System and method for controlling vibration of a mandrel of an extruder head

Abstract

A system and method for controlling the vibrations of a mandrel (5) of an extruder head used in the forming of tubular films for food products, which extruder head is of the type immersed inside a coagulation tank (7) and whose rotating elements are driven by an electric motor. The control method comprises: detecting the vibrations undergone by the free end (5b) of the mandrel (5) by means of a proximity sensor (13); sending the signal detected by the proximity sensor (13) to a controller (17) which, on the basis of the signal, calculates the necessary correction of the rotation frequency of the motor so as to move the rotation frequency of the motor away from a harmonic frequency of the natural oscillation frequency of the mandrel (5); and modifying the rotation speed of the motor until said calculated frequency correction is reached, so that the mandrel (5) does not resonate.

Description

Technical Field

[0001] As stated in the title of this specification, the present invention relates to a control system for monitoring and regulating the vibration state induced on the mandrel included in the extruder die head. More specifically, the extruder is a type commonly used in the forming of food tubular films or edible artificial casings, comprising a counter-rotating nozzle. Background Technology

[0002] Currently, casing extrusion technology based on fibrous collagen is used to form the type of meat casings used to wrap foods such as sausages or stuffed foods. With the help of casing extrusion technology, tubular membranes of varying lengths can be obtained.

[0003] Given the requirements for regularity in size and performance of sausage casings used in food, the tubular extrusion of such casings is an extremely delicate process, and the uniformity of diameter along the variable length of the casing—also known as specifications—is one of the most important parameters.

[0004] Size uniformity allows for sausages with a uniform appearance and a constant weight per unit length in the subsequent stage of stuffing meat products into tubular membranes. This, in turn, makes it possible, for example, to entrust the weight of slices to the number of slices to be packaged, which is advantageous compared to weighing the slices after cutting. Furthermore, size uniformity prevents other problems during the stuffing stage, where certain components of the machine, such as the stuffing horns, are adjusted for each size. For all these reasons, size uniformity is one of the primary goals in the manufacture of artificial sausage casings.

[0005] Most casings or tubular membranes are obtained by tubular molding of a fluid material with a certain paste viscosity, extruded through an annular groove, and then solidifying the fluid material at the outlet of the groove by physicochemical means, commonly referred to as coagulation. These collagenous substances consist of natural collagen fibers dispersed in a gel-like fluid material containing a large amount of water, for example, more than 85% water by weight.

[0006] During the initial production of collagen casings, the extrudable collagen material obtained through the same process can be extruded using dry extrusion technology to produce edible or inedible casings, depending on the physical dimensions of the casing, such as specifications, wall thickness, or the rigidity of the tubular membrane. The edibility of the casings is thus adapted to low-specification production when using dry extrusion technology.

[0007] GB471566 describes a general batch production process in which leather is long-filed and then treated with hydrochloric acid to cause collagen swelling. Swelling continues until the material can be mechanically transformed into a plastic and extensible substance, for example, upon reaching 75% water swelling. Furthermore, the document states that the material can be initially digested using hot water, followed by partial hydrolysis using heat, and treated simultaneously or at the end with a swelling agent. Subsequently, the material is finely shredded and the fibers are separated to maintain fiber length. Finally, the resulting paste is homogenized in a mixer, where the water content is adjusted from 75% to 95%.

[0008] However, the fact that it is necessary to start with materials having a higher solids content, for example, 8% to 11%, also greatly limits the manufacture of casings with thin walls and low specifications. This is mainly due to the need for higher pressure to extrude the material through a nozzle with a narrow slit and all the resulting technical defects, as well as the undesirable increase in heat due to friction on the material and rheological problems caused by the high heterogeneity of the fibers present, which leads to possible clogging in the nozzle, discontinuous flow or pulsating material in the nozzle, which in turn can lead to variations in uniformity and specifications on the surface of the casing.

[0009] In the search for solutions, not only were improvements to the nozzle design proposed, but it was also discovered that attention must be paid to the preparation of the material. Improvements typically aim to maximize fiber separation of the natural fibrous structure through intense mechanical processing of the material. This helps to soften the material, but it also leads to shorter collagen fibers, resulting in a weakened membrane obtained from the extrusion of these collagen fibers.

[0010] In this regard, reference is made to Johnson & Johnson's early 1960s U.S. patents US3123653 and US3123482, which proposed a new method for producing edible casings from rubber raw materials. This new method alters the properties of the material by utilizing the more fibrous or less fibrous portions of those materials, i.e., releasing the protofibrils from the encapsulation that groups the fibers, and thereby releasing the fibers into the final material.

