Thread feeding device of a sewing machine

Abstract

A thread feeding device of a sewing machine includes a needle bar movable vertically to pull an upper thread through a fabric, and movable between left and right terminal positions. An imaginary plane to which the needle bar is normal is defined, and includes left and right boundary lines which pass through the left and right terminal positions. An inner rotary hook includes a thread tensing unit disposed on a hook surrounding wall. A lower thread passes through and abuts against the thread tensing unit to define at least one thread abutting point. A final abutting point where the lower thread passes through the thread tensing unit immediately before reaching the fabric is defined, and is projected on the imaginary plane at a point that is interposed between the boundary lines.

What is claimed is: 
     
         1 . A thread feeding device of a sewing machine for feeding upper and lower threads to a fabric, the lower thread being supplied from a lower thread bobbin, said thread feeding device comprising:
 a needle bar driven to move in an up-and-down direction between an upper position and a lower position to pull the upper thread through the fabric, said needle bar being movable in a left-and-right direction which is perpendicular to the up-and-down direction between a left terminal position and a right terminal position, said needle bar defining an imaginary plane to which said needle bar is normal and which extends in a front-and-rear direction that is perpendicular to both the up-and-down direction and the left-and-right direction, the imaginary plane including a left boundary line which extends in the front-and-rear direction and passes through the left terminal position, and a right boundary line which extends in the front-and-rear direction and passes through the right terminal position; and   an inner rotary hook disposed below the fabric, said inner rotary hook including a hook base wall, a hook surrounding wall which surrounds said hook base wall to cooperatively define an accommodation chamber with an upwardly facing opening, and a thread tensing unit which is disposed on said hook surrounding wall;   the lower thread bobbin being disposed in said accommodation chamber to supply the lower thread such that the lower thread is pulled out from the lower thread bobbin and passes through said thread tensing unit to reach the fabric, said thread tensing unit being provided with at least one thread abutting point where the lower thread abuts against and is tensed, said at least one thread abutting point including a final abutting point where the lower thread passes through said thread tensing unit immediately before the lower thread reaches the fabric, said final abutting point being projected on the imaginary plane in the up-and-down direction at a projected point, the projected point being interposed between the left boundary line and the right boundary line.   
     
     
         2 . The thread feeding device as claimed in  claim 1 , wherein a distance from the projected point of said final abutting point to the left boundary line is substantially the same as a distance from the projected point of said final abutting point to the right boundary line. 
     
     
         3 . The thread feeding device as claimed in  claim 1 , wherein said thread tensing unit includes a thread tensing plate which is disposed on an inner circumferential surface of said hook surrounding wall, said thread tensing plate including a fixed portion which is fixed on said hook surrounding wall, a thread pull-out portion which extends from said fixed portion and which is spaced apart from said inner circumferential surface of said hook surrounding wall, a thread hole which is formed in and penetrates said thread pull-out portion, and a thread cutout which is formed in an upper edge of said thread pull-out portion and which is not in communication with said thread hole for the lower thread that is pulled out of the lower thread bobbin to pass through said thread hole and abut against said thread pull-out portion in said thread cutout. 
     
     
         4 . The thread feeding device as claimed in  claim 3 , wherein said thread tensing unit further includes a thread tensing spring which is interposed between said inner circumferential surface of said hook surrounding wall and said thread tensing plate, said thread tensing spring having a fixed end which is fixed on said fixed portion of said thread tensing plate, and a suspending end which is spaced apart from both said inner circumferential surface of said hook surrounding wall and said thread pull-out portion such that a segment of the lower thread that extends from said thread hole to said thread cutout is gripped by said suspending end and said thread pull-out portion so as to impart a tension to the lower thread. 
     
     
         5 . The thread feeding device as claimed in  claim 3 , wherein said thread tensing plate further includes a guiding slit which is a cutout from an upper edge of said fixed portion and extends downwardly and to said thread pull-out portion to communicate with said thread hole. 
     
     
         6 . The thread feeding device as claimed in  claim 3 , wherein said thread tensing plate is arc in shape and extends along said inner circumferential surface of said hook surrounding wall to have said fixed portion and said thread pull-out portion, said thread tensing plate being mounted such that said thread pull-out portion is a leading side of said fixed portion in a counterclockwise direction in a view from a top of said inner rotary hook. 
     
     
         7 . The thread feeding device as claimed in  claim 3 , wherein said thread tensing plate is arc in shape and extends along said inner circumferential surface of said hook surrounding wall to have said fixed portion and said thread pull-out portion, said thread tensing plate being mounted such that said thread pull-out portion is a leading side of said fixed portion in a clockwise direction in a view from a top of said inner rotary hook. 
     
     
         8 . The thread feeding device as claimed in  claim 3 , wherein said thread tensing unit further includes an abutting member which is disposed on said hook surrounding wall, said abutting member having a thread abutting portion which is located at a route of the lower thread and interposed between said thread tensing plate and the fabric such that a segment of the lower thread that passes through said thread cutout abuts against said thread abutting portion to define said final abutting point at said thread abutting portion.