Patent Description:
One of the top challenges in the oil and gas industry is the periodic inspection of elevated assets found in refineries, gas plants, offshore platforms, and other plants and facilities. These assets include high-elevation pipes and other structures that are difficult to access during inspection jobs. Often, the only practical way to inspect them is to erect scaffolding in order for the inspector to access the asset and perform a manual inspection. Such scaffolding is not only expensive and introduces a significant cost barrier for frequent inspection, but also poses safety concerns mainly in the form of falling and tripping hazards.

It is in regard to these and other problems in the art that the present disclosure is directed to provide a technical solution for an effective UAV having bi-stable and switchable magnetic legs for landing on curved ferromagnetic surfaces. As described in <CIT>, a UAV includes a body constructed to enable the UAV to fly and three or more legs connected to the body and configured to land and perch the UAV on a curved ferromagnetic surface. In <CIT>, a UAV for landing and perching on a curved ferromagnetic surface is disclosed.

According to a first aspect of the disclosure, an unmanned aerial vehicle (UAV) configured to land, take off, and magnetically perch on a ferromagnetic cylindrical surface is provided. The
UAV comprises a body and a plurality of articulated magnetic legs configured to land the UAV on the ferromagnetic cylindrical surface and to magnetically perch the UAV on the ferromagnetic cylindrical surface after the landing. Each magnetic leg has a fixed portion coupled to the body and a pivoting portion pivotably coupled to the fixed portion at a pivot axis. The pivoting portion comprises a switchable magnet and a single articulation joint configured to provide the pivoting portion with a single degree of freedom about the pivot axis in order to passively orient the pivoting portion inward and tangent to the cylindrical surface in response to the pivoting portion contacting the cylindrical surface during the landing, and to passively maintain the inward orientation of the pivoting portion during the takeoff. The magnetism of the switchable magnet is switched on to magnetically attach the UAV to the ferromagnetic cylindrical surface at an end of the landing and throughout the perching, and switched off to magnetically detach the UAV from the ferromagnetic cylindrical surface at a beginning of the takeoff.

In an embodiment consistent with the above, the fixed portion of each magnetic leg comprises an inward rotation limiter configured to limit the inward rotation of the pivoting portion during the landing and the takeoff.

In an embodiment consistent with the above, the UAV is further configured to land on and take off from a flat surface, and the articulation joint of each magnetic leg is further configured to provide the pivoting portion with the single degree of freedom about the pivot axis in order to passively orient the pivoting portion flat and parallel to the flat surface in response to the pivoting portion contacting the flat surface during the landing on the flat surface, and to passively maintain the flat orientation of the pivoting portion during the takeoff from the flat surface.

In an embodiment consistent with the above, the fixed portion of each magnetic leg comprises an outward rotation limiter to limit the outward rotation of the pivoting portion to a mostly flat orientation during the landing on and the takeoff from the flat surface.

In an embodiment consistent with the above, the pivoting portion of each magnetic leg further comprises a switch actuator at a top of the switchable magnet and configured to actuate the magnet in order to switch the magnet between on and off, the center of gravity of the switch actuator being on an outward side of the pivot axis during the takeoff from the cylindrical surface, and on an inward side of the pivot axis during the takeoff from the flat surface.

Each magnetic leg further comprises an angle rotation sensor configured to measure a pivot of the pivoting portion about the pivot axis after the pivoting portion contacts the cylindrical surface.

In an embodiment consistent with the above, the UAV further comprises a control circuit configured to determine when to switch on the magnets of the magnetic legs at the end of the landing using the measured pivots of the pivoting portions of the magnetic legs.

In an embodiment consistent with the above, for each magnetic leg, the pivoting portion comprises a switch actuator coupled to a top of the magnet and configured to actuate the magnet in order to switch the magnet between on and off, and the control circuit is further configured to control the switch actuator to switch on the magnet when the measured pivots of the pivoting portions of the magnetic legs are the same inward angle.

The UAV further comprises a control circuit configured to determine the diameter of a cylinder corresponding to the cylindrical surface using the measured pivots of the pivoting portions of the magnetic legs.

The UAV further comprises a control circuit configured to determine a distance from the body to the cylindrical surface using the measured pivots of the pivoting portions of the magnetic legs.

In an embodiment consistent with the above, the ferromagnetic cylindrical surface is part of a carbon steel pipe or vessel.

According to another aspect of the disclosure, a method of landing, taking off, and magnetically perching an unmanned aerial vehicle (UAV) on a ferromagnetic cylindrical surface is provided. The UAV comprises a body and a plurality of articulated magnetic legs each having a fixed portion coupled to the body and a pivoting portion pivotably coupled to the fixed portion at a pivot axis. The pivot portion comprises a switchable magnet and a single articulation joint having a single degree of freedom about the pivot axis. The method comprises: landing the UAV on the ferromagnetic cylindrical surface using the magnetic legs; passively orienting, for each magnetic leg using the single articulation joint with the single degree of freedom about the pivot axis, the pivoting portion inward and tangent to the cylindrical surface in response to the pivoting portion contacting the cylindrical surface during the landing; magnetically attaching the UAV to the ferromagnetic cylindrical surface at an end of the landing by switching on the switchable magnet in each magnetic leg; magnetically perching the UAV on the ferromagnetic cylindrical surface after the landing using the magnetic legs while their respective switchable magnets remain switched on; magnetically detaching the UAV from the ferromagnetic cylindrical surface at a beginning of the takeoff by switching off the switchable magnet in each magnetic leg; taking off with the UAV from the cylindrical surface after the perching; and passively maintaining, for each magnetic leg using the articulation joint and with the center of gravity of the pivoting portion being on an outward side of the pivot axis, the inward orientation of the pivoting portion during the takeoff.

