Panagiotis Artemiadis - Academia.edu (original) (raw)

Papers by Panagiotis Artemiadis

2020 8th IEEE RAS/EMBS International Conference for Biomedical Robotics and Biomechatronics (BioRob), 2020

Locomotion is essential for a person’s ability to function in society. When an individual has a c... more Locomotion is essential for a person’s ability to function in society. When an individual has a condition that limits locomotion, such as a lower limb amputation, the performance of a prosthetic often determines the quality of life an individual regains. In recent years, powered prosthetic devices have shown nearly identical replication for human leg motion on non-compliant terrains. However, they still face numerous functional deficits such as increased metabolic cost and instability for walking on surfaces of varying compliance and complexity. This paper proposes joint angles of the biological leg are uniquely altered by surface compliance regardless of a subject’s individual walking pattern. These differences are then displayed and quantified as a way to better characterize able-bodied walking compensation typical with three common terrains: sand, grass and gravel. This study also collects data outdoors using IMU sensors and is not limited by lab setup and conditions. These resul...

Wearable Technologies

This review meta-analysis combines and compares the findings of previously published works in the... more This review meta-analysis combines and compares the findings of previously published works in the field of soft wearable robots (SWRs) that provide active methods of actuation for assistive and augmentative purposes. A thorough investigation of major contributions in the field of an SWR is made to analyze trends in the field focused on fluidic and cable-driven systems, prevalent and successful approaches, and identify the future direction of SWRs and active actuation strategies. Types of soft actuators used in wearables are outlined, as well as general practices for fabrication methods of soft actuators and considerations for human–robot interface designs of garment-like exosuits. An overview of well-known and emerging upper body (UB)- and lower body (LB)-assistive technologies is categorized by the specific joints and degree of freedom (DoF) assisted and which actuator methodology is provided. Different use cases for SWRs are addressed, as well as implementation strategies and desi...

Neurocomputing

Abstract This paper presents a framework to classify motor imagery in the context of multi-class ... more Abstract This paper presents a framework to classify motor imagery in the context of multi-class Brain Computer Interface based on electroencephalography (EEG). Covariance matrices are extracted as the EEG signal descriptors, and different dissimilarity metrics on the manifold of Symmetric Positive Definite (SPD) matrices are investigated to classify these covariance descriptors. Specifically, we compare the performance of the Log Euclidean distance, Stein divergence, Kullback–Leibler divergence and Von Neumann divergence. Furthermore, inspired from the conventional Common Spatial Pattern, discriminant analysis performed directly on the SPD manifold using different mentioned metrics are proposed to improve the classification accuracy. We also propose a new feature, namely Heterogeneous Orders Relevance Composition (HORC), by combining different relevance matrices, such as Covariance, Mutual Information or Kernel Matrix under the Tensor Framework and Multiple Kernel fusion. Multi-Class Multi-Kernel Relevance Vector Machine is adopted to provide a sparse classifier and Bayesian confidence prediction. Finally, we compare the performance of total 16 methods on the dataset IIa of the BCI Competition IV. The results shows that the mentioned dissimilarity metrics perform quite equally on the original manifold, whereas the proposed discrimination methods can improve the accuracy by 3–5% on the reduced dimension manifold.

Applied bionics and biomechanics, 2018

In the last years, several studies have been focused on understanding how the central nervous sys... more In the last years, several studies have been focused on understanding how the central nervous system controls muscles to perform a specific motor task. Although it still remains an open question, muscle synergies have come to be an appealing theory to explain the modular organization of the central nervous system. Even though the neural encoding of muscle synergies remains controversial, a large number of papers demonstrated that muscle synergies are robust across different tested conditions, which are within a day, between days, within a single subject, and between subjects that have similar demographic characteristics. Thus, muscle synergy theory has been largely used in several research fields, such as clinics, robotics, and sports. The present systematical review aims at providing an overview on the applications of muscle synergy theory in clinics, robotics, and sports; in particular, the review is focused on the papers that provide tangible information for (i) diagnosis or path...

