Rotary ultrasonic assisted machining high-precision frequency tracking device and method

Abstract

The application relates to a high-precision frequency tracking device and method for rotary ultrasonic auxiliary machining, and the tracking device comprises a microcontroller, an upper computer, a signal generating module, a power amplification module, a compensation circuit, a loosely coupled transformer, a dynamometer, a sampling module and a signal conditioning module; the microprocessor is connected with the upper computer, the signal generator module, a first band-pass filter circuit and a second band-pass filter circuit respectively; the signal generating module is connected with the power amplification module; the power amplification module is sequentially connected with a voltage sensor and a primary side of the loosely coupled transformer; the dynamometer measures the cutting force in the machining process, and the counterforce of the force is a load force received by a transducer. The application fully considers the problem that static matching failure caused by load force change in the rotary ultrasonic machining process further leads to the decline of frequency tracking precision, and improves the frequency tracking precision. The application has the advantages of low cost, fast frequency tracking speed, high precision and strong adaptability.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of ultrasonic assisted machining and frequency tracking, and more particularly, to a high-precision frequency tracking device and method for rotary ultrasonic assisted machining. BACKGROUND

[0002] Rotary ultrasonic assisted machining is a high-efficiency and high-precision machining technology, which is widely used in the machining of hard and brittle materials. The existing ultrasonic machining system mainly consists of an ultrasonic power supply, a non-contact power transmission unit, a transducer, and a clamped tool. The function of the ultrasonic power supply is to convert the 50Hz commercial power into an alternating current with adjustable frequency and matching the resonant frequency of the transducer in series. The non-contact power transmission unit is mainly composed of a loosely coupled transformer, which transmits electrical energy to the transducer in a non-contact manner. The transducer is a device that converts high-frequency alternating current into high-frequency vibration. In actual ultrasonic assisted machining process, the resonant frequency of the transducer often changes due to sudden changes in load force, temperature rise of the transducer, tool wear, etc., which leads to a decrease in output amplitude and affects the machining quality. Long-term misalignment can even reduce the service life of the transducer. In addition, when the resonant frequency of the transducer changes, the matching circuit of the non-contact power transmission unit is invalid. At this time, the phase difference between the voltage and current at the resonant frequency of the transducer is often not zero. Therefore, a high-precision frequency tracking method and device are needed.

[0003] The commonly used frequency tracking technology at present is based on the hardware phase-locked loop method. First, the phase difference between the voltage signal and the current signal in the transducer circuit is detected, and then the output frequency is adjusted to the frequency point where the phase difference is zero through methods such as bisection and variable step size algorithm. However, since the transducer works at series resonance frequency and parallel resonance frequency, the phase difference between the voltage signal and the current signal is zero, and only when it works at series resonance frequency, the output power of the ultrasonic machining system can reach the maximum. Therefore, the existing phase-locked loop technology often appears the situation of false locking frequency. In addition, a Chinese patent with the patent number CN110702971B discloses an ultrasonic driving power supply and real-time frequency tracking method for automatically tracking the series resonance frequency of the transducer. The method acquires the peak value of the current flowing through the filter capacitor and the sampling resistor and their phase difference, and then calculates the relationship that the current needs to satisfy when the transducer dynamic branch is in series resonance. Whether the relationship is zero is used as the basis for adjusting the frequency. Although this method avoids the false locking of the ultrasonic power supply to the parallel resonance frequency of the transducer, the calculation accuracy of the relationship is seriously dependent on the accuracy of the filter capacitor value and the accuracy of the transducer static capacitance. SUMMARY

[0004] The technical problem solved by the present application is to provide a rotating ultrasonic auxiliary machining frequency tracking device and method capable of tracking the series resonance frequency of a transducer with high precision and in real time.

[0005] The technical solution adopted by the present application to solve its technical problem is to construct a rotating ultrasonic auxiliary machining high-precision frequency tracking device, which comprises a microcontroller, an upper computer, a signal generation module, a power amplification module, a compensation circuit, a loosely coupled transformer, a dynamometer, a sampling module and a signal conditioning module; the compensation circuit is composed of a first compensation capacitor and a second compensation capacitor;

[0006] The microprocessor is connected with the upper computer, the signal generator module, the first band-pass filter circuit and the second band-pass filter circuit respectively, the signal generation module is connected with the power amplification module, the power amplification module is connected with the voltage sensor and the primary side of the loosely coupled transformer respectively, the first compensation capacitor is connected with the primary side of the loosely coupled transformer in parallel, the secondary side of the loosely coupled 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 counterforce of the cutting force is the load force received by the transducer, the current sensor is connected with the second signal amplification circuit and the second band-pass filter circuit in sequence, and the voltage sensor is connected with the first signal amplification circuit and the first band-pass filter circuit in sequence.

