System and method for aligning the optical axis of an optical assembly perpendicular to the surface of a workpiece using multi-point autofocus

Abstract

To align the optical axis of an optical assembly portion to a workpiece surface vertically.SOLUTION: A metrology system includes an optical assembly portion; an adjustment mechanism configured to change a distance and an angular orientation between the optical assembly portion and a workpiece surface; and a processor. The processor is configured to: control the adjustment mechanism to move the optical assembly portion to position a workpiece surface within a focal Z autofocus range; capture an image stack of the workpiece surface wherein each image of the image stack corresponds to a different autofocus height; determine an autofocus height for at least three locations of the workpiece surface; control the adjustment mechanism based on the autofocus heights to rotate the optical assembly portion relative to the workpiece surface to nominally align an optical axis of the optical assembly portion with a surface normal of the workpiece surface and adjust a distance between the optical assembly portion and the workpiece surface; and execute a defined operation on the workpiece surface.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to precision measurement, and more specifically, to aligning an optical axis perpendicular to a workpiece surface using multi-point autofocus to improve the accuracy of subsequent operations (such as measurement operations) performed on the workpiece surface.

Background Art

[0002] Precision measurement systems such as precision machine vision inspection systems (or simply "vision systems") can be used to obtain precise dimensional measurements of objects and to inspect various other object features, and may include a computer, a camera, an optical system, and a precision stage that moves to enable traversal and inspection of a workpiece. One exemplary prior art system is the QUICK VISION® series of PC-based vision systems and QVPAK® software available from Mitutoyo America Corporation (MAC) located in Aurora, Illinois. The functions and operations of the QUICK VISION® series of vision systems and QVPAK® software are generally described, for example, in the QVPAK 3D CNC Image Measuring Machine User Guide published in January 2003. This is hereby incorporated by reference in its entirety into the present application. This type of system utilizes a microscope-type optical system and moves the stage to provide inspection images of small or relatively large workpieces.

[0003] General-purpose precision machine vision inspection systems are generally programmable to perform automated video inspection. Such systems typically include selectable operating modes and GUI functions and predefined image analysis "video tools" so that "non-expert" operators can perform operations and programming. For example, U.S. Patent No. 6,542,180 teaches a vision system that utilizes automated video inspection including the use of various video tools.

[0004] A variable focal length (VFL) optical system can be used for observing and precisely measuring surface heights and can be incorporated, for example, into a precision machine vision inspection system or other optical systems as disclosed in U.S. Patent No. 9,143,674. Briefly stated, a VFL lens can acquire multiple images at multiple focal lengths. Various types of VFL lenses are known, for example, a mechanical VFL lens that mechanically moves a multi-lens system to change its focal length, or a non-mechanical VFL lens such as a tunable acoustic gradient (TAG) lens that generates a lens effect using sound waves in a fluid medium (to change the focal length). A VFL lens in a precision machine vision inspection system can be used, for example, to acquire images of a workpiece at multiple surface heights, i.e., "Z heights," of a machine coordinate system (MCS). SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0005] Such a configuration often enables only the execution of a specific type of operation (e.g., acquisition of an image stack) from a single orientation (e.g., along the Z-axis of the MCS). There is a desire for a system that can provide improvements to such operations (e.g., with respect to workpieces having inclined and / or complex surfaces).

[0006] This summary is presented to introduce, in a simplified form, some concepts that are further described below in the "DETAILED DESCRIPTION OF THE INVENTION." This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used to determine the scope of the claimed subject matter. MEANS FOR SOLVING THE PROBLEMS

[0007] According to one aspect, a measurement system is provided that includes an optical assembly unit, an adjustment mechanism, one or more processors, and a memory coupled to the one or more processors and storing program instructions.

[0008] The optical assembly unit includes a light source, an objective lens that inputs image light generated from the surface of a workpiece illuminated by the light source and transmits the image light along an imaging optical path, the objective lens defining an optical axis of the optical assembly unit that extends at least between the objective lens and the workpiece surface, and a camera that receives the imaging light transmitted along the imaging optical path and provides an image of the workpiece surface.

[0009] The adjustment mechanism is configured to change the distance between the optical assembly unit and the workpiece surface and further to rotate the optical assembly unit with respect to the workpiece surface to change the angular orientation of the optical axis of the optical assembly unit with respect to the workpiece surface.

[0010] When the program instructions stored in the memory are executed by the one or more processors, control the adjustment mechanism to move the optical assembly unit so as to place the workpiece surface within the autofocus range of focus Z of the optical assembly unit; capture an image stack of the workpiece surface within the autofocus range of focus Z using the optical assembly unit, the image stack including a plurality of images of the workpiece surface, each image of the image stack corresponding to a different autofocus height; determine the autofocus heights of at least three positions on the workpiece surface based on at least three corresponding regions of interest of the captured image stack; control the adjustment mechanism to rotate the optical assembly unit with respect to the workpiece surface so as to nominally align the optical axis of the optical assembly unit with the surface normal of the workpiece surface and further to adjust the distance between the optical assembly unit and the workpiece surface, based at least in part on the autofocus heights of the at least three positions. Performing a defined operation on the workpiece surface and causing one or more processors to execute it.

[0011] According to another aspect, the optical assembly further includes a variable focal length (VFL) lens included in the imaging optical path. The objective lens transmits image light along the imaging optical path via the VFL lens. The camera receives the imaging light transmitted by the VFL lens along the imaging optical path. The VFL lens can be a variable acoustic refractive index distribution type (TAG) lens configured to non-mechanically vary the focal length. By periodically changing the optical power of the TAG lens, the periodically changed focusing position of the optical assembly is controlled. The defined operation performed on the workpiece surface may include using the VFL lens to capture one or more images of the workpiece surface. The defined operation performed on the workpiece surface may include using the VFL lens to capture an image stack while nominally aligning the optical axis of the optical assembly with the surface normal of the workpiece surface. The image stack includes a plurality of images of the workpiece surface, and each image of the image stack corresponds to a different focusing position of the optical assembly along the direction of the optical axis.

[0012] According to another aspect, determining the autofocus height at at least three positions on the workpiece surface includes determining the focus curve data of each region of interest based at least in part on the analysis of the images of the image stack. At each of the at least three positions, the peak of the focus curve data of the corresponding region of interest indicates the corresponding autofocus height.

[0013] According to another aspect, when the program instructions are executed by one or more processors, determining the surface normal of the workpiece surface based at least in part on the autofocus height at at least three positions, and determining adjustment information for controlling an adjustment mechanism to rotate the optical assembly based at least in part on the determined surface normal. Cause it to be executed by one or more additional processors.

[0014] According to another aspect, the defined operation may include a measurement operation for determining dimensions of elements on the workpiece surface.

[0015] According to another aspect, the defined operation is obtaining an image stack including a plurality of images, each image corresponding to a focusing position of an optical assembly along an imaging optical axis that coincides with the optical axis, and obtaining the image stack; determining focus curve data indicating three-dimensional positions of a plurality of surface points on the workpiece surface, based at least in part on an analysis of the images in the image stack; and a point-from-focus (PFF) operation including the above.

[0016] According to another aspect, the defined operation may include a machining operation performed on the workpiece surface. The machining axis of the machining operation is at least one of nominally coinciding with or nominally parallel to the optical axis of the optical assembly.

[0017] According to another aspect, the adjustment mechanism may include a rotation mechanism and a Z-axis movement mechanism. The Z-axis movement mechanism is coupled to move the optical assembly along the Z-axis direction. The rotation mechanism is coupled between the Z-axis movement mechanism and the optical assembly and is configured to rotate the optical assembly relative to the workpiece surface to change the angular orientation of the optical axis of the optical assembly relative to the workpiece surface. The measurement system may be embodied in a precision machine vision inspection system. The adjustment mechanism includes a rotary stage, and the rotary stage includes a rotation mechanism and is coupled between the Z-axis movement mechanism and the optical assembly.

[0018] According to another aspect, the measurement system may be embodied in a coordinate measuring machine system. The adjustment mechanism An x-axis slide mechanism, a y-axis slide mechanism, and a z-axis slide mechanism configured to move an optical assembly unit in the x-axis, y-axis, and z-axis directions that are mutually orthogonal in a machine coordinate system, A rotation mechanism configured to rotate the optical assembly unit with respect to the workpiece surface, and includes.

[0019] According to another aspect, the measurement system can be embodied in a robot system. The adjustment mechanism is included in a robot arm having at least three degrees of freedom for moving the optical assembly unit.

[0020] According to yet another aspect, a method for operating a measurement system including an optical assembly unit is provided. The optical assembly unit a light source, an objective lens that inputs image light generated from the surface of a workpiece illuminated by the light source and transmits the image light along an imaging optical path, the objective lens defining an optical axis of the optical assembly unit that extends at least between the objective lens and the workpiece surface, a camera that receives the imaging light transmitted along the imaging optical path and provides an image of the workpiece surface, and includes.

[0021] This method includes moving the optical assembly unit to place the workpiece surface within the autofocus range of focus Z of the optical assembly unit, capturing an image stack of the workpiece surface within the autofocus range of focus Z using the optical assembly unit, the image stack including a plurality of images of the workpiece surface, each image of the image stack corresponding to a different autofocus height, determining the autofocus height of at least three positions of the workpiece surface based on at least three corresponding regions of interest of the image stack, To rotationally align the optical assembly unit with respect to the workpiece surface so that the optical axis of the optical assembly unit is nominally aligned with the surface normal of the workpiece surface, at least partially based on the autofocus heights at at least three positions, and further to determine adjustment information for adjusting the distance between the optical assembly unit and the workpiece surface, To rotationally align the optical axis of the optical assembly unit with the surface normal of the workpiece surface, and further to use adjustment information for adjusting the distance between the optical assembly unit and the workpiece surface, To perform a defined operation on the workpiece surface, including.

[0022] According to another aspect, the method further includes determining the surface normal of the workpiece surface at least partially based on the autofocus heights at at least three positions, and the adjustment information is determined at least partially based on the determined surface normal.

[0023] According to another aspect, the workpiece surface is the first workpiece surface of the workpiece, and after performing the defined operation on the first workpiece surface, the method includes Moving the optical assembly unit to place the second workpiece surface of the workpiece within the focus Z autofocus range of the optical assembly unit, Capturing an image stack of the second workpiece surface within the focus Z autofocus range using the optical assembly unit, where the image stack includes a plurality of images of the second workpiece surface, and each image of the image stack corresponds to a different autofocus height, Determining the autofocus heights at at least three positions of the second workpiece surface based on at least three corresponding regions of interest of the image stack, Rotating the optical assembly relative to the second workpiece surface to nominally align the optical axis of the optical assembly with the surface normal of the second workpiece surface, at least partially based on the autofocus height at at least three positions, and further determining adjustment information for adjusting the distance between the optical assembly and the second workpiece surface. Rotating the optical assembly to nominally align the optical axis of the optical assembly with the surface normal of the second workpiece surface, and further using adjustment information for adjusting the distance between the optical assembly and the second workpiece surface. Performing a defined operation on the second workpiece surface. Further comprising.

[0024] According to yet another aspect, a measurement system is provided. The measurement system includes an optical assembly, a Z-axis movement mechanism configured to change the distance between the optical assembly and the workpiece surface, a rotation mechanism configured to rotate the optical assembly relative to the workpiece surface to change the angular orientation of the optical axis of the optical assembly relative to the workpiece surface, one or more processors, and a memory coupled to the one or more processors and storing program instructions.

[0025] The optical assembly includes a variable focal length (VFL) lens, a light source, and an objective lens that receives image light generated from the surface of the workpiece illuminated by the light source and transmits the image light along an imaging optical path passing through the VFL lens, the objective lens defining the optical axis of the optical assembly that extends at least between the objective lens and the workpiece surface, and a camera that receives the imaging light transmitted by the VFL lens along the imaging optical path and provides an image of the workpiece surface.

[0026] When the program instructions stored in the memory are executed by one or more processors, Controlling the Z-axis movement mechanism or the rotation mechanism to move the optical assembly to place the workpiece surface within the autofocus Z range of the optical assembly. Capturing an image stack of the workpiece surface within the automatic focus range of the optical assembly along the Z-axis, wherein the image stack includes a plurality of images of the workpiece surface, and each image of the image stack corresponds to a different autofocus height; Determining the autofocus heights of at least three positions on the workpiece surface based on at least three corresponding regions of interest in the image stack; Based at least in part on the autofocus heights of the at least three positions, controlling a rotation mechanism to rotate the optical assembly with respect to the workpiece surface so as to nominally align the optical axis of the optical assembly with the surface normal of the workpiece surface, and further controlling a Z-axis movement mechanism to adjust the distance between the optical assembly and the workpiece surface; Performing a specified operation on the workpiece surface; Causing one or more processors to execute.

[0027] Thus, according to the principles disclosed in the present invention, a system and method are provided that include using multi-point autofocus to nominally align the optical axis of an optical assembly perpendicular to any workpiece surface. The system and method can quickly perform multi-point autofocus on the workpiece surface to derive adjustment information necessary to adjust the optical axis of the optical assembly nominally perpendicular to the workpiece surface. The system and method are useful when inspecting various types of workpiece surfaces, such as freeform workpiece surfaces (e.g., turbine blades) where the surface normal varies constantly along various portions of the surface or across various surfaces, because the optical axis is (re)-oriented nominally perpendicular to the workpiece surface. The system and method are also useful for automatically aligning / placing the workpiece surface for subsequent non-optical operations, such as machining (e.g., milling) operations performed on the workpiece surface. In this case, the machining operation axis coincides with the optical axis. BRIEF DESCRIPTION OF THE DRAWINGS

[0028]

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BEST MODE FOR CARRYING OUT THE INVENTION

[0029] FIG. 1 is a block diagram of one exemplary machine vision inspection system 10 that can be used as or includes a VFL(TAG) lens system (also referred to herein as an imaging system) according to the present disclosure. Machine vision inspection system 10 includes an image measuring machine 12 operably connected to exchange data and control signals with a control computer system 14. Control computer system 14 is further operably connected to exchange data and control signals with a monitor or display 16, a printer 18, a joystick 22, a keyboard 24, and a mouse 26. Monitor or display 16 can display a user interface suitable for controlling and / or programming the operation of machine vision inspection system 10. In various embodiments, it will be appreciated that any one or all of the functions of elements 14, 16, 22, 24, and 26 can be substituted and / or redundantly provided by, for example, a touch screen tablet. Various embodiments of machine vision inspection system 10 are also described in U.S. Pat. Nos. 7,454,053, 7,324,682, 8,111,905, and 8,111,938, which are assigned to the present applicant.

[0030] It will be appreciated by those skilled in the art that the control computer system 14 can generally be implemented using any suitable computing system or device, including, for example, a distributed or networked computing environment. Such a computing system or device can include one or more general-purpose processors or special-purpose processors (e.g., non-custom or custom devices) that execute software to implement the functions described herein. The software can be stored in a memory such as random access memory (RAM), read-only memory (ROM), flash memory, or a combination of such components. Additionally, the software can be stored in one or more storage devices such as optical-based disks, flash memory devices, or any other type of non-volatile storage medium for storing data. The software can include one or more program modules that include routines, programs, objects, components, data structures, etc., that perform specific tasks or implement specific abstract data types. In a distributed computing environment, the functionality of the program modules can be combined or distributed across multiple computing systems or devices in either a wired or wireless configuration and accessed via service calls.

[0031] The image measuring machine 12 includes a movable workpiece stage 32 and an optical imaging system 34 that can include a zoom lens or an interchangeable objective lens. The zoom lens or interchangeable objective lens generally provides various magnifications to the image obtained by the optical imaging system 34. As will be described in detail below with reference to FIGS. 2A and 2B, the optical imaging system 34 can include an optical assembly portion 205 (which can include, for example, a zoom lens and / or an interchangeable objective lens), and in some embodiments, this can be coupled to a rotary stage 297.

