EP3653771A1

EP3653771A1 - Sewing machine for making seams in a programmed, measured and controlled way

Info

Publication number: EP3653771A1
Application number: EP19205638.0A
Authority: EP
Inventors: Bruno Mancini
Original assignee: Derim Srl
Current assignee: Derim Srl
Priority date: 2018-11-14
Filing date: 2019-10-28
Publication date: 2020-05-20
Also published as: JP2020081859A; CN111188131A; TW202024423A

Abstract

Sewing machine (100) for making seams on fabrics (11, 12, 13, 14) in a programmed, measured and controlled way; the sewing machine (100) of the invention provides for easily and accurately sewing fabrics (11, 12, 13, 14) with edges with a different radius of curvature, making very accurate seams, wherein the stitch pitch coincides with a preset pitch; the sewing machine (100) comprises: a needle (A), a claw, a blocking unit (4, 41) that firmly blocks the fabrics (11, 12, 13, 14) in the vicinity of the place where the needle (A) makes the seam, a dragging assembly (2) suitable for dragging the fabrics (11, 12, 13, 14) along a work surface (PL), a clamp (3) that is integral with the dragging assembly (2), and a detector (R) to detect the length between two adjacent stitches, in such a way to measure and check the accuracy of the seam made by the needle (A).

Description

The present patent application for industrial invention relates to a sewing machine used for making seams between two or more fabrics in a programmed, measured and controlled way.
In this patent, the expression "programmed seam" refers to a seam with a trajectory that is partially programmed before the sewing machine actually makes the seam. The programming of the seam refers to the single pitch between consecutive stitches and also to the trajectory of the seam.
The present invention relates to the field of sewing machines, which are a mechanical or electro-mechanical apparatus used to join fabrics, leather, or cloth materials with a seam, by passing one or more threads made of cotton or other materials by means of one or more needles that make alternate oscillations from up downwards.
The inventive idea of the present invention is the result of a necessity that is experienced in several applications in which at least two fabrics are to be sewn, the seam is to be made along a programmed trajectory and a constant pitch is to be maintained for the entire trajectory.
In particular, such a necessity is encountered when sewing the fabrics that are used for the upholstery of car seats.
As it is known, for the safety of car drivers and passengers, motor vehicles are to be provided with an airbag that can be contained inside a seat.
Fig. 2 shows four fabrics used as upholstery of a car seat, comprising an internal airbag.
As shown in Fig. 2, the upholstery of a seat comprises a first fabric (11), which is used to cover a backrest of the seat, and a second fabric (12) with U-shape, which is used to cover the side of the seat.
Still with reference to Fig. 2, the edges of the first fabric (11) and of the second fabric (12) have a different radius of curvature, in such a way that, when they are joined with a seam that runs in parallel direction to the edges of both fabrics, the second fabric (12) has a curving portion that permits its correct positioning on the side of the seat.
Moreover, it must be noted that, after being sewn on said first fabric (11), the second fabric (12) is folded over along the edge of the seam in such a way to cover the seam.
Still with reference to Fig. 2, the upholstery of the seat comprises a third fabric (13) and a fourth fabric (14).
The third fabric (13) is presewn on said second fabric (12), whereas said fourth fabric (14) is presewn on said first fabric (11).
The third fabric (13) and the fourth fabric (14) are positioned in such a way that, after folding over the second fabric (12) along the edge of the seam, the third fabric (13) and the fourth fabric (14) are disposed side-by-side.
More precisely, the third fabric (13) and the fourth fabric (14) are sewn in such a way not to be visible when said upholstery is applied on said seat.
Said third fabric and fourth fabric (14) act as housing and/or support for said airbag. In order to be ejected in case of an accident, the airbag must break the portion of the seam where said third fabric (13) and said fourth fabric (14) are sewn.
In view of the above, the seam of such a portion must withstand the stress in normal conditions and guarantee at the same time the free ejection of the airbag in case of an accident.
In such a portion, the seam must be made in a very accurate way and must have an exact number of stitches that is programmed in advance, with a programmed stitch pitch.
The sewing machines of the prior art comprise at least one electric motor actuated by means of an actuation control that in the majority of the sewing machines consists in a pedal pressed by the operator with his or her foot.
A sewing machine of the prior art comprises an operating station with a work surface where the fabrics to be sewn are positioned.
The sewing machine of the prior art comprises a sewing head disposed above the work surface, one or more needles connected to said sewing head by means of supporting and moving means that move the needle or the needles along a vertical trajectory, upwards and downwards, when the motor of the sewing machine is actuated by said actuation command.
Still in said operating station, the machine comprises one or more claws disposed under the work surface, which are suitable for dragging along the fabric/s in the operating station.
It must be noted that the claw/s is/are in contact with the lower side of the fabric/s that is/are momentarily disposed under the needle or needles.
Advantageously, the supporting and moving means can also move the needle or needles in a horizontal direction, in such a way that said needle or needles cooperate with the claws and the supports while the fabric is dragged along.
Still in said operating station, the sewing machine comprises one or more feet that alternately press the fabric against the claws and contribute to moving the fabric along the work surface.
The making of a very accurate seam on the edges of two fabrics with a different radius of curvature is extremely difficult and complicated with a sewing machine according to the prior art. In fact, in order to make such a seam, the operator must position the fabrics upstream the needle, constantly and correctly, by hand.
More precisely, in order to sew the edges of the two fabrics (11, 12, 13, 14) with a different radius of curvature, the operator must move and pull either one of the two fabrics upstream the needle in such a way that the edges of the two fabrics coincide. Due to the fact that the feet used to press the claw are not sufficiently stable to firmly maintain the fabric under the needle, the movement of the fabrics upstream the needle or needles determines a movement of the fabrics also in correspondence of the needle or needles, consequently causing the inaccuracy of the seam.
Moreover, in order to keep a constant, accurate stitch pitch, the operator must exert a constant force of traction on the fabrics.
The stitch pitch obtained with such a sewing machine will depend on the tension exerted on said fabrics under the needle.
The incorrect tensioning of the fabrics will inevitably result in an inaccurate seam. More precisely, the stitch pitch will be reduced if the fabrics are excessively held upstream the operating station, whereas the stitch pitch will be increased if the fabric or fabrics are insufficiently held upstream the operating station.
In view of the above, regardless of the manual ability and experience of the operator, it is practically impossible to maintain a perfectly constant traction, while moving the fabrics in the correct direction during sewing. Therefore, the seams made by such a sewing machine may be inaccurate.
An inaccurate seam may be caused by other factors, such as for example a different thickness or a different characteristic of the fabric that are moved under the needle.
The purpose of the present invention is to solve the aforesaid problems by disclosing a new sewing machine that permits to:

