An integrated calibration tool for six-axis spatial allocation of an optical instrument entrance pupil

Abstract

A system for calibrating a device includes a beamsplitter; a first reticle configured to be removably attached to the device; and an image capture device including an image plane, wherein an image of the first reticle is configured to be received at the image plane along an optical axis of the beamsplitter through the beamsplitter, wherein a direction indicated by the first reticle is compared to a direction of the image plane, and if the direction indicated by the first reticle is different from the direction of the image plane, the device is rotated about the optical axis of the beamsplitter so that the direction indicated by the first reticle matches the direction of the image plane.

Description

TECHNICAL FIELD

[0001] The present invention relates to a calibration tool having six-axis spatial partitioned imaging capability; in particular, the present invention relates to an instrument entrance pupil calibration tool having six-axis partitioned imaging capability. BACKGROUND

[0002] In an application, a calibration tool is required to measure depth or distance in the Z direction, where the Z direction is the direction of the optical path of the calibration tool. For example, the output of a conventional chromatic confocal sensor can generate position measurements of a device based on the Z direction measurements. The conventional chromatic confocal sensor can be arranged at various X-Y positions in the X-Y coordinate plane to obtain Z direction data, thereby extending its use to populate position data of a device whose position is measured as distance from the X-Y plane to produce position data in the (X, Y, Z) coordinate system, or in directions specified by the rotational angles about the X, Y, and Z axes, respectively. However, the conventional chromatic confocal sensor can only produce a three-dimensional position that can be specified in the (X, Y, Z) coordinate system or in directions (RX, RY, RZ), where RX represents the angle of tilt about the X axis, RY represents the angle of tilt about the Y axis, and RZ represents the angle of rotation about the Z axis, if the feature of the device to be detected is symmetric about the Z axis, i.e., the axis that is coaxial with the optical axis of the chromatic confocal sensor, then the three-dimensional position is specified as the rotational values about two of the three axes of the base coordinate. Thus, in the use of the conventional chromatic confocal sensor in conjunction with a device having an entrance pupil that is coaxially aligned with the optical axis of the conventional chromatic confocal sensor, there is no RZ or rotational data available since the feature of the entrance pupil or other features about the entrance are symmetric about the optical axis of the sensor. Furthermore, the acquisition cost of the chromatic confocal sensor is relatively high.

[0003] Therefore, there is a need for a calibration tool that can provide rotational angles about all X, Y, and Z axes, and can provide position information in the X, Y, and Z coordinate space, where the acquisition cost of the calibration tool is within a relatively affordable range for optical device manufacturers. SUMMARY

[0004] Summary of the Invention: It is an object of the present invention to provide a tool that can provide an indicator so that the rotational direction of a device about the optical axis of the tool can be obtained or indicated; it is another object of the present invention to provide a tool that can provide position data and rotational data, including an indication of rotational angles about all X, Y, and Z axes.

[0005] Technical solution: A system for calibrating a device, the system comprising: a beam splitter; a first reticle configured to be removably attached to the device; and an image capturing device comprising an image plane, wherein an image of the first reticle is configured to be received at the image plane along an optical axis of the beam splitter by the beam splitter, wherein a direction indicated by the first reticle is compared to a direction of the image plane, and if the direction indicated by the first reticle is different from the direction of the image plane, the device is rotated about the beam splitter optical axis such that the direction indicated by the first reticle matches the direction of the image plane.

[0006] In one embodiment, the system further comprises a second reticle, wherein the second reticle is configured to be removably attached to the beam splitter, and an image of the second reticle is configured to be received at the image plane along the beam splitter optical axis by the beam splitter, wherein a direction indicated by the second reticle is compared to the direction of the image plane, and if the direction indicated by the second reticle is different from the direction of the image plane, at least one of a position and an orientation of the image capturing device is adjusted such that the direction indicated by the second reticle matches the direction of the image plane.

[0007] In one embodiment, the direction indicated by the first reticle is compared to the direction of the image plane, and if the direction indicated by the first reticle is different from the direction of the image plane, the device is rotated about the beam splitter optical axis such that the direction indicated by the first reticle matches the direction of the image plane.

