Marvin K. Bugeja | University of Malta (original) (raw)
Papers by Marvin K. Bugeja
2022 20th International Conference on Mechatronics - Mechatronika (ME)
2017 25th Mediterranean Conference on Control and Automation (MED), 2017
This work compares the use of three different artificial neural networks (ANNs) to estimate shoul... more This work compares the use of three different artificial neural networks (ANNs) to estimate shoulder and elbow kinematics using surface electromyographic (EMG) signals for proportional and simultaneous control of multiple degrees of freedom (DOFs). The three different networks considered include a multilayer perceptron (MLP) neural network, a time delay neural network (TDNN), and a recurrent neural network (RNN). In each case, surface EMG signals from agonist and antagonist arm muscles detected during seven different movements, three of which involve the simultaneous activation of the shoulder and elbow, were used as inputs to the neural networks. The three configurations were trained to estimate angular displacements of the shoulder and/or elbow. The average correlation coefficient (CC) between the true and the estimated angular position for simultaneous movements for the elbow and shoulder combined was 0.866 ± 0.050 when using the MLP structure, 0.830 ± 0.130 for the TDNN structure and 0.840 ± 0.058 when using the RNN architecture. These results show that all three neural networks are plausible alternatives to model the EMG to joint angle relationship of the upper arm with the MLP being the most computationally efficient option.
Proceedings of the 13th International Conference on Informatics in Control, Automation and Robotics, 2016
This paper proposes a practical solution to the autonomous exploration and mapping problem using ... more This paper proposes a practical solution to the autonomous exploration and mapping problem using a single mobile robot. Moreover, the authors implement the proposed scheme within the Robot Operating System (ROS), and validate it experimentally using PowerBot, a real wheeled mobile robot equipped with a 2D laser scanner. In essence, the proposed scheme integrates an efficient particle-filter-based SLAM algorithm, two different exploration strategies, and a path-planning and navigation module. The modular nature of the proposed scheme is intentional and advantageous. It allows the authors to compare the two exploration strategies under investigation objectively and with ease. Finally, hypotheses testing is also used to strengthen the results of the comparative analysis.
IEEE Journal on Miniaturization for Air and Space Systems, 2020
Attitude control for CubeSats and small satellites has been widely researched. Nonetheless, most ... more Attitude control for CubeSats and small satellites has been widely researched. Nonetheless, most of the literature is based on simulations, with limited availability of actual implementation results. This article tries to fill this gap by highlighting implementation difficulties and proposing appropriate workable solutions. The difficulty of direct reaction wheel (RW) torque feedback for attitude control of a 1p PocketQube (PQ) pico-satellite is noted and addressed. A simple control strategy implementable on a microcontroller is then proposed, showing how direct RW torque control can be achieved through angular velocity measurement without using derivative feedback. A linear quadratic Gaussian controller with integral action in quaternion formulation is used for attitude control, and a reference input boundary caused by the use of the standard integral action scheme is highlighted. A simple solution is then proposed, showing how using the error quaternion removes this boundary. An extended Kalman filter in quaternion formulation is used for attitude determination by fusing data from three sensors, namely, a magnetometer, solar cells, and a gyroscope. An accelerometer is used in place of the solar cells for simplified laboratory testing. Magnetometer error due to surrounding interference is addressed through calibration. A string-suspended model of the UoMBSat-1 PocketQube pico-satellite is used for attitude control testing. Preliminary single-axis tests are performed using a PID controller to determine the satellite parameters and actuators verification. The proposed linear quadratic Gaussian controller is then tested and validated experimentally in the laboratory setting.
Sensors
Electroencephalogram (EEG)-based brain–computer interfaces (BCIs) provide a novel approach for co... more Electroencephalogram (EEG)-based brain–computer interfaces (BCIs) provide a novel approach for controlling external devices. BCI technologies can be important enabling technologies for people with severe mobility impairment. Endogenous paradigms, which depend on user-generated commands and do not need external stimuli, can provide intuitive control of external devices. This paper discusses BCIs to control various physical devices such as exoskeletons, wheelchairs, mobile robots, and robotic arms. These technologies must be able to navigate complex environments or execute fine motor movements. Brain control of these devices presents an intricate research problem that merges signal processing and classification techniques with control theory. In particular, obtaining strong classification performance for endogenous BCIs is challenging, and EEG decoder output signals can be unstable. These issues present myriad research questions that are discussed in this review paper. This review cov...
