Inspection method using perching UAV with releasable crawler

Abstract

To provide a method of inspection or maintenance of a curved ferromagnetic surface using an unmanned aerial vehicle (UAV) having a releasable crawler.SOLUTION: The method includes: flying a UAV 100 from an initial position to a pre-perching position in the vicinity of the ferromagnetic surface; autonomously perching the UAV 100 on the ferromagnetic surface; maintaining magnetic attachment of the perched UAV 100 to the ferromagnetic surface; releasing a crawler 130 from the magnetically attached UAV 100 onto the ferromagnetic surface; moving the crawler 130 over the curved ferromagnetic surface while maintaining magnetic attachment of the released crawler 130 to the ferromagnetic surface; inspecting or maintaining the ferromagnetic surface using the magnetically attached crawler 130; and re-docking the released crawler 130 with the perched UAV 100.SELECTED DRAWING: Figure 1A

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 62 / 772,700, filed November 29, 2018, and entitled "PERCHING UAV WITH RELEASABLE CRAWLER," and claims the benefit under 35 U.S.C. §120 of U.S. Application No. 16 / 694,092, filed November 25, 2019, and entitled "INSPECTION METHOD USING A PERCHING UAV WITH RELEASABLE CRAWLER," each of which is incorporated herein by reference in its entirety.

[0002] The present disclosure relates generally to inspection and maintenance of structures, and more particularly to an inspection method using a perching unmanned aerial vehicle (UAV) having releasable and redockable crawlers for inspecting and maintaining structures. [Background technology]

[0003] Inspection and maintenance of exposed metal assets such as pipes, storage tanks, etc. can be difficult or impractical for humans to perform in some environments. In such situations, the use of automated UAVs (drones) can be an aid, providing a viable alternative. However, such inspection and maintenance tasks are often best performed using direct contact with the asset or by piloting the UAV over the asset, rather than hovering at a distance from the asset. In particular, performing a full circumferential scan of a pipe (or other asset) using a drone is a challenging task. Summary of the Invention [Problem to be solved by the invention]

[0004] With regard to these and other problems in the art, the present disclosure aims to provide a technical solution for an effective inspection method using a perching UAV with releasable and redockable crawlers. [Means for solving the problem]

[0005] According to one embodiment, a method is provided for inspecting or maintaining a curved ferromagnetic surface using an unmanned aerial vehicle (UAV) having releasable crawlers. The method includes flying the UAV into the vicinity of the ferromagnetic surface and perching the UAV on the ferromagnetic surface. Perching the UAV includes passively articulating legs of the UAV to a curved portion of the ferromagnetic surface using corresponding magnets on the legs while approaching the ferromagnetic surface, magnetically attaching the articulated legs of the UAV to the ferromagnetic surface using corresponding magnets, and maintaining the magnetic attachment of the legs to the ferromagnetic surface throughout the perching. The method further includes detaching the crawlers from the perched UAV to the ferromagnetic surface and maneuvering the detached crawlers on the ferromagnetic surface while magnetically attaching the crawlers to the ferromagnetic surface using magnetic wheels on the crawlers.

[0006] In one embodiment, the curved ferromagnetic surface comprises a pipe, and steering the separated crawler includes performing a circumferential scan of the pipe using the separated crawler.

[0007] In one embodiment, the method further includes inspecting or maintaining the ferromagnetic surface during maneuvering using a probe or tool on the crawler.

[0008] In one embodiment, the method further includes wirelessly communicating from the separated crawler with the UAV or a base station.

[0009] In one embodiment, the method further includes, after the maneuver, disengaging the crawler from the ferromagnetic surface and redocking the detached crawler to the perched UAV.

[0010] In one embodiment, the method includes magnetically decoupling the articulated legs from the ferromagnetic surface and flying the magnetically decoupled legs of the UAV away from the ferromagnetic surface.

[0011] In one embodiment, the corresponding magnet comprises a switchable permanent magnet, and demagnetizing comprises switching the permanent magnet from a magnetized state to a non-magnetized state.

[0012] In one embodiment, breaking the magnetization includes applying leverage to the magnetized legs using one or more separate actuators of the UAV.

[0013] In one embodiment, the method further includes scanning the nearby ferromagnetic surface using a laser scanner on the flying UAV.

[0014] According to one embodiment, a method for inspecting or maintaining a curved ferromagnetic surface using an unmanned aerial vehicle (UAV) having releasable crawlers is provided, the method includes flying the UAV from an initial position to a pre-perched position near the ferromagnetic surface, autonomously perching the UAV on the ferromagnetic surface, maintaining magnetic attachment of the perched UAV to the ferromagnetic surface, releasing the crawler from the magnetically attached UAV to the ferromagnetic surface, moving the crawler across the curved ferromagnetic surface while maintaining magnetic attachment of the released crawler to the ferromagnetic surface, inspecting or maintaining the ferromagnetic surface using the magnetically attached crawler, and redocking the released crawler with the perched UAV.

[0015] In one embodiment, the method further includes wirelessly communicating with the UAV from the released crawler.

[0016] In one embodiment, the method further includes magnetically separating the perched UAV from the ferromagnetic surface and flying the magnetically separated UAV away from the ferromagnetic surface to a pre-perched position.

[0017] In one embodiment, flying the magnetically separated UAV includes not carrying the redocked crawler, and the method further includes wirelessly communicating from the released crawler to the flying UAV.

[0018] In one embodiment, inspecting or maintaining the ferromagnetic surface includes marking locations of interest on the ferromagnetic surface.

[0019] In one embodiment, inspecting or maintaining the ferromagnetic surface includes measuring a thickness of the ferromagnetic surface, and the locations of interest include locations where the measured thickness is less than a critical value.

[0020] In one embodiment, the method further includes magnetically isolating the perched UAV from the ferromagnetic surface, flying the magnetically separated UAV away from the ferromagnetic surface, and detecting the marked locations of interest on the ferromagnetic surface from the magnetically separated UAV.

[0021] In one embodiment, the method further includes magnetically separating the perched UAV with the redocked crawler from the ferromagnetic surface, flying the perched UAV with the redocked crawler to a pre-perched position away from the ferromagnetic surface, and flying the magnetically separated UAV with the redocked crawler to another pre-perched position near a second ferromagnetic surface to be inspected or maintained by the redocked crawler.

[0022] In one embodiment, the method includes magnetically isolating the perched UAV with the redocked crawler from the ferromagnetic surface, and flying the magnetically separated UAV with the redocked crawler away from the ferromagnetic surface to an initial position.

[0023] In one embodiment, autonomously perching the UAV includes sensing a ferromagnetic surface using a depth camera or laser scanner of the UAV and touching down on the ferromagnetic surface using the sensed depth camera or laser scanner data.

[0024] In one embodiment, autonomously perching the UAV includes aligning the UAV to a pre-touchdown position using the sensed ferromagnetic surface data, magnetically separating the perching UAV with the redocked crawler from the ferromagnetic surface, and flying the magnetically separated UAV with the redocked crawler away from the ferromagnetic surface to an initial position.

