Patent Description:
While they originated mostly in military applications, the use of unmanned aerial vehicle has rapidly expanded to commercial, scientific, recreational, agricultural, and other applications, such as for instance policing, peacekeeping, and surveillance, but also product deliveries, aerial photography, agriculture, and drone racing.

Also, in the recent times, have been developed omnidirectional drones for physical interaction. A normal drone will need to be tilted to exert forces on the environment the environment, which is an unstable configuration. A small wind gust or any disturbance could rapidly lead to a crash of a normal drone. Therefore, current use for MAVs is most of the time limited to remote sensing tasks.

The main problem lies in the fact that currently existing MAVs cannot be robustly controlled when in physical contact with the environment. In recent years, fully actuated MAVs have started to gain attention as promising platforms for reliable aerial physical interaction. Equipped with an aerial manipulator, these platforms have the potential to achieve a high degree of versatility, robustness and stability.

Notably, there is a need not yet correctly fulfilled for omnidirectional drones or omnidirectional aerial vehicles that can interact with the environment, including applying force, while also staying in a stable position. Such type of omnidirectional aerial vehicles could be used for instance to do inspections of infrastructures, or to do painting or cleaning on high-rise buildings or any other difficult to reach places. Physical interaction with drones would be also useful for many other applications, notably industrial applications, such as non-destructive testing of bridges, tunnels, silos, or pipes, or other concrete structures, also for inspection of storage tanks or cavities. that can further more be implemented by the human being remotely from the inspection site.

Document <CIT> presents a non-destructive inspection ("NDI") system that includes an unmanned aerial vehicle ("UAV") comprising a body structure. The body structure comprises one or more support structures with a releasable end structure; and one or more non-destructive inspection sensors integrated to a respective releasable end structure. This system also includes a location tracking system. A manipulator arm that can comprises a gripper allows implementation of specific tasks. The propulsion system is not detailed.

Document <CIT> concerns a rotor-based remote flying vehicle platform which comprises a central frame with a control center that is configured to control motors mounted to the vehicle platform. Four arms are connected to the central frame and extend outward. A unique motor is mounted on the distal end of each arm and is controlled by a tilt actuator capable of tilting the motor according to different configurations. This configuration becomes highly inefficient when interacting with environnement.

Document <CIT> relates to an aircraft with a stationary flight capability comprising a contact device. More precisely, in this arrangement, there is a central section to which are attached two segments rigidly joined to each other, with a counterweight and a gripper. For propulsion, eight engines are used, equipped with propellers that are fixedly mounted with a predetermined inclination at an angle of between <NUM> ° and <NUM> ° on the horizontal plane. This configuration requires additional actuators to orient an end-effector in any orientation because it cannot tilt its body completely. Furthermore, it is not agile in changing the applied force and moment and requires a high thrust to weight ratio for stable control.

Document <CIT> concerns a multi-rotor type unmanned aerial vehicle includes: a main body including the battery module and the control module; a plurality of frames (four main frames and four auxiliary frames) connected to a side surface of the main body and extending therefrom; a first motor connected to a distal end of each of the frames; and a drive unit connected to the first motor, wherein the drive unit includes a rotary frame and a stationary frame each having a circular shape and connected to each other in the form of a gyroscope, a second motor supported at the center of the rotatable frame, and a propeller connected to the second motor, and a vector of thrust generated by rotation of the propeller is variable according to rotation of the first and second motors. This arrangement having a lot of motors to be controlled, the driving of this aerial vehicle is quite complex and sensitive.

Document <CIT> presents a system including a first coaxial rotor spaced from an aircraft body and a second coaxial rotor spaced from the aircraft body and opposite the first coaxial rotor; the first coaxial rotor having a first top propeller aligned with a first bottom propeller along a first rotational axis; the second coaxial rotor having a second top propeller aligned with a second bottom propeller along a second rotational axis. A gyroscopic moment to maintain pitch stability is controlled by modulating the first and second top propellers having a different angular speed or different torque from the first and second bottom propellers and tilting the first and second coaxial rotors towards the central axis with a common tilt angle and a common tilt rate.

