阅读说明：本技术 用于检测丝上的涂层的设备以及使用该设备的方法 (Apparatus for detecting a coating on a wire and method of using the same ) 是由 B·万兰德格赫姆 W·范雷滕 K·莫蒂尔 T·贝克兰特 于 2019-02-26 设计创作，主要内容包括：本发明涉及一种测量单元,用于光学地验证丝上涂层的存在,尤其是钢丝或钢帘线上涂层的存在。由于钢丝或钢帘线一般是细而圆的,因而很难测量从丝的表面反射或发射的光。涂层具有光学活性,因为其响应于入射光而吸收或发射辐射。测量单元包括暗腔,暗腔具有入口孔和出口孔。两个或更多个源朝中央点照射丝。从涂层反射或发射的辐射由两个或更多个检测器检测。提出了用于定位源和检测器的不同布置。本发明还描述了一种用于使用测量单元的方法以及一种用于可控地涂覆丝表面的设备。(The invention relates to a measuring unit for optically verifying the presence of a coating on a wire, in particular a steel wire or a steel cord. Since steel wires or cords are generally thin and round, it is difficult to measure the light reflected or emitted from the surface of the wire. The coating is optically active in that it absorbs or emits radiation in response to incident light. The measurement unit comprises a dark chamber having an inlet aperture and an outlet aperture. Two or more sources illuminate the filament toward a central point. Radiation reflected or emitted from the coating is detected by two or more detectors. Different arrangements for positioning the source and detector are proposed. The invention also describes a method for using the measuring cell and an apparatus for controllably coating a wire surface.)

1. A measurement cell for optically verifying the presence of a coating on a wire, comprising:

-a lumen having an entry aperture and an exit aperture for guiding the wire through the lumen, the entry aperture and the exit aperture defining a reference axis;

-two or more sources;

-two or more detectors;

the source for emitting light towards a center point on the reference axis, the detector for detecting light,

it is characterized in that the preparation method is characterized in that,

the source and/or the detector are located on the surface of a first cone with the reference axis as axis and on the surface of a second cone with the reference axis as axis, the tops of the first and second cones meeting at a central point, the source and the detector being oriented towards the central point.

2. The measurement unit of claim 1, wherein the apex angle of the first cone is equal to the apex angle of the second cone.

3. The measurement unit of claim 2, wherein the surface of the first cone and the surface of the second cone are a single plane perpendicular to the reference axis.

4. The measurement unit of claim 1, wherein the apex angle of the first cone is different from the apex angle of the second cone.

5. The measurement unit of claim 4, wherein one of the surface of the first cone and the surface of the second cone is a single plane perpendicular to the reference axis.

6. The measurement unit of any one of claims 1 to 5, wherein the number of sources and the number of detectors are even, the sources being arranged in pairs opposite the reference axis in a source plane, the detectors being arranged in pairs opposite the reference axis in a detector plane, the source plane and the detector plane comprising the reference axis.

7. The measurement unit of claim 6, wherein for each source plane there is a detector plane orthogonal to said each source plane.

8. The measurement unit according to claims 6 and 7, wherein two sources are arranged in pairs opposite the reference axis in a source plane and two detectors are arranged in pairs opposite the reference axis in a detector plane, the detector plane being orthogonal to the source plane, the two detectors and the two sources being in a plane perpendicular to the reference axis.

9. The measurement unit of claim 6, wherein each source plane coincides with an associated detector plane.

10. The measurement unit of any one of claims 7 to 9, wherein the source plane and the detector plane are disposed equiangularly about the reference axis.

11. The measurement unit according to any one of claims 1 to 10, wherein a light-transmissive tube is placed between the inlet aperture and the outlet aperture, the tube comprising the reference axis.

12. The measurement unit of any one of claims 1 to 11, wherein the source emits light in an excitation wavelength band and the detector detects light in a receive wavelength band, wherein the excitation wavelength band and the receive wavelength band do not intersect.

13. A method of optically verifying the presence of a coating on a wire using one, two or more measurement units according to any one of claims 1 to 12, the method comprising the steps of:

-providing a filament comprising a coating which emits or absorbs light in response to incidence of light;

-guiding the wire through the one, two or more measurement units;

-electronically driving the source and detector of the one, two or more measurement units with a period comprising the following time intervals:

i. illuminating at least one of said sources during a first time interval while recording the illumination levels respectively detected by all detectors;

in a second time interval, all of the sources are extinguished, while the dark levels detected by all detectors respectively are recorded,

-extracting information about the presence of the coating by processing the light and dark levels recorded by all the light detectors.

