EP3725929B1

EP3725929B1 - Industrial sewing machine

Info

Publication number: EP3725929B1
Application number: EP20169729.9A
Authority: EP
Inventors: Dario MORANDIN
Original assignee: TorMec Ambrosi SRL
Current assignee: TorMec Ambrosi SRL
Priority date: 2019-04-16
Filing date: 2020-04-15
Publication date: 2021-11-17
Anticipated expiration: 2040-04-15
Also published as: EP3725929A1; IT201900005890A1

Description

TECHNICAL FIELD

The present invention relates to an auxiliary device for controlling the upper sewing yarn, which intervenes during the formation of a double chain stitch, for reverse arm industrial sewing machines.
More in particular, the present invention relates to an auxiliary device applicable to a reverse arm industrial sewing machine, which comprises an assembly for the mechanical control of the formation of the stitch and the tension of the upper sewing yarns, where such auxiliary device works in synergy with an original mechanical thread tensioning device applied to the needle bar.
This auxiliary device is displaced dynamically between a work position and a rest position, on the basis of the work phases of the sewing machine on which it is installed.
The auxiliary device is further provided internally with a dynamic control assembly for controlling the tension of the upper sewing yarns during the formation of the stitch.
The auxiliary device is advantageously applied and used in the sector of industrial sewing machines of the reverse arm type.

PRIOR ART

It is known that sewing machines operate the mechanical sewing of particular types of superposed fabric in order to obtain items of clothing or even other products of various kinds, e.g. those used in upholstery, curtains and the like, and they are made according to different construction techniques for the purpose of the different operations that they must perform.
Sewing machines, including industrial ones, in their most common construction, comprise an upper head in which the needle is arranged, which moves alternatively with respect to the work surface, a fabric advancement system and below which the means is arranged that contributes to the formation of the sewing stitch.
In the specific case in which the device according to the invention is applied, for the stitch class 400 or 401, a looper is provided into which the lower sewing yarn is threaded.
Class 400 stitches are formed by two or more sewing yarns, coming from spools external to the machine.
The seam has a front (upper) and back side (lower) with the consequent constraints on the positioning of the details for the seam.
Class 400 stitches have an excellent hold on the item of clothing and their formation takes place every two penetrations of the needle.
Another similar stitch to the class 400 one is the class 401 one, which is formed by the linking of two sewing yarns, an upper one carried by the needle and the lower one by a looper, where both threads come from spools.
As the 401 stitch is also formed every two penetrations of the needle, the closure of the stitch and therefore the formation of the quality of the seam itself is performed during the second penetration.
Consequently, in order to obtain the desired quality it is important to adjust the tension and the mechanical control of the upper sewing yarn, which must be compared to the tension applied to the lower sewing yarn.
According to the prior art it is envisaged that in the first step, with the first penetration of the needle into the material, the upper sewing yarn is wound around the lower looper.
In the second step, with the second penetration of the needle into the material, the upper sewing yarn is dropped from the looper.
Currently, with reference to Figures 8 and 9, the devices of the state of the art envisage that the adjustment of the tension of the upper sewing yarn is obtained by using mechanical devices 11, comprising two discs placed in mutual contrast with an upper compression spring and an adjustment nut into which the upper sewing yarn passes.
Still with reference to figures 8 and 9 the control of the upper sewing yarn, during the formation of the stitch, is performed by means of a mechanical thread tensioning device and a series of thread guides, one of which is indicated by number 15, which normally comprise a rigid plate provided with holes crossed by sewing yarns that come from the sewing members.
The mechanical thread tensioning device and the thread guides are not adapted to dynamically compensate for the different tensions of the upper sewing yarns in the steps of penetration of the needle into the material, as the material in the same sewing cycle can have different processing thicknesses, with the result that such traditional processing causes the formation of stitches with a tension that may be:

too high causing the upper sewing yarns to break, and increasing the tension of the thread with respect to the fabric;
too loose causing the formation of knots on the lower part of the material.