[0008] In one embodiment, an image of the first reticle is focused on the image plane, and a first magnification of the image of the first reticle is obtained by comparing a size of the image of the first reticle with a corresponding size of the first reticle, the second reticle further comprises a known position, an image of the second reticle is focused on the image plane, and a second magnification of the image of the second reticle is obtained by comparing a size of the image of the second reticle with a corresponding size of the second reticle, a position of the first reticle relative to the second reticle is calculated based in part on the first magnification and the second magnification.

[0009] In one embodiment, the system further comprises a directional light source configured to be transmitted by the beam splitter and projected onto the image plane at a first point, and configured to be reflected by the beam splitter and directed to the device, the light source reflected by the device is directed by the beam splitter onto the image plane at a second point, wherein if the second point does not fall on the first point, the device is said to be arranged in a direction that is not perpendicular to the beam splitter optical axis.

[0010] In one embodiment, the directional light source comprises a laser beam.

[0011] In one embodiment, the first reticle includes an aperture to enable the light source to image the device area within the first reticle.

[0012] In one embodiment, the device is an optical imaging system with an external entrance pupil, an optical imaging system with rotational alignment requirements, or a combination thereof.

[0013] In one embodiment, the image capture device is a charge-coupled device (CCD) camera.

[0014] Advantages: The system of the present invention can be used not only to determine the position of the device in the X, Y and Z axes, where these axes are orthogonal to each other, but also to determine the angle of rotation around these axes; the system of the present invention can be used to determine whether a part of the device to be measured is arranged orthogonally with respect to the optical axis of the system of the present invention, and if it is not, to adjust the orientation of the device to be measured, so that a simple orthogonal indicator can be used to ensure that the orientation is at the target position. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a schematic diagram depicting the system of the present invention for calibrating a device with an external entrance pupil;

[0016] Figure 2 is a schematic diagram depicting Figure 1 the system of the present invention for self-calibration of the orientation of the system around its optical axis and for obtaining the distance between the optical lens group of the camera and the second reticle;

[0017] Figure 3 is a top view of the reticle used herein;

[0018] Figure 4 is a schematic diagram depicting Figure 1 the system of the present invention for obtaining the distance between the optical lens group of the camera and the first reticle;

[0019] Figure 5 is a schematic diagram depicting Figure 1 the system of the present invention for obtaining the orientation of the device around an axis perpendicular to the optical axis of the beamsplitter;

[0020] wherein the light source 2; the beamsplitter 4; the image capture device or camera 6; the instrument or device to be measured or calibrated 8; the optical lens group 10; the image plane 12; the surface of the device to be measured or calibrated 14; the entrance pupil of the device 16; the projected image of reticle A 18; the projected image of reticle B 20; the point at which the image of the transmitted beam is projected 22; the point at which the image of the reflected beam is projected by the beamsplitter 24; the optical axis of the beamsplitter 26; the center of the image plane 28; the aperture 30; the optically reflective surface 32; the crosshairs 34. DETAILED DESCRIPTION

[0021] As used herein, the term "about" is used in the sense of approximately, roughly, around, or in the range or area of. When the term "about" is used in conjunction with a numerical value, it modifies that numerical value by expanding the upper and lower boundaries of the numerical value. Generally, the term "about" as used herein is used to modify a value by a variance of plus or minus 20% of the stated value.

