FI106745B - Method for measuring of the shape of a surface and the measuring arrangement - Google Patents

Description

106745

Method for measuring the shape of the surface and measuring apparatus

Field of the Invention

The present invention relates to a method for measuring the shape of a surface, which method comprises forming a grating line or the like for optically moire measurement on the surface under consideration and determining the shape of the surface by an interference-type line pattern formed by a reference lattice line.

The invention also relates to a surface shape measuring apparatus adapted to form a grating line or the like used for moire measurement on an optically observable surface and to determine the shape of a surface by means of an interference type line pattern formed by a reference grid line and a surface reflected lattice line.

Background of the Invention

Surface shape measurement technique is required, for example, when measuring the flatness of steel sheets. Traditionally, such surface flatness measurement has been performed visually or by hand. In prior art automated measuring arrangements, flatness measurement is based, for example, on laser triangle measurement or moire technique, where a grid line is projected or otherwise formed on a surface such as a steel plate. This surface-reflected lattice grid is viewed through the reference grid grid. In this case, the lattice line on the surface and the "reference lattice line" form a phenomenon similar to interference, resulting in a band pattern accurately representing the shape of the surface. A typical planar gauge of prior art • · ·: V comprises a lattice line forming unit and an image processing and central unit.

A disadvantage of such a measuring arrangement, especially when measuring large surfaces, is that the measuring apparatus with its fastening structures becomes considerably large and the measuring range remains small compared to the size of the apparatus. When measuring '. · ... for example, a 3.5 m wide steel plate requires up to 7 m of space in the factory hall, up to 7 m. The reason for the size is, among other things, that forming a uniform 3.5 m wide lattice line , 1 ·! With the lattice line forming device, only: ·: · 1: when the distance between the lattice line device and the camera to the surface to be measured is at least. just as much and preferably clearly more than the width of the lattice line. If lattice! 35 lines are attempted to project closer to the surface to be measured with wide-angle • · 2 106745 optics, the lattice line is distorted, and when using white light, the lattice line projection optics cause color errors. Prior art solutions require the use of high quality lattice components manufactured in special processes in railings. Prior art solutions 5 also require precision machined parts and optics as well as precise tolerances. These requirements are difficult to implement. The luminance of the lattice line remains poor, which increases the measurement uncertainty. In addition, the luminous efficacy is not uniform throughout the lattice line. It is demanding to change the maximum measuring range of the equipment to measure different sized surfaces.

Brief Description of the Invention

It is thus an object of the invention to provide a method and apparatus implementing the method so that the above problems can be solved. The solution according to the invention can make the equipment much faster with cheaper components and simpler structural solutions 15 than the solutions according to the prior art, and at the same time the inventive solution is easier to install on the production line and smaller in size.

This is achieved by a method of the type disclosed in the introduction, characterized in that the lattice line is formed on the surface under consideration with at least two separate lattice line means, the lattice line comprising essentially parallel lattice lines from different lattice means and reflected from the surface under consideration. with at least one camera in substantially one direction.

The measuring apparatus according to the invention, in turn, is characterized in that the measuring apparatus comprises at least two separate lattice line means to form a lattice line on the surface of the desired size, the lattice line comprising parallel lattice lines from different lattice means and describe the view: · ;; in a manner substantially from one direction of imaging of the lattice line on the surface.

The method and apparatus of the invention provide many advantages. The inventive solution is less sophisticated in the state of the art, ** **], with precision manufacturing of optics and mechanics for lighting and imaging. . Relatively less demanding, faster, more reliable and easier to install on a production line. In addition, a wide measuring range is easier to implement *. 'and lower equipment and development costs. Also, the luminous power and the contrast of the constants are better than the prior art. This enables • 4 «« · «· 3 106745 line patterns to be interpreted by the simplest and faster algorithms known in the art, which results in more reliable operation.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail with reference to the preferred embodiments, with reference to the accompanying drawings, in which:

Figure 1 shows a lattice line means;

Fig. 2 illustrates the formation of a lattice grid line of the surface under consideration by more than one lattice grid means;

Figure 3 shows a surface shape measurement arrangement using a camera 10 and a computer;

Figure 4 shows a measuring arrangement in which the surface is illuminated by a separate light;

Fig. 5 shows the slot used in the measuring arrangement and Fig. 6 shows the fiber row used in the measuring arrangement.

