Vibrator motor for wireless silent alerting device

A small dc vibrator motor for use in a wireless alerting device includes a housing, a non-rotatable shaft fixed to the housing, a cylindrical magnet fixedly mounted on the shaft, and a rotor which is rotatably mounted on the shaft. The rotor includes a cylindrical coreless winding assembly between the magnet and the housing, and eccentric bearings, or combinations of concentric bearings and eccentric weights, on both ends of the winding assembly. The eccentric bearings, or the combinations of concentric bearings and eccentric weights, cause vibrations when the rotor rotates.

BACKGROUND OF THE INVENTION 
1. FIELD OF THE INVENTION 
This invention relates to a small-size coreless dc vibrator motor for use 
in a wireless silent alerting device. The alerting device is vibrated by 
the vibrator motor upon receiving a radio call signal and transmits the 
vibration to the wearer of the device so that the wearer becomes aware 
that he is being called without being noticed by others and, therefore, 
without disturbing others. 
2. DESCRIPTION OF THE PRIOR ART 
FIG. 5 shows one of the conventional small-size vibrator motors. In FIG. 5, 
letter M denotes a cylindrical dc motor which has a rotatable output shaft 
denoted by letter S. Letter W denotes an eccentric weight and mounted on 
the shaft S. The motor vibrates as the shaft turns because of the 
eccentric and unbalanced mass distribution about the axis of the shaft S. 
Such a conventional vibrator motor having an eccentric weight on the 
rotatable shaft, however, requires an extra length of the shaft on which 
the weight is mounted and an additional space for the weight to occupy for 
rotation. The weight is normally made of a high density metal, such as a 
tungsten-based alloy, so as to create a maximum unbalanced centrifugal 
force out of a very small size eccentric weight. Since such a high density 
metal for the eccentric weight is very costly, the overall production cost 
of the vibrator motor has to be substantially increased because of the 
cost of the weight. 
Furthermore, this type of conventional vibrator motor normally employs a 
cylindrical permanent magnet and a pair of bearings for holding the 
rotatable shaft. The bearings are normally disposed diametrically inside 
the cylindrical magnet. In case the bearings are made of an 
oil-impregnated iron, the bearings themselves can serve as magnetic paths. 
However, if the bearings are made of an oil-impregnated bronze-based 
alloy, which is not magnetically conductive but is typical as a bearing 
material, an iron tube has to be additionally disposed between the 
bearings and the inside periphery of the permanent magnet in order to 
provide magnetic paths. 
On the other hand, it is desired that the radial thickness of the 
cylindrical permanent magnet is as large as practically possible. However, 
in the case of the above described conventional motor, the radial 
thickness of the cylindrical magnet has to be considerably curtailed not 
only because of the presence of the rotatable shaft and a clearance 
immediately around the shaft but also because of the additional room 
necessary for accommodating the bearings and the iron tube, if any; all of 
these are normally present diametrically inside the cylindrical magnet. 
Whereas the outside diameter of the cylindrical permanent magnet must 
naturally be limited because of the inevitable limit of the diameter of 
the motor which has to be made as small as possible. 
The loss of the radial thickness of the cylindrical magnet gives rise to a 
decrease in the permeance at the operating point because the ratio of the 
radial thickness of the cylindrical magnet to the amount of the air gap 
(i.e. the distance between the outside periphery of the cylindrical magnet 
and the internal periphery of the case of the motor, wherein a cylindrical 
coreless winding assembly is disposed) is decreased. Accordingly, the 
effective magnetic flux density across the air gap is minimized and the 
cylindrical coreless winding assembly disposed therein is subjected to a 
less amount of magnetic flux, thereby causing the amperage for a required 
torque to be increased. 
Furthermore, because the eccentric bearing is mounted on one end of the 
shaft, the bearing closer to the eccentric weight is subjected to a 
greater amount of unbalanced centrifugal force created by the eccentric 
weight and this gives rise to an accelerated wear to one bearing as 
compared to the wear to the other bearing, thereby shortening the life of 
the motor. 
