GB2162552A - Lower hook of a sewing machine suitable for forming whipstitches - Google Patents

Abstract

A lower hook 3 for a whipstitch type sewing machine in which the blade 9 is supported in cantilevered fashion on a spindle 8 and is shaped with its lower edge 16 in the form of an arc generated about the axis of the spindle. <IMAGE>

Description

SPECIFICATION Lower hook of a sewing machine suitable for forming whipstitches The present invention relates to the lower hook of a sewing machine suitable for forming whipstitches with two or three threads (Nos. 503 and 504 of the Federal Standard Catalog). The said lower hook is also particularly suitable for sewing operations where heavy fabrics are used.

Background of the Invention As is known, the lower hook of sewing machines of the industrial type cooperates with the needle and upper hook to form the so-called whipstitch, which consists of two or three threads and is made on the edges of a fabric. The lower hook is always provided with thread and performs an oscillatory movement which always takes place below the plane on which the fabric lies.

The main operating phases performed by the lower hook are as follows: it penetrates, with its own tip, between the needle ascending from its bottom dead point and its associated thread, oscillating angularly in the direction of the upper hook; then, when it has stopped oscillating, it assumes a position alongside the upper hook which in turn wedges itself between the lower hook and its associated thread. The lower hook then returns to its initial position.

During a large part of its oscillatory movement, the lower hook is therefore inserted into the thread of the needle, and the thread itself forms a loop which runs along the blade of the lower hook; during some parts, however, the thread attempts to run along the blade, but is prevented, and hence more thread is drawn out (thread which can no longer be recovered).

It must then be pointed outthatthe said movements of the lower hook are performed by a series of kinematic mechanisms which include a support piece interlocked at one end with the said hook and at the other end with a spindle, the axis of which is substantially perpendicular to the plane in which the blade of the lower hook lies and to its trajectory.

The technical solutions described above are very widespread and have generally been adopted for forming a whipstitch on any type of fabric, be it lightweight or heavy. Despite this, it is known that a lower hook of the type described above can have serious drawbacks as regards operation and, in particular, can give rise to irregular tensioning of the stitches formed. In fact, the hook itself during its trajectory tensions the thread of the needle in a generally non-uniform manner and in a particular variant, in accordance with the position which it assumes along its trajectory: the tension increases as the lower hook moves closerto the upper hook.

This situation can have serious consequences particularly when the lower hook is large in size and when, most of all, heavy fabrics are being sewn. In fact, in the case of the latter, the thickness of which can be as much as 15 mm for example, the needle thread passing through the fabric itself is held tightly in position: any spontaneous movement of the needle thread is prevented, owing to friction with the fabric which it passes through. As a result, the irregularities in tensioning, produced by the lower hook, are unable to offset each other as in the case of iightweight fabrics. Tight stitches may thus exist alongside loose stitches.

In the case of heavy fabrics, the present lower hooks may not only cause the formation of loose stitches alternating with tight stitches, but may also give rise to a continuous series of loose stitches when too much thread is taken up from the needle.

It must in fact be remembered that sewing machines of the industrial type used for making whipstitches are not equipped with devices for pulling, tensioning or even recovering the thread and that any excess in the amount of th read taken up is in no way compensated for.

In view of the above, the general aim of the present invention is to design the lower hook of a sewing machine suitable for forming whipstitches, such that the abovementioned drawbacks can be overcome. Within the scope of this general aim, an important object of the present invention is to design a lower hook which has a particularly simple structure and can be easily produced by the industries in the sector.

Another important object is to design a lower hook which is able to use the same kinematic chain generally used for controlling its movements.

These and other objects, which will become clearer below, are achieved by means of the lower hook of a sewing machine suitable for forming whipstitches, of the type comprising a blade which is mounted in cantilever fashion on a tang supported by a support piece oscillating about the axis of a spindle which is substantially perpendicular to the plane in which the said blade lies, wherein the lower edge of the said blade extends, in the said plane in which the blade lies, along the arc of a circle, the centre of which lies on the said axis.

Description of the Drawings Further characteristic features and advantages will become clearer from the description of a preferred embodiment of the invention, illustrated by way of example in the attached drawings in which: Fig. 1 shows a perspective view of the components of a sewing machine which cooperate with each other so as to form a whipstitch with two threads (continuous lines) or three threads (broken lines);; Fig. 2 also shows a perspective view of some of the components shown in Fig. 1, along with their trajectories, Fig. 3 shows the trajectory of the needle in relation to the upper hook and lower hook, Figs. 4 to 7 show the structure of the lower hook, which is the subject of the present invention, on its own, Figs. 8 to 10 show, In schematic form, certain phases during formation of a whipstitch with three threads, involving a lower hook structured as in Figure 4.

Description of the Invention With reference to the abovementioned figures, provision is made for a sewing machine which, in a manner known peruse, has a needle 1, an upper hook 2 and a lower hook 3.

