JPS60144150A - Speed control circuit of motor - Google Patents

Abstract

PURPOSE:To readily control at variable speed with high linearity by a digital signal by altering the conversion constant of the frequency of a frequency/voltage converter to the voltage output. CONSTITUTION:The voltages outputted from a tachometer generator 2 for detecting the rotating speed of a motor 1, a frequency/voltage converter 3 for converting the output of the generator 2 to a voltage are compared with a reference voltage ES, and power supply amount to a motor is controlled in response to an error therebetween. The first resistor 9 for deciding the conversion constant of the frequency to the voltage output of the converter 3, the second resistor 13 connected in parallel with the resistor 9 and in series with each other, and a transistor 12 are provided, and a pulse width modulation signal is supplied to the base 14 of the transistor, thereby equivalently varying the resistance value.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention detects the rotational speed of a motor using a frequency generator such as a tacho generator, and supplies power to the motor in accordance with the detected output. Regarding the motor speed control circuit that controls the motor so that it always rotates at a set speed,
In particular, the set speed can be freely varied, making it useful for application to, for example, speed control circuits for floppy disk drive motors and the like.

<Background technology and its problems> Conventionally, a frequency generator such as a tacho generator, which is installed in a motor and outputs its rotational speed as a frequency signal, has been used as a speed control circuit for a motor for rotating a floppy disk or the like. A frequency-to-voltage converter converts the output of this frequency generator into a voltage output at a level corresponding to the frequency, and the voltage output of this frequency-to-voltage converter is compared with a reference voltage, and the voltage is calculated according to the mutual error. There is a known device that includes an operational amplifier that increases or decreases the amount of power supplied to the motor, and controls the power supply based on the rotation period of the motor to maintain an accurate rotational speed of the motor at all times. There is. The frequency-voltage converter provided in this speed control circuit applies a voltage to a circuit in which a resistor and a capacitor are connected in series, and forms a ramp wave signal having a constant slope at the time of rising. This ramp wave signal is sequentially reset by a pulse signal obtained by waveform shaping the frequency signal, and is formed as a plurality of ramp wave signals that rise sequentially corresponding to the frequency of this pulse signal, and the signal level of these ramp wave signals is is compared with a reference level to form a rectangular wave signal having a width corresponding to the frequency of the pulse signal, and this rectangular wave signal is further passed through a low-pass filter. By converting the voltage level into a voltage level corresponding to the pulse width ratio, a voltage level corresponding to the frequency of the pulse signal, that is, the frequency of the frequency signal output from the frequency generator is obtained.

By the way, in a speed control circuit with such a configuration, in order to change the set speed of the motor and perform multi-step variable speed control, the reference voltage is variably adjusted and the reference value for power supply to the motor is adjusted. There is a way to change it.

However, in this method, if this speed control circuit is installed in a device that is controlled by a digital signal by a microprocessor, etc., the analog reference voltage cannot be controlled by a digital signal. Since digital-to-analog conversion is required for this purpose, the circuit configuration becomes complicated and linearity is difficult to obtain.

<Object of the Invention> In view of the above-mentioned circumstances, the present invention aims to provide a motor speed control circuit that can easily perform highly linear variable speed control using digital signals and has a simple configuration. shall be.

<Summary of the Invention> In other words, in order to achieve the above-mentioned object, the present invention supplies the output of a frequency generator whose frequency changes depending on the rotational speed of the motor to a frequency-voltage converter', and converts the frequency -
In a motor speed control circuit that controls the speed of the motor according to the voltage output of the voltage converter, a first resistor that determines a conversion constant between the frequency and the voltage output in the frequency-voltage converter; A second resistor and a switching element are provided which are connected in parallel to this resistor and connected in series with each other, and the resistance value is changed isometrically by supplying a pulse width modulation signal to the switching element. This is how it was done.

<Example> Hereinafter, specific examples of the present invention will be described in detail with reference to the drawings.

As shown in FIG. 1, the speed control circuit for a motor 1 according to the present invention includes a frequency generator 2, such as a tacho generator, provided in the motor 1 for detecting the rotational speed of the motor 1.
Then, the frequency signal outputted from the frequency generator 2 (see Fig. 3) is outputted from the frequency-voltage converter 3 to a frequency-voltage converter 3 that converts the frequency signal outputted from the frequency generator 2 into a voltage corresponding to the frequency of this frequency signal. and an operational amplifier 4 that compares the voltage applied to the reference voltage Es with a reference voltage Es and controls the amount of power supplied to the motor according to the mutual error. The power supply is controlled accordingly to ensure that the motor 1 always has an accurate rotational speed.

