Fabric Touch Tester The New Standard in Comfort Measurement Rycobel NV - Nijverheidslaan 47-8540 Deerlijk 3934 Airway Drive Rock Hill, SC 29732 Phone: 803-329-2110 Fax: 803-329-2133 Tel.: +32 56 78 21 70 Fax.: +32 56 77 30 40 3J. Garment Centre, 576 Castle Peak Road, Kowloon, Hong Kong info@rycobel.be - www.rycobel.com Phone: 852-3443-4888 Fax: 852-3443-4999 www.sdlatlas.com info@sdlatlas.com
Introduction In consumer behavior research, it is found that a key factor affecting the consumer s clothes buying decision process (for both males and females) is the comfort attribute. Comfort is a highly subjective perception. You may define comfort perception based on your feeling and experience when touching the clothes. However, how do you effectively communicate these perceptions with another person? For example, how can a designer sitting in New York office tell a fabric mill in India what type of comfort fabric that he/she needs via some qualitative descriptions and quantified requirements, and then get the correct supply? Many researchers have developed various objective measurement methods to quantify the sensations when touching a fabric. The way that the fabric feels has been described as fabric hand, which has been traditionally used in the textile and clothing industries as a description of fabric quality and prospective performance. The most well-known objective measurement method is the KES-FB (Kawabata Evaluation System of Fabric Hand), invented by HESC in 1980. The KES-FB measurement method involves totally 5 very sensitive testing instruments for measuring the mechanical and surface properties of fabrics. The drawbacks of this instrumentation are the expensive costs and the need for a highly trained operator to carry out the tests and interpret the test results. Now, an innovative Fabric Touch Tester (FTT) is co-developed by Prof. Li Yi, et al. of Hong Kong Polytechnic University (HKPU) and SDL Atlas, funded by the Hong Kong Research Institute for Textiles and Apparel (HKRITA), to measure the skin touch comfort objectively and quantitatively. The comprehensive, sophisticated design of the FTT enables it to measure all the mechanical and surface properties of a fabric in one simple test which takes about 2-3 minutes. Research studies showed the FTT has good correlations to KES-FB, and human panel subjective evaluation studies covering a wide range of fabrics.
Basic Principle and Conceptual Design When we touch a fabric, the receptors in our skin are stimulated and the encoded neural information is subjectively interpreted, i.e. our perception of sensations. Fig. 1 Neurophysiology of sensory perceptions..hatch et al, 2000 This same process is instrumented in FTT via the use of 5 types of sensors, namely: - Heatflux - Temperature - Pressure - Friction - Displacement With these 5 types of sensors, the hand properties of a fabric are measured simultaneously, all in about 2-3 minutes, including: - Fabric thickness - Fabric compression - Fabric bending - Fabric shearing - Fabric surface friction - Fabric thermal properties.
Design and structure of FTT Figure 2 shows the photo and structural design of the FTT: US Patent No. 6,601,457 China Patent App. No.: 201210275485.6 / 201210275648.0 / 201210278839.2 Fig. 2 Fabric Touch Tester (FTT) appearance and structure. Fig. 3 Testing specimen dimensions The testing area of the FTT consists of an upper plate and a lower plate, and specimen to be tested is prepared as per Fig. 3, includes both the warp and weft directions. A heater is installed in the upper plate; a constant 10 deg C temperature difference between the upper and lower plates is maintained before a test is started. A Heatflux sensor is also installed in the upper plate (Fig. 4) hence the heat flow during a test is measured.
Fig. 4 Design of FTT upper plate When 10 deg. C temperature difference is achieved between the upper and lower plates, the upper plate will be moved downwards to compress the testing specimen, and then upwards by the use of a step motor. The testing specimen on the lower plate is compressed and then released, and the travel distance of the upper plate is measured by a laser displacement sensor; whilst the pressure (of compression) is measured by the load cells underneath the lower plate. Through this process, the following parameters are measured: Compression Measurement Initial thickness Thickness at max. pressure Standard thickness Compression work Compression recovery work Compression recovery rate Compression linearity Max. compression rigidity Max. recovery rigidity Thermal Measurements The max. hear flux in the compression Heat conductivity without pressure Heat conductivity with standard pressure Heat conductivity with max. pressure Heat resistance without pressure Heat resistance with standard pressure Heat resistance with max. pressure While the upper plate is moving downwards, the specimen on the lower plate is pressed, and forced downwards, dragging the warp and weft sections of the specimen through other measurement modules which are adjacent to the lower testing plate for surface friction and surface roughness measurements (Fig. 5).
