Method for controlling a fiberizing device

Abstract

The present invention relates to a method for forming glass fibers using a rotating assembly (1) comprising a shaft (2) driven in rotation about an axis of rotation (A), a centrifuge (3) fixed to the shaft (2) and provided with a primary annular wall (30) having a plurality of primary orifices (31), and means for feeding molten glass (20) to the centrifuge (3), Here, under the effect of centrifugal forces resulting from the rotation of the rotating assembly (1), a primary reserve (R1) of glass is formed against the primary annular wall (30) of the centrifuge (3), which comprises acquiring at least one primary image of the centrifuge (3) by means of a camera (7), processing the at least one primary image by means of an image processing system (72) and evaluating a parameter representative of the volume of the primary reserve (R1) by means of a system (74) for processing data from the primary images.

Description

[Technical field]

[0001] The present invention relates to a method for forming glass fibers. [Background technology]

[0002] The method according to the invention applies in particular to the industrial production of mineral wool, intended for use, for example, in the construction of thermal and / or acoustic insulation products.

[0003] Glass fiber forming devices, i.e. fiberizers, typically have a centrifuge, also called a fiberizer spinner, which includes an annular wall, called a "primary" wall or "strip," through which a number of orifices (hereinafter, primary orifices) penetrate. The fiberizer also has a shaft, which is intended to be rotated by a motor and on which the centrifuge is attached.

[0004] There are various types of fiberizers: in some cases, the so-called "bottom" centrifuges are closed at their lower end. In this case, during operation, the flow of molten glass originating from a suitable feed means flows directly into the bottom of the centrifuge. Under the action of centrifugal force, the molten glass is blown onto the primary annular wall, where a primary reserve of glass is formed.

[0005] In other cases, so-called "bottomless" spinners are open at their lower end. In such cases, the shaft is generally hollow and is connected at its upper end to a molten glass supply means. At its lower end, the shaft is connected to a basket that is disposed within the centrifuge and is intended to rotate together with the centrifuge and the shaft. The basket has a secondary annular wall with a number of orifices passing through it.

[0006] When the glass fiber forming apparatus is in operation and the centrifuge, shaft and basket rotate about the axis of the shaft, molten glass flows into the shaft, into the basket, and under the effect of the rotation, the molten glass is sprayed onto the secondary annular wall of the basket, forming a secondary reserve, passes through a number of secondary orifices in the basket and, in the form of lofty filaments, onto the primary peripheral wall of the centrifuge, forming a primary reserve.

[0007] In both cases (bottom centrifuge or bottom-less centrifuge), under the effect of centrifugal force, the glass of the primary reserve is blown by the primary orifice in the form of filaments. These filaments are then subjected, while traveling along the wall of the spinner, to the action of an annular entrainment flow at high temperature and high speed, which attenuates them and transforms them into fibers. The formed fibers are entrained by this gaseous entrainment flow into a receiving device, generally consisting of a gas-permeable strip. This method is called "internal centrifugation".

[0008] This process has been the subject of numerous improvements, particularly with regard to the centrifuges, aimed at improving the quality of the fibres.

[0009] For example, it has been demonstrated that distributing the primary orifices over an annular row and decreasing the diameter of the orifices from the row located at the top of the strip towards its lower part makes it possible to improve the quality of fiberization.

[0010] This basic principle has been further improved, in particular as taught in French patent specification No. 2 443 436, by means of which it is possible to obtain a laminar flow of molten material from the top to the bottom of the spinner strip.

[0011] Another modification described in EP 1 370 496 A1 has been made to improve fiber quality and efficiency by distributing the orifices of the strip into a number of annular regions arranged in an overlapping fashion, at least two of the annular regions having a number of orifices per unit surface area that differs by 5% or more. Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention also aims to improve the quality of the fibers obtained. [Means for solving the problem]

[0013] It proposes an improvement in the above-mentioned glass fiber forming method.

