Patent ID: 8302547
Filing Date: 2012-11-06
Classification: D05B

Abstract:
1. A thread cutting device for a sewing machine which includes a table fitted with a needle plate, and a hook assembly spaced apart from the needle plate in an upright direction to define a thread fetching zone, comprising: a mount adapted to be mounted under the table of the sewing machine, and having a marginal region which extends in a direction transverse to the upright direction, and which is disposed to confront the thread fetching zone, said mount having a lower major surface and an upper major surface which defines a stroke path that extends toward said marginal region in a longitudinal direction transverse to the upright and transverse directions, said upper major surface having a guide slot which extends through said lower major surface, and which extends parallel to said stroke path; a fixed knife disposed on said marginal region and including a blade which is oriented in alignment with said stroke path; a movable knife including a shank body which extends in the longitudinal direction to terminate at an actuated end and a hook end that has a hook cavity, and which is disposed to be movable along said stroke path between a fetching position, where said hook end takes up a thread tensed in the thread fetching zone by engaging the thread in said hook cavity, and a thread cutting position, where the cavity-engaging thread is cut by virtue of sweeping movement of said hook end relative to said blade; a drive unit with an output shaft disposed under said lower major surface of said mount to deliver a rotational force; and a rotation/translation conversion mechanism which is disposed to convert the rotational force into a translational force, and which is configured to transmit the translation force through said guide slot so as to actuate a translation of said actuated end of said movable knife to thereby move said shank body between the fetching and thread cutting positions, wherein said rotation/translation conversion mechanism includes: a pivot axle mounted on said mount and extending downwardly from said lower major surface, a rotary unit rotatably mounted on said pivot axle and having driving and driven regions angularly spaced apart from each other about said pivot axle, said driven region being coupled with said output shaft to receive the rotational force to turn said driving region about said pivot axle, and a key coupled to said actuated end and extending through said guide slot to be engaged with said driving region of said rotary unit such that turning of said driving region brings said key to guidingly move along said guide slot so as to move said shank body between the fetching and thread cutting positions.