Patent Description:
The primary field of the present invention is a two degrees of freedom (DoF) actuator.

More specifically, the present invention concerns the field of such actuators used in different applications. In the present description, the main illustrative examples and embodiments will relate to applications in the field of aircrafts such as helicopters and drones but this should not be regarded as limiting as regards the teaching of the present invention as will be discussed in detail in the present application.

More specifically, embodiments of the present invention concern a two degrees of freedom actuator for example for multi-bladed rotor of an aircraft with at least two blades that are driven in rotation about a main rotation axis by primary actuator, and a secondary actuator that is arranged to rotate each of said blades about the respective blades' longitudinal axis, with a synchronization means that is operatively arranged for driving the secondary actuator based on an azimuth of the rotor about the main axis for obtaining a predetermined cyclic pitch of a given amplitude for each blade depending on the azimuth of the rotor.

Quadrotor helicopter systems, or other multirotor systems including a plurality of coplanar rotary wings are known to be very agile, simple, and reliable. They are, however aerodynamically inefficient once downscaled, thereby substantially reducing flight time.

Another class of rotary-wing aircraft includes the so-called coaxial helicopters, that are compact, and downscale efficiently, preserving flight time.

Conventional full scale helicopters use complex swashplate mechanisms to achieve cyclic and collective blade pitch control. However, swashplate mechanisms are difficult to miniaturize as they become fragile, maintenance intensive and unreliable. Accordingly, they cannot be applied efficiently, for example to build small scale helicopters or drones and other similar flying machines.

<CIT> describes a variable-pitch propeller with two coaxial electric motors driving two drive gears, which are arranged on the axis. This system acts collectively on the propeller blades.

<CIT> describes a propeller system with electronically controlled cyclic and collective pitch control, using a plurality of electromagnets positioned in a ring adjacent the rotor's hub.

<CIT> describes a passive rotor control mechanism for micro air vehicles. The behavior and benefits of traditional cyclic control in one rotor may be implemented with a simple under-actuated passive mechanism. An air vehicle employing the disclosed technology maintains lifting thrust by regulating the average rotor speed and generates control moments through coordinated pulsing of the motor torque.

The documents <CIT> and <CIT> describe tilting mechanisms adapted to tilt the blades of a propeller.

The document <CIT> describes an arrangement related to contra-rotating propellers.

An aim of the present invention is to improve the known actuation systems and methods.

A further aim of the present invention is to provide a system that is simple and allow an efficient miniaturization, for example in applications related to flying machines such as drones.

A further aim of the present invention is to combine the advantages of known quadrotor systems and conventional helicopters by using a simple system to achieve cyclic blade pitch control.

Another object of the present invention is a system for varying the pitch angle of the blades of a propeller during rotation.

Another object of the present invention is a system for varying the pitch angle of a plurality of blades of a propeller cyclically.

Another object of the present invention is a system for varying the pitch angle of a plurality of blades of a propeller cyclically not necessarily in a sinusoidal manner.

Another object of the present invention is a system for varying the pitch angle of a plurality of blades of a propeller cyclically without any swash-plate or complex mechanics.

Another object of the present invention is an electronic control system for simultaneously varying the pitch of a plurality of blades of a propeller cyclically.

Another object of the present invention is a steering and propulsion system for precision steering of an aircraft in six degrees of freedom (DoF).

Another object of the present invention is a rotary wing aircraft, for example a helicopter or an aerial drone capable of decoupling vehicle rotational motion from translational motion. Of course, the present invention is not limited to these applications and to models.

According to the invention, these and other aims are achieved by means of non-limiting embodiments of the invention described herein, illustrated in the figures and as defined in the appended claims.

In an embodiment, the invention concerns a two-degree of freedom actuator as defined in appended claim <NUM>.

The invention also concerns a method of controlling an aircraft as defined in claim <NUM>.

Dependent claims define preferred embodiments.

In an embodiment, the present invention stems from the preferred synergistic combination of several elements:.

In conventional helicopters, the propulsion is ensured with a main rotor, while the steering is done with a swashplate and a tail rotor. The swashplate has typically two main functions: collective blade- pitch-control for the up and down movements of the vehicle (helicopter) and cyclic blade-pitch-control for the forward or back movement of the helicopter. In embodiments, the present invention presents a swashplate-less system, based on the separation of the cyclic and the collective controls. The cyclic control is implemented thanks to the use of a two degrees-of-freedom actuator, while the collective control is simply and preferably achieved by accelerating or decelerating the rotor.