U.S. Pat. Nos. 3,623,064, issued Nov. 23, 1971, and 3,911,416, issued Oct. 
7, 1975, disclose small motors for wireless silent paging devices having 
add-on unbalanced weights mounted on the output shafts. U.S. Pat. No. 
4,030,246, issued July 5, 1977, discloses a comparatively large industrial 
vibrator motor including a rotor shaft having a pair of fixed eccentric 
weights and a pair of eccentric weights which are angularly adjustable 
about the rotor axis, so that the amount of the vibration of the motor can 
be controlled. 
SUMMARY OF THE INVENTION 
In view of the above, it is an object of the present invention to provide a 
small-size dc coreless vibrator motor for use in a wireless silent 
alerting device which requires neither an add-on eccentric weight nor an 
extended part of the rotor shaft on which the eccentric weight is mounted, 
thereby requiring no external space in which such eccentric weight 
rotates. 
Another object of the present invention is to provide a small-size coreless 
vibrator motor for said use which features a simple construction, a low 
production cost, and yet requires low power consumption because of a 
greater permeance at the operating point. 
A further object of the present invention is to provide a small-size 
coreless vibrator motor for said use having a pair of bearings which are 
subjected to a substantially equal amount of unbalanced centrifugal force, 
thereby obviating unbalanced wear between the two bearings, and 
consequently, extending the life of the motor. 
The vibrator motor of the present invention includes a 
generally-cylindrically shaped housing; a non-rotatable shaft which is 
fixed to the housing; a cylindrically-shaped permanent magnet fixedly 
mounted directly or indirectly on the shaft; and a generally 
cylindrically-shaped rotor. The rotor includes a cylindrical coreless 
winding assembly disposed in an air gap formed between the magnet and the 
housing, a pair of holders disposed on both sides of the winding assembly, 
each holder containing an eccentric bearing mounted on the shaft, or a 
combination of a concentric bearing and an eccentric weight, and a 
commutator disposed at one end of the rotor. The motor further includes a 
pair of brushes slidably in contact with the commutator and fixed to a 
electrically-insulating brush base which also serves as a closure material 
on one side of the housing. More specifically, the housing consists of a 
case, having an open end and a closed end, the brush base which is fixedly 
attached to the case so as to close the open end thereof, a 
support-terminal which is securely attached, and electrically connected, 
to the closed end of the case, and a bracket-terminal which is rigidly 
secured to the brush base. The case and the bracket-terminal are 
electrically insulated from each other by the brush base. One of the 
brushes is electrically connected to the case and the other brush to the 
bracket-terminal. Thus, the support-terminal and the bracket-terminal 
serve as power input terminals, which can be directly connected to a power 
supply circuit on a circuit board. 
This arrangement also obviates a possible mechanical damage to a power 
supply wiring which may be otherwise caused by the vibrations of the 
alerting device and further facilitates the fabrication of the alerting 
device in a mass production. 
The pair of the eccentric bearings, or the eccentric weights, cause 
vibrations when the rotor is rotated. Since the eccentric bearings, or the 
eccentric weights, are completely contained in the rotor of the motor, no 
extra space external to the vibrator motor need to be considered in 
fitting the motor to the alerting device, as opposed to the case of a 
conventional vibrator motor having an external eccentric weight. This 
substantially facilitates the design of the alerting device which employs 
the vibrator motor. Furthermore, the radial thickness of the fixed 
cylindrical magnet can be made large, to increase the permeance at the 
operating point, thereby causing the required amount of current to be 
lowered and minimizing power consumption.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 is a longitudinal cross section of one embodiment of a coreless dc 
vibrator motor according to the present invention. A vibrator motor 1 has 
a generally cylindrically-shaped housing 2 which consists of a generally 
cylindrically-shaped case 3, a support-terminal 4, a brush base 5, and a 
bracket-terminal 6. The case 3 is made of an 
electrically-magnetically-conductive material: i.e. tinplate, in this 
embodiment. One end 3a (the left-side end as viewed in FIG. 1) of the case 
3 per se is closed and the other end 3b thereof is open. 