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](IEEE Control Systems, 2017
Abstract-This paper presents a novel dual adaptive dynamic controller for trajectory tracking of ... more Abstract-This paper presents a novel dual adaptive dynamic controller for trajectory tracking of nonholonomic wheeled mobile robots. The controller is developed entirely in discretetime and the and the robot's nonlinear dynamic functions are assumed to be unknown. A Gaussian radial basis function neural network is employed for function approximation, and its weights are estimated stochastically in real-time. In contrast to adaptive certainty equivalence controllers hitherto published for mobile robots, the proposed control law takes into consideration the estimates' uncertainty, thereby leading to improved tracking performance. The proposed method is verified by realistic simulations and Monte Carlo analysis. Index Terms-Nonholonomic mobile robots, trajectory tracking, dual adaptive control, neural networks.
2017 25th Mediterranean Conference on Control and Automation (MED)
The CubeSat form factor was very successful at reducing development and launch costs for spacecra... more The CubeSat form factor was very successful at reducing development and launch costs for spacecraft. The PocketQube (PQ)-one eighth the size of a CubeSataims to further reduce these costs. However, the question remains on whether it is feasible to implement a fully-featured satellite within the far tighter constraints imposed by a PQ. This paper explores the implications of including a 3-axis attitude determination and control system with provisions for desaturation and detumbling within the confines of a PQ. The hardware technology available is outlined and the applicable control laws and techniques are reviewed. This paper presents the approach that is actually being adopted in the development of the UoMBSat-1 picosatellite at the University of Malta.
Proceedings of the 15th International Conference on Informatics in Control, Automation and Robotics
This paper presents the design and implementation of a training simulator for the teleoperated ro... more This paper presents the design and implementation of a training simulator for the teleoperated robot Telemax. Telemax is used at CERN for inspection and maintenance operations to reduce the exposure of personnel to radiation. The robot is modelled using a robot description format and spawned in the robotic simulator Gazebo. Control schemes are implemented in ROS in order to actuate the robotic arm in both joint-by-joint space and operational-space. Control of the robot base is also modelled. A graphical user interface is used in order to interface with the simulation, and control the robot with the help of live images coming from the robot's on-board cameras. The resulting simulator was tested by robot operators at CERN and is envisaged to be of great help in the training of new operators, as well as in the testing of robot interventions in new scenarios and environments.
IFAC-PapersOnLine
Multi-robot systems are becoming widely popular in applications where a rapid response is require... more Multi-robot systems are becoming widely popular in applications where a rapid response is required or where various different robotic capabilities are required. Applications such as surveillance, or search and rescue, would require an efficient team that can be deployed and optimally dispersed over the environment. This is known as the coverage control problem. The solution to this research optimization problem is affected by several external aspects, such as characteristics of the environment as well as factors that pertain to the robotic team. This work proposes a novel solution to the complete coverage problem where the team of robots is restricted with energy limitations, and must cover an environment that has time-varying regions of importance. Our results show that in a realistic scenario, where the robots have limited energy for the task in question, the proposed solution performs significantly better than a typical coverage algorithm which disregards the energy considerations of the robotic team.
2017 25th Mediterranean Conference on Control and Automation (MED)
Literature reviews on Multi-Robot Systems (MRS) typically focus on fundamental technical aspects,... more Literature reviews on Multi-Robot Systems (MRS) typically focus on fundamental technical aspects, like coordination and communication, that need to be considered in order to coordinate a team of robots to perform a given task effectively and efficiently. Other reviews only consider works that aim to address a specific problem or one particular application of MRS. In contrast, this paper presents a survey of recent research works on MRS and categorises them according to their application domain. Furthermore, this paper compiles a number of seminal review works that have proposed specific taxonomies in classifying fundamental concepts, such as coordination, architecture and communication, in the field of MRS.
