BACKGROUND OF THE INVENTION
Field of the Invention
[0001] The present invention relates to a circuit for driving a liquid drop spraying or
ejecting apparatus, which may have a variety of uses, the apparatus treating a liquid
or operating by spraying or ejecting the liquid as small liquid drops.
Description of Prior Art
[0002] A liquid drops spraying apparatus is generally composed as shown in a longitudinal
cross section of FIG. 7. A piezoelectric or electrostrictive element 1 (piezoelectric
/ electrostrictive element) acts as pressurizing means for spraying liquid. The piezoelectric
/ electrostrictive element 1 is provided on a wall face of a pressurizing chamber
2 for pressurizing liquid to be sprayed; a liquid drops spraying nozzle 3 is provided
at the tip end of the pressurizing chamber; and an introducing hole 5 for supplying
liquid to the pressurizing chamber 2 is formed at its proximal end, thereby entirely
constituting a liquid drops spraying unit 6. This liquid drops supply unit 6 is concurrently
formed in plurality, and an introducing hole 5 for a plurality of the adjacent liquid
drops spraying units 6, 6,.. is coupled with a common liquid supply path 7.
[0003] A drive circuit for driving a liquid drops spraying apparatus deforms the wall of
the pressurizing chamber 2 by applying a predetermined voltage signal to the piezoelectric
/ electrostrictive element 1 and charging the element. In this manner, the drive circuit
generates a pressure at the pressurizing chamber 2, and causes the liquid supplied
to the pressurizing chamber from the liquid drops spraying nozzle 3. In addition,
the drive circuit causes power discharge and release deformation, thereby restoring
the deformation of the pressurizing chamber 2, and causes liquid from the introducing
hole 5 to the pressurizing chamber.
[0004] In the meantime, in the liquid drops spraying apparatus, a large amount of liquid
must be supplied according to uses. In order to cope with such uses, the apertures
of the nozzle and introducing hole have been increased in size.
Object of the Invention
[0005] If the aperture of the liquid drops spraying nozzle 3 is too large, however, an only
small amount of liquid can be sprayed. The introducing hole 5 is not a mere path through
which liquid is supplied to the pressurizing chamber 2, and serves to prevent back
flow even if pressurization is performed so as to spray a small amount of liquid drops
from the liquid spraying nozzle 3. Thus, the aperture cannot be widened infinitely.
[0006] Therefore, it is considered that a time interval for applying a predetermined voltage
signal to the piezoelectric / electrostrictive element 1 nozzle 3 is shortened; the
number of signal applications per unit time is increased; and the number of supplies
to the liquid drops spraying apparatus is increased. In that case, if the time interval
for applying the voltage is shortened, there occurs a new problem that a delay in
liquid supply from the introducing hole 5 to the pressurizing chamber 2 occurs, and
a large amount of liquid cannot be constantly supplied.
[0007] In addition, the piezoelectric / electrostrictive element acts as a capacitor. Charging
/ discharging is repeated when spraying operation is repeated. Thus, when an operating
period is shortened, power consumption is further increased, and a calorific value
is increased.
[0008] A technique to cope with the above increased power consumption is described in Japanese
Patent Application Laid-open No. 10-107335 or Patent No. 2909150. A technique for
shortening the application period of a voltage signal per unit time is disclosed in
Japanese Patent Application Laid-open No. 8-300646. In Japanese Patent Application
Laid-open No. 10-107335, there is disclosed an arrangement in which an external capacitor
is provided for power recollection, a coil that is an inductance is interposed in
a charge / discharge circuit, and part of a discharge of the piezoelectric / electrostrictive
element is effectively stored in the external capacitor and utilized for next charge,
thereby ensuring power saving. In Patent No. 2909150, there is disclosed an arrangement
in which piezoelectric elements to be driven at different timings are mutually utilized
as power recollecting means, thereby reducing power consumption without additionally
providing an external circuit.
[0009] However, in all of these arrangements, although there is provided an advantageous
effect on saving power consumption, a technique for constantly spraying a large amount
of liquid is not described. Thus, a delay in liquid supply from the introducing hole
to the pressurizing chamber is not solved.
[0010] In addition, in Japanese Patent Application Laid-open No. 8-300646, there is disclosed
an arrangement in which the rise of a drive voltage wavelength is divided into two
stages and/or three stages, the stability of meniscus is improved, thereby suppressing
an occurrence of a satellite. As a result of reducing a constant during discharge
when the waveform is divided into three stages, the printing speed is increased, thereby
making it possible to increase an ink discharge quantity. However, discharge start
characteristics are not smooth at the respective stages. Thus, the printing speed
cannot be significantly increased, and the discharge quantity cannot be significantly
increased.
[0011] In view of the foregoing problems, even in the case where a large amount of liquid
is sprayed, it is a object of the present invention to provide a circuit for driving
a liquid drops spraying apparatus capable of smoothly supplying liquid to the pressurizing
chamber.
SUMMARY OF THE INVENTION
[0012] According to a first aspect of the present invention, the following is provided.
A liquid drops spraying apparatus comprising: a plurality of units for spraying a
small amount of liquid drops that comprises a liquid drops spraying nozzle; a pressurizing
chamber for pressurizing liquid to be sprayed from the nozzle; an introducing hole
for supplying liquid to the pressurizing chamber; and a piezoelectric / electrostrictive
element for operating the pressurizing chamber to be pressurized, a liquid introducing
hole of a plurality of the adjacent liquid drops spraying units being coupled with
a common liquid supply path, there is provided a liquid drops spraying apparatus driving
circuit for applying a predetermined voltage signal to the piezoelectric / electrostrictive
element, thereby deforming the wall of the pressurizing chamber, and discharging from
the nozzle the liquid to be supplied to the pressurizing chamber by a pressure produced
at the pressurizing chamber, wherein a rate between an introducing hole diameter and
a nozzle hole diameter (introducing hole diameter / nozzle hole diameter) is 0.6 or
more and 1.6 or less; a rate between a nozzle hole diameter and nozzle thickness (nozzle
hole diameter / nozzle thickness) is 0.2 or more and 4 or less; an applied voltage
signal supplies a current to the piezoelectric / electrostrictive element and charge
power, and then, holds a final charge voltage for a predetermined time after a current;
discharging with two or more kinds of constants during discharge is then performed
sequentially; a constant during first discharging is greater than a constant during
second discharging; and the second discharging is started at a voltage that is 35%
to 70% in a voltage difference between the charging start voltage and the final charge
voltage when the charging start voltage is defined as a reference, whereby an inductance
and a resistor are interposed in at least one discharge circuit in series relevant
to the piezoelectric / electrostrictive element.
