Multi-band resonant frequency tracking circuit and method for ultrasonic machining

Abstract

The present invention discloses a multi-band resonant frequency tracking circuit applied to ultrasonic machining, including an output current voltage phase difference direction detection circuit and a multi-band resonant frequency tracking circuit, wherein the detection signal output end of the output current voltage phase difference direction detection circuit is connected to the signal input end of the multi-band resonant frequency tracking circuit, and adopts the above technical scheme, the present invention realizes a rapid determination of the system detuning condition through the current voltage phase difference direction detection signal output by the D trigger in the SN74HC74D chip, and can timely change the dead zone resistance between the 5th pin and the 7th pin in the EG3525 chip according to the detuning degree of the piezoelectric transducer, thereby changing the system driving frequency to track the resonant frequency of the piezoelectric transducer, and realizing rapid and accurate tracking. The realization process of the circuit function is simple and fast, and the ability to quickly and accurately track the forward resonant frequency point of the piezoelectric transducer is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of ultrasonic machine tools, and in particular to a multi-band resonant frequency tracking circuit and method for ultrasonic machining. Background Art

[0002] The piezoelectric transducer is the core component of the entire ultrasonic system. Under the excitation of the external high-frequency driving signal, the piezoelectric transducer generates vibrations of the same frequency. When the driving signal frequency is the same as the natural frequency of the piezoelectric transducer, the output vibration amplitude of the piezoelectric transducer is the largest. However, during the ultrasonic machining process, the resonant frequency of the piezoelectric transducer drifts due to the change of the external load force. Therefore, during the ultrasonic machining process, it is necessary to continuously adjust the driving signal frequency to track the resonant frequency of the piezoelectric transducer, so that the piezoelectric transducer can always output with the maximum amplitude and ensure the highest electromechanical conversion coefficient. Therefore, designing a stable, fast and accurate automatic resonant frequency tracking strategy is one of the research hotspots in the ultrasonic machining system. However, in the existing more mature technical methods, when the piezoelectric transducer is detuned, the speed of judging the direction of the forward resonant frequency is still not fast enough, and the judgment of the degree of detuning of the forward resonant frequency is not sensitive enough, and the resonant frequency cannot be tracked in time.

[0003] At present, the methods for realizing resonant frequency tracking in ultrasonic machining systems mainly include acoustic feedback method, composite frequency tracking method, maximum current method and automatic frequency tracking method based on fuzzy PI control strategy, etc. Among them, the implementation scheme most similar to the present invention is a resonant frequency tracking method of a piezoelectric transducer using a phase-locked loop method disclosed by Wei Qian et al. in 2018. The controller controls the frequency of the driving signal by detecting the phase difference between the voltage and current signals of the piezoelectric transducer loop. The phase-locked loop technology determines the phase difference between the voltage and current signals of the piezoelectric transducer loop through a phase detector, and linearly converts the phase difference into a voltage output to the filter for filtering, and then adjusts the output frequency through a voltage-controlled oscillator.

[0004] However, the frequency adjustment of the phase-locked loop technology is limited in range. For different types of piezoelectric transducers with different resonant frequencies, it is necessary to adjust the phase-locked loop hardware parameters to change the output frequency range. Therefore, the use of phase-locked loop technology to achieve resonant frequency tracking has the disadvantages of poor flexibility, poor structure and high cost. The composite frequency tracking method can speed up the resonant frequency tracking to a certain extent, but the composite frequency tracking method also has certain defects, that is, it only uses the phase difference of zero to determine whether the resonant frequency is tracked, while the piezoelectric transducer actually has positive and negative resonant frequencies. At the forward resonant frequency point F of the piezoelectric transducer, the phase difference of the piezoelectric transducer is zero. s and the reverse resonance frequency F p, their phases are all zero. At this time, the composite resonant frequency tracking strategy will not be able to distinguish whether the tracked resonant frequency is the forward resonant frequency or the reverse resonant frequency; the biggest disadvantage of the maximum current method for tracking the resonant frequency is that the tracking is slow. When the load changes suddenly, the resonant frequency tracking often cannot keep up with the load change. Therefore, the maximum current method for tracking the resonant frequency is not suitable for application scenarios with drastic load changes; the disadvantage of the resonant frequency tracking method of the fuzzy PI strategy is that under load conditions, when the impedance characteristics of the piezoelectric transducer change greatly, since the fuzzy PI only uses the phase difference as the control signal, the fuzzy PI cannot distinguish whether the tracked resonant frequency is the forward resonant frequency or the reverse resonant frequency. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention proposes a multi-band resonant frequency tracking circuit and method for ultrasonic machining. The circuit divides the different detuning conditions during the loading process of the piezoelectric transducer, and quickly determines the resonant frequency tracking direction and tracking degree when the resonant frequency is lost, thereby greatly shortening the judgment time during the resonant frequency loss process and improving the ability to quickly and accurately track the forward resonant frequency point.

