Measuring device and method

Abstract

The subject of the invention is a measuring device (1) for more accurate measurement of the Biot parameters of acoustic materials. The measuring device according to the invention is characterised by a horizontal and vertical frame (2, 3), an upper pressure plate (6) moving on the vertical frame (3), a computer- controlled (21) actuating mechanism, and control electronics (16) moving the upper pressure plate (6).

Description

[0001] MEASURING DEVICE AND METHOD

[0002] The subject of the invention is a measuring device and method for more accurately measuring the Biot parameters of acoustic materials, including the determination of data necessary for more accurate determination of the Biot parameters.

[0003] Materials with noise-reducing and sound-absorbing properties are used in many industries, especially in the automotive industry. The behavior of such materials can be described and simulated using specific material properties, such as Biot parameters. These include, for example, porosity, airflow resistance, tortuosity, etc. Among the Biot parameters, the Young's modulus, damping, and Poisson's ratio are of great importance, and the so-called state-of-the-art QMA (Qiasi-static mechanical analysis - analyser) measurement method is used to measure them accurately. The known method and the equipment used for this purpose operate on the principle that the measured sample is compressed under preload, and then the force acting on the material and the associated deformation are measured by generating a pulsating vibration. From these, the magnitude of the Young's modulus, damping, and Poisson's ratio are concluded. This method is used by the Canadian company Mecanum [see Langlois, C , Panneton, R., Atalla, N.: Polynomial relations for quasi-static mechanical characterization of isotropic poroelastic materials "Journal": The Journal of the Acoustical Society of America, 110 (6) (2001), pp. 3032-3040; https: / / www.researchgte.net / publication / 235331996_Polynomial_relations_for_quasi- static_mechanical_characterization_of_isotropic_poroelastic_materials]

[0004] The disadvantage of the known method and apparatus is that

[0005] 1) the preload force, the initial thickness, the CR [compression ratio or compression rate, i.e. the strain (or the equivalent of strain, only in the case of pressure and not tension), i.e. the ratio of the displacement or length (or height, as the case may be) change to the initial length (or height) of the sample, i.e. dl / L (dl=length change, or height change, or displacement of the top of the sample) divided by the initial or original, i.e., unloaded length or, if desired, height of the sample = L], which is measured and determined using a dynamic sensor rather than a static method, as contact detection can lead to inaccuracy depending on how rigid the material is.

[0006] 2) since the thickness / force-thickness / force-displacement / stiffness-strain (CR) / stress-strain curves are not displayed correctly, the measured material properties (Young's modulus, damping, Poisson's ratio) are also insufficient, which negatively affects the material properties obtained. 3) the Poisson's ratio is not measured geometrically but is inferred indirectly, which can yield incorrect results due to material inhomogeneity if the material is significantly inhomogeneous, which also depends on the manufacturing technology of the examined sample.

[0007] The objective of the present invention is to develop a measuring device that overcomes the disadvantages of known solutions, is accurate, and provides results that accurately reflect material properties.

[0008] The present invention is based on the recognition that measuring the applied force with a static load cell - e g., a mg-accurate balance - ensures accurate measurement. The accuracy of the measurement can be increased by precise electronic control of the displacement, and the determination of Poisson's ratio becomes more accurate with a more precise determination of the geometry.

[0009] The objective of the present invention is achieved by a measuring device which is characterized in that it has a horizontal and vertical frame, an upper pressure plate mounted on the vertical frame, a computer-controlled drive mechanism for moving the upper pressure plate, and control electronics.

[0010] In a preferred embodiment of the measuring device according to the invention, the drive mechanism is formed by a linear guide built into the vertical frame, a ball screw connected to a stepper motor via a coupling between the linear guides, a ball nut which is connected to the linear carriages of the carriage moving along the ball screw and which drives the upper pressure plate.

[0011] In another preferred embodiment of the measuring device according to the invention, a load cell is built into the horizontal frame.

[0012] In a further preferred embodiment of the measuring device according to the invention, the control electronics comprise a stepper motor controller connected to the stepper motor and equipped with a separate power supply, a motion control card equipped with a separate power supply, and a computer.

