U.S. patent number 3,631,556 [Application Number 04/879,844] was granted by the patent office on 1972-01-04 for automatic toothbrush.
This patent grant is currently assigned to U.S. Philips Corporation. Invention is credited to Peter Leendert Holster, Cornelis Johannes Theresia Potters, Hendricus Franciscus Gerardus Smulders.
United States Patent |
3,631,556 |
Holster , et al. |
January 4, 1972 |
AUTOMATIC TOOTHBRUSH
Abstract
An automatic fluid-powered toothbrush provided with a fluid
vibrator motor having a power chamber with a movable wall such as a
piston or a membrane connected to the brush member for causing
vibrating movement thereof. At least one fluid port is arranged in
the fluid path, and a valve is arranged with each port for opening
and closing same. The closed or opened condition of each valve is
determined by a bistable fluid switch controlled by the fluid
pressure in the power chamber. The fluid switch may have a movable
switching component which acts as a valve body. An auxiliary
chamber is preferably provided in constant fluid communication with
the fluid supply aperture and also has a movable wall. The movable
walls of the power chamber and the auxiliary chambers are coupled
to one another for the transmission of movement to one another. The
chambers and passages may be arranged in a plurality of plates,
such as, of a plastic, which are stacked with rubber packing plates
between them, parts of which may act as a diaphragm-type movable
wall or as a valve body.
Inventors: |
Holster; Peter Leendert
(Emmasingel, Eindhoven, NL), Smulders; Hendricus
Franciscus Gerardus (Emmasingel, Eindhoven, NL),
Potters; Cornelis Johannes Theresia (Emmasingel, Eindhoven,
NL) |
Assignee: |
U.S. Philips Corporation (New
York, NY)
|
Family
ID: |
19805290 |
Appl.
No.: |
04/879,844 |
Filed: |
November 25, 1969 |
Foreign Application Priority Data
|
|
|
|
|
Nov 29, 1968 [NL] |
|
|
6817187 |
|
Current U.S.
Class: |
15/22.1; 91/468;
601/96; 601/141 |
Current CPC
Class: |
A61C
17/38 (20130101); A61C 17/34 (20130101) |
Current International
Class: |
A61C
17/16 (20060101); A61C 17/34 (20060101); A61C
17/38 (20060101); A46b 013/06 () |
Field of
Search: |
;15/22R,22A
;128/38,39,47,50,53,62A,65,66 ;91/468 ;60/51,52 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Roberts; Edward L.
Claims
What is claimed is:
1. A vibrating fluid-powered toothbrush comprising a handle, a
brush member detachably connected to said handle and arranged for
vibrating motion with respect thereto, a fluid vibrator motor
housed within said handle for driving said brush, said motor
comprising a power chamber, a movable wall bounding one side of
said chamber, fluid-supply port for supplying fluid under pressure
to said handle, a fluid-discharge port for discharging fluid from
said toothbrush, a fluid path connecting said supply port to the
chamber of said motor and the chamber with said discharge port, a
first primary port arranged in the fluid path, a bistable fluid
switch the operation of which being activated by the pressure
prevailing in said power chamber, a valve arranged for opening and
closing said primary port, said switch arranged for controlling the
operation of said valve, and means connecting said movable wall to
said brush for causing oscillatory vibrating motion thereof.
2. The vibrating fluid-powered toothbrush according to claim 1
wherein said bistable fluid switch comprises a movable switching
member adapted to move under the influence of fluid pressure forces
and further comprising at least one stop for said switching member,
at least one passage terminating in said stop forming a switch port
arranged to be closed by said switching member, said fluid pressure
forces acting on at least a first projected area (F.sub.1) of said
switching member, substantially constant fluid pressure
continuously acting on said first projected area, said fluid
pressure forces also acting on a second projected area (F.sub.2)
located opposite said first projected area and being continuously
influenced by the fluid pressure in said chamber, and upon a third
projected area (F.sub.3), which in one position of the fluid switch
is subjected either to at east substantially the same fluid
pressure as is exerted on said first projected area, in which case
it is located on the same side of said first projected area, or to
at least substantially the same fluid pressure as is exerted on
said second projected area, in which case, it is located on the
same side thereof, and in the other position of the fluid switch is
subjected to the fluid pressure in a space being in fluid
communication with a fluid discharge aperture.