Document <CIT> relates to an unmanned aerial and underwater vehicle, and more precisely to a sea-air-land-dive quadrangle tilting three-rotor unmanned aerial vehicle with the capacity of vehicle take-off and landing. This vehicle has a tail equipped with a tail rotor, where the rear motor rotor is fixed on a rear tilt swivel connected to the tail of the fuselage through a rear tilt shaft. There are two arms constituting forward tilt pivots, on which is mounted a forward tilting swivel with one front motor rotor. The speeds of the two front motor rotors and of the rear motor rotor are independently controlled to achieve vertical take-off and landing and fixed-wing modes.

<CIT> discloses another type of VTOL aircraft.

One of the main problems lies in the unstable dynamics of aerial vehicles in contact with the environment and equipped with tools and sensors so as to perform as robots, which complicates the control performance.

In view of above considerations, there exist a need to propose an aerial vehicle that overcomes at least some of the drawbacks of the existing aerial vehicles.

There also exists a need to propose an improved aerial vehicle with respect of the existing aerial vehicles.

Also, some embodiments of the present invention aims to provide an aerial vehicle with advanced manipulation capabilities that can be employed in various tasks that require interaction with the environment, such as contact-based inspection, cleaning and lightweight maintenance.

According to the invention, these aims are achieved by means of an aerial vehicle comprising:.

The proposed aerial vehicle is able to exert forces and torques in all directions with high capability of the system to control position and orientation independently. It means the aerial vehicle can take any orientation (including for instance, level position, vertical position or inclined position of the central frame of the aerial vehicle), and stay stabilised in that orientation, with the possibility of moving in that orientation and have possibly contact with a surface, with or without exerting a force on that surface.

Therefore, the proposed aerial vehicle is capable for physical interaction with environment, including for instance contact-based inspection.

The central frame <NUM> is a platform in the form of a flat box, elongated along and parallel to the first X axis, and parallel to the second axis Y. The central frame <NUM> contains on-board notably the electronical and control parts of the aerial vehicle <NUM>. The central frame <NUM> defines a front face <NUM> for reversible attachment with equipment. The central frame <NUM> defines a rear face <NUM> from which extends a tail <NUM> equipped with a tail rotor <NUM>. The central frame <NUM> also defines two lateral faces <NUM>, <NUM> from each of which extends one arm <NUM> (as illustrated) or several arms (situation not shown). The central frame <NUM> also defines a top face <NUM> and a bottom face <NUM>. Also, in a variant (not shown), the aerial vehicle <NUM> further comprises bumpers forming extension at the front part of the central frame <NUM>.

Unlike classic aerial vehicles where the arms <NUM> are fixed with respect to the frame, according to the invention, the arms are able to tilt or to rotate around at least one axis, which is named the second axis in the present text. Also, the angular position of the arm <NUM> around this second axis, with respect to the third axis Z, defines an arm rotation angle (A1) (see <FIG>). In the illustrated embodiment, this second axis is coaxial with the arm's direction (Y axis) to that the orientation of the arms <NUM> with respect to the central frame <NUM> is fixed. The arm rotation angle A1 is controlled by a first actuator <NUM>. In <FIG>, this actuator <NUM> is visible within the central frame <NUM>.

In <FIG>, this arm rotation angle A1 is <NUM>°; in <FIG> and <FIG>, this arm rotation angle A1 is +<NUM>°; in <FIG> and <FIG>, this arm rotation angle A1 is +<NUM>°. Preferably, said arm rotation angle A1 is contained within the range -<NUM>° to + <NUM>° so as to take any angular position around the second axis. In a possible embodiment, said arm rotation angle A1 can take any angular value in the <NUM>° to <NUM>° range, with a possible continuous rotation by using a slip ring that avoids the cable twisting.

