Probe alignment and surface following for non-destructive test (NDT)

Abstract

A non-contact sensing approach can be used to adjust a position or orientation (or both) of a non-destructive test (NDT) probe assembly relative to a surface of an object under test. Such sensing can include use of respective range sensors (e.g., laser- based range sensors or acoustic sensors, or combinations thereof). For example, an NDT acquisition, such as an acoustic inspection acquisition, can include use of a machine-implemented (e.g., automated) technique. In such a technique, sensed data can be acquired, indicative of at least one of a location or an orientation of a surface relative to a surface of an object under test such as a curved surface. In response, a representation of a correction (e.g., one or more "offset" values) can be determined to steer at least one of a location or an orientation of the probe assembly.

Description

PROBE ALIGNMENT AND SURFACE FOLLOWING FOR NONDESTRUCTIVE TEST (NDT)CLAIM OF PRIORITY

[0001] This patent application claims the benefit of priority of Badeau, et al., U.S. Provisional Patent Application Number 63 / 487,315, titled “PROBE ALIGNMENT AND SURFACE FOLLOWING FOR NON-DESTRUCTIVE TEST (NDT),” filed on February 28, 2023 (Attorney Docket No. 6409.257PRV), which is hereby incorporated by reference herein in its entirety.FIELD OF THE DISCLOSURE

[0002] This document pertains generally, but not by way of limitation, to apparatus and techniques for non-destructive inspection and more particularly, to apparatus and techniques for performing automated or semi-automated scanning of a probe assembly including performing probe alignment to follow a contour of a surface of an object under test, using at least one non-contact distance sensor.BACKGROUND

[0003] Non-destructive testing (NDT) can refer to use of one or more different techniques to inspect regions on or within an object, such as to ascertain whether flaws or defects exist, or to otherwise characterize the object being inspected. Examples of non-destructive test approaches can include use of an eddy current testing approach where electromagnetic energy is applied to the object and resulting induced currents on or within the object are detected, with the values of a detected current (or a related impedance) providing an indication of the structure of the object under test, such as to indicate a presence of a crack, void, porosity, or other inhomogeneity.

[0004] Another approach for NDT can include use of an acoustic inspection technique, such as where one or more electroacoustic transducers are used to insonify a region on or within the object under test, and acoustic energy that is scattered or reflected can be detected and processed. Such scattered or reflected energy can be referred to as an acoustic echo signal. Generally, such an acoustic inspection scheme involves use of acoustic frequencies in an ultrasonic range of frequencies, such asincluding pulses having energy in a specified range that can include value from, for example, a few hundred kilohertz, to tens of megahertz, as an illustrative example.SUMMARY OF THE DISCLOSURE

[0005] Non-destructive testing techniques can be used to inspect objects in relation to a wide variety of applications, such as in relation to manufacturing or field inspection. Acoustic inspection is one such approach, using one or more transducers to direct acoustic energy into a target and then receiving and processing any reflected energy. The received signals can be processed and imaged to facilitate inspection and evaluation. For example, such ultrasonic inspection data can be processed to provide time-series or imaging data in a specified format. Acquired acoustic inspection imaging data is generally reviewed to identify indications of flaws, defects, or other anomalies. Similarly, an eddy current inspection technique can be used for inspecting metallic structures, such as to identify cracks or porosities, for example.

[0006] For large structures (e.g., metal or composite), performing associated scanning (e.g., moving of the probe assembly across a surface to perform an acquisition) can present challenges. If scanned by hand, such an approach can be labor intensive and sensitive to scan path variation and probe lift-off, as illustrative examples. A robotic manipulator can be used to facilitate scanning. Programming of the robotic manipulator can be complex and may involve establishing a nominal scan path (e.g., a raster or other pattern) based on nominal dimensions and nominal positioning of an object under test. In practice, the actual dimensions or actual positioning of the object under test may vary relative to such nominal dimensions or positioning.

[0007] In one approach, such variation may be compensated for by using a force sensor that physically touches a surface of the object under test. Contact between the sensor and the surface can be used to adjust a probe orientation or position. However, use of such a force sensor may limit a velocity of the probe head and may exhibit other challenges such as providing noisy or unreliable data. Use of a force sensor also generally adds significant cost to the scanning equipment, because such apparatus is generally application and vendor specific.

[0008] The present inventors have recognized, among other things, that a non-contactsensing approach can be used to adjust a position or orientation (or both) of a probe assembly relative to a surface of an object under test, such as to align the probe assembly in a dynamic manner during scanning. Such sensing can include use of respective range sensors (e.g., laser-based range sensors or acoustic sensors, or combinations thereof). For example, anon-destructive test (NDT) acquisition, such as an acoustic inspection acquisition, can include use of a machine-implemented (e.g., automated) technique. In such a technique, sensed data can be acquired, indicative of at least one of a location or an orientation of a surface relative to a probe assembly, such as a curved surface. In response, a representation of a correction (e.g., one or more “offset” values) can be determined to steer at least one of a location or an orientation of the probe assembly. Use of non-contacting range sensors can avoid challenges mentioned above associated with using a contact-based force sensor. In an example, laser range sensors can be included on or within, such as affixed to, an acoustic inspection probe assembly that used as an end effector of a robotic manipulator to perform automated non-destructive inspection including mechanical scanning across a surface of an object under test.

[0009] In an example, a machine-implemented method can be used for controlling an alignment of a non-destructive test (NDT) inspection probe, the machine- implemented method comprising receiving range data corresponding to three locations on an object under test relative to an initial probe position and an initial probe orientation, determining a vector that is normal to a plane defined by the three locations on the object under test, determining an offset from a nominal value of at least one parameter corresponding to a degree of freedom of movement by a manipulator using the vector that is normal to the plane, and adjusting at least one of a probe position or a probe orientation using the manipulator and using the determined offset from the nominal value. For example, adjusting at least one of the probe position or the probe orientation can align an active surface of the probe with a surface of the object under test.

[0010] In an example, a system can be used for controlling an alignment of a nondestructive test (NDT) inspection probe, the system comprising at least one sensor configured to acquire range data corresponding to three locations on an object undertest relative to an initial probe position and an initial probe orientation, at least one processor circuit, and at least one memory circuit comprising instructions that, when executed by the at least one processor circuit, cause the system to perform the machine-implemented method above or a machine-implemented method as described elsewhere herein. For example, the at least one sensor can include a laser range sensor or the at least one sensor comprises an acoustic sensor (or combinations of such sensors).

