JP2001129989A - Drive circuit for liquid droplet atomizing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a drive circuit for a liquid droplet atomizing device capable of smoothly supplying liquid to a pressurizing chamber, even when a large volume of the liquid is atomized. SOLUTION: A coil L1 is provided in series with a resistor R1 which decides the charge characteristics of a charging circuit 12 of a piezoelectric/ electrostriction element 1 and thereby the start characteristics of charging voltage during its rise shows a slow start. Further, a discharging circuit is provided in two stages and time required for electric discharge of a unit voltage in a second discharging circuit 13b is made shorter than time required for electric discharge of a unit voltage in a first discharging circuit 13a. In addition, coils L2, L3 are installed in series with resistors R2, R3 for deciding discharging characteristics of the circuits 13a, 13b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving circuit for a liquid droplet spraying device used in various machines for processing or operating the liquid by spraying the liquid as fine liquid droplets.

[0002]

2. Description of the Related Art A droplet spraying apparatus is usually constructed as shown in a vertical sectional view of FIG. 7, and uses a piezoelectric or electrostrictive element 1 (piezoelectric / electrostrictive element) as a pressurizing means for spraying a liquid. Have been. The piezoelectric / electrostrictive element 1 is provided on a wall surface of a pressurizing chamber 2 for pressurizing a liquid to be sprayed, a nozzle 3 for spraying a droplet is provided at a distal end of the pressurizing chamber 2, and a base end portion. Is formed with an introduction hole 5 for supplying a liquid to the pressurizing chamber 2, and constitutes a droplet spraying unit 6 as a whole. The plurality of droplet supply units 6 are formed continuously, and the introduction holes 5 of the plurality of adjacent droplet spray units 6, 6,... Are connected to a common liquid supply path 7.

A driving circuit for driving the droplet spraying device applies a predetermined voltage signal to the piezoelectric / electrostrictive element 1 to charge the piezoelectric / electrostrictive element 1, thereby deforming the wall of the pressurizing chamber 2 and thereby applying a voltage. A pressure is generated in the pressure chamber 2, and the liquid supplied to the pressure chamber is sprayed from the droplet spray nozzle 3. Further, the deformation of the pressurized chamber 2 is returned to the original state by releasing the deformation by discharging, and at this time, the liquid is supplied to the pressurized chamber from the introduction hole 5. By the way, some droplet spraying apparatuses need to supply a large amount of liquid depending on the application, and such an application has been dealt with by increasing the diameter of the nozzle and the introduction hole.

[0004]

However, if the diameter of the droplet spraying nozzle 3 is too large, the liquid to be sprayed will not be fine droplets, and the supply hole 5 will supply the liquid to the pressurizing chamber 2. It is not a simple path, but also has a function of preventing backflow even if it is pressurized so as to spray fine droplets from the droplet spray nozzle 3, so that the diameter cannot be increased without limit. To cope with this, it is conceivable that the time interval for applying a predetermined voltage signal to the piezoelectric / electrostrictive element 1 is shortened to increase the number of times of application per unit time, thereby increasing the number of times of supply to the droplet spraying device. In this case, if the time interval of the applied voltage is shortened, the supply of the liquid from the introduction hole 5 to the pressurizing chamber 2 is delayed, and a new problem that the liquid cannot be stably supplied in a larger amount. Had occurred. Also, the piezoelectric / electrostrictive element acts as a capacitor,
Since charging and discharging are repeated each time the spraying operation is repeated, the power consumption is further increased and the heat generation is increased when the operation cycle is shortened.

As a countermeasure against the above-mentioned increase in power consumption, there is a technique described in Japanese Patent Application Laid-Open No. 10-107335 and Japanese Patent No. 2909150. As a technique for shortening the voltage signal application cycle per unit time, JP-A-8-30
There is a technology disclosed in Japanese Patent No. 0646. JP-A-10-
In JP-A-107335, an external capacitor is provided for power recovery, and a coil, which is an inductance, is interposed in a charge / discharge circuit to effectively store a part of the discharge charge of the piezoelectric / electrostrictive element in the external capacitor. A configuration for saving power by using the battery for charging is disclosed in Japanese Patent No. 299091.
No. 50 discloses a configuration in which piezoelectric elements driven at different timings are used as power recovery means, and power consumption is reduced without providing an external capacitor separately. However, although all of them have an effect on saving power consumption, there is no description about a technique for spraying a large amount of liquid stably, and a delay in supply of liquid from the introduction hole to the pressurizing chamber is solved. Not. Also, JP-A-8-3006
No. 46 discloses that the falling of the drive voltage waveform is two steps /
A configuration is shown in which the generation of satellites is suppressed by improving the stability of the meniscus in three stages. By reducing the discharge time constant in the three stages, the printing speed is increased and the ink ejection amount is increased as a result. Is possible,
Since the discharge start characteristics at each stage are not smooth, the printing speed cannot be significantly increased, and the discharge amount cannot be increased significantly.

In view of the above problems, it is an object of the present invention to provide a driving circuit for a liquid droplet spraying device capable of smoothly supplying a liquid to a pressurizing chamber even when a large amount of liquid is sprayed. And

[0007]

Means for Solving the Problems To solve the above problems, the invention of claim 1 comprises a nozzle for spraying a droplet, a pressurizing chamber for pressurizing a liquid sprayed from the nozzle, and a pressurizing chamber. And a plurality of fine droplet spraying units each having a piezoelectric / electrostrictive element for pressurizing the pressurizing chamber, and a plurality of adjacent droplet spraying units having a common liquid introducing hole. In the droplet spraying device connected to the liquid supply path, a predetermined voltage signal is applied to the piezoelectric / electrostrictive element, thereby deforming the wall of the pressurizing chamber, and A droplet spraying device driving circuit for ejecting a liquid supplied to the pressurizing chamber from the nozzle, wherein a ratio of an introduction hole diameter to a nozzle hole diameter (introduction hole diameter / nozzle hole diameter) is 0.6 or more and 1.6 or less, and Ratio of nozzle hole diameter to nozzle thickness (nozzle hole diameter / Is between 0.2 and 4, the applied voltage signal supplies current to the piezoelectric / electrostrictive element and charges it, holds the final charging voltage for a certain period of time, and then discharges two or more types of discharge time constants Are sequentially performed, and the first first discharge time constant is larger than the second second discharge time constant, and a voltage difference between the charge start voltage and the final charge voltage with reference to the charge start voltage. 35% to 70% of
% Of the piezoelectric / electrostrictive element in series with the piezoelectric / electrostrictive element in at least one discharge circuit.

