Abstract:
An ink jet recorder of the continuous jet type has a mounting block defining a reference surface. Nozzle units from which the ink streams are ejected are releasably keyed to the reference surface. An ink reservoir supplies electrically conductive ink to the nozzle units which selectively charge segments of the ink streams issuing from the nozzle units. Each unit also includes provision for accurately aiming the ink stream in both the x and y directions using simple knob controls. A deflection unit also releasably keyed to the reference surface downstream from the nozzle units. 
     The ink stream is directed through a deflection unit mounted on the reference surface. Mating members are provided in said mounting block which corresponds with mating members on the deflection unit. This unit generates an electrical field which deflects the selectively charged segments of the ink stream issuing from the nozzle unit, from their predetermined paths so that they do not reach the recording medium; the undeflected portions of the ink streams form the printing on the medium. The deflection unit also includes provision for removing extraneous ink from the regions of the deflection field so as to minimize background coloration in the printing on the medium. A charged mist shield is provided in said deflection unit to further attract extraneous ink in and about said deflection unit. Vacuum means are provided to withdraw extraneous ink from said deflection unit, nozzle unit, and mist shield.

Description:
This invention relates to an ink jet recorder and more particularly to an ink jet recorder which is capable of high resolution and faithful reproduction of images, yet permits user maintenance, replacement, installation and adjustment of the ink jet nozzle and deflection units. The invention also relates to a nozzle unit having an improved reliability, as well as to a deflection unit which minimizes background coloration of the recorded images. 
     BACKGROUND OF THE INVENTION 
     Ink jet recorders have been the subject of an intense development effort for a number of years. The recorders fall generally into two categories, namely drop-on-demand and continuous stream types. The present invention is directed to the latter type of recorder whose operation is described in detail in U.S. Pat. No. 3,416,153. In general, a continuous ink jet recorder produces a liquid jet by pumping the ink under high pressure through a capillary nozzle unit and directing the jet along a path toward a recording medium such as a paper sheet. As the jet issues from the nozzle it is selectively charged. A transverse electric field deflects the charged portions of the ink jet from the path into a gutter so that they are prevented from reaching the recording medium. The uncharged, and thus undeflected, portions of the jet reach the recording medium and form the printing thereon. 
     In continuous jet printers, the voltage of the deflection field is quite high. Particles from the ink stream which rebound upon impact with the recording surface instead of adhering to that surface, as well as particles from the ink stream which were deflected, cause an ink mist to develop in the region of the field. The ink mist particles of the different color inks are entrained in the segments of the ink streams that reach the recording surfaces and thus contaminate the color printing on that surface giving it a pronounced background coloration. This ink mist also reduces the voltage of the deflection field and sometimes causes arcing in the field region resulting in improper deflection of the ink streams and irregular printing on the recording surface. 
     In addition, prior printers of this type are plagued by clogging of their nozzle units by the recording liquid while the ink jet recorder is in operation. This gives rise to increased down-time and increased nozzle relacement costs. Further, none of the prior recorders of which we are aware have permitted simple adjustments by the user of the directions of the ink streams. Nor do they have low cost nozzle and deflection units which are easily removed and positioned. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide an improved ink jet recorder. 
     Another object is to provide improved units for use in such a recorder. 
     Another object is to provide a recorder whose nozzle and deflection units are quite reliable yet are easily repaired or replaced in the event that becomes necessary. 
     The nozzle units of this recorder are less prone to clogging and they can be targeted easily by the user to produce high quality printing on the recording surface which is free of background colorations. 
     Thus, this recorder incorporates a set of nozzle units in modular form each of which is adjustable and replacable separately from the others. The deflection unit is also made as a module which is replacable as a unitary structure. The nozzle units and the deflection unit are all separately keyed to a mounting block so that they can be installed and replaced quite easily. The mounting block also has all the necessary electrical and pneumatic connections for the nozzle units and these are automatically connnected to the units when the units are keyed to the mounting block. Likewise, the mounting block has all necessary pneumatic connections for the deflection unit, and these are automatically connected to the unit which the unit is keyed to the mounting block. 
