DC brushless motor having eccentric rotor

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DC BRUSHLESS MOTOR HAVING ing north and South poles, angled partially, about the rota ECCENTRIC ROTOR tional axis. The rotor additionally includes a tubular yoke to provide magnetic flux paths.

BACKGROUND OF THE INVENTION

1. Field of the Invention SUMMARY OF THE INVENTION This invention relates to a Self-vibrating dc-operated It is a primary object of the present invention to provide brushless vibrator motor used for a pocketable wireless a light, compact dc brushleSS Vibrator motor having an alerting or communication device Such as a pager or a eccentrically-weighted rotor.

portable phone. The motor has a rotor having eccentric mass It is an additional object of the present invention to distribution that causes vibration. provide a vibrator motor having a cored Stator, but Simple in 2. Description of the Prior Art construction and low in production cost. A typical prior known dc vibrator motor has an eccentric In order to achieve the above objects, a dc brushless weight made of a tungsten alloy fixedly mounted on an Vibrator motor according to the present invention has a base output shaft of the motor. The motor vibrates as the shaft 15 member, a shaft connected to the base member, the Shaft rotates because of the unbalanced distribution of the mass of having a longitudinal center axis, a Stator fixedly connected the rotor about the rotational axis. to the base member, the Stator having plurality of magneti However, a danger of mechanical interference pertains to cally conductive cores angularly evenly disposed about the this type of vibrator motor because of the existence of the center axis and respective armature coils mounted thereon, externally rotating eccentric weight. In addition, the alerting a rotor mounted on the Shaft having an eccentric mass device requires an extra Space in which the eccentric weight distribution with respect to the center axis. The rotor has a rotates, and the high density material for the weight, Such as magnet holder, an annular permanent magnet fixedly con tungsten alloy, is costly. nected to the magnet holder and disposed concentrically As disclosed in U.S. Pat. No. 5,036,239 (issued Jul. 30, with the center axis and radially outside the stator. The 1991, one of the present applicants invented a flat coreleSS 25 annular magnet has alternate north and South magnetic poles dc vibrator motor having neither output shaft nor external magnetarranged at an even angular pitch about the center axis. The weight. This vibrator motor has a rotor which incorporates nal holder has a top generally flat part disposed orthogo generally Sector Shaped non-overlapping flat armature coils to the center axis.

arranged angularly partially about the shaft of the rotor, So In one embodiment, that magnet holder has a cylindrical that the center of mass of the rotor is off the rotational axis Side wall disposed concentrically with the center axis and of the rotor. the rotor has an arcuate weight fixed to the cylindrical side As disclosed in U.S. Pat. No. 5,107,155 (issued Apr. 21, wall on the inside thereof but radially outside the annular magnet. The flat top part of the magnet holder has a plurality 1992), the same applicant of the present invention invented a dc vibrator motor without an output shaft. This vibrator 35 of through-holes So as to reduce the weight of the magnet motor has a fixed shaft on which a cylindrical magnet is holder. The magnet holder further has an arcuate groove fixedly mounted, and an eccentrically-weighted rotor having between its cylindrical Side wall and the annular magnet in a cylindrical coreleSS winding, enclosing the fixed magnet, a manner that the arcuate weight and the arcuate groove are is mounted on the fixed shaft. The rotor has either eccentric disposed angularly 180° about the center axis in angularly bearings or a combination of eccentric bearings and eccen 40 non-overlapping relation with each other. The magnet holder tric weights, So that the center of mass of the rotor is off its may be made of a low-friction type Synthetic resin and be rotational axis. Although the motor has been favorably rotatably mounted on the Shaft in a manner that the resin accepted in the market, the rotor of this motor requires a shaft.made magnet holder is in a direct Sliding contact with the Substantial number of production proceSS Steps.

