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  • Costas S. Tzafestas is an Associate Professor of Robotics at the School of Electrical and Computer Engineering, Natio... moreedit
This paper presents ORB-LINE-SLAM, a real-time hybrid point-line and only-line based visual SLAM system for stereo cameras which can operate in standard CPUs. This work is based on the ORB-SLAM3 open-source library, which is here expanded... more
This paper presents ORB-LINE-SLAM, a real-time hybrid point-line and only-line based visual SLAM system for stereo cameras which can operate in standard CPUs. This work is based on the ORB-SLAM3 open-source library, which is here expanded and adapted to further cope with line features. The main contribution of this paper concerns the introduction of an adaptation scheme, based on an experimentally tuned adapting factor, which aims to achieve a more efficient fusion of point and line features during the SLAM process. Furthermore, to the best of our knowledge, this work constitutes the first open-source visual SLAM system that has the ability to perform effectively by using exclusively line features. This paper also performs a systematic comparison of different error functions used in the bundle adjustment process, to deduce which ones are the more efficient for the visual SLAM problem. The experimental results obtained indicate that the proposed point-line method significantly improv...
This paper presents assessment findings of the “i-Walk” robotic rehabilitation assistant. i-Walk provides support to target groups of people with cognitive and/or mobility deficits via a pioneer robotic rollator that utilizes innovation... more
This paper presents assessment findings of the “i-Walk” robotic rehabilitation assistant. i-Walk provides support to target groups of people with cognitive and/or mobility deficits via a pioneer robotic rollator that utilizes innovation in multimodal robot perception, user-adaptive robot autonomy and natural human-robot interaction. The i-Walk rollator was thoroughly evaluated in terms of its usability and acceptance from its intended end users (patients and therapists) in a rehabilitation centre. i-Walk was tested (i) as a whole, and in terms of (ii) its navigation and human-robot interaction functionalities, (iii) the provided walking support, and (iv) the rehabilitation exercises it offers. In total, twenty-two patients and twelve therapists evaluated the device under real conditions. The paper presents the findings from the evaluation testing of the i-Walk platform. A systematic methodology and protocol were used to test the intelligent robotic rehabilitation assistant in three ...
This paper presents a contribution to the active field of robotics research to support the development of social skills and capabilities in children with Autism Spectrum Disorders as well as Typically Developing children. We present... more
This paper presents a contribution to the active field of robotics research to support the development of social skills and capabilities in children with Autism Spectrum Disorders as well as Typically Developing children. We present preliminary results of a novel experiment where classical roles are reversed: children are here the teachers giving positive or negative reinforcement to the Kaspar robot to make it learn arbitrary associations between toys and locations where to tidy them. The goal is to help children change perspective, and understand that sometimes a learning agent needs several repetitions before correctly learning something. We developed a reinforcement learning algorithm enabling Kaspar to verbally convey its uncertainty along learning, so as to better inform the interacting child of the reasons behind successes and failures made by the robot. Overall, 30 children aged between 7 and 8 (19 girls, 11 boys) performed 16 sessions of the experiment in groups, and manage...
This paper presents a contribution aiming at testing novel child–robot teaching schemes that could be used in future studies to support the development of social and collaborative skills of children with autism spectrum disorders (ASD).... more
This paper presents a contribution aiming at testing novel child–robot teaching schemes that could be used in future studies to support the development of social and collaborative skills of children with autism spectrum disorders (ASD). We present a novel experiment where the classical roles are reversed: in this scenario the children are the teachers providing positive or negative reinforcement to the Kaspar robot in order for it to learn arbitrary associations between different toy names and the locations where they are positioned. The objective is to stimulate interaction and collaboration between children while teaching the robot, and also provide them tangible examples to understand that sometimes learning requires several repetitions. To facilitate this game, we developed a reinforcement learning algorithm enabling Kaspar to verbally convey its level of uncertainty during the learning process, so as to better inform the children about the reasons behind its successes and failu...
Fast adaptation to changes in the environment requires both natural and artificial agents to be able to dynamically tune an exploration-exploitation trade-off during learning. This trade-off usually determines a fixed proportion of... more
Fast adaptation to changes in the environment requires both natural and artificial agents to be able to dynamically tune an exploration-exploitation trade-off during learning. This trade-off usually determines a fixed proportion of exploitative choices (i.e. choice of the action that subjectively appears as best at a given moment) relative to exploratory choices (i.e. testing other actions that now appear worst but may turn out promising later). The problem of finding an efficient exploration-exploitation trade-off has been well studied both in the Machine Learning and Computational Neuroscience fields. Rather than using a fixed proportion, non-stationary multi-armed bandit methods in the former have proven that principles such as exploring actions that have not been tested for a long time can lead to performance closer to optimal - bounded regret. In parallel, researches in the latter have investigated solutions such as progressively increasing exploita- tion in response to improve...
