U.S. patent application number 09/905953 was filed with the patent office on 2001-12-13 for control system for atomizing liquids with a piezoelectric vibrator.
Invention is credited to Denen, Dennis J..
Application Number | 20010050317 09/905953 |
Document ID | / |
Family ID | 22413112 |
Filed Date | 2001-12-13 |
United States Patent
Application |
20010050317 |
Kind Code |
A1 |
Denen, Dennis J. |
December 13, 2001 |
Control system for atomizing liquids with a piezoelectric
vibrator
Abstract
There is described a battery driven atomizer in which an
alternating voltage is applied to a piezoelectric actuation element
to cause it to expand and contract and vibrate an atomizing
membrane. The alternating voltage is controlled to produce a high
amplitude vibration during a first portion of a drive period, to
initiate atomization, and thereafter to produce a lower amplitude
vibration to sustain atomization during the remainder of the drive
period. The frequency of the alternating voltage is swept
repeatedly during each drive period.
Inventors: |
Denen, Dennis J.;
(Westerville, OH) |
Correspondence
Address: |
J. WILLIAM FRANK III
S.C. JOHNSON & SON INC.
1525 HOWE STREET MS 077
RACINE
WI
53404-2236
US
|
Family ID: |
22413112 |
Appl. No.: |
09/905953 |
Filed: |
July 17, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09905953 |
Jul 17, 2001 |
|
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09519560 |
Mar 6, 2000 |
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60124155 |
Mar 5, 1999 |
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Current U.S.
Class: |
239/102.1 ;
239/102.2; 239/142; 239/99 |
Current CPC
Class: |
B05B 17/0684 20130101;
B05B 17/0646 20130101; A01M 1/205 20130101; A61L 9/14 20130101 |
Class at
Publication: |
239/102.1 ;
239/102.2; 239/99; 239/142 |
International
Class: |
B05B 001/08 |
Claims
1. A drive circuit for a liquid atomizer in which a piezoelectric
actuator is coupled to an orifice plate to vibrate the plate to
atomize a liquid being supplied to one side of said plate, said
drive circuit comprising: a pair of terminals across which a
voltage is applied, and between which said piezoelectric actuator
is connected; an electronic switch also connected between said
terminals in parallel with said piezoelectric actuator, said
electronic switch being switchable between conducting and
non-conducting states; and a switch operating circuit connected to
switch said electronic switch between said conducting and
non-conducting states.
2. A drive circuit according to claim 1, wherein said switch is a
field effect transistor.
3. A drive circuit according to claim 1, wherein a coil is
connected in series with said piezoelectric actuator between said
terminals.
4. A drive circuit according to claim 3, wherein said switch is
connected in parallel with a portion of said coil and said
piezoelectric actuator.
5. A drive circuit according to claim 1, wherein said switch
operating circuit comprises an oscillator.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a division of Application No. 09/519,560 filed Mar.
6, 2000, which is a Continuation-in-Part of Provisional Application
No. 60/124,155 filed Mar. 5, 1999.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the invention
[0003] This invention relates to the atomization of liquids by
means of a piezoelectric vibrator and more specifically it concerns
novel methods and apparatus for controlling such atomization in an
efficient and effective manner.
[0004] The present invention also relates to means for the
distribution of a liquid active material, such as a perfume, air
freshener, insecticide formulation, or other material, in the form
of fine particles or droplets, as in a fine spray, by means of a
piezoelectric device. In particular, the invention is directed to a
piezoelectric liquid delivery system for production of droplets of
liquid, or liquid suspensions, by means of an electromechanical or
electroacoustical actuator. Even more specifically, the present
invention relates to an improved control circuit for use with such
devices.
[0005] 2. Description of the Related Art
[0006] The use of piezoelectric vibrators to atomize liquids is
well known; and examples of such devices are described in U.S. Pat.
Nos. 5,164,740, 4,632,311 and 4,533,082. In general, these devices
apply an alternating voltage to a piezoelectric element to cause it
to expand and contract. The piezoelectric element is coupled to a
perforated membrane, which in turn is in contact with a liquid
source. The expansion and contraction of the piezoelectric element
causes the membrane to vibrate up and down whereupon liquid is
driven into the membrane's perforations and is then thrown upwardly
in the form of a fine mist.
[0007] It is desired to provide a battery driven piezoelectric
atomizer which operates over a long period of time without
deterioration of its performance and which permits the use of
inexpensive alkaline batteries whose voltage output is known to
decrease over the operating life of the battery.
[0008] One way in which a piezoelectric atomizer can be driven
economically is to control it to operate during drive periods which
are separated by sleep periods, so that liquid becomes atomized
during the drive periods in successive short puffs. However, during
the sleep periods between puffs, liquid accumulates on the
membrane; and in order to start a successive puff at the next drive
period, the membrane must be driven at a large amplitude.
[0009] Another way in which a battery operated piezoelectric
atomizer can be operated economically is to drive it at the
resonant frequency of its vibrating system, which includes the
membrane, the piezoelectric element and any mechanical coupling
between the membrane and the element. A problem occurs, however,
because the resonant frequency may vary somewhat from device to
device so that a different driving frequency must be set for each
unit.
[0010] The distribution of liquids by formation of a fine spray, or
atomization, is well known. One method for such distribution is to
atomize a liquid by means of the acoustic vibration generated by an
ultrasonic piezoelectric vibrator. An example of such a method is
shown in U.S. Pat. No. 4,702,418, which discloses an aerosol
dispenser including a nozzle chamber for holding fluid to be
dispensed and a diaphragm forming at least a portion of the
chamber. An aerosol dispensing nozzle is disposed therein, with a
restrictive passage for introducing liquid from the reservoir to
the nozzle. A pulse generator in combination with a low voltage
power source is used to drive a piezoelectric bender, which drives
fluid from the reservoir through the nozzle to create an aerosol
spray.
[0011] Another atomizer spraying device is shown in U.S. Pat, No.
5,518,179, which teaches a, liquid droplet production apparatus
comprising a membrane which is vibrated by an actuator which has a
composite thin-walled structure, and is arranged to operate in a
bending mode. Liquid is supplied directly to a surface of the
membrane and sprayed therefrom in fine droplets upon vibration of
the membrane.
[0012] U.S. Pat. Nos. 5,297,734 and 5,657,926 teach ultrasonic
atomizing devices comprising piezoelectric vibrators with a
vibrating plate connected thereto.
[0013] In U.S. Pat. No. 5,297,734, the vibrating plate is described
as having a large number of minute holes therein for passage of the
liquid.
[0014] While a number of additional patents disclose means for the
dispersion of liquids by ultrasonic atomization, or for timed
intervals of dispersion, they have achieved only moderate success
in the efficient atomization of such materials as perfumes. See,
e.g., U.S. Pat. Nos. 3,543,122, 3,615,041, 4,479,609, 4,533,082,
and 4,790,479. The disclosures of these patents, and of all other
publications referred to herein, are incorporated by reference as
if fully set forth herein.
