Chromatic range sensor system for measuring workpiece thickness

Abstract

A chromatic range sensor (CRS) system is provided that determines workpiece thickness and includes an optical pen, an illumination source, a wavelength detector, and a processing portion. The optical pen includes an optical device portion that provides axial chromatic dispersion, the illumination source is configured to generate multi-wavelength light, and the wavelength detector includes a plurality of pixels distributed along a measurement axis. In operation, the optical pen inputs a spectrum from the illumination source and outputs corresponding radiation to a first workpiece surface and a second workpiece surface of a workpiece (e.g., the workpiece may be transparent), and outputs reflected radiation to the wavelength detector that provides output spectral data. The processing portion processes the output spectral data to determine the thickness of the workpiece. In various embodiments, the processing for determining the thickness may be independent of determining the distance to the workpiece and / or may utilize a transform process, etc.

Description

Technical Field

[0001] The present invention relates to precision measuring instruments and more particularly to chromatic range sensors and similar optical distance determining devices and uses thereof. Background Art

[0002] It is known to use chromatic confocal techniques in optical range sensors (e.g., sensors including height, distance, etc.). As described in U.S. Pat. No. 7,876,456 (the '456 patent), which is incorporated herein by reference in its entirety, an optical element with axial chromatic aberration (also known as axial or longitudinal chromatic dispersion) can be used to focus a broadband light source so that the axial distance to the focus varies with wavelength. Therefore, only one wavelength will be accurately focused on the surface, and the surface height or distance relative to the focusing element determines which wavelength is best focused. After reflecting from the surface, the light will be refocused onto a small detector aperture, such as a pinhole or the end of an optical fiber. Only the wavelengths that are well focused on the surface can be well focused on the aperture when reflecting from the surface and passing back through the optical system to the input / output optical fiber. All other wavelengths are poorly focused on the aperture and therefore do not couple much power into the optical fiber. Therefore, for the light returning through the optical fiber, the signal level of the wavelength corresponding to the surface height or distance to the surface will be the largest. A spectrometer-type detector measures the signal level of each wavelength to determine the surface height.

[0003] Some manufacturers refer to practical and compact chromaticity range sensing (CRS) systems that operate as described above and are suitable for use in industrial environments as chromaticity point sensors (CPS) or chromaticity line sensors, etc. Compact chromaticity dispersion optical assemblies used with such systems are referred to as "optical pens" or "pen". The optical pen is connected to the electronic part of the chromaticity range sensor by an optical fiber. The electronic part includes a light source that transmits light through the optical fiber to output from the optical pen, and also provides a spectrometer that detects and analyzes the returned light. The returned light forms a wavelength-dispersed intensity spectrum received by the detector array of the spectrometer. The pixel data corresponding to the wavelength-dispersed intensity spectrum is analyzed to determine the "dominant wavelength position coordinate" as indicated by the peak or centroid of the intensity spectrum, and the resulting pixel coordinates of the peak and / or centroid are used together with a lookup table to determine the distance to the surface. This pixel coordinate can be determined with sub-pixel resolution and can be referred to as a "coordinate indicating distance" or a "pixel coordinate indicating distance".

[0004] Also known in the art are “line sensor” CRS that use a slit aperture and focus light along a line rather than a point, thereby providing the ability to measure the distance to a surface at multiple points along the line, as disclosed in U.S. Patent No. 8,773,757, which is hereby incorporated by reference in its entirety. Summary of the invention

[0005] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0006] Prior art CRS systems have exhibited certain problems (e.g., measurement errors, etc.) associated with thickness measurements, which typically involve determining a measured distance to two opposing surfaces of a workpiece and determining a difference between the two measured distances. For example, when measuring the thickness of a transparent workpiece such as glass (e.g., molten silica), the CRS illumination will be reflected from both the top and bottom surfaces of the glass, resulting in two corresponding wavelength peaks. Certain measurement errors arise from the difficulty associated with separating two peaks of the intensity spectrum that are indicative of the two corresponding measured distances, where for thin workpieces, the two peaks tend to merge together. For example, the width of the two peaks may be such that the peaks at least partially overlap / merge due to insufficient separation between the two peaks (e.g., Figure 5A The dashed measured spectrum signal 510a and Fig. 10A , 10B , 10D, 10E and 10G, as will be described in more detail below).

[0007] Specifically about Figures 10A-10G , showing seven corresponding intensity spectra, each containing two measured peaks (e.g., merged into Fig. 10A A single peak in the graph indicates the measured distances to the top and bottom surfaces of a workpiece having different thicknesses. For example, Fig. 10A and 10D For a workpiece with a thickness of 25 μm, Fig. 10B and 10E corresponds to a workpiece thickness of 50 μm, and Fig. 10C and 10F Corresponds to a workpiece with a thickness of 100 μm. Figures 10A-10G The intensity spectrum includes the intensity or "signal level" (vertical axis) as a function of the pixel coordinates or "pixel position" (horizontal axis) of the CRS wavelength detector, where the pixel position corresponds to the wavelength measured by the CRS wavelength detector, and the CRS is calibrated to convert the wavelength peak to the CRS measurement distance. Correspondingly, according to certain previously known methods, the thickness of the workpiece can be determined based on the difference between the measured distances to the two workpiece surfaces.

[0008] In some embodiments, such as Figures 10A-10C As shown in the example of FIG. , the merging of the two peaks in the blue portion of the Z range of the CRS system (i.e., the blue light wavelength portion) is similar to that in FIG. Figures 10D-10FThe problem of merging may become more severe in the red portion of the Z range (i.e., the red wavelength portion) as shown in the example of FIG. 1 , which is closer to the optics of the CRS system's optical pen along the distance measurement optical axis (Z axis) than in the blue portion. Therefore, one possible technique for providing a certain amount of improvement related to the merging problem is to place the workpiece to be measured in the red portion of the CRS system's Z range (i.e., at a sufficient distance from the optical pen). In addition, as Figure 10G Another technique for providing a certain amount of improvement related to the wavelength peak merging problem, best shown in , is to set a higher signal level threshold (e.g., threshold B) to thereby separate the two peaks and detect both peaks, rather than setting a lower signal level threshold (e.g., threshold A), which does not separate the two peaks and therefore only one (merged) peak may be detected. Figure 5A Some of the related concepts are described in more detail. This technique has certain limitations (e.g., it is not always easy to place a specific artifact in the red portion of the CRS system's Z range, when the detection threshold is set too high, more signal levels will become undetectable, etc.).

[0009] Various aspects of the present invention are directed to providing improvements with respect to such problems. One aspect of the present invention is to achieve more accurate thickness measurements (eg, for smaller thicknesses where wavelength peak merging may occur, and over an increased range of possible distances between the optical pen and the workpiece, etc.).

[0010] According to an embodiment of the present invention, a chromatic range sensor (CRS) system configured to determine the thickness of a workpiece is provided. The CRS system comprises:

[0011] an optical pen comprising a confocal optical path including an optics portion that provides axial chromatic dispersion and is configured to focus different wavelengths at different distances proximate a workpiece;

[0012] an illumination source configured to generate a multi-wavelength input light comprising an input spectrum input to the optical pen;

[0013] a CRS wavelength detector comprising a plurality of pixels, respective pixel positions of the plurality of pixels being distributed along a measurement axis of the CRS wavelength detector, wherein the CRS system is configured such that when the optical pen is operably positioned relative to the workpiece to perform a measurement operation, the optical pen inputs the input spectrum and outputs corresponding radiation to a first workpiece surface and a second workpiece surface of the workpiece, and receives reflected radiation from the first workpiece surface and the second workpiece surface and outputs the reflected radiation to the CRS wavelength detector providing output spectrum data; and

[0014] A processing portion is configured to process the output spectral data to determine a thickness of the workpiece, the thickness corresponding to a separation between the first workpiece surface and the second workpiece surface of the workpiece, wherein the process for determining the thickness includes utilizing a transform process.

[0015] According to one aspect, the transform processing includes at least one of a Fourier transform processing or a Fourier correlation transform processing. The utilizing the transform processing includes: determining a transform of the output spectral data; and determining the thickness of the workpiece based at least in part on a first characteristic of the transform of the output spectral data. According to another aspect, the first characteristic corresponds to a first dip of the transform of the output spectral data.

[0016] According to another aspect, the output spectral data includes a distance-dependent spectral component having a first wavelength peak and a second wavelength peak corresponding to the first workpiece surface and the second workpiece surface, respectively, and the determining the thickness of the workpiece is independent of processing the output spectral data to determine the corresponding first and second measured distances to the first and second workpiece surfaces. According to further aspects, the first and second wavelength peaks appear visually as a single peak in a representation of the output spectral data provided by the CRS wavelength detector.

[0017] According to another aspect, for a workpiece having a spacing between the first workpiece surface and the second workpiece surface of 5 microns, the utilizing the transform process enables the processing portion to accurately determine the thickness of the workpiece with an error of less than 10%.

[0018] According to another aspect, the processing portion is further configured to process the output spectral data to determine a measured distance to the workpiece. According to a further aspect, the processing for determining the measured distance to the workpiece includes processing the output spectral data to determine a centroid indicating the measured distance to the workpiece, and the processing for determining the thickness of the workpiece is independent of the determination of the centroid. According to a further aspect, the determined measured distance is to a point within the workpiece that is between the first workpiece surface and the second workpiece surface. According to a still further aspect, the determined measured distance is determined based on coordinates indicating a distance, the coordinates indicating the distance corresponding to an average of a first wavelength peak and a second wavelength peak, the first wavelength peak and the second wavelength peak corresponding to respective first workpiece surfaces and second workpiece surfaces. According to a further aspect, the processing portion is further configured to utilize the determined measured distance and the determined thickness of the workpiece to determine at least one of a first measured distance to the first workpiece surface or a second measured distance to the second workpiece surface.

[0019] According to another aspect, the utilizing the transform process comprises:

[0020] determining a Fourier transform of the output spectral data;

[0021] dividing the Fourier transform of the output spectral data by the Fourier transform of a reference to obtain a Fourier transform of target spectral data;

[0022] calculating an inverse Fourier transform of the Fourier transform of the target spectral data to determine first and second wavelength peaks corresponding to respective first and second measured distances to the first and second workpiece surfaces; and

[0023] The thickness of the workpiece is determined based at least in part on a difference between the respective measured distances to the first and second workpiece surfaces.

