U.S. patent application number 12/488733 was filed with the patent office on 2009-12-31 for electric toothbrush.
This patent application is currently assigned to PANASONIC ELECTRIC WORKS, CO., LTD.. Invention is credited to Yoshinori MASUKO.
Application Number | 20090320221 12/488733 |
Document ID | / |
Family ID | 41119967 |
Filed Date | 2009-12-31 |
United States Patent
Application |
20090320221 |
Kind Code |
A1 |
MASUKO; Yoshinori |
December 31, 2009 |
ELECTRIC TOOTHBRUSH
Abstract
An electric toothbrush is provided with a brush portion, a motor
including a rotary shaft, a battery, which supplies the motor with
power supply voltage, and an eccentric shaft, which rotates
together with the rotary shaft. The eccentric shaft has a center of
gravity located at a position deviated from an axis of the rotary
shaft of the motor. An oscillation transmission mechanism transmits
oscillations generated by the rotation of the eccentric shaft. An
oscillation amplitude regulation circuit regulates an oscillation
amplitude of the brush portion to be constant regardless of changes
in the power supply voltage in a state in which the brush portion
is free from external loads.
Inventors: |
MASUKO; Yoshinori; (Hikone,
JP) |
Correspondence
Address: |
Workman Nydegger;1000 Eagle Gate Tower
60 East South Temple
Salt Lake City
UT
84111
US
|
Assignee: |
PANASONIC ELECTRIC WORKS, CO.,
LTD.
Osaka
JP
|
Family ID: |
41119967 |
Appl. No.: |
12/488733 |
Filed: |
June 22, 2009 |
Current U.S.
Class: |
15/22.1 |
Current CPC
Class: |
A61C 17/221 20130101;
A61C 17/3481 20130101 |
Class at
Publication: |
15/22.1 |
International
Class: |
A46B 13/02 20060101
A46B013/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 27, 2008 |
JP |
2008-168727 |
Claims
1. An electric toothbrush comprising: a brush portion; a motor
including a rotary shaft; a battery which supplies the motor with
power supply voltage; an eccentric shaft which rotates together
with the rotary shaft, in which the eccentric shaft has a center of
gravity located at a position deviated from an axis of the rotary
shaft of the motor; an oscillation transmission mechanism which
transmits oscillations generated by the rotation of the eccentric
shaft to the brush portion; and an oscillation amplitude regulation
circuit which regulates an oscillation amplitude of the brush
portion to be constant regardless of changes in the power supply
voltage in a state in which the brush portion is free from external
loads.
2. The electric toothbrush according to claim 1, wherein the
oscillation amplitude regulation circuit includes a pulse
generation circuit which supplies the motor with the power supply
voltage in pulses of a predetermined pulse duration period set to
regulate the oscillation amplitude of the brush portion to be
constant in accordance with the value of the power supply voltage
supplied from the battery.
3. The electric toothbrush according to claim 1, wherein the
oscillation amplitude regulation circuit converts the power supply
voltage supplied from the battery into constant voltage for
regulating the oscillation amplitude of the brush portion to be
constant, and supplies the motor with the constant voltage.
4. The electric toothbrush according to claim 2, wherein the
oscillation amplitude regulation circuit: detects load current
applied to the motor when external load is applied to the motor;
and supplies the motor with the power supply voltage in pulses of
the predetermined pulse duration period set to regulate the
oscillation amplitude of the brush portion to be constant in
accordance with both the value of the power supply voltage supplied
from the battery and the value of the detected load current.
5. The electric toothbrush according to claim 2, wherein the
oscillation amplitude regulation circuit: detects rotation speed of
the motor when external load is applied to the motor; and supplies
the motor with the power supply voltage in pulses of the
predetermined pulse duration period set to regulate the oscillation
amplitude of the brush portion to be constant in accordance with
both the value of the power supply voltage supplied from the
battery and the detected rotation speed.
6. The electric toothbrush according to claim 2, wherein the
oscillation amplitude regulation circuit: detects back
electromotive force of the motor when external load is applied to
the motor; and supplies the motor with the power supply voltage in
pulses of the predetermined pulse duration period set to regulate
the oscillation amplitude of the brush portion to be constant in
accordance with both the value of the power supply voltage supplied
from the battery and the value of the detected electromotive
force.