[0015] Such atomizers fail to provide an easily portable, battery
operated dispenser employing an orifice plate in mechanical
connection with a piezoelectric element, capable of long periods of
use with little or no variation in the delivery rate. Furthermore,
the efficiency of these atomizers may differ due to manufacturing
differences in the atomizer piezoelectric pump components. Thus, a
need exists for improved atomizers or dispensers for use in
distribution of active fluids such as fragrances and insecticides,
which atomizers are highly efficient and consume minimal electrical
power while providing wide dispersal of the liquid.
SUMMARY OF THE INVENTION
[0016] The present invention in is various aspects, overcomes the
above problems.
[0017] In one aspect, the present invention involves a novel method
for operating a vibratory liquid atomizer of the type in which a
membrane, to which liquid to be atomized is supplied, vibrates to
drive the liquid from its surface in the form of a mist. This novel
method includes the steps of initially vibrating the membrane at a
high amplitude to initiate atomization of the liquid: and
thereafter vibrating the membrane at a lower amplitude sufficient
to sustain the atomization.
[0018] In another aspect, the invention involves a novel method for
operating a piezoelectric vibratory liquid atomizer of the type in
which a piezoelectric actuating element is energized by an
alternating voltage to expand and contract and thereby to vibrate a
membrane, to which a liquid to be atomized is supplied, so that the
vibration of the membrane atomizes said liquid and ejects it from
the membrane in the form of a mist. This novel method comprises the
steps of first applying a high alternating voltage to said the
piezoelectric actuating element to cause it to vibrate the membrane
at a high amplitude to initiate atomization of the liquid; and
thereafter applying a lower alternating voltage to the
piezoelectric actuating element to sustain atomization.
[0019] In a further aspect the invention involves a novel vibratory
liquid atomizer which comprises a membrane, a liquid conduit which
is arranged to supply liquid to be atomized to the membrane, and a
vibration actuator connected to first vibrate the membrane during a
drive period at a high amplitude to initiate atomization of the
liquid and thereafter, during the same drive period, to vibrate the
membrane at a lower amplitude sufficient to sustain the
atomization.
[0020] In a still further aspect, the present invention involves a
novel vibratory liquid atomizer which comprises a membrane mounted
which is mounted to be vibrated, a liquid supply conduit arranged
to supply liquid to the membrane while it is vibrating, a
piezoelectric actuating element coupled to the membrane to cause it
to vibrate when the piezoelectric element expands and contracts,
and an electric power supply system connected to supply an
alternating voltage to the actuating element during a drive period
to cause it to expand and contract and thereby to vibrate the
membrane to atomize the liquid and eject it in the form of a mist.
The electric power supply system includes circuits which are
connected to first apply a high alternating voltage to said the
piezoelectric actuating-element to cause it to vibrate the membrane
at a high amplitude to initiate atomization of the liquid and
thereafter to apply a lower alternating voltage to the
piezoelectric actuating element to sustain atomization.
[0021] A primary purpose of the present invention is to provide, a
highly efficient method for dispensing such liquids as perfumes,
air fresheners, or other liquids. Such other liquids include
household cleaning materials, sanitizers, disinfectants,
repellents, insecticides, aroma therapy formulations, medicinals,
therapeutic liquids, or other liquids or liquid suspensions which
benefit from atomization for use. These compositions may be
aqueous, or comprise various solvents.
[0022] It is an object of the present invention to provide improved
control circuits for use with an easily portable, battery operated
dispenser employing a domed Orifice plate in mechanical connection
with a piezoelectric element. The piezoelectric pump is capable of
operating efficiently for months, on low voltage batteries, while
maintaining consistency of delivery throughout the period. A
piezoelectric atomizer is capable for use with such electrical
sources as 9 volt batteries, conventional dry cells such as "A",
"AA", "AAA", "C", and "D" cells, button cells, watch batteries, and
solar cells. The preferred energy sources for utilization in
combination with the present invention are "AA" and "AAA"
cells.
[0023] The piezoelectric pump has circuitry to compensate for
manufacturing differences in the pump components. The electronics
of such circuitry may be programmable, and may be used to set a
precise delivery rate (in milligrams per hour, hereinafter mg/hr).
Alternatively, the electronic circuitry may allow the consumer to
adjust intensity or effectiveness to a desired level for personal
preference, efficacy, or for room size.
[0024] In the preferred embodiment of the present invention, these
and other objects of this invention are achieved by an atomizer for
fragrances, insecticide formulations, and other liquids such as set
forth previously, wherein the atomization system includes a chamber
for the liquid to be dispensed, means to supply the liquid from
said chamber to an orifice plate for dispersal of the liquid, a
piezoelectric element, an energy source, and the improved circuitry
to drive and control the piezoelectric element. It has been found
that by controlling the amplitude and frequency of the signal
driving the piezoelectric element, superior results are attained.
The present invention thus provides a means for more uniform
atomization of the liquid to be dispensed throughout the total
period of dispersion, such that the amount dispersed per time unit
at the commencement of dispersion does not vary as greatly from the
amount dispersed near or at the finish of dispersion. These and
still other objects and advantages of the present invention will be
apparent from the description which follows, which is, however,
merely of the preferred embodiments. Thus, the claims should be
looked to in order to understand the full scope of the
invention.
[0025] The invention also involves other specific features which
are described hereinafter; and which in combination with the
foregoing features, provide additional advantages.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a sectional elevation view of an atomizing device
with the invention may be used;
[0027] FIG. 2 is a timing diagram showing the operation of the
device of FIG. 1 according to the invention;
[0028] FIG. 3 is a simplified block diagram showing the arrangement
of elements of a control system according to the present
invention;
[0029] FIG. 4 is a partial isometric view of a circuit board
suitable for use in a piezoelectric atomizer in accordance with a
preferred embodiment of the present invention;
[0030] FIG. 5 is an isometric view of a liquid container and liquid
transport means suitable to bring the liquid to the surface of the
orifice plate;
[0031] FIG. 6 is a cross sectional view showing the relationship of
the liquid container, a feed means, and the piezoelectric element
when assembled together;
[0032] FIG. 7 is a magnified detail of the area of FIG. 6 enclosed
within the circle.
[0033] FIG. 8 is a top view of the piezoelectric element and the
printed circuit board mounted on the chassis of a preferred
embodiment;
[0034] FIG. 9 illustrates a much simplified cross-sectional diagram
of a piezoelectric pump assembly suitable for use with a preferred
embodiment of the present invention;
[0035] FIG. 10 is a block diagram of a preferred control circuit
for driving the piezoelectric element;
[0036] FIG. 11 illustrates the details of the state machine in FIG.
10; and
[0037] FIG. 12 graphically depicts the modulation of the output
signal of the control circuit.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0038] FIG. 1 shows a vibratory atomizing device which may be
operated according to the present invention. This device comprises
an annularly shaped piezoelectric actuator 10 having a center hole
12 and a circular membrane 14 which extends across the hole 12 on
the underside of the actuator and slightly overlaps an inner region
15 of the actuator. The membrane 14 is fixed to the underside of
the actuator 10 in the overlap region 15. Any suitable cementing
means may be used to fix the member 14 to the piezoelectric element
10; however, in cases where the device may be used to atomize
liquids which are corrosive, it is preferred that the membrane be
soldered to the piezoelectric element.
