JPS59104946A - Ink jet recording apparatus - Google Patents

Abstract

PURPOSE:To provide the titled apparatus capable of performing the control for detecting the liquid pressure of the ink in a recording head and the detection of an ink residual amount with high accuracy in good reliability, constituted by forming a part of the wall of an ink supply chamber by a specific flexible membrane. CONSTITUTION:The displacement amount of a flexible membrane 19 for bringing the opening part of the common ink chamber 3 in a recording head to a hermetically sealed state with respect to the change in the liquid pressure of ink is set to 0.1mum/cmH2O-1m/cm H2O. The flexible membrane 19 is provided so as to hold a height +H from the liquid level of an ink tank and a non-contact position detecting means 20 for detecting the displacement amount of the height H is fixedly provided to the predetermined position on a head substrate 18. When the ink residual amount in the ink tank becomes small, the liquid pressure of the ink in the recording head is lowered and, when the ink liquid pressure reaches a definite value or less by monitoring ink pressure, an alarm is issued or printing operation is stopped.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inkjet recording apparatus, and particularly to detection of changes in ink fluid pressure within a recording head.

Inkjet recording devices generally have the advantage of being able to perform high-speed recording with extremely low noise, being able to use inexpensive plain paper, and not requiring complex processing such as development and fixing. Furthermore, the small-diameter dots and reduced dot spacing enable high-resolution image recording, and are also effective for recording kanji characters, figures, etc.

Regarding the ejection method in inkjet recording devices,
Several methods have been developed and put into practical use. For example, an inkjet recording method called an on-demand method, as disclosed in Japanese Patent Publication No. 53-12138, has been developed in recent years and is attracting attention.

This is an inkjet recording device that ejects ink droplets from a nozzle.

The feature of this on-demand method is that in response to the image signal,
Since ink is ejected only when needed, there is no need for a system to collect unnecessary ink, resulting in low ink consumption and high reliability.The recording device itself is also smaller, lighter, and less expensive. It is possible to do so. Also,
Another advantage is that a large number of channels can be easily mounted on one recording head, so high resolution and high-speed printing performance can be obtained, and color printing is also easy.

Furthermore, Japanese Patent Publication No. 35936/1983 is an on-demand type inkjet recording device in which the above method is put into practical use. This method uses a method in which a plurality of nozzles are mounted within one recording head. FIGS. 1 and 2 are schematic diagrams illustrating this method, showing a cross-sectional view and a plan view, respectively.

In the figure, a plurality of nozzles I, a plurality of pressure chambers 2 communicating with the nozzles IK, and a common common ink chamber 3 for distributing and supplying ink from an ink tank 6 into the pressure chambers 2, and the above-mentioned portions are shown. 1.2.3 are arranged in the same plane.

Recording ink is supplied from the ink tank 6 through the valve means 5 and the ink supply pipe 4 to the common ink chamber 3 of the recording head. The common ink chamber 3 is branched into a plurality of pressure chambers 2 that communicate with a plurality of nozzles IK corresponding to pixels in the vertical direction of the image. Furthermore, a piezoelectric transducer 7 electrically connected to an electronic pulse generator 8 is adhered to a part of the wall of each pressure chamber 2 .

The piezoelectric transducer 7 is a suitable flexible plate that can be bent toward the inside of the pressure chamber 2 when receiving a drowsiness signal from the generator 8.
It consists of a piezoelectric crystal, for example, and is glued to the outer wall of the pressure chamber by means of a conductive thin film.

