Microprocessor-based elastic feed systems for sewing applications

The manufacture of certain garments, such as underwear and T-shirts, requires the attachment of tensioned elastics and tapes to workpieces which make up the garment. If the tape is incorrectly tensioned, when it returns to its original length after attachment to the workpiece the final garment will be too tight or too loose, and a sub-standard garment is produced. This thesis describes the design and development of two microprcessor-based systems which control the feed of elastic tape to sewing machines for such operations. The first uses an open-loop control approach, and can maintain tension to within 2% of that required for correct workpiece sizing during normal operation. However, any loss of tension due to outside factors, such as slippage of the elastic through the feed mechanism, cannot be recovered sufficiently quickly to prevent incorrect sizing of one or more workpieces. To overcome this problem, a second system was developed which employs closed-loop control to maintain the correct tension. A transducer senses the tension in the elastic, and provides feedback which allows the control algorithm to compensate rapidly for changes in tension. An adaptive control loop is also employed to compensate for practical problems encountered such as operator workpiece feed rate, elastic feed path friction, and variations in the physical characteristics of the elastic tape itself. Workpiece sizing can be maintained to within a pre-defined tolerance, usually ± 10mm.Test data from laboratory and factory tests is included, and the performance of the two systems is compared.