Patent Description:
It is important that in a manufacturing or processing phase a width, a thickness, a shape and/or a location of at least one of the edges of a moving metal sheet is measured. In the prior art, there have been several methods to measure at least one of these features.

An imaging system that typically has a camera may capture images of the moving metal sheet, and an image processing computer program may be used to determine a value for any measured feature detectable in the images. However, dust and steam, such as an emulsion steam deteriorate the visibility of the moving metal sheet and the heat may cause heat distortion to image. The heat may also cause a high requirement to the optics. Additionally, an imaging system is structurally and operationally complicated.

Ultrasound measurement systems suffer from a low accuracy, and the ultrasound waves are detracted with the moving air, which causes errors in the measurement results.

Properties such as thickness of the metal sheet have been measured using radioactivity, X-rays, lasers, eddy-currents, test contact probes, and microwave resonators. A use of a radioactivity source requires a permission, and a massive protection against the radiation which results in a challenging technical and economic situation in order to be a realistic measurement. It also requires a separate calibration for each metal, and the measurement is slow. The radioactivity measurements are receding technologies.

The X-ray measurements are rather similar to the measurements based on radioactivity except that the X-ray radiation can be switched off when a measurement is not performed. Additionally, the X-ray tubes need to be renewed.

The probes that are in a physical contact with the metal sheet are not perfectly non-invasive and may scratch the surface. Additionally, the measurement with a physical contact is slow.

The measurements based on the lasers expressly require that the specular reflection is directed to the detector, which is not fulfilled when a direction of the bright metal surface i.e. a direction of a normal of the metal surface varies. Thus, the variation in a tilt angle of the metal sheet must be prevented or compensated leading to a technical complexity. Also dust and vapours cause problems to optical radiation of the lasers.

The measurement with eddy-currents does not work with ferrous metals. Additionally, the measurement range and gap are narrow.

The measurements based on microwaves are sensitive to a variation of a tilting of the metal surface i.e. to a tilt of a normal of the metal surface. This leads to similar technical problems as the measurement with a laser.

Patent document <CIT> presents a baffle plate unit and a gas wiping device using the baffle plate unit. Patent document <CIT> presents a device for determining the positions of the edges and the width of a metal strip. Patent document <CIT> presents an apparatus and a method for a thickness and velocity measurement of flat moving materials using high frequency radar technologies. Patent document <CIT> present an arrangement for determining the width of a plate with a measuring device with a first sensor device.

Hence, there is a need to find an improvement to the measurement.

Furthermore, words "comprising" and "including" should be understood as not limiting the described embodiments to consist of only those features that have been mentioned and such embodiments may also contain features/structures that have not been specifically mentioned. All combinations of the embodiments are considered possible if their combination does not lead to structural or logical contradiction.

It should be noted that while Figures illustrate various embodiments, they are simplified diagrams that only show some structures and/or functional entities. The connections shown in the Figures may refer to logical or physical connections. It is apparent to a person skilled in the art that the described apparatus may also comprise other functions and structures than those described in Figures and text. It should be appreciated that details of some functions, structures, and the signalling used for measurement and/or controlling are irrelevant to the actual invention. Therefore, they need not be discussed in more detail here.

Dimensions in the document refer to spatial directions that are orthogonal to each other.

<FIG> illustrate an example of an apparatus for measuring a surface of a sheet <NUM>. Sensor arrangements <NUM> in <FIG>, <FIG>, <FIG> and <FIG> are shown from two orthogonal viewing angles, side and top. A curved arrow illustrates a turn from top to side. In <FIG>, the sensor arrangements shown side and top do not show the same arrangement <NUM>, <NUM>' but two different but possible arrangements. The sheet <NUM> may be electrically conductive and moving. In an embodiment, the sheet <NUM> may be a metal sheet. In an embodiment, the sheet <NUM> may have an electrically conductive surface but material below or within the electrically conductive surface may be an electrical insulator. Alternatively in an embodiment, the sheet <NUM> may be an insulator without an electrically conductive surface. It is also possible, in an embodiment, that the sheet <NUM> is not moving but is immobile while the measurement is performed. However, the claims define a moving, not immobile, surface. Although many of the measurements are described to be performed to the sheet <NUM>, particularly a measurement of thickness, a measured object does not necessarily need to be a sheet but it may be an object of any shape (see an example relating to a roll in <FIG>). However, the claims are directed to a moving surface in the context of a sheet and not to any object as such.

At least two first sensors <NUM>, <NUM>, <NUM> are distributed parallel with a longitudinal extent of a first edge <NUM> of the sheet <NUM>. The two sensors in <FIG> are <NUM> and <NUM>, for example, the two sensors being useful to understand the invention. It can be considered that the at least two sensors <NUM>, <NUM> have a distance therebetween, the distance being in a single dimension such that the two first sensors <NUM>, <NUM> are distributed one-dimensionally in space. The single dimension is at least approximately parallel to the longitudinal extent i.e. length of the first edge <NUM>. The single dimension can be considered and it typically is horizontal.