[0011] In the preparation of the material, the hide is shredded and cut into a fine paste, then placed in a weak acid solution, such as 1% to 1.2% lactic acid, which causes the fibers to swell to more than 100% of their original volume. This breaks down the sheaths surrounding the fibrils, and these sheaths are removed, for example, by filtration. For the decomposition to be effective, the ratio of collagen to the acid solution must be very low, much lower than that used in previous dry processes, for example, containing 2.5% to no more than 6% solids. The swollen acidic paste is homogenized and dispersed in a homogenizer, and finally filtered to remove fiber residues, etc. Therefore, the final product before extrusion is a very homogeneous material with a low solids content.

[0012] Patent US3681093 provides clear examples demonstrating that by influencing the smoothness of the material during extrusion, in addition to achieving a significant increase in dimensional uniformity, a beneficial effect of reducing fibril size is obtained, which is accompanied by an increase in the thickness uniformity of the produced film. This patent describes an enzymatic process for reducing fibril size in acidic collagen material by co-proliferating the material with an Aspergillus enzyme prior to extrusion, wherein one of the main objectives mentioned is the production of collagen casings with a constant diameter and wall thickness. In the description of the preferred embodiment of the patent, particularly in Example XII, the preparation of the extrudable material is described in detail, wherein an enzyme is added to an aqueous dispersion of finely chopped collagen prior to the formation of a fine dispersion of finely chopped collagen and acidification, so as to transform the finely chopped collagen into a swollen and extrudable material. The most representative figures in this literature represent comparative measurements of dimensional changes (measured as width-flatness) observed in casings produced using undigested material or using enzymatically digested material, demonstrating that the enzymatically treated material exhibits smoother and more uniform dimensional uniformity compared to the untreated material.

[0013] Similarly, while altering the properties of the material, the processing conditions at the extruder exit are also changed by utilizing the instantaneous solidification system of the newly formed tube, in order to provide the extrusion force required to withstand subsequent processing. For this purpose, extrusion is carried out directly in a coagulation bath, typically a brine solution.

[0014] However, solidification by the solidification of a fluid does not immediately produce a hard film. Instead, it produces a film that is sufficiently self-supporting to move while maintaining its tubular shape, yet still possesses very good plastic characteristics. This film develops to become more rigid with increasing residence time under solidification conditions. This phenomenon may be due, among other reasons, to the large amount of water still remaining in the film, which facilitates molecular movement and passage; or it may be due to incomplete solidification reactions occurring overall, or incomplete solidification reactions occurring internally relative to the exterior of the variable-thickness film itself, and so on.

[0015] Therefore, the new membrane is still deformable during the first, more plastic stage. Thus, a key aspect of manufacturing collagen casings is the extrusion nozzle. The nozzle has several uses. On one hand, the nozzle is an element through which a plastic material, such as swollen fibrous collagen, takes a tubular shape before solidifying into a solid membrane. Using this element, the radial distribution of the casing's outer and inner diameters, as well as the membrane wall thickness, is determined. On the other hand, when the walls defining the nozzle are independent moving elements rotating about the same axis, the fibers of the collagen material deviate from the machine direction towards a more lateral direction, generating a three-dimensional structure with less anisotropy in mechanical properties. Finally, the nozzle is also the element through which the coagulating liquid flows towards both the exterior and interior of the resulting casing.

[0016] Another fundamental component of an extruder is the mandrel, a hollow metal tube extending through the central bore of the nozzle. The mandrel's primary purpose is to determine the casing's dimensions, as it is enclosed during extrusion, thus defining the casing's inner diameter by its own outer diameter. The mandrel includes a fixed end, which can be threaded or unthreaded, through which it is attached to the body of the extruder head, while the other end remains free and determines the height of the internal coagulation bath. Therefore, the length and width of the mandrel are variable; they depend on the height of the coagulation bath and the inner diameter to be imparted to the casing, resulting in a set of mandrels with different diameters.

[0017] A rotary disc extruder can be seen in detail in the aforementioned patent US3122788 of Johnson & Johnson, which is cited herein by way of example only. This die head attempts to overcome the problems inherent in the extrusion of collagen plastic materials with well-known rheological properties, and particularly the effects of preferred fiber guidance and memory in the machine direction, which are primarily generated by weakening the casing wall in the transverse direction. In the patent, a central mandrel can be seen, and how the central mandrel is connected to the extruder die head, in this case, how it is connected to the extruder die head via a threaded section.

