Drone-based determination of bulk material height

Abstract

The invention relates to a measurement system for determining a bulk material height (L) or a bulk material profile (Lx,y), which comprises the following components. An in particular unmanned multicopter (1) having a measuring unit which emits radar signals (SHF) in particular according to the FMCW principle and in a frequency band of at least 100 GHz towards the bulk material (2) and receives them, after their reflection there, as received signals (RHF); and having a control unit for controlling the position ([x; y]), flying height (h) and trajectory of the multicopter (1). An internal or external evaluation unit (1, 3, 4) determines, on the basis of the received signal (RHF), corresponding distance values (d) of the multicopter (1) from the bulk material (2) and determines the bulk material height (L) on this basis in conjunction with the flying height (h) of the multicopter (1). Provided this is done at several positions ([x; y]) along a defined trajectory over the bulk material (2), it is possible to determine a bulk material profile (Lx,y) using the corresponding group of distance values (d). As a whole, it is advantageous that, in contrast to conventional filling level measuring equipment, rigid fastening is not necessary.

Description

[0001] DRONE-BASED FILLING HEIGHT DETERMINATION

[0002] The invention relates to radar-based filling material determination using drones, in particular multicopters.

[0003] In process automation technology, various types of field devices are used to record relevant process parameters. To record the respective process parameters, suitable measurement principles are implemented in the corresponding field devices to record process parameters such as level, flow, pressure, temperature, pH value, redox potential, or conductivity. The Endress + Hauser Group manufactures and distributes a wide variety of field device types and variants.

[0004] Non-contact measuring methods have become established for level measurement of filling materials in containers because they are robust and low-maintenance. A further advantage of non-contact measuring methods is their ability to measure the fill level virtually continuously. In the field of continuous level measurement, radar-based measuring methods are therefore predominantly used. In the context of this invention, the term "radar" refers to signals or electromagnetic waves with frequencies between 0.03 GHz and 300 GHz. Due to the principle, the higher the frequency, the higher the measurement resolution can be achieved. The pulse transit time method and FMCW ("Frequency Modulated Continuous Wave") have become established measuring methods. Radar-based level measurement is described in more detail, for example, in "Radar Level Detection, Peter Devine, 2000".

[0005] Typical frequency bands approved for radar-based level measurement are 26 GHz, 60 GHz, 80 GHz, and 120 GHz, and increasingly also 180 GHz and 240 GHz. Higher frequency bands are advantageous for many applications because, for given antenna dimensions, greater beam focusing is achieved and generally more bandwidth is available, which can be used for greater distance resolution. One such application area is, for example, high-precision level measurement in refinery tanks.

[0006] In the case of liquid products with a homogeneous fill level, a point-based level measurement is sufficient. In these cases, the level gauge is attached to the container and aligned so that the radar beam cone of the level gauge is directed approximately vertically downwards towards the fill material, determining the distance to the fill material. However, with solid-like products such as gravel or grain, the fill material height can be inhomogeneous, for example due to bulk material cones, so that the value for the fill material height determined by the level gauge is only of limited significance. Especially in such cases, it is therefore desirable to be able to determine the fill material height in the form of a two- or three-dimensional fill material profile.

[0007] To achieve this, the radar beam cone emitted by the level gauge can be swiveled either mechanically or electrically to determine the corresponding distance or level values ​​depending on the solid angle. Mechanical swiveling of the beam cone can be achieved, for example, using an actuatable mirror, which redirects the beam cone to the desired points on the product surface.

[0008] Electronic beam steering can be implemented, for example, using the MIMO (“Multiple Input Multiple Output”) principle. This principle is based on the appropriate control of an antenna arrangement consisting of column-shaped transmitting antennas and row-shaped receiving antennas in order to digitally shape the resulting radar signal. On the hardware side, this can be achieved, for example, using appropriately programmed MMICs (“Monolithic Microwave Integrated Circuits”). MIMO-based radar systems are described in more detail, for example, in “MIMO Radar Signal Processing” (Jian Li, 2009). Independent of electronic or mechanical beam steering, the product profile is created by assigning the individual product height values ​​to the corresponding lateral position. The lateral position on the product surface is described, for example, using the Cartesian coordinate system.Depending on the type of beam deflection, the solid angle must be converted into the corresponding Cartesian spatial coordinate.

