| 摘要 |
An improved thread control mechanism for sewing machines adapted to minimize breakage and entanglement of the needle thread in a two-thread sewing machine, and which insures the formation of a uniform and desirable line of stitching at high speeds of operation. It is particularly advantageous in connection with a lockstitch sewing machine, which at one stage in a cycle of operation of the machine must subject said thread to a quick take-up action when a loop of the thread has been passed around half of the circumference of a bobbin case. The improved mechanism eliminates the need for a coiled check spring which heretofore has been provided to present an arm in the path of movement of the thread after it leaves a thread tensioning device. By eliminating the need for the check spring, the extent of movement of a thread eyelet at the outer end of a take-up lever is reduced, from the extent that was required in prior constructions involving a check spring. A plurality of cams are provided on a shaft which is rotated at the same speed as the main drive shaft of the sewing machine. These cams act upon different portions of the needle thread as the latter passes through a succession of eyelets provided on certain prongs of rockable members. Normally these members are retained in an active position, but they are shifted to an inactive position upon the lifting of the pressure foot. The thread control means of the present invention exercises the desired control over the needle thread when the machine is used on a variety of types of work which have normally, heretofore, required special adjustments and even changes in the mechanism when variations in the thickness and the nature of the work pieces being dealt with are involved.
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