detecting beam offsets in laser welding of closed square butt joints by wavelet analysis of an optical process signal

Abstract Robotized laser beam welding of closed-square-butt joints is sensitive to the positioning of the laser beam with respect to the joint since even a small offset may result in a detrimental lack of sidewall fusion. An evaluation of a system using a photodiode aligned coaxial to the processing laser beam confirms the ability to detect variations of the process conditions, such as when there is an evolution of an offset between the laser beam and the joint. Welding with different robot trajectories and with the processing laser operating in both continuous and pulsed mode provided data for this evaluation. The detection method uses wavelet analysis of the photodetector signal that carries information of the process condition revealed by the plasma plume optical emissions during welding. This experimental data have been evaluated offline. The results show the potential of this detection method that is clearly beneficial for the development of a system for welding joint tracking

Synthesis of highly brominated diphenyl ethers and aspects on photolysis and indoor spreading

Adding chemicals to materials to decrease flammability can be dated back to as early as 450 BC when the Egyptians used alum to reduce flammability of wood. Almost 2500 years later brominated flame retardants (BFRs) are used to prevent ignition of textiles, electronics and polymers. BFRs in major use today are polybrominated diphenyl ethers (PBDEs), hexabromocyclododecane (HBCDD) and tetrabromobisphenol A (TBBPA), including derivatives. There have been three industrial PBDE mixtures produced. Extensive scientific reporting has shown increasing concentrations of PBDEs in wildlife and in humans. This in combination with reports on their physico-chemical characteristics and chemical reactivity have led to that two of the PBDE products have been classified as being persistent, bioaccumulative and toxic, which has led to legislative measures, in e.g. EU, Norway and the USA. The availability of pure reference standards is a prerequisite for much toxicologically related research. Hence the main objective of this thesis was to develop additional methods for synthesis of highly brominated diphenyl ethers. Further, to quantify and identify photolysis products of decabromodiphenyl ether (decaBDE) and to perform a case study regarding PBDE exposure in aircrafts. Synthesis of highly brominated BDE congeners by perbromination of mono- or diaminodiphenyl ethers followed by diazotization of the amino group(s) and introduction of hydrogen(s) in the molecules is a convenient route for synthesis of some octaBDEs and all nonaBDEs. Selective bromination of diaminodiphenyl ether, followed by diazotization of the amino groups and substitution with bromines yielded a hexaBDE or a heptaBDE which were then further brominated to octaBDE congeners. Even though several studies have been performed on photolysis of decaBDE a new study with a more quantitative approach was performed as part of this thesis. Debrominated PBDE products were identified and quantified and a marker PBDE for UV degradation of DecaBDE was identified i.e., 2,2’,3,3’,5,5’,6,6-octabromodiphenyl ether (BDE-202). Polybrominated dibenzofuranes, methoxlated brominated dibenzofuranes, pentabromophenol and hydroxylated bromobenzenes were also detected. The PBDEs accounted for approximately 90% of the total amount of substances in each sample and the PBDFs for about 10%. Also, a case study on potential exposure to PBDEs in humans travelling long distances by aircraft was done. It was shown that PBDE concentrations in dust onboard aircrafts may be high and increased PBDE serum levels were indicated in a majority of the travellers. The present thesis has contributed to make higher brominated diphenyl ethers available as reference standards, allowing better quantitative assessments possible regarding both abiotic studies and exposure assessments. New toxicological testing can also be pursued

A Unified Framework for Mixed Continuous/Discrete-time H_inf-Control

This thesis presents a unified and general state-space framework for mixed continuous/discrete-time H_inf-controller design. H_inf-design considers robust and optimal control of multivariable systems. A versatile unified notation for signals and systems in continuous and discrete time is introduced, providing a means to show a very close relationship between the continuous-time and discrete-time solutions. In fact they are two different interpretations of the general result. The solution is mainly Riccati equation based, and in the periodic case, the continuous-time state evolution over the period is achieved from a discretised (or "lifted") system model. Typical applications are control of continuous-time or discrete-time (periodic) systems, as well as (multirate) sampled-data control, including mixed continuous and sampled-data measurements. Especially the sampled-data application with a hold-circuit at controller output implies significant simplifications in the solutions, and this is presented to its full extent. The results are also applied to the loop-shaping situation, where no so called ?-iteration is needed. The controller order becomes with these methods the same as that of the augmented plant, and this is often unacceptably high. A parametric numeric optimisation approach for achieving a lower order controller is presented by means of bilinear matrix inequalities. To achieve good robustness and performance for the closed loop, it is necessary to use appropriate weight functions in the augmented plant. For this choice, a versatile genetic algorithm is used, based on fair evaluation criteria for the closed loop. Simulation results are presented for two example plants throughout the thesis, one SISO-plant and a MIMO model of a jet engine

Experimental validation of an inductive probe for narrow gap measurement based on numerical modelling

Experimental validation of numeric results for an inductive probe shows that narrow gaps between two plates can be measured with accuracy suitable for laser beam welding. A two-coil inductive probe for measurement of the gap was built based on finite element modelling results. The individual coils were calibrated using a complex response method, and results from the physical coils closely match the numerical results regarding distance to gap and lift-off above the plate. The measurement of a realistic gap shows results that can be used in industrial applications for position, plate height and height alignment.

"Vad har du på hjärtat"? Betydelsen av vanlighet och genomskinlighet för idiomförståelse hos normalspråltiga skolbarn

Idiom är en typ av språkliga uttryck som vi ofta använder i vårt tal t ex "jag ska hålla tummarna". Vissa forskare menar att ju vanligare ett idiom är desto lättare har barn att förstå det. Andra forskare anser att graden av genomskinlighet i idiomet är avgörande för förståelsen. Vårt syfte var att undersöka om det fanns något samband mellan förståelse av idiom hos 51 normalspråkiga barn i åldern 8 till l O år och vuxnas skattning av vanlighet och genomskinlighet hos idiomen. En videofilm med scener där 16 idiom användes i vardagssituationer utgjorde underlag för bedömning av idiomförståelse. Ett skattningsformulär utformades och studenter och lärare ombads skatta vanlighet och genomskinlighet hos idiomen enligt en 5-gradig skala. Vi fann att barnen hade en god förståelse av idiomen. Vi fann inget signifikant samband mellan barnens resultat på idiomförståelse och skattningarna av idiomens vanlighet och genomskinlighet när samtliga vuxnas skattningar användes som underlag för beräkningarna. Lärare verksamma i Skåne och lärare verksamma i Småland skiljde sig dock signifikant beträffande uppfattning av idiomens vanlighet och genomskinlighet. När vi renodlade skattningarna geografiskt, det vill säga när skattningar gjorda av lärare verksan1ma i Skåne relaterades till barnens resultat på idiomförståelse fann vi en tendens till samband. I framtida studier av idiomförståelse bör därför hänsyn tas till regionala skillnader

Low Order Sampled-Data H_inf Control

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