In an embodiment consistent with the method described above, the method further comprises limiting, for each magnetic leg using an inward rotation limiter of the fixed portion of the magnetic leg, the inward rotation of the pivoting portion during the landing and the takeoff.

In an embodiment consistent with the method described above, the method further comprises: landing the UAV on a flat surface using the magnetic legs; passively orienting, for each magnetic leg using the single articulation joint with the single degree of freedom about the pivot axis, the pivoting portion flat and parallel to the flat surface in response to the pivoting portion contacting the flat surface during the landing on the flat surface; taking off with the UAV from the flat surface; and passively maintaining, for each magnetic leg using the articulation joint and with the center of gravity of the pivoting portion being on an inward side of the pivot axis, the flat orientation of the pivoting portion during the takeoff from the flat surface.

In an embodiment consistent with the method described above, the method further comprises limiting, for each magnetic leg using an outward rotation limiter of the fixed portion of the magnetic leg, the outward rotation of the pivoting portion to a mostly flat orientation during the landing on and the takeoff from the flat surface.

The method further comprises, for each magnetic leg, measuring a pivot of the pivoting portion about the pivot axis after the pivoting portion contacts the cylindrical surface using an angle rotation sensor of the magnetic leg.

In an embodiment consistent with the method described above, the method further comprises determining, by a control circuit of the UAV, when to switch on the magnets of the magnetic legs at the end of the landing using the measured pivots of the pivoting portions of the magnetic legs.

In an embodiment consistent with the method described above, the method further comprises for each magnetic leg, actuating the magnet, using a switch actuator of the pivoting portion and coupled to a top of the magnet, in order to switch the magnet between on and off, and controlling, by the control circuit, the switch actuator to switch on the magnet when the measured pivots of the pivoting portions of the magnetic legs are the same inward angle.

The method further comprises determining, by a control circuit of the UAV, the diameter of a cylinder corresponding to the cylindrical surface using the measured pivots of the pivoting portions of the magnetic legs.

The method further comprises determining, by a control circuit of the UAV, a distance from the body to the cylindrical surface using the measured pivots of the pivoting portions of the magnetic legs.

These and other aspects and features can be appreciated from the following description of certain embodiments together with the accompanying drawings and claims.

It is noted that the drawings are illustrative and not necessarily to scale, and that the same or similar features have the same or similar reference numerals throughout.

Example embodiments of the present disclosure are directed to a mechanical system design that enables an unmanned aerial vehicle (UAV or drone) to use switchable magnetic legs in order to magnetically land or perch on both curved ferromagnetic surfaces (such as carbon steel pipes) and flat ferromagnetic surfaces (such as a home base or base of operations, or the tops of many structures such as storage tanks). Some such embodiments utilize switchable magnets and constrained joints to, for example, help improve stability and reduce wobbling during takeoff and landing. In some such example embodiments, these features provide for a bi-stable design (e.g., exhibiting stability during takeoff from and landing on both curved surfaces and flat surfaces). This bi-stability provides for less oscillation during flight. In some example embodiments, one or more angle rotation sensors are provided to, for example, determine pipe diameter after contact when landing or perching on carbon steel pipes.

As discussed earlier, one of the top challenges in the oil and gas industry is the periodic inspection of elevated assets found in refineries, gas plants, offshore platforms, and other plants and facilities. These assets include high-elevation pipes and structures which are difficult to access during inspection jobs. While UAVs can be employed to help with the access, landing on such structures with a UAV poses its own set of obstacles. For example, these structures are often elevated pipes, having relatively narrow diameters (for example, six inches). Landing, taking off, and perching on such curved surfaces can be a difficult task for a UAV.

Accordingly, in example embodiments, systems and methods are provided for an effective way that allows drones (e.g., battery-powered drones or UAVs) to magnetically land and perch on these assets in order to, for example, perform inspection tasks while saving battery energy. In example embodiments, the UAVs include switchable magnetic legs that allow the UAVs to magnetically perch on ferromagnetic surfaces after landing and before takeoff. This allows such UAVs to, for example, preserve their battery power by landing on pipes instead of hovering during missions that require long time (such as surveillance or monitoring for gas leaks), perform jobs that require contact with the pipe such as inspection (e.g., ultrasonic, magnetic) or light maintenance (e.g., coating), and deliver payloads to the pipe (such as small sensing devices and crawlers) or retrieve samples (such as corrosion coupons). Example embodiment provide for a UAV to land on operational assets found in oil and gas facilities such as pipes, vessels, and structures. In some such embodiments, magnetic attachment (e.g., switchable magnetic legs) is employed by the UAV since most of these assets are made of carbon steel.