     The present invention accordingly comprises the features of construction, combinations of elements, and arrangements of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings in which 
     FIG. 1 is a top plan view of an ink-jet recorder embodying the invention; 
     FIG. 2 is a side elevational view thereof; 
     FIG. 3 is a front elevational view with a part broken away taken through plane 3--3 of FIG. 1; 
     FIG. 4 is a sectional view thereof with a part broken away taken through plane 4--4 of FIG. 1; 
     FIG. 5 is a similar view on a larger scale thereof taken through plane 5--5 of FIG. 1; and 
     FIG. 6 is a sectional view taken through plane 6--6 of FIG. 5. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to FIGS. 1 and 2, an ink jet recorder includes four nozzle units 1a-1d which are a mounted on a mounting block 3. Ink streams or jets 5a-5d are projected from the nozzle units 1a-1d through a deflection unit 7 toward a recording surface 9 which in illustrated recorder is a paper sheet wrapped around a rotary drum. Some segments of each of the ink streams 5a-5d are charged in the corresponding nozzle units 1a-1d. These charged segments are deflected downward into a gutter (not shown) by an electric field in the deflection unit 7 and discarded. The uncharged segments of the ink streams 5a-5d pass through deflection unit 7 to the recording surface 9 forming printing thereon. The surface 9 rotates about a central axis 11, while the mounting block 3, with the nozzle units 1a-1d and deflection unit 7 mounted thereon, is moved in the longitudinal direction relative to the recording surface (ie. parallel to the axis 11). This causes the ink streams 5a-5d to sweep over the recording surface in a raster type of operation. 
     As is customary in recorders of this type, one of the ink streams is black and the other three have the three primary subtractive colors, i.e. cyan, magenta and yellow. Thus by selectively charging various segments of the ink streams and thereby controlling the color densities of corresponding segments of the raster lines traced by them, the colored inks can be laid down one over the other so as to imprint a full-color image on the recording surface 9. A vacuum system, described in detail below, incorporates a suction pump 13 to evacuate extraneous ink from the nozzle units 5a-5d and the deflection unit 7. 
     Referring now to FIGS. 1 and 5, nozzle units 1a to 1d are all more or less identical. Therefore, we will describe only one unit, namely unit 1b in detail. It includes a tubular capillary housing 15 having an elongated capillary holder 17 mounted axially therein. A capillary 19, consisting of a brass sheathing 21 and a glass capillary containted therein and ending in an exposed tip 23 mounted on one end and a stainless steel barrel 25 mounted on its opposite end, is retained within holder 17. A charge adapter 27 is plugged into the free end of barrel 25 inside holder 17. As best seen in FIG. 1, a pump 29b pumps an electrically conductive ink from a reservoir 31b through a conduit 33b to the charge adapter 27. From the adapter 27 the ink flows through the barrel 25 and the tube 21 to tip 23. The ink leaves the tip 23 in a stream 5b which shortly breaks up into individual droplets. 
     As shown in FIG. 5, the capillary 19 is inserted into capillary holder 17 from the right end in that figure until barrel 25 seats on an internal shoulder provided in the capillary holder. The inside wall of the holder is tapered to guide the nozzle end of tube 19 into a frustoconical ejection chamber 32 formed at the left end of the capillary holder 17. An electrically conductive 0-ring 34 is provided between the tube and the chamber wall to seal the joint between the two. After the capillary 19 is inserted into holder 17, the charge adapter is threaded into the barrel end of the capillary. The capillary 19 is secured there by tightening of a screw 35 received in two registering threaded apertures 36 in the capillary holder 17 which are separated by a slot 38 in the holder. 
