Collision avoidance system

Abstract

A rotary wing drone communicates its altitude (determined by an onboard GPS receiver) and an air pressure (from multiple onboard barometers) to a ground station which has a known height above sea leve

Description

The present invention relates to a collision avoidance system, in particular a collision avoidance system suitable for use with drones. Background The use of drones, otherwise termed micro aerial vehicles, are becoming increasingly prevalent and exist in large numbers. It is therefore important, as with any aerial vehicle, to ensure that collisions between aerial vehicles are avoided. Collision avoidance of aerial vehicles is well established and includes visual guidance, which is generally not applicable to drones in the same sense as it is to conventional aircraft, and in particular not applicable to autonomous drones. Another mechanism of collision avoidance is the use of prearranged flightpaths and flight schedules. This is effective but drones are often required to go into areas which are not normally frequented by aerial vehicles, such as low altitudes and built-up areas. It therefore impractical to have an established flightpath and flight planning to the doorstep of every potential recipient of a drone delivery system, for example. Another mechanism for collision avoidance is the sharing of position information with a flight controller. Flight controllers provide direction and prioritisation to aerial vehicles but it is not practical to use human flight controllers for the number and density of drones, particularly the large numbers that are envisaged in built-up areas. Automatic flight controllers can be envisaged and for them to work effectively they need accurate input data. Drones are typically equipped with a form of global positioning system. These are well established, such as the GPSystems. These are GPS: Operated by the United States; GLONASS: Operated by Russia; Galileo: Operated by the European Union; BeiDou: Operated by China and regional systems such as: QZSS (Quasi-Zenith Satellite System): operated by Japan and NavIC (Navigation operated by India): Operated by India. Such systems provide position information in the form of latitude, longitude and altitude and may be used individually or in combination so as to provide a drone with accurate position information. The very systems offer position information in the order of US GPS (Global Positioning System): with the Standard Positioning Service (SPS) providing an accuracy of about 5-10 meters with the Augmented with WAAS (Wide Area Augmentation System) providing an accuracy of about 1-3 meters. GLONASS (Global Navigation Satellite System) providing an accuracy for the Standard Positioning providing an accuracy of about 5-10 meters and the Augmented system providing an accuracy of about 2-4 meters particularly when used in combination with GPS or other systems. Galileo provides an accuracy by means of the Open Service providing an accuracy of about 1 meter and the High Accuracy Service (HAS) providing an accuracy of predicted to provide an accuracy of about 20 centimetres. BeiDou (BDS) Satellite System providing an accuracy of about 2.5-5 meters and the Augmented Serviceproviding an accuracy of about 1-2 meters. As will be evident, given that a drone may have a typical dimension of less than 1m and a drop-off point, such as for delivery being a doorway with a width of around 1m, the need for higher accuracy remains. A further mechanism which can be used in conjunction with GPS systems is a Differential Global Positioning System. Differential Global Positioning System (DGPS) is an enhancement to the standard Global Positioning System (GPS) that provides improved location accuracy, from the 15-meters to about 1 meter to 10 cm in case of the best implementations. DGPS requires ground stations which provide reference points to enable a form of triangulation of aerial vehicle position between a satellite ground station and the aerial vehicle. Whilst the timescale at which the typically 24 satellites plus redundant satellites, can be deployed for any given system and the extensive cost is relatively long the provision of ground stations can be more quickly and economically implemented and this is a desirable route to improving navigation. Aerial vehicles, for example drones, can convey the position information for the purposes of air traffic control by means of communication such as Automatic Dependent Surveillance-Broadcast" (ADS-B) and variants thereof needs to be relied upon. This is because primary and secondary surveillance radar do not normally have the resolution or the coverage for providing accurate information regarding drones and similar micro aerial vehicles. Multi-lateration is another method and this uses multiple ground stations to detect signals from aircraft transponders. By measuring the time difference of arrival (TDOA) of these signals, the system can triangulate the position of the aircraft. ADS-B is a further method of reporting and as with the previous methods ultimately uses GPS (Global Positioning System) to determine an aircraft's precise position with ADS-B then broadcasting that information to ground stations and other aircraft equipped with ADS-B receivers. This and related systems allow air traffic controllers to have a more accurate and realtime view of aircraft positions, which enhances situational awareness and safety in the airspace. ADS-B is becoming a standard in modern air traffic management systems worldwide, as it provides improved efficiency, reduced separation standards, and more comprehensive traffic information for both pilots and controllers. One common factor will all of the above systems, particularly in the area urban environment is that with large buildings and transit of drones et cetera through what might be termed an urban canyon there are issues with reflected signals. Reflected signals deviate from line of sight and therefore the same signal may be received twice or a signal may take longer to arrive than it would otherwise and errors can arise. In addition, due to the issues, among others, of radio signal communication in such locations as the urban environment there can be situations where a drone cannot be readily