2015 IEEE International Conference on Robotics and Automation (ICRA), 2015

As the expansion of the field of robotics has continued, the physical interaction between robots ... more As the expansion of the field of robotics has continued, the physical interaction between robots and humans has become an increasingly important area of study. Many of these physical interactions can be seen as a cooperative task conducted by both the robot and the human. Often, when two humans are interacting, one of them will act as the leader of some aspect of the task and the other will act as a follower. This cooperation may require the switching of roles between leader and follower. This can be further complicated by the fact that different participants may be the leaders of different aspects of the task. Previous research in human-robot cooperation focused on the switching of only a single role. In this paper, we investigate a novel method for the simultaneous switching of two roles between a robot and a human participant. This switching method was examined using both fixed and adaptive parameters that control role switching. Overall, human-robot cooperation was successful in the task 85% of the time when using a non-adaptive method and 95% when using an adaptive control method.

Journal of Biomechanics, 2015

Locomotion involves complex neural networks responsible for automatic and volitional actions. Dur... more Locomotion involves complex neural networks responsible for automatic and volitional actions. During locomotion, motor strategies can rapidly compensate for any obstruction or perturbation that could interfere with forward progression. In this pilot study, we examined the contribution of interlimb pathways for evoking muscle activation patterns in the contralateral limb when a unilateral perturbation was applied and in the case where body weight was externally supported. In particular, the latency of neuromuscular responses was measured, while the stimulus to afferent feedback was limited. The pilot experiment was conducted with six healthy young subjects. It employed the MIT-Skywalker (beta-prototype), a novel device intended for gait therapy. Subjects were asked to walk on the split-belt treadmill, while a fast unilateral perturbation was applied mid-stance by unexpectedly lowering one side of the split-treadmill walking surfaces. Subject's weight was externally supported via the bodyweight support system consisting of an underneath bicycle seat and the torso was stabilized via a loosely fitted chest harness. Both the weight support and the chest harness limited the afferent feedback. The unilateral perturbations evoked changes in the electromyographic activity of the non-perturbed contralateral leg. The latency of all muscle responses exceeded 100 ms, which precludes the conjecture that spinal cord alone is responsible for the perturbation response. It suggests the role of supraspinal or midbrain level pathways at the inter-leg coordination during gait.

Frontiers in human neuroscience, 2015

Sensorimotor control theories propose that the central nervous system exploits expected sensory c... more Sensorimotor control theories propose that the central nervous system exploits expected sensory consequences generated by motor commands for movement planning, as well as online sensory feedback for comparison with expected sensory feedback for monitoring and correcting, if needed, ongoing motor output. In our study, we tested this theoretical framework by quantifying the functional role of expected vs. actual proprioceptive feedback for planning and regulation of gait in humans. We addressed this question by using a novel methodological approach to deliver fast perturbations of the walking surface stiffness, in conjunction with a virtual reality system that provided visual feedback of upcoming changes of surface stiffness. In the "predictable" experimental condition, we asked subjects to learn associating visual feedback of changes in floor stiffness (sand patch) during locomotion to quantify kinematic and kinetic changes in gait prior to and during the gait cycle. In the...

Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2014

Despite holding promise for advances in prostheses and robot teleoperation, myoelectric controlle... more Despite holding promise for advances in prostheses and robot teleoperation, myoelectric controlled interfaces have had limited impact in commercial applications. Simultaneous multifunctional controls are desired, but often lead to frustration by users who cannot easily control the devices using state-of-the-art control schemes. This paper proposes and validates the use of implicit motor control training systems (IM-CTS) to achieve practical implementations of multifunctional myoelectric applications. Subjects implicitly develop muscle synergies needed to control a robotic application through an analogous visual interface without the associated physical constraints which may hinder learning. The learning then naturally transfers to perceived intuitive and robust control of the robotic device. The efficacy of the method is tested by comparing performance between two groups learning controls implicitly via the visual interface and explicitly via the robotic interface, respectively. The...

