A machine vision-based contactless electroluminescent detection probe inclination angle adjusting device and method

Abstract

The application discloses a kind of based on machine vision's contactless electroluminescence detection probe inclination adjustment device and method, wherein device includes: for carrying detection probe's probe adjustment mechanism, probe adjustment mechanism includes the vertical rotation axis of control detection probe in X axis and / or Y axis direction is rotated and is used for the horizontal rotation axis of control detection probe in Z axis direction is rotated;Probe adjustment mechanism below is provided with machine vision unit, machine vision unit includes CCD camera, lens and light source, light source is used to irradiate detection probe, CCD camera and lens are used to collect the image of the bottom surface of detection probe, lens is parallel with the Micro-LED chip to be detected;Probe adjustment mechanism and machine vision unit are connected with control unit respectively;Control unit is used to carry out image processing to the image collected and generates angle adjustment instruction control probe adjustment mechanism adjusts detection probe.The application improves the precision and efficiency of probe adjustment, reduces the error of manual operation.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of detection, in particular to a contactless electroluminescence detection probe inclination adjustment device and method based on machine vision. BACKGROUND

[0002] Micro-LED is a microstructure of traditional LED, and the pixel size is generally not more than 50 μm. Each pixel can be independently positioned and individually lighted. Micro-LED is considered as a disruptive next-generation display technology as an important branch of LED technology. Detecting wafer-level Micro-LED chips to intercept bad pixels is a key link to improve the yield of Micro-LED display screens. At present, wafer-level Micro-LED detection is divided into contact detection and non-contact detection. Among them, contactless electroluminescence detection is considered as the most efficient and accurate detection method. This technology can not only avoid the problem of false high yield caused by photoluminescence detection, but also does not need to ensure the accurate contact between the probe and the chip, so the inspection speed is the fastest. Patent (202310674572.7) proposes a method for contactless mass detection of Micro-LED chips by using a probe structure. In the detection process, in order to ensure the uniformity of the applied electric field, the bottom surface of the detection probe needs to be parallel to the sample surface. However, in the prior art, the adjustment of the probe inclination relies on manual operation, and the precision and efficiency are low, and there is a large operation error. Therefore, an automatic and accurate probe inclination adjustment device and method are needed. SUMMARY

[0003] In view of the above part of the defects of the prior art, the technical problem to be solved by the present application is to provide a contactless electroluminescence detection probe inclination adjustment device and method based on machine vision, which aims to improve the precision and efficiency of probe adjustment, reduce the error of manual operation, and make the device suitable for high-precision requirements in Micro-LED contactless electroluminescence detection.

[0004] To achieve the above object, the application discloses a machine vision-based contactless electroluminescent detection probe inclination adjustment device, which comprises a probe adjustment mechanism for carrying a detection probe, the probe adjustment mechanism comprising a vertical rotation shaft and a horizontal rotation shaft, the vertical rotation shaft being used for controlling the detection probe to rotate in the X-axis and / or Y-axis direction, and the horizontal rotation shaft being used for controlling the detection probe to rotate in the Z-axis direction; a machine vision unit is arranged below the probe adjustment mechanism, the machine vision unit comprising a CCD camera, a lens and a light source, the light source being used for irradiating the detection probe, and the CCD camera and the lens being used for collecting an image of the bottom surface of the detection probe, the lens being parallel to a Micro-LED chip to be detected; and the probe adjustment mechanism and the machine vision unit are connected with a control unit respectively.

[0005] The inclination adjustment device is configured to: in response to the detection probe being mounted on the probe adjustment mechanism, control the light source to irradiate the bottom surface of the detection probe, and control the CCD camera to collect a first image of the bottom surface of the detection probe through the lens; perform image processing on the first image through the control unit to obtain the inclination of the detection probe in each direction; generate an angle adjustment instruction according to the inclination of the detection probe in each direction through the control unit; and control the probe adjustment mechanism to adjust the inclination angle of the detection probe according to the angle adjustment instruction, so that the bottom surface of the detection probe is parallel to the lens.

