TWI863697B - An optimal diffuser position adjustment method for kohler illumination system - Google Patents

Abstract

An optimal diffuser position adjustment method for Kohler illumination system is used to adjust the Kohler illumination system. Firstly, when a diffuser rotates, an image sensor is used to capture an initial dynamic image of a diffuser at an initial position, and the initial dynamic image is analyzed whether a vector of deviation displacement of at least one speckle remains converged at a predetermined range; then, if the vector of deviation displacement of the speckle remains converged within the predetermined range, an initial diffuser position is defined as an optimal diffuser position with the best uniformity of the light field , otherwise, the diffuser position is adjusted until the deviation displacement of the speckle converges within the predetermined range. The corrected diffuser position is then defined as the optimal diffuser position for field uniformity optimization.

Description

Optimized diffuser position adjustment method for Kohler illumination system

The present invention relates to a method for adjusting an illumination system, and more particularly to a method for adjusting the object distance of a Kohler illumination system.

In existing optical measurement technology, in order to effectively capture the image of the sample, a suitable light source must be used for illumination. The illumination methods are divided into two categories: critical illumination and Kohler illumination (Kohler is the English translation of the original German Köhler). Critical illumination will cause the characteristics of the light source itself to be displayed in the image of the sample, overlapping and causing interference. Therefore, in the existing optical field, Kohler illumination technology is mainly used to provide uniform illumination.

Please refer to the first figure, which is a schematic diagram of a Kohler illumination system of the prior art. As shown in the first figure, a Kohler illumination system PA100 includes an illumination light source PA1, a light collecting lens PA2, a diffuser PA3, a focusing lens PA4, a spectroscope PA5, an objective lens PA6, a tube lens PA7 and an image sensor PA8; wherein the diffuser PA3 is rotatably disposed between the illumination light source PA1 and the light collecting lens PA2, so that the light projected by the illumination light source PA1 After being uniformly diffused by the rotation of the diffuser PA3, an emitted laser beam PALB is sequentially irradiated to the object to be measured located on an illuminated surface PAIP through the collecting lens PA2, focusing lens PA4, spectroscope PA5 and objective lens PA6, and then the image sensor PA8 captures the image of the object to be measured reflected on the illuminated surface PAIP through the tube lens PA7, spectroscope PA5 and objective lens PA6.

Please continue to refer to the second figure, which shows the random speckle image presented by the illuminated surface when the diffuser PA3 is stationary when the existing Kohler illumination system uses laser as the illumination light source. As shown in the first and second figures, in some optical applications, in order to achieve sufficient power density (generally known as brightness), a high coherence laser must be used as the illumination light source PA1. However, when the laser is used as the illumination light source PA1, when the diffuser PA3 is stationary, the image sensor PA8 will capture a speckle image SI containing multiple speckle noises on the illuminated surface PAIP, and the presence of speckle will cause severe uneven illumination, making the image captured by the image sensor PA8 almost unrecognizable.

As mentioned above, in order to reduce the negative impact of speckle, the conventional technology generally sets a diffuser PA3 between the illumination light source PA1 and the light collecting lens PA2, and utilizes the rotation of the diffuser PA3 to make the laser light pass through the rotating diffuser PA3 to form an equivalent light source, and then pass through the light collecting lens PA2 and the focusing lens PA4 to focus on the back focal plane of the objective lens PA6, and then projected onto the object to be measured (not shown) located on the illuminated surface PAIP through the objective lens PA6; thereby, from the equivalent light source to the illuminated surface PAIP is a typical Kohler illumination architecture. The light then passes through the objective lens PA6, the beam splitter PA5 and the tube lens PA7 to form an image on the image sensor PA8. The image observed is effectively uniformed during the exposure time due to the rotation of the diffuser PA3. This type of technology is generally known as despeckle technology.

From the above description, we can know that the purpose of rotating the diffuser PA3 is to achieve the effect of eliminating speckles (achieving uniform illumination on a smaller scale), while the purpose of the Kohler illumination system PA100 is to achieve uniform illumination at a macroscopic level. In order to achieve uniform illumination at a macroscopic level, the position of the diffuser PA3 (i.e., the equivalent light source) must be properly adjusted so that the diffuser PA3 and the illuminated surface PAIP satisfy the Fourier plane relationship in optics.

Generally speaking, people with knowledge in this field can preliminarily set the relative positions of the diffuser PA3, image sensor PA8 and the above objects according to the nominal specifications of the light collecting lens PA2, focusing lens PA4, objective lens PA6 and tube lens PA7 through optical components. However, in practice, due to various processing and assembly errors, the position of the diffuser PA3 usually fails to form the best macroscopic uniform illumination on the illuminated surface PAIP (equivalent to the concentric surface of the image sensor PA8). At this time, a standard object to be tested needs to be placed on the illuminated surface PAIP, and the image sensor PA8 is used to observe the illumination distribution on the standard object to be tested, and then the position of the diffuser PA3 is fine-tuned to make the illumination distribution on the standard object to be tested present the best macroscopic uniform illumination. However, since the laser beam passing through the diffuser PA3 will cause the image observed by the image sensor PA8 to have strong random speckles, it is difficult to judge whether the standard object to be tested presents macroscopic uniform illumination. Therefore, an effective judgment and adjustment method is needed to judge and adjust the optimal setting position of the diffuser PA3.