In this speed control circuit, the frequency-voltage converter 3
For example, as shown in FIG. 2, the frequency signal of the frequency generator 2 supplied to the input terminal 5 is waveform-shaped to obtain a pulse signal C synchronized with the frequency (see FIG. 3). A container 6 is provided. The pulse signal output from the waveform shaper 6 is supplied to the base terminal of a ramp wave reset transistor 70. The emitter terminal of this transistor 7 is grounded, and the collector terminal is connected to only one power terminal of the operational amplifier 8.

Further, a first resistor 9 and a capacitor 10 connected in series with each other are connected to the frequency-voltage converter 3 in order to obtain a ramp wave signal C (see FIG. 3) that always rises at a constant angle of inclination. There is a samurai. The first resistor 9 has one end connected to a power source 11 to be supplied with power, and the other end of the capacitor 10 is grounded. Further, a second resistor 12 and a transistor 13 serving as a switching element, which are connected in series with each other, are connected to the first resistor 9.
are connected in parallel. The base terminal of the transistor 13 is a pulse width modulation signal (hereinafter referred to as a PWM signal).
is connected to the PWM input terminal 14 supplied with the signal, and its collector terminal and emitter terminal are connected to the power supply 11 and the second resistor 12, and the base terminal receives the pulse input of the PWM signal. Sometimes the above power supply 1
1 and the second resistor 12. That is, the instantaneous resistance value R between the capacitor 13 and the power supply 11 during the operation period corresponding to the pulse width of the PWM signal of the transistor 13 is
' is the resistance value of the first resistor 9 and the second resistor 12, respectively. Therefore, the first resistor 9 and the second resistor between the power source 11 and the capacitor 10
The resistance value R given by the resistor 12 is the above PwM
It changes with equal constraints depending on the ratio of the pulse width to the pulse period of the signal, that is, the duty ratio. The connection ends of the first resistor 9 and the second resistor 12 connected in this way and the capacitor 10 are connected to the collector terminal of the ramp wave reset transistor γ, and the connection terminal of the operational amplifier 8 is connected to the collector terminal of the ramp wave reset transistor γ. One input terminal has nine connected to it. That is, this input terminal has the capacitor 10
The charges charged in the ramp wave reset transistor 7 sequentially reset and fall by the operation corresponding to the pulse signal, and after this reset, a ramp wave signal is generated that sequentially rises at a certain slope angle. It will be supplied. The inclination angle at the rise of this ramp wave signal is set by the resistance value R given by the first resistor 9 and the second resistor 12. It is assumed that the frequency of the PWM signal is sufficiently thicker than the frequency of the pulse signal.

Further, a pair of reference resistors 15 and 16 are connected to the power source 11 and are connected in series with each other and grounded. The connection terminals of these reference resistors 15 and 16 are connected to the other input terminal of the operational amplifier 8, and a reference voltage for obtaining the time constant of the ramp wave signal is applied to the operational amplifier 8.

The operational amplifier 8 compares the levels of the ramp wave signal supplied to both input terminals and the reference voltage, and generates a step output at the output terminal when the ramp wave signal exceeds the reference voltage. In this case, a rectangular wave signal (see FIG. 3) having a pulse width corresponding to the time constant and generation period of the ramp wave signal is output.

The rectangular wave signal output from the operational amplifier 8 is integrated by a low-pass filter 19 consisting of a resistor 17 and a capacitor 18, and an integrated waveform voltage output having a voltage level corresponding to the pulse width of this rectangular wave signal is output. (See FIG. 3), the signal is outputted from the output terminal 25 of this frequency-voltage conversion circuit. Therefore, this voltage output is further waveform-shaped by a waveform shaping circuit (not shown) to obtain a voltage at a nearly constant level, and the operational amplifier 4 compares the voltage with the reference voltage ES.