[0039] The piezoelectric actuator 10 may be made from any material
having piezoelectric properties which cause it to change
dimensionally in a direction perpendicular to the direction of an
applied electric field. Thus in the illustrated embodiment, the
piezoelectric actuator 10 should expand or contract in a radial
direction when an electrical field is applied across its upper and
lower surfaces. The piezoelectric actuator 10 may, for example, be
a ceramic material made from a lead zirconate titanate (PZT) or
lead metaniobate (PN). In the embodiment illustrated herein, the
piezoelectric actuator has an outer diameter of about 0.382 inches
and a thickness of about 0.025 inches. The diameter of the center
hole 12 is about 0.177 inches. These dimensions are not critical
and they are given only by way of example.
[0040] The membrane 14 in the illustrated embodiment is about 0.250
inches in diameter and has a thickness of about 0.002 inches. The
membrane 14 is formed with a slightly domed center region 16 and a
surrounding flexible flange region 18 which extends between the
domed center region 16 and the region where the membrane is affixed
to the actuator 10. The domed center region 16 has a diameter of
about 0.103 inches and it extends out of the plane of the membrane
by about 0.0065 inches. The domed center region contains several
(for example 85) small perforations 20 which have a diameter of
about 0.000236 inches and which are spaced from each other by about
0.005 inches. A pair of diametrically opposed holes 22 are formed
in the flange region 18. These holes have a diameter of about 0.029
inches.
[0041] Again, these dimensions are not critical and only serve to
illustrate a particular embodiment.
[0042] It will be noted that the doming of the center region 16,
which contains the perforations 20, makes this region stiff so that
it does not bend during actuation, whereas the flange region 18,
which contains the holes 22, remains flexible so that it does bend
during actuation. While the domed center region is spherical in
configuration, any configuration which will maintain stiffness in
this region may be used. For example, the center region 16 may have
a parabolic or arcuate shape.
[0043] The membrane 14 is preferably made by electroforming with
the perforations 20 and the holes 22 being formed in the
electroforming process. However, the membrane may be made by other
processes such as rolling; and the perforations and holes may be
formed separately. For ease in manufacture, the center region 16 is
domed after the perforations 18 have been formed in the
membrane.
[0044] The membrane 14 is preferably made of nickel, although other
materials may be used, provided that they have sufficient strength
and flexibility to maintain the shape of the membrane while being
subjected to flexing forces. One such material is a
magnesium-zirconium alloy.
[0045] The piezoelectric actuator 10 may be supported in any
suitable way which will hold it in a given position and yet not
interfere with its vibration. thus, the actuator may be supported
in a grommet type mounting (not shown).
[0046] The piezoelectric element 10 is coated on its upper and
lower surfaces with an electrically conductive coating such as
aluminum. As shown, electrical leads 26 and 28 are soldered to the
electrically conductive coatings on the upper and lower surfaces of
the actuator 10. These leads extend from a source of alternating
voltages (not shown).
[0047] A liquid reservoir 30, which contains a liquid 31 to be
atomized, is mounted below the actuator 10 and membrane 14. A wick
32 extends up from within the reservoir to the underside of the
membrane 14 so that it lightly touches the membrane in the center
region 16 and so that it contacts the perforations 20. However, the
wick should not touch the holes 22 and these holes should be
laterally displaced from the wick. The wick 32 may be made of a
porous flexible material which provides good capillary action to
the liquid in the reservoir 30 so as to cause the liquid to be
pulled up to the underside of the membrane 14. At the same time the
wick should be sufficiently flexible that it does not exert
pressure against the membrane which would interfere with its
vibratory motion. Subject to these conditions, the wick 32 may be
made of any of several materials, for example, paper, nylon,
cotton, polypropylene, fiberglass, etc. A preferred form of wick 30
is strand of woven cotton material that is bent back on itself
where it touches the membrane. This causes very thin fibers of the
strand to extend up to the membrane surface. These very thin fibers
are capable of producing capillary action so as to bring liquid up
to the membrane; however, these thin fibers do not exert any
appreciable force on the membrane which would interfere with its
vibratory movement.
[0048] In operation of the atomizer, alternating electrical
voltages from an external source are applied through the leads 26
and 28 to the electrically conductive coatings on the upper and
lower surfaces of the actuator 10. This produces a piezoelectric
effect in the actuator material whereby the actuator expands and
contracts in radial directions. As a result, the diameter of the
center hole 12 increases and decreases in accordance with these
alternating voltages. These changes in diameter are applied as
radial forces on the membrane 14; and as a result, the flange
region 18 flexes and pushes the domed center region 16 up and down.
This produces a pumping action on the liquid which is brought up
against the underside of the center region 16 by the wick 32. The
capillary action of the wick causes the pressure of the liquid on
the underside of the membrane 14 to be slightly higher than the
atmospheric pressure above the membrane. As a result, the liquid 31
is forced upwardly through the perforations 20 and is ejected from
the upper surface of the membrane as a mist into the
atmosphere.
[0049] FIG. 2 shows the driving sequence of the piezoelectric
actuation element 10 according to the invention. As shown in FIG.
2, the driving sequence is divided into alternate drive periods of
5.5 milliseconds duration, and sleep periods of from 9 to 18
seconds duration.
[0050] During the 5.5 millisecond drive periods, the voltage used
for driving the piezoelectric actuation element 10 decreases
exponentially from 3.3 volts down to about 1.2 volts. Thus the
piezoelectric actuating element 10 is initially driven at a high
amplitude, which clears liquid from its surface and initiates
atomization; and then it is driven at significantly lower
amplitudes, which are sufficient to maintain actuation but which
consume only minimal amounts of driving power.
[0051] After each drive period, the system goes into a sleep period
of from 9 to 18 seconds. During the first 4 seconds of each sleep
period the system recharges back to 3.3 volts and this voltage is
maintained for use during the next drive period.
[0052] It will be noted that the actuation element 10 is capable of
driving the membrane 14 at a sufficient amplitude to atomize the
liquid 31 when the element 10 is driven from a supply voltage
source of only 1.2 volts; however in order to initiate atomization,
the element 10 must be driven using a higher supply source voltage,
such as 3.3 volts, in order to vibrate the membrane 14 at a
sufficient amplitude to clear a film of liquid which had
accumulated on its outer surface during the previous sleep period.
Thus the membrane 14 is initially driven at high power to produce
high amplitude vibrations which initiate atomization; but once
atomization has begun, a much lower vibrational amplitude may be
used to sustain atomization. By having the driving voltage decrease
from 3.3 volts to 1.2 volts at an exponential rate, the total
energy expended is reduced and battery life can thereby be extended
significantly.
[0053] At the end of each 5.5 millisecond drive period, the system
enters a "sleep period" of from 9 to 18 seconds. The length of this
sleep period can be set at 9 seconds, 13.5 seconds or 18 seconds by
means of a selector switch as described hereinafter.