[0025] Any combination of the various embodiments and implementations disclosed herein may be used. These and other aspects and features can be understood from the following description of specific embodiments, taken in conjunction with the accompanying drawings and claims. [Brief description of the drawings]

[0026] [Figure 1A] 1A-1C are diagrams of an example of a UAV perching on a structure (e.g., a pipe), where the UAV has releasable crawlers for inspecting or maintaining the structure, according to one embodiment. [Figure 1B] 1A-1C are diagrams of an example of a UAV perching on a structure (e.g., a pipe), where the UAV has a releasable crawler for inspecting or maintaining the structure, according to one embodiment. FIG. 1B shows the crawler unattached to the UAV (e.g., crawling on the structure). [Figure 2A] FIG. 1 illustrates an exploded and cross-sectional view of an exemplary UAV or drone, according to one embodiment, comprising an undercarriage having perching legs for perching on a structure. [Figure 2B]FIG. 1 illustrates an exploded and cross-sectional view of an exemplary UAV or drone, according to one embodiment, configured with an undercarriage having crawlers for releasing the UAV from a perched on a structure for inspecting or maintaining the structure. [Figure 3A] FIG. 2C is a cross-sectional view of an exemplary UAV having modular mounting points for attaching the undercarriage of FIGS. 2A and 2B, according to one embodiment. [Figure 3B] A cross-sectional view of a UAV having a substructure attached in a lateral orientation relative to the UAV, according to one embodiment. [Figure 3C] A cross-sectional view of a UAV having a lower structure mounted in an upward orientation relative to the UAV, according to one embodiment. [Figure 4A] A cross-sectional view of an exemplary UAV having a rotatable mounting point for mounting the undercarriage of Figures 2A to 3C, with the undercarriage mounted in a bottom orientation relative to the UAV, in accordance with one embodiment. [Figure 4B] A cross-sectional view of an exemplary UAV having a rotatable mounting point for mounting the undercarriage of Figures 2A to 3C, with the undercarriage mounted in an upward orientation relative to the UAV, in accordance with one embodiment. [Figure 4C] A cross-sectional view of an exemplary UAV having a rotatable mounting point for mounting the undercarriage of Figures 2A to 3C, with the undercarriage mounted in a lateral orientation relative to the UAV, in accordance with one embodiment. [Figure 5A] 1 is an illustration of an exemplary method of inspecting a structure of interest (e.g., a pipe) using a perching UAV having releasable crawlers, according to one embodiment. [Figure 5B] 1 is a flowchart corresponding to an illustration of an exemplary method for inspecting a structure of interest (e.g., a pipe) using a perching UAV having releasable crawlers, according to one embodiment. [Figure 6]FIG. 1 is an illustration illustrating an example releasable crawler that visually marks interesting (e.g., suspicious) portions of a structure (e.g., a pipe) encountered during inspection or maintenance of the structure, along with an example UAV that detects the visual markers left by the crawler, according to one embodiment. [Figure 7A] FIG. 1 is an illustration illustrating an example technique for a releasable crawler to visibly mark interesting (e.g., suspicious) portions of a structure (e.g., a pipe) encountered during inspection or maintenance of the structure, in conjunction with a UAV performing wireless localization using virtual markers, according to one embodiment. [Figure 7B] FIG. 1 is an illustration illustrating an example technique for a releasable crawler to visibly mark interesting (e.g., suspicious) portions of a structure (e.g., a pipe) encountered during inspection or maintenance of the structure, in conjunction with a UAV performing wireless localization using virtual markers, according to one embodiment. [Figure 8] 1 is an exemplary structure for deploying a UAV having releasable crawlers to inspect or maintain the structure, according to one embodiment. [Figure 9] 1 is a flowchart of an exemplary method for inspecting or maintaining a structure (such as a pipe) having a curved ferromagnetic surface using a UAV with releasable crawlers, according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Please note that the drawings are illustrative and are not necessarily to scale, and that like or similar features have the same or similar reference numbers throughout.

[0028] In various exemplary embodiments, a perching UAV with releasable crawlers is provided for inspecting or maintaining structures such as elevated or otherwise inaccessible pipes or storage tanks. The UAV is a hybrid UAV with advanced capabilities for performing contact inspection operations on ferromagnetic surfaces such as carbon steel pipes, structures, and the like. The UAV can fly toward and autonomously land (commonly referred to as perching) the pipe to be inspected, and deploy the releasable crawlers to crawl around the pipe, for example, to perform intricate inspection operations at any orientation angle. The crawlers can also be configured to perform maintenance on the pipe. As will be appreciated from the discussion below, the UAV can land, for example, on top of, to the side of, or directly underneath the pipe or other structure, and in each instance is said to have landed on the structure.

[0029] As mentioned previously, it can be difficult or impractical for people to inspect and maintain exposed metal assets such as pipes, storage tanks, etc. For example, one of the biggest challenges in the oil and gas industry is the regular inspection of elevated assets found in refineries, gas plants, offshore platforms, and other plants and facilities. These assets include elevated pipes and structures that are difficult to access during inspection or maintenance work. Sometimes the only way for people to inspect or maintain them is to erect scaffolding so that an inspector or engineer can access the asset and perform manual inspections, for example, using ultrasonic inspection (UT) sensors for thickness measurements. Such scaffolding is expensive, posing a significant cost barrier to frequent inspections, as well as raising safety concerns, primarily in the form of fall and tripping hazards.

[0030] Thus, in an exemplary embodiment, a perching UAV with releasable crawlers provides a solution to the aforementioned technical problem by having two vehicles in a mother-son configuration. Each vehicle is designed or optimized to perform the most suitable performance. The vehicles include a perching UAV that can fly over and land on the pipe, and a small magnetic crawler that is carried by the UAV and released from the UAV after landing or perching. The crawler can move around on the pipe to perform inspection scans, such as thickness measurements using a UT sensor. For example, in some embodiments, both the UAV and the crawler magnetically attach to the curved surface of the pipe or other asset being inspected or maintained. As such, the crawler can perform a complete longitudinal or circumferential scan of the asset (even upside down with respect to gravity).

[0031] This provides a more feasible approach than having the entire UAV crawl around the pipe, which requires larger and heavier motors and risks collision with nearby pipes and assets, especially when clearance constraints are limited. A perching UAV also saves energy (electrical energy, battery energy, etc.) by perching on (e.g., on top of) the pipe as opposed to hovering close to the pipe. Perching the UAV on the pipe surface also makes it easier to release or redock the releasable crawler from the UAV than when the UAV is hovering next to the pipe. Additionally, perching provides more stability and reduces risk compared to hovering.

[0032] 1A and 1B are diagrams of an exemplary UAV 100 perched on a structure 50 (e.g., a pipe) according to one embodiment, the UAV 100 having a releasable crawler 130 for inspecting or maintaining the structure 50. The crawler 130 is shown attached to the UAV 100 in FIG. 1A and not attached to the UAV 100 (e.g., crawling on the structure 50) in FIG. 1B. For ease of explanation, the structure 50 is assumed throughout to be larger (e.g., significantly larger) than the UAV 100. For example, the structure 50 is larger in all dimensions than the UAV 100. Or, the proposed landing area provided by the structure 50 is larger than the proposed landing area of ​​the UAV 100. Additionally, for ease of explanation, the structure 50 (or any structure described herein) is assumed to be a pipe, such as a pipe with a diameter of 8 inches or more.

[0033] 1A and 1B show the mother-son configuration in operation. FIG. 1A shows the UAV 100 after landing on the pipe 50 with the crawler 130 still docked. FIG. 1B shows the crawler 130 after being released from the UAV 100 to perform inspection operations. The crawling capability provided by the releasable crawler 130 gives the UAV 100 important features for inspection and maintenance operations such as easier accessibility (e.g., no need to land at the exact spot where the inspection or maintenance is to be performed). Crawling further provides circumferential and longitudinal scanning. For example, in the oil and gas industry, it is important to perform a full scan of the pipe 50 to find the minimum steel thickness in a particular area of ​​the pipe 50. Such scanning often includes circumferential and longitudinal scanning, for which crawling is well suited. Crawling further provides power efficiency during multiple inspections (e.g., crawling between multiple inspection sites on the same pipe is more power efficient than flying).

