JP2000258142A - Non-contact method for measuring surface shape - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the surface shape of an object with high accuracy by scanning white light interference by calculating the peak position of the intensities of interference fringes at each measuring point by finding phases with respect to the intensities of interference fringes and correcting the calculated peak position. SOLUTION: While interference fringes are generated in the measuring range of a work W by producing white light interference by removing a filter 28 from a white light source (lamp) 21 and displacing a detector 20 in a direction Za the detector 20 is fixed to a prescribed position in the measuring range. Then single-wavelength interference is produced by putting the filter 28 on the lamp 21 and the intensities of interference fringes at each measuring point is measured and used as the intensities of interference fringes at initial detecting points. Then the intensities of interference fringes at three or more spots in the one-period range of the intensities of interference fringes are detected from the initial detecting points by minutely displacing a reference mirror 24 at every measuring point and the phases of the initial detecting points are found from the minutely displaced amount at every measuring point. Thereafter, interference fringe generating positions are detected by means of a length measuring instrument 30 at every measuring point by removing the filter 28 and displacing the detector 20 in the direction Za and the relative height between the measuring points is roughly calculated. Then the order of interference fringes corresponding to the relative height is found and the relative height between the measuring points is calculated from the order and the phases of the initial detecting points.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a non-contact surface shape measuring method using a white interference scanning method.

[0002]

2. Description of the Related Art As a method for measuring the surface shape (roughness, waviness, etc.) of a work in a non-contact manner, the applicant of the present invention has disclosed a method disclosed in Japanese Patent Application Laid-Open No. Hei 9-3.
No. 18329, "Non-contact surface shape measuring method and apparatus"
And Japanese Patent Application No. 9-147244, entitled "Method and Apparatus for Non-Contact Surface Shape Measurement". Since these use white light as a light source, they are referred to herein as “white interference scanning method”. In this method, light from a light source is split into a work direction and a reference mirror direction, interference fringes are generated by the reflected light, and the interference fringe intensity is detected by a CCD camera. Since this intensity changes due to the difference in the distance between the work and the reference mirror from the reference position in the detector, the distance from the reference position to the work or the distance to the reference mirror is relatively displaced for each measurement point, The difference in the distance between the workpiece and the reference mirror when the strength is maximized is detected by a length measuring device or the like. Accordingly, the height between the measurement points (the displacement amount in the measurement direction is referred to as “height” in the present specification).
) Is detected to determine the workpiece surface shape. Since white light has an extremely narrow interference range, it is suitable for precise detection.

[0003]

However, in the white light interference scanning method, the position detected by the detector is not necessarily the peak position of the interference fringe intensity, so that there is a problem that an error occurs. FIG. 7 illustrates the interference fringe intensity at two measurement points. The vertical direction is the measurement direction, and the horizontal direction is the interference fringe intensity. The detected value is the height difference Hd between the position D and the position E. Since the true value is the distance Ho between the peak positions of the interference fringe intensity, the distances δd and δe from the peak positions are the measurement errors and Become.

The present invention has been made in view of such circumstances, and has as its object to provide a highly accurate white interference scanning type measuring method.

[0005]

According to the present invention, in order to achieve the above object, the phase of the interference fringe intensity at each measurement point is obtained, and the peak position of the interference fringe intensity is calculated and corrected. To find the phase,
As disclosed in, for example, Japanese Patent Application Laid-Open No. 9996, entitled "Method and Apparatus for Wavefront Measurement", it is necessary to generate interference fringes with a single wavelength or a wavelength close thereto (hereinafter, simply referred to as "single wavelength" in the present specification). Therefore, a detector of the "white interference scanning system" is provided with a function of switching the light source from white light to a single wavelength. In addition, a mechanism that can perform minute “scanning” is required.

The measurement is performed as follows. (1) Switch the light source to a single wavelength. (2) Fix the detector at a predetermined position in the measurement range, detect the interference fringe intensity at each measurement point, and store this as the interference fringe intensity at the initial detection point of each measurement point. (3) The distance from the reference position inside the detector to the work and the distance to the reference mirror are relatively slightly displaced, and for each measurement point of the work, the range of one cycle of the interference fringe intensity from the initial detection point. The interference fringe intensity is detected at three or more locations. (4) From the detected three or more interference fringe intensities and the amount of slight displacement, the phase of the initial detection point is calculated for each measurement point assuming that the interference fringe intensity is a sin curve. (5) Switch the light source to white light. (6) The detector is displaced in the measurement direction, the position where interference fringes are generated at each measurement point is detected by long-term measurement or the like, and the approximate relative height between the measurement points is calculated from this. (7) Calculate the order of interference fringes corresponding to the approximate relative height. (8) The relative height between each measurement point is calculated from the phase of the initial detection point and the order of the interference fringes.

