Vittorio Lippi | Universitätsklinikum Freiburg (original) (raw)

Papers by Vittorio Lippi

Sensors, 2024

Using lower-limbs exoskeletons provides potential advantages in terms of productivity and safety ... more Using lower-limbs exoskeletons provides potential advantages in terms of productivity and safety associated with reduced stress. However, complex issues in human-robot interaction are still open, such as the physiological effects of exoskeletons and the impact on the user’s subjective experience. In this work, an innovative exoskeleton, the Wearable Walker, is assessed using the EXPERIENCE benchmarking protocol from the EUROBENCH project. The Wearable Walker is a lower-limb exoskeleton that enhances human abilities, such as carrying loads. The device uses a unique control approach called Blend Control that provides smooth assistance torques. It operates two models simultaneously, one in the case in which the left foot is grounded and another for the grounded right foot. These models generate assistive torques combined to provide continuous and smooth overall assistance, preventing any abrupt changes in torque due to model switching. The EXPERIENCE protocol consists of walking on flat ground while gathering physiological signals such as heart rate, its variability, respiration rate, and galvanic skin response and completing a questionnaire. The test was performed with five healthy subjects. The scope of the present study is twofold: to evaluate the specific exoskeleton and its current control system to gain insight into possible improvements and to present a case study for a formal and replicable benchmarking of wearable robots.

Human and humanoid posture control models usually rely on single or multiple degrees of freedom i... more Human and humanoid posture control models usually rely on single or multiple degrees of freedom inverted pendulum representation of upright stance associated with a feedback controller. In models typically focused on the action between ankles, hips, and knees, the control of head position is often neglected, and the head is considered one with the upper body. However, two of the three main contributors to the human motion sensorium reside in the head: the vestibular and the visual system. As the third contributor, the proprioceptive system is distributed throughout the body. In human neurodegenerative brain diseases of motor control, like Progressive Supranuclear Palsy PSP and Idiopathic Parkinson’s Disease IPD, clinical studies have demonstrated the importance of head motion deficits. is work sp ecifically addresses the control of the head during a perturbed upright stance. A control model for the neck is proposed following the hypothesis of a modular posture control from previous studies. Data from human experiments are used to fit the model and retrieve sets of parameters representative of the behavior obtained in different conditions. e result of the analysis is twofold: validate the model and its underlying hypothesis and provide a system to assess the differences in posture control that can be used to identify the differences between healthy subjects and patients with different conditions. Implications for clinical pathology and application in humanoid and assistive robotics are discussed.

Frontiers in Human Neuroscience

IntroductionGait disturbances are a common consequence of polyneuropathy (PNP) and a major factor... more IntroductionGait disturbances are a common consequence of polyneuropathy (PNP) and a major factor in patients’ reduced quality of life. Less is known about the underlying mechanisms of PNP-related altered motor behavior and its distribution across the body. We aimed to capture whole body movements in PNP during a clinically relevant mobility test, i.e., the Timed Up and Go (TUG). We hypothesize that joint velocity profiles across the entire body would enable a deeper understanding of PNP-related movement alterations. This may yield insights into motor control mechanisms responsible for altered gait in PNP.Methods20 PNP patients (61 ± 14 years) and a matched healthy control group (CG, 60 ± 15 years) performed TUG at (i) preferred and (ii) fast movement speed, and (iii) while counting backward (dual-task). We recorded TUG duration (s) and extracted gait-related parameters [step time (s), step length (cm), and width (cm)] during the walking sequences of TUG and calculated center of mas...

9TH INTERNATIONAL POSTURE SYMPOSIUM, 2023

slows down"-Polyneuropathy as a model for gait disturbances leading to reduced gait speed 9 th In... more slows down"-Polyneuropathy as a model for gait disturbances leading to reduced gait speed 9 th International Posture Symposium 207 frontiersin.org

Frontiers in Human Neuroscience, 2023

Introduction: Gait disturbances are a common consequence of polyneuropathy (PNP) and a major fact... more Introduction: Gait disturbances are a common consequence of polyneuropathy (PNP) and a major factor in patients’ reduced quality of life. Less is known about the underlying mechanisms of PNP-related altered motor behavior and its distribution across the body. We aimed to capture whole body movements in PNP during a clinically relevant mobility test, i.e., the Timed Up and Go (TUG). We hypothesize that joint velocity profiles across the entire body would enable a deeper understanding of PNP-related movement alterations. This may yield insights into motor control mechanisms responsible for altered gait in PNP.

