JP2003341090A - Supply ink tank for reciprocative inkjet print head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stabilize a pressure in a supply chamber for a print head. <P>SOLUTION: A header ink tank mounted on a reciprocative carriage supplies ink to the reciprocating inkjet print head. The various kinds of functional elements are provided to be symmetric with respect to a central face perpendicular to the reciprocating direction. An ink level sensor is equipped with an ink supply exit to the print head, a supply inlet to an ink chamber, and a float. An adequate negative pressure is applied to the ink tank by using a controlled vacuum source having a predetermined volume. Two ink tanks having a common side wall are combined. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to an apparatus having improved recording quality in an ink jet printing system having a reciprocating printhead, and more particularly to having such a stable pressure in the supply chamber to such a printhead. Regarding the device.

[0002]

2. Description of the Related Art (Inkjet printing) At present, many printed materials on which a copy of a color image is mounted are produced. While most of these color prints are made using offset printing, in office and home environments large amounts of color prints are made using relatively small printing devices. One of the possible printing presses used is the ink jet printing press. In an ink jet printer, ink drops
For example, it is ejected from a nozzle toward an image receiving layer which can be a special coated paper. Ink jet printheads typically have an array of nozzles, each nozzle ejecting ink at different locations at the same time.

Ink is ejected from a nozzle, for example by the use of heat or piezoelectric actuators which produce pressure waves.

It is generally contemplated that the drop size can be held constant, or that there is good control of drop size in a printing machine that can record variable drop sizes.

Printhead FIG. 1 shows an ink jet printhead having a capillary 1 with a nozzle end and an inlet end. An actuator 2 is provided for each tube 1 for causing the pressure wave to push the ink out of the nozzle at the end. At the other end, ink is supplied from the ink tank to the print head.

In the normal rest state, the ink forming the meniscus 3 at the nozzle end of the capillary 1 is affected by the surface tension. Another force acting on the ink is the "hydrostatic pressure" created by gravity due to the height of the ink above the meniscus 3. Since the ink jet print head is completely filled with ink and is connected to the ink tank, the height of the ink level in the ink tank determines the ink pressure at the print head. When the ink tank is placed above the printhead, a positive ink pressure will result due to the vertical height difference between the ink surface and the nozzle.

Some types of printheads require a stable negative ink pressure in the nozzle area for good printing.

In order to finally reach the negative pressure at the nozzle, this positive pressure can be neutralized by applying a negative pressure on the ink in the header tank.

The problem is that the negative pressure in the head and in the tank must be kept constant or within a small range in order to obtain a constant or manageable recording quality.

(Reciprocating print head with header tank) Recently, the ink jet printing technology in a large plate type, large capacity printing machine is used.

The ink jet printhead can be sized to be similar to the transverse dimension of the image or text to be printed, but typically the printhead is smaller. Pagewidth printheads are still more expensive and less reliable than their smaller counterparts.

FIG. 2 is a diagram showing how the ink jet printing machine constructs the entire image. The image-receiving sheet 4, for example a sheet, is transported in one direction (transport direction is indicated by arrow A) and gradually passes below the printing station.

A printhead 5 of a smaller size than the image-receiving sheet 4 reciprocates above it in the transverse direction (indicated by arrow B), one line or a plurality of lines when reciprocating above the paper of the sheet 4. Record continuously. The image is constructed gradually.

Color images can be recorded by overlaying different color images using several printheads to record various colors.

In order to enable continuous operation of the print head 5, an ink tank containing an ink supply source is used as the print head 5.
Combined with. Small presses usually have small cartridges with some limited amount of ink. The cartridge is optionally integrated with the printhead nozzles.

These cartridges must be replaced when empty.

However, high end ink jet printers with large print volumes or large plate forms consume large amounts of ink.

The ink jet printhead of a high-end printing press is combined with an ink tank mounted on a reciprocating carriage that carries the printhead.

This ink tank is called a header tank and can be replenished from a stationary high capacity ink tank.

A possible replenishment arrangement (replenishment of the header tank) can be found in Patent Document 1. If the ink level in the header tank drops too low, the reciprocating cartridge will be transported to the refill station outside the printing area,
Here the header tank is refilled.

A major problem with this method is the difficulty of maintaining a constant ink pressure in the printhead. The height of the ink level in the header tank is constantly lowered to reduce the pressure due to gravity, which causes fluctuations in recording quality. The liquid level can be maintained relatively constant by replenishing it very frequently, but since the cartridge must be stopped each time, recording cannot be performed during replenishment, and the amount of printing per unit time decreases.

