INK JET PRINTER

Abstract: An ink jet printer in which a movable ink reservoir (24) carries a plurality of ink jet print heads (40) and supplies ink to the heads (40) by means of separate conduits (30, 70, 72, 74). The reservoir (24) includes baffle means (76, 78, 80) therein formed to provide individual ink tanks for the print heads and to prevent or substantially reduce the extent of agitated motion of the ink within the reservoir (24), as the latter is accelerated and decelerated in printing operations.

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 deflected 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 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 re- quiring neither deflecting means for controlling the flight of the droplets nor the provision of an ink recovery system. Multiple print head printers using this method are simple and compact and are relatively easy to manufacture. A problem arising with ink jet printers in which several print heads are mounted on a common ink reservoir and are arranged to move therewith in a side- to-side manner during the printing operation, is that excessive changes in pressure may result from the agitated "sloshing" motion of the ink within the reser¬ voir due to the rapid acceleration and deceleration of the latter. Such acceleration and deceleration results from the changing horizontal movement associated with the print carriage during printing, but may also arise from accidental shaking, jarring or moving of the entire printer. Pressure changes may lead to uneven ink supply to the individual print heads, to failure of maintaining the ink at predetermined levels during printing, and may generally interfere with the faultless operation of the printer. Disclosure of Invention It is an object of the invention to provide an ink jet printer in which the above disadvantages are alleviated and in which means are provided for control- ling movement of the ink in a reciprocating reservoir carrying a plurality of ink jet print heads. Thus, according to the invention, there is provided an ink jet printer including reservoir means for containing a supply of ink, a plurality of ink jet print heads movable with said reservoir means in a side- to-side manner during printing operation, and a plurality of conduit means for carrying ink in individual manner from the supply of ink to each of the print heads, characterized by baffle means within said reservoir means forming individual compartments of ink for the respective conduit means and reducing the extent of agitated motion of the ink within the reservoir means during printing operation.. Brief Description of the Drawing One embodiment of the invention will now be described, by way of example, with reference to the accompanying drawing, in which: Fig. 1 is a diagrammatic view, partly in section, of an ink jet printer according to the present invention and taken along the line 1-1 of Fig. 2, and Fig. 2 is a sectional view taken along the line 2-2 of Fig. 1. Best Mode for Carrying Out the Invention Referring now to the drawing, Fig. 1 shows a portion of a main or primary reservoir 10 which contains a supply of printing ink 12 sufficient for printing in excess of several million characters. A length of flexible tubing 14 is connected at one end 16 to an outlet 18 of the reservoir 10 and the tubing is connected at the other end 20 to an inlet 22 of a secondary reser- voir 24. The tubing 14, shown broken in form, may include a constriction device for limiting the volume of ink flowing between the reservoirs 10 and 24 and thereby prevent pressure surges in the ink within the reservoir 24 upon rapid movement thereof during printing operat * ions. The reservoir 24 has a filter-type vent 26 suitably dis¬ posed in the top for access to the atmosphere in the manner of allowing equalizing of pressure between the reservoir and the atmosphere over an extended period of time, to prevent entry of dust or foreign particles into the reservoir, and to reduce evaporation of any water or like constituent of the ink from the reservoir. A suitable reservoir carrier 27 is provided to move the reservoir 24 in rapid back and forth reciprocating manner, in the direction as viewed by the observer, during printing operation. The local or movable reservoir 24 also in¬ cludes an opening 28 in one side wall thereof for re¬ ceiving a molded elastomer member 30 which is formed to include an enlarged portion 32 on the outer side of the reservoir wall and a similar enlarged portion 34 on the inner side of the reservoir wall and wherein such en¬ larged portions provide a fluid-tight connection with the wall of the reservoir. The elastomer member 30 is in the form of a conduit or tube which terminates with one end 36 outside the reservoir 24 and which