JPH01275147A - Ink jet recording method - Google Patents

Abstract

PURPOSE:To perform stable discharge of ink droplet and rapid stop of the motion of a meniscus by abruptly contracting an electromechanical converter, holding it for a predetermined period of time, then generating the expansion of a predetermined level at it, and then setting a driving voltage for gradually releasing its contraction. CONSTITUTION:A piezoelectric element 3 mounted in an ink pressure chamber 1 is disposed at the intermediate between an ink supply port 6 and an ink discharge port 2, and a driving voltage is applied by a driving circuit 18. When an abrupt voltage is applied to the element 3, the element 3 is contracted, held while the applied voltage maintains a predetermined value, and the free vibration of the element 3 is suppressed. A positive pressure part is formed at the moment that the element 3 is contracted, and propagated as a pressure wave toward the ports 6 and 7. When the positive pressure part is left to stand for as it is, the ink mightly be discharged. Accordingly, the driving voltage is reduced at the moment that the positive pressure part passes inside the element 3, the element 3 is expanded, and a negative pressure part is generated. In this case, the pressure of the negative pressure part is regulated by selecting the reducing amplitude of the voltage so that the positive pressure part and the negative pressure part cancel each other.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an inkjet recording method used in an inkjet recording apparatus and for driving an electromechanical transducer provided in an inkjet recording head thereof.

[Conventional technology]

As shown in FIG. 7, the inkjet recording apparatus includes a nozzle 2 for discharging ink at the end of an ink pressure chamber 1, and a piezoelectric element 3 as an electromechanical transducer provided near the nozzle 2. An inkjet recording head 10 is used. By applying a driving voltage according to recording data to the piezoelectric element 3, the ink pressure chamber l is kept at a steady state.
Expansion→steady or steady-shrink constant operation is performed, and ink droplets are ejected by the pressurizing force generated in the ink pressure chamber 1. The ink droplets that fly due to this ejection are attached to the surface of the recording medium (recording paper, film, etc.) to form dots.

The driving voltage has a rising part a, a constant value part, and a falling part C as shown in FIG.
The ink droplet is ejected by the pressure generated during the contraction. The constant value part maintains its contracted state, and is returned to its original state by the expansion caused by the rising part a at the falling part C.

Next, with reference to FIGS. 7 and 9 to 11, the operation of ejecting ink droplets using the drive voltage shown in FIG. 8 will be described in detail.

As shown in FIG. 7, the ink pressure chamber 1 contracts at the rising edge a of the driving voltage, and the ink pressure in the ink pressure chamber 1 decreases △
Increases by Q. Furthermore, since a pressure difference occurs between the ink pressure chamber 1 and the ink flow path at the boundary surfaces 4 and 5, pressure waves are generated and propagate toward the ink supply path 6 and the ink discharge lower direction.

After a while after the piezoelectric element 3 contracts, as shown in FIG. 9, areas 8 and 9 closer to the ink supply port 6 and the ink discharge lower, respectively, than the piezoelectric element 3 reach a pressure value of 1/2ΔP. There is. The lengths of these two high voltage portions are approximately equal to the length l of the piezoelectric element 3. Due to the mechanical properties (mass, elastic constants, etc.) of the piezoelectric element 3, it is difficult to clearly delineate the boundary of the high voltage portion 8.9 as shown in FIG.
This is done for convenience of explanation. At this point, the ink located inside the piezoelectric element 3, which continues to contract, has been returned to the pressure before the contraction (for example, atmospheric pressure).

Here, when the voltage applied to the piezoelectric element 3 reaches a falling point C in FIG. 8, the piezoelectric element 3 expands.

Therefore, the pressure of the ink located inside the piezoelectric element 3 decreases to -ΔP as shown in FIG.

Then, as in the case at the moment when the piezoelectric element 3 contracts, 2 with a pressure of 2 1/2 ΔP is created in the ink flow path.
Two negative pressure sections 11 and 12 are generated as pressure waves as shown in FIG. In addition, since the period during which the constant value part of the drive voltage occurs is long, it is assumed that regions 8 and 9 in FIG. 9 completely leave the ink pressure chamber 1, but in reality the constant value part is short. , regions 8 and 9 and negative pressure sections 11 and 1
2 may overlap with each other, but because of their linearity, they can be considered as two parts.

