JP3890487B2 - Control method of vibrator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a vibration conveying apparatus that supplies parts using vibration, for example, a vibrator such as a bowl feeder, a so-called parts feeder, and a frequency (frequency) of a resonance frequency (natural frequency) of the vibration conveying apparatus (vibration system). The control device for the vibrator and the control method of the vibrator for controlling and driving the vibratory conveying device.
[0002]
[Prior art]
A component feeder using vibration such as a bowl feeder (hereinafter referred to as a vibrator) will continue to vibrate at the natural frequency of the vibrator in terms of component supply efficiency and low power consumption. Is advantageous.
Conventionally, when the vibrator is vibrated at the natural frequency of the vibration system, one of the following methods has been proposed (see Japanese Patent Laid-Open No. 8-48413).
[0003]
The vibrating machine that is stopped is hit with a pulse current of a predetermined frequency, for example, 50/60 Hz half-wave sine wave or triangular wave. That is, power is supplied to the excitation means for a short time to vibrate the vibrator, and the natural frequency of the vibrator is picked up (detected) by a vibration sensor such as an acceleration sensor.
The vibrator control device divides the vibration detection signal from the vibration sensor (acceleration sensor) by half and shifts (delays) a predetermined phase, specifically, π / 2, to the vibrator. Give feedback.
[0004]
Note that delaying this phase by π / 2 is determined from the viewpoint of vibration engineering, and dividing the signal from the vibration sensor by ½ means that the vibration is vibrated in the case of full-wave control of the vibrator. This is necessary when an acceleration sensor is used as the sensor and has been conventionally known and practiced by those skilled in the art.
In other words, this vibrator control method is intended to control the drive frequency of the vibrator by shifting the output signal from the vibration sensor by a predetermined phase and feeding it back to the vibrator.
[0005]
[Problems to be solved by the invention]
The above-described conventional vibrator control device has the following problems.
The frequency of the current applied to the actuator (that is, the excitation means) is determined based on the signal from the vibration sensor. The frequency of the signal from the vibration sensor is the frequency at which the vibration system (that is, the entire vibration mechanism) vibrates (the frequency at which the vibration system vibrates is simply referred to as the vibration frequency of the vibration system).
[0006]
The resonance frequency of the vibration system changes as the parts are sent out, and may change due to fluctuations in other conditions (for example, changes in the spring constant).
The control of the vibration frequency of the vibrator in the conventional vibrator control device is fixed by hardware, and cannot be finely adjusted.
That is, the signal detected by the vibration sensor is used as a vibration machine drive signal after adjusting the phase and level, but the vibration frequency is determined and adjusted by the detection signal of the vibration sensor. I couldn't.
That is, the frequency of the signal detected by the vibration sensor is output to the vibrator substantially as it is (although it is divided by half).
[0007]
Further, the signal of the vibration sensor is divided by ½, delayed by π / 2, and applied to the excitation means.
In terms of vibration engineering, theoretically, it is known that the difference between the driving force of the vibration system and the phase of the vibration at resonance is π / 2, but in reality, the response of the signal of each part (circuit) When there is a delay, when the vibration system is vibrated at the resonance frequency, the phase difference between the vibration sensor signal input to the control device (CPU) and the control device (CPU) signal output to the power conversion means is calculated. There was a question as to whether it should be π / 2.
[0008]
Therefore, the conventional vibrator control device cannot vibrate the vibrator at the resonance frequency of the vibrator, for example, when a large amount of work is put into the vibrator at a time, and temporarily lowers the conveyance efficiency. There was a problem of becoming.
[0009]
[Means for Solving the Problems]
The invention of claim 1 solves the above-mentioned problems in a control device for vibrating a vibrator to which a vibration sensor is attached by means of excitation means provided in the vibrator, and is as follows. .
[0010]
Similar to the conventional vibrator control device, this vibrator control device is an A / D conversion means for A / D converting the vibration detection signal from the vibration sensor, and the vibration detection signal is passed through the A / D conversion means. And a power conversion means (power amplification / control means) for outputting an analog signal for driving the excitation means based on a pulse signal output from the microcomputer system.