[0032] FIG. 2A is a block diagram of a control system unit 120 and a vision component unit 200 of a machine vision inspection system 100 that includes some of the features described herein, similar to the machine vision inspection system of FIG. 1. As will be described in detail below, the control system unit 120 is used to control the vision component unit 200. The vision component unit 200 includes an optical assembly unit 205, light sources 220, 230, 240 (which can be part of the optical assembly unit 205 or provided separately from the optical assembly unit 205), and a workpiece stage 210 having a transparent portion 212 at the center. The workpiece stage 210 (corresponding to the workpiece stage 32 of FIG. 1) is controllably movable along X and Y axes that are in a plane generally parallel to the surface of the stage on which the workpiece 20 is placed. The optical assembly unit 205, which may include at least a portion of the light sources 220, 230, 240, further includes a camera system 260, an interchangeable objective lens 250, and a variable focal length (VFL) lens 270.

[0033] One type of known VFL lens is a variable acoustic refractive index distribution type (「TAG」) lens that generates a lens effect using sound waves in a fluid medium. By applying an electric field at the resonance frequency to a piezoelectric tube surrounding the fluid medium, sound waves can be generated, creating a profile of density and refractive index that varies over time within the lens's fluid. This changes the refractive power of the lens, thereby altering the focal length (or effective focusing position) of the optical system. Using a TAG lens, a range of focal lengths can be periodically swept (i.e., its refractive power can be periodically changed) at high speeds, for example, at a resonance frequency higher than 30 kHz, or higher than 70 kHz, or higher than 100 kHz, or higher than 400 kHz, up to a maximum of 1.0 MHz. Such lenses can be understood in detail from "High speed varifocal imaging with a tunable acoustic gradient index of refraction lens" (Optics Letters, Vol. 33, No. 18, September 15, 2008). The TAG lens and the associated controllable signal generator are available, for example, from Mitutoyo Corporation (Kanagawa, Japan). As a specific example, the SR38 series of TAG lenses can be periodically modulated at a modulation frequency of up to 1.0 MHz. The operating principle and various features of the TAG lens are described in more detail in U.S. Patents Nos. 9,930,243, 9,736,355, 9,726,876, 9,143,674, 8,194,307, and 7,627,162, as well as U.S. Patent Publication Nos. 2017 / 0078549 and 2018 / 0143419. A TAG lens with a high-speed variable focus imaging function is particularly suitable for use as the VFL lens 270 to perform high-speed autofocusing according to various embodiments. Instead of a TAG lens, a mechanical VFL lens that mechanically moves a multi-lens system to change its focal length can also be used as the VFL lens 270.

[0034] In various embodiments, the optical assembly 205 may further include a turret lens assembly 223 having lenses 226 and 228. Instead of a turret lens assembly, in various embodiments, a fixed or manually replaceable magnification-altering lens, or a zoom lens configuration, etc. may be included. In various embodiments, the interchangeable objective lens 250 can be selected from a set of fixed magnification objective lenses (e.g., a set of objective lenses corresponding to magnifications such as 0.5x, 1x, 2x or 2.5x, 5x, 7.5x, 10x, 20x or 25x, 50x, 100x, etc.) included as part of the variable magnification lens section.

[0035] The optical assembly 205 can be controllably moved along the Z-axis (i.e., the Z-axis) of the MCS, which is generally orthogonal to the X-axis and Y-axis (i.e., the X-axis and Y-axis) of the MCS, by using a controllable motor 294. The controllable motor 294 drives an actuator to move the optical assembly 205 along the Z-axis. M axis and Y M axis) of the MCS. M axis) of the MCS. MMove along the axis (for example, this can change the distance between the optical assembly 205 and the workpiece 20, and thereby also change the focus of the image of the workpiece 20). The controllable motor 294 is connected to the input / output interface 130 via the signal line 296. As will be detailed below, the VFL (TAG) lens 270 is controlled by the lens control interface 134 via the signal line 234' to periodically change the refractive power of the VFL lens 270, thereby enabling the effective focusing position (or focal length) of the optical assembly 205 to be changed (for example, in some embodiments / orientations, this can be used to change the focus of the image over a relatively small range, or it can be used instead of moving the optical assembly 205 to change the focus of the workpiece image). The lens control interface 134 can include a VFL lens control unit 180 as will be detailed below. The workpiece stage 210 on which the workpiece 20 is disposed is controlled to move relative to the optical assembly 205 (for example, in the X and Y directions, and / or in the Z direction as part of a rotatable stage), so that the field of view of the interchangeable objective lens 250 can move (for example, between the surfaces and / or surface positions of the workpiece 20, and / or between multiple workpieces 20).

[0036] One or more of the transmitted illumination light source 220, the epi-illumination light source 230, and the oblique illumination light source 240 (for example, ring illumination) can emit the source lights 222, 232, and / or 242 respectively to illuminate one or more workpieces 20. In various exemplary embodiments, stroboscopic illumination can be used. For example, during image exposure, the epi-illumination light source 230 can emit stroboscopic source light 232 along a path including a beam splitter 290 (for example, a partial mirror). The source light 232 is reflected or transmitted as image light 255, and the image light used for imaging passes through the interchangeable objective lens 250, the turret lens assembly 223, and the VFL (TAG) lens 270 and is collected by the camera system 260. The workpiece image exposure including the image of one or more workpieces 20 is captured by the camera system 260 and output onto the signal line 262 to the control system unit 120.

[0037] Various light sources (for example, light sources 220, 230, 240) can be connected to the illumination control interface 133 of the control system unit 120 via associated signal lines (for example, buses 221, 231, 241 respectively). The control system unit 120 can control to select one of the turret lenses via the signal line or bus 223' by rotating the turret lens assembly 223 along the axis 224 to change the magnification of the image.

[0038] As described above, in various embodiments, the relative position, distance, etc. of the optical assembly unit 205 (for example, the objective lens 250 of the optical assembly unit 205) with respect to the workpiece surface WPS1 and / or WPS2 of the workpiece 20 to be measured can be adjusted along the Z-axis of the MCS (for example, using the controllable motor 294), and also along the X-axis and Y-axis of the MCS (for example, by moving the workpiece stage 210). In various embodiments, both the controllable motor 294 and the movable workpiece stage 210 can be part of an adjustment mechanism configured to change at least the distance, position, and / or orientation between the optical assembly unit 205 and the workpiece surfaces WPS1 and / or WPS2.

[0039] According to various embodiments of the present disclosure, the adjustment mechanism may further include a rotation mechanism 295. The rotation mechanism 295 is configured to rotate the optical assembly unit 205 with respect to the workpiece surface WPS1 of the workpiece 20 to change the orientation (for example, angular orientation) of the optical axis OA of the optical assembly unit 205 with respect to the workpiece surface WPS1. In various embodiments, rotating the optical assembly unit 205 to change the orientation of the optical axis OA with respect to the workpiece surface WPS1 can correspond to at least roll rotation and / or pitch rotation.

[0040] As shown in FIG. 2A, the optical assembly unit 205 has a local coordinate system (LCS: local coordinate system) including the X-axis, Y-axis, and Z-axis (i.e., X L , Y L , and Z L axis). The LCS can move and rotate together with the optical assembly unit 205, and the optical axis OA is aligned with the Z L axis (for example, defines the Z L axis). In the orientation shown in FIG. 2A, the LCS is generally aligned with the MCS (i.e., the optical axis OA is aligned with the Z M axis of the MCS). In some conventional systems, the orientation of the optical axis OA of the optical assembly unit is always the Z MIt was relatively fixed so as to be aligned with the axis. With respect to the LCS, yaw rotation, pitch rotation, and roll rotation can correspond to rotations about each axis. In the illustrated configuration, X L A rotation about the axis (for example, referred to as the first rotation axis) is called roll, and Y L A rotation about the axis (for example, referred to as the second rotation axis) is called pitch, and Z L A rotation about the axis can be called yaw.

[0041] In some embodiments, the rotation mechanism 295 can perform a rotation of the optical assembly portion 205 corresponding to a rotation about at least one of the first rotation axis (for example, roll) and / or the second rotation axis (for example, pitch). Therefore, as used herein, the first rotation axis “and / or” the second rotation axis means only the first rotation axis, only the second rotation axis, or both the first rotation axis and the second rotation axis. The first rotation axis and the second rotation axis can be, for example, the X L axis and the Y L axis that are perpendicular to each other, but it is not essential that they are perpendicular to each other, nor is it essential that they are perpendicular to the Z L axis. The first rotation axis and the second rotation axis only need to be non-parallel to each other and to the Z L axis (including not being on the same line). Generally, in various embodiments, the rotation mechanism 295 can perform a rotational movement (for example, at least one of roll or pitch, or a combination thereof) that is “out-of-plane with respect to the Z L axis”.

[0042] As will be described in detail below, FIG. 2B shows a configuration in which the optical assembly portion 205 is rotated with respect to the workpiece surface WPS1 using the rotation mechanism 295 so that the optical axis OA of the optical assembly portion 205 is nominally perpendicular (ie, substantially orthogonal) to the workpiece surface WPS1. Thus, the angular orientation of the optical axis OA is changed. Further, using the motor 294, the distance between the optical assembly portion 205 and the workpiece surface WPS1 is adjusted (for example, the relative position of the workpiece surface is nominally at a desired Z with respect to the optical assembly portion 205L is in a position, e.g., at a nominal desired focus position). As used herein, the term "nominal" encompasses variations that fall within the acceptable tolerances of one or more parameters. As an example, in one specific embodiment, an element (e.g., the optical axis OA) is perpendicular (i.e., orthogonal) to the workpiece surface (which can be defined according to the surface plane of the calculated surface), or within 5 degrees of perpendicular (e.g., having an angular orientation of 85 degrees to 95 degrees with respect to the workpiece surface), this element can be defined as being nominally perpendicular (i.e., nominally orthogonal) to the workpiece surface. As another example, in one specific embodiment, all areas of the workpiece surface (which can be defined according to the surface plane of the calculated surface. In some cases, the workpiece surface is relatively flat and is located at or near the best focus position of the optical assembly) within the field of view (FOV) of the optical assembly are at an average position or other specified position or the best Z L (i.e., in focus) within the 4 depth of field (DOF) of the position, the optical axis OA of the optical assembly can be defined as being nominally perpendicular (i.e., substantially orthogonal) to the workpiece surface. In one embodiment, this can correspond to at least a portion of the workpiece surface within the FOV being at the best focus position and all other portions of that workpiece surface being within the 4 DOF of the best focus position (i.e., correspondingly, the optical axis OA of the optical assembly is nominally perpendicular to the workpiece surface). As another example, when all portions of the workpiece surface within the FOV are within the 4 DOF of the best focus position, the workpiece surface can be defined as being nominally at the best focus position. In other examples, the system and / or specifications may be more stringent (e.g., within 2 DOF, within 2 degrees, within 2 percent, etc.).

[0043] The rotation that causes the orientation of FIG. 2B with respect to the orientation of FIG. 2A is X LIt corresponds to the roll rotation centered on the axis (for example, the first rotation axis). In other configurations, such rotation (for example, nominally aligning the optical axis OA with the surface normal of the workpiece surface) is additionally or alternatively, Y L It may include a pitch rotation centered on the axis (for example, the second rotation axis). As shown in FIG. 2B, following the rotation of the optical assembly unit 205, the LCS also rotates (for example, with respect to the MCS), and the optical axis OA is Z L axis aligned (for example, Z L axis defined).

[0044] Various embodiments of the rotation mechanism 295 are possible. For example, as shown in FIGS. 1 and 2A, the rotation mechanism 295 can be provided as part of the rotation stage 297 of the image measuring machine 12, to which the optical assembly unit 205 is attached. Thus, in various embodiments, by driving an actuator (for example, as part of the rotation mechanism 295) to move (for example, rotate) the rotation stage 297, the optical assembly unit 205 can be controllably rotated. The rotation stage 297 (for example, including the rotation mechanism 295) is connected to the input / output interface 130 via the signal line 298.

[0045] Alternatively or additionally, the movable workpiece stage 210 can be configured to embody a rotation stage (for example, including a rotation mechanism not shown) that can be configured and controlled in the same manner as the above-described rotation stage 297. Similar to the above-described rotation stage 297, the movement (for example, rotation) of the workpiece stage 210 additionally configured as a rotation stage is controlled by the control system unit 120 via a signal line (for example, similar to the signal line 298) to perform a desired rotation (for example, the angular orientation of the workpiece 20 located on the workpiece stage 210).

[0046] As shown in FIG. 2A, in various exemplary embodiments, the control system unit 120 includes a control unit 125, an input / output interface 130, a memory 140, a workpiece program generator and executor 170, and a power supply unit 190. Each of these components and additional components described below can be interconnected by one or more data / control buses and / or application programming interfaces, or by direct connections between various elements. The input / output interface 130 includes an imaging control interface 131, a movement control interface 132, an illumination control interface 133, and a lens control interface 134. The lens control interface 134 includes or is connected to a VFL lens control unit 180 that includes circuits and / or routines for controlling the operation of the VFL(TAG) lens 270 (as detailed below with reference to FIG. 4, for example). The illumination control interface 133 can include illumination control elements 133a - 133n, which control applicable selection, power, on / off switching, and strobe pulse timing, for example, for the various corresponding light sources of the machine vision inspection system 100, where applicable.

[0047] The movement control interface 132 is configured to transmit control signals via signal lines 296 and 298 to move the optical assembly unit 205. In various embodiments, the movement control interface 132 may include a surface normal movement control unit 132sn. Using the surface normal movement control unit 132sn, a specific process can be implemented to adjust and / or change the orientation of the optical axis OA of the optical assembly unit 205 to be nominally perpendicular to the workpiece surface (e.g., workpiece surfaces WPS1 and / or WPS2). Also, control signals (e.g., from the movement control interface 132 or the surface normal movement control unit 132sn) can also be transmitted to adjust and / or change the distance between the optical assembly unit 205 and the workpiece surfaces WPS1 and / or WPS2 (e.g., to nominally position the optical assembly unit 205 at a desired in-focus position with respect to the workpiece surface according to the process performed on the workpiece surface, such as a PFF operation, or acquisition of an extended depth of field (EDOF) image, or a machining operation).

[0048] The memory 140 can include an image file memory unit 141, an edge detection memory unit 140ed, a workpiece program memory unit 142 that can include one or more part programs, etc., and a video tool unit 143. The video tool unit 143 includes various tools 143a - 143n, and in particular, includes an autofocus video tool 143af that determines a GUI for each corresponding video tool, image processing operations, etc. Also, the video tool unit 143 also includes a region of interest (ROI) generator 143roi, which supports automatic, semi-automatic, and / or manual operations that define various ROIs operable in various video tools such as the autofocus video tool 143af included within the video tool unit 143.

[0049] The autofocus video tool 143af uses the VFL lens 270 controlled via the input / output interface 130 for the focus height (i.e., the effective focus position (Z LDetermine a GUI for the height measurement operation, image processing operations, etc. In various embodiments, as described in detail in U.S. Patent No. 9,143,674, the autofocus video tool 143af can further include a high-speed autofocus height tool that can be used to measure the focus height at high speed. High-speed autofocus and / or focus positioning for one or more image regions of interest can be based on analyzing images of various regions according to known methods to determine corresponding focus characteristic values (e.g., quantitative contrast scale values and / or quantitative focus scale values). For example, such methods are described in U.S. Patents Nos. 8,111,905, 7,570,795, and 7,030,351.