According to various embodiments, a UAV is provided having passively articulated landing legs with embedded switchable magnets. These magnets are selectively turned on or off, which facilitates easy detachment during take-off from the pipe by switching the magnet off. According to some embodiments, a magnetic perching mechanism is provided, such as part of a UAV. The mechanism tolerates landing on various pipe diameters (such as six inches and larger) and misalignment due to imperfect landing (e.g., up to <NUM>°, or in some cases, <NUM>°, off from vertical). The mechanism uses landing legs that are lightweight (such as light as possible or practical) since payload weight is an important restriction of most UAVs. There are numerous variations of the UAV and articulated magnetic legs, example embodiments of which are illustrated in <FIG> and described in the text that follows.

<FIG> illustrate assembled and exploded views, respectively, of an example articulated magnetic leg <NUM> for landing an unmanned aerial vehicle (UAV) or drone on a curved ferromagnetic surface (such as a carbon steel pipe), according to an embodiment. For instance, the drone or UAV may have four or six such magnetic legs <NUM>, such as one for each propeller of the drone.

With reference to the exploded view of <FIG>, the magnetic leg <NUM> includes a fixed portion <NUM> that normally remains fixed and attaches the magnetic leg <NUM> to the main body (or just body) of the UAV. The fixed portion <NUM> includes a fixed leg body <NUM> rigidly attached to the drone through a carbon fiber tube <NUM>. The leg body <NUM> holds a rotating holder (also referred to as a pivoting portion <NUM>) that houses a switchable magnet <NUM> and acts as one of the drone's feet. A single degree of freedom (such as inward-to-outward with respect to the drone's body) allows the magnetic leg <NUM> to adapt to any inward surface curvature (such as for pipes six inches or larger), including a flat surface. For example, a pivot pin <NUM> can serve as an inward rotation axle that allows the pivoting portion <NUM> to rotate inwardly with one degree of freedom about a pivot axis coinciding with the rotation axle.

In one or more embodiments, the switchable magnet <NUM> includes two stacked disk magnets, one static and one rotatable (such as the top disk magnet). The rotatable disk magnet is rotated or oriented to one of two positions. In a first position, the rotatable disk magnet cancels the other disk magnet's magnetic field, which effectively switches off the magnetism of the switchable magnet <NUM>. In a second position (e.g., rotated <NUM>° from the first position), the rotatable disk magnet is oriented the same way as the other disk magnet's magnetic field, which intensifies the total magnetism and switches on the switchable magnet <NUM>.

In order to perform this disk magnet rotation, an actuator such as a servo motor <NUM> is used. The servo motor <NUM> is capable of rotating the rotatable disk magnet through a mechanical coupling (such as a servo horn <NUM> and an adapter <NUM>) A servo-magnet holder <NUM> holds the top disk magnet and has embedded rotation limiters to limit the rotatable disk magnet (e.g., the top disk magnet) to <NUM> degrees. This limitation allows the servo motor rotation direction to be linked with switching on or off the switchable magnet <NUM>. In some other embodiments, different types of switchable magnets are used, such as electromagnets or electro-permanent magnets.

The switchable magnet <NUM> of each magnetic leg <NUM> is switched on at some point in the landing maneuver. For example, this switching can take place at the beginning of the landing while the UAV is approaching the landing target (e.g., pipe), or at the end of the landing after the feet (e.g., pivoting portions <NUM>) settle after touching down on the pipe. To activate the switching, in one embodiment, an onboard controller (on the drone) is programmed or otherwise configured to a signal to the servo motor <NUM> to allow the UAV to stick to (or magnetically perch on) the pipe. When the time comes to takeoff (such as at the beginning of the takeoff), the switchable magnets <NUM> are switched off (e.g., by the onboard controller that is further programmed to send such a signal to the servo motor <NUM>). This makes the propeller's job easier and avoids the need to overcome the magnetic pull force while taking off.

<FIG> illustrate an example UAV <NUM> having articulated magnetic legs <NUM> landing on flat and curved surfaces (e.g., flat surface <NUM> and pipe <NUM>), respectively, according to an embodiment. The UAV <NUM> includes a body (or UAV body) <NUM> to which the articulated magnetic legs <NUM> (in this case, four such legs) are attached. The UAV <NUM> also includes a plurality of propellers <NUM> attached to the body <NUM>. In different embodiments, the number of articulated magnetic legs can vary (such as six) and the number of propellers can vary (such as six). In some embodiments, the number of articulated magnetic legs is the same as the number of propellers. In some embodiments, the articulated magnetic legs are arranged symmetrically about a longitudinal (e.g., lengthwise) axis of the UAV. For ease of description throughout, the number of articulated magnetic legs of the UAV is four, the number of propellers of the UAV is four, and the articulated magnetic legs are arranged symmetrically about the longitudinal axis of the UAV. Other embodiments are not necessarily so limited.

<FIG> show the UAV <NUM> that has landed on two different surfaces, namely a flat surface <NUM> (such as a home base or the top of a vertically-arranged cylinder) and a curved pipe <NUM> (such as a carbon steel pipe or the top of a horizontally-arranged cylinder or cylindrically curved portion of a structure), respectively. Here, "top" is in reference to gravity, and the articulated magnetic legs <NUM> of the UAV <NUM> in <FIG> are arranged symmetrically about the top of the pipe <NUM> (e.g., about a longitudinal axis of the top of the pipe <NUM>). In some embodiments, the articulated magnetic legs <NUM> adapt to allow landings on any pipe diameter larger than six inches. That is, the articulated magnetic legs <NUM> are adaptable (e.g., can land securely on with all articulated magnetic legs <NUM>) to multiple diameters of pipe.

