JP2008170280A - Shape measuring apparatus and shape measuring method - Google Patents

Abstract

An object of the present invention is to provide a three-dimensional shape measuring apparatus having high measurement accuracy by reducing the influence of distortion and the like in a projection optical system and an imaging optical system.
A projection unit that projects a predetermined projection pattern onto a projection target, an imaging unit that images the projection target onto which the pattern is projected, and a relative position of the imaging unit with respect to the projection target in the optical axis direction are adjusted. A position adjustment unit, a calibration data storage unit for projecting the projection pattern onto a calibration plate having a planar shape, and storing data for each position in the optical axis direction from a plate captured image captured by the imaging unit; A pattern is projected onto the inspection object, and a shape calculation unit that calculates the height in the optical axis direction of the test object from the captured object captured image, and for each height obtained by the shape calculation unit, A calibration image acquisition unit that calibrates the data of the test object image used for calculating the height using the stored calibration data and acquires a calibration image. Providing measurement equipment To.
[Selection] Figure 1

Description

  The present invention relates to an apparatus and method for measuring a three-dimensional shape of a test object by pattern projection.

  Various techniques for measuring the surface shape of an object such as an industrial product have been proposed, and one of them is an optical three-dimensional shape measuring apparatus. There are various types of optical three-dimensional shape measurement devices and configurations, but a predetermined projection pattern (a striped pattern or a lattice pattern) is projected onto the test object, and the test object is imaged. From the above, there is a method for calculating the height of each image position by calculating the phase of the stripes at each image position (each pixel) and measuring the three-dimensional surface shape of the test object (see Patent Document 1).

  In such an apparatus, for example, a projection pattern composed of a fringe pattern is projected onto the surface of the test object, and a fringe pattern projected onto the test object from an angle different from the projection direction is imaged. The phase distribution of the fringe pattern is calculated from the captured image of the surface, and the three-dimensional shape of the surface of the test object is obtained using the principle of triangulation or the like.

  An example of the configuration is shown in FIG. 3, and the light from the light source 51 is projected onto the surface of the test object 54 through the projection pattern mask 52 having a striped pattern and the projection lens 53. The stripe pattern of the projection pattern mask 52 projected on the surface of the test object 54 is deformed according to the three-dimensional shape of the surface of the test object 54, and the pattern of the surface of the test object 54 thus deformed is projected. The image is picked up by an image pickup device 56 (for example, a CCD sensor) through an image pickup lens 55 from an angle different from the direction, and sent to the arithmetic processing device 57, where the picked-up image data is processed. The arithmetic processing unit 57 calculates the phase distribution of the fringe pattern from the captured image data of the surface of the test object imaged in this way, and calculates the three-dimensional shape of the test object surface using the triangulation principle or the like. Processing is performed.

JP 2000-9444 A

  By the way, in the above-described three-dimensional measurement, in the projection optical system and the imaging optical system, due to the influence of distortion due to the projection lens and the imaging lens being interposed, the influence of the shift of the telecentric optical system, the influence of coma aberration, etc. There is a problem that the imaging pattern deviates from the projection pattern. Of course, when three-dimensional measurement is performed using such an imaging pattern, the measurement result has an error.

  The present invention has been made in view of such problems, and can perform accurate three-dimensional shape measurement without being affected by the above-described effects in the projection optical system and the imaging optical system. An object of the present invention is to provide a measuring apparatus and a measuring method.

In order to solve the above problems and achieve the object, a shape measuring apparatus according to the present invention includes a projection unit that projects a predetermined projection pattern onto a projection target, and an imaging unit that captures the projection target onto which the projection pattern is projected. And a position adjusting unit that adjusts a relative position of the imaging unit in the optical axis direction with respect to the projection target, and the projection unit projects the projection pattern onto a calibration plate having a planar shape, and the imaging unit captures an image. A calibration data storage unit that stores calibration data for each position in the optical axis direction from the plate captured image, and the projection pattern projected onto the test object by the projection unit, and the captured object image captured by the imaging unit A shape calculation unit for calculating the height of the test object in the optical axis direction, and the calibration data stored in the calibration data storage unit for each of the heights obtained by the shape calculation unit. Using data, the calibrated data of the object captured image used for calculating the height, and a calibration image acquiring unit for acquiring calibration image.

  The calibration data storage unit is preferably configured to store a difference between a phase of a captured pattern of the plate captured image and a theoretical phase as the calibration data.

