Chromatic Range Sensor System

Abstract

To provide a configuration for calibrating an optical probe of a chromatic range sensor connected to a coordinate measurement machine.SOLUTION: A calibration component for a chromatic range sensor (CRS) optical probe of a coordinate measurement machine (CMM) includes a calibration member. The calibration member includes at least a first cylindrical calibration surface. A central axis of the first cylindrical calibration surface is along a Z direction, and is aligned so as to be substantially parallel to a rotational axis of a CRS optical probe. The first cylindrical calibration surface is provided at a distance of a known first radius R1 from the central axis along the Z direction. A first set of angle reference feature parts are formed on the surface of or in the inside of the first cylindrical calibration surface. The angle reference feature parts are formed to be detectable by a radial distance detection beam, and are mutually arranged at a known angle or at an angle interval around the central axis in the surface or the inside of the first cylindrical calibration surface.SELECTED DRAWING: Figure 7C

Description

[Technical field]

[0001] The present invention relates generally to precision measurement equipment, and more particularly to chromatic range sensor optical probes for coordinate measuring machines (CMMs) used to determine measurements of workpieces. [Background technology]

[0002] One type of coordinate measuring machine scans the surface of a workpiece with a probe and calculates the 3D profile of the workpiece after the scan. One type of scanning probe measures the workpiece directly by mechanically contacting the probe with various points along the workpiece surface, often with balls.

[0003] Other CMMs use optical probes to measure the workpiece without contacting the workpiece surface. Some optical probes (e.g. triangulation probes) use light to measure points on the workpiece surface and are coupled with a video camera (e.g. stereo vision or structured light systems) for imaging two-dimensional (2D) cross-sections of the workpiece surface. Some systems use image processing software to determine the coordinates of geometrical parts of the workpiece.

[0004] Also known are "hybrid" coordinate measuring machines that use both optical and mechanical measurement detectors. One such machine is described in U.S. Pat. No. 4,908,951 and has two spindles. One spindle is for carrying a mechanical contact probe and the other spindle is for holding a video camera. The optical path of the video camera is set up so that the laser probe can measure simultaneously with the video camera along the Z axis, i.e. the optical axis of the video camera.

[0005] US Patent No. 5,825,666 (Patent Document 2) describes an optical three-dimensional coordinate measuring machine, in which an optical contact probe of the machine sets the distal end of a contact of a standard probe to a first target. The standard probe is attached to a video camera, which images the target on the camera. The movement and position of the target in the XY coordinate system are displayed on a computer image processing device of the machine. A second target is attached to the proximal end of the probe, which displays the movement and position of the Z coordinate. The second target may obscure the photodetector, but can be focused on the camera by a light beam parallel to the XY plane. Here, the two second targets can be illuminated by beams parallel to the XY plane and orthogonal to each other. And, when using star probes, the rotation about the Z axis is calculated by a computer. Also disclosed is an automatic exchange rack for holding multiple probes, a probe holder, and multiple lenses for selective attachment to the camera, respectively. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent No. 4,908,951 [Patent Document 2] U.S. Patent No. 5,825,666 [Patent Document 3] U.S. Patent No. 7,876,456 [Patent Document 4] U.S. Patent No. 7,990,522 [Patent Document 5] US Patent Publication No. 20120050723 Summary of the Invention [Problem to be solved by the invention]

[0007] The optical probe and / or coordinate measuring machine may include, for example, a rotation mechanism for rotating an optical pen of the optical probe about an axis. In addition, the optical pen may include a reflective element disposed in the light path of the light source, which directs the measurement light in a different direction than the light source light.

[0008] Problems in this regard include errors in measurements taken with a rotating optical pen coordinate measuring machine, which may have nonlinear components, such as radius error, azimuth error, and z-distance error. Traditionally, interferometric calibrations are used to deal with such errors. However, interferometric calibrations are difficult to perform accurately, especially for rotating probes. In addition, such calibrations are difficult to perform at the measurement site, such as in a manufacturing plant.

[0009] What is needed is an arrangement and method that can address these issues, namely, an arrangement and method for calibrating the optical probe of a chromatic range sensor connected to a coordinate measuring machine. [Means for solving the problem]

[0010] A method according to the present invention is a method for providing calibration data for correcting misalignment errors in a rotary chromatic range sensor configured to direct a radial distance sensing beam along a radial direction relative to an axis of rotation and configured to rotate the radial distance sensing beam about the axis of rotation. The calibration member of the present invention has at least one cylindrical first calibration surface, the central axis of which extends along the Z direction and is aligned to be substantially parallel to the rotation axis, the first cylindrical calibration surface is located at a first known radius R1 from the central axis extending in the Z direction, and includes a first set of angular reference features formed on or within the first cylindrical calibration surface. The set of angular reference features are configured to be detected by the radial distance detection beam and are disposed on or within the first cylindrical calibration surface at known angles or angular intervals about the central axis. The calibration member is disposed in a relationship to the rotating chromatic range sensor. The direction of the rotation axis and the direction of the central axis have a constant angular relationship to each other and are parallel to each other within 5 degrees.

[0011] The rotating chromatic range sensor rotates a radial distance detection beam about a rotation axis at a first Z coordinate position in a Z direction relative to the calibration member to acquire and provide a first radial distance data set during operation, where the radial distance data set references a sensed rotation angle of the radial distance detection beam about the rotation axis. The first radial distance data set referenced to the sensed rotation angle is processed to determine calibration data. The calibration data is configured for use in characterizing or compensating for radial distance measurement errors as a function of a sensed rotation angle of the radial distance detection beam about the rotation axis.

[0012] In some embodiments, a system is provided that includes a coordinate measuring machine (CMM), a chromatic range sensor (CRS) optical probe, and a calibration member. The CMM includes a light generating circuit, a wavelength detecting circuit, and a CMM control circuit. The CRS optical probe is configured to be connectable to the CMM and includes an optical pen having a confocal optical system including at least a confocal aperture and a chromatic dispersion optical member. The optical pen is configured to direct a radial distance detection beam along a radial direction relative to an axis of rotation and to rotate the radial distance detection beam about the axis of rotation such that different wavelengths of light are focused at different distances near a measured surface of the workpiece along the measurement axis. The calibration member is for providing calibration data to correct misalignment errors of the CRS optical probe. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a block diagram of an exemplary chromatic range sensor (CRS) system having an optical pen. [Diagram 2] FIG. 1 is a block diagram of a coordinate measurement system including a coordinate measuring machine, a CRS optical probe including an optical pen, a controller, and a user interface. [Diagram 3] 3A and 3B are diagrams showing the internal structure of the CRS optical probe of FIG. 2 according to the first embodiment. [Figure 4] 4A and 4B are diagrams illustrating the structure of an optical pen including the exchange mount and replaceable optical mechanism of FIGS. 3A and 3B. [Diagram 5] FIG. 3 is a block diagram showing the structure of the probe controller of FIG. 2. [Figure 6] FIG. 1 is a block diagram illustrating one embodiment of an optical pen that includes a rotor of interchangeable optical mechanisms and an encoder for measuring and reporting position information. [Figure 7] 7A-7C are cross-sectional views showing representative calibration components of the optical pen of FIG. [Figure 8] 8A-8C are conceptual diagrams showing examples of misalignment that can cause measurement errors when measuring with a rotating optical pen, and examples of parameters that may be taken into account to compensate for such errors. [Figure 9] 9A to 9D are diagrams showing a calibration member in the shape of a ring gauge according to one embodiment. [Figure 10] FIG. 2 illustrates a calibration member in the form of a stepped ring gauge according to one embodiment. [Figure 11] 11A to 11C are cross-sectional views and conceptual diagrams showing a calibration member in the shape of a stepped ring gauge according to another embodiment. [Figure 12] 12A-12C are diagrams showing calibration members in the form of one or more precision glass tubes according to an embodiment. [Figure 13] 13A to 13E are diagrams showing a calibration member in which a plurality of precision metal tubes are nested together according to the embodiment. [Figure 14] 1 is a graph of an example radius measurement data set associated with an optical pen. [Figure 15]15 is a graph of corrected slope and offset determined based on the example radial distance measurement data set of FIG. 14. [Figure 16] 13A-13C are graphical illustrations of radial distance data obtained at gauge distance (at multiple locations) and at multiple locations of offset of the rotation axis of the optical pen relative to the central axis of the calibration member according to one embodiment. [Figure 17] FIG. 1 illustrates the calibration procedure for the rotating chromatic range sensor structure of a CMM. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] FIG. 1 is a block diagram showing the basic components of a representative chromatic range sensor (CRS) system 100 with a desired operating principle for a coordinate measuring machine. The CRS system 100 has some similarities to the devices described in U.S. Pat. No. 7,876,456 and U.S. Pat. No. 7,990,522. The CRS system 100 shown in FIG. 1 is a chromatic point sensor system including an optical mechanism 120 and electronics 160, which may measure one point at a time. Hereinafter, the optical mechanism 120 of FIG. 1 is also referred to as an optical pen. However, various embodiments may utilize alternative chromatic range systems, such as a chromatic line sensor.

[0015] The optical pen 120 includes a fiber optic connector 109, a housing 131 (e.g., an assembly hollow tube), and a color dispersive optical element 150. The fiber optic connector 109 is attached to an end of the housing 131. In various embodiments, the fiber optic connector 109 may be oriented at an angle relative to the housing 131. The fiber optic connector 109 carries input and output optical fibers (not shown in detail) through an integrated input and output fiber optic cable 112. The input and output optical fibers output measurement light from a light source through a fiber aperture 195 and receive reflected measurement signal light through the fiber aperture 195.

[0016] During the measurement operation, broadband source light (e.g., white light) emitted from the end of the fiber through a fiber aperture 195 is collected by a chromatic dispersion optical element 150, which may include a simple or compound lens that promotes axial chromatic dispersion, so that the focus along the optical axis OA is at a different distance depending on the wavelength of the light, as is well known in confocal chromatic sensor devices. The source light forms a measurement light 196 that includes wavelengths of light that are focused on a work surface 190 at a position Z from the optical pen 120. The reflected light from the work surface 190 is again focused on the fiber aperture 195 by the chromatic dispersion optical element 150. The measurable measurement light and reflected light are bounded by limiting rays LR1, LR2. Due to the axial chromatic dispersion, only one wavelength will exhibit a forward focal distance FF that corresponds to the measurement distance from the optical pen 120 to the work surface 190. The optical pen 120 is configured such that the wavelength that is best focused on the work surface 190 is also the wavelength that is best focused on the fiber aperture 195. Fiber aperture 195 spatially filters the reflected light so that the best focused light passes through aperture 195 and into the core of fiber optic cable 112. As described in more detail below, fiber optic cable 112 conveys the reflected signal light to wavelength detector 162, which is used to determine the wavelength of predominant intensity that corresponds to the measured distance to work surface 190.

[0017] FIG. 1 also shows a schematic representation of an optional reflective element 155, shown in dashed lines. A reflective element, as described in detail in U.S. Patent Publication No. 20120050723, may be disposed in the path of the source light SB of the present invention. In such an embodiment, rather than a measurement axis MA that is coaxial with the optical axis OA, the reflective element may reflect the measurement light 196' in a different direction along the measurement axis MA' (e.g., orthogonal to the optical axis) as required by the measurement application. Such an orthogonal direction is used in the embodiments shown in the other figures, as described in more detail below.

[0018] The electronics 160 includes a fiber coupler 161, a wavelength detector 162, a light source 164, a signal processor 166, and a memory 168. In various embodiments, the wavelength detector 162 includes a spectrometer or spectrometer arrangement. A dispersive optical element, such as a diffraction grating, in the wavelength detector 162 receives the reflected light through the fiber optic cable 112 and communicates the resulting spectral intensity profile to a detector array 163. The wavelength detector 162 may also include associated signal processing functionality, such as functionality provided by the signal processor 166 in some embodiments, such as removing detector-specific error components from the profile data or compensating the profile data. Thus, certain aspects of the wavelength detector 162 and the signal processor 166 may be integrated or may be indistinguishable.

