Method of air-coupled guided wave inspection and system thereof

Abstract

A method of air-coupled guided wave inspection, including: moving an ultrasonic-wave- emitting probe and an ultrasonic-wave-receiving probe, via a first robotic arm and a second robotic arm respectively, relative to a surface of a to-be-inspected article to iteratively vary an incident angle and a receiver angle; selecting an optimal combination of the incident angle of the ultrasonic-wave-emitting probe and the receiver angle of the ultrasonic-wave-receiving probe from different combinations of the incident angle of the ultrasonic-wave-emitting probe and the receiver angle of the ultrasonic-wave-receiving probe based on a detection signal of the ultrasonic-wave-receiving probe having a maximum amplitude; and performing scanning of the to-be-inspected article by moving the ultrasonic-wave-emitting probe and the ultrasonic- wave-receiving probe relative to the surface of the to-be-inspected article along a scanning path and with the ultrasonic-wave-emitting probe and the ultrasonic-wave-receiving probe respectively oriented at the optimal combination of the incident angle and the receiver angle.

Description

METHOD OF AIR-COUPLED GUIDED WAVE INSPECTION AND SYSTEM THEREOFCross-references to related applicationsrooon The present application claims the benefit of the Singapore Patent Application No. 10202500781U filed on 25 March 2025, the entire contents of which are incorporated herein by reference for all purposes.Technical Field

[0002] Various embodiments relate to a method of air-coupled guided wave inspection, and a system for air-coupled guided wave inspection.Background

[0003] Composites such as CFRP / GFRP (carbon or glass fibre reinforced polymer) based components are seeing increasing usage in the aerospace industry. As the usage increases, there is a pressing need for a large coverage inspection methodology for detection of buried defects such as delaminations and disbonds which significantly affect material properties. Some examples of technologies used include water-coupled phase array or single element probes. However, both technologies are more suited for thicker composites samples and have smaller coverage.

[0004] Ultrasonic guided wave technology is one example of technology which can perform large area inspection for thin composites. It also has an air-coupled option which increases the usability of the technology. Guided wave is preferred since conventional piezoelectric ultrasonic inspection of composites samples requires immersion or spraying a fluid medium which could adversely affect material properties. Air-coupled options eliminate the drawbacks of conventional ultrasonic inspection.

[0005] However, the challenge with implementing ultrasonic guided wave technology i the lengthy process for the understanding of how the guided wave propagates through the sample. This generally includes a sequence of steps, starting from (1) sample definition, (2) simulation of sample and ultrasonic guided wave propagation, (3) optimisation of ultrasonic guided wave, (4) experimental validation, and finally (5) translation of input parameters to automated platform. The process is lengthy and requires a diverse range of expertise relating to ultrasonic simulations, automation, and inspection.

[0006] Therefore, there is a need to have a simpler and effective solution to address some of the issues identified above.Summary

[0007] According to various embodiments, there is provided a method of air-coupled guided wave inspection. The method includes moving an ultrasonic-wave-emitting probe and an ultrasonic-wave-receiving probe, via a first robotic arm and a second robotic arm respectively, relative to a surface of a to-be-inspected article to iteratively vary an incident angle and a receiver angle. The incident angle is between an emission axis of the ultrasonicwave-emitting probe and a normal of a transmitting point on the surface of the to-be-inspected article, and the receiver angle is between a detection axis of the ultrasonic-wave-receiving probe and a normal of a receiving point on the surface of the to-be-inspected article. The transmitting point is an intersection point of the emission axis of the ultrasonic- wave-emitting probe and the surface of the to-be-inspected article, and the receiving point is an intersection point of the detection axis of the ultrasonic-wave-receiving probe and the surface of the to-be-inspected article. The method further includes selecting an optimal combination of the incident angle of the ultrasonic-wave-emitting probe and the receiver angle of the ultrasonic-wavereceiving probe from different combinations of the incident angle of the ultrasonic-wave-emitting probe and the receiver angle of the ultrasonic-wave-receiving probe based on a detection signal of the ultrasonic-wave-receiving probe having a maximum amplitude. The method also includes performing scanning of the to-be-inspected article by moving the ultrasonic-wave-emitting probe and the ultrasonic-wave-receiving probe relative to the surface of the to-be-inspected article along a scanning path and with the ultrasonic-wave-emitting probe and the ultrasonic-wave-receiving probe respectively oriented at the optimal combination of the incident angle of the ultrasonic-wave-emitting probe and the receiver angle of the ultrasonic-wave-receiving probe.

[0008] According to various embodiments, there is provided a system for air-coupled guided wave inspection. The system including a first robotic arm with an ultrasonic-waveemitting probe; a second robotic aim with an ultrasonic-wave-receiving probe; and a processor configured to control the first robotic arm and the second robotic arm to move the ultrasonic -wave-emitting probe and the ultrasonic-wave-receiving probe respectively relative to a surface of the to-bc-inspcctcd article to perform the method as described herein.Brief description of the drawings

[0009] In the drawings, like reference characters generally refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments are described with reference to the following drawings, in which:

[0010] FIG. 1 shows a block diagram illustrating a system connectivity and architecture of an example of a system for air-coupled guided wave inspection according to various embodiments;

[0011] FIG. 2 shows a visualization of the system of FIG. 1 according to various embodiments;

[0012] FIG. 3 shows a block diagram of the operation of the system for air-coupled guided wave inspection according to various embodiments;

[0013] FIG. 4A shows a schematic diagram of the ultrasonic-wave-emitting probe and the ultrasonic-wave-receiving probe of the system of FIG. 1 being moved to determine an optimal parameter during the iterative process according to various embodiments;

[0014] FIG. 4B shows an example of processing / analyzing of the set of recorded detection signals (e.g. data / signals) associated with the different combinations of the incident angle and the receiver angle for determining the optimal combination of the incident angle and the receiver angle according to various embodiments;

[0015] FIG. 4C shows a schematic diagram of the ultrasonic-wave-emitting probe and the ultrasonic-wave-receiving probe being moved to determine another optimal parameter during the iterative process according to various embodiments;

[0016] FIG. 4D shows an example of processing / analyzing of the set of recorded detection signals (e.g. data / signals) associated with the different combinations of the emission distance and the reception distance (or changes in lift off distances) for determining the optimal combination of the emission distance and the reception distance according to various embodiments;

[0017] FIG. 4E shows a schematic diagram of the ultrasonic-wave-emitting probe and the ultrasonic-wavc-rccciving probe being moved to determine another optimal parameter during the iterative process according to various embodiments;

[0018] FIG. 4F shows a schematic diagram of the ultrasonic-wavc-cmitting probe and the ultrasonic-wave-receiving probe being moved to determine another optimal parameter during the iterative process according to various embodiments;

[0019] FIG. 4G shows an example of processing / analyzing of the set of recorded detection signals (e.g. data / signals) associated with the different with the different lateral distances apart between the transmitting point and the receiving point on the surface of the to-bc-inspcctcd article for determining the optimal combination of the lateral distances apart between the transmitting point and the receiving point on the surface of the to-be-inspected article;

[0020] FIG. 5A and FIG. 5B show the scanning paths according to various embodiments; and

[0021] FIG. 6 shows an example of the charts of the post-processing process of the inspection process according to various embodiments.Detailed description

[0022] Embodiments described below in context of the apparatus are analogously valid for the respective methods, and vice versa. Furthermore, it will be understood that the embodiments described below may be combined, for example, a part of one embodiment may be combined with a part of another embodiment.

[0023] It should be understood that the terms “on”, “over”, “top”, “bottom”, “down”, “side”, “back”, “left”, “right”, “front”, “lateral”, “side”, “up”, “down” etc., when used in the following description are used for convenience and to aid understanding of relative positions or directions, and not intended to limit the orientation of any device, or structure or any part of any device or structure. In addition, the singular terms “a”, “an”, and “the” include plural references unless context clearly indicates otherwise. Similarly, the word “or” is intended to include “and” unless the context clearly indicates otherwise.

[0024] According to various embodiments, there is provided a method of air-coupled guided wave inspection, and a system for air-coupled guided wave inspection. In the various embodiments, the air-coupled guided wave inspection may be anon-contact and nondestructive method for inspecting an article, whereby sound wave (e.g. ultrasound) in air may be used to excite guided waves through the article to detect defects in the article. According to various embodiments, the method and / or system may enable air-coupled guided wave inspection to be perform on an article without requiring the conventional steps of conducting simulation based on the article and / or generating a toolpath (or scanning path) customized for the article from the simulation step prior to performing the inspection step of the air-coupled guided wave inspection.

[0025] According to various embodiments, instead of performing the conventional steps of conducting simulation and generating the toolpath based on the simulation, the method and / or system of the various embodiments may include an iterative optimization step to replace those conventional steps. In the various embodiments, the iterative optimization step may include performing optimization of positional / orientation parameters of the inspection component / equipment relative to the article by physically moving the inspection component / equipment relative to the article so as to detect the signal strength of the inspection component / equipment at the various relative positions / orientations and to select an optimal position / orientation based on an optimal signal strength for the inspection component / equipment. The optimal position / orientation information obtained via the iterative optimization step may then be applied to update a toolpath for subsequent inspection of the article. Accordingly, various embodiments may provide an iterative and adaptative method and / or system for conducting air-coupled guided wave inspection, whereby the toolpath may be adapted to the geometry of the article by iteratively obtaining the optimized parameters to update the toolpath for performing inspection of the article. With the method and / or system of the various embodiments, the air-coupled guided wave inspection may be automated and may be applied to inspect different articles (having different geometries) one after another directly, without having to conduct the conventional simulation for each specific geometry and generate the toolpath based on the simulation. According to various embodiments, the method and / or system may accelerate inspection and / or simplify automation for detection of defects in an article and / or be applicable for a wide-range of geometries for the article. According to various embodiments, the method and / or system may utilize ultrasound for performing the air-coupled guided wave inspection. According to various embodiments, the article for inspection may include, but not limited to, carbon-fiber reinforced polymer (CFRP) article and / or glass-fiber reinforced polymer (GFRP). According to various embodiments, the defects of the article may include, but not limited to, delaminations, disbands and / or surface discontinuities. According to various embodiments, the positional / orientation parameters may include, but note limited to, angle, height and / or distance parameters.

[0026] According to various embodiments, the method and / or system may perform the iterative process to determine one or more optimized parameters for conducting the air-coupled wave inspection on the fly (without going through the conventional simulation step and / or the conventional toolpath generation step based on the conventional simulation). The iterative process may involve moving an ultrasonic-wave-emitting probe and an ultrasonic-wavereceiving probe (i.e. the inspection component / equipment) relative to a surface of the to-be-inspected article to vary the relative positions / orientations. The ultrasonic-wave-emitting probe may direct an ultrasonic wave at the surface of the to-be-inspected article to excite a guided ultrasonic wave within the to-be-inspected article. The guided ultrasonic wave may propagate along a propagation direction, and exit or leak from the surface of the to-bc-inspcctcd article downstream which may be received by the ultrasonic-wave-receiving probe for measuring a strength of the ultrasonic wave. The strength of the ultrasonic wave associated with the different positions / orientations of the ultrasonic-wave-emitting probe and the ultrasonic-wave-receiving probe relative to a surface of the to-be-inspected article may be obtained via the iterative process, and the optimal position / orientation may be determined. The optimal position / orientation may then be applied to the toolpath for conducting the actual inspection of the article subsequently.

[0027] According to various embodiments, the iterative process may determine one or more optimized parameter including, but not limited to, an optimal incident angle of the ultrasonic-wave-emitting probe and an optimal receiver angle of the ultrasonic-wave -receiving probe; an optimal emission distance of the ultrasonic-wave-emitting probe and an optimal reception distance of the ultrasonic-wave-receiving probe; an optimal relative offset distance between the transmitting point for the ultrasonic-wave-emitting probe and the receiving point for the ultrasonic-wave-receiving probe; and an optimal lateral distance apart between the transmitting point for the ultrasonic-wave-emitting probe and the receiving point for the ultrasonic-wave-receiving probe.

[0028] FIG. 1 shows a block diagram illustrating a system connectivity and architecture of an example of a system 100 for air-coupled guided wave inspection according to various embodiments. According to various embodiments, the system 100 may be configured for conducting air-coupled guided wave inspection according to the method as described in the various embodiments. In particular, the system 100 may be configured to perform an iterative process to optimized parameters and to apply the optimized parameters in a toolpath for conducting the inspection process of the air-coupled guided wave inspection.