[0024] According to yet another aspect, the CRS system is operable in a plurality of modes including a thickness measurement mode, for which the processing portion performs the processing to determine the thickness as part of the thickness measurement mode. According to a further aspect, the plurality of modes further includes a distance measurement mode for measuring a distance to a workpiece; the CRS system is configured such that during the distance measurement mode, when the optical pen is operably positioned relative to the workpiece to perform a measurement operation, the optical pen inputs the input spectrum and outputs corresponding radiation to the workpiece, and receives reflected radiation from the workpiece and outputs the reflected radiation to the CRS wavelength detector that provides the output spectrum data; and the output spectrum includes a distance-dependent spectral component having a wavelength peak that indicates a measured distance to the workpiece. According to a further aspect, the thickness measurement mode is only operable to determine a thickness such as corresponding to a spacing between a first workpiece surface and a second workpiece surface, and is not operable to determine spacing between three or more workpiece surfaces.

[0025] According to another aspect, the CRS system is at least one of a chromaticity point sensor system or a chromaticity line sensor system.

[0026] According to another aspect, a method for operating a chromatic range sensor (CRS) system to determine a thickness of a workpiece is provided. The CRS system comprises: an optical pen comprising a confocal optical path comprising an optical device portion providing axial chromatic dispersion and configured to focus different wavelengths at different distances proximate to a workpiece; an illumination source configured to generate a multi-wavelength input light comprising an input spectrum input to the optical pen; and a CRS wavelength detector comprising a plurality of pixels having respective pixel positions distributed along a measurement axis of the CRS wavelength detector, the plurality of pixels receiving respective wavelengths and providing output spectral data. The method comprises:

[0027] operating the CRS system with the optical pen operably positioned relative to the workpiece to perform measurement operations, the measurement operations comprising the optical pen inputting the input spectrum and outputting corresponding radiation to first and second workpiece surfaces of the workpiece, and receiving reflected radiation from the first and second workpiece surfaces and outputting the reflected radiation to the CRS wavelength detector providing the output spectrum data; and

[0028] The output spectral data is processed to determine a thickness of the workpiece, the thickness corresponding to a separation between the first workpiece surface and the second workpiece surface of the workpiece, wherein the process for determining the thickness includes utilizing a transform process.

[0029] According to another aspect, a method for operating a chromatic range sensor (CRS) system is provided. The CRS system comprises: an optical pen comprising a confocal optical path, the confocal optical path comprising an optical device portion, the optical device portion providing axial chromatic dispersion and configured to focus different wavelengths at different distances close to a workpiece; an illumination source, the illumination source configured to generate a multi-wavelength input light, the multi-wavelength input light comprising an input spectrum input to the optical pen; and a CRS wavelength detector, the CRS wavelength detector comprising a plurality of pixels, the respective pixel positions of the plurality of pixels being distributed along a measurement axis of the CRS wavelength detector, the plurality of pixels receiving respective wavelengths and providing output spectral data. The method comprises:

[0030] operating the CRS system with the optical pen operably positioned relative to the workpiece to perform a measurement operation, the measurement operation comprising the optical pen inputting the input spectrum and outputting corresponding radiation to a first workpiece surface and a second workpiece surface of the workpiece, and receiving reflected radiation from the first workpiece surface and the second workpiece surface and outputting the reflected radiation to the CRS wavelength detector providing the output spectrum data;

[0031] processing the output spectral data to determine a measured distance to the workpiece, wherein the processing for determining the measured distance comprises determining coordinates indicative of the distance, the coordinates indicative of the distance corresponding to pixel locations of the CRS wavelength detector indicative of the measured distance; and

[0032] The output spectral data is processed to determine a thickness of the workpiece, the thickness corresponding to a separation between the first workpiece surface and the second workpiece surface of the workpiece, wherein the processing for determining the thickness is independent of a determined measured distance to the workpiece. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The foregoing aspects and many of the attendant advantages of the present invention will become more readily understood and better appreciated when reference is made to the following detailed description taken in conjunction with the accompanying drawings, in which:

[0034] Figure 1 is a block diagram of one embodiment of an exemplary CRS system.

[0035] Figure 2is a graph of the system noise (bias) spectrum from a CRS system showing the wavelength-dependent voltage offset signal level of the pixels in the detector array when no measurement surface is present.

[0036] Figure 3 is a graph of an intensity spectrum from a CRS system showing effective wavelength peaks resulting from wavelengths reflected by a top surface of a workpiece (eg, a non-transparent workpiece), wherein the pixel location of the peak corresponds to the measured distance to the top surface.

[0037] Figure 4A is a map of CRS distance calibration data that relates pixel coordinates indicating distance to the known measured distance to the workpiece surface being measured.

[0038] Figure 4B is an example CRS distance calibration lookup table that references distance indicated coordinates (DIC) to corresponding measured distances of a CRS system.

[0039] Figure 5A is a graph of the intensity spectrum from a CRS system showing two effective wavelength peaks resulting from wavelengths reflected from the top and bottom surfaces of a transparent workpiece, where the pixel positions of the peaks correspond to the measured distances to the surfaces.

[0040] Figure 5B It is a graph showing the measured distances to the top and bottom surfaces of a transparent workpiece, including the actual measured distance and the apparent measured distance to the bottom surface.

[0041] Figure 6 is a flow chart illustrating a method of operating a CRS system to determine the thickness of a workpiece.

[0042] Figures 7A-7D The process of workpiece thickness measurement using transform processing is demonstrated.

[0043] Figure 8 Demonstrates workpiece thickness measurement using Fast Fourier Transform (FFT) processing as part of a deconvolution approach.

[0044] Figures 9A-9H Examples are shown for which, regardless of the position of the workpiece relative to the optical pen within the operable measurement range, Figure 8 Both FFT processing methods determine the location of the first valley in the Fourier transform of the signal, which can be used to determine the thickness of the workpiece.

[0045] Figures 10A-10G is a graph depicting intensity spectra of workpieces having different thicknesses (eg, 25 μm, 50 μm, and 100 μm) measured by a CRS system, showing the different extents to which the two wavelength peaks merge together depending on the thickness of the workpiece and the distance from the optical pen. DETAILED DESCRIPTION

[0046] Figure 1 1 is a block diagram of an exemplary embodiment of a chromatic range sensor (CRS) system 100 that includes an optical element 120 (e.g., an optical pen), an electronics portion 160, and a user interface portion 171. An embodiment of the electronics portion 160 includes a signal processor 166, a memory portion 168, and a source and detector subsystem 161 including a wavelength detector 162 and a broadband light source 164. Figure 1 The CRS system 100 shown in FIG. 1 is a chromaticity point sensor (CPS) system that measures a single measurement point at a time, but it will be understood that in other embodiments, other sensor systems (e.g., chromaticity line sensors, etc.) may be utilized. In various embodiments, the wavelength detector 162 includes a detector array 163 of a spectrometer. The detector array 163 may include a plurality of pixels distributed along a measurement axis of the wavelength detector 162, wherein corresponding pixels receive corresponding wavelength signals and provide corresponding output spectral data.

[0047] The electronics portion 160 is coupled to the optical element 120 through an optical path including a fiber optic cable 112. An optional or alternative aspect of the optical path is shown, the optical path including a fiber optic cable 112 having a first segment 112A and a second segment 112B connected at a connector CONNECT-D at an optical segment 112B, and a coupler COUPLER-O connecting segment 112B to segment 112C coupled to the electronics portion 160. A light source 164 controlled by a signal processor 166 is connected to input an input multi-wavelength light including an input spectrum to the optical element 120 through a path including an illumination fiber segment 165I, a 2x1 coupler COUPLER-E, CONNECT, and the fiber optic cable 112. The optical element 120 includes an input / output fiber subassembly 105, a housing 130, and an optics portion 150. The input / output fiber subassembly 105 includes an input / output optical fiber 113 carried through the fiber optic cable 112 and a fiber optic connector 108. The input / output optical fiber 113 outputs the output beam through the aperture 195 , and receives the reflected measurement signal light through the aperture 195 .

[0048] In operation, light emitted from the fiber end through the aperture 195 is focused by the optics portion 150, which includes a lens that provides axial chromatic dispersion so that the focus point along the optical axis OA is located at different distances depending on the wavelength of the light, as is known for CRS systems. During measurement operations, the light is focused near a workpiece 170 having a first workpiece surface 190-1 and a second workpiece surface 190-2 (i.e., a top workpiece surface and a bottom workpiece surface). In various embodiments, the workpiece 170 can be transparent or can otherwise include a material such that the bottom surface 190-2 can be at least partially seen through the top surface 190-1 (i.e., some of the light from the optical element 120 can pass through the top surface 190-1 to reach the bottom surface 190-2). For purposes of simplicity in the following description, initially a case is described where the workpiece 170 is non-transparent or otherwise has characteristics such that only the top surface 190-1 reflects light to the CRS system 100.

[0049] In embodiments where only the top surface 190-1 reflects light, during measurement operations, the light is focused by the optics portion 150 on the top surface 190-1 (i.e., as opposed to also focusing light on the bottom surface 190-2, as will be described with respect to other examples below). The light reflected from the top surface 190-1 is refocused by the optics portion 150 onto the aperture 195. Due to its axial chromatic dispersion, only one wavelength will have a focus distance that matches the measurement distance "Z1", which is the distance from a reference position RP fixed relative to the optical element 120 to a location on the workpiece surface 190-1. The wavelength that is best focused at the location on the workpiece surface 190-1 is the wavelength that is best focused at the aperture 195. Therefore, it is primarily the best focused wavelength that passes through the aperture 195 and enters the core of the optical fiber 113 of the optical fiber cable 112. The fiber optic cable 112 routes the signal light to a wavelength detector 162 which is used to determine the wavelength having the dominant intensity corresponding to the measured distance Z1 to the location on the workpiece surface 190 - 1 .

[0050] In the illustrated embodiment, the reflected wavelength-dependent light intensity passes back through the electronics portion 160 via an optical fiber path including a coupler COUPLER-E, so that a certain percentage (e.g., approximately 50% in some embodiments) of the light is directed through the signal fiber segment 165S to the wavelength detector 162. The wavelength detector 162 receives the wavelength-dependent light intensity as an output spectral intensity spectrum (also referred to simply as an output spectrum) distributed over the pixel array along the measurement axis of the detector array 163, and operates to provide corresponding output spectral data based on the pixel data output from the detector array 163.