According to this configuration, in the case of a configuration in which liquid droplets are sprayed at the time of charging the piezoelectric / electrostrictive element, the discharging time constant of the first discharge circuit is large when discharging the charged electric charge. When deformation can be started gently and droplets are ejected simultaneously from multiple droplet spray units,
The operation of introducing the liquid into the plurality of pressurized chambers is reliably performed. Thereafter, the operation shifts to a quick suction operation in which the time required to discharge the unit voltage value is short, so that the liquid supply to the pressurizing chamber can be performed smoothly and in a short time, and the liquid supply amount can be increased.

When the discharge starting voltage is 35% or less,
Discharge with a large discharge time constant, that is, gentle suction occupies most of the entire suction process, and the suction itself is surely performed, but the suction amount per unit time can not be large, and as a result, The spray cycle cannot be shortened and a large amount of spray cannot be secured. Further, if the time constant of the first discharge is set to be relatively small within a range larger than the time constant of the second discharge so as to increase the suction amount per unit time, the start of suction becomes unstable, and poor spraying is caused. On the other hand, when it is 70% or more, the discharge time constant is large, that is, the rate of gentle suction is too small, so that the suction of the liquid cannot be started quickly, and the discharge from the liquid introduction hole to the liquid pressurizing chamber after the discharge is performed. The suction amount of the liquid decreases, and bubbles are entangled from the liquid discharge nozzle, and the spray becomes unstable.

Further, when spraying with the above-mentioned driving waveform, the ratio of the nozzle to the introduction hole (introduction hole diameter / nozzle hole diameter) is a good direction in consideration of suction as the ratio increases, but the rate at which the pressure during spraying escapes to the introduction hole side is high. If the spraying power becomes large and the spraying power becomes small, and if it becomes small, the supply amount becomes insufficient, the ratio of the inlet hole diameter to the nozzle hole diameter (inlet hole diameter / nozzle hole diameter) is preferably 0.6 to 1.6. Further, the ratio of the nozzle hole diameter to the nozzle thickness (nozzle hole diameter / nozzle thickness) is preferably 0.2 or more and 4 or less, and if it is 4 or less, the residual vibration of the liquid surface immediately after spraying due to the contact resistance with the fluid on the nozzle wall surface. It is possible to quickly converge, and furthermore, it is possible to prevent air bubbles from entering the pressurized chamber due to pressure fluctuations in the pressurized chamber at the time of electric discharge, thereby improving the spraying stability. As a result, the spraying can be performed in a short cycle, and the spray amount can be increased. Further, when it is 0.2 or more, poor spraying caused by insufficient spraying force due to large contact resistance of the liquid on the nozzle wall surface can be prevented. Further, when three of the ratio of the introduction hole to the nozzle hole, the ratio of the nozzle hole to the nozzle thickness, and the discharge voltage ratio are simultaneously satisfied, it is possible to prevent poor spraying due to the intrusion of bubbles and to secure a large amount of spraying.

[0011] The invention of claim 2 is the invention according to claim 1,
The time (t) from when the discharge is started with the first discharge time constant to when the next predetermined voltage signal is applied to the piezoelectric / electrostrictive element
4) a nozzle for ejecting liquid, a pressurizing chamber for pressurizing the liquid to be ejected from the nozzle, an introduction hole for supplying the liquid to the pressurizing chamber, and a piezoelectric / electrode for pressurizing the pressurizing chamber. A discharge time at a first discharge time constant that is equal to or more than ４ and not more than 20 times the natural oscillation period (To) when the liquid is supplied to the flow path in the structure constituted by the strain element; t3) and the ratio (t3 / t4) of the time (t4) from the start of the discharge with the second discharge time constant to the application of the next predetermined voltage signal to the piezoelectric / electrostrictive element is 0.1 or more. 20 or less.

With this configuration, the time (t4) from the time when the piezoelectric / electrostrictive element starts discharging at the second discharging time constant to the time when the next predetermined voltage signal is applied becomes equal to the natural frequency (T).
In the case of o) or less, the suction speed of the liquid from the liquid inlet into the liquid pressurizing chamber after spraying is too high. Due to the suction at the time of the second discharge, the supply of the liquid from the introduction hole cannot be made in time, and bubbles enter the pressurizing chamber from the droplet spray nozzle, resulting in poor spraying. On the other hand, when it is 20 times or more of To, the suction amount per unit time cannot be increased, and as a result, the spray cycle cannot be shortened and a large spray amount cannot be secured. Further, the time (t3) of the discharge with the first discharge time constant and the time (t4) between the time when the discharge is started with the second discharge time constant and the time when the predetermined voltage signal is applied to the next piezoelectric / electrostrictive element. When the ratio is 0.1 or less, the ratio of the first discharge having a large time constant is small, the ratio of the liquid suction amount at the first discharge to the total suction amount is reduced, and the suction catches up at the time of the second discharge suction. Gone
Bubbles may enter the pressurizing chamber from the droplet spray nozzle, resulting in poor spraying. When the above ratio is 20 or more,
A large amount of suction per unit time cannot be obtained, and as a result, the spray cycle cannot be shortened, and a large amount of spray cannot be secured.

According to a third aspect of the present invention, in the first or second aspect, an inductance and a resistance are interposed in series with the charging circuit in addition to the discharging circuit. With this configuration, the voltage / time gradient at the time of spraying becomes linear, and the stability of spraying droplets is improved.

