JPH0591779A - Motor controller - Google Patents

Abstract

(57) [Summary] [Purpose] When the motor is switched from high-speed rotation to low-speed rotation, the reduction of the voltage applied to the DC motor is prevented from being applied to the motor drive circuit. [Arrangement] An arithmetic circuit 11 calculates a detection signal a indicating the rotation speed of the motor 1 from the FG 3 and a control signal VE indicating a difference from the target value of the rotation speed of the motor 1 from the filter amplifier 5 to obtain a calculation result. Create a voltage Vref. Voltage control circuit 1
2 controls the power supply voltage guided to the power supply input terminal 2b of the motor drive IC 2 in accordance with the calculation result Vref. As a result, the voltage control circuit 12 reduces the DC voltage V'cc supplied to the motor drive IC 2 when the motor is switched to the low speed rotation. It can be prevented from being added to the circuit of the IC 2 for use.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor control device for controlling a motor so as to maintain a constant number of rotations, and more particularly to a motor control device capable of controlling the motor in a wide range from low speed rotation to high speed rotation.

[0002]

2. Description of the Related Art Generally, a DC motor is used as a power source for paper feeding of a printing machine and tape feeding of a computer because of its excellent torque efficiency and controllability. A motor control device for controlling such a DC motor uses a feedback control system to keep the rotation speed of the DC motor constant.

FIG. 3 is a circuit diagram showing a control circuit for performing feedback control of such a conventional DC motor.

In FIG. 3, reference numeral 1 is a DC motor, and this motor 1 is driven by a current IM, which will be described later, supplied from an integrated circuit for motor drive (hereinafter referred to as IC for motor drive) 2. A frequency generator (hereinafter referred to as FG) 3 arranged around the motor 1 detects the rotation of the motor 1 and uses a detection signal a indicating a frequency proportional to the angular velocity of the rotating shaft of the motor 1 as a feedback signal. It is supplied to the first input terminal of the frequency detector 4. Further, the target value b of the frequency of the detection signal a is led to the second input terminal of the frequency detector 4. The frequency detector 4 is FG
The comparison detection signal c in which the frequency of the detection signal a from 3 and the target value b are compared, and the voltage is proportional to the difference between the frequencies.
Is supplied to the filter amplifier 5. The filter amplifier 5 is
The phase and gain of the comparison detection signal c from the frequency detector 4 are corrected and the motor drive IC is used as the control signal VE.
2 control input terminals 2a. I for motor drive
The DC voltage Vcc from the power source is introduced to the power source input terminal 2b of the C2, and the ground terminal 2c is connected to the reference potential point via the current detection resistor RF. Also, I for motor drive
On the output side of C2, the positive output terminal 2d is connected to the positive terminal 1a of the motor 1, and the negative output terminal 2e is connected to the negative terminal 1b of the motor 1. With such a connection,
The motor drive IC 2 divides the DC voltage Vcc based on the control signal VE from the control input terminal 2a and applies the voltage to the motor 1 via the output terminal pair 2d and 2e.
A current IM proportional to E is supplied to the motor 1.

Explaining the motor drive IC 2 in more detail, the input terminal 2a to which the comparison detection signal VE from the filter amplifier 5 is guided is connected to the non-inverting input terminal of the mix amplifier 21. The output terminal of the mix amplifier 21 is connected to the bases of the transistors Tr1 and Tr2. The power supply input terminal 2b to which the voltage Vcc is introduced is connected to the positive output terminal 2d via the collector-emitter path of the transistor Tr1. On the other hand, the negative output terminal 2e
Is connected to the ground terminal 2c and the inverting input terminal of the mix amplifier 21 via the collector-emitter path of the transistor Tr2.

The inside of the broken line of the motor 1 shows an equivalent circuit of the motor 1. The positive polarity input terminal 1a has a resistance RM indicating an internal resistance RM of the motor 1 and a counter electromotive force V of the motor 1.
The negative output terminal 2d is connected through a series connection with a power source VM indicating M.

