Tactile Transducer Research Articles

Event-related potential responses to differences in vibrotactile frequency: Evidence for continuous encoding of tactile information during early perception

Perception of vibrotactile frequency is driven by activation of different types of mechanoreceptors embedded in the skin, which respond to vibrations in a frequency range of approximately 0.4 to 500 Hz. While previous behavioral work has measured participants’ sensitivity to differences in vibration frequency, it is unclear how this information is encoded in neural representations during perception. This issue was addressed in an event-related potential (ERP) experiment investigating responses to vibrotactile stimuli. EEG data were recorded while participants rested their hand on a tactile transducer. On each trial, the transducer delivered a sinusoidal vibration with a duration of 1000 ms. Frequency of vibration ranged from 30 to 70 Hz in 10 Hz steps. Results revealed that frequency is encoded in early somatosensory ERP responses recorded at Cz. Specifically, the amplitude of a negative-going ERP component, centered at approximately 50 ms post-stimulus onset, increased as stimulus frequency increased from 40 to 70 Hz. These results demonstrate that vibrotactile frequency is encoded continuously during perception and that these responses can be measured using scalp-recorded EEG.

Agar-based soft tactile transducer with embedded optical fiber specklegram sensor

Tactile transducers monitor physical variables like force and texture through direct contact, featuring indispensable in human–computer interaction and biomedical applications. This work proposes an optical fiber tactile sensor based on specklegram analysis. A soft matrix made of agar embeds a concatenated multimode/single-mode/multimode fiber structure. Forces exerted over the tactile surface disturb the probe mechanically, modulating the output speckle patterns for further processing through image correlation techniques. Experiments evaluated the sensor response as a function of the probe position and the agar matrix composition. Static and dynamic characterizations yielded average force and spatial resolutions of 0.006 N and 0.0008 mm, respectively, with a time response of 34.7 ms, exceeding most of the available optical fiber tactile devices. Compared with intensity and spectral approaches, the specklegram analysis provides high sensitivity (∼1.65 N−1) and relies on a straightforward interrogation system. Furthermore, as a biocompatible, degradable, and easy-to-manipulate material, the agar-based transducer shows perspectives for developing artificial skins and implantable sensors.

Highly pixelated, untethered tactile interfaces for an ultra-flexible on-skin telehaptic system

Realizing highly immersive tactile interactions requires a skin-integrated, untethered, high-definition tactile transducer devices that can record and generate tactile stimuli. However, the rigid and bulky form factor, and insufficient resolution of existing actuators are hindering the reproduction of sophisticated tactile sensations and immersive user experiences. Here, we demonstrate an ultra-flexible tactile interface with high spatial resolution of 1.8 mm for telehaptic communication on human skin. Dual mechanism sensors and sub-mm scale piezoceramic actuators are designed to record and generate the static and dynamic pressures in a wide frequency range (1 Hz to 1 kHz). Moreover, actuators are integrated on ultra-flexible substrate with chessboard pattern to minimize stress during mechanical deformations. Finally, remote transmissions of various tactile stimuli, such as shapes, textures, and vibration patterns were demonstrated by the telehaptic system with low latency (<1.55 ms) and high fidelity as proven by the short-time Fourier-transform analysis.

A Fetal Movement Simulation System for Wearable Vibrational Sensors.

This paper introduces a low-cost phantom system that simulates fetal movements (FMVs) for the first time. This vibration system can be used for testing wearable inertial sensors which detect FMVs from the abdominal wall. The system consists of a phantom abdomen, a linear stage with a stepper motor, a tactile transducer, and control circuits. The linear stage is used to generate mechanical vibrations which are transferred to the latex abdomen. A tactile transducer is implemented to add environmental noise to the system. The system is characterized and tested using a wireless sensor. The sensor recordings are analyzed using time-frequency analysis and the results are compared to real FMVs reported in the literature. Experiments are conducted to characterize the vibration range, frequency response, and noise generation of the system. It is shown that the system is effective in simulating the vibration of fetal movements, covering the full frequency and magnitude ranges of real FMV vibrations. The noise generation test shows that the system can effectively create scenarios with different signal-to-noise ratios for FMV detection. The system can facilitate the development of fetal movement monitoring systems and algorithms.