[0029] According to various embodiments, the system 100 may include a first robotic arm 102 and a second robotic aim 104. Further, an ultrasonic-wave-emitting probe 110 may be at an end of the first robotic arm 102, whereby the ultrasonic-wavc-cmitting probe 110 may serve as the end-of-arm-tooling (EOAT) or end-effector of the first robotic aim 102. Furthermore, an ultrasonic-wavc-rccciving probe 120 may be at an end of the second robotic arm 104, whereby the ultrasonic-wave-receiving probe 120 may serve as the end-of-arm-tooling (EOAT) or end-effector of the second robotic arm 104. According to variousembodiments, the ultrasonic-wave-emitting probe 110 may include an ultrasonic-wavetransmitter or an ultrasonic-wave-transducer. According to various embodiments, the ultrasonic-wave-receiving probe 120 may include an ultrasonic-wave-receiver or an ultrasonic -wavc-transduccr. According to various embodiments, each of the first robotic arm 102 and the second robotic arm 104 may be a articulated robot or any multi- axis robotic arm.

[0030] According to various embodiments, the system 100 may include a processor 105. The processor 105 may be electrically coupled to the first robotic arm 102, the second robotic arm 104, the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave -receiving probe 120 for controlling and / or communicating with the first robotic arm 102, the second robotic arm 104, the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave -receiving probe 120. For example, the processor 105 may receive positional information of the first robotic arm 102 and / or the second robotic arm 104, as well as send control signals to control movements of the first robotic arm 102 and / or the second robotic arm 104. Further, the processor 105 may send control signals to the ultrasonic-wave-emitting probe 110 for emission of the ultrasonic wave and receive detection signals from the ultrasonic -wave-receiving probe 120 as feedback on the guided wave propagated through a to-be-inspected article 106.

[0031] As shown, according to some embodiments, the system 100 may include a router 107. The router 107 may be configured to direct the instructions from the processor 105 respectively to the first robotic arm 102, the second robotic arm 104, the ultrasonic-waveemitting probe 110 and / or the ultrasonic-wave-receiving probe 120, as well as direct the data / signals from the first robotic arm 102, the second robotic arm 104, the ultrasonic-wave-emitting probe 110 and / or the ultrasonic-wave -receiving probe 120 to the processor 105. In an example, the router 107 may implement TCP / IP (transmission control protocol / internet protocol) for communication between the processor 105 and each of the first robotic arm 102, the second robotic arm 104, the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120.

[0032] According to some embodiments, the system 100 may include a first local controller 101 (or first robot controller) associated with the first robotic arm 102 and a second local controller 103 (or second robot controller) associated with the second robotic aim 104. The first local controller 101 may control a movement of the first robotic arm 102, as well as receive positional data / signals from the first robotic ami 102. Similarly, the second local controller 103 may control a movement of the second robotic arm 104, as well as receive positional data / signals from the second robotic arm 104. In an example, the router 107 may be electrically coupled to the first local controller 101 and the second local controller 103.Accordingly, the router 107 may receive instructions from the processor 105 and rely the instructions respectively to the first local controller 101 for controlling the first robotic arm 102 and the second local controller 103 for controlling the second robotic aim 104. Further, the router 107 may receive data / signals relating to the position / oricntation of the first robotic arm 102 from the first local controller 101 and data / signals relating to the position / orientation of the second robotic arm 104 from the second local controller 103, and relay to the processor 105.

[0033] According to some embodiments, the system 100 may include a probe controller 109 associated with the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave -receiving probe 120. The probe controller 109 may be configured to control the ultrasonic-wave-emitting probe 110 to generate the ultrasonic wave for directing at the surface 108 of the to-be-inspected article 106, and configured to receive detection data / signals relating to the guided wave propagated through the to-be-inspected article 106 from the ultrasonic- wave-receiving probe 120. In an example, the router 107 may be electrically coupled to the probe controller 109. Accordingly, the router 107 may receive instructions from the processor 105 and rely the instructions to the probe controller 109 for controlling the ultrasonic-wave-emitting probe 110 to generate the ultrasonic wave. Further, the router 107 may receive data / signals associated with the guided wave propagated through the to-be-inspected article 106 detected by the ultrasonic- wave-receiving probe 120 from the probe controller 109.

[0034] According to various embodiments, the processor 105 may execute a program 105a comprising instructions to control the first robotic arm 102 and the second robotic arm 104, and / or to process the data / signals received from the first robotic arm 102 and the second robotic arm 104. According to various embodiments, the processor 105 may execute a program 105b comprising instructions to control the ultrasonic-wave-emitting probe 110 and / or to process the data / signals received from the ultrasonic-wave-receiving probe 120. According to various embodiments, the processor 105 may then execute a program comprising instructions to process the data / signals respectively from the first robotic arm 102 and the second robotic arm 104 as well as from the ultrasonic-wave-receiving probe 120 for determining the optimal position / orientation information and / or to apply the optimal position / orientation information to the toolpath for subsequent conduct of the inspection process of the air-coupled guided wave inspection. According to various embodiments, the system 100 may include a display 105c for displaying the control information as well as data / signal information processed by the processor 105.

[0035] In various embodiments, the "processor 105" may be understood as any kind of a logic implementing entity, which may be special purpose circuitry or a processor executing software stored in a memory, firmware, or any combination thereof. Thus, in an embodiment, the "processor 105" may be a hard-wired logic circuit or a programmable logic circuit such as a programmable processor, e.g. a microprocessor (e.g. a Complex Instruction Set Computer (CISC) processor or a Reduced Instruction Set Computer (RISC) processor). The "processor 105" may also be a processor executing software, e.g. any kind of computer program, e.g. a computer program using a virtual machine code such as e.g. Java. Any other kind of implementation of the respective functions which will be described in more detail below may also be understood as the "processor 105" in accordance with various embodiments. In various embodiments, the “processor 105” may be part of a computing system or a controller or a microcontroller or any other system providing a processing capability. According to various embodiments, such systems may include a memory which is for example used in the processing carried out by the device or system. A memory used in the embodiments may be a volatile memory, for example a DRAM (Dynamic Random Access Memory) or a non-volatile memory, for example a PROM (Programmable Read Only Memory), an EPROM (Erasable PROM), EEPROM (Electrically Erasable PROM), or a flash memory, e.g., a floating gate memory, a charge trapping memory, an MRAM (Magnetoresistive Random Access Memory) or a PCRAM (Phase Change Random Access Memory).

[0036] According to various embodiments, the processor 105 may be configured to generate the various control signals for operating the various components (e.g. the first robotic arm 102, the second robotic arm 104 and the ultrasonic-wave-emitting probe 110 via the first local controller 101, the second local controller 103, and the probe controller 109) of the system 100. According to various embodiments, the processor 105 may be configured to process the various data / signals from the various components (e.g. the first robotic arm 102, the second robotic arm 104 and the ultrasonic-wave-receiving probe 120 via the first local controller 101, the second local controller 103, and the probe controller 109) of the system 100 for performing the iterative process and / or the inspection process.

[0037] FIG. 2 shows a visualization of the system 100 of FIG. 1 according to various embodiments. According to various embodiments, the control / proccssing sub-system 205a may be electrically coupled to the first robotic aim 102, the second robotic aim 104, the ultrasonic-wavc-cmitting probe 110 and the ultrasonic-wavc-rccciving probe 120 for controlling and / or communicating with the first robotic arm 102, the second robotic arm 104, the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120.Referring back to FIG. 1, the control / processing sub-system 205a may include, but not limited to, the processor 105, the router 107, the first local controller 101, the second local controller 103, the probe controller 109, the programs 105a, 105b, and the display 105c as described with reference to FIG. 1.

[0038] As also shown in FIG. 2, the to-be-inspected article 106 may be placed between the ultrasonic- wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120. The first robotic arm 102 and the second robotic arm 104 may be controlled to move the ultrasonicwave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 relative to the to-be-inspected article 106. During the iterative process, the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 may be moved relative to the to-be-inspected article 106 such that the control / processing sub-system 205a may determine the optimal positional / orientation information for updating the toolpath. During the inspection process, the ultrasonic-wave-emitting probe 110 and the ultrasonic- wave-receiving probe 120 may be moved relative to the to-be-inspected article 106 along the updated toolpath for inspecting the to-be-inspected article 106.

[0039] As shown in FIG. 2, according to some embodiments, the system 100 may include an acoustic barrier 199 disposed between the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120. Accordingly, the acoustic barrier 199 may mitigate the sound travelling between the ultrasonic-wave-emitting probe 110 and the ultrasonic-wavereceiving probe 120 so as to minimize or eliminate error due to direct sound transmission between the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120. According to some embodiments, the acoustic banner 199 may be in the form of the acoustic foam.

[0040] FIG. 3 shows a block diagram of the operation 370 of the system 100 for aircoupled guided wave inspection according to various embodiments. According to various embodiments, the operation 370 of the system 100 may commence with an initial toolpath generation process 371. During the initial toolpath generation process 371, a toolpath for synchronized movement between the first robotic arm 102 and the second robotic arm 104 for respectively moving the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave -receiving probe 120 may be generated. The toolpath may be generated manually or automatically using toolpathing software. In the various embodiments, the initial toolpath generation may be based on initial user input parameters. The initial user input parameters may be based on assumptions (e.g. angle assumption, height assumption, distance assumption, etc.) or may be based on simple adaption to the geometry of the to-be-inspected article 106. In the various embodiments,the initial toolpath generation process 371 may generate the initial toolpath which may be updated in subsequent process of the operation 370. According to various embodiments, the initial toolpath generation process 371 may be performed by the processor 105 of the system 100.

[0041] According to various embodiments, after the initial toolpath is generated, the operation 370 of the system 100 may proceed with the robotic system control process 373. In the various embodiments, the processor 105 of the system 100 may control the movement of the first robotic arm 102 and the second robotic arm 104 based on the initial toolpath generated. According to some embodiments, the processor 105 of the system 100 may continuously send control instructions according to the initial toolpath generated for controlling the movement of the first robotic arm 102 and the second robotic arm 104. According to some embodiments, the processor 105 of the system 100 may export the initial toolpath generated and send the initial toolpath to the first local controller 101 and the second local controller 103, such that the first local controller 101 and the second local controller 103 may respectively control the movement of the first robotic am 102 and the second robotic aim 104.

[0042] In an example, the first robotic arm 102 and the second robotic arm 104 may respectively be connected to the processor 104 via input / output (I / O) ports. Further, the first robotic am 102 and the second robotic arm 104 may be controlled using Universal Robot (UR) teach pendent human machine interface (HMI), which may be fully controlled using external interface, e.g. computing device / workstation serving as the processor 105. In the example, the system 100 may be set to run a program with some time -based synchronization function (e.g. to wait for I / O trigger or send I / O trigger.

[0043] According to various embodiments, the operation 370 of the system 100 may include the ultrasonic system control process 375. The ultrasonic system may include the ultrasonic-wave-emitting probe 110, the ultrasonic-wave-receiving probe 120, the probe controller 109 (e.g. oscilloscope), the router 107 and the processor 105. The ultrasonic system may control the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120, and capture data / signals. The ultrasonic system control process 375 may include capturing the data / signals, recording the data / signals, and visualizing (or processing or analyzing) the data / signals for evaluation of the inspection process or for determining the optimal parameters during the iterative process.

[0044] According to various embodiments, the operation 370 of the system 100 may include the iterative process 377. The iterative process 377 may interact with the ultrasonic system control process 375 and the robotic system control process 373. In the variousembodiments, the robotic system control process 373 may move the first robotic arm 102 and the second robotic arm 104 so as to vary the positions / orientations relative to the to-be-inspected article 106, and the ultrasonic system control process 375 may obtain the data / signals relating to the guided wave propagated through the to-bc-inspcctcd article 106 when the first robotic arm 102 and the second robotic arm 104 are at the different positions / orientations. The iterative process 377 may interact with the ultrasonic system control process 375 to extract the data / signals from the ultrasonic system control process 375. Further, the iterative process 377 may process the data / signals so as to determine the optimal parameters for positioning / orientating (e.g. height, angle, distance) the first robotic arm 102 and the second robotic arm 104, so as to position and / orientate (e.g. height, angle, distance) the ultrasonicwave-emitting probe 110 and the ultrasonic-wave-receiving probe 120, based on determining the optimal data / signal. Subsequently, the iterative process 377 may update the initial toolpath based on the optimal parameters determined through the interaction with the ultrasonic system control process 375. Accordingly, the iterative process 377 may generate or output an optimized toolpath (e.g. optimized with the optimal position and / or orientation of the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave -receiving probe 120). In FIG. 3, the dashed lines show the interaction of the various processes to arrive at the generation of the optimized toolpath.

[0045] With the optimized toolpath, the robotic system control process 373 may control the first robotic arm 102 and the second robotic arm 104 to follow the optimized toolpath for conducting the inspection process, and the ultrasonic system control process 375 may control the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 to obtain the data / signals relating to the guided wave propagated through the to-be-inspected article 106 for detecting defect in the to-be-inspected article 106.

