Patent ID: 7490567

Claim:
A seam puckering preventing shuttle device of a sewing machine, which uses an upper thread inserted into a needle moving upward and downward while drawing a trace vertically of a throat plate, and a lower thread accommodated in a full rotation hook, which is disposed below the throat plate and accommodates the lower thread, and which picks up the upper thread, at the time when the upper thread inserted into the needle extending through a work placed on the throat plate and performing reciprocating movements in the vertical direction is raised from the lower dead center of the needle for each feed of the work, with a loop-taker point of the full rotation hook to interlace the upper thread and the lower thread thereby to form lock stitches in the work, wherein the full rotation hook includes: an inner hook accommodating a shuttle bobbin having the lower thread wound thereon and fixed removably, and prevented from rotating relative to the frame by an inner hook stopper; and an outer hook mounting the inner hook therein, having the loop-taker point and rotated by a rotation driving portion; wherein the inner hook is arranged to have its rotation center eccentric to the rotation center of the rotation driving portion so that an upper thread entrance and an upper thread exit are formed between the inner hook stopper and the inner hook at circumferentially different positions where clearances are formed to guide in and guide out the loop of the upper thread on the outer circumference of the inner hook after the loop of the upper thread picked up by the loop-taker point for every predetermined rotations of the outer hook rotationally driven as pulled out to the maximum by the outer circumference of the inner hook; wherein the upper thread entrance is arranged at the position where the loop of the upper thread picked up by the loop-taker point is guided in on the outer circumference of the inner hook whereas the upper thread exit is arranged at the position where the loop of the upper thread is guided out on the outer circumference of the inner hook and pulled upward of the throat plate; wherein the upper thread entrance and the upper thread exit are arranged at an angular space of 120 degrees to 160 degrees; and wherein the rotation center of the inner hook is eccentric in the direction at the angular space between the upper thread entrance and the upper thread exit with respect to the rotation center of the rotation driving portion.