Vibratory motor

A vibratory motor is provided with a detecting member for detecting rotational speed of a rotor member and a control circuit for stopping oscillation of a stator member of the motor when the rotational speed of the rotor member becomes less than a predetermined speed. When the rotational speed of the rotor member is less than the predetermined speed, the control circuit stops oscillation of the stator member. When the stator member stops oscillating, slippage is not generated between the rotor member and the stator member and deterioration of the motor due to friction is successfully decreased.

BACKGROUND OF THE INVENTION 
This invention relates to a motor which utilizes vibrations on a stator 
member as a driving source. 
Conventionally, a motor which utilizes vibrations on a stator member is 
well known in the art. The motor rotates a rotor member due to transmitted 
vibrational energy from the stator member to the rotor member by 
frictional force. Accordingly, rotational speed of the rotor may be 
decreased due to an increased slippage between the stator member and the 
rotor member as a load connected to the rotor, is increased, i.e., as the 
load on the motor, is increased. 
Thus, the conventional vibratory motor deteriorates in efficiency due to 
the slippage between the stator member and the rotor member if an 
excessive load is connected to the rotor member. 
SUMMARY OF THE INVENTION 
One of the objects of this invention is to obviate the above drawbacks of 
the conventional motors. 
It is also an object of this invention to provide a system to restart a 
rotor member after dissipating an excessive load. 
To achieve the above objects, and in accordance with the principles of the 
invention as embodied and broadly described herein, the vibratory motor, 
includes an arrangement for detecting rotational speed of a rotor member, 
and for stopping oscillation of a stator member if the rotational speed 
becomes less than a predetermined speed. 
Preferably, the vibratory motor includes a control arrangement for 
restarting oscillation of the stator member after elapse of a 
predetermined period of time.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Reference will now be made in detail to the present preferred embodiment of 
the invention, an example of which is illustrated in the accompanying 
drawings. In accordance with the invention, a stator member is defined by 
a stator 3, a vibrating member is defined by a vibrator 2, a rotor member 
is defined by rotor 6, an oscillator is defined by the oscillation circuit 
50. A detector arrangement is defined by a ring magnet 61 and a 
Hall-effect element 62, and a control system is defined by control 
circuits 60, 70 and 80. 
Referring now to FIG. 1, a vibratory motor 100 of the first embodiment will 
be explained. A central opening 4a is provided at the center of a disc 
shaped base 4. A bearing 16 is press fit into the central opening 4a. 
An inner portion of a disc shaped stator 3 is supported by the base 4. The 
stator 3 is fixed to the base 4 by screw or fastening member 11. The 
stator 3 comprises a ring-shaped elastic member 1 and a ring-shaped 
piezoelectric vibrator 2. The piezoelectric vibrator 2 is adhered to the 
elastic member 1 by use of a conductive adhesive. 
The elastic member 1 includes an outer ring portion 1a, an inner ring 
portion 1b, and a thin portion 1c. The outer portion 1a and the inner 
portion 1b are connected integrally with the thin portion 1c. The elastic 
member 1 is fixed to the base 4 by supporting the inner portion 1b with 
the screw or fastening member 11. The projections 1e are provided on the 
outer portion 1a. Each projection 1e has a constant gap therebetween. The 
elastic member 1 is made of a conductor, i.e., phosphor-bronze. Thus the 
elastic member 1 is electrically connected to the base 4. 
The piezoelectric vibrator 2 generates a travelling wave on the stator 3. A 
piezoelectric vibrator 2 for generating such a traveling wave is well 
known in the art. Therefore, the detailed explanation for the 
piezoelectric vibrator 2 is herein omitted. The piezoelectric vibrator 2 
has a pair of elements 2a and 2b. Further, a pair of conductive wires 17 
and 18 are connected to the piezoelectric vibrator 2. The element 2a is 
contracted and expanded when a source supplies A.C. power between the 
conductive wire 17 and the base 4. The element 2b is contracted and 
expanded when a source supplies A.C. power between the conductive wire 18 
and the base 4. When the elements 2a and 2b are contracted and expanded 
due to proper A.C. power, travelling waves are generated on the elastic 
member 1. 
A cylindrical member 12 is threadly engaged and fixed to the base 4. A 
cover member 5 is threadly engaged with the cylindrical member 12 so as to 
define a screw connection between the cover member 5 and the cylindrical 
member 12. Accordingly, the cover member 5 moves in the axial direction of 
the shaft 9 when the cover member 5 is rotated. The base member 4, the 
cylindrical member 12 and the cover member 5 constitute a housing for the 
vibratory motor 100. 