2013 IEEE/RSJ International Conference on Intelligent Robots and Systems, 2013

IEEE Transactions on Robotics, 2015

ABSTRACT Proportional myoelectric control has been proposed for user-friendly interaction with pr... more ABSTRACT Proportional myoelectric control has been proposed for user-friendly interaction with prostheses, orthoses, and new human–machine interfaces. Recent research has stressed intuitive controls that mimic human intentions. However, these controls have limited accuracy and functionality, resulting in user-specific decoders with upper-bound constraints on performance. Thus, myoelectric controls have yet to realize their potential as a natural interface between humans and multifunctional robotic controls. This study supports a shift in myoelectric control schemes toward proportional simultaneous controls learned through the development of unique muscle synergies. A multiple day study reveals natural emergence of a new muscle synergy space as subjects identify the system dynamics of a myoelectric interface. These synergies correlate with long-term learning, increasing performance over consecutive days. Synergies are maintained after one week, helping subjects retain efficient control and generalize performance to new tasks. The extension to robot control is also demonstrated with a robot arm performing reach-to-grasp tasks in a plane. The ability to enhance, retain, and generalize control, without needing to recalibrate or retrain the system, supports control schemes promoting synergy development, not necessarily user-specific decoders trained on a subset of existing synergies, for efficient myoelectric interfaces designed for long-term use.

Bio-Inspired Computing and Networking, 2011

IEEE Transactions on Biomedical Engineering, 2014

Humans have the inherent ability to perform highly dexterous tasks with their arms, involving mai... more Humans have the inherent ability to perform highly dexterous tasks with their arms, involving maintenance of posture, movement, and interaction with the environment. The latter requires the human to control the dynamic characteristics of the upper limb musculoskeletal system. These characteristics are quantitatively represented by inertia, damping, and stiffness, which are measures of mechanical impedance. Many previous studies have shown that arm posture is a dominant factor in determining the end point impedance on a horizontal plane. This paper presents the characterization of the end point impedance of the human arm in 3-D space. Moreover, it models the regulation of the arm impedance with muscle cocontraction. The characterization is made by route of experimental trials where human subjects maintained arm posture while their arms were perturbed by a robot arm. Furthermore, the subjects were asked to control the level of their arm muscles' cocontraction, using visual feedback, in order to investigate the effect of muscle cocontraction on the arm impedance. The results of this study show an anisotropic increase of arm stiffness due to muscle cocontraction. These results could improve our understanding of the human arm biomechanics, as well as provide implications for human motor control-specifically the control of arm impedance through muscle cocontraction.

2012 IEEE International Conference on Robotics and Automation, 2012

Walking impairments are a common sequela of neurological injury, severely affecting the quality o... more Walking impairments are a common sequela of neurological injury, severely affecting the quality of life of both adults and children. Gait therapy is the traditional approach to ameliorate the problem by re-training the nervous system and there have been some attempts to mechanize such approach. We have recently presented the MIT-Skywalker; a novel device to deliver gait therapy, which, in contrast to previous approaches, takes advantage of the concept of passive walkers and the natural dynamics of the lower ...

ASME Dynamic Systems and Control Conference, 2010

Walking impairments are a common sequela of neurological injury, severely affecting the quality o... more Walking impairments are a common sequela of neurological injury, severely affecting the quality of life of both adults and children. Gait therapy is the traditional approach to ameliorate the problem by re-training the nervous system and there have been some attempts to mechanize such approach. In this paper, we present a novel impedance controller for the MIT-Skywalker. In contrast to previous approaches in mechanized gait therapy, the MIT-Skywalker does not impose a rigid kinematics pattern of normal gait on ...

… on Robotics and …, May 14, 2012

Reaching and grasping of objects in an everyday-life environment seems so simple for humans, thou... more Reaching and grasping of objects in an everyday-life environment seems so simple for humans, though so complicated from an engineering point of view. Humans use a variety of strategies for reaching and grasping anything from the simplest to the most complicated objects, achieving high dexterity and efficiency. This seemingly simple process of reach-to-grasp relies on the complex coordination of the musculoskeletal system of the upper limbs. In this paper, we study the muscular co-activation patterns during a variety of reach-to- ...