As disclosed in U.S. Pat. No. 5,341,057 (issued Aug. 23, 45 In other embodiments, the magnet holder has a cutout, 1994), the present applicants and another inventor jointly which may be a through-hole in a top flat part thereof, in a invented an additional dc vibrator motor without an output manner that the magnet holder per Se has an eccentric mass shaft. This vibrator motor has an eccentric armature rotor distribution with respect to the center axis. The annular having three-pole armature iron cores and coils that are all magnet is totally or partially adjoined by a part of the magnet Situated within an angular range of 180 about its rotational 50 holder on radially outside thereof. The rotor may have an XS. arcuate weight fixedly attached to the magnet holder in a A Sector-shaped eccentric armature rotor having all of the manner that the arcuate weight and the cutout in the mag armature poles within an angular range of 180 provides a netic holder are disposed diametrically opposite to each good mass imbalance. However, the iron armature cores of other with respect to the center axis So that the eccentric the motor disclosed in U.S. Pat. No. 5,341,057 cause a 55 mass distribution about the center axis is enhanced. The cogging torque, a magnetic Sticking effect, and, therefore, magnet holder in these embodiments is made of a magneti requires comparatively high Voltage for Starting. cally conductive material, but it may alternatively be made Furthermore, all of the above vibrator motors disclosed in of a synthetic resin. The vibrator motor of these embodi the U.S. patents have commutator brushes, thereby giving ments further has a cup-like Stationary rotor cover fixed to the base member in a manner that rotor is protectively rise to a life span problem. 60 capped with the rotor cover.

As disclosed in U.S. Pat. No. 5,373.207 (issued Dec. 13, 1994), the present applicants invented a dc brushless vibra BRIEF DESCRIPTION OF THE DRAWINGS tor motor having neither an output shaft nor brushes. This

Vibrator motor employs a cylindrically-shaped coreleSS Sta FIG. 1 is a vertical sectional view of a vibrator motor of tor winding unit having at least three Stator coils arranged at 65 the fir embodiment according to the present invention; an even pitch angle and a rotor including an axially extended FIG. 2 is a horizontal section taken along lines II-II eccentrically-weighted permanent magnet having alternat shown in FIG. 1;

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FIG. 3 is a plan view of a magnet holder employed in the posed at an equal distance from the center axis X and at an vibrator motor shown in FIG. 1; even pitch angle of 60 thereabout. The cutouts 6c cause the FIG. 4 is a vertical sectional view of a vibrator motor of weight of the magnet holder 6 to be minimized. The number the Second embodiment according to the present invention; of the cutouts 6c may alternatively be any of one or more. FIG. 5 is a plan view of the rotor and a part of the stator One or more of the cutouts 6c may be arranged only on the employed in the vibrator motor shown in FIG. 4; Side diametrically opposite to the arcuate weight 8 with FIG. 6 is a vertical sectional view of a vibrator motor of respect to the center axis X in order to cause the center of mass of the rotor R1 to deviate further from the center axis the third embodiment, which is alternative to the second X.

embodiment, according to the present invention; and The magnet holder 6 in this embodiment is made of a FIG. 7 is a plan view of the rotor and a part of the stator low-friction Synthetic resin and is rotatably mounted on the employed in the vibrator motor shown in FIG. 6. shaft 2 in a manner that the resin magnet holder 6 is in a DETAILED DESCRIPTION OF THE direct sliding contact with the shaft 2. W1 and W2 in FIG. PREFERRED EMBODIMENTS 1 denote a slide washer and a rotor holding washer, respec

tively.

