Needle bar drive for a buttonhole sewing machine

A counter-weighted eccentric or crank is clamped to an end of the upper drive shaft. A link is pivoted between the eccentric and an end of a short leg on a V-shaped rocker. The base of the V-shaped rocker is pivoted on a fixed pin. The long arm of the V-shaped rocker is connected to a needle bar to drive the needle bar up and down. The movement of the needle bar carries a main needle and thread through a workpiece to make stitches in the cloth.

BACKGROUND OF THE INVENTION 
The present invention relates to an improved needle bar drive used to 
facilitate stitching in sewing machines to make buttonholes. Specifically, 
this invention allows the main needle, bearing the thread, to move upward 
and downward through a workpiece to create stitches. 
A strength of the present invention is the use of a rocker to transfer the 
motion of an eccentric to an upward and downward motion of the sewing 
needle. The rocker is pivoted about a stationary point and provides extra 
stability to the mechanism. The extra stability helps reduce vibrations in 
the needle bar drive mechanism and reduces vibration in the sewing machine 
in general. 
Another strength is the use of two connecting links to allow a separate 
bight motion to be applied to the needle bar assembly to create bight 
stitches. The separate bight motion swings the needle bar assembly back 
and forth to create the stitches along the sides of a buttonhole. This 
bight motion cannot interfere with the upward and downward motion of the 
main needle in creating a stitch. The double linkage allows this motion to 
be coupled into the upward and downward motion of the main needle without 
interference. 
The prior art does not demonstrate the same stability as the present needle 
bar drive mechanism. While many previous inventions allow for proper 
stitching to occur with the main needle, the greater stability and 
simplicity of coupling other motions with the main sewing motion are not 
found in these inventions. 
SUMMARY OF THE INVENTION 
An objective of the present invention is to remedy the disadvantages of the 
prior art by providing a reliable apparatus that allows users to form 
buttonholes in garments. A counter-weighted eccentric or crank is clamped 
to an end of an upper drive shaft. A link is pivoted between the eccentric 
and an end of a short leg on a V-shaped rocker. The base of the V-shaped 
rocker is pivoted on a fixed pin. The long arm of the V-shaped rocker is 
connected to a needle bar to drive the needle bar up and down. The 
movement of the needle bar carries a main needle and thread through a 
workpiece to make stitches in the cloth. 
In a preferred embodiment, a needle bar drive for a button hole sewing 
machine has a drive shaft connected with a crank having a counter-weighted 
side. A smaller side of the crank is connected to a smaller end of a crank 
link. A larger end of the crank link is connected to a crank leg of a 
V-shaped rocker. The rocker pivots on a fixed pin through a first opening 
in the base of the rocker. Another leg of the rocker is connected to a 
middle section of a needle bar that also has a needle end. A main needle, 
connected to the needle holder at the needle end, carries thread through a 
workpiece in creating stitches. 
The embodiment also has a needle bar holder which receives the needle bar 
and allows the needle bar to move upward and downward. The holder has an 
oblong end and two smaller block-like ends forking off the oblong end. The 
oblong side has a large opening passing through it. A bight shaft passes 
through and connects to the large opening to support the needle bar holder 
and to allow for bight stitches to be made. The block-like ends both have 
passages which run transverse to the large opening and lie along the same 
axis. These two passages in the block-like ends accommodate the needle bar 
and allow it to slide through the passages. 
The preferred embodiment also has a needle bar clamp that clamps onto the 
needle bar. A needle leg of the rocker is pivotally connected to a 
cylindrical section of the needle bar clamp and communicates the rocking 
of the rocker into an upward and downward motion of the needle bar. Two 
needle bar guide rails are attached to the needle bar holder at the 
block-like ends. The rails have a separation to allow a slat of the needle 
bar clamp to pass through and guide the motion of the needle bar clamp and 
needle bar. 
Additionally, a connecting link pivotally connects to the cylindrical 
section of the needle bar clamp and pivotally connects to the needle leg 
of the rocker. This additional linkage is important to allow the needle 
bar assembly to rock along with the rocking of the bight shaft. 
Also, two flanged bushings are inserted at each end of the first opening of 
the rocker to facilitate the rocking of the rocker on the fixed pin. Rings 
of ball bearings connected to clevis pins aid in creating the pivotal 
connection between the crank and the crank link and the pivotal connection 
between the crank link and the rocker. 
