Multidirectional airflow sensor

Abstract

An airflow sensor unit 1 for an aerial vehicle (50, figure 2A) The airflow sensor unit comprises a housing 80, with a plurality of openings 30-35 defined in the housing. Each opening faces in a differ

Description

[0002] Unmanned Aerial Vehicles (UAVs) are powered aerial vehicles that do not carry a human operator. UAVs may be autonomous or piloted remotely. Types of UAVs include multicopters, fixed-wing aircraft, or Vertical Take-Off and Landing (VTOL) vehicles.

[0003] A UAV may comprise sensors configured to determine parameters relating to the flight of the UAV. Parameters relating to flight may include, for example, the air speed of the UAV, the velocity of the UAV, the position of the UAV, etc.

[0004] For example, a UAV may comprise one or more accelerometers. An accelerometer may be configured to measure the acceleration of the UAV. While accelerometers are useful for detecting changes in velocity, they do not provide direct measurements of airspeed (or the direction of airflow over / around the UAV). Measurements of acceleration of the UAV may be integrated with respect to time to provide an estimate of a geospatial position of the UAV. However, when acceleration data is used to in this way, errors in the acceleration data are compounded over time, which means that the determined geospatial position quickly becomes inaccurate.

[0005] A UAV may comprise a pitot tube. Pitot tubes are configured to measure a differential pressure, i.e. a difference between a total pressure and a static pressure. The total pressure (which may also be referred to as a stagnation pressure) is dependent on the speed of the air arriving at an entrance to the pitot tube. Thus, from the differential pressure measured by the pitot tube, an estimate for the airspeed of a UAV may be determined.

[0006] Pitot tubes suffer from a number of disadvantages. For example, to provide an accurate measurement of the airspeed of an aerial vehicle, a pitot tube must be aligned with the direction in which air flows towards the UAV (from the reference-point of the UAV). In reality, the direction in which air flows towards the UAV may not be perfectly aligned with the pitot tube. This is especially the case for copter-type UAVs. Further, pitot tubes provide no information regarding the direction of airflow over / around the UAV. Further, pitot tubes do not account for changes in air pressure and temperature, leading to inaccuracies in varying atmospheric conditions. Further, pitot tubes can become blocked by debris or ice, and thus unable to provide any indication of airspeed. Further, classic pitot tubes are unsuitable for use on copter-type UAVs due to the effect of turbulent flow from the rotors. Generally, implementing air speed sensors on copter-type UAVs poses significant challenges due to the turbulent airflow generated by the motors and propellers.

[0007]

[0008] A UAV may comprise a satellite navigation system. Satellite navigation systems, such as GPS (global positioning system), can provide data relating to the position and velocity of the UAV. However, the data provided by the satellite navigation systems may be compromised by signal loss, interference, or jamming. Further, satellite navigation systems are unable to provide information about local airflow conditions (i.e. the speed and direction of air flowing over / around the UAV). Knowledge of local airflow conditions is critical for precise navigation and control of UAV.

[0009] A navigation system of a UAV may utilise the output of a satellite navigation system and / or the output of one or more sensors for the navigation and control of the UAV. However, due to the drawbacks of satellite navigation systems and conventional sensors, navigation and control of a UAV in this way may be ineffective. SUMMARY OF THE INVENTION

[0010] An object of the present invention is to provide an improved airflow sensor unit for use in aerial vehicles. One particular object of the present invention is to provide an airflow sensor unit which outputs data which allows a navigation system of a UAV to operate more accurately.

[0011] According to an aspect of the present invention, there is provided an airflow sensor unit for an aerial vehicle, the airflow sensor unit comprising: a housing; a plurality of sensor arrangements; a plurality of openings defined in the housing; and a plurality of conduits. Each conduit connects a sensor arrangement with a corresponding opening. Each sensor arrangement is configured to measure a pressure within the conduit which connects the sensor arrangement with the corresponding opening. Further, each opening faces in a different direction to the other openings.

[0012] According to another aspect of the present invention, there is provided an aerial vehicle comprising the airflow sensor unit described above.

[0013] In the airflow sensor unit described above, each of the sensor arrangements may be able to measure the stagnation pressure (and therefore velocity) of airflow arriving at the airflow sensor unit from a given direction. Because each opening faces in a different direction to the other openings, each sensor arrangement may be able to measure the stagnation pressure of airflow arriving at the airflow sensor unit in a different direction to that measured by the other sensor arrangements. Thus, the sensor unit is able to measure the airspeed in multiple directions / orientations. By measuring the airspeed in multiple directions / orientations, an overall direction of the airflow arriving at the airflow sensor unit can be determined.

[0014] In preferred embodiments, each sensor arrangement of the airflow sensor unit comprises a piezoelectric pressure sensor configured to measure the total pressure within one of the conduits. Thus, there may be a plurality of piezoelectric sensors, each arranged and configured to measure a total pressure associated with a different direction. Use of a plurality of piezoelectric pressure sensors in this way (e.g. as opposed to arrangements comprising a plurality of pitot-static tubes) eliminates moving parts and the need for complex conduit geometries. Moreover, the use of piezoelectric sensors improves the speed of at which the airflow sensor unit is able to respond to dynamic pressure changes. This is especially the case under turbulent or low-speed conditions.

[0015] Ideally, each sensor arrangement of the airflow sensor unit comprises a piezoelectric pressure sensor configured to measure total pressure within one of the conduits, and the airflow sensor unit further comprises a reference pressure sensor configured to measure local static pressure. By integrating multiple piezoelectric sensors with a dedicated static pressure sensor, the airflow sensor unit enables the extraction of highly accurate dynamic pressure data.

[0016] According to another aspect of the present invention, there is provided a method of determining a geospatial position of an aerial vehicle. The method comprises receiving, from a sensor unit, pressure data recorded by a plurality of sensor arrangements of a sensor unit, wherein each sensor arrangement is associated with a different direction. The method further comprises determining a geospatial position of the aerial vehicle using the pressure data received from the sensor unit.

[0017] By using the pressure data (which is recorded by a plurality of different sensors arrangements associated with different directions), the geospatial vehicle of the aerial vehicle can be more accurately determined (compared to, for example, the case where only accelerometers or satellite navigation systems are used).

