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| 2. |
- Fredenberg, Erik, 1979-
(författare)
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Spectral Mammography with X-Ray Optics and a Photon-Counting Detector
- 2009
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Doktorsavhandling (övrigt vetenskapligt)abstract
- Early detection is vital to successfully treating breast cancer, and mammography screening is the most efficient and wide-spread method to reach this goal. Imaging low-contrast targets, while minimizing the radiation exposure to a large population is, however, a major challenge. Optimizing the image quality per unit radiation dose is therefore essential. In this thesis, two optimization schemes with respect to x-ray photon energy have been investigated: filtering the incident spectrum with refractive x-ray optics (spectral shaping), and utilizing the transmitted spectrum with energy-resolved photon-counting detectors (spectral imaging).Two types of x-ray lenses were experimentally characterized, and modeled using ray tracing, field propagation, and geometrical optics. Spectral shaping reduced dose approximately 20% compared to an absorption-filtered reference system with the same signal-to-noise ratio, scan time, and spatial resolution. In addition, a focusing pre-object collimator based on the same type of optics reduced divergence of the radiation and improved photon economy by about 50%.A photon-counting silicon detector was investigated in terms of energy resolution and its feasibility for spectral imaging. Contrast-enhanced tumor imaging with a system based on the detector was characterized and optimized with a model that took anatomical noise into account. Improvement in an ideal-observer detectability index by a factor of 2 to 8 over that obtained by conventional absorption imaging was found for different levels of anatomical noise and breast density. Increased conspicuity was confirmed by experiment. Further, the model was extended to include imaging of unenhanced lesions. Detectability of microcalcifications increased no more than a few percent, whereas the ability to detect large tumors might improve on the order of 50% despite the low attenuation difference between glandular and cancerous tissue. It is clear that inclusion of anatomical noise and imaging task in spectral optimization may yield completely different results than an analysis based solely on quantum noise.
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| 3. |
- Tegin, Johan, et al.
(författare)
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Demonstration based learning and control for automatic grasping
- 2008
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Ingår i: Intelligent Service Robotics. - Berlin / Heidelberg : Springer. - 1861-2776. ; 2:1, s. 23-30
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Tidskriftsartikel (refereegranskat)abstract
- We present a method for automatic grasp generation based on object shape primitives in a Programming by Demonstration framework. The system first recognizes the grasp performed by a demonstrator as well as the object it is applied on and then generates a suitable grasping strategy on the robot. We start by presenting how to model and learn grasps and map them to robot hands. We continue by performing dynamic simulation of the grasp execution with a focus on grasping objects whose pose is not perfectly known.
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| 4. |
- Trincavelli, Marco, et al.
(författare)
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Towards environmental monitoring with mobile robots
- 2008
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Ingår i: IEEE/RSJ International Conference on Intelligent Robots and Systems, IROS 2008. - New York : IEEE. - 978-1-4244-2057-5 ; s. 2210-2215
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Konferensbidrag (refereegranskat)abstract
- In this paper we present initial experiments towards environmental monitoring with a mobile platform. A prototype of a pollution monitoring robot was set up which measures the gas distribution using an “electronic nose” and provides three dimensional wind measurements using an ultrasonic anemometer. We describe the design of the robot and the experimental setup used to run trials under varying environmental conditions. We then present the results of the gas distribution mapping. The trials which were carried out in three uncontrolled environments with very different properties:an enclosed indoor area, a part of a long corridor with open ends and a high ceiling, and an outdoor scenario are presented and discussed.
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| 5. |
- Ericsson, Mikael
(författare)
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Simulation of robotic TIG-welding
- 2003
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Licentiatavhandling (övrigt vetenskapligt)abstract
- Robotised welding is one of the most important robot tasks used in manufacturing industry. The operator usually performs the programming of the robot manually, i.e. by jogging the robot arm to each coordinate pose in space. Programming can, however, be made more accurate by the use of simulation, using so called Computer Aided Robotics. Simulation can also be a powerful tool to evaluate and control welding heat effects, such as unwanted stresses and deformation. The objective of this thesis was to develop a simulation tool and a method by which robot trajectories, temperature histories, residual stresses and distortion can be analysed and optimised off-line. This was performed by integrating robot simulation software with finite element analysis software. A special interface was created allowing information exchange between the two software programs. The method was used to program welding trajectories both for planar plates and for a part of an aerospace component. The trajectories was downloaded to the finite element analysis software where temperature and residual stress prediction were performed. Good agreement was found between the programmed robot trajectory, and the actual trajectory and only small adjustments were necessary. Temperature measurements were performed using both thermocouples and infrared imaging. Good agreement was also found between the results using these two methods. The method developed provides a powerful tool to construct and optimise robot trajectories and welding process parameters off-line.
