WO2010104466A1

WO2010104466A1 - Method and means for non-contact measuring thickness of non-metal coating on surface of metal matrix

Info

Publication number: WO2010104466A1
Application number: PCT/SE2010/050278
Authority: WO
Inventors: Bengt ÅKERBLOM
Original assignee: Daprox Ab
Priority date: 2009-03-12
Filing date: 2010-03-12
Publication date: 2010-09-16
Also published as: EP2406579A4; EP2406579A1

Abstract

The present invention relates to a material thickness of a web (1) of non-magnetic material applied to a magnetic material (2) measuring means. A sensor assembly (4) comprises an optical sensor (6), for interaction with a first side (10) of said web (1) and a reluctance transducer (8), which is arranged close to said first side of the web (1) for interaction with said magnetic material (2) as a magnetic reference element on the opposite side (12) of the web (1). Said optical sensor, preferably a confocal senor (6), is provided for interaction with said first side (10) of the web (1) as an optical reference element and said sensor assembly (4) is configured with said confocal sensor (6) and said reluctance transducer (8) in combination and related to a reference point (r p). The confocal sensor (6) emits optical signals (30) as input to an optical controller (20), which optical signals are representative of a first distance (d1) from said reference point (r p ) to the web (1). The reluctance transducer (8) emits electric signals (32) as input to an electric control unit (22), which electric signals are representative of a second distance (d2) from said reference point (r p ) to said magnetic material (2). Said optical controller (20) and said electric control unit (22) are individually connected to a processor (24), in which a third distance (d3), which represents the material thickness of the web (1), is calculated.

Description

Method and means for non-contact measuring thickness of non-metal coating on surface of metal matrix

Description

Technical field

The invention relates to on one hand a method for measuring material thickness ac- cording to the precharacterizing clause of claim 1 and on the other a means for measuring material thickness according to the precharacterizing clause of claim 8.

State of the art

In the production of materials in webs, it is desirable to measure the material thickness in the web so as to be able to control the production in various aspects. In the case of a non-magnetic layer applied on a magnetic layer as, a web of sheet metal for example, there is a requirement to be able to measure the thickness the applied non-magnetic layer, for example paint or film, with a high degree of accuracy.

Over the years, many different measuring methods and forms of measuring equipment have been developed. In this connection, measurement has been performed in a free web section, in the space between the various rollers over which the web runs. However it has proved to be increasingly difficult to obtain sufficiently dis- tinct fixing of the web in order to be able to perform reliable measurements. The web tends, especially at increasing rates, to have a variable position in one direction across the web and this of course results in difficulties in measuring thickness. In this connection use has been made of e.g. inductive transducers and eddy-current transducers. By performing the measurement where the web runs in a curved manner over a roller, the result is on the one hand that the roller defines the position of the web well and on the other hand that the web is smoothed out effectively in the transverse direction where measurement is performed. Further, with a transducer which works according to the reluctance principle, different types of reference elements can be selected in measurement, as required. Transducers of this type are well-known and have been described in, for example, Swedish patent 7904903-7, for which reason a detailed description of the operation and construction of the transducer is not required in this context.

Therefore, in the present field of application reluctance transducers are preferred before inductive transducers or eddy-current transducers. Further, eddy-current transducers involve temperature sensitive resistance materials, which are sensitive to temperature variations in the measuring point, while reluctance transducers have a better stability against temperature variations and are capable of producing a relatively thin, substantially coherent pattern of flux and thanks to the iron core is configured to concentrate said pattern of flux and direct it to a relatively limited spot of the web and beyond said spot.

EP-Al -0959324 discloses a method and arrangement for measuring material thickness of this latter kind. The thickness of a web of non-magnetic material, e.g. a paint layer, is measured by a transducer of the reluctance type with respect to a reference element on the other side of the web at a curved section of the web. The shell of a roller or a support for the web can be used as the reference element. The transducer is concave at its end facing towards the web and is coaxial with the roller. The transducer is held at a predetermined spacing from the web by means of a gas cushion produced by gas being introduced into a gas duct. Measurement with respect to the reference element thus takes place according to the reluctance method.

