INK JET PRINTER

Abstract: The control of ink jet printing must deal with rapid starting and stopping of the ink fluid to provide for both correct and high speed printing. Ink droplet ejection is controlled by means of cylindrically-shaped pressure waves generated in the ink close to the nozzle (18). A pair of electrodes (10, 12) is provided in the ink chamber (14) with an insulated conductor (22) extending therebetween and the pressure waves are generated as a result of interaction between discharges between electrodes and the magnetic field produced around the conductor (22) as current flows therethrough, The principal use is an ink jet printer.

Description: INK JET PRINTER Technical Field The invention relates to an ink jet printer. 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 upon the move¬ ment of impact members such as wires or the like and which are typically moved by means of an electromechani¬ cal 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 correct 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. One prior art method of ink jet printing is the pulse-on-demand method, a representative of which is disclosed in the U.S. Patent No. 3,946,398. The drive means for the ink droplets of -the printer disclosed in this patent is in the form of a piezoelectric crystal element which is selectively energizable to eject drop ¬ lets of ink through a nozzle on to a record member. Printers of this kind are easy to control; however, the printing speed achievable therewith is comparatively low. Disclosure of the Invention It is an object of the present invention to provide an ink jet printer having an increased droplet speed and operating at considerably higher frequencies as compared with printers using piezoelectric crystal elements. This is achieved according to the invention by electromagnetically producing cylindrical pressure waves of high amplitude in the ink close to the ink nozzle to cause ejection of ink droplets therefrom. A further advantage of the printer of the invention is that with this type of wave generation, it is possible to arrange a plurality of print heads adjacent and over one another, enabling completely new print head construction. Thus, according to the invention, there is provided an ink jet printer including a body portion having an ink chamber therein for containing ink, a nozzle connected with said ink chamber, and drive means selectively actuatable to eject droplets of ink through said nozzle on to a record medium spaced therefrom, characterized in that said drive means includes first and second electrodes disposed in the ink chamber and spaced from one another for accommodating ink there- between, an insulated electrical conductor extending between said electrodes, said conductor being electri¬ cally connected to said first electrode and passing through and electrically insulated from said second electrode, and circuit means connected to said conduc- tor and to said second electrode for intermittently energizing said electrodes so as to bring about electri¬ cal discharges between said electrodes, whereby pressure waves are generated in the ink chamber as a result of interaction between said discharges and the magnetic field produced around said conductor as current flows therethrough, so as to cause ejection of ink from the nozzle in droplet form. According to another aspect of the invention, there is provided an ink jet printer including a body portion having an ink chamber therein for containing ink, a nozzle connected with said ink chamber, and drive means selectively actuatable to eject droplets of ink through said nozzle on to a record medium spaced there¬ from, characterized in that said drive means includes a flexible wall member separating said ink chamber from a fluid chamber containing fluid therein, first and second electrodes disposed in the fluid chamber and spaced from one another for accommodating fluid therebetween, an insulated electrical conductor extending between sai electrodes, said conductor being electrically connected to said first electrode and passing through and electri¬ cally insulated from said second electrode, and circuit means connected to said conductor and to said second electrode for intermittently energizing said electrodes so as to bring about electrical discharges between said electrodes, whereby pressure waves are generated in the fluid chamber as a result of interaction between said discharges and the magnetic field produced around said conductor as current flows therethrough, so as to cause flexing of said wall member and ejection of ink from the nozzle in droplet form. In one embodiment of the invention, permanent magnets are disposed adjacent the ink chamber for caus¬ ing the pressure waves to assume a preferred direction towards the nozzle. In another embodiment the pressure waves are concentrated in the direction of the nozzle by means of a curved formation of the conductor to increase the speed of ink droplets from the nozzle of the printer. Some pressure waves reflected from the walls of the ink chamber or travelling away from the nozzle tend to flow into the ink. supply and damping means is utilized to minimize the effect of such back pressure waves. Examples of damping means which may be used in the practice of the present invention include a flexible or pliant member having exponential shaping in one por- tion thereof, porous material placed in a conduit with air chambers on either side of the material, and the use of plastic or non-metallic foil in the ink chamber to limit the recurring pressure waves. 