[0018] Further advantages of the present invention will become apparent from the Detailed Description below. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which corresponding reference symbols indicate corresponding parts. Figure 1A depicts a top view of an airflow sensor unit in accordance with an embodiment. Figure IB depicts a bottom view of an airflow sensor unit in accordance with an embodiment. Figure 2A depicts a side view of an airflow sensor unit mounted on a UAV. Figure 2B depicts an airflow sensor unit mounted on a UAV from the opposite side to that depicted in Figure 2A. Figure 3 depicts a plot of pressure data obtained from a plurality of sensors of the airflow sensor unit. Figure 4 depicts a functional block diagram for the airflow sensor unit. Figure 5 depicts a data processing flow for determining a velocity vector. Figure 6 depicts a mechanical filter covering an orifice. Figure 7 depicts the arrangement of a conduit.

[0020] The features shown in the Figures are not necessarily to scale, and the size and / or arrangement depicted is not limiting. It will be understood that the Figures include optional features which may not be essential to the invention. Furthermore, not all of the features of the apparatus are depicted in each of the figures, and the Figures may only show some of the components relevant for describing a particular feature. In the various figures, like parts are donated by like references. DETAILED DESCRIPTION

[0021] Figures 1A and IB depicts an airflow sensor unit 1 in accordance with an embodiment. The airflow sensor unit 1 may be for an aerial vehicle. Figure 1A depicts a top view of the airflow sensor unit 1 (i.e. a view from above the airflow sensor unit 1 looking down at the airflow sensor unit 1). Figure IB depicts a bottom view of the airflow sensor unit (i.e. a view from below the airflow sensor unit 1 looking up at the airflow sensor unit 1).

[0022] The airflow sensor unit may be mounted on any suitable aerial vehicle, such as a copter-type aerial vehicle (e.g. a helicopter or a multicopter), a fixed wing aircraft, or a vertical take-off and landing aerial vehicle. The aerial vehicle may be a manned or an unmanned aerial vehicle.

[0023] The airflow sensor unit comprises a housing 80. The housing 80 may be constructed of a durable material to withstand various environmental conditions and mechanical stresses encountered during flight. The housing 80 may be constructed from a lightweight material to minimise the extent to which the presence of the airflow sensor unit 1 increases the overall weight of the aerial vehicle on which the airflow sensor unit 1 is provided. The housing 80 may be formed of plastic. For example, the housing 80 may be formed of Acrylonitrile Butadiene Styrene (ABS), Polyethylene terephthalate glycol (PETG). Generally, the housing 80 may be formed of any other durable type of plastic that is resistant to stress and / or resistant to long-term exposure to ultraviolet radiation.

[0024] The airflow sensor unit 1 comprises a plurality of sensor portions 10-15. In the present context, the term “sensor portion” is used to refer to a collection of associated features which allow sensor data to be recorded.

[0025] The sensor portions 10-15 may each comprise a sensor arrangement (not shown), such that the airflow sensor unit 1 comprises a plurality of sensor arrangements. The plurality of sensor arrangements may be disposed within the housing 80. In some embodiments, the plurality of sensor arrangements may be fixedly coupled to the housing 80 (e.g. fixedly coupled to an interior surface of the housing 80). Each sensor arrangement may comprise one or more sensors.

[0026] The sensor portions 10-15 may each comprise an opening 30-35. The opening of each sensor portion 10-15 may be defined in (i.e. formed in) the housing 80, such that the airflow sensor unit 1 comprises a plurality of openings 30-35 defined in the housing. The direction in which an opening 30-35 faces may be referred to as a facing direction. The direction in which an opening 30-35 faces may be a direction which is perpendicular to the plane in which the opening 30-35 extends.

[0027] The sensor portions 10-15 may each comprise a conduit (not shown). Each conduit may be in fluid communication with one of the openings 30-35. Thus, each sensor portion 10-15 may comprise an opening 30-35 in fluid communication with a conduit. The conduits may extend into a main body of the airflow sensor unit 1 from an outer surface of the housing 80. In some embodiments, the conduits may extend substantially perpendicularly to the outer surface of the housing 80. The direction in which a conduit extends may be substantially parallel to (and / or coaxial with) the facing direction of the opening 30-35 with which said conduit is in fluid communication.

[0028] The plurality of sensor arrangements may be configured to measure one or more quantities (e.g. pressure) associated with the air in the plurality of conduits. That is, in a sensor portion 10-15, a sensor arrangement may be configured to measure one or more quantities associated with air in the conduit of that sensor portion 10-15. The quantities associated with the air in a conduit may be dependent on characteristics (e.g. speed) of the airflow arriving at the airflow sensor unit in the facing direction of the opening 30-35 which is in fluid communication with said conduit.

[0029] The plurality of sensor portions 10-15 may be distributed around the airflow sensor unit 1. The plurality of openings 30-35 may be distributed around the airflow sensor unit 1. In some embodiments, the plurality of openings 30-35 are distributed around the housing 80. This may be such that each opening 30-35 faces in a different direction to the other openings 30-35. By distributing the plurality of openings 30-35 around the housing such that each opening 30-35 faces in a different direction to the other openings 30-35, each sensor arrangement may be able to measure quantities associated with airflow arriving from different directions. Thus, the airflow sensor unit 1 is able to measure quantities associated airflow arriving at the airflow sensor unit 1 from different directions.

[0030] In some embodiments, the plurality of openings 30-35 are uniformly distributed around the housing 80. This may mean that the airflow sensor unit 1 is able to measure quantities associated airflow arriving at the airflow sensor unit 1 from all different directions.

[0031] The airflow sensor unit 1 depicted in Figures 1A and IB comprises six sensor portions 10-15 (i.e. six sensor arrangements, each with a corresponding conduit and opening 30-35). In general, the airflow sensor unit 1 may comprise six or more sensor portions 10-15. By providing six or more sensor portions 10-15 (each having with an opening facing in a different direction), the airflow sensor unit 1 may be able to measure quantities associated with airflow arriving at the airflow sensor unit 1 from all different directions. Further, by providing six or more sensor portions 10-15 (each having with an opening facing in a different direction), the airflow sensor unit 1 may be able to establish how the measured quantities vary as a function of arrival direction. In some embodiments, the airflow sensor unit may comprise exactly six sensor portions 10-15.

