Method of inspecting a surface of a component using a probe

Abstract

A method of inspecting a surface of a component, e.g. a turbine or compressor blade of a gas turbine engine. The method comprises (a) providing a probe for inspecting the component surface; (b) defining a reference surface that is offset from the component surface; (c) moving the probe so as to contact a plurality of discrete spaced apart inspection points on the component surface, each contact of the probe with an inspection point comprising a first movement of the probe from the reference surface to the inspection point; (d) retracting the probe from the component surface after each contact with an inspection point; and (e) inspecting the component surface each time the probe contacts an inspection point.

Claims

1. A method of inspecting a surface of a component, the method comprising the steps of: providing a probe for inspecting the component surface, wherein the probe is an eddy current probe; defining a reference surface that is offset from the component surface; moving the probe so as to contact a plurality of discrete spaced apart inspection points on the component surface, each contact of the probe with an inspection point comprising a first movement of the probe from the reference surface to the inspection point; retracting the probe from the component surface after each contact with an inspection point; and inspecting the component surface each time the probe contacts an inspection point, wherein the inspection comprises eddy current testing.

2. The method of claim 1, wherein movement of the probe is along a tool path and the method further comprises defining the tool path.

3. The method of claim 1, wherein the probe is spring loaded.

4. The method of claim 1, wherein the probe includes a camera and an illuminated camera system.

5. The method of claim 1, wherein the component is a blade or vane of a gas turbine engine.

6. The method of claim 1, further comprising receiving a continuous time-based signal from the probe and identifying portions of the signal that are associated with the probe being in contact with an inspection point of the component surface.

7. The method of claim 6, further comprising determining, for each of the portions of the signal, whether the portions of the signal are indicative of a defect in the component surface.

8. The method of claim 1, wherein each contact of the probe with an inspection point further comprises a second movement of the probe from the inspection point to the reference surface.

9. The method of claim 8, wherein the first and second movements of the probe are each in a direction that is normal to the component surface at the inspection point.

10. The method of claim 8, wherein the first and second movements of the probe are each in a direction that is at an angle to a direction normal to the component surface at the inspection point.

11. The method of claim 8, wherein each contact of the probe with an inspection point further comprises a third movement of the probe along the reference surface.

12. The method of claim 1, wherein the probe is mounted to a robotic device.

13. The method of claim 12, wherein the probe is moved relative to the robotic device.

14. The method of claim 12, wherein movement of the probe is by the robotic device and the probe is maintained in a fixed position relative to the robotic device throughout the movement of the probe.

15. The method of claim 14, wherein movement of the probe along the reference surface is provided by moving the robotic device while maintaining the probe in a fixed position relative to the robotic device, and each movement of the probe towards or away from the component surface is performed by moving the probe relative to the robotic device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments will now be described by way of example only, with reference to the Figures, in which:

(2) FIG. 1 is a schematic view showing a probe mounted to a robotic device;

(3) FIG. 2 is a schematic view depicting a method of inspecting a surface according to a first embodiment;

(4) FIG. 3 is a schematic view depicting a method of inspecting a surface according to a second embodiment; and

(5) FIG. 4 illustrates the method of the present disclosure in an impedance plane.

(6) FIG. 5 illustrates scans and a component surface map constructed from such scans.

(7) FIG. 6 is a schematic side view of a first embodiment of a probe that is suitable for use in the method of the present disclosure. The probe is an eddy current probe.

(8) FIG. 7 is a schematic perspective view of the eddy current probe of FIG. 6.

(9) FIG. 8 is a schematic side view of a blade of a gas turbine engine showing the path of the eddy current probe of FIG. 6 when inspecting the surface of a fir tree portion of the blade in the method of the present disclosure.

(10) FIG. 9 is a schematic side view of a blade of a gas turbine engine showing the path of the eddy current probe of FIG. 6 when inspecting the surface of a fir tree portion of the blade in the method of the present disclosure.

(11) FIG. 10 is a schematic perspective view of a second embodiment of an eddy current probe that is suitable for use in the method of the present disclosure.

(12) FIG. 11 is a sectional view along the line A-A of the eddy current probe shown in FIG. 10.

