JP2000270529A - Motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize flexible control of rotating velocity and rotation output through effective control of rush current of a commutator type motor, with a simplified structure introducing mechanical control. SOLUTION: A brush 3 slides in contact with a commutator 4 and supplies a drive current to a motor 2 via this commutator 4. A field torque controller 5 integrally and turnably supports a magnetic field 1 with respect to the axial line that is almost in common with the motor 2 to operate a torque against the reaction of rotation of the motor 2, and also adjusts and controls the torque of this field 1. The torque adjusting part adjusts a rotating torque against the reaction of the field 1 based on the control of controller. With adjustment of rotating torque against the reaction of the field 1 through adjustment of this torque adjusting part, the rotation angle position of the field 1, based on the rotation of motor 2 is also controlled. The field holding part integrally holds the field 1 to operate the rotating torque adjusted with the torque adjusting part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electric motor,
In particular, the present invention relates to a commutator type AC motor that supplies power to an armature via a brush and a commutator.

[0002]

2. Description of the Related Art A commutator-type AC motor that supplies power to an armature via a brush and a commutator is widely used in electric appliances such as a vacuum cleaner. This type of commutator-type AC motor is often used as a large-sized motor having a high rotation speed and a high rotation output for power use.

In this type of commutator type AC motor,
The inrush current at the time of start-up is large, and there is a risk of damaging the drive power supply and components, and these must be configured with a high withstand current. Further, in the commutator type AC motor, it is difficult to flexibly control the rotation speed and the rotation output.

Conventionally, in order to cope with these problems in the commutator type AC motor, a resistor for suppressing an inrush current is inserted into a drive control circuit to prevent an excessive inrush current from flowing. The frequency control or the phase control of the driving power supply is performed.

[0005]

However, the inrush current does not occur constantly or statically, but rather is a phenomenon that occurs dynamically, so that excessive rush current can be suppressed simply by inserting a suppressing resistor. Has limitations, such as requiring a complex configuration. In addition, in order to perform complicated control such as frequency control and phase control of a drive power supply, an extremely complicated configuration is required, and even if such control is performed, a fine rotation speed and rotation output can be reduced. Coordination is difficult.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described circumstances, and has a simple structure that mainly uses mechanical control to effectively suppress the inrush current of a commutator-type motor and reduce the rotational speed and the rotational output. An object of the present invention is to provide an electric motor capable of performing flexible control.

[0007]

In order to achieve the above object, a motor according to a first aspect of the present invention comprises one of a field and an armature as a stator and the other as a rotor. A stator holding means for rotatably holding the stator, the stator being provided with the rotation of the rotor, And torque adjusting means for adjusting the torque in accordance with the load while giving a torque against the reaction of.

[0008] The torque adjusting means may include means for controlling torque so as to obtain at least one of a required rotor rotation speed and a required rotor rotation output. The torque adjusting means may include means for controlling the torque so as to suppress the inrush current at the time of starting to a predetermined value or less.

In a motor according to a second aspect of the present invention, one of a field and an armature is configured as a stator, and the other is configured as a rotor, and a commutator that supplies power to the armature via a brush and a commutator. A biasing operation means for rotating the brush around a rotation axis of the rotor by using a load current for at least one of the field and the armature as a drive source to change a rotation angle position of the brush; A bias adjusting means for controlling the bias operating means in accordance with a load to adjust a rotational bias amount of the brush.

[0010] The bias operation means may include a solenoid operated by the load current.

[0011] The deviation adjusting means may include means for controlling the deviation control means to obtain at least one of a required rotor rotation speed and a rotor rotation output.

[0012] The deviation adjusting means may include means for controlling the deviation control means so as to suppress the inrush current at the time of starting to a predetermined value or less.

A motor according to a third aspect of the present invention is a commutator in which one of a field and an armature is configured as a stator and the other is configured as a rotor, and power is supplied to the armature via a brush and a commutator. And a stator holding means for rotatably holding the stator, and applying a torque to the stator against a reaction of the stator accompanying rotation of the rotor and adjusting the torque. Torque adjusting means, and bias operating means for rotating the brush around a rotation axis of the rotor by using a load current for at least one of the field and the armature as a drive source to change a rotation angle position of the brush. A bias adjusting means for controlling the bias operating means to adjust the rotational bias amount of the brush; and a cooperative control means for cooperatively controlling the torque adjusting means and the bias adjusting means according to the load. To.