[0009] Conventional level gauges have so far been permanently mounted on the container containing the material to be examined. However, due to regulatory requirements, among other things, there are also applications that require the determination of the material profile even for materials that are not stored in containers, such as excavated material or gravel dumps. A further problem with such applications is the vastness of the area to be examined. Conventional level gauges are therefore not suitable for such applications, as they require permanent installation. The invention is therefore based on the object of being able to determine the material height or the material profile even in such applications.

[0010] The invention solves this problem by a measuring system for determining a filling material height or a filling material profile, which comprises at least the following components:

[0011] A multicopter, in particular an unmanned one, comprising o a measuring unit designed to transmit radar signals, in particular according to the FMCW principle and in a frequency band of at least 20 GHz, towards the filling material and to receive them as received signals after reflection there, and o a control unit designed to control the position or flight path of the multicopter, and an evaluation unit designed o to determine a distance value of the multicopter to the filling material based on the received signal, and o to determine the filling material height at least based on the distance and at least the flight height of the multicopter at the position of the multicopter

[0012] A fundamental advantage of the measuring system according to the invention is that no static mounting above the filling material is required. The evaluation unit can be designed as a component of the measuring unit. Alternatively, a local base station or a higher-level unit, such as a server or process control center, can act as the evaluation unit of the measuring system. In this case, the multicopter and the evaluation unit must each be designed to communicate with each other via a common communication interface in order to transmit the possibly preprocessed received signal, individual distance or filling material height values, or the entire filling material profile.

[0013] In relation to the measuring system according to the invention, the term "unit" is understood to mean any circuit group intended for a specific application, e.g., as an interface or for high-frequency signal processing. Depending on the application, the respective unit can therefore comprise corresponding analog circuits for generating or processing corresponding analog signals. However, the respective unit can also comprise digital circuits, such as FPGAs, microcontrollers, or storage media in conjunction with corresponding programs. The program is designed to carry out the required method steps or apply the necessary computing operations. In this context, various electronic circuits of the unit within the meaning of the invention can potentially also access a common physical memory or be operated using the same physical digital circuit.It is irrelevant whether various electronic circuits within the unit are located on a common circuit board or on several connected circuit boards. If the measuring system includes a base station at the location of the product, the control unit and the base station can preferably be designed so that the current position of the multicopter is controlled relative to the local base station. This allows the absolute position and flight altitude of the multicopter to be recorded and controlled more precisely. Thus, the evaluation unit also determines the product height or profile relative to the corresponding local coordinate system.

[0014] If the multicopter or measuring unit is designed to variably adjust the beam direction of the beam cone, under which the radar signals are transmitted and received, at least over a defined angular range, the evaluation unit can determine corresponding angle-dependent distance values ​​in order to create an at least two-dimensional filling material profile. In the context of the present invention, the term "beam cone" refers to the solid angle under which the antenna or measuring unit has a defined, equal transmission intensity or reception sensitivity of, for example, -3 dB. The "beam direction" is described by the spatial vector under which the beam cone has maximum intensity.

[0015] Such beam steering can be achieved, for example, by rigidly attaching the measuring unit to the multicopter, and the control unit adjusting the orientation or flight attitude of the multicopter relative to the vertical accordingly, thus changing the beam direction. For beam steering, however, it is also conceivable for the measuring unit to include a radar mirror actuated by the control unit, by means of which the beam direction of the measuring unit can be changed within the angular range. Another alternative to beam steering is to design the measuring unit so that it can adjust the beam direction electronically, in particular using the MIMO principle.

[0016] In conjunction with beam steering, a special embodiment of the measuring system according to the invention involves setting a lateral beam direction of the beam cone in a separate operating mode. This can be used to detect any objects in the area of ​​the filling material, such as trees or construction machinery, that pose a collision risk. For this purpose, the evaluation unit must be upgraded to output a collision warning to the higher-level unit based on the corresponding received signal when the beam direction is set laterally.

[0017] The measuring system according to the invention can be used in various ways to determine the filling material height or a filling material profile: The following procedure is used to determine a single filling material height value: Flying to a defined position,

[0018] Recording the distance value at this position, and

[0019] Calculation of the corresponding location-related filling material height based on the distance value and the flight altitude.

