Ehab Al Khatib | American University of Sharjah (original) (raw)

Papers by Ehab Al Khatib

IEEE robotics and automation letters, Apr 1, 2020

Neurological or biomechanical disorders may distort ankle mechanical impedance and thereby impair... more Neurological or biomechanical disorders may distort ankle mechanical impedance and thereby impair locomotor function. This paper presents a quantitative characterization of multivariable ankle mechanical impedance of young healthy subjects when their muscles were relaxed, to serve as a baseline to compare with pathophysiological ankle properties of biomechanically and/or neurologically impaired patients. Measurements using a highly backdrivable wearable ankle robot combined with multi-input multi-output stochastic system identification methods enabled reliable characterization of ankle mechanical impedance in two degrees-of-freedom (DOFs) simultaneously, the sagittal and frontal planes. The characterization included important ankle properties unavailable from single DOF studies: coupling between DOFs and anisotropy as a function of frequency. Ankle impedance in joint coordinates showed responses largely consistent with a second-order system consisting of inertia, viscosity, and stiffness in both seated (knee flexed) and standing (knee straightened) postures. Stiffness in the sagittal plane was greater than in the frontal plane and furthermore, was greater when standing than when seated, most likely due to the stretch of bi-articular muscles (medial and lateral gastrocnemius). Very low off-diagonal partial coherences implied negligible coupling between dorsiflexion-plantarflexion and inversion-eversion. The directions of principal axes were tilted slightly counterclockwise from the original joint coordinates. The directional variation (anisotropy) of ankle impedance in the 2-D space formed by rotations in the sagittal and frontal planes exhibited a characteristic "peanut" shape, weak in inversion-eversion over a wide range of frequencies from the stiffness dominated region up to the inertia dominated region. Implications for the assessment of neurological and biomechanical impairments are discussed.

Robotics and Autonomous Systems

An external magnetic field can be used to remotely control small-scaled robots, making them promi... more An external magnetic field can be used to remotely control small-scaled robots, making them promising candidates for diverse biomedical and engineering applications. In previous study, we showed that our magnetically actuated millirobot is highly agile and can perform a variety of locomotive tasks such as pivot walking, tumbling, and tapping in a horizontal plane. In this study, we focus on the controlling of the locomotion outcomes of this millirobot in the pivot walking mode. A mathematical model of the system is developed and the kinematic model is derived. The role of the sweep and tilt angles in robot's motion is also investigated. We propose two controllers to regulate the gait of the pivot walker. The first one is a proportional-geometric controller, which determines the correct pivot point that the millirobot should use. Then, it regulates the angular velocity proportionally based on the error between the center of the millirobot and the reference trajectory. The second controller is based on a gradient descent optimization technique, which expresses the control action as an optimization problem. These control algorithms enable the millirobot to generate stable gait while tracking a desired trajectory. A low-cost high-performance magnetic actuator is built to validate the proposed controllers. We conduct a set of different experiments and simulation runs to establish the effectiveness of proposed controllers for different sweep and tilt angles in terms of the tracking error. The two controllers exhibit an appropriate performance, but it is observed that gradient descent based controller yields faster convergence time, smaller tracking error, and fewer number of steps. Finally, we perform an extensive experimentally parametric analysis on the effect of the sweep angle, tilt angle, and step time on the tracking error. As we expect, the optimization-based controller outperforms the geometric based controller.

Autonomous Robots

Small-size robots offer access to spaces that are inaccessible to larger ones. This type of acces... more Small-size robots offer access to spaces that are inaccessible to larger ones. This type of access is crucial in applications such as drug delivery, environmental detection, and collection of small samples. However, there are some tasks that are not possible to perform using only one robot including assembly and manufacturing at small scales, manipulation of micro- and nano- objects, and robot-based structuring of small-scale materials. In this article, we focus on tasks that can be achieved using a group of small-scale robots like pattern formation. These robots are typically externally actuated due to their size limitation. Yet, one faces the challenge of controlling a group of robots using a single global input. In this study, we propose a control algorithm to position individual members of a group in predefined positions. In our previous work, we presented a small-scaled magnetically actuated millirobot. An electromagnetic coil system applied external force and steered the milli...

