JPS62157507A - Apparatus for measuring three-dimensional shape - Google Patents

Abstract

PURPOSE:To measure a three-dimensional shape due to a minute spot at a high speed with high accuracy and high stroke, by arranging a support means so that the center of the curvature of the surface to be inspected of an object almost coincides with a rotary axis. CONSTITUTION:Difference is generated between lights reaching a sensor 38 by the angle of inclination of the surface of an article 50 to be measured. That is, when it is assumed that the surface of the article 50 to be measured is inclined by an angle alpha with respect to the surface vertical to the optical axis X at the position on the optical axis X, the reflected beam from a projected light spot has the center in a direction forming an angle 2alpha with respect to the optical axis X to be incident to an objective lens 20. The beam incident to the objective lens 20 advances in parallel to the optical axis X and the center of said beam is separated by h fsin2alpha from the optical axis X. As the sensor 38, a sensor for detecting the center of gravity position of the beam, a called position sensor is used and, by measuring the above mentioned (h) by said sensor, the angle alpha can be calculated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a three-dimensional shape measuring device, and particularly to a three-dimensional shape measuring device that can perform shape measurement at high speed in a non-contact manner.

[Prior art]

Conventionally, various methods have been used to measure the three-dimensional shape of an object in a non-contact manner. As such a measurement method, an interferometric method using a coherent source, a method of reading a light cut image by a slit source, etc. are used. -However, while interferometry has the advantage of being able to simultaneously measure the entire surface of the object to be measured with high precision, it is difficult to measure when the irregularities on the surface of the object are significantly larger than the wavelength of the light. There are drawbacks.

Furthermore, the method of reading a photocut image has the disadvantage that it is difficult to measure the uneven shape on the order of the wavelength of light, and therefore high accuracy cannot be expected.

Therefore, by placing a focusing state determination optical system having an internal light source on a movable table and moving the movable table so as to bring the optical system into contact with the surface of the object to be measured, the amount of movement of the movable table can be adjusted. A method for measuring three-dimensional shapes has been proposed (Japanese Patent Publication No. 46-40231). According to this, shape measurement can be performed with an accuracy of kana υ, regardless of the degree of unevenness of the surface of the object to be measured.

However, in this method of relatively scanning a movable table, if the object to be measured has a large aperture angle, such as an aspherical lens or a lens with a large curvature, the inclination angle of the surface to be measured in the scanning direction becomes larger. Therefore, in this type of optical measuring device, the reflected light from the surface to be measured cannot enter the pupil of the objective lens of the device, and measurement cannot be performed. or.

Even if measurement is possible, it has the disadvantage that the stroke of the sub-length must be large.

On the other hand, a device that improved this kind of problem was published in Japanese Patent Application Laid-open No. 60-1
It is disclosed in Japanese Patent No. 04206.

According to the publication, there is a device that measures a surface shape by focusing a laser beam onto a surface to be measured using an objective lens and detecting the Doppler shift of the frequency of the reflected light that occurs as the surface to be measured moves. The object to be measured is rotatable and the X direction and θ
By moving the object to be measured in the above-described method, it is possible to measure the entire surface of the object even when the angle of inclination of the surface of the object to be measured is large.

However, this method utilizes the Doppler shift caused by the movement of the surface to be measured, and the light directly reflected from the surface to be measured is emitted from the same light source as room light with positional information, and other optical paths are transmitted. However, if there are defects such as scratches or dust on the surface to be measured, the reflected light will be scattered, making continuous measurement impossible. It became.

[Purpose of the invention]

In view of the above-mentioned various drawbacks of the conventional art, the present invention is capable of measuring any surface shape to be measured with high accuracy and high speed, and is capable of continuously measuring even if there are scratches, dust, etc. on the surface to be measured. An object of the present invention is to provide a three-dimensional shape measuring device capable of performing measurements.

