GB2262717A

GB2262717A - Electro-magneto-hydrodynamic ink drop generator.

Info

Publication number: GB2262717A
Application number: GB9206382A
Authority: GB
Inventors: Yoon-Soo Kim
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 1991-12-23
Filing date: 1992-03-24
Publication date: 1993-06-30
Also published as: KR930012307A; FR2685251A1; IT1254832B; ITMI920648A0; GB9206382D0; CA2062711A1; ITMI920648A1

Abstract

The printhead comprises an array of tubular ink-projecting tubes which have internally thereof respective pairs of spaced electrodes, and which has means for generating a magnetic field in the vicinity of the electrodes. When a current is passed through a conductive ink in a said tube, the interaction between the current through the ink and the magnetic field causes movement of the ink, whereby a droplet is ejected from the open end of the tube. As shown (Fig 1) a printhead comprises a row of tubes (14) of rectangular (square) cross section in an insulator (24). The electrodes (16, 18) are applied to opposed walls of the tubes (14) and the magnetic field is generated between laminar magnets (20, 22) which sandwich the insulator (24). It is stated that the printhead is able to produce recordings with continuous tonal gradation. <IMAGE>

Description

INK-lET PRINT HEAD This invention relates to print heads of ink-jet printers of drop-ondemand type, and more particularly to an ink-jet print head for ejecting ink by an electromagnetic force responding to an externally applied voltage.

In general, an ink-jet recording technique is a method of reproducing a certain visible pattern on a recording medium such as paper by a group of electronically controlled ink drops. In ink-jet recording, ink drops from a nozzle (orifice) adhere to the printing medium which faces the ink-nozzle, thereby resulting in a visible pattern.

Although there are more than twenty ink-jet printing methods, most ink-jet printers can be categorized into either one of: (1) Drop-on-Demand type (DOD) or (2) Continuous Ink-jet type, wherein among several different DOD-type ink-jet printing methods, the most popular types of this category may be: (A) Thermal Ink-jet or Bubble-jet or (B) Piezo-electric element type.

The heart of the thermal ink-jet (or bubble-jet) (A) is a resistive heating element placed inside an ink-chamber. One face of the ink-chamber has a hole connected to an orifice which is a tiny hole through which an ink drop is ejected toward the recording media. Enormous heat generated instantaneously from the heating element due to current flow through the heating element evaporates ink and the pressure from the ink vapor accelerates the ink inside the ink-chamber toward the orifice to form a high speed ink drop when it escapes from the orifice.

An ink-jet head of this type has a complicated shape and has problems in reproducing continuous tone since the size of the ink-drop is hard to control.

An ink-jet head of type (B) has a piezo-electric crystal which vibrates in accordance with a voltage signal applied across the crystal. The vibrating energy is transferred to the motion energy of the ink-drop to form ink-drops.

A drawback of this type is that the rate of ink-drop formation is low (2-3 KHz) causing low printing speed.

A continuous stream of ink drops is formed in the type (2) by using an ink pump and a vibrating nozzle. The flight path of the ink drops is modified when they pass through a deflecting electrode following a charging electrode.

The rate of the ink-drop formation is high (100KHz or above) and it enables the reproduction of continuous tone. However, since the system is complicated, the system tends to be large and high in price. In addition, maintaining a steady stream of ink-drops still remains a problem.

Preferred embodiments of the present invention aim to provide an electromagnetic pumping ink-jet print head capable of effective continuous tonal gradation of print image in response to an input print signal.

Another aim is to provide an ink-jet print head with simpler structure for ejecting the ink by means of an electromagnetic pumping method.

According to one aspect of the present invention, there is provided an ink jet print head of drop-on-demand type for ejecting conductive ink by electromagnetic pumping, the print head comprising: a magnetic field generating means for generating a uniform magnetic field from a first space to a second space; and a pumping tube member comprising a plurality of pumping tubes each having isolated first and second electrodes and disposed in said magnetic field, wherein said conductive ink is selectively ejected from each said pumping tube by applying a voltage to the respective said first and second electrodes.

Preferably, each said pumping tube is of quadrangular section.

Preferably, said first and second electrodes of each said pumping tube are of metal and coated on opposite inner walls of said tube.

Preferably, said pumping tubes are formed separately in a center of an insulation panel at regular intervals.

According to another aspect of the present invention, there is provided an ink jet print head of drop-on-demand type for ejecting conductive ink by electromagnetic pumping, the print head comprising: a pumping tube member incorporating a plurality of pumping tubes each having isolated first and second electrodes and being formed separately at regular intervals in a center of an insulation panel; and a first magnet panel and a second magnet panel installed on opposite sides of said pumping tube member for applying a uniform magnetic field to said pumping tube member.

Preferably, said insulation panel comprises a glass or a silicon wafer.

Preferably, each said pumping tube is of quadrangular section.

Preferably, said first and second magnetic panels each have a South and North magnetic pole aligned in a common direction.

The invention extends to an ink jet printer having a print head according to any of the preceding aspects of the invention.