[0032] Increasing the number of sensor portions 1-15 may increase extent to which the airflow sensor unit 1 is be able to measure quantities associated with airflow arriving at the airflow sensor unit 1 from all different directions. Further, increasing the number of sensor portions 1-15 may improve the extent to which the variation in the measured quantities quantities as a function of direction can be determined. However, increasing the number of sensor portions may result in an increase in the complexity, mass and cost of the airflow sensor unit 1. It has been found that an airflow sensor unit 1 having nine sensor portions (e.g. exactly nine sensor portions or nine sensor portions only) provides data that can be used effectively for, e.g. navigational purposes, without unnecessarily increasing the complexity of the airflow sensor unit 1.

[0033] The sensor arrangement of each of the sensor portions 10-15 may be configured to measure pressure. That is, the sensor arrangement of a sensor portion 10-15 may be configured to measure a pressure within the conduit of that sensor portion 10-15. The sensor arrangement of each sensor portion 10-15 may comprise a pressure sensor.

[0034] The pressure within each conduit may be a stagnation pressure. In other words, the pressure within the conduit may be equal to the sum of the local static pressure and the dynamic pressure of the airflow arriving at the UAV from the facing direction of the opening. The dynamic pressure of the airflow arriving at the UAV from the facing direction of the opening is a function of the speed of that airflow. Thus, from the difference between the pressure within the conduit and the local static pressure (i.e. the differential pressure or gauge pressure), it is possible to determine a speed of the airflow arriving at the UAV from the facing direction of the opening 30-35.

[0035] The speed of the airflow arriving at the UAV from the facing direction of the opening 30-35 may be determined from the differential pressure measurement made by the sensor arrangement using Bernoulli’s law, as shown in Equation 1, where: v is the speed of the airflow arriving at the UAV from the facing direction of the opening 30-35; AP is the differential pressure measurement made by the sensor arrangement; and p is the density of the air in the conduit. |2AP v = ---- J P Equation 1

[0036] In some embodiments, a sensor arrangement of a sensor portion 10-15 (or the pressure sensor thereof) is configured to measure a differential pressure of the conduit of that sensor portion 10-15 directly. That is, the sensor arrangement may be configured to measure directly a difference between the pressure within the conduit and the local static pressure. In such embodiments, the sensor arrangement may comprise a pitot tube. Figure 3 depicts a plot of differential pressure data obtained from the plurality of sensor arrangements of the airflow sensor unit 1.

[0037] In some embodiments, the airflow sensor unit may comprise a reference pressure sensor configured to measure (e.g. continuously measure) the local static pressure. The reference pressure sensor may be in the interior of the airflow sensor unit. A reference pressure sensor may alternatively be provided on the UAV on which the airflow sensor unit 1 is mounted. In embodiments in which the airflow sensor unit 1 or the UAV comprises a reference pressure sensor, the plurality of sensor arrangements of the airflow sensor unit 1 may be configured to measure the total pressure within the conduits (i.e. the sum of the local static pressure and the dynamic pressure of the airflow arriving at the airflow sensor unit 1 from the facing direction of the opening). The local static pressure measurements made by the reference pressure sensor may be subtracted from the total pressure measurements made by the sensor arrangements of the airflow sensor unit 1 to obtain differential pressure values corresponding to each of the sensor arrangements. This may allow different types of pressure sensor to be used in the airflow sensor unit 1.

[0038] It will be appreciated that many types of mechanical, electromechanical and electrical pressure sensors may be implemented in the sensor arrangements of the airflow sensor unit 1. Examples include capacitive pressure sensors, piezoelectric pressure sensors, piezoresistive films, MEMS, optical film sensors, differential pressure sensors, and strain gauge pressure sensors.

[0039] Piezoelectric pressure sensors may be particularly advantageous in some embodiments. That is, in preferred embodiments, each sensor arrangement of the airflow sensor unit comprises a piezoelectric pressure sensor configured to measure the total pressure within one of the conduits. Thus, there may be a plurality of piezoelectric sensors, each arranged and configured to measure total pressure associated with a different direction. Each piezoelectric sensor may be configured to convert forces exerted on the sensor by the total pressure in a conduit directly into an electrical signal which is indicative of the total pressure in the conduit.

[0040] Use of a plurality of piezoelectric pressure sensors in this way (e.g. as opposed to arrangements comprising a plurality of pitot-static tubes) eliminates moving parts and improves the speed of at which the airflow sensor unit is able to respond to dynamic pressure changes. This is especially the case under turbulent or low-speed conditions.

[0041] Piezoelectric sensors may also have an improved resolution, i.e. piezoelectric sensors may be able to detect smaller changes in pressure (e.g. as compared to Pitot-static tubes). Additionally, the use of piezoelectric pressure sensors enables a compact, solid-state design that is especially suited to UAV applications. The piezoelectric pressure sensors may have very low noise (e.g. in the the order of 1-3 Pa (RMS)) in highest-resolution modes. This means that small pressure differences can be reliably detected.

[0042] The dynamic pressure associated with each of the plurality of directions (i.e. each of the directions in which the plurality of openings face), processing may be determined based on: (i) the total pressure associated with each of the plurality of directions, as measured by the plurality of piezoelectric sensors which are each associated with one of the different directions; and (ii) the local static (i.e. ambient) pressure, as measured by the reference pressure sensor. For example, to determine the dynamic pressure associated with a particular direction, the local static pressure may be subtracted from the total pressure associated with the particular direction (i.e. the total pressure as measured by the piezoelectric sensor which measures pressure in the conduit with an opening facing in the particular direction). The use of the reference pressure sensor in conjunction with the plurality of piezoelectric pressure sensors allows the airflow sensor unit 1 to effectively compute true airspeed and angle-of-attack even in variable atmospheric conditions.

[0043] Use of piezoelectric sensors for the purpose of airspeed / airflow determination is not obvious, because, unlike pitot-static tubes, piezoelectric sensors do not provide a direct measurement of dynamic pressure. However, by using the piezoelectric sensors in conjunction with the reference sensor, total pressure can be determined while using piezoelectric sensors. Thus, the advantages of piezoelectric sensors can be obtained.

[0044] Figure 7 depicts an arrangement of a conduit inside the airflow sensor unit. A portion of the conduit extending from the opening may be a decompression / filtering chamber. A pressure channel nozzle may be in fluid communication with the decompression / filtering chamber so that the pressure sensor for the conduit is able to measure the pressure within the decompression / filtering chamber. A silicone gasket may seal against a gasket face to provide a pressure seal.

