The matrix inequalities are in fact linear in either the Lyapunov matrix or the static controller matrix, why the solution to the non convex problem fundamentally is given by a bilinear matrix inequality (BMI). The order of the controller is reduced until the closed loop performance degrades too much. Simulations are shown for the control of a time delayed SISO-plant where the controller order can be reduced from 8th to 3rd order. Results are also shown from control of a MIMO-model of a jet engine where the reduction is successful from 15th to 4th order. It is argued that the non convexity is handled efficiently since the procedure uses a model reduction of the full-order controller as initial value.

  • 7.
    Christiansson, Anna-Karin
    et al.
    University West, Department of Engineering Science, Division of Automation and Computer Engineering.
    Lennartson, Bengt
    Chalmers University of Technology, Control Engineering Lab, SE-41 2 96 Goteborg, Sweden .
    Toivonen, H.
    Åbo Akademi University, Department of Chemical Engineering, FIN-20500 Abo, Finland .
    Continuous-, discrete- and sampled-data- H∞ˆž control - a unified framework2000In: IEEE Proceedings: Conference on Decision and Control (CDC), ISSN 0191-2216, Vol. 2, p. 1936-1941Article in journal (Refereed)
    Abstract [en]

    We present a unified and general framework for H∞-control in both continuous time, discrete time and combinations of these. The general result is a hybrid continuous-/discrete-time H∞ˆž-controller. Using a compact hybrid notation, the work shows a close relationship between the continuous-and discrete-time solutions. In fact, the pure continuous and discrete time equations may be obtained as two similar interpretations of the general result. There are no assumptions made on certain system matrices being zero or normalised, e.g. D11 = 0. The method is Riccati equation (RE) based, and it is shown how the continuous REs can be "lifted" into discrete ones reflecting the system behaviour during the period. Typical applications are control of continuous-time or discrete-time periodic systems, as well as multirate and sampled-data control, including mixed continuous and sampled-data measurements.

  • 8.
    Christiansson, Anna-Karin
    et al.
    University West, Department of Engineering Science, Division of Automation and Computer Engineering.
    Lennartson, Bengt
    Chalmers University of Technology, Control Engineering Lab, Göteborg, Sweden.
    Toivonen, H.T.
    Åbo Akademi University, Department of Chemical Engineering, Åbo, Finland..
    Sampled-data H∞ˆž-control for time-varying hybrid systems2001In: Dynamics of continuous, discrete and impulsive systems, ISSN 1201-3390, E-ISSN 1918-2538, Dynamics of Continuous, Discrete and Impulsive Systems Series B: Applications and Algorithms, ISSN 1492-8760, Vol. 8, no 4b, p. 427-444Article in journal (Refereed)
    Abstract [en]

    This paper presents sampled-data H∞ˆž-control of linear mixed continuous-time and discrete-time systems, including a mix of continuous-time and discrete-time performance signals and disturbances. However, neither continuous-time control signals nor continuous-time measurements are included. The sampling may well be multirate, i.e. different signals may be sampled by different rates, as long as a periodic pattern is repeated over the period, consisting of a number of sampling steps. In fact, the results are applicable even to arbitrary linear time-varying systems. The sampled-data system is discretised such that the continuous-time performance is reflected in the discretised or "lifted" system. This lifted system is combined with discrete-time updates at the sampling instants to achieve the sampled-data controller. The "hold-states" case is presented as a special application, when there is also a hold circuit at the controller output. The continuous-time Riccati equations with discrete-time updates then can be replaced by one discrete-time static feedback and filter Riccati equation respectively, which also reflect the intersample behaviour. Furthermore, convergence results between the discretised Riccati solutions and the corresponding continuous-time solutions are shown, when the sampling interval decreases towards zero. Simulations are shown when the results are applied to the control of a MIMO jet-engine model.