3. The vibrating fluid-powered toothbrush according to claim 2
wherein said switch port is a primary port.
4. The vibrating fluid-powered toothbrush according to claim 3
further comprising two stops arranged in said bistable switch for
said switching member and wherein said second projected area is
greater than the sum of said first and third projected areas, and
wherein said third projected area is located on the same side of
said switching member as is said first projected area.
5. The vibrating fluid-powered toothbrush according to claim 4
further comprising a fluid passageway in said stops of said
bistable switch, one of said stops being located upstream in the
fluid path with respect to said power chamber and the other stop
being located downstream with respect thereto, the terminating
orifice of the passageway in the stop located upstream being in
fluid communication with a supply aperture and having an area equal
to said first projected area, and the terminating orifice of the
passageway in the stop located downstream forming a primary port in
the fluid discharge path of the power chamber.
6. The vibrating fluid-powered toothbrush according to claim 5
further comprising an auxiliary chamber in fluid communication with
the fluid supply port and having a movable wall with a projected
area less than the projected area of the movable wall of said power
chamber, means coupling the movable wall of said auxiliary chamber
with the movable wall of said power chamber for transferring
movement of one to the other, and a pair of stops arranged for
limiting the movement of the coupled pair of movable walls.
7. The vibrating fluid-powered toothbrush according to claim 6
wherein the projected area of the movable wall of the auxiliary
chamber is approximately one-half of the projected area of the
movable wall of the power chamber.
8. The vibrating fluid-powered toothbrush according to claim 6
wherein the chambers and passages of the fluid vibrator motor are
defined within a plurality of stacked plates in local relative
fluid communication and otherwise insulated for fluid from one
another and are made of a material impermeable to fluid, and
wherein the movable walls of said power chamber and of said
auxiliary chamber are formed by resilient diaphragms which are
impermeable to fluid, and wherein said switch member of the
bistable fluid switch is disposed between two such diaphragms.
Description
The invention relates generally to an automatic toothbrush and more
particularly to such a toothbrush provided with a fluid vibrator
motor having at least one chamber which acts as a power chamber
having a movable wall.
U.S. Pat. No. 3,213,471 describes an automatic toothbrush of this
kind which is equipped with a water vibrator motor. The appliance
can be connected to the water supply mains by means of a hose; the
energy required for the brushing action is supplied by the
pressurized water of the water supply mains. The vibrator motor
comprises a fluid oscillator of the type in which a fluid flow can
be switched from one state to the other under the sole action of
the fluid itself. The fluid oscillator is provided with two output
ducts of which one is connected to the power chamber and the other
to the discharge port of the motor. Switching the fluid flow back
and forth is effected by means of two control jets which each are
tapped from the main flow in the output ducts by way of a feedback
duct having a given resistance value and a given fluid capacity.
The frequency of the oscillator depends upon its geometry and upon
the pressure and the density of the fluid supplied.
A characteristic of this known automatic toothbrush is that the
fluid oscillator will have a high frequency. This is due to the
fact that the frequency of the oscillator is determined by the
velocity at which the fluid signal propagates in the feedback
passage, which velocity in a first approximation is equal to the
velocity of sound in the respective fluid, in this case water.
Hence, pressure pulses of very short duration are applied to the
power chamber, and during these short periods only small amounts of
water can flow to the power chamber.
