EP0605386B1

Movatterモバイル変換

Info

Publication number: EP0605386B1
Application number: EP94101081A
Authority: EP
Inventors: Takashi C/O Seiko Epson Corporation Suzuki; Yoshinori C/O Seiko Epson Corporation Miyazawa; Masanao C/O Seiko Epson Corporation Matsuzawa
Original assignee: Seiko Epson Corp
Current assignee: Seiko Epson Corp
Priority date: 1984-05-22
Filing date: 1984-10-09
Publication date: 2001-03-14
Anticipated expiration: 2004-10-09
Also published as: DE3486334D1; EP0605386A3; DE3486482T2; DE3486481T2; EP0605388A3; DE3486334T2; HK73395A; EP0406982A3; DE3486337T2; DE3486480T2; DE3486485D1; DE3486485T2; EP0406983A3; SG26403G; EP0605388A2; SG52578A1; EP0605387A2; EP0749839A2; EP0605387A3; EP0605389A2

Description

The present invention relates to an inktank. The invention is exemplified in the following byreferring to an ink tank for a wire dotmatrix printer head. Such wire dot printerhead has wires supplied with ink at distal end facesand movable against a sheet of print paper fortransferring ink to the sheet in the form of dots torecord a character, a figure, a graphic image or thelike on the sheet.
An ink supply system for a wire dot matrix printeris known in which an ink ribbon is not used, but ink issupplied from an ink tank to the distal ends of the wireand transferred from the wires directly to a sheet ofprint paper. One known ink guide mechanism for such anink supply system is disclosed in US-A-4,194,846 andcomprises a porous member capable of absorbing ink froman ink tank, the ink guide mechanism having wirescontacting the porous member. The porous member containsfine holes whose sizes or diameters vary in a certainrange, with the result that the ink absorbing capabilityvaries from porous member to porous member, and bothexcessive and insufficient quantities of ink are liableto be supplied to the distal ends of the wires. Thequantities of ink retained in the vicinity of the distalends of the wires differ widely, and the porous memberis liable to vary in dimensions or to be deformed due tocoaction with the sides of the wires. Consequently, theink densities of the so-formed dots are irregular.
EP-A-97,009 discloses another ink supply mechanismin which ink is supplied from an ink tank to the distalends of wires by means of a pump. The ink supply mechanism of EP-A-97,009 has, however, the disadvantagethat the construction of the connection between the pumpand a printer head is complex and results in increasedcost. It is necessary to provide a good seal so as toobtain good pump performance, and a large-torque drivesource is required for driving the pump. The ink supplymechanism is particularly complex in the case of amulti-colour printer head, and such an ink supplymechanism is not suitable for use with a small printerhead.
In DE-A-2,546,835 there is disclosed a wire dotmatrix printer head comprising an ink tank; a wire guidemeans having a portion which is arranged to receive inkfrom the ink tank; and a printing wire a distal endportion of which is mounted in a hole in the wire guidemeans, the wire guide means having a capillary ink pathwhich communicates both with the said portion of thewire guide means and with a distal end portion of theprinting wire so as to supply ink to the latter.
In DE-A-2,546,835, however, the ink tank containsliquid ink which enters one end of the capillary inkpath, with the result that ink flow is liable to vary orto be interrupted if the liquid ink contains particlesof dust etc. which clog the capillary ink path.Furthermore, the wire guide means is so constructed thatany air which has been drawn into the ink by capillaryforce cannot escape therefrom prior to reaching thedistal end surface of the wire guide means, with theresult that the air can expand under the low pressurewhich is present and cause flow problems. Additionally,no means are provided for preventing excessive inkaccumulating on the distal end surface of the wire guidemeans.
In EP-A-0,042,293 there is disclosed a wire dotmatrix printer head comprising an ink supply means; awire guide means having a portion which is arranged toreceive ink from the ink supply which and which has adistal end surface; and a printing wire a distal endportion of which is mounted in a hole in the wire guidemeans with a gap therebetween, the wire guide meanshaving a capillary ink path which communicates both withthe said portion and the distal end surface of the wireguide means and with the distal end portion of theprinting wire so as to supply ink to the latter, thesaid hole communicating with at least one inkcollection groove situated in the distal end surface ofthe wire guide means into which ink collection grooveany excessive ink on the distal end surface of the wireguide means is drawn under capillary attraction, the oreach ink collection groove being open to theatmosphere. In this construction, however, there is noprovision for ensuring that the force of capillaryattraction increases in the direction from the inksupply means to the said distal end surface with theresult that there can be wastage of ink in the said inksupply means, especially if air is trapped in thelatter.