[0018] The existing literature cited so far proposes improvements that ensure the uniformity of casing dimensions by physicochemically altering the properties of the material or by adjusting certain structural aspects of the extruder head. However, the literature does not consider other external factors affecting this process, such as vibrations transmitted from the rotating elements included in the extruder and generated in the die head assembly. These rotating elements are primarily the gears of the rotation drive system of the motor shaft and the counter-rotating nozzle—a nozzle commonly used in the extrusion technology of synthetic collagen casings.

[0019] Specifically, these vibrations become even more significant in the mandrel because of its free end, allowing it to easily begin oscillating at its natural frequency, thus vibrating like a tuning fork. This vibration not only affects the regularity of the specifications and thus produces the negative effects already mentioned, but it also affects the recirculation of the coagulated liquid inside the casing. This continuously updated liquid, injected from the base of the extruder, rises along the outer wall of the mandrel until it reaches the free end, where it overflows and the excess is collected inside the hollow tube defining the mandrel.

[0020] In this way, a narrow space is formed between the outer surface of the mandrel and the inner surface of the casing, through which the internal coagulated liquid circulates. In this situation, the forming casing, which is in continuous upward motion, can move at a specific point or area and approach the mandrel, sufficient to cause the internal fluid flow to collapse or reduce its thickness and decrease the degree of internal coagulation in the contact area, or approach for a moment, thereby resulting in a subsequent weak area in the casing.

[0021] The density of the internal coagulant fluid also changes during its ascent because it is diluted upon contact with the new casing due to the amount of coagulant diffusing into the casing and the water absorbed from it. Accordingly, the ascending casing becomes increasingly coagulated and contains less water, thus narrowing the casing walls and causing the space between the casing and the mandrel walls to gradually increase. Consequently, the volume of fluid between the mandrel and the casing also tends to increase as it rises toward the distal end of the mandrel.

[0022] All the phenomena described result in the fact that, during extrusion, neither the plastic state of the casing nor the mass of the casing-inner bath-mandrel assembly is distributed uniformly, and therefore varies along the longitudinal axis of the mandrel.

[0023] Therefore, the vibration or lateral oscillation of the mandrel affects the thickness of the internal coagulant liquid, which in turn can cause the casing to move or oscillate, a movement or oscillation that can be suppressed by the liquid from the external bath. Similarly, circumferential vibration of the mandrel can occur in the radial direction, creating spiral regions with different degrees of coagulation, which will cause very characteristic deformations in the casing. The vibration of the mandrel also acts mechanically on the casing, which is still deformable at its new height, causing changes in the inner diameter of the casing and thus changes in the nominal size of the casing.

[0024] Considering the problems caused by vibration, a solution is needed. These problems mainly include variations in the final casing specifications, differences in additive absorption (crosslinking agents, liquid or natural smoke, plasticizers, etc.), and differences in the permeability of materials to gases such as water vapor and to the deformed pleats formed. Summary of the Invention

[0025] The control system of this invention solves the aforementioned problems of the prior art because it provides an integrated system for detecting and controlling vibrations generated in the mandrel based on the oscillation frequencies of the various electric components involved. This system allows for efficient, economical, and output-ready control of most extrusion systems currently used in the extrusion of casings for food filling, while ensuring casing uniformity.

[0026] More specifically, the operating principle of this method is based on preventing the mandrel from entering a resonant state, a phenomenon that occurs when the frequency of the wave source coincides with the natural frequency of the oscillating object or resonator. Under resonant conditions, the physical system tends to oscillate with a larger amplitude, amplifying the effects of the vibration, which is detrimental in this situation.

[0027] If the frequency difference between the emitter (the rotating element of the extruder) and the resonator (mandrel) is large, the amplitude of the resonator system will be minimal; and the greater the difference between the two frequencies, the greater the energy required to produce an oscillation of a specific amplitude. However, under resonance conditions, when the frequency difference becomes minimal, a small amount of force applied by the emitter can achieve a large oscillation amplitude in the resonator system, thereby generating significant interference in the resonator system.

[0028] When an element vibrating at a specific frequency is placed at the base of a mandrel, i.e., used as a transmitter, if the element is in sync with or excited to the inherent oscillation frequency of the mandrel, the mandrel will enter a resonant vibration state until a movement is produced in which the amplitude of the movement mechanically affects the casing.