DETAILED DESCRIPTION OF THE INVENTION

The solution according to the invention is suitable for measuring the shape of the surface and especially for checking the flatness of the plate-like products using the moirö technique or the like.

Considering now the lattice line means 14 in Fig. 1, which comprises a light source 10, a slit means 11, a lens 12 and a lattice 13. Between the light source 10 and the slit means 11, a lens (not shown) usually collects an optical power from the light source normally operate any single or multi-colored source of optical power. The optical power can be at least ultraviolet light, visible light or infrared light, but most commonly visible light is used. In the solution according to the invention, the light source 10 is preferably a halogen lamp. The small gap in the gap means 11 spatially filters the optical radiation from the light source 10, i.e., reduces the divergence of the radiation, resulting in a uniform beam for the lens 12. The lens 12 can be any optically good quality light-gathering lens. Preferably, lens 12 is a cheap, plastic Fresnel lens. The gap of the slot means 11 should preferably be at the focal point of the lens 12, whereupon the lens 12 collimates, i.e. aligns, the light rays on the lattice 13. However, the light rays may also be diverging according to the known moire technique. The lattice 13 is a metal or other light-impermeable plate 35 material or the like having a large number of narrow beams in the form of granules or light. These narrow gaps form a lattice line over the surface under consideration. In the solution according to the invention, the lattice can be quite coarse, for example 3 mm / line pair.

Fig. 2 illustrates a measuring arrangement of the object under consideration 5 comprising a light source 10, a slit means 11, a lens 12, a lattice 13, a viewable surface 20 and a camera 21. The lattice line means 22 is projected from the lattice line means 14 the characteristic feature is modular lattice illumination.

That is, two or more gate line means 14 are used to measure the shape of the surface, providing a gate line 22 for a desired area, comprising a plurality of lattice lines originating from different gate line means. Different lattice line means 14 may illuminate surface 20 at different angles to each other. The overall width of the lattice line 22 is easily convertible to narrow or wide according to the number of lattice line means 14, whereby the apparatus can be easily installed on production lines of different widths. In the inventive solution, the distance of the lattice line means 14 from the collimating lens 13 to the viewable surface 20 is substantially smaller than the total width of the lattice line 22 produced by the lattice line means 14 on the viewable surface 20.

The lattice line 22 produced by one of the lattice line means 14 is typically 400 mm wide and, when at least two lattice line means 14 are used, the lattice line 22 has a total width of at least 800 mm. The usual distance from grid 13 to the surface to be considered is 150 mm regardless of the required width of grid line 22: · * ·· in the surface under consideration 20. In the solution of the invention, the collimating lens 12 and grid 13 are adjacent or the distance between surface 20 remains small. In prior art solutions, this distance is typically much larger and depends on the required width of the lattice grid 22. In the solution of the invention, the total length of the lattice line means 14 from the lattice 13 to the illumination means 10 is typically less than 1 m. Thus, the distance farthest 30 from the lattice line means 14 to the observed surface 20 is about 1 m. This is significantly less than in prior art • · ··· * solutions.

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In the solution according to the invention in Figure 2, the camera 21 depicts • · ·: ··· first the lattice line on the reference surface, followed by the camera 21. \ 35 lattice lines formed on surfaces 20 to be considered 22. As a reference surface • · »; a piece of known surface shape is used, typically of good quality