[0046] According to various embodiments, the system 100 may further include a postprocessing process 379 to visualise / locate / size the defect in the to-be-inspected article 106 based on the data / signals captured in the ultrasonic system control process 375. In FIG. 3, the solid lines show the interaction between the various processes for conducting inspection based on the optimized toolpath. As shown, the robotic system control process 373 may control the first robotic arm 102 and the second robotic arm 104 based on the optimized toolpath generated by the iterative process 377, the ultrasonic system control process 375 may capture the data / signals while the ultrasonic-wavc-cmitting probe 110 and the ultrasonic-wavc-rccciving probe 120 are being moved based on the optimized toolpath, and the data / signals may be processed by the post-processing process 379 to visualise / locate / size the defect in the to-be-inspected article 106. According to various embodiments, the post-processing process 379 may compress each data / signal into a single value, and map the single value to corresponding coordinate of the to-be-inspected article 106 so as to determine a location of the defect in the to-bc-inspcctcd article 106.

[0047] Accordingly, the operation 370 of the system 100 as illustrated by FIG. 3 may be a complete (or full) inspection operation suitable for inspecting any to-be-inspected article 106 without requiring the conventional step of simulation and generating toolpath based on the simulation. As shown, the operation 370 of the system 100 may utilize the iterative process 377 as part of the inspection operation to optimize the toolpath for conducting an effective and accurate inspection. Accordingly, the to-be-inspected article 106 may be fed into the system 100 and the operation 370 may be run to optimized the toolpath specifically adapted to the geometry of the to-be-inspected article 106 (e.g. via the initial toolpath generation process 371, the robotic system control process 373, the ultrasonic system control process 375, and the iterative process 377), and subsequently conduct inspection along the optimized toolpath (e.g. via the robotic system control process 373, the ultrasonic system control process 375, and the post-processing process 379).

[0048] FIG. 4A shows a schematic diagram of the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 being moved to determine an optimal parameter during the iterative process 377 according to various embodiments. According to various embodiments, the iterative process 377 may involve moving the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave -receiving probe 120 relative to the surface 108 of the to-be-inspected article 106. The ultrasonic-wave-emitting probe 110 may direct an ultrasonic wave at the surface 108 of the to-be-inspected article 106 to excite a guided ultrasonic wave within the to-be-inspected article 106. The guided ultrasonic wave may be guided between the surface 108 of the to-be-inspected article 106 and an opposite surface of the to-be-inspected article 106 in a manner so as to be kept a body of the to-be-inspected article 106. Further, the guided ultrasonic wave may propagate along a propagation direction. The ultrasonic-wave-receiving probe 120 may be disposed downstream of the guided ultrasonic wave propagating within the to-be-inspected article 106. Accordingly, the ultrasonic-wave-receiving probe 120 may be spaced apart from the ultrasonic-wavc-cmitting probe 110 along the propagation direction of the guided ultrasonic wave (or spaced laterally apart with respect to the scanning path). The ultrasonic-wavc-rccciving probe 120 may receive and / or sense and / or detect an ultrasonic wave that exits or leaks from the surface 108 of the to-be-inspected article 106 downstream of the guided ultrasonic wave propagating within the to-be-inspected article 106. The ultrasonic-wave-receiving probe 120 may measure a strength (or amplitude) of the ultrasonic wave that exits or leaks from the surface 108 of the to-be-inspected article 106.

[0049] According to various embodiments, by moving the ultrasonic-wave-emitting probe 110 and the ultrasonic-wavc-rccciving probe 120, an optimal orientation and / or position of the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 with respect to each other, for optimal guided ultrasonic wave propagation within the to-be-inspected article 106 and / or detection of the ultrasonic wave that exits or leaks from the surface 108 of the to-be-inspected article 106 downstream of the guided ultrasonic wave propagating within the to-be-inspected article 106, may be determined through the iterative process 377.

[0050] According to various embodiments, during the iterative process 377, the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 may be moved to determine the optimal incident angle 114 of the ultrasonic-wave-emitting probe 110 and the optimal receiver angle 124 of the ultrasonic-wave-receiving probe 120 (as an example of the optimal parameters for positioning / orientating the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120), for example as shown in FIG. 4A.

[0051] According to various embodiments, the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 may be moved, via the first robotic aim 102 and the second robotic arm 104 respectively, relative to the surface 108 of the to-be-inspected article 106 to iteratively vary an incident angle 114 and a receiver angle 124. Accordingly, the ultrasonic-wave-emitting probe 110 and the ultrasonic- wave-receiving probe 120 may be moved by small and / or incremental steps over a series of motion of the first robotic arm 102 and the second robotic aim 104 to vary the incident angle 114 of the ultrasonic-wave-emitting probe 110 and the receiver angle 124 of the ultrasonic-wave-receiving probe 120. In the various embodiments, the incident angle 114 may be between an emission axis 112 of the ultrasonicwave-emitting probe 110 and a normal 132 of a transmitting point 130 on the surface 108 of the to-be-inspected article 106, and the receiver angle 124 may be between a detection axis 122 of the ultrasonic-wave-receiving probe 120 and a normal 142 of a receiving point 140 on the surface 108 of the to-be-inspected article 106. The transmitting point 130 may be an intersection point of the emission axis 112 of the ultrasonic-wave-emitting probe 110 and the surface 108 of the to-bc-inspcctcd article 106. The receiving point 140 may be an intersection point of the detection axis 122 of the ultrasonic-wave -receiving probe 120 and the surface 108 of the to-bc-inspcctcd article 106. Accordingly, the incident angle 114 may be an angle of the ultrasonic-wave-emitting probe 110 off the normal 132 of the surface 108 of the to-be-inspected article 106, and the receiver angle 124 may be an angle of the ultrasonic-wavereceiving probe 120 off the normal 142 of the surface 108 of the to-be-inspected article 106.

[0052] In the various embodiments, as the ultrasonic-wave-emitting probe 110 and the ultrasonic-wavc-rccciving probe 120 arc iteratively moved to vary the incident angle 114 and the receiver angle 124, detection signals (e.g. data / signals) captured / measured by the ultrasonic-wave-receiving probe 120 for different combinations of the incident angle 114 and the receiver angle 124 may be recorded. Subsequently, the set of recorded detection signals (e.g. data / signals) associated with the different combinations of the incident angle 114 and the receiver angle 124 may be analyzed and processed using the post-processing process 379.

[0053] According to various embodiments, an optimal combination of the incident angle 114 of the ultrasonic-wave-emitting probe 110 and the receiver angle 124 of the ultrasonic-wave-receiving probe 120 from the different combinations of the incident angle 114 of the ultrasonic-wave-emitting probe 110 and the receiver angle 124 of the ultrasonic-wave-receiving probe 120 may be selected based on the detection signal of the ultrasonic-wavereceiving probe 120 having a maximum amplitude. Accordingly, from the set of recorded detection signals (e.g. data / signals) associated with the different combinations of the incident angle 114 and the receiver angle 124, the detection signal with the maximum amplitude may be selected and the combination of the incident angle 114 and the receiver angle 124 associated with said detection signal may then be the optimal combination of the incident angle 114 and the receiver angle 124.

[0054] According to various embodiments, with the optimal combination of the incident angle 114 of the ultrasonic-wave-emitting probe 110 and the receiver angle 124 of the ultrasonic- wave-receiving probe 120 determined or selected, inspection of the to-be-inspected article 106 may be performed based on the optimal combination of the incident angle 114 and the receiver angle 124. According to various embodiments, during the inspection process, scanning of the to-be-inspected article 106 may be performed by moving the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 relative to the surface 108 of the to-be-inspected article 106 along a scanning path and with the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 respectively oriented at the optimal combination of the incident angle 114 of the ultrasonic-wavc-cmitting probe 110 and the receiver angle 124 of the ultrasonic-wave -receiving probe 120. Accordingly, the optimal combination of the incident angle 114 and the receiver angle 124, serving as the optimal parameters, may be applied to the initial toolpath so as to enhance the initial toolpath to takeinto consideration of the geometry and / or propagation property of the to-be-inspected article 106 for optimal scanning / inspection.

[0055] According to various embodiments, when capturing / measuring the detection signal by the ultrasonic-wavc-rccciving probe 120, an amplitude of the detection signal may be captured / measured. Accordingly, when recording the detection signals (e.g. data / signals) captured / measured by the ultrasonic-wave-receiving probe 120 for different combinations of the incident angle 114 and the receiver angle 124, a set of amplitude data comprising amplitudes of detection signals measured by the ultrasonic-wave-receiving probe 120 when moving the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 to iteratively vary the incident angle 114 and the receiver angle 124 may be compiled. Hence, the set of amplitude data compiled may be associated with changes in angle (i.e. changes in the incident angle 114 of the ultrasonic-wave-emitting probe 110 and the receiver angle 124 of the ultrasonic-wave-receiving probe 120).

[0056] Tn the various embodiments, the set of amplitude data associated with the changes in angle may be obtained via continuous measurement of the amplitudes of the detection signals of the ultrasonic-wave-receiving probe 120 when the incident angle 114 of the ultrasonic-wave-emitting probe 110 and the receiver angle 124 of the ultrasonic -wave-receiving probe 120 are iteratively varied. According to various embodiments, the set of amplitude data associated with the changes in angle may then be mapped to the different combinations of the incident angle 114 of the ultrasonic-wave-emitting probe 110 and the receiver angle 124 of the ultrasonic-wave-receiving probe 120. According to various embodiments, the range of angles for the iterative variation of the incident angle 114 of the ultrasonic- wave-emitting probe 110 may be pre-defined and the range of angles for the iterative variation of the receiver angle 124 of the ultrasonic-wave-receiving probe 120 may be predefined. Accordingly, the continuous measurement of the amplitudes of the detection signals of the ultrasonic-wave-receiving probe 120 may then be mapped to the pre-defined range of the incident angle 114 and the pre-defined range of the receiver angle 124.

[0057] According to various embodiments, selecting the optimal combination of the incident angle 114 of the ultrasonic-wave-emitting probe 110 and the receiver angle 124 of the ultrasonic-wavc-rccciving probe 120 may include comparing the amplitudes of the detection signals mapped to the different combinations of the incident angle 114 of the ultrasonic-wave-cmitting probe 110 and the receiver angle 124 of the ultrasonic-wavc-rccciving probe 120, and selecting the combination of the incident angle 114 of the ultrasonic-wave-emitting probe 110 and the receiver angle 124 of the ultrasonic-wave-receiving probe 120 with the maximumamplitude as the optimal combination of the incident angle 114 of the ultrasonic-wave-emitting probe 110 and the receiver angle 124 of the ultrasonic-wave -receiving probe 120. Accordingly, from the mapped dataset, i.e. the set of amplitude data mapped to the different combinations of the incident angle 114 and the receiver angle 124, the combination of the incident angle 114 and the receiver angle 124 with the maximum amplitude may be selected as the optimal combination of the incident angle 114 and the receiver angle 124.

[0058] According to various embodiments, when iteratively varying the incident angle 114 and the receiver angle 124, the incident angle 114 of the ultrasonic-wave-emitting probe 110 and the receiver angle 124 of the ultrasonic-wave-receiving probe 120 may be iteratively varied to progressively increase and / or decrease. Accordingly, during the iterative process 377, the incident angle 114 of the ultrasonic-wave-emitting probe 110 may be increased incrementally (and / or steadily), or decreased incrementally (and / or steadily), or increased incrementally (and / or steadily) followed by decreased incrementally (and / or steadily), or decreased incrementally (and / or steadily) followed by increased incrementally (and / or steadily), over the pre-defined range of angles. Similarly, during the iterative process 377, the receiver angle 124 of the ultrasonic-wave-receiving probe 120 may be increased incrementally (and / or steadily), or decreased incrementally (and / or steadily), or increased incrementally (and / or steadily) followed by decreased incrementally (and / or steadily), or decreased incrementally (and / or steadily) followed by increased incrementally (and / or steadily), over the pre-defined range of angles.

[0059] According to various embodiments, the incident angle 114 of the ultrasonicwave-emitting probe 110 may be iteratively varied in a pre-defined range, wherein the predefined range may be from 10 degree to 80 degree, or from 15 degree to 75 degree, or from 25 degree to 65 degree, or from 30 degree to 60 degree, or from 35 degree to 55 degree, or from 0 degree to 65 degree. Similarly, the receiver angle 124 of the ultrasonic-wave-receiving probe 120 may be iteratively varied in a pre-defined range, wherein the pre-defined range may be from 10 degree to 80 degree, or from 15 degree to 75 degree, or from 25 degree to 65 degree, or from 30 degree to 60 degree, or from 35 degree to 55 degree, or from 0 degree to 65 degree.

