JPH04339660A - Method for driving liquid jet recording head - Google Patents

Abstract

PURPOSE:To print an image of high quality even by high frequency by stabilizing the jet state of a liquid droplet and eliminating the change of a droplet speed to driving frequency. CONSTITUTION:A signal +Vp1 always holding flow passages so as to contract the volumes thereof is applied to the piezoelectric element of a liquid jet recording head consisting of a plurality of parallel flow passages, the nozzles connected to the parallel flow passages to inject liquid droplets, a connection means supplying a liquid to the parallel flow passages and the piezoelectric element making the volumes of the parallel flow passages variable to displace the piezoelectric element in the direction increasing the volume the selected flow passage and a first pulse (1) displacing said element in the direction contracting the volume is again applied and, after the time delay Td from the point of time emitting a liquid droplet from the nozzle corresponding to the flow passage, second pulse (2) different in pulse width is applied.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for driving a recording head of an on-demand inkjet recording apparatus, and more particularly, to a method for driving a liquid jet recording head that is simple, inexpensive, and greatly improves print quality.

0002

[Prior Art] A droplet ejection pressure control method in which an electric signal is applied to a recording head equipped with a piezoelectric element, converted into a pressure wave, and the droplet is ejected using the pressure wave, in order to eject recording droplets only when necessary. The on-demand inkjet recording method generates pressure pulses in response to electrical signals, so it has the advantage of a simple drive circuit and simple structure. Publicly known documents of the prior art related to the present invention include, for example, Japanese Patent Publication No. 2-
``On-demand type inkjet head driving method'' described in Japanese Patent Publication No. 24218, or JP-A-59-1
There is an "inkjet head driving method" described in Japanese Patent No. 76060.

Japanese Patent Publication No. 2-24218 relates to a method for driving the above-mentioned on-demand type inkjet head, in which a piezoelectric element is charged by applying a voltage in the same direction as the polarization voltage in advance to reduce the volume of the pressure chamber. Then, when ejecting ink, a signal pulse is applied, and after the voltage is gradually discharged to increase the volume by the fall of the signal pulse, the volume of the pressure chamber is decreased by rapidly charging by the rise of the pulse. A technology has been disclosed that can be driven by an inexpensive drive circuit and can eject droplets with a low drive voltage.

Furthermore, Japanese Patent Application Laid-Open No. 59-176060 discloses that a leading edge of a main drive signal that deforms a diaphragm in a direction that reduces ink pressure in a pressure chamber is applied to a piezoelectric element to supply ink to the pressure chamber. By applying the trailing edge of the main drive signal to return the diaphragm to a steady state in accordance with the phase of the natural vibration of the head determined by the ink flow path system, diaphragm, and piezoelectric element, the ink pressure in the pressure chamber is suddenly increased. The ink droplet is ejected from the nozzle by increasing the vibration, and the vibration is
In an inkjet head recording method in which more than one auxiliary drive signal is applied, a technique has been disclosed in which an auxiliary drive signal is applied after a main drive signal is applied in order to improve repetition frequency characteristics when driving the head.

However, according to the above technique, the fall of the applied auxiliary drive signal, that is, the timing of the drive signal in the direction of lowering the ink pressure in the flow path, occurs before ink ejection by the main drive signal is completely completed. , the natural vibration caused by the auxiliary drive signal does not have an opposite phase to the natural vibration excited by the main drive signal, and the natural vibration cannot be completely suppressed. Therefore, when attempting to further suppress the natural vibration, a plurality of auxiliary signals are required one after another, resulting in a disadvantage that the drive circuit becomes complex and expensive.

[0006] Furthermore, since the discharge amount is reduced, the dot diameter when printed becomes smaller, and in the case of graphic printing, the overlap rate between dots is low in the solid printed area, which should have uniform density. This may result in uneven density. Furthermore, the application timing and application time of the auxiliary drive signal are unclear with respect to the natural vibration of the head, and this method lacks practicality.

