Haptic Display Research Articles

Flexible and Transparent Electrovibration-Based Haptic Display with Low Driving Voltage.

Electrovibration haptic technology, which provides tactile feedback to users by swiping the surface with a finger via electroadhesion, shows promise as a haptic feedback platform for displays owing to its simple structure, ease of integration with existing displays, and simple driving mechanism. However, without electrical grounding on a user's body, the frequent requirement of a high driving voltage near 50 V limits the use of electrovibration haptic technology in practical display applications. This study introduces materials and fabrication strategies that considerably reduce the driving voltage. We used a transparent poly(vinylidene fluoride) (PVDF) thin film deposited on transparent conductive polymers through a simple spin-coating process, thereby enabling easy integration with existing display technologies. The high dielectric constant characteristics of PVDF enabled the production of tactile cues at low voltages (approximately 15 V), which are within the safety limits of common electronics. We verified the feasibility of our electrovibration haptic feedback system on the basis of the absolute threshold voltage through two-alternative forced choice psychological tests. The results revealed that the PVDF dielectric layer exhibited a relatively lower absolute threshold than commonly used polymer films, which possess a relatively lower dielectric constant. To validate the tactile attributes, a Likert five-point scale survey was conducted, considering flat, concave, and convex curvatures. The results indicated that our haptic device can render diverse surface textures, such as "hairy" and "groovy", on the fingertips through the control of applied pulse width modulated voltage signals.

Augmenting perceived stickiness of physical objects through tactile feedback after finger lift-off.

Haptic Augmented Reality (HAR) is a method that actively modulates the perceived haptics of physical objects by presenting additional haptic feedback using a haptic display. However, most of the proposed HAR research focuses on modifying the hardness, softness, roughness, smoothness, friction, and surface shape of physical objects. In this paper, we propose an approach to augment the perceived stickiness of a physical object by presenting additional tactile feedback at a particular time after the finger lifts off from the physical object using a thin and soft tactile display suitable for HAR. To demonstrate this concept, we constructed a thin and soft tactile display using a Dielectric Elastomer Actuator suitable for HAR. We then conducted two experiments to validate the effectiveness of the proposed approach. In Experiment 1, we showed that the developed tactile display can augment the perceived stickiness of physical objects by presenting additional tactile feedback at appropriate times. In Experiment 2, we investigated the stickiness experience obtained by our proposed approach and showed that the realism of the stickiness experience and the harmony between the physical object and the additional tactile feedback are affected by the frequency and presentation timing of the tactile feedback. Our proposed approach is expected to contribute to the development of new applications not only in HAR, but also in Virtual Reality, Mixed Reality, and other domains using haptic displays.

Plantar Haptic Display to Estimate the Position of the Projected Center of Gravity of a Humanoid

Humans can perform stable motion with a sense of stability that involves identifying their center of gravity point with plantar sensory system. By contrast, the stability of a humanoid robot is inferior to that of a human. If the sense of stability of a humanoid robot is presented to a human who operates the robot in real time, the operator can control the robot more stably. However, studies wherein humans recognize the projected center of gravity point with a plantar haptic display are lacking. In this study, we investigated the possibility of estimating the projected center of gravity point of a small humanoid robot from only the foot force information. We propose a plantar haptic display to reproduce the foot reaction force on four points of a single sole as large as the force during human running. We conducted an experiment to verify the estimated center of gravity point using the foot reaction forces of a small robot with and without scaling by a weight ratio between an operator and the robot. The results indicated that it is difficult to estimate the projected center of gravity point without scaling; however, it is possible to estimate the movement of the projected center of gravity point with a maximum error of [Formula: see text][Formula: see text]mm with scaling.

Let It Snow: Designing Snowfall Experience in VR

We present Snow, a cross-modal interface that integrates cold and tactile stimuli in mid-air to create snowflakes and raindrops for VR experiences. Snow uses six Peltier packs and an ultrasound haptic display to create unique cold-tactile sensations for users to experience catching snowflakes and getting rained on their bare hands. Our approach considers humans' ability to identify tactile and cold stimuli without masking each other when projected onto the same location on their skin, making illusions of snowflakes and raindrops. We design both visual and haptic renderings to be tightly coupled to present snow melting and rain droplets for realistic visuo-tactile experiences. For multiple snowflakes and raindrops rendering, we propose an aggregated haptic scheme to simulate heavy snowfall and rainfall environments with many visual particles. The results show that the aggregated haptic rendering scheme demonstrates a more realistic experience than other schemes. We also confirm that our approach of providing cold-tactile cues enhances the user experiences in both conditions compared to other modality conditions.

