Two-needle sewing machine and two-needle sewing machine stitch forming method

A method for forming a stitch of a two-needle sewing machine including:

• a bed part on which a material to be sewn is placed;
• a column part erected upward from one side of the bed part;
• an arm part provided substantially parallel to the bed part at an upper portion of the column part;
• a needle shaft provided at a leading part of the arm part to reciprocate vertically by a driving motor;
• two sewing needles mounted on the needle shaft;
• two horizontal hooks provided in the bed part and catch respective loops of needle threads of the two sewing needles;
• and
• a conveyor member that conveys the material to be sewn in a direction approximately orthogonal to the bed part, the sewing needles are arranged at both sides of a direction approximately orthogonal to a conveyance direction of the material to be sewn and a first sewing needle of the sewing needles arranged at a position distant from the column part is provided at a conveyance side of the material to be sewn rather than a second sewing needle of the sewing needles arranged at a position closer to the column part, the method comprising:
• forming a pair of stitches having a common stitch width by the sewing needles by conveying the material to be sewn in a conveyance direction of the conveyor member;
• and
• forming a pair of stitches having a stitch width smaller than the common stitch width by the sewing needles by conveying the material to be sewn in a direction distant from the column part with respect to the conveyance direction of the conveyor member.

A method for forming a stitch on the periphery of a material to be sewn having a convex part by a two-needle sewing machine including:

• a bed part on which a material to be sewn is placed;
• a column part erected upward from one side of the bed part;
• an arm part provided substantially parallel to the bed part at an upper portion of the column part;
• a needle shaft provided at a leading part of the arm part to reciprocate vertically by a driving motor;
• two sewing needles mounted on the needle shaft;
• two horizontal hooks that are provided in the bed part and catch respective loops of needle threads of two sewing needles;
• and
• a conveyor member that conveys the material to be sewn in a direction approximately orthogonal to the bed part,
• wherein the sewing needles are arranged at both sides of a direction approximately orthogonal to a conveyance direction of the material to be sewn and a first sewing needle of the sewing needles arranged at a position distant from the column part is provided at a conveyance side of the material to be sewn rather than a second sewing needle of the sewing needles arranged at a position closer to the column part, the method comprising:
• forming a pair of stitches having a common stitch width by the sewing needles by conveying the material to be sewn in a conveyance direction of the conveyor member;
• and
• forming a pair of stitches having a stitch width smaller than the common stitch width on the periphery of a convex portion by the sewing needles by conveying the material to be sewn in a direction distant from the column part with respect to the conveyance direction of the conveyor member.