  • 9.
    Christiansson, Anna-Karin
    et al.
    University West, Department of Technology, Mathematics and Computer Science, Division for Electrical Engineering and Land Surveying.
    Ottosson, Mattias
    University West, Department of Technology, Mathematics and Computer Science, Division for Electrical Engineering and Land Surveying.
    Sensor and control system for metal deposition using robotised laser welding.2006In: 16th International Conference on Computer Technology in Welding and Manufacturing: Kiev, Ukraine, 2006, p. 328-332Conference paper (Refereed)
  • 10.
    Danielsson, Fredrik
    University West, Department of Technology, Mathematics and Computer Science.
    Off-line programming, verification and optimisation of industrial control systems2002Doctoral thesis, monograph (Other academic)
  • 11.
    Danielsson, Fredrik
    et al.
    University West, Department of Technology, Mathematics and Computer Science.
    Hansbo, Anita
    University West, Department of Technology, Mathematics and Computer Science.
    Control system verification by emulation: an application to off-line pressline throughput rate orpimization2002In: Journal of advanced manufacturing systems, ISSN 0219-6867, Vol. 1, no 2, p. 159-172Article in journal (Refereed)
    Abstract [en]

    This study is part of a research project aims at off-line programming and verification of industrial control systems. In this paper, an off-line method for press line throughput rate optimization and control system verification is proposed, implemented and evaluated. The main tool is a virtual press station, developed by the first author, consisting of an emulated control system for a feeder/extractor robot which communicates with 3D-simulated production equipment. Moreover, several virtual press stations have been coupled and synchronized in a virtual press line. An important feature of the system is that the virtual robot controller is emulated, yielding an exact representation of the control logic and the possibility to run the entire system in virtual real time. The application considered is a sheet metal forming process where it is difficult to achieve maximum capacity utilization. There is much to gain if the control logic is improved and the throughput rate is increased. For this purpose, an automated robot motion optimization method is implemented and evaluated, using the virtual press line.

  • 12.
    Danielsson, Fredrik
    et al.
    University West, Department of Technology, Mathematics and Computer Science.
    Moore, P
    Eriksson, P
    Validation, off-line programming and optimisation of industrial control logic2003In: Mechatronics (Oxford), ISSN 0957-4158, E-ISSN 1873-4006, Vol. 13, no 6, p. 571-585Article in journal (Refereed)
    Abstract [en]

    This article proposes a classification of different methods for validation, off-line programming and optimisation of control logic. The classification is an overview of different methods available and includes advantages and disadvantages for each method. The method overview points out a superior method, control system emulation, which is the most cost-effective and flexible method. The control system emulation method is also general and may be applied to validate and optimise control logic in various applications. Further, the method is compared with several other methods for validation of industrial control systems. However the method requires a standardised system architecture. This article proposes such architecture for the control system emulation method. Here, a control system emulator has also been implemented with the specific system architecture described in this article. An application case is also provided to demonstrate an approach to the integration of a control system emulator into a virtual manufacturing system.

  • 13.
    De Backer, Jeroen
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Robotic Friction Stir Welding for Flexible Production2012Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Friction Stir Welding (FSW) is a modern welding process that joins materials by frictional heat, generated by a rotating tool. Unlike other welding processes, the material never melts, which is beneficial for the weld properties. FSW is already widely adopted in several industries but the applications are limited to simple geometries like straight lines or circular welds, mostly in aluminium. The welding operation is performed by rigid FSW machines, which deliver excellent welds but puts limitations on the system in terms of flexibility and joint geometries. Therefore, several research groups are working on the implementation of the FSW process on industrial robots. A robot allows welding of three-dimensional geometries and increases the flexibility of the whole system. The high process forces required for FSW, in combination with the limited stiffness of the robot brings some extra complexity to the system.  The limitations of the robot system are addressed in this licentiate thesis.

