Sewing machine with pneumatically-operated rotary thread cutter, includes blade, shuttles and needle path in specified geometric arrangement

摘要

The center of rotation of the moving blade (9) lies on a side opposite the center of the needle path (32), relative to the center of rotation of the outer shuttle (22). When the moving blade (9) executes a complete stroke, its path passes over the inner shuttle (23). The front end of the moving blade passes through one side of an outer circumference of the inner shuttle (23), on one side of the center of the needle path (32). The geometrical path of a section of the cutting edge of the moving blade (9), passes through the center of the needle path. At least part of the moving blade is prismatic in form. This blade includes an upper thread relief section. This prevents seizure of the upper thread which is to be cut off, by the moving blade, when it is in the cutting position. Leading angles of upper and lower surfaces of the moving blade, lie in the range 25[deg] -30[deg] .