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5 106745 plane surfaces. The imaging of the reference grid line with the camera 21 is particularly important when the surface 20 is not a planar surface, whereby the grid lines become curved, or when the surface 20 has highly reflective points which obstruct the visibility of the lattice resistors 22. In the surface 20 is, for example levyvalssa-5 uslinjan plate surface, which moves in the direction indicated by the arrow. The flatness of the plates is then monitored by measurement. Disc flatness deviations on the sheet rolling line can also be corrected based on the measurement of the sheet surface shape. Hereby, the measuring apparatus is preferably located in connection with the straightening and cutting machines and, if necessary, also at the end of the production line, where, for example, the rolls correct the shape of the surface 20. The camera 21 may be any electronic camera, but in the solution of the invention, the camera 21 is preferably a line camera, or line camera, and the exposure of the camera 21 is preferably synchronized with the movement of the plate, allowing surface 20 to be imaged. Thus, the use of a line camera allows for flexible inspection of objects of variable length or continuous strip product. A matrix camera can also be used, but the exposure of the matrix camera is not as easily adjustable as that of a line camera because the matrix cameras are usually fitted to the video signal. In addition, the resolution of the matrix camera is lower than that of a linear camera. In the solution of the invention, one or more cameras 20 may be used 21. When more than one camera 21 is used, the distance of the camera 21 from the surface 20 may also be shortened.

Figure 3 further illustrates the rat-r 'embodiment of the invention. Each of the at least two lattice line means 14 comprises a frame structure 31 that protects against diffused light from the environment. Lattice tool; 14 projects the lattice line obliquely on the surface 20 to be viewed. The camera 21 may then be in the normal direction of the surface 20. However, in the solution of the invention, the shooting angle of the camera 21 and the illumination angle of the lattice entertainment device 14 are preferably adjustable according to the luminous efficacy, optical properties of the surface under consideration, required measurement resolution and camera characteristics. From the camera 21, image information of the lattice line is transferred to a computer 32, which, by means of a reference lattice line image and a lattice *: ** line image, forms a line pattern and determines the shape of the surface. lines the surface shape based on a stripe pattern. When the camera 21 is digital, the computer 32 directly receives the images of the lattice lines 22 digital but when using an analog camera, the images are converted from analog to digital “*! for example, an A / D converter on a computer 32. The reference grid line need not necessarily be imaged by the camera 21, but in the solution of the invention the reference grid line may also be a binary memory map stored in the memory of the computer 32. This is possible in particular when the surface is planar and does not exhibit strong hi-5 disturbances that interfere with the lattice line 22. The exposure of the camera 21 is preferably synchronized with the movement of the plate, whereby the camera or cameras 21 depict surface 20 line by line and the rows are stored in the memory of the computer 32. The desired number of rows depicted by the camera or cameras 21 can be used to measure the shape of the surface. The computer 32 may process the grid line images, for example, as grayscale images, but the computer 32 10 will preferably treat the grid lines in binary value, i.e., the dark lines will have the value zero and the light lines will have the value one or vice versa. In this way, the lattice lines and the stripe pattern become more contrast and easy to manipulate with the optically formed moire line and stripe.

Fig. 4 shows an inventive surface shape measuring arrangement 15 in which the surface is illuminated in addition to the lattice line means 14 by the second illumination means 41. The second illumination means 41 comprises one or more luminaires. In this solution, it is essential that the camera 21 be so-called. a color camera, i.e., having detectors for at least two substantially different optical wavelength bands. Instead of a single color camera, it is also possible to use at least two separate cameras with filters which detect different bands of optical radiation. Typically, a color camera distinguishes blue, red, and green. In this case, the lattice line means 14 may use, for example, a puff *** ·· female light to depict the lattice line on the surface 20 and the other illumination means 41 ′ may use blue light for example to illuminate the surface 20. Thus, the camera 21 25 depicts the lattice line on the red light 20 and the blue light only the surface 20 and stores these images in the memory of the computer 32. In prior art solutions, · the texture of the surface 20 to be considered is displayed simultaneously with the lattice lines formed on the surface of the object. This situation significantly complicates the automatic and reliable interpretation of the grid line and increases the processing time of the calculation. Often, applications will be limited to situations where the texture of the surface 20 under consideration occurs in a grid line projected onto the surface at a completely different spatial frequency and: * ·! or the texture is not at all. Typical ·: ··· textures in the steel industry include ruffle and tear patterns and textured 35 Plastic coatings. In the wood panel industry, wood has its own characteristic surface • · · | texture formed. The industry also uses a variety of code and product markings, which interfere with the grid line. If there are markings or patterns on the surface 20 that interfere with the visibility of the lattice line, they can be removed from the lattice line image using image processing programs on the computer 32. Preferably, the inventive method eliminates the effect of ambient diffused light, compensates for differences in the sensitivity of the detector, and subtracts the surface image from the lattice line image to provide a clean lattice line image. The imaging process is fast because both the lattice line and the surface only can be captured simultaneously. The illumination angle of the other illumination means 41 is not essential to the invention, but in the inventive solution the illumination angle can be adjusted as desired according to the luminous efficacy, the optical properties of the surface 20 to be examined and the camera 21. In addition, the optical radiation of the second illumination means 41 allows the computer 32 to accurately determine the width of the surface 20 to be considered.

In Figure 5, the slot 51 of each lattice line means 14 is shown in more detail. In the inventive embodiment, the slot 51 of the slot member 11 is effectively an elongated slot and the narrow portion of the slot 51 is in the same direction as the lattice line lines. By elongation is meant that the slot 51 may be a uniform approximately rectangular hole, for example, also a narrow ellipse or a set of discrete holes located in a substantially rectangular-shaped area. In the inventive solution, the optical radiation band of the lattice line means 14 can be limited, for example, by using a red filter in slot 51. Of course, the filter can also be located anywhere between the light source and the surface under consideration, as long as it does not interfere. Compared to prior art solutions where · '* 25 uses a small circle or square slot, the inventive • · \ * · solution is much lighter, which improves the visibility of the lattice line on the surface under consideration.

Fig. 6 shows a solution according to the invention in which a fiber array 61 is used instead of a slot 51. The fiber array 61 is illuminated by a source of optical power. * · *. 30 and the other end of the fiber row 61 is at the focal point of the lens 12. In this case, the fiber row 61. when the optical power is emitted to the lens 12, the situation is substantially similar to that of the optical power coming from the elongated slot 51.

**. * ·: When using slot 51 or fiber row 61 as a lens 12, a standard cylindrical lens can be used instead of a Fresnel lens because collimation is only required:. 35 in the width direction and not in the direction of the lattice lines (in Figures 5 and 6 [[[. ': The radiation is thus collimated horizontally but not vertically). The Fresnel • · 8 106745 lens incorporates a number of wedge-shaped groove rings to achieve the desired bending force. This way, the Fresnel lens is thin and light compared to a regular lens with a refractive power. The Fresnel lens can be made of, for example, glass or plastic.

5 Instead of a reference lattice line stored in a computer memory, a concrete lattice line can be used as a reference lattice line, through which the surface reflected lattice line is represented by a camera. However, in this case, the second illumination means 41 cannot be utilized, and thus the disturbing patterns on the surface cannot be removed from the image of the lattice line in image processing.

The inventive solution works in particular with the moire technique whereby the lattice forms a line pattern on the surface to be considered, but the solution according to the invention is in principle also possible with any other regular patterning of the lattice. The determination of the surface shape is then based on computer programs other than the moire technique.

While the invention has been described above with reference to the example of the accompanying drawings, it is clear that the invention is not limited thereto, but that it can be modified in many ways within the scope of the inventive idea set forth in the appended claims.

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Claims (32)