7. The electric toothbrush according to claim 2, wherein the pulse
generation circuit includes: a memory which stores the value of the
power supply voltage supplied from the battery in association with
the predetermined pulse duration period set to regulate the
oscillation amplitude of the brush portion to be constant; and a
switch element which functions in accordance with a pulse signal
having a pulse duration period stored in the memory; wherein the
power supply voltage is supplied in pulses to the motor via the
switch element.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of Japanese Patent
Application No. 2008-168727, filed on Jun. 27, 2008, the entire
contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to an electric toothbrush.
[0003] A typical electric brush includes a brush portion that is
oscillated by a motor. Japanese Laid-Open Patent Publication No.
9-173360 describes an electric toothbrush including a motion
conversion mechanism, which converts the rotation produced by a
motor to two types of different motions that are transmitted to the
brush portion so as to move the brush portion in constant
oscillation amplitude. Japanese Laid-Open Patent Publication No.
2008-80099 describes an electric toothbrush including an eccentric
shaft, which generates oscillations when rotated by a motor, and an
oscillation transmission component, which transmits the oscillation
of the eccentric shaft to the brush portion, so as to reduce power
consumption and produce high-speed rotations.
SUMMARY OF THE INVENTION
[0004] In the electric toothbrush of the '360 publication, the
motion conversion mechanism mechanically converts the rotation of
the motor to oscillation of the brush portion so as to oscillate
the brush portion in constant oscillation amplitude. However, due
to the external load applied by the brush portion, it is difficult
for the motor to produce high-speed rotations. Further, this
electric toothbrush consumes much power.
[0005] In the electric toothbrush of the '099 electric toothbrush,
the eccentric shaft is rotated to generate oscillations so as to
produce high-speed rotations. However, as the power supply voltage
decreases, the oscillation amplitude of the brush portion decreases
and lowers the brushing performance.
[0006] It is an object of the present invention to provide an
electric toothbrush that produces high-speed rotations with a motor
and always moves the brush portion in constant oscillation
amplitude even when the power supply voltage decreases.
[0007] One aspect of the present invention is an electric
toothbrush provided with a brush portion, a motor including a
rotary shaft, a battery which supplies the motor with power supply
voltage, and an eccentric shaft which rotates together with the
rotary shaft. The eccentric shaft has a center of gravity located
at a position deviated from an axis of the rotary shaft of the
motor. An oscillation transmission mechanism transmits oscillations
generated by the rotation of the eccentric shaft to the brush
portion. An oscillation amplitude regulation circuit regulates an
oscillation amplitude of the brush portion to be constant
regardless of changes in the power supply voltage in a state in
which the brush portion is free from external loads.
[0008] Other aspects and advantages of the present invention will
become apparent from the following description, taken in
conjunction with the accompanying drawings, illustrating by way of
example the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The invention, together with objects and advantages thereof,
may best be understood by reference to the following description of
the presently preferred embodiments together with the accompanying
drawings in which:
[0010] FIG. 1(a) is a cross-sectional side view and FIG. 1(b) is a
cross-sectional plan view, each showing a first embodiment of an
electric toothbrush;
[0011] FIG. 2 is a block diagram of the electric toothbrush shown
in FIG. 1;
[0012] FIG. 3 is a graph showing the relationship between the
oscillation amplitude of a brush portion, the power supply voltage,
and the rotation speed of a motor;
[0013] FIGS. 4(a) to 4(c) are timing charts showing the
relationship between the time power supply voltage is supplied and
the rotation speed of the motor;
[0014] FIG. 5 is a block diagram of a second embodiment of an
electric toothbrush;
[0015] FIG. 6 is a block diagram of a third embodiment of an
electric toothbrush; and
[0016] FIG. 7 is a block diagram of a fourth embodiment of an
electric toothbrush.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0017] A first embodiment of an electric toothbrush according to
the present invention will now be discussed.
[0018] Referring to FIG. 1, an electric toothbrush 10 includes a
grip, or case 11, and a brush unit 12, which is detachably attached
to the distal end of the case 11. The case 11 may be elongated and
cylindrical. The case 11 accommodates a motor 13 and a battery 20,
which supplies power supply voltage. A switch button 14 arranged on
the case 11 is used to switch the motor 13 ON and OFF.
[0019] The motor 13 includes a rotary shaft 13a, which extends
toward the distal end of the case 11 in the longitudinal direction
of the case 11. An eccentric shaft 15 is attached to the rotary
shaft 13a. The eccentric shaft 15 includes an elongated main shaft
body 15a and a weight 15b, the center of gravity of which is
deviated in the radial direction from the axis of the rotary shaft
13a. The weight 15b is attached to the distal end of the main shaft
body 15a.
