JP2007078635A - Calibration fixture, and offset calculation method of image measuring machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a calibration fixture superior in workability by dispensing with complicated regulation processing and suppressing a price of the fixture at a low price. <P>SOLUTION: A reference sphere 113 is fixedly held on the upper part of a support 112. In the reference sphere 113, previously precisely measured size is a known steel sphere. A reflection plate 114 is fixedly formed by screwing and the other method on the surface of a substrate 111 downward of the reference sphere 113. The reflection plate 114 is formed into size larger than an illumination range when the reference sphere 113 is illuminated upward. The surface of the reflection plate 114 has a prescribed roughness Ra so that the illumination light is scattered. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a calibration jig and an offset calculation method for an image measuring machine.

2. Description of the Related Art Conventionally, there has been known an image measuring apparatus that measures an outline shape or the like of an object to be measured from an image obtained by imaging an object to be measured (work) with an imaging means such as a CCD camera. In addition, in such an image measuring apparatus, an image measuring machine is known that is provided with a non-contact optical probe such as a laser probe in addition to the imaging means in order to improve the measurement accuracy in the vertical direction, that is, the Z direction (for example, patents). Reference 1)
When an offset exists between such an image measurement function by the imaging means and a non-contact displacement detection function by the non-contact optical probe, it is necessary to quantitatively specify the offset. Various jigs are used to calculate the offset value.

  For example, Patent Document 1 proposes a calibration jig in which a trapezoidal pattern metal film having two non-parallel straight knife edges is formed on a flat substrate. In addition, as shown in FIG. 5, a calibration jig in which a hollow cylindrical block 52 having a flat upper surface is formed on a substrate 51, or four-side knife edges on the substrate 51 as shown in FIG. There is also known a calibration jig in which a rectangular metal block 53 having a shape is formed and the periphery thereof is surrounded by an acrylic block 54 to enable image measurement of four sides of the metal block and measurement using an optical probe. However, these calibration jigs require an adjustment process with the assembled parts because the offset calculation error depends on the flatness and squareness of the block, and the jig cost is high. There is a problem. Further, in the case of the calibration jig of Patent Document 1 or FIG. 6, it is necessary to align each side of the block with respect to the measurement coordinates of the measuring machine, and there is a problem that workability is poor.

On the other hand, in a three-dimensional measuring machine using a touch probe, a reference sphere that is precisely measured in advance and has a known radius is used for offset calculation to calibrate the apparatus. Since the reference sphere has no directionality, there is an advantage that alignment with respect to the measurement coordinates is unnecessary. However, in the image measuring machine, the reference sphere is difficult to use for offset adjustment. In the case of image measurement, the edge portion of the reference sphere cannot be clearly identified even when using epi-illumination, transmitted illumination, oblique illumination, etc., and therefore the center position of the reference sphere cannot be accurately calculated.
Japanese Patent Laid-Open No. 11-83438

  In view of this problem, the present invention eliminates the need for complicated adjustment processing, makes it possible to keep the jig price low, and provides a calibration jig excellent in workability and an offset calculation method for an image measuring machine. The purpose is to provide.

  To achieve the above object, a calibration jig according to the present invention includes a reference sphere, a base portion that supports the reference sphere from below, and the reference sphere formed on the surface of the base portion below the reference sphere. And a reflector having a predetermined surface roughness that scatters light when illuminated from above.

  In addition, the offset calculation method of the image measuring machine according to the present invention includes a non-contact optical probe that includes an imaging unit for measuring an image and measures the shape of the object to be measured based on light irradiated to the object to be measured. In the offset calculation method of the provided image measuring machine, a reference sphere that is precisely measured in advance and has a known size is placed on a reflecting plate having a predetermined surface roughness, and then is imaged by the imaging means to capture the reference sphere. Performing image measurement and measuring the reference sphere with a non-contact optical probe; and comparing the measurement result of the image measurement and the measurement result of the non-contact optical probe to calculate an offset. It is characterized by having.

