JPS6233601B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a frequency discrimination circuit used for detecting speed changes in speed control devices and the like.

Conventionally, in equipment that requires constant speed rotation, such as video tape recorder (VTR) rotary head drive motors and tape drive capstan motors,
A so-called servo control method is generally adopted, which detects the rotational speed of a rotating body such as a rotating head or capstan, and controls the drive motor of the rotating body according to the detected speed signal to obtain a predetermined constant speed. There is.

An example of such a servo control system is shown in FIG. That is, the rotational speed of a rotating body 2 (such as a rotating head of a VTR) driven by a drive motor 1 is detected by a detector 4 using a signal from a frequency generator 3 built into the motor 1. , a sine wave signal A with a frequency proportional to the rotational speed of the rotating body 2 is obtained, and this sine wave signal A is supplied to a frequency discrimination circuit 5 for frequency discrimination. By outputting an error voltage E corresponding to the rotational speed of the rotating body 2 as a discrimination output and supplying this error voltage E to the motor drive amplifier 6 to control the rotational speed of the drive motor 1, the rotational speed of the rotating body 2 can be adjusted to a predetermined value. It is configured to be kept at a constant value.

By the way, in such a servo control system, the performance of the frequency discrimination circuit 5 has a great influence on the overall characteristics, and in particular, the controllability of this servo system against disturbances in the motor 1 is improved (i.e., the performance of the frequency discrimination circuit 5 is (reducing rotational speed fluctuations of motor 1)
In order to do this, it is necessary to make the sample rate for finely discriminating frequency fluctuations in the frequency discrimination circuit 5, that is, the frequency of the detection signal A from the frequency generator 3, to be sufficiently high.

Therefore, in the past, a frequency generator 3 that generates a frequency at a sufficiently high rate had to be attached to the motor 1, which resulted in drawbacks such as an increase in the size of the device and an increase in the cost of the device.

Therefore, in order to reduce this rate, a frequency discrimination circuit as shown in FIG. 2, for example, has been conventionally proposed. 2, 101 is an input terminal to which the sine wave signal A from the detector 4 in FIG. 1 is supplied, 102 is an output terminal to which the error voltage E is output, 103 is a limiter amplifier, 104 is a pulse generator, 105 and 106 are monomultis (monostable multivibrators) having time constants of τ ₁ and τ ₂ , respectively, 107 is a triangular wave generator, and 108 is a sample and hold circuit.

Next, the operation will be explained using the waveform diagram shown in FIG.

A sine wave signal A supplied from a terminal 101 is sufficiently amplified by a limit amplifier 103, shaped into a rectangular wave signal P having a duty ratio of approximately 50%, and output. This rectangular wave signal P is input to the pulse generator 104, and pulses Q having a relatively narrow pulse width are alternately generated at the rising and falling portions of the rectangular wave signal P.
is formed and output. Therefore, if the frequency of the input sine wave signal A is ₀ , the frequency of the pulse Q from this pulse generator 104 is twice that frequency, 2.
It becomes ₀ .

The pulse Q multiplied to twice the frequency in this way is supplied to the monomulti 105 and is also supplied to the sample hold circuit 108 as a sampling signal.
sampling input.

First, the monomulti 105 is triggered by an input pulse Q and outputs a rectangular wave signal R with a pulse width of τ ₁ , and then the monomulti 106 is triggered by the falling part of this rectangular wave signal R and outputs a rectangular wave signal R with a pulse width of τ 1. A rectangular wave signal S of τ ₂ is output.

The triangular wave generator 107 is triggered by this signal S and generates a triangular wave signal T that rises at a constant slope in proportion to time from the falling time of the signal S.
This signal T is supplied to the sampled input of the sample and hold circuit 108.

Therefore, the output of the sample and hold circuit 108 is obtained by sampling the triangular wave signal T with the pulse Q and holding the error voltage E during the sampling period.

