Device, method and needle plate for execution of overcasting seams and seams obtained thereby

Abstract

A device ( 1 ) for execution of overcasting seams comprises two needles ( 3, 4 ) carrying respective sewing threads, two support arms ( 6, 9 ) on each of which two lower ( 7, 8 ) and upper ( 10, 11 ) loopers respectively, are mounted. The loopers of each support arm ( 6, 9 ) interact with the loopers of the other arm ( 6, 9 ) and with the needles ( 3, 4 ) to form a first and a second overcasting seam portions superposed on each other. The invention also relates to a method to be put into practice by such a device ( 1 ), a needle plate to be installed on such a device ( 1 ) and a seam consequently obtainable therewith.

What is claimed is:  
     
         1 . A device for execution of overcasting seams comprising: 
 at least one main needle ( 3 ) carrying a respective sewing thread, movable with a rectilinear reciprocating motion through a needle plate ( 5 ) along which a workpiece runs following a sewing direction (“A”)    at least one lower support arm ( 6 ) alternately oscillatable around a rotation axis (“X”) substantially parallel to the sewing direction (“A”) of said workpiece;    at least one main lower looper ( 7 ) mounted on said lower arm ( 6 ) in such a manner that said main lower looper ( 7 ) is alternately movable according to an arched trajectory in a direction transverse to the sewing direction (“A”);    at least one upper arm ( 9 ) oscillatable around an oscillation axis substantially parallel to the sewing direction (“A”) of said workpiece;    at least one main upper looper ( 10 ) mounted on said upper arm ( 9 ) in such a manner that said main upper looper ( 10 ) is alternately movable according to an arched trajectory extending astride a side edge of said workpiece in a direction transverse to the sewing direction (“A”) of the workpiece itself, said main upper looper ( 10 ) interacting with said main lower looper ( 7 ) and main needle ( 3 ) to cause formation of an overcasting seam portion on said workpiece,    characterized in that it further comprises: 
 at least one auxiliary needle ( 4 ) carrying a respective auxiliary sewing thread, movable with a rectilinear reciprocating motion through said needle plate ( 5 );  
 at least one auxiliary lower looper ( 8 ) mounted on said lower arm ( 6 ) in such a manner that said auxiliary lower looper ( 8 ) is alternately movable following an arched trajectory in a direction transverse to the sewing direction (“A”);  
 at least one auxiliary upper looper ( 11 ) mounted on said upper arm ( 9 ) in such a manner that said auxiliary upper looper ( 11 ) is movable according to an arched trajectory extending astride a side edge of said workpiece in a direction transverse to said sewing direction (“A”), said auxiliary upper looper ( 11 ) cooperating with said auxiliary lower looper ( 8 ) and said auxiliary needle ( 4 ) to give rise to formation of an auxiliary overcasting seam portion on said workpiece.  
   
     
     
         2 . The device as claimed in  claim 1 , wherein said auxiliary needle ( 4 ) and main needle ( 3 ) are engaged on one and the same needle bar ( 2 ).  
     
     
         3 . The device as claimed in  claim 1 , wherein said main needle ( 3 ) and auxiliary needle ( 4 ) lie in a plane transverse to the sewing direction (“A”).  
     
     
         4 . The device as claimed in  claim 3 , wherein the lying plane of said needles ( 3 ,  4 ) is oblique to the sewing direction (“A”).  
     
     
         5 . The device as claimed in  claim 4 , wherein the lying plane of said needles ( 3 ,  4 ) is inclined relative to the sewing direction of the workpiece, by an angle included between 1° and 70° measurable on the lying plane of the needle plate ( 5 ).  
     
     
         6 . The device as claimed in  claim 1 , wherein said needle plate ( 5 ) has: 
 a main slot ( 21 ) having an end portion ( 21   c ) arranged to be passed through by the main needle ( 3 );    an auxiliary slot ( 22 ) having an end portion ( 22   c ) arranged to be passed through by the auxiliary needle ( 4 );    at least one main tab ( 23 ) formed at the primary side ( 17 ) of said needle plate ( 5 ) and partly bounding at least one of said slots ( 21 ,  22 );    at least one auxiliary tab ( 24 ) formed along said primary side ( 17 ) of the needle plate ( 5 ) substantially in alignment with the main tab ( 23 ), said auxiliary tab ( 24 ) bounding said auxiliary slot ( 22 ) at least partly.    
     
