WO2014102437A1 - System for controlling rotary-wing unmanned aircraft for vertical landing on moving surfaces by feeding forward forces in the control system - Google Patents

Abstract

The invention relates to an improvement to the control system for landing a VTOL unmanned aircraft on a moving platform, comprising the addition of: a sensor-based control system, said sensors measuring the tension of the cable that connects the aircraft to the landing platform and the angles of orientation of said cable with respect to a system connected to the aircraft; and a control module that receives as input the tension — both in terms of magnitude and direction — obtained from the sensors, as well as the control settings generated by the aircraft controller. Based on the tension in the cable, the control module of the invention calculates corrections to be incorporated into the control settings, which anticipate the disruptions that will occur to the position of the aircraft as a consequence of the changes in the tension of the cable.

Description

 DESCRIPTION

Control system of unmanned rotary wing aircraft for vertical landing on mobile surfaces by pre-feeding forces in the control system.

OBJECT OF THE INVENTION The invention consists in an improvement of the control system for the landing of an unmanned VTOL aircraft on a mobile platform.

The sector of the technique to which the present invention is intended is aerospace, or for landing assistance devices

BACKGROUND IN THE STATE OF THE TECHNIQUE The operation of vertical take-off and landing aircraft from ships has several characteristics that make it a maneuver that is not without difficulties. In the case of unfavorable atmospheric or sea conditions, the problem is exacerbated due to the great disturbances that may occur in the position and attitude of both the aircraft and the landing platform. Various techniques are currently used to increase the safety of such maneuvers in manned aircraft. A solution that has proven to be effective is the use of a cable that connects the aircraft with the landing platform (US3801050, US2453851). Among these cable-based methods, the Beartrap system used by the Canadian navy and RAST used by the US military (US3303807) should be noted. Both are based on maintaining a constant tension in the cable that connects the helicopter with the platform by hydraulic means. The constant tension in the cable increases the stability of the platform-cable-helicopter system against possible disturbances induced by external agents - typically meteorological -, facilitating the work of the pilot during landing. Other systems (JP 5330493 A 19931214), in addition to maintaining constant tension in the cable, also measure the angle that the cable forms with the platform and the aircraft. The system in question consists of a controller whose objective is to keep the cable perpendicular to the aircraft and the platform in order to get it to land at the desired point. This system, however, only allows measuring the effect that possible disturbances have on the position of the aircraft once it has changed, it is not possible to predict this effect from the cause itself (a disturbing force). In addition, in the mentioned systems, only the control of the angle formed by the cable with the aircraft is carried out, the angle measures not being used to increase the accuracy of the relative positioning of the same with respect to the landing platform.

Other methods used to facilitate the maneuver are to stabilize the landing platform, so that its position and attitude is not affected by the movement of the ship. This is achieved by placing the landing surface on a Stewart platform - a platform whose position and attitude is controllable by means of actuators that allow its movement in the 6 possible degrees of freedom. In this regard, it is worth noting Cybaero's recent works aimed mainly at unmanned aircraft, such as the international patent WO 2009/091315 W1, and the thesis on the MALLS system: Mobile Automatic Launch and Landing Station for VTOL UAVs, Andreas Gising, Linkóping Universitet LITH-ISY-EX-08 / 4190— SE. EXPLANATION OF THE INVENTION

The invention consists in an improvement of the control system for the landing of an unmanned VTOL aircraft on a mobile platform. Starting from the method mentioned in the previous section consisting of the deployment of a cable between the aircraft and the platform, the improvement is based on the addition of a control system consisting of sensors, which measure the tension of the cable that joins the aircraft with the landing platform and the orientation angles of said cable with respect to a system associated with the aircraft, and a control module that takes as inputs the voltage - both in magnitude and in direction - obtained from the mentioned sensors, in addition to the control instructions generated by the aircraft controller. The control module object of the invention calculates, based on the tension in the cable, corrections to be introduced in the control instructions. These corrections allow to anticipate the disturbances that will immediately occur in the position of the aircraft as a result of changes in the cable tension. As in the methods mentioned in the study of the prior art, the cable is collected as the aircraft approaches the platform, said collection mechanism not being the object of this invention.

Additionally, the information on the orientation of the cable makes it possible to increase the accuracy of the estimation of the position of the aircraft in relation to the landing platform. Indeed, if the cable is short enough and its tension is high, we can assume that it takes the form of a straight line that connects the aircraft with the platform. In combination with other aircraft sensors, such as a precision altimeter, and inertial sensors that determine the attitude of the aircraft, the relative position of the aircraft can be estimated from its height and the angle it forms. the cable with the vertical. The relative position value obtained by this method can then be used to increase the accuracy of the position estimate provided by the rest of the aircraft's sensors. It should be noted the difference of this method with respect to those described in the prior art, in which the information provided by the angle sensors is only used as input of a control loop whose objective is to keep the cable perpendicular to the aircraft . In the proposed solution, however, angle measurements are used to increase the accuracy of the estimation of the position of the aircraft, said estimate being in turn used to control the position of the aircraft.