     As best seen in FIGS. 5 and 6, the capillary holder 17 is supported within the capillary housing 15 at its rear (i.e. right) end by a spring 37 which extends up from base 3 through an opening into wall of capillary housing 15 and engages under the holder 17. The forward (i.e. left) end of the capillary holder 17 is supported within housing 15 by a pin 39 which extends transversely through the holder 17, the opposite flanged ends of the pin being received in apertures 41 formed in the opposite side walls of the capillary housing 15. Further, lateral support is provided to the capillary holder 17 by pin 39, an interior projection 43 on a sidewall of housing 15 adjacent its right hand and a spring 45 (FIG. 6) fixed to the other housing side wall directly opposite the projection 43. When holder 17 reposes in the housing as shown, spring 45 presses it against projection 43 thereby fixing the lateral position of the holder. 
     The housing 15 is positioned and keyed to the upper surface 51 of block 3 which constitutes a reference surface. More particularly, projections 53 and 55 project down from the underside of housing 15 to apertures 57 and 59 formed in the mounting block 3. 
     Referring now to FIGS. 1,2,5 and 6, the capillary housing 15 is releasably secured to the reference surface 51 by an arm 65 which extends down from the bottom wall of the housing into a cavity provided in the top wall of block 3. Arm 65 is angled rearwardly (i.e. to the right in FIG. 5) parallel to the longitudinal axis of housing 15. Its end engages in a slot 67a of an elongated transverse tube 67 rotatively mounted in block 3 so that it intercepts cavity 68. The arm 65 is positioned within cavity 68. Tube 67 is rotatable between a first angular position shown in FIG. 5 wherein the upper edge of the tube slot 67a engages and holds the end of arm 65 against the bottom of block cavity 68 thereby clamping the nozzle unit 1b to the block and a second position wherein the lower wall of tube slot 67a engages the underside of the arm and the nozzle unit as a whole may be moved away from block 3. The tube is biased to its first, i.e., clamping position by a torsion spring 69 which encircles the tube at one end, one wall of the spring being retained by retainer 71 on the tube and the other being anchored to block 3. Thus by rotating tube 67 clockwise from its first to its second position, using its handle 73, all of the units 11 are jacked away from block 3. Those needing repair can be removed and replaced with operative units. Then all of the units are clamped to the block by rotating of the tube counterclockwise under the action of said spring 69 to its position shown in FIG. 5. 
     Referring now to FIGS. 1, 2, and 5, a passage 75 leads from ejection chamber 32 of capillary holder 17 to a flexible tube 77 which communicates with an axial passage 78 in housing projection 55 when the housing is clamped to block 3 as aforesaid, passage 78 communicates with a conduit 79 which leads from the corresponding block aperture 59 to a port 81 in the mounting block 3, as shown in FIG. 1. An external conduit 83 connects the port 81 with the suction pump 13 which draws a vacuum to suck surplus or extraneous ink from the ejection chamber 32 of each capillary holder 17 to a waste reservoir 85. 
     Referring again to FIG. 5, the present recorder includes means to manually change the orientation of the capillary 19 within the capillary housing 15 so that the path of the ink stream produced by each nozzle unit is altered. More particularly, a vertical hole 87 is provided in the upper wall of housing 15 adjacent its forward or nozzle end. A pin 91 which is rotatively received in that hole has a lower end which is formed as an eccentric which extends into a slightly undersized aperture in the capillary holder 17. A similar aperture is positioned in an adjacent face of the capillary holder 17 creating an L-shaped cavity into which the eccentric end of pin 91 extends. Thus, a wall 95 of the capillary holder 17 between the aforesaid adjacent apertures provides a compression force on the pin 91. An o-ring 97 is engaged around pin 91 in a countersunk portion of hole 87, such that the turning of the pin is inhibited but not prevented. Rotation of pin 91 moves capillary holder 17 and, thus the capillary 19, therein, laterally within its housing 15 about pivot point defined by the housing projection member 43 without backlash or other undesirable consequences due to flexing of parts. Thus, by rotating pin 91 in one direction or the other, the ink stream can be aimed in the transverse direction, i.e. along the X axis. 