[0054] The first 4 seconds of each sleep period is used for
recharging the supply for driving the system back from 1.2 volts to
3.3 volts. Thus when the next successive drive period begins, the
membrane 14 will initially be driven at a high amplitude from a 3.3
volt drive voltage supply.
[0055] The vibratory amplitude of the membrane 14 depends not only
on the voltage used for producing the vibrations, it also depends
on the frequency used to drive the membrane. This is because the
vibratory system which includes the membrane 14, the piezoelectric
driving actuator 10, and any interconnections between these
members, has a natural resonant frequency. When this system is
driven at its natural resonance frequency, the vibrational
amplitude of the membrane is maximized, while the driving power is
minimized. However, because of tolerances of manufacture, the
resonant frequency of the membrane and actuator system differs from
device to device.
[0056] In order to solve this problem, the driving frequency is
varied or swept over a range which includes the resonant frequency
of the membrane and actuator system. Thus, even though the specific
resonant frequency of a particular system is not known, by driving
it through a range of frequencies, it will be caused to resonate at
some point in this frequency range. As shown in FIG. 2, the drive
frequency is swept over a predetermined frequency range of from 120
to 160 kilohertz at a sweep rate of about 2 kilohertz. Thus the
frequency range is swept back and forth at least eleven times
during each 5.5 millisecond drive period.
[0057] FIG. 3 is a simplified block diagram for explaining a
circuit arrangement that may be used for driving the piezoelectric
actuator element 10 according to the invention. For purposes of
explanation, this circuit arrangement is described as a group of
functional units which are shown in dashed outline. These
functional units are as follows:
[0058] (a) an operating power supply unit 40;
[0059] (b) a drive voltage pattern control unit 42;
[0060] (c) a drive signal amplification unit 44;
[0061] (d) the piezoelectric actuator element 10;
[0062] (e) a sleep period control unit 46;
[0063] (f) a frequency pattern control unit 48; and
[0064] (g) a low battery detection and control unit 50.
[0065] Portions of each of these units are formed in a common
integrated circuit 52 (shown in dotted outline) while other
portions are mounted on a printed circuit board (not shown)
together with the integrated circuit 52, as will be described more
fully hereinafter.
[0066] The operation of the circuit arrangement of FIG. 3 will
first be described in regard to the overall operation of the
functional units 40, 42, 44, 46, 48 and 50; and thereafter the
individual operation of each functional unit will be described.
Overall Description of the Functional Units
[0067] The operating power supply unit 40 converts the voltage
output of a 1.5 volt "AA" alkaline battery 54 to a 3.3 volt
operating voltage. The 3.3 volt operating voltage is used to power
the other circuits in the system, including the drive voltage
pattern control unit 42.
[0068] The drive voltage pattern control unit 42 causes the
operating voltage to follow the exponential decrease from 3.3 volts
to 1.2 volts during the successive 5.5 millisecond drive periods
shown in FIG. 2. Here it should be noted that an exponential
decrease is not critical to this invention. Actually once
atomization is initiated at the beginning of each drive period, the
voltage can be lowered as rapidly as possible in order to conserve
battery power, so long as the atomization function is
sustained.
[0069] The voltage from the drive voltage pattern control unit 42
is supplied to the drive signal amplification control unit 44 where
it is amplified and converted into a swept frequency voltage output
which is used to energize the piezoelectric actuator element
10.
[0070] The sleep period control unit 46 controls the duration of
the sleep periods indicated in FIG. 2. In the illustrated
embodiment, these sleep periods can be set for durations of either
9, 13.5 or 18 seconds. The sleep periods may be set for other
durations, provided that they are long enough to allow the
operating power supply unit 40 to bring the drive voltage pattern
control unit 42 back to its 3.3 volt level for the next drive
period. In the present embodiment, the recharging to 3.3 volts
requires about 4.5 seconds.
[0071] The frequency pattern control unit 48 produces an
alternating voltage signal having a frequency which is swept
between 120 and 160 kilohertz at a 2 kilohertz rate. This signal is
applied to the drive signal amplification and frequency control
unit 44 which in turn drives the piezoelectric actuator 10 at these
frequencies and at a decreasing amplitude corresponding to the
drive period voltage pattern set by the drive voltage pattern
control 42.
[0072] The low battery detection and control unit 50 senses the
voltage output of the battery 54; and when this voltage output
decreases to a predetermined level at which the battery no longer
operates reliably, the detection and control unit 50 prevents
further operation of the system. At the same time, the unit 50
causes the battery 54 to drain to a level such that it cannot
recover sufficient output voltage to cause inadvertent sporadic
operation of the atomizer device.
The Operating Power Supply Unit
[0073] The operating power supply unit 40 includes, in addition to
the battery 54, a pumping coil 56, a Zener diode 58 and a storage
capacitor 60. The battery 54 is connected between ground at its
cathode and one end of the pumping coil 56. The other end of the
coil 56 is connected to the anode of the Zener diode 58, while the
diode's cathode is connected to one side of the storage capacitor
60. The other side of the capacitor 60 is connected to ground. A
voltage controlled switch 62 has one side connected between the
coil 56 and the diode 58, while the other side of the switch 62 is
connected to ground. The switch 62 is alternately opened and closed
at a 2 kilohertz rate by the output of a 2 kilohertz pumping
oscillator 64. A voltage detector 66 is connected to sense the
voltage at a point between the Zener diode 58 and the storage
oscillator 60. The voltage detector 66 has a high sensed voltage
output terminal 66a and a low sensed voltage output terminal 66b.
These output terminals are connected to stop and start inputs 64a
and 64b, respectively, of the pumping oscillator 64.
[0074] The start input 64b of the pumping oscillator 64 is also
connected to receive directly the 1.2 output of the battery 54.
Thus the voltage detector low sensed voltage terminal 66b and the
battery 54 output are shown to be connected to the start terminal
of the pumping oscillator 64 via an OR gate 68.
[0075] When the battery 54 is first installed, its 1.2 volt output
is supplied through the OR gate 68 to the start input terminal of
the pumping oscillator 64 to start operation of the oscillator. The
oscillator output causes the switch 62 to open and close at a 2
kilohertz rate. When the switch is closed, current from the battery
54 flows through the pumping coil 56 to ground. Then, when the
switch 62 closes, the flow of current is suddenly interrupted and
the inductance of the pumping coil causes it to experience a sudden
rise in voltage, which allows current to pass through the zener
diode 58 and into the storage capacitor 60. When the switch 62
opens again the voltage of the pumping coil decreases, but because
of the diode effect, current cannot flow back through the coil 56.
As the oscillator 64 continues to operate, the voltage on the
storage capacitor 60 increases until it reaches about 3.3
volts.
[0076] The voltage on the storage capacitor 60 is detected by the
voltage detector 66 which, when the voltage becomes just above 3.3
volts, produces a signal at its high sensed voltage output terminal
66a. This signal is supplied to the stop terminal 64a of the
oscillator 64 causing it to stop oscillating, with the switch 62 in
its open condition. As a result as current is drained from the
storage capacitor, its voltage decreases until it reaches a point
where the voltage detector 66 produces a signal at its low sensed
voltage terminal 66b.