BRIEF DESCRIPTION OF THE FIGURES Figure 1. General view of the aircraft and platform in landing configuration.

An outline of the aircraft and the platform is shown during the landing maneuver. The cable that joins both elements during landing is also represented.

Figure 2. Diagram of the sensor system that allows measuring the angle and tension of the cable. A scheme of the system is shown that allows measuring the tension of the cable that joins the aircraft with the landing platform, as well as the angles that the cable forms with the aircraft.

Figure 3. Block diagram of the control system.

A block diagram of the automatic control system of the aircraft is shown. The diagram highlights the modules that are part of the invention and that improve the behavior of current automatic control systems.

Figure 4. Preferred embodiment representation

An overview of the preferred embodiment is shown. The aircraft are visible, as well as the device attached to it to which the cable connecting the aircraft with the landing platform is attached. The numbered elements in the figures are detailed below: Figure 1

 1 - Vertical landing aircraft

 2 - Cable clamping device in the aircraft

3 - Aircraft-platform junction cable

 4 - Cable clamping device to the platform

 5 - Landing platform

Figure 2

6 - Union zone with the base of the aircraft

 7 - Angle meter on axis 1

 8 - Angle meter on axis 2

 9 - Cable tension meter

 10 - Cable connecting the aircraft with the landing platform

Figure 3

 1 1 - Control 1

12 - Control 2

 13 - Pre-feeding

14 - Driver actuators

 15 - Aircraft

 16 - Estimator

Figure 4 17 - Angle meter A

18 - Angle meter B

19 - Piezoelectric sensor

EXAMPLE OF PREFERRED EMBODIMENT As an explanation of the "Control system of unmanned rotary wing aircraft for vertical landing on mobile surfaces by pre-feeding forces in the control system", Figure 3 shows the scheme of the automatic control system of an unmanned aircraft, to which the components object of the invention have been added, the latter being distinguished by being framed in the dashed box.

The following describes the traditional control system, as well as the operation of the modules object of the invention and how they contribute to improve the behavior of the traditional system.

As can be seen, the control system aims to set the position and attitude of the aircraft from the desired position and attitude P _d and the estimated position and attitude P. The control system represented consists of two nested control loops . The first control module 'Control 1' generates a force setpoint - in module F and direction ά - that the main rotor of the aircraft must exercise. The module F setpoint is used directly to act on the power control of the aircraft. On the other hand, the angle setpoints are the inputs of a second internal control module 'Control 2, which generates setpoints of force pairs T that must be applied to the rotor to orient its plane, based on the difference between the address setpoint φ _ά and the same measure φ.

In a traditional system, in which the modules object of the invention are not included, the instructions T directly feed the module identified as 'Drider actuators'. Said module generates the signals A necessary for the operation of the actuators, which could be, for example, signals modulated in pulse width. The effect of the application of these signals on the system is measured by on-board sensors, which may include, among others, gyroscopes, inertial sensors, satellite positioning. In Figure 3 the data provided by these sensors have been grouped under the nomenclature S. The 'Estimator' module is responsible for providing the P estimate of the position and attitude of the aircraft based on the sensor measurements, thus closing the control loop.

With the present invention, the exposed system is improved by adding an additional module 'Pre-feeding' for the calculation of the correction by pre-feeding, as well as by including the voltage and angle signals [H and _1; oc ₂ respectively) of the cable that connects the aircraft with the platform as new inputs of the 'Estimator' module. The voltage measurement is obtained from a sensor placed for that purpose on the part that connects the cable with the aircraft (element 9, Figure 3). Moreover, the measures of angles _{1; 2} are obtained from two angle sensors located perpendicularly (elements 7 and 8, Figure 3).

The signals H, ai and ₂ allow the pre-feed signal calculation module to generate a correction signal of the actuation signals T. The signals H, ai and ₂ are measurements of the voltage in module and angles in the cable that links the aircraft with the platform. Any disturbing force on the aircraft (such as that generated by a gust of wind) has an immediate effect on the tension in the cable, as well as a first-order effect on the speed of the aircraft and second order on the position, as described in Newton's 2- Law

F = M ^■ v = M ^■ x

Thus, by taking the voltage in the cable as input, the pre-feed correction calculation module can calculate a new corrected action setpoint T, anticipating the effect that the disturbing force will have on the position and attitude S of The aircraft.