in communication with a base station. There is therefore a need to manage this situation effectively so as to avoid collisions either between aerial vehicles between an aerial vehicle and other objects. This problem is particularly significant due to the relative proximity versus velocity of drones and therefore the need for a high level of real-time situational awareness of an anticollision system. In summary, because of the challenges due to the small size of drones and related mini, micro and nano aerial vehicles, their extra flexibility and potential flightpaths this provides there is an ever-extending need for greater accuracy of positioning to enable and facilitate navigation and collision avoidance of those aerial vehicles. The present invention The present invention in its various aspects is as set out in the appended claims. The present invention provides a method of determining the position of rotary wing drone the method comprising: a. providing a ground station , having a known height above sea level, and equipped with GPS positioning; b. providing a drone equipped with GPS positioning and further equipped with a plurality of pressure sensors in the form of barometers; c. communicating an altitude of the drone determined by GPS to the ground station; d. communicating the air pressure from the drone barometers to the ground station; wherein: d. The ground station is configured to augment the determined altitude of the drone by calculating: i) a difference in pressure between a local, ground station air pressure and the communicated air pressure of the drone barometers; ii) an equivalent difference in altitude from i); ii) a difference in communicated GPS altitude of the drone and the GPS altitude of the ground station; iii) an error between i) and iii) e) reporting the error for the purposes of reporting the altitude of the drone. A particular advantage of the present invention is that drones are kept aloft by means of rotary wings and therefore the barometric pressure, as a measure of altitude is unreliable. This is a known problem for rotary wing aircraft, such as helicopters where a barometric altimeter cannot be relied upon particularly at low altitudes these are typically supplemented by radar altimeters. The use of radar altimeters is currently prohibitive for drones and the emission of microwave radiation is undesirable particulars drones may typically fly over persons on a regular basis. In addition, the changes in local air pressure from the so-called down wash from a rotary wing can change very radically in a short period of time for a drone where is that from larger aircraft, such as a helicopter much more slowly and can be more readily accommodated. In the present invention the GPS of the drone may be a Differential GPS (DGPS) between the drone and the ground station. The use of GPS provides a more accurate measure of position and in particular regarding altitude. Altitude being a lesser accurate measure than latitude or longitude from GPS. In the present invention wherein the GPS position of the drone may be supplemented by the drone by a real-time kinematic (RTK) position measurement. This is particular, beneficial in situations where signal strength is low or absent for a period of time and the available GPS measurement may be historic. Given the velocity of a drone compared to typical separation distance this is particularly important. In the present invention a first one or more of the plurality of barometers is located at a level lower than the rotary wing and a second one or more of the plurality of barometers is located at a level above the rotary wing. This enables the differential pressure due to the effect of the rotary wing on the localised environment of the drone to be taken into account. Whilst this differential pressure is the pressure necessary to maintain the drone in flight and is therefore small compared to the overall atmospheric pressure the differences nevertheless significant in terms of the altitude of the drone, such as in particular when close to the ground. In particular, means such as LIDAR in height ranging, whilst feasible have the disadvantage that, in the urban environment the ground, certainly at the centimetre to metre range level is drastically uneven and therefore a measure of absolute height in terms of altitude is required as accurately as possible. In the present invention the communicating of the air pressure from the drone may be the communication of air pressure value intermediate between the first one or more of the plurality of barometers and the second one or more of a plurality of the barometers. The pressure intermediate between the two parameters provides the most accurate reading and may be calculated as a numerical average of the two readings. In the present invention the value intermediate may be calculated by means of a predetermined difference in air pressure between barometers of the drone in flight. By having a predetermined difference in air pressure recorded for the drone and is possible to more accurately determine local air pressure based upon the readings from the barometers and it is if a simple average calculation is carried out. In the present invention the predetermined difference is measured at a plurality of ambient barometric pressures and the intermediate value calculation is based upon the closest available data of the ambient barometric pressure. In particular the ground station air pressure itself may fluctuate, particularly in the urban environment where localised temperatures may vary and, with it, localised air pressure. In the present invention the predetermined difference may be adjusted depending upon whether the drone is elevating or descending at the time of drone air pressure measurement. For greatest accuracy the differential in air pressure due to the drone ascending or descending is taken into account. This may be taken into account using predetermined tables of values using a test setup of the drone prior to implementation and operation with the invention. A further problem which requires addressing is that during transit a drone may lose radio communication with the ground station. This is for example particularly prevalent in urban areas such as in urban canyons where areas