Electricity: motive power systems – Braking
Reexamination Certificate
2000-08-17
2001-08-14
Fletcher, Marlon T. (Department: 2837)
Electricity: motive power systems
Braking
C318S254100, C318S434000, C318S721000, C318S369000
Reexamination Certificate
active
06274992
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a braking method for a single-phase motor and, in particular, to a braking method using a three-phase motor driving IC to drive a single-phase DC brushless motor.
2. Related Art
DC servomotors have superior stability and the relation between the input and output is almost linear, which renders a good controllability; they are therefore widely used in places that require high precision controls. However, the conventional DC motor has a brush and redirector that are subject to erosion. This defect makes the reliability and maintenance of the conventional DC motor worse than other motors. The brushless motor is to replace the rectifier (brush and redirector) of the conventional DC motor with an electronic means so that it is free from the erosion of the brush and redirector and maintenance. Because there is no brush in the structure, it will not generate mechanical and electronic noises in principle. Therefore, such motors have superior properties.
According to the wiring method on the stator, the DC brushless motor can be classified into single-phase type, double-phase ones, three-phase types, five-phase ones, etc. In particular, the three-phase DC brushless motors are more common. Compared with the three-phase DC brushless motor, the single-phase DC brushless motor has the advantages of easy assembly and high yield. Therefore, taking into account the production cost, the single-phase DC brushless motors are more competitive than the three-phase DC brushless motors. Since three-phase motor driving means is still the main stream on the current market and the single-phase motor driving IC is still under development, thus the three-phase motor driving IC has the advantages of mass production and low prices in the motor driving IC industry. If the three-phase motor driving IC can be used to drive the single-phase DC brushless motor, advantages of both of them can be combined to have more competitive power. The time schedule delay in production development due to fewer single-phase motor driving IC manufacturers can be avoided.
Currently, the Opto-Electronics & Systems Laboratories in Industrial Technology Research Institute has successfully applied three-phase motor driving ICs to drive single-phase DC brushless motor. However, the method disturbs the determination of the rotation direction of the main axis motor in the three-phase motor driving IC and results in reverse rotation when the motor braking action stops.
SUMMARY OF THE INVENTION
In view of the foregoing problem of reverse rotation when using a three-phase motor driving IC to drive a single-phase DC brushless motor, it is then a primary object of the invention to provide a braking method for a single-phase motor, which is applied to detect the rotational speed of a single-phase DC brushless motor driven by a three-phase motor driving IC and stop the motor rotation before the motor reverses its rotation.
To achieve the above object, the disclosed braking method for a single-phase motor comprises the steps of: obtaining the magnetic pole position of the single-phase motor rotor; driving the single-phase motor to rotate at the speed set by a user using a motor driving unit according to the rotor magnetic pole position; obtaining a rotation number signal; computing the rotational speed of the single-phase motor according to the rotation number signal using a control unit; stopping the operation of the single-phase motor using the control unit when the rotational speed of the single-phase motor is lower than a threshold.
The braking method for a single-phase motor disclosed herein does not need extra system elements. BY simply modifying the program in the control unit, the problem of unable to determine the rotational direction of a single-phase motor within a three-phase motor driving IC existing in the prior art can be solved. Since currently the single-phase DC brushless motor and the three-phase motor driving IC have competitive superiority in prices, if the three-phase motor driving IC can directly drive the single-phase DC brushless motor without requiring additional system elements the whole system cost can be lower. On the other hand, this method can avoid the delay problem due to fewer single-phase motor driving IC manufacturers on the market.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
REFERENCES:
patent: 3708734 (1973-01-01), Rowe
patent: 4678972 (1987-07-01), Lehnhoff et al.
patent: 5229693 (1993-07-01), Futami et al.
patent: 6020700 (2000-02-01), Tien
Huaug Der-Ray
Kuo Li-Te
Lee Yao-Yu
Wang King Yin
Yu Ming-Jiou
Fletcher Marlon T.
Industrial Technology Research Institute
Liauh W. Wayne
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