The invention will now be described in detail with refer The Six armature coils 5 are energized in Sequence with dc ence to the drawings. power Supplied through the wiring plate Win a prior-known FIG. 1 shows a vertical section of a vibrator motor Ml of method in which different phases of dc pulses are produced the first embodiment according to the present invention in a driver circuit (not shown) and individually Supplied to along the rotational axis X of the rotor thereof. FIG. 2 is a the Six coils 5 in proper Sequence and timing. The Sequence horizontal section taken along lines II-II shown in FIG. 1. and timing of the pulses outputted from the driver circuit are FIG. 3 is a plan view of a magnet holder employed in the controlled by a controller (not shown) So as to cause the coils vibrator motor M1. 5 to produce a rotating magnetic flux in the airgap G between Referring to FIGS. 1 to 3, the vibrator motor M1 has a the stator S and the rotor R1. The rotating magnetic flux base member 1, a shaft 2, having a longitudinal center axis 25 interacts with the magnetic flux produced by the permanent X, fixedly connected to the base member 1, a stator S fixedly magnet 7 so that the rotor R1 rotates in synchronism with the connected to the base member 1, a rotor R1 rotatably rotating magnetic flux. Since this method is in the prior art mounted on the shaft2, and a flexible wiring plate W fixedly and is not involved in the object of the present invention, no attached onto the base member 1. further details thereof will be disclosed. The base member 1 has a bracket 1b that is a center part Since the rotor R1 has an eccentric mass distribution with of the base member 1, raised in of a pressing process. The respect to the center axis X, the motor M1 vibrates as the Stator Sincludes six magnetically conductive armature cores rotor R1 makes rotation.

3 that are fixedly attached to the bracket 1b at their radially FIG. 4 shows a vertical section of a vibrator motor M2 of inner-most ends. The armature cores 3 extend radially the Second embodiment according to the present invention outwardly from the bracket 1b and are disposed at an even 35 along the rotational axis X of the rotor thereof. FIG. 5 is a angular pitch of 60 about the center axis X. Each set of the plan view of the rotor and a part of the Stator employed in cores 3 includes a pair of identically-formed members the vibrator motor M2.

attached to each other back-to-back. The cores 3 have The basic construction and the functional principle of the arcuate blades 4 at their radially outer-most ends. Six vibrator motor M2 are similar to those of the vibrator motor armature coils 5 are individually mounted on the six sets of 40 Ml of the first embodiment.

cores 3. Unless otherwise specifically mentioned, it should be The rotor R1 has a round magnet holder 6, a one-piece understood, throughout this specification, that like reference annular permanent magnet 7 fixedly connected to the mag numerals or characters denote like components or parts, net holder 6, disposed concentrically with the center axis X Structurally and functionally. No duplicate explanation may, and radially outside the Stator SSo that the magnet 7 opposes 45 therefore, be made of the components or parts having the blades 4 of the Stator cores 3 leaving an airgap G reference numerals or characters that have already been therebetween. described above.

The magnet holder 6 has a generally flat top part 6t that Referring to FIGS. 4 and 5, the vibrator motor M2 has a is disposed orthogonal to the center axis X and a cylindrical base member 21, a shaft 22, having a longitudinal center axis side wall 6s that is disposed concentrically with the center 50 X, rotatably connected to the base member 21 with an axis X. The rotor R1 further has an arcuate metal weight 8 oil-impregnated bearing B, a Stator S fixedly connected to that is fixed to the cylindrical side wall 6s of the magnet the base member 21, a rotor R2 fixedly mounted on the shaft holder 6 radially inside thereof and radially outside the 22, a flexible wiring plate W fixedly attached onto the base annular magnet 7. The annular magnet 7 has a total of Six member 21, and a cup-like Stationary rotor cover Rc fixedly north and South magnetic poles alternately arranged at a 55 attached to the base member 21.

uniform angular pitch of 60 about the center axis X. The base member 21 has a bracket 21b that is a centerpart The magnet holder 6 has an arcuate groove 6g disposed of the base member 21, raised by a pressing process. The radially inside the cylindrical side wall 6s and radially Stator S includes Six magnetically conductive cores 3 that outside the annular magnet 7 in a manner that the arcuate extend radially outwardly from the bracket 21b and are weight 8 and the arcuate groove 6g are disposed in angularly 60 disposed at a uniform angular pitch of 60 about the center non-overlapping relation about the center axis X and dia axis X. Each Set of the cores 3 includes a pair of members metrically opposite to each other with respect to the center attached to each other back-to-back. The cores 3 have axis X. The rotor R1 has an eccentric mass distribution with arcuate blades 4 at their radially outer-most ends. Six respect to the center axis X because of the arcuate weight 8 armature coils 5 are individually mounted on the six sets of and the arcuate groove 6g. 65 cores 3. Namely, the construction and function of the Stator As shown in FIGS. 1 and 3, the top part 6t of the magnet S of the vibrator motor M2 are exactly the same as those of holder 6 has six round cutouts 6c, i.e. through-holes, dis the vibrator motor M1 of the first embodiment.