arXiv (Cornell University), Dec 13, 2019

In this paper, we propose a new Robust Nonlinear Quadratic Gaussian (RNQG) controller based on St... more In this paper, we propose a new Robust Nonlinear Quadratic Gaussian (RNQG) controller based on State-Dependent Riccati Equation (SDRE) scheme for continuous-time nonlinear systems. Existing controllers do not account for combined noise and disturbance acting on the system. The proposed controller is based on a Lyapunov function and a cost function includes states, inputs, outputs, disturbance, and the noise acting on the system. We express the RNQG control law in the form of a traditional Riccati equation. Real time applications of the controller places high computational burden on system implementation. This is mainly due to the nonlinear and complex form of the cost function. In order to solve this problem, this cost function is approximated by a weighted polynomial. The weights are found by using a least squares technique and a neural network. The approximate cost function is incorporated into the controller by employing a method based on Bellman's principle of optimality. Finally, an inertially stabilized inverted pendulum example is used to verify the utility of proposed control approach.

2020 IEEE Aerospace Conference

This study aims to investigate the control of a triangular configuration and triple mass tethered... more This study aims to investigate the control of a triangular configuration and triple mass tethered satellite system using a novel robust H2−HinftyH_{2}-H_{\infty}H2−Hinfty Model Reference Adaptive Control (HMRAC) scheme. The system is actuated by thrusters to generate control forces. The dynamical model of the semi-ideal system, which acts as a reference model is described with a known external disturbance, called the J2J_{2}J2 perturbation. The proposed MRAC design methodology is based on the stable semi-ideal nonlinear reference model, which is regulated by a state feedback controller using H2−HinftyH_{2}-H_{\infty}H2−Hinfty State Dependent Riccati Equation (SDRE) techniques. Then, the real system with the unknown disturbances is controlled by the feedback of the reference model control scheme. The main benefit of using the HMRAC is having robustness of the reference model, which decreases the computational burden of the classical MRAC. The numerical simulation results are presented and compared with the Linear Quadratic Regulator to demonstrate the effectiveness of the proposed control method. Also, the effectiveness of the proposed controller in improving attitude maneuverability is demonstrated.

arXiv (Cornell University), Nov 6, 2021

Small-size robots offer access to spaces that are inaccessible to larger ones. This type of acces... more Small-size robots offer access to spaces that are inaccessible to larger ones. This type of access is crucial in applications such as drug delivery, environmental detection, and collection of small samples. However, there are some tasks that are not possible to perform using only one robot including assembly and manufacturing at small scales, manipulation of micro-and nano-objects, and robot-based structuring of smallscale materials. The solution to this problem is to use a group of robots as a swarm system. Thus, in this article, we focus on tasks that can be achieved using a group of small-scale robots. These robots are typically externally actuated due to their size limitation. Yet, one faces the challenge of controlling a group of robots using a single global input. In this study, we propose a control algorithm to position individual members of a swarm in predefined positions. A single control input applies to the system and moves all robots in the same direction. We also add another control modality by using different length robots. In our previous work [1], we developed a small-scaled magnetically actuated millirobot. An electromagnetic coil system applied external force and steered the millirobots. This millirobot can move in various modes of motion such as pivot walking and tumbling. In this paper, we propose two new designs of these millirobots. In the first design, the magnets are placed at the center of body to reduce the magnetic attraction force between the millirobots. In the second design, the millirobots are of identical length with two extra legs acting as the pivot points. This way we vary pivot separation in design to take advantage of variable speed in pivot walking mode while keeping the speed constant in tumbling mode. This paper presents a general algorithm for positional control of n millirobots with different lengths to move them from given initial positions to final desired ones. This method is based on choosing a leader that is fully controllable. Then, the motions of a group of follower millirobots are regulated by following the leader and determining their appropriate pivot separations in order to implement the intended swarm motion. Simulations and hardware experiments validate these results.