Humans perform a wide range of skillful and dexterous motion by adjusting the dynamic characteris... more Humans perform a wide range of skillful and dexterous motion by adjusting the dynamic characteristics of their musculoskeletal system during motion. This capability is based on the non-linear characteristics of the muscles and the motor control architecture that can control motion and exerted force independently. Mechanical impedance (i.e. stiffness, viscosity and inertia) constitutes the most solid characteristic for describing the dynamic behavior of human movements. This paper presents a method for estimating upper limb impedance characteristics in the three-dimensional (3D) space, covering a wide range of the arm workspace. While subjects maintained postures, a seven-degrees-of-freedom (7-DoFs) robot arm was used to produce small displacements of subjects' hands along the three Cartesian axes. The end-point dynamic behavior was modeled using a linear second-order system and the impedance characteristics in the 3D space were identified using the measured forces and motion profiles. Experimental results were confirmed with two subjects.

ieeexplore.ieee.org

There is a great effort during the last decades towards building robotic devices that are worn by... more There is a great effort during the last decades towards building robotic devices that are worn by humans. These devices, called exoskeletons, are used mainly for support and rehabilitation, as well as for augmentation of human capabilities. Providing a control interface for exoskeletons, that would guarantee comfort and safety, as well as efficiency and robustness, is still an issue. This paper presents a methodology for estimating human arm motion and force exerted, using electromyographic (EMG) signals from muscles of the upper limb. The proposed method is able to estimate motion of the human arm as well as force exerted from the upper limb to the environment, when the motion is constrained. Moreover, the method can distinguish the cases in which the motion is constrained or not (i.e. exertion of force versus free motion) which is of great importance for the control of exoskeletons. Furthermore, the method provides a continuous profile of estimated motion and force, in contrast to other methods used in the literature that can only detect initiation of movement or intention of force. The system is tested in an orthosis-like scenario, during planar movements, through various experiments. The experimental results prove the system efficiency, making the proposed methodology a strong candidate for an EMG-based control scheme applied in robotic exoskeletons.

2020 8th IEEE RAS/EMBS International Conference for Biomedical Robotics and Biomechatronics (BioRob), 2020

Locomotion is essential for a person’s ability to function in society. When an individual has a c... more Locomotion is essential for a person’s ability to function in society. When an individual has a condition that limits locomotion, such as a lower limb amputation, the performance of a prosthetic often determines the quality of life an individual regains. In recent years, powered prosthetic devices have shown nearly identical replication for human leg motion on non-compliant terrains. However, they still face numerous functional deficits such as increased metabolic cost and instability for walking on surfaces of varying compliance and complexity. This paper proposes joint angles of the biological leg are uniquely altered by surface compliance regardless of a subject’s individual walking pattern. These differences are then displayed and quantified as a way to better characterize able-bodied walking compensation typical with three common terrains: sand, grass and gravel. This study also collects data outdoors using IMU sensors and is not limited by lab setup and conditions. These resul...

Wearable Technologies

This review meta-analysis combines and compares the findings of previously published works in the... more This review meta-analysis combines and compares the findings of previously published works in the field of soft wearable robots (SWRs) that provide active methods of actuation for assistive and augmentative purposes. A thorough investigation of major contributions in the field of an SWR is made to analyze trends in the field focused on fluidic and cable-driven systems, prevalent and successful approaches, and identify the future direction of SWRs and active actuation strategies. Types of soft actuators used in wearables are outlined, as well as general practices for fabrication methods of soft actuators and considerations for human–robot interface designs of garment-like exosuits. An overview of well-known and emerging upper body (UB)- and lower body (LB)-assistive technologies is categorized by the specific joints and degree of freedom (DoF) assisted and which actuator methodology is provided. Different use cases for SWRs are addressed, as well as implementation strategies and desi...