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S 6

The rotor R2 has a round magnet holder 26, a one-piece center axis X, whereby the rotor R3 has an eccentric mass annular permanent magnet 7, which is the Same magnet as distribution as well. Only a part (angularly 180° about the of the vibrator motor M1, fixedly connected to the magnet center axis X) of the annular magnet 7 is covered by the top holder 26 and disposed concentrically with the center axis X part 36t of the magnet holder 36 on its top and by the side radially outside the Stator S, and an arcuate metal weight 28 wall 26S thereof on its radially outside, and angularly the fixed to the magnet holder 26 and disposed radially outside other half part of the magnet 7 is exposed without being the annular magnet 7 and the magnet holder 26. AS shown covered or adjoined by the magnet holder 36. Nevertheless, in FIGS. 4 and 5, the arcuate metal weight 28 is fixed to the the one-piece annular magnet 7 has enough physical Strength magnet holder 26, axially extending within the rotor R2, so as to withstand the centrifugal force when the rotor R3 farther from the center axis X than the annular permanent rotates. AS in the case of vibrator motor M1 or M2, the magnet 7, and has a height along the axial direction which annular magnet 7 has a total of Six north and South magnetic is substantially the same as the height of the rotor R2. As poles alternately arranged at a uniform angular pitch of 60 shown in FIGS. 1 and 4, in various embodiments, the arcuate about the center axis X.

weight 28 can be located on either side of the wall of the Since the operational principle of the vibrator motor M3 magnet holder 26, farther from or closer to the central axis 15 is identical to those of the vibrator motor M1 or M2, no X than the wall of the magnet holder. The annular magnet 7 duplicate explanation will be made.

has a total of six north and South magnetic poles alternately While the rotor R2 or R3 is in rotation, the magnetic arranged at an even pitch of 60 about the center axis X. interaction between the Stator S and the magnet 7 keeps the The round magnetic holder 26 includes a generally flat top rotor R2 or R3 from axially moving upwardly (as viewed in part 26t that is orthogonal to the center axis X and a FIG. 4 or 6) and touching the rotor cover Rc. No key or cylindrical side wall 26S concentric with the center axis X. Stopper is, therefore, required to keep the Shaft from Slipping The top part 26t has a generally Sectorial cutout 26c, which axially while operation.

is a through-hole. The annular magnet 7 is disposed radially It will be understood that various changes and modifica inside the cylindrical side wall 26s and the arcuate weight 28 tions may be made in the above described embodiments is disposed radially outside the side wall 26s. The arcuate which provide the characteristics of the present invention

weight 28 and the cutout 26c are disposed in angularly without departing from the Spirit and principle thereof non-overlapping relation about the center axis X and dia particularly as defined in the following claims. metrically opposite to each other with respect to the center What is claimed is:

axis X, as better shown in FIG. 5. The rotor R2 has an 1. A dc brushleSS Vibrator motor, comprising: eccentric mass distribution with respect to the center axis X a base member;

because of the arcuate weight 28 and the cutout 26c. a shaft Supporting portion fixed to Said base member and The magnet holder 26 is made of a magnetically conduc having a longitudinal center axis; tive material, but, alternatively, it may be made of a syn thetic resin. a Stator connected to Said base member, Said Stator having The rotor cover Rc is fixedly connected to the base 35 a plurality of magnetically conductive cores and a member 21 in a manner that the rotor R2 is protectively plurality of blades uniformly arranged around the cen ter axis and an armature coil mounted at each of Said capped with the rotor cover Rc. magnetically conductive cores, The operational principle of the vibrator motor M2 is a rotor mounted on a shaft retained in Said shaft Support identical to that of the vibrator motor M1, which is a prior 40 ing portion and having an eccentric mass distribution known art. No duplicate explanation thereon will, therefore, with respect to the center axis, Said rotor having be made.