The thickness of a paint layer may usually amount to approximately 200-300 μm, but considerably smaller values, down to approximately 10 μm, can also be found. However, to enable measurements on e.g. wet paint applied on sheet, there is even a higher requirement on accuracy as the thickness of a paint layer may amount to as little as 1 μm and preferably 5-200 μm and is allowed to vary only some ± 5 μm. To this extent the transducer, when held at a predetermined spacing of 30-100 μm from the web by means of a gas cushion, would not provide a sufficient accuracy for this purpose, even if the transducer is of the reluctance type.

Moreover, the wet paint layer would be blown away by the pressure (gas cushion) of gas leaving the gas duct and irregularities in the paint layer would occur.

The object of the invention

The aim of the invention is to produce an improved method and an improved ar- rangement for measuring the thickness of a material web, in which a solution is provided for existing problems of simplicity and accuracy.

Description of the invention

An improved measuring method and means according to the non-contact measurement principle is achieved and defined in the independent claims. Thus, by performing the measurement by means of an optical sensor in combination with an electromagnetic sensor and particularly a reluctance sensor according to the invention, it is possible to measure, and if desirable, control the thickness of a paint layer applied on e.g. sheet, no matter if the paint is freshly applied and wet or dry.

In previous solutions the thickness of non-magnetic material is measured by a transducer of the reluctance type with respect to a reference element, e.g. a sheet on the other side of the web at a curved section of the web. The transducer is held at a pre- determined spacing from the web by means of a gas cushion. According to the present invention, in stead of a gas cushion at least one linear motor is associated with an optical sensor and used in combination with the transducer in a sensor assembly configured to measure the distance/spacing to the web. The sensor assembly is held at a predetermined spacing from the web by means of said at least one linear motor. By this means, the thickness of non-magnetic material can be measured no matter if the sheet would be thicker than 2 mm or if the measurement is performed at curved or other sections of the web.

Brief description of the drawings

The invention is described in more detail with reference to the accompanying schematic drawings.

Fig. 1 discloses the principle of measuring thickness according to the invention, Fig. 2 discloses a flow chart of a means for realizing the measuring principle,

Fig. 3 discloses an embodiment of a sensor assembly of said means in fig. 2, and Fig 4 schematically illustrates a material thickness measuring means including a reluctance transducer, comprising two magneto resistive elements and comprising a sensor for static fields.

Similar details and details with the same function are given the same reference numerals in the figures.

Description of embodiments

Fig. 1 discloses the principle according to the present invention of measuring the material thickness of a web 1 of non-magnetic material applied to a magnetic material 2. For this purpose, a sensor assembly 4 is provided comprising a combination of an optical sensor 6 and an electromagnetic sensor 8 related to a reference point r_p and arranged close to a first side 10 of said web 1. On one hand said optical sensor 6 is configured for interaction with said first side of the web 1 and on the other said electromagnetic sensor 8 is configured for interaction with said magnetic material 2 as a magnetic reference element on the opposite side 12 of the web 1.

Firstly, by means of the optical sensor 6 which, as will be described later, can be designed according to what is known as the confocal measurement principle, a first distance dl can be determined between the reference point r_p and a first measuring point 14 on the first side 10 of the web 1.

Secondly, by means of the electromagnetic sensor 8, which preferably is a reluctance transducer, a second distance d2 can be determined between the reference point r_p and a second measuring point 16 at the opposite side 12 of the web. Finally, a third distance d3 between the first measuring point 14 and the second measuring point 16 can be determined by subtracting the first distance dl from the second distance d2. The third distance d3 indicates the material thickness of the web 1.

Fig. 2 discloses a flow chart of a means for realizing the principle according to the present invention of measuring the material thickness of a web 1 of non-magnetic material applied to a magnetic material 2. The sensor assembly 4 is associated with a central unit 18 configured with a halogen light source or LED based optical controller 20, an electric control unit 22, a processor 24, a memory media 26 and an in- structions electric control unit 28.

Preferably, the optical sensor of the sensor assembly 4 is a confocal sensor 6, which works according to the confocal measurement principle in a confocal chromatic measurement system comprising said central unit 18 configured with said LED based optical controller 20, which can be connected to said confocal sensor 6 by means of a fiber optical cable 30.

