Horizontal axis full rotary hook with a bobbin case holder having a needle guiding means

A horizontal axis full rotary hook for a sewing machine, including a generally cylindrical hook base having a point of hook, an inner circumferential surface, and a guide groove formed in the inner circumferential surface; and a generally cylindrical bobbin-case holder having an inner circumferential surface, an outer circumferential surface, and a part-circumferential rail provided on the outer circumferential surface, the bobbin-case holder being supported by the hook base such that the bobbin-case holder is freely rotatable relative to the rotary hook while the rail is guided in the guide groove, the bobbin-case holder having a needle aperture which allows a sewing needle with an upper thread to be moved down to a bottom position thereof, the needle aperture having a first inclined inner surface which is opposite to the point of hook with respect to the needle at the bottom position, a distance between the needle at the bottom position and the first inclined inner surface as measured in a direction parallel to a rotation axis of the bobbin-case holder being decreased in a direction from the outer circumferential surface of the bobbin-case holder toward the inner circumferential surface of the bobbin-case holder.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates in general to a full rotary hook for a sewing 
machine and in particular to such a hook suitable for use with a pattern 
or embroidery sewing machine. 
2. Related Art Statement 
A conventional full rotary hook shuttle for such use includes (a) a 
generally cylindrical hook base having a point of hook, an inner 
circumferential surface, and a guide groove provided in the inner 
circumferential surface, and (b) a generally cylindrical bobbin-case 
holder having an inner circumferential surface, an outer circumferential 
surface and a part-circumferential rail provided on the outer 
circumferential surface, the bobbin-case holder being supported by the 
hook base such that the bobbin-case holder is freely rotatable relative to 
the rotary hook while the rail is guided by the guide groove. 
However, this hook has no means for guiding a sewing needle with a top or 
upper thread. The hook produces no problem when it is used in a common 
sewing machine in which a work fabric or cloth is fed in an unchangeable 
direction. However, when the hook is used with a pattern or embroidery 
sewing machine in which directions in which a work cloth is fed are often 
changed, the hook provides a problem that a point of hook fails to catch a 
loop of the upper thread, producing a skipping stitch or a thread 
breakage, if continuous feeding of the work cloth is carried out, or if 
double fabric sewing is carried out using a thick fabric or cloth even by 
intermittent feeding of the work cloth. The reason for this problem is 
that the sewing needle is bent slightly away from the point of hook by 
being pulled by the cloth, depending upon the direction in which the cloth 
is fed, thereby increasing the possibility that the point of hook fails to 
catch the upper thread. 
For solving the above problem, it has been proposed, as indicated in 
two-dot chain line in FIG. 3, to provide, between a throat plate 100 and a 
bobbin-case holder, 20, a needle guide 102 for preventing a sewing needle 
2 from being displaced away from a point of hook 16. Alternatively, it has 
also been proposed to form, in place of a needle hole 104 concentric with 
the needle 2, a needle hole 106 eccentric with the needle 2 in the throat 
plate 100, so that the eccentric hole 106 serves for guiding the needle 2. 
However, even where these needle guides 102, 106 are used, they come into 
contact with the upper thread, thereby exerting resistance to the same and 
reducing tightness of the stitches formed. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a full rotary 
hook shuttle which effectively prevents a sewing needle from being 
displaced away from a point of hook thereof without adversely affecting an 
upper thread. 
The above object has been achieved by the present invention, which provides 
a full rotary hook for a sewing machine, comprising a generally 
cylindrical hook having a point of hook base, an inner circumferential 
surface, and a guide groove formed in the inner circumferential surface; 
and a generally cylindrical bobbin-case holder having an inner 
circumferential surface, an outer circumferential surface, and a 
part-circumferential rail provided on the outer circumferential surface, 
the bobbin-case holder being supported by the rotary hook such that the 
bobbin-case holder is freely rotatable relative to the hook base while the 
rail is guided in the guide groove, the bobbin-case holder having a needle 
aperture which allows a sewing needle with an upper thread to be moved 
down to a bottom position thereof, the needle aperture having a first 
inclined inner surface which is opposite to the point of hook with respect 
to the needle at the bottom position, a distance between the needle at the 
bottom position and the first inclined inner surface as measured in a 
direction parallel to a rotation axis of the bobbin-case holder being 
decreased in a direction from the outer circumferential surface of the 
bobbin-case holder toward the inner circumferential surface of the 
bobbin-case holder. 