A Cable-Based Haptic Interface with a Reconfigurable Structure

Abstract Cable robots have been used as haptic interfaces for several decades now, with the most notable examples being the SPIDAR and its numerous iterations throughout the years, as well as the more recent IPAnema 3 Mini manufactured by Fraunhofer IPA. However, these robots still have drawbacks, particularly their high number of cables required to maintain a high workspace-to-installation-space ratio. Using a hybrid-structure cable robot (HSCR) could prevent some collisions that occur between the cables and the user's body. More specifically, some applications requiring multimodal feedback could benefit from the flexibility that a reduced number of cables offers. Therefore, this paper presents a novel SPIDAR-like VSCR and its sensor-less force control method based on motor current. The purpose of this work is to clarify the advantages that a variable structure can provide for haptic interaction. In this regard, experimental results regarding the device's workspace and its force feedback capabilities are presented. Additionally, since real-time high-frequency updates are required for haptic display, we provide additional data regarding the control algorithm's runtime. Lastly, another experiment was conducted to study changes in user performance when using both the variable and the usual cable configuration. The results showed that feedback accuracy is maintained, and there are no drawbacks to using hybrid configurations.

High-speed fluidic processing circuits for dynamic control of haptic and robotic systems.

Fluidic logic circuits simplify system design for soft robotics by eliminating bulky components while enabling operation in a range of hostile environments that are incompatible with electronics but at the expense of limited computational capabilities and response times on the order of seconds. This paper presents a four-terminal fluidic transistor optimized for fast switching times, reduced component count, low unit cost, and high reproducibility to achieve complex fluidic control circuits while maintaining flow rates of liters per minute. A ring oscillator using three fluidic transistors achieves oscillation frequencies up to a kilohertz with full signal propagation, tolerating billions of cycles without failure. Fundamental processor circuits like a full adder and a 3-bit analog-to-digital converter require just seven transistors each. A decode circuit drives a high-resolution soft haptic display with refresh times below the human perception threshold for latency, and an electronics-free control circuit performs closed-loop position control of a pneumatic actuator with disturbance rejection, demonstrating the value across domains.

Optimizing Setup Configuration of a Collaborative Robot Arm-Based Bimanual Haptic Display for Enhanced Performance

Optimizing Setup Configuration of a Collaborative Robot Arm-Based Bimanual Haptic Display for Enhanced Performance

Head-Up Haptic Display Using Dual-Mode Haptic Actuator for Vehicles

Driving assistance modules are important components to improving driver safety in driving environments, which can create overloaded multisensory information. This paper introduces the concept of a head-up haptic display that assists drivers in keeping their visual attention focused, and then offers a haptic actuator that may be used as the main component in the head-up haptic display. We selected magneto-rheological elastomer (MRE) as the base material and adopted a porous structure to reduce its initial stiffness. Furthermore, we fabricate a haptic actuator based on an MRE having a porous structure (pMRE) and a solenoid. The current to the solenoid generates a magnetic field that causes the pMRE to stiffen, thereby increasing the resistive force. As soon as the current input is removed, the pMRE becomes soft again. We simulated the solenoid coil and the magnetic path to further maximize the magneto-motive force generated by the solenoid coil and experimentally optimized the pMRE. We showed that the proposed haptic actuator creates not only a sufficient resistive force but also vibration to generate various haptic sensations. Moreover, we constructed a head-up haptic display using four haptic actuators and demonstrated the possibility of utilizing a new user interface to increase driving safety.

Model-Free Energy-Based Friction Compensation for Industrial Collaborative Robots as Haptic Displays

Model-Free Energy-Based Friction Compensation for Industrial Collaborative Robots as Haptic Displays

Advancing Haptic Display Technology for Embodied Metaverse Experiences

Advancing Haptic Display Technology for Embodied Metaverse Experiences

PopTouch: A Submillimeter Thick Dynamically Reconfigured Haptic Interface with Pressable Buttons.

The interactions with touchscreens rely heavily on vision: The virtual buttons and virtual sliders on a touchscreen provide no mechanical sense of the object they seek to represent. This work presents PopTouch: a 500µm thick flexible haptic display that creates pressable physical buttons on demand. PopTouch can be mounted directly on touchscreens or any other smooth surface, flat, or curved. The buttons of PopTouch are independently controlled hydraulically amplified electrostatic zipping taxels (tactile pixels) that generate 1.5mm of out of plane displacement. When pressed by the user, the buttons provide intuitive mechanical feedback thanks to a snap-through characteristic in their force-displacement profile. The snap-through threshold can be as high as 4 N, and is tuned by design and actuation parameters. This work presents two versions of PopTouch: a transparent PopTouch for integration on Touchscreens with built-in touch sensing, such as smartphones and a sensorized PopTouch, with embedded thin-film piezoelectric sensors on each taxel, for integration on substrates without built-in touch sensing, such as a steering wheel. PopTouch adds static and vibrating button-like haptics to any device thanks to its thin profile, flexibility, low power consumption (6mW per button), rapid refresh rate (2Hz), and freely configured array format.

