| 摘要 |
A knife drive mechanism of a sewing machine includes a drive assembly 1 for converting rotary motion of a drive shaft 10 into a swing motion and an upper-knife drive assembly 2 for converting the swing motion into an up-and-down motion of an upper knife 20. The upper-knife drive assembly 2 has a clutch 3 for preventing/permitting transmission of the up-and-down motion to the knife 20. Even during stitching, engagement/disengagement of the clutch 3 can be effected, which permits the knife 20 to be connected to and disconnected from its drive assembly, thereby permitting the scissoring cutting to be started or stopped. When a surface 42 of the first swing member 4 urges a projection 52 of a second swing member 5 to cause the knife 20 to move downward at the completion of cutting, the knife 20 itself serves as a cloth-feed guide to prevent misalignment of the cloth and breakage of the sewing needle or upper and lower loopers.
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