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 s a diagrammatic view of an arrangement for generating shaped pressure waves for producing ink droplets; Fig. 2 is a diagrammatic view of another arrangement for generating shaped pressure waves; Fig. 3 is a view taken along the plane 3-3 of - Fig. 2; Fig. 4 is a diagrammatic view of a further arrangement for generating the shaped pressure waves; Fig. 5 is a diagrammatic view of an arrangement similar to Fig. 1 along with a portion of a flexible or pliable hose for damping the pressure waves; Fig. 6 is a view showing the extended form of the pliable hose partially shown in Fig. 5; Fig. 7 is a view showing another form of damping arrangement; Fig. 8 is a view showing a further form of damping arrangement; Fig. 9 is a diagram showing an alternate method of enabling the ink droplet drive means; and Fig. 10 is a timing diagram in graphic form of the input/output signals of the switching means of the invention. * Best Mode of Carrying Out the Invention Fig. 1 of the drawing shows an arrangement for producing cylindrically shaped pressure waves of ink which are electromagnetically initiated and which effect the ejection of ink droplets from an outlet of an ink jet printer. Two flat circular electrode plates 10 and 12 made of stainless steel and maintained in spaced relationship are disposed in an ink chamber 14 which is formed in the shape of a rectangular parallelepiped or like configuration within a plastic body 16 of cylindri¬ cal shape. A nozzle 18 is provided as the outlet from the ink chamber 14 to one end 20 of the plastic body 16 for serving as the orifice through which the ink is ejected in droplet form 21 for printing on paper or other record material 17 spaced from the nozzle and as enabled by the actuation, of the ink drive means. A bore or like opening 19 is provided for an ink supply line connected to the body 16 for supplying ink to the chamber 14. A central conductor 22 of brass material ex¬ tends between the electrode plates 10 and 12, the con¬ ductor 22 passing through the electrode plate 12 and having one end connected to a lead 24 of a supply volt¬ age E and the other end connected to the electrode plate 10. The conductor 22 is coated with a suitable plastic material 25 such as manufactured by DuPont and sold under the registered trademark "Teflon", and is also insulated from a conductor 26 of brass material having one end connected with the plate 12 and the other end connected with a lead 28 connected to ground potential. A switching device 30 is inserted in the lead 24 and an R-C circuit including a resistor 32 and a • capacitor 34 is placed across the leads 24 and 28. In this manner, the plates 10 and 12 serve as electrodes between which the charged capacitor 34 discharges upon closing the switch 30. The discharge current takes the path of least resistanc .and will appear as a surface discharge spark along the insulated central conductor 22. The current flowing in the direction as indi¬ cated by the arrow 36 through the central conductor 22 produces an azimuthal magnetic field (a field directed in a horizontal plane and in a clockwise direction) which by interaction with the charged layer directed axially with the conductor 22 as indicated by the arrow 38 in the liquid ink- in the chamber 14 generates a radially outwardly directed force as indicated by the arrow 40, by virtue of the reverse pinch effect. Thus, a cylindrical-shaped pressure wave is produced in the chamber 14 which causes ejection of ink in droplet form from the nozzle 18. A damped oscillating circuit is provided by the capacitor 34, the resistor 32, and the inductance which is inherent in the leads 24 and 28. Actuation of the switoh 30, produces one or more pressure waves upon each closure thereof, dependent upon the resistance losses in the circuit. " Fig. 2 shows another arrangement for gener- ating directed pressure waves wherein a plastic body 42 contains an ink chamber 44 and metallic electrode plates 46 and 48 along with a central conductor 50 for moving ink from a supply tube 52 into the chamber 44 and out through an ink nozzle 54, all in similar manner as shown in Fig. 1. Additionally, as seen in Fig. 3, a magnetic field is provided by means of permanent magnets 56 and 58, adjacent the ink cavity 44 and more specifically ferrite-type magnets, for causing a preferred direction of movement for spreading the produced pressure waves toward the nozzle 54, as shown by the arrows in Fig. 2. With the arrangement shown in Figs. 2 and 3, pressure pulses of 50 atmospheres can be produced in about one microsecond. Fig. 4 shows a pressure wave concentration arrangement by means of electrohydraulic impact wave generation for increased ink ejection. A plastic body 60 contains an ink chamber 62 and metallic plates 64 and 66 along with a central conductor 68 for moving ink from a suitable supply tube into the chamber 62 and through an ink nozzle 70, all in similar manner as seen in Figs. 1 and 2. In this arrangement the central con- ductor 68 is formed in concave shape with respect to the nozzle 70 and provides a pressure wave concentrator effect to form and eject the ink droplets, as 21 in Fig. 1. It should readily be seen that the geometry of the ink chamber tends to enable pressure waves to be reflected and flow back into the ink supply means. It is desirable that the return pressure waves be of minimum amplitude and therefore the effect of these return pressure waves is substantially diminished or . almost eliminated by damping means which may take the shape and form of several arrangements. Fig. 5 shows the plastic body 16 of Fig. 1 containing the plates 10 and 12 along with the central conductor 22 in the ink chamber 14 for ejecting ink droplets 21 from the nozzle 18. A hose 72 of soft wall material is connected into the bore 19 of the plastic body 16 for damping the pressure waves travelling in the direction of the ink supply means. Fig. 6 shows the hose 72 which has a wall thickness of about 10 microns connected to the plastic body 16 of the print head and shaped to include a section 74 in exponential form. The section 74 of ex¬ ponential form is located in the supply line near the print head and provides pressure wave sump means for damping the returning pressure waves in the ink chamber 14 of Fig. 1. Fig. 7 shows another arrangement for damping or absorbing the pressure waves which are travelling in the direction of the ink supply means. An ink carry- ing conduit or passageway 76 is connected to the plastic body 16 of the print head and includes a portion 78 having porous material; for example, clay, inserted in the conduit between a pair of air chambers 80 and 82. The geometric connections of the air chambers 80 and 82 and the hydraulic resistance to the flow of ink deter¬ mine the damping effect required on the recurrent or back flow of the pressure waves. Fig. 8 shows a further embodiment of the print¬ er according to the invention which includes a plastic body 86 containing plates 88 and 90 along with a central conductor 92 arranged in similar manner as shown in Figs. 1, 2, 4 and 5. The plastic body 86 has a fluid chamber 94 therein containing oil or like viscous fluid and an ink chamber 96 at right angles to chamber 94 and separated by a flexible plastic member 98. A nozzle 100 is provided in a wall of the plastic body 86 opposite the chamber 94 and the member 98. The pressure waves generated in the fluid chamber 94 will cause flexing of the plastic member 98 and thereby ejection of ink from the nozzle 100 in droplet form. The amount of damping and the oscillating behaviour of the fluid in the chamber 94 in relation to the plastic member 98 can be adjusted or changed by the choice of material used for member 98 and the types of viscous fluid placed in chamber 94. Certain chemical additives can be added to the viscous liquid to provide a gaseous atmosphere in the chamber 94. Additionally, certain liquids, such as alcohol, can be added in the damping fluid to influence the effectiveness of the damping system. Fig. 9 shows a different circuit arrangement for enabling the ink droplet drive means and which in¬ cludes a capacitor 102 and a resistor 106 along with a transistor or like semiconductor switch 104 correspond¬ ing to switch 30 of Fig. 1. The discharge path of the ink droplets is diagrammatically shown in the form of a print head 108. The transistor 104 may be utilized in a manner to provide signals as indicated in graphic form in the Fig. 10 timing diagram with a time parameter to derive optimum separation of the-ink droplets. V s is a function of V_ a and V-,, the latter being the potential across the capacitor 102 in Fig. 9. In the upper timing dia¬ gram (a), if the input voltage V of the transistor 104 (Fig. 9) is a square-wave impulse signal, then the dis- charge function of the capacitance is like that of the voltage V g of the timing diagram (a) . In the lower timing diagram (b) , if the voltage V_ of the transistor 104 (Fig. 9) is a peak-shaped impulse signal, then the discharge function is like that of the voltage V of the timing diagram (b) , therefore making it possible to modify the output voltage V s of such transistor 104 (Fig. 9). In the latter case (b) , g results from the superposition of V_ and V c in the manner wherein V_ determines the rise and V- determines the decline of V g ..

Claims: CLAIMS : 1. An ink jet printer including a body por¬ tion (16) having an ink chamber (14) therein for con¬ taining ink, a nozzle (18) connected with said ink chamber (14), and drive means selectively actuatable to eject droplets of ink through said nozzle (18) on to a record medium spaced therefrom, characterized in that said drive means includes first and second electrodes (10, 12) disposed in the ink chamber (14) and spaced from one another for accommodating ink therebetween, an * insulated electrical conductor (22) extending between said electrodes, said conductor (22) being electrically connected to said first electrode (10) and passing through and electrically insulated from said second electrode (12), and circuit means (30, 32, 34) connected to said conductor (22) and to said second electrode (12) for intermittently energizing said electrodes so as to bring about electrical discharges between said electrodes, whereby pressure waves are generated in the ink chamber (14) as a result of interaction between said discharges and the magnetic field produced around said conductor (22) as current flows therethrough, so as to cause ejection of ink from the nozzle (18) in droplet form. 2. An ink jet printer including a body por¬ tion (86) having an ink chamber (96) therein for con-, taining ink, a nozzle (100) connected with said ink chamber (96), and drive means selectively actuatable to eject droplets of ink through said nozzle (100) on to a record medium spaced therefrom, characterized in that said drive means includes a flexible wall member (98) separating said ink chamber (96) from a fluid chamber (94) containing fluid therein, first and second elec- trodes (88, 90) disposed in the fluid chamber (94) and spaced from one another for accommodating fluid there¬ between, an insulated electrical conductor (92) extend- 2 . ( concluded ) ing between said electrodes, said conductor (92) being electrically connected to said first electrode (88) and passing through and electrically insulated from said second electrode (90), and circuit means connected to said conductor (92) and to said second electrode (90) for intermittently energizing said electrodes so as to bring about electrical discharges between said elec- trodes whereby pressure waves are generated in the fluid chamber (94) as a result of interaction between said discharges and the magnetic field produced around said conductor (92) as current flows therethrough, so as to cause flexing of said wall member (98) and ejection of ink from the nozzle (100) in droplet form. 3. An ink jet printer according to either claim 1 or 2, characterized in that said electrodes are circular metal plate members (10, 12). 4. An ink jet printer according to either claim 1 or 2, characterized in that said electrical conductor (22, 92) extends through said ink chamber (14) or fluid chamber (94) perpendicularly to the axis of the nozzle (18, 100). 5. An ink jet printer according to either claim 1 or 2, characterized in that said electrical conductor (68) is formed in concave shape with respect to the nozzle (70). . 6. An ink jet printer according to either claim 1 or 2, characterized in that said circuit means includes a switch (30) in series with a capacitor (34), whereby closure of said switch (30) causes the capacitor (34) to discharge between said pair of electrodes (10, 12; 88, 90). 7. An ink jet printer according to claim 6, characterized in that said capacitor (34) is connected with a resistor (32) to provide a damped oscillating circuit. 8. An ink jet printer according to claim 1, characterized by permanent magnets (56, 58) disposed adjacent said ink chamber (44) for causing the pressure waves to assume a preferred direction towards the noz- zle (54). 9. An ink jet printer according to claim 1, characterized by resilient means (72) connected to an inlet of said ink chamber and shaped for damping pressure waves travelling in the direction of said inlet. 10. An ink jet printer according to claim 1, characterized by a passageway (76) connected to an inlet of said ink chamber and having a portion thereof disposed between a pair of air chambers (80, 82), said portion containing porous material (78) for damping pressure waves travelling in the direction of said inlet. 11. An ink jet printer according to claim 2, characterized in that the fluid contained in said fluid chamber (94) is an oil or like viscous liquid. 12. An ink jet printer according to claim 11, characterized in. that said fluid has added thereto a chemical additive to provide a gaseous atmosphere in said fluid chamber (94). ■ - ~ -

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