According to a fourth aspect of the present invention, there is provided a droplet spray nozzle,
Microdroplets provided with a pressurizing chamber for pressurizing liquid ejected from the nozzle, an introduction hole for supplying liquid to the pressurizing chamber, and a piezoelectric / electrostrictive element for pressurizing the pressurizing chamber. In a droplet spraying device having a plurality of spraying units, in which liquid introduction holes of a plurality of adjacent droplet spraying units are connected to a common liquid supply path, the piezoelectric / electrostrictive element to which a predetermined voltage signal is applied is repeatedly different. By applying a voltage signal,
A droplet spraying device driving circuit that changes a wall of the pressurizing chamber and ejects a liquid supplied to the pressurizing chamber from the nozzle by a pressure generated in the pressurizing chamber. The ratio (nozzle hole diameter / nozzle hole diameter) is 0.6 or more and 1.6 or less, and the ratio of the nozzle hole diameter to the nozzle thickness (nozzle hole diameter / nozzle thickness) is 0.2 or more and 4 or less. After the current is discharged from the piezoelectric / electrostrictive element to which the discharge starting voltage is applied, the final discharge voltage is held for a certain period of time, and then the charge is sequentially performed with two or more types of charge time constants, and the first charge is performed. The second charge is started at a voltage having a time constant larger than the second charge time constant and 30% to 65% of a voltage difference between the final discharge voltage and the discharge start voltage with respect to the final discharge voltage. And at least one charge Characterized in that said piezoelectric / electrostrictive element in series inductance and resistance to the road is interposed.

According to this configuration, in the case of a configuration in which droplets are sprayed at the time of discharging the piezoelectric / electrostrictive element, the time constant is large at the start of charging of the first charging circuit when charging. Can start deforming slowly, and when spraying droplets simultaneously from multiple droplet spray units,
The operation of introducing the liquid into the plurality of pressurized chambers is reliably performed. Thereafter, the operation shifts to a quick suction operation in which the time required to charge the unit voltage value is short, so that the liquid supply to the pressurizing chamber can be performed smoothly and in a short time, and the liquid supply amount can be increased.

When the final discharge voltage is 65% or more, charging with a large charging time constant, that is, gentle suction occupies most of the entire suction process, and the suction is reliably performed. Not enough suction per hour
As a result, the spray cycle cannot be shortened. For this reason, it is not possible to secure a large amount of spraying, and if the initial charging time constant is set to be relatively small in a range larger than the second time constant so as to increase the suction amount per unit time, the suction start becomes unstable. Causes poor spraying. On the other hand, when the charging time is 30% or less, the charging time constant is large, that is, the rate of gentle suction is too small, so that the suction of the liquid cannot be started quickly, and the spray becomes unstable. Furthermore, when spraying with the above drive waveform, the ratio of the diameter of the introduction hole to the diameter of the nozzle (introduction hole diameter / nozzle hole diameter)
Although it is a good direction to consider suction when it becomes large, the rate at which the pressure during spraying escapes to the introduction hole side is large, and the spraying power becomes insufficient. In addition, if the diameter becomes smaller, the supply amount becomes insufficient with respect to the spray amount. Therefore, the ratio of the introduction hole diameter to the nozzle hole diameter (introduction hole diameter / nozzle hole diameter) is preferably from 0.6 to 1.6.

Further, the ratio of the nozzle hole diameter to the nozzle thickness (nozzle hole diameter / nozzle thickness) is preferably 0.2 or more and 4 or less, and if it is 4 or less, the liquid level immediately after spraying due to the contact resistance with the fluid on the spray nozzle wall surface. Residual vibration can quickly converge, and the pressure fluctuation in the pressurizing chamber during discharge can prevent bubbles from entering the pressurizing chamber and improve the spraying stability. As a result, it is possible to spray in a short cycle and increase the spraying amount. Can be. Further, when it is 0.2 or more, poor spraying caused by insufficient spraying force due to large contact resistance of the liquid on the nozzle wall surface can be prevented.
Furthermore, when three of the ratio of the introduction hole and the nozzle hole, the ratio of the nozzle hole and the nozzle thickness, and the charging voltage ratio are simultaneously satisfied, it is possible to prevent poor spraying due to intrusion of bubbles and to secure a large amount of spraying.

According to a fifth aspect of the present invention, in the fourth aspect, 2
The time (t) from when charging is started with the first charging time constant to when the next predetermined voltage signal is applied to the piezoelectric / electrostrictive element
40) a liquid ejecting nozzle, a pressurizing chamber for pressurizing the liquid ejected from the nozzle, an introduction hole for supplying liquid to the pressurizing chamber, and a piezoelectric / A time for charging at a first charging time constant that is not less than ４ and not more than 20 times the natural oscillation period (To) when a liquid is supplied to the flow path in the structure composed of the electrostrictive element. (T3
0) and the time (t40) from the start of charging with the second charging time constant to the application of the next predetermined voltage signal to the piezoelectric / electrostrictive element (t30 / t40) is 0.1 or more and 2
0 or less.

With this configuration, t40 is one-fourth of To.
In the following cases, the suction speed is too fast, so even if suction starts at the beginning of the bend without any problems, the supply of the liquid from the introduction hole cannot be made in time due to the suction at the second charge, and air bubbles are added from the nozzle holes. Intrusion into the pressure chamber prevents spraying. Also, t
When 40 is equal to or more than 20 times To, the suction amount per unit time cannot be increased, and as a result, the spray cycle cannot be shortened, and a large spray amount cannot be secured.

According to a sixth aspect of the present invention, in the fourth or fifth aspect, an inductance and a resistance are interposed in series with the discharging circuit in addition to the charging circuit. By doing so, the voltage / time gradient during spraying becomes linear, and the stability of droplet spraying is improved.

According to a seventh aspect of the present invention, there is provided a droplet spray nozzle,
Microdroplets provided with a pressurizing chamber for pressurizing the liquid to be sprayed from the nozzle, an introduction hole for supplying the liquid to the pressurizing chamber, and a piezoelectric / electrostrictive element for pressurizing the pressurizing chamber. In a droplet spraying device having a plurality of spraying units and the liquid introduction holes of adjacent multiple droplet spraying units connected to a common liquid supply path, a predetermined voltage signal is applied to the piezoelectric / electrostrictive element. A liquid droplet spraying device driving circuit for deforming a wall of the pressurized chamber and ejecting a liquid supplied to the pressurized chamber from the nozzle by pressure generated in the pressurized chamber, wherein an applied voltage signal is: After the current is supplied to the piezoelectric / electrostrictive element for charging, the final charging voltage is held for a certain period of time, and then discharge having two or more types of discharge time constants is sequentially performed. At least one greater than the th discharge time constant A circuit for interposing an inductance and a resistor in series with the piezoelectric / electrostrictive element in the discharge circuit, dividing the piezoelectric / electrostrictive element into at least two or more groups, and charging and discharging current to each group; At least part of the discharge current of one group is used as part of the charge current of the other group.

