Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-10-26
2001-04-17
Enad, Elvin (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C338S03200R, C324S207210
Reexamination Certificate
active
06218750
ABSTRACT:
BACKGROUND OF THE INVENTION
Detailed Description of the Invention
1. Technical Field of the Invention
The present invention relates to a driving device for a brushless motor that is having a polyphase structure, and more particularly to a driving device for a polyphase motor excellent in temperature characteristic and capable of simplifying the circuit structure through the use of a magnetoresistance effect element for a rotation detector.
2. Prior Art
FIG. 14
is a structural view showing a driving device for a three-phase brushless motor as an example of a conventional driving device for a polyphase motor, and
FIG. 15
is a timing chart for the Hall signal and phase current in FIG.
14
.
In
FIG. 14
, a reference numeral
1
designates a brushless three-phase motor consisting of driving coils
1
U (U-phase),
1
V (V-phase) and
1
W (W-phase).
In this three-phase motor
1
, a rotor is rotatably supported on a stator, which is located on the fixed portion side. The stator is provided with the driving coils
1
U,
1
V and
1
W, and in positions adjacent these coils, with hole elements H
1
, H
2
and H
3
respectively. On the inner surface of a rotor case (not shown), there are provided ring-shaped rotor magnets, in which N-poles and S-poles are alternately arranged, and the Hall elements H
1
, H
2
and H
3
are provided in positions opposed to these rotor magnets respectively. When the rotor rotates, each magnetic pole of the rotor magnet passes the Hall elements H
1
, H
2
and H
3
respectively, and at this time, the Hall elements H
1
, H
2
and H
3
detect changes in the magnetic field.
Output signals from the Hall elements H
1
, H
2
and H
3
are inputted into driving means
2
. As shown in
FIG. 14
, the driving means
2
comprises voltage follower means
3
, control means
4
and phase current generating means
5
.
By receiving the output signals from the Hall elements H
1
, H
2
and H
3
by a high-input impedance element consisting of an operational amplifier and the like, the voltage follower means
3
plays a part of accurately transmitting the output signals of the Hall signals to the control means
4
in the next stage. Also, within the control means
4
, there is provided amplification means (not shown) to amplify the output signals from the Hall elements H
1
, H
2
and H
3
having a low signal level into such hole signals Hu, Hv and Hw which are prone to be signal-processed as shown in FIG.
15
.
Also, the control means
4
generates driving signals
4
u
,
4
v
and
4
w
for which timing adjustment has been performed on the basis of each Hall signal Hu, Hv and Hw. Thus, in the phase current generating means
5
, driving signals
4
u
,
4
v
and
4
w
are voltage-current converted into phase current Iu, Iv and Iw respectively. At this time, each phase current Iu, Iv and Iw is converted in line with the timing of the driving signals
4
u
,
4
v
and
4
w
respectively, and is supplied to each driving coil
1
U,
1
V and
1
W of the three-phase motor
1
.
In this manner, the construction of three-phase motor
1
makes it possible to always maintain the rotational speed and rotational phase of the rotor with high accuracy by performing feedback control in which the rotational speed and rotational phase of the rotor are detected to supply optimum phase current Iu, Iv and Iw to the driving coils
1
U,
1
V and
1
W for each phase in real time.
Problems to be solved by the Invention
The driving device for the motor has, however, the following problem.
The Hall elements used in the foregoing include a chemical semiconductor such as InSb (indium antimony) and GaAs (gallium arsenic).
Generally, since the Hall element including InSb (indium antimony) has a defect in that it has large fluctuations in temperature characteristic, the problem results because it is difficult to maintain the rotational speed and phase of the rotor with high accuracy.
On the other hand, since it has a low output level although it has smaller fluctuations in temperature characteristic than InSb, the Hall element made of GaAs (gallium arsenic) requires means for amplifying the output signal from the Hall element. Therefore, the problem is that the structure of the motor driving device becomes complicated.
Also the problem exists that when a plurality of Hall elements are provided within a polyphase motor, the outside dimensions of the entire polyphase motor increase because the outside dimensions of the Hall element are prone to become comparatively large.
SUMMARY OF THE INVENTION
The present invention solves the above-described conventional problems, and its object is to provide a driving device for a polyphase motor that is excellent in temperature characteristic and capable of simplifying the structure of a motor driving device.
Also, it is another object of the present invention to provide a polyphase motor capable of preventing the outside dimensions of the polyphase motor itself from being increased.
Means for solving the Problems
The present invention comprises a polyphase motor whose rotor magnet rotates when each phase current is supplied to a stator having a plurality of driving coils; a magnetoresistance effect element sensor provided for each phase for detecting an output signal corresponding to the rotational phase of the rotor magnet; offset removing means for removing offset voltage contained in an output signal from the magnetoresistance effect element sensor; driving signal generating means for generating a difference signal between phases of the output signal corresponding to each phase, from which the offset voltage has been removed; and phase current supplying means for generating phase current which is applied to the driving coils for each phase on the basis of the driving signal.
A driving device for a polyphase motor according to the present invention is, for example, used for a three-phase brushless motor, and may be for a two-phase motor, a four-phase motor and the like in addition. Generally, the magnetoresistance effect element is capable of suppressing the power consumption because it has a higher output level than the Hall element. Or when the current consumption is set to the same degree the Hall element, the magnetoresistance effect element can be operated in a more stable state. Also, since the magnetoresistance effect element is capable of generating a high output signal to a very weak magnetic field, the rotor magnet can also be formed by a weakly magnetic material, and it becomes possible to supply a low-priced three-phase motor.
In a driving device for a polyphase motor according to the present invention, a magnetoresistance effect sensor is used for detecting rotational speed or rotational phase of a polyphase motor consisting of a plurality of phases, whereby it is possible to obtain a signal at a higher output level than when the Hall element is used. Accordingly, it becomes possible to control the polyphase motor from low-speed rotation to high-speed rotation with high accuracy.
In the foregoing, the magnetoresistance effect sensor is a sensor comprising a first magnetoresistance effect element and a second magnetoresistance effect element in series connected through an output unit at the mid-point. The first magnetoresistance effect element has a fixed magnetic layer magnetized in one direction and a free magnetic layer whose direction of magnetization fluctuates under the influence of an external magnetic field, while the second magnetoresistance effect element has a fixed magnetic layer magnetized in a direction opposite to the one direction and a free magnetic layer whose direction of magnetization fluctuates under the influence of the external magnetic field. The directions of magnetization of the fixed magnetic layers of the first and second magnetoresistance effect elements, which are opposite to each other, are set in parallel to the direction of the magnetic field of the rotor, and predetermined voltage is applied to the magnetoresistance effect elements in series connected. The offset removing means has preferably subtraction means for subtracting, f
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Dinh Le Dang
Enad Elvin
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