[Summary of the invention]

According to the present invention, the above objects include: a focus state determination optical system having a movable part that has an internal light source and is movable at least in part; a means for measuring the displacement IDt of the movable part; a support means for a test object that is rotatable about a rotation axis that intersects with the optical axis of the objective lens of the focus state determination optical system and is substantially orthogonal to the optical axis, and a center of curvature of the test object. This is achieved by the fact that the rotation axis is located at the rotating shaft.

[Embodiments of the invention]

Hereinafter, embodiments of the present three-dimensional shape measuring device will be described with reference to the drawings.

1(A) and 1(B) are schematic configuration diagrams showing a first embodiment of a three-dimensional shape measuring device according to the present invention, FIG. 1(A) is a top view, and FIG. (B) shows a side view. In addition, in FIG. 1 (Bl), a schematic configuration of the optical system is shown for the sake of understanding. Here, 2 is a focus state determination optical system,
4 is a tilt angle measuring optical system. Optical systems 2 and 4 are incorporated into casing 6.

In the focus state determination optical system 2, 8 is a light source, 10
is a collimator lens, 12 is a knife lens, 14 is a polarizing beam splitter, and 16 is a half mirror.

18 is a quarter wavelength plate, 20 is an objective lens,
22 is a band pass filter, 24 is a lens, and 26 is an optical sensor.

In the tilt angle measurement optical system 4, 28 is a light source;
and 32 are lenses; 34 is a polarizing beam splitter; 36 is a bandpass filter;
8 is an optical sensor. In this optical system 4Vc, the half mirror 16, quarter wavelength plate 18, and objective lens 20 are shared with the optical system 2.

The casing 6 has an actuator 40 fixed to the outside.
It is connected to the. By driving the actuator 40, the casing 6 can be moved along the optical axis X of the objective lens 20. Actuator 4
It is preferable to use a device equipped with a fluid movement bearing slide mechanism to achieve highly accurate control of the amount of movement.

The casing 6 is also provided with length measuring means 42 for measuring the amount of movement thereof. The length measuring means 42 may be, for example, one based on a grating interferometric length measuring method (Oplns Fi,
(April 1981 issue, p. 84~) is used; in this case, 44 in FIG. 1 is a reference grid fixed to the casing 6, and 46 is a grid pitch reading device fixed outside.

50 is an object to be measured whose shape is to be measured.

Reference numeral 60 denotes a mount on which an object to be measured 50 such as an aspherical lens is mounted, and as shown in the figure, the object to be measured 50 can be rotated in the θ direction with respect to a rotation axis passing through its center of curvature. Therefore, the object to be measured 5o is rotated in the θ direction by the driving means built into the mount 60, and at this time, in order to measure a predetermined cross-sectional shape (surface shape) of the object to be measured 50, a focusing state discriminating optical System 2 scans the cross section from one end to the other end with a spot light, so that the spot light is focused on the surface to be measured at each scanning position. A predetermined member (objective lens 20) is moved in the direction of the original axis. Then, by sequentially detecting the amount of movement of this predetermined member, it is possible to finally obtain the surface shape at an arbitrary cross section of the surface to be measured.

By rotating the object to be measured 50 around its center of curvature as described above, even if there is a large inclination angle on the surface of the object to be measured 50 with respect to the optical axis of the objective lens 20, which will be described later. , the inclination of the surface to be measured during measurement becomes qualitatively smaller. Therefore, it becomes easy to measure lenses with large aperture angles such as aspherical lenses and lenses with large curvatures.

Furthermore, in this embodiment, as will be described in detail later, the length measuring system for measuring the amount of movement of members such as the objective lens 20 is connected to the object to be measured 50.
The optical system is separated from the optical system for determining the focusing state, and is composed of a system different from the optical system for determining the focusing state.

Therefore, whereas in the conventional apparatus, the measurement is interrupted when there are scratches, dust, etc. on the surface to be measured of the object to be measured 50, according to the present invention, the measurement is interrupted by continuous scanning of the spot light. It is measurable.