In the horizontal axis full rotary hook constructed as described above, the 
sewing needle is guided by the first inclined inner surface of the needle 
aperture, so that the needle is prevented from being displaced in a 
direction away from the point of hook. Since the first inclined inner 
surface guides the sewing needle only, the first inclined inner surface 
does not come into contact with the upper thread and does not adversely 
affect the same. Therefore, even in the case where sewing is carried out 
at a high operational speed by continuous feeding of a work cloth on a 
pattern or embroidery sewing machine in which the directions of feeding of 
the cloth are often changed, or in the case where double fabric sewing is 
carried out using a thick fabric or cloth by intermittent feeding of the 
cloth, the hook securely catches a loop of the upper thread, without 
producing a skipping stitch or a thread breakage. In addition, since the 
upper thread is fed forward smoothly, the sewing is carried out with 
"well-locked" stitches. A "well-locked" stitch means a stitch formed by an 
upper and a bobbin thread locking each other in the middle of the 
thickness of the work cloth. 
In a preferred embodiment of the present invention, the needle aperture is 
an elongate aperture extending in a circumferential direction of the 
bobbin-case holder, the first inclined inner surface extending in a 
longitudinal direction of the elongate aperture. The first inclined inner 
surface extending in the longitudinal direction of the elongate aperture, 
exhibits the above-indicated advantages even in the event that the sewing 
needle is bent in that longitudinal direction of the elongate aperture. 
In another embodiment of the present invention, the needle aperture has a 
second inclined inner surface which surface is located on a side of the 
point of hook with respect to the needle at the bottom position, a 
distance between the needle at the bottom position and the second inclined 
inner surface as measured in the direction parallel to the rotation axis 
of the bobbin-case holder being decreased in the direction from the outer 
circumferential surface of the bobbin-case holder toward the inner 
circumferential surface of the bobbin-case holder. The second inclined 
inner surface serves for preventing the sewing needle from colliding with 
the point of hook due to elastic deformation of the needle. 
In yet another embodiment of the present invention, the needle aperture is 
an elongate aperture extending in a circumferential direction of the 
bobbin-case holder, the first and second inclined inner surfaces extending 
in a longitudinal direction of the elongate aperture. This embodiment 
provides the advantages produced by both the above two preferred 
embodiments of the invention. 
In a further embodiment of the present invention, the bobbin-case holder 
has a straight elongate groove formed in the outer circumferential surface 
thereof so as to extend in a direction perpendicular to the rotation axis 
of the bobbin-case holder and have a depth which does not reach the inner 
circumferential surface of the bobbin-case holder, the bobbin-case holder 
having an elongate hole formed through a bottom of the elongate groove so 
as to extend parallel to the elongate groove, the needle aperture 
including the elongate hole and a surrounding portion of the elongate 
groove which portion surrounds the elongate hole, at least an inner 
surface of the elongate groove which surface is opposite to the point of 
hook being inclined with respect to the needle at the bottom position and 
providing the first inclined inner surface. This needle aperture is easily 
produced by forming the elongate groove such that at least an inner 
surface thereof is inclined with respect to the needle at the bottom 
position and forming the elongate hole through the bottom of the elongate 
groove. In this case, the elongate hole has a non-inclined inner surface 
which is not inclined with respect to the sewing needle and which is 
aligned with the inclined inner surface of the elongate groove. This 
arrangement serves for increasing the durability of the elongate hole or 
needle aperture. If the elongate hole or needle aperture has no such 
non-inclined inner surface, the shape of the hole or aperture as viewed in 
the direction of reciprocation of the sewing needle is subject to 
deformation due to wear caused by the friction between the needle and the 
inner edge of the first inclined inner surface, because the first inclined 
inner surface has no thickness at the inner edge thereof. In contrast, in 
the present embodiment, the shape of the elongate hole is hardly changed 
even if the first inclined inner surface is worn to an appreciable extent. 
According to a feature of the present invention, the bobbin-case holder has 
a recess adjacent to an opening thereof through which a bobbin, around 
which a bobbin thread is wound, and a bobbin case are inserted in the 
bobbin-case holder, the recess being engageable with the bobbin thread, 
the needle aperture being located adjacent to the recess. 
