CN116872375A - High-precision frequency tracking device and method for rotary ultrasonic auxiliary processing - Google Patents
High-precision frequency tracking device and method for rotary ultrasonic auxiliary processing Download PDFInfo
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Abstract
The invention relates to a high-precision frequency tracking device and a high-precision frequency tracking method for rotary ultrasonic auxiliary processing, wherein the tracking device comprises a microcontroller, an upper computer, a signal generating module, a power amplifying module, a compensating circuit, a loose coupling transformer, a dynamometer, a sampling module and a signal conditioning module; the microprocessor is respectively connected with the upper computer, the signal generator module, the first band-pass filter circuit and the second band-pass filter circuit, the signal generator module is connected with the power amplification module, the power amplification module is sequentially connected with the voltage sensor and the primary side of the loose coupling transformer, and the dynamometer measures the cutting force in the processing process and the counterforce of the cutting force is the load force received by the transducer. The invention fully considers the problem that the frequency tracking precision is reduced due to static matching failure caused by load force change in the rotary ultrasonic processing process, and improves the frequency tracking precision. The invention has the advantages of low cost, high frequency tracking speed, high precision and strong adaptability.
Description
Technical Field
The invention relates to the technical field of ultrasonic-assisted machining and frequency tracking, in particular to a high-precision frequency tracking device and method for rotary ultrasonic-assisted machining.
Background
Rotary ultrasonic assisted machining is a high-efficiency, high-precision machining technique that is widely used in the machining of hard and brittle materials. The existing ultrasonic processing system mainly comprises an ultrasonic power supply, a non-contact electric energy transmission unit, a transducer and a clamping tool. The ultrasonic power supply is used for converting the commercial power with the frequency of 50Hz into alternating current with adjustable frequency and matched with the serial resonance frequency of the transducer. The non-contact power transmission unit mainly comprises a loose coupling transformer, and the function of the non-contact power transmission unit is to transmit power to a transducer in high-speed rotation in a non-contact mode, and the transducer is a device for converting high-frequency alternating current into high-frequency vibration. In the actual ultrasonic auxiliary processing process, the resonance frequency of the transducer is often greatly changed due to reasons such as abrupt change of load force, temperature rise of the transducer, abrasion of a cutter head and the like, so that the output amplitude of the transducer is reduced to influence the processing quality, and the service life of the transducer is even reduced when the long-time detuning is serious. In addition, when the resonant frequency of the transducer changes, the matching circuit of the non-contact power transmission unit fails, at this time, the phase difference between the voltage and the current at the resonant frequency point of the transducer is often not 0, and at this time, the frequency tracking is performed with the 0 phase difference as a target, which has the problem of low tracking precision, so a high-precision frequency tracking method and device are required.
The current frequency tracking technology is based on a hardware phase-locked loop method, firstly, the phase difference between a voltage signal and a current signal in a transducer loop is detected, then, the output frequency is regulated to a frequency point with zero phase difference by a dichotomy method, a variable step algorithm and the like, and the phase difference between the voltage signal and the current signal is zero when the transducer works at a series resonance frequency and a parallel resonance frequency and the output power of an ultrasonic processing system can be maximum only when the transducer works at the series resonance frequency, so that the traditional phase-locked loop technology often has the situation of frequency error locking. In addition, chinese patent No. CN110702971B discloses an ultrasonic driving power supply and a real-time frequency tracking method for automatically tracking the series resonant frequency of a transducer, which are implemented by collecting peak values of current flowing through a filter capacitor and a sampling resistor and a phase difference between them, and then calculating a relational expression to be satisfied by the current when a dynamic branch of the transducer is in series resonance, and taking whether the relational expression is zero as a basis for adjusting the frequency. Although the method avoids the situation that the ultrasonic power supply is frequency-locked to the parallel resonant frequency of the transducer by mistake, the calculation accuracy of the relation is seriously dependent on the accuracy of the capacitance value of the filter capacitor and the accuracy of the static capacitance of the transducer.