[0011] In an example, a system can be used for controlling an alignment of a nondestructive test (NDT) inspection probe, the system comprising a means for receiving range data corresponding to three locations on an object under test relative to an initial probe position and an initial probe orientation, a means for determining a vector that is normal to a plane defined by the three locations on the object under test, a means for determining an offset from a nominal value of at least one parameter corresponding to a degree of freedom of movement by a manipulator using the vector that is normal to the plane, and a means for adjusting at least one of a probe position or a probe orientation using the determined offset.

[0012] This summary is intended to provide an overview of subject matter of the present patent application. It is not intended to provide an exclusive or exhaustive explanation of the invention. The detailed description is included to provide further information about the present patent application.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In the drawings, which are not necessarily drawn to scale, like numerals may describe similar components in different views. Like numerals having different letter suffixes may represent different instances of similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document.

[0014] FIG. 1 illustrates generally an example comprising an acoustic inspection system, such as can be used to perform at least a portion one or more techniques as shown and described herein.

[0015] FIG. 2A illustrates generally an example comprising a probe assembly relativeto a target (e.g., an object under test), and a corresponding coordinate system, such as for illustration of a probe alignment technique including using respective range sensors, and for determination of a normal vector relative to a location on the surface of the target, such as using range data corresponding to three locations.

[0016] FIG. 2B illustrates generally rotational variables (corresponding to rotational degrees of freedom), such as for performing probe alignment using the normal vector determined in relation to FIG. 2A and to correct an orientation or position (or both) of the probe assembly.

[0017] FIG. 3A and FIG. 3B illustrate generally side views of different hypothetical probe assembly locations relative to a target (e.g., an object under test), and a corresponding coordinate system, such as for illustration of z direction (e.g., distance) offset compensation, where a positive (+z) offset value in the z direction indicates a distance between the probe assembly and the target.

[0018] FIG. 4 illustrates generally a control architecture including feedback to perform probe orientation adjustment or position adjustment (or both) to achieve a nominal probe orientation or position (or both) relative to an object under test.

[0019] FIG. 5 A shows an illustrative example of a coordinate system, acoustic inspection probe assembly, and robotic manipulator relative to an object under test.

[0020] FIG. 5B, FIG. 5C, FIG. 5D, and FIG. 5E show different views of an illustrative example of an acoustic inspection probe assembly.

[0021] FIG. 6A and FIG. 6B shows respective Z-axis (in FIG. 6A) and Y-axis (in FIG. 6B) positional errors relative to a nominal probe position, for various scanning velocities.

[0022] FIG. 7A, FIG. 7B, and FIG. 7C shows respective Z-axis (in FIG. 7A) and Y- axis (in FIG. 7B) and X-axis (in FIG. 7C) positional errors relative to a nominal probe position, for various scanning velocities, including examples where an initial “pathbuilding” operation is performed to acquire a contour of an object under test at an initial probe velocity that is lower than a velocity used for later scanning.

[0023] FIG. 8 illustrates generally how a radius of curvature of a surface of an object under test can create a slight error when a planar approximation is used for probealignment.

[0024] FIG. 9 illustrates generally a technique, such as a machine-implemented method, for performing adjustment of at least one of a probe orientation or a probe position relative to an object under test.

[0025] FIG. 10 illustrates a block diagram of an example comprising a machine upon which any one or more of the techniques (e.g., methodologies) discussed herein may be performed.DETAILED DESCRIPTION

[0026] Non-destructive testing of manufactured structures can be performed using various approaches, such as an using an eddy current or acoustic inspection technique. In an example, for acoustic inspection, a phased-array transducer architecture and associated processing (e.g., beamforming and imaging) can be performed. Similarly, for eddy current inspection, an eddy current array (ECA) probe can be used, such as scanned across a surface of an object under test. The present subject matter can be used to perform probe alignment, such as on a dynamic basis, as the probe assembly is manipulated (e.g., translated) by a robotic manipulator in support of a scanning operation.

[0027] FIG. 1 illustrates generally an example comprising an acoustic inspection system 100, such as can be used to perform at least a portion one or more techniques as shown and described herein. The inspection system 100 can include a test instrument 140, such as a hand-held or portable assembly. The test instrument 140 can be electrically coupled to a probe assembly 150, such as using a multi -conductor interconnect 130. The probe assembly 150 can include one or more electroacoustic transducers, such as a transducer array 152 including respective transducers 154A through 154N. The transducers array can follow a linear or curved contour or can include an array of elements extending in two axes, such as providing a matrix of transducer elements. The elements need not be square in footprint or arranged along a straight-line axis. Element size and pitch can be varied according to the inspection application.

[0028] A modular probe assembly 150 configuration can be used, such as to allow atest instrument 140 to be used with various different probe assemblies. Generally, the transducer array 152 includes piezoelectric transducers, such as can be acoustically coupled to a target 158 (e.g., a test specimen or “object-under-test”) through a coupling medium 156. The coupling medium can include a fluid or gel or a solid membrane (e.g., an elastomer or other polymer material), or a combination of fluid, gel, or solid structures. For example, an acoustic transducer assembly can include a transducer array coupled to a wedge structure comprising a rigid thermoset polymer having known acoustic propagation characteristics (for example, Rexolite® available from C-Lec Plastics Inc.), and water can be injected between the wedge and the structure under test as a coupling medium 156 during testing, or testing can be conducted with an interface between the probe assembly 150 and the target 158 otherwise immersed in a coupling medium.

[0029] The test instrument 140 can include digital and analog circuitry, such as a front-end circuit 122 including one or more transmit signal chains, receive signal chains, or switching circuitry (e.g., transmit / receive switching circuitry). The transmit signal chain can include amplifier and filter circuitry, such as to provide transmit pulses for delivery through an interconnect 130 to a probe assembly 150 for insonification of the target 158, such as to image or otherwise detect a flaw 160 on or within the target 158 structure by receiving scattered or reflected acoustic energy elicited in response to the insonification.

