A Comparison of Pneumatic Actuators for Soft Growing Vine Robots.

Soft pneumatic actuators are used to steer soft growing "vine" robots while being flexible enough to undergo the tip eversion required for growth. In this study, we compared the performance of three types of pneumatic actuators in terms of their ability to perform eversion, quasi-static bending, dynamic motion, and force output: the pouch motor, the cylindrical pneumatic artificial muscle (cPAM), and the fabric pneumatic artificial muscle (fPAM). The pouch motor is advantageous for prototyping owing to its simple manufacturing process. The cPAM exhibits superior bending behavior and produces the highest forces, whereas the fPAM actuates fastest and everts at the lowest pressure. We evaluated a range of dimensions for each actuator type. Larger actuators can produce more significant deformations and forces, but smaller actuators inflate faster and can evert at a lower pressure. Because vine robots are lightweight, the effect of gravity on the functionality of different actuators is minimal. We developed a new analytical model that predicts the pressure-to-bending behavior of vine robot actuators. Using the actuator results, we designed and demonstrated a 4.8 m long vine robot equipped with highly maneuverable 60 × 60 mm cPAMs in a three-dimensional obstacle course. The vine robot was able to move around sharp turns, travel through a passage smaller than its diameter, and lift itself against gravity.

Leveraging Haptic Feedback to Improve Data Quality and Quantity for Deep Imitation Learning Models.

Learning from demonstration is a proven technique to teach robots new skills. Data quality and quantity play a critical role in the performance of models trained using data collected from human demonstrations. In this paper we enhance an existing teleoperation data collection system with real-time haptic feedback to the human demonstrators; we observe improvements in the collected data throughput and in the performance of autonomous policies using models trained with the data. Our experimental testbed was a mobile manipulator robot that opened doors with latch handles. Evaluation of teleoperated data collection on eight real conference room doors found that adding haptic feedback improved data throughput by 6%. We additionally used the collected data to train six image-based deep imitation learning models, three with haptic feedback and three without it. These models were used to implement autonomous door-opening with the same type of robot used during data collection. A policy from a imitation learning model trained with data collected while the human demonstrators received haptic feedback performed on average 11% better than its counterpart trained with data collected without haptic feedback, indicating that haptic feedback provided during data collection resulted in improved autonomous policies.

Stiffness Change for Reconfiguration of Inflated Beam Robots.

Abstract Active control of the shape of soft robots is challenging. Despite having an infinite number of passive degrees of freedom (DOFs), soft robots typically only have a few actively controllable DOFs, limited by the number of degrees of actuation (DOAs). The complexity of actuators restricts the number of DOAs that can be incorporated into soft robots. Active shape control is further complicated by the buckling of soft robots under compressive forces; this is particularly challenging for compliant continuum robots due to their long aspect ratios. In this study, we show how variable stiffness enables shape control of soft robots by addressing these challenges. Dynamically changing the stiffness of sections along a compliant continuum robot selectively "activates" discrete joints. By changing which joints are activated, the output of a single actuator can be reconfigured to actively control many different joints, thus decoupling the number of controllable DOFs from the number of DOAs. We demonstrate embedded positive pressure layer jamming as a simple method for stiffness change in inflated beam robots, its compatibility with growing robots, and its use as an "activating" technology. We experimentally characterize the stiffness change in a growing inflated beam robot and present finite element models that serve as guides for robot design and fabrication. We fabricate a multisegment everting inflated beam robot and demonstrate how stiffness change is compatible with growth through tip eversion, enables an increase in workspace, and achieves new actuation patterns not possible without stiffening.

Development and Evaluation of a Learning-based Model for Real-time Haptic Texture Rendering.

