WO2020072484A1

WO2020072484A1 - An auxiliary focus measurement for a laser radar 3d scanner

Info

Publication number: WO2020072484A1
Application number: PCT/US2019/054054
Authority: WO
Inventors: Daniel Gene Smith
Original assignee: Nikon Corp
Current assignee: Nikon Corp
Priority date: 2018-10-01
Filing date: 2019-10-01
Publication date: 2020-04-09
Anticipated expiration: 2021-04-01

Abstract

An auxiliary focus system is coupled to a focus adjustment mechanism to simplify laser radar focusing. An auxiliary focus beam, a fringe projector, or a camera can be used to determine target distance so that focus can be set at an initial distance. In some cases, an electrical measurement beam modulation is used to determine the initial focus. A laser radar (LR) (400) includes a transceiver (402) that includes an LR laser (404), an LR detector (406), and a coupler (408) that directs an LR measurement beam from the LR laser (404) along an axis (410) and directs a return portion of an LR beam from a target to the LR detector (406). The laser radar (400) also includes an auxiliary (focus) transceiver (412) that includes a focus laser (414), a focus detector (416), and a focus coupler (418) that directs a focus beam from the focus laser (414) along an axis (420) and directs a return portion of a focus beam from a target to the focus detector (416). A beam scanner (422) is coupled to scan the beams over a region of interest at the target. A beam splitter (424) combines and separates focus and LR beams and a common objective (430) directs both beams to the target. The axes (410, 420) are displaced from each other so that the LR beam and the focus beam are incident to different portions of the target.Typically, the focus beam is directed to a target area in advance of exposure of the target area to the LR beam so that a focus estimate can be obtained prior an LR measurement. Both the LR detector (406) and the focus detector (416) produce electrical signals that are coupled to a controller (432) and are processed to establish a preliminary focus and recording a sample surface profile, respectively. Based on the focus signal, the controller (432) couples a control signal to a focus mechanism (434). Alternatively, a fringe projector directs a patterned beam to the target, the fringe image of which is used to estimate distance and initiate a focus adjustment. The methods and apparatus disclosed above can be used in a variety of manufacturing systems, such as for producing one or more components of a ship, airplane, or part of other systems or apparatus, and for evaluating and reprocessing such manufactured components

Description

AN AUXILIARY FOCUS MEASUREMENT FOR A LASER RADAR 3D SCANNER

FIELD

The disclosure pertains to laser surface profile and distance measurement apparatus.

BACKGROUND

Laser radar systems (LR) provide simple, convenient, non-contact measurements that aid single-operator object inspection. Laser radar systems are particularly useful for inspection applications in which large objects are to be measured such as in the manufacture and assessment of aircraft, automobile, wind turbine, satellite, and other oversized parts. Some conventional laser radar systems are described in U.S. Patents 4,733,609; 4,824,251; 4,830,486; 4,969,736; 5,114,226; 7,139,446; 7,925,134; and Japanese Patent 2,664,399 which are incorporated herein by reference. In such laser radar systems, a laser beam is directed to and scanned over a target surface, and portions of the laser beam that are reflected or scattered back to the laser radar are detected and processed to provide target information.

LRs that use optical heterodyne signals to determine range can provide measurement accuracies of less than 5 pm/meter. Heterodyne LR is particularly well suited to very near objects (e.g., closer than one meter) such as might be encountered inside a 3D scan box.

However, heterodyne and other types of LR typically require directing a tightly focused laser beam to a target to achieve both fine spatial resolution and high SNR for strongly scattering objects. Unfortunately, in the absence of any surface measurements upon initiation of LR surface scanning, it is difficult to establish a proper focus location for the laser beam, and actual surface measurements are preceded by a delay period during which a focus position is determined. Approaches are needed that can permit rapid, initial acquisition of surface data so that LR focus can be set, and LR measurements initiated promptly.

SUMMARY

Auxiliary focus systems permit rapid initial focus of optical measurement apparatus prior to final focusing. In some examples, optical measurement apparatus include an auxiliary focus system situated to estimate a distance to at least a portion of a target and a focus mechanism situated to adjust a focus of a measurement beam at the target in response to the distance estimate. In some examples, the auxiliary focus system includes an auxiliary laser situated to direct an auxiliary beam to the portion of the target, and the distance is estimated based on a portion of the auxiliary beam returned from the target. In other examples, the auxiliary focus system includes an auxiliary detector situated to receive the portion of the auxiliary beam returned from the target. In further examples, the auxiliary focus system includes a modulator that applies an electrical amplitude modulation, frequency modulation, phase modulation, pulse modulation, or any combination thereof to the auxiliary beam, and the distance estimate is based on a detected modulation. In some embodiments, a measurement laser is situated to direct a measurement beam to the portion of the target, wherein the auxiliary focus system includes an auxiliary laser situated to direct an auxiliary beam to the portion of the target, and the estimated distance is based on a portion of the auxiliary beam returned to the target. In other examples, a measurement laser is situated to produce and direct a measurement beam and an auxiliary beam to the portion of the target. In still other examples, a focus element is coupled to the focus mechanism so as to be translated by the focus mechanism, wherein the focus element includes one or more of a lens, a prism, or a mirror. In still other alternatives, the measurement laser and the auxiliary laser emit respective beams at different wavelengths.

In other approaches, the auxiliary focus system includes a fringe projector situated to project a fringe pattern on at least the portion of the target, and the focus mechanism is adjustable in response to a detected fringe pattern. In some embodiments, an objective lens is situated to direct the measurement beam to the target and an image sensor is situated to image the projected fringe pattern through the objective lens or along the axis of the objective lens. In typical examples, a beam scanner is situated to scan the auxiliary beam over the target area prior to the measurement beam. In some examples, the beam scanner is configured to scan the auxiliary beam at least one scan line prior to the measurement beam. In other examples, the auxiliary focus system includes an image sensor situated to produce at least two images of the target area and a processor coupled to receive the at least two images and establish at least one distance estimate based on the at least two images.

