Data visualization benefits from non-visual cues to enable people to understand information by engaging with it through multimodality, yet most approaches rely on cumbersome technologies or large scale artifacts, making them difficult to adapt to dynamic or complex datasets. In this paper, we explore the use of cutaneous haptics as a lightweight quantitative channel for visualization tasks, allowing users to feel data and interact with it dynamically. We present Haptixel, an open-source DIY encountered-type wearable providing force-feedback on the users’ fingertips’ pulp. We propose an interaction framework illustrating how Haptixel can be used to complement visualization tasks through combinations of force levels and contact types. We evaluate our approach in a pixel-art-like VR user study (n=16) where pixels color/height are associated to forces as a univariate value mapping. Results show that participants can retrieve information with Haptixel, and significantly discriminate 3D-data with at least four levels of forces; suggesting that cutaneous force-feedback can function for quantitative distinctions in visualization tasks.

Safe and intuitive telemanipulation of multiple microrobots is limited by visual occlusions that compromise control and task success. This paper introduces a shared control framework that guarantees safety and visibility by formulating the control problem as a constrained optimization problem. Our framework combines Control Lyapunov Functions (CLFs) for operator-driven stability with High-Order Control Barrier Functions (HOCBFs) to enforce collision and occlusion avoidance, all resolved within a real-time Quadratic Program (QP). A key innovation is a rendering technique based on the QP’s Lagrange multipliers, which are used to decompose the optimal control solution. This method isolates the effects of individual constraints to provide the human operator with distinct, interpretable visuohaptic cues for navigation and avoidance. The architecture also includes a viewpoint optimization system with a virtual autonomous camera to maximize task visibility. The framework is validated via two user studies in simulation and a demonstration on a real-world electromagnetic microrobotics actuation system. Results confirm that our visuo-haptic shared control strategies significantly improve user performance and task completion rates, while the control design provably prevents the microrobots from colliding or entering occluded regions.

The perceived realism of virtual body illusions, such as arm elongation, is dependent on congruent sensory feedback. This paper explores the effects of visio-haptic stimulation on the sense of embodiment in Virtual Reality (VR). We conducted three experiments. The first identified the optimal parameters for vibrotactile feedback by varying stimulation location and motor activation duration (250, 500, 750 ms) during a fixed visual task of 40% arm elongation over 18 seconds. We found that sequential stimulations along the entire arm with a 500ms duration per motor were the most effective. From this, we derived a formula to generalize the optimal haptic timing based on elongation velocity. The formula was then validated in two follow-up experiments: one varying the elongation percentage (26% to 80%) and another varying the elongation duration (9s to 27s). Our findings offer validated guidelines for designing more immersive haptic experiences for virtual body deformations.

Variable stiffness of a remote robot is crucial for a teleoperation system to deal with challenging tasks. External stiffness command interfaces have emerged as a promising solution to regulating the remote robot stiffness because of the benefits of their accuracy, ergonomics, and avoidance of the “coupling effect” that usually exists in muscle activity-based stiffness interfaces. However, the use of an external stiffness command interface requires good coordination between two limbs of an operator, which take care of the teleoperation task and the stiffness regulation task, respectively, at the same time, which is demanding for novice operators in dynamic situations necessitating agile and timely stiffness adjustments. In this paper, a new concept of Stiffness Regulation Co-pilot was proposed to facilitate the use of these interfaces. A co-pilot is a virtual agent that consists of a Stiffness Regulation Policy, which infers a reasonable stiffness regulation action from the task performance, and a feedback modality, which conveys the suggested stiffness regulation action to the operator. A preliminary user study was conducted to evaluate the efficacy of the co-pilot and the effect of different modalities of the co-pilot. The results showed that the cutaneous feedback or combined with another modality can potentially improve the task performance of the system and reduce the cognitive load of the operator compared to a teleoperation system without using the co-pilot.

Microrobotics implies actuation-related constraints that make safe telemanipulation particularly challenging. We present a haptic shared control system for electromagnetic-based telemanipulation of a pair of microrobots using a constrained optimization framework. Our contributions include: (1) a Quadratic Programming formulation with Control Lyapunov Functions and Control Barrier Functions, for safe and stable navigation in cluttered environments; (2) a shared control architecture, combining a haptic interface and simulation environment, to teleoperate the microrobots and enable micromanipulation capabilities; and (3) haptic shared control strategies offering visuo-haptic cues for task execution. The approach is validated through a user study, highlighting better navigation accuracy, control stability and task efficiency.

The precise manipulation of microrobots presents challenges arising from their small size and susceptibility to external disturbances. To address these challenges, we present the experimental evaluation of a haptic shared control teleoperation framework for the locomotion of multiple microrobots, relying on a kinesthetic haptic interface and a custom electromagnetic system. Six combinations of haptic and shared control strategies are evaluated during a safe 3D navigation scenario in a cluttered environment. 18 participants are asked to steer two spherical magnetic microrobots among obstacles to reach a predefined goal, under different conditions. For each condition, participants are provided with different obstacle avoidance and navigation guidance cues. Results show that providing assistance in avoiding obstacles guarantees safer performance, regardless if the assistance is autonomous or delivered through a haptic repulsive force. Moreover, autonomous obstacle avoidance also reduces the completion time by 30% compared to haptic obstacle avoidance and no obstacle avoidance cases, although haptic feedback is preferred by the users. Finally, providing haptic guidance towards the target improves by the 65% the positioning accuracy of the microrobots with respect to not providing this guidance. We also present some illustrative scenarios to generalize the presented haptic shared control strategies to arbitrary formations of N microrobots, while showing the effectiveness of the method for a clinical use-case of endovascular navigation in simulated environment. Note to Practitioners—The recent increasing interest in microrobotics arises from its potential applications in fields like medicine, manufacturing, and environmental monitoring, enabling highly precise control of minimally invasive tools. By enabling users to teleoperate microscale tools with partial autonomous support, these systems facilitate safe access to confined spaces, enhance task efficiency, and enable navigation in otherwise inaccessible environments. Our presented solution serves as an experimental platform to evaluate the efficacy of different combinations of tactile feedback and partial autonomy during safe navigation tasks, with potential applications spanning microsurgery, drug delivery, microscale manufacturing, and environmental remediation. Further practical adaptation of the system will require defining specific application objectives and specifications, along with potential modifications to the actuation system to accommodate environmental constraints of targeted scenarios.

