Piezoelectric ceramic multi-position self-calibration device and method for intrinsic safety type inertial navigation system

Abstract

The invention relates to a piezoelectric ceramic multi-position self-calibration device and method for an intrinsic safety type inertial navigation system, and relates to the technical field of inertial navigation system calibration, the self-calibration device comprises a base, a biaxial piezoelectric driving assembly, a rotating unit and an angle measuring unit, the base is used for fixing the self-calibration device on an underground platform or other fixing equipment, the biaxial piezoelectric driving assembly comprises an X-axis piezoelectric ceramic driver, a Y-axis piezoelectric ceramic driver and a flexible hinge, the rotating unit comprises a rotating shaft and a rotating platform, the rotating platform is used for installing the inertial navigation system, and the rotating shaft is used for rotating the inertial navigation system. The angle measuring unit is arranged on the rotating platform and used for monitoring the rotating angle in real time. According to the device and the method disclosed by the invention, the inverse piezoelectric effect of the piezoelectric ceramic can meet the requirement of an inertial navigation system for multi-position angle calibration.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of inertial navigation system calibration, in particular to a self-calibration device and method for an intrinsically safe inertial navigation system in a coal mining underground scene. BACKGROUND

[0002] The coal mine underground environment has extremely poor characteristics, which poses a severe challenge to the calibration of inertial navigation systems. The temperature of the working face in the underground mine is usually maintained at 25-35°C, and the relative humidity is as high as 80-95%. The temperature of deep mines can reach 30-50°C, and the humidity increases with the increase of mining depth. The cross section of the underground roadway is small, and the working space is narrow and crowded. The space of some coal mining working faces is even narrower, and personnel activities are limited, making equipment operation difficult.

[0003] The calibration of inertial navigation systems is a key technology to ensure their accurate work in underground environments. Traditional calibration methods mainly include six-position method and twelve-position method. The six-position method is to point the x, y and z axes upward and downward respectively, a total of six positions, which can only calibrate the zero offset and scale factor of the X, Y and Z axes, a total of 6 parameters. The twelve-position method contains 36 axial positions.

[0004] The existing calibration method of mine inertial navigation system usually needs to fix the system on a calibration turntable, collect 4-azimuth initial alignment data, 12-azimuth static calibration data and 4-azimuth dynamic calibration data. However, this traditional mechanical calibration method has many limitations in the underground environment: first, the large calibration turntable is difficult to deploy in the narrow space of the underground mine; second, the mechanical device is easily affected by dust and humidity in the harsh underground environment, which reduces the precision; third, the traditional calibration method needs to disassemble the inertial navigation system from the equipment, which affects the normal production operation.

[0005] In addition, in the coal mine underground transportation scene, the inertial navigation system measures the acceleration, angular velocity and attitude angle of the vehicle in real time through the three-axis accelerometer and gyroscope, and realizes continuous positioning combined with the dead reckoning algorithm. The cooperative positioning technology of inertial navigation and odometer further optimizes the precision, and the experimental results show that the straightness measurement error of the working face can be controlled within 90mm. This puts higher requirements on the calibration accuracy of the inertial navigation system.

[0006] Piezoelectric ceramics have unique technical advantages in the field of inertial navigation system calibration. The piezoelectric nanometer rotary table is driven based on the inverse piezoelectric effect of piezoelectric ceramics, and the input voltage causes the material to produce nanoscale deformation, with nanoscale resolution, no friction and ultra-fast response speed, perfectly meeting the needs of IMU calibration. The piezoelectric nanometer rotary table can produce and stabilize extremely small angular steps (micro-radian level) to accurately calibrate the non-linear error of the sensor, and the piezoelectric drive has the advantages of millisecond-level response speed and no magnetic and friction.

[0007] At present, the application of piezoelectric ceramics in the calibration field of inertial navigation system mainly concentrates in the laboratory environment, and there is still a blank in the special calibration device for the harsh environment in the mine. In particular, how to realize the double-axis rotation by using the inverse piezoelectric effect of piezoelectric ceramics to meet the requirements of inertial navigation self-calibration, and how to realize large-angle torsion by combining piezoelectric ceramics and flexible hinge, and other key technical problems still need further technical breakthrough.

[0008] More importantly, there is a serious explosive gas and dust environment in the mine. When the methane (CH4) concentration released by the coal seam reaches 5%-16%, an explosion hazard is formed, and the combustible coal dust concentration generated in the mining and transportation reaches 30-2000 g / m 3 , and has an explosion risk when suspended, and there is a double explosion risk. Therefore, the equipment in the mine must meet the strict intrinsic safety explosion-proof standard, and the core requirement is that the electric spark or thermal effect generated by the circuit in the normal and fault states cannot ignite the explosive mixture. There are methane, coal dust and other flammable gases in the mine, and all electrical equipment must meet the intrinsic safety (intrinsic safety) explosion-proof standard. The core of the standard is to limit the electric spark energy generated by the circuit in any normal or fault state, so that it is insufficient to ignite a specific dangerous gas (for example, the minimum ignition energy of IIC class gas methane is about 200 μJ). The intrinsic safety device prevents ignition by limiting the circuit energy, and the key parameters include the maximum allowed current (I max ), the maximum allowed voltage (U max ) and the maximum allowed power (P max ), the device needs to pass the intrinsic safety explosion-proof certification, adopt a sealed structure and an anti-interference communication protocol (such as CAN bus), and the protection level should reach IP65 and above. SUMMARY

[0009] The main technical problems to be solved by the present application include: The traditional mechanical rotating device has problems such as large size, low precision and difficult maintenance in the mine environment, and needs to realize precise double-axis rotation movement by the inverse piezoelectric effect of piezoelectric ceramics. How to design a double-axis rotating device by using the inverse piezoelectric effect of piezoelectric ceramics to meet the angle requirements of multi-position calibration of the inertial navigation system is one of the technical problems to be solved by the present application.

[0010] According to the prior art, the maximum static rotation angle of the piezoelectric torsion device is usually between 4.935 mrad (about 0.28°) and 2.73°, which is far from meeting the requirement of a rotation angle of more than 90° required by the calibration of the inertial navigation system. How to realize large-angle torsion by combining piezoelectric ceramics and flexible hinge, especially to solve the problem of angle limitation of the piezoelectric torsion device, is also one of the technical problems to be solved by the present application.

[0011] The intrinsically safe device must pass the intrinsically safe explosion-proof certification, adopt a sealed structure and an anti-interference communication protocol, and the protection level should reach IP65 or above. How to ensure that the entire device meets the explosion-proof requirements of the intrinsically safe environment in the well, including circuit energy limitation, shell protection level, temperature control and other key technical indicators, is also a problem to be considered.

[0012] In addition, it is also necessary to consider how to realize the engineering application of the device, including the rationality of the structure design, the feasibility of the manufacturing process, the economy of the cost control and other aspects.

[0013] In order to solve the above problems, the technical scheme of the present application provides a piezoelectric ceramic multi-position self-calibration device for an inertial navigation system, which comprises a base, a dual-axis piezoelectric drive assembly, a rotating unit and an angle measurement unit, wherein: the base is used to fix the self-calibration device on a downhole platform or other fixed equipment; the dual-axis piezoelectric drive assembly comprises an X-axis piezoelectric drive assembly and a Y-axis piezoelectric drive assembly, which are respectively used to control the rotational movement of the rotating unit around the X-axis and the Y-axis, wherein: the X-axis piezoelectric drive assembly comprises an X-axis piezoelectric ceramic driver and an X-axis flexible hinge; the Y-axis piezoelectric drive assembly comprises a Y-axis piezoelectric ceramic driver and a Y-axis flexible hinge; the rotating unit comprises a rotating shaft and a rotating platform, the rotating shaft is fixedly connected with the X-axis flexible hinge and the Y-axis flexible hinge, and the rotating platform is used to install the inertial navigation system; the angle measurement unit is arranged on the rotating platform and is used to monitor the rotation angle in real time.