[0030] While FIG. 1 shows a single probe assembly 150 and a single transducer array 152, other configurations can be used, such as multiple probe assemblies connected to a single test instrument 140, or multiple transducer arrays 152 used with a single probe assembly 150 or multiple probe assemblies for pitch / catch inspection modes. Similarly, a test protocol can be performed using coordination between multiple test instruments 140, such as in response to an overall test scheme established from a master test instrument 140 or established by another remote system such as a compute facility 108 or general -purpose computing device such as a laptop 132, tablet, smartphone, desktop computer, or the like. The test scheme may be established according to a published standard or regulatory requirement and may be performed upon initialfabrication or on a recurring basis for ongoing surveillance, as illustrative examples.

[0031] The receive signal chain of the front-end circuit 122 can include one or more filters or amplifier circuits, along with an analog-to-digital conversion facility, such as to digitize echo signals received using the probe assembly 150. Digitization can be performed coherently, such as to provide multiple channels of digitized data aligned or referenced to each other in time or phase. The front-end circuit can be coupled to and controlled by one or more processor circuits, such as a processor circuit 102 included as a portion of the test instrument 140. The processor circuit 102 can be coupled to a memory circuit 104, such as to execute instructions that cause the test instrument 140 to perform one or more of acoustic transmission, acoustic acquisition, processing, or storage of data relating to an acoustic inspection, or to otherwise perform techniques as shown and described herein. The test instrument 140 can be communicatively coupled to other portions of the system 100, such as using a wired or wireless communication interface 120.

[0032] For example, performance of one or more techniques as shown and described herein can be accomplished on-board the test instrument 140 or using other processing or storage facilities such as using a compute facility 108 or a general- purpose computing device such as a laptop 132, tablet, smart-phone, desktop computer, or the like. For example, processing tasks that would be undesirably slow if performed on-board the test instrument 140 or beyond the capabilities of the test instrument 140 can be performed remotely (e.g., on a separate system), such as in response to a request from the test instrument 140. Similarly, storage of imaging data or intermediate data such as A-scan matrices of time-series data or other representations of such data, for example, can be accomplished using remote facilities communicatively coupled to the test instrument 140. The test instrument can include a display 110, such as for presentation of configuration information or results, and an input device 112 such as including one or more of a keyboard, trackball, function keys or soft keys, mouse-interface, touch-screen, stylus, or the like, for receiving operator commands, configuration information, or responses to queries.

[0033] Generally, the probe assembly 150 can be manipulated by hand, such as scanned across the target 158 by a user. Alternatively, or in addition, the probeassembly 150 can be positioned or oriented (or both) using a manipulator 170, such as a robotic arm supporting multiple mechanical degrees of freedom, or using other equipment such as a gantry, crane, or other apparatus including one or more linear or rotary actuators. A wrist region 174 (e.g., defining or including a mounting plate or flange) can be coupled to the probe assembly 150, where the probe assembly 150 serves as an end effector. A manipulator controller 172 (e.g., a hardware platform that can execute a manipulator control routine, such as to control one or more linear or rotary actuators to guide the probe assembly 150 in support of an inspection acquisition). While the system 100 of FIG. 1 shows an acoustic inspection application, such a configuration can be similar for eddy current inspection, such as where the probe assembly 150 comprises an eddy current transducer array.

[0034] As mentioned above, the present subject matter can be used to align a probe assembly to facilitate non-destructive inspection. The techniques described herein are generally applicable to performing probe alignment (e.g., through controlling one or more of a probe orientation or a probe position, or both) to track a varying or even unknown geometry of a surface of an object under test. Generally, as described herein, such a surface can be tracked in the context of an automated scanning operation using range sensors such as distance measurement lasers. Other sensing modalities can be used, such as acoustic range sensors. FIG. 2A illustrates generally an example 200A comprising a probe assembly 250 relative to a target 258 (e.g., an object under test), and a corresponding coordinate system (showing x,y, and -z directions), such as for illustration of a probe alignment technique including using respective range sensors, and for determination of a normal vector (n) relative to a location on the surface of the target 258, such as using range data corresponding to three locations 278A, 278B, and 278C (labeled A, B, and C).

[0035] As shown illustratively in FIG. 2A, respective laser range sensors 276A, 276B, and 276C can be used to obtain respective distance values (or analog representations thereof) or other range data corresponding to three respective locations 278 A, 278B, and 278C on a surface of the target 258. For example, the range data corresponding to three locations 278A, 278B, and 278C can be used to define a plane having a corresponding normal vector (n). Using three range measurements provided byrespective laser range sensors 276A, 276B, and 276C on the probe assembly 250 allows compensation corresponding to three degrees of freedom. Use of three range measurements and three degrees of freedom is merely an illustration, and other approaches could include different (e.g., higher) counts of degrees of freedom based on other data or constraints.

[0036] For example, FIG. 2B illustrates generally an example 200B showing rotational variables (corresponding to two rotational degrees of freedom), such as for performing probe alignment using the normal vector (n) determined in relation to FIG. 2A and to correct an orientation or position (or both) of the probe assembly 250. As shown in FIG. 2B, the orientation of the probe assembly 250 can be corrected relative to the target 258 surface such as in directions defined by angle w (about x) and angle p (about y). A third degree of freedom can be defined as the distance (z) between a datum associated with probe the assembly 250, such as Tool Center Position (TCP) and a surface of the target 258, such as corresponding to a distance from an active surface 252 of the probe assembly 250 to the surface of the target 258. For example, FIG. 3A and FIG. 3B illustrate generally side views 300A and 300B of different hypothetical probe assembly 250 locations relative to a target 258 (e.g., an object under test), and a corresponding coordinate system, such as for illustration of Z (e.g., distance) offset compensation. The probe assembly 250 can include respective range sensors such as laser range sensors 276A, 276B (with 276C not shown due to the orientation of the views 300A and 300B of FIG. 3 A and FIG. 3B).