[0020] In order to record a filling material profile using the measuring system, the following procedure can be used:

[0021] Flying a particularly meandering or circular flight path, recording distance values ​​along the flight path with a fixed beam direction, in particular vertically downwards, and

[0022] Creation of the filling material profile based on o the recorded distance values, and o the respective positions of the multicopter on the flight path.

[0023] If the jet cone can be pivoted at least along one axis in relation to the measuring unit, the following process steps can also be carried out to determine the filling material profile:

[0024] Flying a straight trajectory above the filling material at a defined altitude, simultaneously changing the beam direction orthogonal to the straight trajectory so that the beam cone of the radar signal describes a zigzag trajectory,

[0025] Recording distance values ​​along the trajectory,

[0026] Creation of the filling material profile based on o the recorded distance values, o the respective radiation direction, and o the respective position of the multicopter on the straight-line flight path.

[0027] Due to the straight flight path, this method is particularly suitable for filling materials that are distributed over an elongated area.

[0028] If the filling material has a rather round basic shape, the following procedure can preferably be used so that the filling material profile to be created

[0029] Covers the base area of ​​the filling material as completely as possible:

[0030] Flying to a defined position above the filling material, stationary rotation of the measuring unit or the multicopter around the vertical axis, simultaneous swiveling of the beam direction in relation to the measuring unit along the

[0031] axis, o where the beam direction is constantly changed so that the beam cone describes a spiral trajectory, or o where the beam direction is changed step by step so that the beam cone describes a trajectory with circles or circle segments running concentrically around the position,

[0032] Recording distance values ​​along the spiral or circular segment trajectory, and

[0033] Creation of the filling material profile based on o the recorded distance values, o the respective beam direction, and o the position and flight altitude of the multicopter.

[0034] The invention is explained in more detail with reference to the following figures. They show:

[0035] Fig. 1 : A measuring system according to the invention for determining the filling material profile, and

[0036] Fig. 2: possible methods for operating the measuring system.

[0037] For a basic understanding of the invention, Fig. 1 shows a bulk material 2, such as a gravel dump or excavated earth. A three-dimensional profile of the surface of the material is to be determined, for example, in order to be able to determine the volume or mass of the material 2 based thereon. According to the invention, a multicopter 1, in particular an unmanned one, is used for this purpose, which flies over the material 2 at a defined altitude h along a defined flight path or hovers above the material 2 at a stationary position [x; y; h].

[0038] In addition to a standard control unit for controlling the position [x; y], flight altitude h, and flight path of the multicopter 1, a radar-based measuring unit is installed there, analogous to stationary level measurement: Using the measuring unit, it is possible to determine the distance d of the multicopter 1 to a point below it on the filling material surface based on the current flight altitude h. For this purpose, radar signals SHF are emitted towards the surface of the filling material 2 via a radar antenna of the measuring unit within a predefined frequency band. The beam direction v of the beam cone emanating from the antenna is directed exactly vertically downwards in the illustration shown in Fig. 1.

[0039] After the transmitted radar signals SHF are reflected by the product surface, the measuring unit receives the reflected received signals RHF via the measuring unit's antenna. The signal propagation time t between transmission and reception of the respective radar signal S, RHF is determined according to proportional to the distance d, where c represents the propagation speed of the respective radar signal S, RHF, known in air.

[0040] The signal propagation time t can be determined, for example, using the FMCW or the pulse propagation time method. Accordingly,

[0041] L = h — d the filling material height L can be determined.

[0042] How the measuring unit of the multicopter 1 is to be designed with regard to the generation and processing of the radar signals SHF depends on the implemented radar method: Using an appropriately designed phase-locked loop (PLL), the FMCW method, for example, can be implemented on the transmit side. In this case, a mixer and subsequent Fourier transformation logic are used on the receive side. To ensure the antenna and measuring unit are designed as compactly as possible, it is advantageous if the radar signal SHF, RHF is generated or transmitted in a frequency band with a center frequency of at least 100 GHz: The higher the frequency, the more compact the antenna can be designed with the same beam width.Furthermore, a correspondingly high frequency band is advantageous, as the absolute value of the bandwidth can be increased, for example, to 2 GHz. This, in turn, increases the range resolution.