[0019] The white light source 164 is controlled by a signal calculator 166 and is connected to the fiber cable 112 via an optical coupler 161 (e.g., a 2×1 optical coupler). As described above, light travels through the optical pen 120 which generates axial chromatic aberration, the focal length of which varies depending on the wavelength of the light. The wavelength of light that is most efficiently transmitted when passing backward through the fiber is the wavelength that is focused on the work surface 190 at position Z. The wavelength-dependent reflected light intensity then passes again through the fiber coupler 161 such that approximately 50% of the light is directed to a wavelength detector 162 which operates to receive the spectral intensity profile distributed on the pixel array along the measurement axis of the detector array 163 and provide corresponding profile data. In brief, the sub pixel-resolution distance indicating coordinates of the profile data, e.g., peak position coordinates, are calculated by the signal calculator 166. The distance indicating coordinates (DIC) corresponding to the wavelength peaks then determine the measured distance to the surface via a distance calibration look-up table. The calibration look-up table is stored in memory 168. The distance indicating coordinate (DIC) may be determined in a variety of ways, such as by determining the center of gravity of the profile data within a peak region of the profile data. The rotational systems described herein may also utilize calibration data (e.g., stored in memory 168 or other storage) to provide an indication or adjustment of a measured distance based at least in part on the angular orientation of the optical pen 120.

[0020] Typically, the optical pen 120 has a measurement range R defined by a minimum and maximum distance ZMIN and ZMAX in the Z-axis direction. In some known examples of optical pens, the measurement range R is preferably approximately 1 / 10 of the nominal standoff or operable distance from the end of the pen (e.g., in the range of tens of microns to a few millimeters). Figure 1 shows that when a reflective element 155 is used, the measurement range R' is determined along a measurement axis MA' defined by the location of the reflective element 155 (e.g., the x-axis). In this case, the measurement range R' is defined by a minimum and maximum distance XMIN and XMAX in the X-axis direction.

[0021] In some embodiments, the electronics 160 is separate from the optical pen 120. It is known to mount an optical pen similar to the optical pen 120 of FIG. 1 to a CMM using a custom designed bracket and to route optical fibers similar to the fiber optic cable 112 along temporary paths external to the CMM machine to remote electronics similar to the electronics 160.

[0022] 2, 3A, and 3B, a group of light source / wavelength detector components 160A (e.g., including wavelength detector 162 and light source 164) may be included in the CRS optical probe assembly in some embodiments. A group of components in measurement signal processing control circuit 160B (e.g., including signal processor 166 and memory unit 168) may be located external to the CRS optical probe assembly if necessary (e.g., to maintain a lightweight probe and compact size).

[0023] FIG. 2 is a block diagram of a three-dimensional coordinate measuring system 200 and a CRS optical probe device 215 that can be automatically connected and replaced. That is, the CRS optical probe device 215 can be automatically replaced with another type of CMM probe. Here, the CRS optical probe device is simply called a CRS optical probe. Unless otherwise specified in the specification, a reference numeral having a similar suffix in a plurality of drawings (for example, a reference numeral 2XX having the same suffix XX as a reference numeral 1XX) basically has a similar configuration. And, a change to a configuration 2XX based on a description of a similar configuration 1XX is generally easily inferred from a well-known technique. However, despite such an inference, it is obvious that different aspects of various configurations naturally exist in different embodiments, so the configuration of the present invention should not be interpreted as being limited to one of the well-known techniques.

[0024] The three-dimensional coordinate measuring system 200 includes a three-dimensional coordinate measuring machine (CMM) controller 202, a computer and user interface 206, a probe signal processing and control circuitry 207, and a three-dimensional coordinate measuring machine (CMM) 210. The CMM controller 202 includes a probe head controller 203, a position latch 204, and a motion controller 205. The CRS optical probe 215 includes an auto-exchange joint element 236 and is connected to the CMM 210 via a mating joint element of an auto-exchange joint connection mechanism 230 (also referred to as an auto-joint connection).

[0025] The CMM 210 communicates with all of the other components through a data transfer line 201 (e.g., a bus). The data transfer line 201 is connected by a connector 208 (e.g., a "micro-D" connector) to a probe head cable 211 which carries input and output signals to the CRS optical probe 215. The CRS optical probe 215 is controlled by a probe signal processing control circuit 207 which includes a measurement signal processing control circuit 260B, as described for example for the measurement signal processing control circuit 160B in FIG. 1, and exchanges data with this control circuit 207, but the CMM 210 is controlled by a CMM controller 202. A user can control all of the components through a computer and user interface 206.

[0026] 2, the CRS optical probe 215 includes a probe electronics 275 including a light source / wavelength detector component 260A (e.g., a light source and a wavelength detector as described for component 160A in FIG. 1) and an optical pen 220 for projecting a measurement light 296 onto a surface 290 to be measured. In one particular embodiment, the surface 290 to be measured is the inner surface of a screw hole. Such surfaces are difficult or impossible to measure completely and reliably using known CMM probes (e.g., contact probes). The CRS optical probe of the present invention can scan and measure such surfaces with improved measurement completeness, accuracy, and versatility.

[0027] 5, in one embodiment, data relating to the optical pen 220 and / or replaceable optical mechanism 280 (e.g., identification data, calibration data, compensation data, etc.) is preferably stored external to the CRS optical probe 215 (e.g., in the probe signal processing and control circuitry 207). Alternatively, some of such data may be stored within the CRS optical probe 215 or as other coded data.

[0028] Figures 3A and 3B are schematic diagrams of a CMM 210 and a CRS optical probe 215', which is similar to the CRS optical probe 215 of Figure 2. Figure 3A is a front view, and Figure 3B is a view of the CMM 210 and the CRS optical probe 215 from different angles. As shown in Figures 3A and 3B, the CMM 210 includes a probe head 213. The probe head 213 transmits and receives probe signals through a probe head cable 211. The probe head 213 is fixed to the spindle 217 of the CMM. A probe 215' is connected to the probe head 213 using a probe automatic joint connection mechanism 230.

[0029] In one embodiment, the probe head 213 rotates 360 degrees in a horizontal plane and includes a U-shaped joint. The probe automatic joint connection mechanism 230 is an electromechanical connection mechanism that mechanically clamps and secures the CRS optical probe 215' to the probe head 213, allowing the probe to be removed and another probe to be attached. In one embodiment, the probe automatic joint connection mechanism 230 includes first and second automatic exchange joint elements 234, 236, where the first automatic exchange joint element 234 is attached to the probe head 213 and the second automatic exchange joint element 236 is attached to the CRS optical probe 215'. In one embodiment, the probe automatic joint connection mechanism 230 includes a mating electrical contact or electrical connection portion 235, where the electrical contacts are automatically connected when the probe is attached to the probe head 213 and an electrical connection is established.

[0030] The CRS optical probe 215' receives power and control signals through an automatic joint connection mechanism 230. Signals sent to the CRS optical probe 215' through the automatic joint connection mechanism 230 pass through an electrical connection 235. As shown in Figures 3A and 3B, the CRS optical probe 215' includes a probe assembly 216 and an automatic exchange joint element 236 attached to the probe assembly 216 for automatically connecting the probe to the CMM using the probe automatic joint connection mechanism 230. The probe 215' may also include a protective cover or probe housing 269 (shown diagrammatically). The probe assembly 216 includes an optical pen 220 and a probe electronics section 275 having a light source 264 and a wavelength detector 262, all of which are supported by various structural members of the probe assembly 216.

[0031] 3A and 3B, the structural member extends from a base member 218 secured to an auto-interchange joint element 236. An optical pen 220 (or an optical mechanism similar to the optical pen 120) includes a fiber optic connector 209 and a confocal optical system having an aperture 295 and a chromatic dispersion optical element 250, and outputs a measurement light 296. In some embodiments, the optical pen 220 may include a repeatable, rapid-interchangeable interchange mount 285 to allow for interchangeability of the chromatic dispersion optical element 250. A powered light source 264 (e.g., a broad spectrum LED light source) may be powered through the auto-interchange joint element and interfaced with known circuitry (e.g., circuitry used in commercially available chromatic distance measurement systems) included in a probe power and signal control circuit portion 276 of the probe electronics unit 275. In several embodiments, the probe electronics unit 275 includes a serial converter 277S that serializes various data signals and transmits them to a parallel converter (e.g., included in the probe signal processing control circuit 207) over a relatively small number of wires in the automatic joint connection mechanism 230.

[0032] 3A, the serializer 277S is included in the probe power supply and signal control circuitry 276. However, in other configurations, where most of the serialized data to be transmitted is measured spectral profile data generated in the CRS wavelength detector 262, it is better to include the serializer 277S in the CRS wavelength detector 262. In general, the serializer 277S should be located in a desired position in the probe electronics section 275, i.e., a position that can provide sufficiently low noise levels and crosstalk characteristics.

[0033] The light source 264 generates the light required by the CRS optical probe assembly 216. The light has an input spectral profile in the wavelength range that is transmitted to the optical pen 220 through the fiber optic cable 212. The CRS wavelength detector 262 may include known circuitry (such as that used in commercially available chromatic distance measurement systems) that interfaces with the spectrometer arrangement 262' and the detector array 263. The detector array 263 is comprised of a number of pixels distributed along the detection axis of the CRS wavelength detector 262, each of which is illuminated with a respective wavelength of light reflected from the surface to be measured back to the confocal optical system, such that the CRS wavelength detector 262 can provide output spectral profile data.

[0034] As described above, the configuration of the present invention allows the CRS optical probe assembly 216 to perform the functions of generating measurement light and processing reflected light from the workpiece, thereby enabling self-contained and automatic replacement of the CRS optical probe assembly 216. Such a CRS optical probe device does not require or include an optical fiber connection from the CRS optical probe assembly through the automatic joint connector to an external element, or an optical fiber connection along any other temporary path, such as parallel to the automatic joint connector. In other words, such a CRS optical probe assembly is not connected to or does not include an optical fiber extending from the CRS optical probe assembly to the outside.

[0035] In various embodiments, the CRS optical probe assembly 216 is configured by mounting an optical pen 220 to a distal end of the CRS optical probe assembly 216 relative to the probe head 213. In the embodiment of Figures 3A and 3B, the CRS optical probe 215' includes a base member 218, a wavelength detector mounting member 219A coupled to the base member 218, and an optical pen mounting member 219B coupled to the base member 218. The optical pen mounting member 219B holds the optical pen 220 without holding the wavelength detector 262. This allows heat and mass associated with flexing and vibration to be isolated from the optical pen 220. In some embodiments, one or both of the mounting members 219A and 219B may include a hollow tube (e.g., a carbon fiber tube) extending from the base member 218 toward the distal end of the CRS optical probe assembly 216.

[0036] In one embodiment, the center of mass of the optical pen 220 is located on or near an axis defined by the center of mass CMPA of the rest of the CRS optical probe 215' and the central axis CAJ of the probe automatic joint connection mechanism 230. Using this configuration, the CRS optical probe 215' can be moved to allow smooth operation of the probe head 213 (e.g., avoidance of unnecessary additional torque, vibration, deflection, etc.). In one aspect of the invention, the optical pen 220 is mounted relative to the probe automatic joint connection mechanism 230 such that the central axis CAOP (e.g., reference axis for measurement) of the optical pen 220 is coaxial with the central axis CAJ of the automatic exchange joint connection mechanism 230. In such a configuration, when the CMM rotates the probe automatic joint connection mechanism 230 about its axis, the optical pen 220 can be rotated about its axis without lateral movement of the measurement reference axis in the XY plane. Such a configuration provides advantages such as improved mechanical stability and simplified calculation of the measurement position of the optical pen 220 relative to the positioning by the CMM.

[0037] 4A and 4B are diagrams specifically illustrating the configuration of the optical pen 220 of FIGS. 3A and 3B described above, and will be used to explain an embodiment including a representative replacement mount 285. In the embodiment illustrated in FIGS. 4A and 4B, the optical pen 220 includes a base member 282 and a replaceable optical mechanism 280. The replaceable optical mechanism 280 includes a front plate 286, a hollow tube 231, and a color dispersion optical member 250. The base member 282 of the optical pen includes a base housing 282A including a surface that becomes a first engagement half member 285A of the replacement mount 285. Corresponding to this surface, the front plate 286 also includes a surface that becomes a second engagement half member 285B of the replacement mount 285. In one embodiment, the second engagement piece 285B is forcibly attached to the first engagement piece 285A by a retention arrangement formed by a permanent magnet 285C attached to one or both of the first and second engagement pieces 285A, 285B. More generally, the retention arrangement may be a spring-loaded mechanical tab or other known mechanism. Such an arrangement allows the second engagement piece 285B to be automatically connected to and disconnected from the first engagement piece 285A under program control (e.g., under control of the computer and user interface 206).