For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings, in which: Figure 1 is an exploded view of one example of an electromagnetic pumping ink-jet print head according to this invention; Figures 2A and 2B are a front and a plan view respectively of the print head shown in Figure 1; Figures 3A and 3B is a detailed and enlarged view of an essential part of the exploded view as shown in Figure 1; Figure 4 is a front view of an electromagnetic pumping tube; and Figures 5A and 5B are graphs of variation of tone respectively with time and applied voltage.

A pumping tube member incorporating a plurality of pumping tubes comprising isolated first and second electrodes in its body at regular intervals is located in an electromagnetic space of a given and uniform magnetic field, generated from a first space to a second space.

By applying a positive voltage to the first electrode and a negative voltage to the second electrode, a given amount of current flows from the first electrode to the second electrode. Due to the current flow between the two electrodes, a conductive ink in the pumping tube is accelerated and ejected toward an exit side according to Fleming's left-hand rule.

For à pumping tube of the pumping tube member, a quadrangle shape of tube is desirable, and the first and second electrodes are fitted or coated separately on a right and left inner wall of the quadrangle tube. The first and second electrodes are of good conductive metal and extend in an axial direction.

By placing the pumping tube in an electromagnetic space where a uniform magnetic field is applied from the first space to the second space, the conductive ink of the pumping tube is ejected by applying a drive voltage to the electrodes of the pumping tubes.

With reference to Figure 1, an electromagnetic pumping ink-jet print head comprises a pumping tube member 24 comprising an insulation panel 12 and a plurality of pumping tubes 14 having first and second electrodes 16, 18 installed in the center of the insulation panel 12 at regular intervals, and first and second magnet panels 20, 22 installed on the top and bottom side of the pumping tube member 24 for applying a uniform magnetic field to it.

The insulation panel 12 is an insulating material of glass or silicon wafer, which is treated equivalently. The first and second electrodes 16, 18 are a positive electrode (+) and a negative electrode (-) respectively, and are of good conductive material.

The first and second electrodes 16, 18 are coated on an inner wall of right and left side of each pumping tube 14 by a plating method.

With reference to Figures 2A and 2B, said N magnetic poles of the first and second magnet panels 20, 22 are arrayed from top to bottom in order, and each pumping tube 14 has a given height H and width L3.

With reference to Figure 3A, the insulator 12 of hexahedron shape, having a given height H, length L and width L2 forms an elongate tube 14, and the first and second electrodes 16, 18 are coated on opposite left and right inner sides of the tube 14.

Figure 3B shows in more detail the position of the first and second electrodes 16, 18 in the insulation panel 12. Figure 4 is a front view of the tube 14 as shown in Figure 3A and for describing a principle of electromagnetic pumping. Figures SA and SB are graphs showing tone of an electromagnetic pumping ink-jet print head and show a correlation with an applied voltage V to the first and second electrodes 16, 18 (Figure 5B), and with variation of time (Figure SA). The shape of the tube is illustrated as a quadrangle for convenience and simplifying the model in Figure 1 to Figure 4.

For describing an example of operation, it is assumed that a uniform magnetic field is applied to the pumping tube member 24 by the first and second magnetic panels 20, 22, and each tube 14 is filled with an ink of conductive material.

When a given state of voltage V corresponding to a print signal is applied across the first electrode 16 and second electrode 18 of the pumping tube 14, current flows from the first electrode 16 (positive electrode +) to the second electrode 18(negative electrode -).

Assuming that a magnetic field strength of the pumping tube member 24 is B (shown as a vector B), current density per unit length from the first electrode 16 to the second electrode 18 is I (shown as a vector I), and the conductive ink in the pumping tube 14 experiences a force along the axis of the tube, by Fleming's left-hand rule. If this axial force is indicated as F (shown as a vector F), F may be expressed as an equation: F=L3IxB (l) wherein L3 is the inner width of the pumping tube 14.

Assuming that the voltage applied between the two electrodes 16 and 18 of the pumping tube 14 is V, the current I in the equation (1) is expressed as: I= V ...... (2) R wherein R is the resistance per unit length of the conductive ink filled in the tube 14.

The resistance R of the equation (2) is expressed as: R=# L3/H ....... (3) wherein p is a coefficient of resistance of the conductive ink filled in the pumping tube 14, L3 is its inner width and H is its height.

Arranging the equations (1),(2),and (3), F can be expressed as an equation:

= L3VH XB pL3 = VH xB ......... (4) p Consequently, the conductive material in the pumping tube 14 is accelerated by the force F calculated by the equation (4) in the pumping tube member 24 installed between the first and second magnet panels 20, 22.

Assuming that the density of the conductive ink in the tube 14 is "d" and friction and viscosity resistance are negligible, the acceleration "a" of the conductive material caused by the force F is expressed as: a = VHB = V#B ..... (5) dHL3# d#L3 The conductive ink in the pumping tube 14 of the pumping tube member 24 is ejected toward the exit of the tube 14 with an acceleration a determined by the equation (5).

