CN111473911A - Inherent frequency measuring clamp and method for micro-range cross beam type force sensor - Google Patents

Abstract

The invention discloses a natural frequency measuring clamp of a micro-range cross beam type force sensor and a method thereof.

Description

Inherent frequency measuring clamp and method for micro-range cross beam type force sensor

Technical Field

The invention belongs to the technical field of sensor calibration, and particularly relates to a natural frequency measuring clamp and a method of a micro-range cross beam type force sensor.

Background

The force sensor can simultaneously measure dynamic data of three-dimensional force in space, and is widely applied to the fields of robots, aerospace, national defense construction and the like. Before the force sensor is put into use after being manufactured, due to the influences of manufacturing, assembly, patch errors, circuit noise interference and the like, static and dynamic calibration needs to be carried out on the force sensor to obtain the actual performance index of the sensor, the relation between the input and the output of the sensor is determined, the inherent frequency of each aspect of the force sensor is obtained, and therefore the working frequency band of the force sensor is determined, and the method has important significance for the actual application of the force sensor. The convenience, the practicability and the accuracy of the natural frequency measuring clamp have direct influence on the measuring precision and the efficiency of the force sensor, so that the measuring clamp which is convenient and effective to research and design has high practical significance.

At present, the inherent frequency measuring device of the force sensor of the domestic external force sensor mainly comprises a weight type, a vibration table type and the like. The weight type utilizes a combined pulley and a weight to realize negative step force loading on a force sensor, and a patent with the patent number of CN106706207B discloses a step force generating device for dynamic calibration of the force sensor, which is suitable for dynamic calibration experiments of the force sensor with an irregular load end tool structure or needing to carry out multi-direction force/moment loading, and comprises a calibration table, a directional loading component, a force transmission steel wire, a force source, a pulley suspension system, an impact shearing device and a step edge detection circuit, but the calibration device is difficult to obtain accurate step input signals. The vibration table type excitation is to adopt a vibration exciter to carry out frequency sweep excitation on the force sensor, but the calibration method has the disadvantages of complex device, large direct loading force on the force sensor and high requirement on equipment. In addition, although the method of measuring the natural frequency by pulse excitation is widely used, since pulse excitation can only excite a force sensor that can withstand a large impact force, there is no method of pulse excitation for a force sensor that is subject to a small range and structural damage.

Disclosure of Invention

In order to solve the defects of the prior art, the invention provides a natural frequency measuring clamp of a micro-range cross beam type force sensor and a method thereof, so that the natural frequency of the force in three directions of the cross beam type force sensor can be measured, and the complexity of exciting force application of the natural frequency of the force sensor in the measuring process is reduced.

In order to achieve the purpose, the invention adopts the following technical scheme:

the invention relates to a natural frequency measuring clamp for a micro-range cross beam type force sensor, which is characterized by comprising the following components: a first fixed structure and a second fixed structure;

fan-shaped concave platforms are arranged at four corners of the center of the inner side surface of the first fixing structure, and a linear deep groove is arranged on the inner side surface of the first fixing structure along the radial direction and used for placing cables; through holes are formed in four corners of the inner side face of the first fixing structure;

fan-shaped bosses are arranged at four corners of the center of the inner side surface of the second fixing structure, and a cross-shaped deep groove is arranged on the inner side surface of the second fixing structure along the radial direction and used for placing cables or other acquisition sensors; the four corners of the inner side surface of the second fixing structure are provided with the same through holes;

the cross beam type force sensor is arranged on the fan-shaped concave platform on the inner side surface of the first fixing structure, and the bolts penetrate through the four pairs of through holes to form a fixing structure with the fan-shaped convex platform on the inner side surface of the second fixing structure, so that a clamping structure for the cross beam type force sensor is formed, and a gap is formed between the inner side surfaces around the cross beam type force sensor.