[0060] Referring back to FIG. 4A, according to various embodiments, when the determining the optimal incident angle 114 of the ultrasonic-wavc-cmitting probe 110 and the optimal receiver angle 124 of the ultrasonic-wave-receiving probe 120, the emission axis 112 of the ultrasonic-wavc-cmitting probe 110 and the detection axis 122 of the ultrasonic-wavc-receiving probe 120 may lie in a same plane and may be converging. In the various embodiments, the emission axis 112 of the ultrasonic-wave-emitting probe 110 may be acenterline of emission of the ultrasonic wave from the ultrasonic-wave-emitting probe 110. Further, the detection axis 122 of the ultrasonic-wave-receiving probe 120 may be a centerline of detection of the ultrasonic-wave-receiving probe 120 for detecting the ultrasonic wave. Accordingly, in the various embodiments, the ultrasonic-wavc-cmitting probe 110 and the ultrasonic-wave-receiving probe 120 may be aligned in the same plane. Further, the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 may be pointing towards the to-be-inspected article 106 in a converging manner.

[0061] FIG. 4B shows an example of processing / analyzing of the set of recorded detection signals (e.g. data / signals) associated with the different combinations of the incident angle 114 and the receiver angle 124 for determining the optimal combination of the incident angle 114 and the receiver angle 124. The top left chart shows a plot of the angular positions (y-axis of the chart) of the first robotic arm 102 as a measure of the incident angle 114 of the ultrasonic-wave-emitting probe 110 at the different data point (x-axis of the chart). The top middle chart shows a plot of the angular positions (y-axis of the chart) of the second robotic aim 104 as a measure of the receiver angle 124 of the ultrasonic-wave -receiving probe 120 at the different data point (x-axis of the chart). The top right chart shows a plot of the detection signals (y-axis of the chart) captured / measured by the ultrasonic-wave-receiving probe 120 over time (x-axis of the chart). The bottom left chart shows a plot of the positions of the first robotic arm 102 and the second robotic arm 104 in the same chart. The bottom right chart shows a plot of the amplitude (y-axis of the chart) of the detection signals against the angular positions (x-axis of the chart) for determining the optimal angle. As shown, the process / analysis may be an angular-based optimization process / analysis, which may determine the best angle between the sensors (i.e. the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave -receiving probe 120) and the component surface (i.e. the surface 108 of the to-be-inspected article 106). From the plots as shown, the peak of the plot of the bottom right chart may be determined to be the optimal angle. In particular, the bottom right chart illustrates that the robots (i.e. the first robotic arm 102 and the second robotic arm 104) may start from the angle of 20° from the normal of the surface 108 and be moved 25°, with an optimal angle of 40° having the maximize signal.

[0062] FIG. 4C shows a schematic diagram of the ultrasonic-wavc-cmitting probe 110 and the ultrasonic- wave-receiving probe 120 being moved to determine another optimal parameter during the iterative process 377 according to various embodiments. According to various embodiments, during the iterative process 377, the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 may be moved to determine the optimal emissiondistance 116 of the ultrasonic-wave-emitting probe 110 and the optimal reception distance 126 of the ultrasonic- wave-receiving probe 120 (as an example of the optimal parameters for positioning / orientating the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-rccciving probe 120).

[0063] According to various embodiments, the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 may be moved, via the first robotic arm 102 and the second robotic arm 104 respectively, relative to the surface 108 of the to-be-inspected article 106 to iteratively vary an emission distance 116 of the ultrasonic-wave-emitting probe 110 along the emission axis 112 from the transmitting point 130 and a reception distance 126 of the ultrasonic-wave-receiving probe 120 along the detection axis 122 from the receiving point 140. Accordingly, the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 may be moved by small and / or incremental steps over a series of motion of the first robotic arm 102 and the second robotic arm 104 to vary the emission distance 116 of the ultrasonic-wave-emitting probe 110 and the reception distance 126 of the ultrasonic-wave-receiving probe 120 with reference to the surface 108 of the to-be-inspected article 106. According some embodiments, the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 may be moved to iteratively vary the emission distance 116 and the reception distance 126 after the optimal combination of the incident angle 114 of the ultrasonic-wave-emitting probe 110 and the receiver angle 124 of the ultrasonic-wave-receiving probe 129 is determined. Accordingly, when moving the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 iteratively to vary the emission distance 116 and the reception distance 126, the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 may respectively be oriented and maintained at the optimal combination of the incident angle 114 of the ultrasonic-wave-emitting probe 110 and the receiver angle 124 of the ultrasonic-wave-receiving probe 129. Thus, the ultrasonic-wave-emitting probe 110 may be moved towards and / or away from the surface 108 of the to-be-inspected article 106 while maintaining the optimal incident angle 114 of the ultrasonic-wave-emitting probe 110. Similarly, the ultrasonic-wave-receiving probe 120 may be moved towards and / or away from the surface 108 of the to-be-inspected article 106 while maintaining the optimal receiver angle 124 of the ultrasonic- wave-receiving probe 129.

[0064] In the various embodiments, as the ultrasonic-wave-emitting probe 110 and the ultrasonic-wavc-rccciving probe 120 arc iteratively moved to vary the emission distance 116 and the reception distance 126, detection signals (e.g. data / signals) captured / measured by the ultrasonic-wave-receiving probe 120 for different combinations of the emission distance 116and the reception distance 126 may be recorded. Subsequently, the set of recorded detection signals (e.g. data / signals) associated with the different combinations of the emission distance 116 and the reception distance 126 may be analyzed and processed.

[0065] According to various embodiments, an optimal combination of the emission distance 116 of the ultrasonic-wave-emitting probe 110 and the reception distance 126 of the ultrasonic-wave-receiving probe 120 may be selected from the different combinations of the emission distance 116 of the ultrasonic-wave-emitting probe 110 and the reception distance 126 of the ultrasonic-wave-receiving probe 120 based on the detection signal of the ultrasonicwave-receiving probe 120 having a maximum amplitude. Accordingly, from the set of recorded detection signals (e.g. data / signals) associated with the different combinations of the emission distance 116 and the reception distance 126, the detection signal with the maximum amplitude may be selected and the combination of the emission distance 116 and the reception distance 126 associated with said detection signal may then be the optimal combination of the emission distance 116 and the reception distance 126.

[0066] According to various embodiments, with the optimal combination of the emission distance 116 of the ultrasonic-wave-emitting probe 110 and the reception distance 126 of the ultrasonic-wave-receiving probe 120 determined or selected, inspection of the to-be-inspected article 106 may be performed based on the optimal combination of the emission distance 116 and the reception distance 126. According to various embodiments, during the inspection process, scanning of the to-be-inspected article 106 may be performed by moving the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 relative to the surface 108 of the to-be-inspected article 106 along a scanning path and with the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 respectively maintained at the optimal combination of the emission distance 116 of the ultrasonic -wave-emitting probe 110 and the reception distance 126 of the ultrasonic-wave-receiving probe 120. Accordingly, the optimal combination of the emission distance 116 and the reception distance 126, serving as the optimal parameters, may be applied to the initial toolpath so as to enhance the initial toolpath for optimal scanning / inspection.

[0067] According to various embodiments, when recording the detection signals (e.g. data / signals) capturcd / mcasurcd by the ultrasonic-wavc-rccciving probe 120 for different combinations of the emission distance 116 and the reception distance 126, a set of amplitude data comprising amplitudes of detection signals measured by the ultrasonic-wavc-rccciving probe 120 when moving the ultrasonic-wave-emitting probe 110 and the ultrasonic-wavereceiving probe 120 to iteratively vary the emission distance 116 and the reception distance126 may be compiled. Hence, the set of amplitude date compiled may be associated with changes in lift off distance (i.e. changes in the emission distance 116 of the ultrasonic-wave-emitting probe 110 and the reception distance 126 of the ultrasonic-wave-receiving probe 120).

[0068] In the various embodiments, the set of amplitude data associated with the changes in lift off distance may be obtained via continuous measurement of the amplitudes of the detection signals of the ultrasonic-wave-receiving probe 120 when the emission distance 116 of the ultrasonic-wave-emitting probe 110 and the reception distance 126 of the ultrasonicwave-receiving probe 120 are iteratively varied. According to various embodiments, the set of amplitude data associated with the changes in lift off distance may then be mapped to the different combinations of the emission distance 116 of the ultrasonic-wave-emitting probe 110 and the reception distance 126 of the ultrasonic-wave-receiving probe 120. According to various embodiments, the range of distances for the iterative variation of the emission distance 116 of the ultrasonic-wave-emitting probe 110 may be pre-defined and the range of distances for the iterative variation of the reception distance 126 of the ultrasonic-wave-receiving probe 120 may be pre-defined. Accordingly, the continuous measurement of the amplitudes of the detection signals of the ultrasonic-wave-receiving probe 120 may then be mapped to the predefined range of the emission distance 116 and the pre-defined range of the reception distance 126.

[0069] According to various embodiments, selecting the optimal combination of the emission distance 116 of the ultrasonic-wave-emitting probe 110 and the reception distance 126 of the ultrasonic-wave-receiving probe 120 may include comparing the amplitudes of the detection signals mapped to the different combinations of the emission distance 116 of the ultrasonic-wave-emitting probe 110 and the reception distance 126 of the ultrasonic-wave-receiving probe 120, and selecting the combination of the emission distance 116 of the ultrasonic-wave-emitting probe 110 and the reception distance 126 of the ultrasonic-wave-receiving probe 120 with the maximum amplitude as the optimal combination of the emission distance 116 of the ultrasonic-wave-emitting probe 110 and the reception distance 126 of the ultrasonic-wave-receiving probe 120. Accordingly, from the mapped dataset, i.e. the set of amplitude data mapped to the different combinations of the emission distance 116 and the reception distance 126, the combination of the emission distance 116 and the reception distance 126 with the maximum amplitude may be selected as the optimal combination of the emission distance 116 and the reception distance 126.

[0070] According to various embodiments, when iteratively varying the emission distance 116 and the reception distance 126, the emission distance 116 of the ultrasonic-wave-emitting probe 110 and the reception distance 126 of the ultrasonic-wave-receiving probe 120 may be iteratively varied to progressively increase and / or decrease. Accordingly, during the iterative process 377, the emission distance 116 of the ultrasonic-wave-emitting probe 110 may be increased incrementally (and / or steadily), or decreased incrementally (and / or steadily), or increased incrementally (and / or steadily) followed by decreased incrementally (and / or steadily), or decreased incrementally (and / or steadily) followed by increased incrementally (and / or steadily), over the pre-defined range of distances. Similarly, during the iterative process 377, the reception distance 126 of the ultrasonic-wave-receiving probe 120 may be increased incrementally (and / or steadily), or decreased incrementally (and / or steadily), or increased incrementally (and / or steadily) followed by decreased incrementally (and / or steadily), or decreased incrementally (and / or steadily) followed by increased incrementally (and / or steadily), over the pre-defined range of distances.

[0071] According to various embodiments, the emission distance 116 of the ultrasonicwave-emitting probe 110 may be iteratively varied in a pre-defined range, wherein the predefined range may be from 0.01m to 0.2m, or from 0.01m to 0.15m, or from 0.01m to 0. Im, or from 0.01m to 0.08m. Similarly, the reception distance 126 of the ultrasonic-wave -receiving probe 120 may be iteratively varied in a pre-defined range, wherein the pre-defined range may be from 0.01m to 0.2m, or from 0.01m to 0.15m, or from 0.01m to 0.1m, or from 0.01m to 0.08m.

[0072] FIG. 4D shows an example of processing / analyzing of the set of recorded detection signals (e.g. data / signals) associated with the different combinations of the emission distance 116 and the reception distance 126 (or changes in lift off distances) for determining the optimal combination of the emission distance 116 and the reception distance 126. The top left chart shows a plot of the height (y-axis of the chart) of the first robotic arm 102 as a measure of the emission distance 116 of the ultrasonic-wave-emitting probe 110 at the different data point (x-axis of the chart). The top middle chart shows a plot of the height (y-axis of the chart) of the second robotic arm 104 as a measure of the reception distance 126 of the ultrasonicwave-receiving probe 120 at the different data point (x-axis of the chart). The top right chart shows a plot of the detection signals (y-axis of the chart) captured / measured by the ultrasonic -wavc-rccciving probe 120 over time (x-axis of the chart). The bottom left chart shows a plot of the positions of the first robotic arm 102 and the second robotic arm 104 in a same chart. The bottom right chart shows a plot of the amplitude (y-axis of the chart) of the detection signals against the height (x-axis of the chart) for determining the optimal height. As shown, the process / analysis may be an height-based optimization process / analysis, which may determinethe best height of the sensors (i.e. the ultrasonic-wave-emitting probe 110 and the ultrasonicwave-receiving probe 120) from the component surface (i.e. the surface 108 of the to-be-inspected article 106). From the plots as shown, the peak of the plot of the bottom right chart may be determined to be the optimal height. In particular, the bottom right chart illustrates that the robots (i.e. the first robotic arm 102 and the second robotic arm 104) may start from the distance of 0.01m from the surface 108 and be moved 0.1m away, with an optimal height of 0.07m (0.06 + 0.01) to maximize signal while ensuring sufficient lift-off for automation. In the example, the height of 0.06m may be selected when the objective is to maximize distance from the surface 108 without significant decrease in the signal amplitude. As shown, the significant drop may be at the height of 0.07 to 0.08m. Thus, the height of 0.06m may be selected.