Methods comprise obtaining an initial distance estimate associated with at least one target area and based on the initial distance estimate, adjusting a focus element associated with a measurement beam. An initially focused measurement beam is directed to the at least one target area based on the adjustment of the focus element and a final focus of the measurement beam is determined based on a returned portion of the measurement beam. A target surface profile is obtained based on a returned portion of a finally focused measurement beam. In some cases, the initial distance is obtained by directing an auxiliary beam to the at least one target area, and detecting a time-of-flight of the auxiliary beam to the at least one target area. In other examples, the initial distance is obtained by directing an auxiliary beam to the at least one target area, and detecting a time-of-flight of the auxiliary beam to the at least one target area, wherein the auxiliary beam is a portion of the measurement beam. In some embodiments, the initial distance is obtained by directing an auxiliary beam to the at least one target area, and detecting a modulation of a detected portion of the auxiliary beam received from the at least one target area. In representative examples, the modulation of the detected portion of the auxiliary beam is an electrical phase modulation, amplitude modulation, frequency modulation, or a combination thereof. Typically, the final focus of the measurement beam is obtained based on a detected portion of the measurement beam returned from the target. In some alternatives, the final focus of the measurement beam is obtained based on an optical frequency modulation of a detected portion of the measurement beam returned from the target. In other cases, the initial distance is obtained by projecting a fringe pattern on the at least one target area, and detecting at least a portion of the projected fringe pattern. In some examples, the initial distance is obtained by obtaining at least one image that includes the target area, and processing the at least one image to obtain the initial distance.

The foregoing and other objects, features, and advantages will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a laser radar system (LR) that includes an auxiliary focus system having two image sensors.

FIG. 2 illustrates an LR that includes an auxiliary focus system having a single image sensor.

FIG. 3 illustrates an LR that includes an auxiliary focus system having an auxiliary laser that propagates to a target via an LR objective and scanning system.

FIG. 4 illustrates another representative LR having an auxiliary focus system.

FIG. 5 illustrates another representative LR having an auxiliary focus system that uses a common laser and detector with the LR.

FIG. 6 illustrates a representative LR focus method.

FIG. 7 illustrates another representative LR focus method.

FIGS. 8-9 illustrate auxiliary focus systems for LR using external LIDAR systems. FIG. 10 illustrates a representative LR having an auxiliary focus system that uses a fringe projector.

FIG. 11 illustrates another representative LR having an auxiliary focus system that uses a fringe projector.

FIG. 12 is a block diagram illustrating a representative manufacturing method that includes profile measurement to determine whether manufactured structures or components are acceptable, and if one or more such manufactured structures can be repaired.

FIG. 13 is a block diagram of a representative method of tracking a tooling ball that is secured to a substrate or target.

FIG. 14 is a block diagram of a representative manufacturing system that includes a laser radar or other profile measurement system to manufacture components, and assess whether manufactured parts are defective or acceptable.

FIG. 15 is a schematic illustration of a laser radar system that includes an auxiliary focus system as disclosed herein.

FIG. 16 is a front view of a preferred type of laser radar system that can include an auxiliary focus system as disclosed herein.

FIG. 17 is a schematic illustration raster scanning associated with an auxiliary beam and a measurement beam.

FIG. 18 illustrates a representative scan system.

DETAILED DESCRIPTION

As used in this application and in the claims, the singular forms“a,”“an,” and“the” include the plural forms unless the context clearly dictates otherwise. Additionally, the term “includes” means“comprises.” Further, the term“coupled” does not exclude the presence of intermediate elements between the coupled items.

The systems, apparatus, and methods described herein should not be construed as limiting in any way. Instead, the present disclosure is directed toward all novel and non-obvious features and aspects of the various disclosed embodiments, alone and in various combinations and sub-combinations with one another. The disclosed systems, methods, and apparatus are not limited to any specific aspect or feature or combinations thereof, nor do the disclosed systems, methods, and apparatus require that any one or more specific advantages be present or problems be solved. Any theories of operation are to facilitate explanation, but the disclosed systems, methods, and apparatus are not limited to such theories of operation. Although the operations of some of the disclosed methods are described in a particular, sequential order for convenient presentation, it should be understood that this manner of description encompasses rearrangement, unless a particular ordering is required by specific language set forth below. For example, operations described sequentially may in some cases be rearranged or performed concurrently. Moreover, for the sake of simplicity, the attached figures may not show the various ways in which the disclosed systems, methods, and apparatus can be used in conjunction with other systems, methods, and apparatus. Additionally, the description sometimes uses terms like“produce” and“provide” to describe the disclosed methods. These terms are high-level abstractions of the actual operations that are performed. The actual operations that correspond to these terms will vary depending on the particular implementation and are readily discernible by one of ordinary skill in the art.

In some examples, values, procedures, or apparatus’ are referred to as“lowest”,“best”, “minimum,” or the like. It will be appreciated that such descriptions are intended to indicate that a selection among many used functional alternatives can be made, and such selections need not be better, smaller, or otherwise preferable to other selections.

As used herein,“image” refers to a viewable, displayed, or projected image of an object, or a stored digital representation associated therewith. Stored digital representations can be arranged as, for example, JPEG, TIFF, BMP, PDF or other formats, or as sequences of images such as MPEG or other formats. In some examples, one or more stored digital representations are processed to provide an initial distance estimate for use in focusing.

For convenience, beams are described as propagating along one or more axes. Such axes generally are based on one or more line segments so that an axis can include a number of non- collinear segments as the axis is bent or folded or otherwise responsive to mirrors, prisms, lenses, and other optical elements. The term“lens” is used herein to refer to a single refractive optical element (a singlet) or a compound lens that includes one or more singlets, doublets, or other elements. In some examples, beams are shaped or directed by refractive optical elements, but in other examples, reflective optical elements such as mirrors are used, or combinations of refractive and reflective elements are used. Such optical systems can be referred to as dioptric, catoptric, and catadioptric, respectively. Other types of refractive, reflective, diffractive, holographic and other optical elements can be used as may be convenient.