    One part of the thesis studies the effect of robot deflections on the weld quality. A sensor-based solution is presented that measures the path deviation and compensates this deviation by modifying the robot trajectory. The tool deviation is reduced to an acceptable tolerance and root defects in the weld are hereby eliminated. The sensor-based method provided better process understanding, leading to a new strategy that uses existing force-feedback for path compensations of the tool. This method avoids extra sensors and makes the system less complex. Another part of this work focuses on the extra complexity to maintain a stable welding process on more advanced geometries. A model is presented that allows control of the heat input in the process by control of the downforce. Finally, the robot’s limitations in terms of maximal hardness of the materials to be welded are investigated. Parameter tuning and implementation of preheating are proposed to allow robotic FSW of superalloys.

  • 14.
    Därnemyr, Johan
    University West, Department of Engineering Science.
    Åtgärder för att minimera kommunikationsstörningar vid avläsning av elmätare via elnätet2009Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    This report handles the issue of communication problems that appears between the components in the ADDAX system, mainly between the router and meter. The system is built around a hierarchy with the ADDAX server at the top and the meter at the bottom. The system uses the power grid as communication medium, this is called PLC “power line communication. The task has bin to se how the system works, witch geographical areas that have problems with communication, localization of source for the disturbing of the communication, attend to the disturbing and to make a flow chart that the electricians can use when they are conducting a measurement. A program called “TC Meter Surv SA Edition 0.61” was used for finding which areas that have problems with the communication. Two areas were chosen, one in the countryside and one in central Grästorp. The program firs showed that some meters where missing but when the measurements where don the program showed that all meters where missing. The reason for this problem is unknown. The problem in the central Grästorp area is not in the LV butt in the MV. The conclusion will be that al of the software must be updated and that the master routers could be replaced with a never versions before any new measurements are to be done. The power quality measurement instruments that has bin used are PL-monitor and HF+. On other conclusion that can bi don is that HF+ is superfluous because it chows the same information that PL-monitor dose but it’s harder to interpret. In the area on the countryside the solution to the communication problem can bi to install a filter. Other solutions to PLC problems can bi to switch the phase the meter uses for communication, move the meter farther from the customer, installing a repeater or in consultation with the customer get him or here to turn of the devise that disturb the communication under some ours in a 24-hour period.

  • 15.
    Ericsson, Mikael
    et al.
    University West, Department of Technology, Mathematics and Computer Science.
    Nylén, Per
    University West, Department of Technology, Mathematics and Computer Science.
    Danielsson, Fredrik
    University West, Department of Technology, Mathematics and Computer Science.
    Carlsson, Henrik
    University West, Department of Technology, Mathematics and Computer Science.
    Off-line programming of robots for metal deposition2005In: Trends in welding research: Proceedings of the 7th international conference, May 16-20. Pine Mountain, Georgia, 2005, p. 629-634Conference paper (Other academic)
    Abstract [en]

    Metal Deposition (MD) is a rapid prototyping technique to build parts by depositing metal in a required fashion. When a complex-shaped part is to be built, a simulation tool is needed to define robot trajectories. Three different simulation-based methods for robot trajectory generation are introduced and compared in this study. The methods are; reversed milling, adapted rapid prototyping and application programming in a computer aided robotics software. All methods were shown capable of creating robot paths for complex shapes, with the CAR software approach being the most flexible. Using this method, the geometry to be built is automatically sliced into layers and a robot path is automatically generated. The method was tentatively evaluated and appears to provide a powerful technique in the design and optimisation of robot paths for MD. Experiments showed that it is possible to manufacture fully dense parts using an Nd-Yag laser.

     

  • 16.
    Hagqvist, Petter
    et al.
    University West, Department of Engineering Science, Division of Automation Systems.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Automation Systems.
    Heralic, Almir
    GKN Aerospace.
    Automation of a laser welding system for additive manufacturing2015In: Proceedings of the 2015 IEEE International Conference on Automation Science and Engineering / [ed] Kazuhiro Saitou, Univ. of Michigan, IEEE, 2015, p. 900-905Conference paper (Refereed)
    Abstract [en]