end is connected with an ink jet print head 40. The reservoir 24 carries two or more of the print heads 40 and the close proximity of such heads minimizes the tendency to eject ink unintentionally or to ingest air into the heads when such print heads are caused to be moved in rapid acceleration and deceleration manner by the car¬ rier 27 during printing operation. The print head 40 includes a body portion 42 of cylindrical form having a glass tube or glass-lined passageway 44 through the body portion and terminating in a nozzle 46 for ejecting a droplet 48 of printing ink to be applied to record media 50, 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 40 includes a piezoelectric device or tubular type transducer 52 for causing ejec¬ tion of the ink droplets 48, either in synchronous or asynchronous manner, from the print head nozzle 46. * The ink droplets 48, so produced from the nozzle 46, are essentially the same or constant in size and are nor¬ mally ejected at a constant velocity. Leads 56 and 58 are appropriately connected to the print head 40 for actuating the transducer 52 to cause ejection of the ink droplets 48 in well-known manner. The elastomer member 30, in the form of an L- shaped ink supply tube, is formed with an inside opening 60 which is substantially constant throughout the length of the tube and running from the outer end 36 connected to the print head 40 and extending to a downturned opposite end 62 which is immersed in the printing ink 12 within the reservoir 24. Starting at a point upstream from the enlarged portion 34 of the member 30, the wall thickness thereof gradually decreases and results in a decreasing outside diameter portion 64 down to the end 62. The decreasing wall thickness provides a flexible and pliant portion of the tube generally beyond the bend 66 thereof, which portion 64 allows the pressure waves returning from the nozzle 46, after actuation of the print head 40 in ejecting an ink droplet 48, to expend energy in stretching or flexing the tube radially out¬ wardly along the wall portion 64 above the reduced diameter inlet end 62. " Since there is at least minimal or no great change in the dimensions of the tube 30 over a distance along the length thereof comparable to the wave lengths of sound associated with pressure waves, such pressure waves are absorbed by the flexible and pliant portion 64 of the tube, rather than being re- fleeted back in the direction toward the nozzle 46. The elastomer member or tube 30 utilized in the reser¬ voir 24 may be made of Tygon (a polyvinyl chloride material manufactured by The Norton Chemical Company) . Since the tube 30 is almost totally within the reservoir 24 and in the vaporous ink atmosphere thereof, the ink carried by the tube maintains its composition or con * - stituency for maximum effective printing. Further, it r QM is seen that the tapered wall portion 64 enables the use of a shorter tube for carrying the ink and at the same time absorb the return pressure waves in the ink from the nozzle 46. Fig. 2 is a rear view taken generally along the line 2-2 of Fig. 1 and shows the elastomer member or ink supply tube 30 along with several additional elasto¬ mer members or supply tubes 70, 72 and 74 substantially identical with tube 30 except for the length thereof. As illustrated, while the reduced diameter inlet end of each of such tubes is located at a like distance from the bottom of the reservoir 24, the enlarged upper portion of each of such tubes extends through the side wall of such reservoir 24 at an elevation slightly dif- ferent from the remaining such tubes. It is thus appar¬ ent that the several print heads (not shown) associated with the tubes 70, 72 and 74 are at slightly different heights with respect to print head 40. In this manner, the ink droplets 48 ejected from the respective print heads 40 are at different vertical positions for print¬ ing a line of characters as the print heads are moved in the lateral direction by the well-known carrier means 27 (Fig. 1) along a line of printing. When the reservoir 24 along with the several print heads (one of which is designated 40 in Fig. 1) are moved from side to side (Fig. 2) in the printing operation, the ink 12 within such reservoir is subjected to forces of rapid acceleration and deceleration and the ink is caused to undergo an agitated "sloshing" motion in a back-and-forth manner. Means for reducing the sloshing or agitated motion of the ink 12 is accomplished by use of baffles positioned between the ink supply tubes 30, 70, 72 and 74 for the respective print heads 40. The preferred baffles 76, 78 and 80 are in the form of plates extending from the front wall to the rear wall of the reservoir 24 and are formed as an integral part of such reservoir 24 at the floor