A device and method for measuring natural frequency of a force sensor

Abstract

The invention provides a device and method for measuring the natural frequency of a force sensor. The device comprises a loading device, a base plate, an extensometer and a host computer electrically connected to the extensometer. A hoop is provided on the base plate, a plurality of protrusions are equidistantly provided on the hoop, a push rod is sleeved on the protrusion, a spring is sleeved on one end of the push rod, and a push plate is fixed on one end of the push rod. A clamping mechanism is provided on the cutter head of the extensometer. The method comprises the following steps: measuring the mass of the force sensor; applying a force F0 of 20% of the full scale to the force sensor by using the loading device, and then clearing the extensometer; applying a target load F1 to the force sensor, and measuring the deformation L of the force sensor by the extensometer, and finally calculating the natural frequency of the force sensor. The invention fixes the force sensor and measures the natural frequency by using the device provided by the invention in a static state, thereby overcoming the influence of the position factor in the dynamic measurement method and improving the measurement accuracy of the natural frequency of the force sensor.

Description

Technical Field

[0001] The invention relates to the field of measuring devices, in particular to a device and method for measuring the natural frequency of a force sensor. Background Art

[0002] Force sensors are sensitive devices used to measure force parameters. They can be used to measure both static and dynamic forces. For the measurement of static force, force sensors and their indicating instruments only need to be calibrated for indication. However, for the dynamic measurement process, not only the static sensitivity of the force sensor needs to be calibrated, but also the natural frequency of the sensor must be calibrated to determine whether the dynamic characteristics of the force sensor meet the dynamic measurement requirements. According to the requirements of JJG 556-2011 "Verification Procedure for Axial Loading Fatigue Testing Machines", when measuring dynamic force, the natural frequency of the measuring sensor system must be at least 15 times the measured frequency. This is the basic technical requirement for force sensors used for dynamic measurement. If the natural frequency of the force sensor does not meet the technical requirements, it will lead to large measurement errors and the amplitude of the dynamic force value cannot be accurately measured.

[0003] The current technical specifications only have a simple description of the natural frequency measurement method. The measurement of natural frequency in JJF 1053-1996 "Load Sensor Dynamic Characteristics Calibration Specification" can be obtained from the resonant peak of the amplitude-frequency characteristic; the draft "Dynamic Force Sensor Calibration Specification" points out that the natural frequency can be measured by a force hammer and a dynamic signal analyzer.

[0004] The above two measurement methods are both dynamic measurement methods. At present, the common measurement methods for natural frequency generally adopt random vibration method and pulse vibration method.

[0005] The random vibration method is to install the force sensor under test on the vibration test bench, give a random vibration signal, measure the vibration signal at the response point, and use FFT transformation to convert the signal time domain curve into a frequency domain curve. According to the frequency domain curve, the natural frequency of the sensor under test is measured.

[0006] The pulse vibration method is to suspend the force sensor to be measured with a suspension device. For sensors with a small range, a pulse hammer can be used to give the sensor an impact pulse; for force sensors with a larger range, a drop hammer standard device is required to measure the frequency response characteristics of the signal and obtain the natural frequency of the sensor to be measured.

[0007] Although the natural frequency of the force sensor can be measured in theory using the above method, there are many influences in the actual measurement process, which will lead to low measurement accuracy or large measurement uncertainty.

[0008] 1) Different installation positions of sensors, vibrations and uncertainties introduced by measuring devices will affect the measurement results. Whether using the random vibration method or the pulse vibration method, the different installation positions of the force sensor on the vibration test bench or the suspension mechanism will lead to large deviations in the measurement results; the distortion, uniformity, stability of the vibration table and the uncertainty introduced by the frequency response measuring instrument are also large.

[0009] 2) Exciting the force sensor at different positions will also have a significant impact. Whether the force sensor natural frequency test is performed using the random vibration method or the pulse vibration method, if the position of the excitation point is changed, the natural frequency measurement result will also change to a certain extent.