[0043] The evaluation of the received signal RHF to determine the signal propagation time t and the filling material height L based thereon can, within the scope of the invention, either be carried out in the measuring unit itself or this is implemented in an external evaluation unit that is not on board the multicopter 1.

[0044] As shown in Fig. 1, the evaluation unit can be, for example, a local base station 3 or a higher-level unit 4, such as a decentralized server or a process control center. In this case, the multicopter 1 and the evaluation unit communicate via a suitable interface in order to transmit the possibly already pre-processed received signal RHF ZU. The interface must be designed wirelessly, for example "Bluetooth", "WLAN" or "GSM", at least in the case of the higher-level unit 4. In the case of wireless data transmission, it is also possible for the evaluation unit 3, 4, with appropriate design, to create the filling material profile in real time during the flight. Regardless of whether the base station 3 functions as an evaluation unit, the base station 3 can also be used for recharging or as a hangar for the multicopter 1.Furthermore, with appropriate design, the base station 3 can serve as a local reference, so that the multicopter 1 or its control unit determines the position [x; y] and altitude h of the multicopter 1 relative to the local base station 3. This variant, in which the position [x; y] or altitude h does not refer to the global GPS coordinate system, offers the advantage of more precise positioning with a resolution of up to the centimeter, so that the control unit can control the flight path of the multicopter 1 more precisely.

[0045] The design of the flight path determines how the filling material profile is created using the measuring system according to the invention, or vice versa: In the simplest case, the control unit is instructed to fly to a defined position [x; y] and flight height h above the filling material 2 in order to determine a corresponding distance value d there, provided that it is only necessary to know the filling material height L at this position [x; y]. In this case, this location-specific filling material height L is calculated according to the above formula based on the distance value d and the flight height h. For this purpose, the beam direction v of the beam cone does not have to be pivotable; rather, the beam direction can be fixed.

[0046] A fixed beam direction v is also possible if the control unit is instructed to fly over the area to be examined or the filling material 2 in a defined trajectory in order to measure not only the filling material height at a selected position [x; y], but also as a filling material profile L x , y In this case, according to the measurement principle mentioned above, distance values ​​d are to be recorded at regular time or distance intervals along the flight path and assigned to the position [x; y] and flight altitude h that the multicopter 1 occupies when recording the respective distance value d. This assignment determines the filling material profile L x , y If a straight trajectory is chosen, the resulting filling material profile L x , y only two-dimensional. To achieve the highest possible area coverage and a three-dimensional filling material profile L x , yTo reach this area, the area can be flown over in a meandering or circular flight path, for example.

[0047] Fig. 2 shows two possible methods for creating three-dimensional filling material profiles L x , y visualized based on the measuring system according to the invention, by means of which the intended flight path can be shortened: In both cases, the prerequisite is that the measuring unit can change the beam direction v of the beam cone, under which the radar signals SHF and RHF are transmitted and received, relative to the normal along an axis over a defined angular range. The extent of the angular range depends, among other things, on the form in which the beam deflection is implemented, i.e., mechanically or electronically. The control of the measuring unit with regard to the currently set beam direction v of the beam cone is, in turn, subject to the control unit.

[0048] In the embodiment shown on the left in Fig. 2, the multicopter 1 is controlled such that it flies a straight flight path y at a defined flight altitude h above the area to be examined. During this time, the beam direction v is changed orthogonally x to the flight path y, so that the beam cone of the radar signal SHF, HF describes a zigzag-shaped trajectory b, as shown in Fig. 2. For a better overview, the flight path in the illustration on the left in Fig. 2 is drawn slightly offset from the filling material 2. Along the zigzag-shaped trajectory b, distance values ​​d are again recorded by the measuring unit: Together with the respective associated beam direction v, the respective associated position [x; y] and the flight altitude h of the multicopter 1 on the straight flight path y, the filling material profile L can be determined based on the distance values ​​d recorded in this way. x , y create.

