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  • 1.
    Andersson, Tom
    et al.
    Mälardalen University.
    Persson, Niklas
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Fattouh, Anas
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Ekström, Martin C.
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    A loop shaping method for stabilising a riderless bicycle2019In: 2019 European Conference on Mobile Robots, ECMR 2019 - Proceedings, Institute of Electrical and Electronics Engineers Inc. , 2019, article id 8870965Conference paper (Refereed)
    Abstract [en]

    Several control methods have been proposed to stabilise riderless bicycles but they do not have sufficient simplicity for practical applications. This paper proposes a practical approach to model an instrumented bicycle as a combination of connected systems. Using this model, a PID controller is designed by a loop shaping method to stabilise the instrumented riderless bicycle. The initial results show that the bicycle can be stabilised when running on a roller. The work presented in this paper shows that it is possible to self stabilise a riderless bicycle using cascade PI/PID controllers.

  • 2.
    Bergblomma, Marcus
    et al.
    Mälardalen University, School of Innovation, Design and Engineering.
    Ekström, Martin
    Mälardalen University, School of Innovation, Design and Engineering.
    Björkman, Mats
    Mälardalen University, School of Innovation, Design and Engineering.
    Ekström, Mikael
    Mälardalen University, School of Innovation, Design and Engineering.
    Gerdtman, Christer
    Motion Control AB, Västerås, Sweden .
    Lindén, Maria
    Mälardalen University, School of Innovation, Design and Engineering.
    A wireless low latency control system for harsh environments2012In: IFAC Proceedings Volumes (IFAC-PapersOnline): Vol. 11, PART 1, 2012, p. 17-22Conference paper (Refereed)
    Abstract [en]

    The use of wireless communication technologies in the industry offer severaladvantages. One advantage is the ability to deploy sensors where they previously could noteasily be deployed, for instance on parts that rotate. To use wireless communication in industrialcontrol loops, demands on reliability and latency requirements has to be met. This in anenvironment that may be harsh for radio communication. This work presents a reliable, lowlatency wireless communication system. The system is used in a wireless thyristor control loopin a hydro power plant generator. The wireless communication is based on Bluetooth radiomodules. The work shows a latency analysis together with empirical hardware based latencyand packet error rate measurements. The background noise of a hydro power plant station isalso investigated. The average latency between the Bluetooth modules for the proposed systemis 5.09 ms. The packet error rate is 0.00288 for the wireless low latency control system deployedin a hydro power plant.

  • 3.
    Ehn, Maria
    et al.
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Derneborg, Mattias
    Region Västmanland, Sweden.
    Ekström, Martin
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Johansson, Ann-Christin
    Mälardalen University, School of Health, Care and Social Welfare, Health and Welfare.
    Inter- disciplinary and -sectorial cooperation for development of technology supporting behavioral change: Peer reviewed poster abstract2017Conference paper (Other academic)
  • 4.
    Ekström, Martin
    et al.
    Mälardalen University, School of Innovation, Design and Engineering.
    Bergblomma, Marcus
    Mälardalen University, School of Innovation, Design and Engineering.
    Lindén, Maria
    Mälardalen University, School of Innovation, Design and Engineering.
    Björkman, Mats
    Mälardalen University, School of Innovation, Design and Engineering.
    Ekström, Mikael
    Edith Cowan University, Bunbury, Australia.
    A Bluetooth Radio Energy Consumption Model for Low Duty-Cycle Applications2012In: IEEE Transactions on Instrumentation and Measurement, ISSN 0018-9456, E-ISSN 1557-9662, Vol. 61, no 3, p. 609-617Article in journal (Refereed)
    Abstract [en]

    This paper presents a realistic model of the radio energy consumption for Bluetooth-equipped sensor nodes used in a low-duty-cycle network. The model is based on empirical energy consumption measurements of Bluetooth modules. This model will give users the possibility to optimize their radio communication with respect to energy consumption while sustaining the data rate. This paper shows that transmission power cannot always be directly related to energy consumption. Measurements indicate that, when the transmission power ranges from $-$5 to $+$10 dBm, the difference in consumed energy can be detected for each transmission peak in the sniff peak. However, the change is negligible for the overall energy consumption. The nonlinear behavior of the idle state for both master and slave when increasing the interval and number of attempts is presented. The energy consumption for a master node is in direct relation to the number of slaves and will increase by approximately 50% of the consumption of one slave per additional slave, regardless of the radio setting.