Disclosure of Invention
The invention aims to solve the technical problem of providing a rotary ultrasonic auxiliary processing frequency tracking device and a method capable of tracking the series resonant frequency of a transducer in high precision and in real time.
The technical scheme adopted for solving the technical problems is as follows: the rotary ultrasonic auxiliary processing high-precision frequency tracking device comprises a microcontroller, an upper computer, a signal generation module, a power amplification module, a compensation circuit, a loose coupling transformer, a dynamometer, a sampling module and a signal conditioning module; the compensation circuit consists of a first compensation capacitor and a second compensation capacitor;
the microprocessor is respectively connected with the upper computer, the signal generator module, the first band-pass filter circuit and the second band-pass filter circuit, the signal generator module is connected with the power amplification module, the power amplification module is respectively connected with the voltage sensor and the primary side of the loose coupling transformer, the first compensation capacitor is connected with the primary side of the loose coupling transformer in parallel, the secondary side of the loose coupling transformer is connected with the second compensation capacitor, the second compensation capacitor is connected with the transducer in parallel, the dynamometer measures the cutting force in the machining process, the counter force of the cutting force is the load force received by the transducer, the current sensor is sequentially connected with the second signal amplification circuit and the second band-pass filter circuit, and the voltage sensor is sequentially connected with the first signal amplification circuit and the first band-pass filter circuit;
the microcontroller control signal generation module outputs a PWM signal with adjustable frequency; the microcontroller utilizesThe internal ADC function detects voltage and current signals amplified and filtered by the signal conditioning module; the microcontroller is communicated with the upper computer and receives the phase-locked target phase difference theta sent by the upper computer Target object The method comprises the steps of carrying out a first treatment on the surface of the A program control algorithm is arranged in the microcontroller, a voltage expression at two ends of the primary side of the loose coupling transformer and a current expression flowing through the primary side of the loose coupling transformer are obtained through the program algorithm, and then a phase difference between the voltage and the current is obtained through the voltage and the current expressions; finally, the frequency of the control signal is regulated through a PI algorithm to enable the phase difference of the voltage and the current to be equal to the target phase difference sent by the upper computer, and the frequency of the control signal corresponding to the target phase difference is the series resonance frequency of the transducer.
According to the above scheme, the upper computer receives the cutting force data measured by the force measuring instrument, and then substitutes the cutting force data into a formula of change of the resonant frequency of the loose coupling transformer and the transducer loop along with the load force, so as to obtain the phase value of the loose coupling transformer and the transducer loop under the cutting force, namely the phase-locking target phase difference theta Target object And sent to the microcontroller.
According to the scheme, the signal generation module comprises the DDS generator and the grid driving chip, the microcontroller controls the DDS generator to generate a single-path PWM signal, and the single-path PWM signal is processed by the grid driving chip to form two paths of inverted PWM signals with dead time as control signals of the power amplification module.
According to the scheme, the power amplification module comprises a full-bridge inverter circuit, and alternating current output by the full-bridge inverter circuit is transmitted in a non-contact mode through the loose coupling transformer and then drives the energy converter to work.
According to the scheme, the compensating circuit is used for carrying out bilateral compensation on the loose coupling transformer, and the resonance frequency of the loose coupling transformer and the transducer loop after bilateral compensation is equal to the series resonance frequency of the transducer in the no-load state.
According to the scheme, the force measuring instrument collects the cutting force in the current processing state and receives cutting force data from the upper computer.
According to the scheme, the sampling module comprises a voltage and current sensor, and the voltage and current sensor is used for collecting the voltage and current values of the primary side of the loosely coupled transformer.
According to the scheme, the signal conditioning module comprises a signal amplifying circuit and a band-pass filter circuit, wherein the signal amplifying circuit and the band-pass filter circuit are used for amplifying sampled voltage and current signals, filtering out higher harmonics and transmitting the higher harmonics to the microcontroller for detection.
