INK JET PRINTER

Abstract: An ink jet printer in which the level of ink in a reciprocating reservoir (28) is automatically controlled for both printing and non-printing conditions. The reciprocating motion creates forces to cause the ink to move back and forth between the reciprocating reservoir (28) and a main reservoir (10) and a pump (50) maintains the ink at one level during printing. The pump (50) controls the direction and flow of the ink moving between the reservoirs by continuous operation during printing and the ink is allowed to rise in the first-mentioned reservoir (28) during non-printing. In a second embodiment, the main reservoir (10) is raised or lowered respectively by a hydraulic or solenoid operated device (106) to establish the two ink levels in the reciprocating reservoir (28). The advantage of these arrangements is that a negative meniscus is maintained at the nozzles (78) of the printer.

Description: -1 - INK JET PRINTER Technical Field The present invention relates to ink jet printers, and, more particularly, to ink jet printers which utilize the so-called drop-on-demand method of operation. Background Art Non-impact printers have recently become very popular due to their quiet operation resulting from the absence of mechanical printing elements impacting on record media during printing. Among such printers, ink jet printers are particularly important as they permit high speed recording on plain untreated paper. Various ink jet printing methods have been developed over the past years. In the so-called con¬ tinuous ink jet method, such as disclosed in U.S. Patent No. 3,596,275, the ink is delivered under pressure to nozzles in a print head to produce a continuous jet of ink emitted through each nozzle. The ink jet is separ- ated by vibration into a stream of droplets which are charged, and the flying droplets are either allowed to impact on a record medium or are electrostatically de¬ flected for collection in a gutter for subsequent recir- culation. A second method, known as the electrostatic method, is disclosed, for example, in U.S. Patent No. 3,060,429. In this method the ink in the nozzles is under zero pressure or low positive pressure, and the droplets are generated by electrostatic pull and caused to fly between two pairs of deflecting electrodes ar¬ ranged to control the direction of flight of the droplets and their deposition in desired positions on the record medium. A third method, which is known as the drop-on- demand method, is described, for example, in U.S. Patent No. 4,125,845. The droplets in this method are emitted - - under the control of an electronic character generator by means of volume displacement brought about in an ink chamber or channel by means of energization of a piezo¬ electric element. The volume displacement generates a pressure wave hich propagates to the nozzles causing the ejection of ink droplets. The drop-on-demand method has several advan¬ tages over the other above-mentioned methods. Ink jet printers using this method have a simpler structure requiring neither deflecting means for controlling the flight of the droplets nor the provision of an ink re¬ covery system. Multiple nozzle print heads using this method are simple and compact and are relatively easy to manufacture. A multiple nozzle print head of this type is disclosed in U.S. Patent No. 4,126,868 in which ink is supplied from a stationary ink reservoir to a common reservoir or manifold incorporated in the print head and supplying ink to the individual nozzles. A problem arising with ink jet print heads which incorporate a common ink reservoir or manifold supplied with ink from a remote ink reservoir is that such print heads are sensitive to acceleration or de¬ celeration of the head resulting from the reciprocating side-to-side motion thereof during printing operation. Surges in the ink caused by the reciprocating motion bring about pressure changes in the manifold which may . cause ink to be unintentionally ejected through the nozzles or may cause air to be ingested therein. Even a small air bubble can interrupt or fault the performance of transducers or like devices that expel ink droplets from a nozzle by means of pressure pulses created within an ink-filled chamber or channel. In normal operation of an ink jet print head, it is well-known that a negative (convex) meniscus of ink should be maintained at the nozzle, that the rela¬ tive levels of ink in the various parts or areas of the system have an effect on the printing operation, and further, that the movement of the several printer ele¬ ments affects the flow of ink during the printing cycle^. Disclosure of the Invention It is an object of the present invention to provide an ink jet printer in which unwanted surges of the ink in the common manifold are reduced and in which the ink level in the manifold is automatically con¬ trolled during both the printing and non-printing periods . Thus, according to the invention, there is provided an ink jet printer including first reservoir means for containing a supply of ink, second reservoir means for containing a supply of ink, printing means for ejecting ink in droplet form and movable with said second reservoir means in a reciprocating manner relative to said first reservoir means