Electrical generator or motor structure – Dynamoelectric – Rotary
Patent
1987-04-07
1989-04-04
Salce, Patrick R.
Electrical generator or motor structure
Dynamoelectric
Rotary
318138, H02K 2906
Patent
active
048189081
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a brushless motor capable of positioning operations and high-speed rotation.
BACKGROUND OF THE INVENTION
Responding to the development of recent semiconductor technology and digital technology, industrial apparatuses are making increased use of microcomputers. As a driving source for such apparatuses, a motor capable of digital positioning operations is useful, and hitherto a stepping motor or a servo motor has been used.
However, the stepping motor is not suitable for high-speed rotation since the increase of current is delayed at high-speed, and since the torque it not timely generated because of the influence of iron loss and the time constant of the coil. Particularly when the magnetic pole pitch is made small in order to improve the positional resultion capability, the iron loss influence appears, since the switching frequency per one rotation is increased.
Further, in order to compensate the disadvantages of the stepping motor, there is a method that can be executed where an encoder is provided outside the motor and switching of the conducting phase is carried out at an advanced time corresponding to the motor speed to thereby overcome the delay of the current increasing. However, in this method, there is the disadvantage that the size of the apparatus becomes large because the encoder is provided outside of the motor, and the encoder is expensive.
On the other hand, in the case of the positioning servo system, high-speed running is executed corresponding to digital position instructions, and therefore proper positioning characteristics can be obtained. However, even in such systems there are disadvantages, such as the encoder being expensive and the circuit scale of the control system being large and expensive.
As described above, the stepping motor is incapable of high-speed rotation, and the stepping motor provided with an encoder has the disadvantages of large size and an expensive encoder. Further, the servo motor has the disadvantage of using an expensive control system and an expensive encoder.
In view of the above-mentioned problems, the present invention offers a brushless motor having positioning functions and high-speed rotation characteristics with a size corresponding to the conventional stepping motor size, and considerably simpler circuit construction.
SUMMARY OF THE INVENTION
In order to overcome the above problems, the brushless motor of the present invention comprises
(a) a rotor having a magnetic body or a permanent magnet,
(b) a stator comprising at least a stator core facing the rotor across an air gap, and plural coils,
(c) a bearing for rotatably supporting the rotor,
(d) a position sensor, mounted on the stator, for detecting the variation of the position of the rotor and converting it to electric signals thereby issuing positional signals of almost sine waves of different phase to each other,
(e) velocity detecting means for converting the variation of the positional signals to velocity signals,
(f) electronic switching means for receiving step advance instruction signals from outside and selecting polyphase positional signals in order depending on the number of the step advance instruction signal,
(g) phase advance means for advancing the phase of the positional signal by an advancing amount of the sum of the velocity signal and the selected positional signal,
(h) a driving circuit for exciting plural coils by the advanced positional signal.
By the above construction, the present invention provides a brushless motor that provides, with regard to the position signal being obtained by the position sensor built in the motor, a positional signal for phase switching which is phase-advanced corresponding to the positional signal itself selected by the electric switching means, and wherein the step advance function and positioning function are obtained by exciting the coil by the phase-advanced positional signal. Further, the delay of the current increase is overcome by wholly increasing the phase-advance amount of the positio
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Ashizaki Yoshihiro
Tamae Hiroaki
Matsushita Electric - Industrial Co., Ltd.
Rebsch D. L.
Salce Patrick R.
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