The present invention relates to a sewing machine for forming running-stitch seams.

Sewing machines for forming a seam with a so-called running stitch are known; such seam is formed with a single thread of preset length, known as draw, and is composed of stitches that are alternately visible on either side of the fabric being sewn.

A machine of this kind is disclosed in US-4,122,787 and is substantially composed of a needle that has a substantially vertical axis and is provided, proximate to its tip, with an open eye and is orientated so that its axis is substantially perpendicular to a supporting surface on which the item being sewn is deposited.

The needle can be actuated with a reciprocating motion along its axis in order to pass cyclically through the item deposited on the supporting surface. Below the supporting surface there is a thread take-up wheel, which is arranged on a plane that is substantially parallel to the axis of the needle and is orientated so that its axis is substantially perpendicular to the axis of the needle. Such wheel is composed of a fixed part, in which there is a magazine for the taken-up thread, and a rotatable part, which can be actuated with a rotary motion about its own axis. The rotatable part of the wheel is mounted coaxially on an actuation shaft, which can be rotationally actuated about its own axis synchronously with the movement of the needle, and has, in a peripheral region, a looper or lower looper which, as a consequence of the rotation of the rotatable part of the wheel and of the movement of the needle, engages the thread carried below the supporting surface by the needle and takes it up, making it pass inside the magazine provided in the fixed part of the wheel.

The machine is completed by thread handling elements, which are located below the supporting surface, and by another looper, or upper looper, which is arranged above the supporting surface laterally to the needle and is adapted to engage the loop of thread carried by the needle above the supporting surface and retain it while it is taken up by the lower looper.

Substantially, this machine works with a draw of thread that is clamped at one of its ends. During a first step of the operating cycle, the needle, threaded with the thread proximate to its clamped end, passes through the item being sewn, carrying a loop of thread below the supporting surface.

Said loop of thread is engaged by the lower looper as a consequence of the rotation of the rotatable part of the wheel, and all the excess thread of the draw is loaded into the magazine located in the fixed part of the wheel and disengaged from the needle, which is extracted above the supporting surface.

After the item being sewn has been advanced by one step, the needle descends again with its eye below the supporting surface and engages the thread, carrying in the subsequent return step a loop of thread above the item being sewn. This loop of thread is engaged by the upper looper and, after the item has been advanced by another step, the needle again passes through the item, carrying a loop of thread below the supporting surface. Said loop of thread is engaged by the lower looper and disengaged from the needle. The lower looper, by continuing its rotation, takes up the portion of thread that lies between the eye of the needle and the free end of the draw, extracting it and reloading it into the magazine of the fixed part of the wheel. In this manner, the machine produces a seam with a single thread composed of stitches that are alternatively visible on the outer side and inner side of the item being sewn, i.e. a seam formed with so-called running stitches.

Over time, this machine has proved to be susceptible of improvements aimed mainly at improving the quality and precision of the seam.

The aim of the present invention is to provide a sewing machine for forming running-stitch seams that ensures highly regular execution of the stitches.

Within this aim, an object of the invention is to provide a sewing machine for forming running-stitch seams that ensures a substantially uniform tension of the thread during the forming of the stitches.

Another object of the invention is to provide a sewing machine for forming running-stitch seams that can use for the seam almost the entire length of the draw of thread, thus allowing to save both time and material.

Another object of the invention is to provide a sewing machine that can be obtained, with modifications that are relatively simple to provide and have a modest cost, from known types of sewing machine for forming running-stitch seams.

This aim and these and other objects that will become better apparent hereinafter are achieved by a sewing machine for forming running-stitch seams, comprising a needle provided, proximate to its tip, with an open eye and orientated so that its axis is substantially perpendicular to a surface for supporting the item being sewn, said needle being actuatable with a reciprocating motion along its own axis in order to pass cyclically through said supporting surface and the item being sewn; a thread take-up wheel being provided below said supporting surface, being arranged on a plane that is substantially parallel to the axis of said needle and being orientated so that its axis is substantially perpendicular to the axis of said needle; said wheel being composed of a fixed part, in which there is a magazine for the taken-up thread, and a rotatable part, which can be rotationally actuated about its own axis; said rotatable part of the wheel being mounted coaxially on an actuation shaft that can be rotationally actuated about its own shaft axis synchronously with the movement of said needle and being provided with a lower looper that can engage the loop of thread carried below said supporting surface by said needle in order to load the thread in said magazine formed in the fixed part of the thread take-up wheel; characterized in that it comprises tensioning means for the pneumatic tensioning of the portion of thread that lies below said supporting surface between the item being sewn and said taken-up thread magazine.

Further characteristics and advantages of the invention will become better apparent from the description of a preferred but not exclusive embodiment of the machine according to the invention, illustrated only by way of non-limitative example in the accompanying drawings, wherein:

• Figure 1 is a front elevation view of some of the elements that compose the machine according to the invention, arranged below the supporting surface of the item being sewn, with the fixed part of the thread take-up wheel shown only partially;
• Figure 2 is a partially sectional enlarged-scale front elevation view, similar to Figure 1, of the fixed part of the thread take-up wheel;
• Figure 3 is a reduced-scale sectional view of Figure 2, taken along the line III-III;
• Figure 4 is an enlarged-scale view of a detail of Figure 3.

With reference to the figures, the machine according to the invention, shown only partially for the sake of simplicity, comprises in a per se known manner a needle 1 that has, proximate to its tip, an eye 2 that is open at the front and is orientated so that its axis 1a is substantially perpendicular to a supporting surface 3 for the item 4 being sewn.