Further, the microcomputer system outputs a start pulse signal to the excitation means via the power conversion means to displace and open, that is, move the vibrator. Next, the microcomputer system detects the resonance frequency of the vibrator by the vibration sensor and continuously vibrates the vibrator at the resonance frequency, that is, the vibration at that time detected by the vibration sensor. The pulse signal is output to the power conversion means so that the analog signal having a frequency equal to the resonance frequency of the machine is output to the excitation means.
[0011]
In the control device having such a configuration, the microcomputer system is configured to be able to detect the voltage level, frequency, phase of the vibration detection signal and the phase of the analog signal.
Further, the microcomputer system is configured to be able to control the pulse signal so as to cancel the fluctuation of the voltage level of the vibration detection signal or the phase difference between the vibration detection signal and the analog signal.
That is, when the phase difference between the vibration detection signal immediately after the start pulse signal is output and the analog signal output from the power conversion unit to the excitation unit varies, the microcomputer system changes the voltage level. Alternatively, the voltage level or frequency of the analog signal can be changed in a direction that reduces the fluctuation of the phase difference.
[0012]
Here, the microcomputer system is configured by storing a predetermined program in a memory (ROM) that is a component of the microcomputer system so that the microcomputer, substantially the CPU, can perform a desired operation. It means to keep.
[0013]
The invention of claim 1 is the above-mentioned In the control device for a vibrator, the A / D conversion unit includes a comparator as a component, the power conversion unit includes a PWM inverter as a component, and the microcomputer system includes a PWM wave generation unit. Therefore, the pulse signal is a method for controlling the vibrator when it includes a PWM wave, and is the following method.
[0014]
In the microcomputer system, the vibration detection signal is output from a reference time (t0) at which the phase of the analog signal is a predetermined value until a period T of the analog signal that is the driving means driving signal elapses. The PWM wave is PI controlled so that the ratio τ / T between the time τ until the time when the threshold level of the comparator is cut (crossed) and the period T of the analog signal becomes a constant value.
That is, the frequency (cycle) of the duty fluctuation of the PWM wave is changed by PI control.
The microcomputer system, as a result, controls the frequency of the analog signal by performing PI control on the frequency of the duty fluctuation of the PWM wave, substantially the PWM wave.
[0015]
Of course, the PWM wave generation means may be included in the power conversion means, or may be provided between the microcomputer system and the power conversion means. Further, the PWM wave may be generated by software by a microcomputer system.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
As is well known, the power conversion means includes an AC-DC converter (forward converter), an AC-AC converter (AC power regulator and frequency converter), a DC-AC converter (inverse converter, so-called inverter). ) And DC-DC converters.
Which kind of device is used as the power conversion means of the control device of the vibrator is a design choice for those skilled in the art. Since the excitation means is usually driven by alternating current, it is common to use an alternating current-alternating current converter or a direct current-alternating current converter, that is, an inverter.
The following description will be made assuming that an inverter is used as the power conversion means of the control device for the vibrator.
[0017]
First, The microcomputer system is configured to generate a start pulse. That is, it has a program that can perform such an operation. When the vibrator is stopped, the microcomputer system outputs the start pulse to the power conversion means for a short period of time, for example, about half the period of the power supply current, and the power conversion means receives the power from the microcomputer system. In accordance with the start pulse signal, the excitation means is driven at a power supply frequency, for example. The exciting means displaces the vibrator and freely vibrates by releasing from the displacement.
[0018]
The vibrator starts to vibrate when it is struck at the power frequency, but as soon as no current is supplied to the excitation means, it vibrates at the natural frequency, and if a signal is output from the microcomputer system. If not, it will stop. However, as will be described later, the microcomputer system continues to output a pulse signal for generating an analog signal having a predetermined frequency (that is, the resonance frequency of the vibrator) to the power conversion means, so that the vibrator does not stop.
[0019]
On the other hand, the signal from the vibration sensor is an analog signal, converted into a digital signal by the A / D conversion means, and taken into the microcomputer system.
The microcomputer system outputs a pulse signal having a predetermined cycle to the power conversion means based on the signal from the vibration sensor subjected to A / D conversion.
Note that pulse signals (pulse signals whose duty fluctuation frequency is the resonance frequency of the vibration system) output from the microcomputer system to the power conversion means may be complementarily output by two to four signal lines. In general, it is desirable in terms of efficiency.