In view of the fact that in the prior art, although the existing Kohler illumination system can provide higher illumination brightness through a laser light source, in order to eliminate the speckle generated when using the laser light source, a diffuser is usually set, and the light field is made uniform by rotating the diffuser. However, in actual use, the setting position of the diffuser may not necessarily make the illuminated surface align with the object to be tested, so that the object to be tested cannot receive the most uniform illumination; therefore, the main purpose of the present invention is to provide a method for adjusting the optimal diffuser position of the Kohler illumination system, which can effectively find the optimal diffuser setting position so that the object to be tested can receive uniform light field illumination.

The present invention is to solve the problems of the prior art. The necessary technical means adopted is to provide a method for adjusting the position of an optimized diffuser of a Kohler illumination system, which is used to calibrate a Kohler illumination system. The Kohler illumination system includes a laser light source, a collector, a diffuser, a focusing lens, a spectroscope, an objective lens, a tube lens, and an image sensor. The diffuser is rotatably disposed between the laser light source and the collector, so that a laser beam projected by the laser light source is uniformly diffused by the rotation of the diffuser, and then irradiated to a device under test (device under test, image sensor) through the collector, the focusing lens, the spectroscope, and the objective lens in sequence. DUT), so that the image sensor captures the image reflected by the object under test through the tube lens, the spectroscope and the objective lens. The calibration method of the Kohler illumination system includes the following steps (A) to (C).

First, step (A) is to use the image sensor to capture an initial dynamic image of the object under test when the diffusion sheet is located at an initial position when the diffusion sheet rotates, and analyze whether a deviation displacement vector of at least one speckle in the initial dynamic image of the object under test remains convergent within a predetermined range.

Next, step (B) is to define the initial position of the diffuser as an optimized diffuser position with the best light field uniformity if the deviation displacement vector of the at least one speckle in step (A) remains converged within the predetermined range; otherwise, step (C) is continued.

Finally, step (C) is to adjust the position of the diffuser if the deviation displacement vector of the at least one speckle in step (A) exceeds the predetermined range until the deviation displacement vector of the at least one speckle remains converged within the predetermined range, and define a corrected position of the diffuser after adjustment as the optimized diffuser position with the best light field uniformity.

In an auxiliary technical means derived from the above necessary technical means, the laser light source has an optical axis, and the step (C) further includes the following steps (C1) to (C4).

Step (C1) is to move the diffusion sheet to a first calibration position along a first direction parallel to the optical axis, so as to capture a first calibrated dynamic image of the object to be measured by using the image sensor, and to analyze the first calibrated dynamic image to determine whether the deviation displacement vector of the at least one speckle remains converged within the predetermined range.

In step (C2), if the deviation displacement vector of the at least one speckle in step (C1) remains converged within the predetermined range, the first correction position of the diffuser is defined as the optimized diffuser position with the best light field uniformity; otherwise, step (C3) is continued.

Step (C3) is to move the diffusion sheet along the first direction or a second direction opposite to the first direction to a second calibration position to capture a second calibration dynamic image of the object to be measured by the image sensor if the deviation displacement vector of the at least one speckle in step (C1) exceeds the predetermined range, and analyze the second calibration dynamic image to determine whether the deviation displacement vector of the at least one speckle remains converged within the predetermined range. If the deviation displacement vector of the at least one speckle remains converged within the predetermined range, the calibrated position of the diffused sheet at the second calibration position is defined as the optimized diffusion sheet position with the best light field uniformity; otherwise, step (C4) is continued.

Step (C4) is to repeatedly perform step (C1) to step (C3) until the deviation displacement vector of the at least one speckle remains converged within the predetermined range, and the diffuser position is defined as the optimized diffuser position with the best light field uniformity.

As described above, in step (C3), when the vector magnitude of the deviation displacement vector of the at least one speckle in step (C1) exceeds the predetermined range, and the vector direction of the deviation displacement vector of the at least one speckle in step (C1) is opposite to the vector direction of the deviation displacement vector measured when the diffusion sheet is located at the previous position, the diffusion sheet is moved along the second direction opposite to the first direction to the second calibration position.

In addition, in step (C3), when the vector magnitude of the deviation displacement vector of the at least one speckle in the step (C1) exceeds the predetermined range, if the direction of the deviation displacement vector of the at least one speckle in the step (C1) is the same as the direction of the deviation displacement vector measured when the diffusion sheet is located at a previous position, but the deviation displacement vector magnitude of the at least one speckle in the step (C1) is smaller than the vector magnitude of the deviation displacement vector measured when the diffusion sheet is located at the previous position, then the diffusion sheet is moved along the first direction to the second correction position.