[0045] In some embodiments, at least one of the sensor arrangements is further configured to measure temperature. For example, the sensor arrangement of each sensor portion 10-15 may be configured to measure temperature. For example, the sensor arrangement of each sensor portion 10-15 may be configured to measure temperature within the conduit of that sensor portion 10-15.

[0046] It will be appreciated that many types of temperature sensor may be implemented in the sensor arrangement of the airflow sensor unit 1. For example, Negative Temperature Coefficient (NTC) Thermistors, Resistance Temperature Detectors (RTDs), thermocouples and semiconductor-based sensors may all be used as a temperature sensor in the airflow sensor unit 1.

[0047] In some embodiments, at least one of the sensor arrangements is further configured to measure humidity, e.g. relative humidity. That is, at least one of the sensor arrangements may comprise a humidity sensor. For example, the sensor arrangement of each sensor portion 10-15 may be configured to measure relative humidity. For example, the sensor arrangement of a sensor portion 10-15 may be configured to measure relative humidity within the conduit of that sensor portion 10-15.

[0048] It will be appreciated that many types of humidity sensor may be implemented it the sensor arrangement of the airflow sensor unit 1. For example, the sensor arrangements may comprise a capitative humidity sensor, a thermal conductivity humidity sensor or a resistive humidity sensor.

[0049] The housing 80 may define an outer profile of the airflow sensor unit 1. The outer profile may be the general shape defined by the housing 80, ignoring any local features. The plurality of openings may be recessed below the outer profile of the airflow sensor unit. In other words, the housing 80 comprises a plurality of recesses 20-25, and each opening 30-35 may be defined in a recess 20-25. The recesses 20-25 may be considered to be a part of the sensor portions 10-15.

[0050] The recesses 20-25 may alternatively be referred to as localised depressions in the surface of the housing 80. A distance between a centre of the airflow sensor unit 1 and the outer surface of the housing may be smaller where a recess is present (than a distance between the centre of the airflow sensor unit 1 and the outer surface of the housing may be smaller where a recess is not present).

[0051] The airflow sensor unit 1 depicted in Figures 1A and IB is substantially spherical. That is, the housing 80 of airflow sensor unit 1 depicted in Figures 1A and IB defines a substantially spherical profile. The plurality of openings 30-35 may be recessed below the substantially spherical profile of the housing 80.

[0052] By recessing the plurality of openings below the outer profile of the airflow sensor unit 1 (irrespective of the shape of the housing 80), the extent to which turbulent air flows (and lateral air flows in general) around the airflow sensor unit interfere with the measurements made by the plurality of sensor arrangements is decreased. Consequently, the plurality of sensor arrangements are able to record more accurate data. This may be particularly important on copter-type UAVs, in which rotors generate a large amount of turbulence in the air surrounding the UAV. Thus, the airflow sensor unit 1 may be suitable for use in copter-type UAVs in a way that conventional sensor units are not.

[0053] Moreover, by recessing the plurality of openings below the outer profile of the airflow sensor unit 1 (irrespective of the shape of the housing 80), the sensor arrangements are protected from direct impacts.

[0054] Such recessed openings may preferably be provided in an airflow sensor unit which comprises piezoelectric pressure sensors and a reference pressure sensor, as described above. This combination of features provides especially high accuracy and robustness.

[0055] The plurality of recesses 20-25 formed in the housing may be conical recesses. The recesses may have a circular perimeter at the outer profile of the airflow sensor unit 1. Moving in the radially inward direction (i.e. towards the centre of the airflow sensor unit 1), a diameter of the circular perimeter of the recesses may decrease, such that the recesses are conical. Each opening 30-35 may be disposed at or near the vertex (i.e. apex) of the conical recess 20-25 in which it is positioned. In some embodiments, the apex angle of the conical recess 20-25 may be greater than 90°, preferably greater than 100°, and less than 150°. By providing a conical recess with an apex angle within this range, the effects of turbulence around the airflow sensor unit 1 on the measurements made by the sensor arrangements may be effectively reduced.

[0056] In some embodiments, the airflow sensor unit 1 may not be spherical. For example, the airflow sensor unit 1 may be cylindrical. That is, the housing 80 may define a substantially cylindrical outer profile. In general, the shape of the airflow sensor unit 1 is not particularly limited, as long as it allows the plurality of openings 30-35 to face in different directions in the manner described above. For instance, the airflow sensor unit may be ovoidal, cuboidal, ellipsoidal or oblate spheroidal. Alternatively, the outer profile of the airflow sensor unit may be a dodecahedron, an icosahedron, or a prism.

[0057] A distance between an opening 30-35 and the outer profile of the airflow sensor unit 1 may be greater than 10 mm, and preferably greater than 15 mm. That is, each of the openings may be recessed below the outer profile of the airflow sensor unit 1 by a distance of greater than 10 mm and preferably greater than 15 mm. This may ensure that the effects of turbulence around the airflow sensor unit 1 on the measurements made by the sensor arrangements are effectively reduced.

[0058] The airflow sensor unit may further comprise a plurality of filter members (see Figure 6). The filter members may cover the plurality of openings 30-35. That is, each opening 30-35 may be covered by a filter member. The filter member depicted in Figure 6 may be a mechanical filter member. The filter members may have an ingress protection (IP) rating of 68 or more. This may provide good protection for the sensors, e.g. the piezoelectric sensors (which may require more protection from dust and other contaminants than other types of sensors).

[0059] Additionally, or alternatively, a filter member may be disposed within one or more of the plurality of conduits. The filter member may be a filter or a protective mesh. The filter members may be configured to prevent debris entering the conduits through the openings 30-35. Consequently, the filter members prevent the conduits from becoming blocked. Consequently, a risk that the sensor arrangements become unable to provide data relating to quantities of the airflow arriving at the airflow sensor unit 1 is reduced. Consequently, the airflow sensor unit 1 is more robust.

[0060] The airflow sensor unit 1 may comprise a processing module 70. The processing module may be a microcontroller unit (MCU). The processing module may be disposed within the housing 80. The processing module may comprise any suitable hardware and software for performing the functionality described below. It will be recognised that, in some embodiments, the processing of the processing module described below may be performed by a processing module that is independent of the airflow sensor unit 1. For example, the processing of the processing module described below may be performed by a processing module of the UAV to which the airflow sensor unit 1 is mounted. Alternatively, the processing of the processing module described below may be performed by a processing module in a remote server with which the airflow sensor unit 1 is in wireless communication.