Current Virtual Reality (VR) environments lack the haptic signals that humans experience during real-life interactions, such as the sensation of texture during lateral movement on a surface. Adding realistic haptic textures to VR environments requires a model that generalizes to variations of a user's interaction and to the wide variety of existing textures in the world. Current methodologies for haptic texture rendering exist, but they usually develop one model per texture, resulting in low scalability. We present a deep learning-based action-conditional model for haptic texture rendering and evaluate its perceptual performance in rendering realistic texture vibrations through a multi-part human user study. This model is unified over all materials and uses data from a vision-based tactile sensor (GelSight) to render the appropriate surface conditioned on the user's action in real-time. For rendering texture, we use a high-bandwidth vibrotactile transducer attached to a 3D Systems Touch device. The results of our user study shows that our learning-based method creates high-frequency texture renderings with comparable or better quality than state-of-the-art methods without the need to learn a separate model per texture. Furthermore, we show that the method is capable of rendering previously unseen textures using a single GelSight image of their surface.

Design and Evaluation of a 3-DoF Haptic Device for Directional Shear Cues on the Forearm.

Wearable haptic devices on the forearm can relay information from virtual agents, robots, and other humans while leaving the hands free. We introduce and test a new wearable haptic device that uses soft actuators to provide normal and shear force to the skin of the forearm. A rigid housing and gear motor are used to control the direction of the shear force. A 6-axis force/torque sensor, distance sensor, and pressure sensors are integrated to quantify how the soft tactor interacts with the skin. When worn by participants, the device delivered consistent shear forces of up to 0.64 N and normal forces of up to 0.56 N over distances as large as 14.3 mm. To understand cue saliency, we conducted a user study asking participants to identify linear shear directional cues in a 4-direction task and an 8-direction task with different cue speeds, travel distances, and contact patterns. Participants identified cues with longer travel distances best, with an 85.1% accuracy in the 4-direction task, and a 43.5% accuracy in the 8-direction task. Participants had a directional bias, with a preferential response in the axis towards and away from the wrist bone.

A Comparative Analysis of Smartphone and Standard Tools for Touch Perception Assessment Across Multiple Body Sites.

Tactile perception plays an important role in activities of daily living, and it can be impaired in individuals with certain medical conditions. The most common tools used to assess tactile sensation, the Semmes-Weinstein monofilaments and the 128 Hz tuning fork, have poor repeatability and resolution. Long term, we aim to provide a repeatable, high-resolution testing platform that can be used to assess vibrotactile perception through smartphones without the need for an experimenter to be present to conduct the test. We present a smartphone-based vibration perception measurement platform and compare its performance to measurements from standard monofilament and tuning fork tests. We conducted a user study with 36 healthy adults in which we tested each tool on the hand, wrist, and foot, to assess how well our smartphone-based vibration perception thresholds (VPTs) detect known trends obtained from standard tests. The smartphone platform detected statistically significant changes in VPT between the index finger and foot and also between the feet of younger adults and older adults. Our smartphone-based VPT had a moderate correlation to tuning fork-based VPT. Our overarching objective is to develop an accessible smartphone-based platform that can eventually be used to measure disease progression and regression.

Haptic Guidance and Haptic Error Amplification in a Virtual Surgical Robotic Training Environment.

Teleoperated robotic systems have introduced more intuitive control for minimally invasive surgery, but the optimal method for training remains unknown. Recent motor learning studies have demonstrated that exaggeration of errors helps trainees learn to perform tasks with greater speed and accuracy. We hypothesized that training in a force field that pushes the user away from a desired path would improve their performance on a virtual reality ring-on-wire task. Thirty-eight surgical novices trained under a no-force, guidance, or error-amplifying force field over five days. Completion time, translational and rotational path error, and combined errortime were evaluated under no force field on the final day. The groups significantly differed in combined error-time, with the guidance group performing the worst. Error-amplifying field participants did not plateau in their performance during training, suggesting that learning was still ongoing. Guidance field participants had the worst performance on the final day, confirming the guidance hypothesis. Observed trends also suggested that participants who had high initial path error benefited more from guidance. Error-amplifying and error-reducing haptic training for robot-assisted telesurgery benefits trainees of different abilities differently, with our results indicating that participants with high initial combined error-time benefited more from guidance and error-amplifying force field training.

Design and Evaluation of Haptic Guidance in Ultrasound-Based Needle-Insertion Procedures.