According to a feature of the present invention, the recess provides a 
recessed portion of the bobbin-case holder which portion is engageable 
with a bobbin holder position bracket for stopping rotation of the 
bobbin-case holder.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring first to FIG. 1, there is shown an embroidery sewing machine in 
which a horizontal axis full rotary hook in accordance with the present 
invention is used. On a machine table 50, there is disposed a sewing head 
52. A needle bar 54 carrying a sewing needle 2 is reciprocated vertically 
by being driven by a main motor (not shown) via a main shaft (not shown). 
A pair of first support members 56, 56, each fixed to the machine table 
50, support a pair of first guide rails 58, respectively, which extend in 
a Y direction indicated at arrow Y in the figure. A first rack 60 is fixed 
to each first guide rail 58, and a first slide member 62 is mounted on 
each first rack 60. The two first slide members 62, 62 cooperate with each 
other to support a movable frame 64 and a second rack 66 such that the 
frame and rack 64, 66 are movable in the Y direction. A first drive motor 
68 drives, via a first shaft 70, a pinion (not shown) threadedly engaged 
with each first rack 60, thereby moving the frame 64 in a positive and a 
negative direction of the Y direction. 
A pair of second support members 72, 72 support a spline shaft 74 such that 
the spline shaft 74 extends in the Y direction and is freely rotatable 
about a rotation axis thereof. A second drive motor 76 drives the spline 
shaft 74 via a wheel 78. The spline shaft 74 is engaged with a spline 
bearing 82 supported by a second slide member 80. When the spline shaft 74 
is driven by the second drive motor 76, the spline bearing 82 and a pinion 
(not shown) are rotated, so that the second slide member 80 and a carriage 
84 are moved in an X direction perpendicular to the Y direction while 
being guided by the frame 64. A pallet 90 is secured to the carriage 84 by 
means of a clamp member 86 and a clamp cylinder 88, and a work fabric or 
cloth 4 is held by the pallet 90. 
The first and second drive motors 68, 76 cooperate with each other to move 
the work cloth 4 relative to the sewing needle 2 to a desired position in 
a plane defined by the X and Y directions or axes, so as to form stitches 
on the work cloth 4. The manner of loop-catching and stitch formation by 
the sewing machine of this type is disclosed in U.S. Pat. No. 2,680,417. 
Referring next to FIGS. 2 and 3, there is shown a horizontal axis full 
rotary hook in accordance with the present invention. The shuttle includes 
a base hook 12. The hook base 12 has a boss portion 14 fixed to a rotary 
shaft 10, so that the rotary hook base 12 is rotatable with the rotary 
shaft 10. The hook base 12 has a beak or point of hook 16 for catching a 
loop of an upper thread 6 (FIG. 5), and a cam plate 18 for guiding the 
upper thread 6 caught by the point of hook 16. The hook base 12 has a 
generally cylindrical shape and has a raceway or guide groove 22 formed in 
an inner circumferential surface thereof. The guide groove 22 guides a 
bobbin-case holder 20 such that the bobbin-case holder 20 is freely 
rotatable relative to the hook base 12. 
As shown in FIG. 4, the bobbin-case holder 20 has a generally cylindrical 
shape and has a part-circumferential ridge or rail 24 provided on an outer 
circumferential surface thereof. The rail 24 is engaged with the guide 
groove 22 of the hook base 12. The bobbin-case holder 20 has, at its 
central portion, a stud support shaft 26 for supporting a bobbin 28 via a 
bobbin case 30. A bobbin thread 8 is wound around the bobbin 28. The 
rotary shaft 10, hook base 12, central stud support shaft 26 of the 
bobbin-case holder 20, bobbin case 30, and bobbin 28 are coaxial with each 
other. The bobbin-case holder 20 has, at an upper end portion thereof, an 
engagement recess 32 adjacent to an opening thereof through which the 
bobbin 28 and bobbin case 30 are inserted to the bobbin-case holder 20. A 
bobbin holder position bracket 34 is engageable, at an extension 36 
thereof, with the engagement recess 32 of the bobbin-case holder 20, for 
stopping rotation of the bobbin-case holder 20. The engagement recess 32 
is also engageable with the bobbin thread 8. The bobbin-case holder 20 
has, at the upper end portion thereof, an elongate aperture 40, 41, 42 
adjacent to the engagement recess 32. The elongate aperture 40, 41, 42 
allows an end portion of the sewing needle 2 carrying the upper thread 6, 
to be moved down to a bottom position thereof. 