Methods: 20 PNP patients (61 ± 14 years) and a matched healthy control group (CG, 60 ± 15 years) performed TUG at (i) preferred and (ii) fast movement speed, and (iii) while counting backward (dual-task). We recorded TUG duration (s) and extracted gait-related parameters [step time (s), step length (cm), and width (cm)] during the walking sequences of TUG and calculated center of mass (COM) velocity [represents gait speed (cm/s)] and joint velocities (cm/s) (ankles, knees, hips, shoulders, elbows, wrists) with respect to body coordinates during walking; we then derived mean joint velocities and ratios between groups.

Results: Across all TUG conditions, PNP patients moved significantly slower (TUG time, gait speed) with prolonged step time and shorter steps compared to CG. Velocity profiles depend significantly on group designation, TUG condition, and joint. Correlation analysis revealed that joint velocities and gait speed are closely interrelated in individual subjects, with a 0.87 mean velocity ratio between groups.

Discussion: We confirmed a PNP-related slowed gait pattern. Interestingly, joint velocities in the rest of the body measured in body coordinates were in a linear relationship to each other and to COM velocity in space coordinates, despite PNP. Across the whole body, PNP patients reduce, on average, their joint velocities with a factor of 0.87 compared to CG and thus maintain movement patterns in terms of velocity distributions across joints similarly to healthy individuals. This down-scaling of mean absolute joint velocities may be the main source for the altered motor behavior of PNP patients during gait and is due to the poorer quality of their somatosensory information.

Clinical Trial Registration: https://drks.de/search/de, identifier DRKS00016999.

Gait & Posture

Background For humans, control of upright standing posture is a prerequisite for many physical ac... more Background For humans, control of upright standing posture is a prerequisite for many physical activities. Experimentally, this control is often challenged by the motion of the support surface presented as tilt or translation, or some combination thereof. In particular, we have investigated subjects balancing in situations where tilt and translation stimuli were presented in isolation and compared it to a situation where such stimuli occurred simultaneously. Research questions Is the human posture control system in the case of two or more superimposed external disturbances responding to these as if it were dealing with one disturbance? Or does it identify the disturbances individually and as such and respond to them specifically, as suggested in a current concept of disturbance-specific estimations and compensations? Methods We had healthy human subjects controlling their balancing of upright stance on a motion platform while we presented them with different combinations of pseudorandom support surface tilt and translation stimuli alone or in superposition (with peak-to-peak amplitude of 0.5° and 1° for tilt, and 0.8 cm and 1.5 cm for translation). In one set of trials they kept their eyes closed and in a second set open. Furthermore, a simulation was performed to qualitatively evaluate the impact of sensory non-linearities and joint stiffness modulation. Results We found that the experimental conditions 'eyes open' vs. 'eyes closed' always created significant differences (p<0.05) between the frequency response functions. In contrast to this, with different combinations of the tilt and translation stimuli, significant differences between the responses were observed only in 5 cases over the 24 that have been tested. Significance The superposition of translation and tilt can be used to characterize the responses to both stimuli with one trial. When the amplitude of the stimuli is unbalanced (e.g. very small tilt superimposed with a larger translation) the effect of stiffness modulation can be studied.

Gait & Posture, Volume 100, 2023, Pages 139-148, ISSN 0966-6362,, 2023

Background For humans, control of upright standing posture is a prerequisite for many physical ac... more Background For humans, control of upright standing posture is a prerequisite for many physical activities. Experimentally, this control is often challenged by the motion of the support surface presented as tilt or translation, or some combination thereof. In particular, we have investigated subjects balancing in situations where tilt and translation stimuli were presented in isolation and compared it to a situation where such stimuli occurred simultaneously. Research questions

Robotics, Computer Vision and Intelligent Systems, 2022

Similarly to humans, humanoid robots require posture control and balance to walk and interact wit... more Similarly to humans, humanoid robots require posture control and balance to walk and interact with the environment. In this work posture control in perturbed conditions is evaluated as a performance test for humanoid control. A specific performance indicator is proposed: the score is based on the comparison between the body sway of the tested humanoid standing on a moving surface and the sway produced by healthy subjects performing the same experiment. This approach is here oriented to the evaluation of a human-likeness. The measure is tested using a humanoid robot in order to demonstrate a typical usage of the proposed evaluation scheme and an example of how to improve robot control on the basis of such a performance indicator score.

Sportmotorik, 2022

Geschmeidige Bewegungen gelten als energieeffizientes Ergebnis gut koordinierter neuromuskulärer ... more Geschmeidige Bewegungen gelten als energieeffizientes Ergebnis gut koordinierter neuromuskulärer Interaktion (Wong et al., 2021), dagegen kann eine Reduktion der Bewegungsgeschmeidigkeit (Smoothness) auf sensomotorische Störungen hindeuten (Figueiredo et al., 2020). Während herkömmliche Bewegungsanalysen vorranging zeitliche und räumliche Parameter wie Amplitude und Dauer quantifizieren, erlauben neue Smoothness-Maße Rückschlüsse auf die Bewegungsqualität unabhängig von Amplitude oder Geschwindigkeit (Figueiredo et al., 2020) und liefern damit möglicherweise neue Erkenntnisse zur Bewegungskontrolle.
Das Ziel dieser Querschnittsstudie ist es, die Smoothness von Patienten mit sensomotorischem Defizit (Polyneuropathie, PNP) zu untersuchen.

