JPH0813193B2 - Motor control device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor control device that prevents an excessive inrush current when starting a motor.

2. Description of the Related Art In general, in order to control the rotation speed of a DC motor, a means for varying the supply voltage is used. Recently, a so-called switching regulator method, which controls the power supply voltage by pulse width modulation, is used because of its high efficiency. Often.

FIG. 2 is a configuration diagram showing a conventional switching regulator type motor control device, in which 1 is a sawtooth wave generation circuit and 2 is a sawtooth wave generation circuit.
Is a pulse width control circuit, 3 is a drive circuit, and 4 is a preamplification circuit. The pulse width control circuit 2 punches out the sawtooth wave output from the sawtooth wave generation circuit 1 by using the rotation speed control voltage as a threshold level, and performs a waveform shaping operation to obtain a pulse signal having a pulse width proportional to the rotation speed control voltage. Is producing. The drive circuit 3 receives the output pulse signal of the pulse width control circuit 2 as an input, performs a switching operation, and performs pulse width modulation of the power supply voltage. The output portion of the drive circuit 3 is provided with a large-capacity capacitor, and by integrating the pulse voltage, an output voltage proportional to the pulse width is created, and the rotation speed of the motor 5 is voltage-controlled. The preamplifier circuit 4 is composed of a differential amplifier and amplifies the rotation speed control voltage to a value suitable for the input level of the pulse width control circuit 2 and supplies feedback voltage to the negative input side for feedback control. I have to. Reference numeral 6 in the figure is a detection device for detecting the number of rotations of the motor 5 and is fed back to the preamplification circuit 4. 7
Is a power supply circuit.

Problems to be Solved by the Invention However, in the conventional configuration, a large inrush current peculiar to the DC motor flows through the circuit at the time of starting the motor, and in order to cope with this, it is necessary to increase the current rating of the circuit element. In particular, during feedback control, since the gain of the preamplifier circuit 4 is set to a large value, the preamplifier circuit 4 is in a state close to the maximum drive during the shortage of the feedback input rising caused by the delay time of the control system, and therefore the motor is not driven. There is a problem that the applied voltage is close to the maximum and a larger inrush current flows.

In order to solve the above-mentioned problems, the present invention controls the rotational speed control voltage gradually by changing the reference operating point voltage of the preamplifier circuit in conjunction with the motor start signal to reduce the inrush current of the motor. An object of the present invention is to provide a motor control device capable of performing the above.

Means for Solving the Problems In order to achieve the above object, a motor control device of the present invention changes a output voltage in proportion to a pulse width of an input pulse signal, and a drive circuit for controlling a rotation speed of a motor. The sawtooth wave generating circuit that is the signal source of the control pulse signal is compared with the output sawtooth wave of the sawtooth wave generating circuit and the rotation speed correction voltage, and the sawtooth wave has a pulse width proportional to the rotation speed correction voltage. A pulse width control circuit that converts the pulse signal into a pulse signal and supplies it as an input to the drive circuit; a rotation speed detection device that generates a DC voltage proportional to the rotation speed of the motor; and a DC voltage and rotation speed of the rotation speed detection device. A preamplifier circuit that amplifies the difference in control voltage to perform feedback control, and a reference operating voltage of the preamplifier circuit that is gradually increased by a CR circuit in conjunction with a motor start signal, and an output supplied from the preamplifier circuit No. was increasing from a low voltage, but having a soft start circuit for controlling the rotational speed correction voltage corresponding to the rotation speed control voltage after the CR time constant.

With the above configuration, the present invention gradually increases the reference operating voltage of the preamplifier by the CR circuit in conjunction with the motor start signal, and gradually increases the output signal supplied from the preamplifier from a low voltage, so that the motor is low. Start from voltage to prevent excessive inrush current. Further, since the reference potential maintains a steady value after the CR time constant, the rotation speed correction voltage is controlled by the difference between the rotation speed control voltage and the output voltage of the rotation speed detection device, and shifts to normal feedback control.

