Design and Evaluation of Identifiable Key-Click Signals for Mobile Devices

A 2-DOF Impact Actuator for Haptic Application

The demand for realistic haptic feedback actuators has increased as mobile devices have increased in popularity. However, most current haptic actuators provide limited 1-DOF tactile sensations, such as vibrations. This paper presents a 2-DOF haptic impact actuator that can provide planar directional (e.g., x and y directional) and magnitude tactile cues to a user. We built an impact actuator that was designed to be of such a size that a user can grasp it with one hand. Multiple electromagnets of the actuator drive a permanent magnet to hit the actuator housing, creating an impact. For the control of the impact direction, we assumed the direction of a magnetic field vector at the centre of the actuator would follow that of a reference vector formed by voltage heading into the electromagnet array. The results of magnetic field measurements support our assumption by showing that the trend of the magnetic field vector coincided with that of the reference voltage vector. Furthermore, the measurement of the impact acceleration showed the trend that the impact direction follows the reference voltage vector.

Effect of 2.5D haptic feedback on virtual object perception via a stylus

As touch screen technologies advanced, a digital stylus has become one of the essential accessories for a smart device. However, most of the digital styluses so far provide limited tactile feedback to a user. Therefore we focused on the limitation and noted the potential that a digital stylus may offer the sensation of realistic interaction with virtual environments on a touch screen using a 2.5D haptic system. Thus, we developed a haptic stylus with SMA (Shape Memory Alloy) and a 2.5D haptic rendering algorithm to provide lateral skin-stretch feedback to mimic the interaction force between fingertip and a stylus probing over a bumpy surface. We conducted two psychophysical experiments to evaluate the effect of 2.5D haptic feedback on the perception of virtual object geometry. Experiment 1 investigated the human perception of virtual bump size felt via the proposed lateral skin-stretch stylus and a vibrotactile stylus as reference. Experiment 2 tested the participants’ ability to count the number of virtual bumps rendered via the two types of haptic styluses. The results of Experiment 1 indicate that the participants felt the size of virtual bumps rendered with lateral skin-stretch stylus significantly sensitively than the vibrotactile stylus. Similarly, the participants counted the number of virtual bumps rendered with the lateral skin-stretch stylus significantly better than with the vibrotactile stylus. A common result of the two experiments is a significantly longer mean trial time for the skin-stretch stylus than the vibrotactile stylus.

Development of a Human-Display Interface with Vibrotactile Feedback for Real-World Assistive Applications

It is important to operate devices with control panels and touch screens assisted by haptic feedback in mobile environments such as driving automobiles and electric power wheelchairs. A lot of consideration is needed to give accurate haptic feedback, especially, presenting clear touch feedback to the elderly and people with reduced sensation is a very critical issue from healthcare and safety perspectives. In this study, we aimed to identify the perceptual characteristics for the frequency and direction of haptic vibration on the touch screen with vehicle-driving vibration and to propose an efficient haptic system based on these characteristics. As a result, we demonstrated that the detection threshold shift decreased at frequencies above 210 Hz due to the contact pressure during active touch, but the detection threshold shift increased at below 210 Hz. We found that the detection thresholds were 0.30–0.45 gpeak with similar sensitivity in the 80–270 Hz range. The haptic system implemented by reflecting the experimental results achieved characteristics suitable for use scenarios in automobiles. Ultimately, it could provide practical guidelines for the development of touch screens to give accurate touch feedback in the real-world environment.

Usability study of multiple vibrotactile feedback stimuli in an entire virtual keyboard input

With advances in information technology, people spend more time on touchscreen-based virtual keyboards than physical keyboards. However, typing on touchscreens usually lacks informative tactile feedback and anchoring references to locate the right keys, and thus requires more visual attention. Most prior tactile keyboard research used single stimulus pattern, which was not enough to recognize different keys. The purpose of this study was to investigate the usability of multiple vibrotactile feedback patterns in an entire virtual QWERTY keyboard input. A set of highly discriminable vibration patterns was designed and associated with different regions of a virtual keyboard to help users to locate the right keys. However, the number of stimulus patterns might also affect the typing performance. A user study was conducted to evaluate the effectiveness of the multiple vibrotactile feedback. The results showed that an appropriate number of stimulus patterns provided higher typing speed, higher typing efficiency, and lower error rate.

Multitouch Vibrotactile Feedback on a Tactile Screen by the Inverse Filter Technique: Vibration Amplitude and Spatial Resolution

Nowadays, tactile surfaces, such as smartphones, provide haptic feedback to signify that a task has been performed correctly or more generally to enrich the interaction. However, this haptic feedback induces vibrations in the surface that propagate to the whole surface, reverberate and attenuate, thus making multi-finger interaction, with different feedbacks, difficult. Recently, the Inverse Filter Method has been proposed to control the propagation of these vibrations, and thus enable to product localized multitouch on a glass surface. This way, a user can put several fingers on a tactile surface and yet feel stimuli independently on his/her different fingers. This article continues this work and demonstrates that a localized multitouch haptic feedback can be delivered in real time using a capacitive screen. To achieve this, this article presents the two necessary steps: a calibration step and an interpolation calculation in order to save calculation and learning time. Furthermore, the paper describes the performance of the device through a study on the behaviour of the screen subjected to the Inverse Filter Method, indicating the movement of the whole screen and the voltage requirement for any haptic feedback.