[0006] Optionally, when obtaining the inclination of the detection probe, the control unit is specifically configured to:

[0007] perform preprocessing on the image; wherein the preprocessing comprises graying and binarization;

[0008] take two end points on the edge arc of the bottom surface of the detection probe in the first image, the two end points being symmetrical and having luminance difference values within a preset range, and determine the arc with higher luminance between the two end points as a reference arc;

[0009] obtain the inclination θ z of the detection probe around the Z-axis according to the position of the reference arc in the first image;

[0010] calculate the inclination θ x of the detection probe around the X-axis or the inclination θ y of the detection probe around the Y-axis according to the arc height of the reference arc and the depth of field of the lens.

[0011] Optionally, the formula for obtaining the inclination θ y is wherein D is the depth of field of the lens, and H is the arc height of the reference arc.

[0012] Optionally, the light source in the machine vision unit is a ring-shaped LED light source, which is used to provide uniform and adjustable illumination to reduce shadow and reflection interference in the first image.

[0013] Optionally, the probe adjustment mechanism comprises an electric motor and a precision screw rod, and the electric motor is used to drive the precision screw rod to adjust the tilt angle.

[0014] Optionally, the probe adjustment mechanism further comprises a locking structure, which is used to lock the position of the detection probe after the tilt angle adjustment is completed, so as to prevent the detection probe from being deviated during the detection process.

[0015] The second aspect of the present application discloses a machine vision-based contactless electroluminescent detection probe tilt angle adjustment method, which is suitable for the tilt angle adjustment device described above, and the method comprises:

[0016] Step S1, the detection probe is installed on the probe adjustment mechanism, and the tilt angle adjustment device controls the light source to irradiate the bottom surface of the detection probe;

[0017] Step S2, the tilt angle adjustment device controls the CCD camera to collect a first image of the bottom surface of the detection probe through the lens;

[0018] Step S3, the CCD camera sends the first image to the control unit, so that the control unit processes the first image to obtain the tilt angle of the detection probe in each direction;

[0019] Step S4, the control unit generates an angle adjustment instruction according to the tilt angle of the detection probe in each direction;

[0020] Step S5, the control unit sends the adjustment instruction to the probe adjustment mechanism, so that the probe adjustment mechanism adjusts the tilt angle of the detection probe according to the angle adjustment instruction;

[0021] Step S6, the tilt angle adjustment device determines that the adjustment is completed in response to the bottom surface of the detection probe being parallel to the lens.

[0022] Optionally, in step S3, the control unit processes the first image to obtain the tilt angle of the detection probe in each direction, which comprises:

[0023] The control unit pre-processes the image; wherein the pre-processing comprises grayscale and binarization;

[0024] The control unit takes two end points on the edge arc of the bottom surface of the detection probe in the first image, the end points have brightness difference in a preset range and are symmetrical, and determines the arc line brighter between the end points as a reference arc;

[0025] The control unit obtains the inclination angle θ z of the detection probe around the Z axis according to the position of the reference arc in the first image

[0026] The control unit calculates the inclination angle θ x of the detection probe around the X axis or the inclination angle θ y of the detection probe around the Y axis according to the arc height of the reference arc and the depth of field of the lens.

[0027] Optionally, the formula for obtaining the inclination angle θ y is as follows Wherein, D is the depth of field of the lens, and H is the arc height of the reference arc.

[0028] The present application has the following advantages: the present application completes the adjustment of the inclination angle of the probe through the machine vision unit, the control unit and the probe adjustment mechanism, reduces the manual intervention, and improves the efficiency and consistency of the adjustment. The device and method are suitable for various precision detection occasions, especially in the Micro-LED non-contact electroluminescence detection, can make the electric field applied by the probe more uniform, and avoid the misjudgment caused by the non-uniform electric field due to the non-parallelism between the probe and the sample surface. The present application integrates machine vision technology and automatic control technology, provides a high-efficiency, accurate and automatic probe inclination angle adjustment solution for Micro-LED non-contact electroluminescence detection, and has wide application prospect and significant technical advantages. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a structural schematic diagram of a non-contact electroluminescence detection probe inclination angle adjustment device based on machine vision provided by an embodiment of the present application;

[0030] Figure 2 is a schematic diagram of different inclination angles of a detection probe provided by an embodiment of the present application;