Dynamic average estimation is a critical problem in multi-agent systems, enabling agents to collaboratively estimate time-varying signals using only local information exchange. Traditional model-based approaches often face challenges related to convergence speed and sensitivity to network topology changes. This article introduces a novel learning-based solution leveraging Gated Graph Neural Networks (GGNNs) for fast-convergent dynamic average estimation in a fully distributed manner. Taking advantage of the inherent structure of GGNNs, the proposed method models the estimation process as a distributed autoregressor, ensuring rapid convergence while maintaining stability. We incorporate a regularization term during training to enforce convergence guarantees and introduce an encoding–decoding mechanism to reduce communication overhead without sacrificing accuracy compared to standard GGNNs. Extensive numerical experiments demonstrate that our approach significantly outperforms conventional model-based estimators in terms of both convergence speed and precision, making it a promising alternative for multi-agent applications that require dynamic average estimation.

The ability to manipulate and physically feel virtual objects without any real object being present and without equipping the user has been a long-standing goal in virtual reality (VR). Emerging ultrasound mid-air haptics (UMH) technology could potentially address this challenge, as it enables remote tactile stimulation of unequipped users. However, to date, UMH has received limited attention in the field of haptic exploration and manipulation in virtual environments. Existing work has primarily focused on interactions requiring a single hand and thus the delivery of unimanual haptic feedback. Despite being fundamental to a large part of haptic interactions with our environments, bimanual tasks have rarely been studied in the field of UMH interaction in VR. In this paper, we propose the use of non-coplanar mid-air haptic devices for providing simultaneous tactile feedback to both hands during bimanual VR manipulation. We discuss coupling schemes and haptic rendering algorithms for providing bimanual haptic feedback in bimanual interactions with virtual environments. We then present two human participant studies, assessing the benefits of bimanual ultrasound haptic feedback in a two-handed grasping and holding task and in a shape exploration task. Results suggest that the use of multiple non-coplanar UMH devices could be an interesting approach for enriching unencumbered haptic manipulation in virtual environments.

Ultrasound mid-air haptic (UMH) interfaces focus acoustic energy to generate high-pressure focal points in mid-air, creating tactile sensations. When these focal points are modulated over time, they can render tactile patterns with various properties in a 3D workspace. While UMH has been used to render curves and 2D shapes, such as tactile icons, rendering 3D objects in full is nowadays an open problem, as it would require more powerful devices. To overcome this limitation, designers typically only render a representation of the intersection between the user’s hand and the virtual object. However, there is no consensus in the literature on how best to compute this intersection.

Multi-robot systems have gained increasing interest across various fields such as medicine, environmental monitoring, and more. Despite the evident advantages, the coordination of the swarm arises significant challenges for human operators, particularly concerning the cognitive burden needed for efficiently controlling the robots. In this study, we present a novel approach for enabling a human operator to effectively control the motion of multiple robots. Leveraging a shared control data-driven approach, we enable a single user to control the 9 degrees of freedom related to the pose and shape of a swarm. Our methodology was evaluated through an experimental campaign conducted in simulated 3D environments featuring a narrow cylindrical path, which could represent, e.g., blood vessels, industrial pipes. Subjective measures of cognitive load were assessed using a post-experiment questionnaire, comparing different levels of autonomy of the system. Results show substantial reductions in operator cognitive load when compared to conventional teleoperation techniques, accompanied by enhancements in task performance, including reduced completion times and fewer instances of contact with obstacles. This research underscores the efficacy of our approach in enhancing human-robot interaction and improving operational efficiency in multi-robot systems.

In this paper, we study how thermal haptic feedback can influence social interactions in virtual environments, with an emphasis on persuasion, focus, co-presence, and friendliness. Physical and social warmth have been repeatedly linked in psychological literature, which allows for speculations on the effect of thermal haptics on virtual social interactions. To that effect, we conducted a study on thermal feedback during simulated social interactions with a virtual agent. We tested three conditions: warm, cool, and neutral. Results showed that warm feedback positively influenced users’ perception of the agent and significantly enhanced persuasion and thermal comfort. Multiple users reported the agent feeling less ‘robotic’ and more ‘human’ during the warm condition. Moreover, multiple studies have previously shown the potential of vibrotactile feedback for social interactions. A second study thus evaluated the combination of warmth and vibrations for social interactions. The study included the same protocol and three similar conditions: warmth, vibrations, and warm vibrations. Warmth was perceived as more friendly, while warm vibrations heightened the agent’s virtual presence and persuasion. These results encourage the study of thermal haptics to support positive social interactions. Moreover, they suggest that some haptic feedback are more suited to certain types of social interactions and communication than others.

Wearable haptic devices can modify the haptic perception of an object touched directly by the finger in a portable and unobtrusive way. In this paper, we investigate whether such wearable haptic augmentations are perceived differently in Augmented Reality (AR) vs. Virtual Reality (VR) and when touching with a virtual hand instead of one’s own hand. We first designed a system for real-time rendering of vibrotactile virtual textures without constraints on hand movements, integrated with an immersive visual AR/VR headset. We then conducted a psychophysical study with 20 participants to evaluate the haptic perception of virtual roughness textures on a real surface touched directly with the finger (1) without visual augmentation, (2) with a realistic virtual hand rendered in AR, and (3) with the same virtual hand in VR. On average, participants overestimated the roughness of haptic textures when touching with their real hand alone and underestimated it when touching with a virtual hand in AR, with VR in between. Exploration behaviour was also slower in VR than with real hand alone, although subjective evaluation of the texture was not affected. We discuss how the perceived visual delay of the virtual hand may produce this effect.

Cutaneous haptic feedback has recently received great attention from researchers in the robotic teleoperation field, as it has been proven to convey rich information to the human operator while guaranteeing the safety and stability of the control loop. In fact, delivering ungrounded cutaneous cues keeps the teleoperation system stable even in the presence of time-varying destabilizing factors such as hard contacts or communication delays. This aspect is particularly relevant for all the applications and scenarios where the safety of the system is of paramount importance, as in medical robotics. This article presents an overview on cutaneous haptic interaction followed by a review of the literature on cutaneous/tactile feedback systems for robotic teleoperation, categorizing the considered systems according to the type of cutaneous stimuli they can provide to the human operator. This article ends with a discussion on the role of cutaneous haptics in robotics and the perspectives of the field.

