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
  • G01B11/24—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures
  • G01B11/245—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures using a plurality of fixed, simultaneously operating transducers

Definitions

• the invention relates to a method for optoelectronic measurement of the shape, in particular cross-sectional shape, of objects, e.g. Workpieces, or for calibrating optoelectronic
• At least one light strip is projected onto the object to be measured and / or onto the calibration body by at least one light source, preferably laser light sources (light section method), which light strips preferably have a number corresponding to the number of light sources
• Video cameras preferably CCD semiconductor cameras, are recorded and imaged on their sensor element, the camera signals of an evaluation unit comprising a computer for image evaluation and calculation of the dimensions of the object or for determining the
• the invention further relates to an arrangement for performing this
• the image processing systems used in such methods and arrangements have disadvantages in terms of their limited resolution, which limits the maximum achievable accuracy.
• Conventional systems for example, resolve an image in 512 x 512 pixels. If objects of different sizes are to be measured with a measuring arrangement in the light section method, small objects are naturally imaged on the available sensor element, or the existing measuring field is not fully utilized, so that the accuracy of the evaluation suffers; Smaller objects only use part of the measuring field and are therefore resolved with less than 512 x 512 pixels, which reduces the relative measuring accuracy.
• the aim of the invention is to achieve maximum accuracy in image processing in measuring methods and measuring arrangements which operate according to the light section method.
• Sensor element of the imaging scale is changed or varied or the measuring field size of the respective camera depending on the size of the light strips generated on the object and / or calibration body are changed or adapted to them.
• the size of the sensor element of the camera remaining the same, a significantly improved evaluation of small objects or small light strips can be carried out, which are just magnified and are imaged on the sensor element of the camera such that all light strips necessary for evaluation are always imaged together or simultaneously become. Whether one or more light strips from the calibration body and / or from the object are imaged on the sensor element depends on the evaluation method selected. If the image of the light strips is larger than the sensor element, it is of course also possible to choose a smaller image scale and thus adapt the image size of the light strips to the size of the sensor element.
• ZOOM devices of the video cameras are adjusted, if necessary by motor, and / or camera lenses with different focal lengths are connected upstream of the video cameras and / or the distance between the video cameras and the object to be measured and / or calibration body is changed, possibly by a motor.
• At least one calibration body of a predetermined size is measured for calibration and the data obtained from the imaging of this at least one calibration body on the sensor element is stored in the evaluation unit and used for evaluating the data obtained when measuring an object.
• the magnification or reduction scale selected for imaging the respective light strip on the object and / or calibration body is determined and taken into account in the evaluation of the camera signals.
• the devices for adjusting the image size or the image scale or the measuring field size can be controlled by the evaluation unit, depending on the comparison of the data of the calibration body with the data of the object to be measured or on the determined size of the images of the light strips the sensor element. This enables an almost fully automatic measuring process with optimal accuracy.
• At least one light section imaged on a calibration body or a calibration mark is imaged on the sensor element, that the Size of the image of the at least one light section strip is adapted to the size of the sensor element, that the light strips generated on the calibration body or the calibration marks are measured and the image scale or the measurement field size are determined, that the data and parameters relating to the size of the light strips and the image scale in the evaluation device can be stored so that when measuring at least one light strip generated on an object, the size of the image of the at least one light strip is adapted to the size of the sensor element, that using the same imaging scale or an imaging scale that deviates from it in a known or predetermined manner the object is measured at this imaging scale and that the dimensions of the object are calculated with the aid of the imaging parameters determined during the measurement and calibration.
• the evaluation unit comprises a comparator for data and parameters originating from at least one measured calibration body with the evaluation device in the course of measuring an object and that the evaluation unit is connected to the devices for changing the imaging scale or the measuring field size and applies a control signal, which is dependent on the comparison result, for setting the imaging scale or the measuring field size.
• Fig. 1 shows schematically the structure of an arrangement according to the invention