[0031] Figure 3 is a non-contact electroluminescence detection probe inclination angle calculation diagram based on machine vision provided by an embodiment of the present application;

[0032] Figure 4 is a non-contact electroluminescence detection probe inclination angle adjustment flowchart based on machine vision provided by an embodiment of the present application;

[0033] Figure 5 is an image processing algorithm flowchart provided by an embodiment of the present application;

[0034] Figure 6 is a probe bottom surface graph collected by a CCD before adjustment of a detection probe provided by an embodiment of the present application;

[0035] Figure 7 is a probe bottom surface gray scale graph collected by a CCD before adjustment of a detection probe provided by an embodiment of the present application;

[0036] Figure 8 is a probe bottom surface binary graph collected by a CCD before adjustment of a detection probe provided by an embodiment of the present application;

[0037] Figure 9 is a calculation graph of a probe inclination angle θZ and θY provided by an embodiment of the present application;

[0038] Figure 10 is a probe bottom surface graph collected by a CCD after adjustment of a detection probe provided by an embodiment of the present application;

[0039] Figure 11 is a probe bottom surface gray scale graph collected by a CCD after adjustment of a detection probe provided by an embodiment of the present application;

[0040] Figure 12 is a probe bottom surface binary graph collected by a CCD after adjustment of a detection probe provided by an embodiment of the present application;

[0041] Figure 13 is a flowchart of a non-contact electroluminescent detection probe inclination angle adjustment method based on machine vision provided by an embodiment of the present application. DETAILED DESCRIPTION

[0042] The present application discloses a non-contact electroluminescent detection probe inclination angle adjustment method based on machine vision, and those skilled in the art can refer to the content herein and appropriately improve technical details for implementation. It is particularly important to note that all similar substitutions and changes are obvious to those skilled in the art, and they are considered to be included in the present application. The method and application of the present application have been described by the preferred embodiments, and the relevant personnel can obviously modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit and scope of the present application, to realize and apply the present application technology.

[0043] The applicant has found that in the prior art, the adjustment of the probe inclination angle in the non-contact detection of wafer-level Micro-LEDs relies on manual operation, has low precision and efficiency, and has a large operation error.

[0044] Therefore, the embodiment of the present application provides a non-contact electroluminescent detection probe inclination angle adjustment device based on machine vision, as shown in Figure 1As shown, the tilt adjustment device includes: a probe adjustment mechanism for mounting a detection probe, the probe adjustment mechanism including a vertical rotation axis and a horizontal rotation axis, the vertical rotation axis for controlling the rotation of the detection probe in the X-axis and / or Y-axis direction, and the horizontal rotation axis for controlling the rotation of the detection probe in the Z-axis direction; a machine vision unit is arranged below the probe adjustment mechanism, the machine vision unit including a CCD camera, a lens and a light source, the light source for illuminating the detection probe, the CCD camera and lens for acquiring images of the bottom surface of the detection probe, and the lens being parallel to the Micro-LED chip to be detected; the probe adjustment mechanism and the machine vision unit are respectively connected to the control unit.

[0045] The tilt adjustment device is configured to: respond to the detection probe being mounted on the probe adjustment mechanism, control the light source to illuminate the bottom surface of the detection probe, control the CCD camera to acquire a first image of the bottom surface of the detection probe through the lens; perform image processing on the first image through the control unit to obtain the tilt angle of the detection probe in various directions; generate angle adjustment commands through the control unit based on the tilt angle of the detection probe in various directions; and control the probe adjustment mechanism to adjust the tilt angle of the detection probe according to the angle adjustment commands so that the bottom surface of the detection probe is parallel to the lens.

[0046] It should be noted that the vertical and horizontal rotation axes are set separately and rotate independently.

[0047] In another specific embodiment, the lens is parallel to the device under test.

[0048] It should be noted that aligning the lens with the Micro-LED chip under test (the device under test) ensures that the bottom surface of the adjusted detection probe is parallel to the Micro-LED chip (the device under test).

[0049] In this specific embodiment, the control unit is specifically configured to, when obtaining the tilt angle of the detection probe:

[0050] The image is preprocessed; the preprocessing includes grayscale conversion and binarization.