[0038] For example, in one embodiment, the optical pen 220 may be provided with a collar 232 guided by program control. This allows the optical pen 220 to be inserted into an arm of an engagement fork provided on a probe rack within the movable range of the CMM. The CMM then moves the CRS optical probe 215' so that the arm of the engagement fork hooks the collar 232, hooking the exchangeable optical mechanism 280 onto the probe rack, and the two engagement half members 285A, 285B of the exchange mount 285 can be separated. Also, by performing the reverse operation, the exchangeable optical mechanism 280 can be attached again to the base member 282. Furthermore, with such a configuration, in the event of a side collision with the workpiece, the exchangeable optical mechanism 280 is separated from the base member 282, preventing damage to the exchangeable optical mechanism 280.

[0039] In one embodiment, the exchange mount 285 may include three spheres or balls 285D fixed to the first engagement piece 285A in a first triangular pattern (e.g., an equilateral triangle). The exchange mount 285 may also include three radial V-grooves 285E formed in the same engagement pattern to the second engagement piece 285B. With this configuration of the exchange mount 285, the exchangeable optical mechanism 280 can be mounted so that the measurement light 296 directed horizontally from the exchangeable optical mechanism 280 is oriented in a direction selected from three directions spaced 120 degrees apart around the axis. The above embodiment is a representative configuration, but the present invention is not limited thereto. Various other known exchange mount configurations may be employed to provide an exchange mount with suitable mounting and dismounting repeatability.

[0040] The interchangeable optical mechanism 280 includes a color dispersive optical element 250 (e.g., similar to the color dispersive optical element 150 of FIG. 1). In one embodiment, the base member 282 includes an end of an optical fiber 212 that is connected to an LED light source 264 and a spectrometer arrangement 262′ through a fiber connector 261. The end of the optical fiber is typically located near the confocal aperture 295, fixed relative to a first mating half 285A of an exchange mount 285 that is positioned around the confocal aperture 295. In some embodiments, the end of the optical fiber forms the confocal aperture 295. In some embodiments, the confocal aperture 295 can be a thin aperture that is glued in close proximity to the end of the optical fiber (e.g., on a holder or connector that supports the optical fiber) or a thin aperture adjacent to the end of the optical fiber. 4A, the base member 282 includes a fiber optic end positioning mechanism 283 having a fiber optic holding member 283A (such as a fiber optic connector that mates with the connector 209 in this embodiment) and a fiber optic end positioning arrangement 283B that is secured (e.g., glued) to the base member 282 in a position adjacent to a first mating half member 285A of an exchange mount 285.

[0041] In this embodiment, the optical fiber end positioning mechanism 283 has an optical fiber holding member that holds an optical fiber (e.g., an optical fiber passing through the connector 209). The optical fiber holding member fixes the optical fiber end and the confocal aperture 295 in a position relative to the first engagement half member 285A of the exchange mount 285. However, in other embodiments, the confocal aperture 295 may be fixed to the base member 282, and the end of the optical fiber may be fixed in a position adjacent to the confocal aperture 295 separately by an appropriate optical fiber end positioning mechanism 283 as needed.

[0042] The interchangeable optical mechanism 280 receives measurement light from the confocal aperture 295 and reflects the measurement light back to the confocal aperture 295. It provides axial chromatic dispersion of the measurement light at each measurement distance along the measurement axis. In one embodiment, the chromatic dispersion optical member 250 also includes a reflective element 294 for irradiating the measurement light in a direction perpendicular to the axis of the optical pen 220 (e.g., transverse to the central axis of the hollow tube 231).

[0043] Fig. 5 is a block diagram of the computer and user interface 206 and the probe signal processing control circuit 207 shown in Fig. 2. As shown in Fig. 5, the probe signal processing control circuit 207 includes a parallel converter 277D, a position latch 515, a CRS optical probe ID 520, and an optical pen ID 525. Each component of the probe signal processing control circuit 207 is connected to each other and also to the computer and user interface 206 by a data transfer line 201.

[0044] The deserializer 277D works in conjunction with the serializer 277S of FIG. 3A to serialize various data signals and transmit them through the auto-joint connection mechanism 230, which consists of a relatively small number of wires. The serializer 277S and the deserializer 277D are related to the use of low voltage differential signaling (LVDS) for use in several embodiments. In brief, a synchronization signal is provided between the serializer and the deserializer to ensure synchronization between the serializer and the deserializer. After the relevant data signal is provided to the signal line, a clock signal (e.g., a clock signal that is the exact opposite of the previous clock signal) is sent to the corresponding signal line until the deserializer operation is completed, at the point where the synchronization signal is turned on.

[0045] The position latch 515 is associated with the XYZ latch signals. Briefly, the XYZ latch signals are provided to synchronize the measurement positioning operations of the CRS optical probe with the measurement positioning operations of the CMM controller 202. In one embodiment, the position latch 515 communicates with the position latch 204 of the CMM controller 202 to ensure that the coordinate positions of the CMM 210 are properly synchronized. In other words, the position latch 515 and the position latch 204 are coupled to ensure that all of the derived measurements have their measurement accuracy. This ensures that the CMM machine coordinates (which reflect the position of the CRS optical probe during a particular measurement) are properly coupled to the CRS optical probe measurements (measurements related to the CRS optical probe position).

[0046] The CRS optical probe ID 520 is utilized to identify the CRS optical probe 215' (e.g., by reading and processing an identification signal obtained from an identification element included in the CRS optical probe 215'), and the optical pen ID 525 is utilized to identify the replaceable optical mechanism 280 (e.g., by reading and processing an identification signal obtained from an identification element included in the replaceable optical mechanism 280). Proper identification of the CRS optical probe 215' and the replaceable optical mechanism 280 allows for the use of appropriate configuration and calibration data to verify correct operation and resulting measurements from the CRS optical probe 215' and the replaceable optical mechanism 280.

[0047] FIG. 6 is a structural diagram of an optical pen 220A according to an embodiment. The optical pen 220A includes a non-rotating or fixed part 605, a rotation mechanism 610 for rotating the orientation of the replaceable optical mechanism 280A and the measurement light 296, and an encoder 630 for measuring and reporting position information. The position information is, for example, a rotation azimuth angle and Z-axis position information for the optical pen, and position information of the calibration member, and will be described in detail with reference to FIGS. 7A to 13E. As shown in FIG. 6, the base member 282A includes components of the non-rotating part 605, the rotation mechanism 610, and the encoder 630.

[0048] FIG. 6 shows some representative "bounding" confocal rays (or ray segments). In particular, rays R1 and R2 are shown between the transfer lens 251 and the aperture 295, and rays R3 and R4 are shown between the transfer lens 251 and the chromatic dispersion optics 250. In some embodiments, the transfer lens 251 is a collimating lens or a lens similar to a collimating lens. The rays R3 and R4 are then approximately parallel or collimated, which provides benefits in some embodiments, as described in more detail below. Rays R5 and R6 are shown within the chromatic dispersion optics 250, which provide rays R7 and R8 as the measurement light 296. Here, the operating position 297 of the confocal aperture can be positioned close to or at the best focus position of the lenses of the optical pen 220. In particular, in this embodiment, it can be positioned close to or at the focus position of the transfer lens 251. The transfer lens 251 may be disposed within the range of the extension portion 282AX of the base member 282A.

[0049] As shown in FIG. 6, the rotation mechanism 610 includes a rotating portion 612. In this embodiment, the rotating portion 612 includes a surface that is to be the first half of the exchange mount 285. The first half can be coupled to the second half of the exchange mount 285 located on the front plate 286 in a similar configuration as described in FIG. 4A and 4B. The rotation mechanism 610 also includes a bearing 614 as well as a motor 616 and a gear 618 for rotational drive to rotate the rotating portion 612. Alternatively, a motor and a rotation actuator (e.g., a motor sleeve mechanism, etc.) may be used. When the transfer lens 251 is located on the base member 282A, the error / effect due to rotation is small. This is because the transmission of the large diameter parallel light shown as parallel light R3 and R4 through the rotation joint is less sensitive to changes in alignment.

[0050] The encoder 630 detects configuration position information (eg, rotational position information, Z-axis position information) of the optical pen 220A and reports the position information, for example, via one or more cables (eg, the probe head cable 211 of FIG. 2).

[0051] In one embodiment, the replaceable optical mechanism 280A may include an ID element 233 (e.g., mounted on the front plate 286). A corresponding reader 233R is disposed in the optical pen base member 282A. The ID element 233 may be encoded with a specific identification information representative of the replaceable optical mechanism 280. In one embodiment, the ID element 233 may include a radio frequency identification device (RFID), which may be a passive RFID. The reader 233R (e.g., an RFID reader) is positioned close enough to the ID element 233 to read data from it. If the reader 233R is not positioned adjacent to the ID element 233, a hole may be provided in the base member 282A. This allows the material of the base member to not block signal exchange (e.g., radio signals, optical signals, optical images, etc.) between the ID element 233 and the reader 233R. The ID element 233 may include an identifying mark (e.g., a simple bar code) or color, and the reader 233R may include a photodetector that provides a signal corresponding to the identifying mark or color. The ID element 233 may also include a passive resonant circuit at a specific frequency, and the reader 233R may include an exciter / detector that provides a signal responsive to the specific frequency. The reader 233R reports identification information based on the response signal, for example, through one or more cables (see probe head cable 211 in FIG. 2).

[0052] For ease of illustration, the rotation mechanism 610 and the encoder 630 are shown in functional block form. The arrangement of the rotation mechanism 610 and the encoding element 630 is exemplary only and not limiting. Various configurations may be modified to similar configurations for rotating and telescoping interchangeable optical mechanisms and reporting position information with minor adaptations that are obvious from this disclosure.

[0053] For calibration and accuracy purposes, the optical pen may be characterized by calibration data or information that includes or is based on radial distance data, and that may be associated with, for example, the following values: Multiple rotation positions of interchangeable optical mechanisms, Various focal lengths and measurement distances for the optical pen 220A, the interchangeable optical mechanism 280, the chromatic dispersion optical element 250, and the exchange mount 285, etc. Such calibration data or information compensates for various misalignments, which may be functions of rotational position, Z-axis position, and CRS measurement distance, as well as other errors (rotary encoder error, Z stage error, etc.).

[0054] 7A-7C are diagrams illustrating an exemplary calibration component 740 for the optical pen 220A of FIG. 6 that can be used to obtain radial distance and other data for use in calibrating the optical pen 220A. FIG. 7A is a conceptual diagram showing an overview of an optical pen configuration including a calibration component, and FIGS. 7B-7C are detailed diagrams of an embodiment. The optical pen 220A of FIG. 7A has a non-rotating or fixed portion 605 and a rotating portion 610. The calibration component 740 includes a calibration gauge extension 744 that moves and is attached to the non-rotating portion 605, and a calibration gauge or calibration member 746. As shown, the calibration gauge 746 is held in place relative to the rotating portion 610 of the optical pen 220A by the calibration gauge extension 744. As the rotation mechanism 610 rotates around the central axis of the optical pen 220A (the reference axis for obtaining measurements), a measurement of the calibration member (e.g., using the measurement light 296 shown in FIG. 7C) is performed to obtain a radial distance measurement for calibration of the optical pen 220A.

[0055] The retention force of the calibration gauge extension 744 can be variously arranged to hold the calibration member 746 in place relative to the rotating chromatic range sensor structure of the optical pen 220A. For example, a similar mechanism can be used for the exchange mount 285. With this arrangement, the calibration member 746 can be automatically connected, positioned, and disconnected from the calibration extension 744 under program control (e.g., under control of the computer and user interface 206).

[0056] As shown in Figures 7B and 7C, the calibration component 740 includes an extended actuator 742. The extended actuator 742 may include bearings, motors, and gears (not shown for ease of illustration, but similar to the bearings 614, motors 616, and gears 618 of the rotation mechanism 610 in Figure 6). The extended actuator 742 facilitates positioning of the calibration gauge extension 744 between the stowed position (Figure 7B) and the extended calibration position (Figures 7A and 7C). Figure 7B shows an example of a structure in which the calibration gauge extension 744 is in the stowed position and is not connected to the calibration member 746'. During a calibration operation using the calibration gauge or the calibration member 746', the calibration gauge extension 744 moves and extends to the calibration position. Alternatively, the calibration gauge extension 744 is stowed in the stowed position to avoid interference with other measurements using the optical pen 220A (e.g., measuring the inner surface of the screw hole shown in Figure 2). As discussed above, in one embodiment, when the calibration gauge extension 744 is moved to the calibration position and extended, the calibration gauge extension 744 connects with the calibration member 746', as shown in Figure 7C.

