Multi-piezoelectric yarn sliding sensor for weaving machine and automatic assembling method of multi-piezoelectric yarn sliding sensor

Abstract

A multi-piezoelectric yarn slip sensor comprising a plurality of independent piezoelectric sensors, each piezoelectric sensor consisting of a piezoelectric element (P) in stable association with a yarn guide eyelet (4) and an electronic printed circuit board (1) comprising a flexible portion (2), the piezoelectric element (P) being electrically connected to the electronic printed circuit board by the flexible portion (2), and the piezoelectric element (P) being electrically connected to the electronic printed circuit board by the flexible portion (2). Electric signals emitted by piezoelectric elements (P) of the independent piezoelectric sensors are transmitted on an electronic printed circuit board.

Description

Technical Field

[0001] This invention relates to a multi-piezoelectric yarn sliding sensor for textile machines and a related method for its automated assembly. Such multi-piezoelectric yarn sliding sensors are used in most textile machines; a particularly noteworthy application is in tufting machines, where it is practically necessary to simultaneously monitor a large number of different yarns and then quickly and definitively identify any yarn breakage, thereby stopping the machine and repairing the broken yarn. Piezoelectric yarn sliding sensors provide a particularly satisfactory answer to this need, thanks to their small size and the possibility of close-packing them without mutual interference. However, the following description of the multi-piezoelectric yarn sliding sensor of this invention will be given only with reference to such a multi-piezoelectric sensor, whose inherent characteristics are virtually entirely independent of the specific textile machine in which it is used. Background Technology

[0002] Piezoelectric yarn sliding sensors utilize the well-known properties of piezoelectric materials, such as certain ceramic materials, which, when subjected to mechanical stress, generate a potential difference between two positions of the same element at a certain distance from each other. This potential difference between the two positions of the element can be detected, and by analyzing the electrical signal, it can be verified whether the piezoelectric element is under mechanical stress or in a stationary state.

[0003] Therefore, from a theoretical perspective, applying this general concept to a piezoelectric yarn slip sensor is relatively simple, as it is sufficient to rigidly associate the aforementioned type of piezoelectric element with a normal yarn guide eyelet. The yarn to be checked for regular slippage passes through the inside of the yarn guide eyelet, ensuring continuous contact between the surface of the yarn guide eyelet and the slipping yarn. In fact, the slippage of the yarn thus generates continuous mechanical stress, such as vibration, on the yarn guide eyelet and consequently on the piezoelectric element integrated therewith. An electronic control circuit is connected to the piezoelectric element to detect the presence of a continuous electrical signal at its poles with an amplitude greater than a predetermined threshold. If present, the regular slippage of the yarn is confirmed, while when the electrical signal is absent or below the predetermined threshold, it means that the vibrational stress on the piezoelectric element has ceased; therefore, the yarn slipping through the yarn guide eyelet causing this vibration has clearly broken or become blocked.

[0004] However, the practical implementation of this principle involves overcoming several difficulties, not only in miniaturizing the yarn guide eye (which actually needs to have a sufficiently small mass to vibrate as the yarn passes through), but more importantly, in the mechanical support of the yarn guide eye and the electrical connection of the piezoelectric element. The mechanical support of the yarn guide eye should actually allow it to vibrate freely, suppressing the vibration to the smallest possible extent; and the electrical connection between the poles of the piezoelectric element and the associated electronic control board must be made of extremely thin and flexible conductors, again with the aim of not suppressing the vibration of the yarn guide eye / piezoelectric element assembly. In fact, applying a general principle, the more freely the yarn guide eye / piezoelectric element assembly can vibrate, the better the signal quality obtained for subsequent signal processing, in which the condition of yarn breakage or unexpected stopping must be distinguished from regular slippage with minimal possible error.