[0014] Further, the X-axis and Y-axis flexible hinges are both multi-segment flexible hinge structures, which are composed of a plurality of flexible hinge segments connected in series.

[0015] Further, the X-axis and Y-axis flexible hinges and the rotating unit are integrally formed by using an overall machining process.

[0016] Further, the base and the dual-axis piezoelectric drive assembly further comprise a metal substrate for fixing the piezoelectric drive assembly on the base.

[0017] Further, the X-axis and Y-axis piezoelectric ceramic drivers are both composed of a plurality of piezoelectric ceramic sheets stacked together, the piezoelectric ceramic sheets are fixed on the metal substrate by epoxy resin to form a piezoelectric stack structure.

[0018] Further, the base is internally designed with a sealed chamber for installing a control circuit of the piezoelectric ceramic driver, and the control circuit meets the intrinsically safe explosion-proof requirements.

[0019] Further, the X-axis piezoelectric drive assembly further comprises an X-axis limiting device, and the Y-axis piezoelectric drive assembly further comprises a Y-axis limiting device.

[0020] Further, the self-calibration device and the calibrated inertial navigation system are placed in a sealed shell, both of which meet the requirements of intrinsic safety equipment, and the sealed shell is designed with an IP65 protection level.

[0021] Further, the device further comprises an electrical interface for connecting with an external control system.

[0022] Further, the method comprises the following steps: S1. Calibration initialization, the inertial navigation system is installed on a rotating platform, all electrical interfaces are connected, and the self-calibration device is initialized after the inertial navigation system is started or the control system receives a calibration instruction; S2. Initial position calibration, the inertial navigation system is placed at an initial position, and data output by an angle measurement unit at this time is recorded as a calibration reference; S3. Angle planning, the control system loads a pre-stored calibration position sequence; S4. Rotation control, the motion of the rotating unit is controlled according to the angle sequence planned in S3; S5. Data acquisition, inertial navigation system data is acquired after stabilization at each calibration position; S6. Judgment of whether all positions are completed, if not, returning to S4, and the selection of the rotating position needs to ensure that the main postures in the working range of the inertial navigation system are covered; S7. Data processing, the acquired data is preprocessed, and the preprocessing includes filtering and denoising; S8. Parameter estimation, least square method or other optimization algorithms are used to estimate error parameters of the inertial navigation system; S9. Error compensation, the parameters estimated in S8 are substituted into a calibration mathematical model of the inertial navigation system for error compensation, and the data measured multiple times is fused; S10. Calibration verification, the calibration effect is verified through experiments, and if the effect does not meet the requirements, the calibration is re-performed.

[0023] Further, S8 comprises: S81. Establishment of an error model of the inertial navigation system and compensation, the error model comprises accelerometer error, gyroscope error, temperature error, lever arm error and installation error; S82. Establishment of an observation equation in multi-position calibration, in the multi-position calibration, error parameters are estimated by measuring gravitational acceleration and earth rotation angular velocity at different postures; S83. Least square method or iterative calculation is used to continuously optimize the estimated error parameters.

[0024] Further, S9 comprises: S91. Simplification of an error model of the inertial navigation under small-angle rotation; S92. Fusion processing of the data measured multiple times using the simplified error model by using Kalman filtering or particle filtering algorithm, to further improve the estimation accuracy of the parameters.

[0025] Further, the specific steps of S3 and S4 are: (1) receiving calibration instructions, determining the target rotation angle and rotation axis; (2) calculating the required control voltage according to the target rotation angle; (3) outputting the control voltage, converting the digital signal to an analog voltage signal through a D / A converter; (4) piezoelectric ceramic generates deformation and generates a torsional moment under the action of voltage; (5) flexible hinge amplifies displacement, amplifies the small deformation of piezoelectric ceramic to a larger rotation angle; (6) angle feedback detection, angle sensor real-time monitoring rotation angle; (7) closed-loop control, comparing the actual angle with the target angle, adjusting the control voltage; (8) judging whether the target angle is reached, if not, returning to step (2) to continue adjusting.

[0026] The beneficial effects of the present application are: 1. The innovative combination of piezoelectric ceramic inverse piezoelectric effect and flexible hinge is realized: the present application first combines the inverse piezoelectric effect of piezoelectric ceramic with the flexible hinge technology and applies it to the self-calibration field of inertial navigation system. This combination fully utilizes the high precision and fast response characteristics of piezoelectric ceramic, and solves the problem of small output displacement of piezoelectric ceramic through the elastic amplification of flexible hinge.

[0027] 2. Innovative structural design of dual-axis rotation device: the present application designs a dual-axis rotation device based on piezoelectric ceramic, which realizes independent rotation control of X-axis and Y-axis through two groups of orthogonally arranged piezoelectric ceramic drivers. This design can meet the demand for different angle positions in multi-position calibration of inertial navigation system, and has the advantages of small size, high precision and fast response compared with traditional mechanical rotation devices.

[0028] 3. Innovative method to solve the problem of piezoelectric torsion angle limitation: in view of the small torsion angle of piezoelectric torsion device, the present application proposes an innovative method of multi-position combined calibration. By decomposing large-angle rotation into multiple small-angle rotations and combining with the optimization of calibration algorithm, the multi-point positioning function under the limitation of piezoelectric torsion device torsion angle is realized.

[0029] 4. Innovative scheme of intrinsic safety explosion-proof design: the present application fully considers the special requirements of underground intrinsic safety environment in device design, and ensures that the whole device meets the explosion-proof standard of coal mine underground through circuit energy limitation, sealing structure design, temperature control and other measures. Especially in the circuit design of piezoelectric ceramic driver, the intrinsically safe circuit is adopted to limit the maximum energy output of the circuit.

[0030] 5. Innovative design concept with engineering application: the design of the present application fully considers the demand of engineering application, adopts modular design concept in structural design, which is convenient for manufacturing, installation and maintenance; adopts corrosion-resistant and impact-resistant materials suitable for underground environment in material selection; and reduces manufacturing cost through optimization design in cost control. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the drawings needed to be used in the following embodiment or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can also obtain other drawings from the structures shown in the drawings without any creative effort.

[0032] Figure 1 The schematic diagram of the overall structure of the piezoelectric ceramic multi-position self-calibration device of the present application; Figure 2 The front view of the piezoelectric ceramic driver and flexible hinge structure diagram of the present application; Figure 3 The top view of the piezoelectric ceramic driver and flexible hinge structure diagram of the present application; Figure 4 The flow chart of the working principle of the piezoelectric ceramic biaxial rotation of the present application; Figure 5 The flow chart of the working principle of the piezoelectric ceramic biaxial rotation of the present application;

[0033] The implementation of the object of the present application, functional features and advantages will be further described with reference to the embodiments and the accompanying drawings. DETAILED DESCRIPTION

[0034] The exemplary embodiments will be described in detail herein with reference to the accompanying drawings. The following description refers to the accompanying drawings in which the same numbers in different drawings represent the same or similar elements unless otherwise represented. The embodiments described in the following exemplary embodiments are not meant to represent all implementations consistent with the present disclosure. Rather, they are merely examples of apparatuses and methods consistent with some aspects of the present disclosure as detailed in the appended claims.

[0035] The terms "first", "second", and the like in the description and claims of the present disclosure are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the use of such terms in the description and claims is solely intended to distinguish the corresponding use of the same terms in the description and claims unless otherwise indicated.

[0036] In addition, the terms "comprising" and "having" and any variations thereof are intended to cover a non-exclusive inclusion, for example, a process, method, system, product, or apparatus that comprises a list of steps or units is not necessarily limited to those steps or units that are clearly listed, but can include other steps or units that are not clearly listed or inherent to such processes, methods, products, or apparatuses.