The calibration data storage unit divides the stored calibration data into common calibration data common to each position in the optical axis direction and dependent calibration data depending on each position in the optical axis direction, and acquires the calibration image A projection unit that calibrates the projection pattern using the common calibration data, and a calibration projection pattern that is calibrated by the pattern calibration unit, and is captured by the imaging unit. The shape calculation unit calculates the height of the test object in the optical axis direction, and the image calibration unit calibrates the phase of the captured image using the dependence calibration data for each height. It is preferable to comprise so that it may comprise.

  The calibration data storage unit maintains uniformity of the reflected light of the light projected on the surface of the calibration plate, and rotates the calibration plate with a perpendicular line of a surface formed by the projection optical axis and the imaging optical axis. It is preferable that the calibration data is acquired by inclining as follows.

The shape measurement method according to the present invention includes a projection unit that projects a predetermined projection pattern onto a projection target, an imaging unit that captures the projection target on which the projection pattern is projected, and the imaging unit for the projection target. A method for measuring a three-dimensional shape of a test object using a shape measuring device having a position adjusting unit for adjusting a relative position in an optical axis direction, wherein a calibration plate having a planar shape is formed by the position adjusting unit. The projection unit is positioned at a plurality of positions in the optical axis direction with respect to the projection unit, the projection pattern is projected onto the calibration plate by the projection unit, and the plate captured image captured by the imaging unit is Obtaining for each position; obtaining calibration data for each position in the optical axis direction from the plate-captured image; and projecting the projection pattern onto the object by the projection unit. Capturing the projection pattern projected onto the test object by the projection unit by the imaging unit to obtain a test object captured image; and the test object from the test object captured image. Calculating the shape height in the optical axis direction, determining calibration data to be used for calibrating the test object captured image for each shape height, and using the calibration data determined for each shape height And calibrating the captured image of the test object to obtain a calibration image, and obtaining a three-dimensional shape of the test object from the calibration image.

Preferably, the step of acquiring the calibration data is configured to acquire a difference between the phase of the captured pattern of the plate image and the theoretical phase as the calibration data.

When the calibration data is acquired, the calibration data is divided into common calibration data common to each position in the optical axis direction and dependent calibration data depending on each position in the optical axis direction; and the common calibration Calibrating the projection pattern using data, projecting the calibration projection pattern calibrated to the test object by the projection unit, capturing the captured image by the imaging unit, and acquiring the captured image Calculating the height of the test object in the optical axis direction, determining dependence calibration data used for calibration of the captured image for each height, and the dependence calibration data determined for each shape height And calibrating the captured image to obtain a calibration image.

  The step of acquiring the calibration data maintains the uniformity of the reflected light of the light projected on the plane of the calibration plate, and the normal of the plane formed by the projection optical axis and the imaging optical axis on the calibration plate. It is preferable that the calibration data is acquired by inclining as the rotation center.

  According to the present invention configured as described above, calibration data is acquired for each position in the projection optical axis direction using the calibration plate, the captured image is calibrated for each position in the projection optical axis direction, and triangulation is performed. The three-dimensional shape of the test object can be obtained based on the principle of the above, and the influence of distortion and the like in the projection optical system and the imaging optical system can be reduced, and a three-dimensional shape measuring apparatus with high measurement accuracy can be provided. .

  Hereinafter, preferred embodiments of the present invention will be described. FIG. 1 shows a schematic configuration of a three-dimensional shape measuring apparatus according to the present invention. First, the shape measuring apparatus will be described with reference to FIG.

  The shape measuring device projects a light source 1, a projection pattern mask 2 for giving a stripe pattern to the light from the light source 1, and light from the light source 1 that has passed through the projection pattern mask 2 onto the surface of the test object 20. A pattern projection unit including the projection lens (group) 3 and an imaging unit including the imaging device 5 that captures the reflected light from the test object 20 via the imaging lens (group) 4 are configured. .

  In the pattern projection unit, the projection pattern mask 2 is constituted by, for example, a liquid crystal element, and the projection pattern generator 6 can generate a pattern having an arbitrary shape and pitch (in this embodiment, a sinusoidal fringe pattern is generated). Thereby, the light from the light source 1 passes through the projection pattern mask 2, is condensed by the projection lens 3, and a desired projection pattern formed by the projection pattern mask 2 is projected onto the surface of the test object 20. it can.

