JP2006017613A - Interference image measuring instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an interference image measuring instrument capable of extracting phase information at a satisfactory S/N ratio, even when portions different in light intensities exist within the same view field, in measurement of an interference fringe. <P>SOLUTION: In this interference image measuring instrument 10 provided with an image detecting means 12 for detecting interference light to image an interference fringe image, and for acquiring the phase information based on the imaged interference fringe image, the one interference fringe image regulated to conform a range of a light intensity amplitude in each area with a signal level range of the image detecting means 12 is acquired from the interference lights having the light intensity amplitudes different in every of the areas within the same view field, by regulating luminous energy incident into the image detecting means 12, based on light intensity amplitude information in every of areas of the detecting interference lights, and based on spatial arrangement information of the areas, or by regulating the signal level range of the image detecting means 12 to image the interference fringe image. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an interference image measurement apparatus used for optical wave interference measurement and the like, and more particularly to an interference image acquisition mechanism thereof.

In light wave interferometry, which measures the length and shape of an object to be measured using light interference, an interference detector is used to image an interference fringe using an image detector such as a CCD camera, and measurement is necessary from the obtained interference image. Accurate phase information is obtained. For example, in non-contact optical interference measurement as described in Patent Document 1, the phase information necessary for calculating the length of the object to be measured (GB: block gauge) is obtained in the region of the end face of the object to be measured. It is obtained from the interference fringes and the interference fringes in the surrounding area. That is, as shown in FIG. 1, it is necessary to extract phase information from a plurality of points in the same field of view on the interference image. Specifically, the phase difference information Φ in the peripheral region and the GB region on one end face, the phase information ΦA ₁ and ΦA ₂ at two points A ₁ and A ₂ on the peripheral region, and the phase information at the GB region center point B From ΦB,
Φ = (ΦA ₁ + ΦA ₂ ) / 2−ΦB
And calculate.
JP 2003-194523 A

Here, a problem arises when the light intensity amplitude widths of the interference fringes in the surrounding region and the GB region are different from each other. That is, an interference signal due to the passing light and the reference light is obtained in the surrounding area, whereas an interference signal due to the reflected light from the GB end surface and the reference light is obtained in the GB area. Considering the light intensity, as shown in FIG. 2, when the reflectance of the GB surface is x%, the amplitude of the signal obtained in the GB region is x% of the surrounding region.
By the way, in order to acquire a signal with high resolution, it is effective that the maximum and minimum values of the light intensity amplitude fall within the gradation range of the image detector and can be used without waste. However, the steel GB surface has a reflectivity of almost 100%, while the zirconia ceramic GB has a reflectivity of about 10% and the glass reaches about 5%. There is a risk that the light intensity will be extremely reduced. That is, as shown in FIG. 3, the light intensity amplitude A in the _{steel GB} region is substantially equal to the _periphery of the light intensity amplitude A in the _surrounding region, whereas the light intensity in the GB region of the ceramics with low reflectance is low. The amplitude A _{Sera GB} is smaller than the light intensity amplitude A _{surrounding area} .

As described above, when parts with extremely different reflectances are mixed in the same field of view, it is necessary to match the gradation range of the camera to a part with a large light intensity amplitude, so the resolution may be lowered at a part with a small intensity amplitude. Conceivable. Therefore, as shown in FIG. 4, in a region where the light intensity amplitude is small, the light intensity amplitude is strongly affected by noise caused by the performance of the camera and noise generated in an optical system such as a lens, resulting in high accuracy. It becomes a factor that hinders measurement. In other words, if there are regions with significantly different light intensity amplitudes in the same image, it is impossible to fully use the gradation of the image detector, resulting in a risk that the S / N ratio of the phase signal deteriorates. There is sex.
The present invention has been made in view of the above problems, and its purpose is to extract phase information with a high S / N ratio even when locations with different light intensities coexist in the same field of view when measuring interference fringes. It is an object of the present invention to provide an interference image measurement apparatus capable of performing the above.

  In order to achieve the above object, an interference image measurement apparatus according to the present invention includes an image detection unit that detects interference light and captures an interference fringe image, and obtains phase information based on the captured interference fringe image. An apparatus that adjusts the amount of light incident on the image detection unit based on light intensity amplitude information for each region of interference light to be detected and spatial arrangement information on the region, or a signal level of the image detection unit By adjusting the range and picking up the interference fringe image, the light intensity amplitude range in each region is matched with the signal level range of the image detection means from the interference light having different light intensity amplitude for each region in the same field of view. One interference fringe image adjusted so as to be acquired is obtained.