(13) The following table lists the reference numerals used in the drawings with the features to which they refer:

(14) TABLE-US-00001 Ref no. Feature 10 Probe 12 Surface of a component 14 Engagement portion 16 Robotic arm 18 Biasing device 20 Tool path 22 Inspection point(s) 24 Reference surface 26 Reference point 28 Mid-point 30 Axis 32 Curved path D Stand-off distance 40 Scan noting no defects 42 Scan noting defects 44 Component surface map 46 Spike on scan indicating defect 48 Spot on component surface map indicating defect 50 End effector 52 Snake robot 54 Linear translation system 56 Eddy current coils 58 Camera 60 Light emitting diode (LED) 62 Root of gas turbine engine blade 64 Gas turbine engine blade

DETAILED DESCRIPTION OF THE DISCLOSURE

(15) Aspects and embodiments of the present disclosure will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art.

(16) FIG. 1 shows a probe, in the form of an eddy current probe 10, for inspecting a surface 12 of a component for defects. The probe 10 is mounted to an engagement portion 14 at the distal end of a robotic device in the form of a robotic arm 16. The probe 10 is mounted to the engagement portion 14 by way of a biasing device 18. The biasing device 18 provides resilient mounting of the probe 10 and allows movement of the probe 10 relative to the robotic arm 16 in the direction of the longitudinal axis of the probe 10. The biasing device 16 biases the probe 10 in a direction away from the engagement portion 14. In this way, when the probe 10 is moved against the component surface 12 there is some yield in the probe 10, i.e. to ensure contact between the probe 10 and the surface 12 can be maintained without the requirement of extremely tight tolerances.

(17) Although not apparent from FIG. 1, the probe 10 may be mounted to the engagement portion 14 in such a way that it is moveable, i.e. other than the biasing, relative to the robotic arm 16. For example, the probe 10 may be moveable by an actuator, e.g. a motor, in the direction along a longitudinal axis of the probe 10, i.e. towards and away from the surface 12 as depicted. In other words, the probe 10 may be extendable and retractable relative to the robotic arm 16.

(18) The probe 10 is configured to induce eddy currents in the component surface 12 and detect differences in those eddy currents, e.g. caused by the presence of surface defects. The probe 10 is configured to provide a signal that can be used to determine the presence of a defect, such as a crack, in the component surface 12. Although not shown, the probe 10 comprises one or more coils for inducing eddy currents in the component surface 12. The signal provided by the probe 10 may, for example, be a voltage signal proportional to, or at least related to, impedance changes in the coil or coils.

(19) FIG. 2 schematically depicts a method of inspecting a surface 12, according to a first embodiment, using a probe and robotic arm, such as those shown in FIG. 1. In particular, FIG. 2 shows a tool path 20 along which the probe is moved by the robotic arm to inspect the surface 12.

(20) The tool path 20 is defined such that the probe contacts a plurality of discrete spaced apart inspection points 22 on the component surface 12. At each inspection point 22, the component surface 12 is inspected. As should be apparent from the figure, the tool path 20 is such that, after each contact with an inspection point 22, and inspection, the probe is retracted from the component surface 12.

(21) By contacting the plurality of discrete inspection points 22, rather than e.g. dragging across the surface 12, and by retracting the probe between each contact, the probe is substantially stationary when it is in contact with the component surface 12. As such, the wear of the probe may be eliminated or at least significantly reduced. Thus, the method may minimise probe wear, while maintaining the accuracy of any measurements that are made in the inspection.

(22) In order to provide the tool path 20, a reference surface 24 is defined, which is offset from the component surface 12 by a stand-off distance D. As is apparent from the figure, the reference surface 24 follows the shape of the component surface 12, but is spaced therefrom by the stand-off distance D. As such, the curvature of the reference surface 24 has a greater radius than that of the component surface 12, i.e. because of the nature of the offset. The reference surface 24 is not a physical surface, it merely acts as a guide for defining the tool path 20. In the illustrated embodiment, the stand-off distance D is 1 mm.

(23) The reference surface 24 comprises a plurality of reference points 26. Although not apparent from the figure, the reference points 26 are arranged in an organised array or grid so as to be evenly spaced from one another. Each reference point 26 is located so as to be aligned with a mid-point 28 between two inspection points 22. That is, each reference point 26 lies on a line extending in a normal direction from each mid-point 28, e.g. as is shown in the FIG. 2. Also highlighted by the reference line extending from mid-point 28 is the fact that the movement is such that the probe is normal to the component surface 12 throughout its movement, and, importantly, at all inspection points 22.