[0006] In order to solve the above technical problems, the technical solution of the present invention is:

[0007] A multi-band resonant frequency tracking circuit for ultrasonic machining comprises an output current voltage phase difference direction detection circuit and a multi-band resonant frequency tracking circuit, wherein a detection signal output terminal of the output current voltage phase difference direction detection circuit is connected to a signal input terminal of the multi-band resonant frequency tracking circuit.

[0008] The signal input end of the multi-band resonant frequency tracking circuit includes a PWM control chip U1, a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a resistor R6, a resistor R8, a resistor R9, a resistor R10, a resistor R11, a resistor R12, a transistor Q1, a transistor Q2, a sliding rheostat Rw1, an optical coupler U2, a capacitor C1, a capacitor C2, a capacitor C3, a capacitor C4, a capacitor C5, and a capacitor C6.

[0009] One end of the resistor R4 is connected to the detection signal output end of the output current voltage phase difference direction detection circuit, and the other end of the resistor R4 is connected to one end of the resistor R3 and connected to the base of the transistor Q1; one end of the resistor R3 is connected to the other end of R4, and the other end of the resistor R3 is connected to one end of R1 and connected to the emitter of the transistor Q1; the other end of the resistor R1 is grounded; one end of the resistor R9 is connected to +3.3V and connected to one end of the capacitor C5, and the other end of the resistor R9 is connected to the first pin of the optocoupler U2; the other end of the capacitor C5 is grounded; one end of the resistor R5 is connected to the third pin of the optocoupler U2, and the other end of the resistor R5 is connected to the seventh pin of the PWM control chip U1; one end of the capacitor C6 is connected to the fifth pin of the PWM control chip U1, and the other end of the capacitor C6 is grounded; one end of the sliding rheostat Rw1 is connected to the sixth pin of the PWM control chip U1, and the other end of the sliding rheostat Rw1 is connected to one end of the resistor R11, and the other end of the resistor R11 is grounded; one end of the capacitor C4 is connected to the The 8th pin of the PWM control chip U1, the other end of the capacitor C4 is grounded; one end of the resistor R12 outputs a level signal; the other end of the resistor R12 is connected to the base of the transistor Q2; one end of the resistor R10 is connected to the emitter of the transistor Q2; one end of the capacitor C1 is connected to +12V and connected to the 13th and 15th pins of the PWM control chip U1, and the other end of the capacitor C1 is grounded; one end of the resistor R2 is connected to the 2nd pin of the PWM control chip U1, the other end of the resistor R2 is connected to +5.1V and connected to the 16th pin of the PWM control chip U1; the 1st pin of the PWM control chip U1 is grounded; one end of the capacitor C2 is connected to the 16th pin of the PWM control chip U1, and the other end of the capacitor C2 is grounded; one end of the capacitor C3 is connected to the 13th pin of the PWM control chip U1, and the other end of the capacitor C3 is grounded; the 12th pin of the PWM control chip U1 is grounded; one end of the resistor R6 is connected to the 10th pin of the PWM control chip U1; one end of the resistor R8 is connected to the 9th pin of the PWM control chip U1.