In US-A-4 095 237 an ink reservoir or cartridge is disclosedwhich contains a porous filter and has an air hole. Thereservoir may be completely filled with the filter or onlypartially. However, no embodiment with a partially filledreservoir is described as well as no advantage beingmentioned.
It is therefore an object of the present invention toprovide a high-quality and highly reliable ink tank, which hasa simple construction which is capable of supplying a stableand appropriate quantity of ink from an ink tank and which isless subjected to the influence of environmental changes suchas temperature variations than prior constructions.
According to the present invention, therefore there isprovided an ink tank according to independent claim 1. Furtheradvantageous features and aspects of this ink tank are evidentfrom the dependent claims.
The ink tank comprises a top wall, a bottom walland walls extending therebetween. An ink supplyport is arranged in the bottom wall to receive inkfrom at least one porous member, which isimpregnated with ink under subatmospheric pressure and havingsubstantially no air layer or pocket enclosed by the ink. Theat least one porous member is arranged in theink tank such that only a projecting portion ofat least one wall contacts the at leastone porous member so that the remaining portionof the at least one wall is spaced at adistance from the at least one porous member andthat an air hole in one of the ink tank wallscommunicates air in the space with ambient air. The at leastone porous member has pores which progressivelyreduce in size.
The ink tank is preferably formed as a detachably mountedunit, said ink-supply tank being formed with a pluralityof ink-supply sections, each of said ink-supply sectionshaving an ink-supply delivery port. Each of said ink-supplysections contain an ink absorbing member formed by said porousmember and impregnated with ink,and at least two of said ink-supply sections carryingink of different colors.
Advantageously the unitary ink supply tank is formed with aplurality of ink-supply sections. Each of said ink-supplysections have an ink supply port. Said unitary ink supply tankcontains an ink absorbing member in each of said ink-supplysections formed by the porous member and impregnated with ink.
At least two of said ink-supplysections carry ink of different colors, said ink in said ink-supplysections are of a color other than black. Further, afurther separate ink supply tank is formed with an ink supplyport. A separate ink absorbing member is formed of a porousmaterial contained within said separate ink supply tank andimpregnated with ink,and the ink contained insaid separate ink supply tank is black.
Preferably, the ink absorbing member is compressed by the topwall of the ink supply tank.
Preferably, the ink absorbing member has a tapered portion.
Preferably, the ink absorbing member has a thicker portion inthe vicinity of the ink supply port.
The at least one porous member has preferably beenimpregnated with ink at a pressure lower than atmosphericpressure.
Preferably, the pressure at which the ink is impregnatedis in the range of 666 to 1333 Pa (5 to 10 mmHg).
Preferably, the pores of the porous member areprogressively reduced in size in a direction towards the inksupply port of the ink supply tank.
The ink absorbing means may comprise first andsecond porous members which are in contact with eachother so that ink may flow from one to the other.Moreover, the ink supply tank has an ink supplyport which is arranged to receive ink from the secondporous member, the first porous member having porestherein whose average diameter is greater than those ofthe second porous member.
The porous member is compressed in the vicinity of thesaid ink supply port.
A printer head suitable for using the ink tank accordingto the invention may comprise a printing wire, a distal endportion of which is mounted in a wire guide hole orholes of a wire guide means, portion of the wire guidemeans being arranged to receive ink from the inkabsorbing means, and the wire guide means having acapillary ink path which communicates both with the saidportion of the wire guide means and with the distal endportion of the printing wire.
The said ink absorbing means reduces the chance ofparticles of dust being carried into the capillary ink path. Moreover, air which has been drawn into the ink bycapillary force can escape therefrom through inkcollection groove or grooves, while the latter may serveto prevent excessive ink building up on the distal endsurface of the wire guide means.
The invention is illustrated, merely by way ofexample, in the accompanying drawings, in which:-
Figure 1 is an exploded perspective view of aprinter head using an ink tank according to the invention;
Figure 2 is an exploded perspective view, partlycut away, of an ink tank and ink supply guide formingpart of the printer head of Figure 1;
Figure 3 is a side elevational view illustratingthe manner in which an ink tank is mounted in place in ahead body of the printer head of Figure 1;
Figure 4 is an exploded perspective view of an inkguide which can be used with the ink tank according to theinvention;
Figure 5 is an exploded perspective view of an inktank according to the invention which may form part of aprinter head,
Figure 6 is a perspective view, partly brokenaway, of an ink tank previously known to the applicants;
Figure 7 is a schematic view to illustrate the wayin which air trapped in the ink tank of Figure 6 isexpanded; and
Figure 8 is a schematic view of a seven-columnprinter to illustrate an arrangement of wires thereof.