[0029] Next, a more specific analysis is conducted on the case of an extrusion system with counter-rotating nozzles, where two hollow cylindrical components used to expel the extruded material from the trough or nozzle rotate in opposite directions. The vibrations induced in the mandrel are regulated by the rotation of an electric motor that drives the rotating elements of the extruder, primarily the motor shaft and gears in the rotation drive system of the counter-rotating nozzles. Typically, as the motor speed increases, the mandrel gradually approaches a resonant vibration state, and the oscillations are amplified. After a certain limit, the oscillations begin to weaken with further increases in motor speed.

[0030] To keep the mandrel away from resonance, one possible solution is to determine the natural frequency of the element to prevent the motor from operating near a threshold, thereby establishing a safe operating range. However, putting this idea into practice, mathematically calculating the theoretical natural frequency of oscillation for each mandrel used in different extruders is tedious and complex, as this frequency depends on the mandrel's geometry and composition.

[0031] Furthermore, it must be considered that the vibration state of the mandrel is usually not determined by a single frequency, but by the superposition of harmonics with different frequencies and lower amplitudes and a fundamental harmonic with a larger amplitude. This superposition implies greater complexity, causing the calculated theoretical frequencies to differ from the observed empirical frequencies.

[0032] For all the aforementioned cases, the inherent oscillation frequency of the mandrel can be predicted in an approximate manner, i.e., the oscillation frequency of the mandrel is isolated from the rest of the extruder components; however, such a prediction does not possess the certainty necessary for its application in extrusion practice, especially considering the complex interactions of other variable factors during actual casing extrusion, such as: the solidified liquid, which contacts the inner and outer surfaces of the mandrel and can suppress mandrel vibration or alter the mandrel's resonant frequency; and the casing itself, which is in a new state of increased solidification and also acts as an elastic diaphragm that can suppress or alter the vibration conditions of the mandrel it encloses.

[0033] All these interactions will cause the mandrel under its operating conditions to resonate at a frequency different from its inherent frequency, that is, a frequency that can be theoretically calculated for isolated elements.

[0034] Figure 3 The figure shows the mandrel vibration spectrum obtained from tests conducted using an extruder die submerged in a coagulation tank under normal operating conditions, thus taking into account the external factors mentioned above. This figure should be interpreted as a non-limiting example, as different spectra will be obtained for mandrels with different specifications or materials and under different operating conditions. The tests conducted included vibrations of the free end of the mandrel at different rotational modes relative to the electric motor, detected by a proximity sensor.

[0035] In other words, the frequency of the motor's rotation, equivalent to its rotational speed and expressed in Hz on the horizontal axis, is gradually varied, for example, within a range of 10 rpm, and the vibration of the mandrel is recorded for each of these frequencies. The positioning signal detected by the sensor at the free end of the mandrel is a voltage signal described as an approximately sinusoidal curve; Figure 3The vertical axis represents the maximum peak-to-peak value of the voltage, expressed in mV. The larger the amplitude of the resulting sine wave, the greater the vibration caused by the rotating elements of the extruder within the mandrel. Therefore, other representative values ​​of the amplitude of the sine signal can be collected, namely the peak-to-peak value, the effective value, or the amplitude itself.

[0036] exist Figure 3 In the diagram, we can see the highest vibration peak corresponding to the fundamental resonant frequency at the motor rotation frequency of 1.7 Hz, and at the same time, we can see a second vibration peak with a lower amplitude corresponding to one of its harmonic frequencies at the frequency of 0.8 Hz.

[0037] This test is performed on each extruder and under specific operating conditions (temperature, solidified liquid, etc.) to determine the frequency at which the mandrel enters resonance. Once determined, the motor speed is adjusted so that the motor does not operate at these frequencies and remains under safe operating conditions. This control method is a simple and economical solution to be implemented in extruders.

[0038] Alternatively, the present invention proposes a second solution comprising a control system that continuously monitors the mandrel's vibration state in a non-invasive but reliable and adjustable manner during extrusion operation, and simultaneously regulates the vibration state in response to specific critical frequencies deemed dangerous. When the mandrel's vibration amplitude exceeds a specific preset threshold, the controller gradually increases or decreases the extruder's rotational speed until the mandrel's vibration amplitude is reduced below the preset threshold. In this way, the mandrel can be moved away from its resonant frequency without performing prior tests to experimentally determine the resonant frequency for each type of mandrel or extruder considered.

[0039] Therefore, the control system has three main components: a proximity sensor, which is preferably positioned at a height consistent with the free end of the mandrel and a few millimeters away from the outer surface of the casing, where oscillations are most pronounced and most problematic; a digital controller that receives signals from the sensor; and a frequency converter connected to a gear motor that drives the rotating elements of the extruder.

