Motor control device

This Non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No(s). 096120524, filed in Taiwan, Republic of China on Jun. 7, 2007, the entire contents of which are hereby incorporated by reference.

1. Field of Invention

The present invention relates to a control device and in particular to a motor control device.

2. Related Art

In the field of motor controlling, a Hall sensor can be used in sensing the positions of rotating magnetic poles (magnets in the rotor) in a motor. Therefore, the rotation of the motor can be monitored by appropriately positioning the Hall sensors in the motor.

As shown in FIG. 1 and FIG. 2 . A Hall sensor 11 is disposed at a position P 1 to sense variations in the magnetic poles (magnets in the rotor) during the rotation of the motor 12 . A controller 13 is connected to the hall sensor 11 for adjusting the driving current 121 of the motor 12 according to the sensing result of the Hall sensor 11 .

However, if the Hall device 11 is still disposed at the position P 1 , it is easy to generate a surge during the driving current 121 being close to its reverse point when the rotation speed of the motor 12 increases ( FIG. 2 ). Moreover, the phase of the driving current 121 will fall behind the phase of the driving voltage of the motor 12 . Therefore, the motor 12 is likely to produce noises and operates with a worse efficiency.

To improve the above-mentioned situation, the Hall sensor 11 is disposed at a position P 2 . As a result, the phase difference between the driving current 121 and the driving voltage can be reduced, and the surge occurring when the driving current 121 is close to its reverse point during high-speed operations of the motor 12 can be improved. Therefore, the motor 12 produces fewer noises and operates more efficiently. Nevertheless, the motor 12 has lower efficiency and larger noises during low-speed operations. Consequently, the best position of the Hall sensor 11 varies with the rotation speed of motor 12 . Whether it is disposed at the appropriate position affects the control efficiency of the controller 13 over the motor 12 .

In view of the foregoing, the present invention is to provide a motor control device that can eliminate the effect caused by the position of the sensor at various rotation speeds of the motor, and properly adjust the rotation speed of the motor, thereby improving the efficiency and lifetime of the motor and significantly reducing the noises.

To achieve the above, the present invention discloses a motor control device including a sensing circuit, a phase-shifting circuit, a comparing circuit and a control circuit. The sensing circuit senses the motor to generate a sensing signal. The phase-shifting circuit is electrically connected to the sensing circuit for receiving the sensing signal and generating a phase-shifting signal according to the sensing signal. The comparing circuit is electrically connected to the phase-shifting circuit for receiving the phase-shifting signal and generating a comparing signal according to the phase-shifting signal. The control circuit is electrically connected to the comparing circuit and the motor for receiving the comparing signal and generating a control signal to control the rotation speed of the motor according to the comparing signal.

As mentioned above, the motor control device of the present invention includes the phase-shifting circuit and the comparing circuit. The phase-shifting circuit makes the sensing signal phase shifted, producing the phase-shifting signal. The comparing circuit compares the phase-shifting signal to produce the comparing signal. The sensing circuit can be disposed at a fixed position adjacent to the motor and is accordingly capable of sensing the rotation speed of motor. This method not only can immediately adjust the rotations speed of the motor in an appropriate way by using the phase-shifting circuit according to the sensing signal, but also does not need to change the sensing position of the sensing circuit. Therefore, the working efficiency and lifetime of the motor can be increased, while the noises thereof are reduced.

The present invention will become more fully understood from the detailed description and accompanying drawings, which are given for illustration only, and thus are not limitative of the present invention, and wherein:

FIG. 1 is a schematic illustration of a conventional motor and a controller;

FIG. 2 shows the wave form of a motor driving current;

FIG. 3 is a schematic illustration of a motor control device according to a preferred embodiment of the present invention;

FIG. 4 shows the equivalent circuit of FIG. 3 ; and

FIG. 5 shows the wave forms of the sensing signal, phase-shifting signal and comparing signal of the motor control device according to the embodiment of the present invention.

The present invention will be apparent from the following detailed description, which proceeds with reference to the accompanying drawings, wherein the same references relate to the same elements.

With reference to FIGS. 3 and 4 , a motor control device 2 of a motor M according to a preferred embodiment of the present invention includes a sensing circuit 21 , a phase-shifting circuit 22 , a comparing circuit 23 and a control circuit 24 . In the embodiment, the motor M in practice can be used or applied to various electronic devices, such as a fan.

The sensing circuit 21 includes a Hall sensor 211 and a resistor R. The Hall sensor 211 is disposed at a fixed position adjacent to the motor M for sensing variations in the magnetic poles (magnets in the rotor) as the motor M rotates and then generating a sensing signal S 1 . Besides, the sensing signal S 1 has a first sensing sub-signal S 1 A and a second sensing sub-signal S 1 B that are output respectively by two terminals of the Hall sensor 211 of the sensing circuit 21 (as shown in FIG. 4 ). In practice, the phase difference between the first sensing sub-signal S 1 A and the second sensing sub-signal S 1 B is 180 degrees (as shown in FIG. 5 ).

With reference to FIGS. 3 and 4 , the phase-shifting circuit 22 is electrically connected to the sensing circuit 21 . In the embodiment, the phase-shifting circuit 22 receives the sensing signal S 1 and generates a phase-shifting signal S 2 according to the sensing signal S 2 . The phase-shifting signal S 2 has a first phase-shifting sub-signal S 2 A and a second phase-shifting sub-signal S 2 B. In practice, the phase difference between the first phase-shifting sub-signal S 2 A and the second phase-shifting sub-signal S 2 B is 180 degrees.