The natural frequency measuring clamp is also characterized in that a wide-range force hammer is used for carrying out pulse excitation on the natural frequency measuring clamp, so that the force sensor generates translation under the clamping of the first fixing structure and the second fixing structure, and an elastic element of the force sensor is driven to vibrate.

The whole natural frequency formed by the first fixing structure and the second fixing structure under clamping is far higher than the natural frequency of the force sensor to be measured in each direction.

The method for measuring the natural frequency of the sensor to be measured by using the natural frequency measuring clamp is characterized by comprising the following steps of:

step 1, rigidly connecting an elastic element of a force sensor to be measured with a three-way acceleration sensor;

step 2, after the force sensor is clamped by the fan-shaped concave platform of the first fixing structure and the fan-shaped boss of the second fixing structure, the whole body is hung by an elastic rope or placed on an elastic base;

step 3, knocking the inherent frequency measuring clamp by using a wide-range force hammer, and acquiring an input signal of the wide-range force hammer and an output signal of a three-way acceleration sensor, so that a frequency response function H (jw) of the inherent frequency measuring clamp and the force sensor is obtained by using a formula (1);

in the formula (1), Y (w) is a frequency domain form of an output signal of the three-way acceleration sensor after Fourier transform, and X (w) is a frequency domain form of an input signal of the wide-range force hammer after Fourier transform;

and 4, obtaining the natural frequency of the force sensor to be measured according to the first-order frequency of the frequency response function H (jw).

Compared with the prior art, the invention has the beneficial effects that:

1. the invention designs a pulse excitation loading clamp, which directly applies larger pulse excitation to the clamp, drives the vibration of the elastic element part of a force sensor to be measured through the integral translation of a clamp body, and acquires an output signal, thereby avoiding the structural damage of a micro-range cross beam type force sensor; the complexity of applying the exciting force in the process of measuring the natural frequency of the force sensor is reduced; therefore, the problems that the existing measuring device cannot carry out pulse excitation on the micro-range cross beam type force sensor, the calibration device is complex, the loading mode is complex and the like are solved.

2. The force sensor to be measured is clamped and fixed, and threaded connection between the clamp and the force sensor to be measured is avoided, so that inherent frequencies of cross beam type force sensors with different sizes can be measured, and the force sensor to be measured has the advantages of simple structure, convenience in disassembly and assembly and certain universality;

3. the invention has the advantages of convenient assembly of each part of the structure, simple and easily obtained used equipment, accurate and convenient input and output acquisition and convenience for loading the force sensor in three directions of Fx, Fy and Fz.

Drawings

FIG. 1 is a front view of the clamp of the present invention;

FIG. 2 is a top view of FIG. 1;

FIG. 3 is a perspective view of a first fastening structure of the clamp of the present invention;

FIG. 4 is a perspective view of a second fixing structure of the clamp according to the present invention;

FIG. 5 is an exploded view of a three-dimensional structure of the present invention with a load cell shown in phantom;

FIG. 6 is a schematic diagram of a test system for the method of the present invention;

reference numbers in the figures: 1 a first fixed structure; 2 a second fixation structure.

Detailed Description

In this embodiment, a natural frequency measuring jig of a micro-range cross beam type force sensor includes: a first fixed structure 1 and a second fixed structure 2;

as shown in fig. 3, fan-shaped concave platforms are arranged at four corners of the center of the inner side of the first fixing structure 1, and a linear deep groove is arranged on the inner side of the first fixing structure 1 along the radial direction for placing cables; through holes are arranged at four corners of the inner side surface of the first fixing structure 1;

as shown in fig. 4, fan-shaped bosses are arranged at four corners of the center of the inner side of the second fixing structure 2, and a cross-shaped deep groove is arranged on the inner side of the second fixing structure 2 along the radial direction for placing cables or other acquisition sensors; the four corners of the inner side surface of the second fixing structure 2 are provided with the same through holes;

as shown in fig. 5, a cross beam force sensor is mounted on a fan-shaped concave platform on the inner side surface of the first fixing structure 1, and bolts are inserted between four pairs of through holes and fan-shaped convex platforms on the inner side surface of the second fixing structure 2 to form a fixing structure, so that a clamping structure for the cross beam force sensor is formed, and a gap is formed between the inner side surfaces around the cross beam force sensor.

