THREAD TENSIONING DEVICE FOR SEWING MACHINES AND SEWING

MACHINE COMPRISING A THREAD TENSIONING DEVICE

Specification

The present invention relates generally to a thread tensioning device for sewing machines and to a sewing machine comprising one or more thread tensioning devices. More particularly, it relates to a thread tensioning device, and to a related sewing machine, which allows the tension of a sewing thread to be adjusted conveniently and quickly.

As is well known, sewing machines have one or more thread tensioning devices to keep the thread taut so that an optimal seam is achieved.

In addition to electric thread tensioners, which are generally very bulky, the most commonly used thread tensioning devices consist of two discs between which the thread passes, which are spring-loaded and spring-loaded.

The spring's spring coefficient is adjusted by means of an adjusting screw around which the spring itself is arranged.

As the screw is tightened, the length of the spring is decreased, increasing the pressure of the spring itself on one of the two discs on which it stops.

In order to free the thread between the two discs, the known technique provides a few solutions.

A first method involves inserting a sort of wedge between the two discs in order to separate them and let the thread pass through.

A second method involves the arrangement of a plate, interposed between the second disc and the spring on which the same plate goes. This plate is controlled by an actuator or pneumatic cylinder. When the thread must be free to move and thus pass between the two discs, the plate is moved, pushing the spring away from the two discs, which are then free to move away from each other.

These modes therefore only provide the possibility of releasing the two discs to let the thread pass through. The thread is clamped solely by the spring, the tension of which can be altered by turning the adjustment screw.

This adjustment, as well as taking time, cannot, however, be done continuously and especially during a sewing cycle.

Furthermore, there may be cases where the spring tension is not sufficient to keep the thread locked.

There are, in fact, cases in which it is desirable for the thread to be well tensioned, for example in the case of sewing by means of mechanical devices.

It is an object of the present invention to provide a thread tensioning device for sewing machines and a sewing machine with such a device, which overcomes the problems of the known technique.

A further scope of the invention is to provide a thread tensioning device for adjusting the tension of a sewing thread conveniently and quickly.

A further purpose of the invention is to provide a thread tensioning device which allows the thread clamping tension to be decreased or increased according to different operational requirements.

These and other purposes are achieved, according to the invention, by a thread tensioning device for sewing machines capable of adjusting the tension of a sewing thread F.

The thread tensioning device comprises:

- a pin attached to a block;

- a first disc arranged around the pin and having a first face and a second face which are opposite to each other; - a second disc arranged around the pin, having a first face and a second face which are opposite to each other, and capable of engaging with its first face on the second face of the first disc;

- a plate having a first face and a second face opposite to each other, and capable of engaging with its first face on the second face of the second disc;

- half-pressure plates capable, at rest, of placing the plate under pressure on the second disc, so as to place the second disc under pressure on the first disc;

- a first actuator with a movable rod, capable of engaging the first face of the disc, so as to be able to move the disc away from the second disc by actuating said first actuator.

Thanks to this configuration, the thread F, being arranged between the first disc and the second disc, is kept in tension when the thread tensioning device is in the working configuration, i.e. the plate is under pressure on the second disc.

When the first actuator is actuated, its stem pushes the plate away from the second disc. In this way, the first disc and the second disc are not pressurised against each other and the thread F is free to move.

In particular, the thread tensioning device according to the invention is characterised in that it comprises at least one second actuator with a respective second rod having its free end in contact with the first face of the first disc.

When said second actuator is actuated, the first disc is further placed under pressure on the second disc, increasing the pressure between the two discs and holding the thread F with greater force.

Advantageously, the thread tensioning device may comprise a third actuator with a respective third rod having its free end against the first face of the first disc.

Thus, through the action of the second actuator and the third actuator, it is possible to move the first disc in a desired direction.

Advantageously, in order to guide the first disc in a direction parallel to the pin, the second actuator and the third actuator can move in synchronism.

Furthermore, the stem of the first actuator can be coaxial to the pivot, so that the plate can be moved smoothly.

In particular, for this purpose, a cavity can be cut into the pin in which the stem of the first actuator is accommodated.

The plate may comprise a bridging element arranged in the cavity and capable of being pressurised by the stem of the first actuator. In this way, the displacement of the plate is defined according to the direction of development of the cavity.

Advantageously, the pressurising means acting on the disc may comprise a spring comprising a first end against the second face of the disc and a second end against a nut screwed onto a threaded end of the stud.

Due to the presence of the spring, the plate is abutting the second disc.

Alternatively, the half-pressure plates acting on the plate can comprise a fourth actuator with a pressure rod on the second face of the plate. In this way, the pressure of the plate on the second disc can be varied by varying the action of this fourth actuator.

The purposes and advantages of the invention are also achieved by a sewing machine characterised by comprising at least two thread tensioning devices as defined above.