Anthropogenic substrate-borne vibrations impact anuran calling

Anthropogenic disturbance is a major cause of the biodiversity crisis. Nevertheless, the role of anthropogenic substrate vibrations in disrupting animal behavior is poorly understood. Amphibians comprise the terrestrial vertebrates most sensitive to vibrations, and since communication is crucial to their survival and reproduction, they are a suitable model for investigating this timely subject. Playback tests were used to assess the effects of substrate vibrations produced by two sources of anthropogenic activity– road traffic and wind turbines– on the calling activity of a naïve population of terrestrial toads. In their natural habitat, a buried tactile sound transducer was used to emit simulated traffic and wind turbine vibrations, and changes in the toads’ acoustic responses were analyzed by measuring parameters important for reproductive success: call rate, call duration and dominant frequency. Our results showed a significant call rate reduction by males of Alytes obstetricans in response to both seismic sources, whereas other parameters remained stable. Since females of several species prefer males with higher call rates, our results suggest that anthropogenically derived substrate-borne vibrations could reduce individual reproductive success. Our study demonstrates a clear negative effect of anthropogenic vibrations on anuran communication, and the urgent need for further investigation in this area.

Noise Reduction Using Active Vibration Control Methods in CAD/CAM Dental Milling Machines

Used in close proximity to dental practitioners, dental tools and devices, such as hand pieces, have been a possible risk factor to hearing loss due to the noises they produce. Recently, additional technologies such as CAD/CAM (Computer Aided Design/Computer Aided Manufacturing) milling machines have been used in the dental environment and have emerged as a new contributing noise source. This has created an issue in fostering a pleasant hospital environment. Currently, because of issues with installing and manufacturing noise-reducing products, the technology is impractical and insufficient relative to its costly nature. In this experiment, in order to create a safe working environment, we hoped to analyze the noise produced and determine a practical method to attenuate the noises coming from CAD/CAM dental milling machines. In this research, the cause for a noise and the noise characteristics were analyzed by observing and measuring the sound from a milling machine and the possibility of reducing noise in an experimental setting was examined using a noise recorded from a real milling machine. Since a milling machine generates noise mainly due to vibration of the dust collector, the possibility of reducing noise was examined by controlling vibration. This study was conducted to understand the cause for noise from the milling machine and verify the possibility of improving noise by a tactile transducer.

Biomechanically Optimized Distributed Tactile Transducer Based on Lateral Skin Deformation

In this paper we describe a tactile transducer device that is optimized from biomechanical data and that has a compact, yet modular design. The tactile transducer comprises a 6 × 10 piezoelectric bimorph actuator array with a spatial resolution of 1.8 mm × 1.2 mm and has a wide temporal bandwidth. The actuator mounting method was improved from a conventional cantilever method to a dual-pinned method, giving the actuator the ability to deform the glabrous skin maximally during laterotactile stimulation. The results were validated by asking subjects to detect tactile features under a wide range of operating conditions. The tactile display device is modular, makes use of ordinary fabrication methods, and can be assembled and dismantled in a short time for debugging and maintenance. It weighs 60 g, it is self-contained in a 150 cm 3 volume and may be interfaced to most computers, provided that two analog outputs and six digital I/O lines are available. Psychophysical experiments were carried out to assess its effectiveness in rendering virtual tactile features.