Biomedical Engineering / Biomedizinische Technik
The use of foot mounted inertial and other auxiliary sensors for kinematic gait analysis has been... more The use of foot mounted inertial and other auxiliary sensors for kinematic gait analysis has been extensively investigated during the last years. Although, these sensors still yield less accurate results than those obtained employing optical motion capture systems, the miniaturization and their low cost have allowed the estimation of kinematic spatiotemporal parameters in laboratory conditions and real life scenarios. The aim of this work was to present a comprehensive approach of this scientific area through a systematic literature research, breaking down the state-of-the-art methods into three main parts: (1) zero velocity interval detection techniques; (2) assumptions and sensors’ utilization; (3) foot pose and trajectory estimation methods. Published articles from 1995 until December of 2018 were searched in the PubMed, IEEE Xplore and Google Scholar databases. The research was focused on two categories: (a) zero velocity interval detection methods; and (b) foot pose and traject...
Proceedings of the 16th International Conference on Informatics in Control, Automation and Robotics, 2019
Wheelchairs have improved the lives of many people with limited mobility. Yet, to this day, conve... more Wheelchairs have improved the lives of many people with limited mobility. Yet, to this day, conventional wheelchairs are still not a viable option for mobility independence in cases of people with severe weakness or poor coordination e.g. Amyotrophic Lateral Sclerosis (ALS). Smart wheelchairs (SWs) overcome many of these limitations by adding an extra layer of intelligence to the system. SWs have so far remained mostly inaccessible to the general public, due to a limited market presence and steep costs. This paper thus presents the design and implementation of a novel SW which makes the upgrade of a commercially available motorised wheelchair to a SW a much simpler process. The system is a complete implementation offering low-level hardware control, a specialised ROS architecture and autonomous navigation algorithms allowing shared user control or fully-autonomous movement. Contrary to most other published works, the focus of this paper is to implement a fully-featured working prototype with minimal hardware complexity and an efficient modular software development environment. Initial practical tests in typical use scenarios showcased the successful operation of the complete system. The developed prototype SW has the potential to restore autonomy to people who are unable to use conventional or powered wheelchairs.
Gait & Posture
BACKGROUND Kinematic gait analysis employing multi-segment foot models has been mainly conducted ... more BACKGROUND Kinematic gait analysis employing multi-segment foot models has been mainly conducted in laboratories by means of optical motion capture systems. This type of process requires considerable setup time and is constrained by a limited capture space. A procedure involving the use of multiple inertial measurement units (IMUs) is proposed to overcome these limitations. RESEARCH QUESTION This study presents a new approach for the estimation of the trajectories of a multi-segment foot model by means of multiple IMUs. METHODS To test the proposed method, a system consisting of four IMUs attached to the shank, heel, dorsum and toes segments of the foot, was considered. The performance of the proposed method was compared to that of a conventional method using IMUs adopted from the literature. In addition, an optical motion capture system was used as a reference to assess the performance of the implemented methods. RESULTS Employing the suggested method, all trajectory directions of the shank, heel and dorsum segments, as well as the Z (yaw) direction of the toes segment, have exhibited an error reduction varying between 8% and 55%. However, X (roll) and Y (pitch) direction of the toes segment presented an error increase of 17% and 26%, respectively. The estimation of the vertical displacement, corresponding to the foot clearance, was improved for all segments, resulting in a final mean accuracy and precision of 3.5 ± 2.8 cm, 2.7 ± 2.1 cm, 0.8 ± 0.7 cm and 1.1 ± 0.9 cm for the shank, heel, dorsum and toes segments, respectively. SIGNIFICANCE It has been demonstrated that as an alternative to tracking each foot segment separately, the fusion of multiple IMU measurements using kinematic equations, considerably improves the estimated trajectories, especially when considering vertical foot displacements. The proposed method could complement the use of smaller and cheaper sensors, while still matching the same performance of other published methods, making the suggested approach very attractive for real life applications.