Acquisition and annotation of a multimodal-multisensory data set of human-passive rollator-carer interactions have enabled the analysis of related human behavioural patterns and the definition of the MOBOT human-robot communication model.... more
Acquisition and annotation of a multimodal-multisensory data set of human-passive rollator-carer interactions have enabled the analysis of related human behavioural patterns and the definition of the MOBOT human-robot communication model. The MOBOT project has envisioned the development of cognitive robotic assistant prototypes that act proactively, adaptively and interactively with respect to elderly humans with slight walking and cognitive difficulties. To meet the project’s goals, a multimodal action recognition system is being developed to monitor, analyse and predict user actions with a high level of accuracy and detail. In the same framework, the analysis of human behaviour data that have become available through the project’s multimodal-multisensory corpus, have led to the modelling of Human-Robot Communication in order to achieve an effective, natural interaction between users and the assistive robotic platform. Here, we discuss how the project’s communication model has been integrated in the robotic platform in order to support a natural multimodal human-robot interaction.
This paper reports on work related to the modelling of Human-Robot Communication on the basis of multimodal and multisensory human behaviour analysis. A primary focus in this framework of analysis is the definition of semantics of human... more
This paper reports on work related to the modelling of Human-Robot Communication on the basis of multimodal and multisensory human behaviour analysis. A primary focus in this framework of analysis is the definition of semantics of human actions, i.e. verbal and non-verbal signals, in a specific context with distinct Human-Robot interaction states. These states are captured and represented in terms of communicative behavioural patterns that influence, and in turn are adapted to the interaction flow with the goal to feed a multimodal human-robot communication system. This multimodal HRI model is defined upon, and ensures the usability of a multimodal sensory corpus acquired as a primary source of data retrieval, analysis and testing of mobility assistive robot prototypes.
Elderly and mobility impaired people need special attention during bathing activities, since these tasks are demanding in body flexibility. Our aim is to build an assistive robotic bathing system, in order to increase the independence and... more
Elderly and mobility impaired people need special attention during bathing activities, since these tasks are demanding in body flexibility. Our aim is to build an assistive robotic bathing system, in order to increase the independence and safety of this procedure. Towards this end, the expertise of professional carers for bathing sequences and appropriate motions have to be adopted, in order to achieve natural, physical human - robot interaction. In this paper a Navigation Function (NF) approach is proposed in order to reproduce the way an expert clinical carer executes the bathing activities by means of construction repulsive potential fields ("virtual obstacles") for an assistive bath robot. The produced vector field, constructed based on the demonstration procedure, is used for real-time motion behavior planning tasks, which exploits the visual information from Depth sensors and the advantages of the NF approach, to estimate the reference pose for the end- effector of the assistive robotic system. The proposed method guarantees globally asymptotic convergence to the learned from demonstration washing motion, within the deformable and moving body-part limits, while in addition, restricted areas on the body surface are avoided. The proposed method is evaluated using real experimental data, obtained from human subjects during pouring water task demonstration.
This paper presents the concept and the architecture of the I-SUPPORT service robotics system. The goal of the I-SUPPORT system is to support and enhance older adults mobility, manipulation and force exertion abilities and assist them in... more
This paper presents the concept and the architecture of the I-SUPPORT service robotics system. The goal of the I-SUPPORT system is to support and enhance older adults mobility, manipulation and force exertion abilities and assist them in successfully, safely and independently completing the entire sequence of showering tasks, such as properly washing their back, their upper parts, their lower limbs, their buttocks and groin, and to effectively use the towel for drying purposes. Adaptation and integration of state-of-the-art, cost-effective, softrobotic arms will provide the hardware constituents, which, together with advanced human-robot force/compliance control will form the basis for a safe physical human-robot interaction that complies with the most up-to-date safety standards. Human behavioural, sociological, safety, ethical and acceptability aspects, as well as financial factors related to the proposed service robotics system will be thoroughly investigated and evaluated so tha...
We present a robot following behavior, which enables a mobility assistance robot to follow the user from the front. Although this behavior is desirable in various circumstances, it has received scarce attention. Our proposed solution... more
We present a robot following behavior, which enables a mobility assistance robot to follow the user from the front. Although this behavior is desirable in various circumstances, it has received scarce attention. Our proposed solution consists of a kinematic control scheme, tied to a human position estimator based on a Laser Range Finder. Experiments have been performed in an indoor environment with ten users, and the results have been analyzed and presented. We show that the control is feasible but inserts a cognitive load on the users, who tend to “drive” the robot to the optimal paths they would take under normal conditions.