According to this configuration, when the piezoelectric / electrostrictive element is configured to spray liquid droplets at the time of charging, when discharging the charged electric charge, the discharge time constant of the first discharge circuit is large. When deformation can be started gently and droplets are ejected simultaneously from multiple droplet spray units,
The operation of introducing the liquid into the plurality of pressurized chambers is reliably performed. Thereafter, the operation shifts to a quick suction operation in which the time required to discharge the unit voltage value is short, so that the liquid supply to the pressurizing chamber can be performed smoothly and in a short time, and the liquid supply amount can be increased. Further, since the discharge power of the piezoelectric / electrostrictive element is directly used as the charging current of another piezoelectric / electrostrictive element, it is not necessary to newly provide a power storage means, and power consumption can be further reduced.

[0023] The invention according to claim 8 is characterized in that a nozzle for spraying a droplet is provided,
Microdroplets provided with a pressurizing chamber for pressurizing liquid ejected from the nozzle, an introduction hole for supplying liquid to the pressurizing chamber, and a piezoelectric / electrostrictive element for pressurizing the pressurizing chamber. In a droplet spraying device having a plurality of spraying units, in which liquid introduction holes of a plurality of adjacent droplet spraying units are connected to a common liquid supply path, the piezoelectric / electrostrictive element to which a predetermined voltage signal is applied is repeatedly different. By applying a voltage signal,
A droplet spraying device driving circuit for changing a wall of the pressurizing chamber and ejecting a liquid supplied to the pressurizing chamber from the nozzle by a pressure generated in the pressurizing chamber, wherein the different applied voltage signal Is the piezoelectric / electrode to which the discharge starting voltage is applied.
After discharging the current from the electrostrictive element, the final discharge voltage is held for a certain period of time, and then charging with two or more types of charging time constants is sequentially performed. At least one charging circuit is connected in series with the piezoelectric / electrostrictive element. The piezoelectric / electrostrictive element is divided into at least two or more groups by interposing an inductance and a resistance, and each of the groups has a circuit for charging and discharging a current. Is used for a part of the charging current of the group.

According to this configuration, in the case of a configuration in which droplets are sprayed at the time of discharging the piezoelectric / electrostrictive element, the time constant at the start of charging of the first charging circuit during charging is large. Can start deforming slowly, and when spraying droplets simultaneously from multiple droplet spray units,
The operation of introducing the liquid into the plurality of pressurized chambers is reliably performed. Thereafter, the operation shifts to a quick suction operation in which the time required to charge the unit voltage value is short, so that the liquid supply to the pressurizing chamber can be performed smoothly and in a short time, and the liquid supply amount can be increased. Further, since the discharge power of the piezoelectric / electrostrictive element is directly used as the charging current of another piezoelectric / electrostrictive element, it is not necessary to newly provide a power storage means, and power consumption can be further reduced.

A ninth aspect of the present invention is characterized in that, in the seventh aspect of the present invention, an inductance and a resistance are interposed in series with the charging circuit in addition to the discharging circuit. By doing so, the voltage / time gradient during spraying becomes linear, and the stability of droplet spraying is improved.

According to a tenth aspect, in the eighth aspect, an inductance and a resistance are interposed in series with the discharge circuit in addition to the charging circuit. By doing so, the voltage / time gradient during spraying becomes linear, and the stability of droplet spraying is improved.

[0027]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows an example of a droplet spraying device driving circuit according to the present invention, and shows a circuit in a case where a spraying operation is performed when a piezoelectric / electrostrictive element is charged. 10
(10a to 10c) are Schmitt trigger ICs for converting a signal from a control unit (not shown) such as a microcomputer into drive circuit operation signals, R6, R7, and R8 are resistors for limiting the output current of the Schmitt trigger IC 10, M2 Is a charge switch composed of a P-MOSFET for passing a charging current to a piezoelectric / electrostrictive element 1 (hereinafter referred to as a pressure element), and M3 and M4 are first and second N-MOSFETs for discharging the pressure element 1 respectively. It is a discharge switch.

The charging switch M2 forms a charging circuit 12 together with a coil L1 and a resistor R1 provided in series at its output, and a Schmitt trigger IC 10 via a switch M5.
a. Also, the first discharge switch M3
Is controlled by the Schmitt trigger IC 10b, and the first discharge circuit 13a is formed by the first discharge switch M3 and the coil L2 and the resistor R2 provided in series with the discharge circuit. The second discharge switch M4 is connected to the Schmitt trigger I
Controlled by C10c, a second discharge circuit 13b is formed by the second discharge switch M4 and the coil L3 and the resistor R3 provided in series with the discharge circuit. Here, in the second discharge circuit 13b, the time T4 required for discharging the unit voltage value at the start of discharge (which is determined by the coil L3, the resistor R3, and the capacitor C1) is the discharge start in the first discharge circuit. Sometimes, it is set shorter than the time T3 required to discharge the unit voltage value (this is determined by the coil L2, the resistor R2, and the capacitor C1). In addition, Vp
Is a power supply voltage, and Vd is a voltage applied to the pressure element.

FIG. 2 (a) shows the characteristics of the voltage applied to the pressure element of the drive circuit of FIG. 1, and t1 is the rise time when the charging circuit charges the pressure element 1, and rises slowly by the action of the coil L1. , The rise time t1 is the applied voltage Vd
Is adjusted by the coil L1 and the resistor R1 as a time for causing the voltage to reach a desired voltage value. Then, the pressurizing element 1 is deformed by this charging operation, and pressurizes the pressurizing chamber 2 to spray droplets from the droplet spray nozzle 3. Further, t2 is a holding time for maintaining the pressurized chamber 2 or a state in which the liquid is completely sprayed in order to stabilize the liquid in the pressurized chamber for a certain time.