[0007] The microcontroller controls the signal generation module to output a PWM signal with adjustable frequency; the microcontroller detects the voltage and current signals amplified and filtered by the signal conditioning module by using the internal ADC function; the microcontroller communicates with the upper computer and receives the target phase difference θ 目标 sent by the upper computer; the microcontroller is internally provided with a program control algorithm, by which the voltage expression at both ends of the primary side of the loosely coupled transformer and the current expression flowing through the primary side of the loosely coupled transformer are obtained, and then the phase difference of the voltage and current is obtained through the voltage and current expressions; finally, the frequency of the control signal is adjusted and controlled through the PI algorithm so that the voltage and current phase difference is equal to the target phase difference sent by the upper computer, and the control signal frequency corresponding to the target phase difference is the series resonance frequency of the transducer.

[0008] According to the above scheme, the upper computer receives the cutting force data measured by the dynamometer, and then substitutes the cutting force data into the formula for the change of the resonance frequency of the loosely coupled transformer and transducer circuit with the load force, and further obtains the phase value of the loosely coupled transformer and transducer circuit under the cutting force, i.e. the target phase difference θ 目标 of the phase-locked loop, and sends it to the microcontroller.

[0009] According to the scheme, the signal generation module includes a DDS generator and a gate drive chip, the microcontroller controls the DDS generator to generate a single-channel PWM signal, the single-channel PWM signal is processed by the gate drive chip to form two reverse PWM signals with a dead time as the control signal of the power amplifier module.

[0010] According to the scheme, the power amplifier module includes a full-bridge inverter circuit, and the alternating current output by the full-bridge inverter circuit drives the transducer to work after being transmitted by the loosely coupled transformer.

[0011] According to the scheme, the compensation circuit is used for double-side compensation of the loosely coupled transformer, and the resonance frequency of the loosely coupled transformer and the transducer loop after the double-side compensation is equal to the series resonance frequency of the transducer in the no-load state.

[0012] According to the scheme, the dynamometer collects the cutting force in the current machining state, and the cutting force data is received by the upper computer.

[0013] According to the scheme, the sampling module includes voltage and current sensors, and the voltage and current sensors are used to collect the voltage and current values on the primary side of the loosely coupled transformer.

[0014] According to the scheme, the signal conditioning module includes a signal amplification circuit and a band-pass filter circuit, and the signal amplification circuit and the band-pass filter circuit are used to amplify the sampled voltage and current signals and filter out high-order harmonics before transmitting them to the microcontroller for detection.

[0015] The application also provides a high-precision frequency tracking method for rotary ultrasonic auxiliary machining, and the high-precision frequency tracking method for rotary ultrasonic auxiliary machining comprises the following steps:

[0016] S1, determining the series resonance frequency of the transducer in the no-load state and calculating the compensation circuit parameters, and determining the change value of the series resonance frequency of the transducer under different force loads through a loading test;

[0017] S2, setting the excitation voltage frequency as the series resonance frequency of the transducer under different force loads, calculating the phase value of the loosely coupled transformer and the transducer loop under different force loads through an equivalent circuit method, and then fitting the value into a formula of the phase of the loosely coupled transformer and the transducer loop changing with the force load;

[0018] S3, setting the initial excitation frequency in the microcontroller, generating the excitation voltage through the control signal generation module and the power amplifier module, collecting the voltage and current values on the primary side of the loosely coupled transformer through the voltage and current sensors and transmitting them to the microcontroller for detection, and finally obtaining the phase difference of the voltage and current through a phase difference solving algorithm.

[0019] S4, start the machine tool to start processing, through the force gauge to collect the cutting force in the processing process, process the cutting force data in the host computer, and substitute the cutting force data into the formula of the change of the phase of the loosely coupled transformer and the transducer circuit with the load force to obtain the target phase difference θ of the phase-locked loop 目标 Then send θ 目标 to the microcontroller as the target value of the PI regulation algorithm;

[0020] S5, set the PI regulation algorithm in the microcontroller to take θ 目标 as the target value, adjust the excitation frequency to make the phase difference of the voltage and current equal to θ 目标 At this time, the excitation frequency is the series resonance frequency of the transducer, and the frequency tracking is completed.