[0034] 1A and 2B, the UAV 100 utilizes four articulated magnets 120 (such as permanent magnets or switchable permanent magnets). To accommodate landing of the UAV 100 on the pipe 50, each magnet 120 (or, more precisely, its magnetic field) is articulated in a perpendicular orientation relative to the pipe 50 when the UAV 100 lands on or is perched on the pipe 50.

[0035] In some embodiments, the magnetic field of the joint magnet 120 can be actively switched on and off (e.g., to allow for easy removal after work is completed). A laser scanner 110 (e.g., light detection and ranging, or LIDAR) is included as a form of real-time feedback to measure the relative position of the pipe to the UAV 100 during the automatic landing maneuver, etc. In some embodiments, the miniature crawler 130 is connected by wires (e.g., for power and communication) and includes the UT sensor, four magnetic wheels 140, and two motors for driving the wheels 140 in corresponding pairs (e.g., front and rear). The wires also allow the remaining electronics and batteries for performing inspection or maintenance to be located within the UAV body 100. This reduces the size, weight, and complexity of the crawler 130.

[0036] In some other embodiments, the crawler 130 includes a different number of wheels 140 (e.g., two or three wheels, or four or more) and their types (omni wheels, mecanum wheels, etc., to name a few). Unlike an unmanned ground vehicle (UGV), the magnetic crawler 130 must contend with the various curvatures and various orientations (as shown throughout) of a pipe inspection or maintenance. Thus, in some embodiments, the magnetic crawler 130 has a specialized locomotion system for navigating the curvature of a pipe (or similar curvatures from other curved structures or vessels).

[0037] In some embodiments, communication between the crawler 130 and the UAV 100 is wired. For example, using a small spool of thin cord, the crawler 130 can be connected to the UAV 100 for power and communications. This can, for example, eliminate the need to carry batteries and other electronics within the crawler 130, allowing the crawler to be smaller and save overall weight by utilizing some components already present in the UAV 100.

[0038] In some other embodiments, the communication between the crawler 130 and the UAV 100 is wireless. Here, the crawler 130 includes its own battery and electronics to provide a more independent vehicle. This may be useful, for example, when the UAV 100 picks up the crawler 130 from the ground and deploys it to the pipe 50. At that point, the UAV 100 can fly off and do some other inspection work and then return to pick up the crawler 130. This is also useful when multiple crawlers 130 (e.g., a fleet of crawlers 130) are inspecting multiple assets. The UAV 100 picks them up from the ground, one by one or in batches, to their destination and then retrieves them when the work is completed. In different embodiments, the wireless connection may be between the crawler 130 and either the UAV 100 or the operator's control station, or both the UAV 100 and the operator's control station.

[0039] In one embodiment, the UAV 100 includes a body (e.g., having rotors, control devices, and guidance devices, etc.) constructed to enable flight of the UAV 100. The UAV 100 also includes three or more legs connected to the body and configured to land and perch the flying UAV 100 on a curved ferromagnetic surface 50. Each leg includes an upper (or main) portion connected to the body and a lower portion including a permanent magnet 120. The bottom portion is configured to magnetize the leg to the ferromagnetic surface 50 upon landing and to remain magnetized to the ferromagnetic surface while perching. Additionally, a passive articulation joint connection connects the upper and lower portions of the legs and passively articulates (e.g., pivots) the lower portion relative to the upper portion in response to the lower portion approaching the ferromagnetic surface 50 during landing. The UAV 100 further includes a releasable crawler 130 having magnetic wheels 140. The magnetic wheels 140 allow the crawler 130 to be separated from the UAV 100 during perching, and after separation, allow the crawler 130 to move over the ferromagnetic surface 50 while remaining magnetically attached to the ferromagnetic surface 50.

[0040] In different embodiments, different landing mechanisms for the UAV 100 can be used. These can include various types of attachment mechanisms, such as magnetic or non-magnetic. Examples of magnetic landing mechanisms include magnets that can be blocked or overcome by mechanical means during takeoff from the pipe 50. Such magnets include switchable permanent magnets, permanent magnets with actuating levers to aid in detachment during takeoff, electro-permanent magnets, and electromagnets. However, it is noted that continuous power consumption can be a disadvantage for electromagnets. Non-magnetic attachment mechanisms can be used on non-ferromagnetic surfaces such as stainless steel, composite pipes, concrete walls, etc. Such mechanisms include microspine, suction cups, grippers, and crawlers, which are gecko-inspired dry adhesives (such as synthetic bristles).

[0041] Different embodiments use different crawler loads or designs. For simplicity, these loads or designs are categorized into two basic categories: inspection and maintenance. Inspection loads and designs include various types of sensors commonly used in the oil and gas industry to inspect pipes and structures. For example, in some embodiments, UT sensors are used for thickness measurement. For ease of explanation, UT sensors for thickness measurement are sometimes used throughout to represent exemplary devices and applications for inspection and maintenance. However, other embodiments are not limited to such devices or applications. For example, other inspection sensors or probes can be used in place of or in addition to UT sensors depending on the task, including (but not limited to) eddy current sensors and alternating current field measurement (ACFM) sensors.

[0042] In yet other embodiments, the crawler 130 is configured with one or more tools and used for maintenance purposes. For example, the crawler 130 can be used to perform light maintenance tasks such as cleaning, surface preparation, and coating repair. In yet other embodiments, the crawler 130 is configured with one or more cameras and used for visual inspection. For example, in some embodiments, the cameras are used for simple visual inspection tasks, such as areas where only video or photos of the area of ​​interest need to be obtained, but where the area is difficult to inspect directly by the UAV 100.

[0043] In some embodiments, the crawler 130 is configured to leave markers (such as paint or QR codes) in areas of interest (where sensor readings are outside normal levels, where faults are detected, etc.). For example, these locations may be where critical thickness levels are detected. In some such embodiments, the UAV 100 scans these markers after the crawler 130 redocks and the UAV 100 flies away, and creates a 3D reconstruction of the environment showing the exact locations of these markers. In some such embodiments, the UAV 100 detects the markers using an on-board RGB-D camera and calculates their location relative to the UAV 100. The GPS location of the UAV can be used to calculate or otherwise determine the absolute location of the markers. It should be noted that while the UAV 100 is scanning the markers, the crawler 130 can remain on the pipe 50 or redock with the UAV 100, for example.

[0044] In some embodiments, the crawler 130 uses radio localization to identify where there are problems on the asset, such as with virtual markers. In other words, the location of the defects can be identified without physical markers, although with less accuracy. This is because the position of the crawler relative to the UAV 100 can be calculated (or otherwise determined) using radio sensors. For example, in some such embodiments, the UAV 100 carries an ultra-wide band (UWB) sensor array that receives radio signals from another UWB transmitter mounted on the crawler 130. The relative position of the crawler can then be measured regardless of whether the UAV 100 is in flight or attached to the pipe 50. In some embodiments, whenever the operator finds an obstacle during the crawl, the position of the crawler relative to the UAV 100 is tagged and captured. Using the UAV's GPS sensors, the absolute location of these defects can be identified. In some embodiments, when GPS is unavailable, the position of the UAV is estimated based on flight trajectory and IMU data from a home base where GPS is available.

[0045] In some embodiments, the pre-calculated (or determined) inspection positions are transferred from the UAV 100 to an operational computer or ground station. The inspection positions are then visualized in a 3D model, which can be built, for example, on a pre-created 3D model of the plant to be inspected or on the UAV's on-board sensors (e.g., depth camera or 3D LIDAR). Furthermore, in some such embodiments, the visualized positions are annotated with the corresponding measurement thickness (or other sensed values ​​or information).