T3 and t4 are the first discharge circuit 13a and the second
The time T4 required to discharge the unit voltage at the start of the discharge of the second discharge circuit 13b is the fall time when the discharge circuit 13b is sequentially activated, and the unit voltage is discharged at the start of the discharge of the first discharge circuit 13a. , The discharge characteristic at time t4 becomes lower than the discharge characteristic at time t3. However, the coil L2
Due to the action of L3, the change at the start of discharge is gradual. In addition, the circuit provided with the coil L2 and without the coil L3 also considers the balance between the spray amount and the supply amount,
It can be suitably used.

As described above, the discharge circuit is provided in two stages, and the change of the applied voltage Vd at the time of the fall is set to be gentle at first and then to a steep slope from the middle.
The liquid flows into the pressurizing chamber 2 from the beginning, but the supply speed becomes slow at first, and the suction can be started uniformly from the plurality of introduction holes 5. The suction speed is accelerated so that a large amount can be sucked, and the drive cycle time T can be shortened as compared with the case where the suction is performed at the first suction speed to the end, and the spray amount from the nozzle is increased in proportion thereto. Can be. Therefore, it is possible to increase the droplet spray per unit time.

Further, by interposing the coil L1 in the charging circuit 12, the applied voltage Vd does not rise sharply at the start of charging, so that residual vibration after spraying due to deformation of the pressurizing element 1 can be eliminated. In addition, the voltage / time gradient can be made constant, the spraying of the liquid droplets can be stabilized, and the occurrence of poor spraying due to entrainment of air bubbles from the nozzle during the suction operation can be prevented. Therefore, the holding time t2 can be shortened, the spray amount of the liquid can be further increased, and the liquid can be smoothly supplied to the pressurizing chamber. Also,
Since the coils L2 and L3 gradually change the applied voltage even at the start of discharge, the liquid can be sucked more efficiently, and the supply amount of the liquid can be further increased to increase the spray amount.

FIG. 2B shows a control signal of the drive circuit. In the figure, (1) shows a Schmitt trigger IC 10
a, the output signal of the Schmitt trigger IC 10b, the output signal of the Schmitt trigger IC 10c, and the charging circuit 12 outputs the Lo signal from the Schmitt trigger IC 10a as shown in FIG. The charging switch M2 is turned on to perform a droplet spraying operation, and the two discharge circuits 13a and 13b are respectively connected to the Schmitt trigger IC.
Hi signals are sequentially output from 10b and 10c, and the switches M3 and M4 are turned on to perform the liquid suction operation.

Although the discharge time constant for supplying the liquid is switched between two stages, the discharge time constant may be set to two or more stages and gradually shortened. The charge / discharge characteristics can be changed by changing the resistors R1 to R3, and a desired waveform can be set at low cost. In addition, while the pressure element 1 is charged for spraying the liquid droplets and the pressure chamber 2 is deformed, the discharge of the pressure element 1 causes the pressure chamber 2 to be deformed and the droplets are deformed. Is sprayed, it is only necessary to provide two stages of charging circuits having different charging characteristics and form a single stage discharging circuit.

FIG. 5 shows an example of a droplet spraying device operated by the above-mentioned drive circuit, and is an explanatory longitudinal sectional view of a central portion of a droplet discharging unit. The droplet spraying device includes a pressurizing unit for discharging the liquid, a pressurizing chamber 2 for pressurizing the discharged liquid,
A droplet discharge unit 6 having a liquid discharge nozzle 3 connected below the pressurizing chamber 2 for discharging liquid to a processing unit of the liquid droplet spraying apparatus, and an introduction hole 5 for supplying liquid to the pressurizing chamber 2. Is used as one unit, and a plurality of units from several to several hundred units are provided according to the usage mode. The droplet discharge unit 6 includes a plurality of adjacent pressure chambers 2, 2... Connected by a common liquid supply path 7 through an introduction hole 5, and a part of an upper wall of the pressure chamber 2. The piezoelectric / electrostrictive element 1 is provided as a pressing means. The piezoelectric / electrostrictive element 1 is formed by laminating an upper electrode 16, a piezoelectric / electrostrictive layer 18, and a lower electrode 17, and is generated between the upper electrode 16 and the lower electrode 17 by applying a predetermined voltage signal. The piezoelectric / electrostrictive layer 18 is deformed by the electrolysis, and the wall of the pressurized chamber 2 is deformed and the liquid supplied to the pressurized chamber 2 is discharged from the nozzle 3 by the pressure generated in the pressurized chamber 2. I do.

The ratio of the diameter of the introduction hole 5 to the diameter of the nozzle 3 (introduction hole diameter / nozzle hole diameter) is set to a value between 0.6 and 1.6, for example, 1.0, and the ratio of the nozzle hole diameter to the thickness of the nozzle (nozzle diameter) The hole diameter / nozzle thickness) is between 0.2 and 4, for example, 2. The ratio between the diameter of the introduction hole 5 and the diameter of the nozzle 3 is set to 0.
By setting the ratio from 6 to 1.6, the spraying force and the suction force are balanced, and there is no shortage of the spraying force and no shortage of the suction force. If the ratio of the introduction hole diameter / nozzle hole diameter exceeds 1.6, suction works well, but the rate at which the pressure during spraying escapes to the introduction hole side becomes large, resulting in insufficient spraying power. On the other hand, if it is smaller than 0.6, the supply amount is insufficient for the spray amount. Further, if the nozzle hole diameter / nozzle thickness is 4 or less, the residual vibration of the liquid surface immediately after spraying can be quickly converged due to the contact resistance with the fluid on the nozzle wall, and the pressure due to the fluctuation of the pressure inside the pressurizing chamber 2 at the time of discharge is further increased. It is possible to prevent air bubbles from entering the pressure chamber 2 and improve the spraying stability. As a result, the spraying can be performed in a short cycle, and the spraying amount can be increased. It is possible to prevent the occurrence of insufficient spraying due to the large contact resistance of the above, resulting in poor spraying. In the above embodiment, the nozzle hole diameter is 25 μm.
m to 100 μm.