If the knots emerge from the fabric and are formed by an upper sewing yarn, they create thicknesses that can cause irritation to the skin of whoever wears the item of clothing sewn with traditional methods, with all the negative consequences.
Normally, to obtain seams with the traditional method the knot formed by the upper sewing yarn with the lower one must be buried or hidden inside the material to be sewn.
To bring the upper sewing yarn into the material, the current technique teaches increasing the tension applied to the upper sewing yarn, and using further mechanical devices directly connected to the mechanical movement provided by the sewing head.
The increased tension given to the upper sewing yarn, during the advancement movement of the material, implies adding further tension to the transported material, and this is noted further in the case of light or very elastic materials.
It follows that this tension of the upper sewing yarns during sewing limits the extension of the sewn materials and/or causes creases/ripples on the surface, which jeopardise the quality of the seam itself.
The use of this method has therefore been shown to be unsuited to quality seams with the use of elasticated materials.
Document DE 102008016774 A1 discloses a sewing machine including a coupling mechanism with a regulation section. This is moved in correspondence with vertical movement of a pressure rod, which is mounted on the machine body for vertical reciprocation. A thread guide lies on the thread path from the spool to the thread puller. A coupling mechanism couples the thread guide with the pressure rod, such that the thread guide is pushed by the regulation section in a first or a second, opposite direction.
Document DE 102009048794 A1 discloses a device having a thread release-electromagnet arranged on a rear side of a base plate and provided with a movement pin that is pressed against a thread release plate. A thread tension-primary control device is arranged on the base plate and has a support pin. The support pin is pressed against the thread release plate for tension release of the primary control device during operation of the thread release-electromagnet. A thread tension-secondary control device is arranged on the base plate. A thread drawing-electromagnet is provided on a side of the base plate.
Document JP 2019017666 A discloses a sewing machine in which the shape of a loop of a thread is maintained even when a looper is miniaturized, and which can execute single chain stitches smoothly. The sewing machine includes a balance for supplying a thread to a sewing needle, a needle bar reciprocating in a direction orthogonal to a predetermined plane by holding the sewing needle a needle plate having a pinhole through which the sewing needle can pass, and for supporting a sewing object a looper rotating around a rotation axis in a predetermined plane, and for scraping the thread from the sewing needle which has passed through the sewing object and the pinhole and a thread tension device for imparting a tensile force to the thread between the balance and the needle bar.
A further example of thread tensioning in sewing machines is disclosed in JPS 53111858 A .

