Patent ID: 8069799
Filing Date: 2011-12-06
Classification: D05B

Abstract:
1. A thread cutting device used for cutting both upper and lower threads in a sewing machine, the sewing machine including a base housing which has needle-bar side and bobbin side surfaces opposite to each other in an upright direction, a needle plate which is fitted in the needle-bar side surface, and which has a needle hole, a needle which is threaded with an upper thread, and which is disposed to reciprocate through the needle hole along a piercing path to thereby bring the upper thread to upper and lower limits alternately, a hook assembly which is spaced apart from the needle plate to define a thread fetching zone, and which has a rotating hook configured to travel around a first axis in a longitudinal direction that is transverse to the upright direction so as to form a looped segment of the upper thread by hooking up the upper thread from the needle, and a bobbin which is disposed to be reelable about the first axis in the hook assembly, and which is configured to tensely deliver a lower thread into the thread fetching zone so as to enable the lower thread to be interlocked with the upper thread through tying of the looped segment while the upper and lower threads are tensed, said thread cutting device comprising: a drive motor which is a servomotor and which has an output shaft; a fixed knife adapted to be disposed proximate to the bobbin side surface, and having a working-side wall which is disposed to face away from the bobbin side surface, which extends towards the thread fetching zone, and which terminates at a first cutting edge; a mounting post which has an actuated end coupled with said drive motor so as to be moved angularly about a second axis that is parallel to the first axis, and a mount end that is opposite to said actuated end in the longitudinal direction; a movable knife including a base end connected to said mount end so as to be movable between a fetching position and a thread cutting position, a probe end opposite to said base end in a lengthwise direction, and an intermediate segment interposed between said base end and said probe end, said movable knife having a driving gear disposed to be rotated with said output shaft; a mounting shaft disposed to extend along the second axis; a driven gear including a pivoted end rotatably mounted on said mounting shaft about said second axis, a toothed segment which is opposite to said pivoted end radially, and which is meshed with said driving gear, and a web portion interposed between said pivoted end and said toothed segment; and a positioning member which is disposed to locate said actuated end of said mounting post at said web portion proximate to said toothed segment so as to angularly move said mounting post about the second axis.