[0014] Thus, the present invention relates to a method of forming glass fibers by a rotating assembly comprising: - a shaft rotating around an axis of rotation, - a centrifuge, the centrifuge being provided with a primary annular wall fixed to a shaft and having a plurality of primary orifices; - Means for feeding the molten glass to the centrifuge. where, under the effect of centrifugal forces resulting from the rotation of the rotating assembly, a primary reserve of glass is formed against the primary annular wall of the centrifuge; The method comprises the steps of: (a) acquiring at least one primary image of the centrifuge with a camera; (b) processing the at least one primary image by an image processing system; and (c) evaluating a parameter representative of the volume of the primary reserve by a system for processing data from the primary images.

[0015] The invention proposes to automatically evaluate one parameter of the fiber formation process, which has been established as influencing the quality of the fibers obtained and the successful operation of the centrifuge; namely the volume of the reserve of molten glass formed against the annular wall of the centrifuge.

[0016] As explained above, as the centrifuge rotates and molten glass is dispensed, a primary permanent reserve of molten glass is formed against the peripheral strip and dispensed into a number of primary orifices of the centrifuge.

[0017] The volume of glass contained in the primary tank of the centrifuge is an important parameter in the operation of the fiberizer. This volume defines the pressure that is applied to the molten glass. This pressure, however, determines the speed at which the glass exits through the primary orifice, which as such affects the quality of the filaments produced. It has therefore been established that:

[0018] If the pressure applied to the molten glass is too low, the filaments exiting the spinner will have a hook shape and the resulting fibers will be of poor quality.

[0019] If the pressure is too high, the volume of the reserve becomes too large, so that the molten glass furthest from the burner and toward the inside of the centrifuge begins to cool or even solidify, which can damage the centrifuge. In some cases, the molten glass can even project out of the centrifuge through its lower opening, with the attendant risk of fire.

[0020] Controlling a parameter representative of the volume of the primary reserve makes it possible to control this pressure and, optionally, to adjust the operation of the glass fiber former in real time.

[0021] The evaluated parameter is a parameter representative of the volume of the reserve. The actual volume is not necessarily calculated within the scope of the claimed method. The evaluated parameter may in particular be proportional to this volume. This is for example the (horizontal) thickness of the reserve, calculated geometrically from the height of the glass measured on the primary image and the characteristics of the centrifuge and the camera.

[0022] The method according to the invention applies to all types of fiberizing equipment.

[0023] In particular, the primary image acquired by the camera may be an image of at least a portion of the bottom of the rotating assembly, the image showing at least the lower portion of the centrifuge.

[0024] According to one example, the centrifuge comprises an opening at its lower end, through which the primary image is acquired in step (a). This centrifuge is said to be "bottomless". For example, the primary annular wall comprises a free lower edge, or the primary annular wall is extended at its lower end by a lower wall or cuff (turn-up), which extends towards the interior of the centrifuge and forms an angle with the annular wall, and the opening is bounded by the free edge of the cuff.

[0025] In this case, in particular, the camera used in step (a) preferably has a viewing direction that forms an angle with the axis of rotation, in this way the camera can directly view the free surface of the primary reserve, which in particular faces towards the axis of the centrifuge.

[0026] According to another configuration, the centrifuge comprises a bottom (solid) and the image acquired is an image of at least a part of the bottom of the centrifuge. In this case, the volume of the primary reserve can be evaluated from the color change on the bottom of the centrifuge, in particular obtained by either an optical camera operating with visible light or an infrared camera: the bottom of the centrifuge has a higher temperature at the position where the glass flow falls vertically than at the position where it falls along the reserve (the glass has time to cool a little when it is blown against the primary annular wall). The boundaries of the reserve can be obtained by image processing (contrast, thresholding, etc.).

[0027] Alternatively, especially in the case of centrifuges with a (solid) bottom, images may possibly be taken from the top of the centrifuge.

[0028] According to one example, in step (b), the image processing comprises identifying at least one boundary of the primary reserve on the primary image.