  The imaging unit includes an imaging device 5 (for example, a CCD camera) that captures an image of the test object 20 through the imaging lens 4 with reflected light from the test object 20. The image data of the test object 20 imaged by the imaging device 5 is sent to the arithmetic processing device 7, where the image arithmetic processing described below is performed, and the surface shape of the test object 20 is measured. Although the pattern projection unit and the imaging unit are integrally fixed by a single frame, the test object 20 is placed on a support table (not shown). A position adjuster (not shown) is provided that moves relative to the integrally coupled frame in the direction of the projection optical axis. For this reason, it is possible to adjust the position in the optical axis direction by relatively moving the test object 20 in the direction of the projection optical axis with respect to the pattern projection unit and the imaging unit by the position adjuster.

  The arithmetic processing unit 7 includes a calibration data storage unit 8 that stores a difference between a theoretically obtained phase and a phase of an imaging pattern of a captured image obtained by the imaging device 5 as calibration data for each position in the projection optical axis direction, and a projection A pattern calibration unit 9 that calibrates the projection pattern mask 2 using common calibration data common at each position in the optical axis direction, and a shape height in the projection optical axis direction of the object 20 in the projection optical axis direction. An image calibration unit 10 that calibrates the phase of the captured image using dependency calibration data that depends on each position, and a height of the test object 20 in the direction of the projection optical axis from the image data of the test object 20 captured by the imaging device 5. And a shape calculation unit 11 for calculating the shape.

  A method of measuring the surface shape of the test object 20 using the surface shape measuring apparatus configured as described above will be described below with reference to the flowchart of FIG.

  In this measurement, first, as shown in FIG. 1B, a calibration plate 30 having a planar shape is placed on a support base. The calibration plate 30 is positioned at a position in the predetermined projection optical axis direction (hereinafter referred to as the first Z position Z1) by the position adjuster (step S1). In this state, light from the light source 1 is irradiated onto the calibration plate 30 through the projection pattern mask 2 (sinusoidal fringe pattern) and the projection lens 3 to project the projection pattern onto the surface of the calibration plate 30. The light thus projected and reflected from the calibration plate 30 is collected through the imaging lens 4, and the projection pattern projected onto the calibration plate surface by the imaging device 5 is imaged (step S2).

  The plate captured image obtained by the imaging device 5 is sent to the arithmetic processing device 7. In the calibration data storage unit 8 in the arithmetic processing unit 7, the difference between the theoretically obtained phase and the phase of the imaging pattern of the plate captured image is obtained as calibration data (calibration data at the first Z position Z1) (step S3).

  Next, the calibration plate 30 is positioned by the position adjuster at a position (second Z position Z2) different from the first Z position Z1 in the projection optical axis direction (step S4). Then, similarly to the case of the first Z position Z1, the phase of the projection pattern mask 2 and the plate captured image (the captured image obtained by the imaging device 5 with the calibration plate 30 positioned at the second Z position Z2). The phase difference is obtained as calibration data (calibration data at the second Z position Z2) (step S5).

  Further, the calibration plate 30 is positioned at a plurality of positions in the projection optical axis direction by the position adjuster (in the range in which the shape height of the test object 20 in the projection optical axis direction can be covered) In the same manner as described above, the plate-captured image (the calibration plate 30 is positioned at a plurality of positions in the projection optical axis direction, and the imaging device 5 is positioned at each position. The error of the phase of the imaging pattern of each captured image) obtained as described above is obtained as calibration data (calibration data at each position in the direction of the projection optical axis) (step S6).

  The calibration data is acquired at a sufficiently small interval with respect to the shape height of the test object 20 in the direction of the projection optical axis in a range that can cover the shape height of the test object 20 in the direction of the projection optical axis. It is desirable to acquire calibration data at regular intervals. When the uniformity of the reflected light of the projected light is maintained in the plane of the calibration plate 30, the calibration plate 30 is tilted with respect to the plane formed by the projection optical axis and the imaging optical axis. Thus, the calibration data at each position in the projection optical axis direction can be acquired at a time without positioning the calibration plate 30 at a plurality of positions in the projection optical axis direction by the position adjuster.

  Furthermore, by installing the calibration plate 30 in the shape measuring device so that it can be inserted and removed, the calibration data can be reacquired whenever the components of the device (for example, illumination lamps, objective lenses, etc.) change or periodically. is there.

  The calibration data at each position in the projection optical axis direction includes calibration data that is common at each position in the projection optical axis direction (hereinafter referred to as Z-position common calibration data) and each calibration data that depends on each position in the projection optical axis direction. (Hereinafter referred to as Z position-dependent calibration data) can be divided as described below (step S7).