Localizable Button Click Rendering via Active Lateral Force Feedback

In this article, we have developed a novel button click rendering mechanism based on active lateral force feedback. The effect can be localized because electroadhesion between a finger and a surface can be localized. Psychophysical experiments were conducted to evaluate the quality of a rendered button click, which subjects judged to be acceptable. Both the experiment results and the subjects' comments confirm that this button click rendering mechanism has the ability to generate a range of realistic button click sensations that could match subjects' different preferences. We can, thus, generate a button click on a flat surface without macroscopic motion of the surface in the lateral or normal direction, and can localize this haptic effect to an individual finger.

A Review of Surface Haptics: Enabling Tactile Effects on Touch Surfaces

In this article, we review the current technology underlying surface haptics that converts passive touch surfaces to active ones (machine haptics), our perception of tactile stimuli displayed through active touch surfaces (human haptics), their potential applications (human-machine interaction), and finally, the challenges ahead of us in making them available through commercial systems. This article primarily covers the tactile interactions of human fingers or hands with surface-haptics displays by focusing on the three most popular actuation methods: vibrotactile, electrostatic, and ultrasonic.

Detection of Friction-Modulated Textures is Limited by Vibrotactile Sensitivity

Modulation of the frictional force of a fingertip sliding over a surface-haptic device can produce compelling sensations of texture and relief. The virtual sensation is particularly apparent and feel as fixed in space if the stimulus is rigorously correlated with the displacement of the finger. While frictional textures tactually resemble their real counterparts, some exploratory conditions under which the sharpness of the texture declines exist. We postulate that this decline in sharpness is caused by the perceptual limitation of the attempt to interpret the variation in friction as an out-of-plane sinusoidal topography. To investigate these questions, we measured the detection thresholds of sinusoidal friction-modulated gratings for a wide range of spatial periods explored at two different speeds. We compared the results with the detection thresholds, reported in the literature, of real gratings and vibrotactile stimuli. We found that the detection of spatial friction-modulated textures does not follow the same trend as that of real textures but is more similar to the vibrotactile rendering, which is strongly influenced by the exploratory speed. This article provides a better understanding of the perception of friction-modulated textures and provides insight into how to design impactful stimuli on surface-haptic devices.

Haptic Enchanters: Attachable and Detachable Vibrotactile Modules and Their Advantages

This paper showcases attachable/detachable haptic modules, nicknamed haptic enchanters, by presenting their conceptual prototypes and quantifying their information transmission capacity. Haptic enchanters can be attached to ordinary devices and wearables to endow them with the ability of creating programmable haptic stimuli, thereby transforming them to effective haptic communication devices. In particular, our prototype enchanters are designed to localize vibrotactile stimulation to the neighborhood of attachment site, and this spatial isolation allows for effective spatiotemporal information delivery using multiple enchanters. We demonstrate that haptic enchanters enable very high capacity of information transfer (4.55-7.06 bits) for spatiotemporal vibration sequences rendered with two, three, and four enchanters. We also assert that haptic enchanters provide better user experiences by using location-enabled feedback in a game application than the whole-device feedback. These results instantiate the performance of haptic enchanters as effective and convenient communication accessories and their potential for applications.

VR-MDS: multidimensional scaling for classification tasks of virtual and real stimuli

Evaluating the perceptual similarity between virtual and real sensory stimuli has been a serious problem for virtual reality interface researchers for a long time. One of the most commonly used evaluation methods is a classification task where assessors classify randomly presented stimuli into multiple candidate types. The results of this method are summarized using two types of confusion matrices, which have different stimulus sets. The present study developed a method that computes the locations of simulated and real stimuli in a perceptual space on the basis of the two confusion matrices. The spatial distribution of the stimuli allows us to visually interpret the perceptual relationships between stimuli and their perceptual dimensionality. This method is recommended when the guidance index based on the answer ratios of the confusion matrices is fairly high.

Application of psychophysical techniques to haptic research

Various psychophysical methods have been used to study human haptic perception, although the selection of a particular method is often based on convention, rather than an analysis of which technique is optimal for the question being addressed. In this review, classical psychophysical techniques used to measure sensory thresholds are described as well as more modern methods such as adaptive procedures and those associated with signal detection theory. Details are provided as to how these techniques should be implemented to measure absolute and difference thresholds and factors that influence subjects' responses are noted. In addition to the methods used to measure sensory thresholds, the techniques available for measuring the perception of suprathreshold stimuli are presented. These scaling methods are reviewed in the context of the various stimulus and response biases that influence how subjects respond to stimuli. The importance of understanding the factors that influence perceptual processing is highlighted throughout the review with reference to experimental studies of haptic perception.