[0007]

FIG. 1 shows a preferred embodiment 1 of a measuring mechanism used in a non-contact surface shape measuring method according to the present invention. The measuring mechanism shown in FIG. 1 includes a detector 20 and a length measuring device 30 for detecting a displacement amount thereof. Detector 2
0 is a lamp 21 as a white light source, a collimating lens 2
2, half mirror 23, reference mirror 24, piezoelectric element 2
5, imaging lens 26, CCD camera 27, filter 2
8. In this case, the lamp 21, the collimating lens 22, the half mirror 23, the piezoelectric element 25, the imaging lens 26, and the CCD camera 27 are fixed in the detector 20. The filter 28 is driven in a perpendicular direction (Xa direction), and the filter 28 is driven in the Ua direction by a mechanism (not shown).

The principle of detection by the detector 20 is as follows.
That is, the light emitted from the lamp 21 is
2 and enters the half mirror 23 and the half mirror 23
Reflected by the mirror and heading toward the work surface Wa and the half mirror 2
The light is divided into light passing through 3 and traveling toward the reference mirror 24.
Light directed toward the work surface Wa is reflected by the work surface Wa, and then passes through the half mirror 23 and enters the CCD camera 27 via the imaging lens 26. The light that has passed through the half mirror 23 and travels toward the reference mirror 24 is reflected by the reference mirror 24, and then reflected by the half mirror 23 and enters the CCD camera 27 via the imaging lens 26. As a result, interference fringes occur due to the difference between the distance La from the half mirror 23, which is the reference position inside the detector, to the workpiece surface Wa, and the distance Lb to the reference mirror 24.

The detector 20 is in the measuring direction (Za direction).
The displacement amount is detected by the length measuring device 30. The length measuring device 30 detects the displacement by projecting a laser beam onto a reflecting mirror 29 fixed to the upper end of the detector 20 using a laser.

The first embodiment of the measuring mechanism used in the non-contact surface shape measuring method according to the present invention is configured as described above, and detects the height of each measuring point of the work as shown in the flowchart of FIG. (1) The filter 28 is removed from the light source to make a white interference state (step S1). (2) The detector 20 is displaced in the Za direction, and it is confirmed that interference fringes occur in the measurement range of the work (Step S)
2). (3) Set the detector 20 to the predetermined work measurement range (approximately at the middle, etc.)
(Step S3). (4) Put the filter 28 in the light source to make it a single-wavelength interference state (step S4).

(5) The interference fringe intensity at each measurement point is detected, and this is stored as the interference fringe intensity at the initial detection point of each measurement point (step S5). This state is shown in FIG. In FIG. 3, three measurement points A,
B and C are shown. Since the light source has a single wavelength, the interference range is wide, interference fringes can be detected at all measurement points at the same position, and the interference fringe intensity is almost si.
It becomes an n curve. Ao, Bo, Co are the initial detection points,
The detected interference fringe intensities are Ia, Ib, and Ic. The phases determined by a method described later are θa, θb, and θc.

(6) At each measurement point, the reference mirror is minutely displaced in the Xa direction by the piezoelectric element 25, and the interference fringe intensity is detected at three or more locations within one cycle of the interference fringe intensity from the initial detection point ( Step S6). (7) Assuming that the interference fringe intensity is a sin curve, the phase θ of the initial detection point is calculated for each measurement point from the detected three or more interference fringe intensities and the amount of slight displacement (step S7). . In this case, when the calculated phase θ is larger than π (half cycle), 2π (one cycle) is added or subtracted so as to be smaller than π.

FIG. 4 shows this state. FIG. 4 shows the measurement point A among those shown in FIG. Here, one cycle of the interference fringes (1/2 of the wavelength λ in the measurement length, 2π in the phase) is divided into four, and four points A1, A2, A are provided at intervals of π / 4.
3, the interference fringe intensities I1, I2, I3, and I4 of A4 are detected, and the phase θa of the A0 point is calculated based on the detected intensity.