OBJECTIVE: This article presents two haptic guidance systems designed to help a clinician keep an ultrasound probe steady when completing ultrasound-assisted needle insertion tasks. These procedures demand spatial reasoning and hand-eye coordination because the clinician must align a needle with the ultrasound probe and extrapolate the needle trajectory using only a 2D ultrasound image. Past research has shown that visual guidance helps the clinician align the needle, but does not help the clinician keep the ultrasound probe steady, sometimes resulting in a failed procedure. METHODS: We created two separate haptic guidance systems to provide feedback if the user tilts the ultrasound probe away from the desired setpoint using (1) vibrotactile stimulation provided by a voice coil motor or (2) distributed tactile pressure provided by a pneumatic mechanism. RESULTS: Both systems significantly reduced probe deviation and correction time to errors during a needle insertion task. We also tested the two feedback systems in a more clinically relevant setup and showed that the perceptibility of the feedback was not affected by the addition of a sterile bag placed over the actuators and gloves worn by the user. CONCLUSION: These studies show that both types of haptic feedback are promising for helping the user keep the ultrasound probe steady during ultrasound-assisted needle insertion tasks. Survey results indicated that users preferred the pneumatic system over the vibrotactile system. SIGNIFICANCE: Haptic feedback may improve user performance in ultrasound-based needle-insertion procedures and shows promise in training for needle-insertion tasks and other medical procedures where guidance is required.

Haptics: The Science of Touch As a Foundational Pathway to Precision Education and Assessment.

ABSTRACT: Clinical touch is the cornerstone of the doctor-patient relationship and can impact patient experience and outcomes. In the current era, driven by an ever-increasing infusion of point-of-care technologies, physical exam skills have become undervalued. Moreover, touch and hands-on skills have been difficult to teach due to inaccurate assessments and difficulty with learning transfer through observation. In this article, the authors argue that haptics, the science of touch, provides a unique opportunity to explore new pathways to facilitate touch training. Furthermore, haptics can dramatically increase the density of touch-based assessments without increasing human rater burden-essential for realizing precision assessment. The science of haptics is reviewed, including the benefits of using haptics-informed language for objective structured clinical examinations. The authors describe how haptic devices and haptic language have and can be used to facilitate learning, communication, documentation and a much-needed reinvigoration of physical examination, and touch excellence at the point of care. The synergy of haptic devices, artificial intelligence, and virtual reality environments are discussed. The authors conclude with challenges of scaling haptic technology in medical education, such as cost and translational needs, and opportunities to achieve wider adoption of this transformative approach to precision education.

Evaluation of a Passive Wearable Device for Post-Stroke Shoulder Abduction Support.

Post-stroke upper extremity function can be improved by devices that support shoulder abduction. However, many of these devices provide limited assistance in activities of daily living due to their complexity and encumbrance. We developed and evaluated a passive, lightweight (0.6 kg) wearable device consisting of an aluminum frame and elastic bands attached to a posture vest to aid in shoulder abduction. The number and thickness of bands can be adjusted to provide supportive forces to the affected arm. We measured reachable workspace area and Wolf Motor Function Test (WMFT) performance in people with a history of stroke (n = 11) with and without the wearable. The device increased workspace area in 6 participants and improved average WMFT functional and timing scores in 7 and 12 tasks, respectively, out of 16 total tasks. On average, participants increased their arm motion within 20 cm of shoulder level by 22.4% and decreased their hand's average distance from trunk by 15.2%, both improvements in the device case.

Relief of post-stroke spasticity with acute vibrotactile stimulation: controlled crossover study of muscle and skin stimulus methods.

Background: Prior work suggests that vibratory stimulation can reduce spasticity and hypertonia. It is unknown which of three predominant approaches (stimulation of the spastic muscle, antagonist muscle, or cutaneous regions) most reduces these symptoms. Objective: Determine which vibrotactile stimulation approach is most effective at reducing spastic hypertonia among post-stroke patients. Methods: Sham-controlled crossover study with random assignment of condition order in fourteen patients with post-stroke hand spasticity. All patients were studied in four conditions over four visits: three stimulation conditions and a sham control. The primary outcome measure was the Modified Ashworth Scale, and the secondary outcome measure was the Modified Tardieu Scale measured manually and using 3D motion capture. For each condition, measures of spastic hypertonia were taken at four time points: baseline, during stimulation, after stimulation was removed, and after a gripping exercise. Results: A clinically meaningful difference in spastic hypertonia was found during and after cutaneous stimulation of the hand. Modified Ashworth and Modified Tardieu scores were reduced by a median of 1.1 (SD = 0.84, p = 0.001) and 0.75 (SD = 0.65, p = 0.003), respectively, during cutaneous stimulation, and by 1.25 (SD = 0.94, p = 0.001) and 0.71 (SD = 0.67, p = 0.003), respectively, at 15 min after cutaneous stimulation. Symptom reductions with spastic muscle stimulation and antagonist muscle stimulation were non-zero but not significant. There was no change with sham stimulation. Conclusions: Cutaneous vibrotactile stimulation of the hand provides significant reductions in spastic hypertonia, compared to muscle stimulation. Clinical trial registration: www.ClinicalTrials.gov, identifier: NCT03814889.

Between-Tactor Display Using Dynamic Tactile Stimuli for Directional Cueing in Vibrating Environments.

Torso-worn vibrotactile devices have been used in many studies on directional cueing and navigation in environments where visual feedback is limited. These devices aim to indicate directions with high resolution while using the smallest possible number of vibration motors (tactors). Resolution can be increased using between-tactor displays, but their performance in vibrating environments (e.g., a helicopter) are unknown. This study proposes a between-tactor display using dynamic stimuli and verifies its effectiveness when the user sits in a vibrating chair. We developed a waist belt device that displays 12 directions using 6 tactors. Static stimuli display virtual (between-tactor) locations by constantly vibrating two adjacent tactors equally, whereas dynamic stimuli move the virtual vibration position back and forth between tactors. We performed two studies in which participants felt tactile stimuli and used a joystick to move a cursor on a screen to a target in the perceived direction. Direction recognition accuracy and task completion time were measured under combined conditions of two belt orientations (tactor alignments), with and without chair vibration, and with and without audio white noise to mask tactor sound. In all conditions, dynamic stimuli increased recognition accuracy while maintaining task completion time compared to static stimuli.

Wearable Sensory Substitution for Proprioception via Deep Pressure.

We propose a sensory substitution device that communicates one-degree-of-freedom proprioceptive feedback via deep pressure stimulation on the arm. The design is motivated by the need for a feedback modality detectable by individuals with a genetic condition known as PIEZO2 loss of function, which is characterized by absence of both proprioception and sense of light touch. We created a wearable and programmable prototype that applies up to 15 N of deep pressure stimulation to the forearm and includes an embedded force sensor. We conducted a study to evaluate the ability of participants without sensory impairment to control the position of a virtual arm to match a target angle communicated by deep pressure stimulation. A participant-specific calibration resulted in an average minimum detectable force of 0.41 N and maximum comfortable force of 6.42 N. We found that, after training, participants were able to significantly reduce angle error using the deep pressure haptic feedback compared to without it. Angle error increased only slightly with force, indicating that this sensory substitution method is a promising approach for individuals with PIEZO2 loss of function and other forms of sensory loss.

A Modular 3-Degrees-of-Freedom Force Sensor for Robot-Assisted Minimally Invasive Surgery Research.

Effective force modulation during tissue manipulation is important for ensuring safe, robot-assisted, minimally invasive surgery (RMIS). Strict requirements for in vivo applications have led to prior sensor designs that trade off ease of manufacture and integration against force measurement accuracy along the tool axis. Due to this trade-off, there are no commercial, off-the-shelf, 3-degrees-of-freedom (3DoF) force sensors for RMIS available to researchers. This makes it challenging to develop new approaches to indirect sensing and haptic feedback for bimanual telesurgical manipulation. We present a modular 3DoF force sensor that integrates easily with an existing RMIS tool. We achieve this by relaxing biocompatibility and sterilizability requirements and by using commercial load cells and common electromechanical fabrication techniques. The sensor has a range of ±5 N axially and ±3 N laterally with errors of below 0.15 N and maximum errors below 11% of the sensing range in all directions. During telemanipulation, a pair of jaw-mounted sensors achieved average errors below 0.15 N in all directions. It achieved an average grip force error of 0.156 N. The sensor is for bimanual haptic feedback and robotic force control in delicate tissue telemanipulation. As an open-source design, the sensors can be adapted to suit other non-RMIS robotic applications.