<FIG> illustrate an example articulated magnetic leg <NUM> of a UAV (such as UAV <NUM>) making initial and final contacts, respectively, of a curved surface <NUM> (such as a pipe or other partial or fully cylindrically curved surface having a radius of curvature, as in pipe <NUM>), according to an embodiment. <FIG> illustrate the articulated magnetic leg <NUM> of <FIG> making initial and final contacts, respectively, of a flat surface <NUM>. The articulated magnetic leg <NUM> includes a fixed portion <NUM> (coupled to the body of a UAV) and a pivoting portion <NUM> coupled to the fixed portion <NUM> through a pivot point <NUM> (e.g., a pivot axis defining a single degree of freedom rotation of the pivoting portion <NUM> with respect to the fixed portion <NUM>, as in pivot pin <NUM>).

Here, with reference to <FIG>, the pivot axis <NUM> is parallel to the longitudinal axis of the UAV in order to impart an inward (or outward) rotation of the pivoting portion <NUM> with respect to the curved surface <NUM> when the longitudinal axis of the UAV is aligned with or parallel to a longitudinal axis of the pipe or other cylindrically curved surface. Accordingly, the initial contact of the pivoting portion <NUM> with the curved surface <NUM> causes a contact force <NUM> to be imparted on the pivoting portion <NUM>. This in turn causes a corresponding clockwise rotation <NUM> (inward) of the pivoting portion <NUM> about the pivot axis <NUM>. The inward rotation <NUM> continues until the pivoting portion (or more specifically, the bottom of the pivoting portion) <NUM> is tangent to the curved surface <NUM> at a final contact of the pivoting portion <NUM> with the curved surface <NUM>.

In addition, and with reference to <FIG>, the pivot axis is parallel to the flat surface <NUM>. Accordingly, the initial contact of the pivoting portion <NUM> with the flat surface <NUM> causes a contact force <NUM> to be imparted on the pivoting portion <NUM>. This in turn causes a corresponding counterclockwise rotation <NUM> (downward) of the pivoting portion <NUM> about the pivot axis <NUM>. The downward rotation <NUM> continues until the pivoting portion (or more specifically, the bottom of the pivoting portion) <NUM> aligns with the flat surface <NUM> at a final contact of the pivoting portion <NUM> with the flat surface <NUM>.

The legs <NUM> have one degree of freedom around the pivot axis <NUM> (or pivot point) shown in <FIG> to allow them to rotate and adapt to surfaces with different curvatures. Upon contact when the leg <NUM> rotates to face a flat surface, the leg <NUM> keeps pointing that way even after detachment. Similarly, when the leg <NUM> rotates to face the curved surface or a small pipe, the leg <NUM> keeps pointing to that direction even after detachment. This makes the joint stable in these two positions (e.g., bi-stable), reducing oscillations and wobbling in the leg joint during flight.

In further detail, and with reference to <FIG>, when the leg <NUM> contacts the curved surface <NUM> at a contact point, the surface <NUM> pushes the leg <NUM> (and in particular, the pivoting portion <NUM>) at the contact point. This causes the pivoting portion <NUM> to rotate along or about its pivot axis <NUM> up until the pivoting portion <NUM> faces (e.g., is tangent to) the surface <NUM>. The contact force <NUM> generates a rotating torque in the correct direction (in this case, clockwise) <NUM> due to the flat design of the bottom contact surface of the pivoting portion <NUM> of the leg <NUM>.

By contrast, and with reference to <FIG>, the leg <NUM> (and, in particular, the pivoting portion <NUM>) contacts the flat surface <NUM> at a contact point. In addition, the flat bottom of the pivoting portion <NUM> is not parallel to the flat surface <NUM>. Accordingly, the rotating portion <NUM> of the leg <NUM> rotates (in this case, counterclockwise <NUM>) around or about its pivot axis <NUM> until the flat bottom of the rotating portion <NUM> faces the flat surface <NUM>. This is due to the pushing force <NUM> from the surface <NUM> at the contact point. This contact force <NUM> generates a (counterclockwise) rotating torque in the correct (counterclockwise) direction <NUM> due to the flat design of the bottom contact surface of the pivoting portion <NUM> of the leg <NUM>.

<FIG> illustrate an example articulated magnetic leg <NUM> of a UAV (such as UAV <NUM>) prior to take off from flat and curved surfaces (such as flat surface <NUM> and curved surface <NUM>), respectively, according to an embodiment. The leg <NUM> (and more specifically, the pivoting portion <NUM>) has only one degree of freedom, namely inward (e.g., clockwise or rotation direction <NUM> as shown in <FIG>) or outward (e.g., counterclockwise or rotation direction <NUM> as shown in <FIG>) around a pivot point (or about a pivot axis) <NUM> to allow the leg -<NUM> to land flat on flat surfaces or tangent to curved surfaces. These curved surfaces can include different size (or diameter) pipes with corresponding different curvatures (or radii of curvature).