[0037] Generally, referring to FIG. 2A, FIG. 2B, FIG. 3A and FIG. 3B, the alignment technique as described herein approximates an unknown surface section of the target 258 as planar. For example, for surfaces having a reasonably low curvature, an assumption can be made that the surface is effectively flat, at least locally. By doing so, a position of the surface section and its orientation can be determined using as few as three range determinations corresponding to three respective locations 278 A, 278B, and 278C shown illustratively in FIG. 2A. The coordinates in the x and y directions of the respective laser range sensors 276A, 276B, and 276C are generally known because they are at fixed positions with respect to a known datum, such as with respect to the TCP of the probe assembly 250, where the TCP defines the (0, 0, 0)coordinate. The range determinations can be in the z direction (as positive z-distances to each respective laser range sensor 276A, 276B, and 276C).

[0038] Referring to FIG. 2A, the x and y coordinates of each of the three respective locations 278A (xo, yo) , 278B (xy, yi), and 278C (xz, yz) correspond to the x andy coordinates of the respective sensors 276 A, 276B, and 276C shown in FIG. 2 A, and the respective z coordinates of each of the three respective locations 278 A (zo) , 278B (zy), and 278C (zz) correspond to the range determinations. With these values, two surface vectors can be determined, represented by the following:AC (the plane approximating the inspected surface) can be computed with a vector cross product:

[0040] Referring to FIG. 2B, an inclination of the plane can be computed using a projection of the unit normal (n) on a reference coordinate system. To obtain the unit value normal n and angles w offset and poffset relative to reference axes, the following expressions can be used:

[0041] The determined values for w offset and poffset can be parameters representing offsets from a nominal probe alignment and can be used for adjusting probe alignment using two rotational degrees of freedom of movement of the probe assembly 250 (e.g., where movement is performed by a robotic manipulator). For example, as shown and ndescribed below, such adjustment can align a face (e.g., an active surface) of a transducer array with a surface of the target 258 (e.g., to orient the transducer array in a direction parallel to the surface of the target 258).

[0042] Referring to FIG. 3A and FIG. 3B, a third parameter can be determined, such as distance between a specified datum (e.g., a probe assembly 250 TCP) and a surface of the target 258. For example, in the expression below, TCP represents a coordinate of the of Tool Center Position with respect to an end effector coupling plate or other portion of a robotic manipulator, which can serve as a system reference location. A shortest distance (e.g., in a direction normal to the target 258 surface) separating the robot TCP and the surface can be represented as:

[0043] To determine a direction of the distance in the corrected axis (±z), a verification can be performed using a vector characterizing the TCP passing through the conceptualized plane (defined by a surface of the target 258) as defined by the following equation: ni(x - x0) + nj(y - y0) + nk(z - z0) = 0

[0044] Solving the equation above for an unknown z value that is on the plane results in the following expression:

[0045] A vector describing a nominal TCP can be represented as the following, for example:

[0046] A distance in the z direction can be assigned as positive (too far from the surface, as shown in the view 300 A of FIG 3 A) or negative (interfering with the surface as shown in the view 300B of FIG. 3B) depending on the following conditions:

[0047] The determined z distance value (e.g., signed as plus or minus | distance |) can be used to adjust a position the probe assembly 250 to track a nominal distance relative to the surface of the target 258. The determined values for w and p (e.g., or corresponding angular offset values), the determined z distance value (e.g., a distance offset value), both probe orientation and position can be adjusted to drive the offset values towards zero or towards other target values. Determinations of parameters as mentioned above can be performed successively for different locations as the probe assembly 250 is translated in the x or y directions (or both) along the target 258, such as in a closed-loop manner using a path modification control routine as discussed below and in relation to FIG. 4.

[0048] FIG. 4 illustrates generally a control architecture 400 including feedback to perform probe orientation adjustment or position adjustment (or both) to achieve a nominal probe orientation or position (or both) relative to an object under test. As described in this document, use of non-contact (e.g., laser-based or acoustic) ranging can provide more reliable determination of orientation or positional error, such as at a faster rate, as compared to using other robotic scan control techniques, such as force contouring. Data from laser ranging can be fed into a robotic manipulator control system to provide modification of a nominal path in a dynamic manner. For example, a Dynamic Path Modification (DPM) package from Fanuc (Japan) supports modification of a preprogrammed path using the technique described above. Such modification as described herein can provide enhanced alignment and placement of a non-destructive inspection probe on or nearby a surface.

[0049] As an illustration, a probe orientation is generally specified to be normal to an inspected surface and in contact with such a surface, and such constraints can be represented by the following assignments and provided as an input at 448 in FIG. 4(such as assigned by register value or other stored data): w 0°distance 0 millimeters (mm)

[0050] A proportional, integral, and differential (PID) control architecture 464 can be used to drive the probe alignment and distance toward the assignments provided at 448 (or other specified orientation and specified distance). Use of the PID control architecture 464 is merely illustrative and other control topologies can be used. As shown in FIG. 4, range determinations can be provided at 442 as analog inputs (e.g., corresponding to distances as measured by three respective non-contact sensors such as laser range sensors) and converted to digital representations. Analog signals representing distance determinations can be filtered, such as using a low pass filter. For example, the analog signals can be linearly proportional to a distance between the range sensor and a surface of the object under test. The analog signals can be converted to distance value data using a calibration technique to determine slope and offset values corresponding to the respective sensors. A current state determination can be made at 446, such as describing the coordinates of one more locations on a surface of the target being inspected as discussed above or using a representation of angular and positional offset values (e.g., w offset and poffset, and z) with respect to nominal values provided at 448. An error estimation can be performed at 462, such as to compare a robotic manipulator state (e.g., position or orientation, or both) to a desired position or orientation (or both), to produce an error vector, e[k], where k represents an iteration index, or other representation of error.

[0051] The control architecture 464 can apply a proportional component at 466A, an integral component at 466B, and a differential or “derivative” component at 466C, using respective gain values Kp, K,. Kd, to provide an input vector u[k] to a dynamic correction interface, such as a path modification routine, at 480. For example, the input vector u[k] can be provided as an input to registers associated with DPM where a Fanuc system is used as the manipulator controller. The gain values Kp, K,. Kd affect the dynamic performance of the probe orientation and position adjustment, and suitable gain values will generally depend on specific test configuration, such asdegree of curvature of the surface being inspected, a velocity of the translation of the probe assembly across the surface, and dynamic behavior of the robotic manipulator system.

