INK JET PRINTER

Abstract: An ink jet printer in which a short tapered elastomer tube (18) carries ink from a reservoir (10) to an ink jet print head (26). The tube (18) has a substantially constant inside diameter throughout the length thereof and a decreasing outside diameter along a portion (48) of the length to provide a thin wall section at an ink inlet end (46) thereof. Due to the flexible nature of the thin wall section, return pressure waves generated from the nozzle of the print head and tending to cause faulty operation of the printer, are absorbed by this wall section.

Description: INK JET PRINTER • 1 Technical Field The present invention relates to ink jet printers, and, more particularly, to ink jet printers 5 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 10 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 15 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 20 separated 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. 25 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 30 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- 35 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 jection 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 observed in the operation of an ink jet printer of the drop-on-demand type is that each time a drop of ink is ejected from the nozzle, a pressure wave originates thereat and travels back toward the reservoir of ink. Such pressure wave then may return toward the nozzle in a reflected manner of action and movement and cause faulty performance in the printing operation. United States Patent No. 3,832,579 discloses ink jet printers in which the above problem is alleviated. The described ink jet printers are provided with energy absorbing means coupled to the liquid for absorbing pres¬ sure waves therein. Such means include conduit walls of visco-elastic material which deform and absorb energy, and also several forms of acoustic resistance elements inserted within the conduit at the inlet end. However, the provision of such means tends to increase the com¬ plexity and the cost of manufacture of the printer. Disclosure of Invention It is an object of the present invention to provide an ink jet printer having means for absorbing back pressure waves of ink from the ink jet nozzle, which means do not rely on the use of special materials OW for the conduit wall nor on the insertion of separate acoustic resistance elements therein. Thus, according to the present invention, there is provided an ink jet printer including reservoir means for containing a supply of ink therein, printing means operably associated with said reservoir means for ejec¬ ting ink in droplet form, and conduit means connected with said printing means and extending therefrom to the supply of ink, characterized in that said conduit means has an elongated wall portion terminating in an ink inlet end immersed in operation in said supply of ink and whose thickness decreases in a direction away from said printing means for providing a pliant portion to absorb return pressure waves in the ink resulting from the operation of said printing means. Brief Description of the Drawing An embodiment of the invention will now be described, by way of example, with reference to the single figure of the accompanying drawing which is a diagrammatic view, in cross-section, of an ink jet printer according to the present invention. Best Mode for Carrying Out the Invention As seen in the single figure of the drawing, an ink reservoir 10 contains a supply of ink 12 which is sufficient for printing in excess of several million characters. The ink reservoir 10 has a filter-type vent 14 suitably disposed in the top thereof for access to the atmosphere. The reservoir 10 also includes an opening 16 in one side wall thereof for receiving a molded elastomer member 18 which is formed to include an enlarged portion 20 on the outer side of the reservoir wall and a similar enlarged portion 22 on the inner side of the reservoir wall and wherein such enlarged portions provide a fluid-tight connection with the wall of th «e reservoir. The elastomer member 18 is in the form of a conduit or tube which terminates with one end 24 outside the reservoir 10 and which is connected with an ink jet print head 26. The print head 26 includes a body portion 28 of cylindrical form having a glass tube or glass-lined passageway 30 through the body portion and terminating in a nozzle 32 for ejecting a droplet 34 of printing ink to be applied to record media 36, 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 26 includes a piezoelectric device or tubular type transducer 38 for causing ejec¬ tion of the ink droplets 34, either in synchronous or asynchronous manner, from the print head nozzle 32. The ink droplets, so produced from the nozzle 32, are essen¬ tially the same or constant in size and are normally ejected at a constant velocity. Leads 40 and 42 are appropriately connected to the print head 26 for actu¬ ating the transducer 38 to cause ejection of the ink droplets 34 in well-known manner. The elastomer member 18, in the form of an L- shaped ink supply tube, is formed with an inside opening 44 which is substantially constant throughout the length of the tube and running from the outer end 24 connected to the print head 26 and extending to a downturned opposite end 46 which is immersed in the printing ink 12 within the reservoir 10. Starting at a point upstream from the enlarged portion 22 of the member 18, the wall thickness thereof gradually decreases and results in a decreasing outside diameter portion 48 down to the end 46. The decreasing wall thickness provides the flexible and pliant elongated portion 48 of the tube generally beyond the bend 50 thereof, and the smooth variation of the wall thickness of this portion 48 allows the pres- sure waves returning from the nozzle 32, after actuation of the print head in ejecting an ink droplet 34, to expend energy in stretching or flexing the tube radially outwardly along the wall portion 48 above the reduced diameter inlet end 46. Since there is at least minimal or no great change in the dimensions of the tube 18 over a distance along the length thereof comparable to the 5 wave lengths of sound associated with pressure waves, such pressure waves are absorbed by the flexible and pliant portion 48 of the tube, rather than being reflec¬ ted back in the direction toward the nozzle. The elas¬ tomer member or tube 18 utilized in the reservoir 10 may 10 be made of Tygon (a polyvinyl chloride material manu¬ factured by The Norton Chemical Company) . •T OMP '

Claims: CLAIMS Ϊ 1. An ink jet printer including reservoir means (10) for containing a supply of ink (12) therein, printing means (26) operably associated with said reservoir means (10) for ejecting ink in droplet form, and conduit means (18) connected with said printing means (26) and extending therefrom to the supply of ink (12), characterized in that said conduit means (18) has an elongated wall portion (48) terminating in an ink inlet and immersed in operation in said supply of ink and whose thickness decreases in a direction away from said printing means (26) for providing a pliant portion to absorb return pressure waves in the ink resulting from the operation of said printing means (26). 2. An ink jet printer according to claim 1, characterized in that said conduit means (18) is a tubular member having a substantially constant inside diameter extending throughout the length thereof. 3. An ink jet printer according to claim 2, characterized in that the outside diameter of said por¬ tion (48) of said tubular member (18) approaches the inside diameter at said inlet end (46) of the tubular member (18) . 4. An ink jet printer according to claim 1, characterized in that said reservoir means (10) has an aperture (16) in one wall thereof and said conduit means (18) includes a section (20, 22) fitting in said aperture (16) and supporting said printing means (26). 5. An ink jet printer according to claim 4, characterized in that said aperture (16) is formed in a side wall of said reservoir means (10), and said conduit means (18) is an L-shaped tubular member having one leg f OMP 5 . ( concluded ) thereof extending through said aperture (16), and having said wall portion (48) along the other leg thereof de¬ fining said inlet end (46). 6. An ink jet printer according to claim 1, characterized in that said printing means (26) includes one or more piezoelectric transducers (38). 7. An ink jet printer according to claim 1, characterized in that said conduit means (18) is made of an elastomeric material.

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