     Still referring to FIG. 5, a second vertical hole 89 is present in housing 15 adjacent its rear or right hand end. This hole is threaded to accept threaded pin 93. The pin 93 contacts a flexible, insulating strip 99 which is secured at its upper end to the upper wall of housing 15 and extends downward and along the top of capillary holder 17. The spring 37 described previously is positioned within housing projection 53 and extends upward and contacts the capillary holder 17 approximately opposite the pin 93. It thus urges the holder 17 upwardly against the pin 93. An anti-rotation spring clip 100 is provided around the upwardly raised portion aroung aperture 89 and contacts the pin 93 through a void in said upwardly raised portion to inhibit unintended movement of the pin 93. 
     Rotation of pin 93 results in the pivoting of the capillary holder 17, and thus the capillary 19 therein, about a pivot point defined by the pin 39 that supports the nozzle end of this holder 17. The strip 99, further, operates as a insulating member preventing the circular motion of the pin 93 from being transmitted to the capillary holder 17. Thus by rotating the pin in one direction or the other, the ink stream ejected from the capillary 19 can be aimed vertically along the y axis. 
     Thus, using both pins 91 and 93, the ink stream can be aimed in two mutually perpendicular x and y directions that are orthogonal to the longitudinal axis of the nozzle unit. Preferably, the outer ends of the pins are formed as knobs so that these adjustments can be made without requiring any tools or other special apparatus. 
     Referring now to FIGS. 1,2 and 5, a switch controller 101 selectively charges or discharges the ink in the capillary. The switch controller 101 is connected to an electrical source 103 and to ground at 105 which it selectively connects to conductors 107a-107d leading to the nozzle units 1a to 1d. As best seen in FIG. 5, a rod-like spring-loaded contact 109 is mounted to each capillary holder 17. It extends through housing projection 53 into the aperture 57 in block 3. Contact 109 is spring-loaded downwards into engagement with an electrical contact 111 mounted at the bottom of aperture 57. The four aforementioned conductors 107a-107d are connected separately to the contacts 111 of the four nozzle units 1a to 1d. Thus, using switch controller 101, a charge may be applied selectively to or discharged from segments of the ink while the ink is passing through each of the nozzle units. In this connection, it should be noted that the stainless steel charge adaptor 27, the stainless steel barrel 25 and conductive O-ring 34 all contact the capillary holder 17 which is made of a conductive plastic and to which electrical contact 109 is connected. 
     Referring now to FIGS. 1, 5 and 6, the deflection unit 7 of the recorder is mounted on reference surface 51 of mounting block 3 downstream from the ejection end of the nozzle units 1a-1d. The ink streams 5a-5d pass through corresponding apertures 119 in an upwardly extending wall of a ground electrode 120. The apparatus is positioned such that the &#34;droplet formation point&#34; of the ink streams 5a-5d occur while the ink streams are passing through these apertures. The four separate ink streams 5a-5d then enter an intense electrical field generated between the ground electrode 120 and a deflection electrode 122 whose polarity is such as to repel the selectively charged segments of the ink streams 5a-5d. Thus, the charged segments of the ink streams 5a-5d are deflected toward the ground electrode 120, while passing through the electric field, and these deflected portions of the ink streams are then inhibited or otherwise stopped by a knife edge 124 mounted to the top of electrode 120 and which forms a gutter for the ink. Undeflected portions of the ink streams 5a-5d exit the electric field and pass through four similar apertures 125 in a mist shield 126 which is positioned on the forward edge of the deflection unit 7. Only the ink droplets passing through the apertures in mist shield 126 strike recording surface 9. Extraneous ink building up on the mist shield 126, deflection electrode 122, and ground electrode 120 is removed therefrom by the action of suction pump 13, as described hereafter. 
