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Feeling fine – the effect of topography and friction on perceived roughness and slipperiness
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
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2016 (English)Manuscript (preprint) (Other academic)
Abstract [en]

To be able to design materials with specific haptic qualities, it is important to understand not only the contribution of physical attributes from the surfaces of the materials, but also the perceptions that are involved in the haptic interaction with the materials. A series of 16 wrinkled surfaces with two different materials (Young’s modulus of 1,600 and 20,000 psi, respectively) and 8 different wrinkle wavelengths (30‑120 µm, and two unwrinkled reference surfaces) were thus characterized in terms of surface roughness and finger friction coefficient. Sixteen participants scaled the perceived Roughness and Slipperiness of the surfaces using the method of free magnitude estimation. Five of the sixteen participants conducted friction measurements during their perceived slipperiness session, and an experimenter conducted friction measurements in a separate experiment with higher experimental control. The trends in friction properties were similar for the group of participants performing the friction measurements in an uncontrolled way and the experiments performed under well-defined conditions, showing that the latter type of measurements represent the general friction properties well. The results point to slipperiness as the key perception dimension for textures below 100 µm and roughness above 100 µm. In the interval between 30 and 50 µm it is hard to discriminate between the wavelengths, these surfaces also exhibit the highest slipper­iness and the lowest roughness. Furthermore, it is apparent that roughness and slipperiness perception of these types of structures are not indepen­dent; which is also supported by an increased friction between 80‑100 µm that corresponds well with both a change in slipperiness and in roughness. The increased friction in this specific wavelength region is related to an increased contact area between finger and material. Somewhat surprising was the fact that the material with the higher Young’s modulus was perceived as more slippery, especially for the smaller wavelengths, this is also the range where it was difficult to differentiate between the wave­lengths. A concluding finding was that the flat (high friction) references surfaces were scaled as rough, supporting the theory that perceived roughness itself is a multidimensional construct with both surface rough­ness and friction components.

Place, publisher, year, edition, pages
2016.
Keyword [en]
tactile perception, roughness, slipperiness, friction, textures
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-183994OAI: oai:DiVA.org:kth-183994DiVA: diva2:926279
Note

QC 20160509

Available from: 2016-05-05 Created: 2016-03-22 Last updated: 2016-05-09Bibliographically approved
In thesis
1. Adhesion and Friction - a Study on Tactility
Open this publication in new window or tab >>Adhesion and Friction - a Study on Tactility
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Although we are surrounded by hundreds of surfaces we can still distinguish them from each other simply by touch. The tactile information, interpreted by our brain and given by our fingers, is precise, but to put words to the sensation is very difficult — is it smooth, sticky or harsh? We do not only perceive surfaces differently, we also describe them in our own way. Luckily the forces and deformations that the skin are exposed to when sliding over a surface is ruled by laws of nature.

This thesis investigates the contact between finger and surface and how it is affected by, for example, material properties, surface texturing or changes in climate. By measuring contact area, friction coefficient, and adhesion, using different materials and under different conditions, conclusions could be drawn. Also, a model for the contact between a finger and a sinus­oidal surface was developed, which could be used to estimate contact area, deformation and resulting friction coefficient.

Results showed how differences in for example material, surface topography and environ­ment affect the interaction between finger and surface, and what consequences it has. If the objective is to change the feel of a surface or to alter the grip, this thesis could work as a support.

Paper A investigates the area and friction between finger and glass surface under different conditions.

Paper B presents a model for the contact area and deformation for a finger in contact with a sinusoidal surface.

Paper C is a validation of the contact area model. Here it was used on new surfaces and compared with new finger friction measurements.

Paper D mainly examines whether the adhesion or stickiness of different surfaces is distinguishable by a test panel and how this affects the perceived pleasantness of the surface.

Paper E relates to the adhesion and friction for a bioskin probe and skin. Tests were made to evaluate how an artificial probe can be used to evaluate the tactile properties of a surface.

Abstract [sv]

Även om vi omges av hundratals olika ytor kan vi fortfarande skilja dem åt med hjälp av känseln. Den taktila informationen från fingertopparna som tolkas av hjärnan är precis, men att sätta ord på hur ytan känns är väldigt svårt. Len, sträv eller grov? Vi upplever inte bara ytorna olika utan beskriver dem också på olika sätt. Krafterna och deformationerna som huden utsätts för när den glider över en yta styrs dock av naturlagar.

Denna avhandling utreder kontakten mellan fingertopp och yta och hur den påverkas av exempelvis materialval, ytstruktur eller förändringar i klimat. Genom mäta kontaktarea, friktionskoefficient och adhesion för olika material i varierande omgivning kunde slutsatser dras. En modell för kontakten mellan fingertopp och sinusformad yta togs fram vilken kunde användas till att uppskatta kontaktarea, deformation och resulterande friktionskoefficient.

Resultaten visade hur skillnader i exempelvis material, yttopografi och omgivning påverkar kontakten mellan finger och yta och vilka kon­sekvenser detta får. Om målet är att förändra känslan eller friktionen för en yta kan denna avhandling fungera som stöd.

Artikel A undersöker kontakten och friktionen mellan fingertopp och glasyta för olika förhållanden.

Artikel B presenterar en modell för arean och deformationen som sker för fingertopp och sinusformad yta i kontakt.

Artikel C är en validering av modellen. Här användes den för nya ytor och jämfördes med nya mätningar av fingerfriktion.

Artikel D undersöker i huvudsak huruvida en testpanel kan särskilja adhesionen för olika ytor och hur detta påverkar hur den känns.

Artikel E arbetar vidare med adhesion och undersöker och hur en testkropp av artificiell hud kan användas för adhesionsmätningar av en yta. Detta för att med relativt enkla mätningar kunna uppskatta ytans taktila egenskaper.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. xii, 42 p.
Series
TRITA-MMK, ISSN 1400-1179 ; 2016:03
Keyword
Adhesion, finger, friction, humidity, material, model, tactile friction, tactility
National Category
Mechanical Engineering
Research subject
Machine Design
Identifiers
urn:nbn:se:kth:diva-186208 (URN)978-91-7595-955-9 (ISBN)
Public defence
2016-05-27, F3, Lindstedtsvägen 26, KTH Campus, Stockholm, 14:00 (English)
Opponent
Supervisors
Note

QC 20160504

Available from: 2016-05-09 Created: 2016-05-04 Last updated: 2016-05-09Bibliographically approved

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