[0013] In one preferred embodiment of the measuring device according to the invention is also equipped with a camera.

[0014] The measuring device according to the invention is described in detail with reference to the accompanying drawings, in which

[0015] Figure 1 shows an axonometric view of the measuring device according to the invention,

[0016] Figure 2 shows a front view of the measuring device shown in Figure 1,

[0017] Figure 3 shows a rear view of the vertical stand of the measuring device shown in Figure 1, and

[0018] Figure 4 is a block diagram of the electronics of the measuring device shown in Figure 1. Figure 1 shows an axonometric representation of measuring device 1 according to the invention. Measuring device 1 enables more accurate determination of the Biot parameters that define a poroelastic material's sound-absorption capabilities, particularly measuring Young's modulus, damping, and Poisson's ratio more precisely.

[0019] Measuring device 1 consisting essentially of horizontal frame 2 ensuring the stability of the device, vertical frame 3 connected to the horizontal frame 2, upper pressure plate 6 that can be moved up and down by a carriage 7 on the vertical frame 3, linear guides 8 that ensure the movement of the pressure plate 6 and form the vertical frame 3, and ball nut 13 and ball screw 9 placed between the linear guides 8, coupling 15 located above the vertical frame 3 and ensuring the operation of the ball screw 9, stepper motor 11 connected to the coupling 15, and load cell 4 integrated into the horizontal frame 2, functioning as static balance with milligram resolution (optionally equipped with a display) (see Figure 2), and electronics 16 for operating the measuring device 1.

[0020] Figure 2 shows the measuring device 1 according to the invention in a front view.

[0021] The horizontal frame 2 is essentially a square body, where the integrated load cell 4 serves as the lower pressure plate and is installed in front of the vertical frame 3 in the plane of the horizontal frame 2. The lower pressure plate itself, i.e., the load cell 4, is permanently installed and connected to the electronics 16 of the measuring device 1.

[0022] The upper pressure plate 6 is attached to the bottom of the carriage 7, which carriage 7 consists essentially of two linear carriages 14 (see Figure 3). The linear carriages 14 surround the movable ball nut 13 of the ball screw 9 arranged between the linear guides 8 of the vertical frame 3.

[0023] The sensor 12 is located at the top of the vertical frame 3, which is preferably an inductive sensor, essentially a limit switch, which can also be used to determine the exact position of the upper pressure plate 6 and to determine the exact thickness, displacement, and elongation of the element to be measured.

[0024] Bearing housing 10 is above the vertical frame 3, which, on the one hand, secures the ball screw 9 and, on the other hand, via coupling 15, provides rotational motion to the ball screw 9 under the action of stepper motor 11, whereby the upper pressure plate 6 is moved via the carriage 7.

[0025] The rotational motion provided by the stepper motor 11 to the ball screw 9 is converted into linear motion by means of the ball nut 13, causing the upper pressure plate 6 to move upwards or inwards, whereby the material to be measured, i.e., the sample, arranged on the lower pressure plate, the load cell 4, is compressed by the applied force.

[0026] The measuring device 1 according to the invention also comprises an electronics, which is used to control the operation of the measuring device 1, the ball screw 9, the ball nut 13, and the movement of the carriage 7 connected to the ball nut 13, and measuring the properties of the material to be examined - the sample - held and compressed between the lower 5 and upper 6 pressure plates, and evaluating the measured results.

[0027] The block diagram of the electronic 16 is shown in Figure 4. The electronics itself comprises a power supply 17 and the stepper motor controller 18 controlling the operation of the stepper motor 11, a motion control card 20 also supplied by power supply 19, and a computer 21. In addition to controlling the device, the computer 21 also comprises an evaluation module. The evaluation module is used to receive and process the data generated during measurement, including, in particular, the signal from load cell 4 and the displacement of the upper pressure plate 6. The module organizes incoming signals into a uniform data format, taking calibration settings into account, and prepares them for further calculations and display.