Haptic exoskeleton gloves are a widespread solution for providing force-feedback in Virtual Reality (VR), especially for 3D object manipulations. However, they are still lacking an important feature regarding in-hand haptic sensations: the palmar contact. In this paper, we present PalmEx, a novel approach which incorporates palmar force-feedback into exoskeleton gloves to improve the overall grasping sensations and manual haptic interactions in VR. PalmEx's concept is demonstrated through a self-contained hardware system augmenting a hand exoskeleton with an encountered palmar contact interface - physically encountering the users' palm. We build upon current taxonomies to elicit PalmEx's capabilities for both the exploration and manipulation of virtual objects. We first conduct a technical evaluation optimising the delay between the virtual interactions and their physical counterparts. We then empirically evaluate PalmEx's proposed design space in a user study (n=12) to assess the potential of a palmar contact for augmenting an exoskeleton. Results show that PalmEx offers the best rendering capabilities to perform believable grasps in VR. PalmEx highlights the importance of the palmar stimulation, and provides a low-cost solution to augment existing high-end consumer hand exoskeletons.

Rich, informative and realistic haptic feedback is key to enhancing Virtual Reality (VR) manipulation. Tangible objects provide convincing grasping and manipulation interactions with haptic feedback of e.g., shape, mass and texture properties. But these properties are static, and cannot respond to interactions in the virtual environment. On the other hand, vibrotactile feedback provides the opportunity for delivering dynamic cues rendering many different contact properties, such as impacts, object vibrations or textures. Handheld objects or controllers in VR are usually restricted to vibrating in a monolithic fashion. In this article, we investigate how spatialiazing vibrotactile cues within handheld tangibles could enable a wider range of sensations and interactions. We conduct a set of perception studies, investigating the extent to which spatialization of vibrotactile feedback within tangible objects is possible as well as the benefits of proposed rendering schemes leveraging multiple actuators in VR. Results show that vibrotactile cues from localized actuators can be discriminated and are beneficial for certain rendering schemes.

Nonverbal communication is paramount in daily life, as well as in populated virtual reality (VR) environments. In this paper, we focused on gaze behaviour, which is key to initiate and drive social interactions. Previous work on photographs and on virtual agents showed the importance of gaze, even in the presence of multiple stimuli, by demonstrating the stare-in-the-crowd effect: humans detect faster and observe gazes directed towards them longer than the averted ones. While previous studies focused on static scenarios, which fail in representing the complexity of real-life social interactions, we propose to explore the stare-in-the-crowd effect in dynamic situations. To this end, we designed a within-subject experiment where 21 users navigated a virtual street through an idle or moving crowd of virtual agents. Agents’ gaze was manipulated to display averted, directed, or shifting gaze. We analysed the user’s gaze (fixations, dwell time) and locomotor behaviours (path decisions, proximity to agents) as well as their social anxiety. Results showed that the stare-in-the-crowd effect is preserved when walking through both types of crowd, and that social anxiety decreases gaze interaction time and affects proximity behaviours in case of agents with directed gazes. However, virtual agents’ gaze did not elicit significant changes on users’ locomotion. These findings highlight the importance of considering virtual agents’ gaze when creating VR environments, and open future work perspectives to better understand factors that would strengthen or decrease this effect at gaze and locomotor levels.

We present a decentralized connectivity-maintenance algorithm for controlling a group of quadrotor UAVs with limited field of view (FOV) and not sharing a common reference frame for collectively expressing measurements and commands. This is in contrast to the vast majority of previous works on this topic which, instead, make the (simplifying) assumptions of omnidirectional sensing and presence of a common shared frame. For achieving this goal, we design a gradient-based connectivity-maintenance controller able to take into account the presence of a limited FOV. We also propose a novel (to our knowledge) decentralized estimator of the relative orientation among neighboring robots, which is a necessary quantity for correctly implementing the connectivity-maintenance action. We validate the framework in realistic simulations that show the effectiveness of our approach.

In Virtual Reality (VR), a growing number of applications involve verbal communications with avatars, such as for teleconference, entertainment, virtual training, social networks, etc. In this context, our paper aims to investigate how tactile feedback consisting in vibrations synchronized with speech could influence aspects related to VR social interactions such as persuasion, co-presence and leadership. We conducted two experiments where participants embody a first-person avatar attending a virtual meeting in immersive VR. In the first experiment, participants were listening to two speaking virtual agents and the speech of one agent was augmented with vibrotactile feedback. Interestingly, the results show that such vibrotactile feedback could significantly improve the perceived co-presence but also the persuasiveness and leadership of the haptically-augmented agent. In the second experiment, the participants were asked to speak to two agents, and their own speech was augmented or not with vibrotactile feedback. The results show that vibrotactile feedback had again a positive effect on co-presence, and that participants perceive their speech as more persuasive in presence of haptic feedback. Taken together, our results demonstrate the strong potential of haptic feedback for supporting social interactions in VR, and pave the way to novel usages of vibrations in a wide range of applications in which verbal communication plays a prominent role.

Ultrasound mid-air haptic (UMH) devices are a novel tool for haptic feedback, capable of providing localized vibrotactile stimuli to users at a distance. UMH applications largely rely on generating tactile shape outlines on the users’ skin. Here we investigate how to achieve sensations of continuity or gaps within such two-dimensional curves by studying the perception of pairs of amplitude-modulated focused ultrasound stimuli. On the one hand, we aim to investigate perceptual effects that may arise from providing simultaneous UMH stimuli. On the other hand, we wish to provide perception-based rendering guidelines for generating continuous or discontinuous sensations of tactile shapes. Finally, we hope to contribute toward a measure of the perceptually achievable resolution of UMH interfaces. We performed a user study to identify how far apart two focal points need to be to elicit a perceptual experience of two distinct stimuli separated by a gap. Mean gap detection thresholds were found at 32.3-mm spacing between focal points, but a high within- and between-subject variability was observed. Pairs spaced below 15 mm were consistently (>95%) perceived as a single stimulus, while pairs spaced 45 mm apart were consistently (84%) perceived as two separate stimuli. To investigate the observed variability, we resort to acoustic simulations of the resulting pressure fields. These show a non-linear evolution of actual peak pressure spacing as a function of nominal focal point spacing. Beyond an initial threshold in spacing (between 15 and 18 mm), which we believe to be related to the perceived size of a focal point, the probability of detecting a gap between focal points appears to linearly increase with spacing. Our work highlights physical interactions and perceptual effects to consider when designing or investigating the perception of UMH shapes.