[0021] According to the above scheme, in the step S3, the method for obtaining the phase difference of the voltage and current through the phase difference solving algorithm includes the following steps:

[0022] Sa, record the frequency f s of the electrical signal driving the transducer in the microcontroller control program, and set the mathematical expressions of the voltage and current collected at this time as

[0023] V(t)=A1cos(ωt+θ1)+C1

[0024] I(t)=A2cos(ωt+θ2)+C2

[0025] Wherein, A1 and A2 are the amplitudes of the voltage and current signals respectively, ω is the circular frequency of the signal, θ1 and θ2 are the initial phases of the voltage and current signals respectively, and C1 and C2 are the DC offsets of the voltage and current signals respectively.

[0026]

[0027] A0 and B0 are the coefficients in the expansion, wherein

[0028]

[0029]

[0030] From formulas (2) and (3), we can get

[0031] A0=A1cos(θ1) (11)

[0032] B0=-A1sin(θ1) (12)

[0033] Sc, set the sampling time t n, let the sampling value be y(n), wherein n=1, 2, 3...N, N is the number of sampling points, then

[0034] y(n)=A0cos(ωt n )+B0sin(ωt n )+C1 (13)

[0035] The frequency of the sampling voltage signal is known as f s , then ω=2πf s , the values of A0, B0 and C1 can be obtained by the least square method as shown in the following formula

[0036]

[0037] Wherein

[0038]

[0039] Sd, the values of A0 and B0 are substituted into (4) and (5) to obtain the initial phase θ1 of the sampling voltage signal, and the calculation method of the initial phase θ2 of the sampling current signal is same as that of the sampling voltage signal;

[0040] Se, the phase difference Δθ=θ2-θ1 of the sampling current and voltage signals, if Δθ>θ 目标 , at this time, the sampling current phase leads the sampling voltage, and the transducer loop is capacitive; if Δθ<θ 目标 , at this time, the sampling voltage phase leads the sampling current, and the transducer loop is inductive; if Δθ=θ 目标 , at this time, the transducer loop is purely resistive, and is at the resonance point, and the transducer is in the no-load state, θ 目标 =0.

[0041] The rotating ultrasonic auxiliary machining high-precision frequency tracking device and method implemented by the application have the following beneficial effects:

[0042] 1. The application calculates the phase difference of voltage and current by using software algorithm instead of obtaining the phase difference of voltage and current by the traditional hardware phase discrimination circuit, simplifies the hardware circuit part of the frequency tracking device, and saves the cost;

[0043] 2. The frequency tracking speed of the application is fast, and the phase difference values of voltage and current can be calculated by sampling three groups of voltage and current values respectively, while the traditional zero-crossing comparison method needs to compare the voltage and current waveforms of one period to obtain the phase difference values;

[0044] 3. The application fully considers the problem that the static matching failure caused by the load force change in the rotating ultrasonic machining process further leads to the decrease of frequency tracking precision, takes the phase change value of the primary side of the loosely coupled transformer as the phase locking target value, and improves the frequency tracking precision;

[0045] 4、The application has strong adaptability, and when the hard and brittle materials with different mechanical properties are processed by ultrasonic auxiliary processing, the series resonance frequency of the transducer after the current load force value is accurately tracked;

[0046] 5、The application has the advantages of low cost, fast frequency tracking speed, high precision and strong adaptability. BRIEF DESCRIPTION OF DRAWINGS

[0047] The application will be further described below in combination with the drawings and examples, and the drawings are as follows:

[0048] Figure 1 It is a schematic diagram of the rotating ultrasonic auxiliary processing frequency tracking device of the application;

[0049] Figure 2 It is an equivalent circuit diagram of the loose coupling transformer, transducer, etc. of the application;

[0050] Figure 3 It is an amplitude and phase characteristic curve diagram of the loose coupling transformer and transducer loop after double-side compensation of the application;

[0051] Figure 4 It is a schematic diagram of the change value of the series resonance frequency of the transducer with the load force of the application;

[0052] Figure 5 It is an algorithm flowchart in the frequency tracking process of the application;

