JP2965587B2 - Motor speed control circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor speed control circuit that detects a rotation speed of a motor, performs a feedback control based on the detection signal, and controls the motor speed to a constant speed or a desired speed.

[Conventional technology]

Conventionally, as disclosed in Japanese Patent Application Laid-Open No. 61-69384, there has been proposed a motor speed control circuit that detects the rotation speed of a motor and controls the motor at a constant speed (PWM control).

That is, as shown in FIG. 4, a sine wave signal having a cycle corresponding to the rotation speed of the DC motor 7 is output from the rotation detecting unit 1 (FIG. 6, i).
It is shaped into a pulse signal by 11 (FIG. 6, j). Then, in synchronization with the rise of this pulse signal, the integration circuit
The integration is started by 12 and a sawtooth wave is generated (the sixth wave).
Figure, k). The peak voltage of the sawtooth wave is held by the sample hold circuit 13 (FIG. 6, l), and the voltage between the hold voltage VL and the speed setting voltage VM (FIG. 6, m) from the speed setting voltage generating circuit 18 is applied. The difference is amplified by the differential amplifier circuit 14. The amplified voltage VN (FIG. 6, n) and the reference triangular wave voltage VO (FIG. 6, FIG.
o) is compared by the comparator 16, and a pulse is output while the amplified voltage VN is on the reference triangular wave voltage VO (the sixth pulse).
Figure, p).

During the output period of the pulse p, the switching circuit
17 is turned on, and the motor current is supplied to the motor 7 from the power supply Vcc. Therefore, the switching circuit
A torque is generated according to the ON period of 17, and the rotation speed is controlled according to the torque.

Thus, for example the rotational speed of the motor 7 is reduced by the load of the motor 7 becomes heavier, as shown in waveform I ₂ of Figure 6,
When the period of the sine wave signal from the rotation detecting unit 1 is longer than the waveform I ₁ , the sawtooth wave K ₂
Peak voltage is increased in comparison with the waveform K _1. Therefore, the amplified voltage VN from the differential amplifier circuit 14 is
Period equal to or greater than the voltage VO of the reference triangular wave from 5 becomes longer, as shown in waveform P ₂ of FIG. 6, the pulse width of the output pulse p from the comparator 16 is wider than the waveform P _1.

As a result, the period during which the motor current is supplied from the power supply Vcc to the motor 7 is prolonged, and the torque of the motor 7 is increased. Therefore, the rotation speed of the motor 7 is increased to return to the initial rotation speed.

On the other hand, when the load on the motor 7 is reduced and the rotation speed of the motor 7 is increased, and the period of the sine wave signal from the rotation detector 1 is shortened, the peak voltage of the sawtooth wave k from the integration circuit 12 is reduced. As a result, the period during which the amplified voltage VN from the differential amplifier circuit 14 is higher than the reference triangular wave voltage VO is shortened,
, The pulse width of the output pulse p becomes narrower. As a result,
The period during which the motor current is supplied from the power supply Vcc to the motor 7 is also shortened, the torque of the motor 7 is reduced, and the rotation speed of the motor 7 is reduced to return to the desired rotation speed.

As described above, the rotation speed of the motor 7 is controlled steplessly according to the fluctuation of the rotation speed of the motor 7 so that the motor 7 rotates at a constant speed.

[Problems to be solved by the invention]

However, in the conventional motor speed control circuit, as shown in the circuit diagram of FIG. 5, the number of parts is large and the production cost is increased by using a dedicated IC.

Further, since the hold timing of the sample hold circuit 13 is delayed by one cycle of the sine wave signal, the response is poor.

Further, for example, even if the rotation of the motor 7 is stopped due to an overload on the motor 7, the motor 7 continues to be supplied with the motor current from the power supply Vcc.
Etc. may be damaged or burnt.

