JPS61139286A - Servo controller - Google Patents

Abstract

PURPOSE:To normally start a motor constantly by supplying a voltage of the prescribed level for starting and accelerating the motor to a motor drive circuit at motor stopping time. CONSTITUTION:When a drive command signal S is L, a motor drive circuit 6 is in nonoperating state. Since a control signal SD becomes L at this time, a transistor 14 is in ON state. Thus, the output of a speed detector 10 is flowed to an earth, and the output voltage VE of an error voltage forming circuit 4 is held at sufficiently large level H. When the signal S becomes H, the circuit 6 becomes an operating state, and a motor 1 is normally started. When the prescribed time is elapsed, the signal SC becomes H, and the transistor 14 becomes OFF state. Thus, the output signal FI of the detector 10 is input to an error amplifier 8, and the output of the circuit 4 is pulse-width-modulated in response to the signal FI.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a servo control device suitable for controlling the rotation of a motor used in a video tape recorder or the like.

[Background of the invention]

Motors whose rotational speed must be kept constant, such as the drum motor or capstan motor of a video tape recorder, generally have their rotational speed controlled by a servo controller.

Conventionally, such a servo control device has 1 as shown in FIG.
The motor 1 is controlled by negative feedback, and the motor 11C is provided with a frequency generator (not shown), for example.
A signal F'I with a frequency corresponding to the rotational speed of the motor 1 (hereinafter referred to as a frequency signal) is generated from , and this frequency signal FI is supplied to the speed control circuit 5 to determine the current rotational speed of the motor 1 (hereinafter referred to as a frequency signal). An error voltage VB is generated according to the difference between the current rotation speed (referred to as the current rotation speed) and a rotation speed below the to-be-set rotation speed (referred to as the specified rotation speed), and this error voltage VB is supplied to the motor drive circuit 6, so that the motor 1 reaches the specified rotation speed. A drive voltage VD is generated so that the motor rotates at a constant speed.

By the way, in such a servo control device, for the purpose of achieving high integration and improving reliability, for example, National
l Tealinical Rap) rt VoL 2
8 Nn 5 June 1982 by Hashimoto et al.
Recently, digital IC technology has enabled
A digital processing method has been introduced. In this digital method, the frequency of a frequency signal corresponding to the rotational speed of the motor or the phase difference with respect to a predetermined reference signal is measured using a high-precision clock, and the error data obtained by this is digitally processed. A commonly used method is to perform pulse width modulation using a low-pass filter, demodulate the output using a low-pass filter, etc. to form a control voltage, and then feed this negative feedback to the motor to control the motor.

When such a digital system is adopted in the conventional technique shown in FIG. It is equipped with a frequency discrimination circuit 3 that outputs a width modulated (width modulated) wave vPt and an error voltage forming circuit 4 that smooths this PWM wave vp and generates a DC error voltage VE, but the frequency signal FId is generally a minute sine wave. However, in order for the frequency discrimination circuit 5 to respond to this, it is necessary to waveform-shape this frequency signal into a rectangular wave with a logic level (that is, high and low levels). A gain amplifier (eg, a differential amplifier) 2 is provided.

Note that a drive command signal S is supplied from the input terminal 7 to the motor drive circuit 6. When this drive command signal S is "Fl" (high level), the motor drive circuit 6 is in an operating state, and the motor drive circuit 6 is at a drive voltage VDt corresponding to the error voltage vE from the error voltage forming circuit 4. - occurs and the motor 1 is drive-controlled, and when the interlocking command signal S is "L" (low level), the motor drive circuit 6 is in an inactive state and the motor 1 is in a stopped state.

Next, the operation of the servo control device shown in FIG. 5 will be explained using the waveform diagram shown in FIG.

Now, if the drive command signal S is "L" and the motor 1 is stopped, of course the amplifier 2
If the μ frequency signal FI is not supplied to the circuit, but if no noise is also supplied, the output VP of the frequency discrimination circuit 5 will be "H#" as shown in FIG. 6, and this output vP will be the error voltage. It is supplied to the motor drive circuit 6 via the formation circuit 4.Then, the drive command signal S becomes H'', and
The motor drive circuit 6 outputs the next operating voltage VD in response to the error voltage vE of H', and the motor 1 is thereby started and accelerated. When the motor 1 is started and accelerated, the frequency signal FI
is generated and the waveform is shaped by amplifier 2.