In US Pat. No. 6,037,086, a header tank replenishment system that can be replenished during printing is described. The header tank of the reciprocating cartridge is connected to the supply tank by a flexible tube. The main tank is pressurized, and when the refill valve is opened, the ink is pneumatically pumped from the supply tank to the header tank during the printing run. The refill valve is located between the header tank and the printhead.

Maintaining a constant pressure in the printhead is a general problem. The "hydrostatic pressure" must be canceled during printing, even if the header tank is being replenished with a large amount of ink. -During a reciprocating motion, the "hydrostatic pressure" may change due to the acceleration force. It is clear that during acceleration the ink surface will be leveled and that acceleration creates a pressure gradient in the header tank. -A reliable method of measuring the ink level in the header tank is needed to ensure the correct replenishment of the header tank.
Float measurements may not be reliable due to ink movement in the header tank.

It is desirable to have a system that can accurately measure the amount of ink supplied to the header tank.

Another problem is that during the reciprocating motion of the cartridge supporting the header tank, the ink may be bubbled and trapped air bubbles may form in the ink. These bubbles can be transported into the printhead along with the ink flow and cause defects in the printed image. In the prior art, there is no special measure to avoid the influence of bubbles and cancel them.

When the ink tank reciprocates simultaneously with the print head, a mechanism should be provided to damp the pressure fluctuations in the ink connection to the print head due to the movement of the cartridge. Pressure fluctuations adversely affect print quality.

A further problem is that the size of the ink tank must be smaller than the printhead itself to allow for small stagger movements of the printhead.

Up to now, the following related documents are known. Patent Document 1, Inkjet Recording Device Patent Document 3, Ink Cartridge for Inkjet Recording Device Patent Document 4, Inkjet Recording Device, Subtank Unit Suitable for the Same, and Ink Drop Ejection Capacity Recovery Method Patent Document 5, Ink Cartridge Inkjet recording device of JP-A-2003-242242, ink jet recording device, method of supplying ink to sub-tank by this device, and method of collating ink amount supplied to sub-tank by this device

[0029]

[Patent Document 1] European Patent Application Publication No. 1097814

[0030]

[Patent Document 2] European Patent Application Publication No. 1142713

[0031]

[Patent Document 3] European Patent Application Publication No. 1199178

[0032]

[Patent Document 4] European Patent Application Publication No. 1055520

[0033]

[Patent Document 5] European Patent Application Publication No. 812693

[0034]

[Patent Document 6] European Patent Application Publication No. 1142713

[0035]

SUMMARY OF THE INVENTION The drawbacks mentioned above are avoided by a device having the features stated in claim 1. Special features for preferred embodiments of the invention are set out in the dependent claims.

Further advantages and embodiments of the present invention will be apparent from the following description and drawings.

[0037]

DETAILED DESCRIPTION OF THE INVENTION The present invention solves the above-mentioned drawbacks by providing a header tank having functional elements symmetrically arranged in a central plane perpendicular to the direction of movement of the reciprocating carriage of the printing press.

Next, a preferred embodiment of the ink tank according to the present invention will be described.

FIG. 3A shows a header tank 6 according to the present invention.
2 shows a cross section perpendicular to the reciprocating direction of.

FIG. 3B shows a combination of two tanks with additional features that will be explained later.

FIG. 5 gives a horizontal cross section of a combination of two tanks. Line B with arrows on both sides indicates the direction of reciprocal movement of the print cartridge with the print head and header tank. The plane P is a center plane perpendicular to this direction.

The ink tank 6 has an ink chamber 7 and comprises or is connected to several functional elements.

The functional elements are considered to be all the mechanisms that influence the operation of the ink tank 6. All the mechanisms that affect the operation of the ink tank 6 are considered to be functional elements.

Several functional mechanisms can be seen from this point of view. The ink is sent from the bottom of the ink chamber 7 to the ink jet print head 5 via the ink supply outlet 8. The height difference between the ink surface and the print head defines the pressure due to gravity at the print head, and the height difference should be minimized. The position of the outlet 8 should be kept constant to avoid pressure fluctuations. The pressure in the print head 5 is directly determined by the pressure at the supply outlet 8 of the header tank 6.

The supply inlet 10 of the header tank 6 enables the replacement of the ink in the ink chamber 7 with the ink from the main tank to the header tank during the replacement. The inlet is formed by a tube reaching below the ink level in the header tank 6 to allow smooth refilling. Care must be taken during the displacement not to create pressure fluctuations due to the inflow of new ink. At the vacuum inlet 9 at the top of the ink chamber 7, a stable negative pressure is applied to the ink chamber 7 of the header tank 6 to offset the positive "hydrostatic pressure" due to gravity. This is realized by extracting the air at the top of the ink chamber 7 above the ink surface. A system for providing a vacuum or negative pressure to the ink chamber 7 will be described later. A reflux inlet 11 is connected to the print head 5 so that the bubbles generated in the print head 5 can flow back to the ink chamber 7. A small passage 12 provides a connection with the ink chamber above the ink surface.

4A to 4C show the ink level in the ink tank 6 during the three stages. -Acceleration to the left, -acceleration to the right, -no acceleration (for example, when reciprocating motion is stopped) In these three cases, the amount of ink in the header tank 6 is the same.

As shown, during state L in FIG. 4A and during state R in FIG. 4C, the ink surface in the ink chamber is tilted due to the acceleration of the ink tank and the inertia of the ink in the ink chamber. A hydrostatic gradient is created in the ink. Since the supply outlet 8 is provided in the center plane perpendicular to the movement direction of the cartridge, the outlet 8 of the ink chamber 7
The height of the ink level at the position of
Not affected as seen in. The inclination of the ink surface (due to the acceleration and deceleration of the cartridge) swings symmetrically, and the height h of the liquid level at the center of each tank remains constant. By positioning the ink outlet 8 on the printhead along the center plane, pressure fluctuations due to head reciprocation can be minimized.

Inlet 10 for replenishing ink into chamber 7
When considering the position of, the inflow of ink must avoid pressure changes. The most neutral position of the inlet 10 is also in the center plane of the ink chamber 7. The inlet 10 is configured to ensure that the drop of ink into the tank supplies below the ink level to avoid causing, for example, entrapment of air in bubbles.

A further functional feature is a system for adjusting the ink level in the ink chamber 7. -A constant ink level is realized by the ink level sensor. Inside the ink chamber 7, a float 13 having an integrated magnet 14 is provided. A liquid level detection system is provided in combination with a reed switch contact piece 15 fixed to the outside of the ink chamber 7.

The ink tank 6 is adapted to inks having different specific gravities by choosing a large volume float 13 dimensioned for low specific gravity inks (ie oil based inks).

By choosing a float 13 that is large with respect to the size of the ink tank 6, a considerable damping of the ink movement is obtained.

The float 13 can be attached to the ink chamber 7 using a hinge with a small tolerance to ensure that its position remains centered inside the ink chamber 7 during reciprocating motion. The float 13 is also preferably symmetrical in itself.

The ink level h is the reed switch contact piece 1
By adjusting the fixed height of No. 5, it can be kept constant regardless of the type of ink.

By configuring the float 13 symmetrically with respect to the center plane perpendicular to the direction B of reciprocation, the ink level sensor system readings are shown in FIGS. 4A and 4C. Not affected by height position.

The reed switch contact piece 15 commands the pump to force ink from the main tank to the header tank 6 during replacement of the header tank 6.

Furthermore, an ink motion damper 16 is integrated in the ink tank 6 in order to damp the further pressure deformation due to the reciprocating motion. This ink motion damper 16 is located between the ink chamber 7 and the ink outlet 8 to the printhead 5. In order to limit the movement of the ink inside the attenuator 16, the dimensions are chosen to be smaller than the width dimension of the ink chamber 7. The size in the reciprocating direction B is preferably smaller than half the size of the ink chamber 7. The attenuator 16 can be implemented in the form of a labyrinth, mesh or porous member that limits the movement of the ink near the outlet opening 18 of the ink chamber 7. In FIG. 3, a maze is shown on the right side of the ink chamber 7. There are several partitions 17 with holes at different heights and the ink cannot move to the outlet opening 8 in a straight path. In order to avoid pressure and flow fluctuations due to reciprocating movement, the attenuator 16 is constructed symmetrically with respect to the center plane of the ink tank 6.

The attenuator 16 also has an important function of degassing the ink flowing from the ink chamber 7 into the print head.

As the ink is sent from the ink chamber 7 to the outlet 8, the ink flow is guided through the attenuator 16. The ink is forced so that the path is bent several times through the maze formed by the partition 17. Bubbles trapped in the ink have a tendency to rise to the top where they become associated with the air above the ink surface in the ink layer 6. The air outlet of the ink attenuator 16 must reach above the ink level.

By applying a constant negative pressure, the trapped air is more likely to form larger bubbles than at atmospheric pressure, and larger bubbles are more likely to rise more quickly, thus allowing easier separation. it can.