[0013] With this arrangement, in the case of an arrangement in which liquid drops are sprayed
during charging of the piezoelectric / electrostrictive element, when a charge is
discharged, the constant during discharging of the first discharge circuit is large,
and thus, the piezoelectric element, i.e., piezoelectric / electrostrictive element
can start deformation gently. In the case where liquid drops are sprayed simultaneously
from a plurality of liquid drops spraying units, an operation for introducing liquid
into a plurality of pressure chambers is reliably performed. Then, this operation
goes to a suction operation in which a time required for discharging a unit voltage
value is short. Thus, liquid is supplied to the pressurizing chamber smoothly and
within a short time, and an amount of liquid supply can be increased.
[0014] In addition, when the discharge start voltage is 35% or less, discharging with its
large discharge constant, i.e., gentle suctioning dominates a majority of the entire
suctioning steps. Suctioning itself is reliably performed, but a large amount of suctioning
per unit time cannot be provided. As a result, the spraying period cannot be shortened,
and a large amount of spray cannot be ensured. In addition, if the time constant of
the first discharging is comparatively small in a range which is greater than the
time constant during the second discharging so as to provide the suction quantity
per unit time, unstable suctioning starts, resulting in a spray fault. In addition,
when the voltage is 70% or more, discharging with its large discharge constant, i.e.,
gentle suction rate is too small to smoothly start liquid suctioning. Then, a suction
quantity of liquid from a liquid introducing hole to a liquid pressurizing chamber
after discharge is decreased, the entrapment of air bubbles from the liquid spraying
nozzle occurs, resulting in unstable spraying.
[0015] Further, when spraying is done in the above drive waveform, a large rate between
the nozzle and the introducing hole (introducing hole diameter / nozzle hole diameter)
is preferable in consideration of suctioning. However, a rate of which the pressure
during spraying escapes to the introducing hole side is large, and the spraying force
is shortened. Alternatively, if the above rate is small, it causes shortage of the
quantity of liquid supply against the spray quantity. Thus, a rate between the introducing
hole diameter and the nozzle hole diameter (introducing hole diameter / nozzle hole
diameter) is preferably 0.6 to 1.6.
[0016] Furthermore, a rate between the nozzle hole diameter and nozzle thickness (nozzle
hole diameter / nozzle thickness) is preferably 0.2 or more and 4 or less. When the
rate is 4 or less, the residue vibration of the liquid level immediately after spraying
can be converged speedily by a contact resistance between the liquids on the nozzle
wall face. Still furthermore, air bubbles can be prevented from entry into the pressurizing
chamber with the pressure change in the pressurizing chamber during discharge, and
the spray stability can be improved. As a result, spraying can be done at a short
period of time, and the spray quantity can be increased. In addition, when the rate
is 0.2 or more, there can be prevented a spray fault generated due to the shortage
of the spraying force with a large contact resistance of the liquid on the nozzle
wall face.
[0017] Yet furthermore, a rate between the introducing hole and the nozzle hole, a rate
between the nozzle hole and the nozzle thickness, and a discharge voltage rate are
met simultaneously, the spray fault due to air bubble entry is prevented, whereby
a large amount of spray can be ensured.
[0018] According to a second aspect of the present invention, as in the first aspect, there
is provided a circuit for driving a liquid drops spraying apparatus, wherein a time
(t4) from a time when discharging is started at a second discharge constant to a time
when a next predetermined voltage signal is applied to a piezoelectric / electrostrictive
element is 1/4 or more and 20 times or less of a specific vibration period (To) when
liquid is supplied to a flow path in a structure composed of a liquid spraying nozzle;
a pressurizing chamber for pressurizing the liquid discharged from the nozzle; an
introducing hole for supplying liquid to the pressurizing chamber; and a piezoelectric
/ electrostrictive element for operating the pressurizing chamber to be pressurized;
and a rate (t3 / t4) between a time (t3) when discharging is effected at a first discharge
constant and a time (t4) is 0.1 or more and 20 or less.
[0019] With this arrangement, when the time (t4) from a time when the piezoelectric / electrostrictive
element starts discharging at the second discharge constant to a time when the next
predetermined voltage signal is applied is 1/4 or less of the specific vibration period
(To), a suction speed of liquid from the liquid introducing hole to the liquid pressurizing
chamber after spraying is too fast. Even if suctioning is started at the first charging
without any fault, liquid supply from the introducing hole is too late when suctioning
is effected during the second discharging. Thus, air bubbles enter the pressurizing
chamber from the liquid drops spraying nozzle, resulting in a spray fault. In addition,
when the rate is 20 times or more of To, a large amount of suction per unit time cannot
be provided. As a result, the spray period cannot be shortened, and a large amount
of spray cannot be ensured.
[0020] Further, when a rate between a time (t3) when discharging is effected at the first
discharge constant to a time (t4) when a predetermined voltage signal is applied to
the next piezoelectric / electrostrictive element is 0,1 or less, the rate of the
first discharging with its large time constant is small. Thus the rate of the liquid
suction quantity during the first discharging to the entire suction quantity decreases,
suctioning is too late during the second discharge suctioning. Then, air bubbles enter
the pressurizing chamber from the liquid drops spraying nozzle, causing a spray fault.
In addition, when the above rate is 20 or less, a large amount of suction quantity
per unit time cannot be provided. As a result, the spray period cannot be shortened,
and a large amount of spray cannot be ensured.
[0021] According to a third aspect of the present invention, as in the first and second
aspects thereof, in addition to a discharge circuit, an inductance and a resistor
are interposed in series relevant to the charge circuit.
[0022] With this arrangement, the voltage / time gradient during spraying is made linear,
and the stability of liquid spraying is improved.