14. The method of claim 13, wherein the period of driving the one, two or more measurement units comprises the following time intervals:

-sequentially illuminating said sources one by one in the same time interval, while recording said illumination levels respectively detected by all detectors at each respective time interval;

-in a last time interval, turning off all of the light sources while recording the dark levels detected by all light detectors respectively.

15. An apparatus for coating a wire, the apparatus comprising:

-means for providing a coating in a controlled manner on the axially moving wire based on the device input;

-one, two or more measuring units according to any of claims 1 to 12;

-a processor for extracting information from the measurement unit according to the method of any one of claims 13 to 14;

wherein the processor controls an amount of coating applied by the device on the axially moving wire via the device input based on the information extracted from the measurement unit.

Technical Field

The present invention relates to a measuring cell to detect a coating on a wire, more particularly a round wire (on which an optically active coating is present) made of metal, such as steel or copper, such as a monofilament, a bundle or a cord. The invention also relates to methods of using such apparatus and to filaments particularly suitable for use with the apparatus.

Background

Apparatus for detecting the presence of coatings are well known in the industry for processing foils and webs. For example, in the paper industry, it is very common to perform online gloss measurements to determine the presence of a coating in which added fluorescence is present (US 4250382). This measurement is performed by means of a device that emits UV radiation and determines the amount of fluorescence generated (US 6603126).

The measurement of such fluorescent radiation on the foil or web (and thus the presence of the coating and the amount of coating) is straightforward, since the fluorescent radiation leaves the foil or web only in half-space on the side of incidence of the excitation beam. Furthermore, the foil or web allows excitation over a large area due to the wide foil. The total collectable fluorescence radiation is proportional to the illuminated surface.

Detecting fluorescence on curved surfaces (such as that of a round wire) is more difficult because not only does the fluorescent radiation leave the surface in all directions, but the surface itself is also bent in one direction, thereby propagating the radiation in all directions. Since the filaments are typically very thin (less than one millimeter wide), too much fluorescence radiation cannot be collected unless measured over a very long length.

Although US6597455 describes a measuring device for detecting defects on enamelled wires by varying the reflectivity of the enamelled wire, this device does not allow to measure much weaker fluorescence radiation. Furthermore, the device does not give an indication of the circumferential distribution of the coating.

US5469252 describes an apparatus for detecting defects in an optical fibre. The device is based on the variation of the direction of reflection of light incident perpendicular to the axis of the optical fiber. In the presence of a defect, the apparatus detects light reflected out of the plane perpendicular to the optical fiber.

Thus, no measuring device is available for reliably measuring fluorescence radiation excited from a filament having a fluorescent coating. The inventors therefore set their task to design such a device.

Disclosure of Invention

A first object of the invention is to provide a measuring cell for checking the presence of a thin coating on a wire. It is a further object of the invention to provide a method of operating such a measurement unit. It is a further object of the present invention to provide an apparatus for controlling the amount of coating applied to a wire. Finally, it is an object of the invention to provide a steel cord in which the amount of coating is well controlled by means of the above-mentioned apparatus.

According to a first aspect of the invention, a measuring unit having the features of claim 1 is claimed. The measurement unit for optically verifying the presence of a coating on a wire, comprising:

-a lumen having an entry aperture and an exit aperture for guiding a wire through the lumen, the entry aperture and the exit aperture defining a reference axis;

-two or more sources for emitting light;

-two or more detectors for detecting light,

thereby, the source emits light towards a central point on the reference axis. The measuring unit is characterized in that the source and/or the detector are located on the surface of a first cone and a second cone, both cones having an axis of reference, and wherein the tops of the first cone and the second cone meet at a central point. All sources and detectors are oriented towards the center point. Preferably, the sources and detectors are evenly distributed circumferentially about the reference axis.

The measuring unit is used for detecting the presence of a coating on the filaments. The measuring unit is based on optical principles, by which is meant that the measuring unit uses electromagnetic waves in the infrared, visible or ultraviolet spectrum (for convenience, referred to as "light" elsewhere in this application) that interact with the coating. The measurement unit does not detect the physical thickness of the coating (e.g., by measuring the diameter of the coated and uncoated filaments). The coating may be very thin, e.g. thinner than 10 microns, or even thinner than 5 microns, e.g. thinner than 1 micron.

