Humans continuously adapt to new sensorimotor environments, wherein we create motor commands to execute movements properly, such as picking up the telephone or riding a bike. Generalization of motor commands means that a learned movement, such as grasping a bottle, transfers to similar but new environments, such as grasping a carton of milk. However, it remains unclear to what extent we are able to learn an uncertain variable environment and to what extent these learned movements transfer to a new environment. We compared generalization to a new environment after learning a fixed (F) or trial-by-trial variable (V) velocity-dependent clockwise force field. Selecting the damping coefficients from a predefined distribution on a trial-by-trial basis introduced the variability for the variable group during the training trials, while the fixed group had a fixed damping coefficient during training. After training, both groups made reaching movements in a new force field that was fixed over all trials. Due to the uncertainty in the force field strengths, we hypothesized that the variable group would have more difficulties with adapting compared to the fixed group. However, because the variable group would experience more different force fields during the training, we hypothesized that they would perform better in the new environment. Based on the force field compensation factors, the adaptation to the training fields was: 79.8% (F) and 79.7% (V), p = 0.982. The generalization learning was similar for both groups: 78.8% (F) and 78.9%, p = 0.986. Interestingly, the trajectory measurements showed that the variable group was less accurate than the fixed group in the training fields, but more accurate in the generalization field. Therefore, our results show that variable force field perturbations can be learned and generalized in a similar manner as fixed perturbations and that the variable group, despite a more inaccurate performance in the training block, reached more accurately than the fixed group in the new environment.

Objectives – Over the past decades, more and more cardiac diseases have been treated in interventional cardiology. Catheters are generally used to access the heart through the blood vessels. The previously developed steerable Sigma catheter at Delft University of Technology, tackles cable related challenges of conventional mechanically controlled catheters by an improved tip and shaft design. With its two finger-controlled joysticks, the handle allows full actuation of the four degrees of freedom catheter tip. However, this input control method is not specifically designed for optimal user experience. Therefore, the aim of this research is to design an input control method for the Sigma catheter tip and shaft design to improve task performance while reducing workload for the interventionist. Methods – A theoretical framework was composed and analysed to form design requirements. After detailing the functional and geometrical design, a functional prototype, the Epsilon catheter, was fabricated. To evaluate the proposed control method, an experimental setup was prepared and the control method of both catheters were compared. Six participants were asked to conduct the task, which consisted of contacting targets with the catheter end-point. Target-to-target times were measured and a self-report questionnaire was conducted. Results – The theoretical analysis was divided in the interventional environment, the interventionist who controls the catheter, and the instrumentation. A functional design was made, including catheter control through combining multiple fingers and the wrist using positive input-output coupling. The geometrical design achieved these functionalities through bending flexures and a 180° bended shaft. Data analysis of the experiment showed differences in target-to-target times and self-reported measures. Conclusion – The Epsilon prototype showed to fulfil on the requirements in a functionality test. The prototype allows steering the catheter tip in five degrees of freedom, single-handed in a handheld design. In the experimental setup, participants using the control method of the Epsilon catheter, performed the targeting task faster than using the Sigma catheter with reduced workload. Significance – Allowing the interventionist to control all manoeuvrability of the catheter tip single handed, may change the operational procedure during interventional cardiology. A single interventionist could perform extended treatment using two individually controlled multi-steerable catheters. Further developments will be towards design optimisations to further improve user experience and evaluation of the fifth degree of freedom.

Endoscopic instruments are integral components of minimally invasive procedures, widely used for diagnoses and treatment of diseases. When navigating the endoscope, it should experience a minimum of friction, while an increase in friction is beneficial for performing the medical procedure. Friction can be reduced by squeeze film levitation, where air is trapped and pressurized between two surfaces by vibrating one of these surfaces. The squeeze film levitates the two surfaces away from each other, hereby reducing friction. Squeeze film levitation between a rigid curved surface and a soft surface is still poorly understood. Also, a proof of concept of a friction modulation mechanism for endoscopes is not yet available in the research literature. Therefore, this paper describes the design and experimental validation of an ultrasonic vibrating ring that can actively modulate friction by generating a squeeze film. On a steel surface, the friction is reduced considerably. However, on the two soft surfaces described in this paper, the reduction of friction is absent.