The leg <NUM> has two stable positions and is thus sometimes referred to as bi-stable. When the leg <NUM> rotates to face a flat surface (e.g., as shown in <FIG>), the leg <NUM> keeps pointing that way even during and after detachment (e.g., as part of taking off from the flat surface). Similarly, when the leg <NUM> rotates to face a curved surface or a small pipe (e.g., as shown in <FIG>), the leg <NUM> keeps pointing in that direction even after during and after detachment (e.g., as part of taking off from the curved surface or small pipe). This makes the joint (e.g., pivoting portion <NUM>) stable in these two positions (bi-stable), which helps reduce oscillations and wobble in the leg joint during flight.

In further detail, when landing on a flat surface, the leg <NUM> remains in a vertical orientation (e.g., bottom of pivoting portion <NUM> is parallel to the flat surface) even after takeoff. This is due to a servo motor <NUM> being located off-centered on a top of the pivoting portion <NUM>. The servo motor <NUM> is off-centered with respect to the pivot axis <NUM>, such that the servo motor center of gravity <NUM> is shifted to the left of the pivot axis <NUM> (while the center of gravity of the remainder of the pivoting portion <NUM> remains centered with respect to the pivot axis <NUM>). The leftward shift of the center of gravity of the servo motor <NUM> causes the leg <NUM> to rotate outwardly (in a counterclockwise direction <NUM> as illustrated in <FIG>).

However, the fixed portion of the leg <NUM> (e.g., the leg frame) acts as a rotation limiter <NUM> to prevent the pivoting portion <NUM> from rotating much further in this direction. For instance, the rotation limiter <NUM> prevents the pivoting portion <NUM> from rotating more than a few degrees (e.g., no more than three degrees, or no more than five degrees) in an outward direction, effectively keeping the bottom of the pivoting portion <NUM> mostly flat during the takeoff from the flat portion. In some embodiments, the same effect is achieved by keeping the center of gravity of the pivoting portion <NUM> on the inward side of the pivot axis <NUM> when perching and taking off from a flat surface. In some such embodiments, the center of gravity of the pivoting portion is also above the pivot axis <NUM> when perching and taking off from the flat surface. Here, directions such as "above" are with respect to a gravity direction.

Furthermore, when landing on a curved surface, the contact force from the surface on the bottom part of the leg <NUM> creates a torque that causes the leg <NUM> to rotate and achieve the rotated (inward) orientation shown in <FIG>. The leg <NUM> remains in this orientation even after takeoff because the center of gravity <NUM> of the servo motor <NUM> (or the center of gravity of the pivoting portion <NUM>) has shifted to an outward side of the pivot axis <NUM> (and in some embodiments, above the pivot axis <NUM>) such that the weight creates an opposite torque (in a clockwise direction <NUM> as illustrated in <FIG>), keeping the pivoting portion <NUM> in this (inward) orientation. Here, the fixed portion of the leg <NUM> (e.g., the leg body) also acts as a rotation range limiter <NUM> to prevent excessive (inward) rotation. For example, in some embodiments, the rotation limiter <NUM> limits inward rotation to no more than <NUM>°, while in some other embodiments, the rotation limiter <NUM> limits inward rotation to no more than <NUM>°.

<FIG> illustrates an example UAV <NUM> having articulated magnetic legs <NUM> landing in a centered orientation on a pipe <NUM>, according to an embodiment. <FIG> illustrate the UAV <NUM> of <FIG> landing in a non-centered orientation on the pipe <NUM>, making initial and final contacts, respectively. In accordance with the invention, measuring the rotation angle of the legs <NUM> due to their singular degree of freedom before or after contacting a surface (such as the pipe <NUM>) is done through rotation angle sensors such as a potentiometer, rotary encoder, or shaft encoder in each magnetic leg <NUM>. Determining the rotation angle of each leg <NUM> helps with determining an orientation of the legs <NUM> or the UAV <NUM> with respect to the surface. In some embodiments, the rotation angle sensors measure the angular rotation of the pivoting portions of the legs <NUM> with respect to gravity, while in some embodiments, the rotation angle sensors measure the angular rotation of the pivoting portions of the legs <NUM> with respect to the fixed portions of the legs <NUM>. In some such embodiments, the rotation angle sensors measure the angular rotation of the pivoting portions of the legs <NUM> with respect to both gravity and the fixed portions of the legs <NUM>.

For example, in some embodiments, rotation angle sensors are implemented on the legs <NUM>, with control circuitry provided to signal if all of them have the same orientation (e.g., the same measured inward angles of their pivoting portions) when lending on a surface before switching on the switchable magnets of the magnetic legs <NUM>. This helps detect situations where one or more legs are not touching the surface or not touching the surface at the appropriate (inward) angle, which are indicative of an incomplete or imperfect landing attempt on the surface. In some embodiments, this indication of the same inward angle is further combined with a level sensor in the body of the UAV <NUM> to detect in the body of the UAV <NUM> is level with respect to gravity.

For example, the pivoting portions of the legs <NUM> of the UAV <NUM> of <FIG> are not at the same angular rotation, which indicates a problem with the landing (in this case, the UAV <NUM> is off-centered with respect to the top of the pipe <NUM>). If the UAV <NUM> continues to land to try to force the pivoting portions to have the same angular rotation, at least with respect to the fixed portions, as in <FIG>, the UAV <NUM> is no longer level with respect to gravity. This can be detected with, for example, a level sensor in the body of the UAV <NUM>, or rotation angle sensors in the legs <NUM> that measure angular rotation of the pivoting portions with respect to gravity. At this point, in some embodiments, automated control circuitry is programmed to determine the amount of off-center, and whether to re-attempt the landing or if the amount of off-center is within a tolerance of a safe landing (such as <NUM> degrees, <NUM> degrees, or <NUM> degrees off-center).