Transactions of the Institute of Measurement and Control
This paper proposes three novel neural network controllers for dual adaptive control of a class o... more This paper proposes three novel neural network controllers for dual adaptive control of a class of functionally uncertain, nonlinear, multiple-input/multiple-output stochastic systems. Both Gaussian radial basis function and sigmoidal multilayer perceptron neural networks are considered for approximation of the unknown dynamic functions. Control and estimation are effected through optimization of a stochastic cost function which elicits the dual effects of caution and probing, resulting in control laws that take into consideration the interactions between estimation and control, leading to improved control performance. The Kalman filter is used for estimation of the weights of the radial basis function network, while the extended and unscented Kalman filter are used for the multilayer perceptron case. The performances of the three schemes are compared and evaluated through extensive Monte Carlo simulations and statistical significance tests.
Journal of Dynamic Systems, Measurement, and Control, 2016
Current research in offshore wind turbines is proposing a novel concept of using seawater-based h... more Current research in offshore wind turbines is proposing a novel concept of using seawater-based hydraulics for large-scale power transmission and centralized electrical generation. The objective of this paper is to investigate the control of such an open-loop circuit, where a fixed line pressure is desirable for the sake of efficiency and stability. Pressure control of the open-loop hydraulic circuit presents an interesting control challenge due to the highly fluctuating flow rate along with the nonlinear behavior of the variable-area orifice used by the pressure controller. The present analysis is limited to a single turbine and an open-loop hydraulic line with a variable-area orifice at the end. A controller is proposed which uses a combination of feed-forward compensation for the nonlinear part along with a feedback loop for correcting any errors resulting from inaccuracies in the compensator model. A numerical model of the system under investigation is developed in order to obse...
Abstract: Adaptive control involves both estimation and control, which are generally interdepende... more Abstract: Adaptive control involves both estimation and control, which are generally interdependent and partly in conflict. Yet, the majority of adaptive controllers separate the two by assuming that certainty equivalence holds, even if this is not the case. In contrast a ...
Abstract: This paper presents experimental results which validate the use of a novel dual adaptiv... more Abstract: This paper presents experimental results which validate the use of a novel dual adaptive controller for mobile robots operating in the presence of dynamic uncertainty. The control scheme, recently proposed by the same authors, has so far been tested by simulations ...
Volume 9: Ocean Renewable Energy, 2015
The viability of offshore wind turbines is presently affected by a number of technical issues per... more The viability of offshore wind turbines is presently affected by a number of technical issues pertaining to the gearbox and power electronic components. Current work is considering the possibility of replacing the generator, gearbox and electrical transmission with a hydraulic system. Efficiency of the hydraulic transmission is around 90% for the selected geometries, which is comparable to the 94% expected for conventional wind turbines. A rotor-driven pump pressurises seawater that is transmitted across a large pipeline to a centralised generator platform. Hydroelectric energy conversion takes place in Pelton turbine. However, unlike conventional hydro-energy plants, the head available at the nozzle entry is highly unsteady. Adequate active control at the nozzle is therefore crucial in maintaining a fixed line pressure and an optimum Pelton turbine operation at synchronous speed. This paper presents a novel control scheme that is based on the combination of proportional feedback co...
Proceedings of the 12th International Conference on Informatics in Control, Automation and Robotics, 2015
This paper proposes and investigates the application of sliding mode control to the ball and plat... more This paper proposes and investigates the application of sliding mode control to the ball and plate problem. The nonlinear properties of the ball and plate control system are first presented. Then the experimental setup designed and built specifically for the purpose of this research is discussed. The paper then focuses on the implementation and thorough evaluation of the experimental results obtained with two different control schemes: the linear full-state feedback controller and the sliding mode controller. The latter control strategy was selected for its robust and order reduction properties. Finally the control performance of the two controllers is analysed. The sliding controller manages to obtain a faster and more accurate operation for continuously changing reference inputs. The robustness of the proposed control scheme is also verified, since the system's performance is shown to be insensitive to parameter variations.