It is an object of the invention to obviate this characteristic and
the invention is characterized in that in the part of the fluid
trajectory from a fluid supply port through the power chamber to a
fluid discharge port, along which part the fluid always flows in
substantially the same direction during the operation of the fluid
vibrator motor, at least one primary port is located which is
adapted to be closed under the influence of a bistable fluid switch
arranged to be controlled by the fluid pressure in the power
chamber.
The term "primary port" is used herein to means any port which is
disposed in the above-mentioned part of the trajectory of what
might be termed the main flow of the fluid through the motor.
The expression "a bistable fluid switch arranged to be controlled
by the fluid pressure in the working chamber" is to be understood
to mean: a device operating solely with fluid as the energy medium
and as the information-carrying medium, the input signal to which
device is the fluid pressure in the power chamber or another
pressure directly related thereto, which device provides one or
more output signals in the form of a fluid pressure or a
displacement, which output signals can have only two values, which
correspond to a logical 0 or a logical 1, the invention further
having the property that switching takes place solely if the input
signal either exceeds a high limit or falls below a low limit, the
switching action on the high limit being exceeded taking place only
if the preceding switching of the switch was due to the signal
falling below the low limit, and conversely the switching action on
the signal falling below the low limit taking place only if the
preceding switching of the switch was due to the high limit being
exceeded.
It should be remarked here that for a clear understanding of the
fluid vibrator motor in the automatic toothbrush according to the
invention it should be kept in mind that each fluid passage has a
certain resistance value, the shape and the dimensions of the flow
channel being two of the factors determining this value. In the
description hereinafter, when the term "a fluid resistance" is
used, it is not intended to mean a distinct component part which
acts as such a resistance.
In the automatic toothbrush according to the invention, the fluid
pressure in the power chamber of the fluid vibrator motor will vary
between limits which are determined by the static characteristic of
the bistable fluid switch, which limits obviously must lie between
the pressures under which the fluid is supplied to the motor and
discharged from the motor, but which otherwise may be freely
chosen. By widely spacing these limits a comparatively large power
can be generated in the working chamber.
Bistable fluid switches suited for use in the fluid vibrator motor
of the automatic toothbrush according to the invention may be
designed in a variety of manners and may consist or be composed of
commercially available fluidic elements. An embodiment of the
invention which is highly suitable for the intended use is
characterized in that the bistable fluid switch includes a
switching member arranged to be moved under the influence of fluid
pressure forces and at least one stop for the switching member, in
which stop at least one passage terminates, the orifice of which is
a switching port adapted to be closed by the switching member, the
said fluid pressure forces acting at least on a projected area
F.sub.1 which is continuously influenced by an at least
substantially constant fluid pressure, on a projected area F.sub.2
located opposite F.sub.1 and continuously influenced by the fluid
pressure in the power chamber, and on a projected area F.sub.3
which in one position of the fluid switch is influenced either by
at least substantially the same fluid pressure as is F.sub.1 and
then lies on the same side as F.sub.1 or by at least substantially
the same fluid pressure as is F.sub.2 and then lies on the same
side as F.sub.2, and in the other position of the fluid switch is
influenced by the fluid pressure in a space which is in fluid
connection with a fluid discharge aperture.
The automatic toothbrush can be compactly and simply built if
according to a further embodiment the or each switching port also
is a primary port.
One of the advantage of a still further embodiment of the invention
is that the fluid switch is operated by the sole influence of fluid
pressure forces, and this embodiment is characterized in that two
stops are provided one on each side of the switching member, that
F.sub.2 is greater than the sum of F.sub.1 and F.sub.3 and that
F.sub.3 lies on the same side as F.sub.1.
In the water vibrator motor of the known automatic toothbrush
one-half of the water supplied is directly discharged through one
of the output passages of the fluid oscillator, namely through the
passage leading to the discharge aperture. In the automatic
toothbrush according to the invention an important saving in the
consumption of fluid is obtainable, and also the bistable fluid
switch can be given a very simple form, if according to a preferred
embodiment of the invention there terminates in each of the stops a
passage, the orifice in the stop situated upstream with respect to
the power chamber being in fluid communication with a fluid supply
aperture, and having a projected area F.sub.1, and the orifice in
the stop situated downstream with respect to the power chamber
forming a primary port in the fluid discharge trajectory of the
working chamber.
