Virtual zoom lens

Abstract

To provide an optical imaging system for a dimensional measuring machine.SOLUTION: The optical imaging system comprises a digital sensor 130 having an array of addressable pixels, a lens system 108 forming an image of a test object on the digital sensor, and a variable size aperture 150 that changes an F-number of a lens for imaging points of the test object on the digital sensor 130 at different spot sizes. An aperture controller 152 varies the size of the aperture 150. An image controller 154 groups contiguous clusters of one or more of the pixels having a common output such that the number of pixels within each of the clusters having a common output can be varied. A magnification controller 156 that works in conjunction with the aperture controller 152 and the image controller 154 increases / decreases the number of pixels within each of the clusters having a common output in accordance with an increase / decrease in the spot sizes at which points of the test object are imaged.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to optical dimension measurement systems, and more particularly to optical dimension measurement systems that operate at different effective magnifications for purposes such as adjusting field of view, depth of field, and optical resolution. [Background technology]

[0002] Conventional optical dimension measurement systems include zoom lenses to acquire images of the test object at different magnifications. For purposes such as identifying features of interest or taking less precise measurements, a lower magnification allows an image of the test object to be acquired with a wider field of view and a greater depth of field. For purposes such as identifying smaller features or taking more precise measurements, a higher magnification allows an image of the test object to be acquired with a narrower field of view and a shallower depth of field. Different magnifications are provided for feature identification and resolution according to different measurement purposes.

[0003] Conventional zoom lenses require additional components to move the optical elements, but these components are prone to failure and can result in undesirable variations in optical performance between different magnification positions. For example, conventional zoom lenses can exhibit varying amounts of distortion across the zoom range. Also, zoom lenses must be designed to be coaxial and parfocal to avoid additional adjustments between different magnification settings, which tends to increase costs.

[0004] A zoom lens, as part of an optical imaging system, forms an image of the test object on a digital sensor with an array of pixels. The optical dimensional measurement system analyzes these images to precisely determine (measure) where edges and other transition features of the test object are located. Typically, edge detection algorithms process contrast changes that span several pixels at the transition to obtain accurate and reproducible results. Variations in image resolution between different magnification settings (including variations across the field of view) can degrade the performance of edge detection algorithms and may require different adaptation strategies for different magnification settings. Summary of the Invention

[0005] Instead of using a conventional zoom lens to change the field of view and depth of field, an optical imaging system for a dimensional measurement system can be constructed using a fixed lens system with a variable-sized aperture, as described herein, along with additional controls for extracting and processing pixelated image data from a digital sensor. The optical imaging system disclosed herein can be constructed to significantly reduce axial movement between lens components and maintain both coaxiality and cofocality at different digital magnifications. Furthermore, the optical imaging system disclosed herein can effectively maintain image resolution optimally during edge detection at different digital magnifications.

[0006] For example, an optical imaging system for a dimension measuring machine includes a digital sensor having an array of addressable pixels, a lens system operable to form an image of a test object on the digital sensor, and a variable-size aperture of the lens system that varies the F-number of the lens system to image points of the test object onto the digital sensor at different spot sizes. An aperture controller varies the size of the variable-size aperture. An image controller groups one or more contiguous clusters of the addressable pixels into a common output. The number of pixels in each cluster having a common output is variable. A magnification controller operates in conjunction with the aperture controller and the image controller to (a) increase the number of pixels in each cluster having a common output in response to an increase in the spot size onto which the points of the test object are imaged, and (b) decrease the number of pixels in each cluster having a common output in response to a decrease in the spot size onto which the points of the test object are imaged.

[0007] The one or more clusters of pixels occupy sub-regions of the digital sensor according to the number of pixels in each sub-region, and the magnification controller varies the size of the sub-regions in response to changes in spot size onto which a point of the test object is imaged. The magnification controller changes the size of the sub-regions to more closely maintain the size of the sub-regions as a given fraction of the spot size onto which the point of the test object is imaged. The magnification controller fills spot sizes associated with different aperture sizes with substantially the same number of sub-regions.

[0008] Similarly, the magnification controller may be configured to (a) increase the size of the sub-regions as the F-number of the optical system increases, and (b) decrease the size of the sub-regions as the F-number of the optical system decreases. Preferably, the magnification controller increases the linear dimension of the sub-regions substantially proportional to an increase in the F-number of the lens system.

[0009] The imaging system further includes a display that displays the test object at different magnifications, and the magnification controller (a) increases the magnification of the test object on the display as the size of the sub-area decreases, and (b) decreases the magnification of the test object on the display as the size of the sub-area increases. The magnification of the test object on the display may be inversely proportional to the size of the image pixel. An increase in the size of the sub-area may be associated with an increase in the area of ​​the digital sensor on which the test object is displayed, and a decrease in the size of the sub-area may be associated with a decrease in the area of ​​the digital sensor on which the test object is displayed. The same number of sub-areas may be displayed, resulting in different display magnifications.

[0010] In another example, an optical measurement system for performing dimensional measurements of a test object can be configured to include a digital sensor having an array of addressable pixels, a lens system that forms an image of the test object on the digital sensor, and a variable-size aperture operable to change the F-number of the optical system. An aperture controller varies the size of the aperture. An image controller groups contiguous clusters of one or more pixels having a common output into respective sub-regions of the digital sensor. The size of the sub-regions varies depending on the number of pixels in each sub-region. A magnification controller operates in conjunction with the aperture controller and the image controller to (a) increase the size of the sub-regions as the size of the aperture decreases, and (b) decrease the size of the sub-regions as the size of the aperture increases. The measurement controller includes an edge detector that detects the edge of the test object imaged on the digital detector as a variation in output between the sub-regions, whereby as the size of the sub-regions increases, the edge of the test object can be detected with a greater depth of field, and as the size of the sub-regions decreases, the edge of the test object can be resolved with greater precision.