• Fig. 2 shows a schematic diagram of the measurement of an object or calibration body
• Fig. 3a, 3b, 3c different arrangements for changing the imaging scale
• Fig. 4a, b, c and d the measurement of calibration bodies.
• Fig.l illustrates the principle of the measuring method.
• the object 4 to be examined is illuminated with a number of light sources 5, in the present case with four laser light sources, the laser light sources 5 possibly emitting light of different wavelengths.
• the light beam from the lasers 5 is expanded into a plane by means of optics (not shown), so that a light contour or a light stripe 6 is imaged on the measurement object.
• Each laser 5 forms a bright stripe 6, which usually overlap partially on the object.
• Each light plane which is spanned by a laser 5, is advantageously perpendicular to the longitudinal axis of the body (Angle / 5);
• the light planes of the individual lasers 5 are aligned in such a way that they are again adjusted as far as possible in a common plane in order to overlap the strips imaged by the individual lasers as far as possible or to place them in a defined cutting plane with the object to avoid evaluation errors based on positional inaccuracies from the outset.
• each camera 7 can be preceded by a filter 8 which only transmits light of the wavelength which is emitted by the associated laser 5, so that each
• Camera 7 can only receive light from the laser light source 5 assigned to it. This prevents any camera 7 from being influenced by light emitted by other light sources 5. At the same time, the contour of the strips 6 can be evaluated very precisely or
• Basic data of a calibration object can be evaluated precisely, which also increases the subsequent measurement accuracy.
• control lines for the light sources 5 and the cameras 7 are indicated by 11; the control unit 10 from which the
• the lighting and cameras can be switched on with the
• Evaluation unit 9 for the camera signals can be coupled or cooperates with it.
• the evaluation device 9 comprises a computer to which the digitized video signals from the cameras 7 are fed and which stores them.
• the computer looks for those points from the image matrix which represent the light section.
• the position data of the object and the position and orientation of the camera relative to the light plane as well as the focal length of the lens are known, so that the pixels found can be geometrically corrected and recalculated into the actual object coordinates.
• the light sources 5 are white light sources, with corresponding color filters, lasers, laser diodes or the like which can be tuned or frequency-adjusted with regard to their wavelength. in question. Appropriate optics are known for forming the very narrow light sections on the object.
• Video cameras semiconductor cameras, in particular CCD cameras, cameras that respond to certain colors or have color-sensitive sensor elements, so-called color cameras, are suitable as cameras.
• CCD cameras are used for image recording, which comprise a semiconductor sensor element which is made up of a matrix of approximately 500 x 500 photodiodes and which delivers essentially distortion-free images.
• the image is usually searched for contour starting points by checking the brightness contrasts of the image points and polygonizing the lines found. After the determination of appropriate polygons, each separated for the individual signals of the video cameras, each determined polygon is transformed into the object coordination and then the polygons obtained from the individual cameras are combined to form the overall contour and the desired dimensions are calculated therefrom.
• the imaging or equalization parameters are determined in the course of the calibration process, for which purpose a calibration body is brought into the measuring field of the cameras, the exact dimensions of the calibration body being stored in the computer. If the light section of the calibration body is recorded using the method described above, the equalization parameters can be calculated from the comparison of the stored dimensions with the measured light sections.
• the unit for processing the signals of the individual cameras relating to the polygon sections recorded by each camera is indicated by 12 in FIG. With 13, the unit for joining the individual polygons to the outline or cross section of the object is indicated.
• a monitor for displaying the measured object is indicated at 14, a printer for printing out the dimensions of the object or other measured data is indicated at 15 and a plotter for graphic recording of the examined object is indicated at 16.
• Layers of laser light spanned by each laser 5 lie in a common overall plane.
• FIGS. 3a, 3b and 3c show various possibilities for changing the imaging scale or for adjusting the size of the measuring field of the cameras in relation to the object or calibration body to be measured.
• a camera 7 is equipped with a ZOOM lens 18 and it is made clear that measurement objects 23 of different sizes or light sections or strips 6 of different sizes, as shown on the left and right in Figure 3a, each are mapped in such a way that they fill the measuring field 30 or 31 of the camera 7 as large as possible or that the size of the measuring field 30 or 31 is adapted to the objects or light strips 6 to be measured.
• Fig.3b an arrangement corresponding to Fig.3a is shown, in which a lens changing device 18 ', e.g., to adapt or vary the imaging scale or the measuring field size of the video camera 7. a rotating drum lens system is provided.