[0005] In current methods for assembling piezoelectric yarn sliding sensors, each yarn guide eyelet and its associated piezoelectric element are simply arranged on a corresponding rubber seat, which allows the yarn guide eyelet to vibrate to its maximum extent in response to the stress exerted by the yarn sliding through it. The two metallized electrodes of the piezoelectric element are then manually soldered to two corresponding contact pads on an electronic printed circuit board (hereinafter also referred to as the PCB), which processes the electrical signals emitted by the multiple piezoelectric elements. Therefore, for each installed yarn guide eyelet, four manual soldering operations are required using two conductors (two on the PCB side and two on the piezoelectric element side), and these conductors must be as flexible and adaptable as possible, as described above.

[0006] Therefore, the assembly method briefly described above is particularly lengthy and labor-intensive, and requires a highly specialized workforce. This is both because it involves tiny components and very thin and flexible conductors, and because, for obvious space-saving reasons, the guide holes must be installed at very short intervals, laterally grouped and aligned on the corresponding support shells. Consequently, the workspace is very limited.

[0007] EP-0139231 discloses a piezoelectric yarn sensor suitable for spinning and weaving machines, which represents the closest prior art to the present invention, and its features have been incorporated into the preamble of the independent claims of the present invention.

[0008] DE 2152907 discloses another yarn sensor for spinning and weaving machines that uses an electroacoustic transducer to detect the presence of yarn.

[0009] US-2022 / 0282416 discloses a system for monitoring yarn breakage in a textile machine.

[0010] In the context of the prior art, the technical problem solved by the present invention is to provide a multi-piezoelectric yarn sliding sensor equipped with an innovative wiring system for piezoelectric elements, which allows it to be manufactured using a fully automated and rapid assembly method.

[0011] In light of this technical problem, the first objective of the present invention is to provide a multi-piezoelectric yarn sliding sensor in which the wiring from the piezoelectric element to the electronic board no longer requires manual soldering.

[0012] A second objective of this invention is to provide a multi-piezoelectric yarn sliding sensor, wherein the piezoelectric elements are mechanically connected to a PCB with high degrees of freedom to vibrate.

[0013] Finally, a third objective of the present invention is to provide a multi-piezoelectric yarn sliding sensor, wherein in the event of a break or failure in the wiring, the wiring from the piezoelectric element to the PCB can be quickly replaced by manually soldering a flexible conductor. Summary of the Invention

[0014] This problem is solved and these objectives are achieved by an assembly method of a multi-piezoelectric yarn sliding sensor having the features defined in claim 1 and the multi-piezoelectric sensor having the features defined in claim 10. Further preferred features of the multi-piezoelectric yarn sliding sensor and related assembly methods are defined in the dependent claims. Attached Figure Description

[0015] Other features and advantages of the multi-piezoelectric yarn sliding sensor according to the invention will become more apparent from the following detailed description of preferred embodiments of the invention, given only by way of non-limiting example and shown in the accompanying drawings, wherein:

[0016] Figure 1 This is a front view of a rigid-flexible PCB suitable for automated soldering of multiple piezoelectric components arranged side by side;

[0017] Figure 1A yes Figure 1 A magnified view of the end of the PCB;

[0018] Figure 2 It is similar to Figure 1 The view shows piezoelectric elements soldered to a detachable flexible portion of the PCB;

[0019] Figure 3 yes Figure 2 A three-dimensional view of the PCB, in which each piezoelectric element has a corresponding guide hole bonded to it;

[0020] Figure 4 It is a three-dimensional view of two PCBs and related yarn guide eyelets set in the corresponding support shell;

[0021] Figure 5 It is a magnified three-dimensional view of the yarn guide eye; and

[0022] Figure 6 yes Figure 5 Axial cross-sectional view of the center guide yarn eyelet. Detailed Implementation

[0023] According to the present invention, in order to solve the above-mentioned prominent problems with a simple and immediately applicable solution, the applicant has introduced some substantial innovations into the currently known assembly methods shown in the introduction of the specification, with the aim of making them fully automated, thereby increasing their output.

[0024] The first innovation involves the use of flat piezoelectric elements with contact electrodes of a so-called "folded" or "wrapped" type. In this type of piezoelectric element (which is well-known in itself but has only recently been used in piezoelectric sensors), the two connected metallized electrodes of the piezoelectric element are expected to be arranged on the same surface of the piezoelectric element, rather than on two opposing surfaces as is the case with piezoelectric elements used in known piezoelectric yarn sliding sensors. Therefore, this first innovation allows for easy and automated soldering of piezoelectric elements onto PCBs using surface mount technology (SMT).