Further, the electromagnetic sensor is preferably a reluctance transducer 8, which can be connected to said electric control unit 22 by means of an electric cable 32. Consequently, the sensor assembly 4 according to fig. 2 is provided with a combination of the confocal sensor 6 and the reluctance transducer 8. Even if not explicitly disclosed in fig. 2, the sensor assembly 4 with the combination of the two sensors is also here related to the same reference point r_p as in fig.1. Further, the sensor assembly 4 is associated with at least one not shown linear motor and held at a predetermined spacing from the web by means of said at least one linear motor. The opti- cal controller 20 is in turn preferably electrically connected 34 to said processor 24, which means signals representative of the first distance dl can be transferred to the processor 24. Moreover, even the electric control unit 22 is preferably electrically connected 36 to the processor 24, which means signals representative of the second distance d2 can be transferred to the processor 24.

In the processor 24 the difference between the second distance d2 and the first distance dl is calculated resulting in the third distance d3, which is representative of the thickness of the web 1. This value d3 can, via an electric cable 46, be transferred to and continuously stored in said memory media 26 together with a reference value R of a desired thickness of the web 1. Then the processor 24 can communicate with the memory media 26 and determine if an actual value A for the thickness of the web 1 lies within an allowed limit of tolerance. If not, said instructions control unit 28 which is associated with the memory media 26 is activated by the memory media and can produce an output 48 to e.g. an automatic painting machine with instruc- tions to adjust the thickness e.g. of a web 1 in the form of wet paint or similar.

Fig. 3 discloses in more detail than fig. 2 the sensor assembly 4 provided with the combination of the confocal sensor 6, which can be designed according to what is known as the confocal measurement principle, and the reluctance transducer 8. The confocal measurement system comprises the halogen light source or LED based optical controller 20 and said sensor 6 interconnected by means of the fiber optic cable 30. The light source emitter of the optical controller 20 emits polychromatic white light, which is transferred through the fiber optic cable 30 and focused onto the first side 10 of the web by means of a not shown multi-lens optical system of the sensor 6. The lenses are arranged so that the white light is dispersed into monochromatic light by controlled chromatic aberration. As appear best in fig. 1 , a specific distance, e.g. the first distance dl, to the web 1 can be assigned to each wavelength e.g. by a factory calibration. Only the wavelength which is exactly focused on the web 1 is used for the measurement. This light reflected from the web 1 is passed through a likewise not shown confocal aperture and through the fiber optic cable 30 onto a re- ceiver in form of a not shown spectrometer of the optical controller 20, which detects and processes the spectral changes. This measuring principle enables first distances dl to be measured with high precision and extreme spatial resolution. As a matter of fact an accuracy better than 0,1 μ might be achievable.

Further, since the emitter and receiver are arranged in one axis C, shadowing is avoided. In contrast to conventional triangulation sensors, the confocal sensor 6 is able to measure in narrow apertures and through narrow passages onto e.g. a web 1.

The reluctance transducer 8, provided in combination with the confocal sensor of the sensor assembly 4, comprises an iron core 38 around which at least two counteracting coils 40 are arranged on each side of at least one magneto resistive element 42. In a known manner the magneto resistive element is constituted of a DC field meter 42, which together with said coils 40 are connected to the electric control unit 22 by means of conductors indicated by the electric cable 32.

Said iron core 38 is provided with a so called beam hole 44 for a beam of rays emitted of the not shown optical light source of the optical controller 20 and transferred to the combined confocal sensor 6 and reluctance transducer 8. The beam axis of said rays is directed through said beam hole, essentially parallel to the centre axis C of the beam hole 44, to hit onto the web 1. The web 1 is reflecting back at least a part of said beam of rays through a not shown slot in the likewise not shown lens system in the beam hole 44 of the iron core 38 and through the fiber optical cable 30 to a not shown spectrometer of the optical controller 20.