The disclosure pertains generally to auxiliary measurement systems, apparatus, and methods that can provide approximate ranges so that an LR focus can be established. In some examples disclosed herein, such auxiliary measurements can be obtained by auxiliary beam scanning, line scanning, photogrammetry, fringe projection, or other approaches as described below. An auxiliary focus signal can be provided using the scanning LR beam (or a portion of the LR beam scan, such as a scan line) or using a separate beam, using the LR optics or different optics. Auxiliary focus scanning can direct an auxiliary beam (such as a line beam) along the LR beam path or a separate path, typically to irradiate a target portion prior to scanning with the LR measurement beam. In some cases, auxiliary focus is determined for only a portion of the target surface just in advance of LR measurement, or, alternatively, a larger or complete target area is imaged to establish an initial LR beam focus. A photogrammetric system can be used, using one or more cameras that image at least portions of a surface to be scanned in advance of the LR measurement beam. In other examples, fringe projection systems can be used. Fringe projection can use a separate illumination system or can use the same optical system or objective lens as an LR. A low-NA imaging channel can be used on a first scan of the object to sense fringes, and then a second scan can use the resulting information to set focus and scan with the LR. In other examples, a spatially displaced imaging channel is used that is one or more scan lines ahead of the LR scan. In another approach, range measurements can be made coaxially with the LR scan, if desired. For example; a LIDAR signal can be used that is obtained with the LR scan beam or an auxiliary beam. The LIDAR signal can be acquired in advance of LR scanning. A LIDAR beam could be directed along a common axis with the LR beam using a dichroic or polarizing or other beam splitter. Returned portions of the LIDAR beam can be detected with the LR detector or a separate detector using a beam splitter such as a fiber coupler, a beam splitter cube, or a plate beam splitter. The LIDAR beam can be produced using the LR source prior to LR scanning or along with LR scanning based on a beam modulation that differs from that of LR scan. For example, the LIDAR modulation can be an AM or FM modulation that is different from an optical heterodyne swept modulation used by the LR. An FM

modulation at electrical frequencies (< 1 GHz) can be used that can be detected without an optical reference optical signal such as required by LR in swept frequency, heterodyne LR.

These and other approaches are described below with reference to the disclosed examples.

The disclosed technology is described herein in connection with a laser radar systems of the type described in U.S. Pat. Nos. 4,733,609, 4,824,251, 4,830,486, 4,969,736, 5,114,226, 7,139,446, 7,925,134, and Japanese Patent No. 2,664,399, which are incorporated herein by reference, but the disclosed methods and apparatus can be used in other measurement systems.

In heterodyne laser radar, measurement beam wavelength is varied. For convenience, such a variation is referred to herein as an optical modulation. Amplitude, phase, or frequency modulations of a measurement beam at frequencies less than about 1 GHz are referred to as electrical modulations. For electrical modulations, change of laser wavelength is generally not intended.

Example 1

FIG. 1 is a perspective view of a laser rangefinder 100 that includes a laser radar 102 secured to an altitude rotational stage 108 that is configured to rotate about an altitude axis 110. The altitude stage 108 is secured to an azimuthal rotational stage 111 that is configured to rotate about an azimuthal axis 116. The axes 110, 116 are generally intersecting orthogonal axes, and are described herein as azimuthal and altitude axes for convenience, as such axes may be arranged so as to be in arbitrary directions. For convenient illustration, control systems used for adjustment of rotation angles are not shown in FIG. 1.

The laser radar 102 includes optical and electrical systems configured to deliver an interrogation beam to a target from an aperture 104 along a laser radar axis 106. The laser radar typically 102 includes a housing 103 that is secured to the altitude stage 108 so that the laser radar axis 106 can be scanned over the target with the altitude stage 108 and the azimuth stage 111. Some portions of the laser radar 102 can be provided separately from the housing 103, and are not rotatable. For example, control electronics, fiber coupled lasers and/or detectors and associated transmitter and detector electronics, and signal processors can be located remotely. Typically, a housed portion of the laser radar 102 includes transmit and receive optical systems. The azimuthal stage 111 includes a rotatable platform 112 to which the altitude stage 108 is secured and a fixed platform 114. Rotation of the rotatable platform 112 about the axis 116 permits scanning of the laser radar axis 104 over a target.

The laser rangefinder 100 also includes a first camera 130 and a second camera 140 that are secured to rotate with the laser radar housing 103. The cameras 130, 140 are configured to image through apertures 132, 142 along imaging axes 134, 144, respectively, and provide images of at least some portions of a target or of areas situated about the laser radar axis 104. In typical examples, the camera axes 134, 144 are substantially parallel to the laser radar axis and are orthogonal to and intersect the altitude axis 110. However, other arrangements can be used, as may be convenient. For example, the camera axes 134, 144 can be arranged to be intersecting or skew.

Images from the cameras 130, 140 are typically provided to a focus processor 150 that estimates a target distance based on the images. The focus processor 150 is coupled to a focus mechanism (not shown in FIG. 1) that is situated to adjust a focus of a measurement beam at the target. Estimated distance can be obtained photogrammetrically, and focus is typically adjusted again based on a portion of the measurement beam returned from the target during LR operation. In most cases, final target surface data is acquired primarily based on the measurement beam, and the cameras 130, 140 permit a rapid initial focus which can reduce total measurement time. In other examples, measurement beam based distances are combined with camera-based estimates to obtain suitable surface measurements.

In the example of FIG. 1, two cameras are used, but a single camera can be used if images are acquired from different vantage locations. A camera need not be situated to rotate in both azimuth and elevation, but only to image a portion of a target for which focus data is to be obtained.

In the example of FIG. 1, the relationship between the camera axes of the cameras 130 and 140 and the laser radar axis 106 (the optical axis of the laser radar optical system) may be fixed. The camera axes of the cameras 130 and 140 and the laser radar axis 106 may be parallel to each other. The cameras 130 and 140 may move together with the housing 103. Note that the relationship between the camera axes of the cameras 130 and 140 and the laser radar axis 106 may be changeable.

Also in the example of FIG. 1, the focus processor 150 controls the focus mechanism (not shown) based on the images obtained by the cameras 130 and 140, so that the irradiation spot of the measurement beam irradiated by the laser radar 102 is focused on the target.

Thereby, the intensity of light from the irradiation spot received by the laser radar 102 can be increased. As a result, the S/N ratio of signals associated with the received measurement beam can be improved and measurement accuracy can be improved.