[0025] The second innovation involves using rigid-flexible or fully flexible PCBs instead of traditional rigid PCBs; the definition naturally refers to the mechanical properties of the substrate on which printed circuits are formed.

[0026] In fact, traditional rigid PCBs typically consist of insulating and conductive layers, which are laminated together onto a rigid substrate on which electronic components are mounted. The rigidity of this substrate is primarily due to the use of rigid insulating layers, usually composed of glass fibers impregnated with epoxy resin. A significant characteristic of rigid PCBs is their flatness; therefore, as a preliminary approximation, rigid PCBs can be considered as two-dimensional structures.

[0027] Rigid-flex or fully flexible PCBs are characterized by the use of substrates that are inherently highly flexible, allowing them to be easily bent or rolled, such as polyimide films. For this purpose, rigid substrates that can also be deformed (even if only a limited number of times) if properly handled have also been proposed. Therefore, depending on the position and extension of the flexible and rigid substrate portions, fully flexible PCBs or PCBs that include only some flexible portions within the original rigid substrate can be obtained.

[0028] Clearly, conductive substrates can be integrated into both rigid and flexible parts of a PCB, where electrical connections suitable for connecting different parts and components of the PCB are defined using methods known per se.

[0029] A typical characteristic of partially or fully flexible PCBs is that they can not only be placed in a two-dimensional plane, but can also occupy available space in a three-dimensional configuration.

[0030] According to the present invention, a rigid-flexible or fully flexible PCB is used by placing contact pads for electrical connections of piezoelectric elements on the free ends of flexible portions of the printed circuit (the opposite ends of which are connected to the remainder of the PCB). Thanks to this particular solution, each piezoelectric element can vibrate freely after it has been soldered to its corresponding flexible portion of the PCB, and can obviously be conveniently positioned relative to the rest of the PCB over the length of the flexible portion, thereby eliminating the conductor pairs used in the prior art for electrically connecting piezoelectric elements to the PCB.

[0031] Finally, the last innovation involves the steps of assembling the different components of a multi-piezoelectric yarn sliding sensor, which are the reverse of those steps in conventional assembly methods. In fact, in the latter method, the yarn guide eye / piezoelectric element assembly is first obtained by bonding and then soldered onto a PCB. In the assembly method of this invention, all piezoelectric elements are first soldered collectively to the PCB, and then the yarn guide eye is bonded to the piezoelectric elements already soldered to the PCB. This allows all steps of the assembly method to be automated, thereby achieving production volumes suitable for meeting market demands.

[0032] Now refer to the attached diagram, Figure 1 A rigid-flex PCB 1 is schematically shown, containing electronic circuitry that collects electrical signals emitted by a number of parallel piezoelectric elements P. The rigid substrate of the rigid-flex PCB 1 is coated with a flexible film in a manner known per se, and then the flexible film is partially pre-cut in a predetermined area to form a partially removable flexible portion 2 of the rigid-flex PCB 1. Components requiring a degree of placement freedom relative to the rigid substrate of the rigid-flex PCB 1 are then attached to the removable flexible portion. Alternatively, the same result can be achieved using a fully or partially flexible PCB.

[0033] Figure 1AThe flexible portion 2 is shown in more detail, which is partially detachable from the rigid substrate of the rigid-flexible PCB 1 because its fixed ends 2f are firmly anchored to the rigid substrate of the rigid-flexible PCB 1, while the remaining portion (particularly the free end 2c opposite the fixed end 2f) is free to move relative to the rigid substrate of the PCB. Two contact pads 3 are soldered onto the surface of the free end 2c for electrical connection of the piezoelectric element P. The flexible portion 2 is obviously equipped with internal electrical connections that connect the contact pads 3 to the printed circuit of the rigid-flexible PCB 1 via its fixed end 2f. The middle portion of the PCB flexible portion 2 (i.e., included between the fixed end 2f and the free end 2c) has a serpentine shape, which is specifically designed to give the piezoelectric element P soldered to the contact pads 3 as many degrees of freedom as possible, thereby minimizing vibrations suppressed by the flexible portion 2 of the PCB 1. Finally, on the rigid-flexible PCB 1, near each flexible portion 2, there are two additional contact pads (not shown in the figure) connected to the printed circuit parallel to the contact pad 3, for any manual repair of the electrical connection between the piezoelectric element P and the rigid-flexible PCB 1 in the event of a failure of the flexible electrical connection, as better illustrated below.

