| 1. |
- Björsell, Niclas, 1964-
(författare)
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Modeling Analog to Digital Converters at Radio Frequency
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Det här arbetet handlar om att ta fram beteendemodeller av analog till digital omvandlare avsedda för tillämpningar i radiofrekvensområdet. Det gäller tillämpningar inom telekommunikation men även in test- och mätinstrument där omvandlingen från analoga till digitala signaler ofta är en prestandamässig flaskhals. Modellerna är avsedda att användas för att efterbehandla utdata från omvandlaren och på så sätt förbättra prestanda på den digitala signalen. Genom att skapa modeller av verkliga omvandlare och hur dessa avviker från ett idealt beteende kan ofullständigheter korrigeras genom så kallad postkorrigering. Beteendemodeller innebär att genererar en lämplig insignal, mäta utdata och beräkna en modell. För omvandlare i radiofrekvensområdet ställs höga krav på instrumentering. Den testutrustningen som används är baserad på moderna högprestanda instrument som har kompletterats med specialbyggd utrustning för signalkonditionering och datainsamling. I avhandlingen har även olika insignaler utvärderats med såväl teoretisk som experimentell analys. Det finns ett flertal olika varianter av modeller för att modulera ett olinjär, dynamisk system. För att få en parametereffektiv modell har utgångspunkten varit att utgå från en Volterramodell som på ett optimalt sätt beskriver svagt olinjära dynamiska system, så som analog till digital omvandlare, men som är alltför omfattande i antal parametrar. Volterramodellens har sedan reducerats till en mindre parameterintensiv, modellerstruktur på så sätt att Volterrakärnans symmetriegenskaper jämförts med symmetrierna hos andra modeller. En alternativ metod är att använda en Kautz-Volterramodell. Den har samma generella egenskaper som Volterramodellen, men är inte lika parameterkrävande. I den här avhandlingen redovisas experimentella resultat av Kautz-Volterramodellen som i framtiden kommer att vara intressanta att använda för postkorrigeringen. För att kunna beskriva beteenden som en dynamiska olinjära modellen inte klarar av har modellen kompletterats med en statisk styckvis linjär modellkomponent. I avhandlingen presenteras en sluten lösning för att identifiera samtliga paramervärden i modellen. Vidare har det i avhandlingen genomförs en analys av hur respektive komponent påverkar prestanda på utsignalen. Därigenom erhålls ett mått på den maximala prestandaförbättring som kan uppnås om felet kan elimineras.
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| 2. |
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| 3. |
- Osa, Joseba, et al.
(författare)
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60 GHz mmWave Signal Propagation Characterization in Workshop and Steel Industry
- 2023
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Ingår i: IEEE International Workshop on Factory Communication Systems - Proceedings, WFCS. - : IEEE. - 9781665464321
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Konferensbidrag (refereegranskat)abstract
- Communication systems are a key element for the industry 4.0 revolution, where the remote access to the machinery is a fundamental part for the automation of tasks related to monitoring and control of the different industrial processes. There is an increasing interest in performing such communications using a wireless medium, as they offer several advantages as a lower cost, greater flexibility or the ability to operate in moving elements. However, existing works have showed that the achievable performance in the sub-6 GHz frequency bands is insufficient to cope with all the requirements, which motivated the analysis of the millimeter wave spectrum for these use cases. Industrial environments present a harsh condition for electromagnetic wave propagation, where the abundance of reflective surfaces can present difficulties to properly exchange information. Thus, a thorough analysis and characterization of the propagation through this kind of environment is necessary to develop protocols and standards accordingly. This work provides the results of measurements carried out in two industrial facilities, which are a university workshop and a pit oven building from a steel company. Metrics of the results are computed and discussed as well, where a significantly larger losses can be seen for the pit oven measurements compared to other industrial scenarios.
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| 4. |
- Andersson, Daniel, et al.
