JPH0630573A - Motor controlling circuit and motor system using this circuit - Google Patents

Abstract

PURPOSE:To suppress an influence on a motor by a ripple contained in an output signal by installing a current controller which, according to a motor control command signal, changes the current flowing into a constant current device which determines the current flowing into a differential amplifier which amplifies an input signal. CONSTITUTION:A base of a transistor for controlling current 30 is connected to a base of a transistor 14a, 14b of a current mirror 14 to make an amount of current flowing into the transistor 30 proportional to the current flowing into the current mirror 14 or an input signal T for controlling a torque of the motor. Therefore, when the input signal T is small, an amount of current flowing into the transistor 30 becomes small and as a result, an amount of current flowing into a transistor 18a becomes small and a gain of an error amplifier 10 is small. Eventually, an amplification factor to a ripple component contained in the input signal T becomes small and thereby a bad influence on a motor can be held down. When there is no input signal T, the amplifier 10 doen not work and the erroneous output does not appear.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor control circuit used to control the driving of a motor, and more particularly to improvement of its control characteristics.

[0002]

2. Description of the Related Art Conventionally, electric motors have been widely used as drive sources for various devices. In particular, a motor is widely used as a drive source for controlling the number of revolutions because it can control the number of revolutions by supplying electric power.

In controlling such a motor, the number of rotations of the motor is detected and the drive current is changed according to the number of rotations. For example, in the control of a DC servo motor, the rotation speed of the motor 100 is detected by an FG coil (frequency generating coil) 102 as shown in FIG. 2, and the supply current to the motor 100 is controlled according to this rotation speed detection signal. is doing. That is, the FG coil 102
The rotation speed detection signal obtained by is first supplied to the rotation speed control unit 104. The rotation speed control unit 104 outputs a voltage signal for the current supplied to the motor 100 according to the input rotation speed detection signal. Then, this voltage signal is converted into a torque signal of a current signal by the voltage / current converter 106 and supplied to the error amplifier 108.

The error amplifier 108 amplifies the input torque signal and supplies it to the motor driver 112 via the current feedback amplifier 110. Since the motor driver 112 controls the current supplied to the motor 100 according to the input signal, it is possible to supply a predetermined electric power to the motor 100 and drive the motor 100 at a desired rotation speed. it can.

Further, the current feedback amplifier 110 is connected with a phase compensation capacitor C0 and is supplied with a signal about the current supplied to the motor 100 by the current detector 114. Therefore, the current feedback amplifier 110 can feedback control the current supplied to the motor 100. In this application, the error amplifier including the current feedback amplifier 110 is called.

An example of such a conventional error amplifier will be described with reference to FIG.

The error amplifier 10 receives an input signal T about the drive current value and outputs an output current I corresponding to the input signal T.

The input signal T is input to the input current regulator 12 whose one end is connected to the power supply. This input current regulator 1
Reference numeral 2 controls the current flowing therethrough according to this input signal. Then, on the downstream side of the input current regulator 12, a current mirror 1 including a pair of transistors 14a and 14b is provided.
4 are arranged. Therefore, the resistor 1 having the other end connected to the output side of the current mirror 14 connected to the power supply
The same current as that of the current regulator 12 also flows through 6. Therefore,
The potential on the downstream side of the resistor 16 corresponds to the input signal.

The downstream end of the resistor 16 is connected to the base of the transistor 18a on the differential amplification input side. The emitter of the transistor 18a is connected to the transistor 18b on the differential amplification output side and is also connected to the ground via the constant current source 20. A variable power supply 22 that changes in accordance with the output current from the output current detection unit is connected to the base of the transistor 18b on the differential amplification output side, and current feedback is performed so that the current value becomes the same as the current value of the detection unit. Takes. Further, the collectors of the transistors 18a and 18b are connected to a power supply via a pair of transistors 24a and 24b connected so as to form a current mirror.

Therefore, as the base potential of the transistor 18a changes, the amount of current flowing through the transistor 18a changes, and the transistor 24 forming a current mirror.
The current flowing through a and b changes.