©2012 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for... more ©2012 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. DOI: 10.5555/3523760.3523899 Abstract—This work presents a description of the EXOSMOOTH project, oriented to the benchmarking of lower limb exoskeletons performance. In the field of assisted walking by powered lower limb exoskeletons, the EXOSMOOTH project proposes an experiment that targets two scientific questions. The first question is related to the effectiveness of a novel control strategy for smooth assistance. Current assist strategies are based on controllers that switch the assistance level based on the gait segmentation provided by a finite state machine. The proposed strategy aims at managing pha...

The human-derived sensorimotor control concept DEC (for Disturbance Estimation and Compensation) ... more The human-derived sensorimotor control concept DEC (for Disturbance Estimation and Compensation) is here considered with three issues: (1) DEC can be used in a modular control architecture for multi-DoF applications. (2) DEC can easily be implemented on humanoid robotics platforms that have human-inspired sensors and force-controlled actuations. (3) Comparing different bio-inspired control concepts with each other on the same robot helps to define criteria for human-likeness of control algorithms—with potential benefits for user acceptance in assistive robotics.

This paper introduces a human-derived humanoid control concept that allows voluntary movements wi... more This paper introduces a human-derived humanoid control concept that allows voluntary movements with automatic posture control. The concept consists of a modular control architecture, where each DOF is served by one control module. The control modules are based on the DEC model (DEC, Disturbance Estimation and Compensation). The DEC model combines sensory-derived disturbance estimates for re-active disturbance compensation with predicted-sensory disturbance estimates for compensation of self-produced disturbances. The control modules are interconnected, forming a network whose functionality dynamically reflects the robot’s current state of kinematic activity and its interaction with the external forces that are acting on it. By this, the DEC control allows superposition of several postural and voluntary activities. Keywords—Humanoid; Multi-Task Control; DEC model

Proceedings of the 16th International Conference on Informatics in Control, Automation and Robotics

This paper describes some applications of an incremental implementation of the principal componen... more This paper describes some applications of an incremental implementation of the principal component analysis (PCA). The algorithm updates the transformation coefficients matrix on-line for each new sample, without the need to keep all the samples in memory. The algorithm is formally equivalent to the usual batch version, in the sense that given a sample set the transformation coefficients at the end of the process are the same. The implications of applying the PCA in real time are discussed with the help of data analysis examples. In particular we focus on the problem of the continuity of the PCs during an on-line analysis.

Proceedings of the 10th International Conference on Pattern Recognition Applications and Methods, 2021

This work presents a system to benchmark humanoid posture control and balance performances under ... more This work presents a system to benchmark humanoid posture control and balance performances under perturbed conditions. The specific benchmarking scenario consists, for example, of balancing upright stance while performing voluntary movements on moving surfaces. The system includes a motion platform used to provide the perturbation, an innovative body-tracking system suitable for robots, humans and exoskeletons, control software and a set of predefined perturbations, a humanoid robot used to test algorithms, and analysis software providing state of the art data analysis used to provide quantitative measures of performance. In order to provide versatility, the design of the system is oriented to modularity: all its components can be replaced or extended according to experimental needs, adding additional perturbation profiles, new evaluation principles, and alternative tracking systems. It will be possible to use the system with different kinds of robots and exoskeletons as well as for...

Proceedings of the 18th International Conference on Informatics in Control, Automation and Robotics, 2021

Proceedings of the 16th International Conference on Informatics in Control, Automation and Robotics, 2019

Proceedings of the 17th International Conference on Informatics in Control, Automation and Robotics, 2020

This work describes a tracking system designed for humanoid robots, exoskeletons and humans orien... more This work describes a tracking system designed for humanoid robots, exoskeletons and humans oriented to posture control and balance experiments. The system aims to provide a tool that allows for repeatability of balance experiments across different robotics platforms and control algorithms with the ultimate aim of providing a standardized framework for performance benchmarking. To make the system suitable for different geometries and materials, it relies just on inertial sensors. The system is evaluated with a marker-based optical tracking, performing a trial of a typical posture control and balance experiment. In particular the frequency response function of the body segments respect to the support surface tilt is evaluated.