2022 20th International Conference on Mechatronics - Mechatronika (ME)
2017 25th Mediterranean Conference on Control and Automation (MED), 2017
This work compares the use of three different artificial neural networks (ANNs) to estimate shoul... more This work compares the use of three different artificial neural networks (ANNs) to estimate shoulder and elbow kinematics using surface electromyographic (EMG) signals for proportional and simultaneous control of multiple degrees of freedom (DOFs). The three different networks considered include a multilayer perceptron (MLP) neural network, a time delay neural network (TDNN), and a recurrent neural network (RNN). In each case, surface EMG signals from agonist and antagonist arm muscles detected during seven different movements, three of which involve the simultaneous activation of the shoulder and elbow, were used as inputs to the neural networks. The three configurations were trained to estimate angular displacements of the shoulder and/or elbow. The average correlation coefficient (CC) between the true and the estimated angular position for simultaneous movements for the elbow and shoulder combined was 0.866 ± 0.050 when using the MLP structure, 0.830 ± 0.130 for the TDNN structure and 0.840 ± 0.058 when using the RNN architecture. These results show that all three neural networks are plausible alternatives to model the EMG to joint angle relationship of the upper arm with the MLP being the most computationally efficient option.
Proceedings of the 13th International Conference on Informatics in Control, Automation and Robotics, 2016
This paper proposes a practical solution to the autonomous exploration and mapping problem using ... more This paper proposes a practical solution to the autonomous exploration and mapping problem using a single mobile robot. Moreover, the authors implement the proposed scheme within the Robot Operating System (ROS), and validate it experimentally using PowerBot, a real wheeled mobile robot equipped with a 2D laser scanner. In essence, the proposed scheme integrates an efficient particle-filter-based SLAM algorithm, two different exploration strategies, and a path-planning and navigation module. The modular nature of the proposed scheme is intentional and advantageous. It allows the authors to compare the two exploration strategies under investigation objectively and with ease. Finally, hypotheses testing is also used to strengthen the results of the comparative analysis.
IEEE Journal on Miniaturization for Air and Space Systems, 2020
Attitude control for CubeSats and small satellites has been widely researched. Nonetheless, most ... more Attitude control for CubeSats and small satellites has been widely researched. Nonetheless, most of the literature is based on simulations, with limited availability of actual implementation results. This article tries to fill this gap by highlighting implementation difficulties and proposing appropriate workable solutions. The difficulty of direct reaction wheel (RW) torque feedback for attitude control of a 1p PocketQube (PQ) pico-satellite is noted and addressed. A simple control strategy implementable on a microcontroller is then proposed, showing how direct RW torque control can be achieved through angular velocity measurement without using derivative feedback. A linear quadratic Gaussian controller with integral action in quaternion formulation is used for attitude control, and a reference input boundary caused by the use of the standard integral action scheme is highlighted. A simple solution is then proposed, showing how using the error quaternion removes this boundary. An extended Kalman filter in quaternion formulation is used for attitude determination by fusing data from three sensors, namely, a magnetometer, solar cells, and a gyroscope. An accelerometer is used in place of the solar cells for simplified laboratory testing. Magnetometer error due to surrounding interference is addressed through calibration. A string-suspended model of the UoMBSat-1 PocketQube pico-satellite is used for attitude control testing. Preliminary single-axis tests are performed using a PID controller to determine the satellite parameters and actuators verification. The proposed linear quadratic Gaussian controller is then tested and validated experimentally in the laboratory setting.
Sensors
Electroencephalogram (EEG)-based brain–computer interfaces (BCIs) provide a novel approach for co... more Electroencephalogram (EEG)-based brain–computer interfaces (BCIs) provide a novel approach for controlling external devices. BCI technologies can be important enabling technologies for people with severe mobility impairment. Endogenous paradigms, which depend on user-generated commands and do not need external stimuli, can provide intuitive control of external devices. This paper discusses BCIs to control various physical devices such as exoskeletons, wheelchairs, mobile robots, and robotic arms. These technologies must be able to navigate complex environments or execute fine motor movements. Brain control of these devices presents an intricate research problem that merges signal processing and classification techniques with control theory. In particular, obtaining strong classification performance for endogenous BCIs is challenging, and EEG decoder output signals can be unstable. These issues present myriad research questions that are discussed in this review paper. This review cov...