[0046] 2A and 2B are exploded and cross-sectional views, respectively, of an exemplary UAV 200 or drone, according to one embodiment, comprising (1) a substructure 220 having perching legs 280 for perching on a structure 150 (such as a carbon steel pipe or other curved ferromagnetic surface 150) and (2) a substructure 220 having crawlers 260 for release from the UAV 200 perched on the structure 150 for inspection and maintenance of the structure 150. The crawlers 260 have magnetic wheels 270 for steering while adhering to the curved ferromagnetic surface 150 (e.g., regardless of orientation relative to gravity, even upside down). For ease of explanation, a pipe is used throughout as an example structure having a curved ferromagnetic surface. However, the described embodiments are equally applicable to other such structures, such as cylindrical or spherical storage tanks having curved ferromagnetic surfaces. The UAV 200 or drone may include rotors (such as four or six rotors) and a control unit for adjusting the rotational speed of each rotor to balance the load of the UAV 200 or move the UAV 200 in a desired direction.

[0047] 2A and 2B, the UAV 200 includes a set of attachment points 210 for mating with a set of similar attachment points 230 on the undercarriage 220. In this manner, any compatible UAV / undercarriage combination (e.g., compatible attachment points and payload capacity / weight) can be assembled for a desired purpose, in this case a releasable crawler 260 for deploying to the structure 150 and inspecting or maintaining the structure 150. To this end, the undercarriage 220 includes a set of perching legs 280 (e.g., four such legs 280), each having an articulated magnet 290. The articulated magnets 290 are attached to the legs 280 such that they can be oriented toward and adhere to the curved ferromagnetic surface 150 as the UAV 200 approaches and perches on the surface 150.

[0048] Thus, as shown in FIG. 2A , the articulating joint allows for the magnet 290 to pivot within the housing of the magnet 290 relative to the surface 150 where the leg 280 just perches, such as when the joint includes a universal joint. As shown, the pivoting can be about the axis of the leg 280 or the joint, and can assume angles relative to the axis, such as angle φ and optionally an additional angle θ. The UAV 200 and undercarriage 220 are primarily configured to perch and deploy or retrieve the crawler 260 on (or near) a structure (e.g., to keep the rotor of the UAV 200 at an appropriate level before, during, or after perching).

[0049] Additionally, the undercarriage 220 includes a height adjustment mechanism 240 (e.g., a motor or other actuator) for lowering the crawler 260 from the perched UAV 200 to the surface 150 or for raising the crawler 260 from the surface 150 to the perched UAV 200. To assist with this, a docking mechanism 250 connects the height adjustment mechanism 240 to the crawler 260, such as with a docking port. The docking port allows the crawler 260 to disengage (e.g., be flipped off) from the perched UAV 200 after it has been deployed to the surface 150, or to engage (e.g., run into or onto) the perched UAV 200 when it is ready to leave the surface 150, such as for returning to a home base or other structure or component to be inspected or maintained. The docking mechanism 250 may also allow for the transfer of information or energy between the UAV 200 and the crawler 260. For example, instrumentation data may be downloaded from the crawler 260 to the UAV 200 or the crawler 260's batteries may be recharged from the UAV 200.

[0050] More specifically, in some embodiments, the height adjustment mechanism 240 is used to adjust the height of the crawler 260 based on the pipe diameter (e.g., for successful release at the surface 150). For example, on a large pipe (or plane), the docked crawler 260 will be at a higher height to the surface 150 than on a small diameter pipe. Thus, for a large pipe (or plane), the crawler 260 is deployed at a lower height to reach the surface 150, whereas for a small diameter pipe, the crawler 260 is deployed and released at a higher point. Additionally, in some embodiments, the height adjustment mechanism 240 is used to redock the crawler 260 after the job is completed. This allows the docking mechanism 250 to be at the correct height relative to the crawler 260. Again, different pipe diameters correspond to different heights. In some embodiments, the height adjustment mechanism 240 is used to pull the crawler 260 and release it from the ferromagnetic surface 150.

[0051] In some embodiments, height adjustment mechanism 240 is actuated by a motor or the like. In some embodiments, height adjustment mechanism 240 is passive when not used to separate crawlers 260. For example, in one such embodiment, height adjustment mechanism 240 is spring loaded so that it can always push pipe 150 at its maximum possible extension when UAV 200 perches to deploy crawlers 260.

[0052] For a UAV 200 with a substructure 220, it is desirable to approach and land near the top of the pipe 150 (e.g., at or near the 12 o'clock position) at a vertical or near vertical angle, typically providing for attachment of the legs 280 and appropriate perching. The perching legs 280 have features useful for successful perching and attachment to the pipe 150. For example, each leg 280 of the perching mechanism features an articulated magnet 290 (such as a permanent magnet or a switchable permanent magnet). The articulation of the legs 280 is passive when the UAV 200 (more precisely, the attached substructure 220) is in close proximity to the ferromagnetic surface 150 of interest, such as in response to initial contact of the magnet 290 with the ferromagnetic surface 150, in that the articulated magnet 290 is designed to articulate about the axis shown in FIG. 2A in response to the magnetic attraction of the magnet 290 and the ferromagnetic surface 150. It should be noted that undercarriage 220 can be attached to any UAV having suitable attachment points (e.g., for mating with attachment points 230) and payload capacity (e.g., for carrying and deploying undercarriage 220 during flight).

[0053] In some embodiments, after deployment and completion of the operation, the crawler 260 redocks with the UAV 200, or more specifically, with the docking mechanism 250. The process of redocking and takeoff from the ferromagnetic surface 150 by the UAV 200 using the crawler 260 also includes magnetically isolating the crawler 260 from the surface 150. In some such embodiments, the UAV 200 uses the height adjustment mechanism 240 to lever the crawler 260 away from the magnetic attraction of the magnetic wheels 270 of the crawler 260 and the ferromagnetic surface 150. In some other such embodiments, the magnetic wheels 270 use switchable magnets to disable adhesion to the ferromagnetic surface 150 after redock. In still other such embodiments, the docking mechanism 250 includes a ramp on the pipe 150 and attached to the UAV 200. In such embodiments, the crawler 260 climbs the ramp while redocked (such as parking on a sloped roadway). In this manner, the crawler's wheel motors are used to forcefully separate the magnets of the magnetic wheels 270 using the drive torque of the crawler 260. The ramp can be made of metallic materials (e.g., steel) or non-magnetic materials depending on factors such as weight, strength, etc. In each such embodiment, magnetic attraction of the UAV 200 is achieved to enable the UAV 200 to fly to its next location, with the crawler 260 as a payload safely held by the UAV 200.

[0054] 3A is a cross-sectional view of an exemplary UAV 300 having modular mounting points 310 for mounting the undercarriage 220 of FIGS. 2A and 2B, while FIGS. 3B and 3C are cross-sectional views of a UAV 300 having the undercarriage 220 mounted in a lateral and upper orientation, respectively, relative to the UAV 300, according to one embodiment. This modular approach allows for the undercarriage 220 (payload) to be mounted, for example, at the bottom, front, or top of the UAV 300 to be able to perch on the top, side, or bottom of the pipe 150, respectively.

[0055] One of the biggest challenges in inspecting pipes in refineries is that many of the pipes are not accessible from above due to obstacles such as racks, structures, other pipes, etc. In these cases, it is desirable to access or perch such surfaces from other positions, such as the side or bottom of the structure. The UAV 300, along with the undercarriage 220 attached to an appropriate set of mounting points 310, can perch on the top, side, or bottom of the pipe 150 using the adaptable perching legs 280, as shown in Figures 3A, 3B, and 3C, respectively.