[0010] Preferably, the other end of the resistor R5 is also connected to a resistor R7, one end of which is connected to the 7th pin of the PWM control chip U1; the other end of the resistor R7 is connected to the 4th pin of the optocoupler U2 and to one end of the capacitor C6; one end of the capacitor C6 is connected to the 5th pin of the PWM control chip U1, and the other end of the capacitor C6 is grounded.

[0011] Preferably, the PWM control chip U1 is a chip EG3525.

[0012] Preferably, the resistance value of the resistor R5 is 1KΩ, and the resistance value of the resistor R7 is 100Ω.

[0013] Preferably, the output current voltage phase difference direction detection circuit comprises a trigger U3, a capacitor C7, a capacitor C8, a capacitor C9, and a resistor R13;

[0014] One end of the capacitor C7 is connected to the first pin of the trigger U3, and the other end of the capacitor C7 is grounded; one end of the resistor R13 is connected to the first pin of the trigger U3, and the other end of the resistor R13 is connected to +3.3V; the second pin of the trigger U3 is input with a voltage square wave signal; the third pin of the trigger U3 is input with a current square wave signal; the sixth pin of the trigger U3 outputs a detection signal and is connected to one end of the resistor R4; the seventh pin of the trigger U3 is grounded; one end of the capacitor C8 is connected to the 14th pin of the trigger U3, and the other end of the capacitor C8 is grounded; one end of the capacitor C9 is connected to +3.3V and is connected to the 14th pin of the trigger U3, and the other end of the capacitor C9 is grounded.

[0015] Preferably, the trigger U3 is a D trigger SN74HC74D.

[0016] The present invention also discloses a multi-band resonant frequency tracking method for ultrasonic machining, which is characterized by comprising the following cyclic steps:

[0017] S1. Start the equipment, and the piezoelectric transducer works at normal frequency;

[0018] S2, real-time detection of the voltage and current signals of the piezoelectric transducer loop by means of an output current and voltage phase difference direction detection circuit;

[0019] S3. According to the detection result, the multi-band resonant frequency tracking circuit drives the piezoelectric transducer to adjust the frequency.

[0020] Preferably, in S2, a system detuning duration threshold is preset, wherein a maximum value of the time threshold is set to 5-20 ms.

[0021] Preferably, in S2, when the system is out of tune at time t2, the output current and voltage phase difference direction detection circuit outputs a high level, and the duration of the output high level signal is within the time threshold, S3 drives the piezoelectric transducer to increase the frequency slightly, and returns to S2 after the adjustment is completed;

[0022] In S2, when the system is out of tune at time t2, the output current and voltage phase difference direction detection circuit outputs a low level, and the duration of the output low level signal is within the time threshold, S3 drives the piezoelectric transducer to reduce the frequency slightly, and returns to S2 after the adjustment is completed.

[0023] Preferably, after completing the small adjustment, if S2 continues to output a high level and the duration exceeds the time threshold, the piezoelectric transducer is driven to increase the frequency significantly;

[0024] After completing the small adjustment, S2 continues to output a low level and the duration exceeds the time threshold, which drives the piezoelectric transducer to significantly reduce the frequency.

[0025] The present invention has the following characteristics and beneficial effects:

[0026] By adopting the above technical scheme, the present invention realizes the rapid determination of the system detuning situation through the current voltage phase difference direction detection signal output by the D flip-flop in the SN74HC74D chip, and can timely change the dead zone resistance between the 5th pin and the 7th pin in the EG3525 chip according to the detuning degree of the piezoelectric transducer, thereby changing the system driving frequency to track the resonant frequency of the piezoelectric transducer and realize rapid and accurate tracking. The realization process of the circuit function is simple and fast, and the ability to quickly and accurately track the forward resonant frequency point of the piezoelectric transducer is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0028] Figure 1 4 is a circuit diagram of a multi-band resonant frequency tracking circuit in an embodiment of the present invention.