[0037] Plurality, including two or more.

[0038] And / or, it should be understood that for the term "and / or" used in the present disclosure, it is only a description of the association relationship of the associated objects, which means that there can be three relationships. For example, A and / or B can represent three cases: A exists alone, A and B exist together, and B exists alone.

[0039] The basic principle of the present application for realizing biaxial rotation motion by using the inverse piezoelectric effect of piezoelectric ceramics is that when an electric field is applied in the polarization direction of piezoelectric ceramics, the piezoelectric ceramics will produce mechanical deformation, which includes elongation, shortening or torsion and other forms. In the present application, the torsional deformation of piezoelectric ceramics is mainly used to generate a rotation torque.

[0040] 1. Principle of inverse piezoelectric effect of piezoelectric ceramics: The inverse piezoelectric effect of piezoelectric ceramics refers to the rearrangement of internal electric dipole moments when an external electric field is applied to the piezoelectric ceramics, resulting in mechanical deformation of the material. For a piezoelectric ceramic driver of torsional mode, when a voltage is applied to the electrodes of the piezoelectric ceramic, a shear stress is generated, which causes the torsional deformation of the material. The torsion angle θ is proportional to the applied voltage V, which can be represented as θ = k·V, where k is the torsion coefficient.

[0041] Implementation mechanism of biaxial rotation: The present application adopts two groups of piezoelectric ceramic drivers to control the rotation motion of X and Y axes respectively. Each group of piezoelectric ceramic drivers is composed of multiple piezoelectric ceramic pieces arranged in a specific way. For X-axis rotation control, when a voltage is applied to the X-axis piezoelectric ceramic driver, the piezoelectric ceramic generates a torsional torque around the X-axis, which is transmitted to the rotating platform through a flexible hinge mechanism, causing the platform to rotate around the X-axis. The control principle of Y-axis is the same as that of X-axis. By controlling the voltage size and direction of the two groups of drivers, the rotation motion of the rotating platform in any direction can be realized.

[0042] Generation mechanism of torsional torque: The generation mechanism of torsional torque of piezoelectric ceramics is based on the shear strain in the inverse piezoelectric effect. When an electric field is applied in a specific direction of the piezoelectric ceramic, a shear stress T is generated, which is proportional to the electric field strength E: T = e·E, where e is the piezoelectric stress constant. The shear stress generates shear strain γ in the piezoelectric ceramic, which in turn generates a torsional torque M. The size of the torsional torque is related to the geometric size of the piezoelectric ceramic, the material parameters and the applied voltage.

[0043] For a piezoelectric ceramic torsional driver with a circular cross section, the torsional torque M can be represented as: , where d 36 is the piezoelectric strain constant, V is the applied voltage, r is the average radius of the piezoelectric ceramic, t is the thickness of the piezoelectric ceramic, G is the shear modulus, and h is the length of the polarization direction of the piezoelectric ceramic (electrode spacing).

[0044] Dual-axis coordinated control strategy: In order to realize precise dual-axis rotation control, the application adopts a closed-loop control system, which monitors the angle position of the rotation platform in real time through an angle sensor and compares it with the set value to form a feedback control loop. The control system adjusts the voltage of the piezoelectric ceramic driver according to the deviation signal to realize precise angle control.

[0045] In actual application, different angle rotation movements can be realized by controlling the phase difference of the voltage of the two groups of piezoelectric ceramic drivers. For example, when the phase difference of the voltage of the two groups of drivers is 90°, circular trajectory rotation movement can be realized; when the phase difference is 0° or 180°, linear trajectory swing movement can be realized.

[0046] The application establishes a complete mathematical model of the piezoelectric ceramic torsion device, which is based on the constitutive equation of piezoelectric material and the theory of elasticity, and can accurately describe the electromechanical coupling characteristics of the device.

[0047] I. Mathematical model of piezoelectric ceramic torsion device (1) Constitutive equation of piezoelectric ceramic: The constitutive equation of piezoelectric ceramic describes the coupling relationship between mechanical quantities and electrical quantities. For piezoelectric torsion mode, the equation can be expressed as follows:

[0048] (1) Where S is the strain tensor, T is the stress tensor, E is the electric field intensity, D is the electric displacement, s E is the elastic compliance coefficient under constant electric field, d is the piezoelectric strain constant matrix, is the dielectric constant under constant stress.

[0049] For a circular ring piezoelectric ceramic torsion driver, in the cylindrical coordinate system, the main stress component is the shear stress T θz , and the corresponding strain component is the shear strain S θz . When an electric field E Z is applied in the axial direction of the piezoelectric ceramic, according to the inverse piezoelectric effect, shear strain will be generated: (2) Where d 36 is the piezoelectric strain constant (unit: m / V), E Z is the axial electric field intensity (unit: V / m), and S θz is the dimensionless strain.

[0050] (2) Calculation model of torsional moment: The relationship between the torsional moment M generated by the piezoelectric ceramic torsion driver and the applied voltage V can be calculated by the following formula: (3) where r is the average radius of the piezoelectric ceramic, t is the thickness of the piezoelectric ceramic, G is the shear modulus, and h is the length of the polarization direction of the piezoelectric ceramic (the electrode spacing). Formula (3) shows that the torsional moment is proportional to the piezoelectric constant d 36 , the voltage V, and the cube of the radius r, and inversely proportional to the thickness t. Therefore, increasing the radius of the piezoelectric ceramic or reducing its thickness can significantly improve the torsional moment.

[0051] The modified formula considering actual efficiency is: (4) where η is the efficiency coefficient (considering hysteresis, loss, etc., typical value 0.8-0.95) (3) Elastic model of flexible hinge: The elastic deformation of the flexible hinge can be described by the bending theory of beam. For a straight circular flexible hinge, its torsional stiffness K can be expressed as: (5) where E is the elastic modulus of the material, about 2×10 11 Pa for stainless steel, b is the width of the hinge, t h is the thickness of the hinge, and l is the length of the hinge. This formula is applicable to straight circular flexible hinges with thickness t h much smaller than length l (t h / l < 0.1), and when t h / l > 0.1, nonlinear correction needs to be considered: (6) where α is the correction coefficient (typical value 0.2-0.5).

[0052] When a torsional moment M is applied, the torsional angle generated by the flexible hinge is: (7) (4) Overall model of piezoelectric torsional device: Considering the characteristics of piezoelectric ceramic driver and flexible hinge, in the overall mathematical model of piezoelectric torsional device, θ piezo and θ hinge are in series, and the total torsional angle is determined by the amplification factor of the flexible hinge, expressed as: (8) where θ total is the total torsional angle, θ piezo is the torsional angle directly generated by the piezoelectric ceramic, and M amplification is the amplification factor of the flexible hinge.

[0053] The amplification factor is shown in the following formula: (9) Wherein, L1 is the distance from the piezoelectric ceramic action point to the hinge center, L2 is the distance from the hinge center to the rotating platform, and β is the structure efficiency coefficient (0.9-0.98).

[0054] The total amplification multiple of multi-stage amplification (the amplification multiple of each stage is the same) is: (10) In the formula: n is the amplification stage.

[0055] (5) Dynamic characteristic model: the dynamic characteristic of the piezoelectric torsion device can be described by a second-order vibration system: (11) Wherein, J is the rotational inertia of the system , c is the damping coefficient , K total is the total stiffness of the system , and M(t) is the applied torsional moment.

[0056] The natural angular frequency ω n and the damping ratio ζ of the system are respectively: ζ (12)

[0057] The critical damping coefficient : (13) II. Mathematical model of biaxial rotation motion The biaxial rotating device of the application relates to rotation motions in two orthogonal directions, and a corresponding mathematical model needs to be established to describe the coupling relationship and coordinated control strategy of biaxial motion.

