JPH0580361B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ultrasonic cleaning machine equipped with a control circuit.

[Prior art]

Traditionally, so-called B-class push-pull circuits using transistors have often been used in output circuits that supply particularly powerful energy, such as in ultrasonic oscillators used in ultrasonic cleaning machines, but in recent years, the performance has improved. With the development of excellent switching transistors, class B and class C single-ended push-pull circuits (hereinafter referred to as class B and C SEPP circuits) using these transistors and class D push-pull circuits that use these transistors for switching operation have been developed. Circuits (hereinafter referred to as D-class PP circuits) are more efficient than conventional B-class circuits, so they are replacing B-class circuits as the mainstream.

By the way, B and C class SEPP circuits and D class PP circuits are constant voltage drive circuits, and the oscillator output P ₀ is B and C class SEPP circuits: P ₀ ≒ V ² _CC /8R _L ...... (1) D class In the PP circuit, P ₀ ≒ 8V ² _T / π ² R _L ......(2) However, in the formula, R _L : Load impedance of the oscillator V _CC : Power supply voltage V _T : As is well known, it is expressed by the output voltage. It is.

In equations (1) and (2), since the voltages V _CC and V _T are constant, the output circuit P ₀ is inversely proportional to the load impedance R _L as shown in Figure 6, and as the value of R _L increases, As a result, the output _P0 gradually becomes smaller.

Therefore, when such an output circuit is used, there is a problem in that the output becomes maximum at the point where the impedance is the lowest or the admittance is the highest, regardless of the resonance point of the vibrator.

Further, there are also the following problems regarding the vibration frequency.

Looking at the characteristics of the load electrically, it can be assumed that the majority of the load is impedance L for the magnetostrictive type and capacitance C for the electrostrictive type. Therefore, by canceling the respective L and C components and setting the phase difference to zero, from the oscillator side. In order to make the overall impedance seen appear to be pure resistance, a circuit is constructed as shown in FIG.

That is, FIG. 7 shows the case of a magnetostrictive type, where 21 is an oscillator, 22 is a vibrator, and C is a resonant matching capacitor for canceling the inductance component of the vibrator 22. FIG. 8 shows the case of an electrostrictive type, in which 23 is a vibrator, and L is a reciprocal matching inductance for canceling the capacitance component of the vibrator 23.

Thus, the free impedance Z _f on the load side in the magnetostrictive type shown in Fig. 7 is as shown by the solid line in Fig. ₉ when the frequency _f is plotted on _the The free admittance Y _f on the load side of the electrostrictive type shown in Figure 8 is the 10th
As shown by the solid line in the figure, it reaches a maximum at B ₁ and B ₂ .

The curves shown by dotted lines in Figures 9 and 10 are the frequency characteristics of impedance and admittance determined only for each vibrator, and the vicinity of the frequency where the value is minimum or maximum is the so-called physical resonance frequency. corresponds to

[Problem that the invention seeks to solve]

Here, when using a class D SEPP circuit (class D single-ended push-pull circuit) or a class D PP circuit, the output will be at A ₁ or A ₂ , which corresponds to the frequency at which the impedance is minimum for the magnetostrictive type, and at the electrostrictive type. In this type, the maximum output is obtained at B ₁ or B ₂ , which corresponds to the frequency where the admittance is maximum, but since these frequencies are deviant values that do not match the physical resonance frequency unique to the vibrator, In terms of vibration, this is less efficient than driving at a resonant frequency, and therefore cannot be said to be the optimum driving frequency.

However, if you adjust the frequency using an oscillator with a frequency adjustment function, the frequency will be adjusted to the frequency that minimizes the load impedance or the frequency that maximizes the admittance, and even automatic frequency tracking systems will operate to obtain the apparent maximum output. Therefore, there is a problem that the vibrator cannot be driven at the physical resonance frequency of the vibrator, which is the most desirable vibration efficiency at the maximum.

Furthermore, in conventional automatic frequency tracking, a bandpass filter has been used to adjust the oscillation frequency to a desired frequency. When using this filter, there was a problem that if the frequency deviated from the optimum frequency, the phase would shift and the filter would no longer operate at the optimum resonance frequency.