[0020] The eccentric shaft 15 is enclosed in an oscillation
transmission member 16, which functions as an oscillation
transmission mechanism. The oscillation transmission member 16 is
fixed to the case 11 via a vibration suppression member, or
resilient damper 17. The eccentric shaft 15 has a distal end
rotatably supported by a bearing 16a formed in the oscillation
transmission member 16. Rotation of the eccentric shaft 15
oscillates the oscillation transmission member 16 relative to the
case 11.
[0021] The oscillation transmission member 16 is enclosed in the
brush unit 12. The brush unit 12 includes a tube 18, in which the
oscillation transmission member 16 is arranged, and a brush portion
19, which is fixed to the distal end of the tube 18. The brush unit
12 is a consumable product and detachable from the oscillation
transmission member 16 to enable replacement. Oscillation of the
oscillation transmission member 16 oscillates the brush portion 19.
A user holds the case 11, switches the power ON, and brushes his or
her teeth with the oscillating brush portion 19 to clean the teeth.
The oscillation amplitude S of the brush portion 19 is shown by the
double-headed arrow in FIG. 1(b).
[0022] An electrical circuit for oscillating the brush unit 12 will
now be discussed.
[0023] As shown in FIG. 2, the motor 13 is connected to a
transistor 21, which serves as a switch element. A terminal of the
motor 13 may be connected to the positive terminal of a battery 20
and another terminal of the motor 13 may be connected to the
collector terminal of the transistor 21. The emitter terminal of
the transistor 21 is connected to the negative terminal of the
battery 20. Thus, the motor 13 is connected in series with the
battery 20 via the transistor 21. When the base terminal of the
transistor 21 is provided with a voltage signal (flow of current),
the motor 13 is supplied with power supply voltage from the battery
20.
[0024] The battery 20 is connected to a power supply circuit 22.
The power supply circuit 22 may include a booster circuit, which
increases the power supply voltage from the battery 20. Further,
the power supply circuit 22 is connected to a control unit 23,
which functions as an oscillation amplitude regulation circuit. The
control unit 23 detects the power supply voltage supplied to the
motor 13 from the battery 20.
[0025] The control unit 23 is connected to the base terminal of the
transistor 21. Based on the value of the detected power supply
voltage from the battery 20, the control unit provides the base
terminal with a predetermined voltage signal to switch ON and OFF
the transistor 21 (duty-control). That is, the control unit 23
outputs a voltage signal over pulse duration periods that are based
on the value of the detected power supply voltage from the battery
20. This supplies the motor 13 with the power supply voltage from
the battery 20 in pulses of a pulse duration period that is based
on the value of the power supply voltage and thereby produces
rotation with the motor 13. Such a process will now be discussed in
further detail.
[0026] Referring to FIG. 3, the oscillation amplitude S of the
brush portion 19 usually decreases as the power supply voltage
supplied to the motor 13 increases, and the oscillation amplitude S
increases as the power supply voltage decreases. Further, the
rotation speed of the motor 13 usually increases as the power
supply voltage supplied to the motor 13 increases, and the rotation
speed of the motor 13 decreases as the power supply voltage
supplied to the motor 13 decreases. Factors such as the length and
diameter of the eccentric shaft 15 and the heaviness of the weight
15b vary the relationship between the power supply voltage supplied
to the motor 13 and the rotation speed of the motor 13. For
example, the rotation speed of the motor 13 may decrease as the
power supply voltage increases. In other situation, the rotation
speed of the motor 13 may reach a peak when the power supply
voltage is intermediate. It is thus apparent that the oscillation
amplitude S of the brush portion 19 varies as the rotation speed of
the motor 13 varies. In the first embodiment, the oscillation
amplitude S of the brush portion 19 decreases as the rotation speed
of the motor 13 increases.
[0027] Based on the value of the detected power supply voltage from
the battery 20, the control unit 23 provides the base terminal of
the transistor 21 with pulses of a voltage signal (pulse signal),
which is generated to keep the rotation speed of the motor 13
constant. For example, when the value of the detected power supply
voltage from the battery 20 increases, the control unit 23 shortens
the pulse duration period during which the voltage signal is
provided. When the value of the detected power supply voltage from
the battery 20 decreases, the control unit 23 lengthens the pulse
duration period during which the voltage signal is provided.
[0028] In one example, pulse duration periods set to keep the
rotation speed of the motor 13 constant based on the value of the
power supply voltage from the battery 20 are stored beforehand in a
memory of the control unit 23. A pulse duration period PD is
illustrated in FIG. 4(a). The control unit 23 provides the base
terminal with a voltage signal over a pulse duration period
corresponding to the value of the detected power supply voltage
from the battery 20.
