JPH05284780A - Controller for dc motor - Google Patents

Abstract

PURPOSE:To provide a controller for a DC motor in which a variation in torque can be reduced only by adding a simple circuit. CONSTITUTION:The controller for a DC motor comprises a control amount regulator Q2 for regulating a control amount signal of a main current controller Q1 based on an output command signal Vi to a motor M, a current detecting resistor Rd for detecting a motor current, a first feedback circuit C1 for negatively feeding back a current detection signal to the control amount signal, a second feedback circuit C2 for negatively feeding back an input voltage signal to the control amount signal, and feedback amount distributors R2, R3 for setting distribution of negative feedback amounts of the first and second feedback circuits. A variation in torque can be reduced by a simple configuration by suitably setting a distribution ratio of the distributors R2, R3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC motor controller, and more particularly to a controller for reducing fluctuations in torque generated by a DC motor.

[0002]

2. Description of the Related Art As a control device for controlling the output of a DC motor, there is a constant voltage system shown in FIG. 2 or a constant current system shown in FIG.

In FIG. 2, M is a three-phase bipolar brushless motor, and its rectifying circuit and the like are omitted. Q1 is a transistor forming a main current control circuit for controlling the motor current. The transistor Q1 receives the power source + V at its emitter, and its collector is connected to one input end of the motor M. Q2 is a transistor for adjusting the controlled variable signal of the transistor Q1. OP1 is an operational amplifier whose + terminal is grounded and whose − terminal divides the voltage difference between the torque command value VS (= Ii R1) due to the current Ii through the resistor R1 and the motor terminal voltage VM with the resistors R1 and R2. The voltage corresponding to the above is received and its output is given to the base of the transistor Q2. + V1 and -V2 are control voltages. A
r is the armature of the motor M, Ra is the resistance of the armature Ar, EM
Is the speed electromotive force of the armature Ar.

In the control circuit of FIG. 2, the motor terminal voltage VM becomes VM = -Vi R2 / R1 and is constant with respect to the torque command value VS. The generated torque τ is τ = KT sin θ × IM (1) Here, KT is a torque constant generated by the maximum magnetic flux, assuming that the magnetic flux distribution characteristic of the field magnetic poles of the motor M has a sinusoidal waveform. The unit of the generated torque τ is KE (Nm / m /), where n is the number of revolutions of the motor M and k is a value for each current A using the velocity electromotive force KE (V / n) per number of revolutions n. It is represented by A). θ is an electrical angle and repeats a value of 60 ° to 120 ° at every commutation period (60 °) accompanying the rotation of the motor M. IM is an armature current and is represented by IM = (VM-EM sin .theta.) / Ra (2). EM is the speed electromotive force corresponding to the maximum magnetic flux.

Next, FIG. 3 will be described. In FIG. 3, the same parts as those in FIG. 2 are designated by the same reference numerals, and different parts will be described below.

D is a current detector for detecting the current IM of the motor M. Rd is a current detecting resistor, which is connected between the other input end of the motor M and the ground potential. OP2 is an operational amplifier which receives a voltage divided by the resistors R4 and R5 of the potential of the current detecting resistor Rd at its + terminal, and divides its output potential VI by resistors R4 and R5 at its-terminal. The output voltage VI is applied to the negative terminal of the operational amplifier OP1 via the resistor R3.

In the control circuit of FIG. 3, the output potential VI
Is VI = -Vi R3 / R1 and VI = IM Rd R5 / R4.
The armature current IM is expressed as follows: IM = -Vi R3 R4 / (R5 Rd) (3) Alternatively, in place of the formula (2), IM = (VM-EM sin .theta.) / (Ra + Rd). … (4) The generated torque τ is represented by the equation (1) as in FIG.

[0008]

However, since the armature resistance Ra is generally a small value in order to improve the motor characteristics, in the control device of FIG. 2, the motor terminal voltage VM is constant. , And the value of sin θ becomes small, the armature current IM according to the equation (2) significantly increases compared to the decrease of KT sin θ according to the equation (1), and the generated torque τ increases. Therefore, the torque fluctuation due to this repetition becomes large.

Further, in the control device of FIG. 3, since the armature current IM is constant, the torque τ generated by the equation (1) varies depending on sin θ.

For a load such as a mechanism for scanning a mirror of a laser printer, which requires smooth rotation, it is necessary to reduce these torque fluctuations as much as possible.

It is an object of the present invention to provide a DC motor control device that can reduce torque fluctuations by adding a simple circuit.

[0012]

In order to solve the above problems, the present invention provides a main current control circuit connected to one input terminal of a motor for controlling a motor current, and a main current control circuit based on an output command signal to the motor. In a DC motor control device including a control amount adjusting circuit for adjusting a control amount signal of a current control circuit, a current detecting resistor connected to the other input end of the motor to detect a motor current and a current detecting resistor A first feedback circuit that negatively feeds back the generated current signal to the control amount signal; a second feedback circuit that negatively feeds back a voltage signal at one input end of the motor to the control amount signal; and the control amount signal. A feedback amount distributor that sets the distribution of the negative feedback amounts of the first and second feedback circuits with respect to.