during printing operation, and ink supply means connecting said first reservoir means with said second reservoir means, characterized by actuating means for causing the ink to assume a pre¬ determined ink level in said second reservoir means during operation of the printer, said ink supply means allowing flow of ink from said first reservoir means to said second reservoir means to establish therein an ink level during non-operation of the printer, which ink level is higher than said predetermined ink level . Brief Description of the Drawings Embodiments of the invention will now be des¬ cribed, by way of example, with reference to the accom¬ panying drawings, in which: Fig. 1 is a diagrammatic view, partly in sec¬ tion, of an ink jet printer according to the present invention; and Fig. 2 is a modification of the printer of Fig. 1. Best Mode of Carrying Out the Invention As seen in Fig. 1 of the drawing, an ink reservoir 10 contains a supply of printing ink 12 which f * Oy PI _ _ is sufficient for printing in excess of several million characters. The reservoir 10 has a filter-type vent 14 suitably disposed in the top thereof for access to the atmosphere. A length of flexible tubing 16 is connected at one end 18 thereof to the outlet 20 of the reservoir 10 and is connected at the other end 22 thereof to an inlet 24 of a constricting-type device 26 which is formed of suitable material to dampen or impede the flow of ink from the main or remote reservoir 10 to a second or 0 local reservoir 28. The reservoir 28 also has a filter- type vent 29 disposed in the top thereof. A second flexible tube 30 is connected at one end 32 thereof to an outlet 34 of the device 26 and is connected at the other end 36 to an inlet 38 of the reservoir 28. The 5 tubes 16 and 30 provide an ink supply passageway for flow of ink from the main reservoir 10 to the device 26 and from such device to the local reservoir 28. A return path for the flow of ink is provided from the reservoir 28 to the reservoir 10. A flexible tube 40 is connected at one end 42 thereof to an outlet 44 (above the inlet 38) of the reservoir 28 and is connected at the other end 46 thereof to the inlet 48 of a pump 50 which is suitable for causing ink to flow from the reservoir 28 to the reservoir 10 in continuous manner under printing operation or conditions. The pump 50 may be a common and well-known, electrically ener¬ gized, type for causing a negative pressure in the reser¬ voir 28 and producing a continuous flow between the two reservoirs 10 and 28 in the arrangement for establishing the proper ink level at the proper time for printing operations. Actuation of the pump 50 during printing operations establishes a level for the ink in reservoir 28, which is a condition required for proper operation of the ink jet printer. A flexible tube 56 is connected at one end 58 thereof to the outlet 60 of the pump 50 and is connected at the other end 62 thereof to an inlet 64 of the main reservoir 10. r CC-fPI V.T -5- The secondary or local reservoir 28 is secured to or supported from a movable carriage 66 which causes the reservoir to be moved in a reciprocating manner in a direction to and from the observer, as viewed in the drawing. A feed tube 68, of a length and extending from near the bottom of the reservoir 28 to a height which is above the normal level of ink in the main reservoir 10, includes an upper outlet portion 69 which extends through a wall portion or grommet 70 of the reservoir 28 to an ink jet print head 72. The several tubes utilized in the system may be made of Tygon (a polyvinyl chloride material manufactured by The Norton Chemical Company) . The print head 72 includes a body portion 74 of cylindrical form having a glass tube or glass-lined passageway 76 through the body portion for receiving and connecting to the feed tube portion 69 and terminating in a nozzle 78 for ejecting a droplet 80 of printing ink to be applied to record media 82, which media may be in the form of paper or the like and supported in suitable manner around a drum or from a platen (not shown). The print head 72 includes a piezoelectric device or tubular type transducer 84 for causing ejec¬ tion of the ink droplets 80, either in synchronous or asynchronous manner, from the print head nozzle 78. The ink droplets 80, so produced from the nozzle 78, are essentially the same or constant in size and are nor¬ mally ejected at a constant velocity. Leads 86 and 88 are appropriately connected to the print head 72 for actuating the transducer 84 so as to cause ejection of the ink droplets 80 in well-known manner. In the operation of the printing system, the pump 50 is turned on along with the printer and the reservoir 28 is caused to be moved by the reciprocating motion of the carriage 66 in a printing condition wherein the motion of the carriage creates forces which tend to cause the ink to be moved back and forth, or in a some¬ what defined supply-and-return cycle between the OMT' reservoirs 10 and 28. Prior to printing operation, i.e. when the reservoir 28 along with the print head 72 are rapidly moving or reciprocating in the back-and-forth direction, the pump 50 is called into operation and causes the level of ink 12 in the local reservoir 28 to be lowered and then maintained