[0011] The variable size aperture of the optical system can change its F-number to image points of the test object onto the digital sensor with different spot sizes, and the magnification control The roller (a) increases the number of pixels in each subregion in accordance with an increase in the spot size onto which the test object point is imaged, and (b) decreases the number of pixels in each subregion in accordance with a decrease in the spot size onto which the test object point is imaged. The magnification controller changes the size of the subregions to more closely maintain the size of the subregions as a given fraction of the spot size onto which the test object point is imaged. The magnification controller can fill the spot sizes associated with different aperture sizes with the same number of subregions. For example, the linear dimension of the spot size associated with different aperture sizes is filled by five subregions. The magnification controller can direct output from the same number of subregions at different aperture sizes to the edge detector.

[0012] The magnification controller can (a) increase the size of the subregions as the F-number of the optical system increases, and (b) decrease the size of the subregions as the F-number of the optical system decreases. The magnification controller can increase a linear dimension of the subregions substantially proportional to an increase in the F-number of the optical system.

[0013] The measurement system may further include a display operable to display the test object at different magnifications. The magnification controller may (a) increase the magnification of the test object on the display as the size of the sub-region decreases, and (b) decrease the magnification of the test object on the display as the size of the sub-region increases. The magnification of the test object on the display may be inversely proportional to the size of the sub-region. Both the edge detector and the display may receive output from the same sub-region of the digital sensor.

[0014] The optical system may include a front lens and a back lens that are fixed relative to the variable-size aperture. In one configuration, the front lens and the back lens are positioned telecentrically relative to the variable-size aperture. However, it should be understood that many of the benefits of the present invention can be achieved in non-telecentric configurations. Thus, in one configuration, the front lens and the back lens are not telecentric. In one embodiment, the measurement controller is configured to detect two edges of a test object and measure the distance between the two edges based on the number and size of subregions between the two edges. The measurement controller can detect the edges of the test object, construct a polyhedron feature, and determine the dimensions of the polyhedron.

[0015] An exemplary method for measuring dimensions of a test object using an optical measurement machine begins by aligning the test object with an optical system. The optical system has a variable-size aperture and forms an image of the test object on a digital sensor having an array of addressable pixels. The variable-size aperture is set to a first size. Contiguous clusters of pixels having a common output are grouped into subregions of the digital sensor having a first size according to the number of pixels in each subregion. Two or more edges of the test object imaged onto the digital detector can be identified based on output variations between the subregions of the first size. The two or more edges of the test object are focused at a first depth of field and a first resolution. If a wider field of view of the test object is required, the optical measurement machine can be used with the first depth of field and the first resolution. For example, a wider field of view is required to determine where on the test object to measure.

[0016] The variable-size aperture can be set to a second, larger size. Contiguous clusters of pixels with a common output are regrouped into subregions of the digital sensor having a second, smaller size according to the reduced number of pixels in each subregion. Dimensional measurements are performed using two different fields of view at a higher resolution by moving the stage on which the test object is positioned. For example, two or more edges of the test object imaged on the digital detector are identified based on the output variation between the second, smaller-sized subregions. The two or more identified edges of the test object are focused at a second, shallower depth of field and a second, higher resolution. The distance between two of the two or more edges can be measured based on the number and size of the second, smaller-sized subregions between the two edges.

[0017] In one embodiment, the edge detection software is operable to use a low magnification (wider field of view) to identify a feature of the test object to be measured, followed by dimensional measurements at a higher magnification (narrower field of view). Setting the variable-size aperture to a second, larger size reduces the F-number of the optical system to image the point of the test object onto the digital sensor at a smaller spot size. The regrouping step reduces the size of the pixel subregions in accordance with the smaller spot size at which the point of the test object is imaged. The regrouping step reduces the size of the pixel subregions to more closely maintain the size of the subregions as a given fraction of the spot size at which the point of the test object is imaged. [Brief explanation of the drawings]

[0018] The accompanying drawings are incorporated as part of this specification. The drawings illustrate embodiments of the disclosed subject matter and illustrate selected principles and teachings of the present disclosure. However, the drawings do not depict every possible embodiment of the disclosed subject matter, and are not intended to limit the scope of the present disclosure in any way.

[0019] [Figure 1] 1 is a schematic perspective view of a dimensioning machine according to an exemplary embodiment of the presently disclosed subject matter; FIG.

[0020] [Figure 2] 1 is a schematic diagram of an optical imaging system according to an exemplary embodiment of the disclosed subject matter.

[0021] [Figure 3] 1 is a table of design parameters for four available magnifications of an optical imaging system according to an exemplary embodiment of the disclosed subject matter.

[0022] [Figure 4] 1 is a schematic diagram illustrating different areas of a digital sensor array utilized by an optical imaging system at different effective magnifications in an exemplary embodiment of the disclosed subject matter.

