| 摘要 |
PROBLEM TO BE SOLVED: To control a thread tension to be at a desired value in a thread tension regulating device for a sewing machine, stabilize the sewing quality, and improve the reproducing property. SOLUTION: This thread tension regulating device 20 is equipped with a tension regulating tray 22 which imparts a tension to a thread, and a solenoid 30 which changes the thread tension. When the stroke of a plunger 31 is taken as S, the thrust is taken as F, the quantity of electricity to be applied is taken as C, infinitesimal amounts for the stroke and the thrust are respectively taken asΔS andΔF, the solenoid 30 has a specified stroke zone, which satisfiesΔF/ΔS≈0 when C is uniform. Thus, a tension which is imparted to a thread can be changed by controlling the quantity of electricity which is applied to the solenoid 30 by the bobbin thread tension- regulating device 20 of a sewing machine 1. Such a bobbin thread tension-regulating device 20 is equipped with a control device 50. In this case, the control device 50 controls in such a manner that when the thread tension is lowered to a specified target value in the specified stroke zone, a current value corresponding with a thread tension, which is lower than the specified target value, is applied to the solenoid, and then, a current value corresponding with the specified target value is applied.
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