[0034] As will be described more broadly below, in the first step of the assembly method of the present invention, a piezoelectric element P is placed correspondingly to each flexible portion 2 on each rigid-flexible PCB 1, and then a single automatic soldering operation is performed between the contact pad 3 and the corresponding contact electrode of the piezoelectric element P, as described above, with both corresponding contact electrodes located on the surface of the piezoelectric element P, facing the rigid-flexible PCB 1 and therefore towards the surface on which the free end 2c of the contact pad 3 is located. When soldering is complete, the rigid-flexible PCB 1 is thus as Figure 2 The process is as shown. At this point, the corresponding guide holes 4 are bonded to the piezoelectric element 3, thus completing the rigid-flexible PCB 1 as shown. Figure 3 The presentation is as shown.

[0035] The yarn guide eye 4 used in the multi-piezoelectric yarn sliding sensor of the present invention has some innovative shapes, such as Figure 5 and Figure 6 As clearly shown, these innovations are particularly useful for improving the performance of the sensor.

[0036] The first innovation involves the internal contour (4i) of the yarn guide eyelet 4, as in Figure 6 As can be clearly seen in the cross-sectional view, the inner contour (4i) is continuously raised, thus forming the inner surface of the guide eye without any abrupt changes in tilt, and the cross section gradually decreases from the opposite opening to its center, which allows for a larger contact surface with the yarn passing through the eye, even if the yarn entry direction forms an angle with respect to the axis of the guide eye 4.

[0037] The second innovation relates to the shape of the circular opening 7 of the yarn guide eye, which has an outwardly facing circular annular protrusion to prevent the yarn from sliding against the rubber seat supporting the yarn guide eye 4 when the yarn entry direction forms a protruding angle relative to the axis of the yarn guide eye, and to keep it in a predetermined position within the support shell.

[0038] The third innovation involves providing a large, flat outer wall 6 on one side of the yarn guide eye 4, preferably parallel to the axis of the yarn guide eye, to allow it to adhere stably to the corresponding flat surface of the piezoelectric element P. Finally, in the fourth innovation, the flat outer wall 6 also includes two longitudinal angular protrusions 8, which prevent the yarn guide eye 4 from rotating about its axis when it is inserted into the corresponding rubber seat, wherein one or the other of the angular protrusions 8 engages with the rubber seat.

[0039] The assembly method of the multi-piezoelectric yarn sliding sensor according to the present invention involves the following steps:

[0040] a) An SMT step of soldering piezoelectric element P onto a rigid-flexible PCB 1, wherein a "pick and place" positioning device (hereinafter referred to as "P&P") is used to place the piezoelectric element P onto a corresponding contact pad 3 provided at the free end 2c of the flexible portion 2 of the rigid-flexible PCB 1. Then, all the piezoelectric elements P thus placed are simultaneously soldered to the corresponding contact pads 3 in a reflow oven in the same manner as known in SMD electronic components;

[0041] b) The step of bonding the ceramic guide eyelet 4 to the corresponding piezoelectric element P that has been soldered to the flexible portion of the rigid-flexible PCB 1. The guide eyelet 4 is positioned corresponding to the piezoelectric element P that has been soldered to the rigid-flexible PCB 1 using a specific P&P positioning device, then an adhesive layer is applied, and finally it is adhered to the piezoelectric element P, as shown below. Figure 3 As shown;

