JP2009025119A - Profile measuring apparatus and operating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a profile measuring apparatus which projects a fringe pattern onto an object (22) and is equipped also with an optical unit for acquiring an image of a distorted fringe pattern and which performs thereby accurate measurement of the object, and an operating method. <P>SOLUTION: The profile measuring apparatus (12) includes a fringe projecting device (32) so constituted as to project the fringe pattern onto the object (22) and the optical unit (34) so constituted as to acquire the image of the distorted fringe pattern modulated by the object (22). Besides, the profile measuring apparatus (12) includes a signal processing unit (60) which is so constituted that it processes the image acquired from the optical unit (34), filters noise from the image and determines real-time estimate values as to parameters relating to manufacture or repair of the object (22). <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates generally to a profile measurement apparatus, and more particularly to a profile measurement apparatus for performing real time measurement of parameters of an object in a machining process. .

  Various types of machining processes are known and used to manufacture and repair parts. For example, a laser consolidation system is used to form functional components that are built layer by layer from computer-aided design (CAD) without the use of any mold or mold. Typically, such systems use a laser beam to melt a controlled amount of the injected powder onto the substrate to deposit the first layer, and then to the previously deposited layer. The next layer is produced sequentially by melting the powder on top. Unfortunately, due to the complexity of the process of such a system, it is very difficult to determine the accumulated layer height and to obtain an instantaneous three-dimensional (3D) measurement of the weld pool volume. Have difficulty.

Certain systems use a two-dimensional (2D) observation system to monitor the weld pool boundary while the system is operating. However, such an observation system provides a rough estimate of the weld area and does not measure the weld pool volume and accumulated layer height. Certain other systems use an off-machine measurement method to measure the 3D volume of the weld pool. Such measurement techniques require stopping the machining process and removing parts from the system to measure the weld pool volume. In addition, certain systems use sensors to measure the accumulated layer height. However, such sensors do not have the required measurement resolution, accuracy, or measurement range and cannot perform reliable measurements.
US Patent Application Publication No. 2005/0103767

  In view of the above, there is a need for a contour measuring device that accurately measures the volume of the 3D weld pool and the accumulated layer height for parts formed by the laser consolidation process. Furthermore, it is possible to provide a contour measuring device that can be used to control process parameters of a machining process and that can measure on-line parameters of an object formed by the machining process. desirable.

  Briefly, according to one embodiment, a contour measuring device is provided. The contour measuring apparatus includes a fringe projection device configured to project a fringe pattern onto an object, and an optical unit configured to acquire an image of a distortion fringe pattern modulated by the object. Including. The contour measurement device is also configured to process the acquired image from the optical unit, filter noise from the image, and determine real-time estimates for parameters associated with the manufacture or repair of the object. Including a signal processing unit.

  In another embodiment, a manufacturing assembly is provided. The manufacturing assembly has a process parameter and is configured to manufacture or repair an object from a machining system configured to manufacture or repair the object and a single image generated by the contour measuring device. And a contour measuring device configured to perform real-time estimation of parameters associated with. The contour measuring apparatus is a) a fringe projection device configured to project a fringe pattern onto an object, and b) an optical unit configured to acquire an image of a distortion fringe pattern modulated by the object. And c) a signal configured to process the acquired image from the optical unit to filter noise from the image and to determine real-time estimates for parameters associated with the manufacture or repair of the object. Includes processing units. The manufacturing assembly also includes a control system configured to adjust process parameters of the machining system based on the estimated parameters from the contour measurement device.

  In another embodiment, a laser consolidation system is provided. The laser consolidation system includes a laser consolidation nozzle configured to form an object by supplying a powder material into a laser-generating molten pool, and coupled to the laser consolidation nozzle. A fringe projection arm configured to produce a fringe pattern on the upper surface. The laser consolidation system also includes an optical unit configured to acquire an instantaneous image of a distorted fringe pattern corresponding to the object, and is coupled to the optical unit, and the instantaneous image from the optical unit is captured. A signal processing unit configured to process and filter noise from the image and to estimate parameters associated with the manufacture or repair of the object by Fourier transform analysis.

