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
  • G01B11/25—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures by projecting a pattern, e.g. one or more lines, moiré fringes on the object
  • G01B11/2536—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures by projecting a pattern, e.g. one or more lines, moiré fringes on the object using several gratings with variable grating pitch, projected on the object with the same angle of incidence
• • 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
  • G01B11/25—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures by projecting a pattern, e.g. one or more lines, moiré fringes on the object
  • G01B11/2513—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures by projecting a pattern, e.g. one or more lines, moiré fringes on the object with several lines being projected in more than one direction, e.g. grids, patterns

Definitions

• the invention relates to a method for determining the absolute coordinates of an object, in which the object is irradiated with light through a projection grating, the light reflected by the object is recorded by a sensor and the recording of the sensor is evaluated.
• the invention further relates to a device for determining the absolute coordinates of an object with projection optics for projecting a projection grating onto the object and sensor optics with a sensor for recording the light reflected by the object.
• the three-dimensional geometry of the surface of an object can be determined with the Moire technique and with projected lines.
• the contour line images can be evaluated by a computer, for example using the so-called phase shift method.
• phase-shifted images that is sensor recordings
• the evaluation can also be carried out using other techniques in which only a contour line image, that is to say only a sensor image or only a video image, is necessary. Examples are given in DE 39 07 430 B1 and DE 38 43 396 B1.
• the moire technique only provides the relative shape of the object surface. It generally cannot be used to determine the absolute distance between the sensor or the camera and the object from a contour line image. It is therefore not possible to determine the absolute coordinates (ie the absolute coordinates) of the object surface using the techniques and methods mentioned.
• these absolute coordinates of the object are required to determine the absolute size of the object or, in the case of step-shaped cross sections, the depth of the object. Since there is no information about the imaging scale in the contour line image, additional information going beyond the contour line image is required for determining the absolute coordinates.
• This additional information can be obtained by distance sensors or by changing the contour line distance or by moving the object or the camera. For this, however, masses have to be moved, which requires a stable construction of the test facility and takes a relatively long time. The mechanical effort is very high if a certain precision is to be achieved.
• EP 0 181 553 A Another device, used in a triangulation method, is known from EP 0 181 553 A.
• US 4,564,295 A discloses a method in which a grating is projected onto an object. The object is then imaged and overlaid with a reference grid (moire). For the evaluation, the reference grid is moved, or the projection grid and the reference grid are moved synchronously, which causes stationary contour lines on the object.
• US 4,349,277 discloses a method in which colored gratings with at least two different wavelengths are projected onto the object.
• the recording is made using color filters for wavelength selection on two rows of diodes.
• Equidistant grids in different colors that are shifted from each other are projected in parallel.
• the evaluation takes place via the ratio of the intensities of the respective colors.
• An absolute coding of the light planes can also be achieved via color information of the projected grating, which however is bought with a dependency on the color properties of the object.
• patterns are used that work with local coding, for example binary patterns or color patterns.
• adjacent image elements are viewed in the sensor image and the projected light plane is identified by means of a neighborhood analysis.
• US 4,802,759 discloses a method for determining the coordinates of an object, in which the object is irradiated with light through a projection grating and the light reflected by the object is recorded by a sensor.
• a method for determining the absolute coordinates of an object according to the preamble of claim 1 is known from EP 0 534 284 B1 which, when the projection grating and the sensor are in a first position, a first recording and evaluation are carried out and in which the projection grating and / or the sensor are subsequently rotated by a certain angle and a second recording and evaluation of the sensor are carried out.
• the absolute coordinates of the object can be determined from the evaluations.
• the object of the invention is to propose an improved method and an improved device for determining the absolute coordinates of an object.
• the projection grating comprises a first grating with a first grating vector and a second grating with a different second grating vector
• the sensor is arranged at a distance from the projection grating such that the projections of the first and second grids base vector leading to the sensor on the associated gitters are of different sizes.
• the projection grid can be applied to a slide or a glass plate or a similar device and can be projected onto the object with one or more light sources via one or more lenses. However, it can also be generated by the superimposition (interference) of coherent light radiation or in some other way.
• the sensitivity increases with increasing base length and thus increasing triangulation angle.