Referring to FIGS. 1 and 4, the support-terminal 4 is 
electrically-conductive and is securely attached to the closed end 3a of 
the case 3. The brush base 5, made of an electrically-insulating synthetic 
resin, is securely fixed to the case 3 in such a manner that the brush 
base 5 caps and closes the open end 3b of the case 3. The bracket-terminal 
6 is electrically-conductive and is rigidly attached to the brush base 5, 
so that the bracket-terminal 6 and the case 3 are fixedly held together, 
but electrically insulated from each other, by the brush base 5. 
Referring to FIG. 1, numeral 7 denotes a non-rotatable shaft made of a 
magnetically-conductive metal: i.e. magnetically-conductive stainless 
steel (SUS420J2), in this embodiment. One end 7a of the shaft 7 is fixedly 
engaged with a bore 3c formed in the diametrical center of the end 3a of 
the case 3. The other end 7b of the shaft 7 is fixed to the brush base 5 
in a diametrical center of the housing 2. The end 7b of the shaft 7 has a 
D-shaped section so that the shaft 7 is securely locked to the brush base 
5 and is prevented from accidental rotation. The D-shaped end 7b of the 
shaft 7 is also utilized for the purpose of obtaining a precise angular 
alignment of the shaft 7 in the course of production. A 
cylindrically-shaped permanent magnet 8, made of a rare earth metal, is 
fixedly mounted on the shaft 7. The magnet 8 may be formed in a segmented 
construction. 
FIG. 1A shows a shaft-magnet assembly in longitudinal vertical cross 
section which can be alternatively used for the shaft-magnet assembly of 
the vibrator motor shown in FIG. 1. In FIG. 1A, a magnetically-conductive 
tube 8a is fixedly mounted on the shaft 7 and the permanent magnet 8 is 
fixedly mounted on the magnetically-conductive tube 8a. In other words, 
the magnetically conductive tube 8a is fixedly interposed between the 
shaft 7 and the magnet 8. The magnetically-conductive tube 8a serves as a 
path for magnetic flux. Therefore, the shaft 7 may be made magnetically 
non-conductive in this alternative embodiment as explained later. 
Referring back to FIG. 1, rotor 9 includes a cylindrically-shaped coreless 
winding assembly 10 and a pair of holders 11 and 12 which are made of 
light-weight epoxy resin and disposed on both sides of the winding 
assembly 10 and securely fixed thereto. A pair of oil-impregnated 
eccentric bearings 13 and 14, made of a bronze-based alloy, are disposed 
in the holders 11 and 12, respectively, and securely fixed thereto. The 
bearings 13 and 14 are rotatably mounted on the shaft 7 so that the rotor 
9 is rotatable about the axis of the shaft 7 while the shaft 7 and the 
magnet 8 remain stationary. Although the bearings 13 and 14 are eccentric 
in terms of their mass distributions about the axis of the shaft 7, the 
winding assembly 10 and the magnet 8 are concentrically disposed with 
respect to the axis of the shaft 7 so that the winding assembly 10 stays 
in an air gap 15 formed between the circumferential surface of the magnet 
8 and the inner circumferential surface of the case 3. Spacers 16, 17 are 
disposed on both sides of the magnet 8 in order to prevent a longitudinal 
(axial) movement of the rotor 9. 
FIG. 2 is a cross section of the vibrator motor 1 taken along the lines 
II--II or II'--II' of FIG. 1. 
In reference to FIGS. 1 and 2, the eccentric bearings 13 and 14 have a 
generally fan-shaped cross section, as shown in FIG. 2, in a plane 
perpendicular to the axis of the shaft 7, and are press-fit or otherwise 
fixedly secured to the holders 11 and 12, respectively. The centers of 
mass (or, the centers of gravity) of the eccentric bearings 13 and 14 are 
off the axis of the shaft 7. Each of the bearings 13 and 14 is so designed 
and formed that the deviation of the center of mass thereof from the axis 
of the shaft 7 is as large as practically possible so as to create a 
maximum unbalanced centrifugal force, yet the distance between the 
outermost part thereof and the axis of the shaft may not exceed the 
outside radius of the magnet 8. Therefore, the distance from the axis of 
the shaft 7 to a radially farthest part of each of the eccentric bearings 
13 and 14 is substantially equal to the outside radius of the cylindrical 
magnet 8. 