Additionally, the measurement of the cable angle can be used to improve the estimation of the relative position between the aircraft and the platform, by sensory fusion with the rest of the position and attitude estimation sensors of the aircraft.

Thus, an example of embodiment of the invention is described below without said proposal of embodiment assuming the optimal option or limiting in any way the possibilities of realization thereof.

For this embodiment, the aerial platform is an unmanned helicopter to which a cardan joint has been incorporated into its base at whose end the cable connecting the aircraft to the platform. To measure the angles formed by the cable with the platform, there are two encoders, which could be optical or otherwise, to measure the angle of each joint of the cardan joint. There is also a force sensor for measuring the tension in the cable. As an exemplary embodiment, a piezoelectric sensor could be used. Figure 4 shows the previously described set, including the encoders (17, 18), as well as the force sensor (19).

The electrical signals provided by the aforementioned sensors are adapted by the electronics on board the aircraft and read by a microcontroller that converts them into digital format. The microcontroller provides the values of the angle and voltage signals to the aircraft control system, which runs on a computer on board it.

It is not considered necessary to make this description more extensive so that any person skilled in the art understands the scope of the invention and the advantages derived therefrom. The materials used, dimensions and joining procedures, including its fixing system on the user, will be subject to variation as long as this does not imply an alteration in the essentiality of the invention.

Claims

Control system of unmanned rotary wing aircraft for vertical landing on mobile surfaces by pre-feeding forces in the control system, characterized by the use of a cable that joins the aircraft with the landing platform and by the use of voltage measurements on said cable to correct the control instructions of the aircraft based on said measures. 2. Automatic aircraft control system according to claim 1, characterized by the use of both the module and angle measures of the tension in the cable that connects the aircraft with the landing platform for the correction of the setpoints of control. Automatic aircraft control system, according to claim 1 and 2, wherein the measurement of the angle formed by the cable with the aircraft is used to improve the estimation of the relative position between the aircraft and the landing platform, for the subsequent use of said estimate in the position control of the aircraft. Control system of unmanned rotary wing aircraft for vertical landing on mobile surfaces by pre-feeding forces in the control system according to claim 1, 2 and 3, characterized in that it incorporates a control system consisting of sensors, which measure the tension of the cable that joins the aircraft with the landing platform and the orientation angles of said cable with respect to a system associated with the aircraft; and also a control module that takes as inputs the voltage - both in magnitude and in direction - obtained from the indicated sensors, in addition to the control setpoints generated by the aircraft controller. The indicated control system calculates, based on the tension in the cable, corrections to be introduced in the control instructions. Control system of unmanned rotary wing aircraft for vertical landing on mobile surfaces by pre-feeding forces in the control system according to claims 1, 2, 3 and 4, characterized in that in combination with other sensors of the aircraft, as could be a precision altimeter, and the sensors inertials that determine the attitude of the aircraft, an estimate of the relative position of the aircraft is made through a data fusion algorithm, based on the height of the aircraft and the angle formed by the cable with the vertical. The relative position value obtained by this method is then used to increase the accuracy of the position estimate provided by the rest of the aircraft's sensors. Control system of unmanned rotary wing aircraft for vertical landing on mobile surfaces by pre-feeding forces in the control system according to claims 1, 2, 3, 4 and 5, characterized in that the control system, which fixes the position and aircraft attitude from the desired position and attitude Pd and the estimated position and attitude P, consists of two nested control loops. The first control module 'Control Γ (1 1) generates a force setpoint - in module F and direction φ _ά - which must be exercised by the main rotor of the aircraft. The module F setpoint is used directly to act on the power control of the aircraft. On the other hand, the angle setpoints are the inputs of a second internal control module 'Control 2' (12), which generates setpoints of force pairs T that must be applied on the rotor to orient its plane, starting from of the difference between the address setpoint φ _ά and the same measure φ. Control system of unmanned rotary wing aircraft for vertical landing on mobile surfaces by pre-feeding forces in the control system according to claims 1, 2, 3, 4, 5, 6 and 7, characterized by the addition of a module (13) for the calculation of the pre-feed correction. The signals the voltage signals and angles in the cable that connects the aircraft with the platform [H and to ₂ respectively) allow the pre-feed signal calculation module (1 3) to generate a correction signal of the actuation signals T that feed the actuators of the rotor of the aircraft. Control system of unmanned rotary wing aircraft for vertical landing on mobile surfaces by means of pre-feeding of forces in the control system according to claims 1, 2, 3, 4, 5, 6 and 7, characterized in that by taking as input the voltage in the cable, the pre-feed correction calculation module (1 3) can calculate a new corrected action setpoint Γ, anticipating the effect that will have a disturbing force on the position and attitude S of the aircraft (15).