Neurocomputing

Abstract This paper presents a framework to classify motor imagery in the context of multi-class ... more Abstract This paper presents a framework to classify motor imagery in the context of multi-class Brain Computer Interface based on electroencephalography (EEG). Covariance matrices are extracted as the EEG signal descriptors, and different dissimilarity metrics on the manifold of Symmetric Positive Definite (SPD) matrices are investigated to classify these covariance descriptors. Specifically, we compare the performance of the Log Euclidean distance, Stein divergence, Kullback–Leibler divergence and Von Neumann divergence. Furthermore, inspired from the conventional Common Spatial Pattern, discriminant analysis performed directly on the SPD manifold using different mentioned metrics are proposed to improve the classification accuracy. We also propose a new feature, namely Heterogeneous Orders Relevance Composition (HORC), by combining different relevance matrices, such as Covariance, Mutual Information or Kernel Matrix under the Tensor Framework and Multiple Kernel fusion. Multi-Class Multi-Kernel Relevance Vector Machine is adopted to provide a sparse classifier and Bayesian confidence prediction. Finally, we compare the performance of total 16 methods on the dataset IIa of the BCI Competition IV. The results shows that the mentioned dissimilarity metrics perform quite equally on the original manifold, whereas the proposed discrimination methods can improve the accuracy by 3–5% on the reduced dimension manifold.

Applied bionics and biomechanics, 2018

In the last years, several studies have been focused on understanding how the central nervous sys... more In the last years, several studies have been focused on understanding how the central nervous system controls muscles to perform a specific motor task. Although it still remains an open question, muscle synergies have come to be an appealing theory to explain the modular organization of the central nervous system. Even though the neural encoding of muscle synergies remains controversial, a large number of papers demonstrated that muscle synergies are robust across different tested conditions, which are within a day, between days, within a single subject, and between subjects that have similar demographic characteristics. Thus, muscle synergy theory has been largely used in several research fields, such as clinics, robotics, and sports. The present systematical review aims at providing an overview on the applications of muscle synergy theory in clinics, robotics, and sports; in particular, the review is focused on the papers that provide tangible information for (i) diagnosis or path...

2015 IEEE International Conference on Robotics and Automation (ICRA), 2015

As the expansion of the field of robotics has continued, the physical interaction between robots ... more As the expansion of the field of robotics has continued, the physical interaction between robots and humans has become an increasingly important area of study. Many of these physical interactions can be seen as a cooperative task conducted by both the robot and the human. Often, when two humans are interacting, one of them will act as the leader of some aspect of the task and the other will act as a follower. This cooperation may require the switching of roles between leader and follower. This can be further complicated by the fact that different participants may be the leaders of different aspects of the task. Previous research in human-robot cooperation focused on the switching of only a single role. In this paper, we investigate a novel method for the simultaneous switching of two roles between a robot and a human participant. This switching method was examined using both fixed and adaptive parameters that control role switching. Overall, human-robot cooperation was successful in the task 85% of the time when using a non-adaptive method and 95% when using an adaptive control method.

Journal of Biomechanics, 2015

Locomotion involves complex neural networks responsible for automatic and volitional actions. Dur... more Locomotion involves complex neural networks responsible for automatic and volitional actions. During locomotion, motor strategies can rapidly compensate for any obstruction or perturbation that could interfere with forward progression. In this pilot study, we examined the contribution of interlimb pathways for evoking muscle activation patterns in the contralateral limb when a unilateral perturbation was applied and in the case where body weight was externally supported. In particular, the latency of neuromuscular responses was measured, while the stimulus to afferent feedback was limited. The pilot experiment was conducted with six healthy young subjects. It employed the MIT-Skywalker (beta-prototype), a novel device intended for gait therapy. Subjects were asked to walk on the split-belt treadmill, while a fast unilateral perturbation was applied mid-stance by unexpectedly lowering one side of the split-treadmill walking surfaces. Subject's weight was externally supported via the bodyweight support system consisting of an underneath bicycle seat and the torso was stabilized via a loosely fitted chest harness. Both the weight support and the chest harness limited the afferent feedback. The unilateral perturbations evoked changes in the electromyographic activity of the non-perturbed contralateral leg. The latency of all muscle responses exceeded 100 ms, which precludes the conjecture that spinal cord alone is responsible for the perturbation response. It suggests the role of supraspinal or midbrain level pathways at the inter-leg coordination during gait.