The coating on the filament whose presence is to be detected must interact with the light incident on the coating. This means that the coating should not reflect light completely, but that absorption and/or emission processes of the light radiation have to take place in the coating. For example, the incident light may have a bandwidth, some frequencies of which are absorbed by the coating, but others of which are not. The emitted light will then show absorption lines that can be detected by the detector. Alternatively, the coating may emit light of low energy after excitation with light of high energy, a process known as fluorescence.

When light to be detected is reflected (possibly with some absorption) on and/or emitted by the coating of the surface of the substantially cylindrical body, the light propagates in all possible directions. Thus, the amount of light falling into a single detector is very small. Thus, the cavity is designed to exclude all stray light that may interfere with coating measurements, and the material from which the cavity is made is not light transmissive. To limit the light entering the cavity, the entrance and exit apertures are made long and narrow compared to the filaments, the inner surfaces of which may be coated with a light absorbing coating.

"first taper" and "second taper" should be interpreted as describing the geometric configuration of the present invention. Thus, it is not necessarily related to a physical object. By "the source and/or detector are located on the surface of the first cone and the second cone" it is meant that the optical axis of the detector or source is on the cone. The optical axis of the detector or source passes through the center point.

All sources may be located on the first cone and all detectors on the second cone, although this is not required for the practice of the invention. If the number of sources and detectors is even, it may be beneficial to mount half of the sources and half of the detectors on a first cone and the other half of the sources and detectors on a second cone.

Preferably, the sources have the same light intensity when "on". Also, it is highly preferred that all sources are located at the same distance from the center point ("source distance"). This is to prevent that different light source distances would result in different illumination at the centre point. Also, the detectors are preferably mounted at the same distance from the center point ("detector distance") such that each detector collects light at the same solid angle. The source distance may, but need not, be equal to the detector distance. Preferably, the detector distance is shorter than the source distance to capture as much light as possible.

For the purposes of this application, the silk must be understood broadly: can be anything long and thin as a filament. Preferably, the minimum and maximum caliper diameters of the cross-section of the filament do not differ much. This does not mean that the filaments must be round: filaments or cords having non-circular cross-sections may equally well be used in the present invention. Although the invention is designed with a maximum caliper of about 1 mm of wire in mind, the principle can be extended to larger diameters of up to 5 mm. Since the emitted light decreases significantly with decreasing diameter, the use of the measuring cell is limited in the following to a filament with a diameter of 50 micrometer.

The material from which the filaments are made is not critical to the invention. Although the invention has been designed particularly for use with metal filaments such as steel filaments or steel cords, the inventors believe that the measuring cell can equally well be used with organic fibres which may be of artificial or natural origin.

This arrangement of sources and detectors allows the presence of a coating on the filament to be detected at one single point (i.e. the centre point) in all circumferential directions of the filament. The amount of coating present at various points along the length of the filament can be detected as the filament moves through the measuring unit.

According to the first modified embodiment of the present invention, the apex angles of the first taper and the second taper are equal to each other. Since the surface of the filament can be considered as a cylinder, a light beam incident on this cylinder and at an angle α to the reference axis will be reflected in all directions falling on a cone forming an apex angle 2 α with the top of the cone corresponding to the point of incidence. Light is only reflected in the half-space direction on the source side. This makes optical measurements on the wire particularly cumbersome, since the reflection of the light beam is scattered on a half cone, making all scattered light difficult to detect. However, by mounting, for example, a series of detectors on the half cone of reflection, the reflected light can be integrated.

In a further preferred embodiment, the first cone and the second cone may be degenerate cones. By "degenerate cone" is meant a cone having a 90 ° half apex angle (i.e., forming a plane perpendicular to the reference axis). For the purposes of this application, a "degenerate cone" is still considered to be a cone having a 180 ° apex angle. All sources and detectors are then located in this plane and oriented towards a centre point, which is then the intersection of the plane with the reference axis. This is a highly preferred orientation of the cones because it is very simple.

In an alternative embodiment, the first cone and the second cone have different apex angles. Since some coating measurements are based on the emission of absorbed light (e.g., fluorescence), these processes are random processes. This means that the light is emitted in random directions, independent of the direction of the incident light. The reflected light is diffusely reflected. In these cases, the cones need not have equal apex angles, since the reflection is diffuse instead of specular. When the reflection is diffuse, it is beneficial to angle the source and reference axis while the detector is mounted in a plane perpendicular to the incident spot, i.e. one of the cones is a plane perpendicular to the reference axis. Fluorescence can be better detected because oblique incidence creates a large incidence surface.

