EP0031323B1

EP0031323B1 - Rotary hook for sewing machine

Info

Publication number: EP0031323B1
Application number: EP79900750A
Authority: EP
Inventors: Wayne E. Starr
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-07-02
Filing date: 1979-07-10
Publication date: 1986-04-02
Also published as: SE8101313L; GB2063939A; JPS56500757A; GB2063939B; JPS6147114B2; EP0031323A4; WO1981000120A1; NL7920001A; SE440671B; EP0031323A1

Abstract

A rotary hook (11) and bobbin (12) assembly for a single needle lock-stitch sewing machine (9). he bobbin (11) has no case but has a flat end plate (12b) and a convexly curved end plate (12a).The bobbin older (11) has a post (14) with a means (13) for locking the bobbin (12) and a relatively wide undergroove (16) in its wall for adjusting tension.

Description

The invention relates to lock-stitch sewing machines. In particular, it relates to a rotary hook and bobbin assembly for a single-needle lock-stitch sewing machine.
An example of the basic type of assembly to which the invention relates is described in U.S. Patent Specification No. 3,476,068. Such prior art assembly comprises a rotary driving shaft, a bobbin holder engageable with said shaft and with the sewing machine, a bobbin engageable with the bobbin holder, and a rotary hook mounted on said shaft for rotational movement relative to the bobbin holder, said bobbin holder having a needle opening, an opening for positioning the bobbin holder on the sewing machine positioner, a bevelled guide surface for the needle thread, a bobbin post on which the bobbin is freely rotatably mounted, and means for applying force axially on the bobbin so as to drive and maintain the flat bobbin end plate in frictional contact with the bottom wall of the bobbin holder.
Other examples of the prior art in rotary hook sewing machines are disclosed in German Patent Specification No. 50727, British Specification No. 700,306 and U.S. Specifications Nos. 1,966,432, 2,830,550 and 4,009,670.
The object of the present invention is to provide a hook and bobbin assembly having higher thread capacity, ease of threading, self-adjusting tension, less stalling, and higher speed than the prior art.
According to the invention, a rotary hook and bobbin assembly of the basic type first referred to is characterised in that the bobbin has a convexly curved outer end plate, that the bobbin holder has an undergroove adjacent the opening for engaging the bobbin thread passing from the bobbin outwardly of the bobbin holder, and that the convexly curved outer end plate of the bobbin and the bevelled surface of the bobbin holder are so disposed as to contact and support the needle thread looped around the bobbin holder.
In an assembly according to the invention, automatic tension control for the bobbin thread is provided by the combination of the continuous curved outer surface, the undergroove and the flat surface of the bobbin. The flat side of the bobbin makes total contact with the back wall of the holder, with the curved end out. As the bobbin thread is drawn off the bobbin the bobbin spins in a clockwise direction which is opposite to the counterclockwise rotation of the assembly. This permits the bobbin to thread itself in the holder. The operator simply puts in a bobbin and starts to sew with no need to pick up the bobbin thread manually as in previous hook assemblies. The opposite directions of rotation provide inertial balance and smooth, quiet operation.
The forces on the holder would tend to make the holder rotate in the same direction as the bobbin. This occurs when thread is drawn off the bobbin in short pulses as each stitch is formed. However since the assembly rotates in a counterclockwise direction the forces on the holder would tend to make it rotate in the same direction. At sewing speeds the opposing forces tend to cancel leaving the holder neutral and stable,.thus enabling improved stitches to be formed.
Said means for applying force axially on the bobbin may comprise a curved spring-loaded arm means which confirms to the curvature of the bobbin end plate. Alternatively said means may comprise magnetic means, such as magnetic discs on the floor of the bobbin holder.
Further objects and advantages of this invention will be apparent from the description which follows taken together with the appended drawings. In the specific examples which follow, the invention is illustrated with reference to undertrimming, but can be used with other single-needle lock-stitch sewing machines.

Brief Description of Drawings

Figs. 1, 1A and 7 refer to the invention generally, while Figs. 2-6 refer to one embodiment and Figs. 8-12 refer to a second embodiment of this invention.
Fig. 1 is a perspective view in semi-diagrammatic form of a single needle lock-stitch sewing machine using undertrimming, showing where the rotary hook and bobbin assembly of this invention would be installed.
Fig. 1A is a diagrammatic view of the interlocking of the bobbin thread and needle thread.
Fig. 2 is a plan view of the front portion showing a bobbin in place and indicating the position of the bobbin thread and needle thread.
Fig. 3 is a perspective view of the bobbin holder with the bobbin removed and the arm up.
Fig. 4 is a top view with partial sectioning showing attachment of the assembly to a sewing machine.
Fig. 5 is a side view in a different position.
Fig. 6 is a section through the assembly.
Fig. 7 is a side sectional view of the bobbin.
Fig. 8 is a plan view of the front portion of the second embodiment.
Fig. 9 is a perspective view of the bobbin holder with the bobbin removed.
Fig. 10 is a top view with partial sectioning. showing attachment of the assembly to a sewing machine.
Fig. 11 is a side view in a different position.
Fig. 12 is a section through the assembly.

Specific Examples of the Invention

Referring now to the drawings, there are illustrated therein two embodiments of the rotary hook-bobbin assembly of this invention as applied to an undertrimming, lock-stitch sewing machine.