At the connection point between the collectors of the transistor 24b and the transistor 18b, a pair of transistors 26a, 26b forming a currant mirror for output.
Is connected to the common base and the collector of the transistor 26a. Therefore, the amount of current flowing through the transistor 26, that is, the output current I changes according to the amount of current flowing into the connection point between the collectors of the transistor 24b and the transistor 18b.

As described above, the error amplifier 10 is
An output current I that changes according to a change in the input signal is output. The voltage drop in the transistor 18a is only the dynamic resistance, and this amount of current is determined by the voltage drop in the resistor 16. Therefore, if the resistance value of the resistor 16 and the value of the constant current source 20 are properly selected, the input signal The current gain for can be predetermined.

[0013]

In the conventional motor control circuit having the above-mentioned error amplifier, the output control signal contains ripples, which causes ripples in the motor drive current, resulting in output torque of the motor. There was a problem in that

Originally, the error amplifier 10 ideally does not output an output when a control signal is not input, but in the conventional circuit, even if there is no input control signal due to an input offset of the error amplifier 10 or the like. There was a case where output current was generated. Therefore, conventionally, it is necessary to set a negative offset and design so that the output current is generated only when the level of the input control signal is higher than the set value.

Further, when the input signal input to the error amplifier 10 is formed by integrating a PWM (pulse width modulation) wave based on the result obtained by comparing the detected value of the rotation speed of the motor with the set value. There are many. In such a case, the influence of the PWM wave remains on the input signal and ripples are added. Also, in other cases, the detected value of the rotation speed and the like are basically digital pulse outputs, and the arithmetic processing is also performed as digital data. Therefore, when digital data is converted into an analog voltage value or the like, ripples often occur.

In the case of the above-mentioned conventional example, the current gain in the error amplifier 10 is a fixed value determined by the setting of the circuit. Therefore, the same amplification is performed regardless of the level of the input signal. For example, if the current gain is 20 times and the ripple width (width between the maximum value and the minimum value of the ripple) in the current (input current) in the input current regulator 12 is 0.1 μA regardless of the magnitude of the input current, The ripple width on the output current is 2 μA regardless of the magnitude of the output current I. Since the ripple width on the input current depends on the voltage value of the digital data pulse at the high level, it does not depend on the magnitude of the input signal in many cases. Therefore, the ripple rate (ratio of the magnitude of the ripple width to the output level) in the output signal increases as the input current decreases, that is, the output current I decreases.

The ratio of the output current to the input current in the error amplifier 108 shown in FIG.
Since current feedback is applied at 0, it should be constant regardless of the current conversion gain. However, the phase compensation capacitor C0 connected to the current feedback amplifier 110 is
Has a problem that, when the conversion gain is large during the transient change, the amount of residual ripple increases accordingly.

The present invention has been made to solve the above-mentioned problems, and can effectively suppress the influence of ripples contained in an output signal on a motor.
Another object of the present invention is to provide a motor control circuit capable of preventing a malfunction due to an offset when a control input is not input, that is, an output.

[0019]

According to the present invention, in a motor control circuit having an error amplifier for amplifying an input signal for motor drive control and outputting a DC control signal, the error amplifier amplifies the input signal. The differential amplifier, constant current means for determining the current flowing through the differential amplifier, and current control means for changing the current flowing through the constant current means in accordance with the input signal. It is characterized in that the error amplifier is controlled so that the amplification factor is small when it is small and is large when it is large.

A motor system according to the present invention is characterized by utilizing the above motor control circuit.

[0021]

When the motor control signal for controlling the motor torque is small, the amount of current flowing through the constant current means is reduced. Therefore, the amount of current flowing through the differential amplifier is reduced, and the gain of the error amplifier is reduced. For this reason,
The amplification factor for the ripple component on the input signal is reduced, and the adverse effect on the output of the motor can be suppressed low. If there is no input signal, the error amplifier does not work and no error output occurs.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, one embodiment of a motor control circuit according to the present invention will be described with reference to the drawings.

