Rotationally symmetrical L-shaped composite piezoelectric three-axis acceleration sensor

Abstract

The invention relates to the technical field of sensors, in particular to a rotationally symmetrical L-shaped composite piezoelectric three-axis acceleration sensor which comprises a stainless steel base body frame, a central inertia mass block, a plane sensing unit, a shearing sensing unit and a signal leading-out system. Through the rotationally symmetrical L-shaped cantilever beam structure, the single inertial mass block is used for sensing the three-axis acceleration, the size and the mass of the sensor are remarkably reduced, the sensor is suitable for application scenes with extremely high requirements for the weight and the space, and on the basis of the single center inertial mass block, the three-axis acceleration can be sensed. The low-coupling, high-sensitivity and wide-band measurement of the three-axis acceleration is realized, and meanwhile, the sensor has the characteristics of small volume, light weight and high reliability, so as to solve the dilemma of a traditional orthogonal combined type and an existing integrated type MEMS sensor in high-end precision measurement application, and the suppression of common-mode interference is realized by combining differential output and a symmetrical structure. And the output stability of the sensor in a variable-temperature environment is improved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sensors, in particular to a rotationally symmetrical L-shaped composite piezoelectric three-axis acceleration sensor. BACKGROUND

[0002] The piezoelectric acceleration sensor is widely applied to the vibration signal measurement in the fields of industrial monitoring, aerospace, bionic robots and the like due to its good dynamic characteristics, strong impact resistance and wide frequency range. The traditional three-axis piezoelectric acceleration sensor is usually composed of three independent single-axis piezoelectric acceleration sensors, and has a large volume and redundant quality. For a bionic flapping wing aircraft (MAV) with a quality of only 20-80 grams, the three-axis piezoelectric acceleration sensor can change the center of mass distribution and the aerodynamic characteristics. The MEMS acceleration sensor (such as a capacitive or piezoresistive type), the dual-mode three-axis piezoelectric acceleration sensor and the three-axis MEMS piezoelectric acceleration sensor with a T-shaped folded beam can integrate the three-axis sensitive structure on a single chip, and realize significant reduction in volume and weight.

[0003] However, the above acceleration sensor still has the following problems:

[0004] (1) High inter-axis coupling: due to the structural asymmetry or unreasonable layout, mechanical or electrical interference exists between the multiple axial sensitive elements, so that when measuring the acceleration in a certain direction, the acceleration in other directions will also produce a response, thereby affecting the measurement accuracy. For example, the transverse sensitivity of the T-shaped beam structure can be as high as 30% of the main sensitivity, which seriously affects the measurement accuracy.

[0005] (2) Sensitivity and bandwidth contradiction: it is difficult to ensure high sensitivity while obtaining a wide working bandwidth. The working bandwidth is generally low (usually between 60 Hz and 400 Hz), and it is difficult to meet the measurement requirements of high-frequency vibration (harmonic up to 800 Hz) or high-intensity transient impact (peak value up to 200g) of flapping wing flight.

[0006] (3) Uneven stress distribution: the strain energy of the traditional cantilever beam structure is concentrated in the root area. The piezoelectric material is prone to depolarization or mechanical damage under strong impact, which easily leads to local fatigue damage, thereby affecting the stability and service life of the sensor during long-term operation.

[0007] (4) Poor temperature stability: the piezoelectric performance of the piezoelectric material is greatly affected by temperature. The traditional structure lacks an effective temperature compensation mechanism, which leads to output drift. Moreover, the output signal of the MEMS sensor is weak, and needs to rely on a complex integrated circuit for amplification and processing. SUMMARY

[0008] In order to solve the above technical problems in the prior art, the application provides a rotationally symmetrical L-shaped composite piezoelectric triaxial acceleration sensor.