[0053] In the drawings: 1, microcontroller, 2, upper computer, 3, signal generation module, 4, power amplification module, 5, current sensor, 6, first compensation capacitor, 7, loose coupling transformer, 8, second compensation capacitor, 9, transducer, 10, force gauge, 11, voltage sensor, 12, first signal amplification circuit, 13, first band-pass filter circuit, 14, second signal amplification circuit, 15, second band-pass filter circuit, 16 loose coupling transformer equivalent circuit, 17, transducer equivalent circuit, U i , primary side voltage of loose coupling transformer, I i , primary side current of loose coupling transformer, C p1 , first compensation capacitor, L p , primary side leakage inductance, R p , primary side equivalent series resistance, L m , magnetizing inductance, R m , magnetic core loss, R s , secondary side equivalent series resistance, L s , secondary side leakage inductance, C p2 , second compensation capacitor, C0, static capacitance of transducer, R1, dynamic resistance of transducer, C1, dynamic capacitance of transducer, L1, dynamic inductance of transducer. DETAILED DESCRIPTION

[0054] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0055] like Figure 1 As shown, the high-precision frequency tracking device for rotary ultrasonic-assisted machining of the present invention comprises a microcontroller 1, a host computer 2, a signal generation module 3, a power amplification module 4, a compensation circuit, a loosely coupled transformer 7, a force gauge 10, a sampling module, and a signal conditioning module. The microcontroller 1 consists of a microprocessor chip and its peripheral circuits; the microcontroller 1 controls the signal generation module to output a frequency-adjustable PWM signal; the microcontroller 1 uses its internal ADC function to detect the voltage and current signals amplified and filtered by the signal conditioning module; the microcontroller 1 communicates with the host computer 2 and receives the phase difference θ of the phase-locked target sent by the host computer 2. 目标 The microcontroller 1 internally sets up a control algorithm to obtain the voltage expression across the primary side of the loosely coupled transformer 7 and the current expression flowing through the primary side of the loosely coupled transformer 7. Then, the phase difference between the voltage and current can be obtained from these expressions. Finally, a PI algorithm is used to adjust the frequency of the control signal so that the phase difference between the voltage and current equals the target phase difference θ sent by the host computer. 目标 θ 目标 The corresponding control signal frequency is the series resonant frequency of the transducer.

[0056] The host computer 2 receives the cutting force data measured by the force measuring instrument 10, and then substitutes the current cutting force data into the formula for the change of the resonant frequency of the loosely coupled transformer and transducer circuit with the load force, thereby obtaining the phase value of the loosely coupled transformer and transducer circuit under the current cutting force, i.e., the phase difference θ of the phase-locked loop. 目标And sent to the microcontroller 1. Signal generation module 3 is composed of DDS generator, gate drive chip (such as EG2104), microcontroller 1 controls DDS generator to generate single channel PWM signal, the signal is processed by gate drive chip to form two-way reverse and dead time PWM signal as the control signal of power amplifier module 4. Power amplifier module 4 is composed of full-bridge inverter circuit, the output of which drives transducer 9 to work after non-contact transmission through loosely coupled transformer 7. Compensation circuit is composed of first compensation capacitor 6 and second compensation capacitor 8, which is used to compensate the loosely coupled transformer 7 from both sides. After double side compensation, the resonant frequency of loosely coupled transformer 7 and transducer 9 loop is equal to the series resonant frequency of transducer 9 in no load state. Force measuring instrument 10 collects the size of cutting force under current processing state, and receives cutting force data by host computer 2. Sampling module is composed of voltage sensor 11 (such as CHV-50P) and current sensor 5 (such as LT58-S7), which is used to collect the voltage and current value of the primary side of loosely coupled transformer 7. Signal conditioning module is composed of first signal amplification circuit 12, first band-pass filter circuit 13, second signal amplification circuit 14 and second band-pass filter circuit 15, which is used to amplify and filter the sampling voltage and current signal to the microcontroller 1 for detection.

[0057] The phase difference solving algorithm in controller 1 is as follows:

[0058] Sa, first record the driving signal frequency f of transducer 9 in the microcontroller 1 control program s , suppose the mathematical expression of the collected voltage and current at this time is

[0059] V(t)=A1cos(ωt+θ1)+C1、

[0060] I(t)=A2cos(ωt+θ2)+C2;

[0061] Wherein, A1, A2 are the amplitude of voltage and current signal respectively, ω is the circular frequency of signal, θ1, θ2 are the initial phase of voltage and current signal respectively, C1, C2 are the DC bias of voltage and current signal respectively.

