Fill volume measurement

Abstract

The invention relates to a measuring system for determining a filling volume of a filling material (4) in a container (3). To this end, the measuring system comprises a 3D camera (2) and a radar-based level measurement device (1). The 3D camera (2) is used to first capture at least one 3D image ([pi,j]) of at least one portion of the interior of an empty container. On the basis of this 3D image ([pi,j]), a data set or digital space model is created which represents the geometry of at least this portion of the interior of the empty container. In order to create the desired three-dimensional surface or level profile (L(a, #)), the level measurement device (1) is based on the digital beamforming principle, such as the MIMO principle. Thus, on the basis of the data set which reflects the geometry in the interior of the container and on the basis of the level profile (L(a, #)), the filling volume in the container (3) can be determined.

Description

Technical Field

[0001] This invention relates to a measurement system and a method for determining the filling volume of a filling material in a container. Background Technology

[0002] In process automation, corresponding field devices are used to capture relevant process parameters. To capture these parameters, appropriate measurement principles are implemented within the field devices to obtain information such as level, flow rate, pressure, temperature, pH, redox potential, or conductivity. Endress+Hauser manufactures and sells a wide variety of field devices.

[0003] Non-contact measurement methods have been established for measuring the level of fill material in containers because they are robust and require minimal maintenance. Another advantage of non-contact measurement methods is their ability to measure level semi-continuously. Therefore, radar-based measurement methods are primarily used in the field of continuous level measurement (in the context of this patent application, "radar" refers to signals or electromagnetic waves with frequencies between 0.03 GHz and 300 GHz). One established measurement method is FMCW ("Frequency Modulated Continuous Wave"). For example, an FMCW-based level measurement method is described in published patent application DE 10 2013 108 490 A1.

[0004] Using the FMCW method, distance or level can be measured at least selectively. The point at which the level is measured depends on the orientation of the transmitting / receiving antenna or the direction of its lobes (due to the general reciprocal nature of antennas, the characteristics of the corresponding antenna lobes or its beam angle are independent of whether transmission or reception is in progress). For the purposes of this patent application, the term "angle" or "beam angle" refers to the angle at which the lobes have maximum transmission strength or receiving sensitivity.

[0005] In the case of liquid filler material with a uniform level, selective level measurement is sufficient. In these cases, the level measuring device is oriented such that the antenna lobe is approximately vertically downward, and the distance to the filler material is determined. If the internal container geometry is known, the filling volume of the filler material in the container can also be determined based on the selectively determined level value and the known container geometry. For this purpose, the container geometry can be presented in tabular form as a so-called tank table. The tank table links the level value to the corresponding filling volume. Tank tables can be created using a corresponding calibration filler material of a known quantity or volume of liquid filler material type. Theoretically, a tank table can be created if the container geometry or its dimensions are known.

[0006] In the case of solid fill materials, such as gravel or granules, the material level may be uneven due to the cone-shaped structure of the blocky material, making the intermittent level values ​​determined by the level measuring device meaningful only within a limited range. Therefore, especially in this case, it is desirable to be able to determine the distance or level in the form of a three-dimensional level profile. To this end, the level measuring device must be designed to assign the input radar signal to the associated solid angle. This can be achieved, for example, by means of digital beamforming principles, particularly by means of the MIMO ("Multiple-Input Multiple-Output") principle.

[0007] This principle is based on an antenna arrangement consisting of multiple transmitting and receiving antennas. Therefore, orthogonal radar signals are transmitted via each transmitting antenna to the other transmitting antennas, with the corresponding reflected signals received via each receiving antenna and digitized if necessary to determine the material level profile from the digitized received signals. In particular, the MIMO method is characterized by its effectively enlarged aperture. Therefore, compared to systems without an effectively enlarged aperture, MIMO-based radar systems improve spatial resolution. However, a drawback of digital beamforming methods is the potential for ambiguity and angular errors. According to existing technology, the entire hardware required to implement the MIMO principle can be compactly integrated, allowing the transmitting and receiving antennas to be housed together with the transmit / receive unit as patch antennas, on a common printed circuit board, or even as a co-packaged IC (“integrated circuit”). MIMO-based radar systems are described in more detail, for example, in “MIMO radar signal processing” (Jian Li), 2009.