[0009] In order to solve the above technical problems, the application provides the following technical scheme: a rotationally symmetrical L-shaped composite piezoelectric triaxial acceleration sensor, comprising a stainless steel base frame, a central inertial mass block, a planar sensitive unit, a shear sensitive unit and a signal leading system, the central inertial mass block is arranged at a central position of the stainless steel base frame, the planar sensitive unit is rotationally symmetrically arranged inside the stainless steel base frame, the shear sensitive unit is arranged at a central position of the central inertial mass block, and the planar sensitive unit and the shear sensitive unit are connected with a charge amplifier through the signal leading system.

[0010] Preferably, the stainless steel base frame comprises a fixed frame and L-shaped cantilever beams, and the fixed frame is internally provided with four L-shaped cantilever beams which are rotationally symmetrically distributed.

[0011] Preferably, the central inertial mass block is elastically suspended inside the fixed frame through the L-shaped cantilever beams to form an elastic vibration system, a middle fixed seat is arranged on the fixed frame inside the central inertial mass block, and the central inertial mass block is made of high-density material which is integrally formed with the fixed frame.

[0012] Preferably, the shear sensitive unit is a piezoelectric ceramic tube which is interference-fitted between the middle fixed seat and the central inertial mass block, the piezoelectric ceramic tube is fixed on the sensor base on the outside, and the piezoelectric ceramic tube is a ceramic ring tube with an outer diameter of 8.4 mm, an inner diameter of 4.5 mm and a thickness of 1.5 mm.

[0013] Preferably, the planar sensitive unit is four piezoelectric ceramic sheets which are fixed on the middle part of the surface of the L-shaped cantilever beam, the length of each piezoelectric ceramic sheet is 10 mm, the thickness is 0.7 mm, and the width is the same as the thickness of the L-shaped cantilever beam.

[0014] Preferably, the signal leading system comprises wires and conductive silver adhesive, one end of the wires is respectively adhered and fixed on the piezoelectric ceramic sheets and the piezoelectric ceramic tube through the conductive silver adhesive, and the other end is connected to the charge amplifier.

[0015] Preferably, the fixed frame and the L-shaped cantilever beam are integrally formed stainless steel sheets, and the outer edge of the fixed frame is square.

[0016] Preferably, each two opposite L-shaped cantilever beams form a measurement axis, the polarization directions of the two piezoelectric ceramic sheets on the same axis are opposite, and the signal lines of the two piezoelectric ceramic sheets on the same axis are connected in a differential mode.

[0017] Compared with the prior art, the application has the following beneficial effects:

[0018] 1. The application uses a single inertial mass block to realize the perception of three-axis acceleration through a rotationally symmetrical L-shaped cantilever beam structure, significantly reducing the volume and mass of the sensor, making it suitable for applications with extremely high weight and space requirements, and enabling low coupling, high sensitivity, and wide frequency band measurement of three-axis acceleration based on a single central inertial mass block, while also having the characteristics of small size, light weight, and high reliability, to solve the difficulties faced by traditional orthogonal combination type and existing integrated MEMS sensors in high-end precision measurement applications.

[0019] 2. In the application, the rotationally symmetrical structure and differential output principle are used to realize the decoupling of three-axis signals, improve the independence and accuracy of each axis measurement, and realize the suppression of common mode interference (such as temperature drift) by combining differential output and symmetrical structure, thereby improving the output stability of the sensor in a variable temperature environment.

[0020] 3. In the application, the L-shaped cantilever beam structure optimizes the stiffness ratio of the main beam and the auxiliary beam, realizes the uniformization of the surface strain distribution of the main beam, effectively avoids stress concentration, improves the mechanical reliability and service life of the sensor, overcomes the defect that the traditional cantilever beam structure is prone to fatigue damage due to root stress concentration, makes the sensor have superior fatigue resistance, improves the sensitivity, ensures a high first-order resonance frequency, and widens the working bandwidth. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a structural schematic diagram of the three-axis acceleration sensor of the application;

[0022] Figure 2 is a force analysis schematic diagram of the three-axis acceleration sensor of the application during signal perception;

[0023] Figure 3 is an X-axis coupling sensitivity curve of the three-axis acceleration sensor of the application;

[0024] Figure 4 is a Z-axis coupling sensitivity curve of the three-axis acceleration sensor of the application;

[0025] Figure 5 is a flowchart of the three-axis acceleration sensor of the application during signal perception.