Example 2

FIG. 2 illustrates a representative laser rangefinder 200 that includes a laser radar 202 situated to have a scan axis 204 that is directed to a target 205. A camera 220 includes a lens 212 that is configured to form images at an image sensor 214. As shown in FIG. 2, the camera 220 has an axis 216 that is parallel to the scan axis 206. The camera axis 216 can be fixed or variable with respect to the scan axis 204. An image processor 230 is coupled to receive image data from the image sensor 214 and estimate a target distance for use in focus adjustment. A laser radar controller 232 processes laser radar data and controls the laser radar 202 to scan the target 205 and provide range estimates. Images can be obtained during scanning of either the laser radar 202 or the target 205 as indicated at 250, 251, respectively, and processed to determine distance estimates for focus adjustment.

In the example of FIG. 2, the distance of the target 205 is estimated by moving the focus lens 212 (moving along the camera axis 216). In the example of FIG. 2, the distance of the target 205 is estimated based on information of the position of the focus lens 212 in a direction along the camera axis 216 when the contrast of the image on the image sensor 214 is the best. Thereby, the focus when the laser radar 202 performs the measurement can be adjusted to the target 205. As a result, the intensity of light generated at the target 205 by irradiating the measurement beam can be increased, so that the S/N ratio can be improved and the measurement accuracy can be improved.

Example 3

With reference to FIG. 3, a laser radar system 300 includes a transmitter system 302 that is configured to couple an optical beam from one or more laser diodes or other light sources to an optical fiber 304 through a beam splitter 305 such as a beam splitter cube, a plate beam splitter, or a fiber coupler. The optical beam exits the optical fiber 304 at a fiber end 306, typically at a cleaved or plane polished fiber end, and is directed along an axis 308 to a right angle prism 310 and a return mirror 332. The return mirror 332 is situated along the axis 308 as folded by the right angle prism 310 to return the beam through the right angle prism 310 to an objective lens 314 that produces a focused beam that is directed to a target 316 and scanned over a region of interest with a scanning assembly 310. Focus is typically adjusted by translating the right angle prism 310 along the axis 308. At least some portions of the beam are scattered, reflected, or otherwise returned to the objective lens 314 and coupled via the right angle prism 310 and the return mirror 332 to the fiber end 306 and to a receiver system 322. The right angle prism 310 is secured to a focus mechanism 326 that is configured to translate the right angle prism 310 along the axis 308 to focus the beam at particular distance. The returned portion of the beam can be used in laser radar processing to provide target coordinates.

The laser radar system 300 also includes a processing system 350 that is coupled to the transmitter system 302 and the receiver system 322. Based on transmitted and received optical signals, the processing system 350 can estimate distances and other coordinates associated with the target, or selected portions of the target 316. Measurement results are provided directly for user inspection or relayed to analysis systems. The laser radar system 300 can be configured as a frequency modulated continuous wave system, as an amplitude or phase modulated system, or a combination of such systems as discussed further below. The example of FIG. 3 is illustrated with a right angle prism used to provide focus adjustment. Corner cubes or roof prisms (solid or air spaced) are generally superior, but a right angle prism permits convenient illustration.

Generally, the fiber 304 is a polarization maintaining fiber and the beam splitter 305 is a polarizing beam splitter.

The transmitter system 302 includes a swept frequency laser 302A (i.e., a measurement laser), an auxiliary laser 302B, and a pointing laser 302C that produce a swept frequency beam, an auxiliary focus beam, and a visible pointing beam, respectively, that are coupled by a coupler 303 such as a fiber coupler, dichroic beam splitter, or polarizing beam splitter to the fiber 304. The visible pointing beam is available for visual alignment by an operator, and the swept frequency beam is used in swept frequency laser radar. The auxiliary beam (and the other beams) are directed along the axis 308 to the target 316, and portions of each can be returned from the target 316 to the beam splitter 305. Any returned portion of the pointing beam is generally unused, and is typically blocked by one or more optical filters or is not coupled downstream by components used for the swept frequency and auxiliary beams.

A coupler 323 receives returned portions of the swept frequency beam and the auxiliary beam and couples portions to a swept frequency detector 322A and an auxiliary detector 322B, respectively. If the swept frequency beam and the auxiliary beam are at different wavelengths, the coupler 323 can be a wavelength dependent coupler such as a fiber coupler or a dichroic beam splitter. In heterodyne laser radar, a portion of the swept frequency beam is directed to the swept frequency detector 322A as a local oscillator (LO) beam along an LO path 342 to produce a heterodyne output signal at the swept frequency detector 322A. Signals associated with the detected beam portions are coupled to a controller/signal processor 350.

The signal associated with the auxiliary laser beam is used to produce a range estimate. For example, the auxiliary laser beam can be a pulsed beam and a time of flight to the target 316 can be estimated. In generally, the auxiliary beam can be amplitude modulated or frequency modulated, and modulation in the detected signal used to estimate target distance. Amplitude or frequency modulation is usually at electronic frequencies (less than a few 100 MHz). Based on the estimated target distance, the controller 350 directs a focus signal to the focus adjustment mechanism 326 so that the swept frequency laser beam is suitably focused at the target 316.

With an initial beam focus established, measurements using the swept frequency beam are used to obtain more precise target data. In the example of FIG. 3, an auxiliary measurement (time of flight (TOF) method) which has high robustness can be used to concentrate the irradiation spot of the measurement beam irradiated on the target, thereby increasing the intensity of light from the irradiation spot. As a result, the S/N ratio can be improved and measurement accuracy can be improved. Further, the example of FIG. 3 has an advantage that the distance of the target 316 can be estimated without driving the focus mechanism.

Example 4

Referring to FIG. 4, a laser radar 400 includes a transceiver 402 that includes an LR laser 404, an LR detector 406, and a coupler 408 that directs an LR measurement beam from the LR laser 404 along an axis 410 and directs a return portion of an LR beam from a target to the LR detector 406. The laser radar 400 also includes an auxiliary (focus) transceiver 412 that includes a focus laser 414, a focus detector 416, and a focus coupler 418 that directs a focus beam from the focus laser 414 along an axis 420 and directs a return portion of a focus beam from a target to the focus detector 416. A beam scanner 422 is coupled to scan the beams over a region of interest at the target. A beam splitter 424 combines and separates focus and LR beams and a common objective 430 directs both beams to the target. The axes 410, 420 are displaced from each other (and need not be parallel) so that the LR beam and the focus beam are incident to different portions of the target. Typically, the focus beam is directed to a target area in advance of exposure of the target area to the LR beam so that a focus estimate can be obtained prior an LR measurement. Both the LR detector 406 and the focus detector 416 produce electrical signals that are coupled to a controller 432 and are amplified, buffered, or otherwise processed to establish a preliminary focus and recording a sample surface profile, respectively. Based on the focus signal, the controller 432 couples a control signal to a focus mechanism 434.