A bearing member 15 is fixed to the cover member 5 so that the shaft 9 is 
rotatably mounted in the bearings 15 and 16. The bearing 15 is in contact 
with a flange portion 9a of the shaft 9. The flange portion 9a prevents 
movement of the shaft 9 toward the cover member 5. 
The rotor 6, a rubber seat 14 and a cone spring 13 are positioned between 
the bearing 15 and the elastic member 1. The rotor 6 and the rubber seat 
14 are pressed toward the stator 3 by the spring force of the cone spring 
13. The rubber seat 14 prevents aural noises from being generated between 
the rotor 6 and the cone spring 13 due to oscillation of the rotor 6. 
The cone spring 13 is in contact with and positioned by the flange portion 
9a of the shaft 9, thus the cone spring 13 is supported by the flange 
portion 9a coaxially with the bearing 15. Further, the pressure between 
the stator 3 and the rotor 6 can be adjusted by rotating the cover member 
5 as the cover member 5 is movable along the axial direction of the shaft 
9. 
A sliding portion 6a is formed at an outer extent of the rotor 6. One 
surface of the sliding portion 6a faces toward the outer portion 1a of the 
elastic member 1. A friction film 7 is pinched or held between the sliding 
portion 6a and the outer portion 1a. As the rotor 6 is pressed toward the 
stator 3, the sliding portion 6a is pressed against the projections 1e 
formed on the outer portion 1a through the friction film 7. 
The travelling waves are generated on the elastic member 1 due to the 
oscillation of the piezoelectric vibrator 2 when the A.C. power is 
supplied to the conductive wires 17, 18 and the base 4. The travelling 
waves go around the outer portion 1a of the elastic member 1. During this 
time, the amplitude of the travelling wave is amplified by the projections 
1e. Thus, the travelling wave feeds a moment of rotation to the rotor 6. 
Accordingly, the rotor 6 rotates with the shaft 9 when the traveling wave 
is generated on the elastic member 1. 
A ring magnet 61 is fixed to one end of the shaft 9. The magnet 61 rotates 
together with the shaft 9. The ring magnet 61 provides a predetermined 
number, i.e., 20, magnetic poles around circumference thereof. A 
Hall-effect element 62 is provided close to the ring magnet 61. The 
Hall-effect element 62 is fixed to a circuit board 10. The circuit board 
10 includes an oscillating circuit 50 and a control circuit 60. The 
circuit board 10 is fixedly attached to a lower cover 8. The lower cover 8 
is fixedly attached to the base 4. 
Referring now to FIG. 2, the oscillation circuit 50 and the control circuit 
60 will be explained. 
The oscillation circuit 50 includes an oscillator 51, phase shifter 52, 
drivers 53 and 54, and transformers 55 and 56. An oscillation signal, 
generated by the oscillator 51 is supplied to the phase shifter 52. The 
phase shifter 52 generates two separate signals based on the supplied 
oscillation signal. The two separate signals have a mutual difference of 
phase corresponding to 90 degrees. The two separate signals are applied to 
the elements 2a and 2b through the drivers 53, 54 and transformers 55, 56. 
The piezoelectric vibrator 2 generates the traveling wave on the stator 3 
in order to rotate the rotor 6 when the two separate signals are applied 
to the elements 2a and 2b. 
The control circuit 60 includes the ring magnet 61, the Hall-effect element 
62, an amplifier 63, an F/V converter 64, a comparator 65 and delay 66. 
The rotational speed of the rotor 6 is converted into an A.C. signal by 
the ring magnet 61 and the Hall-effect element 62. 
The A.C. signal from the Hall-effect element 62 has a frequency 
corresponding to the rotational speed of the rotor 6. The A.C. signal is 
amplified by the amplifier 63. Then, the A.C. signal is converted into a 
D.C. signal by the F/V converter 64. The D.C. signal from the F/V 
converter 64 has a voltage level which corresponds to the rotational speed 
of the rotor 6. 
The D.C. signal from the F/V converter 64 is supplied to the comparator 65. 
The comparator 65 has a predetermined reference voltage. The reference 
voltage is based on a rotational speed detected just before stoppage of 
the rotor 6. The comparator 65 generates an "H" or high level signal when 
the D.C. signal from the F/V converter 64 exceeds the reference voltage. 
