Fringe calibration system and method

Abstract

To provide a method for evaluating quality of a component in real time.SOLUTION: A system includes: an additive manufacturing machine having a reference plane and an object plane; at least one camera device for capturing the reference plane; at least one projector device for projecting onto a reference plane; a memory that stores computer-readable instructions; and at least one processor. The at least one processor executes instructions to move the reference plane above or below the highest point of the object plane, and use the at least one camera device and the at least one projector device to move the reference plane downward until entire measurement volume has phase map data, and acquire a digital fringe projection phase map of the reference plane.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT The invention described herein was made with U.S. Government ("Government") support under Contract No. FA864922P0933 awarded by the U.S. Air Force. Accordingly, the Government has certain rights in this invention. Summary of the Invention [Problem to be solved by the invention]

[0002] Additive manufacturing can produce complex, high-performance parts, but determining part quality, fit, and performance is extremely challenging. Assessing part quality through post-mortem inspection is often expensive and time-consuming, making a method for assessing part quality in real time valuable. Post-mortem inspection techniques aimed at finding defects in additive manufacturing are time-consuming, expensive, and inaccurate when inspecting large parts, creating additional challenges for quality assurance.

[0003] Real-time or "in-situ" inspection (e.g., inspection of additively manufactured parts while they are being printed) is more cost-effective, efficient, and accurate than inspection after the part is manufactured. However, some techniques, such as image analysis, temperature monitoring, humidity monitoring, and thermal monitoring, cannot accurately and efficiently determine whether defects are present in real time. Furthermore, these traditional techniques generate vast amounts of data, waste storage space, and result in computational tasks that are very difficult to perform efficiently, wasting processor cycles and time.

[0004] Height mapping techniques such as digital fringe projection, electronic speckle interferometry, phase profilometry, and touch probes can locate defects during the printing process, but establishing a calibration method for good measurement is difficult.

[0005] It is with these problems, among others, in mind that various aspects of the present disclosure have been devised. [Means for solving the problem]

[0006] According to one aspect, a fringe calibration system and method are provided that acquire objective height information using a single frequency, e.g., pitch, sequence of fringe projections. Previously, multi-frequency, e.g., pitch, digital fringe projection sequences were used to acquire height information, resulting in a large number of fringe images that were time-consuming to acquire and difficult to store efficiently. The fringe calibration system calibrates height mapping techniques, and can perform calibration at one of a powder surface, a melt surface, a bond surface, a slurry surface, a base plate, and a calibration plate, among others.

[0007] In one example, a system may include an additive manufacturing machine having a reference surface and an object surface, at least one camera device for capturing the reference surface, at least one projector device for projecting onto the reference surface, a memory storing computer-readable instructions, and at least one processor, wherein the at least one processor may execute instructions to move the reference surface above or below a highest point of the object surface and use the at least one camera device and the at least one projector device to move the reference surface until the entire measurement volume has phase map data and acquire a digital fringe projection phase map of the reference surface.

[0008] In another example, a method may include capturing a reference surface of an additive manufacturing machine with at least one camera device; projecting onto the reference surface of the additive manufacturing machine using at least one projector device; moving, by at least one processor, the reference surface above or below a highest point of an object surface of the additive manufacturing machine; and moving, by the at least one processor, the reference surface using the at least one camera device and the at least one projector device until the entire measurement volume has phase map data, and obtaining a digital fringe projection phase map of the reference surface.

[0009] In another example, a non-transitory computer-readable storage medium may store instructions that, when executed by at least one computing device, cause the computing device to perform operations including capturing a reference surface of an additive manufacturing machine with at least one camera device; projecting onto the reference surface of the additive manufacturing machine using at least one projector device; moving the reference surface above or below the highest point of the object surface of the additive manufacturing machine; and using at least one camera device and at least one projector device, moving the reference surface until the measurement volume has phase map data and obtaining a digital fringe projection phase map of the reference surface.

[0010] These and other aspects, features, and advantages of the present disclosure will become apparent from the following detailed description of the preferred embodiments and aspects, read in conjunction with the following drawings, to which variations and modifications can be made without departing from the spirit and scope of the novel concepts of the present disclosure.

[0011] The accompanying drawings illustrate embodiments and / or aspects of the present disclosure and, together with the written description, serve to explain the principles of the disclosure. Wherever possible, the same reference numerals are used throughout the drawings to refer to the same or like elements of an embodiment. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a block diagram of a fringe calibration system according to an example of the present disclosure. [Figure 2] FIG. 1 is a block diagram of a fringe calibration system according to an example of the present disclosure. [Figure 3] 1 is a flowchart of a process for physical calibration with a fringe calibration system according to an example of the present disclosure. [Figure 4] FIG. 10 illustrates calibration artifacts in an initial pose according to an example of the present disclosure. [Figure 5] 10 is a graph illustrating exemplary poses according to an example of the present disclosure. [Figure 6] 10 is a graph illustrating an example wrapped phase plotted against the nominal height of each pose according to an example of the present disclosure. [Figure 7] 10 is a graph showing ffwd(znom) evaluated at [x,y]=[1000,1000] according to an example of the present disclosure. [Figure 8] 10 is a graph showing frev(φwbiased) evaluated at [x,y]=[1000,1000] according to an example of the present disclosure. [Figure 9] 1 is a flowchart of a process for software calibration by a fringe calibration system according to an example of the present disclosure. [Figure 10] FIG. 1 illustrates an example system for implementing certain aspects of the present technology. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present disclosure is more fully described below with reference to the accompanying drawings. While the following description is exemplary in that it describes certain embodiments (e.g., by use of the terms "preferably," "for example," or "in one embodiment"), such description should not be considered as limiting solely to the embodiments of the present disclosure or as defining the only embodiments of the present disclosure, as the present disclosure encompasses other embodiments not specifically enumerated in this description, including alternatives, modifications, and equivalents within the spirit and scope of the present invention. Furthermore, throughout the description, the use of terms such as "invention," "present invention," "embodiments," and similar terms is used broadly and is not intended to imply that the invention requires or is limited to the particular aspects described or that such description is the only way the invention can be made or used. Furthermore, while the present invention may be described in connection with particular applications, the present invention can be used in a variety of applications not specifically described.