This open access book constitutes the proceedings of the 12th International Conference on Human Haptic Sensing and Touch Enabled Computer Applications, EuroHaptics 2020, held in Leiden, The Netherlands, in September 2020. The 60 papers presented in this volume were carefully reviewed and selected from 111 submissions. The were organized in topical sections on haptic science, haptic technology, and haptic applications. This year's focus is on accessibility. @en

The provision of somatosensory information may play a fundamental role in the recovery of stroke patients. Particularly, tactile information is known to influence motor control by contributing to the perception of the weight, friction, and slip condition of objects. Despite this, the inclusion of tactile information through haptic rendering in robotic neurorehabilitation systems remains largely unexplored. In this study, we present a tactile interface to extend the kinesthetic rendering capabilities of an existing hand rehabilitation robot. The developed solution relies on skin stretch stimulation of the fingerpads, which allows the rendering of interaction forces with tangible virtual objects, e.g., friction, weight, and inertia. In contrast with previous skin stretch devices, our system uses closed-loop force control for accurate force rendering, relying on a custom magnetic field-based three-axis force sensor. A three-axis positioning stage in combination with a reference force sensor was used for calibrating and characterizing the sensor, as well as evaluating the interface response. The sensor achieves shear force accuracies of 0.2 N, influenced by hysteresis and viscoelastic creep effects. The tactile interface achieves a steady-state error of 0.2–0.4N and rise times of 20–70 ms during step response tests. Frequency response tests show that the interface can successfully track signals up to 5–7 Hz. The novel use of force-controlled skin stretch stimulation aims to open a new avenue for the accurate rendering of interaction forces through the tactile sense. Moreover, through purposeful design for usage in the rehabilitation domain, we hope that this study will serve as a stepping stone toward the inclusion of tactile information in robot-assisted therapies.

Incipient slip detection plays an important role in human and robotic grasping. With the growing use of deep learning in vision-based tactile sensing, the black-box nature of these deep neural networks (DNNs) makes it difficult to analyze, debug, and validate their behavior and learned patterns. To fill this gap, eXplainable AI (XAI) methods have been introduced to shed light into the DNN’s reasoning regarding incipient slip detection. These methods generate saliency maps, highlighting the relevant regions in the input tactile image that resulted in the predicted degree of incipient slip. Temporal difference images have been used to enhance the visualization of incipient slip and make saliency maps easier for human viewers to understand. Additionally, this research evaluates several XAI methods based on criteria such as high-resolution, smoothness, and faithfulness. The experiment examined 42 samples from the ChromaTouch tactile dataset, focusing on contact interactions with a flat object. The results showed that Poly-CAM satisfies all three criteria by accurately highlighting markers while emphasizing their relative importance in the DNN’s decision-making process. Overall, through visual analysis of saliency maps, our findings confirm that DNNs have successfully learned to localize crucial deformation features for detecting incipient slip.

Navigating touchscreens in vehicles becomes increasingly challenging when subjected to external perturbations like air turbulence or bumpy roads. These perturbations can lead to a loss in task performance, reduced finger accuracy, and increased frustration among users. To address these issues, electrovibration has emerged as a promising technology to enhance touchscreen interactions by providing users with better feedback and maintaining touch stability even under challenging conditions. Before we investigate if electrovibration helps users in challenging conditions, first the effects of external perturbations on tactile perception by electrovibration must be found. To investigate the impact of external perturbations on electrovibration perception, we conducted psychophysical experiments with 18 participants interacting with an electrostatic display mounted on the cockpit of the SIMONA flight simulator. We measured participants’ absolute detection thresholds for electrovibration pulses generated using 100 Hz input voltage for durations of 0.2 and 0.5 seconds, simulating a ridge and a button or slider. The measurements were taken under no-turbulence conditions and two different turbulence conditions. Our results revealed that turbulence significantly affects vertical finger movement, average normal force, and the change in force applied to the screen by participants. This combination of factors, along with the 0.2-second pulse duration, makes electrovibration more difficult to perceive or even imperceptible. The 0.5-second electrovibration pulse was perceived better overall and remained unaffected by turbulence. This highlights the strong significance of pulse duration on the absolute threshold of electrovibration. Therefore, to counteract the negative effects of perturbations on perception, electrovibration should be employed for longer durations when perturbations are present.