<FIG> illustrate the principle of a possible embodiment of the cyclic propeller control system. The system comprises a main motor (<NUM>), typically an electric motor, which drives the shaft <NUM> to spin (motion A) the rotor comprising the blades <NUM> and <NUM> and the rotor-attached parts: namely a magnet <NUM>, mechanical parts <NUM> and <NUM>, and shaft <NUM>.

A secondary actuator comprising the axially wounded air-cored coil <NUM> and the magnet <NUM> control the tilting of the blades (motion B). The part <NUM> is fixed to the shaft <NUM>. The magnet <NUM> is fixed to the part <NUM>. Part <NUM> can tilt relatively to part <NUM> around the longitudinal axis of shaft <NUM>. The parts <NUM> and <NUM> can rotate about a main axis ("motion A"), essentially vertical and tilting about a secondary axis, essentially orthogonal to the main axis ("motion B"). <FIG> illustrate section views of the system shown in <FIG>. Part <NUM> represents a Printed Circuit Board ("PCB") that comprises sensors <NUM> and <NUM> which allow to detect the angular position of the shaft <NUM> ("azimuth"). The part <NUM> is a mechanical support to the coil <NUM>.

Preferably, the main motor <NUM> spins the rotor about a main axis, essentially vertical (motion A). The blades are driven by the secondary actuator in such a manner that they rotate simultaneously and in the same direction about a transversal axis (motion B), essentially orthogonal to the main axis. The desired cyclic pitch (for example sinusoidal) can be obtained by a suitable control of the secondary actuator dependent on the azimuth (angular position) of the rotor (shaft <NUM>) around the main axis, for example detected by sensors <NUM>/<NUM>. By an appropriate current injection in the coil <NUM> and the resulting magnetic field, the magnet <NUM> which is diametrically-magnetized will be driven (i.e. tilted) to transmit a tilting motion to the parts <NUM> around the axis of shaft 107and thus produce the pitch/motion B to the blades. This tilting motion is possible notably via the bearings <NUM>' placed between shaft <NUM> and part <NUM>. This construction gives a maximum torque through push-pull effect on the pitch rotation of the magnet <NUM> which is transmitted to the blades <NUM>, <NUM>.

A combination of typically magnetic, optical, or similar sensors <NUM>, <NUM> may be used to detect the rotation of the main motor in order to command the secondary actuator to act (tilt) at the right azimuth and with the right amplitude. The combination of sensors is also used to detect the tilt angle of the blades.

Preferably, at every rotor revolution, , the cyclic blade pitch control algorithm ("CPCA") energizes the coil at the azimuth and with the amplitude commanded by the ADA drone stabilization algorithm ("ADAA"). The generated coil's magnetic field will cause the diametrically-magnetized magnet to tilt around the longitudinal axis of the shaft <NUM>, trying to align its magnetic field with the magnetic field of the coil.

As an example, exactly half a rotor revolution later, the CPCA algorithm energizes the coil in the opposite direction by inverting the current. This way, the magnet will, in every rotor revolution tilt at the commanded: azimuth, direction and amplitude.

There exist several configurations of helicopters and drones, ranging from single rotor, tandem rotors, quadrotors and multi-rotors in general. The present invention combines two cyclic propeller control (CPC) systems in a <NUM> DoF propulsion and steering system. The two CPC systems are laid out head to tail ("tête-bêche") in an embodiment illustrated in <FIG>.

<FIG> illustrates a possible embodiment of a system <NUM> for propulsion and steering of an aerial drone in <NUM> DoF. It combines two cyclic propeller control (CPC) systems <NUM> as illustrated in <FIG> with blades <NUM>, <NUM>, motors <NUM> which rotate the shaft <NUM> (<FIG>) and some structural elements <NUM> and <NUM>, such as support plates (for example in metal, plastic or carbon, or a mix therefrom). This forms a unit that can be used in an aerial vehicle such as a drone as illustrated in the next <FIG>.

The Aerial Drone Aircraft (ADA) <NUM> comprises at least one (SPS) system <NUM> as disclosed above in <FIG>, mechanically linked to an external ring <NUM>, as illustrated in <FIG> as an exemplary embodiment. The ring <NUM> is not only protecting the blades <NUM>, <NUM>, but serves also as a support for various components like a camera, a battery and several sensors, or other elements as desired as will be described later in the present specification. A battery (such as a rechargeable battery) is identified by reference <NUM>, and placed in the middle of the system <NUM> (<FIG> shows the system <NUM> without the battery <NUM>).