In this method, the piezoelectric transducer 7 is suddenly deflected inward into the pressure chamber 2 due to the drowsiness signal from the electronic pulse generator 8, and the resulting rapid decrease in the volume of the pressure chamber 2 causes the ink inside to be transferred to the nozzle 1. Dot recording is achieved by ejecting ink droplets from the ink, causing them to fly, and reaching the opposing recording paper. The decrease in ink in the pressure chamber 2 due to ink droplet ejection is:
Ink stored in the common ink chamber 3 flows into the pressure chamber 3 to supplement it. Further, the decrease in ink in the common ink chamber 3 is caused by the flexible membrane 9 forming a part of the wall of the common ink chamber 3 and the flexible membrane 1j! This is detected as a pressure decrease by a hydraulic pressure detection means provided outside the i9. The hydraulic pressure detection means consists of a long cantilever-shaped beam 10 whose tip end is glued to the displacement detection portion of the flexible opening 9, and a strain O gauge 11 provided at the base of the beam 100. When the liquid pressure detection means detects that the liquid pressure in the common ink chamber 3 has fallen below a predetermined lower limit value, an electric signal is generated, the valve means 5 is opened, and the ink in the ink tank 6 is discharged. It is introduced into the common ink chamber 3 through the conduit 4 .

Further, when the liquid pressure in the common ink chamber 3 detected by the liquid pressure detection means exceeds a predetermined upper limit value, the valve means is opened and the ink flow from the ink tank 6 to the common ink chamber 3 is stopped. Ru. In this way, the hydraulic pressure of the ink in the common ink chamber 3 is always maintained within the above-mentioned lower limit value, and in this hydraulic pressure state, it is possible to continue stably ejecting ink droplets from the nozzle 1. It is.

The flexible opening 9 is fitted over the opening of the common ink chamber 3 of the recording head to form an upper wall and seal the ink inside the chamber 3.

The common ink chamber 3 configured in this way is filled with ink and absorbs the return pressure of the ink due to the deformation of the pressure chamber 2 during ink ejection, and interacts with other pressure chambers (channel interaction). It acts to prevent this from occurring.

FIG. 3 shows an inkjet recording apparatus specifically constructed using the above-mentioned recording method and consisting of seven nozzle arrays.

In the above-described inkjet recording device, the flexible liquid 9
Since the amount of change in response to changes in fluid pressure is set to be minute, fluid pressure detection by detecting the amount of change has had no choice but to use a highly sensitive sensing element such as a strain gauge, which is also unstable. For this reason, when this detection system is used for a long period of time, there are problems such as changes over time.

One example of a conventional method for stabilizing the liquid pressure of ink in the printhead is the so-called hydrostatic ink supply method, in which the height of the ink tank is maintained at a constant height relative to the position of the printhead. Although there is a method, it is difficult to constantly maintain a predetermined pressure in response to changes in ink consumption, changes in ink remaining amount, etc. Further, even in the above-mentioned ink supply method in which the ink in the ink tank is pressurized and fed, it is difficult to constantly maintain the liquid pressure in the common ink chamber 3 at a constant level.

Therefore, the ink pressure in the print head fluctuates widely due to factors such as changes in ink consumption due to changes in dot density during printing and changes in the amount of ink remaining in the ink tank. Therefore, it has been difficult to stabilize the flight characteristics of ink droplets ejected from the nozzle. In severe cases, the supply of ink could not keep up with the consumption, and the liquid pressure dropped, causing air bubbles to be sucked in from the nozzles, resulting in the inability to eject and record.

In addition, in a print head that uses an ink supply method using hydrostatic pressure, when the ink tank and the print head are connected by an ink supply system, changes in the volume of ink within the print head are caused by the flow of ink between the print head and the ink tank. The recording head is absorbed by the recording device (printer)
When removing the ink from the ink and storing it as a single unit, the ink inlet passage of the recording head is sealed to prevent air bubbles from entering, so ink may leak from the nozzles during storage due to temperature changes or evaporation. , inhale the bubbles.

In a conventional inkjet recording device, which has a valve means for adjusting fluid pressure in the middle of an ink supply system that connects an ink tank and an ink jet channel in the recording head to replenish ink, the temperature of the ink in the recording head is There was no means between the valve means and the nozzle to accommodate changes in ink volume caused by evaporation or evaporation. For this reason, ink may leak from the nozzle forming the opening, or air bubbles may be sucked into the nozzle, resulting in poor recording.

That is, in any type of infusier recording apparatus, defects often occur due to the above-mentioned change in ink volume. Therefore, the deformable volume t1'7 of the flexible membrane that covers the opening of the common ink chamber must be made such that it can sufficiently absorb the volume change q of the ink.

An object of the present invention is to accurately detect and control the liquid pressure of ink within a recording head, thereby solving the drawback of unstable liquid pressure in the prior art.

The present invention provides a means for detecting the liquid pressure within the recording head, a means for detecting an abnormality in the liquid pressure and a lack of remaining wink.

The present invention will be explained below with reference to illustrated embodiments.

FIGS. 4 and 5 are a sectional view and a plan view showing an embodiment of the present invention. In the figure, the flexible film 19 that seals the opening of the common ink chamber 3 in the recording head is attached to the head base plate 18 when the ink is supplied from the ink tank 6.
It maintains a height of +H from the surface. This flexible membrane 19
Above the head substrate 18, a non-contact position detection means for detecting the displacement needle of the height H of the flexible membrane 19 is fixed at a predetermined position on the head substrate 18.

The flexible film 19 is made of a thin film-like member made of a flexible material so as to be able to absorb changes in the volume of the ink caused by changes in the temperature of the ink in the recording head and evaporation in the nozzle portion. .

The flexible membrane 19 is configured to absorb pressure changes propagating from the pressure chamber 2. That is, in a multi-nozzle recording head, a pressure wave generated from the pressure chamber of one channel spreads to the pressure chamber of another channel via the common ink chamber, and the ink droplets of the other channel are affected. This produces so-called channel inter-rough silane which deteriorates the jet flight characteristics. By constructing a part of the wall surface constituting the common ink chamber with a flexible film, it is possible to prevent such pressure waves from going around.

The above problem is solved by making the flexible film for detecting ink pressure according to the present invention also serve as the flexible film for preventing pressure waves from wrapping around, and by utilizing the space above the recording head, At the same time, it has a compact structure, making it possible to reduce costs.

As for the shape of the flexible membrane 19, various cross-sectional views can be considered as shown in FIGS. 6 to 9. Here, Figure 6 shows a water pillow shape, Figure 7 shows a dome shape, and Figure 8 shows a corrugated shape (
FIG. 9 is a cross-sectional view of each flexible membrane having a small waveform at the periphery.

The plan view of the movable wall having each of the above-mentioned cross-sectional shapes may be rectangular, circular, oval, or other shapes depending on the configuration of the recording head.

The flexible film 19 having each of the above shapes is formed so as to be able to be displaced in response to the liquid pressure of the ink within the recording head, and is adhered to the surface of the head base 18 in a fluid-tight manner.

As for the material used for the flexible film, a single thin film or a laminate of plastic materials such as vinylidene chloride, polyethylene, nylon, and polypropylene are used. Moreover, those obtained by laminating or vapor-depositing metal thin films such as aluminum are also used. Furthermore, consideration was given to thermal deformation when the flexible film 19 was bonded to the head base 18 and then heated and cured.
C1 It is also effective to heat the flexible film 19 in advance.

Metal materials used for flexible membranes include aluminum,
N& materials such as stainless steel and brass can also be used, but materials that change the composition upon contact with the ink or have a negative effect on the ink are not allowed.

The flexible film described above is used to control the liquid pressure of ink within the recording head with a configuration as shown in the block diagram of FIG. That is, the height of the flexible film changes in response to changes in the liquid pressure within the recording head. This change in the height of the flexible film is detected by measuring the gap distance between the flexible film 19 and a non-contact position detection means fixedly installed above the recording head, and its output signal is input to the control circuit. The control circuit processes the signal and outputs a control signal to a circuit that drives the valve means.

The valve means is operated in response to a signal from the valve means drive circuit, and ink sent from the ink tank is injected into the recording head. When the amount of ink in the recording head decreases due to printing operations, etc., and the liquid pressure decreases, the above system detects the position where the flexible membrane is lowered, and injects an appropriate amount of ink from the ink tank to fill the inside of the recording head. The amount or pressure of ink is always kept within certain upper and lower limits, ensuring stable ink droplet ejection flight characteristics.

Figure 11 fAl, (B), (C1 shows the above-mentioned decrease in the ink liquid pressure in the recording head and the deformation process of the flexible film 19, and H,, t+,, H, in each figure are respectively It shows the distance from the reference position on the top surface of the head base 18 to the predetermined detection position of the flexible film 19.The height position of the flexible film 19 can be determined using a non-contact position detection means fixed on the top of the recording head. It is detected by measuring the gap with the flexible membrane 19.

The deformation of the flexible membrane 19 due to the hydraulic pressure P is as shown in FIG. That is, for example, if the hydraulic pressure is gradually lowered from a sufficiently high hydraulic pressure P3, the central part will first begin to dent, and as the hydraulic pressure is further lowered (near P), the dent will spread to the surrounding area, When the hydraulic pressure becomes sufficiently low (pl), the entire flexible membrane becomes depressed.

FIG. 12 shows the change in the liquid pressure of the ink in the recording head (
P, ~P, ~) and the height change of the flexible membrane 19 (H1 to H8
~) shows the characteristic curve of t). This characteristic curve forms a hysteresis curve as shown in the figure due to the unique stiffness (roughness) that varies depending on the material, plate thickness, and processing method of the flexible membrane. If you draw a tangent line at any point A on this curve, the slope (tangent) of that line is d
It is given in H/dP. When designing the flexible film, the flexible film η) at the hydraulic pressure P1 used for inkjet recording.
Pressure sensitivity is important. This pressure sensitivity is the ratio of the change in the height H of the flexible membrane to the change in the hydraulic pressure P. This a
The larger the value of Jap, the more accurate pressure detection can be obtained and the easier it is to control pressure. Conversely, if the drt/ap value is small, pressure detection over a wide range becomes possible, but the accuracy of pressure measurement and pressure control decreases.

In order to increase the dH/dP value, it is preferable to use a shape with a large number of concentric or spiral corrugations (waveforms) as shown in FIG. Further, in order to have a certain degree of hysteresis as shown in the curve shown in FIG. 12, a spherical shape as shown in FIG. 7 is preferable.

When actually recording by ink jetting, the liquid pressure P of the ink inside the recording head used is a slightly negative pressure (for example, -5 to -
Good droplet jet flight characteristics can be obtained near Pl set to 10 crn HtO), but near that liquid pressure P1, dTvd
In order to make P thicker, it is better to give K a certain degree of hysteresis.

The present inventors previously made it possible to realize this by repeating trial production and experiments in the range of dtMd P value from 0 to 20 dtMd/cx rho. Furthermore, by changing the structure of the recording head and the shape/size/material of the flexible film,
/cm Chicken.

It was possible to achieve a range from 1000 mN/cr/LIItO to 1000 mN/cr/LIItO. In addition, the above d I
The ap value is detected by a flexible membrane detector 2 that deforms due to changes in fluid pressure.
This is the value measured at the part where 0 force "-ta is exerted. Also, regarding the t-5 characteristic curve, it is the part used to determine the displacement on the characteristic curve (in most cases, the part with the steepest slope) is the value at which the measured pressure is used.

When designing a flexible membrane, it is necessary to ensure that the characteristic curve shown in FIG. 12 has good reproducibility. Furthermore, it is preferable that the hysteresis of the loop-shaped characteristic curve be as small as possible. The characteristic curve of the flexible film after printing or running-in operation is continued for a sufficient length of time at °C is the height H of the flexible film relative to the liquid pressure P1, which is approximately equal to the upper loop and lower loop in Fig. 12. It becomes stable at an intermediate position.

Appropriately select the cross-sectional shape of the flexible membrane shown in Figures 6 to 9, i.e. the dimensions and curvature of the trapezoid, spherical, corrugated, peripheral waveform, etc., as well as the hardness and stickiness of the flexible membrane material. By doing so, a predetermined dll/dP value can be obtained near the hydraulic pressure P used for recording.

It is also possible to apply the liquid pressure detection ability based on the displacement characteristics of the flexible membrane according to the present invention and use it to detect the remaining amount in an ink tank of a hydrostatic ink supply system. That is.

