JPH04295709A - Intereference measuring apparatus and method for receiving image data of interference fringe - Google Patents

Abstract

PURPOSE:To realize the analysis of fringes at resolution higher than the resolution of a sensor by moving a sensor part stepwise at an equal interval in the two directions wherein the pixels of an image sensing element are aligned, receiving a plurality of fringe image data, and thereafter combining the data into one image datum. CONSTITUTION:A CCD camera 1 is mounted on an X-Y stage 2 which is driven with a PZT piezoelectric element. The PZT piezoelectric element is controlled with a PZT controller 6, and a sensor part is moved at steps which are 1/N (N is an integer) of the pitch of the CCD pixel. The total of (N-1) sheets of the images are sequentially stored in a memory 5 through a video interface 4. Thereafter, the image data are transferred into the memory of a computer 8, and the data are combined. Thus, the interference-fringe image data are obtained. Therefore, the resolution which is N times the ordinary resolution can be obtained.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is applicable to measurements of aspherical shapes, etc.
The present invention relates to an interference measurement device and a method for capturing interference fringe image information for measuring the surface shape of an object.

0002

[Prior Art] Conventionally, as a device used for measuring aspherical shapes, etc., the surface of a measurement object is irradiated with light, and a television camera is used to image the interference fringes generated by the wavefronts of the light and another light. 2. Description of the Related Art An interference measuring device is known that identifies the surface shape of the object by image processing interference fringes.

0003

[Problems to be Solved by the Invention] However, a drawback of the interferometry method is that the interference fringes cannot be measured using a CCD (Charge CCD).
Since the information is read using an image sensor such as an image sensor such as an image sensor (e.g. This point will be explained in detail below. The phase difference corresponding to the fringe spacing of the interference fringes is equal to λ (the wavelength of the laser light). For example, in order to obtain the cross-sectional shape of the interference fringes as shown in FIG. 6(a), first find the intersection of the cross-section AA' and the peak of the interference fringes, and then set the height in advance as shown in FIG. 6(b). All you have to do is display it on a graph scaled by wavelength and connect it with a smooth curve. However, in this method, when the number of interference fringes is small, the number of measurement points decreases and the accuracy deteriorates. In other words, the problem with this method is that no information between the measurement points can be read from the interference fringe image. Therefore, in order to increase the information density, a method of introducing a tilt component as shown in FIG. 7 is generally used. With this method, the information density is considerably higher than in the case of Fig. 6(a), but if too many tilt components are introduced, the CCD
A new problem arises in that the fringe density becomes too high relative to the pixel resolution. In other words, since the light receiving area of a CCD pixel has a certain width, it is impossible to specify the interference fringe peak position with an accuracy greater than the width of that pixel.

Furthermore, in recent years, the so-called sub-fringe analysis method has become mainstream as a fringe analysis method. The subfringe analysis method differs from the method of determining the interference fringe peak as described above, in that it allows the phase angle of the interference fringe to be determined at points other than the peak point of the interference fringe.An example is the fringe scanning method. . In this method, the shape of the wavefront to be measured is determined from M pieces of interference fringe data obtained by changing the optical path of the reference light in M steps in steps of λ/M. Usually, in order to shorten the measurement time, fringe scanning is often performed with M=4. In this case, the phase angle φ is calculated from the following equation. However, I1 to I4 are the fringe intensities at certain points when the optical path length of the reference light is changed in four steps in steps of λ/4. tan φ={(I2-I4)/(I1-I3)} Here, φ takes a value between -π/2 and π/2, so the CCD
The value of φ determined for each point corresponding to a pixel is usually discontinuous in some places. It is necessary to connect these patterns continuously, but to do so, one cycle of interference fringes must be received by four or more CCD pixels. Therefore, if the fringe density becomes higher than that, it becomes impossible to connect φ. In addition, there is a method of enlarging the fringe image using an optical system so that the fringe interval does not become too small, but there is a problem in that the measurement range becomes narrower by the amount of enlargement.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an interference measuring device and a method for capturing interference fringe image information that make it possible to realize fringe analysis with a resolution higher than that of the sensor body. With the goal.

[0006]

[Means for Solving the Problems] In order to achieve the above object, the invention according to claim 1 of the present application irradiates the surface of a measurement object with light, and monitors the interference fringes generated by the wavefronts of the light and another light. In an interference measuring device that identifies the surface shape of the object by capturing an image with a camera and processing the interference fringes, if a sensor unit such as an image sensor that receives the interference fringes is movable within a plane perpendicular to the optical axis. The image pickup device has a closing mechanism, and means for capturing a plurality of striped image data while moving the sensor part stepwise at equal intervals in two directions in which the pixels of the image pickup device are lined up, and then stitching the striped image data together into one image data. do.

