JPS6028237B2 - Constant speed control device for rotating bodies - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for controlling the rotation speed of a controlled rotating body such as a capstan in a magnetic recording/reproducing device at a constant speed and stably, and includes, for example, an internal gear attached to a capstan shaft; After detecting the capacitance of the gap between the externally fixed external gear and creating a high-frequency electrical signal proportional to the capstan's rotation speed, this signal is added to a frequency discrimination circuit to determine the capstan's rotation speed. In addition to creating an error signal proportional to the fluctuation, a rectangular wave having a width corresponding to the magnitude of the error signal is generated, and the control voltage obtained by smoothing this is supplied to the DC motor for driving the capstan. In a constant speed control device, etc., which is capable of accurately maintaining the rotation speed of the capstan at a constant speed by supplying the rotation speed, when the output level of the rotation speed detector is smaller than a specified value, the output level of the rotation speed detector oscillates at a predetermined frequency, It is an object of the present invention to provide a constant speed control device for a rotating body whose startup is stable at all times by providing an amplitude limiter that supplies this oscillation signal to a frequency discriminator and limits the amplitude during normal times.

Various methods for controlling the capstan in a magnetic recording/reproducing device at a constant speed have been proposed and put into practical use, but it is extremely difficult to control the rotational speed with a small and simple circuit configuration and with high precision. It was difficult.

In response to this, the applicant of the present invention proposed the following constant speed control device for a rotating body in an attempt to solve this problem.

Referring to the drawings below, FIG. 1 shows a schematic block system diagram of an example of the above-mentioned constant power control device for a rotating body. In the figure, 1 is a capstan in a magnetic recording and reproducing device, 2 is a flywheel, 3 is a gear, and 4 is a pulley. The capstan 1 is rotated by a driving force transmitted from a pulley 6 directly connected to a DC motor 7 to the pulley 4 via a belt 5. The rotational speed is detected by the rotational frequency detector 8 via the gear 3.
Its output is applied to a frequency discriminator 9. As a result, fluctuations in the rotation speed of the capstan 1 are detected by the discriminator 9 as an error voltage signal. The signal is sent to motor drive amplifier 1
After being amplified by 0', V is supplied to the DC motor 7, thereby controlling the capstan 1 to suppress variations in the rotational speed. In this way, the above device operates to stabilize the rotational speed of the capstan 1 by means of an open loop constant speed control system, and specific examples of each circuit configuration will be described below. FIG. 2 is a diagram for explaining the rotational frequency detector 8, its related parts, and the frequency discriminator 9, and shows the plane of the rotational frequency detection mechanism, the odor-like circuit of the rotational frequency detector 8, and the frequency discriminator 9. The block system is shown.

In the figure, the same components as in FIG. 1 are given the same reference numerals. The gear 3 includes an internal gear 31 attached to a capstan shaft and an external gear 32 fixed to the outside. These gears 31 and 32 have the same number of teeth n
, with a certain gap between them.
Since the internal gear 31 is attached to the capstan shaft, it rotates at the same number of rotations as the capstan 1. Now, when the capstan 1 rotates once, the capacitance Co between the internal gear 31 and the external gear 32 changes n times in a sinusoidal manner. Therefore, when the capstan 1 rotates at a frequency of n2, the capacitance Co becomes fo=n.・Varies with peak (Hz) frequency. This capacitance Co is the rotational frequency detector 8
The gate of the field effect transistor FETQ. connected between sources.

The voltage of the power supply B is connected to the gate of the transistor Q by a resistor B2.
and R3 are applied across resistor R, the source being grounded via resistor R4 and bypass capacitor C2. On the other hand, a tank circuit consisting of a coil L and a capacitor C, the resonance frequency of which is equal to the aforementioned fo, is connected to its drain. In a circuit configured in this way, if the capacitance Co changes at a certain frequency, only when this frequency matches a certain frequency band centered on the resonant frequency fo of the tank circuit consisting of L and C. An output signal is obtained from the drain of transistor Q.

Note that even if disturbances such as noise or hum occur on the input side, the output signal will not be disturbed. According to this circuit, the number of rotations n2 (day 2) of the capstan 1 is n, and the frequency f which is twice as high as that is
It can be detected as an electrical signal of o. Further, in the figure, the output eo of the rotational frequency detector 8 is applied directly to one input terminal of the NAND circuit 14, and at the same time,
It is applied to the other input terminal of the NAND circuit 14 through the phase shifter 11.