  In another embodiment, a method for controlling a process for manufacturing an object is provided. The method includes projecting a fringe pattern onto an object and obtaining an instantaneous image of a distorted fringe pattern corresponding to the object. The method also processes the acquired image, filters noise from the image, and estimates parameters associated with the manufacture or repair of the object by Fourier transform analysis, and relates to the manufacture or repair of the object. Responsive to the estimated parameters, controlling process parameters for the manufacturing process.

  These and other features, aspects and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings, in which: In the drawings, like parts are designated by like reference numerals throughout the drawings.

  As described in detail below, various embodiments of the present technique function to perform real-time measurements of parameters associated with manufacturing or repair operations of objects by machining processes. Specifically, the method of the present invention uses pattern interval analysis to estimate parameters from a fringe pattern corresponding to an object. Such real time measurement of parameters is further utilized to control process parameters of the machining process. Referring now to FIG. 1, FIG. 1 illustrates a machining system such as a laser consolidation system 10 having a contour measuring device 12 coupled to a laser consolidation nozzle 14. The laser consolidation nozzle 14 includes a laser source 16 that is configured to generate a molten pool 17 on a substrate 18. In addition, the laser consolidation system 10 includes a nozzle 20 that is configured to form the object 22 by supplying a powder material 24 to the laser produced molten pool 17. Specifically, the laser consolidation system 10 uses a laser beam to melt a controlled amount of powder 24 injected onto the substrate 18 to deposit a first layer 26, and then The next layer (not shown) is sequentially formed by melting the powder 24 on the previously deposited layer to form the object 22.

  In the illustrated embodiment, the contour measurement device 12 is coupled to or physically attached to the laser consolidation nozzle 14 and is configured to determine parameters related to the manufacture or repair of the object 22. Specifically, the contour measurement device 12 is configured to determine parameters associated with the weld pool 17 that can be further utilized for process control of the machining process. Examples of such parameters include the molten pool 17 volume, the accumulated layer 26 height, the accumulated layer 26 thickness, and the like. As described in detail below, the contour measurement device 12 uses a contour measurement method, such as Fourier transform analysis, to measure such parameters without interfering with the manufacturing or repair process.

  FIG. 2 is a schematic diagram illustrating an exemplary configuration 30 of the laser consolidation nozzle 14 of FIG. In the illustrated embodiment, the laser consolidation nozzle 14 includes two arms 32 and 34 having optical components for fringe projection and image acquisition from the object 22 (see FIG. 1). Two arms 32 and 34 are located on either side of the high processing laser 16. In the illustrated embodiment, the arm 32 is configured to project a fringe pattern onto the object 22 and the arm 34 is configured to acquire an image of the distorted fringe pattern from the object 22. As will be appreciated by those skilled in the art, different types of patterns can be projected onto the object 22 via the arm 32. For example, in one embodiment, the fringe pattern includes a linear pattern. In one exemplary embodiment, the fringe projection arm 32 has a substantially large cross section to cover the targeted area, whereas the laser 16 provides a high power density to melt the powder. In order to converge to one point on the object 22. The optical components of the two arms 32 and 34 for fringe projection and image acquisition are described in detail below.

  FIG. 3 is a schematic diagram illustrating an exemplary configuration 40 of the contour measuring device 12 of FIG. The contour measurement device 40 includes a fringe projection device 42 configured to project a fringe pattern onto an object 44 being formed or repaired via a machining system. The fringe projection device 42 projects a continuous sinusoidal fringe pattern on the surface of the object. In one embodiment, the fringe projection device 42 projects the fringe pattern via a digital projector, such as a liquid crystal display (LCD), digital micromirror device (DMD) or liquid crystal on silicon (LCOS) projector. To do. In an alternative embodiment, the fringe projection device 42 projects the fringe pattern by a combination of a light source such as a laser, light emitting diode (LED) or lamp, and diffractive components such as gratings and holographic components. In certain other embodiments, the fringe projection device 42 projects the fringe pattern with an optical interferometer layout.