The frequency discrimination circuit 3 generates a PWM wave vP having a Hals width according to the frequency of the output of the amplifier 2. This Pw Mmvp
is smoothed by the error voltage forming circuit 4 to form an error voltage VB.This error voltage 1/E is supplied to the motor drive circuit B, and the rotational speed of the motor 1 is controlled.

However, normally, even when the motor 1 is stopped, the frequency generator generates noise, although it is weak. Consequently, the amplifier 2 will be supplied with noise even when the frequency signal F is not supplied. The amplifier 2 shapes the weak sinusoidal frequency signal FI into a rectangular wave, and has a sufficiently high gain, so it can sufficiently amplify even weak noise, and even when the motor 1 is stopped, As shown in FIG. 6, the output signal FO when driving the motor 1
Outputs a signal with the same amplitude as . Therefore, the frequency discrimination circuit 5 outputs a PWM signal corresponding to the frequency of this signal. In the end, the 9-frequency discrimination circuit 3 outputs a pw double signal shown as vp' in FIG.

For this reason, when the motor 1 is stopped, the error voltage WE supplied to the motor drive circuit 6 is very low, and the drive command signal S becomes H' and the motor drive circuit 6 starts operating. However, the driving voltage 1/D is not high enough to drive the motor 1t sufficiently, and in the worst case, the motor 1 cannot be driven.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a servo control device that eliminates the drawbacks of the prior art described above, prevents the influence of noise, always starts the motor normally, and can stably control the motor.

[Summary of the invention]

To achieve this objective, the present invention prohibits the supply of voltage affected by noise to the motor drive circuit at least when the motor is stopped, and instead prevents the motor from starting and accelerating. Embodiments of the invention The embodiments of the invention will be described below with reference to the drawings. 1 is a block diagram showing an embodiment of a servo control device according to the invention, in which 8 is a differential amplifier, 9 is a rotating disk, 10 is a detector, 11 is a mode designation circuit, a 12μ delay circuit, and 15
．． 14i) transistor, 15.16 is capacitor, 17
~22 is resistance.

Reference numeral 23 denotes a power supply voltage supply terminal, and parts corresponding to those in FIG. 5 are given the same reference numerals and redundant explanations will be omitted.

In FIG. 1, when the drive command signal S from the mode designation circuit 11 is L'', the motor drive circuit 6 is in an inactive state and the motor 1 is in a stopped state.

On the other hand, the drive command signal S is supplied to the delay circuit 12.
A well-delayed control signal SD is formed, and the resistor 22t
l- to the base of transistor 130. At this time, since the drive command signal S is 'L', the control signal SD is 'L' and the transistor 13 is in the off state. In this case, the transistor 14 is in the on state because its base voltage is H''.
Noise is generated even when the motor is stopped. However, since transistor 14 is in the on state, this noise flows to ground through transistor 14 and is not supplied to differential amplifier 8.

Therefore, the output signal FO of the differential amplifier 8 is kept at "L#".
l The output signal vp of the frequency discrimination circuit 3 is held at 'H' as shown in FIG.
is maintained at a sufficiently large level of "H#" Next, by specifying motor start, when the drive command signal S becomes "H", the motor drive circuit 6 becomes operational, but the error voltage has already been formed. Since the error voltage of 1H# is supplied from the circuit 4, the motor 1 is started normally by the motor drive circuit 6.At the same time, the rotating disk 9 starts to rotate and the detector 10 detects the voltage of the motor 1. A frequency signal FI of the next station wave number is output according to the rotation speed.