[0050] In various embodiments, the autofocus video tool 143af can include and / or be associated with a surface normal determination unit 143sn. The surface normal determination unit 143sn can be used to perform a specific process (e.g., including or used in combination with a multipoint autofocus process) for determining the surface normal of the workpiece surface. In a particular embodiment, the surface normal determination unit 143sn can also be implemented as an independent process or mode from the autofocus video tool 143af, and according to the methods disclosed herein, the multipoint autofocus process and / or subsequent processing for determining the surface normal (e.g., in some embodiments, also for determining the corresponding desired focus position) can be started independently or by other means. This will be described in detail below.

[0051] According to various embodiments, the control unit 125 cooperates with the VFL lens control unit 180 and the surface normal determination unit 143sn to capture an image stack including a plurality of images at various focal lengths of the workpiece surface WPS1, and the autofocus height (e.g., Z) at at least three positions of the workpiece surface WPS1 LThe height) can be calculated based on at least three corresponding regions of interest (ROIs) of the image stack. In various embodiments, it may not be necessary to change the relative orientation between the optical assembly 205 and the workpiece surface WPS1 to calculate at least three autofocus heights. This will be further described in more detail below with reference to FIGS. 6A and 6B. In various embodiments, by calculating / determining at least three autofocus heights, a surface can be defined / determined (e.g., according to a defined / determined plane or other representation that may include three autofocus heights and / or their calculated average value or other determined value), and thereby the surface normal of this calculated / defined surface can be calculated. As long as the extra computational load and processing time are acceptable for a particular application, it will be understood by those skilled in the art that more than three autofocus heights, such as dozens (10, 20, 50, etc.) or hundreds of autofocus heights, can be calculated, and the surface can be defined more precisely according to this large number of calculated autofocus heights.

[0052] In various embodiments, adjustment information can be calculated using a surface normal and / or other data (e.g., regarding a defined / determined surface) calculated at least partially based on at least three autofocus heights (e.g., by a surface normal determination unit 143sn, a control unit 125, and / or a surface normal movement control unit 132sn, etc.). In accordance with the calculated adjustment information, the surface normal movement control unit 132sn and / or the movement control interface 132 can control an adjustment mechanism (e.g., a controllable motor 294 and a rotation mechanism 295) to move / rotate the optical assembly unit 205 so that the optical axis OA of the optical assembly unit 205 is nominally aligned with the surface normal SN of the workpiece surface WPS1, and also to adjust the distance between the optical assembly unit 205 and the workpiece surface WPS1. For example, FIG. 2B shows that the adjustment mechanism is used to (re)orient the optical assembly unit 205 so that the optical axis OA of the optical assembly unit 205 is nominally coincident with the calculated surface normal SN of the workpiece surface WPS1. As will be described in detail below, in the example of FIG. 2B, the adjustment mechanism is also controlled to adjust the distance between the optical assembly unit 205 and the workpiece surface WPS1 (e.g., so that the workpiece surface WPS1 is nominally at a desired Z L (i.e., in-focus) position relative to the optical assembly unit 205). In various embodiments, the surface normal determination unit 143sn and the surface normal movement control unit 132sn and / or various processes associated therewith may be implemented as separate parts / components and / or merged and / or may not be distinguishable.

[0053] The control unit 125 or other component can then perform a defined operation, such as an optical measurement operation (e.g., including imaging) or a machining operation (e.g., milling) of the workpiece surface, on the workpiece surface WPS1 that is nominally perpendicular to the optical axis OA and at a desired Z L position. When performing a specific imaging operation, as described above, the distance between the optical assembly unit and the workpiece surface (i.e., adjusted by the adjustment mechanism and Z LThe (which corresponds to the position) nominally corresponds to the desired focus position, which is the best focus position that nominally focuses on the workpiece surface, or may desirably correspond to different focus positions (for example, positions out of focus in a specific type of EDOF operation, etc.). When performing a machining operation, in various embodiments, the machining operation axis (for example, a drilling operation, etc.) is assumed to coincide with and / or be parallel to the optical axis OA of the optical assembly 205 such that the machining operation is performed along an axis that is nominally perpendicular to the calculated surface of the workpiece.

[0054] Generally, in various embodiments, the control unit 125 and the memory 140 include circuits and / or routines necessary to implement the method of the present disclosure, which is further described in more detail below. The method of the present disclosure includes arranging the optical assembly 205 with respect to the workpiece surface WPS1, capturing an image stack of the workpiece surface at a plurality of focal lengths, determining the autofocus height at at least three positions of the workpiece surface based on at least three corresponding ROIs of the image stack (for example, the surface normal and the corresponding adjustment information can be determined based on these autofocus heights), rotating the optical assembly 205 with respect to the workpiece surface WPS1 to nominally align the optical axis of the optical assembly 205 with the (for example, calculated) surface normal SN of the workpiece surface WPS1, and further adjusting the distance between the optical assembly and the workpiece surface WPS1 (for example, nominally setting the workpiece surface WPS1 to the desired / specified / determined Z L position) by controlling the adjustment mechanism, and performing a defined operation with respect to the workpiece surface WPS1.

[0055] One or more display devices 136 (e.g., display 16 in FIG. 1) and one or more input devices 138 (e.g., joystick 22, keyboard 24, and mouse 26 in FIG. 1) can be connected to the input / output interface 130. Using the display device 136 and the input device 138, a user interface that may include various GUI functions can be displayed. These functions can be used for performing inspection operations, and / or generating and / or modifying part programs, viewing images captured by the camera system 260, and / or directly controlling the vision component section 200.

[0056] In various exemplary embodiments, when a user generates a part program for the workpiece 20 using the machine vision inspection system 100, the user causes part program instructions to be generated by operating the machine vision inspection system 100 in a learning mode to provide a desired image acquisition training sequence. For example, the training sequence may include placing a specific workpiece element of a representative workpiece within the field of view (FOV), setting the illumination level, performing focusing or autofocusing, acquiring an image, and providing an inspection training sequence applied to the image (e.g., using one instance of a video tool for that workpiece element). Such operations can include processes such as those described herein, aligning the optical axis of the optical assembly nominally perpendicular to the workpiece surface using multipoint autofocus and adjusting the distance between the optical assembly and the workpiece surface, and performing subsequent operations (e.g., imaging and measurement) with respect to the workpiece surface. The learning mode operates such that this one or more sequences are captured or recorded and converted into corresponding part program instructions. When the part program is executed, these instructions cause the machine vision inspection system to reproduce the image acquisition trained during training and perform inspection operations to automatically inspect specific workpiece elements (i.e., corresponding elements at corresponding positions) on one or more execution mode workpieces equivalent to the representative workpiece used during part program generation.

[0057] Figure 3A is a schematic diagram of a VFL (TAG) lens system 300 including an optical assembly portion 305 that includes a TAG lens 370 corresponding to the VFL lens 270 of FIG. 2A. The TAG lens system 300 and / or the optical assembly portion 305 can be adapted to a machine vision system of the type shown in FIGS. 1, 2A, and 2B, or can be adapted to the robot system of FIG. 7 or the coordinate measuring machine (CMM) system of FIGS. 8A to 8E as described below. Some of the components numbered 3XX in FIG. 3A correspond to the components numbered 1XX or 2XX of the same or similar operation or function in FIG. 2A, and it will be recognized that they can be understood in the same way unless otherwise indicated.

[0058] The imaging optical path OPATH (also referred to herein as the workpiece imaging optical path) includes various optical components arranged along a path that transmits image light 355 from the workpiece 320 to the camera 360. The image light is transmitted generally along the direction of their optical axes. In the embodiment shown in FIG. 3A, all the optical axes are aligned. However, it will be recognized that this embodiment is for illustrative purposes only and not limiting. More generally, the imaging optical path OPATH includes mirrors and / or other optical elements and can take any form that operates to image the workpiece 320 using a camera (e.g., camera 360) according to known principles. In the illustrated embodiment, the imaging optical path OPATH includes a TAG lens 370 (which can be included in a 4f imaging configuration) and is utilized, at least in part, to image the surface of the workpiece 320 during workpiece image exposure.

[0059] As shown in FIG. 3A, the TAG lens system 300 includes an optical assembly unit 305 including a light source 330, an objective lens 350, a tube lens 351, a relay lens 352, a VFL(TAG) lens 370, a relay lens 356, and a camera 360. The TAG lens system 300 may also include an exposure (strobe) time control unit 333es, a VFL(TAG) lens control unit 380, a movement control unit 332 (including, for example, a surface normal movement control unit 332sn), and a surface normal determination unit 343sn. In various embodiments, the movement control unit 332, the surface normal movement control unit 332sn, and / or the surface normal determination unit 343sn may operate substantially in the same manner as the control unit / parts 132, 132sn, and 143sn, respectively, as described above with reference to FIGS. 2A and 2B. In various embodiments, the various components may be interconnected directly, or by means of one or more data / control buses (such as a system signal and control bus 395), and / or application programming interfaces, etc.

[0060] As detailed below (including, for example, referring to FIG. 4), in various embodiments, the VFL lens control unit 380 can control the drive signal of the TAG lens 370 to periodically change the refractive power of the TAG lens 370 over a certain refractive power range, and these refractive powers occur at each phase timing within the periodic change. The objective lens 350 inputs the image light generated from the workpiece 320 during image exposure, and transmits the image light along the imaging optical path OPATH through the TAG lens 370 to the camera 360 during this image exposure, providing a workpiece image in the corresponding camera image. The effective focusing position EFP in front of the objective lens 350 during image exposure corresponds to the refractive power of the TAG lens 370 during that image exposure. The exposure time control unit 333es is configured to control the image exposure timing used for the camera image.

[0061] Regarding the general configuration shown in FIG. 3A, the light source 330 is an "epi-illumination light source" or other light source, and is configured to emit the light source light 332 to the surface of the workpiece 320 through the objective lens 350 along a path including a beam splitter 390 (e.g., a partial reflection mirror as part of the beam splitter) (e.g., by stroboscopic illumination or continuous illumination). The objective lens 350 receives the image light 355 (e.g., workpiece light) that converges at the effective focal position EFP close to the workpiece 320, and outputs the image light 355 to the tube lens 351. The tube lens 351 receives the image light 355 and outputs it to the relay lens 352. In other embodiments, the same light source can be used to illuminate the field of view non-coaxially. For example, the field of view can be illuminated by a ring light source.

[0062] In various embodiments, the objective lens 350 can be a replaceable objective lens, and the tube lens 351 can be included as part of a turret lens assembly (e.g., similar to the replaceable objective lens 250 and the turret lens assembly 223 in FIG. 2A). In the embodiment shown in FIG. 3A, the image light 355 generated from the nominal focal plane of the objective lens 350 is focused by the tube lens 351 to form an intermediate image at the nominal intermediate image plane IIPnom. When the TAG lens 370 has no lens effect (no refractive power), the nominal focal plane of the objective lens 350, the nominal intermediate image plane IIPnom, and the image plane of the camera 360 form a set of conjugate planes according to the known microscope imaging principle. In various embodiments, any of the other lenses referred to in this specification can be formed from individual lenses, compound lenses, etc., or can operate in cooperation with those lenses.

[0063] The relay lens 352 receives the image light 355 from the tube lens 351 (or more generally from the intermediate image plane in various alternative microscope configurations) and outputs it to the TAG lens 370. The TAG lens 370 receives the image light 355 and outputs it to the relay lens 356. The relay lens 356 receives the image light 355 and outputs it to the camera 360. In various embodiments, the camera 360 can capture a camera image during image exposure (e.g., during the integration period of the camera 360) and provide the corresponding image data to the control system unit. Some of the camera images can include workpiece images (e.g., of a certain region of the workpiece 320) provided during workpiece image exposure. In some embodiments, the image exposure (e.g., workpiece image exposure) can be limited or controlled by the strobe timing of the light source 330 within the image integration period of the camera 360. In various embodiments, the camera 360 can have a pixel array larger than 1 megapixel (e.g., 1.3 megapixels, a 1280×1024 pixel array, 5.3 microns per pixel).

[0064] In the example of FIG. 3A, the relay lenses 352 and 356 and the VFL(TAG) lens 370 are shown as being included in a 4f optical configuration, the relay lens 352 and the tube lens 351 are shown as being included in a Keplerian telescope configuration, and the tube lens 351 and the objective lens 350 are shown as being included in a microscope configuration. It will be understood that the configurations shown herein are all merely exemplary and not limitations on the present disclosure. In various embodiments, the illustrated 4f optical configuration enables the VFL(TAG) lens 370 (which can be a device with a small numerical aperture (NA), for example) to be placed at the Fourier plane of the objective lens 350. This configuration can maintain telecentricity at the workpiece 320 and minimize scale change and image distortion (e.g., including providing a constant magnification at each effective focus position (Z L height) of the workpiece 320).

[0065] In various embodiments, the lens control unit 380 may include a drive signal generation unit 381, a timing clock 381', and an imaging circuit / routine 382. The drive signal generation unit 381 can operate (e.g., in cooperation with the timing clock 381') to provide a periodic drive signal to the high-speed VFL (TAG) lens 370 via the signal line 380'. In various embodiments, the TAG lens system 300 (or the optical assembly unit 205') can include a control system (e.g., the control system unit 120 of FIG. 2) configured to operate in cooperation with the lens control unit 380 for coordinated operation.

[0066] In various embodiments, the lens control unit 380 can generally perform various functions related to imaging the workpiece 320 so as to be synchronized with the desired phase timing of the TAG lens 370, and controlling, monitoring, and adjusting the drive and response of the TAG lens 370. In various embodiments, the image circuit / routine 382 performs standard imaging operations of the optical system synchronized with the phase timing of the TAG lens 370.

[0067] In various examples, there may be a drift in the operating characteristics of the VFL lens due to undesirable temperature variations. As shown in FIG. 3A, in various embodiments, the TAG lens system 300 can optionally include a lens heater / cooler 337 associated with the TAG lens 370. The lens heater / cooler 337 can be configured to facilitate heating and / or cooling of the TAG lens 370 by inputting a certain amount of thermal energy to the TAG lens 370 and / or performing a cooling function according to some embodiments and / or operating conditions. Further, in various embodiments, a temperature sensor 336 associated with the TAG lens 370 can provide a TAG lens monitoring signal to monitor the operating temperature of the TAG lens 370.

[0068] Regarding the overall operation of the TAG lens 370, in various embodiments as described above, the lens control unit 380 can periodically and rapidly adjust or change its refractive power to realize a high-speed VFL lens that periodically changes the refractive power at a high speed, such as the TAG lens resonance frequencies of 400 kHz, 250 kHz, 70 kHz, or 30 kHz. As shown in FIG. 3A, by using the periodic modulation of the signal for driving the TAG lens 370, the effective focusing position EFP of the TAG lens system 300 (i.e., the focusing position in front of the objective lens 350) can be rapidly moved within the range Refp (e.g., the focusing range or the autofocus search range, etc.). The range Refp can be defined by the effective focusing position EFP1 (or EFPmax or peak focal length Z1max+) corresponding to the maximum refractive power of the TAG lens 370 combined with the objective lens 350 and the effective focusing position EFP2 (or EFPmin or peak focal length Z1max-) corresponding to the maximum negative refractive power of the TAG lens 370 combined with the objective lens 350. In various embodiments, the effective focusing positions EFP1 and EFP2 can approximately correspond to the phase timings of 90 degrees and 270 degrees, respectively. This will be described in detail below with reference to FIG. 4. For consideration, the center of the range Refp can be shown as EFPnom, which can approximately correspond to the zero refractive power of the TAG lens 370 combined with the nominal refractive power of the objective lens 350. According to this description, EFPnom can approximately correspond to the nominal focal length of the objective lens 350 in some embodiments (this can correspond to the working distance WD of the objective lens 350).