FIG. 1 shows the configuration of an error amplifier 10 suitable for the motor control circuit according to the present invention. Note that FIG.
The same members as those in the conventional example are given the same reference numerals and the description thereof will be omitted.

A feature of this embodiment is that a current adjusting transistor 30 as a constant current means is provided in place of the constant current source 20 in the conventional example. The base of the current adjusting transistor 30 is connected to the bases of the transistors 14a and 14b of the current mirror 14.

Therefore, the current adjusting transistor 30
The amount of current flowing in is proportional to the current flowing in the current mirror 14, that is, the input signal. Therefore, both the current flowing through the transistor 18a and the current flowing through the current adjusting transistor 30 are proportional to the input signal. Therefore, the current gain of the error amplifier 10 becomes proportional to the input current, and the output current I becomes 2 of the input current.
It is proportional to the power.

Therefore, the relationship between the level of the input signal and the level of the output signal is low when the input signal is small and high when the input signal is large, as shown in FIG. here,
In the error amplifier 10 of the present invention, when the signal level of the input signal is low, the signal level of the input signal needs to be increased to obtain the same output value as in the conventional example.

That is, the current gain in the conventional example is 2
Assuming that the input current is 1 μA, the output current I is 20 μA. If the ripple width included in the input current is 0.1 μA, the ripple width included in the output current I is 2 μA. In contrast,
According to the error amplifier 10 of the present invention, the input current is 3.16.
Output current is 20μA at μA, ripple width is 0.6
It will be about 3 μA. Therefore, the ripple rate at the time of normal use can be suppressed to be much lower than the conventional one. Therefore, the torque fluctuation of the motor due to the ripple can be suppressed.

Further, when the signal level of the input signal is high, the current gain rises accordingly, and the error amplifier 1
The maximum output of 0 can be retained as before. Therefore, responsiveness at the time of large acceleration such as driving the motor can be made sufficient.

When there is no input signal, the current of the transistor 30 also disappears, so that the transistors 18a, 18a
The differential amplifier circuit by b does not operate either. Therefore, even if the transistors 18a and 18b have an offset, the output is not affected.

By applying the error amplifier 10 to the system shown in FIG. 2, suitable control of the motor 100 can be achieved.

[0031]

As described above, according to the motor control circuit of the present invention, the current gain of the error amplifier is reduced when the signal level of the input signal is small. Therefore, the effect of ripple on the motor control signal is effective. Can be suppressed. Further, the output when there is no input can be completely eliminated. Thereby, suitable motor control can be achieved.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an error amplifier suitable for a motor control circuit according to the present invention.

FIG. 2 is a block diagram showing a system to which a motor control circuit is applied.

FIG. 3 is a circuit diagram showing an example of a conventional error amplifier.

FIG. 4 is a characteristic diagram showing an input characteristic of an error amplifier.

[Explanation of symbols]

 10 error amplifier 100 motor 110 motor control circuit T input signal I output current

Claims (2)

[Claims] 1. A motor control circuit having an error amplifier for amplifying an input signal for drive control of a motor and outputting a DC control signal, wherein the error amplifier is a differential amplifier for amplifying the input signal, A constant current means for determining the current flowing through the differential amplifier, and a current control means for changing the current flowing through the constant current means in accordance with the motor control command signal are provided, and the amplification factor is set when the input signal is small. A motor control circuit characterized by controlling an error amplifier so that the amplification factor becomes large when is small and large. 2. A system including a motor and a motor control circuit for controlling the drive of the motor, wherein the motor control circuit amplifies an input signal for drive control of the motor and outputs a DC control signal. The error amplifier includes an amplifier for amplifying an input signal, a constant current unit for determining a current flowing through the differential amplifier, and a current flowing through the constant current unit according to the motor control command signal. And a current control means for changing the input signal, and controlling the error amplifier such that the amplification factor is small when the input signal is small and is large when the input signal is large.