[0008] In the case of solid filler materials, it is of interest to be able to determine the material level in the container in addition to the material level profile.

[0009] However, tank tables cannot be used to determine the filling volume of rough filler surfaces or corresponding filler materials because determining the filling volume based on tank tables requires smooth, horizontal filler surfaces, which is only the case for liquids.

[0010] Furthermore, depending on the application and type of filling material, solid containers are typically not formed from geometrically simple bodies: to avoid the accumulation of filling material, for easier filling and emptying, or for stability reasons, container walls are often curved, inclined, or wavy. In addition, containers often include fixtures such as supports, heating, cleaning, or maintenance equipment. Therefore, theoretical derivations of the internal geometry of a container based on its surface profile are only possible for precisely known container geometries. Subsequent changes due to modifications and alterations make determining the container geometry from planning documents even more difficult. Summary of the Invention

[0011] Therefore, the object of the present invention is to provide a measurement system by means of which the filling volume in a container can be determined even in the case of non-liquid filling materials.

[0012] This invention achieves this objective through a measuring system for determining the filling volume of a container's filling material, the system comprising the following components:

[0013] - A 3D camera, designed, for example, as a ToF sensor, and capable of being positioned to record at least one 3D image of at least one partial region inside the container.

[0014] - A radar-based level measurement device for creating a three-dimensional level profile of the surface of the filling material in a container. This device has:

[0015] ○ Antenna arrangement: Based on digital beamforming principles (such as MIMO), this antenna arrangement can transmit radar signals in the direction of the filling material, and can receive the corresponding received signals after the radar signals are reflected from the surface of the filling material.

[0016] The transmitting / receiving unit is designed to generate radar signals based on beamforming principles, and, based on these beamforming principles, at least on the received signals, to create a solid angle-dependent material level profile.

[0017] - Evaluation unit, which is designed as follows:

[0018] A dataset is created based on at least one 3D image, representing the geometry of at least a partial region inside the container, and

[0019] The filling volume is determined based on the dataset and material level profile.

[0020] Therefore, if the container is empty at least in the corresponding partial area, it is necessary to record a 3D image.

[0021] According to the present invention, the level measuring device can be designed, for example, to have a grommets for a 3D camera, wherein the antenna arrangement is preferably formed particularly around the circular grommets of the level measuring device. This allows a corresponding compact 3D camera to be guided or lowered into the container via the grommets to record 3D images when the level measuring device is installed. As an alternative to the grommets in the level measuring device or antenna arrangement, the 3D camera can also be designed as an integral part of the antenna arrangement. Furthermore, the evaluation unit can also be designed as a component of the level measuring device or the transmit / receive unit.

[0022] Corresponding to the measurement system or the level measuring device according to the present invention, the objective of the present invention is also achieved through a corresponding measurement method for operating the level measuring device. Therefore, the method includes at least the following steps:

[0023] - Record at least one 3D image of at least one partial area inside the container using a 3D camera.

[0024] - Create a dataset based on at least one 3D image, representing the geometry of at least a portion of the interior of the container.

[0025] -Using a level measurement device to create a solid angle-dependent level profile of the filling material surface, and

[0026] - Determine the filling volume based on the dataset and material level profile.

[0027] Within the framework of this application, the term "3D camera" includes any system by which the distance value of the nearest object is recorded as a corresponding pixel value in a selected image area. Thus, for example, a so-called ToF camera ("time-of-flight") can be used for this purpose, which includes a corresponding semiconductor-based sensor (also known as a PMD sensor, "photonic hybrid device"). However, the same function can also be achieved, for example, by means of a so-called light field camera or at least two interconnected conventional digital cameras.

