Stiffness Compensation and External Control of Gantry-Tau Robots

This master thesis describes how to compensate for the compliance of the Gantry-Tau robot. The main reason for this is to improve the performance of the robot. The compliance is modeled as nine springs, one for each cart and each link. The model seems promising but has only been tested in homing position of the robot but shows a positive result in decreasing the compliance. External control of the CNC software ISG and its drivers for a Gantry-Tau robot F1 is also investigated. A way to add external measurement equipment and adding external position references was implemented

Robotic friction stir welding—Seam-tracking control, force control and process supervision

Purpose – This study aims to enable robotic friction stir welding (FSW) in practice. The use of robots has hitherto been limited, because of the large contact forces necessary for FSW. These forces are detrimental for the position accuracy of the robot. In this context, it is not sufficient to rely on the robot’s internal sensors for positioning. This paper describes and evaluates a new method for overcoming this issue.Design/methodology/approach – A closed-loop robot control system for seam-tracking control and force control, running and recording data in real-time operation, was developed. The complete system was experimentally verified. External position measurements were obtained from a laser seam tracker and deviations from the seam were compensated for, using feedback of the measurements to a position controller.Findings – The proposed system was shown to be working well in overcoming position error. The system is flexible and reconfigurable for batch and short production runs. The welds were free of defects and had beneficial mechanical properties.Research limitations/implications – In the experiments, the laser seam tracker was used both for control feedback and for performance evaluation. For evaluation, it would be better to use yet another external sensor for position measurements, providing ground truth.Practical implications – These results imply that robotic FSW is practically realizable, with the accuracy requirements fulfilled.Originality/value – The method proposed in this research yields very accurate seam tracking as compared to previous research. This accuracy, in turn, is crucial for the quality of the resulting material.Keywords Friction stir welding, Robotics, Force control, Seam-tracking control, Control, Sensors, Robot weldin

Congener patterns of polychlorinated dibenzo-p-dioxins, dibenzofurans and biphenyls as a useful aid to source identification during a contamination incident in the food chain

Polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and biphenyls (PCBs) are still considered among the most important groups of contaminants in the food chain. Self-control by food producers and official control by authorities are important activities that allow contaminant sources to be traced and promote further reduction in food and feed levels. Strict but feasible maximum levels were set by the EU Commission for food and feed to support this strategy, as well as action levels and thresholds. When products exceed these levels, it is important to trace the source of contamination and take measures to remove it. Congener patterns of PCDD/Fs and PCBs differ between sources and are important tools for source identification. Therefore, patterns associated with different sources and incidents relating to various feed matrices and certain agricultural chemicals were collated from published scientific papers, with additional ones available from some laboratories. The collection was evaluated for completeness by presentations at workshops and conferences. Primary sources appear to derive from 5 categories, i) by-products from production of organochlorine chemicals (e.g. PCBs, chlorophenols, chlorinated pesticides, polyvinyl chloride (PVC)), ii) the result of combustion of certain materials and accidental fires, iii) the use of inorganic chlorine, iv) recycling/production of certain minerals, and v) certain naturally occurring clays (ball clay, kaolinite). A decision tree was developed to assist in the identification of the source

Ett köpcentrums dilemma : En studie om skillnader i varumärkesidentitet och image

Avsikten med studien är att beskriva vilka problemområden som kan uppstå vid skillnader mellan varumärkesidentitet och image hos ett köpcentrum. För att undersöka detta har vi valt att studera hur Galleria Duvan i Karlstad arbetar med sin varumärkesidentitet. Därefter har vi undersökt hur konsumenterna uppfattar denna identitet och vilken image denna organisation har hos dem. För att genomföra våra studier har vi använt oss av en kvalitativ metod där de intervjuer vi har utfört har varit djupintervjuer. En intervju på en representant från Galleria Duvans marknadsgrupp har genomförts samt tio stycken intervjuer på konsumenter.  Resultatet av studien har gett indikationer på att det finns skillnader mellan köpcentrumets identitet och den image som konsumenterna upplever. Dessa skillnader ligger främst i kommunikationen av budskapet via sin marknadskommunikation. Konsumenterna upplevde ingen gemensam image för organisationen och associationerna till denna som helhet var olika. De emotionella nyttorna var kopplade till de enskilda butikerna och konsumenterna hade svårt att se det samlade utbudet av butiker och produkter. Sammanfattningsvis var det svårt för konsumenter att uppfatta en organisations önskvärda identitet

Robotic Seam Tracking for Friction Stir Welding under Large Contact Forces

Friction stir welding (FSW) is a solid-state welding process where metals are joined without melting. Heat is generated by friction between a rotating non-consumable tool and the work-piece material, and by mechanical deformation of the material. The process, invented in 1991, provides several benefits over arc welding and other fusion processes: No filler material has to be added, low energy consumption, low distortion and excellent mechanical properties, similar to those of the parent material. The FSW process has hitherto been performed mostly by stiff machines of gantry-type. In this work, however, the use of a 6 DOF robot arm for FSW was explored. This allows for processing of a wider range of seam shapes. However, the compliance of the robot introduces challenges in terms of positioning of the tool subject to large external forces. In the FSW process, large contact forces are necessary to produce frictional heat, to move the tool along the seam, and to counteract the torque induced by the rotating tool. In this context, it is not enough to rely on the robot's internal sensors for positioning, and therefore, an external laser sensor was attached adjacent to the tool in order to detect and measure the position of the seam.The measurements propagated through a PI-controller, yielding changes of the reference positions for the robot. The approach was verified experimentally at TWI Technology Centre Yorkshire, UK, through FSW of thin section aluminium alloys with an ABB IRB 7600 robot