IEEE Control Systems, 2017
Abstract-This paper presents a novel dual adaptive dynamic controller for trajectory tracking of ... more Abstract-This paper presents a novel dual adaptive dynamic controller for trajectory tracking of nonholonomic wheeled mobile robots. The controller is developed entirely in discretetime and the and the robot's nonlinear dynamic functions are assumed to be unknown. A Gaussian radial basis function neural network is employed for function approximation, and its weights are estimated stochastically in real-time. In contrast to adaptive certainty equivalence controllers hitherto published for mobile robots, the proposed control law takes into consideration the estimates' uncertainty, thereby leading to improved tracking performance. The proposed method is verified by realistic simulations and Monte Carlo analysis. Index Terms-Nonholonomic mobile robots, trajectory tracking, dual adaptive control, neural networks.
2017 25th Mediterranean Conference on Control and Automation (MED)
The CubeSat form factor was very successful at reducing development and launch costs for spacecra... more The CubeSat form factor was very successful at reducing development and launch costs for spacecraft. The PocketQube (PQ)-one eighth the size of a CubeSataims to further reduce these costs. However, the question remains on whether it is feasible to implement a fully-featured satellite within the far tighter constraints imposed by a PQ. This paper explores the implications of including a 3-axis attitude determination and control system with provisions for desaturation and detumbling within the confines of a PQ. The hardware technology available is outlined and the applicable control laws and techniques are reviewed. This paper presents the approach that is actually being adopted in the development of the UoMBSat-1 picosatellite at the University of Malta.
Proceedings of the 15th International Conference on Informatics in Control, Automation and Robotics
This paper presents the design and implementation of a training simulator for the teleoperated ro... more This paper presents the design and implementation of a training simulator for the teleoperated robot Telemax. Telemax is used at CERN for inspection and maintenance operations to reduce the exposure of personnel to radiation. The robot is modelled using a robot description format and spawned in the robotic simulator Gazebo. Control schemes are implemented in ROS in order to actuate the robotic arm in both joint-by-joint space and operational-space. Control of the robot base is also modelled. A graphical user interface is used in order to interface with the simulation, and control the robot with the help of live images coming from the robot's on-board cameras. The resulting simulator was tested by robot operators at CERN and is envisaged to be of great help in the training of new operators, as well as in the testing of robot interventions in new scenarios and environments.
IFAC-PapersOnLine
Multi-robot systems are becoming widely popular in applications where a rapid response is require... more Multi-robot systems are becoming widely popular in applications where a rapid response is required or where various different robotic capabilities are required. Applications such as surveillance, or search and rescue, would require an efficient team that can be deployed and optimally dispersed over the environment. This is known as the coverage control problem. The solution to this research optimization problem is affected by several external aspects, such as characteristics of the environment as well as factors that pertain to the robotic team. This work proposes a novel solution to the complete coverage problem where the team of robots is restricted with energy limitations, and must cover an environment that has time-varying regions of importance. Our results show that in a realistic scenario, where the robots have limited energy for the task in question, the proposed solution performs significantly better than a typical coverage algorithm which disregards the energy considerations of the robotic team.
2017 25th Mediterranean Conference on Control and Automation (MED)
Literature reviews on Multi-Robot Systems (MRS) typically focus on fundamental technical aspects,... more Literature reviews on Multi-Robot Systems (MRS) typically focus on fundamental technical aspects, like coordination and communication, that need to be considered in order to coordinate a team of robots to perform a given task effectively and efficiently. Other reviews only consider works that aim to address a specific problem or one particular application of MRS. In contrast, this paper presents a survey of recent research works on MRS and categorises them according to their application domain. Furthermore, this paper compiles a number of seminal review works that have proposed specific taxonomies in classifying fundamental concepts, such as coordination, architecture and communication, in the field of MRS.