[0051] Spectral data (see, for example, Figure 3) is calculated by the signal processor 166, and the DIC (in sub-pixel units) indicates the measured distance Z1 (in microns) stored in the calibration portion 173 of the memory portion 168 to the position on the workpiece surface 190-1 via the distance calibration lookup table, as shown below with respect to Figure 4A and 4B According to previously known methods, DIC can be determined based on the centroid of the intensity spectrum data contained in the peak region. In various embodiments, the spectrum data can be used to determine DIC with sub-pixel resolution, as described in more detail below.

[0052] It should be understood that in embodiments where the workpiece 170 is transparent, operating principles similar to those described above may be applied to the determination of the measured distances to the workpiece surfaces 190-1 and 190-2. More specifically, during the measurement operation, light is focused by the optics portion 150 on the workpiece surfaces 190-1 and 190-2 (i.e., for the focusing, some of the light passes through the workpiece surface 190-1 to the workpiece surface 190-2). Light reflected from the workpiece surfaces 190-1 and 190-2 is refocused by the optics portion 150 onto the aperture 195. Due to its axial chromatic dispersion, only one wavelength will have a focused distance that matches the measured distance "Z1", which is the distance from the reference position RP fixed relative to the optical element 120 to the location on the workpiece surface 190-1, and similarly, only one wavelength will have a focused distance that matches the measured distance "Z2", which is the distance from the reference position RP to the location on the workpiece surface 190-2. The wavelength that is best focused at the locations on the workpiece surfaces 190-1 and 190-2 is the wavelength that is best focused at the aperture 195. Therefore, it is primarily the best focused wavelength that passes through the aperture 195 and enters the core of the optical fiber 113 of the fiber optic cable 112. The fiber optic cable 112 routes the signal light to the wavelength detector 162, which is used to determine the wavelength having the dominant intensity that corresponds to the measured distance to the corresponding location on the workpiece surfaces 190-1 and 190-2. As will be described below with respect to Figure 5B As described in more detail, due to the refractive index of the workpiece material, in various embodiments, the indicated measured distance to the workpiece surface 190 - 2 may be an apparent measured distance Z2 ′ that is related to the measured distance Z2 (eg, as presented in Equations 3-5, etc.).

[0053] In the illustrated embodiment, the reflected wavelength-dependent light intensity passes back through the electronics portion 160 via an optical fiber path including a coupler COUPLER-E, so that a certain percentage (e.g., approximately 50% in some embodiments) of the light is directed through the signal fiber segment 165S to the wavelength detector 162. The wavelength detector 162 receives the wavelength-dependent light intensity as an output spectral intensity spectrum (also referred to simply as an output spectrum) distributed over the pixel array along the measurement axis of the detector array 163, and operates to provide corresponding output spectral data based on the pixel data output from the detector array 163.

[0054] Spectral data (see, for example, Figure 5A ) are calculated by the signal processor 166, and the two DICs (in sub-pixels) indicate corresponding measured distances (in microns) stored in the calibration portion 173 of the memory portion 168 via a distance calibration lookup table or the like, as described below with respect to Figure 4A and 4B As described. According to previously known methods, two DICs can be determined based on the centroid of the intensity spectrum data contained in each of the two corresponding peak regions. In various embodiments, the spectral data can be used to determine two DICs with sub-pixel resolution, as described in more detail below. In various embodiments, a DIC corresponding to an apparent measured distance Z3' (e.g., calculated by the centroid of the two merged wavelength peaks) can also or alternatively be determined, and the DIC is related to the actual measured distance Z3 (e.g., as shown in equations 6-10, etc.). As will be described in more detail below, distance Z3 can be located between distances Z1 and Z2 and can correspond to a position inside the workpiece 170, such as a distance to a position at the midpoint between workpiece surfaces 190-1 and 190-2.

[0055] like Figure 1As further shown, the user interface portion 171 is coupled to the electronics portion 160 and is configured to receive user input for operation of the CRS system 100, such as user commands for selecting various operating parameters by any suitable means, such as a keyboard, a touch sensor, a mouse, etc. In an exemplary embodiment, the user interface portion 171 may include one or more operating mode selection elements (e.g., user selectable buttons) that can be operated by a user to select one of a plurality of operating modes (e.g., a thickness measurement mode and / or a distance measurement mode, etc.) of the CRS system 100. The user interface portion 171 is also configured to display information on a screen, such as a distance and / or thickness successfully determined / measured by the CRS system 100. As will be described in more detail below, in various embodiments, the memory portion 168 may include a thickness measurement portion 169 and a distance measurement portion 172, such as corresponding modes may be implemented and / or corresponding operations may be provided in addition. Such corresponding modes and / or operations may be used to measure the thickness of a workpiece (e.g., a thickness corresponding to the interval between a first workpiece surface and a second workpiece surface) and / or a distance to a workpiece surface, etc. In various embodiments, the thickness measurement portion 169 and the distance measurement portion 172 and / or operations associated therewith may be combined and / or otherwise possibly not differentiated.

[0056] Figure 1 The Z direction is defined as being parallel to the optical axis (OA) of the optical element 120, which is the distance measurement axis. Figure 1 As shown, during operation, the workpiece 170 is positioned along the optical axis OA and may be mounted on a translation stage 175 which may advantageously be aligned so that it translates along the Z-axis constrained by guide bearings 175A.

[0057] Figure 2 The following description outlines certain known background signal processing and / or calibration operations. Figure 2 200 is a graph of the system noise (bias) spectrum from the CRS system, which shows the voltage offset signal level Voffset(p) for pixels in the detector array 163 when there is no measurement surface within the nominal total measurement range of the CRS system. In this case, there is no intentionally reflected light, and therefore there is no significant or dominant wavelength peak in the resulting intensity spectrum. For each of the 1,024 pixels along the "wavelength" measurement axis, the voltage offset signal Voffset(p) is plotted in units of normalized volts. "Normalized Volts" assigns a value of 1.0 to the saturation voltage of the detector array 163. The voltage offset signal Voffset(p) includes a bias signal level Vbias that is relatively consistent across the detector array and a background signal component Vback(p) that appears to vary across the detector array.

[0058] The following Figure 3 , 4A The descriptions of 4A, 4B, 5A, and 5B outline certain signal processing operations that determine distance indicating coordinates (DIC) with sub-pixel resolution based on effective wavelength peaks produced in the wavelength-dispersed intensity spectrum of the CRS system and determine a measured distance (e.g., in microns) to a workpiece surface based on the determined DIC. Certain operations outlined herein are described in greater detail in the '456 patent. The purpose of this description is to provide additional background information that may be useful in fully understanding certain CRS measurement operations as described herein.

[0059] Figure 3 300 is a graph of a wavelength-dispersed intensity spectrum from a CRS system showing effective wavelength peaks 302 generated by a subset of the measured spectral signals MS(p), indicating wavelengths focused on and reflected by a single measured surface of a workpiece (e.g., opaque). In this example, the graph 300 includes a single wavelength peak 302 corresponding to a single reflective surface (e.g., top surface) of the non-transparent workpiece. Each of the measured spectral signals MS(p) has a signal level (expressed in normalized volts) associated with each pixel p of a detector array (e.g., detector array 163). The wavelength peaks 302 have sufficient height (good signal-to-noise ratio), are relatively symmetrical, and allow for good estimation of the peak position along the measurement axis of the detector array or measurement of distance-indicating coordinates (DIC) 304. Figure 3 Also shown are a bias signal level MVbias (in normalized volts), a peak pixel coordinate (ppc), and a data threshold MVthreshold defining a lower limit for a subset of the indicated distances of the measured spectral signal MS(p) forming the wavelength peak 302. All values ​​(e.g., including "MV" values) are in normalized volts.

[0060] Briefly, in one embodiment, the measurement operations for determining distance indicating coordinates (DIC) (in pixels) and determining the corresponding measured distance (in microns) based on the determined DIC may include the following:

[0061] • Position the target surface along the optical axis OA and capture the resulting wavelength-dispersed intensity spectrum as in FIG300.

[0062] • Determine the peak pixel coordinate (ppc), which is the pixel with the highest signal.

[0063] ●Determine the measurement bias signal level MVbias at a given sampling rate.

[0064] • Determine a data threshold MVthreshold (eg, as a percentage of the peak height).

[0065] - Determining distance-indicating coordinates (DIC) with sub-pixel resolution based on a subset of distance-indicating measured spectral signals MS(p) forming wavelength peaks having values ​​greater than MVthreshold.

[0066] ● By comparing DIC with stored distance calibration data (e.g. Figure 4A The distance calibration curve in Figure 4B The measured distance is determined by associating the measured distance with the corresponding distance in the lookup table in the flow chart, etc.

[0067] In the foregoing operation, DIC can be determined with sub-pixel resolution based on a subset of the measured spectrum signals MS(p) indicating distances above a data threshold MVthreshold. According to previously known methods, DIC can be determined as the centroid X of the subset of the signal MS(p) indicating distances. C For example, for a detector with 1024 pixels (i.e., each pixel has a corresponding pixel number (p) from 1 to 1024), the centroid X C This can be determined based on:

[0068]

[0069] in,

[0070]

[0071] In one specific example, n=2 in Equation 1. It should be appreciated that Equation 2 restricts the signal MS(p) used in the centroid calculation to a subset indicating the distance.

[0072] Figure 4A 400A is a graph of CRS measured distance calibration data 410A that compares coordinates of indicated distances (DIC) with sub-pixel resolution to known measured distances (ZOUT) along the optical axis (OA) of the CRS in microns (e.g., stored in Figure 3 It should be understood that Figure 4A The specific values ​​of are intended to be illustrative only and may not correspond to specific values ​​indicated in other examples (e.g., Figure 1-3 Certain values ​​described and / or as will be described in more detail below Figure 4B Specific table values ​​are not provided, but it should be understood that these concepts are similar). Figure 4AThe example shown in is for an optical element (e.g., an optical pen) having a nominal total measurement range MR of 300 microns, which corresponds to a DIC range of approximately 150 pixels-490 pixels. However, if desired, the CRS system can be calibrated over a larger pixel range of the detector array 163. An exemplary laboratory calibration method for determining CRS measurement distance calibration data 410A employs a mirror (e.g., in place of a lens) that moves along the optical axis OA (e.g., in steps of approximately 0.1 or 0.2 microns). Figure 1 For each actual mirror position, the corresponding calibration DIC of the CRS system is based on the above description of Figure 3 The corresponding intensity spectrum data is determined. The calibration DIC and the corresponding actual position (in microns along the optical axis OA) are then recorded to provide calibration data 410A. During a workpiece measurement operation (e.g., to determine a measured distance to a workpiece surface, such as workpiece surface 190-1), the measured DIC obtained by the CRS system is referenced to the stored calibration data 410A to determine a measured distance ZOUT corresponding to the measured DIC. Although the distance calibration data 410A appears to form a smooth curve, it should be understood that in some cases, the distance calibration data and / or output spectral data of a typical CRS system, especially an economical CRS system, may exhibit some short-range variations / irregularities (e.g., as described in part in U.S. Patent No. 7,876,456, which is hereby incorporated by reference in its entirety).

