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  • 1.
    Pahlberg, Tobias
    et al.
    Luleå University of Technology, Campus Skellefteå, Skellefteå, Sweden.
    Thurley, Matthew
    Luleå University of Technology, Luleå, Sweden.
    Popovic, Djordje
    Jönköping University, School of Engineering, JTH, Supply Chain and Operations Management. Jönköping University, School of Engineering, JTH, Industrial Product Development, Production and Design.
    Hagman, Olle
    Luleå University of Technology, Campus Skellefteå, Skellefteå, Sweden.
    Crack detection in oak flooring lamellae using ultrasound-excited thermography2018In: Infrared physics & technology, ISSN 1350-4495, E-ISSN 1879-0275, Vol. 88, p. 57-69Article in journal (Refereed)
    Abstract [en]

    Today, a large number of people are manually grading and detecting defects in wooden lamellae in the parquet flooring industry. This paper investigates the possibility of using the ensemble methods random forests and boosting to automatically detect cracks using ultrasound-excited thermography and a variety of predictor variables. When friction occurs in thin cracks, they become warm and thus visible to a thermographic camera. Several image processing techniques have been used to suppress the noise and enhance probable cracks in the images. The most successful predictor variables captured the upper part of the heat distribution, such as the maximum temperature, kurtosis and percentile values 92–100 of the edge pixels. The texture in the images was captured by Completed Local Binary Pattern histograms and cracks were also segmented by background suppression and thresholding. The classification accuracy was significantly improved from previous research through added image processing, introduction of more predictors, and by using automated machine learning. The best ensemble methods reach an average classification accuracy of 0.8, which is very close to the authors’ own manual attempt at separating the images (0.83).

  • 2.
    Popovic, Djordje
    Jönköping University, School of Engineering, JTH, Supply Chain and Operations Management. Jönköping University, School of Engineering, JTH, Industrial Product Development, Production and Design.
    Off-site manufacturing systems development in timber house building: Towards mass customization-oriented manufacturing2018Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The need for housing in Sweden has been showing a constant increase over the past couple of years. However, this situation might change in 2018 since there are indications that the increase in demand will reach its peak. On the other hand, the use of timber as a load bearing structure has become more popular in the multi-family house building sector. It is competing with concrete and steel frames, and its market share might even reach 50% by the year of 2025. Adding the involvement of customers in house design decisions and a high level of customization, the conclusion is that timber house building must continue the development towards mass customization. There is a lack of knowledge on how mass customization is developed and implemented regarding off-site manufacturing systems. In this thesis, a contribution is made to manufacturing system development in timber house building by proposing a novel approach to aligning off-site manufacturing systems to the requirements of production strategy, market needs, product design, and manufacturing processes. The proposed conceptual framework is a synthesis of the knowledge gained from three empirical studies and different methods found in theories of changeable manufacturing systems, mass customization, and manufacturing system development. The research purpose addressed by the presented work, is to increase the knowledge on how the development potential of off-site manufacturing systems can be identified in mass customization-oriented timber house building. Case study research was applied to gather the empirical data. The data collection and analysis methods used in the empirical studies can be useful when discussing the potential improvements. However, these data are not comprehensive enough in terms of presenting a holistic view of off-site manufacturing and consideration of the market as well as variation in product and processes. Therefore, a comprehensive set of requirements is proposed in the conceptual framework together with a step by step description of how the development potential of off-site manufacturing systems can be identified.

  • 3.
    Popovic, Djordje
    et al.
    Luleå tekniska universitet.
    Broman, Olof
    Luleå tekniska universitet, Träteknologi.
    Hagman, Olle
    Luleå tekniska universitet, Träteknologi.
    Optimizing the cross cutting operation using research design metod2014Conference paper (Refereed)
    Abstract [en]

    A cost efficient process is the goal of every part of the wood processing chain. It is directly related to a yield that is gained out of a raw material. On the other hand these processes have to deliver a certain product quality in order to satisfy customer needs. Very often a tradeoff has to be made between the yield and theproduct quality through optimization processes. The main objective of this work was to study if the research design can be used for the purpose of predictingscanning operation parameters, in order to maximize the yield and keep the mean length of the accepted pieces of center boards at a desired value. The obtained partial least squares (PLS) regression models quite accurately predicted optimum operating settings for the given material. This method can be used to achieve the goal of optimizing the cross cutting operation. Nevertheless the knowledge about the origin of processed boards in terms of the log type they were sawn from is significant, since developed models differed between each other accordingly.

