CN113325778A - Method for controlling elongation of piezoelectric ceramic - Google Patents

Abstract

The invention relates to the technical field of piezoelectric ceramic driving, in particular to a method for controlling the elongation of piezoelectric ceramic, which comprises the following steps: s1, controlling a high-power synchronous half-bridge driving circuit by the MCU as a hardware structure, and establishing a model relation between piezoelectric ceramic stack voltage and a driving waveform; s2, establishing PWM duty ratio D and ceramic driving voltage V output by MCU by using set volt-second product model_outThe relationship of (1); s3, collecting voltage and current in real time, modulating and outputting a driving signal according to the model, and correcting an output waveform by using a fuzzy PID algorithm; modifying the output waveform for the fuzzy PID algorithm of S3, including: s31, the controller determines the target voltage value V of the drive voltage waveform according to the dispensing parameters_t(ii) a S32, determining fuzzy subsets and domains thereof of the deviation E and the deviation change rate EC, establishing a fuzzy rule base, and designing a fuzzy controller; s33, obtaining a proportional coefficient Kp, an integral coefficient Ki and a differential coefficient Kd through cleaning; and S34, calculating a correction value according to the incremental PID. The voltage driving waveform of the piezoelectric ceramic is accurately controlled and corrected by a fuzzy PID algorithm, so that the piezoelectric ceramic dispensing valve is ensuredThe accurate glue output amount is obtained during the field application.

Description

Method for controlling elongation of piezoelectric ceramic

Technical Field

The invention relates to the technical field of piezoelectric ceramic driving, in particular to a method for controlling the elongation of piezoelectric ceramic.

Background

The piezoelectric ceramic stack has large thrust and rapid micromotion, and is widely applied to the fields of electronic equipment, finish machining and the like; the piezoelectric injection dispensing valve is a non-contact injection dispensing valve, and the piezoelectric ceramic stack is a core component for realizing high-efficiency, high-precision and non-contact dispensing and is increasingly widely applied in the field of electronic packaging; the main structure of the piezoelectric ceramic injection valve is composed of a valve body, a piezoelectric actuator, an amplifying mechanism, a flow channel assembly and the like, and the main principle is as follows: at the beginning of the piezoelectric valve jet valve, the colloid fills the valve body channel, the upper part of the firing pin is pressed to abut against the bottom of the nozzle and seal the outlet of the nozzle, the piezoelectric brake is applied with high electric frequency, the piezoelectric actuator transversely extends, the firing pin is lifted upwards, the nozzle is opened at the moment, the glue solution is driven by external air pressure to fill the valve body gap formed by the upward movement of the firing pin, and a certain amount of glue solution flows out of the nozzle, the piezoelectric brake is applied with low electric frequency, the piezoelectric brake and the rhombic amplification mechanism contract, and simultaneously, under the action of the restoring force of the spring, the firing pin downwards impacts the inner cavity of the nozzle at high speed and seals the nozzle, and the cavity extruded in the nozzle is ejected out under the action of inertia force to form glue drops; under the alternate action of high and low electric frequencies of a driving signal, the striker continuously vibrates up and down in a reciprocating manner, so that high-speed injection dispensing is realized, the amplitude and the frequency of the striker can be adjusted by changing the amplitude, the frequency, the duty ratio and the like of the driving voltage, and the control on the injection performance of the glue drops is further realized; the existing piezoelectric driving technology is a technical core of a piezoelectric jet dispensing valve, and the driving control technology directly influences the excellent rate of dispensing products.

Disclosure of Invention

The problems existing in the prior art are solved: the invention accurately controls the voltage driving waveform of the piezoelectric ceramic, and corrects the voltage driving waveform through a fuzzy PID algorithm, thereby ensuring that the precise glue output amount is obtained when the piezoelectric ceramic dispensing valve is applied in the field of piezoelectric ceramic dispensing valves.