approximately at or slightly above the level indicated at 90, which is slightly above the height of the outlet 44 and the end 42 of the tube 40, and which level is substantially below the level 92 of the ink 12 in the main reservoir 10. The pump 50 thus provides a continuous circulating flow of ink 12 between the two reservoirs 10 and 28 during printing operations and in a manner wherein the flow of ink is dampened or reduced and the ink is also continuously filtered by the device 26. An added f ature may include an ink level sensor or automatic level sen¬ sing device (not shown) which may be connected inside the local reservoir 28 and used to control the pump 50 in an arrangement to allow the proper level of ink during printing operation or conditions, but would turn the pump off at a low ink level condition. When the printing operation ceases or when the reservoir 28 along with the print head 72 are not moving or reciprocating, as in the non-printing or rest condi- tion, the ink 12 in the local reservoir 28, by reason of gravity, slowly rises above the height of the outlet 44 and may rise to a level indicated at 94, corresponding generally with the level 92 of ink 12 in the main reservoir 10 and approximately to or slightly below the height of the print head 72. This ensures that a nega¬ tive meniscus is maintained at the nozzle 78 reducing the tendency of the meniscus to draw back from the nozzle when surface tension reducing contaminants coat the nozzle. In this respect, the ink levels 92 and 94 tend to be equalized through the ink supply tubes 16 and 30 and since the level of ink 12 in the reservoir 28 is above the outlet 44 thereof, the pump 50 is ineffective in a WA ,. Vl non-running condition and due to the increasing level of ink in the reservoir 28, the gravitational flow of ink 12 is in the direction from the main reservoir 10 to the local reservoir 28 for substantially filling the latter. It is seen that the system provides for simple pumping means with two distinct levels of ink in the ink reservoir 28 directly associated with the operation of and directly supplying the ink jet print head 72- The idle or non-printing level at 94 in the local reservoir 28 is approximately at print head height and the oper¬ ating or printing level at 90 is about 5 centimetres lower or at approximately the height of the outlet 44 and of the return tube 40. The motion of the carriage 66, on which the print head 72 and the reservoir 28 are mounted, along with the continuous operation of the pump 50 provide the driving force to pump the ink 12 from the local reservoir 28 to the main reservoir 10 and addi¬ tionally, the pump 50 ensures that the ink 12 moves only in the proper direction during certain conditions, all in a manner and arrangement wherein the ink level con¬ trol is considered to be automatically controlled during both idle or non-printing periods and operating or printing periods. It is seen that the constriction device 26 in the supply line to the local reservoir 28, the pump 50 in the return line to the main reservoir 10, and the location of the inlet 44 for the return tube 40 all provide for and prevent unwanted surges in the ink 12 which are caused by motion of the carriage 66. If such surges were allowed to occur, the pressure in the reser¬ voir 28 would suddenly change and cause ink to be unin¬ tentionally ejected from the nozzle 78 or to cause air to be .ingested therein. In an alternative system or modification of the above-described arrangement, the pump has been omitted (as seen in Fig. 2) along with the return line which included the flexible conduits or tubes 40 and 56 connected to the local reservoir 28 and to the main reservoir 10 for carrying ink 12 therebetween, as seen in Fig. 1. Since the same reference numerals are used for the identical elements in Fig. 2 as were used in Fig. 1, the complete detailed description is not re¬ peated. In the alternate system of Fig. 2, means is provided for raising and lowering the main reservoir 10 in relation to the local reservoir 28 and thereby estab¬ lish the two levels of ink in the local reservoir. The particular means employed for raising and lowering the reservoir 10 may be a simple hydraulic lift mechanism or a solenoid operated device, such as dia¬ grammatically illustrated at 106, which mechanism or device is capable of operating in a raising and lowering range of several centimeters. The reservoir 10 is raised or elevated to the position shown in " Fig. 2, and under idle or non-printing conditions, the level of the ink 12 is approximately at ink jet nozzle 72 height. Under operating or printing conditions, the main reser- voir 10 is lowered by operation of the mechanism or device 106 so that the level 92 of ink 12 therein cor¬ responds generally to the ink level 90 in the local reservoir 28. Thus, the level of ink in the moving reservoir 28 will descend to a predetermined point and settle or stop at that point. In similar manner as mentioned above, when the carriage 66 and the reservoir 28 are not moving, the ink level will slowly rise by flowing through the supply tubes 16 and 30 until the two reservoirs 10 and 28 have approximately equal ink levels, or rather, the ink 12 in the two reservoirs 10 and 28 is at approximately the same height.

