Finger pad friction and its role in grip and touch

Festkörpergleitreibung und verschleiss von eisen, kobalt, kupfer, silber, magnesium und aluminium in einem sauerstoff-stickstoff-gemisch zwischen 760 und 2 × 10 −7 torr

The dense mechanoreceptors in human fingertips enable texture discrimination. Recent advances in flexible electronics have created tactile sensors that effectively replicate slowly adapting (SA) and rapidly adapting (RA) mechanoreceptors. However, the influence of dermatoglyphic structures on tactile signal transmission, such as the effect of fingerprint ridge filtering on friction-induced vibration frequencies, remains unexplored. A novel multi-layer flexible sensor with an artificially synthesized skin surface capable of replicating arbitrary fingerprints is developed. This sensor simultaneously detects pressure (SA response) and vibration (RA response), enabling texture recognition. Fingerprint ridge patterns from notable historical figures - Rosa Parks, Richard Nixon, Martin Luther King Jr., and Ronald Reagan - are fabricated on the sensor surface. Vibration frequency responses to assorted fabric textures are measured and compared between fingerprint replicas. Results demonstrate that fingerprint topography substantially impacts skin-surface vibrational transmission. Specifically, Parks' fingerprint structure conveyed higher frequencies more clearly than those of Nixon, King, or Reagan. This work suggests individual fingerprint ridge morphological variation influences tactile perception and can confer adaptive advantages for fine texture discrimination. The flexible bioinspired sensor provides new insights into human vibrotactile processing by modeling fingerprint-filtered mechanical signals at the finger-object interface.

A noncontact tactile stimulus can be presented by focusing airborne ultrasound on the human skin. Focused ultrasound has recently been reported to produce not only vibration but also static pressure sensation on the palm by modulating the sound pressure distribution at a low frequency. This finding expands the potential for tactile rendering in ultrasound haptics as static pressure sensation is perceived with a high spatial resolution. In this study, we verified that focused ultrasound can render a static pressure sensation associated with contact with a small convex surface on a finger pad. This static contact rendering enables noncontact tactile reproduction of a fine uneven surface using ultrasound. In the experiments, four ultrasound foci were simultaneously and circularly rotated on a finger pad at 5 Hz. When the orbit radius was 3 mm, vibration and focal movements were barely perceptible, and the stimulus was perceived as static pressure. Moreover, under the condition, the pressure sensation rendered a contact with a small convex surface with a radius of 2 mm. The perceived intensity of the static contact sensation was equivalent to a physical contact force of 0.24 N on average, 10.9 times the radiation force physically applied to the skin.

Friction in sheet-metal-forming processes not only affects the values of the force parameters of the process but also determines the quality of the surface of the drawpieces. This paper presents an approach to reducing the coefficient of friction by directly applying pressurized oil to the contact zone. For this purpose, a special test stand was built to carry out the strip draw test, commonly used to model the phenomenon of friction in the deep-drawing process. This test consisted of pulling a strip between flat countersamples made of 145Cr6 cold-work tool steel covered with an abrasion-resistant Mtec (AlTiN) coating. During the pilot tests, various contact pressures, lubricants with different viscosities, and different lubricant pressures were used. The influence of friction conditions on the surface roughness of the samples and the relationship between the friction conditions and the value of the coefficient of friction were determined. The supply of the lubricant under pressure into the contact zone has a beneficial effect on reducing friction. The coefficient of friction decreases with increasing lubricant pressure for contact pressures of 2–6 MPa. For a contact pressure of 8 MPa, the lubricant pressure is the least favorable for reducing the coefficient of friction. At higher lubricant pressures (12 and 18 bar), the lubrication efficiency depends on the viscosity of the lubricant and decreases with increasing contact pressure.

A mechanical model for particle motion in the micro-scale abrasion wear test

During tactile perception, the electrical system in the brain will respond to the changes in vibration, friction, and surface properties between the perceived surface and human skin. To establish the relationship between tactile perception and friction, 64-channel Neuroscan event-related potential (ERP) system and a three-axis force sensor were used to obtain electroencephalograph (EEG) and friction signals during fingers exploring surfaces. An oddball variation mode was applied to produce the late positive component (LPC) of ERP. Three fabric samples with different friction coefficient were chosen. The results indicate that LPC amplitude is affected by friction. High friction leads to high LPC amplitude. LPC latency is related to difference of friction. Large difference of friction between samples induces small LPC latency. During tactile perception, the applied normal load of male is larger than that of female. Tactile perception is effected by gender. Female has larger LPC latency than male, indicating female are more sensitive to recognize fabrics. This fundamental study could provide theory support to the related researches.

