Device For Retention Of Ink Jet Nozzle Clogging And Ink Spraying

Abstract

A device for use in an ink jet printing system which comprises a vapor chamber and means for moving said chamber to enclose the jet nozzles during shut-down period to prevent ink from drying at the nozzle. A sharp edge wall is provided to keep the charging electrodes and deflection plates free from ink spraying at pressure shut-off and means are provided for mounting the charging electrodes for movement out of the jet path prior to shutdown of the printer to prevent ink spraying thereon at pressure shut-off.

Description

BACKGROUND OF THE INVENTION

Ink jet printing has been known in the prior art as exemplified by the system shown and described in U.S. Pat. No. 3,596,275 which issued on July 27, 1971. In the system described in this patent, a jet of writing fluid or ink is caused to issue from a nozzle in the form of a succession of tiny individual droplets which are directed toward the surface of a record member. As the individual droplets are formed, they are given an electrostatic charge which is a function of the instantaneous value of an input signal which is to be recorded. The charged droplets are caused to pass between a pair of electrostatic deflection plates. Constant high voltage charges are applied to the deflection plates to produce a constant high voltage electric field between adjacent plates. As the charged droplets pass through the electric field, they are deflected from their normal path by an amount which is a function of the magnitude of the charge on each of the droplets and in a direction which is a function of the polarity of the charge on the individual droplets. Each droplet of the ink or writing fluid has its own unique charge characteristic for directing it to the desired print position on the record member.

In a printing system of the type described above, nozzle clogging has presented a well known problem. One of the reasons of clogging is due to the ink drying in the nozzle over a standstill period, such as the weekend. The nozzles have an inside diameter in the order of 0.001 or 0.002 of an inch and ink allowed to stand therein tends to clog the opening when the ink has dried. Prior attempts have been made to solve this problem. For example, the aforementioned U.S. Pat. No. 3,596,275 discloses a system for removing the residual ink from the nozzle by flushing it out with a suitable solvent such as water. A reservoir is provided which contains rinse water and a pressure source is connected to the reservoir to establish a suitable pressure head. Another system is disclosed in U.S. Pat. No. 3,346,869 wherein a solenoid-operated silicone-coated pad is brought up to close the nozzle opening to prevent the ink from drying. Both these systems are relatively expensive and complex to operate.

Another problem which exists is that of ink spraying. When the jet pressure is turned off to shut down the printer, the residual pressure in the ink supply line usually causes irregular sideway spraying that wets and messes up the charging electrodes and the deflection plates. From practical experience, it is known that it is imperative to keep the electrodes and deflection plates dry lest arcing and short circuits occur and cause machine breakdown. Therefore, every time before the printer is turned on, it is necessary to dry up the ink mess on the electrodes and deflection plates left by the ink spraying of the last shutdown. This is an extremely cumbersome and time-consuming task because there are generally 66 charging electrodes and 67 deflection plates in a line printer and they are of small dimensions with a tiny space in-between.

In view of the above, it was considered desirable to devise an improved device which would not only prevent nozzle clogging but which also would keep the electrodes and deflection plates free from ink spraying.

SUMMARY OF THE INVENTION

In one preferred embodiment of the present invention a support member is provided on which is mounted the row of charging electrodes. This support member is fastened to another member having a hollow chamber portion with an opening or mouth in alignment with the electrodes and spaced therefrom. The chamber is partially filled with ink or water with a chemical additive such that a high vapor pressure is maintained in the remaining portion of the chamber. The electrode and chamber assembly is movably mounted and transducer means, such as a solenoid, is provided to move the assembly.

A row of ink jet nozzles is fixedly mounted and when the electrode and chamber assembly is positioned for a printing operation, the row of charging electrodes is positioned in alignment with the row of nozzles so that the ink droplets are directed between the electrodes and the opening in the chamber is spaced away from the nozzles. When the printer is shut down and prior to turning off the pressurized ink, the transducer is activiated to move the electrode and chamber assembly so that the row of charging electrodes is moved out of the discharge path of the nozzles and the chamber is moved so that its mouth will intercept the nozzles and the jet stream, after which the ink pressure is turned off. Thus, ink spray is prevented from reaching the electrodes and the deflection plates mounted in alignment with the electrodes and also the nozzles which are now enclosed in the mouth of the vapor chamber are kept damp enough to prevent ink drying and clogging. A sharp edged side wall is also provided on the assembly against which the mouth of the chamber moves, said wall serving to contain the vapor in the chamber and also to further prevent the ink spray from reaching the electrodes and the deflection plates.

In another embodiment of the invention, the charging electrodes are mounted on a movable support along with a trough containing water or water and a detergent. Activation of a transducer will move the electrodes out of the discharge path of the nozzles and the trough will move into position to intercept the nozzles with the nozzle tips extending below the water line.