[0056] More specifically, each leg 280 is designed with an articulated magnet 290 that divides the leg 280 into two separate parts, a main body that is firmly attached to the undercarriage 220 and a movable (or articulated) magnet 290. This provides the legs 280 with at least a rotational degree of freedom, which allows the magnets 290 to passively readjust their orientation (e.g., vertical) towards the pipe 150 during landing, allowing for full or near-perfect adhesion.

[0057] Note that for ease of illustration of the 2D side view, features such as rotors of UAV 300 may be shown touching other portions of UAV 300 (such as perching legs 280). However, this is because the depth dimension (where such features do not overlap) is not shown. The rotors of UAV 300 do not interfere with undercarriage 220 in any configured orientation of undercarriage 220 (e.g., undercarriage 220 is between the rotors when viewed from above).

[0058] It should also be noted that changing the location of the undercarriage 220 changes the center of gravity of the UAV 300. Therefore, the UAV 300 needs to compensate for this change. In some embodiments, the on-board flight controller of the UAV 300 is configured (e.g., by logic, code, etc.) to keep the UAV 300 in a stable hover regardless of weight distribution. For example, if the UAV 300 becomes front-heavy, the controller is configured to sense a slight tilt and increase the thrust or rotational speed of the heavy side to compensate for the tilt in order to keep the UAV 300 level and stable. In some embodiments (as shown in Figures 4A to 4C), to reduce the effect of the change in center of gravity, heavy components such as batteries are placed on the rotating rail opposite the undercarriage 220. This makes it easier for the flight controller to keep the UAV 200 stable even in situations where the undercarriage 220 is not directly underneath the UAV 200.

[0059] 4A, 4B, and 4C are cross-sectional views of an exemplary UAV 400 having a rotatable mounting point 410 for mounting the undercarriage 220 of FIGS. 2A-3C, with the undercarriage 220 mounted in bottom, top, and side orientations, respectively, relative to the UAV 400, according to one embodiment. In some embodiments, the UAV 400 includes a motor or actuator for rotating the mounting point 410 to the appropriate orientation, including during flight (e.g., dynamic rotation). In some other embodiments, the mounting point 410 can be manually rotated to a desired orientation prior to a mission (e.g., static rotation).

[0060] In an exemplary motorized embodiment, a motorized system (e.g., motorized attachment points 410 and a motor for rotating attachment points 410 to orbit around the UAV 400) allows an operator to change the orientation of the undercarriage 220 (payload) at the push of a button. In another embodiment, the UAV 400 automatically changes the orientation of the undercarriage 220 (e.g., during flight) in response to factors such as observed or known obstacles around the pipe 150. With this in mind, FIGS. 4A, 4B, and 4C show how the motorized system changes the orientation of the perching legs 280 to land on the top, bottom, or side of the pipe 150, respectively.

[0061] For example, in one embodiment, the UAV has a controller configured (e.g., by computer code) to plan the safest location on the pipe 150 to perch, such as the top, side, or bottom of the pipe 150, or somewhere in between. In the exemplary motorized embodiment shown in Figures 4A-4C, rotation is accomplished via a circular rail around the body 400 of the UAV. Thus, to maintain a proper center of gravity during rotation, heavy components such as batteries can be placed on the rail (e.g., opposite the mounting point 410) to act as a counterweight.

[0062] In an exemplary user adjustable (e.g., manual) embodiment, the rotation of the undercarriage 220 is manually adjusted by a user instead of being motorized. For example, this may be done to save weight, complexity, power, etc. An exemplary technique for achieving this manual adjustment is by loosening a hand screw to unlock the manual rotation of the undercarriage 220 about the circular rail, which can then be relocked once the undercarriage 220 is in the desired position.

[0063] 5A and 5B are a diagram and corresponding flow chart, respectively, of an exemplary method 500 for inspecting a structure of interest 555 (e.g., a pipe) using a perching UAV 505 having releasable crawlers 535, according to one embodiment. FIG. 5A illustrates the method 500, showing steps 1 through 9, which correspond, respectively, to steps 510 through 590 of the flow chart of FIG. 5B. For ease of explanation, the method 500 will be described with reference to steps 510 through 590 of FIG. 5B, but may also be visualized with corresponding reference to FIG. 5A at any point.

[0064] 5A and 5B illustrate an inspection method 500 for inspecting assets, such as assets in the oil and gas industry, including pipes, tanks, and other structures, using a perching UAV 505 with a releasable crawler 535 system, as described throughout in the exemplary embodiment. The system includes a UAV 505 used to carry a releasable crawler 535 that is deployed on an elevated structure, such as a steel tube (e.g., pipe 555), to perform contact inspection operations. The use of such advanced systems in critical industrial environments requires a high level of safety assurance and reliability of the system. In this manner, the method 500 performs inspection operations in a systematic and safe manner. Additionally, the method 500 can be programmed or coded, for example, in system software, to automate the process 500 as much as possible.

[0065] The method 500 illustrates a multi-stage mission to enable successful and safe inspection of an object, a pipe 555. FIG. 5A illustrates the steps of the method in an exemplary order. Several key steps include flying the UAV 505 autonomously or manually close to the inspection object 555 (called a pre-perch waypoint). Once the object 555 is close enough and detectable by the UAV's 505 sensors, such as a depth camera or laser scanner (LIDAR), the operator initiates an autonomous landing on the object 555 by confirming the automatically detected object 555 or by selecting a different object on the screen. The UAV 505 is programmed (or otherwise configured) to autonomously perform a perch maneuver (e.g., land on the target 555) so that the UAV 505 can safely approach and autonomously attach to the object 555.

[0066] After landing, the crawler 535 is released from the UAV 505. In one embodiment, the crawler 535 is manually driven over the surface 555 of the object by an operator to perform the inspection operation. In another embodiment, the crawler 535 is programmed or otherwise configured to navigate over the pipe 555 and perform the inspection (or maintenance) operation autonomously. Once completed, the crawler 535 is redocked (e.g., by an operator or autonomously using pre-programmed code or logic) to the UAV 505 and then flown to another inspection area or back to the home takeoff and landing site 515.

[0067] In more detail, and with further reference to FIG. 5B, the method 500 begins with a pre-flight phase, such as step 510, of positioning the UAV system 505 (or drone) at a designated take-off (and landing) location 515. In one embodiment, an operator positions the UAV 505 at the designated take-off location 515 with the rotors (or propellers) removed. At this point, the method 500 includes step 520 of powering up the UAV 505 and performing pre-flight checks and initialization. In one embodiment, the operator performs the checks and initialization. If any checks fail, the mission should not proceed.

[0068] In an exemplary embodiment, the inspection may include, but is not limited to, checking the battery degradation of the UAV 505, checking that the propulsion system is functioning as expected, checking communications between the operator's control station and the UAV / crawler 505 / 535, checking the functionality of the perch mechanism, checking the functionality of the crawler 535 and its docking mechanism, inspecting and calibrating inspection tools (e.g., UT sensors), installing rotors or propellers on the UAV 505, placing the UAV 505 into position mode (e.g., to stabilize its position in the air), enabling obstacle avoidance mode (e.g., to allow the UAV 505 to safely navigate the environment during an autonomous mission via waypoints), and selecting a flight guidance mode for the UAV 505 (e.g., selecting manual, autonomous, or mixed mode, since some waypoints are navigated autonomously and some waypoints are navigated manually).