[0069] Similar to the precision machine vision inspection system of FIG. 2A, the TAG lens system 300 of FIG. 3A is also associated with or includes an adjustment mechanism. The adjustment mechanism is configured to change the distance between the optical assembly 305 and the workpiece surface WPS1 of the workpiece 320 (e.g., using a motor 294 or a similar mechanism as in the configuration of FIG. 2A), and to rotate the optical assembly 305 relative to the workpiece surface WPS1 of the workpiece 320 (e.g., using a rotation mechanism 295). In the example shown in FIG. 3A, the adjustment mechanism includes a rotation mechanism 295 configured to rotate the optical assembly 305 (including the optical axis OA of the optical assembly 305) relative to the workpiece surface WPS1. As shown in FIG. 3A, the rotation mechanism 295 can be provided as part of a rotating stage 297 to which the optical assembly 305 is attached. Alternatively, it is also possible to configure the stage on which the workpiece 320 is disposed as a rotating stage.

[0070] In the example of FIG. 3A, the adjustment mechanism is controlled to move the optical assembly unit 305 so that the workpiece surface WPS1 is disposed within the autofocus range of the optical assembly unit 305 in the Z-axis direction. In the example of FIG. 3A, this may correspond to disposing the optical assembly unit 305 at a distance D-3A from a position on the workpiece surface WPS1. For example, the distance D-3A can nominally correspond to the working distance WD, and the working distance WD can correspond to the midpoint or other part of the autofocus range in the Z-axis direction (e.g., can correspond to a part or all of the range REFP). As shown in FIG. 3A, at the distance D-3A, since all parts of the workpiece surface WPS1 are within the range REFP, the autofocus height at different positions (e.g., at least three positions) of the workpiece surface WPS1 can be determined using an autofocus process including capturing an image stack. Also, it will be appreciated that the workpiece 320 and / or the optical assembly unit 305 are arranged such that the workpiece surface WPS1 is within the field of view of the optical assembly unit 305. As will be described in detail below, in the example of FIG. 3B, the workpiece 320 can likewise be arranged such that the workpiece surface WPS1 is within the field of view of the optical assembly unit 305, and the optical axis OA can be directed towards a position on the workpiece surface WPS1 that is similar or identical to that shown in FIG. 3A (e.g., in the X M and Y M axis direction, etc., a workpiece stage or other moving mechanism can be used to arrange the workpiece 320).

[0071] Similar to the precision machine vision inspection system of FIG. 2A, the method of the present disclosure can be implemented. This method includes placing the optical assembly 305 with respect to the workpiece surface 320A (e.g., controlled by the movement control unit 332 and / or 332sn), capturing an image stack of the workpiece surface at a plurality of focal lengths (e.g., by controlling the VFL(TAG) lens 370 controlled by the lens control unit 380 and / or the exposure time control unit 333es, and / or by moving the optical assembly 305 controlled by the movement control unit 332 and / or 332sn), determining the autofocus height at at least three positions of the workpiece surface WPS1 based on at least three corresponding ROIs of the image stack (e.g., the surface normal and the corresponding adjustment information can be determined based on this calculated autofocus height), rotating the optical assembly 305 with respect to the workpiece surface WPS1 so that the optical axis of the optical assembly 305 is nominally aligned with the calculated surface normal SN of the workpiece surface WPS1, further controlling the adjustment mechanism to adjust the distance between the optical assembly and the workpiece surface, and performing a defined operation with respect to the workpiece surface WPS1.

[0072] For example, FIG. 3B shows that when the workpiece surface WPS1 of the workpiece 320 is inclined with respect to the horizontal plane as shown or oriented at an angle in another way, the adjustment mechanism including the rotation mechanism 295 can be used to (re)orient the optical assembly unit 305 so as to nominally align the determined (e.g., calculated) surface normal SN of the workpiece surface WPS1 with the optical axis OA of the optical assembly unit 305. Further, the distance between the optical assembly unit 305 and the workpiece surface WPS1 can be adjusted using an adjustment mechanism (e.g., including the motor 294 or other corresponding mechanisms). As shown in FIG. 3B, this distance is adjusted such that the distance D-3B between the optical assembly unit 305 and the workpiece surface WPS1 nominally corresponds to the working distance WD (e.g., the working distance WD can be near the center or at the center of the range REFP, and / or can correspond to the best focus position, etc.). In particular, in embodiments that do not include a VFL lens or in embodiments where a VFL lens is included but not operating, the working distance WD of the objective lens 350 can correspond to the best focus position (i.e., the workpiece surface WPS1 is in focus at this position). In embodiments where the VFL lens 370 is included and operating, in some cases the working distance WD can be designated to correspond to the approximate "focus position" of the optical assembly unit and / or can be designated to correspond to the "best focus position" (e.g., near the center or at the center of the operating range REFP of the VFL lens 370, and the phase timing corresponding to the zero refractive power of the VFL lens 370 can nominally correspond to the workpiece surface WPS1 that is in focus).

[0073] When the optical assembly unit 305 rotates from the orientation of FIG. 3A to the orientation of FIG. 3B by the rotation mechanism 295, it will be recognized that during the rotation, the distance between the optical assembly unit 305 and the workpiece surface WPS1 changes substantially according to the principle of triangulation. Therefore, even in an example where the distance D-3B in FIG. 3B can be substantially the same as the distance D-3A in FIG. 3A, in response to the rotation, the adjustment mechanism adjusts the distance between the optical assembly unit 305 and the workpiece surface WPS1 as part of the process to achieve the orientation and position shown in FIG. 3B. Also, in various embodiments, it will be recognized that the distance D-3B may generally not be the same as the distance D-3A. More specifically, in the tilted orientation of the workpiece surface WPS1 in FIG. 3A, the surface position of the workpiece surface WPS1 that intersects the optical axis OA (i.e., at the distance D-3A) is within the focus Z autofocus range, but may not be at the desired Z L position (for example, the desired focusing position, or other distances that may correspond to the distance D-3B, etc.). In some cases, one or more other surface positions of the workpiece surface WPS1 in FIG. 3A may be at the desired Z L position, or none of the other surface positions may be at the desired Z L position (for example, corresponding to the distance D-3B). According to the method described herein, in the example of FIG. 3A, the autofocus process is used to determine (for example, thereby defining and indicating the position of) the autofocus heights at different positions (for example, at least three positions) of the workpiece surface WPS1. Based at least in part on the determined autofocus heights, the adjustment mechanism rotates the optical assembly unit and adjusts the distance of the optical assembly unit with respect to the workpiece surface to obtain the orientation and distance D-3B as shown in FIG. 3B (for example, this corresponds to the desired Z L position. One or more of the positions of the workpiece surface WPS1 in FIG. 3A may have been at the distance D-3B or the corresponding desired Z L position before the adjustment in FIG. 3B, or none of the positions may have been at the desired Z L position).

[0074] Figure 4 is a timing diagram showing the phase timing for the periodically modulated control signal PMCS and the optical response RSP of the VFL lens system of FIGS. 3A and 3B. In the example of FIG. 4, an ideal case is shown where the control signal PMCS and the optical response RSP have the same phase timing and are thus represented as the same signal, but it will be understood that in some cases these signals may be separated by only a phase offset. In various embodiments, the control signal PMCS is related to the drive signal (e.g., including an amplitude drive signal) generated by the drive signal generator 381 of FIG. 3A, and the optical response RSP can represent the periodically changed focus position of the optical assembly that is controlled by periodically changing the refractive power of the TAG lens 370 as outlined above.

[0075] In various embodiments, the sinusoidal shape of the curves PMCS and RSP may depend on a series of lenses (e.g., the objective lens 350 and the TAG lens 370 shown in FIGS. 3A and 3B, etc.). The refractive power of the TAG lens 370 changes in the cycle shown in FIG. 4 and is equal to 1 / f (f = focal length). As will be detailed below, each Z L height is associated with each phase timing signal value. The Z L height-to-phase calibration can be established by calibration according to known principles (e.g., according to a mathematical model and / or by repeatedly advancing the surface to a known Z L height and then manually or computationally determining the phase timing at which the image is in best focus at this known Z L height and storing the relationship in a look-up table or the like of an effective focus position (Z L height-to-phase) calibration section that may be included as part of the lens control unit 380 or others).

[0076] Timing diagram 400A shows each Z LCorresponding to the height (e.g., zφ0, zφ90, zφ180, zφ270, etc.), it shows phase timings (e.g., φ0, φ90, φ180, φ270, etc.) equal to the respective phase timing signal values (e.g., t0, t90, t180, t270, etc.) of the control signal PMCS. In various embodiments, the phase timing signal values (e.g., t0, t90, t180, t270, etc.) can be determined according to a phase timing signal (e.g., given by a clock or by other techniques such as establishing timing for periodic modulation, etc.). It should be understood that the phase timing signal values shown in the timing diagram are merely illustrative and not limiting. More generally speaking, for any phase timing signal value, the focus position Z within the illustrated focus position range L is associated with the height (e.g., in the illustrated example, the range is from a maximum Z L height zφ90 to a minimum Z L height zφ270).

[0077] As described above, various techniques (e.g., as part of the utilization of multi-point autofocus, point from focus, maximum confocal brightness determination, etc.) are used to determine when a certain imaging surface area is in focus, and the Z L height measurement value of that imaging surface area can be associated. For example, when a certain imaging surface area is in focus, it can be determined that this imaging surface area is at a Z L height zφsurf. In the illustrated example using the principle of phase versus Z L height, at the phase timing φsurf_ind(-) equal to the phase timing signal value Tsurf_ind(-), the focus position is at Z L height zφsurf, and the workpiece surface area located at this Z L height zφsurf is in focus. Similarly, at the phase timing φsurf_ind(+) equal to the phase timing signal value Tsurf_ind(+), the focus position is at Z L height zφsurf, and the workpiece surface area located at this Z L height zφsurf is in focus. Such values are for each Z LEffective focusing position (Z that associates height with each phase timing signal value L By including it in the height-phase calibration unit, when it is determined that a certain imaging surface area is in focus, the corresponding phase timing signal value (e.g., Tsurf_ind(-)) is used to measure the corresponding Z of that imaging surface area L height (e.g., Z L height zφsurf) can be found.

[0078] In the illustrated example, the phase timing signal values Tsurf_ind(-) and Tsurf_ind(+) correspond to the movement of the modulated focusing position in opposite directions. More specifically, the phase timing signal value Tsurf_ind(-) corresponds to the movement of the modulated focusing position in the first direction (e.g., downward), and the phase timing signal value Tsurf_ind(+) corresponds to the movement of the modulated focusing position in the second direction opposite to the first direction (e.g., upward).

[0079] Also, FIG. 4 qualitatively shows how to adjust the timing of the strobe illumination (controlled by the exposure time control unit 333es in FIG. 3A) to correspond to each phase timing (e.g., φ0, φ90, φ180, φ270, etc.) of the periodically changing focusing position in order to expose the image focused at each Z L height (e.g., zφ0, zφ90, zφ180, zφ270, etc.). That is, in the illustrated example, when a short strobe pulse is given at the phase timing φ0 while the digital camera is acquiring an image during the integration period, the focusing position becomes the height zφ0, and in the resulting image, the workpiece surface located at the height zφ0 is in focus. The same applies to the other exemplary phase timings and Z L heights shown in FIG. 4. According to such a principle, an image stack can be obtained using the images captured corresponding to different phase timings and thus different Z L heights.

[0080] According to such a principle, the TAG lens system 300 is suitable for performing an autofocus operation (e.g., a multi-point autofocus operation) at high speed. Specifically, using the TAG lens system 300, the refractive power of the TAG lens 370 that sweeps a focus Z L range (e.g., the focus Z L autofocus range) is periodically changed, and while finding the best focus image corresponding to the Z L height of the workpiece surface position, an image stack of the workpiece surface including a plurality of surface positions can be captured. More specifically, as part of a multi-point autofocus process, at least three regions of interest (ROIs) of the image stack are analyzed to find at least three Z L heights of three corresponding workpiece surface positions (e.g., which can be performed simultaneously in some embodiments), then this is used to calculate / determine the workpiece surface (e.g., corresponding to the calculated surface or other representation), and further, the surface normal of the workpiece surface can be calculated / determined accordingly.

[0081] FIG. 5A shows a sample workpiece WP1 having various workpiece surfaces WPS1, WPS2, and WPS3. In the example of FIG. 5A, when associated with the machine coordinate system (MCS), the workpiece surface WPS2 is parallel to the horizontal plane, the workpiece surface WPS3 is parallel to the vertical plane, and the workpiece surface WPS1 can be in a relatively inclined orientation. Regions of interest ROI1, ROI2, and ROI3 are shown on the workpiece surface WPS1, and each of these has surface points SP1, SP2, and SP3 that can be arranged at the relative centers of the corresponding regions of interest. As will be detailed below, the regions of interest represent regions of interest within the image stack as part of the autofocus process, and the autofocus height (e.g., Z L height) of each of these corresponding surface points SP1, SP2, and SP3 can be determined (e.g., using these, the surface or other representation of the workpiece surface WPS1 and the corresponding surface normal can be determined).

[0082] Figure 5B is a schematic view showing the distal end of the optical assembly unit 305. The optical axis OA and the image stack acquisition axis ISAA of the optical assembly unit 305 are oriented in a direction substantially perpendicular to the surface (e.g., the stage) on which the workpiece WP1 is disposed (i.e., the optical axis OA is parallel to the Z M axis of the MCS). Figure 5C is a schematic view showing the distal end of the optical assembly unit 305. The optical axis OA and the image stack acquisition axis ISAA of the optical assembly unit 305 are oriented at an angle so as to be substantially / nominally perpendicular (orthogonal) to the inclined workpiece surface WPS1 of the workpiece WP1.

[0083] To achieve the orientation of Figure 5C, a specific process can be executed according to the principles disclosed herein. For example, to achieve the configuration of Figure 5B, the optical assembly unit 305 can be moved and the adjustment mechanism can be controlled so that the workpiece surface WPS1 is disposed within the autofocus range of the focus Z (i.e., the Z L autofocus range) of the optical assembly unit 305. In the example of Figure 5B, this may correspond to disposing the optical assembly unit 305 at a distance D1 from a position on the workpiece surface WPS1 (e.g., the position where the optical axis OA intersects the workpiece surface WPS1, and in some cases, generally the midpoint or other central position of the workpiece surface WPS1). In the example of Figure 5B, the focus Z L autofocus range is represented by the range SR1. As will be described in detail below with reference to Figures 6A and 6B, as part of the autofocus process, an image stack of the workpiece surface WPS1 within the focus Z L autofocus range can be captured using the optical assembly unit 305. The autofocus height of each of at least three positions (e.g., surface points SP1, SP2, and SP3) of the workpiece surface WPS1 can be determined based on at least three corresponding regions of interest ROI1, ROI2, and ROI3 of the image stack. This will also be described in detail below with reference to Figures 6A and 6B. As shown in Figure 5B, the surface normal SN of the workpiece surface WPS1 is at an angle ANG1 with respect to the optical axis OA of the optical assembly unit 305.