[0014] Described embodiments, and references herein to "one embodiment," "embodiment," "exemplary embodiment," etc., indicate that the described embodiment may include a particular feature, structure, or characteristic. Such phrases do not necessarily refer to the same embodiment. When a particular feature, structure, or characteristic is described in connection with an embodiment, one skilled in the art can implement such feature, structure, or characteristic in connection with other embodiments, whether or not explicitly described.

[0015] In some figures, the same reference numerals may be used for similar elements with similar functions, even in different figures. The described embodiments and their detailed structures and elements are provided merely to facilitate a comprehensive understanding of the present invention. Thus, it is apparent that the present invention can be embodied in various forms, and none of the specific features described herein are essential. Also, well-known functions or structures will not be described in detail as they would obscure the present invention in unnecessary detail. Signal arrows in the figures / drawings should be considered merely illustrative and not limiting, unless otherwise specified. Furthermore, the description should not be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the present invention, since the scope of the present invention is best defined by the appended claims.

[0016] Although terms such as first, second, etc. may be used herein to describe various elements, it will be understood that these elements are not limited by these terms. These terms are used merely to distinguish one element from another. As a purely non-limiting example, a first element could also be termed a second element, and similarly, a second element could also be termed a first element, without departing from the scope of the exemplary embodiments. As used herein, the term "and / or" includes any of the associated listed items and any combination of one or more of the items. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly dictates otherwise. It should also be noted that in some alternative implementations, the functions and / or acts described may occur out of the order depicted in at least one of the figures. As a purely non-limiting example, two figures shown in succession may in fact be executed substantially concurrently or may be executed in reverse order depending on the functions and / or acts described or depicted.

[0017] In particular, conditional language such as "can," "could," "might," or "may," unless otherwise specified or as understood within the context in which it is used, is intended to generally convey that certain embodiments include certain features, elements, and / or steps, while other embodiments do not include certain features, elements, and / or steps. Thus, such conditional language is not generally intended to imply that features, elements, and / or steps are more or less required for one or more embodiments, or that one or more embodiments necessarily include logic for determining whether those features, elements, and / or steps are included in or performed in a particular embodiment, with or without user input or prompts.

[0018] Described herein are fringe calibration systems and methods that use a single frequency, e.g., pitch, sequence of fringe projections to obtain objective height information. Conventionally, multi-frequency, e.g., pitch, sequences of digital fringe projections have been used to obtain height information, resulting in many fringe images that are time-consuming to acquire and difficult to store efficiently.

[0019] Additive manufacturing traditionally uses visual inspection, such as human visual inspection, which involves a person looking through a window in a three-dimensional (3D) printer to look for visual signs of defects that may occur within the printer's powder bed chamber.

[0020] There are several commercially available in-situ monitoring systems. One, the melt pool monitoring system manufactured by EOS, uses a photodiode in the optical path to measure the "temperature" of the melt pool. However, traditional methods generate very large amounts of data (e.g., terabytes of data), making it difficult to extract useful information. The data is not very useful, and the system is limited to use only with EOS 3D printers. Furthermore, it does not work with printers from different makes and models.

[0021] Another monitoring system is the melt pool monitoring system, but this conventional method relies on the accumulation of objects in the printer beamline, which voids the warranty. This modification is also not a suitable solution as it generates a very large amount of data that is too large to process in real time.

[0022] While visual inspection can assess the health of the print process or detect defects, it relies on a human's subjective opinion, can only be applied to the current layer, requires costly labor to observe the build, and may miss defects if a human (e.g., a technician) is not observing the process. Current drawbacks of in-process monitoring melt pool analysis techniques include high financial costs, an inability to provide actionable real-time information, the need for specialized knowledge, the generation of large datasets, non-real-time monitoring, and, in some circumstances, the use of traditional solutions to void printer warranties.

[0023] The fringe calibration system includes a structured light monitoring system for detecting defects in additive manufacturing processes. The system can use structured light monitoring measurements and information to determine the statistical likelihood of a defect occurring. Additive manufacturing (AM) systems, commonly referred to as 3D printers, add layers of build material, which then solidify. As layers are added, defects can occur in the final product.

[0024] The fringe calibration system spatially encodes unique phase values ​​for the unidirectional data of each measurement surface. This can be achieved by projecting a predefined pattern onto the measurement surface, which can be a build plate, powder layer, fused layer, bonded layer, or sintered layer, among others. The phase values ​​encoded on the measurement surface can detect process anomalies during the printing process. Anomalies during the printing process can include and / or be related to recoater cross-sectional information, build surface distortion, plate distortion, build plate flatness, build plate vibration, build plate vertical accuracy, powder coating thickness, powder coating roughness, powder coating streaking, powder coating hopping, powder coating short feed, powder coating clumping, powder coating agglomeration, changes in powder coating after melting or solidification or bonding, non-uniform powder particles, thermal distortion, over-melting, under-melting, component protrusion, absolute layer height from reference, material collapse, support structure distortion, bulk distortion, surface distortion, particle breakage, particle aggregation, particle agglomeration, uneven melting, uneven sintering, laser spacing effects, laser spot size, laser power, binder ballistic effects, binder powder interactions, binder solidification at pile height, or anything else that shifts the encoded spatial phase from a reference plane that can be measured or mathematically determined.

[0025] The features appear in the spatially encoded phase data or can be extracted using matched filters. These features can be extracted using kernel convolution techniques, absolute phase difference measurements, separable convolution, dilated convolution, atlas convolution, deformable convolution, demodulation, Fourier transform, Hilbert transform, Gaussian filtering, flat-box filtering, Sobel filter, Sobel operator, Sobel-Fieldman operator, Prewitt operator, and Laplace operator, among others.

[0026] In addition to generating a spatially phase-encoded surface map, the system can generate a height map of the powder bed chamber that determines the height of each deposited powder layer and / or solidified layer, classify the height map as in-specification or out-of-specification, and provide warnings when height anomalies may exist.

