CN111188942A - Piezoelectric valve capable of sensing force and displacement automatically and displacement control method - Google Patents
Piezoelectric valve capable of sensing force and displacement automatically and displacement control method Download PDFInfo
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16K—VALVES; TAPS; COCKS; ACTUATING-FLOATS; DEVICES FOR VENTING OR AERATING
- F16K37/00—Special means in or on valves or other cut-off apparatus for indicating or recording operation thereof, or for enabling an alarm to be given
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16K—VALVES; TAPS; COCKS; ACTUATING-FLOATS; DEVICES FOR VENTING OR AERATING
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Abstract
A piezoelectric valve capable of self-sensing force and displacement and a displacement control method are provided, a relation model among valve core displacement, output force, piezoelectric charge of a piezoelectric actuator and driving voltage of the piezoelectric actuator is established, and an algorithm for self-sensing estimation of the valve core displacement and the output force according to the piezoelectric charge and the driving voltage is provided. The piezoelectric valve comprises a piezoelectric stack actuator, an upper cover, a base, a moving end, a disc spring gasket for pre-tightening, and a regular octagonal cushion block, and is matched with a sampling resistor, a current integrator and a feedforward PID controller with a hysteresis compensation algorithm in a control system, so that the valve core displacement closed-loop control and the output force real-time measurement without a sensor are realized. The piezoelectric actuator is used as a driver and a sensor, and can detect the displacement and the output force of the valve core at the same time without an additional sensor; a hysteresis compensation algorithm is added in the controller, so that the control precision and the response speed are improved; the piezoelectric charge is obtained by adopting a current integration method, and parameters can be flexibly adjusted to compensate piezoelectric leakage current so as to stably work for a long time.
Description
Technical Field
The invention belongs to the technical field of fluid measurement and control, relates to an electric control piezoelectric valve technology in an automobile gearbox, and particularly relates to a method for realizing closed-loop displacement control without an additional sensor by acquiring a valve core displacement and an output force signal from a piezoelectric actuator by adopting a decoupling algorithm.
Background
The electromagnetic valve is a key component in the gearbox, generally, the electromagnetic valve can only realize two-position control and cannot be continuously adjusted, so that the gear shifting is controlled by the opening and closing actions of a plurality of electromagnetic valves together. With the development of intelligent valve technology, piezoelectric valves become ideal substitutes for electromagnetic valves. The piezoelectric valve has the advantages of high precision, quick response, low power consumption, long service life, compact structure, environmental protection, energy conservation and the like. Through changing the driving voltage, the valve core position of the piezoelectric valve can be continuously changed, and the number of the required piezoelectric valves is greatly reduced compared with that of the electromagnetic valves.
The valve core of the piezoelectric valve needs to be accurately positioned in the working process so as to realize multi-position control; at the same time, the pressure in the cavity needs to be sensed, and the pressure data is transmitted to an Electronic Control Unit (ECU) of the vehicle. Normally the displacement and pressure needs to be measured by additional sensors, patent CN 1434217a discloses a piezo-electrically driven servo valve in which the position signal needs to be measured by an external displacement sensor. Patent CN 101319688A discloses an intelligent piezoelectric electrohydraulic servo valve, which measures the displacement of a valve core by a displacement sensor in a closed-loop piezoelectric ceramic driver. Patent CN 103032296a discloses a piezoelectric pump based on a butterfly sensor valve, which measures the output pressure and flow rate of the valve while the piezoelectric stack pumps liquid. However, the piezoelectric valve needs to be provided with an independent sensor, and the volume and the complexity of the valve are increased.
The piezoelectric self-sensing method is introduced, the piezoelectric valve is used as the actuator and also used as the sensor to work, an external sensor is not needed, and the piezoelectric self-sensing actuator has the advantages of saving the space of a gearbox, reducing the cost and reducing the difficulty in installation and maintenance.
Disclosure of Invention
The invention aims to provide a valve core displacement and force self-sensing measuring method and a displacement control method in a piezoelectric valve, and also provides a novel displacement-force self-sensing piezoelectric valve. The force and displacement of the mechanical port are estimated by using the voltage and the charge of the electrical port of the piezoelectric valve, and the closed-loop displacement control is realized without using an additional sensor.