In specific implementation, the natural frequency measuring clamp is subjected to pulse excitation by using a wide-range force hammer, so that the force sensor generates translation under the clamping of the first fixing structure 1 and the second fixing structure 2, and the elastic element with the force sensor vibrates. The force applied to the clamp is large pulse excitation, and the elastic element of the force sensor is small force, so that micro force loading of the micro force sensor is realized. The three-way acceleration sensor collects vibration of the elastic element, pulse excitation is used as an input signal of the test system, acceleration output collected by the three-way acceleration sensor is used as an output signal of the test system, and the integral frequency response function formed by clamping the first fixing structure 1 and the second fixing structure 2 is obtained according to the formula 1.

The clamp material uses aluminum alloy, rigidity is high, and the quality is little, and anchor clamps all adopt solid construction, makes anchor clamps quality evenly distributed on the space to this natural frequency that improves for the whole natural frequency that constitutes under the centre gripping of first fixed knot structure 1 and second fixed knot structure 2 is far higher than the natural frequency of the each side of the force sensor that awaits measuring. Therefore, the first-order frequency of the frequency response function of the whole body formed by clamping the first fixing structure 1 and the second fixing structure 2 is the natural frequency of the load cell.

In the present embodiment, the method for measuring the natural frequency of the force sensor using the natural frequency measuring jig is performed as follows:

step 1, rigidly connecting an elastic element of a force sensor to be measured with a three-way acceleration sensor;

step 2, after the fan-shaped concave table of the first fixing structure 1 and the fan-shaped boss of the second fixing structure 2 are used for clamping the force sensor, the whole body is hung or placed on an elastic base by an elastic rope;

step 3, knocking the inherent frequency measuring clamp by using the wide-range force hammer, and acquiring an input signal of the wide-range force hammer and an output signal of the three-way acceleration sensor, so that a frequency response function H (jw) of the inherent frequency measuring clamp and the force sensor is obtained by using a formula (1);

in the formula (1), Y (w) is a frequency domain form of an output signal of the three-way acceleration sensor after Fourier transform, and X (w) is a frequency domain form of an input signal of the large-range force hammer after Fourier transform;

and 4, obtaining the natural frequency of the force sensor to be measured according to the first-order frequency of the frequency response function H (jw).

The technical effects of the embodiment are as follows: by the arrangement, the indirect excitation of the elastic element of the force sensor can be realized by directly applying excitation to the clamp, so that the loading force is in the range of the force sensor, and the structure of the force sensor is prevented from being damaged; and secondly, the clamp can calibrate force sensors with different sizes by a connection mode of the clamping force sensors instead of threaded connection.

The calibration experiment of the Fx, Fy and Fz force of the force sensor comprises the following specific steps:

step 1: when the natural frequency of the force sensor in the positive X direction or the negative X direction is measured, the force sensor is clamped by the first fixing structure 1 and the second fixing structure 2, the X beam direction of the cross beam type force sensor to be measured is perpendicular to the side faces of the first fixing structure 1 and the second fixing structure 2, the force hammer strikes the side face of the first fixing structure along the positive X direction or the negative X direction of the force sensor, the direction of a pulse force is consistent with the positive X direction or the negative X direction of the force sensor, input and output signals are collected, a frequency response function is calculated according to the formula 1, the first-order frequency of the frequency response function is obtained and is the natural frequency of the force sensor to be measured in the positive X direction or the negative X direction, and the measurement of the natural frequency of the force sensor in the positive X direction or the.