Aerospace Science and Technology, 2021

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

A Master of Science thesis in Mechatronics Engineering by Ehab Al Khatib entitled, "A Naviga... more A Master of Science thesis in Mechatronics Engineering by Ehab Al Khatib entitled, "A Navigation and Control System for a Robot in Indoor/Outdoor Environments," submitted in May 2016. Thesis advisor is Dr. Mohammad A. Jaradat and thesis co-advisor is Dr. Mamoun Abdel-Hafez. Soft and hard copy available.

2020 American Control Conference (ACC), 2020

Journal of Micro-Bio Robotics, 2020

An external magnetic field can be used in remotely controlling magnetic microrobots, making them ... more An external magnetic field can be used in remotely controlling magnetic microrobots, making them promising candidates for diverse biomedical applications, including cell manipulation and therapy. This paper presents a teleoperation scheme to control magnetically actuated microrobots. The system was developed to allow human operators to control the motion for magnetically actuated microrobots and feel their interactions with the environment. The potential applications of the presented system will be in targeted drug delivery, micro-assembly, and biopsy procedures. A haptic interface constituted the core of the teleoperation system. It was used to provide the operator with force feedback to control the microrobots. In particular, virtual interaction forces were computed and transmitted to the human operators to guide them in performing path following tasks. The operating field of the microrobots was haptically rendered to avoid contacts with obstacles. Finally, a basic set of experimental trials were conducted, demonstrating that the average path tracking error was reduced by 67% when haptic feedback was used.

IEEE Access, 2020

This paper presents a low-cost based approach for solving the navigation problem of wheeled mobil... more This paper presents a low-cost based approach for solving the navigation problem of wheeled mobile robots to perform required tasks within indoor and outdoor environments. The presented solution is based on probabilistic approaches for multiple sensor fusion utilizing low-cost visual/inertial sensors. For the outdoor environment, the Extended Kalman Filter (EKF) is used to estimate the robot position and orientation, the system consists of wheel encoders, a reduced inertial sensor system (RISS), and a Global Positioning System (GPS). For the indoor environment, where GPS signals are blocked, another EKF algorithm is proposed using low cost depth sensor (Microsoft Kinect stream). EKF indoor localization is based on landmarks extracted from the depth measurements. A hybrid low-cost reduced navigation system (HLRNS) for indoor and outdoor environments is proposed and validated in both simulation and experimental environments. Additionally, an input-output state feedback linearization (I-O SFL) technique is used to control the robot to track the desired trajectory in such an environment. According to the conducted validation simulation and experimental testing, the proposed HLRNS provides an acceptable performance to be deployed for real-time applications. INDEX TERMS Extended kalman filter, Kinect depth sensor, low-cost navigation, mobile robot, sensor fusion.

Nonlinear Dynamics, 2019

This paper introduces a unique hopping robot based on the inertial actuation concept that can nav... more This paper introduces a unique hopping robot based on the inertial actuation concept that can navigate in three-dimensional environments. Inertial actuators are used to drive the robot. Rotating mass spinners provide the jumping thrust, while flywheels stabilize and control the orientation of the robot. The robot has two modes of motion: flying and ground contact modes. A mathematical model is developed, and equations of motion for both modes are obtained using both Lagrangian method and Euler's moment equations. An adaptive control scheme is developed in order to generate periodic jumping during the ground contact mode. Tracking controllers are used during the flight mode to modify the orientation of the robot. Two tracking controllers are considered in this paper. First, sliding mode control is designed based on Lyapunov approach. Second, state-dependent Riccati equationbased optimal controller is also developed. Then, nonlinear stability of the system is analyzed. We demonstrate that successful control action that drives the system toward a stable periodic orbit is possible. Finally, the simulation results validate the proposed controllers

