Lever Mechanism for Diaphragm-Type Vibrators to Enhance Vibrotactile Intensity.

Thin and light vibrators that leverage the inverse piezoelectric effect with a diaphragm mechanism are promising vibrotactile actuators owing to their form factors and high temporal and frequency response. However, generating perceptually sufficient displacement in the low-frequency domain is challenging. This study presents a lever mechanism mounted on a diaphragm vibrator to enhance the vibrotactile intensity of low-frequency vibrotactile stimuli. The lever mechanism is inspired by the tactile contact lens consisting of an array of cylinders held against the skin on a sheet that enhances micro-bump tactile detection. We built an experimental apparatus including our previously developed thin-film diaphragm-type vibrator, which reproduced the common characteristic of piezoelectric vibrators: near-threshold displacement (10 to 20 µm) at low frequency. Experiments demonstrated enhanced vibrotactile intensity at frequencies less than 100 Hz with the lever mechanism. Although the arrangement and material of the mechanism can be improved, our findings can help improve the expressiveness of diaphragm-type vibrators.

Validity of Accelerometer-Based Sensor System for Muscle Tightness Estimation through Vibration on the Upper Limb.

Spasticity is a condition that profoundly impacts the ability to perform everyday tasks. However, its diagnosis requires trained physicians and subjective evaluations that may vary depending on the evaluator. Focal vibration of spastic muscles has been proposed as a non-invasive, pain-free alternative for spasticity modulation. We propose a system to estimate muscular tightness based on the propagation of elastic waves in the skin generated by focal vibration of the upper limb. The developed system generates focalized displacements on the biceps muscle at frequencies from 50 to 200 Hz, measures the vibration acceleration on the vibration source (input) and the distant location (output), and extracts features of ratios between input and output. The system was tested on 5 healthy volunteers while lifting 1.25 - 11.25 kg weights to increase muscle tone resembling spastic conditions, where the vibration frequency and weight were selected as explanatory variables. An increase in the ratio of the root mean squares proportional to the weight was found, validating the feasibility of the current approach to estimating muscle tightness.Clinical Relevance- This work presents the feasibility of a vibration-based system as an alternative method to objectively diagnose the degree of spasticity.

Interpersonal Transmission of Vibrotactile Feedback Via Smart Bracelets: Mechanics and Perception.

The importance of interpersonal touch for social well-being is widely recognized, and haptic technology offers a promising avenue for augmenting these interactions. We presented smart bracelets that use vibrotactile feedback to augment social interactions, such as handshakes, by transmitting vibrations between two people. This work conducts mechanical and perceptual experiments to investigate key factors affecting the delivery of interpersonal vibrotactile feedback via bracelets. Our results show that low-frequency vibrations elicited through tangential actuation are efficiently transmitted from the wrist to the hand, with amplitude varying based on distance, frequency, and actuation direction. We also found that vibrations transmitted to different locations on the hand can be felt by a second person, with perceptual intensity correlated with oscillation magnitude at the touched location. Additionally, we demonstrate how wrist-interfaced devices can elicit spatial vibration patterns throughout the hand surface, which can be manipulated by the frequency and direction of actuation at the wrist. Our experiments provide important insights into the human factors associated with interpersonal vibrotactile feedback and have significant implications for the design of technologies that promote social well-being.

Can Facial Expressions Induce Haptic Perception?

A key challenge in haptics is designing human-human communications involving touch to facilitate positive effects on social interactions. An important consideration in designing social touch is understanding the effect of social stimuli on perception, in addition to that of a physical stimulus, because social touch always involves a partner. This study presents an experiment to demonstrate that facial expressions induce haptic perception. We developed a human-agent interaction system on a display in which participants moved the mouse cursor to click the target icon while the agent behaved as if it pulled the cursor back in the opposite direction, showing either a negative or neutral face. The perceived force during the interaction was quantified by the control display ratio using a psychophysical approach. The results show that the negative face induced a significantly greater perceived force than the neutral face. In addition, the perceived force correlated with the individual's evaluation of the facial expression; that is, the more unpleasant or aroused they perceived the facial expression to be, the more force they perceived. This study sheds light on the design of social touch performed by people who have physical or mediated contact with each other in physical space or cyberspace.