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    fulltext
  • 5.
    Folke, Mia
    et al.
    Mälardalen University, Department of Computer Science and Electronics.
    Cernerud, Lars
    Mälardalen University, School of Health, Care and Social Welfare, Health and Welfare.
    Ekström, Martin
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Hök, Bertil
    Hök Instrument AB, Västerås, Sweden.
    Critical review of non-invasive respiratory monitoring in medical care2003In: Medical & Biological Engineering & Computing, Vol. 41, no 4, p. 377-383Article in journal (Refereed)
    Abstract [en]

    Respiratory failure can be difficult to predict. It can develop into a life-threatening condition in just a few minutes, or it can build up more slowly. Thus continuous monitoring of respiratory activity should be mandatory in clinical, high-risk situations, and appropriate monitoring equipment could be life-saving. The review considers non-invasive methods and devices claimed to provide information about respiratory rate or depth, or gas exchange. Methods are categorised into those responding to movement, volume and tissue composition detection; air flow, and blood gas concentration. The merits and limitations of the methods and devices are analysed, considering information. content and their ability to minimise the rate of false alarms and false non-alarms. It is concluded that the field of non-invasive respiratory monitoring is still in an exploratory phase, with numerous reports on specific device solutions but less work on evaluation and adaptation to clinical requirements. Convincing evidence of the clinical usefulness of respiratory monitors is still lacking. Devices responding only to respiratory rate, and lacking information about actual gas exchange, will have limited clinical value. Furthermore, enhancement in specificity and sensitivity to avoid false alarms and non-alarms will be necessary to meet clinical requirements. Miniature CO2 sensors are identified as one route towards substantial improvement.

  • 6.
    Hellstrom, Per Anders Rickard
    et al.
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Carlén Eriksson, Lennie
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Scharff Willners, Jonatan
    Folke, Mia
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Ekström, Martin
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Intelligent Wireless Body Area Network System for Human Motion Analysis2015Conference paper (Refereed)
    Abstract [en]

    Human motion analysis provides several important applications. Examples are fall risk assessment, sports biomechanics, physical activity monitoring and rehabilitation. This work in progress paper proposes an intelligent wireless body area network system for motion and gait symmetry analysis. A Bluetooth network with accelerometers, gyroscopes and in-shoe force sensing resistors gathers data and sends it to a web server after intelligent pre-processing and filtering. The system is flexible and adaptable for different use cases including combinations of gait analysis, gait symmetry and pressure measurements between foot and shoe.

  • 7.
    Hellstrom, Per Anders Rickard
    et al.
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Folke, Mia
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Ekström, Martin
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Wearable Weight Estimation System2015In: Procedia Computer Science, vol. 64, 2015, Vol. 64, p. 146-152Conference paper (Refereed)
    Abstract [en]

    Heavy working conditions, as well as sedentary behaviour, are risk factors for health. There is a lack of wearable measurement systems for monitoring carried loads while walking. Pedobarography, the study of force fields acting between the plantar surface of the foot and a supporting surface, is supposed to be useable for estimating carried loads. Purpose. The aim of this paper is to present a novel method for selecting appropriate measurement samples for weight estimation of carried load during walk and a wearable system, based on pedobarography, consisting of commercial off the shelf components. The main idea is to choose samples when half of the total weight is on the forward sensors and the other half is on the heel sensor “equipoise” in one foot while the other foot not touches the ground. Methods. The system consists of insoles with force sensing resistors, data acquisition with IOIO-OTG and analysis in Excel. Each subject was weighed on an electronic floor scale. Three walks were performed on level ground. The first walk without any added load and then with two increases of carried load. Equipoise was defined as having half the weight distributed on the heel and the other half over the metatarsal pad. An equipoise value of 0.5 represents equilibrium regarding the weight distribution on one foot, with the other foot in the air. Samples were chosen in the equipoise region of 0.5±0.1 and then the average of the samples collected during one minute estimated the total weight. Results. The system can detect increases in carried loads but has a tendency to overestimate them. The estimated value was always larger with increased weight but the system was not always linear. The average overestimation error was 16.7 kg. Discussion. This study shows that this type of wearable system is usable for estimating carried load during walk after calibration of the system to the body weight force distribution on the sensors. There is still need for future development to obtain real-time analysis and direct feedback. A smaller and lighter measurement system is also desirable. Conclusion. This study shows that the novel method, equipoise, is usable for selecting appropriate measurement samples for weight estimation of carried load during walk. This study also shows that the wearable system, consisting of commercial off the shelf components, can be used for these measurements. However, there is a tendency to overestimate the loads.