SUMMARY OF THE INVENTION An object of the present invention is to provide a motor speed control circuit which solves the above-mentioned problem, is low in cost, has good responsiveness, and can prevent overcurrent to the motor.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a battery as a power supply connected to a motor and a means for generating a predetermined set level, and a means for generating the motor and the set level. A constant voltage power supply for supplying power from the battery via a constant voltage circuit to a means for outputting a sawtooth wave to be compared with a set level, and a periodic signal corresponding to the rotation speed of the motor. Periodic signal generating means, pulse shaping means for shaping the periodic signal into a pulse signal, sawtooth wave generating means for outputting a sawtooth wave synchronized with the pulse signal, and the level of the sawtooth wave and the set level And motor power supply means for supplying drive power to the motor while the sawtooth wave is at or above the set level.

Further, the motor speed control circuit according to the second aspect of the present invention includes a bias means for biasing the level of the sawtooth wave, and the lowest level of the sawtooth wave is set higher than the set level.

The motor speed control circuit according to claim 3, further comprising a level comparing means for comparing the level of the sawtooth wave with the regulation level, and supplying the drive power to the motor when the level of the sawtooth wave exceeds the regulation level. To stop.

(Operation) According to the motor speed control circuit having the above configuration, a periodic signal corresponding to the rotation speed of the motor is shaped into a pulse signal, and a sawtooth wave synchronized with the pulse signal is formed by being supplied with power from a low-voltage power supply. During the period when the level of the sawtooth wave is higher than the set level, the drive power is supplied to the motor. Then, when the rotation speed of the motor decreases, the supply period of the drive power to the motor increases, the rotation speed of the motor increases to the desired rotation speed, and when the rotation speed of the motor exceeds the desired rotation speed, The supply period of the drive power to the motor is shortened, and the rotation speed of the motor is reduced to the desired rotation speed.

In addition, when the load on the motor becomes heavy and the rotation speed of the motor decreases, and the power supply from the battery to the motor increases, the battery voltage decreases, that is, the set level decreases. As a result, the period of current supply to the motor becomes longer, and the increase in the rotation speed of the motor is promoted.

Further, the level of the sawtooth wave is biased so that the lowest level of the sawtooth wave is higher than the set level, and the setting can be made up to the maximum of the motor rotation speed.

Also, when the level of the sawtooth wave exceeds the regulation level,
The supply of drive power to the motor is stopped, and overcurrent to the motor is prevented.

〔Example〕

FIG. 1 is a circuit diagram of one embodiment of a motor speed control circuit according to the present invention.

The rotation detecting section 1 is composed of, for example, a frequency oscillator (FG), and outputs a sine wave signal (FIG. 2, a) having a cycle corresponding to the rotation speed of the motor 7 in order to detect the rotation speed of the motor 7. . The waveform shaping circuit 3 shapes the sine wave signal from the rotation detecting section 1 into a pulse signal. That is, the resistors R ₁ and R ₂ and the capacitor C ₁ constitute a low-pass filter for removing noise from the sine wave signal a from the rotation detecting unit 1. The resistors R ₃ and R ₄ apply a bias to the sine wave signal from which the DC component has been removed by the capacitor C ₂ and input it to the non-inverting input terminal of the comparator 31. resistance
R ₅ and R ₆ divide the voltage from the constant voltage circuit 9 and input it to the inverting input terminal of the comparator 31. The comparator 31 compares the biased sine wave signal with the divided voltage, and outputs a pulse during a period when the biased sine wave signal is equal to or higher than the divided voltage (FIG. 2, b). is there.

The sawtooth wave generating circuit 4 generates a sawtooth wave synchronized with the output pulse from the waveform shaping circuit 3. That is, the capacitor C ₄ and the resistor R ₇ is for differentiating the output pulses from the comparator 31. Then, a positive differential pulse is formed at the rise of the output pulse of the comparator 31, and a negative differential pulse is formed at the fall (second
Figure, waveform c). Diode D ₁ is intended for output only the positive trace amount pulse to the base of the transistor Q _1.