In a conventional rotary wing aircraft, rotation and translation motions are inherently coupled. In fact, when the vehicle pitches or rolls, it causes the vehicle to translate in longitudinal or lateral directions. In some applications this coupling might be undesirable. In order to avoid this coupling, the aircraft (ADA) according to the present invention is constructed in a way to achieve roll or pitch without necessarily a translation. This is obtained through the combination of the head to tail ("tête-bêche") layout of the SPS system of <FIG>/<FIG> and the central positioning of the aerial drone center of gravity between the two CPC systems forming the system <NUM> and by using appropriate sensors and control algorithms. This way, the horizontal components of the thrust forces compensate each other and the system remains on the spot despite the tilt motion. The motion of the ADA <NUM> is controlled through an appropriate control algorithm. This provides the unique ability of setting at will and controlling the attitude of the aircraft while hovering on the spot.

<FIG> illustrates the Aerial Drone Aircraft (ADA) in a possible embodiment. Parts <NUM> are structural elements such as tubes, for example to link the external ring <NUM> to the plates <NUM>/<NUM> (see <FIG>). Part <NUM> is a structural element protecting the propellers <NUM>, <NUM> from colliding with humans or objects. Part <NUM> is typically made out of foam or carbon as an example.

<FIG> is a schematic representation of the free force diagram of the SPS and ADA systems. The vertical components of the two thrust forces compensate the weight, while the horizontal components of the two thrust forces compensate each other. Using an appropriate control system, the tilt on the spot of the SPS and ADA systems is achieved.

<FIG> and <FIG> illustrate another embodiment of a system for propulsion and steering (SPS) <NUM>. This system is basically similar to the one described previously and comprises the same features as described in reference to <FIG>. The one difference with respect to the embodiment of <FIG> is that the shafts <NUM> of each unit are placed coaxially. This brings a very compact construction.

A frame holds the motors <NUM> in position, the frame comprising mainly four pillars <NUM>, and two crosses <NUM> at each end to build a stable structure. The crosses <NUM> also hold the PCBs <NUM> used for the control of the motors and the tilting system of the present invention.

At the end of the pillars <NUM>, there are four apertures <NUM> that will be explained later.

<FIG> illustrates the same embodiment as <FIG>, but with a battery <NUM> which is inserted in the middle of the structure and held by appropriate means, for example clip <NUM> (one being on the other side of the battery <NUM> and not visible in <FIG>). Appropriate connecting means are of course provided so that introduction of the battery allows the energy of the battery <NUM> to be brought to the motors <NUM> and tilting system.

<FIG> illustrates another embodiment of an aerial drone aircraft <NUM> according to the present invention. This drone <NUM> comprises the SPS <NUM> of <FIG> and <FIG> which is held by tubes <NUM> in a ring <NUM>. Both ends of the tubes <NUM> are attached to the ring and the SPS <NUM> is fixed on the tubes via the apertures <NUM> which are used to clamp the tubes, once the SPS <NUM> is at the proper position in the ring <NUM>. This principle is of course applicable to the structure illustrated in <FIG> as well.

The ring may be made with synthetic / plastic materials, foam, carbon fibers and/or a mix therefrom. In one embodiment, the ring may comprise reinforcing means, for example a carbon ring.

The embodiment of <FIG> also comprises an optical camera <NUM>, a thermal camera <NUM> with are shielded by protections <NUM>. Of course, only one camera may be used and these means are applicable to all embodiments disclosed herein.

<FIG> illustrates the ADA <NUM> of <FIG> seen from the bottom.

<FIG> illustrates another embodiment of an ADA. For example, this may be the ADA <NUM> of <FIG> and <FIG>, on which a grid or wire mesh <NUM> has been added for protection purposes. This grid may also participate to the rigidity of the ADA. Of course, such a grid <NUM> may be used in the ADA of <FIG> and other embodiments not specifically illustrated herein but falling within the scope of the present specification.

The exemplary embodiments in a drone system (ADA) presented above and herein may be used in, but not limited to applications like: aerial photography, inspection, payload delivery, surveillance, aerial filming, mapping, entertainment. Unlike many other existing aircraft, the tilt on the spot feature removes the need for attaching a gimbal system when a camera or a payload is used.

