Cycle sewing machines

The fundamental principle behind a computerised sewing machine is the synchroniser, a device that monitors and counts the rotation of a hand wheel. While the synchroniser acts as the logic provider to the electronic circuit, the solenoids or pneumatic cylinders move the machine parts. With one complete rotation of the hand wheel, the needle bar completes one cycle of needle up/down movement. For example, when the needle is at topmost position, and the electronic marker is set at 90° position on the hand wheel, every time the electronic marker come to 90° position on the hand wheel the needle will be at topmost position. Using this logic, the synchroniser can... 

Figure 12.10 Needle thread-force waveforms on an industrial over-edge sewing machine over five stitch cycles, with occurrence of a skipped stitch in the fourth cycle. 

As the synchroniser can monitor the rotation of the hand wheel, it can also count the number of rotations of the hand wheel. One complete rotation of the hand wheel equates to one stitch formation. To ensure that thread is not slipped out of the needle hole while starting the next sewing cycle, all generations of computerised machines have one thread catcher and thread wiper fitted near the needle point. While the thread wiper swipes away the thread tail towards the right side of the stitch line, the thread catcher holds the thread end by suction or pinch force to ensure that the thread is not shpped out of the needle hole while starting the next sewing cycle. 

Figure 12.11 shows presser-foot vertical displacement during two stitch cycles on the same machine at two different sewing speeds, measured with an linear variable differential transformer (LVDT) attached to the machine. 

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