Transistor Q ₁ is are those turned on by the input of the positive trace amount pulse. Then, by turning on the transistor Q _1, the capacitor C ₅ is discharged to a predetermined discharge voltage. That is, the discharge of the capacitor C ₅ is the base of the transistor Q _1, is performed to the emitter voltage to a voltage obtained by adding the ON voltage of the diode D _2. The diode D ₂ may be one that a plurality of diodes connected in series, it may be a Zener diode. In this case, the discharge voltage is set by the number of diodes or the Zener voltage of the Zener diode.

With the capacitor C ₅ is discharged by turning on the transistor Q ₁ as described above, is intended to be charged by the current from the constant voltage circuit 9 through a resistor ₉ during the off period of the transistor Q _1. That is, the voltage between the terminals of the capacitor C ₅ is after the discharge, it is charged with a slope determined by the time constant of the capacitor C ₅ and the resistor _9, the sawtooth waveform (Fig. 2, d).

The comparator 51 of the comparison circuit 5 compares the sawtooth voltage with the set voltage. That is, the terminal voltage of the capacitor C ₅ is input to the non-inverting input terminal of the comparator 51,
On the other hand, a voltage obtained by dividing the battery voltage of the battery 2 by the resistors R ₁₀ and R ₁₁ and the variable resistor VR is input to the inverting input terminal. Then, the comparator 51 outputs a time high inter-terminal voltage of the capacitor C ₅ is the divided voltage higher (FIG. 2, e). The variable resistor VR is used to set the voltage applied to the inverting input terminal of the comparator 51 in order to set the motor 7 to the desired rotational speed.

When the battery voltage from the battery 2 decreases, the voltage to the inverting input terminal of the comparator 51 decreases in accordance with the decrease. That is, for example, when the load of the motor 7 becomes heavy and the rotation of the motor 7 becomes slow and the current to the motor 7 increases, the battery voltage of the battery 2 decreases and the voltage to the inverting input terminal of the comparator 51 decreases. . For this reason, as will be described later, the supply period of the drive power to the motor 7 is lengthened, and the rotation speed of the motor 7 is increased.

The discharge voltage of the capacitor C ₅ because it is biased to a positive voltage, the input voltage to the non-inverting input terminal of the comparator 51 becomes also a positive voltage at the lowest voltage level. Therefore,
By adjusting the variable resistor VR, the duty ratio of the output pulse from the comparator 51 can be adjusted to almost 100%. That is, the rotation speed of the motor 7 can be set continuously and up to the maximum.

FET8 the comparator 5 which is divided by the resistors R _12, R ₁₃ to the gate
One of the output pulses is input. During the output period of the output pulse, the output pulse is turned on to supply a current from the battery 2 to the motor 7. The motor 7 is composed of a DC motor or the like, and rotates at a rotation speed according to a current supply period. That is,
The rotation speed of the motor 7 increases as the current supply period increases, and decreases as the current supply period decreases. Low voltage circuit 9
Is to output the battery voltage from the battery 2 at a constant voltage. The diode D ₃ is a spike noise prevention generated when the motor 7 is turned off.

The comparator 61 of the protection circuit 6 compares the sawtooth voltage with the regulation voltage. That is, the terminal voltage of the capacitor C ₅ is input to the non-inverting input terminal of the comparator 61,
On the other hand, the low voltage circuit 9 is connected to the inverting input terminal by resistors R ₁₄ and R _15.
A voltage obtained by dividing this voltage is input as a regulated voltage. Then, the comparator 61 outputs a time high inter-terminal voltage of the capacitor C ₅ is the regulating voltage or more (Figure 3, f). Transistor Q ₂ is intended to output of the comparator 61 is inputted through a resistor R _16, and outputs a period ON of the output pulse, FET 8
The gate of is turned to a low level to forcibly turn off the FET8.

Next, the operation of the motor speed control circuit having the above configuration will be described with reference to FIGS.