Also in the example of FIG. 4, the same effect as the effect of the example of FIG. 3 is achieved.

Example 5

Referring to FIG. 5, an LR system 500 includes an LR laser modulator 502 that is coupled to a laser driver 504 to activate an LR laser 506 to direct an LR beam along an axis 510 via a coupler 508. In addition, a focus modulator 512 is coupled to the laser driver 504 to apply a focus modulation to the LR laser output beam along with or in addition to a modulation associated with LR measurement. Portions of the LR beam returned from the target are coupled

- it - by the beam splitter 508 to an LR detector 516 and modulations associated with one or both of the LR modulation and the focus modulation are detected at a demodulator 518. In swept frequency, heterodyne LR, an optical frequency difference between the portion of the LR beam returned from a target and an LO beam is used to provide a distance estimate. A controller 550 is coupled to direct a focus signal to a focus mechanism 552 based on the portion of the detected LR signal having the focus modulation. In the system of FIG. 5, a single laser (the LR laser) is provided with different modulations and separate focus laser and detector are not needed.

However, a second detector can be used if desired so that there are dedicated detectors for LR measurement and focus adjustment.

In swept frequency heterodyne LR, control of laser frequency can be challenging and applying an additional focus modulation can interfere with swept frequency control. As shown in FIG. 5, it may be preferable to apply a focus modulation to an external modulator 505 such as an electro-optic, acousto-optic, electro-absorption, or other modulator implemented in a bulk material or a waveguide configuration. Such an external optical modulator is situated outside of a laser cavity, but can be integrated on a common substrate with a laser diode. Generally, laser gain modulation can introduce additional (unwanted) laser wavelength changes that are avoided with external modulation.

The example of FIG. 5 has the following effects in addition to the same effects as the effects of the examples of FIGS. 3 and 4. Since the LR laser output beam (measurement beam) and the auxiliary measurement beam (auxiliary beam) are supplied from a common irradiation source, the configuration can be simplified. As a result, it is possible to suppress degradation of measurement accuracy due to, for example, manufacturing errors. Further, the light generated by irradiating the target with the LR laser measurement beam and the light generated by irradiating the target with the auxiliary beam are received by the common light receiver 516, the configuration can be simplified. As a result, it is possible to suppress degradation of measurement accuracy due to, for example, manufacturing errors. Example 6

In other implementations, two or more laser diodes or other sources and corresponding detectors are used for LR measurement and focus measurements, respectively. The sources can produce beams that differ in wavelength or polarization, and can have the same or different modulations that are independently selected. A focus laser can be operated as a pulsed laser or can be amplitude and/or frequency modulated and pulse timing or amplitude and/or frequency modulation in a beam portion returned from a target used to adjust focus. LR measurements can use the same or other approaches such as swept frequency heterodyne measurements. Of course, as discussed above, a single LR laser can be used for LR and focus measurements.

Example 7

Referring to FIG. 6, a representative method 600 includes directing an auxiliary focus beam to a target at 602, and establishing a distance estimate for one, some, or all target locations of interest based on a returned portion of the auxiliary focus beam at 604. At 606, a focus of an LR beam is adjusted, and at 608, an LR measurement of some or all target locations is obtained. In some alternatives, two or more images of the target are used to estimate focus.

Note that 604 is not essential in the example of FIG 6. The relationship (model) between information obtained by receiving the light generated by irradiating the target with the auxiliary beam and the driving amount of the focus mechanism can be obtained in advance, and the focusing operation 606 may be performed using the relationship (model) and the information obtained by receiving the light.

In addition, a table showing the above relationship can be prepared in advance, and the focusing operation (606) may be performed using the table and the information obtained by receiving the light.

Example 8

Referring to FIG. 7, a focus method 700 includes selecting a scan area at 702. At 704, an auxiliary focus beam is directed to a scan area or two or more images of the scan are obtained.

At 706, distance estimates are obtained for some or all locations in the scan area based on the auxiliary focus beam or the two or more images. At 708, an LR beam is applied with a focus based on the previously determined distance estimate, and at 710, LR-based target

measurements are obtained. At 712, it is determined if additional target areas are to be measured, and if so, processing returns to 702. In some examples, the auxiliary focus beam is scanned over a selected number (one or more) scan lines, and the LR beam is then scanned over the same line or lines (such as a raster scan) with a pre-focus based on the prior scan. The LR beam may require additional focusing but the total range of possible focus settings is reduced, permitting more rapid LR data acquisition. Other pre-scan areas can be selected (or a vector scan can be used), or an entire target area of interest can be investigated to estimate LR focus.

In the example of FIG. 7, the focus estimation at 706 is not required as in the example of FIG. 6. Instead of focus estimation, the driving amount of the focus mechanism can be directly obtained.

Example 9

In some examples, light detection and ranging systems (LIDAR) can be combined with heterodyne or other LR for use in beam focus. The LIDAR can provide an approximate distance that is used to establish an initial LR focus to reduce a range of focus needed for LR

measurements. Referring to FIG. 8, an LR system 800 includes an LR such as a heterodyne LR 802 having an objective lens 806 that is coupled to a focus mechanism 804 that is adapted to displace the objective lens 806 along an LR axis 808. A LIDAR 810 is situated to direct an auxiliary beam along the axis 808 or along a displaced or tilted axis such as axis 814. An LR measurement beam and the LIDAR beam can be combined with a beam splitter 816 and directed to a target along the common axis 808 or axes 808, 814, respectively. The LIDAR 810 is coupled to the LR 802 to provide an auxiliary focus signal so that the LR can be approximately focused, typically increasing the speed with which the fine focus needed for LR can be adjusted.

In an example shown in FIG. 9, an LR system 900 includes an LR 902 having an objective lens 906 that is coupled to a focus mechanism 904 that is adapted to displace the objective lens 906 along an LR axis 908. A LIDAR 910 is situated to direct an auxiliary beam to the LR 902 for combination with an LR measurement beam using a beam splitter. The LIDAR beam and the LR measurement beam are directed to a target along the axis 908 with the objective lens 906. The LIDAR 910 is also coupled to the LR 902 to provide an auxiliary focus signal so that the LR can be approximately focused prior to LR measurement.