[0029] Figure 2 1 is a circuit diagram for detecting the phase difference direction of output current and voltage in an embodiment of the present invention.

[0030] Figure 3 The figure is a flow chart of a multi-band synchronous resonance tracking method according to an embodiment of the present invention.

[0031] Figure 4 It is a schematic diagram of multi-band resonance tracking according to an embodiment of the present invention. DETAILED DESCRIPTION

[0032] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0033] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and the like are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0034] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0035] Example 1

[0036] This embodiment provides a multi-band resonant frequency tracking circuit for ultrasonic machining, such as Figure 1 As shown, it includes an output current voltage phase difference direction detection circuit and a multi-band resonant frequency tracking circuit, wherein the detection signal output end of the output current voltage phase difference direction detection circuit is connected to the signal input end of the multi-band resonant frequency tracking circuit,

[0037] The signal input end of the multi-band resonant frequency tracking circuit includes a PWM control chip U1, a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a resistor R6, a resistor R8, a resistor R9, a resistor R10, a resistor R11, a resistor R12, a transistor Q1, a transistor Q2, a sliding rheostat Rw1, an optical coupler U2, a capacitor C1, a capacitor C2, a capacitor C3, a capacitor C4, a capacitor C5, and a capacitor C6.

[0038] One end of the resistor R4 is connected to the detection signal output end of the output current voltage phase difference direction detection circuit, and the other end of the resistor R4 is connected to one end of the resistor R3 and connected to the base of the transistor Q1; one end of the resistor R3 is connected to the other end of R4, and the other end of the resistor R3 is connected to one end of R1 and connected to the emitter of the transistor Q1; the other end of the resistor R1 is grounded; one end of the resistor R9 is connected to +3.3V and connected to one end of the capacitor C5, and the other end of the resistor R9 is connected to the first pin of the optocoupler U2; the other end of the capacitor C5 is grounded; one end of the resistor R5 is connected to the third pin of the optocoupler U2, and the other end of the resistor R5 is connected to the seventh pin of the PWM control chip U1; one end of the capacitor C6 is connected to the fifth pin of the PWM control chip U1, and the other end of the capacitor C6 is grounded; one end of the sliding rheostat Rw1 is connected to the sixth pin of the PWM control chip U1, and the other end of the sliding rheostat Rw1 is connected to one end of the resistor R11, and the other end of the resistor R11 is grounded; one end of the capacitor C4 is connected to the The 8th pin of chip U1, the other end of capacitor C4 is grounded; one end of resistor R12 outputs a level signal; the other end of resistor R12 is connected to the base of transistor Q2; one end of resistor R10 is connected to the emitter of transistor Q2; one end of capacitor C1 is connected to +12V and connected to the 13th and 15th pins of PWM control chip U1, and the other end of capacitor C1 is grounded; one end of resistor R2 is connected to the 2nd pin of PWM control chip U1, and the other end of resistor R2 is connected to +5.1V and connected to the 16th pin of PWM control chip U1; the 1st pin of PWM control chip U1 is grounded; one end of capacitor C2 is connected to the 16th pin of PWM control chip U1, and the other end of capacitor C2 is grounded; one end of capacitor C3 is connected to the 13th pin of PWM control chip U1, and the other end of capacitor C3 is grounded; the 12th pin of PWM control chip U1 is grounded; one end of resistor R6 is connected to the 10th pin of PWM control chip U1; one end of resistor R8 is connected to the 9th pin of PWM control chip U1. Wherein, the PWM control chip U1 is chip EG3525.

[0039] Furthermore, the other end of the resistor R5 is also connected to a resistor R7, one end of the resistor R7 is connected to the 7th pin of the PWM control chip U1; the other end of the resistor R7 is connected to the 4th pin of the optocoupler U2 and to one end of the capacitor C6; one end of the capacitor C6 is connected to the 5th pin of the PWM control chip U1, and the other end of the capacitor C6 is grounded. The resistance value of the resistor R5 is 1KΩ, and the resistance value of the resistor R7 is 100Ω.