[0062] Sb, take the expression of each unknown parameter of sampling voltage signal V i as an example:

[0063]

[0064] A0, B0 are the coefficients in the expansion, wherein

[0065]

[0066]

[0067] From equation (2), (3)

[0068] A0 = A1 cos(θ1) (4)

[0069] B0 = -A1 sin(θ1) (5)

[0070] Sc, set the sampling time t of ADC in microcontroller 1 n , set the sampling value as y(n), where n = 1, 2, 3...N, N is the number of sampling points, then

[0071] y(n) = A0 cos(ωt n )+B0sin(ωt n )+C1 (6)

[0072] Given the frequency of the sampling voltage signal V i is f s , then ω = 2πf s , the values of A0, B0, C1 can be obtained by least square method as shown in the following equation

[0073]

[0074] Where

[0075]

[0076] Sd, substitute A0, B0 into (4), (5) to obtain the initial phase θ1 of the sampling voltage signal, and the calculation method of the initial phase θ2 of the sampling current signal is the same as that of the sampling voltage signal;

[0077] The phase difference Δθ = θ2- θ1 of the sampling current I i and the sampling voltage V i , if Δθ > θ 目标 , the sampling current I i leads the sampling voltage V i at this time, the transducer circuit is capacitive; if Δθ < θ 目标 , the sampling voltage V i leads the sampling current I i at this time, the transducer circuit is inductive; if Δθ = θ 目标 , the transducer circuit is purely resistive at this time, at the resonance point. In particular, when the transducer 9 is in the no-load state, θ 目标 = 0.

[0078] As shown in Figure 2 , 16 is the equivalent circuit of a loosely coupled transformer, 17 is the equivalent circuit of a transducer, C p1 is the first compensation capacitor, C p2The second compensation capacitor is C0. When the double-side compensation capacitor value is selected reasonably, the series resonance frequency of the transducer in the no-load state is the resonance frequency of the entire circuit.

[0079] In the preferred embodiment of the present application, a set of parameters are selected as an illustration, the transducer equivalent parameters include: R1=19.372Ω, C1=1.281nF, L1=23.464mH, C0=6.963nF, the loosely coupled transformer parameters include: L p =1.83mH, R p =0.9885Ω, L m =0.899mH, R m =30050Ω, R s =0.5754Ω, L s =1.3mH, the first compensation capacitor C p1 =244.57nF, C p2 =161.9nF. At this time, the impedance characteristic curve and the phase frequency characteristic curve of the loosely coupled transformer and the transducer circuit are as shown in Figure 3 The lowest point f s =29029.83Hz of the impedance characteristic curve is the resonance frequency of the loosely coupled transformer and the transducer circuit, as shown in Figure 3 The horizontal coordinate is the frequency of the excitation voltage, the left axis vertical coordinate is the total impedance of the loosely coupled transformer and the transducer circuit after the double-side compensation, and the right axis vertical coordinate is the phase of the loosely coupled transformer and the transducer circuit. The change value of the transducer series resonance frequency with the load force after the loading experiment of the transducer is as shown in Figure 4 The horizontal coordinate is the load force, and the left axis vertical coordinate is the series resonance frequency of the transducer. Figure 4

[0080] The present application also provides a high-precision frequency tracking method for rotary ultrasonic auxiliary machining, which adopts the high-precision frequency tracking device for rotary ultrasonic auxiliary machining.

[0081] S1, determine the series resonance frequency of the transducer 9 in the no-load state, calculate the compensation circuit parameters, and determine the change value of the transducer series resonance frequency with the load force under different force load conditions through a loading experiment.

[0082] S2, set the excitation voltage frequency as the series resonance frequency of the transducer under different force load conditions, calculate the phase value of the loosely coupled transformer and the transducer circuit with the load force after the double-side compensation through the equivalent circuit method, and then fit the value into a formula of the phase of the loosely coupled transformer and the transducer circuit with the load force.

[0083] ​S3, the initial excitation frequency is set in the microcontroller 1, and the excitation voltage is generated through the control signal generation module 3 and the power amplifier module 4. Then the voltage and current values on the primary side of the loosely coupled transformer are collected by 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 current is obtained through the phase difference solving algorithm.