The at least two first sensors <NUM>, <NUM>, <NUM> have an interaction with the surface of the edge <NUM> of the sheet <NUM> in a contactless manner using a microwave range of electromagnetic signals. Wavelengths of the microwave signals may be in a millimeter range. In an embodiment, a frequency range of the microwave signals may start from a minimum frequency about <NUM>. In an embodiment, a frequency range of the microwave signals may start from a minimum frequency about <NUM>. In an embodiment, a frequency range of the microwave signals may start from a minimum frequency about <NUM>. In an embodiment, a frequency range of the microwave signals may start from a minimum frequency about <NUM>. In an embodiment, a frequency range of the microwave signals may start from a minimum frequency about <NUM>. In an embodiment, a frequency range of the microwave signals may go upto about <NUM>. In an embodiment, a frequency range of the microwave signals may go upto about <NUM>.

At least one of the at least two first sensors <NUM>, <NUM>, <NUM> receives and/or detects at least two of the signals of the interaction as a reflection from the first edge <NUM>. The reflected signals also carry information relating to distances between the at least two first sensors <NUM>, <NUM>, <NUM> and the first edge <NUM> at different longitudinal sections <NUM>, <NUM> of the sheet <NUM>. The microwave signals reflect from the first edge <NUM> in a direction parallel to a normal of the first edge <NUM> of the sheet <NUM>. The rectangle angle of the normal opens on a plane a normal of which is parallel to a normal of a first main surface <NUM> (see rectangle angle <NUM>° in <FIG>).

A data processing unit <NUM> receives the information relating to distances between the at least two first sensors <NUM>, <NUM>, <NUM> and the first edge <NUM> at different longitudinal sections <NUM>, <NUM> of the sheet <NUM>. The data processing unit <NUM> also determines at least one geometrical parameter of the first edge <NUM>. In an embodiment, the at least one geometrical parameter may include information on a geometry of the first edge <NUM>. In an embodiment, the at least one geometrical parameter may include a location of the first edge <NUM> of the moving sheet <NUM> based on the information on the distances. The location may be determined in a horizontal direction, in a vertical direction or in a vertical and horizontal directions.

The location may mean a location of the first edge <NUM> with respect to the at least two first sensors <NUM>, <NUM>, <NUM>. However, as it is possible that the position of the at least two first sensors <NUM>, <NUM>, <NUM> is known with respect to an external coordinate system. The data processing unit <NUM> may then determine the location of the first edge <NUM> according to the external coordinate system. The external coordinate system may refer to measures of a system that is used to manufacture of the sheet <NUM>, for example. The external coordinate system may refer to global coordinates, for example.

A desired direction DD may be parallel to a longitudinal axis of the sheet <NUM> or a direction of movement M of the sheet <NUM>. The desired direction DD is the same as the single dimension that is at least approximately horizontal. In an embodiment, the at least one geometrical parameter may include information on a direction of the first edge <NUM> of the sheet <NUM> with respect to the desired direction DD. Alternatively or additionally, the at least one geometrical parameter may include information on a variation of a direction of the first edge <NUM>, which may refer to or be based on a variation of the distance between the first edge <NUM> and the at least two sensors <NUM> to <NUM>. Alternatively or additionally, the at least one geometrical parameter may include information on waviness or curviness of the first edge <NUM>. The waviness or curviness may mean a random or determined variation with respect to a straight line. The straight line, in turn, may refer to an averaged and constant position of the first edge <NUM> or a predetermined straight line.

The direction of the first edge <NUM> may be computed on the basis of the distances the microwaves travel between a transmitter and a receiver. Consider for simplicity that sensors <NUM> and <NUM> are transceivers i.e. the same sensor transmits and receives the microwaves. Then the microwave from the sensor <NUM> travels <NUM> between transmission and reception as can be seen in <FIG>. Correspondingly, the microwaves from the sensor <NUM> travels <NUM>' between transmission and reception. As can easily be understood on the basis of elementary geometry, <NUM> is longer than <NUM>', and a difference between <NUM> and <NUM>' depends deterministically on an angle α which is a deviation of the first edge <NUM> from the desired direction. Thus, the direction of the first edge <NUM> may be computed on the basis of the distances L and L' in the data processing unit <NUM>. A corresponding result can easily be achieved in the case the sensors <NUM>, <NUM> are not transceivers. In general, the sensors <NUM>, <NUM> do not need to be transceivers in order to compute the direction of the first edge <NUM>.

To measure any surface of the sheet <NUM>, the apparatus may comprise at least three first sensors <NUM> to <NUM>; <NUM> to <NUM>, which are distributed two-dimensionally in space (see <FIG>). The at least three first sensors <NUM> to <NUM> may be called at least three first main surface sensors <NUM> to <NUM> when they measure a first main surface <NUM> or a second main surface <NUM>. Then the at least three first sensors <NUM> to <NUM> may be considered to measure and a first edge <NUM>. The at least three first sensors <NUM> to <NUM>; <NUM> to <NUM> may have a component also in a third dimension. The microwave sensors <NUM> to <NUM> refer to the sensor that are explained earlier in conjunction with <FIG>. In an embodiment, there may be four or more of the at least three first sensors.

