Technical Field

The present invention relates to an ink jet print head, and to a method of controlling the flight path of ink droplets ejected therefrom.

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 for example in U.S. Patent No. 3,596,275, the ink is delivered under pressure to nozzles in a print head to produce a con¬ tinuous jet of ink emitted through each nozzle. The ink jet is 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 recirculation. 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 arranged to control the direction of flight of the drop¬ lets 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. 3,871,004. The droplets in this method are emitted

by means of volume displacement brought about in an ink chamber or channel by energization of a piezoelectric element. The volume displacement generates a pressure wave which propagates to the nozzles causing the ejec- tion of ink droplets. The ink jet print head described in this patent is provided with electrode plates in the area of the nozzles for producing an electrical field causing a deflection of ejected ink droplets for the purpose 'of increasing the resolution and quality of the produced dot matrix characters or images.

In all the abovementioned printers and print¬ ing methods, the deflection of the ejected ink droplets, that is to say, the control of the flight path of the droplets, is achieved by the provision of deflection plates or electrodes positioned between the nozzles and the record media to be printed upon. It should be clear that ink jet print heads requiring such external deflection means are of a complex construction and costly to manufacture.

Disclosure of the Invention

It is an object of the invention to provide an ink jet print head which is of a simple and robust construction and which does not require external de¬ flection plates or electrodes to control the flight path of the ejected ink droplets.

Thus, according to the invention, there is provided an ink jet print head including at least one ink conduit extending through a body portion and ending in a nozzle, and driving means for moving ink along said ink conduit causing ejection of droplets of ink through said nozzle, characterized in that said body portion incorporates a resilient portion, and further charac¬ terized by tilting means for deforming said resilient portion so as to bring about a tilting movement of said nozzle and thereby change the flight path of droplets of ink ejected from said nozzle.

According to another aspect of the invention, there is provided a method of controlling the flight path of ink droplets ejected from the nozzle of an ink jet print head having a supply of ink fluid thereto, comprising the steps of providing a conduit to define a path for ink fluid to be moved from said supply to said nozzle, moving said ink fluid in stream-like manner from said supply to said nozzle, and forming droplets of ink at said nozzle in a path aligned with said con- duit, characterized by providing said print head with a resilient portion, and by deforming said resilient por¬ tion so as to tilt the nozzle whereby droplets of ink are caused to be moved in a path at an angle with respect to said conduit. In a preferred embodiment of the invention, the tilting movement of the nozzle or nozzle plate of a pulse-on-demand type print head is effected by use of an electromagnet which is positioned in the vicinity of the nozzle plate and operated to cause tilting of the plate for controlling the flight path of ink droplets from the nozzle or nozzles. The nozzle plate is attached to a metal vane which in turn is attached to a resilient layer portion of the print head. The metal vane has a portion adjacent the electromagnet and is moved or tilted by actuation of the electromagnet wherein the vane is controlled in attitude thereby and is easily moved with respect to the resiliency of the resilient layer portion. The ink which passes through the nozzle and is ejected therefrom in ink droplet form is directed in a path which is dependent upon the angle or incline of the orifice in the nozzle plate. The nozzle plate, in effect, is subject to movement about a pivot located at the center of the orifice therethrough.

Another embodiment of the invention includes the use of an electrical conductor adjacent the nozzle plate, which plate is in the form of a permanent magnet. A magnetic field is generated by an electric current flowing through the conductor which field induces an

oscillating movement of the nozzle plate and of the nozzles. The pivot point of the nozzle plate movement is the center of gravity of the plate so as to minimize the mass and forces required to move the plate.

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 is a side elevational view, partly in section, of a print head according to the present invention;

Fig. 2 is a rear perspective view in partial section of a print head similar to that of Fig. 1 and showing a record medium; Fig. 3 is a non-proportional functional view showing a nozzle plate of the print head in a normal or at rest position;

Fig. 4 is a similar view showing the nozzle plate in a tilted position; Fig. 5 is a non-proportional view showing certain details of one form of connection of the nozzle plate assembly and the print head;

Fig. 6 is a view of a modification of the nozzle plate arrangement; Fig. 7 is a diagram of ink droplets on record media which is advancing at a predetermined velocity past the print head; and

Fig. 8 is a similar diagram of ink droplets on record media which is advancing at a lesser velocity past the print head.