Advantageously, by means of this sensor assembly 4, the combination of the reluctance transducer 8 with a confocal measurement system 6, 30, 20 will result in a thinner pattern of flux compared to a combination with a tri-laser measurement system. Thanks to the fact that the iron core can be extended closer to the web 1 with no hindering of any offset located light sensor, it can transfer and direct a more concentrated pattern of flux to the web 1 to hit on a more concentrated area around the measuring spot (the first measuring point 14) of the confocal measurement system and beyond said spot (the second measuring point 16).

Hence, the present sensor assembly combination 4 enables measurements to be performed by the reluctance transducer 8 at almost the same spot (or beyond) as the wavelength of light which is exactly focused on the web 1 by the confocal sensor 6 or at least as close to each other as is technically possible.

Fig 4 schematically illustrates a material thickness measuring means 3 according to a preferred embodiment. It comprises a reluctance transducer 8 including two mag- neto resistive elements 40 and comprises a sensor 42 for measuring static fields. The two magneto resistive elements 40 are, during use of the material thickness measuring means 3, caused by an algorithm stored on a data memory (not shown) of the control unit 22 to work in opposite directions. This is made for achieving a balanced system not being disturbed by the magnetic field present in and caused by the mag- netic material layer, here a sheet metal 2, upon which the non-magnetic layer (here paint layer 1 of 5 to 300 μm and preferably 20-200 μm) has been applied. By this embodiment is achieved that the thickness is allowed to vary only some ± 5 μm by means of the measuring means 3. The magneto resistive elements 40 are thus arranged to co-operate with a DC field meter (sensor 42), which together with the elements 40 are connected to the control unit 22 by means of conductors 32. This implies that the resulting flux through the sensor 42 all the time is kept equal to zero. By means of the reluctance transducer 8, a second distance d2 can be determined between a pre-determined and suitable reference point r_p and a measuring point corresponding with the side 12 (underside of the paint) of the paint layer 1. Le, by using an upper side 60 (which upper side 60 is defined as the side of the sheet metal facing and being in contact with the paint layer 1) to provide the meas- uring point (by means of the reluctance transducer 8 measuring the second distance d2), the underside or side 12 (defined as the side of the paint layer 1 facing the 60 of the sheet metal 2) of the paint layer 1 can be used together with a first distance dl (distance from said reference point r_p to an upper surface 10 (first side) of the paint layer 1) measured by a confocal chromatic sensor 6, further explained below. In case of difference in distance between the reference point r_p and the upper side 60 of the sheet metal 2, i.e. a variation of the second distance d2 so that the reluctance fed from one of the magneto resistive elements 40 is changed, a magnetic flux is started through the sensor 42. The sensor 42 reacts to the flux and directs, via a zero detector (not shown), a current supply (not shown but used for the application) to change its current to the other magneto resistive element 40 so that the resulting flux through the sensor 42 again becomes equal to zero. An output signal is obtained by measuring the difference between the currents supplied to the magneto resistive elements 40. This method with zero detection of the magnetic flux through the measuring element 30 involves that no greater demands on the stability of the material thickness measuring means 3 need to be put. This type of measuring means is not sensitive to magnetic fields and can be designed not bulky, which is preferable when for example being mounted on a robot arm (not shown).

In Fig. 4 is also shown schematically a confocal chromatic sensor 6 being adapted to co-operate with the reluctance transducer 8 for calculation of the thickness of the paint layer 1 by subtracting the first distance dl (achieved by the confocal chromatic sensor 6) from the second distance d2 (achieved by the reluctance transducer 8). By means of the confocal chromatic sensor 6, the first distance dl can be deter- mined between said reference point r_p and a first measuring point on the first side 10 of the paint layer 1 (paint surface).

The reluctance transducer 8 further comprises a core 38 around which the two magneto resistive elements 40 (counteracting coils) are arranged on each side of the magneto resistive element. The core 38 is provided with a beam hole 44 and an optical light source (not shown) of the confocal chromatic sensor 6 for emitting a beam of rays. The beam axis of the rays is directed through the beam hole 44 essentially parallel to a centre axis of the beam hole 44 and is directed to hit on the first measuring point of the first side of the paint layer 1 (the upper surface 10). At least a part of the beam of rays is reflected back from the upper surface 10 of the paint layer 1 through a slot in a lens system (not shown) in the beam hole 44 of the core 38 and further through a fiber optical cable 30 to a spectrometer (not shown) of the optical controller 20.