DESCRIPTION OF THE INVENTION

The present invention proposes to provide an industrial sewing machine of the reverse arm type, comprising an auxiliary device for the mechanical control of the formation of the stitch and the tension of the upper sewing yarns, where such device works in synergy with the original thread tensioning device applied to the needle bar.
This auxiliary device comprises mechanical components crossed by the sewing yarns which are displaced dynamically between a work position and a rest position, where these two positions are determined on the basis of where the sewing cycle is performed, on the material in the "work" condition or outside the material in the "rest" condition.
Such auxiliary device according to the invention for the mechanical control of the formation of the stitch and the tension of the upper sewing yarns, internally has a dynamic control of the tension of the upper sewing yarns during the formation of the stitch, and therefore is able to eliminate or at least reduce all the drawbacks highlighted above.
The auxiliary device according to the invention is made to guarantee the loosening of the tension of the upper sewing yarn, through an adjustment performed using the upper double discs in the opposite way with respect to the current technique in use but, at the same time, thanks to the mechanical control exerted during the formation of the stitch and the dynamic tension system of the upper sewing yarn, it allows an ideal type 401 seam to be obtained, formed visually only by the lower flat chain, without the presence of knots, and very elastic as during the formation of the stitch the upper sewing yarn does not transfer any tension to the material being sewn.
The invention in particular makes use of an auxiliary device, to be positioned on the upper sewing head, which works in synergy with the original thread tensioning device of the machine.
This auxiliary device is composed of a main support onto which two thread guide assemblies are fixed, an upper one and a lower one, said thread guide assemblies being placed on two different levels, with the interposition between the two lower thread guide assemblies of a flexible element whose position/inclination can be adjusted independently through its block fixed to the main support.
The main support of the auxiliary device is automatically arranged between two positions, one defined as an active work position and the other a rest position. The arrangement of these two mechanical positions is performed by means of a pneumatic cylinder.
The operation of the auxiliary device and the characteristics are described in claim 1.
The dependent claims outline advantageous embodiments of the invention.
One of the advantages offered by the auxiliary device according to the invention is that of allowing the formation of a sewing stitch with minimum tension between the two sewing yarns, and at the same time with an optimal formation of the chain, as the sewing is performed inside or outside the material to be sewn, obtaining a result that is impossible without such auxiliary device.
A further advantage proposed by the invention is that of being able to maintain the seam flat to touch and very elastic, also allowing elasticated materials to be sewn.
Using the auxiliary device according to the invention it is also possible to hide the connection knot between the two sewing yarns within the material and therefore simulate the effect of sewing stitch 301, the lock stitch, and therefore increase the resistance of the double chain seam also to heavy duty washing.
The auxiliary device according to the invention is formed by a system with an upper thread guide and two lower thread guides, placed on two different mechanical levels with respect to the main support.
The upper thread guide with respect to the original thread tensioning device of the machine is adjustable in its work or rest position based on the type of seam performed (whether the sewing machine is sewing inside or outside the sewing material).
The pair of lower thread guides assumes a fixed position with respect to the main support and the distance between them is also fixed.
Between the two lower thread guides an elastic element is positioned for controlling the tension of the upper sewing yarns.
This elastic element is fixed to a block thereof which has the possibility to change the work position and/or angle with respect to the support thereof.
The main support of the thread guide is fixed to a stem of the pneumatic cylinder. This pneumatic cylinder enables the device to operate between a work position and a rest position, in order to make the auxiliary device for controlling the compensation stitch formation intervene when necessary.

ILLUSTRATION OF THE DRAWINGS

Further characteristics and advantages of the invention will become apparent from reading the following description of an embodiment of the invention provided by way of non-limiting example, with the aid of the figures illustrated in the appended tables of drawings, in which:

figure 1 represents a front schematic view of an industrial sewing machine according to the invention as a whole, comprising the original thread tensioning device with the auxiliary device applied in the rest position;
figure 2 illustrates a perspective schematic view of an industrial sewing machine according to the invention as a whole, comprising the original thread tensioning device with the auxiliary device applied in the work position;

figures 3 and 4 represent perspective schematic views of an auxiliary device for controlling the upper sewing yarn according to the invention arranged raised during the work step and lowered during the rest or work break step, respectively;
figure 5 is a detailed schematic view of the auxiliary device for controlling the upper sewing yarn according to the invention arranged in the work position;
figure 6 is an even more detailed schematic view of the auxiliary device for controlling the upper sewing yarn according to the invention arranged in the work position;
figure 7 illustrates an exploded schematic view of the components of the auxiliary device for controlling the upper sewing yarn according to the invention arranged in the work position;
figures 8 and 9 represent schematic views inherent to the state of the art comprising thread guide devices of the traditional type.

DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

Initially with reference to figures 1 and 2, an industrial sewing machine according to the invention, indicated as a whole with reference sign 10, is of the reverse arm type and is made using some components of the traditional type with which the devices according to the invention are associated, which compose the new sewing yarn guide and traction system.
The industrial sewing machine according to the invention of the reverse arm type comprises some traditional components, such as:

an assembly 11 for adjusting the tension of the upper sewing yarn obtained using mechanical devices represented by two discs into which the upper sewing yarn passes. A pressure spring pushes the upper disc onto the lower one; in this case there are three systems that supply three upper sewing yarns that are made to reach an
upper head 12 which has a mechanical thread tensioning device 13 for controlling the upper sewing yarn;
an advancement system 14 for advancing the fabric on a work surface below which a looper means is arranged not represented as it is known per se, which controls the lower sewing yarn which, together with the needle, contributes to the formation of a sewing stitch 401.