The invention also provides a method for tracking the high-precision frequency of the rotary ultrasonic auxiliary processing, which adopts the device for tracking the high-precision frequency of the rotary ultrasonic auxiliary processing, and comprises the following steps:
s1, determining the series resonance frequency of the transducer in an empty load state, calculating compensation circuit parameters, and carrying out a loading test to determine the variation value of the series resonance frequency of the transducer along with the loading force under different force loading conditions;
s2, setting excitation voltage frequency as the series resonance frequency of the transducer under different force loading conditions, calculating to obtain a phase value of the loose coupling transformer and the transducer loop, which changes along with the load force, after bilateral compensation by an equivalent circuit method, and then fitting the phase value into a formula of the loose coupling transformer and the transducer loop, which changes along with the load force;
s3, setting an initial excitation frequency in the microcontroller, generating excitation voltage through a control signal generating module and a power amplifying module, acquiring voltage and current values of the primary side of the loose coupling transformer through a voltage and current sensor, transmitting the voltage and current values to the microcontroller for detection, and finally obtaining a phase difference of the voltage and the current through a phase difference solving algorithm;
s4, starting the machine tool to start machining, collecting cutting force in the machining process through a dynamometer, processing cutting force data in an upper computer, substituting the cutting force data into a change formula of the phase of a loose coupling transformer and a transducer loop along with load force, and obtaining a phase-locked target phase difference theta Target object Then θ is taken Target object The target value is sent to a microcontroller as a target value of a PI regulation algorithm;
s5, setting a PI regulating algorithm in the microcontroller to theta Target object For the target value, the exciting frequency is regulated to make the phase difference of voltage and current equal to theta Target object At this time, the excitation frequency is the serial resonance frequency of the transducer, and frequency tracking is completed.
According to the above scheme, in the step S3, the method for obtaining the phase difference between the voltage and the current through the phase difference solving algorithm includes the following steps:
sa, record the frequency f of the electric signal driving the transducer to work in the control program of the microcontroller s Let the mathematical expression of the voltage and current acquired at this time be
V(t)＝A 1 cos(ωt+θ 1 )+C 1
I(t)＝A 2 cos(ωt+θ 2 )+C 2
Wherein A is 1 、A 2 The amplitude of the voltage and current signals respectively, omega is the circular frequency of the signals, theta 1 、θ 2 The initial phases of the voltage and current signals are respectively C 1 、C 2 The dc bias of the voltage and current signals, respectively. Sb, taking calculation of each unknown parameter of the expression of the sampled voltage signal as an example:
A 0 、B 0 coefficients in the expansion respectively, wherein
From formulae (2), (3)
A 0 ＝A 1 cos(θ 1 ) (11)
B 0 ＝-A 1 sin(θ 1 ) (12)
Sc, in microcontrollersSetting the sampling time t of the ADC n Let the sample value be y (N), where n=1, 2, 3..n, N is the number of sample points, then there is
y(n)＝A 0 cos(ωt n )+B 0 sin(ωt n )+C 1 (13)
The frequency of the sampled voltage signal is known to be f s ω=2pi f s A is obtained by least square method 0 、B 0 、C 1 The value of (2) is shown in the formula
Wherein the method comprises the steps of
Sd, will A 0 、B 0 Substituting the values into (4) and (5) to obtain the initial phase theta of the sampling voltage signal 1 Sampling the primary phase theta of the current signal 2 The calculation method of (1) samples the voltage signal;
se, phase difference Δθ=θ of sampling current and voltage signals 2 -θ 1 If delta theta>θ Target object At this time, the sampling current phase advances the sampling voltage, and the transducer loop is capacitive; if delta theta is less than theta Target object At this time, the sampling voltage phase advances the sampling current, and the transducer loop presents an inductance; if Δθ=θ Target object At this time, the transducer loop is purely resistive, is at the resonance point, and when the transducer is in an unloaded state, θ Target object ＝0。
The rotary ultrasonic auxiliary processing high-precision frequency tracking device and method have the following beneficial effects:
1. according to the invention, the phase difference between the voltage and the current is calculated by using a software algorithm instead of the traditional hardware phase detection circuit, so that the hardware circuit part of the frequency tracking device is simplified, and the cost is saved;
2. the frequency tracking speed is high, the phase difference value of the voltage and the current can be obtained by calculating by sampling three groups of voltage and current values respectively at least, and the phase difference value can be obtained by comparing the voltage and the current waveforms of one period according to the traditional zero-crossing comparison rule;
3. the method fully considers the problem that the frequency tracking precision is reduced due to static matching failure caused by load force change in the rotary ultrasonic processing process, takes the phase change value of the primary side of the loose coupling transformer as a phase locking target value, and improves the frequency tracking precision;
4. the invention has strong adaptability, and can accurately track the serial resonance frequency of the energy converter after drifting according to the value of the current load force when the ultrasonic auxiliary processing of the hard brittle materials with different mechanical properties is performed;
5. the invention has the advantages of low cost, high frequency tracking speed, high precision and strong adaptability.