ArXiv, 2020

Human posture control models are used to analyse neurological experiments and control of humanoid... more Human posture control models are used to analyse neurological experiments and control of humanoid robots. This work focuses on a well-known nonlinear posture control model, the DEC (Disturbance estimate and Compensation). In order to compensate disturbances, unlike other models, DEC feedbacks signals coming from sensor fusion rather than raw sensory signals. In previous works, the DEC model is shown to predict human behavior and to provide a control system for humanoids. In this work, the stability of the system in the sense of Lyapunov is formally analysed. The theoretical findings are combined with simulation results, in which an external perturbation of the support surface reproduces a typical scenario in posture control experiments.

Biosystems & Biorobotics, 2021

Posture control and maintaining balance are fundamental elements of humanoid robot control and ha... more Posture control and maintaining balance are fundamental elements of humanoid robot control and have a significant impact for the performance of robots. The evaluation of robotic performance, at the state of the art, is mostly evaluated at goal level, e.g. with robot competitions. While falling is a typical reason beyond the failure of the humanoid operation, the failure itself does not provide many details about the nature of the underlying problem that can be used to improve the control. In order to provide a more specific analysis of posture control and balance, this contribution presents a set of performance indicators, i.e. indexes that can be used to compare the performance of robots with the human control systems. The inspiration for the proposed tests and indicators comes from human experiments and particular emphasis is placed on human-robot comparison.

Sensors, 2024

Using lower-limbs exoskeletons provides potential advantages in terms of productivity and safety ... more Using lower-limbs exoskeletons provides potential advantages in terms of productivity and safety associated with reduced stress. However, complex issues in human-robot interaction are still open, such as the physiological effects of exoskeletons and the impact on the user’s subjective experience. In this work, an innovative exoskeleton, the Wearable Walker, is assessed using the EXPERIENCE benchmarking protocol from the EUROBENCH project. The Wearable Walker is a lower-limb exoskeleton that enhances human abilities, such as carrying loads. The device uses a unique control approach called Blend Control that provides smooth assistance torques. It operates two models simultaneously, one in the case in which the left foot is grounded and another for the grounded right foot. These models generate assistive torques combined to provide continuous and smooth overall assistance, preventing any abrupt changes in torque due to model switching. The EXPERIENCE protocol consists of walking on flat ground while gathering physiological signals such as heart rate, its variability, respiration rate, and galvanic skin response and completing a questionnaire. The test was performed with five healthy subjects. The scope of the present study is twofold: to evaluate the specific exoskeleton and its current control system to gain insight into possible improvements and to present a case study for a formal and replicable benchmarking of wearable robots.

Human and humanoid posture control models usually rely on single or multiple degrees of freedom i... more Human and humanoid posture control models usually rely on single or multiple degrees of freedom inverted pendulum representation of upright stance associated with a feedback controller. In models typically focused on the action between ankles, hips, and knees, the control of head position is often neglected, and the head is considered one with the upper body. However, two of the three main contributors to the human motion sensorium reside in the head: the vestibular and the visual system. As the third contributor, the proprioceptive system is distributed throughout the body. In human neurodegenerative brain diseases of motor control, like Progressive Supranuclear Palsy PSP and Idiopathic Parkinson’s Disease IPD, clinical studies have demonstrated the importance of head motion deficits. is work sp ecifically addresses the control of the head during a perturbed upright stance. A control model for the neck is proposed following the hypothesis of a modular posture control from previous studies. Data from human experiments are used to fit the model and retrieve sets of parameters representative of the behavior obtained in different conditions. e result of the analysis is twofold: validate the model and its underlying hypothesis and provide a system to assess the differences in posture control that can be used to identify the differences between healthy subjects and patients with different conditions. Implications for clinical pathology and application in humanoid and assistive robotics are discussed.

Frontiers in Human Neuroscience

IntroductionGait disturbances are a common consequence of polyneuropathy (PNP) and a major factor... more IntroductionGait disturbances are a common consequence of polyneuropathy (PNP) and a major factor in patients’ reduced quality of life. Less is known about the underlying mechanisms of PNP-related altered motor behavior and its distribution across the body. We aimed to capture whole body movements in PNP during a clinically relevant mobility test, i.e., the Timed Up and Go (TUG). We hypothesize that joint velocity profiles across the entire body would enable a deeper understanding of PNP-related movement alterations. This may yield insights into motor control mechanisms responsible for altered gait in PNP.Methods20 PNP patients (61 ± 14 years) and a matched healthy control group (CG, 60 ± 15 years) performed TUG at (i) preferred and (ii) fast movement speed, and (iii) while counting backward (dual-task). We recorded TUG duration (s) and extracted gait-related parameters [step time (s), step length (cm), and width (cm)] during the walking sequences of TUG and calculated center of mas...

