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 stationary reservoir (10) and to maintain the ink at one level during printing. A check valve (50) controls direction and flow of ink moving between the reservoirs and ink is allowed to rise in the first-mentioned reservoir (28) during non-printing. The advantage of this arrangement is that unwanted surges of ink are reduced in the reciprocating reservoir and a negative meniscus is maintained at the nozzles of the printer.

Description: 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 re- circulation. 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 O PI 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 which 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- o-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 relative levels of ink in the various parts or areas of the system have an effect on the printing operation, and further, -3- that the movement of the several printer elements 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 controlled 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 the first reservoir means and the second reservoir means, characterized by ink return means connecting the two reservoir means and having valve means associated therewith actuatable to permit ink to be pumped intermittently from said second reservoir means to said first reservoir means in re¬ sponse to reciprocating movement of said second reser¬ voir means so as to establish a predetermined 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 an ink level which is higher than said predetermined ink level in said second reservoir means during non-operation of the printer. Brief Description of the Drawing An embodiment of the invention will now be described, by way of example with reference to the accompanying drawing in which the single figure is a diagrammatic view, partly in section, of an ink jet printer according to the invention. - ■ $\JRE. Best Mode of Carrying Out the Invention As seen in the single figure of the drawing, an ink reservoir 10 contains a supply of printing ink 12 which is sufficient for printing in excess of several million characters. The reservoir 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 there- of to an inlet 24 of a cons ricting-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 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 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 normally-closed, pressure actuated check valve 50 which is suitable for allowing ink to flow from the reservoir 28 to the reservoir 10 during normal printing operation. The check valve 50 may be a common and well- known type which includes a ball operably associated with a valve seat for permitting intermittent flow of ink through the valve from the reservoir 28 to the reservoir 10 upon reciprocating movement of the reservoir 28 as described hereinafter. A flexible tube 56 is connected at one end 58 thereof to the outlet 60 of the check valve 50 and is connected at the other end 62 thereof to an inlet 64 of the reservoir 10. -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 reciprocating manner in a direction to and from the observer, as viewed in the drawing. Such reciprocating movement of the reservoir 28 results in increased ink pressure therein and thus inter¬ mittently operates said check valve 50 upon each accel¬ eration portion of such movement. A feed tube 68, of a length and extending from near the bottom of the reser- voir 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 manufac¬ tured 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 reservoir 28 is caused to be moved by the reciprocating motion of the carriage 66 in a printing condition where¬ in the motion of the carriage creates forces which tend to cause the ink to be moved back and forth, or in a somewhat defined supply-and-return cycle, between the reservoirs 10 and 28. During printing conditions, i.e., when the printer is ready for actual printing of char- acters or the like and when the reservoir 28 along with the print head 72 are rapidly moving or reciprocating in the back-and-forth direction, the level of ink 12 in the local reservoir 28 is maintained approximately at or slightly above the level indicated at 90, which corres- ponds generally with 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. 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 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 approxi¬ mately to or slightly below the height of the print head 72. This ensures that a negative meniscus is maintained at the nozzle 78 reducing the tendency of the meniscus to draw back from the nozzle when surface tension redu- cing contaminants coat the nozzle. In this respect, the ink levels 92 and 94 tend to be equalized and since the level of ink 12 in the reservoir 28 is above the outlet 44 thereof, the check valve 50 is responsive to the increasing level of ink in the reservoir 28 and allows flow of ink in the direction of the arrow, shown with the check valve 50, from reservoir 28 to reservoir 10. An alternate ink level 96 is shown as being slightly above the outlet 44 of the reservoir 28 wherein the ink level may attain an upper point of the operating range- When the ink level in local reservoir 28 is maintained between levels 90 and 96, no gas bubbles are present or created within the system. -7- It is seen that the system provides for simple self-pumping means with two distinct levels of ink in the ink reservoir 28 directly associated with the oper¬ ation of 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 operating 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, provides the driving force to pump the ink 12 from the local reservoir 28 to the main reservoir 10 and the check valve 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 control is considered to be automatically controlled during both idle or non-printing periods and operating or printing periods. The result of the ink supply system is that a circulating flow of ink is maintained or is taking place when the reservoir 28 moves back and forth in the print¬ ing operation. Since the local reservoir 28 moves in reciprocating manner relative to the main reservoir 10, acceleration of reservoir 28 away from reservoir 10 causes valve 50 to open and thereby permit flow of ink from reservoir 28 to reservoir 10, thus lowering the level of ink in reservoir 28. When the reservoir 28 accelerates back toward reservoir 10, the check valve 50 closes and there is no flow of ink from reservoir 28 to reservoir 10. Further, it is noted that when the ink in reservoir 28 is at the low level 90, the force of gravity causes a small flow of ink from reservoir 10 to reservoir 28, except during accelerating conditions. The net result is a substantially steady flow of ink 12 from reservoir 10 to reservoir 28 through the filter and constricting device 26, and a pulsating flow of ink 12 from reservoir 28 to reservoir 10 through the check • valve 50. -A-VO It is seen that the constriction device 26 in the supply line to reservoir 28, the check valve 50 in the return line to 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 the reciprocating motion of the carriage 66. If such surges were allowed to occur, the pressure in the moving reservoir 28 would suddenly change and cause ink to be unintentionally 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 check valve 50 could be spring or gravity-loaded to control the differences in pressures between the two reservoirs 10 and 28 and thereby change the location of the flexible tubes 40 and 56 so that both tubes can be connected to inlets.and outlets located at the bottom of the reservoirs. In the case of a spring or weight-loaded check valve 50, the force tending to open the valve is the force on the ink 12 caused by the motion of the carriage 66, reduced by the spring force or weight of the ball and also the force caused by the difference in level between the two reservoirs 10 and 28. When the differ¬ ence in the ink levels is sufficiently large, such ink level difference and the spring force or weight of the ball together balance the force due to carriage motion and under these conditions, the valve will not open to permit flow of ink therethrough. Thus, the level of ink 12 in the moving reservoir 28 will descend to a prede- termined point and settle or stop thereat. In similar manner, as mentioned above, when the carriage and the reservoir are not moving, the ink level in reservoir 28 will slowly rise by flow of ink through the supply tubes 16 and 30 until the two reservoirs have approximately equal ink levels, or otherwise stated, the ink in the two reservoirs is at approximately the same height by reason of gravity. It should be noted that the distance between ink level 90 and ink level 94 in the reservoir 28 is in the range of 5-6 centimeters. ■ gJRE OMP -9- It is seen that the check valve 50 allows flow of the ink 12 from the local reservoir 28 to the main reservoir 10 only when the ink level in the reservoir 28 is at or slightly above the level of outlet 44. The reciprocating motion of the reservoir 28 creates the pumping forces which cause a negative pressure within the reservoir 28 and which cause the ink 12 to move back and forth between the two reservoirs, however the check valve 50 allows ink flow only in the indicated direction. G*.-. ' t-I • .- VΪΪ-