Drawings
The invention will be further described with reference to the accompanying drawings and examples, in which:
FIG. 1 is a schematic diagram of a rotary ultrasonic-assisted machining frequency tracking device of the present invention;
FIG. 2 is a diagram of a loosely coupled transformer, transducer equivalent circuit of the present invention;
FIG. 3 is a graph of amplitude-phase characteristics of a double-sided compensated loosely-coupled transformer and transducer loop of the present invention;
FIG. 4 is a graph showing the variation of the series resonant frequency of the transducer according to the present invention with load force;
FIG. 5 is a flowchart of an algorithm in the frequency tracking process of the present invention;
in the figure: 1. the micro controller comprises a micro controller, 2, an upper computer, 3, a signal generating module, 4, a power amplifying module, 5, a current sensor, 6, a first compensation capacitor, 7, a loose coupling transformer, 8, a second compensation capacitor, 9, a transducer, 10, a dynamometer, 11, a voltage sensor, 12, a first signal amplifying circuit, 13, a first band pass filter circuit, 14, a second signal amplifying circuit, 15, a second band pass filter circuit, 16, a loose coupling transformer equivalent circuit, 17, a transducer equivalent circuit and U i Primary side voltage of loose coupling transformer，I i Primary side current of loosely coupled transformer, C p1 A first compensation capacitor L p Primary side leakage inductance, R p Equivalent series resistance at primary side, L m Magnetization inductance, R m Loss of magnetic core, R s Equivalent series resistance of secondary side, L s Secondary side leakage inductance, C p2 A second compensation capacitor C 0 Static capacitance of transducer, R 1 Dynamic resistance of transducer, C 1 Dynamic capacitance of transducer, L 1 Transducer dynamic inductance.
Detailed Description
For a clearer understanding of technical features, objects and effects of the present invention, a detailed description of embodiments of the present invention will be made with reference to the accompanying drawings.
As shown in fig. 1, the rotary ultrasonic auxiliary processing high-precision frequency tracking device comprises a microcontroller 1, an upper computer 2, a signal generating module 3, a power amplifying module 4, a compensating circuit, a loose coupling transformer 7, a dynamometer 10, a sampling module and a signal conditioning module. The microcontroller 1 consists of a micro-processing chip and a peripheral circuit thereof; the microcontroller 1 controls the signal generation module to output a PWM signal with adjustable frequency; the microcontroller 1 detects voltage and current signals amplified and filtered by the signal conditioning module by utilizing an internal ADC function; the microcontroller 1 communicates with the upper computer 2 to receive the phase-locked target phase difference theta sent by the upper computer 2 Target object The method comprises the steps of carrying out a first treatment on the surface of the The microcontroller 1 is internally provided with a program control algorithm, and a voltage expression at two ends of the primary side of the loose coupling transformer 7 and a current expression flowing through the primary side of the loose coupling transformer 7 are obtained through the algorithm. Then the phase difference of the voltage and the current can be obtained through the expression of the voltage and the current. Finally, the frequency of the control signal is regulated through a PI algorithm to enable the voltage phase difference and the current phase difference to be equal to the target phase difference theta sent by the upper computer Target object ，θ Target object The corresponding control signal frequency is the series resonant frequency of the transducer.
