JPS58224592A - Speed controller for motor - Google Patents

Abstract

PURPOSE:To accurately automatically control the rotating speed of a motor by employing as the detection signal of the rotating speed of the motor the counterelectromotive force of the motor. CONSTITUTION:A gate unit 10 is conducted at the moment that a pulse of a shifting phase pulse generator 8 is inputted to the gate unit 10, and it becomes the state that the output signal of a voltage detector 4 is fed to a filter 11. The filter 11 is charged by the reverse voltage of a motor 2. The voltage of the filter 11 is added by an adder 6 in reverse polarity to the set speed voltage set by a speed setter 5, and the voltage is amplified by an amplifier 7. The output of the amplifier 7 is inputted to the shifting phase pulse generator 8, and the output pulse is outputted via a timer 9 as the trigger pulse of a triac 3.

Description

[Detailed description of the invention] The present invention relates to a speed control device for an electric motor.

Conventionally, in motor speed control devices, a tacho generator for rotation speed detection is generally attached to the shaft of the motor, the speed setting voltage is compared and amplified with the output voltage of the tacho generator as an actual speed signal, and this voltage is used to generate moving phase pulses. In addition to the gates of switching elements such as triacs, the power supply voltage supplied to the electric motor was automatically controlled through the device.

However, this device requires a tachometer generator for rotation speed detection to be attached to the electric motor, and also requires wiring from the tachometer generator to a control device with a speed setting circuit, which has the disadvantage of making this type of speed control device expensive. .

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and to provide a device that can control the speed of an electric motor at low cost without using a tachometer generator for detecting rotational speed, which has been conventionally used in electric motors.

In order to achieve this object, according to the present invention, a switching element that controls the switching of the power supply voltage supplied to the motor is provided with an intermittent control signal that compares the set speed of the rotary motor with the actual speed and corresponds to the deviation. A voltage detector is provided to detect a terminal voltage of the motor during a period in which the switching element is off, and the detected voltage of the voltage detector is used as a signal indicating the actual speed. It is used for feedback control of electric motors.

The structure of the present invention will be explained below based on illustrated embodiments. FIG. 1 is a block diagram showing one embodiment of the present invention. FIG. 2 is a circuit diagram of an embodiment embodying the contents of the block diagram shown in FIG.

In FIG. 1, 1 is an AC power supply, 2 is an AC motor, 3 is a triac which is a type of switching element that switches the AC power supply voltage supplied to the motor 2, and 4 is a voltage detector connected to both ends of the motor 2. The detector detects the back electromotive force of the motor 2 when the triac 8 is off. Since the back electromotive voltage is a voltage that is approximately proportional to the rotation speed of the motor, the output voltage of the voltage detector 8 when the triac is off can be considered to be approximately the rotation speed of the motor. 5 is a speed setting device that sets the speed of the electric motor 2, 6 is an adder-17 is an amplifier that amplifies the output of the adder 6, and 8 is a ignition of the triac 8 at a phase according to the output of the amplifier 7. 9 is a delay timer for delaying the pulses outputted from the pulse generator 8 so that the pulses are outputted in the time layer; 10 is a gate device for generating pulses from the pulse generator 8; When a pulse is input to the gate of the gate device 10, this device 10 becomes conductive, and when a signal is input from the delay timer 9, it becomes non-conductive. Reference numeral 11 denotes a filter that stores the output of the voltage detector 4 via the gate device 10 to maintain the voltage.

To explain the operation of the embodiment shown in FIG. 1, the moment the pulse from the moving phase pulse generator 8 is input to the gate device 10 in the figure, the gate device 10 becomes conductive, and the output signal of the voltage detector 4 is transferred to the filter 11. The filter 11 is charged by the back electromotive force of the electric motor 2, which is in a proportional relationship with the electric motor 2, that is, the back electromotive force increases when the rotational speed of the electric motor 2 is high. Furthermore, after a certain period of time has elapsed after the pulse is output from the moving phase pulse generator 8, a pulse is output from the delay timer 9, and at the same time the gate device 10 becomes non-conductive, the triac 8 is fired. The triac 8 becomes conductive and a voltage is applied to the motor 2 from the power supply l. However, at this time, since the gate device 10 is non-conductive as described above, the voltage detected by the voltage detector 4 is the same as that of the filter 1.
1, and as described above, the back electromotive voltage of the electric motor 2, that is, the voltage approximately proportional to the rotational speed remains in the filter 11 from before, that is, when the triac 8 was non-conducting (off). The voltage of this filter 11 is added with an opposite polarity to the speed setting voltage set by the speed setting device 6 by an adder 6, and the voltage is amplified by an amplifier 7. The output of this amplifier 7 is transferred to a phase pulse generator 8.
receives power and simultaneously outputs a pulse for controlling the phase of the triac 8.