Advances in Space Research, 2019

Since space debris is a problem that has been continuously increasing, removal missions should be... more Since space debris is a problem that has been continuously increasing, removal missions should be considered. Tethered space system (TSS) has wide application prospects in the future on-orbit missions such as debris removal. However, it is rather complex and difficult for TSS to realize stabilization of tumbling combinations after connecting to the debris. In this paper, the stabilization problem of this combination is studied. An adaptive sliding mode and State-Dependent Riccati Equation control methods are applied on a TSS to stabilize the system and de-orbit the space debris. The tether tension and stability of the in-plane and out-of-plane libration angles of the system are taken into account. The tether can only resist axial stretching. The thrusters, which are the sources of the system inputs are equipped on the satellite. The controllers regulate the tether to remain fully stretched and to decrease the altitude of the orbit continuously. The numerical simulation validates the proposed control schemes for de-orbiting the debris and put it in lower altitude orbit. This makes the debris retrieve to the atmosphere in less time than the actual orbit lifetime. The comparison between two control schemes is discussed.

2015 10th International Symposium on Mechatronics and its Applications (ISMA), 2015

Navigation is an important topic in mobile robots. In this paper, an Extended Kalman Filter (EKF)... more Navigation is an important topic in mobile robots. In this paper, an Extended Kalman Filter (EKF) is used to localize a mobile robot equipped with an encoder, compass, IMU and GPS utilizing three different approaches. Subsequently, an input output state feedback linearization (I-O SFL) method is used to control the robot along the desired robot trajectory. The presented algorithms are verified when the robot was steered along two different track shapes. Additionally, the performance of the method is demonstrated when a fault was simulated on the sensors.

2015 10th International Symposium on Mechatronics and its Applications (ISMA), 2015

Two adaptive trajectory tracking controllers for wheeled mobile robots are tested in this work. A... more Two adaptive trajectory tracking controllers for wheeled mobile robots are tested in this work. Adaptively tuned proportional control is one approach, where as the other controller uses a Universal Adaptive Stabilization (UAS) based technique. Using simulations, the robustness of the above controllers is quantified in the presence of measurement noise. The robustness is measured in terms of the Integral of absolute magnitude of the error (IAE), the Integral of square of the error (ISE), and the Integral of time multiplied by the absolute value of the error (ITAE) criteria. It is observed that the UAS based technique shows fast convergence in the absence of noise. To combat the effect of noise, the authors reset the adaptation gains after the adaptation gains reach a preset bound. With this technique it is found that the UAS based technique converges to the trajectory being tracked faster than the adaptively tuned proportional controller, and also faster than a traditional inputoutput state feedback linearization based controller.

IEEE Robotics and Automation Letters, 2020

Neurological or biomechanical disorders may distort ankle mechanical impedance and thereby impair... more Neurological or biomechanical disorders may distort ankle mechanical impedance and thereby impair locomotor function. This paper presents a quantitative characterization of multivariable ankle mechanical impedance of young healthy subjects when their muscles were relaxed, to serve as a baseline to compare with pathophysiological ankle properties of biomechanically and/or neurologically impaired patients. Measurements using a highly backdrivable wearable ankle robot combined with multi-input multi-output stochastic system identification methods enabled reliable characterization of ankle mechanical impedance in two degrees-of-freedom (DOFs) simultaneously, the sagittal and frontal planes. The characterization included important ankle properties unavailable from single DOF studies: coupling between DOFs and anisotropy as a function of frequency. Ankle impedance in joint coordinates showed responses largely consistent with a second-order system consisting of inertia, viscosity, and stiffness in both seated (knee flexed) and standing (knee straightened) postures. Stiffness in the sagittal plane was greater than in the frontal plane and furthermore, was greater when standing than when seated, most likely due to the stretch of bi-articular muscles (medial and lateral gastrocnemius). Very low off-diagonal partial coherences implied negligible coupling between dorsiflexion-plantarflexion and inversion-eversion. The directions of principal axes were tilted slightly counterclockwise from the original joint coordinates. The directional variation (anisotropy) of ankle impedance in the 2-D space formed by rotations in the sagittal and frontal planes exhibited a characteristic "peanut" shape, weak in inversion-eversion over a wide range of frequencies from the stiffness dominated region up to the inertia dominated region. Implications for the assessment of neurological and biomechanical impairments are discussed.