When the driving of the motor 7 is started, the waveforms A ₁ and A in FIG.
As shown in _2, corresponding from the rotation detecting section 1 to the rotational speed of the motor 7, for example, a sine wave signal with a period T ₁ is outputted.
The sine wave signals A ₁ and A ₂ are input to the inverting input terminal of the comparator 31 after being biased by the resistors R ₃ and R ₄ . Then, the comparator 31 compares the biased sine wave signals A ₁ and A ₂ with the divided voltage V ₂ by the resistors R ₅ and R ₆ , as shown in waveforms B ₁ and B ₂ in FIG. 2B. During the period in which the sine wave signals A ₁ and A ₂ are equal to or higher than the divided voltage V ₂ , the comparator 31 outputs high.

The output pulse B _1, B ₂ of the comparator 31 is differentiated by the capacitor C ₄ and a resistor R _7, as shown in waveform C ₁ -C ₄ in FIG. 2 c, positive trace amount pulse C _1, C ₂ and the negative electrode Differential pulse C ₃ ,
C ₄ is applied to the diode D _1. And the diode D ₁
Only positive trace amount pulse C _1, C ₂ is applied to the base of the transistor Q _1, the transistor Q ₁ is the capacitor C ₅ is turned on are discharged up to discharge voltages described above through. After this discharge,
Capacitor C ₅ is charged, as shown in waveform D _1, D ₂ of FIG. 2 d, the voltage between the terminals of the capacitor C ₅ is a sawtooth waveform.

These saw-tooth waveform voltages D ₁ and D ₂ are input to a comparator 51,
As shown by a dashed line D in FIG. D, the voltage is compared with a voltage obtained by dividing the battery voltage of the battery 2 by the variable resistor VR or the like. Then, as shown by waveforms E ₁ and E ₂ in FIG. 2E, a high is output from the comparator 31 while the sawtooth voltage is equal to or higher than the divided voltage D. During the output period of the output pulse, the FET 8 is turned on and the current from the battery 2 is supplied to the motor 7 so that the motor 7
Rotates at a rotation speed corresponding to this output period.

On the other hand, for example, the motor 7
When the rotation of the drops, as shown in waveform A ₃ in FIG. 2 a,
Cycle of the sine wave signal from the rotation detecting section 1 is T ₁ from T ₂ (T ₁ <
T ₂ ). For this reason, as shown by the waveforms B ₃ and B ₄ in FIG. 2B, the period of the output pulse of the comparator 31 also becomes longer. Therefore, as shown in waveform D ₃ in FIG. 2 d, a capacitor C ₅
Is longer, the sawtooth voltage becomes equal to the divided voltage D.
The above period becomes longer. Then, the output period of the output pulse of the comparator 31 becomes longer, and the ON period of the FET 8 becomes longer.

Thus, when the on period of FET8 becomes longer, the battery voltage of the battery 2 is reduced by a current from the battery 2 to the motor 7, as shown in dashed line D ₀ in FIG. 2 d, inversion of the comparator 51 The divided voltage to the input terminal decreases. Therefore, as shown in waveform E ₃ in FIG. 2 e, the ON period of the output period becomes longer FET8 of the output pulse of the comparator 31 is T _3. That is, when the rotation of the motor 7 decreases, the period of the sawtooth waveform increases, and the divided voltage D decreases, so that the ON period of the FET 8 increases. Therefore, the current to the motor 7 is further increased, and the increase in the rotation speed of the motor 7 is promoted.
As a result, the motor 7 is controlled to return to the desired rotation speed in a short time.

Further, for example, when the rotation of the motor 7 increases, the period of the sine wave signal from the rotation detecting unit 1 becomes shorter, and the period of the output pulse of the comparator 31 also becomes shorter. Then, the period during which the sawtooth waveform voltage is equal to or higher than the divided voltage D is also shortened, and the ON period of the FET 8 is shortened. For this reason, the current supply period to the motor 7 is shortened, and the rotation speed of the motor 7 is reduced. As a result, the motor 7 is controlled to return to the desired rotation speed.