The technical scheme adopted by the invention for solving the technical problems is as follows: a method for controlling the elongation of piezoelectric ceramics comprises the following steps:

s1, controlling a high-power synchronous half-bridge driving circuit by the MCU through a hardware structure, and establishing a model relation between the piezoelectric ceramic driving voltage and the PWM duty ratio output by the MCU;

under the excitation action of voltage, the piezoelectric ceramic can extend due to the inverse piezoelectric effect; when the piezoelectric ceramic is shortened by external pressure, due to the positive piezoelectric effect, charges can be generated at two ends of the piezoelectric ceramic to counteract the deformation of the piezoelectric ceramic; therefore, the PWM duty ratio output by the MCU needs to be adjusted along with the working state of the piezoelectric ceramics so as to ensure that the driving waveform is intact, thereby realizing accurate control;

s2, establishing PWM duty ratio D and ceramic driving voltage V output by MCU by using set volt-second product model_outThe relationship of (1);

and measuring a corresponding table of the driving voltage of the piezoelectric ceramic and the PWM duty ratio output by the MCU, and obtaining a fitting curve relation according to the volt-second product relation so as to obtain an accurate model, wherein an inductance volt-second product relation equation is as follows:

V_on·t_on＝V_off·t_off (1)

the voltage drop of the inductor when the half-bridge lower tube is switched on is equal to the driving voltage:

V_off＝V_out (2)

half-bridge top tube open time inductance voltage and MCU mains voltage, drive voltage relation:

V_power＝V_on+V_out (3)

PWM duty ratio:

from the above relationship, it can be deduced that:

V_out＝V_power·D (5)

the piezoelectric ceramic has positive piezoelectric effect to increase its voltage V_outThe PWM driving output dead zone is related to the external pressure, the PWM driving output dead zone, the component parameters, the leakage inductance and other influence results are complex, and therefore the PWM duty ratio D and the driving voltage value V are measured according to experiments on the basis of the relationship_outThe linear adjustment is carried out, and the adjustment method comprises the following steps:

V_out＝k·V_power·D+b (6)

calculating an adjustment coefficient by using the measured value to obtain a volt-second product model, wherein k is a slope and b is a control quantity;

the values of k and b are determined by several sets of large PWM duty cycles D and corresponding drive voltages V_outOf the arithmetic mean, a number of groups of small PWM duty cycles D and corresponding drive voltages V_outIs calculated as the arithmetic mean fit of.

S3, collecting the driving voltage value of the piezoelectric ceramics in real time, and correcting the output PWM duty ratio D by using a fuzzy PID algorithm in combination with a formula (6) to obtain an accurate driving waveform of the piezoelectric ceramics;

further, the flow of the output PWM duty ratio D corrected by the fuzzy PID algorithm is as follows:

s31, determining the target voltage value V of the drive voltage waveform by the MCU controller according to the set dispensing parameters_t；

The dispensing parameters comprise four stage time of piezoelectric ceramic driving voltage value and driving voltage waveform, including: t is t₁Rise time of voltage, t₂High voltage holding time, t₃Voltage drop time, t₄A low voltage hold time;

s32, determining fuzzy subsets and domains thereof of the deviation E and the deviation change rate EC, establishing a fuzzy rule base, and designing a fuzzy PID controller;

s33, obtaining a proportionality coefficient K by cleaning_pIntegral coefficient K_iAnd a differential coefficient K_d；

S34, calculating a correction value according to the incremental PID, weighting with the PWM duty ratio D corresponding to the model in the step S2 to obtain the adjusted PWM duty ratio D, using the MCU as a controller, and adopting a discrete incremental PID algorithm, wherein the formula is as follows:

ΔU＝Kp·(E(l)-E(l-1))+Ki·E(l)+Kd·(E(l)-2·E(l-1)+E(l-2)) (7)

where l is the sample number, E (l) is the offset signal of the l-th sample, E (l-1) is the offset signal of the l-1-th sample, Δ E ═ E (l) -E (l-1), i.e., Δ E ═ V_t-V_out；

The formula (6) gives Δ U ═ kV_powerΔ D + b, whereinAnd delta D is a PWM duty ratio D increment value calculated by a PID algorithm.

The invention has the beneficial effects that:

1. detecting the driving voltage of the piezoelectric ceramics in real time, and correcting the output quantity through a fuzzy PID algorithm to enable the MCU controller to set a driving voltage value V_tAnd the actual output driving voltage value V_outThe deviation value is smaller, so that the stable dispensing effect and the accurate dispensing amount of the piezoelectric injection dispensing valve are ensured.

Drawings

FIG. 1 is a logic diagram of a control method of the present invention;

FIG. 2 is a hardware block diagram of the present invention;

FIG. 3 is a waveform diagram of the driving output t of the present invention₁Rise time of voltage, t₂High voltage holding time, t₃Voltage drop time, t₄Low voltage hold time.

Detailed Description

Embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

Referring to fig. 1, the method for controlling the elongation of a piezoelectric ceramic according to the present invention includes the following steps:

s1, outputting a PWM signal with a fixed duty ratio D to the half-bridge synchronous buck circuit through the MCU, and outputting a fixed voltage to the piezoelectric ceramic (as shown in FIG. 2); establishing a model relation between the piezoelectric ceramic driving voltage and the PWM duty ratio output by the MCU; measuring driving voltage values V corresponding to multiple groups of PWM duty ratios D_outIn this example, 16 sets of data are taken, and the duty ratio range is [ 20%, 95%]Step size 5%.

D(％)	20	25	30	35	40	45	50	55
									Vout(v)	31	38.4	46.3	53.9	61.5	69	76.7	84.3
D(％)	60	65	70	75	80	85	90	95
									Vout(v)	92	99.5	107.2	114.8	122.5	130.1	137.7	145.3

S2, establishing PWM duty ratio D and ceramic driving voltage V output by MCU by using set volt-second product model_outThe relationship of (1);

carrying out linear adjustment on the measured value, taking 5 groups of numbers with small duty ratio as arithmetic mean, and taking 5 groups of numbers with large duty ratio as arithmetic mean; two sets of averaged data solve the coefficients k and b of equation (6), where the MCU supply voltage V_powerDC150V, and thereby calculates the volt-second product driving model V_out＝1.5253·D+0.4364。

S3, collecting a piezoelectric ceramic driving voltage value (namely, a voltage value in a voltage detection circuit) in real time, modulating and outputting a PWM duty ratio D according to a formula (6), and correcting an output driving waveform by using a fuzzy PID algorithm;

the input variables of the fuzzy PID algorithm are deviation E and deviation change rate EC; the fuzzy subsets are { NB, NM, NS, ZO, PS, PM, PB }, wherein the fuzzy subsets are sequentially expressed as negative big, negative middle, negative small, zero, positive small, middle and positive big; the membership degree is defined as a certain number in an open interval (0, 1); the argument field corresponding to the input variables E and EC is defined as: -3, -2, -1, 0, 1, 2, 3 }; the analog voltage measurement range is defined as V_min,V_max]The range of the deviation E is [ (V)_min-V_max),(V_max-V_min)]The range of the deviation change rate EC is [2 (V) ]_min-V_max),2(V_max-V_min)]。

Deviation E quantization function:

quantitative function of the rate of change of deviation EC:

the effect of Kp, Ki, Kd is as follows:

(1) coefficient of proportionality K_pThe function of the system is to accelerate the response speed of the system and improve the adjustment precision of the system; k_pThe larger the system is, the faster the response speed of the system is, and the higher the adjustment precision of the system is, but the overshoot is easy and even unstable; k_pIf the value is too small, the adjustment precision is reduced, and the response speed is reduced.

(2) Integral coefficient K_iThe function of (1) is to eliminate the steady-state error of the system; k_iThe larger the system, the faster the static error of the system is eliminated, but the integral saturation phenomenon is generated in the early stage of the response, thereby causing the overshoot, K_iAnd if the static error is too small, the static error is difficult to eliminate, and the adjustment precision is influenced.