[0040] The proximity sensor will preferably be an electromagnetic detector, so as to take advantage of the sensitivity of magnetic detection to the metallic material forming the mandrel, and the fact that magnetic detection is insensitive to both the coagulating liquid and the new casing, to clearly detect the oscillation of the mandrel. The greater the degree of this oscillation, the more unstable, irregular, or dangerous the coagulation process is considered, and the more likely it will lead to undesirable changes in the production of casings that are expected to be as regular as possible.

[0041] The signal sensed by the sensor—which detects the distance between the free end of the mandrel and the sensor itself—is approximated as a sine wave with a specific oscillation frequency; the amplitude of the wave is more or less highly dependent on how close the oscillation is to the resonant frequency. In practice, a considerable number of harmonics and overlapping frequencies have been observed, indicating the complexity of the process.

[0042] Sensor signals are sent to an intelligent system or controller that integrates the frequency signals from the detectors and calculates the necessary frequency correction for the motor to move away from the resonant frequency of the mandrel, which is understood to be the frequency at which the mandrel enters resonance during the extrusion operation. The signal calculated by the controller commands, for example, a frequency converter, to change the speed of the motor reducer driving the rotating elements of the extruder until the oscillation frequency is far from the harmonic of the mandrel's resonant frequency. Attached Figure Description

[0043] To supplement the ongoing description and to aid in a better understanding of the features of the invention, this specification is accompanied by a set of drawings that form an integral part of the specification. These drawings, which are illustrative and not restrictive in nature, illustrate the following:

[0044] Figure 1 The present invention illustrates a mandrel vibration control system installed in the die head of an extruder for use with tubular films for food.

[0045] Figure 2 A longitudinal cross-sectional view of the extruder head for use in food tubular films is shown, along with details of the mandrel.

[0046] Figure 3 An example of the vibration spectrum of the mandrel obtained in the test is shown. Detailed Implementation

[0047] In view of the above figures and according to the reference numerals used, examples of preferred embodiments of the invention can be seen in the figures, including the parts and elements described and labeled in detail below.

[0048] Specifically, Figure 2 A preferred embodiment of an extruder head for forming tubular food films is illustrated by way of example. Specifically, the wet extrusion of the collagen casing 9, including internal coagulation, is carried out directly in a coagulation bath outside the casing 9. The external coagulation liquid is recirculated from the external coagulation bath to the casing 9 via a recirculation pipe 6 to refresh the external coagulation liquid.

[0049] The extruder has a body 1, which is immersed in a coagulation tank 7 containing an external coagulating liquid. The body 1 includes multiple chambers into which collagen paste 8 is introduced under pressure through conduits (not shown), the paste being driven through the conduits by a pumping system. The paste 8 rises through a channel 2 defined by the walls of two concentric hollow cylindrical elements 3, 4—this has already… Figure 2 The longitudinal section represents the extruder, which then exits through a tubular nozzle 2a defined by the end of the groove 2 itself, the groove 2 determining the thickness of the tubular film.

[0050] Once it has passed through the tubular nozzle 2a, the casing 9 continues its upward movement until it reaches the roller 12, where the extruded tubular film is flattened.

[0051] At least one of the two hollow cylindrical elements 3, 4—although typically both of the two hollow cylindrical elements 3, 4—can be driven to rotate on their respective axes by a drive shaft of a gear or electric motor connected to the stem (not shown in the figures). For example, in an extrusion system with a counter-rotating nozzle typically used for forming casings, the inner hollow cylindrical element 3 rotates in the opposite direction to the outer hollow cylindrical element 4.

[0052] To better understand, Figure 2 In this design, the lengths of the hollow cylindrical elements 3 and 4 in the region encompassed outside the body 1 of the extruder have been enlarged. These hollow cylindrical elements 3 and 4 are inserted into the body 1 of the extruder and attached to a disc 10, which is rotated by a gear connected to the same motor shaft (not shown).

[0053] The tube or mandrel 5 extends inside the inner hollow cylindrical element 3, such that a gap 11 is defined between the outer wall of the mandrel 5 and the inner wall of the inner hollow cylindrical element 3, through which the internal coagulated liquid of the casing 9 rises, and is injected through a conduit (not shown) located at the base of the extruder body 1.

[0054] like Figure 2 As shown in the details, the mandrel 5 is a hollow metal element with radial and elongated symmetry. The mandrel 5 is securely and hermetically attached at one end to the base of the extruder body 1. This end will be referred to as the fixed end 5a, and this end is centered such that its axis coincides with the axis of the hollow cylindrical elements 3 and 4. The opposite end is the free end 5b, which determines the height of the internal coagulation bath. In this way, the mandrel 5 or hollow tube includes a section extending inside the extruder and a section extending through the coagulation tank 7, which is typically longer.

