Patent ID: 6378448
Filing Date: 2002-04-30
Classification: D05B

Abstract:
A thread cutting device for a sewing machine, the sewing machine including a horizontal thread-engaging needle, which is in front of said thread cutting device, said thread cutting device being adapted to cut a row of threads, which are located on one side of the needle, and comprising:a horizontal base plate; an elongated horizontal swing plate disposed on and above said base plate and having a pivot hole formed through a rear end portion thereof, and an inclined slide slot which is formed through said swing plate and in front of said pivot hole and which extends in a direction that is inclined with respect to longitudinal and transverse directions of said swing plate; an elongated horizontal cutting plate disposed slidably on and above said swing plate and including a cutter that is fixed to a front end thereof and that is formed with a barb-shaped blade portion, an open-ended transverse slide slot, a front slide slot that is formed through an intermediate portion of said cutting plate, and a rear slide slot that is formed through a rear end portion of said cutting plate and that extends in a longitudinal direction of said cutting plate, said front slide slot having a longitudinal rear portion that extends in the longitudinal direction of said cutting plate and an inclined front portion that extends in a direction that is inclined with respect to the longitudinal direction and a transverse direction of said cutting plate, each of said front and rear slide slots having closed front and rear ends; a front pivot member extending through said front slide slot in said cutting plate and said inclined slide slot in said swing plate and attached to said base plate; a rear pivot member extending through said rear slide slot in said cutting plate and said pivot hole in said swing plate so as to mount said cutting plate and said swing plate rotatably on said base plate, thereby permitting rotation of said cutting plate and said swing plate about said rear pivot member; a driving rod mounted pivotally on said base plate and having a rounded end, which is received slidably within said transverse slide slot in said cutting plate, said rounded end of said driving rod being rotatable about a vertical axis between a front limit position, where said blade portion of said cutter is adapted to be located in front of the needle and where said front and rear pivot members are located respectively in said rear ends of said front and rear slide slots in said cutting plate, and a rear limit position, where said front pivot member is located in said inclined front portion of said front slide slot and where said rear pivot member is located in said front end of said rear slide slot in said cutting plate; a driving unit for activating said driving rod to swing on said base plate; and means for rotating said cutting plate and said swing plate synchronously, forward swinging movement of said rounded end of said driving rod from said rear limit position resulting in movement of said front pivot member from said inclined front portion of said front slide slot in said cutting plate toward said longitudinal rear portion of said front slide slot so as to rotate said cutting plate and said swing plate about said rear pivot member in a first direction until said rounded end of said driving rod moves to a cutter-feeding position, where said front pivot member moves into a front end of said longitudinal rear portion of said front slide slot and where said cutter is located at a stand-by position so as to be adapted to be aligned with the needle, continued forward swinging movement of said rounded end of said driving rod from said cutter-feeding position to said front limit position resulting in forward movement of said cutter in such a manner that said front and rear pivot members move to said rear ends of said front and rear slide slots in said cutting plate, rearward swinging movement of said rounded end of said driving rod from said front limit position to said cutter-feeding position resulting in rearward movement of said cutter back to said stand-by position, continued rearward movement of said rounded end of said driving rod from said cutter-feeding position to said rear limit position resulting in rotation of said cutting plate and said swing plate about said rear pivot member in a second direction that is opposite to said first direction in such a manner that said front pivot member moves from said longitudinal rear portion of said front slide slot in said cutting plate back to said inclined front portion of said front slide slot.