By the way, the region 9 pushes out ink from the ink ejection lower and converts the wave energy into kinetic energy of ink droplets. Although the positive pressure 1/2△P in this area 9 does not completely lose energy, it is considerably weakened compared to 1/2△P, and is reflected by the wall surface of the nozzle 2 and the ink discharge lower, and is reflected in the direction of the ink supply port 6. Head to. On the other hand, area 8
The positive pressure 1/2ΔP and the negative pressure portion 11.12 reciprocate within the ink pressure chamber l. At this time, when the region 8 is reflected by the ink supply port 6, it becomes a negative pressure part of -1/2ΔP and heads toward the nozzle 2, and conversely, the negative pressure part 11 becomes a positive pressure part and moves toward the nozzle. going in two directions (this is because the ink supply port 6 is an open end)
. On the other hand, the negative pressure portion 12 is similarly reflected by the ink discharge lower and heads toward the ink supply port 6 .

(Problem to be Solved by the Invention) However, in such a conventional inkjet recording method, the diameter d2 of the ink discharge lower is sufficiently smaller than the diameter d1 of the ink pressure chamber 1, so that it cannot be used as an open end. It functions as a closed end.

Therefore, even after being reflected, the negative pressure portion 12 propagates as a negative pressure portion and heads toward the ink supply port 6 .

Therefore, each pressure wave of the positive pressure and negative pressure portions 11.12 of the area 8 is reflected by the ink supply port 6 and the ink discharge lower and moves back and forth, and each time it reaches the ink discharge lower,
As shown in FIG. 12, the meniscus 14 formed in the ink discharge lower moves in the direction 15 or 16, and the area L!
The positive pressure and negative pressure 11 and 12 of 3i8 reciprocate between the ink supply port 6 and the ink discharge lower many times and do not stop until they weaken. Therefore, it takes time to eject the next ink droplet, which deteriorates the frequency characteristics of the head. Also,
When the positive pressure wave reaches the ink ejection lower
This causes droplets to be ejected, deteriorating the image quality. Furthermore, when the negative pressure wave reaches the ink ejection lower, air may be sucked in and bubbles may be generated within the ink flow path, resulting in inability to eject ink.

In order to solve the above problem, it is possible to apply a second pulse voltage to the piezoelectric element 3. That is, the positive pressure 1/2ΔP in the region 8 shown in FIGS. 9 and 10 is reflected at the ink supply port 6, becomes a negative pressure part 17 as shown in FIG. It is most effective to cancel the negative pressure portion 17 by making the rise time of the second pulse voltage coincide with the time when the second pulse voltage passes. However, since two new positive pressure waves and one negative pressure wave are generated, although it is possible to suppress the ejection of the second droplet, it takes time for the meniscus to recover, and there is still a risk of bubbles being taken in. There are some defects that remain.

An object of the present invention is to provide an inkjet recording method that can solve the problems of the prior art, eject ink droplets stably, and quickly stop the movement of the meniscus.

[Means to solve the problem]

The present invention provides an on-demand ink diisotope recording device that ejects ink droplets from the nozzle using pressure waves generated in the ink pressure chamber by contraction and expansion of an electromechanical transducer provided in the ink pressure chamber having a nozzle at its tip. , the driving voltage is applied to the electromechanical transducer to cause the contraction to occur rapidly, to hold the contraction for a certain period of time, to cause the expansion to occur rapidly to release the contraction to a certain level, and to gradually release the contraction. The above object is achieved by applying the voltage to the element.

Furthermore, the drive voltage when contraction occurs may be set to a value that corresponds to the amount of ink droplet ejection.

Further, the driving voltage during expansion can be made proportional to the amount of contraction when contraction occurs.

Further, the time t from the occurrence of the contraction to the occurrence of the expansion
, t=2 CIt l+2j22) /C (however,
11: Distance from the placement position of the electromechanical transducer element to the ink discharge port, β2: Distance from the placement position of the electromechanical conversion element to the ink supply port, C: Speed at which pressure waves propagate within the ink pressure chamber) It is desirable to set this.

[Effect]

By using a driving voltage that causes the electromechanical transducer to rapidly contract and hold it for a certain period of time, then rapidly expand to a predetermined level, and then gradually release the contraction, the positive pressure caused by the movement of negative pressure can be reduced. It is possible to prepare for ejection of the next ink droplet while preventing pressure from being generated and ejecting unnecessary ink droplets.

This makes it possible to prevent deterioration of image quality while also preventing deterioration of frequency characteristics.