[0023] [Figure 5A] 5 is a schematic diagram of the central 24×24 pixels of the digital sensor array of FIG. 4 in one of different binnings. [Figure 5B] FIG. 5 is a schematic diagram of the central 24×24 pixels of the digital sensor array of FIG. 4 with alternative binning. [Figure 5C] FIG. 5 is a schematic diagram of the central 24×24 pixels of the digital sensor array of FIG. 4 with alternative binning. [Figure 5D] FIG. 5 is a schematic diagram of the central 24×24 pixels of the digital sensor array of FIG. 4 with alternative binning.

[0024] [Figure 6] FIG. 5 is a schematic diagram of the central 24×24 pixels of the digital sensor array of FIG. 4 with non-square binning.

[0025] [Figure 7A] 1 is a schematic diagram of a lens system having a pair of doublets operable to move along an optical axis, according to an exemplary embodiment of the disclosed subject matter. [Figure 7B] FIG. 2 is a schematic diagram of the lens system.

[0026] [Figure 8A] FIG. 1 is a schematic perspective view of a dimension measuring machine with a lens turret, according to an exemplary embodiment of the presently disclosed subject matter.

[0027] [Figure 8B] 8B is a schematic diagram of the optical imaging system of the dimension measuring machine of FIG. 8A with the objective lens positioned along the optical axis. [Figure 8C] 8B is a schematic diagram of an optical imaging system in the dimension measuring machine of FIG. 8A with an objective lens at a different position along the optical axis than in FIG. 8B.

[0028] [Figure 9A] 1 is a schematic diagram of a portion of an optical imaging system having a compound lens operable to change the magnification of the system, according to an embodiment of the disclosed subject matter. [Figure 9B] FIG. 9B is a schematic diagram of a portion of an optical imaging system showing the compound lens of FIG. 9A in an inverted position.

[0029] [Figure 10] 1 is a schematic diagram of an optical imaging system according to an embodiment of the disclosed subject matter.

[0030] [Figure 11A] 1 is a schematic diagram of an optical imaging system according to an embodiment of the disclosed subject matter.

[0031] [Figure 11B] 1 is a schematic diagram of an optical imaging system according to an embodiment of the disclosed subject matter.

[0032] [Figure 11C] 1 is a schematic diagram of an optical imaging system according to an embodiment of the disclosed subject matter. Detailed Description of the Invention

[0033] It is to be understood that the present invention may assume various alternative orientations and steps unless expressly stated otherwise. It is also to be understood that the specific assemblies and systems illustrated in the accompanying drawings and described in the specification are merely exemplary embodiments of the inventive concepts defined. Accordingly, specific dimensions, orientations, or other physical characteristics relating to the disclosed embodiments are not to be considered limiting, unless expressly stated otherwise. Also, where not otherwise stated, like elements in the various embodiments described herein are commonly referred to by like reference numerals.

[0034] As used herein, terms such as "first," "second," etc., do not necessarily indicate an order or priority, unless otherwise specified, but are merely used to clearly distinguish one element or set of elements from another element or set of elements.

[0035] As used herein, the term "exemplary" refers to an "example" and is not intended to suggest a preferred or ideal embodiment.

[0036] The present disclosure provides, among other things, a dimensional measurement video system capable of operating with a wide field of view ("FOV"), high effective magnification, and high focus repeatability. The dimensional measurement video system of one embodiment includes an optical imaging system having a fixed lens used at multiple f / numbers in combination with different regions of the camera (i.e., a digital sensor array) to generate the desired magnification. The dimensional measurement video system of one embodiment includes an optical imaging system having a movable lens operable to generate high-quality images over a range of focal lengths with a large zoom ratio.

[0037] As shown in FIGS. 1 and 2 , in one embodiment, a dimension measuring machine 100 is operable to measure a test object 10 mounted on a worktable (i.e., stage) 102. The dimension measuring machine 100 includes an optical imaging system 104 having an illumination system 106. In one embodiment, the illumination system 106 comprises a ring light having a central aperture for capturing images of the worktable 102 and the test object 10. An annular portion surrounding the central aperture of the illumination system 106 includes a plurality of light sources. For example, the illumination system 106 may include a selectively activatable, essentially monochromatic light source operable to illuminate the test object 10. The light sources include, but are not limited to, a plurality of light emitting diodes (LEDs). Those skilled in the relevant art will recognize that the dimension measuring machine 100 may utilize a variety of illumination systems.

[0038] 2, the optical imaging system 104 includes an objective lens 122 (i.e., a front lens) positioned to collect at least a portion of the light illuminating the test object 10. The objective lens 122 collects light reflected from the surface of the test object 10 by specular reflection, diffuse reflection, or a combination of specular reflection and diffuse reflection.

[0039] The light collected by the objective lens 122 is referred to as the image light beam 116. A portion of the image light beam 116 propagates through focusing optics 124 (i.e., a back lens) on its way to the camera system 126. In one embodiment, the focusing optics 124 comprises a fixed lens operable to form an image of the test object 10 on the digital sensor array 130. The lens system 108 of the optical imaging system 104 comprises the objective lens 122 and the focusing optics 124. The camera system 126 includes a digital sensor array 130, which comprises an image sensor such as an area charge-coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS). As described in more detail below, the digital sensor array 130 includes a plurality of addressable pixels 200.

[0040] 2 , in one embodiment, a variable-size aperture 150 is positioned at a telecentric position of the focusing optical lens 124. The variable-size aperture 150 is operable to change the F-number of the lens system 108 and, therefore, the optical imaging system 104. Because the variable-size aperture 150 is positioned at a telecentric position of the optical imaging system 104, all FOVs are telecentric. Each size of the variable-size aperture 150 utilizes a different area of ​​the digital sensor array 130 for imaging. The focusing optical lens 124 is parfocal with the variable-size aperture 150 within a depth of field (“DOF”) d for each size. In one embodiment, because the optical imaging system 104 does not include any optical elements that move in the z-axis, there is no need to recalibrate the magnification of the optical imaging system 104 when the effective magnification of the dimension measuring machine 100 is changed.

