JP2016024067A - Measurement method and measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a measurement method advantageous in view of increasing measurement accuracy.SOLUTION: This measurement method measures the position of a surface to be inspected by using the principle of a trigonometrical survey, the method including: a first step for irradiating the surface to be inspected with illumination light and detecting the light strength distribution of the illumination light from the surface to be inspected; a second step S101 for finding, for each of a plurality of peak portions, a peak width at a specific threshold and the peak position of a peak portion when there exist a plurality of peak portions in the light strength distribution detected in the first step; a third step S103 for setting, for each of the plurality of peak portions, a reference peak width differing for each of the plurality of peak portions on the basis of the peak position; and a fourth step S104 for specifying a peak position, among the plurality of peak portions, that is needed for finding the position of the surface to be inspected on the basis of a difference between the peak width obtained in the second step and the reference peak width set in the third step, and finding the position of the surface to be inspected from the specified peak position.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a measurement method and a measurement apparatus.

  As a measuring device for measuring the size and shape of a subject, there is a three-dimensional measuring device using a non-contact type measuring probe capable of acquiring high-density multi-point measurement data at a time. As the non-contact probe, for example, a triangulation type can be used. A triangulation type non-contact probe first irradiates a subject with laser light emitted from an illumination unit, and forms an image of the reflected light on an image sensor by a light receiving lens. The non-contact probe converts the received light intensity into digital image information corresponding to the received light intensity, and measures the position of the subject by performing arithmetic processing based on the principle of triangulation from the position of the bright spot image. However, in the measurement apparatus as described above, the light irradiated on the subject may be reflected a plurality of times on the surface (the subject surface) of the subject, and the light reflected a plurality of times is reflected on the light receiving surface of the image sensor. When incident, a plurality of peaks appear in the digital image information corresponding to the received light intensity. Here, the peak in the digital image information is not limited to the vertex, but may include the entire mountain profile. The generation of stray light due to such multiple reflections is undesirable because it prevents the acquisition of an accurate three-dimensional shape of the subject. Therefore, Patent Document 1 removes stray light by determining that the peak portion is normal signal light as a measurement signal when the width at the peak portion of the received light intensity distribution exceeds a fixed width. An optical sensor is disclosed.

Japanese Patent No. 3695170

  However, the width of the light intensity peak corresponding to stray light varies greatly depending on the relative position and orientation of the triangulation sensor and the subject or the roughness of the subject. Therefore, even if the fixed width is set by using the technique disclosed in Patent Document 1, there is a possibility that the signal light is determined despite the stray light.

  The present invention has been made in view of such a situation, and an object of the present invention is to provide a measurement method that is advantageous for improving measurement accuracy, for example.

  In order to solve the above problems, the present invention is a method for measuring the position of a test surface using the principle of triangulation, and illuminating the test surface with illumination light and illuminating from the test surface A first step of detecting a light intensity distribution of light, and when there are a plurality of peak portions in the light intensity distribution detected in the first step, for each of the plurality of peak portions, a peak width at a specific threshold value and A second step of obtaining a peak position of the peak portion, a third step of setting a different reference peak width for each of the plurality of peak portions based on the peak position for each of the plurality of peak portions, Based on the difference between the peak width determined in the step and the reference peak width set in the third step, identify the peak position for determining the position of the test surface among the plurality of peak portions, The position of the test surface from the specified peak position A fourth step of obtaining a, characterized in that it comprises a.

  According to the present invention, for example, it is possible to provide a measurement method advantageous for improving measurement accuracy.

It is a figure which shows the structure of the measuring device which concerns on 1st Embodiment of this invention. It is a figure which shows the structure of a non-contact probe. It is a figure which shows the state in which signal light and stray light image-form on an image sensor simultaneously. It is a graph which shows the image signal according to the light intensity of signal light and stray light. It is a flowchart which shows the flow of the signal light specific process in 1st Embodiment. It is a graph which shows the relationship between a stage position and a peak position.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

(First embodiment)
First, a measurement method according to the first embodiment of the present invention and a measurement apparatus to which the measurement method is applied will be described. FIG. 1 is a schematic perspective view showing a configuration of a measuring apparatus 1 according to the present embodiment. The measurement apparatus 1 is a non-contact three-dimensional measurement apparatus that uses a part or a mold for manufacturing the part as a subject W and measures the position of the subject W in a non-contact manner. In each of the following drawings, an X axis and a Y axis perpendicular to each other are taken in a plane in a state where the subject W is placed on the surface plate 2, and perpendicular to the XY plane (in this embodiment, a non-contact probe) 11 and the subject W are facing each other). The measuring device 1 includes a drive stage and a control unit 12.

