Apparatus for detecting thread breakage in sewing machine

摘要

The invention relates to an apparatus for detecting thread breakage in a sewing machine. The sewing machine comprises a looper (3) reciprocating laterally across a leading end of a needle, a thread-controlling cam (11) fixed on a rotary shaft (S) interlocked with the reciprocal motion of the looper and varying in the extent of projection from the thread take-up stand (10) along with rotation of the shaft, and thread guides (12) disposed on the thread take-up stand at both sides of the thread-controlling cam. Said thread guides have thread eyelets (12a) for inserting the looper thread (6). Other thread guides having thread pass eyelets (15a) for inserting the looper thread are fixed and disposed on the looper thread route between the thread-controlling cam and the looper. A thread breakage-detecting member (13) detects presence or absence of vibration of looper thread inserted in the thread pass eyelets of other thread guides between the other thread guides. A control circuit stops the sewing machine from driving on the basis of the detection of absence of thread vibration by this thread breakage-detecting member. In this constitution, breakage of looper thread while the sewing machine is being driven is securely detected, and the sewing machine is stopped immediately when the looper thread is broken, so that lowering of the sewing operation efficiency is effectively prevented. <IMAGE>