<FIG> illustrate an example UAV <NUM> having articulated magnetic legs <NUM> landing on flat and curved surfaces (pipe <NUM> and flat surface <NUM>), respectively, according to an embodiment. The legs <NUM> are coupled to a UAV body <NUM>. Here, rotation angle sensors in the legs <NUM> are used to measure the curvature of the surface that the legs <NUM> land on. In some embodiments, measurement is used to determine the distance between the body <NUM> (or top of the legs <NUM>, or bottom of payload) and the surface. Based upon this distance, the amount that a payload of the UAV <NUM> needs to be lowered (e.g., from the body <NUM>, such as distance <NUM> to the pipe <NUM> or the distance <NUM> to the flat surface <NUM>) to the surface can be established. Determining this distance can be especially useful when a controller is used (e.g., configured by code) to deploy the payload through a feedback loop between the controller and the sensors.

With reference to <FIG>, in some example embodiments, an unmanned aerial vehicle (UAV, such as UAV <NUM>, <NUM>, or <NUM>) that lands, takes off, and magnetically perches on a ferromagnetic cylindrical surface (such as pipe <NUM> or curved surface <NUM>) is provided. The UAV includes a body (such as UAV body <NUM> or <NUM>) and a plurality (such as four or six) of articulated magnetic legs (such as articulated magnetic legs <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>). The magnetic legs land the UAV on the ferromagnetic cylindrical surface and magnetically perch the UAV on the ferromagnetic cylindrical surface after the landing. Each magnetic leg has a fixed portion (such as fixed portion <NUM> or <NUM>) coupled to the UAV body and a pivoting portion (such as pivoting portion <NUM>, <NUM>, or <NUM>) pivotably coupled to the fixed portion at a pivot axis (such as pivot pin <NUM> or pivot axis <NUM> or <NUM>).

The pivoting portion includes a switchable magnet (such as switchable magnet <NUM>) whose magnetism is switched on to magnetically attach the UAV to the ferromagnetic cylindrical surface at an end of the landing and throughout the perching, and switched off to magnetically detach the UAV from the ferromagnetic cylindrical surface at a beginning of the takeoff. The pivoting portion further includes only a single articulation joint (such as pivot pin <NUM>) that provides the pivoting portion with only a single degree of freedom (such as inward and outward) about the pivot axis in order to passively orient the pivoting portion inward and tangent to the cylindrical surface in response to the pivoting portion contacting the cylindrical surface during the landing. The single articulation joint with the single degree of freedom also passively maintain the inward orientation of the pivoting portion during the takeoff.

In an embodiment, the fixed portion of each magnetic leg includes an inward rotation limiter (such as rotation limiter <NUM>) that limits the inward rotation of the pivoting portion during the landing and the takeoff. In an embodiment, the UAV lands on and takes off from a flat surface (such as flat surface <NUM>). In addition, the articulation joint of each magnetic leg further provides the pivoting portion with the single degree of freedom about the pivot axis in order to passively orient the pivoting portion flat and parallel to the flat surface in response to the pivoting portion contacting the flat surface during the landing on the flat surface. Further, the articulation joint with the single degree of freedom also passively maintain the flat orientation of the pivoting portion during the takeoff from the flat surface.

In an embodiment, the fixed portion of each magnetic leg includes an outward rotation limiter (such as rotation limiter <NUM>) to limit the outward rotation of the pivoting portion to a mostly flat (such as within a few degrees of flat, as in no more than three degrees or no more than five degrees off from flat) orientation during the landing on and the takeoff from the flat surface. In an embodiment, the pivoting portion of each magnetic leg further includes a switch actuator (such as servo motor <NUM> or <NUM>) at a top of the switchable magnet. The switch actuator actuates the magnet in order to switch the magnet between on and off. In addition, the center of gravity of the switch actuator is on an outward side (such as center of gravity <NUM>) of the pivot axis during the takeoff from the cylindrical surface, and on an inward side (such as center of gravity <NUM>) of the pivot axis during the takeoff from the flat surface.

In an embodiment, each magnetic leg further includes an angle rotation sensor that measures a pivot of the pivoting portion about the pivot axis after the pivoting portion contacts the cylindrical surface. In an embodiment, the UAV further includes a control circuit configured (such as programmed by code) to determine when to switch on the magnets of the magnetic legs at the end of the landing using the measured pivots of the pivoting portions of the magnetic legs to make the determination. In an embodiment, for each magnetic leg, the pivoting portion includes a switch actuator coupled to a top of the magnet and that actuates the magnet in order to switch the magnet between on and off. The control circuit is further configured (such as by code) to control the switch actuator to switch on the magnet when the measured pivots of the pivoting portions of the magnetic legs are the same inward angle.

