Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B11/00—Measuring arrangements characterised by the use of optical techniques
  • G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
  • G01B11/06—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material
  • G01B11/0616—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material of coating
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B21/00—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant
  • G01B21/02—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant for measuring length, width, or thickness
  • G01B21/08—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant for measuring length, width, or thickness for measuring thickness
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
  • G01B7/02—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness
  • G01B7/06—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness for measuring thickness
  • G01B7/10—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness for measuring thickness using magnetic means, e.g. by measuring change of reluctance
  • G01B7/105—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness for measuring thickness using magnetic means, e.g. by measuring change of reluctance for measuring thickness of coating
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B2210/00—Aspects not specifically covered by any group under G01B, e.g. of wheel alignment, caliper-like sensors
  • G01B2210/40—Caliper-like sensors
  • G01B2210/42—Caliper-like sensors with one or more detectors on a single side of the object to be measured and with a backing surface of support or reference on the other side
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B2210/00—Aspects not specifically covered by any group under G01B, e.g. of wheel alignment, caliper-like sensors
  • G01B2210/50—Using chromatic effects to achieve wavelength-dependent depth resolution

Definitions

• 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.
• reluctance transducers are preferred before inductive transducers or eddy-current transducers.
• 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
• 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 ⁇ m, but considerably smaller values, down to approximately 10 ⁇ m, 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 ⁇ m and preferably 5-200 ⁇ m and is allowed to vary only some ⁇ 5 ⁇ m. To this extent the transducer, when held at a predetermined spacing of 30-100 ⁇ m 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.
• 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 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• said optical sensor 6 is configured for interaction with said first side of the web 1
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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 ⁇ might be achievable.
• 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.
• 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.
• 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).
• 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 ⁇ m and preferably 20-200 ⁇ m) has been applied.
• the non-magnetic layer here paint layer 1 of 5 to 300 ⁇ m and preferably 20-200 ⁇ m
• the thickness is allowed to vary only some ⁇ 5 ⁇ m 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.
• 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.
• 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.
• 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.
• 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).
• 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).
• 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.
• 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.
• 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.
• 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).
• 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 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.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Length Measuring Devices By Optical Means (AREA)
• Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)

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• 2010
  • 2010-03-12 EP EP10751099.2A patent/EP2406579A4/de not_active Withdrawn
  • 2010-03-12 WO PCT/SE2010/050278 patent/WO2010104466A1/en active Application Filing

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