The first object of the present invention is to solve the above-mentioned problems of the conventional cleaners and to provide an ultrasonic cleaner that is driven at the optimal resonance frequency of the vibrator.

A second object of the present invention is to provide an ultrasonic cleaner that automatically tracks a resonance frequency and performs efficient cleaning using the resonance frequency.

[Means for solving problems]

The present invention provides a phase shift circuit, a phase lock loop circuit including a phase comparator and a voltage controlled oscillator, a power supply voltage control circuit, an output circuit using a class D single-ended push-pull circuit or a class D push-pull circuit, An ultrasonic cleaning machine comprising an ultrasonic vibrator as a load of the output circuit, the ultrasonic cleaner being disposed between the output circuit and the vibrator,
a current detection circuit that detects an output current from the output circuit; and a current detection circuit that receives a signal based on the detected current from the current detection circuit, and adjusts a power supply voltage of the output circuit according to the signal so that the output circuit maintains a constant output current. a power supply voltage control circuit that controls the current detection circuit so that the current detection circuit and the vibrator have a vibration detection circuit that detects a signal proportional to the vibration speed of the vibrator; A phase shift circuit that receives an output voltage signal and changes the phase of the voltage signal, and an oscillation frequency that maintains a phase difference of 90 degrees between the output f _i of the phase shift circuit and the output f _v of the phase lock loop circuit. This ultrasonic cleaning machine is characterized by being equipped with an automatic frequency tracking circuit including a phase lock loop circuit for controlling.

〔Example〕

Embodiments of the present invention will be described using the drawings.

In Figure 1, 1 is a phase shift circuit, 2 is a phase lock loop circuit (hereinafter referred to as a PLL circuit), 3 is a power supply voltage control circuit, and 4 is a class D SEPP circuit or a class D
An output circuit using a push-pull circuit such as a PP circuit, 5 a current detection circuit, 6 a vibration detection circuit, and 7 an ultrasonic vibrator.

In this system, the current output from the output circuit 4 is detected by the current detection circuit 5, and the detection signal is fed back to the power supply voltage control circuit 3 as a voltage.
The power supply voltage of the output circuit 4 is controlled so that the output current of the output circuit 4 becomes a constant value. That is, the output circuit 4, the current detection circuit 5, and the power supply voltage control circuit 3 operate while forming a loop.

In addition, the voltage detected by the vibration detection circuit 6 changes its phase through the phase shift circuit 1, and is fed back to the PLL circuit 2, so that the frequency of the built-in frequency oscillator automatically tracks the input frequency, and the optimum value for the vibrator 7 is set. It is designed to provide a resonant frequency.

FIG. 2 shows an example in which each of the circuits shown in FIG. 1 is implemented.

To explain the output circuit 4, Fig. 2 shows
An example of a SEPP circuit is shown with the bias circuit omitted. 51 is an input transformer, 52
and 53 are transistors, 54 and 55 are resistors, 56
is a capacitor, 57 is a smoothing circuit that serves as a DC power source, and 58 is an output transformer.

Input signals of opposite phases are applied to the two transistors 52 and 53 through the input transformer 51, and one of the two transistors operates alternately for each positive and negative half cycle of the input signal.

That is, when the transistor 52 is operating and the collector current I _C1 is flowing, the capacitor 56 is charged from the smoothing circuit 57 as a current power source through the transformer 58, and when the transistor 53 is operating next, the capacitor 56 is charged. The stored charge is discharged through the output transformer 58, and a collector current I _C2 flows. In this way, the positive and negative half cycles are combined to reproduce the input waveform.

In the current detection circuit 5, 62 is a reciprocal matching capacitor, which transmits the input voltage signal through the transformer 58, detects the current, and sends it as a voltage signal to the power supply voltage control circuit 3 through the transformer 64. I am learning to give.

In the power supply voltage control circuit 3, 40 is a diode, 41 is a thyristor, 42 is a pulse transformer, 43 is a unidirectional transistor, 4
4, 46, 49 are resistors, 47 is a variable resistor, 4
8 and 50 are transistors, and 61 is a Zener diode.