[0058] (1) Kinematic model of biaxial rotation: let the rotation angles of X-axis and Y-axis directions be θ x and θ y , respectively, and the attitude of the rotating platform is described by Euler angles, the application is X, Y biaxial rotation, and the order is to rotate θ y around Y-axis first, and then rotate θ x around X-axis.

[0059] For the biaxial rotating device, the rotation motions around X-axis and Y-axis are mainly involved, and the corresponding rotation matrix is: (14) (15) When two rotations are performed simultaneously, the total rotation matrix is: (16) Rotation matrix multiplication does not satisfy the commutative law, the above expression represents first rotating θ y around the Y axis and then rotating θ x around the X axis; if first rotating around the X axis and then rotating around the Y axis, the rotation matrix is , the two poses are different, and the rotation sequence of Y first and then X is adopted in the embodiment of the application.

[0060] (2) Coupling effect of biaxial motion: in an actual biaxial rotation system, there is a coupling effect between the two rotation axes, and the coupling mainly comes from the asymmetry of the mechanical structure and the installation error. The coupling effect can be described by a coupling matrix C: (17) Where θ x eff and θ y eff are actual rotation angles, θ x cmd and θ y cmd are command rotation angles, and C is a coupling matrix.

[0061] The general form of the coupling matrix C is: (18) Where c xy is the coupling coefficient of the X axis to the Y axis, c yx is the coupling coefficient of the Y axis to the X axis, c xy represents the associated rotation angle of the Y axis when the X axis rotates a unit angle, and c yx is the same; in the ideal case, c xy =c yx =0, and the actual value is generally less than 0.01 (1%).

[0062] (3) Biaxial coordinated control model: in order to realize accurate biaxial rotation control, a coordinated control model needs to be established. Let the control voltages of the two piezoelectric ceramic drivers be V x and V y , according to the mathematical model of the piezoelectric torsion device, we have:

[0063] (19) Where k x and k y are the voltage-angle conversion coefficients of the X axis and the Y axis respectively, For the error term caused by temperature, δ(V): voltage nonlinearity error term.

[0064] In practical control, the required control voltage needs to be calculated based on the target rotation angle: (20) In the formula: θ ref From the target angle.

[0065] Considering the dynamic characteristics and control delay of the system, the control algorithm needs to adopt predictive control or feedforward control strategies to improve response speed and control accuracy.

[0066] For complex rotational trajectories, such as circular or spiral trajectories, it is necessary to establish corresponding trajectory planning models.

[0067] III. Mathematical Model for Inertial Navigation System Calibration The present invention also establishes a mathematical model for the calibration of an inertial navigation system applicable to a piezoelectric ceramic self-calibration device. This model takes into account the characteristics of small-angle rotation and the statistical characteristics of multiple measurements.

[0068] (1) Error Model of Inertial Navigation System: The error model of inertial navigation system includes the accelerometer error model and the gyroscope error model. The accelerometer error model can be expressed as: (twenty one) in, The measured value is from the accelerometer. For the true acceleration, ΔKa is a 3×3 scaling factor and installation error matrix, where the diagonal elements represent the scaling factor error and the off-diagonal elements represent the installation error. The zero bias error vector For measuring white noise, I is a 3×3 identity matrix. , , , Both are 3×1 vectors, expanded as follows: (twenty two) The error model of a gyroscope can be expressed as: (twenty three) in, This is the measurement value from the gyroscope. For true angular velocity, This is a 3×3 scaling factor and installation error matrix, where the diagonal elements represent scaling factor errors and the off-diagonal elements represent installation errors. This is the drift error vector. Measure white noise for a gyroscope.

[0069] Simplified form (ignoring installation error): (24) The error model includes accelerometer error, gyroscope error, temperature error, rod arm error and installation error; the installation error, rod arm error and temperature error are ignored in the above error model formula and can be compensated in the host computer software.

[0070] (2) Observation equation of multi-position calibration: In multi-position calibration, error parameters are estimated by measuring the gravitational acceleration and the earth rotation angular velocity in different attitudes. Under static calibration conditions, the accelerometer should measure the local gravitational acceleration, and the gyroscope should measure the component of the earth rotation angular velocity in the carrier coordinate system.

[0071] For the i-th calibration position, the observation equation of the accelerometer is: (25) For the i-th calibration position, the observation equation of the gyroscope is: (26) In the formula: : gravitational vector (navigation coordinate system); : earth rotation angular velocity, ; : gravitational acceleration; L: local latitude.

[0072] where, is a 3x3 orthogonal rotation matrix from the navigation coordinate system to the carrier coordinate system, satisfying (inverse matrix is equal to transpose matrix), g is the gravitational acceleration vector, is the earth rotation angular velocity vector, and are measurement noises; the navigation coordinate system n uses the North East Down (NED) coordinate system, and the carrier coordinate system b uses the Front-Right-Up (FRU) coordinate system.

[0073] (3) Model simplification under small angle rotation: Considering the torsion angle limitation of the piezoelectric torsion device, the angle of each rotation is usually small (less than 10°), and the small angle approximation can be used: ,

[0074] Under the small angle condition, the rotation matrix can be simplified as: ; (27) This simplification can greatly simplify the calculation process and improve the real-time performance of the calibration algorithm.

[0075] Approximation error analysis: When (0.087 rad), the approximation error is <0.1%; when (0.175 rad), the approximation error is <0.5%.

[0076] (4) Data fusion model for multiple measurements: Due to the use of multiple small-angle rotation calibration strategy, it is necessary to fuse the data of multiple measurements. The least squares method is adopted, and the objective function is: (28) The weighting matrix W a and W g is usually taken as the inverse matrix of the measurement noise covariance matrix:

[0077]

[0078] By minimizing the objective function J, the error parameters of the inertial navigation system can be estimated.

[0079] (5) Observability analysis of calibration parameters: The observability of calibration parameters determines the accuracy and stability of parameter estimation. Under the condition of small-angle rotation, some parameters may become unobservable or have poor observability.

[0080] Observability matrix: (29) Where: h i is the i-th observed output (or measurement); p is the parameter vector to be identified; is the gradient (or Jacobian row vector) of h i with respect to the parameter vector p.

[0081] Observability criterion: if , all parameters are observable; if , there are unobservable parameters.

[0082] Note: rank( ) represents the amount of information (dimension) that can be independently determined from the observation data, dim( ) represents the total number of parameters to be identified. If the rank of the matrix is equal to the number of parameters, it means that each parameter can be uniquely determined by the observation data. If the rank is less than the number of parameters, there are some parameters that cannot be distinguished from the data (i.e., there are parameters that cannot be identified).

[0083] Four, error analysis and compensation model The complete error analysis and compensation model is established in the application, which is used for evaluating the calibration accuracy and performing error compensation, so as to ensure that the calibration result of the inertial navigation system meets the accuracy requirement of the downhole application.

[0084] (1) Analysis of the source of calibration error: the calibration error mainly comes from the following aspects: hysteresis error of piezoelectric ceramic driver, elastic deformation error of flexible hinge, measurement error of angle sensor, temperature and vibration interference of downhole environment, and model error of calibration algorithm. The measurement error of the angle sensor is the index item that can be seen in the selected sensor, and the vibration interference of the downhole environment and the model error of the calibration algorithm can be ignored compared with the hysteresis error. Among them, the hysteresis error of piezoelectric ceramic is the main factor affecting the calibration accuracy, and its hysteresis rate is usually between 5%-10%; the elastic deformation error of the flexible hinge can be compensated by the temperature error, because this error is mainly caused by the deformation caused by temperature.