[0029] According to one example, the at least one boundary comprises an edge of the opening of the centrifuge and an upper edge of the primary reserve.

[0030] According to one example, identifying at least one boundary comprises determining at least one series of points by digital methods for detecting contours, in particular by thresholding, and fitting said series of points to an ellipse.

[0031] According to one example, the image acquisition in step (a) is performed using an infrared camera.

[0032] According to one example, the method includes, prior to step (c), a step (b') of calibrating the data processing system by measuring elements of the rotating assembly on the acquired primary images and by comparing the measurements with known dimensions of said elements.

[0033] According to one example, the method further comprises a step (d) of determining, at the end of at least one succession of steps (a) to (c), a deviation of the volume of the reserve from a nominal value and adjusting the rotation speed of the rotating assembly as a function of said deviation.

[0034] According to one example, prior to step (d), steps (a) to (c) are performed at least N times in succession, in particular N times in succession, with regular intervals in time, for example at least 30 seconds between each.

[0035] According to one example, when the rotational speed of the rotating assembly reaches a predetermined maximum value at the end of step (d), a warning is issued.

[0036] If the centrifuge comprises an opening at its lower end, the rotating assembly usually comprises a basket, which is arranged below the shaft, fixed to it and provided with a secondary annular wall having a number of secondary orifices, against which a secondary reserve of glass forms under the effect of the centrifugal forces resulting from the rotation of the rotating assembly. In this case, advantageously, the bottom of the basket may also be viewed by a camera (or another camera) and the method may further comprise evaluating, by a system for processing data obtained from said at least one primary image or another so-called secondary image of the centrifuge, a parameter representative of the volume of the secondary reserve.

[0037] In particular, the volume of the secondary reserve can be evaluated from a color change on the bottom of the basket, obtained in particular by either an optical camera operating with visible light or an infrared camera: the bottom of the basket, at the position where the glass flow falls vertically, has a higher temperature than at the position where it falls along the secondary reserve. The boundaries of the reserve can be obtained by image processing (contrast, thresholding, etc.).

[0038] The present invention also relates to a fiberglass forming apparatus having a rotating assembly including: - a shaft rotating around an axis of rotation, - A centrifuge, provided with a primary annular wall fixed to a shaft and having a plurality of primary orifices. the rotating assembly is configured such that under the influence of centrifugal forces resulting from rotation thereof, a primary reserve of glass is formed against the primary annular wall; The apparatus further comprises: - means for acquiring at least one primary image of the centrifuge; - a system for processing said at least one primary image, and - a data processing system configured to estimate a parameter representative of the volume of the primary reserve from data from the primary images.

[0039] The invention also relates to a computer program comprising instructions for carrying out at least steps (b) and (c) of the method defined above, when said program is run on a computer.

[0040] According to one example, the computer program further comprises instructions for carrying out step (d) above when said program is executed on a computer.

[0041] The invention also relates to a computer readable medium having such a computer program recorded thereon.

[0042] Further features and advantages of the present invention will be explained in conjunction with the drawings, in which: [Brief description of the drawings]

[0043] [Figure 1] FIG. 1 shows a cross-section of a glass fiber forming device according to the invention along an axial plane; [Diagram 2] FIG. 2 is a detailed view of FIG. 1; [Diagram 3] FIG. 3 is an example of an image captured by the camera of FIG. 1 (shown in negative for ease of viewing); [Figure 4]Figure 4 shows test results showing the effect of variations in the rotational speed of the rotating assembly on the volume of the secondary reserve; [Diagram 5] FIG. 5 is a schematic diagram of the basket as seen by an axis-oriented camera. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] FIG. 1 depicts a cross-sectional view of a glass fiber forming apparatus 100 according to the present invention.

[0045] The glass fiber forming apparatus 100 has a rotating assembly 1 which rotates about an axis A under the influence of a drive motor 8 .

[0046] The rotating assembly 1 has a shaft 2 of axis A, intended to be rotated by a motor 8 .