In such a conventional control circuit, when the rotation speed of the motor 1 is lower than the target rotation speed, the frequency of the detection signal a becomes smaller than the target value b and the voltage of the control signal VE becomes positive. It becomes sex + AV. In this case, the voltage at the inverting input terminal of the mix amplifier 21 is the current detection resistor R
It is the same as the voltage drop due to the current flowing through F, and the mix amplifier 21 reduces the difference between the voltage drop due to the current detection resistor RF and the voltage of the control signal VE so as to reduce the difference.
It controls the transistors Tr1 and Tr2. That is, the current IM of the motor 1 is controlled. This indicates that the motor drive IC 2 increases the current flowing through the motor 1 in response to the decrease in the rotation speed of the motor 1 from the target value b, and thus the rotation speed of the motor 1 is increased. Is controlled so that the target speed is reached.

When the rotation speed of the motor 1 is higher than the target rotation speed, the frequency of the detection signal a becomes higher than the target value b, and the voltage of the control signal VE becomes a negative polarity -BV. The voltage at the inverting input terminal of the mix amplifier 21 in this case is
Since it is always 0 V or more, the mix amplifier 21 controls the transistors Tr1 and Tr2 to be off. This allows
No current flows in the motor 1, and the motor 1 has a reduced rotation speed due to friction of bearings and the like.

As described above, the conventional control circuit raises the rotation speed of the motor 1 to control the rotation speed of the motor 1 to reach the target rotation speed when the rotation speed of the motor 1 is lower than the target rotation speed. When the number of revolutions is higher than the target number of revolutions, no current is passed through the motor 1 to reduce the number of revolutions.

Here, in the above-mentioned conventional control circuit,
The power supply voltage Vcc is set so as to satisfy the following formula.

Vcc> IM (max) · RM + VM (max) + V1 + V2 + IM (max) · RF (1) However, in the formula (1), IM (max) is the maximum current flowing through the motor 1, VM (max) max) is the maximum back electromotive force of motor 1, R
F and RM are the resistance values of the resistors RF and RM, V1 and V, respectively.
Reference numeral 2 denotes the collector-emitter voltage of the transistors Tr1 and Tr2, respectively.

Here, the maximum back electromotive force VM (ma) of the motor 1 is
x) [V] is the induced voltage constant of the motor 1 in Ke [V / rpm
], And the maximum number of rotations is N (max) [rpm], it can be expressed by the following equation.

VM (max) = Ke.N (max) (2) Substituting this formula (2) into the formula (1), Vcc> IM (max) .RM + Ke.N (max) + V1 + V2 + IM ( max) ・ RF ... (3)

Here, assuming that N is the actual number of revolutions of the motor 1, the power consumption P of the motor drive IC 2 is given by the following equation.

P = {Vcc- (IMRM + KeN) -IMRF} IM (4) In general, the resistance value of the resistance RF is 0.2 to 1Ω.
Since the one with a small value is used,

[0016]

[Equation 1]

Then, the equation (4) can be approximated to the following equation.

P = {Vcc- (IM * RM + Ke * N)} * IM (6) From this equation (6), when the load of the motor 1, that is, the current IM of the motor 1 is always constant, Number of rotations of motor 1 N
Becomes smaller, the voltage applied to the motor 1 (IM · RM +
Since the amount of decrease of Ke · N) is added to the circuit of the motor drive IC 2, the power consumption P of the motor drive IC 2 increases.

Here, in such a conventional control circuit,
In order to cope with high-speed rotation, that is, in order to set the maximum rotation speed N (max) of the motor 1 to a large value, the voltage Vcc must be set to a value as large as possible so that the equation (3) holds. However, when the voltage Vcc is set to a large value and the motor 1 is rotated at a low speed, the decrease in the voltage applied to the motor 1 is added to the circuit of the motor drive IC 2 as shown in the equation (6), and the motor drive IC 2 is driven. The power consumption P of the IC2 approaches the product of the voltage Vcc and the current IM flowing through the motor 1. As a result, the power consumption P of the motor drive IC 2 increases. Therefore, especially when the load of the motor 1 is large, that is, when a large torque is generated by the motor 1, the current IM of the motor 1 also increases, and the power consumption P of the motor drive IC 2 during low speed rotation further increases. It was difficult to control the motor 1 in a wide range from low speed rotation to high speed rotation.