[0027] The system can include hardware devices and at least one computing device operably coupled to many types of 3D printers, such as additive manufacturing printers, to provide real-time measurements of exposed surfaces of parts and raw materials. Height measurements, separate from phase measurements, can be used to detect process anomalies during the printing process. Anomalies during the printing process can include or be related to recoater cross-sectional information, build surface distortion, plate distortion, build plate flatness, build plate vibration, build plate vertical accuracy, powder coating thickness, powder coating roughness, powder coating streaking, powder coating hopping, powder coating short feed, powder coating clumping, powder coating agglomeration, changes in powder coating after melting or solidification or bonding, non-uniform powder particles, thermal distortion, over-melting, under-melting, component protrusion, absolute layer height from reference, material collapse, support structure distortion, bulk distortion, surface distortion, particle splitting, particle clumping, particle agglomeration, uneven melting, uneven sintering, laser spacing effects, laser spot size, laser power, binder ballistic effects, binder powder interactions, binder solidification at pile height, or any other physical phenomenon that shifts the encoded spatial phase from a reference plane that can be measured or mathematically determined.

[0028] These features appear in the height data or can be extracted using matched filters, among others: kernel convolution techniques, absolute height difference measurements, separable convolution, dilated convolution, atlas convolution, deformable convolution, demodulation, Fourier transform, Hilbert transform, Gaussian filtering, flat-box filtering, Sobel operator, Sobel-Fieldman operator, Prewitt operator, or Laplace operator.

[0029] The system can generate a unique spatially encoded phase value for each pixel on the measurement area. Areas of non-uniform phase may contain process anomalies during 3D printing. The system can also generate a height map. The height map of the exposed surface can be used to detect height anomalies (dimples or clamps) in the raw material layer that may contribute to final part failure, as well as newly solidified layers that may contribute to final part defects and / or printer damage.

[0030] The system may include hardware devices and software executed by at least one computing device that can couple to numerous 3D printers, e.g., additive manufacturing printers, to provide real-time measurements of exposed surfaces of parts and raw materials. The system generates spatially encoded phase values ​​for each pixel on the measurement area. The hardware devices may include a structured light system such as a digital fringe projection (DFP). The DFP may include one or more projectors, one or more camera devices, and at least one computing device that timing, triggering, and collecting data to control and perform mathematical operations on images captured by the camera devices. The DFP obtains 3D measurements by projecting a pattern onto the surface of the part or raw material being created or printed, records deformation of the pattern, and spatially encodes phase onto the surface while obtaining a height map representing the 3D measurement surface. The height map can reveal many different types of in-situ defects that could cause overall part failure downstream. In-situ defects include, among others, warpage, over-fusion, under-fusion, thermal distortion, poor fusion bonding, recoater blade hopping, powder streaks, powder pitting, and part protrusions. The system can assess and make decisions about the impact of defects detected in-situ on the quality of the final part.

[0031] Detected defects can be compared to a library of 3D prints where similar defects were identified and led to defects in the final part, allowing for an estimate of the likelihood of the defect occurring in the final part.

[0032] The system may include a DFP monitoring system and can be used for powder bed fusion (PDF), binder jetting (BJ), or selective laser sintering (SLS) polymer additive manufacturing (AM), among others. The system can be used for DFP height measurements and can be used to provide an indication of the uncertainty associated with other types of optical or light-based measurement techniques, such as digital image correlation, contact scanner, and coherent light imaging techniques.

[0033] The system geometrically measures layer height before and after solidification, detecting, among other things, warpage, powder bed defects, poor fusion bonding, and delamination. By projecting a pattern onto the part surface before and after laser irradiation, a 3D height map can be determined based on the pattern deformation. The system determines a modular spatial measurement density, where each pixel represents a height measurement, providing micron-level resolution of height features.

[0034] The system provides actionable information in real time and stores a height map of each layer to detect defects without storing vast amounts of data or requiring robust analysis, thereby saving storage space and increasing computational efficiency. The system can measure a variety of features, including powder bed and fused layer height maps, to provide a real-time estimate of part quality and provide a pass / fail decision.

[0035] The system can be operably coupled to the printer via a mounting mechanism and can determine the accuracy of each measurement point by using a neutral density filter on one or more camera devices and a computing device to filter the image and then create a phase map that can be converted to a topography, and estimate the density of the part based on the phase or topography information, thereby using previous data regarding defects in the final part to estimate the presence of internal defects based on the in-situ topography.

[0036] This system is associated with fringe calibration and can be used to calibrate a fringe projection inspection system. Fringe calibration can include physical steps and processes by at least one computing device to jointly obtain phase and height calibration matrices. As an example, fringe calibration can include physical steps including placing a calibration plate at the height of the surface to be measured; then focusing at least one camera device on the calibration plate; then focusing at least one projector on the calibration plate; placing the calibration plate above or below the print surface; acquiring digital fringe projection phase map measurements; and moving the calibration plate toward the print surface until the complete measurement volume is obtained. Then, performing software calibration on the computing device.

[0037] Fringe calibration improves upon previous solutions by enabling objective height information to be obtained with a single frequency (or pitch) projection sequence. Previously, multi-frequency (or pitch) digital fringe projection sequences were used to obtain objective height information, resulting in a large number of fringe images and slow acquisition times.

[0038] As a result, fringe projection can be used to obtain highly accurate height maps in minimal time, which can be used for inspection of manufacturing processes.

[0039] In one example, a system may include an additive manufacturing machine having a reference surface and an object surface, at least one camera device for capturing the reference surface, at least one projector device for projecting onto the reference surface, a memory storing computer-readable instructions, and at least one processor, wherein the at least one processor may execute instructions to move the reference surface above or below a highest point of the object surface and use the at least one camera device and the at least one projector device to move the reference surface until the entire measurement volume has phase map data and acquire a digital fringe projection phase map of the reference surface.