[0007]

[Objective] The present invention was made in view of the above-mentioned problems, and provides a method for driving a liquid jet recording head that stabilizes the ink jetting state and eliminates fluctuations in the ink jetting speed with respect to the driving frequency. It was done for the purpose of

[0008]

[Structure] In order to achieve the above objects, the present invention provides (1)
A plurality of parallel channels arranged at intervals in the longitudinal direction of the channels, a nozzle connected to each of the parallel channels to eject liquid droplets, and a connecting means for supplying liquid to the parallel channels. and,
a piezoelectric element that changes the volume of the flow path by applying displacement in a direction perpendicular to the longitudinal direction of the parallel flow path, and applying a signal to the piezoelectric element to maintain the flow path volume so that the volume of the flow path is constantly reduced; After displacing the selected channel in a direction that increases the channel volume, a pulse signal is applied again to cause a displacement that reduces the channel volume, and droplets are ejected from the nozzle corresponding to the channel. In the method for driving a liquid jet recording head, after ejecting a droplet by applying the pulse signal, a second pulse signal having a different pulse width is applied, or (2)
A plurality of parallel channels arranged at intervals in the longitudinal direction of the channels, a nozzle connected to each of the parallel channels to eject liquid droplets, and a connecting means for supplying liquid to the parallel channels. and,
a piezoelectric element that changes the volume of the flow path by applying displacement in a direction perpendicular to the longitudinal direction of the parallel flow path, and applying a signal to the piezoelectric element to maintain the flow path volume so that the volume of the flow path is constantly reduced; After displacing the selected channel in a direction that increases the channel volume, a pulse signal is applied again to cause a displacement that reduces the channel volume, and droplets are ejected from the nozzle corresponding to the channel. In the method for driving a liquid jet recording head, after ejecting droplets by applying the pulse signal, applying a second pulse signal having a different peak value, and (3) in (1) or (2) above. , the second pulse signal is applied such that the second pulse signal rises with a time delay of (3/2)T from the rise of the pulse signal, assuming that the residual vibration period due to the application of the pulse signal is T. This is a characteristic feature. Hereinafter, the present invention will be explained based on examples.

First, an on-demand type ink jet recording head (hereinafter simply referred to as a head) will be explained. FIGS. 5(a) and 5(b) are diagrams for explaining the configuration of the recording head, where FIG. 5(a) is a cross-sectional view and FIG. 5(b) is an A--
It is an enlarged view taken along the line A. In the figure, 1 is a substrate, 2 is a piezoelectric element, 3 is a channel plate, 3a is a channel (pressure chamber), 3b is a wall, 4
4a is a common liquid chamber component, 4a is a common liquid chamber, 5 is an ink supply pipe, 6 is a nozzle plate, 6a is a nozzle, 7 is a driving circuit printed board (PCB), 8 is a lead wire, 9 is a driving electrode, 10 is a filler, 11 is a protection plate, 12 is a fluid resistance,
13 and 14 are electrodes, and 15 is an upper partition.

In the integrated head, the electrodes 13,
The laminated piezoelectric element 2 having a piezoelectric element 14 is grooved in the direction of the flow path 3a in correspondence with the flow path 3a, and is divided into a groove 10, a driven piezoelectric element 2b, and a non-driven piezoelectric element 2a. Groove 1
0 contains a filler. A channel plate 3 is joined to the grooved piezoelectric element 2 via an upper partition wall 15. That is, the upper partition wall 15 is supported by the wall portion 3b separating the non-driven piezoelectric element 2a and the adjacent flow path 3a. The width of the driving piezoelectric element 2a is selected to be slightly narrower than the width of the flow path 3a. A constant voltage is applied to the drive piezoelectric element 2b by a drive circuit on a drive circuit printed board (PCB), thereby reducing the volume of the flow path 3a. When a pulsed signal voltage (signal pulse) is applied to the drive piezoelectric element 2b selected in printing, the fall of the signal pulse causes the flow path 3a to
The volume of the nozzle plate increases and sucks ink, and the driving piezoelectric element 2b is displaced in the thickness direction by the rise of the signal pulse, and the volume of the flow path 3a is rapidly reduced through the upper partition wall 15. As a result, the nozzle plate Ink droplets are ejected from nozzle 6a.

FIGS. 6(a) and 6(b) are similar to the above-mentioned FIG. 3(a).
, (b) are diagrams showing the drive voltage waveforms of the recording head shown in Figure (a) is the drive voltage waveform, and Figure (b) is the residual vibration (
Part A) is shown. In driving the above head, Figure (a)
In the drive voltage waveform illustrated in , the peak value Vp1 and the pulse width P
Only the pulse signal w1 was applied to the driving piezoelectric element 2b. At the falling edge of the pulse signal (in the direction of arrow Pd), the volume of the flow path 3a increases due to the reduction in the thickness direction of the drive piezoelectric element 2b, creating negative pressure, and as a result, ink is sucked from the ink supply pipe 5, The rise of the pulse signal (in the direction of arrow Pu) causes a displacement in the thickness direction and conversely presses and compresses the channel 3a, and this pressurization causes ink droplets to be ejected from the nozzle 6a. When driving the drive piezoelectric element 2b by applying such a single pulse signal, changing the frequency of the pulse signal causes the ejection speed Vj of the ink droplets to vary, which impairs the image quality when printed on the record. There was a problem.

The present inventors believe that the causes of this variation in the velocity of ink droplets are the structure of the flow path 3a consisting of the size, material, shape, etc. of the flow path, the elastic modulus of the piezoelectric element 2, the viscosity of the ink liquid, It was thought that this is because the ink liquid resonates with the natural frequency determined by the vibration system including mass, etc., and pressure waves are generated. In addition, after the drive pulse signal as shown in Figure (a) is raised (arrow Pu) to the drive piezoelectric element 2b, a residual vibration waveform is generated in part A of Figure (a), and it is observed as in Figure (b). be done.

This residual vibration occurs after the ink liquid in the flow path 3a is pressurized by the rise of the pulse signal (arrow Pu) in Figure (a) and ink droplets are ejected from the nozzle.
This is because the pressure waves generated in the ink liquid pressurize the piezoelectric element 2, and the voltage waveform generated at the drive piezoelectric element 2b due to the piezoelectric effect due to the pressurization is superimposed on the drive voltage waveform. Therefore, it is considered that the residual vibration seen on the drive voltage waveform is synchronized with the pressure waveform of the ink liquid in the flow path 3a.

FIG. 2 shows the amplitude Vm and pulse width P of the residual vibration.
This is a diagram showing the relationship between w and the peak value Vp, and if the peak value Vp of the pulse signal is constant, the amplitude Vm of the residual vibration is maximum when the pulse width Pw=Pw1. Therefore, if the pulse width Pw is a constant value Pw1, the maximum amplitude Vm is Vm1 when the peak value Vp=Vp1, and the maximum amplitude Vm is Vm2 when the peak value Vp=Vp2. As shown in the figure, the maximum vibration Vm of the residual vibration increases as the peak value Vp of the pulse signal increases. The ejection speed Vj of ink droplets is the maximum vibration Vm
The larger the size, the faster the speed. Therefore, if an attempt is made to increase the ink droplet ejection speed Vj, the residual vibration amplitude also increases, resulting in a disadvantage that fluctuations in the ejection speed Vj become large.

The present invention eliminates the above-mentioned disadvantage by apparently eliminating the residual amplitude, and reduces the frequency f of the drive pulse signal.
The ejection velocity Vj of the ink droplet is made to have a flat characteristic without fluctuation. FIGS. 1(a) and 1(b) are diagrams for explaining the drive voltage waveform according to the present invention, and FIG.
The voltage waveform on the time axis applied to the piezoelectric element. 2
(called a pulse). In addition, Figure (b) is a diagram showing the residual vibration waveform when the first pulse ■ in Figure (a) is applied to the driving piezoelectric element 2b, and ■ (solid line) and ■ (dotted line) in the figure are shown in the figure. This corresponds to ■ and ■ in (a).

The first pulse (■) in FIG. 6(a) is a voltage signal pulse waveform having a peak value Vp1 and a pulse width Pw1 shown in FIG. 6, and is generated by applying this first pulse (■) to the drive piezoelectric element 2b. The residual vibration is caused by the first pulse ■
The damped vibration is shown by a solid line from the time of rise (arrow Pu), and the second pulse (2) is applied with a phase difference of an odd multiple of a half wavelength in order to cancel the residual vibration (2) caused by the first pulse (2). Here, the pulse width Pw2 of the second pulse (2) must be such as to generate a residual vibration such that the amplitude of the residual vibration is Vm=Vm2, as shown in Figure (b). Since the pulse peak value Vp=Vp1 in this case, in the characteristic diagram of FIG. 2, on the curve of the pulse peak value Vp=Vp1, the pulse width corresponding to the residual vibration amplitude Vm=Vm2 is Pw2.
It is determined that Above, wave height value Vp1, pulse wave height value Pw
As a result of applying the second pulse of 2, the residual vibration in figure (b)
The residual vibration ■ of the pulse ■ and the residual vibration ■ of the second pulse ■ become a composite wave and are canceled out.

[0017] Also, the fall of the second pulse (arrow Pd)
must be applied with a time delay Td so as not to interrupt the ejection of ink droplets due to the rising of the next applied first pulse (arrow Pu). From the above, the phase delay time Td of the second pulse ■ with respect to the first pulse ■, that is, the time delay Td from the rise of the pulse ■ to the rise of the second pulse ■ is Td=(3/
2) When T (T is the period of residual vibration) and pulse width Pw is Pw=Pw2, the residual vibration waveform in part B, which is a combination of residual vibrations (■) and (2), becomes least efficient (attenuates).

Next, an example will be explained. Figure 3(a),(b)
) and (c) are diagrams for explaining the driving results of a conventional liquid jet recording head for comparison with the present invention.
a), (b), and (c) are diagrams for explaining an embodiment of the head drive according to the present invention. Figure (a) is a diagram showing the driving waveform, and diagram (b) is a diagram showing the ejected droplet. Diagrams showing shapes, diagrams (
c) is a diagram showing the frequency characteristics of the droplet velocity Vj.

The conventionally used signal pulse waveform shown in FIG. 1A is as follows: first pulse; peak value Vp=22 (V); pulse width Pw1=14 (μs). At this time, after the pulse is started, the droplets flow from the nozzle over time as shown in Figure (b) (1) → (2) → (
Although the droplets are ejected as shown in 3), unnecessary droplets are ejected as shown in (4) -> (5) -> (6) due to the influence of residual vibration, which impairs the image quality. In addition, the velocity fluctuation of the droplet is shown in Figure (c).
As shown in FIG. 2, as the driving frequency f becomes higher, the amount of fluctuation increases, and ejection becomes impossible near f=8 (kHz), resulting in a limit to the recording speed.

FIGS. 4(a), 4(b), and 4(c) are diagrams for explaining head driving results according to the liquid jet recording head driving method of the present invention. In the illustration, the wave value Vp and pulse width Pw1 of the first pulse are the same signal pulse waveform for comparison with the case of the prior art shown in FIG.

[0021] That is, the first pulse, the second pulse, and the time delay Td are as follows: First pulse Peak value Vp = 22 (V) Pulse width P
w1=14 (μs) 2nd pulse Pulse width Pw2=7 (μs) Time delay Td=(3/2)T=(μs) (However,
Residual vibration period T = 28 (μs)) In this case, the ejection of droplets changes from (1) → (2) → (3) as shown in FIG. 4(b).
Therefore, unnecessary droplets as in cases (4), (5), and (6) of FIG. 3(b) are not ejected.

In the above, the rising timing of the second pulse (2) is applied with a time delay (Td) of a phase difference that is an odd multiple of the half wavelength of the residual vibration in order to cancel the residual vibration (2) caused by the first pulse. It has been stated that =(3/2)T (T is the period of residual vibration) is the optimal value. On the other hand, the phase difference or delay of an odd multiple of the half-wave number in the vicinity of the optimal time delay is Td = (
The influence on droplet jetting will be described for the cases of 1/2)T and (5/2)T.

(1) When Td=(1/2), the pressure wave generated by reducing the volume of the flow path 3a due to the rise (Pu) of the first pulse (2) begins to eject droplets, and further The droplet grows in the form of a liquid column. During the period when the vibration wave reaches 1/2T, the volume of the flow path 3a increases, and at the time of 1/2T, the volume of the flow path 3a increases.
The volume of the flow path 3a becomes maximum, and the pressure inside the flow path 3a also becomes minimum. During this time, the droplet continues to move, but is maintained in equilibrium by the meniscus (surface tension) of the liquid between the flow path 3a and the droplet. The pressure is applied again in the next half cycle, and the droplet moves in the state of a liquid column. However, at point P after time T, the pressure in the flow path 3a decreases, and the liquid column changes as shown in FIG. 3(b). The liquid is ejected as droplets shown in (3). Therefore, if the second pulse (2) is started at Td=(1/2)T, the droplet formed by the first pulse will be cut off midway through its formation by application of the second pulse. As a result, (1) the droplet ejection amount (Mj) becomes small, and the ejection efficiency decreases. ■ The meniscus (surface tension) of the recording liquid in the flow path becomes unstable, making it easier for air to be absorbed into the flow path, making it impossible to record.

(2) When Td=(5/2)T■ At the position of points P and Q where the trailing end of the droplet leaves, (4) in FIG. 3(b)
), (5), and (6), unnecessary droplets are ejected and stain the paper surface, which deteriorates the image quality. ■
The sum (Tw1+Td) of the pulse width Pw1 of the first pulse and the time delay Td, which is the driving time, becomes long, which is disadvantageous for high-frequency driving.

FIG. 4(c) shows the frequency characteristics of the droplet velocity Vj, and the velocity fluctuation seen in FIG. 3(c) is almost eliminated, stable ejection is performed, and the drive frequency f>10kHz.
It became possible to respond up to The second pulse (■) according to the above embodiment has a pulse width of Pw1>Pw2, but as mentioned earlier, it is sufficient if the residual vibration amplitude Vm=Vm2, so even if the pulse width is the same as that of the first pulse (2), the pulse width as shown in FIG. A similar effect can be obtained by setting the pulse height value Vp to Vp=Vp2, which is lower than Vp1, as shown in FIG.

Next, a specific example of a drive circuit for applying the first pulse and the second pulse will be described. Figure 7(a)
, (b) are diagrams showing a specific example of a drive circuit, (a) is a circuit configuration diagram, and (b) is a waveform timing chart. In the diagram, 21, 22, 23 are monostable multivibrators. (hereinafter referred to as mono-multi), 24 is an OR circuit, 25
~30 is a resistor, 31 is a PNP transistor, 32 is an N
PN type transistor, 33 is a power supply, 34 is a piezoelectric element (P
ZT) element.

In Figure (a), the selected piezoelectric element 3
4 is applied to the monomulti 21. The monomulti 21 determines the pulse width Pw1 for forming the first pulse, and inputs the pulse a shown in FIG. On the other hand, Monomulti 2
The pulse a output from 1 passes through monomultis 22 and 23 connected in series, and outputs a pulse b for forming a second pulse having a time delay Td and a pulse width Pw2. Pulse b is input to the other input terminal of OR circuit 24, and pulse c, which is the sum of pulse a and pulse b, is obtained from OR circuit 24.

The NPN transistor 32 is always open, and the power supply voltage Vp is applied to the piezoelectric element 34 via the PNP transistor 31 and the resistor 29. The positive pulse train c output from the OR circuit 24 is applied to the resistors 25 and 27.
When the voltage is applied to the bases of the PNP type transistor 31 and the NPN type transistor 32 via the voltage Vp, the NPN type transistor 32 is closed and the PNP type transistor is opened. A first pulse with a pulse width Pw1 having a value and a second pulse voltage with a pulse width Pw2 that is output with a delay time Td are output. The piezoelectric element 34 charged to the power supply voltage Vp is discharged via the resistor 30 at the falling edge of the pulse Pd, and charged via the resistor 29 at the rising edge of the pulse Pu. Therefore, the discharge time and charge time settings can be changed by selecting the resistance values of resistors 30 and 29. The circuit in FIG. 7A is illustrated in principle, and it is also possible to configure these circuits using an integrated circuit.