[0023] According to a fourth aspect of the present invention, in a liquid drops spraying
apparatus comprising: a liquid drops spraying nozzle; a pressure chamber for pressurizing
liquid discharged from the nozzle; and a piezoelectric / electrostrictive element
for operating the pressure chamber to be pressurized, a liquid introducing hole of
a plurality of the adjacent liquid drops spraying units being coupled with a common
liquid supply path, there is provided a circuit for driving a liquid drops spraying
apparatus for repeatedly applying a different voltage signal to the piezoelectric
/ electrostrictive element to which a predetermined voltage signal is applied, thereby
changing the wall of the pressurizing chamber and discharging from the nozzle the
liquid supplied to the pressurizing chamber with a pressure generated in the pressurizing
chamber, wherein a rate between an introducing hole and a nozzle hole diameter (introducing
hole diameter / nozzle hole diameter) is 0.6 or more and 1.6 or less; a rate between
a nozzle hole diameter and nozzle thickness (introducing hole diameter / nozzle thickness)
is 0.2 or more and 4 or less; the different applied voltage signal discharges a current
from the piezoelectric / electrostrictive element to which the discharge start voltage
is applied, and then, holds the final discharge voltage for a predetermined time;
charging with two or more kinds of charge constants is then performed sequentially;
and second charging is started at a voltage that is 30% to 65% of a voltage difference
between the final discharge voltage and the discharge start voltage when the final
discharge voltage is defined as a standard; and an inductance and a resistor are interposed
in series relevant to the piezoelectric / electrostrictive element in at least one
charge circuit.
[0024] With this arrangement, in the case where liquid drops are sprayed during discharge
of the piezoelectric / electrostrictive element, a time constant is large when first
charging of the charge circuit is started. Thus, the piezoelectric element, i.e.,
the piezoelectric / electrostrictive element can start deformation gently. In the
case where liquid drops are sprayed from a plurality of liquid drops spraying units
simultaneously, an operation for introducing liquid to a plurality of pressure chambers
are reliably performed. Then, this operation goes to a suction operation in which
a time required to charge a unit voltage value is short. Thus, liquid supply to the
pressure chambers can be performed smoothly and within a short time, and the liquid
supply quantity can be increased.
[0025] When the final discharge voltage is 65% or more, charging with its large charge constant,
i.e., gentle suctioning dominates a majority of the entire suctioning steps, and suctioning
is reliably performed. However, a large amount of suctioning per unit time cannot
be provided. As a result, the spraying period cannot be shortened. Therefore, a large
amount of splay cannot be ensured. If the first charging constant is comparatively
smaller within the range that is greater than the second time constant so as to provide
the suction quantity per unit time, unstable suctioning is started, resulting in a
spray fault. In addition, when the voltage is 30% or less, a rate of charging with
its charge constant, i.e., gentle suctioning is too small to perform liquid suctioning
start speedily, unstable spraying occurs.
[0026] Further, when spraying is performed in the drive waveform, a large rate between the
introducing hole diameter and the nozzle hole diameter (introducing hole diameter
/ nozzle hole diameter) is preferable in view of suctioning. However, a rate at which
the spraying pressure escapes to the introducing hole side, the spraying force becomes
short. Alternatively, if the rate is small, it causes the shortage of quantity of
liquid supply to the spray quantity. Thus, a rate between the introducing hole diameter
and the nozzle hole diameter (introducing hole diameter / nozzle hole diameter) is
preferably 0.6 to 1.6.
[0027] Further, the rate between the introducing hole and the nozzle hole, the rate between
the nozzle hole and nozzle thickness, and the charge voltage rate are met simultaneously,
a spray fault due to air bubble entry is prevented, and a large amount of spray can
be ensured.
[0028] According to a fifth aspect of the present invention, as in the fourth aspect thereof,
a time (t40) from a time when charging is started at the second charging constant
to a time when the next predetermined voltage signal is applied to the piezoelectric
/ electrostrictive element is 1/4 or more and 20 times or less of a specific vibration
period (To) when liquid is supplied to a flow path in a structure composed of: a liquid
spraying nozzle; a pressurizing chamber for pressurizing liquid discharged from the
nozzle; an introducing hole for supplying liquid to the pressurizing chamber; and
a piezoelectric / electrostrictive element for operating the pressurizing chamber
to be pressurized, and a rate (t30 / t40) between a time (t30) when charging is performed
at the first charging constant and a time (t40) is 0.1 or more and 20 or less.
[0029] With this arrangement, when t40 is 1/4 or less of (To), the suctioning speed is too
high. Thus, even if suctioning is started at the first charging without any failure,
liquid supply from the introducing hole is too late when suctioning is performed at
the second charging. Then, air bubbles enters the pressurizing chamber from the nozzle
hole, and spraying cannot be performed. In addition, when t40 is 20 times or more
of (To), a large amount of suction per unit time cannot be provided. As a result,
the spraying time cannot be shortened, and a large amount of spray cannot be ensured.
[0030] According to a sixth aspect of the present invention, as in the fourth and fifth
aspects thereof, in addition to a charge circuit, an inductance and a resistor are
interposed in series relevant to the discharge circuit.
[0031] By doing this, the voltage / time gradient during spraying becomes linear, and the
stability of liquid drops spraying is improved.
[0032] According to a seventh aspect of the present invention, in a liquid drops spraying
apparatus comprising: a liquid drops spraying nozzle; a pressurizing chamber for pressurizing
liquid sprayed from the nozzle; an introducing hole for supplying liquid to the pressurizing
chamber; and a piezoelectric / electrostrictive element for operating the pressurizing
chamber to be pressurized, a liquid introducing hole of a plurality of the adjacent
liquid drops spraying units being coupled with a common liquid supply path, there
is provided a circuit for driving a liquid drops spraying apparatus for applying a
predetermined voltage signal to the piezoelectric / electrostrictive element, thereby
deforming the wall of the pressurizing chamber, and discharging from the nozzle the
liquid supplied to the pressurizing chamber, wherein the applied voltage signal supplies
a current to the piezoelectric / electrostrictive element and charges power, and then,
holds a final charge voltage for a predetermined time; discharging with two or more
kinds of discharge constants is then performed sequentially; and the first charging
constant is greater than the second discharge time constant; an inductance and a resistor
are interposed in series relevant to the piezoelectric / electrostrictive element
in at least one discharge circuit; the piezoelectric / electrostrictive elements are
divided into at least two groups; a circuit for charging and discharging a current
is provided at their respective groups; and at least part of the discharge current
of one group is used for part of the charge current of the other group.