Embodiment of Figs. 2-6

The sewing machine 9 has a conventional reciprocating needle 31 which extends through the pressure foot 32 and bottom plate 33 into the assembly 10 through needle opening 19.
The assembly 10 of the bobbin holder 11 and bobbin 12 are attached to the machine by a holding means 23 which consists of a removable plate 25 and a cup portion 24. The cup portion 24 has a back opening 24b to receive the rotary driving shaft (not illustrated) and hold it by means of bolt 24a. Cup portion 24 also has a raceway 24c which cooperates with the ridge 22 of the holder 11 to hold it in position. The removable portion 25 permits the insertion and locking of the holder 11 with its ridge into the groove.
The holder 11 has a center hollow post 14 on which the bobbin 12 is mounted. The holder 11 has a ridge 22 for mounting the holding means 23, an upper, rear bevelled surface 20, a needle opening 19, a finger 17, a relatively wide undergroove 16 in which the bobbin thread moves, an opening 18 which is engageable with the positioner 41 which is normally attached to the sewing machine, and a floor 11 a in which there is an opening 15.
The center post 14 of the holder has a spring 27 held with locking rod 27a against arm 13 which pivots on rod 28. Arm 13 is curved so as to register with the curvature of end wall 12a of bobbin 12 and it extends over the bobbin so as to lock into groove 21 in the holder. The other end wall 12b of the bobbin 12 is flat and seats against the bottom wall 11 a of the holder 11.
In operation, the needle 31 goes down and after reaching its lowest point on the downward stroke forms a little loop as it rises. This loop of needle thread 40 is picked up by the point of the hook 23a (Fig. 2) and carried around the holder 11 (Fig. 5) and then draws the bobbin thread up to form the proper stitch. As indicated in Fig. 4, the ridge 22 has an interruption 22a to permit the smooth flow of the needle thread around the holder. As the holder means 23 rotates in synchronization with the needle, the bobbin holder 11 is held in fixed position by the sewing machine positioner 41 but the bobbin 12 is free to rotate.
It should be noted that the bobbin has no case and that the spring-held, curved arm cooperates in forming the non-snagging surface for the needle thread. No adjustments are needed in changing from one thickness of thread to another. The tension is directly on the bobbin and regardless of any bumps or the like that might be in the thread, the tension is automatically adjusted by the drag caused by the arm and the frictional engagement of the thread on the undergroove 16.

Embodiment of Figs. 8-12

In the embodiment represented by Figs. 8 to 12 the bobbin 112 is of the same configuration having a curved outer wall 112a and a flat inner wall 112b. However, in this case the bobbin must be made of ferro-magnetic material at least with respect to wall 112b.
The assembly 110 of the bobbin holder 111 and bobbin 112 are attached to the machine by a similar holding means 123 which consists of a removable plate 125 and a cup portion 124. The cup portion 124 has a back opening 124b to receive the rotary driving shaft (not illustrated) and hold it by means of a bolt 124a. Cup portion 124 also has a raceway 124c to latch 122 of the holder 111 to hold it in position. The removable portion 125 permits the insertion and locking of the holder 111 when it is latched into the groove. The holder 111 has a ridge 122 for mounting the holding means 124, an upper rear bevelled surface 120, a needle opening 119, a finger 117, a relatively wide undergroove 116 in which the bobbin thread moves, an opening 118 which is engageable with the finger position 141 which is normally attached to the sewing machine and floor 111 a in which there is an opening 115.
The floor 111a of the holder 111 has two magnetic discs 141. A suitable magnetic disc would be a rare earth cobalt magnet of the order of 3/16 inches (4.8 mm) in diameter with an energy product of fifteen million gauss-oersteds and having a composition of approximately 65% cobalt and 35% samarium. Sources of such rare earth magnets include Emm Indiana General, a division of Electronic Memories and Magnetics Corp. of Valpariso, Indiana, Crucible Magnetics Division of Colt Industries, Elizabethtown, Kentucky and Hitachi Magnetics Corp. of Edmore, Michigan. The bobbin 112 is held on the holder 111 by the magnetic forces of the discs 141 and thus provides the tension for the bobbin thread. The bobbin 112 is removed from the holder 111 by inserting a finger into the slot 121 and pulling forward.
The operation of this embodiment is similar to that of the preceding embodiment.

Claims

1. A rotary hook and bobbin assembly for a single needle lock-stitch sewing machine comprising a rotary driving shaft, a bobbin holder (11) engageable with said shaft and with said sewing machine, a bobbin (12) engageable with the bobbin holder, and a rotary hook (23, 23a) mounted on said shaft for rotational movement relative to the bobbin holder (11), said bobbin holder having a needle opening (19), an opening (18) for positioning the bobbin holder (11) on the sewing machine positioner (41), a bevelled guide surface (20) for the needle thread (40), a bobbin post (14) on which the bobbin (12) is freely rotatably mounted, and means (13) for applying force axially on the bobbin (12) so as to drive and maintain the flat bobbin end plate (12b) in frictional contact with the bottom wall (11 a) of the bobbin holder (11), characterised in that the bobbin (12) has a convexly curved outer end plate (12a), that the bobbin holder (11) has an undergroove (16) adjacent the opening (18) for engaging the bobbin thread (30) passing from the bobbin (12) outwardly of the bobbin holder (11), and that the convexly curved outer end plate (12a) of the bobbin (12) and the bevelled surface (20) of the bobbin holder (11) are so disposed as to contact and support the needle thread (40) around the bobbin holder (12).

. 2. The assembly of claim 1 wherein said means (13) for applying force axially on said bobbin comprises a curved spring-loaded arm means which conforms to the curvature of said bobbin end plate (12a).

3. The assembly of claim 1 wherein the means 13 for applying force axially on said bobbin comprises magnetic means (141).

4. The assembly of claim 3 wherein said magnetic means comprises magnetic discs in the floor (111 a) of the bobbin holder.