  For example, in the present embodiment, the components up to the third order are corrected (in general, the higher the order, the smaller the error component, so in the present embodiment, the components up to the third order are corrected). The calibration data at each position in the direction of the projection optical axis is obtained from a measured value for each pixel of the plate image, for example, by a least square method to obtain a cubic equation. Calibration data obtained by averaging the coefficients of the cubic equation (calibration data) at each position in the projection optical axis direction is obtained as Z-position common calibration data, and the cubic equation (calibration data) at each position in the projection optical axis direction is obtained. ) And the calibration data obtained by subtracting the respective coefficients of the Z position common calibration data are obtained as Z position dependent calibration data for each position in the projection optical axis direction.

  Here, the main purpose of dividing the calibration data at each position in the direction of the projection optical axis into the Z-position common calibration data and the Z-position dependent calibration data is to compress the calibration data, and measurement by distortion of each lens. The error component does not depend on the Z position, and the measurement error component due to the displacement of the telecentric optical system in the projection unit and the imaging unit and coma aberration tends to depend on the Z position.

  Next, a procedure for measuring the shape of the test object 20 using the calibration data at each position in the projection optical axis direction obtained above will be described.

  Calibration data at each position in the projection optical axis direction obtained by the calibration data storage unit 8 is sent to the pattern calibration unit 9 and the image calibration unit 10 in the arithmetic processing unit 7. The pattern calibration unit 9 in the arithmetic processing unit 7 calibrates the phase of the projection pattern mask 2 using the Z position common calibration data (step S8).

  And as shown to FIG. 1 (A), the to-be-tested object 20 is mounted on a support stand. The surface of the test object 20 is calibrated by irradiating the test object 20 with light from the light source 1 via the calibration projection pattern mask 2 (projection pattern mask 2 calibrated using the Z-position common calibration data) and the projection lens 3. Projection pattern mask 2 is projected. The light thus projected and reflected from the test object 20 is collected through the imaging lens 4, and the calibration projection pattern mask 2 projected onto the test object surface is imaged by the imaging device 5 (step S9).

  Imaging by these imaging devices 5 is performed a plurality of times (for example, phase 1, phase 2, and phase 3 in FIG. 2) while changing the phase of the calibration projection pattern mask 2 to obtain a set of captured image groups. The image data obtained in this way is sent from the imaging device 5 to the arithmetic processing device 7.

  When the image data is sent as described above, the object imaging image obtained by projecting the projection pattern mask 2 calibrated using the Z-position common calibration data in the shape computation unit 11 in the computation processing device 7. Based on the phase value, the shape height in the direction of the projection optical axis of the test object 20 is calculated using the principle of triangulation (the temporary shape measurement of the test object 20 is performed) (step S10).

Then, in the image calibration unit 10 in the arithmetic processing unit 7, for each shape height (for each Z position) of the test object 20 in the direction of the projection optical axis, using the Z position-dependent calibration data for each position in the direction of the projection optical axis. Next, the phase of the captured image of the test object (the captured image obtained by projecting the projection pattern mask 2 calibrated using the Z position common calibration data) is calibrated (step S11).

  Here, since the Z position-dependent calibration data is obtained for each position in the projection optical axis direction (for each Z position), the projection pattern mask 2 (calibration) calibrated using the Z position common calibration data as described above. From the captured image obtained by projecting the projection pattern mask 2), it is first necessary to calculate the shape height of the test object 20 in the direction of the projection optical axis.

  Further, the phase value of the calibration image calibrated using the Z position-dependent calibration data for each shape height in the direction of the projection optical axis of the test object 20 as described above, the principle of triangulation is used. The shape measurement is performed again (step 12).

  As described above, the test object is obtained from the test object captured image obtained by projecting the projection pattern mask 2 (calibration projection pattern mask 2) calibrated on the test object 20 using the Z-position common calibration data. 20 calculates the shape height in the direction of the projection optical axis (provisional shape measurement of the test object 20), and uses the Z position-dependent calibration data for each shape height of the test object 20 in the direction of the projection optical axis. The three-dimensional shape of the test object 20 can be accurately measured by calibrating the phase of the test object image and calculating the shape height of the test object 20 in the projection optical axis direction again.

  Therefore, the phase of the captured image obtained by projecting the projection pattern mask 2 onto the test object 20 is calibrated using the calibration data for each position in the direction of the projection optical axis obtained using the calibration plate 30. In order to measure the shape of the test object 20, a three-dimensional shape measuring apparatus with high measurement accuracy by reducing the influence of distortion in the projection optical system and the imaging optical system, the influence of displacement of the telecentric optical system, the influence of coma aberration, etc. Can be provided.