[0020]
This pulse signal output from the microcomputer system to the power conversion means (that is, the power conversion means drive signal) is a pulse signal that causes the power conversion means to generate an analog signal having a frequency half that of the signal from the vibration sensor. The power conversion means outputs an analog signal having a frequency half that of the signal from the vibration sensor to the excitation means.
At this time, the vibration system can be regarded as having almost the same vibration conditions as when it was struck by the start pulse, so that the vibration system is vibrated at the resonance frequency. At this time, the phase difference between the vibration detection signal and the analog signal is an appropriate value θ, possibly π / 2.
[0021]
That is, the phase of the vibration detection signal depends on the frequency of the analog signal, and when the analog signal is the resonance frequency of the vibration system, the above-described value θ is obtained.
The microcomputer system stores the value of θ, and controls the frequency of the analog signal to the excitation means by controlling the pulse signal using θ as a target value (PI control may be used).
[0022]
In this way, the microcomputer system has a phase difference θ between the analog signal that is the excitation means driving signal and the vibration detection signal (a signal obtained by dividing the frequency by 1/2) when the vibration system vibrates at the resonance frequency. Is stored, and when the value of θ changes, the frequency of the analog signal is changed through control of a pulse signal output to the power conversion means in a direction to cancel the change.
[0023]
The microcomputer system can also adjust the frequency of the analog signal output to the excitation means by monitoring (detecting) the voltage level of the signal (vibration detection signal) from the vibration sensor. Of course, the voltage level can also be adjusted.
Immediately after the start pulse signal is output, the analog signal output to the excitation means generated by the microcomputer system outputting the pulse signal to the power conversion means is half the frequency of the signal detected by the vibration sensor. The microcomputer system can be configured such that the frequency (or voltage level) of the analog signal can be adjusted according to the voltage level of the vibration detection signal.
[0024]
In other words, if the voltage level of the signal from the vibration sensor decreases, the microcomputer system can be configured to adjust the frequency of the analog signal in the direction of increasing the voltage level.
[0025]
Claim 1 The control method of the vibrator is a method in which the frequency of the pulse signal, and thus the analog signal output from the power conversion means to the excitation means, is simply matched with the resonance frequency of the vibration system. Claim 1 The control method of the vibrator has the configuration as described above. Vibratory In the control device, when the A / D conversion means is provided with a comparator, the microcomputer system is provided with PWM wave generation means (hereinafter referred to as PWM circuit), and the power conversion means is provided with a PWM inverter, The frequency of the modulated wave of the PWM wave output to the power conversion means by the computer system, that is, the frequency of the duty fluctuation is controlled.
[0026]
The microcomputer system can measure the time when the signal from the vibration sensor cuts the threshold level of the comparator of the A / D conversion means, that is, crosses.
Now, it is assumed that the vibration system vibrates at the resonance frequency. The time when the voltage waveform of the signal from the vibration sensor cuts the threshold level from the low voltage side to the high voltage side is defined as t1. If the time when the voltage waveform of the signal from the vibration sensor cuts the threshold level from the low voltage side to the high voltage side after t1 is t2, the frequency and period of the vibration detection signal, and hence the vibration of the vibrator You can see the frequency and period. Let the period of the vibration detection signal be S (= t2-t1). Naturally, the frequency of the vibration detection signal is 1 / S, and the resonance frequency of the vibrator is 1 / 2S.
[0027]
For convenience of explanation, the rising edge from the low voltage side to the high voltage side is used as the direction in which the vibration detection signal cuts the threshold level of the comparator. However, the falling edge may of course be used.
[0028]
The microcomputer system outputs a PWM wave having a modulation wave (modulation signal) having a cycle of 2 × S (this cycle is T) through the PWM circuit. That is, a PWM wave having a PWM wave duty cycle of 2 × S = T is output.
[0029]
For example, when the phase of the modulated wave of the PWM wave is 0, the reference time (t0) is set, and by the time T elapses, the vibration detection signal has a threshold level of the comparator 2 from below to above or from top to bottom. Can intersect. This is because T = 2S.
Assuming that the above-described times t1 and t2 are between 0 and T, τ / T when the vibration system resonates, that is, the initial τ / T, where τ is the time from 0 to time t2. Using the value of T as a target value for control, the microcomputer can perform PI control on the frequency of the analog signal output to the excitation means by controlling the frequency of the pulse signal, that is, the modulation wave of the PWM wave.