Step 2: when the natural frequency of the force sensor in the positive Y direction or the negative Y direction is measured, the force sensor is clamped by the first fixing structure 1 and the second fixing structure 2, the Y beam direction of the cross beam type force sensor to be measured is perpendicular to the side faces of the first fixing structure 1 and the second fixing structure 2, the force hammer strikes the side face of the first fixing structure along the positive X direction or the negative Y direction of the force sensor, the direction of a pulse force is consistent with the positive Y direction or the negative Y direction of the force sensor, input and output signals are collected, a frequency response function is calculated according to the formula 1, the first-order frequency of the frequency response function is obtained and is the natural frequency of the force sensor to be measured in the positive Y direction or the negative Y direction, and the measurement of the natural frequency of the force sensor in the positive Y direction or the.

And step 3: when the natural frequency of the force sensor in the positive Z direction or the negative Z direction is measured, the force sensor is clamped by the left clamp and the right clamp, the Z direction of the cross beam type force sensor to be measured is made to coincide with the axial lines of the first fixing structure and the second fixing structure, the force hammer is knocked on the clamp body along the space positive Z direction or the negative Z direction of the force sensor, the direction of a pulse force is made to be consistent with the space positive Z direction or the space negative Z direction of the force sensor, input and output signals are collected, a frequency response function is calculated according to the formula (1), the first-order frequency of the frequency response function is obtained and is the natural frequency of the force sensor to be measured in the positive Z direction or the negative Z direction, and the measurement of the natural frequency of the force.

Claims (4)

1. A natural frequency measurement fixture for a micro-scale cross beam force sensor, comprising: a first fixed structure (1) and a second fixed structure (2);

fan-shaped concave tables are arranged at four corners of the center of the inner side surface of the first fixing structure (1), and a linear deep groove is arranged on the inner side surface of the first fixing structure (1) along the radial direction and used for placing cables; through holes are formed in four corners of the inner side face of the first fixing structure (1);

fan-shaped bosses are arranged at four corners of the center of the inner side surface of the second fixing structure (2), and a cross-shaped deep groove is arranged on the inner side surface of the second fixing structure (2) along the radial direction and used for placing cables or other acquisition sensors; the four corners of the inner side surface of the second fixing structure (2) are provided with the same through holes;

the cross beam type force sensor is arranged on a fan-shaped concave platform on the inner side surface of the first fixing structure (1), and a bolt penetrates through four pairs of through holes to form a fixing structure with a fan-shaped boss on the inner side surface of the second fixing structure (2), so that a clamping structure for the cross beam type force sensor is formed, and a gap is formed between the inner side surfaces around the cross beam type force sensor.

2. The natural frequency measuring clamp according to claim 1, characterized in that the pulse excitation of the natural frequency measuring clamp is performed by using a wide-range force hammer, so that the force sensor generates translation under the clamping of the first fixing structure (1) and the second fixing structure (2), and the elastic element of the force sensor is driven to vibrate.

3. The natural frequency measuring jig according to claim 1, wherein the whole natural frequency of the first fixing structure (1) and the second fixing structure (2) under clamping is much higher than the natural frequency of the force sensor to be measured in each direction.

4. The method for measuring the natural frequency of a load cell using the natural frequency measuring jig of claim 1, comprising the steps of:

step 1, rigidly connecting an elastic element of a force sensor to be measured with a three-way acceleration sensor;

step 2, after the force sensor is clamped by the fan-shaped concave table of the first fixing structure (1) and the fan-shaped boss of the second fixing structure (2), the whole body is suspended by an elastic rope or placed on an elastic base;

step 3, knocking the inherent frequency measuring clamp by using a wide-range force hammer, and acquiring an input signal of the wide-range force hammer and an output signal of a three-way acceleration sensor, so that a frequency response function H (jw) of the inherent frequency measuring clamp and the force sensor is obtained by using a formula (1);

in the formula (1), Y (w) is a frequency domain form of an output signal of the three-way acceleration sensor after Fourier transform, and X (w) is a frequency domain form of an input signal of the wide-range force hammer after Fourier transform;

and 4, obtaining the natural frequency of the force sensor to be measured according to the first-order frequency of the frequency response function H (jw).

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