Electricity: motive power systems – Motor load – armature current or force control during... – Initial – 'cracking' or 'starting from rest' torque control
Reexamination Certificate
1999-07-07
2001-03-20
Ro, Bentsu (Department: 2837)
Electricity: motive power systems
Motor load, armature current or force control during...
Initial, 'cracking' or 'starting from rest' torque control
C318S254100
Reexamination Certificate
active
06204618
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates a starting method for a brushless DC motor and a device for implementing the same. More specifically, the present invention relates to a starting method to be adapted in a single-phase DC brushless motor for use in an open circuit and a device for implementing the same, which can induce the rotor of a motor to be triggered away from the dead initiating position for an easier start when actuating the motor.
BACKGROUND OF THE INVENTION
Single-phase brushless DC motors are extensively used in the manufacturing the CPU cooler fan because it has the advantage of a lowered fabrication cost due to the easier assembly process and the higher fabrication reliability. However, the main concern over the motor design turns to how to lower the cogging torque and prevent the motor from being blocked on the dead initiating position when the motor of such kind is adapted for use under the conditions of a required low cogging torque (for example, the spindle motor in a CD-ROM). The lower cogging torque will require a greater precision in the assembly process. On the contrary, the higher cogging torque will induce the larger vibration in rotation to inevitably reduce the maneuverability of the motor. The problem that the rotor of a motor can be retained at the dead initiating position and thus become not easy to be re-started after the stop of the motor is therefore taken into account. The measure as known to the art is to resolve the problem by adopting the concept of detouring the magnetic flux and there are two ways of the most adopted. The first of which is to trim every pole of the stator into the asymmetrical shape while leaving the polar plates from trimming (as disclosed in the U.S. Pat. No. 5,093,599, U.S. Pat. No. 4,987,331, and U.S. Pat. No. 5,492,458). The cogging torque curve
16
as formed by such way is as illustrated in the FIG.
1
. The rotor will stay at the point C as referred to
FIG. 1
when the motor stops. By that, the problem caused by the dead initiating position will be avoided; however, the cogging torque for the motor is also increased. The second way is to keep the shapes of the poles of the stator in symmetric while trimming the edges of the polar plates into the arcs (as disclosed in the U.S. Pat. No. 5,744,889). The stopping position of the rotor will appear in two conditions as illustrated in FIG.
1
. (1) When the stator is overly trimmed or inaccurately assembled, the cogging torque of the motor can probably turn to be inverse (as referred to the inverse curve
17
in FIG.
1
). The stopping position of the rotor can be displaced to the dead initiating position A or E, which will cause to a difficult start for the motor. (2) Even if the polar plates of the motor are properly trimmed to lead the rotor to stop at point B or point D, the actual stop position of the rotor can be possibly close to or even exactly located on the dead initiating position A or E due to the mechanical friction, which has great influences on the manufacturing reliability in the mass-production. The cogging torque curve
18
for the motor assembly with the trimmed stator is as shown in
FIG. 1
, which presents a substantial shift on the stopping position compared to the motor with an untrimmed stator. A severe demand on the exact tolerances for the parts and the high accuracy on the assembly process should be therefore adopted to avoid the occurrence of such problems. From that, it can be concluded that the disclosure as known to the art cannot practically resolve the problems on the difficult start of the motor simply by detouring the magnetic flux to prevent the rotor from staying at the dead initiating position when the motor stops. Moreover, additional problems like the severe demand on the quality of the products and high accuracy on the assembly procedure are still raising to reduce the manufacturing reliability in the mass-production.
In the two disclosures as known to the art for resolving the problems caused by the dead initiating position in the single-phase DC brushless motor, the additional problems like the increasing of the cogging torque or the increasing probability on the rotor's stopping at the dead initiating position will be still rising no matter the shape of the stator is trimmed to an asymmetrical one or the shape of the stator is kept symmetrical while the edges of the polar plates are trimmed into arcs and yet the problems cannot be resolved.
SUMMARY OF THE INVENTION
It is the main objective of the present invention to provide a starting control method to trigger the rotor of a motor to be away from the dead initiating position when the motor is starting and a device for implementing the same. The present invention especially aims at triggering the rotor of a single-phase DC brushless motor out of the dead initiating position to allow the motor to rotate smoothly in case that the rotor stops at the dead initiating position. By realizing the method disclosed in the present invention, the motor's manufacturing reliability can be substantially raised and the single-phase DC brushless motor can be adopted with a more accurate phase control.
The start procedure for a motor comprises two steps according to the present invention. When starting a single-phase DC brushless motor, the motor is driven to do self-oscillation (as called by oscillating step) at first. The motor is then driven to rotate normally in one direction (as called by starting operation step) once the rotor is out of the dead initiating position. By that the rotor of the single-phase DC brushless motor can be triggered out of the dead initiating position even under a low cogging torque.
According to the art as disclosed in the present invention, an oscillator signal is firstly sent to a driver by a signal generator to drive the rotor of the motor to oscillate in both clockwise and counter-clockwise direction. The driver is sent with an operation signal to drive the rotor in one direction once the rotor is out of the dead initiating position. The oscillator signal and the operation signal can be integrated into a sequence of a start command and sent sequentially by the signal generator unit when starting the motor to drive it operating by steps. Alternatively, a triggering signal (comprising a period of high voltage and a period of low voltage) is firstly sent to a multiplexer by an oscillator. Then the multiplexer sends an oscillator signal to the driver, which produces an alternate current in the motor coils to form an oscillation and causes the stator and the rotor to expel each other. When the rotor is expelled away from the dead initiating position, the multiplexer is triggered by the simultaneous change on the voltage level of the trigger signal (for example, high voltage turns to be low voltage or vice versa) to transmit the operating signal to lead the motor to rotate in one direction.
REFERENCES:
patent: 3609487 (1971-09-01), Allison
patent: 3972535 (1976-08-01), Bleiman
patent: 4096420 (1978-06-01), Gosling et al.
patent: 4891537 (1990-01-01), Shiraki et al.
patent: 6072652 (2000-06-01), Lee
Huang Der-Ray
Huang Jieh-Yee
Kuo Li-Te
Wang King Yin
Wang Shyh-Jier
Industrial Technology Research Institute
Liauh W. Wayne
Ro Bentsu
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