By setting the drive voltage during contraction and expansion according to the amount of ink discharged and the amount of contraction, it becomes possible to determine the amount of discharged Q-wise, and prevents the occurrence of complicated pressure wave movements. Discharge can be performed stably.

In addition, by setting the contraction duration t based on the placement position of the electromechanical transducer with respect to each of the ink supply port and the ink discharge port, the negative pressure generated by the change in the drive voltage during expansion is adjusted. It can be canceled to such an extent that ink droplets are not ejected.

〔Example〕

The present invention will be specifically described below with reference to FIGS. 1 to 6.

FIGS. 1(a) and 1(b) are a time-voltage characteristic diagram of a drive voltage and a pressure wave propagation characteristic diagram in an ink pressure chamber for explaining the driving method according to the present invention. Further, FIG. 2 is a schematic cross-sectional view of a head applied to the present invention.

As shown in FIG. 2, the piezoelectric element 3 installed in the ink pressure chamber 1 is located in the middle between the ink supply port 6 and the ink discharge port 2, and is applied with a driving DJ lightning voltage from the drive circuit 18. .

As shown in FIG. 1(a), when a sudden voltage is applied to the piezoelectric element 3 at time 1=0, the piezoelectric element 3 contracts. In this state, the applied voltage is a constant value (approximately 85V in this example)
, and the free vibration of the piezoelectric element 3 is suppressed. At the moment when the piezoelectric element 3 contracts, a high pressure area (positive pressure area) is formed as shown in FIG. 7, and immediately two positive pressure areas (area 8.9) are formed as shown in FIG.
becomes a pressure wave and propagates toward the ink supply port 6 and the ink discharge lower at a speed C. The propagation of this pressure wave is as shown in FIG. 1(b).

In FIG. 1(b), d indicates that the positive pressure 1/2ΔP in the region 9 is directed toward the nozzle 2, and e indicates that it has reached the ink discharge lower. At the moment of this arrival, the ink liquid is pushed out from the ink ejection lower to the outside of the nozzle, and the ink droplet 1
7 is formed. Thereafter, a portion of the positive pressure is reflected by the ink discharge lower and heads toward the ink supply port 6, and thereafter reciprocates between the ink supply port 6 and the ink discharge lower. This is Figure 1 (
fj shown in b). This wave has a small energy because most of the wave energy given by the piezoelectric element 3 when 1=0 is applied to the ink droplet 17.

In FIG. 1(b), k indicates that the positive pressure in the region 8 is directed toward the ink supply port 6, and the point at which the positive pressure reaches the ink supply port 6 is l. Reflection occurs at these four points (reflection at the opening end), and the positive pressure portion conversely becomes a portion (negative pressure portion) with lower pressure than Po and moves toward the ink discharge lower (
wave m). Further, at this time, a part of the wave is sent from the ink supply port 6 to an ink tank (not shown) or the like. Therefore, the energy of the reflected wave toward the ink ejection lower reaches the ink ejection lower at point n while being somewhat weakened, and is re-reflected here. The reflection at this time is considered to be a reflection at the closed end, and therefore, the negative pressure portion directly goes toward the ink supply port 6 (O in FIG. 1(b)). At the time when the wave n occurs, the distance between the ink supply port 6 and the ink discharge lower is 20
In the case of about mm to 60+s, the ink droplet 17 is often connected to the ink in the ink pressure chamber. Therefore, part of the reflected energy of the negative pressure portion is absorbed by the ink droplet 17, and this reflected wave energy is somewhat weakened and reflected again at P. At this time, reflection of the opening end occurs at the ink supply port 6, resulting in a positive pressure portion (wave q). If left as is, this positive pressure portion may reach the ink ejection lower and cause ink to be ejected. This second ink droplet is undesirable because it degrades image quality.

Further, as the second droplet is ejected, it takes time to replenish ink between the ink supply port 6 and the ink ejection lower from an ink supply system (not shown), which causes deterioration of frequency characteristics. Therefore, when this positive pressure portion reaches r, that is, the moment when the positive pressure portion passes inside the piezoelectric element 3, that is, time 2(1+2β2)/C (however, the distance from the piezoelectric element 3 to the ink discharge lower 11 and jl!2, respectively, and the velocity of the pressure wave in the ink pressure chamber 1 is C), the driving voltage is lowered to expand the piezoelectric element 3 and generate a negative pressure portion.

