Measurement of Frictional Coefficients between Fabric
Surfaces and Fingertip by Using Multi-component Load Cell
Hyun Joon Kwon, Young Ha Kwon, Kyung Hee Park
College of Advanced Technology Kyung Hee Univirsity, Yongin city,
Gyeonggido, 449-701, Korea
ABSTRACT: The tactile feeling of fabric is sensed by physical and dynamic phenomenon; friction, temperature and
vibration between human’s skin and fabric.
the tactile feeling.
The frictional coefficients are the most important factor to determine
This paper describes the real time high precision and stable operating system to measure the
frictional coefficients between human fingertips and wool fabric for man. The range of the frictional coefficients
between fingertips and fabric surface are distributed from 0.54 to 0.74 and calculated SMD of the frictional
coefficients are averaged 0.05. The frictional coefficients are decreased in according to the increased speed.
Also,
the current paper presents that the variation of the frictional coefficients depends on the moving speed and pressure.
Key words: multi-component load cell, linear motor, frictional coefficient
1. Introduction
A measurement of the mechanical properties of fabric is important factor to find out the
handle of fabric.
The tactile sensation of fabric is sensed by physical and dynamic
phenomenon; friction, temperature and vibration. Therefore, the frictional coefficients are
very important factor to sense the tactile mechanism.
The previous surface frictional measurement system such as KES-F measures friction by
using a contactor as a steel piano wire [1]. However, it is difficult to compare with subjective
test.
Hence the current measurement system applies fingertip to a contactor for in vivo
condition.
It is useful to compare with subjective test effectively.
This research is to measure a kinetic frictional coefficient in the dry for the real time.
condition of friction is related to the continuous motion after moving.
The
The condition of a
kinetic friction is maintained for sliding on sample and the frictional force during a
measurement is smaller than the maximum of the frictional force to a standstill. The frictional
force is corresponded to the normal force in proportion, so the normal force and the frictional
force is necessary to be measured simultaneously.
The frictional coefficients represents a surface roughness that textile fabric into connecting
with fingertip and involves geometrical properties of a contact surface.
Though the
measurement by using a fingertip has a concern in oil, dust, a different thing, change of local
temperature, the hardness of the contact point and viscoelastic, it is not considered in this work.
2 The Measurement of Frictional Coefficients
The measuring system that is used to obtain the fabric coefficient is shown in figure 1. It is
consisted of multi-component load cell and linear motor. Linear motor is moved smoothly and
can automatically change velocity of sliding from 0.001m/s to 3m/s. Multi-component load cell
measures simultaneously the normal force, Fz, and the frictional force, Fx, with the strain gauge
while linear motor is moved with a sample as the fixed fingertip on. Capacity of horizontal
direction, Fx, is 1 N, accuracy and precision is 0.1% and vertical direction, Fz, is 10N, accuracy
and precision is 0.04%.
Fx = Fxm – 0.015 * Fzm
(1)
Fx is obtained from calibration.
Fxm is measured force of Fx and Fzm is measured force of Fz.
AC motor or DC motor is unstable speed and vibration with general bearing translators.
Therefore linear motor is moved to translate with constant speed without vibration.
Fig 1. Constitution of Measuring System
In this work, we measured the frictional coefficients between human fingertip and fabric.
The frictional coefficient of a fabric is measured with mounted sample in size as 120 X 20 mm.
An aluminum flat plate holds the sample fabric under a tension of 20 gf and it is fixed on multicomponent load cell. Fabrics is woven by warp and weft, it has an anisotropy. Therefore,
frictional coefficients are measured over 55 mm length along each direction of warp and weft.
The result is stored 200 data per a second with microprocessor and whole system is interfaced
with a PC.
3. Result and Discussion
It is important to confirm experimental variables on fabric friction.
Therefore, the current
work attempts various trials on experiment. Spectrum of frictional force and frictional coefficient
is shown in figure 2.
Fig 2. Spectrum of friction force and frictional coefficient
The friction may depend on the repeat in which the fabric is rubbed.
of friction for fabric, how it can be change during repeat.
To obtain a clear value
Fixed fingertip is located on the
same point of fabric for accurate measuring and its load is maintained regular force for three
times.
The experimental condition is a different normal load and velocity, i.e. 0.02 N, 0.05 N,
0.1N; 1 mm/s, 5 mm/s, 10 mm/s. The result in repeat is changed within 1 % with the exception
of the first and final value. This effect may be related to alignment of fibers in the surface of
fabrics in the repeat of rubbing.
3.1. Effect of the Normal Load and Contact Area
By increasing the normal pressure the coefficient for fabric are decreased.
frictional coefficients of fabrics.
Table 1. shows
Because fingertip is viscoelastic, by increasing the normal
load, the contact area is increased. It is therefore the area of contact between fingertip and fabric
surfaces in important in fabric friction coefficient. Increasing of contact area is changed slowly
than increasing of the normal load. Hence the change of the frictional coefficient is less than the
change of the normal load.
3.2. Effect of Velocity of Sliding
Textile materials are viscoelastic in nature and their frictional properties are expected to be
time-dependent[2,3], thus an increase in the velocity of sliding causes a decrease in the time of
contact between the sliding parts.
Therefore, an increase in the velocity of sliding causes a
decrease in the time of contact between the sliding parts.
fabric are decreased.
By increasing velocity coefficient of
Thus the velocity of sliding can affect the frictional properties of fabrics.
3.3 Effect of Warp and Weft Directions of Rubbing
Fabric is woven by warp and weft so it has anisotropy. Thus, each direction is measured to
confirm its effect in same fabric. The value of weft direction has smaller than the value of warp
direction. It represents warp direction is rougher than weft direction by the properties of
weaving for fabric.
Table 1 Frictional properties of the fabrics (Sample #2)
1mm/s
Velocity
Warp
Weft
SMD
load
5mm/s
(μ)
Warp
SMD
(μ)
10mm/s
Weft
SMD
(μ)
Warp
SMD
(μ)
Weft
SMD
(μ)
SMD
(μ)
0.02N
0.667
0.083
0.586
0.063
0.665
0.062
0.586
0.073
0.585
0.067
0.550
0.070
0.05N
0.632
0.063
0.572
0.043
0.569
0.048
0.600
0.060
0.536
0.033
0.515
0.048
0.1N
0.599
0.057
0.515
0.048
0.565
0.052
0.535
0.040
0.519
0.026
0.523
0.044
4. Conclusion
The current work shows the friction measuring system is applied fingertip as a contactor is
available to obtain frictional coefficient.
The range of a frictional coefficient between
fingertips and fabric surface is distributed from 0.54 to 0.74 and calculated SMD of a frictional
coefficient is averaged 0.05.
Thus, the measuring system is stable.
Reference
1. Sueo Kawabata, "The Standardization and Analysis of Hand Evaluation", 2nd Ed., pp.3134, the Textile Machinery Society of Japan, 1980.
2. Ajayi, J.O., “ Fabric Smoothness, Friction and Handle”, Textile Research Journal,
62(52), 1992.
3. Schick, M.J., “Surface Characteristics of Fibres and Textiles”, part 1, Marcel Dekke Inc.,
New York, 1975.
4. Luis Virto and Arun Naik ., “ Frictional Behavior of Taxtile Fabrics.”, Textile
Res.j.70(30), 256-260(2000)