  The drive stage includes a surface plate 2 on which the subject W is mounted, a Y carriage 3, an X slider 4, and a Z spindle 5, which allows the non-contact probe 11 to move in the three axial directions of XYZ. The Y carriage 3 has a pair of leg portions extending in the Z-axis direction, and the upper ends (Z-axis direction plus side) of each other are connected by the X beam 6. The lower end of each leg of the Y carriage 3 (minus side in the Z-axis direction) is connected to air guides arranged on both sides of the surface plate 2, and the air guide can move the Y carriage 3 in the Y-axis direction. To support. The X beam 6 supports the X slider 4 movably in the X axis direction via an air guide. The X slider 4 supports the Z spindle 5 movably in the Z-axis direction via an air guide. The Z spindle 5 supports the non-contact probe 11 at the lower end thereof via the rotary head 10.

  The drive stage includes a Y-coordinate measuring linear encoder 7 that reads the XYZ position coordinates of the non-contact probe 11 and X-coordinate measuring and Z-coordinate measuring linear encoders (not shown). The linear encoder 7 for Y coordinate measurement is installed in the vicinity of one leg of the Y carriage 3. A linear encoder for X coordinate measurement is installed on the X beam 6. A linear encoder for measuring the Z coordinate is installed on the Z spindle 5.

  In addition, as a drive unit for moving the Y carriage 3 in the Y-axis direction, the drive stage has a Y shaft 13 installed on the surface plate 2 and a Y movable unit 8 installed on the Y carriage 3. As a drive unit for moving the X slider 4 in the X-axis direction, the drive stage has an X shaft 14 installed on the Y carriage 3 and an X movable unit 9 installed on the X slider 4. As a drive unit for moving the Z spindle 5 in the Z-axis direction, the drive stage has a Z shaft (not shown) installed on the X slider 4 and a Z movable unit (not shown) installed on the Z spindle 5. . The drive stage also has a rotary head 10 for changing the posture of the non-contact probe 11 at the tip of the Z spindle 5. The rotary head 10 enables rotation around the Z axis and rotation around the XY axis. A non-contact probe 11 is installed at the tip of the rotary head 10. Note that the configuration of the drive stage described above is an example, and for example, it may be configured by only some of the mechanisms.

  FIG. 2 is a schematic diagram showing the configuration of the non-contact probe 11. In this embodiment, the non-contact probe 11 is a measurement probe that employs a light cutting method (line light projection type triangulation method). The length measurement principle of the light section method is that the subject W is illuminated with line light (illumination light in which the illuminated shape becomes a line shape) 30, and the line generated according to the surface (test surface) shape of the subject W is generated. The distortion amount is detected by peak detection, and the height information of the subject W is obtained based on the distortion amount of the line. The non-contact probe 11 includes an illumination unit 15 that illuminates the subject W with line light, and an imaging unit 16 that captures an image of the line illuminated on the subject W from an angle different from that of the illumination unit 15. The illuminating unit 15 includes a semiconductor laser 20 and a cylindrical lens 21, passes the light emitted from the semiconductor laser 20 through the cylindrical lens 21, and illuminates the subject W with the line light 30. The imaging unit 16 includes a first lens 22, a second lens 23, and an image sensor 24. The image sensor 24 is a light receiving element in which a plurality of pixels are gathered. Note that it is desirable that the imaging unit 16 be arranged so as to satisfy the conditions of the Scheimpflug optical system in which the sensor surface of the image sensor 24, the object surface, and the main plane of the second lens 23 intersect on the same straight line. The line light 30 illuminating the subject W is scattered by the surface to be examined, and a part of the light becomes normal signal light 31 as a measurement signal, and passes through the first lens 22 and the second lens 23. The image is formed on the sensor surface of the image sensor 24. Also, the convergence angle φ in FIG. 2 is an angle formed by the line light 30 and the signal light 31.