A common problem for the elderly population with mobility impairment is the difficulties in performing Activities of Daily Living (ADLs), that consequently leads to restrictions and the degradation of the living standards of the elders.... more
A common problem for the elderly population with mobility impairment is the difficulties in performing Activities of Daily Living (ADLs), that consequently leads to restrictions and the degradation of the living standards of the elders. When designing a user-centered assistive device for mobility constrained people, the variable spectrum of disabilities is a factor that should affect the design process, since people with different impairments have different needs to be covered by the device, thus an adaptive behavior of those systems to real user needs is necessary. In this paper, we present the methodological principles and technologies, for the designing of the robotic rollator platform Human Robot Interaction (HRI) environment. The reported work builds upon experience gained from previous engagement with development of the multimodal HRI communication model of an assistive robotic rollator and its end-user evaluation, leading to our enhanced methodology for identifying and priori...
Using assistive robots for educational applications requires robots to be able to adapt their behavior specifically for each child with whom they interact.Among relevant signals, non-verbal cues such as the child’s gaze can provide the... more
Using assistive robots for educational applications requires robots to be able to adapt their behavior specifically for each child with whom they interact.Among relevant signals, non-verbal cues such as the child’s gaze can provide the robot with important information about the child’s current engagement in the task, and whether the robot should continue its current behavior or not. Here we propose a reinforcement learning algorithm extended with active state-specific exploration and show its applicability to child engagement maximization as well as more classical tasks such as maze navigation. We first demonstrate its adaptive nature on a continuous maze problem as an enhancement of the classic grid world. There, parameterized actions enable the agent to learn single moves until the end of a corridor, similarly to “options” but without explicit hierarchical representations.We then apply the algorithm to a series of simulated scenarios, such as an extended Tower of Hanoi where the r...
Online human leg tracking and gait analysis are crucial functionalities for mobility assistant robots, like intelligent walkers. Usually, such walkers are equipped with various sensors for the extraction of human-related features for... more
Online human leg tracking and gait analysis are crucial functionalities for mobility assistant robots, like intelligent walkers. Usually, such walkers are equipped with various sensors for the extraction of human-related features for adaptive human-robot interaction and assistance. We treat the gait detection problem jointly, presenting a novel method for detecting and recognizing gait features from 2D range data produced by a laser sensor mounted on a robotic walker. We propose an effective Convolutional Neural Network (CNN) as a powerful feature extractor for detecting the user’s leg centers in range data represented as occupancy grid maps. We couple the CNN with a Long Short Term Memory (LSTM) network for learning the legs’ motion temporal dynamics while walking, improving the prior detection, and providing better leg occlusion handling. Moreover, we perform gait analysis by recognizing gait phases over both legs by feeding the leg tracking output to a subsequent LSTM. Our proposed lightweight framework has been trained and tested on real patients-data. The presented experimental results show our method’s efficiency in providing accurate detections compared to state-of-the-art and application to an online system due to its high frequency, making it a competitive method for gait detection on robotic mobility assistants.
Mobility impairment is a common problem for the elderly population which relates to difficulties in performing Activities of Daily Living (ADLs) and consequently leads to restrictions and the degradation of the living standards of the... more
Mobility impairment is a common problem for the elderly population which relates to difficulties in performing Activities of Daily Living (ADLs) and consequently leads to restrictions and the degradation of the living standards of the elders. When designing a user-friendly assistive device for mobility constrained people, the variable spectrum of disabilities is a factor that should affect the design process, since people with different impairments have different needs to be covered by the device, thus an adaptive behavior of those systems is necessary. Also, the performance of bathing activities includes several challenges for the elderly people, since such tasks require body flexibility. In this paper, we present current frameworks and solutions for intelligent robotic systems for assistive living involving human robot interaction in a natural interface. Our aim is to build such systems, in order to increase the independence and safety of these procedures. To achieve human - robot interaction in a natural way, we have to adapt the expertise of carers regarding bathing motions and walking assistance. The main goal of this work is to present recent research results towards the development of two real-life use cases incorporating intelligent robotic systems, aiming to support mobility and bathing activities for the elderly in order to provide context-aware and user-adaptive assistance.
The MOBOT project has envisioned the development of cognitive robotic assistant prototypes that act proactively, adaptively and interactively with respect to elderly humans with slight walking and cognitive difficulties. To meet the... more
The MOBOT project has envisioned the development of cognitive robotic assistant prototypes that act proactively, adaptively and interactively with respect to elderly humans with slight walking and cognitive difficulties. To meet the project's goals, a multimodal action recognition system is being developed to monitor, analyse and predict user actions with a high level of accuracy and detail. Here we discuss how the analysis of human behaviour data that have become available through the annotation and study of the project's multimodal-multisensory corpus, have led to the modelling of Human-Robot Communication in order to achieve an effective, natural interaction between users and the assistive robotic platform, intending to show how the project's communication model has been integrated in the robotic platform in order to support a natural multimodal human-robot interaction as verified by systematic end user validation cycles.