As is usual in the field, particular of drones but not limited thereto, the aircraft may be remote controlled, for example by a user. Accordingly, a remote control system (<NUM>, see <FIG>) and capabilities may be provided in an embodiment of the invention, with appropriate antennas/transmission means (used for remote control and/or data transmission, <NUM>, <NUM> see <FIG>), remote control unit (<NUM>), remote vision and/or Virtual reality (VR) for example using parts/sensors of the device on which the actuator according to the invention is mounted, GPS capabilities to guide the device (such as an aircraft) to a desired position (as an aim, or for a safe landing or emergency landing), distance evaluation means (such as optical sensors or distance sensors) may be provided on the device to avoid collisions with obstacles. Also patterns may be stored in the system to define a predetermined functioning of the actuator. In the case of the application to an aircraft, a pattern could be a predetermined flight to reach a certain point, the pattern following a route determined (for example) by GPS coordinates which are then transformed into automatic or semi-automatic flight controls of the aircraft.

Although not specifically, described, it is clear for a skilled person that the present invention comprises electronic means, such as a chip (or IC, such as <NUM>, <NUM>) for example, in which the necessary programs/codes/routines are stored and/or accessible via radio/remote command as appropriate for proper monitoring and control. Other electronic parts such as wires, energy sources, antenna <NUM>, <NUM> etc. are also present as necessary to operate the system of the invention, notably as a remote controlled object, all being within the scope of the present specification and invention.

Preferably, the parts of the system described herein are made in material that are light and rigid. For example, the parts forming the actuator <NUM>, <NUM>-<NUM>, <NUM>, <NUM>, <NUM> or the supports <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> are made of metal (for example aluminum or another light metal/material), the blades <NUM>, <NUM>, protections <NUM>, <NUM>, <NUM> are made of synthetic materials as non-limiting examples. Carbon may also be used alone or in combination with other materials for any part of the system, as appropriate.

There are several control algorithms needed to ensure a good operation of the ADA drone. The main ones are: Cyclic blade pitch control (CPCA) at the right azimuth; ADA drone <NUM> DoF stabilization (ADAA); Tilt on the spot control algorithm (TOSA).

The Cyclic blade pitch control algorithm (CPCA) executes the following steps:.

Of course, other control algorithms may be used in embodiments of the invention, depending on the application of the actuator described herein. Also the signal energizing the coil <NUM> may be a sinusoidal signal or it may have another shape which is not sinusoidal or it may by symmetrical or non-symmetrical or a combination thereof.

The embodiments and features of the present invention are given as illustrative examples and should not be construed in a limiting manner. The principle of the present invention may be applied to any vehicle, in particular aerial vehicles such as drones, helicopter or the like aircrafts, with no size limitation.

Also, the main examples and embodiments given herein relate to drones and flying aircrafts but the present invention is not limited to this application. The principles of a two degree of freedom actuator or support according to the present invention may be used in other applications such as a support for a functionalized head such as cameras and other similar devices, for a laser and laser head, for a mirror, for a cutting head (for example jet cutting head), for a painting head, for optical or illumination means etc. <FIG> and <FIG> illustrate the principle of a device with a functionalized head <NUM> able to carry out the functions listed above as application examples. The actuator is the one described herein and as illustrated in <FIG> and the blades <NUM>, <NUM> are replaced by the desired functionalized head <NUM>. The description above thus applies correspondingly to this embodiment. Head <NUM> may be the functionalized head per se or a support for the head.

Claim 1:
A two-degree of freedom actuator, for example for a two-bladed rotor of an aircraft, said actuator comprising :
- a motor (<NUM>) adapted to drive a primary shaft (<NUM>) around a primary axis (A),
- a secondary shaft (<NUM>) oriented along a secondary axis (B) perpendicular to said primary axis (A),
- an axially wound air-cored coil (<NUM>) which is fixed on a mechanical support (<NUM>),
- wherein said secondary shaft (<NUM>) is pivotally coupled to said primary shaft (<NUM>) by means of a first mechanical part (<NUM>) and a second mechanical part (<NUM>) wherein the second mechanical part (<NUM>) is fixed to the primary shaft (<NUM>) and the first mechanical part (<NUM>) is fixed to said secondary shaft (<NUM>) and arranged so as to tilt relatively to said second mechanical part (<NUM>), and
- the actuator further comprising a magnet (<NUM>), said magnet being attached to said first mechanical part (<NUM>) so that said first mechanical part (<NUM>) and said magnet (<NUM>) can rotate about said primary axis (A) and tilt about said secondary axis (B), wherein said magnet rotates in said axially wounded air-cored coil (<NUM>),
- characterized in that
- bearings (<NUM>') are arranged between said second shaft (<NUM>) and said second mechanical part (<NUM>),
- the magnet (<NUM>) has a cylindrical wall facing an inner surface of said axially wound air-cored coil and is diametrically magnetized, the position of the secondary rotating parts about the secondary axis (B) being set by the magnetic field of the coil.