[0028] In a preferred embodiment, the electronics 16 comprises a closed-loop control unit that controls the movement of the upper pressure plate 6 based on continuous feedback. The control unit uses the output signal of the load cell 4 to determine the force acting on the sample, and calculates the actual displacement of the upper pressure plate 6, thereby calculating the change in thickness of the sample, from the number of steps of the stepper motor 11 and / or from the lead of the ball screw 9.

[0029] The control can be implemented in two modes. In one mode, the control unit maintains the force exerted on the sample at a constant value, while in the other mode, it compresses the sample to a specified compression ratio relative to its initial thickness. The compression ratio is calculated from the ratio of the initial thickness recorded when the sample contact is detected and the actual thickness.

[0030] The sample contact is detected by the electronics 16 by comparing the signal from the load cell 4 with a preset force threshold, and the initial thickness of the sample is then recorded. For this purpose, the electronics 16 preferably comprise a force threshold comparison input that directly compares the load cell 4 signal with the set reference value This input ensures that the sample contact is detected accurately and automatically, without operator intervention. According to a preferred embodiment, the closed-loop control unit is further preferably suitable for setting a preloading step that creates a small preload on the sample before the measurement begins. This preload ensures that the starting point of the measurement is recorded under the same conditions for each test, thereby increasing the reproducibility of the measurement data. The control unit controls the stepper motor 11 via the stepper motor controller 18, which drives the ball screw 9 via the coupling 15, thereby ensuring precise and reproducible movement of the upper pressure plate 6. Parameterization and operating mode selection are accessible from computer 21, via motion control card 20.

[0031] With this design, the measuring device 1, by combining static, milligram -resolution force measurement by the load cell 4 with closed-loop control, enables stable, reproducible loading conditions over a wide range of stiffnesses. This eliminates the uncertainties of dynamic preload measurement and allows the device to accurately determine the Poisson's ratio based on a single sample, and parameters that ensure a more accurate determination of the Biot parameters of the material under examination.

[0032] The measuring device 1 according to the invention is primarily used to determine the material properties of acoustic materials used in vehicles. The purpose of the application of the measuring apparatus 1 is to determine the exact material properties - Biot parameters - for simulations. The measuring machine 1 is primarily used to measure small cylindrical samples made of foam- like / sponge-like or fibrous materials, e.g., felt-like materials. As mentioned above, a cylindrical sample is usually prepared from the material to be examined and placed on the lower pressure plate, i.e., load cell 4, of the measuring device 1. The upper surface of the load cell 4, which is integrated into the horizontal frame 2 and functions as a static balance with milligram resolution, forms the lower pressure plate 5, on which the sample is supported, and accurate, reproducible force measurement is performed. The load cell 4 is in direct data communication with the control electronics, and its signal serves as the feedback quantity for the control loop. Owing to this high- precision balance - i.e., a milligram-resolution balance - the force can be measured accurately.

[0033] Machine 1, according to the invention, also comprises an upper pressure plate 6 that can be moved vertically via the drivetrain.

[0034] The signal from computer 21 is transmitted via motion sensor card 20 or stepper motor controller 18 to stepper motor 11, which results in rotational motion.

[0035] The shaft of the stepper motor 11 is connected to the ball screw 9 via the couplings 15, causing the ball screw 9 to rotate. The rotational motion of the ball screw 9 is converted into linear motion by virtue of the interaction between the ball screw 9 and the ball nut 13, thereby causing the upper pressure plate 6 to move. When the movement of the upper pressure plate reaches the top of the sample to be examined, the load cell 4 displays a value other than 0. During the measurement, the force exerted perpendicular to the sample is determined by the load cell 4 integrated into the horizontal frame 2, which functions as a static balance with milligram resolution. The signal from load cell 4 is displayed in units of mass, which the control electronics automatically convert to the force acting on the sample. The initial thickness is the height of the sample recorded directly upon detection of the sample contact. The control electronics detect the sample contact when the signal from load cell 4 exceeds a preset force threshold. During the measurement, the thickness of the sample decreases under the applied load. The actual thickness is determined from the displacement of the upper pressure plate 6, which the device calculates from the number of steps of the stepper motor 11 and / or the rise of the ball screw 9, taking into account the calibrated transmission ratios of the drivetrain.