[0057] In some embodiments, the optical pen 220A and the calibration member 746' are configured such that the calibration member 746' is held by the optical pen. For example, the calibration member 746' may be held by the calibration gauge extension in its retracted position during the retracted period. This ensures that the calibration gauge extension 744 and the calibration member 746' do not block or interfere with the radial distance detection beam (i.e., the measurement light 296) during normal measurement operations during the retracted period. During the calibration period, the calibration member 746' moves and is held by the calibration gauge extension in its calibration position.

[0058] The calibration gauge extension 744 may be positioned by the extension actuator 742 at one of a number of calibration positions in its extension direction, facilitating collection of calibration radial distance data at different CRS measurement distances or focal lengths. In such a situation, the encoder reports Z-axis position information of the optical pen 220A relative to the position of the calibration member. In a manner similar to the interchangeable optical mechanism 280A described above, the calibration member 746' may include an ID element and the calibration gauge extension 744 may include a reader corresponding to the ID element.

[0059] Alternative configurations for the extension actuator 742 may be utilized (e.g., a motor sleeve mechanism, etc.) The calibration gauge extension 744 also positions the calibration gauge or calibration member 746' in a constrained relationship with respect to the rotating CRS structure of the optical pen 220A.

[0060] As shown in FIG. 7C, the calibration gauge or member 746′ comprises a ring gauge having an inner circumferential surface 748 and an outer circumferential surface 750. Other calibration members may be used, and various materials (e.g., metal, glass, etc.) may be used for the calibration member. One or more of the inner circumferential surface 748 and the outer circumferential surface 750 may include a printed texture or patterned surface (see, e.g., FIGS. 9A-9D) or various combinations thereof, thereby providing calibration data that may be used to generate calibration information for the optical pen 220A upon scanning with the measurement light 296.

[0061] The conceptual diagrams shown in Figures 8A-8C show, in an exaggerated manner, examples of misalignments that result in measurement errors when measuring with an optical pen, and examples of parameters that may be taken into account to compensate for such errors. As shown in Figure 8A, in the ideal case, an optical pen (see optical pen 220A in Figure 6) has a reference central axis 820. When measuring the surface of an ideal cylinder 830, the reference central axis 820 is aligned with the central axis of the cylinder 830. The angle of incidence of the measurement light (see measurement light 296 in Figure 7C) with respect to the normal to the surface of the ideal cylinder 830 is ideally constant. An ideal measurement represents the distance from the ideal center C to an ideal point along an ideal trace 870 of the cylinder 830. An example of an ideal point along the ideal trace 870 is shown in Figures 8A and 8B. This includes the ideal point Pideal 850 at a rotation angle ω = 0.

[0062] However, misalignment of the optical pen or other components can cause measurement errors (due to a variety of factors, such as misalignment of the exchange mount 285). For example, the optical pen's optical axis may have an xy offset 810 from the nominal central axis 820, and the optical pen's axis of rotation 860 along the optical pen length L may be misaligned with respect to the nominal central axis 820 of the optical pen 220A. In addition, the reflective element 294 (see Figs. 2, 7B) may be misaligned from the optical pen's optical axis. As a result, measurements taken of the measurement points are measured from positions S that pivot about a non-ideal center S', as shown in detail in Fig. 8B. These, along with other possible misalignments, can result in the measurement points being on a non-ideal or erroneous trace 890, as shown in Fig. 8B. An example of a measurement point associated with a misalignment error is shown in Figs. 8A and 8B, including a measurement point 840 at a rotation angle ω=0. It should be noted that the illustrated examples contain geometric exaggeration (e.g., the Z axis is reduced to scale to better illustrate potential misalignments and errors).

[0063] FIG. 8B shows an example of misalignment that causes harmonic errors. Here, the reference central axis m (i.e., the mount axis) corresponds to the reference central axis 820 in FIG. 8A. The rotation axis r corresponds to the rotation axis 860 in FIG. 8A. The optical axis o is collinear with the optical axis of the pen along the optical length L of the pen. The axis designations m, r, and o are used in subscripts of the various misalignment parameters, some of which are shown in FIG. 8B. The mount axis misalignment angle θ represents the misalignment angle of the mount axis m with respect to the rotation axis r, occurring in a plane that contains the rotation axis and is oriented by the mount axis misalignment azimuthal orientation angle φ (not shown). The rotation axis misalignment angle θ represents the misalignment angle of the optical axis o with respect to the rotation axis r, occurring in a plane that contains the rotation axis and is oriented by the azimuthal misalignment orientation angle φ (not shown). The measurement light emitted by the pen also has a pointing error. The pointing error is indicated by the output normal elevation error δθo (in the vertical direction) and by the output normal azimuth axis error δφo (in the horizontal direction).

[0064] FIG. 8C uses the same exaggerated geometry as FIG. 8B to show an example of first harmonic error caused by various misalignments of the optical pen. As shown in the table, in this example the optical pen has an X-axis offset δx of 50 μm and a Y-axis offset δy of −40 μm, which constitute the x and y components of the xy offset 810 of FIG. 8A. The other parameters shown in the table are defined in the description of FIG. 8B above, with (exaggerated) values ​​as an example. For example, The mount axis misalignment angle θm is 6 degrees, The mount axis misalignment azimuth orientation angle φm is 240 μm, The mount axis clock error δφm (not shown) is 5 degrees, The ideal optical pen length L is 2000 μm (shortened in FIG. 8B to exaggerate the error), The rotation axis misalignment angle θr is 8 degrees, The rotation axis misalignment orientation angle φr is 40 degrees, The output normal azimuth axis error δφo is 10 degrees, The output normal elevation error δθo is 5 degrees, The ideal calibration measurement distance is 1000 μm. To some extent, the azimuth related error (symbol φ) is coupled to the phase of the azimuth offset error and the harmonic errors. The axial misalignment and elevation errors (symbol θ) are coupled to the radial offset, Z offset and harmonic amplitude errors. As shown, the radial error is primarily a first harmonic oscillating about a constant Z error offset, which is an offset constant of about 180 μm. The azimuth error is primarily a first harmonic oscillating about an azimuth offset constant of about -50 μm. All three curves have slight but higher order harmonic content. Various points are exaggerated in this example to better illustrate the potential misalignments and the errors they introduce. The actual misalignment in one embodiment is on the order of 0.1 to 1 degree, and the actual error (other than xy offsets) is on the order of single micrometers or less.

[0065] As described elsewhere, radial distance measurements obtained by measuring a calibration member at a given rotation angle ω and a given Z position are used to generate calibration data. The calibration data can similarly be used to adjust measurement data (e.g. radial distance data) obtained by measuring a workpiece with an optical pen of a coordinate measuring machine. The calibration data added to the radial distance data generated using the calibration member can be used as part of the calibration information or can be used to generate the calibration information. For example, measurements obtained using an interferometer (e.g. distances measured at various light wave frequencies) or measurements of the calibration member can be used to determine the CRS distances relative to the optical pen. In another example, the Z axis information of the optical pen relative to the position of the calibration member can be used.

[0066] 9A-9D show a calibration member 946 in the form of a ring gauge according to a first embodiment. FIG. 9A shows a perspective view of the cylindrical ring gauge 946, and FIG. 9B shows a cross-sectional view thereof. The inner peripheral surface 904 of the cylindrical ring gauge 946 has a number of known features, such as a printed or machined pattern 906, in a known positional relationship to one another. The inner peripheral surface 904 is a cylindrical calibration surface, and a central axis 905 of the inner peripheral surface 904 along the Z direction is aligned to be approximately parallel to the rotation axis of the CRS optical pen during calibration measurements (see, for example, the reference central axis 820 and the rotation axis 860 in FIG. 8A). The illustrated first cylindrical calibration surface 904 is located at a known distance of a first radius Rc from the central axis 905 along the Z axis.

[0067] 9C and 9D conceptually show examples of patterns, and show a printed or processed pattern applied (printed) or formed on the inner peripheral surface 904 in a flat printed or processed view. The printed or processed pattern 906 may include a first set of angular reference features (e.g., reference lines, etc.). The angular reference features are formed on or within the first cylindrical calibration surface. That is, the angular reference features are configured to be detectable by a radial distance detection beam on or within the first cylindrical calibration surface, and are arranged at known angles or angular intervals from each other around the central axis. The features of the pattern are configured to be detectable by an optical pen, such as the optical pen 220A in FIGS. 7A to 7C. For example, a printed pattern may be black and white, grayscale, or multicolored, and a processed pattern may be changed in depth or shape. Various combinations of these may also be used.

[0068] As shown in FIG. 9C, the pattern 906 has azimuth indicators or vertical reference lines 908 spaced at known intervals, either regularly or irregularly. The pattern 906 also has Z-axis indicators or tilted reference lines 910 spaced at known intervals, either regularly or irregularly. The vertical lines 908 provide calibration information for the azimuth position. The tilted lines 910, in relation to the azimuth indicators or vertical reference lines 908, provide calibration information for the Z-axis position. The lines 908, 910 may be formed with a constant thickness or with a variable thickness. For example, as shown, one of the vertical lines 908 may be a reference line with a different thickness than the other vertical lines to indicate a specific azimuth position on the calibration gauge 946. Multiple reference lines may be used to indicate multiple specific positions (e.g., midpoints) on the calibration gauge. In the case of a machining pattern, the pattern 906 in FIG. 9C represents a machining diagram showing the positions of indentations or protrusions to be formed on the inner circumferential surface 904 of the calibration member. In other embodiments, the inner periphery 904 is flat.

[0069] For ease of illustration, the vertical lines 908 of the pattern 906 in Fig. 9C are shown as white bars and the inclined lines 910 as black bars. In the case of a printed pattern, in practice the two types of bars can be the same color (e.g. black) or different colors (e.g. indicating an angular position relative to the bars), or various combinations of these are also possible. As mentioned above, in the case of an engineered pattern, depressions of different widths and depths can be used to facilitate measuring the calibration information.

[0070] Also shown in Figure 9C is an example of a calibration measurement trace 920. Position information of the trace 920 acquired by the optical pen 220A (e.g., position information provided by the encoder 630 in Figure 6 as a measurement on the trace 920) may be used as calibration data or information together with the measurement results on the trace 920 (e.g., radial distance measurement data and Z position measurement data), or may be used to create calibration data or information based on, for example, a difference between the measurement results for each measurement position and an ideal result.

[0071] Pattern 906' in Figure 9D is similar to pattern 906 in Figure 9C, except that it does not include the slanted lines 910, and trace 920' measures calibration information for the calibration member using only the vertical lines 908. If Z-axis calibration information is required, it can be obtained in other ways, such as by detecting the top or bottom edges of calibration member 946 as the calibration member is moved into position. Other patterns may also be used in conjunction with or substituted for the calibration (e.g., a slanted grid, horizontal and slanted lines, etc.).

[0072] FIG. 10 is a cross-sectional view of a calibration member 1046 having a central axis 1005 according to the second embodiment. The calibration member 1046 is a ring gauge having a stepped diameter, and has a first inner peripheral surface 1048 having a first diameter and a second inner peripheral surface 1048' having a second diameter smaller than the first diameter. One or both of the first and second inner peripheral surfaces 1048, 1048' may be provided with a pattern surface for calibration measurement (e.g., a printed or machined pattern surface, see FIGS. 9C and 9D). The use of the ring gauge 1046 having a stepped diameter facilitates calibration measurements at multiple measurement distances simultaneously with calibration measurements regarding the Z axis. The calibration gauge extension 744 (see FIGS. 7A to 7C) can position the calibration gauge 1046 relative to the measurement light 296 in a first extended position, which facilitates calibration reading of the first inner peripheral surface 1048. Additionally, the calibration gauge extension 744 can position the calibration gauge 1046 relative to the measurement beam 296 in a second extended position, which can facilitate a calibration reading of the second inner circumferential surface 1048'. Additionally, in other embodiments, detection of the change from the first inner circumferential surface 1048 to the second inner circumferential surface 1048' can be used to obtain Z-axis calibration information.