The needle 1 can be actuated with a reciprocating motion along its axis 1a, which is preferably orientated vertically, in order to pass cyclically through the supporting surface 3, which is preferably arranged horizontally.

Below the supporting surface 3 there is a thread take-up wheel, generally designated by the reference numeral 5, which is arranged on a plane that is substantially parallel to the axis 1a of the needle 1 and is orientated so that its axis 5a is substantially perpendicular to the axis 1a of the needle 1.

The wheel 5 is composed of a fixed part 6 and a rotatable part 7, which can be rotationally actuated about the axis 5a. The fixed part 6 of the wheel 5 has a circular contour around the axis 5a, with a discontinuity along its contour. Said discontinuity is located proximate to the working area of the needle 1.

Proximate to the peripheral region of the fixed part 6 of the wheel 5 there is a magazine 8 for the taken-up thread, with an inlet 8a located at one of the ends of the fixed part 6 at said discontinuity.

The rotatable part 7 of the wheel is mounted coaxially on an actuation shaft 10, which can be rotationally actuated about its own axis, which coincides with the axis 5a, synchronously with the movement of the needle 1. The rotatable part 7 supports a looper 11, which constitutes the lower looper of the machine and can engage a portion 12a of the thread 12 that protrudes from the eye 2 along one side of the needle 1 when the thread 12 is carried by the needle 1 below the supporting surface 3 after passing through the item 4 being sewn, which rests on the supporting surface 3.

According to the invention, the sewing machine comprises pneumatic tensioning means for tensioning the portion of thread 12 that lies below the supporting surface 3 between the item 4 being sewn and the magazine 8 for the taken-up thread.

More particularly, the magazine 8 comprises a channel 13, which traces a circular path around the axis 5a and is formed proximate to the perimeter of the fixed part 6 of the wheel 5. Said channel 13 is open at the discontinuity of the fixed part 6 of the wheel 5 and on the lateral surface of said fixed part 6.

The pneumatic tensioning means comprises means for injecting a stream of pressurized air into the channel 13 in a direction that corresponds to the direction in which the thread 12 is loaded into the channel 13 by the lower looper 11.

Preferably, the air injection means comprises an air supply duct 14, which is formed in the fixed part 6 of the wheel 5. Said duct 14, which runs preferably along an arc that is centered on the axis 5a and has a smaller radius than the channel 13, can be connected by means of a connector 15, connected to the fixed part 6, to means for supplying pressurized air, such as for example a pressurized air distribution line or a compressor.

The duct 14 is communicated with the channel 13 through at least one delivery duct 16. The outlet of the delivery duct 16 into the channel 13 is orientated in a delivery direction that corresponds to the direction in which the thread 12 is inserted in the channel 13 by the lower looper 11.

Preferably, multiple delivery ducts 16 are provided which start from the duct 14 and lead into the channel 13, with delivery directions that correspond to the direction in which the thread 12 is inserted in the channel 13 by the lower looper 11.

The channel 13 has, on its side directed toward the axis 5a, a raised portion 17 that partially divides the channel 13 into two contiguous portions: a first portion 13a, which is closer to the rotatable part 7 and is contiguous to the lateral opening 20 of the channel 13, and a second portion 13b, which is located further away from the rotatable part 7. These two portions 13a and 13b are in any case mutually connected so as to allow the thread 12, inserted in the channel 13 through the lateral opening 20 as a consequence of the rotation of the looper 11, to pass from the portion 13a to the portion 13b. The delivery ducts 16 lead into the second part 13b of the channel 13.

The machine is completed by thread handling elements, which are located below the supporting surface 3, and by another looper, or upper looper, which is arranged above the supporting surface 3 laterally to the needle 1 and is meant to engage the thread carried by the needle 1 above the supporting surface 3 and retain it when it is taken up by the lower looper 11, for example as disclosed and illustrated in US-4,122,787 . Said thread handling elements have not been illustrated for the sake of simplicity.

As regards the formation of the stitches, the sewing machine according to the invention operates substantially like the machine disclosed in US-4,122,787 , except that when the thread 12 is loaded into the channel 13, the pressurized air delivered inside said channel 13, through the ducts 16, tensions the thread 12 and this tension is transmitted to the portion of thread that lies between the item 4 being sewn and the channel 13.

Through this tension, abnormal slackening of the thread 12 is avoided and the stitches are more regular.

Furthermore, thanks to the tensioning of the thread 12, the machine according to the invention can use, for sewing, almost the entire length of the draw of thread, thus reducing the number of draws required to form a seam and also reducing the sewing time and the amount of thread that is required.

It should also be noted that the pneumatic tensioning of the thread 12 facilitates its arrangement within the portion 13a while it is loaded in the fixed part 6 by the rotatable part 7 and its arrangement inside the portion 13b while it is extracted from the fixed part 5. In this manner one avoids interference between the portion of thread 12 that enters the magazine 8 and the portion of thread 12 that exits from the magazine 8.

In practice it has been found that the sewing machine according to the invention fully achieves the intended aim and objects, since it ensures high regularity in the formation of the stitches by way of the pneumatic tensioning of the sewing thread.

The sewing machine thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims; all the details may further be replaced with other technically equivalent elements.

In practice, the materials used, as well as the dimensions, may be any according to requirements and to the state of the art.

Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.