[0028] Within the scope of this invention, the term "unit" generally refers to any electronic circuit designed in a manner suitable for its intended purpose. Thus, depending on the need, it can be an analog circuit for generating or processing corresponding analog signals. However, it can also be a digital circuit, such as an FPGA, or a storage medium that interacts with a program. In this case, the program is designed to perform corresponding method steps or apply the necessary computational operations of the corresponding unit. In this context, various electronic units of the measuring device in the sense of this invention can also potentially access common physical memory or operate by means of the same physical digital circuitry. Attached Figure Description

[0029] The invention will now be explained in more detail with reference to the accompanying drawings. In the drawings:

[0030] Figure 1 : This illustrates a measuring system according to the invention on a container.

[0031] Figure 2 : Shows a front view of the antenna arrangement of the material level measuring device according to the present invention. Detailed Implementation

[0032] To understand the present invention, Figure 1A container 3 with filling material 4 is shown, the filling volume of which is to be captured. The determination of the filling volume according to the invention is based on a preliminary determination of the internal geometry of the container (at least up to the maximum level L of the filling material 4) using a measuring system in the empty state of the container 3. max The height h). In subsequent operations, the current filling volume can be determined by using the stored container geometry and the currently measured level value L(α, β) with the (partially) filled container 4.

[0033] In this case, the height of container 3 can reach over 100m, depending on the type and application area.

[0034] like Figure 1 As schematically shown, dead zones often occur inside the container, for example, due to the external mounting location of container 3, which is necessary. Therefore, at least in this case, it is impractical to theoretically determine the container geometry by means of which the filling volume can be set with respect to the material level L(α, β). Therefore, the measurement system includes a 3D camera 2, by means of which a 3D image of the corresponding partial area inside the container [p] is obtained when container 3 is empty. i，j [was initially recorded. From 3D images [p] i，j Create a dataset that represents at least reaching the maximum level L. max The 3D coordinates or geometry inside the container. For further processing, it is also possible to create a complete digital space model from such a dataset. To be able to record 3D images, the 3D camera 2 can optionally be positioned at a variable location inside the container 3 or at a suitable opening of the container 3, such that recording 3D images [p] i，j Afterwards, no shadowed areas will remain inside the container due to any blind spots. In order to determine the corresponding position and / or orientation of the 3D camera 2 within the container 3 so that geometric data or spatial models can be subsequently calculated, for example, the corresponding acceleration or inertial sensors can be assigned to the 3D camera 2.

[0035] To determine the material level L(α, β), the measurement system includes a radar-based material level measuring device 1, which is attached to the container 3 at a known mounting height h above the filling material 4. The material level measuring device 1 is aligned and fixed to the container 3 such that it transmits a corresponding radar signal S via an antenna arrangement 11 along a vertical axis relative to the surface 2 of the filling material. HF In radar signal S HF After reflection at the surface of the filling material, the level measuring device 1 receives, via antenna arrangement 11, the radar signal R reflected by the distance d(α, β) between the level measuring device 1 and the surface of the filling material, according to the following formula. HF

[0036] d(α,β)=hL(α,β)

[0037] like Figure 1 As indicated, the surface of the filler material 4 is not planar. This is especially possible in the case of blocky filler material 4, for example, when a blocky cone is formed during filling of container 3. Furthermore, when the filler material 4 is pumped out, a conical depression can appear on the surface of the filler material. For this purpose, the level measuring device 1 is designed to determine the level L within a defined solid angle range [α; β] in the form of a three-dimensional level profile L(α, β). As the main measurement result, the level measuring device 1 determines the corresponding coordinate data of the grid of points on the surface of the filler material for each measurement. Thus, by means of interpolation of the coordinate data, the level profile L(α, β) is generated as a three-dimensional surface model. Since the angles α and β that travel perpendicularly to each other in the solid angle range [α; β] each refer to the vertical axis emanating from the level measuring device 1, the level profile L(α, β) or the underlying coordinate data initially appears in the form of polar coordinates α; β. To convert the polar coordinate-based material level profile L(x, y) to a Cartesian coordinate system, common coordinate transformation methods can be used to transform the corresponding angles α, β (since they are known as well as the corresponding measurement distance d(α, β) as measured by the material level measuring device 1).