sew two fabrics with edges having a different radius of curvature in an easy, accurate way;
obtain a very accurate seam, in which the stitches are separated by the same distance and the stitch pitch coincides with a preset pitch;
make a very accurate seam also in case of a different thickness and of different characteristics of the fabrics that are moved under the needle;
allow the operator to pull the edges of two fabrics closer, upstream the needle, without changing the position of the fabrics under the needle;
make a seam that can be applied in a portion of the upholstery of a seat, which can withstand the stress in normal conditions, and at the same time permits the free ejection of an airbag contained in the car seat in case of an accident;
sew multiple fabrics with a curvilinear seam and a constant stitch pitch.

An additional purpose is to disclose a method for making a programmed seam on two fabrics with a different radius of curvature, with a very high accuracy and in compliance with the programmed pitch between two adjacent stitches.
These purposes are achieved according to the invention, with the characteristics of the appended independent claim 1.
Advantageous embodiments will appear from the dependent claims.
The sewing machine of the invention is defined by claim 1.
For the sake of clarity, the description of the sewing machine according to the invention continues with reference to the appended drawings, which have a merely illustrative, not limiting value, wherein:

Fig. 1 is an axonometric top view of the sewing machine according to the invention;
Fig. 2 illustrates a first fabric, a second fabric, a third fabric and a fourth fabric, which are all suitable for being sewn by means of the sewing machine according to the invention and for covering a car seat;
Figs. 3 to 27 are axonometric views of the sewing machine according to the invention in different operating steps while sewing the four fabrics;
Fig. 28 is an axonometric view of a portion of the sewing machine according to the invention, wherein said sewing machine comprises a detection device;
Fig. 28A is an enlarged view of the detail enclosed in the circle O of Fig. 28;
Fig. 29 is an axonometric view of a portion of the sewing machine of Fig. 28, wherein said detection device is in the first position;
Fig. 30 is an axonometric view of a portion of the sewing machine of Fig. 28, wherein said detection device is in the second position;
Fig. 31 is an axonometric view of a portion of the sewing machine, wherein the disk of the detection device is positioned in the slot of the foot;
Fig. 31A is an enlarged view of the detail enclosed in the broken line circle K of Fig. 31;
Fig. 32 shows the portion of the sewing machine of Fig. 31 from a different angle;
Fig. 32A is an enlarged view of the detail enclosed in the broken line circle K1 of Fig. 32;
Fig. 33 shows the portion of the sewing machine of Fig. 31, wherein the disk of the detection device is omitted;
Fig. 33A is an enlarged view of the detail enclosed in the broken line circle K2 of Fig. 33;
Fig. 34 shows the portion of the sewing machine of Fig. 33 from a different angle;
Fig. 34A is an enlarged view of the detail enclosed in the broken line circle K3 of Fig. 34;
Fig. 35 is an axonometric view of the foot according to a preferred embodiment of the invention.

With reference to Fig. 1, a sewing machine according to the present invention is disclosed, which is generally indicated with reference numeral (100).
The sewing machine (100) of the invention is suitable for making a programmed seam on two or more fabrics (11, 12, 13, 14).
The sewing machine (100) comprises:

an operating station (SO);
a work surface (PL), in correspondence of the operating stations (SO), where the fabrics (11, 12, 13, 14) are disposed;
a sewing head (1) disposed above said operating station (SO);
a needle (A) connected to said sewing head (1) and disposed in correspondence of said operating station (SO);
supporting and moving means for said needle (A), which move the needle (A) along a vertical trajectory closer and farther to/from said work surface (PL);
a claw (not shown in the appended figures) disposed under the work surface (PL) in correspondence of said needle (A); said claw is used to move the fabrics (11, 12, 13, 14) and is synchronized with the movement of the needle (A). Although only one needle (A) is shown in the appended figures, the sewing machine (100) according to the invention can be provided with multiple needles (A). Likewise, the sewing machine according to the invention can be provided with multiple claws, instead of only one claw. For convenience purposes, the description refers to a sewing machine (100) provided with one needle (A) and one claw.