Ultrasound mid-air haptic (UMH) devices can remotely render vibrotactile shapes on the skin of unequipped users, e.g., to draw haptic icons or render virtual object shapes. Spatio-temporal modulation (STM), the state-of-the-art UMH shape-rendering method, provides large freedom in shape design and produces the strongest possible stimuli for this technology. Yet, STM shapes are often reported to be blurry, complicating shape identification. Dynamic tactile pointers (DTP) were recently introduced as a technique to overcome this issue. By tracing a contour with an amplitude-modulated focal point, they significantly improve shape identification accuracy over STM, but at the cost of much lower stimulus intensity. Building upon this, we propose spatio-temporally-modulated Tactile Pointers (STP), a novel method for rendering clearer and sharper UMH shapes while at the same time producing strong vibrotactile sensations. We ran two human participant experiments, which show that STP shapes are perceived as significantly stronger than DTP shapes, while shape identification accuracy is significantly improved over STM and on par with that obtained with DTP. Our work has implications for effective shape rendering with UMH and provides insights that could inform future psychophysical investigation into vibrotactile shape perception in UMH.

Pseudo-Haptic techniques, or visuo-haptic illusions, leverage user's visual dominance over haptics to alter the users' perception. As they create a discrepancy between virtual and physical interactions, these illusions are limited to a perceptual threshold. Many haptic properties have been studied using pseudo-haptic techniques, such as weight, shape or size. In this paper, we focus on estimating the perceptual thresholds for pseudo-stiffness in a virtual reality grasping task. We conducted a user study (n = 15) where we estimated if compliance can be induced on a non-compressible tangible object and to what extent. Our results show that (1) compliance can be induced in a rigid tangible object and that (2) pseudo-haptics can simulate beyond 24 N/cm stiffness (k > 24N/cm, between a gummy bear and a raisin, up to rigid objects). Pseudo-stiffness efficiency is (3) enhanced by the objects' scales, but mostly (4) correlated to the user input force. Taken altogether, our results offer novel opportunities to simplify the design of future haptic interfaces, and extend the haptic properties of passive props in VR.

Neural Style Transfer (NST) refers to a class of algorithms able to manipulate an element, most often images, to adopt the appearance or style of another one. Each element is defined as a combination of Content and Style: the Content can be conceptually defined as the “what” and the Style as the “how” of said element. In this context, we propose a custom NST framework for transferring a set of styles to the motion of a robotic manipulator, e.g., the same robotic task can be carried out in an “angry”, “happy”, “calm”, or “sad” way. An autoencoder architecture extracts and defines the Content and the Style of the target robot motions. A Twin Delayed Deep Deterministic Policy Gradient (TD3) network generates the robot control policy using the loss defined by the autoencoder. The proposed Neural Policy Style Transfer TD3 NPST3 alters the robot motion by introducing the trained style. Such an approach can be implemented either offline, for carrying out autonomous robot motions in dynamic environments, or online, for adapting at runtime the style of a teleoperated robot. The considered styles can be learned online from human demonstrations. We carried out an evaluation with human subjects enrolling 73 volunteers, asking them to recognize the style behind some representative robotic motions. Results show a good recognition rate, proving that it is possible to convey different styles to a robot using this approach.

This paper considers a multi-robot team tasked with monitoring an environmental field of interest over long time horizons. The approach is based on a control-theoretic measure of the information collected by the robots, namely a norm of the constructability Gramian. This measure is leveraged in order to learn a distributed multi-robot control policy using the reinforcement learning paradigm. The learned policy is then combined with energy constraints using the constraint-driven control framework in order to achieve persistent environmental monitoring. The proposed approach is tested in a simulated multi-robot persistent environmental monitoring scenario where a team of robots with limited availability of energy is to be controlled in a coordinated fashion in order to estimate the concentration of a gas diffusing in the environment.

Nonverbal cues are paramount in real-world interactions. Among these cues, gaze has received much attention in the literature. In particular, previous work has shown a search asymmetry between directed and averted gaze towards the observer using photographic stimuli, with faster detection and longer fixation towards directed gaze by the observer. This is known as the stare-in-the-crowd effect. In this study, we investigate whether stare-in-the crowd effect is preserved in Virtual Reality (VR). To this end, we designed a within-subject experiment where 30 human users were immersed in a virtual environment in front of an audience of 11 virtual agents following 4 different gaze behaviours. We analysed the user’s gaze behaviour when observing the audience, computing fixations and dwell time. We also collected the users’ social anxiety score using a post-experiment questionnaire to control for some potential influencing factors. Results show that the stare-in-the-crowd effect is preserved in VR, as demonstrated by the significant differences between gaze behaviours, similarly to what was found in previous studies using photographic stimuli. Additionally, we found a negative correlation between dwell time towards directed gazes and users’ social anxiety scores. Such results are encouraging for the development of expressive and reactive virtual humans, which can be animated to express natural interactive behaviour.

The use of electrotactile feedback in Virtual Reality (VR) has shown promising results for providing tactile information and sensations. While progress has been made to provide custom electrotactile feedback for specific interaction tasks, it remains unclear which modulations and rendering algorithms are preferred in rich interaction scenarios. In this paper, we propose a unified tactile rendering architecture and explore the most promising modulations to render finger interactions in VR. Based on a literature review, we designed six electrotactile stimulation patterns/effects (EFXs) striving to render different tactile sensations. In a user study (N=18), we assessed the six EFXs in three diverse finger interactions: 1) tapping on a virtual object; 2) pressing down a virtual button; 3) sliding along a virtual surface. Results showed that the preference for certain EFXs depends on the task at hand. No significant preference was detected for tapping (short and quick contact); EFXs that render dynamic intensities or dynamic spatio-temporal patterns were preferred for pressing (continuous dynamic force); EFXs that render moving sensations were preferred for sliding (surface exploration). The results showed the importance of the coherence between the modulation an the interaction being performed and the study proved the versatility of electrotactile feedback and its efficiency in rendering different haptic information and sensations.