[0029] The motor 13 applies drive force to the rotary shaft 13a
over the pulse duration periods during which it is supplied with
power supply voltage. The interval is extremely short between the
pulse duration periods during which power supply voltage is
supplied. Thus, fluctuations in the rotation produced by the motor
13 are subtle and ignorable, and the rotation may be approximated
as rotation at a constant speed. When the pulse duration periods
during which the power supply voltage is supplied are relatively
short as shown in FIG. 4(a), the constant speed may be slightly
lower than when the motor 13 is continuously supplied with the
power supply voltage.
[0030] In the first embodiment, the control unit 23 function to
shorten the pulse duration period Pd during which the motor 13 is
supplied with power supply voltage (refer to FIG. 4(a)) as the
power supply voltage from the battery increases and lengthen the
pulse duration period Pd during which the motor 13 is supplied with
power supply voltage as the power supply voltage from the battery
decreases. This regulates the motor 13 to a constant rotation
speed. In this manner, the oscillation amplitude S of the brush
portion 19 is regulated to be constant. In the first embodiment,
the control unit 23 and the transistor 21 function as a pulse
generation circuit.
[0031] FIG. 4 shows the power supply voltage, which is supplied in
pulses, and the rotation speed of the motor 13. FIGS. 4(a), 4(b),
and 4(c) show situations in which the state of charge of the
battery (battery capacitance or remaining battery level) are
respectively high, intermediate, and low, for example, 100%, 50%,
and about 0%. The power supply voltage of the battery 20 in the
first embodiment is related to the state of charge of the battery
20.
[0032] The control unit 23, which is connected to the switch button
14, starts the motor 13 when the switch button 14 is switched ON.
The battery 20 may be connected to a charging circuit 24. In such a
case, the charging circuit 24 charges the battery 20 when the
charging circuit 24 is connected to an external power supply.
[0033] The first embodiment has the advantages described below.
[0034] (1) The oscillation amplitude regulation circuit detects the
value of the power supply voltage supplied from the battery 20 and
supplies the motor 13 with the power supply voltage in pulses of a
pulse duration period set in accordance with the value of the power
supply voltage. In one example, the oscillation amplitude
regulation circuit regulates the rotation speed of the motor 13 to
be constant by shortening the pulse duration period during which
the power supply voltage is supplied when the value of the detected
power supply voltage increases, and lengthening the pulse duration
period during which the power supply voltage is supplied when the
value of the detected power supply voltage decreases. Thus, the
oscillation amplitude regulation circuit regulates the oscillation
amplitude S of the brush portion 19 to keep it constant regardless
of changes in the power supply voltage of the battery 20. This
allows for the oscillation amplitude regulation circuit to produce
high-speed rotations with the motor 13, while regulating the
oscillation amplitude S of the brush portion 19 to always be
constant even when the power supply voltage decreases. Thus, even
when used for a long time, the brushing performance of the electric
toothbrush 10 is not lowered.
[0035] A second embodiment of the present invention will now be
discussed. Like or same reference numerals are given to those
components that are the same as the corresponding components of the
first embodiment. Such components will not be described below.
[0036] Referring to FIG. 5, the battery 20 is connected via the
switch button 14 to a constant voltage circuit 31, which functions
as an oscillation amplitude regulation circuit. When the switch
button 14 is switched ON, the constant voltage circuit 31 is
supplied with power supply voltage from the battery 20. When the
switch button 14 is switched OFF, the supply of power supply
voltage to the constant voltage circuit 31 is stopped (cut).
[0037] The constant voltage circuit 31 is connected to the motor
13. The constant voltage circuit 31 converts the power supply
voltage supplied from the battery 20 into a predetermined constant
voltage and supplies the motor 13 with the constant voltage. The
constant voltage supplied from the constant voltage circuit 31
rotates the rotary shaft 13a of the motor 13.
[0038] In the second embodiment, the constant voltage circuit 31
converts the power supply voltage to voltage C (constant voltage),
which is shown in FIG. 3. The voltage C is predetermined as a value
that is lower than the maximum value A of the power supply voltage
and drives the motor 13 at a rotation speed that is high and
satisfactory. This allows for the motor 13 to produce high-speed
rotations. When the value of the power supply voltage supplied from
the battery 20 is higher than the voltage C, the constant voltage
circuit 31 converts (lowers) the power supply voltage to the
voltage C. When the value of the power supply voltage supplied from
the battery 20 decreases to the voltage C or lower, the constant
voltage circuit 31 converts (increases) the power supply voltage to
the voltage C. This regulates the oscillation amplitude S of the
brush portion 19 to be constant regardless of the decrease in the
power supply voltage of the battery 20.