Therefore, the surface shape of the cross section where the defect exists can also be corrected and obtained based on the information of the surface shape where the defect occurs at a certain location on the surface to be measured.

In this embodiment, the object to be measured 50 is rotated in the direction in the plane of the paper in FIG. It may be in any direction as long as it is on the optical axis of the objective lens 200.

Furthermore, the various members and drive mechanism for rotating the object to be measured by 5 ot may have any configuration.

Furthermore, in order to measure the shapes of multiple cross sections on the surface to be measured of the object to be measured 50, for example, the object to be measured 50 is placed under the objective lens 20.
What is necessary is to provide a mechanism for rotating the optical axis relative to the rotation axis of the optical axis. By providing such a mechanism, as soon as the scanning of the spot light beam in a predetermined direction of the surface to be measured of the object to be measured 5o is completed, the object to be measured 50 can be moved to the objective lens 2 at an arbitrary angle.
By rotating it about the original axis of 0 and scanning the surface to be measured again with the spot light beam, it is possible to obtain surface shapes of a plurality of cross sections.

In this embodiment, as described later, the focusing and state determining optical system 2
In addition, an inclination angle measuring optical system 4 for measuring the inclination of the surface to be measured of the object to be measured 50 is arranged to further improve the accuracy of surface shape measurement. These two optical systems will be explained in detail below.

The focus state determination method of the focus state determination optical system 2 in this embodiment will be described below.

The light emitted from the light source 8 is converted into a parallel light beam by the collimator lens 10, and the parallel light beam is transmitted through the polarizing beam splitter 14 and reflected by the half mirror 16.
The light passes through the quarter-wave plate 18 and enters the objective lens 20.

Note that the parallel light beam exiting the collimator lens 10 is partially blocked by the knife lens 12, and the objective lens 20 has one of two zones divided into two by a boundary plane passing through the optical axis X (in the figure). is the upper half zone) Only K is incident. Thus, the light focused by the objective lens 20 forms a spot on the surface of the object to be measured 50. The light reflected from the spot passes through the objective lens 20 again,
The light passes through the quarter-wave plate 1B, is reflected by the half mirror 16, is reflected by the beam splitter 14, and passes through the bandpass filter 22 and lens 24 before reaching the sensor 26.

At this time, the surface of the object to be measured 50 and the objective lens 2
A difference occurs in the light reaching the sensor 26 depending on the distance from the sensor 26. That is, as shown in FIG. 2, when the surface of the object to be measured 500 is located exactly at the focal position of the objective lens 20 (
At position A in the figure), the spot on the surface of the object to be measured 50 is located at the ninth position, whose center is exactly on the optical axis X.
The reflected light is centered on the optical axis Y at the sensor 26. Furthermore, when the surface of the object to be measured 50 is located far away from the focal point of the objective lens 20 (the position of the mouth in the figure), the spot on the surface of the object to be measured 50 is located at a position shifted from the original axis X. Since the center is located within the A zone, the reflected light is reflected by the sensor 26.
The center of the optical axis is located at 1/ in the diagram deviated from the optical axis Y. On the other hand, when the surface of the object to be measured 50 is located closer to the focal point of the objective lens 20 (position C in the figure), the spot on the surface of the object to be measured 50 is shifted from the optical axis X. Since the center will be located in the B zone, the reflected light will be centered in the A zone in the diagram shifted from the optical axis Y in the sensor 26.

The sensor 26 is COD (Charge C!o
An array sensor such as an upledDeyice') is used. FIG. 3 is a plan view of such a sensor 26.

This figure shows the sensor 26 in FIG. 2 viewed from the left. In the figure, the shaded area shows a part of the channel stopper that separates the sensor segments. The sensor 26 in FIG. 3 detects the surface position of the object to be measured 50 as shown in FIG. 2.

A graph of the spot position and its light intensity distribution in the case of mouth or ha is shown.