Assuming that an initial speed of the ink ejected from the tube 14 of the pumping tube member 24 is "0" (zero), the amount of ink Q ejected for a time t at an acceleration determined by the equation (5) is expressed as: 1 BVt Q=-at= .... (6) 2 2d#L3 Accordingly the conductive ink in the pumping tube 14 of height "H" and width "L3" is ejected by the force "F" and acceleration "a" determined in the equations (4) and (5) owing to a voltage "V" applied between the first and second electrodes 16, 18 of the pumping tube 14. So it is shown that the amount of ink Q ejected with the force F and the acceleration a is controlled by adjusting the applied voltage V or the time tin the equation (6).

The ink is ejected from the tube and adheres to a printing paper (not shown in drawings) facing the pumping tube 14, so that a pictorial image is formed on the paper. The tone of the pictorial image formed on the paper is varied greatly by the ejected amount of ink Q.

For simplicity, assuming that the tone is proportional to the amount of ink, expression of tone of the pictorial image is possible by changing the voltage V applied to the first and second electrodes 16, 18 and the time (t) of applying the voltage V in the equation (6).

By applying a voltage V of square wave across the two electrodes 16, 18 of the pumping tube 14 of the pumping tube member 24 and changing the time (t), the amount of ink to be ejected can be controlled, the printed tone having the characteristic illustrated in Figure SA.

Accordingly, the tone of the pictorial image is related to time (t) as shown in Figure SA, if an input signal is applied to the two electrodes 16, 18 of the pumping tube 12 of the pumping tube member 24 after modulating the input signal by a method of pulse width modulation.

If the time of applying a voltage to the two electrodes 16, 18 is fixed and the voltage applied to the two electrodes 16, 18 is changed, a more linear feature of tone is obtained as shown in Figure 5B. For example, a linear feature of tone is produced as shown in Figure 5B, if a print input signal is applied to the two electrodes 16, 18 of the pumping tube 14 after modulating the print input signal by a method of pulse height modulation.

The acceleration a in the equation (5) does not count for loss factors such as viscosity of the ink filling the tube 14, friction force between the ink and the inner wall of the tube 14, gravity, air resistance, etc. under real conditions. Assuming that the loss caused by these factors is f(v), the pumping acceleration Pa in the equation (5) needs to be modified as the following equation: 1 ( VHB -f(v)) ....(7) p wherein v represents speed.

The pumping acceleration Pa in fact should be considered in the relation between the ejected amount of ink Q and the applied voltage V, or the ejected amount of ink Q and the time of ejection (t). An expert skilled in the art will be able to determine the pumping acceleration by experiment.

Consequently the ink in the pumping tube 14 is ejected when the signal responding to a print signal is applied to the pumping tube 14 of the pumping tube member 24.

In this embodiment, a uniform magnetic field is applied to the pumping tube member by attaching a permanent magnet on the top and bottom side of the pumping tube member 24. However, the permanent magnet can be replaced by, for example, an electromagnet comprising a coil winding.

In conclusion, the print head ejects conductive ink by electromagnetic pumping and can express continuous tone by regulating an amount of ejected ink by modulating the print signal in an electromagnetic pumping drop-ondemand ink jet print head.

While preferred embodiments of the present invention have been described in the foregoing, various modifications, alternate constructions and equivalents thereof may be employed without departing from the true spirit and scope of the invention. Therefore, the above description and illustration should not be construed as limiting the scope of the invention.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. An ink jet print head of drop-on-demand type for ejecting conductive ink by electromagnetic pumping, the print head comprising: a magnetic field generating means for generating a uniform magnetic field from a first space to a second space; and a pumping tube member comprising a plurality of pumping tubes each having isolated first and second electrodes and disposed in said magnetic field, wherein said conductive ink is selectively ejected from each said pumping tube by applying a voltage to the respective said first and second electrodes.

2. An ink jet print head as claimed in Claim 1, wherein each said pumping tube is of quadrangular section.

3. An ink jet print head as claimed in Claim 1 or 2, wherein said first and second electrodes of each said pumping tube are of metal and coated on opposite inner walls of said tube.

4. An ink jet print head claim as claimed in 1, 2 or 3, wherein said pumping tubes are formed separately in a center of an insulation panel at regular intervals.

5. An ink jet print head of drop-on-demand type for ejecting conductive ink by electromagnetic pumping, the print head comprising: a pumping tube member incorporating a plurality of pumping tubes each having isolated first and second electrodes and being formed separately at regular intervals in a center of an insulation panel; and a first magnet panel and a second magnet panel installed on opposite sides of said pumping tube member for applying a uniform magnetic field to said pumping tube member.

6. An ink jet print head as claimed in Claim 5, wherein said insulation panel comprises a glass or a silicon wafer.

7. An ink jet print head as claimed in Claim 5 or Claim 6, wherein each said pumping tube is of quadrangular section.

8. An ink jet print head as claimed in Claim 5, 6 or 7, wherein said first and second electrodes of each said pumping tube are of metal and coated on opposite inner walls of said tube.

9. An ink jet print head as claimed in any of Claims 5 to 8, wherein said first and second magnetic panels each have a South and North magnetic pole aligned in a common direction.

10. An ink jet print head substantially as hereinbefore described with reference to the accompanying drawings.

11. An ink jet printer having a print head according to any of the preceding claims.