  In the illustrated embodiment, fringe projection device 42 includes a light source, such as a lamp 46 or LED 48, and an optical head 50 coupled to the light source via optical fibers 52 to project light onto an object 44. In addition, the contour measuring device 40 includes an optical unit 54 configured to acquire an image of a distorted fringe pattern modulated by the object 44. In this exemplary embodiment, the optical unit 54 includes a wide-pass filter 56 and a camera 58 for acquiring a fringe pattern image, which is further fed to the signal processing unit 60 via a cable 62. Is transmitted. In certain embodiments, the optical unit 54 includes a plurality of lenses configured to acquire an image of a distorted fringe pattern. In one embodiment, the optical unit 54 includes a borescope.

  The signal processing unit 60 is configured to process the acquired image from the optical unit 54, filter noise from the acquired image, and determine real-time estimates for parameters associated with the manufacture or repair of the object. Has been. Examples of such parameters include molten pool volume, accumulated layer height, accumulated layer thickness, and the like. It should be noted here that the signal processing unit 60 can be a general purpose computer with appropriate programming to estimate parameters and facilitate control of the process based on the estimated parameters. In certain embodiments, the signal processing unit 60 may include a microcomputer. In one exemplary embodiment, the contour measurement device 40 uses computer numerical control (CNC) to estimate the formed height of the object 44, thereby eliminating the need to add a height sensor to the system 40. Exclude. In operation, the signal processing unit 60 filters noise from the image acquired by the optical unit 54 using pattern interval analysis. In this exemplary embodiment, pattern spacing analysis includes Fourier transform analysis. However, other types of pattern interval analysis can be envisaged. More specifically, the signal processing unit 60 extracts a phase map of the distortion fringe pattern and estimates parameters from this phase map. The point which extracts a phase map from a fringe pattern using a Fourier transform and estimates parameters from the phase map will be described below.

  In this exemplary embodiment, the fringe pattern image acquired by the optical unit 54 is represented by the following equation:

I _k (i, j) = I ₀ (i, j) [1 + γ (i, j) cos (φ (i, j) + δ _k )],
k = 1,2,3, ... K (1)
here,
k is the index number of the image used in the phase measurement method,
I is the intensity at pixel (i, j)
γ is a fringe modulation degree representing image contrast,
δ _k is the initial phase for each individual image k;
K is the total number of images.

  For the image represented by equation (1),

で表されるような２次元フーリエ変換を得ることができる。

A two-dimensional Fourier transform represented by

Furthermore, after applying the bandpass filter F (u, v), only C (u, v) remains, which is expressed by the following equation C (u, v) = M (u, v) F (u, v) ( 3)
Represented by

  After the inverse Fourier transform, c (i, j) can be obtained as follows.

ここで、Ｉ及びＪはピクセル・インデックスのディメンジョンである。

Here, I and J are pixel index dimensions.

Further, the phase value at each pixel (i, j) is expressed by the following equation: φ (i, j) = tan ⁻¹ [I _m c (i, j) / R _e c (i, j)] (5)
Can be calculated with Here, I _m and R _e represent the imaginary part and the real part of the complex number c (i, j).

Further, the contour of the weld pool is obtained from the phase map, and the following formula (x, y, z) = fx _{, y, z} (i, j, φ (i, j)) (6)
It is represented by

  Accordingly, the weld pool contour, including parameters associated with the weld pool, can be determined from a single instantaneous image via Fourier transform analysis as previously described.

  In certain embodiments, the signal processing unit 60 is configured to divide the instantaneous image from the optical unit 54 into a plurality of images, and the pattern of each image is shifted relative to the other images. Is done. Furthermore, the signal processing unit 60 is configured to create a phase map from the plurality of images in order to estimate the parameters. It should be noted here that the combination of light fringe projection and Fourier transform makes it relatively easy to filter to remove noise such as that generated from powder and background illumination. The phase information generated from the fringe pattern has substantially high resolution and accuracy. Moreover, the Fourier transform contour measurement method allows the creation of a phase map from a single image, resulting in relatively little time for image processing and estimation of weld pool parameters.