  The control unit 12 transmits a drive command to each drive unit for each axial direction in the measuring apparatus 1, the rotary head 10, and the non-contact probe 11, and obtains measurement information of each axis obtained in accordance with these operations. ,To analyze. In particular, the control unit 12 obtains image information output from the image sensor 24 in the non-contact probe 11, obtains the position of the test surface based on the amount of line distortion, and obtains the height information of the subject W. Finally, the shape of the subject W can be obtained.

  Next, the measurement operation (measurement method) of the measurement apparatus 1 will be described. First, a state where stray light is generated will be described. FIG. 3 is a schematic diagram showing a state in which the signal light 31 and the stray light 32 are simultaneously imaged on the sensor surface of the image sensor 24 corresponding to the configuration of the non-contact probe 11 shown in FIG. As described above, the line light 30 illuminating the subject W is scattered by the shape of the subject W, and a part of the light is imaged on the sensor surface as the signal light 31 indicated by a solid line in the drawing. On the other hand, the light regularly reflected by the subject W reaches the subject W again and is scattered, and a part of the light is imaged on the sensor surface as stray light 32 indicated by a broken line in the drawing. In this manner, the signal light 31 reflected only once by the subject W and the stray light 32 that has been reflected multiple times (reflected multiple times) can be incident on the sensor surface of the image sensor 24. And it is not desirable for the control unit 12 to recognize the stray light 32 as the signal light 31 because the accurate position of the test surface is hindered from being measured.

  Next, a method for specifying the signal light 31 from the light detected by the image sensor 24 will be described. FIG. 4 is a graph showing an image signal 40 (light intensity distribution) corresponding to the light intensity of the signal light 31 and stray light 32 obtained by the image sensor 24 with the horizontal axis representing pixel coordinates and the vertical axis representing signal values. Here, a specific threshold value 41 is set as a reference for the signal value. In this case, when the image signal 40 is viewed, there are a plurality of peak portions exceeding the threshold value 41 (two peak portions are illustrated in FIG. 4). The peak portion is a convex portion that is larger than the surrounding light intensity in the light intensity distribution on the pixel coordinate axis. Note that the threshold 41 is not limited to a predetermined value, and may be sequentially derived using the image signal 40 corresponding to the light intensity. For example, if the ratio is constant with respect to the maximum signal value of the image signal 40, it is possible not to detect a small signal value as a peak with respect to the signal light 31 or the stray light 32. Hereinafter, the process of specifying the signal light 31 when a plurality of peaks are detected will be described.

  FIG. 5 is a flowchart showing a process flow for identifying the signal light 31. First, after acquiring the image signal 40 as a first step, the control unit 12 obtains a peak width and a peak position for each of a plurality of peak portions with respect to the threshold value 41 shown in FIG. 4 as a second step ( Step S101). Specifically, the control unit 12 calculates and stores a first peak width 44 and a second peak width 45 that are distances between the intersections of the image signal 40 and the threshold value 41 for each peak (see FIG. 4). Moreover, the control part 12 calculates | requires and memorize | stores the 1st peak position 42 and the 2nd peak position 43 about each peak by the gravity center calculation of a pixel coordinate (refer FIG. 4). The peak position is a position where the light intensity shows the maximum value or its vicinity in the peak portion on the pixel coordinate axis. In calculating the peak widths, only the threshold value 41 is used in the above description. However, the peak widths may be calculated by approximating the signal light 31 to a mathematical model. For example, approximation to a Gaussian distribution may be performed on the image signal between the intersections of the image signal 40 and the threshold value 41, and the half width may be used as the peak width. By approximating the mathematical model in this way, it is possible to reduce the influence of spatially high frequency speckle noise and the like.

  Next, as a fifth step, the control unit 12 obtains a subject angle θ (see FIG. 3) that is a relative angle between the line light and the subject W (test surface) (step S102). Specifically, the control unit 12 obtains the three-dimensional information of the subject W and the relative position between the subject W and the non-contact probe 11, and the subject to which the line light 30 is irradiated based on the relative position. Find the irradiation position on the surface. Further, the control unit 12 obtains, for example, the inclination ψ (see FIG. 3) at the irradiation position on the test surface as the angle information of the test surface, and derives and stores the subject angle θ from the tilt ψ. Here, the three-dimensional information and the inclination ψ of the subject W are, for example, design values such as CAD data, actual measurement values obtained using a measurement device different from the measurement device 1, or the like. Of these, the actual measurement value is used for obtaining the subject angle θ, and therefore may be less accurate than the accuracy required for the non-contact probe 11. Further, the actual measurement value may be only angle information based on the coordinate system of the measuring apparatus 1 at the irradiation position on the surface to be irradiated with the line light.