[0061] The processing module may be configured to process data recorded by the plurality of sensor arrangements. For example, the processing module may be configured to process pressure data recorded by the plurality of sensor arrangements. In some embodiments, the processing module is configured to process temperature data and / or relative humidity data recorded by the plurality of sensor arrangements. As shown in Figure 4, the processing module may communicate with the plurality of sensor arrangements via a communication protocol such as I2C, i.e. a two-wire serial communication protocol using a serial data line (SDA) and a serial clock line (SCL).

[0062] The processing module may be configured to integrate (i.e. combine or fuse) different types of data measured by different types of sensor. The integration of different types of data from different types of sensor may be referred to as data fusion or sensor fusion. Sensor fusion can significantly improve the accuracy and reliability of airflow measurements made by the plurality of sensor arrangements of the airflow sensor unit 1.

[0063] For example, the processing module may be configured to integrate (i.e. combine or fuse) pressure data with one or more of temperature data and relative humidity data. As a specific example, one or more of the temperature data and the relative humidity data may be integrated with the pressure data during the calculation of airspeed using Equation 1. This may be achieved by calculating the density of the air in the conduit based on the measured values of temperature and / or relative humidity. An air density that is based on measured values of temperature and relative humidity may be more accurate than, for example, assuming the density of the air based on an altitude.

[0064] In some embodiments, one of the sensor arrangements (which may be representative of all of the sensor arrangements) comprises a pressure sensor, a temperature sensor and a relative humidity sensor. The processing module of the airflow sensor unit 1 may be configured to fuse the data recorded by the pressure sensor, the temperature sensor and the relative humidity sensor by taking the data recorded by the pressure sensor, the temperature sensor and the relative humidity sensor into account when calculating the airspeed associated with that sensor arrangement (i.e. the speed of the airflow in the direction in which the opening corresponding to the sensor arrangement faces). The processing module may do this for each of the sensor arrangements individually.

[0065] In some embodiments, the processing module may be configured to integrate (i.e. combine or fuse) data (e.g. pressure data and / or temperature data and / or relative humidity data) recorded by different sensor arrangements of the plurality of sensor arrangements. By cross-referencing data by different sensor arrangements of the plurality of sensor arrangements, it may be possible to increase the accuracy of the data as a whole (e.g. by identifying and / or correcting and / or discounting erroneous / inaccurate data).

[0066] In some embodiments, the processing module is configured to use the data measured by the plurality of sensor arrangements to obtain the overall speed and velocity of the airflow arriving at the airflow sensor unit 1. This may comprise integrating (i.e. combining or fusing) the different airspeed values for the different sensor portions 10-15 having different facing directions.

[0067] In some embodiments, the sensor arrangements each comprise a piezoelectric pressure sensor, and the airflow sensor unit further comprises a reference pressure sensor configured to measure local static pressure. As such, the processing module may be suitably configured to fuse data from the piezoelectric sensors with data from the reference pressure sensor. A suitable calibration routine may be used to optimize the co-operative performance of these different sensor types.

[0068] Figure 5 depicts a data processing flow for determining a velocity vector from the pressure data recorded by the plurality of sensor arrangements of the airflow sensor module 1. At step SI, a raw data array is obtained. The raw data array comprises, for each of the plurality of sensors, differential pressure values over time. At step S2, the raw data array is filtered using a bandpass filter. This reduces the amount of noise in the data. At step S3, the data is calibrated. The calibration of the data may comprise the application of correction coefficients. Different correction coefficients may correspond to different ones of the plurality of sensor arrangements.

[0069] The correction coefficients may be determined through an initial calibration procedure. The initial calibration procedure may comprise measuring values from the plurality of sensor arrangements while the airflow sensor 1 is stationary and in a steady state. These measurements may allow baselines and biases to be determined, from which correction coefficients can be calculated.

[0070] Additionally or alternatively, the correction coefficients may be adapted dynamically during use of the airflow sensor (i.e. as the aerial vehicle is in flight). For instance, the correction coefficients may be adapted based on the temperature of the air around the sensors. For example, each sensor arrangement may comprise a pressure sensor and a temperature sensor. The correction coefficient for a given pressure sensor may be adapted based on temperature measurements made by a temperature sensor which accompanies the given pressure sensor (i.e. which is a part of the same sensor arrangement).

[0071] At step S4, an airspeed is calculated for each of the sensor arrangements. Thus, at step S4, a plurality of airspeeds is obtained, with each airspeed corresponding to a different direction. At step S5, the airspeeds are combined to obtain a velocity vector which represents the overall speed and direction of the airflow arriving at the airflow sensor 1.

[0072] The processing module may be configured to determine one or more characteristics of the flight of the aerial vehicle. For example, in some embodiments, the processing module is configured to determine an airspeed of the UAV. The airspeed of the UAV may be equal to the overall speed and velocity of the airflow arriving at the airflow sensor unit 1.

[0073] In some embodiments, the processing module is configured to determine a geospatial velocity of the UAV (i.e. a speed and direction of the UAV relative to a spatially fixed reference point, e.g. the Earth). The geospatial velocity of the UAV may be determined based at least in part on the overall speed and velocity of the airflow arriving at the airflow sensor unit 1.

[0074] In some embodiments, the processing module is configured to determine a wind drift of the UAV (i.e. an amount (e.g. distance) by which the UAV drifts as a result of wind). The wind drift of the UAV may be determined based at least in part on the overall speed and velocity of the airflow arriving at the airflow sensor unit 1.

[0075] In some embodiments, the processing module may collate and store data recorded by the plurality of sensor arrangements. This data may be used in the modelling of the airflow around the UAV. The model of the airflow around the UAV may be used to improve navigational accuracy and in aerodynamic analysis. Knowledge of the airflow around the UAV during flight may be useful in the design and development of future UAVs. The design of the UAV on which the airflow sensor unit 1 is disposed may be adapted based on the data collated by the processing module.