[0055] The length and width of the mandrel 5 are variable; the length and width of the mandrel 5 depend on the height of the coagulation bath and the desired inner diameter to be imparted to the casing 9, respectively, thus resulting in a series of mandrels 5 with different diameters. The configuration of the mandrel 5 can also be variable; in its simplest form, the mandrel 5 can resemble a cylindrical tube with a uniform diameter and thickness throughout its length. However, the mandrel 5 can also be composed of segments with different compositions and dimensions, for example, the mandrel 5 may terminate at its fixed end 5a with a threaded or bayonet fitting for secure mounting into the extruder, or the mandrel 5 may have a more complex structure, such as the mandrel 5 comprising different segments along its length or segments whose diameter varies gradually or discontinuously along its length.

[0056] As the internal coagulated liquid rises to the outer wall of the mandrel 5, it reaches the free end 5b of the mandrel and overflows, thus entering the mandrel 5 which is partially filled with the liquid. Furthermore, a narrow space is formed between the outer surface of the mandrel 5 and the inner surface of the casing 9 being produced, through which the internal coagulated liquid circulates.

[0057] Preferably, the opening of the free end 5b of the mandrel 5 is at the level of the surface of the outer coagulation bath to facilitate adjustment of the height of the inner bath and prevent the height of the inner bath from exceeding the height of the outer bath or from falling below the level of the outer bath. In the first case, the casing 9 will experience internal overpressure, causing the diameter of the casing 9 to expand; in the second case, the opposite occurs, and the tubular membrane will contract. Similarly, the mandrel 5 tube will preferably be wide enough to quickly discharge excess internal bath liquid, the renewal or recycling rate of which is determined by the extrusion speed.

[0058] on the other hand, Figure 1 The diagram illustrates a control system capable of adjusting and reducing the vibrational motion of the mandrel 5. The system comprises three main components: a proximity sensor 13 positioned at a height of 5b at the free end of the mandrel 5, close to the outer surface of the casing 9, which transmits received signals to a digital controller 17, which in turn acts on a frequency converter 15 connected to a geared motor that drives the rotating elements of the extruder.

[0059] It can be observed that the proximity sensor 13 is submerged in the solidification tank 7 closer to the free end 5b of the mandrel 5, which does not protrude above the horizontal level of the bath. Therefore, the magnetic detector must be enclosed and isolated in a housing 16, preferably plastic and tightly sealed, to prevent the proximity sensor 13 from contacting the liquid in the bath and to prevent subsequent corrosion of the proximity sensor 13. Similarly, the proximity sensor 13 can be anchored to the wall of the solidification tank 7 by means of a fastening element 14.

[0060] In addition, the control system may include means for adjusting the distance from the proximity sensor 13 to the mandrel 5 to prevent the detector from coming into contact with the very fragile new gel, for example, when the diameter of the mandrel 5 is changed to produce casings with larger or smaller dimensions, and to move the detector closer to have sufficient signal sensitivity.

[0061] In a preferred embodiment of the invention, the proximity sensor 13 may be an inductive electromagnetic detector, the operation of which is described below. These sensors internally consist of a detection zone, a coil, an oscillator, a trigger circuit, and an output circuit. When current flows through the oscillator and the coil with very fine copper wire, the current generates a magnetic field. When a metal element approaches the detection zone of the sensor, the coil induces a magnetic field in the object through eddy currents. This magnetic field formed in the metal element is opposite to the original magnetic field, which reduces the inductance of the original magnetic field and thus reduces its impedance. When the material moves away from the sensor, the oscillator generates the original magnetic field again. This phenomenon repeats when the metal element approaches again. This phenomenon repeats repeatedly as the material moves closer to and further away from the sensor. These distance changes are monitored by external units that process the information to show the user values ​​that can be used for positioning, metal detection, and other applications.

[0062] For a mandrel 5 in a state of vibration, the signal obtained from the proximity sensor 13 is approximately a sine wave with a specific oscillation frequency, the amplitude of which is more or less highly dependent on the proximity of the oscillation to the resonant frequency. That is, the mandrel positioning signal 5 always reflects the vibration state.