Also, each arm <NUM> is equipped with two thrust motors <NUM> controlling the spinning in opposite direction of two coaxial rotors <NUM>. In the illustrated embodiment, the free end of each arm <NUM> is equipped with said two thrust motors <NUM>. In another possible arrangement, not shown, the two double rotors <NUM> are located at the end portion of the arm <NUM>, which can be distant of the free end of said two arms <NUM>. These thrust motors <NUM> allows the spinning of the double rotors <NUM> to generate lift force for the aerial vehicle <NUM>. Therefore, according to the invention, when considering each one of the two arms <NUM>, his two rotors <NUM> (top rotor and bottom rotor of the same arm <NUM>) are spinning in opposite directions.

Also, the two coaxial rotors <NUM> define a double rotor axis R. The thrust motors <NUM> rotate around this double rotor axis R, in opposite directions, which also make the two coaxial rotors <NUM> rotate around this double rotor axis R, in opposite directions. For each pair of rotors <NUM>, the the respective angular position of the rotors <NUM> is not determined, and not defined (can be any relative rotate around this double rotor axis R, in opposite directions). The two coaxial rotors <NUM> can tilt together with respect to another tilting axis T (see <FIG>),. Said tilting axis T is perpendicular to the second axis (Y axis). The angular position of the double rotor <NUM> or double rotor axis R with respect to the plane orthogonal to the second axis, is defining a double rotor tilting angle A2. In the illustrated embodiment, this second axis is coaxial with the arm's direction (Y axis) so that the double rotor tilting angle A2 is measured with respect to the plane (Z, T). In <FIG>, this double rotor tilting angle A2 is <NUM>°; in <FIG>, , this double rotor tilting angle A2 is +<NUM>° for both double rotors <NUM> which double rotor tilting angle A2 are parallel. In other words, the two double rotors <NUM> tilt together the same amount with respect to the third axis Z, or more precisely with respect to a plane parallel to the third axis Z and secant with the tilting axis T. Preferably, said double rotor tilting angle (A2) is contained within the range -<NUM>° to + <NUM>°. In a possible embodiment, said double rotor tilting angle (A2) is contained within the range -<NUM>° to + <NUM>°. The arm double rotor tilting angle A2 is controlled by a second actuator <NUM>. In <FIG> and <FIG>, this second actuator <NUM> is visible at the tip of the arm <NUM>.

This way, changing the generated force direction or thrust vectoring, which provides omni-directionality, is possible notably through the tilting (rotation) of the arms <NUM> around at least one axis, named the second axis in the present text (Y axis in the figure), with respect to the central frame <NUM>.

In the illustrated embodiment, said second axis (Y) is coaxial with the corresponding arm <NUM>.

In the illustrated embodiment, the aerial vehicle <NUM> comprises two coaxial arms <NUM>, extending from opposite faces (two lateral faces <NUM> and <NUM>) of said central frame, along said second axis (Y). Therefore, these two arms <NUM> are parallel and coaxial to each other.

In some other embodiments (not shown), the aerial vehicle <NUM> comprises more than two coaxial arms, namely four, six or eight arms, extending symmetrically from opposite faces of said central frame.

The tail <NUM> extends along the first axis X from the rear of the central frame <NUM>, according to a relative long dimension, for instance <NUM> from the central point O. This long tail provides a good lever arm which is efficient for rapidly change the orientation of the aerial vehicle <NUM>, namely to change the pitch angle of the central frame <NUM>, notably when the rotor is decelerating or inversely accelerating. The tail <NUM> is equipped with a tail rotor <NUM> spinning around a tail rotor axis P, said tail rotor axis P being parallel to a third axis Z.

In a first alternative of the invention, the direction of rotation of the tail rotor <NUM> can be inverted.

In that respect, the profile of the two airfoils of the tail rotor <NUM> is double symmetric, meaning symmetric with two planes of symmetry, a first plane of symmetry between the leading edge and the trailing edge of the foil, and a second plane of symmetry being the chord line. Such a geometry leads to a continuous identical section of the tail rotor <NUM> along the length of the foils: the upper camber being the same than the lower camber along the length of the two foils of the tail rotor <NUM>, and the leading edge and the trailing edge having the same shape along the length of the two foils of the tail rotor. Thus, the tail rotor <NUM> has the same dynamics independent of the direction of rotation. In that configuration, the tail rotor <NUM> is in one piece, the two airfoils being not movable one with respect to the other.