[0073] Figure 4B is used to refer the coordinates of the indicated distance to the measured distance of the chromaticity point sensor (e.g., stored in Figure 3 FIG. 400B of the CRS distance calibration lookup table 410B of the calibration section 173 of FIG. As described above, it should be understood that Figure 4B The table values ​​are intended to be illustrative only and may not correspond to specific values ​​indicated in other examples, such as Figure 4A However, it should be understood that the concepts are similar for the other examples. Figure 4B , in the left column, the calibration DIC entries cover pixel coordinates from 1 to 1,024 in increments of 0.1 pixel steps, and in the right column, the corresponding measured distance in microns is entered (ZOUT). In operation, the measured DIC calculated by the CRS system is referenced to a stored calibration lookup table to determine the corresponding measured distance in microns. If the measured DIC falls between adjacent calibrated DIC values, the measured distance can be determined by interpolation. Figure 4B In the example of FIG. 5 , some specific example values ​​are shown for some small ranges of DIC near pixel positions of approximately 104, 604, and 990, where the corresponding measured distances are in the range of approximately 37 microns, 381 microns, and 486 microns.

[0074] In operation (for example, Figure 3 The optical pen 120 is connected to the CRS electronics portion 160 and is operably positioned relative to the workpiece surface 190-1 to perform a measurement operation. The measurement operation includes the optical pen 120 inputting an input spectrum from the illumination source 164 and outputting corresponding radiation to the workpiece surface 190-1, and receiving reflected radiation from the workpiece surface 190-1 and outputting the reflected radiation to provide an output spectrum to the CRS wavelength detector 162 which then provides output spectrum data. The output spectrum includes a distance-dependent spectral component and a distance-independent spectral component. The distance-dependent spectral component has a wavelength peak (e.g., Figure 3 The peak 302 in the wavelength indicates the measured distance (e.g., measured distance Z1) from the optical pen 120 to the workpiece surface 190-1. As described above, the calibration data (e.g., Figure 4A or 4B) to determine a measured distance (e.g., measured distance Z1) corresponding to the measured DIC. If the measured DIC falls between adjacent calibrated DIC values, the measured distance corresponding to the measured DIC may be determined by interpolation (e.g., between the measured distances corresponding to adjacent calibrated DIC values).

[0075] and Figure 3 In contrast to the example of determining the measured distance to a single workpiece surface, as will be described in more detail below, Figure 5A A method for determining a measured distance to a first workpiece surface and a second workpiece surface (e.g., Figure 1 Such techniques (e.g., sometimes referred to herein as "centroid-type techniques") can be used to determine the thickness of a workpiece (e.g., based at least in part on the difference between the measured distances Z1 and Z2' as corresponding to the DIC determined by the centroid calculation). However, as will be described in more detail below (e.g., specifically with respect to Figure 6-9H As described herein, certain alternative techniques may be utilized to determine workpiece thickness according to the principles disclosed herein, which may have certain advantages (eg, including more accurate thickness determination for certain workpieces, etc.).

[0076] Figure 5A500A is a graph of an intensity spectrum of wavelength dispersion from a CRS system, which shows effective wavelength peaks 502-1 and 502-2. Wavelength peak 502-1 is generated by a first subset of measurement spectrum signals MS(p), the wavelength peak indicating a first wavelength focused on and reflected by a first measurement surface (e.g., surface 190-1 of workpiece 170). Effective wavelength peak 502-2 is generated by a second subset of measurement spectrum signals MS(p), the effective wavelength peak indicating a second wavelength focused on and reflected by a second measurement surface (e.g., surface 190-2 of workpiece 170). In this example, the workpiece (e.g., workpiece 170) may be transparent, thus allowing viewing of the second measurement surface 190-2 through the first measurement surface 190-1 (e.g., for the viewing, some of the light from the optical pen 120 passes through the first measurement surface 190-1 to be reflected by the second measurement surface 190-2).

[0077] Each of the measured spectral signals MS(p) has a signal level (expressed in normalized volts) associated with each pixel p of a detector array (e.g., detector array 163). Each of the effective wavelength peaks 502-1 and 502-2 has sufficient height (good signal-to-noise ratio), is relatively symmetrical, and allows for a good estimate of the relative peak positioning along the measurement axis of the detector array and determination of the distance indicating coordinate (DIC) 504-1 or 504-2 (i.e., using a centroid calculation). Figure 5A The bias signal level MVbias (in normalized volts), the peak pixel coordinates (ppc1 and ppc2), and the data threshold MVthreshold defining the lower limit of the subset of the indicated distances of the measured spectrum signal MS(p) forming the corresponding wavelength peaks 502-1 and 502-2 are shown. All values ​​(e.g., including the "MV" value) are in normalized volts.

[0078] In operation (e.g., for two workpiece surface measurements), the optical pen 120 is connected to the CRS electronics portion 160 and operably positioned relative to the workpiece 170 (i.e., including the workpiece surfaces 190-1 and 190-2) to perform a measurement operation. The measurement operation includes the optical pen 120 inputting an input spectrum from the illumination source 164 and outputting corresponding radiation to the workpiece surfaces 190-1 and 190-2, and receiving reflected radiation from the workpiece surfaces 190-1 and 190-2 and outputting the reflected radiation to provide an output spectrum to the CRS wavelength detector 162 which then provides output spectrum data. The output spectrum includes a distance-dependent spectral component and a distance-independent spectral component. The distance-dependent spectral component has a wavelength peak (e.g., Figure 5AAs described above, the measured DIC 504-1 and 504-2 calculated by the CRS system (i.e., using the centroid calculation) are referenced to stored calibration data (e.g., Figure 4A or 4B) to determine the measured distances corresponding to the measured DICs (e.g., measured distances Z1 and Z2'). If either or both of the measured DICs fall between adjacent calibrated DIC values, the measured distances corresponding to the measured DICs may be determined by interpolation. In various embodiments, and in accordance with previously known techniques, the thickness d of the workpiece 170 may be determined based on the difference between the determined measured distances, as will be described below with respect to Figure 5B Described in more detail.

[0079] Figure 5B FIG. 500B is a diagram showing the measured distances to the top surface 190-1 and the bottom surface 190-2 of the transparent workpiece 170, including the actual measured distance Z2 and the apparent measured distance Z2' to the bottom surface 190-2. Figure 5B As shown in FIG. 1 , rays R1A and R1B (eg, from optics portion 150 ) are shown as being focused at workpiece surface 190 - 1 (ie, corresponding to wavelengths that are best focused at workpiece surface 190 - 1 ), and produce Figure 5A The wavelength peak 502-1 in FIG. 5 has a corresponding DIC 504-1 indicating a measurement distance Z1. Figure 5B As shown in FIG. 1 , rays R2A and R2B (eg, from optics portion 150) are shown as being focused at workpiece surface 190-2 (ie, corresponding to wavelengths that are best focused at workpiece surface 190-2), and produce Figure 5A 5. The wavelength peak 502-2 in FIG. 5 has a corresponding DIC 504-2 indicating an apparent measured distance Z2'. Due to the refractive index of the workpiece material at the corresponding wavelength (ie, corresponding to the wavelength peak 502-2), the apparent measured distance Z2' is different from the actual measured distance Z2.

[0080] More specifically, if Figure 5B As shown, once rays R2A and R2B enter the workpiece 170, the rays pass through the workpiece material with an angular change due to the refractive index resulting in a focus at the workpiece surface 190-2 corresponding to the actual measured distance Z2 as shown by ray portions R2A' and R2B'. However, the projected ray portions R2A-P and R2B-P within the workpiece (i.e., no angular change) indicate a focus corresponding to the apparent measured distance Z2', which corresponds to the wavelength peak 502-2 with the corresponding DIC 504-2. Some equations that explain the relationship between the various distances will be described in more detail below.

[0081] The relationship between the actual measured distances Z1 and Z2 and the actual workpiece thickness d can be characterized by the following equation 3:

[0082] d = Z2 - Z1 (Equation 3)

[0083] Similarly, the relationship between the actual measured distance Z1 and the apparent measured distance Z2' and the apparent workpiece thickness d' can be characterized by the following equation 4:

[0084] d'=Z2'-Z1 (Equation 4)

[0085] The relationship between the actual workpiece thickness d and the apparent workpiece thickness d' can be characterized by the following equation 5:

[0086] d = (d')(n) (Equation 5)

[0087] Where n is the refractive index of the workpiece material at the corresponding wavelength (eg, corresponding to wavelength peak 502-2). The above equation enables the use of Figure 5A The measured spectrum signals MS(p) are used to determine the workpiece thickness d. More specifically, Figure 5A The determined DIC 504-1 and 504-2 indicate the corresponding measured distances Z1 and Z2' stored in the calibration portion 173 of the memory portion 168 via a distance calibration lookup table or the like, as described above with respect to Figure 4A and 4B The measured distances Z1 and Z2' can be used to determine the measurement of the apparent workpiece thickness d' according to calculations such as those of Equation 4. The measurement of the apparent workpiece thickness d' can then be used to determine the measurement of the actual workpiece thickness d according to calculations such as those of Equation 5. As will be described in more detail below, the distance Z3 can be located between the distances Z1 and Z2 (e.g., can be the average of the distances Z1 and Z2 and can extend to the midpoint of the actual thickness d), and the related distance Z3' can be located between the distances Z1 and Z2' (e.g., can be the average of the distances Z1 and Z2' and can extend to the midpoint of the apparent thickness d').

