GB2162553A

GB2162553A - Device for adjusting the tension of a whipstitch in a sewing machine

Info

Publication number: GB2162553A
Application number: GB08505723A
Authority: GB
Inventors: Franco Marchesi
Original assignee: Rockwell-Rimoldi SpA
Current assignee: Rockwell-Rimoldi SpA
Priority date: 1984-07-31
Filing date: 1985-03-06
Publication date: 1986-02-05
Also published as: DE3512656C2; IT1176511B; GB8505723D0; CH662591A5; DE3512656A1; IT8422138A0; JPS6141491A; GB2162553B; FR2568597A1; FR2568597B1

Abstract

An improved whipstitch sewing device wherein the presser foot 4 on the end of the presser bar 5 is provided with an attachment 18 that is shaped like, overlies the tongue on the machine needle plate, and has the same function as the tongue. <IMAGE>

Description

SPECIFICATION Device for adjusting the tension of a whipstitch in a sewing machine BACKGROUND OF THE INVENTION The invention falls within the technical sector of sewing machines for industrial usage and in particular relates to a device for adjusting the tension of a whipstitch. According to the invention, provision is made for a device comprising an auxiliary plate which is mounted on a presser bar, arranged above the fabric and the needle plate through which the feed teeth pass and provided with an attachment similar to the tongue of the needle plate which is surrounded by the whipstitch.

The said attachment is positioned above the said tongue so as to be also surrounded by the whipstitch.

Provision is also made for the said attachment to be fastened to the said auxiliary plate by means of removable connection elements.

As is known, sewing machines of theindustrial type comprise, among other things, a needle plate which is fixed to the sewing surface and is coplanar therewith and through which the teeth of the feed dog for feeding the fabric pass. In addition to the recesses for the teeth, the needle plate also has an opening into which the needle is inserted. This opening is partially defined by a tongue which is located on one edge and in the region of the upper hook and a lower hook which in addition to the needle cooperate to form a whipstitch.

The whipstitch is made along one edge of the fabrics so as to prevent fraying thereof. This edge is arranged to coincide substantially with the free edge of the needle plate and of the tongue on the needle plate. Provision is also made for a fixed blade and a mobile blade which cut and trim the edge of the fabric to be sewn, before the latter is arranged on the said tongue in the sewing area. In practice, the fixed blade is integral with the needle plate.

Above the needle plate and the fabric being sewn, provision is also made for an auxiliary plate commonly called a presser foot, which is mounted on a presser bar. The auxiliary plate is indispensable for keeping the fabric still during sewing and for preventing it bunching up when the feed teeth move it forward.

To prevent this presser foot from interfering with the needle and with the various sewing operations, the said foot is provided with a large opening in the region of the working zone of the needle.

Particularly significant is the function of the said tongue of the needle plate. The same tongue, in fact, replaces and simulates the fabric when the latter is not present to prevent the stitches formed at the start and at the end of the sewing machine's operation from causing entanglement of the threads, which would otherwise require remedial action on the part of the operator. The whipstitch is in fact formed on either side of the tongue and, on account of the latter having the shape of a truncated cone, the formed stitches can be easily removed or unthreaded.

In addition, and in particular, the said tongue determines, by means of its size, the final tension of the whipstitch on the fabric during sewing. In fact, almost all fabrics possess at least a certain degree of softness and deformability and therefore, when they are directly surrounded by the whipstitch, the latter tensions them locally and causes them to bunch up partially and form a series of depressions and swellings. The presence of the tongue which is surrounded by the whipstitch, together with the overlying fabric, reduces this phenomenon since the whipstitch is formed so as to have a greater width than that of the section of fabric being sewn. As a result, once removed from the tongue, the whipstitch does not tension excessively the fabric and create the said irregularities on the surface.

It must be noted that generally there is no danger of creating stitches which are too loose or too wide, on account of the presence of the Bbovementioned tongue. In fact, on the one hand, the fabric is partially squashed and gripped, during sewing, between the needle plate and the presser foot, and, on the other hand, the threads which form the stitch are at least partially elastic and stretch during sewing. As a result, after the sewing operation, the threads tend to assume their initial length and contract.