In the illustrated embodiment, said arms <NUM> and said tail <NUM> define a main plane (X, Y) for said aerial vehicle <NUM>, said central frame <NUM> being secant with said main plane (X, Y). Said main plane (X, Y) is also defined by the first axis (X) and the second axis (Y) which are orthogonal to each other. Also, these first axis (X) and the second axis (Y) are secant to a central point (O) which is contained within the central frame <NUM>. A third axis Z defines with the first axis (X) and the second axis (Y) an orthogonal geometrical system (see <FIG>). Said first axis (X), said second axis (y) and said third axis (Z) are therefore secant into said central point (O).

The control of the change of rotation direction for the tail rotor <NUM> with a double symmetric shape of the two airfoils of the tail rotor <NUM> provides in an efficient way the inversion of the lift direction for the aerial vehicle <NUM>.

The decoupling of attitude and position makes it possible to control the position of any equipment mounted on the central frame <NUM> very precisely.

As can be seen in <FIG>, a clutch element <NUM> having a tube shape with a lateral opening at of its end for cable passage, connects the actuator <NUM> and the arm <NUM>. As a possible embodiment, this clutch element <NUM> is designed (shape and material) so as to provide a relative mechanical flexibility : in that situation, the mechanical stress applied in the arm <NUM> is not transmitted to the actuator <NUM>, except for the one rotation around the arm axis which is controlled by the actuator <NUM>. In case of impact on the arm <NUM>, such a flexible clutch element <NUM> prevents some serious damage of the arm <NUM>, or at least of the actuator <NUM> while also making the rotation of the arm <NUM> possible. Such a clutch element <NUM> also compensates for small misalignment between actuator <NUM> axis and arm <NUM> axis. In that respect, the clutch element <NUM> can tolerate a radial, axial and angular misalignment between the actuator and the arm <NUM> but is relative stiff in torsion, which is important for precise control.

In a second alternative of the invention, here is a variant implementation for the tail rotor <NUM>', which is shown on <FIG>, the two airfoils or blades <NUM>' of the tail rotor <NUM>' have opposite inclination, which means opposite angle of attack and are moveable with respect to each other. Among the possible positions for the orientation of the two blades <NUM>' which have a continuous motion, can be defined the following extreme or remarkable positions:.

An elongated member <NUM> is visible on the <FIG>, at the front face <NUM> of the central frame. In this illustrated embodiment, the elongated member <NUM> is telescopic and can receive some piece of equipment through its end fixing part. Preferably, this elongated member <NUM> is compliant.

In another embodiment, not shown, the front face <NUM> of the central frame <NUM> has no elongated member but the central frame <NUM> is directly equipped with supporting means for removably attaching an equipment.

A lot of possible equipment can be mounted onto the front face <NUM> of the central frame <NUM>. Among the possibilities, the following pieces of equipement can be, taken alone or in combination, as follows : manipulator, sensor, nozzle.

Within the central frame, among other things, there are the following pieces of gear, forming on-board sensors:.

The aerial vehicle <NUM> can be powered with a battery or from power coming over a tether.

The sensor data can be synchronized in time, namely taking the measure at the same moment(s), which allows to collect the date in a more accurate way. In another data collection mode, the sensor data can also be measured and collected at different moments between them but with accurate known timing with respect to a "wall clock". Data from these sensors are fused using sensor fusion algorithms running on the onboard computer. The onboard computer placed also within the central frame generate actuators command signals to control the drone behavior.

Preferably, as visible on <FIG>, when the aerial vehicle <NUM> has no equipment, the center of mass C0 of the aerial vehicle <NUM> is placed within the central frame <NUM>, and on particular within the half portion of the central frame <NUM> which is the closest to the tail <NUM> (Rear half portion H1 of the central frame).