It is schematic structure explanatory drawing which shows the structure of the three-dimensional shape measuring apparatus which concerns on embodiment of this invention, (A) places the test object 20 on a support stand, (B) shows the plate 30 for a calibration. This is a case where it is placed on a support base. It is a flowchart which shows the shape measuring method which concerns on the said invention. It is schematic structure explanatory drawing which shows the structure of the conventional shape measuring apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Projection pattern mask 3 Projection lens 4 Imaging lens 5 Imaging device 6 Projection pattern generation device 7 Arithmetic processing device 8 Calibration data storage unit 9 Pattern calibration unit 10 Image calibration unit 11 Shape calculation unit 20 Test object 30 Calibration plate

Claims (8)

A projection unit that projects a predetermined projection pattern onto a projection target;
An imaging unit that images the projection target onto which the projection pattern is projected;
A position adjusting unit that adjusts the relative position of the imaging unit in the optical axis direction with respect to the projection target;
A calibration data storage unit that projects the projection pattern onto a calibration plate having a planar shape by the projection unit, and stores calibration data for each position in the optical axis direction from the plate captured image captured by the imaging unit;
A shape calculation unit that projects the projection pattern onto the test object by the projection unit, and calculates the height in the optical axis direction of the test object from the test object captured image captured by the imaging unit;
For each of the heights obtained by the shape computation unit, the calibration data stored in the calibration data storage unit is used to calibrate the data of the captured object image used for computing the height. A calibration image acquisition unit for acquiring a calibration image;
A shape measuring apparatus comprising:   The shape measurement apparatus according to claim 1, wherein the calibration data storage unit stores, as the calibration data, a difference between a phase of a captured pattern of the plate captured image and a theoretical phase. The calibration data stored by the calibration data storage unit is divided into common calibration data common at each position in the optical axis direction and dependent calibration data depending on each position in the optical axis direction,
The calibration image acquisition unit projects the projection pattern calibrated by the pattern calibration unit onto the test object, and shoots the image by the imaging unit. An image for calculating the height of the test object in the optical axis direction by the shape calculation unit using the captured image thus obtained, and calibrating the phase of the captured image using the dependence calibration data for each height. The shape measuring apparatus according to claim 1, further comprising a calibration unit.   The calibration data storage unit maintains uniformity of the reflected light of the light projected on the surface of the calibration plate, and rotates the calibration plate with a perpendicular line of a surface formed by the projection optical axis and the imaging optical axis. The shape measurement apparatus according to claim 1, wherein the calibration data is acquired by inclining as follows. A projection unit that projects a predetermined projection pattern onto the projection target, an imaging unit that images the projection target on which the projection pattern is projected, and a position adjustment that adjusts the relative position of the imaging unit with respect to the projection target in the optical axis direction A method for measuring a three-dimensional shape of a test object using a shape measuring device comprising a part,
The position adjusting unit causes a calibration plate having a planar shape to be positioned at a plurality of positions in the optical axis direction with respect to the projection unit, and the projection unit projects the projection pattern onto the calibration plate, and the imaging unit Obtaining a plate-captured image picked up by each position in the optical axis direction;
Obtaining calibration data for each position in the optical axis direction from the plate captured image;
Projecting the projection pattern onto the object by the projection unit;
Capturing the projected pattern projected onto the test object by the projecting unit by capturing an image of the test object captured by the imaging unit;
Calculating a shape height in the optical axis direction of the test object from the test object captured image, and determining calibration data used for calibration of the test object captured image for each of the shape heights;
Using the calibration data determined for each shape height, calibrating the test object captured image, obtaining a calibration image;
A shape measuring method, comprising: obtaining a three-dimensional shape of the test object from the calibration image.   The shape measurement method according to claim 5, wherein the step of acquiring the calibration data includes acquiring a difference between a phase of a captured pattern of the plate captured image and a theoretical phase as the calibration data.   When the calibration data is acquired, the calibration data is divided into common calibration data common at each position in the optical axis direction and dependent calibration data depending on each position in the optical axis direction; and the common calibration Calibrating the projection pattern using data, projecting the calibration projection pattern calibrated to the test object by the projection unit, capturing the captured image by the imaging unit, and acquiring the captured image Calculating the height of the test object in the direction of the optical axis, determining dependence calibration data used for calibration of the captured image for each height, and the dependence calibration data determined for each height. The shape measuring method according to claim 5, further comprising a step of calibrating the captured image and acquiring a calibration image.   The step of acquiring the calibration data maintains the uniformity of the reflected light of the light projected on the plane of the calibration plate, and the normal of the plane formed by the projection optical axis and the imaging optical axis on the calibration plate. The shape measurement method according to claim 5, wherein the calibration data is acquired by inclining as a rotation center.

Images