In the above-mentioned known automatic toothbrush, during the time
in which the power chamber is emptied the diaphragm constituting
the movable wall of the working chamber is moved by a relaxing
compression spring. This spring will have to exert a comparatively
large force, since otherwise during the emptying period of the
power chamber insufficient energy will be delivered to move the
brush over the teeth. Further, the force exerted by the spring must
show no large variations over the distance travelled by the
diaphragm, so that the spring must have a comparatively level
characteristic. The said requirements cannot readily be satisfied
by a conventional spring in the restricted space available in an
automatic toothbrush.
An embodiment of the invention obviates this difficulty and is
characterized in that the fluid vibrator motor has an auxiliary
chamber which is in fluid communication with a fluid supply
aperture and has a movable wall having a projected area smaller
than that of the power chamber, and in that the movable walls of
the power chamber and of the auxiliary chamber are coupled to one
another for transferring movements to one another, the movements of
the coupled pair of movable walls being limited by stops.
In this embodiment the movable wall of the power chamber is moved
in both directions under the influence of fluid pressure forces
only. Since the fluid pressure in the auxiliary chamber is equal to
that of the fluid supplied to the fluid motor, which latter
pressure usually will be constant, for example will be equal to the
water-supply mains pressure, the auxiliary chamber performs the
function of a spring having a perfectly level characteristic. The
stops for the coupled pair of movable walls are necessary in order
to obtain fluid pressure variations in the power chamber which are
required for controlling the bistable fluid switch. Important
additional advantages are that the variation in time of the fluid
pressure in the power chamber may closely approximate to the square
wave shape desired for generating a high power in the available
space, that it is readily possible to cause the movable walls to
make a comparatively large stroke, and that variations in the fluid
supply pressure do not affect the symmetrical operation of the
motor. In view of the fact that the water-supply pressure may
differ by several atmospheres from town to town, the last of the
above properties can be regarded as important in automatic
toothbrushes having water vibrator motors.
An automatic toothbrush of the said kind capable of delivering a
maximum force which is independent of the direction of movement of
the brush, is characterized in that the movable wall of the
auxiliary chamber of the fluid vibrator motor has a projected area
which is substantially one-half of that of the movable wall of the
power chamber.
An embodiment which is attractive specifically in view of mass
production of the automatic toothbrush is characterized in that the
chambers and the passages of the fluid vibrator motor are formed in
a number of stacked plates which locally are in fluid communication
with one another but otherwise are insulated from one another with
respect to fluid, in that the said movable walls are in the form of
resilient fluid-impermeable diaphragms, and in that the switching
member of the bistable fluid switch is disposed between two such
diaphragms.
The invention will now be described more fully with reference to a
number of embodiments, given by way of example only, and to the
partly schematic drawings, in which:
FIG. 1 is a schematic side elevation of an automatic toothbrush
according to the invention equipped with a water vibrator
motor,
FIG. 2 is a graph showing the variation of the pressure in the
power chamber of the water vibrator motor of the automatic
toothbrush shown in FIG. 1 without an external load,
FIG. 3 schematically shows a bistable water switch,
FIG. 4 shows the locations of the areas F.sub.1, F.sub.2 and
F.sub.3 in the switching member of the water switch of FIG. 3,
FIG. 5 shows the static characteristic of the water switch of FIG.
