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EP-4058866-B1 - SYSTEMS AND METHOD OF CONTROLLING SELF-PROPELLED FLYING DEVICES

EP4058866B1EP 4058866 B1EP4058866 B1EP 4058866B1EP-4058866-B1

Inventors

  • O' SULLIVAN, Sean

Dates

Publication Date
20260506
Application Date
20201105

Claims (11)

  1. A method of controlling a self-propelled flying device (1) that seeks a target, the method comprising the steps of: obtaining (101) a desired arrival time for the device to reach the target; acquiring (104) the position of the target; calculating (105) a bias value; and adjusting (106) the direction of flight of the device towards the target for a period of time using the bias value to lengthen the path of the device to the target by adding curvature to the path so that the device takes a greater amount of time to travel to the target; wherein the bias value is calculated so that the device reaches the target at the desired arrival time; and characterised in that the step of calculating a bias value comprises: providing (201) an initial candidate for the bias value; estimating (202) an arrival time at the target using the initial candidate as the bias value; determining (203) a difference between the estimated arrival time and the desired arrival time; and setting (204) the initial candidate as the bias value when the difference is less than a threshold, otherwise, providing (205) a new candidate for the bias value close to the initial candidate and estimating (206) an arrival time at the target using the new candidate; using the estimated arrival times for the initial candidate and the new candidate to calculate the gradient of an error function (207), the error function being a function of the difference between the estimated arrival time and the desired arrival time; using the gradient with the Newton-Raphson method to determine a new initial candidate for the bias value (208), and then repeating the previous steps (202 onwards) using that new initial candidate.
  2. A method as claimed in claim 1, wherein the flight of the device (1) is controlled by adjusting the rate of change of the device's sightline to the target, and wherein the sightline rate is adjusted by the bias value.
  3. A method as claimed in claim 1, wherein the flight of the device (1) towards the target is adjusted by adjusting the position the device flies towards by the bias value.
  4. A method as claimed in any preceding claim, wherein the device (1) is arranged to seek the target using proportional navigation.
  5. A method as claimed in claim 4, wherein the device (1) is arranged to seek the target using generalised explicit guidance (GENEX).
  6. A method as claimed in any preceding claim, wherein the period of time during which the flight of the device (1) towards the target is adjusted by the bias value begins when the devices acquires the position of the target.
  7. A method as claimed in any preceding claim, wherein the period of time during which the flight of the device (1) towards the target is adjusted by the bias value ends when the device is a predetermined distance from the target.
  8. A method as claimed in any of claims 1 to 6, wherein the period of time during which the flight of the device (1) towards the target is adjusted by the bias value ends a predetermined length of time before the desired time to reach the target.
  9. A method as claimed in any preceding claim, wherein the device (1) is a missile.
  10. A self-propelled flying device (1) arranged to seek a target in accordance with any of the methods of claims 1 to 9.
  11. A computer program product arranged, when executed by a computer processor of a self-propelled flying device (1), controls the self-propelled flying device to seek a target in accordance with any of the methods of claims 1 to 9.

Description

Field of the Invention The present invention concerns methods of controlling self-propelled flying devices. More particularly, but not exclusively, the invention concerns controlling a self-propelled flying device that seeks a target so that it reaches the target at a desired arrival time. Background of the Invention It can be desirable to control the arrival time at which a self-propelled flying device, such as a missile, reaches its target. A key application is to control the arrival time of multiple missiles, so that they all reach the target at the same time, or at specified intervals, to maximise their effect. However, it can also be desirable to control the arrival time of a single missile or other self-propelled flying device. While the arrival time can be controlled simply by controlling the time at which a device is launched, unintended effects such as launch positions/time errors, environmental conditions and non-nominal device performance can cause significant inaccuracies in arrival time. It is common for self-propelled flying devices such as missiles to have a control based upon proportional navigation (PN). PN is a well-known guidance law that is based upon the fact that when a device is on a collision course with a target, the direct line-of-sight of the device to the target does not change direction as the device approaches the target. PN requires that the velocity vector of the device rotates at a rate proportional to, and in the same direction as, the line-of-sight. Proposed system to control the arrival time of a device that is controlled using PN have been considered, for example in Cooperative Guidance for Multimissile Salvo Attack, Zhao S et al, Chinese Journal of Aeronautics, December 2008; Robust Cooperative Guidance Law for Simultaneous Arrival, Li Z et al, IEEE Transactions on Control Systems Technology, May 2019; Distributed cooperative guidance for multiple missiles with fixed and switching communication topologies, Zhao Q et al, Chinese Journal of Aeronautics, August 2017; and Three-dimensional cooperative guidance laws against stationary and maneuvering targets, Zhao J et al, Chinese Journal of Aeronautics, August 2015. However, the problem is simplified to a two-dimensional system and/or using unrealistic assumptions such as that velocity is constant. Consequently, such proposals cannot be implemented in a real-life system. Another example is in A Three-Dimensional Cooperative Guidance Law of Multimissile System, Wei X et al, International Journal of Aerospace Engineering, September 2015, which uses an artificial neural network which is trained using machine learning. However, this solution is complicated, and the training time for the artificial neural network can be slow to obtain acceptable accuracy. A common aspect to all these proposed systems is that the arrival time is varied by adjusting the PN guidance coefficient. US 2013/092785 A1 is also a relevant prior art document with regard to the control of a missile. The present invention seeks to solve and/or mitigate some or all of the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide improved methods of controlling a self-propelled flying device and improved methods of controlling a plurality of self-propelled flying devices. Summary of the Invention In accordance with a first aspect of the invention there is provided a method of controlling a self-propelled flying device that seeks a target, the method comprising the steps of: obtaining a desired arrival time for the device to reach the target;acquiring the position of the target;calculating a bias value; andadjusting the direction of flight of the device towards the target for a period of time using the bias value; wherein the bias value is calculated so that the device reaches the target at the desired arrival time,and wherein the step of calculating a bias value comprises: providing an initial candidate for the bias value;estimating an arrival time at the target using the initial candidate as the bias value;determining a difference between the estimated arrival time and the desired arrival time; andsetting the initial candidate as the bias value when the difference is less than a threshold, otherwise, repeating the estimating the arrival time with a new candidate for the bias value and determining the bias value via the Newton-Raphson method. By having the flight of the device towards the target adjusted by a bias value, the path of the device to the target is lengthened, as the bias value effectively adds curvature to the path of the missile. The longer path takes the device a greater amount of time to travel. Thus, by selecting an appropriate bias value, the device can be made to reach the target at the desired arrival time. Advantageously, the flight of the device is controlled by adjusting the rate of change of the device's sightline to the target, and wherein the sightline rate is adjusted by the bias value. A device'