  • 4.
    Popovic, Djordje
    et al.
    Jönköping University, School of Engineering, JTH. Research area Industrial Production. Jönköping University.
    Fast-Berglund, Åsa
    Chalmers University of Technology.
    Winroth, Mats
    Chalmers University of Technology.
    Production of customized and standardized single family timber houses – A comparative study on levels of automation2016Conference paper (Refereed)
    Abstract [en]

    Industrialization of house building implies a higher pre-fabrication level where companies have moved from the traditional on-site to the off-site assembly. Currently in Sweden there is an increasing demand for all types of households and the companies from this construction sector lack the capacity to respond to these needs. Increasing the productivity through automation is one of the ways to address this problem. Nevertheless, introducing automation solutions without the structured analysis of the production system can lead to sub-optimization. In the analysis of processes, obtaining the current state of levels of automation has proven to be a useful step towards the identification of possible automation solutions. Producers of single family timber houses often have different business strategies, therefore their processes can differ with respect to how standardized the products are. The single case study was used as a research method and has the following research question: How different are the processes and current levels of physical and cognitive automation within the off-site assembly of exterior walls in ETO and SV projects? Both assembly lines currently have rather low physical and cognitive automation levels. However, there are tasks with higher levels of physical and cognitive automation in the ETO assembly line.

  • 5.
    Popovic, Djordje
    et al.
    Jönköping University, School of Engineering, JTH, Industrial Engineering and Management.
    Meinlschmidt, Peter
    Fraunhofer Institute for Wood Research, Wilhelm-Klauditz-Institut WKI.
    Plinke, Burkhard
    Fraunhofer Institute for Wood Research, Wilhelm-Klauditz-Institut WKI.
    Dobic, Jovan
    Tarkett Eastern Europe, BU WOOD.
    Hagman, Olle
    Luleå University of Technology, Wood Science and Engineering.
    Crack Detection and Classification of Oak Lamellas Using Online and Ultrasound Excited Thermography2015In: Pro Ligno, ISSN 1841-4737, E-ISSN 2069-7430, Vol. 11, no 4, p. 464-470Article in journal (Refereed)
    Abstract [en]

    On-line thermography and ultrasound-excited thermography have been evaluated for the detection of cracks in oak lamellae of flooring top layers. Image acquisition accompanied the tests and the objects were identified by post-processing and the evaluation of lamella images. The results were validated by comparing these findings with the actual state of the lamellae in terms of cracks and the classification accuracy of the method was calculated. The classification accuracy of the ultrasoundexcited thermography method was three times greater than that of on-line thermography. The main conclusion is that the ultrasound-excited thermography method is the more suitable for the detection of cracks and the classification of lamellae.

  • 6.
    Popovic, Djordje
    et al.
    Jönköping University, School of Engineering, JTH, Supply Chain and Operations Management. Jönköping University, School of Engineering, JTH, Industrial Product Development, Production and Design.
    Rösiö, Carin
    Jönköping University, School of Engineering, JTH, Supply Chain and Operations Management. Jönköping University, School of Engineering, JTH, Industrial Product Development, Production and Design.
    Product and manufacturing systems alignment: a case study in the timber house building industry2019In: 10th Nordic Conference on Construction Economics and Organization / [ed] Irene Lill & Emlyn Witt, Emerald Group Publishing Limited, 2019, p. 357-364Chapter in book (Refereed)
    Abstract [en]

    Purpose

    The purpose of the study was to investigate the alignment between current product and manufacturing systems and how it could be achieved.

    Design/Methodology/Approach

    Case study research method was chosen for the collection and analysis of empirical data. The data was of qualitative nature and was collected using research techniques such as observations through video recordings of processes, documents and open and semi-structured interviews.

    Findings

    The variation of outer side sub-element of the exterior wall element was found to not be aligned with its corresponding assembly. A hybrid assembly of outer side sub-elements characterised by flexibility and reconfigurability can be developed.

    Research Limitations/Implications

    The study is limited to the exterior wall element and corresponding manufacturing system. Practical Implications The presented approach was formulated with the aim to be used both for the analysis of existing products and manufacturing systems as well as for the design of new manufacturing systems.

    Originality/Value

    So far, this is the first study in the context of timber house building where the alignment between product and manufacturing systems was investigated by considering product variety and flexibility of manufacturing systems.