In another preferred embodiment, the number of sources and the number of detectors are even numbers. The sources are arranged in pairs opposite the reference axis, i.e. the two sources are in a source plane including the reference axis but on opposite sides of the reference axis. Likewise, the detectors are arranged in pairs opposite the reference axis in the detector plane. The source plane(s) or the detector plane(s) comprise a reference axis, i.e. all planes have a common reference axis. On the "opposite side of the reference axis", two possibilities may occur:

meaning that the first pair of members coincides with the second pair of members after a 180 ° rotation about the reference axis, or

Meaning that the first pair of members coincides with the second pair of members after being specularly reflected by the centre point.

The limitation of the source and detector on the first and second cones still exists. A further limitation is that the number of sources equals the number of detectors.

In a particularly preferred embodiment of the above construction, for each source plane, there is a detector plane orthogonal to the source plane. In this case, the illumination spot formed by one source in the source plane on the reference axis can be observed by two detectors in a plane orthogonal to the source plane. The two detectors also detect light emanating from a spot formed by the opposing source in the source plane.

In an alternative embodiment, each source plane coincides with an associated detector plane. Thus, each of the detectors can be found in the same plane of the source. The advantage of this configuration is that the detector can see all the spots, but this arrangement does not allow the coating information to be extracted for each quadrant of the wire unless the number of sources and detectors is doubled. Since at least one source and at least one detector are then required for each quadrant, a total of four sources and four detectors are required. This configuration is particularly useful when the emission of light is specular to the incident light, for example when the coating absorbs certain wavelengths.

In another preferred embodiment, the source plane and the detector plane are arranged equiangularly about the reference axis. This means that the planes can be found at an angle of 180 divided by the total number of planes (including the source and detector planes). In this way, the circumferential distribution can be determined with higher angular resolution (e.g., not only in each quadrant, but also within each hexagon).

In another preferred embodiment of the aforementioned embodiment, the two sources are oppositely positioned in each source plane and the two detectors are oppositely positioned in a corresponding detector plane orthogonal to each source plane, and the two sources and the two detectors further lie in the same plane perpendicular to the reference axis. This configuration is particularly useful because it allows the extraction of coating information for each quadrant of the wire. Thus, with a minimum of two sources and two detectors, the coating information for each quadrant can be extracted. This is a very preferred embodiment.

In a further improved embodiment, a light-transmissive tube is placed between the entrance aperture and the exit aperture, wherein the reference axis is contained within the light-transmissive tube, more preferably the light-transmissive tube is coaxial with the reference axis. The light pipe provides physical protection (e.g., in the event of a filament break) and prevents contamination of the detector or source.

In a particularly preferred embodiment, the source emits light that is not detectable by the detector, i.e., the source emits light in the excitation wavelength band and the detector detects light in the receive wavelength band, wherein the receive wavelength band and the excitation wavelength band do not intersect. This preferred embodiment is particularly useful when the coating is a fluorescent coating, since the fluorescent radiation band has a lower frequency than the excitation wavelength band, which is typically ultraviolet radiation.

In a particularly preferred arrangement, two or more measuring units according to any of the embodiments described above are placed one after the other along the path of the filament. The measurement units are spaced apart from each other by a length "L". In particular, two measuring cells may be placed in series. By arranging two or more measuring units one after the other, a better measurement coverage can be obtained both in angle and in length. Possibly and preferably, the outlet aperture of the first measuring cell coincides with the inlet aperture of the second measuring cell.

According to a second aspect of the invention, a method of operating one, two or more measurement units as presently described is disclosed. The method allows extracting coating information on the filament, e.g. whether such a coating is present or not.

The method begins with providing a filament having a coating that emits or absorbs light in response to light incidence. The guide wire passes through one, two or more measurement units from the entry aperture to the exit aperture. The wire can be measured in a stationary position so that a light spot can be measured accurately. Preferably, the wire is moved through one, two or more measuring units at a speed "v" (in meters per second), for example during a coating operation, thereby providing information on the longitudinal distribution of the coating.