(3) Differential coefficient K_dThe function of (1) is to improve the dynamic characteristic of the system, and the function of the system is mainly to inhibit the change of the deviation to any direction in the response process and to adjust the deviation change in advance. But K_dIf the size is too large, the response process is braked in advance, and the anti-interference performance is reduced.

K_p、K_i、K_dIs based on the last output, so the adjustment calculation relationship is as follows:

Δ Kp, Δ Ki, Δ Kd are three outputs derived by the fuzzy controller according to fuzzy inference, for correcting three control parameters of PID; v_p1、V_i1、V_d1Is an initial value which is an empirical value manually called by the traditional PID control parameter; a fuzzy inference rule table is defined according to the above analysis:

the fuzzy PID control algorithm adopts a weighted average method widely applied in industrial control, and the output form is as follows:

wherein coefficient t_iThe choice of (1) is determined by the actual circumstances and is here given by 1; p_i、P_oTo resolve the input and output values of the fuzzy PID control algorithm.

As shown in figure 3, when the control method of the invention is used for controlling the piezoelectric ceramic injection valve, the MCU controller controls two direct current power supplies V_max＝144V，V_min24V, the maximum voltage at two ends of the piezoelectric ceramic is V_max-V_minAnd (3) controlling and outputting a trapezoidal wave of 500Hz, correcting the volt-second product model by using a fuzzy PID algorithm, obtaining a straight driving waveform, and measuring that the ripple wave is less than 0.3V.

The invention has the advantages that the driving voltage of the piezoelectric ceramics is detected in real time, the output quantity is corrected through a fuzzy PID algorithm, and the driving waveform with the set parameters as the standard is realized, so that the stable dispensing effect and the accurate dispensing quantity of the piezoelectric injection dispensing valve are ensured.

In light of the foregoing description of the preferred embodiment of the present invention, many modifications and variations will be apparent to those skilled in the art without departing from the spirit and scope of the invention. The technical scope of the present invention is not limited to the content of the specification, and must be determined according to the scope of the claims.

Claims (2)

1. A method for controlling the elongation of piezoelectric ceramics is characterized by comprising the following steps:

s1, controlling a high-power synchronous half-bridge driving circuit by the MCU through a hardware structure, and establishing a model relation between the piezoelectric ceramic driving voltage and the PWM duty ratio output by the MCU;

s2, establishing PWM duty ratio D and ceramic driving voltage V output by MCU by using set volt-second product model_outObtaining a relation model of the accurate driving voltage and the duty ratio, wherein the formula is V_out＝k·V_powerD + b, wherein k is a slope and b is a controlled variable;

the values of k and b are determined by several sets of large PWM duty cycles D and corresponding drive voltages V_outOf the arithmetic mean, a number of groups of small PWM duty cycles D and corresponding drive voltages V_outThe arithmetic mean fitting of (1) is calculated;

s3, collecting the driving voltage value of the piezoelectric ceramic in real time and combining the formula V_out＝k·V_powerD + b corrects the output PWM duty ratio D by using a fuzzy PID algorithm to obtain an accurate piezoelectric ceramic driving waveform.

2. The method for controlling the elongation of the piezoelectric ceramics according to claim 1, wherein the step of correcting the output PWM duty ratio D by the fuzzy PID algorithm of S3 comprises the following steps:

s31, determining the target voltage value V of the drive voltage waveform by the MCU controller according to the set dispensing parameters_t；

S32, determining fuzzy subsets and domains thereof of the deviation E and the deviation change rate EC, establishing a fuzzy rule base, and designing a fuzzy PID controller;

s33, obtaining a proportionality coefficient K by cleaning_pIntegral coefficient K_iAnd a differential coefficient K_d；

And S34, calculating a PWM duty ratio D correction value according to the incremental PID, and weighting the PWM duty ratio D correction value with the PWM duty ratio D corresponding to the model in the step S2 to obtain the adjusted PWM duty ratio D.

Images