[0085] (2) Establishment of error compensation model: in order to improve the calibration accuracy, the corresponding error compensation model needs to be established. For the hysteresis error of piezoelectric ceramic, Preisach hysteresis model is adopted for compensation, which can accurately describe the hysteresis characteristics of piezoelectric ceramic. The expression of Preisach hysteresis model is: (30) Among them, is the Preisach density function, is the unit hysteresis operator, and α and β are the upper and lower thresholds of hysteresis characteristics, respectively.

[0086] Simplified implementation (piecewise linear model): (31) In the formula: K up ,b up : the slope and bias of the rising branch; k down ,b down : the slope and bias of the falling branch.

[0087] Hysteresis compensation algorithm: (32) Among them: V cmd : the ideal voltage corresponding to the expected output angle (assuming no hysteresis); : the voltage correction term added to offset the hysteresis effect, which depends on the last state (θ prev ,V prev ) and the voltage change direction.

[0088] For temperature error, a polynomial fitting method is used to establish a temperature compensation model. Let the temperature be T, and the torsion angle error of the piezoelectric ceramic be Δθ(T), then the temperature compensation model is: (33) Where: θ raw is the original measured or calculated angle (without temperature compensation), is the fitting coefficient of temperature error, and T0 is the reference temperature (usually the room temperature at calibration).

[0089] Typical second-order model: (34) This is the specificization of formula (33) when n=2, .

[0090] Temperature sensitivity coefficient: (unit: ppm / °C) Where k is the torsional stiffness, and TC k is the temperature coefficient of the material / structure.

[0091] (3) Implementation steps of error compensation: The implementation steps of error compensation include: first, measuring error data at different voltages and temperatures through experiments; second, establishing an error model based on the measured data and determining the model parameters; third, integrating the error model into the calibration algorithm to calculate and compensate the error in real time during the calibration process; finally, verifying the compensation effect through experiments and continuously optimizing the error model parameters.

[0092] In the embodiments of the present application, referring to Figure 1 , the piezoelectric ceramic biaxial rotation device structure of the present application, which adopts modular design and mainly includes a base, an X-axis piezoelectric driving assembly, a Y-axis piezoelectric driving assembly, a flexible hinge mechanism, a rotating platform and other core components. Specifically: (1) Base: The base is the basic support structure of the device, made of high-strength stainless steel material, with good corrosion resistance and impact resistance (maintaining certain rigidity and stability). The base is provided with mounting holes for firmly fixing the entire device on the downhole platform or equipment base through bolts. The base is also provided with a standard mounting interface, which can be used in cooperation with the mounting bracket of the downhole inertial navigation system to realize fast, accurate and reliable mechanical docking.

[0093] The base is internally designed with a sealed chamber for installing the control circuit of the piezoelectric ceramic driver, ensuring that the circuit meets the intrinsic safety explosion-proof requirements.

[0094] (2) X-axis piezoelectric driving assembly: the X-axis piezoelectric driving assembly is responsible for controlling the rotary motion of the rotating platform around the X-axis, and the assembly comprises an X-axis piezoelectric ceramic driver, an X-axis flexible hinge mechanism and an X-axis limiting device. The X-axis piezoelectric ceramic driver is responsible for controlling the rotary motion of the rotating platform around the X-axis, and the X-axis piezoelectric ceramic driver is composed of a plurality of piezoelectric ceramic sheets stacked together, adopts high-performance piezoelectric materials such as PZT-5H, and has a large piezoelectric coefficient. The piezoelectric ceramic sheet is fixed on the metal substrate by epoxy resin bonding to form a piezoelectric stack structure.

[0095] (3) Y-axis piezoelectric driving assembly: the structure of the Y-axis piezoelectric driving assembly is similar to that of the X-axis, and is responsible for controlling the rotary motion of the rotating platform around the Y-axis. The X-axis and Y-axis piezoelectric driving assemblies are arranged orthogonally to ensure that the two rotary shafts are perpendicular to each other, meeting the orthogonality requirement of the inertial navigation system calibration. The Y-axis piezoelectric ceramic driver is responsible for controlling the rotary motion of the rotating platform around the Y-axis, and has the same structure as the X-axis driver and is arranged orthogonally with the X-axis driver.

[0096] (4) Flexible hinge mechanism: comprising an X-axis flexible hinge and a Y-axis flexible hinge, respectively connecting the X-axis, Y-axis piezoelectric ceramic driver and the rotating platform, the flexible hinge mechanism is a key component connecting the piezoelectric ceramic driver and the rotating platform, and the flexible hinge mechanism and the piezoelectric ceramic end driver are connected by epoxy resin glue, while the flexible hinge and the rotating platform are integrally formed by the whole machining process. The flexible hinge mechanism amplifies the small displacement of the piezoelectric ceramic through elastic deformation. Preferably, the present application adopts a straight circular flexible hinge or an asymmetric triangular circular arc flexible hinge structure.

[0097] The design structure parameters of the flexible hinge include hinge thickness t, length l, width b, etc., which directly affect the torsion angle and the size of the output torque. According to the theoretical model of the flexible hinge, the flexible deformation angle a around the z-axis z and the torque M z are related as follows: M z = K z ·a z , wherein K z is the torsional stiffness of the flexible hinge. By optimizing the structure parameters of the flexible hinge, the torsion angle can be accurately controlled. The amplification factor of the flexible hinge can be calculated by the lever principle, and the amplification factor M = L2 / L1, wherein L1 is the distance from the action point of the piezoelectric ceramic driver to the center of the hinge, and L2 is the distance from the center of the hinge to the rotating platform.

[0098] (5) Rotary platform: The rotary platform is used to install the inertial navigation system (IMU) and is made of lightweight aluminum alloy material with good rigidity and stability. A standard inertial navigation system installation interface is provided on the rotary platform, which can adapt to different types of inertial navigation systems. A high-precision angle sensor is provided at the center of the platform to monitor the rotation angle in real time.

[0099] (6) Angle sensor: installed on the rotary platform coaxially with the inertial measurement unit, used to monitor the rotation angle in real time, using high-precision optical encoder or capacitive sensor.

[0100] (7) Sealed housing: The protective housing of the entire device is designed with IP65 protection level to prevent dust and water from entering.

[0101] (8) Electrical interface: including power interface, signal interface, communication interface, etc., used to connect with external control system.

[0102] Referring to Figure 2 and Figure 3 , the connection structure of the piezoelectric ceramic driver and the flexible hinge is shown in detail, wherein the piezoelectric ceramic sheet stack is composed of multiple piezoelectric ceramic sheets (such as PZT-5H); the metal substrate is used to fix the piezoelectric ceramic stack, which is made of stainless steel; the electrode and electrode lead are used to connect the driving circuit, which is made of high-temperature resistant wire. Since the piezoelectric ceramic needs to input +5V and -5V voltage to realize bending, the driving circuit needs to convert the input voltage; the X-axis flexible hinge body is connected with the rotary platform, and the rotary motion is realized through flexible deformation; the Y-axis flexible hinge structure is the same as the X-axis flexible hinge, but the direction is orthogonal.

[0103] The structural design of the entire device fully considers the special requirements of the downhole environment, adopts a compact structural layout, and ensures that the complex dual-axis rotation function is realized in a limited space.

[0104] The piezoelectric ceramic and the flexible hinge are organically combined in the present application, the elastic deformation of the flexible hinge amplifies the small displacement of the piezoelectric ceramic, and the large-angle torsional motion is realized. This combination fully utilizes the high-precision characteristics of the piezoelectric ceramic and the amplification effect of the flexible hinge, which is one of the core innovations of the present application. Mainly: 1. Amplification principle of flexible hinge: The flexible hinge is a kind of elastic mechanical structure, which transmits motion and force through its elastic deformation. In the present application, the flexible hinge is used as the connecting mechanism between the piezoelectric ceramic driver and the rotary platform, which mainly amplifies the small torsional displacement of the piezoelectric ceramic to a larger rotation angle.

