The present invention provides a thread feeding device of a decorative stitching sewing machine. The thread feeding device feeds a needle thread, an upper looper thread, and a lower looper thread in the amounts required for sewing one stitch such that the position of a stitch looping point of the threads changes. The thread feeding device includes: a thread accumulator 500 having thread accumulating elements 13a to 13d and 14a to 14d which measure the thread accumulation amounts of predetermined lengths of the needle thread, the upper looper thread, and the lower looper thread, and thread accumulation amount control elements 15 to 18 which adjust the amounts of the threads required for sewing one stitch in an increasable and decreasable manner within the range of thread accumulation amounts of predetermined lengths at the time of fabric feeding, and which release the threads to a stitch forming device when a stitch is formed; a thread feed drive mechanism 600 which drives each of the elements; and a thread feed control unit having a program which dives the thread accumulation amount control elements for each stitch to feed the threads in an increasable and decreasable manner so as to increase or decrease the threads within the range of a total thread feeding amount that is maintained constant, including a fabric feeding amount, a fabric thickness and an overlocking width, thereby to change the position of the stitch looping point of the needle thread, the upper looper thread, and the lower looper thread, thus controlling the decorative stitching according to a stitching decoration pattern.

The present invention provides a thread feeding device of a decorative stitching sewing machine. The thread feeding device feeds a needle thread, an upper looper thread, and a lower looper thread in the amounts required for sewing one stitch such that the position of a stitch looping point of the threads changes. The thread feeding device includes: a thread accumulator 500 having thread accumulating elements 13a to 13d and 14a to 14d which measure the thread accumulation amounts of predetermined lengths of the needle thread, the upper looper thread, and the lower looper thread, and thread accumulation amount control elements 15 to 18 which adjust the amounts of the threads required for sewing one stitch in an increasable and decreasable manner within the range of thread accumulation amounts of predetermined lengths at the time of fabric feeding, and which release the threads to a stitch forming device when a stitch is formed; a thread feed drive mechanism 600 which drives each of the elements; and a thread feed control unit having a program which dives the thread accumulation amount control elements for each stitch to feed the threads in an increasable and decreasable manner so as to increase or decrease the threads within the range of a total thread feeding amount that is maintained constant, including a fabric feeding amount, a fabric thickness and an overlocking width, thereby to change the position of the stitch looping point of the needle thread, the upper looper thread, and the lower looper thread, thus controlling the decorative stitching according to a stitching decoration pattern.

With a overlock sewing machine, when a switching mechanism is switched to a threading-enabled state, and a looper cover is closed, the looper cover is slid toward one side in the hinge shaft axial direction so as to operate a detection lever. In the non-operating state, the detection lever is set to an initial position where it does not press an operation protrusion of a switch. When a side cover is closed, and the detection lever is operated, the operation lever is set to an operation-enabled position where it presses the operation protrusion. When the operation lever is operated, and the side cover is opened, the detection lever is set by passing through the operation-enabled to the operation-disabled position where it does not press the operation protrusion.

With a overlock sewing machine, when a switching mechanism is switched to a threading-enabled state, and a looper cover is closed, the looper cover is slid toward one side in the hinge shaft axial direction so as to operate a detection lever. In the non-operating state, the detection lever is set to an initial position where it does not press an operation protrusion of a switch. When a side cover is closed, and the detection lever is operated, the operation lever is set to an operation-enabled position where it presses the operation protrusion. When the operation lever is operated, and the side cover is opened, the detection lever is set by passing through the operation-enabled to the operation-disabled position where it does not press the operation protrusion.

A overlock sewing machine includes a switch limiting arm rockable integrally with a main shaft fixing operating arm and an arm including arms which are actuated by operating a threading switching knob to engage with the switch limiting arm to rock a rocking lever portion and being engageable with a slide plate to move the position of the slide plate to a sewing executable position upon operating the threading switching knob to the sewing executing position side.

A overlock sewing machine includes a switch limiting arm rockable integrally with a main shaft fixing operating arm and an arm including arms which are actuated by operating a threading switching knob to engage with the switch limiting arm to rock a rocking lever portion and being engageable with a slide plate to move the position of the slide plate to a sewing executable position upon operating the threading switching knob to the sewing executing position side.

A sewing machine includes an upper shaft rotatable so as to drive a needle bar, a lower shaft rotatable so as to drive a hook, an upper-shaft pulley attached to the upper shaft, a lower-shaft pulley attached to the lower shaft, a belt linking the upper-shaft pulley and the lower-shaft pulley, and synchronizing a rotation of the upper-shaft pulley and a rotation of the lower-shaft pulley with each other, a belt adjusting mechanism contacting the belt and changing a belt length at a tensioned side at which the belt is drawn, and a tensioner tensioning the belt in accordance with the change in the belt length of the belt at the tensioned side.

A sewing machine includes an upper shaft rotatable so as to drive a needle bar, a lower shaft rotatable so as to drive a hook, an upper-shaft pulley attached to the upper shaft, a lower-shaft pulley attached to the lower shaft, a belt linking the upper-shaft pulley and the lower-shaft pulley, and synchronizing a rotation of the upper-shaft pulley and a rotation of the lower-shaft pulley with each other, a belt adjusting mechanism contacting the belt and changing a belt length at a tensioned side at which the belt is drawn, and a tensioner tensioning the belt in accordance with the change in the belt length of the belt at the tensioned side.