Here, the time constant τ of monomulti 105, 106
If the relationship between ₁ , τ ₂ and the frequency 2 ₀ of the pulse Q is determined as 1/2 ₀ > τ ₁ + τ ₂ , then the pulse Q becomes the triangular wave signal T
Therefore, we will sample the sloped part of
The error voltage E is a voltage that corresponds to a change in the frequency of the pulse Q, that is, a change in the rotational speed of the rotating body 2.

Since this error voltage E is supplied from the motor drive amplifier 6 to the motor 1, the motor 1 is subjected to negative feedback control, and the rotating body 2 is controlled so that its rotational speed becomes a predetermined constant value.

As is clear from the above operation, according to this conventional example, even if the frequency of the input signal A is ₀ , frequency discrimination can be performed at a sample rate of ₂₀ , which is twice that frequency, and the configuration is simple. It is possible to obtain a sufficiently fine speed error even by using a frequency generator of This method was widely adopted.

However, in this conventional method, the duty ratio of the rectangular wave signal P output from the limiter amplifier 103 is increased due to so-called limiter imbalance in the limiter amplifier 103 and distortion of the generated signal in the frequency generator 3. As shown by the broken line in Figure 3, it is no longer 50%, so the pulse former 1
There was a problem in that the input signal A with a frequency of ₀ leaked into the pulse Q output from the 04, causing a fluctuation of the frequency ₀ in the interval between the pulses Q.

Therefore, in this conventional example, as shown in Fig. 3, the leaked frequency ₀ component is discriminated and output, and an error voltage E' is generated in which the voltage alternately fluctuates for each sample by the pulse Q. For this reason, when applied to a servo control system, the leaked component disturbs the control state of the motor 1, causing rotational unevenness.

An object of the present invention is to eliminate the drawbacks of the prior art described above, and to provide a circuit in which the sample rate is twice that of the input signal so that frequency fluctuations can be finely discriminated. To provide a frequency discriminator circuit which can prevent leakage.

To achieve this object, the present invention obtains a pulse signal with twice the frequency of the input signal, and alternately applies an error signal having a value proportional to the time interval of this pulse signal every half cycle of the input signal. It is characterized in that a discrimination output signal is obtained by adding the first and second signals obtained separately.

Embodiments of the present invention will be described below based on the drawings.

FIG. 4 shows an embodiment of the frequency discrimination circuit according to the present invention, and FIG. 5 is a waveform diagram for explaining its operation.

In addition, in the example of FIG. 4, 101, 10
2, 103, 105, 106, and 107 are respectively an input terminal, an output terminal, a limiter amplifier, a monomulti, a monomulti, and a triangular wave generator, and these are all the same as the conventional example shown in Fig. 2, and their operation is as follows. The case is also exactly the same as that shown in Fig. 2.

In the figure, 110 and 111 are both pulse generators, 112 is an OR gate, 113 and 114 are both sample and hold circuits, and 115 is an adder circuit.

Next, the operation will be explained.

First, a sine wave input signal A supplied from a terminal 101 is amplified by a limiter amplifier 103, shaped into a rectangular wave signal P with a duty ratio of approximately 50%, and output.

This rectangular wave signal P is generated by pulse formers 110 and 11.
1.

As a result, as shown in FIG. 5, the pulse generator 110 outputs
Further, from the pulse former 111, a first pulse having a relatively narrow pulse width is output at the falling portion of the rectangular wave signal P.
and second pulses Q ₁ and Q ₂ are formed and output.

Pulses Q ₁ and Q ₂ from these pulse generators 110 and 111 are supplied to an OR gate 112, which
The OR gate 112 outputs a pulse Q ₀ which is the logical addition of pulses Q ₁ and Q ₂ as shown in FIG. This pulse Q ₀ changes the frequency of input signal A to
Needless to say, if it is ₀ , the frequency will be twice as high as ₂₀ .

