Balancing structure for motor

A motor includes a fixed portion, a rotor, and at least one balancing plate fixed on the fixed portion. The fixed portion includes a stator having at least one pole plate that extends to form a plurality of pole faces, with a gap being defined between a pair of the pole faces adjacent to each other. The rotor includes a shaft and an annular magnet facing the pole faces. The balancing plate includes at least two magnetically conductive faces respectively aligned with the gaps. Each magnetically conductive face includes a length not smaller than that of an associated gap. The pole faces face at least one face of the annular magnet. When the rotor turns, the annular magnet of the rotor induces the alternating magnetic fields created by the stator and attracts the magnetically conductive faces to thereby maintain rotational balance of the rotor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a balancing structure for a motor. In particular, the present invention relates to a balancing structure for maintaining stable rotation of a rotor of a motor.

2. Description of Related Art

A wide variety of structures for maintaining rotational balance for a rotor of a motor have been proposed. One of these structures comprises a fixed portion, a rotor, an attracting portion, and a magnetically conductive portion. The fixed portion includes a base, an axial tube fixed on the base, a bearing received in the axial tube, a stator, and a circuit board. The stator includes a coil with axial winding or radial winding and a plurality of pole plates (or pole arms). The rotor includes a shaft rotatably extending through the bearing and an annular magnet surrounding the pole faces of the pole plates. The attracting portion is provided on a bottom of the rotor or a top end of the axial tube. Alternatively, the attracting portion is provided by the annular magnet or the alternating magnetic fields created by the pole plates of the stator. The magnetically conductive portion is made of a magnetically conductive material and may be comprised of a disc with two arcuate edges, a casing fixed in a rotor housing of the rotor, an annular plate, a plurality of arcuate plates, or a rotor housing of a spindle motor. The magnetically conductive portion may be provided on the circuit board, an inner periphery of the rotor, or the bottom of the rotor, and associated with the attracting portion. Such a structure is disclosed in, e.g., Taiwan Utility Model Publication Nos. 383818, 422365, 428838, and M241969, U.S. Pat. Nos. 6,097,120; 6,483,209; 6,700,241; and 6,727,626, and U.S. Patent Publication No. 2005/0006962.

When the motor turns, alternating magnetic fields are created by the pole faces of the magnetic pole plates (or pole arms). The magnetically conductive portion is attracted by the attracting portion during rotation of the rotor, thereby maintaining rotational balance of the rotor, avoiding disengagement of the rotor shaft from the stator, reducing rotational friction of the bearing, and prolonging the life of the motor.

It is common to make the size of the metal plate consisting of the magnetically conductive portion as large as possible so as to provide a large area facing the magnet of the attracting portion (such as the annular magnet). This may result in excessive attracting force between the magnetically conductive portion and the attracting portion for balancing the rotor. In a case that the attracting portion is provided by the annular magnet and the magnetically conductive portion is provided on the fixed portion, the magnetically conductive portion often extends across the alternating magnetic fields created by the pole faces of the stator, adversely affecting the alternating magnetic fields and lowering the rotational efficiency of the rotor. On the other hand, alternating magnetic fields do not exist in the gap between two adjacent pole faces. Thus, it is most desirable to provide the attracting portion in the gap. However, none of the conventional designs provides the attracting portion in the gap. At best, the gap is covered by an attracting portion with an excessively large area, leading to unsatisfactory balancing effect for the rotor.

OBJECTS OF THE INVENTION

An object of the present invention is to provide a balancing structure for assuring rotational efficiency for a rotor of a motor.

Another object of the present invention is to provide a balancing structure for obtaining stable starting of a rotor of a motor.

A further object of the present invention is to provide a balancing structure for maintaining stable rotation of a rotor of a motor.

SUMMARY OF THE INVENTION

A motor in accordance with the present invention includes a fixed portion, a rotor, and at least one balancing plate. The fixed portion includes a stator having at least one winding and at least one pole plate. The at least one pole plate extends to form a plurality of pole faces, with a gap being defined between a pair of the pole faces adjacent to each other. The at least one winding is energizable to make the pole faces create alternating magnetic fields.

The rotor includes a shaft and an annular magnet. The shaft rotatably extends through the fixed portion, and the annular magnet is mounted to an inner periphery of the rotor and face the pole faces of the stator.

The at least one balancing plate is mounted on the fixed portion. The at least one balancing plate includes at least two magnetically conductive faces that are respectively aligned with the gaps of the stator and that are spaced from each other. Each magnetically conductive face includes a length not smaller than that of an associated one of the gaps. The pole faces face at least one face of the annular magnet.