[0026] NUMERALS IN THE DRAWINGS

[0027] 1. Fixed frame; 2. L-shaped cantilever beam; 3. Central inertial mass block; 4. Piezoelectric ceramic tube; 5. Middle fixed seat; 6. Piezoelectric ceramic sheet. DETAILED DESCRIPTION

[0028] The above and other technical features and advantages of the present invention will be further described below with reference to the accompanying drawings and embodiments. However, the following embodiments are merely preferred embodiments of the present invention and are not exhaustive.

[0029] Example:

[0030] like Figures 1-5 As shown, this invention provides a rotationally symmetric L-shaped composite piezoelectric triaxial accelerometer, comprising a stainless steel substrate frame, a central inertial mass block 3, a planar sensing unit, a shear sensing unit, and a signal extraction system. The central inertial mass block 3 is disposed at the center of the stainless steel substrate frame, and the planar sensing unit is rotationally symmetrically disposed inside the stainless steel substrate frame. The shear sensing unit is disposed at the center of the central inertial mass block 3. The stainless steel substrate frame, the central inertial mass block 3, the planar sensing unit, and the shear sensing unit are fixed to the object being measured by a sensor base. Both the planar sensing unit and the shear sensing unit are connected to a charge amplifier through the signal extraction system.

[0031] In this embodiment, the stainless steel base frame includes a fixed frame 1 and an L-shaped cantilever beam 2. The fixed frame 1 is processed by precision wire cutting to form four L-shaped cantilever beams 2 that are distributed in a rotationally symmetrical manner (90° interval), which serve as the mechanical support and fixed foundation for the entire sensor and transmit external acceleration to the sensitive unit. The fixed frame 1 and the L-shaped cantilever beam 2 are integrally formed stainless steel sheets, and the outer edge of the fixed frame 1 is square.

[0032] In this embodiment, the central inertial mass block 3 is elastically suspended inside the fixed frame 1 by an L-shaped cantilever beam 2, forming an elastic vibration system for sensing external acceleration and generating inertial force. A central fixed seat 5 is provided on the fixed frame 1 inside the central inertial mass block 3. When there is acceleration on the Z-axis, the central fixed seat 5 can generate relative displacement with the central inertial mass block 3. Shear stress will be generated on the inner and outer surfaces of the piezoelectric ceramic tube 4 between them. The piezoelectric ceramic tube 4 will convert the shear stress into voltage or charge output through the piezoelectric effect. The central inertial mass block 3 is a high-density material integrally formed with the fixed frame 1, which can be tungsten alloy or stainless steel.

[0033] In this embodiment, the shear-sensitive unit is a piezoelectric ceramic tube 4 that is interference-fitted between the central fixed seat 5 and the central inertial mass block 3. The piezoelectric ceramic tube 4 is a ceramic annular tube with an outer diameter of 8.4 mm, an inner diameter of 4.5 mm, and a thickness of 1.5 mm.

[0034] In this embodiment, the planar sensitive unit is four piezoelectric ceramic sheets 6 fixed by epoxy glue on the middle of the surface of the L-shaped cantilever beam 2. Each two opposite L-shaped cantilever beams 2 form a measuring axis. The polarization directions of the two piezoelectric ceramic sheets 6 on the same axis are opposite. The signal lines of the two piezoelectric ceramic sheets 6 on the same axis are connected in a differential manner, i.e. the positive and negative poles are reversely connected. The length of each piezoelectric ceramic sheet 6 is 10 mm, the thickness is 0.7 mm, and the width is the same as the thickness of the L-shaped cantilever beam 2.