In order to achieve the purpose, the invention adopts the technical scheme that:
the piezoelectric valve 1 comprises a moving end 2, a disc spring gasket 3 for pre-tightening, an upper cover 4, internal and external threads 5, a pre-tightening screw 6, a base 7, a regular octagonal cushion block 8 and a piezoelectric stack actuator 9.
The piezoelectric stack actuator 9 is a driving element, and needs to apply a pre-tightening force of about 750N during use because the tensile strength of piezoelectric ceramics is low.
The upper cover 4 is connected with the base 7 through the internal and external threads 5, and the upper cover 4 is of a cylindrical structure.
The piezoelectric stack actuator 9 is a driving element and is arranged inside the upper cover 4, the upper end of the piezoelectric stack actuator 9 is provided with a moving end 2, the moving end 2 outputs displacement and force outwards under the voltage driving, the lower end of the piezoelectric stack actuator 9 is padded with a regular octagonal cushion block 8, and a square groove is formed in the regular octagonal cushion block 8 and used for keeping the piezoelectric stack 9 stable.
The moving end 2 is of a T-shaped structure, the large end of the moving end is in contact with the piezoelectric stack actuator 9, the small end of the moving end extends out of the upper cover 4, and the metal disc spring gasket 3 is arranged between the middle of the moving end 2 and the upper cover 4 and used for providing required pre-tightening force and simultaneously does not excessively block the movement of the moving end 2.
A displacement control method of a piezoelectric valve capable of sensing force and displacement comprises the following steps.
The first step is as follows: a displacement control system for a piezoelectric valve is assembled. The displacement control system of the piezoelectric valve comprises a controller 10, the piezoelectric valve 1, a sampling resistor 11, a software integrator 12, a displacement self-perception calculator 13 and a force self-perception calculator 14.
The controller 10 is used for outputting a voltage signal for setting the displacement to drive the piezoelectric valve 1 and accurately control the displacement thereof.
The sampling resistor 11 is a precision resistor and is connected in series with the piezoelectric valve 1 to convert the current signal of the piezoelectric valve 1 into a voltage signal.
The integrator 12 is connected with the sampling resistor 11, and collects and integrates the voltage signal on the sampling resistor 11, so as to obtain the piezoelectric charge.
The displacement self-sensing calculator 13 obtains the piezoelectric charge from the integrator 12 and obtains the driving voltage from the controller 10, so as to calculate the self-sensing displacement signal of the piezoelectric valve 1, and the self-sensing displacement signal is used as a feedback to be input into the controller 10, thereby forming closed-loop displacement control.
The force self-sensing calculator 14 also obtains the piezoelectric charge from the integrator 12 and the driving voltage from the controller 10, so as to calculate the self-sensing output force signal of the piezoelectric valve 1 for real-time monitoring.
The second step is that: and calculating the displacement and output force of the piezoelectric valve according to a self-sensing measuring method. The self-sensing measurement method can estimate the displacement and the output force of the valve core, namely the moving end 2, by utilizing the driving voltage and the surface charge of the piezoelectric stack actuator 9. The self-perception measurement method comprises the following steps:
(2.1) according to the driving voltage U and the external force F of the loadsAnd obtaining the axial displacement y of the multilayer piezoelectric stack.
The piezoelectric stack 9 does length expansion movement under the voltage driving, and the strain S, the stress T, the electric displacement D and the electric field strength E of the piezoelectric stack conform to a first piezoelectric equation, as shown in the formula (1) and the formula (2):
in the formula, D3And T3Respectively, the electric displacement and stress, S, of the piezoelectric material3And E3Respectively the strain and the electric field strength,
and d33Respectively, the dielectric coefficient, the elastic compliance coefficient and the piezoelectric constant of the piezoelectric material.
Equations (1) and (2) are applied to the piezoelectric stack 9, and abstract mechanical and electrical quantities are converted into an intuitive displacement y, force F, drive voltage U, and charge Q.