FIG. 6 shows that the driving voltage of the piezoelectric / electrostrictive element is constant at 40 V and t1 = 2 in the applied voltage waveform of FIG.
0 μS, t2 = 5 μS, t3 = 20 μS, t4 = 10 μS
It is measurement data showing the stability of the spraying operation of the droplet spraying device by changing the voltage at which the discharge is changed from the discharge with the first discharge time constant to the discharge with the second discharge time constant, assuming that it is constant at S. As shown in the figure, the spraying operation is good when the transition voltage to the discharge by the second discharge time constant is between 38% and 63% of the final charging voltage, but no good operation is shown at 25% and 75%. As described above, the voltage at which the second discharge is started has a range, and the applied voltage, that is, the final charge voltage, is 3 times.
It is preferable to start the second discharge at a voltage of 5% to 70%, and the above-mentioned three ratios of the introduction hole diameter and the nozzle hole diameter, the ratio of the nozzle hole diameter and the nozzle thickness, and the second discharge start voltage are simultaneously satisfied. In addition, it is possible to prevent poor spraying due to entrainment of air bubbles from the nozzle for spraying droplets, and to secure a large amount of spray.

When the second discharge starting voltage is 35% or less, discharge having a large discharge time constant, that is, gentle suction occupies most of the entire suction process, and the suction itself is surely performed. It will be performed, but the suction amount per unit time can not be large, as a result, the spray cycle can not be shortened,
If it is not possible to secure a large amount of spray, and if the first discharge time constant is set to be larger than the second discharge time constant and the suction time is set relatively small so as to increase the suction amount per unit time, suction starts. Unstable, leading to insufficient spray volume,
When the discharge time is 70% or more, the discharge time constant is large, that is, the rate of the gentle suction is too small to start the liquid suction promptly, and the liquid introduction hole 5 to the liquid pressurized chamber after the discharge is discharged.
The amount of liquid sucked from the nozzle 3 is reduced, and bubbles are trapped in the nozzle 3 and the spray becomes unstable.

Further, the discharge time t4 at the second discharge time constant is determined by the nozzle 3 for spraying the droplet, the pressurizing chamber 2 for pressurizing the liquid sprayed from this nozzle, and the pressurizing chamber 2 Four minutes of the natural oscillation period To when the liquid is supplied to the flow path in the structure constituted by the introduction hole 5 for supplying the liquid and the piezoelectric / electrostrictive element 1 for pressurizing the pressure chamber 2. 1 or more of 20
It is preferable that the ratio t3 / t4 of the first discharge time t3 and the second discharge time t4 is 0.1 to 20 or less, and by setting the ratio to this range, the suction speed is reduced from the introduction hole. The liquid can be smoothly supplied, and the spraying operation can be favorably performed without air bubbles entering the pressurized chamber from the nozzle.

If the time t4 is equal to or less than To / 4, the suction speed is too high.
In the second suction operation at the time of discharge, the supply of the liquid from the introduction hole cannot be made in time, and bubbles enter the pressurizing chamber 2 from the nozzle 3 to cause poor spraying. On the other hand, if it is 20 T or more, a large suction amount per unit time cannot be obtained, and as a result, the spray cycle cannot be shortened, and a large discharge amount cannot be secured. Also, t
When 3 / t4 is 0.1 or less, the ratio of the first discharge having a large time constant is small, the suction ratio of the liquid at the first discharge to the entire suction amount is reduced, and the ratio at the time of suction during the second discharge is reduced. Suction cannot catch up and it is easy to have poor spraying.
If the value is set to 0 or more, the effect of setting the second discharge time constant is lost, and the effect of increasing the drive frequency is more effective in terms of mass spraying. Note that the discharge time constant for supplying the liquid is switched between two stages, but it is also preferable to set the discharge time constant to two or more stages and gradually increase. In addition, while the piezoelectric / electrostrictive element is charged to spray the droplet and deforms the pressurized chamber, the piezoelectric / electrostrictive element is discharged to deform the pressurized chamber to spray the droplet. In this case, the charging by the second charging time constant is started at a voltage of 30% to 65% of the discharge starting voltage.

FIG. 8 shows an MLP (stacked actuator) used as a piezoelectric / electrostrictive element, which operates in the opposite manner to the droplet spraying device shown in FIG. 3A and 3B are explanatory views of a droplet spraying unit for spraying a liquid crystal, wherein FIG. 3A is a longitudinal sectional view, and FIG.
In the figure, 23 is a fixing member for fixing the piezoelectric / electrostrictive element, 20 is a positive electrode, 21 is a negative electrode, and 22 is a piezoelectric / electrostrictive layer. The same components as those in FIG. 5 are denoted by the same reference numerals. In this case, the ratio between the inlet hole diameter and the nozzle hole diameter, and the ratio between the nozzle hole diameter and the nozzle thickness may be the same as in the above embodiment, and the second charge start voltage is based on the discharge final voltage. It is preferable that the difference between the final voltage and the discharge starting voltage is 30 to 65%. Also,
The charging time t40 at the second charging time constant is equal to or more than one-fourth of the natural oscillation period To as in the above-described embodiment.
A charging time t3 that is equal to or less than 0 times and based on the first charging time constant
The ratio t30 / t40 of 0 to the second charging time is set to 0.1 to
It should be 20.

FIG. 3 is a main part circuit diagram showing a second embodiment of the present invention.
Are provided. The charging circuit includes three FETs, a first charging switch M12, a second charging switch M15, and a third charging switch M16. The discharging circuit includes a first discharging switch M13 and a second discharging switch M16.
14 and a third discharge switch M17. The resistors R11 to R16 determine the charge / discharge characteristics of each circuit in combination with the capacitance components of both the pressure elements 1 and 11. The first charge switch M12 and the first discharge switch M13 have the coil L11 and the coil L
12 is inserted in series with the resistors R11 and R12. D1 to D4 are diodes.