[0007] Furthermore, the invention according to claim 2 of the present application irradiates light onto the surface of a measurement object, images interference fringes generated by both wavefronts of the light and another light with a television camera, and performs image processing on the interference fringes. In an interference measurement device that identifies the surface shape of the object by It has a mechanism that can horizontally shift the interference light incident on the television camera by mechanically moving optical components such as, and horizontally shifts the interference light stepwise at equal intervals along the two directions in which the pixels are lined up. The present invention is characterized in that it includes a means for joining a plurality of striped image data captured while capturing them into one image data after capturing them.

[0008] Furthermore, the invention according to claim 3 of the present application irradiates light onto the surface of a measurement object, images interference fringes generated by both wavefronts of the light and another light with a television camera, and performs image processing on the interference fringes. A method for capturing interference fringe image information in an interferometric measurement device that identifies the surface shape of an object by determining the surface shape of an object, the method includes a mechanism that allows a sensor unit such as an image sensor that receives the interference fringes to move within a plane perpendicular to the optical axis. The present invention is characterized in that a plurality of pieces of striped image data are taken in while moving the sensor section stepwise and at equal intervals in two directions in which the pixels of the image pickup device are lined up, and then combined into one piece of image data.

[0009] Furthermore, the invention according to claim 4 of the present application irradiates light onto the surface of a measurement object, images interference fringes generated by both wavefronts of the light and another light with a television camera, and performs image processing on the interference fringes. In a method for capturing interference fringe image information in an interferometric measurement device that identifies the surface shape of an object by It has a mechanism that can horizontally shift the interference light incident on the TV camera by mechanically moving optical components such as mirrors, parallel plates, lenses, etc., and the interference light incident on the TV camera can be shifted horizontally in equal steps along the two directions where the pixels are lined up. The method is characterized in that a plurality of pieces of fringe image data are captured while laterally shifting the interference light at intervals, and then combined into one image data.

0010

[Operation] In both cases, the interference measuring device and method for capturing interference fringe image information of the present invention orient either the television camera (or image sensor) or the fringe image orthogonally to the optical axis when capturing interference fringes. While driving in two directions, striped images are captured multiple times and stored in the image memory, and then the multiple striped image data that are slightly shifted from each other are combined into one image data. Fringe analysis can be achieved with a resolution higher than that of .

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained in detail below with reference to the drawings. First, the principle of a method for capturing interference fringe image information in an interferometer of the present invention will be explained using FIG. 1. Figure 1 shows the interference fringe intensity distribution along the line AA' in Figure 6 and the CC
D is a schematic representation of the amount of light received by each pixel, and
In FIG. 1, one cycle of interference fringe intensity change is received by 4/3 CCD pixels. However, in such a state, it is no longer possible to determine the peak position of the fringe or apply the fringe scanning method. Therefore, let us consider a case where the CCD is moved in steps of 1/5 of the pixel pitch in the direction in which the pixels are lined up to capture interference fringe data. First, when focusing on the CCD pixel X, its output value changes as shown in FIG. The change in the amount of light received by the pixel X shown in FIG. 2 changes at the same period as the interference fringe intensity distribution shown in FIG. This is the same for all other pixels, and if you connect the CCD output values for all pixels when moving by 1/5 of the pixel pitch, you can capture interference fringe data with 5 times the original resolution. It becomes possible. That is, according to the above example, it is possible to capture data equivalent to the case where one cycle of interference fringes is received by 20/3 pixels. Of course, the amount of CCD movement is not limited to 1/5 of the pixel pitch. Furthermore, although this example has been described in one dimension for simplicity, if a two-dimensional CCD is used, the CCD will be moved in two directions along the pixel arrangement.

[0012] Next, a mechanism for enabling the above-mentioned interference fringe information acquisition method will be explained. First, the first method is to move the CCD camera itself. In other words, the CC is placed on an XY stage that moves in the direction of the CCD pixels.
Install the D camera. In this case, since the pixel pitch of the CCD is usually about 10 μm, the positioning accuracy of the stage needs to be on the order of submicrons. There is. Next, in the second method, the CCD camera is fixed and the interference fringe image itself is laterally shifted in a direction orthogonal to the optical axis. For example, as shown in Figure 3, before entering the imaging lens of a CCD camera, the interference light is reflected twice by mirror 1, which has its surface normal in the xz plane, and mirror 2, which has its surface normal in the yz plane. and move each mirror in the direction of the arrow (z direction) in FIG. 3 using a piezoelectric element. That is, by moving mirror 1 in the z direction, the interference light incident on the CCD camera is laterally shifted in the x direction, and by moving mirror 2 in the z direction, the light incident on the CCD camera is laterally shifted in the z direction. Alternatively, as shown in Figures 4(a) and (b), by combining a mirror, a lens, and a half mirror, and rotating the mirror placed at the imaging position of the lens around the x and y axes, the interference light can be shifted laterally. You can also. Furthermore, Figure 3
, FIG. 4, the interference light must be parallel light.