We present a decentralized connectivity-maintenance control framework for a heterogeneous human–robot team. The algorithm is able to manage a team composed of an arbitrary number of mobile robots (drones and ground robots in our case) and humans, for collaboratively achieving exploration and patrolling tasks. Differently from other works on the subject, here the human user physically becomes part of the team, moving in the same environment of the robots and receiving information about the team connectivity through wearable haptics or audio feedback. Although human explores the environment, robots move so as to keep the team connected via a connectivity-maintenance algorithm; at the same time, each robot can also be assigned with a specific target to visit. We carried out three human subject experiments, both in virtual and real environments. Results show that the proposed approach is effective in a wide range of scenarios. Moreover, providing either haptic or audio feedback for conveying information about the team connectivity significantly improves the performance of the considered tasks, although users significantly preferred receiving haptic stimuli w.r.t. the audio ones. Note to Practitioners—Exploration, patrolling, and search-and-rescue are highly dynamic and unstructured scenarios. When considering the operative conditions of such environments, the benefits of multirobot systems are evident. Most tasks can be carried out faster and more robustly by a team of robots with respect to a single unit. There are also situations explicitly requiring the presence of a multirobot team, e.g., using one drone for surveillance of the ground team and one ground mobile robot for carrying supplies. Of course, if the operator(s) in charge of the operation could share the same environment of the robots (i.e., be together with the robots in the field), they would be provided with a level of situational awareness that no teleoperation technology can match as of today. This work presents a framework for controlling heterogeneous teams composed of one human operator and an arbitrary number of aerial and ground mobile robots. The operator moves together with the robotic team and, at the same time, he or she receives meaningful information about the status of the formation. The algorithm only uses the relative position of the drones and humans with respect to each other, and all computations are designed in a decentralized fashion. Decentralization avoids relying on any absolute positioning system (e.g., GPS) or centralized command centers. These features make the proposed framework ready for deployment in different high-impact applications, such as in surveillance, search-and-rescue, and disaster response scenarios.

This article proposes a shared-control teleoperation architecture for robot manipulators transporting an object on a tray. Differently from many existing studies about remotely operated robots with firm grasping capabilities, we consider the case in which, in principle, the object can break its contact with the robot end-effector. The proposed shared-control approach automatically regulates the remote robot motion commanded by the user and the end-effector orientation to prevent the object from sliding over the tray. Furthermore, the human operator is provided with haptic cues informing about the discrepancy between the commanded and executed robot motion, which assist the operator throughout the task execution. We carried out trajectory tracking experiments employing an autonomous 7-degree-of-freedom (DoF) manipulator and compared the results obtained using the proposed approach with two different control schemes (i.e., constant tray orientation and no motion adjustment). We also carried out a human-subjects study involving 18 participants in which a 3-DoF haptic device was used to teleoperate the robot linear motion and display haptic cues to the operator. In all experiments, the results clearly show that our control approach outperforms the other solutions in terms of sliding prevention, robustness, commands tracking, and user’s preference.

Research on robotic manipulation of fragile, compliant objects, such as food items, is gaining traction due to its game-changing potential within the food production and retailing sectors, currently characterized by manually intensive and highly repetitive tasks. Food products exhibit high levels of frailness, biological variation, and complex 3-D shapes and textures. For these reasons, introducing greater levels of robotic automation in the food and agricultural sectors remains an important challenge. This article addresses this challenge by developing a human-centered, haptic-based, learning from demonstration (LfD) policy that enables pretrained autonomous grasping of food items using an anthropomorphic robotic system. The policy combines data from teleoperation and direct human manipulation of objects, embodying human intent and interaction areas of significance. We evaluated the proposed solution against a recent state-of-the-art LfD policy as well as against two standard impedance controller techniques. Results show that the proposed policy performs significantly better than the other considered techniques, leading to high grasping success rates while guaranteeing the integrity of the food at hand.

Virtual reality (VR) is a valuable experimental tool for studying human movement, including the analysis of interactions during locomotion tasks for developing crowd simulation algorithms. However, these studies are generally limited to distant interactions in crowds, due to the difficulty of rendering realistic sensations of collisions in VR. In this article, we explore the use of wearable haptics to render contacts during virtual crowd navigation. We focus on the behavioral changes occurring with or without haptic rendering during a navigation task in a dense crowd, as well as on potential after-effects introduced by the use haptic rendering. Our objective is to provide recommendations for designing VR setup to study crowd navigation behavior. To the end, we designed an experiment (N=23) where participants navigated in a crowded virtual train station without, then with, and then again without haptic feedback of their collisions with virtual characters. Results show that providing haptic feedback improved the overall realism of the interaction, as participants more actively avoided collisions. We also noticed a significant after-effect in the users' behavior when haptic rendering was once again disabled in the third part of the experiment. Nonetheless, haptic feedback did not have any significant impact on the users' sense of presence and embodiment.

While user's perception and performance are predominantly examined independently in virtual reality, the Action-Specific Perception (ASP) theory postulates that the performance of an individual on a task modulates this individual's spatial and time perception pertinent to the task's components and procedures. This paper examines the association between performance and perception and the potential effects that tactile feedback modalities could generate. This paper reports a user study (N=24), in which participants performed a standardized Fitts's law target acquisition task by using three feedback modalities: visual, visuo-electrotactile, and visuo-vibrotactile. The users completed 3 Target Sizes × 2 Distances × 3 feedback modalities = 18 trials. The size perception, distance perception, and (movement) time perception were assessed at the end of each trial. Performance-wise, the results showed that electrotactile feedback facilitates a significantly better accuracy compared to vibrotactile and visual feedback, while vibrotactile provided the worst accuracy. Electrotactile and visual feedback enabled a comparable reaction time, while the vibrotactile offered a substantially slower reaction time than visual feedback. Although amongst feedback types the pattern of differences in perceptual aspects were comparable to performance differences, none of them was statistically significant. However, performance indeed modulated perception. Significant action-specific effects on spatial and time perception were detected. Changes in accuracy modulate both size perception and time perception, while changes in movement speed modulate distance perception. Also, the index of difficulty was found to modulate all three perceptual aspects. However, individual differences appear to affect the magnitude of action-specific effects. These outcomes highlighted the importance of haptic feedback on performance, and importantly the significance of action-specific effects on spatial and time perception in VR, which should be considered in future VR studies.