  Estimated parameters associated with the manufacture or repair of the object 44 can be utilized for process control of a machining system, such as the laser consolidation system 10 described with reference to FIG. Specifically, the process parameters of the laser consolidation system 10 can be adjusted in response to estimated parameters associated with the manufacture or repair of the object 44. Exemplary process parameters include laser powder, powder flow rate, focal position, laser translation speed, slot dimensions, and combinations thereof. In certain embodiments, a control system (not shown) can be coupled to the machining system 10 to achieve closed loop control of the system 10 based on the estimated parameters. Advantageously, estimation of the phase map from a single instantaneous image by Fourier transform contour measurement allows immediate process control based on the estimated parameters.

  Generation of the structured light pattern in the contour measuring apparatus 40 described above can be achieved through a plurality of configurations as described below with reference to FIGS. Specifically, such an exemplary configuration is used for a laser consolidation nozzle 30 (see FIG. 2) for generating a structured light pattern on an object 22 (see FIG. 2). be able to.

  FIG. 4 is a schematic diagram illustrating an exemplary configuration 70 for generating a structured light pattern in the contour measurement device 40 of FIG. In the illustrated embodiment, a laser 72 is projected to form a spot on the surface of the object 74 to be measured. In addition, an imaging lens 76 disposed at a given angle with respect to the laser beam 72 forms an image or image of the laser spot, which is acquired by the camera 78. Due to the change 80 (D) of the surface height of the object 74, the spot to be imaged is shifted laterally on this image plane by a distance (d) 82. This distance is used to estimate the surface height change 80 by the triangle formed by the laser 72, laser spot and camera 78.

  FIG. 5 is a schematic diagram illustrating another exemplary configuration 100 for generating a structured light pattern in the contour measurement device 40 of FIG. As previously described with respect to FIG. 4, this exemplary configuration 100 includes a laser 72, an imaging lens 76 and a camera 78. Further, in the illustrated embodiment, the fringe pattern is projected by the laser 72 and the diffractive component 102. The diffractive component includes, for example, a grating and a holographic component.

  As previously mentioned, the fringe projection device 42 (see FIG. 3) of the contour measuring device 40 can project a fringe pattern via an optical interferometer layout that projects the fringes. 6-9 illustrate exemplary system configurations for optical interferometer layouts for projecting fringe patterns.

  FIG. 6 is a schematic diagram illustrating an exemplary configuration 120 of a full field interferometer for generating a fringe pattern in the contour measurement apparatus 40 of FIG. In the illustrated embodiment, the interferometer includes a Michelson interferometer. In operation, a beam emitted from a light source such as a laser 122 with a beam expander 124 is split by a beam splitter 126 into two beams of approximately equal intensity. One of these beams is directed to the reference mirror 128 and the other beam is directed to the object surface 130. Furthermore, the light generated by the reflection of these two beams is made to interfere. When observed from an observation window such as the camera 132, interference occurs between the image of the mirror 128 and the image of the object surface 130. Since the light waves reflected by the object surface 130 and the mirror 128 are caused by splitting the beams emitted by the same light source 122, these waves are mutually coherent, so that the two-beam interference pattern is Generated. Further, interference phase recovery can be performed by phase shift due to phase stepping of the piezoelectric transducer (PZT) 134. However, other known techniques can be used to create the phase map.

  FIG. 7 is a schematic diagram illustrating another exemplary configuration 150 of a full field interferometer for generating a fringe pattern in the contour measurement apparatus 40 of FIG. In this exemplary embodiment, interferometer 150 includes a digital holographic interferometer that generates a fringe pattern by interference between a wave reflected or transmitted from an object to be imaged and a reference wave. Similar to the configuration shown in FIG. 6, the digital holographic interferometer 150 includes a light source 122 with a beam expander 124 to generate a fringe pattern on the object 130. In addition, interferometer 150 includes mirrors 152 and 154 and beam splitters 156 and 158 to generate an object beam and a reference beam that are combined to generate a fringe pattern.

  FIG. 8 is a schematic diagram illustrating another exemplary configuration 170 of a full field interferometer for generating a fringe pattern in the contour measurement apparatus 40 of FIG. In the illustrated embodiment, interferometer 170 includes a shearing interferometer. The shearing interferometer 170 includes a light source 122 with a beam expander 124 to generate a fringe pattern on the object 130. Further, the shearing interferometer 170 includes a shearing plate 172. The wavefront from the object 130 is incident on the shearing plate at an angle of about 45 degrees, and the reflected wavefront from the shearing plate 172 is sheared laterally by the finite thickness of the plate. In addition, fringe patterns are generated as a result of interference of the reflected wave fronts.