thereof, as best shown in Fig. 2. Such baffles 76, 78 and 80 are thus formed within the reservoir 24 to provide a separate ink tank or chamber for each of the ink supply tubes 30, 70, 72 and 74 for the print heads 40. A plurality of aper- tures 82, 84 and 86 are provided in the baffle plates 76, 78 and 80, respectively, near the bottom thereof and located near the rear wall of the reservoir 24 for equalizing the levels of ink 12 in the respective baf¬ fle-formed chambers or tanks. While apertures 82, 84 and 86 are shown in the plates 76, 78 and 80, any suit¬ able opening at or near the bottom of the plates could serve the purpose of allowing the ink to flow between the chambers. The operating ink level for the print heads 40, indicated as 88 in the reservoir 24, is maintained within an allowable range, as indicated by the arrow 90 at the right side of Fig. 1. The difference in the ink level 88 indicated in reservoir 24 and the level of ink 12 in reservoir 10 may be attained by means of a suit- able valve or pump located in the flexible line 14 between the reservoirs. It has been found in actual operation that without some type of baffle or damping means or the like in the reservoir 24, the rapid accel¬ eration of reservoir 24 during printer operation would cause the ink 12 to actually leave a void at the lower end of the tube 74, while climbing the wall adjacent the tube 30 almost to the height of the print head 40 there¬ of. On the other hand, through use of the baffles within the reservoir 24, the locations of the ink sur- faces in the respective ink chambers or tanks formed by such plates 76, 78 and 80 have been found to be as indicated by the dotted lines 92, 94, 96 and 98 during such conditions of rapid acceleration of the reservoir 24, for example, to the right in Fig. 2. Such ink locations, it is seen, maintain an ink 12 level above the inlet ends of the supply tubes 30, 70, 72 and 74 throughout the overall operation of the printer. f OM An additional baffle, perpendicular to the baffles 76, 78 and 80, may also be located within the reservoir 24 at the position indicated by the line 100 in Fig. 1. Such baffle further restricts ink level change at the inlets to the tubes 30, 70, 72 and 74 during any excessive movement of the reservoir 24 in a direction parallel with the print head nozzles 46 as may be caused by accidental jarring or movement of the print¬ er.

Claims: n -9- CLAIMS : 1. An ink jet printer, including reservoir means (24) for containing a supply of ink (12), a plurality of ink jet print heads (40) movable with said reservoir means (24) in a side-to-side manner during 5 printing operation, and a plurality of conduit means (30, 70, 72, 74) for carrying ink in individual manner from the supply of ink (12) to each of the print heads (40), characterized by baffle means (76, 78, 80) within said reservoir means (24) forming individual compartments 10* of ink for the respective conduit means (30, 70, 72, 74) and reducing the extent of agitated motion of the ink within the reservoir means (24) during printing opera¬ tion. 2. An ink jet printer according to claim 1, characterized in that said baffle means includes one or more plate members (76, 78, 80) each disposed between the respective print head conduit means (30, 70, 72, 74). 3. An ink jet printer according to claim 2, characterized in that said reservoir means (24) is rec¬ tangular and in that said one or more plate members (76, 78, 80) are arranged to join opposed walls of said 5 reservoir means (24). 4. An ink jet printer according to claim 3, characterized in that said one or more plate members (76, 78, 80) are arranged to extend upwardly from the floor of said reservoir means (24) to form separate ink 5 supply tanks for the print heads (40), and in that each plate member (76, 78, 80) includes an aperture (82, 84, 86) positioned near the said floor to allow passage of ink therethrough for equalizing ink levels (88) within the tanks. 5. An ink jet printer according to claim 4, characterized by a further plate member (100) extending perpendicularly to said plate members (76, 78, 80) between opposed walls of said reservoir means (24) . 6. An ink jet printer according to any one of claims 3 to 5, characterized in that said plate members (76, 78, 80, 100) are integral with the floor and re- spective walls of said reservoir means (24) . 7. An ink jet printer according to claim 1, characterized in that each conduit means (e.g. 30) includes a tapered wall portion (60) extending into the supply of ink (12) at the inlet end thereof. 8. An ink jet printer according to claim 1, characterized in that said ink jet print heads (40) are piezoelectric transducers energizable to eject ink in droplet form.

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