Said at least three first sensors <NUM> to <NUM>; <NUM> to <NUM> interact with the surface of the sheet <NUM> in a contactless manner using a microwave range of electromagnetic signals. At least two of the at least three first sensors <NUM> to <NUM>; <NUM> to <NUM> receive at least two of the microwave signals of the interaction. The at least two of the microwave signals of the interaction are reflected from the surface of the sheet <NUM>. The two of the microwave signals carry information relating to distances between the at least three first sensors <NUM> to <NUM>; <NUM> to <NUM> and the surface of the sheet <NUM>. The microwave signals reflect in a direction parallel to a normal of the surface of the sheet <NUM> at the first edge <NUM> (and at second edge <NUM>). The beam widths of the sensors are wide enough for transmission and reception such that the reflection can be measure even when the surface is tilted.

The transmitting and receiving sensors of the at least three first sensors <NUM> to <NUM>; <NUM> to <NUM> are selected two-dimensionally such that microwave signals of the interaction represent both dimensions of the space of two-dimensional distribution of the at least three first sensors <NUM> to <NUM>; <NUM> to <NUM>.

The data processing unit <NUM> then receives said information on the distances, and determines at least one geometrical parameter of the sheet <NUM>. The at least one geometrical parameter may be a geometrical feature of the sheet <NUM> or a location of the sheet <NUM> for example.

In an embodiment, the at least two or three sensors <NUM> to <NUM>, which are used to measure the first edge <NUM>, may use linear polarization a direction of which is parallel to a longitudinal axis of the sheet <NUM>. The polarization allows a strong reflection from the first edge <NUM>.

In an embodiment, the at least two or three sensors <NUM> to <NUM>, which are used to measure the first edge <NUM>, may use linear polarization a direction of which is at about <NUM>° angle with respect to the longitudinal axis of the sheet <NUM>. In this embodiment, a field of the microwave transmission induce an electric current in a direction of the longitudinal axis of the sheet <NUM> at the first edge <NUM>. The electric current then radiates linearly polarized microwaves a direction of which is orthogonal to that of the transmitted microwaves. Interfering reflections from other electrically conducting surfaces may be attenuated or eliminated when either of the polarizations is utilized.

In an embodiment, a width of the sheet <NUM> may be measured using only the at least two or three sensors <NUM> to <NUM> at one side of the sheet <NUM>. The microwaves reflect then from both the first edge <NUM> and the second edge <NUM> as surface waves. A temporal difference between receptions of the microwaves then is comparable to the width of the sheet <NUM>. A property that depends on the temporal difference may be detected using a direct time measurement, a phase measurement of the microwave signals or the like that is known, per se, in the prior art.

In an embodiment, the transmitted microwaves may be circularly polarized. The reception may then be performed in a linearly polarized manner or in a circularly polarized manner. An advantage in this approach is that interfering reflections from other electrically conducting surfaces may be attenuated or eliminated.

In an embodiment, the at least three first sensors <NUM> to <NUM>; <NUM> to <NUM> may comprise at least two first sensors <NUM> to <NUM>, which are distributed parallel with a longitudinal extent of a first edge <NUM> of the sheet <NUM> for making it possible for the data processing unit <NUM> to determine the at least one geometrical parameter of the first edge <NUM> as already explained.

In an embodiment, the data processing unit <NUM> may determine an angle of the first edge <NUM> with respect to a direction of the desired direction of the sheet <NUM> as the at least one geometrical parameter of the sheet <NUM> based on the information relating to the difference of the distances between the at least three first sensors <NUM> to <NUM>; <NUM> to <NUM> and the surface of the sheet <NUM>. The desired direction of the sheet <NUM> may be a predetermined direction at which the sheet <NUM> is moving or should move during its processing such as manufacturing or later treatment, for example.

In an embodiment an example of which is illustrated in <FIG>, the apparatus may comprise at least two second sensors <NUM>, <NUM>, <NUM>, which are distributed parallel to a longitudinal extent of a second edge <NUM> of the sheet <NUM>. The at least two second sensors <NUM>, <NUM>, <NUM> are located opposite to the first edge <NUM> and on an opposite side of the sheet <NUM> with respect to the at least first two or three sensors <NUM> to <NUM>. The at least two second sensors <NUM> to <NUM> may have the interaction with the surface of the second edge <NUM> in the contactless manner using the microwave range of the electromagnetic signals. Sensor arrangements <NUM> in <FIG> are shown from two orthogonal viewing angles, side and top. A curved arrow illustrates a turn from top to side.

The at least two second sensors <NUM> to <NUM> may receive at least two of the microwave signals of the interaction, the microwave signals carrying information relating to distances between the at least two second sensors <NUM> to <NUM> and the second edge <NUM> at different sections <NUM>, <NUM> of the sheet <NUM> spaced in a longitudinal direction of the sheet <NUM> from each other. The data processing unit <NUM> may receive the information on the distances, and determine at least one geometrical parameter of the second edge <NUM> based on the information. In an embodiment, the at least one geometrical parameter may include information on a geometry of the second edge <NUM>. In an embodiment, the at least one geometrical parameter may include a location of the second edge <NUM> of the moving sheet <NUM> based on the information on the distances.

In an embodiment, the at least one geometrical parameter may include information on a direction of the second edge <NUM> of the sheet <NUM> with respect to the desired direction DD. Alternatively or additionally, the at least one geometrical parameter may include information on a variation of a direction of the second edge <NUM>, which may refer to or be based on a variation of the distance between the second edge <NUM> and the at least two sensors <NUM> to <NUM>. Alternatively or additionally, the at least one geometrical parameter may include information on waviness of the second edge <NUM>.

