Electricity: motive power systems – Switched reluctance motor commutation control
Patent
1995-03-06
1996-09-03
Ro, Bentsu
Electricity: motive power systems
Switched reluctance motor commutation control
318439, H02P 616
Patent
active
055526829
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
a) Field of the Invention
The present invention relates to a detector for detecting the position of the rotor of a brushless motor.
b) Description of the Related Art
An existing drum driving motor (brushless motor) of a VTR (Video Tape Recorder), for instance, has a rotational position detector for generating a rotational position signal of one pulse per turn of the motor in order to change image heads.
FIG. 6 shows an example of the rotational position detector in which a rotational position detecting step of a motor is formed by the fact that a magnetic field generated by a PG (Pulse Generator) magnet 21a set on the outer periphery of a rotor 21 of the motor is detected by a PG sensor 22 arranged at a position facing the outer periphery of the rotor 21, a signal provided as an output from PG sensor 22 is amplified by an amplifier 23 to obtain a waveform having a peak shown in FIG. 7(a), and the signal is compared with a threshold V.sub.th by a voltage comparison circuit 24 to obtain a pulse signal whose one cycle corresponds to one turn of rotor 21 as shown in FIG. 7(b).
However, the rotational position detector of the above brushless motor has the following problems.
That is, the number of parts increases and therefore the cost increases because the rotational position detector of the brushless motor requires the above-mentioned PG magnet 21a and the PG sensor 22.
Moreover, when a magnetic detector such as PG sensor 22 is used, electric wiring is necessary on a board (printed circuit board) and the operation is complicated. Further, the board cannot be downsized because the magnetic detector is arranged at a position facing the outer periphery of the rotor magnet 21 and a large space for electric wiring is necessary on the board.
OBJECT AND SUMMARY OF THE INVENTION
The present invention is made to solve the above problems of the prior art and its primary object is to provide a rotational position detector of a brushless motor which makes it possible to decrease the number of components and thereby decrease the component cost. Further, the manufacturing cost can be decreased and a corresponding board downsized as a result of the invention.
To achieve the above object, a first aspect of the present invention comprises an m-phase driving coil which is reciprocally electrified in the positive and negative directions, a driving magnet which faces the driving coil and rotates together with a rotary shaft by the fact that N and S driving magnetic poles are alternately polarized, position-detecting magnetic means which is provided on at least one of the driving magnetic poles and has homopolarity, a magnetic detector which is arranged so as to face the driving magnet and detects the magnetic fields of both the driving magnetic poles and position detecting means, a brushless motor driving circuit for applying a driving current to the driving coil in accordance with an output signal of the magnetic detector, and synthesizing means for synthesizing a rotational position signal with an output signal of the magnetic detector, a counter electromotive voltage of the driving coil and a reference voltage.
A second aspect of the present invention provides that an output of the magnetic detector of the first aspect described above protrusively changes once per turn of a motor.
A third aspect of the present invention provides that the synthesizing means of the first aspect of the invention comprises an amplifier for amplifying output signals for one phase among those of a magnetic detector, a counter electromotive synthesizing circuit for providing a predetermined pulse signal as an output in accordance with a counter electromotive voltage waveform of a driving coil and a reference voltage, a sample-and-hold circuit for sampling and holding an output signal of an amplifier in accordance with a pulse signal sent from a counter electromotive synthesizing circuit, a potential dividing circuit for dividing the amplitude of the potential of an output signal of the amplifier by n, a comparator for
REFERENCES:
patent: 4529918 (1985-07-01), Muller
patent: 4740733 (1988-04-01), Epars
patent: 5160873 (1992-11-01), Tukiyama et al.
patent: 5291104 (1994-03-01), Okada et al.
Ro Bentsu
Sankyo Seiki Mfg. Co. Ltd.
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