Here, although it is conceivable to increase the allowable amount of the power consumption P of the motor drive IC 2, that is, the maximum rating of the power consumption P, usually the motor drive IC 2 is used.
Realizes various circuits and functions such as a constant current circuit, a power transistor, a switching circuit (in the case of a multi-phase motor) by a Hall element, etc. on one chip, and although it is small, the maximum rating of the power consumption P is Since it is smaller than discrete components (power transistor, field effect transistor), it is not suitable for applications that require a wide range of control from low speed rotation to high speed rotation with a high load on the motor 1.

[0021]

In such a conventional motor control device, in order to cope with high speed rotation,
The power supply voltage of the motor drive IC must be set to a large value, but if the motor is rotated at a low speed in this state, the amount of decrease in the voltage applied to the DC motor is added to the circuit of the motor drive IC, so the motor drive IC The power consumption of the IC for use becomes large and it is difficult to control the motor 1 in a wide range from low speed rotation to high speed rotation.

Therefore, it is an object of the present invention to provide a motor control device capable of preventing a decrease in voltage applied to a DC motor from being applied to a motor drive circuit when the motor is switched from high speed rotation to low speed rotation.

[0023]

According to a first aspect of the present invention, there is provided a motor control device including a frequency generator for generating a signal having a frequency proportional to the number of revolutions of a motor, and a frequency of the signal from the frequency generator. , A frequency detector that compares the target frequency and detects the difference in frequency, a motor drive circuit that controls the current flowing to the motor based on the detection output of this frequency detector, and the detection of the frequency detector A control circuit that creates a control signal from the output and the detection signal from the frequency generator, and a path that supplies a voltage from the power supply to the motor drive circuit. The motor drive circuit responds to the control signal from the control circuit. And a voltage control circuit for controlling the voltage supplied to the circuit.

[0024]

According to this structure, a control signal is generated by calculating the detection output of the frequency detector and the frequency of the detection signal from the frequency generator by the arithmetic circuit, and the voltage control circuit causes the motor to operate. When the high-speed rotation is switched to the low-speed rotation, the control signal can reduce the DC voltage from the power supply supplied to the motor drive IC. It can be prevented from joining the circuit.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A description will be given below with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of a motor control device according to the present invention. The same components as those of the conventional example of FIG. 3 are designated by the same reference numerals and their description is omitted.

In FIG. 1, the difference between the present embodiment is that the arithmetic circuit 11 calculates the detection signal a from the FG 3 and the control signal VE from the filter amplifier 5 and the resulting voltage V
The ref is created, and the voltage control circuit 12 corresponds to this operation result Vref and the power supply input terminal 2b of the motor drive IC 2
That is, the power supply voltage guided to is controlled.

More specifically, the FG 3 supplies the detection signal a indicating the frequency proportional to the rotation speed of the motor 1 to the first input terminal of the frequency detector 4 and the first signal of the arithmetic circuit 11. Supplying to the input terminal. The control signal VE from the filter amplifier 5 is led to the second input terminal of the arithmetic circuit 11. The arithmetic circuit 11 calculates the detection signal a and the control signal VE with a coefficient to be described later, and supplies the voltage Vref as the calculation result to the control signal input terminal of the voltage control circuit 12. In the voltage control circuit 12, a DC voltage of a voltage Vcc from a DC power supply is introduced to the power supply input terminal, and this voltage Vcc is controlled so as to be proportional to the voltage Vref to obtain V'cc.
Is led to the power input terminal 2b of the motor drive IC 2.