A motor according to the present invention is a commutator type AC motor in which one of a field and an armature is configured as a stator and the other is configured as a rotor, and power is supplied to the armature via a brush and a commutator. A structure for holding a stator rotatably, applying a torque to the stator against a reaction of the stator accompanying rotation of the rotor and adjusting the torque, and driving a brush with a load current At least one of a configuration for adjusting the amount of deviation of the rotation angle position of the brush by rotating and deviating around the rotation axis of the rotor is provided as a source. In this motor, the inrush current of the commutator motor is effectively suppressed by mechanical control adjustment using a simple configuration, and it is possible to flexibly control the rotation speed and the rotation output.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an electric motor according to an embodiment of the present invention will be described with reference to the drawings.

FIGS. 1 and 2 show the configuration of a commutator type motor according to a first embodiment of the present invention. FIG.
FIG. 2 schematically shows a principle configuration of a commutator type electric motor, and FIG. 2 schematically shows a configuration of a drive control system thereof.

The commutator type motor shown in FIG. 1 includes a field 1, an armature 2, a brush 3, a commutator 4, and a field torque controller 5.

The field 1 forms, for example, a stator having a pair of magnetic poles. The field 1 applies a magnetic field to the armature 2 via the magnetic poles. The field 1 is constituted by an electromagnet.

The armature 2 is rotatably supported by a rotating support (not shown), and forms a rotor that rotates in the magnetic field generated by the stator consisting of the field 1. The armature 2
Has, for example, a pair of magnetic poles for generating a magnetic repulsive force and a magnetic attraction force with the magnetic poles of the field 1 to obtain a predetermined rotational force.

The brush 3 comes into sliding contact with the commutator 4, and supplies a drive current to the armature 2 via the commutator 4. Commutator 4
Supplies the drive current supplied from the brush 3 to the armature 2 at a required timing and polarity for obtaining a rotational force.

The field torque control unit 5 integrally supports the field 1 so as to be rotatable about an axis substantially common to the armature 2 and controls a torque against a reaction of rotation of the armature 2. And the torque of the field 1 is adjusted and controlled.

This motor is configured to have an AC inductance because the driving current is AC and the armature 2 and the like are configured as electromagnets and use a wire (coil).

That is, in the first state, when the magnetic path between the magnetic pole of the field 1 and the magnetic pole of the armature 2 is the shortest distance, it is generated by the magnetic pole of the field 1 and the magnetic pole of the armature 2. The brushes 3 are arranged so that the directions of the magnetic flux are the same. In this state, the AC inductance viewed from the brush 3 is the largest, and the armature current supplied to the armature 2 is the smallest. In the second state, the magnetic pole of the field 1 and the magnetic pole of the armature 2 are the most distant as usual. For example, in the case of FIG. 1, the direction of the magnetic flux on the magnetic pole of the field 1 and the magnetic pole of the armature 2 The direction of the magnetic flux makes an angle of 90 °.

By changing the two states of the first and second states by adjusting the rotational torque against the reaction of the field 1 based on the rotation of the armature 2 and the mechanical arrangement associated therewith, the inrush current is increased. Limit and rotation speed / rotation output can be controlled.

That is, the brush 3 is usually arranged at a position where the magnetic pole of the armature 2 is formed at an angle of 90 ° with respect to the magnetic pole of the field 1, that is, at a position where the phase is shifted by 90 °. . On the other hand, by adjusting the rotation torque of the field 1,
When the magnetic pole position of the field 1 is shifted and the magnetic pole of the armature 2 is relatively shifted in the rotating direction, the magnetic pole of the field 1 and the magnetic pole of the armature 2 approach the same direction (the phase difference decreases), Gradually, the inductance increases and the rotation speed decreases.
Furthermore, when the magnetic pole positions are relatively shifted and the same direction, that is, the phase difference becomes 0 °, the rotation of the armature 2 stops. Further, if the position is shifted by more than 0 °, the armature 2 will rotate reversely.

On the other hand, a normal position, that is, an angle of 90 ° with respect to the magnetic pole of the field 1, that is, a position whose phase is shifted by 90 °,
From the position where the magnetic poles of the armature 2 are formed in a direction in which the phase difference exceeds 90 ° (eg, when the phase difference is
If the magnetic poles of the armature 2 are shifted in the direction of 0 °, the inductance decreases, and while the phase difference is less than 180 ° (until it reaches 180 °), the current increases and the rotation speed increases. To rise.

The control system of the motor configured as shown in FIG.
For example, the configuration is as shown in FIG. The motor control system shown in FIG. 2 includes a drive power supply 11, a control device 12, a torque adjustment unit 13, and a field holding unit 14. The torque adjustment unit 13 and the field holding unit 14 constitute the field torque control unit 5.

The drive power supply 11 applies a drive current to the armature 2 via the brush 3 and the commutator 4. Control device 12
Controls the torque adjustment unit 13 of the field torque control unit 5 to control the rotation torque against the above-described reaction of the field 1 according to the required rotation speed and rotation output.

The torque adjusting section 13 adjusts the rotational torque against the reaction of the field 1 under the control of the control device 12. Along with the adjustment of the rotation torque against the reaction of the field 1 by the adjustment of the torque adjustment unit 13, the rotation angle position of the field 1 based on the rotation of the armature 2 is also controlled. The field holding unit 14 integrally holds the field 1 and applies a rotational torque adjusted by the torque adjusting unit 13 on an axis substantially common to the armature 2.

The torque adjusting unit 13 and the field holding unit 1
4 is a rotational torque control of the reaction of the field 1, the rotational torque given to the field 1 depends on the magnitude of the reaction accompanying the rotation of the armature 2, Balance in position. For this reason, when the inrush current becomes excessive and the reaction is to be increased, the rotational position of the field 1 is changed, which acts in a direction to suppress the reaction and the inrush current. The rush current may be further suppressed by controlling the torque adjusting unit 13 according to the armature current supplied from the drive power supply 11.

Next, the function and operation of the motor configured as described above will be described in detail.

When a driving current is supplied from the driving power supply 11 to the armature 2 via the brush 3 and the commutator 4 with a predetermined polarity and phase, the driving current is included in the magnetic flux generated from the magnetic pole of the field 1 as the stator. Magnetic flux is generated at the magnetic poles of the armature 2 disposed. The magnetic field generated by the magnetic poles of the armature 2 causes the field 1
A magnetic repulsion force and a magnetic attraction force are generated between the magnetic poles of the armature 2 and the armature 2, and the armature 2 as a rotor rotates. During rotation of the armature 2, the commutator 4 with which the brush 3 is in sliding contact changes the polarity phase of the drive current supplied to the armature 2 to maintain the armature 2 rotating continuously.

In the drawings, for easy understanding, the field 1 and the armature 2 are shown as two-pole motors each having two magnetic poles. In some cases, it is necessary to provide a starting means for starting the rotation operation. Therefore, it is generally preferable to configure the motor as a multi-pole motor having three or more poles.

With the rotation of the armature 2, a reaction against the rotation of the armature 2 occurs in the field 1. The rotation torque against this reaction is generated by the field torque control unit 5 by the torque adjustment unit 13 and the field 1 held by the field holding unit 14.
Act on. As described above, the rotational torque applied to the field 1 is balanced when the field 1 is at an appropriate rotational position with respect to the magnitude of the reaction accompanying the rotation of the armature 2. If the inrush current becomes excessive and the reaction is about to increase, the rotational position of the field 1 changes, thereby suppressing the reaction and the inrush current.

For this reason, when the torque adjusting unit 13 is controlled by the control device 12 to adjust the rotational torque of the field 1 against the reaction, the rotational speed and the rotational output of the armature 2 can be set to desired values. it can.

That is, under the control of the field torque control section 5 (torque adjustment section 13) by the control device 12, at least one of the rotation speed and the rotation output can be freely controlled and adjusted according to the state of the load. Can be suppressed. Therefore, good motor control is possible without performing semiconductor control that is weak against inductance load.

FIG. 3 schematically shows a configuration of a drive control system of a commutator type motor according to a second embodiment of the present invention. In this case, the commutator type electric motor itself has the same configuration as that shown in FIG.

The motor control system shown in FIG. 3 is a motor control system for controlling at least one of the rotation speed and the rotation output of the motor with high accuracy. The motor control system shown in FIG. 3 includes a drive power supply 11, a torque adjustment unit 13 and a field holding unit 14 similar to those in FIG. 2, a control device 12 'substantially similar to the control device 12 in FIG. Armature 2 that is a child
And a sensor 15 for detecting at least one of the rotation speed and the rotation output of the motor.

The sensor 15 detects at least one of the rotation speed and the rotation output of the armature 2 of the electric motor, and
Feedback to 2 '. The control device 12 'controls the torque adjustment unit 13 of the field torque control unit 5 so that at least one of the rotation speed and the rotation output detected by the sensor 15 has a separately set value.

With such a configuration, the control device 12 '
By controlling the torque adjusting unit 13 in accordance with the output of the sensor 15 to adjust the rotational torque of the field 1 against the reaction, at least one of the rotational speed and the rotational output of the armature 2 can be adjusted to a desired value. Control and adjustment can be performed with high accuracy according to the value.

FIGS. 4 and 5 show a configuration of a commutator type motor according to a third embodiment of the present invention. FIG.
FIG. 5 schematically shows a principle configuration of a commutator type motor, and FIG. 5 schematically shows a configuration of a drive control system thereof.

The commutator type electric motor shown in FIG. 4 has a brush 2 in addition to a field 1, an armature 2 and a commutator 4 similar to those of FIG.
1, an urging device 22, a solenoid 23, and an adjusting resistor 24.

The brush 21 has substantially the same function as the brush 3 of FIG. 1, and can change the rotational angular position of the brush 21 with respect to the commutator 4. The urging device 22 is made of, for example, a spring or the like, and urges the brush 21 to a predetermined position. The solenoid 23 constitutes a biasing operation means, and an actuator 23a is connected to an intermediate portion of the brush 21 to suck and bias the intermediate portion of the brush 21 so that a rotational angle position of the brush 21 in sliding contact with the commutator 4 is determined. The armature 2 is turned around the rotation axis. A load current such as an electric current supplied to the armature 2 through the brush 21 is supplied to the exciting coil of the solenoid 23, and the solenoid 23 is driven to be excited according to the load current. Further, an adjusting resistor 24 as a displacement adjusting means is inserted in parallel with the exciting coil of the solenoid 23, and by changing the resistance value of the adjusting resistor 24, the exciting current of the solenoid 23 is controlled and the amount of attraction of the solenoid 23 is controlled. That is, the amount of rotational deviation of the brush 21 is controlled and adjusted.

This motor is also configured to have an AC inductance because the drive current is AC and the armature 2 and the like are configured as electromagnets and use wires. In the first state, when the magnetic path between the magnetic pole of the field 1 and the magnetic pole of the armature 2 is the shortest distance, the direction of the magnetic flux generated by the magnetic pole of the field 1 and the magnetic pole of the armature 2 The brush 21 is arranged so that
In this state, the AC inductance becomes the largest, and the armature current supplied to the armature 2 becomes the smallest. In the second state, the magnetic pole of the field 1 is farthest from the magnetic pole of the armature 2. For example, in the case of FIG. 4, the direction of the magnetic flux on the magnetic pole of the field 1 and the direction of the magnetic flux on the magnetic pole of the armature 2 Form a 90 ° angle. The first and second states 2
By changing these two states by adjusting the mechanical arrangement of the brush 21, that is, adjusting the amount of rotation deviation, it is possible to control the inrush current and control the rotation speed / rotation output.

That is, the brush 21 normally has an angle of 90 ° with respect to the magnetic pole of the field 1, that is, a phase of 90 °.
It is arranged at a position where the magnetic pole of the armature 2 is formed at the shifted position. On the other hand, by adjusting the position of the brush 21,
The magnetic pole of the armature 2 is moved to the
When the magnetic poles of the field 1 and the armature 2 are shifted in the rotational direction relative to the magnetic pole of the armature, the magnetic poles of the armature 2 approach the same direction, the phase difference decreases, the inductance gradually increases, and the rotational speed increases. descend. Further, when the relative magnetic pole position is shifted by the rotational bias of the brush 21 and the same direction, that is, the phase difference becomes 0 °, the rotation of the armature 2 stops. further,
If the position is shifted by more than 0 °, the armature 2 will now rotate in the reverse direction.

On the other hand, a normal position, that is, an angle of 90 ° with respect to the magnetic pole of the field 1, that is, a position whose phase is shifted by 90 °,
When the magnetic poles of the armature 2 are shifted from the position where the magnetic poles of the armature 2 are formed by the rotational deviation of the brush 21 in a direction in which the phase difference increases beyond 90 ° in the direction opposite to the rotation direction, Until the inductance decreases and the phase difference reaches 180 °, the current increases and the rotation speed increases.

The control system of the motor configured as shown in FIG.
For example, the configuration is as shown in FIG. The motor control system shown in FIG. 5 includes an armature current control unit 31 and a brush position control unit 32 in addition to the drive power supply 11 and the control device 12 similar to those in FIG. The brush position control unit 32 includes the solenoid 23
And a solenoid current adjusting unit 24a.

The armature current control unit 31 controls the armature current supplied from the drive power supply 11 to the brush 21. The armature current control unit 31 transfers a part of the armature current to the brush position control unit. 32 solenoid current adjusting units 24
a.

The brush position control unit 32 controls and adjusts a part of the armature current supplied from the armature current control unit 31 by the solenoid current adjusting unit 24a and supplies the adjusted current to the solenoid 23. The solenoid current adjustment unit 24a controls and adjusts a part of the armature current supplied from the armature current control unit 31 in accordance with the control of the control device 12, supplies the solenoid current to the solenoid 23, and drives the 21 is controlled.

The exciting current of the solenoid 23 is a load current,
For example, since it is proportional to the armature current, the amount of rotation deviation of the brush 21 becomes a value corresponding to the load current, and automatic control can be performed so that the load current, that is, the inrush current does not become excessive.

In the motor configured as above,
The driving current is supplied from the driving power supply 11 to the brush 21 and the commutator 4.
When a predetermined polarity and phase are supplied to the armature 2 via the magnetic field, a magnetic flux is generated in the magnetic poles of the armature 2 arranged in the magnetic flux generated from the magnetic poles of the field 1 which is the stator. Due to the magnetic flux generated at the magnetic poles of the armature 2, a magnetic repulsion force and a magnetic attraction force are generated between the field 1 and the magnetic poles of the armature 2, and the armature 2 as a rotor rotates. During rotation of the armature 2, the polarity phase of the drive current supplied to the armature 2 changes due to the commutator 4 with which the brush 21 is in sliding contact, and the armature 2 maintains continuous rotation. In FIG. 1 also, for easy understanding, a two-pole motor having two magnetic poles for the field 1 and the armature 2 is shown. However, in the case of the two-pole motor, the motor is separately rotated. In some cases, starting means for starting the operation may be required. Therefore, it is desirable to configure the motor as a multi-pole motor having three or more poles in a normal case.

With the rotation of the armature 2, the armature current supplied from the armature current control unit 31 to the armature 2 changes, and accordingly, is supplied to the solenoid 23 via the solenoid current adjustment unit 24a. The exciting current changes. For this reason, when the load current becomes excessive due to the rush current and the reaction tends to increase, the rotational angle position of the brush 21 with respect to the commutator 4 changes, and the rush current is effectively suppressed.

For this reason, the controller 12 controls the solenoid current adjuster 24a of the brush position controller 32 to
When the amount of rotation of the contact rotation angle of the brush 21 is adjusted,
The rotation speed and the rotation output of the armature 2 can be controlled and adjusted to desired values.

That is, under the control of the brush position control unit 32 (solenoid current adjustment unit 24a) by the control device 12, at least one of the rotation speed and the rotation output can be freely controlled and adjusted in accordance with the state of the load. Can be suppressed. Even in this case, good motor control can be performed without using semiconductor control weak in inductance load.

FIG. 6 schematically shows a configuration of a drive control system of a commutator motor according to a fourth embodiment of the present invention. In this case, the commutator type electric motor itself has the same configuration as that shown in FIG.

The motor control system shown in FIG. 6 is a motor control system for controlling at least one of the rotation speed and the rotation output of the motor with high accuracy. The motor control system shown in FIG. 6 includes a drive power supply 11 and an armature current control unit 31 similar to those in FIG.
In addition to the control unit 32 of FIG.
2 and a sensor 15 for detecting at least one of the rotational speed and the rotational output of the armature 2 which is the rotor of the electric motor.

The sensor 15 detects at least one of the rotation speed and the rotation output of the armature 2 of the electric motor, and
Feedback to 2 '. The control device 12 'controls the solenoid current adjustment unit 24a of the brush position control unit 32 so that at least one of the rotation speed and the rotation output detected by the sensor 15 has a separately set value.

With such a configuration, the control device 12 '
By controlling the solenoid current adjusting unit 24a in accordance with the output of the sensor 15 to adjust the amount of rotational deviation of the brush 21, at least one of the rotational speed and the rotational output of the armature 2 is set to a desired value. The control and adjustment can be performed with high accuracy in accordance with this.

The field torque control shown in FIGS. 1 to 3 and the brush bias control shown in FIGS. 4 to 6 may be combined.

[0060]

As described above, according to the present invention, with a simple configuration mainly using mechanical control,
It is possible to provide a motor capable of effectively suppressing the inrush current of the commutator type motor and performing flexible control of the rotation speed and the rotation output.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of a commutator type electric motor according to a first embodiment of the present invention.

FIG. 2 is a schematic block diagram showing a configuration of a control system used in the electric motor of FIG.

FIG. 3 is a schematic block diagram showing a configuration of a control system of a commutator motor according to a second embodiment of the present invention.

FIG. 4 is a schematic diagram showing a configuration of a commutator type electric motor according to a third embodiment of the present invention.

FIG. 5 is a schematic block diagram showing a configuration of a control system used in the electric motor of FIG.

FIG. 6 is a schematic block diagram showing a configuration of a control system of a commutator motor according to a fourth embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 field 2 armature 3 brush 4 commutator 5 field torque controller 11 drive power supply 12 controller 12 ′ controller 13 torque regulator 14 field holder 15 sensor 21 brush 22 biasing device 23 solenoid 23 a actuator 24 adjustment Resistance 31 Armature current control unit 32 Brush position control unit

Claims (8)

[Claims] 1. A commutator-type AC motor in which one of a field and an armature is configured as a stator, and the other is configured as a rotor, and power is supplied to the armature via a brush and a commutator. A stator holding means for rotatably holding, and a torque adjusting means for applying a torque to the stator against a reaction of the stator accompanying the rotation of the rotor and adjusting the torque according to a load; An electric motor comprising: 2. The electric motor according to claim 1, wherein said torque adjusting means includes means for controlling torque so as to obtain at least one of a required rotor rotation speed and a rotor rotation output. 3. The electric motor according to claim 1, wherein said torque adjusting means includes means for controlling torque so as to suppress an inrush current at startup to a predetermined value or less. 4. A commutator type AC motor in which one of a field and an armature is configured as a stator and the other is configured as a rotor, and power is supplied to the armature via a brush and a commutator. Biasing means for rotating and biasing around the rotation axis of the rotor by using a load current for at least one of the field and the armature as a drive source to change the rotational angle position of the brush; And a bias adjusting means for adjusting the amount of rotational bias of the brush by controlling the rotation of the brush. 5. The electric motor according to claim 4, wherein said biasing operation means includes a solenoid operated by said load current. 6. The apparatus according to claim 4, wherein said bias adjusting means includes means for controlling said bias operating means to obtain at least one of a required rotor rotation speed and a rotor rotation output. Electric motor. 7. The electric motor according to claim 4, wherein said bias adjusting means includes means for controlling said bias operating means so as to suppress an inrush current at start-up to a predetermined value or less. 8. A commutator-type AC motor in which one of a field and an armature is configured as a stator and the other is configured as a rotor, and the armature is supplied with power through a brush and a commutator. A stator holding means for rotatably holding, a torque adjusting means for applying a torque to the stator against a reaction of the stator accompanying the rotation of the rotor, and adjusting the torque; and the brush. A bias operating means for rotating and biasing around a rotation axis of the rotor by using a load current for at least one of the field and the armature as a drive source to change a rotational angle position of the brush; and controlling the bias operating means. An electric motor comprising: a bias adjusting means for adjusting an amount of rotational deviation of the brush; and a cooperative control means for cooperatively controlling the torque adjusting means and the bias adjusting means according to a load.