[0049] Due to the rectilinear flight path y, this design variant is in principle preferably suitable for an elongated filling material 2. If the filling material 2, as indicated on the right in Fig. 2, has a predominantly round base, it is more suitable to fly the multicopter 1 to a central position [x; y] above the filling material 2 at a defined flight altitude h and to have the multicopter 1 or at least the measuring unit rotate around the vertical axis. The measuring unit is controlled by the control unit in such a way that during the rotation around the vertical axis, the beam direction v is simultaneously changed in a straight line along the axis with respect to the measuring unit, whereby the beam cone describes a spiral trajectory a as a whole, as illustrated on the right in Fig. 2. For reasons of clarity, the spiral trajectory a on the right in Fig. 2 is again not shown centrally above the filling material 2, but offset from it.

[0050] In the variant shown on the right in Fig. 2, distance values ​​d are recorded at regular intervals along the spiral trajectory a and assigned to the respective beam direction v. This and the known position [x; y] or flight altitude h of the multicopter 1 allow the respective distance value d to be assigned to the corresponding point [x; y] on the spiral trajectory a. This assignment, in turn, determines the filling material profile L. x , y A significant advantage of the method shown in Fig. 2 is that the measuring unit only needs to be designed for a one-dimensional swivel of the jet cone in order to create a three-dimensional product profile L x , y which significantly simplifies their construction. Instead of the variants shown in Fig. 2 for creating the filling material profile L x , yIt is, of course, also possible to design the measuring unit to allow the beam cone to be swiveled two-dimensionally. This also makes it possible to measure the filling material profile L x , y To do this, the system simply flies to one or more positions [x; y] above the filling material 2 in a stationary manner, in order to be able to determine the distance d in a spatially resolved manner in a corresponding solid angle range from there at a known flight altitude h by swiveling the beam cone in two dimensions. For this purpose, the MIMO principle, for example, can be implemented in the measuring unit. Based on the spatially resolved distance values ​​d x , y The unit 1, 3, 4 acting as an evaluation unit can in turn determine the corresponding spatially resolved level values ​​in order to calculate the three-dimensional filling material profile L x , y to create.

[0051] Regardless of the method implemented for recording the distance values ​​d or the choice of the trajectory / position [x; y], the distance values ​​d are assigned to the corresponding position [x; y] and the filling material profile L is created based on this. x , y in the evaluation unit 1, 3, 4.

[0052] The filling material profile L created according to the invention x , y can be used not only to determine the volume or, if the product density is known, the mass. In addition, based on the product profile L x , yWith the appropriate design of the evaluation unit 1, 3, 4, a more extensive object identification can be implemented using appropriate 3D or solid-body-based software, for example to detect rocks, broken edges or any foreign bodies on the filling material surface. In this context, it is conceivable to expand the measuring system according to the invention with an optical camera. This allows at least in selected areas of the filling material surface, in which, based on the determined filling material profile L x , y If a foreign body is expected, a photo should be taken to verify this. It goes without saying that the inventive recording of the filling material profile L x , y can also be repeated in predefined cycles in order to detect any changes in the filling quantity. List of reference symbols

[0053] 1 level gauge

[0054] 2 Filling material 3 Base station

[0055] 4 Superior unit a Zigzag trajectory b Spiral trajectory c Radar signal propagation speed d Distance h Altitude

[0056] L Filling height

[0057] RHF reception signals

[0058] SHF radar signals v beam direction x, y axes

Claims

Patent claims 1 . Measuring system for determining a filling material height (L) or a filling material profile (L x , y ), including: A multicopter (1), in particular an unmanned one, comprising: a measuring unit designed to transmit radar signals (SHF), in particular according to the FMCW principle and in a frequency band of in particular at least 20 GHz, towards the filling material (2) and to receive them as received signals (RHF) after reflection there, and comprising: a control unit designed to control at least the position ([x; y;]) and the flight altitude (h) of the multicopter (1), and an evaluation unit (1, 3, 4) designed: to determine a distance value (d) of the multicopter (1) to the filling material (2) on the basis of the received signal (RHF), and to determine the filling material height (L) at the position ([x; y;]) at least on the basis of the distance (d) and at least the flight altitude (h) of the multicopter (1).

2. Measuring system according to claim 1, wherein the evaluation unit is designed as a component of the measuring unit.

3. Measuring system according to claim 1, comprising: A local base station (3) and / or a higher-level unit (4) which functions as an evaluation unit, wherein the multicopter (1) and the evaluation unit (3, 4) are each designed to communicate with each other via a common communication interface.