    This paper presents the benefits and challenges ofusing a standard robotised laser welding cell for additive manufacturing(AM). Additive manufacturing, sometimes denoted3D-printing or rapid prototyping, has lately met strong interestin several areas of society, and a variety of technologies andmaterials have been in focus. The current paper summarisesautomation efforts for AM of advanced aero engine componentsusing high power laser with welding optics as power source formelting metal wire and using an industrial robot for obtaininga 3-dimensional feature shape. The challenges are related to theprocess itself encountering high and repeated temperatures withmelting and solidification of the metal as the main players. Themajor research solutions discussed in this paper are relatedto automation issues for obtaining a stable process and tohave control of the temperatures and temperature changes thatthe metals encounter during the process. The solutions aresuccessfully implemented in an industrial laser welding cell.

  • 17.
    Heralic, Almir
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Monitoring and Control of Robotized Laser Metal-Wire Deposition2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The thesis gives a number of solutions towards full automation of the promising manufacturing technology Robotized Laser Metal-wire Deposition (RLMwD). RLMwD offers great cost and weight saving potentials in the manufacturing industry. By metal deposition is here meant a layered manufacturing technique that builds fully-dense structures by melting metal wire into solidifying beads, which are deposited side by side and layer upon layer. A major challenge for this technique to be industrially implemented is to ensure process stability and repeatability. The deposition process has shown to be extremely sensitive to the wire position and orientation relative to the melt pool and the deposition direction. Careful tuning of the deposition tool and process parameters are therefore important in order to obtain a stable process and defect-free deposits. Due to its recent development, the technique is still manually controlled in industry, and hence the quality of the produced parts relies mainly on the skills of the operator. The scientific challenge is therefore to develop the wire based deposition process to a level where material integrity and good geometrical fit can be guaranteed in an automated and repeatable fashion. This thesis presents the development of a system for on-line monitoring and control of the deposition process. A complete deposition cell consisting of an industrial robot arm, a novel deposition tool, a data acquisition system, and an operator interface has been developed within the scope of this work. A system for visual feedback from the melt pool allows an operator to control the process from outside the welding room. A novel approach for automatic deposition of the process based on Iterative Learning Control is implemented. The controller has been evaluated through deposition experiments, resembling real industrial applications. The results show that the automatic controller increases the stability of the deposition process and also outperforms a manual operator. The results obtained in this work give novel solutions to the important puzzle towards full automation of the RLMwD process, and full exploitation of its potentials.

  • 18.
    Heralic, Almir
    et al.
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Charles Murgau, Corinne
    University West, Department of Engineering Science, Division of Production Engineering.
    Dzevad, Imamovic
    Volvo Aero Coorporation.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Lennartson, Bengt
    Dep of signal and systems, Chalmers.
    Towards stable high-speed metal-wire deposition, Part I: Parameter studyIn: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387Article in journal (Refereed)
  • 19.
    Heralic, Almir
    et al.
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Automatic in-process control of laser metal-wire deposition based on sensor feedback2011In: 30th Interantional Congress on Applications of Lasers & Electro-Optics, ICALEO 2011: Orlando October 23-27, 2011. Code 87581|, 2011, p. 211-220Conference paper (Refereed)
    Abstract [en]

    This paper describes alasermetaldepositionsystem that isbasedon robotizedlaserwelding andwirefiller material. The system has been found suitable for the manufacture of simple but large shapes with high metallurgical requirements such as bosses or flanges found on aero engine components. Several benefits have been identified with the usage ofwirefiller compared to powderized feedstock, such as betterprocessefficiency, higherdepositionrates, and cleaner working environment. Thewirebaseddepositionprocessis however sensitive to disturbances and thus requires continuous monitoring and adjustments.Inthis work a 3D scanning system is described forautomaticin-processcontrolof thedeposition. The goal is to obtain a flat surface for each deposited layerinorder to ensure stabledeposition. The deviationsinthe layer height are compensated by controlling thewirefeed rate. The system is tested throughdepositionof small cylindrical bosses and the results show that the proposedcontrolapproach is suitable forautomaticdepositionof such structures. The material consideredinthis paper is Ti-6Al-4V deposited on plates of same material. The paper presents the equipment and thecontrolstrategy and discusses practical issues regarding thesensorused.