IEEE robotics and automation letters, Apr 1, 2020

Neurological or biomechanical disorders may distort ankle mechanical impedance and thereby impair... more Neurological or biomechanical disorders may distort ankle mechanical impedance and thereby impair locomotor function. This paper presents a quantitative characterization of multivariable ankle mechanical impedance of young healthy subjects when their muscles were relaxed, to serve as a baseline to compare with pathophysiological ankle properties of biomechanically and/or neurologically impaired patients. Measurements using a highly backdrivable wearable ankle robot combined with multi-input multi-output stochastic system identification methods enabled reliable characterization of ankle mechanical impedance in two degrees-of-freedom (DOFs) simultaneously, the sagittal and frontal planes. The characterization included important ankle properties unavailable from single DOF studies: coupling between DOFs and anisotropy as a function of frequency. Ankle impedance in joint coordinates showed responses largely consistent with a second-order system consisting of inertia, viscosity, and stiffness in both seated (knee flexed) and standing (knee straightened) postures. Stiffness in the sagittal plane was greater than in the frontal plane and furthermore, was greater when standing than when seated, most likely due to the stretch of bi-articular muscles (medial and lateral gastrocnemius). Very low off-diagonal partial coherences implied negligible coupling between dorsiflexion-plantarflexion and inversion-eversion. The directions of principal axes were tilted slightly counterclockwise from the original joint coordinates. The directional variation (anisotropy) of ankle impedance in the 2-D space formed by rotations in the sagittal and frontal planes exhibited a characteristic "peanut" shape, weak in inversion-eversion over a wide range of frequencies from the stiffness dominated region up to the inertia dominated region. Implications for the assessment of neurological and biomechanical impairments are discussed.

Robotics and Autonomous Systems

An external magnetic field can be used to remotely control small-scaled robots, making them promi... more An external magnetic field can be used to remotely control small-scaled robots, making them promising candidates for diverse biomedical and engineering applications. In previous study, we showed that our magnetically actuated millirobot is highly agile and can perform a variety of locomotive tasks such as pivot walking, tumbling, and tapping in a horizontal plane. In this study, we focus on the controlling of the locomotion outcomes of this millirobot in the pivot walking mode. A mathematical model of the system is developed and the kinematic model is derived. The role of the sweep and tilt angles in robot's motion is also investigated. We propose two controllers to regulate the gait of the pivot walker. The first one is a proportional-geometric controller, which determines the correct pivot point that the millirobot should use. Then, it regulates the angular velocity proportionally based on the error between the center of the millirobot and the reference trajectory. The second controller is based on a gradient descent optimization technique, which expresses the control action as an optimization problem. These control algorithms enable the millirobot to generate stable gait while tracking a desired trajectory. A low-cost high-performance magnetic actuator is built to validate the proposed controllers. We conduct a set of different experiments and simulation runs to establish the effectiveness of proposed controllers for different sweep and tilt angles in terms of the tracking error. The two controllers exhibit an appropriate performance, but it is observed that gradient descent based controller yields faster convergence time, smaller tracking error, and fewer number of steps. Finally, we perform an extensive experimentally parametric analysis on the effect of the sweep angle, tilt angle, and step time on the tracking error. As we expect, the optimization-based controller outperforms the geometric based controller.

Autonomous Robots

Small-size robots offer access to spaces that are inaccessible to larger ones. This type of acces... more Small-size robots offer access to spaces that are inaccessible to larger ones. This type of access is crucial in applications such as drug delivery, environmental detection, and collection of small samples. However, there are some tasks that are not possible to perform using only one robot including assembly and manufacturing at small scales, manipulation of micro- and nano- objects, and robot-based structuring of small-scale materials. In this article, we focus on tasks that can be achieved using a group of small-scale robots like pattern formation. These robots are typically externally actuated due to their size limitation. Yet, one faces the challenge of controlling a group of robots using a single global input. In this study, we propose a control algorithm to position individual members of a group in predefined positions. In our previous work, we presented a small-scaled magnetically actuated millirobot. An electromagnetic coil system applied external force and steered the milli...