[0010] The reason for the above influence is that the structure of the sensor being measured is not a completely regular structure, which results in a great influence on the measurement results regardless of the installation position or the excitation point position, making the measurement uncertainty of the natural frequency larger. Summary of the invention

[0011] The purpose of the present invention is to overcome the deficiencies of the prior art and to provide a device and method for measuring the natural frequency of a force sensor to solve the technical problems raised in the above-mentioned background technology.

[0012] The objective of the present invention is achieved through the following technical solutions:

[0013] A force sensor natural frequency measuring device comprises a loading device, a base plate, an extensometer and a host computer electrically connected to the extensometer;

[0014] The base plate is provided with a hoop, and a plurality of convex parts are equidistantly arranged on the hoop, and a push rod is sleeved on the convex part, and a spring is sleeved on one end of the push rod, and a push plate is fixed to one end of the push rod, and a locking nut is provided on the other end of the push rod, and the push rod is fixed to the hoop through the locking nut;

[0015] A clamping mechanism is provided on the cutter head of the extensometer, and the clamping mechanism includes a fixing rod and an adjusting rod. The fixing rod includes a fixing portion and an adjusting portion which are perpendicular to each other. The adjusting rod is slidably connected to the adjusting portion. A clamping cavity for clamping a force sensor is formed between the adjusting rod and the fixing portion. The adjusting rod adjusts the size of the clamping cavity by sliding along the adjusting portion. The adjusting rod is also provided with an installation groove for installing the cutter head of the extensometer.

[0016] In the above invention, further, the adjusting portion is provided with a slide groove, and one end of the adjusting rod passes through the slide groove and is fixed to the adjusting portion through an adjusting nut.

[0017] In the above invention, further, the push plate and the inner wall of the fixing portion are respectively provided with a first arc groove and a second arc groove.

[0018] In the above invention, further, the inner wall of the push plate, the inner wall of the fixing portion, the inner wall of the first arc-shaped groove and the inner wall of the second arc-shaped groove are all provided with anti-slip patterns.

[0019] In the above invention, further, the loading device is a deadweight loading device, an electric loading device or a hydraulic loading device.

[0020] A method for measuring a natural frequency measurement device of a force sensor, the method comprising the following steps:

[0021] S1. Measure the mass m of the force sensor, then fix the force sensor on the base plate and fix the extensometer on the force sensor;

[0022] S2. Use a loading device to apply a force F0 of 20% of the full scale to the force sensor, and then clear the extensometer to zero.

[0023] S3, then applying the target load F1 to the force sensor, and the extensometer measures the deformation L of the force sensor;

[0024] S4. Calculate the natural frequency f of the measured force sensor. The calculation formula is as follows:

[0025]

[0026] Wherein, F is the static load value of the force sensor, that is, the difference between F1 and F0;

[0027] L is the deformation of the sensor when subjected to static load F;

[0028] m is the mass of the force sensor.

[0029] The beneficial effects of the present invention are:

[0030] The present invention fixes the force sensor and uses the device provided by the present invention to measure the natural frequency in a static state, thereby overcoming the influence of the position factor in the dynamic measurement method and improving the measurement accuracy of the natural frequency of the force sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a structural schematic diagram of the present invention;

[0032] Figure 2 It is a schematic diagram of the hoop structure of the present invention;

[0033] Figure 3 It is a schematic diagram of the clamping structure of the present invention;

[0034] Figure 4 It is a schematic diagram of the connection structure between the clamping mechanism and the cutter head of the present invention.

[0035] In the figure, 1-loading device, 2-base plate, 3-extensometer, 3.1-cutter head, 4-host computer, 5-hoop, 5.1 raised part, 6-push rod, 7-spring, 8-push plate, 8.1-first arc groove, 9-locking nut, 10-fixing rod, 10.1-fixing part, 10.2-adjusting part, 10.3-slide groove, 10.4-second arc groove, 11-adjusting rod, 11.1-installing groove, 12-clamping cavity, 13-adjusting nut, 14-force sensor. DETAILED DESCRIPTION

[0036] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0037] It should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention, and thus the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0038] Example:

[0039] A force sensor natural frequency measurement device, please refer to the attached Figure 1 -Attached Figure 3 As shown, it includes a loading device 1, a base plate 2, an extensometer 3 and a host computer 4 electrically connected to the extensometer 3; the loading device 1 is a deadweight loading device, an electric loading device or a hydraulic loading device.