[0036] The compression ratio expresses the degree of compression of the sample, that is, the extent to which the height of the sample has decreased relative to the initial thickness. This quantity is derived directly from the ratio of the initial and actual thicknesses. The measuring device 1 supports two control modes: on the one hand, constant-force control, and on the other hand, prescribed-compression-ratio control. In both cases, the control unit controls the movement of the upper pressure plate 6 based on continuous feedback, ensuring stable and reproducible measurement conditions.

[0037] It is noted that, although in the illustrated embodiment the load cell 4 is a balance, and thus the display will show milligrams or grams, this can be converted according to the measurement conditions, and we can accurately determine the magnitude of the force exerted on the test sample and with the computer 21 we can accurately control the compression or length change created in the test sample by the upper plate 6.

[0038] By accurately determining the magnitude of the force and displacement, the measured sample can be defined by the following parameters:

[0039] - sample thickness, volume, bulk density,

[0040] - force-displacement curve, stiffness-strain curve, stress-strain curve

[0041] Note that the curves can be displayed automatically using a suitable program or in the traditional way by recording the measurement points,

[0042] - static stiffness, static elastic modulus,

[0043] - for dynamic machines and dynamic measurements, the preload / initial elongation / initial compression can be determined using the measuring device according to the invention.

[0044] The evaluation module automatically generates force-displacement, stress-strain, and stiffness-strain curves based on the measurement data and displays them on the computer 21 interface or exports them to a file format.

[0045] It should be noted that one embodiment of the measuring device according to the invention can be combined with a camera, Poisson's ratio, even for a single sample, can be determined using the finite element method. In a preferred embodiment, the measuring device 1 is equipped with a camera that takes high-resolution images of the sample placed between the lower pressure plate 5 formed by the load cell 4 and the upper pressure plate 6. The camera is capable of continuously documenting the deformation of the sample under load and supplying data to the computer 21. In addition to controlling the measuring device 1, the computer 21 may optionally comprise additional functional units. These include, for example, an image processing unit that analyzes the images from the camera, extracts the outer contour of the sample from the images, and determines the actual thickness of the sample, i.e., the distance between the upper and lower 6, 5 pressure plates. The computer 21 may further preferably comprise a model -fitting unit that compares the geometric data obtained from image processing and the load data provided by the load cell 4 with the results of finite element simulations. The simulations can be run with different Poisson's ratios, so that the degree of lateral deformation actually observed on the sample, known as “barreling”, can be directly compared with the deformations in the simulation. With this method, the Poisson's ratio of the sample can be unambiguously determined even from a single sample, eliminating errors arising from inhomogeneity across multiple samples.

[0046] Advantages of the measuring device according to the invention:

[0047] - the thickness of the sample can be accurately determined from a single sample

[0048] - determination of Poisson's ratio

[0049] - accurate determination of displacement and elongation.

[0050] During the measurement method according to the invention, a sample taken from an acoustic material is placed on the lower pressure plate 5, forming the upper surface of the load cell 4. The upper pressure plate 6 is moved towards the sample by the actuating mechanism until the signal from the load cell 4 reaches the preset force threshold. At the same time, the initial thickness of the sample is determined. Subsequently, according to a preferred embodiment, the electronics 16 move the upper pressure plate 6 with closed-loop control based on either a predetermined force or a compression ratio relative to the initial thickness. However, the invention is not limited to the closed-loop control. During loading, the signals from the load cell 4 and the displacement of the upper pressure plate 6 are recorded. Mechanical characteristics such as the elastic modulus and static stiffness can be determined from the recorded data, and the Biot parameters can then be calculated from these. In a preferred embodiment, the deformation of the sample is recorded by an integrated camera, and the recorded images are compared by the computer 21 model-fitting unit with preliminary finite element simulations, from which the Poisson's ratio of the sample can be determined. The displacement of the upper pressure plate 6 can be determined from the number of steps of the stepper motor 11 or the rise of the ball screw 9, which provide accurate feedback on the compression of the sample.