arXiv (Cornell University), Dec 13, 2019

In this paper, we propose a new Robust Nonlinear Quadratic Gaussian (RNQG) controller based on St... more In this paper, we propose a new Robust Nonlinear Quadratic Gaussian (RNQG) controller based on State-Dependent Riccati Equation (SDRE) scheme for continuous-time nonlinear systems. Existing controllers do not account for combined noise and disturbance acting on the system. The proposed controller is based on a Lyapunov function and a cost function includes states, inputs, outputs, disturbance, and the noise acting on the system. We express the RNQG control law in the form of a traditional Riccati equation. Real time applications of the controller places high computational burden on system implementation. This is mainly due to the nonlinear and complex form of the cost function. In order to solve this problem, this cost function is approximated by a weighted polynomial. The weights are found by using a least squares technique and a neural network. The approximate cost function is incorporated into the controller by employing a method based on Bellman's principle of optimality. Finally, an inertially stabilized inverted pendulum example is used to verify the utility of proposed control approach.

2020 IEEE Aerospace Conference

This study aims to investigate the control of a triangular configuration and triple mass tethered... more This study aims to investigate the control of a triangular configuration and triple mass tethered satellite system using a novel robust H2−HinftyH_{2}-H_{\infty}H2−Hinfty Model Reference Adaptive Control (HMRAC) scheme. The system is actuated by thrusters to generate control forces. The dynamical model of the semi-ideal system, which acts as a reference model is described with a known external disturbance, called the J2J_{2}J2 perturbation. The proposed MRAC design methodology is based on the stable semi-ideal nonlinear reference model, which is regulated by a state feedback controller using H2−HinftyH_{2}-H_{\infty}H2−Hinfty State Dependent Riccati Equation (SDRE) techniques. Then, the real system with the unknown disturbances is controlled by the feedback of the reference model control scheme. The main benefit of using the HMRAC is having robustness of the reference model, which decreases the computational burden of the classical MRAC. The numerical simulation results are presented and compared with the Linear Quadratic Regulator to demonstrate the effectiveness of the proposed control method. Also, the effectiveness of the proposed controller in improving attitude maneuverability is demonstrated.

arXiv (Cornell University), Nov 6, 2021

Small-size robots offer access to spaces that are inaccessible to larger ones. This type of acces... more Small-size robots offer access to spaces that are inaccessible to larger ones. This type of access is crucial in applications such as drug delivery, environmental detection, and collection of small samples. However, there are some tasks that are not possible to perform using only one robot including assembly and manufacturing at small scales, manipulation of micro-and nano-objects, and robot-based structuring of smallscale materials. The solution to this problem is to use a group of robots as a swarm system. Thus, in this article, we focus on tasks that can be achieved using a group of small-scale robots. These robots are typically externally actuated due to their size limitation. Yet, one faces the challenge of controlling a group of robots using a single global input. In this study, we propose a control algorithm to position individual members of a swarm in predefined positions. A single control input applies to the system and moves all robots in the same direction. We also add another control modality by using different length robots. In our previous work [1], we developed a small-scaled magnetically actuated millirobot. An electromagnetic coil system applied external force and steered the millirobots. This millirobot can move in various modes of motion such as pivot walking and tumbling. In this paper, we propose two new designs of these millirobots. In the first design, the magnets are placed at the center of body to reduce the magnetic attraction force between the millirobots. In the second design, the millirobots are of identical length with two extra legs acting as the pivot points. This way we vary pivot separation in design to take advantage of variable speed in pivot walking mode while keeping the speed constant in tumbling mode. This paper presents a general algorithm for positional control of n millirobots with different lengths to move them from given initial positions to final desired ones. This method is based on choosing a leader that is fully controllable. Then, the motions of a group of follower millirobots are regulated by following the leader and determining their appropriate pivot separations in order to implement the intended swarm motion. Simulations and hardware experiments validate these results.