[0088] As another example, Figure 5AAlso shown is a dashed representation of a wavelength-dispersed intensity spectrum from a CRS system, with wavelength peaks 502-1a and 502-2a having corresponding peak pixel coordinates ppc1a and ppc2a. Wavelength peaks 502-1a and 502-2a are similar to wavelength peaks 502-1 and 502-2, except that they are closer together, so that the corresponding first and second subsets of the peak and measurement spectrum signals 510a are partially merged. In various embodiments, this example can correspond to a version of a relatively thin workpiece 170 (i.e., for which there is almost no spacing between the top and bottom surfaces that are relatively closer together). As shown, according to previously known techniques (e.g., using centroid calculations to determine DIC), this may present certain problems for determining the measured distances to the corresponding surfaces, and for determining the workpiece thickness as corresponding to the difference between the determined measured distances. For example, in one embodiment, processing as described above may result in an evaluation of partially merged wavelength peaks 502-1a and 502-2a, which evaluation (e.g., based on the centroid calculation as described above with respect to equations 1 and 2) may enable a determination of a single DIC 504a as corresponding to only a single determined measured distance to the workpiece. In other embodiments, the processing may enable a determination of two DICs, but with respect to the determination, it will be understood that the partial merging of wavelength peaks 502-1a and 502-2a may enable a determination of a corresponding DIC in some cases and / or may provide an error message for the determination (e.g., indicating that there is a problem with the determination of the corresponding DIC) in some cases. In any of the above cases, the corresponding determination of the thickness of the workpiece may be problematic (e.g., may have some inaccuracy or may not be determined in other ways, etc.).

[0089] According to various embodiments of the present invention, the CRS system is equipped with a novel method for determining workpiece thickness that produces a high degree of accuracy even for relatively thin workpieces (e.g., having a thickness as small as 7 microns, or 5 microns, or 3 microns in various embodiments). Specifically, in one example embodiment, the CRS electronics portion 160 ( Figure 1) includes a thickness measurement portion 169 that can be used by the CRS system to perform a thickness measurement of a workpiece according to the principles disclosed herein, and a distance measurement portion 172 that can be utilized by the CRS system 100 to perform one or more distance measurements to one or more surfaces of the workpiece (e.g., according to previously known techniques). In various embodiments, selection of a thickness measurement mode or operation (e.g., using the thickness measurement portion 169) or a distance measurement operation or mode (e.g., for the distance measurement portion 172) can be performed in response to user input received through the user interface 171 or automatically. For example, in response to positioning the optical pen relative to a workpiece (e.g., a transparent workpiece), a thickness operation or mode can be automatically or manually selected to determine the thickness of the workpiece.

[0090] As will be described in more detail below, in various embodiments of the thickness measurement operation or mode, the signal processor 166 can execute an algorithm (e.g., including a transform or other process) as stored in the thickness measurement portion 169 of the memory portion 168. The algorithm (e.g., using a transform process) is executed on the spectral data output from the wavelength detector 162 to determine the thickness of the workpiece. In operation, the optical pen 120 is connected to the CRS electronics portion 160 and is operably positioned relative to the workpiece 170 to perform a thickness measurement operation. The thickness measurement operation includes the optical pen 120 outputting an input spectrum from the illumination source 164 and outputting corresponding radiation to two surfaces 190-1 and 190-2 (i.e., "surface 1" and "surface 2") of the workpiece 170. The optical pen 120 receives reflected radiation from the two surfaces and outputs the reflected radiation to the CRS wavelength detector 162, which then provides output spectral data for which the workpiece thickness is determined based on processing of the output spectral data (e.g., using a transform process, such as a Fourier transform process or a Fourier correlation transform process, etc.).

[0091] Figure 66 is a flow chart illustrating an exemplary method 600 of operating a CRS system 100 to determine a thickness of a workpiece. At block 610, a CRS system is provided that includes: an optical pen 120 that includes a confocal optical path that includes an optics portion 150 that provides axial chromatic dispersion and is configured to focus different wavelengths at different distances proximate to a workpiece 170; an illumination source 164; and a CRS wavelength detector 162 that includes a plurality of pixels having respective pixel locations distributed along a measurement axis of the CRS wavelength detector, wherein the plurality of pixels receive respective wavelengths and provide output spectral data. At block 620, the CRS system 100 is operated with the optical pen operably positioned relative to a workpiece to perform a measurement operation that includes the optical pen inputting the input spectrum and outputting corresponding radiation to a first workpiece surface and a second workpiece surface of the workpiece, and receiving reflected radiation from the first workpiece surface and the second workpiece surface and outputting the reflected radiation to the CRS wavelength detector that provides the output spectral data.

[0092] At decision block 630, a determination is made as to whether one or more measured distances are to be determined. If one or more measured distances are not to be determined, the method proceeds to block 650, as described in greater detail below. If one or more measured distances are to be determined, the method proceeds to block 640, where the output spectral data is processed to determine one or more measured distances to the workpiece (e.g., where the processing for determining the measured distances may include determining coordinates of the indicated distances that indicate pixel locations corresponding to the indicated measured distances of the CRS wavelength detector).

[0093] Starting from box 640, or if one or more measured distances are not determined at box 630, the method proceeds to box 650, where the output spectral data is processed to determine the thickness of the workpiece corresponding to the spacing between the first workpiece surface and the second workpiece surface of the workpiece (e.g., wherein the processing for determining the thickness is independent of the determined measured distance to the workpiece and / or can utilize a transform process such as a Fourier transform process or other Fourier-related transform process). In various embodiments, the Fourier-related transform process can include a linear transform of a function related to Fourier analysis (e.g., a function can be mapped to a set of coefficients of a basis function, where the basis function can be sinusoidal and can be located in the spectrum). Some examples include cosine transforms, sine transforms, Laplace transforms, etc.

[0094] As mentioned above (for example, Figure 5AIn various embodiments, it may be difficult to determine coordinates that accurately indicate distances relative to the surface of the workpiece (e.g., a thin workpiece due to at least partially merged wavelength peaks). In some cases, wavelength peaks may be merged to the point where only a single coordinate indicating distances may be determined (e.g., Figure 5A In other cases, two coordinates indicative of distance may be determined, but there may be inaccuracies and / or processing issues with the determination due to the merging of wavelength peaks (e.g., for the determination, a centroid calculation for a first wavelength peak used to determine a corresponding coordinate indicative of distance may be partially skewed or otherwise affected by the merged second wavelength peak, or vice versa). Due to such potential issues, in some cases it is desirable to be able to determine the thickness of a workpiece without using centroid calculations such as those previously known techniques described above to make distance determinations. As will be described in more detail below, alternative techniques for determining the thickness of a workpiece (e.g., using a transform process) are disclosed herein.

[0095] In various embodiments, one or more distances determined by previously known techniques may still provide useful information (e.g., which may in some cases be used in combination with a thickness determined according to the principles disclosed herein). For example, as will be described in more detail below (e.g., with respect to Equations 6-10), in some cases, a measured distance to a workpiece determined (e.g., at block 640) may be used in combination with a thickness of a workpiece determined according to the principles disclosed herein (e.g., at block 650).

[0096] As described above, in some cases, wavelength peaks corresponding to two opposing workpiece surfaces may merge to a coordinate from which only a single indicative distance may be determined (e.g., Figure 5A In some embodiments, this coordinate (e.g., Figure 5A The DIC 504a) can represent the measured distance, such as Figure 5B The distance Z3' is between the distances Z1 and Z2' (e.g., and may correspond to the average of the distances Z1 and Z2' and may extend to the midpoint of the apparent thickness d'). The distance Z3' is related to the distance Z3, which is similar to a point inside the workpiece 170 between the first workpiece surface 190-1 and the second workpiece surface 190-2. In some embodiments, the point inside the workpiece corresponding to the distance Z3 may be located at the midpoint between the first workpiece surface 190-1 and the second workpiece surface 190-2, for which the distance Z3 corresponds to the average of the first distance Z1 and the second distance Z2 to the corresponding first workpiece surface 190-1 and the second workpiece surface 190-2 (e.g., for which the distance Z3 extends to the midpoint of the actual thickness d).

[0097] For example, about Figure 5A As shown in the dashed measured spectral signal 510a corresponding to the thin version of the workpiece 170, if the wavelength peaks 502-1a and 502-2a corresponding to the workpiece surfaces 190-1 and 190-2 (e.g., having peak pixel coordinates ppc1a and ppc2a) have similar characteristics (e.g., have similar sizes, etc.), then the centroid or similar calculation may produce a coordinate indicating a distance (e.g., DIC 504a) that is approximately / nominally located at the midpoint between the two wavelength peaks. In this case, the corresponding measured distance (e.g., distance Z3') is approximately the average of the first distance Z1 and the second distance Z2'. In some embodiments, this determined measured distance (e.g., distance Z3') can be used in combination with the determined thickness d of the workpiece (e.g., determined at box 650) to determine the first measured distance Z1 and / or the second measured distance Z2 to the first workpiece surface 190-1 and the second workpiece surface 190-2. For example, if it is assumed that the distance Z3' is located at the midpoint between the distances Z1 and Z2', and if the apparent thickness d' corresponds to the difference between the distances Z1 and Z2' (for which the apparent thickness d'=Z2'-Z1), and if it is assumed that the thickness d of the workpiece 170 and the interval between the workpiece surface 190-1 and 190-2 correspond (for which the thickness d=Z2-Z1), the following equations represent some of the relationships between the respective distances:

[0098] Z1=Z3-(d / 2) (Equation 6)

[0099] Z2=Z3+(d / 2) (Equation 7)

[0100] Z1=Z3'-(d' / 2) (Equation 8)

[0101] Z2'=Z3'+(d' / 2) (Equation 9)

[0102] According to the above equation, in various embodiments, the determined workpiece thickness d can be used in combination with the determined distance (e.g., distance Z3' as the average of distances Z1 and Z2') to determine the distance to the workpiece surface (e.g., distance Z1 to the workpiece surface 190-1). For example, the following equation 10 is generated by combining equations 5 and 8:

[0103] Z1=Z3'-(d / 2n) (Equation 10)

[0104] And for said equation Z2 can then also be determined (eg, according to equation 3).

[0105] As described above, in some cases, according to previously known techniques, processing may produce two DICs corresponding to two wavelength peaks that are partially merged. In some cases, the two determined DICs may have some inaccuracy (e.g., due to the merged peaks). In some such embodiments, (e.g., for such embodiments, it may be assumed that the two DICs have been skewed toward the midpoint by similar amounts due to the merged peaks) the two measured distances corresponding to the two DICs may be averaged to determine an approximate midpoint measured distance (e.g., similar to distance Z3'), which may then be used in combination with the determined thickness d of the workpiece (e.g., determined at block 650) to provide a more accurate determination of distances Z1 and Z2 (e.g., by utilizing processing such as Equation 10).

