Abstract
An artificial neural network (ANN) model is constructed to derive the surface temperature of e-textile structures developed for cold weather clothing. A series of textile transmission lines made of different types of conductive yarns, insulated by using different types of seam tapes, were enclosed in a thermoplastic textile structure via hot air welding technology, and then they were powered with different levels of specific voltages in order to obtain different heating levels. The surface temperatures of the powered e-textile structures were measured using a thermal camera. The experimental input variables, sample type, temperature, feeding speed, resistance of samples, applied voltage and current were used to construct an ANN model and the outputs of surface temperature and electric power dissipated were used to test the prediction performance of the developed model. It was concluded that the ANN provided substantial predictive performance. Simulations based on the developed ANN model can estimate the surface temperature distributions of powered e-textile structures under different conditions. The ANN model developed for prediction of electric power dissipated was very successful and can be useful for e-textile product designers as well as textile manufacturers, particularly for cold weather protection products such as jackets, gloves and outdoor sleeping mats.
Keywords
Many prediction-related problems in textiles are computed by artificial neural network (ANN) architecture. ANN applications have mainly focused on fiber and yarn production issues, that is, prediction of cotton yield with supplemental nitrogen, 1 fiber identification with NIR (near-infrared) light without destruction of the fiber,2–6 formulating physical/molecular structure property relationships of man-made fibers,7,8 inspection of textured yarn packages, 9 determination of the degree of spinnability from fiber and process properties with an accuracy of over 90%, 10 yarn inspection to classify trash and neps with an accuracy of over 97%, 11 determination of the performance of a spinning unit from the number of yarns, ring frames, utilization levels of machines, etc., with an average error of around 1% 12 and prediction of the relationship between fiber properties, yarn count and/or yarn tensile and elongation properties with errors of less than 7% or correlation coefficients of over 0.84.13–17 Moreover, ANN studies concerning fabric properties, including prediction of the relationship between fabric manufacturing process parameters and fabric properties, such as strength, bending rigidity, thickness, drape, shear, wrinkle, etc., with average absolute errors of around 2% and coefficient of correlation of 0.95,18–26 fabric defect detection with a level of success around 90%,27–34 fabric pattern classification 35 and prediction of stitch formation and sewability from fabric and sewing machine properties with a level of success of over 97%,36–38 as well as those on prediction of color recipes/dyestuff concentration from absorbance,39–44 were of great interest in the literature. However, it is apparent that there is not much work on ANN application to electronic textiles (e-textiles).
The concept of e-textiles explains interactive reactions that can sense the signals, process the information and give actuation with responses via the textile structure.45,46 Today's innovative e-textile manufacturing approaches let the textiles and fabrics have applications mainly in wearable computing systems, medical and healthcare, sportswear and the military.47–51 For instance, textile electrodes integrated into clothing that can be worn comfortably can gather clinical physiological data comparable to gel electrodes in order to monitor the health of the wearer in both sports and healthcare settings. 52 Garment-based gesture controls or muscle fatigue detection can be realized by textile-based electromyography sensors.53,54 Beyond sportswear or healthcare, the attention on connecting people through clothing-based wearable technology has been recently pioneered by incorporating micro-light emitting diode (LED) arrays to create wearable displays and tactile or touching textile sensors 55 and color-tunable textiles for illumination or decoration56,57 in the fashion and entertainment sectors. Indeed, the product range and vision of the e-textile technology market is constantly improving and enabling more commercial product developments. For instance, electric resistance heating textile applications especially for cold weather protection like jackets, gloves and outdoor sleeping mats have attracted great interest in the market recently. 58
The interface layout or design of e-textiles is generally realized using conductive textile yarns or fibers. From a textile perspective, the textile-based transmission/power lines can be formed by designing conductive tracks on the textile structure based on different textile production techniques, such as printing, welding, knitting, weaving, embroidery, etc.59–64 However, the current passing through these conductive tracks might cause a vital problem, since electrical energy is converted to heat on top of conductive tracks while transmitting power. On the other hand, based on the resistance values of conductive yarns with the current passing through, these conductive yarns can be used for heating purposes. In both cases, the surface temperature distribution on textile structures is critical and vital to be known as a design parameter before manufacturing e-textile structures, since they might cause burns on human skin. Another design constraint is the very high cost of e-textiles, which must be kept in mind at all times. Moreover, precise measurement of surface temperature and heat dissipation are time consuming, and demand highly sophisticated equipment as well as well-trained personnel.