  Next, as a third step, the control unit 12 obtains a reference peak width W2 for each peak using each peak position obtained in step S101 and the subject angle θ obtained in step S102. (Step S103). Specifically, the control unit 12 first determines the first peak position 42 from the axial position of the line light 30 corresponding to the first peak position 42 to the beam waist (spot) position based on the principle of triangulation. The distance L1 is obtained. Next, the control unit 12 calculates the beam width W1 when the subject angle θ at the first peak position 42 is 90 ° from the beam waist propagation equation (1).

  Here, λ is the wavelength of the line light, and W0 is the beam width at the beam waist position. Next, the control unit 12 uses the convergence angle φ and the beam width W1 to calculate the beam width W1 at the subject angle θ from the expression (2) indicating the relationship of the beam width to the subject angle θ. A beam width W2 when calculated on the sensor surface is calculated. This beam width W2 is set as a reference peak width W2.

  Here, α is the optical magnification of the imaging unit 16. Similarly, the control unit 12 derives a reference peak width for the other peak using the second peak position 43 and the subject angle θ.

  Then, as a fourth step, the control unit 12 determines whether the light having the peak is the signal light 31 based on the peak width obtained in step S101 and the reference peak width obtained in step S103. (Step S104). Specifically, the control unit 12 takes a difference between the first peak width 44 and the reference peak width, and when the difference is equal to or less than an arbitrarily set allowable value, the light having the peak is the signal light 31. And the first peak position 42 is stored as a normal measurement value. On the other hand, when the difference exceeds the allowable value, the control unit 12 determines that the light having the peak is the stray light 32 and deletes the first peak position 42 from the recording. Similarly, for the other peak, the control unit 12 determines whether the light having the peak is the signal light 31 or the stray light 32 and stores it or deletes it from the recording.

  After specifying the signal light 31, the control unit 12 obtains the height information of the subject W based on the principle of triangulation from the peak position, that is, the position of the subject W (test surface). In the above description, the reference peak width is obtained using the equation (1) of beam waist propagation and the equation (2) of the relationship of the beam width with respect to the object angle θ. A database may be created and referenced. A database of reference peak widths can be created by acquiring peak widths at a plurality of peak positions and subject angles θ using a reference sample having a known shape in advance.

  As described above, in the measurement method and the measurement apparatus according to the present embodiment, the absolute value of the peak width of the signal light 31 is considered as the reference peak width. Therefore, even if the peak width of the stray light 32 varies greatly depending on the surface roughness, position, or orientation of the subject W, and the magnitude relationship with the signal light 31 also changes, the signal light 31 can be accurately identified. As a result, the position of the subject W and the size and shape of the subject W can be measured with high accuracy.

  As described above, according to the present embodiment, it is possible to provide a measurement method and a measurement apparatus that are advantageous for improving measurement accuracy.

(Second Embodiment)
Next, a measurement method according to the second embodiment of the present invention will be described. In step S102 in the first embodiment, the subject angle θ is obtained from the three-dimensional information of the subject W such as CAD data. On the other hand, the feature of the measurement method according to the present embodiment is that instead of this, as a sixth step, the object angle θ is obtained from measurement data at a plurality of stage positions (a plurality of peak positions). is there. Here, the stage position refers to, for example, a position (XY coordinate position) where the surface plate 2 (that is, the subject W) and the non-contact probe 11 are relatively moved. In addition, since the structure of the measuring device to which the process other than that and the measuring method which concerns on this embodiment can be applied is the same as that of the measuring device 1 which concerns on 1st Embodiment, description is abbreviate | omitted.

  In the measurement method according to the present embodiment, first, referring to the flowchart of FIG. 5, the steps up to step S101 are the same as the steps in the first embodiment. Next, the control unit 12 obtains the subject angle θ as the process of step S102. First, the third peak position at the reference stage position traced an arbitrary distance in the X axis direction of the drive stage from the current stage position X1. Refer to Here, for the sake of simplicity, it is assumed that the stage drive is only in the X-axis direction.

