Buttonhole sewing machine

A buttonhole sewing machine for the production of buttonholes on a workpiece (32), comprising

• a needle (12) mounted in an arm (4),
• which is reciprocatingly drivable in a Z direction for the production of stitches by means of a driving motor (6),
• which is drivable by a jogging drive (23) for the production of a zigzag seam by a motion of the needle (12) relative to the workpiece (32), and
• which is drivable to pivot about an axis by means of a pivot drive (18);
• a hook bearing (13), which is disposed in a base plate (2), and
• which is drivable by a pivot drive (18) to pivot synchronously and equiangularly relative to the needle (12) about a pivot axis (17) which extends in the Z direction;
• and
• a thread feeding mechanism (33) in the path of a needle thread (34);
• wherein the thread feeding mechanism (33) comprises a closed cam (53, 54) for guidance of the needle thread (34), which is drivable by a thread feeding drive (45) to rotate about an axis of rotation (43a), the cam (53, 54) comprising two different cam sections (53, 54) for tensioning and releasing the needle thread (34), which extend over angles at circumference a, b of 180°, and
• the cam (53, 54) performing a rotation during two stitches of the needle (12).