In contrast, in step (C3), when the vector magnitude of the deviation displacement vector of the at least one speckle in step (C1) exceeds the predetermined range, if the direction of the deviation displacement vector of the at least one speckle in step (C1) is the same as the direction of the deviation displacement vector measured when the diffusion sheet is in the previous position, but the deviation displacement vector magnitude of the at least one speckle in step (C1) is greater than the vector magnitude of the deviation displacement vector measured when the diffusion sheet is in the previous position, then the diffusion sheet is moved along the second direction opposite to the first direction to the second correction position.

In one embodiment, the diffuser moves along the first direction to approach the light collecting lens, and the diffuser moves along the second direction to move away from the light collecting lens; in another embodiment, the diffuser moves along the first direction to move away from the light collecting lens, and the diffuser moves along the second direction to approach the light collecting lens.

Preferably, the step (A) is to use a computer host electrically connected to the image sensor to perform image analysis on the initial dynamic image of the object being tested, the step (C1) is to use the computer host to perform image analysis on the first dynamic image, and the step (C3) is to use the computer host to perform image analysis on the second dynamic image.

In addition, the first corrected dynamic image includes two first corrected static images, and the two first corrected static images have a time difference between each other. The second corrected dynamic image includes two second corrected static images, and the two second corrected static images have a time difference between each other.

In an auxiliary technical means derived from the above necessary technical means, the initial dynamic image of the object to be measured includes two initial static images, and there is a time difference between the two initial static images.

As described above, the present invention mainly uses an image sensor to capture the initial dynamic image of the object to be measured when the diffusion sheet rotates, so as to analyze whether the deviation displacement vector of the speckle remains convergent within a predetermined range, and then judge whether the diffusion sheet is in an optimized position. If not, the position is continuously adjusted until the speckle position of the captured image is in a state of disappearing in situ, which means that the corrected position of the diffusion sheet is the optimized position with the best light field uniformity.

The specific embodiments of the present invention will be further described by the following embodiments and drawings.

Please refer to the third FIG. 3 , which is a plan view showing a Kohler illumination system used in the method for adjusting the position of the diffuser of the Kohler illumination system of the present invention and placing the object to be measured on the illuminated surface.

As shown in the third figure, a Kohler illumination system 100 includes a laser light source 1, a collector 2, a diffuser 3, a condenser 4, a spectroscope 5, an objective 6, a tube lens 7 and an image sensor 8; wherein the diffuser 3 is rotatably disposed between the laser light source 1 and the collector 2, so that a laser beam LB projected by the laser light source 1 is uniformly diffused by the rotation of the diffuser 3, and then sequentially irradiates a device under test (device under test, DUT) DUT, and then the image sensor 8 captures the image reflected by the object under test DUT through the tube lens 7, the spectroscope 5 and the objective lens 6.

As mentioned above, the method for adjusting the position of the diffuser of the Kohler illumination system of the present invention is mainly used to calibrate the position of the object under test DUT in the Kohler illumination system 100 so that the object under test DUT can be illuminated by the most uniform light field.

Please continue to refer to the fourth and fifth figures. The fourth figure is a schematic diagram showing the initial dynamic image of the object to be measured captured by the image sensor in the method for optimizing the position adjustment of the diffuser of the Kohler illumination system of the present invention; the fifth figure is a schematic diagram showing the deviation displacement vector generated by the cross-correlation function analysis of the initial dynamic image of the object to be measured in the method for optimizing the position adjustment of the diffuser of the Kohler illumination system of the present invention. As shown in the third to fifth figures, in order to optimize the position of the diffuser 3, the method for optimizing the position adjustment of the diffuser of the Kohler illumination system of the present invention includes the following steps S110 to S130.

First, in this embodiment, step S110 is to capture an initial dynamic image SI1 of the object under test DUT when the diffusion sheet 3 is located at an initial position P0 using the image sensor 8 when the diffusion sheet 3 rotates, and analyze a deviation displacement vector dV0 of a plurality of speckles S1 (there are a plurality of speckles in the figure, only one of which is marked) for the initial dynamic image SI1 to determine whether the deviation displacement vector dV0 remains convergent within a predetermined range SR; wherein step S110 is to perform image analysis on the initial dynamic image SI1 of the object under test using a cross-correlation operation using a computer host (not shown) electrically connected to the image sensor 8 to obtain a cross-correlation operation result image CC1, thereby displaying the deviation displacement vector dV0. Although in this embodiment, the deviation displacement vector dV0 of the speckle S1 is obtained by cross-correlating the variation characteristics of a plurality of speckles S1, in other embodiments, cross-correlation can also be performed if there is only one speckle S1.