The upper computer 2 receives cutting force data measured by the force measuring instrument 10, and then substitutes the current cutting force data into the change of the resonance frequency of the loose coupling transformer and the transducer loop along with the load forceThe formula is used for further obtaining the phase value of the loose coupling transformer and the transducer loop under the current cutting force, namely the phase locking target phase difference theta Target object And sent to the microcontroller 1. The signal generating module 3 is composed of a DDS generator and a grid driving chip (such as EG 2104), and the microcontroller 1 controls the DDS generator to generate a single-path PWM signal, and the signal is processed by the grid driving chip to form two paths of PWM signals which are reverse and have dead time as control signals of the power amplifying module 4. The power amplification module 4 is composed of a full-bridge inverter circuit, and the output alternating current of the full-bridge inverter circuit drives the transducer 9 to work after non-contact transmission through the loose coupling transformer 7. The compensating circuit is composed of a first compensating capacitor 6 and a second compensating capacitor 8, and is used for carrying out bilateral compensation on the loose coupling transformer 7, and the resonance frequency of the loop of the loose coupling transformer 7 and the transducer 9 after bilateral compensation is equal to the series resonance frequency of the transducer 9 in an idle state. The force measuring instrument 10 collects the cutting force in the current machining state and receives cutting force data from the upper computer 2. The sampling module is composed of a voltage sensor 11 (such as CHV-50P) and a current sensor 5 (such as LT 58-S7) and is used for collecting the voltage and current values of the primary side of the loose coupling transformer 7. The signal conditioning module is composed of a first signal amplifying circuit 12, a first band-pass filter circuit 13, a second signal amplifying circuit 14 and a second band-pass filter circuit 15, and is used for amplifying sampled voltage and current signals, filtering out higher harmonics and transmitting the higher harmonics to the microcontroller 1 for detection.
The phase difference solving algorithm in the controller 1 is as follows:
sa, first, the frequency f of the electric signal driving the transducer 9 to operate is recorded in the control program of the microcontroller 1 s Let the mathematical expression of the voltage and current acquired at this time be
V(t)＝A 1 cos(ωt+θ 1 )+C 1 、
I(t)＝A 2 cos(ωt+θ 2 )+C 2 ；
Wherein A is 1 、A 2 The amplitude of the voltage and current signals respectively, omega is the circular frequency of the signals, theta 1 、θ 2 The initial phases of the voltage and current signals are respectively C 1 、C 2 The dc bias of the voltage and current signals, respectively.
Sb by sampling voltage signal V i The calculation of each unknown parameter of the expression of (a) is exemplified:
A 0 、B 0 coefficients in the expansion respectively, wherein
From formulae (2), (3)
A 0 ＝A 1 cos(θ 1 ) (4)
B 0 ＝-A 1 sin(θ 1 ) (5)
Sc, setting the sampling time t of the ADC in the microcontroller 1 n Let the sample value be y (N), where n=1, 2, 3..n, N is the number of sample points, then there is
y(n)＝A 0 cos(ωt n )+B 0 sin(ωt n )+C 1 (6)
Known sample voltage signal V i Has a frequency f s ω=2pi f s A is obtained by least square method 0 、B 0 、C 1 The value of (2) is shown in the formula
Wherein the method comprises the steps of
Sd, will A 0 、B 0 Value generationThe initial phase theta of the sampling voltage signal can be obtained by the input (4) and (5) 1 Sampling the primary phase theta of the current signal 2 The calculation method of (1) samples the voltage signal;
sampling current I i Sampling voltage V i Phase difference Δθ=θ of (a) 2 -θ 1 If delta theta>θ Target object At this time, the current I is sampled i Phase-advanced sampling voltage V i The transducer loop is capacitive; if delta theta is less than theta Target object At this time sample voltage V i Phase advance sampling current I i The transducer loop presents an inductance; if Δθ=θ Target object The transducer loop is now purely resistive, at the resonance point. In particular, θ when the transducer 9 is in an unloaded state Target object ＝0。
As shown in fig. 2, 16 is a loosely coupled transformer equivalent circuit, 17 is a transducer equivalent circuit, C p1 For the first compensation capacitor C p2 Is the second compensation capacitance. When the bilateral compensation capacitance value is selected reasonably, the series resonance frequency of the transducer in the no-load state is the resonance frequency of the whole circuit.