[0069] The method 500 further includes a step 530 of performing different mission planning depending on factors such as the type of flight guidance mode. In one embodiment, an autonomous guidance mode is selected (if the UAV 505 is programmed to fly autonomously to different waypoints). Here, the operator defines the waypoints and associated operations (e.g., a takeoff waypoint at a given altitude, a pre-perch waypoint at a given distance from the target 555, and a fail-safe waypoint in case of an unplanned event). Furthermore, in one embodiment, the mission planner provides an estimate of the expected mission time. For example, this can be based on the estimated power consumption given in the mission plan entered by the operator (e.g., estimated flight time to and from the target 555, estimated maximum time for inspection operations, etc.).

[0070] In another embodiment, a manual guidance mode is selected, where the operator plans the mission by visually identifying the best and safest path to fly from the takeoff point 515 towards the vicinity of the inspection object 555. Furthermore, in one embodiment, the mission planner plans the mission time with enough battery life to return to home 515. For example, the mission planner can set geofence limits that should not be exceeded during manual operation.

[0071] In yet another embodiment, a mixed guidance mode is selected, which is similar to the autonomous mode (where the mission is fully planned by the control station), but differs in that it allows the operator to manually select some of the waypoints to navigate (e.g., if there are obstacles or difficult environments ahead of the UAV 505 on the way to those waypoints). This is useful, for example, when the operator's confidence in the automated flight is not high enough for certain waypoints.

[0072] The method 500 further includes a step 540 of initiating a flight mission and flying the UAV 505 near the inspection target 555. In an exemplary autonomous guidance mode embodiment, this includes commanding the UAV 505 to go to a takeoff waypoint and commanding the UAV 505 to go to a pre-perch waypoint (e.g., near the inspection target 555). For example, in one embodiment, the UAV 505 is configured (e.g., programmed) to automatically transition from one mission waypoint to the next, while in another embodiment, the UAV 505 is configured to wait for operator confirmation each time it arrives at a waypoint before proceeding. In an exemplary manual guidance mode embodiment, this includes manually flying the UAV 505 near the inspection target 555 in preparation for the perch. In an exemplary mixed guidance mode embodiment, the initiating and flying step 540 is similar to the autonomous mode, but the operator is alerted by the system to take over when the manual portion of the mission begins.

[0073] The method 500 further includes a step 550 of performing a perch maneuver, which includes defining an object of interest (e.g., using an operator control station) with object detection and locating software configured (e.g., programmed) to detect and locate the object 555 in order to plan a perch using the defined object 555. Here, in one embodiment, the operator confirms detection of the object and issues a perch command.

[0074] In an exemplary embodiment, the UAV 505 is programmed to autonomously perform the perch in two steps. In a first step, the UAV 505 autonomously approaches the target 555 at a pre-touchdown position; in one embodiment, the operator verifies its exact position before final touchdown; and (2) in one embodiment, the UAV 505 autonomously performs a final alignment using an on-board sensor (e.g., 2D LIDAR) and is also verified by the operator. In an exemplary verification embodiment, if both positioning and final alignment are not verified, the UAV 505 is commanded to fall back to a fail-safe waypoint (e.g., a point where the perch can be re-performed) or a mission abort is safely commanded (the UAV 505 is configured to return home). In a second step, the UAV 505 waits for a pre-touchdown confirmation, at which point the UAV 505 is programmed to autonomously touch down while the perch mechanism is configured to provide a confirmation of perch completion. If no confirmation of perch completion is displayed, the UAV 505 goes to a fail-safe waypoint. At the failsafe waypoint, the perch can be retried or the mission can be commanded to be aborted (and UAV505 returns home).

[0075] Method 500 further includes a step 560 of releasing crawler 535. In one embodiment, once the perch is successful, the operator commands the release of the crawler. Once crawler 535 is deployed on object 555 and confirmation is displayed by the system, the operator initiates an inspection step. Method 500 further includes a step 570 of inspecting object 555. In one embodiment, the operator controls crawler 535 to perform an inspection operation on object 555. In one embodiment, crawler 535 is operated via a cable connected to UAV 505. In another embodiment, crawler 535 is operated via a wireless connection and the crawler movement is restricted within a predefined secure communication area.

[0076] In one embodiment, the UAV system 505 is programmed or otherwise configured to monitor overall conditions and provide an estimate of a maximum allowable inspection time, for example, depending on available power. Additionally, the UAV system 505 is further programmed to continuously store inspection data (e.g., from the UAV 505, or from the crawler 535, or from the UAV 505 acquired by the crawler 535) in a system memory and to transfer the stored inspection data in real time to an operator control and monitoring station.

[0077] The method 500 further includes a step 580 of redocking the crawler and separating the UAV. In one embodiment, once the inspection is complete, the crawler 535 is retracted by the operator to the UAV 505 and a command for autonomous redocking is issued. For example, the crawler 535 may be programmed or otherwise configured to perform an autonomous redocking with the UAV 505. Once redocking is confirmed, the UAV 505 transitions to a separated state (e.g., pulls away from the magnetic attraction of the target 555). In one embodiment, the operator commands the UAV 505 to a hover state and the latching mechanism is disengaged. At this point, the operator commands the UAV 505 to go to a predefined fail-safe waypoint near the target 555. From here, the method 500 further includes a step 585 of determining whether to safely return the UAV 505 to the takeoff and landing location 515 or to command the UAV 505 (with attached and redocked crawler 535) to proceed to another inspection task target.

[0078] Method 500 further includes step 590 of flying UAV 505 back home (e.g., to takeoff and landing location 515). In one embodiment, unless another test is commanded (e.g., in step 585), UAV 505 goes to landing location 515 at a predefined landing altitude and then descends vertically to the ground. Once landing is confirmed, the rotors or propellers are removed and the mission ends.

[0079] 6 is a diagram of an example releasable crawler 620 visibly marking interesting (e.g., suspect) portions 640 of a structure (e.g., a pipe 650) encountered during inspection or maintenance of the structure 650, in conjunction with an example UAV 610 that detects the visible markers 640 left by the crawler 620, according to one embodiment. In FIG. 6, the crawler 620 has marked a number of inspection points 640 (e.g., where sensor measurements were outside of normal ranges) for identification by the UAV 610 (e.g., via a camera view 630 sensed by the UAV 610).

[0080] More specifically, the crawler 620 can be programmed to leave physical markers 640 (such as paint or a QR code) at inspected locations on the pipe 650 where failures (e.g., thickness levels below a critical threshold) are detected. The UAV 610 is programmed to detect the markers 640 using an on-board RGB-D camera (with view 630) and calculate (or otherwise determine) their location relative to the UAV 610. Using the UAV's GPS location, the UAV 610 is further programmed to calculate (or otherwise determine) the absolute location of the markers 640 from these detections. In one embodiment, the crawler 620 remains on the pipe 650 while the UAV 610 is scanning for the markers 640. In another embodiment, the crawler 620 is docked to the UAV 610 while the UAV 610 is scanning for the markers 640.

[0081] 7A and 7B are diagrams of an exemplary technique in which a releasable crawler 620 visibly marks interesting (e.g., suspect) portions of a structure (e.g., a pipe 650) encountered during inspection or maintenance of the structure 650, in conjunction with a UAV 610 performing radio localization using virtual markers, according to one embodiment. In FIG. 7A, the UAV 610 is perched on the pipe 650, while in FIG. 7B, the UAV 610 is hovering near the pipe 650, such as at a waypoint prior to perching.