[0040] A hoop 5 is provided on the base plate 2, and a plurality of protrusions 5.1 are equidistantly provided on the hoop 5. A push rod 6 is sleeved on the protrusion 5.1. A spring 7 is sleeved on one end of the push rod 6. A push plate 8 is fixed to one end of the push rod 7. A locking nut 9 is provided on the other end of the push rod 6. The push rod 6 is fixed to the hoop 5 by the locking nut 9. In a specific implementation, four push rods 6 can be provided on the hoop 5, and the push plate 8 connected with the four push rods 6 can form a rectangular holding space to clamp the force sensor to be measured.

[0041] The cutter head 3.1 of the extensometer 3 is provided with a clamping mechanism, and the clamping mechanism includes a fixed rod 10 and an adjusting rod 11. The fixed rod 10 includes a fixed portion 10.1 and an adjusting portion 10.2 which are perpendicular to each other. The adjusting rod 11 is slidably connected to the adjusting portion 10.2. A clamping cavity 12 for clamping a force sensor is formed between the adjusting rod 11 and the fixed portion 10.1. The adjusting rod 11 adjusts the size of the clamping cavity 12 by sliding along the adjusting portion 10.2. The adjusting rod 11 is also provided with an installation groove 11.1 for installing the cutter head 3.1 of the extensometer 3. Specifically, a slide groove 10.3 is provided on the adjusting portion 10.2. One end of the adjusting rod 11 passes through the slide groove 10.3 and is fixed to the adjusting portion 10.2 through an adjusting nut 13. For specific usage, please refer to the attached Figure 4 As shown, first install the two blades 3.1 of the extensometer 3 in the mounting grooves 11.1 of the adjusting rod 11, loosen the adjusting nut 13, make the adjusting rod 11 slide in the slide groove 10.3 and adjust the opening size of the clamping cavity 12 to match the force sensor 14 to be measured, and finally tighten the adjusting nut 13 to fix the force sensor 14 on the two clamping mechanisms.

[0042] Specifically, during the use of the present invention, the bottom of the force sensor 14 to be tested is first placed in the clamping space enclosed by the push plate 8. The push plate 8 presses the force sensor 14 under the action of the spring 7, and then the locking nut 9 is tightened to prevent the force sensor 14 from moving during the test. Then, the two blades 3.1 of the extensometer 3 are inserted into the slide groove 10.3. Finally, the force sensor 14 is fixed on the two clamping mechanisms so that the extensometer 3 can be used to measure the force sensor 14.

[0043] In the above embodiment, preferably, the push plate 8 and the inner wall of the fixing portion 10.1 are respectively provided with a first arc groove 8.1 and a second arc groove 10.4, so as to facilitate the fixing and clamping of the force sensor with an arc-shaped outer wall. More preferably, the inner wall of the plate 8, the inner wall of the fixing portion 10.1, the inner wall of the first arc groove 8.1 and the inner wall of the second arc groove 10.4 are all provided with anti-slip grooves to enhance the clamping and fixing effect.

[0044] When measuring the force sensor 14, the measuring method specifically includes the following steps:

[0045] S1, measuring the mass m of the force sensor, then fixing the force sensor 14 on the base plate 2, and fixing the extensometer 3 on the force sensor 14;

[0046] S2. Use a loading device to apply a force F0 of 20% of the full scale to the force sensor, and then clear the extensometer to zero.