In still another embodiment of the present invention, the print head or row of ink jet nozzles is rotatably mounted and transducer means is provided to rotate the nozzles away from the electrodes and into a trough containing water or water and a detergent.

The present invention advantageously solves the aforementioned problems of nozzle clogging and ink spraying by making use of arrangements which are simple, reliable and inexpensive.

It is, then, a primary object of the present invention to provide a novel and improved arrangement for preventing nozzle clogging and ink spraying when an ink jet printing system is shut down.

A further object of the present invention is to provide in an ink jet printing system means for enclosing the ink jet nozzles in a vapor chamber when the system is shut down.

A still further object of the present invention is to provide in an ink jet printing system means for moving the charging electrodes out of the discharge path of the ink jet nozzles when the system is to be shut down.

Another object of the present invention is to provide a novel and improved arrangement for printing nozzle clogging and ink spraying when an ink jet printing system is shut down which comprises a movable assembly having a row of charging electrodes and a vapor chamber.

A further object of the present invention is to provide an ink printing system means for submerging the ink jet nozzles in a liquid when the system is shut down.

Another object of the present invention is to provide a novel and improved arrangement for preventing nozzle clogging and ink spraying when an ink jet printing system is shut down which comprises a movable assembly having a row of charging electrodes and a container of liquid.

A still further object of the present invention is to provide in an ink jet printing system means for moving the ink jet nozzles away from the charging electrodes and into a container of liquid.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a portion of an ink jet printing system shown in printing position and including the embodiment of the vapor chamber of the present invention.

FIG. 2 is an isometric view of the ink jet printing system of FIG. 1 shown in non-printing position with the vapor chamber in position to prevent nozzle clogging.

FIG. 3 is a schematic diagram of an ink jet printing system shown in printing position and including the embodiment of the movable liquid container of the present invention.

FIG. 4 is a schematic diagram of the ink jet printing system of FIG. 3 shown in non-printing position with the liquid container in position to prevent nozzle clogging.

FIG. 5 is a schematic diagram of an ink jet printing system shown in printing position and including the embodiment of the liquid container and the movable print head of the present invention.

FIG. 6 is a schematic diagram of the ink jet printing system of FIG. 5 shown in non-printing position with the print head in position to prevent nozzle clogging.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIG. 1 there is partially shown the previously described ink jet printing system which exemplifies one type of system for which the present invention is adapted for use. A support bracket 10 is provided which has a row of spring blade support tabs 11 and fastened to each tab is a support block 13 and a piezoelectric transducer 14. Running through each block and transducer assembly is an ink pipe 15 having a nozzle 16 and each ink pipe is connected by way of a tubing 17 to a suitable source of ink under pressure. The transducers 14, which may be excited by a suitable sinusoidal oscillator, are used to introduce varicosities in the jet streams by vibrating the nozzle 16 at the desired frequency to produce a succession of ink droplets 18 which are substantially uniform in dimension and frequency.

Each droplet stream 18 passes through a U-shaped charging electrode 19 with the row of electrodes being fastened to a U-shaped support member 20 via the contact pins 21. The electrodes 19 are used to variably charge the individual ink droplets in accordance with input data information. From the charging electrodes, each stream of droplets passes between a pair of deflection plates 22 with the row of deflection plates mounted on a support bracket 23. The deflection plates are oppositely charged to a constant voltage and they deflect the charged droplets onto the record medium to effect printing. Not all of the ink droplets will be charged and those that are not are deflected into a suitable gutter 24 to be returned back to the supply.

In accordance with the present invention, means are provided for preventing ink from drying at the nozzles during printer shutdown and to keep the charging electrodes and deflection plates free from ink spraying at pressure shut off. In the present embodiment, this is accomplished by slideably mounting the charging electrode support member 20 on a pair of end rods 25 mounted in a pair of end brackets 26. Attached to the bottom of the support member 20 by suitable screws (not shown) is a vapor chamber 27 with an opening 28 having a partially closed lip portion 29. The chamber is partially filled with a vapor-forming liquid 30 such as water with a chemical additive or ink which will produce a mist or vapor 31 in the remaining upper portion of the chamber. If desired, the chamber may be provided with a suitable drain hose at the bottom. Connected to the side of the chamber by way of a bracket 32 is the shaft of a solenoid 33 mounted in a support bracket 34. As the system is shown in FIG. 1, the solenoid has been activated to move the support member 20, the charging electrodes 19, and the vapor chamber 27 downward into a printing position. In this position, the row of charging electrodes is in alignment with the row of nozzles to receive the droplet streams and the mouth or opening 28 of the vacuum chamber is down and away from the nozzles.