[0106] In some embodiments, for a given set of output spectral data, a selection may be made and / or processing may be performed to determine whether the thickness of the workpiece should be determined according to the principles disclosed herein, or alternatively according to previously known methods (e.g., using a centroid calculation to determine the corresponding difference between the coordinates indicating the distance and the measured distance, as described above with respect to Figure 5A 4 and 5). For example, for a certain workpiece (e.g., a relatively thin workpiece with little separation between wavelength peaks and corresponding peak merging or other issues), a user may select and / or may perform processing (e.g., automatically) to determine whether the thickness should be determined using techniques as disclosed herein. Alternatively, for a certain workpiece (e.g., a relatively thick workpiece with relatively significant separation between wavelength peaks and without any significant peak merging issues, etc.), a user may select and / or may perform processing (e.g., automatically) to determine whether the thickness should be determined using previously known methods. In some embodiments, such a determination may be made at least in part based on processing the output spectral data using both previously known methods and the techniques disclosed herein, and for a given embodiment, comparing / analyzing the different results to determine which thickness determination technique may be preferred / usable (e.g., most accurate, most practical, etc.) (e.g., this may also depend on additional factors, such as the measurement range of the particular optical pen / CRS system utilized, etc.).

[0107] Figures 7A-7D A thickness measurement process using a transform process as part of a deconvolution method is presented. Deconvolution is used to improve the determination of the location of two wavelength peaks that may not be well defined and / or well separated from each other. Specifically, in one aspect, deconvolution is used to reduce the peak width so that the distance between the two peaks can be better and more accurately determined (e.g., based on corresponding calculations, etc.).

[0108] Fig. 7AAn intensity spectrum (or "output spectral data") 701 output from wavelength detector 162 is shown, the intensity spectrum comprising signal level or intensity (vertical axis) as a function of pixel coordinates or "pixel position" (horizontal axis), similar to Figure 3 , 5A and 10A-10F, as described above. Intensity spectrum 701 includes intensity spectra corresponding to the first work surface and the second work surface (e.g., Figure 1 The first wavelength peak 702-1 and the second wavelength peak 702-2 of the workpiece surfaces 190-1 and 190-2).

[0109] In various embodiments, the transformation process performed to determine the thickness of a workpiece (eg, workpiece 170) may include calculating Figure 7B The Fourier transform of the output spectral data 701 in can then be divided by the Fourier transform of the reference (e.g., Figure 7C ) to thereby obtain the Fourier transform of the target spectral data. In various embodiments, the reference can be a mathematical reference function (e.g., a Lorentzian reference, etc.). In other embodiments, the reference can be obtained, for example, in the form of output spectral data of a "reference" workpiece (e.g., for the workpiece, its top surface is located at the same distance from the optical pen as the distance from the workpiece surface 190-1), the reference workpiece This can be a thick glass workpiece, so that only reflections from the top surface are presented in the output spectral data (e.g., for the workpiece, the bottom surface of the thick glass workpiece may be beyond the range of the optical pen, or otherwise such that reflections from the bottom surface are not included in the output spectral data). Finally, the inverse Fourier transform of the Fourier transform of the target spectral data is calculated to recover as Fig.7D The first wavelength peak 702-1x and the second wavelength peak 702-2x in the image, for which the pixel location can be more easily / more accurately determined and thereby enable enhanced and improved detection of the image contained in the image. Fig. 7A The corresponding pixel locations of the original two peaks 702-1 and 702-2 in the output spectral data 701 are determined. In various embodiments, the locations of the peaks as indicated by the pixel locations can then be referenced to a distance calibration lookup table or the like (e.g., as described above with respect to Figure 4A and 4B As described above, the distances Z1 and Z2' are determined, for which the thickness d of the workpiece can be determined according to calculations such as those of equations 4 and 5.

[0110] As follows, Figure 8-9H As described in more detail, further techniques are disclosed herein that may have advantages over, in some embodiments, Figures 7A-7DFor example, reference Figures 7A-7D The deconvolution type techniques described can improve and enhance the determination of the pixel locations of the two peaks in the output spectral data, but for said determination, in some embodiments, dividing by a reference (e.g., Figure 7C ) may increase the portion of the signal associated with high frequency noise in the Fourier transform of the spectral data. Although this high frequency noise can be mitigated by using a low pass filter, fine tuning this low pass filter may present certain challenges (e.g., fine tuning the filter requires balancing narrow peaks with signal stability, etc.). In various embodiments, at least some of these potential problems can be addressed by alternatively utilizing the following Figure 8-9H Those techniques are described in more detail to address this.

[0111] Figure 8 Certain aspects of a thickness measurement process using transform processing (eg, including Fast Fourier Transform (FFT) processing) are presented. Figure 8 Some of the curves shown in Figures 7A-7D Some of the curves shown in are similar and / or related, as will be described in more detail below. Figure 8 The raw data Fourier transform curve 801 is shown as a Fourier transform of an intensity spectrum (or "output spectral data"), which contains the intensity of the raw data as a function of frequency (pixel -1 )(horizontal axis) of the signal level (logarithmic scale of absolute value) (vertical axis), and the Fourier transform of the curve is determined as curve 801 similar to the determination Figure 7B The deconvolution output curve 802 shows the same Fourier transform curve as above. Figure 7C The result of a similar process as those described, where for the process, the Fourier transform curve 801 is divided by the Fourier transform of the reference, and for the process in this example, no low pass filter is utilized to mitigate high frequency noise, and therefore the noise component in curve 802 is shown to increase (e.g., exponentially or otherwise) for higher frequency components. Techniques for avoiding such problems are described in more detail below with respect to curve 803.

[0112] With respect to curve 803, it should be appreciated that for a spectrum containing two wavelength peaks corresponding to two reflections of equal intensity (i.e., from two workpiece surfaces), where the measured distance Z1 corresponding to the top surface and the apparent measured distance Z2' corresponding to the bottom surface are indicated as being at equal distances of +d' / 2 and -d' / 2 from the corresponding midpoints (e.g., corresponding to the apparent midpoint measured distance Z3') (e.g., see Equations 8 and 9), the ideal Fourier transform of the intensity spectrum data containing two reflections of equal intensity is the Fourier transformed cosine curve 803, as shown in Figure 8And according to the following equation 11:

[0113] F(δ(x-d' / 2)+δ(x+d' / 2))=2cos(k(d' / 2)) (Equation 11)

[0114] where d' is the apparent thickness of the workpiece, and k is the spatial frequency.

[0115] In various embodiments, Figures 7A-7D The process can be characterized as an attempt to recover something like Figure 8 A cosine curve of cosine curve 803 of FIG. 804 is shown, but a low pass filter is required for the curve as described above to mitigate the increased high frequency noise as shown in curve 802, and there may be certain challenges in fine tuning the low pass filter for the curve. According to the principles disclosed herein, since it is expected that the ideal final result will be a cosine curve, an alternative approach is to determine the first valley of the absolute value of the Fourier transform (e.g., the absolute value of the FFT of the output complex number), which indicates the cosine period and correspondingly the workpiece thickness, as indicated by the following equation 12:

[0116]

[0117] where d is the thickness of the workpiece, n is the refractive index of the workpiece material at the corresponding wavelength (ie, according to Equation 5, for the thickness d = (d')(n)), and f 谷 The unit of is 1 / λ. is related to the rate of change of z with respect to pixel position / wavelength, for which Figure 4A As shown in the graph portion of the CRS measured distance calibration data 410A, the change in pixel change unit z is higher for lower wavelengths / pixel positions (e.g., closer to the blue wavelength portion of the range) and lower for higher wavelengths / pixel positions (e.g., closer to the red wavelength portion of the range). This is shown by Figure 4B The example values ​​in the distance calibration lookup table 410B are similarly illustrated, for which the change in z (i.e., the measured distance) for a DIC change of 0.1 is higher for lower DIC (e.g., the change in z between DICs of 104.1 and 104.2 is 37.0303 μm-36.9029 μm=0.1274 μm) and lower for higher DIC (e.g., the change in z between DICs of 990.1 and 990.2 is 486.6733 μm-486.6540 μm=0.0193 μm). As described above, the portion of the range utilized is determined based on the distance of the workpiece from the optical pen (e.g., based on the wavelength of best focus at the aperture 195, as described above with respect to Figure 1-3In some specific example values, in one embodiment, in the blue wavelength portion of the range and in the red wavelength portion of the range

[0118] In accordance with Equation 12 and Figure 8 In the case of some specific example values ​​of the illustration, if the workpiece material is fused silica having a refractive index such that n=1.46, and the workpiece is positioned relative to the optical pen at part of the range, and Figure 8 f along the x-axis 谷 The value / positioning of corresponds to 0.16, then according to Equation 12, the thickness can be determined according to d=(1.46(5.49μm / pixel)) / (2(0.16 / pixel))=25μm. Therefore, according to various exemplary aspects of the present invention, a transform process (e.g., using a fast Fourier transform (FFT)) can be used to determine the first valley 804 of the Fourier transform curve 801 (e.g., which indicates a cosine period), and based on this, the thickness "d" of the workpiece can be determined (e.g., according to a calculation such as example Equation 12).

[0119] In various embodiments, f 谷 The value of can be determined according to a valley finding algorithm (e.g., which in some embodiments can be similar to or include a peak finding algorithm that has been re-used as a valley finding algorithm). In various embodiments, such an algorithm can include operations such as taking derivatives and searching for zero crossings (e.g., the first zero crossing corresponding to the first valley, etc.). In various embodiments, false peaks / valleys that may otherwise occur due to noise or similar factors can be suppressed or otherwise addressed through smoothing and / or thresholding operations, etc.

[0120] As described above, in various embodiments, certain techniques disclosed herein (e.g., as demonstrated by Equation 12) can enable accurate thickness measurement / determination of thinner workpieces than can be measured using previously known techniques. As some examples, some calculations of minimum thicknesses that can be measured using previously known techniques will be described in more detail below and compared to the minimum thickness that can be measured using the techniques disclosed herein.