[0033] With this arrangement, in the case of an arrangement in which liquid drops are sprayed
during piezoelectric / electrostrictive element charging, when a charge is discharged,
the discharge time constant of the first discharge circuit is large. Thus, the piezoelectric
element, i.e., piezoelectric / electrostrictive element can start deformation gently.
In the case where liquid drops are sprayed from a plurality of liquid drops spraying
units simultaneously, an operation for introducing liquid to a plurality of pressure
chambers can be reliably performed. Then, this operation goes to a suction operation
in which a time required to discharge a unit voltage value is short. Thus, liquid
can be supplied to the pressure chamber smoothly and within a short time, and the
liquid supply quantity can be increased.
[0034] In addition, the discharge power of one piezoelectric / electrostrictive element
is directly employed as a charge current of the other piezoelectric / electrostrictive
element. Thus, there is no need to newly provide discharging means, and further, power
consumption can be saved.
[0035] According to an eighth aspect of the present invention, in a liquid drops spraying
apparatus comprising: a liquid drops spraying nozzle; a pressurizing chamber for pressurizing
liquid sprayed from the nozzle; an introducing hole for supplying liquid to the pressurizing
chamber; and a piezoelectric / electrostrictive element for operating the pressurizing
chamber to be pressurized, a liquid introducing hole of a plurality of the adjacent
liquid drops spraying units being coupled with a common liquid supply path, there
is provided a circuit for driving a liquid drops spraying apparatus for applying a
predetermined voltage signal to the piezoelectric / electrostrictive element, thereby
deforming the wall of the pressurizing chamber, and spraying from the nozzle the liquid
supplied to the pressurizing chamber with a pressure generated at the pressurizing
chamber, wherein the different applied voltage signal discharges a current from the
piezoelectric / electrostrictive element to which the discharge start voltage is applied,
and then, holds a final discharge voltage for a predetermined time; charging with
two or more kinds of charge constants is then performed sequentially; and the first
charging constant is greater than the second charge time constant; an inductance and
a resistor are interposed in series relevant to the piezoelectric / electrostrictive
element in at least one charge circuit; the piezoelectric / electrostrictive elements
are divided into at least two groups; a circuit for charging and discharging a current
is provided at their respective groups; and at least part of the discharge current
of one group is used for part of the charge current of the other group.
[0036] With this arrangement, in the case of an arrangement in which liquid drops are sprayed
during piezoelectric / electrostrictive element charging, when charging, the charge
time constant of the first charge circuit is large. Thus, the piezoelectric element,
i.e., piezoelectric / electrostrictive element can start deformation gently. In the
case where liquid drops are sprayed from a plurality of liquid drops spraying units
simultaneously, an operation for introducing liquid to a plurality of pressure chambers
can be reliably performed. Then, this operation goes to a suction operation in which
a time required to charge a unit voltage value is short. Thus, liquid can be supplied
to the pressure chamber smoothly and within a short time, and the liquid supply quantity
can be increased.
[0037] In addition, the discharge power of one piezoelectric / electrostrictive element
is directly employed as a charge current of the other piezoelectric / electrostrictive
element. Thus, there is no need to newly provide discharging means, and further, power
consumption can be saved.
[0038] According to a ninth aspect of the present invention, as in the seventh aspect thereof,
in addition to a discharge circuit, an inductance and a resistor are interposed in
series relevant to a charge circuit.
[0039] By doing this, the voltage / time gradient during spraying is made linear, and the
stability of liquid drops spray is improved.
[0040] According to a tenth aspect of the present invention, as in the eighth aspect thereof,
in addition to a charge circuit, an inductance and a resistor are interposed in series
relevant to a discharge circuit.
[0041] By doing this, the voltage / time gradient during spraying is made linear, and the
stability of liquid drops spray is improved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0042] For a better understanding of the present invention, reference is made to the following
detailed description of the invention, taken in conjunction with the following drawings
in which:
FIG. 1 is a circuit diagram illustrating an example of a circuit for driving a liquid
drops spraying apparatus according to the present invention;
FIG. 2A and FIG. 2B each show operating characteristics of the driving circuit shown
in FIG. 1, wherein FIG. 2A shows voltage waveforms when the piezoelectric / electrostrictive
element is applied, and FIG. 2B shows a control signal;
FIG. 3 is a circuit diagram of a circuit for driving a liquid drops spraying apparatus
showing a second embodiment of the present invention;
FIG. 4 is a view showing applied voltage wavelengths;
FIG. 5 is an illustrative view illustrating a longitudinal cross section of the center
of a liquid drops spraying unit driven by the circuit for driving the liquid drops
spraying apparatus shown in FIG. 1;
FIG. 6 is a view investigating the stability of the liquid drops spraying apparatus
when the discharge time constant of the voltage waveform shown in FIG. 2 is changed;
FIG. 7 is an illustrative view illustrating a central cross section of a liquid drops
spraying unit of the liquid drops spraying apparatus;
FIG. 8 is a longitudinal cross section illustrating the center illustrating another
example of the liquid drops spraying unit driven by the circuit for driving the liquid
drops spraying apparatus shown in FIG. 1.
PREFERRED EMBODIMENTS OF THE INVENTION
[0043] Hereinafter, preferred embodiments of the present invention will be described in
detail with reference to the accompanying drawings. FIG. 1 shows an example of a circuit
for driving a liquid drops spraying apparatus according to the present invention,
the circuit causing spraying operation during piezoelectric / electrostrictive element
charging. Reference numbers (10a to 10c) denotes a Schmidt trigger IC for converting
a signal from a control unit (not shown) such as microcomputer to a drive circuit
operating signal; reference numerals R6, R7, and R8 each denote a resistor for limiting
a charge of a Schmidt trigger IC 10, reference numerals M2 denotes a charge switch
consisting of P-MOSFET that supplies a charge current to a piezoelectric / electrostrictive
element 1 (hereinafter, referred to as a pressurizing element); and reference numerals
M3 and M4 denote first and second discharge switches each consisting of N-MOSFET for
discharging the pressurizing element 1.