As shown in FIGS. 1 and 2, the holders 11 and 12 have air spaces 11a and 
12a, respectively, on the opposite side of the centers of mass of the 
eccentric bearings 13 and 14, respectively, with respect to the axis of 
the shaft 7 so that the centers of the total masses of the holders 11, 12 
and the bearings 13, 14, respectively, are effectively away from the axis 
of the shaft 7. 
In this embodiment, the centers of mass of the eccentric bearing 13 and the 
eccentric bearing 14 are angularly aligned to each other about the axis of 
the shaft 7 within a tolerance of + 10 degrees so that the unbalanced 
centrifugal forces created by the bearings 13 and 14, when the rotor 9 is 
rotated, are always directed in angularly the same direction. Such angular 
alignment between the bearings 13 and 14 is effective in creating maximum 
vibrations to be felt by the wearer of the alerting device for a given 
power input to the motor 1. 
The air spaces 11a, 12a are a plurality of longitudinally (axially) 
elongated columnar holes as shown in FIGS. 1 and 2 and the respective 
holes are angularly aligned to each other between the holders 11 and 12. 
Conversely, the air spaces 11a, 12a can also be utilized for obtaining an 
angular alignment between the holders 11 and 12 in the production of the 
motor 1. The construction and the arrangement of the components of the 
rotor 9 are in order for maximizing the vibration of the alerting device 
with limited dimensions, weight and power consumption and for ensuring the 
reception of the vibration by the wearer of the alerting device. 
FIG. 3 shows a cross section of a rotor of a vibrator motor of the second 
embodiment according to the present invention. A rotor 9a of the second 
embodiment has a similar construction to that of the rotor 9 of the first 
embodiment described above except that the eccentric bearings 13 and 14 of 
the first embodiment are replaced by combinations of oil-impregnated 
concentric bearings 13a and 14a, respectively, made of a bronze-based 
alloy, and eccentric weights 13b and 14b, respectively, made of a high 
density metal such as lead. The concentric bearings 13a, 14a and the 
eccentric weights 13b, 14b are securely held in the holders 11b and 12b, 
respectively, and the concentric bearings 13a, 14a are rotatably mounted 
on the shaft 7. The eccentric weights 13b and 14b have a generally 
fan-shaped cross section, as shown in FIG. 3, in a plane perpendicular to 
the axis of the shaft 7. The eccentric weights 13b and 14b are eccentric 
in terms of their mass distributions about the axis of the shaft 7. 
Therefore, the center of the mass (the center of gravity) of each of the 
eccentric weights 13b, 14b is off the axis of the shaft 7 so that the 
eccentric weights 13b, 14b cause vibrations when the rotor is rotated. 
The distance from the axis of the shaft 7 to a radially farthest part of 
each of the eccentric weights 13b and 14b is substantially equal to the 
outside radius of the cylindrical magnet 8, as is the case of the 
eccentric bearings 13, 14 in the first embodiment. 
The holders 11b and 12b of the second embodiment also contain air spaces 
11c and 12c, respectively, on the opposite side of the centers of mass of 
the eccentric weights 13b and 14b, respectively, with respect to the axis 
of the shaft 7 so that the centers of the total masses of the holder 11b 
and the eccentric weight 13b and the holder 12b and the eccentric weight 
14b, respectively, are effectively away from the axis of the shaft 7. 
In the second embodiment, the centers of mass of the eccentric weight 13b 
and the eccentric weight 14b are angularly aligned to each other about the 
axis of the shaft 7 within a tolerance of .+-. 10 degrees so that the 
unbalanced centrifugal forces created by the eccentric weights 13b, 14b, 
when the rotor 9a is rotated, are always directed in angularly the same 
direction. The air spaces 11c and 12c are angularly aligned to each other 
about the axis of the shaft 7, as is the case of the first embodiment. 