Next, FIG. 5 shows an embodiment of an interference measurement apparatus using the interference fringe information acquisition method of the present invention. In this device, a CCD camera 1 is mounted on an XY stage 2 driven by a PZT piezoelectric element, and a PZT controller 6 controls the PZT piezoelectric element to perform XY scanning in steps of 1/N (N is an integer) of the CCD pixel pitch. The stage 2 is moved and a total of (N-1) two images are sequentially stored in the frame memory 5 via the video interface 4. Thereafter, the image data is transferred to the memory of the computer 8, and the data is connected to obtain interference fringe image information. In this way, in the interference measurement device of the present invention, parallel light and CCD
Data is captured sequentially while horizontally shifting the camera in steps of 1/N of CCD pixels, and then these data are combined into one image data.
A resolution N times higher than normal resolution can be obtained.

[0014]

[Effects of the Invention] As explained above, in both the interference measuring device and the method for capturing interference fringe image information of the present invention, when capturing interference fringes, either the television camera (or image sensor) or the fringe image is used. A method of capturing striped images multiple times while driving one side in two directions perpendicular to the optical axis and storing them in image memory, and then joining multiple pieces of striped image data that are slightly shifted from each other into one image data. Therefore, it is possible to realize fringe analysis with a resolution higher than that of the sensor body. Therefore, according to the present invention, it is possible to accurately measure the surface shape of an object, such as the measurement of an aspherical surface shape.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining the principle of the present invention, and is a diagram showing the interference fringe intensity distribution and the amount of light received by a CCD pixel.

FIG. 2 is a diagram for explaining the principle of the present invention,
FIG. 6 is a diagram showing changes in the amount of received light when CD pixels are moved by 1/5 of the pixel pitch.

FIG. 3 is a diagram showing an example of an interference light lateral shifting method applied to the interference fringe image information acquisition method according to the present invention.

FIG. 4 is a diagram showing another example of the interference light lateral shifting method applied to the interference fringe image information acquisition method according to the present invention.

FIG. 5 is a system block diagram showing an example of an interference measurement device using the present invention.

FIG. 6 is a diagram showing an example of fringe analysis, in which (a) is a diagram showing an example of interference fringes, and (b) is a diagram showing a wavefront shape read from the interference fringes shown in (a).

FIG. 7 is a diagram showing an example of interference fringes when tilt is introduced.

[Explanation of symbols]

1 TV camera 2 XY stage 3 Laser interferometer 4 Video interface 5 Frame memory 6 PZT controller 7 Input/output interface 8 Computer

Claims (4)

[Claims] [Claim 1] Light is irradiated onto the surface of the object to be measured, interference fringes generated by the wavefronts of the light and another light are imaged with a television camera, and the surface shape of the object is determined by image processing the interference fringes. The interference measurement device to be specified has a mechanism that allows a sensor unit such as an image sensor that receives the interference fringes to be movable in a plane orthogonal to the optical axis, and is configured to move the sensor unit, such as an image sensor that receives the interference fringes, in a stepwise manner in two directions in which the pixels of the image sensor are lined up. An interference measurement device characterized by comprising means for capturing a plurality of striped image data while moving a sensor section at intervals and then joining them together into one image data. [Claim 2] Light is irradiated onto the surface of the object to be measured, interference fringes generated by both the wavefronts of the light and another light are imaged with a television camera, and the surface shape of the object is determined by image processing the interference fringes. In the interference measurement device to be identified, a mirror or parallel plate is placed on the optical path from the time the two wavefronts interfere until the interference light enters the television camera whose position is fixed.
It has a mechanism that can horizontally shift the interference light incident on the TV camera by mechanically moving optical components such as lenses, and it shifts the interference light horizontally at equal intervals in stages along the two directions where the pixels are lined up. An interference measuring device characterized by comprising means for combining a plurality of striped image data captured while shifting them into one image data after capturing. 3. The surface shape of the object is determined by irradiating light onto the surface of the object to be measured, imaging the interference fringes generated by the wavefronts of the light and another light with a television camera, and processing the interference fringes as images. In a method for capturing interference fringe image information in an interference measurement device to be specified, a sensor unit such as an image sensor that receives the interference fringes has a mechanism that allows it to move within a plane perpendicular to the optical axis, and pixels of the image sensor are arranged A method for capturing interference fringe image information characterized by capturing a plurality of pieces of fringe image data while moving a sensor unit stepwise at equal intervals in two directions and then combining them into one image data. 4. The surface shape of the object is determined by irradiating light onto the surface of the object to be measured, capturing an image of the interference fringes generated by the wavefronts of the light and another light with a television camera, and processing the interference fringes as images. In the method of capturing interference fringe image information in the specified interference measurement device, a mirror, parallel plate, lens, etc. is used on the optical path after the two wavefronts interfere until the interference light enters a television camera whose position is fixed. It has a mechanism that can horizontally shift the interference light incident on the television camera by mechanically moving optical components, and the system shifts the interference light stepwise and at equal intervals along the two directions in which the pixels are lined up. A method for capturing interference fringe image information, which is characterized by combining a plurality of captured fringe image data into one image data after capturing.