[0044] The charge switch M2 forms a charge circuit 12 together with a coil L1 and a resistor
R1 provided in series at its output, and is controlled by a Schmidt trigger IC 10a
via a switch M5. In addition, a first discharge circuit 13a is formed by the first
discharge switch M3 and the coil L2 and resistor R2 provided in series at its discharge
circuit, and is controlled by a Schmidt trigger IC 10b. In addition, a second discharge
circuit 13b is formed by the second discharge switch M4 and the coil L3 and resistor
R3 provided in series at its discharge circuit, and is controlled by a Schmidt trigger
IC 10c. Here, in the second discharge circuit 13b, a time T4 required to discharge
a unit voltage value when discharging is started (this is determined by the coil L3,
resistor R3, and capacitor C1) is set to be shorter than a time T3 required to discharge
a unit voltage value when discharging is started in the first discharge circuit. 'Vp'
denotes a power supply voltage, and 'Vd' denotes a voltage applied to the pressurizing
element.
[0045] FIG. 2(a) shows the characteristics of a voltage applied to the pressurizing element
of the driving circuit shown in FIG. 1, wherein 't1' denotes a rise time for the charge
circuit to charge the pressurizing element 1, the pressurizing element is gently risen
by action of the coil L1, and the rise time 't1' is adjusted by the coil L1 and resistor
R1 as a time to ensure that the applied voltage 'Vd' reaches a desired voltage value.
The pressurizing element 1 is deformed by this charging operation, the pressurizing
chamber 2 is pressurized, and liquid drops are sprayed from the liquid drops spraying
nozzle 3. In addition, 't2' denotes a hold time for maintaining for a predetermined
time a state in which the liquid has been sprayed in order to stabilize the pressure
chamber 2 and the liquid contained in the pressurizing chamber.
[0046] 't3' and 't4' are fall times for sequentially operating the first discharge circuit
13a and the second discharge circuit 13b. Time 'T4' required to discharge a unit voltage
value when discharging of the second discharge circuit 13b is started is smaller than
time 'T3' required to discharge a unit voltage when discharging of the first discharge
circuit 13a is started. Thus, the discharge characteristics at time 't4' are protruded
to be smaller than the discharge characteristics at time 't3'. However, in any of
these characteristics, a change when discharging is started becomes gentle by action
of the coils L2 and L3. In addition, the coil L2 is provided, thereby a circuit without
the coil L3 can be preferably used in consideration of a balance between the spray
quantity and the supply quantity.
[0047] In this manner, discharge circuits are provided at two stages, a change in the applied
voltage 'Vd' during rise is first gentle and rapid in the middle, whereby the liquid
is supplied from the introducing hole 5 to the pressurizing chamber 2 because the
pressurizing element 1 is deformed. The supply speed is first low, suctioning can
be started uniformly from a plurality of introducing holes 5. The liquid suction speed
at which the change is rapid in the middle, and the flow to the pressurizing chamber
is started is accelerated, and a large amount of liquid can be suctioned. In comparing
a case in which the liquid is suctioned to the end at the first suction speed, the
drive period time T can be shortened, and the spray quantity from the nozzle can be
increased in proportion to such shortening. Therefore, the liquid drop spray per a
unit time can be increased.
[0048] In addition, the coil L1 is interposed in the charge circuit 12, wherein the applied
voltage 'Vd' does not rise rapidly when charging is started. Thus, the residual vibration
followed by spraying with deformation of the pressurizing element 1 can be eliminated,
the gradient of voltage / time can be stabilized, the spraying of liquid drops is
stabilized, air bubbles are involved from the nozzle during suctioning operation,
and an occurrence of a spray failure can be prevented. Therefore, the hold time 't2'
can be shortened, the liquid spray quantity can be further increased, and the liquid
can be supplied smoothly to the pressurizing chamber.
[0049] In addition, a change in applied voltage is made gentle by the coils L2 and L3 when
discharging is started. Thus, the liquid can be further suctioned efficiently and
the liquid supply quantity is further increased, and the spray quantity can be increased.
[0050] FIG. 2(b) shows a control signal of a drive circuit. In the figure, (1) denotes an
output signal of a Schmidt trigger IC 10a, (2) denotes an output signal of a Schmidt
trigger IC 10b, and (3) denotes an output signal of a Schmidt trigger IC 10c. As shown,
in the charge circuit 12, a 'Lo' signal is output from the Schmidt trigger IC 10a,
whereby the charge switch M2 is turned ON, causing liquid drops spraying operation.
In two discharge circuits 13a and 13b, a 'Hi' signal is output sequentially from a
respective one of the Schmidt trigger ICs 10b and 10c, whereby the switches M3 and
M4 are turned ON, causing liquid drops spraying operation.
[0051] Although a discharge time constant for liquid supply is switched at two stages, the
time constant may be set so as to be reduced at two or more stages and gradually.
In addition, in order to change charge and discharge characteristics, resistors R1
to R3 may be changed, and a desired waveform can be set inexpensively.
[0052] Further, the pressurizing element 1 is charged in order to spray liquid drops, and
deformation occurs in the pressurizing chamber 2. In contrast, in the case where deformation
is caused to occur in the pressurizing chamber 2 by discharging from the pressurizing
element 1, thereby spraying liquid drops, charge circuits with their different charge
characteristics are provided at two stages, and the discharge circuit may be formed
as one stage.
[0053] FIG. 5 shows an example of a liquid drops spraying apparatus that operates at the
above driving circuit, and is a longitudinal cross section illustrating the center
of a liquid drops discharging unit. This liquid drops spraying apparatus comprises
a plurality from several units to some hundreds of units according to the use mode
by defining as one unit a liquid drops discharge units 6 each comprising: pressurizing
means for discharging liquid; a pressurizing chamber 2 for pressurizing liquid to
be discharged; a liquid discharge nozzle 3 coupled downwardly with the pressurizing
chamber 2, the nozzle discharging liquid to a treatment unit of the liquid drops spraying
apparatus; and an introducing hole 5 for supplying liquid to the pressurizing chamber
2.
[0054] In the liquid drops discharge unit 6, a plurality of the adjacent pressurizing chambers
2, 2... are coupled with each other by means of a common liquid supply path 7 via
the introducing hole 5, and a piezoelectric / electrostrictive element 1 is provided
as pressurizing means at a part of the upward wall of the pressurizing chamber 2.