Two vibrations with slightly different frequencies induce the beats phenomenon. In tactile perception, when two pins of different frequencies stimulate the fingertips, an individual perceives a beats caused by a summation stimulus of the two vibrations. The present study demonstrates experimentally that humans can perceive another vibration based on the beats phenomenon when two tactile stimuli with slightly different frequencies are stimulated on the finger pad with a small contactor in different locations at the same time. Moreover, we examined the amplitude of the detection threshold to be able to perceive beats phenomenon on the index finger with 5 carrier frequency (63.1, 100, 158.5, 251.2, and 398.1 Hz) and 4 beats frequency (2.5, 3.98, 6.31, and 10 Hz) when two stimuli 1 mm distance apart are vibrated at a slightly different frequency. From the experiments, it is concluded that the amplitude threshold to be able to perceive beats decreases as the standard frequency increases under 398 Hz. Furthermore, from comparing the absolute detection threshold and beats detection threshold, as the carrier frequency increases, the required amplitude at two pins for the detection of beats decreases compared to absolute vibration.

This chapter means to explain the tribological behavior of polymer-based materials, to support a beneficial introducing of those materials in actual applications based on test campaigns and their results. Generally, the designers have to take into consideration a set of tribological parameters, not only one, including friction coefficient, wear, temperature in contact, contact durability related to application. Adding materials in polymers could improve especially wear with more than one order of magnitude, but when harder fillers are added (as glass beads, short fibers, minerals) the friction coefficient is slightly increased as compared to neat polymer. In this chapter, there are presented several research studies done by the authors, from which there is point out the importance of composite formulation based on experimental results. For instance, for PBT sliding on steel there was obtained a friction coefficient between 0.15 and 0.3, but for the composite with PBT + micro glass beads, the value of friction coefficient was greater. Adding a polymer playing the role of a solid lubricant (PTFE) in these composites and also only in PBT, decreased the friction coefficient till a maximum value of 0.25. The wear parameter, linear wear rate of the block (from block-on-ring tester) was reduced from 4.5 μm/(N⋅km) till bellow 1 μm/(N⋅km) for a dry sliding regime of 2.5…5 N, for all tested sliding velocities, for the composite PBT + 10% glass beads +10% PTFE, the most promising composite from this family of materials. This study emphasis the importance of polymer composite recipe and the test parameters. Also there are presented failure mechanisms within the tribolayer of polymer-based materials and their counterparts.

Steel sheet surface topography and its influence on friction in a bending under tension friction test

Friction consumes about a third of the world’s primary energy, wear causes about 80% of machine parts to fail, and the economic losses caused by friction and wear account for about 2%–7% of its gross domestic product (GDP) for different countries every year. For large manufacturing countries such as China, the loss caused by friction and wear is relatively high. If we only calculate by 5%, the loss caused by friction and wear in China in 2019 may reach 4.95 trillion RMB. Therefore, how to reduce friction and wear is a widely concerned problem, and it is also one of the key factors that affect the human society to go green, environmental protection, and effective use of resources and energy. In present paper, advancements in the research of the origin of friction and in superlubricity have been reviewed, in which most is from my group. In the part of the origin of friction, the energy dissipation mechanism of micro-friction has been introduced firstly. The works on such area by molecular dynamics simulation showed that the friction generation process will be accompanied by the energy dissipation of phonons, electrons and acoustic-electric coupling modes. The dissipative form of sliding kinetic energy is mainly that the sliding process produces lattice vibration, which makes the energy irreversibly dissipated in the form of phonons. However, the phonon dissipation measurements of the tribo-process have not been reported at present and all these results need to be proved. Our group developed a friction energy dissipation measurement system, which can realize the measurement of various emission of friction process, phonon and electron dissipation process, molecular orientation change, micro friction force and ultra-low friction coefficient. By such system, it is found that the defects will trap neutral excitons and cause the excitons to dissipate energy faster, and also can reduce the exciton diffusion length significantly. Superlubricity is a new technique that reduces the friction coefficient by several orders of magnitude, accompanied by orders of magnitude decrease in wear rate. It is divided into three sides, one is solid superlubricity, and another is liquid superlubricity, and then is the combine superlubricity of liquids and solids. In the part of solid superlubricity, the introduction of the concept of superlubricity and the latest research progress on the superlubricity properties of 2D materials, such as molybdenum disulfide, boron nitride, graphite, and graphene, are introduced. The lowest friction coefficient for 2D materials about 0.00002 has been gotten in my group. In the amorphous carbon system we achieve superlubricity state with friction coefficient about 0.0001 under low temperature (−110°C) and high pressure (>2 GPa). In the field of liquid superlubricity, it has developed very rapidly in the past 20 years. We conclude three mechanisms for liquid superlubricity: Fluid hydrodynamic effects, double layer force and hydration force. Sometimes one mechanism can lead to superlubricity, and sometimes it requires the joint action of two or three mechanisms. Supported by these three mechanisms, the liquid superlubricity bearing capacity has been improved from about 10 MPa 20 years ago to more than 300 MPa; the system composed of water agent has been extended to solutions (acid, alkali, salt), alcohol-based liquids, oil-based system etc.; and the materials of friction pair are extended from mica, ceramics to sapphire, metal, DLC (diamond-like carbon) film, etc. In addition, recently 2D materials as additives have been added to liquid to form a liquid-solid combined superlubricity state in my group and the bearing pressure has greatly increased to the GPa level, which is a big step forward for the application of liquid superlubricity. Therefore, the time has come for the engineering application of superlubricity, and the concept of “superlubricitive engineering” has been proposed.