  In the interference image measuring apparatus, the detection level setting means for setting the detection signal level of the image detection means based on the information of the light intensity amplitude for each region, and a part is extracted from the plurality of interference images and synthesized. Image processing means for making one interference fringe image, and the detection level setting means changes the gradation range of the image detection means to match the range of the light intensity amplitude in each region, and It is preferable that an interference fringe image is captured, and the image processing unit obtains one interference fringe image by synthesizing the plurality of interference fringe images in which gradation ranges are appropriately set for each region.

  In the above interference image measuring device, based on the information on the light intensity amplitude for each region, an incident light amount adjusting unit that adjusts the incident light amount incident on the image detecting unit, and a plurality of images captured at an appropriate detection level for each region Image processing means for extracting a part from the interference fringe image and combining them into a single interference fringe image, and adjusting the incident light quantity from the predetermined area by the incident light quantity adjusting means, The light intensity amplitude is adjusted to match the gradation range of the image detector, and the plurality of interference fringe images in which the gradation range is appropriately set for each region are synthesized by the image processing means. It is preferable to acquire two interference fringe images.

The interference image measuring apparatus includes a light dividing unit that divides measurement interference light into a plurality of light beams, and the image detection unit includes a plurality of image detectors that detect the light beams divided by the light dividing unit. It is preferable to provide a plurality of sets of interference images appropriately adjusted with respect to the light intensity amplitude for each region having a specific light intensity amplitude by the plurality of image detectors.
The interference image measuring apparatus includes an attenuation region selection unit that selectively attenuates light in a specific region, and adjusts the light intensity amplitude in the specific region by inserting the attenuation region selection unit into the optical path. Thus, it is preferable that the light intensity amplitude of the interference light in each region within the same field of view is substantially the same.

  The interference image measurement device of the present invention is an interference image measurement device that includes image detection means for detecting interference light and capturing an interference fringe image, and acquires phase information based on the captured interference fringe image, The image detecting means sets the gain and / or exposure time for each pixel or each region of the light receiving surface based on the light intensity amplitude information for each region of the interference light to be detected and the spatial arrangement information of the region. It is configured to be possible.

  According to the present invention, the amount of light incident on the image detection unit is adjusted based on the light intensity amplitude information for each region of the interference light to be detected and the spatial arrangement information of the region, or the detection of the image detection unit. By picking up the interference fringe image by adjusting the signal level, the range of the light intensity amplitude in each region from the interference light having different light intensity amplitude for each region in the same field of view is defined as the gradation range of the image detection means. Since one interference fringe image adjusted to fit is acquired, phase information can be extracted with a high S / N ratio even when locations with different light intensities are mixed in the same field of view. .

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the following embodiments, the light intensity amplitude of each region and information for adapting it to the gradation range of the detector have been acquired in advance and are known.
Embodiment 1
FIG. 5 is a schematic configuration diagram of the interference image measuring apparatus according to the first embodiment of the present invention. The interference image measurement apparatus 10 of the embodiment of FIG. 5 sets image detection means (image detector 12) for acquiring interference fringe images by detecting interference light, and a detection signal level of the image detector 12. Detection level setting means 14 and image processing means 16 for extracting a part from a plurality of interference images and combining them into one interference fringe image are provided. The detection level setting means 14 adjusts the gradation range of the image detector 12 so as to be approximately equal to the light intensity amplitude range of a predetermined region of the interference fringe image, and captures an interference image. In other words, adjustment is made so that the gradation range of the image detector and the range of the light intensity amplitude of the region are matched so that the gradation range of the image detector can be used without waste in that region. Further, an interference image is picked up by changing the region to be adjusted, a plurality of interference fringe images are acquired, and the region adjusted by the image processing means 16 is cut and pasted from the plurality of interference images obtained in this way to obtain one interference. An image is created.