In an embodiment an example of which is illustrated in <FIG>, the apparatus may comprise a first additional transceiver sensor <NUM> that may transmit a microwave signal over the sheet <NUM>. The transceiver sensor <NUM> may comprise an integrated transceiver or a combination of a separate transmitter and receiver. The microwave signal may travel over the first main surface <NUM> or the second main surface <NUM>. The microwave signal may be directed to a first reflecting reference <NUM> that has a known location with respect to the at least two second sensors <NUM> to <NUM> or the second edge <NUM>. The microwave signal may travel in a direction that has a component parallel to a normal of the first and second edges <NUM>, <NUM>. The first additional transceiver sensor <NUM> may receive a reflection of the microwave signal from the first reflecting reference <NUM>. The reflection from the first reflecting reference <NUM> carries a transverse information relating to a distance between the first additional transceiver sensor <NUM> and the first reflecting reference <NUM>. The data processing unit <NUM> may receive the transverse information, and determine a width of the sheet <NUM> based on the transverse information, the location of the first edge <NUM> and the location of the second edge <NUM>. In an embodiment of <FIG> and <FIG>, dust and steam that may disturb the microwave measurement can be compensated in the measurement because of the reflection from the first reflecting reference <NUM> or the detection with a receiver microwave sensor used instead of the first reflecting reference <NUM> (explained later).

In an embodiment, the at least two or three sensors <NUM> to <NUM>, which are used to measure the second edge <NUM>, may use linear polarization a direction of which is parallel to a longitudinal axis of the sheet <NUM>. The polarization allows a strong reflection from the second edge <NUM>. This is an advantage when a thin sheet <NUM> is measured. A sheet <NUM> is thin when its thickness is smaller than a wavelength of the microwave transmission. In an embodiment, the at least two or three sensors <NUM> to <NUM>, which are used to measure the second edge <NUM>, may use linear polarization a direction of which is at about <NUM>° angle with respect to the longitudinal axis of the sheet <NUM>. In this embodiment, a field of the microwave transmission induce an electric current in a direction of the longitudinal axis of the sheet <NUM> at the second edge <NUM>. The electric current then radiates linearly polarized microwaves the polarization of which is orthogonal to that of the transmitted microwaves.

In an embodiment an example of which is shown in <FIG>, the apparatus may comprise a receiving reference sensor <NUM>' instead of the first reflecting reference <NUM>. Then the received microwave signal received by the receiving reference sensor <NUM>' carries a transverse information relating to a distance between the first additional transmitter sensor <NUM>' and the receiving reference sensor <NUM>', this transverse information being similarly usable as that carried by the reflection from the first reflecting reference <NUM>.

In an embodiment an example of which is illustrated in <FIG>, the at least two or three first sensors <NUM> to <NUM> may transmit microwaves in a direction that has a component parallel to a normal of the first edge <NUM> to a second reflecting reference <NUM> that is located over the sheet <NUM>. Here the word "over" means that the second reflecting reference <NUM> has a distance from the first main surface <NUM> or the second main surface <NUM> in a direction of a normal of the first main surface <NUM> or the second main surface <NUM>. Hence, the word "over" should also be understood to cover the situation where of the second reflecting reference <NUM> is located under the sheet <NUM>. Said at least two or three first sensors <NUM> to <NUM> may also receive a reflection of the microwaves from the second reflecting reference <NUM>. The reflection carries a first reference information relating to a distance between said one of the at least two or three first sensors <NUM> to <NUM> and the second reflecting reference <NUM>. The second reflecting reference <NUM> is in a known position, which may be a constant position. In that way the first edge <NUM> of the sheet <NUM> may be determined accurately.

In an embodiment, said at least two or three second sensors <NUM>, <NUM>, <NUM> may transmit a microwave signal in a direction that has a component parallel to a normal of the second edge <NUM> to a third reflecting reference <NUM>. Said at least two second sensors <NUM>, <NUM>, <NUM> may receive a reflection of the microwave signal from the third reflecting reference <NUM>. The reflection carries a second reference information relating to a distance between said at least two second sensors <NUM>, <NUM>, <NUM> and the third reflecting reference <NUM>. The data processing unit <NUM> may receive the first reference information and the second reference information, and determine a width W of the sheet <NUM> based on the first transverse information, the second reference information, distance between the second reflecting reference <NUM> and the third reflecting reference <NUM>, the location of the first edge <NUM> and the location of the second edge <NUM>. The third reflecting reference <NUM> is in a known position, which may be a constant position. In that way the second edge <NUM> of the sheet <NUM> may be determined accurately. In an embodiment, the stability of the position of the second and third reflecting references <NUM>, <NUM> may be ensured and/or corrected by measuring their temperature in order to compensate an effect of the thermal expansion.

The second reflecting reference <NUM> and the third reflecting reference <NUM> may be separated from each other by a distance T in a direction at least approximately parallel to a normal of the first edge <NUM> and/or the second edge <NUM>. The second reflecting reference <NUM> and the third reflecting reference <NUM> may be connected to each other by a solid material. The solid material, which may be a bar or the like, may be made of thermally stable material. The thermally stable material may comprise invar, for example. The thermally stable material allows a thermally immobile location for the second reflecting reference <NUM> and the third reflecting reference <NUM>.

