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(11) | EP 0 265 267 A3 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Automatic needle thread supply control system |
| (57) An automatic needle thread supply control system having a pair of clamping members
(152A) disposed between the needle thread supply source and the needle thread take-up
member (138), for clamping and releasing the needle thread (114). The moment when
the clamping members start moving apart from each other and the period in which the
clamping members are held apart from each other are controlled by control means according
to the thickness of the work fabric or the thickness of the needle thread. While the
clamping members are separated from each other, the needle thread is supplied from
the needle thread supply source without restraint as the work fabric is fed. The needle
thread is thus supplied under a tension conforming to the type of the work fabric
in tightening the needle thread. During the free supply of the needle thread, the
thread take-up member is held at the uppermost position, and hence the needle thread
of an amount corresponding to the needle thread demand of the shuttle is supplied
properly. After the supply of the needle thread has been accomplished, the clamping
members are engaged to clamp the needle thread to prevent the excessive supply of
the needle thread, while the thread take-up member starts its motion in phase with
the vertical reciprocatory motion of the needle. To control the motion of the clamping
members according to the thickness of the needle thread instead of the thickness
of the work fabric, the control means is provided with proportional control means
for engaging and for disengaging the clamping members at a speed proportional to the
rotating speed of the arm shaft (128) of the sewing machine, |