3,
FIG. 6 is a schematic diagram of a water vibrator motor in which
the water switch of FIG. 3 is used,
FIG. 7 is a modified embodiment of the schematic diagram of FIG. 6
employing a water switch which is operated solely by the influence
of water pressure forces,
FIG. 8 shows the static characteristic of the water switch used in
the motor of FIG. 7,
FIG. 9 is a schematic diagram of a water vibrator motor having two
primary ports and an auxiliary chamber,
FIG. 10 is a graph of the variation of the pressure in the power
chamber of the symmetrically loaded water vibrator motor shown in
FIG. 9, and finally,
FIG. 11 shows a practical embodiment of the automatic toothbrush of
FIG. 1 in part top plan view and part cross-sectional view.
An automatic toothbrush 1 shown schematically in FIG. 1 has a part
2 which serves as the handle and on which, as is usual in automatic
toothbrushes, a brush 3 proper is removably provided. The automatic
toothbrush shown is intended to be driven by water from the
water-supply mains and for this purpose it is provided with a
water-supply hose 4 and a water-discharge hose 5. For the sake of
clarity, in the drawing the direction of flow of the water towards
the toothbrush and that away from it are indicated by arrows.
A water piston motor is shown schematically in the handle 2. A
power chamber 6 has a movable wall in the form of a piston 7 which
is connected to a connecting rod 8. The motor has a single primary
port in a stop valve shown symbolically by 9. The primary port can
be closed under the influence of a bistable water switch 10 which
is controllable by the water pressure in the power chamber and is
shown symbolically as a rectangle enclosing its static
characteristic. Broken lines 11 and 12 represent the input and
output signals, respectively, of the water switch 10. The piston 7
is unilaterally loaded by a compression spring 13. Water
resistances are symbolically shown at 14 and 15. The connecting rod
8 through a crank pin 16 and an eccentric 17 drives a shaft 18
rotatably mounted in the handle 2, so that in operation the brush 3
is given an oscillating reciprocating movement.
The operation of the motor shown in FIG. 1 will be described more
fully with reference to the graph of the pressure variation in the
power chamber with unloaded motor (FIG. 2), time being plotted
along the horizontal axis and the pressure in the working chamber
along the vertical axis. At t.sub.1 a cycle begins; at this instant
the stop valve 9 is operated under the influence of the water
switch 10 so that the primary port opens and water can flow from
the supply hose 4 through the valve 9 and the resistance 14 to the
power chamber 6. However, simultaneously water from the power
chamber can flow through the resistance 15 to the discharge hose 5,
but the resistances 14 and 15 are chosen so that the pressure in
the power chamber 6 can rise in order to move the piston against
the force of the compression spring 13. The pressure in the power
chamber will continue to rise in accordance with the spring
characteristic of the spring 13 until at an instant t.sub.2 a
pressure is reached which is indicated by P.sub.b. At this instant
the switch 10 changes state and the valve 9 is operated so that the
primary port is closed. The water contained in the power chamber 6
now is expelled from this chamber by the spring 13 and flows away
to the atmosphere through the resistance 15 and the discharge hose
5. The piston 7 returns to its starting position, and the pressure
in the power chamber 6 falls until at an instant t.sub.3 the
pressure has fallen to a value shown by P.sub.o in the graph. At
this instant the bistable water switch 10 again changes state so
that the stop valve 9 is again operated, and the cycle is
repeated.
FIG. 3 shows schematically a bistable water switch 10 with its
connections. It comprises a switching member 19 and a stop 20 for
the switching member, a passage 21 terminating in this stop. The
orifice 22 of this passage can be closed by the switching member
19. The switching member 19 is arranged to move in the enclosure 23
and seals the spaces above and beneath it from one another. Above
the switching member 19 a compression spring 24 is disposed. A
passage 25 is connected to the power chamber 6. The space remaining
beneath the switching member 19 and around the stop 20 when the
switching member bears on the stop is connected to the discharge
hose 5 of the motor through passages 26 and 28 and consequently to
the atmosphere through resistances R.sub.1 and R.sub.2. These
resistances form a fluid pressure equivalent of an electric voltage
divider, passage 27 is connected between R.sub.1 and R.sub.2. The
water pressure in the passage 27 is the output signal of the switch
and is designated by p.sub.2 ; the pressure in the passage 21 is
equal to the pressure under which the water is supplied to the
motor, i.e., the supply pressure of the motor. This latter pressure
is designated by P.sub.v and may be regarded as constant in
practice. The pressure in the passage 25 is equal to the pressure
p.sub.a in the power chamber. The pressures in the passages 21 and
25 may alternatively be derived from p.sub.a and p.sub.v through
voltage fluid pressure dividers.