The angle β, which is a deviation between the microwave signals with respect to first edge <NUM> and the second reflecting reference <NUM>, may be taken into account in the measurement of the width W of the sheet <NUM>. The angle θ, which is a deviation between the microwave signals with respect to second edge <NUM> and the third reflecting reference <NUM>, may also be taken into account in the measurement of the width W of the sheet <NUM>. The width W of the sheet <NUM> may be expressed mathematically in a following manner, for example: <MAT> where T is the distance between the second reflecting reference <NUM> and the third reflecting reference <NUM>, U1 is a distance between the at least two or three first sensors <NUM> to <NUM> and the first edge <NUM>, U2 is a distance between the at least two or three second sensors <NUM> to <NUM> and the second edge <NUM>, U3 is a distance between the at least two or three first sensors <NUM> to <NUM> and the second reflecting reference <NUM>, and U4 is a distance between the at least two or three second sensors <NUM> to <NUM> and the third reflecting reference <NUM>. The data processing unit <NUM> may perform an algorithm that corresponds to the mathematical expression.

In an embodiment an example of which is represented in <FIG>, the apparatus comprises the at least three first sensors <NUM> to <NUM>. The at least three first sensors <NUM>, <NUM>, <NUM> may receive at least two of the microwave signals of the interaction with information relating to distances between the at least three first sensors <NUM>, <NUM>, <NUM> and the first edge <NUM> of the sheet <NUM> as a reflection in a direction parallel to a normal of the first edge <NUM>, the microwave signals of the interaction representing both dimensions of the space of two-dimensional distribution of the at least three first sensors <NUM>, <NUM>, <NUM>. The data processing unit <NUM> may receive said information on the distances, and determine a shift of the sheet <NUM> in a vertical direction as a geometrical parameter on the basis of the information on the distances. The same can also be expressed such that the data processing unit <NUM> may receive said information on the distances, and determine a shift of the sheet <NUM> in a transverse direction to both a normal of the first edge <NUM> and the direction of a longitudinal axis of the sheet <NUM> as a geometrical parameter on the basis of the information on the distances. Often, but not always, the sheet <NUM> is on rolls or a conveyer belt, and thus it can shift only upward from the rolls or the conveyer belt.

The vertical shift may be detected and indicated based on the following geometrical features. Assume first that the sheet <NUM> is a position A which is for simplicity in the middle of the sensors <NUM>, <NUM>, for example. Then the distance between the sensor <NUM> and the first edge <NUM> of the sheet <NUM> is x. The distance between the sensor <NUM> and the first edge <NUM> of the sheet <NUM> is also x. Then distance the microwaves travel from the sensor <NUM> via the first edge <NUM> to the sensor <NUM> is 2x. Assume now that the sheet <NUM> is a position B, which deviates from the position A. Then the distance between the sensor <NUM> and the first edge <NUM> of the sheet <NUM> is x'. The distance between the sensor <NUM> and the first edge <NUM> of the sheet <NUM> is x". Then distance the microwaves travel from the sensor <NUM> via the first edge <NUM> to the sensor <NUM> is x' + x", which is longer than 2x. The difference between the distances 2x and x' + x" depends deterministically from the vertical shift S, which can easily be shown with elementary geometry.

In an embodiment, not claimed as such, an example of which is shown in <FIG>, the at least three first sensors <NUM> to <NUM> may receive, due to reflection, at least two of the microwave signals of the interaction with the first main surface <NUM> of the sheet <NUM>. Alternatively (or additionally), the interaction may take place with the second main surface <NUM> of the sheet <NUM> (see <FIG>; this embodiment is also not claimed as such). The microwave signals may carry information relating to distances between the at least three first sensors <NUM> to <NUM> and the first main surface <NUM> of the sheet <NUM>. The reflection of the microwave signals may have a component in a direction parallel to a normal of the first main surface <NUM>. The microwave signals of the interaction represent both dimensions of the space of two-dimensional distribution of the at least three first sensors <NUM> to <NUM>. The data processing unit <NUM> may receive said information on the distances, and compare the first main surface <NUM> to a desired reference based on the distances between the at least three first sensors <NUM> to <NUM> and the first main surface <NUM> included in the information. Then the data processing unit <NUM> may determine a deviation of the first main surface <NUM> from a desired reference based on differences of the distances between the at least three first sensors <NUM> to <NUM> and the first main surface <NUM> included in the information. The deviation may be considered the at least one geometrical parameter. The at least three sensors <NUM> to <NUM> may be correspondingly over the second main surface <NUM> and the data processing unit <NUM> may determine a deviation of the second main surface <NUM> in a similar manner.

The desired reference may be a flat surface, for example. The desired reference may be a deterministically curved surface, for example. Namely, the sheet <NUM> may be curved. In an embodiment an example of which is illustrated in <FIG>, it is also possible to measure a surface of a roll <NUM> as the first main surface, for example. The roll <NUM> may be a part of a manufacturing machine of a steel factory or a paper mill, for example.

The at least one geometrical parameter may, in the examples of <FIG> and <FIG>, represent a tilt angle of the first main surface <NUM> in one direction or in two orthogonal directions.

