| 1. |
- Andersen, Olav, et al.
(författare)
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A Test-Bed Designed to Utilize Zhu’s General Sampling Theorem to Characterize Power Amplifiers
- 2009
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Ingår i: Instrumentation and measurement technology conference 2009 I2MTC '09 IEEE. - Singapore. - 9781424433537 ; , s. 201-204
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Konferensbidrag (refereegranskat)abstract
- Characterizing power amplifiers require test set-ups with performance superior to the power amplifiers. A commonly used method is to use an IQ-demodulator. However, problem arises due to imperfections in the demodulator such as IQ-imbalance; an alternative method is to use a direct down converter to intermediate frequency. The drawback then is the limited bandwidth. However, the required bandwidth of the ADC does not need to be exceptional. According to Zhu’s general sampling theorem is it enough to sample the output signal at the Nyquist rate of the input. However, even though the required sampling rate is reduced the demands on the analog bandwidth remains. Unfortunately, commercially available instruments such as vector signal analyzers can not be used for this purpose since their analog bandwidth is too small. In this paper a test-bed is designed to utilize the Zhu’s general sampling theorem. The RF front-end has frequency range of 500 MHz – 2.7 GHz and a bandwidth of 1 GHz. All performance data are verified with measurements.
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| 2. |
- 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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| 3. |
- 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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| 4. |
- 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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| 5. |
- 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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| 6. |
- 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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| 7. |
- 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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| 8. |
- 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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| 9. |
- Bemani, Ali, 1986-, et al.
(författare)
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Aggregation Strategy on Federated Machine Learning Algorithm for Collaborative Predictive Maintenance
- 2022
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Ingår i: Sensors. - : MDPI. - 1424-8220. ; 22:16
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Tidskriftsartikel (refereegranskat)abstract
- Industry 4.0 lets the industry build compact, precise, and connected assets and also has made modern industrial assets a massive source of data that can be used in process optimization, defining product quality, and predictive maintenance (PM). Large amounts of data are collected from machines, processed, and analyzed by different machine learning (ML) algorithms to achieve effective PM. These machines, assumed as edge devices, transmit their data readings to the cloud for processing and modeling. Transmitting massive amounts of data between edge and cloud is costly, increases latency, and causes privacy concerns. To address this issue, efforts have been made to use edge computing in PM applications., reducing data transmission costs and increasing processing speed. Federated learning (FL) has been proposed a mechanism that provides the ability to create a model from distributed data in edge, fog, and cloud layers without violating privacy and offers new opportunities for a collaborative approach to PM applications. However, FL has challenges in confronting with asset management in the industry, especially in the PM applications, which need to be considered in order to be fully compatible with these applications. This study describes distributed ML for PM applications and proposes two federated algorithms: Federated support vector machine (FedSVM) with memory for anomaly detection and federated long-short term memory (FedLSTM) for remaining useful life (RUL) estimation that enables factories at the fog level to maximize their PM models’ accuracy without compromising their privacy. A global model at the cloud level has also been generated based on these algorithms. We have evaluated the approach using the Commercial Modular Aero-Propulsion System Simulation (CMAPSS) dataset to predict engines’ RUL Experimental results demonstrate the advantage of FedSVM and FedLSTM in terms of model accuracy, model convergence time, and network usage resources.
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| 10. |
- Bemani, Ali, 1986-
(författare)
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Collaborative Predictive Maintenance for Smart Manufacturing : From Wireless Control to Federated Learning
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Industry 4.0 represents a significant shift in the industrial landscape, aimed at improving efficiency, productivity, and competitiveness. This shift involves the digitalization of industries, impacting manufacturing and maintenance processes. A pivotal element of this transformation is the development of Cyber-Physical Systems (CPS) that seamlessly connect the physical factory floor with the digital realm. These systems monitor real-time data from the physical world and prepare feedback from the digital space, necessitating the harmonious integration of computation and communication, especially through wireless technology. Simultaneously, Machine Learning (ML) methods are advancing across various domains. The proliferation of wireless sensors and the Internet of Things, particularly within the CPS framework, generates substantial data. To address challenges such as latency, device resource limitations, and privacy concerns associated with centralized cloud processing, there is a shift towards edge computing, enabling distributed learning algorithms.This dissertation tackles these challenges with four innovative methods that combine wireless technology, control systems, and distributed ML in the context of Industry 4.0. These methods aim to harness the potential of this digital transformation, making Predictive Maintenance (PdM) in industries smarter and more efficient. The first method, parallel event-triggering, is designed for multi-agent systems in industrial environments. It utilizes distributed event-based state estimation to enhance control performance and reduce network resource consumption. The second and third methods are developed for collaborative PdM using wireless communication in a federated approach. The second method focuses on real-time anomaly detection while preserving asset privacy at the edge level, and the third method optimizes remaining useful life prediction from sequential data within a federated learning framework. Both federated approaches enhance efficiency, simplify communication, and improve local model convergence. The fourth method introduces an innovative approach to collaborative PdM, utilizing over-the-air computation at the edge level. This approach offers low latency and improved spectral efficiency. The optimization challenges at the edge level are addressed by using a modified gradient descent approach, which effectively handles noisy communication channels and improves the convergence of ML algorithms. All four methods proposed in this thesis underwent a comprehensive evaluation,and the experimental findings demonstrate their effectiveness in achieving their intended objectives.
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