This results in a negative pressure section 11.12 shown in FIG. Of these, the negative pressure portion 12 overlaps the above-mentioned positive pressure portion. At this time, by selecting the voltage drop height, the pressure of the two newly generated negative pressure parts can be adjusted,
The positive pressure portion and the negative pressure portion can function so as to cancel each other out.

The driving voltage that achieves this is shown in Figure 1 (a), where the voltage drop section y is stopped at a certain voltage value (about 40 V in this example) without reducing it to zero volts, and the negative pressure section is newly generated. This is done so that the degree of pressure drop is small. The reason for this is that the positive pressure portion has already traveled back and forth between the ink supply port 6 and the ink discharge lower and each time it is reflected, the pressure difference with Po becomes smaller, and the viscous resistance of the ink itself decreases.
This is because the pressure difference with Po is also reduced due to internal resistance, etc., so in order to cancel this, the voltage drop needs to be smaller than the rising voltage of the drive voltage (approximately 85 V in this example). . As a result, among the newly generated negative pressure portions, the negative pressure portion 12 becomes the only pressure wave left within the ink pressure chamber 1. This is the wave S indicated by the broken line shown in FIG. 1(b), which moves toward the ink supply port 6. This is reflected by U, becomes a positive pressure part, and becomes a wave (■) again toward the ink ejection lower, but it does not have enough energy to eject ink droplets.

By the way, after the drive voltage is lowered to two points, the voltage is gradually lowered to near zero volts. The reason for the gradual drop is that if the applied voltage is suddenly lowered, the piezoelectric element 3 will undergo complex vibrations, and corresponding pressure waves will be generated within the ink pressure chamber 1. , if the voltage at two points continues to be maintained, the driving voltage for the next ink ejection cannot be applied, so it is necessary to reduce the voltage to - and zero volts). Specifically, when the distance between the ink supply port 6 and the ink discharge lower is 180 or less, the voltage may be set to zero volts after approximately 250.17 seconds have passed from the start point of application of the drive voltage. This means that ink ejection is stable in the frequency range from 0 to 4 to 11z.

FIG. 3 is a circuit diagram showing details of the drive circuit 18 that generates the drive voltage shown in FIG. 1(a).

41 is an input terminal to which the voltage shown in FIG. 4(a) is applied, 42 is a resistor connected to the input terminal 41, and 43 is an NP with a grounded emitter whose base is connected to the other end of the resistor 42.
It is an N-type transistor.

44 is a resistor inserted between the power supply +■ and the collector of the transistor 43, 45 is a diode whose anode is connected to the collector of the transistor 43, 46 is a resistor connected to the cathode of the diode 45, and 47 is the other end of the resistor 46. This is a capacitor connected between 48 is a resistor connected in parallel to the capacitor 47; 49 is a resistor whose one end is connected to the other end of the resistor 46; 50 is an N P N type transistor whose collector is connected to the other end of the resistor 49 and whose emitter is grounded; 51 is a resistor whose one end is connected to the base of the transistor 50, and 52 is an input terminal connected to the other end of the resistor 51 and to which the voltage shown in FIG. 4(b) is applied. Note that 53 is an output terminal.

In FIG. 3, when the voltage shown in FIG. 4(a) is applied to the input terminal 41, the transistor 43 turns on and off in synchronization with the fall of the voltage, and a voltage is generated at the collector of the transistor 43. , a current flows to the capacitor 47 via the diode 45 and the resistor 46. When the voltage applied to the input terminal 41 becomes "H" level after a certain period of time has elapsed, the transistor 43 turns off. At the same time, a pulse voltage having the waveform shown in FIG. 4(b) is applied to the input terminal 52, and the transistor 50 is turned on. transistor 5
0 instantaneously turns on, the charge in the capacitor 47 drops instantaneously.

The charge in the capacitor 47 is prevented from being discharged because the transistor 50 is turned off and the diode 45 exists in the transistor 43, and the discharge is performed only through the resistor 48. Therefore, by appropriately selecting the resistor 48, the time of the drooping portion can be determined.

Note that the rise of the output waveform (drive voltage) is controlled by the resistor 44.
46, and the voltage width of the sudden voltage drop is determined by the fourth
It is determined by the pulse width shown in Figure (b). Furthermore, by changing the height vL of the bottom of the voltage waveform in FIG. 4(a), the height (■) of the constant value portion in FIG. 4(c) can be adjusted, and the amount of ink ejected can be adjusted.

