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Measurements and feature in sewing

Measurements and feature in sewing

Software development environment For software development, National Instruments Labview graphical programming language was chosen. This environment offers not only a seamless integration of the software with the data acquisition board, but also a great variety of tools for graphical display and analysis, with many third-party add-on products which might be useful in the present context. The development of an application for instrumentation and of an adequate graphical interface turned out to be very quick and easy, especially concerning interfacing with the hardware, although also some limitations were found. Fig.1 shows the main window (panel) of the developed software, showing an acquisition of force on the needle bar. The area filled with white represents the difference between a signal acquired with and without the presence of fabric, resulting from slight sewing speed variations, but mainly from needle-fabric interaction. The next sections give a brief description of the modules developed. B. Configuration of software and hardware All information about hardware (both on the LAB-PC+ and on the external conditioner) and general software configuration is set on the configuration panel and stored into a configuration file. C.Calibration of the sensors The calibration process consists of simply applying a number of known force values to the sensor and calculating the calibration factors, being force related to a digital value by a linear relationship. This process must be independent of the gain settings, that is, the conversion of voltage readings are recalculated taking the current gain settings into account. The software comprises a calibration panel (Fig.2), by which the user can easily calibrate each sensor. Calibration factors will be stored in the configuration file, being used later to perform the conversion of digital into force values. All values obtained in the calibration process can be stored in a specific fileThe Analysis Panel The analysis panel was created to experiment different signal analysis tools which will be described in the next section. VS Enterprises

Measurements and feature in sewing

This paper will focus mainly on the analysis of the needle-bar force. Other authors have done work on the analysis of presser-foot forces and needle penetration [1][4][5] and thread tensions [2][3]. Fig.3 shows the force signal in two sewing cycles (stitches) with the machine operating with and without fabric. Clearly, the signal obtained shows the inertial forces developed on the needle bar due to its typical movement. Some of the discontinuities result from mechanical imperfections in the movement. The effect of the fabric on the needle can be observed in Fig.3 at points 1 to 4 marked in the graph corresponding to operation with fabric. Points land 3 represent the force peak on the needle bar when first contact of the needle tip with the fabric occurs. Points 2 and 4 show the force necessary to achieve full penetration – the needle shaft is making its way through the yarns. Fig.4 shows the result of an average of force calculatedover 14 stitches (one acquisition, in this case). The first effect is important to determine penetration force at first contact. Too high penetration force can lead to yam breakage in the fabric. Penetration forces can have a very great variance, depending on the textile structure under analysis. It is important not only to determine mean values of these forces, but also to know its variance. This is of utmost importance, as textiles have irregular structures and textures, in which there might be a majority of penetrations without any kind of problem, but a few with very high values resulting in yam breakage. The second effect allows conclusions about the interaction of the needle with the fabrics structure. The use of needles that are too thick can lead to structural jamming (distortion of the textile structure), resulting in seam pucker (low-quality seam). Irregularity of these effects can be observed in fig.3: The second penetration of the needle is done with a higher force at first contact, but with lower friction of the shaft, This variation increases in knitted structures and it is very important to describe it. Several possibilities arise to measure the effects described above. A. Manual measurement of needle tip penetration and automatic peak detection The first approach to the measurement of the first effect is to analyse each of the waveforms manually, measuring the peaks introduced during penetration of the needle. This has been done in earlier works [ 11, using a standard spreadsheet program, and revealed itself to be a very difficult and time-consuming task. Nevertheless, this was very important to establish a relationship between this disturbance and the textile materials’ characterisation. In the new environment, this work is eased with Labview’s graphical display tools through use of cursors and the multiple zooming capabilities offered by it. The next step is to automate the detection and measurement of this disturbance using a strategy based on the following : Sewing speed is measured during an acquisition and is sufficiently stable; The peaks occur at well defined points of the sewingcycle; 0 If there is a peak, there is also an inversion of the derivative of the signal at that point. This derivative is greater than the derivative of the base signal, which is basically a sinusoid. The software would define a region where the peak is expected to occur, find its exact starting point by the inversion of the derivative, and its maximum by the next inversion point of the derivative. This strategy has been implemented in the saftware. Several problems arose at the course of its implementation. One of these problems is signal noise, which produces a rather noisy derivative, where zero cross-overs do not necessarily indicate the beginning or end of the peak. To solve this problem, the derivative is smoothed by calculating it as a mean value of several derivatives in its neighbourhood. Two parameters are used to control the calculation of the derivative: https://www.vssewingmachine.in/

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