[0040] It can be understood that one end of the resistor R4 is connected to the output current voltage phase difference direction detection circuit, recorded as / Phase_Direction, one end of the resistor R12 is connected to the MCU, recorded as Fre_DA_3525; the 14th pin of the chip EG3525 is recorded as PWM_A; one end of the resistor R6 is connected to the 10th pin of the chip EG3525, and the other end is recorded as Shutdown_3525; one end of the resistor R8 is connected to the 9th pin of the chip EG3525, and the other end is recorded as Duty_DA_3525.

[0041] In the above technical solution, the multi-band resonant frequency tracking circuit is mainly controlled by the EG3525 chip, which is a relatively mature product with a built-in 5.1V reference voltage source, a 100Hz-500KHz wide frequency oscillator, a soft start circuit, an error amplifier, a PWM comparator, an undervoltage lockout circuit, and a power tube output drive circuit. Adding a resistor between the CT pin and the Discharge pin can achieve the dead time adjustment function. In addition, changes in external signals can drive the transistor to turn on and off, thereby affecting the dead zone resistance between the 5th and 7th pins in the EG3525 chip, changing the output frequency of the two complementary PWM signals, and the power ultrasonic wave generated by the PWM-driven IGBT also changes accordingly.

[0042] Therefore, the key changing factor in the circuit is the dead zone resistance of the 5th and 7th pins in the chip EG3525. When the / Phase_Direction signal is at a high level, the transistor Q1 is turned on, and through the optocoupler U2, the dead zone resistance of the 5th and 7th pins of the chip EG3525 is connected in parallel with a 1K ohm resistor, the total resistance value is reduced slightly, the CT discharge time is reduced, and the frequency is changed slightly by changing the duty cycle. Then, the voltage analog control signal Fre_DA_3525 output by ARM controls the ultrasonic frequency. When Fre_DA_3525 is at a high level, the transistor Q2 is turned on, and the dead zone resistance of the 5th and 7th pins of the chip EG3525 is connected in parallel with a 100 ohm resistor, and the frequency changes greatly.

[0043] In addition, the chip EG3525 has a synchronous clock function and can work in master-slave mode or synchronize with an external system clock signal.

[0044] Therefore, in the above technical solution, when the system is detuned in a small range, the driving frequency is less than the system frequency, the / Phase_Direction signal is high, and the driving frequency increases slightly; when the driving frequency is greater than the system frequency, the / Phase_Direction signal is low, and the driving frequency decreases slightly. This rule is repeated, and the frequency tracking process presents an overall stable state. When the system is detuned in a large range, the driving frequency is less than the system frequency, Fre_DA_3525 is high, and the driving frequency increases significantly; when the driving frequency is greater than the system frequency, the Fre_DA_3525 signal is low, and the driving frequency decreases significantly, and then turns to an overall stable state in a small amplitude oscillation. The system driving frequency is thereby changed to track the resonant frequency of the piezoelectric transducer, achieving fast and accurate tracking.

[0045] The present invention is further configured as follows: Figure 2 As shown, the output current voltage phase difference direction detection circuit includes a trigger U3, a capacitor C7, a capacitor C8, a capacitor C9, and a resistor R13;

[0046] One end of the capacitor C7 is connected to the first pin of the trigger U3, and the other end of the capacitor C7 is grounded; one end of the resistor R13 is connected to the first pin of the trigger U3, and the other end of the resistor R13 is connected to +3.3V; the voltage square wave signal is connected to the second pin of the trigger U3 and input with the voltage square wave signal; the third pin of the trigger U3 is input with the current square wave signal; the sixth pin of the trigger U3 outputs the detection signal and is connected to one end of the resistor R4; the seventh pin of the trigger U3 is grounded; one end of the capacitor C8 is connected to the 14th pin of the trigger U3, and the other end of the capacitor C8 is grounded; one end of the capacitor C9 is connected to +3.3V and connected to the 14th pin of the trigger U3, and the other end of the capacitor C9 is grounded. Wherein, the trigger U3 is a D trigger SN74HC74D.