[0013]

According to the present invention, the first feedback circuit controls the motor current flowing through the current detection resistor so as to have a constant current, and the second feedback circuit causes the motor terminal voltage to have a constant voltage. Control operation. Then, the respective operations are canceled based on the distribution ratio of each of the negative feedback amounts by the feedback amount distributor.

[0014]

1 is a circuit diagram of a DC motor controller showing an embodiment of the present invention. This circuit is similar to that of FIG. 2 and FIG.
These circuits are supplemented with circuit elements that are not common to these circuits.

In the figure, C1 is the first feedback circuit, and C1 is
2 is a constituent element of the second feedback circuit, and the set of the resistors R2 and R3 forms a feedback amount distributor of each of the feedback circuits.

In the configuration of FIG. 1, the armature current IM is
IM = VM-EM sin .theta.) / (Ra + Rd), and the motor terminal voltage VM is VM = R2 (Ii-).
VI / R3), the output potential VI is VI = IM Rd R5 /
Since it is R4, the armature current IM becomes IM = (R2 Ii -EM sin .theta.) / [Ra + Rd {1+ (R5 / R4) (R2 / R3)}] ... (5). The generated torque τ is represented by the equation (1) as in FIG.

In the present embodiment, for example, the rotation speed of the motor M is 1 krpm, the resistance Ra is 18Ω, the resistance Rd is 2Ω, and the resistance R2 is 15 KΩ in order to reduce the fluctuation of the generated torque τ. It is assumed that the resistance R3 is set to 30 KΩ and the resistance ratio R5 / R4 is set to 50. still,
The torque command value VS (= Ii R1) is determined by the torque command current Ii for an appropriate resistor R1. When the torque command current Ii is, for example, 1 mA, the maximum value of the motor terminal voltage VM is calculated based on the formula (4) using the armature current IM when sin θ in the formula (5) is set to 1, It becomes 10V. The generated torque τ is about 0.008 N when calculated by the equation (1) using this armature current IM.
・ It becomes m.

Next, the motor terminal voltage VM in accordance with the change of the rotation phase θ of the motor M is calculated as follows:
It is obtained by sequentially changing from ° to 120 ° and based on the equation (4). FIG. 4A shows the motor terminal voltage VM
It is a figure which shows the characteristic of. Similarly, the generated torque τ is
It is obtained from the equations (5) and (1). FIG. 4B is a diagram showing the characteristic of the generated torque τ. As shown in the figure, the generated torque τ is substantially constant even if the rotation phase θ of the motor M changes. In order to obtain such torque characteristics, the values of the above-mentioned elements are calculated and set.

In FIGS. 4A and 4B, the broken lines show the respective characteristics when the resistance R2 of the circuit of FIG. 2 is 10 KΩ.
Then, the resistance R3 of the circuit of FIG.
The characteristics when / R4 is set to 30 are also shown by the alternate long and two short dashes line with the values at the electrical angle θ of 90 ° being the same. In the circuit of FIG. 2, the motor terminal voltage VM
Is controlled to a constant voltage, the generated torque τ increases as the electrical angle θ deviates from 90 °, and in the circuit of FIG. 3, the motor current is controlled to a constant current. Although θ decreases as it deviates from 90 °, it becomes almost constant in this embodiment.

[0020]

As described above, according to the present invention, the motor current detection signal and the motor terminal voltage signal are negatively fed back to the control amount signal with a certain distribution ratio.
By setting the distribution ratio appropriately, it becomes possible to reduce torque fluctuations associated with motor rotation. Since the distribution ratio can be set by a simple resistance element or the like, it can be configured with a simple configuration.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a DC motor control device showing an embodiment of the present invention.

FIG. 2 is a circuit diagram of a conventional DC motor control device.

FIG. 3 is a circuit diagram of a conventional DC motor control device.

FIG. 4 is a diagram showing a characteristic of a motor terminal voltage and a characteristic of a generated torque.

[Explanation of symbols]

M ... Motor, Q1, Q2 ... Transistor, OP1, OP
2 ... Operational amplifier, Ra ... Armature resistance, Rd ... Current detection resistance, R2, R3 ... Feedback amount distribution resistance, VS ... Torque command value, Ii ... Torque command current, VM ... Motor terminal voltage,
EM ... speed electromotive force.

Claims (1)

[Claims] 1. A main current control circuit connected to one input end of a motor for controlling a motor current, and a control amount adjustment circuit for adjusting a control amount signal of the main current control circuit based on an output command signal to the motor. A DC motor control device provided with: a current detection resistor connected to the other input end of the motor for detecting a motor current; and a first current feedback resistor for negatively feeding back a current signal detected by the current detection resistor to the control amount signal. A feedback circuit; a second feedback circuit that negatively feeds back a voltage signal at one input terminal of the motor to the control amount signal; and a distribution of negative feedback amounts of the first and second feedback circuits to the control amount signal. A direct current motor control device comprising: a set feedback amount distributor.