The members that move the needle and the original thread tensioning device are placed in the upper head and comprise a shaft connected to a motor, the rotation of which is converted, through eccentric, into alternating rectilinear motion, which is transferred to a needle holder support bar.
Between the assembly 11 for controlling the tension of the upper sewing yarn and the upper original thread tensioning device 13, a thread tensioning device is normally arranged which, as can be seen in figures 8 and 9, which refer to the state of the art, is represented, according to the traditional solutions, by a rigid plate 15, which works physically on a predefined position, even if it is slightly adjustable.
The traditional rigid plate 15 is provided with holes through which the threads are made to pass which reach the original thread tensioning device 13 and then the sewing needle of the upper head. It is therefore a solution that envisages a very distant position from the original thread tensioning device and a minimum very rigid adjustment during the formation of the stitch, as highlighted in the introduction with all the operating limits already mentioned.
According to the invention shown in figure 1 and in the finer details of figures 3 to 6, between the assembly 11 for adjusting the tension of the upper sewing yarn and the original mechanical thread tensioning device 13, an auxiliary device 16 for controlling the formation of the stitch and for compensating the tension of the upper sewing yarn is applied to the machine body, which passes between the two lower thread guides.
As represented in figure 5 and in the detail of figure 6, said auxiliary upper sewing yarn tension compensation device 16 comprises a plate 17 fixed parallel to a projection 18 being orthogonal with respect to the front surface of the machine, which is provided, in the upper end 17' thereof, with a first group of holes 19 and an appendage 20, arranged parallel to the plate 17, and in turn provided with a second group of holes 21 arranged in alignment with said first group of holes 19.
The holes 19 and 21 are crossed by the upper sewing yarns and represent the lower thread guides thereof.
Between said plate 17 provided with the first group of holes 19 and said appendage 20 provided with said second group of holes 21, there is an elastic compensation element represented by a flexible element 22, which has an elongated conformation, and is supported at the centre by a pin 23, with a preferably cylindrical section which, in this embodiment, can be represented by a spring.
According to the embodiment represented in figure 7 in an exploded view, it can be noted that said plate 17 is provided in the upper end 17' thereof of said first group of holes 19 and an appendage 20, arranged parallel to the plate 17, and in turn provided with a second group of holes 21 arranged in alignment with said first group of holes 19.
In the same figure 7 said elastic compensation element is represented by the elongated flexible element 22 which, in its central part, has a bunching supported by said pin 23 that causes a certain flexibility between the two half-parts that make up the body of the flexible element 22.
More precisely, the half-part 22' turned towards the outside of the machine is inserted into a fixed part inside a block 24, while the opposite half-part 22" is free and able to intercept the path of the threads that pass through the holes 19 and 21 of the lower thread guides.
From the operating point of view, as represented in figure 6, the threads 25 coming from the assemblies 11 for adjusting the tension of the upper sewing yarn are introduced by the operator through the first group of holes 19 of the plate 17, then made to pass above the flexible element 22, in particular at the free half-part 22" and then through the second group of holes 21 present on the said appendage 20.
The sewing yarns at the exit from the holes 21 of the lower thread guide 20, are channelled through further holes 26 afforded on an appendage 27 of the upper thread guide which is placed on an extension 28 of the plate 17, in a position such as to reach the original thread tensioning device 13 positioned on the upper sewing head 12.
Furthermore, the extension 28 of the plate 17 is hinged onto a pin 29 and can rotate angularly through the intervention of a pneumatic cylinder (not shown in the figures) whose stem acts on another pin located in the lower part of the extension 28.
As can be noted, the passage of the threads 25 through the holes 19 and 21 while they are made to pass over the flexible elements 22, causes the ideal condition so that the threads themselves are always maintained in a controlled and compensated work tension, i.e. an ideal condition to obtain maximum quality sewing stitches, as the compensation assembly of the flexible element 22 causes the loosening or stiffening of the threads according to the operating conditions.
According to the invention, it is possible to adjust the position of the flexible element 22.
The flexible element 22 between the two lower thread guides has its working point adjustable to allow the auxiliary device to always find the perfect balance thereof between two sewing yarn construction factors, the elongation factor (elasticity) of the sewing yarn itself and the breaking load of the sewing yarn.
Furthermore, the working point of the upper thread guide 27 is variable as a function of the type of seam that the machine is to perform, whether it is inside or outside the material to be sewn. Such variability is caused by the pneumatic cylinder which acts on the extension 28 bearing the thread guide 26.
When the upper sewing yarn is dropped from the looper, i.e. during the second penetration into the formation of a sewing stitch 401, it is necessary to mechanically pull the upper sewing yarn in order to tighten as much as possible the knot formed between the upper and the lower sewing yarn, through the intervention of the pneumatic cylinder.
Definitively, to tighten the knot a mechanical leverage is created between three points, defined by a triangle in figure 5, instead of between the two original points, where the three specific points are thus defined:

a first vertex A corresponding to the upper position (in height) of the original thread tensioning device 13 of the needle bar;
a second vertex B corresponding to the position of the upper thread guide 27;
a third vertex C corresponding to the position of the left appendage 20 of the pair of lower thread guides placed at the flexible element 22.

As can be noted, the ideal condition for controlling the formation of the stitch is that the upper thread guide 27 is placed close to the original thread tensioning device 13.
In fact, the working stitch of the upper thread guide 27 is positioned on the right-hand side of the original thread tensioning device 13.
The mechanical compensation device according to the invention works in combination with the flexible element 22 for compensating for any differences in tension of the upper sewing yarn 26, which are due to the type of sewing yarn used (size and elasticity of the fibres) and the thickness of the material.
When it is in the working position, the upper thread guide 27 is normally almost aligned with the original thread tensioning device 13 present in the sewing machine, when the latter, during its oscillatory movement, is positioned in the upper apex point thereof.
In summary, the device according to the invention envisages the use of:

an upper thread guide 27, which works in synergy with the original thread tensioning device 13 present in the upper sewing head 12;
a pair of lower thread guides 19 and 21 that work in synergy with the fixed thread tensioner and have a flexible element 22 positioned inside them;
an elastically oscillating flexible element 22 for dynamically controlling the tension of the upper sewing yarns during the formation of the stitch and adjustable in the work position thereof, with respect to the pair of thread guides at the sides thereof;
a pneumatic cylinder, combined with a respective device holding support.

In turn, the original thread tensioning device allows the entire auxiliary device to be moved between two positions:

a work position, when the sewing machine performs a seam on the material;
a rest position, when the sewing machine performs a seam outside the material.

The auxiliary device according to the invention definitively enables the sewing machine to obtain a double chain seam, with stitch 400 or 401, having all the optimal characteristics required.
When the auxiliary device is in the work position, it has the cylinder extended (figure 3), the chain formed by the lower sewing yarn has a visual appearance with a very wide loop, and to touch it is soft and flat as there are no knots formed by the upper sewing yarn.
The loop of the chain is arranged on the back side of the material.
By placing in tension the seam performed on the material it is possible to note how every single loop of the chain is closed, thus contributing to making the seam very elastic.
When the device is in the rest position (figure 4) the cylinder is retracted to allow the formation of the double chain seam when the machine operates outside the material.
Without this movement of the device, it would not be possible to perform the formation of the stitch as the upper sewing yarn would not allow the formation of the stitch while the sewing machine is operating outside the material.
The advantage of creating a "triangle" displayed in figure 5, with the upper sewing yarn is to have a mechanical "lever" that at the appropriate moment physically pulls the upper sewing yarn upwards when this upper sewing yarn is released from the looper.
It is possible to note that, during the mentioned second step of the formation of the stitch, i.e. when the upper sewing yarn is dropped off the looper, thanks to the "triangle" displayed in figure 5 a different type of mechanical tension applied to the upper sewing yarn is automatically set.
To obtain the correct formation of the stitch it is necessary to form with the upper sewing yarn two straight lines similar to a tip of a triangle, the vertex of which corresponds, indicatively, to the top dead centre of the stroke of the original thread tensioning device 13 and a distance of about 10/15 mm.
With this system there is the advantage that through this mechanical action on the upper sewing yarn the "knot" is pulled into the material to be sewn, hiding it inside the fibres of the material itself.
Furthermore, the flexible element placed in the auxiliary device, between the two lower threads, prevents any excessive tension being created during the mechanical action which potentially could break the upper sewing yarn.
Such flexible element is able to work with a different mechanical stroke on the basis of the length of the stitch performed by the sewing assembly and by the tension and elasticity of the yarn during use.
As already mentioned above, the advantages of the auxiliary device are therefore those related to the possibility to form the sewing stitch with minimum tension between the two sewing yarns, which can only happen using the flexible element 22 according to the invention.
A further advantage is offered by the possibility to maintain a flat and very elastic seam, also allowing elasticated materials to be sewn.
However, using the flexible element according to the invention it is possible to make the lower sewing yarn penetrate into the material, hide the connection knot between the two sewing yarns and therefore, in washing, increase the resistance of the seam.