Fig. 5 Fabric surface friction and roughness evaluation module The friction forces are measured when the specimen is dragged through the Friction Measurement Module (Fig. 6). Fig. 6 Surface Friction Measurement The upward and downward motions of the roughness sensors are induced by the surface profiles of the tested fabric while it is being dragged. The displacement of these motions are measured by the use of another set of laser displacement sensors (Fig. 7), then conveyed to the surface condition parameters as the following for both warp and weft directions:
Fig. 7 Surface Roughness Measurement Friction Evaluation Static friction coefficient Kinetic friction coefficient Deviation of kinetic friction coefficient Kinetic friction work Roughness Evaluation Base line of roughness wave Peak height of roughness wave Trough depth of roughness wave Wavelength of roughness wave Amplitude of roughness wave Average amplitude of roughness wave The testing fabric passed through the surface friction and roughness measurement modules will then be bent as the lower testing plate is pressed downwards, which activates another 2 torque sensors of the bending evaluation module (Fig. 8). The bending angles are then calculated, with the following bending parameters for both warp and weft directions: Bending Parameters Initial bending angle Bending work Bending linearity Average bending rigidity Max. bending rigidity angle
Fig. 8 Bending properties evaluation module and measuring mechanism Test Results Fig. 9 Test screens before (left) and after (right) test. The repeatability and reproducibility study for the key parameters of FTT based on 24 fabric samples are summarized as the following table: Parameter Total Gage % (Repeatability + Reproducibility) Average Bending Rigidity (Warp) 12.16 Average Bending Ridigity (Weft) 4.28 Thickness 0.60 Compression Work 2.97
Qmax 3.79 Thermal Resistance 1.73 Thermal Conductivity 1.51 Static Friction Coefficient (Warp) 34.73 Static Friction Coefficient (Weft) 7.69 Dynamic Friction Coefficient (Warp) 22.45 Dynamic Friction Coefficient (Weft) 11.02 Roughness Peak-trough Distance 4.7 (Warp) Roughness Peak-trough Distance 5.16 (Weft) Remark: Variations in friction measurements for warp direction is larger than the weft s, indicating that the testing principles are working. Correlation studies Correlation studies of this FTT with similar testing equipment, KES-FB and PhabrOmeter, and human subjective evalutaion were conducted by Prof. Yi Li et al. In their study, (2) a comparison study using KES-FB and PhabrOmeter (based on different measurement principles) to measure 20 selected 100% silk fabric smoothness properties. Subjective evaluation on the fabric samples was also conducted among 23 subjects. No significant relationship between these two methods was found through statistical analysis. When the researchers compared both the objective measurement results from KES-FB and PhabrOmeter to subjective evaluation, the smoothness value obtained by KES-FB showed significant correlation between subjective evaluation scores. The PhabrOmeter did not, possibly due to its different approach. For correlation between the FTT and the KES-FB, it was found that most of the key indexes have significant correlation, except the Compression Linearity and Roughness peak-trough Distance because they have different physical meanings. For correlation of the FTT to subjective perceptions, regression studies confirm that the indexes measured by FTT have significant correlation with all the subjective sensations tested. Based on the preliminary study of Prof. Li et al., it can be summarized that the measurements by FTT demonstrated better correlations with the subjective touch sensations than the measurements from other similar instruments such as KES-FB and PhabrOmeter. More detailed check-up and validation are underway.
Detailed research data per the aforementioned studies are available upon request. The data cited in the paper are based on the preliminary study of the FTT. More research studies with the industrial partners are continued. Application of FTT With more understanding on how our body perceives sensation stimuli for comfort, we are able to categorize such stimuli and simulate these with the corresponding mechanical and thermal test modules in FTT. All such simulation tests are integrated in a single test in FTT, making it simple to operate. The powerful software enables the users to easily interpret the test results. Therefore, the FTT will be an indispensable device for multi-levels of users, from fabric mills to designers and retailers. Fabric mills can use it to determine the most appropriate processing conditions for their products; designers can rely on the FTT to predict the consumer reaction on the comfort of the clothes, and retailers can have an objective, precise device to facilitate the communication with their vendors on the comfort parameters of the clothes. Furthermore, since the FTT test results are parameterized, the comfort communication between all the related parties can be in electronic format, making on-site (face-to-face) communication not necessary all the time, saving time and money, and of course, fewer disputes on comfort. Summary The SDL Atlas Fabric Touch Tester (FTT) is an innovative testing equipment that enables measurement of multiple fabric hand properties in a single test which takes about 2-3 minutes. Preliminary studies showed the measurements from FTT have significant correlation with human subjective touch sensations, hence is able to measure and distinguish fabric touch comfort properties. Good repeatability and reproducibility of the FTT was also demonstrated during the study of Prof. Li et al. This innovative equipment, permits quality control and research and development laboratories to measure and predict the comfort perception of fabrics, from product designs, to processing control, and end products for consumers. The precise, objective measurements make the FTT an excellent communication device among designers, retailers, and their vendors about comfort requirements.
References 1/ J.Y, Hu, et al. Fabric Touch Tester: Integrated evaluation of thermal-mechanical sensory properties of polymeric material, Polymer Testing 25 (2006), 1081-1090, Elservier 2/ Xiao Liao, et al. A comparison study of measuring fabric smoothness using KES-FB and PhabrOmeter, Textile Bioengineering and Informatics Symposium (TBIS) 2012, Binary Information Press 3/ Y.H. Hu, et al. Presentations for the Fabric Touch Tester workshop, Textile Bioengineering and Informatics Symposium (TBIS) 2012. 3934 Airway Drive Rock Hill, SC 29732 Phone: 803-329-2110 Fax: 803-329-2133 Rycobel NV - Nijverheidslaan 47-8540 Deerlijk 3J. Garment Tel.: Centre, +32 56 576 78 21 Castle 70 Fax.: Peak +32 Road, 56 77 Kowloon, 30 40 Hong Kong Phone: info@rycobel.be 852-3443-4888 - www.rycobel.com Fax: 852-3443-4999 www.sdlatlas.com info@sdlatlas.com