Next, in step S120, if the deviation displacement vector dV0 of the speckle S1 in step S110 remains converged within the predetermined range SR, the position of the diffuser 3 at the initial position P0 is defined as an optimized diffuser position with the best light field uniformity, otherwise, step S130 is continued. In this embodiment, since it is determined in step S120 that the deviation displacement vector dV0 of the speckle S1 in step S110 does not remain converged within the predetermined range SR, that is, the deviation displacement vector dV0 of the speckle S1 exceeds the predetermined range SR, step S130 is then performed.

Step S130 is to move the diffuser 3 to adjust the position of the diffuser 3 if the deviation displacement vector dV0 of the speckle S1 in step S130 exceeds the predetermined range SR, until the deviation displacement vector dV0 of the speckle S1 remains converged within the predetermined range SR, and define the corrected position of the diffuser 3 as the optimized diffuser position with the best light field uniformity.

As mentioned above, when the initial position P0 of the diffusion sheet 3 is set so that the ideal illuminated surface IP (equivalent to the focusing surface of the objective lens 6) is not aligned with the surface of the object under test DUT as shown in the third figure, the initial dynamic image SI1 of the object under test captured by the image sensor 8 will include two initial static images SI1a and SI1b as shown in the fourth figure; wherein the two initial static images SI1a and SI1b have a time difference between each other.

It should be particularly noted that when the image sensor 8 captures the initial object dynamic image SI1 by capturing one image per second, the two initial static images SI1a and SI1b can be, for example, adjacent frames separated by one second, that is, the initial static image SI1b is captured one second after the initial static image SI1a is captured; but not limited to this, the two initial static images SI1a and SI1b can also be interval frames separated by two seconds, that is, after the initial static image SI1a is captured, the next frame of the initial static image SI1a is skipped and the next frame is taken as the initial static image SI1b.

In addition, in actual use, the peak value of speckle S1 (similar to the weighted average position of all speckles S1 in the picture) and the peak value of S1a are calculated respectively by the above-mentioned computer host, and then the change of the peak value is calculated by cross-correlation to obtain the deviation displacement vector dV0. For example, the initial static images SI1a and SI1b of the present invention can be 100x100 pixels, and when the speckle S1 is about 4 to 6 pixels, the predetermined range SR can be 6 to 9 pixels as the allowable deviation, and the peak value of the speckle S1 is used as the origin and the allowable deviation is used as the positive and negative value boundary to divide the tolerance range, and whether the deviation displacement vector dV0 remains convergent in the predetermined range SR is mainly judged based on whether the peak value of the speckle S1a is located in the predetermined range SR.

From the above two initial static images SI1a and SI1b, it can be seen that the position of the speckle S1 in the initial static image SI1a is significantly different from the position of the speckle S1a in the initial static image SI1b, and the displacement deviation vector dV0 between the peak of the speckle S1a and the peak of the speckle S1 has exceeded the predetermined range SR set with the peak of the speckle S1 as the center. Therefore, corresponding to the above step S120, it can be seen that the initial position P0 set by the diffusion sheet 3 in the third figure is not the position with the best light field uniformity, so it is necessary to proceed to step S130. Specifically, in addition to taking the peak of the speckle S1 as the center, the predetermined range SR can be set to, for example, 100% to 200% of the original range of the speckle S1, and the smaller the range setting, the more accurate it is.

In this embodiment, the above step S130 may further include the following detailed steps S131 to S134.

Please continue to refer to Figures 6 to 8. Figure 6 is a plane diagram showing that when the deviation displacement vector of the speckle of the initial dynamic image of the object under test is analyzed and does not remain converged within a predetermined range, the diffusion sheet is moved along the first direction to the first correction position; Figure 7 is a schematic diagram showing the first correction dynamic image captured by the image sensor using the optimal diffusion sheet position adjustment method of the Kohler illumination system of the present invention; Figure 8 is a schematic diagram showing the deviation displacement vector generated by the cross-correlation function analysis of the first correction dynamic image using the optimal diffusion sheet position adjustment method of the Kohler illumination system of the present invention.

As shown in the third to eighth figures, after it is determined in step S120 that the initial position P0 of the diffusion sheet 3 is not the position with the best light field uniformity, step S131 is to move the diffusion sheet 3 along a first direction D1 parallel to an optical axis OA of the laser beam LB to a first calibration position P1 as shown in the sixth figure, so as to capture a first calibration dynamic image SI2 of the object under test DUT at the first calibration position P1 using the image sensor 8, and analyze the first calibration dynamic image SI2 to see whether the deviation displacement vector dV1 of the speckle S2 remains converged within the predetermined range SR. In step S131, the first calibration dynamic image SI2 is analyzed by a computer host through a cross-correlation operation to obtain a cross-correlation operation result image CC2 showing the deviation displacement vector dV1.