[0052] Various empirical techniques can be used to establish gain values Kp, K,. Kd, such as a Ziegler-Nichols technique or other approach (e.g., an example of a manual approach can include increasing Kpuntil oscillation is observed, dividing that Kpvalue by a factor of 2, then increasing Kt until stability is achieved, then tuning Kd for dynamic performance). As mentioned above, an output of the path modification routine at 480 can be used to establish a new robotic manipulator position at 482, and the coordinates or other representation of the new robotic manipulator position at 482 can be fed back for use with distance measurement (or measurements) at 442 to provide an updated determination of a current state 446 (e.g., orientation or position or both), for use in another error determination at 462 in a closed-loop manner, such as for successive different locations where range data is received and successive determinations of parameters such as offset values are established for comparison with the desired target values at 462. Such updates can be performed in discrete iterations such that the loop formed by the architecture 400 forms an auxiliary control loop independent of primary motion control of the robotic manipulator. For example, such an auxiliary control loop can function to modify a path and orientation established by a primary control loop where the primary control loop is providing motion control according to a nominal path or orientation. The dynamic correction interface at 480 can provide an interface between the loop defined by the control architecture 400 and a separate primary control architecture.

[0053] FIG. 5 A shows an illustrative example of a coordinate system, acoustic inspection probe assembly 550, and robotic manipulator 570 relative to an object under test 558. As shown in FIG. 5A, the acoustic inspection probe assembly 550 includes or defines an active surface 552. Generally, in acoustic inspection applications, the active surface 552 is placed in contact with the object under test 558, such as acoustically coupled with a couplant (e.g., water or other liquid). Accordingly, if a gasket or other structure as present at the active surface 552, the active surface552 is to be kept in constant contact (e.g., to avoid lift-off or loss of couplant).

[0054] Even using a control scheme as shown in FIG. 4 and discussed elsewhere above, some amount of error in orientation and positioning of the probe can occur, particularly as scan velocity is increased (e.g., to beyond 250 mm / second), due to finite non-zero latency and dynamic effects in any tracking scheme. The probe assembly 250 can be configured to provide some degree of compliance and movement relative to the robotic manipulator 570 using springs or pneumatics. FIG. 5B, FIG. 5C, FIG. 5D, and FIG. 5E show different views of an illustrative example of an acoustic inspection probe assembly 550. The probe assembly 550 can include one or more spring-loaded elements and pivot locations, such as allowing free or directed rotation of the probe assembly 550 (e.g., about locations 588A or 588B) or displacement of an active surface 552 of the probe assembly 550, relative to a coupling region 574 where the probe assembly 550 is affixed to a manipulator as an end effector. Accordingly, use of a configuration such as shown in FIG. 5B, FIG. 5C, FIG. 5D, and FIG. 5E can provide some flexibility with respect to error in probe alignment or position. For example, an error that can be tolerated and accommodated by such a probe assembly 550, so that probe adjustment by the closed loop scheme in FIG. 4 need to be perfect, can be as follows: z -» ±15 mm relative to a nominal z distance valuePoff set &woffset ±10° relative to nominal angular positions

[0055] For the illustrative examples of the data presented below, two SICK laser ranging devices, model WTT12L, available from SICK AG (Germany), and a Keyence laser ranging device, model LR-TB5000C, available from Keyence Corporation (Japan) were used. As shown illustratively in FIG. 5B, FIG. 5C, FIG. 5D, and FIG. 5E, the SICK laser ranging device 576A is generally placed at a distance greater than or equal to 50mm from a corresponding location 578 A on the object under test 558. Similarly, other laser ranging sensors such as at 576B and 576C can be placed to provide a specified nominal or minimum distance from corresponding locations on the object under test 558.

[0056] The configuration shown in FIG. 5A, FIG. 5B, FIG. 5C, FIG. 5D, and FIG. 5E can be used, for example, for airfoil inspection such as in support of phased-arrayacoustic inspection of wind turbine blades or other similar structures such as wing or stabilizer structures. This approach can help to provide adequate alignment and placement of a phased-array probe (e.g., acoustic inspection probe assembly 550) on an inspected surface (e.g., object under test 558). This approach can help to maintain pressure between the phased-array probe active surface 552 and the object under test 558 to avoid any loss of couplant medium (such as water). Such an approach does not require a force control solution that involves a force or contact sensor. As such, as an illustrative example, use of the non-contact approach for range sensing and path modification can increase a probe velocity for acoustic inspection to around 500 mm / s (or more), such as more than doubling a scan velocity in comparison to a force control approach.

[0057] As an illustration of performance, FIG. 6A and FIG. 6B shows respective Z- axis (in FIG. 6A) and Y-axis (in FIG. 6B) positional errors relative to a nominal probe position, for various scanning velocities. The Y-axis error of FIG. 6B corresponds to an angular error about the y direction. The x, y. and z directions correspond to those shown in FIG. 5A using a control scheme as shown in FIG. 4 and using the plane approximation discussed above for correction in two angular directions and one distance direction. The parameters used for controlling the z direction and angle about the y direction are low-pass filter time constant Tau = 0.3, Kp= 0.075, Kt= 0, Kd= 0, and Fanuc exponential filter coefficient registers set to default (0.5). Note that these values are specific to implementation using a Fanuc DPM.

[0058] For applications where the object under test has a relatively consistent profile in at least one direction, such as a slowly-changing profile in a longitudinal direction, an autonomous or semi-autonomous scanning approach can be used, where an initial scan path is established using an initial velocity, such as corresponding to a first location or “index” location. The initial path can be established by translating the probe along the surface of the object under test to successive different locations. The initial path can be established without foreknowledge or based upon a nominal configuration taking into account a nominal probe position and nominal object-under- test profile, where the initial path is adjusted or modified using the approach described in this document to provide an updated baseline path. The probe can then be re-indexed to the next scan position, and probe alignment can be adjusted (e.g., in orientation or in position, or both) starting from the updated baseline path, with the probe moving at a velocity that is higher than the initial probe velocity.