     
         7 . The device as claimed in  claim 6 , wherein each tab ( 23 ,  24 ) has an end edge ( 23   a,    24   a ) spaced apart from the end portion ( 21   c,    22   c ) of the respective slot ( 21 ,  22 ) and facing away from said slot, the end edges ( 23   a,    24   a ) of said tabs ( 23 ,  24 ) being mutually aligned along the same direction.  
     
     
         8 . The device as claimed in  claim 7 , wherein said main slot ( 21 ) and auxiliary slot ( 22 ) are disposed in mutual side by side relationship in a direction transverse to said sewing direction (“A”).  
     
     
         9 . The device as claimed in  claim 8 , wherein the end portion ( 21   c ) of the main slot ( 21 ) is spaced apart from the end edge ( 23   a ) of said main tab ( 23 ) by a lower distance than the distance existing between the end edge ( 24   a ) of said auxiliary tab ( 24 ) and the end portion ( 22   c ) of the auxiliary slot ( 22 ).  
     
     
         10 . The device as claimed in  claim 9 , wherein the end portion ( 21   c ) of the main slot ( 21 ) is spaced apart from the end edge ( 23   a ) of said main tab ( 23 ) by a distance greater than the distance existing between the end edge ( 24   a ) of said auxiliary tab ( 24 ) and the end portion ( 22   c ) of the auxiliary slot ( 22 ).  
     
     
         11 . The device as claimed in  claim 10 , wherein the end portion ( 21   c ) of the main slot ( 21 ) is spaced apart from the end edge ( 23   a ) of said main tab ( 23 ) by the same distance as the distance existing between the end edge ( 24   a ) of said auxiliary tab ( 24 ) and the end portion ( 22   c ) of the auxiliary slot ( 22 ).  
     
     
         12 . The device as claimed in  claim 6 , wherein said slots ( 21 ,  22 ) are mutually aligned along a direction substantially parallel to said primary side ( 17 ).  
     
     
         13 . The device as claimed in  claim 7 , wherein the end edge ( 23   a,    24   a ) of each tab ( 23 ,  24 ) has at least one tail portion ( 23   b,    24   b ) oriented obliquely of said primary side ( 17 ) with an inclination converging towards the respective slot ( 21 ,  22 ), away from the end portion ( 21   c,    22   c ) of the slot itself.  
     
     
         14 . The device as claimed in  claim 6 , wherein said needle plate ( 5 ) further comprises a lead-in portion ( 25 ) interposed between said main tab ( 23 ) and said auxiliary tab ( 24 ) to convey the main seam portion moving forward along the main tab ( 23 ), towards and upon the auxiliary tab ( 24 ).  
     
     
         15 . The device as claimed in  claim 14 , wherein said lead-in portion ( 25 ) has a first end ( 25   a ) disposed below said main tab ( 23 ) and a second end ( 25   b ) opposite to the first end ( 25   a ), of one piece construction with said auxiliary tab ( 24 ).  
     
     
         16 . A method of executing overcasting seams comprising the steps of: 
 carrying out a main seam portion of a predetermined sewing pitch on a workpiece according to its sewing direction;    carrying out an auxiliary seam portion superposed on the main seam portion and of a predetermined sewing pitch, on said workpiece,    characterized in that each stitch of the main seam portion is formed simultaneously with the formation of a corresponding stitch of the auxiliary seam portion, said main seam portion being executed with the same sewing pitch as the sewing pitch of said auxiliary seam portion.    
     
     
         17 . The method as claimed in  claim 16 , wherein each stitch of said auxiliary seam portion is formed at a predetermined offsetting distance from the corresponding stitch of the main seam portion preceding it, the offsetting distance being the same for all stitches of said seam.  
     
     
         18 . The method as claimed in  claim 17 , wherein the offsetting distance between each sewing stitch of the auxiliary seam portion and the corresponding sewing stitch of the main seam portion corresponds to half the sewing pitch.  
     