[0077] The low sensed voltage is applied to the start terminal 64a
of the oscillator 64 which causes the switching action of the
switch 62 to resume and to begin further pumping of current into
the storage capacitor 60.
[0078] It will be seen that the voltage at the capacitor 60 is thus
caused to dither between slightly above and slightly below 3.3
volts depending on the high and low voltage settings of the voltage
detector 66. The 3.3 volts on the capacitor 60 is supplied to
operate the remaining components, as represented by the output
power supply terminal 70.
The Drive Voltage Pattern Control Unit
[0079] The drive voltage pattern control unit 42 comprises a
resistor 72 connected at one end to the storage capacitor 60 in the
operating power supply unit 40. The other end of the resistor 72 is
connected to one side of a voltage pattern control capacitor 74.
The other side of this capacitor is connected to ground. The
resistor 72 and the capacitor 74 form a standard RC timing circuit;
and the voltage at a junction 76 between the resistor and capacitor
decreases at an exponential rate when it is connected to a finite
impedance. In the present embodiment, the voltage at the junction
76 decreases from 3.3 to about 1.2 volts in about 5.5
milliseconds.
The Drive Signal Amplification Unit
[0080] The drive signal amplification unit 44 comprises an
autotransformer 78 and a smoothing coil 80 connected in series
between the junction 76 in the drive voltage pattern control unit
42 and one side of the piezoelectric actuator element 10. Also,
there is provided a field effect transistor 82 which is connected
between a point 78a along the autotransformer 78 and ground. The
field effect transistor 82 acts as a switch, and when it receives a
positive voltage from the frequency pattern control unit 48, it
becomes conductive and connects the point 78a to ground.
[0081] Point 78a is located near the upper end of the
autotransformer 78 closest to the drive voltage pattern control
unit 42 such that only a minor portion of the autotransformer's
coils are between the point 78a and the drive voltage pattern
control unit 42. When the point 78a becomes disconnected from
ground, the autotransformer effect produces a very high voltage at
its end closest to the actuation element 10 and causes the element
to expand and contract. The voltage signal from the autotransformer
first passes through the smoothing coil 80 to convert it to a
pattern corresponding more closely to that of the oscillation
pattern of the actuator element 10.
The Sleep Period Control Unit
[0082] The sleep period control unit 46 comprises a three position
selector switch 84 whose common terminal is connected to ground and
two of whose three switch terminals are connected through time
control resistors 86 and 88 to a sampling switch 90. The switch 90
in turn is connected to the 3.3 volt supply voltage. The third
switch terminal is not connected.
[0083] The resistors 86 and 88 are also connected to supply
different voltages to a sleep period logic circuit 92, depending on
the particular switch terminal that is connected to ground. The
logic circuit 92 compares the voltages which it receives from the
resistors 86 and 88; and it outputs one of three different voltages
at an output terminal 92a. This voltage is supplied to a sleep duty
cycle circuit 94 which acts as a timer to produce an output at an
output terminal 94a at either 9, 13.5 or 18 seconds after receiving
a signal from the logic circuit 92.
[0084] There is provided a system timing clock 96 which provides
clock signals at a 2 kilocycle rate. These clock signals are used
for all of the timing circuits and table reading circuits in the
device, including the duty cycle circuit 94.
[0085] When the duty cycle circuit 94 reaches the 9, 13.5 or 18
second interval to which it has been set, it produces a signal at
an output terminal 94a which is supplied to the frequency pattern
control unit 48 to initiate driving of the piezoelectric actuation
element 10. The manner in which this is done is explained
hereinafter in connection with the description of description of
the frequency pattern control unit 48.
[0086] The signal at the output terminal 94a of the sleep duty
cycle circuit is also applied to a drive timer 98 which sets the
driving time period for the piezoelectric actuator element 10. In
the illustrative example, this driving time period is 5.5
milliseconds. At the end of this period, the drive timer 98 outputs
a signal from an output terminal 98a. This signal is transmitted to
the frequency pattern control unit 48 to discontinue driving of the
piezoelectric actuator element 10.
[0087] The signal from the output 98a of the drive timer is also
transmitted to the sampling switch 90 to cause it to close
momentarily. This causes a voltage drop to occur across the
resistor 86 or 88 which has been selected by the setting of the
selector switch 84. If the selector switch is set to its
unconnected terminal, no voltage drop will occur. Thus, either a
zero voltage, a first voltage, or a second voltage is produced each
time the sample switch 90 is closed. This voltage is applied to the
sleep time select logic unit 92 to initiate a sleep time duration
corresponding to the position of the sleep selector switch 84. Thus
at the end of each drive period of the piezoelectric actuator
element 10, a new sleep period ins initiated; and the length of
this sleep period depends on the position of the selector switch at
the time the sleep period begins.
The Frequency Pattern Control Unit
[0088] The frequency pattern control unit 48 includes a swept
frequency oscillator 100, which in the present example, produces a
triangular waveform output at a frequency which sweeps between 120
and 160 kilohertz at a 2 kilohertz rate. This output is applied to
a drive period on and off switch 102. The switch 102 is connected
to be closed by a signal from the output terminal 94a of the sleep
duty cycle circuit 94, and to be opened by a signal from the output
terminal 98a of the drive timer 98. Thus, the variable frequency
outputs from the oscillator 100 pass through the drive period on
and off switch 102 only during the 5.5 millisecond drive periods
for the piezoelectric actuator 10.
[0089] The variable frequency outputs which pass through the switch
102 are applied to a wave voltage threshold detector 104. This
device produces an output signal at an output terminal 104a at a
particular point in each output cycle from the swept frequency
oscillator 100, namely the point in each cycle when the output
voltage from the oscillator reaches a predetermined threshold.
[0090] This output signal from the wave voltage threshold detector
104 is applied to a driver switch 106 to cause it to close. The
driver switch 106, when closed, connects a positive voltage, such
as the 3.3 volt power supply, to the gate terminal of the field
effect transistor 82 to make it conductive.
[0091] The signal from the output of the voltage threshold detector
104 is also supplied to a wave segment control timer 108. This
timer produces an output signal after a fixed duration, less than
the duration of one cycle of the swept frequency oscillator
100.
[0092] The output signal from the timer 108 is applied to the
driver switch 106 and causes it to open. the opening of the driver
switch 106 causes the field effect transistor 82 to become
non-conductive so that current may no longer flow from the upper
portion of the autotransformer 78 to ground. During this time the
autotransformer causes a very large voltage to be imposed on the
piezoelectric actuator 10.
[0093] It will be seen from the foregoing, that during each output
cycle of the swept frequency oscillator 100, the drive control
switch 106 is closed for a fixed duration to produce a fixed amount
of energy to cause the driving of the piezoelectric actuator
element 10. At the same time, the spacing in time between
successive ones of these fixed durations varies according to the
frequency of the variable frequency oscillator 100. This fixed
driving duration for each drive cycle permits the piezoelectric
actuator 10 to be driven at a variable frequency while keeping the
driving energy independent of the frequency. Thus the driving
energy or amplitude of driving of the piezoelectric actuator 10 is
made solely dependent on the voltage at any particular time at the
junction 76 between the capacitor 74 and the resistor 72 in the
drive voltage pattern control unit 42. As a result, during each
drive period, the piezoelectric actuator 10 is driven at a varying
frequency at a decreasing amplitude. It will be appreciated that
this frequency is swept between 120 and 160 kilohertz approximately
11 times during each driving period, while the driving amplitude
decreases once.