In some cases, optical path lengths to a target for an auxiliary beam and an LR beam differ due to, for example, placement of beam splitters or how beams are combined. Any difference in auxiliary beam path length can be compensated in focus estimates to provide a more accurate focus for an LR. In FIGS. 8-9, focus is adjusted with translation of an objective lens, but focus can be adjusted in other ways such as translation of a corner cube as illustrated above. Example 10

Referring to FIG. 10, a measurement system 1000 comprises a fringe projector 1002 situated to direct a patterned beam to a target along an axis 1004. In FIG. 10, an LR 1006 directs a measurement beam from a laser diode 1007 along an axis 1008 and an image sensor 1010 is situated to produce an image of the projected fringes along the axis 1008. A beam splitter 1020 is situated to separate the LR measurement beam and radiation associated with fringe imaging. The fringe image is used by a processor 130 to estimate distance and initiate a focus adjustment.

Example 11

Referring to FIG. 11, a measurement system 1100 comprises a fringe projector 1102 is coupled to a first beam splitter 1104 and a second beam splitter 1106 to direct a patterned beam to a target along an axis 1108. An LR 1120 directs a measurement beam along the axis 1108 via the second beam splitter 1106. An image sensor 1130 is situated to receive radiation associated with the fringe pattern from the first beam splitter 1104, and produce an image of the projected fringe pattern. Based on the fringe pattern, LR focus can be adjusted. In still other examples, the projected fringes are imaged and/or projected using an LR objective lens 1122.

Example 12

The methods and apparatus disclosed above can be used in a variety of manufacturing methods and systems. FIG. 12 is a flowchart showing a representative manufacture method 1200 that can incorporate manufacturing systems such as illustrated in FIG. 14. At 1202, design information is obtained or created corresponding to a shape of a structure to be manufactured.

At 1204, the structure is manufactured or“shaped” based on the design information. At 1206, coordinates, dimensions, or other features of the manufactured structure are measured with a profile measurement system such as the laser radar systems described above to obtain shape information corresponding to the structure as manufactured. At 1208, the manufactured structure is inspected based on a comparison of actual and design dimensions, coordinates, manufacturing tolerance, or other structure parameters. At 1210, if the manufactured structure is determined to be non-defective, the manufactured part is accepted and processing ends at 1214. If the manufacture part is determined to be defective at 1210 by, for example, the manufacture inspector 1432 of the controller 1430 as shown in FIG. 14, then at 1212 it can be determined whether the manufacture part is repairable. If repairable, the manufactured part is reprocess or repaired at 1216, and then measured, inspected, and reevaluated at 1206, 1208, 1210, respectively. If the manufactured part is determined to be unrepairable at 1212, the process ends at 1214.

According to the method of FIG. 12, using a profile measurement system to accurately measure or assess coordinates or other features of a manufactured structure, a manufactured structure can be evaluated to determine if the structure is defective or non-defective. Further, if a manufactured structure is determined to be defective, reprocessing can be initiated if the part is deemed to be repairable based on design and actual structure dimensions and features. By repeating the measurement, inspection, and evaluation processes, defective parts can be reprocessed, and parts that are defective but that are not repairable can be discarded. The particular systems and methods of FIGS. 12 and 14 are exemplary only, and other arrangements can be used. However, in many cases, inclusion of auxiliary focus can produce measurement more rapidly.

Example 13

FIG. 13 illustrates a representative method of tracking a tooling ball that is secured to a substrate or target. One or more tooling balls can be secured to a target to provide reference points for coordinate determinations. Tooling balls generally include a reflective ball-shaped surface in order to provide ample reflection of an interrogation beam in a laser-based

measurement apparatus such as a laser radar.

As shown in FIG. 13, at 1302 a tooling ball location is identified and recorded based on returned portions of a scanned interrogation optical beam. The optical beam can be scanned in a variety of patterns such as circles, spirals, w’s, or zig-zags so as to track a tooling ball. At 1304, the identified location is evaluated to determine a position with respect to a primary scan. The primary scan is adjusted at 1306 so that the tooling ball location is at a preferred location with respect to the primary scan. Typically, the primary scan is adjusted so that the tooling location is approximately centered within a primary scan range. At 1308, a determination is made regarding additional scanning. In some cases, an auxiliary focus system is used to establish an initial focus for scanning an interrogation beam. Example 14

FIG. 14 illustrates a representative manufacturing system 1400 suitable for producing one or more components of a ship, airplane, or part of other systems or apparatus, and for evaluating and reprocessing such manufactured components. The system 1400 typically includes a shape or profile measurement system 1405 such as the laser radar system as discussed above. The manufacturing system 1400 also includes a design system 1410, a shaping system 1420, a controller 1430, and a repair system 1440. The controller 1430 includes coordinate storage 1431 configured to store measured and design coordinates or other characteristics of one or more manufactured structures as designed and/or measured. The coordinate storage 1431 is generally a computer readable medium such as hard disk, random access memory, or other memory device. Typically, the design system 1410, the shaping system 1420, the shape measurement system 1405, and a repair system 1440 communicate via a communication bus 1415 using a network protocol.

The design system 1410 is configured to create design information corresponding to shape, coordinates, dimensions, or other features of a structure to be manufactured, and to communicate the created design information to the shaping system 1420. In addition, the design system 1410 can communicate design information to the coordinate storage 1431 of the controller 1430 for storage. Design information typically includes information indicating the coordinates of some or all features of a structure to be produced.

The shaping system 1420 is configured to produce a structure based on the design information provided by the design system 1410. The shaping processes provided by the shaping system 1420 can include casting, forging, cutting, or other process. The shape measurement system 1405 is configured to measure the coordinates of one or more features of the manufactured structure and communicate the information indicating measured coordinates or other information related to structure shape to the controller 1430.