  • 20.
    Heralic, Almir
    et al.
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Lennartson, Bengt
    Dep of signal and systems, Chalmers.
    Height control of laser metal-wire deposition based on iterative learning control and 3D scanning2012In: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 50, no 9, p. 1230-1241Article in journal (Refereed)
    Abstract [en]

    Laser Metal-wire Deposition is an additive manufacturing technique for solid freeform fabrication of fully dense metal structures. The technique is based on robotized laser welding and wire filler material, and the structures are built up layer by layer. The deposition process is, however, sensitive to disturbances and thus requires continuous monitoring and adjustments. In this work a 3D scanning system is developed and integrated with the robot control system for automatic in-process control of the deposition. The goal is to ensure stable deposition, by means of choosing a correct offset of the robot in the vertical direction, and obtaining a flat surface, for each deposited layer. The deviations in the layer height are compensated by controlling the wire feed rate on next deposition layer, based on the 3D scanned data, by means of iterative learning control. The system is tested through deposition of bosses, which is expected to be a typical application for this technique in the manufacture of jet engine components. The results show that iterative learning control including 3D scanning is a suitable method for automatic deposition of such structures. This paper presents the equipment, the control strategy and demonstrates the proposed approach with practical experiments.

  • 21.
    Heralic, Almir
    et al.
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Automation and Computer Engineering.
    Lennartson, Bengt
    Dep of signal and systems, Chalmers.
    Towards stable high-speed metal-wire deposition, Part II: Automatic deposition using feedback controlArticle in journal (Refereed)
  • 22.
    Heralic, Almir
    et al.
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Ottosson, Mattias
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Lennartson, Bengt
    Chalmers Tekniska Högskola.
    Increased stability in laser metal wire deposition through feedback from optical measurements2010In: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 48, no 4, p. 478-485Article in journal (Refereed)
    Abstract [en]

    Robotized laser metal-wire deposition is a fairly new technique being developed at University West in cooperation with Swedish industry for solid freeform fabrication of fully densed metal structures. It is developed around a standard welding cell and uses robotized fiber laser welding and wire filler material together with a layered manufacturing method to create metal structures. In this work a monitoring system, comprising two cameras and a projected laser line, is developed for on-line control of the deposition process. The controller is a combination of a PI-controller for the bead width and a feed-forward compensator for the bead height. It is evaluated through deposition of single-bead walls, and the results show that the process stability is improved when the proposed controller is used.

  • 23.
    Heralic, Almir
    et al.
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Ottosson, Mattias
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Lennartson, Bengt
    Dep of signal and systems, Chalmers.
    Automation of laser metal deposition for the manufacture of fully dense structures2011In: 4th International Swedish Production Symposium, SPS11: 3-4 May, Lund, Sverige / [ed] Jan-Eric Ståhl, Swedish Productio Academy , 2011, p. 219-227Conference paper (Refereed)
  • 24.
    Heralic, Almir
    et al.
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Ottosson, Mattias
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Norlander, Torbjörn
    Volvo Aero Coorporation.
    Geometry control of laser metal deposition for the manufacture of complex structures in the aero industry2011In: 20th International Society for Airbreathing Engines Conference, ISABE 2011: September 12-16, 2011 Gothenburg, 2011, p. 1666-1674Conference paper (Refereed)
  • 25.
    Heralic, Almir
    et al.
    University West, Department of Technology, Mathematics and Computer Science, Division for Electrical Engineering and Land Surveying.
    Wolff, Krister
    Chalmers University of Technology.
    Wahde, Mattis
    Chalmers University of Technology.
    Central Pattern Generators for Gait Generation in Bipedal Robots2007In: Humanoid Robots: New Developments, I-Tech Education and Publishing , 2007, p. 285-304Chapter in book (Other academic)
  • 26.
    Lennartson, Bengt
    et al.
    University West, Department of Engineering Science, Division of Automation Systems. Chalmers University of Technology, Department of Signals and Systems, Gothenburg, Sweden.
    Bengtsson, Kristofer
    Sekvensa AB.
    Wigstrom, Oskar
    Chalmers.
    Riazi, Sarmad
    Chalmers.
    Modeling and Optimization of Hybrid Systems for the Tweeting Factory2016In: IEEE Transactions on Automation Science and Engineering, ISSN 1545-5955, E-ISSN 1558-3783, Vol. 13, no 1, p. 195-205Article in journal (Refereed)
    Abstract [en]