[0047] In the above technical solution, the processing is mainly performed through a D flip-flop. According to the working principle of the D flip-flop, it can be understood that at the rising edge of the current signal, if the voltage signal is at a high level, the output is high, otherwise it is low. When the voltage signal is at a high level at the rising edge of the current signal, it means that the current lags behind the voltage, and the piezoelectric transducer presents an inductive characteristic; when the voltage signal is at a low level at the rising edge of the current signal, it means that the current leads the voltage, and the piezoelectric transducer presents a capacitive characteristic.

[0048] Therefore, the high level of the D flip-flop output indicates that the piezoelectric transducer exhibits inductive characteristics, and the low level of the D flip-flop output indicates that the piezoelectric transducer exhibits capacitive characteristics. Therefore, the circuit uses the current square wave as the clock signal of the D flip-flop and the voltage square wave as the input to obtain the D flip-flop output signal that can characterize the impedance characteristics of the piezoelectric transducer.

[0049] Example 2

[0050] This embodiment discloses a multi-band resonant frequency tracking method for ultrasonic machining, such as Figure 3 As shown, the cycle steps include:

[0051] S1. Start the equipment, and the piezoelectric transducer works at normal frequency;

[0052] S2, real-time detection of the voltage and current signals of the piezoelectric transducer loop by means of an output current and voltage phase difference direction detection circuit;

[0053] S3. According to the detection result, the multi-band resonant frequency tracking circuit drives the piezoelectric transducer to adjust the frequency.

[0054] In the above technical solution, it is assumed that at time t1 the ultrasonic power supply operates normally with the driving signal frequency f and the frequency tracking is good, and at time t2 the piezoelectric transducer begins to be affected by the outside world and its characteristics change.

[0055] At time t2, when the system is slightly detuned, such as Figure 4 In the state represented by the dashed and dotted lines, the driving frequency is less than the system frequency, the current-voltage phase difference direction detection signal output by the D flip-flop is high, the transistor Q1 is turned on, a 1k ohm resistor is connected in parallel to the EG3525 dead zone resistor, and the driving frequency increases slightly;

[0056] When the driving frequency is greater than the system frequency, the current-voltage phase difference direction detection signal output by the D flip-flop is at a low level, transistor Q1 is cut off, and the driving frequency is slightly reduced. This rule is repeated, and the frequency chasing process presents an overall stable state.

[0057] It can be understood that by real-time detection and synchronous adjustment, the system driving frequency is changed to track the resonant frequency of the piezoelectric transducer, thereby achieving fast and accurate tracking, thereby ensuring the normal operation of the system.

[0058] Furthermore, in S2, a system detuning duration threshold is preset, wherein the maximum value of the time threshold is set to 5 ms.

[0059] Wherein, in S2, when the system is out of tune at time t2, the output current voltage phase difference direction detection circuit outputs a high level, and the duration of the output high level signal is within the time threshold, in S3, the piezoelectric transducer is driven to increase the frequency slightly, and the frequency is returned to S2 after the adjustment is completed;

[0060] Specifically, at time t2, the current-voltage phase difference direction detection signal output by the D flip-flop is high level and lasts for more than 5ms, indicating that the system is detuned to a large extent. Figure 4In the figure, the initial state curve suddenly changes to the dot-half-line, the software controls the driving voltage to a high level, turns on the transistor Q2, and connects a 100-ohm resistor in parallel with the EG3525 dead zone resistor. The driving frequency increases significantly, and then turns to an overall stable state in a small amplitude oscillation.

[0061] Among them, in S2, when the system is detuned at time t2, the output current and voltage phase difference direction detection circuit outputs a low level, and the duration of the output low level signal is within the time threshold, S3 drives the piezoelectric transducer to reduce the frequency slightly, and returns to S2 after the adjustment is completed.