[0038] For the solid angle determination of the material level L(α, β), the MIMO principle is implemented as a digital beamforming principle in the transmit / receive unit 12 of the material level measuring device 1 with control antenna arrangement 11. This means that the transmit / receive unit 12 generates the radar signal S to be transmitted according to the defined MIMO principle. HF And based on the MIMO principle and R HF The received signal creates a solid angle-dependent level profile L(α, β). As a result, the level measuring device 1 can assign a corresponding level value L(α, β) to each solid angle α; β within the solid angle range [α; β]. It goes without saying that, within the scope of this invention, any other principle of (digital) beamforming other than the MIMO principle can be implemented in the transmit / receive unit 12.

[0039] The level measuring device 1 can be connected to a higher-level unit 4, such as a process control system or a distributed data storage device, via an interface such as "PROFIBUS," "HART," or "Wireless HART." Level profiles L(x, y) and L(α, β) can be transmitted via this interface, for example, to control any inflow or outflow from the container 3. Furthermore, other information, such as information about the general operating status of the level measuring device 1, can also be conveyed. However, within the scope of this invention, this interface can also be used specifically to establish direct communication with the 3D camera 2 within the measuring system when necessary.

[0040] In the case of direct communication between the level measuring device 1 and the 3D camera 2, for example, a 3D image determined by the 3D camera 2 for determining the geometry of the container [p] i，j The data may be transmitted to the level measuring device 1. In this case, for example, the evaluation unit 12 of the level measuring device 1, which is designed accordingly, can be based on at least one 3D image of the digital spatial model. i，j A dataset is created to represent the geometry of relevant regions inside the container, which is then used to determine the current filling volume in conjunction with the corresponding current material level profile L(α, β). Correspondingly, it is also conceivable that the dataset or spatial model has been created in the corresponding evaluation unit of the 3D camera 2 before being transmitted to the material level measuring device 1 used to determine the filling volume, using the dataset or spatial model to describe the geometry of relevant regions inside the container.

[0041] Compared to direct communication between the level measuring device 1 and the 3D camera 2, it is also possible to transmit data from the level measuring device 1 and the 3D image [p] i，j The current material level profile L(α, β) of the already calculated container geometry dataset is emitted from 3D camera 2 to the parent unit 5.

[0042] In this case, the upper-level unit 5 can act as an evaluation unit so as to evaluate based on the 3D image [p i，j Determine the geometry of the container, or based on this, determine the current filling volume using the current material level profile L(α, β).

[0043] Depending on the unit that determines the filling volume based on the internal geometry of the container and the material level profile L(α, β), any angular errors and / or ambiguities of the material level measuring device 1 can also be compensated there, in particular by matching the material level profile L(α, β) with the internal geometry of the container.

[0044] like Figure 1 As indicated, the level measuring device 1 is designed with continuous loops 13, allowing the 3D camera 2 to descend via the loops 13, for example, on a telescopic rod, into the interior of the container to record the desired 3D images. i，j And rotate accordingly. In recording 3D images [p i，j Afterwards, or before filling container 3, remove 3D camera 2 from inside the container. A front view of the antenna arrangement 11 designed for this purpose is shown in... Figure 2 As shown in the diagram: In this embodiment, the transmitting and receiving antennas of antenna arrangement 11 are arranged around a circular grommet 13. Each transmitting or receiving antenna is arranged in two straight rows, extending tangentially outside the circular grommet 13 and facing each other on the grommet 13. (The last sentence appears to be incomplete and possibly refers to a different embodiment.) Figure 1 and Figure 2Compared to the embodiment of the 3D camera with integrated cable loops 13 shown in the invention's level measuring device 1, it is also conceivable that the 3D camera could be designed as a fixed component of the antenna arrangement 11, for example, replacing the cable loops 13 arranged in rows between the transmitting and receiving antennas. However, for this embodiment, which is not shown in more detail, the recording of 3D images [p] i，j The potential field of view is reduced, so that the material level profile L(α, β) can be determined only on container 3 with low geometric complexity.