The image detector 12 includes an image detector such as a CCD camera. In this embodiment, the image detector 12 is connected to a computer 18 or the like, and the computer 18 performs setting of the detector, recording of acquired data, and the like. The interference fringe image information obtained by the image detector 12 is stored in the storage means 20 of the computer 18. The image processing unit 16 performs image processing on the interference fringe image stored in the storage unit 20.
The detection level setting means 14 is for setting the detection level of the image detector 12. The detection level may be adjusted by a method such as switching the gain of the detector or switching the shutter speed (exposure time, that is, the light accumulation time).
The above is the schematic configuration of the present embodiment, and the operation thereof will be described below. Here, the description will be given assuming dimension measurement by non-contact optical interference measurement described in Patent Document 1.

  In this embodiment, an image in the same field of view (entire imaging area) is divided into a plurality of areas (however, the intensity of light intensity is divided within one area so as to be substantially constant), and an interference image is acquired for each area. I do. That is, in the example of non-contact light wave interference measurement, acquisition of the interference fringe image in the GB region and acquisition of the interference fringe image in the surrounding region are performed separately. Then, the gradation range of the image detector 12 is set by the detection level setting means 14 so as to match the range of the light intensity amplitude in each region, and a plurality of interference fringe images are respectively captured. Then, the interference fringe image in which the gradation is appropriately adjusted in the surrounding area as shown in FIG. 6A and the gradation in the block gauge area as shown in FIG. 6B are appropriately adjusted. The interference fringe image thus obtained is obtained and stored in the storage unit 20 of the computer 12.

The image processing means 16 cuts out the image of the surrounding area from the image (FIG. 6A) in which the gradation is appropriately set in the surrounding area (FIG. 6C). Similarly, an image of the GB area is cut out from an image (FIG. 6B) in which the gradation is appropriately set in the GB area (FIG. 6D). The two images ((c) and (d) in FIG. 6) obtained in this way are combined to synthesize one interference fringe image ((e) in FIG. 6).
If the interference fringe image obtained in this way is used, an image in which the gradation is appropriately adjusted in all the regions in the image can be obtained, so that measurement with a good S / N ratio is possible. That is, the problem of the prior art is solved by separately acquiring interference images adjusted so that the gradation of the camera is used up only in each of the surrounding area and the GB area, and combining them for each area.

FIG. 7 is an explanatory diagram of gradation adjustment by switching the gain of the image detector. Here, it is assumed that the light intensity amplitude A _{GB in} the region of the end face of the block gauge is smaller than the _surroundings of the light intensity amplitude A in the _surrounding region. FIG. 7A shows a case where the gradation range of the image detector is matched with the _periphery of the light intensity amplitude A in the _{surrounding area} . In FIG. 7B, the gain of the detector is made larger than that in FIG. 7A, and the detection signal of the light intensity amplitude A _GB in the area of the block gauge end face is adapted to the gradation range of the detector. I am doing so. In the case of FIG. 7B, the periphery of the light intensity amplitude A in the _{surrounding area} is saturated because it exceeds the gradation range of the detector, but in the area of the block gauge end face, the gradation range of the detector is It is set properly.

FIG. 8 is an explanatory diagram of a method of adjusting by changing the shutter speed of the detector. FIG. 8A shows a case where the gradation range of the image detector is matched with the _periphery of the light intensity amplitude A in the _{surrounding area} . In FIG. 8B, the shutter speed of the detector is slow (exposure time is long), and the detected light intensity amplitude A _GB of the interference light from the GB region is adapted to the gradation range of the detector. In the case of FIG. 8B, the periphery of the light intensity amplitude A in the _{surrounding area} is saturated because it exceeds the gradation range of the detector, but in the area of the block gauge end face, the gradation range of the detector is It is set properly.
Further, when performing light wave interference measurement by the phase shift method, it is necessary to capture a plurality of images having different phase shift amounts, but there is no particular limitation on the order of image acquisition. That is, as shown in FIG. 9A, even if a plurality of images are acquired at each step during one phase shift, the phase shift is performed a plurality of times for each group as shown in FIG. 9B. Or a combination thereof.

Embodiment 2
In the first embodiment, the detector is adjusted in accordance with the light intensity. However, the incident light intensity itself may be adjusted. Next, this case will be described.
FIG. 10 is a schematic configuration diagram of an interference image measuring apparatus according to the second embodiment of the present invention. The interference image measurement apparatus 110 in FIG. 10 includes an image detection unit (image detector 112), an incident light amount adjustment unit 114 that adjusts an incident light amount incident on the image detection unit based on information on the light intensity amplitude for each region, and , Image detecting means (image detector 112), and image processing means 116 for extracting a part from a plurality of interference images and combining them into one interference fringe image.