[0062] Specifically, at time t2, the drive frequency is greater than the system frequency, the software controls the drive voltage to be low level, and the duration is greater than 5ms, indicating that the system is detuned to a large extent. Figure 4 In the figure, the initial state curve suddenly changes to the half-drawn line, the transistor Q2 is cut off, the driving frequency is greatly reduced, and then it turns to an overall stable state in a small amplitude oscillation.

[0063] In the above technical solution, by setting the time threshold, the detuning state can be further accurately judged, and then fast and accurate tracking can be performed, thereby improving the ability to quickly and accurately track the forward resonant frequency point of the piezoelectric transducer.

[0064] Example 3

[0065] The difference between this embodiment and embodiment 2 is that in S2, a system detuning duration threshold is preset, wherein the maximum value of the time threshold is set to 20 ms.

[0066] In the above technical solution, by setting the maximum range of the time threshold to 20ms, there is enough time to monitor the level signal, so the judgment result of the system detuning state is more accurate, the error rate of detuning judgment is greatly reduced, and adjustments are made quickly, and then the overall stable state is presented in a small amplitude oscillation.

[0067] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions and variations of these embodiments including components are made without departing from the principles and spirit of the present invention, and still fall within the scope of protection of the present invention.

Claims

1. A multi-band resonant frequency tracking circuit for ultrasonic machining, characterized in that: It includes an output current voltage phase difference direction detection circuit and a multi-band resonant frequency tracking circuit, wherein the detection signal output end of the output current voltage phase difference direction detection circuit is connected to the signal input end of the multi-band resonant frequency tracking circuit. The signal input end of the multi-band resonant frequency tracking circuit includes a PWM control chip U1, a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a resistor R6, a resistor R8, a resistor R9, a resistor R10, a resistor R11, a resistor R12, a transistor Q1, a transistor Q2, a sliding rheostat Rw1, an optical coupler U2, a capacitor C1, a capacitor C2, a capacitor C3, a capacitor C4, a capacitor C5, and a capacitor C6. One end of the resistor R4 is connected to the detection signal output end of the output current voltage phase difference direction detection circuit, and the other end of the resistor R4 is connected to one end of the resistor R3 and connected to the base of the transistor Q1; one end of the resistor R3 is connected to the other end of R4, and the other end of the resistor R3 is connected to one end of R1 and connected to the emitter of the transistor Q1; the other end of the resistor R1 is grounded; one end of the resistor R9 is connected to +3.3V and connected to one end of the capacitor C5, and the other end of the resistor R9 is connected to the first pin of the optocoupler U2; the other end of the capacitor C5 is grounded; one end of the resistor R5 is connected to the third pin of the optocoupler U2, and the other end of the resistor R5 is connected to the seventh pin of the PWM control chip U1; one end of the capacitor C6 is connected to the fifth pin of the PWM control chip U1, and the other end of the capacitor C6 is grounded; one end of the sliding rheostat Rw1 is connected to the sixth pin of the PWM control chip U1, and the other end of the sliding rheostat Rw1 is connected to one end of the resistor R11, and the other end of the resistor R11 is grounded; one end of the capacitor C4 is connected to the The 8th pin of the chip U1, the other end of the capacitor C4 is grounded; one end of the resistor R12 outputs a level signal; the other end of the resistor R12 is connected to the base of the transistor Q2; one end of the resistor R10 is connected to the emitter of the transistor Q2; one end of the capacitor C1 is connected to +12V and connected to the 13th and 15th pins of the PWM control chip U1, and the other end of the capacitor C1 is grounded; one end of the resistor R2 is connected to the 2nd pin of the PWM control chip U1, and the other end of the resistor R2 is connected to +5.1V and connected to the 16th pin of the PWM control chip U1; the 1st pin of the PWM control chip U1 is grounded; one end of the capacitor C2 is connected to the 16th pin of the PWM control chip U1, and the other end of the capacitor C2 is grounded; one end of the capacitor C3 is connected to the 13th pin of the PWM control chip U1, and the other end of the capacitor C3 is grounded; the 12th pin of the PWM control chip U1 is grounded; one end of the resistor R6 is connected to the 10th pin of the PWM control chip U1; one end of the resistor R8 is connected to the 9th pin of the PWM control chip U1; The output current voltage phase difference direction detection circuit includes a trigger U3, a capacitor C7, a capacitor C8, a capacitor C9, and a resistor R13; One end of the capacitor C7 is connected to the first pin of the trigger U3, and the other end of the capacitor C7 is grounded; one end of the resistor R13 is connected to the first pin of the trigger U3, and the other end of the resistor R13 is connected to +3.3V; the second pin of the trigger U3 is input with a voltage square wave signal; the third pin of the trigger U3 is input with a current square wave signal; the sixth pin of the trigger U3 outputs a detection signal and is connected to one end of the resistor R4; the seventh pin of the trigger U3 is grounded; one end of the capacitor C8 is connected to the 14th pin of the trigger U3, and the other end of the capacitor C8 is grounded; one end of the capacitor C9 is connected to +3.3V and is connected to the 14th pin of the trigger U3, and the other end of the capacitor C9 is grounded.