By means of the reluctance transducer 8, a second distance d2 can be determined between the reference point r_p and a second measuring point at the opposite side 12 (underside of the paint layer facing the upper side 60 of the sheet metal 2) of the paint layer 1 (upper surface). The opposite side coincides with the upper side 60 of the sheet metal 2. Finally, a third distance d3 between the first measuring point and the second measuring point can be determined by subtracting the first distance dl from the second distance d2. The third distance d3 indicates the material thickness of the paint layer 1. On one hand the confocal chromatic sensor 6 is configured for interaction with the first side of the paint layer 1 (the upper surface 10) and on the other hand the reluctance transducer 8 is configured for interaction with the sheet metal 2 as a magnetic reference element applied to the opposite side 12 of the paint layer 1 (coincides with the 60).

By using the reluctance transducer 8 (not sensitive to magnetic fields eventually generated by the object to be measured) for measure of the distance from the reference point to the upper side 60 of the sheet metal 2, the opposite side (facing the sheet metal) of the layer automatically can be determined and by using the confocal chromatic sensor 6 high accuracy can be achieved at the same time regarding the measurement of the distance from the reference point to the first side (upper surface 10) of the paint.

The present invention is of course not in any way restricted to the preferred embodiments described above, but many possibilities to modifications, or combina- tions of the described embodiments, thereof should be apparent to a person with ordinary skill in the art without departing from the basic idea of the invention as defined in the appended claims. For example, the layer of non-magnetic material can be other layers than paints or films. The number of magneto resistive elements can be of any suitable amount.

Claims

1. Method for measuring the material thickness of a layer (1) of non-magnetic material applied to a magnetic material (2) for adherence thereto, the measuring is made by means of a sensor assembly (4), comprising a positioning means, for interaction with a first side of the layer (1) and an electromagnetic sensor (8), which is arranged close to said first side (10) of the layer (1) for interaction with said magnetic material (2) as a magnetic reference element on the opposite side (12) of the layer (1), characterized by the following steps: -providing the electromagnetic sensor configured as a reluctance transducer (8) comprising at least one magneto resistive element constituted of a sensor for static fields (42);

-configuring said positioning means with a confocal chromatic sensor (6) for interaction with the first side of the layer (1) as an optical reference element; -configuring said sensor assembly (4) with the confocal chromatic sensor (6) and the reluctance transducer (8) in combination and related to a reference point (r_p); -configuring a central unit (18) comprising an optical controller (20) and an electric control unit (22) in combination with a processor (24); by means of the confocal chromatic sensor (6) emitting optical signals (30) as input to said optical controller (20), which optical signals are representative of a first distance (dl) from said reference point (r_p) to the layer (1);

-by means of the reluctance transducer (8) emitting electric signals (32) as input to said electric control unit (22), which electric signals are representative of a second distance (dl) from said reference point (r_p) to said magnetic material (2); and -by means of said central unit (18) calculating a third distance (d3), which represents the material thickness of the layer (1).

2. Method according to claim 1, characterized by the following steps: evaluation of said first distance (dl) by means of the optical controller (20), evaluation of said second distance (d2) by means of the electric control unit (22) and by means of said processor (24) calculating said third distance (d3) as the difference between the second distance (dl) and the first distance (dl).

3. Method according to claim 1 or 2, characterized by the following steps: providing an electromagnetic sensor configured as a reluctance transducer (8) comprising a core (38) around which at least two counteracting coils (40) are arranged on each side of at least one magneto resistive element (42), configuring said core (38) with a beam hole (44) and an optical light source of the confocal chromatic sensor (6) for emitting a beam of rays, directing the beam axis of which through said beam hole essentially parallel to a centre axis (C) of the beam hole (44) and to hit on a first measuring point (14) of the first side (10) of the layer (1) and from the layer (1) reflecting back at least a part of said beam of rays through a slot in the lens system in the beam hole (44) of the core (38) and through a fiber optical cable (30) to a spectrometer of the optical controller (20).