Frontiers in human neuroscience, 2015

Sensorimotor control theories propose that the central nervous system exploits expected sensory c... more Sensorimotor control theories propose that the central nervous system exploits expected sensory consequences generated by motor commands for movement planning, as well as online sensory feedback for comparison with expected sensory feedback for monitoring and correcting, if needed, ongoing motor output. In our study, we tested this theoretical framework by quantifying the functional role of expected vs. actual proprioceptive feedback for planning and regulation of gait in humans. We addressed this question by using a novel methodological approach to deliver fast perturbations of the walking surface stiffness, in conjunction with a virtual reality system that provided visual feedback of upcoming changes of surface stiffness. In the "predictable" experimental condition, we asked subjects to learn associating visual feedback of changes in floor stiffness (sand patch) during locomotion to quantify kinematic and kinetic changes in gait prior to and during the gait cycle. In the...

Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2014

Despite holding promise for advances in prostheses and robot teleoperation, myoelectric controlle... more Despite holding promise for advances in prostheses and robot teleoperation, myoelectric controlled interfaces have had limited impact in commercial applications. Simultaneous multifunctional controls are desired, but often lead to frustration by users who cannot easily control the devices using state-of-the-art control schemes. This paper proposes and validates the use of implicit motor control training systems (IM-CTS) to achieve practical implementations of multifunctional myoelectric applications. Subjects implicitly develop muscle synergies needed to control a robotic application through an analogous visual interface without the associated physical constraints which may hinder learning. The learning then naturally transfers to perceived intuitive and robust control of the robotic device. The efficacy of the method is tested by comparing performance between two groups learning controls implicitly via the visual interface and explicitly via the robotic interface, respectively. The...

2013 IEEE/RSJ International Conference on Intelligent Robots and Systems, 2013

IEEE Transactions on Robotics, 2015

ABSTRACT Proportional myoelectric control has been proposed for user-friendly interaction with pr... more ABSTRACT Proportional myoelectric control has been proposed for user-friendly interaction with prostheses, orthoses, and new human–machine interfaces. Recent research has stressed intuitive controls that mimic human intentions. However, these controls have limited accuracy and functionality, resulting in user-specific decoders with upper-bound constraints on performance. Thus, myoelectric controls have yet to realize their potential as a natural interface between humans and multifunctional robotic controls. This study supports a shift in myoelectric control schemes toward proportional simultaneous controls learned through the development of unique muscle synergies. A multiple day study reveals natural emergence of a new muscle synergy space as subjects identify the system dynamics of a myoelectric interface. These synergies correlate with long-term learning, increasing performance over consecutive days. Synergies are maintained after one week, helping subjects retain efficient control and generalize performance to new tasks. The extension to robot control is also demonstrated with a robot arm performing reach-to-grasp tasks in a plane. The ability to enhance, retain, and generalize control, without needing to recalibrate or retrain the system, supports control schemes promoting synergy development, not necessarily user-specific decoders trained on a subset of existing synergies, for efficient myoelectric interfaces designed for long-term use.

Bio-Inspired Computing and Networking, 2011

IEEE Transactions on Biomedical Engineering, 2014

Humans have the inherent ability to perform highly dexterous tasks with their arms, involving mai... more Humans have the inherent ability to perform highly dexterous tasks with their arms, involving maintenance of posture, movement, and interaction with the environment. The latter requires the human to control the dynamic characteristics of the upper limb musculoskeletal system. These characteristics are quantitatively represented by inertia, damping, and stiffness, which are measures of mechanical impedance. Many previous studies have shown that arm posture is a dominant factor in determining the end point impedance on a horizontal plane. This paper presents the characterization of the end point impedance of the human arm in 3-D space. Moreover, it models the regulation of the arm impedance with muscle cocontraction. The characterization is made by route of experimental trials where human subjects maintained arm posture while their arms were perturbed by a robot arm. Furthermore, the subjects were asked to control the level of their arm muscles' cocontraction, using visual feedback, in order to investigate the effect of muscle cocontraction on the arm impedance. The results of this study show an anisotropic increase of arm stiffness due to muscle cocontraction. These results could improve our understanding of the human arm biomechanics, as well as provide implications for human motor control-specifically the control of arm impedance through muscle cocontraction.

