JPH09168290A - Motor drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize rotational speed control of a motor, free from the influence of the load by providing a bridge circuit incorporating an armature, a differential amplifier circuit for amplifying the unbalance voltage of the bridge circuit, and a circuit for comparing the control voltage of the motor with the output from the differential amplifier circuit and feeding the output from the comparison circuit to the bridge circuit. SOLUTION: A bridge circuit is formed of resistors 3, 4, 5 having resistances R1 , R2 , R3 and the internal resistance Rm of a motor having counter electromotive force Em. Resistances R4 , R5 of resistors 10, 8 are set sufficiently higher than Rm , R1 , R2 , R3 . Assuming the resistance 13 of a differential amplifier circuit 6 is R6 , resistances 20, 23 of a comparator circuit 16 are R8 , R10 , control voltage of a control voltage output circuit 14 is Ei, and respective resistances are set to satisfy the following relations; (R10 /R8 )Ei≫(Rm +R3 )Im , following relationship is obtained; Em=[ (R10 /R8 )/1+(R10 /R8 ).(R6 /R4 ).(R3 /(R1 +R3 ))}]Ei. The counter electromotive force Em, and thereby the r.p.m. of motor, is determined by the control voltage Ei of the control voltage output circuit 14 and not affected by the load.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit suitable for an electric motor used in a feeder of an optical pickup for optically reading a signal recorded on a disc.

[0002]

2. Description of the Related Art A reproducing operation is performed by reading out a signal recorded on a disc, which is recorded with information data such as music by a digital signal and is rotated at a constant linear velocity, by using an optical pickup. The disc player having the above-mentioned structure is in widespread use, and a CD player is known as a typical one of such disc players.

Further, in such a disc player, the main body of the optical pickup is constructed so as to be moved in the radial direction of the disc by a feeding device. There are various devices for moving the main body of such an optical pickup, but there is a technique in which the pickup feeding shaft having a feed groove formed on the outer periphery is rotated to move the main body of the optical pickup. It is described in Japanese Patent Publication No.

A device for feeding the pickup main body by rotating a pickup feeding shaft having a feed groove formed on the outer circumference can feed the pickup accurately, but it can feed at high speed. There is a problem that you cannot do it. There is one that uses a rack gear as a drive mechanism of a pickup that solves such a problem, and as such a technique, for example, Japanese Patent Laid-Open No. 6-252510.
Is disclosed in Japanese Patent Application Laid-Open Publication No. HEI 9-203 (1995).

[0005]

The moving operation of the optical pickup main body is performed by the rotational force of the pickup electric motor. However, when performing the search operation, a high-speed and stable moving operation is required. Although there is a method of using a stepping electric motor to perform such an operation, such a method has a problem that it is expensive and consumes a large amount of power. Further, as another method, there is a method of using an electric motor having a large torque, but such a method has a problem that the electric motor becomes expensive and the shape of the electric motor becomes large.

If the reduction gear ratio of the gear mechanism used as the feed mechanism of the optical pickup is increased, an electric motor having a small torque can be used, but in this case, there is a problem that the search operation becomes slow. As a method of solving such a problem, there is a method of providing a rotation speed detection element such as a hall element outside the electric motor and controlling the rotation drive voltage of the electric motor based on a signal corresponding to the rotation speed obtained from the detection element. However, such a method has a problem that the cost is high and the shape is large.

The present invention is intended to provide an electric motor drive circuit that solves the above problems.

[0008]

A motor drive circuit according to the present invention is provided in a bridge circuit in which an armature is incorporated in one side and resistors are respectively incorporated in three sides, and the bridge circuit. First and second signals to which signals obtained from the first and second unbalanced voltage detection terminals are respectively input
A differential amplifier circuit for amplifying an unbalanced voltage and a control voltage for controlling a rotation speed of a motor are input to a first input terminal and an output signal of the differential amplifier circuit is a second signal. It is composed of a comparison circuit which is inputted to the input terminal and whose output signal is supplied to the bridge circuit.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of the motor drive circuit of the present invention. In the figure, reference numeral 1 denotes an armature of an electric motor, which is incorporated in one side of the bridge circuit 2. 3, 4 and 5
Are resistors incorporated in the other three sides of the bridge circuit 2. 6, the first input terminal 7 is a resistor 8
The second unbalanced voltage which is connected to the first unbalanced voltage detection terminal a provided in the bridge circuit 2 via the resistor and the second input terminal 9 is provided in the bridge circuit 2 via the resistor 10. It is a differential amplifier circuit connected to the voltage detection terminal b, and has a resistor 1 between the first input terminal 7 and the ground.
1 is connected, and a resistor 13 is connected between the second input terminal 9 and its output terminal 12.