The piezoelectric / electrostrictive element 1 laminates an upper electrode 16, a
piezoelectric / electrostrictive layer 18, and a lower electrode 17. By applying a
predetermined voltage signal, the piezoelectric / electrostrictive layer 18 is deformed
by electrophoresis generated between the upper and lower electrodes 16 and 17. Then,
the liquid supplied to the pressurizing chamber 2 is discharged from the nozzle 3
by the pressurizing force generated at the pressurizing chamber 2 by deforming the
wall of the fixed pressurizing chamber 2.
[0055] A rate in diameter between the introducing hole 5 and the nozzle 3 (introducing hole
diameter / nozzle hole diameter) is between 0.6 and 1.6, for example, 1.0; and a rate
between the nozzle hole diameter and nozzle thickness (nozzle hole diameter / nozzle
thickness) is between 0.2 and 4, for example, 2.
[0056] A rate in diameter between the introducing hole 5 and the nozzle 3 is between 0.6
and 1.6, whereby a balance in spraying force and suction force is obtained, and the
shortage of the spray force or suction force is not eliminated. If the introducing
hole diameter / nozzle hole diameter exceeds 1.6, it acts well to suctioning. However,
a rate of which the pressure during spraying escapes to the introducing hole side
is increased, and the shortage of the spraying force occurs. In addition, if the rate
is smaller than 0.6, it causes the shortage of the quantity of liquid supply to the
spray quantity.
[0057] Further, if the nozzle hole diameter / nozzle thickness is 4 or less, the residual
vibration of the liquid level immediately after spraying can be converged speedily
by a liquid contact resistance on the nozzle wall face. Further, air bubbles are prevented
from entry into the pressurizing chamber 2 due to the vibration in internal pressure
of the pressurizing chamber during discharge, and the spray stability can be improved.
As a result, the liquid can be sprayed within a short period, and the spray quantity
can be increased. If the above rate is 0.2 or more, the shortage of the spraying force
due to an increased liquid contact resistance on the nozzle wall face occurs, and
a spray fault can be prevented. In the above embodiment, the nozzle hole diameter
is from 25 microns to 100 microns.
[0058] In addition, FIG. 6 is measurement data indicative of stability of spraying operation
of the liquid drops spraying apparatus by changing a voltage from discharge due to
the first discharge time constant to discharge due to the second discharge time constant
when the drive voltage of the piezoelectric / electrostrictive element is constant
at 40 V, and is constant when t1 = 20 microseconds, t2 = 5 microseconds, t3 = 20 microseconds,
and t4 = = 10 microseconds.
[0059] As shown, when a voltage migrating to discharge due to the second discharge time
constant is between 38% and 63% of the final discharge voltage, spraying operation
can be preferably performed, and preferable operation is not indicated at 25% and
75%. In this way, a voltage for starting second discharge is ranged, second discharging
is preferably started at a voltage from 35% to 70% of the applied voltage, that is,
of the final charge voltage. A rate between the introducing hole diameter and the
nozzle hole diameter, a rate between the nozzle hole diameter and nozzle thickness,
and second discharge start voltage are met simultaneously, whereby a spray fault due
to entrapment of air bubbles from the liquid drops spraying nozzle is prevented, and
a large amount of spray can be ensured.
[0060] When the second discharge start voltage is 35% or less, discharging with its discharge
time constant, i.e., gentle suctioning dominates a majority of the entire suctioning
steps. Suctioning itself is reliably performed, but a large amount of suction quantity
per unit time cannot be provided. As a result, the spray period cannot be shortened,
and a large amount of spray cannot be ensured. In addition, if a comparative suction
time is set to be small in a range in which the first discharge time constant is greater
than the second discharge time constant so as to provide a suction quantity per unit
time, unstable suctioning is started, and the shortage of spray quantity is caused.
In addition, the above rate is 70% or more, discharging with its discharge time constant,
i.e., a rate of gentle suction is too small to speedily start liquid suctioning. A
liquid suction quantity from the liquid introducing hole 5 to the liquid pressurizing
chamber after discharge decreases, the entrapment of air bubbles in the nozzle 3 occurs,
resulting in unstable spraying.
[0061] Further, a time 't4' at which discharging is performed at the second discharge time
constant is 1/4 or more and 20 or less of the specific vibration period 'To' when
liquid is supplied to a flow path in a structure composed of: a liquid drops spraying
nozzle 3; a pressurizing chamber 2 for pressurizing liquid sprayed from this nozzle;
an introducing hole 5 for supplying liquid to the pressurizing chamber 2; and a piezoelectric
/ electrostrictive element 1 for operating the pressurizing chamber 2 to be pressurized;
and a rate 't3 / t4' between the first discharge time 't3' and the second discharge
time 't4' is preferably 0.1 to 20. By setting this range, the liquid from the introducing
hole can be supplied smoothly relevant to the suction speed, and spraying operation
can be well performed without air bubble entry from the nozzle to the pressurizing
chamber.
[0062] When the time 't4' is To / 4 or less, the suction speed is too high. Thus, even if
the first discharge is well performed, liquid supply from the introducing hole is
too late because of suctioning operation during the second discharge, air bubbles
enter the pressurizing chamber 2 from the nozzle 3, and a spray fault occurs. In addition,
when the time is 20T or more, a large amount of suction quantity per unit time cannot
be provided. As a result, the spray period cannot be shortened, and a large amount
of discharge cannot be ensured. Further, in the case where the t3 / t4 is 0.1 or less,
a rate of the first discharge with its large time constant is small, and a rate of
the liquid suction rate during the first discharge to the entire suction quantity
decreases. Thus, suctioning is too late when suctioning is performed during second
discharge, and a spray fault is likely to occur. When the above rate is 20 or more,
an advantageous effect due to the setting of the second discharge time constant is
eliminated. In view of a large amount of spray, an advantageous effect due to increasing
the drive frequency can be utilized as more effective means.
[0063] The discharge time constant for liquid supply is switched into two stages. It is
preferable to set the discharge time constant so as to be increase at two or more
stages and gradually. In addition, a piezoelectric / elecrostrictive element is charged
for the purpose of liquid drop spraying, and a pressurizing chamber is deformed. In
contrast, in the case where discharging is performed from the piezoelectric / electrostrictive
element, thereby causing deformation in the pressurizing chamber, and spraying liquid
drops, charging with the second charge time constant is started at a voltage that
is 30% to 65% of the discharge start voltage.