Best Mode for Carrying Out the Invention

Referring now to the drawing. Fig. 1 is a side elevational view of a print head, generally designated as 10, which includes a plastic body or major portion 12 of cylindrical form incorporating at one end thereof a resilient portion or layer 14, preferably made of

silicone rubber and in the cylindrical form to match the major portion 12. An ink supply tube 16 carries ink into the rearward area of the plastic body 12 through a passageway 17 and into a circular chamber 18 formed as a cavity in the body portion. The ink supply tube 16 and its associated passageway 17 may be oriented in a hori¬ zontal position (Fig. 2) or any other position different therefrom as per the tube position of Fig. 1. A piezo¬ electric element 20 is secured to the rear face 22, as seen in Fig. 2, of the body portion 12 and includes a diaphragm element 24 covering and overlapping the chamber 18 and also includes a washer-like element 26 along with screws 28 for attaching to the body portion 12. A pair of electrical leads 30 and 32 are attached respectively to the center portion of the diaphragm element 24 and to the washer element 26 for use in pulsing the piezo¬ electric element 20.

A conduit or like passageway 34 is connected with the ink chamber 18 and extends forwardly through the center of the body portion 12 and through the front resilient portion 14 to a metal vane or like member 36 of generally rectangular form and which includes an orifice 37 therethrough connected and aligned with conduit 34. The metal vane 36 extends from near the bottom of the front surface of the resilient portion 14 upwardly across the face thereof and therebeyond to provide a portion 38 in upstanding manner. The vane 36 is secured to the resilient portion 14 by suitable means such as, for example, through use of an adhesive material and/or in the manner illustrated in Fig. 1 which includes pressing small portions of the resilient portion 14 into depres¬ sions 40 of the vane 36. Suffice it to say that the vane 36 may also include projections which are inserted into depressions in the portion 14 for securing the vane on the face of the member (see also Fig. 5). A plastic tube 42 is provided along a major length of the conduit or passageway 34 to improve the channelling of ink from the body portions 12 to the resilient portion 14 and

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thereby prevent ink leakage at the junction between such two portions 12 and 14.

A nozzle plate 44 is secured to the metal vane 36 and includes an orifice 46 therein fo ejecting droplets 48 of ink from the print head 10 and onto paper or like record media 50 spaced therefrom and appearing thereon as one or more dots 51 (Fig. 2). The direction and flight path of the droplets 48 emitted from the orifice 46 are controlled by the attitude of the nozzle plate 44 on the metal vane 36. The flight path of the ink droplets 48 can be changed or selectively controlled by moving or tilting the orifice 46 of the nozzle plate 44 a predetermined amount relative to the normal ink channel 34 direction, which is permitted by the flexi- bility of the plastic tube 42. The tilting movement of the nozzle plate 44 is accomplished by an electro-magnet 52 which is supported by the body portion 12 of the print head by means of an angular bracket member *>4. A pair of electrical wire leads 56 and 58 are connected to the electromagnet 52 for energization thereof during operation of the print head 10. Figs. 1 and 2 show the movement of the metal vane 36 caused by association of the upper portion 38 thereof with the electromagnet 52 to deform the resilient portion 14 so as to bring about a tilting motion of the nozzle plate 44 to direct the ink droplet 48 from the solid line path to the dotted line path.

Figs. ^' 3 and 4 are detailed views of the major portions of the print head 10 which include the body portion or element 12, the resilient layer portion 14 and the metal vane 36 along with the electromagnet 52 (shown in diagrammatic form) . The ink is caused to be driven by the piezoelectric element 20 along the passageway 34 through an aperture 37 in the metal vane 36 and then through the orifice 46 in the nozzle plate 44 and ejected as a droplet 48. In Fig. 3 the electromagnet

52 is illustrated in its non-energized state whereby the metal vane 36 along with the nozzle plate 44 assume a

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nor al position or relationship with respect to the path of the ink through the passageway 34. In Fig. 4 the electromagnet 52 is shown energized with the upstanding portion 38 of the metal vane 36 attracted by the " electromagnet in a manner to deform the resilient portion 14 and to tilt the vane 36 and the nozzle plate 44 to cause ejection of the ink droplets 48 in a different path toward the record media.