[0059] As an illustration, FIG. 7A, FIG. 7B, and FIG. 7C shows respective Z-axis (in FIG. 7 A) and Y-axis (in FIG. 7B) and X-axis (in FIG. 7C) positional errors relative to a nominal probe position, for various scanning velocities, including examples where an initial “path-building” operation is performed to acquire a contour of an object under test at an initial probe velocity that is lower than a velocity used for later scanning. The Y-axis error of FIG. 7B corresponds to an angular error about the y direction, and the Z-axis error of FIG. 7C corresponds to an angular error about the z direction, using directions as shown illustratively in FIG. 5 A. The parameters used for controlling the z direction are low-pass filter time constant Tau = 0.15, Kp= 0.075, Kt= 0, Kd= 0.025, and Fanuc exponential filter coefficient registers set to default (0.5). The parameters used for controlling the angles about the y and x directions (w and p) are low-pass filter time constant Tau = 0.15, Kp= 0.075, KL= 0, Kd= 0, and Fanuc exponential filter coefficient registers set to default (0.5).

[0060] For the examples annotated “with pathbuilding,” an initial path is built using N = 10 points in the scan direction at an initial index location along a wind turbine blade. The initial path building is performed at a probe translational velocity of 100 mm / s, for a duration of the first six seconds. The remainder of the data in each of FIG. 7 A, FIG. 7B, and FIG. 7C use probe translational velocities as shown, and the examples without path building (annotated “w / o pathbuilding”) are performed entirely at the probe translation velocity as shown without the initial lower velocity.

[0061] FIG. 8 illustrates generally an example 800 of how a radius of curvature, R, of a surface of an object under test 858 can create a slight error when a planar approximation is used for probe alignment. However, such error need not be large enough to preclude use of the planar approximation, and such error can be controlled to some extent by reducing a distance, b, between the ranging devices (e.g., laser range sensors 876A and 876B as shown here). As an illustration, the distance approximation and associated error be described as follows:Approximation = dReal = d + d2Error = d2

[0062] A value of d2, the error in the measurement can be defined analytically as:where R is the blade radius between two beams, and b is the baseline (physical distance between the lasers). As an illustrative example, for a wind blade turbine R = 1750 mm and a probe assembly can establish b = 200mm, then:Error = 1750 —= 2.85mm. 4

[0063] As mentioned above, some degree of compliance in the probe assembly can be tolerated by spring-loaded or pneumatic structures (e.g., supporting pivoting or displacement relative to a rigid end-effector coupling plate), and the 2.85mm error in this illustration is within the specified + / -15mm tolerance mentioned in relation to another example above.

[0064] FIG. 9 illustrates generally a technique 900, such as a machine-implemented method, for performing adjustment of at least one of a probe orientation or a probe position relative to an object under test. For example, at 905, range data corresponding to three locations (or more) on an object under test can be received. Such range data can be acquired when the probe is an initial probe position and an initial probe orientation. At 910, a vector can be determined that corresponds to a normal direction from a plane defined by the three locations on the object under test. For example, as shown elsewhere herein, the three locations can be used to establish a plane approximating a surface of the object under test. At 915, an offset from a nominal value of at least one parameter can be determined using the vector determined at 910. Such a parameter can correspond to a positional degree of freedom such as a z direction distance between a reference location on the probe assembly and the surface of the object under test, or an angular displacement from a nominal probe orientation about an x direction or a y direction, as illustrative examples. At 920, the determined parameter (or parameters) can be used to adjust at least one of a probe orientation or a probe position. As discussed above, such parameters can be used asinputs to a path modification routine of a manipulator control system. The technique 900 need not be performed using a single processor or within a single system. For example, the determination of one or more parameters at 910 can be performed using one system, and the adjustment of the probe orientation or position at 920 can be performed using another system (such as the manipulator control system and manipulator actuators). As shown illustratively in FIG. 9, a loop 925 can exist such that range data can be received and probe orientation or position can be updated on an ongoing basis in cycles as the probe performs a scanning operation.

[0065] Generally, the apparatus and techniques shown and described herein can be used to maintaining a specified probe alignment relative to an object under test, including preserving contact between the probe assembly and the object under test for certain applications such as acoustic inspection. For large objects like wind turbine blades or airplane wing structures, placement of such objects relative to the manipulator can present uncertainties that can be addressed by the present apparatus and techniques, such as to help avoid misalignment of the probe and the unwanted loss of the coupling medium, or otherwise helping to avoid acquisition of unreliable data.

[0066] The present apparatus and techniques shown and described herein can avoid cumbersome programming or path-definition operations, particularly where differences exist between the 3D CAD models and objects as manufactured. For example, the apparatus and techniques shown herein do not require acquisition of or interpolation between large numbers of points defining the inspection surface. As discussed above, as few as a handful (e.g., ten) locations can be used to establish an initial path at an index location, and such a path can then be modified dynamically using the range sensing approach described herein. The present subject matter does require use of force sensors, where such force sensors might limit a probe velocity to 250 mm / s or less. Such force sensors may also be proprietary or specific to a particular manipulator vendors or configuration, unlike the generic non-contact range sensors that can be used as described herein.

[0067] FIG. 10 illustrates a block diagram of an example comprising a machine 1000 upon which any one or more of the techniques (e.g., methodologies) discussed hereinmay be performed. Machine 1000 (e.g., computer system) may include a hardware processor 1002 (e.g., a central processing unit (CPU), a graphics processing unit (GPU), a hardware processor core, or any combination thereof), a main memory 1004 and a static memory 1006, connected via an interlink 1030 (e.g., link or bus), as some or all of these components may constitute hardware for systems or related implementations discussed above.

[0068] Generally, the hardware processor 1002 may, for example, include at least one of a Central Processing Unit (CPU), a Reduced Instruction Set Computing (RISC) Processor, a Complex Instruction Set Computing (CISC) Processor, a Graphics Processing Unit (GPU), a Digital Signal Processor (DSP), a Tensor Processing Unit (TPU), a Neural Processing Unit (NPU), a Vision Processing Unit (VPU), a Machine Learning Accelerator, an Artificial Intelligence Accelerator, an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA), a Radio- Frequency Integrated Circuit (RFIC), a Neuromorphic Processor, a Quantum Processor, or any combination thereof. A processor circuit may further be a multi-core processor having two or more independent processors (sometimes referred to as "cores") that may execute instructions contemporaneously. Multi-core processors contain multiple computational cores on a single integrated circuit die, each of which can independently execute program instructions in parallel. Parallel processing on multi-core processors may be implemented via architectures like superscalar, VLIW, vector processing, or SIMD that allow each core to run separate instruction streams concurrently. A processor circuit may be emulated in software, running on a physical processor, as a virtual processor or virtual circuit. The virtual processor may behave like an independent processor but is implemented in software rather than hardware.