[0073] FIG. 11A is a perspective view of a calibration member 1146 in the shape of a ring gauge according to another embodiment. FIGS. 11B and 11C are conceptual diagrams showing an embodiment of a calibration member 1146' in the shape of a ring gauge similar to that of FIG. 11A. The calibration member 1146 in FIG. 11A has a plurality of cylindrical inner circumferential surfaces 1148i to 1148n, the diameters of which change stepwise from 1149i to 1149n. Similarly, the calibration member 1146' in FIGS. 11B and 11C has a plurality of cylindrical inner circumferential surfaces 1148i' to 1148n' having diameters 1149i' to 1149n' which change stepwise. A pattern surface for calibration measurement may be provided on one or more of the cylindrical inner circumferential surfaces 1148i to 1148n or 1148i' to 1148n' (for example, a printed or processed pattern surface, see FIGS. 9C, 9D, 13D, and 13E). In FIG. 11A, seven steps of the inner peripheral surface are provided, while in FIGS. 11B and 11C, ten steps of the inner peripheral surface are provided. FIG. 11B shows a processing diagram of the ten steps of the inner peripheral surface of the ring gauge 1146'. FIG. 11C shows a 3D plot of representative measurement data of stepped inner diameters 1149i'-1149n' of the cylindrical inner peripheral surface 1148i'-1148n' of the ring gauge 1146' collected during a spiral scan in the Z direction with a rotating optical pen. This facilitates a calibration read of the first inner peripheral surface 1048. The stepped surfaces of the calibration members 1146, 1146' facilitate the acquisition of measurements over the entire measurement range for distance (e.g., radial distance measurements) simultaneously with the acquisition of Z-axis calibration data. The acquired measurements can be used to generate calibration information for the measurement range of CRS distances of the optical pen.

[0074] As shown in FIG. 11A, the outer peripheral surface 1150 of the ring gauge 1146 includes a flat surface 1152 with a recess 1154. The flat surface 1152 and recess 1154 facilitate the positioning of the ring gauge 1146 in a constrained relationship with respect to the rotational CRS structure of the optical pen by the calibration gauge extension (see calibration gauge extension 744 of optical pen 220A in FIGS. 7A-7C). Specifically, when the optical pen is mounted on a measurement platform (set for azimuth rotation angle ω=0), the flat surface 1152 provides a reference surface for the azimuth rotation angle ω of the optical pen. Additionally, the orthogonal surface of the recess 1154 provides a reference for alignment in the Z-axis direction. For example, the flat surface 1152 and recess 1154 are sized and shaped to receive a corresponding tab or protrusion (not shown) on the calibration gauge extension. This allows the calibration gauge extension to hold the ring gauge 1146 in a constrained relationship with respect to the rotational CRS structure. Other positioning schemes may be used (eg, flat surfaces on opposite sides of the ring gauge, differently shaped recesses, tabs on the calibration member and corresponding recesses on the calibration gauge extension, etc., as well as various combinations thereof).

[0075] FIG. 12A shows a perspective view of a calibration member 1246 in the form of a precision glass tube according to another embodiment, and FIG. 12B shows a cross-sectional view thereof. According to FIG. 12B, the precision glass tube 1246 has a cylindrical inner circumferential surface 1204 and a cylindrical outer circumferential surface 1250. One or both of the inner circumferential surface 1204 and the outer circumferential surface 1250 may be provided with a pattern surface for calibration measurement (e.g., a printed or machined pattern surface, see FIGS. 9C, 9D, 13D and 13E). The pattern of the cylindrical surface may include non-patterned portions (e.g., gaps or windows between reference lines), which facilitates the measurement of the pattern of the other cylindrical surface. For example, the pattern of the cylindrical inner circumferential surface 1204 may have gaps or windows (see window 1374 in FIG. 13D) through which features of the pattern of the cylindrical surface 1250 may be observed, measured or otherwise detected.

[0076] The inner peripheral surface 1204 and the outer peripheral surface 1205 are cylindrical calibration surfaces with a central axis 1205 along the Z direction. During calibration measurements, the central axis 1205 is aligned as parallel as possible to the rotation axis of the CRS optical pen (see, for example, reference central axis 820 and rotation axis 860 in FIG. 8A). The first cylindrical calibration surface 1204 is located at a first known radius Ri from the central axis 1205 in the Z direction as shown. The second cylindrical calibration surface 1250 is located at a second known radius Ro from the central axis 1205 in the Z direction as shown.

[0077] In some embodiments, the inner circumferential surface 1204 has a pattern for measuring one type of calibration information (e.g., a pattern that facilitates measuring angular position information), and the outer circumferential surface 1250 has a pattern for facilitating measuring another type of calibration information (e.g., a pattern that facilitates measuring Z-axis position information). In some embodiments, the outer circumferential surface 1250 may have a patterned surface, while the inner circumferential surface 1204 may be unpatterned and may be a transparent or semi-transparent surface. Distance measurements (radial distance) are obtained by sensing the inner circumferential surface 1204 and the outer circumferential surface 1250 (e.g., a known or measured refractive index for the material may be used to convert from optical thickness to physical thickness, if necessary). Angular position and Z-axis position measurements are obtained by sensing features of the pattern on the outer circumferential surface 1250.

[0078] FIG. 12C illustrates a calibration member 1246′ comprising two nested precision glass tubes, an inner tube 1258 and an outer tube 1260, according to an embodiment. The inner tube 1258 has a calibration surface 1262 formed of a cylindrical inner circumferential surface and a calibration surface 1264 formed of a cylindrical outer circumferential surface. The outer tube 1260 has a calibration surface 1266 formed of a cylindrical inner circumferential surface and a calibration surface 1268 formed of a cylindrical outer circumferential surface. The calibration surfaces 1262, 1264, 1266, and 1268 have a central axis 1205 along the Z direction. During the calibration measurement, the central axis 1205 is aligned as parallel as possible to the rotation axis of the CRS optical pen (see, for example, the reference central axis 820 and the rotation axis 860 in FIG. 8A). The calibration surface 1262 is located at a known radius R1i from the central axis 1205 in the Z direction, as shown. As shown, the calibration surfaces 1264 and 1266 are each disposed at a distance of approximately known radius R2i from the central axis 1205 in the Z direction (for simplicity of explanation, it is assumed that the difference in radius between the two calibration surfaces 1264 and 1266 is negligible). The calibration surface 1268 is disposed at a position of known radius R2o from the central axis 1205 in the Z direction, as shown.

[0079] A pattern surface for calibration measurements may be provided on one or more of the cylindrical inner surface 1262 of the inner tube 1258, the cylindrical outer surface 1264 of the inner tube 1258, the cylindrical inner surface 1266 of the outer tube 1260, and the cylindrical outer surface 1268 of the outer tube 1260 (e.g., a printed or machined pattern surface, see Figures 9C, 9D, 13D, and 13E).

[0080] A cylindrical surface pattern may include non-patterned portions (e.g., gaps or windows between reference lines) that facilitate measuring patterns on other cylindrical surfaces. For example, the pattern on the cylindrical inner circumferential surface 1262 of inner tube 1258 may have gaps or windows through which features of the pattern on the cylindrical inner circumferential surface 1266 of outer tube 1260 may be viewed, measured, or otherwise detected, similar to the description of FIG. 12B.

[0081] In some embodiments, the outer periphery 1268 of the outer tube 1260 is patterned, while the remaining surfaces of the inner tube 1258 and outer tube 1260 are unpatterned and transparent or semi-transparent. Distance measurements (radial distance) are obtained by detecting one or more of the inner periphery 1262 of the inner tube 1258, the outer periphery 1264 of the inner tube 1258, the inner periphery 1266 of the outer tube 1260, and the outer periphery 1268 of the outer tube 1260. Additionally, azimuth and Z-axis position measurements are obtained by detecting pattern features on the outer periphery 1268 of the outer tube 1260. Various combinations of patterned and non-patterned surfaces and / or types of patterns may be used. Nested tubes may also be added. A bottom cap or other retaining structure may be used to hold the nested tubes 1258, 1260 in place relative to one another. The nested glass tube embodiment facilitates acquisition of calibration information covering the full measurement range of the optical pen CRS measurement distances simultaneously with acquisition of Z-axis calibration data, allowing multiple gauge distance measurements without repositioning the calibration member. As described in FIG. 12B, optical distances or optical thicknesses may be converted to physical distances, if desired.

[0082] Figures 13A-13E show an embodiment of a nested calibration member 1346 made of multiple precision metal tubes 1358, 1360, 1370. In Figures 13A-13E, for ease of illustration, the nested metal tubes 1358, 1360, 1370 are exaggerated in size and the spacing between the metal tubes is negligible or exaggerated. More than three nested metal tubes can also be used (e.g., seven or more tubes).

[0083] FIG. 13A is a longitudinal cross-sectional view of the calibration member 1346. Precision metal tube 1358 has an inner circumferential surface 1362, precision metal tube 1360 has an inner circumferential surface 1366, and precision metal tube 1370 has an inner circumferential surface 1372. The inner circumferential surfaces 1362, 1366, and 1372 have a central axis 1305 extending in the Z direction that is aligned to be approximately parallel to the rotation axis of the CRS optical pen during calibration measurements (see, for example, reference central axis 820 and rotation axis 860 in FIG. 8A). The cylindrical calibration surfaces 1362, 1366, and 1372 are located at known radial distances (such as R1, R2, and R3 shown) from the central axis 1205 in the Z direction.

[0084] 13B is a cross-sectional view of an embodiment of nested metal tubes 1358, 1360, 1370 having different lengths L1, L2, L3 along the Z-axis 1305. A portion of one or more of the inner circumferential surface 1362 of metal tube 1358, the inner circumferential surface 1366 of metal tube 1360, and the inner circumferential surface 1372 of metal tube 1370 may be provided with a patterned surface for calibration measurements (e.g., a printed or machined patterned surface, see FIGS. 9C and 9D). Calibration measurements are performed in a similar manner as described for graduated diameter ring gauge 1046 of FIG. 10 and graduated diameter ring gauges 1146, 1146' of FIGS. 11A-11C.

[0085] The calibration gauge extension 744 (see FIGS. 7A-7C) can position the calibration gauge 1346 at a first extended position relative to the measurement beam 296 to facilitate taking a calibration reading of the inner circumferential surface 1362. The calibration gauge extension 744 can also position the calibration gauge 1346 at a second extended position relative to the measurement beam 296 to facilitate taking a calibration reading of the inner circumferential surface 1366. The calibration gauge extension 744 can also position the calibration gauge 1346 at a third extended position relative to the measurement beam 296 to facilitate taking a calibration reading of the inner circumferential surface 1372. Detection of changes in the inner circumferential surfaces 1362, 1366, 1372 can be used to obtain Z-axis calibration information in addition to or instead of Z-axis calibration information based on the surface patterns of one or more of the inner circumferential surfaces 1362, 1366, 1372. Other configurations may also be used in conjunction with or substituted for the calibration (e.g., including a pattern on the inner surface of the outer tube and viewing the pattern through an opening or window in the inner tube, as detailed in FIG. 13D).

[0086] 13C-13E show an embodiment of a calibration gauge 1346 that includes nested metal tubes 1358, 1360, 1370 that generally have the same length L1 along the Z axis 1305. These may be tapered slightly in the length direction (not shown) to help provide a calibration gauge with good concentricity and alignment. The side surface of the inner tube (such as the metal tubes 1358, 1360 shown) is provided with a pattern in the form of windows or segments that penetrate the side wall of the tube, as shown conceptually in FIGS. 13D-13E below. Measurement light 296 can pass through these windows or segments to reach the larger diameter tube wall. At least a portion of the remaining portions of inner surface 1362 of tube 1358, inner surface 1366 of tube 1360, and inner surface 1372 of tube 1370 may be provided with a patterned surface (e.g., a printed or machined patterned surface; see Figures 9C and 9D) for calibration measurements in a manner similar to that described above.

[0087] The illustrated calibration member 1346 includes a cap 1380 that holds the tubes 1358, 1360, and 1370 in place relative to one another. A calibration gauge extension 744 (see FIGS. 7A-7C) can engage the cap 1380 to position the calibration gauge 1346 in a constrained relationship to the rotating CRS structure. The nested metal tube embodiment shown in FIGS. 13D and 13E facilitates obtaining calibration information over the measurement range of the optical pen's CRS distances simultaneously with obtaining the Z-axis calibration information without having to reposition the calibration member at each of the gauge distances R1, R2, and R3.