In particular, the two or more thread tensioning devices in the sewing machine according to the invention can be controlled synchronously or independently of each other, as required. Further features and details will be better understood from the following description, given by way of non-limiting example, as well as from the accompanying drawing plates in which: figure 1 is a sectional side view of a thread tensioning device, according to the invention, of a sewing machine, when said thread tensioning device is in the working configuration;

Figure 2 is an axonometric view of some components of the thread tensioning device of figure 1 ; figures 3 and 4 are cross-sectional side views of the thread tensioning device according to figure 1 , when it is in the open and closed configuration respectively.

With reference to the appended figures, a thread tensioning device 10 is referred to as a whole, according to the invention, for sewing machines.

The thread tensioner device 10 comprises a pin 12 fixed on a block 11 and around which are arranged a first disc 14 and a second disc 16 between which a thread F can pass.

In particular, as illustrated in figure 2, the pin 12 comprises two longitudinal elements 13 separated from each other by a gap 15 and connected to the base by a perforated cylindrical support 17.

Adjacent to the second disc 16 there is also arranged a plate 18 crossed by the two longitudinal elements 13 and on which the first end of a spring 20 is abutted.

The plate 18, as shown in Figure 2, comprises a bridging element 19 arranged in the gap 15 between the two longitudinal elements 13.

The opposite end of the spring 20 is in contact with a nut 22 which can be screwed onto the upper threaded end of the pin 12, i.e. of the two longitudinal elements 13.

Screwing nut 22 onto the threaded upper end increases the tension of spring 20, increasing the pressure on plate 18 and thus also between the first disc 14 and the second disc 16.

The thread F is thus more tightly clamped between the two discs 14, 16.

A first pneumatic actuator 24 is arranged in the block 11 in which a first piston 26 joined to a first rod 28 can move.

The first rod 28 passes through the drilled cylindrical support 17, arranging itself in the gap 15 between the two longitudinal elements 13 and goes into contact with the bridge element 19 of the plate 18.

In this way, the first actuator 24 can push the plate 18.

Also arranged in the block 11 are a second pneumatic actuator 30 and a third pneumatic actuator 32, arranged more externally than the first actuator 24 which is coaxial to the pin 12.

The second actuator 30 comprises a corresponding second piston 34 joined to a second piston rod 36.

The third actuator 32 includes a corresponding third piston 38 joined to a third rod 40.

The second piston rod 36 and the third piston rod 40 are abutting the first disc 14.

A cylindrical element 42 is, in addition, fixed to the block 11 which can be accommodated in the cavity 44 formed in the first disc 14 and in the second disc 16, so as to prevent undesired rotation thereof.

The thread tensioning device 10 according to the invention is thus capable of varying the tension on the thread F as required.

Firstly, the pressure between the first disc 14 and the second disc 16 can be adjusted by screwing or unscrewing the nut 22 on the upper threaded end of the pin 12.

Furthermore, according to what is illustrated in figure 3, the thread tensioning device 10 provides that, when it is necessary to decrease the tension on the thread F, the first actuator 24 is activated, so as to raise the first rod 28 which, pushing on the bridge element 19, moves the plate 18 away from the second disc 16.

According to this configuration, the first disc 14 and the second disc 16 are free to move on the pin 12, even moving away from each other to leave the thread F free to move.

This configuration is particularly useful, for example, in the case of using an electric stitching system, when it is necessary for the thread to remain tension- free, in practice free from brakes. This is, in fact, the moment when the needles are high and the auxiliary conveyor moves the fabric to which the threads are still attached. If the threads are free of tension, the fabric is transported better and it is possible to cut one or more threads more comfortably.

Furthermore, as illustrated in figure 4, the thread tensioning device 10 is able to increase the tension beyond what is already possible by tightening the nut 22. In fact, it is possible to activate the second actuator 30 and the third actuator 32 which, through their respective stems 36, 40, push the first disc 14 against the second disc 16 and the plate 18, which is also pushed, but in the opposite direction, by the spring 20.

In this case, the thread F is clamped with greater pressure than the simple action of the spring 20 as described above and illustrated in figure 1 .

Such a configuration is useful in the case of a mechanical unravelling of the fabric, when the opening of the loop is to be prevented with certainty, making the formation of the stitch almost impossible.

It should also be noted that a sewing machine may comprise more than one thread tensioning device to control the tensioning of several threads, e.g. four devices. Such thread tensioning devices may be controlled synchronously or may be independent of each other.

Variants are provided which are to be considered included in the scope of protection of the present invention.

For example, a thread tensioning device may comprise a single actuator for increasing tension on the thread F. In this case, the stem of this single actuator acts on a first disc capable of translating, without tilting, on a central pivot.

Furthermore, the means of moving the two discs or the plate can be not only pneumatic actuators, but also devices of a different type.

Again, as an alternative to the spring or other elastic means fixed by the position of the nut, a thread tensioning device may comprise an additional actuator acting directly on the plate adjacent to the second disc. In this way, it is possible to vary the pressure of the plate on the second disc by acting on this actuator.