The output signal SD from the t1 delay circuit 12 becomes 'H'' later than the drive command signal S by the delay amount of the delay circuit 12, so that the transistor 13 is turned on.
Transistor 14 is turned off. Next, the frequency signal FI is supplied to the non-inverting input terminal of the differential amplifier 8 via a capacitor 15 that blocks the DC component, and an appropriate bias voltage is applied by a resistor 17 and 18.
Ru. The output signal F0 is divided by resistors 19 and 20 and fed back to the inverting input terminal of the differential amplifier 8. This differential amplifier 8 operates so that the level of the signal supplied to the inverting input terminal is equal to the level of the signal supplied to the non-inverting input terminal, and for this purpose, the resistance value ratio of the resistors 19 and 20 is adjusted appropriately. By setting the gain, the gain can be sufficiently increased, and by increasing the gain sufficiently, the single output signal FO becomes a rectangular wave signal having the same frequency as the frequency signal F'I.

This rectangular wave signal FO is supplied to the frequency discrimination circuit 3, and pulse width modulated according to the frequency of the rectangular wave signal FO.
M-wave VP is obtained〇Hereafter, the motor 1 is
1 servo control is performed to keep the rotation speed of n constant.
Ru.

When the drive command signal S becomes "L#", the motor drive circuit 6 becomes inactive and the motor 1 stops, but at the same time, the control signal SD also becomes "L" and the transistor 14 is turned on. Noise generated by the detector 10 is blocked.
Then, the error voltage VE supplied to the motor drive circuit 6 becomes a sufficiently high level 'H'.

As described above, even if noise is generated from the frequency generator when the motor 1 is stopped, even if the amplifier 8 with a sufficiently high gain is used to shape the frequency signal TI, the frequency The level of the output signal of the discrimination circuit 3 is then set to a sufficiently high level of the error voltage vm supplied to the motor drive circuit 6.
This allows the motor 1 to be started reliably.

Wear.

Note that the delay circuit 12 has a delay amount that is approximately equal to the period from when the motor 1 is started until it rotates at approximately the specified rotational speed, and this delay circuit 12 uses the delay circuit 12 to convert the rise of the control signal SD into a drive command signal. By also delaying S, the servo control at the time of starting the motor 1 is prohibited, allowing the motor 1 to start smoothly. ◎ Fig. 2 shows another embodiment of the servo control device according to the present invention. In the block diagram shown, 23 is a switch, and parts corresponding to the gI diagram are denoted by the same reference numerals, and redundant explanations will be omitted.

FIG. 3 is a waveform diagram showing the signals of each part in FIG. 2. It is something.

In FIGS. 2 and 3, if it is assumed that the drive command signal S is 'L#' and the motor 1 is in a stopped state, the control signal SD from the delay circuit 12 is also 'L#'.
The switch 25 is turned on by the control signal SD, and the resistor 19 is generally short-circuited.As a result, the differential amplifier 8 has a signal supplied to its non-inverting input terminal and its output signal FO. Almost equal, no amplification effect is performed.

Therefore, the noise generated in the detection circuit 10 is supplied as is (without being amplified) to the frequency discrimination circuit 3. However, since this noise signal is weak, the frequency discrimination circuit 3 does not respond to this signal, and therefore, the input signal of the frequency discrimination circuit 3 is kept at "L" and its output signal vP is kept at "H". Next, the error voltage supplied to the motor drive circuit 6 is also kept at "H".

At this time, when the drive command signal S becomes 1'' and the motor drive circuit 6 enters the operating state, the motor 1 is reliably and smoothly started.

Thereafter, the control signal SD becomes "H" and the switch 23 is turned off), the gain of the differential amplifier 8 becomes sufficiently high, and the servo control of the motor 1 is performed.

Note that the switch 23 significantly reduces the time constant of the time constant circuit determined by the capacitor 21 and the high resistance value resistor 19, and changes the operating voltage of the differential amplifier 8 during the "also" period of the control signal SD. Achieve a predetermined value in an instant. As a result, the amplifying operation of the differential amplifier 8 starts quickly when the motor 1 starts driving. Changeover switch, 2
Reference numeral 5 designates an input terminal, and portions corresponding to FIGS. 1 and 5 are marked with a 4- symbol, and the redundant explanation 8A is omitted.