The Low Battery Detection and Control Unit
[0094] The low battery detection and control unit 50 operates to
maintain the system in operation for so long as the battery 54 is
capable of having its voltage pumped to a 3.3 volt level within a
predetermined duration, namely within the first 4 seconds of each
sleep period. The unit 50 comprises a low battery timer 110 which
is connected to receive a start timing input signal from the low
voltage output terminal 66b of the voltage detection circuit 66 in
the operating power supply unit 40, and to receive a stop timing
signal from the high voltage output terminal 66a of the voltage
detection circuit 66. Thus whenever an operation is initiated to
begin pumping the supply voltage to 3.3 volts, the timing operation
of the low battery timer 110 is initiated.
[0095] If the pumping action is completed within the duration set
for the timer, for example 4 seconds, the signal from the high
voltage terminal of the voltage detector 66 will stop timing
action. If however, the pumping action continues for a longer
duration, which occurs when the battery condition has deteriorated,
the low battery timer 110 will produce a signal at an output
terminal 110a.
[0096] The signal from the low battery timer 110a is applied to a
close terminal 106a of the drive switch 106 to hold the switch
closed. This locks the gate of the field effect transistor 82 to
the 3.3 volt supply to hold the transistor in a conductive state.
As a result, the voltage on the capacitors 60 and 74 is drained and
current is drawn from the battery 54 through the field effect
transistor 82 to ground. This action forcibly drains the remaining
life out of the battery so that is prevented from sporadically
operating the piezoelectric actuator 10 in the event it should
recover a slight amount of voltage, as often happens when batteries
wear down.
[0097] It will be appreciated that with the drive system of this
invention, an inexpensive low voltage alkaline battery may be used
to drive a piezoelectric actuator; and the operation of the
actuator is maintained uniform even though the battery itself is
wearing down. When the battery has deteriorated to a predetermined
level, the device shuts off positively without having experienced
any tailing off in its operation.
[0098] It is to be understood that the Figures, and the discussion
herein, are directed to preferred embodiments of the invention, but
that, the invention itself is broader than the illustrations given.
Specifically, the invention is equally applicable to other forms of
piezoelectric atomization, such as the use of cantilever beams
and/or amplifying plates, as well as atomizers driven by
conventional electric power, i.e. wall plug, rather than battery
powered.
[0099] It will be appreciated that the specific circuit
configurations shown herein are not critical to the invention and
that possible modifications will readily be seen by those skilled
in the art. The circuit arrangements shown herein are presented to
most clearly illustrate and explain the important concepts of the
present invention.
[0100] FIG. 4 illustrates the general relationship between the
printed circuit board, 201, and the piezoelectric element 202
located therein. It is to be understood that the circuit board may
be, in use, attached to the chassis of the dispenser, which chassis
may in turn be placed in a decorative shell-like housing or
receptacle (not shown) for use. The chassis board 211 is shown in
top view in FIG. 8, while the housing is not illustrated. The
decorative receptacle or housing may be of any form or shape
suitable for the purpose of retaining and protecting the elements
of the dispenser while providing a pleasing appearance to the
consumer, and permitting passage of the liquid, in spray form, from
the dispenser to the atmosphere. As such, the dispenser housing may
be advantageously produced by high speed molding of any material
suitable for use with, and contact with, the liquid to be
dispensed.
[0101] Piezoelectric element 202 may be mounted as illustrated in
the circuit board 201, held in place by grommet 204, or by any
similar suitable means which does not inhibit vibration of the
element. The piezoelectric element 202, in the form of a ring, is
positioned in an annular relationship to the orifice plate 203, and
is attached to the orifice plate flange so as to be in vibratory
communication therewith. The piezoelectric element generally
comprises a piezoelectric ceramic material, such as a lead
zirconate titanate (PZT) or lead metaniobate (PN), but may be any
material exhibiting piezoelectric properties.
[0102] The orifice plate comprises any conventional material
suitable for the purpose, but is preferably comprised of an
electroplated nickel cobalt composition formed upon a photoresist
substrate which is subsequently removed in conventional manner to
leave a uniform porous structure of nickel cobalt having a
thickness of from about 10 to about 100 microns, preferably from
about 20 to about 80 microns, and most preferably about 50 microns.
Other suitable materials for the orifice plate may be utilized,
such as nickel, magnesium-zirconium alloy, various other metals,
metal alloys, composites, or plastics, as well as combinations
thereof. By forming the nickel cobalt layer through electroplating,
a porous structure having the contour of the photoresist substrate
may be produced, in which permeability is achieved by formation of
conical holes having a diameter of about 6 microns on the exit
side, and a larger diameter on the entrance side. The orifice plate
is preferably dome shaped, i.e. somewhat elevated at the center,
but may vary from flat to parabolic, arc shaped, or hemispherical
in shape, or any other suitable shape which enhances performance.
The plate should have a relatively high bending stiffness, to
assure that the apertures therein still be subject to essentially
the same amplitude of vibration, so as to simultaneously eject
droplets of liquid which are uniform in diameter.
[0103] While shown in the form of an annular ceramic piezoelectric
element surrounding an orifice plate or aperture, it is also
conceived that the present invention is also suitable for use with
a conventional piezoelectric element comprising an oscillator and a
cantilever beam in contact with a diaphragm, nozzle, or orifice
plate suitable for dispersion of liquid droplets or fog.
[0104] Also shown in FIG. 4 is the liquid container 205 for storage
and provision of the fragrance, air freshener, insect control
liquid, or other material to be dispensed. As illustrated, the
container is closed by a closure 208. Also shown are bayonet clips
206, which are present to hold a removable top closure, or cap, not
shown, which is used in transport and storage of the container, and
may be removed easily when it is desired to put the container into
the dispenser and permit use of the contents thereof. From
bottle-opening 209, exiting through the closure 208, projects the
liquid supply means 207, a wick or dome shaped liquid feed medium.
For convenience, we shall refer to the liquid supply means as a
wick, although it may comprise a number of varying shape materials,
from hard capillary systems to soft porous wicks. The function of
the wick is to transport liquid from container 205 to a position in
contact with the orifice plate. Accordingly, the wick should be
unaffected by the liquid being transported, porous, and permit
compliance with the orifice plate. The porosity of the wick should
be sufficient to provide a uniform flow of liquid throughout the
range of flexibility of the wick, and in any configuration thereof.
To best transport the liquid to the surface of the orifice plate,
it has been found necessary that the wick itself physically-contact
the plate to transfer the liquid to the orifice plate. Liquid is
preferably delivered to the orifice plate in such a manner that
essentially all delivered liquid will adhere to and transfer to the
plate surface by surface tension. Among suitable wick materials, we
have found it preferable to utilize such materials as paper, or
fabrics of nylon, cotton, polypropylene, fiber glass, etc. The wick
may preferably be shaped to conform to the surface of the orifice
plate to which it is juxtaposed, and held in the correct position
by a wick holder or positioner, 210, located in the bottle opening
209, of the closure 208 of liquid container 205. Liquid will flow
readily from the wick to the plate as a result of the viscosity and
surface tension of the liquid. It is to be noted that the wick is
intended to be included as an integral part of a liquid resupply
unit, which will comprise the container, the liquid, the bottle
closure, the wick, and the wick holder or positioner, as well as a
top closure to seal the unit for storage and shipment. Such a unit
may thus comprise a refill bottle for the dispenser, suitable to be
placed in the dispenser at the consumers convenience. To this end,
the liquid container 205 may have attachment means 201 the bottle
closure 208, for insertion into a suitable receiving means in the
chassis 211 to lock it in operative position, after removal of the
top closure or cap.
[0105] FIG. 6 illustrates, in cross sectional view, the assembled
relationship between the liquid container 205, the wick 207, the
piezoelectric element 202, and the orifice plate 203 of a specific
preferred embodiment of the invention. The piezoelectric element
202 is positioned, for example, in printed circuit board 201, by
grommets 204, or by any suitable means which does not restrict
vibration of the piezoelectric element. In a preferred embodiment
of the invention, the annular piezoelectric element surrounds the
orifice plate 203, in mechanical connection therewith. The orifice
plate is, in turn, in contact with the wick 207, permitting the
liquid to be dispensed from the container 205 to the orifice plate,
where transfer occurs through surface tension contact. Not shown is
the chassis ball of the dispenser, which holds the circuit board
and the liquid container in the appropriate position to bring wick
207 into juxtaposition with the orifice plate 203. Wick 207 is held
in the opening of closure 8 by the wick holder 210, which permits a
degree of freedom to the flexible wick 207, so as to allow a range
of adjustment thereof, while wick tail 215 assures complete
utilization of all the liquid in the container 205. This degree of
freedom permits self-adjustment of the wick relative to the surface
of the orifice plate, to compensate for variations in position
resulting from the vagaries of manufacture, and provides for a
compliant feed means for transfer of the liquid from the container
to the face of the orifice plate. As will be apparent to one
skilled in the art, the height of the wick, as shown in FIGS. 6 and
7, may be adjusted to vary the liquid gap 214, as shown in FIG. 7,
and to assure an appropriate degree of contact between the wick and
the plate. For a more detailed view of the relationship between the
wick and the orifice plate, attention is directed to FIG. 7, a
magnified detail of a section of FIG. 6, wherein is shown the
looped wick 207, in juxtaposition with domed orifice plate 203,
thereby creating a liquid gap 214, in which the liquid to be
transferred is in surface tension contact with the orifice plate.
While FIG. 7 shows the wick and the plate as not actually in
contact, it is to be understood that this gap is for illustration
only, and that plate 203 does in fact contact the wick 207 for
transfer of the liquid. As shown, the passage of the wick 207
through the opening 209 in the closure element 208 is controlled by
the wick holder/positioner 210. FIG. 7 also shows the mounting
grommet 204 for the piezoelectric element 202, orifice plate 203,
and the orifice plate flange 212, as well as the clips 206 which
hold the removable cap (not shown) to the bottle closure 208.
[0106] FIG. 8 is a top view, showing the relationship of circuit
board 201, piezoelectric element 202, orifice plate 203, mounting
grommet 204, and the chassis board 211. As previously indicated,
the piezoelectric element 202, in annular relationship to the
orifice plate 203, is held in place in the circuit board 201 by the
grommet 204. The circuit board is mounted on chassis board 211 in
conventional manner, such as with clips 217 and positioning
brackets 218.
[0107] In FIG. 9, a simplified cross sectional diagram of the
invention illustrates the overall relationship of various elements.
The orifice plate 203 is shown as including orifice plate flanges
212, which are in turn attached to the piezoelectric element 202 by
suitable attachment means 213, such as epoxy adhesive. The wick 207
is illustrated in partial contact with the orifice plate 203,
creating liquid gap 214, by which the liquid to be dispensed is
transferred to the orifice plate. The wick is shown as also
comprising fabric tails 215, which extend into the liquid container
205, not shown.
[0108] The piezoelectric element 202 is controlled by control
circuitry on the circuit board 201 to provide consistent
performance over an extended period. With reference to FIG. 10 the
control circuitry is implemented by an application specific
integrated circuit (ASIC) 300 which receives power from a battery
102. The battery 302 is connected to a charge pump 304 which,
together with external components 305, acts as a DC-to-DC step up
converter. Operation of the charge pump is controlled by a state
machine 306 which receives timing signals from an oscillator 308
which produces a 20 MHz clock signal, for example, that is applied
to the charge pump 304. The state machine also receives an
indication from a low battery indicator circuit 310.
[0109] The functionality of the control circuit, and specifically
the state machine 306 is determined by a set of three selector
switches 312 which produce input signals A, B, C to the state
machine 306. The state machine inputs from the selector switches
312 are connected to individual pull-up resistors 313 which are
selectively coupled to the positive supply voltage Vcc by the
ENABLE signal from the state machine 306. This allows the voltage
to be disconnected from the pull-up resistors 313 to conserve
battery power during inactive periods of the control circuit. As
will be described, the operation of state machine produces an
output signal on line 314 which has an amplitude and a 301
frequency for driving the piezoelectric element 202. That output
signal on line 314 is coupled through an output driver 216 to
produce the output of the ASIC 300. The output driver 216 controls
the conductive state of metal oxide field effect transistor
(MOSFET) 316 which in turn controls the flow of electric current
from the charge pump 304 to the piezoelectric element 202.
[0110] The details of the state machine 306 are shown in FIG. 11.
The preferred embodiment of the state machine 306 utilizes hardware
circuitry in an application specific integrated circuit but
alternatively could be implemented by a programmable device such as
a microprocessor and associated circuitry. The state machine 306
has decision logic 320 to which the selector input A, B and C are
applied. The decision logic 306 also is interfaced to storage
devices 322 and 324 which respectively contain data regarding the
period and the duty cycle for the output signal that drives the
piezoelectric element 202. The decision logic selects appropriate
period and duty cycle values from the storage devices 322 and 324,
respectively and transfers them to the preload inputs of a
frequency counter 326 and an amplitude counter 328, respectively.
These counters 326 and 328 receive a clock signal from the
oscillator 308 and are enabled by a signal from the decision logic
320. As will be described, when the frequency counter 326 counts
down to zero, it produces an output pulse designated PERIOD which
is applied to the set of a flip/flop 330. Similarly, when the
amplitude counter 328 reaches zero, it produces a DUTY signal that
is o the reset input of flip/flop 330. The flip/flop is enabled by
the signal from the decision logic 320 and produces the output
signal on line 314.