• the "base” is understood to mean the vector from the respective grating to the sensor.
• the triangulation angle is the angle between the distance from the object point to the respective grid and the distance from the object point to the sensor.
• Decisive for the sensitivity is the projection of the base vector, i.e. the vector from the respective grating to the sensor, on the associated grating / ector.
• a grid projection method can be carried out, in which two phase images with freely selectable sensitivities are generated with a single image using the direct phase shift algorithm.
• the invention is based on the knowledge that only the projection of the base vector onto the grid vector is included in the sensitivity, which increases with increasing base length.
• the projection of the base vector leading from the first grid to the sensor onto the first grid vector is different from the projection of the base vector leading from the second grid to the sensor onto the second grid vector, so that consequently different sensitivities can be achieved.
• two freely selectable independent sensitivities can be achieved.
• the distance of the sensor from the grids is preferably selected such that the object or an essential region of interest of the object or a disc continuity of the object is covered by a period of the grating evaluated with less sensitivity.
• the base vector for this grid is thus chosen such that the object or a substantial region of interest of the object or a discontinuity of the object is covered by a period of this grid.
• the arrangement can be selected in such a way that the largest possible object, that is to say the entire measuring volume of the device, or the largest possible essential region of interest of the object or the largest possible discontinuity is covered by a period of this grating.
• the sensitivity of the other grating can be set to a sufficient or the greatest possible evaluation accuracy.
• a further advantageous development is accordingly characterized in that the distance of the sensor from the grids is selected such that the grating evaluated with greater sensitivity is evaluated with sufficient evaluation accuracy or with the greatest possible evaluation accuracy.
• the distance of the sensor from the grids is selected such that the object or a substantial area of the object or a discontinuity of the object from a first number of periods of the first grating and from a different second number of periods of the second Grid is covered. If the first number and the second number are prime to each other, a clear assignment of the phases and thus a clear determination of the absolute coordinates is obtained via the selected area. In one example, the first number is 7 and the second number is 9. The ratio of the lattice periods is then 7: 9, which corresponds to a fractionally rational number.
• the first number and the second number can be chosen such that the selected area is covered by a period of the beat frequency of the periods of the grids. In an example, this can be achieved by the first number being 8 and the second number being 9, so that the periods of the grids are in the ratio 8: 9.
• the ratio of the first number and the second number corresponds to a transient number, that is to say a number that cannot be described by a fraction and whose decimal representation is not repeated, for example the Euler number e or the circle number ⁇ .
• Transient numbers can only be approximated numerically. If the ratio of the first number to the second number corresponds to a transient number, the result is theoretically an infinitely large measurement volume. In practice, this possibility is limited by the measurement noise.
• a further advantageous development is characterized in that the distance of the sensor from the grids is selected such that a period of the grating evaluated with lower sensitivity and / or of the grating evaluated with higher sensitivity covers four pixels on the sensor.
• a particularly simple evaluation algorithm results.
• other configurations can also be used with advantage.
• the grids can be different from one another.
• the grids forming the projection grid, ie the first grid and the second grid, can therefore be different from one another, in particular spaced apart.
• the recording of the sensor can be evaluated by a phase shift.
• a temporal and / or spatial phase shift can be used.
• a colored projection grid is preferably used. This is particularly advantageous if the evaluation of the sensor's recording is carried out by a phase shift.
• the projection grating is rotated.
• FIG. 1 shows a device for determining the absolute coordinates of an object in a schematic perspective view
• FIG. 5 shows a device for determining the absolute coordinates of an object with two projectors in a schematic view from above
• FIG. 6 shows a modification of the device according to FIG. 5 with a projector and three cameras in a representation corresponding to FIG. 5 and
• FIG. 7 shows a further modification of the devices according to FIGS. 5 and 6 with a projector and two cameras in a representation corresponding to FIGS. 5 and 6.
• an object 1 is irradiated with light 3 through a projection grating 2.
• the light 4 reflected by the object 1 is picked up by a sensor 5, namely a surface sensor, in particular a CCD sensor.
• the recording of the sensor 5 is evaluated (not shown in the drawing).
• FIG. 3 An exemplary embodiment of the grating 2 is shown in FIG. 3, namely an ideal sine grating with two grating vectors Gi and G 2 running at right angles to one another.
• the right-angled cross grating shown in FIG. 4 could also be used, a sine grating with two grating vectors Gi and G 2 running at right angles to one another with local, rough screening of the gray value curve.