The tendency, after sewing, of the fabric to expand and of the thread to contract are such that the abovementioned tongue must be of a suitable size. The size of the latter must be related to the fabric being sewn and must increase, at least as regards thickness, in accordance with increase in the softness and height of the fabric being sewn.

However, the abovementioned tongue is an integral part of the needle plate. Therefore, each variation in the size of the tongue, in accordance with the fabric being sewn, involves replacement of the entire needle plate, together with the resultant costs. The needle plate is relatively complex since it is also integral with a fixed cutting element provided for trimming the fabric before sewing. The said presence of this cutting element in practice makes it impossible to remove and exchange the tongue since there is not sufficient space on the needle plate for removable connection elements.

Moreover, it must also be noted that, when the fabrics are very thick and soft, the abovementioned plate tongue is unable to prevent the said irregular tensioning even if it is designed so as to be large in size. This is due, among other things, to the fact that the presence of the teeth and of the various elements connected to the needle plate prevent the tongue being excessively large in size.

Overall, therefore, the existing technology is relatively inadequate both on account of the fact that a relatively complex element such as the needle plate must be replaced each time there is the slightest variation in the thickness of the fabric to be sewn, and on account of the fact that in any case particularly thick and soft fabrics tend to be overtensioned when the whipstitch is made on them, with the consequent negative aesthetic effects precisely in the vicinity of the edges, i.e., the most visible parts of the fabric. As already mentioned, this negative situation cannot be remedied by making the said tongue interchangeable and, moreover, the removability of the said tongue gives rise to serious technical problems in relation to the structure of the needle plate. In this situation, the general aim of the present invention is to overcome the abovementioned drawbacks.

Within the context of this general aim, another important object of the present invention is to design a device which, in addition to ensuring a high standard of workmanship, has a particularly simple and economical structure.

These aims and other aims which will become more apparent below are substantially achieved by a device for adjusting the tension of a whipstitch in a sewing machine, of the type comprising a needle plate through which teeth for feeding the fabric pass and which is provided with a tongue suitable for being surrounded by the whipstitch, together with the overlying fabric, and comprising an auxiliary plate or presser foot mounted on a presser bar and arranged above the fabric and the said needle plate, wherein the said auxiliary plate is provided with an attachment which is similar to the said tongue and located above the latter so as to be surrounded by the whipstitch, together with the fabric and the said tongue.

DESCRIPTION OF THE DRAWINGS Further characteristic features and advantages will become more apparent from the description of a preferred embodiment of the device according to the invention illustrated by way of a non-limiting example in the attached drawings in which: Figure 1 shows a perspective and overall view of the device according to the invention; Figure 2 shows a perspective view of a needleplate in a substantially isolated position; Figure 3 shows a perspective view of an auxiliary plate or presser foot, again in a substantially isolated position; Figure 4 shows a perspective view of all the elements which cooperate to form a whipstitch during sewing of a fabric.

With reference to the abovementioned figures, the device is indicated in its entirety by the number 1. It comprises, in brief, a needle plate 2 fixed to a sewing surface 3, and an auxiliary plate 4 mounted on a presser bar 5. The needle plate 2 is shown in Figure 2 and is of the type known peruse. It has a series of recesses 6through which extend teeth 7 for feeding the fabric 8 (Figure 2). The needle plate 2 is integral with a fixed blade 9 opposite which a mobile blade 10, also known per se, operates.

Adjacent to the fixed blade 9, there is a tongue 11 which has the shape of a truncated cone and partially defines an opening 12 into which a needle 13 is inserted. The latter, cooperating with an upper hook 14 is provided with thread. In Figure 4, the needle 13, the upper hook 14 and the lower hook 15 are all provided with threads 13A, 14A, 15A, respectively. The auxiliary plate 4 is shown in detail in Figures 3 and 4. The said plate, also called the presser foot has as its main element a lamina 16, also called the sole of the foot, which is provided with a rounded tip 1 6A and extends above the needle plate 2 opposite the zorie where the feed teeth 7 are located.