(24) The reference surface 24 may be generated from 3D data representing the component surface 12. Such 3D data may, for example, be data representing the component surface 12 as designed, such as CAD data used in the manufacture and/or design of the component. The reference surface 24 may be generated from the 3D data by applying an offsetting function to the 3D data. Such offsetting functions are known in e.g. CAD applications.

(25) The reference points 26 aid in defining the tool path 20, which alternates, i.e. zig-zags, between the reference points 26 of the reference surface 24 and inspection points 22 on the component surface 12.

(26) In particular, the tool path 20 is such that each contact of the probe with an inspection point 22 on the component surface 12 comprises first and second movements of the probe. The first movement is movement of the probe from a reference point 26 of the reference surface 24 to an inspection point 22 on the component surface 12. This movement is a diagonal movement of the probe, i.e. so as to be at an angle to a normal direction extending from the component surface 12. The second movement is a retraction of the probe from the inspection point 2 on the component surface 12 to a subsequent reference point 26 of the reference surface 24. Again, this movement is diagonal, with the orientation of the probe being continuously adjusted so as to be normal to the component surface 12.

(27) Between the first and second movements, the probe is positioned so as to be in contact with the component surface 12, at an inspection point 22. The probe does not move across the component surface 12, which reduced wear of the probe. When the probe is in this position, a signal provided by the probe allows the determination of whether there is a defect in the component surface 12 at or near to the inspection point 22.

(28) In the illustrated embodiment, movement of the probe along the tool path 20 may be performed entirely by movement of the robotic arm. In other words, the robotic arm may be controlled to move the probe along the tool path 20 in order to perform inspection of the component surface 12.

(29) FIG. 3 schematically depicts a method of inspecting a surface 12, according to a second embodiment. The method, again, may make use of a probe and robotic arm as depicted in FIG. 1. The embodiments of FIGS. 2 and 3 share similar features and such features have been given the same reference numerals accordingly.

(30) Again, the method comprises defining a reference surface 24 which comprises a plurality of reference points 26. The reference surface 24 is offset from the component surface 12 by a stand-off distance D.

(31) This embodiment differs from the first embodiment, depicted in FIG. 2, in that each reference point 26 is located so as to lie on a line extending in a normal direction from a corresponding inspection point 22 on the component surface 12. As will be described further below, this means that the tool path 20 does not have a zig-zag profile such as that of the previously described embodiment.

(32) This embodiment also differs in that movement of the probe along the tool path 20 is performed by a combination of movement of the robotic arm and movement of the probe relative to the robotic arm, whereas in the previous embodiment the probe remained fixed relative to the robotic arm. It should be appreciated, however, that the depicted movement could alternatively be performed by movement of the robotic arm exclusively, as per the previous embodiment.

(33) Each contact of the probe with an inspection point 22 is formed of first, second and third movements along the tool path 20. Unlike the previous embodiment, the first and second movements are along an axis that is normal to the component surface 12 at the corresponding inspection point.

(34) In the first movement, the probe is moved from a reference point 26 of the reference surface 24 to an inspection point 22 on the component surface 12 along an axis 30 that is normal to the component surface 12 at the inspection point 22. At the inspection point 22, the probe is able to perform an inspection of the component surface 12.

(35) In the second movement, the probe is moved from the inspection point 22 to a reference point 26 on the reference surface 24. The second movement is a reverse of first movement. That is, the second movement is along the axis 30 normal to the component surface 12 at the inspection point, and thus returns the probe to the same reference point 26 at which the first movement began.

(36) In the third movement, the probe is moved from the reference point 26, i.e. defining the end of the second movement, to a subsequent, adjacent, reference point 26 along a curved path 32 that follows the reference surface 24. The first, second and third movements may then be repeated to inspect all of the inspection point 22 of the component surface 12.

(37) The first and second movements are performed by moving the probe relative to the robotic arm. In particular, the robotic arm is maintained in a stationary position while the probe is extended (first movement) and then retracted (second movement) along a probe path, i.e. corresponding to the axis 30 discussed above. As noted above, the first and second movements could alternatively be performed by movement of the robotic arm rather than the probe, i.e. the probe remaining fixed relative to the robotic arm. In such embodiments, each of the first, second and third movement would be performed by movement of the robotic arm.