The sewing machine (100) of the invention also comprises a motor connected to the supporting and moving means of the needle (A), as well as transmission means that transmit the movement of the supporting and moving means of the needle (A) to the claw, in such a way to permit the synchronized motion of the needle (A) and of the claw.
With reference to Fig. 1, the sewing machine (100) of the invention also comprises a blocking assembly (4, 41) for the fabrics (11, 12, 13, 14).
The blocking assembly (4, 41) comprises a presser (4) that can is suitable for being in an idle position, wherein the presser (4) is distant from the work surface (PL), and in an operating position, wherein the presser (4) is in contact with the work surface (PL) and firmly holds the fabrics (11, 12, 13, 14) near the place where the needle (A) makes the seam when said fabrics (11, 12, 13, 14) are disposed under said sewing head.
With reference to Fig. 1, the blocking assembly (4, 41) comprises a foot (41) connected to the sewing head (1); the foot (41) can be in an idle position, wherein the foot (41) is distal from the work surface (PL) and in an operating position, wherein the foot (41) is close to the work surface (PL) and presses the fabrics (11, 12, 13, 14) against the claw.
In order to move both the presser (4) and the foot (41) from the idle position to the operating position, the sewing machine (100) comprises moving means for the presser (4) and moving means for the foot (41), which are separate to permit the independent movement of the presser (4) and of the foot (41).
The presser (4) and the foot (41) press the fabrics (11, 12, 13, 14) in different positions on the work surface (PL).
In order to adjust the pressure of the foot (41) when pressing the fabrics (11, 12, 13, 14) against the claw, the sewing machine (100) is provided with a pressure regulation device (8) for the foot.
According to the preferred embodiment shown in Figs. 31 to 35, the blocking assembly of the sewing machine (100) comprises two feet that alternately press the fabrics (11, 12, 13, 14) against the claw, in such a way to cooperate with the claw to drag the fabrics (11, 12, 13, 14) along.
With reference to Fig. 35, said two feet comprise a first foot (41a) and a second foot (42b). The first foot (41 a) comprises two lateral bases (411a, 412a) joined by a central portion. The lateral bases (411a, 412a) and the central portion define a U-shaped seat with concavity upstream the operating station. The second foot (41b) comprises a single horizontal base (411b) that is contained in the U-shaped seat defined by the first foot (41), which presses the point where the seam is made by said needle (A). A hole (FR) is obtained in the horizontal base (411b) of the second foot (41b) and is suitable for being penetrated by the needle (A) when the fabrics (11, 12, 13, 14) are sewn.
Preferably, the movement of the fabrics (11, 12, 13, 14) by means of the movement of the claw is assisted by said two feet (41a, 41b) and/or by the needle (A).
More precisely, the moving means of the feet (41) can be configured in such a way that, in addition to pressing the fabrics (11, 12, 13, 14) against the claw, the feet (41) are also moved along a horizontal direction that is parallel to the dragging direction of the fabrics (11, 12, 13, 14).
Likewise, the moving means of said needle (A) can be configured in such a way that, in addition to being moved vertically, the needle (A) can be also moved horizontally, in a parallel direction relative to the sewing direction.
With reference to Figs. 1 and 4, the presser (4) has a stop surface (40) suitable for stopping against said work surface (PL) when said presser (4) is in operating position.
In such a configuration, the stop surface (40) firmly holds the fabrics (11, 12, 13, 14) on the work surface (PL) when said presser (4) is in operating position.
According to a preferred embodiment of the invention, the moving means of said presser (4) consist in a linear actuator (M4).
With reference to Figs. 1, 3, 8 and 9, the sewing machine (100) also comprises a dragging assembly (2) suitable for dragging the fabrics (11, 12, 13, 14) along the work surface (PL).
Said dragging assembly (2) is disposed on the work surface downstream said needle (A).
Said sewing machine (100) also comprises a clamp (3) that is integral with the dragging assembly (2) and suitable for holding the fabrics (11, 12, 13, 14), and comprises a first element and a second element in opposite position. The sewing machine (100) of the invention is provided with opening/closing means for the clamp (3), which are connected to the clamp (3) in such a way that the clamp (3) can be in an open position, wherein the opposite elements are in distal position, and in a closed position, wherein said opposite elements are in mutual contact so that the clamp (3) can hold the fabrics (11, 12, 13, 14) disposed between said first element and said second element of the clamp (3).
In the embodiment of the invention shown in the appended figures, said clamp (3) comprises an upper body (31a) and a lower plate (31b).
Said opening/closing means of the clamp (3) are disposed inside said upper body (31a) and consist in a linear actuator with a cylinder-piston assembly.
Said cylinder-piston assembly comprises a cylinder and a piston that is slidingly mounted in said cylinder; a stem (not shown in the appended figures) is connected in said piston and projects from the upper body (31a) towards the lower plate (31b).
Said first element of the claw (3) comprises the stem, whereas said second element of the clamp (3) comprises said lower plate (31b).
More precisely, when the clamp (3) is in the closed position, the stem is stopped against the lower plate (3), whereas when the clamp (3) is in the open position, the stem is retracted inside the upper body (31a).
The sewing machine (100) is provided with moving means for the dragging assembly (2), which are configured in such a way to move the dragging assembly (2) along two horizontal axes that lay on a plane that is parallel to the work surface (PL).
The moving means of the dragging assembly (2) can be configured in such a way to also permit the movement of the dragging assembly (2) along a third vertical axis that is orthogonal to the work surface (PL), more precisely in proximal and distal position relative to the work surface (PL).
Advantageously, the moving means of the dragging assembly (2) also comprise first rotational means and second rotational means that are configured in such a way to rotate the dragging assembly (2) and consequently the clamp (3) around an axis that is orthogonal to the work surface (PL) and around one of the two horizontal axes.
Because of said moving means, the clamp (3), which is integral with the dragging assembly (2), can trace a curvilinear trajectory in the space downstream the needle (A), considering that the dragging assembly (2) can move freely in five ways, i.e. three translation movements and two rotational movements.
It must be noted that, if a rectilinear seam, and not a curvilinear seam, is to be made, the moving means can be configured in such a way to move the dragging assembly (2) along a single direction that is parallel to the work surface (PL).
The sewing machine (100) comprises a control unit to program the movement of the clamp (3) in the space downstream the needle (A).
The sewing machine (100) of the invention also comprises synchronization means to synchronize the speed of the supporting and moving means of the needle (A) with the speed of the moving means of the dragging assembly (2).
The anticipated programming of the movement of the moving means of the dragging assembly (2) and the synchronization with the supporting and moving means of the needle (A) allow obtaining a very accurate seam according to the programming mode.
More precisely, in view of the fact that the dragging assembly (2) constantly transports the fabrics (11, 12, 13, 14) at a preset speed, the pitch of the stitches made by the needle (A) is constant and very accurate.
For illustrative purposes, in order to obtain a seam with 0.5 cm stitch pitch, the dragging assembly (2) will be programmed with such a speed that the fabrics (11, 12, 13, 14) are dragged along by exactly 0.5 cm at every vertical travel of the needle (A).
Therefore, because of the provision of the dragging assembly (2) and of the clamp (3), and because of the cooperation with the supporting and moving means of the needle (A), the sewing machine (100) of the invention permits to make a very accurate seam, where the stitch pitch perfectly coincides with the preset pitch.
The sewing machine (100) is provided with three detection devices (5, 6, 7), which are connected to said sewing head (1), are suitable for detecting the fabrics (11, 12, 13, 14) on the work surface (PL) and sending the detected signal to said control unit.
More precisely, the three detection devices (5, 6, 7) consist in optical devices with a radius that is collimated towards the work surface (PL).
The sewing machine (100) preferably comprises a measurement device (9) to measure the number of stitches made by the needle (A). According to the embodiment of the invention, the measurement device (9) consists in an incremental encoder.
In addition to programming the movement of the clamp (3) in advance, said control unit receives signals from the detection devices (5, 6, 7) and from the measurement device (9).
Moreover, said control unit is electronically connected to the moving means of said blocking assembly (4, 41), in such a way to control the movement of the presser (4) and the movement of the feet (41).
In order to display and monitor the number of stitches made by the needle (A), the sewing machine (100) is also provided with a display device (V). In the embodiment of the invention illustrated in the appended figures, the display device (V) consists in a monitor connected to the sewing machine (100) and to the control unit.
According to an additional embodiment, the display device (V) may consist in a portable device that is not connected to the sewing machine (100); in such a case, the sewing machine (100) is provided with a wireless transmission system.
Because of the provision of the measurement device (9) and of the display device (V), an operator can display and control the accuracy of the seams in a rapid, easy way.
Considering that the fabrics (11, 12, 13, 14) may have folds, defects and different elastic properties, although the clamp (3) guarantees a preset, constant travel, the stitch pitch may not correspond to a preset pitch.
Therefore, a system must be provided to control the stitch pitch. In order to do so, it is necessary to:

acquire the realization of a first stitch by the needle (A);
acquire the realization of a second stitch by the needle (A), in a consecutive adjacent position relative to the first stitch;
detect the pitch between said first stitch and said second stitch by means of a detection device;
compare the detected pitch with a preset pitch;
send an error signal when the detected pitch does not correspond with said preset pitch.

To that end, with reference to Figs. 28, 29 and 30, according to a preferred embodiment of the invention, the sewing machine (100) can be provided with a detector (R) that is operatively connected with said control unit and detects the length of a portion of the two fabrics (11, 12, 13, 14) sewn by the needle (A). Specifically, said detector (R) detects the length between two adjacent stitches. According to an embodiment of the invention, said detector (R) comprises:

an incremental encoder reader (RE);
a disk (RD) disposed in the vicinity of the needle (A) and suitable for going in contact with the fabrics (11, 12, 13, 14), in such a way that the disk rotates if the fabrics are moved along the work surface (PL);
a rotary shaft (RA) that transmits the rotary motion of the disk (RD) to the encoder (RE);
a device (RV) to activate/deactivate the detector (R); specifically, the device (RV) moves the detector (R) between a first position, wherein the disk (RD) is in contact with the fabrics (11, 12, 13, 14), and a second position, wherein the disk (RD) is not in contact with the fabrics (11, 12, 13, 14).