  • 8.
    Hellstrom, Per Anders Rickard
    et al.
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Åkerberg, Anna
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Ekström, Martin
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Folke, Mia
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Evaluation of the IngVaL Pedobarography System for Monitoring of Walking Speed2018In: Healthcare Informatics Research, ISSN 2093-3681, E-ISSN 2093-369X, ISSN 2093-3681, Vol. 24, no 2, p. 118-124Article in journal (Refereed)
    Abstract [en]

    Objectives

    Walking speed is an important component of movement and is a predictor of health in the elderly. Pedobarography, the study of forces acting between the plantar surface of the foot and a supporting surface, is an approach to estimating walking speed even when no global positioning system signal is available. The developed portable system, Identifying Velocity and Load (IngVaL), is a cost effective alternative to commercially available pedobarography systems because it only uses three force sensing resistors. In this study, the IngVaL system was evaluated. The three variables investigated in this study were the sensor durability, the proportion of analyzable steps, and the linearity between the system output and the walking speed.

    Methods

    Data was collected from 40 participants, each of whom performed five walks at five different self-paced walking speeds. The linearity between the walking speed and step frequency measured with R2 values was compared for the walking speed obtained ‘A’ only using amplitude data from the force sensors, ‘B’ that obtained only using the step frequency, and ‘C’ that obtained by combining amplitude data for each of the 40 test participants.

    Results

    Improvement of the wireless data transmission increased the percentage of analyzable steps from 83.1% measured with a prototype to 96.6% for IngVaL. The linearity comparison showed that the methods A, B, and C were accurate for 2, 15, and 23 participants, respectively.

    Conclusions

    Increased sensor durability and a higher percentage of analyzed steps indicates that IngVaL is an improvement over the prototype system. The combined strategy of amplitude and step frequency was confirmed as the most accurate method.

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    Hellstrom_2018
  • 9.
    Hellstrom, Per Anders Rickard
    et al.
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Åkerberg, Anna
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Ekström, Martin
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Folke, Mia
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Walking Intensity Estimation with a Portable Pedobarography System2016In: Studies in Health Technology and Informatics, IOS Press , 2016, Vol. 224, p. 27-32Conference paper (Refereed)
    Abstract [en]

    The aim of this pilot study was to investigate the possibility to find a correlation between the output from a portable pedobarography system and the walking intensity expressed as walking speed. The system uses shoe insoles with force sensing resistors and wireless transmission of the data via Bluetooth. The force-time integral, at the toe-off phase of the step, for the force sensors in the forward part of the right foot was used to measure impulse data for 10 subjects performing walks in three different walking speeds. This data was then corrected by multiplication with the step frequency. This pilot study indicates that the portable pedobarography system output shows a linear relationship with the walking intensity expressed as walking speed on an individual level.

  • 10.
    Hozhabri, Melika
    et al.
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Otterskog, Magnus
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Petrović, Nikola
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Ekström, Martin
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Experimental Comparison Study of UWB Technologies for Static Human Detection2016In: IEEE International Conference on Ubiquitous Wireless Broadband (ICUWB 2016) ICUWB 2016, 2016Conference paper (Refereed)
    Abstract [en]

    This paper compares two dominant Ultra Wide Rand(UWB) radar technologies Impulse and M-sequence for static human being detection in free space. The hardware and software platform for each system is described separately. These two radar platform performances are tested in real conditions and the results show that M-sequence UWB radar is better suited for detecting the static human target in larger distances.

  • 11.
    Koshmak, Gregory
    et al.
    Mälardalen University, School of Innovation, Design and Engineering.
    Ekström, Martin
    Mälardalen University, School of Innovation, Design and Engineering.
    Lindén, Maria
    Mälardalen University, School of Innovation, Design and Engineering.
    A smart-phone based monitoring system with health device profile2012Conference paper (Refereed)
  • 12.
    Koshmak, Gregory
    et al.
    Mälardalen University, School of Innovation, Design and Engineering.
    Ekström, Martin
    Mälardalen University, School of Innovation, Design and Engineering.
    Lindén, Maria
    Mälardalen University, School of Innovation, Design and Engineering.
    A smart-Phone Based Monitoring System with Health Device Profile for Measuring Vital Physiological parameters2012Conference paper (Refereed)
  • 13. Persson, Niklas
    et al.
    Andersson, Tom
    Fattouh, Anas
    Mälardalen University, School of Innovation, Design and Engineering, Innovation and Product Realisation.
    Ekström, Martin
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Papadopoulos, Alessandro
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    A Comparative Analysis and Design of Controllers for Autonomous Bicycles2021In: 2021 EUROPEAN CONTROL CONFERENCE (ECC), - IEEE , 2021, p. 1570-1576Conference paper (Refereed)
    Abstract [en]