This pulse Q ₀ is input to the monomulti 105, and the operations of the monomulti 105, the subsequent monomulti 106, and the triangular wave generator 107 are exactly the same as those described in FIG. is triggered by the pulse Q ₀ and outputs a rectangular wave signal R with a pulse width of τ ₁ , and the monomulti 106 is triggered by the signal R and outputs a rectangular wave signal R with a pulse width of τ
₂ rectangular wave signal S is output, and the triangular wave generator 10
7 outputs a triangular wave signal T which is triggered by the signal S and rises at a constant slope in proportion to time.

This triangular wave signal T is then supplied to sampled inputs of the first and second sample and hold circuits 113 and 114.

On the other hand, these sample and hold circuits 113, 1
As the sampling signal No. 14, the pulse Q ₁ from the pulse forming circuit 110 is supplied to the sampling input of the sample hold circuit 113, and the pulse Q ₂ from the pulse forming circuit 111 is supplied to the sampling input of the sample hold circuit 114.

Therefore, these sample and hold circuits 113,
The triangular wave signal T is sampled with pulses Q ₁ and Q ₂ respectively, and error voltages E ₁ and E ₂ held during the sampling period are obtained as outputs of 114.

Of these, the error voltage E ₁ has a value proportional to the time error of the low level period of the rectangular wave signal P, that is, one half period T ₂ of the input signal A, as is clear from the waveform diagram in FIG. On the other hand, the error voltage E ₂ is output with a value proportional to the time error of the high level period of the rectangular wave signal P, that is, the other half period T ₁ of the input signal A. Therefore, the time error over one cycle of the input signal A is discriminated alternately every half cycle, and the error voltages E ₁ ,
It will be output as E ₂ .

Thereafter, these error voltages E ₁ and E ₂ are supplied to an adder circuit 115 and added together to generate an error voltage E ₀ at the output terminal 102.

As a result, the limiter of the limiter amplifier 103
Due to unbalance or distortion of the signal A generated by the frequency generator 3 (Fig. 1), the duty ratio of the rectangular wave signal P from the limiter amplifier 103 may be 50.
%, and therefore, even if an unnecessary component of frequency ₀ leaks into the pulse Q ₀ output from the OR gate 112, these sample and hold circuits 113,
114, the unnecessary components are not discriminated at all, and therefore, the adding circuit 115 detects the rotating body 2 (FIG. 1).
An error voltage E ₀ (E ₀ in FIG. 5) is output, in which the time error for each half period of the input signal A, which is based only on the speed fluctuation of the input signal A, is correctly discriminated.

By the way, in the conventional example shown in Fig. 2, when the duty ratio of the square wave signal P is no longer 50%, the leakage of the frequency ₀ component begins to appear as the error voltage E'. As is clear from Fig. 3, only one sample and hold circuit 1
08, directly by a pulse Q of frequency ₂₀ ,
This is because sampling is performed at a sample rate of ₂₀ . However, in the embodiment shown in FIG.
Two sample and hold circuits 113 and 114 are used, and one of these sample and hold circuits 113
performs sampling using the pulse Q ₁ of only the rising edge of the square wave signal P, and the other sample hold circuit 114 samples using the pulse Q ₂ of only the falling edge of the rectangular wave signal P. , these sample and hold circuits 1
13 and 114 have a phase difference of approximately 180° in their sampling timings, but the sampling rate of both of them is ₀ . As a result of the sampling rate being ₀ , the outputs of these circuits have a period T ₀ = (1/
₀ ), it cannot change, and as a matter of course, a component of frequency ₀ does not appear.

In this manner, according to the embodiment shown in FIG. 4, the outputs E ₁ and E ₂ are added together in the adder circuit 115 after preventing the frequency ₀ component from appearing in the outputs of the sample and hold circuits 113 and 114. However, as a result, an error voltage E ₀ having a sample rate of ₂₀ and containing no frequency ₀ component is obtained.

Since this error voltage E ₀ is supplied from the motor drive amplifier 6 to the motor 1 (Fig. 1), the motor 1 is controlled by negative feedback, and the rotating body 2 is controlled so that its rotational speed becomes a predetermined constant value. will be done.