In a preferred embodiment of the present invention, a set of parameters is chosen as an illustration, and the equivalent parameters of the transducer include: r is R 1 ＝19.372Ω、C 1 ＝1.281nF、L 1 ＝23.464mH、C 0 = 6.963nF, loosely coupled transformer parameters include: l (L) p ＝1.83mH，R p ＝0.9885Ω，L m ＝0.899mH，R m ＝30050Ω，R s ＝0.5754Ω，L s =1.3 mH, calculate to obtain the first compensation capacitance C p1 ＝244.57nF，C p2 = 161.9nF. The impedance and phase frequency characteristics of the loosely coupled transformer and transducer loop are shown in fig. 3. The lowest point f of the impedance characteristic curve in the figure s The frequency of the loosely coupled transformer and the transducer loop is 29029.83Hz, and as shown in fig. 3, the abscissa is the frequency of the excitation voltage, the ordinate on the left axis is the total impedance of the loosely coupled transformer and the transducer loop after bilateral compensation, and the ordinate on the right axis is the phase of the loosely coupled transformer and the transducer loop. After the loading experiment is carried out on the transducer, the change value of the series resonant frequency of the transducer along with the loading force is determined as a graph4. Referring to fig. 4, the abscissa is the load force and the left axis is the series resonant frequency of the transducer.
The invention also provides a method for tracking the high-precision frequency of the rotary ultrasonic auxiliary processing, which adopts the device for tracking the high-precision frequency of the rotary ultrasonic auxiliary processing, and comprises the following specific steps:
s1, determining the series resonance frequency of the transducer 9 in an empty state, and calculating compensation circuit parameters; carrying out a loading test to determine the variation value of the series resonant frequency of the transducer along with the loading force under different force loading conditions;
s2, setting the excitation voltage frequency as the series resonance frequency of the transducer under different force loading conditions, calculating by an equivalent circuit method to obtain a phase value of the loose coupling transformer and the transducer loop, which changes along with the loading force, after bilateral compensation, and then fitting the phase value into a formula of the loose coupling transformer and the transducer loop, which changes along with the loading force.
S3, setting an initial excitation frequency in the microcontroller 1, and generating excitation voltage through the control signal generation module 3 and the power amplification module 4. And then the voltage and current values of the primary side of the loose coupling transformer are collected through the voltage sensor 11 and the current sensor 5 and transmitted to the microcontroller 1 for detection, and finally the phase difference of the voltage and the current is obtained through a phase difference solving algorithm.
S4, starting the machine tool to start machining, collecting cutting force in the machining process through the dynamometer 10, processing cutting force data in the upper computer 2, substituting the cutting force data into a change formula of the phase of the loose coupling transformer and the transducer loop along with the load force, and obtaining a phase-locked target phase difference theta Target object . Then will theta Target object And sending the target value to the microcontroller as a target value of the PI regulating algorithm.
S5, setting a PI regulating algorithm in the microcontroller 1 to theta Target object For target value, the excitation frequency is adjusted to the voltage V i Current I i Is equal to theta in phase difference Target object At this time, the excitation frequency is the serial resonance frequency of the transducer, and frequency tracking is completed.
As shown in FIG. 5, f 0 Is the initial frequency of the excitation voltage signal; delta theta is pineThe phase difference of the primary side voltage and current of the coupling transformer; θ Target object To compensate for the bilateral, the phase of the loosely coupled transformer and the transducer loop changes with the load force, and in particular, the value of the loosely coupled transformer and the transducer loop is equal to 0 when the transducer is unloaded. As shown with reference to fig. 5, when Δθ=θ Target object Time-frequency tracking is completed, otherwise, the PI adjustment algorithm is always called to ensure delta theta=theta Target object 。
The embodiments of the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to the above-described embodiments, which are merely illustrative and not restrictive, and many forms may be made by those having ordinary skill in the art without departing from the spirit of the present invention and the scope of the claims, which are to be protected by the present invention.