Aerospace Science and Technology, 2021

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

A Master of Science thesis in Mechatronics Engineering by Ehab Al Khatib entitled, "A Naviga... more A Master of Science thesis in Mechatronics Engineering by Ehab Al Khatib entitled, "A Navigation and Control System for a Robot in Indoor/Outdoor Environments," submitted in May 2016. Thesis advisor is Dr. Mohammad A. Jaradat and thesis co-advisor is Dr. Mamoun Abdel-Hafez. Soft and hard copy available.

2020 American Control Conference (ACC), 2020

Journal of Micro-Bio Robotics, 2020

An external magnetic field can be used in remotely controlling magnetic microrobots, making them ... more An external magnetic field can be used in remotely controlling magnetic microrobots, making them promising candidates for diverse biomedical applications, including cell manipulation and therapy. This paper presents a teleoperation scheme to control magnetically actuated microrobots. The system was developed to allow human operators to control the motion for magnetically actuated microrobots and feel their interactions with the environment. The potential applications of the presented system will be in targeted drug delivery, micro-assembly, and biopsy procedures. A haptic interface constituted the core of the teleoperation system. It was used to provide the operator with force feedback to control the microrobots. In particular, virtual interaction forces were computed and transmitted to the human operators to guide them in performing path following tasks. The operating field of the microrobots was haptically rendered to avoid contacts with obstacles. Finally, a basic set of experimental trials were conducted, demonstrating that the average path tracking error was reduced by 67% when haptic feedback was used.

IEEE Access, 2020

This paper presents a low-cost based approach for solving the navigation problem of wheeled mobil... more This paper presents a low-cost based approach for solving the navigation problem of wheeled mobile robots to perform required tasks within indoor and outdoor environments. The presented solution is based on probabilistic approaches for multiple sensor fusion utilizing low-cost visual/inertial sensors. For the outdoor environment, the Extended Kalman Filter (EKF) is used to estimate the robot position and orientation, the system consists of wheel encoders, a reduced inertial sensor system (RISS), and a Global Positioning System (GPS). For the indoor environment, where GPS signals are blocked, another EKF algorithm is proposed using low cost depth sensor (Microsoft Kinect stream). EKF indoor localization is based on landmarks extracted from the depth measurements. A hybrid low-cost reduced navigation system (HLRNS) for indoor and outdoor environments is proposed and validated in both simulation and experimental environments. Additionally, an input-output state feedback linearization (I-O SFL) technique is used to control the robot to track the desired trajectory in such an environment. According to the conducted validation simulation and experimental testing, the proposed HLRNS provides an acceptable performance to be deployed for real-time applications. INDEX TERMS Extended kalman filter, Kinect depth sensor, low-cost navigation, mobile robot, sensor fusion.

Nonlinear Dynamics, 2019

This paper introduces a unique hopping robot based on the inertial actuation concept that can nav... more This paper introduces a unique hopping robot based on the inertial actuation concept that can navigate in three-dimensional environments. Inertial actuators are used to drive the robot. Rotating mass spinners provide the jumping thrust, while flywheels stabilize and control the orientation of the robot. The robot has two modes of motion: flying and ground contact modes. A mathematical model is developed, and equations of motion for both modes are obtained using both Lagrangian method and Euler's moment equations. An adaptive control scheme is developed in order to generate periodic jumping during the ground contact mode. Tracking controllers are used during the flight mode to modify the orientation of the robot. Two tracking controllers are considered in this paper. First, sliding mode control is designed based on Lyapunov approach. Second, state-dependent Riccati equationbased optimal controller is also developed. Then, nonlinear stability of the system is analyzed. We demonstrate that successful control action that drives the system toward a stable periodic orbit is possible. Finally, the simulation results validate the proposed controllers