This embodiment consists of an error voltage forming circuit 4 and a motor drive circuit 6.
A changeover switch 24 is provided between the error voltage forming circuit 4 and
Error voltage '/E supplied to contact A from input terminal 25
This voltage is selectively supplied to the motor drive circuit 6 in addition to the ``H'' voltage supplied to the contact B from the contact B.

First, when the drive command signal S is "L" and the motor 1 is in a stopped state, the control signal SD is also "L", the changeover switch 24 is closed to the contact B side, and the input terminal 25 is connected to the motor drive circuit 6. A voltage of H'' is supplied. At this time,
The noise generated by the frequency scattering of the motor 1 (not shown) is amplified by the amplifier 2 and supplied to the frequency discrimination circuit 3, so the error voltage VB is at a relatively low level ◇ Therefore, the drive command signal When S becomes "H#", at this time, the control signal SD is 1L, the changeover switch 24 is closed to the contact B@, and the input terminal 2 is connected to the motor drive circuit 6.
Since the voltage of 5 to 1H# is supplied, the motor 1 starts up reliably and smoothly.

When the motor 1 begins to rotate at the specified rotational speed, the error voltage vFV becomes the difference between the current rotational speed of the motor 1 and the specified rotational speed.

The changeover switch 24 is closed to the contact A side in response to the control signal SDh''H#.As a result, the error voltage vF! is supplied to the motor drive circuit 6, and the motor 1 is servo-controlled.

〔Effect of the invention〕

As explained above, according to the present invention, when the motor is started, the motor driving voltage required to start the motor can be supplied to the motor, so that the motor can be started reliably. Moreover, it is possible to provide a servo control device with superior n-order functions, which can be operated smoothly and eliminates the drawbacks of the above-mentioned conventional technology.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the servo control device according to the present invention, FIG. 2 is a block diagram showing another embodiment of the servo control device according to the present invention, and FIG. 3 shows signals of each part of FIG. 2. FIG. 4 is a block diagram showing still another embodiment of the servo control device according to the present invention, FIG. 5 is a block diagram showing an example of a conventional servo control device, and FIG.
FIG. 3 is a waveform diagram showing signals at each part in the figure. DESCRIPTION OF SYMBOLS 1... Motor, 2... Amplifier, 3... Frequency discrimination circuit, 4... Error voltage formation circuit, 6... Motor drive circuit, 7... Drive command signal input terminal, 8...・Differential amplifier, 12-...delay circuit, 23...switch, 2
4... Selector switch, 25... High level voltage input terminal.

Claims (5)

[Claims] (1) a first means for generating a frequency signal having a frequency corresponding to the rotational speed of the motor; a second means for amplifying the frequency signal with a high amplification gain and shaping the waveform; a third means for digitally frequency-discriminating the output signal; and a fourth means for driving the motor based on the output signal of the third means in the operating state, the motor being switched between an operating state and a non-operating state by a drive command signal. In the servo control device, the servo control device is configured to control the rotational speed of the motor to a constant level, and further includes a switching device that is controlled to turn on and off based on the drive command signal. A servo control device, characterized in that the servo control device is configured such that a voltage of a predetermined level or higher is applied to the fourth means immediately before the start of driving. (2) The servo control device according to claim (1), wherein the signal for controlling the switching means on and off is a signal obtained by delaying the drive command signal by a predetermined time. (3) In claim (1) or (2), the switching means is provided on the input side of the second means, and during a drive stop period of the motor, the switching means is provided on the input side of the second means. A servo control device characterized in that supply of an output signal from the first means is prohibited. (4) In claim (1) or (2), the second means is a feedback differential amplifier, and the switching means switches a feedback resistor of the feedback differential amplifier. . A servo control device, characterized in that the feedback differential amplifier is configured to be able to reduce its gain during a drive stop period of the motor. (5) In claim (1) or (2), the switching means receives, as an input to the fourth means, a voltage based on the output signal of the third means and a voltage equal to or higher than the predetermined level. A servo control device characterized in that the servo control device is configured to switch between the voltage and the voltage.