Patent ID: 8640637

Claim:
A sewing-machine bobbin thread tension controller, comprising: an outer shuttle that has a circular-arc inner peripheral surface and includes a guide groove formed on a front side which is one side of the inner peripheral surface in an axial direction; a middle shuttle that rotates along the guide groove of the outer shuttle, to thus hook a needle thread, and that includes a race formed into a circular arc along a circumferential edge of the middle shuttle and slidably supported by the guide groove, a rear portion continually extending from a rear-side edge of an inner circumferential edge of the race, and a shaft formed on a front surface of the rear portion and along a center of rotation of the rear portion, wherein at least the rear portion and the shaft are made of a non-magnetic substance; a middle shuttle presser that is provided on a front side of the outer shuttle in order to prevent the middle shuttle accommodated in the outer shuttle from falling from the outer shuttle; a bobbin that has a hole through which the shaft of the middle shuttle passes, that is axially supported in the middle shuttle as a result of the shaft being inserted into the hole, and that has a first magnet provided on a rear surface which is a surface opposing a rear portion of the middle shuttle when the bobbin is axially supported by the shaft; and a bobbin thread tension control mechanism that includes a bobbin thread tension control motor which is provided at a rear of the middle shuttle, which has a rotary shaft concentric to the center of rotation of the middle shuttle, and which rotates the rotary shaft in a direction opposite to a rotating direction of the bobbin achieved when a bobbin thread wound around the bobbin is withdrawn and a second magnet which is rotated by the bobbin thread tension control motor, which is disposed in close proximity to the rear portion of the middle shuttle, and which rotates the first magnet.