     The deflection unit 7 includes an upper support 128 positioned on a base 130 along with ground electrode 120. The base 130 is, in turn, positioned on mounting block 3. The upper support 128 supports deflection electrode 122. Lower, exposed faces 132 of the upper support 128 are tapered toward the deflection electrode 122 so that extraneous ink accumulating thereon is urged toward the deflection electrode 122. Lips 134 are also provided on the upper support 128 to urge ink forming thereon to migrate downward and thus reduce the potential for arcing that is commonly associated with the buildup of extraneous ink. 
     An airtight seal is provided over the upper support 128 by a cover 136 which is secured on the support. The mist shield 126 is secured along its upper edge to the cover 136 and along its lower edge to the base 130. The cover 136 is provided with a downwardly-forwardly tapered projection 138 between the upper support 128 and the mist shield 126 which encourages extraneous ink forming thereon to go to the mist shield 126. 
     As shown in FIGS. 2,3, and 4, the base 130 is located on the reference surface 51 by projections 140,142,144 extending down from base 130 into corresponding apertures 146,148,150 in the top of mounting block 3. The upper support 128 is, in turn, located on the base 130 by projections 152 and 154 extending down from support 128 into corresponding apertures 156 and 158 in the base 130. 
     Deflection electrode 122 receives the vacuum drawn by suction pump 13 through a vertical passage 160 which abuts the deflection electrode 122 and extends down through projection 152 and communicates with a passage 162 through projection 140 in base 130. A gas-tight fit between the projection 152 and aperture 156 is provided by an o-ring 164 engaged around projection 152. Passage 162 extends through the projection 140 and communicates with a conduit 165 which extends from aperture 146 into a couter-bored aperture l66a extending upwardly from the bottom of the block 3.A gas tight fit is provided between male projection 140 and the aperture 146 by o-ring 168 encircling projection 140 and engaging the wall of the aperture 146. The conduit 165 is connected to the vacuum pump 13 through a conduit l70a. 
     The ground electrode 120 receives the vacuum drawn by pump 13 by way of a conduit 174 which abuts the open space beneath the ground electrode 120 which is sealed. Conduit 174 extends down through projection 142 and communicates with a conduit 175 which extends from aperture 148 into counter-bored aperture l66b, which extends upwardly from the bottom of said block 3. A gas tight fit is provided between the projection 142 and the aperture 148 wall by an o-ring 176 encircling the projection 142. The conduit 175 is connected via a conduit 170b to the vacuum pump 13. 
     Extraneous ink is extracted from the mist shield 126 to the suction pump 13 through a conduit 178 which has one end abutting the mist shield 126 as shown in FIG. 6. That conduit extends through base 130 and down through projection 144 so as to communicate with conduit 179 which extends from the aperture 150 into a counterbored aperture 166b which extends upwardly from the bottom of the block 3. A gas tight fit between the male member 144 and aperture 150 is provided by an o-ring 180 encircling projection 144 ensures a gas-tight fit at that location. The conduit 179 is connected via a conduit 170c to the vacuum pump 13. 
     As shown in FIGS. 1 to 3, a pair of levers 182 are pivotally mounted to opposite sides of the deflection unit 7 on pivot pins 184 which are secured between members 186 projecting laterally from the unit. Each lever 182 an inwardly turned foot 188 which is adapted to engage in a recess 189 provided in the adjacent side wall of the mounting block 3. A spring (not shown) is secured at one end to the deflection unit 7 and its other end to the lever 182 in a known manner such that the upper end of each lever 182 is urged away from the deflection unit 7. Thus, the spring loaded levers operate to releasably clip the deflection unit 7 to the mounting block 3. When the upper ends of the levers are pressed toward unit 7, their feet are retracted from the block apertures whereby the deflection unit 7 may be removed from the mounting block 3. 
     An electrical contact 190 is positioned along the upper edge of the deflection electrode 122. It is connected at one end to an electrical conductor 192 which is, in turn, connected to the voltage source 103 so that an electrical potential of the polarity which repels the charged portions of the ink streams 5a-5d is applied to the deflection electrode 122. Another electrical conductor 194 connected to ground at 196 leads to the ground electrode 120. A third electrical conductor 198 is connected at one end to the source 103 and at the opposite end to the mist shield 126, whereby the mist shield 126 is electrically charged so as to attract the extraneous ink mist. 