Claims (10)
1. The rotary ultrasonic auxiliary processing high-precision frequency tracking device is characterized by comprising a microcontroller, an upper computer, a signal generation module, a power amplification module, a compensation circuit, a loose coupling transformer, a dynamometer, a sampling module and a signal conditioning module; the compensation circuit consists of a first compensation capacitor and a second compensation capacitor;
the microprocessor is respectively connected with the upper computer, the signal generator module, the first band-pass filter circuit and the second band-pass filter circuit, the signal generator module is connected with the power amplification module, the power amplification module is respectively connected with the voltage sensor and the primary side of the loose coupling transformer, the first compensation capacitor is connected with the primary side of the loose coupling transformer in parallel, the secondary side of the loose coupling transformer is connected with the second compensation capacitor, the second compensation capacitor is connected with the transducer in parallel, the dynamometer measures cutting force in the machining process, the current sensor is sequentially connected with the second signal amplification circuit and the second band-pass filter circuit, and the voltage sensor is sequentially connected with the first signal amplification circuit and the first band-pass filter circuit;
the microcontroller control signal generation module outputs a PWM signal with adjustable frequency; the microcontroller detects voltage and current signals amplified and filtered by the signal conditioning module by utilizing an internal ADC function; the microcontroller is communicated with the upper computer and receives a phase-locked target phase difference theta target sent by the upper computer; a program control algorithm is arranged in the microcontroller, a voltage expression at two ends of the primary side of the loose coupling transformer and a current expression flowing through the primary side of the loose coupling transformer are obtained through the program algorithm, and then a phase difference between the voltage and the current is obtained through the voltage and the current expressions; finally, the frequency of the control signal is regulated through a PI algorithm to enable the phase difference of the voltage and the current to be equal to the target phase difference sent by the upper computer, and the frequency of the control signal corresponding to the target phase difference is the series resonance frequency of the transducer.
2. The rotary ultrasonic-assisted machining high-precision frequency tracking device according to claim 1, wherein the upper computer receives cutting force data measured by the force measuring instrument, substitutes the cutting force data into a formula of change of resonant frequency of the loose coupling transformer and the transducer loop along with load force, and further obtains phase values of the loose coupling transformer and the transducer loop under the cutting force, namely phase-locked target phase difference, and sends the phase values to the microcontroller.
3. The rotary ultrasonic-assisted machining high-precision frequency tracking device according to claim 1, wherein the signal generation module comprises a DDS generator and a grid driving chip, the microcontroller controls the DDS generator to generate a single-path PWM signal, and the single-path PWM signal is processed by the grid driving chip to form two paths of inverted PWM signals with dead time as control signals of the power amplification module.
4. The rotary ultrasonic-assisted machining high-precision frequency tracking device according to claim 1, wherein the power amplification module comprises a full-bridge inverter circuit, and alternating current output by the full-bridge inverter circuit is transmitted in a non-contact mode through a loose coupling transformer and then drives the transducer to work.
5. The rotary ultrasonic-assisted machining high-precision frequency tracking device according to claim 1, wherein the compensation circuit is used for performing bilateral compensation on the loose-coupling transformer, and the resonance frequency of the loose-coupling transformer and the transducer loop after bilateral compensation is equal to the series resonance frequency of the transducer in an idle state.
6. The rotary ultrasonic-assisted machining high-precision frequency tracking device according to claim 1, wherein the force measuring instrument collects the cutting force in the current machining state and receives cutting force data from an upper computer.
7. The rotary ultrasonic-assisted machining high-precision frequency tracking device according to claim 1, wherein the sampling module comprises a voltage and current sensor for acquiring voltage and current values of a primary side of the loosely-coupled transformer.
8. The rotary ultrasonic-assisted machining high-precision frequency tracking device according to claim 1, wherein the signal conditioning module comprises a signal amplifying circuit and a band-pass filter circuit, wherein the signal amplifying circuit is used for amplifying sampled voltage and current signals, filtering out higher harmonics and transmitting the sampled voltage and current signals to the microcontroller for detection.