Infrared detection of water ingress in a composite laminate crevice based on room temperature evaporation

We introduce a new generation of 3D imaging devices based on quantum plenoptic imaging. Position-momentum entanglement and photon number correlations are exploited to provide a scan-free 3D image after post-processing of the collected light intensity signal. We explore the steps toward designing and implementing quantum plenop- tic cameras with dramatically improved performances, unattainable in standard plenoptic cameras, such as diffraction-limited resolution, large depth of focus, and ultra-low noise. However, to make these new types of devices attractive to end-users, two main challenges need to be tackled: the reduction of the acquisition times, that for the commercially available high-resolution cameras would be from tens of seconds to a few minutes, and a speed-up in processing the large amount of data that are acquired, in order to retrieve 3D reconstructions or refocused 2D images. To address these challenges, we are employing high-resolution SPAD (single photon avalanche diode) arrays and high-performance low-level programming of ultra-fast electronics, combined with compressive sensing and quantum tomography algorithms, with the aim of reducing both the acquisition and the elaboration time by one or possibly two orders of magnitude. Moreover, in order to achieve the quantum limit and further increase the volumetric resolution beyond the Rayleigh diffraction limit, we explored dedicated pro- tocols based on quantum Fisher information. Finally, we discuss how this new generation of quantum plenoptic devices could be exploited in different fields of research, such as 3D microscopy and space imaging.

Theoretical investigation of air vitiation effects on hydrogen fuelled scramjet performance

Controlled self-assembly of colloidal nanoparticles onto an electrically nanopatterned electret film is presented (see figure; EFM: electrostatic force microscopy). An unprecedented reolution of 30 nm is achieved for both charge patterning and nanoparticle assembly. Furthermore, only a close-packed monolayer of nanoparticles is assembled, allowing better structural control and the possibility of forming hierarchical nanoparticle structures. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2089/2006/c1542_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

The lack of digital floor plans is a huge obstacle to pervasive indoor location based services (LBS). Recent floor plan construction work crowdsources mobile sensing data from smartphone users for scalability. However, they incur long time (e.g., weeks or months) and tremendous efforts in data collection. In this paper, we propose BatMapper , which explores a previously untapped sensing modality–acoustics–for fast, fine grained, and low cost floor plan construction. We design sound signals suitable for heterogeneous microphones on commodity smartphones, and acoustic signal processing techniques to produce accurate distance measurements to nearby objects. We further develop robust probabilistic echo-object association, recursive outlier removal, and probabilistic resampling algorithms to identify the correspondence between distances and objects, thus the geometry of corridors and rooms. We compensate minute hand sway movements to identify small surface recessions, thus detecting doors automatically. Experiments in real buildings show BatMapper achieves $1-2$ 1 - 2 $cm$ c m distance accuracy in ranges up around 4 $m$ m ; a $2\sim 3$ 2 ∼ 3 minute walk generates fine grained corridor shapes, detects doors at 92 percent precision and $1\sim 2$ 1 ∼ 2 $m$ m location error at 90-percentile; and tens of seconds of measurement gestures produce room geometry with errors $ 0 . 3 $m$ m at 80-percentile, at $1-2$ 1 - 2 orders of magnitude less data amounts and user efforts.