(38) The third movement is performed by moving the robotic arm while maintaining the probe in a fixed position relative to the robotic arm. Thus, the robotic arm follows a path, e.g. robotic device path, which provides movement of the probe along the curved path 32, i.e. along the reference surface 24.

(39) By using the combination of these movements, inspection of the component surface 12 can be achieved without relying on providing highly accurate stand-off between the robotic arm and the component surface 12. Rather, any tolerance issues are addressed by movement of the probe and, at least partly, by the probe being spring loaded. In some embodiments, the probe may also be configured to detect contact with the component surface 12, such that once contact is detected, further extension of the probe may be prevented.

(40) Although the embodiments provided above discuss movement of the probe or robotic arm separately, other embodiments may encompass a tool path formed by moving the probe and robotic arm concurrently.

(41) Signal Processing:

(42) The method of the present disclosure uses a probe to inspect the surface of a component, for example a gas turbine engine blade or vane. In embodiments of the present disclosure the probe generates signals as it contacts inspection points on the surface of the component. These signals are processed to provide meaningful information with regard to the presence of any defects, e.g. cracks, in the surface of the component being inspected.

(43) Known methods of inspecting the surface of components using eddy currents tend to suffer from poor signal-to-noise ratios (SNR). This is generally due to continuously monitoring the impedance measured by an eddy current coil as it traverses steadily over a surface, usually remaining in direct contact the surface. When the eddy current coil is on the component, the impedance value will typically vary if there is a defect in the component but also if there is a contact error, for example because the surface contacted is rough, dirty or topologically-complex. This means signals indicating defects are often masked by signals caused by other factors. This significantly limits the defects that can be reliably detected. It also typically encourages undamaged or lightly damaged components to be scrapped, thereby creating unnecessary waste and expensive replacements.

(44) Instead of scraping the probe along a surface and continuously observing relatively small variations in the measured impedance, the method of the present disclosure discretises the inspected surface into inspection spots or points and uses the relatively large impedance difference between the component and air, as well as the fact that the trajectory of this difference varies according to whether a defect is present or not, to map the whole area and more-sensitively detect defects.

(45) FIG. 4 illustrates the method of the present disclosure as represented in an impedance plane. At each inspection spot, the probe moves from air to the component and the measured impedance varies along one of the two paths in the chart, i.e. a trajectory. The point at which this trajectory intersects the defect amplitude axis (whose rotation is optimised for maximum SNR) determines whether a defect is present at that spot or not. The probe is then retracted from the surface and moved over the next inspection spot, ready for the process to be repeated. The impedance still varies because of either a defect in the component (i.e. a signal) or because a contact error (i.e. noise), however the contribution of noise is significantly reduced, and hence the SNR is appreciably improved even if only a small reduction in the signal amplitude is observed.

(46) Repeating the process over a target area of the surface of a component enables a detailed, high-resolution map to be created that shows any defects present. FIG. 5 shows the results of a scan 40 along a line A of the surface of a gas turbine engine blade where no defects are detected in the surface, a scan 42 along a line B of the surface of a gas turbine engine blade where some defects are detected in the surface, and a component surface map 44 constructed from multiple scans that identifies the location of defects in the surface of the gas turbine engine blade. A spike 46 in the scan 42 that results from a defect in the surface of the component is shown as a spot 48 in the map. Each spot represents a trajectory intersecting a defect amplitude axis.

(47) By making point-by-point component and air impedance measurements and observing the trajectory intersection with a defect amplitude axis, the method of the present disclosure maximises the available impedance data to greatly increase signal-to-noise ratio and significantly reduce sensitivity to extraneous influences, such as surface condition and probe placement precision. This enables the method of the present disclosure to be easily, rapidly and cost-effectively industrialised both for either components that have been fully removed from a machine or for components still in situ.

(48) The defect amplitude axis can be set in various ways. The method may be optimised using reference test pieces or suitable numerical calculations. When desired, the trajectory can be measured from another reference, i.e. not air. If desired, trajectory data may be stored for future diagnoses and intelligence.

(49) Probe Construction and Operation:

(50) As mentioned above, the probe used in the method of the present disclosure may be an eddy current probe, i.e. a configured to induce eddy currents in the component surface and detect changes in those eddy currents, e.g. due to surface defects. Various eddy current probes are known however FIGS. 6 to 11 depict eddy current probes that are especially useful in performing the method of the present disclosure.