Ultrasound mid-air haptic interfaces can display highly reconfigurable vibrotactile shapes in mid-air for human-computer interaction (HCI) applications. The choice of stimulus shape, spatial, temporal and modulation parameters yields a complex design space, yet relatively little is known about the impact of these design choices on perceived stimulus properties. We define the combination of a spatial discretization of an abstract shape and a set of rules for the temporal display order and intensity modulation of the resulting points as a sampling strategy. We developed DOLPHIN, an open-source framework to aid in designing mid-air stimuli. DOLPHIN allows the study of the impact of rendering parameters on perceived stimulus properties. This platform-agnostic framework standardizes stimulus descriptions as a step toward more replicability and easier communication in the field. It enables reproduction of stimuli between perceptual experiments and ensures stimuli used in applications correspond to those evaluated in prior perceptual studies. We validated DOLPHIN’s usability by conducting a user study assessing the impact of sampling strategy design on curvature discrimination for dynamic mid-air haptic stimuli. The Weber fractions for just-noticeable differences (JNDs) in curvature were found to range between 1 and 1.4, yet no significant effect of the number of spatial sampling points on curvature discrimination was found. This result shows a practical use-case for DOLPHIN and provides insight into rendering mid-air haptic curvature.

Non-verbal communication body cues are paramount to interact. In this preliminary work, we explore ways to let Intelligent Virtual Agents (IVAs) simulating nonverbal communication capabilities. We propose an approach to control IVAs' reactive behaviour from the analysis of other agents' apparent motions, in a situation of "observed" IVAs that act and "observers" that react. For that, first a viewpoint-driven analysis of the observed agent's motion is done, and then a synthesis of this analysis induces the observers' reaction.

This article presents the design of a decentralized connectivity-maintenance algorithm for the teleoperation of a team of multiple UAVs, together with an extensive human subject evaluation in virtual and real environments. The proposed connectivity-maintenance algorithm enhances earlier works by improving their applicability, safety, effectiveness, and ease of use, by including: 1) an airflow-avoidance behavior that avoids stack downwash phenomena in rotor-based aerial robots; 2) a consensus-based action for enabling fast displacements with minimal topology changes by having all follower robots moving at the leader’s velocity; 3) an automatic decrease of the minimum degree of connectivity, enabling an intuitive and dynamic expansion/compression of the formation; and 4) an automatic detection and resolution of deadlock configurations, i.e., when the robot leader cannot move due to counterbalancing connectivity- and external-related inputs. We also devised and evaluated different interfaces for teleoperating the team as well as different ways of receiving information about the connectivity force acting on the leader. The results of two human subject experiments show that the proposed algorithm is effective in various situations. Moreover, using haptic feedback to provide information about the team connectivity outperforms providing both no feedback at all and sensory substitution via visual feedback.Note to Practitioners—The control of one drone is usually performed with a remote controller (similar to a joypad) that uses radio-wave signals. When controlling more than one drone, even a simple task, such as moving the whole team around, becomes very challenging. Developing an easy, yet efficient way to impart commands to a formation of drones is necessary to achieve any complex task. This article proposes a framework to control a fleet of drones (quadrotors) in an intuitive way while receiving meaningful and effective information on the state of the formation. The proposed technique does not rely on any absolute positioning system (e.g., GPS) or centralized command center. Instead, it only uses the relative position of the drones with respect to each other, and all computations are designed in a decentralized fashion. These features make the proposed framework ready for deployment in different high-impact applications, such as in surveillance, search-and-rescue, and disaster response scenarios.

We combine tracking information from a tangible object instrumented with capacitive sensors and an optical tracking system, to improve contact rendering when interacting with tangibles in VR. A human-subject study shows that combining capacitive sensing with optical tracking significantly improves the visuohaptic synchronization and immersion of the VR experience.

As robotic systems become more flexible and intelligent, they must be able to move into environments with a high degree of uncertainty or clutter, such as our homes, workplaces, and the outdoors. In these unstructured scenarios, it is possible that the body of the robot collides with its surroundings. As such, it would be desirable to characterise these contacts in terms of their location and interaction forces. This paper addresses the problem of detecting and isolating collisions between a robotic manipulator and its environment, using only on-board joint torque and position sensing. The algorithm is based on a particle filter and, under some assumptions, is able to identify the contact location anywhere on the robot body. It requires the robot to perform small exploratory movements, progressively integrating the new sensing information through a Bayesian framework. The approach was tested and benchmarked in simulation, with respect to its accuracy and robustness. Validation using a robot with joint torque sensing in a real environment demonstrated the applicability of the method to real-world scenarios.

Robot-assisted cutting is considered an important task in several fields, such as robotic surgery, nuclear decommissioning, waste management, and manufacturing. Despite the complex dexterity requirements of cutting tasks, very simple mechanically-linked master-slave manipulators still dominate many of the above fields (e.g., nuclear robotics). Moreover, even when more dexterous manipulators are available (e.g., in robot-assisted surgery), the employed systems show little or no autonomy, delegating all control to the experience of the human operator. To ameliorate this situation, we present two haptic shared-control approaches for robotic cutting. They are designed to assist the human operator by enforcing different nonholonomic-like constraints representative of the cutting kinematics. To validate our approach, we carried out a human-subject experiment in a real cutting scenario. We compared our shared-control techniques with each other and with a standard haptic teleoperation scheme. Results show the usefulness of assisted control schemes in complex applications such as cutting. However, they also show a discrepancy between objective and subjective metrics.