Here, the calculation in the calculation circuit 11 will be specifically described by using mathematical expressions.

First, the power consumption of the motor drive IC 2 is P = {V'cc- (IM * RM + Ke * N)} * IM by setting Vcc in the conventional expression (6) to V'cc. (7) If the maximum rating of the power consumption P of the motor drive IC 2 is P (MAX), the following formula must be satisfied.

P (max)>{V'cc- (IM * RM + Ke * N)} * IM ... (8) where V'cc is V'cc = α + IM * RM + Ke * N ... (9) Suppose In this case, α is a constant that satisfies the following equation.

Α> V ′ 1 + V ′ 2 (10) where V ′ 1 + V ′ 2 is the transistor Tr 1 or Tr 2 when the maximum current IM (max) flows through the motor 1.
The collector-emitter voltage of the transistor Tr1
, Tr2 is the minimum voltage required for constant current operation.

The power consumption P when V'cc is controlled by the equation (9) becomes the following equation by substituting the equation (9) into the equation (7).

P = αIM (11) From the equation (11), if IM is constant, the power consumption P is constant regardless of the rotation speed.

Here, assuming that the maximum current value flowing in the motor 1 is IM (MAX), the condition to be satisfied by the maximum rating P (MAX) of power consumption is to substitute the formula (9) into the formula (8). Therefore, the following formula is obtained.

P (MAX)> α · IM (MAX) (12) If the voltage V'cc is controlled by the equation (9) within the range satisfying the equation (12), the equation (11) yields The power consumption of the motor drive IC 2 can always be kept within the rating.

Here, the number of teeth of FG3 (the number of pulses generated by one rotation of the motor) is n, the conversion coefficient when VE is converted to IM is g [A / V], and the frequency of the detection signal of FG3 is f [H
z],

[0038]

[Equation 2]

Substituting equations (13) and (14) into equation (9) gives the following equation.

[0040]

[Equation 3]

Here, the voltage control circuit 12 controls so that V'cc is proportional to the operation result Vref, and if this proportional constant is k, then V'cc = k.Vref (16) ) Substituting equation (16) into equation (15),

[0042]

[Equation 4]

In equation (17), k, α, Ke, n,
RM.g is a constant, and V'cc can be controlled by the control signal VE and the rotation speed N of the motor 1.

As described above, according to the present embodiment, by controlling the power supply voltage of the motor drive IC 2 in accordance with the rotation speed n of the motor 1 and the control signal VE,
As shown in 1), the power consumption of the motor drive IC 2 can be controlled so as to be proportional to the current flowing through the motor regardless of the rotation speed n of the motor, so that the motor is switched from high speed rotation to low speed rotation. At this time, it is possible to prevent a decrease in the voltage applied to the motor 1 from being applied to the circuit of the motor drive IC 2, reduce the power consumption of the motor drive IC 2 during low speed rotation, and achieve a wide range from low speed rotation to high speed rotation. Can be easily controlled for the motor 1.

FIG. 2 is a circuit diagram showing another embodiment of the motor control device according to the present invention. The same components as those of the embodiment of FIG. 1 are designated by the same reference numerals and their description is omitted. ..

In FIG. 2, the difference between the present embodiment is that the current detection circuit 31 detects the current flowing from the voltage control circuit 12 to the terminal 2b of the motor drive IC 2 to detect the motor current IM, and this detection is performed. The output is supplied as VI to the arithmetic circuit 32, and the arithmetic circuit 32 calculates the detection signal a from the FG 3 and the detection output VI of the current detection circuit 31, and creates the voltage Vref of this calculation result, and the voltage control circuit The control means 12 controls the power supply voltage guided to the power supply input terminal 2b of the motor drive IC 2 in accordance with the calculation result Vref. Here, the current detection circuit 31 detects the current value output from the voltage control circuit 12, and various measuring methods can be adopted.
As such a method, for example, a method of detecting the current value by detecting the potential of the output terminal of the voltage control circuit 12 can be considered.