[0022] Figure 1 is a schematic diagram depicting the inventive system for calibrating a device 8 having an external entrance pupil 16. In one example, the device 8 is an optical imaging system having an external aperture 16 (e.g., entrance pupil). In another example, the device is an optical imaging system having rotational alignment requirements. Figure 2 is a schematic diagram depicting Figure 1 the inventive system for self-calibration of the inventive system around the direction of its optical axis 26 and for obtaining the distance between the optical lens group 10 of the camera 6 and the second reticle or reticle B or the object distance of the reticle B and the distance between the imaging distance or the imaging plane 12 and the optical lens group 10 of the camera 6. Here, the image 20 of the reticle B is projected on the image plane 12. Figure 4 is a schematic diagram depicting Figure 1 the inventive system for obtaining the distance between the optical lens group 10 of the camera 6 and the first reticle or object distance. Here, the image 18 of the reticle A is projected on the image plane 12. In the embodiment shown in Figure 1 the beam splitter 4 is in central alignment with the camera 6 such that the image of an object aligned with the beam splitter optical axis 26 can be projected on the image plane 12 of the camera 6. In another embodiment not shown, the camera can be selectively aligned with its optical axis aligned with the Z-axis. However, as will be shown elsewhere herein, the beam splitter is used to allow the use of another input without the need to re-arrange the components of the present system. Also shown here are two reticles, namely reticle A and reticle B. The purpose of the reticle B is twofold. First, the alignment of the camera 6 can be self-calibrated using this reticle if necessary. The reticle B is configured to be removably attached to the beam splitter 4 and the image of the reticle B is configured to be received by the beam splitter 4 at the image plane 12 along the beam splitter optical axis 26, to compare the direction indicated by the reticle B with the direction of the image plane 12, and to adjust the position or direction of the camera or image capture device 6, e.g., a charge-coupled device (CCD) camera, such that the direction indicated by the reticle B matches the direction of the image plane 12 if the direction indicated by the reticle B is different from the direction of the image plane 12. Any grid line disposed on the image plane 12 can be used to establish the direction of the image plane 12. Second, the reticle B can be used to obtain the distance between its position and the optical lens group 10, i.e., the distance represented by the sum of Lo-B-1 and Lo-B-2, or Figure 2the distance or image distance represented by Li-B. It is noted here that with these distances, the distance between the reticles A and B can be obtained. This distance is important because when the positional information on the Z-axis is available, this information can be established. In use, reticle B can be removed so that it does not obstruct the light beams from other parts of the device surface 14 and can be projected to the image plane 12. However, if needed, reticle B can be left in place for the entire remainder of the calibration process after reticle A is no longer needed for use because reticle B also has the aperture 30 that allows the entire calibration process to be performed.

[0023] Figure 3 is a top view of the reticle used here. Reticle A is configured to be removably attached to the surface 14 of the device to be measured or tested. Its function is also dual. First, reticle A is arranged coaxially with respect to the entrance pupil 16 of the device. Reticle A includes an aperture 30 to allow the imaging of the inner portion of the entrance pupil of the device. Either reticle A or reticle B includes a reflective surface 32 having two pairs of peripheral crosshairs 34. In this way, the direction represented by each reticle can be easily distinguished. Second, the distance between reticle A and the image plane 12 can be calculated. This distance is the sum of Lo-A-l, Lo-A-2, and Li-A-2.

[0024] In obtaining the orientation of the device, the image of reticle A is configured to be received at the image plane along the optical axis of the beam splitter 4 by the beam splitter 4. The camera focus function is adjusted to obtain a focused image of reticle A on the image plane 12. This direction is then compared to the direction of the image plane 12. This direction can be the direction adjusted based on reticle B or the direction not adjusted based on reticle B. The direction indicated by reticle A is compared to the direction of the image plane 12, and if the direction indicated by reticle A is different from the direction of the image plane, the device is rotated about the beam splitter optical axis 26 or the Z-axis so that the direction indicated by reticle A matches the direction of the image plane 12.

[0025] Optical equations can be used to solve for the distance between two reticles, namely, reticles A and B. The distance between an object (e.g., reticle A or B) and optical lens assembly 10, or Lo, or the distance between the object and its projected image 18 and optical lens assembly 10, or Li, or the image distance, is related by the equation 1 / Lo + 1 / Li = 1 / EFL, where EFL represents the effective focal length. Lo and Li are also related by the equation M = Lo / Li, where M represents the magnification. EFL is a constant value of the optical lens assembly, and M can be obtained by comparing the size of the image projected on the image plane with the known physical dimensions of the reticles having the image projected on the image plane. Although Lo = Lo-A-1 + Lo-A-2 and Li = Li-A for reticle A, and Lo = Lo-B-1 + Lo-B-2 and Li = Li-B for reticle B, it is not necessary to solve all parts of these relationships to find the distance between the two reticles. Substituting Li = (1 / M) * Lo in the equation 1 / Lo + 1 / Li = 1 / EFL yields Lo = (1 + M) * EFL. Since M can be calculated and EFL is a known quantity, Lo can be obtained. Li can also be obtained from the equation M = Lo / Li. With the total distance between each reticle and the image plane, the difference between these distances yields the distance between the two reticles, or the distance between the device and the top surface of reticle B, or the quantity in the Z direction.