A method for measuring the shape of a surface, in which a grid line system or equivalent (22) used in moire measurement is optically imaged on the surface (20) examined and the shape of the surface is determined by a line figure of interference type formed by a reference grid line system and the grid line system (22) reflected from the surface, characterized in that the grid line system (22) is formed at the desired width on the surface (20) which is examined by at least two separate grid line system means (14). comprises substantially parallel grid grid system originating from the various grid line system means (14) and the grid line system (22) reflected from the examined surface (20) is imaged with at least one camera (21) substantially in one imaging direction. Method according to claim 1, characterized in that respective grid line system means (14) use collimated optical radiation to form the grid line system (22). Method according to claim 1, characterized in that the reference grid line system is a binary memory map stored in the memory of a computer (32), wherein the reference grid line system stored in the memory functions as the second grid line system needed to form an interference type line figure. 20 Method according to claim 1, characterized in that the reference grid line system is imaged from the reference surface with at least one camera (21) and stored in the memory of the computer (32), the reference grid stored in the memory. the line system acts as the second grid line system needed to form ·: ··: an interference type line figure. · * · *: 25 5. A method according to claim 3 or 4, characterized in that: ·. : the grid line system (22) reflected from the examined surface (20) is depicted:. * with at least one camera (21) and stored in the memory of the computer (32) and the computer (32) forms, by means of the grid line system and the reference grid system reflected from the examined surface (20), a line figure of the interference type, which determines the shape of the surface . The method according to claim 5, characterized in that the dark and light lines of the grid line system (22) are processed digitally as two separate binary values, whereby a sharp contrast is obtained for the grid line system and the line figure formed. • I • · · • «106745 Method according to claim 5, characterized by the angle of incidence of the grid-line system (14) and the angle of imaging of the camera (21) differing from each other, at least the angle of incidence of the grid-line system (14) differs from the angle of incidence of the surface and the grid-line system (14). image angle is controlled in the desired manner according to the optical radiation effect, the optical properties of the surface (20) being investigated, the required measurement resolution and the characteristics of the camera (21). 10 8. A method according to claim 5, characterized in that the method is applied when measuring a moving surface, e.g. on a spot selection line when measuring the flatness of a plate and as a camera (21) a single-line camera is used, the exposure of which is synchronized with the movement of the surface. Method according to Claim 8, characterized in that on the plaque selection line deviations in the flatness of the plaque are corrected on the basis of measurements of the shape on the plaque surface. Method according to claim 5, characterized in that the optical path path length band used by the grid line system (14) is limited, the surface (20) being examined is also illuminated by optical radiation from other illumination means (41), whose path length band differs substantially from the path length band used by the grid line system means (14), at least one camera (21) forms a grid line system image on the path length band used by the grid line system means (14), and said at least one camera (21) separately forms an image of the surface (20) which is examined on the path length band of the other illumination means (41) and • ·: by utilizing the image obtained from the surface illuminated by 'the other illumination means (41), the computer (32) removes from the grid line system the image disturbances in the examined surface (20). *** '30 11. A method according to claim 10, characterized in that when the camera (21) discs detects a first, second and third color, which is in any order e.g. blue, green and red, the grid line system means (14) use the first color and the second illumination means (41) the second and: third color. 35 Method according to claim 10, characterized in that the computer (32) measures the width of the surface (20) which is examined by using an image taken from the surface (20). ) which is examined when illuminated with the other illuminating means (41). The method of claim 1, characterized in that when the grid line system means (14) comprise a collimating lens (12), the grid line system means (14) are spaced from the collimating lens (12) to the surface (20) which is substantially smaller than that of the grid line system means. (14) generated the total width of the grid line system on the surface (20) being investigated. 14. A method according to claim 1, characterized in that the optical radiation of the lattice system means (14) is spatially filtered into a slot (51) of a slot member 10 (11) which is elongated to its effective form and which is parallel to the lines of the lattice system ( 13). 15. A method according to claim 10 or 14, characterized in that the gap (51) of the gap means (11) has a color filter, thereby forming the optical wavelength band used by the grid line system means (14). 