As mentioned above, the first corrected dynamic image SI2 includes two first corrected static images SI2a and SI2b, and the two first corrected static images SI2a and SI2b are captured in a similar manner to the two initial static images SI1a and SI1b, and also have a time difference. The difference mainly depends on the different positions of the diffusion sheet 3. After the first corrected static images SI2a and SI2b are analyzed through a cross-correlation function, the displacement deviation between the peak value of the speckle S2 and the peak value of the speckle S2a can be obtained. The difference vector dV1 and the displacement deviation vector dV1 still exceed the predetermined range SR but fail to converge within the predetermined range SR. Therefore, it can be seen that when the diffuser 3 is moved along the first direction D1 to the first correction position P1, the overall light field uniformity generated is not optimal. Moreover, since the direction of the displacement deviation vector dV1 is opposite to the direction of the displacement deviation vector dV0, it can be seen that the diffuser 3 should then be moved along a second direction D2 opposite to the first direction D1, so that the diffuser 3 may be close to the position with the best light field uniformity.

Next, step S132 is to define the corrected position of the diffuser 3 at the first correction position P1 as the optimized diffuser position with the best light field uniformity when the deviation displacement vector dV1 of the speckle S2 in step S131 remains converged within the predetermined range SR; however, in this embodiment, since the deviation displacement vector dV1 of the speckle S2 does not converge within the predetermined range SR, it is necessary to continue to execute the following step S133.

Please continue to refer to Figures 9 to 11. Figure 9 is a plane diagram showing that when the deviation displacement vector of the speckle in the first correction dynamic image is analyzed and does not remain converged within a predetermined range, the diffusion plate is moved along the second direction to the second correction position by the optimized diffusion plate position adjustment method of the Kohler illumination system of the present invention; Figure 10 is a schematic diagram showing the second correction dynamic image captured by the image sensor by the optimized diffusion plate position adjustment method of the Kohler illumination system of the present invention; Figure 11 is a schematic diagram showing the deviation displacement vector generated by the second correction dynamic image analyzed by the cross-correlation function by the optimized diffusion plate position adjustment method of the Kohler illumination system of the present invention.

As shown in the third to eleventh figures, step S133 is to move the diffusion sheet 3 to a second calibration position P2 along a second direction D2 opposite to the first direction D1 when the deviation displacement vector dV1 of the speckle S2 in step S131 exceeds the predetermined range SR, so as to capture a second calibration dynamic image SI3 of the diffusion sheet 3 at the second calibration position P2 by using the image sensor 8, and analyze whether the deviation displacement vector dV2 of the speckle S3 remains converged within the predetermined range SR for the second calibration dynamic image SI3. If the deviation displacement vector dV2 of the speckle S3 remains converged within the predetermined range SR, the calibrated position of the diffusion sheet 3 at the second calibration position P2 is defined as the optimized diffusion sheet position with the best light field uniformity, otherwise, step S134 is continued to be executed. Among them, step S133 also utilizes the host computer to perform image analysis on the second corrected dynamic image SI3 through cross-correlation operation to obtain a cross-correlation operation result image CC3 showing a deviation displacement vector dV2.

As mentioned above, the second corrected dynamic image SI3 includes two second corrected static images SI3a and SI3b, and the two second corrected static images SI3a and SI3b are captured in a similar manner to the two initial static images SI1a and SI1b, and also have a time difference, and the difference mainly depends on the different positions of the diffusion sheet 3; wherein, after the second corrected static images SI3a and SI3b are analyzed through a cross-correlation function, a displacement deviation vector dV2 between the peak value of the speckle S3 and the peak value of the speckle S3a can be obtained, and since the displacement deviation vector dV2 remains convergent within a predetermined range SR, the position of the diffusion sheet 3 after correction (the second correction position P2) can be defined as the optimized diffusion sheet position with the best light field uniformity.

Please continue to refer to FIG. 12, which is a plane diagram showing the deviation displacement vector corresponding to the movement of the diffuser from the initial position along the first direction to the first calibration position, and from the first calibration position along the second direction to the second calibration position in the method for adjusting the position of the optimal diffuser of the Kohler illumination system of the present invention. As shown in FIG. 3 to FIG. 12, since the deviation displacement vector dV0 obtained by the operation of the cross-correlation function when the diffuser 3 is at the initial position P0 exceeds the predetermined range SR, according to the above-mentioned step S130, the diffuser 3 needs to be moved along the first direction D1, and the first direction D1 refers to the direction of the first movement of the diffuser 3 in step S130, and the first direction D1 can be close to the collecting mirror 2 or away from the collecting mirror 2, and in this embodiment, the first direction D1 is the direction close to the collecting mirror 2.

As mentioned above, in this embodiment, the deviation displacement vector dV0 exceeds the predetermined range SR mainly means that the vector size of the deviation displacement vector dV0 exceeds the allowable offset from the center to the boundary of the predetermined range SR. In more detail, the optimal ideal position of the diffuser 3 will make the spot S1 almost disappear in situ, and the deviation displacement vector dV0 is determined by the offset and direction between the spot S1 and the spot S1a. Therefore, in the calculation The deviation displacement vector dV1 and the predetermined range SR both take the speckle S1 (or the peak value of the speckle S1) as the origin, and the predetermined range SR is the positive and negative error range set with the origin as the center. Thus, when the deviation displacement vector dV0 obtained by the diffusion sheet 3 at the initial position is a positive vector compared to the above-mentioned origin, the deviation displacement vector dV1 centered at the origin and opposite to the deviation displacement vector dV0 is a negative vector.