of dead space may be found in radio communication. This is addressed by the present invention by providing in addition to or as an alternative to the aforementioned method, a method of determining the position of rotary wing drone the method comprising: a. providing a second drone with a known location, having a known height above sea level, and equipped with GPS positioning; b. providing a drone equipped with GPS positioning and further equipped with a plurality of pressure sensors in the form of barometers; c. communicating an altitude of the drone determined by GPS to the second drone; d. communicating the air pressure from the drone barometers to the second drone; wherein: d. The second drone is configured to augment the determined altitude of the drone by calculating: i) a difference in pressure between a local, ground station air pressure and the communicated air pressure of the drone barometers; ii) an equivalent difference in altitude from i); ii) a difference in communicated GPS altitude of the drone and the GPS altitude of the second drone; iii) an error between i) and iii) e) reporting the error for the purposes of reporting the altitude of the drone. In a preferred embodiment of the present invention there is provided an anticollision system wherein a system of is provided configured to operate the method of the invention as previously described. The anticollision system is preferably a tactical anticollision system, i.e. a system operating in real time to provide active direction to aerial vehicles, including drones to avoid collision. The anticollision system provides computing means, such as located at the ground station wherein the altitude determined according to the previous method or methods is communicated between any two of: the drone; any second drone and the ground station. Wherein when the altitude so determined is within a preset distance and the vertical axis a collision avoidance algorithm is operated. At algorithm then expends the further time in processing power necessary to determine if the latitude and longitude of the first and second drone in proximity and if within a predetermined proximity an instruction to either the drone or the second drone to alter course is provided by the ground station. This is particularly beneficial as processing power and time required the determination of latitude and longitude is only carried out after the altitude has been determined to be relevant. This makes the processing more suitable to be carried out in a drone which typically has lower processing power available on any ground station. It also speeds up processing which is significant given the speed to separation ratio of drones in flight were milliseconds can represent several metres of movement at separations themselves in the order of metres. The method and methods of the present invention are preferably carried out in real time. This again emphasises the importance of optimising processing time since whilst relatively speaking the velocity of drones is aerial vehicles is relatively low the proximity is extremely close and therefore response times and their optimisation are crucial. The problem is arising due to the relative proximity versus velocity of drones and therefore the need for a high level of real-time situational awareness of an anticollision system. Whilst recreational drones may have speeds in the range of 5 to 10 m / s commercial drones may have typical speeds of 15 to 30 m / s, racing drones are 40 to 50 m / s and military drones may reach speeds over 50 m / s. Given that the separation of drones may be in the order of metres which could mean 20 ms to cover 1 m. Given that the inertia of an aerial vehicle also needs to be considered along with the power available to reorient orientate the flight trajectory then this provides a very short time indeed in which calculations need to be undertaken. The situation is even more important that a GPS receiver, even one which has recent information about its position, time, and satellite information (ephemeris and almanac data are up-to-date). The time to fix position, TTFF, is usually in the order of 1-5 seconds. Therefore, even a commercial drone can reasonably travel 100 m and high-performance drones up to 250 m and the time necessary to obtain a GPS reading. The time required to find a differential GPS reading is even longer. The present invention therefore addresses these issues regarding anticollision by providing a system which obtains the relevant altitude data by means of the method of the present invention and disputes that data and act upon it so as to avoid a predicted collision. In the present invention the information communicated between a drone in the ground station, ground station and a drone and between drones will typically be accompanied by identification information to identify the source of the information. This may be considered as a remote ID and may for example be in the form of an ADS-B signal. This may be achieved using a remote ID broadcast module which may convey information, particularly send information by means of a radiofrequency signal, such as Wi-Fi or Bluetooth. In the present invention the word drone is used to encapsulate mini, micro and nano aerial vehicles as a general class of vehicle. The following definitions are provided: Mini aerial vehicles are small unmanned aircraft with dimensions typically ranging from several centimetres to a few meters in length or wingspan. They are larger than micro and nano UAVs but smaller than traditional manned aircraft or larger drones. The term drone is mostly colloquially used for such mini aerial vehicles. The lateral dimensions of such vehicles normally less than 1 m. Micro aerial vehicles (MAVs) are very small unmanned aircraft characterized by their miniature size and lightweight construction. They are smaller than mini UAVs and often resemble insects or small birds in appearance. The lateral dimensions of such vehicles are normally less than 30cm. Nano aerial vehicles (NAVs), also known as micro aerial vehicles (pAVs), are the smallest category of unmanned aircraft, characterized by their extremely tiny size, often resembling insects or small birds. The lateral dimensions of such vehicles are normally less than 10 cm.

