Gas carrying threading device of sewing machine

A gas carrying threading device of sewing machine comprising:

• at least one looper having a hollow structure from a looper thread inlet to a looper loop-taker point thread outlet,
• a looper thread introduction mechanism inserting a looper thread which is led to said looper,
• a hollow looper thread guide extending from said looper thread introduction mechanism to said looper thread inlet and having a looper thread guide outlet,
• a gas supply pump that a looper threading of said looper thread is performed from said looper thread introduction mechanism to said looper thread guide outlet through said hollow looper thread guide by the gas carrying,
• a clutch for respectively transmitting power from the sewing machine motor to a drive shaft driving a stitch forming device including said looper at the time of the stitch formation or to said gas supply pump at the time of the looper threading,
• a looper threading/stitch forming changeover mechanism for changing over said clutch so that the transmission of the power to said stitch forming device is interrupted and the power is transmitted to said gas supply pump at the time of the looper threading and so that the power is transmitted to said stitch forming device and the transmission of the power to said gas supply pump is interrupted at the time of the stitch formation,
• a changeover prohibition mechanism for prohibiting an abnormal changeover to a stitch forming state of said looper threading/stitch forming changeover mechanism during a gas supply operation of said gas supply pump;
• and
• wherein:
• said changeover prohibition mechanism comprises a front cover opening and closing detection piece which is attached pivotally at a sub-frame, detects the opening and closing of the front cover and is attached pivotally at an axis which is formed at a front face cover,
• a prohibition active arm which is attached pivotally at a prohibition active arm attaching pedestal which is fixed at said sub-frame by resisting elastic repulsion of a spring and is pivoted depending on a pivot of said front cover opening and closing detection piece, and
• a prohibition driven arm which is fixed at said looper threading/stitch forming changeover mechanism and prohibits an abnormal changeover to a stitch forming state of said looper threading/stitch forming changeover mechanism depending on a pivot of said prohibition active arm during the opening of said front cover,
• at the time of said looper threading, said front cover is opened, said front cover opening and closing detection piece releases a press of said prohibition active arm by a release of the press of a pressing end which is formed in an inner surface of said front cover, said prohibition active arm is pivoted by the spring, a tongue piece of said prohibition driven arm is latched together at a tip plane portion of said prohibition active arm, the looper threading/stitch forming changeover manual operating portion is changed over to the looper threading state, said stitch forming device is locked by rotating a pulley manually, simultaneously, a threading connecting device is operated, said prohibition driven arm is latched together at a side surface portion from the tip plane portion of said prohibition active arm, and the abnormal changeover to the stitch forming state of said looper threading/stitch forming changeover mechanism is prohibited,
• at the time of said stitch formation, after said looper threading/stitch forming changeover manual operating portion is changed over to the stitch forming state, said front cover is closed and said front cover opening and closing detection piece which is pivoted by the press of said pressing end which is formed at an inner surface of said front cover is pivoted, said prohibition active arm is pivoted, said prohibition driven arm is released from said side surface portion of said prohibition active arm onto said tip plane portion, the changeover to the stitch forming state of said looper threading/stitch forming changeover mechanism is activated, and said stitch forming device is operated.