     The operation and use of the ink jet recorder of the present invention involves a flow of conductive ink under pressure generated by the pumps 29a-29d from the ink reservoirs 31a-31d to the nozzle units 2a-2d through passage 33a-33d. The ink pushed by the pumps 29a-29d reaches the charge adaptors 9 through passages 33a-33d. The conductive charge adaptors are secured in the conductive capillary holders 17. The ink is then delivered to the capillaries 19. Electrical current of between 30 and 200 volts are selectively imparted to the ink as it passes through the capillaries 19 from the electrical source 103 by way of the switching means 101 which selectively connects the electrical contact 111 to the ground conductor 105 or to the source 103 via the electrical conductors 107a--107d. 
     The ink streams 5a-5d which are ejected from the capillaries 19 enter the deflection unit 7 which is positioned so that the droplet formation point occurs while the ink streams 5a-5d are passing through the apertures in the ground electrode 120. The droplets of the ink streams 5a-5d then enter an electrical field generated between the deflection electrode 122 and ground electrode 120. A high intensity as a high electrical potential between 500 and 2,200 volts is applied to the deflection electrode from source 103, while the ground electrode 120 is maintained at ground potential. The electrical field thus generated causes the portions of the ink streams 5a-5d, which have been selectively charged, to be repelled by the deflection electrode 122 and directed towards the ground electrode 120 and thereby into the knife edge 124. The knife edge 124, which in the preferred embodiment is an ultra thin razor blade, is set at a substantial angle between 45° and 75° to the ground electrode 120 and extends upward to a height just below the predetermined paths of the ink streams 5a-5d to the recording surface 9. Ink building up on the angled knife edge 124, is thereby urged downward along the opposite faces of the knife edge 124 toward the ground electrode 120. 
     Ink deflected into the knife edge 124 is also dispersed upon impact in the form of ink mist into the region in and about the deflection unit 7. The ground electrode 120, deflection electrode 122, and mist shield 126 are therefore preferably formed of a porous, electrically conductive material such as sintered carbon, so that extraneous ink (e.g. the ink mist formed within the deflection unit as well as ink mist condensate, misaimed ink, the ink deflected by the knife edge 124 not being dispersed or other ink not following the predetermined path) which strikes or otherwise contacts the deflection electrode 122, ground electrode 120, or mist shield 126, is removed from the deflection units by the action of the pump 13. Further, as previously described the internal structure of the deflection unit 7 encourages migration of extraneous ink to the ground electrode 120, deflection electrode 122 and mist shield 126. 
     Undeflected ink which follows the predetermined trajectory toward the recording suface 9 then passes through the aperture in the mist shield 126 and strikes the recording surface 9 forming the printing thereon. Additional extraneous ink may be formed upon impact of segments of the ink streams 5a-5d with the recording surface 9 because part of the ink may rebound therefrom. Such extraneous ink is collected by the mist shield 126, from which it is extracted by the action of the pump 13 in a manner described previously. 
     The present recorder disclosed herein thus provides improved resolution by reducing the background color effects due to the presence of extraneous ink. Yet the recorder is simple to make and maintain in that its deflection and nozzle units can be installed, and the latter aligned quite easily, Accordingly, it allows nontechnical persons to intervene and rectify problems with the recorder. The simplicity of the recorder also allows greater efficiency in mass producing of its components. A further advantage is gained from providing an frustoconical ink ejection chamber having the described flared construction to reduce clogging in the nozzle unit and the buildup of extraneous ink. The aforementioned improved geometry of the deflection unit likewise minimizes the problems associated with buildup of extraneous ink. 
     It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and that certain changes may be made in the above arrangement of the components or other alterations apparent to those skilled in the art, without departing from the scope of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limited sense.