Advances in Space Research, 2019

Since space debris is a problem that has been continuously increasing, removal missions should be... more Since space debris is a problem that has been continuously increasing, removal missions should be considered. Tethered space system (TSS) has wide application prospects in the future on-orbit missions such as debris removal. However, it is rather complex and difficult for TSS to realize stabilization of tumbling combinations after connecting to the debris. In this paper, the stabilization problem of this combination is studied. An adaptive sliding mode and State-Dependent Riccati Equation control methods are applied on a TSS to stabilize the system and de-orbit the space debris. The tether tension and stability of the in-plane and out-of-plane libration angles of the system are taken into account. The tether can only resist axial stretching. The thrusters, which are the sources of the system inputs are equipped on the satellite. The controllers regulate the tether to remain fully stretched and to decrease the altitude of the orbit continuously. The numerical simulation validates the proposed control schemes for de-orbiting the debris and put it in lower altitude orbit. This makes the debris retrieve to the atmosphere in less time than the actual orbit lifetime. The comparison between two control schemes is discussed.

2015 10th International Symposium on Mechatronics and its Applications (ISMA), 2015

Navigation is an important topic in mobile robots. In this paper, an Extended Kalman Filter (EKF)... more Navigation is an important topic in mobile robots. In this paper, an Extended Kalman Filter (EKF) is used to localize a mobile robot equipped with an encoder, compass, IMU and GPS utilizing three different approaches. Subsequently, an input output state feedback linearization (I-O SFL) method is used to control the robot along the desired robot trajectory. The presented algorithms are verified when the robot was steered along two different track shapes. Additionally, the performance of the method is demonstrated when a fault was simulated on the sensors.

2015 10th International Symposium on Mechatronics and its Applications (ISMA), 2015

Two adaptive trajectory tracking controllers for wheeled mobile robots are tested in this work. A... more Two adaptive trajectory tracking controllers for wheeled mobile robots are tested in this work. Adaptively tuned proportional control is one approach, where as the other controller uses a Universal Adaptive Stabilization (UAS) based technique. Using simulations, the robustness of the above controllers is quantified in the presence of measurement noise. The robustness is measured in terms of the Integral of absolute magnitude of the error (IAE), the Integral of square of the error (ISE), and the Integral of time multiplied by the absolute value of the error (ITAE) criteria. It is observed that the UAS based technique shows fast convergence in the absence of noise. To combat the effect of noise, the authors reset the adaptation gains after the adaptation gains reach a preset bound. With this technique it is found that the UAS based technique converges to the trajectory being tracked faster than the adaptively tuned proportional controller, and also faster than a traditional inputoutput state feedback linearization based controller.

IEEE Robotics and Automation Letters, 2020

Neurological or biomechanical disorders may distort ankle mechanical impedance and thereby impair... more Neurological or biomechanical disorders may distort ankle mechanical impedance and thereby impair locomotor function. This paper presents a quantitative characterization of multivariable ankle mechanical impedance of young healthy subjects when their muscles were relaxed, to serve as a baseline to compare with pathophysiological ankle properties of biomechanically and/or neurologically impaired patients. Measurements using a highly backdrivable wearable ankle robot combined with multi-input multi-output stochastic system identification methods enabled reliable characterization of ankle mechanical impedance in two degrees-of-freedom (DOFs) simultaneously, the sagittal and frontal planes. The characterization included important ankle properties unavailable from single DOF studies: coupling between DOFs and anisotropy as a function of frequency. Ankle impedance in joint coordinates showed responses largely consistent with a second-order system consisting of inertia, viscosity, and stiffness in both seated (knee flexed) and standing (knee straightened) postures. Stiffness in the sagittal plane was greater than in the frontal plane and furthermore, was greater when standing than when seated, most likely due to the stretch of bi-articular muscles (medial and lateral gastrocnemius). Very low off-diagonal partial coherences implied negligible coupling between dorsiflexion-plantarflexion and inversion-eversion. The directions of principal axes were tilted slightly counterclockwise from the original joint coordinates. The directional variation (anisotropy) of ankle impedance in the 2-D space formed by rotations in the sagittal and frontal planes exhibited a characteristic "peanut" shape, weak in inversion-eversion over a wide range of frequencies from the stiffness dominated region up to the inertia dominated region. Implications for the assessment of neurological and biomechanical impairments are discussed.