[0088] FIGURE 13D conceptually illustrates calibration member 1346. A nested inner tube 1358 of calibration member 1346 has a pattern in the shape of a window 1374 extending therethrough. A nested central tube 1360 has a pattern in the shape of a window 1376 extending therethrough. FIGURE 13D illustrates example patterns shown as printed / machined views of the windows, which are planar developments of one or more patterns applied (printed) or formed on the inner surfaces 1362, 1366, 1372 of tubes 1358, 1360, 1370.

[0089] The window 1374 of inner tube 1358 and the window 1376 of central tube 1360 are sized and the inner and central tubes 1358, 1360 are positioned such that, during a measurement operation, the rotating CRS structure (see FIGS. 7A-7C) can sense the window 1376 of tube 1360 through the opening of window 1374 in tube 1358 and can also sense a portion of the inner surface 1372 of outer tube 1370. Sensing of the windows 1374, 1376 and inner surfaces 1362, 1366, 1372 by the rotating CRS structure (see FIGS. 7A-7C) provides calibration measurement data or is used to generate calibration data or information.

[0090] Additionally, one or more of the inner surfaces 1362, 1366, 1372 may have a patterned surface (e.g., a printed or machined patterned surface, see FIGS. 9C and 9D) that can also be used for calibration measurements. The inner surface 1362 of the illustrated tube 1358 includes vertical patterned lines 1308, the inner surface 1366 of the tube 1360 includes slanted lines 1310, and the inner surface 1372 of the tube 1370 includes slanted lines 1310. The illustrated windows 1374, 1376 are rectangular, but some or all of the windows may have slanted sides. The slanted sides may provide Z-axis calibration measurement data (e.g., instead of or in addition to the slanted lines 1310).

[0091] The embodiment of Figure 13E is similar to the embodiment of Figure 13D, except that nested inner tube 1358 has a pattern in the shape of a segment 1382 passing through tube 1358 instead of a window, and nested central tube 1360 has a pattern in the shape of a segment 1384 passing through tube 1360 instead of a window. Figure 13E shows example patterns shown as printed / machined views of segments that are flattened out from one or more patterns printed or formed on inner surfaces 1362, 1366, 1372 of tubes 1358, 1360, 1370.

[0092] In a measurement operation, the segment 1382 of the inner tube 1358 and the segment 1384 of the central tube 1360 are sized and the inner and central tubes 1358, 1360 are positioned relative to each other such that the rotating CRS structure (see FIGS. 7A-7C) can detect segment 1384 of tube 1360 through the opening of segment 1382 of tube 1358 and detect a portion of the inner surface 1372 of the outer tube 1370 through the openings of segments 1382, 1384 in at least partial alignment. Detection of segments 1382, 1384 and inner surfaces 1362, 1366, 1372 by the rotating CRS structure (see FIGS. 7A-7C) can provide calibration measurement (distance) data that can be used as or to generate calibration data or information. Additionally, as described above, one or more of the inner circumferential surfaces 1362, 1366, 1372 may be provided with a patterned surface (eg, a printed or machined patterned surface such as the sloping lines 1310) that can also be used for calibration measurements.

[0093] FIG. 14 shows a graph of calibration test data collected using a calibration member to measure seven calibration steps and plotted in a cylindrical coordinate system (with the page as the Z axis). For example, a calibration ring gauge with seven or more concentric calibration surfaces may be used, such as a stepped calibration surface (see, e.g., FIGS. 11A-11C, 13B) and / or multiple calibration surfaces generally aligned perpendicular to the Z axis of the rotating CRS device (see, e.g., FIGS. 12C, 13C-13E). The vertical axis represents radial distance measurements and the horizontal axis represents the rotation angle of the optical pen plotted in units of rotation cycles. Measurements at different radial distance conditions can be plotted using the following methods: repositioning the calibration member in the Z-axis direction (e.g., using the calibration gauge extension 744 of FIGS. 7A-7C to align a calibration member having a stepped surface, such as in the embodiment of FIGS. 11A-11C and 13B); adjusting control parameters of a probe signal processing control circuit (see probe signal processing control circuit 207 in Figs. 2 and 5) as much as possible; and / or and scanning a Z-axis stage incorporated in the telescopic section or the base section to perform a spiral scan.

[0094] Table 1 illustrates the error sources in a rotated CRS configuration. See also Figure 8C above.

[0095] [Table 1]

[0096] The errors due to misalignment may also be expressed by a set of mathematical equations. The errors may be compared to measurement data collected from the calibration components to generate calibration data or information for correcting the errors (e.g., adjusting test measurement results). For example, curve fitting to the measurement data may be used to determine coefficients in the equations that represent the errors.

[0097] As an example, the error of the measurement value is expressed by the following relational expression (1).

[0098]

number

[0099] Here, D C ,ω C (,Z C ) is the data variable for the measured input value (Z C is a third measurement input that is not in the equation above but can be collected. ΔR, Δφ, and ΔZ are the measurement errors. The fitting coefficients up to the second harmonic are the remaining symbols, all defined below. D C represents the corrected distance measurement data from an optical pen and is calibrated to be non-rotational and linear, but may have offset and scaling errors as a result of various mechanical misalignments of the measurement device during rotational measurements. ω C represents the corrected rotation angle output value of the optical pen's rotary encoder. ZC represents the corrected Z-axis stage position output value of the optical pen rotary encoder platform.

[0100] ΔR represents the radial distance measurement error and includes terms with coefficients: Ro represents the constant term of the radial offset. R L represents the coefficient of the radial linear (scaling) term. C R1 represents the amplitude coefficient of the radial first harmonic term. θ R1 represents the phase coefficient of the radial first harmonic term. C R2 represents the amplitude coefficient of the radial second harmonic term. θ R2 represents the phase coefficient of the radial second harmonic term.

[0101] Δφ represents the azimuth measurement error and includes terms with coefficients: φo represents the constant term of the azimuth offset. φ L represents the coefficient of the azimuth linear (scaling) term. Cφ1 represents the amplitude coefficient of the azimuth first harmonic term. θφ1 represents the phase coefficient of the azimuth angle first harmonic term. Cφ2 represents the amplitude coefficient of the azimuth second harmonic term. θφ2 represents the phase coefficient of the azimuth angle second harmonic term.

[0102] ΔZ represents the Z-axis measurement error and includes terms with the following coefficients: Zo represents the constant term for the Z-axis offset. Z L represents the coefficient of the Z-axis linear (scaling) term. C Z1 represents the amplitude coefficient of the Z-axis first harmonic term. θ Z1 represents the phase coefficient of the Z-axis first harmonic term. C Z2 represents the amplitude coefficient of the Z-axis second harmonic term. θ Z2represents the phase coefficient of the Z-axis second harmonic term. In some embodiments, the second harmonic term here is treated as negligible, while other embodiments may include second and higher order harmonic terms.

[0103] The fully corrected measurements of the rotational CRS measurement device are expressed in a cylindrical coordinate system according to the relationship in equation (2).

number

[0104] The terms on the right are as defined above. R RCPS,c represents the fully corrected radial distance measurement. φ RCPS,c represents a fully corrected azimuth angle measurement. Z RCPS,c represents the Z-axis distance measurement. Figure 14 shows an example of the Z-axis projection of the corrected data for the calibration element of Figure 11B plotted in a cylindrical coordinate system, where the data has been corrected for at least the radial offset.

[0105] The data is transformed from cylindrical to Cartesian coordinates using equation (3).

number

[0106] Transformations are useful for visualizing data. Figure 11C is an example of the data from Figure 14 transformed and plotted in a Cartesian coordinate system. Transformations can also be used to normalize the data. For example, the data may be transformed into a Cartesian coordinate system, and then a rotation and translation transformation may be performed to align the data with the Z axis, and then a transformation back to a cylindrical coordinate system may be performed.

[0107] In some cases, measurements of small radii are of interest, and calibration to the radius measurement of one calibration element is sufficient. In these cases, the linear coefficient R L ,φL ,Z L are set to zero and the fit only needs to include the constant offset terms Ro, φo, Zo, together with harmonic terms if necessary (e.g. only the first and second harmonic terms for radius are needed). In other cases, measurements are performed over the entire radius range of the optical pen. The entire range of radius measurements is then calibrated using separate ring gauges, or preferably one multi-stage ring gauge. If necessary, potential azimuth and Z-axis errors at different radii can be calibrated out using a calibration element having marks or shapes required for azimuth and Z-axis calibration. In such cases, the linear fit is performed using the linear coefficients R L ,φ L ,Z L and constant offset terms Ro, φo, and Zo. The fit is done simultaneously to these parameters as well as the harmonic coefficients. In some cases it may be desirable to average the radial data over a regular integer number of rotation cycles (which averages out the harmonic content) (see Figure 14, labelled "Average Radial Distance"). The linear and offset terms are then fitted only to the average radial data over multiple gauge radii Ri to obtain the linear correction coefficients R L ,φ L ,Z L and determine the constant offset correction terms Ro, φo, and Zo.

[0108] As an example, FIG. 15 shows a graph of the calibration test data of FIG. 14 along with an indication of the traceable tolerances. The vertical axis of FIG. 15 represents the mean radial distance and the horizontal axis represents the gage number (step number in the case of a stepped gage) of the calibration member. At a given radial distance or step, the difference between the test data and the traceable tolerance corresponds to the radial error ΔR at that distance or step. A straight line fit to the test data shows good linearity, but some offset and slope errors from the traceable tolerances of the multi-step calibration member. A linear fit of the measured mean radial distance (dashed line) and its relationship to the traceable tolerances for each step radius (i.e., ΔR=Ro+R from Equation (1)) is shown. L DC ) to obtain the corrected slope R L A method is derived to calibrate the measurements to the trace tolerance using the calibration coefficients for slope and offset Ro. By using the corrected slope and offset to calibrate the rotating CRS structure, the radius measurements can be performed with high accuracy in the entire measurement range. Similar corrections are preferably applied to the Z axis and azimuth as well, using Z axis or azimuth reference patterns of the calibration members at different radial positions.

[0109] FIG. 16 graphically illustrates obtaining more consecutive calibration distance measurements at a range of different distances (four gauge distance positions shown) and at a range of different offsets (N offset positions shown). By comparing measurements at different gauge distances and offset positions, e.g., by performing simultaneous curve fitting, errors due to mechanical rotation (errors that have a common mode with respect to the rotation angle) can be separated from errors due to CRS pen calibration (errors that have a common mode with respect to the CRS distance measurements).

[0110] The use of XY offsets from the axis of the gauge (e.g., multiple distance gauges) and multiple gauge distance steps provides measured distance data for each CRS distance within the CRS measurement range. This facilitates continuous calibration of the CRS distances as opposed to piecewise linear calibrations based solely on the radius of each ring gauge distance or step. For example, a first calibration performed with the ideal axis of the optical pen centered on the calibration member can remove harmonic errors. As shown in FIG. 16, at the first offset, the ideal axis of the optical pen is aligned with the central axis of the calibration member. This data can be used to correct specific radius measurements with small deviations. Calibrated distance measurements are then performed at multiple offsets from the central axis of the calibration member to the ideal axis of the optical pen (e.g., offsets 2 through N). The generated data may include measurements at successive radial distances. The XY offsets introduce small vibration deviations in the alignment of the sensor with respect to the ring gauge or similar work surface. Depending on the type of surface of the calibration member, such deviations may result in radius measurement errors. In such an embodiment, if the surface type is known and the angular deviation is deterministic, a look-up table or similar calculation can be used to correct for such errors.

[0111] The ring gauge (i.e., calibration member) described herein is particularly advantageous for calibrating the optical pen when the axis of the optical pen can be aligned to the axis of the ring gauge and subsequent workpiece measurements are performed in that aligned state (e.g., the same alignment). These configurations can be realized on a variety of platforms (e.g., SCARA-type assembly robots, image processing systems, CMMs, etc., each with a fixed automatic joint). For example, in these configurations, the probe is held in a fixed orientation (e.g., vertical) (i.e., the probe can be used for the calibration process as well as for performing workpiece measurements), and the ring gauge can be mounted on the platform in a corresponding fixed orientation (e.g., vertical) for the calibration process.