[0045] Reference tag list

[0046] 1. Material level measuring equipment

[0047] 2 3D cameras

[0048] 3 containers

[0049] 4. Filling material

[0050] 5. Upper-level unit

[0051] 11 Antenna Arrangement

[0052] 12 Evaluation Units

[0053] 13. Gripping ring

[0054] d Distance, separation distance

[0055] h Installation height

[0056] L(α, β) material level profile

[0057] [p i，j 3D images

[0058] R HF Reflected radar signals

[0059] S HF radar signals

[0060] α, β solid angles

Claims

1. A level measuring device (1) for creating a level profile (L(α, β)) of the surface of a filling material (4) in a container (3), comprising the following components: - Antenna arrangement (11), by means of which, according to the principle of digital beamforming, radar signals (S) in the direction of the filling material (4) can be emitted. HF And by means of the antenna arrangement, the radar signal (S) can be reflected on the surface of the filling material. HF After receiving the corresponding received signal (R) HF ), - Transmit / receive unit (10), the transmit / receive unit being designed to generate the radar signal (S) according to the beamforming principle. HF ), and according to the beamforming principle, at least based on the received signal (R) HF ), to create the solid angle-related material level profile (L(α, β)). The antenna arrangement (11) of the material level measuring device (1) is formed around the circular cable ring (13) of the material level measuring device (1), such that the 3D camera (2) passing through the cable ring (13) inside the container is oriented.

2. The material level measuring device according to claim 1, wherein, The transmitting / receiving unit (10) is designed to generate the radar signal (S) according to the MIMO principle. HF And create the material level profile (L(α, β)) according to the MIMO principle.

3. A measuring system for determining the filling volume of filling material (4) in a container (3), comprising the following components: - 3D camera (2), said 3D camera being positioned such that it records at least one 3D image of at least one partial region inside the container ([p i，j ]), - The radar-based level measuring device (1) according to claim 1 or 2, wherein the radar-based level measuring device is used to create a level profile (L(α, β)) on the surface of the filling material, and - Evaluation unit (12), the evaluation unit is designed as follows: ○ Based on at least one 3D image ([p i，j Create a dataset that represents the geometry of at least a portion of the region inside the container, and ○ Determine the filling volume based on the dataset and the material level profile (L(α,β)).

4. The measurement system according to claim 3, wherein, The 3D camera (2) is designed as a component of the antenna arrangement (11) of the material level measuring device (1).

5. The measurement system according to claim 3, wherein, The evaluation unit (12) is designed as a component of the material level measuring device (1).

6. The measurement system according to any one of claims 3 to 5, wherein, The 3D camera is designed as a ToF sensor.

7. A method for determining the filling volume of filling material (4) in a container (3) by means of a measuring system according to any one of claims 3 to 6, the method comprising the following process steps: - Using the 3D camera (2), at least one 3D image of at least one partial area inside the container is recorded ([p i，j ]), - Based on at least one 3D image ([p i，j Create a dataset that represents the geometry of at least a portion of the region inside the container. - The solid angle-dependent level profile (L(α, β)) of the filling material surface is created using the level measuring device (1), and - The filling volume is determined based on the dataset and the material level profile (L(α, β)).

8. The method according to claim 7, wherein, The at least one 3D image is recorded when the container (3) is empty at least in the corresponding partial area.

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