Sewing – Elements – Thread sensing
Patent
1984-10-23
1987-07-21
Nerbun, Peter
Sewing
Elements
Thread sensing
112186, 112180, 112273, D05B 4500, D05B 5904
Patent
active
046810501
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a bobbin run-out detector for a lockstitch sewing machine and to an automatic bobbin changing mechanism incorporating the run-out detector.
It is known to provide lockstitch sewing machines, particularly industrial sewing machines, with a bobbin run-out detector in order to detect when the bobbin thread is substantially depleted. Upon detection of this condition, a signal may be given to the operator to stop sewing and to change the bobbin. Alternatively, the signal may be used to initiate operation of a bobbin rewinding mechanism. One previously proposed run-out detector intended for use with machines having manual bobbin change comprises a sensor in the form of a light beam which is responsive to decreasing bobbin diameter. A run-out detector of this type is disclosed for example in U.S. Pat. Nos. 4,212,257; 4,178,866; and 4,163,158. This previously proposed sensor does not have a high degree of sensitivity and cannot be used for accurately determining when the bobbin thread is at the point of depletion. The result of this is that this previously proposed sensor may trigger when there is still a substantial length of thread remaining on the bobbin.
This residual thread tends to cause difficulties during subsequent operation of the bobbin after rewinding, and therefore with manual bobbin change systems the residual thread is usually manually removed before the bobbin is rewound. Apart from the inherent wastage of thread, this leads to a reduction in efficiency. If this run-out detector were to be incorporated in a mechanism for automatically rewinding the bobbin, it would not usually be possible to remove any residual thread from the bobbin with the result that subsequent operation of the machine may be impaired.
A requirement accordingly exists for a run-out detector for accurately determining when the bobbin is empty, both for use in machines with manual bobbin change and for use in machines having provision for automatic bobbin change and/or rewinding.
There has been proposed a mechanism for rewinding the bobbin of a lockstitch sewing machine while the bobbin is in situ in the hook of the sewing machine. This means that the sewing machine cannot be operated during rewinding of the bobbin, and as mechanisms of this nature are primarily intended for use on industrial sewing machines, the benefits resulting from automatic rewinding are offset by the down-time of the machine. U.S. Pat. No. 4,216,733 describes such a mechanism.
A requirement accordingly exists for mechanism which can automatically change and rewind a bobbin without causing significant down time of the sewing machine. It is also necessary that the mechanism includes a run-out detector for accurately determining when the bobbin is empty so that the change and winding cycle is initiated only when the bobbin is empty in order to avoid difficulties arising from the presence of residual thread on the bobbin to be rewound. Finally, it is necessary that the run-out detector is such that it can operate effectively within the very confined space in the zone of the hook.
According to the invention, there is provided a run-out detector for sensing when the bobbin of a lockstitch sewing machine is empty, said detector comprising means engageable with the thread extending from the bobbin such that the thread-engaging means is responsive to bobbin thread tension and moves as a result of loss in thread tension, means for transmitting an energy beam, means for receiving an energy beam, and means responsive to the thread-engaging means and movable relative to the path of said energy beam upon movement of the thread-engaging means consequent on loss of thread tension, whereby to influence said beam, said beam receiving means being responsive to such influence of the beam to provide a signal indicative of a run-out condition.
Further according to the invention, there is provided a mechanism for automatically changing and winding the bobbin of a lockstitch sewing machine, said mechanism comprising means responsive to bobbin thre
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