(51) In the eddy current probes of FIGS. 6 to 11 miniaturised eddy current coils and an illuminated camera system are embedded into the end effector of a snake robot to allow targeted eddy current inspection of gas turbine engine components in situ. Such eddy current probes are particularly suitable for inspecting the surface of a blade or vane of a gas turbine engine. The miniaturised nature of the eddy current probes enables access to surfaces that are generally difficult to access within a gas turbine engine.

(52) FIG. 6 is a schematic side view of a first embodiment of a probe that is suitable for use in the method of the present disclosure. The probe 10 is an eddy current probe embedded in the end effector 50 of a snake robot 52. The snake robot 52 includes a linear translation system 54 in the form of a linearly retractable rod that is configured to move the end effector with respect to the snake robot. The end effector 50 houses eddy current coils 56 and an illuminated camera system that are suitably connected to an externally located signal processing system. In use the end effector 50 lightly taps the surface of the component being inspected. The illuminated camera system can take a variety of forms. In the embodiment shown the illuminated camera system comprises a camera 58 and a plurality of light-emitting diodes 60. If desired the light-emitting diodes or other suitable illumination means can be integrated into the camera. If desired, the eddy current coils may be operated differentially. This lowers the sensitivity to positional accuracy but requires the smooth translation offered by the probe to reliably detect defects. Four eddy current coils can be provided in a square configuration and a switching system may be provided at the control end of the equipment to allow a multitude of operating modes: absolute, differential, and pulse-receive. This would allow a breadth of inspection applications. In the first embodiment of the probe 10 the eddy current 56 coils do not contact the surface of the component being inspected however they are brought in very close proximity to it. The end effector may be made from a non-conductive material, e.g. DELRIN® acetal homopolymer available from DuPont.

(53) FIG. 7 is a schematic perspective view of the eddy current probe of FIG. 6 with the end effector 50 shown in an extended position. The linear translation system can be provided in various alternative forms. For example the linear translation system can be in the form of a conduit that has both the flexibility to not inhibit gross positioning but the stiffness required to bridge the gap from deployment tube to blade/disc gap once actuated from outside the engine. Alternatively the conduit may have a stiff section that bridges this gap only, and is connected to a more flexible section that cannot extend outside of the deployed probe. In another alternative the conduit may be spring loaded such that the probe is moved into the gap along an internalised rail such that only a highly flexible cable will be needed to withdraw it.

(54) FIG. 8 is a schematic side view of a blade of a gas turbine engine showing the path of the eddy current probe of FIG. 6 when inspecting the surface of a root 62 of a gas turbine engine blade 64 in the method of the present disclosure. The end effector 50 is shown in its retracted position. Whilst in that position, the probe can be navigated to the surface to be inspected, aided by the illuminated camera system provided in the probe, and optionally assisted by a positioning system (not shown). Once the probe is positioned sufficiently close to the surface to be inspected, the linear translation system is activated to move the end effector 50 adjacent the surface of the root in a manner that enables the end effector to contact a plurality of discrete spaced apart inspection points on the surface of the root. The inspection of the surface of the root can be made on either the extension or retraction of the end effector. In FIG. 8 the inspection is shown to be made on extension of the end effector is extended.

(55) FIG. 9 is a schematic side view of a blade of a gas turbine engine showing the path of the eddy current probe of FIG. 6 when inspecting the surface of a fir tree portion of the blade in the method of the present disclosure. The end effector 50 is shown in its extended position. In FIG. 9 the inspection is shown to be made on retraction of the end effector is extended. Choosing whether to inspect the surface on extension or retraction of the end effector will typically be determined by whichever the skilled person judges to provide the more controlled inspection.

(56) FIG. 10 is a schematic perspective view of a second embodiment of an eddy current probe that is suitable for use in the method of the present disclosure. The probe is embedded in the end effector 50 of a snake robot (not shown). The snake robot includes a linear translation system 54 that is configured to move the end effector with respect to the snake robot. The end effector 50 houses eddy current coils 56 and an illuminated camera system that comprises a camera 58 and a plurality of light-emitting diodes 60.

(57) FIG. 11 is a sectional view along the line A-A of the eddy current probe shown in FIG. 10. It shows the end effector 50 houses a pair of eddy current coils 56.

(58) It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein.