JP3069155B2 - Driving method of liquid jet recording head - Google Patents

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 liquid jet recording head, and more particularly, to a method for driving a liquid jet recording head which enables high-speed printing.

[0002]

2. Description of the Related Art A droplet discharge pressure control method in which an electric signal is applied to a recording head provided with a piezoelectric element to convert the pressure droplet into a pressure wave and the droplet is ejected by the pressure wave in order to discharge a recording droplet only when necessary. The on-demand type ink jet recording method has advantages that a driving circuit is simple and a structure is simple because a pressure pulse is generated according to an electric signal. Examples of known documents of the prior art according to the present invention include, for example,
No. 24218 discloses an “on-demand type ink jet head driving method”.

Japanese Patent Publication No. 2-24218 relates to a method of driving the above-mentioned on-demand type ink jet head, in which a piezoelectric element is charged by applying a voltage in the same direction as a polarization voltage in advance to reduce the volume of the pressure chamber. In advance, a signal pulse is applied at the time of ink ejection, the voltage is gradually discharged by falling of the signal pulse from the voltage, the volume is increased, ink is sucked into the pressure chamber, and then rapidly charged by rising of the signal pulse, A technique for ejecting ink by reducing the volume of a pressure chamber, which can be driven by an inexpensive drive circuit, and which ejects droplets at a low drive voltage is disclosed.
This driving method has been described with respect to one head portion provided with an independent pressure chamber. Further, the pulse width of the signal pulse to be applied is from the time when the signal pulse falls to the time when the amplitude when the wall surface of the pressure chamber oscillates to the maximum value during ink suction at the time of the fall of the signal pulse. Is set to

The present applicant has previously proposed a "method for driving a liquid jet recording head". In this method, a second signal pulse is applied a predetermined time after the application of the first signal pulse for ejecting ink droplets. This is a driving method for eliminating unnecessary ink droplet ejection due to residual vibration generated in the flow path after ink droplet ejection, and greatly improving printing quality by simple and low-cost means. As the pulse width of the first signal pulse in the driving method, a pulse width that maximizes the speed of the droplet at a predetermined peak value is selected. Figure 4 is a graph showing the relationship between the amplitude Vm and the pulse width Pw and the peak value Vp of the residual vibration, the maximum amplitude Vm of the residual vibration when the pulse width Pw = Pw ₁ if the peak value Vp of the pulse signal is constant Becomes Accordingly, if the pulse width Pw is a constant value Pw _1, the maximum amplitude V when the wave height Vp = Vp ₁
m is Vm ₁ , the maximum amplitude Vm when the peak value Vp = Vp ₂ is Vm ₂ , and the maximum vibration Vm of the residual vibration increases as the peak value Vp of the pulse signal increases. The ejection speed Vj of the ink droplet increases as the magnitude of the maximum vibration Vm increases.

[0005] That is, the residual vibration generated in the channel is
The ink liquid resonates at the natural frequency determined by the vibration system including the flow path structure, the pressure element elastic modulus, the ink liquid viscosity and the mass, which is composed of the flow path dimensions, material, shape, etc., and generates a pressure wave. However, it is shown that the ink droplet velocity increases as the peak value of the signal pulse increases, and increases as the residual vibration amplitude increases. It also shows that the pulse width of the signal pulse having the maximum vibration amplitude is uniquely determined.

However, the driving method disclosed in Japanese Patent Publication No. 2-24218 describes a case in which a single pressure chamber is provided, and a multi-nozzle head provided with a plurality of flow paths having nozzles serving as pressure chambers. Does not relate to the liquid ejecting nozzle. In driving the multi-nozzle head, mutual interference caused by mechanical action such as distortion generated between flow paths and hydrodynamic action such as pressure wave applied to adjacent flow paths through a common liquid chamber that supplies ink is considered. The pulse width of the signal pulse must be set in consideration of this. Similarly, the "driving method of the liquid jet recording head" proposed earlier by the present application does not take mutual interference into consideration.

In a multi-head fluid jet recording head,
If the head is driven by a signal pulse having a pulse width determined by itself, the droplet speed is reduced when a plurality of heads are driven simultaneously. This means that in printing, the head moves relatively to the paper on the carriage, so that if the droplet speed is different, the position of the dot printed on the paper will be shifted, and the image quality will be degraded. Such disadvantages are significant in high-speed printing.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and considers mutual interference in driving a liquid jet recording head of a multi-nozzle head so as to minimize the influence of drop speed due to the mutual interference. It is intended to enable high-speed printing by setting the pulse width of the voltage pulse.

[0009]

According to the present invention, in order to achieve the above object, a plurality of parallel flow paths arranged at intervals in a longitudinal direction of the flow path, and a droplet connected to each of the parallel flow paths A nozzle for jetting, connecting means for supplying liquid to the parallel flow path, and a piezoelectric element for changing the volume of the flow path by applying a displacement in a direction perpendicular to the longitudinal direction of the parallel flow path; A pulse that gives a signal to the element to keep the flow path volume constantly reduced, displaces the selected flow path in a direction to increase the flow path volume, and then gives a displacement that reduces the flow path volume again In a method for driving a liquid jet recording head, in which a signal is applied to eject a droplet from a nozzle corresponding to a flow path and then a second pulse is applied, when the pulse signal is simultaneously applied to the plurality of piezoelectric elements, Injected from the nozzle of the parallel flow path corresponding to the element As the speed of the droplets is maximum, it is characterized in that setting the pulse width of the pulse signal. Hereinafter, a description will be given based on examples of the present invention.
First, an on-demand type liquid jet recording head to which the present invention is applied (hereinafter, simply referred to as a head) will be described.

FIGS. 3A and 3B are views for explaining the structure of the head, wherein FIG. 3A is a sectional view, and FIG. 3B is an enlarged view taken along line AA of FIG. FIG. In the figure, 1 is a substrate,
2 is a piezoelectric element, 2a is a non-driven piezoelectric element, 2b is a driven piezoelectric element, 3 is a flow path plate, 3a is a flow path (pressurizing chamber), 3b is a wall, 4 is a common liquid chamber constituent member, and 4a is common. Liquid chamber, 5 is an ink supply pipe, 6 is a nozzle plate, 6a is a nozzle, 7
Is a drive circuit printed circuit board (PCB), 8 is a lead wire, 9
Is a drive electrode, 10 is a filler, 11 is a protective 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 14 is grooved in the direction of the flow path 3a corresponding to the flow path 3a, and is divided into the groove 10, the drive voltage element 2b, and the non-drive piezoelectric element 2a. Groove 1
0 is filled with a filler. The channel plate 3 is joined to the grooved piezoelectric element 2 via an upper partition 15. That is, the upper partition 15 is provided with the non-drive piezoelectric element 2a.
And the wall 3b separating the adjacent flow path. The width of the driving piezoelectric element 2b is selected to be slightly smaller 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 circuit board (PCB) to reduce the volume of the flow path 3a. When a pulse-like signal electricity (signal pulse) is applied to the driving piezoelectric element 2b selected in printing, the volume of the flow path 3a increases due to the fall of the signal pulse, ink is sucked, and the rise of the signal pulse causes the volume to increase. The driving piezoelectric element 2b is displaced in the thickness direction, and the upper partition 15
The volume of the flow path 3a is reduced via the
Ink droplets are ejected from the nozzle 6a.

However, when a single signal pulse is applied as described above, if the frequency of the pulse signal is changed, the droplet speed Vj fluctuates and image quality is impaired. The present inventors have considered that the cause is that the ink liquid resonates at the natural frequency of the vibration system determined by the physical properties of the flow path and the ink, and a pressure wave is generated. These pressure waves press the piezoelectric element 2 and are superimposed on the drive voltage waveform as residual vibrations.
In the present invention, a compensating signal pulse is applied after a signal pulse is applied in order to eliminate the inconvenience by apparently canceling the residual vibration.

FIGS. 2A and 2B are diagrams for explaining a drive voltage waveform applied in the present invention.
Is the voltage waveform on the time axis applied to the piezoelectric element.
Is a main drive pulse signal (shown by a solid line, hereinafter, referred to as a first pulse), and is a compensation pulse wave signal (shown by a dotted line;
(Referred to as a second pulse). FIG. 2B is a diagram showing a residual vibration waveform when the voltage waveform of FIG. 2A is applied to the piezoelectric element, and (solid line) and (dotted line) in the diagram.
Corresponds to, in FIG.

To cancel the residual vibration, the first pulse
The half-wavelength odd period from the rise of the second pulse to the rise of the second pulse
A second pulse having a several times phase difference is applied.
Here, the pulse width Pw of the second pulse_TwoIs shown in Figure (b)
The amplitude of the residual vibration is Vm = Vm_TwoLike
It must generate residual vibration. in this case
Pulse peak value Vp = Vp₁Therefore, the characteristic diagram of FIG.
, The pulse peak value Vp = Vp₁On the curve
Motion amplitude Vm = Vm_TwoIs Pw_TwoAnd decide
Is done. Above, the peak value Vp₁, Pulse peak value Pw_TwoApplication of
As a result, the residual vibration in FIG.
Cancels out as a composite wave of the residual vibration of the second pulse
Is done. When the second pulse falls (arrow Pd)
The period is the ink liquid by the rise of the first pulse (arrow Pu)
Must be applied without interrupting drop ejection
No. The delay time of the second pulse from the first pulse
Is short, the meniscus becomes unstable, and long, the response is poor.
It becomes. From the above, the second pulse is the first pulse
, The delay time of the first pulse.
The optimum value of the time from the rise to the rise of the second pulse is Td = (3/2) T (T is the period of the residual vibration), and the pulse width Pw is Pw = Pw_Two  Residual vibration in part B, which combines residual vibration with
The waveform is most efficiently lost (attenuated).

However, when the flow path is driven by a signal pulse having the same waveform, the speed of droplets ejected from the nozzle is faster when driven alone than when driven simultaneously. The reason for this is that the volume reduction rate of the flow path in the case of simultaneous driving is reduced. When the driving piezoelectric element 2b is simultaneously driven, the filler 10 is also pushed up, and as a result, the wall 3b is also displaced upward. This is because mutual interference occurs. Therefore, when the multi-head is driven independently and simultaneously, the droplet speeds are not the same.

FIG. 1 is a graph showing the dependence of the droplet speed pulse width upon single driving and upon simultaneous driving. In the figure, a circle mark indicates that the No. 16 channel of the multi-nozzle head (32 channels) is driven independently. The mark ● indicates the pulse width dependency of the drop speed of the No. 16 channel when all the channels (32 channels) are simultaneously driven. As shown in the figure, in the case of single drive, the drop speed increases as the pulse width is increased, and then the drop speed decreases.However, in the case of simultaneous drive, the drop is caused by mutual interference. There is a phenomenon that the speed decreases.

Accordingly, the first pulse in the case of independently driving the flow path of the illustrated multi-head has a pulse width P at which the voltage Vm of the residual vibration becomes maximum in order to maximize the droplet velocity.
Although w ₁ was selected, it is the pulse width at points A, B, and C indicated by ○ in FIG. 1 and has different pulse widths. Simultaneous drive for this pulse width (●
Comparing the cases where there is mutual interference (mark), the drop speed of the mark is small and the difference between the drop speeds is large in the pulse width of the points A and B having the maximum drop speed by the single drive. When a signal pulse having a pulse width at which point D of the mark, that is, the simultaneously driven droplet speed becomes maximum, is selected, the pulse width of the single drive is equivalent to the point C, the droplet speed is maximum, and the speed difference is small. As described above, the first pulse of the single drive should be determined to have a pulse width of the point C in consideration of a drop speed change (indicated by ● in the drawing) due to mutual interference of the simultaneous drive. That is, by changing the pulse width under the simultaneous driving condition, the first pulse at the optimum pulse width D point considering the mutual interference is easily determined because the rate of the speed change due to the pulse width change is large.

[0018]

As is apparent from the above description, according to the driving method of the liquid jet recording head of the present invention, the residual vibration is suppressed by applying the second pulse having the predetermined pulse width after the application of the first pulse, and the droplet velocity is reduced. To reduce the fluctuation of
When multiple heads drive the pulse width simultaneously,
Since the pulse width at which the droplet speed is maximized is set, the difference from the droplet speed when driven alone is small, and the dot position on the paper is shifted due to the difference in droplet speed between single driving and simultaneous driving. Image quality can be prevented from deteriorating.

[Brief description of the drawings]

FIG. 1 is a diagram showing the drop speed pulse width dependence during single driving and simultaneous driving.

FIG. 2 is a diagram for explaining a drive voltage waveform applied in the present invention.

FIG. 3 is a diagram illustrating a configuration of a head.

FIG. 4 is a diagram illustrating a relationship among an amplitude Vm of a residual vibration, a pulse width Pw, and a peak value Vp.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Piezoelectric element, 2a ... Non-drive piezoelectric element, 2b
... Driving piezoelectric element, 3 ... Channel plate, 3a ... Channel (pressurizing chamber),
3b: wall portion, 4: common liquid chamber constituent member, 4a: common liquid chamber,
5 ... Ink supply pipe, 6 ... Nozzle plate, 6a ... Nozzle, 7 ... Drive circuit printed board (PCB), 10 ... Filler, 11 ... Protective plate, 12 ... Fluid resistance, 13,14 ... Electrode, 15 ... Top Partition walls.

Continuation of the front page (72) Inventor Toshiharu Hirata 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (56) References JP-A-3-108549 (JP, A) JP-A-57- 59774 (JP, A) JP-A-58-55253 (JP, A) JP-A-57-176055 (JP, A) JP-A-63-94850 (JP, A) (58) Fields investigated (Int. ⁷ , DB name) B41J 2/045 B41J 2/055

Claims (1)

(57) [Claims] A plurality of parallel flow paths arranged at intervals in a longitudinal direction of the flow path; a nozzle connected to each of the parallel flow paths for ejecting a droplet; Connecting means for supplying a liquid, and a piezoelectric element for changing the volume of the flow path by applying a displacement in a direction perpendicular to the longitudinal direction of the parallel flow path, so that the flow path volume is always reduced in the piezoelectric element. After the signal to be retained is given to the selected flow path, the flow path is displaced in a direction to increase the volume of the flow path, and then a pulse signal is applied again to give a displacement to reduce the volume of the flow path to correspond to the flow path. In a method for driving a liquid jet recording head for applying a second pulse after ejecting a droplet from a nozzle, when the pulse signal is simultaneously applied to the plurality of piezoelectric elements, the nozzles of a parallel flow path corresponding to the piezoelectric elements are used. In order to maximize the velocity of the ejected droplet, A method for driving a liquid jet recording head, wherein a pulse width of the pulse signal is set.