[0041] 1, in one embodiment, optical imaging system 104 is mounted on a carriage 170 that is movable along a vertical z-axis. Carriage 170 is mounted on rails 172, 174 to facilitate movement along the z-axis to adjust the distance between camera system 126 and test subject 10. Worktable 102 is mounted on another carriage 176 and is movable along the y-axis via rails 178, 180 and along the x-axis via rails 182, 184.

[0042] In one embodiment, the optical imaging system 104 includes a 2592 x 1944 pixel digital sensor array 130 with addressable pixels 200 that are 2 μm square. The active sensor size of the digital sensor array 130 may be 5.4 mm x 4.2 mm. In one embodiment, the dimensioner 100 includes a visual display 160 that has 640 x 480 pixels (i.e., VGA resolution). The visual display 160 may be an image display screen.

[0043] In one embodiment, the dimension measuring machine 100 includes a measurement controller 158 with edge detection software. This edge detection software performs optimally when the measured edge has five image pixels 202, 204, 206, 208, 210 within the diffraction-limited spot size Sd of the optical imaging system 104. The edge detection software processes contrast changes across several pixels and optimizes the number of image pixels in transition to achieve accurate and repeatable results. Therefore, the variable-size aperture 150 is adjusted at each magnification to maintain approximately five image pixels 202, 204, 206, 208, 210 within the diffraction-limited spot size Sd of the optical imaging system 104 to optimize the edge detection algorithm. The design parameters for four effective magnifications are shown in the table in FIG. 3. Column 1 shows the one-dimensional (1D) image of the digital sensor array 130 binned by magnification. The binnings indicate the number of pixels 200 in a pixel array 130 (e.g., x-axis). The binnings are 1x1, 2x2, 3x3, and 4x4 groups (e.g., square groups) of pixels in the digital sensor array 130, respectively. The "image pixel size" is the size of one side of a square binned pixel and is equal to the pixel size of the digital sensor array 130 (e.g., 2 μm) multiplied by the number of pixels in each binned group. The "spot size" required to optimize the edge detection algorithm (i.e., the diffraction-limited spot size Sd) is equal to the "image pixel size" multiplied by the number of pixels in the digital sensor array 130 required to optimize the edge detection algorithm (e.g., 5 image pixels).

[0044] 4, in one embodiment, the highest effective magnification of the optical imaging system 104 can be achieved by utilizing a 640×480 pixel 200 located in the center of the digital sensor array 130. Lower effective magnifications of the optical imaging system 104 can be achieved by binning 2×2, 3×3, or 4×4 groups of the pixels 200 of the digital sensor array 130 and creating enlarged image pixels 202, 204, 206, and 210, while maintaining 640×480 pixels in the image displayed via the image display screen 160. Because the size of the displayed image remains the same, as the size of the image pixels 202, 204, 206, 208, 210 increases, the effective magnification of the displayed image decreases to half (1 / 2), 1 / 3, or 1 / 4 of the maximum effective magnification as the number of pixels 200 of the digital sensor array 130 that are binned within the size of each image pixel 202, 204, 206, 208, 210 increases.

[0045] 5A-5D show schematic diagrams of the central 24×24 pixel 200 of the digital sensor array 130 at different binnings. The binning pattern is repeated across the digital sensor array 130 until the required number of image pixels 202, 204, 206, 208, and 210 for binning is reached. As shown in FIG. 5A, in binning 4, a 4×4 square region of pixels 200 is binned to generate one output image pixel 202. As shown in FIG. 5B, in binning 3, a 3×3 square region of pixels 200 is binned to generate one output image pixel 204. As shown in FIG. 5C, in binning 2, a 2×2 square region of pixels 200 is binned to generate one output image pixel 206. As shown in FIG. 5D, in binning 1, a 1×1 square region of pixels 200 is binned to generate one output image pixel 208.

[0046] As shown in Figures 5A-5D, the pixels 200 are binned into square groups for ease of implementation in electronic devices, but the groups of pixels 200 need not be square. Any binning pattern that covers the required pixel area can be used. For example, as shown in Figure 6, the columns of binned pixels 200 may be offset and staggered. In this example, an alternative binning pattern Binning 1 has 8 sensor pixels 200 within the image pixel 210. Binnings 2, 3, and 4 will have 32, 72, and 128 sensor pixels 200 per image pixel 210, respectively.

[0047] The diffraction-limited spot size Sd on the digital sensor array 130 is represented by the diameter of the Airy disk and is: Sd=2.44λF i =2.44λmF0(1) where λ is the wavelength of the light generated by the light source 106. In one embodiment, the wavelength λ is 0.6 μm, as shown in FIG. i is the F-number of the imaging system 104 on the digital sensor array 130 side of the fixed lens 124, and F o The test pair of fixed lenses is 124. The variable m is the magnification of the imaging system 104. Equation (1) is the F-number F i , F o can be solved.