[0069] Specific examples of main memory 1004 include Random Access Memory (RAM), and semiconductor memory devices, which may include storage locations in semiconductors such as registers. Specific examples of static memory 1006 include non-volatile memory, such as semiconductor memory devices (e.g., Electrically Programmable Read-Only Memory (EPROM), Electrically Erasable Programmable Read-Only Memory (EEPROM)) and flash memory devices; magnetic disks, such asinternal hard disks and removable disks; magneto-optical disks; RAM; or optical media such as CD-ROM and DVD-ROM disks.

[0070] The machine 1000 may further include a display device 1010, an input device 1012 (e.g., a keyboard), and a user interface (UI) navigation device 1014 (e.g., a mouse). In an example, the display device 1010, input device 1012, and UI navigation device 1014 may be a touch-screen display. The machine 1000 may include a mass storage device 1008 (e.g., drive unit), a signal generation device 1018 (e.g., a speaker), a network interface device 1020, and one or more sensors 1016, such as a global positioning system (GPS) sensor, compass, accelerometer, or some other sensor. The machine 1000 may include an output controller 1028, such as a serial (e.g., universal serial bus (USB), parallel, or other wired or wireless (e.g., infrared (IR), near field communication (NFC), etc.) connection to communicate or control one or more peripheral devices (e.g., a printer, card reader, etc.).

[0071] The mass storage device 1008 may comprise a machine-readable medium 1022 on which is stored one or more sets of data structures or instructions 1024 (e.g., software) embodying or utilized by any one or more of the techniques or functions described herein. The instructions 1024 may also reside, completely or at least partially, within the main memory 1004, within static memory 1006, or within the hardware processor 1002 during execution thereof by the machine 1000. In an example, one or any combination of the hardware processor 1002, the main memory 1004, the static memory 1006, or the mass storage device 1008 comprises a machine readable medium.

[0072] Specific examples of machine-readable media include, one or more of nonvolatile memory, such as semiconductor memory devices (e.g., EPROM or EEPROM) and flash memory devices; magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; RAM; or optical media such as CD-ROM and DVD-ROM disks. While the machine-readable medium is illustrated as a single medium, the term "machine readable medium" may include a single medium or multiple media (e.g., a centralized or distributed database, or associated caches and servers) configured to store the one or more instructions 1024.

[0073] An apparatus of the machine 1000 includes one or more of a hardware processor 1002 (e.g., a central processing unit (CPU), a graphics processing unit (GPU), a hardware processor core, or any combination thereof), a main memory 1004 and a static memory 1006, sensors 1016, network interface device 1020, antennas, a display device 1010, an input device 1012, a UI navigation device 1014, a mass storage device 1008, instructions 1024, a signal generation device 1018, or an output controller 1028. The apparatus may be configured to perform one or more of the methods or operations disclosed herein.

[0074] The term “machine readable medium” includes, for example, any medium that is capable of storing, encoding, or carrying instructions for execution by the machine 1000 and that cause the machine 1000 to perform any one or more of the techniques of the present disclosure or causes another apparatus or system to perform any one or more of the techniques, or that is capable of storing, encoding or carrying data structures used by or associated with such instructions. Non-limiting machine- readable medium examples include solid-state memories, optical media, or magnetic media. Specific examples of machine-readable media include: non-volatile memory, such as semiconductor memory devices (e.g., Electrically Programmable Read-Only Memory (EPROM), Electrically Erasable Programmable Read-Only Memory (EEPROM)) and flash memory devices; magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; Random Access Memory (RAM); or optical media such as CD-ROM and DVD-ROM disks. In some examples, machine readable media includes non-transitory machine-readable media. In some examples, machine readable media includes machine readable media that is not a transitory propagating signal.

[0075] The instructions 1024 may be transmitted or received, for example, over a communications network 1026 using a transmission medium via the network interface device 1020 utilizing any one of a number of transfer protocols (e.g., frame relay, internet protocol (IP), transmission control protocol (TCP), user datagram protocol (UDP), hypertext transfer protocol (HTTP), etc.). Example communication networks include a local area network (LAN), a wide area network (WAN), a packet data network (e.g., the Internet), mobile telephone networks (e.g., cellular networks), PlainOld Telephone (POTS) networks, and wireless data networks (e.g., Institute of Electrical and Electronics Engineers (IEEE) 802.11 family of standards known as WiFi®), IEEE 802.15.4 family of standards, a Long Term Evolution (LTE) 4G or 5G family of standards, a Universal Mobile Telecommunications System (UMTS) family of standards, peer-to-peer (P2P) networks, satellite communication networks, among others.

[0076] In an example, the network interface device 1020 includes one or more physical jacks (e.g., Ethernet, coaxial, or other interconnection) or one or more antennas to access the communications network 1026. In an example, the network interface device 1020 includes one or more antennas to wirelessly communicate using at least one of single-input multiple-output (SIMO), multiple-input multiple-output (MIMO), or multiple-input single-output (MISO) techniques. In some examples, the network interface device 1020 wirelessly communicates using Multiple User MIMO techniques. The term “transmission medium” shall be taken to include any intangible medium that is capable of storing, encoding or carrying instructions for execution by the machine 1000, and includes digital or analog communications signals or other intangible medium to facilitate communication of such software.Various Notes

[0077] The above detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the invention can be practiced. These embodiments are also referred to generally as “examples.” Such examples can include elements in addition to those shown or described. However, the present inventors also contemplate examples in which only those elements shown or described are provided. Moreover, the present inventors also contemplate examples using any combination or permutation of those elements shown or described (or one or more aspects thereof), either with respect to a particular example (or one or more aspects thereof), or with respect to other examples (or one or more aspects thereof) shown or described herein.

[0078] In the event of inconsistent usages between this document and any documentsso incorporated by reference, the usage in this document controls.