When the amount of ink remaining in the ink tank becomes low, the ink pressure in the print head decreases.The system monitors the ink pressure in the print head and issues an alarm when the liquid pressure falls below a certain value. and then stop the printing operation. For example, FIG. 13 shows the fluid pressure change characteristics on the print head side in a hydrostatic ink tank and print head.

This represents the change in the liquid pressure of ink within the recording head when ink is consumed by printing at a constant consumption rate from a full ink tank. At first, the hydraulic pressure is kept almost constant, but when the residual force drops below a certain level, the hydraulic pressure begins to drop rapidly. Here, the hydraulic pressure is P. When the printer reaches a certain level, an alarm will be issued or the printing operation will be stopped. Here, the process may be divided into two stages, with an alarm being issued at Po and a printing operation being stopped at Pot.

Further, in the case of application to remaining amount detection, the height of the flexible membrane may be configured to change rapidly near the hydraulic pressure P0. For example, hydraulic pressure P. When reaching the vicinity, the characteristic curve abruptly changes from sufficiently convex to sufficiently concave.

By forming such a η-characteristic curve, it is possible to use an inexpensive hydraulic pressure detection means with low accuracy.

FIG. 14 is a sectional view showing the ink liquid pressure detection means used in the present invention. The structure is such that a part of the ink chamber is provided with a flexible film 31, and the height of the flexible film 31 is directly detected by a photodetector. A part of the wall of the ink chamber is provided with a flexible film. It's now 31.

On the other hand, a bottle is glued to the upper surface of the flexible film 31 at approximately the center to prevent the pin 35 from tilting due to the C1 regulating plate, and a light shielding plate is attached to the tip of the bottle 35. 3
A photodetector, such as a photointerrupter, consisting of a light-emitting element and a light-receiving element 39 is installed on both sides of the light-emitting element 7. With this configuration, when the ink liquid pressure in the ink chamber changes, the pin 35 and the photometric plate 37 move up and down.
A photointerrupter detects this vertical movement.

In addition to the above-mentioned photoelectric detection means, the ink liquid pressure detection means used in the present invention includes, for example, a magnetic detection means in which the light-shielding plate is a magnet and a photointerrupter is a magnetic sensing element;
Various detection means can be used, such as electrical detection means that uses electrodes provided on the flexible membrane and changes in static capacitance due to the upper and lower positions of the electrodes.

As described above, by using the flexible film having the characteristics according to the present invention and the non-contact position detection means, the liquid pressure detection control of the ink in the recording head and the detection of the remaining amount of ink are realized with high precision and high reliability. It is possible to do so.

[Brief explanation of drawings]

1 and 2 are schematic diagrams of an on-demand inkjet recording device, with a sectional view and a plan view, respectively, and FIG. The perspective view, FIG.
9 to 9 are cross-sectional views showing various shapes of the flexible membrane according to the present invention, FIG. 10 is a block diagram showing the hydraulic pressure detection control according to the present invention: Step A, and FIG. 11 is a cross-sectional view showing various shapes of the flexible membrane according to the present invention. A cross-sectional view showing the change process of the flexural membrane and hydraulic pressure, Fig. 12 is a characteristic curve of the hydraulic pressure in the record-\RAD and flexible membrane displacement, and Fig. 13 is the hydraulic pressure of the hydrostatic pressure type fink supply system. Characteristic curve No. 141'fl is a sectional view of the hydraulic pressure sensing means according to the present invention. 1...Nozzle 3...Common ink chamber 5...Valve 8 6-=...Ink tank 9.19...Flexible membrane 18...・
・Head base 2 ()...Representative of non-contact position detection means Yoshi Kuwahara Misaki 111c (C) Ward 6μ diagram

Claims (1)

[Claims] In an ink jet recording head in which a part of the wall forming an ink supply chamber for supplying ink to an ink jet nozzle is formed of a flexible film, the amount of displacement of the flexible film with respect to a change in ink liquid pressure is 0.1 μm/α10-1 m, / mTT,
0. An inkjet recording head characterized in that the flexible film is formed such that the flexible film is 0.