In the sensor 26, if the sum of the outputs of all sensor segments in the A' zone is denoted by At, and the sum of the outputs of all the sensor segments in the W zone is denoted by IB/, then ΔI=
AA/-rB/ changes.

The relationship is shown in FIG. As can be seen from FIG. 4, ΔI changes almost linearly in the vicinity of the case where 7 orcasings are completely filled (state A above). By utilizing this characteristic, it can be determined whether the optical system 2 is in a front out-of-focus state, in a complete focusing state, or in a rear out-of-focus state.

Therefore, automatic focusing can be realized by servo-driving the actuator 40 to make the Δwork 0 based on the output Δ1. Konono's casing 6
By measuring the amount of movement by the length measuring means 42, the position of the portion of the surface of the object to be measured 500 that intersects with the original axis X is measured.

By performing this position measurement on the entire surface of the object to be measured, the three-dimensional shape can be measured.

Next, a method for measuring the tilt angle of the tilt angle measuring optical system 4 in this embodiment will be explained below.

After the light emitted from the light source 2 passes through lenses 30 and 32, it becomes a parallel beam of light and is sent to a polarizing beam splitter 34.
is reflected by the half mirror 16 and 1/
The light passes through the four-wavelength plate 1B and is focused by the objective lens 20.

In this optical system 4, the light beam incident on the objective lens 20 is centered on the optical axis X and is incident parallel to the optical axis X. The light thus focused by the objective lens 20 connects a spot centered on the X-axis on the surface of the object to be measured 50. The light beam reflected from the spot passes through the objective lens 20 again, and passes through the 174 wavelength plate 18, the half mirror 16, and the polarizing beam splitter 3.
4 and a bandpass filter 36, it reaches a sensor 38.

At this time, a difference occurs in the amount of light that reaches the sensor on the third day depending on the inclination angle of the surface of the object to be measured 500. That is, as shown in FIG. 5, if the surface of the object to be measured 50 is tilted at an angle α with respect to a plane perpendicular to the optical axis at a position on the optical axis enters the objective lens 20 with its center in a direction forming an angle 2α with respect to the optical axis X. In this way, the light beam incident on the objective lens 20 travels parallel to the optical axis, and the center of light velocity is h*f from the original axis
They are separated by sin2α (here, the focal length of the objective lens 20).

As the sensor 3B, a sensor for detecting the position of the center of gravity of the light flux, ie, a so-called position sensor, is used, and by measuring the above h, the above α can be obtained.

As can be seen from the above explanation, when measuring the inclination angle, it is necessary that the surface of the object to be measured 50 be at the focal point of the objective lens 20. However, due to the action of the optical system 2 and the actuator 40, Since focusing is performed, this condition is a normal pressure groove.

In addition, since the focusing state determining optical system 2 and the tilt angle measuring optical system 4 have some parts in common, the wavelength bands of the light sources used in each optical system are made different, and the polarization states are made different. , to prevent crosstalk from occurring. For this purpose, bandpass filters 22 and 36, as well as polarizing beam splitters 14 and 34 and a 174-wave plate 18 are used.

An attempt will be made below to evaluate the performance of the three-dimensional shape measuring apparatus of the above embodiment.

First, the accuracy of position measurement is determined by the focusing state determination resolution of the optical system 2 and the measurement accuracy of the length measuring means 42. for example,
The objective lens 20 has a focal length f=2.1 mm,
NA = 0.9, lens 10 with focal length fl = 6.6 m, lens 24 with focal length f, = 85 sn, and sensor 26 with a COD sensor array. %IJ in the graph of Figure 4 The slope of the near part is 200 to 10
00 mV/μm is obtained, and furthermore, the noise of the output of the Δ device at this time is 1 to 2 mV or less. As a result, the focusing state determination resolution of the optical system 2 is 0.01 to 0.
．． 02 μm is obtained. Furthermore, if the length measuring means 42 is based on a grating interference length measuring method, the
An accuracy of m is achieved. The length measuring means 42 may be one based on the narrow-light heterodyne interference method (for example,
Hewlstt Packard laser length measuring machine,
(PluaK, December 1982 issue, p. 86~) or a method based on a wave number reading method using a laser interferometer can also be used, and similar accuracy can be achieved by these methods as well.

