Patent ID: 6269760
Filing Date: 2001-08-07
Classification: D05B

Abstract:
In a sewing machine including a needle oscillating along a linear direction and threaded with a needle thread forming a loop, a bobbin threaded with a bobbin thread, and an oscillating hook having a hook finger engaging and moving the loop so that the loop surrounds and is pulled tight against the bobbin thread for each stitch, a drive mechanism for driving the oscillating hook, the drive mechanism including:a rotating driving wheel;a rack coupled to the driving wheel and oscillating transversely between two extreme positions in response to rotation of the driving wheel; anda pinion engaging the rack, the pinion being coupled to and driving the oscillating hook, wherein the pinion has a radius that varies over a first part of a circumference of the pinion and has an average radius over a second part of the circumference of the pinion that is larger than an average of the radius over the first part of the circumference, and the rack has a width that varies with position to accommodate the radius of the pinion that varies, whereby, in response to a constant rotation speed of the driving wheel, the hook is oscillated at a rotational velocity that varies with rotational position of the hook so that swing amplitude of the needle transverse to the linear direction may be increased.