[0029]

[Effects] As is clear from the above explanation, according to the method for driving a liquid jet recording head of the present invention, (1) After applying the first pulse, a second pulse having a predetermined pulse width and a peak value is applied. Since residual vibration can be suppressed, fluctuations in droplet velocity can be significantly reduced, and unnecessary discharge of droplets can also be prevented. Therefore, printing quality can be greatly improved easily and at low cost. (2) The application of the second pulse while changing the pulse width can be easily realized using a logic IC (integrated circuit) by only controlling the time of the drive circuit, so that compensation can be achieved at low cost. (3) By changing the peak value of the second pulse, the variation in the amplitude value of the residual vibration is small relative to the change in the pulse peak value, so there is a wide margin for variation in the peak value. (4) Residual vibration can be eliminated more efficiently by simply delaying the application of the second pulse by (3/2) T relative to the residual vibration period T from the first pulse.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining a drive voltage waveform according to the present invention.

FIG. 2 is a diagram showing the relationship between the amplitude Vm of residual vibration, the pulse width Pw, and the peak value Vp.

FIG. 3 is a diagram for explaining the driving results of a head in conventional liquid jet recording.

FIG. 4 is a diagram for explaining head driving results by the liquid jet recording head driving method of the present invention.

FIG. 5 is a diagram for explaining the configuration of a liquid jet recording head.

FIG. 6 is a diagram showing a drive voltage waveform of a conventional liquid jet recording head.

FIG. 7 is a diagram showing a specific example of a drive circuit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1...Substrate, 2...Piezoelectric element, 2a...Non-driven piezoelectric element, 2b
... Drive piezoelectric element, 3... Channel plate, 3a... Channel, 4... Common liquid chamber constituent member, 5... Ink supply pipe.

Claims (3)

[Claims] 1. A plurality of parallel flow channels arranged at intervals in the longitudinal direction of the flow channels, a nozzle connected to each of the parallel flow channels to eject droplets, and a nozzle connected to each of the parallel flow channels to eject droplets; It consists of a connecting means for supplying liquid, and a piezoelectric element that changes the volume of the flow path by applying displacement in a direction perpendicular to the longitudinal direction of the parallel flow path, and the piezoelectric element is configured such that the volume of the flow path is constantly reduced. After applying a signal to hold the selected channel and displacing the selected channel in a direction that increases the channel volume, apply a pulse signal that causes a displacement that reduces the channel volume again to correspond to the channel. A method for driving a liquid jet recording head that jets droplets from a nozzle, characterized in that after the droplets are ejected by applying the pulse signal, a second pulse signal having a different pulse width is applied. Driving method. 2. A plurality of parallel flow channels arranged at intervals in the longitudinal direction of the flow channels, a nozzle connected to each of the parallel flow channels to eject a droplet, and a nozzle connected to each of the parallel flow channels to eject droplets; It consists of a connecting means for supplying liquid, and a piezoelectric element that changes the volume of the flow path by applying displacement in a direction perpendicular to the longitudinal direction of the parallel flow path, and the piezoelectric element is configured such that the volume of the flow path is constantly reduced. After applying a signal to hold the selected channel and displacing the selected channel in a direction that increases the channel volume, apply a pulse signal that causes a displacement that reduces the channel volume again to correspond to the channel. A method for driving a liquid jet recording head that jets droplets from a nozzle, characterized in that after the droplets are ejected by applying the pulse signal, a second pulse signal having a different peak value is applied. Driving method. 3. Let T be the residual vibration period due to the application of the pulse signal, and (3/2) from the rising edge of the pulse signal.
3. The method of driving a liquid jet recording head according to claim 1, wherein the second pulse signal is applied so that the second pulse signal rises with a time delay of T.