[0047] The apparatus further includes a centrifuge 3 having an annular side wall (hereinafter primary wall) 30 pierced by a number of orifices (hereinafter primary orifices) 31, and a web 32 forming the top of the centrifuge 3. In the example, the centrifuge 3 is fixed to the shaft 2 via a tulip 4, which is in the extension of the web 32. When the glass fiber forming apparatus 100 is in the fiberization position, the axis A is vertical.

[0048] In the remainder of this specification, the terms "top", "bottom", "upper" and "lower" as well as the "upper" and "lower" portions are defined relative to a vertical axis when the centrifuge 1 is in the centrifugal position, i.e., when the centrifuge's rotation axis A lies on the vertical axis as in FIG. 1.

[0049] In the particular example shown, the primary annular wall 30 is extended at its lower end by a lower wall or cuff 33, which extends towards the interior of the centrifuge 3 and forms an angle with the primary annular wall 30. Here, the cuff 33 extends approximately horizontally within the fiberization location. A central opening 34 (here of circular cross section) is defined by the free edge of the cuff 33. The centrifuge 1 is said to be "bottomless".

[0050] As shown in Figure 1, the shaft 2 is hollow. It has a central channel 20 at its upper end which is connected to a means for supplying molten glass (not shown). At its lower end, the shaft 2 is connected to a basket 5 having a secondary annular side wall 50 pierced by a number of orifices, called secondary orifices 51, and a bottom 52. The basket 5 is located inside the centrifuge 3, as can be seen in Figure 1.

[0051] The glass fiber forming apparatus 100 also has at least one annular burner 6 which generates a hot gaseous drawing jet. The gas drawing jet is a hot gas stream (typically 1350°C to 1600°C) which exits the annular burner 6 through its outlet 60 such that the gas drawing jet is tangential to the annular wall 30 of the centrifuge 3. In the fiberization position, the outlet 60 of the annular burner 6 is located above the primary annular wall 30 of the centrifuge 3.

[0052] During operation of the glass fiber forming apparatus 100, the centrifuge 3, the shaft 2 and the basket 5 rotate about the axis A. Molten glass flows from the molten glass supply means into the shaft 2 and into the basket 5. Under the effect of the rotation, the molten glass is blown onto the secondary annular wall 50 of the basket 5 and forms a permanent reserve R2 (hereinafter, secondary reserve) relative to said annular wall 50. The molten glass obtained from said secondary reserve R2 passes through a number of secondary orifices 51 (having a diameter of about 1.5 mm to 3 mm) of the basket 5 and is blown in the form of bulky filaments V1 (diameter of about 2 mm) onto the primary annular side wall 30, usually called "strip", of the centrifuge 3. A primary permanent reserve of molten glass R1 is then formed in the centrifuge 3, which is thereby fed into a number of orifices 31 pierced in the primary annular side wall 30. The molten glass finally passes through a number of primary orifices 31 (having a diameter of about 0.5 mm to 1 mm) of the centrifuge 3 to form the pre-fibers V2. Under the action of the gaseous drawing jet from the burner 6, the pre-fibers V2 are elongated and their end portions generate discontinuous fibers V3, which are then collected below the centrifuge 3.

[0053] According to the invention, the device taken as an example comprises means intended to estimate in an automated manner the volume of the primary reserve R1 of the centrifuge.

[0054] These measures include: means for acquiring at least one primary image of the centrifuge 3; a system 72 for processing said at least one primary image; and A data processing system 74 configured to estimate a parameter representative of the volume of the primary reserve from data from the images.

[0055] The image acquisition means here comprises a camera 7 directed towards the bottom of the rotating assembly 1 .

[0056] The parameters representative of the volume of the primary reserve R1 are explained in relation to FIG. 2, which is a detailed view of FIG.

[0057] In a cross-sectional view of the rotating assembly 1 in an axial plane (i.e., including the axis A), a first reference point P1 is identified, which corresponds to an inner joint line between the side wall 30 of the centrifuge 3 (which generally extends substantially vertically) and a rounded web 32 having a radius of curvature RC.