[0042] b1) Possible steps for cutting the rigid-flexible PCB 1 from a multilayer board. To facilitate processing the rigid-flexible PCB 1 in automated machines, larger multilayer boards are typically used, thus each multilayer board contains multiple PCBs 1. In this case, at the end of step b), each rigid-flexible PCB 1 is cut from the multilayer board by a milling cutter. During the cutting step, each individual guide eyelet 4 is held in place with a special clamp to prevent excessive stress on the flexible portion 2 of the rigid-flexible PCB 1;

[0043] c) The rigid-flexible PCB 1, equipped with piezoelectric element P and guide eyelet 4, is mechanically assembled onto a specific support shell 5. Figure 4In the step shown (in the shaded area), a conventional rubber seat has been inserted into the support housing 5 to accommodate the yarn guide eyelet 4. In the illustrated embodiment, two rigid-flex PCBs 1 are mounted on corresponding seats provided in the support housing 5, and then the individual yarn guide eyelets 4 are inserted into their adjacent rubber seats by removing the corresponding flexible portions 2 from the rigid-flex PCBs 1 (except for the fixed end 2f). Thus, the flexible portions 2 form a multi-degree-of-freedom electrical connection between the rigid-flex PCBs 1 and the yarn guide eyelet 4 / piezoelectric element P assembly, thereby allowing the assembly to vibrate freely as the yarn passes through the yarn guide eyelet 4.

[0044] This result was achieved using a fully automated assembly method, requiring no manual soldering. During use, if the flexible portion 2 is damaged or broken, it can be easily replaced with a pair of flexible conductors manually soldered to the piezoelectric element and the additional contact pads disposed on the rigid substrate of the rigid-flexible PCB 1, thus eliminating the need to replace the entire multi-piezoelectric yarn sliding sensor. Therefore, all the intended objectives of the invention have been achieved.

[0045] However, it should be understood that the present invention should not be considered as limited to the specific arrangements shown above. These arrangements are merely exemplary embodiments of the present invention and there may be different variations. All of these variations are within the scope of skill of those skilled in the art and do not depart from the protection scope of the present invention itself, which is defined only by the appended claims.

Claims

1. A multi-piezoelectric yarn slide sensor comprising a plurality of independent piezoelectric sensors, each piezoelectric sensor consisting of a piezoelectric element (P) stably associated with a guide eye (4), an electronic printed circuit board and an electrical connection between the piezoelectric element (P) and the electronic printed circuit board, the electrical signals emitted by the piezoelectric elements (P) of the independent piezoelectric sensors being transmitted on the electronic printed circuit board, characterized in that, The electronic printed circuit board (1) comprises flexible portions (2) partially detachable from the electronic printed circuit board (1) with their free ends (2c) and the electrical connections are made by said flexible portions (2).

2. The multi-piezoelectric yarn sliding sensor according to claim 1, wherein said piezoelectric elements (P) are provided with two metallized poles for electrical connection and said two metallized poles are arranged on the same surface of the piezoelectric element (P).

3. The multi-piezoelectric yarn slide sensor of claim 2, wherein, Said flexible portions (2) of the electronic printed circuit board (1) are provided with two contact pads (3) on the surface of said free ends (2c) for electrical connection of said piezoelectric elements (P).

4. The multi-piezoelectric yarn slide sensor of claim 3, wherein, The intermediate portion of each flexible portion (2) of the electronic printed circuit board (1), comprised between its fixed end (2f) and said free end (2c), is serpentine.

5. The multi-piezoelectric yarn slide sensor of claim 3, wherein, On the electronic printed circuit board (1) in the vicinity of each flexible portion (2) are provided two additional contact pads connected to the printed circuit parallel to said contact pads (3).

6. The multi-piezoelectric yarn sliding sensor according to claim 1, wherein said yarn guide eyelet (4) has a continuously convex inner profile (4i) so that its inner surface has no abrupt inclination and has a cross section that gradually decreases from opposite openings to its center.

7. The multi-piezoelectric yarn sliding sensor according to claim 1, wherein the shape of the circular opening (7) of said yarn guide eyelet (4) comprises an external circular annular protrusion.