A manufacture inspector 1432 of the controller 1430 is configured to obtain design information from the coordinate storage 1431, and compare information such as coordinates or other shape information received from the profile measuring apparatus such as described above with design information read out from the coordinate storage 1431. The manufacture inspector 1432 is generally provided as a processor and a series of computer-executable instructions that are stored in a tangible computer readable medium such as random access memory, a flash drive, a hard disk, or other physical devices. Based on the comparison of design and actual structure data, the manufacture inspector 1432 can determine whether or not the manufacture structure is shaped in accordance with the design information, generally based on one or more design tolerances that can also be stored in the coordinate storage 1431. In other words, the manufacture inspector 1432 can determine whether or not the manufactured structure is defective or non-defective. When the structure is not shaped in accordance with the design information (and is defective), then the manufacture inspector 1432 determines whether or not the structure is repairable. If repairable, then the manufacture inspector 1432 can identify defective portions of the manufactured structure, and provide suitable coordinates or other repair data. The manufacture inspector 1432 is configured to produce one or more repair instructions or repair data and forward repair instructions and repair data to the repair system 1440. Such repair data can include locations requiring repair, the extent of re-shaping required, or other repair data. The repair system 1440 is configured to process defective portions of the manufactured structure based on the repair data. Use of auxiliary focus methods and apparatus permit more rapid detection of locations in need of repair.

Example 15

FIG. 15 shows a laser radar system 1500 that can be used with any or all of the disclosed embodiments. As shown in FIG. 15, the laser radar system 1500 includes a pointing laser 1502 that produces a pointing beam in a visible (e.g., red) wavelength range, and a measurement laser 1504 that produces a measurement beam in a different (e.g., infrared or IR) wavelength range, and directs (transmits) the pointing and measurement beams to an output 1520 of the laser radar system 1500. The pointing beam is used to identify a point on a target 1506 at which the measurement beam is directed. The pointing beam laser source and the measurement beam laser source are generally different. A control unit 1508 can control the laser radar system 1500. In this embodiment, the laser radar system 1500 includes a control unit, but in other examples, a control unit can be provided separately and coupled to the laser radar system 1500.

The measurement beam may pass through a beam splitter 1510 which directs the measurement beam (and the pointing beam) along a measurement path 1512 to the target 1506.

A portion of the measurement beam is directed by the beam splitter 1502 through a free space or fiber optic optical path so that a portion of the measurement beam is processed as described in U.S. Pat. Nos. 4,733,609, 4,824,251, 4,830,486, 4,969,736, 5,114,226, 7,139,446, 7,925,134, and Japanese Patent No. 2,664,399. The measurement beam portion that is directed along the measurement path 1512 is reflected from the target 1506 and a portion of the reflected or scattered measurement beam is received back at the laser radar system 1500, where it is directed to a detector 1513 by a beam splitter 1514. This beam portion is detected and processed to provide information about the target 1506. The detection and processing of the reflected or scattered radiation is provided in a base of the laser radar system 1500, and processing can be performed as described in U.S. Pat. Nos. 4,733,609, 4,824,251, 4,830,486, 4,969,736, 5,114,226, 7,139,446, 7,925,134, and Japanese Patent No. 2,664,399, which are incorporated herein by reference. Briefly, optical heterodyne detection provides a source light beam which is directed to a target, and a portion is reflected or scattered from the target and returned. The returned light beam is then mixed with a local oscillator light beam on a photodetector to provide optical interference signals which may be processed to provide detailed information about the target.

As shown in FIG. 16, a laser radar assembly 1600 incudes a scan assembly 1604 in which an objective lens 1606 directs a measurement beam (and a pointing beam) and an auxiliary beam to a target. A rotary stage 1608 permits rotation about an azimuthal axis 1610 and a rotational actuator 1612 permits rotation about an elevation axis 1614. One or more electrical and/or optical cables 1616 couples electrical and optical signals to and from a base 1620 that contains electronics 1622 (such as photodetector amplifiers, scan controllers, laser drivers) and optical components 1624 (such as fiber components, laser diodes, detectors). If image based auxiliary focusing is intended, one or more image sensors and associated optics such as camera 1630 can be secured to the scanning assembly 1604.

In the above embodiments, measurements are carried out by a laser radar by directing a measurement beam to a target surface. In other examples, a laser based tool such a laser radar or laser tracker can direct one or more beams to suitable targets such as mirrors, corner cubes, tooling balls, or other reflectors.

Example 16

Referring to FIG. 17, a target area 1700 is scanned as defined by a raster pattern 1702 that includes representative scan lines 1704, 1706. An auxiliary beam is directed to an area 1709 to scan along the scan line 1706 as shown by arrow 1708. With such a scan, initial focal distances for a subsequent measurement beam scan can be obtained. A measurement beam is directed to an area 1711 that is scanned along the scan line 1704 as shown by arrow 1710. Thus, each scan line is scanned by the auxiliary beam to provide a focus estimate prior to scanning with a measurement beam. The auxiliary scan can be one, two, or more scan lines ahead of the measurement beam. Alternatively, the auxiliary beam can be scanned along the scan line 1704 just in advance of the measurement beam scan as indicated by arrow 1718. In some examples, initial focus estimates for the entire target area 1700 are obtained prior to measurement beam scanning. Such pre-scan approaches can also be used with other scan patterns such as arbitrary scans, vector scanning, or“W” shaped scans. In systems using target area images to establish an initial focus as a function of location, some or all image portions can be obtained or processed in advance of measurement beam scanning.

Example 17

A representative system 1800 for scanning an auxiliary beam and a measurement beam is illustrated in FIG. 18. An objective lens 1802 receives the auxiliary beam and the measurement beam and directs the beams at different angles with respect to an axis 1803. A scan mirror 1808 that is coupled to a rotary stage 1810 receives the beams and directs the beams to a target. In the example of FIG. 18, the beams can be co-planar but need not be. In other examples, the measurement and auxiliary beams are directed along the same or parallel axes to a target.

In view of the many possible embodiments to which the principles of the disclosure may be applied, it should be recognized that the illustrated embodiments are only preferred examples and should not be taken as limiting the scope of the disclosure. I claim all that comes within the scope and spirit of the appended claims.

Claims

I claim:

1. A distance measurement apparatus which irradiates a target with a first measurement beam through a measurement optical system, receives light from the target irradiated with the first measurement beam, and measures a distance of the target in a direction along the optical axis of the measurement optical system, the apparatus comprising:

an irradiation source configured to emit a second measurement beam which is different from the first measurement beam, the second measurement beam being directed to the target via the measurement optical system;

a receiver configured to receive light from the target generated by irradiating the target with the second measurement beam; and

a controller configured to control a focusing optical system of the measurement optical system so as to focus the first measurement beam on the target.