Tangible objects are a simple yet effective way for providing haptic sensations in Virtual Reality. For achieving a compelling illusion, there should be a good correspondence between what users see in the virtual environment and what they touch in the real world. The haptic features of the tangible object should indeed match those of the corresponding virtual one in terms of, e.g., size, local shape, mass, texture. A straightforward solution is to create perfect tangible replicas of all the virtual objects in the scene. However, this is often neither feasible nor desirable. This paper presents an innovative approach enabling the use of few tangible objects to render many virtual ones. The proposed algorithm analyzes the available tangible and virtual objects to find the best grasps in terms of matching haptic sensations. It starts by identifying several suitable pinching poses on the considered tangible and virtual objects. Then, for each pose, it evaluates a series of haptically-salient characteristics. Next, it identifies the two most similar pinching poses according to these metrics, one on the tangible and one on the virtual object. Finally, it highlights the chosen pinching pose, which provides the best matching sensation between what users see and touch. The effectiveness of our approach is evaluated through a user study. Results show that the algorithm is able to well combine several haptically-salient object features to find convincing pinches between the given tangible and virtual objects.

Robotic telemanipulators are already widely used in nuclear decommissioning sites for handling radioactive waste. However, currently employed systems are still extremely primitive, making the handling of these materials prohibitively slow and ineffective. As the estimated cost for the decommissioning and clean-up of nuclear sites keeps rising, it is clear that one would need faster and more effective approaches. Towards this goal, in this paper we present the user evaluation of a recently proposed haptic-enabled shared-control architecture for telemanipulation. An autonomous algorithm regulates a subset of the slave manipulator degrees of freedom (DoF) in order to help the human operator in grasping an object of interest. The human operator can then steer the manipulator along the remaining null-space directions with respect to the main task by acting on a grounded haptic interface. The haptic cues provided to the operator are designed in order to inform about the feasibility of the user's commands with respect to possible constraints of the robotic system. In this paper we compared this shared-control architecture against a classical 6-DOF teleoperation approach in a real scenario by running experiments with 10 subjects. The results clearly show that the proposed shared-control approach is a viable and effective solution for improving currently-available teleoperation systems in remote telemanipulation tasks.

This paper presents a novel optimization-based passivity control algorithm for haptic-enabled bilateral teleoperation systems involving multiple degrees of freedom. In particular, in the context of energy-bounding control, the contribution focuses on the implementation of a passivity layer for an existing time-domain scheme, ensuring optimal transparency of the interaction along subsets of the environment space which are preponderant for the given task, while preserving the energy bounds required for passivity. The involved optimization problem is convex and amenable to real-time implementation. The effectiveness of the proposed design is validated via an experiment performed on a virtual teleoperated environment.

Haptic systems have only recently started to be designed with wearability in mind. Compact, unobtrusive, inexpensive, easy-to-wear, and lightweight haptic devices enable researchers to provide compelling touch sensations to multiple parts of the body, significantly increasing the applicability of haptics in many fields, such as robotics, rehabilitation, gaming, and immersive systems. In this respect, wearable haptics has a great potential in the fields of virtual and augmented reality. Being able to touch virtual objects in a wearable and unobtrusive way may indeed open new exciting avenues for the fields of haptics and VR. This work presents a novel wearable haptic system for immersive virtual reality experiences. It conveys the sensation of touching objects made of different materials, rendering pressure and texture stimuli through a moving platform and a vibrotactile abbrv-doi-hyperref-narrowmotor. The device is composed of two platforms: one placed on the nail side of the finger and one in contact with the finger pad, connected by three cables. One small servomotor controls the length of the cables, moving the platform towards or away from the fingertip. One voice coil actuator, embedded in the platform, provides vibrotactile stimuli to the user.

This paper studies the combination of tangible objects and wearable haptics for improving the display of stiffness sensations in virtual environments. Tangible objects enable to feel the general shape of objects, but they are often passive or unable to simulate several varying mechanical properties. Wearable haptic devices are portable and unobtrusive interfaces able to generate varying tactile sensations, but they often fail at providing convincing stiff contacts and distributed shape sensations. We propose to combine these two approaches in virtual and augmented reality (VR/AR), becoming able of arbitrarily augmenting the perceived stiffness of real/tangible objects by providing timely tactile stimuli at the fingers. We developed a proof-of-concept enabling to simulate varying elasticity/stiffness sensations when interacting with tangible objects by using wearable tactile modules at the fingertips. We carried out a user study showing that wearable haptic stimulation can well alter the perceived stiffness of real objects, even when the tactile stimuli are not delivered at the contact point. We illustrated our approach both in VR and AR, within several use cases and different tangible settings, such as when touching surfaces, pressing buttons and pistons, or holding an object. Taken together, our results pave the way for novel haptic sensations in VR/AR by better exploiting the multiple ways of providing simple, unobtrusive, and low-cost haptic displays.

Untethered miniature robotics have recently shown promising results in several scenarios at the microscale, such as targeted drug delivery, microassembly, and biopsy procedures. However, the vast majority of these small-scale robots have very limited manipulation capabilities, and none of the steering systems currently available enables humans to intuitively and effectively control dexterous miniaturized robots in a remote environment. In this paper, we present an innovative micro-teleoperation system with haptic assistance for the intuitive steering and control of miniaturized self-folding soft magnetic grippers in 2-D space. The soft grippers can be wirelessly positioned using weak magnetic fields and opened/closed by changing their temperature. An image-guided algorithm tracks the position of the controlled miniaturized gripper in the remote environment. A haptic interface provides the human operator with compelling haptic sensations about the interaction between the gripper and the environment as well as enables the operator to intuitively control the target position and grasping configuration of the gripper. Finally, magnetic and thermal control systems regulate the position and grasping configuration of the gripper. The viability of the proposed approach is demonstrated through two experiments involving 26 human subjects. Providing haptic stimuli elicited statistically significant improvements in the performance of the considered navigation and micro-manipulation tasks.

Robotic teleoperation in cluttered environments is attracting increasing attention for its potential in hazardous scenarios, disaster response, and telemaintenance. Although haptic feedback has been proven effective in such applications, commercially-available grounded haptic interfaces still show significant limitations in terms of workspace, safety, transparency, and encumbrance. For this reason, we present a novel robotic teleoperation system with wearable haptic feedback for telemanipulation in cluttered environments. The slave system is composed of a soft robotic hand attached to a 6-axis force sensor, which is fixed to a 6-degrees-of-freedom robotic arm. The master system is composed of two wearable vibrotactile armbands and a Leap Motion. The armbands are worn on the upper arm and forearm, and convey information about collisions on the robotic arm and hand, respectively. The position of the manipulator and the grasping configuration of the robotic hand are controlled by the user's hand pose as tracked by the Leap Motion. To validate our approach, we carried out a human-subject telemanipulation experiment in a cluttered scenario. Twelve participants were asked to teleoperate the robot to grasp an object hidden between debris of various shapes and stiffnesses. Haptic feedback provided by our wearable devices significantly improved the performance of the considered telemanipulation tasks. All subjects but one preferred conditions with wearable haptic feedback.