9TH INTERNATIONAL POSTURE SYMPOSIUM, 2023

slows down"-Polyneuropathy as a model for gait disturbances leading to reduced gait speed 9 th In... more slows down"-Polyneuropathy as a model for gait disturbances leading to reduced gait speed 9 th International Posture Symposium 207 frontiersin.org

Frontiers in Human Neuroscience, 2023

Introduction: Gait disturbances are a common consequence of polyneuropathy (PNP) and a major fact... more Introduction: Gait disturbances are a common consequence of polyneuropathy (PNP) and a major factor in patients’ reduced quality of life. Less is known about the underlying mechanisms of PNP-related altered motor behavior and its distribution across the body. We aimed to capture whole body movements in PNP during a clinically relevant mobility test, i.e., the Timed Up and Go (TUG). We hypothesize that joint velocity profiles across the entire body would enable a deeper understanding of PNP-related movement alterations. This may yield insights into motor control mechanisms responsible for altered gait in PNP.

Methods: 20 PNP patients (61 ± 14 years) and a matched healthy control group (CG, 60 ± 15 years) performed TUG at (i) preferred and (ii) fast movement speed, and (iii) while counting backward (dual-task). We recorded TUG duration (s) and extracted gait-related parameters [step time (s), step length (cm), and width (cm)] during the walking sequences of TUG and calculated center of mass (COM) velocity [represents gait speed (cm/s)] and joint velocities (cm/s) (ankles, knees, hips, shoulders, elbows, wrists) with respect to body coordinates during walking; we then derived mean joint velocities and ratios between groups.

Results: Across all TUG conditions, PNP patients moved significantly slower (TUG time, gait speed) with prolonged step time and shorter steps compared to CG. Velocity profiles depend significantly on group designation, TUG condition, and joint. Correlation analysis revealed that joint velocities and gait speed are closely interrelated in individual subjects, with a 0.87 mean velocity ratio between groups.

Discussion: We confirmed a PNP-related slowed gait pattern. Interestingly, joint velocities in the rest of the body measured in body coordinates were in a linear relationship to each other and to COM velocity in space coordinates, despite PNP. Across the whole body, PNP patients reduce, on average, their joint velocities with a factor of 0.87 compared to CG and thus maintain movement patterns in terms of velocity distributions across joints similarly to healthy individuals. This down-scaling of mean absolute joint velocities may be the main source for the altered motor behavior of PNP patients during gait and is due to the poorer quality of their somatosensory information.

Clinical Trial Registration: https://drks.de/search/de, identifier DRKS00016999.

Gait & Posture

Background For humans, control of upright standing posture is a prerequisite for many physical ac... more Background For humans, control of upright standing posture is a prerequisite for many physical activities. Experimentally, this control is often challenged by the motion of the support surface presented as tilt or translation, or some combination thereof. In particular, we have investigated subjects balancing in situations where tilt and translation stimuli were presented in isolation and compared it to a situation where such stimuli occurred simultaneously. Research questions Is the human posture control system in the case of two or more superimposed external disturbances responding to these as if it were dealing with one disturbance? Or does it identify the disturbances individually and as such and respond to them specifically, as suggested in a current concept of disturbance-specific estimations and compensations? Methods We had healthy human subjects controlling their balancing of upright stance on a motion platform while we presented them with different combinations of pseudorandom support surface tilt and translation stimuli alone or in superposition (with peak-to-peak amplitude of 0.5° and 1° for tilt, and 0.8 cm and 1.5 cm for translation). In one set of trials they kept their eyes closed and in a second set open. Furthermore, a simulation was performed to qualitatively evaluate the impact of sensory non-linearities and joint stiffness modulation. Results We found that the experimental conditions 'eyes open' vs. 'eyes closed' always created significant differences (p<0.05) between the frequency response functions. In contrast to this, with different combinations of the tilt and translation stimuli, significant differences between the responses were observed only in 5 cases over the 24 that have been tested. Significance The superposition of translation and tilt can be used to characterize the responses to both stimuli with one trial. When the amplitude of the stimuli is unbalanced (e.g. very small tilt superimposed with a larger translation) the effect of stiffness modulation can be studied.

Gait & Posture, Volume 100, 2023, Pages 139-148, ISSN 0966-6362,, 2023

Background For humans, control of upright standing posture is a prerequisite for many physical ac... more Background For humans, control of upright standing posture is a prerequisite for many physical activities. Experimentally, this control is often challenged by the motion of the support surface presented as tilt or translation, or some combination thereof. In particular, we have investigated subjects balancing in situations where tilt and translation stimuli were presented in isolation and compared it to a situation where such stimuli occurred simultaneously. Research questions

Robotics, Computer Vision and Intelligent Systems, 2022

Similarly to humans, humanoid robots require posture control and balance to walk and interact wit... more Similarly to humans, humanoid robots require posture control and balance to walk and interact with the environment. In this work posture control in perturbed conditions is evaluated as a performance test for humanoid control. A specific performance indicator is proposed: the score is based on the comparison between the body sway of the tested humanoid standing on a moving surface and the sway produced by healthy subjects performing the same experiment. This approach is here oriented to the evaluation of a human-likeness. The measure is tested using a humanoid robot in order to demonstrate a typical usage of the proposed evaluation scheme and an example of how to improve robot control on the basis of such a performance indicator score.