[0084] S4, start the machine tool to process, collect the cutting force in the processing process through the force sensor 10, process the cutting force data in the upper computer 2, and substitute the cutting force data into the formula of the change of the phase of the loosely coupled transformer and the transducer circuit with the load force to obtain the target phase difference θ of the phase-locked loop. 目标 Then θ 目标 is sent to the microcontroller as the target value of the PI regulation algorithm.

[0085] S5, the PI regulation algorithm is set in the microcontroller 1, and θ 目标 is taken as the target value to adjust the excitation frequency so that the phase difference of the voltage V i , the current I i equals θ 目标 , at this time the excitation frequency is the series resonance frequency of the transducer, and the frequency tracking is completed.

[0086] As shown in Figure 5 , f0 is the initial frequency of the excitation voltage signal; Δθ is the phase difference of the voltage and current on the primary side of the loosely coupled transformer; θ 目标 is the change of the phase of the loosely coupled transformer and the transducer circuit with the load force after double-sided compensation, and in particular, when the transducer is unloaded, its value is equal to 0. Referring to Figure 5 , when Δθ = θ 目标 , the frequency tracking is completed, otherwise the PI regulation algorithm will be called to make Δθ = θ 目标 .

[0087] The embodiments of the application are described above in combination with the drawings, but the application is not limited to the above specific embodiments, and the above specific embodiments are only illustrative but not restrictive, and those skilled in the art can make many forms under the inspiration of the application without departing from the purpose of the application and the scope protected by the claims, which are all within the protection of the application.

Claims

1. A high-precision frequency tracking device for rotary ultrasonic machining, characterized by The device comprises a microcontroller, a host computer, a signal generating module, a power amplifier module, a compensation circuit, a loosely coupled transformer, a force measuring instrument, a sampling module and a signal conditioning module; the compensation circuit is composed of a first compensation capacitor and a second compensation capacitor; The sampling module comprises voltage and current sensors for collecting voltage and current values on the primary side of the loosely coupled transformer; the signal conditioning module comprises a first band-pass filter circuit, a second band-pass filter circuit, a first signal amplifier circuit and a second signal amplifier circuit; The microcontroller is connected with the host computer, the signal generator module, the first band-pass filter circuit and the second band-pass filter circuit; the signal generating module is connected with the power amplifier module; the power amplifier module is connected with the voltage sensor and the primary side of the loosely coupled transformer; the first compensation capacitor is connected in parallel with the primary side of the loosely coupled transformer; the secondary side of the loosely coupled transformer is connected with the second compensation capacitor; the second compensation capacitor is connected in parallel with the transducer; the force measuring instrument measures the cutting force in the machining process; the current sensor is connected with the second signal amplifier circuit and the second band-pass filter circuit in sequence; the voltage sensor is connected with the first signal amplifier circuit and the first band-pass filter circuit in sequence; The microcontroller controls a signal generation module to output a frequency-adjustable PWM signal; the microcontroller detects a voltage and current signal amplified and filtered by a signal conditioning module by using an internal ADC function; the microcontroller communicates with a host computer to receive a phase difference θ sent by the host computer 目标 ; the microcontroller is internally provided with a program control algorithm, which obtains a voltage expression across the primary side of a loosely coupled transformer and a current expression through the primary side of the loosely coupled transformer, and then obtains a phase difference of the voltage and the current through the voltage and current expressions; finally, the PI algorithm is used to adjust the frequency of the control signal to make the phase difference of the voltage and the current equal to the target phase difference sent by the host computer, and the control signal frequency corresponding to the target phase difference is the series resonance frequency of the transducer.

2. The high-precision frequency tracking device for rotary ultrasonic machining according to claim 1, characterized in that The host computer receives the cutting force data measured by the force measuring instrument, and then substitutes the cutting force data into the formula of the phase value of the loosely coupled transformer and transducer loop changing with the load force, so as to obtain the phase value of the loosely coupled transformer and transducer loop under the cutting force, i.e. the phase difference of the locking target, and sends it to the microcontroller.

3. The high-precision frequency tracking device for rotary ultrasonic machining according to claim 1, characterized in that, The signal generating module comprises a DDS generator and a gate drive chip; the microcontroller controls the DDS generator to generate a single-channel PWM signal; the single-channel PWM signal is processed by the gate drive chip to form two-channel reverse PWM signals with dead time as the control signal of the power amplifier module.