8. The multi-piezoelectric yarn sliding sensor according to claim 1, wherein one side of said yarn guide eyelet (4) comprises a flat outer wall (6) for adhesion to a corresponding flat surface of said piezoelectric element (P).

9. The multi-piezoelectric yarn sliding sensor according to claim 8, wherein said flat outer wall (6) is parallel to the axis of said yarn guide eyelet (4) and comprises at least one longitudinal angular protrusion (8) adapted to engage within the rubber support seat of said yarn guide eyelet (4).

10. A method for the automatic assembly of a multi-piezoelectric yarn sliding sensor of the type comprising a plurality of independent piezoelectric sensors, each consisting of a piezoelectric element (P) stably associated with a guide eye (4), an electronic printed circuit board and an electrical connection between said piezoelectric element (P) and said electronic printed circuit board, the electronic printed circuit board processing the electrical signals emitted by the piezoelectric elements (P) of said independent piezoelectric sensors, characterized in that, The method comprises the following steps: a) a soldering step by surface mounting technology SMT, wherein the metallized poles of a plurality of piezoelectric elements (P) are soldered on respective flexible portions (2) of an electronic printed circuit board (1) comprising flexible portions (2) partially detachable from the electronic printed circuit board (1) with their free ends (2c) and provided with contact pads (3) for electrical connection of said piezoelectric elements (P); and b) an adhesion step, wherein a yarn guide eyelet (4) is adhered to said piezoelectric elements (P) soldered to said rigid-flex electronic printed circuit board (1) in step a).

11. The automatic assembly method for a multi-piezoelectric yarn sliding sensor according to claim 10, wherein said piezoelectric elements are each provided with two metallized poles for electrical connection and said two metallized poles are arranged on the same surface of the piezoelectric element (P).

12. The automatic assembly method for a multi-piezoelectric yarn sliding sensor according to claim 11, wherein the flexible portion (2) of the electronic printed circuit board (1) is provided, on the surface of its free end (2c), with contact pads (3) for the electrical connection of the piezoelectric elements (P).

13. The automatic assembly method for a multi-piezoelectric yarn sliding sensor according to claim 12, wherein, in the welding step a), the piezoelectric elements (P) are placed on the contact pads (3) by means of a "pick and place" positioning device, which then simultaneously welds them to the contact pads (3).

14. The automatic assembly method for a multi-piezoelectric yarn sliding sensor according to claim 12, wherein, in the gluing step b), the guide eyelets (4) are placed in correspondence with the piezoelectric elements (P) welded to the electronic printed circuit board (1) by means of a "pick and place" positioning device, the guide eyelets (4) being provided with a layer of glue, which then adheres them to the piezoelectric devices (P).

15. The method for automatic assembly of a multi-piezoelectric yarn sliding sensor according to claim 12, wherein, The intermediate portion comprised between the fixed end (2f) and the free end (2c) of each flexible portion (2) of the electronic printed circuit board is serpentine.

16. The automatic assembly method for a multi-piezoelectric yarn sliding sensor according to claim 14, wherein the guide eyelets (4) comprise flat outer walls (6) for gluing to the corresponding flat surfaces of the piezoelectric elements (P).

17. The automatic assembly method for a multi-piezoelectric yarn sliding sensor according to claim 10, wherein the following additional steps are provided: c) a mounting step, wherein, - mechanically mounting the electronic printed circuit board (1) equipped with the piezoelectric elements (P) and the guide eyelets (4) in the respective seats of a support shell (5), wherein i. the electronic printed circuit board (1) is mounted in a first seat, and ii. the guide eyelets (4) are mounted in a second seat, separate and adjacent to the first seat, partially detaching the free end (2c) of the flexible portion (2) from the electronic printed circuit board (1).

18. The automatic assembly method for a multi-piezoelectric yarn sliding sensor according to claim 17, wherein the second seat is made of rubber and the guide eyelets (4) are provided with flat outer walls (6) parallel to the axis of the guide eyelets (4), which comprise at least one longitudinal angular protrusion (8) engaged inside the second seat.

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