[0082] More specifically, the location of the defect can be determined using virtual markers (e.g., without using physical markers), although with potentially reduced accuracy. Here, the UAV 610 is programmed (or configured) to calculate the location of the crawler relative to the UAV 610 using wireless sensors. More specifically, in one embodiment, the UAV 610 carries an ultra-wide band (UWB) sensor array that receives wireless signals broadcast from a UWB transmitter mounted on the crawler 620. The relative location of the crawler is measured regardless of whether the UAV 610 is airborne (e.g., FIG. 7B) or attached to the pipe 650 (e.g., FIG. 7A).

[0083] In one embodiment, the UAV 610 is programmed (or otherwise configured) such that whenever defects are detected by the crawler 620 while crawling (e.g., maneuvering and inspecting on the pipe 650), the UAV 610 is programmed (or otherwise configured) to tag and capture the location of the crawler relative to the UAV 610. Together with the UAV's GPS sensor, the UAV 610 is further programmed to find (e.g., calculate, determine) the absolute location of these defects. In one embodiment, in situations where GPS is not available, the UAV 610 is programmed (or otherwise configured) to estimate the location of the UAV based on sensors or flight trajectory and other instrumentation data such as IMU data from a home base (e.g., where GPS is available).

[0084] FIG. 8 is an exemplary structure 800 for deploying a UAV with releasable crawlers to inspect or maintain the structure, according to one embodiment. In the structure 800 of FIG. 8, more specifically on a hard-to-reach pipe of the structure 800, the UAV has deployed crawlers to perform thickness determination (e.g., using a UT sensor). The crawlers have marked two exemplary locations 810 and 820. Location 810 corresponds to a section of the pipe where the thickness has reached a very low value (in this case 2 millimeters (mm)). On the other hand, location 820 corresponds to a section of the pipe where the thickness is at a normal value, in this case 5 mm.

[0085] More specifically, these inspection points 810 and 820 are part of the mapping and annotation of the structure 800. The UAV and crawler are programmed (or configured) to perform some or all of this mapping and annotation. In one embodiment, pre-calculated inspection locations are transferred from the UAV to an operational computer or ground station. The computing system is then programmed (or otherwise configured) to visualize the inspection locations (e.g., 810 and 820) on a pre-built 3D model of the inspected plant 800. In another embodiment, the UAV is programmed (or otherwise configured) to build a 3D model of the portion of the plant 800 using data acquired by the UAV's on-board sensors, e.g., a depth camera or 3D LIDAR. Furthermore, in one embodiment, the UAV is further programmed to annotate the visualized locations with the corresponding measured thicknesses obtained by the crawler when inspecting the structure 800.

[0086] FIG. 9 is a flowchart of an exemplary method 900 for inspecting or maintaining a structure having a curved ferromagnetic surface (such as a pipe like pipe 50, 150, 555, or 650) using a UAV (such as UAV 100, 200, 300, 400, 505, 610) having a releasable crawler (such as releasable crawler 130, 260, 535, or 620) according to one embodiment.

[0087] Part or all of method 900 may be performed using components and techniques illustrated in Figures 1A-8. Parts of this method and other methods disclosed herein may be performed on or using custom or pre-programmed logic devices, circuits, or processors, such as programmable logic circuits (PLCs), computers, software, or other circuits (e.g., ASICs, FPGAs), configured with code or logic to perform assigned tasks. The device, circuit, or processor may be, for example, a dedicated or shared hardware device (such as a laptop, a workstation, a tablet, a smartphone, a portion of a server, or a dedicated hardware circuit such as an FPGA or ASIC), a computer server, a portion of a server, or a computer system. The device, circuit, or processor may include a non-transitory computer readable medium (CRM, such as a read-only memory (ROM), a flash drive, or a disk drive) that stores instructions that, when executed on one or more processors, cause portions of method 900 (or other disclosed methods) to be performed. It should be noted that in other embodiments, the order of operations may be changed and some of the operations may be omitted. Some or all of the method 900 may also be performed using logic, circuitry, or a processor located on a UAV configured to perform the method 900.

[0088] In the exemplary method 900, processing begins with step 910 of flying a UAV near a ferromagnetic surface, followed by step 920 of perching the UAV to the ferromagnetic surface. The perching step 920 includes passively articulating a leg of the UAV (such as perching leg 280) toward a curved portion of the ferromagnetic surface using a corresponding magnet of the leg (such as articulated magnet 120 or 290) while approaching the ferromagnetic surface. The perching step 920 also magnetically attaches the articulated leg of the UAV to the ferromagnetic surface using a corresponding magnet. The method 900 further includes step 930 of maintaining the magnetic attachment of the leg to the ferromagnetic surface throughout the perching, and step 940 of decoupling the crawler from the perching UAV onto the ferromagnetic surface. Method 900 further includes a step 950 of steering the separated crawler over the ferromagnetic surface while magnetically attracting the crawler to the ferromagnetic surface using a magnetic wheel (such as magnetic wheel 140 or 270) of the crawler.

[0089] In a further embodiment, the method 900 includes inspecting or maintaining the ferromagnetic surface during the maneuver using a probe or tool (such as a UT sensor) on the crawler. In yet another embodiment, the method 900 includes demagnetizing the crawler from the ferromagnetic surface after the maneuver and redocking the detached crawler to the perched UAV.

[0090] The methods described herein may be performed in part or in whole by software or firmware in machine-readable form on a tangible (e.g., non-transitory) storage medium. For example, the software or firmware may be in the form of a computer program adapted to perform some or all steps of any method described herein, and the computer program may be embodied on a computer-readable medium when the program is executed on a computer or a suitable hardware device (e.g., FPGA). Examples of tangible storage media include computer storage devices, including computer-readable media such as disks, thumb drives, memory, etc., and do not include propagated signals. Although propagated signals may reside on tangible storage media, the propagated signals themselves are not examples of tangible storage media. The software may be suitable for execution on a parallel or serial processor, such that the method steps may be performed in any suitable order or simultaneously.

[0091] It should be further understood that like numerals in the drawings represent like elements throughout the several drawings, and that not all of the components and / or steps described and illustrated in connection with the drawings are required in all embodiments or configurations.

[0092] The terms used herein are for the purpose of describing particular embodiments only and are not intended to be limiting of the disclosure. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising", as used herein, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0093] Orientation terms are used herein merely for convention and reference purposes and should not be construed as limiting. However, it is recognized that these terms may be used relative to the viewer. Thus, no limitation is implied or inferred. Furthermore, the use of ordinal numbers (e.g., first, second, third) is for distinction and not for counting. For example, "third" does not suggest that there is a corresponding "first" or "second". Additionally, the phraseology and terminology used herein are for descriptive purposes and should not be considered as limiting. The use of "including," "comprising," or "having," "containing," "involving," and variations thereof herein is intended to encompass the items listed thereafter, and equivalents thereof, as well as additional items.