[0058] A high point M of the reserve R1 is also identified, which corresponds to the upper boundary of the primary reserve R1. High point M is typically a point on the web 32, but could be a point on the sidewall 30 if the reserve R1 is zero.

[0059] Finally, a second reference point P2 corresponding to the upper boundary of the edge 33a of the cuff 33 is identified.

[0060] The parameter representative of the volume of the reserve R1 evaluated by the data processing system 72 is, for example, the thickness e of the reserve, which corresponds to the distance between the reference point P1 and the high point M, measured horizontally.

[0061] According to the invention, the thickness e of the reserve is determined by acquiring, by means of the camera 7, a primary image of the centrifuge 3 and using said image.

[0062] In the example, the camera 7 is oriented so as to acquire images showing at least a part of the upper boundary of the edge 33a of the cuff 33 and a part of the upper boundary of the primary reserve R1. The observation direction of the camera forms an angle φ different from 0° or 90° with the horizontal and therefore forms an axis 90-φ together with the axis of rotation A. In practice, the optical axis of the camera is directed towards the centre O of the lower face of the basket 5, as shown in FIG.

[0063] An example of an image thus acquired by a matrix camera (negative) is shown in FIG. 3 and is explained in more detail below.

[0064] The camera 7 can be a matrix camera or, particularly advantageously, an infrared camera.

[0065] The camera is connected to a computer 70 containing a computer program executing a processing system 72 for one or more images acquired by the camera, and a data processing system 74 in communication with the image processing system 72 .

[0066] In practice, the computer program contains the following instructions: When run on a computer, - Acquisition of an image, here of the primary reserve R1, - processing of the image by an image processing system 72; - Processing of data from the image processing by a data processing system 74.

[0067] For each image acquired by the camera 7, the image processing system 72 detects the upper boundary of the reserve R1 and the upper boundary of the edge 33a of the cuff 33, for example by a method of the "contour detection" type. This type of detection is well known and consists in identifying a point in the image which corresponds to an abrupt change in light intensity. Several methods exist, including for example thresholding or determining the contrast gradient of the image.

[0068] The contour detection is very advantageously completed by a step of elliptical adjustment of the contour thus determined.

[0069] 3, the ellipse E1 corresponds to the upper boundary of the primary reserve R1. The ellipse E2 corresponds to the upper boundary of the edge 33a of the cuff 33. The ellipse E3 corresponds to the outer contour of the bottom 52 of the basket 5.

[0070] Once the contour of the reserve R1 has been identified, the data processing system 72 can calculate the thickness of the reserve R1 from the known geometric characteristics of the centrifuge 3, the characteristics of the camera 7 used to acquire the image of the reserve R1, and the height h measured on the image between the upper boundary of the reserve and the top of the edge 33a of the cuff 33.

[0071] The geometric characteristics of the centrifuge 3 that can be used for the calculation are as follows: - the coordinates x1,y1 of the reference point P1 in the reference frame x,y, whose origin is the centre of the lower surface of the basket 5; - coordinates x2, y2 of reference point P2 in the reference frame x, y; - radius of curvature RC of the inner surface of the web 32; - the distance DC, measured horizontally, between the center of curvature C of the web E2 and the axis A of the centrifuge 3.

[0072] The characteristics of the camera 7 that can be used in the calculation are:

[0073] - the distance D between the camera 7 and the basket 5; - angle φ between the line of sight and the horizontal; - focal length f; - The size of each pixel.

[0074] From all these parameters, the system can calculate the height h0 according to Equation 1 below:

[0075]

number

[0076] The system may then calculate e in a reference frame (u,v) of origin P1, where u is parallel to the camera's line of sight, using Equations 2-5 below:

[0077] The ordinate v of point M in the reference frame u,v M is given by Equation 2 below:

[0078]

number

[0079] Then, as follows:

[0080]

number

[0081] The abscissa u of point M in the reference frame u,v M is given by Equation 4 below:

[0082]

number

[0083] Then, e is obtained using Equation 5:

[0084]

number

[0085] Advantageously, the data processing system 74 is configured to undergo a calibration before operation or in a periodic manner. The contours of the basket 5 identified on the acquired images can be used to perform this calibration, from the actual dimensions of the basket 5, which are known, and the dimensions of the contours identified in the images.