[0079] In this document, the terms “a” or “an” are used, as is common in patent documents, to include one or more than one, independent of any other instances or usages of “at least one” or “one or more.” In this document, the term “or” is used to refer to a nonexclusive or, such that “A or B” includes “A but not B,” “B but not A,” and “A and B,” unless otherwise indicated. In this document, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Also, in the following claims, the terms “including” and “comprising” are open-ended, that is, a system, device, article, composition, formulation, or process that includes elements in addition to those listed after such a term in a claim are still deemed to fall within the scope of that claim. Moreover, in the following claims, the terms “first,” “second,” and “third,” etc., are used merely as labels, and are not intended to impose numerical requirements on their objects.

[0080] Method examples described herein can be machine or computer-implemented at least in part. Some examples can include a computer-readable medium or machine- readable medium encoded with instructions operable to configure an electronic device to perform methods as described in the above examples. An implementation of such methods can include code, such as microcode, assembly language code, a higher-level language code, or the like. Such code can include computer readable instructions for performing various methods. The code may form portions of computer program products. Such instructions can be read and executed by one or more processors to enable performance of operations comprising a method, for example. The instructions are in any suitable form, such as but not limited to source code, compiled code, interpreted code, executable code, static code, dynamic code, and the like. Further, in an example, the code can be tangibly stored on one or more volatile, non- transitory, or non-volatile tangible computer-readable media, such as during execution or at other times. Examples of these tangible computer-readable media can include, but are not limited to, hard disks, removable magnetic disks, removable optical disks (e.g., compact disks and digital video disks), magnetic cassettes, memory cards or sticks, random access memories (RAMs), read only memories (ROMs), and the like.

[0081] The above description is intended to be illustrative, and not restrictive. Forexample, the above-described examples (or one or more aspects thereof) may be used in combination with each other. Other embodiments can be used, such as by one of ordinary skill in the art upon reviewing the above description. The Abstract is provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Also, in the above Detailed Description, various features may be grouped together to streamline the disclosure. This should not be interpreted as intending that an unclaimed disclosed feature is essential to any claim. Rather, inventive subject matter may he in less than all features of a particular disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description as examples or embodiments, with each claim standing on its own as a separate embodiment, and it is contemplated that such embodiments can be combined with each other in various combinations or permutations. The scope of the invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

Claims

WHAT IS CLAIMED IS:

1. A machine-implemented method for controlling an alignment of a nondestructive test (NDT) inspection probe, the machine-implemented method comprising: receiving range data corresponding to three locations on an object under test relative to an initial probe position and an initial probe orientation; determining a vector that is normal to a plane defined by the three locations on the object under test; determining an offset from a nominal value of at least one parameter corresponding to a degree of freedom of movement by a manipulator using the vector that is normal to the plane; and adjusting at least one of a probe position or a probe orientation using the manipulator and using the determined offset from the nominal value.

2. The machine-implemented method of claim 1, wherein the adjusting at least one of the probe position or the probe orientation aligns an active surface of the probe with a surface of the object under test.

3. The machine-implemented method of claim 2, wherein the adjusting at least one of the probe position or the probe orientation orients the active surface in a direction more parallel to a surface of the object under test and positions the active surface of the probe within a specified distance of the surface of the object under test.

4. The machine-implemented method of any of claims 2 or 3, wherein the adjusting at least one of the probe position or the probe orientation maintains the active surface of the probe at a specified distance from the surface of the object under test during inspection.

5. The machine-implemented method of any of claims 1 through 4, comprising determining respective offsets corresponding to different degrees of freedom of movement by the manipulator using the vector that is normal to the plane.

6. The machine-implemented method of claim 5, wherein the respective offsets comprise adjustments for at least two rotational degrees of freedom of the manipulator.

7. The machine-implemented method of any of claims 5 or 6, wherein the respective offsets include a distance between the probe and the object under test.

8. The machine-implemented method of any of claims 1 through 7, wherein the receiving the range data includes acquiring range data from respective sensors on or near an end effector of the manipulator.

9. The machine-implemented method of claim 8, wherein the respective sensors comprise at least one laser range sensor.

10. The machine-implemented method of any of claims 8 or 9, wherein the respective sensors comprise at least one acoustic sensor.

11. The machine-implemented method of any of claims 1 through 10, wherein the determined offset comprises an error term in closed-loop control topology for the adjusting at least one of the probe position or the probe orientation.

12. The machine-implemented method of claim 11, comprising receiving range data for successive different locations for respective successive determinations of respective normal vectors and corresponding adjustments of at least one of the probe position or the probe orientation using the manipulator and using offsets determined using the respective normal vectors.

13. The machine-implemented method of claim 12, wherein the probe position is moved to the successive different locations along an initial path using an initial probe velocity; andwherein, using the corresponding adjustments, the initial path is modified to provide a corrected path corresponding to a profile of a portion of the object under test.

14. The machine-implemented method of claim 13, wherein the probe is translated along a length of the object under test to a new index location; and wherein the method comprises repeating the receiving range data for successive different locations for respective successive determinations of respective normal vectors and corresponding adjustments of at least one of the probe position or the probe orientation using the manipulator and using offsets determined using the respective normal vectors, starting from the corrected path, and using a probe velocity that is higher than the initial velocity.

15. A system for controlling an alignment of a non-destructive test (NDT) inspection probe, the system comprising: at least one sensor configured to acquire range data corresponding to three locations on an object under test relative to an initial probe position and an initial probe orientation; at least one processor circuit; at least one memory circuit comprising instructions that, when executed by the at least one processor circuit, cause the system to perform the machine-implemented method of any of claims 1 through 14.

16. The system of claim 15, further comprising a manipulator.

17. The system of any of claims 15 or 16, further comprising the non-destructive test (NDT) inspection probe.

18. The system of any of claims 15 through 17, wherein the at least one sensor comprises a laser range sensor.

19. The system of any of claims 15 through 17, wherein the at least one sensor comprises an acoustic sensor.

20. A system for controlling an alignment of a non-destructive test (NDT) inspection probe, the system comprising: a means for receiving range data corresponding to three locations on an object under test relative to an initial probe position and an initial probe orientation; a means for determining a vector that is normal to a plane defined by the three locations on the object under test; a means for determining an offset from a nominal value of at least one parameter corresponding to a degree of freedom of movement by a manipulator using the vector that is normal to the plane; and a means for adjusting at least one of a probe position or a probe orientation using the determined offset.

Images