Patent DE-10025852-A1 (DE)
Title: Opening mechanism for the bobbin housing of a double lockstitch sewing machine has a moving limit stop with controlled movement speeds between the end positions and structured limit surfaces for a quiet and low-wear operation
Inventor: PAPAJEWSKI GERD
IPC: D05B57/26
Filed: 2000-05-25
Abstract: The mechanism to open the bobbin housing (2), at a double lockstitch sewing machine, has a moving limit stop (3) which travels from one end position (4) to the other at a faster speed than in the reverse direction. The limit surface (11), at a time, moves so quickly from the housing limit surface (10) in front of the lower thread loop passage to the end position so that the mass of the bobbin housing prevents it from keeping up with the increased rotary speed of the looper body (1).  The bobbin housing opening mechanism, at a double lockstitch sewing machine, forms a gap between the limit surfaces of the limit stop and the bobbin housing at the time of the lower thread loop passage. After the thread loop passage, the limit stop returns to the first end position, so that on a high rotary speed the bobbin housing makes only a slight relative rotation and turns back through the limit surface against the direction of the looper body rotation. The forces are low on the bobbin housing in a quiet operation. The limit stop reaches the second end position when the thread loop is passed between the limit surfaces. As the limit stop is moved from the second end position to the first, the maximum acceleration forces are greater in the first section of the movement path than in the remainder of the movement. A stop unit (7) has a limit surface (9), working with a limit surface (8) at the bobbin housing. When the limit surfaces are in contact with each other, the friction drive on the bobbin housing is blocked in the direction (23) of looper rotation. All the limit surfaces are positioned in relation to each other so that, when the limit surfaces at the stop are in contact with the limit stop in the second end position, there is a gap between the limit stop and housing limit surfaces and a gap is between the stop limit surfaces when the limit stop is in the first end position. They are also located so that a lower thread loop initially passes between the stop limit surfaces and then between the limit stop and housing limit surfaces as it passes around the bobbin housing. The drive for the moving limit stop is a cam disk (16) coupled to the looper shaft, which trips a cam follower (17) at the limit stop. The limit stop has a limit surface (14) working with a limit surface (13) at the bobbin housing, which blocks housing rotation when they are together. As the thread loop is passed around the bobbin housing, it passes initially through this set of limit surfaces (13,14) before moving between the other pair of limit surfaces (10,11). The limit stop is moved by a spring (19) from the first end position to the second, and it is returned by the action of the cam on the limit stop cam follower. The cam can have three cam zones to give a rapid movement from the first end position, a slower return movement and a relatively slower movement before reaching the first end position.