Embodiment FIG. 1 is a block diagram showing an embodiment of the present invention. The components having the same functions as those of the conventional motor control device shown in FIG. 2 are designated by the same reference numerals and detailed description thereof will be omitted. 8 shows the whole soft start circuit, 9 is a switch interlocked with the motor start signal, 10 is a reference power source, 11 is a capacitor, 12 is a resistor,
13 is a diode. The switch 9 is closed when the motor is stopped. When the switch 9 is opened in conjunction with the motor start signal, the capacitor 11 is charged by the reference power source 10 and its voltage is resistance.
The resistance value of 12 and the capacity of the capacitor 11 gradually increase according to a time constant formula. The reference operating point voltage of the operational amplifier 41 in the preamplifier circuit 4 is determined by the voltage of the positive input terminal, and since the positive input terminal is read close to the capacitor 11, the reference operating point voltage also gradually increases, resulting in rotation. The number control voltage gradually increases. For this reason, the pulse width control circuit 2 starts punching out the output sawtooth wave of the sawtooth wave generation circuit 1 from a low threshold level, raises the threshold level as the rotational speed control voltage gradually increases, and gradually expands the pulse width. Then, the output voltage of the drive circuit 3 starts from a low potential, and the voltage gradually increases in proportion to the expansion of the pulse width, so that an excessive rush current is prevented. The switch 9 is closed again when the motor is stopped, the accumulated charge in the capacitor 11 is quickly discharged through the diode 13, and the soft start circuit 8 is immediately ready for the next start.

In this embodiment, since the positive input terminal of the operational amplifier 41 is used as the variable means of the reference operating point voltage, the rotation speed control voltage is added as the inversion voltage to the negative input terminal, and the feedback input is added to the differential input to perform differential amplification It has an effect. (The inverting circuit is not shown.) Effects of the Invention As is apparent from the above embodiments, according to the present invention, the following effects can be obtained.

(1) Since the motor is started from a low voltage, smooth starting characteristics can be obtained.

(2) The inrush current at the time of starting the motor can be suppressed to a low level, the current rating of the circuit can be reduced, the cost can be reduced, and failures due to an excessive current can be reduced to improve reliability.

(3) Since the rotation speed control is performed by direct current, the feedback loop can be configured by a differential amplifier circuit with a simple circuit configuration, and the soft start circuit also has a simple configuration such as resistors and capacitors, which is technically easy and inexpensive. A circuit can be realized.

(4) After the reference potential reaches the steady value, the normal feedback control is performed without any switching means.

[Brief description of drawings]

FIG. 1 is a block diagram of a motor controller showing an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional motor controller. 1 ... Sawtooth wave generation circuit, 2 ... Pulse width control circuit, 3
...... Drive circuit, 4 …… Preamplifier circuit, 8 …… Soft start circuit.

Claims (1)

[Claims] 1. A drive circuit for changing the output voltage in proportion to the pulse width of an input pulse signal to control the number of revolutions of a motor, a sawtooth wave generating circuit as a signal source of a control pulse signal, and the sawtooth waveform. A pulse width control that compares the output sawtooth wave of the wave generation circuit with the rotation speed correction voltage, converts the sawtooth wave into a pulse signal having a pulse width proportional to the rotation speed correction voltage, and supplies it as an input to the drive circuit. A circuit, a rotation speed detection device that generates a DC voltage proportional to the rotation speed of the motor, and a feedback control that amplifies the difference between the DC voltage of the rotation speed detection device and the rotation speed control voltage to obtain the rotation speed correction voltage. The preamplifier circuit to perform, and the reference operating voltage of the preamplifier circuit is gradually increased by the CR circuit in conjunction with the motor start signal, the output signal supplied from the preamplifier circuit is gradually increased from a low voltage, and the CR time constant is increased. Later the above times A rotation speed DC feedback type motor control device having a soft start circuit for controlling a rotation speed correction voltage corresponding to a rotation speed control voltage.