Cognitive and Physical Activities Impair Perception of Smartphone Vibrations.

Vibration feedback is common in everyday devices, from virtual reality systems to smartphones. However, cognitive and physical activities may impede our ability to sense vibrations from devices. In this study, we develop and characterize a smartphone platform to investigate how a shape-memory task (cognitive activity) and walking (physical activity) impair human perception of smartphone vibrations. We measured how Apple's Core Haptics Framework parameters can be used for haptics research, namely how hapticIntensity modulates amplitudes of 230 Hz vibrations. A 23-person user study found that physical ( ) and cognitive ( p=0.012) activity increase vibration perception thresholds. Cognitive activity also increases vibration response time ( ). This work also introduces a smartphone platform that can be used for out-of-lab vibration perception testing. Researchers can use our smartphone platform and results to design better haptic devices for diverse, unique populations.

Daily Vibrotactile Stimulation Exhibits Equal or Greater Spasticity Relief Than Botulinum Toxin in Stroke.

OBJECTIVE: To test the feasibility and efficacy of the VibroTactile Stimulation (VTS) Glove, a wearable device that provides VTS to the impaired limb to reduce spastic hypertonia. DESIGN: Prospective 2-arm intervention study-including 1 group of patients who use Botulinum toxin (BTX-A) for spasticity and 1 group of patients who do not use BTX-A. SETTING: Participants were recruited through rehabilitation and neurology clinics. PARTICIPANTS: Patients with chronic stroke (N=20; mean age=54 years, mean time since stroke=6.9 years). Patients who were previously receiving the standard of care (BTX-A injection) were eligible to participate and started the intervention 12 weeks after their last injection. INTERVENTION: Participants were instructed to use the VTS Glove for 3 hours daily, at home or during everyday activities, for 8 weeks. MAIN OUTCOME MEASURES: Spasticity was assessed with the Modified Ashworth Scale and the Modified Tardieu Scale at baseline and then at 2-week intervals for 12 weeks. Primary outcomes were the difference from baseline and at week 8 (end of VTS Glove use) and week 12 (4 weeks after stopping VTS Glove use). Patients who were receiving BTX-A were also assessed during the 12 weeks preceding the start of VTS Glove use to monitor the effect of BTX-A on spastic hypertonia. Range of motion and participant feedback were also studied. RESULTS: A clinically meaningful difference in spastic hypertonia was found during and after daily VTS Glove use. Modified Ashworth and Modified Tardieu scores were reduced by an average of 0.9 (P=.0014) and 0.7 (P=.0003), respectively, at week 8 of daily VTS Glove use, and by 1.1 (P=.00025) and 0.9 (P=.0001), respectively, 1 month after stopping VTS Glove use. For participants who used BTX-A, 6 out of 11 showed greater change in Modified Ashworth ratings during VTS Glove use (mean=-1.8 vs mean=-1.6 with BTX-A) and 8 out of 11 showed their lowest level of symptoms during VTS Glove use (vs BTX-A). CONCLUSIONS: Daily stimulation from the VTS Glove provides relief of spasticity and hypertonia. For more than half of the participants who had regularly used BTX-A, the VTS Glove provided equal or greater symptom relief.

Human Perception of Wrist Flexion and Extension Torque During Upper and Lower Extremity Movement.