Tracking human gait accurately and robustly constitutes a key factor for a smart robotic walker, aiming to provide assistance to patients with different mobility impairment. A context-aware assistive robot needs constant knowledge of the... more
Tracking human gait accurately and robustly constitutes a key factor for a smart robotic walker, aiming to provide assistance to patients with different mobility impairment. A context-aware assistive robot needs constant knowledge of the user's kinematic state to assess the gait status and adjust its movement properly to provide optimal assistance. In this work, we experimentally validate the performance of two gait tracking algorithms using data from elderly patients; the first algorithm employs a Kalman Filter (KF), while the second one tracks the user legs separately using two probabilistically associated Particle Filters (PFs). The algorithms are compared according to their accuracy and robustness, using data captured from real experiments, where elderly subjects performed specific walking scenarios with physical assistance from a prototype Robotic Rollator. Sensorial data were provided by a laser rangefinder mounted on the robotic platform recording the movement of the user...
We present the i-Walk system1, a novel framework for intelligent mobility assistance applications. The proposed system is capable of automatically understanding human activity, assessing mobility and rehabilitation progress, recognizing... more
We present the i-Walk system1, a novel framework for intelligent mobility assistance applications. The proposed system is capable of automatically understanding human activity, assessing mobility and rehabilitation progress, recognizing human intentions and communicating with the patients by giving meaningful feedback. To this end, multiple sensors, i.e. cameras, microphones, lasers, provide multimodal data in order to allow for user monitoring, while state-of-theart and beyond algorithms have been developed and integrated into the system to enable recognition, interaction and assessment. More specifically, i-Walk performs in real-time and consists of four main sub-modules that interact automatically to provide speech understanding, activity recognition, mobility analysis and multimodal communication for seamless HRI. The i-Walk assessment system is evaluated on a database of healthy subjects and patients, who participated in carefully designed experimental scenarios that cover esse...
When designing a user-friendly Mobility Assistive Device (MAD) for mobility constrained people, it is important to take into account the diverse spectrum of disabilities, which results to completely different needs to be covered by the... more
When designing a user-friendly Mobility Assistive Device (MAD) for mobility constrained people, it is important to take into account the diverse spectrum of disabilities, which results to completely different needs to be covered by the MAD for each specific user. An intelligent adaptive behavior is necessary. In this work we present experimental results, using an in house developed methodology for assessing the gait of users with different mobility status while interacting with a robotic MAD. We use data from a laser scanner, mounted on the MAD to track the legs using Particle Filters and Probabilistic Data Association (PDA-PF). The legs' states are fed to an HMM-based pathological gait cycle recognition system to compute in real-time the gait parameters that are crucial for the mobility status characterization of the user. We aim to show that a gait assessment system would be an important feedback for an intelligent MAD. Thus, we use this system to compare the gaits of the subj...
We present a feedback equivalence transformation for the Dubins airplane model, which maps a monotone reference curve in space, to a straight line. This enables one to reduce path following and trajectory tracking for UAVs to the... more
We present a feedback equivalence transformation for the Dubins airplane model, which maps a monotone reference curve in space, to a straight line. This enables one to reduce path following and trajectory tracking for UAVs to the following and tracking of a straight line. We show that under this equivalence map, the system’s equations remain invariant. Thus, in the new transformed space, one can use existing controllers, simplify them for straight lines, and apply them for tracking. We analyse the requirements of the reference curves which allow bijectivity and showcase simulation results using existing controllers.
For a user-friendly Mobility Assistive Device (MAD) aiming to assist mobility constrained people, it is important to take into account the different gait disabilities. Thus, an intelligent MAD should recognize and adapt to the particular... more
For a user-friendly Mobility Assistive Device (MAD) aiming to assist mobility constrained people, it is important to take into account the different gait disabilities. Thus, an intelligent MAD should recognize and adapt to the particular needs of each user. In this work we present a thorough experimental analysis, using an on-line gait tracking and analysis system, to examine the impact of different control designs on the gait performance of elderly subjects who use an intelligent robotic rollator. The augmented human gait state estimates are provided by a system, that exploits laser data from a single Laser RangeFinder (LRF) sensor, mounted on the robotic MAD and capturing the users’ legs motion. This augmented gait state estimation is the tool for online gait analysis, in order to detect gait cycles and extract certain gait parameters which are crucial for the mobility status characterization of the user. We compare statistically the gait performance of subjects with different mob...

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