2. The distance measurement apparatus of claim 1, wherein the irradiation source emits a pulsed light as the second measurement beam.

3. The distance measurement apparatus of claim 2, wherein the controller estimates the distance of the target based on a time of flight of the second measurement beam.

4. The distance measurement apparatus of any one of claims 1 to 3, wherein the irradiation source emits the first measurement beam and the second measurement beam.

5. The distance measurement apparatus of claim 4, wherein the first and second measurement beams have different frequency modulations.

6. The distance measurement apparatus of claim 5, wherein the second

measurement beam includes at least a pulsed light portion.

7. The distance measurement apparatus of any one of claims 4 to 6, wherein the first and second measurement beams have different wavelengths.

8. The distance measurement apparatus of any one of claims 4 to 7, wherein the first and second measurement beams have different polarizations.

9. The distance measurement apparatus of any one of claims 4 to 8, wherein the first measurement beam is directed to the target via the measurement optical system.

10. The distance measurement apparatus of any one of claims 1 to 9, wherein the receiver receives light from the target generated by irradiating the target with the first measurement beam.

11. The distance measurement apparatus of any one of claims 1 to 10, wherein the controller is configured to

estimate the distance of the target based on an output from the receiver; and

control the focusing optical system based on the estimated distance.

12. The distance measurement apparatus of claim 11, wherein the controller is configured to control the irradiation source so as to irradiate the first measurement beam from the irradiation source after the first measurement beam is focused on the target.

13. The distance measurement apparatus of claim 11, wherein the controller is configured to control the irradiation source so as to direct the first measurement beam from the irradiation source to the target after the focusing optical system is controlled based on the estimated distance.

14. A laser radar system, comprising:

an auxiliary focus system situated to estimate a distance to at least a portion of a target; and

a focus mechanism situated to adjust a focus of a measurement beam at the target in response to the distance estimate.

15. The optical measurement system of claim 14, wherein the auxiliary focus system includes an auxiliary laser situated to direct an auxiliary beam to the portion of the target, and the distance is estimated based on a portion of the auxiliary beam returned from the target.

16. The optical measurement system of claim 15, wherein the auxiliary focus system includes an auxiliary detector situated to receive the portion of the auxiliary beam returned from the target.

17. The optical measurement system of any of claims 14 to 16, wherein the auxiliary focus system includes a modulator that applies an amplitude modulation, a frequency modulation, a phase modulation, a pulse modulation, or any combination thereof to the auxiliary beam, and the distance estimate is based on a detected modulation.

18. The optical measurement system of claim 14, further comprising a measurement laser situated to direct a measurement beam to the portion of the target, wherein the auxiliary focus system includes an auxiliary laser situated to direct an auxiliary beam to the portion of the target, and the estimated distance is based on a portion of the auxiliary beam returned to the target.

19. The optical measurement system of claim 14, further comprising a measurement laser situated to produce and direct a measurement beam and an auxiliary beam to the portion of the target.

20. The optical measurement system of any of claims 14 to 19, further comprising a focus element coupled to the focus mechanism so as to be translated by the focus mechanism, wherein the focus element comprises one or more of a lens, a prism, or a mirror.

21. The optical measurement system of any of claims 14 to 20, wherein the measurement laser and the auxiliary laser emit respective beams at different wavelengths.

22. The optical measurement system of any of claims 14 to 21, wherein the auxiliary focus system includes a fringe projector situated to project a fringe pattern on at least the portion of the target, and the focus mechanism is adjustable in response to a detected fringe pattern.

23. The optical measurement system of any of claims 14 to 22, further comprising: an objective lens situated to direct the measurement beam to the target; and an image sensor situated to image the projected fringe pattern through the objective lens or along the axis of the objective lens.

24. The optical measurement system of any of claims 14 to 23, further comprising a beam scanner situated to scan the auxiliary beam over the target area prior to the measurement beam.

25. The optical measurement system of any of claims 14 to 24, wherein the beam scanner is configured to scan the auxiliary beam at least one scan line prior to the measurement beam.

26. The optical measurement system of any of claims 14 to 25, wherein the auxiliary focus system includes an image sensor situated to produce at least two images of the target area and a processor coupled to receive the at least two images and establish at least one distance estimate based on the at least two images.

27. A method, comprising:

obtaining an initial distance estimate associated with at least one target area;

based on the initial distance estimate, adjusting a focus element associated with a measurement beam; and

directing an initially focused measurement beam to the at least one target area based on the adjustment of the focus element and determining a final focus of the measurement beam; and obtaining a target surface profile based on a returned portion of a finally focused measurement beam.

28. The method of claim 27, wherein the initial distance is obtained by directing an auxiliary beam to the at least one target area, and detecting a time-of-flight of the auxiliary beam to the at least one target area.

29. The method of any of claims 27 to 28, wherein the initial distance is obtained by directing an auxiliary beam to the at least one target area, and detecting a time-of-flight of the auxiliary beam to the at least one target area, wherein the auxiliary beam is a portion of the measurement beam.

30. The method of any of claims 27 to 29, wherein the initial distance is obtained by directing an auxiliary beam to the at least one target area, and detecting a modulation of a detected portion of the auxiliary beam received from the at least one the at least one target area.

31. The method of any of claims 27 to 30, wherein the modulation of the detected portion of the auxiliary beam is an electrical phase modulation, amplitude modulation, frequency modulation, or a combination thereof.

32. The method of any of claims 27 to 31, wherein the final focus of the

measurement beam is obtained based on a detected portion of the measurement beam returned from the target.

33. The method of any of claims 27 to 32, wherein the final focus of the

measurement beam is obtained based on an optical frequency modulation of a detected portion of the measurement beam returned from the target.

34. The method of any of claims 27 to 33, wherein the initial distance is obtained by projecting a fringe pattern on the at least one target area, and detecting at least a portion of the projected fringe pattern.

35. The method of any of claims 27 to 34, wherein the initial distance is obtained by obtaining at least one image that includes the target area, and processing the at least one image to obtain the initial distance.