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| 2. |
- Holmberg, Jonas, 1976-
(författare)
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Surface integrity on post processed alloy 718 after nonconventional machining
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- There is a strong industrial driving force to find alternative production technologies in order to make the production of aero engine components of superalloys even more efficient than it is today. Introducing new and nonconventional machining technologies allows taking a giant leap to increase the material removal rate and thereby drastically increase the productivity. However, the end result is to meet the requirements set for today's machined surfaces.The present work has been dedicated to improving the knowledge of how the non-conventional machining methods Abrasive Water Jet Machining, AWJM, Laser Beam Machining, LBM, and Electrical Discharge Machining, EDM, affect the surface integrity. The aim has been to understand how the surface integrity could be altered to an acceptable level. The results of this work have shown that both EDM and AWJM are two possible candidates but EDM is the better alternative; mainly due to the method's ability to machine complex geometries. It has further been shown that both methods require post processing in order to clean the surface and to improve the topography and for the case of EDM ageneration of compressive residual stresses are also needed.Three cold working post processes have been evaluated in order to attain this: shot peening, grit blasting and high pressure water jet cleaning, HPWJC. There sults showed that a combination of two post processes is required in order to reach the specified level of surface integrity in terms of cleaning and generating compressive residual stresses and low surface roughness. The method of high pressure water jet cleaning was the most effective method for removing the EDM wire residuals, and shot peening generated the highest compressive residual stresses as well as improved the surface topography.To summarise: the most promising production flow alternative using nonconventional machining would be EDM followed by post processing using HPWJC and shot peening.
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| 3. |
- Olsson, Tomas
(författare)
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Bootstrapping and decentralizing recommender systems
- 2003
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis consists of three papers on recommender systems.The first paper addresses the problem of making decentralized recommendations using a peer-to-peer architecture. Collaborating recommender agents are connected into a network of neighbors that exchange user recommendations to find new items to recommend. We achieved a performance comparable to a centralized system.The second paper deals with the bootstrapping problem for centralized recommender systems. Most recommender systems learn from experience but initially there are no users and no rated items to learn from. To deal with this problem we have developed the Genesis method. The method bootstraps a recommender system with artificial user profiles sampled from a probabilistic model built from prior knowledge. The paper describes how this was done for a k-nearest neighbor recommender algorithm in the movie domain. We were able to improve the performance of a k-nearest neighbor algorithm for single predictions but not for rank ordered lists of recommendations.The third paper identifies a new domain for recommendations – product configuration – where new recommender algorithms are needed. A system that helps users configuring their own PCs is described. Recommendations and a cluster-based help system together with a rule-based configurator assist the users in selecting appropriate features or complete PC configurations. The configurator ensures that users cannot choose incompatible components while the recommender system adds social information based on what other users have chosen. This introduces new complexity in the recommendation process on how to combine the recommendations from the configurator and the recommender system. The paper proposes (1) three new recommender algorithms on how to make recommendations in the domain of product configuration, (2) a method for adding social recommendations to a rule-based configurator and (3) a method for applying the Genesis method in this domain. In this case the Genesis method is implemented by a Bayesian belief net that captures the designers' prior knowledge on how to configure PCs. Then instances of complete configurations are sampled from the model and added to the recommender algorithm.
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| 4. |
- Olsson, Tomas
(författare)
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Feedback Control and Sensor Fusion of Vision and Force
- 2004
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with feedback control using two different sensor types, force sensors and cameras. In many tasks robotics compliance is required in order to avoid damage to the workpiece. Force and vision are the most useful sensing capabilities for a robot system operating in an unknown or uncalibrated environment. An overview of vision based estimation, control and vision/force control is given. Two different control algorithms based on a hybrid force/vision structure are presented, using image-based and position-based visual servoing, respectively. The image-based technique is suitable in situations with simple contact geometry in uncalibrated environments, and in situations where the positioning task is naturally specified relative to some visible structure in image space. The position-based technique can handle more complex motions, which require more information about the environment. For a process with linear dynamics in task space, an edge-based visual estimation technique can be used to design an observer with linear error dynamics, which avoids the high computational complexity of the Extended Kalman Filter. In a dynamic visual tracking system, many different choices of the parameterization of the state space exist. If the actuator- and measurement coordinate systems are rigidly attached, a dual quaternion parameterization can be used to express linear constraints on the estimated motion. This increases robustness when the intrinsic camera parameters are time-varying. For real-time control applications in general, it is important to minimize the input-output latency, which may otherwise compromise the performance of the control system. In vision-based control systems the latency is dominated by the image processing. A method for multiple cameras, which aims at maximizing the achieved accuracy of the measurements given a fixed computation time, is presented.
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| 5. |
- Olsson, Tomas
(författare)
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Physical and morphological aspects of linseed oil impregnated pine (Pinus Sylvestris)
- 1999
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This work has investigated the possibilities of increasing wood durability using environmentally friendly chemicals. The chemical used in this study was linseed oil. The study also investigated flow paths during impregnation in pine and spruce. The first order voids of wood samples were impregnated with a low viscosity epoxi which was subsequently thermally cured. By observing the solid epoxi with a scanning electron microscopy (SEM), it was possible to determine the critical features which limit the flow in the selected species. The take up of linseed oil was measured using an X-ray microdensitometry technique. Quantification of the impregnant (within annual rings) was made by comparing densitometric curves from the impregnated samples with curves from the same specimens after the impregnated oil had been removed. Observations of fracture surfaces in scanning electron microscopy (SEM) revealed evidence of microstructural damage caused by the impregnation process.
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- Unga, Johanna, 1973-
(författare)
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Det är en spricka i allt, det är så ljuset kommer in… : Matematik och förskolebarns experimenterande och potentialitet
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In preschools it is common that mathematics mainly focuses on how children learn mathematics through everyday activities, or on children´s understanding of mathematical concepts. However, views on mathematics-learning are today deepened and extended, and embrace children’s own mathematical signs, visual representations and bodily experiences. The overall aim of this thesis is to experiment with how this extended view in which children´s engagement and creativity is affirmed, simultaneously as they are developing knowledge about the world of mathematics with its procedures and rules. With inspiration from the French philosophers Gilles Deleuze´s and Félix Guattari´s immanent ontology and transcendental empiricism, and from the pedagogical philosophy of the preschools in Reggio Emilia, I have experimented both with mathematics, and with toddlers’ explorations and potentiality. The research-material primarily consists of video observations and documentations, and it is taken from a project with a mathematical topic through a cooperative work by me, preschool teachers and children aged 1–3 years. Methodologically the work is based on one example from the project where some children explores and experiment on geometric objects. In relation to the example some concepts from Reggio Emilia’s pedagogical thinking and Deleuze´s and Guattari´s immanent ontology are put to work, by focusing on the connections that emerge. The study make visible that children explore and experiment with mathematics in what in the study has called “a relational field of potentiality”. In relation to preschool didactics the study stresses the importance of teachers paying attention to and “listening” to children’s experimentations and sign-making, in order not to interrupt what is emerging/becoming. This requires an environment that embraces “the hundred languages” and enables collective experimentation for thoughts and ideas to be shared in “togetherness”.
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