| 摘要 |
A mechanism for coupling and uncoupling a driven rotatable drive wheel from a rotatable shaft, particularly, the arm shaft of a sewing machine from its associated drive wheel in order to spool up the lower thread, comprises a rotatable shaft which has an annular collar portion which is frictionally engageable by a drive wheel which is freely rotatable on the shaft. The drive wheel is continuously driven from a drive, such as a belt, and it may be urged into engagement with the collar by means of a nut which is threaded onto the end of the shaft. The arrangement includes a stop disc which has a cam surface which is engageable with a stop defined on the nut end face in a recess thereof. The cam surface and the stop define a cam structure which permits rotation of the nut so as to permit frictional engagement of the drive wheel with the shaft collar for driving the shaft and the disengagement thereof by rotation of the nut in a reverse direction. The amount of movement permitted to the nut is such to permit easy engagement or disengagement of the drive shaft without moving the nut to such a degree that, for example, it may cause the drive wheel to disengage from the frictional drive with another rotatable mechanism, such as a spooling device. |