The auxiliary plate 4 has an opening 17 in the area where the needle 13 passes through.

Advantageously, this opening 17 is partially occupied by an attachment 18 which has a shape identical to that of the tongue 11 and is located above it.

Moreover, provision is made for the attachment 18to befastenedtothe lamina 16 by means of removable connection elements consisting, for example, of a screw 19, as shown in detail in Figure 3. The attachment 18 is provided in a large number of sizes and faces an oblique portion 20 of the lamina 16, which portion is inclined so as to facilitate feeding of the fabric and removal of the stitches.

Operation of the device according to the invention can be understood in particular from the above description and is illustrated in Figure 4.

The needle 13, upper hook 14 and lower hook 15 form, with their respective threads, the whipstitch by entwining the latter not only around the fabric 8 and the tongue 11, but also around the attachment 18. These threads 13A, 14A, 1 5A a re therefore arranged in a particularly loose manner and, when the fabric 8 leaves the operating zone of the needle and expands whereas the threads themselves tend to contract, the whipstitch remains attached to the fabric 8 without creating depressions or irregularities on the latter.

The dual presence of the tongue 11 and of the attachment 18 makes it possible to achieve this result not only on account of the increased thickness of the elements in question, but also because the stitch is initially formed on either side of two rigid elements completely enclosing the fabric.

Previously, only one rigid element, the tongue 11, was provided and hence the threads tended to sink into the fabric, particularly if the latter had a considerable degree of softness.

A second important feature of the invention consists in the fact that the attachment 18 can be immediately and simply exchanged by screwing and unscrewing the screw 19. This makes it possible to vary the width of the stitch being formed, in accordance with the fabric being sewn, without removing the needle plate 2 or even the auxiliary plate 4.

Attention is drawn to the original and practical nature of the device which has been created and which, unlike the prior art, is arranged on the auxiliary plate 4, the later hitherto being provided only with a view to correct positioning of the fabric 8 opposite the feed teeth 7. As a result of a new attachment 18 being provided in the region of the opening 17, formation of the stitches can be completely controlled and the latter gradually removed. Furthermore, the removable nature of the attachment 18 means that the device can be immediately and economically adapted to any type of fabric. Replacement of the attachment 18 can be performed even by non-specialized personnel.

It is also worth emphasizing that the device created does not result, as one might at first think, in the formation of loose stitches, in particular on account of the compression effect to which the fabric 8 is subjected when it is inserted between the tongue 11 and the attachment 18.

The invention in its present form is subject to numerous modifications and variations all of which come within the scope of the inventive idea.

Moreover, all of the details can be replaced by technically equivalent elements. In practice, the materials used and the dimensions may be of any kind or magnitude, as required.

Claims

1. In a sewing machine for forming whipstitching which includes a needle plate through which teeth for feeding the fabric pass, a tongue on the needle plate for being surrounded by the whipstitch and a presser base, the combination comprising an auxiliary plate mounted on the presser bar and an attachment shaped like the plate tongue and secured to said auxiliary plate to overlie said tongue to be surrounded by the whipstitch at the same time as the tongue.

2. The device as claimed in claim 1, wherein the said attachment is fastened to the said a auxiliary plate by means of removable connection elements.

3. The device as claimed in claim 2, wherein the said attachment is fastened to the said auxiliary plate by means of a screw.

4. The device as claimed in claim 2, wherein the said attachment is provided in a large number of sizes so as to be able to vary, as required, the width of the whipstitch, depending on the fabric being sewn.

5. The device as claimed in claim 1, wherein the said auxiliary plate comprises an oblique guiding portion which follows the said attachment and is suitable for facilitating feeding of the fabric and removal of the stitch.

6. Device for adjusting the tension of a whipstitch in a sewing machine, substantially as hereinbefore described with reference to the accompanying drawings.