• the amounts of the grid vectors Gi and G 2 in FIGS. 3 and 4 are each of the same size.
• the sensor 5 is arranged at a distance from the projection grid 2.
• the base vector leading from the projection grid 2 to the sensor is denoted by b.
• the sensor 5 is arranged at a distance b from the projection grid 2 such that the projection b x of the base vector b onto the first grid vector Gi is greater than the projection b y of the base vector b onto the second grid vector G 2 .
• the vector a x of the evaluation in the x direction runs parallel or approximately parallel to the first grating factor Gi and the vector a y of the evaluation in the y direction runs parallel or approximately parallel to the second grating vector G 2 . It is important to ensure that the information of the grids can be separated sufficiently well.
• the described choice of the base vector b ensures that the evaluation in the direction of. first grating vector G- t or in the x direction with a greater sensitivity than the evaluation in the direction of the second grating vector G 2 or in the y direction.
• the sensitivity increases with increasing base length, that is to say with increasing length of the projection of the base vector b onto the respective grating vector or with increasing triangulation angle y, the triangulation angle y being the angle between the path 3 from the object point 6 to the grating 2 and the path 4 from object point 6 to sensor 5.
• the distance b of the sensor 5 from the grids of the projection grating 2 is selected such that the object 1 is covered by a period of the grating evaluated with less sensitivity, that is to say the grating with the grating vector G 2 .
• This distance b is also selected such that the evaluation of the grating evaluated with greater sensitivity, that is to say the grating with the grating vector Gi, is carried out with the greatest possible evaluation accuracy.
• FIG. 6 there is a projector 8 which lies at the origin of the X-Y coordinate plane.
• a first camera 10, a second camera 1 and a third camera 12 are arranged on the X axis at a distance from one another.
• a projector 8 is arranged in the origin of the XY coordinate system.
• the first camera 13 is located in the first quadrant of this coordinate system, closer to the X axis than to the Y axis.
• the second camera 14 is also in the first quadrant of the XY plane, and also closer to the X axis than to the Y axis.
• Projector 8 first camera 13 and second camera 14 lie approximately on one line, whereby however, the first camera 13 is located somewhat outside the connecting line between the projector 8 and the second camera 14, and is somewhat closer to the X axis.
• the invention creates a method with which absolute coordinates of an object can be measured in terms of area, with only a single image having to be recorded. This is made possible using a grid which is static and which need not be manipulated at any time. In contrast to the known "single image" method, the method according to the invention does not require a colored grid or a color camera; so it is independent of the object color.
• the transmission function of a grating for example the grating shown in FIG. 2, can be described as follows:
• the sensitivity increases with increasing base length and thus increasing triangulation angle y and with a decreasing lattice constant.
• the projection of the base vector onto the grid vector is included in the sensitivity.
• the base vector is perpendicular to the grid vector, this results in zero sensitivity.
• T (r) a + b * sin (G ⁇ * r) + c * sin (G 2 * r)
• gectors are perpendicular to one another.
• the sensitivity k is greater than for the first grating.
• the projector with the projection grating 2 is at the coordinate origin.
• the two grid vectors Gi and G 2 lie on the X-axis and the Y-axis, respectively.
• the camera node, ie the sensor 5 of the camera, has the location vector in this coordinate system
• FIG. 6 Another way of obtaining multiple phase images with different sensitivities is to use a projector with a grid vector and. to use two or more cameras that have different base vectors, as shown in an example in FIG. 6.
• a projector 8 with a grating which has a grating vector G for example a grating of the type shown in FIG. 2 (ie in a line grating).
• the evaluation is carried out by at least two cameras, in the example in FIG. 6 by three cameras which have different base vectors, the distance from which is different from the projector 8.
• the method according to the invention can be implemented with a projection grating which has two grids which are preferably perpendicular to one another.
• two projectors each of which has a strip grating (with a grating vector), the grating vectors of the strip grids preferably being perpendicular to one another.
• Another possibility is to use a projector with a cross grating and to take the picture with several cameras, whereby a higher accuracy can be achieved.
• the invention can also be implemented in that several projectors, each with a cross grating, are used and the evaluation is performed by a camera.

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• Engineering & Computer Science (AREA)
• Computer Vision & Pattern Recognition (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Length Measuring Devices By Optical Means (AREA)

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• 2002
  • 2002-03-20 DE DE10212364A patent/DE10212364A1/de not_active Ceased
• 2003
  • 2003-03-19 EP EP03712057A patent/EP1485670A2/de not_active Withdrawn
  • 2003-03-19 JP JP2003576887A patent/JP2005520142A/ja active Pending
  • 2003-03-19 WO PCT/EP2003/002877 patent/WO2003078920A2/de active Application Filing
  • 2003-03-19 US US10/478,121 patent/US6876458B2/en not_active Expired - Lifetime

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