[0073] FIG. 4E shows a schematic diagram of the ultrasonic-wave-emitting probe 110 and the ultrasonic- wave-receiving probe 120 being moved to determine another optimal parameter during the iterative process 377 according to various embodiments. According to various embodiments, during the iterative process 377, the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 may be moved to determine the optimal relative offset distance 162 between the transmitting point 130 for the ultrasonic- wave-emitting probe 110 and the receiving point 140 for the ultrasonic-wave-receiving probe 120 (as an example of the optimal parameters for positioning / orientating the ultrasonic- wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120).

[0074] According to various embodiments, the ultrasonic- ave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 may be moved, via the first robotic arm 102 and the second robotic arm 104 respectively, relative to the surface 108 of the to-be-inspected article 106 to iteratively vary the relative offset distance 162 between the transmitting point 130 and the receiving point 140 on the surface 108 of the to-be-inspected article 106 with respect to a reference alignment line 160 perpendicular to a scanning direction 192 of the scanning path 190. In the various embodiments, the ultrasonic-w'ave-emitting probe 110 and the ultrasonicwave-receiving probe 120 may on opposite sides of the scanning path. Accordingly, the ultrasonic-wave-emitting probe 110 may be on one side of the scanning path and the ultrasonicwave-receiving probe 120 may be on the opposite side across the scanning path. The ultrasonic-wavc-cmitting probe 110 may be directing the ultrasonic 'avc tow'ards the transmitting point 130 on the surface 108 of the to-be-inspected article and the ultrasonic -wave-receiving probe 120 may be pointing to the receiving point 140 on the surface 107 of the to-bc-inspcctcd article 106 so as to detect guided wave exiting from the receiving point 140. When the ultrasonicwave-emitting probe 110 and the ultrasonic-w'ave-receiving probe 120 are aligned to each other(i.e. the relative offset distance 162 is 0) with respect to the scanning direction 192 of the scanning path 190, a straight line extending between the transmitting point 130 and the receiving point 140 may be perpendicular' to the scanning direction 192 of the scanning path 190. On the other hand, when the ultrasonic-wavc-cmitting probe 110 and the ultrasonic-wavc-receiving probe 120 are offset relative to each other, either the ultrasonic-wave-emitting probe 110 is ahead of the ultrasonic- wave-receiving probe 120 in the scanning direction 192 of the scanning path 190 or the ultrasonic-wave-receiving probe 120 is ahead of the ultrasonic-wave-emitting probe 110 in the scanning direction 192 of the scanning path 190. Hence, a straight line extending between the transmitting point 130 and the receiving point 140 may be nonperpendicular to the scanning direction 192 of the scanning path 190. To quantify the offset between the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120, the reference alignment line 160 perpendicular to a scanning direction 192 of the scanning path 190 may be taken as reference. For example, by extending the reference alignment line 160 through the transmitting point 130, the relative offset distance 162 between the transmitting point 130 and the receiving point 140 may be measured as the perpendicular distance from the receiving point 140 to the reference alignment line 160. Similarly, by extending the reference alignment line through the receiving point 140, the relative offset distance 162 between the transmitting point 130 and the receiving point 140 may be measured as the perpendicular distance from the transmitting point 130 to the reference alignment line 160. In the various embodiments, a y-axis of a reference coordinate system may be aligned to the scanning path 190. Accordingly, the relative offset distance 162 between the transmitting point 130 for the ultrasonic-wave-emitting probe 110 and the receiving point 140 for the ultrasonic-wave-receiving probe 120 may be a y-axis distance between the transmitting point 130 for the ultrasonic-wave-emitting probe 110 and the receiving point 140 for the ultrasonic-wave-receiving probe 120.

[0075] In the various embodiments, the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 may be moved by small and / or incremental steps over a series of motion of the first robotic arm 102 and the second robotic arm 104 to vary the relative offset distance 162 between the transmitting point 130 and the receiving point 140 on the surface 108 of the to-bc-inspcctcd article 106 with respect to the reference alignment line 160 perpendicular to the scanning direction 192 of the scanning path 190. According some embodiments, the ultrasonic-wavc-cmitting probe 110 and the ultrasonic-wavc-rccciving probe 120 may be moved to iteratively vary the relative offset distance 162 between the transmitting point 130 and the receiving point 140 after the optimal combination of the incident angle 114of the ultrasonic-wave-emitting probe 110 and the receiver angle 124 of the ultrasonic-wave-receiving probe 129 is determined. Accordingly, when moving the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 iteratively to vary the relative offset distance 162 between the transmitting point 130 and the receiving point 140, the ultrasonicwave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 may respectively be oriented and maintained at the optimal combination of the incident angle 114 of the ultrasonicwave-emitting probe 110 and the receiver angle 124 of the ultrasonic-wave-receiving probe 129. Thus, the ultrasonic-wave-emitting probe 110 may be moved forward or rearward with respect to the scanning direction 192 of the scanning path 190 while maintaining the optimal incident angle 114 of the ultrasonic-wave-emitting probe 110. Similarly, the ultrasonic-wave-receiving probe 120 may be moved forward or rearward with respect to the scanning direction 192 of the scanning path 190 while maintaining the optimal receiver angle 124 of the ultrasonic-wave-receiving probe 129.

[0076] In the various embodiments, as the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 are iteratively moved to vary the relative offset distance 162 between the transmitting point 130 and the receiving point 140 on the surface 108 of the to-be-inspected article 106 with respect to the reference alignment line 160 perpendicular' to the scanning direction 192 of the scanning path 190, detection signals (e.g. data / signals) captured / measured by the ultrasonic-wave-receiving probe 120 for different relative offset distances 162 between the transmitting point 130 and the receiving point 140 may be recorded. Subsequently, the set of recorded detection signals (e.g. data / signals) associated with the different relative offset distances 162 between the transmitting point 130 and the receiving point 140 may be analyzed and processed.

[0077] According to various embodiments, an optimal relative offset distance 162 between the transmitting point 130 and the receiving point 140 with respect to the reference alignment line 160 may be selected from the different relative offset distances 162 between the transmitting point 130 and the receiving point 140 with respect to the reference alignment line 160 based on the detection signal of the ultrasonic-wave-receiving probe 120 having a maximum amplitude. Accordingly, from the set of recorded detection signals (e.g. data / signals) associated with the different relative offset distances 162 between the transmitting point 130 and the receiving point 140 on the surface 108 of the to-be-inspected article 106 with respect to the reference alignment line 160 perpendicular to the scanning direction 192 of the scanning path 190, the detection signal with the maximum amplitude may be selected and the relative offset distance 162 between the transmitting point 130 and the receiving point 140 associatedwith said detection signal may than be the optimal relative offset distance 162 between the transmitting point 130 and the receiving point 140 on the surface 108 of the to-be-inspected article 106 with respect to the reference alignment line 160 perpendicular to the scanning direction 192 of the scanning path 190.

[0078] According to various embodiments, with the optimal relative offset distance 162 between the transmitting point 130 and the receiving point 140 determined or selected, inspection of the to-be-inspected article 106 may be performed based on the optimal relative offset distance 162 between the transmitting point 130 and the receiving point 140. According to various embodiments, during the inspection process, scanning of the to-be-inspected article 106 may be performed by moving the ultrasonic-wave-emitting probe 110 and the ultrasonicwave-receiving probe 120 relative to the surface 108 of the to-be-inspected article 106 along a scanning path and with the ultrasonic-wave-emitting probe 110 and the ultrasonic-wavereceiving probe 120 maintained at the optimal relative offset distance 162 between the transmitting point 130 and the receiving point 140 on the surface 108 of the to-be-inspected article 106 with respect to the reference alignment line 160 perpendicular to the scanning direction 192 of the scanning path 190. Accordingly, the optimal relative offset distance 162 between the transmitting point 130 and the receiving point 140, serving as the optimal parameters, may be applied to the initial toolpath so as to enhance the initial toolpath for optimal scanning / inspection.

[0079] According to various embodiments, when recording the detection signals (e.g. data / signals) captured / measured by the ultrasonic-wave-receiving probe 120 for different relative offset distances 162 between the transmitting point 130 and the receiving point 140 on the surface 108 of the to-be-inspected article 106 with respect to the reference alignment line 160 perpendicular to the scanning direction 192 of the scanning path 190, a set of amplitude data comprising amplitudes of detection signals measured by the ultrasonic-wave-receiving probe 120 when moving the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 to iteratively vary the relative offset distance 162 between the transmitting point 130 and the receiving point 140 may be compiled. Hence, the set of amplitude data compiled may be associated with changes in relative offset distance 162 between the transmitting point 130 and the receiving point 140 (i.c. changes in the relative offset distance 162 between the transmitting point 130 and the receiving point 140 on the surface 108 of the to-bc-inspcctcd article 106 with respect to the reference alignment line 160 perpendicular to the scanning direction 192 of the scanning path 190).

[0080] In the various embodiments, the set of amplitude data associated with the changes in relative offset distance 162 between the transmitting point 130 and the receiving point 140 may be obtained via continuous measurement of the amplitudes of the detection signals of the ultrasonic-wavc-rccciving probe 120 when the relative offset distance 162 between the transmitting point 130 and the receiving point 140 is iteratively varied. According to various embodiments, the set of amplitude data associated with the changes in relative offset distance 162 between the transmitting point 130 and the receiving point 140 may then be mapped to the different relative offset distances 162 between the transmitting point 130 and the receiving point 140. According to various embodiments, the range of distances for the relative offset distance 162 between the transmitting point 130 and the receiving point 140 may be pre-defined. Accordingly, the continuous measurement of the amplitudes of the detection signals of the ultrasonic-wave-receiving probe 120 may then be mapped to the pre-defined range of the relative offset distance 162 between the transmitting point 130 and the receiving point 140.

[0081] According to various embodiments, selecting the optimal relative offset distance 162 between the transmitting point 130 and the receiving point 140 may include comparing the amplitudes of the detection signals mapped to the different corresponding relative offset distances 162 between the transmitting point 130 and the receiving point 140, and selecting a relative offset distance 162 between the transmitting point 130 and the receiving point 140 with the maximum amplitude as the optimal relative offset distance 162 between the transmitting point 130 and the receiving point 140. Accordingly, from the mapped dataset, i.e. the set of amplitude data mapped to the different relative offset distances 162 between the transmitting point 130 and the receiving point 140, the relative offset distance 162 between the transmitting point 130 and the receiving point 140 with the maximum amplitude may be selected as the optimal relative offset distance 162 between the transmitting point 130 and the receiving point 140.

[0082] According to various embodiments, when iteratively varying the relative offset distance 162 between the transmitting point 130 and the receiving point 140, the relative offset distance 162 between the transmitting point 130 and the receiving point 140 may be iteratively varied to progressively increase and / or decrease. Accordingly, during the iterative process 377, the relative offset distance 162 between the transmitting point 130 and the receiving point 140 may be increased incrementally (and / or steadily), or decreased incrementally (and / or steadily), or increased incrementally (and / or steadily) followed by decreased incrementally (and / orsteadily), or decreased incrementally (and / or steadily) followed by increased incrementally (and / or steadily), over the pre-defined range of distances.

[0083] FIG. 4F shows a schematic diagram of the ultrasonic-wave-emitting probe 110 and the ultrasonic- wave-receiving probe 120 being moved to determine another optimal parameter during the iterative process 377 according to various embodiments. According to various embodiments, during the iterative process 377, the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 may be moved to determine the optimal lateral distance apart 150 between the transmitting point 130 for the ultrasonic- wave-emitting probe 110 and the receiving point 140 for the ultrasonic-wave-receiving probe 120 (as an example of the optimal parameters for positioning / orientating the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120).