(8) The filter 28 is removed from the light source to make a white interference state (step S8). (9) The detector 20 is displaced in the Za direction, the position where the interference fringe is generated at each measurement point is detected by the length measuring device 30, and the approximate relative height K between each measurement point is calculated and stored from this. (Step S9). (10) The order N of the interference fringes corresponding to the approximate relative height K is calculated as follows (step S10). N = K / (λ / 2) In this case, those whose remainder is smaller than λ / 4 are discarded. (11) The relative height H between the measurement points is calculated as follows from the phase θ of the initial detection point of each measurement point and the order N of the interference fringes (step S11). H = (2πN−θ) λ / (4π)

A specific example of the method for calculating the relative height H will be described with reference to FIG. In FIG. 5, the measurement point A shown in FIG.
And the relative height Ha between two points of the measurement point B and the measurement point B. That is, when the phase of the initial detection point Ao is θa, the phase of the initial detection point Bo is θb, and the relative height is Ka, the order Na of the interference fringes and the relative height Ha between the measurement point A and the measurement point B are as follows. Become like Na = Ka / (λ / 2) However, those having a remainder smaller than λ / 4 are discarded. Ha = {2πNa− (θa−θb)} λ / (4π) In the conventional method, Ja is calculated as a relative height.

FIG. 6 shows a second embodiment of the measuring mechanism used in the non-contact surface shape measuring method according to the present invention. The measurement mechanism shown in FIG. 6 is different from the first embodiment shown in FIG. 1 in the configuration of the detector. Basically, the method of relatively slightly displacing the distance from the reference position inside the detector to the workpiece and the distance to the reference mirror is different, and the distance La from the reference mirror to the surface Wa of the workpiece is displaced. ing. In addition, the positions of the light source and the CCD camera are changed.

That is, the detector 40 is composed of two stages, upper and lower, and a lamp 41, a collimating lens 42, a half mirror 43, a mirror 44,
5, a CCD camera 46 and a filter 47. The lower part is composed of a reference mirror 51 and a half mirror 52, and the upper and lower parts are connected by a piezoelectric element 48. The lower portion is driven by the piezoelectric element 48 in the measurement direction (Za direction). Filter 47 is detector 2
As in the case of 0, it is driven in the Ub direction by a mechanism not shown. Further, the upper portion is movable in the Za direction, and a laser is projected onto the reflection mirror 49 fixed to the upper end, and the displacement is detected by the length measuring device 30. When the upper part is displaced, the lower part is also displaced.

The principle of detection by the detector 40 is as follows.
That is, the light emitted from the lamp 41 is
2 enters the half mirror 43 via the half mirror 43
And is directed downward (toward the workpiece surface Wa side). This light is divided into light that passes through the half mirror 52 at the lower portion and travels toward the work surface Wa, and light that is reflected by the half mirror 52 and travels toward the reference mirror 51. The light directed toward the work surface Wa is reflected by the work surface Wa, and is again returned to the half mirror 5.
Pass 2 Then, the light passes through the half mirror 43, is reflected by the mirror 44, and passes through the imaging lens 45 to the CCD camera 4.
Enter 6. The light reflected by the half mirror 52 and traveling toward the reference mirror 51 is reflected by the reference mirror 51 and is reflected again by the half mirror 52. And the half mirror 43
Passes through the mirror 44 and is refracted by the mirror 44 via
Enter the CD camera 46. As a result, an interference fringe is generated due to the difference between the distance La from the half mirror 52 to the work surface Wa and the distance Lb to the reference mirror 51.

