The Development Of LabVIEW-Based Virtual Clothing Pressure Measurement System

Clothing pressure comfort is an important part of clothing comfort, and the clothing pressure measurement is the base of objective evaluation of clothing pressure comfort. So clothing pressure measurement is particularly important. With the rapid development of computer technology, the combination of computer technology and measurement system has achieved new breakthrough, which has changed the concept of traditional instruments and the function and role of test instruments. Therefore, the concept of virtual instruments emerged.It was discussed in this thesis that how to apply the concept of virtual instrument to clothing pressure measurement. And a virtual clothing pressure measurement system based on LabVlEW was developed. The system consists of both hardware and software. Hardware platform is composed of a pressure sensor, an amplifier, a signal conditioner, a data acquisition card and a computer. FlexiforceA201had been chosen as the pressure sensor, which was developed by the Tekscan sensor company and suitable for testing small pressure on flexible contact surface. Its function is to convert the input variable into measurable signal. An amplifier circuit recommended by the Tekscan was used. The role of the amplifier is transforming output impedance into output voltage, which will help the data acquisition. SCXI series of signal conditioner had been chosen, which was exploited by "National Instruments. The function of signal conditioner is to filter the sensor output signal. PCI-6024E data acquisition card was used. It is a member of E Series data acquisition cards developed by NI, its role is to collect the external analog signals into the computer. After the hardware platform was set up, static calibration of the pressure sensor was done, including sensor adaptation, repeatability, linear relationship between input load and output voltage, hysteresis tests, etc., to prepare for data acquisition.The programs of the clothing pressure measurement system were written by using underlying VI-DAQmx of LabVIEW. The programs involves five modules:controlling and timing module, data acquisition module, data storage module, data display and analysis module and error handling module. The specific procedures and operating principles of each module was intoduced, and clothing pressure measurement system operating instructions was provided.The precision and accuracy of LabVIEW-based virtual clothing pressure measurement system were evaluated in this thesis. The R&R method (Repeatability and Reproducibility Assessment Method) was used to evaluate the precision of the system. The (R&R)%of LabVIEW-based virtual clothing pressure measurement system was calculated based on the clothing pressure test results of20samples from the same stretch fabric used for making girdles and the calculated value of (R&R)%was19.93%. According to R&R evaluation criteria, the precision of LabVIEW-based virtual clothing pressure measurement system is well. The precision of AMI air-pack pressure measurement system was also evaluated by using the same method. The (R&R)%was19.21%and slightly less than that of LabVIEW-based virtual clothing pressure measurement system. And this shows that the precision of LabVIEW-bascd virtual clothing pressure measurement system is slightly worse than that of AMI air-pack pressure measurement system, but the difference is not obvious. To compare the degree of variation, the coefficients of variation were calculated according to the clothing pressure test results of20samples from the same stretch fabric used for making girdles by using these two measurement systems. The CV value of LabVIEW-based virtual clothing pressure measurement system is5.0%. The CV value of AMI air-pack pressure measurement system is3.9%. This indicates that the former is somewhat less stable than the latter. However. the difference is small.Accuracy evaluation includes two steps. First, ajusting the programs of LabVIEW-based virtual clothing pressure measurement system by using AMI air-pack pressure measurement system as the criterion. The clothing pressure of samples from other4stretch fabrics used for making girdles and at different elongation rates (10%,20%,30%,40%and50%) were tested by using the two measurement systems.Fitting curve analysis was carried out using SPSS on the test results. The fitting curve equation is Y=1.171x3-4.336x2+6.315x-0.177, where Y represents clothing pressure test results of AMI air-pack pressure measurement system (kPa). X is on behalf of clothing pressure test results of LabVIEW-based virtual clothing pressure measurement system(kPa). The R2is0.939for the fitting curve equation, which indicates that the fitting effect is remarkable. Second, adjusting the programs of the LabVIF.W-based virtual clothing pressure measurement system according to the fitting curve equation. The ajusted measurement system was used to re-measure the clothing pressure of the4stretch fabrics used for making girdles and at different elongation rates (10%,20%,30%,40%and50%), and the test results were compared with the results that obtained from the AMI air-pack pressure measurement system by using paired T test. According to the result of paired T-test, it was found that there is significant correlationship but no obvious difference between the test results from the adjusted LabVIHW-based virtual clothing pressure measurement system and those from AMI air-pack pressure measurement system. In addition, the relative error between the test results from the adjusted LabVIEW-based virtual clothing pressure measurement system and those from AMI air-pack pressure measurement system was calculated. It was found that the error is ranged from2%to27%. The error is not large and the ajusted system can meet the requirements of data acquisition accuracy.