FIG. 4 shows that the area F.sub.1 on the lower surface of the
switching member 19 is equal to the projected area of the orifice
22 in the stop 20. F.sub.2 is the upper surface area of the
switching member 19 and F.sub.3 is the lower surface area decreased
by F.sub.1. Both in the condition in which the orifice 22 is closed
and in the condition in which it is open, the area F.sub.1 is
influenced by the supply pressure p.sub.v and hence is continuously
influenced by a constant fluid pressure. The area F.sub.2 is
continuously influenced by the water pressure in the power chamber
6, and the area F.sub.3 in the condition in which the orifice 22 is
not closed by the switch member 19 is influenced by the same or
substantially the same water pressure as is F.sub.1, namely the
supply pressure, and in the other condition is influenced by the
water pressure in the space around the stop 20 and under the switch
member 19, which space is connected to the water discharge hose 5
of the motor through the passages 26 and 28.
The operation of the water switch will now be discussed with
reference to the static characteristic shown in FIG. 5. In the
position shown in FIG. 1, i.e., the position in which the orifice
22 is not closed, there will be in the passage 27, assuming this
passage not to be loaded, a water pressure
The switch member 19 will only move downward when the pressure in
the power chamber has reached a value p.sub.b such that the
downward force p.sub.b F.sub.2 +K.sub.v, where K.sub.v is the force
of the spring, exceeds the upward force p.sub.v (F.sub.1 +F.sub.3).
In this case the switch member 19 is urged onto the stop 20,
whereupon F.sub.1 continues to be influenced by P.sub.v, but
F.sub.3 is influenced by the atmospheric pressure p.sub.at. Thus,
the upward force exerted on the switch member is reduced to the
value p.sub.v F.sub.1, and the switch member will only move again
when the pressure in the power chamber has fallen to so low a
pressure p.sub.o that the upward force p.sub.v F.sub.1 exceeds the
downward force p.sub.o F.sub.2 +K.sub.v.
In view of the small movements which the switch member 19 performs
in practice, in the above discussion K.sub.v has been assumed to be
constant and the pressures referred to are excess pressures above
atmospheric pressure.
The output signal p.sub.s of the water switch of FIG. 3 can be used
to energize the stop valve 9 (FIG. 1). Another possibility is to
use the movements of the switch member 19 for this purpose. FIG. 6
shows a use of the water switch of FIG. 3 which results in a very
compact and simple construction of the water motor in that the
switch port 22 is also used as a primary port. In FIG. 6,
corresponding passages have been designated by the same numerals as
in FIG. 3.
FIG. 7 shows the water motor of FIG. 6 with the difference that the
water switch 10 is not equipped with a compression spring 24, since
it is operated by the sole influence of water pressure forces.
Further, in addition to the stop 20 there is a second stop 29, and
F.sub.2, is greater than F.sub.1 +F.sub.3.
FIG. 8 shows the static characteristic of the water switch 10 of
FIG. 7, and just as in FIG. 5 p.sub.s is the water pressure in the
passage 26. Owing to the coupling of the passage 26 to the power
chamber 6 of the motor the extreme values of p.sub.s will be equal
to the extreme values p.sub.o and p.sub.b of the water pressure
p.sub.a in the power chamber. The width of the static
characteristic is shown in the drawing, namely
The pressures indicated are excess pressures above atmospheric
pressure. To generate a maximum power in the power chamber 6 the
water pressure in the power chamber must be variable within the
widest possible limits, so that F.sub.1 must be small. In FIG. 7 in
principle it would be possible to interchange the connection of the
passages 20 and 26 to the water switch 10, but it would than be
more difficult to make the area F.sub.1 small. Further it should be
noted that p.sub.b cannot be greater than
The passage 30 communicates with the atmosphere and serves to
conduct away any leakage water and to exhaust the air from the
space 31, which contributes to a short response time of the water
switch.