The piezo-stack 9 consists of a multilayer piezo-ceramic (PZT) with a displacement y for a single PZT layernComprises the following steps:
in the formula, AsIs the cross-sectional area of the piezoelectric stack, tnThickness of single-layer PZT, U applied voltage, FsIs the total external force.
For a piezoelectric stack 9 consisting of n layers of PZT, the total axial displacement y is:
in the formula, the total external force FsComprising two parts, the transmission amplifying chamber initial pressure F0And effective output force F generated to the hydraulic chamber during stack movementeff。
(2.2) establishing a spool displacement yeffOutput force FeffA model of the relationship between the piezoelectric charge Q and the drive voltage U of the piezo stack actuator 9.
The initial position of the valve core is taken as a starting point, and the displacement variation of the valve core is defined as effective displacement yeffAs shown in equation (5):
the piezoelectric charge generated by the n layers of PZT is Q, as shown in equation (6):
Q＝-nd33Feff+CpU (6)
in the formula, CpIs a piezoelectric capacitor, and has a specific expression of
Further, the effective output force F can be obtained from the formula (6)effThe relationship between the piezoelectric charge Q and the piezoelectric actuator driving voltage U is modeled as shown in equation (7):
the formula (7) is driven into the formula (5), and finally the valve core displacement y is obtainedeffA model of the relationship between the piezoelectric charge Q and the piezoelectric actuator drive voltage U, as shown in equation (8):
as can be seen from equations (7) and (8), the displacement y of the piezoelectric valve 1 can be obtained from the drive voltage U and the piezoelectric charge QeffAnd the output force Feff。
The third step: and obtaining the self-sensing displacement and the output force of the piezoelectric valve 1 according to the step two, and applying the self-sensing displacement and the output force to the self- sensing calculators 13 and 14 in the step one to realize displacement control and output force monitoring of the piezoelectric valve.
The invention has the advantages that: the piezoelectric self-sensing algorithm is adopted, so that the piezoelectric actuator is used as a driver and a sensor, the displacement and the output force of the valve core can be detected simultaneously without an additional sensor, and the cost and the installation space are saved; a hysteresis compensation model is added in the controller, so that the control precision and the control speed are improved; the piezoelectric charge is obtained by adopting a software current integration method, and parameters can be flexibly adjusted to compensate piezoelectric leakage resistance.
Drawings
Fig. 1 is a block diagram of a displacement-force self-sensing piezoelectric valve. Figure (a) is an isometric view of a piezoelectric valve; fig. b is a sectional view of the piezoelectric valve.
FIG. 2 is a schematic diagram of a displacement-force self-sensing piezoelectric valve control system.
Fig. 3 is a schematic diagram of a displacement control experimental device of the displacement-force self-sensing piezoelectric valve.
FIG. 4 is a diagram illustrating the self-sensing result of displacement under the closed-loop displacement control of the piezoelectric valve in one embodiment. The abscissa is time in seconds(s); the ordinate is the displacement in micrometers (μm). The amplitude of the displacement was set at 7 μm and the frequency at 1 Hz. Graph (a) is a comparison between the set displacement, the measured displacement of the sensor and the self-sensing displacement when the set displacement is a sinusoidal signal; in the graph (b), when the set displacement is a triangular signal, the set displacement, the measured displacement of the sensor, and the self-sensing displacement are compared with each other.
FIG. 5 is a diagram illustrating the force self-sensing result under the closed-loop displacement control of the piezoelectric valve in one embodiment. The abscissa is time in seconds; the ordinate is force in newtons (N). The maximum amplitude of the output force is 85N, and the frequency is 1 Hz. Graph (a) is a comparison between the measured force of the sensor and the self-sensing force when the displacement is set to be a sinusoidal signal; the graph (b) is a comparison between the measured force and the self-sensing force of the sensor when the displacement is set to the triangular signal.
In the figure: 1, a piezoelectric valve; 2, a mobile terminal; 3 pre-tightening a disc spring gasket; 4, covering the cover; 5, internal and external threads; 6 pre-tightening the screw; 7, a base; 8, a regular octagonal cushion block; 9 piezoelectric stack actuator; 10 a controller; 11 sampling resistance; 12 an integrator; 13 displacement self-sensing calculator; a 14-force self-sensing calculator; 15 a control algorithm; 16 hysteresis compensation models; 17 an eddy current displacement sensor; 18 a top plate; 19 an optical extension bar; 20 an optical bench; 21 a force sensor; a disc spring washer is loaded at 22.
Detailed Description
The following detailed description of the embodiments of the invention is provided in connection with the accompanying drawings.
According to the first aspect, the piezoelectric valve capable of sensing force and displacement automatically is provided, and the piezoelectric valve 1 comprises a moving end 2, a disc spring gasket 3 for pre-tightening, an upper cover 4, internal and external threads 5, a pre-tightening screw 6, a base 7, a regular octagonal cushion block 8 and a piezoelectric stack actuator 9.
The piezoelectric stack actuator 9 is a driving element, and needs to apply a pre-tightening force of about 750N during use because the tensile strength of piezoelectric ceramics is low.
The upper cover 4 is connected with the base 7 through the internal and external threads 5, the thread pitch is 1mm, and the upper cover 4 is of a cylindrical structure.
The piezoelectric stack actuator 9 is a driving element and is arranged inside the upper cover 4, the upper end of the piezoelectric stack actuator 9 is provided with a moving end 2, the moving end 2 outputs displacement and force outwards under the voltage driving, the lower end of the piezoelectric stack actuator 9 is padded with a regular octagonal cushion block 8, and a square groove is formed in the regular octagonal cushion block 8 and used for keeping the piezoelectric stack 9 stable.
The moving end 2 is of a T-shaped structure, the large end of the moving end is in contact with the piezoelectric stack actuator 9, the small end of the moving end extends out of the upper cover 4, and the metal disc spring gasket 3 is arranged between the middle of the moving end 2 and the upper cover 4 and used for providing required pre-tightening force and simultaneously does not excessively block the movement of the moving end 2.
In a second aspect, a displacement control method of a piezoelectric valve that is self-sensing of force and displacement is provided, comprising the following steps.
The first step is as follows: a displacement control system for a piezoelectric valve is assembled. The displacement control system of the piezoelectric valve comprises a controller 10, the piezoelectric valve 1, a sampling resistor 11, a software integrator 12, a displacement self-perception calculator 13 and a force self-perception calculator 14.
The experimental set-up is shown in FIG. 3. The piezoelectric valve 1 is installed on an optical experiment table 20, clamped under a top plate 18, and two optical connecting rods 19 are used as supports.
The piezoelectric valve moving end 2 is provided with a force sensor 21 for calibrating force, an eddy displacement meter 17 for measuring and calibrating displacement, and a disc spring gasket 22 as an elastic load.
The controller 10, the integrator 12, the displacement self-perception calculator 13 and the force self-perception calculator 14 are all completed by matching LabVIEW programs with a computer; all the set displacement control signals, the position signals measured by the displacement meter and the output force signals measured by the force sensor are output or collected by the NI collection card. The controller 10 is used for setting a required displacement signal, and the output voltage signal is amplified by the driving power supply and then applied to two ends of the piezoelectric valve 1.
The controller 10 is specifically a feedforward PID algorithm composed of a control algorithm 15 and a hysteresis compensation algorithm 16. Wherein the control algorithm 15 is a conventional PID algorithm; the hysteresis compensation algorithm 16 adopts a Prandtl-Ishlinskii (PI) model, and before the experiment, least square method off-line identification is carried out on model parameters, so that a corresponding PI inverse model is established as the hysteresis compensation algorithm. The output of the PI hysteresis compensation algorithm is used as feedforward, and meanwhile, the traditional PID is used for correcting the feedforward, so that the control precision can be improved, the response speed is accelerated, and the piezoelectric valve hysteresis is reduced.
The sampling resistor 11 is a precision resistor of 75 Ω, is connected in series with the piezoelectric valve 1, and converts a current signal of the piezoelectric valve 1 into a voltage signal.
The integrator 12 is connected with the sampling resistor 11, the voltage on the resistor 11 is collected by an NI data acquisition card, the voltage is divided by the resistance value to obtain piezoelectric current, and the piezoelectric current is integrated point by point in the integrator 12 to obtain piezoelectric charge. The piezoelectric material has leakage resistance, and the integrated charge can drift due to the effect of leakage current in long-term operation. Different from the traditional hardware integrating circuit, the integrator adopts software integration, and can flexibly adjust integration parameters in the running process and eliminate the influence of leakage current.
The displacement self-sensing calculator 13 obtains the piezoelectric charge from the integrator 12 and obtains the driving voltage from the controller 10, so as to calculate the self-sensing displacement signal of the piezoelectric valve 1, and the self-sensing displacement signal is used as a feedback to be input into the controller 10, thereby forming closed-loop displacement control.
The force self-sensing calculator 14 also obtains the piezoelectric charge from the integrator 12 and the driving voltage from the controller 10, so as to calculate the self-sensing output force signal of the piezoelectric valve 1 for real-time monitoring.
The second step is that: and calculating the displacement and output force of the piezoelectric valve according to a self-sensing measuring method. The self-sensing measurement method can estimate the displacement and the output force of the valve core, namely the moving end 2, by utilizing the driving voltage and the surface charge of the piezoelectric stack actuator 9. The self-perception measurement method comprises the following steps:
(2.1) according to the driving voltage U and the external force F of the loadsAnd obtaining the axial displacement y of the multilayer piezoelectric stack.
The piezoelectric stack 9 does length expansion movement under the voltage driving, and the strain S, the stress T, the electric displacement D and the electric field strength E of the piezoelectric stack conform to a first piezoelectric equation, as shown in the formula (1) and the formula (2):
in the formula, D3And T3Respectively, the electric displacement and stress, S, of the piezoelectric material3And E3Respectively the strain and the electric field strength,
and d33Respectively, the dielectric coefficient, the elastic compliance coefficient and the piezoelectric constant of the piezoelectric material.
Equations (1) and (2) are applied to the piezoelectric stack 9, and abstract mechanical and electrical quantities are converted into an intuitive displacement y, force F, drive voltage U, and charge Q.
The piezo-stack 9 consists of a multilayer piezo-ceramic (PZT) with a displacement y for a single PZT layernComprises the following steps:
in the formula, AsIs the cross-sectional area of the piezoelectric stack, tnThickness of single-layer PZT, U applied voltage, FsIs the total external force.
For a piezoelectric stack 9 consisting of n layers of PZT, the total axial displacement y is:
in the formula, the total external force FsComprising two parts, the transmission amplifying chamber initial pressure F0And effective output force F generated to the hydraulic chamber during stack movementeff。
(2.2) establishing a spool displacement yeffOutput force FeffA model of the relationship between the piezoelectric charge Q and the drive voltage U of the piezo stack actuator 9.
The initial position of the valve core is taken as a starting point, and the displacement variation of the valve core is defined as effective displacement yeffAs shown in equation (5):
the piezoelectric charge generated by the n layers of PZT is Q, as shown in equation (6):
Q＝-nd33Feff+CpU (6)
in the formula, CpIs a piezoelectric capacitor, and has a specific expression of
Further, the effective output force F can be obtained from the formula (6)effThe relationship between the piezoelectric charge Q and the piezoelectric actuator driving voltage U is modeled as shown in equation (7):
the formula (7) is driven into the formula (5), and finally the valve core displacement y is obtainedeffA piezoelectric charge Q and a piezoelectric actuator drive voltage UThe relationship between them is shown in formula (8):
as can be seen from equations (7) and (8), the displacement y of the piezoelectric valve 1 can be obtained from the drive voltage U and the piezoelectric charge QeffAnd the output force Feff。
The third step: and obtaining the self-sensing displacement and the output force of the piezoelectric valve 1 according to the step two, and applying the self-sensing displacement and the output force to the self-sensing calculators 13 and 14 in the step one to realize displacement control and output force monitoring of the piezoelectric valve.
