| 摘要 |
Monitoring of the rotation speed and stationary state of the lower thread bobbin in a sewing machine is performed using a light emitter and two reflected light receivers. The light rays reflected at the surface of the front flange of the bobbin are incident in a sequence which differs in time on the reflected light receivers. These data are evaluated by a computer, which can be the computer of the sewing machine, and are used to stop the machine or the sewing process before the thread end leaves the stitch plate of the sewing machine. It can also be determined from the observed direction of rotation of the bobbin whether the bobbin is correctly placed in the bobbin housing. From the relationship of kind of stitch, stitch speed, and bobbin rotation speed, the bobbin thread supply can also be calculated.
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