Real-world application of haptic feedback from kinesthetic devices is implemented while the user is in motion, but human wrist torque magnitude discrimination has previously only been characterized while users are stationary. In this study, we measured wrist torque discrimination in conditions relevant to activities of daily living, using a previously developed backdrivable wrist exoskeleton capable of applying wrist flexion and extension torque. We implemented a torque comparison test using a two-alternative forced-choice paradigm while participants were both seated and walking on a treadmill, with both a stationary and a moving wrist. Like most kinesthetic haptic devices, the wrist exoskeleton output torque is commanded in an open-loop manner. Thus, the study design was informed by Monte Carlo simulations to verify that the errors in the wrist exoskeleton output torque would not significantly affect the results. Results from ten participants show that although both walking and moving wrist conditions result in higher Weber Fractions (worse perception), participants were able to detect relatively small changes in torque of 12-19% on average in all grouped conditions. The results provide insight regarding the torque magnitudes necessary to make wrist-worn kinesthetic haptic devices noticeable and meaningful to the user in various conditions relevant to activities of daily living.

Design of a Wearable Vibrotactile Stimulation Device for Individuals With Upper-Limb Hemiparesis and Spasticity.

Vibratory stimulation may improve post-stroke symptoms such as spasticity; however, current studies are limited by the large, clinic-based apparatus used to apply this stimulation. A wearable device could provide vibratory stimulation in a mobile form, enabling further study of this technique. An initial device, the vibrotactile stimulation (VTS) Glove, was deployed in an eight-week clinical study in which sixteen individuals with stroke used the device for several hours daily. Participants reported wearing the glove during activities such as church, social events, and dining out. However, 69% of participants struggled to extend or insert their fingers to don the device. In a follow-up study, eight individuals with stroke evaluated new VTS device prototypes in a three-round iterative design study with the aims of creating the next generation of VTS devices and understanding features that influence interaction with a wearable device by individuals with impaired upper-limb function. Interviews and interaction tasks were used to define actionable design revisions between each round of evaluation. Our analysis identified six new themes from participants regarding device designs: hand supination is challenging, separate finger attachments inhibit fit and use, fingers may be flexed or open, fabric coverage impacts comfort, a reduced concern for social comfort, and the affected hand is infrequently used. Straps that wrap around the arm and fixtures on the anterior arm were other challenging features. We discuss potential accommodations for these challenges, as well as social comfort. New VTS device designs are presented and were donned in an average time of 48 seconds.

Data-Driven Sparse Skin Stimulation Can Convey Social Touch Information to Humans.

During social interactions, people use auditory, visual, and haptic cues to convey their thoughts, emotions, and intentions. Due to weight, energy, and other hardware constraints, it is difficult to create devices that completely capture the complexity of human touch. Here we explore whether a sparse representation of human touch is sufficient to convey social touch signals. To test this we collected a dataset of social touch interactions using a soft wearable pressure sensor array, developed an algorithm to map recorded data to an array of actuators, then applied our algorithm to create signals that drive an array of normal indentation actuators placed on the arm. Using this wearable, low-resolution, low-force device, we find that users are able to distinguish the intended social meaning, and compare performance to results based on direct human touch. As online communication becomes more prevalent, such systems to convey haptic signals could allow for improved distant socializing and empathetic remote human-human interaction.

Effects of Peripheral Haptic Feedback on Intracortical Brain-Computer Interface Control and Associated Sensory Responses in Motor Cortex.

Intracortical brain-computer interfaces (iBCIs) provide people with paralysis a means to control devices with signals decoded from brain activity. Despite recent impressive advances, these devices still cannot approach able-bodied levels of control. To achieve naturalistic control and improved performance of neural prostheses, iBCIs will likely need to include proprioceptive feedback. With the goal of providing proprioceptive feedback via mechanical haptic stimulation, we aim to understand how haptic stimulation affects motor cortical neurons and ultimately, iBCI control. We provided skin shear haptic stimulation as a substitute for proprioception to the back of the neck of a person with tetraplegia. The neck location was determined via assessment of touch sensitivity using a monofilament test kit. The participant was able to correctly report skin shear at the back of the neck in 8 unique directions with 65% accuracy. We found motor cortical units that exhibited sensory responses to shear stimuli, some of which were strongly tuned to the stimuli and well modeled by cosine-shaped functions. In this article, we also demonstrated online iBCI cursor control with continuous skin-shear feedback driven by decoded command signals. Cursor control performance increased slightly but significantly when the participant was given haptic feedback, compared to the purely visual feedback condition.