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| 6. |
- Ericsson, Mikael, 1975-, et al.
(författare)
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Three dimensional simulation of robot path, heat transfer and residual stresses of a welded part with complex geometry
- 2005
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Ingår i: International jourrnal for the joining of materials. - 0905-6866. ; 17:2, s. 42-51
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Tidskriftsartikel (refereegranskat)abstract
- In this article a simulation system is presented that combines computer aided robotics software used to define the welding operation, with a finite element model that predicts temperature-time histories and residual stress distributions for welding applications. The objective is to develop a tool for engineering processes in which robot trajectories and welding process parameters can be optimized off-line on parts with complex geometries. The system was evaluated on a stainless steel gas turbine component. Temperature dependent properties and phase change were included in the analysis. The turbine component was welded using an in-house TIG welding cell. The assumptions and principles that underpin the modeling techniques are presented together with predicted temperature histories, residual stresses, and fixture forces. Predicted residual stresses were compared with neutron diffraction measurements.
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| 7. |
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| 8. |
- Ericsson, Mikael, 1975-, et al.
(författare)
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Non-contact Temperature Measurements using an Infrared Camera in Aerospace Welding Applications
- 2002
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Ingår i: 6th International Conference on Trends in Welding Research : Phoenix, AZ; 15-19 April 2002. - Materials Park : ASM International. ; s. 930-935
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Konferensbidrag (refereegranskat)abstract
- This paper describes the application of infrared (IR) thermal imaging and temperature measurements in welding applications, both on single plane plates and on an aero engine turbine component with complex geometry. Temperature profiles were measured on the plates using thermocouples (T/C) in combination with an IR camera system, and the results were compared. The IR camera was used both in line scan mode (270 Hz scan frequency) and in full frame mode (1 Hz frame rate). Different methods of surface treatments have been tested to handle the problem of the surface emissivity variations due to oxidation during welding. Results from measurements using thermocouples and IR camera is presented in the paper as well as temperature measurements using the IR camera on an turbine exhaust case (TEC) engine component.
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| 9. |
- Ericsson, Mikael, et al.
(författare)
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Three Dimensional Simulation of Robot path, Heat Transfer and Residual Stresses of a TIG-welded Part with Complex Geometry
- 2002
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Ingår i: Trends in Welding Research: Proceedings of the 6th International Conference : Phoenix, AZ, 15-19 April, 2002. ; s. 973-978
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Konferensbidrag (övrigt vetenskapligt)abstract
- In this paper a system is presented that combines a robot off-line programming software with a finite element model that predicts temperature-time histories and residual stress distributions. The objective is to develop a tool for the engineer where robot trajectories and welding process parameters can be optimized on parts with complex geometry. The system was evaluated on a stainless steel gas turbine component. Robot weld paths were defined off-line and automatically downloaded to the finite element program, where transient temperatures and residual stresses were predicted. Temperature dependent properties and phase change, were included in the analysis. Assumptions and principles behind the modeling techniques are presented together with predicted temperature histories, residual stresses, and fixture forces.
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| 10. |
- Fahlen, Elsa, et al.
(författare)
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Assessment of absorption cooling as a district heating system strategy - A case study
- 2012
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Ingår i: Energy Conversion and Management. - Elsevier. - 0196-8904. ; 60:SI, s. 115-124
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Tidskriftsartikel (refereegranskat)abstract
- Heat load variations, daily as well as seasonal, are constraining co-generation of high-value energy products as well as excess heat utilisation. Integration of heat-driven absorption cooling (AC) technology in a district heating and cooling (DHC) system raises the district heat (DH) demand during low-demand periods and may thus contribute to a more efficient resource utilisation. In Sweden, AC expansion is a potentially interesting option since the cooling demand is rapidly increasing, albeit from low levels, and DH systems cover most of the areas with potential cooling demand. This study aims to assess the potential for cost and CO2 emission reduction due to expansion of DH-driven AC instead of electricity-driven compression cooling in the DHC system of Goteborg, characterised by a high share of low-cost excess heat sources. The DHC production is simulated on an hourly basis using the least-cost model MARTES. Despite recent advances of compression chillers, the results show potential for cost-effective CO2 emission reduction by AC expansion, which is robust with regards to the different scenarios applied of energy market prices and policies. While the effects on annual DHC system results are minor, the study illustrates that an increased cooling demand may be met by generation associated with low or even negative net CO2 emissions - as long as there is high availability of industrial excess heat in the DHC system, or if e.g. new biomass-based combined heat and power capacity is installed, due to the avoided and replaced marginal power generation.
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