FIG. 3 is an explanatory diagram of the operation, and when no signal is applied to the gate, the thyristor 41 is in a cut-off state and no voltage is supplied to the smoothing circuit 57, but for half a cycle of the power supply voltage (see a in FIG. 3). When a signal (see Fig. 3b) is applied to the gate at a certain phase shift α, the thyristor 41 becomes conductive at that phase, and the smoothing circuit 57 receives the power supply voltage (see Fig. 3c) through the thyristor 41 and the diode 40. ) is supplied.

Therefore, by changing the timing of applying voltage to the gate of the thyristor 41, it is possible to control the output power supply voltage to be changed.

When the input voltage at the transformer 64 becomes larger than a certain predetermined value, voltage is applied from the Zener diode 61 to the transistor 50, lowering the internal resistance of the transistor 50, and the voltage applied to the base of the transistor 48 decreases, causing the internal resistance of the transistor 48 to decrease. As shown in FIG. 5, the pulse width of the unijunction transistor 43 is widened and the timing of applying voltage to the gate of the thyristor 41 is changed, and the smoothing circuit 5
The output voltage to 7 is lowered. The voltage obtained by the smoothing circuit 57 is applied to the output circuit 4 as a DC power source.

In the vibration detection circuit 6, a bridge circuit that detects a signal proportional to the vibration speed of the magnetostrictive vibrator 63 as the vibrator 7 includes capacitors 68, 69,
It is formed by an inductance 70 and a transformer 71.

The voltage taken out by the transformer 71 is input to the phase shift circuit 1.

In the phase shift circuit 1, a variable resistor 66 and a capacitor 67 are provided, and by changing the value of the variable resistor 66, the phase angle can be changed.

In the PLL circuit 2, a phase comparator (PC) 75, a low pass filter (LPF) 76, and a voltage controlled oscillator (VCO) are installed using a phase lock loop IC.
A closed loop is formed by 77, and the oscillation frequency f _v (different from the free run frequency f ₀ ) of the power supply voltage oscillator ₇₇ follows and matches the frequency f i of the input voltage to be compared, and the phase difference between the two is 90°. It has become stable in its normal state.

Since this embodiment is configured as described above,
When the load impedance becomes low, the current detection circuit 5 detects that the output current of the output circuit 4 increases.
This is detected by the power supply voltage control circuit 3, which lowers the power supply voltage of the output circuit 4.
On the other hand, if the load impedance is high, the power supply voltage is increased accordingly to suppress the decrease in the output current of the output circuit 4, and the maximum output is obtained when the impedance is maximum. Do it like this.

In this way, the property that is inversely proportional to the impedance seen in the output of the PP circuit is suppressed, so by setting the operating conditions of the detection circuit and power supply voltage control circuit appropriately, the output can be maximized at a certain impedance as shown in Figure 4. If we create a load characteristic such that the impedance value at maximum output is equal to or greater than the dynamic impedance R _n at the time of resonance of the ultrasonic transducer, the maximum output will be reached at the resonance frequency of the ultrasonic transducer. It can be driven at a resonant frequency.

Furthermore, this embodiment has the following automatic frequency tracking effect.

That is, a signal proportional to the vibration speed of the vibrator detected by the vibration detection circuit 6 enters the phase shifter of the phase shift circuit 1, where the phase is shifted by 90 degrees with respect to the vibrator drive voltage, and the signal is output to the PLL circuit. For phase lock loop 2
Enter the IC. This PLL circuit 2 includes a phase comparator 75,
It is equipped with a voltage controlled oscillator 77 and has a characteristic of automatically adjusting the oscillation frequency so that the phase difference between the input signal f _i and the reference signal f _v becomes 90°.

The signal f _i from the phase shift circuit 1 is compared with the phase of the drive voltage by the internal phase comparator 75 of the PLL circuit 2, and a phase-corresponding control voltage is generated, and the oscillation frequency f _v of the internal voltage controlled oscillator 77 is is controlled.

This automatic frequency tracking circuit allows the vibrator current and voltage to always be in the same phase point, allowing the vibrator to be driven at the optimum resonance point.