[0121] The following numerical examples relate to previously known centroid-type techniques for determining DIC from calculated centroid values ​​(e.g., Figure 5A In one specific example embodiment, an optical pen of a CRS system may be provided, for which the optical pen is in the blue wavelength portion of the range. and in the red wavelength portion of the range In one embodiment, it can be determined that when utilizing previously known centroid-type techniques as described above, wavelength peaks can be measured (i.e., pixel locations can be accurately determined for said wavelength peaks) when the peaks are separated by at least one full width half maximum (FWHM) value, which in the blue wavelength portion of the range can correspond to FWHM=3 pixels, and in the red wavelength portion of the range can correspond to FWHM=6 pixels. In this embodiment, with n=1.5 for a glass workpiece, the minimum thickness of the workpiece that can be accurately measured is For the values ​​indicated above for the blue wavelength portion of the range, the thickness may correspond to d 最小 =36 μm, and for the values ​​indicated above for the red wavelength portion of the range, the thickness may correspond to d 最小 =18μm.

[0122] In contrast, according to certain techniques disclosed herein (e.g., as demonstrated by Equation 12 for certain “first valley” type techniques), assuming the same CRS system with the same optical pen is used, the minimum thickness of a workpiece that can be accurately measured can approximately correspond to the Nyquist frequency, for which f 谷 may be approximately equal to 0.5, and for the frequency equation 12 can therefore be simplified to The frequency for the blue wavelength portion of the range may correspond to d 最小 = 12 μm (i.e., approximately the same as the d of the previously known centroid technique described above). 最小 = 1 / 3 of 36 or 33.3%), and the frequency for the red wavelength portion of the range may correspond to d 最小 = 3 μm (i.e., it is approximately the same as the d of the previously known centroid technique as described above). 最小 =1 / 6 of 18μm or 16.7%).

[0123] In addition, according to another technique disclosed herein (for example, for some "deconvolution" type techniques above relative to Figures 7A-7D Assuming the same CRS system with the same optical pen is used, in one embodiment, it has been experimentally determined that the minimum thickness of the workpiece that can be accurately measured may correspond to a peak separation of approximately (0.85) FWHM, for which the blue wavelength portion of the range may correspond to d 最小 = 30.6 μm (i.e., the d of the previously known centroid technique as described above) 最小 = 85% of 36), and for the optical pen, the red wavelength portion of the range may correspond to d 最小= 15.3 μm (ie, it is the d of the previously known centroid technique as described above). 最小 =85% of 18). It should be appreciated that this increase in the measurable thickness range is difficult to obtain given the complexity of the optical pen of the CRS system, and may be particularly advantageous in certain embodiments (e.g., for which accurate measurement of the thickness of certain thin workpieces and / or workpiece portions may be desired, etc.).

[0124] Further information about the above Figure 8 Some of the "first valley" type of technologies described, Figures 9A-9D Some additional examples of identified first valleys are shown in . Figures 9A-9D The example of FIG. 1 shows that, regardless of the position of the workpiece (eg, thickness = 25 μm) relative to the operable measurement range of the optical pen 120, Figure 8 The processing method results in a Fourier transform of a signal having a first valley, and for the method, the location of the first valley can be used to determine the thickness of the workpiece (e.g., according to calculations such as those of Equation 12). Figures 9A-9D In the example of FIG. 1 , the workpiece 170 may be placed on the stage 175 of the CRS system 100 (see FIG. Figure 1 ), for which the top surface 190-1 is located at 300μm, 400μm, 500μm and 800μm, respectively, from the measurement reference position RP of the optical pen 120 of the CRS system 100 (i.e., for which the wavelength peaks are shown to be positioned at different corresponding relative positions along the pixel / wavelength range of the detector, as shown by the corresponding x-axis positions).

[0125] Figures 9A-9D The corresponding intensity spectra 902A, 905A, 908A, 911A output from the wavelength detector 162 are shown, and the corresponding intensity spectra include signal level or intensity (vertical axis) as a function of pixel coordinates or "pixel position" (horizontal axis), which is similar to the above-mentioned Figure 3 , 5A , 7A and 10A-10F. It should be noted that in the blue wavelength portion of the Z range of the CRS system 100 closer to the optical pen 120, the two wavelength peaks of the intensity spectrum appear to have completely merged together, as shown in FIG. Fig.9A and 9B As shown, in the red wavelength portion of the Z range of the CRS system 100 that is further away from the optical pen 120, the two wavelength peaks of the intensity spectrum are at least somewhat identifiable / distinguishable, as shown in FIG. Fig. 9C and 9D shown. Figures 9A-9DAlso shown are intensity spectra 903A, 906A, 909A, 912A corresponding to a "reference" workpiece, which may be a thick glass workpiece such that only reflections from the top surface of the reference workpiece are represented in the intensity spectrum, as described above with respect to Figure 7C As described.

[0126] Fig.9E Shown Fig.9A Fourier transform 902B / 903B of intensity spectrum 902A / 903A. Fig.9F Shown Fig. 9B Fourier transform 905B / 906B of the intensity spectrum 905A / 906A. Figure 9G Shown Fig. 9C Fourier transform 908B / 909B of the intensity spectrum 908A / 909A. Figure 9H Shown Fig.9D Fourier transform 911B / 912B of intensity spectrum 911A / 912A.

[0127] Figures 9E-9H It is shown that regardless of the positioning of the workpiece relative to the optical pen 120 of the CRS system 100, the Fourier transforms 902B, 905B, 908B, 911B of the measured intensity spectrum of the workpiece include first valleys 904, 907, 910, 913, which can be used to determine the thickness of the workpiece, as described above. Note that, on the other hand, the Fourier transforms 903B, 906B, 909B, 912B of the intensity spectrum of the reference workpiece do not include any prominent valleys. In various embodiments, it has been experimentally determined that utilizing the "first valley" type techniques disclosed herein (e.g., including calculations as shown by Equation 12) enables the thickness of a workpiece (e.g., a 25 micron workpiece) to be determined with little error or no error (e.g., an error of less than 10% or 5%, etc.) up to (e.g., 90% or 75%) over a wavelength range corresponding to the range of the workpiece of the CRS system including the optical pen, including for example. Figures 9A-9D , where the wavelength peaks have been merged (e.g., and specifically in Fig.9A and 9B , where the two peaks appear visually as a single peak).

[0128] Due to the principles of operation of the first valley type techniques as disclosed herein (e.g., including utilizing a transform such as a Fourier transform as a sum of sines), as described above, such techniques may be particularly effective for determining the thickness of a workpiece such as corresponding to the spacing between a first workpiece surface and a second workpiece surface, but in some embodiments, they may be less effective for simultaneously determining the thickness between multiple layers of a workpiece (i.e., the multiple layers may include a top workpiece surface and a bottom workpiece surface and additional intermediate workpiece surfaces as separating layers). Therefore, in certain embodiments, corresponding thickness measurement operations and / or modes as implemented according to the principles disclosed herein may only be operable to determine the thickness such as corresponding to the spacing between a first workpiece surface and a second workpiece surface, and may not be operable to determine the spacing (e.g., of multiple layers) between three or more workpiece surfaces.

[0129] As described above, in some embodiments, the thickness of a workpiece determined according to the techniques disclosed herein can be used in combination with the distance to the workpiece determined according to previously known methods. Figures 9A-9D A graphical representation of two merged wavelength peaks in (e.g., specifically Fig.9A and 9B , where the two peaks appear visually as a single peak), it will be appreciated that while previously known centroid-type techniques for determining DIC in this case may not accurately determine the two distances to the two surfaces, they can be used to accurately determine the distance (e.g., distance Z3') to the approximate midpoint (e.g., between the centroid distances Z1 and Z2' determined for the merged peaks). The distance calculated in this manner (e.g., distance Z3') can be referenced or otherwise used in combination with a thickness measurement performed in accordance with the techniques disclosed herein (e.g., as described above with respect to equation 10 for determining distance Z1, etc.).

[0130] In some exemplary embodiments, the CRS system 100 may be included in and / or otherwise used in a machine system (e.g., a vision inspection system or a coordinate measuring machine, etc.). In some cases, corresponding functions may be automatically performed in the machine system, such as measuring the thickness of a workpiece along the optical axis OA of the CRS system 100. As some examples of such machine systems, suitable machine vision inspection systems are described in U.S. Pat. Nos. 8,085,295 and 7,454,053, the entire contents of which are hereby incorporated by reference in their entirety.

[0131] Although preferred embodiments of the present invention have been shown and described, the arrangement of features and the order of operations shown and described in this disclosure will become apparent to those skilled in the art. For example, although some types of Fourier transform processing (e.g., Figures 7A-9HCertain techniques related to colorimetric analysis are not disclosed herein, but it should be understood that other types of transform processing can be similarly utilized to achieve similar results based on the disclosed concepts (for example, utilizing Fourier-related transform processing such as cosine transforms, sine transforms, Laplace transforms, etc.). As another example, a CRS system including a chromaticity point sensor (optical pen) has been demonstrated herein. However, a CRS system including a chromaticity line sensor can be configured to operate according to the systems and methods disclosed herein. It should be understood that these and various other alternative forms can be used to implement the principles disclosed herein. In addition, the various embodiments described above can be combined to provide additional embodiments. All U.S. patents and U.S. patent applications mentioned in this specification are incorporated herein by reference in their entirety. If it is necessary to adopt the concepts of various patents and applications to provide additional embodiments, various aspects of the embodiments can be modified.

[0132] These and other changes can be made to the embodiments in light of the above detailed description. In general, in the following claims, the terms used should not be interpreted to limit the claims to the specific embodiments disclosed in the specification and claims, but should be interpreted to encompass all possible embodiments and the full scope of equivalents to which these claims are entitled.

Claims

1. A chromatic range sensor (CRS) system for determining a thickness of a workpiece, the CRS system comprising: an optical pen comprising a confocal optical path including an optics portion that provides axial chromatic dispersion and is configured to focus different wavelengths at different distances proximate a workpiece; an illumination source configured to generate a multi-wavelength input light comprising an input spectrum input to the optical pen; a CRS wavelength detector comprising a plurality of pixels, respective pixel positions of the plurality of pixels being distributed along a measurement axis of the CRS wavelength detector, wherein the CRS system is configured such that when the optical pen is operably positioned relative to the workpiece to perform a measurement operation, the optical pen inputs the input spectrum and outputs corresponding radiation to a first workpiece surface and a second workpiece surface of the workpiece, and receives reflected radiation from the first workpiece surface and the second workpiece surface and outputs the reflected radiation to the CRS wavelength detector providing output spectrum data; as well as A processing portion is configured to process the output spectral data to determine a thickness of the workpiece, the thickness corresponding to a separation between the first workpiece surface and the second workpiece surface of the workpiece, wherein processing the output spectral data for determining the workpiece thickness includes utilizing a transform process.