The needle 1 is mounted on a lever4which is able to oscillate, the upper hook 2 on a system comprising a connecting rod 5 and crank 6, and the lower hoot"3 on a support piece 7 located at the end of a spindle 8.

The needle 1, upper hook 2 and associated support and control components are known per se.

The figures show, next to an upper hook 2 drawn in continuous lines, another hook drawn in broken lines and varying slightly from the first hook: this is to indicate that the upper hook 2 may or may not be provided with thread so as to form a whipstitch with either two threads or three threads.

With reference to Figures 1 and 2 in particular, it can be seen that the lower hook 3, which is the subject of the present invention, consists of a blade 9 which atone end has a tip 10 and at the other end is integral with a tang 11. The blade 9 lies in a substantially vertical plane and the tang 11 is integrally fixed, at its end, to the said support piece 7 which is interlocked with the spindle 8. It can be seen that the support piece 7 is perpendicular to the spindle 8 and that the axis of the latter is substantially perpendicular to the plane in which the blade 9 lies as well as the the trajectory of the latter.

The lower hook 3 is provided with a thread 33a similarly to the needle 1 which is provided with an associated thread 1 a and the upper hook 2 which is provided, in the case of an upper hook with a hole, with an associated thread 2a, as Figures 8 to 10 show.

Figures 5 to 7 show that the lower hook 3 is advantageously provided with a tip 10 with a convex side 12 and with a blade 9 with, in the vicinity of the convex side 12, a series of chamfers designed to ensurethatthe lowerhook3 engages properlywith the upper hook 2 at all times. In particular, the figures show a first chamfer 13 tapering the blade 9 in the direction of the tip 10, a second chamfer 14 tapering the upper edge of the blade 9, and a third chamfer 15 also tapering the upper edge of the blade 9 and partially flanking, on the opposite side, the second chamfer 14.

According to the invention, as can be seen in particular from Figure 4, the lower edge 16 of the blade 9 advantageously has a rounded shape with the cavity facing the axis of the spindle 8.

Moreover, in an original manner, the rounded profile of the lower edge 16 of the blade 9 is the art of a circle, the centre of which is located on the said axis of the spindle 8.

Operation of the lower hook which is the subject of the present invention is clear from the mainly structural description given above.

In particular, it is emphasized that, on account of the lower edge 16 being rounded in the manner of a circumferential arc, any tensioning of the thread 1 a of the needle 1 can be avoided. In fact, as Figures 8 to 10 show, the lower hook 3 inserts its tip 10 between the needle 1 and the thread 1 a, separating the thread 1 a with its swelling 12, and then moves forward so as to cause the loop formed by the thread 1a to run along the blade 9. In actual fact, after inserting itself in the loop of thread lea, the lower hook 3 moves towards the upper hook 2, interacting with the said thread 1 a.

In the prior art, this displacement or movement forwards of the lower hook 3, which was always performed with a straight blade, gave rise to undesired tensioning of the thread 1 a. In fact, the tip 10 was at a greater radial distance from the axis of the spindle 8 than the middle part of the blade 9.

Consequentiy, the latter pulled thethread 1 a, tensioning the previously made stitches or, alternatively, drawing out an excessive amount of new thread 1 a. As a result, the previously formed stitches were greatly tensioned or, alternatively, an excessive amount of new th read was drawn out, with the subsequent formation of loose stitches. In neither case was the situation normalized again after the formation of the stitches, owing to the friction between the fabric and thethread 1a and owing to the absence of devices for pulling the thread, tensioning it, etc.

Now, however, any possibility of the thread 1 a being drawn out in irregularfashion after insertion ofthetip 10 is prevented on account of the profile of the lower edge 16. It is in fact clear that the radial distance between the blade 9 and the axis about which the trajectory of the latter develops, always remains constant. In practice, the simple technical solution described is sufficient to eliminate all of the abovementioned problems during formation of a whipstitch, in particular on heavy fabrics.

It is obvious that it is also possible for the lower edge 16 to have profiles other than the arc of a circle, for example rounded profiles with cavities which vary in size and face the axis of the spindle 8.

All of the detailed features can be replaced by technically equivalent elements.

In practice, the material used can be of any type and the dimension of any magnitude, as required.

Claims (2)

1. A lower hook of a sewing machine suitable for forming whipstitches, of the type comprising a blade which is mounted in cantilever fashion on a tang supported by a support piece oscillating about the axis of a spindle which is substantially perpendicular to the plane in which the said blade lies, said lower hook having the lower edge of the blade thereof shaped in the form of an arc generated about the axis of the spindle and wherein said edge lies facing the axis of the spindle.

2. A lower hook of a sewing machine suitable for forming whipstitches, substantially as hereinbefore described with reference to the accompanying drawings.