On the other hand, at a substantially stopped state rotation of the motor 7 is reduced extremely due to an overload of the motor 7, the period of the third, as shown in waveform A ₄ in FIG. A _1, a sine wave signal from the rotation detecting section 1 Becomes extremely long, and the amplitude becomes extremely small. Then, the level of the sine wave signal input to the inverting input terminal of the comparator 31 is no longer exceeds the divided voltage V _2, as shown in the latter half of the waveform of Figure 3 b, is not output pulse from the comparator 31 . Therefore, the capacitor C ₅ continues to be charged and the charging voltage is regulated voltage V ₃ or more comparators 61 of the protective circuit 6, as shown in Figure 3 f, the high from comparator 61 at t ₀ point is output to the base of the transistor Q _2, transistor Q ₂
Turn on.

As a result, the gate of the FTE 8 becomes low level, the FET 8 is forcibly turned off, and the supply of the current to the motor 7 is stopped. After time t ₀ , the motor 7 is completely stopped, so that no signal is output from the rotation detecting unit 1. That is, the capacitor C ₅ is continued to be further charged, the charge voltage comparator
Remains in a state higher than the regulated voltage V ₃ of 61, the comparator 61
High from is retained. As a result, the transistor Q ₂ is kept turned on, for example, blocking the current of the battery 2 to the motor 7 to turn off the switch or the like is followed.

〔The invention's effect〕

The present invention has a simpler circuit configuration than the conventional motor speed control circuit, but when the rotation speed of the motor fluctuates, the motor is steplessly controlled to return to the desired rotation speed. Circuit manufacturing cost can be reduced.

In addition, when the load on the motor becomes heavy and the rotation speed of the motor decreases, and the power supply from the battery to the motor increases, the battery voltage decreases, that is, the set level decreases. The current supply period to the motor becomes longer, the time required for the motor to reach the desired rotation speed can be further shortened, and the responsiveness to fluctuations in the rotation speed of the motor can be improved.

Furthermore, since the bias is applied so that the lowest level of the sawtooth wave is equal to or higher than the set level, the rotation speed of the motor can be set up to the maximum.

Also, when the level of the sawtooth wave exceeds the regulation level,
Since the current supply to the motor is stopped, it is possible to prevent a long-term short-circuit current when the motor is stopped or at low rotation speeds, and it is possible to protect the motor and prevent thermal destruction due to a rise in the temperature of switching elements. Become.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a motor speed control circuit according to the present invention, FIGS. 2 and 3 are timing charts showing the operation of the motor speed control circuit, and FIG. 4 is a conventional motor speed control circuit. FIG. 5 is a circuit diagram of a conventional motor speed control circuit, and FIG. 6 is a timing chart showing the operation of the conventional motor speed control circuit. 1 ... rotation detection unit, 2 ... battery, 3 ... waveform shaping circuit,
4 ... sawtooth wave generation circuit, 5 ... comparison circuit, 6 ... protection circuit, 7 ... motor, 8 ... FET, 9 ... constant voltage circuit, 3
1,51,61 ... Comparator.

Claims (3)

(57) [Claims] 1. A battery as a power supply connected to a motor and a means for generating a predetermined set level, and a sawtooth wave which is means other than the motor and the means for generating the set level and which is compared with the set level. A constant voltage power supply for supplying power from the battery via a constant voltage circuit to the output means, a periodic signal generating means for outputting a periodic signal corresponding to the rotation speed of the motor, and a pulse for shaping the periodic signal into a pulse signal Shaping means, sawtooth wave generating means for outputting a sawtooth wave synchronized with the pulse signal, comparing means for comparing the level of the sawtooth wave with the set level, and setting the level of the sawtooth wave to the setting level A motor power supply means for supplying drive power to the motor during a period equal to or higher than a level. 2. The motor speed control circuit according to claim 1, further comprising bias means for biasing a level of the sawtooth wave, wherein a minimum level of the sawtooth wave is higher than a set level. 3. The motor speed control circuit according to claim 1, further comprising a level comparing means for comparing the level of the saw-tooth wave with the regulation level, and when the level of the saw-tooth wave exceeds the regulation level, the motor is controlled. A motor speed control circuit characterized in that the supply of drive power is stopped.