METHOD AND APPARATUS FOR INK JET PRINTING

Abstract: Apparatus and method for ink jet printing in which ink (14) circulated in a continuous moving stream in a closed capillary tube (10) is caused to be deflected at a point inside the circulating ink system by deflecting means (18) arranged to produce pressure pulses to effect a printing operation by deflecting ink from the stream towards a nozzle (20). The deflected ink is ejected through the nozzle (20) in the form of droplets. The velocity (V<uD>u) of the ejected droplets depends upon the velocity of the continuously-flowing ink (V<uT>u) and on the velocity of the deflection pulse (V<uP>u).

Description: _METHOD AND APPARATUS FOR INK JET PRINTING Technical Field The invention relates to an apparatus and method for ink jet printing on record media. Background Art In the field of non-impact printing, the most common types of printers have been the thermal printer and the ink jet printer. When the performance of a non-impact printer is compared with that of an impact printer, one of the problems in the non-impact machine has been the control of the printing operation. As is well-known, the impact operation depends on the movement of impact members such as wires or the like and which are typically moved by means of an electromechanical system which is believed to enable a more precise control of the impact members. The advent of non-impact printing, as in the case of thermal printing, brought out the fact that the heating cycle must be controlled in a manner to obtain maximum repeated operations. Likewise, the control of ink jet printing in at least one form thereof must deal with rapid starting and stopping movement of the ink fluid from a supply of the fluid. In each case, the precise control of the thermal elements and of the ink droplets is necessary to provide for both direct and high-speed printing. In the matter of ink jet printing, it is extremely important that the control of the ink droplets be accurate from the time of formation of the droplets to the depositing of such droplets on paper or like record media. Prior art ink jet printing methods generally fall into two categories. In the pulse-on-demand method, such as disclosed for instance in the U.S. Patent No. 3,946,398, the drive means for the ink droplets is generally in the form of a piezoelectric crystal element which is selectively energizable to eject a droplet of ink through the nozzle onto a record medium. Printers of this kind are easy to control; however, the printing speed achievable therewith is comparatively low. In. the continuous jet method-, such as disclosed for instance in the U.S. Patent No. 3,769,624, a jet of ink is caused to issue from a nozzle in the form of a succession of minute individual droplets directed towards a record medium. The droplets are charged and are caused to pass between electrostatic deflection plates which will deflect the droplets either to the record medium or to a gutter from which the ink is returned to the reservoir. The printing speed of this kind of printer is much higher than the speed of the pulse-on-demand printers; however, the control of the ink jet is rather more complex and the ink droplets issuing from the nozzle have a long way to travel before impinging on the record medium and are affected by the contaminants (dust, moisture, etc.) of the surrounding atmosphere. Disclosure of the Invention It is an object of the present invention to provide an ink jet printing apparatus and method which provide printing speeds comparable to those achieved with continuous jet methods, yet are easy to control and are not affected by the surrounding environment. This object is achieved according to the inven¬ tion by providing an ink jet printing apparatus and method in which deflection of ink occurs within a cir¬ culating ink system and only the deflected ink is ejected through the nozzle in the form of ink droplets. Thus, according to the invention, there is provided an apparatus for ink jet printing, including conduit means for carrying ink, and actuating means operative to eject droplets of ink through a nozzle connected with said conduit means, characterized by cir¬ culating means arranged to circulate the ink in a con¬ tinuous stream in said conduit means, said actuating OMPI means being arranged to generate pressure waves through the stream, causing the ink to be deflected from said stream towards and through said nozzle. According to another aspect of the invention, there is provided a method of printing in dot matrix form, wherein droplets of ink are ejected through a nozzle onto a record medium, characterized by circulating a quantity of ink in a continuous stream, and deflecting ink from said stream by pressure waves transmitted through the ink stream, said pressure waves causing ink to be ejected through said nozzle in droplet form onto said record medium. In a preferred embodiment of the invention, ink is caused to be driven in a closed system along a path by a pump wherein a portion of the ink is deflected at one point in its travel to eject ink droplets through a nozzle which is located downstream of the one point in the direction of ink travel. The ink is driven in continuous movement around the closed system and timely short pressure pulses from a deflection element deflect the ink stream in a manner to cause ejection of the ink droplets. The ink is circulated at a certain velocity and the deflection element is moved at a precise velocity to cause the ink droplet to be ejected at a high velocity from the nozzle. One variation of the preferred arrangement for ejection of ink droplets from a continuously moving stream of ink includes the use of oppositely-positioned deflection elements to produce an ink droplet from one or another side of the ink path. Another variation provides that the ink is moving in a free flow state or condition and the pressure pulse caused by the deflec¬ tion element drives the ink jet to the nozzle for eject¬ ing an ink droplet. The deflection element may be in the form of a piezoelectric element, it may be in the form of an elec¬ trode generating a discharge, or the deflection may be effected through a lateral channel with hydraulic O PI energization. Further,, the deflection of the ink stream may be effected by means of an electrohydraulic pressure wave chamber or by means of applying pressure waves in a . counter direction to the normal direction of ink stream flow. Brief Description of the Drawings Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 shows a diagrammatic view of the principle of the present invention in a preferred arrangement thereof; Fig. 2 is a view similar to Fig. 1 and showing a modification thereof; Fig. 3 is a diagrammatic view of an arrange¬ ment showing the flow of ink in a free state and in position to be deflected toward the nozzle; Fig. 4 is a diagrammatic view of the ink flow and showing a particular deflecting element; Fig. 5 is a view showing an alternate deflec¬ tion element arrangement; Fig. 6 is a view showing a further alternate deflection means; Fig. 7 is a view showing a still further alternate deflection means; Fig. 8 is a view showing a counter-directed deflection means; and Fig. 9 is a view showing a feedback channel arrangement of the ink system. Best Mode of Carrying Out the Invention Fig. 1 shows the principle of the circulating ink system with an arrangement for deflection of ink droplets from liquid ink 14 which is carried in a closed capillary tube 10 supported in a plastic body 12. The tube 10 contains the liquid ink in a closed environment or atmosphere free from effects of the surrounding medium such as dust, gas, or moisture. The ink 14 is caused to be moved or driven in a continuous movement or flow in the closed system by means of a high pressure pump 16 and with pro .ision for the . ink to be deflected at a certain point in the stream by a deflecting element 18. The element 18 is caused to produce a pressure pulse or wave into the path of the ink stream and perpendicu¬ lar thereto at a velocity V p at the time the traveling ink is moving at a velocity V_. By reason of the pres- sure pulses being directed into the ink stream, droplets 21 of the ink 14 are caused to be moved through a nozzle 20 at a velocity V D . In the absence of pressure pulses being direc¬ ted into the ink stream, due to the Coanda effect the ink tends to adhere to the convex wall portion 22 of the tube 10 and flows past the nozzle 20 in a stable manner. The velocity V_ of the ink droplets 21 from the nozzle 20 depends upon the velocity V„ of the travel¬ ing ink 14 and upon the velocity V p of the pressure pulses from the deflecting element 18 to produce the wave motion to eject the ink in the form of such drop¬ lets 21 from the nozzle 20. Since the ink droplet velocity V Q is dependent in part on the velocity of the circulating ink 14, the pump pressure can be varied within wide limits to change the velocity of the moving ink within the tube 10. It is important to note that the deflection of the ink 14 occurs within the closed system and only the deflected ink in the form of droplets 21 are ejected through the nozzle 20. Fig. 2 shows an ink jet system with two stable ink flow paths. The closed capillary tube 10 is suppor¬ ted in a plastic mold 26 for carrying the ink 14 in a circulating and continuous moving manner by means of the high pressure pump 16. A pair of deflecting elements 30 and 32 are disposed on either side of the flow of ink 14 upstream from an .ink ejection nozzle 34 formed as an outlet of a cavity 36 in the plastic mold 26. The cavity 36 adjacent the deflecting element 30 OMPI_ includes a convex wall portion 38 and the cavity 36 in¬ cludes a further convex wall portion 40 adjacent the deflecting element 32. In this arrangement, for an ink droplet to be produced it is necessary for the element 30 to be actuated to cause the ink jet stream to be deflected from one ink flow path adjacent the wall por¬ tion 38 to the other ink flow path adjacent the wall portion 40. Actuation of the element 32 will cause the ink jet stream to be deflected back to its original path. Both ink flow paths are stable, since both wall portions 38 and 40 of the cavity 36 adjacent the res¬ pective deflecting elements 30 and 32 are convex causing the ink stream to adhere to one or the other of these wall portions. Fig. 3 shows an arrangement of a closed ink system with the capillary tube 10 being supported in a plastic mold 42 for carrying the ink 14 in a circulating and continuous moving manner by means of the high pressure pump 16. A deflecting element 44 is provided upstream of an ink ejection nozzle 46 which is formed as an outlet of a cavity 48 in the plastic mold 42. In this arrangement, the ink stream 14 is in a free flowing state and is considered to be in a stable condition as it is caused to be continuously driven in its path through the cavity 48. The ink 14 in the stream thereof is not affected by wall adhesion as in Figs. 1 and 2 but rather is affected by characteristic dynamic or inertia forces for stability in the free flow condition. When the element 44 is actuated the pressure pulse moves the free flowing jet of ink to turn over to the nozzle 46 so as to eject the ink in the form of droplets therefrom. Fig. 4 shows another arrangement of ink flow deflection wherein the ink 14 is caused to be driven or moved in the direction of the arrow and the deflec- tion is actuated by means of a piezoelectric device 52 * carried in a plastic mold 54. The deflection device 52 comprises a piezo-ceramic element 56 and a steel plate 58 adjacent the ink stream for causing pressure pulses O PI or waves to form the ink droplets. The ceramic element 56 is energized from an electric voltage which causes bending or deforming of the element and acts upon the plate 58 to produce the pressure pulses or waves. Fig. 5 shows the stream of ink 14 carried in a plastic mold 62 and deflected by an electric spark between electrodes 64 and 66 to generate the pressure waves necessary for ejection of the ink droplets. Fig. 6 shows the stream of ink 14 carried in a plastic mold 70 and including a channel or passageway 72 disposed laterally from the ink stream and positioned for carrying fluid to deflect the ink stream into a cavity 74 and then eject ink in the form of droplets from a nozzle 76. Unless the deflecting fluid is ink, a flexible membrane is used to separate the fluid from the ink stream. Fig. 7 shows the stream of ink 14 carried in a plastic mold 80 and includes means for deflecting the ink from the stream and out through the nozzle 82. The deflecting means includes an oil or like viscous liquid contained in a chamber 84 which has a central conductor 86 disposed through the chamber and connecting with a plate element 88. A second plate 90 is used as a por¬ tion of an R-C circuit for actuating the fluid in the chamber 84 to cause a foil element 92 to move and to generate pressure waves in the ink stream 14 and thus cause ejection of ink droplets through the nozzle 82. Fig. 8 shows means for deflecting the ink 14 by applying pressure waves in a counter or opposite direction to the normal flow of the ink through the tubular portion formed in the plastic mold 94. The stream of ink 14 is caused to flow upwardly and is sub¬ jected to pressure pulses 96 to cause the ink flow to take the form as shown in the cavity 98 and to eject ink as ink droplets through the nozzle 100. The ink passes through a reduced diameter or narrowed portion 101 prior to reaching the cavity 98. O PI Fig. 9 shows the stream of ink 14 carried in a plastic mold 102 and a deflection element 104 is provided upstream of a nozzle 106 formed as an outlet of a cavity 108 in the plastic mold. A feed back channel 110 is formed in the plastic mold 102 for measurably controlling and thereby determining the duration of the run of the ink stream through the outlet nozzle 106. The feed back channel is filled with ink upon the deflec¬ tion of the ink stream to the left side and the hy- draulic effect is used to "turn over" the ink jet from the left side to the right side. The duration of the ink jet run at the left side is determined by the volume of the channel 110. It will be appreciated that in each of the ink jet systems described above the ink in the conduit is replenished from a suitable reservoir to compensate for ink droplets ejected through the nozzle.

Claims: CLAIMS : 1. Apparatus for ink jet printing, including conduit means for carrying ink, and actuating means operative to eject droplets of ink through a nozzle connected with said conduit means, characterized by circulating means (16) arranged to circulate the ink (14) in a continuous stream in said conduit means (10), said actuating means (18) being arranged to generate pressure waves through the stream, causing ink (14) to be deflected from said stream towards and through said nozzle (20). 2. Apparatus according to claim 1, charac¬ terized by a body member (12) for containing said conduit means (10) and cavity means interconnecting said conduit means (10) with said nozzle (20). 3. Apparatus according to either claim 1 or 2, characterized in. that said circulating means includes a pump (16) . 4. Apparatus according to either claim 1 or 2, characterized in that said actuating means includes a deflection element (18) upstream of said nozzle (20). 5. Apparatus according to either claim 1 or 2, characterized in that said actuating means includes a pair of opposed deflection elements (30, 32) upstream of said nozzle (34). 6. Apparatus according to either claim 1 or 2, characterized in that said actuating means includes a piezoelectric element (52). 7. Apparatus according to either claim 1 or 2, characterized in that said actuating means includes 7. ( concluded ) a pair of opposed electrodes (64, 66) for producing an electric spark therebetween. 8. Apparatus according to claim 2, charac¬ terized in that said actuating means includes a channel (72) carrying fluid laterally of said stream of ink (14) to deflect said stream into said cavity means (74), 9. Apparatus according to claim 2, charac¬ terized in that said conduit means (10) includes a reduced diameter portion (101) and said cavity means includes an enlarged portion (98) for enabling deflec- tion of said ink (14) by fluid flow counter to the flow of said stream. 10. Apparatus according to claim 2, charac¬ terized in that-said cavity means (108) includes a feed back channel (110) for controlling the duration of the flow of ink (14) through the nozzle (106). 11. A method of printing in dot matrix form, wherein droplets of ink are ejected through a nozzle onto a record medium, characterized by circulating a quantity of ink (14) in a continuous stream, and deflec- ting ink (14) from said stream by pressure waves trans¬ mitted through the ink stream, said pressure waves caus¬ ing ink (14) to be ejected through said nozzle (20) in droplet form onto said record medium. 12. A method according to claim 11, charac¬ terized in that deflection of ink (14) from the stream is accomplished by means of hydraulic pressure applied laterally of said stream and upstream of said nozzle (76, 82). 13. A method according to claim 11, charac¬ terized in that deflection of ink (14) from the stream OMPI lS. (concluded) is accomplished by means of fluid flow (96) counter to the flow of said stream. OMPI ι/

Inventors: REITBERGER P
Applicants: NCR CO, NCR CORP
Application year: 1981
Main classification: G01D5
IPC codes: B41J2, G01D5, G01D15