[0086] The steps of acquiring an image, processing this image in order to extract therefrom the edge of the reserve, and processing the image data to determine the thickness of the reserve are advantageously repeated several times at regular time intervals, for example at intervals of about 30 seconds.

[0087] At the end of one or, advantageously, several successive runs of these steps, the data processing system 74 determines the deviation of the volume of the primary reserve R1 from its nominal value and sends a signal, typically via a PID, to the drive motor 8 of the shaft 2 to adjust the rotational speed of the rotating assembly in proportion to said deviation.

[0088] Figure 4 shows test results illustrating the effect of variations in the rotation speed of the rotating assembly 1 on the volume of the primary reserve R1: the solid curve represents the rotation speed of the centrifuge 3 (units: revolutions per minute) and the dotted curve represents the variations in the thickness e of the primary reserve R1, e in units of pixels. It should be noted that there is a direct correlation between the variations in the rotation speed and the variations in the volume of the reserve.

[0089] If the volume of the primary reserve R1 is too large, the rotation speed of the rotating assembly may be increased up to the maximum operating value of the machine (typically 2000 rpm, or even 3000 rpm). If this maximum speed value is exceeded, the data processing system 74 may be configured to send a signal to a warning device 9, which may be any device capable of indicating to an operator the need to adjust other parameters, in particular the temperature of the glass fed to the fiber manufacturing machine.

[0090] In addition, it is also conceivable to evaluate the volume of the secondary reserve in the basket 5 .

[0091] On the image acquired by the camera, reproduced in FIG. 3, the lower face 52 of the basket 5 is visible.

[0092] This image (here a negative) reveals a dark central ring G (which is actually bright) and a relatively bright peripheral ring H (which is actually relatively dark).

[0093] The central bright ring G is the area of ​​basket 5 that is in direct contact with the molten flow of glass falling vertically through feed channel 20, and whose temperature T is very high.

[0094] The relatively dark peripheral ring H is the area at the bottom of the basket 5 in contact with the molten glass in the secondary reserve R2, the temperature of which has already been reduced and is below T.

[0095] In one variant embodiment, the camera 7 or the auxiliary camera can be configured to acquire an image other than the primary image and the secondary image of the basket 5, for example an image in a viewing direction along the rotation axis A of the rotating assembly 1. Such a secondary image of the basket seen from the bottom is shown diagrammatically in FIG.

[0096] Advantageously, the image processing system 72 is adapted to detect the boundaries of the peripheral ring H by thresholding and to approximate these boundaries by ellipses or, as in FIG. 5, by concentric circles H1, H2 (in this case the camera line of sight is vertical).

[0097] The data processing system 74 can then determine the thickness e' of the ring H, in other words the distance between the contours H1 and H2, which represents the volume of the secondary reserve R2.

[0098] The evaluation of the secondary reserve thus described may be replaced in the same way by an evaluation of the volume of the primary reserve R1 in the case of a centrifuge of the "with bottom" type. The image of the bottom of the centrifuge, acquired by the camera, will in principle be the same as the image of the basket bottom shown in figures 3 and 5: it will show a central bright ring and a comparatively dark peripheral ring, the thickness of which will be representative of the volume of the primary reserve R1. It will therefore not be elaborated on further here.