[0051] In the first image, two symmetrical endpoints with a brightness difference within a preset range are selected on the edge arc of the probe bottom surface, and the brighter arc between the endpoints is determined as the reference arc; there are two arcs between the endpoints, one darker and one brighter.

[0052] Based on the position of the reference arc in the first image, the tilt angle θ of the detection probe around the Z-axis is obtained. z ;

[0053] Based on the arc height of the reference arc and the depth of field of the lens, the tilt angle θ of the detection probe around the X-axis is calculated. x Or detect the tilt angle θ of the probe around the Y-axis. y .

[0054] Further, the inclination angle θ y The formula is Wherein, D is the depth of field of the lens, and H is the arc height of the reference arc.

[0055] It should be noted that the embodiment of the present application can process the image in the above manner, and then obtain the inclination angle of the detection probe. This processing method is accurate and efficient, which effectively improves the image processing efficiency of the embodiment of the present application.

[0056] In this specific embodiment, as shown in Figure 2 The inclination angles formed by the probe around different axes will have different imaging in the machine vision system. Figure 2 The semicircle in the middle can be a reference arc and its endpoint connecting line, Figure 2 The three inclination angles and their imaging in the first image are shown.

[0057] In this specific embodiment, as shown in Figure 3 Different inclination angle adjustments can be made by first adjusting the inclination angle θ z around the Z axis, and then adjusting the inclination angle θ y around the Y axis.

[0058] In another specific embodiment, different inclination angle adjustments can be made by first adjusting the inclination angle θ z around the Z axis, and then adjusting the inclination angle θ x around the X axis. Figure 3 Wherein, D is the depth of field of the lens, and H is the arc height of the reference arc.

[0059] In this specific embodiment, the adjustment steps of the inclination angle adjustment device of the embodiment of the present application are as shown in Figure 4 The overall adjustment steps are as follows: (1) install the probe on the probe adjustment mechanism, and visually perpendicular; (2) control the machine vision system to obtain the probe bottom surface image information; (3) the control unit calculates the inclination angles of the probe around the Z axis and the Y axis through image processing algorithm; (4) the control unit of the probe adjustment mechanism generates adjustment instructions to control the probe adjustment mechanism to adjust the inclination angle. (5) adjustment is completed.

[0060] In another specific embodiment, as shown in Figure 5 The image processing algorithm flow is as follows: (1) read the probe bottom surface image; (2) pre-process the image, including grayscale and binarization; (3) find the outer contour of the image; (4) fit the outer contour arc; (5) calculate the inclination angles around the Z axis and the Y axis, respectively.

[0061] In a specific application process, Figure 6 is the detection probe bottom surface image before adjustment (i.e., the first image without processing). Figure 7The gray scale image of the detection probe bottom surface image before adjustment. Figure 8 The binary image of the gray scale image of the detection probe bottom surface image before adjustment. Figure 6 、 Figure 7 and Figure 8 The schematic of the same detection probe bottom surface image at different processing stages.

[0062] As Figure 9 shown, the outer contour arc (reference arc) is fitted after image algorithm processing, and the inclination angles θ z = 92.9° and θ y = 2.83° are calculated. Figure 9 A and B are two endpoints with coordinates for calculating the inclination angles θ z = 92.9° and θ y = 2.83°, the arc with brighter A and B two endpoints is the reference arc, D is the depth of field of the lens, H is the arc height of the reference arc, and pixelsize is the pixel size.

[0063] Figure 10 The detection probe bottom surface image after adjustment (i.e., the first image without processing). Figure 11 The gray scale image of the detection probe bottom surface image after adjustment. Figure 12 The binary image of the gray scale image of the detection probe bottom surface image after adjustment. Figure 10 、 Figure 11 and Figure 12 The schematic of the same detection probe bottom surface image at different processing stages.

[0064] In this specific embodiment, the light source in the machine vision unit is a ring-shaped LED light source, which is used to provide uniform and adjustable illumination to reduce shadow and reflection interference in the first image.