[0076] The airflow sensor unit 1 may comprise a communication module. The communication controller may be part of the microcontroller. The communication module may be configured to interface with (i.e. communicate with) an autonomous navigation system 100 (i.e. a flight controller) of the UAV on which the airflow sensor unit 1 is mounted. As shown in Figure 4, the communication module may be configured to communicate with the autonomous navigation system 100 suing a communication protocol such as Mavlink (Micro Air Vehicle Link). Additionally or alternatively, the communication module may be configured to communicate wirelessly with, for example, a server or a remote operation centre.

[0077] Figures 2A and 2B depict the airflow sensor unit 1 mounted on a UAV 50. Figure 2A depicts one side view of the airflow sensor 1 and UAV 50, and Figure 2B depicts the airflow sensor 1 and UAV 50 from the opposite side.

[0078] The UAV depicted in Figures 2A and 2B is a multicopter comprising one or more rotating blades (not shown) configured to generate a lift force in a downward direction. The airflow sensor unit 1 may be disposed above the one or more rotating blades. This means that the airflow sensor unit 1 is not disposed in the downwash generated by the rotating blades of the multicopter. If disposed in the turbulent downwash generated by the rotating blades, the accuracy of the measurements made by the plurality of sensor arrangements of the airflow sensor unit 1 would be impaired. Consequently, by positioning the airflow sensor unit above the one or more rotating blades the accuracy of the measurements made by the plurality of sensor arrangements of the airflow sensor unit 1 is improved.

[0079] As shown in Figures 2A and 2B, the airflow sensor unit 1 may be connected to an upper surface of a main body of the UAV 50 by a connecting rod 60. The airflow sensor unit 1 may comprise a coupling interface 40 (see Fig. IB) configured to facilitate the connection of the airflow sensor unit 1 to the rod. The coupling interface 40 may be a hole in the housing 80. The coupling interface 40 may be configured to receive the connecting rod 60 and / or one of more fittings 61.

[0080] The connecting rod 60 means that the airflow sensor unit is displaced from (i.e. separated from) the main body of the UAV. This means that the impact of the main body of the UAV 50 on the airflow around the UAV 50 has a lesser effect on the measurements made by the plurality of sensor arrangements of the airflow sensor unit 1.

[0081] In other embodiments, the UAV 50 may comprise a main airframe, and the airflow sensor unit 1 may be integrated within the main air frame.

[0082] The compact, lightweight design of the airflow sensor unit of the present disclosure, combined with its rapid and accurate measurement capabilities, makes it particularly suitable for UAVs. The airflow sensor unit can provide real-time data on airspeed, airflow direction, and other parameters crucial for flight stability and autonomous navigation, even in environments where conventional sensors may struggle, such as in turbulent or GPS-denied conditions.

[0083] The aerial vehicle 50 to which the airflow sensor unit 1 is coupled may comprise an autonomous navigation system. The autonomous navigation system may be configured to receive the data recorded by the plurality of sensor arrangements of the airflow sensor unit via the communication module of the airflow sensor unit 1. Additionally or alternatively, the autonomous navigation system may be configured to receive the one or more characteristics of the flight of the aerial vehicle determined by the processor of the airflow sensor unit 1 (e.g. the airspeed, the velocity of the UAV, the wind drift of the UAV, etc.)

[0084] The autonomous navigation system may be configured to use the data recorded by the plurality of sensor arrangements and / or the one or more characteristics of flight determined by the processor in a position determining process. The position determining process may be a process in which a geospatial position of the aerial vehicle is determined.

[0085] As part of the position determining process, the autonomous navigation system may be configured to obtain a first estimation of the position of UAV based on the velocity of the UAV. The velocity of the UAV may be determined based on the data recorded by the plurality of sensor arrangements, as described above. Computation of the velocity of the UAV may be performed by the processing module of the airflow sensor unit 1, or by the autonomous navigation system. To obtain the first estimation of geospatial position from the velocity of the UAV, a displacement of the UAV may be computed by integrating the velocity of the UAV with respect to time. The computed displacement of the UAV may then be combined with (e.g. added to) a known initial geospatial position of the UAV to obtain the first estimation. It will be recognised that, in some embodiments, the computation of the first estimation may be performed by the processing module of the airflow sensor unit 1, rather than the autonomous navigation system of the UAV.

[0086] As part of the position determining process, the autonomous navigation system may be configured to obtain a second estimation of the geospatial position of the aerial vehicle based on data other than that received from the plurality of sensor arrangements of the airflow sensor unit 1. For example, the autonomous navigation system may be configured to obtain a second estimation of the geospatial position of the aerial vehicle based on at least one of GPS data, inertial data, meteorological data and celestial data.

[0087] As part of the position determining process, the autonomous navigation system may be configured to obtain a refined estimation of the geospatial position of the aerial vehicle based on the first estimation and the second estimation. This may comprise combining the first estimation and the second estimation. The combining of the first estimation and the second estimation may comprise Kalman filtration. In some embodiments, the first estimation may be used to calibrate (i.e. correct) the second estimation to produce the refined estimation. In other embodiments, the second estimation may be used to calibrate (i.e. correct) the first estimation to produce the refined estimation.

[0088] Integrating an Inertial Navigation System (INS) and other sensors of UAV with airflow sensors and using Kalman filtration for drift correction is a powerful approach to improve the accuracy of navigation in aerial vehicles. The INS provides high-frequency data about the vehicle’s motion, but it suffers from drift over time due to the accumulation of small errors. Airflow sensors can provide additional data that helps correct these drifts, ensuring more accurate positioning and velocity estimations.

[0089] In some emboddiments, the INS provides continuous high-rate data on the vehicle's motion (acceleration and angular rates), which may be used in a prediction step of a geospatial position determining process comprising Kalman filtration. The airflow sensor may provide periodic data on the true airspeed and, optionally, on the angle of attack and / or sideslip angle. The geospatial position determining process comprising Kalman filtration may comprise an updating step, in which any drift in the INS-based state estimate is corrected based on the periodic data on the true airspeed, and, optionally, on the angle of attack and / or sideslip angle. By continuously correcting the INS estimates with the airflow sensor data, the geospatial position determining process comprising Kalman filtration mitigates the drift that typically accumulates in INS-only systems, resulting in more accurate and reliable position and velocity estimates. In summary, using Kalman filtration to combine INS and airflow sensor data allows for accurate, drift-free estimation of an aerial vehicle's state, improving overall navigation performance and reliability.

