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Adhesion and Friction - a Study on Tactility
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
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 [en]
Adhesion, finger, friction, humidity, material, model, tactile friction, tactility
National Category
Mechanical Engineering
Research subject
Machine Design
Identifiers
URN: urn:nbn:se:kth:diva-186208ISBN: 978-91-7595-955-9 (print)OAI: oai:DiVA.org:kth-186208DiVA: diva2:926187
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
List of papers
1. Towards simultaneous measurements of skin friction and contact area: Results and experiences
Open this publication in new window or tab >>Towards simultaneous measurements of skin friction and contact area: Results and experiences
2015 (English)In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 229, no 3, 230-242 p.Article in journal (Refereed) Published
Abstract [en]

This article investigates one of the important parameters when designing for feel, namely the friction coefficient. An experiment was performed to evaluate how fringe projection could be used to investigate the topography of the fingertip, especially while in contact and sliding on a smooth surface. By allowing this smooth surface to be a small sheet of glass, a topographic camera could take pictures through it. The glass was also connected to a universal force gauge to measure normal and tangential forces from which the coefficient of friction could be calculated. The intention was to get dependable data on the forces, coefficient of friction, apparent contact area and actual contact area. This set-up was tested using 66 students who used one and three fingers in both dry and wet conditions and with a rubber glove. In order to measure natural everyday friction, they were not given any particular instructions on how to clean or slide their fingers. This method resulted in a much higher variation in friction coefficients than has been found in previous research. In particular, many higher values were noticed. This illustrates that the friction coefficient is a very hard parameter to rely on when it comes to designing surfaces for feel.

Place, publisher, year, edition, pages
Sage Publications, 2015
Keyword
Biotribology, finger, tactility, adhesion, friction test methods, water, glass
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-162947 (URN)10.1177/1350650114521798 (DOI)000349985500002 ()2-s2.0-84923361088 (Scopus ID)
Note

QC 20160413

Available from: 2015-04-02 Created: 2015-03-26 Last updated: 2017-12-04Bibliographically approved
2. Model for contact between finger and sinusoidal plane to evaluate adhesion and deformation component of friction
Open this publication in new window or tab >>Model for contact between finger and sinusoidal plane to evaluate adhesion and deformation component of friction
2016 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 96, 389-394 p.Article in journal (Refereed) Published
Abstract [en]

One of the main parameters affecting finger friction, friction-induced vibrations in the finger, and consequently tactility is surface topography. Recently Skedung et al. performed finger friction measurements on fine controlled surfaces. These surfaces were sinusoidal with wavelengths from 0.27 to 8.8 mu m and amplitudes from 0.007 to 6 mu m. Building on those tests an analytical model for the contact was developed to explain the differences in friction coefficient. The contact was modelled as trapezoids in a circular pattern pressed against a sinusoidal plane. Results showed that the calculated contact area and therefore friction coefficient corresponded well with the measurements. This model can be used to see how the different surface parameters influence friction.

Place, publisher, year, edition, pages
Elsevier, 2016
Keyword
Finger, Friction, Contact area, Adhesion
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-184014 (URN)10.1016/j.triboint.2014.12.020 (DOI)000371100800036 ()2-s2.0-84959542022 (Scopus ID)
Note

QC 20160330

Available from: 2016-03-30 Created: 2016-03-22 Last updated: 2017-11-30Bibliographically approved
3. Feeling fine – the effect of topography and friction on perceived roughness and slipperiness
Open this publication in new window or tab >>Feeling fine – the effect of topography and friction on perceived roughness and slipperiness
Show others...
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.

Keyword
tactile perception, roughness, slipperiness, friction, textures
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-183994 (URN)
Note

QC 20160509

Available from: 2016-05-05 Created: 2016-03-22 Last updated: 2016-11-29Bibliographically approved
4. Four similar surfaces with different feel – a tactile study on adhesion, friction, Young’s modulus and thermal conductivity
Open this publication in new window or tab >>Four similar surfaces with different feel – a tactile study on adhesion, friction, Young’s modulus and thermal conductivity
2016 (English)Manuscript (preprint) (Other academic)
Abstract [en]

Even surfaces that look the same and have the same topography have a different feel to them. How is this difference related to material properties? In this paper four surfaces (aluminosilicate glass, soda‑lime glass, polycarbonate and polyurethane) were evaluated by a test panel. The purpose was to study whether the panel could distinguish different material parameters, in particular the adhesion. Results showed that the test panel could sense differences in thermal conductivity, Young’s modulus and adhesion. The results also showed that the measured friction coefficients did not correspond to the test panels’ subjective opinion, unlike the perceived and measured adhesion force.

Keyword
finger, friction, tactility, adhesion, biotribology
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-183996 (URN)
Note

QC 20160509

Available from: 2016-05-05 Created: 2016-03-22 Last updated: 2016-05-09Bibliographically approved
5. Friction and adhesion on smooth surfaces in different climates – an evaluation of a polymer bioskin for tactile measurements
Open this publication in new window or tab >>Friction and adhesion on smooth surfaces in different climates – an evaluation of a polymer bioskin for tactile measurements
2016 (English)Manuscript (preprint) (Other academic)
Abstract [sv]

Whether a surface feels good or not is obviously up to personal preference but the physical interaction between finger and surface can be measured and explained. For a smooth surface the sensation of touching is mainly determined by perceived friction and stickiness. Therefor would it be useful with an easy way to measure these properties and being able to specify the tactile properties of a surface without measuring finger friction and doing subjective tests with a test panel. For this have a polymer bioskin probe been tested in friction and adhesion measure­ments in three different climates. Results showed that tests with bioskin correlated better for tests on glass than on polymer surfaces and better in dry conditions than warm and humid. This means that in the right environment even a simple adhesion test can be used to grade tactile properties of smooth surfaces.

Keyword
finger, friction, adhesion, tactility
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-183997 (URN)
Note

QC 20160509

Available from: 2016-05-05 Created: 2016-03-22 Last updated: 2016-05-09Bibliographically approved

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