Now, Fig. 5 shows the case where the input signal A does not include frequency fluctuation (or even if it does, it is so small that it does not appear in the figure). , rotation speed fluctuation appears in motor 1,
Assume that the frequency of input signal A fluctuates in an upward direction.

Then, in this case, as shown in FIG. 6, the period T ₀ of the input signal A increases, the sampling value of the triangular wave signal T also increases, and the error voltages E ₁ and E ₂ each increase in steps. rises like a figure. As a result of combining these error voltages E ₁ and E ₂ , an error voltage E ₀ that follows the change in the input signal A in a stepwise manner is obtained.

As is clear from the above explanation, according to this embodiment, frequency discrimination can be performed at a sample rate of ₂₀ , which is substantially twice that of the frequency ₀ of the input signal A. Since the generation of unnecessary components with frequency ₀ can be completely suppressed, only the true speed error based on the speed fluctuation of the controlled object can be finely discriminated at a high rate, which improves the control performance of the servo system. can be significantly increased.

Although FIG. 4 shows an embodiment of the present invention constructed from so-called analog circuits, monomulti 105,
106 and the triangular wave generator 107, a conventionally known counter circuit that counts a predetermined clock according to the time interval between adjacent pulses of the pulse Q ₀ is used, and the sample and hold circuits 113, 1
14 consists of a latch circuit that latches and holds the data counted by the counter circuit in accordance with the sampling inputs Q ₁ and Q ₂ , and an adder circuit 115.
is configured with a so-called full adder circuit, the output data from the latch circuit is digitally added, the added output data from this full adder circuit is digital-to-analog (D/A) converted, and the output data is calculated according to the analog amount. It is also possible to use a digital circuit configuration in which the voltage is output to the terminal 102. According to this embodiment, exactly the same effect as the embodiment shown in FIG. 4 can be obtained, and since it can be integrated into an IC, the cost can be reduced. An excellent effect can be expected in that miniaturization becomes easy.

As explained above, according to the present invention, it is possible to perform frequency discrimination at twice the sampling rate of the input signal, and it is also possible to completely prevent the frequency components of the input signal from leaking to the discrimination output. ,
Eliminating the drawbacks of the conventional technology, when applied to a servo control type speed control device, sufficient control responsiveness can be obtained without increasing the frequency of the frequency generator for rotation detection, and moreover, it is suitable for motor control. A high-performance frequency discrimination circuit that does not cause disturbance can be provided.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an example of a rotation speed control device using a servo control method, Fig. 2 is a block diagram showing a conventional example of a frequency discrimination circuit, Fig. 3 is a waveform diagram for explaining its operation, and Fig. 4 is a block diagram showing an example of a rotation speed control device using a servo control method. A block diagram showing an embodiment of the frequency discrimination circuit according to the present invention, FIG. 5 is a waveform diagram for explaining its operation, and FIG. 6 is a waveform diagram showing the operation when an error occurs. 103... Limiter amplifier, 105, 106...
...Mono multi, 107...Triangle wave generator, 11
0, 111...pulse former, 112...OR gate, 113, 114...sample hold circuit, 115...addition circuit.

Claims (1)

[Claims] 1. A first pulse generator that generates a first pulse signal at the rising edge of a signal to be discriminated shaped into a rectangular wave, and a second pulse generator that generates a second pulse signal at the falling edge of the signal to be discriminated. a pulse former; a first sample and hold circuit that samples an error signal having a value proportional to the time interval from the second pulse signal to the first pulse signal, using the first pulse signal; from the first pulse signal to the second pulse signal
and a second sample-and-hold circuit for sampling an error signal having a value proportional to the time interval up to the pulse signal using the second pulse signal, and outputs of the first and second sample-and-hold circuits are provided. A frequency discrimination circuit characterized in that it is configured to perform addition to obtain a discrimination output signal.