[0064] FIG. 8 is an illustrative view of a liquid drops spraying unit that causes reverse
operation relevant to the liquid drops spraying apparatus shown in FIG. 5 and that
deforms the pressurizing chamber during discharge to spray liquid drops by employing
an MLP (laminated actuator) for the piezoelectric / electrostrictive element, wherein
FIG. 8(a) is a longitudinal cross section; and FIG. 8(b) is an arrow view of the cross
section taken along line A-A. In the figures, reference numeral 23 denotes a fixing
member for fixing the piezoelectric / electrostrictive element; reference numeral
20 denotes a positive electrode; reference numeral 21 denotes a negative electrode;
and reference numeral 22 denotes a piezoelectric / electrostrictive layer. Like constituent
elements identical to those shown in FIG. 5 are denoted by like reference numbers.
[0065] In the case of the illustrative embodiment, a ratio between an introducing hole diameter
and a nozzle hole diameter and a ratio between a nozzle hole diameter and nozzle thickness
may be similar to that shown in the above-described illustrative embodiment, the second
charge start voltage may be 30 to 65% of a voltage difference between the final discharge
voltage and the discharge start voltage when the final discharge voltage is defined
as a reference. In addition, the time 't40' at which charging is performed at the
second charge time constant may be 1/4 or more and 20 times or less of the specific
vibration period To as is the case with the above-described illustrative embodiment;
and a rate 't30 / t40' between the charge time 't30' with the first charge time constant
an the charge time may be 0.1 to 20.
[0066] FIG. 3 is a circuit diagram of essential portions illustrating a second embodiment
of the present invention, wherein a second pressurizing element 11 is provided as
power storage means for power saving. A charge circuit consists of three FETs with
a first charge switch M12, a second charge switch M15, and a third charge switch M16.
A discharge circuit is formed of three FETs with a first discharge switch M13, a second
discharge switch M14, and a third discharge switch M17. In addition, resistors R11
to R16 each determine charge and discharge characteristics of each circuit together
with both of the pressurizing elements 1 and 11. In first charge switch M12 and the
first discharge switch M13, coils L11 and L12 are inserted in series into resistors
R11 and R12. D1 to D4 each denotes a diode.
[0067] An operation of this circuit will be described with reference to the applied voltage
characteristic chart shown in FIG. 4. FIG. 4(a) shows an applied voltage waveform
of a first pressurizing element 1, and FIG. 4(b) shows an applied voltage waveform
of a second pressurizing element 11. At a first charge period 't21', a first charge
switch M12 is first turned ON, thereby discharging a second pressurizing element 11,
and the first pressurizing element 1 is charged by its discharge charge. At a second
charge time 't22', a second charge switch M15 is then turned ON, thereby charging
the shortage of charge, and a third discharge switch M17 is turned ON, thereby completely
discharging the pressurizing element 11.
[0068] Then, at a period 't23', after its state has been held for a predetermined time,
the first discharge switch M13 is turned ON at the first discharge time 't24', thereby
discharging power, and its discharge charge is charged with the second pressurizing
element 11. At a second discharge time 't25', the second discharge switch M14 is turned
ON, thereby discharging the residual capacity, and the third charge switch M16 is
turned ON, thereby charge the shortage of the charge of the second pressurizing element
11, and its state is held at a time 't26'. In this time, when the time 't21' is started,
't21' to 't26' are defined as one period for charging and/or discharging, the first
and second pressurizing elements 1 and 11 operate in synchronism with each other,
and the voltage waveform is repeatedly applied.
[0069] In this manner, when pressurizing elements operated by shifting a half period are
provided, these mutual elements can be employed as power storage means, and a discharge
charge can be efficiently utilized without additionally providing power storage means
such as capacitor. Therefore, in the case where a plurality of pressurizing elements
are provided, these pressurizing elements are divided into two or more groups. When
the elements are operated by shifting about a half period, at least part of the discharge
current of one group can be used for at least part of the charge current of the other
group, and power consumption can be further saved.
[0070] Although the above illustrative embodiment is composed of an analog circuit, the
drive waveform is generated by means of a digital signal. This digital signal can
be converted into an analog signal, and the drive waveform can be preferably set.
In addition, although a charge switch or a discharge switch is fully MOS shaped FET,
the driving circuit may be composed of a transistor without being limited thereto.
Advantageous Effect of the Invention
[0071] As has been described above in detail, according to the present invention, liquid
can be supplied to a plurality of pressurizing chambers smoothly and within a short
time, and the liquid supply quantity can be increased. In addition, liquid suctioning
can be started gently, the liquid can be suctioned efficiently, and the liquid supply
quantity can be further increased. Therefore, the application period can be further
shortened, the liquid ejection quantity can be further increased, and the liquid can
be supplied to the pressurizing chambers smoothly.
1. A liquid drop spraying apparatus comprising: a plurality of units for spraying liquid
drops which each comprise a liquid drop spraying nozzle; a pressurizing chamber for
pressurizing liquid to be sprayed from the nozzle; an introducing hole for supplying
liquid to the pressurizing chamber; and a piezoelectric/electrostrictive element for
operating the pressurizing chamber, the liquid introducing holes of a plurality of
adjacent spraying units being coupled with a common liquid supply path; a circuit
for applying a predetermined voltage signal to the piezoelectric/electrostrictive
element, thereby deforming the wall of the pressurizing chamber, and discharging from
the nozzle the liquid to be supplied to the pressurizing chamber by a pressure produced
at the pressurizing chamber, a ratio between an introducing hole diameter and a nozzle
hole diameter (introducing hole diameter/nozzle hole diameter) to 0.6 or more and
1.6 or less; a ratio between a nozzle hole diameter and nozzle thickness (nozzle hole
diameter/nozzle thickness) to 0.2 or more and 4 or less; said driving circuit comprising
being arranged for applying a voltage signal supplying a current to the piezoelectric/electrostrictive
element and charge power, and then, holding a final charge voltage for a predetermined
time after a current; and then, sequentially performing discharging with two or more
kinds of discharge time constant; setting the first discharge time constant to be
greater than a second discharge time constant; and starting the second discharging
at a voltage that is 35% to 70% in a voltage difference between the charging start
voltage and the final charge voltage when the charging start voltage is defined as
a reference, wherein an inductance and a resistor are interposed in at least one discharge
circuit in series with the piezoelectric/electrostrictive element.