[0030]
If for some reason τ / T deviates from the stored initial value, the microcomputer system controls the frequency of the modulated wave of the PWM wave so as to restore the deviation.
[0031]
It is known that when a vibration system is vibrated at a resonance frequency, the phase difference between vibration force and vibration must be π / 2.
However, the vibration control device can obtain and recognize information about the phase of vibration in the vibration system from the input vibration detection signal and the pulse signal output to the power conversion means. Even if the control device can control the phase difference between the vibration detection signal and the pulse signal output to the power conversion means (strictly, the above-described modulation signal) to be exactly π / 2, the vibration force of the vibration system Whether the phase difference between the vibration and the vibration is exactly π / 2 corresponding to it or not is not actually known by the control device.
[0032]
When the vibration system vibrates at the resonance frequency, the present invention provides a vibration detection signal input to the microcomputer system controlling the vibration of the vibration system and a pulse signal output from the microcomputer system to the power conversion means. Data representing the phase difference from the analog signal (and thus the analog signal output to the excitation means) is detected in the form of τ / T using the threshold level of the comparator.
[0033]
Since data τ / T representing the phase difference between the vibration detection signal and the modulation signal of the PWM wave when the vibration system is resonating is known, the τ / T is used as a target value to obtain a PWM wave. By performing PI control on the frequency of the modulation signal of the pulse signal, the vibration system is maintained in a resonance state without directly considering that the phase difference between the vibration force and the vibration is π / 2. Can do.
That is, according to the vibrator control method of claim 2, it is only necessary to control the frequency of the analog signal, and it is not necessary to control the phase.
[0034]
【Example】
FIG. 1 is a block diagram showing an embodiment of the invention of claim 1, and FIG. 1 3 is a block diagram for explaining one embodiment of the present invention, FIG. 3 is a schematic diagram showing waveforms of carrier waves of pulse signals and PWM waves, and FIG. 4 is a schematic diagram showing waveforms of vibration detection signals and excitation means drive signals. . Embodiments of the present invention will be described with reference to these drawings.
[0035]
The vibrator 6 is a conveying device (for example, a bowl feeder) that has been conventionally used. The vibrator 6 has an excitation means 5 and a vibration sensor 1. For the excitation means 5, for example, an electromagnet can be used. As the vibration sensor 1, for example, a piezoelectric acceleration sensor can be used.
The vibrator 6, the excitation means 5, and the vibration sensor 1 with the work (parts) placed therein form one vibration system. In the present invention, the vibration system starts to vibrate at the resonance frequency and continues to vibrate at the resonance frequency.
[0036]
In order to configure the present invention, the microcomputer system 3 having a normal configuration generally used in the past is sufficient. Accordingly, although not shown, various circuits or elements constituting the microcomputer system such as a clock circuit, a reset circuit, an input / output port, and a power supply circuit are naturally provided.
To configure the present invention, A / D conversion means is required. FIG. 1 shows a configuration in which A / D conversion means 2 a is provided outside the micron computer system 3. Of course, the microcomputer system 3 may include the A / D conversion means 2a.
[0037]
The power conversion means 4 is a power supply circuit that switches a power supply current based on a pulse signal of the microcomputer system 3 (CPU 7), and is a power amplification circuit that uses a power element such as a thyristor, FET, or power transistor as a switching element. . That is, it is a circuit conventionally used in a vibration machine control device.
[0038]
The CPU 7 outputs the start pulse for a short time to the vibrator 6 (substantially the excitation means 5) that is stopped via the power conversion means 4. The excitation means 5 strikes (pulls) the vibrator 6 at the frequency of the power supply frequency. That is, the vibrator 6 is moved (displaced). When no current is supplied to the excitation means 5, the vibrator vibrates at free vibration, that is, at a resonance frequency. This vibration of the vibrator 6 is detected by the vibration sensor 1 and taken into the CPU 7 via the A / D conversion means 2a.
[0039]
The vibrator 6 is pulled by an analog signal in which the start pulse from the CPU 7 is output to the excitation means 5 via the power conversion means 4. As soon as the start pulse is not output, the pulled vibrator 6 starts to vibrate at its resonance frequency.