[0026] Figure 5 It is a depiction Figure 1 Schematic diagram of the system of the present invention for obtaining the orientation of the device around an axis perpendicular to the optical axis 26 of the beam splitter. In one embodiment, the system also includes a directional light source 2, which is configured to be transmitted by the beam splitter 4 and projected onto the image plane 12 at a first point 22, and is configured to be reflected by the beam splitter 4 and directed to the device, the light reflected by the device being directed by the beam splitter onto the image plane of a second point 24, wherein if the second point 24 is not incident on the first point 22, the device is said to be arranged in a direction that is not perpendicular to the optical axis of the beam splitter 4. Here, an angle of rotation about the Y axis is determined and this angle can be adjusted. It can be seen that, although not shown, the angle of rotation about the X axis can also be determined similarly. In one embodiment, the directional light source includes a laser beam for generating a light source with a small coverage area.

[0027] In one embodiment, when performing calibration of the device, first the position of the device is adjusted relative to the system of the present invention. The camera 6 is first powered on so that the entrance pupil 16 can first be positioned and oriented. The device to be measured, calibrated or tested should be moved until the reticle A appears in the center of the image plane 12. If the system of the present invention needs to be calibrated, this step should be performed before other steps including the positioning and orientation of the entrance pupil 16. When calibrating the system, an image of the reticle B will be obtained when the reticle B is attached to the top surface of the beamsplitter 4 along the optical axis 26. The image should be centered on the image plane at the center 28 and the image plane should be oriented relative to the directional indicators of the reticle B, for example, by aligning the grid lines of the image plane with the crosshairs of the reticle B. The positioning and / or orientation of either assembly, i.e. the beamsplitter 4 and the camera 6, should be adjusted. The reticle A can then be used to calibrate the orientation of the device about the Z axis or the angle of rotation about the Z axis or RZ. The tilt of the device can be calibrated using the associated strategy. Figure 5 If desired, the position of other surface features of the device can be identified in the same manner as the identification of the reticle.

Claims

1. A system for calibrating a device, characterized in that The system includes: a beam splitter; a first reticle configured to be attached to the device; and an image capture device including an image plane, wherein an image of the first reticle is configured to be received at the image plane through the beam splitter along an optical axis of the beam splitter, wherein a direction indicated by the first reticle is compared with a direction of the image plane, and if the direction indicated by the first reticle is different from the direction of the image plane, the device is rotated about the optical axis of the beam splitter so that the direction indicated by the first reticle matches the direction of the image plane; the system also includes a second reticle, wherein the second reticle is configured to be attached to the beam splitter, and an image of the second reticle is configured to be received at the image plane through the beam splitter along the optical axis of the beam splitter, wherein the direction indicated by the second reticle is compared with the direction of the image plane, and if the direction indicated by the second reticle is different from the direction of the image plane, at least one of a position and an orientation of the image capture device is adjusted so that the direction indicated by the second reticle matches the direction of the image plane.

2. The system according to claim 1, wherein: The direction indicated by the first reticle is compared with the direction of the image plane, and if the direction indicated by the first reticle is different from the direction of the image plane, the device is rotated about the optical axis of the beam splitter so that the direction indicated by the first reticle matches the direction of the image plane.

3. The system according to claim 1, wherein: wherein the image of the first reticle is focused on the image plane, and a first magnification of the image of the first reticle is obtained by comparing a size of the image of the first reticle with a corresponding size of the first reticle, the second reticle further comprises a known position, the image of the second reticle is focused on the image plane, and a second magnification of the image of the second reticle is obtained by comparing a size of the image of the second reticle with a corresponding size of the second reticle, and the position of the first reticle relative to the second reticle is calculated in part based on the first magnification and the second magnification.

4. The system according to claim 1, wherein: It also includes a directional light source, which is configured to be transmitted by the beam splitter and projected onto the image plane at a first point, and is configured to be reflected by the beam splitter and directed to the device, and the reflection of the light source by the device is directed to the image plane at a second point by the beam splitter, wherein if the second point is not incident on the first point, the device is arranged in a direction that is not perpendicular to the optical axis of the beam splitter.