  According to the present invention, the reflector having a predetermined surface roughness is disposed below the reference sphere, and the illumination light from above the reference sphere is scattered by the reflector. For this reason, even when image measurement is performed, the edge of the reference sphere is clearly specified, and the offset value can be accurately calculated. Further, since this reference sphere is used, complicated adjustment processing is not required, and the price of the jig can be kept low, and the workability is excellent.

  Next, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows the configuration of a calibration jig 100 according to an embodiment of the present invention. The calibration jig 100 includes a steel substrate 111, a support column 112, a reference sphere 113, a reflection plate 114, and a reference block 115. The support column 112 is fixed to the substrate 111 by being screwed to the substrate 111 from the back side. Further, the reference sphere 113 is fixedly held on the upper portion of the support column 112. The reference sphere 113 is a steel sphere whose dimension is precisely measured in advance, and has a diameter D = 25 mm as an example.

  The reflector 114 is fixed to the substrate 111 below the reference sphere 113 by screwing or other methods on the surface of the substrate 111. The reflector 114 is formed in a size larger than the illumination range when the reference sphere 113 is illuminated from above by epi-illumination or the like. The surface of the reflecting plate 114 is given a predetermined surface roughness Ra (arithmetic mean roughness) so that the illumination light is scattered. This surface roughness Ra is determined in consideration of the diameter D of the reference sphere 113 and the height h (see FIG. 2) of the equator plane of the reference sphere 113 from the surface of the reflector 114. As an example, when the diameter D = 25 mm and the height h = 20 mm, the surface roughness Ra = 0.4 μm can be set. For example, when h is set larger than 20 mm, the surface roughness Ra is set smaller than 0.4 μm. The reference block 115 is a steel rectangular block formed so that the surface thereof is a flat surface.

  In the calibration jig 100 according to the present embodiment, the sphericity of the reference sphere 113 and the flatness of the reference block 115 cause an error in calculating the offset value. This eliminates the need for adjustment processing in the above-described state, so that the price can be kept low.

  Next, an example of an image measuring machine using the calibration jig 100 will be described with reference to FIG. This image measuring machine is configured as follows. That is, a measurement table 13 on which a workpiece is placed is mounted on the gantry 11, and this measurement table 13 is driven in the Y-axis direction by a Y-axis drive mechanism (not shown). Support arms 14 and 15 extending upward are fixed to the center of both side edges of the gantry 11, and an X-axis guide 16 is fixed so as to connect both upper ends of the support arms 14 and 15. An imaging unit 17 is supported on the X-axis guide 16. The imaging unit 17 is driven along the X-axis guide 16 by an X-axis drive mechanism (not shown). The imaging unit 17 includes a slider 31 that can move along the X-axis guide 16. A Z-axis guide 32 is integrally fixed to the slider 31. A support plate 33 is provided on the Z-axis guide 32 so as to be slidable in the Z-axis direction. The support plate 33 is provided with a CCD camera 34 as an imaging means for image measurement, and a laser probe as a non-contact displacement meter. 35. As a result, the CCD camera 34 and the laser probe 35 can move simultaneously in the three axial directions of X, Y, and Z while maintaining a fixed positional relationship. An illumination device 36 for illuminating the imaging range is added to the CCD camera 34. In order to confirm the measurement position of the workpiece by the laser beam of the laser probe 35 in the vicinity of the laser probe 35, a CCD camera 38 for imaging the periphery of the measurement position and illumination for illuminating the measurement position of the laser probe 35 A device 39 is provided. The laser probe 35 is supported by a vertical movement mechanism 40 for retracting the laser probe 35 when the imaging unit 17 is moved, and a rotation mechanism 41 for adapting the directivity of the laser beam to an optimum direction. .

    When calculating such an offset between the CCD camera 34 and the laser probe 35 of the image measuring machine 1, the calibration jig 100 shown in FIG. 1 is placed on the measurement table 13. Then, after calculating the center coordinates Pc (x, y) of the reference sphere 113 by image measurement with the CCD camera 34, the coordinates Pc ′ (x ′, x ′, center coordinates of the reference sphere 113 are subsequently measured by the laser probe 35. y ′) is calculated.

