Ink Supply System for an Ink Jet Printer

This invention relates generally to the art of non-impact ink jet printing, and more particularly to ink supply systems for ink jet print heads.

An asynchronous volume displacement droplet ejection type of ink jet head is described in U.S. Pat. No. 3,946,398--Kyser et al (1976) and co-pending patent application Ser. No. 489,985, filed July 19, 1974, both assigned to the assignee of the present application. A piezoelectric element is associated with an ink jet chamber, resulting in ejecting a droplet of ink from a nozzle of the chamber with sufficient velocity for it to travel to a recording medium. One such droplet forms a portion of a character to be printed. A plurality, such as seven of nine, print heads of this type are preferably built as a single structure that is mechanically swept across a recording medium upon which the printing is taking place line by line. At each column of the printing line the appropriate number of the independently controllable ink jet chambers are fired by pulsing their respective piezoelectric elements to eject ink drops therefrom.

Such ink jet heads require, of course, a supply of ink to their chambers to replace the ink that is ejected as droplets. An ink supply system for the asynchronous type of ink jet head which utilizes a pre-filled insertable ink cartridge is described in co-pending patent application Ser. No. 807,219, filed June 16, 1977, a division of co-pending application Ser. No. 694,064, filed June 7, 1976, both of which are assigned now U.S. Pat. No. 4,074,284, issued Feb. 14, 1978, to the same assignee as the present application. The goal of prior ink supply design efforts have been to deliver ink under constant pressure and free of bubbles and impurities. Other efforts have been directed toward making ink containers refillable or interchangeable. However, much of this prior work is not entirely effective for many particular applications.

It is an objective of the present invention to provide an improved technique for supplying ink to an ink jet printer under constant pressure over time that is above atmospheric pressure.

It is another objective of the present invention to deliver ink free from contamination by bubbles and impurities.

It is a further objective of the present invention to supply ink in a manner that the ink container can readily be removed and replaced by another container.

In accordance with this invention, an ink container takes the form of an ink cartridge including a piston, a piston housing forming most of the body of the cartridge, and a flexible diaphragm to seal the piston with respect to the housing. All of these are made of fluid impervious materials. A septum is provided in the piston to allow fluid communication between the interior of the cartridge and the supply line to the ink jet print head through a hollow needle mounted in the cartridge receptacle. A shroud biased upward by a spring in the receptacle engages the piston upon the cartridge's insertion into the receptacle and pressurizes the cartridge. The cartridge is then rotated and detents on the receptacle engage the cartridge housing to hold it in place. Further rotation or rotation in the opposite direction disengages the detents and the cartridge is lifted off and removal is complete. As ink is withdrawn from the cartridge, the piston moves upward under influence of the spring to maintain the reduced volume of ink under pressure.

Also mounted on the shroud is a vertically movable coupling which is also biased upward by a spring. The coupling contains a rubber cap which moves over the hollow needle upon the removal of the ink cartridge from the receptacle. This seals the ink supply line from unwanted air bubbles and impurities. The sliding coupling further guides the cartridge into the correct position with respect to the needle and receptacle and allows the needle to pierce the septum of the cartridge before it is pressed down completely and rotated to engage the container detents for mounting. Fluid communication is therefore established before the cartridge piston is loaded upward for full pressurization of the ink cartridge and ink spillage is thus avoided. No ink is stored in the cartridge under pressure before installation on the receptacle.

In addition, ink leakage prevention is enhanced with the use of a rounded, hollow needle through a prepunctured septum in place of the standard needle and septum in the prior art.

Thus, by the above means, ink can be supplied to an ink jet printer with constant pressure until exhaustion of the ink cartridge. The cartridge is readily removed and another inserted for continued printing. The cartridge and receptacle are both completely sealed when they are separated from each other. No contamination of the ink by air or impurities can occur. One further result is that there is little chance of staining the operator's hands in the cartridge replacement operation.

Additional objects, advantages and features of the various aspects of the present invention will become apparent from the following description of its preferred embodiments which should be taken in conjunction with the accompanying drawings.

FIG. 1 is a vertical sectional view of an ink cartridge receptacle with a ink cartridge mounted thereon;

FIG. 2 is a sectional view of the ink cartridge receptacle of FIG. 1 but with the ink cartridge removed therefrom;

FIGS. 3 and 4 illustrate variations of certain receptacle components of the embodiments of FIGS. 1 and 2;

FIG. 5 illustrates a preferred structure of a component of the ink cartridge embodiment of FIGS. 1 and 2 in top view;

FIG. 6 is a sectional view of the component of FIG. 5 taken across section 6--6 thereof; and

FIGS. 7 and 8 illustrate in an enlarged scale two specific alternative structures of a component of the receptacle embodiment shown in FIGS. 1 and 2.