15 Method according to claim 1, characterized in that when the grid line system means (14) comprises an optical beam source (10), a fiber line (61), a lens (12) and a grid (13), the radiation from the optical beam source ( 10) to the fiber line (61), from which the radiation advances via the lens (12) and the grating (13) to the surface (20) being examined, which fiber line (61) is parallel to the lines of the grid line system (14). Apparatus for measuring the shape of a surface, which is arranged to form on the surface (20) which is optically formed a grid line system or the equivalent (22) used in moire measurement, and determine the shape of the surface by a interference-type line figure formed by a reference grid line system and the surface line grid system reflected from the surface, characterized in that the measuring device comprises at least two separate grid line means (14) to form a grid line system (22) of the desired width on the surface (20) being examined, wherein the grid line system (22) comprises substantially parallel grid grid systems originating from the various grid line system means (14) and at least one camera (21) is arranged to image grid line. the system (22) on the examined surface (20) substantially in an imaging direction. accession. Measuring device according to claim 17, characterized in that the respective grid line system means (14) are arranged to form a grid line system ·: ··: 35 (22) by means of collimated optical radiation. • »• · · •« «•» · · • «18 106745 The measuring device of claim 17, characterized in that the reference grid line system is a binary memory map stored in the memory of a computer (32), wherein the reference grid line system stored in memory functions as the second grid line system needed to form an interference type line figure. 5 Measuring device according to claim 17, characterized in that a camera (21) is arranged to image both the grid line system (22) on the surface being examined (20) and the reference grid line system, wherein the memory grid line system stored in memory functions as the second grid line system needed to form an interference type line figure. 10 Measuring device according to claim 19 or 20, characterized in that the device comprises at least one camera (21), a computer (32) and a memory belonging to the computer (32), from which the camera (21) is arranged to image the grid line system ( 22) on the surface (20) being examined, the memory is arranged to store the images of the grid line systems and the computer (32) is arranged to form, by means of the grid line systems stored in the memory, an interference type line figure, which determines the shape of the surface. Measuring device according to claim 21, characterized in that the computer (32) is arranged to treat the dark and light lines of the grid line system (22) as binary values, the grid line system and the line figure formed being sharply contrasted. Measuring device according to claim 21, characterized in that the angle of incidence of the grid line system (14) is adjustable and the angle of imaging of the camera (21) is adjustable in the desired manner according to the optical effect: the optical properties of the surface (20) being investigated , the required measurement resolution and the characteristics of the camera (21), where the grid line system angle of incidence and the imaging angle of the camera (21) differ from each other and at least the angle of incidence of the grid line system (14) deviates from the normal surface. • Measuring device according to claim 21, characterized in that the surface (20) being examined is a movable pian surface, e.g. on a spot selection line and can. ···. the meran (21) is a single-line camera whose exposure is synchronized with • · IV. ' surface movement. 25. Measuring device according to claim 24, characterized in that it is arranged on the basis of measurements of the shape of the plate surface to control ·: ··: the rolls of the platen rolling line so that the rollers correct deviations in the flatness of the plate. * · · * · · • 1 · · · 106745 26. Measurement device according to claim 21, characterized in that the wavelength band used for optical straining is limited by the grating line system means (14), the measuring device also comprises other illuminating means (41) arranged to illuminate the surface (20) which is examined by optical straining, whose path longitudinal strips differ substantially from the path length band used by the grid line system means (14), at least one camera (21) is arranged to form a grid line system image of the wavelength band the grid line system means (14) is used, and said at least one camera (21) is arranged to form a image of the surface (20) examined on the wavelength band of the second illuminating means (41) and by utilizing the image obtained by the surface illuminated by the other illuminating means (41), the computer (32) is arranged to remove interference from the grid line system image. the examined surface (20) for improving the quality of the line figure. Measuring device according to claim 26, characterized in that when the camera (21) is arranged to separately detect a first, second and third color, which is in an arbitrary order e.g. blue, green and red, the grid line system means (14) are arranged to use the first color and the second illumination means (41) are arranged to use the second or third color. 28. Measuring device according to claim 26, characterized in that the computer (32) is arranged to measure the width of the surface (20) which is examined by utilizing an image obtained by the surface (20) which is examined during illumination "with the other lighting means. (41). 25 Measuring device according to claim 17, characterized in that the distance of the grid line system means (14) from the collimating lens (12) to the surface (20) examined is substantially smaller than that of the grid line system ( 14) generated the total width of the grid line system on the surface (20) being examined. 30. Measuring device according to claim 17, characterized in that. when the grid line system means (14) comprises an optical radiation source (10), a gap member (11), a lens (12) and a grid (13), the gap (51) of the gap member (11) is elongated to its effective shape and the gap (51) is parallel to the lines of the grid line system (22). Measuring device according to claim 17 or 26, characterized in that the gap (51) of the gap means (11) comprises a color filter to form the optical path length band used by the grid line system means (14). Measurement device according to claim 17, characterized in that the grid line system means (14) comprise an optical radiation source (10), a fiber line (61), an iris (12) and a grid (13), said fiber line (61) being parallel. with the lines in the grid line system (22). · · · · · · · · · · · · ♦ ♦ · · · · ··· · · · · · ··· · · · · · ··· • ♦ • · ·· · · · · · · · · · · · · · · · · · ♦