2. A circuit for driving a liquid drop spraying apparatus, comprising means for ensuring
that a time (t4) from a time when discharging is started with the second discharge
time constant to a time when a next predetermined voltage signal is applied to a piezoelectric/electrostrictive
element is 1/4 or more and 20 times or less of a specific vibration period (To) when
liquid is supplied to a flow path in a structure composed of a liquid spraying nozzle;
a pressurizing chamber for pressurizing the liquid discharged from the nozzle; an
introducing hole for supplying liquid to the pressurizing chamber; and a piezoelectric/electrostrictive
element for operating the pressurizing chamber to be pressurized; and a ratio (t3/t4)
between a time (t3) when discharging is effected with the first discharge time constant
and the time (t4) is 0.1 or more and 20 or less.
3. A circuit for driving a liquid drop spraying apparatus as claimed in claim 1 or claim
2, wherein, in addition to a discharge circuit, an inductance and a resistor are interposed
in series relevant to a charge circuit.
4. A liquid drop spraying apparatus comprising: spraying units each having a liquid drop
spraying nozzle; a pressure chamber for pressurizing liquid discharged from the nozzle;
and a piezoelectric/electrostrictive element for operating the pressurizing chamber
to be pressurized, liquid introducing holes of a plurality of the adjacent spraying
units being coupled with a common liquid supply path, a driving circuit for repeatedly
applying a different voltage signal to the piezoelectric/electrostrictive element,
thereby changing the wall of the pressurizing chamber and discharging from the nozzle
the liquid supplied to the pressurizing chamber with a pressure generated in the pressurizing
chamber, wherein the ratio between an introducing hole and a nozzle hole diameter
(introducing hole diameter/nozzle hole diameter) is 0.6 or more and 1.6 or less; a
ratio between a nozzle hole diameter and nozzle thickness (introducing hole diameter/nozzle
thickness) is 0.2 or more and 4 or less; said driving circuit being arranged so that
an applied voltage signal discharges a current from the piezoelectric/electrostrictive
element to which the discharge start voltage is applied, and then, holds the final
discharge voltage for a predetermined time; charging with two or more kinds of charge
constants is then performed sequentially; and second charging is started at a voltage
that is 30% to 65% of a voltage difference between the final discharge voltage and
the discharge start voltage when the final discharge voltage is defined as a standard;
and an inductance and a resistor are interposed in series with the piezoelectric/electrostrictive
element in at least one charge circuit.
5. A circuit for driving a liquid drop spraying apparatus as claimed in claim 4, wherein
a time (t40) from a time when charging is started at the second charging constant
to a time when the next predetermined voltage signal is applied to the piezoelectric/electrostrictive
element is 1/4 or more and 20 times or less of a specific vibration period (To) when
liquid is supplied to a flow path in a structure composed of: a liquid spraying nozzle;
a pressurizing chamber for pressurizing liquid discharged from the nozzle; an introducing
hole for supplying liquid to the pressurizing chamber; and a piezoelectric/electrostrictive
element for operating the pressurizing chamber to be pressurized, and a ratio (t30/t40)
between a time (t30) when charging is performed at the first charging constant and
the time (t40) is 0.1 or more and 20 or less.
6. A circuit for driving a liquid drop spraying apparatus as claimed in claim 4 or claim
5, wherein, in addition to a charge circuit, an inductance and a resistor are interposed
in series with a discharge circuit.
7. A liquid drop spraying apparatus comprising; spraying units each having a liquid drop
spraying nozzle; a pressurizing chamber for pressurizing liquid sprayed from the nozzle;
and introducing hole for supplying liquid to the pressurizing chamber; and a piezoelectric/electrostrictive
element for operating the pressurizing chamber to be pressurized, liquid introducing
holes of a plurality of adjacent liquid drop spraying units being coupled with a common
liquid supply path, a driving circuit for applying a predetermined voltage signal
to the piezoelectric/electrostrictive element, thereby deforming the wall of the pressurizing
chamber, and discharging from the nozzle the liquid supplied to the pressurizing chamber,
said driving circuit comprising means for arranging that the applied voltage signal
supplies a current to the piezoelectric/electrostrictive element and charges power,
and then, holds a final charge voltage for a predetermined time; discharging with
two or more kinds of discharge constants is then performed sequentially; and the first
charging constant is greater than the second discharge time constant; an inductance
and a resistor are interposed in series with the piezoelectric/electrostrictive element
in at least one discharge circuit; the piezoelectric/electrostrictive elements are
divided into at least two groups; a circuit for charging and discharging a current
is provided for the respective groups; and at least part of the discharge current
of one group is used for part of the charge current of the other group.
8. A liquid drop spraying apparatus comprising; spraying units each having a liquid drop
spraying nozzle; a pressurizing chamber for pressurizing liquid sprayed from the nozzle;
an introducing hole for supplying liquid to the pressurizing chamber; and a piezoelectric/electrostrictive
element for operating the pressurizing chamber to be pressurized, a liquid introducing
hole of a plurality of adjacent spraying units being coupled with a common liquid
supply path, a driving circuit for applying a predetermined voltage signal to the
piezoelectric/electrostrictive element, thereby deforming the wall of the pressurizing
chamber, and spraying from the nozzle the liquid supplied to the pressurizing chamber
with a pressure generated at the pressurizing chamber, said driving circuit comprising
means for arranging that the different applied voltage signal discharges a current
from the piezoelectric/electrostrictive element to which the discharge start voltage
is applied, and then, holds a final discharge voltage for a predetermined time; charging
with two or more kinds of charge constants is then performed sequentially; and the
first charging constant is greater than the second charge time constant; an inductance
and a resistor are interposed in series relevant to the piezoelectric/electrostrictive
element in at least one charge circuit; the piezoelectric/electrostrictive elements
are divided into at least two groups; a circuit for charging and discharging a current
is provided for the respective groups; and at least part of the discharge current
of one group is used for part of the charge current of the other group.
9. A circuit for driving a liquid drop spraying apparatus as claimed in claim 7, wherein,
in addition to a discharge circuit, an inductance and a resistor are interposed in
series relevant to a charge circuit.
10. A circuit for driving a liquid drop spraying apparatus as claimed in claim 8, wherein,
in addition to a charge circuit, an inductance and a resistor are interposed in series
relevant to a discharge circuit.