[0065] It should be noted that the light source is first used to provide illumination for the detection probe. Secondly, the ring-shaped LED light source is more uniform, which reduces the shadow and reflection interference in the first image and improves the quality of the first image.

[0066] In this specific embodiment, the probe adjustment mechanism includes an electric motor and a precision screw, and the electric motor is used to drive the precision screw to adjust the inclination angle.

[0067] The precision screw can be a vertical rotation shaft and a horizontal rotation shaft. The electric control is more accurate and convenient.

[0068] In this specific embodiment, the probe adjustment mechanism further includes a locking structure, which is used to lock the position of the detection probe after completing the inclination angle adjustment to prevent the detection probe from being deviated during the detection process.

[0069] The embodiment of the present application also provides a machine vision-based contactless electroluminescent detection probe inclination angle adjusting method, which is suitable for the inclination angle adjusting device. Figure 13 As shown in the figure, the method comprises the following steps:

[0070] In step S1, the detection probe is installed on the probe adjusting mechanism, and the inclination angle adjusting device controls the light source to irradiate the bottom surface of the detection probe;

[0071] In step S2, the inclination angle adjusting device controls the CCD camera to collect a first image of the bottom surface of the detection probe through the lens;

[0072] In step S3, the CCD camera sends the first image to the control unit, so that the control unit processes the first image to obtain the inclination angle of the detection probe in each direction;

[0073] In step S4, the control unit generates an angle adjusting instruction according to the inclination angle of the detection probe in each direction;

[0074] In step S5, the control unit sends the adjusting instruction to the probe adjusting mechanism, so that the probe adjusting mechanism adjusts the inclination angle of the detection probe according to the angle adjusting instruction;

[0075] In step S6, the inclination angle adjusting device determines that the adjustment is completed in response to the bottom surface of the detection probe being parallel to the lens.

[0076] In this specific embodiment, the processing of the first image by the control unit in step S3 to obtain the inclination angle of the detection probe in each direction comprises the following steps:

[0077] The control unit pre-processes the image; wherein the pre-processing comprises graying and binarization;

[0078] The control unit detects two end points on the edge arc of the bottom surface of the detection probe in the first image, wherein the two end points are symmetrical and have luminance difference values within a preset range, and determines the arc with higher luminance between the two end points as a reference arc;

[0079] The control unit obtains the inclination angle θ z of the detection probe around the Z axis according to the position of the reference arc in the first image;

[0080] The control unit calculates the inclination angle θ x of the detection probe around the X axis or the inclination angle θ y of the detection probe around the Y axis according to the arc height of the reference arc and the depth of field of the lens.

[0081] In this specific embodiment, the formula for obtaining the inclination angle θ y is as follows: Wherein, D is the depth of field of the lens, and H is the arc height of the reference arc.

[0082] The embodiment of the present application adjusts the probe inclination angle through the machine vision unit, the control unit and the probe adjustment mechanism, reduces manual intervention, and improves the efficiency and consistency of the adjustment. The device and method are suitable for various precision detection occasions, especially in Micro-LED non-contact electroluminescence detection, can make the electric field applied by the probe more uniform, and avoid the misjudgment caused by the uneven electric field due to the non-parallelism between the probe and the sample surface. The embodiment of the present application integrates machine vision technology and automatic control technology, provides an efficient, accurate and automatic probe inclination angle adjustment solution for Micro-LED non-contact electroluminescence detection, and has wide application prospect and significant technical advantages.

[0083] It should be noted that, in this document, relational terms such as first and second and the like can be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without limitation, an element preceded by "comprises... a" does not, without more constraints, foreclose the existence of additional identical elements in the process, method, article, or apparatus.

[0084] Each of the embodiments in the specification is described in a relevant manner, and the same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the difference from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the part of the method embodiment.