4. Measuring system according to claim 1, wherein the control unit is designed to control the position ([x; y]) and flight altitude (h) of the multicopter (1) in relation to the local base station (3), and wherein the evaluation unit (1, 3, 4) is designed to determine the filling material height (L) or a filling material profile (L x , y ) with respect to a corresponding local coordinate system.

5. Measuring system according to one of claims 1 to 4, wherein the multicopter (1) is designed to pivot or changeably adjust the beam direction (v) of the beam cone, under which the radar signals (SHF, RHF) are transmitted and received, at least over a defined angular range, and wherein the evaluation unit (1, 3, 4) is designed to provide corresponding angle-dependent distance values (d x , y ) and to calculate from this at least a two-dimensional filling material profile (L x ,y).

6. Measuring system according to claim 5, wherein the measuring unit is rigidly attached to the multicopter (1) and the control unit is designed to control the orientation of the multicopter (1) with respect to the plumb line such that the beam direction (v) is changed.

7. Measuring system according to claim 5, wherein the measuring unit comprises a radar mirror which can be actuated by the control unit and by means of which the beam direction (v) of the measuring unit can be changed within the angular range.

8. Measuring system according to claim 5, wherein the measuring unit is designed to adjust the beam direction (v) electronically, in particular by means of the MIMO principle.

9. Measuring system according to claim 5 to 8, wherein the multicopter (1) is designed to adjust a lateral beam direction (v) of the beam cone, and wherein the evaluation unit (1, 3, 4) is designed to output a collision warning depending on the received signal (RHF).

10. Measuring system according to one of the preceding claims, comprising: an optical camera, by means of which an image can be recorded at at least one defined position ([x; y]) of the filling material surface.

11. Method for determining a filling material height (L) by means of the measuring system according to at least one of the preceding claims, comprising the following method steps: Approaching a defined position ([x; y]) at a defined altitude (h), recording the distance value (d) at this position ([x; y]) from this altitude (h), and Calculation of the corresponding location-related filling material height (L) based on the distance value (d) and the flight height (h).

12. Method for determining a three-dimensional filling material profile (L x , y ) by means of the measuring system according to at least one of claims 1 to 10, comprising the following method steps: Flying a particularly meandering or circular flight path, recording distance values (d) along the flight path under a fixed jet direction (v), in particular vertically downwards, and creating the filling material profile (L x , y) based on the recorded distance values (d), and o the respective corresponding positions ([x; y]) and flight altitude (h) of the multicopter (1 ) on the flight path.

13. Method for determining a three-dimensional filling material profile (L x , y ) by means of the measuring system according to at least one of claims 5 to 10, comprising the following method steps: Flying a straight-line flight path (y) at a defined flight altitude (h), simultaneously changing the beam direction (v) orthogonal (x) to the straight-line flight path (y), so that the beam cone of the radar signal (SHF, RHF) describes a zigzag trajectory (b), Recording distance values (d) along the trajectory (b), Creation of the filling material profile (L x , y) based on o the recorded distance values (d), o the respective associated radiation direction (v), and o the respective associated position ([x; y]) and flight altitude (h) of the multicopter (1) on the straight-line flight path (y).

14. Method for determining a three-dimensional filling material profile (L x , y ) by means of the measuring system according to at least one of claims 5 to 10, comprising the following method steps: Approaching a defined position ([x; y)] and flight altitude (h), stationary rotation of the measuring unit or the multicopter (1) around the vertical axis, simultaneous pivoting of the beam direction (v) in relation to the measuring unit along the axis, o wherein the beam direction (v) is constantly changed so that the beam cone describes a spiral trajectory (a), or o wherein the beam direction (v) is gradually changed so that the beam cone describes a trajectory with circles or circle segments running concentrically around the position ([x; y)], Recording of distance values (d) along the spiral (a) or Circle segment-shaped trajectory, and Creation of the filling material profile (L x , y ) based on o the recorded distance values (d), o the respective associated beam direction (v), and o the position ([x; y]) and the flight altitude (h) of the multicopter (1).

Images