[0084] As shown in FIG. 5C, by controlling the adjustment mechanism based at least in part on the autofocus height at at least three positions (e.g., surface points) of the workpiece surface WPS1, the optical assembly 305 is rotated with respect to the workpiece surface WPS1 so that the optical axis OA of the optical assembly 305 is nominally aligned with the surface normal SN of the workpiece surface WPS1, and the distance between the optical assembly 305 and the workpiece surface WPS1 can be adjusted (e.g., to distance D2). In various embodiments, before controlling the adjustment mechanism as shown in FIG. 5C, the surface normal SN of the workpiece surface WPS1 can be calculated or otherwise determined using the determined autofocus heights of the surface points SP1, SP2, and SP3. For example, three surface points SP1, SP2, and SP3 can be determined to geometrically define a plane (or other representation) corresponding to the workpiece surface WPS1, and the surface normal SN can be calculated and / or otherwise determined as the normal (i.e., perpendicular) to this calculated / determined plane (or other representation). Once such a surface normal SN is determined, adjustment information can be calculated or otherwise determined. The adjustment information can be used to control the adjustment mechanism to rotate the optical assembly 305 from the orientation shown in FIG. 5B to the orientation shown in FIG. 5C or otherwise move it (e.g., rotate it by an amount of angle ANG1). In FIG. 5C, the optical axis OA is shown as nominally coinciding with the surface normal SN. Further, the distance between the optical assembly 305 and the workpiece surface WPS1 can be adjusted using an adjustment mechanism (e.g., including motor 294 or other corresponding mechanism). As shown in FIG. 5C, this adjustment results in a distance D2 between the optical assembly 305 and the workpiece surface WPS1. As described above with reference to FIGS. 3A and 3B, in various embodiments, the distance D2 can correspond to the workpiece surface WPS1 at a desired Z L position (e.g., nominally at the center of the range SR2, and / or at or near the working distance of the objective lens of the optical assembly 305, and / or at the best focus position, etc.).

[0085] Once in the orientation and position shown in FIG. 5C, defined operations can be performed on the workpiece surface WPS1. For example, a measurement operation using the optical assembly 305 can be performed on the workpiece surface WPS1. As part of such a process or others, a point from focus operation can be performed on the workpiece surface WPS1 (e.g., to determine a surface profile). As part of the point from focus operation, an image stack can be captured by the optical assembly 305 in the orientation shown in FIG. 5C. In various embodiments, the process can be repeated / continued (e.g., to perform defined operations on other parts of the workpiece surface WPS1 or on other workpiece surfaces of the workpiece WP1). In this case, the optical assembly 305 can be rotated from the orientation shown in FIG. 5C to be nominally perpendicular to another part of the workpiece surface or another surface of the workpiece (e.g., to proceed and measure various parts of a workpiece such as a turbine blade with a continuously curving shape).

[0086] As an additional aspect, FIGS. 5B and 5C can be understood to show the scan range (e.g., of FIG. 5C compared to FIG. 5B) necessary to cover the three - dimensional surface topography of the workpiece surface WPS1 depending on the orientation of the optical assembly 305 with respect to the workpiece surface WPS1 being measured. For example, the scan range SR1 in the orientation of FIG. 5B is significantly larger than the scan range SR2 in the orientation of FIG. 5C so as to cover the three - dimensional surface topography of the workpiece surface WPS1. Thus, it can be technically advantageous to adjust the angle / orientation of the optical assembly 305 so that the optical axis OA is nominally perpendicular (i.e., substantially orthogonal) to the workpiece surface WPS1 as in FIG. 5C to reduce the required scan range. This reduction in the scan range enables a reduction in the scan time and / or a reduction in the number of images required to form an image stack (e.g., of a desired image density).

[0087] As shown in FIG. 5B, in addition to the scanning range SR1 for the image stack being significantly larger than the scanning range SR2 in FIG. 5C, the orientation of the optical assembly unit 305 is relatively acute with respect to the workpiece surface WPS1, which may reduce the image quality or prevent imaging of some parts / aspects of some workpiece elements. For example, this acute angle may cause a decrease in imaging quality due to, among other things, less imaging light being reflected back towards the optical assembly unit 305. In contrast, in FIG. 5C, by orienting the optical assembly unit 305 so as to be nominally perpendicular (i.e., substantially orthogonal) to at least a part of the workpiece surface WPS1, the optical assembly unit 305 can be at a better angle for imaging the workpiece surface WPS1 (e.g., at a better angle with respect to the reflected imaging light and / or being able to see some workpiece elements better, etc.).

[0088] In various embodiments, as described above, it may be desirable to continue to rotate / align the optical assembly 305 in various orientations to perform processes on various workpiece surfaces or various portions of the workpiece surface of the workpiece. For example, the workpiece WP1 of FIGS. 5A - 5C is shown as including workpiece surfaces WPS1, WPS2, and WPS3. In one embodiment, the optical assembly 305 can be positioned / aligned (or adjusted as such) as shown in FIG. 5B to perform some operations (such as measurement operations or image stack acquisition for PFF scanning etc.) on the workpiece surface WPS2 (for example, the optical axis OA has an inclination of 0 degrees with respect to the vertical direction and is nominally perpendicular to the workpiece surface WPS2). Next, perform multi - point autofocus on the workpiece surface WPS1 and rotate the optical assembly 305 so that the optical axis OA is oriented as shown in FIG. 5C (for example, having an inclination of 45 degrees with respect to the vertical and being nominally perpendicular to the workpiece surface WPS1) to perform some operations (such as measurement operations or image stack acquisition for scanning etc.) on the workpiece surface WPS1, thus enabling the processes disclosed herein to be executed. Then, move the optical assembly to place the workpiece surface WPS3 within the focus Z autofocus range, perform multi - point autofocus on the workpiece surface WPS3, and rotate the optical assembly 305 so that the optical axis OA is oriented (for example, having an inclination of 90 degrees with respect to the vertical and being nominally perpendicular to the workpiece surface WPS3) to perform some operations (such as performing measurement operations or acquiring an image stack for PFF scanning etc.) on the workpiece surface WPS3, thereby enabling the processes disclosed herein to be executed again. In various embodiments, the processes disclosed herein may first be executed to achieve the orientation of FIG. 5B (for example, the optical axis OA is nominally perpendicular to the workpiece surface WPS2 and the specified operations (i.e., can be implemented) can be performed on the workpiece surface WPS2).

[0089] In various embodiments, as part of such a process, the optical axis OA of the optical assembly 305 may be nominally perpendicular (i.e., approximately orthogonal) to only a portion of the workpiece surface, or, in some cases, may not be nominally perpendicular (i.e., not approximately orthogonal) to any particular portion of the workpiece surface, but may be recognized as being nominally perpendicular only to the overall orientation or average (e.g., calculated) orientation of the workpiece surface, etc. For example, if the workpiece surface has particular undulations and / or includes a number of workpiece elements forming a complex or otherwise non-uniform three-dimensional profile / surface topography, the optical axis OA may not be strictly or nominally perpendicular / orthogonal to any particular portion of the workpiece surface, but may be approximately / nominally perpendicular / orthogonal to the overall orientation, average orientation, and / or approximate (e.g., calculated) orientation of the workpiece surface, etc. In this case, as described herein, it can be said that the optical axis OA is nominally perpendicular to the workpiece surface.

[0090] Figures 6A and 6B illustrate how an image stack including images at various focal lengths obtained by the optical assembly 205 or 305 can be used to L determine the autofocus height (i.e., autofocus position or Z L position or Z L height) of at least three points on the workpiece surface along the Z L axis. As used herein, the "Z L axis" may correspond to the Z-axis of the local coordinate system (LCS) of the optical assembly 205 or 305 (i.e., corresponding to the optical axis OA of the optical assembly 205 or 305). In various embodiments, the optical assembly 205 or 305 operates in a multi-point autofocus mode (e.g., and / or other modes such as PFF) (e.g., in the orientation shown in FIG. 5B) to determine the autofocus height (i.e., Z L height or Z

[0091] Specifically, FIGS. 6A and 6B show operations related to determining the relative Z L position (i.e., the autofocus height) along the optical axis direction (i.e., coinciding with the Z L axis of the optical assembly 205 or 305) for each of one or more points on the workpiece surface. As shown in FIGS. 6A and 6B, the focus position of the optical assembly 205 or 305 can move along a range of positions Z L (i) along the direction of the image stack acquisition axis corresponding to the optical axis and / or the focusing axis at each image acquisition position. The optical assembly 205 or 305 can capture image (i) at each position Z L (i). In each captured image (i), a focus measure fm(k,i) can be calculated based on a region of interest or sub-region of interest ROI(k) (e.g., a pixel set) within the image (e.g., the corresponding surface point is at the center of the region of interest or sub-region of interest ROI(k)). The focus measure fm(k,i) is associated with the focus position of the optical assembly 205 or 305 along the direction of the optical axis and / or the image stack acquisition axis at the time when image (i) is captured (e.g., according to the phase timing of the VFL lens 270 or 370 and / or the distance to the workpiece surface). As a result, focus curve data (e.g., a set of focus measures fm(k,i) at position Z L (i), which is one type of focus peak determination data set) is obtained. This may also be simply referred to as the "focus curve" or "autofocus curve". In one embodiment, the focus measure value may involve calculating the contrast or sharpness of the region of interest within the image.

[0092] The Z L position corresponding to the peak of the focus curve corresponding to the best focus position along the image stack acquisition axis (e.g., Z L k601 in FIG. 6A) is the Z Lis the position. For illustration purposes, the image stack is shown as including 11 images (images (1) to (11)), but it will be recognized that in actual embodiments, fewer or more images can be used. For example, some autofocus processes can typically acquire an image stack including 5 to 10 images, while some PFF processes can acquire an image stack including more than 200 images. Further, the images in the image stack can be smaller or larger depending on the embodiment (e.g., related to the size of the camera's field of view and / or other factors) (e.g., including fewer or more regions of interest of a given size).

[0093] As shown by the focus curves generated for images (1) to (11), in the illustrated example, image (6) (i.e., having the corresponding focus measure fm(1,6)) appears to be close to or at the best focus. For example, the central element of ROI(1) (e.g., at surface point SP1 in FIG. 5A) appears to be most in focus in image (6). In contrast, in other images, that portion of the workpiece surface gradually loses focus and appears to become more blurred as it moves away from image (6). When the focus measure value is based on contrast as described above, one method includes comparing the pixel at the center of the ROI (e.g., corresponding to surface point SP1) with the color / brightness, etc. of adjacent pixels within that ROI. By finding the image with the highest overall contrast corresponding to the focus position at the time of image acquisition, along the optical axis OA and the image stack acquisition axis, the relative Z L position (i.e., the autofocus height) indication / measurement value of the surface point (e.g., the central surface point SP1 of ROI(1)) can be obtained.

[0094] As described above, in FIG. 6B, the central region of the region of interest ROI(1) is considered to be approximately in focus in image (6) corresponding to position Z L (6). Therefore, the surface point (e.g., surface point SP1) on the workpiece surface corresponding to the center of ROI(1) has a relative position Z that approximately corresponds to the focus position of ROI(1) in image (6) within the image stack.L It can be determined that it is at (6). Similar processing is performed for each of the regions of interest ROI(2) and ROI(3), and the relative Z of the surface points corresponding to the centers of ROI(2) and ROI(3) (for example, surface points SP2 and SP3 respectively) L positions can be determined. Specifically, as shown in FIG. 6A, autofocus curves can be generated for ROI(2) and ROI(3), and the best focus images can be found in each region of interest ROI. For example, assuming that in ROI(2) the image (5) appears to be in best focus and in ROI(3) the image (7) appears to be in best focus, the autofocus height of the surface position at the center of ROI(2) is Z L (5), and the autofocus height of the surface position at the center of ROI(3) can be determined to be Z L (7).

[0095] The Z of the three regions of interest ROI(1), ROI(2), and ROI(3) (for example, having corresponding central surface points SP1, SP2, and SP3) L height / autofocus height (Z L position) can be used to define a plane or other representation corresponding to the surface that includes these Z L positions / surface points or represents them in other ways, and the surface normal SN with respect to this defined / determined surface can be calculated / determined. As described above, at least three Z L positions (i.e., autofocus heights) can be calculated / determined to define the surface, but to more precisely define the surface, four or more Z L positions may be obtained. In various embodiments, multiple regions of interest ROI(1), ROI(2), ROI(3)...ROI(n) can be processed based on the same (single) image stack, and in some cases, multiple Z LIt may not be necessary to obtain multiple image stacks to calculate / determine the position. In some cases, it will be recognized that the determined peak focus position (i.e., corresponding to the autofocus height) can be between two images in the image stack. In this case, the focus peak position may be determined by interpolation or other techniques according to the fitting of the focus curve to the focus scale value determined for the image.

[0096] In various embodiments, the illustrations of FIGS. 6A and 6B show the Z L height (i.e., Z L position) of multiple surface points on the workpiece surface, which may represent an image stack acquired by the optical assembly unit 205 or 305 operating in the point from focus (PFF) mode (or other modes) to determine the 3D surface coordinate set (e.g., corresponding to the surface shape or profile of the workpiece). Processing the PFF image stack to quantitatively show the Z LA height coordinate map (e.g., a point cloud) can be determined or output. Compared to a multi-point autofocus image stack, a PFF image stack typically includes more images and involves calculations / determinations for more surface points (e.g., for precise determinations such as detailed surface profiles), and accordingly, may involve a more time-consuming process. For example, in some embodiments, a PFF image stack may include at least 10 times, 20 times, or 40 times more images than a multi-point autofocus image stack (e.g., as specific values in some examples, in some embodiments, a multi-point autofocus image stack includes 5 - 10 images / camera frame, and a PFF image stack may include more than 200 (e.g., 220, etc.) images / camera frame). According to the principles disclosed herein, in connection with nominally aligning the optical axis of the optical assembly with the surface normal of the workpiece surface, a multi-point autofocus image stack (e.g., captured by fewer images and fewer surface points and corresponding processing) can be acquired and processed relatively quickly. Then, using the thus-aligned optical assembly, a defined operation (e.g., including PFF operation, etc.) can be performed on the workpiece surface. The PFF operation can provide more detailed information regarding the surface profile of the workpiece surface. Nominally aligning the optical axis with the surface normal can have various advantages (e.g., for performing PFF and / or other processes).

[0097] FIG. 7 is a robotic system 400 embodying a measurement system of the present disclosure that includes an optical assembly unit 405 (similar to the optical assembly units 205 and 305). The robotic system 400 includes an adjustment mechanism 401 in the form of a multi-joint arm having a plurality of degrees of freedom. In various embodiments, the adjustment mechanism 401 (i.e., the multi-joint arm) can typically function as a Z-axis movement mechanism configured to change the distance between the optical assembly unit 405 and the workpiece surface 320A (e.g., including the operation of some parts of the multi-joint arm), and can typically function as a rotation mechanism configured to rotate the optical assembly unit to change the angular orientation of the optical axis with respect to the workpiece surface 320A (e.g., including the operation of some parts of the multi-joint arm).

[0098] The optical assembly unit 405 includes a camera 360, a VFL (TAG) lens 370, and an illumination light source 330. In various embodiments, the illumination light source 330 may be, for example, a ring illumination (formed by arranging, for example, LEDs) provided at the distal end of the optical assembly unit 405 in the illustrated embodiment, but the illumination light source 330 may also be, for example, an epi-illumination light source. The robotic system 400 includes a control unit 425 that includes or is coupled to VFL (TAG) lens control software and robot integration software responsible for controlling the optical assembly unit 405 incorporated in the robotic system 400. In the illustrated embodiment, the optical assembly unit 405 is coupled to the distal end of the multi-joint arm 401. The control unit 425 of the robotic system 400 can move the optical assembly unit 405 by controlling the multi-joint arm 401 to change the distance to the workpiece surface 320A (e.g., using the Z-axis movement mechanism part of the multi-joint arm 401), and can further rotate the optical assembly unit 405 to change the angular orientation of the optical axis OA of the optical assembly unit 405 with respect to the workpiece surface 320A (e.g., using the rotation mechanism part of the multi-joint arm 401).

[0099] Similar to the embodiments of FIGS. 2A to 3B described above, the control unit 425 of the robot system 400 can implement the method of the present disclosure. This method includes arranging the optical assembly unit 405 such that the workpiece surface 320A is within the automatic focusing range, capturing an image stack of the workpiece surface at a plurality of focal lengths within the automatic focusing range (e.g., by controlling the TAG lens 370 and / or moving the optical assembly unit 405), determining the automatic focusing height at at least three positions of the workpiece surface based on at least three corresponding ROIs of the image stack (e.g., surface normal and adjustment information can be determined based on this determined automatic focusing height), rotating the optical assembly unit with respect to the workpiece surface to nominally align the optical axis of the optical assembly unit 405 with the surface normal of the workpiece surface 320A, and further controlling the adjustment mechanism based at least in part on the determined automatic focusing height to adjust the distance between the optical assembly unit and the workpiece surface, and performing a specified operation on the workpiece surface 320A.