A further method of connecting the metal vane 36 to the resilient portion 14 and of the portion 14 to the body portion 12 is best understood from Fig. 5. The plastic tube 42 channels the ink through the aperture 37 in the vane 36 and through the orifice 46 in the nozzle plate 44 to effect the ejection of the ink droplets 48. As shown in detail, the resilient portion 14 includes connecting fingers or projections 60 which are embedded in the body portion 12. Likewise, the metal vane 36 includes connecting fingers or projections 62 embedded in the resilient portion 14. Representative diameters of orifice 37 in the vane 36 and of orifice 46 in the plate 44 are 0.6 millimeter and 0.07 millimeter, respectively.

Fig. 6 shows an embodiment in which alter¬ native means are provided for bringing about the tilting movement of the nozzle plate. In this embodiment, a body portion 70 incorporates a resilient layer 72 in¬ cluding two ink conduits 74 for carrying ink to the respective nozzles formed in nozzle plates 76 and 84. The nozzle plates 76, 84 are permanent magnets each including a north pole and a south pole and the tilting thereof is accomplished by means of a magnetic field generated by an electric current flowing through a con¬ ducting wire including portions 78, 80 and 82 and so trained around the nozzle plates 76, 84 that at any time the direction of current flow in the portions 78 and 82 thereof is opposite to the direction of current- flow in the portion 80. Thus, at any time, the two noz¬ zle plates 76 and 84 are tilted in opposite senses in

response to a flow of current through the conducting wire. In Fig. 6, the nozzle plate 76 is shown to be tilted for ejection of a droplet 79 in an upward direc¬ tion, while the nozzle plate 84 is shown to be tilted for ejection of a droplet 86 in a downward direction.

The sense of tilting of the nozzle plates 76, 84 can be reversed by reversing the sense of current flow in the conducting wire. Thus, alternating current passed through the conducting wire will induce an oscillatory movement of the nozzle plates 76, 84 on a pivot which is located at the center of the orifice in the nozzle plate. This is once again permitted through flexibility of a plastic tube 75 extending thereto and of the sup¬ porting resilient layer 72 to which such nozzle plate is secured.

Operation of the print head shown in Fig. 6 is accomplished in rapid manner by tilting of the nozzle plates 76 and 84, which plates are made as small and thin as possible to eject the ink droplets 79, 86, and also by having the pivot point of the tilting movement of the nozzle plate in each instance being in the center of gravity of the plate. In this manner, only very small acceleration forces act on the surface of the ink fluid. Writing or recording with the ink jet print head disclosed herein is done by moving the paper 50

(Fig. 2) in a direction normal to the direction of ink droplet ejection. In this respect, the paper is usually advanced vertically past the print head or printing station and the droplets are ejected and deflected hori- zontally. The velocity of the vertical paper advance¬ ment determines the number of ink dots per unit length printed in a vertical line at a given rate of ink drop¬ let ejection. The faster the paper is advanced, the lower the number of dots per unit length in the vertical direction.

The number of dots per unit length in the horizontal direction is determined by the frequency of oscillation of the nozzle plate and the frequency of

drops emitted therefrom per second. Generally, the resonant oscillating frequency of the nozzle plate and of the elastic layer will be chosen in predetermined manner and the frequency of drop emission will be adjust- ed to obtain a suitable horizontal drop spacing of the horizontal lines. Therefore, a sinusoidal dot spacing is obtained in the horizontal direction unless the drop emission frequency is electronically varied in order to obtain an evenly-spaced dot pattern in the event this is necessary or desirable.

The effect of the vertical velocity ~ Vv and the horizontal velocity V as determined by the resonant oscillating frequency of deflection is illustrated in the dot patterns of Figs. 7 and 8. Both dot patterns are printed at the same oscillating frequency V. , however, the drop emission frequency is higher in the pattern shown in Fig. 8 and results in a higher number of dots per unit length in the vertical direction. The vertical spacing of the dots also may differ by reason of a higher paper advance rate in Fig. 7.

Different dot patterns can be produced by varying either the oscillating characteristics of the nozzle plate and/or the vertical paper advance rate and/or the drop emission frequency. The desired charac- ters are printed by appropriate control of the pulse-on- demand drop emission at a relatively arbitrary resolution as defined by the preselected dot pattern spacing.