SmartSpring: a Low-Cost Wearable Haptic VR Display with Controllable Passive Feedback.

With the development of virtual reality, the practical requirements of the wearable haptic interface have been greatly emphasized. While passive haptic devices are commonly used in virtual reality, they lack generality and are difficult to precisely generate continuous force feedback to users. In this work, we present SmartSpring, a new solution for passive haptics, which is inexpensive, lightweight and capable of providing controllable force feedback in virtual reality. We propose a hybrid spring-linkage structure as the proxy and flexibly control the mechanism for adjustable system stiffness. By analyzing the structure and force model, we enable a smart transform of the structure for producing continuous force signals. We quantitatively examine the real-world performance of SmartSpring to verify our model. By asymmetrically moving or actively pressing the end-effector, we show that our design can further support rendering torque and stiffness. Finally, we demonstrate the SmartSpring in a series of scenarios with user studies and a just noticeable difference analysis. Experimental results show the potential of the developed haptic display in virtual reality.

Soft Wearable Haptic Display and Flexible 3D Force Sensor for Teleoperated Surgical Systems

AbstractHaptic (touch) is important for effective interaction with the surroundings. In teleoperated surgical systems, its absence leads to reduced perception, making delicate tasks difficult and resulting in unexpected damage to surrounding tissues. To enhance safety, a force‐feedback system and haptic device are needed. However, existing haptic prototypes are associated with rigid, bulky, and heavy components, making effective communication with the skin problematic. This paper presents a teleoperated endoscopic surgical system with an integrated 3D force sensor and real‐time haptic feedback. A surgical robotic arm is remotely controlled by a soft haptic glove incorporated 3‐axis cutaneous device and a finger kinesthetic module. The 3D force sensor is constructed from hydraulic filament soft sensors that can induce pressure change under strain. To enable precise motion, the haptic glove is operated by a feedforward controller and a master‐slave architecture. Experiments with human subjects (n = 15) show that cutaneous and kinesthetic feedback significantly improves the user's performance (9.4 out of 10) compared to no haptic feedback (2.27 out of 10). Finally, subjects rank the new system as highly wearable, comfortable, and effective, which is expected to bridge a gap in the surgical field and support the future development of advanced teleoperated systems.

Toward Designing Haptic Displays for Desired Touch Targets: A Study of User Expectation for Haptic Properties via Crowdsourcing.

Things that people desire to touch in daily life are known to be limited to a number of specific targets (e.g., cats). The utilization of haptic displays to provide the experience of touching such desired targets is expected to enhance people's quality of life. However, it is currently unclear which haptic properties (e.g., hardness and weight) of desired targets should be rendered with haptic displays, and how they should be rendered. To address these issues, we conducted an experiment with 600 Japanese participants via crowdsourcing. Among the 600 participants, we identified potential users of haptic displays and analyzed their responses for each target. For each desired target, we identified the haptic properties in relation to which a "need for consistency" was felt by potential users between their expectations and actual impressions during touching. We also identified the haptic properties in relation to which a "biased impression" was held by potential users for each target. For example, potential users responded that cats were soft and that the actual impression of softness during touching needed to be consistent with their impression. Our results provide insights into the design of haptic displays for realizing desired touch experiences.

Wearable High-Resolution Haptic Display Using Suction Stimuli to Represent Cutaneous Contact Information on Finger Pad.

A high-resolution haptic display that reproduces tactile distribution information on the contact surface between a finger and an object realizes the presentation of the softness of the object and the magnitude and direction of the applied force. In this article, we developed a 32-channel suction haptic display that can reproduce tactile distribution on fingertips with high resolution. The device is wearable, compact, and lightweight, thanks to the absence of actuators on the finger. A FE analysis of the skin deformation confirmed that the suction stimulus interfered less with adjacent stimuli in the skin than when pressing with positive pressure, thus allowing more precise control of local tactile stimuli. The optimal layout with the least error was selected from three configurations dividing 62 suction holes into 32 ports.The suction pressures were determined by calculating the pressure distribution by a real-time finite element simulation of the contact between the elastic object and the rigid finger. A discrimination experiment of softness with different Young's modulus and its JND investigation suggested that the higher resolution of the suction display improved the performance of the softness presentation compared to a 16-channel suction display previously developed by the authors.

Wrapping Haptic Displays Around Robot Arms to Communicate Learning.