Reference numeral 14 is a control voltage output circuit for outputting a control voltage for controlling the rotation speed of the electric motor during rotation driving operation to an output terminal 15. Reference numeral 16 is a first input terminal 17 of the control voltage output circuit 14 via a resistor 18. A comparison circuit that is connected to the output terminal 15 and has a second input terminal 19 connected to the output terminal 12 of the differential amplifier circuit 6 via a resistor 20, and is connected between the first input terminal 17 and ground. A resistor 21 is connected, a resistor 23 is connected between the second input terminal 19 and its output terminal 22, and the output terminal 22 is connected to a power supply terminal c of the bridge circuit 2.

The electric motor drive circuit of the present invention is constructed as described above. Next, the drive operation of the electric motor will be described. If the internal resistance of the motor is Rm, the back electromotive force generated by the rotation of the motor is Em, the resistance value of the resistor 3 is R1, the resistance value of the resistor 4 is R2, and the resistance value of the resistor 5 is R3, the balance of the bridge circuit 2 is From the condition, R1 × R3 = Rm × R2 holds.

The resistance value of the resistor 10 is R4, the resistance value of the resistor 8 is R5, and the values of R4 and R5 are Rm, R1, and R.
2 and R3 are sufficiently large, that is, assuming that the differential amplifier circuit 6 does not affect the operation of the bridge circuit 2, the voltage Ea of the first unbalanced voltage detection terminal a, the second
Between the voltage Eb of the unbalanced voltage detection terminal b and the voltage Ec of the power supply terminal c,

[0013]

[Equation 1]

The relationship is established. In the differential amplifier circuit 6, the resistance value of the resistor 10 is R4, the resistance value of the resistor 8 is R5,
When the resistance value of the resistor 13 is R6, the resistance value of the resistor 11 is R7, and R4 = R5 and R6 = R7 are set, the voltage Ed at the point d, which is the output terminal 12 of the differential amplifier circuit 6, is

[0015]

(Equation 2)

It becomes as follows. Substituting equations (1) and (2) into equation (3),

[0017]

(Equation 3)

When the equilibrium condition of the bridge circuit 2 is added to the equation (4) and the right side is rearranged,

[0019]

(Equation 4)

It becomes like this. In the comparison circuit 16, the resistance value of the resistor 20 is R8, and the resistance value of the resistor 18 is R
9, the resistance value of the resistor 23 is R10, the resistance value of the resistor 21 is R
11 and R8 = R9 and R10 = R11 are set, and the control voltage output to the output terminal 15 of the control voltage output circuit 14 is set to Ei, the output terminal 2 of the comparison circuit 16 is set.
2, that is, the voltage Ec of the power supply terminal c provided in the bridge circuit 2 is

[0021]

(Equation 5)

It is expressed as follows. In this equation (6), (5)
Substituting the expression gives

[0023]

(Equation 6)

It becomes like this. The current flowing through the armature 1 is I
m and the voltage Ec for one-cycle transmission,

[0025]

(Equation 7)

It is expressed as follows. From the above equations (7) and (8),

[0027]

(Equation 8)

When the relational expression of is established and this expression (9) is rearranged,

[0029]

(Equation 9)

It becomes as follows. here,

[0031]

(Equation 10)

If the resistance values are set so that the relation of

[0033]

[Equation 11]

It is expressed as follows. When the back electromotive force Em is obtained from the equation (12),

[0035]

(Equation 12)

It becomes as follows. As is clear from the equation (13), the back electromotive force Em, that is, the rotation speed of the motor is determined by Ei, that is, the control voltage output to the output terminal 15 of the control voltage output circuit 14, and is not affected by the load. become. Therefore, the rotation speed of the electric motor can be set and controlled by changing the control voltage Ei.

[0037]

According to the present invention, an armature of an electric motor is incorporated in a bridge circuit, a differential amplifier circuit for amplifying an unbalanced voltage obtained from the bridge circuit is provided, and an output signal and a control voltage output of the differential amplifier circuit are provided. Since the comparison circuit for comparing with the control voltage output from the circuit is provided and the output signal of the comparison circuit is supplied to the bridge circuit to control the rotation speed of the electric motor, it is not affected by the load. The rotation speed of the electric motor can be controlled. Therefore, when the electric motor drive circuit of the present invention is used to perform the rotational drive operation of the electric motor that moves the optical pickup of the disc player, the rotational drive can be quickly performed at a desired rotational speed state. The invention has a very great effect on speeding up a search operation in a disc player.

[Brief description of the drawings]

FIG. 1 is an embodiment of a motor drive circuit of the present invention.

[Explanation of symbols]

 1 Armature 2 Bridge circuit 6 Differential amplifier circuit 14 Control voltage output circuit 16 Comparison circuit

Claims (1)

[Claims] 1. A bridge circuit in which an armature of an electric motor is incorporated in one side and resistors are respectively incorporated in three sides, and first and second unbalanced voltage detections provided in the bridge circuit. A differential amplifier circuit having first and second input terminals to which signals obtained from the terminals are respectively input and amplifying an unbalanced voltage, and a control voltage for controlling the rotation speed of the electric motor are provided at the first input terminal. The output signal of the differential amplifier circuit is input to the second input terminal, and the output of the comparator circuit is supplied to the power supply terminal of the bridge circuit. The electric motor drive circuit.