The construction of other parts of the vibrator motor of the second 
embodiment is identical to that of the vibrator motor of the first 
embodiment. 
In both of the first and the second embodiments, the permanent magnet 8 may 
be a rare-earth-element-based plastic magnet (i.e. bonded magnet) which is 
directly formed onto the shaft 7 or onto the magnetically-conductive tube 
8a shown in FIG. 1A. 
Referring again to FIG. 1, a commutator 18 is concentrically disposed with 
respect to the axis of the shaft 7 and is fixedly secured to the holder 12 
and electrically connected to the winding assembly 10. A pair of brushes 
19 and 20, which are slidably in contact with the commutator 18, are 
fixedly secured to the brush base 5 and electrically connected to the case 
3 and the bracket-terminal 6, respectively. Therefore, a dc power to drive 
the vibrator motor 1 can be input between the support-terminal 4 and the 
bracket-terminal 6. 
In reference to FIGS. 1 and 4, bases 4a and 6a of the support-terminal 4 
and bracket-terminal 6, respectively, can be directly connected to a dc 
power supply circuit on a circuit board. As a matter of course, power 
input to the motor 1 may alternatively be achieved in a conventional 
lead-wire method. 
In the above embodiments, each of the winding assembly 10 and the 
commutator 18 is made up of three segments (120 degrees each), and the 
permanent magnet 8 is made up of two segments (180 degrees each). The loop 
of the magnetic circuit is: an outside periphery (N pole) of the 
magnet--an air gap (including the winding assembly)--case (the magnetic 
flux passes in the case angularly 180 degrees)--another air gap (including 
the winding assembly) on the 180-degree opposite side--another outside 
periphery (S pole) of the magnet on the 180-degree opposite side--inside 
the magnet--magnetically conductive shaft--inside the magnet--the outside 
periphery (N pole) of the magnet. 
In the alternative embodiment of the shaft-magnet assembly as shown in FIG. 
1A, the shaft 7 may be magnetically non-conductive. In that case, the 
magnetic flux passes through the magnetically-conductive tube 8a while 
bypassing the shaft 7. 
The dc currents input to the winding assembly 10 through the input route of 
support-terminal 4--case 3--brush 19--commutator 18--winding assembly 10 
and output from the winding assembly 10 through the output route of 
winding assembly 10--commutator 18--brush 20--bracket-terminal 6, or vice 
versa. Then, according to Fleming's left-hand rule, the 
dc-current-carrying winding assembly 10 electromagnetically interacts with 
the magnetic flux which is present across the air gap 15 between the 
magnet 8 and the case 3, thereby causing the rotor 9 to rotate. As the 
rotor 9 rotates, the eccentric bearings 13, 14, in the first embodiment, 
or the eccentric weights 13b, 14b, in the second embodiment, cause 
vibrations. The vibrations are transmitted from the motor 1 to the 
alerting device, and then to the wearer of the device. 
In an alternative embodiment, the winding assembly 10 and the commutator 18 
may be made up of six segments (60 degrees each), and the magnet 8 may be 
made up of four segments (90 degrees each). However, the basic principle 
of producing electromagnetic force is the same as above. 
Since the rotor of the vibrator motor according to the present invention 
contains a pair of holders, and each of the holders has an eccentric 
bearing, or a combination of a concentric bearing and an eccentric weight, 
in order to produce vibrations, and all of the bearings or the weights are 
disposed completely within the rotor, no space external to the vibrator 
motor need to be considered in designing the alerting device which 
contains the vibrator motor. 
Furthermore, the eccentric bearings may be made of the same material as is 
used for conventional bearings and such material is far less costly as 
compared to the material, such as tungsten alloys, of external eccentric 
weights used in the conventional vibrator motors. In addition, the radial 
thickness of the fixed cylindrical magnet can be made large enough so as 
to increase the permeance at the operating point, thereby causing the 
amount of the current to be lowered and the power requirement to be 
minimized. 
It will be understood that various changes and modifications may be made in 
the above described embodiments which provide the characteristics of the 
present invention without departing from the spirit and principle thereof 
particularly as defined in the following claims.