For the ink supply cartridge (FIG. 1), a piston 10 slides up a cartridge housing 12, consisting of a side housing 14 and a cartridge top 13. A flexible, fluid impermeable diaphragm 16 seals the piston with respect to a housing 12 of the cartridge, while allowing the piston to slide. The seal for the piston occurs in the form of a rolling diaphragm. The edges of the diaphragm, preferably made of soft rubber that is chemically resistant to the ink, such as butyl, are thickened so as to be held by annular protrusions 21 and 22 of the top 13 and a side housing 14, respectively, to form a sealing gasket. Furthermore, since it is preferable to mold side housing 14 and top 13 out of polystyrene plastic, resistant to both high impact and chemical reaction with the ink, the top and side housing can be ultrasonically welded to form a further seal against ink leakage. Lugs 18 are mounted on the top 13 to engage detents 32 on a receptacle 30 to hold the ink supply container in place.

It has been found preferable to attach a septum 17 to the center of the piston 10, although other locations on the housing are possible. The septum 17 is prepunctured to receive a needle 39 therethrough. Furthermore, the septum 17 can conveniently be molded as part of the diaphragm 16 as a unitary, fluid tight element. In molding the septum 17, it is best to make it slightly larger than the piston 10 so as to allow the septum 17 to frictionally engage the sides of the circular inlet 11. The septum 17 can be pushed into the inlet 11 and it will remain there without the use of adhesives. Also, the tight fit between the inlet 11 and septum 17 causes the rubber to be in compression. The compression forces cause the rubber of the septum 17 to close tightly behind the needle 39 as it is extracted from the cartridge, thus resealing the cartridge.

FIGS. 5 and 6 show a preferred embodiment of the septum 17. This design for the septum allows the septum to be in place by frictional force. When a needle is inserted, it spreads the rubber of the septum causing even greater force against the side wall. The frictional retaining force is increased. This helps counteract the axial force on the septum generated by the pressure of the needle pressing through the septum which tends to force the septum out of the inlet. Thus, a feature of the design is that the frictional force of the side wall is made greater than the needle force which tends to push the septum out of the inlet.

Referring to FIGS. 5 and 6, the septum 17 is discussed by three horizontal zones, 62, 64 and 66. A prepunctured hole 60 passes through the center of the septum 17 and through all three zones. This hole is precisely cut with the needle having a sharp point and a longer taper. A hollow needle 39 having a rounded point is then used for establishing fluid communication with the interior of the cartridge. These needles do not cut the rubber, but pry open the walls of the hole previously opened in the rubber. Thus, the hollow needle 39 continually uses the same pathway, avoiding further holes in the septum and allowing a more effective seal. FIGS. 7 and 8 show two embodiments of rounded point, hollow needles that may be employed as the needle 39 (FIGS. 1 and 2).

It is clear that use of a prepunctured septum and a rounded point, hollow needle need not be restricted to pressurizable cartridges as discussed herein, but may be substituted for any previous septum and needle system.

To help steer the hollow needle into previously punctured hole 60, conical inlet 61, a part of zone 62, is placed at the bottom of the hole 60. In the zone 62, the rubber of the septum 17 includes notches 63 which provide room for rubber expansion as the needle passes through. The notches reduce axial force which tend to force the septum out of position. Between the notches, rubber ribs 65 transmit compressive forces to the walls of the piston inlet 11 which increase friction tending to retain the septum in position. When the needle is removed, compressive forces remain in the rubber because of support from the side walls and thus the hole 60 is squeezed shut.

In the zone 64, there is solid rubber backed up by support from the walls. The rubber is in compression before needle insertion and after needle removal. Those forces seal the pre-cut hole. The zone 64 being thin compared to its diameter acts like a diaphragm. When the needle is applied at the center, the rubber stretches. The stretching puts the rubber in tension and reduces the force required for needle penetration. It also reduces the frictional retaining force at the walls in the zone 64, with the retaining force in zone 62 sufficient to prevent dislocation of the septum. If the rubber did not bow and stretch in zone 64, the force required to insert the needle would likely be unacceptably high.

In zone 66, there is no side wall support and thus no compressive force in the rubber initially. When the needle penetrates zone 66, the rubber opens and spreads into the open space provided. The force required to penetrate is low, because there is no resistance to the movement of the rubber other than the tensile forces in the rubber itself. No septum retention force is provided in zone 66. A sealing force is provided when the needle is removed from the zone 66 by the internal tensile forces combined with the pressure of the ink in the cartridge.

The ink cartridge is filled by first piercing the septum 17 with precision with a sharp tapering needle. Through this pre-cut hole, a hollow needle allows ink to flow into a chamber created by the diaphragm 16 and the cartridge top 13. As the cartridge becomes full, the piston reaches its lowest or fullest extended position. At this point, detents on the cartridge housing prevent the piston from disengaging the cartridge housing. Due to the slight slope toward the center of the top 13, air tends to flow into the conically shaped space 15 provided at the center of the top 13. During the process of filling the cartridge with ink, a hollow needle is inserted through the septum. Its tip goes to the top of the space 15 and draws off any gas or air which has collected there.

Referring to FIGS. 1 and 2, the receptacle 30 includes a receptacle housing 31 on which is mounted detents 32 which lock the ink cartridge in place. Locking is accomplished by rotating the cartridge around its axis after it is fully inserted, engaging the detents, as shown in FIG. 1. Through a connector 38, a load spring 33 urges upward a shroud 34 which contains the spring 33 and limits its extension. The shroud 34 has slots accepting lugs on housing 31 to allow vertical movement without rotation. The spring 33 applies a force against the cartridge piston 10 when the cartridge is positioned in the receptacle, thus pressurizing the ink inside the container. The spring 33 also provides a force against the cartridge housing 14 which holds it in the detents of the receptacle housing 14. A slidable coupling 36 mounted at the center of the shroud 34 engages the ink container, and also locates and guides a rounded point, hollow needle 39 in the receptacle to the center of the septum 17 as the cartridge is lowered into the receptacle. Furthermore, the coupling 36 provides a rubber cap 37 over the needle to seal it against air and impurities when the container is removed (see FIG. 2). Also, since the piston inlet 11 of the cartridge for receiving the septum contacts the coupling 36 to guide the cartridge into proper placement in the receptacle and to provide the force path along which the cartridge is pressurized, the load on the piston as the cartridge is inserted is toward the center. Less torque can be transmitted between the cartridge and the receptacle when the cartridge is rotated against spring pressure for locking into the detents.

A connector 38 retains the needle 39 used for penetrating the septum in the container and connects the needle to flexible tubing 40 to supply the ink to an ink jet print head. A coupling spring 35 applies a force between the coupling 36 and the connector 38 to pull a rubber cap 37, which is part of the coupling 36, over the end of the needle 39 and to seal it when a cartridge is not in the receptacle. When a cartridge is inserted into the receptacle, the spring 35 is compressed. The coupling 36 moves relative to the connector 38, causing the needle 39 to emerge from the sealing cap 37 and to penetrate the septum 17 in the cartridge. The coupling spring 35 is chosen to be weaker than the load spring 33 so that the needle will penetrate the septum of the cartridge before the load spring is compressed to fully pressurize the ink in the cartridge. In this manner, ink spillage is greatly reduced since the cartridge is penetrated while only slightly pressurized by the coupling spring. After fluid communication is established, then the load spring is depressed as the cartridge is locked into place on the receptacle to fully pressurize the cartridge.

As a matter of construction, all rigid parts of the receptacle, except the metal springs, are made of easily moldable plastic. A non-inflammable plastic under the name "Noryl", a trademark of the General Electric Corp., is used for the shroud 34 and receptacle housing 31. The coupling 36 and the connector 38 use acetyl plastic for its low friction and strength. Materials which are soft, weather-resistant and have low compression set, such as neoprene and ethylene propylene, should be chosen for the rubber cap 37 and the contact pad 41.

FIGS. 3 and 4 show two different embodiments of the coupling 36 of FIGS. 1 and 2 which prevent a drop of ink from the needle or the septum from being deposited either on the septum or the receptacle at the point of the needle passage when the needle is removed from the ink container and withdrawn to its rubber sheath in two receptacle. Both embodiments place a rubber contact in the receptacle which will contact the septum and be in compression before, during and after passage of the needle tip. Compression will not be released until after other mechanisms in the receptacle and cartridge can seal the interior of the container and receptacle from the interface surface.

FIG. 4 entails one such embodiment. The rubber cap 37 is bonded to the coupling 36. Its length is such that it extends above the surface against which the piston is seated. This causes the cap to be in compression at the interface, performing the sealing function during the passage of the needle. The embodiment of FIG. 3 has a separately protruding rubber contact pad 41 and needle guide 42 directly below fixed to the coupling 36. Of consideration between the two embodiments is that the one in FIG. 4 places the needle guide 42 further away from the point of needle entry into the septum than the embodiment in FIG. 3. However, the spring force provided by the rubber needle sheath tends to force the needle towards the center line for proper entry through the septum. Moreover, this embodiment in FIG. 4 is slightly less expensive because it involves fewer parts.

The various aspects of the present invention have been described with respect to particular embodiments thereof, but it will be understood that the invention is entitled to protection within the full scope of the appended claims. For example, it is easily recognizable that the present invention can be used with liquids other than ink and in areas other than ink jet printing.