[0105] The amplification factor of the flexible hinge mainly depends on its geometric structure parameters and material properties. For a straight circular flexible hinge, its torsional stiffness K can be expressed as: , where E is the elastic modulus of the material, b is the width of the hinge, t is the thickness of the hinge, and l is the length of the hinge.

[0106] The relationship between the torsion angle θ and the applied torque M is given by: When the piezoelectric ceramic generates a torque acting on the flexible hinge, a torsion angle is produced. By adjusting the geometric parameters of the flexible hinge, precise control of the torsion angle can be achieved.

[0107] 2. Integrated design of piezoelectric ceramic and flexible hinge: The invention adopts an integrated design concept, integrating the piezoelectric ceramic driver and the flexible hinge mechanism together. Specifically, the piezoelectric ceramic driver is connected to the flexible hinge through mechanical fixation or adhesive bonding, forming a complete driving unit.

[0108] In terms of structural design, the piezoelectric ceramic driver is installed at the fixed end of the flexible hinge, while the rotating platform is connected to the free end of the flexible hinge. When the piezoelectric ceramic generates a torsional torque, the torque is transmitted to the rotating platform through the flexible hinge, causing the platform to rotate. The design of the flexible hinge needs to consider factors such as stress concentration and fatigue life to ensure that it does not fail during long-term use.

[0109] 3. Multi-section flexible hinge structure: To further improve the torsion angle, the invention proposes a multi-section flexible hinge structure. This structure is composed of multiple flexible hinge sections connected in series, each with a certain amplification factor. Through the cascading amplification of multiple hinge sections, a larger total amplification factor can be achieved.

[0110] Assuming that the amplification factor of each flexible hinge section is M l , then the total amplification factor of n hinge sections in cascade is M total = M l n For example, if the amplification factor of each hinge section is 10, then the total amplification factor of 3 hinge sections in cascade can reach 1000 times.

[0111] 4. Selection of flexible hinge materials: The selection of flexible hinge materials has an important influence on the performance of the entire device. The invention uses high-strength and high-elastic modulus materials such as stainless steel or titanium alloy to manufacture the flexible hinge. These materials have good corrosion resistance and are suitable for use in downhole environments.

[0112] The elastic modulus E and yield strength R eare two key parameters. The elastic modulus determines the stiffness of the flexure hinge, while the yield strength determines the maximum allowable deformation of the flexure hinge. In order to obtain a large amplification factor, a material with a low elastic modulus needs to be selected, but at the same time the yield strength of the material needs to be high enough to avoid plastic deformation during operation. See Figure 4 The working principle flow of the piezoelectric ceramic biaxial rotation device is as follows: 1. System initialization: including parameter setting, sensor calibration, communication establishment, etc. Among them, the parameter setting includes: the initial position of the driving flexible hinge after the piezoelectric ceramic is powered on, the initial parameter setting of the inertial navigation system entering the working mode after self-checking, the input rod arm error, and the installation error information; The sensor calibration refers to the angle sensor restoring zero position to ensure that the inertial navigation system and the rotation platform are at zero position; The communication establishment is that the host computer receives the output data of the inertial navigation system.

[0113] 2. Receive calibration instructions, determine the target rotation angle and rotation axis; 3. Calculate the required control voltage, calculate Vx and Vy according to the target angle and the voltage-angle conversion coefficient; In actual control, the method of calculating the required control voltage according to the rotation angle is as follows: For example, the target angle is = = 45°, the calibration parameter is k x = k y = 0.5 ° / V, and the coupling matrix is c_{xy} = 0.005, c_{yx} = 0.003, then

[0114]

[0115] Ignore temperature and nonlinear error , then the ideal voltage V x_ideal =V y_ideal = 45° / 0.5 ° / V = 90 V, and the feedforward decoupling is performed (substitute formula 20):

[0116] Due to the coupling, in order to achieve 45 degrees on both axes, the actual voltage required to be applied (about 89.55V) is slightly lower than 90V calculated without considering coupling, because the rotation of one axis will "help" the rotation of the other axis through coupling.

[0117] 4. Output control voltage, convert digital signal to analog voltage signal through D / A converter; 5. The piezoelectric ceramic generates deformation and generates a torsional moment under the action of voltage; 6. Flexible hinge amplifies displacement, which amplifies the small deformation of piezoelectric ceramics into a larger rotation angle; 7. Angle feedback detection, angle sensor real-time monitoring rotation angle; 8. Closed-loop control, compare the actual angle with the target angle, adjust the control voltage; 9. Determine whether to reach the target angle, if not, return to step 3 to continue adjustment; 10. Angle stability, and keep the voltage stable after reaching the target angle, wait for the inertial navigation system data acquisition.

[0118] Reference Figure 5 For the complete workflow of multi-position calibration of the present application, the specific steps are as follows: 1. Calibration preparation: install the inertial navigation system on the rotating platform, connect all electrical interfaces, and the intrinsically safe control and processing unit performs initialization operation after the system is powered on or the controller receives external calibration instructions, including parameter zeroing, circuit self-checking, module communication link verification, etc., to ensure the normal work of the intrinsically safe IMU, piezoelectric ceramic multi-axis precision positioning table, angle sensor and other components. Among them: parameter zeroing is to ensure that the parameters read by the inertial navigation system are the parameters of this measurement, circuit self-checking is to confirm that the circuit is not short-circuited or open-circuited, and module communication link verification is to send verification data to verify that the communication is working normally.

[0119] 2. Initial position calibration: record the sensor of the initial position; place the inertial navigation system at the initial position and record the sensor output data at this time as the calibration reference.

[0120] 3. Angle planning: after the data system is powered on, load the pre-stored calibration position sequence, and in this embodiment, 8 calibration positions are selected: position 1: pitch + 90°, azimuth 0°; position 2: pitch - 90°, azimuth 0°; position 3: pitch 0°, azimuth + 90°; position 4: pitch 0°, azimuth - 90°; position 5: pitch + 45°, azimuth + 45°; position 6: pitch + 45°, azimuth - 45°; position 7: pitch - 45°, azimuth + 45°; position 8: pitch - 45°, azimuth - 45°; 4. Rotation control: control the rotating platform motion according to the planned angle sequence; control the rotating platform to rotate by a small angle through the piezoelectric torsion device, and the rotation angle is Δθ each time, and the rotation direction can be X-axis, Y-axis or Z-axis direction; 5. Data acquisition: collect inertial navigation system data after each calibration position is stable; 6. Determine whether all positions are completed, if not, return to step 4; the selection of rotation positions should ensure that the main postures in the working range of the inertial navigation system can be covered; 7. Data processing: pre-process the collected data, including filtering, denoising, etc. 8. Parameter estimation: estimate the inertial navigation error parameters using the least squares method or other optimization algorithms; the error parameters of the inertial navigation system include the accelerometer zero bias, scale factor, installation error, gyroscope zero bias, scale factor, drift, etc.

[0121] The parameter estimation includes the following steps: (1) Establish the error model of the inertial navigation system: the error model of the inertial navigation system includes the accelerometer error model and the gyroscope error model; (2) Establish the observation equation for multi-position calibration: in multi-position calibration, the error parameters are estimated by measuring the gravitational acceleration and the earth rotation angular velocity at different postures; (3) Model simplification under small angle rotation; (4) Since the calibration strategy adopts multiple small angle rotations, the data measured multiple times need to be fused. In this embodiment, the least squares method is adopted, and the objective function is as follows: see formula (28). By minimizing the objective function J, the error parameters of the inertial navigation system can be estimated; 9. Error compensation: substitute the estimated parameters into the inertial navigation system for error compensation; the implementation steps of error compensation include: first, measure the error data under different voltages and temperatures through experiments; second, establish an error model based on the measured data to determine the model parameters; third, integrate the error model into the calibration algorithm to calculate and compensate the error in real time during the calibration process. The calibration error mainly comes from the following aspects: the hysteresis error of the piezoelectric ceramic driver, the elastic deformation error of the flexible hinge, the measurement error of the angle sensor, the temperature and vibration interference of the downhole environment, and the model error of the calibration algorithm. Among them, the hysteresis error of the piezoelectric ceramic is one of the main factors affecting the calibration accuracy, and its hysteresis rate is usually between 5%-10%. For the hysteresis error of the piezoelectric ceramic, the Preisach hysteresis model is used for compensation, and the compensation is performed according to formulas (30)-(32); for the temperature error, a polynomial fitting method is used to establish a temperature compensation model, and the compensation is performed according to formulas (33)-(34).