4. Method according to one of the previous claims, characterized by the following steps: by means of the core (38) directing the magnetic flux of the reluctance transducer (8) to hit on a spot essentially surrounding the first measuring point (14), from where the magnetic flux goes beyond and interacts with the magnetic material (2) at a second measuring point (16) on the opposite side (12) of the layer (1) in relation to said first measuring point (14).

5. Method according to claim 3 or 4, characterized by the following steps: configuring said spectrometer of the optical controller (20) for determining the first distance (dl) by detecting the spectral changes in the received reflected beam.

6. Method according to one of claims 3 - 5, characterized by the following steps: configuring the reluctance transducer (8) with a DC field meter (42) as magneto resistive element and, calculating the second distance (d2) by means of variations in magnetic flux through the sensor for static fields (42).

7. Method according to one of the previous claims, characterized by that the nonmagnetic layer is a paint and the thickness of which is at least 1 μm and preferably 5-200 μm.

8. Method according to one of the previous claims, characterized by the following steps: providing the central unit (18) with a memory media (26) and an instructions control unit (28) connected to an output of the processor (24).

9. Material thickness measuring means (3), which during use measures material thickness of a non-magnetic material layer (1) applied and adhered to a magnetic material (2), the means (3) includes a sensor assembly (4) comprising a positioning means, for interaction with a first side (10) of the layer (1) and an electromagnetic sensor (8), which is arranged close to the first side of the layer (1) for interaction with said magnetic material (2) as a magnetic reference element on the opposite side (12) of the layer (1), characterized in that

-the electromagnetic sensor is configured as a reluctance transducer (8) comprising at least one magneto resistive element constituted of a sensor for static fields (42); -the positioning means is provided with a confocal chromatic sensor (6) for interac- tion with the first side of the layer (1) as an optical reference element;

-the sensor assembly (4) is configured with the confocal chromatic sensor (6) and the reluctance transducer (8) in combination and related to a reference point (r_p); -a central unit (18) is configured comprising an optical controller (20) and an electric control unit (22), individually connected to a processor (24); -the confocal chromatic sensor (6) is arranged to emit optical signals (30) as input to said optical controller (20), which optical signals are representative of a first distance (dl) from said reference point (r_p) to the layer (1); -the reluctance transducer (8) is arranged to emit electric signals (32) as input to said electric control unit (22), which electric signals are representative of a second distance (d2) from said reference point (r_p) to said magnetic material (2); and - the central unit (18) is arranged to calculate a third distance (d3), which represents the material thickness of the layer (1).

10. Material thickness measuring means according to claim 8, characterized in that the electromagnetic sensor is a reluctance transducer (8) comprising a core (38) around which at least two counteracting coils (40) are arranged on each side of at least one magneto resistive element (42) and said core (38) is configured with a beam hole (44), through which an optical light source of the confocal chromatic sensor (6) emits a beam of rays, the beam axis of which is essentially parallel to a centre axis (C) of said beam hole (44) and directed to hit on a predetermined point (14) of the first side (10) of the layer (1) and from the layer (1) at least part of said beam of rays is reflected back through a slot in the lens system in the beam hole (44) of the core (38) and through a fiber optical cable (30) to a spectrometer of the optical controller (20).

11. Material thickness measuring means according to claim 9, characterized in that the core (38) is configured to direct the magnetic flux of the reluctance transducer (8) to hit on a spot essentially surrounding the first measuring point (14), from where the magnetic flux goes beyond and interacts with the magnetic material (2) at a second measuring point (16) on the opposite side (12) of the layer in relation to said first measuring point (14).

12. Material thickness measuring means according to claim 9 or 10, characterized in that said spectrometer of the optical controller (20) is capable of determining the first distance (dl) to the layer (1) by detecting the spectral changes in the received reflected beam.

13. Material thickness measuring means according to one of claims 9 - 11, charac- terized in that the reluctance transducer (8) is provided with a sensor for static fields (42) as magneto resistive element and the second distance (d2) is calculated by means of variations in magnetic flux through the sensor for static fields (42).

14. Material thickness measuring means according to one of the previous claims, characterized in that the central unit (18) is provided with a memory media (26) and an instructions control unit (28) connected to an output of the processor (24).