[0039] The second embodiment has the same advantages as the first
embodiment.
[0040] A third embodiment of the present invention will now be
discussed.
[0041] Referring to FIG. 6, the motor 13 has one terminal connected
to the positive terminal of the battery 20 and another terminal
connected to the collector terminal of the transistor 21. The
emitter terminal of the transistor 21 is connected to the negative
terminal of the battery 20.
[0042] The battery 20 is connected to the power supply circuit 22.
The power supply circuit 22 is connected to the control unit 23,
which includes a CPU and a RAM. The power supply circuit 22
supplies the control unit 23 with drive voltage that is suitable
for driving the control unit 23. The control unit 23 is connected
to the battery 20 and detects the power supply voltage supplied
from the battery 20 to the motor 13. A rotation speed detection
circuit 41 is connected to the control unit 23 to detect the
rotation speed of the motor 13. This allows for the control unit 23
to detect the rotation speed of the motor 13.
[0043] Based on both the value of the detected power supply voltage
from the battery 20 and the rotation speed of the motor 13, the
control unit 23 provides the base terminal of the transistor 21
with a predetermined voltage signal to switch ON and OFF the
transistor 21. This will now be described in further detail.
[0044] The control unit 23 provides the base terminal of the
transistor 21 with a voltage signal over a pulse duration period
that is in accordance with both the value of the detected power
supply voltage from the battery 20 and the rotation speed of the
motor 13. This supplies the motor 13 with the power supply voltage
from the battery 20 in pulses of a pulse duration period that is in
accordance with both the value of the detected power supply voltage
from the battery 20 and the rotation speed of the motor 13 and
thereby produces rotation with the motor 13.
[0045] In one example, pulse duration periods set to keep the
rotation speed of the motor 13 constant in accordance with both the
value of the detected power supply voltage from the battery 20 and
the rotation speed of the motor 13 are stored beforehand in a
memory of the control unit 23. The control unit 23 provides the
base terminal with a voltage signal over a pulse duration period
corresponding to both the value of the detected power supply
voltage from the battery 20 and the rotation speed of the motor 13.
This supplies the motor 13 with the power supply voltage from the
battery 20 in pulses. The motor 13 applies a drive force to the
rotary shaft 13a over the pulse duration period during which it is
supplied with power supply voltage. The interval is extremely short
between the pulse duration periods during which power supply
voltage is supplied. Thus, fluctuations in the rotation produced by
the motor 13 are subtle and ignorable, and the rotation may be
approximated as rotation at a constant speed.
[0046] In the third embodiment, the control unit 23 shortens the
pulse duration period during which the motor 13 is driven when the
value of the power supply voltage from the battery 20 is high.
Further, the control unit 23 lengthens the pulse duration period
during which the motor 13 is driven when the value of the power
supply voltage from the battery 20 is low. When the rotation speed
of the motor 13 becomes lower than a predetermined rotation speed,
the control unit 23 lengthens (prolongs) the pulse duration period
during which the motor 13 is driven. This regulates the rotation
speed of the motor 13 to be constant even when the power supply
voltage of the battery 20 decreases or when an external load
applied to the brush portion 19 impedes the rotation of the rotary
shaft 13a. As a result, the oscillation amplitude S of the brush
portion 19 is regulated to be constant.
[0047] As discussed above in detail, in addition to the advantages
of the first embodiment, the third embodiment has the advantages
described below.
[0048] (2) The oscillation amplitude regulation circuit supplies
the motor 13 with the power supply voltage in pulses of a pulse
duration period set in accordance with the value of the power
supply voltage from the battery 20 and the rotation speed of the
motor 13 detected by the rotation speed detection circuit 41. Thus,
the brush portion 19 always continuously moves in constant
oscillation amplitude even when the external load applied to the
brush portion 19 lowers the rotation speed of the motor 13. This
prevents the brushing performance of the electric toothbrush 10
from being lowered during use. Further, the power supply voltage of
the battery 20 is used without undergoing any conversions. This
suppresses unnecessary drainage of the battery 20 and prolongs the
life of the battery 20.
[0049] A fourth embodiment of the present invention will now be
discussed.