Here, when the conversion coefficient for converting VI into IM is g '[A / V], the following equation is obtained.

IM = VI.g '[A] (18) Since the conversion from VI to IM in the equation (18) is different from the conversion from VE to IM in the equation (14), only the conversion coefficient is different. , The arithmetic circuit 32 changes the conversion coefficient g of the arithmetic operation in the arithmetic circuit 11 of FIG.
The same operation as VE in FIG. 1 may be performed on I. In this way, the conversion coefficient g is changed to g ', and VI is VE
Even if it is changed to the expression (1
Since the equations 5), (16) and (17) are established, the power consumption of the motor drive IC 2 is controlled to be proportional to the current flowing through the motor irrespective of the rotation speed n of the motor in this embodiment as well. It is possible to obtain the same effect as the embodiment of FIG.

Here, as a modification of the embodiment shown in FIG. 2, instead of the current detection circuit 31 detecting the current at the output terminal of the voltage control circuit 12, a terminal of the current detection resistor RF on the side of the motor drive IC 2, that is, Alternatively, the current flowing through the motor may be detected by detecting the potential V2c of the terminal 2c of the motor drive IC 2. In this case, the following equation holds.

[0050]

[Equation 5]

Here, when the conversion coefficient for converting into IM is g ″ [A / V], the following equation holds.

[0052]

[Equation 6]

Since the conversion coefficient g ″ [A / V] in this case is a constant, the following equation holds as in the equation (18).

IM = V2c · g ″ [A] (21) That is, in this modification, the conversion coefficient g ′ in the arithmetic circuit 32 is changed to g ″, and V2c in FIG. By performing the same calculation as VI, the same effect as in FIG. 2 can be obtained.

In the embodiments of FIGS. 1 and 2, as in the conventional example, the mix amplifier 21 reduces the difference between the voltage drop due to the current detecting resistor RF and the voltage of the control signal VE so that the transistors Tr1 and Although Tr2 is controlled, the transistor Tr1 may be controlled by a mere switching operation by determining the control signal VE by a predetermined determination circuit.

[0056]

As described above, according to the present invention, when the motor is switched from the high speed rotation to the low speed rotation, it is possible to prevent the decrease in the voltage applied to the DC motor from being applied to the motor drive circuit. The power consumption of the motor drive circuit at low speed rotation can be reduced, and the motor can be easily controlled in a wide range from low speed rotation to high speed rotation.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram showing another embodiment of the motor control device according to the present invention.

FIG. 3 is a circuit diagram showing a conventional motor control device.

[Explanation of symbols]

 1 DC motor 2 Motor drive IC 3 FG 4 Frequency detector 11 Arithmetic circuit 12 Voltage control circuit

Claims (2)

[Claims] 1. A frequency generator for generating a signal having a frequency proportional to the number of rotations of a motor, and a frequency of a signal from this frequency generator and a target frequency are compared to detect a difference between the frequencies. A control signal is created from the frequency detector, the motor drive circuit that controls the current flowing to the motor based on the detection output of this frequency detector, the detection output of the frequency detector, and the detection signal from the frequency generator. A control circuit and a voltage control circuit provided on a path for supplying a voltage from the power supply to the motor drive circuit and controlling a voltage supplied to the motor drive circuit in response to a control signal from the control circuit. A motor control device characterized by: 2. A frequency generator for generating a signal having a frequency proportional to the number of revolutions of the motor, and the frequency of the signal from this frequency generator is compared with a target frequency to detect the difference between the frequencies. A frequency detector, a motor drive circuit that controls the current that flows in the motor based on the detection output of this frequency detector, a current detection circuit that detects the current that flows in the motor, the detection output of this current detection circuit, and the frequency It is provided in the control circuit that creates a control signal from the detection signal from the generator and the path that supplies the voltage from the power supply to the motor drive circuit, and is supplied to the motor drive circuit in response to the control signal from the control circuit. And a voltage control circuit for controlling the voltage.