[0048] The DOF (depth of field) d is the defocused spot size S at the object plane. f is the diffraction-limited spot size S at the object plane d The defocus spot size S at distance x from the focus is limited to a range smaller than f is as follows: S f = x / F o (2)

[0049] Defocused spot size Sf is mS in the image plane f If the DOF d is spread evenly on both sides of the focus, dividing the DOF d by 2 (d / 2) gives the defocus spot size S f is the diffraction-limited spot size S d (mS f =S d ) is the point where The following equation can be derived from equations (1) and (2): m(d / 2) / F o = 2.44λmF o (3) From equation (3), DOFd is calculated by the F-number F of the fixed lens 124 on the test object 10 side. o It can be calculated as a function of d=4.88λF o 2 (4)

[0050] The resolution of the optical imaging system 104 is not limited by the size of the pixels 200 of the digital sensor array 130. The dimensioning machine 100 does not need to modify its image processing software for each available magnification. Therefore, the edge detection algorithm and the number of image pixels 202, 204, 206, 208, 210 in the image sent to the visual display 160 remain the same at each magnification.

[0051] Aperture controller 152 communicates with variable size aperture 150. As shown in Figure 2, in one embodiment, aperture controller 152 is electrically connected to variable size aperture 150. In other embodiments, aperture controller 152 may be connected via WiFi, Bluetooth, etc. The aperture controller 152 is wirelessly connected to the variable size aperture 150. The aperture controller 152 sends a signal to the variable size aperture 150 to change the diameter of the variable size aperture 150 and produce different diffraction limited spot sizes S d The diameter of the variable size aperture 150 varies the image point of the test object 10 on the digital sensor array 130 at the diffraction limited spot S dThe diameter of the diffraction-limited spot S is adjusted to maintain the aperture diameter according to the size of the image pixels 202, 204, 206, 208, and 210. d The diameter of is determined by the number of image pixels 202, 204, 206, 208, 210 (e.g., five image pixels) required for the optimized edge detection algorithm used in the dimensioning machine 100. The number of image pixels 202, 204, 206, 208, 210 in the diffraction-limited spot does not need to be exactly the same at each magnification.

[0052] In the optical imaging system 104, a low magnification state provides a wide FOV with a large F-number and a large DOFd. In a high magnification state, the F-number is smaller, the DOFd is smaller, and the FOV is narrower. Each size of the aperture 150 uses a different area (i.e., number of pixels 200) of the digital sensor array 130. Each size of the aperture 150 provides a different camera resolution. In a low magnification state (e.g., binning 4), substantially the entire digital sensor array 130 is used. Using substantially the entire digital sensor array 130 provides the largest FOV for the optical imaging system 104. In the low magnification state, the aperture 150 is at its smallest diameter used, providing the largest DOFd and F-number.

[0053] In the high magnification state (e.g., binning 1), only approximately a 640x480 pixel portion of the digital sensor array 130 is used. In the high magnification state, the aperture 150 is at its largest diameter, providing the smallest FOV and F-number. In one embodiment, in the high magnification state, pixels 200 outside the central 640x480 pixel portion of the digital sensor array 130 are ignored by the measurement controller 158. In the high magnification state, the optical imaging system 104 utilizes the full resolution of the digital sensor array 130 by using image data from each sensor pixel 200, while only using image data from the central 640x480 pixel portion of the digital sensor array 130. The high magnification state provides the best edge detection and focus repeatability.

[0054] The effective magnification of the dimensioning machine 100 is determined by the size of the area of ​​the digital sensor array 130 used to create an image on the visual display 160. For example, when the same area of ​​the image display screen 160 is used at different F-stop settings, the effective magnifications associated with different F-stop settings are associated with different sized image pixels 202, 204, 206, 208, 210. The image pixels 202, 204, 206, 208, 210 describe sub-areas of the digital sensor array 130 from which pixel output data (i.e., contiguous clusters of addressable pixels with a common output) are drawn to fill the image display screen 160. When the same number of pixel outputs of the digital sensor array 130 at different F-stop settings are passed to the image display screen 160 via binning, the resolution of the image display screen 160 appears to remain constant. If the change in size of the sub-area of ​​the digital sensor array 130 that fills the image display screen 160 with a given number of pixel outputs (i.e., image pixels 202, 204, 206, 208, 210) remains proportional to the change in the F-stop setting, then both the effective magnification and resolution of the test object on the display screen will remain proportional to the change in the F-stop setting.

[0055] 2, the image controller 154 is in communication with the digital sensor array 130. In one embodiment, the image controller 154 is electrically connected to the digital sensor array 130. The image controller 154 sends signals to the digital sensor array 130 to bin the pixels 200 of the digital sensor array 130 to create image pixels 202, 204, 206, 208, and 210. Binning involves grouping adjacent clusters of the pixels 200 of the digital sensor array 130 into a common output (i.e., image pixel). The number of pixels 200 of the digital sensor array 130 in each cluster can vary.

[0056] Diffraction-limited spot size S dThe number of image pixels 202, 204, 206, 208, 210 in the image plane remains substantially constant as the effective magnification is changed to optimize edge detection. d If is changed for other reasons, the edge detection software can be modified.

[0057] Substantially the same number of image pixels 202, 204, 206, 208, 210 may be imaged at different effective magnifications (i.e., different F-number settings of the optical imaging system 104) to produce diffraction-limited spot sizes S d However, the diffraction-limited spot S d The number of pixels 200 in the digital sensor array varies with different effective magnifications. Equation (1) defines the diffraction-limited spot size S d 210 is proportional to the F-number setting of the optical imaging system 104. The same number of image pixels 202, 204, 206, 208, 210 will have different diffraction-limited spot sizes S at different F-number settings. d satisfies the condition, the size of the image pixels 202, 204, 206, 208, 210 varies proportionally with the F-stop setting. The relative sizes of the image pixels 202, 204, 206, 208, 210 at different F-stop settings can vary slightly without substantially affecting the accuracy of the edge detector.