[0090] Aspects of the invention are described in the following numbered clauses. 1. An airflow sensor unit for an aerial vehicle, the airflow sensor unit comprising: a housing; a plurality of openings defined in the housing, wherein each opening faces in a different direction to the other openings; a plurality of conduits, wherein each conduit is in fluid communication with a corresponding opening; and a plurality of sensor arrangements, wherein each sensor arrangement is configured to measure a pressure within one or more of the conduits. 2. The airflow sensor unit of clause 1, wherein at least one of the sensor arrangements is further configured to measure temperature and / or humidity within the conduit. 3. The airflow sensor unit of clause 1 or 2, wherein the plurality of openings are distributed around the housing, optionally wherein the plurality of openings are uniformly distributed around the housing. 4. The airflow sensor unit of any of the preceding clauses, wherein the housing defines an outer profile of the airflow sensor unit, and the plurality of openings are recessed below the outer profile of the airflow sensor unit. 5. The airflow sensor unit of clause 4, wherein the outer profile is substantially spherical. 6. The airflow sensor unit of any of the preceding clauses, wherein the housing comprises a plurality of recesses, and each opening is defined in a recess. 7. The airflow sensor unit of any of the preceding clauses, wherein the airflow sensor unit further comprises a plurality of filter members, wherein each filter member covers one of the plurality of openings or is disposed within one of the conduits. 8. The airflow sensor unit of any of the preceding clauses, wherein the plurality of sensor arrangements comprises six sensor arrangements. 9. The airflow sensor unit of any of the preceding clauses, wherein the plurality of sensor arrangements comprises nine sensor arrangements. 10. The airflow sensor unit of any of the preceding clauses, further comprising a processing module configured to process pressure data recorded by the plurality of sensor arrangements, optionally wherein the processing module is further configured to process temperature data and / or relative humidity data recorded by the plurality of sensor arrangements. 11. The airflow sensor unit of clause 10, wherein the processing module is configured to integrate data recorded by different sensor arrangements of the plurality of sensor arrangements. 12. The airflow sensor of clause 10 or 11, wherein the processing module is configured to integrate pressure data with one or more of temperature data and or relative humidity data. 13. The airflow sensor unit of any of clauses 10 to 12, wherein the processing module is configured to determine one or more characteristics of the flight of the aerial vehicle, including: an airspeed; a velocity of the aerial vehicle; an airflow around the aerial vehicle; and / or a wind drift. 14. The airflow sensor unit of any of the preceding clauses, further comprising a communication module configured to interface with an autonomous navigation system of the aerial vehicle. 15. An aerial vehicle comprising the airflow sensor unit of any of the preceding clauses. 16. The aerial vehicle of clause 15, wherein the aerial vehicle is an unmanned aerial vehicle. 17. The aerial vehicle of clause 15 or 16 wherein the aerial vehicle is a helicopter, a multicopter, a fixed wing aircraft, or a vertical take-off and landing aerial vehicle. 18. The aerial vehicle of any of clauses 15 to 17, wherein the aerial vehicle is a helicopter or a multicopter comprising one or more rotating blades configured to generate a lift force in a downward direction, and the airflow sensor unit is disposed above the one or more rotating blades. 19. The aerial vehicle of clause 18, wherein the airflow sensor unit is connected to an upper surface of a main body of the aerial vehicle by a connecting rod. 20. The aerial vehicle of any of the preceding clauses, further comprising an autonomous navigation system configured to receive data recorded by the plurality of sensor arrangements via the communication module of the airflow sensor unit and / or to receive one or more characteristics of the flight of the aerial vehicle determined by the processor via the communication module of the airflow sensor unit. 21. The aerial vehicle of clause 20, wherein the autonomous navigation system is configured to use the data recorded by the plurality of sensor arrangements and / or the one or more characteristics of flight determined by the processor in a position determining process, wherein the position determining process is a process in which a geospatial position of the aerial vehicle is determined. 22. The aerial vehicle of clause 21, wherein the processing module and / or the autonomous navigation system is configured to obtain a first estimation of the position of aerial vehicle from the velocity of the aerial vehicle, wherein the velocity of the aerial vehicle is determined based on the data recorded by the plurality of sensor arrangements. 23. The aerial vehicle of clause 22, wherein the autonomous navigation system is configured to obtain a second estimation of the geospatial position of the aerial vehicle based on at least one of GPS data, inertial data, meteorological data and celestial data. 24. The aerial vehicle of clause 23, wherein the position determining process comprises determining a refined estimation of the geospatial position of the aerial vehicle based on the first estimation and the second estimation. 25. The aerial vehicle of clause 24, wherein the determining of the refined estimate of the geospatial position of the aerial vehicle based on the first estimation and the second estimation comprises Kalman filtration. 26. A method of operating an aerial vehicle of any of clauses 15 to 25. 27. A method of determining a geospatial position of an aerial vehicle, the method comprising: receiving, from a sensor unit, pressure data recorded by a plurality of sensor arrangements of a sensor unit, wherein each sensor arrangement is associated with a different direction; and determining a geospatial position of the aerial vehicle using the pressure data received from the sensor unit. 28. The method of clause 27, further comprising recording the data using the one or more sensors of the sensor arrangement. 29. The method of clause 27 or 28, further comprising determining a velocity of the aerial vehicle based on the pressure data received from the sensor unit. 30. The method of any of clauses 27 to 29, wherein the determining of the geospatial position of the aerial vehicle comprises obtaining a first estimation of the geospatial position of the aerial vehicle based on the velocity of the aerial vehicle. 31. The method of clause of any of clauses 30, wherein: the method further comprises receiving at least one of GPS data, inertial data, meteorological data and celestial data, and the determining of the geospatial position of the aerial vehicle comprises obtaining a second estimation of the geospatial position of the aerial vehicle based on at least one of the GPS data, the inertial data, the meteorological data and the celestial data. 32. The method of clause 31, wherein the determining of the geospatial position of the aerial vehicle comprises determining a refined estimation of the geospatial position of the aerial vehicle based on the first estimation and the second estimation. 33. The method of clause 32, wherein the determining of the refined estimation of the geospatial position of the aerial vehicle based on the first estimation and the second estimation comprises Kalman filtration.