[0100] FIGS. 8A to 8E show a coordinate measuring machine (CMM) 500 embodying a measurement system including an optical assembly unit 505 according to another aspect of the present disclosure. As shown in FIG. 8A, the coordinate measuring machine 500 includes a machine body 501 that moves an optical assembly unit 505 (which can be included in, for example, a vision probe), an operation unit 503 having a manually operated joystick 506, and a processing device configuration 509. The machine body 501 includes a surface plate 510 (e.g., a workpiece stage) and an adjustment mechanism 520 that moves the optical assembly unit 505 (see also FIG. 8E). The adjustment mechanism 520 includes an X-axis slide mechanism 525, a Y-axis slide mechanism 526, and a Z-axis slide mechanism 527, which are provided to be placed on the surface plate 510 to hold the optical assembly unit 505 and move it three-dimensionally with respect to the workpiece WP to be measured. The adjustment mechanism 520 also includes a rotation mechanism 595.

[0101] Specifically, the adjustment mechanism 520 adjusts the Y coordinate of the machine coordinate system (MCS) as shown in FIG. M A beam support 521 that can move in the X direction, a beam 522 that connects the beam supports 521, and a machine coordinate system X on the beam 522. M Column 523 can be moved in the Z direction of the machine coordinate system. M 8A are provided between the beam 522 and the column 523, between the surface plate 510 and the beam support 521, and between the column 523 and the Z-axis moving member 524, respectively. The optical assembly section 505 is attached to the probe head 513. The probe head 513 includes a rotation mechanism 595, and is attached to and supported by an end of the Z-axis moving member 524. The rotation mechanism 595 can rotate the optical assembly section 505. The X-axis slide mechanism 525, the Y-axis slide mechanism 526, and the Z-axis slide mechanism 527 are provided in the X-axis, Y-axis, and Z-axis directions (i.e., X-axis, Y-axis, and Z-axis) that are mutually orthogonal within the MCS, respectively. M , Y M , and Z M 5 and 6. The optical assembly portion 505 is configured to move in the forward (or reverse) direction.

[0102] 8E, the X-axis slide mechanism 525, the Y-axis slide mechanism 526, and the Z-axis slide mechanism 527 are provided with an X-axis scale sensor 528, a Y-axis scale sensor 529, and a Z-axis scale sensor 530, respectively. Therefore, the amount of movement of the optical assembly unit 505 in the X-axis, Y-axis, and Z-axis directions of the machine coordinate system (MCS) can be obtained from the outputs of the X-axis scale sensor 528, the Y-axis scale sensor 529, and the Z-axis scale sensor 530. In the illustrated embodiment, the movement directions of the X-axis slide mechanism 525, the Y-axis slide mechanism 526, and the Z-axis slide mechanism 527 are respectively in the X-axis and Y-axis directions of the machine coordinate system (MCS). M Direction, Y M Direction and Z Mis consistent with the direction. In various embodiments, such relatively simple correlations and associated components are X M , Y M , and Z M can be useful for high-precision levels of movement and position control / detection and relatively simple processing in the directions. The probe head 513 with the rotation mechanism 595 includes one or more rotation sensors 515 (see FIG. 8E) for detecting the angular rotation / position / orientation of the optical assembly 505. This will be described in detail below.

[0103] In various embodiments, as shown in FIGS. 8A and 8E, the adjustment mechanism 520 including the X-axis, Y-axis, and Z-axis slide mechanisms 525, 526, and 527, and the rotation mechanism 595 can be controlled to move and align the optical axis OA of the optical assembly 505 to be nominally perpendicular to any workpiece surface. Similar to the embodiments of FIGS. 2A to 3B and FIG. 7 described above, as shown in FIGS. 8C, 8D, and 8E, the optical assembly 505 can include a light source 330 and an optical component unit 306 (for example, can include an objective lens 350, a camera 360, and a VFL (for example, TAG) lens 370).

[0104] As shown in FIGS. 8A and 8E, the operation unit 503 is connected to the command unit 602 of the control unit 625. The control unit 625 includes or is coupled to a movement control unit 540 configured to control the movement of the optical assembly 505. Various commands can be input to the machine body 501 and the control unit 625 via the operation unit 503. As shown in FIG. 8A, the control unit 625 can be embodied in the processing unit of a computer system.

[0105] Similar to the embodiments of FIGS. 2A to 3B and FIG. 7 described above, the control unit 625 of the CMM 500 can implement the method of the present disclosure. This method includes arranging the optical assembly unit 505 with respect to the workpiece surface such that the workpiece surface (WPS1) is within the auto-focus range, capturing an image stack of the workpiece surface at a plurality of focal lengths within the auto-focus range (e.g., by controlling the TAG lens 370 and / or moving the optical assembly unit 505), determining the auto-focus height at at least three positions of the workpiece surface based on at least three corresponding ROIs of the image stack (e.g., surface normal and adjustment information can be determined based on the determined auto-focus height), rotating the optical assembly unit 505 with respect to the workpiece surface WPS1 so as to nominally align the optical axis of the optical assembly unit with the surface normal SN of the workpiece surface WPS1, and further controlling the adjustment mechanism 520 based at least in part on the determined auto-focus height at at least three positions so as to adjust the distance between the optical assembly and the workpiece surface, and performing a prescribed operation with respect to the workpiece surface WPS1.

[0106] As shown in FIG. 8E, the control unit 625 includes a command unit 602, an adjustment mechanism control unit 604, a positioning unit 606, an optical assembly unit control unit 608, an optical assembly unit data unit 610, an analysis unit 612, and a storage unit 614. The command unit 602 shown in FIG. 8E gives a predetermined command to the adjustment mechanism control unit 604. The command unit 602 generates coordinate values in the machine coordinate system for each control cycle, considering, as a position command for the adjustment mechanism 520, for example, the moving direction, moving distance, moving speed, etc. for moving the optical assembly unit 505 to a plurality of positions or orientations. The adjustment mechanism control unit 604 shown in FIG. 8E outputs a drive control signal D in response to the command from the command unit 602, and thereby performs drive control by passing current through the motors of the X-axis, Y-axis, and Z-axis slide mechanisms 525, 526, and 527, and the rotation mechanism 595 within the adjustment mechanism 520.

[0107] To ensure proper synchronization between the coordinates of the CMM500 and the optical assembly unit 505 during image acquisition, in one implementation, a position latch 516 communicates with various sensors and / or drive mechanisms. More specifically, in various embodiments, the position latch 516 can be used to ensure the accuracy of measurements and / or other determinations derived from the images of the image stack. In various embodiments, the operation of the position latch 516 enables proper synthesis of the CMM machine coordinates (reflecting the position of the connection point or other reference point of the optical assembly unit 505 during a particular measurement) with the position data determined from the optical assembly unit image (e.g., regarding the position and orientation of the optical assembly unit 505 itself). In some embodiments, the position latch 516 can be used to trigger measurements from CMM position sensors (such as sensors 515 and 528 - 530, etc.). This CMM position sensor can include a scale, encoder, or other sensing element that tracks the overall position and orientation of the optical assembly unit 505 (including its base position, for example) in the machine coordinate system. In some embodiments, the position latch 516 can also trigger image acquisition from the optical assembly unit 505 (e.g., as part of an image stack. A trigger signal can be provided for each image of the image stack, and the corresponding position of the optical assembly unit 505 and / or the phase timing of the VFL lens 370 can also be synchronized and / or tracked during each image acquisition).

[0108] When utilized with the optical assembly unit 505, the CMM adjustment mechanism 520, particularly its sensors (515 and 528 - 530), can provide the measurement output M to the position determination unit 606. The position determination unit 606 determines the position (or other connection point or reference position) of the probe head 513 of the optical assembly unit 505 within the machine coordinate system (MCS) of the CMM. For example, the position determination unit 606 can provide the X, Y, and Z coordinates (i.e., X M 、Y M 、and Z M coordinates) of the probe head 513 or other connection point or reference point of the optical assembly unit 505 within the machine coordinate system.

[0109] When using the optical assembly 505 as described herein with respect to various exemplary embodiments (e.g., with respect to some defined operations or others), the positioning unit 606 can determine the position of the probe head 513 (or other reference or mounting position) that is on top of the optical assembly 505. To determine the coordinates of the surface points on the workpiece, information from the analysis of the image stack can be used. For example, an image stack (of images at various focus positions) can be acquired by the optical assembly 505. The relative position / focus position of the images within the image stack is represented in the local coordinate system (LCS) of the optical assembly. The local coordinate system can be related to the reference position of the optical assembly within the MCS in some embodiments. To determine the overall position of the surface points within the machine coordinate system (MCS), in some embodiments, the LCS position data of the surface points is converted to MCS position data and / or combined with the MCS position data by other means, whereby the overall positions of all the surface points can be determined.

[0110] When the optical assembly 505 is oriented at an angle (e.g., as shown in FIG. 8D), and thus the Z-axis (i.e., the Z L axis) of the local coordinate system (LCS) of the optical assembly is oriented at an angle (i.e., corresponding to the optical axis OA of the optical assembly 505), the acquired image stack is the relative distance of the surface points of the workpiece along the direction of the Z-axis of the optical assembly oriented at that angle (e.g., the autofocus height or the Z LIt shows the height). In some embodiments, these LCS coordinates can be combined (e.g., converted to or added to the MCS coordinates) with the determined MCS coordinates of the probe head 513 (or other reference position) to determine the overall position of the surface points on the workpiece within the MCS. For example, if it is desired to determine the coordinates of the surface points in the MCS, the measured points determined in the local coordinate system LCS of the optical assembly unit can be converted to MCS coordinates and added to or combined in other ways with the other MCS coordinates of the probe head 513 (or other reference position) of the optical assembly unit 505. Alternatively, if the workpiece has its own coordinate system assigned to it, the determined MCS coordinates and / or LCS coordinates of the probe head 513 (or other reference position) of the optical assembly unit 505 can be converted to the local coordinate system of the workpiece or combined with the local coordinate system. As yet another example, in some cases, additionally or alternatively, other local coordinate systems (e.g., for images of an image stack, etc.) may be established. Generally, the MCS covers the entire large volume of the coordinates of the CMM 500, while the local coordinate system generally covers a smaller volume and may in some cases be generally included within the MCS. In various embodiments, in addition to the X, Y, and Z coordinates, for the determination of the orientation of the optical assembly unit 505 and the coordinates of the measured surface points on the workpiece WP, specific types of cylindrical coordinates, Cartesian coordinates, or other coordinates may be additionally or alternatively utilized as part of the MCS and / or the local coordinate system. Also, it will be recognized that such principles for determining coordinates are applicable and available to other systems described herein (e.g., in relation to FIGS. 2A to 3B, FIGS. 5A to 5C, FIG. 7, etc.).

[0111] In some embodiments, the position data represented by the LCS from the image stack can be utilized relatively independently (e.g., the conversion or composition with the coordinates of the MCS or other coordinate systems is limited or non-existent). For example, the position data determined from the analysis of the image stack provides 3D coordinates indicating the 3D position of the surface points on the workpiece surface represented by the LCS, and thus can represent / correspond to the 3D profile / surface topography of the workpiece surface. As described above, in some embodiments, such data can be combined with other position data represented by the MCS to indicate the overall position of the workpiece surface and the surface points within the MCS. However, in some embodiments, analysis, and / or representation, etc., it may be desirable to primarily use or only use the position data determined from the image stack. For example, when the main purpose of the analysis or inspection is to determine the relative position and / or features of workpiece elements on the workpiece surface (e.g., determining / calculating the relative surfaces / faces together with the surface normal, and / or regarding the distance between workpiece elements on the workpiece surface, and / or the three-dimensional dimensions of the workpiece elements on the surface, etc.), in some embodiments, such data can be mainly determined from the analysis of the image stack. More specifically, in a desired analysis / inspection, when the overall position(s) of the workpiece surface and / or workpiece elements within the MCS is not required, the data determined from the image stack can be utilized with limited or no composition with the coordinates of other MCSs or other coordinate systems. In addition to the analysis of such data, in some operations, it will be recognized that a 3D representation of the workpiece surface can be similarly determined and / or provided (e.g., to a display, etc.) according to the data from the analysis of the image stack (e.g., as part of a PFF process, etc.).

[0112] As shown in FIG. 8E, the optical assembly unit control unit 608 controls the optical assembly unit 505 (for example, to acquire an image of an image stack, controls the illumination configuration 330, the camera 360, the VFL lens 370, etc.). In various embodiments, certain portions of the movement or focusing of the optical assembly unit 505 can be controlled by a CMM adjustment mechanism 520 that moves the optical assembly unit 505 closer to and / or away from the workpiece. To rotate the optical assembly unit 505 to a desired angle / orientation (e.g., nominally perpendicular to the workpiece surface), a rotation mechanism 595 can be used. In various embodiments, the focal length of the optical assembly unit 505 can be determined at least in part by the objective lens 350 (e.g., since the VFL lens 370 is used in combination therewith, the focal length in front of the optical assembly unit 505 can vary during measurement operations according to the operation of the VFL lens 370). The optical assembly unit data unit 610 receives the output of the optical assembly unit 505 (i.e., image data for an image of an image stack). Using the analysis unit 612, related analysis can be performed (e.g., to determine the corresponding surface of the workpiece surface and / or the three-dimensional surface profile of the workpiece surface, etc., a point from focus (PFF) analysis or other image stack analysis for determining the relative autofocus height / position of each surface point on the workpiece surface along the Z-axis direction (i.e., the Z L direction) of the optical assembly unit). The storage unit 614 can include a portion of a computer memory that stores specific software, routines, data, etc. for the operation of the system, etc.

[0113] FIG. 8B is a diagram schematically showing some components of the machine body 501 of the CMM 500 and the optical assembly unit 505. As shown in FIG. 8B, the machine body 501 includes a probe head 513. The probe head 513 receives and transmits signals via a probe head cable 511. The probe head 513 is fixed to the coordinate measuring machine hollow shaft 517, and the hollow shaft 517 is in the Z-axis direction of the MCS (i.e., the Z MIt is attached to the end of the Z-axis moving member 524 (or a slide element such as a spindle) that moves in the [[ID=]] direction). The probe head 513 is connected to the optical assembly unit 505 in the probe autojoint connection 531. An embodiment of the probe autojoint is described in detail in U.S. Patent No. 9,115,982.

[0114] The probe head 513 of the illustrated embodiment includes a rotation mechanism 595. The rotation mechanism 595 rotates 360 degrees in the horizontal plane in some embodiments (for example, the movement / position / orientation of the angle can be detected by the first rotation sensor 515) and may include a certain type of U-joint. This can rotate, for example, the attached optical assembly unit about a corresponding axis in the horizontal plane, and the movement / position / orientation of the angle can be detected by the second rotation sensor 515. Therefore, the rotation mechanism 595 of the probe head 513 in the specific example of FIG. 8B supports the rotation of the optical assembly unit 505 about two different axes. That is, the first is the rotation (spin) of the optical assembly unit 505 in the current orientation about the Z-axis of the MCS, and the second is the rotation of the optical assembly unit 505 about the horizontal axis (that is, the axis in the XY plane of the MCS). In some embodiments, the rotation mechanism 595 including a spherical (or ball-shaped) joint allows the optical assembly unit 505 to rotate about the Z-axis moving member 524 in the column 523 and / or about any horizontal axis, and the optical axis OA of the optical assembly unit 505 is arranged at a desired angle / orientation with respect to the workpiece surface (for example, nominally perpendicular to the workpiece surface). Generally, the rotation mechanism 595 is a mechanism for changing the orientation (that is, the posture) of the optical assembly unit 505.