    In this paper, we develop and compare the performance of different controllers for balancing an autonomous bicycle. The evaluation is carried out both in simulation, using two different models, and experimentally, on a bicycle instrumented with only lightweight components, and leaving the bicycle structure practically unchanged. Two PID controllers, a Linear Quadratic Regulator (LQR), and a fuzzy controller are developed and evaluated in simulations where both noise and disturbances are induced in the models. The simulation shows that the LQR controller has the best performance in the simulation scenarios. Experimental results, on the other hand, show that the PID controllers provide better performance when balancing the instrumented bicycle.

  • 14.
    Persson, Niklas
    et al.
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Ekström, Martin C.
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Ekström, Mikael
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Papadopoulos, Alessandro
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Trajectory tracking and stabilisation of a riderless bicycle*2021In: 2021 IEEE International Intelligent Transportation Systems Conference (ITSC), 2021, p. 1859-1866Conference paper (Refereed)
    Abstract [en]

    Trajectory tracking for an autonomous bicycle is considered in this paper. The trajectory tracking controller is designed using a Model Predictive Controller with constraints on the lean, steer, and heading angle as well as the position coordinates of the bicycle. The output from the trajectory tracking controller is the desired lean angle and forward velocity. Furthermore, a PID controller is designed to follow the desired lean angle, while maintaining balance, by actuation of the handlebar. The proposed control strategy is evaluated in numerous simulations where a realistic nonlinear model of the bicycle is traversing a go-kart track and a short track with narrow curves. The Hausdorff distance and Mean Squared Error are considered as measurements of the performance. The results show that the bicycle successfully can track desired trajectories at varying velocities.

  • 15.
    Persson, Niklas
    et al.
    Mälardalen University, School of Innovation, Design and Engineering.
    Ekström, Martin
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Ekström, Mikael
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Papadopoulos, Alessandro
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    On the Initialization Problem for Timed-Elastic BandsManuscript (preprint) (Other academic)
    Abstract [en]

    Path planning is an important part of navigation for mobile robots. Several approaches have been proposed in the literature based on a discretisation of the map, including A*, Theta*, and RRT*. While these approaches have been widely adopted also in real applications, they tend to generate non-smooth paths, which can be difficult to follow, based on the kinematic and dynamic constraints of the robot. Time-Elastic-Bands (TEB) have also been used in the literature, to deform an original path in real-time to produce a smoother path, and to handle potential local changes in the environment, such as the detection of an unknown obstacle. This work analyses the effects on the overall path for different choices of initial paths fed to TEB. In particular, the produced paths are compared in terms of total distance, curvature, and variation in the desired heading. The optimised version of the solution produced by Theta* shows the highest performance among the considered methods and metrics, and we show that it can be successfully followed by an autonomous bicycle. 

  • 16.
    Tidare, Jonatan
    et al.
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Åstrand, Elaine
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Ekström, Martin C.
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Evaluation of closed-loop feedback system delay a time-critical perspective for neurofeedback training2018In: BIODEVICES 2018 - 11th International Conference on Biomedical Electronics and Devices, Proceedings; Part of 11th International Joint Conference on Biomedical Engineering Systems and Technologies, BIOSTEC 2018, SciTePress , 2018, p. 187-193Conference paper (Refereed)
    Abstract [en]

    Neurofeedback in real-time has proven effective when subjects learn to control a BCI. To facilitate learning, a closed-loop feedback system should provide neurofeedback with maximal accuracy and minimal delay. In this article, we propose a modular system for real-time neurofeedback experiments and evaluate its performance as a function of increased stress level applied to the system. The system shows stable behavior and decent performance when streaming with many EEG channels (36-72) and 500-5000 Hz, which is common in BCI setups. With very low data loads (1 channel, 500-1000 Hz) the performance dropped significantly and the system became highly unpredictable. We show that the system delays did not correlate linearly with the stress-level applied to the system, emphasizing the importance of system delay tests before conducting real-time BCI-experiments. 

1 - 16 of 16
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