In one embodiment, the displacement is set in the controller 10 to be a sinusoidal signal and a triangular signal with amplitude of 7 μm and frequency of 1Hz, and under the driving voltage, the piezoelectric valve stack 9 is elongated, pushing the moving end 2 and compressing the load disc spring 22, where the load disc spring 22 is used to simulate the hydraulic pressure in the amplification chamber. The self-sensing displacement signal is fed back to the controller 10 and the data measured by the eddy current displacement meter 17 and the force sensor 21 are recorded simultaneously and compared with the displacement and force estimated by self-sensing. Under the drive of voltage, the moving end 2 moves according to the set displacement, and meanwhile, corresponding output force is generated. When the set displacement is a sinusoidal signal, the curve of the measured displacement and the self-perception displacement of the moving end 2 is shown in fig. 4(a), and the curve of the measured displacement and the self-perception displacement is shown in fig. 5 (a); when the set displacement is a triangular signal, the curve of the measured displacement and the self-sensing displacement of the moving end 2 is shown in fig. 4(b), and the curve of the measured displacement and the self-sensing force is shown in fig. 5 (b). As can be seen from fig. 4, under two control signals, the self-sensing displacement curve can stably follow the set displacement curve, the actually measured displacement curve and the self-sensing displacement curve are almost overlapped, and the Root Mean Square Error (RMSE) of the actually measured displacement curve and the self-sensing displacement curve is about 2.03% of the maximum displacement, which proves that the self-sensing displacement is accurate enough and the displacement control method is effective. As can be seen from FIG. 5, the output force is 0-85N within the displacement range of 0-7 μm, and the RMSE between the measured force and the self-perception force is only 1.80% of the maximum output force, thus proving that the self-perception force is accurate. In addition, as can be seen from measuring the hysteresis curve of the piezoelectric actuator, the maximum hysteresis of the piezoelectric actuator is reduced from 37% to 3.75%, and the effect of hysteresis compensation is significant. The piezoelectric valve realizes high-precision and stable operation through self-sensing valve core displacement without an external sensor, and can monitor output force in real time, which shows that the displacement-force self-sensing piezoelectric valve has practical engineering application value.
The above-mentioned embodiments only express the embodiments of the present invention, but not should be understood as the limitation of the scope of the invention patent, it should be noted that, for those skilled in the art, many variations and modifications can be made without departing from the concept of the present invention, and these all fall into the protection scope of the present invention.
Claims (2)
1. The piezoelectric valve capable of sensing force and displacement automatically is characterized in that the piezoelectric valve (1) comprises a moving end (2), a disc spring gasket (3), an upper cover (4), a pre-tightening screw (6), a base (7), a regular octagonal cushion block (8) and a piezoelectric stack actuator (9);
the upper cover (4) is of a cylindrical structure and is connected with the base (7) through threads;
the piezoelectric stack actuator (9) is a driving element and is arranged in the upper cover (4), the upper end of the piezoelectric stack actuator (9) is provided with a moving end (2), the moving end (2) outputs displacement and force outwards under the drive of voltage, the lower end of the piezoelectric stack actuator (9) is padded with a regular octagonal cushion block (8), and a square groove is formed in the regular octagonal cushion block (8) and used for keeping the piezoelectric stack actuator (9) stable;
the moving end (2) is of a T-shaped structure, the outer side of the large end part of the moving end (2) is in contact with the piezoelectric stack actuator (9), the small end part of the moving end passes through a central through hole of the end part of the upper cover (4) and extends out of the end part of the upper cover (4), and a metal disc spring gasket (3) is arranged between the inner side of the large end part of the moving end (2) and the upper cover (4) and used for providing required pretightening force and simultaneously does not excessively block the movement of the moving end (2);
regular octagon cushion (8) below install pretension screw (6), pretension screw (6) are located in base (7), rotatory pretension screw (6) can be with regular octagon cushion (8) jack-up, cooperation dish spring gasket (3) can adjust the pretightning force size, regular octagon cushion (8) can not rotate at the pretension in-process, avoid piezoelectric stack executor (9) to receive the shearing force.