FIGS. 5(a) and 5(b) show drive voltage waveforms when a magnetostrictive element or the like having an inductance property is used as the electromechanical transducer.

As shown in FIG. 5(a), a current suddenly flows through the element as shown in FIG. 5(b) due to the positive first pulse voltage, and then the planted state is maintained. Next, by applying a negative second pulse voltage smaller than the first pulse, the current flowing through the element is momentarily reduced to a certain level, and then the current is gradually reduced. Note that the gradual decrease between the first pulse and the second pulse shown in FIG. 5(a) is effective when the value of the internal resistance of the element cannot be ignored. FIG. 6 shows the measurement of the displacement of the meniscus 14 after ejecting an ink droplet of a head having a nozzle with a length of 18n using a driving voltage having a waveform as shown in FIG. 1(a). As is clear from the figure, after ejecting one ink drop, the meniscus 14 is gently returned to an equilibrium state without vibration, and no bubbles or the like are taken into the nozzle.

Therefore, ink can be ejected stably. [Effects of the Invention] As explained above, according to the present invention, the electromechanical transducer is rapidly contracted and held for a certain period of time, then rapidly expanded to a predetermined level, and then the contraction is gradually released ( By setting it as a driving voltage, the 2 that occurs when it is applied
By absorbing and extinguishing one of the two positive pressures, meniscus vibration is effectively suppressed, quickly returning to an equilibrium state, and ink can be ejected stably, resulting in deterioration of image quality and frequency characteristics. Never.

In addition, by setting the drive voltage during contraction and expansion according to the amount of ink ejection and contraction, it is possible to optimize the amount of ink in the ink droplet and suppress the complicated response of pressure waves within the ink pressure chamber. can.

Furthermore, by setting the contraction duration t based on the arrangement position of the electromechanical transducer with respect to each of the ink supply port and the ink discharge port, the negative pressure generated by the change in the driving voltage during expansion can be adjusted. , can be canceled to such an extent that ink droplets are not ejected.

[Brief explanation of the drawing]

FIGS. 1(a) and (b) are time-voltage characteristic diagrams of driving voltage and pressure wave propagation characteristics in the ink pressure chamber for explaining the driving method according to the present invention, and FIG. 2 is a diagram of the head applied to the present invention. 3 is a schematic cross-sectional view, and FIG. 3 is a circuit diagram showing details of the drive circuit 18 that generates the drive voltage shown in FIG. 1, and FIGS.
), (C) are input voltage waveform diagrams and output voltage waveform diagrams of the circuit of FIG. 3, and FIGS. 5(a) and (b) are drive voltage waveform diagrams and element energization diagrams explaining another driving method of the present invention. Waveform diagram, 6th
The figure is a displacement characteristic diagram of the meniscus in the nozzle after ink is ejected according to the present invention, FIG. 7 is a principle explanatory diagram illustrating the ink droplet ejection operation, FIG. Figures 1 to 13 are explanatory views of pressure wave generation within the ink pressure chamber. 1-----ink pressure chamber, 2-----nozzle, 3-- piezoelectric element, 18--------
m-drive circuit.

Claims (4)

[Claims] (1) In an on-demand inkjet recording device that ejects ink droplets from the nozzle using pressure waves generated in the ink pressure chamber by contraction and expansion of an electromechanical transducer provided in the ink pressure chamber having a nozzle at its tip. , the driving voltage is applied to the electromechanical transducer to cause the contraction to occur rapidly, hold this contraction for a certain period of time, then rapidly cause the expansion to release the contraction to a certain level, and then gradually release the contraction. An inkjet recording method characterized by applying voltage to an element. (2) The inkjet recording method according to claim (1), wherein the drive voltage value at the time of occurrence of the contraction is set to a value corresponding to the amount of ink droplet ejection. (3) The drive voltage at the time of expansion is set to a value proportional to the amount of contraction when contraction occurs.
) The inkjet recording method described in item 1. (4) Time t from the occurrence of the contraction to the occurrence of the expansion
, t=2(l1+l2)/C (where l1: distance from the placement position of the electromechanical conversion element to the ink ejection port, l2: distance from the placement position of the electromechanical conversion element to the ink supply port, C The inkjet recording method according to claim 1, wherein: the speed at which the pressure wave propagates within the ink pressure chamber is set.