The second embodiment of the measuring mechanism used in the non-contact surface shape measuring method according to the present invention is configured as described above, and similarly to the first embodiment, the height of each measuring point of the workpiece is as follows. Is detected. The flow chart is the same as FIG. (1) The filter 47 is removed from the light source to make a white interference state (step S1). (2) The detector 40 is displaced in the Za direction, and it is confirmed that interference fringes are generated in the measurement range of the work (Step S)
2). (3) Set the detector 40 to a specified work measurement range (approximately at the middle, etc.)
(Step S3). (4) Put the filter 47 in the light source to make a single-wavelength interference state (step S4). (5) The interference fringe intensity at each measurement point is detected, and this is stored as the interference fringe intensity at the initial detection point at each measurement point (step S5). (6) For each measurement point, the lower part of the detector 40 is minutely displaced in the Za direction by the piezoelectric element 48, and the interference fringe intensity is detected at three or more positions within one cycle of the interference fringe intensity from the initial detection point ( Step S6). (7) Assuming that the interference fringe intensity is a sin curve, the phase θ of the initial detection point is calculated for each measurement point from the detected three or more interference fringe intensities and the amount of slight displacement (step S7). . (8) The filter 47 is removed from the light source to make a white interference state (step S8). (9) The detector 40 is displaced in the Za direction, the position where the interference fringe is generated at each measurement point is detected by the length measuring device 30, and the approximate relative height K between each measurement point is calculated and stored from this. (Step S9). (10) The order N of the interference fringes corresponding to the approximate relative height K is calculated (step S10). (11) The relative height H between the measurement points is calculated from the phase θ of the initial detection point of each measurement point and the order N of the interference fringes (step S11).

In the above-described embodiment, the displacement of the detector 20 and the detector 40 is detected by the laser-type length measuring device 30. However, another detection sensor (for example, an optical linear sensor) may be used. Needless to say.

[0021]

As described above, according to the present invention, in the white interference scanning method, the phase of the interference fringe intensity at each measurement point is obtained, and the peak position of the interference fringe intensity is calculated and corrected. did. Therefore, it is possible to provide a highly accurate white interference scanning method.

[Brief description of the drawings]

FIG. 1 is a first embodiment of a measuring mechanism used in a measuring method according to the present invention.

FIG. 2 is a flowchart of a measuring method according to the present invention.

FIG. 3 is an explanatory diagram of an initial detection point of the measuring method according to the present invention.

FIG. 4 is an explanatory diagram of a phase calculation method of the measurement method according to the present invention.

FIG. 5 is an explanatory diagram of a method for calculating a relative height of a work in the measuring method according to the present invention.

FIG. 6 is a second embodiment of the measuring mechanism used in the measuring method according to the present invention.

FIG. 7 is an explanatory diagram of a conventional measuring method.

[Explanation of Signs] Ao: initial detection point of measurement point A Bo: initial detection point of measurement point B θa: phase of initial detection point Ao θb: phase of initial detection point Bo Ka: measurement point A Rough height relative to measurement point B Ha ... Relative height between measurement point A and measurement point B

Claims (3)

[Claims] 1. A mechanism for relatively slightly displacing a distance from an internal reference position to a workpiece and a distance to a reference mirror, and a function of switching a light source from white light to light of a single wavelength or a light close thereto. A measurement method using a white interference scanning type detector, wherein the light source is switched to a single wavelength or light close to the single wavelength, and the detector is fixed at a predetermined position in a measurement range, and interference fringes at each measurement point of a workpiece. Detecting the intensity, storing this as the interference fringe intensity of the initial detection point of each measurement point, relatively slightly displacing the distance from the reference position inside the detector to the work and the distance to the reference mirror, For each measurement point, 3 of one cycle of the interference fringe intensity from the initial detection point
The interference fringe intensity is detected for more than one location, and from the detected three or more interference fringe intensities and the amount of minute displacement, it is assumed that the interference fringe intensity is a sin curve and the phase of the initial detection point is determined for each measurement point. The light source is switched to white light, the detector is displaced in the measurement direction, the position where interference fringes are generated for each measurement point is detected, and the approximate relative height between each measurement point is calculated from this. Calculating the order of interference fringes corresponding to the approximate relative height, calculating the relative height of each measurement point from the phase of the initial detection point and the order of the interference fringes, and determining the surface shape of the workpiece. A non-contact surface shape measuring method characterized by the above-mentioned. 2. The method according to claim 1, wherein the light source is white light, and the light source is switched from white light to light of a single wavelength or a light having a wavelength close to the white light by providing a filter.
Non-contact surface shape measuring method according to 4. 3. A distance between a reference position inside the detector and a workpiece and a distance between the reference mirror and a reference mirror are relatively displaced by driving the reference mirror with a piezoelectric element. 2. The non-contact surface shape measuring method according to 1.