The ink supply system for the print head 5 is
Realized by two ink connections between the ink tank 6 and the print head 5.

First from ink outlet 8 to print head 5
The connecting part of the is located at the bottom of the ink tank 6 and behind the attenuator 16. This opening supplies ink into the print head 5.

A second connection, which is connected to the reflux inlet 11, will allow air bubbles to return from the printhead 5 into the ink tank 6. This is especially important when the new (empty) printhead 5 has to be filled with ink. The height of the connection between the ink tank 6 and the opening is located above the ink surface in the ink tank 6, via which the negative pressure is also directly applied to the ink jet print head 5.

In order to provide a constant vacuum source, the ink tank 6 is connected to a large volume vacuum container in which the vacuum is maintained by a small volume bleed pump under the control of a precision pressure regulator. To be done. By selecting a container with a large volume, a large amount of ink can be transferred to the header tank 6
It will not change easily during the replacement step added to the. The pressure of the large vacuum holding device will change very little when a relatively small amount of ink is applied to the system. The volume of the vacuum container is preferably at least five times the volume of the ink chamber 7. More preferably, the volume of the vacuum container is 50 to 100 times larger than the volume of the ink chamber 7.

Most of the ink tank 6 can be manufactured by a known method such as injection molding. A special coating can be applied to the inside of the ink chamber 7 to obtain lipophilicity.

To reduce manufacturing costs, it is also possible to make a combined ink tank 6 assembly with common sidewalls. The combination of two ink tanks is shown in FIG.

If a separate tank is to be provided for each color, a combination of ink tanks 6 with a common side wall 18 is a cost advantage.

Another possibility is that a special separable seal 19 is provided on the common side wall 18 of the tank 6, so that a single tank, for example for high-end monochrome printers, can be made from the double tank 6. is there. The ink tanks 6 can also be connected in another direction, for example by providing a separable seal 19 in the special ink passage 20.

In order to prevent fluctuations in the ink level during the reciprocating movement, the dimensions of the unblocked opening should be small so that only a small amount of ink can pass through the opening between the tanks 6 during the reciprocating movement. Is.

The combination of several tanks 6 has a further advantage.

As can be seen from FIGS. 3A, 3B and 5, the ink tank 6 is provided with several mountings to allow easy replacement of the ink tank 6 in the printing machine by the use of screws or other mounting means. Holes / slits are provided. The use of mounting means with a quick release system is preferred. This may be necessary when changing the ink type or color in an ink jet printing device. If several tanks 6 are mounted together in a reciprocating carriage, the replacement can be done faster than if such tanks 6 were mounted separately.

While the preferred embodiment of the invention has been described in detail, it will be apparent to those skilled in the art that many modifications can be made thereto without departing from the scope of the invention as defined by the claims. Will.

[Brief description of drawings]

FIG. 1 shows a cross section of an ink jet print head.

FIG. 2 illustrates the overall printing principle of an ink jet printing machine with a reciprocating print head.

FIG. 3 shows a cross section (A) of an ink tank according to the present invention, giving an isometric view (B) of a dual ink tank assembly.

FIG. 4 shows the ink level in the tank during acceleration and at rest or during continuous motion.

FIG. 5 shows a horizontal cross section of a dual ink tank assembly.

[Explanation of symbols] 1 capillary 2 actuators 3 meniscus 4 Image receiving sheet 5 print head 6 header tank 7 Ink chamber 8 Ink supply outlet 9 Vacuum inlet 10 Supply entrance 11 Reflux inlet 12 passages 13 floats 14 magnets 15 Reed switch contact piece 16 attenuator 17 partitions 18 Common sidewall 19 Separable seal 20 tank passage 21 Mounting holes / slits

Continued front page    (72) Inventor Balt Berghest             Belgium Bee 2640 Maltcell Septes             Trat 27 in Aghua-Gewert F term (reference) 2C056 EA26 EC19 EC32 EC40 FA10                       KC09

Claims (3)

[Claims] 1. An ink tank (6) for supplying ink to an ink jet print head (6) having an ink supply chamber (7) and mounted on a reciprocating carriage and mounted on the same carriage. An ink tank, wherein the functional elements of the ink tank (6) are symmetrically arranged in a center plane for mounting at a right angle to a moving direction of the reciprocating carriage. 2. A reciprocating printhead (5) with a vacuum source for providing a stable negative pressure by the use of an ink tank (6) according to claim 1 and a controlled vacuum source with a large volume. Ink supply system. 3. An ink jet printing machine comprising an ink tank (6) according to any of the preceding claims, wherein the ink tank (6) is preferably replaceable.