(författare)
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Radar Images of Leaks in Building Elements
- 2015
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Ingår i: Energy Procedia. - : Elsevier BV. - 1876-6102. ; 78, s. 1726-1731
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Tidskriftsartikel (refereegranskat)abstract
- Through leakage in the building envelope there is a penetration of air, water vapor and particles. The degree of leakage of air can be quantified by existing methods. However, the location of adventitious openings is often not known. In order to overcome the limitations in existing methods, a non-contact and non-destructive method based on ultra-wide bandwidth radar technology is suggested. A test-bed is designed that can measure with different polarization to be able to detect flaws in different directions. Initial measurements shows promising results for further development of the method of using radar images to find leaks in building elements.
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| 5. |
- Andersson, Rabé, et al.
(författare)
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Robots are a promising investment to fight pandemics
- 2021
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Ingår i: 2021 8th International Conference on Signal Processing and Integrated Networks (SPIN). - : IEEE. - 9781665435642 ; , s. 458-463
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Konferensbidrag (refereegranskat)abstract
- Coronavirus caused pandemics as many viruses did through human history. The current pandemic causes overwhelmed healthcare system, locked down cities, and massive fatality among humans. Thus, different robots have been used since the COVID outbreak worldwide to reduce spreading infectious diseases and support frontline healthcare workers. This paper sets out the different robots implemented for hospital, non-hospital use, and possible use that can be deployed amidst the pandemic. A literature survey of versatile robots during COVID-19 is introduced. Roboticists contributed with wheeled and drone robots with various applications to assist medical care systems and society during the ongoing crisis. Pandemics are common throughout human history and difficult to avoid or prevent; thus, we intend to encourage societies, academia, engineers and innovators to invest more in robots that cannot catch the virus and consequently introduce beneficial solutions to fight such pandemic in the future.
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| 6. |
- Andersson, Rabé, et al.
(författare)
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The Energy Consumption and Robust Case Torque Control of a Rehabilitation Hip Exoskeleton
- 2022
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Ingår i: Applied Sciences. - : MDPI. - 2076-3417. ; 12:21
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Tidskriftsartikel (refereegranskat)abstract
- Gait disorders, muscle weakness, spinal cord injuries (SCIs) and other work-related disorders have increased the need for rehabilitation exoskeletons—specifically, for the hip because a huge percentage of mechanical power comes from the hip joint. However, realising a lightweight rehabilitation hip exoskeleton for mobility and at-home use with reliable control is challenging. The devices developed are restricted by a joint actuator and energy source design and tend to have various uncertainties. Thus, this study tested the robustness of four optimal controller cases in a simulation-based environment. We sought to determine whether the most robust optimal controller consumed less energy and demonstrated better performance in tracking the desired signal. The robustness of the optimal cases was tested with the hip torque signals of healthy subjects. The number of sit-to-stand (STS) instances and the walking distance at various speeds were calculated. The results showed that the most robust case controller was more energy efficient for STS, but not for walking activity. Furthermore, this study provides compelling evidence that various optimal controllers have different degrees of robustness and effects on energy consumption.
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| 7. |
- Andersson, Rabé, et al.
(författare)
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The MATLAB Simulation and the Linear Quadratic Regulator Torque Control of a Series Elastic Actuator for a Rehabilitation Hip Exoskeleton
- 2022
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Konferensbidrag (refereegranskat)abstract
- Almost the half of mechanical energy of a human gait cycle is generated by a hip joint. Therefore, this paper discusses a rehabilitation hip exoskeleton, starting with the modeling, simulation and ending with controlling its hip joints. A MATLAB based simulation environment with the use of Simscape Multibody toolbox was utilized to design and control the robotic hip exoskeleton. More details of adding a series elastic actuators (SEA) to the hip joints with the mathematical model are presented. However, the linearised mathematical model of the entire exoskeleton was found in simulation software which establish the basic need of controlling hip joints. The trajectory tracking is commonly used of controlling rehabilitation exoskeleton and to ensure a safe and reliable motion tracking methods, two desired torque signals were tested and analysed with the optimal linear quadratic regulator (LQR). The experiments with two torque signals–representing the sit-to-stand (STS) and the walking activity, demonstrated good performance of the motion gait tracking based on torque signals of a healthy person, which is carried out in the simulation environment. Furthermore, some studies in a human robot interaction are also mentioned in this paper.