In this document a general concept can be understood to be that an apparatus for measuring a surface comprises first sensors <NUM> to <NUM>; <NUM> to <NUM>, which are distributed two-dimensionally in space, except in the measurement of either of the edges <NUM>, <NUM> it is possible to have a distribution of the sensors in one dimension or two dimensions. Said first sensors <NUM>, <NUM>, <NUM>; <NUM> to <NUM> interact with the surface in a contactless manner using a microwave range of electromagnetic signals. The first sensors <NUM> to <NUM>; <NUM> to <NUM> receive at least two of the microwave signals of the interaction with information relating to distances between the sensors <NUM> to <NUM>; <NUM> to <NUM> and the surface as a reflection. The microwave signals of the interaction represent both dimensions of the space of two-dimensional distribution of the first sensors <NUM> to <NUM>; <NUM> to <NUM>, except in the measurement of either of the edges <NUM> and <NUM> the interaction may cover one dimension or two dimensions although otherwise the measurement of the edge <NUM>, <NUM> is similar. A data processing unit <NUM> receives said information on the distances, and determines at least one geometrical parameter of the surface on the basis of the information.

In an embodiment, the at least three first sensors <NUM> to <NUM> may comprise at least four sensors, which may receive at least three of the microwave signals of the interaction as a reflection, the microwave signals carrying information relating to the distances between the at least four first sensors and a first main surface <NUM>. The microwave signals of the interaction representing both dimensions of the space of two-dimensional distribution of the at least four first sensors. The data processing unit <NUM> may receive said information on the distances, and determine a waviness of the first main surface <NUM> based on differences of the distances between the at least four first sensors and the first main surface <NUM> included in the information. Also in this case, the at least three sensors <NUM> to <NUM> may be correspondingly over the second main surface <NUM> and the data processing unit <NUM> may determine a deviation of the second main surface <NUM> in a similar manner.

In an embodiment an example of which is illustrated in <FIG>, the apparatus may comprise at least three second sensors <NUM>, <NUM>, <NUM>, <NUM> at a known distance D2 from the at least three first sensors <NUM> to <NUM>. The at least three second sensors <NUM> to <NUM> are distributed two-dimensionally in space (may have a component also in third dimension). Said at least three first sensors <NUM> to <NUM> may have an interaction with a second main surface <NUM> of the sheet <NUM> opposite to the first main surface <NUM> in a contactless manner using a microwave range of electromagnetic signals. At least two of the at least three second sensors <NUM> to <NUM> may receive at least two of the microwave signals of the interaction. The microwave signals may carry information relating to distances between the at least three second sensors <NUM> to <NUM> and the second main surface <NUM>. The microwave signals of the interaction represent both dimensions of the space of two-dimensional distribution of the at least three second sensors <NUM> to <NUM>. The data processing unit <NUM> may receive said information on the distances, and determine a thickness P of the sheet <NUM> based on the distance between the at least three first sensors <NUM> to <NUM> and the first main surface <NUM>, the distance between the at least three second sensors <NUM> to <NUM> and the second main surface <NUM> included in the information from both sides of the sheet <NUM>, and the known distance between the at least three first sensors <NUM> to <NUM> and the at least three second sensors <NUM> to <NUM>. By performing the measurement at the same moment, particularly if the sheet <NUM> is moving, and at the same positions on the opposite sides of the sheet <NUM>, the thickness of the sheet <NUM> can be determined more accurately than otherwise. That the measurement is performed at the same positions means that each pair of the measurements of opposite sides of the sheet <NUM> is performed at the same position on a plain determined by a normal N1, N2 of the first main surface <NUM> and/or the second main surface <NUM> (see <FIG>, <FIG>).

In <FIG>, a distance between the sensor arrangement <NUM> and the sheet <NUM>/the first surface <NUM> is K1. A distance between the sensor arrangement <NUM>' and the sheet <NUM>/the second surface <NUM> is K2. The data processing unit <NUM> may determine the thickness P of the sheet <NUM> based on the following mathematical expression: P = D2 - K1 - K2.

In <FIG> and <FIG> the black dots represent separate examples of a single location where distance measurements may be projected on such that a distance between the sensor arrangement <NUM>, <NUM>' and the sheet <NUM> is determined from a single point.

In an embodiment, only one transceiver sensor <NUM> over the first main surface <NUM> and only one transceiver sensor <NUM> over the second main surface <NUM> may be used to measure the thickness of the sheet <NUM>. In an embodiment, only two transceiver sensors <NUM>, <NUM> over the first main surface <NUM> and only two transceiver sensors <NUM>, <NUM> over the second main surface <NUM> may be used to measure the thickness of the sheet <NUM>.

<FIG> illustrates an example, which is not claimed as such, where the at least three sensors <NUM> to <NUM> comprise one transmitter TX1 and two receivers RX1 and RX2 for measuring the edge <NUM> of the sheet. Alternatively, the at least three sensors <NUM> to <NUM> may comprise two transmitters and one receiver in order to have the same measurement configuration and geometry which allows the data processing unit <NUM> to determine the at least one geometrical parameter.

<FIG> illustrates an example of an embodiment, where a transceiver <NUM> may transmit the microwaves towards the first edge <NUM> of the sheet <NUM>. The microwaves reflect back to the transceiver <NUM> from the first edge (see microwaves <NUM>). The distance between the transceiver <NUM> and the first edge <NUM> may be measured by the data processing unit <NUM> on the basis of effects caused by the distance to the microwaves. In this case, the microwaves travel a distance LR, which is measured as explained in conjunction with <FIG>. The transceiver <NUM> may comprise an integrated transmitter and receiver. Alternatively, the transceiver <NUM> may comprise a transmitter and a receiver that are separate. The transceiver <NUM> can be understood to be included in the at least two sensors <NUM>, <NUM>, <NUM>.