The operation of this circuit will be described with reference to the applied voltage characteristic diagram of FIG. FIG. 4A shows an applied voltage waveform of the first pressing element 1, and FIG. 4B shows an applied voltage waveform of the second pressing element 11. First, at the first charging time t21, the first charging switch M12 is turned on to discharge the second pressing element 11, and the first pressing element 1 is discharged by the discharged charge.
Charge. Next, at the second charging time t22, the second charging switch M15 is turned on to charge the insufficient charge,
The discharge switch M17 is turned on to completely discharge the pressure element 11.

Thereafter, after maintaining that state for a certain period of time in a period t23, the first discharge switch M is turned on for a first discharge time t24.
13 is turned on to discharge, and the discharged charge is charged to the second pressure element 11. Then, the second discharge time t25
Then, the second discharging switch M14 is turned on to discharge the remaining capacity, and the third charging switch M16 is turned on to charge the insufficient charge of the second pressurizing element 11, and the state is maintained at time t26. In this case, when time t21 is started, t21 to t26 constitute one cycle of charging and discharging, and the first pressing element 1 and the second pressing element 11 operate in synchronization with each other, and this voltage waveform is repeated. Applied.

As described above, by providing the pressurizing elements that are shifted by a half cycle, the mutual elements can be used as power storage means, and the discharged charge can be efficiently used without providing a separate power storage means such as a capacitor. be able to. Therefore, when a plurality of pressurizing elements are provided, the pressurizing elements are divided into two or more groups and operated by being shifted by about a half cycle, so that at least a part of the discharge current of one group is reduced to the other group. Can be used for at least a part of the charging current, and the power consumption can be further reduced.

Although the above embodiment is configured by an analog circuit, a drive waveform can be generated by a digital signal and converted into an analog signal, and the drive waveform can be set appropriately. Further, although all the charge switches or discharge switches are MOS type FETs, the present invention is not limited thereto, and a drive circuit may be constituted by transistors.

[0047]

As described in detail above, according to the present invention,
The liquid supply to the plurality of pressurizing chambers can be performed smoothly and in a short time, and the liquid supply amount can be increased.
In addition, the start of liquid suction can be started gently, the liquid can be sucked efficiently, and the supply amount of the liquid can be further increased. Therefore, the application cycle can be further shortened, and the ejection amount of the liquid can be further increased,
The supply of the liquid to the pressurizing chamber can also be performed smoothly.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one example of a droplet spray device driving circuit according to the present invention.

2A and 2B show operating characteristics of the drive circuit of FIG. 1, wherein FIG. 2A shows a voltage waveform applied to a piezoelectric / electrostrictive element, and FIG. 2B shows a control signal.

FIG. 3 is a circuit diagram of a droplet spray device driving circuit according to a second embodiment of the present invention.

FIG. 4 is an applied voltage waveform of FIG.

FIG. 5 is an explanatory vertical sectional view of a central portion of a droplet spraying unit driven by the droplet spraying device drive circuit of FIG. 1;

6 is a diagram illustrating the stability of the droplet spraying device when the discharge time constant of the voltage waveform in FIG. 2 is changed.

FIG. 7 is a central sectional explanatory view of a droplet spraying unit of the droplet spraying device.

FIG. 8 is a central vertical sectional view showing another example of the droplet spray unit driven by the droplet spray device drive circuit of FIG. 1;

[Explanation of symbols]

1. Pressurizing element (piezoelectric / electrostrictive element), 2. Pressurizing chamber, 3
..Droplet spray nozzles, 5..introduction holes, 6..droplet spray units, 7..liquid supply paths, 11..pressurizing elements (piezoelectric / electrostrictive elements), 12..charging circuits, 13a .. First discharge circuit, 13b second discharge circuit, M2 charge switch, M3 first discharge switch, M4 second discharge switch, M12 first charge switch, M13 first Discharge switch, M14... Second discharge switch, M15.
Second charge switch, M16... Third charge switch, M1
7. Third discharge switch, L1, L2, L3, L11,
L12 ... coil, R1 to R3, R6 to R16 ... resistance.

Continued on the front page (72) Inventor Juichi Hirota 2-56, Suda-cho, Mizuho-ku, Nagoya Japan Insulator Co., Ltd. F-term (reference) 2C057 AF04 AF54 AG33 AG44 AG75 AR16 BA04 BA14

Claims (10)