Biomedical Engineering / Biomedizinische Technik
The use of foot mounted inertial and other auxiliary sensors for kinematic gait analysis has been... more The use of foot mounted inertial and other auxiliary sensors for kinematic gait analysis has been extensively investigated during the last years. Although, these sensors still yield less accurate results than those obtained employing optical motion capture systems, the miniaturization and their low cost have allowed the estimation of kinematic spatiotemporal parameters in laboratory conditions and real life scenarios. The aim of this work was to present a comprehensive approach of this scientific area through a systematic literature research, breaking down the state-of-the-art methods into three main parts: (1) zero velocity interval detection techniques; (2) assumptions and sensors’ utilization; (3) foot pose and trajectory estimation methods. Published articles from 1995 until December of 2018 were searched in the PubMed, IEEE Xplore and Google Scholar databases. The research was focused on two categories: (a) zero velocity interval detection methods; and (b) foot pose and traject...
Proceedings of the 16th International Conference on Informatics in Control, Automation and Robotics, 2019
Wheelchairs have improved the lives of many people with limited mobility. Yet, to this day, conve... more Wheelchairs have improved the lives of many people with limited mobility. Yet, to this day, conventional wheelchairs are still not a viable option for mobility independence in cases of people with severe weakness or poor coordination e.g. Amyotrophic Lateral Sclerosis (ALS). Smart wheelchairs (SWs) overcome many of these limitations by adding an extra layer of intelligence to the system. SWs have so far remained mostly inaccessible to the general public, due to a limited market presence and steep costs. This paper thus presents the design and implementation of a novel SW which makes the upgrade of a commercially available motorised wheelchair to a SW a much simpler process. The system is a complete implementation offering low-level hardware control, a specialised ROS architecture and autonomous navigation algorithms allowing shared user control or fully-autonomous movement. Contrary to most other published works, the focus of this paper is to implement a fully-featured working prototype with minimal hardware complexity and an efficient modular software development environment. Initial practical tests in typical use scenarios showcased the successful operation of the complete system. The developed prototype SW has the potential to restore autonomy to people who are unable to use conventional or powered wheelchairs.
Gait & Posture
BACKGROUND Kinematic gait analysis employing multi-segment foot models has been mainly conducted ... more BACKGROUND Kinematic gait analysis employing multi-segment foot models has been mainly conducted in laboratories by means of optical motion capture systems. This type of process requires considerable setup time and is constrained by a limited capture space. A procedure involving the use of multiple inertial measurement units (IMUs) is proposed to overcome these limitations. RESEARCH QUESTION This study presents a new approach for the estimation of the trajectories of a multi-segment foot model by means of multiple IMUs. METHODS To test the proposed method, a system consisting of four IMUs attached to the shank, heel, dorsum and toes segments of the foot, was considered. The performance of the proposed method was compared to that of a conventional method using IMUs adopted from the literature. In addition, an optical motion capture system was used as a reference to assess the performance of the implemented methods. RESULTS Employing the suggested method, all trajectory directions of the shank, heel and dorsum segments, as well as the Z (yaw) direction of the toes segment, have exhibited an error reduction varying between 8% and 55%. However, X (roll) and Y (pitch) direction of the toes segment presented an error increase of 17% and 26%, respectively. The estimation of the vertical displacement, corresponding to the foot clearance, was improved for all segments, resulting in a final mean accuracy and precision of 3.5 ± 2.8 cm, 2.7 ± 2.1 cm, 0.8 ± 0.7 cm and 1.1 ± 0.9 cm for the shank, heel, dorsum and toes segments, respectively. SIGNIFICANCE It has been demonstrated that as an alternative to tracking each foot segment separately, the fusion of multiple IMU measurements using kinematic equations, considerably improves the estimated trajectories, especially when considering vertical foot displacements. The proposed method could complement the use of smaller and cheaper sensors, while still matching the same performance of other published methods, making the suggested approach very attractive for real life applications.