When the rotor turns, the annular magnet of the rotor induces the alternating magnetic fields created by the stator and attracts the at least two magnetically conductive faces to thereby maintain rotational balance of the rotor.

In an embodiment of the invention, the fixed portion includes an axial tube, and the at least one balancing plate is a disc with a central hole and mounted around the axial tube. Preferably, the at least two magnetically conductive faces extend from a circumference of the disc and face the inner periphery of the annular magnet.

Preferably, the fixed portion further includes a circuit board with an underside, and the at least one balancing plate is in intimate contact with the underside or a top side of the circuit board.

Preferably, each magnetically conductive face extends across an associated one of the gaps and two mutually facing ends respectively of an associated pair of the pole faces adjacent to each other, with an associated one of the gaps being delimited between the two mutually facing ends.

Preferably, a length of each magnetically conductive face overlaps with an associated pair of the pole faces delimiting the associated gap by a first overlapped length and a second overlapped length. At least one of the first overlapped length and the second overlapped length is smaller than ½ of an overall length of each pole face.

In another embodiment of the invention, the at least one balancing plate includes a plurality of notches aligned with the pole faces, and the at least one balancing plate includes a plurality of extensions respectively aligned with the gaps of the stator. Preferably, the magnetically conductive faces are respectively located on upper faces of distal ends of the extensions, and the magnetically conductive faces face a bottom face of the annular magnet of the rotor. Preferably, each magnetically conductive face extends across an associated one of the gaps and two mutually facing ends respectively of an associated pair of the pole faces adjacent to each other, with an associated one of the gaps being delimited between the two mutually facing ends.

In a further embodiment of the invention, at least two balancing plates are used. Each of the at least two balancing plates is U-shaped and includes an inner magnetically conductive face, an outer magnetically conductive face, and a lower magnetically conductive face. Preferably, the fixed portion includes a circuit board or a base. The at least two balancing plates are mounted on the circuit board or the base and respectively aligned with the gaps of the stator. The inner magnetically conductive face, the outer magnetically conductive face, and the lower magnetically conductive face of each of the at least two balancing plates respectively face the inner periphery, an outer periphery, and a bottom face of the annular magnet of the rotor.

Preferably, each of the inner magnetically conductive face, the outer magnetically conductive face, and the lower magnetically conductive face of each of the at least two balancing plates extend across an associated one of the gaps and two mutually facing ends respectively of an associated pair of the pole faces adjacent to each other, with an associated one of the gaps being delimited between the mutually facing ends.

Preferably, a length of each of the inner magnetically conductive face, the outer magnetically conductive face, and the lower magnetically conductive face of each of the at least two balancing plates overlaps with an associated pair of the pole faces delimiting the associated gap by a first overlapped length and a second overlapped length, at least one of the first overlapped length and the second overlapped length being smaller than ½ of an overall length of each pole face.

In still another embodiment of the invention, each of the at least two balancing plates are rectangular and has an upper side on which the magnetically conductive faces are formed. Preferably, the fixed portion includes a circuit board or a base. The at least two balancing plates are mounted on the circuit board or the base and respectively aligned with the gaps of the stator, with the magnetically conductive faces facing a bottom face of the annular magnet of the rotor.

Preferably, each of the at least two balancing plates extends across an associated one of the gaps and two mutually facing ends respectively of an associated pair of the pole faces adjacent to each other, with an associated one of the gaps being delimited between the mutually facing ends.

Preferably, a length of each of the at least two balancing plates overlaps with an associated pair of the pole faces delimiting the associated gap by a first overlapped length and a second overlapped length, at least one of the first overlapped length and the second overlapped length being smaller than ½ of an overall length of each pole face.

The stator may include radial winding or axial winding.

Other objects, advantages and novel features of this invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring toFIG. 1, a first embodiment of a motor in accordance with the present invention comprises a fixed portion10, a rotor20, and a balancing plate30. The motor can be used as a motor for a heat-dissipating fan, a spindle motor for an optical disk drive, etc.

Referring toFIGS. 1 through 3, the fixed portion10includes a base11, an axial tube12, a bearing13, a stator14, and a circuit board15. The base11may be coupled to a casing of the motor. The axial tube12is fixed on or integrally formed with the base11. At least one bearing13is mounted in the axial tube12whereas as the stator14and the circuit board15are mounted around the axial tube12. The bearing13may be an oily bearing, ball bearing, fluid dynamic bearing, or magnetic bearing.