The source and detector of each, two or more measurement units are driven with a period having the following time intervals:

-illuminating at least one of said sources during a first time interval while recording the illumination levels respectively detected by all detectors. The total duration of the first time interval is denoted by "T_on"means. At T_onDuring which at least one source is turned on. … … after the first time interval;

-in a second time interval, extinguishing all of the sources while recording the dark levels detected by all detectors respectively. The duration of the second time interval is denoted by "T_off"means. At T_offDuring the period, all detectors are switched off;

by processing the dark and light levels recorded by each individual detector, information about the presence of a coating on the wire can be extracted. The use of the terms "first time interval" and "second time interval" does not necessarily imply that the second time interval always has to follow the first time interval. The reverse is also possible. The terms "first" and "second" are used merely as labels, and do not imply an ordering. In addition, the "first time interval" need not be equal in duration to the "second time interval". Preferably, the second time interval "T_offThe duration of "is substantially longer than the first time interval" T_onIs "short" because of the presence of "T_offDuring the "time period, no detection of the presence of the coating is performed.

E.g. at T_onMeanwhile, when the detector detects a light level, only one source may be lit. The brightness level of the detector, together with its angular position, gives the idea of where the coating is circumferentially present. Alternatively, all light sources may be in the first time interval T_onWhile being simultaneously turned on. Due to reflection on the filamentThere is directional scattering so there is no risk of one detector being "blinded" by the light of the source. The sum of all detector levels can give information on whether a coating is present or not.

In an alternative preferred embodiment of the method, at T_onDuring equal time intervals, the light sources may be turned on sequentially. Intermittently, followed by a time interval T_offDuring this time, the dark levels of all detectors are measured. This way it is possible to extract the circumferential distribution of the coating on the filaments. The bright level of the detector allows to reconstruct the angular distribution of the coating.

Completion of a cycle may take between 1 and 1000 milliseconds, more preferably between 10 and 100 milliseconds, for example 20 milliseconds. The duration or period "T" of one cycle is the sum of the first and second time intervals: t ═ T_on+T_off。

Although the inventors realized that recording the dark level by all detectors during the second time interval when one measurement unit is not actively "on" results in a "blind time period" in which the one measurement unit does not detect the presence of the coating when the filament passes, it is not regarded as a major problem by the inventors.

First, the measuring unit is intended to detect the presence of a coating over a considerable length, i.e. to measure the overall presence of a coating, and the local absence of a coating is not considered a major defect.

Secondly, if it is desired to detect the presence of a coating over the entire length of the wire, two or more measurement units may be placed in series along the path of the wire. In the case where there are two measuring units according to the above description and summaries in the claims, the above method is further defined as:

-providing a filament comprising a coating which emits or absorbs light in response to incidence of light;

-guiding the wire through the first measurement unit at a velocity "v";

-guiding the wire through a second measuring unit separated from the first measuring unit by a distance "L", the distance being measured along the path of the wire;

-electronically driving the source and the detector of the first measurement unit according to a first cycle and electronically driving the source and the detector of the second measurement unit according to a second cycle, comprising the following time intervals:

i. at a first time interval of duration "T_on"at least one of said sources is illuminated, while simultaneously recording the illumination levels respectively detected by all the detectors;

at a second time interval "T_off"in, turning off all of the sources while recording the dark levels detected by all detectors respectively;

a time delay "Δ t" where the second period lags the first period by zero or more;

wherein the following requirements are met:

T_off≤|Δt-(L/v)|＜T_on

according to a third aspect of the invention, an apparatus for coating a wire is provided. The apparatus comprises means for providing a coating in a controlled manner on an axially moving wire. By "in a controlled manner" is meant that the amount of coating can be increased or decreased based on device input. The device further comprises one, two or more measurement units as described above. The device further comprises a processor for extracting information from the measurement unit according to any of the methods described above.

Based on information extracted by the processor from the one or more measurement units, the feedback loop is closed towards a specific set point for the coating quantity:

-if the information extracted from the one or more measuring units indicates that the amount of coating present on the passing wire is below the set point, steering the input of the coating device towards a higher coating level;

-if the information extracted from the one or more measurement units indicates that the amount of coating present on the passing filament is above the set point, steering the input of the coating device towards a lower coating level;

those having knowledge of the present disclosure will appreciate that certain time constants must be met in order to avoid feedback loop oscillations. Thus, the processor is programmed, for example, to provide a moving average of the measured output from the measurement unit and is input towards the set point manipulation device with a time constant that takes into account the wire speed and the time required to detect the coating and manipulate the coating quantity.