[0084] According to various embodiments, the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 may be moved, via the first robotic arm 102 and the second robotic arm 104 respectively, relative to the surface 108 of the to-be-inspected article 106 to iteratively vary the lateral distance apart 150 between the transmitting point 130 and the receiving point 140 on the surface 108 of the to-be-inspected article 106 with respect to the scanning path 190. In the various embodiments, as the ultrasonic-wave-emitting probe 110 may be directing the ultrasonic wave towards the transmitting point 130 and the ultrasonic-wave-receiving probe 120 may be pointing to the receiving point 140, the lateral distance apart 150 between the transmitting point 130 and the receiving point 140 on the surface 108 of the to-be-inspected article 106 may be varied by moving the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 towards or away from each other. Accordingly, the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 may be moved closer to each other or further apart from each other so as to vary the lateral distance apart 150 between the transmitting point 130 and the receiving point 140 on the surface 108 of the to-be-inspected article 106 with respect to the scanning path 190. In the various embodiments, the lateral distance apart 150 between the transmitting point 130 for the ultrasonic-wave-emitting probe 110 and the receiving point 140 for the ultrasonic- wavereceiving probe 120 may be a x-axis distance, with reference to the reference coordinate system having the y-axis thereof aligned to the scanning path 190, between the transmitting point (130) for the ultrasonic-wave-emitting probe (110) and the receiving point (140) for the ultrasonic -wavc-rccciving probe (120).

[0085] In the various embodiments, the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 may be moved by small and / or incremental steps over aseries of motion of the first robotic arm 102 and the second robotic arm 104 to vary the lateral distance apart 150 between the transmitting point 130 and the receiving point 140 on the surface 108 of the to-be-inspected article 106 with respect to the scanning path 190. According some embodiments, the ultrasonic-wavc-cmitting probe 110 and the ultrasonic-wavc-rccciving probe 120 may be moved to iteratively vary the lateral distance apart 150 between the transmitting point 130 and the receiving point 140 on the surface 108 of the to-be-inspected article 106 after the optimal combination of the incident angle 114 of the ultrasonic-wave-emitting probe 110 and the receiver angle 124 of the ultrasonic -wave-receiving probe 129 is determined. Accordingly, when moving the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 iteratively to vary the lateral distance apart 150 between the transmitting point 130 and the receiving point 140 on the surface 108 of the to-be-inspected article 106, the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 may respectively be oriented and maintained at the optimal combination of the incident angle 114 of the ultrasonic-wave-emitting probe 110 and the receiver angle 124 of the ultrasonic-wave-receiving probe 129. Thus, the ultrasonic-wave-emitting probe 110 may be moved sideways with respect to the scanning direction 192 of the scanning path 190 while maintaining the optimal incident angle 114 of the ultrasonic-wave-emitting probe 110. Similarly, the ultrasonic-wave-receiving probe 120 may be moved sideways with respect to the scanning direction 192 of the scanning path 190 while maintaining the optimal receiver angle 124 of the ultrasonic-wave-receiving probe 129.

[0086] In the various embodiments, as the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 are iteratively moved to vary the lateral distance apart 150 between the transmitting point 130 and the receiving point 140 on the surface 108 of the to-be-inspected article 106 with respect to the scanning path 190, detection signals (e.g. data / signals) captured / measured by the ultrasonic-wave-receiving probe 120 for different lateral distance apart 150 between the transmitting point 130 and the receiving point 140 may be recorded. Subsequently, the set of recorded detection signals (e.g. data / signals) associated with the different relative lateral distance apart 150 between the transmitting point 130 and the receiving point 140 may be analyzed and processed.

[0087] According to various embodiments, an optimal lateral distance apart 150 between the transmitting point 130 and the receiving point 140 on the surface 108 of the to-be-inspcctcd article 106 may be selected from the different lateral distances apart 150 between the transmitting point 130 and the receiving point 140 on the surface 108 of the to-be-inspected article 106 based on the detection signal of the ultrasonic-wave-receiving probe 120 having amaximum amplitude. Accordingly, from the set of recorded detection signals (e.g. data / signals) associated with the different lateral distances apart 150 between the transmitting point 130 and the receiving point 140 on the surface 108 of the to-be-inspected article 106, the detection signal with the maximum amplitude may be selected and the lateral distance apart 150 between the transmitting point 130 and the receiving point 140 associated with said detection signal may than be the optimal lateral distance apart 150 between the transmitting point 130 and the receiving point 140 on the surface 108 of the to-be-inspected article 106.

[0088] According to various embodiments, with the optimal lateral distance apart 150 between the transmitting point 130 and the receiving point 140 determined or selected, inspection of the to-be-inspected article 106 may be performed based on the optimal lateral distance apart 150 between the transmitting point 130 and the receiving point 140. According to various embodiments, during the inspection process, scanning of the to-be-inspected article 106 may be performed by moving the ultrasonic-wave-emitting probe 110 and the ultrasonicwave-receiving probe 120 relative to the surface 108 of the to-be-inspected article 106 along a scanning path and with the ultrasonic-wave-emitting probe 110 and the ultrasonic-wavereceiving probe 120 maintained at the optimal lateral distance apart 150 between the transmitting point 130 and the receiving point 140 on the surface 108 of the to-be-inspected article 106. Accordingly, the optimal lateral distance apart 150 between the transmitting point 130 and the receiving point 140, serving as the optimal parameters, may be applied to the initial toolpath so as to enhance the initial toolpath for optimal scanning / inspection.

[0089] According to various embodiments, when recording the detection signals (e.g. data / signals) captured / measured by the ultrasonic-wave-receiving probe 120 for different relative lateral distances apart 150 between the transmitting point 130 and the receiving point 140 on the surface 108 of the to-be-inspected article 106, a set of amplitude data comprising amplitudes of detection signals measured by the ultrasonic-wave-receiving probe 120 when moving the ultrasonic- wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 to iteratively vary the relative lateral distance apart 150 between the transmitting point 130 and the receiving point 140 may be compiled. Hence, the set of amplitude data compiled may be associated with changes in relative lateral distance apart 150 between the transmitting point 130 and the receiving point 140 (i.e. changes in the relative lateral distance apart 150 between the transmitting point 130 and the receiving point 140 on the surface 108 of the to-bc-inspcctcd article 106 with respect to the scanning path 190).

[0090] In the various embodiments, the set of amplitude data associated with the changes in relative lateral distance apart 150 between the transmitting point 130 and the receiving point 140 may be obtained via continuous measurement of the amplitudes of the detection signals of the ultrasonic-wavc-rccciving probe 120 when the relative lateral distance apart 150 between the transmitting point 130 and the receiving point 140 is iteratively varied. According to various embodiments, the set of amplitude data associated with the changes in relative lateral distance apart 150 between the transmitting point 130 and the receiving point 140 may then be mapped to the different relative lateral distances apart 150 between the transmitting point 130 and the receiving point 140. According to various embodiments, the range of distances for the lateral distance apart 150 between the transmitting point 130 and the receiving point 140 may be pre-defined. Accordingly, the continuous measurement of the amplitudes of the detection signals of the ultrasonic-wave-receiving probe 120 may then be mapped to the pre-defined range of the relative lateral distance apart 150 between the transmitting point 130 and the receiving point 140.

[0091] According to various embodiments, selecting the optimal lateral distance apart 150 between the transmitting point 130 and the receiving point 140 may include comparing the amplitudes of the detection signals mapped to the different corresponding lateral distance apart 150 between the transmitting point 130 and the receiving point 140, and selecting a lateral distance apart 150 between the transmitting point 130 and the receiving point 140 with the maximum amplitude as the optimal lateral distance apart 150 between the transmitting point 130 and the receiving point 140. Accordingly, from the mapped dataset, i.e. the set of amplitude data mapped to the different lateral distances apart 150 between the transmitting point 130 and the receiving point 140, the lateral distance apart 150 between the transmitting point 130 and the receiving point 140 with the maximum amplitude may be selected as the optimal lateral distance apart 150 between the transmitting point 130 and the receiving point 140.

[0092] According to various embodiments, when iteratively varying the lateral distance apart 150 between the transmitting point 130 and the receiving point 140, the lateral distance apart 150 between the transmitting point 130 and the receiving point 140 may be iteratively varied to progressively increase and / or decrease. Accordingly, during the iterative process 377, the lateral distance apart 150 between the transmitting point 130 and the receiving point 140 may be increased incrementally (and / or steadily), or decreased incrementally (and / or steadily), or increased incrementally (and / or steadily) followed by decreased incrementally (and / or steadily), or decreased incrementally (and / or steadily) followed by increased incrementally (and / or steadily), over the pre-defined range of distances.

[0093] According to various embodiments, the lateral distance apart 150 between the transmitting point 130 and the receiving point 140 may be iteratively varied in a pre -defined range, wherein the pre-defined range may be from 0.05m to 0.5m, or from 0.1m to 0.4m, or from 0.12m to 0.36m.

[0094] FIG. 4G shows an example of processing / analyzing of the set of recorded detection signals (e.g. data / signals) associated with the different with the different offsets or lateral distances apart 150 between the transmitting point 130 and the receiving point 140 on the surface 108 of the to-be-inspected article 106 for determining the optimal combination of the lateral distances apart 150 between the transmitting point 130 and the receiving point 140 on the surface 108 of the to-be-inspected article 106. The top left chart shows a plot of the lateral positions (y-axis of the chart) of the first robotic arm 102 as a measure of the lateral positions of the ultrasonic- wave-emitting probe 110 at the different data point (x-axis of the chart). The top middle chart shows a plot of the lateral positions (y-axis of the chart) of the second robotic arm 104 as a measure of the lateral positions of the ultrasonic-wave-receiving probe 120 at the different data point (x-axis of the chart). The top right chart shows a plot of the detection signals (y-axis of the chart) captured / measured by the ultrasonic-wave-receiving probe 120 over time (x-axis of the chart). The bottom left chart shows a plot of the lateral positions of the first robotic arm 102 and the second robotic arm 104 in a same chart. The bottom right chart shows a plot of the amplitude (y-axis of the chart) of the detection signals against the lateral distance apart (x-axis of the chart) for determining the optimal lateral distance apart. As shown, the process / analysis may be a positional-based optimization process / analysis, which may determine the best interval between the sensors (i.e. the ultrasonicwave-emitting probe 110 and the ultrasonic-wave-receiving probe 120). From the plots as shown, the peak of the plot of the bottom right chart may be determined to be the optimal lateral distance apart. In particular, the bottom left chart illustrates that the robots (i.e. the first robotic arm 102 and the second robotic arm 104) may move towards each other from the distance of 0.36m to 0.12m, with each robot moving approximately 0.12m. For this optimization, the tendency may be for stable signals to dominate and for the sensors to be closer. Hence, as long as there are no step functions representing significant changes, any distance may be acceptable.

[0095] According to various embodiments, during the iterative process 377, the system 100 and / or method may determine at least the optimal incident angle 114 of the ultrasonic -wavc-cmitting probe 110 and the optimal receiver angle 124 of the ultrasonic- wave-receiving probe. According to various embodiments, the system 100 and / or method may additionally determine at least one or a combination of (i) the optimal emission distance 116 of theultrasonic- wave-emitting probe 110 and the optimal reception distance 126 of the ultrasonicwave-receiving probe 120; (ii) the optimal relative offset distance 162 between the transmitting point 130 for the ultrasonic-wave-emitting probe 110 and the receiving point 140 for the ultrasonic-wavc-rccciving probe 120; and (iii) the optimal lateral distance apart 150 between the transmitting point 130 for the ultrasonic-wave-emitting probe 110 and the receiving point 140 for the ultrasonic-wave-receiving probe 120.

[0096] According to various embodiments, the system 100 and / or method may perform one or more cycles of the iterative process 377 (i.e. optimization process) before proceeding with the inspection process. When there are two or more cycles of the iterative process 377, determination of at least one of the optimized parameters may be repeated in the two or more cycles of the iterative process 377. For example, in a first cycle of the iterative process 377, the system 100 and / or method may determine (i) the optimal incident angle 114 of the ultrasonicwave-emitting probe 110 and the optimal receiver angle 124 of the ultrasonic-wave-receiving probe 120; (ii) the optimal emission distance 116 of the ultrasonic-wave-emitting probe 110 and the optimal reception distance 126 of the ultrasonic-wave-receiving probe 120; (iii) the optimal relative offset distance 162 between the transmitting point 130 for the ultrasonic-wave-emitting probe 110 and the receiving point 140 for the ultrasonic-wave-receiving probe 120; and (iv) the optimal lateral distance apart 150 between the transmitting point 130 for the ultrasonic-wave-emitting probe 110 and the receiving point 140 for the ultrasonic-wave-receiving probe 120. In a second cycle of the iterative process 377, the system 100 and / or method may determine (i) the optimal incident angle 114 of the ultrasonic-wave-emitting probe 110 and the optimal receiver angle 124 of the ultrasonic-wave-receiving probe 120; (ii) the optimal lateral distance apart 150 between the transmitting point 130 for the ultrasonic-wave-emitting probe 110 and the receiving point 140 for the ultrasonic-wave-receiving probe 120; and / or (iii) the optimal lateral distance apart 150 between the transmitting point 130 for the ultrasonic-wave-emitting probe 110 and the receiving point 140 for the ultrasonic- wavereceiving probe 120. In the various embodiments, with two or more cycles of the iterative process 377, one or more of the optimized parameters may be refined and / or tuned to be more accurate.