In the field of soft robotics, rigid joints and links are replaced by soft, deformable elements, This causes soft continuum robot arms to excel in unpredictable environments, but to face challenges during control and shape reconstruction. The sensing ability present in octopus suckers provides inspiration for solutions. Octopuses employ their suckers not only to strengthen their grasp but also as tactile sensors to control the shape and position of their soft arms. This has motivated researchers to integrate artificial sensorized suckers in soft continuum robot arms Although various sensorized suckers have already been developed, their employed sensing methods tend to be low in resolution and are often poorly embedded into the overall sucker architecture. In this work, these limits are overcome by presenting an octopus-inspired suction cup with integrated high-resolution tactile sensing abilities. This is achieved by utilizing the Chromatouch Principle, which relies on embedding colored markers in the suction cup membrane. Tracking these markers with a camera produced tactile images containing useful information about forces, deformations and interactions with objects. Fabrication with multi-material additive manufacturing enabled direct integration of these markers into the suction cup membranes. We demonstrated the design’s basic functionality by conducting pull-off and pickup tests. The design exhibited a normal pull-off force of 9.53 N and a shear pull-off force of 5.28 N. It was also able to successfully pick up both flat and curved objects. The sensing ability was showcased by training a Convolutional Neural Network to learn the relationship between the camera images and the orientation of the suction cup with respect to a touching substrate. Using a spherical coordinate system, the orientation could be predicted with an error of less than 2 degrees for latitude and less than 9 degrees for longitude. This performance was validated by using the trained network to successfully correct the orientation when picking up objects under an angle. For a single suction cup, this ability can be utilized to correct the orientation and achieve perpendicular contact with an object, crucial for achieving a seal. On a larger scale, the integration of multiple suction cups in soft continuum robot arms has the potential to form a representation of the arm shape as a whole. It can thereby contribute to overcoming the control challenges faced in the field of soft robotics.

In dangerous environments, teleoperation is needed to enable humans to execute tasks remotely. To assist in these tasks, haptic teleoperation systems provide the human operator with the sense of touch of the telerobot. One way to provide this sense of touch is through high-frequency vibration feedback. State-of-the-art solutions generally rely on integrated hardware, which limits their application to specific telerobots and master devices. The aim of this study is to develop a deployable high-frequency vibration feedback method through an add-on setup. In the presented system, both the vibration recording device and vibration feedback display run on a single microcontroller. Furthermore, all components are small in size and portable by the robotic or human hand. Spectral analysis of the replicated vibrations shows that the presented system is capable of mimicking textures. To evaluate the effectiveness of the texture imitations, a human factors experiment is conducted. Twenty participants executed a texture identification task for two conditions: a manual condition with direct tactile feedback and a teleoperated condition with tactile feedback displayed by the presented system. Results show that 75-85% of the textures were correctly identified in the teleoperated condition. These correctness rates are close to the results of the manual condition (96% correct) and outperform the chances of random guessing by a factor three. In the teleoperated condition, participants took on average 67% longer than in the manual feedback condition. Based on these results, it is concluded that the presented add-on system enables humans to accurately feel high-frequency vibrations in teleoperation.

Creating a lateral force on a finger touching a touch- screen can provide the sensation of a bump in the surface, and generate a pulling sensation, which could enhance the experience of operating a touchscreen. The Ultraloop, a device built to generate such a lateral force on a finger in contact, works by producing flexural traveling waves that push the finger. However, its shape is not simple to manufacture. Moreover, its shape is inconvenient to place in most touch input interfaces, which often appear in flat devices. A flat UltraLoop is proposed providing similar traveling wave force feedback, fitting the form factor of flat human-machine touch interfaces better. Furthermore, the new shape allows for manufacturing from a sheet of aluminum, using a cnc. The flat Ultraloop works by actuating two orthogonal modes at around 38k Hz, with a phase shift of 90 degrees, similarly to the Ultraloop. To validate the performance, force measurements have been conducted showing a maximum lateral force of 0.3N. Also, the influence of the normal force, phase, and finger motion on the lateral force is investigated. Lastly, we present a demo showing application of the flat Ultraloop, simulating a spring and a bump.