Thus, in the above step S131, because the vector magnitude of the displacement deviation vector dV1 (equivalent to the absolute value of the vector when the direction is not considered and only the magnitude is considered) generated by the diffusion plate 3 at the first correction position P1 exceeds the predetermined range SR (i.e., a simple numerical value comparison based on the above-mentioned origin), and the vector direction of the displacement deviation vector dV1 generated by the first correction position P1 is opposite to the vector direction of the deviation displacement vector dV0 measured when the diffusion plate 3 is located at the previous position (initial position P0), it means that the diffusion plate 3 is in the opposite direction and is farther away from the predetermined range SR. Therefore, the diffusion plate 3 needs to be moved in the second direction D2 opposite to the first direction D1 in order to make the diffusion plate 3 approach the ideal position.

Please continue to refer to Figures 13 and 14. As shown in the figures, in step S133 of another embodiment, when the diffusion sheet 3 in step S131 moves from the initial position P0 along the first direction D1 to a first correction position P1a, and the deviation displacement vector dV1a obtained by calculating the correlation function still exceeds the predetermined range SR, if the direction of the deviation displacement vector dV1a is the same as the direction of the deviation displacement vector dV0 measured when the diffusion sheet 3 is at the previous position (initial position P0), but the vector magnitude of the deviation displacement vector dV1a is smaller than the vector magnitude of the deviation displacement vector dV0 of the diffusion sheet 3 at the previous position (initial position P0), it means that the diffusion sheet 3 moves along the first direction D1 to the first correction position P1a, which is closer to the predetermined range SR, and therefore the diffusion sheet 3 needs to continue to move along the first direction D1.

As mentioned above, when the diffuser 3 moves from the first correction position P1a to the second correction position P2a along the first direction D1, and the deviation displacement vector dV2a obtained by the operation of the cross-correlation function converges within the predetermined range SR, the corrected position of the diffuser 3 (the second correction position P2a) can be defined as the optimized diffuser position with the best light field uniformity.

Please continue to refer to FIG. 15 and FIG. 16. As shown in the figure, in step S133 of another embodiment, when the diffusion sheet 3 moves from the initial position P0 along a first direction D1b to a first correction position P1b, if the deviation displacement vector dV1b obtained by the operation of the cross-correlation function still exceeds the predetermined range SR, if the direction of the deviation displacement vector dV1b is the same as the deviation displacement vector dV1b measured when the diffusion sheet 3 is at the previous position (initial position P0), The direction of the diffusion plate 3 is the same as that of dV0, but the vector magnitude of the deviation displacement vector dV1a is greater than the vector magnitude of the deviation displacement vector dV0 of the diffusion plate 3 at the previous position (initial position P0), which means that the diffusion plate 3 moves along the first direction D1 to the first correction position P1b, but not only does it not move within the predetermined range SR but is further away from the predetermined range SR compared to the initial position P0, so the diffusion plate 3 needs to be moved along the second direction D2b opposite to the first direction D1b.

In summary, the method for adjusting the position of the diffuser of the Kohler illumination system of the present invention is mainly to first use the image sensor to capture the initial dynamic image of the object to be measured when the diffuser rotates, so as to analyze whether the deviation displacement vector of the spot is kept convergent in a predetermined range, and then judge whether the diffuser is in the optimized position. If not, the position is adjusted continuously until the spot position of the captured image is eliminated in situ. The increase in the state of the diffuser means that the corrected position of the diffuser is the optimal position for the best light field uniformity. Compared with the prior art which only utilizes the rotation of the diffuser to eliminate speckle but cannot place the object to be tested at a position where it can receive the most uniform illumination, the present invention can indeed place the diffuser at an optimal position that can optimize the uniformity of the illumination light field on the object to be tested, thereby effectively improving the quality of the captured image.

The above detailed description of the preferred specific embodiments is intended to more clearly describe the features and spirit of the present invention, but is not intended to limit the scope of the present invention by the preferred specific embodiments disclosed above. On the contrary, the purpose is to cover various changes and arrangements with equivalents within the scope of the patent application for the present invention.