In order to exactly measure the pitch between two adjacent stitches, when the detector (R) is in the first position, the disk (RD) of the detector (R) must be disposed as close as possible to the place where the seam is made by the needle (A) (see Figs. 28 and 29), preferably at a distance from the needle (A) that is lower than 5 mm.
According to the preferred embodiment of the invention provided with the first foot (41 a) and the second foot (41b), as shown in Figs. 31 to 35, a slot (413) was made by the applicant, it being defined by said first foot (41 a) on one side and by said second foot (41b) on the other side, said slot (413) receiving the disk (RD) of the detector (R) while sewing one or more fabrics. In particular, said slot (413) is defined by a lateral base (411a, 412a) of the first foot (41a) on one side, and by the horizontal base (411b) of the second foot (41b) on the other side.
As shown in Figs. 31A and 32A, when in its first position in contact with the fabrics (11, 12, 13, 14), the disk (RD) of the detector (R) is disposed in said slot (413).
If the sewing machine (100) is provided with only one foot (41), the slot (413) can be obtained in said only one foot (41).
Because of the position of the disk (RD) of the detector (R) in the vicinity of the place where the seam is made by the needle (A), the detector (R) can accurately measure the length between two adjacent stitches of one or more fabrics. Preferably, the disk (RD) of the detector (R) has a thickness of 0.9 mm and a diameter (Rm) of 50 mm, whereas the slot (413) has a width (413L) of 4 mm and a length (413Z) of 42 mm (see Fig. 33A). With such a configuration, a pitch lower than 5 mm is provided between the needle (A) and the disk (RD) of the detector (R), which permits a very high accuracy when measuring the stitch pitch.
When the disk (RD) is in contact with the fabrics, the forward movement of the fabrics (11, 12, 13, 14) involves a rotation of the disk (RD). The rotary shaft (RA), which is integral with the disk (RD), transmits the rotation to the incremental encoder reader (RE) that converts said rotation into a piece of information on the length to the control unit.
The fabrics (11, 12, 13, 14) are dragged along between two adjacent stitches in such a way that the encoder (RE) can measure the stitch pitch.
Although not shown in the appended figures, the sewing machine (100) may also comprise a stitch-skip device, which is configured in such a way to detect stitches that are skipped by the needle. Stitch-skip devices are known to the experts of the field and freely available on the market. For illustrative purposes, the stitch-skip device comprised a nozzle that sends air towards an upper section of the sewing thread, and an optical sensor disposed in an opposite position of the nozzle relative to said upper section of the thread. Said optical sensor is operatively connected to the control unit in order to detect whether the thread crosses the optical beam of the optical sensor. When the needle makes a correct stitch, the thread is tensioned and does not cross the optical beam of the optical sensor in spite of the thrust caused by the air flow emitted by the nozzle. On the contrary, when the needle skips a stitch, the thread loosens and the upper section of the thread, which is pushed by the air flow emitted by the nozzle, is bent and crosses the optical beam of the optical sensor, which sends the signal to the control unit and immediately stops the sewing machine (100).
For instance, such a stitch-skip device is marketed by KINOSHITA with the name "Auto skip catcher".
With reference to Figs. 2 to 27, a method for making a seam is disclosed, said seam being used for making the upholstery of a car seat with an internal air-bag.
With reference to Fig. 2, a first fabric (11) and a second fabric (12) are provided.
A third fabric (13) is presewn in the second fabric (12), whereas a fourth fabric (14) is presewn in the first fabric; the third fabric (13) and the fourth fabric (14) act as support for the airbag.
The first fabric (11) has an edge (B1), whereas the second fabric (12) has a U-shaped profile and comprises an external edge (B2).
The external edge (B2) and the edge (B1) have a different radius of curvature in correspondence of a section (B22) of the external edge (B2) disposed in the vicinity of the place where the third fabric (13) is sewn.
More precisely, when the first fabric and the second fabric (11, 12) are overlapped, the edge (B1) and the external edge (B2) coincide only in an initial portion (I).
The first fabric (11) and the second fabric (12) are disposed on the work surface (PL), upstream the needle (A) relative to the sewing direction, in such a way that the edge (B1) and the external edge (B2) coincide in the initial portion (I).
Although not shown in the appended figures, while the fabrics (11, 12, 13, 14) are arranged on the work surface (PL), the presser (4) is maintained in its operating position, in such a way that the stop surface (40) of the presser (4) is in contact with said work surface (PL), acting as point of reference for the positioning of the fabrics (11, 12, 13, 14).
In particular, the first fabric and the second fabric (11, 12) are disposed on the contact point of the stop surface (40) with the work surface (PL), in such a way that the seam of the initial portion (I) is always started in a preset point.
As shown in Fig. 3, after positioning the fabrics (11, 12, 13, 14), the feet (41) pass from the idle position to the operating position, the presser (4) passes from the operating position to the idle position, the third detection device (7) detects the present of said fabrics (11, 12, 13, 14) and the needle (A) is moved by activating the supporting and moving means of the needle (A) to sew the initial portion (I), as shown in Fig. 4.
When the third detection device (7) detects the presence of the fabrics (11, 12, 13, 14), the third detection device (7) sends the signal to the control unit, which stores the stitches made by the needle (A) by means of the measurement device (9).
With reference to Fig. 4, while sewing the initial portion (I), when the first detection device (5) detects the presence of the third fabric (13), the needle (A) is stopped, deactivating the supporting and moving means of the needle (A), the presser (4) passes from the idle position to the operating position and blocks the fabrics (11, 12, 13, 14) disposed on the work surface (PL), as shown in Fig. 5.
When the fabrics (11, 12, 13, 14) are blocked, the moving means of the dragging assembly (2) are activated, in such a way that the clamp (3) is positioned in the vicinity of the needle (A), as shown in Fig. 6.
When the clamp (3) is disposed in the vicinity of the needle (A), the opening/closing means for the clamp (3) are activated in such a way that the clamp (3) can grab the fabrics (11, 12, 13, 14).
With reference to Fig. 7 and 8, when the fabrics (11, 12, 13, 14) are clamped, the presser (4) passes from its operating position to its idle position; the supporting and moving means of the needle (A) and the moving means of the dragging assembly (2) are simultaneously activated in such a way to sew a proximal portion of fabric in consecutive position relative to the portion that has been previously sewn, wherein the stitches are extremely accurate thanks to the synchronization of the dragging assembly (2) with the needle (A).
The use of the dragging assembly (2) in synchronized mode with the movement of the needle (A) is necessary for the stitches to have a preset pitch.
During the movement of the dragging unit (2), which drags said fabrics (11, 12, 13, 14) along, the pressure regulation device (8) increases or reduces (according to the specific requirements) the pressure of the feet (41), in such a way that said feet (41) cooperate with the dragging assembly (2) in the movement of the fabrics (11, 12, 13, 14).
It must be noted that the movement of the dragging assembly (2) follows a preset trajectory that is programmed in advance.
Still with reference to Fig. 7, while the seam is continued, the second detection device (6) detects the presence of the third fabric (13) and informs the control unit of the starting point with the third fabric (13).
More precisely, the second detection device (6) provides an initial instant to the control unit of the sewing machine (100), starting from which the stitch pitch must be extremely accurate. Such an initial instant is necessary to calculate and track the stitches in the third fabric by means of the measurement device (9).
In the specific application shown in the appended figures, wherein the sewing machine is used to sew the upholstery of a car seat, the stitches in the third fabric (13) must be necessarily accurate so that the seam can withstand the stress in normal conditions, guaranteeing the free ejection of the airbag in case of an accident.
In such a step, in order to ensure a very high precision of the stitch pitch, if the sewing machine (100) is provided with said detector (R) (which is shown in Figs. 28, 29, 30, 31 and 32), the stitch pitch can be accurately controlled. More precisely, during such a step, the device (RV) of the detector (R) is activated in order to move the detector (R) between the second position and the first position, bringing the disk (RD) in contact with the fabrics (11, 12, 13, 14).
With reference to Fig. 9, after completing the travel of the dragging assembly (2), the presser (4) passes from its idle position to its operating position, the clamp (3) releases the fabrics (11, 12, 13, 14) and the needle (A) is stopped by deactivating the supporting and moving means of the needle (A).
With reference to Fig. 10 and 11, the dragging assembly (2) is moved in such a way to re-position the clamp (3) in the vicinity of the needle (A) and the opening/closing means are activated in such a way that the clamp (3) re-grabs the fabrics (11, 12, 13, 14) again.
It must be noted that, in the section (B22), the radius of curvature of the lateral edge (B2) is different from the radius of curvature of the edge (B1). With reference to Figs. 12 to 14, the lateral edge (B2) and the edge (B1) are moved closer in order to be overlapped and the fabrics (11, 12, 13, 14) are grabbed by the clamp (3).
In particular, the fact that the two edges (B1, B2) are moved closer, upstream the needle (A), does not cause the movement of the fabrics (11, 12, 13, 14) in the place where the needle (A) is sewing, because the fabrics (11, 12, 13, 14) are firmly held and position by the presser (4) that presses the fabrics (11, 12, 13, 14) in the vicinity of the needle (A).
After clamping the fabrics (11, 12, 13, 14) the presser (3) passes from its operating position to its idle position, and the fabrics (11, 12, 13, 14) are dragged along by the dragging assembly (2).
In such a step, the measurement device (9) continues on measuring the number of stitches in the section with the third fabric (13).
Likewise, during this step, the detector (R) detects the distance between two consecutive stitches in such a way to check the precision of the seam. The stitch pitch is detected by means of the following operations:

the control unit acquires the realization by the needle (A) of a first stitch and of a second stitch in adjacent consecutive position to the first stitch;
the detector (R) detects the pitch between the first stitch and the second stitch;
the control unit compares the pitch detected by the detector (R) with a preset pitch and sends an error signal when said detected pitch does not coincide with said preset pitch.

The sewing process continues with the iteration of the sewing, dragging, blocking and movement operations of the fabrics (11, 12, 13, 14) until the first detection device (5) detects the end of the third fabric (13), as shown in Figs. 15 to 20.
When the first detection device (5) detects the end of the third fabric (13), the signal is sent to the control unit, which releases the clamp (3) after a preset delay (and consequently after a predefined set of stitches), in such a way that the seam can be made manually without the aid of the dragging assembly (2), as shown in Figs. 22 to 27. If necessary, while the clamp (3) is released, the presser (4) can pass from the idle position to the operating position so that the operator can move the edges (B1, B2) of the fabrics (11, 12, 13, 14) closer, upstream the needle (A).
During such a preset delay, the second detection device (6) detects the end of the third fabric (13) proving the sewing machine (100) with the initial instant in which the stitches are to be extremely accurate.
During such a step, the device (RV) of the detector (R) is activated in order to move the detector (R) from the first position to the second position, moving the disk (RD) away from the fabrics (11, 12, 13, 14).
It must be noted that both during the programmed sewing and during the manual sewing, at every moment the operator can make the presser (4) go from the idle position to the operating position, stopping the sewing machines (100) whenever necessary.
In view of the above, while sewing, at every moment the operator can move the fabrics upstream the needle (A) in a stable, safe way.
It must be noted that, also during the manual sewing shown in Figs. 22 to 27, the pressure regulation device (8) increases or reduces the pressure of the feet (41), in such a way to guarantee the best cooperation of said feet (41) with the clamp while the fabrics (11, 12, 13, 14) are moved.
With reference to Fig. 26, the third detection device (7) detects the end of the first fabric and of the second fabric (11, 12) and the control unit stops the needle (A).
When the sewing is completed, the precision of the seam made by the needle (A) can be assessed by means of the display device (V), with particular reference to the seam made along the section with the third fabric (13) and the fourth fabric (14).
The precision of the seam is ensured by the assistance of the dragging unit (2) and is checked by means of the detector (R). In fact, the stitch pitches detected by the detector (R) are compared with preset length values. If the pitches are correct or acceptable according to the permitted tolerance, the seam will be suitable for being used as seam for the upholstery of a car seat that contains an airbag.
The use of such a sewing machine (100) permits to realize a very precise seam in the portion with the third and the fourth fabric (13, 14). The precision of said seam is necessary because the seam must withstand the stress in normal conditions, guaranteeing at the same time the free ejection of the airbag in case of an accident, according to the calculations and tests made by the car manufacturer.
Because of the provision of the measurement device, of the detector (R) and of the display device, the sewing machine (100) of the invention makes it possible to check the precision and accurateness of the seam during and after sewing.
Although the preceding description refers to a specific application of the sewing machine (100), i.e. for sewing the upholstery of a car seat provided with airbag, said sewing machine (100) can be used for all applications that require to make a very precise programmed seam on two or more fabrics (11, 12, 13, 14).
Because of the provision of the dragging assembly (2), which drags the fabrics along at a preset speed, an extremely accurate seam is obtained regardless of the different thickness, of the different technical features of the fabrics and of the movements made by the operator.
Moreover, thanks to the presser (4) of the blocking unit (4, 41), the operator can arrange the fabrics (11, 12, 13, 14) in a safe, simple way. More precisely, when in its operating position, the presser (4) firmly holds the fabrics (11, 12, 13, 14) in the vicinity of the needle (A); in such a way, the operator can easily move the fabrics (11, 12, 13, 14) upstream the needle (A), without moving the fabrics (11, 12, 13, 14) in the vicinity of the needle (A), with no negative consequences for the precision of the seam.
In view of the preceding description, it appears evident that the simultaneous presence of the presser (4) of the blocking unit (4, 41), of the clamp (3) and of the dragging assembly (2) makes it possible to obtain a very precise programmed seam on two fabrics (11, 12, 13, 14) with different edges; in fact, the presence of the presser (4) permits to place the edges one close to the other, without altering the position of the fabrics (11, 12, 13, 14) in correspondence of the needle (A), whereas the presence of the clamp (3) and of the dragging assembly (2) makes it possible to drag the fabrics (11, 12, 13, 14) along according to the programmed seam.
The sewing machine (100) of the invention can be used use whenever a seam is to be made in parallel direction to a curved lateral edge, or whenever two fabrics are to be sewn in an accurate way, with the need to move either one of the two fabrics upstream the needle in such a way to generate a curving portion on either one of the two fabrics.
In view of the foregoing description, such a sewing machine (100) can be used for all types of seams.
Numerous variations and modifications can be made to the present embodiment of the invention, which are within the reach of an expert of the field, falling in any case within the scope of the invention as disclosed by the appended claims.

Claims

Sewing machine (100) for sewing two fabrics (11, 12, 13, 14) in a programmed, measured and controlled way; said sewing machine (100) comprising:
- an operating station (SO);

- a work surface (PL), in correspondence of said operating stations (SO), where said two fabrics (11, 12, 13, 14) are disposed;

- a sewing head (1) disposed above said operating station (SO);

- at least one needle (A) connected to said sewing head (1) and disposed in correspondence of said operating station (SO);

- supporting and moving means for said needle (A) to move the needle (A) along a vertical trajectory, closer and farther to/from said work surface (PL);

- at least one claw disposed under said work surface (PL) where the seam is made by said at least one needle (A);

- a blocking unit (4, 41) for said two fabrics (11, 12, 13, 14); said blocking unit (4, 41) comprising a presser (4) that can be in an idle position, wherein said presser (4) is distal from said work surface (PL), and in an operating position, wherein said presser (4) is in contact with said work surface (PL) and firmly blocks said two fabrics (11, 12, 13, 14) in the vicinity of the place where the seam is made by said at least one needle (A); said blocking unit comprising at least one foot (41) connected to said sewing head (1); said at least one foot (41) being suitable for being in an idle position, wherein said at least one foot (41) is distal from said work surface (PL), and in an operating position, wherein said at least one foot (41) is proximal to said work surface (PL) and presses said fabrics (11, 12, 13, 14) against said claw; said sewing machine (100) comprising moving means for said foot (41) to move said foot (41) between said idle position and said operating position;

- moving means for said presser (4) of the blocking assembly (4, 41); said moving means for said presser (4) moving said presser (4) between said idle position and said operating position;

- a dragging assembly (2) suitable for dragging said two fabrics (11, 12, 13, 14) along the work surface (PL);

- a clamp (3) integral with said dragging assembly (2), suitable for grabbing said two fabrics (11, 12, 13, 14); said clamp (3) comprising a first and a second element in opposite position;

- opening/closing means for said clamp (3) connected to the clamp (3) in such a way that said clamp (3) can be in an open position, wherein said opposite elements are in distal position, and a closing position, wherein said opposite elements are in mutual contact;

- moving means for said dragging assembly (2); said moving means for said dragging assembly (2) being configured in such a way to move the dragging assembly (2) along a first horizontal axis, which lies on a plane that is coincident or parallel to the work surface (PL);