[0040] FIG. 1 is a block diagram of a fringe calibration system 100 according to an example of the present disclosure. The fringe calibration system 100 is mounted inside and / or outside an additive manufacturing machine chamber 102 as shown in FIG. 1. A computing device is also used to perform fringe calibration. The fringe calibration system 100 may have one or more projector devices 104 and one or more camera devices 106 for capturing images. The one or more projector devices 104 can provide various projections that can be simultaneously overlaid with various fringe wavelengths. The wavelength of the projected light can be changed during or before projection. Each projector device 104 has one or more light sources and is positioned at specific locations inside and outside the additive manufacturing machine chamber 102. Additionally, one or more camera devices 106 are positioned inside and outside the additive manufacturing machine chamber 102. One or more interferometers may also be present. Each camera device 106 may have one or more image sensors for imaging structured light, such as fringes, projected onto the surface of the object to be measured or being measured. The position of the camera device is kept constant across the viewing angle, and the fringe calibration system 100 can trigger the camera image capture to capture fringe images at uniform intervals, eliminating projector draw lines that can otherwise occur out of sync.

[0041] DFP height measurements are performed by projecting a pattern onto a flat reference surface (physical or mathematical), then placing an object in the scene and acquiring information related to how the projected pattern deforms from the object's shape. A phase map can be generated from the calculated deformation of the fringe pattern, which can be converted to a height map through a calibration routine. During in-situ measurements, the reference surface can be a bare base plate or a base plate with a uniform initial powder coating. If the DFP geometry is expected to remain constant, mathematically generating a reference phase map allows for differential height measurements that are independent of the height profile of the reference surface.

[0042] In one example, a reference surface 110, such as a calibration plate, is placed at the height or highest point of the object surface 108. At least one camera device 106 is focused on the reference surface 110. Additionally, at least one projector 104 is focused on the reference surface 110. In one example, the at least one projector device 104 may have a flexible light steering device with brightness and resolution for industrial applications such as additive manufacturing. The at least one camera device 106 may be a BASLER Ace acA4600 GigE camera or another camera device that can be used for industrial applications such as additive manufacturing.

[0043] The reference surface 110 is raised above the initial height of the object surface 108. Digital fringe projection phase map measurements of the reference surface 110 are acquired by a computing device. The reference surface 110 is moved in another direction, such as downward or upward. Digital fringe projection phase map measurements of the calibration plate are acquired as the reference surface 110 is moved until the entire measurement volume has phase measurements. The entire measurement volume may have phase map data. By way of example, the reference surface 110 may be at least one of a powder surface, a melt surface, a bond surface, a slurry surface, a base plate, and a calibration plate, among others. Further by way of example, the object surface 108 may be at least one of a powder surface, a melt surface, a bond surface, a slurry surface, a base plate, and a calibration plate, among others.

[0044] In one example, at least one of focus, aperture, exposure, gain, and brightness is adjusted for the at least one camera device 106 and the at least one projector device 104. When performing fringe calibration with the system 100, this may include first preheating the print volume of the additive manufacturing machine chamber 102 to a particular temperature and pressure before obtaining the measurement volume.

[0045] 2 is another block diagram of a fringe calibration system 100 according to an example of the present disclosure. As shown in FIG. 2, the system 100 may include an additive manufacturing machine chamber 102 and at least one computing device 202. The at least one computing device 202 may be in communication with at least one database 210.

[0046] At least one computing device 202 may be configured to receive data and / or transmit data over communication network 208. Although computing device 202 is shown as a single computing device, it is contemplated that each computing device may include multiple computing devices.

[0047] The communication network 208 can be the Internet, an intranet, or another wired or wireless communication network. For example, the communication network 208 can include a Global System for Mobile Communications (GSM) network, a code division multiple access (CDMA) network, a third generation Generation Partnership Project (GPP) network, an Internet Protocol (IP) network, a wireless application protocol (WAP) network, a Wi-Fi network, a Bluetooth network, a near field communication (NFC) network, a satellite communication network, or an IEEE 802.11 standard network, and variations thereof. Other conventional and / or later-developed wired and wireless networks can also be used.

[0048] Computing device 202 may have a fringe calibration application 206, which may be a component of an application and / or service executable by at least one computing device 202. For example, fringe calibration application 206 may be a single unit of deployable executable code or multiple units of deployable executable code. According to one aspect, fringe calibration application 206 may include a component that may be a web application, a native application, and / or an application (e.g., an app) downloaded from a digital distribution application platform that enables users to browse and download applications developed with a software development kit (SDK), including the APPLE® iOS App Store and GOOGLE PLAY®, among others.

[0049] The fringe calibration system 200 may also include one or more data sources that store and communicate data from at least one database 210. By way of example, the data stored in the at least one database 210 may be fringe projection phase map measurement information, such as measurement volume information including phase map data.

[0050] Computing device 202 may include at least one processor for processing data and memory for storing data. The processor processes communications, constructs communications, retrieves data from memory, and stores data in memory. The processor and memory are hardware. The memory may include computer-readable storage media such as volatile and / or non-volatile memory, e.g., cache, random access memory (RAM), read only memory (ROM), flash memory, or other memory for storing data and / or computer-readable executable instructions. Additionally, computing device 202 further includes at least one communication interface for sending and receiving communications, messages, and / or signals.

[0051] Computing device 202 may be a programmable logic controller, a programmable controller, a laptop computer, a smartphone, a personal digital assistant, a tablet computer, a standard personal computer, or another processing device. Computing device 202 may include a display, such as a computer monitor, for displaying data and / or a graphical user interface. Computing device 202 may also include a Global Positioning System (GPS) hardware device for determining a specific location, one or more cameras or imaging devices for inputting data or interacting with a graphical interface and / or other type of user interface, an input device, such as a keyboard, or a pointing device (e.g., a mouse, trackball, pen, or touchscreen). In an exemplary embodiment, the display and input device may be combined as a touchscreen on a smartphone or tablet computer.

[0052] In one example, the computing device 202 is located on-premise at the location. As another example, the computing device 202 comprises a cloud computing device. In some examples, there may be at least one of a computing device 202 located on-premise and a cloud computing device.