[0058] The magnification controller 156 is in communication with the aperture controller 152 and the image controller 154. In one embodiment, the magnification controller 156 is electrically connected to the aperture controller 152 and the image controller 154. The magnification controller 156 sends signals to the aperture controller 152 and the image controller 154 to control the number of pixels 200 in each image pixel 202, 204, 206, 208, 210 (i.e., a binned cluster of contiguous pixels 200 of the digital sensor array 130) to determine the diffraction-limited spot size S at which a point on the test object 10 is imaged. d Increase or decrease depending on the increase or decrease in diameter.

[0059] Each of the image pixels 202, 204, 206, 208, 210 occupies a sub-area of ​​the digital sensor array 130 according to the number of pixels 200 in the cluster of binned pixels 200. The magnification controller 156 controls the size of the sub-areas (i.e., image pixels 202, 204, 206, 208, 210) according to the number of times a point of the test object 10 is imaged. In addition, the magnification controller 156 varies the size of the sub-areas of the digital sensor array 130 to adjust the diffraction-limited spot size Sd at which points on the test object 10 are imaged. d The magnification controller is operable to more closely maintain the size of the sub-regions as a given (predetermined) fraction of the diameter. The magnification controller controls the spot size S associated with different aperture 150 sizes. d are operable to fill each spot size S with substantially the same number of image pixels 202, 204, 206, 208, 210. However, d The edge detection algorithm does not fail even if the number of image pixels 202, 204, 206, 208, 210 in each spot size S d Variations in the number of image pixels 202, 204, 206, 208, 210 within the image display screen 160 (e.g., variations of half or more of the image pixels 202, 204, 206, 208, 210) do not hinder the performance of the edge detection algorithm for many test objects. Consistent performance of the edge detection software is maintained as the effective magnification changes if each spot size Sd across the edge contains approximately the same number of image pixels 202, 204, 206, 208, 210. The effective magnification of the test object 10 on the image display screen 160 is inversely proportional to the total size of the sub-areas of the digital sensor 130.

[0060] In the low magnification state, the optical imaging system 104 provides both a wide field of view and a deep depth of field to identify the type and location of one or more features on the test object 10 presented for measurement. In the low magnification state, the optical imaging system 104 can video measure a range of feature sizes on the test object 10 within a predetermined accuracy range. In the high magnification state, the optical imaging system 104 provides both a smaller field of view and a smaller depth of field to measure smaller features on the test object 10 and / or measure changes in the surface height of the test object 10 using an autofocus method that correlates the surface height with an optimal focus position. Measurements are performed by translating the worktable 102 and test object 10 relative to the optical imaging system 104 to identify the focus position and measure the translation. Autofocus measurements are performed by moving one or more elements of the optical imaging system 104 along an optical axis (e.g., the z-axis) and measuring the displacement of the elements.

[0061] In embodiments of the presently disclosed subject matter, the zoom range of the dimensioning machine 100 can be extended beyond the zoom range available with a fixed-lens optical imaging system 104 in several ways. Referring to FIGS. 7A and 7B , in one embodiment, the lens system 300 of the optical imaging system 104 comprises an objective lens 122 and a focusing optic 124. The zoom range of the optical imaging system 104 can be extended by allowing one or more elements of the lens system 300 to move along the optical axis. In one embodiment, a pair of doublets 302 of the focusing optic 124 moves along the optical axis to change the magnification of the lens system 300. For example, the optical magnification of the optical imaging system 104 can be changed from 1× to 2× by moving the pair of doublets 302 from position X1 in FIG. 7A to position X2 in FIG. 7B. The doublets 302 move along the optical axis between these two repeatable positions X1, X2. By moving the lens pair 302, the zoom range of the optical imaging system 104 is doubled.

[0062] In another embodiment, as shown in Figures 8A, 8B, and 8C, the optical imaging system 104 includes a lens turret 400. The lens turret 400 includes multiple objective lenses 422A, 422B having different optical magnifications, and the magnification of the optical imaging system 104 is changed by moving or rotating the lens turret 400 to align the objective lenses 422A, 422B that provide the appropriate or desired magnification. In one embodiment, the lens turret 400 includes an objective lens 422A that provides a 0.5x magnification and an objective lens 422B that provides a 1.1x magnification. In another embodiment, additional objective lenses 422 are included in the lens turret 400. Similarly, multiple objective lenses mounted on sliders can be utilized in the same manner as the lens turret 400.

[0063] In one embodiment, as shown in FIGS. 9A and 9B , the optical imaging system 104 includes a focusing optics 124 having a compound lens 500. The zoom of the optical imaging system 104 is increased by flipping / inverting the compound lens 500 along its optical axis. For example, by flipping the compound lens 500 from the position shown in FIG. 9A to the position shown in FIG. 9B , the magnification can be increased from 1.71× to 2×. In other words, the compound lens 500 shown in FIG. 9A is inverted in FIG. 9B , causing the image light beam 116 to pass through the compound lens 500 in the opposite direction. As shown in FIG. 9A , the image light beam 116 enters the second surface 504 of the compound lens 500 and exits through the first surface 502 of the compound lens 500. When the compound lens 500 is inverted, as shown in FIG. 9B , the image light beam 116 enters the first surface 502 and exits through the second surface 504. In one embodiment, the compound lens 500 is a pair of lenses.