5. The system according to claim 4, characterized in that The first reticle includes an aperture to enable the light source to image a device area within the first reticle.

6. The system according to claim 4, characterized in that The directional light source includes a laser beam.

7. The system according to claim 1, wherein: The device is a device selected from the group consisting of an optical imaging system having an external aperture, an optical imaging system having rotational alignment requirements, and combinations thereof.

8. The system according to claim 1, wherein: The image capture device is a charge coupled device camera.

9. A system for calibrating a device, characterized in that The system includes: a beam splitter; a first reticle configured to be attached to the device; an image capture device including an image plane, wherein an image of the first reticle is configured to be received at the image plane through the beam splitter along an optical axis of the beam splitter, and a directional light source, wherein a direction indicated by the first reticle is compared with a direction of the image plane, and if the direction indicated by the first reticle is different from the direction of the image plane, the device is rotated about the optical axis of the beam splitter so that the direction indicated by the first reticle matches the direction of the image plane, and the directional light source is configured to be transmitted by the beam splitter and projected onto the image plane at a first point, and is configured to be reflected by the beam splitter and directed toward the device, A reflection of the light source by the device is directed by the beam splitter to the image plane at a second point, wherein if the second point is not incident on the first point, the device is set in a direction that is not perpendicular to the optical axis of the beam splitter; the system also includes a second reticle, wherein the second reticle is configured to be attached to the beam splitter, and an image of the second reticle is configured to be received at the image plane along the optical axis of the beam splitter through the beam splitter, wherein the direction indicated by the second reticle is compared with the direction of the image plane, and if the direction indicated by the second reticle is different from the direction of the image plane, at least one of the position and direction of the image capture device is adjusted so that the direction indicated by the second reticle matches the direction of the image plane.

10. The system according to claim 9, characterized in that The orientation indicated by the first reticle is compared with the direction of the image plane, and if the direction indicated by the first reticle is different from the direction of the image plane, the device is rotated about the optical axis of the beam splitter so that the direction indicated by the first reticle matches the direction of the image plane.

11. The system according to claim 9, wherein: The image of the first reticle is focused on the image plane, and a first magnification of the image of the first reticle is obtained by comparing a size of the image of the first reticle with a corresponding size of the first reticle, the second reticle further includes a known position, the image of the second reticle is focused on the image plane, and a second magnification of the image of the second reticle is obtained by comparing a size of the image of the second reticle with a corresponding size of the second reticle, and the position of the first reticle relative to the second reticle is calculated in part based on the first magnification and the second magnification.

12. The system according to claim 9, wherein: The first reticle includes an aperture to enable the light source to image a device area within the first reticle.

13. The system according to claim 9, wherein: The directional light source includes a laser beam.

14. The system according to claim 9, wherein: The device is a device selected from the group consisting of an optical imaging system having an external aperture, an optical imaging system having rotational alignment requirements, and combinations thereof.

15. The system according to claim 9, wherein: The image capture device is a charge coupled device camera.

16. A system for calibrating a device, characterized in that The system includes: a beam splitter; a first reticle configured to be attached to the device; an image capture device including an image plane, wherein an image of the first reticle is configured to be received at the image plane along the optical axis of the beam splitter through the beam splitter, and a second reticle configured to be attached to the beam splitter, and an image of the second reticle is configured to be received at the image plane along the optical axis of the beam splitter through the beam splitter, wherein a direction indicated by the second reticle is compared with the direction of the image plane, and if the direction indicated by the second reticle is different from the direction of the image plane, at least one of a position and an orientation of the image capture device is adjusted so that the direction indicated by the second reticle matches the direction of the image plane, and the direction indicated by the first reticle is compared with the direction of the image plane, and if the direction indicated by the first reticle is different from the direction of the image plane, the device is rotated about the optical axis of the beam splitter so that the direction indicated by the first reticle matches the direction of the image plane.

17. The system according to claim 16, wherein: The system also includes comparing the direction indicated by the second reticle to the direction of the image plane, and if the direction indicated by the second reticle is different from the direction of the image plane, adjusting the position of the image capture device so that the direction indicated by the second reticle matches the direction of the image plane.

18. The system according to claim 16, wherein: The image capture device is a charge coupled device camera.

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