Sportmotorik, 2022

Geschmeidige Bewegungen gelten als energieeffizientes Ergebnis gut koordinierter neuromuskulärer ... more Geschmeidige Bewegungen gelten als energieeffizientes Ergebnis gut koordinierter neuromuskulärer Interaktion (Wong et al., 2021), dagegen kann eine Reduktion der Bewegungsgeschmeidigkeit (Smoothness) auf sensomotorische Störungen hindeuten (Figueiredo et al., 2020). Während herkömmliche Bewegungsanalysen vorranging zeitliche und räumliche Parameter wie Amplitude und Dauer quantifizieren, erlauben neue Smoothness-Maße Rückschlüsse auf die Bewegungsqualität unabhängig von Amplitude oder Geschwindigkeit (Figueiredo et al., 2020) und liefern damit möglicherweise neue Erkenntnisse zur Bewegungskontrolle.
Das Ziel dieser Querschnittsstudie ist es, die Smoothness von Patienten mit sensomotorischem Defizit (Polyneuropathie, PNP) zu untersuchen.

©2012 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for... more ©2012 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. DOI: 10.5555/3523760.3523899 Abstract—This work presents a description of the EXOSMOOTH project, oriented to the benchmarking of lower limb exoskeletons performance. In the field of assisted walking by powered lower limb exoskeletons, the EXOSMOOTH project proposes an experiment that targets two scientific questions. The first question is related to the effectiveness of a novel control strategy for smooth assistance. Current assist strategies are based on controllers that switch the assistance level based on the gait segmentation provided by a finite state machine. The proposed strategy aims at managing pha...

The human-derived sensorimotor control concept DEC (for Disturbance Estimation and Compensation) ... more The human-derived sensorimotor control concept DEC (for Disturbance Estimation and Compensation) is here considered with three issues: (1) DEC can be used in a modular control architecture for multi-DoF applications. (2) DEC can easily be implemented on humanoid robotics platforms that have human-inspired sensors and force-controlled actuations. (3) Comparing different bio-inspired control concepts with each other on the same robot helps to define criteria for human-likeness of control algorithms—with potential benefits for user acceptance in assistive robotics.

This paper introduces a human-derived humanoid control concept that allows voluntary movements wi... more This paper introduces a human-derived humanoid control concept that allows voluntary movements with automatic posture control. The concept consists of a modular control architecture, where each DOF is served by one control module. The control modules are based on the DEC model (DEC, Disturbance Estimation and Compensation). The DEC model combines sensory-derived disturbance estimates for re-active disturbance compensation with predicted-sensory disturbance estimates for compensation of self-produced disturbances. The control modules are interconnected, forming a network whose functionality dynamically reflects the robot’s current state of kinematic activity and its interaction with the external forces that are acting on it. By this, the DEC control allows superposition of several postural and voluntary activities. Keywords—Humanoid; Multi-Task Control; DEC model

Proceedings of the 16th International Conference on Informatics in Control, Automation and Robotics

This paper describes some applications of an incremental implementation of the principal componen... more This paper describes some applications of an incremental implementation of the principal component analysis (PCA). The algorithm updates the transformation coefficients matrix on-line for each new sample, without the need to keep all the samples in memory. The algorithm is formally equivalent to the usual batch version, in the sense that given a sample set the transformation coefficients at the end of the process are the same. The implications of applying the PCA in real time are discussed with the help of data analysis examples. In particular we focus on the problem of the continuity of the PCs during an on-line analysis.

Proceedings of the 10th International Conference on Pattern Recognition Applications and Methods, 2021

This work presents a system to benchmark humanoid posture control and balance performances under ... more This work presents a system to benchmark humanoid posture control and balance performances under perturbed conditions. The specific benchmarking scenario consists, for example, of balancing upright stance while performing voluntary movements on moving surfaces. The system includes a motion platform used to provide the perturbation, an innovative body-tracking system suitable for robots, humans and exoskeletons, control software and a set of predefined perturbations, a humanoid robot used to test algorithms, and analysis software providing state of the art data analysis used to provide quantitative measures of performance. In order to provide versatility, the design of the system is oriented to modularity: all its components can be replaced or extended according to experimental needs, adding additional perturbation profiles, new evaluation principles, and alternative tracking systems. It will be possible to use the system with different kinds of robots and exoskeletons as well as for...

