A cutting device for a sewing machine includes an upper-blade positioning device and a lower-blade positioning device. The upper-blade positioning device includes an upper blade upper blade fixed at a head portion of the upper-blade holder, and a spring and a restricting member sleeved on a body portion of the upper-blade holder. A restricting pin is engaged between an upper-blade drive member and the restricting member. A guide member includes a guide hole for insertion of a rod portion of the upper-blade drive member and is fixed to the base. The upper-blade drive member is inserted through a guide member of the base and moved by a connecting rod. The lower-blade positioning device includes a lower-blade holder, an adjustment member. A lower-blade shaft has one end fixed to the base and another end extended out of the base, rotating the adjustment member can adjust the position of the lower-blade holder.

A cutting device for a sewing machine includes an upper-blade positioning device and a lower-blade positioning device. The upper-blade positioning device includes an upper blade upper blade fixed at a head portion of the upper-blade holder, and a spring and a restricting member sleeved on a body portion of the upper-blade holder. A restricting pin is engaged between an upper-blade drive member and the restricting member. A guide member includes a guide hole for insertion of a rod portion of the upper-blade drive member and is fixed to the base. The upper-blade drive member is inserted through a guide member of the base and moved by a connecting rod. The lower-blade positioning device includes a lower-blade holder, an adjustment member. A lower-blade shaft has one end fixed to the base and another end extended out of the base, rotating the adjustment member can adjust the position of the lower-blade holder.

A sewing machine including a detection portion that detects a movement amount of a workpiece, a sewing machine motor that serves as a driving source for vertical movement of a needle bar, and a control device that controls the sewing machine motor based on the detection result by the detection portion and performs control to maintain a constant stitch pitch. The control device lengthens a period for obtaining an output of the detection portion when the movement amount of the workpiece per unit time based on the detection result by the detection portion is decreased, and shortens the period for obtaining the output of the detection portion when the movement amount of the workpiece per unit time based on the detection result by the detection portion is increased.

A sewing machine including a detection portion that detects a movement amount of a workpiece, a sewing machine motor that serves as a driving source for vertical movement of a needle bar, and a control device that controls the sewing machine motor based on the detection result by the detection portion and performs control to maintain a constant stitch pitch. The control device lengthens a period for obtaining an output of the detection portion when the movement amount of the workpiece per unit time based on the detection result by the detection portion is decreased, and shortens the period for obtaining the output of the detection portion when the movement amount of the workpiece per unit time based on the detection result by the detection portion is increased.

An overlock sewing machine includes a first switching part for switching an interlocked state where an upper knife drive part and an upper knife are interlocked and a released state where the upper knife drive part and the upper knife are not interlocked; a second switching part for switching the upper knife between a projection position and a retreat position; and an operation part for switching the first switching part and the second switching part between a first mode, a second mode, and a third mode.

An overlock sewing machine includes a first switching part for switching an interlocked state where an upper knife drive part and an upper knife are interlocked and a released state where the upper knife drive part and the upper knife are not interlocked; a second switching part for switching the upper knife between a projection position and a retreat position; and an operation part for switching the first switching part and the second switching part between a first mode, a second mode, and a third mode.