PA100: Kohler illumination system PA1: Light source PA2: Light collecting lens PA3: Diffuser PA4: Focusing lens PA5: Spectroscope PA6: Objective lens PA7: Cylinder PA8: Image sensor PALB: Laser beam PAIP: Illuminated surface SI: Speckle image 100: Kohler illumination system 1: Laser light source 2: Light collecting lens 3: Diffuser 4: Focusing lens 5: Spectroscope 6: Objective lens 7: Cylinder 8: Image sensor DUT: Object under test LB: Laser beam OA: Optical axis SI1: Initial object under test dynamic image SI1a, SI1b: Initial static image SI2: First calibration dynamic image SI2a, SI2b: First calibration static image SI3: Second corrected dynamic image SI3a, SI3b: Second corrected static image S1, S1a, S2, S2a, S3, S3a: Speckle SR: Predetermined range dV0, dV1, dV1a, dV1b, dV2, dV2a: Deviation displacement vector D1, D1b: First direction D2, D2b: Second direction P0: Initial position P1, P1a, P1b, P1c: First corrected position P2, P2a: Second corrected position CC1, CC2, CC3: Cross-correlation operation result image

The first figure is a plane diagram of the Kohler illumination system of the prior art; The second figure is a plane diagram of the random speckle image presented by the illuminated surface captured when the existing Kohler illumination system uses laser as the illumination light source; The third figure is a plane diagram of the Kohler illumination system used in the optimized diffuser position adjustment method of the Kohler illumination system of the present invention, with the object to be measured placed on the illuminated surface; The fourth figure is a schematic diagram of the initial dynamic image of the object to be measured captured by the image sensor using the optimized diffuser position adjustment method of the Kohler illumination system of the present invention; The fifth figure is a schematic diagram of the deviation displacement vector generated by the cross-correlation function analysis of the initial dynamic image of the object to be measured using the optimized diffuser position adjustment method of the Kohler illumination system of the present invention; The sixth figure is a schematic diagram showing that the object to be measured is moved along the first direction to the first correction position when the deviation displacement vector of the speckle of the initial dynamic image of the object to be measured does not remain converged within the predetermined range when analyzing the optimal diffuser position adjustment method of the Kohler illumination system of the present invention; The seventh figure is a schematic diagram showing the first correction dynamic image captured by the image sensor when the method for adjusting the position of the diffuser of the Kohler illumination system of the present invention is used; The eighth figure is a schematic diagram showing the deviation displacement vector generated by the cross-correlation function analysis of the first correction dynamic image when the method for adjusting the position of the diffuser of the Kohler illumination system of the present invention is used; The ninth figure is a schematic diagram showing that the method for adjusting the position of the diffuser of the Kohler illumination system of the present invention is moved along the second direction to the second correction position when the deviation displacement vector of the speckle of the first correction dynamic image does not remain converged within the predetermined range when analyzing the optimal diffuser position adjustment method of the Kohler illumination system of the present invention; Figure 10 is a schematic diagram showing the second corrected dynamic image captured by the image sensor in the optimized diffuser position adjustment method of the Kohler illumination system of the present invention; Figure 11 is a schematic diagram showing the deviation displacement vector generated by the cross-correlation function analysis of the second corrected dynamic image in the optimized diffuser position adjustment method of the Kohler illumination system of the present invention; Figure 12 is a plane schematic diagram showing the deviation displacement vector corresponding to the diffuser moving from the initial position along the first direction to the first correction position and from the first correction position along the second direction to the second correction position in the optimized diffuser position adjustment method of the Kohler illumination system of the present invention; Figure 13 is a plane schematic diagram showing the diffuser moving along the first direction to the first correction position and then moving along the first direction to the second correction position in the optimized diffuser position adjustment method of the Kohler illumination system of the present invention; FIG14 is a plane diagram showing the deviation displacement vectors corresponding to the first correction position and the second position of the diffuser in FIG13 according to the movement from the initial position along the first direction to the diffuser in FIG13; FIG15 is a plane diagram showing the method for adjusting the position of the diffuser in the Kohler illumination system of the present invention, in which the diffuser is moved along the first direction away from or close to the focusing lens to the first correction position, and the deviation displacement vector still does not converge within the predetermined range and needs to be moved along the opposite second direction; and FIG16 is a plane diagram showing the deviation displacement vectors corresponding to the movement of the diffuser in FIG15 along the first direction away from or close to the focusing lens to the first correction position.

SI3: Second correction dynamic image

SI3a, SI3b: Second calibration static image

S3, S3a: speckle

Claims (10)