Similarly, the same signal is applied to another NAND circuit 15 through phase inversion circuits 12 and 13, respectively. The outputs of the respective NAND circuits 14 and 15 are led through a filter 16 to an output terminal. The phase shifter 11 operates to delay the phase of an input signal with a higher frequency and advance the phase of an input signal with a lower frequency based on the frequency.

So now, for convenience of explanation, let's talk about the input signal. is a rectangular wave with a frequency fo as shown in FIG. 3A, and this is phase-shifted by the phase shifter 11 as shown in FIG. 3C. It is clear that the signals applied to the NAND circuit 14 at this time are the signals A and C mentioned above. Further, rectangular waves B and C, which are the inversions of A and C in the figure, are applied to the NAND circuit 15.
Therefore, the signal obtained by combining the outputs of both NAND circuits 14 and 15 becomes a rectangular wave as shown in FIG. If the rotational speed of the capstan becomes higher than in the steady state, and the center frequency of the input signal eo of the frequency discriminator 9 becomes higher, the output of the phase shift circuit 11 will be slightly delayed in phase, resulting in a signal like F in the same figure. Become. Therefore, the combined output of the NAND circuits 14 and 15 at this time becomes a rectangular wave having a narrower width than the rectangular wave E as shown in FIG. Therefore, the DC error signal obtained by smoothing the G signal will be smaller than in the steady state.
On the other hand, when the rotational speed of the cab stan becomes lower than the steady state, the phase of the input signal eo changes as shown in Figure 3. As a result, the combined output of the NAND circuits 14 and 15 becomes a wide rectangular wave as shown in FIG. 1, and the DC error signal obtained by smoothing this becomes large. That is, according to the circuit configured as described above, an output error voltage Vo whose magnitude is inversely proportional to the frequency of the input signal eo is obtained, and this voltage Vo is supplied to the motor drive amplifier 10.

At this time, the output voltage VN of the motor drive amplifier 10 has a value proportional to the control input voltage Vo, and the DC motor is thereby controlled according to the input voltage Vo. By the way, in the constant speed control device for a rotating body as explained above, the phase characteristics of the resonant circuit of the coil and the capacitor are used when detecting the rotational frequency of the rotating body and discriminating the frequency.
The output error signal characteristics of the frequency discriminator 9 with respect to the rotational frequency of the capstan 1 are actually as shown by a in FIG.
Exhibits S-curve characteristics.

Therefore, the output level of the discriminator 9 when the rotational frequency of the capstan l is zero, that is, just before starting, and the output level of the discriminator 9 when the rotational frequency is a predetermined number of rotations, that is, the output level of the discriminator 9 at a frequency near the resonance frequency of the resonant circuit. are equal or approximate, the input signal level to the motor drive amplifier 10 is not sufficient to start the rotating body, and the starting is unstable (i.e.,
There was a problem with this (sometimes it started, sometimes it didn't).

The present invention has solved the above-mentioned problems, and FIG. 5, together with FIG. shows.

In the figure, the same reference numerals as those in FIG. 1 are given the same reference numerals, and the explanation thereof will be omitted. In the figure, a limiter 17 is inserted and connected between the rotation frequency detector 8 and the frequency discriminator 9. One embodiment of a specific circuit including the limiter 17 and rotational frequency detector 8 is shown in FIG.

In the figure, the left side of the dotted line a shows the rotational frequency detection section 8, and the right side of the dotted line a shows the limiter 17. The coil L and capacitor C, which form part of the rotational frequency detection section 8, are a tank circuit tuned to the frequency f, the resistor R4 is a current limiting resistor, and the capacitor C2 is a bypass capacitor. The output terminal (b in the figure) of the rotational frequency detection section 8 is connected to a capacitor C.
,.

and resistance R2. The output terminal of this amplifier 17a is connected to the input terminal of the amplifier 17a through a series circuit with the resistors R2,
and capacitor C, . amplifier 17a through a series circuit with
Connect the feedback to the input terminal of the Note that the amplifier 17a is configured by, for example, a combination of differential amplifiers. The output signal of the rotational frequency detector 8 is supplied to an amplifier 17a via a capacitor C and a resistor R. The amplifier 17a of the IJ transmitter 17 has a resistor a, a capacitor C, . Relatively weak positive feedback is applied through the input and output signals, so that the input and output signals have the same phase relationship. Therefore, the positive feedback signal from the output and the output signal of the rotational frequency detector 8 are applied to the input of the amplifier 17a. Among the signals supplied to the input of the limiter 17 (that is, the input terminal of the amplifier 17a), the level of the signal supplied from the tank circuit of the coil L and capacitor C is lower than the level of the positive feedback signal. When the capacitor C, . , resistance R2, , capacitor C, o,
It oscillates at an oscillation frequency determined by the resistance 2o, the "Q" of the coil L, and the capacitor C. On the other hand, among the signals supplied to the input of the limiter 17, when the level of the signal supplied from the tank circuit of the coil L and capacitor C is higher than the level of the above-mentioned positive feedback signal, the limiter 17 performs the original amplitude limit. It operates as an amplifier to limit and amplify the amplitude of the input signal.