Proceedings of the 18th International Conference on Informatics in Control, Automation and Robotics, 2021

Proceedings of the 16th International Conference on Informatics in Control, Automation and Robotics, 2019

Proceedings of the 17th International Conference on Informatics in Control, Automation and Robotics, 2020

This work describes a tracking system designed for humanoid robots, exoskeletons and humans orien... more This work describes a tracking system designed for humanoid robots, exoskeletons and humans oriented to posture control and balance experiments. The system aims to provide a tool that allows for repeatability of balance experiments across different robotics platforms and control algorithms with the ultimate aim of providing a standardized framework for performance benchmarking. To make the system suitable for different geometries and materials, it relies just on inertial sensors. The system is evaluated with a marker-based optical tracking, performing a trial of a typical posture control and balance experiment. In particular the frequency response function of the body segments respect to the support surface tilt is evaluated.

ArXiv, 2020

Human posture control models are used to analyse neurological experiments and control of humanoid... more Human posture control models are used to analyse neurological experiments and control of humanoid robots. This work focuses on a well-known nonlinear posture control model, the DEC (Disturbance estimate and Compensation). In order to compensate disturbances, unlike other models, DEC feedbacks signals coming from sensor fusion rather than raw sensory signals. In previous works, the DEC model is shown to predict human behavior and to provide a control system for humanoids. In this work, the stability of the system in the sense of Lyapunov is formally analysed. The theoretical findings are combined with simulation results, in which an external perturbation of the support surface reproduces a typical scenario in posture control experiments.

Biosystems & Biorobotics, 2021

Posture control and maintaining balance are fundamental elements of humanoid robot control and ha... more Posture control and maintaining balance are fundamental elements of humanoid robot control and have a significant impact for the performance of robots. The evaluation of robotic performance, at the state of the art, is mostly evaluated at goal level, e.g. with robot competitions. While falling is a typical reason beyond the failure of the humanoid operation, the failure itself does not provide many details about the nature of the underlying problem that can be used to improve the control. In order to provide a more specific analysis of posture control and balance, this contribution presents a set of performance indicators, i.e. indexes that can be used to compare the performance of robots with the human control systems. The inspiration for the proposed tests and indicators comes from human experiments and particular emphasis is placed on human-robot comparison.

International Conference on Mathematical Analysis and Applications in Science and Engineering, 2024

The frequency response function (FRF) is an established way to describe the outcome of experiment... more The frequency response function (FRF) is an established way to describe the outcome of experiments in posture control literature. The FRF is an empirical transfer function between an input stimulus and the induced body segment sway profile, represented as a vector of complex values associated with a vector of frequencies. Having obtained an FRF from a trial with a subject, it can be useful to quantify the likelihood it belongs to a certain population, e.g., to diagnose a condition or to evaluate the human likeliness of a humanoid robot or a wearable device. In this work, a recently proposed method for FRF statistics based on confidence bands computed with Bootstrap will be summarized, and, on its basis, possible ways to quantify the likelihood of FRFs belonging to a given set will be proposed.

ICINCO , 2023

Timely treatment of stroke is critical to minimize brain damage. Therefore, efforts are being mad... more Timely treatment of stroke is critical to minimize brain damage. Therefore, efforts are being made to educate the public on detecting stroke symptoms, e.g., face, arms, and speech test (FAST). In this position paper, we propose to perform the arm weakness test using the integrated video tracking from an iPhone-some general tests to assess the tracking quality and discuss potential critical points. The test has been performed on 4 stroke patients. The result is compared with the report of the clinician. Although presenting some limitations, the system proved to be able to detect arm weakness as a symptom of stroke. We envisage that introducing a portable body tracking system in such clinical tests will provide advantages in terms of objectivity, repeatability, and the possibility to record and compare groups of patients.

ICINCO, 2023

Human and humanoid posture control models usually rely on single or multiple degrees of freedom i... more Human and humanoid posture control models usually rely on single or multiple degrees of freedom inverted pendulum representation of upright stance associated with a feedback controller. In models typically focused on the action between ankles, hips, and knees, the control of head position is often neglected, and the head is considered one with the upper body. However, two of the three main contributors to the human motion sensorium reside in the head: the vestibular and the visual system. As the third contributor, the proprioceptive system is distributed throughout the body. In human neurodegenerative brain diseases of motor control, like Progressive Supranuclear Palsy PSP and Idiopathic Parkinson’s Disease IPD, clinical studies have demonstrated the importance of head motion deficits. is work sp ecifically addresses the control of the head during a perturbed upright stance. A control model for the neck is proposed following the hypothesis of a modular posture control from previous studies. Data from human experiments are used to fit the model and retrieve sets of parameters representative of the behavior obtained in different conditions. e result of the analysis is twofold: validate the model and its underlying hypothesis and provide a system to assess the differences in posture control that can be used to identify the differences between healthy subjects and patients with different conditions. Implications for clinical pathology and application in humanoid and assistive robotics are discussed.