  FIG. 6 is a graph showing the relationship between the stage position and the peak position, where the horizontal axis is the stage position (X-axis direction) and the vertical axis is the peak position (Z-axis direction). FIG. 6 plots the third peak position 71 at the reference stage position X0 and the first peak position 42 and the second peak position 43 at the current stage position X1 corresponding to the first embodiment. The control unit 12 converts the third peak position 71 and the first peak position 42 into height information of the subject W, and obtains an inclination from the reference stage position X0 to the stage position X1 corresponding to the solid line in FIG. . This inclination is the first inclination of the subject W at the stage position X1. Similarly, the control unit 12 converts the third peak position 71 and the second peak position 43 into the height information of the subject W, and from the reference stage position X0 to the stage position X1 corresponding to the broken line in FIG. Find the slope. This inclination is the second inclination of the subject W at the stage position X1. And the control part 12 calculates | requires and memorize | stores object angle (theta) about each peak based on the relative position of the object W and the non-contact probe 11, and the 1st and 2nd inclination calculated | required previously.

  Hereinafter, similarly to the first embodiment, the control unit 12 executes steps S103 to S104 to identify the signal light 31. Thus, according to the present embodiment, even if the method for obtaining the subject angle θ is changed from the method in the first embodiment, the same effects as in the first embodiment can be obtained. In the present embodiment, it is assumed that the signal light 31 is specified at the reference stage position X0 and there is one peak position. On the other hand, even if a plurality of peak positions are detected successively, the signal light 31 may be specified in order from the reference stage position X0 where the stray light 32 does not exist.

  In each of the above embodiments, the measurement probe is a non-contact probe of a light cutting method (line light projection type triangulation method). However, the present invention is not limited to this, and the measurement probe may be, for example, a point light projection type triangulation type non-contact probe.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

DESCRIPTION OF SYMBOLS 1 Measuring apparatus 11 Non-contact probe 12 Control part 15 Illumination part 24 Image sensor

Claims (7)

A method for measuring the position of a test surface using the principle of triangulation,
A first step of irradiating the test surface with illumination light and detecting a light intensity distribution of the illumination light from the test surface;
When there are a plurality of peak portions in the light intensity distribution detected in the first step, a peak width at a specific threshold value and a peak position of the peak portion are obtained for each of the plurality of peak portions. Two steps;
A third step of setting a different reference peak width for each of the plurality of peak portions based on the peak position for each of the plurality of peak portions;
In order to determine the position of the test surface among the plurality of peak portions based on the difference between the peak width determined in the second step and the reference peak width set in the third step A fourth step of determining the position of the test surface and determining the position of the test surface from the specified peak position;
A measurement method comprising:   The measurement method according to claim 1, wherein, in the third step, the reference peak width is set based on a beam width of the illumination light. Including a fifth step of determining an angle of the test surface;
The measurement method according to claim 1, wherein in the third step, the reference peak width is set based on an angle of the test surface. A sixth step of acquiring a peak position for each of a plurality of different positions on the test surface by relatively moving the test surface and the measurement probe that irradiates the illumination light;
The measurement method according to claim 3, wherein in the fifth step, an angle of the test surface is obtained based on a plurality of peak positions obtained in the sixth step.   The angle of the test surface in the fifth step is obtained based on angle information of the test surface measured by a measurement device different from the measurement probe that irradiates the illumination light. 3. The measuring method according to 3.   The measurement method according to claim 3, wherein, in the fifth step, the angle of the test surface is obtained based on three-dimensional information as a design value existing in advance. A measuring device for measuring the position of a surface to be tested,
An illumination unit that irradiates illumination light to the test surface, and a measurement probe that includes a light receiving element that includes a set of pixels and detects a light intensity distribution of the illumination light from the test surface;
A control unit for obtaining the position based on an output from the measurement probe;
Have
The controller is
When there are a plurality of peak portions in the light intensity distribution detected by the measurement probe, for each of the plurality of peak portions, obtain a peak width at a specific threshold and a peak position of the peak portion,
For each of the plurality of peak portions, a different reference peak width is set for each of the plurality of peak portions based on the peak position,
Based on the difference between the peak width at the specific threshold and the reference peak width, a peak position for determining the position of the test surface is determined from the plurality of peak portions, and the target peak is determined from the specified peak position. A measuring apparatus characterized by obtaining a position of a surface inspection.

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