Tactile synthesis and perceptual inverse problems seen from the viewpoint of contact mechanics

A contact-mechanics analysis was used to explain a tactile illusion engendered by straining the fingertip skin tangentially in a progressive wave pattern resulting in the perception of a moving undulating surface. We derived the strain tensor field induced by a sinusoidal surface sliding on a finger as well as the field created by a tactile transducer array deforming the fingerpad skin by lateral traction. We found that the first field could be well approximated by the second. Our results have several implications. First, tactile displays using lateral skin deformation can generate tactile sensations similar to those using normal skin deformation. Second, a synthesis approach can achieve this result if some constraints on the design of tactile stimulators are met. Third, the mechanoreceptors embedded in the skin must respond to the deviatoric part of the strain tensor field and not to its volumetric part. Finally, many tactile stimuli might represent, for the brain, an inverse problem to be solved, such specific examples of “tactile metameres” are given.

Haptically Enabled Handheld Information Display With Distributed Tactile Transducer

This paper describes the design, construction, and initial evaluation of a handheld information device that supports combined tactile and graphical interaction. The design comprises a liquid crystal graphic display co-located with a miniature, low-power, distributed tactile transducer. This transducer can create electronically-controlled lateral skin deformation patterns which give the sensation of sliding over small shapes. It is integrated within a slider mechanism to control scrolling. It also functions as a detent when pushing on it. Tactile feedback and the combination of visual and tactile feedback in a mobile context enable the development of new functions, such as multimodal navigation within large graphic spaces

Vibration transfer mobility measurements using maximum length sequences

Vibration transfer mobility measurements are required under Federal Transit Administration guidelines when developing detailed predictions of ground‐borne vibration for rail transit systems. These measurements typically use a large instrumented hammer to generate impulses in the soil. These impulses are measured by an array of accelerometers to characterize the transfer mobility of the ground in a localized area. While effective, these measurements often make use of heavy, custom‐engineered equipment to produce the impulse signal. To obtain satisfactory signal‐to‐noise ratios, it is necessary to generate multiple impulses to generate an average value, but this process involves considerable physical labor in the field. To address these shortcomings, a transfer mobility measurement system utilizing a tactile transducer and maximum length sequences (MLS) was developed. This system uses lightweight off‐the‐shelf components to significantly reduce the weight and cost of the system. The use of MLS allows for adequate signal‐to‐noise ratio from the tactile transducer, while minimizing the length of the measurement. Tests of the MLS system show good agreement with the impulse‐based method. The combination of the cost savings and reduced weight of this new system facilitates transfer mobility measurements that are less physically demanding, and more economical when compared with current methods.

Speech perception with tactile support in adverse listening conditions

Since long, different methods of vibrotactile stimulation have been used as an aid for speech perception by some people with severe hearing impairment. The fact that experiments have shown (limited) benefits proves that tactile information can indeed give some support. In our research program on multimodal interfaces, we wondered if normal hearing listeners could benefit from tactile information when speech was presented in adverse listening conditions. Therefore, we set up a pilot experiment with a male speaker against a background of one, two, four or eight competing male speakers or speech noise. Sound was presented diotically to the subjects and the speech-reception threshold (SRT) for short sentences was measured. The temporal envelope (0–30 Hz) of the speech signal was computed in real time and led to the tactile transducer (MiniVib), which was fixed to the index finger. First results show a significant drop in SRT of about 3 dB when using tactile stimulation in the condition of one competing speaker. In the other conditions no significant effects were found, but there is a trend of a decrease of the SRT when tactile information is given. We will discuss the results of further experiments.

Inverse analysis for the recovery of forces applied to photoelastic tactile transducers

In this paper, the forward and inverse analyses of one- and two-layer photoelastic tactile transducers are presented. For such transducers, an applied force profile generates stresses in the photoelastic layer, making it birefringent. Consequently, circularly polarized light input to the transducer becomes elliptically polarized at the output because of the introduction of a phase-lead distribution. Herein, the forward and inverse analyses of a one-layer photoelastic tactile transducer, under ideal conditions, are first presented. The transducer is modeled using closed form equations based on the theories of elasticity and photoelasticity, which allow the calculation of the light intensity distribution corresponding to an applied force profile. However, to recover the force profile from a light intensity distribution (i.e., the inverse problem), the phase-lead distribution must be determined first. A novel technique is described for this purpose. In the second part of the paper, we consider the forward and inverse analyses of a two-layer transducer, under nonideal conditions, where the light-intensity distribution is no longer noise-free. In the forward analysis, the calculation of the stress distribution in the transducer is implemented by finite-element analysis. The recovery of the phase-lead distribution under noisy conditions, however, constitutes an ill-posed inverse problem. A novel algorithm that accurately and effectively determines the phase-lead distribution from a noisy light-intensity distribution is presented. © 1998 John Wiley & Sons, Inc.