[0122] 10. Calibration verification: verify the calibration effect through experiments, and re-calibrate if the requirements are not met.

[0123] In summary, to solve the problem of the limited torsion angle of the piezoelectric torsion device, the present application proposes an innovative multi-position calibration implementation strategy. Through the combination of multiple small-angle rotations and the optimization of the calibration algorithm, the requirements of multi-point positioning of the inertial navigation system are met without requiring a single large-angle rotation.

[0124] The basic principle of multi-position calibration: Calibration of inertial navigation systems usually requires data collection at multiple different attitude positions to determine the error parameters of the sensors. According to existing technologies, commonly used calibration methods include the 6-position method and the 12-position method. The 6-position method involves placing the x, y, and z axes upward and downward, respectively, for a total of six positions. The 12-position method is based on the 6-position method and involves mirror measurement at each position to offset the interference caused by the placement surface tilt. For the piezoelectric torsion device of the present application, due to the limited single torsion angle, it is not possible to directly achieve a large-angle rotation of 90° or more. Therefore, a strategy of multiple small-angle rotations is needed to cover the required angle range through the combination of multiple rotations and measurements.

[0125] Angle decomposition and path planning: The present application decomposes a large-angle rotation into multiple small-angle rotation steps. Specifically, a 90° rotation is decomposed into n small-angle increments Δθ, and the size of each increment depends on the maximum torsion angle of the piezoelectric torsion device. For example, if the maximum torsion angle of the piezoelectric torsion device is 0.22° (under 24V intrinsic safety working conditions), then a 90° rotation can be decomposed into 41 rotation steps of 0.22°. If the maximum torsion angle is 22° (after 3-stage amplification), then it can be decomposed into 5 rotation steps of 4.5°.

[0126] In terms of path planning, the present application adopts a spiral or stepped rotation path to ensure that the entire spherical space can be covered. After each rotation step, the system will stabilize for a period of time before data collection is performed after the vibration has decayed. The design of the rotation sequence takes into account the observability of the error parameters of the inertial navigation system to ensure that each error parameter is fully excited.

[0127] Optimized design of calibration algorithm: To adapt to the multi-small-angle rotation calibration method, the present application optimizes the traditional calibration algorithm. The main optimization measures include: 1. Improvement of error model: Establish an error model suitable for small-angle rotation, considering the non-linear effects of rotation angle and the influence of cumulative error.

[0128] 2. Data fusion algorithm: Use methods such as Kalman filtering or particle filtering to fuse the data from multiple measurements, improving the estimation accuracy of the calibration parameters.

[0129] 3. Iterative optimization algorithm: Use least squares method or other optimization algorithms to continuously optimize the calibration parameters through iterative calculations to reduce estimation errors. Each iteration is based on the results of the previous adjustment until the convergence condition is reached.

[0130] 4. Robust design: Consider noise interference, model error and other uncertain factors in algorithm design to improve the robustness of the calibration results.

[0131] The core technical solution of the present application is to combine the inverse piezoelectric effect of piezoelectric ceramics with flexible hinges to design a biaxial rotating piezoelectric torsion device for multi-position self-calibration of inertial navigation systems. The device mainly includes base, piezoelectric ceramic driver, flexible hinge mechanism, rotating platform and other key components.

[0132] In terms of biaxial rotation, the present application uses two groups of piezoelectric ceramic drivers to control the rotation in two orthogonal directions. Each group of piezoelectric ceramic drivers is composed of multiple piezoelectric ceramic sheets stacked together to generate a torsional moment by applying voltage. The inverse piezoelectric effect of piezoelectric ceramics refers to the rearrangement of internal electric dipole moments when an external electric field is applied to the piezoelectric ceramics, resulting in mechanical deformation of the material. The deformation (ΔL) is proportional to the applied voltage (V), and the mathematical expression is ΔL = d·V, where d is the piezoelectric constant.

[0133] In terms of flexible hinge design, the present application uses flexible hinges as the connecting mechanism between the piezoelectric ceramic driver and the rotating platform, which amplifies the small displacement of the piezoelectric ceramic through the elastic deformation of the flexible hinge, realizing large-angle torsional motion. The design parameters of the flexible hinge include hinge thickness, length, width, etc., which directly affect the torsional angle and the size of the output torque.

[0134] In terms of multi-position calibration, considering the torsional angle limitation of the piezoelectric torsion device, the present application proposes a multi-position combined calibration method. When the piezoelectric torsion device cannot be twisted more than 90°, the combination of multiple small-angle rotations can be used to realize large-angle position changes, combined with the optimization of the calibration algorithm to meet the requirements of multi-point positioning of the inertial navigation system.

[0135] In addition, the device of the present application must meet the strict explosion-proof requirements of the intrinsically safe environment in the well, which is the key to ensuring the safe operation of the equipment in the well. The design of intrinsically safe equipment must comply with the relevant requirements of GB3836 series standards and coal mine safety regulations.

[0136] Circuit energy limitation design: The core requirement of intrinsically safe equipment is that the electric spark or thermal effect generated by the circuit in normal and fault states cannot ignite explosive mixtures. According to GB3836.4 standard, the key parameters of intrinsically safe equipment include maximum allowable current (I max ), maximum allowable voltage (U max) and the maximum allowed power (P max ).

[0137] In terms of circuit design, the invention adopts an intrinsically safe circuit that limits the maximum energy output of the circuit through elements such as current-limiting resistors and Zener diodes. The driving circuit of the piezoelectric ceramic driver uses low-voltage power supply, with a maximum voltage of not more than 24V and a maximum current of not more than 100mA. For methane explosive gas, the maximum allowed energy of the intrinsically safe circuit is usually not more than 20μJ, corresponding to a voltage of 24V, the current-limiting resistor needs to be not less than 28.8kΩ (derived from E=U 2 / (2R)), ensuring that in a fault state, it will not produce a spark energy sufficient to ignite gas.

[0138] Housing protection design: The housing of the device of the invention is made of high-strength aluminum alloy or stainless steel material, with good sealing performance. The housing protection level reaches IP65 and above, which can prevent dust from entering and water from entering. According to the standard requirements, IP65 protection level means that the device can prevent harmful dust from accumulating and can resist water spray in all directions.

[0139] Temperature control design: The surface temperature of the intrinsically safe device must be strictly controlled within the specified range. The T1-T4 temperature group corresponds to the methane environment in the well, the maximum surface temperature of the T1 group is not more than 450℃, and the T4 group is not more than 135℃. The device adapts to the requirements of the T4 group, with a maximum surface temperature of 135℃ or less, which is more suitable for use in high-risk environments in the well. In the downhole environment, the device not only needs to consider its own heat generation, but also needs to consider the influence of environmental temperature. The invention achieves temperature control through the following measures: first, select a low-power piezoelectric ceramic driver and control circuit to reduce self-heating; second, use a heat dissipation design and set up heat dissipation fins or holes on the housing; third, set up a temperature monitoring circuit that automatically cuts off the power supply when the temperature exceeds the set value.