[0097] According to various embodiments, before commencing the iterative process 377, the lateral distance apart 150 between the transmitting point 130 and the receiving point 140 on the surface 108 of the to-bc-inspcctcd article 106 may be set to a prc-dctcrmincd distance 152. Accordingly, prior to moving the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120, via the first robotic arm 102 and the second robotic arm104 respectively, relative to the surface 108 of the to-be-inspected article 106 to iteratively vary the incident angle 114 and the receiver angle 124, the ultrasonic-wave-emitting probe 110 and the ultrasonic- wave-receiving probe 120 may be moved to a starting position / orientation whereby the lateral distance apart 150 between the transmitting point 130 and the receiving point 140 on the surface 108 of the to-be-inspected article 106 is the pre-determined distance 152. Through the iterative process 377, the optimal lateral distance apart 150 between the transmitting point 130 and the receiving point 140 may be subsequently obtained and the position / orientation may be updated for subsequent conduct of the inspection process.

[0098] According to various embodiments, the first robotic arm 102 may be controlled to move the ultrasonic-wave-emitting probe 110 and the second robotic arm 104 may be controlled to move the ultrasonic-wave-receiving probe 120. In the various embodiments, the iterative process 377 may be performed automatically via the processor 105 to control the first robotic arm 102 and the second robotic arm 104 to move the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120, respectively, with respect to the surface 108 of the to-be-inspected article 106. Accordingly, the first robotic aim 102 and the second robotic arm 104 may be controlled by the processor 105 to move the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120, respectively, through the various orientations and / or positions, measure the strength of the corresponding ultrasonic wave received or sensed by the ultrasonic-wave-receiving probe 120 at the various orientations and / or positions, compare the strength of the ultrasonic wave sensed and determine (or select) the optimal orientation and / or position for conducting the inspection process of the air-coupled guided wave inspection.

[0099] Upon determining the optimal orientation and / or position for conducting the inspection process of the air-coupled guided wave inspection, the system 100 and / or method of the various embodiments may proceed with the inspection process of the air-coupled guided wave inspection. According to various embodiments, during the inspection process, the ultrasonic-wave-emitting probe 110 and the ultrasonic- wave-receiving probe 120 may be maintained or kept in the optimal orientation and / or position (as previously determined) relative to each other. Further, the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-rccciving probe 120 may be moved, together, synchronously or simultaneously or concurrently, while maintaining the optimal orientation and / or position relative to each other, along the scanning path 190 during the inspection process. The ultrasonic-wavc-cmitting probe 110 and the ultrasonic-wave-receiving probe 120 may be moved synchronously relative to the surface 108 of the to-be-inspected article 106 so as to scan the surface 108 of the to-be-inspected article106 for inspecting an interior of the to-be-inspected article 106. This scanning may be performed along the scanning direction 192.[000100] According to various embodiments, when the to-be-inspected article 106 has planar geometries like sheets, pipes and aerofoils, the ultrasonic-wavc-cmitting probe 110 and the ultrasonic-wave-receiving probe 120 may be stationary or non-movable with respect to each other during the inspection step. Accordingly, the relative positions and / or orientation between the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120 with respect to each other may be maintained or preserved as the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave -receiving probe 120 are being moved relative to the surface 108 of the to-be-inspected article 106 so as to scan the to-be-inspected article 106. On the other hand, for non-planar geometries, the ultrasonic-wave-emitting probe 110 and the ultrasonicwave-receiving probe 120 may be moved relative to each other in order to maintain / preserve the optimal incident angle 114 of the ultrasonic-wave-emitting probe 110 and the optimal receiver angle 124 of the ultrasonic-wave-receiving probe 120; and / or the optimal emission distance 116 of the ultrasonic-wave-emitting probe 110 and the optimal reception distance 126 of the ultrasonic-wave-receiving probe 120; and / or the optimal relative offset distance 162 between the transmitting point 130 for the ultrasonic-wave-emitting probe 110 and the receiving point 140 for the ultrasonic-wave-receiving probe 120; and / or the optimal lateral distance apart 150 between the transmitting point 130 for the ultrasonic- wave-emitting probe 110 and the receiving point 140 for the ultrasonic-wave-receiving probe 120.[000101] According to some embodiments, the scanning path 190 may be a single straight track across the surface 108 of the to-be-inspected article 106 (e.g. as shown in FIG. 4E). With such a scanning path, the inspection process of the system 100 and / or method of the various embodiments may provide a simple “pass” or “fail” result, whereby the “pass” result may indicate no defect is detected in the to-be-inspected article 106 and the “fail” result may indicate that at least a defect is detected in the to-be-inspected article 106.[000102] According to some embodiments, the scanning path 190 may be a multi-track zig-zag scanning path 190a covering the surface 108 of the to-be-inspected article 106. With such a scanning path, a general location of the defect with reference to the surface 108 of the to-bc-inspcctcd article 106 may be obtained. In these embodiments, the scanning path 190 may be the zig-zag scanning path 190a as shown in FIG. 5A.[000103] According to some embodiments, the system 100 and / or method of the various embodiments may be utilized to pin-point a location of the defect with reference to the surface 108 of the to-be-inspected article 106. For example, two runs of scanning according to thevarious embodiments may be performed. The first run of scanning may be along the zig-zag scanning path 190a with a major axis 194a as shown in FIG. 5A. The second run of the method may be for the zig-zag scanning path 190b with the major axis 194b as shown in FIG. 5B. During each run, the iterative process 377 may be performed before the inspection process. The results of the two runs may then be overlaid, one over the other, to pin-point the location of the defect with reference to the surface 108 of the to-be-inspected article 106. Therefore, according to various embodiments, the scanning path 190 may include the zig-zag scanning path 190a and the further zig-zag scanning path 190b, wherein the zig-zag scanning path 190a and the further zig-zag scanning path 190b may be orthogonal with respect to each other. Accordingly, the major axis 194b of the further zig-zag scanning path 190b may be perpendicular to the major axis 194a of the zig-zag scanning path 190a. Further, the zig-zag scanning path 190a and the zig-zag scanning path 190b may overlap each other in a crisscross manner. In such an example, the location of the defect may be determined with reference to the surface 108 of the to-be-inspected 106.[000104] In the various embodiments, the system 100 with the first robotic aim 102 and the second robotic arm 104 (i.e. a two -robotic-arm system) may handle a wide range of inspection tasks, and may provide ease of integration, repeatability, and cost-effectiveness. To operate the system 100 during the inspection process, two sets of toolpaths may be required for the first robotic arm 102 and the second robotic arm 104 to work in tandem for performing inspection.[000105] According to various embodiments, the automation toolpath for the inspection process may be generated via on-robot programming (e.g. with teach pendant) or offline programming (e.g. through use of tool pathing software). As an example, toolpaths with two-axis movements or less may be programmed directly via on-robot programming, while complex toolpaths involving three-axis movements or more may be generated using offline programming with software. For developing the toolpath for the inspection process, a few key process parameters (variables) for the automation may be required.[0()()l()6] According to some embodiments, one of the parameters may be an angular alignment, a. The first robotic arm 102 and the second robotic arm 104 may be aligned and conformed to the surface 108 of the to-bc-inspcctcd article 106. For example, the first robotic aim 102 and the second robotic aim 104 may respectively be angled from the normal of the surface 108 so as to correspondingly angle the ultrasonic-wavc-cmitting probe 110 and the ultrasonic- wave-receiving probe 120 respectively to a certain angle (depending on the3geometry of the article 106) from the normal of the surface 108 of the article 106. In some embodiments, the article 106 may require an accuracy of ±5°.[000107] According to some embodiments, another parameter may be a lift-off distance (or height), z. The lift-off distance, z, may refer to a distance of each of the ultrasonic-wavc-emitting probe 110 and the ultrasonic-wave-receiving probe 120 from the surface 108 of the article 106.[000108] According to some embodiments, another parameter may be a positional tolerance, y. The position tolerance may be the offset distance between the ultrasonic-waveemitting probe 110 and the ultrasonic-wave-receiving probe 120 respectively held by the first robotic arm 102 and the second robotic arm 104. In some embodiments, the larger the positional tolerance, y, (i.e. the further the offset distance), the lower the signal strength. However, the smaller the positional tolerance, y, (i.e. the closer the offset distance), the higher the signal with higher noise. Therefore, the positional tolerance (i.e. the offset distance) may need to be optimized for best signal-to-noise-ratio (SNR), without saturating the signal with direct air-to-air noise.[000109] According to some embodiments, another parameter may be an inter-sensor distance, d. The inter- sensor distance, d. may be the lateral distance apart between the ultrasonic-wave-emitting probe 110 and the ultrasonic-wave-receiving probe 120. In the various embodiments, the inter-sensor distance may be maximized while ensuring reasonable signal response. According to an example, the range for the inter-sensor distance, d. may be 0.12m to 0.36m.[000110] As discussed previously, the various parameters above may be optimized during the iterative process 377.[000111] According to various embodiments, for robotic synchronization between the first robotic arm 102 and the second robotic arm 104, digital input / output (I / O) may be utilized for controlling the first robotic arm 102 and the second robotic arm 104. The digital input / output (I / O) may allow for synchronization of movement to ensure the first robotic arm 102 and the second robotic arm 104 may be moved in tandem to perform parallel movement to one another during the inspection process. According to some embodiments, the first robotic arm 102 may be assigned as a master robot to ‘lead’ the movement while the second robotic aim 104 may act as a slave robot that waits for commands from the master robot.[000112] For an example, a pseudo code for the master robot and the slave robot may be as show in table 1 below.[000113] Table 1.000114] According to various embodiments, the above loop (of the pseudo code) may repeat for each segment of the toolpath, ensuring handshakes between the robots (i.e. master robot and slave robot) through the digital I / O to ensure both robots (i.e. master robot and slave robot) may be in sync and not lagging or leading one another.[000115] According to various embodiments, the ultrasonic signal captured / measured by the ultrasonic-wave-receiving probe 120 may be encoded together with the coordinates of the robots (e.g. the first robotic arm 102 and the second robotic arm 104). The encoding function may be performed by tracking the scan initialization position and saving this as the start point. All 6 coordinates (x, y, z, rx, ry, rz) from the robotic arm EOAT may be saved into an array. The ultrasonic data may also be saved within a similar anay, with the same index. A pseudo code is provided in table two below as an example.[000116] Table 2[000117] FIG. 6 shows an example of the charts of the post-processing process 379 of the inspection process according to various embodiments. Following from the pseudo code inTable 2, once the N cycles have been completed for the scan during the inspection process, the robot movement may be plotted. As shown in FIG. 6, the top left chart shows a plot of the positions (y-axis of the chart) of the first robotic arm 102 as a measure of the positions of the ultrasonic-wavc-cmitting probe 110 at the different data point (x-axis of the chart). The top middle chart shows a plot of the positions (y-axis of the chart) of the second robotic arm 104 as a measure of the positions of the ultrasonic-wave-receiving probe 120 at the different data point (x-axis of the chart). The top right chart shows a plot of the detection signals (y-axis of the chart) captured / measured by the ultrasonic-wave-receiving probe 120 over time (x-axis of the chart). The bottom left chart shows a plot of the positions of the first robotic arm 102 and the second robotic arm 104 together in a same chart, whereby the plot illustrates the movements of the first robotic arm 102 and the second robotic arm 104. The difference in start coordinate from the toolpath side may be recorded and the difference may be assigned to the whole relative array. This may effectively recreate the live toolpath for both robots (i.e. the first robotic arm 102 and the second robotic arm 104). The final step may be the plotting of the pass / fail criteria, based on the N value for array 1. With the criteria, line is drawn between the N values of array 2, for both robot coordinates, indicating that a defect within the scan region. This may be seen in the bottom right chart in FIG. 6. As shown in the bottom right chart in FIG. 6, the top-most solid bold line and the bottom-most solid bold line may be representations of the positions of the robots (i.e. the first robotic arm 102 and the second robotic arm 104); the areas with oblique hatching may be a representation of defects that have exceeded a predetermined threshold range; the dash lines may be a representation of defects within the predetermined threshold range; and the empty area may be a representation of areas free of defects.[000118] Various embodiments have provided a system and / or method for air-coupled guided wave inspection capable of detecting defects such as delaminations and / or disbonds in an article. The system and / or method of the various embodiments may be an iteratively and adaptive automated system for conducting non-contact air-coupled ultrasonic inspection on materials, such as CFRP and GFRP composite materials. The system and / or method of the various embodiments may be applied to articles with various geometries without being limited to planar' geometries. Various embodiments may also be capable of defect sizing and localization. Further, the system or method of the various embodiments may reduce the need for a lengthy conventional research & development (R&D) process for guided wave inspection of large form composites. According to various embodiments, there may be iterative feedback on parameters such as height, distance, and angle, and applying this feedback to the original toolpath. This may result in capabilities accelerating usage and simplifying automation of grid-based localization for detection of defects such as delaminations, disbonds and surface discontinuities.[000119] According to various embodiments, the system and / or method for air-coupled guided wave inspection as described herein may be versatile and easy to use. For example, the system components may be simplified when the rate of the parts to be inspected are simplified. The system of the various embodiments may also be applicable to a larger range of composite types. Further, the system and / or method of the various embodiments may also provide time saving as compared to the conventional air-coupled guided wave inspection. For example, the system and / or method of the various embodiments may require lesser time to complete inspection after the sample size is above a certain number (e.g. 30). Furthermore, the system and / or method of the various embodiments may be relatively robust and insensitive to minor alignment and displacement changes.[000120] While the invention has been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes, modification, variation in form and detail may be made therein without departing from the scope of the invention as defined by the appended claims. The scope of the invention is thus indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced.