  As will be appreciated by those skilled in the art, depending on the desired resolution in the application, any of the techniques described above can be used to generate a fringe pattern on the object 44 by the fringe projection device 42 of FIG. . In addition, an instantaneous image of a distorted fringe pattern corresponding to the object 44 is acquired by the optical unit 54 and the image is processed by the signal processing unit 60 to estimate parameters related to the manufacture or repair of the object 44. .

  FIG. 9 is a schematic diagram illustrating another exemplary configuration 190 of the contour measuring device 12 of FIG. The contour measuring device 190 includes a fringe projection device 42 configured to project a fringe pattern onto the object 44. In the illustrated embodiment, the fringe projection device 42 includes a light source 192 coupled to a grating 194 and a lens 196 via optical fibers 198. In one exemplary embodiment, the grating 194 has a 250 PLI grating and the lens 196 has a biconvex lens. Further, the contour measuring device 190 includes an optical unit 54 for acquiring an image of a distorted fringe pattern modulated by the object 44. In the exemplary embodiment, optical unit 54 includes borescope 200 and camera 202, which are coupled to signal processing unit 60 via cable 62. As previously mentioned, the acquired image from the optical unit 54 is processed by the signal processing unit 60. The signal processing unit 60 extracts a phase map of the instantaneous image and estimates parameters related to the machining operation of the object 44 without interfering with the machining process. In certain embodiments, typical frame rates and processing allow the system to be updated approximately 10 times per second, which is much faster for feedback and control operations. Furthermore, a dedicated image processing device optimized for this application along with a high frame rate camera can be updated almost 100 times per second.

  Various aspects of the method described above are utilized for different machining applications. The illustrated approach can be used to make real-time measurements of parameters associated with manufacturing or repair operations of objects by machining processes. The approach can also be used for closed-loop control of the machining process based on parameters estimated to achieve the desired output. As stated previously, more generally, the method described herein uses a Fourier transform contour measurement method to estimate parameters from a single instantaneous image by filtering noise from the system. Furthermore, a particular advantage of this approach is to provide a contour measuring device that has good resolution and accuracy, is cost effective and can be used for a wide range of machining applications.

  While only certain specific features have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. Accordingly, it is to be understood that the claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

1 is a schematic diagram illustrating a laser consolidation system having a contour measurement device in accordance with various aspects of the present technique. 2 is a schematic diagram illustrating an exemplary configuration 30 of the laser consolidation nozzle 14 of FIG. 1 with a contour measurement device 12 according to various aspects of the present technique. FIG. 3 is a schematic diagram illustrating an exemplary configuration of the contour measurement apparatus of FIG. 2 in accordance with various aspects of the present technique. 4 is a schematic diagram illustrating an exemplary configuration for generating a structured light pattern in the contour measurement apparatus of FIG. 3 in accordance with various aspects of the present technique. FIG. 4 is a schematic diagram illustrating another exemplary configuration for generating a structured light pattern in the contour measurement apparatus of FIG. 3 in accordance with various aspects of the present technique. FIG. 4 is a schematic diagram illustrating an exemplary configuration of a full field interferometer for generating a fringe pattern in the contour measurement apparatus of FIG. 3 in accordance with various aspects of the present technique. 4 is a schematic diagram illustrating another exemplary configuration of a full field interferometer for generating a fringe pattern in the contour measurement apparatus of FIG. 3 in accordance with various aspects of the present technique. 4 is a schematic diagram illustrating another exemplary configuration of a full field interferometer for generating a fringe pattern in the contour measurement apparatus of FIG. 3 in accordance with various aspects of the present technique. 2 is a schematic diagram illustrating another exemplary configuration of the contour measurement apparatus of FIG. 1 in accordance with various aspects of the present technique.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Laser consolidating system 12 Contour measuring apparatus 14 Laser consolidating nozzle 16 Laser source 17 Weld pool 18 Substrate 20 Nozzle 22 Object 24 Powder material 26 Accumulated layer 32, 34 Arm 40 Contour measuring apparatus 42 Stripe projection device 44 Object 46 lamp 48 LED
DESCRIPTION OF SYMBOLS 50 Optical head 52 Optical fiber 54 Optical unit 56 Wide-pass filter 58 Camera 60 Signal processing unit 62 Cable 70 Structure for generation of structured light pattern 72 Laser 74 Object 76 Imaging lens 78 Camera 80 Object surface height Change 82 Distance 100 Configuration for generation of structured light pattern 102 Diffractive parts 120 Full field interferometer 122 Laser 124 Beam expander 126 Beam splitter 128 Reference mirror 130 Object surface 132 Camera 134 Piezoelectric transducer 150 Full field interference Total 152, 154 Mirror 156, 158 Beam splitter 170 Shearing interferometer 172 Shearing plate 190 Contour measuring device 192 Light source 194 Grating 196 Lens 198 Optical fiber 200 Bore Co-op 202 camera