Vibration energy harvesters have been proposed as a solution to increase the lifetime of wireless and portable medical devices. One example of implantable medical devices for which energy harvesters could be interesting, are pacemakers. With a lifespan of about 6 to 12 years, the battery must be replaced after this period of time. Using an energy harvester instead of a battery is therefore seen as an interesting alternative. However, the human heart rate is usually between 0.6-2Hz and consists of low acceleration peaks (<1g). The use of resonance at low frequency is extremely difficult, especially when the motion amplitude is larger than the device itself. A solution is sought in the non-resonant bistable energy harvesters. When enough force is applied to overcome the potential energy barrier, snap through motion is induced, resulting in a significant increase in power output. However, large threshold accelerations are limiting the usability of these systems. Therefore, stiffness compensation is required. A prototype was fabricated in which buckled flexures were used to add negative stiffness to a piezoelectric cantilever, resulting in a stiffness compensated bistable energy harvester suitable for energy harvesting from low frequency and low force excitations. The dynamical behaviour and practical performance of the prototype was studied in relation to a heartbeat, sawtooth wave and sine waves. The output power of the non-resonant prototype was compared to a resonant device, which in all cases showed that the non-resonant prototype outperformed the resonant device. This shows that stiffness compensated bistable energy harvesters can be used in order to make energy harvesting for low force and low frequency excitations, such as a heartbeat, possible.

Conventional steering systems in passenger vehicles have a mechanically fixed steering ratio. The steering sensitivity, defined as the amount of vehicle response to the driver's steering wheel input, remains fixed with changing road environments. Research has shown that driving comfort and safety can be improved when the vehicle's steering sensitivity is adapted to the road curvature profile. Current vehicle models can adapt the vehicle's steering sensitivity based on vehicle's speed and driver's steering wheel angle (i.e variable gear-ratio systems), or on individual selection of driving mode (i.e sport, comfort). It is hypothesised that adaptation of the steering sensitivity based on frequency measures of individual drivers' steering behaviour could improve driving comfort and safety. In a fixed-base driving simulator experiment involving 24 participants, real-time adaptation of steering wheel sensitivity based on individual drivers' steering behaviour was compared to three different fixed steering sensitivity settings on a road with changing road curvature. Here I show that intermittent switching frequency in drivers' steering movements can be used to adapt the vehicle's steering response to a varying road curvature. Significant differences in intermittent switching were found between different road curvature sections and between different steering sensitivity settings. Driver's positional control and comfort ratings did not significantly increase with the steering sensitivity adaptation strategy.

Vibrotactile wearable devices are a non-intrusive and inexpensive means to provide haptic feedback directly on the user’s skin. These devices utilize one or multiple vibrotactile actuators to generate vibrations across the skin and into the tissue. Combining these vibrations in amplitude can create the illusion of a funneled sensation on the skin at another location than at the actual sites of stimulation. This allows for the placement of virtual actuators on the skin, such that fewer actuators need to be deployed. However, the illusion does not take into account that the waves originating from the actuator attenuate and disperse due to the viscoelastic properties of the skin. We hypothesize that this diffusion of the elastic energy in the skin is affecting the perception of this illusion. Therefore, if we correct for the wave propagation speed, and temporally focus the stimulation, we hypothesized that the specificity of the stimulation on the skin could be drastically improved. In this paper, a novel technique, which is named the inverse filter technique, was introduced that enables to focus the amplitude, frequency and phase of vibrations to one location while cancelling them at the remaining nearby positions. We developed a wearable device for the volar surface of the forearm on which we could independently control arbitrary waveforms at any position between a set of four physical actuators. A human-subject study found that the performance in terms of localization confidence was improved significantly, whereas the precision and accuracy of the task did not improve compared to when we did not correct for the wave attenuation and dispersion. These results show that focusing waves towards a target location has a direct influence on our confidence of localizing vibrotactile stimuli on the arm. Therefore, we anticipate that our findings can benefit industries interested in including localized vibrotactile feedback on the human body surface.

Conventional robots adopt wheels or robotic limbs for locomotion. Wheels are simple to control but not suitable for irregular terrains. On the other hand, robotic feet can overcome a wider variety of surfaces but are less desirable due to their complex design and control system. In nature, we find that invertebrate animals, like snails, can go anywhere without needing the complex control system a rigid robot needs. Instead, they move forward by sending travelling deformations along their soft bodies. Inspired by these animals, we present a soft robot that uses a sequence of deformations for locomotion. This sequence of deformations is driven by a row of vibrating actuators that vibrate with the same frequency but a phase shift between each consecutive actuator. The metachronal wave arising from this vibration pattern offers efficient locomotion due to the continuous movement of the robot. The top speed achieved in this research was 5 mm/s for both forward and backward locomotion. Our study shows how the robot’s locomotion capabilities are affected by its material and how the robot's velocity depends on the mechanical design and the properties of the metachronal wave and provides a next step into soft robots that can efficiently move almost anywhere.