[0053] By way of example, computing device 202 may communicate data in packets, messages, or other communications using common protocols, such as Hypertext Transfer Protocol (HTTP) and / or Hypertext Transfer Protocol Secure (HTTPS). One or more computing devices may communicate based on representational state transfer (REST) ​​and / or Simple Object Access Protocol (SOAP). By way of example, a first computer (e.g., computing device 202) may send a request message that is a REST and / or SOAP request formatted using JavaScript Object Notation (JSON) and / or Extensible Markup Language (XML). In response to the request message, a second computer (e.g., a server computing device) may send a REST and / or SOAP response formatted using JSON and / or XML.

[0054] 3 illustrates an example method 300 for physical calibration by a fringe calibration system 100 according to an example of the present disclosure. Although the example method 300 illustrates a specific order of operations, the order may be changed without departing from the scope of the present disclosure. For example, some of the illustrated operations may be performed in parallel or in a different order without substantially affecting the functionality of the method 300. In other examples, various components of an example device or system implementing the method 300 may perform functions substantially simultaneously or in a specific order.

[0055] According to some examples, the method 300 includes, at block 310, focusing at least one camera device 106 on a reference surface 110 of the additive manufacturing machine. This may include the at least one camera device 106 capturing the reference surface 110. By way of example, the reference surface 110 may be at least one of a powder surface, a melt surface, a bonding surface, a slurry surface, a base plate, and a calibration plate, among others.

[0056] According to some examples, method 300 includes, at block 320, focusing at least one projector device 104 on reference surface 110. This may include projecting onto reference surface 110 using at least one projector device 104. By way of example, at least one of focus, aperture, exposure, gain, and brightness may be adjusted for at least one camera device 106 and at least one projector device 104.

[0057] According to some examples, the method 300 includes moving the reference surface above or below a highest point of the object surface 108 of the additive manufacturing machine at block 330. By way of example, the object surface 108 may be at least one of a powder surface, a melt surface, a bonding surface, a slurry surface, a base plate, and a calibration plate, among others.

[0058] According to some examples, the method 300 includes, at block 340 , determining digital fringe projection phase map measurements of the reference surface 110 .

[0059] According to some examples, the method 300 includes, at block 350, moving the reference surface 110 until the entire measurement volume has phase map data and acquiring a digital fringe projection phase map of the calibration plate.

[0060] According to some examples, the method 300 may include preheating the print volume of the additive manufacturing machine to a predetermined temperature and pressure before obtaining the measurement volume.

[0061] FIG. 4 is a calibration artifact at an initial pose 400 according to an example of the present disclosure.

[0062] FIG. 5 is a graph illustrating an example pose 500 according to an example of the present disclosure.

[0063] FIG. 6 is a graph 600 illustrating an example wrapped phase plotted against the nominal height for each pose according to an example of the present disclosure.

[0064] FIG. 7 shows f evaluated at [x,y]=[1000,1000] according to an example of the present disclosure. fwd (z nom ) is a graph 700 showing

[0065] FIG. 8 shows f evaluated at [x,y]=[1000,1000] according to an example of the present disclosure. rev (φ w 8 is a graph 800 showing the relationship between the saturation and the saturation (biased).

[0066] As an example, the system 100 may generate a phase estimate φ w The estimated height z est It is possible to calibrate the function that maps to

[0067] Calibrate the system and adjust the powder bed height z est There may be several steps to be able to estimate

[0068] As an example, the following assumptions may exist:

[0069] A planar calibration artifact is swept parallel to the z-axis from top to bottom of the measurement volume, and each pose is measured at a nominal height z nom A series of N poses ("pose1.p" ... "poseNp") for which are known are determined.

[0070] The calibration artifact is perpendicular to the z-axis for all pose positions.

[0071] The number of poses, N, is sufficient to characterize the nonlinearity in the optical transfer function. N is at least 2, but typically N is >40, and the Δz between poses is nom The step was 50 μm, which corresponds to a measurement volume range of >2 mm along the z-axis.

[0072] Furthermore, for a given camera pixel, the estimated wrapped phase φ w and height z est The relationship is with the function z est =f(φ w ) can be assumed to be characterized by the function σ. The calibration process therefore aims to optimize the function parameters to fit the observed data.

[0073] As an example, Figure 4 shows the nominal height z nom , which shows calibration artifacts in the initial pose at =0.

[0074] The calibration parameters are defined in an exemplary file config.yaml, which may define reference and object surface information, masking parameters, contrast limits, number of reference measurements, phase and height biases, etc.

[0075] In one example, a folder may have 41 poses corresponding to linearly spaced artifact positions.

[0076] z nom = [0, -50, -100, ..., 2000] μm is illustrated in Figure 5.

[0077] In one example, Figure 5 shows the z function versus pose index. nom 1 shows a plot of

[0078] As an example, consider a single pixel [x,y]=[1000,1000].

[0079] Figure 6 shows the nominal height z for each pose evaluated at [x,y]=[1000,1000]. nom Estimated wrapped phase φ plotted against w An example of this is shown.

[0080] Wrapped phase φ w Note that π can wrap around between the main phase range limits -π rad and +π rad.

[0081] Step 1: The first processing step is to extract the observed wrapped phase value φ w For example, this may involve determining a constant phase bias at each pixel that shifts the observed φ w Formula for value: φ w biased=f fwd (z nom ) The phase bias applied to pixel [x,y]=[1000,1000] can be based on

[0082] φ w biased=φ w -φ bias where φ bias =2.84 rad (see Figure 6). This means that φ w Ensures that the biased value is monotonic across the entire work volume.

[0083] Step 2: For each pixel, we apply a cubic polynomial φ to the observation. w biased=f fwd (z nom ) can be applied.

[0084] For example, [x,y]=[1000,1000], and f fwd The coefficient is

[0085] These are [-0.00238102,-0.01658108,-0.58473124,-0.56542734], which correspond to the cubic, quadratic, linear, and constant terms, respectively.