Claims

Claims1. A method of air-coupled guided wave inspection, comprising:moving an ultrasonic-wave-emitting probe and an ultrasonic-wave-receiving probe, via a first robotic arm and a second robotic arm respectively, relative to a surface of a to-be-inspected article to iteratively vary an incident angle and a receiver angle, the incident angle being between an emission axis of the ultrasonic- ave-emitting probe and a normal of a transmitting point on the surface of the to-be-inspected article and the receiver angle being between a detection axis of the ultrasonic-wave-receiving probe and a normal of a receiving point on the surface of the to-be-inspected article, wherein the transmitting point is an intersection point of the emission axis of the ultrasonic-wave-emitting probe and the surface of the to-be-inspected article, wherein the receiving point is an intersection point of the detection axis of the ultrasonic-wave-receiving probe and the surface of the to-be-inspected article;selecting an optimal combination of the incident angle of the ultrasonic-wave-emitting probe and the receiver angle of the ultrasonic-wave-receiving probe from different combinations of the incident angle of the ultrasonic-wave-emitting probe and the receiver angle of the ultrasonic-wave-receiving probe based on a detection signal of the ultrasonicwave-receiving probe having a maximum amplitude; andperforming scanning of the to-be-inspected article by moving the ultrasonic- waveemitting probe and the ultrasonic-wave-receiving probe relative to the surface of the to-be-inspected article along a scanning path and with the ultrasonic-wave-emitting probe and the ultrasonic-wave-receiving probe respectively oriented at the optimal combination of the incident angle of the ultrasonic-wave-emitting probe and the receiver angle of the ultrasonicwave-receiving probe.

2. The method according to claim 1 , further comprisingcompiling a set of amplitude data associated with changes in angle comprising amplitudes of detection signal measured by the ultrasonic-wave-receiving probe when moving the ultrasonic-wave-emitting probe and the ultrasonic-wave-receiving probe to iteratively vary the incident angle and the receiver angle; andmapping the set of amplitude data associated with changes in angle to the different combinations of the incident angle of the ultrasonic-wavc-cmitting probe and the receiver angle of the ultrasonic-wave-receiving probe,wherein selecting the optimal combination of the incident angle of the ultrasonicwave-emitting probe and the receiver angle of the ultrasonic-wave-receiving probe comprises comparing the amplitudes of the detection signals mapped to the different combinations of the incident angle of the ultrasonic-wavc-cmitting probe and the receiver angle of the ultrasonic-wave-receiving probe and selecting a combination of the incident angle of the ultrasonic-wave-emitting probe and the receiver angle of the ultrasonic-wave-receiving probe with the maximum amplitude as the optimal combination of the incident angle of the ultrasonic-wave-emitting probe and the receiver angle of the ultrasonic -wave-receiving probe.

3. The method according to claim 1, wherein the incident angle of the ultrasonic-wave-emitting probe and the receiver angle of the ultrasonic-wave-receiving probe are iteratively varied to progressively increase and / or decrease.

4. The method according to claim 1, wherein the incident angle of the ultrasonic-wave-emitting probe and the receiver angle of the ultrasonic-wave-receiving probe are iteratively varied in a pre-defined range, wherein the pre-defined range is from 10 degree to 80 degree, or from 15 degree to 75 degree, or from 25 degree to 65 degree, or from 30 degree to 60 degree, or from 35 degree to 55 degree, or from 0 degree to 65 degree.

5. The method according to claim 1, wherein the emission axis of the ultrasonic-wave-emitting probe and the detection axis of the ultrasonic-wave-receiving probe lie in a same plane and are converging.

6. The method according to claim 1, further comprisingmoving the ultrasonic-wave-emitting probe and the ultrasonic-wave-receiving probe, via the first robotic arm and the second robotic arm respectively, relative to the surface of the to-be-inspected article to iteratively vary an emission distance of the ultrasonic-wave-emitting probe along the emission axis from the transmitting point and a reception distance of the ultrasonic-wavc-rccciving probe along the detection axis from the receiving point while maintaining the ultrasonic-wave-emitting probe and the ultrasonic-wave-receiving probe respectively oriented at the optimal combination of the incident angle of the ultrasonic-wave-emitting probe and the receiver angle of the ultrasonic-wave-receiving probe,selecting an optimal combination of the emission distance of the ultrasonic-wave-emitting probe and the reception distance of the ultrasonic-wave-receiving probe from different combinations of the emission distance of the ultrasonic-wave-emitting probe and the reception distance of the ultrasonic-wavc-rccciving probe based on the detection signal of the ultrasonic-wave-receiving probe having a maximum amplitude,wherein the ultrasonic-wave-emitting probe and the ultrasonic- ave-receiving probe are maintained at the optimal combination of the emission distance of the ultrasonic-wave-emitting probe and the reception distance of the ultrasonic-wave-receiving probe during scanning of the to-be-inspected article.

7. The method according to claim 6, further comprisingcompiling a set of amplitude data associated with changes in lift off distance comprising amplitudes of detection signals measured by the ultrasonic- wave-receiving probe when moving the ultrasonic-wave-emitting probe and the ultrasonic-wave-receiving probe to iteratively vary the emission distance of the ultrasonic -wave -emitting probe and the reception distance of the ultrasonic-wave-receiving probe; andmapping the set of amplitude data associated with changes in lift off distance to the different combinations of the emission distance of the ultrasonic- ave-emitting probe and the reception distance of the ultrasonic-wave-receiving probe,wherein selecting the optimal combination of the emission distance of the ultrasonicwave-emitting probe and the reception distance of the ultrasonic-wave-receiving probe comprises comparing the amplitudes of the detection signals mapped to the different combinations of the emission distance of the ultrasonic-wave-emitting probe and the reception distance of the ultrasonic-wave-receiving probe and selecting a combination of the emission distance of the ultrasonic-wave-emitting probe and the reception distance of the ultrasonic-wave-receiving probe with the maximum amplitude as the optimal combination of the emission distance of the ultrasonic- wave-emitting probe and the reception distance of the ultrasonic-wave-receiving probe.

8. The method according to claim 6, wherein the emission distance of the ultrasonicwave-emitting probe and the reception distance of the ultrasonic-wave-receiving probe are iteratively varied to progressively increase and / or decrease.

9. The method according to claim 6, wherein the emission distance of the ultrasonicwave-emitting probe and the reception distance of the ultrasonic-wave-receiving probe are iteratively varied in a pre-defined range, wherein the pre-defined range is from 0.01m to 0.2m, or from 0.01m to 0.15m, or from 0.01m to 0. Im, or from 0.01m to 0.08m.

10. The method according to claim 1, further comprisingmoving the ultrasonic-wave-emitting probe and the ultrasonic-wave-receiving probe, via the first robotic arm and the second robotic arm respectively, relative to the surface of the to-be-inspected article to iteratively vary a relative offset distance between the transmitting point and the receiving point on the surface of the to-be-inspected article with respect to a reference alignment line perpendicular to a scanning direction of the scanning path while maintaining the ultrasonic-wave-emitting probe and the ultrasonic-wave-receiving probe respectively oriented at the optimal combination of the incident angle of the ultrasonic-waveemitting probe and the receiver angle of the ultrasonic-wave-receiving probe,selecting an optimal relative offset distance between the transmitting point and the receiving point with respect to the reference alignment line based on the detection signal of the ultrasonic-wave-receiving probe having a maximum amplitude,wherein the transmitting point and the receiving point are maintained at the optimal relative offset distance during scanning of the to-be-inspected article.

11. The method according to claim 10, further comprisingcompiling a set of amplitude data associated with changes in the relative offset distance between the transmitting point and the receiving point comprising amplitudes of detection signals measured by the ultrasonic-wave-receiving probe when moving the ultrasonic-wave-emitting probe and the ultrasonic-wave-receiving probe to iteratively vary the relative offset distance between the transmitting point and the receiving point; and mapping the set of amplitude data associated with changes in the relative offset distance to different corresponding relative offset distances between the transmitting point and the receiving point,wherein selecting the optimal relative offset distance between the transmitting point and the receiving point comprises comparing the amplitudes of the detection signals mapped to the different corresponding relative offset distances between the transmitting point and the receiving point and selecting a relative offset distance between the transmitting point and thereceiving point with the maximum amplitude as the optimal relative offset distance between the transmitting point and the receiving point.

12. The method according to claim 10, wherein the relative offset distance between the transmitting point and the receiving point are iteratively varied to progressively increase and / or decrease.

13. The method according to claim 1, further comprisingmoving the ultrasonic-wave-emitting probe and the ultrasonic-wave-receiving probe, via the first robotic arm and the second robotic arm respectively, relative to the surface of the to-be-inspected article to iteratively vary a lateral distance apart between the transmitting point and the receiving point on the surface of the to-be-inspected article with respect to the scanning path while maintaining the ultrasonic-wave-emitting probe and the ultrasonic- wavereceiving probe respectively oriented at the optimal combination of the incident angle of the ultrasonic-wave-emitting probe and the receiver angle of the ultrasonic -wave-receiving probe,selecting an optimal lateral distance apart between the transmitting point and the receiving point on the surface of the to-be-inspected article based on the detection signal of the ultrasonic-wave-receiving probe having a maximum amplitude,wherein the transmitting point and the receiving point are maintained at the optimal lateral distance apart during scanning of the surface of the to-be-inspected article.

14. The method according to claim 13, further comprisingcompiling a set of amplitude data associated with changes in the lateral distance apart between the transmitting point and the receiving point comprising amplitudes of detection signals measured by the ultrasonic-wave-receiving probe when moving the ultrasonic-wave-emitting probe and the ultrasonic-wave-receiving probe to iteratively vary the lateral distance apart between the transmitting point and the receiving point; andmapping the set of amplitude data associated with changes in the lateral distance apart to different corresponding distances apart between the transmitting point and the receiving point,wherein selecting the optimal lateral distance apart between the transmitting point and the receiving point comprises comparing the amplitudes of the detection signals mapped to the different corresponding lateral distances apart between the transmitting point and thereceiving point and selecting a lateral distance apart between the transmitting point and the receiving point with the maximum amplitude as the optimal lateral distance apart between the transmitting point and the receiving point.

15. The method according to claim 13, wherein the lateral distance apart between the transmitting point and the receiving point are iteratively varied to progressively increase and / or decrease.

16. The method according to claim 13, wherein the lateral distance apart between the transmitting point and the receiving point are iteratively varied in a pre-defined range.

17. The method according to claim 1, further comprisingsetting a lateral distance apart between the transmitting point and the receiving point on the surface of the to-be-inspected article to a pre-determined distance prior to moving the ultrasonic-wave-emitting probe and the ultrasonic-wave-receiving probe, via the first robotic arm and the second robotic arm respectively, relative to the surface of the to-be-inspected article to iteratively vary the incident angle and the receiver angle.

18. The method according to claim 1, wherein the scanning path is a zig-zag scanning path.

19. The method according to claim 18, wherein the method is repeated for a further zigzag scanning path having a major axis perpendicular to a major axis of the zig-zag scanning path.

20. A system for air-coupled guided wave inspection of a to-be-inspected article, the system comprisinga first robotic arm with an ultrasonic-wave-emitting probe;a second robotic ami with an ultrasonic-wave-receiving probe;a processor configured to control the first robotic arm and the second robotic arm to move the ultrasonic-wave-emitting probe and the ultrasonic-wave-receiving probe respectively relative to a surface of the to-bc-inspcctcd article to perform the method according to claim 1.

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