ABSTRACTS OF THE 8TH INTERNATIONAL POSTURE SYMPOSIUM, 2018

ABSTRACTS OF THE 8 TH POSTURE SYMPOSIUM, 2018

Eurobench Summit 21-22 , 2022

In the field of assisted walking by powered lower limb exoskeletons, the EXOSMOOTH project 1 targ... more In the field of assisted walking by powered lower limb exoskeletons, the EXOSMOOTH project 1 targets an experimental assessment of a novel control strategy for smooth assistance 2. Current assist strategies are based on controllers that switch the assistance level based on the gait segmentation provided by a finite state machine. The proposed strategy manages phase transitions to provide a smoother assistance, thus increasing the device transparency and comfort.

HRI, 2022

This work presents a description of the EXOSMOOTH project, oriented to the benchmarking of lower ... more This work presents a description of the EXOSMOOTH project, oriented to the benchmarking of lower limb exoskeletons performance.
In the field of assisted walking by powered lower limb exoskeletons, the EXOSMOOTH project proposes an experiment that targets two scientific questions. The first question is related to the effectiveness of a novel control strategy for smooth assistance. Current assist strategies are based on controllers that switch the assistance level based on the gait segmentation provided by a finite state machine. The proposed strategy aims at managing phase transitions to provide a smoother assistance to the user, thus increasing the device transparency and comfort for the user. The second question is the role of the actuation at the ankle joint in assisted walking. Many novel exoskeletons devised for industrial applications do not feature an actuated ankle joint. In the EXOSMOOTH project, the ankle joint actuation will be one experimental factor to have a direct assessment of the role of an actuated joint in assisted walking. Preliminary results of 15 healthy subjects walking at different speeds while wearing a lower limb exoskeleton supported the rationale behind this question: having an actuated ankle joint could potentially reduce the torques applied by the user by a maximum value of 85 Nm. The two aforementioned questions will be investigated in a protocol that includes walking on a treadmill and on flat ground, with or without slope, and with a load applied on the back. In addition, the interaction forces measured at the exoskeleton harnesses will be used to assess the comfort of the user and the effectiveness of the control strategy to improve transparency.

ROBOVIS, 2021

Posture control and balance are basic requirements for a humanoid robot performing motor tasks li... more Posture control and balance are basic requirements for a humanoid robot performing motor tasks like walking and interacting with the environment. For this reason, posture control is one of the elements taken into account when evaluating the performance of humanoids. In this work, we describe and analyze a performance indicator based on the comparison between the body sway of a robot standing on a moving surface and the one of healthy subjects performing the same experiment. This approach is here oriented to the evaluation of human likeness. The measure is tested with three human-inspired humanoid posture control systems, the independent channel (IC), the disturbance identification and compensation (DEC), and the eigenmovement (EM) control. The potential and the limitations connected with such human-inspired humanoid control mechanisms are then discussed.

ICPRAM, 2021

Machine learning has shown impressive improvements recently, thanks especially to the results sho... more Machine learning has shown impressive improvements recently, thanks especially to the results shown in deep learning applications. Besides important advancements in the theory, such improvements have been associated with an increment in the complexity of the used models (i.e. the numbers of neurons and connections in neural networks). Bigger models are possible given the amount of data used in the training process is increased accordingly. In medical applications, however, the size of datasets is often limited by the availability of human subjects and the effort required to perform human experiments. This position paper proposes the integration of bioinspired models with machine learning.

IEEE Humanoids Workshop on: performance indicators and benchmarking facilities for bipedal locomotion , 2019

This work describes the technical implementation of a testbed to perform state of the art posture... more This work describes the technical implementation of a testbed to perform state of the art posture control and balance experiments and provides versatile tools for the design of new experiments. The benchmarking is based on measured variables representing body kinematics performed under perturbed conditions. The proposed system is inspired by the experience with human posture control experiments oriented to to characterize and quantify the balancing behavior across subjects of different body size and weight, and to relate balancing problems to insufficiencies in sensors, actuators, or specific disturbances. On this basis it aims to provide quantitative measures of the performance.

8th International Posture Control Symposium, Smolenice, 2018

9th International Posture Symposium, Smolenice Castle, Slovakia, 2023

Lippi, V. Random field theory for testing differences between frequency response functions in pos... more Lippi, V. Random field theory for testing differences between frequency response functions in posturography.