The focus of this study is to offer an ANN-based model for prediction of final average temperature and heat dissipated on e-textile structures, including conductive yarns. Firstly, an experimental study has been conducted based on manufacturing of e-textile structures for heating purposes. Hot air welding technology has been used in order to insulate the conductive tracks over the textile structure, since it can offer a practical solution to prevent the short circuits caused by some of the disturbances resulting from the wearability concept of the textile structures. E-textile structures were used in electric power transmission and distribution to transmit and convert electrical energy into heat. Secondly, based on the experimental results, an ANN model has been designed in order to predict the average surface temperatures and heat dissipation of e-textile structures depending on conductivity level and applied voltage. Hence, the offered model can be a solution for product designers as well as textile manufacturers by eliminating the highly expensive pre-product design process for electric resistance heating product applications.
Experimental study
Electric resistance heating theory
In an electric resistance heating system, the electric current passing through the resistor generates an amount of heat depending on its level; however, the current flow is limited by the resistance and applied voltage in a circuit based on a basic principle of Ohm's law (Figure 1).65,66
Ohm's law illustration.
Production of e-textile structures for heating applications
The properties of the conductive yarns
PA: polyamide
Processing conditions for manufacturing of e-textile power lines
PA: polyamide; PET: polyester
In Figures 2 and 3, the manufacturing process of e-textile structures using an H&H AI-001 hot air welding machine and final e-textile samples are shown, respectively. As shown in Figure 2, the seam tape is sealed on a thermoplastic fabric while passing through the nip point of a stationery roller (at the bottom) and a rotating circular roller (at the top), where the hot air is blown and pressure applied. Thus, thermoplastic fabric is covered by a seam tape, as shown in Figure 3.
Manufacturing welded e-textile structures via hot air welding machine. (Color online only.) Some of the e-textile transmission line samples manufactured by using 100% polyester (yellow) and 100% polyamide (navy) thermoplastic fabrics, welding tapes and conductive yarns. (Color online only.)

Following the production of samples, the resistance (R) values were measured using a Keithley® multimeter.
Testing set up to measure the surface temperature of e-textile structures
In order to test the surface temperature of e-textile samples with high precision and repeatability, the set up shown in Figure 4 was constructed under standardized conditions in a dark room compatible with AATCC 128,
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where any external heat and light reflections are minimized. The set up includes an opaque 45 ° inclined background block inside a dark testing cubicle. The emissivity value of the opaque background block is estimated to have a value of 0.95. E-textile samples are placed on the opaque block and the ends of samples are connected to the power supply. Measurements are taken by a thermal camera located 35 ± 2 cm far away from sample surface; thus, the thermal camera was perpendicular enough to the inclined background block. Measurements were taken via Fluke SmartView® software through a Fluke Ti200 9H2 digital thermal camera at applied voltages of 7.4, 9 and 12 V, respectively, and the average, minimum and maximum temperature values are acquired within a precision of ± 0.005. Following the thermal camera measurements, the actual voltage and current passing through conductive yarn over the sample connected to the power supply were measured using a Keithley multimeter. During observations while applying potential difference to samples, it is found that after around 2 minutes, a relatively stable flow regime is reached where the temperature of the sample becomes almost constant within a precision of ± 0.005. Therefore, with the acquired current value and voltage value, heat dissipation is calculated using Ohm's law, as illustrated in Figure 1.
Testing set up to measure electric resistance heating.
For instance, the thermal image of the e-textile sample together with the sample's original image is shown in Figure 5.
Original e-textile samples (100% polyester – yellow; 100% polyamide – navy) and their thermal images acquired by a thermal camera. (Color online only.)
Analysis of experimental uncertainty
A small experimental set
Artificial neural network model
In this study, the Neural Network Toolbox of MATLAB® 7.10 (R2010a) mathematical software was used to predict average surface temperatures and electric power dissipations on e-textile structures under different applied voltage values. The input variables are Sample Type, Temperature (℃), Feeding Speed (ft/min), Resistance of Sample (Ω), Applied Voltage (V) and Current (A) and the outputs are Average Surface Temperature and Electric Power Dissipated. A small experimental set is shown in Table 3. Here it should be noted that the effects of selected inputs on each of the outputs is highly significant (p < 0.05). Experimental results mainly showed that as the linear resistance increases, the current passing through conductive yarns decreases when the voltage is constant, as expected. Although each input has a significant effect on the resulting average surface temperature and heat dissipated over the e-textile structure, a considerable effect is obtained with inputs of linear resistance and current passing through the samples, as well as applied voltage.