[0094] The subject matter described above is provided merely by way of example and should not be construed as limiting. Various modifications and changes may be made to the subject matter described herein without following the exemplary embodiments and applications described and without departing from the true spirit and scope of the present disclosure as set forth in the following claims. [Additional note 1] 1. A method for inspecting or maintaining a curved ferromagnetic surface using an unmanned aerial vehicle (UAV) having releasable crawlers, comprising: Flying the UAV into the vicinity of the ferromagnetic surface; Perching the UAV on the ferromagnetic surface, passively articulating legs of the UAV toward a curved portion of the ferromagnetic surface using corresponding magnets in the legs while approaching the ferromagnetic surface; magnetically attaching the articulated legs of the UAV to the ferromagnetic surface using the corresponding magnets; and maintaining said magnetic attachment of said legs to said ferromagnetic surface during said perching. detaching the crawler from the perched UAV to the ferromagnetic surface; and and steering the detached crawler over the ferromagnetic surface while magnetically attracting the crawler to the ferromagnetic surface using a magnetic wheel of the crawler. [Additional note 2] 2. The method of claim 1, wherein the curved ferromagnetic surface comprises a pipe, and steering the separated crawler includes performing a circumferential scan of the pipe using the separated crawler. [Additional note 3] 2. The method of claim 1, further comprising inspecting or maintaining the ferromagnetic surface during the maneuver using a probe or tool of the crawler. [Additional note 4] The method of claim 1, further comprising wirelessly communicating with the UAV or a base station from the separated crawler. [Additional note 5] The method of claim 1, further comprising, after the maneuver, detaching the magnetic attraction of the crawler from the ferromagnetic surface and redocking the detached crawler to the perched UAV. [Additional note 6] disengaging the articulated leg from the ferromagnetic surface; and 2. The method of claim 1, further comprising flying the magnetically separated legs of the UAV away from the ferromagnetic surface. [Additional note 7] 7. The method of claim 6, wherein the corresponding magnet comprises a switchable permanent magnet, and the unmagnetizing comprises switching the permanent magnet from a magnetized state to a non-magnetized state. [Additional note 8] The method of claim 6, wherein the releasing of the magnetization includes applying leverage to the magnetized legs using one or more separate actuators of the UAV. [Additional note 9] The method of claim 1, further comprising scanning the nearby ferromagnetic surfaces using a laser scanner on the flying UAV. [Additional Note 10] 1. A method for inspecting or maintaining a curved ferromagnetic surface using an unmanned aerial vehicle (UAV) having releasable crawlers, comprising: flying the UAV from an initial position to a pre-perched position adjacent the ferromagnetic surface; autonomously perching the UAV on the ferromagnetic surface; maintaining a magnetic attachment of the perched UAV to the ferromagnetic surface; and Releasing the crawler from the magnetically attached UAV to the ferromagnetic surface; moving the released crawler across the curved ferromagnetic surface while maintaining magnetic attraction of the released crawler to the ferromagnetic surface; using the magnetized crawler to inspect or maintain the ferromagnetic surface; and and redocking the released crawler with the perched UAV. [Additional Note 11] The method of claim 10, further comprising wirelessly communicating with the UAV from the released crawler. [Additional Note 12] magnetically separating the perched UAV from the ferromagnetic surface; 11. The method of claim 10, further comprising flying the magnetically separated UAV away from the ferromagnetic surface to a pre-perched position. [Additional Note 13] 13. The method of claim 12, wherein flying the magnetically separated UAV includes not carrying the redocked crawler, the method further including wirelessly communicating from the released crawler to the flying UAV. [Additional Note 14] 11. The method of claim 10, wherein inspecting or maintaining the ferromagnetic surface includes marking locations of interest on the ferromagnetic surface. [Additional Note 15] 15. The method of claim 14, wherein inspecting or maintaining the ferromagnetic surface includes measuring a thickness of the ferromagnetic surface, and the locations of interest include locations where the measured thickness is less than a critical value. [Additional Note 16] magnetically separating the perched UAV from the ferromagnetic surface; flying the magnetically decoupled UAV away from the ferromagnetic surface; 15. The method of claim 14, further comprising detecting the marked location of interest on the ferromagnetic surface from the magnetically separated UAV. [Additional Note 17] magnetically decoupling the perched UAV with the redocked crawler from the ferromagnetic surface; flying the magnetically decoupled UAV with the redocked crawler away from the ferromagnetic surface to the pre-perched position; The method of claim 10, further comprising flying the magnetically separated UAV with the redocked crawler to another pre-perch location near a second ferromagnetic surface to be inspected or maintained by the redocked crawler. [Additional Note 18] magnetically decoupling the perched UAV with the redocked crawler from the ferromagnetic surface; 11. The method of claim 10, further comprising flying the magnetically separated UAV with the redocked crawler away from the ferromagnetic surface to the initial position. [Additional Note 19] The method of claim 10, wherein autonomously perching the UAV includes sensing the ferromagnetic surface using a depth camera or laser scanner of the UAV, and touching down on the ferromagnetic surface using the sensed depth camera or laser scanner data. [Additional Note 20] Autonomously perching the UAV, aligning the UAV to a pre-touchdown position using the sensed ferromagnetic surface data; and magnetically separating the perched UAV with the redocked crawler from the ferromagnetic surface. 20. The method of claim 19, further comprising flying the magnetically separated UAV with the redocked crawler away from the ferromagnetic surface to the initial position.

Claims

1. 1. A method for inspecting or maintaining a curved ferromagnetic surface using an unmanned aerial vehicle (UAV) having releasable crawlers, comprising: flying the UAV from an initial position to a pre-perched position proximate the ferromagnetic surface; autonomously perching the UAV on the ferromagnetic surface; maintaining a magnetic attachment of the perched UAV to the ferromagnetic surface; and Releasing the crawler from the magnetically attracted UAV to the ferromagnetic surface to allow the crawler to move along the ferromagnetic surface away from the UAV; moving the released crawler across the curved ferromagnetic surface while maintaining magnetic attraction of the released crawler to the ferromagnetic surface; using the magnetized crawler to inspect or maintain the ferromagnetic surface; and and redocking the released crawler with the perched UAV.

2. The method of claim 1 , further comprising wirelessly communicating with the UAV from the released crawler.

3. magnetically separating the perched UAV from the ferromagnetic surface; The method of claim 1 , further comprising flying the magnetically separated UAV away from the ferromagnetic surface to a position prior to the perching.

4. 4. The method of claim 3, wherein flying the magnetically separated UAV includes not carrying the redocked crawler, the method further including wirelessly communicating from the released crawler to the flying UAV.

5. The method of claim 1 , wherein inspecting or maintaining the ferromagnetic surface comprises marking locations of interest on the ferromagnetic surface.

6. 6. The method of claim 5, wherein inspecting or maintaining the ferromagnetic surface includes measuring a thickness of the ferromagnetic surface, and the locations of interest include locations where the measured thickness is less than a critical value.

7. magnetically separating the perched UAV from the ferromagnetic surface; flying the magnetically separated UAV away from the ferromagnetic surface; The method of claim 5 , further comprising: detecting the marked locations of interest on the ferromagnetic surface from the magnetically separated UAV.

8. magnetically separating the perched UAV with the redocked crawler from the ferromagnetic surface; flying the magnetically separated UAV with the redocked crawler away from the ferromagnetic surface to a pre-perched position; 2. The method of claim 1, further comprising flying the magnetically separated UAV with the redocked crawler to another pre-perch location near a second ferromagnetic surface to be inspected or maintained by the redocked crawler.

9. magnetically separating the perched UAV with the redocked crawler from the ferromagnetic surface; The method of claim 1 , further comprising: flying the magnetically separated UAV with the redocked crawler away from the ferromagnetic surface to the initial position.

10. 2. The method of claim 1, wherein autonomously perching the UAV includes sensing the ferromagnetic surface using a depth camera or laser scanner of the UAV, and touching down on the ferromagnetic surface using the sensed depth camera or laser scanner data.

11. Autonomously perching the UAV, aligning the UAV to a pre-touchdown position using the sensed ferromagnetic surface data; and magnetically separating the perched UAV with the redocked crawler from the ferromagnetic surface. The method of claim 10 , further comprising: flying the magnetically separated UAV with the redocked crawler away from the ferromagnetic surface to the initial position.

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