Claims: 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) dμring printing operation, and ink supply means (16, 30) connecting the first reservoir means (10) and the second reservoir means (28), charac- terized by ink return means (40, 56) connecting the two reservoir means and having valve means (50) associated therewith actuatable to permit ink to be pumped inter¬ mittently from said second reservoir means (28) to said first reservoir means (10) in response to reciprocating movement of said second reservoir means (28) so as to establish 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 an ink level (94) which is higher than said predetermined ink level (90) in said second reservoir means (28) during non-operation of the printer. 2. An ink jet printer according to claim 1, characterized in that said valve means includes a nor¬ mally-closed check valve (50) actuated by pressure of ink thereagainst to allow ink to flow through said return means ( 0, 56). 3. 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). 4. An ink jet printer according to claim 1, characterized in that said ink supply means (16, 30) and said ink return means (40, 56) are flexible tubes allow¬ ing movement of said second reservoir means (28) in relation to said first reservoir means (10). 5. An ink jet printer according to claim 4, characterized in that said first reservoir means (10) is a stationary reservoir. 6. An ink jet printer according to claim 1, characterized in that said second reservoir means (28) carries said printing means (72). 7. An ink jet printer according to claim 6, characterized in that said printing means (72) includes one or more tubular piezoelectric transducers. -flJRE OMPI \ ?

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