Representing Interpersonal Touch Directions by Tactile Apparent Motion Using Smart Bracelets.

We present a novel haptic interaction to vibro-tactually connect an interpersonal touch using bracelet devices. A pair of bracelet devices identifies the user who is actively touching and the other who is passively touched, defining the direction as being from the former to the latter. By controlling the vibrational feedback, the pair induces a tactile apparent motion representing the direction between two hands. The bracelets are comprised of our developed interpersonal body area network module, an acceleration sensor, and a vibrator. The devices communicate with each other through electrical current flowing along the hands to identify the direction by sharing accelerations just before a touch and to synchronize the feedback in less than ten milliseconds. Experiment 1 demonstrates that the vibration propagated from a bracelet device to the wearer's hand is perceivable by another. Experiment 2 determines sets of optimal actuation parameters, stimulus onset asynchrony, and duration of vibration to induce the tactile apparent motion based on a psychophysical approach. In addition, vibration propagation between hands is observed. Experiment 3 demonstrates the capability of the developed device to present the haptic interaction.

SpiroSurface: A Repulsive and Attractive Force Display for Interactive Tabletops Using a Pneumatic System.

We present SpiroSurface, a novel force display for interactive tabletops. SpiroSurface uses a pneumatic system to generate both repulsive and attractive forces. We develop a prototype with 5x5 grid holes on the surface connected to an air compressor and vacuum tanks through electromagnetic valves. The display can output a maximum of +1.0 and -0.08 megapascal (MPa) pressure from a hole that generates 74 and -6 N force. We investigated the latency of the output pressure through pneumatics and an experiment, which indicated a minimum of 50-ms latency. The display allows the creation of three kinds of novel interactions: (1) enhancement of GUI, (2) deformation of soft objects, and (3) three-degree-of-freedom rotation of objects. In the first application, users can feel the force from the display without holding or attaching additional devices. In the second and third applications, the shape and motion of an object on the surface can be manipulated without embedding additional active components in the objects. These aspects allow users to easily experience interaction and expand the freedom of interaction design. We introduce several examples combining video projection and motion tracking. These examples demonstrate the potential of the display.

FaceLooks: A Smart Headband for Signaling Face-to-Face Behavior.

Eye-to-eye contact and facial expressions are key communicators, yet there has been little done to evaluate the basic properties of face-to-face; mutual head orientation behaviors. This may be because there is no practical device available to measure the behavior. This paper presents a novel headband-type wearable device called FaceLooks, used for measuring the time of the face-to-face state with identity of the partner, using an infrared emitter and receiver. It can also be used for behavioral healthcare applications, such as for children with developmental disorders who exhibit difficulties with the behavior, by providing awareness through the visual feedback from the partner’s device. Two laboratory experiments showed the device’s detection range and response time, tested with a pair of dummy heads. Another laboratory experiment was done with human participants with gaze trackers and showed the device’s substantial agreement with a human observer. We then conducted two field studies involving children with intellectual disabilities and/or autism spectrum disorders. The first study showed that the devices could be used in the school setting, observing the children did not remove the devices. The second study showed that the durations of children’s face-to-face behavior could be increased under a visual feedback condition. The device shows its potential to be used in therapy and experimental fields because of its wearability and its ability to quantify and shape face-to-face behavior.

Vibration Feedback Latency Affects Material Perception During Rod Tapping Interactions.

We investigated the effect of vibration feedback latency on material perception during a tapping interaction using a rod device. When a user taps a surface, the perception of the material can be modulated by providing a decaying sinusoidal vibration at the moment of contact. To achieve this haptic material augmentation on a touchscreen, a system that can measure the approach velocity and provide vibration with low latency is required. To this end, we developed a touchscreen system that is capable of measuring the approach velocity and providing vibration feedback via a rod device with latency of 0.1 ms. Using this system, we experimentally measured the human detection threshold of the vibration feedback latency adopting a psychophysical approach. We further investigated the effect of latency on the perception of the material using a subjective questionnaire. Results show that the threshold was around 5.5 ms and the latency made the user feel that the surface is soft. In addition, users reported bouncing and denting sensations induced by the latency.