9. A method for tracking the high-precision frequency of rotary ultrasonic auxiliary processing, which is characterized by adopting the device for tracking the high-precision frequency of rotary ultrasonic auxiliary processing according to any one of claims 1-8, and comprising the following steps:
s1, determining the series resonance frequency of the transducer in an empty load state, calculating compensation circuit parameters, and carrying out a loading test to determine the variation value of the series resonance frequency of the transducer along with the loading force under different force loading conditions;
s2, setting excitation voltage frequency as the series resonance frequency of the transducer under different force loading conditions, calculating to obtain a phase value of the loose coupling transformer and the transducer loop, which changes along with the load force, after bilateral compensation by an equivalent circuit method, and then fitting the phase value into a formula of the loose coupling transformer and the transducer loop, which changes along with the load force;
s3, setting an initial excitation frequency in the microcontroller, generating excitation voltage through a control signal generating module and a power amplifying module, acquiring voltage and current values of the primary side of the loose coupling transformer through a voltage and current sensor, transmitting the voltage and current values to the microcontroller for detection, and finally obtaining a phase difference of the voltage and the current through a phase difference solving algorithm;
s4, starting the machine tool to start machining, collecting cutting force in the machining process through a dynamometer, processing cutting force data in an upper computer, substituting the cutting force data into a change formula of the phase of a loose coupling transformer and a transducer loop along with load force, and obtaining a phase-locked target phase difference theta Target object Then θ is taken Target object The target value is sent to a microcontroller as a target value of a PI regulation algorithm;
s5, setting a PI regulating algorithm in the microcontroller to theta Target object For the target value, the exciting frequency is regulated to make the phase difference of voltage and current equal to theta Target object At this time, the excitation frequency is the serial resonance frequency of the transducer, and frequency tracking is completed.
10. The method for tracking the frequency of high-precision machining assisted by rotary ultrasound according to claim 9, wherein in the step S3, the method for obtaining the phase difference of the voltage and the current by the phase difference solving algorithm comprises the following steps:
sa, record the frequency f of the electric signal driving the transducer to work in the control program of the microcontroller s Let the mathematical expression of the voltage and current acquired at this time be
V(t)＝A 1 cos(ωt+θ 1 )+C 1
I(t)＝A 2 cos(ωt+θ 2 )+C 2
Wherein A is 1 、A 2 The amplitude of the voltage and current signals respectively, omega is the circular frequency of the signals, theta 1 、θ 2 The initial phases of the voltage and current signals are respectively C 1 、C 2 Respectively is a voltage,The dc bias of the current signal.
Sb, taking calculation of each unknown parameter of the expression of the sampled voltage signal as an example:
A 0 、B 0 coefficients in the expansion respectively, wherein
From formulae (2), (3)
A 0 ＝A 1 cos(θ 1 ) (4)
B 0 ＝-A 1 sin(θ 1 ) (5)
Sc setting the sampling time t of ADC in the microcontroller n Let the sample value be y (N), where n=1, 2, 3..n, N is the number of sample points, then there is
y(n)＝A 0 cos(ωt n )+B 0 sin(ωt n )+C 1 (6)
The frequency of the sampled voltage signal is known to be f s ω=2pi f s A is obtained by least square method 0 、B 0 、C 1 The value of (2) is shown in the formula
Wherein the method comprises the steps of
Sd, will A 0 、B 0 Substituting the values into (4) and (5) to obtain the initial phase theta of the sampling voltage signal 1 Sampling the primary phase theta of the current signal 2 The calculation method of (1) samples the voltage signal;
se, phase difference Δθ=θ of sampling current and voltage signals 2 -θ 1 If delta theta>θ Target object At this time, the sampling current phase advances the sampling voltage, and the transducer loop is capacitive; if delta theta is less than theta Target object At this time, the sampling voltage phase advances the sampling current, and the transducer loop presents an inductance; if Δθ=θ Target object At this time, the transducer loop is purely resistive, is at the resonance point, and when the transducer is in an unloaded state, θ Target object ＝0。
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