[0064] In yet another embodiment, as shown in FIG. 10 , the objective lens 122 of the lens system 108 may be supplemented or replaced with an electro-optic lens 622. The focal length of the electro-optic lens 622 can be electrically changed by a factor of two or more without requiring a change in the position of the electro-optic lens 622 within the optical imaging system 104. For example, the electro-optic lens 622 may be one of the Optotune EL series electrically tunable lenses sold by Stemmer Imaging AG, having a place of business at Gutenbergstrasse 9-13, 82178 Puchheim, Germany, the entire contents of which are incorporated herein by reference. The electro-optic lens 622 is operable to change shape using a combination of an optical fluid and a polymer film. In one embodiment, the electro-optic lens 622 includes a container filled with an optical liquid and sealed with an elastic polymer film. A circular ring operable to engage the elastic polymer film facilitates shaping of the electro-optic lens 622. The focal length of the electro-optic lens 622 is changed by using a current-controlled voice coil to force fluid into the center of the lens.

[0065] In another embodiment, the zoom range of the dimensioner 100 can be extended beyond that available with the fixed-lens optical imaging system 104 by utilizing two virtual zoom lenses with different optical magnifications. In other words, the dimensioner 100 employs two camera systems 126A, 126B, each with a digital sensor array 130A, 130B. These digital sensor arrays may comprise, for example, area charge-coupled device (CCD) or complementary metal-oxide semiconductor (CMOS) image sensors, as previously described. In one embodiment, the two camera systems 126A, 126B share the objective lens 122 but have separate focusing optics 124A, 124B (i.e., back lenses) that provide different magnifications for each camera system 126A, 126B. An image controller 154 communicates with the second digital sensor array 130B. In one embodiment, the image controller 154 is operable to determine, in response to predetermined magnification parameters, which digital sensor array 130A, 130B to use to take measurements and create images on the visual display 160. In another embodiment, an operator can manually switch between the digital sensor arrays 130A, 130B used to take measurements and create images on the visual display 160. In one embodiment, a portion of the image light beam 116 collected by the objective lens 122 is directed through a beam splitter 700 to the second focusing optics 124B of the second camera system 126B.

[0066] 11B and 11C, the image light beam 116 collected by the objective lens 122 is selectively directed to the second focusing optics 124B of the second camera system 126B via a specular reflective surface 702. As shown in FIG. 11B, the reflective surface 702 includes, for example, a mirror coupled to a pivot 704. The pivot 704 is operable to rotate the mirror 702 from a first position m1 outside the optical path of the image light beam 116 to a second position m2 within the optical path of the image light beam 116. As shown in FIG. 11C, the reflective surface 702 includes, for example, a mirror coupled to a slide 706. The slide 706 is operable to move the mirror 702 from a first position m1 outside the optical path of the image light beam 116 to a second position m2 within the optical path of the image light beam 116.

[0067] One or more features of the embodiments described herein may be combined to create additional embodiments not shown. While various embodiments have been described in detail above, it should be understood that they are presented by way of example and not limitation. It will be apparent to those skilled in the relevant art that the disclosed subject matter may be embodied in other specific forms, variations, and modifications without departing from the scope, spirit, or essential characteristics thereof. Accordingly, the above-described embodiments are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is indicated by the appended claims, and all changes that come within the meaning and range of equivalents thereof are intended to be embraced therein.

Claims

1. 1. An optical imaging system for a dimension measuring machine, comprising: a digital sensor having an array of addressable pixels; a lens system operable to form an image of a test object on the digital sensor and operable to image points of the test object onto the digital sensor at different spot sizes; an image controller operable to bin one or more of the arrays of addressable pixels into image pixels, the number of pixels within each image pixel being variable; a magnification controller operative in conjunction with the image controller to (a) increase the number of pixels within each image pixel in response to an increase in the spot size onto which the points of the test object are imaged, and (b) decrease the number of pixels within each image pixel in response to a decrease in the spot size onto which the points of the test object are imaged; Equipped with An optical imaging system wherein the number of image pixels at each spot size is maintained substantially constant, and each image pixel contains the same number of pixels.

2. 2. The optical imaging system of claim 1, wherein the image pixels occupy sub-areas of the digital sensor according to the number of pixels in each image pixel, and the magnification controller varies the size of the image pixels according to changes in the spot size onto which a point of the test object is imaged.

3. 3. The optical imaging system of claim 2, wherein the magnification controller is operable to vary the size of the image pixels to maintain the size of the image pixels as a fraction of a spot size onto which a point of a test object is imaged.

4. 3. The optical imaging system of claim 2, wherein the magnification controller (a) increases the size of the image pixels as the F-number of the lens system increases, and (b) decreases the size of the image pixels as the F-number of the lens system decreases.

5. The optical imaging system of claim 4 , wherein the magnification controller increases a linear dimension of the image pixel substantially proportionally to an increase in the f-number of the lens system.

6. a display operable to show the test object at different magnifications; 3. The optical imaging system of claim 2, wherein the magnification controller is operable to (a) increase the magnification of the test object on the display as the size of the image pixels decreases, and (b) decrease the magnification of the test object on the display as the size of the image pixels increases.

7. The optical imaging system of claim 6 , wherein the magnification of the test object on the display is inversely proportional to the size of the image pixels.