Referring now to FIG. 2, when shutting down the printer system and before the ink pressure is turned off, solenoid 33 is released and a coil spring 35 mounted on each of the end slide rods 25 will move the support member 20, the charging electrodes, and the vacuum chamber upward to a non-print position. Instead of the springs, a double-acting solenoid could be used to move the assembly both up and down. In this non-print position, it can be seen that the charging electrodes 19 are moved up out of the path of the jet streams and the vapor chamber is moved up so that the opening 28 encloses the nozzles and intercepts the jet streams. The ink pressure can now be shut-off. The partially closed lip portion 29 protects the charging electrodes and the deflection plates from ink spraying due to residual ink in the nozzles. Also, the vapor pressure in the chamber, either with or without temperature control, will keep the nozzles enclosed in the chamber damp enough to prevent ink drying and clogging during the shutdown period. To further enhance the containment of the vapor and the protection of the plates and electrodes, a sharp edged wall or bar 36 may be fastened to support bracket 10 so that the lip portion 29 will abut against it in the non-print position. Before start-up ink may be forced through the nozzles and into the vapor chamber to expell any air that might be in the nozzles.

A second embodiment of the present invention is shown in FIGS. 3 and 4. Referring to FIG. 3, there is shown, schematically, a print head 37, a plurality of ink jet nozzles 38, a plurality of charging electrodes 39, a plurality of deflection plates 40, an ink gutter 41, and the record medium 42. The charging electrodes are mounted in a suitable movable member 43 and also mounted on the member is a partially open container 44 which is filled with a liquid 45, such as water or water with a detergent. The movable member 43 is connected to a suitable transducer or double acting solenoid 46. As shown in FIG. 3, the system is in a printing position. Referring now to FIG. 4, when shutting the system down, solenoid 46 is activated to move member 43 so that the charging electrodes are out of the path of the jet streams and the container 44 is positioned to intercept the nozzles with the nozzle tips submerged below the water line. Thus, with the nozzles submerged in water, nozzle clogging is prevented during shutdown of the system. Before start-up, ink could be forced through the nozzles into the water container to expel any water that had entered the nozzles.

A third embodiment of the present invention is shown schematically in FIGS. 5 and 6. Referring to FIG. 5, the system comprises a print head 47, a plurality of ink jet nozzles 48, a plurality of charging electrodes 49, a plurality of deflection plates 50, an ink gutter 51, and the record medium 52. The print head is fixed on a rotatable shaft 53 and fastened on the end of the shaft is a hand knob 54. Positioned below the nozzles is an open container 55 which is filled with a liquid 56, such as water or water with a detergent. As shown in FIG. 5, the nozzles have been rotated upward into a printing position. Referring to FIG. 6, when shutting down the nozzles are rotated downward so that the nozzle tips are submerged below the water line in the container to prevent clogging.

The above embodiments of the invention have been applied to one particular type of multiple nozzle printing system, however, they will work equally as well for other types of multiple nozzle systems and also for single nozzle "on demand" types of printing systems.

While the invention has been particulary shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

Claims

1. In an ink jet printing system having nozzles for discharging ink droplets, charging electrodes for charging said droplets, and deflection plates for deflecting the charged droplets onto a record medium, the improvement comprising:

means for subjecting said nozzles to a vapor atmosphere when said system is

2. An ink jet printing system comprising:

a row of ink jet nozzles for discharging ink droplets to carry out a printing operation;

a row of charging electrodes for charging said droplets;

a row of deflection plates for deflecting said charged droplets onto a record medium;

a movable support member on which said row of charging electrodes is mounted;

a vapor chamber mounted on said support member and having an opening;

means for creating a vapor in said chamber;

means for moving said support member into a printing position wherein said row of electrodes is positioned between said nozzles and deflection plates and in the droplet discharge path of said nozzles, and the opening in said vapor chamber is positioned away from said nozzles; and

means for moving said support member to a non-printing position wherein said row of electrodes is positioned out of the droplet discharge path and said row of nozzles is enclosed in the opening in said vapor chamber to prevent clogging of the nozzles by dried ink when the system is shut down.

3. An ink jet printing system as set forth in claim 2 wherein said vapor chamber opening has a partially closed lip portion to contain said vapor and to shield said electrodes and deflection plates from being sprayed by

4. An ink jet printing system as set forth in claim 3 and including a wall against which the partially closed lip portion of said container abuts

5. An ink jet printing system comprising:

a row of ink jet nozzles for discharging ink droplets to carry out a printing operation;

a row of charging electrodes for charging said droplets;

a row of deflection plates for deflecting said charged droplets onto a record medium;

a movable support member on which said row of charging electrodes is mounted;

an open container mounted on said support member;

a supply of liquid in said container;

means for moving said support member into a printing position wherein said row of electrodes is positioned between said nozzles and deflection plates and in the droplet discharge path of said nozzles and said container is positioned away from said nozzles; and

means for moving said support member to a non-printing position wherein said row of electrodes is positioned out of the droplet discharge path and said row of nozzles have their tips submerged in the liquid in said container to prevent clogging of the nozzles by dried ink when the system is shut down.