The transceiver <NUM> may transmit the microwaves towards a fourth reflecting reference <NUM> on the opposite side of the sheet <NUM> with respect to the transceiver <NUM>. The microwaves reflect back to the transceiver <NUM> from the fourth reflecting reference <NUM> (see microwaves <NUM>). The distance between transceiver <NUM> and the the fourth reflecting reference <NUM> may be measured by the data processing unit <NUM> on the basis of effects caused by the distance to the microwaves. In this case, the microwaves travel a distance E, which be expressed mathematically in the following manner and which can be determined by the data processing unit <NUM>: <MAT> Here, the distance LT and the width W remain unknown. If the distance LT between the second edge <NUM> and the fourth reflecting reference <NUM> is separately measured as explained in conjunction of <FIG>, <FIG> and <FIG>, the data processing unit <NUM> may determine the width W of the sheet <NUM> by subtracting two times the known distances LR and LT from measured value E and dividing the result by two. Mathematically this can be expressed as: <MAT> Alternatively, the data processing unit <NUM> may determine the width W of the sheet <NUM> by subtracting a sum of the known distance LR and LT from a value that is half of the measured distance E. Mathematically this can be expressed as: <MAT>.

However, if the distance LT remains unknown, the width W may be determined in the following manner. The transceiver <NUM> may transmit the microwaves towards the fourth reflecting reference <NUM>. In this case the microwaves reflect from the fourth reflecting reference <NUM> to the second edge <NUM> wherefrom the microwaves reflect back to the fourth reflecting reference <NUM>. Then the microwaves reflect from the fourth reflecting reference <NUM> back to the transceiver <NUM> (see microwaves <NUM>). The distance between the transceiver <NUM> and the the fourth reflecting reference <NUM> may be measured by the data processing unit <NUM> on the basis of effects caused by the distance to the microwaves. In this case, the distance F travelled by the microwaves can be expressed mathematically in the following manner: <MAT> The data processing unit <NUM> may determine the width W of the sheet <NUM> by subtracting two times LR and four times LT from the measured distance F and dividing the thus formed result by two or performing any other mathematical equivalent operation. Mathematically this can be expressed in the following manner, for example: <MAT> Because it is also known that the width W is W = E/<NUM> - (LR + LT), it is possible to solve the width W and the width W can be expressed in a mathematical form in a following manner, for example: <MAT> The data processing unit <NUM> may also compute the distance LT from these equations. In a mathematical form it may be expressed as: LT = (F - E)/<NUM>, for example.

The fourth reflecting reference <NUM> may be a separate reflector or it may the same as or a part of the first reflecting reference <NUM>. Any of the reflecting references <NUM>, <NUM>, <NUM>, <NUM> may comprise a retroreflector such as a triangular corner reflector (similar to those used in radar technology), a flat metal surface and/or a spherical surface (if a radius of the spherical surface is at least approximately the same as a distance to a transmitter, the spherical surface will reflect the transmission back to the transmitter).

The sensors <NUM> to <NUM>, <NUM> to <NUM>, <NUM> to <NUM> may comprise lens antennas, which provide narrow beams. In an embodiment, the opening angle of the beam of the microwave transmission and/or reception may be about <NUM>°, for example. In an embodiment, the opening angle of the beam of the microwave transmission and/or reception may be about <NUM>°, for example. The operation frequency of the sensors <NUM> to <NUM>, <NUM> to <NUM>, <NUM> to <NUM> may be in a frequency band about <NUM> to <NUM>, for example.

In an embodiment, the determination of the at least one geometrical parameter may be based on a frequency modulated continuous wave (FMCW) method. Additionally or alternatively, the determination of the at least one geometrical parameter may be based on a method of flight times of one or more microwave pulses, noise correlation method or the like for example.

The FMCW method may allow a high accuracy in the determination of the at least one geometrical parameter on the basis of phase measurements.

In an embodiment, effects of the vapour around the sheet <NUM> may be decreased by a blower <NUM> such as a fan which blows the steam away from the space where the microwaves travel (see <FIG>).

In an embodiment an example of which is shown in <FIG>, with more than one arrangement <NUM>, <NUM> of the at least two first sensors <NUM> to <NUM>, which measure the first edge <NUM>, it is possible to determine a speed of the movement of the sheet <NUM> on the basis of correlation of the microwave signals of the at least two sensors <NUM> to <NUM> or the geometrical parameters when a distance between the arrangements. A time difference it takes for a similar microwave signal to appear in different arrangements that are separated by a known distance reveals the speed v, v = (known distance)/(time difference).

In a similar manner, with more than one arrangement <NUM>, <NUM> of the at least two second sensors <NUM> to <NUM>, which measure the second edge <NUM>, it is possible to determine a speed of the movement of the sheet <NUM> on the basis of correlation of the microwave signals of the at least two sensors <NUM> to <NUM> or the geometrical parameters when a distance between the arrangements.