2. A displacement control method of a self-sensing force and displacement piezoelectric valve according to claim 1, comprising the steps of;
the first step is as follows: the displacement control system of the assembled piezoelectric valve comprises a controller (10), the piezoelectric valve (1), a sampling resistor (11), an integrator (12), a displacement self-sensing calculator (13) and a force self-sensing calculator (14);
the controller (10) is used for setting a displacement output voltage signal to drive the piezoelectric valve (1) and accurately control the displacement of the piezoelectric valve; the sampling resistor (11) is connected with the piezoelectric valve (1) in series and converts a current signal of the piezoelectric valve (1) into a voltage signal; the integrator (12) is a software integrator and is connected with the sampling resistor (11), and collects and integrates voltage signals on the sampling resistor (11) to obtain piezoelectric charges; the displacement self-perception calculator (13) is connected with the integrator (12) and the controller (10), and the force self-perception calculator (14) is connected with the integrator (12) and the controller (10);
the second step is that: calculating the displacement and output force of the piezoelectric valve according to a self-sensing measurement method; the self-sensing measurement method can estimate the displacement and the output force of a valve core by using the driving voltage and the surface charge of a piezoelectric stack actuator (9), wherein the valve core is a moving end (2), and comprises the following steps:
(2.1) according to the driving voltage U and the external force F of the loadsSolving the axial displacement y of the multilayer piezoelectric stack;
the piezoelectric stack actuator (9) does length telescopic motion under the drive of voltage, and the strain S, the stress T, the electric displacement D and the electric field intensity E of the piezoelectric stack actuator accord with a first type of piezoelectric equation; applying a first type of piezoelectric equation to a piezoelectric stack actuator (9), and converting abstract mechanical and electrical quantities into visual displacement y, force F, driving voltage U and charge Q;
the piezoelectric stack actuator (9) is composed of multiple layers of piezoelectric ceramics PZT, and the displacement y of the piezoelectric stack actuator is single-layer PZTnComprises the following steps:
in the formula, AsIs the cross-sectional area of the piezoelectric stack, tnThickness of single-layer PZT, U applied voltage, FsIs the total external force;
for a piezo-stack actuator (9) consisting of n layers of PZT, the total axial displacement y is:
in the formula, the total external force FsComprising two parts, the transmission amplifying chamber initial pressure F0And effective output force F generated to the hydraulic chamber during stack movementeff；
(2.2) establishing a spool displacement yeffOutput force FeffA relation model between the piezoelectric charge Q and the driving voltage U of the piezoelectric stack actuator 9;
the initial position of the valve core is taken as a starting point, and the displacement variation of the valve core is defined as effective displacement yeffAs shown in equation (5):
the piezoelectric charge generated by the n layers of PZT is Q, as shown in equation (6):
Q＝-nd33Feff+CpU (6)
in the formula, CpIs a piezoelectric capacitor, and has a specific expression of
Further, the effective output force F can be obtained from the formula (6)effThe relationship between the piezoelectric charge Q and the piezoelectric actuator driving voltage U is modeled as shown in equation (7):
bringing formula (7) into formula (5) to obtain the final valveCore displacement yeffA model of the relationship between the piezoelectric charge Q and the piezoelectric actuator drive voltage U, as shown in equation (8):
as can be seen from equations (7) and (8), the displacement y of the piezoelectric valve 1 can be obtained from the drive voltage U and the piezoelectric charge QeffAnd the output force Feff。
The third step: and (3) obtaining the self-sensing displacement and the output force of the piezoelectric valve (1) according to the second step, applying the self-sensing displacement and the output force to self-sensing calculators (13) and (14) in the first step, and realizing displacement control and output force monitoring of the piezoelectric valve (1), wherein the self-sensing displacement and the output force monitoring are specifically as follows:
the displacement self-perception calculator (13) obtains piezoelectric charges from the integrator (12), obtains driving voltage from the controller (10), finally calculates a self-perception displacement signal according to a formula (7), and inputs the self-perception displacement signal into the controller (10) as feedback to form closed-loop displacement control;
the force self-perception calculator (14) also obtains piezoelectric charges from the integrator (12), obtains driving voltage from the controller (10), and finally calculates a self-perception output force signal according to a formula (8) for real-time monitoring.
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