System and method for controlling bobbin rotation in a sewing machine

A method of validating the integrity of a sewing process by detecting motion of bobbin used in a chain stitch type sewing machine apparatus of a type using a needle on one side of a textile workpiece and a rotary bobbin positioned on an opposing side of the textile workpiece, and having a bobbin case for enclosing the bobbin having a side panel forming an aperture, the method comprising the steps of:

• providing the bobbin having a side surface with arcuate regions around a perimeter of the side surface, the side surface forming a plurality of first surfaces having a first color or reflectivity and a plurality of second surfaces having a second color or reflectivity;
• providing the first and second surfaces interleaved along arcuate radial regions with respect to an axis of rotation of the bobbin such that upon rotational movement of the bobbin, the first and second surfaces are alternatively exposed through the aperture;
• providing a first optical sensor and aligning the first optical sensor to detect the presence of the first or second surface at a first region of the aperture;
• providing a second optical sensor and aligning the second optical sensor to detect the presence of the first or second surface at a second region of the aperture, the first and second regions separated at differing radial positions with respect to the axis of rotation;
• receiving signals from the first and second optical sensors related to the presence of the first or the second surface in the first or the second regions;
• and
• processing and interpreting the signals to provide the detecting motion of the bobbin.