2. The multi-band resonant frequency tracking circuit for ultrasonic machining according to claim 1, characterized in that: The other end of the resistor R5 is also connected to a resistor R7, one end of which is connected to the 7th pin of the PWM control chip U1; the other end of the resistor R7 is connected to the 4th pin of the optocoupler U2 and to one end of the capacitor C6; one end of the capacitor C6 is connected to the 5th pin of the PWM control chip U1, and the other end of the capacitor C6 is grounded.

3. The multi-band resonant frequency tracking circuit for ultrasonic machining according to claim 1, characterized in that: The PWM control chip U1 is a chip EG3525.

4. The multi-band resonant frequency tracking circuit for ultrasonic machining according to claim 2, characterized in that: The resistance value of the resistor R5 is 1KΩ, and the resistance value of the resistor R7 is 100Ω.

5. The multi-band resonant frequency tracking circuit for ultrasonic machining according to claim 4, characterized in that: The trigger U3 is a D trigger SN74HC74D.

6. A tracking method for a multi-band resonant frequency tracking circuit used in ultrasonic machining according to any one of claims 1 to 5, characterized in that: The cycle includes the following steps: S1. Start the equipment, and the piezoelectric transducer works at normal frequency; S2, real-time detection of the voltage and current signals of the piezoelectric transducer loop by means of an output current and voltage phase difference direction detection circuit; S3. According to the detection result, the multi-band resonant frequency tracking circuit drives the piezoelectric transducer to adjust the frequency.

7. The multi-band resonant frequency tracking circuit for ultrasonic machining according to claim 6, characterized in that: In S2, a system detuning duration threshold is preset, wherein a maximum value of the time threshold is set to 5-20 ms.

8. The multi-band resonant frequency tracking circuit for ultrasonic machining according to claim 6, characterized in that: In S2, when the system is out of tune at time t2, the output current and voltage phase difference direction detection circuit outputs a high level, and the duration of the output high level signal is within the time threshold, in S3, the piezoelectric transducer is driven to increase the frequency slightly, and the frequency is returned to S2 after the adjustment is completed; In S2, when the system is out of tune at time t2, the output current and voltage phase difference direction detection circuit outputs a low level, and the duration of the output low level signal is within the time threshold, S3 drives the piezoelectric transducer to reduce the frequency slightly, and returns to S2 after the adjustment is completed.

9. The multi-band resonant frequency tracking circuit for ultrasonic machining according to claim 8, characterized in that: After completing the small adjustment, S2 continues to output a high level and the duration exceeds the time threshold, which drives the piezoelectric transducer to increase the frequency significantly; After completing the small adjustment, S2 continues to output a low level and the duration exceeds the time threshold, which drives the piezoelectric transducer to significantly reduce the frequency.

Images