Claims

1. A method of determining the position of rotary wing drone the method comprising:a. providing a ground station, having a known height above sea level, and equipped with GPS positioning;b. providing a drone equipped with GPS positioning and further equipped with a plurality of pressure sensors in the form of barometers;c. communicating an altitude of the drone determined by the drone GPS to the ground station;d. communicating air pressures from the drone barometers to the ground station;wherein:d. the ground station is configured to augment the GPS determined altitude of the drone by calculating:i) a difference in pressure between a local, ground station air pressure and the communicated air pressures of the drone barometers;ii) an equivalent difference in altitude from i);ii) a difference in communicated GPS altitude of the drone and the GPS altitude of the ground station;iii) an error between i) and iii)e) reporting the error and optionally utilising the error to provide a corrected altitude of the drone.

2. The method of claim 1 wherein the GPS of the drone is a Differential GPS (DGPS) altitude between the drone and the ground station.

3. The method of claim 2 or claim 3 wherein the GPS altitude of the drone is supplemented by a real-time kinematic (RTK) position measurement.

4. The method of claim 1 or claim 2 wherein:a first one or more of the plurality of barometers is located at a level lower than the rotary wing and a second one or more of the plurality of barometers is located at a level above the rotary wing.

5. The method of any of claims 1 to 3 wherein the communicating of the air pressure from the drone is the communication of air pressure value intermediate between the first one or more of the plurality of barometers and the second one or more of a plurality of the barometers.

6. The method of claim 5 were in the value intermediate is calculated by means of a predetermined difference in air pressure between barometers of the drone in flight.

7. The method of claim 6 were in the predetermined difference is measured at a plurality of ambient barometric pressures and the intermediate value calculation is based upon the closest available data of the ambient barometric pressure.

8. The method of claim or claim 7 wherein the predetermined difference is adjusted depending upon whether the drone is elevating or descending at the time of drone air pressure measurement.

9. The method of any of claims 1 to 8 wherein the method further comprises a second drone in communication with the first drone and the ground station and configured to relay altitude information obtained from the first drone to the ground station.

10. The method of any preceding claim configured to carry out the determination of altitude in real time.

11. Atactical collision avoidance system comprising a ground station configured to carry out the ground station method steps method of any preceding claim.

12. The tactical collision avoidance system of claim 11 further comprising the drone and optionally a second drone, of the method of any preceding claim.

13. The tactical collision avoidance system of claim 11 or claim 12 wherein the system determines a proximity of the drone in comparison to an independent object and upon the altitude being within a predetermined vertical distance between the drone and the object the ground station carries out actions leading to issuing an instruction to the drone to change its course.

14. The tactical collision avoidance system of claim 13 wherein said actions include a subsequent determination of latitude and longitude in the determination of a drone to independent object distance being within a predetermined separation before issuing said instruction.10