According to a fourth aspect of the invention, a steel cord is described. The steel cord comprises a plurality of steel filaments twisted together. The steel cords are provided with a coating following the contour of the steel filaments. The coating includes fluorescence that emits light of an emission wavelength band different from the excitation wavelength band when irradiated with light of the excitation wavelength band.

Preferably, the applied coating is thin, for example less than 10 μm thick, for example less than 5 μm or even less than 1 μm thick. The measurement system is most suitable for thin coatings. The thickness of the coating is the average thickness taken over the appropriate length of the steel cord. The coating mass per unit length "B-a" can be calculated from the mass per unit length "B" after coating and the mass per unit length "a" before coating. The surface per unit length "C" can be calculated from the diameter of one (in the case of a single filament) or more (in the case of a steel cord with different filaments). The mass per surface area (B-A)/C can be obtained by dividing (B-A) by C. The average thickness can then be obtained by dividing by the mass per unit volume of the coating. Note that the mass per unit volume of the coating must be measured in the way the coating is present on the filament, for example in case curing is required, the mass per unit volume must be measured on the coating after curing.

One example of a coating is a lubricating oil for improving the life of steel cords used as window elevator ropes. By mixing the fluorescent agent in the lubricating oil, the existence of oil on the steel cords can be ensured.

Another example of a coating is an adhesive applied as a coating on the steel cord for improving the adhesion between the steel cord and a polymer such as an elastomer. By incorporating the phosphor in the binder, the presence of the phosphor on the coating and thus the binder can be ensured. Furthermore, since the relation between the emitted and measured light and the amount of phosphor in the coating is linear and the ratio of phosphor in the coating and the binder is constant, the amount of binder can be calculated. With the aid of this disclosure, the skilled person will be able to establish this relationship after some experiments.

The detectability of the fluorescent agent depends on the compound used. Preferred are trans-stilbene derived compounds to which polyols may be added to further enhance fluorescence. Very little fluorescent agent is required for detection of the coating: the mass of the phosphor is in any case less than 10% of the total mass of the coating. Even more preferred is that a mass percentage between 0.010 and 5%, for example between 0.015 and 0.3% may be sufficient for detecting the brightener in the measurement cell.

The fourth aspect of the present invention can be summarized as the following expression:

expression 1: a steel cord comprising a plurality of steel filaments twisted together, the steel cord being provided with a coating that follows the contours of the steel filaments,

it is characterized in that the preparation method is characterized in that,

the coating includes a phosphor that emits light at an emission wavelength band different from the excitation wavelength band when irradiated with light at the excitation wavelength band.

Expression 2: a steel cord according to expression 1, wherein the mass of the fluorescent agent in the coating is less than 10% of the total coating mass.

Expression 3: the steel cord according to expression 1 or 2, wherein the coating further comprises an adhesive.

Expression 4: the steel cord according to expression 1 or 2, wherein the coating further comprises a lubricant.

Drawings

FIG. 1 depicts the present invention in its most general form;

FIG. 2 depicts a particular orientation of the source and detector;

FIG. 3 depicts a highly preferred orientation of the source and detector;

FIG. 4 shows another advantageous orientation of the source and detector;

FIG. 5 shows other orientations of the source and detector;

FIG. 6 shows an apparatus for coating wire;

FIG. 7 shows another preferred orientation of the source and detector;

fig. 8 shows a steel cord with a coating provided with a fluorescent agent;

FIG. 9 shows different timing sequences for manipulating the three sources of the measurement cell;

in the drawings, corresponding items in different drawings are identified by the same ten and one digits, and the hundreds digits represent the drawing numbers.

Detailed Description

In fig. 1, a measurement unit 100 is depicted in its most general form. The measuring cell comprises a cavity 102, the cavity 102 having an inlet aperture 104 and an outlet aperture 104'. The inlet and outlet apertures 104, 104' define a reference axis 106. The cavity 102 is used to shield external light from interfering with the measurement and is therefore completely opaque. These holes are used to guide the wire through the lumen. Light is prevented from entering from the hole by using a long entrance hole and/or coating the inside of the hole with a light absorbing substance. In this embodiment, three light sources 108, 108' and 108 "are arranged on the surface of the first cone 112, with the reference axis 106 as the axis. The first cone has an apex angle 2 alpha.