[0047] S3, then applying the target load F1 to the force sensor, and the extensometer measures the deformation L of the force sensor;

[0048] The physical formula for the natural frequency of an object is:

[0049]

[0050] m is the mass of the force sensor;

[0051] K is the force sensor stiffness.

[0052] The sensor stiffness K is equal to the ratio between the load borne by the force sensor and the deformation caused by the force on the force sensor. The ability of the sensor to resist deformation under static load is static stiffness, and the ability of the sensor to resist deformation under alternating load is dynamic stiffness. If the alternating load frequency is much smaller than the natural frequency of the sensor, the values ​​of dynamic stiffness and static stiffness are basically the same. According to JJG 556-2011 "Verification Procedure for Axial Loading Fatigue Testing Machines", the natural frequency should be greater than 15 times the measured frequency, and the static stiffness can be used to represent the stiffness of the sensor. That is,

[0053]

[0054] F is the static load value of the force sensor, that is, the difference between F1 and F0;

[0055] L is the deformation of the sensor when subjected to static load F;

[0056] S4. Calculate the natural frequency f of the measured force sensor. The calculation formula is as follows:

[0057]

[0058] The accuracy level of the above force and mass standards is not greater than 0.1, and the accuracy level of the extensometer is not greater than 0.5. The measurement process is simple and easier to implement than the dynamic method measurement. After comparative verification of the dynamic method measurement, the results obtained by the static method and the dynamic method have good consistency. The static measurement method can more accurately obtain the natural frequency of the force sensor, eliminate the position influence factor in the dynamic measurement method, and improve the measurement uncertainty of the natural frequency of the force sensor. Its measurement uncertainty can be better than 5% (k = 2).

[0059] The above-mentioned embodiments only express the specific implementation of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A force sensor natural frequency measuring device, characterized in that: It includes a loading device, a base plate, an extensometer, and a host computer electrically connected to the extensometer; The base plate is provided with a hoop, and a plurality of convex parts are equidistantly arranged on the hoop, and a push rod is sleeved on the convex part, and a spring is sleeved on one end of the push rod, and a push plate is fixed to one end of the push rod, and a locking nut is provided on the other end of the push rod, and the push rod is fixed to the hoop through the locking nut; A clamping mechanism is provided on the cutter head of the extensometer, and the clamping mechanism includes a fixing rod and an adjusting rod. The fixing rod includes a fixing portion and an adjusting portion which are perpendicular to each other. The adjusting rod is slidably connected to the adjusting portion. A clamping cavity for clamping a force sensor is formed between the adjusting rod and the fixing portion. The adjusting rod adjusts the size of the clamping cavity by sliding along the adjusting portion. The adjusting rod is also provided with a mounting groove for mounting the cutter head of the extensometer; a sliding groove is provided on the adjusting portion, and one end of the adjusting rod passes through the sliding groove and is fixed to the adjusting portion by an adjusting nut; a first arc groove and a second arc groove are respectively provided on the inner walls of the push plate and the fixing portion.

2. A force sensor natural frequency measuring device according to claim 1, characterized in that: The inner wall of the push plate, the inner wall of the fixing portion, the inner wall of the first arc-shaped groove and the inner wall of the second arc-shaped groove are all provided with anti-slip patterns.

3. A force sensor natural frequency measuring device according to claim 1, characterized in that: The loading device is a deadweight loading device, an electric loading device or a hydraulic loading device.

4. A measurement method based on the force sensor natural frequency measurement device according to claim 1, characterized in that: The following steps are involved: S1. Measure the mass m of the force sensor, then fix the force sensor on the base plate and fix the extensometer on the force sensor; S2. Use a loading device to apply a force F0 of 20% of the full scale to the force sensor, and then clear the extensometer to zero. S3, then applying the target load F1 to the force sensor, and the extensometer measures the deformation L of the force sensor; S4. Calculate the natural frequency f of the measured force sensor. The calculation formula is as follows: Wherein, F is the static load value of the force sensor, that is, the difference between F1 and F0; L is the deformation of the sensor when subjected to static load F; m is the mass of the force sensor.

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