The comparator generates an "L" or low level signal when the D.C. signal 
from the F/V converter 64 is less than the reference voltage. The output 
signal from the comparator 65 is transmitted to the oscillator 51 through 
the delay 66. The oscillator 51 oscillates and vibrates the stator 3 as 
long as the "H" level signal is supplied from the delay 66. 
Referring now to FIG. 3, operation of the first embodiment is explained. 
At the time t.sub.1, the rotational speed of the rotor 6 is decreased due 
to an excessive load connected to the shaft 9. When the rotational speed 
of the rotor 6 is decreased, a voltage at a point A in FIG. 2 is 
decreased. At the time t.sub.2, when the voltage at point A becomes less 
than the reference voltage, voltage at point B is changed from the "H" 
level to the "L" level. Thus, the stoppage of the rotor 6 is detected. At 
this time, a large amount of slippage is generated between the rotor 6 and 
the stator 3. As a result of the slippage, deterioration of the rotor 6, 
the stator 3 and the friction film 7 increases. 
After elapse of a predetermined period of time .DELTA.t from detecting 
stoppage of the rotor 6, voltage at a point C is changed from the "H" 
level to the "L" level. At the time, the oscillator 51 stops oscillating. 
Thus, when the rotational speed of the rotor 6 is less than the 
predetermined speed, the control circuit 60 stops the oscillation of the 
oscillation circuit 50. While the oscillation circuit 50 stops 
oscillating, slippage is no longer generated between the rotor 6 and the 
stator 3. Therefore, the deterioration of the rotor 6, the stator 3 and 
the friction film 7, due to the slippage, is successfully decreased. 
In the first embodiment, the oscillation circuit 50 oscillates continuously 
during the period of time .DELTA.t after detecting the stoppage of the 
rotor 6. Therefore, the vibratory motor 100 of the first embodiment avoids 
sudden stoppage of the rotor 6 due to excessive loads applied to the 
output shaft. 
Next, referring to FIG. 4, the second embodiment of the invention will be 
explained. The second embodiment has the same construction as the first 
embodiment except for the control circuit 70. Therefore, only the control 
circuit 70 is explained hereinafter. 
The control circuit 70 includes a square-wave generator 71, a counter 72 
and an OR gate 73 instead of the delay 66 in FIG. 2. Other construction of 
the circuit is the same as the first embodiment in FIG. 2. 
The output signal of the comparator 65 is supplied to the oscillator 51 
through the OR gate 73. The output signal of the comparator 65 is also 
applied to a reset terminal 72R of the counter 72. The square wave 
generator 71 is connected to the counter 72. The counter 72 divides the 
frequency of the square wave generator 71 and generates an output signal 
which is cyclically reversed or changed for every period of time .DELTA.t 
when the comparator 65 generates an "L" level signal. The output signal 
from the counter 72 is applied to the oscillator 51 through the OR gate 
73. The oscillator 51 vibrates the stator 3 as long as the OR gate 73 
generates an "H" level signal. 
Referring now to FIG. 5, operation of the second embodiment is explained. 
At the time t.sub.1, an excessive load is applied to the rotor 6 and 
rotational speed of the rotor 6 is decreased. 
At the time t.sub.2, when the voltage at point A is less than the reference 
voltage, voltage at point B is reversed or changed from the "H" level to 
the "L" level. Thus, stoppage of the rotor 6 is detected. At this time, 
the reset terminal 72R is changed from the "H" level to the "L" level and 
the counter 72 starts the operation. At this time, slippage is generated 
between the rotor 6 and the stator 3. As a result of the slippage, 
deterioration of the rotor 6, the stator 3 and the friction film 7 
increases. 
After elapse of a predetermined period of time .DELTA.t from detecting 
stoppage of the rotor 6, voltage at a point D is reversed or changed from 
the "H" level to the "L" level. Then, the voltage at the point C is also 
inverted from the "H" level to the "L" level, and the oscillator 51 stops 
oscillating. 
Thus, when the rotational speed of the rotor 6 is less than the 
predetermined speed, the control circuit 70 stops the oscillation of the 
oscillation circuit 50. When the oscillation circuit 50 stops oscillating, 
slippage is no longer generated between the rotor 6 and the stator 3. 
Therefore, the deterioration of the rotor 6, the stator 3 and the friction 
film 7 are successfully decreased. 
In the second embodiment, the counter 72 generates the output signal which 
is cyclically reversed or changed for every period of time .DELTA.t. 