FIG. 9 shows a water motor which in several points differs from
that shown in FIG. 7. The stop 29 of the water switch 10 is
provided with a second primary port 32, which lies in the water
discharge trajectory of the power member. The primary ports 22 and
32 are alternately opened and closed by the switch member 19. The
advantage of the primary port 32 is that during the filling of the
power chamber 6 no water can directly flow from the supply hose 4
through the primary port 22 to the discharge hose 5; hence, the
water consumption is reduced. Further, the maximum water pressure
p.sub.b to be reached in the power chamber 6 is no longer
determined by the ratio between the water resistances R.sub.1 and
R.sub.2, but p.sub.b can now become equal to the supply pressure
p.sub.v, which means that a larger power can be generated in the
power chamber than is possible in the motor of FIG. 7. In addition,
the width of the static characteristic of the water switch can be
increased: when the projected area of the primary port 32 is
designated F.sub.4 the switching member 19 has two areas on its
upper surface, namely F.sub.2 and F.sub.4, F.sub.4 being influenced
by the water pressure in the power chamber when the switch part is
in its lower position, and by the atmospheric pressure when the
switch member is in its upper position. As a result, the lowest
water pressure p.sub.o to be achieved in the power chamber is
reduced to
Thus, it is found that, unlike F.sub.1, F.sub.4 need not be small;
hence, an interchange of the passages 25 and 33 in FIG. 2 does not
involve specific disadvantages.
In contradistinction to the water motor shown in FIG. 7, the water
motor of FIG. 9 is provided with an auxiliary space 34 which
through a passage 35 is connected to the water-supply hose, so that
the supply pressure p.sub.v permanently prevails in the auxiliary
chamber 34. The auxiliary chamber has a movable wall the projected
area of which is smaller than that of the power chamber 6 and is
equal to the area of the lower surface of the piston 7 less the
cross-sectional area of the connecting rod 8. Thus, in the case
shown both movable walls are constituted by the piston 7, so that
they are coupled to one another with respect to the transfer of
movements to one another. The movements of the piston 7 are limited
by two stops 36 and 37.
FIG. 10 shows the pressure variation in the power chamber of the
motor shown in FIG. 9. At the instant t.sub.1 the switch member 19
moves upwards so that substantially simultaneously the primary port
22 is opened and the primary port 32 is closed. The piston 7
remains pressed against the stop 36 until the water pressure has
sufficiently risen to move the piston against the load and against
the force exerted on the piston by the water in the auxiliary
chamber 34. At the instant t.sub.2 this pressure, which is
designated p.sub.ab, has been reached. It will be readily
appreciated that the time interval t.sub.1 -t.sub.2, inter alia
owing to the incompressibility of water, will be extremely short.
At the instant t.sub.2 the piston starts moving and, assuming the
load to be constant, the pressure in the power chamber will no
longer change until, at the instant t.sub.3, the piston engages the
stop 37. Thereupon the pressure will rise rapidly until at the
instant t.sub.4 the pressure p.sub.o is reached, to which the
bistable water switch 10 responds by changing its state. The
primary port 22 is closed and the primary port 32 is opened. The
piston 7 remains pressed against the stop 37 until the water
pressure in the power chamber has fallen to the value p.sub.ao, at
which pressure the water pressure in the auxiliary chamber 34 is
capable of moving the piston against the load and against the force
exerted on the piston by the water in the power chamber. The time
interval t.sub.3 -t.sub.5 also will be short. Again the pressure in
the power chamber remains constant, assuming the load to be
constant, until at the instant t.sub.6 the piston again strikes the
stop 36 and subsequently rapidly descends, until at the instant
t.sub.7 the value p.sub.o is reached, the water switch 10 again
changes state and the cycle is repeated. The time interval t.sub.6
-t.sub.7 also is short, so that compared with the total cycle time
t.sub.6 -t.sub.7 the time intervals during which the piston 7 does
not move and hence does no work are small. Consequently, the
pressure variation in the power chamber approximates to the square
wave form desired for a maximum generated power.
The connecting rod 8 of the motor of FIG. 9 has a cross-sectional
area such that the movable wall of the auxiliary chamber 34 has a
projected area which is substantially one-half of that of the
movable wall of the power chamber 6. Thus, the motor is capable of
delivering the same maximum power in both directions, which
naturally is important in an automatic toothbrush. This property of
the motor of FIG. 9 can also be found in FIG. 10; the graph of the
pressure variation in the power chamber has been pictured on the
assumption that the motor load is equal in both directions and is
nearly a maximum, in which case the pressures occurring in the
power chamber are p.sub.ab and p.sub.ao, which are situated
symmetrically with respect to the pressure 1/2(p.sub.b +p.sub.o),
which pressure can be made practically equal to 1/2p.sub.v.
A particular feature of the automatic toothbrush according to the
invention is that the water vibrator motor cannot be stopped by
externally restricting the movements of the movable wall of the
working chamber. If, for example, in the case of the motor of FIG.
9 an obstacle is placed in the path of the connecting rod 8, this
obstacle will only act as a stop, limiting the movements of the
movable wall, i.e., the piston 7. The motor will continue
operating, but with a shortened stroke and a shorter cycle time.
The motor can only be stopped by preventing all movement of the
piston 7.
FIG. 11 shows a practical embodiment of the toothbrush of FIG. 1 in
part top plan view, part cross-sectional view. The chambers and the
passages of the water vibrator motor have been formed in a number
of stacked plates 38 to 42, which are made of a water-impermeable
substance, i.e., a nonporous synthetic material, and are locally in
water communication with one another but otherwise are insulated
from one another. The movable walls of the power chamber 6 and of
the auxiliary chambers 34 are constituted by resilient
water-impermeable diaphragms which form part of water-insulating
rubber sheets 43 and 44. The switch member 19 also is disposed
between two such diaphragms.
The particular positioning of the power chamber 6 and the auxiliary
chamber 34 and the use of diaphragms result in an extremely compact
construction in which no sealing problems crop up. The piston 7,
which here does not have a connecting rod, directly drives the
brush 3 for which purpose the crank pin 16 can move in a
slot-shaped recess 45. Contrary to what is the case in FIG. 1, the
connections for the water supply hose and the water discharge hose,
which obviously may, if desired, by united to form a single hose,
are located within the handle 2; a plug-shaped connecting member
for the water-supply hose is indicated at 46.
It should be noted that the term "switch member" used so far must
be taken in a broad sense and includes embodiments in which the
space 31 does not contain a single discrete member 19 but, for
example, one or more members connected to the diaphragms or several
discrete members, and even embodiments in which the space 31 is
filled with a liquid or a gas.
FIG. 11 clearly shows that the water vibrator motor can readily be
accommodated in the handle 2 of the toothbrush and is
constructionally simple. It is important, especially in view of
mass production, that for satisfactory operation of the motor it
should not be necessary for the various components to be
manufactured within very close dimensional tolerances, and the
absence of this requirement will obviously reduce manufacturing
cost.
With an automatic toothbrush designed according to FIG. 11
satisfactory results were obtained; the frequency of the
oscillating movement of the brush 3 was about 25 Hz. and the force
generated at the brush was amply sufficient for thoroughly cleaning
the teeth. The dimensions of the handle were smaller than those of
some commercially available electric automatic toothbrushes.
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