2012 IEEE International Conference on Robotics and Automation, 2012

Walking impairments are a common sequela of neurological injury, severely affecting the quality o... more Walking impairments are a common sequela of neurological injury, severely affecting the quality of life of both adults and children. Gait therapy is the traditional approach to ameliorate the problem by re-training the nervous system and there have been some attempts to mechanize such approach. We have recently presented the MIT-Skywalker; a novel device to deliver gait therapy, which, in contrast to previous approaches, takes advantage of the concept of passive walkers and the natural dynamics of the lower ...

ASME Dynamic Systems and Control Conference, 2010

Walking impairments are a common sequela of neurological injury, severely affecting the quality o... more Walking impairments are a common sequela of neurological injury, severely affecting the quality of life of both adults and children. Gait therapy is the traditional approach to ameliorate the problem by re-training the nervous system and there have been some attempts to mechanize such approach. In this paper, we present a novel impedance controller for the MIT-Skywalker. In contrast to previous approaches in mechanized gait therapy, the MIT-Skywalker does not impose a rigid kinematics pattern of normal gait on ...

… on Robotics and …, May 14, 2012

Reaching and grasping of objects in an everyday-life environment seems so simple for humans, thou... more Reaching and grasping of objects in an everyday-life environment seems so simple for humans, though so complicated from an engineering point of view. Humans use a variety of strategies for reaching and grasping anything from the simplest to the most complicated objects, achieving high dexterity and efficiency. This seemingly simple process of reach-to-grasp relies on the complex coordination of the musculoskeletal system of the upper limbs. In this paper, we study the muscular co-activation patterns during a variety of reach-to- ...

Humans perform a wide range of skillful and dexterous motion by adjusting the dynamic characteris... more Humans perform a wide range of skillful and dexterous motion by adjusting the dynamic characteristics of their musculoskeletal system during motion. This capability is based on the non-linear characteristics of the muscles and the motor control architecture that can control motion and exerted force independently. Mechanical impedance (i.e. stiffness, viscosity and inertia) constitutes the most solid characteristic for describing the dynamic behavior of human movements. This paper presents a method for estimating upper limb impedance characteristics in the three-dimensional (3D) space, covering a wide range of the arm workspace. While subjects maintained postures, a seven-degrees-of-freedom (7-DoFs) robot arm was used to produce small displacements of subjects' hands along the three Cartesian axes. The end-point dynamic behavior was modeled using a linear second-order system and the impedance characteristics in the 3D space were identified using the measured forces and motion profiles. Experimental results were confirmed with two subjects.

ieeexplore.ieee.org

There is a great effort during the last decades towards building robotic devices that are worn by... more There is a great effort during the last decades towards building robotic devices that are worn by humans. These devices, called exoskeletons, are used mainly for support and rehabilitation, as well as for augmentation of human capabilities. Providing a control interface for exoskeletons, that would guarantee comfort and safety, as well as efficiency and robustness, is still an issue. This paper presents a methodology for estimating human arm motion and force exerted, using electromyographic (EMG) signals from muscles of the upper limb. The proposed method is able to estimate motion of the human arm as well as force exerted from the upper limb to the environment, when the motion is constrained. Moreover, the method can distinguish the cases in which the motion is constrained or not (i.e. exertion of force versus free motion) which is of great importance for the control of exoskeletons. Furthermore, the method provides a continuous profile of estimated motion and force, in contrast to other methods used in the literature that can only detect initiation of movement or intention of force. The system is tested in an orthosis-like scenario, during planar movements, through various experiments. The experimental results prove the system efficiency, making the proposed methodology a strong candidate for an EMG-based control scheme applied in robotic exoskeletons.