Transactions of the Institute of Measurement and Control
This paper proposes three novel neural network controllers for dual adaptive control of a class o... more This paper proposes three novel neural network controllers for dual adaptive control of a class of functionally uncertain, nonlinear, multiple-input/multiple-output stochastic systems. Both Gaussian radial basis function and sigmoidal multilayer perceptron neural networks are considered for approximation of the unknown dynamic functions. Control and estimation are effected through optimization of a stochastic cost function which elicits the dual effects of caution and probing, resulting in control laws that take into consideration the interactions between estimation and control, leading to improved control performance. The Kalman filter is used for estimation of the weights of the radial basis function network, while the extended and unscented Kalman filter are used for the multilayer perceptron case. The performances of the three schemes are compared and evaluated through extensive Monte Carlo simulations and statistical significance tests.
Journal of Dynamic Systems, Measurement, and Control, 2016
Current research in offshore wind turbines is proposing a novel concept of using seawater-based h... more Current research in offshore wind turbines is proposing a novel concept of using seawater-based hydraulics for large-scale power transmission and centralized electrical generation. The objective of this paper is to investigate the control of such an open-loop circuit, where a fixed line pressure is desirable for the sake of efficiency and stability. Pressure control of the open-loop hydraulic circuit presents an interesting control challenge due to the highly fluctuating flow rate along with the nonlinear behavior of the variable-area orifice used by the pressure controller. The present analysis is limited to a single turbine and an open-loop hydraulic line with a variable-area orifice at the end. A controller is proposed which uses a combination of feed-forward compensation for the nonlinear part along with a feedback loop for correcting any errors resulting from inaccuracies in the compensator model. A numerical model of the system under investigation is developed in order to obse...
Abstract: Adaptive control involves both estimation and control, which are generally interdepende... more Abstract: Adaptive control involves both estimation and control, which are generally interdependent and partly in conflict. Yet, the majority of adaptive controllers separate the two by assuming that certainty equivalence holds, even if this is not the case. In contrast a ...
Abstract: This paper presents experimental results which validate the use of a novel dual adaptiv... more Abstract: This paper presents experimental results which validate the use of a novel dual adaptive controller for mobile robots operating in the presence of dynamic uncertainty. The control scheme, recently proposed by the same authors, has so far been tested by simulations ...
Volume 9: Ocean Renewable Energy, 2015
The viability of offshore wind turbines is presently affected by a number of technical issues per... more The viability of offshore wind turbines is presently affected by a number of technical issues pertaining to the gearbox and power electronic components. Current work is considering the possibility of replacing the generator, gearbox and electrical transmission with a hydraulic system. Efficiency of the hydraulic transmission is around 90% for the selected geometries, which is comparable to the 94% expected for conventional wind turbines. A rotor-driven pump pressurises seawater that is transmitted across a large pipeline to a centralised generator platform. Hydroelectric energy conversion takes place in Pelton turbine. However, unlike conventional hydro-energy plants, the head available at the nozzle entry is highly unsteady. Adequate active control at the nozzle is therefore crucial in maintaining a fixed line pressure and an optimum Pelton turbine operation at synchronous speed. This paper presents a novel control scheme that is based on the combination of proportional feedback co...
Proceedings of the 12th International Conference on Informatics in Control, Automation and Robotics, 2015
This paper proposes and investigates the application of sliding mode control to the ball and plat... more This paper proposes and investigates the application of sliding mode control to the ball and plate problem. The nonlinear properties of the ball and plate control system are first presented. Then the experimental setup designed and built specifically for the purpose of this research is discussed. The paper then focuses on the implementation and thorough evaluation of the experimental results obtained with two different control schemes: the linear full-state feedback controller and the sliding mode controller. The latter control strategy was selected for its robust and order reduction properties. Finally the control performance of the two controllers is analysed. The sliding controller manages to obtain a faster and more accurate operation for continuously changing reference inputs. The robustness of the proposed control scheme is also verified, since the system's performance is shown to be insensitive to parameter variations.