[0112] 17 is a flow diagram illustrating a calibration procedure 1700 according to one embodiment of a rotating CRS structure of a CMM. The procedure 1700 may be performed, for example, using one or more embodiments of a CMM with a calibration member described herein. The procedure provides calibration data or information for correcting misalignment errors of the rotating CRS structure. The rotating CRS structure is configured to project a radial distance sensing beam along a radial direction about an axis of rotation and to rotate the radial distance sensing beam about the axis of rotation.

[0113] Procedure 1700 begins in step 1702 by a probe signal processing control circuit (e.g., probe signal processing control circuit 207 of FIGS. 2 and 5) invoking the procedure. Procedure 1700 includes steps 1702 through 1710. In step 1710, a calibration member (e.g., see calibration member 746 of FIGS. 7A-7C, calibration member 946 of FIGS. 9A-9D, calibration member 1046 of FIG. 10, calibration members 1146, 1146' of FIGS. 11A-11C, calibration member 1246 of FIGS. 12A-12B, calibration member 1246' of FIG. 12C, and calibration member 1346 of FIGS. 13A-13E) is positioned with respect to a rotational CRS structure of the CMM (see FIGS. 6, 7A-7C). The calibration member has at least a first cylindrical calibration surface (see, for example, surfaces 1148i-1148n and 1148i'-1148n' in Figures 11A-11C), which has a central axis aligned approximately parallel to the rotational axis of the CMM, with the central axis oriented along the Z direction.

[0114] The cylindrical first calibration surface may include one or more reference features formed on or within the first calibration surface, such as a first set of vertical reference features (e.g., see vertical lines 908 in FIG. 9C ) and / or a first set of tilted reference features (e.g., see tilted lines 910 in FIG. 9C ), that are detectable by the radial distance detection beam and may be at predetermined locations relative to one another (e.g., the tilted reference features may be disposed on or within the first calibration surface at a known angle or angular spacing relative to one another about a central axis).

[0115] The calibration member may be arranged in a constrained relationship with respect to the rotating CRS structure. Here, the direction of the rotation axis and the direction of the central axis have a certain angular relationship with each other, and the parallelism between the two is within a certain threshold, for example, within 5 degrees. The calibration member may be held in a constrained state by, for example, a calibration gauge extension of the rotating CRS structure (see, for example, calibration gauge extension 744 in FIGS. 7A-7C). Procedure 1700 proceeds from step 1710 to step 1720.

[0116] In step 1720, the rotating CRS structure is operated to provide a first set of radial distance measurement data acquired at a first Z coordinate position in the Z direction relative to the calibration member while rotating the radial distance detection beam about the rotation axis and references a sensed rotation angle of the radial distance detection beam about the rotation axis. For example, an encoder (see encoder 630 in FIG. 6) can provide the sensed value of the rotation angle information. Procedure 1700 proceeds from step 1720 to step 1730.

[0117] At step 1730, the procedure 1700 determines whether to obtain an additional set of radial distance measurement data. If at step 1730, it is determined that an additional set of measurement data is to be obtained, then the procedure 1700 proceeds from step 1730 to step 1740.

[0118] In step 1740, optical adjustments are performed to facilitate acquisition of additional sets of radial distance data, such as repositioning a stepped calibration member (e.g., calibration member 1146 of FIGS. 11A-11C) using a calibration gauge extension (e.g., calibration gauge extension 744 of FIGS. 7A-7C), or otherwise adjusting the relative positions of the calibration member and / or the CRS probe, adjusting signal processing routines, etc. From step 1740, procedure 1700 returns to step 1720 to operate the CRS probe to acquire additional sets of radial distance measurement data.

[0119] If, at step 1730, an additional set of radial distance measurement data is not acquired, the procedure proceeds from step 1730 to step 1750. At step 1750, procedure 1700 processes the acquired set of radial distance measurement data referenced to a sensed rotation angle to determine calibration data that is configured for use in characterizing or compensating for radial distance measurement errors as a function of a sensed rotation angle of the radial distance detection beam about the rotation axis. Procedure 1700 proceeds from step 1750 to step 1760 to end or to perform additional processing (e.g., storing the calibration data and / or determining additional calibration data).

[0120] More or fewer operations may be performed in procedure 1700 than those shown, and operations may be performed in various orders. For example, in one embodiment, procedure 1700 may simultaneously acquire sets of radial distance data for multiple measurement distances (e.g., when measuring a calibration member having multiple calibration surfaces generally aligned in a direction perpendicular to the Z axis of a rotating CRS device (see FIGS. 12C, 13C-13E)). Procedure 1700 may process one or more sets of radial distance measurement data before completing acquisition of the sets of radial distance measurement data. In another example, calibration information may include data acquired using an interferometer, such as ideal CRS distance data for an optical pen, radii of one or more cylindrical calibration surfaces, etc. Procedure 1700 may be modified to include operations of retrieving interferometrically acquired data and / or performing interferometric measurements.

[0121] The method described above is for providing calibration data for correcting misalignment errors in a rotating chromatic range sensor configured to direct a radial distance sensing beam along a radial direction relative to an axis of rotation and configured to rotate the radial distance sensing beam about the axis of rotation. A calibration member is provided. The calibration member has at least a first cylindrical calibration surface. The central axis of the first cylindrical calibration surface is aligned along a Z direction and is generally parallel to the rotation axis. The first cylindrical calibration surface is located at a first known radius R1 from the central axis along the Z direction and includes a first set of angular reference features formed on or within the first cylindrical calibration surface. The angular reference features are configured to be detectable by a radial distance detection beam and are located on or within the first cylindrical calibration surface at a known angle or angular interval from one another about the central axis. The calibration member is positioned in a relationship to the range sensor. The direction of the rotation axis and the direction of the central axis are in a constant angular relationship to one another and are parallel to one another within 5 degrees.

[0122] Operation of the rotary chromatic range sensor provides a first set of radial distance data, the data set being acquired while rotating the detection beam about the rotation axis at a first Z coordinate position in a Z direction relative to the calibration member, the radial distance data being referenced to a sensed rotation angle of the detection beam about the rotation axis. The first set of radial distance data referenced to the sensed rotation angle is processed to determine calibration data, the calibration data being configured for use in characterizing or compensating for radial distance measurement errors as a function of a sensed rotation angle of the detection beam about the rotation axis.

[0123] In some embodiments, the method includes obtaining a first set of radial distance data and adjusting a Z positional relationship between the range sensor and the calibration member to a second Z coordinate position in a Z direction relative to the calibration member, where a difference between the first and second Z coordinate positions is known. During the adjustment, the established fixed angular relationship is not altered. The rotating chromatic range sensor is again operated to provide a second set of radial distance data at the second Z coordinate position. The first and second sets of radial distance data referenced to the sensed rotation angle are processed to determine calibration data. The calibration data is configured for use in characterizing or compensating for radial distance measurement errors as a function of the sensed rotation angle of the radial distance sensing beam about the rotation axis.

[0124] In some embodiments, the calibration member is a particular ring gauge, and the method of providing includes mounting at least one of the rotating chromatic range sensor and the ring gauge on a precision Z translation stage constrained to move in a Z direction, and operating the precision Z translation stage such that the difference between the first and second Z positional relationships is known.

[0125] In some embodiments, the first cylindrical calibration surface includes at least one full or partial spiral groove or protrusion formed in a peripheral wall of the calibration surface, and the Z coordinate position of each of the spiral groove or protrusion is known as a function of the circumferential angle of the peripheral wall of the calibration surface.

[0126] In some embodiments, the calibration member is a particular ring gauge, and the rotary chromatic range sensor includes a first ring gauge mounting means associated with the range sensor, and the ring gauge includes a second ring gauge mounting means mated with the first ring gauge mounting means such that the second ring gauge mounting means mates with the first ring gauge mounting means and is configured to align the ring gauge in a constrained relationship.

[0127] In some embodiments, the rotary chromatic range sensor includes an optical pen assembly having a housing that houses a lens mechanism and a rotary bearing mechanism of the range sensor. A first ring gauge attachment means is integrated into the housing of the range sensor.

[0128] In some embodiments, the housing and ring gauge are configured such that the ring gauge is held by the housing in a retracted position during retraction periods and is configured so as not to obstruct or interfere with the radial distance detection beam during normal measurements during the retraction periods. During a calibration period, the ring gauge is moved to hold the ring gauge by the housing in a calibration position where the calibration member is positioned in a positional relationship to the rotating chromatic range sensor.

[0129] In some embodiments, the calibration member includes a second cylindrical calibration surface concentric with the first cylindrical calibration surface, one of the first and second cylindrical calibration surfaces being an inner circumferential surface and the other being an outer circumferential surface, at least a portion of the outer circumferential surface being configured to be viewable through the inner circumferential surface.

[0130] In some embodiments, the calibration member is a glass tube, the first cylindrical calibration surface is an outer wall surface of the glass tube, and the second cylindrical calibration surface is an inner wall surface of the glass tube.

[0131] In some embodiments, the calibration member includes a plurality of concentric glass tubes, the first cylindrical calibration surface being a wall surface of one of the plurality of glass tubes, and the second cylindrical calibration surface being a wall surface of another of the plurality of glass tubes.

[0132] In some embodiments, the inner periphery has a pattern including a plurality of windows or segments, and portions of the outer periphery are configured to be viewable through the windows or segments of the pattern.

[0133] In some embodiments, the calibration member includes a third cylindrical calibration surface that is concentric with the first and second cylindrical calibration surfaces.

[0134] In some embodiments, the calibration member includes a second cylindrical calibration surface having a central axis along the Z direction and aligned to be substantially parallel to the axis of rotation. The second cylindrical calibration surface is located a known distance from the central axis along the Z direction by a second radius R2, the second radius R2 being a different length than the first radius R1.

[0135] In some embodiments, the calibration member includes one or more attachment means configured to connect the calibration member to a calibration gauge extension of a rotary chromatic range sensor such that the calibration member can be positioned in a constrained relationship with respect to the rotary chromatic range sensor such that the orientation of the rotation axis and the orientation of the central axis are in a fixed angular relationship with respect to each other and are parallel to each other within 5 degrees.

[0136] In some embodiments, when the calibration member is connected to the calibration gauge extension, the first cylindrical calibration surface is configured to have a first Z positional relationship with respect to the rotating chromatic range sensor and the second cylindrical calibration surface is configured to have a second Z positional relationship with respect to the rotating chromatic range sensor, the difference between the first and second Z positional relationships being known.

[0137] In some embodiments, the one or more surface features of the calibration member comprise a flat surface and a depression.

[0138] In some embodiments, one of the first and second cylindrical calibration surfaces is an inner circumferential surface and the other is an outer circumferential surface, at least a portion of the outer circumferential surface being observable through the inner circumferential surface.

[0139] In some embodiments, the calibration member is a glass tube, the first cylindrical calibration surface is an outer wall surface of the glass tube, and the second cylindrical calibration surface is an inner wall surface of the glass tube.

[0140] In some embodiments, the calibration member includes a plurality of concentric glass tubes, the first cylindrical calibration surface being a wall surface of one of the plurality of glass tubes, and the second cylindrical calibration surface being a wall surface of another of the plurality of glass tubes.

[0141] In some embodiments, the calibration member has an inner circumferential surface patterned with a plurality of windows or segments through which portions of the outer circumferential surface are viewable.

[0142] In some embodiments, the calibration member includes a third cylindrical calibration surface that is concentric with the first and second cylindrical calibration surfaces.

[0143] In some embodiments, the first cylindrical calibration surface includes at least one full or partial spiral groove or protrusion formed in a circumferential wall of the calibration surface, and the Z coordinate position of each full or partial spiral groove or protrusion is known as a function of the circumferential angle of the circumferential wall of the calibration surface.

[0144] In some embodiments, an apparatus is provided that includes a coordinate measuring machine (CMM), a chromatic range sensor (CRS) optical probe, and a calibration member. The CMM includes a light generating circuit, a wavelength detecting circuit, and a CMM control circuit. The CRS optical probe is configured to be connectable to the CMM and includes an optical pen having a confocal optical system including at least a confocal aperture and a chromatic dispersion optical member. The optical pen is configured to project a radial distance detection beam along a radial direction relative to a rotation axis, and to rotate the radial distance detection beam about the rotation axis, such that different wavelengths of light are focused at different distances near a measured surface of the workpiece along the measurement axis. The calibration member is for providing calibration data for correcting misalignment errors of the CRS optical probe.