This pulse causes the gate device 10 to pass through the timer 9.
becomes non-conductive, the triac 8 is fired, and the electric motor 2 is rotated. The back electromotive force of the motor 2 is stored in the filter 11 via the gate 10 again, and the voltage of this filter 11 is added to the adder 6 with the opposite polarity and subtracted from the voltage set by the speed setting device 5, and the voltage is is added to the amplifier 7. That is, as described above, the filter 11 ensures that the back electromotive force of the motor 2 is proportional to the rotational speed of the motor 2. Furthermore, the adder 6
Since the voltage of motor 1 is subtracted from the speed setting voltage, motor 2
When the rotation of the motor 2 is low, the voltage of the filter 11 becomes small as described above, and therefore the output of the adder 6 becomes large, which acts to increase the rotation of the motor 2. Conversely, when the rotation of the motor becomes high, the output of the adder 6 becomes smaller, which acts to lower the rotation of the motor 2, and the voltage of the filter 11, that is, the back electromotive force of the motor 2, becomes the speed setting voltage. The rotation of the electric motor 2 is automatically controlled so as to be equal.

That is, since the magnitude of the back electromotive force of the electric motor 2 is approximately proportional to the rotation speed of the electric motor 2, the back electromotive force of the electric motor 2 acts as a feedback signal, and the speed of the electric motor 2 is controlled so that it matches the speed setting value. Ru.

FIG. 2 shows a more specific embodiment. The block configuration in FIG. 2 is exactly the same as that in FIG. 1, and the range surrounded by dotted lines in FIG. 2 corresponds to each block in FIG. 1. In FIG. 2, numerals 1 to 11 are exactly the same as those shown in FIG. 12.1B, 14.17°28.28 and 29 are resistors, 15 is an operational amplifier, 16 is a diode, 1
8 is a transistor, 19.24 and chrysanthemum are capacitors, the title is a constant voltage power supply, 21 is a comparator with two power supplies,
The rest and 82 are VΦ elements, the nails are pulse transformers, and 81
88 is a semiconductor switch with a gate electrode, and 88 is a semiconductor switch with a gate electrode.
The element M is a diode bridge.

The speed setter 5 divides a constant negative voltage using a variable resistor, and the adder 6 performs subtraction by adding voltages of different signs through a resistor 12 and a resistance path. The amplifier 7 includes an operational amplifier 15 and a resistor 1814.
It is made up of. The moving phase pulse generator 8 is configured to charge a capacitor 19 from the output of the amplifier 7 through a diode 16 and a resistor 17 to gradually increase the voltage of the capacitor 19.
is turned on by some method at every zero volt point in the voltage waveform of the AC power supply 1, so the voltage of the capacitor 19 gradually increases from zero volts in synchronization with the AC power supply 1. When the output voltage of the amplifier 7 is low, the voltage of the capacitor 19 increases slowly, and when the output voltage of the amplifier 7 is high, the voltage of the capacitor 19 increases quickly, and the voltage of the capacitor 19 increases when the constant voltage power supply is applied. When the voltage becomes higher than the voltage, the output voltage of the comparator 21 changes from zero volts to a positive voltage.

Even if the output voltage of the moving phase pulse generator 8 changes from zero volts to a positive voltage, the output voltage of the delay timer 9 will not change because a resistor and a capacitor are included in the next delay circuit on one side of the input section of the digital element section. The output voltage of the melon element is held at zero volts until the voltage across the capacitor reaches the threshold voltage of the auxiliary element 5.

At this time, the positive output voltage of the phase shift pulse generator 8 is applied to one side of the input of the gate element 82 in the gate device 10, and the zero volt of the output of the delay timer 9 is applied to the other side of the input by the new element. Since it is converted into a positive voltage and is applied, the output of the AND element 82 changes to a positive voltage, so the semiconductor switch 81 becomes conductive, and the output voltage of the diode brittle M in the voltage detector 4 is applied to the filter 11. Added to the resistor and capacitor lead within.

When the voltage next to the capacitor in the delay timer 9 exceeds the threshold voltage of the main element, the output of the main element changes to a positive voltage, the NOT element power becomes zero volts, and the output of the 4MΦ element 82 changes to a positive voltage. It becomes zero volt and semiconductor switch,
The circuit 81 becomes non-conductive. Also, since the output of the exciter changes from zero volts to a positive voltage, this voltage is applied to the gate of the triac 10 through the pulse transformer nail, causing the triac 10 to fire.

The circuit shown in FIG. 1 can be perfectly implemented because the components in each block in FIG. 2 operate as described above and the functions required in each block are fully satisfied.

As described above, according to the present invention, the back electromotive voltage of the motor is used as a signal for detecting the rotation speed, and the fact that this voltage is almost proportional to the rotation speed of the motor is utilized, so feedback is generated. It is extremely effective as a signal and allows automatic control of the rotational speed of the motor with high precision.

Furthermore, since the rotational speed of the motor can be controlled without using a tacho generator, this feedback speed control can be performed at low cost.

Although the above explanation was based on control of a single-phase motor, it goes without saying that three-phase motors, DC motors, etc. can also be controlled in the same way.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a circuit diagram of an embodiment that further embodies FIG. 1. 1... AC power supply, 2... Rotating motor, 8... Triac, 4... Voltage detector, 5... Speed setting device,
6... Subtractor, 8... Moving phase pulse generator.

Claims (1)

[Claims] 1) A switching element that is inserted in series between a power source and an electric motor and controls switching of the power supply voltage supplied to the rotary electric motor is configured to compare the set speed and the actual speed of the electric motor. , in which the speed is controlled by applying an intermittent control signal according to the deviation, a voltage detector is provided to detect the terminal voltage of the motor during the period when the switching element is off, and this voltage A speed control device for an electric motor, characterized in that an output of a detector is used as a signal indicating the actual speed.