Claims: -9- CLAIMS : 1. An ink jet printer including first reser¬ voir means (10) for containing a supply of ink (12), second reservoir means (28) for containing a supply of ink, printing means (72) for ejecting ink in droplet form and movable with said second reservoir means (28) in a reciprocating manner relative to said first reser¬ voir means (10) during printing operation, and ink supply means (16, 30) connecting said first reservoir means (10) with said second reservoir means (28),. character- ized by actuating means (50, 106) for causing the ink to assume a predetermined ink level (90) in said second reservoir means (28) during operation of the printer, said ink supply means (16, 30) allowing flow of ink from said first reservoir means (10) to said second reservoir means (28) to establish therein an ink level (94) during non-operation of the printer, which ink level (94) is higher than said predetermined ink level (90). 2. An ink jet printer according to claim 1, characterized in that said actuating means is in the form of pumping means (50) arranged to pump ink from said second reservoir means (28) to said first reservoir means (10) so as to establish said predetermined ink level (90) in said second reservoir means (28). 3. An ink jet printer according to claim 2, characterized by ink return means (40, 56) connecting said second reservoir means (28) and said first reservoir means (10), said pumping means being in the form of a circulating pump (50) associated with said ink return means (40, 56) and operating during printer operation to establish said predetermined ink level (90) and being non-operative during non-operation of the printer to allow establishment of said higher ink level (94) via said ink supply means (16,30). -10- 4. An ink jet printer according to claim 3, characterized in that said first reservoir means (10) is stationary and in that said ink supply means (16, 30) and said ink return means (40, 56) are flexible tubes allowing movement of said second reservoir means (28) in relation to said first reservoir means. 5. An ink jet printer according to claim 3, characterized by an ink level sensor disposed within said second reservoir means (28) and arranged to control operation of said circulating pump (50) in accordance with the level of ink in said second reservoir means (28). 6. An ink jet printer according to claim 1, characterized in that said actuating means includes moving means (106) for moving said first reservoir means (10) downwardly relative to said second reservoir means (28) for establishing said predetermined ink level (90) in said second reservoir means, and for moving said first reservoir means (10) upwardly relative to said second reservoir means (28) for establishing said higher ink level (94) in said second reservoir means (28) . 7. An ink jet printer according to claim 6, characterized in that said moving means (106) is a hy¬ draulic or a solenoid operated device. 8. An ink jet printer according to claim 1, characterized by constricting means (26) associated with said ink supply means (16, 30) for dampening the flow of and for filtering ink passing from said first reservoir means (10) to said second reservoir means (28) . 9. An ink jet printer according to claim 1, characterized in that said second reservoir means (28) carries said printing means (72). OM 10. An ink jet printer according to claim 9, characterized in that said printing means (72) includes one or more tubular piezoelectric transducers.

Inventors: BANGS RICHARD GORDON, THOMAS JACOB EARL, BANGS, RICHARD, GORDON, THOMAS, JACOB, EARL
Applicants: NCR CO, NCR CORPORATION
Application year: 1983
Main classification: B41J3
IPC codes: B41J2