Figures 6 and 7 of the accompanying drawingsillustrate an ink tank construction previously known tothe applicants comprising an ink-impregnatedmember 160,e.g. of a porous material, which fills atank 140. Theink tank construction of Figures 6 and 7 is of a simpleshape and can supply a suitable amount of ink to a printer head body under appropriate capillary attractionby the ink-impregnatedmember 160. Themember 160 canbe impregnated with a large quantity of ink whilepreventing unwanted ink outflow from anair hole 142 inthetank 140 and from anink supply port 141.
When ink is supplied from theink tank 140 of sucha construction, the ink in theink tank 140 which isremote from the ink supply port is moved toward theinksupply port 141 under a pressure difference which isdeveloped between the ink close to theink supply port141 and the ink remote therefrom as capillary attractionof the ink-impregnatedmember 160 in the vicinity of theink supply port 141 is increased due to ink consumption.However, as can be seen in porous materials, as thequantity of impregnated ink is reduced, ink-impregnatedmembers are generally subjected to an increasedresistance to ink flow and to the fact that interruptedink paths prevent smooth ink flow. If the ink flow isprevented before a pressure difference is produced highenough to move the ink in theink tank 140, then the inkremote from theink supply port 141 remains in positionand unused, resulting in a short ink supply duration.
As shown schematically in Figure 7, theink tank140 frequently has pockets or layers of air trappedtherein. When the ambient temperature rises or theatmospheric pressure is lowered in such circumstances,anair layer 143 communicating directly with theairhole 142 is expanded and is discharged out of theairhole 142 as indicated by arrows A without applying anypressure to the impregnated ink, whereas apocket 144 ofcompletely trapped air is expanded as indicated by thearrows B and thus moves the surrounding ink. Uponarrival of such anair pocket 144 at theink supply port142, the resulting undesired ink outflow can cause a sheet of print paper to be smeared by an ink spot or canallow ink to find its way into the printer headmechanism, with a resulting malfunction of the latter.
A printer head is adapted for use in a multi-colourprinter. Movement is effected of the head of such aprinter or of a sheet of print paper or both, a wirecorresponding to a desired one of the colours beingdirected against the print paper at a prescribedposition thereon to form an ink dot. Desired charactersand figures can thus be produced by repeating the abovecycle. In such a colour image printer using inks ofdifferent colours, a sheet of print paper (or othermaterial) may be scanned by a printer head in adirection normal to the direction of feed of the printpaper to form a one-dot line in one scanning stroke, andthe print paper may be fed along by line pitches torecord images.
The construction of a multi-colour printer isschematically shown in Figure 8. A printer head 70 ismovable back and forth in the directions of an arrow X,and a sheet of print paper (or other material) 71 is fedalong successively at a one line pitch in the directionof an arrow Y. An array ofwire positions 72, 73, 74,75 on the printer head 70 extends along a straight lineinclined at an angle  with respect to the scanningdirections X, the wire positions being spaced in thedirection Y at a pitch of L sin . Yellow-ink, magentaink,cyan-ink, and black-ink wires (not shown) arelocated at thepositions 72, 73, 74 and 75,respectively, to effect colour-image printing free fromundesired colour mixing. Since a dot of one colour isout on top of a dot of another colour for mixed colourformation, multi-colour image printers are generally liable to suffer from unwanted colour mixing because theink of the former colour is applied to the wirecarrying the ink of the latter colour. In the printerconstruction of Figure 8, yellow ink, which is the inkmost affected in colour by inks of the other colours, isfirst applied to the print paper so as to prevent theinks of the other colours from being applied to the tipof the wire carrying the yellow ink, thus avoiding themixture of the yellow ink with the inks of the othercolours.
The present invention is concerned primarily withan ink tank for use in a printer head, and no further detaileddescription of the overall printer construction will thereforebe given.