[0091] The methods of the present invention may be performed by computer systems comprising one or more computers. A computer used to implement the invention may comprise one or more processors, including general purpose CPUs, graphical processing units (GPUs), tensor processing units (TPU) or other specialised processors. A computer used to implement the invention may be physical or virtual. A computer used to implement the invention may be a server, a client or a workstation. Multiple computers used to implement the invention may be distributed and interconnected via a network such as a local area network (LAN) or wide area network (WAN). Individual steps of the method may be carried out by a computer system but not necessarily the same computer system. The methods of the invention may be carried out on a computer system located on the same vehicle as the sensor unit or remote from the vehicle. Results of a method of the invention may be displayed to a user or stored in any suitable storage medium. The present invention may be embodied in a non-transitory computer-readable storage medium that stores instructions to carry out a method of the invention. Any suitable programming language may be used to implement the invention. The present invention may be embodied in a computer system comprising one or more processors and memory or storage storing instructions to carry out a method of the invention.

[0092] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.

Claims

1. An airflow sensor unit for an aerial vehicle, the airflow sensor unit comprising:a housing;a plurality of openings defined in the housing, wherein each opening faces in a different direction to the other openings;a plurality of conduits, wherein each conduit is in fluid communication with a corresponding opening; anda plurality of sensor arrangements, wherein each sensor arrangement is configured to measure a pressure within one or more of the conduits.

2. The airflow sensor unit of claim 1, wherein each sensor arrangement comprises a piezoelectric pressure sensor configured to measure total pressure within one of the conduits.

3. The airflow sensor unit of claim 1 or 2, further comprising a reference pressure sensor configured to measure local static pressure.

4. The airflow sensor unit of any of the preceding claims, wherein at least one of the sensor arrangements is further configured to measure temperature and / or humidity within the conduit.

5. The airflow sensor unit of any of the preceding claims, wherein the plurality of openings are distributed around the housing,optionally wherein the plurality of openings are uniformly distributed around the housing.

6. The airflow sensor unit of any of the preceding claims, wherein the housing defines an outer profile of the airflow sensor unit, and the plurality of openings are recessed below the outer profile of the airflow sensor unit.

7. The airflow sensor unit of any of the preceding claims, wherein the housing comprises a plurality of recesses, and each opening is defined in a recess.

8. The airflow sensor unit of any of the preceding claims, wherein the airflow sensor unit further comprises a plurality of filter members, wherein each filter member covers one of the plurality of openings or is disposed within one of the conduits.

9. The airflow sensor unit of any of the preceding claims, wherein the plurality of sensor arrangements comprises six sensor arrangements, optionally wherein the plurality of sensor arrangements comprises nine sensor arrangements.

10. The airflow sensor unit of any of the preceding claims, further comprising a processing module configured to process pressure data recorded by the plurality of sensor arrangements, optionally wherein the processing module is further configured to process temperature data and / or relative humidity data recorded by the plurality of sensor arrangements.

11. The airflow sensor unit of claim 10, wherein the processing module is configured to determine a dynamic pressure associated with a direction based on a total pressure measured by a piezoelectric pressure sensor and the static pressure measured by the reference pressure sensor.

12. The airflow sensor unit of claim 10 or 11, wherein the processing module is configured to integrate data recorded by different sensor arrangements of the plurality of sensor arrangements.

13. The airflow sensor of any of claims 10 to 12, wherein the processing module is configured to integrate pressure data with one or more of temperature data and or relative humidity data.

14. The airflow sensor unit of any of claims 10 to 13, wherein the processing module is configured to determine one or more characteristics of the flight of the aerial vehicle, including:an airspeed;a velocity of the aerial vehicle;an airflow around the aerial vehicle; and / ora wind drift.

15. The airflow sensor unit of any of the preceding claims, further comprising a communication module configured to interface with an autonomous navigation system of the aerial vehicle.

16. An aerial vehicle comprising the airflow sensor unit of any of the preceding claims, optionally wherein the aerial vehicle is an unmanned aerial vehicle, further optionally wherein the aerial vehicle is a helicopter, a multicopter, a fixed wing aircraft, or a vertical take-off and landing aerial vehicle.

17. The aerial vehicle of any of claim 16, wherein the aerial vehicle is a helicopter or a multicopter comprising one or more rotating blades configured to generate a lift force in a downward direction, and the airflow sensor unit is disposed above the one or more rotating blades,optionally wherein the airflow sensor unit is connected to an upper surface of a main body of the aerial vehicle by a connecting rod.

18. The aerial vehicle of any of the preceding claims, further comprising an autonomous navigation system configured to receive data recorded by the plurality of sensor arrangements via the communication module of the airflow sensor unit and / or to receive one or more characteristics of the flight of the aerial vehicle determined by the processor via the communication module of the airflow sensor unit.

19. The aerial vehicle of claim 18, wherein the autonomous navigation system is configured to use the data recorded by the plurality of sensor arrangements and / or the one or more characteristics of flight determined by the processor in a position determining process, wherein the position determining process is a process in which a geospatial position of the aerial vehicle is determined.

20. The aerial vehicle of claim 19, wherein the processing module and / or the autonomous navigation system is configured to obtain a first estimation of the position of aerial vehiclefrom the velocity of the aerial vehicle, wherein the velocity of the aerial vehicle is determined based on the data recorded by the plurality of sensor arrangements.

21. The aerial vehicle of claim 20, wherein the autonomous navigation system is configured to obtain a second estimation of the geospatial position of the aerial vehicle based on at least one of GPS data, inertial data, meteorological data and celestial data,optionally wherein the position determining process comprises determining a refined estimation of the geospatial position of the aerial vehicle based on the first estimation and the second estimation.

22. The aerial vehicle of claim 21, wherein the determining of the refined estimate of the geospatial position of the aerial vehicle based on the first estimation and the second estimation comprises Kalman filtration.

23. A method of operating an aerial vehicle of any of claims 18 to 22.

24. A method of determining a geospatial position of an aerial vehicle, the method comprising:receiving, from a sensor unit, pressure data recorded by a plurality of sensor arrangements of a sensor unit, wherein each sensor arrangement is associated with a different direction; anddetermining a geospatial position of the aerial vehicle using the pressure data received from the sensor unit.

25. The method of claim 24, further comprising recording the data using the one or more sensors of the sensor arrangement.T +44(0)30 0300 2000A

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