〔Effect of the invention〕

According to the first invention, even if the load impedance changes, the current detection circuit detects the output current, that is, the drive current of the resonator, and feeds it back to the power supply voltage control circuit, while using a class D SEPP or class D PP circuit. By lowering or increasing the power supply voltage of the output circuit, it is possible to suppress the increase or decrease in the output current of the output circuit, thereby keeping the output current of the output circuit constant, realizing the required load characteristics and performing stable operation. Furthermore, in order to obtain a drive current proportional to the vibration amplitude of the transducer and to achieve the required load characteristics, the voltage output proportional to the vibration amplitude is kept at a phase difference of 90 degrees and fed back to the PLL circuit, which is optimal for the ultrasonic transducer. It is possible to provide an ultrasonic cleaning machine that can perform ultrasonic oscillation at a resonant frequency and has high efficiency, which is extremely effective in practical use.

[Brief explanation of drawings]

Fig. 1 is a flowchart of an embodiment of the present invention, Fig. 2 is an example of its circuit diagram, Fig. 3 is an explanatory diagram of the operation of a part of the power supply voltage control device, Fig. 4 is an example of load characteristics, and Fig. 5 is an example of the circuit diagram. Figure 6 shows the operating characteristics of a part of the power supply voltage control device, Figure 6 shows the load characteristics of a conventional general oscillator, Figure 7 shows the matching circuit of the magnetostrictive resonator, and Figure 8 shows the matching circuit of the electrostrictive resonator. In the matching circuit, FIG. 9 shows the frequency characteristics of magnetostrictive free impedance, and FIG. 10 shows the frequency characteristics of electrostrictive free admittance. 1... Phase shift circuit, 2... Phase lock loop circuit (PLL), 3... Power supply voltage control circuit, 4... Output circuit,
5... Current detection circuit, 6... Vibration detection circuit, 7... Vibrator, 21... Oscillator, 22... Vibrator, 23... Vibrator, 40... Diode, 41... Thyristor, 42
...Pulse transformer, 43... Unijunction transistor, 44... Resistor, 46... Resistor, 47... Variable resistor, 48... Transistor, 49... Resistor, 50
...Transistor, 51...Input transformer, 52...Transistor, 53...Transistor, 54...Resistor,
55... Resistor, 56... Capacitor, 57... Smoothing circuit, 58... Transformer, 61... Zener diode, 62... Capacitor, 63... Magnetostrictive vibrator, 6
4...Transformer, 65...Resistance circuit, 66...Variable resistor, 67...Capacitor, 68...Capacitor, 69
...Capacitor, 70...Inductance, 71...Transformer, 75...Phase comparator, 76...Low pass filter, 77...Voltage controlled oscillator.

Claims (1)

[Claims] 1. A phase shift circuit 1, a phase lock loop circuit 2 including a phase comparator 75, and a voltage controlled oscillator 77.
An ultrasonic cleaning machine comprising: a power supply voltage control circuit 3; an output circuit 4 using a class D single-end push-pull circuit or a class D push-pull circuit; and an ultrasonic vibrator 7 as a load of the output circuit 4. A current detection circuit 5 disposed between the output circuit 4 and the vibrator 7 and configured to detect the output current from the output circuit 4; and a current detection circuit 5 configured to receive a signal based on the detected current from the current detection circuit. , a power supply voltage control circuit 3 that controls the power supply voltage of the output circuit according to the signal so that the output current of the output circuit is constant; and a power supply voltage control circuit 3 arranged between the current detection circuit 5 and the vibrator 7. a vibration detection circuit 6 that detects a signal proportional to the vibration speed of the vibrator 7; a phase shift circuit 1 that receives a voltage signal output from the vibration detection circuit and changes the phase of the voltage signal; Equipped with an automatic frequency tracking circuit including a phase lock loop circuit 2 that controls the oscillation frequency so as to maintain the phase difference between the output f _i of the phase circuit 1 and the output f _v of the phase lock loop circuit 2 at 90 degrees. An ultrasonic cleaning machine featuring