• a camera shifting device 18 ′′ is provided to adapt the measuring field size in order to change the distance between the camera 7 and the object 23, but in an alternative way the object relative to the camera 7 or both the camera 7 and the Object or calibration body 23 can be movable relative to each other.
• the same improvement in the accuracy when measuring objects can also be achieved when measuring calibration bodies if the size of the measuring field is adapted to the calibration body or to parts of the same.
• the measuring arrangement is calibrated with a calibration body of a precisely defined shape. By comparing this defined form with image data of the measured calibration body stored in the evaluation device, it is possible to obtain the necessary equalization parameters for equalizing images of objects to be measured.
• the determination of the rectification parameters is also subject to errors which are dependent on the resolving power of the image processing system.
• the measurement of Objects can be reduced or avoided when measuring calibration bodies or when calibrating smaller errors or calibration errors if the light strips that are formed on the calibration body extend over the entire measuring field or the image or the desired image area of the calibration body the entire sensor element extends.
• calibration bodies or calibration bodies with calibration marks intended for different imaging scales for measuring ranges with differently large imaging scales can have different areas with relative positions and / or dimensions of predetermined marks, which are taken into the measuring field or imaged on the sensor element and their known dimensions are evaluated.
• FIGS. 4a and 4b show schematically the measurement of a calibration body 23 'which carries calibration marks 26 and 26'.
• 4b shows a top view of the calibration body 23 'and the peripherally located calibration marks 26 and the centrally located calibration marks 26' can be seen.
• the viewing directions or optical axes of the four video cameras are designated by 22.
• the calibration body shown in FIGS. 4a and 4b is designed for the simultaneous calibration of four cameras. For the calibration process, corresponding light sections 6 are formed on the calibration marks 26 and 26 'or the calibration marks 26 and 26' are cut with the corresponding light planes 33.
• the image transmission system is set to a large imaging scale, ie, for example, the ZOOM lens is in the telephoto setting, then only the four middle calibration marks 26 'lie in the measuring field according to FIG middle calibration marks 26 'shown. If a smaller imaging scale is selected, for example if the ZOOM lenses are in the wide-angle setting, all calibration marks 26 and 26 'can be imaged in accordance with FIG. 4c or the light sections 24 and 24' are imaged on the sensor element 34 '.
• the evaluation device can determine the imaging scale or the image determine field size; it can also be measured by measuring the
• Stripes of light determine the size of the object and measure it with the two image scales. This way, for the
• the image scale is expediently chosen to be as large as possible.
• Image scale during the measurement should be known. Either measurement is carried out at the same imaging scale at which calibration was carried out or the imaging scale during measurement is automatically set to a known value by the evaluation unit or manually.
• a further improvement in the measurement or calibration is achieved if a light strip is imaged and measured over the measurement field planes on an elongated object, for example a ruler or measuring rod.
• the object is then offset and measured in parallel; this is repeated until the measuring field is scanned with measured light strips.
• the same process is carried out again with an object (ruler) rotated by 90 °.
• This measuring grid the spacing of which can be more or less large depending on the measuring accuracy, is used for calibration and is related to the image of the object or compared with the light strips depicted on the object. If certain areas of the object are to be measured more precisely, the grid is drawn closer in this area. The scanning or formation of the calibration light strips is thus locally variable via the measuring or image field.
• the light emanating from the light section imaged on the object is fed directly to the video cameras or directed from the provided imaging devices 18, 18 ', 18 "directly or without deflection to the sensor element.
• the size of the (r ) Light sections (s) to the size of the sensor element or vice versa, which stops light losses and the evaluation can be improved and made more precise by means of an imaging scale that also changes during the measurement.
• variable imaging units are assigned to each video camera that are assigned to the individual video - to map and evaluate light sections assigned to cameras to the various imaging scales.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Length Measuring Devices By Optical Means (AREA)

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Cited By (21)

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Citations (4)

• 1991
  • 1991-10-24 AU AU88691/91A patent/AU8869191A/en not_active Abandoned
  • 1991-10-24 JP JP51812691A patent/JPH05504842A/ja active Pending
  • 1991-10-24 EP EP19910919698 patent/EP0507923A1/de not_active Withdrawn
  • 1991-10-24 CA CA 2070824 patent/CA2070824A1/en not_active Abandoned
  • 1991-10-24 WO PCT/AT1991/000115 patent/WO1992008103A1/de not_active Application Discontinuation

Patent Citations (4)

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