Claims

An industrial sewing machine (10) formed by a machine body of the reverse arm type, comprising:
• a spool assembly (11) for feeding upper sewing yarns (25),

• an upper head (12) in which a sewing needle with the movement members thereof and an original thread tensioning device (13) are arranged,

• an advancement system (14) for advancing a fabric on a work surface below which a looper means is arranged which, together with the sewing needle, contributes to the formation of a sewing stitch,

whereby between said spool assembly (11) and said upper head (12) in which the sewing needle is arranged, an auxiliary device (16) for the dynamic compensation of the sewing yarn tension is applied to the machine body, the auxiliary device having at least two positions for controlling the formation of the sewing stitch and compensating for the tension of said upper sewing yarns (25), said auxiliary device (16) comprising lower thread guides (17', 20) between which at least one flexible element (22) is interposed for compensating for the tension of the threads and an upper thread guide (27), whereby said auxiliary device (16) can be adjusted angularly on a pin (29) to bring said upper thread guide (27) from a work position to a rest position through a pneumatic cylinder,

characterised in that said auxiliary device (16) comprises a support means (17, 18) whose upper end (17'), which represents the first lower thread guide, is provided with a first group of holes (19) and an appendage (20), which represents the second lower thread guide, arranged parallel to the support plate (17) and in turn provided with a second group of holes (21) arranged in alignment with the said first group of holes (19).
The industrial sewing machine (10) according to claim 1, characterised in that said flexible element (22) is elongated and arranged transversally with respect to the advancement of the sewing yarn between said first group of holes (19) and said second group of holes (21).
The industrial sewing machine (10) according to claim 2, characterised in that said elongated flexible element (22) has a partially cylindrical section, comprising a spring (23).
The industrial sewing machine (10) according to any one of claims 2-3, characterised in that said elongated flexible element (22) is arranged symmetrically in a raised position with respect to said first (19) and second (21) group of holes so that the sewing yarn can perform a substantially reverse V-shaped path, such as to allow said elongated flexible element (22) to exert on the sewing yarn itself respective elastic slackenings or tensionings controlled according to a sewing step.
The industrial sewing machine (10) according to claim 1, characterised in that said lower thread guides (17', 20) are located on a support plate (17) and are connected to said upper thread guide (27) through an extension (28) of said support plate (17), and in that said upper thread guide (27) is located close to the original thread tensioning device (13) placed on the upper head (12).
The industrial sewing machine (10) according to claim 5, characterised in that said support plate (17) comprising the extension (28) is hinged onto the pin (29) for rotating angularly through the intervention of said pneumatic cylinder whose stem acts on another pin located in the extension (28), to bring said upper thread guide (27) from the work position to the rest position.
The industrial sewing machine (10) according to any one of the preceding claims characterised in that said auxiliary device (16) forms a mechanical leverage between three points, defined by a triangle (33), thus defined:
• a first vertex (A) corresponding to an upper position, in height, of the original thread tensioning device (13) of the needle bar;

• a second vertex (B) corresponding to a position of the upper thread guide (27);

• a third vertex (C)corresponding to the lower thread guide of the pair of lower thread guides (17', 20) placed at the elongated flexible element (22).