As shown in FIGS. 3 and 5, the needle aperture 40, 41, 42 includes a first 
inclined inner surface 42 which is opposite to the point of hook 16 with 
respect to the needle 2 at the bottom position. A distance 23 between the 
needle 2 at the bottom position and the first inclined inner surface 42 as 
measured in a direction parallel to a rotation axis of the bobbin-case 
holder 20 is decreased in a direction from the outer circumferential 
surface 27 of the bobbin-case holder 20 toward an inner circumferential 
surface 29 of the same 20. More specifically, the bobbin-case holder 20 
has a straight elongate groove 39 formed in the outer circumferential 
surface 27 thereof so as to extend in a direction perpendicular to the 
rotation axis of the bobbin-case holder 20 and have a depth which does not 
reach the inner circumferential surface 29 of the bobbin-case holder 20. 
The needle aperture 40, 41, 42 includes an elongate hole 40 formed through 
a bottom of the elongate groove 39 so as to extend parallel to the 
elongate groove 39. The needle aperture 40, 41, 42 further includes a 
surrounding portion 41, 42 which surrounds the elongate hole 40. The first 
inclined inner surface 42 is an inner surface of the surrounding portion 
41, 42 which surface is opposite to the point of hook 16 and is inclined 
with respect to the needle 2 at the bottom position. When the hook base 12 
is rotated, the point of hook 16 passes adjacent the needle aperture 40, 
41, 42, for catching a loop of the upper thread 6. The surrounding portion 
41, 42 includes a second inclined inner surface 41 which surface is 
located on a side of the point of hook 16 with respect to the needle 2 at 
the bottom position. A distance 25 between the needle 2 at the bottom 
position and the second inclined inner surface 41 as measured in the 
direction parallel to the rotation axis of the bobbin-case holder 20 is 
decreased in the direction from the outer circumferential surface 27 of 
the bobbin-case holder 20 toward the inner circumferential surface 29 of 
the same 20. 
The function of the first inclined inner surface 42 is as follows: When 
sewing is carried out on the work cloth 4 by continuous feeding of the 
cloth 4 in the Y direction, or when double fabric sewing is carried out 
using a thick fabric or cloth 4 by intermittent feeding of the cloth 4, 
the sewing needle 2 is pulled by the work cloth 4 being fed and 
consequently the needle 2 is bent slightly in a direction of feeding of 
the cloth 4, i.e., away from the point of hook 16, thereby increasing a 
distance, X.sub.1, between the point of hook 16 and the needle 2 and 
possibly resulting in that the point of hook 16 fails to catch a loop of 
the upper thread 6. It is desired that distance X.sub.1 fall within the 
range of 0 to 0.1 mm. If distance X.sub. exceeds the upper limit of this 
range, the problem will be encountered with increased probability that the 
point of hook 16 will fail to catch the upper thread 6, thereby producing 
a skipping stitch or a "single-ply" stitch. A "single-ply" stitch means a 
stitch formed by only one or two plies of the upper thread 6 being locked 
by the bobbin thread 8, where the upper thread 6 consist of three plies 
twisted. However, according to the principle of the present invention, 
since the needle aperture 40, 41, 42 of the bobbin-case holder 20 has the 
first inclined inner surface 42, the end portion of the sewing needle 2 is 
guided by the first inclined inner surface 42, so that the needle 2 is 
prevented from being displaced away from the point of hook 16, i.e., 
distance X.sub.1 between the needle 2 and the point of hook 16 is 
prevented from excessively being increased. This arrangement enables the 
point of hook 16 to easily catch the upper thread 6, i.e., prevents the 
point of hook 16 from failing to catch the upper thread 6. Thus, the upper 
thread 6 is caught by the point of hook 16 with high reliability. 
In addition, the first inclined inner surface 42 of the needle aperture 40, 
41, 42 comes into contact only with the end portion of the sewing needle 
2, and does not contact the upper or bobbin thread 6, 8. Consequently, the 
first inclined inner surface 42 does not adversely affect the upper or 
bobbin thread 6, 8, thereby ensuring that the threads 6, 8 are fed forward 
smoothly and therefore that sewing is effected with well-locked stitches 
being produced. 
While the present invention has been described in its presently preferred 
embodiment with detailed particularities, it is to be understood that the 
present invention may be embodied with various changes, improvements and 
modifications that may occur to those skilled in the art without departing 
from the scope and spirit of the invention defined in the appended claims.