Claims (10)

A fringe projection device (32) configured to project a fringe pattern onto the object (22);
An optical unit (34) configured to acquire an image of a distorted fringe pattern modulated by the object (22);
Configured to process the acquired image from the optical unit (34), filter noise from the image, and determine real-time estimates for parameters associated with the manufacture or repair of the object (22); A signal processing unit (60),
A contour measuring device (12) comprising: The contour measuring device (12) according to claim 1, wherein the fringe projection device (32) generates a fringe pattern via a grating (194), an interferometer (120), or a digital fringe projection device. The contour measuring device (12) according to claim 1, wherein the signal processing unit (60) uses pattern interval analysis to filter noise from images acquired from the optical unit (34). The contour measuring device (12) according to claim 3, wherein the pattern interval analysis includes Fourier transform analysis. A machining system (10) having process parameters and configured to manufacture or repair the object (22);
A contour measuring device (12) configured to perform real-time estimation of parameters related to manufacture or repair of an object (22) from a single image generated by the contour measuring device (12). And
A) a fringe projection device (32) configured to project a fringe pattern onto the object (22);
(B) an optical unit (34) configured to acquire an image of a distorted fringe pattern modulated by the object (22); and c) processing the acquired image from the optical unit (34); A contour measuring device (60) comprising a signal processing unit (60) configured to filter noise from the image and to determine real-time estimates for parameters associated with the manufacture or repair of the object (22) 12)
A control system configured to adjust process parameters of the machining system (10) based on estimated parameters from the contour measurement device (12);
Manufacturing assembly having. The machining system (10) includes a laser consolidation system, and the process parameters include laser power, or powder flow rate, or focal position, or velocity, or slot size, or a combination thereof. The manufacturing assembly of claim 5. 6. The parameter associated with manufacturing or repairing an object includes a weld pool volume, or an accumulated material layer height, an accumulated material layer thickness, or a combination thereof. Manufacturing assembly. A laser consolidation nozzle (14) configured to form an object (22) by feeding a powder material (24) into a laser produced molten pool (17);
A fringe projection arm (32) coupled to the laser consolidation nozzle (14) and configured to generate a fringe pattern on an upper surface of the object (22);
An optical unit (34) configured to acquire an instantaneous image of a distorted fringe pattern corresponding to the object (22);
Coupled to the optical unit (34), processes instantaneous images from the optical unit (34), filters noise from the images, and produces or repairs the object (22) by Fourier transform analysis. A signal processing unit (60) configured to estimate associated parameters;
A laser consolidation system (10). A method for controlling a process for manufacturing an object comprising:
Projecting a fringe pattern on the object;
Acquiring an instantaneous image of a distorted fringe pattern corresponding to the object;
Processing the acquired image, filtering noise and estimating parameters associated with the manufacture or repair of the object by Fourier transform analysis;
Responsive to the estimated parameters associated with the manufacture or repair of the object, controlling process parameters for the manufacturing process;
Having a method. A method for estimating parameters of an object formed by a machining system comprising:
Coupling a contour measuring device to the machining system and performing real-time estimation of parameters related to the manufacture or repair of the object by signal processing of a single image generated by the contour measuring device. And the contour measuring device uses a Fourier transform analysis to estimate the parameters from a single image.

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