These and further and other objects and features of the invention are 
apparent in the disclosure, which includes the above and ongoing written 
specification, with the claims and drawings.

DETAILED DESCRIPTION OF THE DRAWINGS 
Referring to FIG. 1, a needle bar drive 1 has a drive housing 3, a bight 
shaft opening 12, and a drive shaft opening 4. A driving means in the 
drive housing turns the drive shaft 5 at a middle section 7. The drive 
shaft 5 has a crank end 9 which is connected to a crank 11 through a large 
aperture 17 in a counter-weighted side 13. A smaller side 15 of the crank 
11 has a smaller aperture 19 through which an upper clevis pin 25 passes. 
Long screws 23 pass through holes 21 to clamp the crank 11 to the drive 
end 9 of the drive shaft 5 and the upper clevis pin 25. A first large ball 
bearing ring 6 secures the drive shaft 5 in the drive shaft opening 4. A 
second large ball bearing ring 8 is connected to the crank end 9 of the 
drive shaft 5. 
The upper clevis pin 25 passes through an upper ball bearing ring 27 which 
is connected to a crank link 29 at a larger hole 35 in a first end 31. A 
lower clevis pin 41 passes though a lower ball bearing ring 39 which is 
connected to a smaller hole 37 in the second end 33. The lower clevis pin 
39 also passes through a second opening 51 in a crank leg 47 of a V-shaped 
rocker 43. The rocker 43 pivots on a fixed pin 55 which passes through one 
of a pair of bushings 57, through a first opening 53 of a base 45 of the 
rocker 43, passes through the second of the bushings 57 and into an 
opening 14 of the drive housing 3. 
A needle leg 49 of the rocker 43 has a third opening 56 which is straddled 
by forked ends 61 of a connecting link 58. A connecting link pin 67 passes 
through a second hole 63 in one of the forked ends 61, the third opening 
56 of the rocker 43, and a third hole 63 in the other forked end 61. 
A cylindrical section 85 of a needle bar clamp 82 passes through a first 
hole 65 in a rounded end 59 of a connecting link 58. A needle bar 79 is 
clamped in a block section of the needle bar clamp 82 through a center 
orifice 83 and the clamping maintained with a screw 90 screwed into the 
needle bar clamp through a small hole 89. A slat section 87 of the needle 
bar clamp passes between two needle bar guides 91. The guides are attached 
to a needle bar holder 69 through small holes 93 in the guides using 
screws 95. 
The needle bar holder has an oblong side 70 and two smaller block-like ends 
71. The oblong side 70 has a large opening 73 used to hold a bight shaft 
24 using a screw 77 to clamp them together. The block-like ends 71 have 
passages 75 passing through them to allow the needle bar 79 to pass 
through. The needle bar 79 has a needle end 81 with a main needle attached 
that pierces a work piece to make stitches. 
In operation, the drive shaft 5 turns and rotates the crank 11 which pushes 
and pulls on the crank link 29. This pushing and pulling rocks the crank 
leg 47 of the V-shaped rocker 43, which pivots on the fixed pin 55. The 
rocking of the rocker 43 moves the connecting link 58 upward and downward. 
The upward and downward motion of the connecting link 58 moves the needle 
bar clamp 82 upward and downward along with the needle bar 79. The clamp 
is guided in its motion by the needle bar guide rails 91 and the needle 
bar 79 passes through passages 75 in the needle bar holder 69. 
The needle bar holder 69 allows a needle to move up and down through the 
workpiece creating stitches. The needle bar holder 69 is also moved by a 
bight shaft 24 passing through the large opening 73, which rotates back 
and forth. The back and forth motion creates a bight pattern to the 
stitching made on the workpiece. 
Referring to FIG. 2, the needle bar drive mechanism 1 of FIG. 1 is shown 
configured in a buttonhole sewing machine. The drive housing 3 supports 
the drive shaft passing through the drive shaft opening 4. Rotation of the 
drive shaft is applied by a belt at the middle section 7 and rotates the 
crank end 9 of the drive shaft. The crank 11 has a counter-weighted side 
13 and a smaller side 15 and is connected to the drive shaft at the large 
aperture 17. 
The crank link 29 is connected to the crank 11 at the first end 31 at the 
larger hole 35. The upper clevis pin 25 passes through the upper ball 
bearing ring 27 and makes the connection to the crank. The second end 33 
of the link 29 pivots around the lower clevis pin 41 through the lower 
ball bearing ring 39 fixed to the second hole 37 of the crank link 29 and 
about the second opening on the crank leg 47 of the V-shaped rocker 43. 