[0145] In some embodiments, the CRS optical pen includes an optical pen assembly having a housing that houses a lens mechanism and a rotary bearing mechanism of a rotary chromatic range sensor, the optical pen assembly including a first calibration member mounting means integrated into the housing of the CRS optical pen.

[0146] In some embodiments, the housing and the first calibration member mounting means are configured such that the first calibration member mounting means is held on the housing in a retracted position during the retraction period and configured so as not to obstruct or interfere with the radial distance detection beam during normal measurement during the retraction period. During the calibration period, the first calibration member mounting means is moved to hold the first calibration member mounting means in the calibration position.

[0147] Although preferred embodiments of the present invention have been described, many variations on the configurations and operational procedures shown herein will be apparent to one of ordinary skill in the art based on this disclosure. For example, the CMMs disclosed herein may be any type of conventional CMM and / or any other type of machine that utilizes an optical probe to determine coordinate values ​​(e.g., a robotic platform that utilizes an optical probe, etc.). As another example, in addition to the CRS optical probes disclosed herein, other types of optical probes may be used with the system arrangements and configurations disclosed herein (e.g., if other non-contact white light optical probes are used, light may be similarly transmitted to the optical probes via the free space fiber optic couplings disclosed herein, etc.).

Claims

1. 1. A method for providing calibration data for correcting misalignment errors in a rotary chromatic range sensor configured to irradiate a radial distance detection beam along a radial direction relative to a rotation axis and rotate the radial distance detection beam about the rotation axis, comprising: a) providing a calibration member having at least a first cylindrical calibration surface having a central axis extending along a Z direction aligned to be substantially parallel to the axis of rotation, the first cylindrical calibration surface being disposed at a first known radius R1 from the central axis extending along the Z direction, and a first set of angular reference features formed on or within the first cylindrical calibration surface, the set of angular reference features being detectable by the radial distance detection beam and disposed on or within the first cylindrical calibration surface at a known angle or angular spacing from one another about the central axis; b) positioning the calibration member relative to the rotary chromatic range sensor such that the direction of the rotational axis and the direction of the central axis are in an angular relationship to one another and are parallel to within 5 degrees of each other; c) providing a first radial distance data set referenced to a sensed rotation angle of the detection beam about the axis of rotation acquired while operating the rotating chromatic range sensor to rotate the radial distance detection beam about the axis of rotation at a first Z coordinate position along the Z direction relative to the calibration member; d) processing the first radial distance data set referenced to the sensed rotation angle to determine the calibration data usable to characterize or compensate for radial distance measurement error as a function of the sensed rotation angle.

2. 2. The method of claim 1, performing steps a) to c) to provide the first radial distance data set at the first Z coordinate position along a Z direction relative to the calibration member; adjusting a Z positional relationship between the rotary chromatic range sensor and the calibration member to align the calibration member with a second Z coordinate position along the Z direction; wherein the difference between the first Z coordinate position and the second Z coordinate position is known and is adjusted without changing the fixed angular relationship established in step b); performing step c) again to provide a second radial distance data set at the second Z coordinate location; In step d), processing the first and second radial distance data sets referenced to the sensed rotation angle to determine the calibration data usable to characterize or compensate for the radial distance measurement error as a function of the sensed rotation angle. A method for providing calibration data comprising the steps of:

3. 3. The method of claim 2, the calibration member is a specific ring gauge; performing step c) again to provide a second radial distance data set at a second Z positional relationship between the rotating chromatic range sensor and the ring gauge, where the difference between the first and second Z positions is known; Furthermore, in the step b), at least one of the rotary chromatic range sensor and the ring gauge is mounted on a precision Z movement stage constrained to move in a Z direction, and the precision Z movement stage is operated so that a difference between the first and second Z positional relationships becomes known. A method for providing calibration data comprising the steps of:

4. 3. The method of claim 2, a first cylindrical calibration surface having at least one complete or partial spiral groove or spiral protrusion formed in a peripheral wall, the Z coordinate position of each of the spiral groove or spiral protrusion being known as a function of a circumferential angle of the peripheral wall; In step d), processing the first and second radial distance data sets to determine the calibration data usable to characterize or compensate for the radial distance measurement error as a function of the sensed rotation angle. A method for providing calibration data comprising the steps of:

5. 5. The method of claim 4, wherein the calibration member is a specific ring gauge; the rotary chromatic range sensor comprising a first ring gauge mounting means integrated into the rotary chromatic range sensor; the ring gauge includes a second ring gauge mounting means mating with the first ring gauge mounting means, and the first and second ring gauge mounting means are adapted to mate with each other in step b) such that the second ring gauge mounting means aligns the ring gauge in a constrained relationship. A method for providing calibration data comprising the steps of:

6. 6. The method of claim 5, wherein the rotary chromatic range sensor includes an optical pen assembly having a housing containing a lens mechanism and a rotary bearing mechanism of the rotary chromatic range sensor; the optical pen assembly includes the first ring gauge mounting means integrated into the housing of the rotary chromatic range sensor; A method for providing calibration data comprising the steps of:

7. 7. The method of claim 6, wherein the housing and the ring gauge are: During a retraction period, the link gauge is held in the housing at a retracted position so as not to obstruct or interfere with the radial distance detection beam during normal measurement during the retraction period; During a calibration period, moving the ring gauge in accordance with step b) and holding the ring gauge in a calibration position on the housing. A method for providing calibration data comprising the steps of:

8. 2. The method of claim 1, wherein the calibration member includes a second cylindrical calibration surface concentric with the first cylindrical calibration surface; one of the first and second cylindrical calibration surfaces is an inner circumferential surface and the other is an outer circumferential surface, and at least a plurality of portions of the outer circumferential surface are configured to be observable through the inner circumferential surface; A method for providing calibration data comprising the steps of:

9. 9. The method of claim 8, wherein the calibration member comprises: a glass tube, the first cylindrical calibration surface being an outer wall surface and the second cylindrical calibration surface being an inner wall surface; a plurality of concentric glass tubes, the first cylindrical calibration surface being a wall surface of one of the plurality of glass tubes, and the second cylindrical calibration surface being a wall surface of another of the plurality of glass tubes; a third cylindrical calibration surface concentric with the first and second cylindrical calibration surfaces; and a pattern on the inner circumferential surface including a plurality of windows or segments through which a plurality of portions of the outer circumferential surface can be viewed; A calibration data providing method comprising at least one of the following steps:

10. A coordinate measuring machine (CMM), a chromatic range sensor (CRS) optical probe, and a calibration member; The CMM includes: A light generating means; A wavelength detection means; and a CMM control means, The CRS optical probe comprises: configured to be connectable to the CMM; an optical pen having a confocal optical system including at least a confocal aperture and a chromatic dispersion optical element, the optical pen being configured to irradiate a radial distance detection beam along a radial direction relative to a rotation axis, rotate the radial distance detection beam around the rotation axis, and focus different wavelengths of light at different distances near a measured surface of the workpiece along the measurement axis; The calibration member is To provide calibration data for correcting misalignment errors of the CRS optical probe; at least a first cylindrical calibration surface having a central axis extending along a Z direction that is aligned to be substantially parallel to the axis of rotation and positioned at a first known radius R1 from the central axis extending along the Z direction; a first set of angular reference features formed on or within the first cylindrical calibration surface, the first set of angular reference features configured to be detectable by the radial distance detection beam, the first set of angular reference features disposed on or within the first cylindrical calibration surface at a known angle about the central axis or at angular intervals from one another; A system characterized by:

11. 11. The system of claim 10, The CRS optical probe includes an optical pen assembly having a housing that houses a lens mechanism and a rotary bearing mechanism of a rotary chromatic range sensor; The optical pen assembly includes a first calibration member mounting means integrated into the housing of the CRS optical probe.

12. 12. The system of claim 11, wherein the housing and the first calibration member mounting means are: the retraction period is configured to hold the first calibration member mounting means on the housing in a retracted position so as not to obstruct or interfere with the radial distance detection beam during normal measurement during the retraction period; A calibration interval is configured to move and hold the first calibration member mounting means in a calibration position.

13. 13. The system of claim 12, the calibration member has a central axis extending along a Z direction aligned to be substantially parallel to the rotation axis, and includes a second cylindrical calibration surface disposed at a distance of a known second radius R2, different from the central axis along the Z direction, the second cylindrical calibration surface being disposed at a distance of a known second radius R2, different from the first radius R1. A system characterized by:

14. 14. The system of claim 13, When the calibration member is connected to the first calibration member attachment means, the first cylindrical calibration surface is configured to have a first Z relationship with the CRS optical probe; the second cylindrical calibration surface is configured to have a second Z positional relationship with the rotating chromatic range sensor; a difference between the first and second Z positional relationships is known.

15. 11. The system of claim 10, The calibration member is a second cylindrical calibration surface having a central axis extending along a Z direction that is aligned to be substantially parallel to the rotation axis, and disposed at a distance of a known second radius R2, different from the first radius R1, from the central axis along the Z direction; one of the first and second cylindrical calibration surfaces is an inner circumferential surface and the other is an outer circumferential surface, and at least a plurality of portions of the outer circumferential surface are configured to be observable through the inner circumferential surface; A system characterized by:

16. 16. The system of claim 15, wherein the inner circumferential surface is patterned to include a plurality of windows or sections, such that a plurality of portions of the outer circumferential surface are observable through the plurality of windows or sections.

17. A calibration member capable of providing calibration data for correcting misalignment errors of a rotary chromatic range sensor configured to irradiate a radial distance detection beam along a radial direction relative to a rotation axis and rotate the radial distance detection beam about the rotation axis, the calibration member comprising: at least a first cylindrical calibration surface having a central axis extending along a Z direction that is aligned to be substantially parallel to the axis of rotation and positioned at a first known radius R1 from the central axis extending along the Z direction; a first set of angular reference features formed on or within the first cylindrical calibration surface, the first set of angular reference features configured to be detectable by the radial distance detection beam, the first set of angular reference features disposed on or within the first cylindrical calibration surface at a known angle or angular spacing from one another about the central axis.

18. The calibration member according to claim 17 comprises: a second cylindrical calibration surface having a central axis extending along a Z direction that is aligned to be substantially parallel to the rotation axis, the second cylindrical calibration surface being positioned at a distance of a known second radius R2, different from the first radius R1, from the central axis along the Z direction.

19. 20. The calibration member according to claim 18, one or more attachment means configured to connect the calibration member to a calibration gauge extension of the rotary chromatic range sensor; a mounting means for mounting the calibration member in a constrained relationship to the rotary chromatic range sensor such that the direction of the rotation axis and the direction of the central axis are in a constant angular relationship to each other and are parallel to each other within 5 degrees of each other.

20. 20. The calibration member according to claim 19, When the calibration member is connected to the calibration gauge extension, the first cylindrical calibration surface is configured to have a first Z positional relationship with the rotating chromatic range sensor; the second cylindrical calibration surface is configured to have a second Z positional relationship with the rotating chromatic range sensor; A calibration member, wherein a difference between the first and second Z positional relationships is known.

21. 20. The calibration member of claim 19, comprising one or more surface features including a flat surface and a depression.

22. 20. The calibration member according to claim 18, one of the first and second cylindrical calibration surfaces is an inner circumferential surface and the other is an outer circumferential surface; A calibration member, characterized in that at least a plurality of portions of the outer circumferential surface are observable through the inner circumferential surface.

23. 23. The calibration member of claim 22, a glass tube, the first cylindrical calibration surface being an outer wall surface and the second cylindrical calibration surface being an inner wall surface; a plurality of concentric glass tubes, the first cylindrical calibration surface being a wall surface of one of the plurality of glass tubes, and the second cylindrical calibration surface being a wall surface of another of the plurality of glass tubes; a third cylindrical calibration surface concentric with the first and second cylindrical calibration surfaces; and a pattern on the inner circumferential surface including a plurality of windows or segments through which a plurality of portions of the outer circumferential surface can be viewed; A calibration member comprising at least one of the following:

24. 20. The calibration member according to claim 18, the first cylindrical calibration surface includes at least one complete or partial spiral groove or spiral protrusion formed on a peripheral wall of the first cylindrical calibration surface; a Z-coordinate position of each of the full or partial spiral grooves or spiral protrusions is known as a function of a circumferential angle of the peripheral wall of the first cylindrical calibration surface; A calibration member characterized by:

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