The three detectors 110, 110 'and 110 "are located on the surface of the second cone 112', sharing the same axis and reference axis 106 as the first cone 112. The second cone 112' has an apex angle 2 beta different from the apex angle 2 alpha. All detectors and sources are oriented towards the center point 112 where the first cone 112 and the second cone 112' meet. The sources are located at angles 0 ° (108'), 120 ° (108), and 240 ° (108") when viewed along the reference axis 106, where 0 ° corresponds to the X-axis direction. The detectors are located at angles of 60 ° (110), 180 ° (110'), and 300 ° (110 "). The light emitted by source 108' is mainly detected by detectors 110 and 110", since the other detectors are blocked by the presence of the filament along reference axis 106. This arrangement is of particular interest when the coating of the filament responds to incident light with a diffuse reflective response (e.g. in the case of a fluorescent coating).

The source is preferably a light emitting diode that can emit in a broad band or preferably in a small band. Light emitting diodes can be switched quickly and easily by electronic current drive. When used to detect fluorescence in a coating, the emission band of the LED should have a wavelength shorter than the excitation threshold wavelength of the fluorescent agent. Thus, UV LEDs emitting below 400nm or even below 385nm are most preferred because the photons emitted are of sufficient energy to excite most fluorescers. The detector may be a photodiode, phototransistor or photomultiplier tube. The choice is determined by the amount of light to be collected and the energy of the collected photons, which in turn depends on the diameter of the filament to be measured and the emission spectrum. For filaments, photomultiplier tubes are most preferred. In order to eliminate the common wavelength between the source and the emission wavelength by the coating, it is proposed to use an optical high-pass filter or band-pass filter in front of the detector that blocks the emission band of the source but allows the emission band of the fluorescent agent to pass.

Fig. 2 shows a second orientation of three sources and three detectors. The apex angles of the first and second cones are now both set equal to the same angle 2 α. Now, the source and detector are aligned with each other: the source 208 "at 0 is combined with the detector 210 at 0. Likewise, source 208 'at 120 ° is combined with detector 210' at 120 °, and source 208 at 108 ° is combined with detector 210 ″ at 180 °. This arrangement is of particular interest when the response to incident light is specular (e.g. when the coating absorbs certain wavelengths of light).

In another preferred embodiment, all detectors and sources may be located in a first cone and a second cone, both having an apex angle of 180 °, i.e. both the first cone and the second cone form a plane perpendicular to the reference axis. An example of such an arrangement is shown in figure 3. Since the two cones must share a center point 312, the first cone and the second cone merge to form a single plane perpendicular to the reference axis 306. The three sources 308, 308' and 308 "are again located at angles 0 °, 120 ° and 240 °. Of course, detectors 310, 310', and 310 "cannot be located at the same angle: they are located at angles 60 °, 180 ° and 300 °, respectively.

Another preferred possibility for mounting the detector and the source is to place the source on a first cone with an apex angle of 2 a and the detector in a cone with an apex angle of 180, that is to say in a plane perpendicular to the reference axis, as shown in fig. 4.

FIG. 5 depicts a particularly preferred embodiment in which sources 508 and 508' are paired and lie in a plane S that includes reference axis 506₁While the detectors 510, 510' are also paired and located in a second plane D that includes the axis₁In (1). In this embodiment, the source plane S₁(corresponding to the plane formed by the reference axis and the Y-axis) is perpendicular to the detector plane D₁(determined by the reference axis and the X-axis).

The embodiment of fig. 3 and 5 is followed immediately by another very preferred embodiment depicted in fig. 7. In this embodiment, both sources 708, 708 'and both detectors 710, 710' lie in one plane perpendicular to the reference axis 706. The source is located at 0 deg. and 180 deg. angles and the detector is located at 90 deg. and 270 deg.. Such an embodiment is preferred because it allows the detection of the presence of an inner coating in four quadrants (0 deg. -90 deg., 90 deg. -180 deg., 180 deg. -270 deg., 270 deg. -0 deg.) around the wire. The inventors have found such an arrangement in which most of the information can be extracted with a minimum number of detectors and sources.

When using a measuring cell, the wire (which may or may not be covered with a coating) is guided along its length from the inlet opening through the measuring cell to the outlet opening. For detectability, the coating must respond to incident light by emitting or absorbing light. If this is not the case, the measuring unit will respond as if no coating is present on the wire. The detector signals are constantly and individually measured, but the sources are driven according to a certain period. A common theme for all cycles is that in each cycle there is a first time interval "T" where at least one source is turned on_on"and a second time interval" T in which all sources are turned off_off". During this time interval, the dark level of the detector is recorded.

