Patent ID: 8245656

Claim:
A sewing machine, comprising: a feed mechanism that is configured to transfer a workpiece cloth; a stitch forming mechanism that is configured to form stitches on the workpiece cloth being transferred by the feed mechanism by interlacing a needle thread and a bobbin thread; a thread tension adjustment mechanism that is configured to adjust at least either a needle thread tension applied on the needle thread and a bobbin thread tension applied on the bobbin thread; an image capturing unit that is disposed at a position capable of capturing images of the stitches formed on the workpiece cloth and that is configured to capture images of the stitches at least either upper and undersides of the workpiece cloth; an extracting section that is configured to extract, from the image data of the stitches captured by the image capturing unit, a region of the image data, which corresponds to a portion that is occupied by an opposite side thread appearing at an interlace of the needle thread and the bobbin thread; a calculating section that is configured to calculate an area of the region of the image data extracted by the extracting section; an evaluating section that is configured to evaluate a tension balance between the needle thread and the bobbin thread based on the area calculated by the calculating section; and a controller that is configured to control the thread tension adjustment mechanism to modify the tension balance of the stitches formed by the stitch forming mechanism based on a result of evaluation by the evaluating section.