In an embodiment, the UAV further includes a control circuit configured by code to determine the diameter of a cylinder corresponding to the cylindrical surface using the measured pivots of the pivoting portions of the magnetic legs. In an embodiment, the UAV further includes a control circuit configured by code or other programmable logic to determine a distance (such as distance <NUM>) from the body to the cylindrical surface using the measured pivots of the pivoting portions of the magnetic legs. In an embodiment, the ferromagnetic cylindrical surface is part of a carbon steel pipe or vessel (such as a storage tank).

The described techniques herein can be implemented using a combination of sensors, cameras, and other devices including computing or other logic circuits configured (e.g., programmed) to carry out their assigned tasks. These devices are located on or in (or otherwise in close proximity to) the body or legs of the UAV for carrying out the techniques. In some example embodiments, the control logic is implemented as computer code configured to be executed on a computing circuit (such as a microprocessor) to perform the control steps that are part of the technique.

<FIG> is a flow diagram of an example method <NUM> of landing, taking off, and magnetically perching a UAV (such as UAV <NUM>, <NUM>, or <NUM>) on a ferromagnetic cylindrical surface (such as pipe <NUM> or curved surface <NUM>), according to an embodiment. The UAV includes a body (such as UAV body <NUM> or <NUM>) and a plurality of articulated magnetic legs (such as magnetic legs <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>). Each leg has a fixed portion (such as fixed portion <NUM> or <NUM>) coupled to the body and a pivoting portion (such as pivoting portion <NUM>, <NUM>, or <NUM>) pivotably coupled to the fixed portion at a pivot axis (such as pivot axis <NUM> or <NUM>). The pivot portion includes a switchable magnet (such as switchable magnet <NUM>) and a single articulation joint (such as pivot pin <NUM>) having a single degree of freedom (such as inward or outward) about the pivot axis.

Some or all of the method <NUM> can be performed using components and techniques illustrated in <FIG>. In addition, portions of this and other methods disclosed herein can be performed on or using a custom or preprogrammed logic device, circuit, or processor, such as a programmable logic circuit (PLC), computer, software, or other circuit (e.g., ASIC, FPGA) configured by code or logic to carry out their assigned task. The device, circuit, or processor can be, for example, a dedicated or shared hardware device (such as a laptop, a single board computer (SBC), a workstation, a tablet, a smartphone, part of a server, or a dedicated hardware circuit, as in an FPGA or ASIC, or the like), or computer server, or a portion of a server or computer system. The device, circuit, or processor can include a non-transitory computer readable medium (CRM, such as read-only memory (ROM), flash drive, or disk drive) storing instructions that, when executed on one or more processors, cause portions of the method <NUM> (or other disclosed method) to be carried out. It should be noted that in other embodiments, the order of the operations can be varied, and that some of the operations can be omitted. Some of the method <NUM> can also be performed using logic, circuits, or processors located on or in electrical communication with a processing circuit configured by code to carry out these portions of the method <NUM>.

In the method <NUM>, processing begins with the step of landing <NUM> the UAV on the ferromagnetic cylindrical surface using the magnetic legs. The method <NUM> further includes the step of passively orienting <NUM>, for each magnetic leg using the single articulation joint with the single degree of freedom about the pivot axis, the pivoting portion inward and tangent to the cylindrical surface in response to the pivoting portion contacting the cylindrical surface during the landing. See, for example, <FIG>. In addition, the method <NUM> includes the step of magnetically attaching <NUM> the UAV to the ferromagnetic cylindrical surface at an end of the landing by switching on the switchable magnet in each magnetic leg. In some embodiments, a servo motor (such as servo motor <NUM> or <NUM>) is used to rotate stacked disk magnets of a switchable magnet in order to turn on the switchable magnet.

Continuing, the method <NUM> includes the step of magnetically perching <NUM> the UAV on the ferromagnetic cylindrical surface after the landing using the magnetic legs while their respective switchable magnets remain switched on. The method <NUM> further includes the steps of magnetically detaching <NUM> the UAV from the ferromagnetic cylindrical surface at a beginning of the takeoff by switching off the switchable magnet in each magnetic leg, and taking off <NUM> with the UAV from the cylindrical surface after the perching. In addition, the method <NUM> includes the step of passively maintaining <NUM>, for each magnetic leg using the articulation joint and with the center of gravity of the pivoting portion being on an outward side of the pivot axis (such as in <FIG>), the inward orientation of the pivoting portion during the takeoff.

In some embodiments, the method <NUM> includes the step of limiting, for each magnetic leg using an inward rotation limiter (such as rotation limiter <NUM>) of the fixed portion of the magnetic leg, the inward rotation of the pivoting portion during the landing and the takeoff. In some embodiments, the method <NUM> includes the steps of: landing the UAV on a flat surface (such as flat surface <NUM>) using the magnetic legs; passively orienting, for each magnetic leg using the single articulation joint with the single degree of freedom about the pivot axis, the pivoting portion flat and parallel to the flat surface in response to the pivoting portion contacting the flat surface during the landing on the flat surface (such as shown in <FIG>); taking off with the UAV from the flat surface; and passively maintaining, for each magnetic leg using the articulation joint and with the center of gravity of the pivoting portion being on an inward side of the pivot axis, the flat orientation of the pivoting portion during the takeoff from the flat surface.