     
         19 . A needle plate for execution of overcasting seams provided with: 
 a main slot ( 21 ) having an end portion ( 21   c ) arranged to be passed through by a main needle ( 3 ) carrying a respective main sewing thread to make a main seam portion on a cloth workpiece moving forward on the needle plate ( 5 ) in a sewing direction (“A”) substantially parallel to a primary side ( 17 ) of the needle plate ( 5 );    an auxiliary slot ( 22 ) having an end portion ( 22   c ) arranged to be passed through by an auxiliary needle ( 4 ) carrying a respective auxiliary sewing thread to make an auxiliary seam portion on said cloth workpiece being fed;    at least one main tab ( 23 ) formed at the primary side ( 17 ) of said needle plate ( 5 ) and partly bounding at least one of said slots ( 21 ,  22 ),    characterized in that it further has at least one auxiliary tab ( 24 ) formed along said primary side ( 17 ) of the needle plate ( 5 ) substantially in alignment with the main tab ( 23 ), said auxiliary tab ( 24 ) bounding said auxiliary slot ( 22 ) at least partly.    
     
     
         20 . The needle plate as claimed in  claim 19 , wherein each tab ( 23 ,  24 ) has an end edge ( 23   a,    24   a ) spaced apart from the end portion ( 21   c,    22   c ) of the respective slot ( 21 ,  22 ) and facing away from said slot, the end edges ( 23   a,    24   a ) of said tabs ( 23 ,  24 ) being mutually aligned along the same direction.  
     
     
         21 . The needle plate as claimed in  claim 20 , wherein said main slot ( 21 ) and auxiliary slot ( 22 ) are disposed in mutual side by side relationship in a direction transverse to said sewing direction (“A”).  
     
     
         22 . The needle plate as claimed in  claim 21 , wherein the end portion ( 21   c ) of the main slot ( 21 ) is spaced apart from the end edge ( 23   a ) of said main tab ( 23 ) by a lower distance than the distance existing between the end edge ( 24   a ) of said auxiliary tab ( 24 ) and the end portion ( 22   c ) of the auxiliary slot ( 22 ).  
     
     
         23 . The needle plate as claimed in  claim 22 , wherein the end portion ( 21   c ) of the main slot ( 21 ) is spaced apart from the end edge ( 23   a ) of said main tab ( 23 ) by a distance greater than the distance existing between the end edge ( 24   a ) of said auxiliary tab ( 24 ) and the end portion ( 22   c ) of the auxiliary slot ( 22 ).  
     
     
         24 . The needle plate as claimed in  claim 23 , wherein the end portion ( 21   c ) of the main slot ( 21 ) is spaced apart from the end edge ( 23   a ) of said main tab ( 23 ) by the same distance as the distance existing between the end edge ( 24   a ) of said auxiliary tab ( 24 ) and the end portion ( 22   c ) of the auxiliary slot ( 22 ).  
     
     
         25 . The needle plate as claimed in  claim 19 , wherein said slots ( 21 ,  22 ) are mutually aligned along a direction substantially parallel to said primary side ( 17 ).  
     
     
         26 . The needle plate as claimed in  claim 20 , wherein the end edge ( 23   a,    24   a ) of each tab ( 23 ,  24 ) has at least one tail portion ( 23   b,    24   b ) oriented obliquely of said primary side ( 17 ) with an inclination converging towards the respective slot ( 21 ,  22 ), away from the end portion ( 21   c,    22   c ) of said slot.  
     
     
         27 . The needle plate as claimed in  claim 19 , further comprising a lead-in portion ( 25 ) interposed between said main tab ( 23 ) and said auxiliary tab ( 24 ) to convey the main seam portion moving forward along the main tab ( 23 ), towards and upon the auxiliary tab ( 24 ).  
     
     
         28 . The needle plate as claimed in  claim 27 , wherein said lead-in portion ( 25 ) has a first end ( 25   a ) disposed below said main tab ( 23 ) and a second end ( 25   b ) opposite to the first end ( 25   a ), of one piece construction with said auxiliary tab ( 24 ).  
     
     
         29 . An overcasting seam comprising: 
 a main overcasting portion having a series of sewing stitches of a predetermined pitch;    an auxiliary overcasting portion superposed on said main seam and having a series of sewing stitches of a predetermined pitch,    characterized in that the pitch of the stitches of said main portion is the same as the pitch of the stitches of said auxiliary portion.    
     
     
         30 . The seam as claimed in  claim 29 , wherein each sewing stitch of said auxiliary seam portion is spaced apart from the preceding stitch of the main seam portion by a distance corresponding to half the sewing pitch.