[0063] The electrical signal generated by proximity sensor 13 is sent to intelligent system or controller 17, which is preferably digital, capable of integrating the signal, and calculating the necessary frequency correction in the motor to move away from the inherent frequency of the spindle 5 based on the vibration frequency detected by the sensor. That is, when the vibration amplitude of the spindle 5 exceeds a predetermined threshold—a threshold set by each user based on the vibration of a tubular diaphragm considered suitable for obtaining the desired uniformity standard—the controller 17's calculation algorithm calculates the necessary frequency change for the motor to reduce the error between the amplitude of the spindle 5's oscillation at that moment and the preset threshold. In this way, the motor's rotational speed is gradually increased or decreased until the vibration amplitude of the spindle 5 decreases below the preset threshold.

[0064] Finally, the signal from controller 17 commands another regulating device, which can modify the speed of the gear motor driving the rotating elements of the extruder. In a preferred embodiment, the device includes a frequency converter 15 that increases or decreases the motor's rotational speed upon receiving a desired correction frequency—information sent from controller 17—so that the motor's rotational frequency matches the desired or corrected frequency, which causes the mandrel 5 to reduce its vibration and move away from its resonant frequency.

[0065] In other words, the control system goes through the following stages:

[0066] - The position of the free end 5b of the mandrel 5 is continuously and in real time detected, thereby enabling the determination of the oscillation frequency and amplitude of the free end 5b;

[0067] - The necessary changes required to calculate the motor's rotational frequency based on the detected oscillations of the mandrel 5, thereby reducing the oscillation amplitude of the free end 5b of the mandrel 5 to below a preset threshold and thus avoiding resonance of the free end 5b; and

[0068] - Modify the motor's rotational speed until it reaches the change in rotational frequency calculated in the previous step.

[0069] This process allows for continuous adjustment of the vibration of the spindle 5, thereby preventing the spindle 5 from entering resonance, without needing to know in advance the value of the spindle 5's inherent oscillation frequency—which would also be affected by other external factors, such as solidified liquids, and would no longer correspond to the frequency of resonance of the spindle 5 during use—because the controller 17 itself calculates, through a computational algorithm, the motor rotation frequency that needs to be increased or decreased to minimize the vibration of the spindle 5.

[0070] In a second preferred embodiment of the invention, not shown in the accompanying drawings, the controller 17 can be omitted; that is, the intelligent system including a mathematical algorithm capable of calculating the necessary frequency correction of the motor based on the electrical signal received from the proximity sensor 13 can be omitted. The algorithm can be executed in a control program of electronic circuitry integrated into the frequency converter 15, such that the frequency converter 15 directly receives and processes the electrical signal from the proximity sensor 13 to calculate the required frequency correction. In this way, the control system of the present invention can include a single regulating element, namely the frequency converter 15, rather than two distinct physical systems serving as the controller, namely the controller 17 and the frequency converter 15.

[0071] On the other hand, an alternative method to a previous method for controlling the vibration of mandrel 5 includes the following steps:

[0072] -The harmonic frequency of the resonant frequency of the free end 5b of the mandrel 5 during the extrusion process is determined by the following steps:

[0073] - Record the vibration of the spindle 5 detected by the proximity sensor 13 for different rotation frequencies of the motor;

[0074] - Determine at which frequency of the motor the vibrations mentioned in the preceding steps would exceed a given threshold, i.e., determine the vibration peak that deviates from the remaining vibrations among a plurality of vibrations and remains above the threshold; and

[0075] -The rotational frequency of the motor determined in the previous step will be established as the harmonic frequency of the resonant frequency of the free end 5b of the spindle 5.

[0076] - Modify the motor's rotational speed until the motor's rotational frequency is far from a given value relative to the resonant frequency determined in the previous step; the predetermined distance value will depend on the vibration of the tubular diaphragm that each user deems suitable for obtaining the desired uniformity standard.

[0077] In a preferred embodiment of this method, the vibration of the free end 5b of the mandrel 5 can be calculated using the following steps:

[0078] - Utilizing at least one proximity sensor 13 to detect real-time changes in the position of the free end 5b of the mandrel 5; and

[0079] - The amplitude of the sinusoidal voltage signal detected by the proximity sensor 13 is established as the vibration of the free end 5b of the mandrel 5.

