JPS639272Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a motor speed control circuit that switches between a first rotational speed and a second rotational speed that is twice the rotational speed. It is suitable for use in

Conventionally, in tape recorders that can change the recording/playback tape speed by switching the rotational speed of the motor, there has been a problem that speed information per unit time is insufficient during low-speed rotation, worsening wow and flutter. Ta. Furthermore, it is necessary to change the gain constant of the speed servo circuit of the motor each time the speed is changed, resulting in a complicated circuit.

Furthermore, a method is known in which the output of a frequency generator that detects the rotational speed of the motor during high-speed rotation is frequency-divided to fix the input frequency of the servo circuit to the frequency during low-speed rotation. According to this method, there is no need to change the servo gain according to the change of rotation speed, and the speed information per unit time is the same at high speed and low speed. Since the output of the frequency generator is frequency-divided and supplied to the servo circuit, the amount of speed information supplied from the frequency generator to the servo circuit becomes insufficient during high-speed rotation. As a result, speed control performance during high-speed rotation deteriorates, and rotational unevenness occurs during high-speed rotation, making it impossible to always perform stable speed control.

The present invention was devised in view of the above-mentioned problems, and is used in tape recorders and the like that can switch the rotational speed of the motor, by changing the frequency supplied to the servo circuit between low-speed rotation and high-speed rotation. To do this, double the frequency output from the frequency generator during low speed rotation to make it the same as the output frequency during high speed rotation, and use this as the input frequency to the servo circuit during low speed rotation. In particular, it is an object of the present invention to prevent the amount of speed information supplied from the frequency generator to the servo circuit from decreasing during high-speed rotation.

An embodiment in which the present invention is applied to a motor speed control circuit of a tape recorder will be described below with reference to the drawings.

FIG. 1 is a block diagram showing this embodiment.

In Fig. 1, motor 1 is a capstan drive motor, and the tape running speed of the tape recorder can be set to two speeds: high speed (4.8 cm/sec) and low speed (2.4 cm/sec).
It is now possible to switch between two speeds. The rotational speed of the motor 1 is detected by a frequency generator 2. The output signal from the frequency generator 2, that is, the speed detection signal is, for example, a sine wave sin t (voltage at point _A ) as shown in FIG. It is also supplied to the limiter 4. Integrator 3 is a resistor
It consists of R ₁ , an operational amplifier, a resistor R ₂ , a capacitor C ₁ and a resistor R ₃ . The signal supplied from the frequency generator 2 is integrated by the integrator 3 and has a phase lead of 90°. That is, as shown in FIG. 2b, the signal voltage at point B in FIG. 1 becomes 1/C ₁ R ₁ cos t. The output from the integrator 3 is waveform-shaped into a rectangular wave as shown in FIG. 2d by the limiter 5 with a phase lead of 90 degrees as shown in FIG. Supplied to the terminal. On the other hand, the speed detection signal supplied to the limiter 4 is waveform-shaped by the limiter 4 and becomes a rectangular wave as shown in FIG. 2c. This signal is supplied to the other terminal of the exclusive OR circuit 6 and also to the fixed contact 7a of the changeover switch 7.

In the exclusive OR circuit 6, the exclusive OR of two rectangular waves having a phase difference of 90 degrees is taken to form a signal having a frequency twice that of the speed detection signal. If we assume that the high level of the two rectangular waves shown in Figure 2c and Figure 2d is "1" and the low level is "0" and take an exclusive OR, we will get a signal with twice the frequency as shown in Figure 2e. can be formed.
This signal is then supplied to the fixed contact 7b of the changeover switch 7 as a speed detection signal when the motor 1 rotates at low speed.

In this embodiment, when the motor 1 is rotating at a low speed, the output of the exclusive OR mentioned above is selected, and the movable contact 7c and fixed contact 7b of the changeover switch 7 are connected, and the frequency of the speed detection signal is doubled. is used as the speed detection signal. When the motor 1 rotates at high speed, a pulse corresponding to the output of the frequency generator mentioned above is selected, and the movable contact 7c and fixed contact 7a of the changeover switch 7 are connected and used as a speed detection signal. As a result, the amount of speed information per unit time of the motor 1 does not change between high speed rotation and low speed rotation, and the speed information amount per one revolution of the motor is fixed to the information amount during high speed rotation.