[0140] Explosion-proof certification requirements: The device of the invention must pass the explosion-proof qualification certificate, with an explosion-proof symbol of Ex ia I Ma. The device must also have a coal mine safety product safety symbol MA, which is a necessary condition for the device to enter the well.

[0141] During the certification process, the device needs to pass a series of strict tests, including spark ignition test, temperature test, housing strength test, and sealing performance test. In particular, the spark ignition test needs to pass 10 discharge verifications to ensure that under any circumstances, no spark will be produced to ignite explosive gas.

[0142] Special design of intrinsic safety circuit: considering the particularity of piezoelectric ceramic driver, the invention adopts special protection measures in circuit design. Piezoelectric ceramic has capacitance characteristics, which will produce instantaneous large current during charging and discharging. In order to prevent such instantaneous current from producing spark, buffer circuit and current limiting circuit are set in the circuit.

[0143] At the same time, in order to ensure the safety in the fault state of cable breakage or short circuit, multiple protection mechanisms are set in the circuit, including overvoltage protection, overcurrent protection, short circuit protection, etc. These protection circuits are independent of each other, even if one of them fails, the other protection circuits can still work normally.

[0144] The above embodiment numbers of the invention are only for description, not representing the advantages and disadvantages of the embodiments.

[0145] Through the above description of the embodiments, those skilled in the art can clearly understand that the above-mentioned implementation methods can be realized by means of software and necessary general hardware platform, of course, they can also be realized by hardware, but in many cases the former is a better implementation method. Based on such understanding, the technical solutions of the present application or the part that contributes to the prior art can be embodied in the form of software product, which is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk), including a plurality of instructions to make a terminal (which can be a mobile phone, computer, server, air conditioner, or network equipment, etc.) execute the method described in each embodiment of the present application.

[0146] The embodiments of the present application are described above in combination with the drawings, but the present application is not limited to the above-mentioned specific embodiments, the above-mentioned specific embodiments are only illustrative, not restrictive, those skilled in the art can make many forms under the inspiration of the present application without departing from the purpose of the present application and the scope protected by the claims, which all belong to the protection of the present application.

Claims

1. A piezoelectric ceramic multi-position self-calibration device for inertial navigation systems, characterized in that, The device includes: a base, a biaxial piezoelectric drive assembly, a rotation unit, and an angle measuring unit, wherein: The base is used to fix the self-calibration device to a downhole platform or other fixed equipment; The biaxial piezoelectric drive assembly is fixed to the base. The biaxial piezoelectric drive assembly includes an X-axis piezoelectric drive assembly and a Y-axis piezoelectric drive assembly, which are used to control the rotational motion of the rotating unit around the X-axis and Y-axis, respectively. The X-axis piezoelectric drive assembly includes an X-axis flexible hinge, and the Y-axis piezoelectric drive assembly includes a Y-axis flexible hinge. The rotating unit includes a rotating shaft and a rotating platform. The rotating shaft is fixedly connected to the X-axis flexible hinge and the Y-axis flexible hinge. The rotating platform is used to install the inertial navigation system. The angle measurement unit is mounted on the rotating platform and is used to monitor the rotation angle of the inertial navigation system in real time.

2. The multi-position self-calibration device according to claim 1, characterized in that, Both the X-axis and Y-axis flexible hinges are multi-segment flexible hinge structures, which are composed of multiple flexible hinge segments connected in series.

3. The multi-position self-calibration device according to claim 2, characterized in that, The flexible hinges of the X-axis and Y-axis are integrally formed with the rotating unit using a single machining process.

4. The multi-position self-calibration device according to claim 1, characterized in that, A metal substrate is also included between the base and the biaxial piezoelectric drive assembly for fixing the biaxial piezoelectric drive assembly to the base.

5. The multi-position self-calibration device according to claim 4, characterized in that, The X-axis piezoelectric drive assembly further includes an X-axis piezoelectric ceramic actuator, and the Y-axis piezoelectric drive assembly further includes a Y-axis piezoelectric ceramic actuator. Both the X-axis and Y-axis piezoelectric ceramic actuators are composed of multiple piezoelectric ceramic sheets stacked together. The piezoelectric ceramic sheets are fixed to the metal substrate by epoxy resin bonding to form a piezoelectric stack structure.

6. The multi-position self-calibration device according to claim 5, characterized in that, The base has a sealed chamber for installing the control circuit of the X-axis and Y-axis piezoelectric ceramic actuators. The control circuit meets the intrinsically safe explosion-proof requirements.

7. The multi-position self-calibration device according to claim 1, characterized in that, The X-axis piezoelectric drive assembly further includes an X-axis limiting device, and the Y-axis piezoelectric drive assembly further includes a Y-axis limiting device.

8. The multi-position self-calibration device according to claim 1, characterized in that, The self-calibration device and the inertial navigation system being calibrated are housed in a sealed enclosure. Both the inertial navigation system and the self-calibration device meet the intrinsically safe equipment requirements. The sealed enclosure is designed with an IP65 protection rating.

9. The multi-position self-calibration device according to claim 1, characterized in that, The device also includes an electrical interface for connecting to an external control system.

10. A method for multi-position self-calibration of piezoelectric ceramics for inertial navigation systems, characterized in that, The method is implemented using the self-calibration device according to any one of claims 1-9, and the method includes the following steps: S1. Calibration and initialization: Install the inertial navigation system on the rotating platform, connect all electrical interfaces, and after the inertial navigation system starts or the control system receives the calibration command, the self-calibration device performs the initialization operation; S2. Initial position calibration: The inertial navigation system is placed at the initial position, and the data output by the angle measurement unit at this time is recorded as the calibration reference; S3. Angle planning: The control system loads a pre-stored calibration position sequence; S4. Rotation control: Control the movement of the rotating unit according to the angle sequence planned in S3; S5. Data Acquisition: Acquire inertial navigation system data after stabilization at each calibration position; S6. Determine if all positions have been completed; if not, return to S4. S7. Data processing: Preprocessing the collected data, including filtering and noise reduction; S8. Parameter estimation: Estimate the error parameters of the inertial navigation system using the least squares method or other optimization algorithms; S9. Error compensation: Substitute the parameters estimated in S8 into the mathematical model for inertial navigation system calibration to compensate for errors in the preprocessed acquired data, and perform fusion processing on the data from multiple measurements. S10. Calibration and verification: Verify the calibration effect through experiments. If the requirements are not met, recalibrate.

11. The self-calibration method according to claim 10, characterized in that, S8 includes: S81. Establish an error model for the inertial navigation system and compensate for it. The error model includes accelerometer error, gyroscope error, temperature error, lever error, and installation error. S82. Establish observation equations for multi-position calibration, in which error parameters are estimated by measuring gravitational acceleration and Earth's rotation angular velocity under different attitudes; S83. Continuously optimize the estimated error parameters using the least squares method or iterative calculation.

12. The self-calibration method according to claim 11, characterized in that, S9 includes: S91. Simplify the error model for inertial navigation under small-angle rotation; S92. The data from multiple measurements using the simplified error model are fused using Kalman filtering or particle filtering algorithms to further improve the accuracy of parameter estimation.

13. The self-calibration method according to claim 10, characterized in that, The specific steps of S3 and S4 are as follows: (1) Receive calibration instructions and determine the target rotation angle and rotation axis; (2) Calculate the required control voltage based on the target rotation angle; (3) Output control voltage, which converts the digital signal into an analog voltage signal through a D / A converter; (4) The piezoelectric ceramic deforms and generates a torsional moment under the action of voltage; (5) Flexible hinges amplify displacement, turning the tiny deformation of piezoelectric ceramics into a larger rotation angle; (6) Angle feedback detection: the angle sensor monitors the rotation angle in real time; (7) Closed-loop control: compare the actual angle with the target angle and adjust the control voltage accordingly; (8) Determine whether the target angle has been reached. If not, return to step (2) to continue adjusting.

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