[0115] The probe auto-joint connection 531 is an electromechanical connection that mechanically and firmly attaches the probe head 513 to the optical assembly section 505 so as to enable the removal of the probe head 513 from one probe (for example, including an optical assembly section) and its attachment to another probe. In one embodiment, the probe auto-joint connection 531 may include first and second mating auto-exchange joint elements 534 and 536. The first auto-exchange joint element 534 is mounted on the probe head 513, and the second mating auto-exchange joint element 536 is mounted on the optical assembly section 505. In one embodiment, the probe auto-joint connection 531 has mating electrical contacts or connections 535, which are automatically engaged to make an electrical connection when the probe is attached.

[0116] The optical assembly section 505 can receive at least some of the power and control signals via the auto-joint connection 531. The power and control signals are sent via the probe head cable 511. The signals sent to the optical assembly section 505 via the auto-joint connection 531 are sent via the connection 535. As shown in FIG. 8E, the optical assembly section 505 includes an auto-exchange joint element 536 and a probe assembly 537 mounted on this auto-exchange joint element 536 for automatically connecting to the CMM 500 via the probe auto-joint connection 531.

[0117] In various embodiments, the optical assembly 505 may additionally or alternatively receive at least some of the power and control signals via cable 511'. In some embodiments, the cable 511' may be used because the number of available wired connections using standard auto-joint connections 531 is limited and because more connections (e.g., provided via optional cable 511') may be desired / used by the optical assembly 505. In various embodiments, the power and / or communication signals (e.g., sent via cable 511 and / or cable 511') for the optical assembly 505 may be transmitted and received between the optical assembly control unit 608 and the optical assembly data unit 610 (see FIG. 8E). The optical assembly data unit 610 receives the output of the optical assembly 505 (i.e., image data for the images of the image stack). Using the analysis unit 612, relevant analysis of the image stack can be performed. This analysis is, for example, an autofocus process for calculating / determining the autofocus height at at least three positions on the workpiece surface (e.g., which can be used to calculate / determine the surface normal of the workpiece surface). The storage unit 614 may include a portion of a computer memory that stores specific software, routines, data, etc. for the operation of the control unit 625 and the like.

[0118] In FIGS. 8A and 8B, the rotation mechanism 595 is illustrated as including a type of U-joint, but the configuration of the rotation mechanism 595 is not limited thereto. For example, the rotation mechanism 595 may be included within the surface plate 510 of the CMM 500 that supports the workpiece WP (see FIG. 8A), or in the form of a rotating stage on the surface plate 510, or in the form of a rotating stage provided at the distal end of the Z-axis moving member 524 of the CMM 500 (similar to the rotating stage 297 in FIGS. 1 to 3B).

[0119] Figures 8C and 8D show some components with respect to Figures 8A and 8B, and include specific parts of an adjustment mechanism 520 that includes a rotation mechanism 595' (embodied within the probe head 513') of the machine body 501 of the CMM500. Figure 8C shows the optical assembly 505 in a vertical orientation (e.g., similar to when a specific prior art system, such as a specific vision system, operates to perform only the up and down focusing position movement along the Z M axis direction of the machine coordinate system). As shown in Figure 8C, the workpiece WP has a workpiece surface WPS1 with an angular orientation (angle A1). Note that in the view of Figure 8C, the Z-axis of the machine coordinate system is parallel to the optical axis OA of the optical assembly 505. When the optical assembly 505 simply moves up and down along the Z M axis of the MCS (including the movement of the Z-axis moving member 524 within the column 523) by a Z-axis slide mechanism 527, it will be recognized that the optical axis (Z L axis) of the optical assembly 505 can be in the same direction as the Z M axis of the machine coordinate system and the image stack acquisition axis ISAA. The workpiece surface WPS1 is shown at an angle A1 with respect to the horizontal plane of the MCS. In contrast, the workpiece surface WPS2 of the workpiece WP is shown substantially parallel to the horizontal plane of the MCS. The surface normal SN of the workpiece surface WPS1 is shown at an angle A2 with respect to the optical axis OA (e.g., as shown in Figure 8D, the optical assembly 505 can rotate by an amount indicated by the angle A2).

[0120] FIG. 8D shows that, according to various embodiments of the present disclosure, the optical assembly 505 is rotated (e.g., by an amount of angle A2) so as to be at an angle (angle "A-H") with respect to the horizontal plane of the MCS and at an angle (angle "A-V") with respect to the vertical plane of the MCS. The optical assembly 505 is rotated about a horizontal rotation axis RA2 passing through the rotation point R2 so as to show the angle A-H (e.g., by another component of the rotation mechanism 595' of the U-joint or probe head 513'). For this reason, the optical axis OA of the optical assembly 505 is nominally perpendicular (i.e., substantially orthogonal) to the workpiece surface WPS1. In FIG. 8D, the rotation mechanism 595' of the probe head 513' enabling the rotation of the optical assembly 505 about the Z-axis of the MCS is shown by the rotation axis RA1 passing through the rotation point R1 at the upper part of the probe head 513' / rotation mechanism 595'. The rotation about the horizontal axis is illustrated by a rotation axis RA2 passing through the rotation point R2 at the center of the probe head 513' / rotation mechanism 595' (i.e., shown as one point since it is in the direction passing through the paper surface) (e.g., according to the operation of the U-joint shown in FIG. 8B).

[0121] FIG. 8D shows an exemplary image stack range SR-3B. This can be, in various embodiments, part or all of the autofocus range, or a PFF range (e.g., for determining the three-dimensional surface profile of the workpiece surface WPS1). The workpiece surface WPS1 can have various workpiece elements (e.g., surface elements) that can be higher or lower than the average plane position of the workpiece surface WPS1. In some embodiments, it may be desirable for the range of the focus position of the image stack to extend a specific distance above and below the workpiece surface. As shown in FIG. 8D, the exemplary image stack range SR-3B can be significantly smaller than the image stack range SR-3A of FIG. 8C (e.g., the image stack range necessary to cover all the surface points of the workpiece surface WPS1 in the orientation shown in FIG. 8C). This is due to the fact that, unlike the relative angular orientation of FIG. 8C, the optical assembly 505 of FIG. 8D is oriented such that the optical axis OA is nominally perpendicular (i.e., substantially orthogonal) to the workpiece surface WPS1. In FIG. 8D, the angle of the optical axis OA (and the image stack acquisition axis ISAA) with respect to at least a portion of the workpiece surface WPS1 is shown as "A-P" and is nominally perpendicular (i.e., approximately 90 degrees / orthogonal) in the example shown. FIG. 8D also shows the angle "A-W" of the workpiece surface WPS1 with respect to the horizontal plane (e.g., corresponding to the angle A1 of FIG. 8C). Depending on the specific angle A-W in each embodiment, the rotation mechanism 595' can be adjusted to ensure that the optical axis OA (and ISAA) of the optical assembly 505 is nominally perpendicular (i.e., substantially orthogonal) to at least a portion of the workpiece surface WPS1.

[0122] To achieve the orientation of FIG. 8D, a specific process can be executed in accordance with the principles disclosed herein (e.g., similar to the examples described above with respect to FIGS. 5B and 5C). For example, to achieve the configuration of FIG. 8C, the adjustment mechanism 520 can be controlled to move the optical assembly 505 and position the workpiece surface WPS1 within the autofocus range of the focus Z of the optical assembly 505. In the example of FIG. 8C, this may correspond to positioning the optical assembly 505 at a distance D-8C from a position on the workpiece surface WPS1 (e.g., the position where the optical axis OA intersects the workpiece surface WPS1, which in some cases may be at or near the midpoint or other central position of the workpiece surface WPS1). In the example of FIG. 8C, the autofocus range of the focus Z is represented by the range SR-3A. As described above with reference to FIGS. 6A and 6B, as part of the autofocus process, an image stack of the workpiece surface WPS1 within the autofocus range of the focus Z can be captured using the optical assembly 505. As described above with reference to FIGS. 6A and 6B, the autofocus height of each of at least three positions of the workpiece surface WPS1 can be determined based on at least three corresponding regions of interest of the image stack.

[0123] As shown in FIG. 8D, by controlling the adjustment mechanism 520 based at least in part on the autofocus heights at at least three surface positions, the optical assembly 505 is rotated with respect to the workpiece surface WPS1 to nominally align the optical axis OA of the optical assembly 505 with the surface normal SN of the workpiece surface WPS1, and the distance between the optical assembly 505 and the workpiece surface WPS1 can be adjusted. In various embodiments, before controlling the adjustment mechanism as shown in FIG. 8D, the surface normal SN of the workpiece surface WPS1 and / or the corresponding adjustment information can be calculated or otherwise determined using the determined autofocus heights at at least three surface positions. Then, the adjustment mechanism 520 is controlled (e.g., using the adjustment information and / or surface normal calculated / determined based on the autofocus height) to rotate the optical assembly 505 from the position and orientation shown in FIG. 8C to the position and orientation shown in FIG. 8D or otherwise move it. In FIG. 8D, the optical axis OA is shown as nominally coinciding with the surface normal SN. Further, the adjustment mechanism 520 can be used to adjust the distance between the optical assembly 505 and the workpiece surface WPS1. As shown in FIG. 8D, this adjustment results in a distance D-8D between the optical assembly 505 and the workpiece surface WPS1 (e.g., measured along the direction of the optical axis OA and / or the corresponding Z L direction). As described above with reference to FIGS. 3A and 3B, in various embodiments, the distance D-8D can correspond to the workpiece surface WPS1 being nominally at the center of the range SR-3B (e.g., the range of the PFF or other defined operations performed on the workpiece surface), and / or at or near the operating distance of the objective lens of the optical assembly 505, and / or at or near the best focus position, etc. Once in the orientation and position shown in FIG. 8D, the defined operation can be performed on the workpiece surface WPS1.

[0124] As an example of a specified operation, a measurement operation using the optical assembly unit 505 can be performed on the workpiece surface WPS1. As part of such an operation or others, a PFF operation (for example, for determining the surface profile of the workpiece surface WPS1) can be performed. As part of the PFF operation, an image stack can be captured by the optical assembly unit 505 in the orientation shown in FIG. 8D (for example, this image stack corresponds to the scanning range SR-3B). As another type of specified operation that can be performed on the workpiece surface WPS1, a machining operation (for example, drilling) can be performed. In this case, it may be desirable for the machining axis (for example, the drilling axis) of the machining operation to coincide with the optical axis OA of the optical assembly unit 505 (for example, to be coaxial or parallel with the optical axis OA), and thus to be nominally perpendicular to the workpiece surface SRF1.

[0125] FIG. 9 is a flowchart of a method 900 for aligning an optical axis perpendicular to a surface using multi-point autofocus according to an aspect of the present disclosure. This method, in block 901, operates a measurement system including an optical assembly unit (205, 305, 405, 505). The optical assembly unit includes a variable focal length (VFL) lens, a light source, and an objective lens. The objective lens receives image light generated from the surface of the workpiece illuminated by the light source and transmits this image light along an imaging optical path passing through the VFL lens. The objective lens defines at least the optical axis of the optical assembly unit extending between the objective lens and the workpiece surface. The optical assembly unit also includes a camera. The camera receives the imaging light transmitted by the VFL lens along the imaging optical path and provides an image of the workpiece surface.

[0126] In block 903, the optical assembly unit is moved to place the workpiece surface to be measured within the focus Z autofocus range of the optical assembly unit.

[0127] In block 905, an image stack of the workpiece surface within the focus Z autofocus range is captured using the optical assembly unit.

[0128] In block 907, the autofocus height at at least three positions on the workpiece surface is calculated based on at least three corresponding regions of interest (ROIs) in the image stack. In various embodiments, surface normal and corresponding adjustment information of the workpiece surface can be determined based at least in part on the autofocus heights at the three positions.

[0129] In block 909, the adjustment mechanism is controlled based at least in part on the autofocus heights at at least three positions so as to rotate the optical assembly relative to the workpiece surface to nominally align the optical assembly with the surface normal of the workpiece surface, and also to adjust the distance between the optical assembly and the workpiece surface.

[0130] In block 911, a defined operation is performed on the workpiece surface that is nominally perpendicular to the optical axis at this point.

[0131] Various defined operations can be performed. All of these operations can utilize the fact that the optical axis of the optical assembly can be quickly and / or precisely aligned to be nominally perpendicular to the workpiece surface to be operated on by a measurement system according to various embodiments.

[0132] For example, after performing the defined operation in block 911, the process from blocks 903 to 911 may be repeated for another portion of the workpiece surface and / or for another workpiece surface of the workpiece (e.g., if the workpiece includes a turbine blade, the process can be repeated to proceed along various sections along the curve of the turbine blade, etc.).

[0133] As another example, non-optical operations such as machining (e.g., drilling) operations can be performed on the workpiece surface. The machining operation axis coincides with the optical axis of the optical assembly that is nominally perpendicular to the workpiece surface.

[0134] As another example, various optical operations such as extended depth of field (EDOF) operation or point from focus (PFF) operation can be performed. The details of the EDOF operation and the PFF operation are shown, for example, in U.S. Patent Publication No. 2020 / 0195836. Briefly stated, in the EDOF operation, the optical assembly section (205, 305, 405, 505) including the VFL(TAG) lens can be operated to expose a preparation image using an EDOF exposure sequence. The EDOF exposure sequence defines a plurality of individual image exposure increments obtained at individual focus positions FP corresponding to each phase of the periodically changing focus position. The preparation image is processed to determine or output an EDOF image having a depth of field larger (e.g., 10 to 20 times or more larger in various embodiments) than that of a VFL(TAG) lens imaging system at a single focus position. The EDOF image is substantially in focus throughout this large depth of field. In various embodiments, the EDOF image can be provided at a high speed suitable for displaying almost in real time. For example, the EDOF image exposure sequence can be configured to acquire the preparation image in less than 500 milliseconds, or less than 250 milliseconds, or less than 100 milliseconds, or less than 50 milliseconds.

[0135] Briefly stated, in the PFF operation, the optical assembly section (205, 305, 405, 505) including the VFL(TAG) lens can be operated to expose a stack of images (image stack) using a PFF exposure sequence. The PFF exposure sequence defines a plurality of individual image exposure increments obtained at individual focus positions FP corresponding to each phase of the periodically changing focus position. The image stack is processed to quantitatively show a set of three-dimensional surface coordinates corresponding to the surface shape of the workpiece as a Z L height coordinate map (e.g., point cloud) is determined or output.

[0136] In various embodiments, it will be appreciated that when a defined operation performed on the workpiece surface requires movement along the direction of the optical axis OA, including a VFL lens (e.g., VFL lenses 220, 370, etc.) can have various advantages. For example, as described above, when including a VFL lens (e.g., a TAG lens), in some embodiments, it is possible to achieve a change in the focus position of the VFL lens without the need for physical movement of components along the direction of the optical axis OA (e.g., such an operation can be performed quickly and repeatedly, and there is no risk of collision. For example, there is no possibility that the moving component collides with the workpiece surface, structure, and / or other components, etc.). In some embodiments, such an aspect can be particularly advantageous when the optical assembly is tilted (e.g., with respect to the Z-axis of the machine coordinate system, as shown in FIGS. 2B, 3B, 5C, and 8D). Typically, in embodiments where a VFL lens is not included and / or movement beyond the modulation limit of the VFL lens along the direction of the optical axis is desired, more complex and various movement sequences may be required.