In some embodiments, the method <NUM> includes the step of limiting, for each magnetic leg using an outward rotation limiter (such as rotation limiter <NUM>) of the fixed portion of the magnetic leg, the outward rotation of the pivoting portion to a mostly flat (such as at most three degrees or at most five degrees) orientation during the landing on and the takeoff from the flat surface. The method <NUM> includes the step of, for each magnetic leg, measuring a pivot of the pivoting portion about the pivot axis after the pivoting portion contacts the cylindrical surface using an angle rotation sensor of the magnetic leg. In some embodiments, the method <NUM> includes the step of determining, by a control circuit of the UAV, when to switch on the magnets of the magnetic legs at the end of the landing using the measured pivots of the pivoting portions of the magnetic legs.

In some embodiments, the method <NUM> includes the step of, for each magnetic leg, the actuating the magnet, using a switch actuator (such as servo motor <NUM> or <NUM>) of the pivoting portion and coupled to a top of the magnet, in order to switch the magnet between on and off, and controlling, by the control circuit, the switch actuator to switch on the magnet when the measured pivots of the pivoting portions of the magnetic legs are the same inward angle. In some embodiments, the method <NUM> includes the step of determining, by a control circuit of the UAV, the diameter of a cylinder (such as pipe <NUM> or cylindrically curved surface <NUM> having a radius of curvature) corresponding to the cylindrical surface using the measured pivots of the pivoting portions of the magnetic legs. In some embodiments, the method <NUM> includes the step of determining, by a control circuit of the UAV, a distance (such as distance <NUM>) from the body to the cylindrical surface using the measured pivots of the pivoting portions of the magnetic legs.

The methods described herein may be performed in part 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 including computer program code adapted to perform some of the steps of any of the methods described herein when the program is run on a computer or suitable hardware device (e.g., FPGA), and where the computer program may be embodied on a computer readable medium. Examples of tangible storage media include computer storage devices having computer-readable media such as disks, thumb drives, flash memory, and the like, and do not include propagated signals. Propagated signals may be present in a tangible storage media, but propagated signals by themselves are not examples of tangible storage media. The software can be suitable for execution on a parallel processor or a serial processor such that the method steps may be carried out in any suitable order, or simultaneously.

It is to be further understood that like or similar numerals in the drawings represent like or similar elements through the several figures, and that not all components or steps described and illustrated with reference to the figures are required for all embodiments or arrangements.

Terms of orientation are used herein merely for purposes of convention and referencing and are not to be construed as limiting. However, it is recognized these terms could be used with reference to a viewer. Accordingly, no limitations are implied or to be inferred. In addition, the use of ordinal numbers (e.g., first, second, third) is for distinction and not counting. For example, the use of "third" does not imply there is a corresponding "first" or "second. " Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

Claim 1:
An unmanned aerial vehicle, UAV (<NUM>, <NUM>, <NUM>), configured to land, take off, and magnetically perch on a ferromagnetic cylindrical surface, the UAV (<NUM>, <NUM>, <NUM>) comprising:
- a body (<NUM>, <NUM>);
- a plurality of articulated magnetic legs configured to land the UAV (<NUM>, <NUM>, <NUM>) on the ferromagnetic cylindrical surface and to magnetically perch the UAV (<NUM>, <NUM>, <NUM>) on the ferromagnetic cylindrical surface after the landing, each magnetic leg (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) having a fixed portion (<NUM>, <NUM>) coupled to the body (<NUM>, <NUM>) and a pivoting portion (<NUM>, <NUM>, <NUM>) pivotably coupled to the fixed portion (<NUM>, <NUM>) at a pivot axis (<NUM>, <NUM>, <NUM>, <NUM>), wherein each magnetic leg (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) further comprises an angle rotation sensor configured to measure a pivot of the pivoting portion (<NUM>, <NUM>, <NUM>) about the pivot axis (<NUM>, <NUM>, <NUM>, <NUM>) after the pivoting portion (<NUM>, <NUM>, <NUM>) contacts the cylindrical surface, the pivoting portion (<NUM>, <NUM>, <NUM>) comprising:
- a switchable magnet (<NUM>) whose magnetism is switched on to magnetically attach the UAV (<NUM>, <NUM>, <NUM>) to the ferromagnetic cylindrical surface at an end of the landing and throughout the perching (<NUM>), and switched off to magnetically detach the UAV (<NUM>, <NUM>, <NUM>) from the ferromagnetic cylindrical surface at a beginning of the takeoff; and
- a single articulation joint configured to provide the pivoting portion (<NUM>, <NUM>, <NUM>) with a single degree of freedom about the pivot axis (<NUM>, <NUM>, <NUM>, <NUM>) in order to passively orient the pivoting portion (<NUM>, <NUM>, <NUM>) inward and tangent to the cylindrical surface in response to the pivoting portion (<NUM>, <NUM>, <NUM>) contacting the cylindrical surface during the landing, and to passively maintain the inward orientation of the pivoting portion (<NUM>, <NUM>, <NUM>) during the takeoff; and
- a control circuit configured to
- determine a diameter of a cylinder corresponding to the cylindrical surface using the measured pivots of the pivoting portions (<NUM>, <NUM>, <NUM>) of the magnetic legs (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) or
- a distance (<NUM>) from the body (<NUM>, <NUM>) to the cylindrical surface using the measured pivots of the pivoting portions (<NUM>, <NUM>, <NUM>) of the magnetic legs (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>).