The input–output data can be actual or normalized. It is obvious that using normalized data leads to better results. The normalized dataset of laboratory experiments is obtained with Equation (1), where X is normalized data, Xi is actual data, Xmin is the minimum value of actual data and Xmax is the maximum value of actual data
A small normalized experimental set
In this study, the feed forward back propagation ANN model is preferred in our multi-layered ANN structure since it is a commonly used approximator and best fitted with the dataset of the ANN model. Levenberg Marquardt
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is used as a training algorithm in the proposed feed forward back propagation ANN model. The Gradient Descent with Momentum (GDM) learning algorithm is applied for the learning algorithm in MATLAB® software. Variables are normalized between 0 and 1, so LOGSIG (Log-Sigmoid), the most widely used transfer function (Equation (2)), is preferred for the ANN model
As a result of tests and analysis, the network's optimum topology has been obtained with a specific iteration. The proposed ANN models consisted of six-neuron input layers that represent inputs, a hidden layer that is made of five and 10 neurons and finally the output layer that is made of two neurons. A sample structure that represents the ANN's input, output and hidden layers (consisting of five neurons) is indicated in Figure 6. Then two proposed ANN models have been trained. Results are simulated and compared with the actual experimental data.
A sample structure of the proposed artificial neural network model (five neurons in the hidden layer).
Results
Mean Absolute Error (MAE), Mean Absolute Percentage Error (MAPE) and Mean Square Error (MSE) values of the two developed artificial neural network models
Figures 7 and 8 show comparisons between experimental and predicted values of the output variables. Correlation coefficient values (R2) and regression equations of the two proposed ANN models are given in the related figure.
Correlation between experimental and predicted values for the tested surface temperature. Correlation between experimental and predicted values for electric power dissipated.

The plot in Figure 7 has correlation coefficients of 0.7399 and 0.8423 for five and 10 neurons, respectively, for prediction of the surface temperature. Moreover, the MSE values were found to be 0.009435 and 0.005692 for five and 10 neurons, respectively. On the other hand, correlation coefficients for prediction of electric power dissipated are about 0.996 for both five and 10 neurons, presenting an almost perfect fit with MSE values of lower than 0.001 (Figure 8). These results confirmed that the neural network model reproduces electric power dissipated values for this system within the experimental ranges adopted in the fitting model.
Conclusions
The potential surface temperature distribution on powered e-textile structures for electric resistance heating was investigated in this study. An ANN model is constructed to derive the surface temperature of e-textile structures. E-textile structures were created using different conductive yarns via welding technology. The measurements were conducted with a set up including a power supply and a thermal camera under different voltage values. Experimental results show that as the linear resistance increases, the current passing through conductive yarns decreases; thus, the resulting heat dissipation and surface temperature over the e-textile structure mainly depends on the resistance, current and applied voltage values. The real test results are used for modeling surface temperature distributions as well as electric power dissipated on powered e-textile structures using the ANN. The straight line obtained for the prediction of electric power dissipated model fits well with the experimental equilibrium data. The correlation coefficient values showed that the ANN model successfully predicted dissipated electric power and surface temperature on e-textile structures by applying a three-layered neural network architecture with 10 neurons in the hidden layer and using a feed forward back propagation algorithm. As a result, it can be concluded that since the values of the determination coefficient and the MSE were found to be 0.996 and less than 0.001, respectively, for both five and 10 neurons in the hidden layer, the ANN model developed for prediction of electric power dissipated was very successful and can be useful for e-textile product designers as well as textile manufacturers, particularly for cold weather protection products, such as jackets, gloves and outdoor sleeping mats. Depending on the end use of the e-textile, careful selection of conductive yarn considering its linear resistance value is crucial. With the ANN model developed, depending on the protection level against cold weather, suitable conductive yarn type and the required voltage can be identified and, thus, the heat dissipation on the textile surface can be predicted as part of the pre-design work.
Footnotes
Declaration of conflicting interests
The authors declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.
Funding
The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the Ministry of Science, Industry and Technology, Republic of Turkey (Grant Agreement No. 0034.TGSD.2015-2) “Design of E-textile Based Thermal Heating Panels via Welding Technology”.