The needle leg 49 of the rocker 43 pivotally connects to connecting link 58 
through a connecting link pin 67 which passes through the forked ends 61 
and the needle leg 49. 
Also, in FIG. 2, the needle bar 79 and the main needle 99 are shown just 
above the base 97 of the buttonhole sewing machine. 
In FIG. 3, an assembled needle drive mechanism is presented. A drive shaft 
is connected to a crank 11 at a larger aperture 17. The crank is connected 
to a crank link 29 at a smaller aperture 19. A V-shaped rocker 43 is 
connected to the crank link at a smaller hole 4, of the crank link. The 
rocker pivots on a fixed pin 55 about the base 45 of the rocker. 
The rocker connects to a connecting link 58 which is attached to a needle 
bar clamp 82 which is connected to a needle bar 79. The needle bar passes 
through passages 75 in block-like ends 71 of a needle bar holder 69. The 
needle bar holder has a large opening 73 where a bight shaft 24 connects 
to wherein the needle bar holder can rock and thus create bight stitches 
in the workpiece. 
FIG. 4 shows four cyclic positions of a needle bar drive as it is making 
stitches: a down position, a mid left position, an up position, and a mid 
right position. A drive shaft spins a crank 11 in complete revolutions. 
Because a link 29 is connected to the crank off the crank's axis of 
rotation, the motion of the crank causes the link to be pulled up and to 
the left between the up and down positions and then down and to the right 
between the down and up positions. A rocker 43 pivots upward between the 
up and down positions. A connecting link 58 communicates the motion of the 
rocker to a needle bar 79, which moves correspondingly upward and 
downward. 
In FIG. 5, a drive shaft 5 has a crank end 9 to connect with a crank and an 
orifice 10 at the other end 8 to mount the shaft for rotation. Rotation of 
the shaft is supplied to the shaft through a belt to a center section 7 of 
the shaft. A keyway 6 cut into the shaft is also shown. 
In FIG. 6, a crank 11 has a large aperture 17 and a smaller aperture 19 and 
transverse countersunk holes 21 to clamp a drive shaft 5 in the large 
aperture and to clamp a clevis pin 25 in the smaller aperture. 
In FIG. 7, a crank link 29 has a first end 31 with a larger hole 35 and a 
second end 33 with a smaller hole 37. A mass-reducing hole 38 is also 
shown. 
In FIG. 8, a crank link 29 is shown assembled with upper 25 and lower 41 
clevis pins and ball bearing rings 27, 39. 
In FIG. 9, a lower clevis pin 41 is detailed. 
In FIG. 10, an upper clevis pin 25 is detailed. 
In FIG. 11, a V-shaped rocker 43 has an extended base 45 with a first 
opening 53, a crank leg 47 with a second opening 51 and a needle leg 49 
with a third opening 53. In addition, each leg has another hole 52, 54 to 
accept set screws. 
In FIG. 12, a V-shaped rocker 43 is shown assembled with bushings 57 
installed at both ends of a first hole 53 that passes through a base 45 of 
the rocker. 
In FIG. 13, a needle bar holder 69 has an oblong end 70 with a large 
opening 73 through the end and an orifice 76 transverse to the large 
opening for clamping a bight shaft 24 in the large opening, and two 
block-like ends 71, each having a passage 75 passing through the 
block-like ends. Holes 72 for connecting needle bar guide rails to the 
needle bar holder are shown. 
In FIG. 14, a needle bar guide rail 91 has upper and lower ends, with each 
end having a small hole 93. 
FIG. 15 shows a needle bar 79 with a notch 80 and a hole 78 for a set screw 
in a needle end 81 of the bar. 
In FIG. 16, a needle bar clamp 82 has a cylindrical section 85, a block 
section 84 with a center orifice 83 and a hole 89 transverse to the center 
orifice for clamping a needle bar, and a slat section 87. 
In FIG. 17, a Y-shaped connecting link 58 has a rounded end 59 with a first 
hole 65 through the end and two forked ends 61 with second and third holes 
63 through the respective forked ends. 
In FIG. 18, a connecting link pin 67 has a recessed center region 68 to 
limit the complete rotation of the pieces it joins. 
While the invention has been described with reference to specific 
embodiments, modifications and variations of the invention may be 
construed without departing from the scope of the invention, which is 
defined in the following claims.