A sensing system for detecting motion of a bobbin used in a chain stitch type sewing machine using a needle on one side of a textile workpiece and a rotary bobbin positioned on an opposing side of the textile workpiece includes the bobbin being held in a bobbin case having a side panel forming an aperture. The rotary bobbin has a side surface with arcuate regions around a perimeter of the side surface. In addition, the sensing system includes the first and second optical sensors aligned to detect the presence of the first or second bobbin surface. The sensing system further includes a controller adapted to receive signals from the first and second optical sensors related to the presence of the first or second bobbin surface in the first or second regions and interpret the signals to provide the detecting motion of the bobbin.