Claims

1. A system for controlling the vibration of a mandrel (5) of an extruder head used in the forming of tubular films for food processing, wherein, The extruder head includes at least one rotating element driven by an electric motor, the mandrel (5) has a free end (5b) that oscillates due to vibrations transmitted by the rotating element, and wherein the extruder head is submerged within a solidification tank (7), characterized in that the system comprises: At least one proximity sensor (13) detects the real-time change in the position of the free end (5b) of the mandrel (5) and determines the oscillation amplitude of the free end (5b); A computing device that receives a signal detected by the proximity sensor (13) and calculates a change in the rotational frequency of the electric motor based on the signal, such that the change reduces the oscillation amplitude of the free end (5b) of the spindle (5) to below a preset threshold; and The variable speed converter of the electric motor modifies the rotational speed of the electric motor until the rotational frequency of the electric motor reaches the variable value, so that the rotational frequency of the electric motor is far away from the harmonic of the natural oscillation frequency of the free end (5b) of the mandrel (5), thereby moving the mandrel (5) away from the resonance state, wherein the resonance state is a phenomenon that occurs when the rotational frequency of the electric motor is consistent with the natural frequency of the oscillation of the free end (5b) of the mandrel (5).

2. The system for controlling the vibration of the mandrel (5) according to claim 1, characterized in that, The computing device is the controller (17) of the transducer that commands the speed of the electric motor.

3. The system for controlling the vibration of the mandrel (5) according to claim 1, characterized in that, The speed changer of the electric motor is a frequency changer (15).

4. The system for controlling the vibration of the mandrel (5) according to claim 3, characterized in that, The computing device is integrated into the frequency converter (15).

5. The system for controlling the vibration of the mandrel (5) according to claim 1, characterized in that, The proximity sensor (13) is an inductive magnetic detector.

6. The system for controlling the vibration of the mandrel (5) according to claim 1, characterized in that, The system also includes a protective housing (16) for the proximity sensor (13), which is connected to the solidification tank (7) via a fastening element (14).

7. The system for controlling the vibration of the mandrel according to claim 6, characterized in that, The system also includes means for adjusting the distance from the proximity sensor (13) to the mandrel (5).

8. A method for controlling the vibration of the mandrel (5) of an extruder head used in the forming of tubular films for food, characterized in that, The method uses a system for controlling the vibration of the mandrel (5) according to any one of claims 1 to 7, and the method includes the following steps: a. Determine the frequency of oscillation at the free end (5b) of the mandrel (5); b. Calculate a correction value for the rotational frequency of the electric motor based on the frequency determined in step a, the correction value being designed to move the rotational frequency of the electric motor away from the harmonic frequency of the resonant frequency of the free end (5b) of the mandrel (5) from a given value; and c. Modify the rotational speed of the electric motor until the rotational frequency of the electric motor reaches the correction value calculated in step b, thereby moving the mandrel (5) away from the resonance state, wherein the resonance state is a phenomenon that occurs when the rotational frequency of the electric motor is consistent with the natural frequency of the free end (5b) of the mandrel (5) oscillating.

9. The method for controlling the vibration of the mandrel (5) according to claim 8, wherein, The frequency of the oscillation in step a is determined by detecting the temporal change in the position of the free end (5b) of the mandrel (5) using a proximity sensor (13).

10. The method for controlling the vibration of the mandrel (5) according to claim 8, wherein, The correction value of the rotation frequency in step b is calculated by the digital controller (17).

11. A method for controlling the vibration of the mandrel (5) of an extruder head used in the forming of tubular films for food, characterized in that, The method uses a system for controlling the vibration of the mandrel (5) according to any one of claims 1 to 7, and the method includes the following steps: Determine the harmonic frequency of the resonant frequency of the free end (5b) of the mandrel (5); and The rotational speed of the electric motor is modified until the rotational frequency of the electric motor is far from a given value relative to the harmonic frequency of the resonance frequency determined in the previous step, thereby moving the mandrel (5) away from the resonance state, wherein the resonance state is a phenomenon that occurs when the rotational frequency of the electric motor is consistent with the natural frequency of the free end (5b) of the oscillating mandrel (5).

12. The method for controlling the vibration of the mandrel (5) according to claim 11, wherein, The harmonic frequency of the resonant frequency of the free end (5b) of the mandrel (5) is determined by the following steps: The vibration of the free end (5b) of the mandrel (5) is recorded for different rotation frequencies of the electric motor; Determine at which frequency of rotation of the electric motor the vibration mentioned in the previous step would exceed a given threshold; and The rotational frequency of the electric motor determined in the previous step is established as the harmonic frequency of the resonant frequency of the free end (5b) of the spindle (5).

13. The method for controlling the vibration of the mandrel (5) according to claim 12, wherein, The vibration of the free end (5b) of the mandrel (5) is determined by the following steps: The real-time change in position of the free end (5b) of the mandrel (5) is detected using at least one proximity sensor (13); and The amplitude of the sinusoidal voltage signal detected by the proximity sensor (13) is established as the vibration of the free end (5b) of the mandrel (5).

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