Next, the stroke of the position measurement is determined by the stroke of the actuator 40 and the stroke of the length measuring means 420. The above-mentioned grating interference length measurement method, optical heterodyne interference method, laser interferometer wave number reading method, etc. are all 10
It is possible to achieve a high stroke of 0 wm or more, and the actuator can also achieve a similar stroke.

Furthermore, the diameter of the projected light spot is determined by the NA of the objective lens 2o. For example, if an objective lens 2o with NA=0.8 is used, the projection spot diameter φ of the optical system 20 will be φ=2.
．． 44 Fλ+2.38 μm (here, F'=2X
i=1.25, λ=0.78 μm) and
Spot measurement of approximately 2 μm is possible.

If it is desired to increase the spot diameter, the diameter of the effective beam projected by the optical system 20 may be reduced to reduce the effective NA of the beam.

Further, the inclination angle measurement accuracy is determined by the sensor 380 snow detection accuracy. For example, the detection accuracy of sensor 3B is 0.3
Focal length of objective lens 2o in μm! = 5.311
In the case of II, an inclination angle measurement accuracy of approximately D can be achieved. Furthermore, the measurement range of the tilt angle is 10 to 30'' if the objective lens 2o is NA=Q, 5 to 0.9.
It becomes possible to measure up to

In the above embodiments, so-called TTL-A"F (Through the Taki
ngLens Active Auto Focus)
Method (Television Shore Society Journal, Vol. 35, No. 8, 1981
Although we have shown an example using the autofocus method (2011, p.637~), other methods such as the method used for video pickup or the method used for camera autofocus may also be used. Ru.

〔Effect of the invention〕

According to the three-dimensional shape measuring device of the present invention as described above, it is possible to perform three-dimensional shape measurement using a micro spot at high speed with high precision and a high stroke, and at the same time, it can be performed regardless of defects on the surface of the object to be measured. Therefore, accurate information regarding the five-dimensional shape can be obtained in a short time.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the device of the present invention, Figs. 2 and 5 are partial views thereof, Fig. 5 is a plan view of the sensor, and Fig. 4 is a graph of the output of the sensor. be. 2: Focus state determination optical system 4: Inclination angle measuring optical system 6: Casing 8, 28, 60: Light source 20: Objective lenses 26.3B, 76.78: Sensor 40 Near actuator 42: Length measuring means 50: Object to be measured 60: Cleaning of mounting drawing 3 (No change in content 1 → SO 1 ζ Captured island Haha procedure correction blind movement type) % formula % 1, Indication of incident 1985 Patent Application No. 297841 2, Name of the invention Three-dimensional shape measuring device 3, relationship with the person making the amendment Patent applicant address 3-30-2 Shimomaruko, Ota-ku, Tokyo Name (100
)Representative of Canon Co., Ltd. Ryu Kaku 3 Part 4 Address of Agent 3-30-2 Shimomaruko, Ota-ku, Tokyo 146 Description and drawings 6, Contents of amendments The specification and drawings originally attached to the application are attached as attached documents. Street engraving. (No change in content)

Claims (1)

[Claims] A focusing state determining optical system having an internal light source and a movable part that can move at least a portion in the optical axis direction, means for measuring the amount of movement of the movable part, and the focusing state determining optical system. a supporting means for a test object that is rotatable about a rotation axis that intersects with the optical axis of the objective lens of the system and is substantially orthogonal to the optical axis, and the support means for the test object is rotatable about a rotation axis that intersects with the optical axis of the objective lens of the system and is substantially perpendicular to the optical axis; A three-dimensional shape measuring device characterized in that the supporting means is arranged so that the supporting means substantially coincides with a rotation axis.