Claims

PATENT CLAIMS1. Measuring device (1) for determining the parameters necessary for the accurate determination of the Biot parameters of acoustic material samples, which comprises a horizontal frame (2), a vertical frame (3), an upper pressure plate (6) movable on the vertical frame (3), a drive mechanism controlled by a computer (21) for moving the upper pressure plate (6) and control electronics (16), characterised in that the device comprises a load cell (4) configured as a lower pressure plate (5) and functioning as a static milligram resolution balance, and the control electronics (16) has a control unit for moving the upper pressure plate (6) according to force or compression ratio.

2. The measuring device according to Claim 1, characterized in that the actuating mechanism comprises linear guide (8), a ball screw (9), a ball nut (13) moving on the ball screw (9) and a carriage (7) connected to the ball nut (13) with linear carriages (14), and a stepper motor (11) driving the ball screw (9) and a coupling (15).

3. A measuring device according to any one of Claims 1 to 2, characterized in that the control electronics (16) comprise a stepper motor controller (18) with a separate power supply (17) and a motion control card (20) with a separate power supply (19).

4. A measuring device according to any one of Claims 1 to 3, characterized in that it comprises a sensor (12) formed as a limit switch and / or reference sensor for determining the position of the upper pressure plate (6).

5. A measuring device according to any one of Claims 1 to 4, characterized in that it comprises a camera for recording the deformation of a sample placed between the pressure plates (5, 6).

6. The measuring device according to Claim 5, characterized in that the computer (21) comprises an image-processing unit and a finite element model-fitting unit, which image-processing unit is formed to process geometric data from the camera, and the model-fitting unit is formed to compare the processed data with the results of finite element simulations in order to determine the Poisson's ratio of the sample.

7. A measuring device according to any one of Claims 1 to 6, characterized in that the control electronics (16) comprises a force threshold comparison input for detecting sample contact and initial thickness.

8. A measuring device according to any of Claims 1 to 7, characterized in that it has a closed-loop control unit for moving the upper pressure plate (6) according to force or compression ratio.

9. A measuring device according to Claim 8, characterized in that the closed-loop control unit is formed for adjusting the preload step.

10. A measuring device according to any one of Claims 1 to 9, characterized in that the computer (21) is equipped with an evaluation module for generating force-displacement, stress-strain and / or stiffness-strain curves.

11. A measuring device according to any one of Claims 1 to 10, characterized in that the evaluation module is configured to determine the parameters required for calculating the Biot parameter set from the specified mechanical characteristics.

12. Method for determining the parameters necessary for calculating the Biot parameters of acoustic material samples using such a measuring device (1), which comprises a horizontal frame (2), a vertical frame (3), a movable upper pressure plate (6) on the vertical frame (3), and a load cell (4) configured as a lower pressure plate, characterized in that- the sample is placed on the load cell (4) configured as a lower pressure plate,- the upper pressure plate (6) is moved towards the sample by means of the actuating mechanism,- the sample contact is determined based on a comparison of the signal of the load cell (4) with a predetermined force threshold, and at the same time, the initial thickness of the sample is determined,- the control electronics (16) then moves the upper pressure plate (6) with a closed-loop control according to a predefined force or a compression ratio relative to the initial thickness,- during the load test, we record the signal of the load cell (4) and the displacement of the upper pressure plate (6),- and from the recorded data, we determine the mechanical characteristics and the parameters necessary for determining the Biot parameters.

13. The method according to Claim 12, characterized in that the deformation of the sample is recorded with a camera and the recorded images are compared with finite element simulations to determine the Poisson's ratio.

14. A measuring device according to Claim 12 or 13, characterized in that the displacement of the upper pressure plate (6) is determined from the number of steps of the stepper motor (11) and / or the rise of the ball screw (9).LIST OF REFERENCE NUMBERS measuring device horizontal frame vertical frame load cell lower pressure plate upper pressure plate carriage linear guide ball screw bearing housing stepper motor sensor ball nut linear carriages coupling electronics power supply stepper motor controller power supply motion control card computer

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