  At the time of measurement by the CCD camera 34, the reference sphere 113 is illuminated by the illumination device 36. The illumination light illuminates the reference sphere 113 and illuminates the reflector 114 existing below the reference sphere 113. The reflecting plate 114 has a predetermined surface roughness Ra, and the light irradiated on the reflecting plate 114 is scattered in various directions as shown in FIG. The scattered light slightly darkens the periphery of the reference sphere 113, that is, the vicinity of the equator plane, while the surrounding reflector 114 becomes brighter due to scattering. Due to this difference in brightness, the outline of the reference sphere 113 is clearly defined by the CCD camera 34. Recognition is possible in the captured image. By performing image processing such as edge detection on the captured image, the center coordinate Pc of the reference sphere 113 can be accurately specified. Unlike the calibration jig such as a rectangular block of the prior art, the reference sphere 113 does not have directionality, and therefore it is not necessary to install the calibration jig 100 in parallel with the measurement coordinate system of the image measuring machine. For this reason, workability | operativity is improved compared with the conventional calibration jig | tool.

  On the other hand, in the measurement by the laser probe 35, a laser beam is irradiated to the measurement range determined by the NA of the light receiving optical system, the reflected light is received, a plurality of points are measured on the surface of the reference sphere 113, and the coordinate values By calculating the center coordinate Pc ′ of the reference sphere 113. By taking the difference between the center coordinates Pc and Pc ′ calculated by the two methods of image measurement and laser probe measurement, offsets in the X direction and the Y direction can be obtained.

  The CCD camera 34 is focused on the upper surface of the reference block 115 by autofocus, and the height of the upper surface of the reference block 115 is measured by specifying the in-focus position based on the count value of an encoder (not shown). At the same time, the laser probe 35 measures the height of the upper surface of the reference block 115 at a plurality of points, for example, about 20 points, and measures the average value. By comparing these two measured values, an offset in the Z direction can also be obtained.

  Although the embodiments of the invention have been described above, the present invention is not limited to these embodiments, and various substitutions, additions, deletions, and the like are possible without departing from the spirit of the invention. For example, in the above-described embodiment, the reference block 115 is provided for calculating the offset value in the Z direction. However, when the CCD camera autofocus to the apex of the reference sphere 113 can be performed with high accuracy, the reference block 115 is provided. 115 may be omitted.

The structure of the calibration jig | tool 100 which concerns on embodiment of this invention is shown. The structure of the calibration jig 100 is shown. 1 shows a configuration example of an image measuring machine in which the calibration jig 100 of FIG. 1 can be used. The operation of the calibration jig 100 of FIG. 1 will be described. An example of a conventional calibration jig is shown. An example of a conventional calibration jig is shown.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 ... Calibration jig | tool, 111 ... Board | substrate, 112 ... Support | pillar, 113 ... Reference sphere, 114 ... Reflector plate, 115 ... Reference block, 11 ... Mounting stand, 13. .... Measurement table 14, 15 ... Support arm, 16 ... X-axis guide, 17 ... Imaging unit, 34, 38 ... CCD camera, 35 ... Laser probe, 36, 39 ... -Illumination device, 40 ... vertical movement mechanism, 41 ... rotation mechanism.

Claims (3)

A reference sphere that has been precisely measured in advance and whose dimensions are known;
A base for supporting the reference sphere from below;
A calibration plate, comprising: a reflector formed on a surface of the base portion below the reference sphere and having a predetermined surface roughness for scattering light when the reference sphere is illuminated from above; Ingredients.   The calibration jig according to claim 1, further comprising a reference block formed on the base portion and having a flat upper surface. In an offset calculation method for an image measuring machine that includes an imaging means for image measurement and includes a non-contact optical probe that measures the shape of the object to be measured based on the light irradiated to the object to be measured.
After a reference sphere that has been measured in advance and has a known size is placed on a reflector having a predetermined surface roughness, the reference sphere is imaged by the imaging means and measured with a non-contact optical probe. Performing a measurement of the reference sphere;
An offset calculation method for an image measuring machine comprising: a step of calculating an offset by comparing a measurement result of the image measurement and a measurement result of the non-contact optical probe.

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