Measurements in high-speed sewing
Several signal-processing implemented and tested algorithms, that aim to automate the detection of some characteristics, will be described. The purpose of this system, that implements some novel strategies, is to develop an add-on kit to apply to different sewing machines, but presently it has been implemented on a PC as a quality assessment system which will be used by textile technicians to build a quality database.VS Sewing Machines
The paper will present an overview of the system, which is a development of earlier hardware and software and will focus on the results concerning the measurement of the force on the needle-bar, parameter is important to investigate on needle penetration force in fabrics during sewing.
During high-speed sewing, several parameters are important for a good performance of the process. Measuring and analysing their behaviour during the sewing process can lead to a better understanding of the process, to the establishment of rules for correct setting of the machines and ultimately to a system which will be able to automatically set itself according to the different materials having the correct feedback to do so. In this work, sensors are used to measure the following parameters: IEEE Catalog Number: 97TH8280 – 961 – Thread tension on the different sewing threads: the correct balance between them, as well as the correct amount of thread tension are very important for the stitch formation; Presser-foot force variations: One of the common sewing problems encountered in high-speed sewing is the bouncing of the presser-foot due to the feeding system, causing contact loss between the material and the presser-foot, which will result in an irregular stitch; Force on the needle bar: This parameter is of utmost importance, because this signal enables the determination of the necessary force for the needle to penetrate the material. Excessive needle penetration forces cause yam breaks, which will lower the seam’s quality and also its strength. Due to the great variety of materials used presently, to the irregularity of some of their structures and difficult physical properties of some yams, it is very important for the apparel manufacturer to evaluate which needle or which limit to the sewing speed should be used. It is a task to be performed prior to the actual production
The first includes four strain gage signal conditioners. Each channel is independently gain programmable. A “base gain”, set by a potentiometer, can be further changed through software from 0 to 255/256 in steps of U256 using an MDAC. Another potentiometer is used to set the offset of the signal. It is also possible to switch a high-pass filter into the signal path to eliminate possible zero-drift if necessary (e.g. :when using cantilever beams which have slowly-varying plastic static strains). The board uses Burr-Brown INA103 integrated instrumentation amplifiers as pre- amplifiers. 0 The second one includes 2 signal conditioners for piezoelectric sensors with similar gain programming functionality. Their outputs can be acquired either directly or through a peak detector for sensor calibration (as will be seen in section 1II.C.). The control of the peak detector is performed by software. High-pass filters are available, but the piezoelectric sensor and its charge amplifier form a high-pass system itself, reacting only to variations of force. This board also includes the necessary conditioning for the synchronisation signal (conversion to TTL-levels). Both boards connect to the input connector of the LAB- PC board, building a bus based on this input. The connection of one output channel to the input channel of the LAB-PC board is not hard-wired; at the time of installation the user can decide on which input to connect a signal, so the system can be flexible, in a way that more boards can be easily installed. Although not implemented in the current software version, more LAB-PC boards can be used in one computer, making the expansion of the system easier. Gain programming, peak detectors control switching on and off of the high-pass filters is achieved communicating through the U0 ports of the board. As each board has its own private address, it is possible to add other types of data “collection” devices later (e.g. thread consumption counters or presser-foot displacement sensing). https://www.vssewingmachine.in/
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