[0035] In this embodiment, the signal leading-out system includes wires and conductive silver glue. The wire is fixed by conductive silver glue on the piezoelectric ceramic sheet 6 and the piezoelectric ceramic tube 4 at one end, and connected to a charge amplifier at the other end. The signals of the piezoelectric ceramic sheet 6 and the piezoelectric ceramic tube 4 are led out from the inside of the sensor through very thin coaxial wires. The inner core and the shielding layer of the coaxial line are used as positive and negative leads respectively. The led-out signals are connected to an external charge amplifier or voltage amplifier circuit, and differential operation is performed to extract effective signals and suppress common-mode noise.

[0036] Working principle: when the measured object vibrates to generate acceleration, the acceleration is transmitted to the sensor through the sensor base, as shown in FIG. 1, the Z axis in the space rectangular coordinate system is defined as the front-back direction, the Y axis is defined as the up-down direction, and the X axis is defined as the left-right direction. Figure 2

[0037] When the acceleration occurs in the X axis or the Y axis: the inertial force forces the center inertia mass block 3 to move in the plane, respectively generating and accelerations, causing the L-shaped cantilever beam 2 to bend and deform, respectively generating and stresses, and the piezoelectric ceramic sheet 6 generates tensile or compressive deformation, generating a charge signal proportional to the acceleration through the positive piezoelectric effect, so as to detect the accelerations of the X axis and the Y axis;

[0038] When the acceleration occurs in the Z axis: the inertial force forces the center inertia mass block 3 to move in the front-back direction, generating acceleration, which applies a shear stress to the middle shear type piezoelectric ceramic tube 4, generating a charge signal through the shear mode;

[0039] In the L-shaped composite piezoelectric three-axis acceleration sensor, the length of the L-shaped cantilever beam 2 is much greater than its thickness, so the amplitude-frequency characteristic curve of the acceleration sensor in the X and Y test axes changes more than that in the Z test axis.

[0040] ​​On the other hand, since the piezoelectric ceramic tube 4 is constrained in both radial and tangential deformation, and the fixed end of the L-shaped cantilever beam 2 mainly limits the shear deformation of the piezoelectric ceramic sheet 6, the piezoelectric ceramic tube 4 is more comprehensively constrained, has greater fixed stiffness, and has a relatively smooth amplitude-frequency characteristic curve.

[0041] By applying a single-axis acceleration, the inter-axis coupling of the L-shaped composite piezoelectric three-axis acceleration sensor is simulated. When the applied single-axis acceleration is Figure 3 , the three-axis voltage sensitivity characteristic curve of the acceleration sensor is as shown in Figure 3 , and the lateral sensitivity of the Y-axis test axis and the Z-axis test axis of the acceleration sensor approaches 0 in the frequency range of 0-12 kHz, which can be regarded as an ideal state.

[0042] Similarly, when the applied single-axis acceleration is , the lateral sensitivity of the X-axis test axis and the Y-axis test axis of the acceleration sensor approaches 0, as shown in Figure 4 , since the sensor is rotationally symmetric in the XOY plane, the amplitude-frequency characteristics of the X-axis test axis and the Y-axis test axis are the same, so only one side axis needs to be analyzed to draw a conclusion,

[0043] In summary, the coupling of the acceleration sensor on the three axes approaches 0.

[0044] The charge signals generated by the piezoelectric ceramic tube 4 and the piezoelectric ceramic sheet 6 are low-lossly led out through the extremely thin lead wire connected by the bumpless lead technology, and after being led out:

[0045] X-axis or Y-axis: the signals generated by the two symmetrical piezoelectric ceramic sheets 6 on the same axis with opposite phases are input into the charge amplifier, which multiplies the effective signal amplitude and simultaneously cancels the common-mode interference such as temperature change and base strain;

[0046] Z-axis: the signal generated by the piezoelectric ceramic tube 4 is directly sent to the charge amplifier for conditioning;

[0047] The three analog voltage signals after amplification and filtering are output to the data acquisition system (such as an oscilloscope or a data acquisition card), and the acceleration time history data in three directions (X, Y, Z) can be obtained, and the user can convert the collected voltage signals into actual acceleration values according to the sensitivity of the sensor calibrated at the factory for subsequent vibration analysis, condition monitoring, etc.