Hand-worn haptic systems must be able to produce high-quality haptics while also being lightweight and energy-efficient. In order to meet market expectations, research is being done into novel drivetrains that may be implemented in hand worn devices. This is being pushed forward by the growing demand in the virtual reality sector, which is placing pressure on the development of new wearable force feedback technology. In order to validate a proof of concept, this thesis proposes a novel force feedback drivetrain with a dual actuator setup-a motor and a brake—that is integrated into a tabletop prototype. Using both a motor and a brake will reduce weight and improve the haptic rendering quality relative to each component when considered separately. To evaluate the presumptive advantages, a theoretical analysis into the suggested hybrid actuation solution is conducted. The analysis comprises of numerous simulations using a model of the hybrid drivetrain's working principle. Additionally, the analysis is employed to investigate and spot any early-stage defects or undesirable behavior. Consequently, a 3D model was created in order to 3D print a functioning prototype in order to apply the theory in a physical version. The prototype is initially used to validate the simulation model and enforce the findings of the theoretical analysis. Force data is measured when using the prototype and in turn is fed into the simulation model to assess whether the output behaviour is consistent with the prototype. Both the model's competence and the prototype's predictability are assessed using the outcomes. Finally, an experiment is conducted to both asses the mechanical performance and predictability as well as the participant's perception; 2 virtual environments and 3 actuation modes (motor, brake, and hybrid) were cross-examined and each repeated 6 times, for a total of 36 trials. This experiment ultimately assesses the prototypes validity and determines whether the theoretically assumed benefits are present in the prototype as well. Finally, the participant completes a questionnaire in the form of a 5-point Likert scale to determine if the experiment data complies with the users experience. The theoretical analysis revealed both reliable behavior and potential problems, such as oscillations in feedback force due to rapid switching between actuator activity. However, the cause of this behaviour was identified and anticipated to be less pronounced during use of the prototype. The prototype was successfully designed and produced, and a comparison to the model revealed consistent findings and, thus, predictable behavior. However, the model occasionally miscalculated the velocity. The experiment also shows that the hybrid drivetrain approach is promising and outperforms the state of the art both in mechanical prowess as well as physical fidelity when providing haptic feedback; the motor fails to render rigid objects and the brake cannot render spring-like objects, while the hybrid approach can render both successfully. The thesis demonstrates that additional investigation into the suggested drivetrain is supported, despite some obvious limitations. When compared to equally powerful DC motors, the hybrid technique, as employed in the prototype, is capable of portraying the largest variety of haptics, including hard walls, impacts, and stiffness while potentially conserving weight.

When a trainee is (re)learning a skilled movement, physical guidance from a trainer is crucial. Yet, providing physical cues to guide movements is highly challenging when training is digitally mediated (e.g.remotely). This work demonstrates the utility of pseudo forces generated by a wearable tactile interface for providing non-intrusive movement guidance. First, we developed hardware to generate pseudo forces using asymmetric vibrations, whose frequency and amplitude can be tuned to vary the acceleration of the pseudo forces. Maximum acceleration of 160 m/sec^2 is obtained at a frequency of 40Hz and amplitude of 1. Second, the utility of the generated pseudo forces to provide movement guidance was explored by involving 19 participants in 4 separate experiments: 1) Symmetric and asymmetric vibration comparison, 2) Duration modulation, 3) Amplitude modulation, 4) Frequency Modulation of asymmetric vibration. For every experiment, the elements of movement guidance: direction and joint angular velocity were investigated. Participants perceive directional cues with 96% accuracy (P<0.001), and translate the perceived pseudo forces into directed arm movements, with a uniform joint angular velocity of 14+/-8 degrees/second for the duration of the provided pseudo force. The joint angular velocity of the arm movement changes until 12 degrees/second with frequency. With these findings, we anticipate pseudo forces to be the foundation for remote guidance of human body movements in fields like rehabilitation and sports.