[Claims] 1. A droplet spray nozzle, a pressurizing chamber for pressurizing a liquid to be sprayed from the nozzle, an introduction hole for supplying a liquid to the pressurizing chamber, and a pressurizing operation of the pressurizing chamber. Piezo /
A droplet spraying device comprising a plurality of micro droplet spraying units each having an electrostrictive element, wherein liquid introduction holes of adjacent plural droplet spraying units are connected to a common liquid supply path; By applying a predetermined voltage signal to the liquid droplet spraying device, the wall of the pressurized chamber is deformed, and the liquid supplied to the pressurized chamber is ejected from the nozzle by the pressure generated in the pressurized chamber. A circuit, wherein the ratio of the inlet hole diameter to the nozzle hole diameter (inlet hole diameter / nozzle hole diameter) is 0.6 or more and 1.6 or less, and the ratio of the nozzle hole diameter to the nozzle thickness (nozzle hole diameter / nozzle thickness) is 0.2 or more 4 In the following, the applied voltage signal supplies a current to the piezoelectric / electrostrictive element, charges the piezoelectric / electrostrictive element, holds the final charging voltage for a certain period of time, then sequentially performs discharge having two or more types of discharge time constants, and The first first discharge time constant is 2 Greater than the second discharge time constant of, and reference to the charging start voltage, 2 in 70% of the voltage from 35% of the voltage difference between the charging start voltage and the final voltage
A driving circuit for a droplet spraying device, wherein a first discharge is started, and an inductance and a resistance are interposed in at least one discharge circuit in series with the piezoelectric / electrostrictive element. 2. A liquid droplet spraying apparatus according to claim 1, wherein a time (t4) from when the discharge is started at the second discharge time constant to when the next predetermined voltage signal is applied to the piezoelectric / electrostrictive element is equal to the time required for spraying the droplet. It comprises a nozzle, a pressurizing chamber for pressurizing a liquid to be sprayed from the nozzle, an introduction hole for supplying liquid to the pressurizing chamber, and a piezoelectric / electrostrictive element for pressurizing the pressurizing chamber. The time (t3) for discharging at a first discharge time constant that is at least 1/4 to 20 times the natural oscillation period (To) when the liquid is supplied to the flow path in the structure, and the second time The ratio (t4) of the time (t4) from the start of discharge with the discharge time constant to the application of the next predetermined voltage signal to the piezoelectric / electrostrictive element.
3 / t4) is 0.1 or more and 20 or less. 3. The drive circuit according to claim 1, wherein an inductance and a resistance are interposed in series with the charging circuit in addition to the discharging circuit. 4. A droplet spray nozzle, a pressurizing chamber for pressurizing a liquid to be sprayed from the nozzle, an introduction hole for supplying liquid to the pressurizing chamber, and pressurizing the pressurizing chamber. Piezo /
A predetermined voltage signal is applied to a droplet spraying device in which a plurality of micro droplet spraying units each including an electrostrictive element are provided, and the liquid introduction holes of adjacent multiple droplet spraying units are connected to a common liquid supply path. By repeatedly applying different voltage signals to the piezoelectric / electrostrictive element, the wall of the pressurizing chamber is changed, and the liquid supplied to the pressurizing chamber by the pressure generated in the pressurizing chamber is supplied to the nozzle. A nozzle sprayer driving circuit, wherein the ratio of the inlet hole and the nozzle hole diameter (inlet hole diameter / nozzle hole diameter) is 0.6 or more and 1.6 or less and the ratio of the nozzle hole diameter and the nozzle thickness (nozzle hole diameter / nozzle) Thickness) is not less than 0.2 and not more than 4 and the different applied voltage signals maintain the discharge final voltage for a certain period of time after discharging current from the piezoelectric / electrostrictive element to which the discharge starting voltage is applied. More charging Sequentially was charged with a constant,
In addition, the first charging time constant is larger than the second charging time constant, and 30% or more and 65% of the voltage difference between the final discharge voltage and the discharge start voltage with respect to the final discharge voltage.
A droplet spraying device driving circuit, wherein a second charging is started at the following voltage, and an inductance and a resistance are interposed in at least one charging circuit in series with the piezoelectric / electrostrictive element. 5. The method according to claim 4, wherein the time (t40) from when charging is started with the second charging time constant to when the next predetermined voltage signal is applied to the piezoelectric / electrostrictive element is equal to the droplet spraying time. Nozzle, a pressurized chamber for pressurizing the liquid to be sprayed from the nozzle, and an introduction hole for supplying the liquid to the pressurized chamber,
When the liquid is supplied to the flow path in the structure composed of the piezoelectric / electrostrictive element for performing the pressurizing operation of the pressurizing chamber, the natural vibration period (To) is not less than ４ and not more than 20 times and The time (t30) for charging with the first charging time constant and the time (t40) from when charging is started with the second charging time constant to when the next predetermined voltage signal is applied to the piezoelectric / electrostrictive element. A liquid droplet spraying device driving circuit, wherein a ratio (t30 / t40) is 0.1 or more and 20 or less. 6. The droplet spraying device driving circuit according to claim 4, wherein an inductance and a resistance are interposed in series with the discharging circuit in addition to the charging circuit. 7. A droplet spray nozzle, a pressurizing chamber for pressurizing a liquid to be sprayed from the nozzle, an introduction hole for supplying a liquid to the pressurizing chamber, and pressurizing the pressurizing chamber. Piezo /
A droplet spraying device comprising a plurality of micro droplet spraying units each having an electrostrictive element, wherein liquid introduction holes of adjacent plural droplet spraying units are connected to a common liquid supply path; By applying a predetermined voltage signal to the liquid droplet spraying device, the wall of the pressurized chamber is deformed, and the liquid supplied to the pressurized chamber is ejected from the nozzle by the pressure generated in the pressurized chamber. A circuit in which an applied voltage signal supplies a current to the piezoelectric / electrostrictive element, charges the same, holds a final charging voltage for a certain period of time, and then sequentially performs discharges having two or more discharge time constants. And the first discharge time constant is larger than the second discharge time constant, and an inductance and a resistance are interposed in series with the piezoelectric / electrostrictive element in at least one discharge circuit, and the piezoelectric / electrostrictive element is connected to at least two discharge circuits. One or more glues And a circuit for charging and discharging current to each group, and using at least a part of the discharge current of one group as a part of the charge current of the other group. Drive circuit. 8. A droplet spray nozzle, a pressurizing chamber for pressurizing a liquid to be sprayed from the nozzle, an introduction hole for supplying liquid to the pressurizing chamber, and pressurizing the pressurizing chamber. Piezo /
A predetermined voltage signal is applied to a droplet spraying device in which a plurality of micro droplet spraying units each including an electrostrictive element are provided, and the liquid introduction holes of adjacent multiple droplet spraying units are connected to a common liquid supply path. By repeatedly applying different voltage signals to the piezoelectric / electrostrictive element, the wall of the pressurizing chamber is changed, and the liquid supplied to the pressurizing chamber by the pressure generated in the pressurizing chamber is supplied to the nozzle. A droplet spraying device driving circuit for spraying from, wherein the different applied voltage signals are:
After discharging the current from the piezoelectric / electrostrictive element to which the discharge starting voltage is applied, the discharge final voltage is held for a certain period of time, and thereafter, charging is sequentially performed with two or more types of charging time constants, and at least one charging circuit is provided. A circuit in which an inductance and a resistance are interposed in series with the piezoelectric / electrostrictive element, the piezoelectric / electrostrictive element is divided into at least two or more groups, and a current is charged and discharged in each group. A driving circuit for a droplet spraying device, wherein at least a part of a discharge current of a group is used as a part of a charge current of another group. 9. The driving circuit according to claim 7, wherein an inductance and a resistance are interposed in series with the charging circuit in addition to the discharging circuit. 10. The driving circuit according to claim 8, wherein an inductance and a resistance are interposed in series with the discharging circuit in addition to the charging circuit.