FIG. 6 is a vertical sectional view of a vibrator motor M3 a magnet holder with a first part having a height parallel of the third embodiment, which is alternative to the the to the center axis and a Second part perpendicular to the vibrator motor M2 of the second embodiment, and FIG. 7 is 45 center axis and having a flat top with a through hole, a plan view of the rotor and a part of the Stator employed in an annular permanent magnet fixedly connected to at least the vibrator motor M3. the first part of Said magnet holder, and Referring to FIGS. 6 and 7, the vibrator motor M3 has a an arcuate metal weight fixed to Said magnet holder, construction identical to that of the vibrator motor M2 axially extending farther from the center axis than Said except that the construction of its rotor R3 is slightly 50 annular permanent magnet and having a height parallel different. Explanation will, therefore, be made of the rotor to the center axis Substantially equal to the height of the R3 only. first part of Said magnet holder, Said annular permanent The rotor R3 has a magnet holder 36, a one-piece annular magnet having a plurality of magnetic poles arranged at permanent magnet 7, which is identical to that of the vibrator a uniform angular pitch around the center axis, and motor M1 or M2, fixedly connected to the magnet holder 36 55 a cup-shaped rotor cover on Said base member covering and disposed concentrically with the center axis X radially Said rotor to prevent foreign matter from entering outside the stator S, which is also identical to that of the through the through hole.

vibrator motor M1 or M2. The rotor R3 has no arcuate metal 2. The dc brushless vibrator motor according to claim 1, weight such as the one included in the rotor R2 of the wherein Said magnet holder is a Synthetic resin and is vibrator motor M2. 60 rotatably mounted on Said Shaft with Said resin magnet AS better shown in FIG. 7, diametrically about one half of holder in direct sliding contact with Said shaft. the magnet holder 36 is cut out. The magnet holder 36 has 3. A dc brushleSS Vibrator motor, comprising: a generally flat top part 36t, which is disposed orthogonal to a base member;

the center axis X, and a Side wall 36S having a form of a part a shaft connected to Said base member, Said shaft having of a cylinder. The top part 36t has a generally anchor form 65 a longitudinal center axis, as viewed from its top. The magnet holder 36 itself has, a Stator fixedly connected to Said base member, Said Stator therefore, an eccentric mass distribution with respect to the having a plurality of magnetically conductive cores

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uniformly angularly disposed about the center axis and 5. The dc brushless vibrator motor according to claim 3, respective armature coils mounted on Said Stator; and further comprising a cup-like Stationary rotor cover fixed to a rotor mounted on Said shaft and having an eccentric Said base member and protectively capping Said rotor. mass distribution with respect to the center axis, Said 6. The dc brushless vibrator motor according to claim 3, rotor having a magnet holder and an annular permanent 5 wherein Said magnet holder has a generally flat top orthogo magnet fixedly connected to Said magnet holder, con nal to the center axis and the cutout is a through-hole in Said centric with the center axis, and located radially outside flat7.top.

The dc brushless vibrator motor according to claim 6,

Said Stator, Said magnet holder having a cutout in a part wherein Said arcuate weight and the through-hole are dis thereof So that Said magnet holder has an eccentric posed diametrically opposite to each other with respect to mass distribution with respect to the center axis, said 10 the center axis.

annular permanent magnet having alternating north and 8. The dc brushless vibrator motor according to claim 7, South magnetic poles arranged at a uniform angular wherein the through-hole is generally Sector-shaped. pitch about the center axis, Said rotor additionally 9. The dc brushless vibrator motor according to claim 6, having an arcuate weight fixedly attached to Said mag wherein Said magnet holder has a cylindrical part concentric net holder radially outside Said annular permanent 15 with the center axis and Said annular permanent magnet is magnet. fixedly adjoined by Said cylindrical part and radially outside 4. The dc brushless vibrator motor according to claim 3, Said cylindrical part.

wherein Said magnet holder is a magnetically conductive materials.