The stator14may be a stator with radial winding. The stator14includes at least one pole plate141with a winding142. In the illustrated embodiment, the stator14includes four pole plates141each having a winding142wound therearound along a radial direction. Each pole plate141includes a pole face140, with a gap143being defined between two mutually facing ends E1and E2respectively of a pair of pole plates141adjacent to each other. At least one sensor151is mounted on the circuit board15for detecting rotational status of the rotor20. When a control circuit of the circuit board15is on, the direction of the electric current of the windings142on the pole plates141are alternately controlled by the control circuit of the circuit board15such that alternating magnetic fields are created by the pole plates141.

Still referring toFIGS. 1 through 3, the rotor20includes a shaft21, a housing22, and an annular magnet23. An end of the shaft21is fixed to a center of an end wall of the housing22, with the other end of the shaft21rotatably extending through the bearing13. The annular magnet23is mounted to an inner periphery of the housing22. The annular magnet23includes a plurality of alternately disposed north pole sections (not shown) and south pole sections (not shown) on an inner periphery thereof, with the pole faces140facing the north and south pole sections. Thus, alternate energizing of the pole faces140drives the rotor20to turn.

Still referring toFIGS. 1 through 3, the balancing plate30is substantially a disc made of a magnetically conductive material. The balancing plate30includes a central hole31and at least two magnetically conductive faces32(four in this embodiment) extending upward (or downward) from a circumference of the balancing plate30. The balancing plate30is mounted around the axial tube12through provision of the central hole31. The balancing plate30is in intimate contact with an underside or a top side of the circuit board15.

In assembly, the magnetically conductive plates32are preferably aligned with the gaps143of the stator14and face the inner periphery of the annular magnet23. Each magnetically conductive face32has a length not smaller than that of the gap143. In a case that a span of each magnetically conductive face32is greater than the length of the gap143, the length of the magnetically conductive face32is overlapped with a pair of the pole faces140of the pole plates141delimiting the associated gap143by a first overlapped length L1and a second overlapped length L2respectively. Preferably, at least one of the first overlapped length L1and the second overlapped length L2of each magnetically conductive face32is smaller than ½ (more preferably ⅓) of the overall length of each pole face140. Thus, an appropriate gap is provided between a pair of magnetically conductive faces32adjacent to each other. By such an arrangement, adverse affect to the alternate energizing of the pole faces140of the stator14by excessive affection from the magnetically conductive faces32is avoided.

Still referring toFIGS. 2 and 3, after assembly, the magnetically conductive faces32of the balancing plate30are fixed on the fixed portion and respectively aligned with the gaps143of the stator14while facing the inner periphery of the annular magnet23of the rotor20. Further, each magnetically conductive face32extends across the ends E1and E2respectively of a pair of pole faces140adjacent to each other and the gap143between the ends E1and E2.

When the motor turns, the inner periphery of the annular magnet23continuously induces the alternating magnetic fields created by the pole faces140of the stator14. The magnetic fields of the annular magnet23also are continuously attracted to all of the magnetically conductive faces32of the balancing plate30, each of which is arranged to radially face the inner periphery of the annular magnet23. In particular, the magnetically conductive faces32and the annular magnet23provide an appropriate magnetically attracting effect for balancing the rotor20without adversely affecting the alternate energizing of the stator14. Shaking, vibration, or wobbling of rotor20is avoided while the pole sections of the rotor20are passing through the gaps143. The rotational balance and the rotational stability of the rotor20are maintained. Further, when the motor is at rest or at the moment of starting, the inner periphery of the annular magnet23still attracts the magnetically conductive faces32of the balancing plate30, avoiding temporary imbalance of the motor at the moment of starting. The starting balance and the starting stability of the rotor20are thus improved.

FIGS. 4 through 6illustrate a second embodiment of the invention. In this embodiment, each magnetically conductive face32is longer. In particular, one of the overlapped length (e.g., the first overlapped length L1) is preferably smaller than ½ (more preferably ⅓) of the overall length of the pole faces140. Further, the other overlapped length (e.g., the second overlapped length) L2is greater than ½ of the overall length of the pole faces140. This embodiment provides advantages similar to those provided by the first embodiment. Further, at least one of the magnetically conductive face32includes a notch321. In assembly, the sensor151of the circuit board150is preferably aligned with the notch321. When the rotor20turns, the sensor151detects the change of magnetism by the angular position of the notch321and a signal is output to the control circuit of the circuit board15.