- a detector (R) to measure the length of a section of said at least one fabric (11, 12, 13, 14) sewn by said at least one needle (A).
The sewing machine (100) of claim 1, wherein said detector (R) comprises:
- an incremental encoder reader (RE);

- a disk (RD) disposed in the vicinity of the needle (A) and suitable for going in contact with the fabrics (11, 12, 13, 14);

- a rotary shaft (RA) to transmit the rotary motion of the disk (RD) to the incremental encoder reader (RE);

- a device (RV) to activate/deactivate the detector (R); said device (RV) moving the detector (R) between a first position, wherein the disk (RD) is in contact with the fabrics (11, 12, 13, 14), and a second position, wherein the disk (RD) is not in contact with the fabrics (11, 12, 13, 14).
The sewing machine (100) of claim 2, wherein, when the detector (R) is in said first position, said disk (RD) is adjacent to the foot (41) at a distance from the needle (A) lower than 5 mm.
The sewing machine (100) of claim 2, wherein said at least one foot (41) comprises a slot (413); when the detector (R) is in said first position, said disk (RD) is disposed inside said slot (413) at a distance from the needle (A) lower than 5 mm.
The sewing machine (100) of claim 4, wherein said at least one foot (41) comprises a first foot (41a) and a second foot (41b); said two feet alternately press the fabrics (11, 12, 13, 14) against said claw; said first foot (41 a) comprises two side bases (411a, 412a) joined by a central portion that define a U-shaped seat with concavity directed upstream the operating station (SO); said second foot (41b) comprises a single horizontal base (411b) that is housed in the U-shaped seat and whereon a hole (FR) is obtained and penetrated by the needle (A) when the fabrics (11, 12, 13, 14) are sewn; said slot (413) being defined by said first foot (41 a) on one side, and by said second foot (41b) on the other side.
The sewing machine (100) of any one of the preceding claims, comprising synchronization means to synchronize the speed of the supporting and moving means of said at least one needle (A) with the speed of the moving means of the dragging assembly (2).
The sewing machine (100) of any one of the preceding claims, comprising a measuring device (9) to calculate the number of stitches made by said at least one needle (A).
The sewing machine (100) of any one of the preceding claims, wherein said moving means for said dragging assembly (2) are configured in such a way to move the dragging unit (2) along:
- a second horizontal axis that is perpendicular to said first axis; and/or

- a third vertical axis that is orthogonal to the work surface (PL).
The sewing machine (100) of any one of the preceding claims, wherein said moving means for said dragging assembly (2) comprise:
- first rotational means for said dragging assembly (2); said first rotational means being configured in such a way to rotate said dragging assembly (2) around an axis that is orthogonal to the work surface (PL); and/or

- second rotational means for said dragging assembly (2); said second rotational means being configured in such a way to rotate said dragging assembly (2) around one of the two horizontal axes.
The sewing machine (100) of any one of the preceding claims, comprising at least one detection device (5, 6, 7) suitable for detecting the presence of said two fabrics (11, 12, 13, 14) in said work surface (PL).
Method for making a programmed seam on two fabrics (11, 12, 13, 14); said method comprising the following steps:
a) providing two fabrics (11, 12, 13, 14);

b) disposing said two fabrics (11, 12, 13, 14) on a work surface (PL);

c) grabbing said two fabrics (11, 12, 13, 14) with a clamp (3);

d) actuating the moving means of a dragging assembly (2) whereon said clamp (3) is fixed; said moving means moving said clamp (3) along two horizontal axes lying on a plane that is coincident or parallel to the work surface (PL); simultaneously actuating a moving means for a needle (A) that moves said needle (A) in synchrony with said moving means of the dragging assembly (2);

e) stopping the step d), blocking the needle (A) and blocking the two fabrics (11, 12, 13, 14) with a blocking assembly (4, 41) suitable for firmly blocking said two fabrics (11, 12, 13, 14) on the work surface (PL);

f) opening the clamp (3) and actuating the moving means of the dragging assembly (2) whereon said clamp (3) is fixed in order to move the clamp (3) towards the needle (A);

g) iterating the steps c), d) and e) until the programmed seam is completed on the two fabrics (11, 12, 13, 14).
The method of claim 11 wherein the following operations are provided between step d) and step g):
- acquiring the realization of a first stitch by the needle (A);

- acquiring the realization of a second stitch by the needle (A), in successive, adjacent position relative to the first stitch;

- detecting the pitch between said first stitch and said second stitch;

- comparing the detected pitch with a preset pitch;

- sending an error signal when the detected pitch does not correspond with said preset pitch.
The method of claim 11 or 12, wherein the following operations are provided during step d):
- moving the dragging assembly (2) along a third vertical axis that is orthogonal to the work surface (PL); and/or

- rotating the dragging assembly (2) along an axis that is orthogonal to the work surface (PL); and/or

- rotating the dragging assembly (2) along an axis that is parallel to the work surface (PL).
The process of any one of claims 11 to 13, wherein said two fabrics (11, 12, 13, 14) comprise a first fabric (11) and a second fabric (12), whereon a fourth fabric (14) and a third fabric (13) are presewn, respectively; said third fabric (13) and said fourth fabric (14) acting as support for an air-bag.
The method of any one of claims 11 to 14, wherein said two fabrics (11, 12, 13, 14) comprise lateral edges with a different radius of curvature; it being provided that, according to the method, said two fabrics (11, 12, 13, 14) are moved closer, upstream the needle (A) during step e) in such a way that the lateral edges of the fabrics (11, 12, 13, 14) are overlapped.