4. The high-precision frequency tracking device for rotary ultrasonic machining according to claim 1, characterized in that, The power amplifier module comprises a full-bridge inverter circuit; the alternating current output by the full-bridge inverter circuit drives the transducer to work after non-contact transmission by the loosely coupled transformer.

5. The high-precision frequency tracking device for rotary ultrasonic machining according to claim 1, characterized in that, The compensation circuit is used for double-side compensation of the loosely coupled transformer; after double-side compensation, the resonant frequency of the loosely coupled transformer and transducer loop is equal to the series resonant frequency of the transducer in the no-load state.

6. The high-precision frequency tracking device for rotary ultrasonic machining according to claim 1, characterized in that The force measuring instrument collects the size of the cutting force in the current machining state, and the host computer receives the cutting force data.

7. A high-precision frequency tracking method for rotary ultrasonic assisted machining, characterized in that, The rotating ultrasonic assisted machining high-precision frequency tracking device and method of any one of claims 1-6 comprise the following steps: S1, determine the series resonant frequency of the transducer in the no-load state and calculate the compensation circuit parameters; perform a loading test to determine the change value of the series resonant frequency of the transducer with the load force under different force load conditions; S2, set the excitation voltage frequency as the series resonant frequency of the transducer under different force load conditions; calculate the phase value of the loosely coupled transformer and transducer loop changing with the load force after double-side compensation by the equivalent circuit method, and then fit the value into the formula of the phase value of the loosely coupled transformer and transducer loop changing with the load force; S3, the initial excitation frequency is set in the microcontroller, the excitation voltage is generated through the control signal generating module and the power amplification module, then the voltage and current values on the primary side of the loosely coupled transformer are collected through the voltage and current sensors and transmitted to the microcontroller for detection, and finally the phase difference of the voltage and current is obtained through a phase difference solving algorithm; S4, start the machine tool to start processing, through the force gauge to collect the cutting force in the processing, process the cutting force data in the host computer, put the cutting force data into the formula of the change of the phase value of the loose coupling transformer and the transducer circuit with the load force, get the target phase difference θ of the phase-locked loop 目标 , then send θ 目标 to the microcontroller as the target value of the PI regulation algorithm; S5, PI regulation algorithm is set in the microcontroller, taking θ 目标 as the target value, adjusting the excitation frequency to make the phase difference of voltage and current equal to θ 目标 At this time, the excitation frequency is the transducer series resonance frequency, and the frequency tracking is completed.

8. The high-precision frequency tracking method for rotary ultrasonic assisted machining according to claim 7, characterized in that, In the step S3, the method for obtaining the phase difference of the voltage and current through the phase difference solving algorithm comprises the following steps: Sa, record the frequency f of the electrical signal driving the transducer in the microcontroller control program s , and the mathematical expression of the voltage and current collected at this time is V(t)=A1cos(ωt+θ1)+C1 I(t)=A2cos(ωt+θ2)+C2 Wherein, A1, A2 are the amplitudes of the voltage and current signals respectively, ω is the circular frequency of the signal, θ1, θ2 are the initial phases of the voltage and current signals respectively, C1, C2 are the direct current biases of the voltage and current signals respectively; Sb, taking the calculation of unknown parameters in the expression of the sampling voltage signal as an example: A0, B0 are the coefficients in the expansion, wherein From equations (2), (3), we can get A0=A1cos(θ1) (4) B0=-A1sin(θ1) (5) Sc, set the sampling time t of the ADC in the microcontroller n Let the sample values be y(n), where n = 1, 2, 3... N, N being the number of sample points, then y(n) = A0cos(ωt n )+B0sin(ωt n + C1 (6) The frequency of the sampled voltage signal is known as f s then ω = 2πf s The values of A0, B0, C1 are obtained from the least squares method as follows Wherein Sd, substituting the values of A0, B0 into equations (4), (5) can obtain the initial phase θ1 of the sampling voltage signal, and the calculation method of the initial phase θ2 of the sampling current signal is the same as that of the sampling voltage signal; Se, phase difference of sampling current and voltage signal Δθ = θ2- θ1, if Δθ > θ 目标 , sampling current phase leads sampling voltage, transducer loop is capacitive; if Δθ < θ 目标 , sampling voltage phase leads sampling current, transducer loop is inductive; if Δθ = θ 目标 , transducer loop is purely resistive, at resonance point, transducer is in no-load state, θ 目标 = 0.

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