FIGS. 7 through 9illustrates a third embodiment of the invention, wherein the balancing plate30includes a plurality of notches33respectively aligned with the pole faces140. Further, the balancing plate30includes a plurality of extensions34respectively aligned with the gaps143of the stator14. Each extension34has a magnetically conductive face32′ on an upper face of a distal end thereof. In assembly, the balancing plate30is in intimate contact with an underside of a top side of the circuit board15.

In assembly, each magnetically conductive face32′ is aligned with an associated gap143of the stator14and faces a bottom face of the annular magnet23. Further, each magnetically conductive face32′ has a length not smaller than that of the gap143. In a case that a span of each magnetically conductive face32′ is greater than the length of the gap143, the length of the magnetically conductive face32′ is overlapped with a pair of the pole faces140of the pole plates141delimiting the associated gap143by a first overlapped length L1and a second overlapped length L2respectively. Preferably, at least one of the first overlapped length L1and the second overlapped length L2of each magnetically conductive face32′ is smaller than ½ (more preferably ⅓) of the overall length of each pole face140. Thus, an appropriate gap is provided between a pair of magnetically conductive faces32′ adjacent to each other. This embodiment provides advantages similar to those provided by the first embodiment.

FIGS. 10 through 12illustrate a fourth embodiment of the invention, wherein the balancing plate30is replaced with at least two (four in this embodiment) smaller balancing plates40. Each balancing plate40is a substantially U-shaped metal plate having an inner conductive face41, an outer conductive face42, and a bottom conductive face43. As illustrated inFIG. 12, a lower portion of the annular magnet23extends beyond a lower edge of the housing22of the rotor20. The balancing plates40are fixed on the base11or the circuit board15of the fixed portion10. Further, the inner conductive face41, the outer conductive face42, and the bottom conductive face43of each balancing plate40respectively face an outer periphery, an inner periphery, and a bottom face of the lower portion of the annular magnet23. Further, each balancing plate40has a length not smaller than that of the gap143. In a case that a span of each balancing plate40is greater than the length of the gap143, the length of the balancing plate40is overlapped with a pair of the pole faces140of the pole plates141delimiting the associated gap143by a first overlapped length L1and a second overlapped length L2respectively. Preferably, at least one of the first overlapped length L1and the second overlapped length L2of each balancing plate40is smaller than ½ (more preferably ⅓) of the overall length of each pole face140. Thus, an appropriate gap is provided between a pair of balancing plates40adjacent to each other. This embodiment provides advantages similar to those provided by the first embodiment.

FIGS. 13 through 15illustrate a fifth embodiment of the invention, wherein the balancing plate30is replaced with at least two (four in this embodiment) smaller balancing plates50. Each balancing plate50is a substantially rectangular metal plate having a magnetically conductive face51on an upper face thereof. The fixed portion10includes a stator14′ with an axial winding. In particular, the stator14′ includes a plurality of pole plates141′ and a winding142′ axially wound between the pole plates141′, with each pole plate141′ extending radially to form a plurality of pole faces140′ and with a gap143′ defined between the pole plates140′.

In assembly, the balancing plates50are fixed on the base11or the circuit board15of the fixed portion10. Further, each balancing plate50is aligned with an associated gap143′ of the stator14′, with the magnetically conductive face51facing a bottom face of the annular magnet23.

Each balancing plate50has a length not smaller than that of the gap143. In a case that a span of each balancing plate50is greater than the length of the gap143, the length of the balancing plate50is overlapped with a pair of the pole faces140of the pole plates141delimiting the associated gap143by a first overlapped length L1and a second overlapped length L2respectively. Preferably, at least one of the first overlapped length L1and the second overlapped length L2of each balancing plate50is smaller than ½ (more preferably ⅓) of the overall length of each pole face140. Thus, an appropriate gap is provided between a pair of balancing plates50adjacent to each other. This embodiment provides advantages similar to those provided by the first embodiment. Further, at least one of the balancing plates50includes a notch52. In assembly, the sensor151of the circuit board150is preferably aligned with the notch52. When the rotor20turns, the sensor151detects the change of magnetism by the angular position of the notch52and a signal is output to the control circuit of the circuit board15.

While the principles of this invention have been disclosed in connection with specific embodiments, it should be understood by those skilled in the art that these descriptions are not intended to limit the scope of the invention, and that any modification and variation without departing the spirit of the invention is intended to be covered by the scope of this invention defined only by the appended claims.