Here, the incident light amount adjusting means 114 is constituted by a light attenuating plate or the like, and adjusts the light amount itself incident on the image detector 112. That is, the amount of transmitted light can be adjusted by changing the light attenuating plate inserted in the optical path. However, the installation position of the light attenuation plate is not particularly limited.
Then, similarly to the first embodiment, the light intensity amplitude of each region in the interference image is adjusted so that the amount of light matches the gradation range of the image detector 112, and a plurality of interference images are captured. The plurality of interference images are appropriately adjusted in gradation range only in different areas. From the plurality of interference fringe images, the image processing means 116 cuts and pastes a region in which the gradation range is appropriately adjusted, as described with reference to FIG. 6, and creates one interference image.

Embodiment 3
Next, a case where a plurality of detectors are used will be described. It is possible to solve the problems of the prior art by dividing the light after interference into the required number of areas and detecting each area with a detector whose characteristics are known in advance or whose characteristics are uniform.
FIG. 11 is a schematic configuration diagram of an interference image measuring apparatus according to the third embodiment of the present invention. The interference image measuring apparatus 210 in FIG. 11 includes a light dividing unit 222 that divides interference light into a plurality of light beams, a plurality of image detectors 212a and 212b that detect each light beam divided by the light dividing unit 222, and an image. And processing means 216. The light dividing means 222 is composed of an element such as a beam splitter. Moreover, although the example divided | segmented into 2 light beams was shown in FIG. 11, what is necessary is just to change according to the number of the area | regions to divide | segment.

The gradation ranges of the image detectors 212a and 212b are set so as to match the light intensity amplitude of each region. For example, the gradation range of the image detector 212a is adjusted to match the light intensity amplitude of the GB region, and the gradation range of the image detector 212b is adjusted to match the light intensity amplitude of the surrounding region. Further, this adjustment may be performed by adjusting the detector itself as in the first embodiment, or by adjusting the amount of incident light itself as in the second embodiment.
Information on the interference fringe images detected by the respective image detectors 212 a and 212 b is sent to the computer 218 and stored in the storage unit 220. Then, as in the first embodiment, the image processing unit 216 obtains one interference fringe image in which the gradation range in each region is appropriately set from the plurality of interference fringe images. Thus, by using a configuration using a plurality of detectors, an image can be acquired in a short time.

In the above embodiment, a case has been described in which an interference image in which the gradation range is appropriately adjusted is obtained using a plurality of images adjusted in different gradation ranges. The gradation range of all the areas in the same visual field can be appropriately set by one imaging.
Embodiment 4
FIG. 12 is a schematic configuration diagram of an interference image measuring apparatus according to the fourth embodiment of the present invention. The interference image measurement apparatus 310 of FIG. 12 includes an image detector 312 and attenuation region selection means 314 that selectively attenuates light in a specific region.
The attenuation region selection means 314 is composed of an optical attenuation plate manufactured according to the shape of the region to be attenuated. The attenuation region selection means 314 is inserted into the optical path as necessary to adjust the light intensity amplitude in the specific region, so that the light intensity amplitude of the interference light in each region in the same field of view is substantially the same. For example, the non-contact light wave interference measurement will be described as an example. As shown in FIG. 13, an attenuation plate having a hole in the GB region is inserted into the optical path to attenuate the surrounding region light and to reduce the light from the GB region. The intensity amplitude is almost the same. Then, by adjusting the gradation range of the image detector 312 to the light intensity amplitude of the GB region, the light intensity amplitude of the surrounding region is automatically adapted. As a result, it is possible to obtain an interference fringe image in which the gradation range in each region is appropriately set only by capturing one interference fringe image.

Embodiment 5
FIG. 14 is a schematic configuration diagram of an interference image measuring apparatus according to the fifth embodiment of the present invention. In the interference image measurement apparatus 410 in FIG. 14, an image detector 412 that can change the exposure time and the gain setting at the time of signal readout for each pixel (or for each predetermined range) on the light receiving surface is used. . For example, a CMOS method may be used.
In the image detector 412 of the present embodiment, based on the light intensity amplitude information for each area of the interference light to be detected and the spatial arrangement information of the area, the exposure time for each pixel (or each area) of the light receiving surface, And / or set gain. As a result, an interference fringe image in which the gradation range in each region is appropriately set can be obtained by capturing an image once, and phase information can be extracted with a high S / N ratio.
As described above, according to the interference image measuring apparatus of the present invention, even when locations with different light intensities are mixed in the same field of view, the interference images in which each location is adjusted to an appropriate gradation range. Therefore, phase information can be extracted with a high S / N ratio.