    In this paper, a predicate transition model for discrete-event systems is generalized to include continuous dynamics, and the result is a modular hybrid predicate transition model. Based on this model, a hybrid Petri net including explicit differential equations and shared variables is also proposed. It is then shown how this hybrid Petri net model can be optimized based on a simple and robust nonlinear programming formulation. The procedure only assumes that desired sampled paths for a number of interacting moving devices are given, while originally equidistant time instances are adjusted to minimize a given criterion. This optimization of hybrid systems is also applied to a real robot station with interacting devices, which results in about 30% reduction in energy consumption. Moreover, a flexible online and event-based information architecture called the Tweeting Factory is proposed. Simple messages (tweets) from all kinds of equipment are combined into high-level knowledge, and it is demonstrated how this information architecture can be used to support optimization of robot stations.

  • 27.
    Lennartson, Bengt
    et al.
    Chalmers University of Technology, Control Engineering Lab, Göteborg, Sweden.
    Middleton, R.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Automation and Computer Engineering.
    Unified, periodic & sampled data H control using the delta operator2004In: Decision and Control, 2004. CDC. 43rd IEEE Conference on, 2004, Vol. 3, p. 2364-2369Conference paper (Refereed)
    Abstract [en]

    A unified and general framework is presented for H<sub>&infin;</sub> control of mixed continuous-time and discrete-time time-varying (periodic) systems. Using the delta operator, a close relationship is shown between the continuous- and discrete-time solutions. No assumptions are made on certain system matrices being zero or normalized, which makes the approach general and easy to apply. A combined continuous/discrete-time lifting procedure is shown to be useful, especially for ill-conditioned systems. This procedure together with the delta formalism results in a numerically robust design method concerning both short and long sampling periods for systems with W-conditioned dynamics, including widely spread eigenvalues.

  • 28.
    Lennartson, Bengt
    et al.
    Chalmers University of Technology, Control Engineering Lab, Göteborg, Sweden.
    Middleton, R.
    Christiansson, Anna-Karin
    University West, Department of Engineering Science, Division of Automation and Computer Engineering.
    McKelvey, T.
    Low order sampled data H control using the delta operator and LMIs2004In: Decision and Control, 2004. CDC. 43rd IEEE Conference on, 2004, Vol. 4, p. 4479-4484Conference paper (Refereed)
    Abstract [en]

    A procedure for H optimization of low order controllers for discrete-time and sampled-data systems is presented in this paper. Generally, low order H controllers may be achieved by solving bilinear matrix inequalities (BMIs). In this paper an iterative alternation between two LMIs gives a suboptimal solution. To avoid local minima in this search the initial controller is obtained by a frequency weighted controller reduction scheme, where the closed loop properties of a full order controller is taken into account. A minimal number of parameters in the state space realization of the controller also reduces the complexity and improves numerical robustness. The complete presentation is based on delta operator models, which shows a close relationship between the continuous- and discrete-time solutions. The sensitivity of the ordinary discrete-time shift operator LMI formulation to small sampling periods is also analyzed.