Therefore, in a speed control circuit having such a configuration, when it is desired to change the set speed of the motor in order to perform variable speed control of the motor, for example, a microprocessor may be used to control the speed of the motor.
This is done by changing the pulse width or pulse period of the PWM signal supplied to the input terminal, and variably adjusting the duty ratio of this PWM signal. That is, if the resistance value of the second resistor 12 is R24 and the duty ratio is D (%), the actual resistance value R34 generated in the second resistor 12 is equivalent to -100R2 R3-□ becomes. Therefore, the time constant T of the ramp wave signal, which is determined by R3, is given by: (R, 1...・Constant) That is, as shown in FIG. 4, the slope of the rising portion of the ramp wave signal changes as the duty ratio is varied as D z D 2 D s . The ratio of the pulse width to the pulse period of the rectangular wave signal determined by the time constant of the signal, that is, the duty ratio of the rectangular wave signal, is changed irrespective of the frequency of the pulse signal.

Therefore, the conversion constant between the frequency of the pulse signal and the voltage output converted to a level corresponding to this frequency is not changed, and the speed of the motor 1 can be adjusted without changing the reference voltage ES. Control becomes possible.

In addition, when the duty ratio of the PWM @ is changed and the rotation speed of the motor 1 is N, (K1.
...constant) is obtained. Therefore, the rotation speed N of the motor 1 changes linearly as the duty ratio of the PWM signal changes.

As described above, according to the speed control circuit of the motor 1 in this embodiment, the conversion constant between the frequency and voltage output of the frequency-voltage converter is changed by changing the duty ratio of the PWM signal. Therefore, the motor 1 is controlled by digital signals from the microprocessor, etc.
variable speed control can be easily performed from time to time. Therefore, there is no need to change the reference voltage Es, and no complicated circuit configuration for digital-to-analog conversion is required.

Further, variable speed control of the motor 1 with extremely high linearity can be realized.

Further, in the above-described embodiment, a case was described in which the frequency of the PWM signal is extremely large compared to one wave number of the pulse signal, that is, the frequency of the frequency signal.
If the frequency of the WM signal is relatively close to the frequency of the pulse signal, and the switching operation of the transistor 13 affects the waveform of the ramp wave signal, causing the ramp wave signal to beat, As shown in FIGS. 5 and 6, it is sufficient to provide a rotor filter 22 consisting of a resistor 20 and a capacitor 21 that absorbs the high frequency component of the PWM @ signal and alleviates the influence on the ramp wave signal. When such a row-nosed filter 22 is provided, the resistor 20 of this row-nosed filter 22 enters the discharge path of the capacitor 10, so in order to ensure reliable discharge of the capacitor 10, for example, A diode 23 and a transistor 24 may be provided, and the diode 23 and transistor 24 may be operated by the above-mentioned pulse signal to form a discharge path with a small time constant.

<Effects of the Invention> As is clear from the description of the embodiments described above, according to the present invention, by changing the duty ratio of the pulse width modulation signal, the conversion constant between the frequency and voltage output of the frequency-voltage converter can be changed. Since the speed of the motor is changed, variable speed control of the motor can be easily performed using a digital signal from a microprocessor or the like, for example. Therefore, there is no need to change the reference voltage, there is no need for a complicated circuit configuration for digital-to-analog conversion, and it is possible to realize variable speed control of the motor with extremely high linearity.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing a frequency-voltage converter, and FIG. 3 is a circuit diagram showing various signal waves obtained by the frequency-voltage converter. FIG. 6 is a circuit diagram showing the main parts of another embodiment of the invention. FIG. 6 is a circuit diagram showing the main parts of still another embodiment of the invention. 1... Motor 2... Frequency generator 3... Frequency-voltage converter 4... Operational amplifier 9... First resistor 12... Second resistor 13... Transistor patent application Person Sony Corporation Representative Patent Attorney Kodo Koike 1) Sakae Mura - Figure 1 Figure 3 t

Claims (1)

[Claims] The output of a frequency generator whose frequency changes depending on the rotational speed of the motor is supplied to a frequency-voltage converter, and this frequency -
In a motor speed control circuit that controls the speed of the motor according to the voltage output of the voltage converter, a first resistor that determines a conversion constant between the frequency and the voltage output in the frequency-voltage converter; A second resistor and a switching element are provided which are connected in parallel to this resistor and connected in series with each other, and the resistance value is changed with equal constraints by supplying a pulse width modulation signal to the switching element. Motor speed control circuit.