[0086] As shown in Figure 7, the plot shows the f evaluated at [x,y]=[1000,1000]. fwd (z nom ) is shown.

[0087] Step 3: Forward polynomial f fwd Once you have found this, invert the function to get the cubic polynomial z nom =f rev (φ w biased).

[0088] For example, [x,y]=[1000,1000], and f rev The coefficient is

[0089] These are [-0.02776195,-0.05832995,-1.7752676,-0.98898422], which correspond to the cubic, quadratic, linear, and constant terms, respectively.

[0090] As shown in Figure 8, the graph is f evaluated at [x,y]=[1000,1000]. rev (φ w biased).

[0091] Step 4: Phase bias φ at each pixel w biased and f rev (φ w Once the polynomial coefficients of the biased function are known, the equation z est =f(φ w ) to estimate the wrapped phase φ w from height z est This provides information to estimate

[0092] z est (x,y)=f rev (φ w (x,y)-φ bias (x,y)).

[0093] So, given a pixel at [x,y]=[1000,1000], the calibration coefficients stored are:

[0094] φ bias =2.84rad, f rev () Coefficients = [-0.02776195,-0.05832995,-1.7752676,-0.98898422].

[0095] 9 illustrates an example method 900 for software calibration by the fringe calibration system 100 and fringe calibration application 206 according to an example of the present disclosure. Although the example method 900 illustrates a specific order of operations, the order may be changed without departing from the scope of the present disclosure. For example, some of the illustrated operations may be performed in parallel or in a different order without substantially affecting the functionality of the method 900. In other examples, various components of an example device or system implementing the method 900 may perform functions substantially simultaneously or in a specific order.

[0096] According to some examples, the method 900 includes, at block 910, determining a constant phase bias at each pixel that shifts the observed wrapped phase value around zero. For example, this may involve shifting the observed phase value φ to achieve the pixel's physical location. w For example, this may involve determining a constant phase bias at each pixel in the image that shifts the observed φ w Formula for value: φ w biased=f fwd (z nom ) may be based on

[0097] According to some examples, method 900 includes fitting either a quadratic or cubic polynomial to each pixel at block 920. By way of example, this may include finding a mathematical surface that is consistent with the observed phase or height values.

[0098] According to some examples, the method 900 includes inverting the function to obtain a third-order polynomial at block 930. By way of example, this may be done by inverting the forward polynomial function f fwd Find f fwd Invert the function to find the cubic polynomial z nom =f rev (φ w biased).

[0099] According to some examples, the method 900 includes determining a calibration coefficient at block 940. By way of example, this may include determining a phase bias φ at each pixel within either the two-dimensional area or the three-dimensional volume. w biased and f rev (φ w This may involve determining polynomial coefficients of a z biased function and estimating height values ​​from the estimated phase using the equation developed for each pixel within the measurement area or volume. est =f(φ w ) where z est (x,y)=f rev (φ w (x,y)-φ bias (x,y)).

[0100] According to some examples, the method 900 includes, at block 950, storing the calibration coefficients in storage, such as the database 210. By way of example, this may include storing the phase bias φ at each pixel. w biased and f rev (φ w The method may include storing information related to the polynomial coefficients of the biased function.

[0101] 10 illustrates an example of a computing system 1000, which may be, for example, computing device 202 or any component thereof, where the components of the system communicate with each other using connections 1005. The connections 1005 may be physical connections via a bus or direct connections to a processor 1010, such as in a chipset architecture. The connections 1005 may also be virtual, network, or logical connections.

[0102] In some embodiments, computing system 1000 is a distributed system, and the functions described in this disclosure may be distributed within a data center, multiple data centers, a peer network, etc. In some embodiments, one or more of the system components described represent many such components, each performing some or all of the functions described. In some embodiments, the components may be physical or virtual devices.

[0103] The exemplary system 1000 includes at least one processing unit (CPU or processor) 1010 and connections 1005 coupling various system components to the processor 1010, including system memory 1015 such as read-only memory (ROM) 1020 and random access memory (RAM) 1025. The computing system 1000 may include a cache of high-speed memory 1012 directly connected to the processor 1010, in close proximity to the processor 1010, or integrated as part of the processor 1010.

[0104] Processor 1010 can include any general-purpose processor and hardware or software services, such as services 1032, 1034, and 1036 stored in storage 1030 configured to control processor 1010 as well as special-purpose processors where software instructions are incorporated into the actual processor design. Processor 1010 can essentially be a completely self-contained computing system, including multiple cores or processors, buses, memory controllers, caches, etc. Multi-core processors can be symmetric or asymmetric.

[0105] To enable user interaction, computing system 1000 includes input devices 1045, which can represent any number of input mechanisms, such as a microphone for audio input, a touch-sensitive screen for gesture or graphical input, a keyboard, a mouse, motion input, voice input, etc. Computing system 1000 can also include output devices 1035, which can be one or more of several output mechanisms known to those skilled in the art. In some cases, a multimodal system allows a user to provide multiple types of input / output for communicating with computing system 1000. Computing system 1000 can include a communications interface 1040, which can generally govern and manage user input and system output. There are no constraints on operation with a particular hardware configuration, and therefore the basic features herein can be easily substituted for improved hardware or firmware configurations as they are developed.

[0106] The storage device 1030 may be a non-volatile memory device, such as a magnetic cassette, a flash memory card, a solid-state memory device, a digital versatile disk, a cartridge, a random access memory (RAM), a read-only memory (ROM), and / or some combination of these devices, and may be a hard disk or other type of computer-readable medium capable of storing data that can be accessed by a computer.

[0107] The storage device 1030 may include software services, servers, services, etc., where code defining such software, when executed by the processor 1010, causes the system to perform functions. In some embodiments, hardware services that perform particular functions may include software components stored on computer-readable media in association with the necessary hardware components, such as the processor 1010, connections 1005, output devices 1035, etc., to perform the functions.

[0108] For clarity of explanation, in some cases, the technology may be presented as including individual functional blocks, including functional blocks comprising devices, device components, method steps or routines embodied in software, or a combination of hardware and software.

[0109] Any of the steps, operations, functions, or processes described herein may be performed or implemented with a combination of hardware and software services, or as services alone or in combination with other devices. In some embodiments, a service may be software that resides in memory of one or more servers of a client device and / or content management system and performs one or more functions when a processor executes the software associated with the service. In some embodiments, a service is a program or collection of programs that perform a particular function. In some embodiments, a service may be considered a server. Memory may be a non-transitory computer-readable medium.

[0110] In some embodiments, computer-readable storage devices, media, and memories can include cables or wireless signals, including bitstreams, etc. However, non-transitory computer-readable storage media, when referred to, explicitly excludes media such as energy, carrier signals, electromagnetic waves, and the signals themselves.

[0111] Methods according to the above examples can be implemented using computer-executable instructions stored on or available from a computer-readable medium. Such instructions may include, for example, instructions and data that cause or configure a general-purpose computer, a special-purpose computer, or a special-purpose processing device to perform a particular function or group of functions. Some of the computer resources used may be accessible over a network. The executable computer instructions may be, for example, binaries, instructions in an intermediate format such as assembly language, firmware, or source code. Examples of computer-readable media that may be used to store instructions and information used and / or created during the execution of methods according to the described examples include magnetic or optical disks, solid-state memory devices, flash memory, USB devices with non-volatile memory, network storage devices, etc.

[0112] Devices implementing methods according to these disclosures may comprise hardware, firmware, and / or software and may take any of a variety of form factors. Typical examples of such form factors include servers, laptops, smartphones, small form factor personal computers, personal digital assistants, etc. The functionality described herein may also be embodied in peripheral devices or add-in cards. Such functionality may also be implemented on a circuit board, as further examples, between various chips or between various processes running on a single device.

[0113] The instructions, media for carrying such instructions, computational resources for executing them, and other structures for supporting such computational resources are means for providing the functionality described in these disclosures.

[0114] Specific examples of the present disclosure include:

[0115] Aspect 1: A system comprising: an additive manufacturing machine having a reference surface and an object surface; at least one camera device for capturing the reference surface; at least one projector device for projecting onto the reference surface; a memory storing computer-readable instructions; and at least one processor, the at least one processor executing instructions to move the reference surface above or below a highest point of the object surface, and use the at least one camera device and the at least one projector device to move the reference surface until the entire measurement volume has phase map data, and acquire a digital fringe projection phase map of the reference surface.

[0116] Aspect 2: The system of aspect 1, wherein the reference surface includes at least one of a powder surface, a melt surface, a bonding surface, a slurry surface, a base plate, and a calibration plate.

[0117] Aspect 3: The system of Aspects 1 and 2, wherein the object surface comprises at least one of a powder surface, a melt surface, a bonding surface, a slurry surface, a base plate, and a calibration plate.

[0118] Aspect 4: A system described in Aspects 1 to 3, wherein at least one of focus, aperture, exposure, gain, and brightness is adjusted for the at least one camera device and the at least one projector device.

[0119] Aspect 5: A system described in Aspects 1 to 4, wherein the at least one processor further preheats the printing volume of the additive manufacturing machine to a particular temperature and pressure before the measurement volume has phase map data.

[0120] Aspect 6: The at least one processor may further calculate the observed phase value φ to achieve the physical location of the pixel. w The system according to any one of the first to fifth aspects, wherein the system determines a constant phase bias at each pixel in the image by shifting the image.

[0121] Aspect 7: A system described in aspects 1 to 6, wherein the at least one processor further finds a mathematical surface that is consistent with the observed phase or height values.

[0122] Aspect 8: The at least one processor further comprises: fwd Find f fwd Invert the function to get f fwd Invert the function to find the cubic polynomial z nom =f rev (φ w The system according to any one of aspects 1 to 7, wherein the system determines a biased value.

[0123] Aspect 9: The at least one processor is further configured to: determine a phase bias φ at each pixel within one of a two-dimensional area and a three-dimensional volume; w biased and f rev (φ wThe system according to any one of aspects 1 to 8, further comprising: determining polynomial coefficients of a biased (or erroneous) function; and estimating a height value from the estimated phase using the equation developed for each pixel in the measurement volume.

[0124] Aspect 10: The at least one processor further comprises: w biased and f rev (φ w The system according to any one of aspects 1 to 9, further comprising: storing information related to polynomial coefficients of a biased (biased) function.

[0125] Aspect 11: A method comprising: capturing a reference surface of an additive manufacturing machine with at least one camera device; projecting onto the reference surface of the additive manufacturing machine using at least one projector device; moving, by at least one processor, the reference surface above or below a highest point of an object surface of the additive manufacturing machine; and moving, by at least one processor, the reference surface using at least one camera device and at least one projector device until the entire measurement volume has phase map data, and obtaining a digital fringe projection phase map of the reference surface.

[0126] Aspect 12: The method of aspect 11, wherein the reference surface comprises at least one of a powder surface, a melt surface, a bonding surface, a slurry surface, a base plate, and a calibration plate.

[0127] Aspect 13: The method of Aspects 11 and 12, wherein the object surface comprises at least one of a powder surface, a melt surface, a bonding surface, a slurry surface, a base plate, and a calibration plate.

[0128] Aspect 14: A method as described in aspects 11 to 13, wherein at least one of focus, aperture, exposure, gain, and brightness is adjusted for the at least one camera device and the at least one projector device.

[0129] Aspect 15: A method as described in aspects 11 to 14, further comprising preheating a print volume of an additive manufacturing machine to a predetermined temperature and pressure before the measurement volume has phase map data.

[0130] Aspect 16: Observed phase value φ to achieve the physical location of the pixel w The method of any one of embodiments 11 to 15, further comprising determining a constant phase bias at each pixel in the image that shifts the image.

[0131] Aspect 17: The method of any one of aspects 11 to 16, further comprising finding a mathematical surface that is consistent with the observed phase or height values.

[0132] Aspect 18: Forward polynomial function f fwd Find f fwd Invert the function to find the cubic polynomial z nom =f rev (φ w The method according to any one of embodiments 11 to 17, further comprising determining the frequency of the variance (biased).

[0133] Aspect 19: Phase bias φ at each pixel within either a two-dimensional area or a three-dimensional volume w biased and f rev (φ w The polynomial coefficients of the (biased) function are calculated, and the wrapped phase φ is estimated using the developed formula for each pixel in the measurement volume. w from height z est The method according to any one of embodiments 11 to 18, further comprising estimating:

[0134] Aspect 20: Phase bias φ at each pixel w biased and f rev (φ w The method according to any one of embodiments 11 to 19, further comprising storing information related to polynomial coefficients of the biased function.

[0135] Aspect 21: A non-transitory computer-readable storage medium having stored thereon instructions that, when executed by at least one computing device, cause the at least one computing device to perform operations including: capturing a reference surface of an additive manufacturing machine with at least one camera device; projecting onto the reference surface of the additive manufacturing machine using at least one projector device; moving the reference surface above or below the highest point of the object surface of the additive manufacturing machine; and using at least one camera device and at least one projector device, moving the reference surface until the entire measurement volume has phase map data, and obtaining a digital fringe projection phase map of the reference surface.

Claims

1. 1. A system comprising: an additive manufacturing machine having a reference surface and an object surface; at least one camera device for capturing said reference surface; at least one projector device for projecting onto said reference surface; a memory for storing computer readable instructions; at least one processor; wherein the at least one processor moving the reference surface above or below the highest point of the object surface; The system executes instructions to use the at least one camera device and the at least one projector device to move the reference surface until an entire measurement volume has phase map data, and acquire a digital fringe projection phase map of the reference surface.

2. The system of claim 1 , wherein the reference surface comprises at least one of a powder surface, a melt surface, a bonding surface, a slurry surface, a base plate, and a calibration plate.

3. The system of claim 1 , wherein the object surface comprises at least one of a powder surface, a melt surface, a bonding surface, a slurry surface, a base plate, and a calibration plate.

4. The system of claim 1 , wherein at least one of focus, aperture, exposure, gain, and brightness is adjusted for the at least one camera device and the at least one projector device.

5. 10. The system of claim 1, wherein the at least one processor is further configured to preheat a print volume of the additive manufacturing machine to a temperature and pressure before the measurement volume has phase map data.

6. The at least one processor further calculates the observed phase value φ to arrive at the physical location of the pixel. ｗ 10. The system of claim 1, wherein the system determines a constant phase bias at each pixel in the image that shifts the image.

7. The system of claim 6 , wherein the at least one processor is further configured to find a mathematical surface that matches the observed phase or height values.

8. The at least one processor further comprises a forward polynomial function f ｆｗｄ and ｆｗｄ Invert the function to get the cubic polynomial z ｎｏｍ = f ｒｅｖ (φ ｗ The system of claim 7, wherein the system determines a biased (or "biased") value.

9. The at least one processor further calculates a phase bias φ at each pixel within either the two-dimensional area or the three-dimensional volume. ｗ biased and f ｒｅｖ (φ ｗ 9. The system of claim 8, wherein the system determines polynomial coefficients of a phase-biased function and estimates height values ​​from the estimated phase using the equation developed for each pixel in the measurement volume.

10. The at least one processor further calculates the phase bias φ at each pixel. ｗ biased and the f ｒｅｖ (φ ｗ 10. The system of claim 9, further comprising: a processor configured to store information related to polynomial coefficients of a polynomial function.

11. 1. A method comprising: capturing a reference surface of an additive manufacturing machine with at least one camera device; projecting onto the reference surface of the additive manufacturing machine using at least one projector device; moving, by at least one processor, the reference surface above or below a highest point of an object surface of the additive manufacturing machine; moving the reference surface using the at least one camera device and the at least one projector device, by the at least one processor, until an entire measurement volume has phase map data, and acquiring a digital fringe projection phase map of the reference surface; A method comprising:

12. The method of claim 11 , wherein the reference surface comprises at least one of a powder surface, a melt surface, a bonding surface, a slurry surface, a base plate, and a calibration plate.

13. The method of claim 11 , wherein the object surface comprises at least one of a powder surface, a melt surface, a bonding surface, a slurry surface, a base plate, and a calibration plate.

14. The method of claim 11 , wherein at least one of focus, aperture, exposure, gain, and brightness is adjusted for the at least one camera device and the at least one projector device.

15. 12. The method of claim 11, further comprising preheating a print volume of the additive manufacturing machine to a temperature and pressure before the measurement volume has phase map data.

16. To achieve the physical location of the pixel, the observed phase value φ ｗ 12. The method of claim 11, further comprising determining a constant phase bias at each pixel in the image that shifts

17. 17. The method of claim 16, further comprising finding a mathematical surface that is consistent with the observed phase or height values.

18. Forward polynomial function f ｆｗｄ and ｆｗｄ Invert the function to get the cubic polynomial z ｎｏｍ = f ｒｅｖ (φ ｗ 18. The method of claim 17, further comprising determining a (biased)

19. The phase bias φ at each pixel within either the 2D area or the 3D volume ｗ biased and f ｒｅｖ (φ ｗ and determining the polynomial coefficients of the (biased) function and estimating the wrapped phase φ using the equation developed for each pixel in the measurement volume. ｗ From height z ｅｓｔ The method of claim 18 , further comprising estimating

20. The phase bias φ at each pixel ｗ biased and the f ｒｅｖ (φ ｗ 20. The method of claim 19, further comprising storing information related to the polynomial coefficients of the (biased) function.

21. When executed by at least one computing device, capturing a reference surface of an additive manufacturing machine with at least one camera device; projecting onto the reference surface of the additive manufacturing machine using at least one projector device; moving the reference surface above or below the highest point of an object surface of the additive manufacturing machine; using the at least one camera device and the at least one projector device to move the reference surface until an entire measurement volume has phase map data, and acquire a digital fringe projection phase map of the reference surface; A non-transitory computer-readable storage medium having stored thereon instructions that cause the at least one computing device to perform operations including:

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