Therefore, the CPU 7 recognizes and stores the resonance frequency of the vibration system, and outputs a pulse signal of the resonance frequency (strictly, a pulse signal whose duty fluctuation frequency is the resonance frequency) to the power conversion unit 4. The CPU 7 also recognizes and stores the phase difference θ between the vibration detection signal and the analog signal output from the power conversion means 4.
The microcomputer system 3 can be controlled to keep this θ constant. That is, the vibrator 6 or the vibration system can continue to vibrate at the resonance frequency.
[0040]
The CPU 7 can easily detect the voltage level of the vibration detection signal from the vibration sensor 1. The CPU 7 can also adjust the frequency of the pulse signal output to the power conversion means 4 with reference to the detected voltage level. For example, when the voltage level decreases, the frequency of the pulse signal (that is, the analog signal) is increased or decreased in the direction in which the voltage level increases.
[0041]
As described above, according to the configuration of FIG. 1, the CPU 7 keeps the phase difference θ between the vibration detection signal fetched via the A / D conversion means 2a and the analog signal output to the excitation means 5 at an initial constant value. In addition, the pulse signal can be controlled.
[0042]
2, the A / D conversion means 2a is provided with a comparator 2, the CPU 7 is provided with a PWM circuit 9, and the power conversion means 4 is provided with a PWM inverter 4a. Of course, the comparator 2 may be provided independently of the A / D conversion means 2a.
Note that the PWM wave is output from the PWM circuit 9 which is one component of the microcomputer system 3 to the PWM inverter 4a. However, since the description is complicated, the PWM wave is output from the CPU 7. The following description will be given.
[0043]
Claim 1 In the present invention, control of the frequency of the PWM wave output from the CPU 7 to the PWM inverter 4a is performed as follows. As for the output of the CPU 7 to the PWM inverter 4a, the PWM signals such as the waveform a and the waveform i b in FIG. Although not shown in FIG. 2, it goes without saying that the opening and closing of the gates of the switching elements (for example, FETs) are complementarily performed by two other signal lines, as is the case with conventional technical common sense. .
[0044]
The signal line A is wired to one gate terminal of a pair of FETs (not shown), and the signal line B is wired to one gate terminal of another pair of FETs (not shown). .
[0045]
Actually, the PWM wave is always output to the signal line A and the signal line B, but when the PWM inverter 4a is viewed from the excitation means 5, analog signals having different polarities are output alternately. Looks like.
Therefore, in FIG. 3, when the waveform a and the waveform i b are considered as a set of signals, it is assumed that PWM waves are alternately output to the signal line A and the signal line B, and the waveform i c of FIG. 3 is obtained. be able to.
Although the output of the CPU 7 to the PWM inverter 4a is actually the waveform a and the waveform i b, it is assumed that the waveform i of the cycle T in FIG. 3 is output.
[0046]
Therefore, the PWM wave output from the CPU 7 to the PWM inverter 4a has a waveform i, and the modulation signal has a waveform a shown by a broken line. The CPU 7 performs PI control on the frequency of the waveform a based on τ and T shown in FIG.
From the reference time t0 when the period of the waveform A is T and the waveform A is in a predetermined phase, the vibration detection signal indicated by the waveform ha a lowers the threshold level of the comparator 2 from the lower (low voltage side) to the upper (high voltage side). ) Is the time until the time (t2) when turning off.
In FIG. 4, the reference time t0 is taken at the zero crossing of the analog signal (waveform b) to the excitation means 5.
[0047]
Further, during the time from the time t0 until the time T elapses, the vibration detection signal (the waveform c and the waveform c a in FIG. 4) crosses the threshold level of the comparator 2 twice from the bottom to the top. It is more preferable to set τ to the time until the time t2 that intersects the second time.
Although it is possible to set τ from t0 to t1, it is better to set the time from t0 to t2 to τ because t0 and t1 may approach and τ may approach 0.
[0048]
At this point, the CPU 7 controls the frequency of the waveform b shown in FIG. 4 while referring to the data of the waveform c. That is, the initial τ / T when the vibration system is resonating is stored, and the τ / T is used as a target value, and the waveform b in FIG. 4 or substantially the duty fluctuation of the waveform i c in FIG. Frequency is PI controlled.
As a result, the CPU 7 performs control equivalent to controlling the phase difference between the waveform C that is the vibration detection signal and the waveform C that is the analog signal output from the power conversion unit 4 (PWM inverter 4a) to the excitation unit 5. It is clear that it can be done.