Therefore, the period from when the capstan 1 is activated and its frequency rises until it reaches the frequency f near the first peak b' of the discrimination characteristic curve b shown in FIG. During the period when the output signal of 8 is smaller than the above feedback signal,
The above IJ filter 17 operates as an oscillator with an oscillation frequency f, and supplies this oscillation signal to the frequency discriminator 9.

This transmission signal is converted into a predetermined DC voltage e2 according to its frequency by the frequency discriminator 9, and this DC voltage is amplified by the motor drive amplifier 10 and then supplied to the motor 7 to drive it. . Therefore, the output signal of the rotational frequency detector 8 is cut off during the period when the rotational speed of the capstan approaches the target value from the time of starting, and a voltage sufficient for starting the DC motor 7 and increasing the rotational speed is eventually applied to the DC motor 7.

Next, the rotational speed of the capstan 1 reaches around the frequency f,
If the output signal of the detector 8 becomes greater than the feedback signal, the limiter 17 resumes its function.

That is, the output signal of the detector 8 is amplified while its amplitude is limited by the limiter 17 and is supplied to the frequency discriminator 9.

As described above, the constant speed control device for a rotating body according to the present invention includes a device between the rotation speed detector and the frequency discriminator that oscillates at a predetermined frequency when the output level of the rotation speed detector is smaller than a predetermined value. Supplying this oscillation signal to the frequency discriminator,
When the above output level is larger than the specified value, a circuit is provided that limits the amplitude of this world's power and then supplies V to the above frequency discriminator.The discrimination characteristic curve allows the rotational speed of the rotating body to reach the target value from the time of startup. During the period approaching , sufficient voltage is applied to the motor to start it and increase its rotational speed, and as a result, the output for the input signal frequency of the frequency discriminator described above, which applies the resonance characteristics of the coil and capacitor, is The S-curve characteristic of the signal voltage level is substantially improved, and stable startup is possible.

[Brief explanation of the drawing]

FIG. 1 is a block system diagram of an example of a constant speed control device previously proposed by the present applicant, and FIG. 2 is a block system diagram of an example of its rotational frequency detection mechanism, rotational frequency detector, and frequency discriminator. 3 A to 1 are waveform diagrams for explaining the operation of the frequency discriminator in FIG. 2, FIG. 4 is a diagram of the output signal voltage characteristic curve for the input signal frequency of the subordinate frequency discriminator, and FIG. 5 is a diagram of the present invention. 6 is a circuit diagram of the limiter portion in the same embodiment, and FIG. 7 is an output signal of the frequency discriminator in accordance with the input signal frequency in the same embodiment. It is a voltage characteristic curve diagram. 1...capstan, 2...flywheel, 3...gear, 3
DESCRIPTION OF SYMBOLS 1... Internal gear, 32... External gear, 7... DC motor, 8... Rotation frequency detector, 9... Frequency discriminator, 10... Motor drive amplifier, 11... - Phase shifter, 12, 13... Polarity inverter, 14, 15... NAND circuit, 16... Filter, 17... Limiter, 17a... Amplifier. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7

Claims (1)

[Claims] 1. A controlled rotating body such as a capstan of a magnetic recording/reproducing device, a rotational speed detector that detects an electrical signal related to the rotation of the rotating body and having a frequency corresponding to the rotational speed of the rotating body, and the rotational speed detector. a frequency discriminator for generating a DC error signal having a magnitude corresponding to the frequency of the output of the frequency discriminator, an amplifier for amplifying the output of the frequency discriminator, and controlling a DC motor for driving the rotating body using the output of the amplifier. In a constant speed control device for a rotating body comprising means for This oscillation signal is then supplied to the frequency discriminator, and when the output level is greater than a specified value, the output is limited in amplitude and then a circuit is inserted and connected to supply the frequency discriminator to the frequency discriminator. A constant speed control device for a rotating body characterized by: