Electricity: measuring and testing – Magnetic – Displacement
Patent
1995-08-30
1997-11-25
Snow, Walter E.
Electricity: measuring and testing
Magnetic
Displacement
32420722, 318653, G01B 730, H02P 616, H02P 700, H02P 602
Patent
active
056916388
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an apparatus for obtaining 3-phase position detecting signals by using a single position detecting element, the apparatus being used as a position detecting apparatus for reluctance type motors, brushless DC motors, or the like.
BACKGROUND ART
A position detecting apparatus for obtaining position detecting signals to detect the position of the rotor of a 3-phase DC motor to control the motor usually requires three position detecting elements. This presents a problem in that the number of electrical parts increases, and the electric circuit is complicated accordingly. This problem is especially remarkable for a small-size motor with a diameter of about 20 mm.
The control of an electric motor by means of a position detecting apparatus using a single position detecting element has been known as disclosed in Unexamined Japanese Patent Publication No. S51-31816. However, the position detecting apparatus of this type poses a problem in that the output torque is unstable when the motor is started.
DISCLOSURE OF THE INVENTION
An object of the present invention relates to a position detecting apparatus for obtaining position detecting signals for controlling an electric motor, and is more particularly to provide a position detecting apparatus which can be applied effectively to a small motor with a small diameter for simplicity of construction, and can generate position detecting signals so that the electric motor can be started and controlled stably.
To achieve the above object, one mode of the present invention comprises a conductor disk rotating in synchronization with the electric motor; a plurality of protrusions each having a width of an electrical angle of 240 degrees, disposed on the circumferential surface of the disk apart from each other by an electrical angle of 120 degrees; a coil constituting a position detecting element which is fixed to the motor body and the coil face of which confronts the rotating surfaces of the protrusions via a slight clearance; means for making the impedance of the coil different by making the clearance between the coil face and a section having a width of 120 degrees electrical angle on the rotating surface of the protrusion different from the clearance between the coil surface and the next section having a width of 120 degrees electrical angle; and an electric circuit for obtaining position detecting signals of first, second, and third phases corresponding to the first, second, and third sections respectively by detecting the difference in impedance among the first section with a width of an electrical angle of 120 degrees, the second section with a width of an electrical angle of 120 degrees, and the third section with a width of an electrical angle of 120 degrees without protrusion, as they pass the coil face, by detecting the change in current value of high-frequency alternate current applied to the coil.
Another mode of the present invention comprises a disk rotating in synchronization with an electric motor; a magnet rotor in which magnets of N and S poles with a width of an electrical angle of 120 degrees are adjacently disposed apart from each other by an electrical angle of 120 degrees on the circumferential surface of the disk; one Hall element consisting of a position detecting element fixed to the motor body and facing the N and S magnetic pole face of the magnet rotor via a slight clearance; and an electric circuit for obtaining position detecting signals of first, second, and third phases without a gap between the adjacent electric signal curves of three electric signals corresponding to first, second, and third sections by detecting first, second, and third output signals of the Hall element when the third section with a width of an electrical angle of 120 degrees without magnetic pole of the magnet rotor passes the Hall element.
According to the present invention, as described above, the first, second, and third sections varying in physical property are disposed at the periphery of the disk rotating in s
REFERENCES:
patent: 4142153 (1979-02-01), Smith
patent: 4774494 (1988-09-01), Extance
Kabushikigaisha Sekogiken
Snow Walter E.
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