[0085] The above only describes the preferred embodiments of the present application, and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A machine vision-based contactless electroluminescent detection probe inclination angle adjustment device, characterized by, The inclination adjustment device comprises a probe adjustment mechanism for carrying the detection probe, the probe adjustment mechanism comprising a vertical rotation shaft for controlling the detection probe to rotate in the X-axis and / or Y-axis direction and a horizontal rotation shaft for controlling the detection probe to rotate in the Z-axis direction; a machine vision unit is arranged below the probe adjustment mechanism, the machine vision unit comprising a CCD camera, a lens and a light source, the light source being used for irradiating the detection probe, the CCD camera and the lens being used for collecting the image of the bottom surface of the detection probe, and the lens being parallel to the Micro-LED chip to be detected; the probe adjustment mechanism and the machine vision unit are connected with a control unit respectively; The inclination adjustment device is configured to: in response to the detection probe being mounted on the probe adjustment mechanism, control the light source to irradiate the bottom surface of the detection probe, and control the CCD camera to collect a first image of the bottom surface of the detection probe through the lens; perform image processing on the first image through the control unit to obtain the inclination of the detection probe in each direction; generate an angle adjustment instruction according to the inclination of the detection probe in each direction through the control unit; and control the probe adjustment mechanism to adjust the inclination angle of the detection probe according to the angle adjustment instruction, so that the bottom surface of the detection probe is parallel to the lens; The control unit is specifically configured to: perform preprocessing on the image; wherein the preprocessing comprises grayscale and binarization; take two end points on the edge arc line of the bottom surface of the detection probe in the first image, the two end points being symmetrical and having two luminance difference values within a preset range, and determine the arc line between the two end points that is brighter as a reference arc; According to the position of the reference arc in the first image, the tilt angle of the detection probe around the Z axis is obtained ; According to the arc height of the reference arc and the depth of field of the lens, the inclination angle of the detection probe around the X axis is calculated or the inclination angle of the detection probe around the Y axis ; wherein the inclination angle is obtained The formula is ; wherein, is the depth of field of the lens, is the arc height of the reference arc. 2.The machine vision based contactless electroluminescent detection probe inclination angle adjustment device according to claim 1, wherein, The light source in the machine vision unit is a ring-shaped LED light source, which is used to provide uniform and adjustable illumination to reduce shadow and reflection interference in the first image. 3.The machine vision based contactless electroluminescent detection probe inclination angle adjustment device according to claim 1, wherein, The probe adjustment mechanism comprises an electric motor and a precision screw, and the electric motor is used to drive the precision screw to adjust the inclination.

4. The machine vision based contactless electroluminescent detection probe angle of inclination adjustment device according to claim 1, characterized in that, The probe adjustment mechanism further comprises a locking structure, which is used to lock the position of the detection probe after completing the inclination adjustment, so as to prevent the detection probe from being deviated in the detection process.

5. A machine vision-based contactless electroluminescent detection probe inclination angle adjustment method, applicable to the inclination angle adjustment device of any one of claims 1-4, characterized in that, The method comprises: Step S1, mounting the detection probe on the probe adjustment mechanism, and controlling the light source of the inclination adjustment device to irradiate the bottom surface of the detection probe; Step S2, controlling the CCD camera of the inclination adjustment device to collect a first image of the bottom surface of the detection probe through the lens; Step S3, sending the first image to the control unit by the CCD camera, so that the control unit performs image processing on the first image to obtain the inclination of the detection probe in each direction; Step S4, generating an angle adjustment instruction according to the inclination of the detection probe in each direction by the control unit; Step S5, the control unit sends the adjustment instruction to the probe adjustment mechanism, so that the probe adjustment mechanism adjusts the tilt angle of the detection probe according to the angle adjustment instruction; Step S6, the tilt angle adjustment device determines that the adjustment is completed in response to the detection probe bottom surface being parallel to the lens; The image processing of the first image by the control unit in the step S3 includes: The control unit pre-processes the image; wherein the pre-processing includes graying and binarization; The control unit takes two end points on the edge arc of the detection probe bottom surface in the first image, which have a brightness difference within a preset range and are symmetrical, and determines the arc line brighter between the end points as a reference arc; The control unit obtains the inclination angle of the detection probe around the Z axis according to the position of the reference arc in the first image ; The control unit calculates the tilt angle of the detection probe around the X-axis based on the arc height of the reference arc and the depth of field of the lens. Or the tilt angle of the detection probe around the Y-axis ; wherein the inclination angle is obtained The formula is ; wherein, is the depth of field of the lens, is the arc height of the reference arc.

Images