[0048] The above only describes the preferred embodiments of the present application, which are only illustrative but not limiting. Those skilled in the art understand that many changes, modifications and even equivalents can be made within the spirit and scope of the present application as defined in the claims, but all will fall within the protection scope of the present application.

Claims

1. A rotationally symmetric L-shaped composite piezoelectric triaxial accelerometer, characterized in that, It comprises a stainless steel base frame, a central inertia mass (3), a plane sensitive unit, a shear sensitive unit and a signal leading system, the central inertia mass (3) is arranged at the central position of the stainless steel base frame, the plane sensitive unit is arranged in the stainless steel base frame in a rotational symmetry, the shear sensitive unit is arranged at the central position of the central inertia mass (3), and the plane sensitive unit and the shear sensitive unit are connected with a charge amplifier through the signal leading system.

2. A rotationally symmetric L-shaped compound piezoelectric three-axis acceleration sensor according to claim 1, wherein The stainless steel base frame comprises a fixed frame (1) and an L-shaped cantilever beam (2), and the fixed frame (1) is internally provided with four L-shaped cantilever beams (2) arranged in a rotational symmetry.

3. The rotationally symmetric L-shaped compound piezoelectric three-axis acceleration sensor according to claim 1, wherein The central inertia mass (3) is elastically suspended in the fixed frame (1) through the L-shaped cantilever beam (2) to form an elastic vibration system, the fixed frame (1) is arranged on the central inertia mass (3) in a middle fixed seat (5), and the central inertia mass (3) is made of a high-density material in an integral manner with the fixed frame (1).

4. A rotationally symmetric L-shaped compound piezoelectric three-axis acceleration sensor according to claim 2, wherein The shear sensitive unit is a piezoelectric ceramic tube (4) in interference fit between the middle fixed seat (5) and the central inertia mass (3), the piezoelectric ceramic tube (4) is fixed on the sensor base on the outside, and the piezoelectric ceramic tube (4) is a ceramic ring tube with an outer diameter of 8.4 mm, an inner diameter of 4.5 mm and a thickness of 1.5 mm.

5. The rotationally symmetric L-shaped compound piezoelectric three-axis acceleration sensor according to claim 2, wherein The plane sensitive unit is four piezoelectric ceramic sheets (6) fixed on the surface of the L-shaped cantilever beam (2) in the middle, the length of each piezoelectric ceramic sheet (6) is 10 mm, the thickness is 0.7 mm, and the width is the same as the thickness of the L-shaped cantilever beam (2).

6. A rotationally symmetric L-shaped compound piezoelectric three-axis acceleration sensor according to claim 1, wherein The signal leading system comprises a wire and conductive silver adhesive, one end of the wire is respectively adhered and fixed on the piezoelectric ceramic sheet (6) and the piezoelectric ceramic tube (4) through the conductive silver adhesive, and the other end is connected to the charge amplifier.

7. A rotationally symmetric L-shaped compound piezoelectric three-axis acceleration sensor according to claim 2, wherein The fixed frame (1) and the L-shaped cantilever beam (2) are made of an integral stainless steel sheet, and the outer edge of the fixed frame (1) is square.

8. A rotationally symmetric L-shaped compound piezoelectric three-axis acceleration sensor according to claim 5, wherein Every two opposite L-shaped cantilever beams (2) form a measuring axis, the polarization directions of two piezoelectric ceramic sheets (6) on the same axis are opposite, and the signal lines of the two piezoelectric ceramic sheets (6) on the same axis are connected in a differential mode.

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