Using of tactile transducer for pressure-distribution measurement on the sole of the foot

This paper deals with a tactile carpet, which is based on conductive rubber of Japanese origin. A brief description of results and experiments with this rubber is introduced. Other problems are also analysed: the dimensions of the carpet for static measurement, for monitoring of human locomotion and other technological aspects.

Distributed-force recovery for a planar photoelastic tactile sensor

In this paper, an efficient force-recovery algorithm is presented for a novel planar photoelastic tactile transducer. A distributed-force profile input to the tactile sensor developed in our laboratory generates stress in the photoelastic layer of the transducer, making it birefringent. Circularly polarized light input to the transducer is elliptically polarized at the output due to phase-lead created in the stressed photoelastic layer. The algorithm presented recovers the phase-lead distribution and correlates it to the input force profile. Since this distribution is a linear function of the force profile, the solution of the inverse-tactile problem is significantly simplified. The paper presents the analytical basis of the algorithm as well as the numerical technique used in its solution.

Methods of processing tactile information based on the solution of Helmholtz's equation

Abstract This paper describes new and original methods of tactile pattern recognition applying the solution of Helmholtz's equation for a tactile transducer. Three groups of methods have been formed, based on: (a) calculation of the A matrix eigenvalue, with the matrix being formed either from the whole pattern, or from the limit points; (b) the scalar characteristic distribution of the components of the pattern's A matrix; (c) the geometrical properties of the A matrix of the pattern. The patterns have been classified into five groups.

Control Aspects of an Integrated Sensor Based Robot System with Novel Tactile Pads

The University of Newcastle upon Tyne, together with its partners, has been developing an intelligent sensor based robot system as part of ESPRIT project 278. A particular aspect of the work at Newcastle is the integration of visual and tactile transducer data into the control algorithms for the determination of robot positioning and movement. This paper discusses the overall strategy adopted for the integrated robot control system and describes its major constituent parts

Soft-Talker: A sound level monitor for the hard-of-hearing using an improved tactile transducer

We describe a small wearable device which enables deaf people to monitor the volume of their voices; it consists of a microphone, amplifier, signal rectifier, smoothing and a level detector connected to a wrist-worn vibrator, and provides vibrotactile feedback of voice level.

Linguistic Approach to the Object Recognition by Grasping

A method for recognizing both the three-dimensional object shapes and their sizes by grasping them with an antropomorfic five-finger artificial hand is described. The hand is equipped with the position sensing elements in the joints of the fingers and with the tactile transducer net on the palm surface. The linguistic method uses formal grammars and languages for the pattern description. The recognition is multilevelly hierarchically arranged, every level being different from the others by the formal language which has been used. On every level the pattern description is generated and verified from the syntactical and semantical points of view. The results of the implementation of the recognition of cones, pyramides, spheres, prisms and cylinders are presented and discussed.

Novel techniques for tactile sensing in a three dimensional environment

A simple, parallel‐mode tactile transducer for extracting three‐dimensional digital representations of complex engineering components is proposed. In addition, algorithms for computer processing of the tactile information to produce a compact structural description of the scrutinised object are evolved. The possibility exists that these techniques might be applied to future generations of robot devices with sensory feedback.

New techniques for tactile imaging

A simple, parallel-mode tactile transducer for extracting three-dimensional digital representations of complex engineering components is proposed. In addition, algorithms for computer processing of the tactile information to produce a compact structural description of the scrutinized object are evolved. The possibility exists that these techniques might be applied to future generations of automatic assembly machines with sensory feedback.