By using different illumination schemes of the source, different information can be extracted from the detector. For the embodiment of fig. 3, different handover schemes are proposed in fig. 9a, 9b and 9 c. With the illumination of the source over time being indicated by the numbered clock periods on the X-axis. When the rank is higher, the corresponding source is set to "on", and when the rank is lower, the source is "off".

In the first scheme shown in fig. 9a, all three sources are simultaneously illuminated during odd numbered clock periods ("first time intervals") and all sources are turned off during even numbered clock periods ("second time intervals"). This timing allows the presence of a small amount of coating to be detected, since all three detectors collect all possible emitted light. However, the circumferential distribution of the coating cannot be determined in this way.

In a second clock scheme, shown in fig. 9b, during the first three clock cycles ("first time interval"), two of the sources are on (S)₁S₂、S₂S₃、S₃S₁And "off"). During a fourth clock cycle ("second time interval"), all sources are in an "off" state and the dark level of the detector is recorded. When for example S₁And S₂When "on", a 300 sector is illuminated, of which 60 is illuminated at twice the intensity. At "on" two sources S₁And S₂The detector in between will detect most of the light over a 180 sector (60 of which is double illuminated). Other detectors will only detect light from a 120 sector. Although the radial distribution can be extracted from these signals, the processing of the signals can be more cumbersome. This has the advantage that more signals can be collected as the filaments are better lit.

In the third clocking scheme of fig. 9c, the sources are alternately lit during the first three clock periods ("first time intervals") and all sources are "off during the fourth clock period (" second time intervals "). Since at this time e.g. S₁Only a 180 sector is illuminated and the two detectors adjacent to the source detect the light emitted on a 120 sector overlapping with 60, respectively. The third detector is in the "shadow" of the source. This allows to more easily reconstruct the circumferential distribution of the coating.

Fig. 6 shows how a measuring unit can advantageously be used in an apparatus 600 for coating a wire. The apparatus comprises means "a" for providing the coating in a controlled manner. Device "a" may be, for example, nozzle 622, which applies an amount of coating based on device input "D". The uncoated wire 620 enters device "a" where it receives the coating and exits the device as coated wire 620'. After coating, the coating amount is measured in the measuring unit "B". The signals of unit B are analyzed in processor "C", where the coating information from measurement unit "B" is extracted. The output of processor "C" manipulates the amount of coating applied by device input "D". This creates a closed loop system that manipulates the coating quantity to a set value that is adjustable in processor "C".

If it is desired to fully inspect the coating over the entire filament length, two (or more) measurement units are placed in series one after the other, spaced apart from each other along the filament by a distance "L". The outputs of the first and second units are combined in processor "C". The two measuring units are driven with the same measuring cycle, wherein the second measuring unit (the unit downstream of the first and second measuring unit) has a delay "Δ t" with respect to the cycle of the first measuring unit. If the filament is moving through the apparatus at a velocity "v", if satisfied

T_off≤|Δt-(L/v)|＜T_on，

The presence of the coating is verified over the entire length of the filament.

Fig. 8 shows a measurement unit 800, which is further provided with a light-transmitting tube 830. In the center of the light-transmitting tube 830, a steel cord 820 is guided from the inlet hole 804 to the outlet hole 804'. Sources 808 and 808' are mounted outside of the light-transmitting tube 830 and illuminate the steel cord at the center point 812. The detectors 810 and 810' are mounted in a plane perpendicular to the steel cord. The center point 812 is illuminated by two sources 808 and 808', which are located in the same plane. The lens shows a cross section of the steel cord 820. Which consists of three steel monofilaments 822 twisted together. The steel cords are coated with a lubricant 824. The lubricant contained 4,4 '-diamino-2, 2' -stilbenedisulfonic acid, a fluorescer, at a concentration of 0.5% of the total coating weight.

An alternative use of the apparatus and method is to determine whether an adhesive coating is present on the filaments. For example, adhesive coatings based on organofunctional silanes, organofunctional zirconates or organofunctional titanates may be applied on steel cords as described in EP 2366047. However, the presence of very thin adhesive coatings can only be determined by time-consuming and expensive adhesion tests. To avoid this adhesion test, a small amount of fluorescent agent 2, 5-thienylbis (5-tert-butyl-1, 3-benzoxazole) of 0.1% by weight was added to the adhesive coating. The presence of the adhesive and the amount of adhesive can then be verified by irradiation with 385nm UV light, which produces a fluorescence emission band of 400nm to 475 nm.