In a similar manner, with more than one arrangement <NUM>, <NUM> of the at least three second sensors <NUM> to <NUM>, which measure the first main surface <NUM>, it is possible to determine a speed of the movement of the sheet <NUM> on the basis of correlation of the microwave signals of the at least two sensors <NUM> to <NUM> or the geometrical parameters when a distance between the arrangements.

In a similar manner, with more than one arrangement <NUM>, <NUM> of the at least three second sensors <NUM> to <NUM>, which measure the second main surface <NUM>, it is possible to determine a speed of the movement of the sheet <NUM> on the basis of correlation of the microwave signals of the at least two sensors <NUM> to <NUM> or the geometrical parameters when a distance between the arrangements.

In an embodiment an example of which is illustrated in <FIG>, the data processing unit <NUM> comprises one or more processors <NUM>, and one or more memories <NUM> including a computer program code. Then the one or more memories <NUM>, the one or more processors <NUM> and a computer program code may cause the data processing unit <NUM> to process the information from the sensors. The data processing unit <NUM> may also control the measurement.

<FIG> is a flow chart of a measurement method of a surface of the sheet <NUM> at the first edge <NUM>. In step <NUM>, electromagnetic signals of a microwave range are transmitted <NUM>, with at least two first sensors <NUM>, <NUM>, <NUM>, to the surface of a sheet <NUM> at a first edge <NUM> for causing an interaction with the surface of the sheet <NUM> in a contactless manner, the at least two first sensors <NUM>, <NUM>, <NUM> being distributed parallel with a longitudinal extent of first edge <NUM> of the sheet <NUM>. In step <NUM>, at least two of the microwave signals of the interaction with information relating to distances between the at least two first sensors <NUM>, <NUM>, <NUM> and the first edge <NUM> as a reflection at different longitudinal sections <NUM>, <NUM> of the sheet <NUM> are received by at least one of the at least two first sensors <NUM>, <NUM>, <NUM>. In step <NUM>, the information is received by a data processing unit <NUM>, and at least one geometrical parameter of the first edge <NUM> of the moving sheet <NUM> is determined based on the information by the data processing unit <NUM>.

<FIG> is a flow chart of the measurement method of a surface. In step <NUM>, electromagnetic signals of a microwave range are transmitted <NUM>, with at least three first sensors <NUM>, <NUM>, <NUM>;<NUM>, <NUM>, <NUM>, to the surface for causing an interaction with the surface in a contactless manner, at least three first sensors <NUM> to <NUM>; <NUM> to <NUM> being distributed two-dimensionally in space. In step <NUM>, at least two of the microwave signals of the interaction with information relating to distances between the at least three first sensors <NUM> to <NUM>; <NUM> to <NUM> and the surface as a reflection are received by at least two of the at least three first sensors <NUM>, <NUM>, <NUM>; <NUM>, <NUM>, <NUM>, the microwave signals of the interaction representing both dimensions of the space of two-dimensional distribution of the at least three first sensors <NUM> to <NUM>; <NUM> to <NUM>. In step <NUM>, said information is received <NUM> by a data processing unit <NUM>, and at least one geometrical parameter of the surface is determined on the basis of the information by the data processing unit <NUM>.

The method steps <NUM> and <NUM> of <FIG> and <FIG> may be implemented as a logic circuit solution or computer program. The computer program may be placed on a computer program distribution means for the distribution thereof. The computer program distribution means is readable by a data processing device, and it encodes the computer program commands, carries out computations required for determining the at least one geometrical parameter, and optionally controls the measurements.

The computer program may be distributed using a distribution medium which may be any medium readable by the controller. The medium may be a program storage medium, a memory, a software distribution package, or a compressed software package. In some cases, the distribution may be performed using at least one of the following: a near field communication signal, a short distance signal, and a telecommunications signal.

Claim 1:
An apparatus for measuring a moving surface, characterized in that the apparatus comprises
at least three first transceivers (<NUM> to <NUM>; <NUM> to <NUM>), which are distributed two-dimensionally in space, said at least three first transceivers (<NUM> to <NUM>; <NUM> to <NUM>) being configured to interact with the surface in a contactless manner using a microwave range of electromagnetic signals and configured to receive microwave signals of the interaction with information relating to distances between the at least three transducers (<NUM> to <NUM>; <NUM> to <NUM>) and the surface as a reflection;
the at least three first transceivers (<NUM> to <NUM>; <NUM> to <NUM>) comprises at least two first transceivers (<NUM> to <NUM>), which are distributed parallel with a longitudinal extent of a surface of a first edge (<NUM>) of a sheet (<NUM>);
the at least two first transceivers (<NUM> to <NUM>) are configured have the interaction with the surface of the first edge (<NUM>) in the contactless manner using the microwave range of the electromagnetic signals;
the at least two first transceivers (<NUM> to <NUM>) are configured to receive at least two of the microwave signals of the interaction with information relating to distances between the at least two first transceivers (<NUM> to <NUM>) and the first edge (<NUM>) at different longitudinal sections (<NUM>, <NUM>) of the sheet (<NUM>), the microwave signals of the interaction representing both dimensions of the space of two-dimensional distribution of the at least three first transceivers (<NUM> to <NUM>; <NUM> to <NUM>); and
a data processing unit (<NUM>) configured to receive the information, and determine at least one geometrical parameter of the first edge (<NUM>) based on the information.