Also, when the aerial vehicle <NUM> has an equipment (shown on <FIG> with zone E), the center of mass C1 is placed preferably within the central frame <NUM> or in front of the central frame <NUM>, and in particular within the half portion H2 (shown on <FIG>) of the central frame <NUM> which contains the front face <NUM> of the central frame <NUM> (Front half portion H2 of the central frame). For instance the equipment is attached to the central frame <NUM> through supporting means that can removeably attach the equipment to the central frame <NUM>. On <FIG>, this supporting means is the telescopic elongated member <NUM>. On <FIG>, the equipment is represented only by a identified zone E at the tip of the elongated member <NUM>.

Also, preferably, as visible on <FIG>, the distance between the tail rotor <NUM> up to the front face <NUM> of the central frame (Length L) is larger than or equal to the distance between the two double rotors <NUM> (width W). This general geometrical relation provides a long tail <NUM> with respect of the size of the aerial vehicle <NUM>, which gives rise to an efficient lever arm effect for the tail when changing the pitch by inverting the rotation direction of the tail rotor <NUM>. In a possible embodiment, the length L is about <NUM>. the width W is about <NUM>, while using a tail rotor of about <NUM> and main propellers of the double rotors <NUM> of the arms <NUM> of about <NUM>. In other possible configurations, not shown, the distance between the tail rotor <NUM> up to the front face <NUM> of the central frame <NUM> (Length L) is larger than or equal to the distance between the two double rotors <NUM> (width W).

In some embodiments, including the embodiment shown in <FIG>, the aerial vehicle <NUM> comprises only one tail <NUM> extending from the central frame <NUM>, this sole tail <NUM> being equipped with the only and sole tail rotor <NUM>. Also, such an aerial vehicle <NUM> comprises only and exactly two arms <NUM>, the latter being each able to tilt or to rotate with respect to the central frame <NUM>, being aligned and being each equipped with said two rotors. Consequently, in this configuration the aerial vehicle <NUM> forms a aerial vehicle having a general T-shape, where the leg of the T is formed by the tail and the two branches of the upper part of the T are formed by the two arms <NUM>. It means that the tail <NUM> is orthogonal to the two arms <NUM>. Also, in this configuration, according to a possible variant corresponding to the aerial vehicle <NUM> shown in <FIG>, the tail <NUM> and the two arms <NUM> are coplanar.

As an example of possible application of the aerial vehicle <NUM> of the invention, is now presented the non-destructive inspection of the reinforcement bars embedded in concrete. For such analysis, a profometer is mounted at the front face of the central frame as the only one element of equipment or one of the pieces of equipment of the aerial vehicle <NUM>. Such a profometer is an instrument for detecting location, size of reinforcement in concrete cover also with thickness of concrete cover. This instrument is also known as rebar locator or a cover meter This is a small, versatile, portable and handy instrument which is normally used to locate the reinforcement via a display, notably an LCD display. In that case, the guiding or controlled navigation, including a possible predefined route, of the aerial vehicle <NUM> allows to have a contact point between the profometer and the surface of the structure to be controlled. This contact point (with or without application of a force applied by the profometer onto the surface) is moreover maintained while moving the aerial vehicle <NUM> and /or for each contact points formed by inspection predefined points where the control and/or measurement is to be implemented.

More generally, inspection of infrastructure, which is a continuous process, can be facilitated with the use of such an aerial vehicle <NUM>. Moreover, sometimes, visual inspection isn't enough and an in-depth inspection is required where sensor placement on the structure is needed. In some situation, an internal structure of the pipe needs to be checked using scaffoldings, having people hanging on ropes or using cranes, which is risky and expensive. With the solution of the present invention, are provided omnidirectional drones that can interact with the environment. In an embodiment, the aerial vehicle <NUM> is equipped with a manipulator and can extend its front elongated member, place a sensor in front of or against (in contact with) the wall and get the measurements needed from the sensor and thus be helpful for inspection tasks. In that application of the aerial vehicle <NUM>, this will help do away with temporary structure of scaffolding and having workers hanging on from ropes or using cranes.

As another example of possible application of the aerial vehicle <NUM> of the invention, for painting surfaces including drawing patterns on both planar and 3D surfaces. In that example, not shown on the drawing, an arm (or an elongated element) plus a spray nozzle are mounted at the front face <NUM> of the central frame <NUM> as elements of equipment of the aerial vehicle <NUM>. In one embodiment, the spray nozzle is connected to a first end of a pipe which other end is mounted on a paint reservoir equipped with an air compressor, so that compressed air pushes the paint along a pipe. Also, a valve is mounted next to the nozzle on the pipe to control the flow of paint. Furthermore, through a system of valves and pipes, mixing multiple colors is possible. With such an equipment, the aerial vehicle <NUM> according to the present invention is capable of painting surfaces and can draw patterns on both planar and 3D surfaces.

According to some embodiments, the aerial vehicle <NUM> interact with a surface while flying with the central frame <NUM> being orientated with any orientation, namely vertically, or being orientated horizontally, or being inclined (orientation of the plane (X, Y) between horizontal and vertical orientation.

According to some embodiments, the aerial vehicle <NUM> can fly <NUM> degrees vertically and tilt horizontal, and do also upside down flights. Such features are coming to the market for the first time. The ability to interact with the environment in unique.

According to some embodiments, the aerial vehicle <NUM> can correct disturbance, be in a stable position and apply force on the environment. Also, the aerial vehicle <NUM> can have compliance to handle collisions and impacts.

According to an embodiment, the aerial vehicle <NUM> further comprises at least three legs <NUM> allowing for support of the aerial vehicle <NUM> on any support such as the floor, said legs <NUM> forming in particular a tripod or a three-legged stand. In the embodiment shown in the figures (see <FIG> and <FIG>), three legs <NUM> are mounted to the central frame <NUM>, from the bottom face <NUM>, with a compliant (flexible) mount <NUM>, so as to be able to absorb harsh landings.

According to some embodiments of the invention, is therefore provided an aerial vehicle <NUM> that is capable of omnidirectional flight and that carries a manipulator which can exert forces and torques in all directions, including a compliant manipulator or even a passively compliant manipulator.

In some embodiments, the aerial vehicle <NUM> can furthermore continuously maintain a target within the sensor field of view or can follow a complex structure.

With an aerial vehicle <NUM> according to some embodiments of the invention, this improves the possibilities of control and planning for aerial robots and therefore elevates the versatility and relevance of aerial robots to many industrial and scientific applications.

In some cases of the prior art aerial vehicle, the presence of internal forces within the aerial vehicle reduces the efficiency of the aerial vehicle as a whole system. With an aerial vehicle <NUM> according to some embodiments of the invention, the configuration reduces or even deletes internal forces within the aerial vehicle.

Claim 1:
Aerial vehicle (<NUM>) comprising:
- a central frame (<NUM>)
- a tail extending from the central frame (<NUM>) along a first axis (X),-,
- at least two arms (<NUM>) extending from the central frame (<NUM>) and able to rotate around at least one second axis (Y), the angular position of the arm (<NUM>) with respect to the second axis (Y) defining an arm rotation angle (A1),
*wherein each arm (<NUM>) is equipped with two thrust motors (<NUM>) controlling the spinning in opposite direction of two coaxial rotors (<NUM>), and
* wherein the two coaxial rotors (<NUM>) define a double rotor axis (R) and can tilt together with respect to another tilting axis (T), said tilting axis (T) being perpendicular to the second axis (Y), the angular position of the double rotor (<NUM>) with respect to the double rotor axis (R) defining a double rotor tilting angle (A2),
wherein said tail (<NUM>) is equipped with a tail rotor (<NUM>) spinning around a tail rotor axis (P), said tail rotor axis (P) being parallel to a third (Z) axis which is orthogonal to both first axis (X) and second axis (Y), and in that said tail rotor (<NUM>) has either the ability to invert its direction of rotation or has a unique direction of rotation and two symmetric blades with opposite angle of attack, the angle of attack of said blades being changeable.