8. 7. The optical imaging system of claim 6, wherein an increase in the size of the image pixels increases the sub-area of ​​the digital sensor on which the test object is displayed, and a decrease in the size of the image pixels decreases the sub-area of ​​the digital sensor on which the test object is displayed.

9. The optical imaging system of claim 6 , wherein the number of image pixels displayed at different magnifications remains substantially constant.

10. The optical imaging system of claim 1 , wherein each image pixel comprises an offset staggered array of said addressable pixels.

11. 1. An optical measurement system for taking dimensional measurements of a test object, comprising: a digital sensor having an array of addressable pixels; a lens system operable to form an image of a test object on said digital sensor, said lens system having a variable focal length; an image controller operable to group contiguous clusters of one or more of the addressable pixels for a common output to respective sub-regions of the digital sensor, the size of the sub-regions varying according to the number of pixels in each sub-region; a magnification controller operable in conjunction with the image controller to (a) increase the size of the sub-regions in response to an increase in the F-number of the lens system, and (b) decrease the size of the sub-regions in response to a decrease in the F-number of the lens system; a measurement controller including an edge detection unit operable to detect edges of the test object imaged on the digital sensor as output variations between the sub-regions, the edge detection unit being capable of detecting test object edges with a greater depth of field as the size of the sub-regions increases and being capable of resolving test object edges with greater precision as the size of the sub-regions decreases; A measurement system comprising:

12. the lens system is operable to image points of the test object onto the digital sensor at different spot sizes; 12. The measurement system of claim 11, wherein the magnification controller is operable to: (a) increase the number of addressable pixels in each sub-region in accordance with an increase in spot size onto which a point of the test object is imaged; and (b) decrease the number of addressable pixels in each sub-region in accordance with a decrease in spot size onto which a point of the test object is imaged.

13. 13. The measurement system of claim 12, wherein the magnification controller is operable to vary the size of the sub-region to substantially maintain the size of the sub-region as a given division of a spot size onto which the point of the test object is imaged.

14. The measurement system of claim 12 , wherein a linear dimension of the spot size is substantially filled by five sub-regions.

15. 14. The measurement system of claim 13, wherein outputs from substantially equal numbers of sub-regions with different spot sizes are directed to the edge detector.

16. The measurement system of claim 11 , wherein the magnification controller increases a linear dimension of the sub-region substantially proportionally to an increase in the f-number of the lens system.

17. further comprising a visual display operable to display the test object at different magnifications; 12. The measurement system of claim 11, wherein the magnification controller is operable to (a) increase the magnification of the test object on the visual display as the size of the sub-area decreases, and (b) decrease the magnification of the test object on the visual display as the size of the sub-area increases.

18. 18. The measurement system of claim 17, wherein the magnification of the test object on the visual display is inversely proportional to the size of the sub-region.

19. 18. The measurement system of claim 17, wherein both the edge detector and the visual display receive output from the same sub-region of the digital sensor.

20. The measurement system of claim 11 , wherein the lens system includes a front lens and a back lens that are in fixed positions relative to the variable size aperture.

21. 21. The measurement system of claim 20, wherein the front lens and the back lens are positioned telecentrically with respect to the variable size aperture.

22. In an edge detection method using an optical measuring instrument, aligning a test object with a lens system having a variable F-number, the lens system operable to form an image of the test object onto a digital sensor having an array of addressable pixels, the lens system operable to image points of the test object onto the digital sensor with different spot sizes; binning the contiguous clusters of addressable pixels into image pixels having a first size according to the number of addressable pixels within each image pixel, wherein the number of image pixels at each spot size is maintained substantially constant; identifying a change in contrast of a test object imaged onto the digital sensor over several image pixels at a first f / number of the lens system, whereby an area of ​​the test object is imaged at a first effective magnification; An edge detection method comprising:

23. moreover, binning the contiguous clusters of addressable pixels into image pixels having a second size according to the number of addressable pixels in each image pixel; identifying a change in contrast of the test object imaged onto the digital sensor at a second f / number of the lens system over substantially the same number of image pixels as at the first f / number of the lens system, thereby imaging an area of ​​the test object at a second effective magnification; 23. The edge detection method of claim 22, comprising:

24. 24. The edge detection method of claim 23, wherein the focal length of the lens system is adjusted at each magnification to maintain substantially the same number of image pixels within the spot size.

25. 24. The edge detection method of claim 23, wherein identifying contrast variations in the test object includes imaging the test object on a visual display, wherein different sized image pixels image the test object at different magnifications.

26. 23. The edge detection method of claim 22, wherein binning the contiguous cluster of addressable pixels of the digital sensor reduces a size of an image pixel to substantially maintain the size of the image pixel as a predetermined division of the spot size at which a point of a test object is imaged.

27. 10. The optical imaging system of claim 1, wherein one or more elements of the lens system are operable to move along an optical axis between a first position and a second position, and wherein a magnification of the test object at the second position is greater than a magnification of the test object at the first position.

28. The optical imaging system of claim 1 , further comprising two or more lens systems having different magnifications, the two or more lens systems operable to be selectively positioned within the optical path of the optical imaging system.

29. 10. The optical imaging system of claim 1, wherein the lens system further comprises a compound lens operable to invert along an optical axis, thereby varying the magnification of the test object.

30. 10. The optical imaging system of claim 1, wherein the lens system further comprises an electro-optic lens having a variable focal length, the focal length of the electro-optic lens operable to be electrically changed without changing the position of the electro-optic lens.

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