Wearable robots have been mostly designed as exoskeletons, with segments and joints corresponding to those of the person they are coupled with. Exoskeletons are mainly employed to augment human body force and precision capabilities, or for rehabilitation purposes. More recently, new wearable robots resembling additional robotic limbs have been developed thanks to the progress in miniaturization and efficiency of mechanical and sensing components. However, wearable robotic extra limbs presented in the literature lack of effective haptic feedback systems. In this paper, we present a robotic extra finger coupled with a vibrotactile ring interface. The human user is able to control the motion of the robotic finger through a switch placed on the ring, while being provided with vibrotactile feedback about the forces exerted by the robotic finger on the environment. To understand how to control the vibrotactile interface to evoke the most effective cutaneous sensations, we executed perceptual experiments to evaluate its absolute and differential thresholds. We also carried out a pick-and-place experiment with ten subjects. Haptic feedback significantly improved the performance in task execution in terms of completion time, exerted force, and perceived effectiveness. All subjects preferred experimental conditions employing haptic feedback with respect to those not providing any force feedback.

Needle insertion in soft-tissue is a minimally invasive surgical procedure which demands high accuracy. In this respect, robotic systems with autonomous control algorithms have been exploited as the main tool to achieve high accuracy and reliability. However, for reasons of safety and acceptance by the surgical community, autonomous robotic control is not desirable. Thus, it is necessary to focus more on techniques enabling clinicians to directly control the motion of surgical tools. In this work we address that challenge and present a novel teleoperated robotic system able to steer flexible needles. The proposed system tracks the position of the needle using an ultrasound imaging system, and, from that, it computes needle's ideal position and orientation to reach a given target. The master haptic interface then provides mixed kinesthetic-vibratory navigation cues about this ideal position and orientation to the clinician as she steers the needle. Six subjects carried out an experiment of teleoperated needle insertion into a soft-tissue phantom. They showed a mean targeting error of 1.36 mm. An additional experiment of remote teleoperation has been carried out to highlight the passivity-based stability of the proposed system.

A study on the role of cutaneous and kinesthetic force feedback in teleoperation is presented. Cutaneous cues provide less transparency than kinesthetic force, but they do not affect the stability of the teleoperation system. On the other hand, kinesthesia provides a compelling illusion of telepresence but affects the stability of the haptic loop. However, when employing common grounded haptic interfaces, it is not possible to independently control the cutaneous and kinesthetic components of the interaction. For this reason, many control techniques ensure a stable interaction by scaling down both kinesthetic and cutaneous force feedback, even though acting on the cutaneous channel is not necessary. We discuss here the feasibility of a novel approach. It aims at improving the realism of the haptic rendering, while preserving its stability, by modulating cutaneous force to compensate for a lack of kinesthesia. We carried out two teleoperation experiments, evaluating (1) the role of cutaneous stimuli when reducing kinesthesia and (2) the extent to which an overactuation of the cutaneous channel can fully compensate for a lack of kinesthetic force feedback. Results showed that, to some extent, it is possible to compensate for a lack of kinesthesia with the aforementioned technique, without significant performance degradation. Moreover, users showed a high comfort level in using the proposed system.

This paper introduces a new approach to haptic feedback during teleoperated robot-assisted surgery. Haptic feedback allows to display to the surgeon the local mechanical properties of the tissue being manipulated, as well as additional information, such as navigation cues. However, when the same end-effector is used to present multiple types of information, there is the risk of confusing the sources of force feedback signals provided to the operator. The objective of this work is to study how to efficiently combine remote tissue sensing and haptic guidance, in order to make the surgeon aware of the source of the stimuli. We propose to use vibrotactile feedback to render navigation cues and kinesthetic feedback to reproduce the mechanical properties of the tissue. The viability of this approach is validated with two experiments where vibrotactile-guided navigation achieves promising performance and allows users to easily disambiguate forces due to the action of guiding constraints and forces due to the interaction with the remote tissue.

A study on the role of cutaneous and kinesthetic force feedback in teleoperation is presented. Cutaneous cues provide less transparency than kinesthetic force feedback but they do not affect the stability of the teleoperation system. On the other hand, kinesthesia provides a realistic illusion of telepresence but it affects the stability of the haptic loop. Several well-established control techniques ensure a stable interaction by scaling down force feedback as and when required, in order to satisfy the controller stability conditions (e.g., passivity). We here discuss the feasibility of a novel approach to improve the realism of the haptic rendering while preserving its stability: can cutaneous stimuli be employed to compensate for the lack of kinesthetic feedback required to guarantee the stability of the teleoperation loop? We carried out two experiments to evaluate the role of cutaneous cues in teleoperation and the performance improvement rate when compensating a lack of kinesthesia with cutaneous force. Results showed improved performance while employing the aforementioned compensation technique and a high comfort in using the proposed system.

A novel idea for improving transparency of teleoperation systems with force feedback is presented. This approach is based on the idea of sensory subtraction presented in [12], and consists of providing the operator with independently controlled kinesthetic and cutaneous feedback to improve the realism of haptic rendering of the remote environment (i.e., transparency), while preserving stability. More specifically, cutaneous force feedback is employed to recover transparency when a lack of kinesthetic feedback has to be enforced to keep the teleoperation loop stable. The viability of this approach is demonstrated with two experiments of teleoperated needle insertion. Results showed improved performance with respect to common control techniques not employing the proposed cutaneous compensation.

This paper presents some preliminary results on RemoTouch, a system allowing to perform experiences of remote touch. The system consists of an avatar equipped with an instrumented glove and a user wearing tactile displays allowing to feel the remote tactile interaction. The main features of RemoTouch are that it is a wearable system and that a human avatar is used to collect remote tactile interaction data. New paradigms of tactile communication can be designed around the RemoTouch system. Two simple experiences are reported to show the potential of the proposed remote touch architecture.