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| 8. |
- Andersson, Rabé
(författare)
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The Robustness and Energy Evaluation of a Linear Quadratic Regulator for a Rehabilitation Hip Exoskeleton
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The implications of gait disorder, muscle weakness, and spinal cord injuries for work and age-related mobility degradation have increased the need for rehabilitation exoskeletons. Specifically, the hip rehabilitation exoskeletons due to a high percentage of the mechanical power is generated by this join during the gait cycle. Additionally, the prolonged hospitalisation after hip replacement and acetabular surgeries that affect human mobility, the social-economic impacts and the quality of life. For these reasons, a hip rehabilitation exoskeleton was our focus in this research, as it will contribute being a sustainable solution to take over the burden of physiotherapy and let patients perform their rehabilitation at home or outdoors. This thesis details an approach of creating a hip rehabilitation exoskeleton, starting with modelling, simulating, and controlling the rehabilitation hip joint in a based-simulation environment. The mathematical model and the reason for using a series elastic actuator in the hip joint to execute the movement in a sagittal plane are more detailed. Because trajectory tracking is commonly used for controlling rehabilitation exoskeletons to ensure safe and reliable motion tracking methods; therefore, two desired torque signals were tested and analysed with the optimal linear quadratic regulator (LQR). The experiments were performed using two torque signals of a healthy hip joint—representing the sit-to-stand (STS) and the walking activity for their importance in lower limb movements. However, the mathematical model used as a basis of the optimal control strategy is usually influenced by multiple sources of uncertainties. Therefore, four case studies of various optimal control strategies were tested for a twofold reason: to choose the most optimal control strategy, and to test the energy consumption of these cases during the STS and walking movements, because the long-term goal is to produce a lightweight and reliable rehabilitation hip exoskeleton.The research showed compelling evidence that tuning the control strategy will not influence the robustness of an optimal controller only, but affect the energy consumption during the STS and walking activity, which needs to be considered in exoskeleton control design regarding its applications.
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| 9. |
- Andersson, Rabé, et al.
(författare)
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The Technical Challenges in Orthotic Exoskeleton Robots with Future Directions: a Review Paper
- 2023
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Konferensbidrag (refereegranskat)abstract
- The robotic wearable exoskeletons have been developed due to various advantages offered by these devices. These advantages are manifested by integrating the human and a robot into one system under the user's control, which motivated researchers to develop different exoskeletons through years. However, several advances in exoskeleton; still, dealing with the various technical challenges in designing these impressive devices is inevitably. This paper aims to introduce informative resources and quick guidance of various technical challenges as such information is critical for exoskeleton development. The constructive discussion is intended to encourage researchers, innovators and academia to be aware of these challenges. Finally, the contemporary research gaps with various challenges have been highlighted, which remain to be solved as well as some future directions in this field that will have far-reaching effects on developing exoskeletons.
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| 10. |
- Barbé, Kurt, et al.
(författare)
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A Simple Nonparametric Preprocessing Technique to Correct for Nonstationary Effects in Measured Data
- 2012
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Ingår i: IEEE Transactions on Instrumentation and Measurement. - 0018-9456 .- 1557-9662. ; 61:8, s. 2085-2094
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Tidskriftsartikel (refereegranskat)abstract
- The general approach for modeling systems assumes that the measured signals are (weakly) stationary, i.e., the power spectrum is time invariant. However, the stationarity assumption is violated when: 1) transient effects due to experimental conditions are dominant; 2) data are missing due to, for instance, sensor failure; or 3) the amplitude of the excitation signals smoothly varies over time due to, for instance, actuator problems. Although different methods exist to deal with each of these nonstationary effects specifically, no unified approach is available. In this paper, a new and general technique is presented to handle nonstationary effects, based on processing overlapping subrecords of the measured data. The proposed method is a simple preprocessing step where the user does not need to specify which nonstationary effect is present, nor the time interval where the nonstationary effect appears. The merits of the proposed approach are demonstrated on an operational wireless system suffering from interrupted link effects.
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