In addition, the phase-shifting circuit 22 includes a first phase-adjusting unit 221 and a second phase-adjusting unit 222 (as shown in FIG. 4 ). The first phase-adjusting unit 221 has a first resistor R 1 , a first capacitor C 1 , a second resistor R 2 , a second capacitor C 2 and a third resistor R 3 . A first end of the first resistor R 1 is electrically connected to a first end of the Hall sensor 211 of the sensing circuit 21 for receiving the first sensing sub-signal S 1 A of the sensing signal S 1 . A first end of the first capacitor C 1 is electrically connected to the first end of the first resistor R 1 , and a second end of the first capacitor C 1 is electrically connected to a second end of the first resistor R 1 . A first end of the second resistor R 2 is electrically connected to the second end of the first resistor R 1 for transmitting the first phase-shifting sub-signal S 2 A of the phase-shifting signal S 2 . The first end of the second capacitor C 2 is electrically connected to a second end of the second resistor R 2 , and the second end of the second capacitor C 2 is electrically connected to the second end of the second resistor R 2 . A first end of the third resistor R 3 is electrically connected to the second end of the second resistor R 2 , and a second end of the third resistor R 3 is grounded.

The second phase-adjusting unit 222 has a fourth resistor R 4 , a third capacitor C 3 , a fifth resistor R 5 , a fourth capacitor C 4 and a sixth resistor R 6 . A first end of the fourth resistor R 4 is electrically connected to a second end of the Hall sensor 211 of the sensing circuit 21 for receiving the second sensing sub-signal S 1 B of the sensing signal S 1 . A first end of the third capacitor C 3 is electrically connected to the first end of the fourth resistor R 4 , and a second end of the third capacitor C 3 is electrically connected to a second end of the fourth resistor R 4 . A first end of the fifth resistor R 5 is electrically connected to the second end of the fourth resistor R 4 for transmitting the second phase-shifting sub-signal S 2 B of the phase-shifting signal S 2 . The first end of the fourth capacitor C 4 is electrically connected to the first end of the fifth resistor R 5 , and the second end of the fourth capacitor C 4 is electrically connected to a second end of the fifth resistor R 5 . A first end of the sixth resistor R 6 is electrically connected to the second end of the fifth resistor R 5 , and a second end of the sixth resistor R 6 is grounded.

With reference to FIGS. 3 and 4 , the comparing circuit 23 in this embodiment includes an operating amplifier 231 having a first input terminal I 1 , a second input terminal I 2 and an output terminal O. The first input terminal I 1 is electrically connected to the first phase-adjusting unit 221 of the phase-shifting circuit 22 for receiving the first phase-shifting sub-signal S 2 A. The second input terminal 12 is electrically connected to the second phase-adjusting unit 222 of the phase-shifting circuit 22 for receiving the second phase-shifting sub-signal S 2 B. The operating amplifier 231 of the comparing circuit 23 compares the first phase-shifting sub-signal S 2 A with the second phase-shifting sub-signal S 2 B, and outputs a comparing signal S 3 via the output terminal O of the operating amplifier 231 .

The comparing signal S 3 in practice is a square wave (as shown in FIG. 5 ) having a high level and a low level. When the first phase-shifting sub-signal S 2 A is greater than the second phase-shifting sub-signal S 2 B, the comparing signal S 3 is at the high level. Otherwise, when the first phase-shifting sub-signal S 2 A is smaller than the second phase-shifting sub-signal S 2 B, the comparing signal S 3 is at the low level.

Please refer to FIG. 5 . The sensing signal S 1 and the phase-shifting signal S 2 differ by a phase θ. The comparing signal S 3 is generated according to the comparison result of the first phase-shifting sub-signal S 2 A and the second phase-shifting signal S 2 B of the phase-shifting signal S 2 . Therefore, when the sensing signal S 1 and the phase-shifting signal S 2 differ by a phase θ, the sensing signal S 1 and the comparing signal S 3 also differ by the phase θ.

In this embodiment, the control circuit 24 can be a programmable chip, an integrated circuit, a processor, a digital signal processor, a microprocessor or a microprocessing chip. It receives the comparing signal S 3 and generates a control signal S 4 according to the comparing signal S 3 so as to adjust the rotation speed of the motor M.

The motor control device 2 of the embodiment is featured in that the phase-shifting circuit 22 and the comparing circuit 23 are disposed between the sensing circuit 21 and the control circuit 24 . The phase-shifting circuit 22 generates the phase-shifting signal S 2 according to the sensing signal S 1 . The comparing circuit 23 generates the comparing signal S 3 according to the phase-shifting signal S 2 . The control circuit 24 generates the control signal S 4 according to the comparing signal S 3 to control the rotation speed of the motor M. In the present invention, the position of the Hall sensor 211 in the sensing circuit 21 does not need to be changed, and the rotation speed of motor M can be immediately changed by adjusting the phase of the sensing signal S 1 by using the phase-adjusting circuit. Therefore, the working efficiency and lifetime of the motor M are increased, and the noises during the operation of motor are reduced.

In summary, the motor control device of the present invention adds the phase-shifting circuit and the comparing circuit. The phase-shifting circuit makes the sensing signal phase shifted, producing the phase-shifting signal. The comparing circuit compares the phase-shifting signal to produce the comparing signal. The sensing circuit can be disposed at a fixed position adjacent to the motor and is accordingly capable of sensing the rotation speed of motor. This method not only can immediately adjust the rotations speed of motor in an appropriate way by using the phase-shifting circuit according to the sensing signal, but also does not need to change the sensing position of the sensing circuit. Therefore, the working efficiency and lifetime of the motor can be increased, while the noises thereof are reduced.

Although the present invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments, will be apparent to persons skilled in the art. It is, therefore, contemplated that the appended claims will cover all modifications that fall within the true scope of the present invention.