  • 7.
    Popovic, Djordje
    et al.
    Jönköping University, School of Engineering, JTH, Industrial Engineering and Management.
    Schauerte, Tobias
    Department of Mechanical Engineering, Linnaeus University, Växjö, Sweden.
    Johansson, Jimmy
    Department of Forestry and Wood Technology, Linnaeus University, Växjö, Sweden.
    Prefabrication of single-family timber houses - Problem areas and wastes2017In: IGLC 2017 - Proceedings of the 25th Annual Conference of the International Group for Lean Construction / [ed] I. Brilakis, K. Walsh & R. Sacks, International Group for Lean Construction (IGLC) , 2017, p. 837-844Conference paper (Refereed)
    Abstract [en]

    Industrialization of house building has shifted the activities traditionally done at building site to the off-site assembly. The design, manufacturing processes and on-site assembly in industrialized house building are defined and documented to form a process platform, but these must be evaluated and improved to constantly develop better and more efficient practice. Lean production and philosophy are still not well understood concepts at the shop floor and wasteful activities that decrease production efficiency are often overseen. Current waste categorizations and descriptions seem not to be addressing problem areas and occurrence of waste in prefabrication of single family timber houses. The research aim is to define problem areas that occur during the prefabrication of wall modules, associate them to eight types of waste and identify key problem areas for possible development and improvement. The study was based on secondary data from five case studies that primarily focused on identifying and proposing possibilities for development of productivity. Four problem areas were identified and the future improvement efforts for the prefabrication of single family houses can be placed on developing the processes of the assembly system problem area. The possible future study can aim at quantifying these problem areas.

  • 8.
    Popovic, Djordje
    et al.
    Jönköping University, School of Engineering, JTH, Supply Chain and Operations Management. Jönköping University, School of Engineering, JTH, Industrial Product Development, Production and Design.
    Thajudeen, Shamnath
    Jönköping University, School of Engineering, JTH, Industrial Product Development, Production and Design, JTH, Product design and development (PDD).
    Vestin, Alexander
    Jönköping University, School of Engineering, JTH, Industrial Product Development, Production and Design.
    Smart manufacturing support to product platforms in industrialized house building2019Conference paper (Refereed)
    Abstract [en]

    Swedish house building companies currently face many challenges in terms of fluctuating market demand, need for flexible product offering, non-uniform governmental regulations, high costs, and long lead times. These challenges affect both internal and external efficiency of companies. Product platforms have been used for more than a decade in this industry to improve both internal and external efficiency. However, the industry is still criticized for its inefficient and costly process. Smart manufacturing has emerged as means to improve the efficiency of internal processes and the question is if and how smart manufacturing can complement and support product platforms in industrialized house building. The aim of this study is to explore the potential of smart manufacturing to complement and support product platforms in theory and practice in the context of industrialized house building. A literature review and a multiple case study were chosen to fulfill the study objective. In total fourteen semi-structured interviews were conducted in two timber house building companies. The data was analyzed within and across cases using four platform assets for categorization: components, processes, knowledge and relationships. The results show that the smart manufacturing technologies are in both theory and practice mainly supporting the process platform asset through developing vertical and horizontal IT systems integration, definition and digitalization of flexible building systems, and transferring explicit drafting and engineering knowledge into parametric modelling tools.

  • 9.
    Popovic, Djordje
    et al.
    Jönköping University, School of Engineering, JTH. Research area Industrial Production.
    Winroth, Mats
    Chalmers University of Technology.
    Industrial timber house building – levels of automation2016In: ISARC 2016, International Association for Automation and Robotics in Construction (IAARC) , 2016, p. 470-477Conference paper (Refereed)
    Abstract [en]

    Swedish industrial timber house building faces a constantly increasing housing demand. In order to respond to the demand, companies in this sector, have to improve their businesses in terms of productivity. At the same time, they need to meet customer requirements, i.e., offering flexible building solutions, thus creating a balance between productivity and flexibility. Off-site assembly of exterior walls is an essential part of the house production, and cutting down lead times at this phase hence, increases the competitiveness. If introduced in a right way, automation can contribute to a higher productivity. Thus, right levels of both physical and cognitive automation are necessary. The objective of this study is to measure the current levels of automation (LoA) within the off-site exterior wall assembly. Research design consisted of a literature study and a case study that was conducted at a Swedish company that is an engineer-to-order producer of single-family timber houses. A case study design was made according to the DYNAMO ++ framework. The framework was used in the assessment of LoA and designing flexible task allocation in many manufacturing industries, but there is a lack of knowledge on how to use this method in the industrial timber house building. The average physical and cognitive LoA of 124 identified tasks are 3 and 1 respectively. Increased physical and cognitive LoA for critical tasks would enable flexible task allocation between human operators and technology. It is believed that this type of flexibility can result in less production disturbances and higher productivity when a high variety of exterior walls is assembled.

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