Therefore, after elapse of the predetermined period of time .DELTA.t, the 
oscillation circuit 50 restarts the oscillation and the rotor 6 is capable 
of restarting the rotation. 
At the time t.sub.3, when the rotor 6 restarts the rotation, the output of 
the comparator 65 is reversed or changed from the "L" level to the "H" 
level. As a result, the counter 72 is initialized. 
As in the first embodiment, in the second embodiment the oscillation 
circuit 5 oscillates continuously for the period of time .DELTA.t, after 
detecting the stoppage of the rotor 6. Therefore, the vibratory motor 100 
of the first embodiment avoids sudden stoppage of the rotor 6 due to 
imposition of an excessive load. 
Furthermore, in the second embodiment, the oscillation circuit 50 restarts 
oscillating cyclically for every period of time .DELTA.t. Therefore, the 
rotor 6 restarts the rotation after removal or otherwise overcoming the 
excessive load. 
Next, referring now to FIG. 6, the third embodiment of the invention is 
explained. The third embodiment has the same construction as the second 
embodiment except for the control circuit 80. Therefore, only the control 
circuit 80 is explained herein below. 
The control circuit 80 includes a counter 74 and an AND gate 75 in addition 
to the circuitry of the second embodiment. The output signal from the 
comparator 65 is applied to the oscillator 51 through the OR gate 73 and 
the AND gate 75. Further, the output signal from the comparator 65 is also 
applied to the reset terminal 72R of the counter 72 and the reset terminal 
74R of the counter 74. The counter 72 divides the frequency of the signal 
from the square wave generator 71 and generates an output signal which is 
cyclically reversed or changed for every period of time .DELTA.t, when the 
comparator 65 generates an "L" level signal. Further, the counter 74 
counts the number of reversing or changing signals from the counter 72. 
The counter 74 closes the AND gate 75 when the signal from the counter 72 
is reversed a predetermined number, e.g., three times. 
The output signal from the counter 72 is applied to the oscillator 51 
through the OR gate 73 and the AND gate 75. The oscillator 51 vibrates the 
stator 3 as long as the output signal from the AND gate 75 is at the "H" 
level. 
Referring now to FIG. 7, operation of the third embodiment is explained. 
At the time t.sub.1, the excessive load is connected to the rotor 6 and the 
rotational speed of the rotor 6 is decreased. 
At the time t.sub.2, when voltage at point A is less than the reference 
voltage, voltage at point B is reversed or changed from the "H" level to 
the "L" level. Thus, stoppage of the rotor 6 is detected. At this time, 
the reset terminals 72R and 74R are reversed from the "H" level to the "L" 
level and the counters 72 and 74 start the operation. 
After elapse of a predetermined period of time .DELTA.t from detecting 
stoppage of the rotor 6, voltages at the points C and D are reversed or 
changed from the "H" level to the "L" level. After voltage at the point D 
is reversed, e.g., three times, the counter 74 closes the AND gate 75. 
Then, the voltage at point C is sustained at the "L" level. As a result of 
this, oscillation circuit 50 stops oscillating continuously. 
Thus, when the rotational speed of the rotor 6 is less than the 
predetermined speed, the control circuit 80 stops the oscillation of the 
oscillator 50. When the oscillation circuit 50 stops oscillating, a large 
amount slippage is no longer generated between the rotor 6 and the stator 
3. Therefore, deterioration of the rotor 6, the stator 3 and the friction 
film 67 are successfully decreased. 
In the third embodiment, the counter 74 closes the AND gate 75 in order to 
prevent the rotor 6 from restarting if the rotor 6 does not start rotating 
after three attempts of restarting. Therefore, in the third embodiment, 
when the rotor 6 temporarily stops the rotation, the rotor 6 could be 
restarted. Further, when the rotor 6 stops the rotation for a long time, 
power which would be used in attempts at restarting the rotor 6 is 
effectively conserved. 
The principles, preferred embodiments and modes of operation of the present 
invention have been described in the foregoing application. The invention 
which is intended to be protected herein should not, however, be construed 
as limited to the particular forms disclosed, as these are to be regarded 
as illustrative rather than restrictive. Variations and changes may be 
made by those skilled in the art without departing from the spirit of the 
present invention. Accordingly, the foregoing detailed description should 
be considered exemplary in nature and not limited to the scope and spirit 
of the invention as set forth in the appended claims.