  • 29.
    Lievain, Guillaume
    et al.
    University West, Department of Technology, Mathematics and Computer Science.
    Rupil, Damien
    University West, Department of Technology, Mathematics and Computer Science.
    Study of different sensor systems and investigation about poseye for positioning2004Report (Other (popular science, discussion, etc.))
  • 30.
    Nia, Nima Khansari
    University West, Department of Engineering Science, Division of Automation and Computer Engineering.
    Efficient simulation and optimization for tandem press lines2012Licentiate thesis, comprehensive summary (Other academic)
  • 31.
    Sikström, Fredrik
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Simulation-based feedback control of welding processes2008Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Fusion welding for joining of metals is an important manufacturing process widely used in industry, and very appreciated for its usefulness. This thesis presents a strategy dealing with the problem of designing feedback control for robotised welding. The idea is to use off-line programming where computer aided robotics for weld sequences is integrated with finite element modelling for simulations and analyses of weld processes. By this approach the design, evaluations, trials and visualisation can be made “off-line”, beside or prior to continuous production. The focus is to reduce the amount of manpower and need for physical experiments. Focuses on the results are to ensure a high quality weld with limited residual stress and deformation. Different models for two types of austenitic steels and two types of weld sources has been calibrated and validated to form a basis for this strategy. Suggestions for systematic model calibration methods have been proposed including global and local optimisation methods. Experimental work has been performed to support and verify the simulation results and the usefulness of the method. The simulation based strategy has been evaluated and proven to work successfully in two different types of applications. The method is not independent of physical experiments since it is based on models that have to be calibrated, but the experiments needed are assumed to be carried out in a simple and cost efficient way. The thesis suggests how these experiments can be performed. The use of all these technologies is assumed to form an efficient tool for the welding engineer in order to obtain high weld quality in robotised welding. The research presented indicates that the methods work well in real situations and that further work for more robust industrialisation will be beneficial for the welding community.

  • 32.
    Svensson, Bo
    et al.
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Danielsson, Fredrik
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Lennartson, Bengt
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Simulation based optimization of a sheet-metal press line2009In: IEEE Conference on Emerging Technologies & Factory Automation, ETFA 2009, 2009, p. 1-8Conference paper (Refereed)
    Abstract [en]

    An off-line optimization of a sheet-metal press line is performed with improved production performances, both in terms of increased production rate and smoother robot motions. Smooth motions prevent the sheet-metal to slide out of position or even fall out, thereby causing lengthy down times. The simulation based method use a process optimizer connected to a time synchronized virtual manufacturing model including real industrial control systems, e.g. PLC. The key benefit herein is that all tuned control system parameters can be directly downloaded to the real press line without any post-processing or transformations. The challenge to find suitable optimization algorithms for a press line that handle highly nonlinear, discontinuous functions; considerable number of parameters; and long evaluation times is reached.

  • 33.
    Svensson, Bo
    et al.
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Danielsson, Fredrik
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Lennartson, Bengt
    University West, Department of Engineering Science, Division of Electrical and Automation Engineering.
    Virtual Real-Time Model: a Tool for Increased Production2005In: Mekatronikmöte 2005, 2005Conference paper (Other academic)
    Abstract [en]

    Increasing the total number of produced components in a pre-existing production line, which is a large-scale mechatronic system, is a continuous and never-ending story in industry. There is a need for tools and methods to develop the control software off-line, i.e. to manage programming, verification, validation, optimisation, training new operators, etc. without using the real production line. Therefore a general Virtual Real-Time Model, VRTM, for simulating industrial production lines is proposed. The VRTM is intended to be used for off-line control software development and is aimed at increase the throughput in highly automated production lines. The main features of the VRTM are that the same control software is used as in the real production line and that virtual real-time is used, implying that everything is time-synchronised and works in the same way as in the real production line (including security functions). An applied VRTM simulating a sheet-metal press line is implemented and validated. A comparison test with the press line at Volvo Car Manufacturing in Göteborg is performed with a satisfactory agreement. This shows that the VRTM can be used for off-line control software development.

  • 34.
    Windfäll, Åsa
    University West, Department of Technology, Mathematics and Computer Science, Division for Mechanical Engineering.
    Principles of robust and accurate computational 3D positioning from 2D image2005Report (Other (popular science, discussion, etc.))
1 - 34 of 34
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