A method for calibrating the position of a diffuser of a Kohler illumination system is provided. The method is used to calibrate a Kohler illumination system. The Kohler illumination system comprises a laser light source, a collector, a diffuser, a condenser, a beam splitter, an objective, a tube lens, and an image sensor. sensor), the diffuser is rotatably disposed between the laser light source and the focusing lens, so that a laser beam projected by the laser light source is uniformly diffused by the rotation of the diffuser, and then irradiates a test object through the focusing lens, the focusing lens, the spectroscope and the objective lens in sequence, and then the image sensor captures the image reflected by the test object through the tube lens, the spectroscope and the objective lens. The calibration method of the Kohler illumination system includes the following steps: (A) When the diffuser rotates, the image sensor is used to capture an initial test object dynamic image of the diffuser at an initial position, and analyzes whether a deviation displacement vector of at least one speckle in the initial test object dynamic image remains convergent within a predetermined range; (B) If the deviation displacement vector of the at least one speckle in the step (A) remains converged within the predetermined range, the initial position of the diffuser is defined as an optimized position with the best light field uniformity; otherwise, the step (C) is continued; and (C) If the deviation displacement vector of the at least one speckle in the step (A) exceeds the predetermined range, the position of the diffuser is adjusted until the deviation displacement vector of the at least one speckle remains converged within the predetermined range, and a corrected position of the diffuser after adjustment is defined as the optimized position with the best light field uniformity. The method for optimizing the object distance adjustment of the Kohler illumination system as described in claim 1, wherein the laser light source has an optical axis, and the step (C) further comprises the following steps: (C1) moving the diffuser along a first direction parallel to the optical axis to a first calibration position, so as to capture a first calibrated dynamic image of the object under test by using the image sensor, and analyzing the first calibrated dynamic image to determine whether the deviation displacement vector of the at least one speckle remains converged within the predetermined range; (C2) if the deviation displacement vector of the at least one speckle in the step (C1) remains converged within the predetermined range, the calibrated position of the diffuser at the first calibration position is defined as the optimized position with the best light field uniformity, otherwise, continuing to execute step (C3); (C3) If the deviation displacement vector of the at least one speckle in step (C1) exceeds the predetermined range, the diffusion sheet is moved to a second calibration position along the first direction or a second direction opposite to the first direction, so as to capture a second calibration dynamic image of the object by using the image sensor, and the second calibration dynamic image is analyzed to determine whether the deviation displacement vector of the at least one speckle remains converged within the predetermined range. If the deviation displacement vector of the at least one speckle remains converged within the predetermined range, the calibrated position of the diffusion sheet at the second calibration position is defined as the optimized position with the best light field uniformity. Otherwise, step (C4) is continued; and (C4) Repeating the steps (C1) to (C3) until the deviation displacement vector of the at least one speckle remains converged within the predetermined range, the corrected position of the diffusion sheet is defined as the optimized position with the best light field uniformity. A method for adjusting the position of an optimized diffuser of a Kohler illumination system as described in claim 2, wherein the step (C3) is to move the diffuser along the second direction opposite to the first direction to the second correction position when the vector magnitude of the deviation displacement vector of the at least one speckle in the step (C1) exceeds the predetermined range and the vector direction of the deviation displacement vector of the at least one speckle in the step (C1) is opposite to the vector direction of the deviation displacement vector measured when the diffuser is in the previous position. A method for optimizing the position adjustment of a diffuser of a Kohler illumination system as described in claim 2, wherein the step (C3) is to move the diffuser along the first direction to the second calibration position if the direction of the deviation displacement vector of the at least one speckle in the step (C1) is the same as the direction of the deviation displacement vector measured when the diffuser is in a previous position, but the magnitude of the deviation displacement vector of the at least one speckle in the step (C1) is smaller than the magnitude of the deviation displacement vector measured when the diffuser is in a previous position when the vector magnitude of the deviation displacement vector of the at least one speckle in the step (C1) exceeds the predetermined range. The method for optimizing the position adjustment of the diffuser of the Kohler illumination system as described in claim 2, wherein the step (C3) is to move the diffuser along the second direction opposite to the first direction to the second calibration position if the direction of the deviation displacement vector of the at least one speckle in the step (C1) is the same as the direction of the deviation displacement vector measured when the diffuser is in the previous position, but the deviation displacement vector of the at least one speckle in the step (C1) is greater than the vector magnitude of the deviation displacement vector measured when the diffuser is in the previous position when the vector magnitude of the deviation displacement vector exceeds the predetermined range. The method for optimizing the position adjustment of the diffuser of the Kohler illumination system as described in claim 2, wherein the diffuser moves along the first direction to approach the focusing lens, and the diffuser moves along the second direction to move away from the focusing lens. The method for optimizing the position adjustment of the diffuser of the Kohler illumination system as described in claim 2, wherein the diffuser moves along the first direction away from the light collecting lens, and the diffuser moves along the second direction toward the light collecting lens. The method for optimizing the position adjustment of the diffuser of the Kohler illumination system as described in claim 2, wherein the step (A) is to use a computer host electrically connected to the image sensor to perform image analysis on the initial dynamic image of the object under test, the step (C1) is to use the computer host to perform image analysis on the first corrected dynamic image, and the step (C3) is to use the computer host to perform image analysis on the second corrected dynamic image. As described in claim 2, the method for optimizing the position adjustment of the diffuser of the Kohler illumination system, wherein the first corrected dynamic image includes two first corrected static images, the two first corrected static images have a time difference between each other, and the second corrected dynamic image includes two second corrected static images, the two second corrected static images have a time difference between each other. The method for optimizing the position adjustment of the diffuser of the Kohler illumination system as described in claim 1, wherein the initial dynamic image of the object under test includes two initial static images, and the two initial static images have a time difference between each other.

Images