Claims

1. 1. A method for forming glass fibers using a rotating assembly (1) comprising: a shaft (2) rotating about an axis of rotation (A), a centrifuge (3) fixed to said shaft (2) and provided with a primary annular wall (30) having a number of primary orifices (31); - means for feeding the molten glass (20) to said centrifuge (3); where, under the effect of the centrifugal forces resulting from the rotation of the rotating assembly (1), a primary reserve (R1) of glass is formed against the primary annular wall (30) of the centrifuge (3), The method comprises the steps of: (a) acquiring at least one primary image of said centrifuge (3) using a camera (7); (b) processing the at least one primary image by an image processing system (72); and (c) estimating, by a system (74) processing data from said primary images, a parameter representative of the volume of said primary reserve (R1); A method comprising:

2. 2. The method of claim 1, wherein the centrifuge (3) comprises an opening (34) at its lower end, and in step (a) the primary image is acquired through this opening (34).

3. The method of claim 1 , wherein the image processing in step (b) comprises identifying at least one boundary of the primary reserve (R1) on the primary image.

4. The centrifuge (3) includes an opening (34) at its lower end, and in step (a), the primary image is acquired through this opening (34); said image processing in step (b) comprising identifying at least one boundary of said primary reserve (R1) on said primary image; 2. The method of claim 1, wherein the at least one boundary comprises an edge of the opening (34) of the centrifuge and an upper edge of the primary reserve (R1).

5. 5. The method according to claim 3 or 4, wherein the identification of the at least one boundary comprises determining at least one series of points by a digital method of contour detection, in particular by thresholding, and elliptical fitting of the series of points.

6. A method according to any one of the preceding claims, wherein the camera (7) used in step (a) has a direction of observation which forms an angle with the axis of rotation (A).

7. The method according to any one of claims 1 to 4, wherein the image acquisition in step (a) is carried out using an infrared camera.

8. The method according to any one of claims 1 to 4, comprising, prior to step (c), a step (b') of calibrating the data processing system (74) by measuring elements of the rotating assembly (1) on the acquired primary images and comparing said measurements with known dimensions of said elements.

9. 2. The method according to claim 1, further comprising a step (d) of determining, at the end of at least one succession of steps (a) to (c), a deviation of the volume of the primary reserve (R1) from a nominal value and adjusting the rotation speed of the rotating assembly (1) as a function of said deviation.

10. 10. The method according to claim 9, wherein, prior to step (d), at least N successions, in particular N successions, of steps (a) to (c) are carried out with regular intervals in time, for example at least 30 seconds.

11. 11. The method according to claim 9 or 10, wherein a warning is issued when the rotational speed of the rotating assembly (1) reaches a predefined maximum value at the end of step (d).

12. The method according to any one of claims 1 to 4, 9 and 10, wherein the rotating assembly further comprises a basket (5) arranged below the shaft (2) and fixed to the shaft (2) and provided with a secondary annular wall (50) having a number of secondary orifices (51), and wherein under the effect of centrifugal forces resulting from the rotation of the rotating assembly (1) a secondary glass reserve (R2) is formed against the secondary annular wall (50), the method further comprising evaluating, by the data processing system (74), from the at least one primary image or another image of the centrifuge, a parameter representative of the volume of the secondary reserve (R2).

13. A glass fiber forming apparatus (10) having a rotating assembly (1) including: a shaft (2) rotating about an axis of rotation (A), a centrifuge (3) fixed to said shaft (2) and provided with a primary annular wall (30) having a number of primary orifices (31); the rotating assembly (1) is configured such that, under the effect of centrifugal forces resulting from its rotation, a primary reserve (R1) of glass is formed against the primary annular wall (30), The apparatus further comprising: - means (7) for acquiring at least one primary image of said centrifuge (3), a system (72) for processing said at least one primary image, and a data processing system (74) adapted to estimate, from data from said primary images, a parameter representative of the volume of said primary reserve (R1); The glass fiber forming apparatus (10) further comprises:

14. A computer program comprising instructions for carrying out at least steps (b) and (c) of claim 1 when said program is run on a computer.

15. 15. The computer program of claim 14, further comprising instructions for carrying out step (d) of claim 9 when the program is run on a computer.

16. A computer readable medium having the computer program of claim 14 recorded thereon.

Images