2. The chromatic range sensor (CRS) system for determining workpiece thickness of claim 1, wherein the transform processing comprises at least one of Fourier transform processing or Fourier correlation transform processing, and the utilizing the transform processing comprises: determining a transformation of the output spectral data; as well as The thickness of the workpiece is determined based at least in part on the transformed first characteristic of the output spectral data.

3. The chromatic range sensor (CRS) system for determining workpiece thickness of claim 2, wherein the first characteristic corresponds to a first dip of the transform of the output spectral data.

4. A chromatic range sensor (CRS) system for determining the thickness of a workpiece according to claim 1, wherein the output spectral data includes a distance-dependent spectral component, the distance-dependent spectral component having a first wavelength peak and a second wavelength peak corresponding to the first workpiece surface and the second workpiece surface, respectively, and determining the thickness of the workpiece is independent of processing the output spectral data to determine the corresponding first measurement distance and second measurement distance to the first workpiece surface and the second workpiece surface.

5. The chromatic range sensor (CRS) system for determining workpiece thickness of claim 4, wherein the first wavelength peak and the second wavelength peak appear visually as a single peak in a representation of the output spectral data provided by the chromatic range sensor wavelength detector for determining workpiece thickness.

6. A chromatic range sensor (CRS) system for determining the thickness of a workpiece according to claim 1, wherein for a workpiece having a spacing of 5 microns between the first workpiece surface and the second workpiece surface, the use of the transformation processing enables the processing portion to accurately determine the thickness of the workpiece with an error of less than 10%.

7. The chromatic range sensor (CRS) system for determining workpiece thickness of claim 1, wherein the processing portion is further configured to process the output spectral data to determine a measured distance to the workpiece.

8. A chromatic range sensor (CRS) system for determining the thickness of a workpiece as described in claim 7, wherein the processing for determining the measured distance to the workpiece includes processing the output spectral data to determine a center of mass indicative of the measured distance to the workpiece, and the processing for determining the thickness of the workpiece is independent of the determination of the center of mass.

9. The chromatic range sensor (CRS) system for determining workpiece thickness of claim 7, wherein the determined measurement distance is to a point inside the workpiece between the first workpiece surface and the second workpiece surface.

10. The chromatic range sensor (CRS) system for determining workpiece thickness according to claim 9, wherein the determined measured distance is determined based on coordinates indicating a distance corresponding to an average value of a first wavelength peak and a second wavelength peak, the first wavelength peak and the second wavelength peak corresponding to respective first workpiece surfaces and second workpiece surfaces.

11. The chromatic range sensor (CRS) system for determining workpiece thickness according to claim 7, wherein the processing portion is further configured to determine at least one of a first measured distance to the first workpiece surface or a second measured distance to the second workpiece surface using the determined measured distance to the workpiece and the determined thickness of the workpiece.

12. The chromatic range sensor (CRS) system for determining workpiece thickness of claim 1, wherein said utilizing said transform process comprises: determining a Fourier transform of the output spectral data; dividing the Fourier transform of the output spectral data by the Fourier transform of a reference to obtain a Fourier transform of target spectral data; calculating an inverse Fourier transform of the Fourier transform of the target spectral data to determine a first wavelength peak and a second wavelength peak corresponding to respective first and second measurement distances to the first and second workpiece surfaces; as well as The thickness of the workpiece is determined based at least in part on a difference between the respective measured distances to the first and second workpiece surfaces.

13. A chromatic range sensor (CRS) system for determining the thickness of a workpiece according to claim 1, wherein the CRS system is capable of operating in multiple modes including a thickness measurement mode, for which the processing portion performs the processing to determine the thickness as part of the thickness measurement mode.

14. The chromatic range sensor (CRS) system for determining workpiece thickness according to claim 13, wherein: The plurality of modes further comprises a distance measurement mode for measuring a distance to a workpiece; The CRS system is configured such that during the distance measurement mode, when the optical pen is operably positioned relative to the workpiece to perform a measurement operation, the optical pen inputs the input spectrum and outputs corresponding radiation to the workpiece, and receives reflected radiation from the workpiece and outputs the reflected radiation to the CRS wavelength detector that provides the output spectrum data; and The output spectrum includes a distance-dependent spectral component having a wavelength peak indicative of a measured distance to the workpiece.

15. The chromatic range sensor (CRS) system for determining workpiece thickness of claim 13, wherein the thickness measurement mode is only operable to determine the thickness as corresponding to the spacing between a first workpiece surface and a second workpiece surface, and is not operable to determine the spacing between three or more workpiece surfaces.

16. The chromatic range sensor (CRS) system for determining workpiece thickness of claim 1, wherein the CRS system is at least one of a chromatic point sensor system or a chromatic line sensor system.

17. A method of operating a chromatic range sensor (CRS) system to determine the thickness of a workpiece, The CRS system comprises: an optical pen comprising a confocal optical path including an optics portion that provides axial chromatic dispersion and is configured to focus different wavelengths at different distances proximate a workpiece; an illumination source configured to generate a multi-wavelength input light comprising an input spectrum input to the optical pen; as well as A CRS wavelength detector, the CRS wavelength detector comprising a plurality of pixels, respective pixel positions of the plurality of pixels being distributed along a measurement axis of the CRS wavelength detector, the plurality of pixels receiving respective wavelengths and providing output spectral data; The method comprises: operating the CRS system with the optical pen operably positioned relative to the workpiece to perform a measurement operation, the measurement operation comprising the optical pen inputting the input spectrum and outputting corresponding radiation to a first workpiece surface and a second workpiece surface of the workpiece, and receiving reflected radiation from the first workpiece surface and the second workpiece surface and outputting the reflected radiation to the CRS wavelength detector providing the output spectrum data; as well as The output spectral data is processed to determine a thickness of the workpiece, the thickness corresponding to a separation between the first workpiece surface and the second workpiece surface of the workpiece, wherein processing the output spectral data to determine the thickness of the workpiece includes utilizing a transform process.

18. The method of operating a chromatic range sensor (CRS) system to determine a thickness of a workpiece as recited in claim 17, wherein said transform process comprises at least one of a Fourier transform process or a Fourier correlation transform process, and said utilizing said transform process comprises: determining a transformation of the output spectral data; as well as The thickness of the workpiece is determined based at least in part on the transformed first characteristic of the output spectral data.

19. The method of operating a chromatic range sensor (CRS) system to determine workpiece thickness as recited in claim 18, wherein said first characteristic corresponds to a first valley of said transform of said output spectral data.

20. A method of operating a chromatic range sensor (CRS) system to determine a thickness of a workpiece according to claim 17, wherein the output spectral data includes a distance-dependent spectral component having a first wavelength peak and a second wavelength peak corresponding to the first workpiece surface and the second workpiece surface, respectively, and determining the thickness of the workpiece is independent of processing the output spectral data to determine corresponding first and second measurement distances to the first and second workpiece surfaces.

21. The method of operating a chromatic range sensor (CRS) system to determine a thickness of a workpiece as recited in claim 17, wherein said utilizing said transform process comprises: determining a Fourier transform of the output spectral data; dividing the Fourier transform of the output spectral data by the Fourier transform of a reference to obtain a Fourier transform of target spectral data; calculating an inverse Fourier transform of the Fourier transform of the target spectral data to determine a first wavelength peak and a second wavelength peak corresponding to respective first and second measurement distances to the first and second workpiece surfaces; as well as The thickness of the workpiece is determined based at least in part on a difference between the respective measured distances to the first and second workpiece surfaces.

22. The method of operating a chromatic range sensor (CRS) system to determine a thickness of a workpiece as recited in claim 17, wherein: The CRS system is operable in a plurality of modes including a thickness measurement mode and a distance measurement mode for measuring the distance to a workpiece; the processing portion performing the processing to determine the thickness as part of the thickness measurement mode; and The method further comprises: operating the CRS system during the distance measurement mode with the optical pen operably positioned relative to a workpiece to perform a measurement operation, the measurement operation comprising the optical pen inputting an input spectrum and outputting corresponding radiation to the workpiece, and receiving reflected radiation from the workpiece and outputting the reflected radiation to the CRS wavelength detector providing output spectral data, the output spectral data including a distance-dependent spectral component having a wavelength peak indicative of a measured distance to the workpiece; as well as The output spectral data is processed to determine a distance to the workpiece.

23. A method of operating a chromatic range sensor (CRS) system to determine a thickness of a workpiece as described in claim 22, wherein the thickness measurement mode is only operable to determine a thickness such as corresponding to a spacing between a first workpiece surface and a second workpiece surface, and is not operable to determine spacing between three or more workpiece surfaces.

24. A method of operating a chromaticity range sensor (CRS) system, The CRS system comprises: an optical pen comprising a confocal optical path including an optics portion that provides axial chromatic dispersion and is configured to focus different wavelengths at different distances proximate a workpiece; an illumination source configured to generate a multi-wavelength input light comprising an input spectrum input to the optical pen; as well as A CRS wavelength detector, the CRS wavelength detector comprising a plurality of pixels, respective pixel positions of the plurality of pixels being distributed along a measurement axis of the CRS wavelength detector, the plurality of pixels receiving respective wavelengths and providing output spectral data; The method comprises: operating the CRS system with the optical pen operably positioned relative to the workpiece to perform a measurement operation, the measurement operation comprising the optical pen inputting the input spectrum and outputting corresponding radiation to a first workpiece surface and a second workpiece surface of the workpiece, and receiving reflected radiation from the first workpiece surface and the second workpiece surface and outputting the reflected radiation to the CRS wavelength detector providing the output spectrum data; processing the output spectral data to determine a measured distance to the workpiece, wherein processing the output spectral data to determine the measured distance to the workpiece comprises determining coordinates indicative of the distance, the coordinates indicative of the distance corresponding to pixel locations of the CRS wavelength detector indicative of the measured distance; and The output spectral data is processed to determine a thickness of the workpiece, the thickness corresponding to a separation between the first workpiece surface and the second workpiece surface of the workpiece, wherein the processing for determining the thickness is independent of a determined measured distance to the workpiece.

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