Explanatory drawing of the acquisition point of the area | region in an interference image, and phase information. Explanatory drawing about the relationship between a reflectance and the light intensity amplitude of an interference fringe. Explanatory drawing about the difference in the light intensity amplitude by a reflectance. Explanatory drawing of the relationship between light intensity and a detector gradation. 1 is a schematic configuration diagram of an interference image measuring apparatus according to a first embodiment of the present invention. Explanatory drawing of the image process in the apparatus of this embodiment. Explanatory drawing of adjustment of the gradation used with a detector. Explanatory drawing of adjustment of the light intensity observed with a detector. Explanatory drawing of the image acquisition order in the case of measuring by a phase shift method. The schematic block diagram of the interference image measuring device concerning the 2nd Embodiment of this invention. The schematic block diagram of the interference image measuring device concerning the 3rd Embodiment of this invention. The schematic block diagram of the interference image measuring device concerning the 4th Embodiment of this invention. Explanatory drawing of the interference image measuring device of 4th Embodiment. The schematic block diagram of the interference image measuring device concerning the 5th Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Interference image measuring device 12 Image detector 14 Image processing means 16 Detection level setting means

Claims (6)

An interference image measurement device that includes an image detection unit that detects interference light and captures an interference fringe image, and obtains phase information based on the captured interference fringe image,
Based on the light intensity amplitude information for each area of the interference light to be detected and the spatial arrangement information of the area, the amount of light incident on the image detection means is adjusted, or the signal level range of the image detection means is adjusted. By capturing the interference fringe image
One interference fringe image adjusted so that the range of the light intensity amplitude in each region matches the signal level range of the image detection means is acquired from the interference light having different light intensity amplitude for each region in the same field of view. An interference image measuring apparatus characterized by that. The interference image measurement apparatus according to claim 1,
Detection level setting means for setting a detection signal level of the image detection means based on information of light intensity amplitude for each region;
Image processing means for extracting a part from a plurality of interference images and combining them into one interference fringe image,
The detection level setting means changes the gradation range of the image detection means so as to match the range of the light intensity amplitude in each area, and captures a plurality of interference fringe images. An interference image measurement apparatus characterized in that a plurality of interference fringe images having a gradation range appropriately set are combined to obtain one interference fringe image. The interference image measurement apparatus according to claim 1,
Based on the information of the light intensity amplitude for each region, the incident light amount adjusting means for adjusting the incident light amount incident on the image detecting means,
Image processing means for extracting a part from a plurality of interference fringe images captured at an appropriate detection level for each region and combining them into one interference fringe image;
With
By adjusting the amount of incident light from a predetermined region by the amount of incident light adjusting means, the light intensity amplitude of the region is adjusted so as to match the gradation range of the image detector, and by the image processing means, An interference image measurement apparatus characterized in that a plurality of interference fringe images having a gradation range appropriately set are combined to obtain one interference fringe image. In the interference image measuring device according to claim 2 or 3,
Comprising a light splitting means for splitting the measurement interference light into a plurality of light fluxes;
The image detecting means includes a plurality of image detectors for detecting each light beam divided by the light dividing means,
An image measurement apparatus for providing a plurality of sets of interference images appropriately adjusted with respect to light intensity amplitude for each region having a specific light intensity amplitude by the plurality of image detectors. The interference image measurement apparatus according to claim 1,
Attenuating area selecting means for selectively attenuating light in a specific area, and adjusting the light intensity amplitude in the specific area by inserting the attenuating area selecting means in the optical path, thereby each area in the same field of view. An interference image measuring apparatus characterized in that the light intensity amplitudes of the interference light beams are substantially the same. An interference image measurement device that includes an image detection unit that detects interference light and captures an interference fringe image, and obtains phase information based on the captured interference fringe image,
The image detecting means sets the gain and / or exposure time for each pixel or each region of the light receiving surface based on the light intensity amplitude information for each region of the interference light to be detected and the spatial arrangement information of the region. An interference image measurement apparatus characterized by being configured.

Images