Humans can leverage physical interaction to teach robot arms. As the human kinesthetically guides the robot through demonstrations, the robot learns the desired task. While prior works focus on how the robot learns, it is equally important for the human teacher to understand what their robot is learning. Visual displays can communicate this information; however, we hypothesize that visual feedback alone misses out on the physical connection between the human and robot. In this paper we introduce a novel class of soft haptic displays that wrap around the robot arm, adding signals without affecting that interaction. We first design a pneumatic actuation array that remains flexible in mounting. We then develop single and multi-dimensional versions of this wrapped haptic display, and explore human perception of the rendered signals during psychophysic tests and robot learning. We ultimately find that people accurately distinguish single-dimensional feedback with a Weber fraction of 11.4%, and identify multi-dimensional feedback with 94.5% accuracy. When physically teaching robot arms, humans leverage the single- and multi-dimensional feedback to provide better demonstrations than with visual feedback: our wrapped haptic display decreases teaching time while increasing demonstration quality. This improvement depends on the location and distribution of the wrapped haptic display.

Extension of Contact Initiation Range in Encountered-Type Haptic Display Using MR Fluid

Extension of Contact Initiation Range in Encountered-Type Haptic Display Using MR Fluid

The Utility of Synthetic Reflexes and Haptic Feedback for Upper-Limb Prostheses in a Dexterous Task Without Direct Vision.

Individuals who use myoelectric upper-limb prostheses often rely heavily on vision to complete their daily activities. They thus struggle in situations where vision is overloaded, such as multitasking, or unavailable, such as poor lighting conditions. Able-bodied individuals can easily accomplish such tasks due to tactile reflexes and haptic sensation guiding their upper-limb motor coordination. Based on these principles, we developed and tested two novel prosthesis systems that incorporate autonomous controllers and provide the user with touch-location feedback through either vibration or distributed pressure. These capabilities were made possible by installing a custom contact-location sensor on the fingers of a commercial prosthetic hand, along with a custom pressure sensor on the thumb. We compared the performance of the two systems against a standard myoelectric prosthesis and a myoelectric prosthesis with only autonomous controllers in a difficult reach-to-pick-and-place task conducted without direct vision. Results from 40 able-bodied participants in this between-subjects study indicated that vibrotactile feedback combined with synthetic reflexes proved significantly more advantageous than the standard prosthesis in several of the task milestones. In addition, vibrotactile feedback and synthetic reflexes improved grasp placement compared to only synthetic reflexes or pressure feedback combined with synthetic reflexes. These results indicate that autonomous controllers and haptic feedback together facilitate success in dexterous tasks without vision, and that the type of haptic display matters.

Effects of Physical Hardness on the Perception of Rendered Stiffness in an Encountered-Type Haptic Display.

Rendering stable hard surfaces is an important problem in haptics; current haptic devices cannot render hard objects and free space together. In our previous work, we addressed these limitations using an encountered-type haptic display system, which showed significant improvements compared to traditional rendering methods. In our approach, we attach a plate with the desired hardness to the kinesthetic device's end-effector, which the user interacts with using an untethered stylus. This method allows us to directly change the hardness of the end-effector based on the rendered object. In this paper, we evaluate how changing the hardness of the end-effector can mask the device's stiffness and affect the user's perception of the interaction. Our human subject experiment results indicate that when the end-effector is made of a hard material, it is difficult for users to perceive the stiffness change rendered by the device. On the other hand, this stiffness change is easily distinguished when the end-effector is made of a soft material. These results show promise for our combined hardness-stiffness display in avoiding the limitations of haptic devices when rendering hard surfaces.

Special Issue on Robotics for Medical Applications

In recent years, the field of robots for medical applications has been expanding rapidly. Robots effectively augment their operators’ skills, enabling them to achieve accuracy and high precision during complex procedures. The use of robots improves the quality of life of patients and the quality of medical research. Therefore, the research and development of robots for medical applications will become more active in aging societies. This special issue focuses on the design and control of robots as well as integrated technologies for robots for medical applications. These include navigation, simulator, image guidance, training, and validation technologies for robots. The special issue consists of 17 papers with various studies related to medical robots. There are 7 papers on assistant robots, including their passive and active controls, devices, and sensors. There are 10 papers related to minimally invasive surgery and neurosurgery involving robots, including papers on sensors, actuators, navigation, haptic display devices, the mechanical design of devices, and other topics. The editors are confident that this special issue will greatly contribute to further progress in robotics We sincerely thank the authors for their fine contributions and the reviewers for their generous contributions of time and effort. We would also like to thank the Editorial Board of the Journal of Robotics and Mechatronics for their help with this special issue.