[0137] For example, with respect to the configuration of FIG. 2B, when attempting to acquire an image stack along a fixed image stack acquisition axis ISAA without using a VFL lens (e.g., as part of a multi-point autofocus or PFF operation), movement for various rearrangements may be required in each image. More specifically, in order to properly align the optical assembly 205 with respect to the workpiece surface WPS1 along the image stack acquisition axis ISAA, at each image acquisition position, adjustment along the Z-axis of the machine coordinate system (e.g., using the motor 294), as well as adjustment along the Y-axis and / or X-axis of the machine coordinate system (e.g., performed by the movable stage 210 that moves the workpiece) may be necessary. Alternatively, in some embodiments, even in the orientation shown in FIG. 2B, image acquisition positions / movements only along the Z-axis of the machine coordinate system (e.g., executed by the motor 294) may be tolerated. In the orientation shown in FIG. 2B, when performing such movement only along the Z-axis direction of the machine coordinate system, the optical axis OA of the optical assembly 205 is not maintained along a fixed image stack acquisition axis ISAA for acquiring each image in the image stack. However, since the stack of captured images has a sufficiently large field of view, one or more desired regions of interest can be included in all images of the image stack. However, the relative position within each image shifts. Through appropriate processing, the desired region of interest can be determined / tracked and used for the desired operation (e.g., multi-point autofocus operation, PFF operation, etc. that can be used according to the methods described herein). It will be appreciated that by including and using a VFL lens (e.g., VFL lens 270), such processing and the need for additional movement can be avoided (i.e., due to the modulation of the VFL lens, the image stack can be captured along a fixed image stack acquisition axis ISAA relatively quickly and iteratively without the need for physical movement of other components and related processing).

[0138] As another example, in the embodiment of FIG. 8D, to capture an image stack along the image stack acquisition axis ISAA without using / include the VFL lens 370, movement along the X, Y, and / or Z-axis directions of the machine coordinate system may be required at each image acquisition position (e.g., performed by the X, Y, and Z-axis slide mechanisms 525, 526, and 527). As described above, such movement may not be necessary when the VFL lens 370 is included and used (i.e., due to the modulation of the VFL lens 370, images of the image stack can be acquired corresponding to various focus positions along a certain image stack acquisition axis ISAA without requiring physical movement of other components).

[0139] As described above, in various embodiments, the adjustment mechanism is controlled to move the optical assembly so as to place the workpiece surface within the autofocus range of the focus Z of the optical assembly. In embodiments where a VFL lens is included and used for autofocus scanning (e.g., no movement of other components for autofocus scanning is performed), the autofocus range of focus Z is mainly determined by and / or may be related to the operating range of the VFL lens (e.g., range Refp). For example, in the case of a specific TAG lens, in some embodiments, this may correspond to a range of approximately 10 DOF (depth of field) of the optical system (thus, it can be arranged, for example, within the 10 DOF of the optical system). As described above, in various embodiments without using / including the VFL lens (and / or when the system moves to increase the scanning range beyond / in addition to the range provided by the operation of the VFL lens), the autofocus range of focus Z is determined by / may correspond to other aspects of the system (e.g., the movement ranges of various components such as the movement range by the motor 294, and / or related to avoiding collisions, etc.).

[0140] As described above, in various embodiments, the multi-point autofocus image stack can be acquired relatively quickly and can include a relatively small number of images (e.g., 5 to 10 images). In various embodiments, it is desirable to move the optical assembly so that the workpiece surface is disposed within the autofocus range of focus Z of the optical assembly such that the multi-point autofocus image stack includes images on both sides of the focus Z position of various portions of the workpiece surface. In some embodiments, this may correspond to having at least a certain number of DOFs (e.g., 1 or 2 DOFs) on both sides of the focus Z position of each portion of the workpiece surface within the field of view of the optical assembly. Such an aspect can be advantageous with respect to determining the peak of the corresponding focus curve data, as described above. More specifically, as described above, determining the autofocus height of the position of the workpiece surface can include determining the focus curve data of that position / corresponding region of interest, at least in part, based on the analysis of the images of the image stack. The focus curve data of the position / region of interest indicates, for example, the autofocus height corresponding to the peak of the focus curve data. By acquiring images corresponding to sufficient focus curve data on both sides of the peak, the peak can be determined with greater / sufficient / desired accuracy and / or precision, etc.

[0141] It will be appreciated that such principles and descriptions may also apply to other processes described herein. For example, as described above, in various embodiments, after determining / calculating the surface normal, the orientation of the optical assembly can be rotated / adjusted and the distance between the optical assembly and the workpiece surface can be adjusted using the movement control unit. In various embodiments, the distance from the workpiece surface at which the adjustment of the optical assembly is performed can be based, at least in part, on principles such as those described above. For example, this distance may desirably be such that the workpiece surface is disposed at a desired position within the scanning range of the system (e.g., corresponding to a desired position within the PFF image stack scanning range such that there are a desired number of images corresponding to the focus data on both sides of each portion of the workpiece surface and / or in accordance with some desired performance characteristics of that portion of the scanning range).

[0142] While the preferred embodiments of the present disclosure have been illustrated and described, based on the present disclosure, numerous variations in the configuration and sequence of operations of the illustrated and described elements will be apparent to those skilled in the art. The principles disclosed herein can be implemented using various alternative forms. Furthermore, it is also possible to combine the various embodiments described above to provide another embodiment.

Claims

1. An optical assembly unit, comprising: a light source; an objective lens that inputs image light generated from the surface of a workpiece illuminated by the light source and transmits the image light along an imaging optical path, the objective lens defining an optical axis of the optical assembly unit that extends at least between the objective lens and the surface of the workpiece; a camera that receives the imaging light transmitted along the imaging optical path and provides an image of the surface of the workpiece; an optical assembly unit including the above; an adjustment mechanism configured to rotate the optical assembly unit with respect to the surface of the workpiece to change the angular orientation of the optical axis of the optical assembly unit with respect to the surface of the workpiece and further change the distance between the optical assembly unit and the surface of the workpiece; one or more processors; a memory coupled to the one or more processors and storing program instructions; a measurement system including the above, wherein when the program instructions are executed by the one or more processors, at least: controlling the adjustment mechanism to move the optical assembly unit so that the surface of the workpiece is disposed within the autofocus range of focus Z of the optical assembly unit; capturing an image stack of the surface of the workpiece within the autofocus range of focus Z using the optical assembly unit, the image stack including a plurality of images of the surface of the workpiece, each image of the image stack corresponding to a different autofocus height; determining the autofocus heights of at least three positions on the surface of the workpiece based on at least three corresponding regions of interest of the captured image stack; controlling the adjustment mechanism to rotate the optical assembly unit with respect to the surface of the workpiece and further adjust the distance between the optical assembly unit and the surface of the workpiece so that the optical axis of the optical assembly unit is nominally aligned with the surface normal of the surface of the workpiece based at least in part on the autofocus heights of the at least three positions; performing a defined operation on the surface of the workpiece; and causing the one or more processors to execute the above. A measurement system.

2. The optical assembly unit further includes a variable focal length (VFL) lens included in the imaging optical path. The objective lens transmits the image light along the imaging optical path through the VFL lens. The camera receives the imaging light transmitted by the VFL lens along the imaging optical path, according to the system of claim 1. **Claim 3** The VFL lens is a variable acoustic refractive index distribution type (TAG) lens configured to non-mechanically vary the focal length, and the periodically changed focusing position of the optical assembly unit is controlled by periodically changing the refractive power of the TAG lens, according to the system of claim 2. **Claim 4** The specified operation performed on the workpiece surface includes using the VFL lens to capture one or more images of the workpiece surface, according to the system of claim 2. **Claim 5** The specified operation performed on the workpiece surface includes using the VFL lens to capture an image stack while nominally aligning the optical axis of the optical assembly unit with the surface normal of the workpiece surface. The image stack includes a plurality of images of the workpiece surface, and each image of the image stack corresponds to a different focusing position of the optical assembly unit along the direction of the optical axis, according to the system of claim 2. **Claim 6** Determining the autofocus height at the at least three positions on the workpiece surface includes determining the focus curve data of each region of interest at least partially based on the analysis of the images in the image stack. At each of the at least three positions, the peak of the focus curve data of the corresponding region of interest indicates the corresponding autofocus height, according to the system of claim 1. **Claim 7** When the program instructions are executed by the one or more processors, determining the surface normal of the workpiece surface at least partially based on the autofocus height at the at least three positions; and determining adjustment information for controlling the adjustment mechanism to rotate the optical assembly unit at least partially based on the determined surface normal; and further causing the one or more processors to execute, according to the system of claim 1. **Claim 8** The specified operation includes a measurement operation for determining the dimensions of the elements on the workpiece surface, according to the system of claim 1. **Claim 9** The specified operation is to obtain an image stack including a plurality of images, each image corresponding to a focus position of the optical assembly unit along an imaging optical axis that coincides with the optical axis, and to obtain the image stack; to determine focus curve data indicating three-dimensional positions of a plurality of surface points on the workpiece surface, based at least in part on an analysis of the images of the image stack; The system according to claim 1, including a point from focus (PFF) operation including the above.

10. The specified operation includes a machining operation performed on the workpiece surface, and a machining axis of the machining operation is at least one of being nominally coincident with or nominally parallel to the optical axis of the optical assembly unit. The system according to claim 1.

11. The adjustment mechanism includes a rotation mechanism and a Z-axis movement mechanism, The Z-axis movement mechanism is coupled to move the optical assembly unit along the Z-axis direction, The rotation mechanism is coupled between the Z-axis movement mechanism and the optical assembly unit, and is configured to rotate the optical assembly unit with respect to the workpiece surface to change an angular orientation of the optical axis of the optical assembly unit with respect to the workpiece surface. The system according to claim 1.

12. The adjustment mechanism includes a rotary stage, The rotary stage includes the rotation mechanism and is coupled between the Z-axis movement mechanism and the optical assembly unit. The system according to claim 11, implemented in a precision machine vision inspection system.

13. The adjustment mechanism is an x-axis slide mechanism, a y-axis slide mechanism, and a z-axis slide mechanism configured to move the optical assembly unit in the x-axis, y-axis, and z-axis directions that are mutually orthogonal in a machine coordinate system, respectively; a rotation mechanism configured to rotate the optical assembly unit with respect to the workpiece surface; The system according to claim 1, implemented in a coordinate measuring machine system, including the above.

14. The adjustment mechanism is included in a robotic arm having at least three degrees of freedom for moving the optical assembly unit, and the system according to claim 1, implemented in a robotic system.

15. A method for operating a measurement system including an optical assembly unit, the optical assembly unit including a light source, An objective lens that inputs image light generated from the surface of a workpiece illuminated by the light source and transmits the image light along an imaging optical path, the objective lens defining an optical axis of the optical assembly unit that extends at least between the objective lens and the surface of the workpiece; A camera that receives the imaging light transmitted along the imaging optical path and provides an image of the surface of the workpiece; and The method includes: Moving the optical assembly unit to place the surface of the workpiece within the autofocus range of focus Z of the optical assembly unit; Capturing an image stack of the surface of the workpiece within the autofocus range of focus Z using the optical assembly unit, the image stack including a plurality of images of the surface of the workpiece, each image of the image stack corresponding to a different autofocus height; Determining the autofocus heights of at least three positions on the surface of the workpiece based on at least three corresponding regions of interest of the image stack; Based at least in part on the autofocus heights of the at least three positions, rotating the optical assembly unit with respect to the surface of the workpiece to nominally align the optical axis of the optical assembly unit with the surface normal of the surface of the workpiece, and further determining adjustment information for adjusting the distance between the optical assembly unit and the surface of the workpiece; Using the adjustment information for adjusting the distance between the optical assembly unit and the surface of the workpiece to rotate the optical assembly unit to nominally align the optical axis of the optical assembly unit with the surface normal of the surface of the workpiece; Performing a prescribed operation on the surface of the workpiece; A method including the above steps.

16. The optical assembly unit further includes a tunable acoustic gradient (TAG) lens included in the imaging optical path; The objective lens transmits the image light along the imaging optical path through the TAG lens; The camera receives the imaging light transmitted by the TAG along the imaging optical path; The method according to claim 15, further including periodically changing the refractive power of the TAG lens to provide a periodically changed focus position of the optical assembly unit.

17. The method according to claim 16, wherein the specified operation performed on the workpiece surface includes using the TAG lens to capture one or more images.

18. The method further includes determining a surface normal of the workpiece surface, at least partially based on the autofocus height at the at least three positions. The adjustment information is determined at least partially based on the determined surface normal, according to the method of claim 15.

19. The method according to claim 15, wherein the specified operation includes a measurement operation for determining dimensions of elements of the workpiece surface.

20. The specified operation is acquiring an image stack including a plurality of images, each image corresponding to a focus position of the optical assembly along an imaging optical axis that coincides with the optical axis, determining focus curve data indicating three-dimensional positions of a plurality of surface points on the workpiece surface, at least partially based on an analysis of the images of the image stack, The method according to claim 15, including a point from focus (PFF) operation.

21. The workpiece surface is a first workpiece surface of the workpiece. After performing the specified operation on the first workpiece surface, moving the optical assembly to place a second workpiece surface of the workpiece within an autofocus range of focus Z of the optical assembly, capturing an image stack of the second workpiece surface within the autofocus range of focus Z using the optical assembly, the image stack including a plurality of images of the second workpiece surface, each image of the image stack corresponding to a different autofocus height, determining the autofocus height at at least three positions of the second workpiece surface, based on at least three corresponding regions of interest of the image stack, rotating the optical assembly with respect to the second workpiece surface, at least partially based on the autofocus height at the at least three positions, to nominally align the optical axis of the optical assembly with the surface normal of the second workpiece surface, and further determining adjustment information for adjusting a distance between the optical assembly and the second workpiece surface. To rotate the optical assembly unit to nominally align the optical axis of the optical assembly unit with the surface normal of the second workpiece surface, and further to use the adjustment information for adjusting the distance between the optical assembly unit and the second workpiece surface. Performing the specified operation on the second workpiece surface. The method according to claim 15, further comprising.

22. An optical assembly unit, comprising: A variable focal length (VFL) lens; A light source; An objective lens that receives image light generated from the surface of a workpiece illuminated by the light source and transmits the image light along an imaging optical path passing through the VFL lens, the objective lens defining an optical axis of the optical assembly unit that extends at least between the objective lens and the workpiece surface; A camera that receives the imaging light transmitted by the VFL lens along the imaging optical path and provides an image of the workpiece surface; An optical assembly unit comprising the above; A Z-axis moving mechanism configured to change the distance between the optical assembly unit and the workpiece surface; A rotating mechanism configured to rotate the optical assembly unit with respect to the workpiece surface to change the angular orientation of the optical axis of the optical assembly unit with respect to the workpiece surface; One or more processors; A memory coupled to the one or more processors and storing program instructions; A measurement system comprising the above; When the program instructions are executed by the one or more processors, at least: Controlling the Z-axis moving mechanism or the rotating mechanism to move the optical assembly unit so that the workpiece surface is disposed within the autofocus range of the focus Z of the optical assembly unit; Capturing an image stack of the workpiece surface within the autofocus range of the focus Z using the optical assembly unit, the image stack including a plurality of images of the workpiece surface, each image of the image stack corresponding to a different autofocus height; Determining the autofocus heights of at least three positions on the workpiece surface based on at least three corresponding regions of interest in the image stack. Based at least in part on the autofocus height at the at least three positions, control the rotation mechanism to rotate the optical assembly relative to the workpiece surface so as to nominally align the optical axis of the optical assembly with the surface normal of the workpiece surface, and further control the Z-axis movement mechanism to adjust the distance between the optical assembly and the workpiece surface, perform a defined operation on the workpiece surface, A measurement system that causes the one or more processors to execute.

23. The system according to claim 22, wherein the VFL lens is a variable acoustic refractive index distribution type (TAG) lens, and the periodically changed focus position of the optical assembly is controlled by periodically changing the refractive power of the TAG lens.

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