[0049]
That is, when an analog signal of the resonance frequency of the vibration system at that time is output to the excitation means 5, the vibration sensor 1 returns a vibration detection signal with a predetermined phase relationship with respect to the analog signal. As a result, / T is controlled so as to coincide with the initial stored value.
[0050]
In this way, the microcomputer system 3 records τ / T (= P), and the CPU 7 keeps P constant, so that the period (frequency) of the duty fluctuation of the waveform i c in FIG. ) To control. It is easy for the CPU 7 to lengthen or shorten the duty fluctuation period of the waveform i c.
[0051]
As long as τ / T = P is maintained at a predetermined ratio, the vibration system can continue to vibrate at the resonance frequency regardless of fluctuations in the vibration conditions of the vibration system.
As a control law for keeping P at a constant value, it is sufficient to use conventional PI control or PID control.
[0052]
【The invention's effect】
According to the present invention Vibratory The control method is as described above. Method Therefore, it has the effects described below. The control device detects the vibration frequency (frequency) of the vibrator 6 with the vibration sensor 1, but vibrates the signal of the frequency as it is (or halved) using fixed hardware. It is not output to the machine 6. Control device Temporarily records (stores) the frequency and phase of the vibration detection signal in the microcomputer system 3 and outputs them to the vibrator 6 as a frequency signal calculated according to a predetermined procedure. Therefore, no matter how the conditions of the vibration system fluctuate, the vibrator can continue to vibrate at the resonance frequency with accuracy and stability according to the predetermined procedure.
[0053]
Claims related to the present invention 1 According to the control method for the vibrator, the microcomputer system 3 (CPU 7) does not have to calculate the current resonance frequency of the vibration system, that is, the resonance frequency itself every time. The CPU 7 sets the time τ until the time when the vibration detection signal from the vibration sensor 1 falls below a predetermined threshold level of the comparator 2 a with reference to the rising time of the pulse signal output to the power conversion means 4. The PI control is performed so that τ / T is kept at a constant value as compared with the period T of the modulation signal of the PWM wave output to.
[0054]
Therefore, it is only necessary to control the frequency of the modulation signal of the PWM wave to the power conversion means 4 (PWM inverter 4a) so as to keep τ / T at a constant value. There is no particular need to consider in controlling the vibrator that the phase difference between the vibration of the machine 6 and its drive signal is kept at π / 2 as in the prior art.
[0055]
Even if the resonance frequency of the vibration system greatly fluctuates for some reason, and the signal from the vibration sensor 1 does not coincide with the resonance frequency of the vibration system, the recorded P is kept in a constant value. By adjusting the frequency of the modulation signal of the PWM wave output to the power conversion means 4 (PWM inverter 4a), the vibration system can be quickly vibrated at the resonance frequency at that time.
Thus, the present invention can provide a simple and reliable control method capable of continuing to vibrate the vibrator at its resonance frequency.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of the invention of claim 1;
FIG. 2 Claim 1 Block diagram for explaining an embodiment of the present invention
FIG. 3 is a schematic diagram showing the waveform of a carrier wave of a pulse signal and a PWM wave.
FIG. 4 is a schematic diagram showing waveforms of vibration detection signals and excitation means drive signals.

Claims (1)

A microcomputer system for taking in a vibration detection signal from a vibration sensor via an A / D conversion means ;
Based on the pulse signal output from the microcomputer system, comprising power conversion means for outputting an analog signal for driving the excitation means ,
The microcomputer system, a start pulse signal through the power conversion means to move the vibrator output to the excitation means, and detects the resonance frequency of the vibrator in the vibration sensor,
The A / D conversion means includes a comparator as a constituent element, the power conversion means includes a PWM inverter as a constituent element, and the pulse signal includes a vibrator configured in the microcomputer system so as to include a PWM wave. In the control device,
The microcomputer system includes a time from a reference time at which the phase of the analog signal is a predetermined value to a time at which the vibration detection signal cuts the threshold level of the comparator during the period T of the analog signal elapses. A method for controlling a vibrator , wherein the frequency of the analog signal is changed by PI control of the PWM wave so that a ratio τ / T between τ and the period T of the analog signal becomes a constant value. .

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