The movable contact 7c of the changeover switch 7 is connected to a frequency-voltage converter 8, to which a speed detection signal is supplied. The output of the frequency-voltage converter 8 is given to the motor 1 via a drive amplifier 9. The frequency-voltage converter 8 increases the voltage applied to the motor 1 to maintain the predetermined rotation speed when the rotation speed of the motor 1 decreases below a predetermined value and the frequency of the speed detection signal becomes small. Operate. Further, when the rotational speed of the motor 1 becomes larger than a predetermined value and the frequency of the speed detection signal increases, the voltage applied to the motor 1 is reduced to maintain the predetermined rotational speed. In this way, the frequency-voltage converter 8
This compensates for fluctuations in the rotational speed of the motor.

Note that as the frequency-voltage converter 8, a conventionally known converter can be used. For example, when using a pulse width modulation type converter, a sawtooth wave is formed in synchronization with the input speed detection signal, and this sawtooth wave is compared with a predetermined reference level, and a sawtooth wave that is more prominent than the reference level is generated. A pulse signal corresponding to the wave portion is formed. Since the pulse of this pulse signal is a PWM wave whose pulse width is modulated according to the frequency of the input speed detection signal, it is possible to obtain a voltage according to the input frequency by integrating this PWM wave.

FIG. 3a shows the gain characteristics of the integrator 3 with respect to the frequency of the speed detection signal, and FIG. 3b shows the phase characteristics of the integrator 3 with respect to the frequency of the speed detection signal.

When the frequency of the speed detection signal is ₀ when the motor 1 in FIG. 1 rotates at a low speed, the integrator 3
If the cutting frequency c is selected so that the phase difference between the input and output of is 90 degrees ahead of the phase, a signal having twice the frequency can be easily formed by using the exclusive OR circuit 6. I can do it. here,
o=1/2πC ₁ R ₁ , c=1/2πC ₁ R ₂ [Sheath frequency]
There is a relationship. It is preferable to set c to approximately 1/5o because the phase advance at o will be 90°.

According to the embodiments described above, the frequency-to-voltage converter 8
Since the speed detection frequency of the input is the same for high speed and low speed, speed switching can be performed without changing the gain of the servo loop and the conversion constant of the frequency-voltage converter 8. Furthermore, since the input frequency of the frequency-voltage converter 8 can be set to always be the same as the output frequency of the frequency generator 2 during high-speed rotation, the wow and flutter during recording/playback will not change even if the tape speed is changed. Since there is no rotation and constant control can be performed using information during high speed rotation with a large amount of speed information per unit time, wow and flutter can be further reduced.

As described above, in the present invention, the frequency of the speed detection signal during low speed rotation is doubled and the frequency used during high speed rotation is used as the motor speed control voltage. Therefore, the input frequency to the frequency-voltage converter that controls the rotational speed of the motor is the same during high-speed rotation and low-speed rotation. As a result, there is no need to switch the gain of the servo system, making circuit switching easy. In addition, even if the amount of speed information during high-speed rotation is not reduced, the amount of speed information per unit time does not change between high-speed rotation and low-speed rotation, so speed control performance during high-speed rotation does not deteriorate, and rotation In addition to being able to further reduce unevenness, speed control performance does not fluctuate due to speed switching, and stable control can be performed at all times.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a motor speed control circuit for a tape recorder to which the present invention is applied, Fig. 2 is a waveform diagram of the speed control signal, and Fig. 3a shows the relationship between the frequency of the speed detection signal and the characteristics of the integrator. The graph shown in FIG. 3b is a graph showing the relationship between the frequency and phase of the speed detection signal. In addition, in the symbols used in the drawings, 1...
...Motor, 2...Frequency generator, 3...Integrator,
4, 5...limiter, 6...exclusive OR circuit,
7...Switchover switch, 8...Frequency-voltage converter.

Claims (1)

[Scope of utility model registration request] A motor speed control circuit configured to switch between a first rotational speed and a second rotational speed that is twice the rotational speed includes a frequency generator that detects the rotational speed of the motor, and an integrator that integrates the output of the frequency generator. , an exclusive OR circuit that performs an exclusive OR of pulses corresponding to the output of the frequency generator and the output of the integrator and outputs a pulse having twice the frequency of the output signal of the frequency generator; a changeover switch that selects the output of the exclusive OR circuit at the first rotational speed and selects a pulse corresponding to the output of the frequency generator at the second rotational speed; and an output of the changeover switch. and a circuit for forming a motor speed control voltage based on the motor speed control voltage.