[0050] Referring to FIG. 7, the motor 13 has one terminal connected
to the positive terminal of the battery 20 and another terminal
connected to the collector terminal of the transistor 21. The
emitter terminal of the transistor 21 is connected to the negative
terminal of the battery 20.
[0051] The battery 20 is connected to the power supply circuit 22.
The power supply circuit 22 is connected to the control unit 23,
which functions as the oscillation amplitude regulation circuit.
The control unit 23 includes a CPU and a RAM. The power supply
circuit 22 supplies the control unit 23 with drive voltage that is
suitable for driving the control unit 23. The control unit 23 is
connected to the battery 20 and detects the power supply voltage
supplied from the battery 20 to the motor 13. A load current
detection circuit 51 is connected to the control unit 23 to detect
the current flowing to the motor 13. This allows for the control
unit 23 to detect the load current of the motor 13.
[0052] Based on both the value of the detected power supply voltage
from the battery 20 and the load current of the motor 13, the
control unit 23 provides the base terminal of the transistor 21
with a predetermined voltage signal to switch ON and OFF the
transistor 21. This will now be described in further detail.
[0053] Duration periods set to keep the rotation speed of the motor
13 constant in accordance with both the value of the power supply
voltage from the battery 20 and the load current of the motor 13
are stored beforehand in a memory of the control unit 23. The
control unit 23 provides the base terminal with a voltage signal
over a pulse duration period corresponding to both the value of the
detected power supply voltage from the battery 20 and the load
current of the motor 13. This supplies the motor 13 with the power
supply voltage from the battery 20 in pulses. The motor 13 applies
a drive force to the rotary shaft 13a over the pulse duration
periods during which it is supplied with power supply voltage. The
interval is extremely short between the pulse duration periods
during which power supply voltage is supplied. Thus, fluctuations
in the rotation produced by the motor 13 are subtle and ignorable,
and the rotation may be approximated as rotation at a constant
speed.
[0054] In the fourth embodiment, the control unit 23 shortens the
pulse duration periods during which the motor 13 is driven when the
value of the power supply voltage from the battery 20 is high.
Further, the control unit 23 lengthens the pulse duration periods
during which the motor 13 is driven when the power supply voltage
is low. Extensions are set beforehand for the pulse duration
periods during which the motor 13 is driven in accordance with the
load current of the motor 13 and stored, for example, the memory of
the control unit 23. This regulates the rotation speed of the motor
13 to be constant even when the power supply voltage of the battery
20 decreases or when an external load applied to the brush portion
19 impedes the rotation of the rotary shaft 13a. As a result, the
oscillation amplitude S of the brush portion 19 is regulated to be
constant.
[0055] As discussed above in detail, in addition to the advantages
of the first embodiment, the fourth embodiment has the advantages
described below.
[0056] (3) The oscillation amplitude regulation circuit detects the
value of the power supply voltage supplied from the battery 20 and
supplies the motor 13 with the power supply voltage in pulses of a
pulse duration period set beforehand in accordance with the load
current of the motor 13 detected by the load current detection
circuit 51. Thus, the brush portion 19 always continuously moves in
constant oscillation amplitude even when external load is applied
to the brush portion 19. This prevents the brushing performance of
the electric toothbrush 10 from being lowered during use. Further,
the power supply voltage of the battery 20 is used without
undergoing any conversions. This suppresses unnecessary drainage of
the battery 20 and prolongs the life of the battery 20.
[0057] It should be apparent to those skilled in the art that the
present invention may be embodied in many other specific forms
without departing from the spirit or scope of the invention.
Particularly, it should be understood that the present invention
may be embodied in the following forms.
[0058] In the second and third embodiments, the oscillation
amplitude regulation circuit detects the rotation speed or load
current of the motor 13, measures the external load applied to the
motor 13, and varies (prolongs) the pulse duration periods during
which power supply voltage is supplied in accordance with the
measured external load. Instead of the rotation speed or load
current, the oscillation amplitude regulation circuit detects back
electromotive force. More specifically, if a external load is
produced, the oscillation amplitude regulation circuit may detect
the back electromotive force generated when the motor 13 is not
supplied with power supply voltage, measure the external load
applied to the motor 13, and vary (prolong) the pulse duration
periods during which power supply voltage is supplied in accordance
with the value of the measured back electromotive force.
[0059] The present examples and embodiments are to be considered as
illustrative and not restrictive, and the invention is not to be
limited to the details given herein, but may be modified within the
scope and equivalence of the appended claims.
* * * * *