[0111] The driver circuit for the piezoelectric element 202
utilizes amplitude and frequency modulation to power the
piezoelectric element 202 thus providing a portable, battery
operated dispenser for continuous use in an air trephener or
pesticide application. The circuitry allows extended operation
utilizing a relatively low-voltage battery 302 and provides a range
of ingredient delivery rates. The circuit drives the piezoelectric
element 202 with amplitude and frequency modulation utilizing an
intermittent duty cycle. The electronic-circuit is programmable and
can be used to set a precise atomizing delivery rate in milligrams
per hour. This is accomplished by selector switch 312 that allows
the user to adjust the off time between cycles and thus change the
intensity/effectiveness to a desired level based on personal
preference or for different room sizes. It has been discovered that
the dispenser's performance is directly related to the excitation
voltage of the piezoelectric element 202. However, it was also
discovered that with increased voltage, the dispenser utilized the
limited battery energy less efficiently. Therefore, by varying the
amplitude of the excitation voltage from a high level to a low
level, the delivery performance was enhanced without incurring
reduced efficiency. This result was due to the momentary high level
excitation that initiates the atomization in a "high-performance"
mode. Thereafter, lower level excitations are merely necessary to
maintain that level of performance.
[0112] The present inventors also found that the optimum operating
frequency for the piezoelectric element 202, varied from unit to
unit due to what are believed to be manufacturing differences in
the circuitry and the dispenser components, such as the
piezoelectric element 202. This phenomenon can be overcome by
sweeping the excitation frequency through a predefined range
thereby compensating for the unit-to-unit variations.
[0113] Another feature of the present driver circuitry is to
provide a constant delivery of active ingredients regardless of the
state of the battery charge. This circuitry includes a portion 318
that accumulates adequate charge to pulse the piezoelectric element
202. As the battery voltage decays, the circuit insures that the
proper amount of energy is available for a consistent pump action.
When the battery voltage decays to the point that the circuit can
no longer provide the proper energy, the circuitry turns the unit
off. Thus, the circuitry provides a constant output delivery
regardless of the state of charge of the battery 302. When the
battery voltage decays to the point that a constant delivery output
is not possible, the dispenser turns off.
[0114] During the operation of the dispenser, the control circuit
spends most of its time in a low-power mode, commonly referred to
as a sleep state. In the sleep state, the signal from the
oscillator 308 is driving a timer within the decision logic 320 of
the state machine 306. During this sleep state, the output signal
on line 314 of the state machine is a low logic level thereby
rendering the piezoelectric element 102 inactive. The period of the
sleep state is determined by the settings of the rate selector
switch 312 and the particular inputs A, B and C to the state
machine 306. The relationship between the switch settings and the
resultant signals A, B and C is shown in Table A.
1TABLE A INPUTS STATE OF A B C OPERATION CLOSED OPEN OPEN UNIT OFF
OPEN OPEN CLOSED UNIT ON, SLEEP TIME = 18 SECS OPEN OPEN OPEN UNIT
ON, SLEEP TIME = 27 SECS CLOSED CLOSED OPEN UNIT ON, SLEEP TIME =
27 SECS CLOSED OPEN CLOSED UNIT ON, SLEEP TIME = 27 SECS OPEN
CLOSED CLOSED UNIT ON, SLEEP TIME = 27 SECS CLOSED CLOSED CLOSED
UNIT ON, SLEEP TIME = 27 SECS OPEN CLOSED OPEN UNIT ON, SLEEP TIME
= 36 SECS
[0115] If the rate selector switch 312 is set so that the dispenser
is off or when the low battery circuit 240 detects that the charge
on the battery 302 had drained to a point where normal operation is
not possible, the modulation sequence is not performed and the
dispenser enters an inactive state.
[0116] When the dispenser is on and the state machine 306 wakes up,
it produces a brief output signal which drives the piezoelectric
element 102. The state machine 306 generates a signal for driving
the piezoelectric element that sweeps through a range of
frequencies and a range of amplitudes. In the preferred embodiment,
there are 19 amplitude values stored in the duty cycle table 322
and 40 frequency values stored in the period table. The decision
logic 320 has an internal timer which every 26.2 microsecond causes
the amplitude and frequency values in the next set of table
locations to be retrieved and loaded in the two counters 326 and
328. Since the number of discrete amplitude and frequency values
are different the amplitude changes so that as a given frequency is
periodically used to drive the piezoelectric element 102 its
amplitude also varies. This concept is depicted in FIG. 12 where as
the frequency sweeps through the 40 values (135 kHz to 155 kHz) in
the period table 322 the amplitude is swept though 19 values from
the duty cycle table 324. Note that since 40 is not evenly
divisible by 19, when the frequency sweep repeats the first
frequency (135 kHz) will have an amplitude value of 3.
[0117] This process is accomplished by the decision logic 306 in
FIG. 11 enabling the frequency and amplitude counters 326 and 328.
The counters 326 and 328 control the period and the duty cycle of
the alternating signal on output line 314. In essence, the two
eight-bit preloadable counters 326 and 328 divide the 20 MHz clock
signal produced by oscillator 308 by the values from the two tables
322 and 324 to control the period and duty cycle of the output
signal. The frequency counter divides the 20 MHz clock signal down
to between 135 KHz and 155 KHz. Every 26.2 microsecond the decision
logic resets the counter by obtaining the next frequency value from
the period table 322 and loading that value via the preload count
line into frequency counter 326. This reloads the counter 326 with
the proper countdown value.
[0118] At the same time a new duty cycle value is obtained from the
table 324 and loaded into the amplitude counter 328. The duty cycle
values vary the pulse width of the output signal on line 314
between 1.4 microseconds and 5.0 microseconds. This duty cycle
controls the amplitude of the output signal and a longer time
period gives a greater amplitude.
[0119] The output signal on line 314 is a digital signal which is
applied through output driver 216 to control the conductive state
of a power MOSFET 316. The counters 326 and 328 control the
operation of Flip/Flop 314 which produces a square wave output
signal that varies in frequency and duty cycle as determined by the
two counters 326 and 328, and shown at 340 and 344 in FIG. 12.
[0120] While the present invention has been described with respect
to what are at present considered to be the preferred embodiments,
it is to be understood that the invention is not to be limited to
the disclosed embodiments. To the contrary, the invention is
intended to cover various modifications and equivalent arrangements
within the spirit and scope of the appended claims. The scope of
the following claims is to be accorded the broadest interpretation
so as to encompass all such modifications and equivalent
formulations and functions.
Industrial Applicability
[0121] The atomization systems of this invention, which are
described in the present application can be used to automatically
dispense such liquids as air fresheners, perfumes, or insecticides,
to any given environment, over an extended period of time, with the
advantage of uniformly dispensing equal amounts of liquid to the
atmosphere over the life span of the battery which drives the
dispenser. Further, the dispenser may be reused at will by means of
refills and replacement batteries, so that the consumer may change
the liquid being dispersed to the atmosphere as desired, with the
added advantage that the amount of liquid being dispersed may be
varied to adjust intensity or effectiveness to a desired level for
personal preference, efficacy, or for room size.
* * * * *