Figure 1 is an exploded perspective view of a printer headusing an ink tank according to the present invention.The ink tank 2 is detachably mounted by a holder ontop of a printer head body 1. The ink tank 2 is of adouble construction composed of an ink tank 2b forcontaining a black ink and an ink tank 2a which is dividedinto three sections for coloured inks. The inks areimpregnated in ink-impregnated members 61, 62 (Figure 2)ormember 60" (Figure 5) of a porous material containedin the ink tank 2.
For each ink, the printer head body 1 has in itsfront portion an ink supply guide 12 (Figure 2) havingink guide grooves 12b with ends leading to therespective ink-impregnatedmember 61, 62 and a wireguide 13 (Figure 4) having a wire guide hole 13a forguiding the tip or distal end portion of a respectiveprinting wire (not shown) therein.
There are thus as shown in Figure 1 four ink tanksand associated wires etc, but in order to simplify thedescription below, reference will normally be made only to a single ink tank and its associated wire etc.
Theink supply guide 12 and thewire guide 13which form no part of the present inventionjointly form an ink path from the ink tank 2 to thedistal end portion of the wire. The printer head shownin Figures 1 and 2 is adapted for use in a four-colourprinter plotter or in a four-colour image printer, andfour wires are employed respectively corresponding tothe four colours.
In a standby position, the distal end portion ofthe wire is located rearwardly of adistal end surface13c of thewire guide 13, and the length of the wire isselected such that an ink meniscus formed in a frontportion of the wire guide hole 13a covers the distal endof the wire.
An ink guide assembly, which comprises aninksupply guide 12" and thewire guide 13, will bedescribed in greater detail with reference to Figure 4.
Theink supply guide 12" has acentral hole 12"ffor guiding the distal end portion of the wire. Theink supply guide 12" also has an axialink guide groove12"b leading to the ink-impregnatedmember 62. Theinkguide groove 12"b has a width and a depth selected suchthat ink will be stably supplied from the ink tank 2 asdescribed later on. Theink supply guide 12" has onafront surface 12"e thereof acircular groove 12"awhich communicates with theink guide groove 12"bthrough an inner portion (not shown). Thewire guide 13has aproximal end 13d thereof placed in thecircular groove12"a. There is only a small gap between the wire andthe peripheral surface defining the wire guide hole 13ain thewire guide 13. The ink is guided from the inktank 2 through theink guide groove 12"b in theinksupply guide 12" and through thewire guide 13 to thedistal end portion of the wire under capillary attraction.
One embodiment of the ink tank 2 according to the presentinvention will now be described in detailwith reference to Figure 2.
The ink tank 2, or each ink tank 2a, 2b, comprises anink tankbody 40, two stacked ink-impregnatedmembers 61, 62 of a porousmaterial which are disposed in the space in theink tank body40 so as to fill the latter, and alid 50. The ink-impregnatedmembers 61, 62 are impregnated with ink at a pressure belowatmospheric pressure ranging from 666 Pa to 1333 Pa (5 to 10mmHg), so that airremaining in the porous ink-impregnated members will bereduced as much as possible to increase the amount ofimpregnated ink. Theink tank body 40 has a bottom orinner wall surface 40a provided with a frontink supplyport 41 and afront wall 40b having anair hole 42defined in a stepped portion thereof. Theink supplyguide 12 has anarm 12d which is inserted in theinksupply port 41 and which projects from the printer headbody 1. The bottom or inner wall surface 40a of theinktank body 40 has a raised or projectingportion 44 inwhich there are a plurality ofslots 45a, 45b, 45c whichcommunicate with theink supply port 41. Theslots 45a,45b, 45c are disposed opposite to and communicate withthe ink supply grooves 12b provided in thearm 12d oftheink supply guide 12. Although not shown, theslots45a, 45b are joined together to form a single slot whichtogether with theslot 45c guides the ink into the inksupply grooves 12b. Theink tank body 40 also has aside wall 40c having on its inner wall surface aplurality ofvertical ridges 47 which project therefrom.Theridges 47 have lower ends held against the bottom40a and upper ends kept out of contact with thetank lid50. Theink tank body 40 further has afront partition48 which is disposed behind theair hole 42 and in front of theink supply port 41, thefront partition 48having one end joined to the side wall 40c. Thetank lid50 has on a lower orinner wall surface 50a thereof aplurality oflongitudinal ridges 51 which project fromthesurface 50a.
The space or hollow interior defined by the bottom40a, the side wall 40c, thepartition 48, and thelid 50of thetank body 50 accommodates therein the twoporousmembers 61, 62 as double layers which are held incontact with only the raisedsurface 44 of the bottom40a, thevertical ridges 47 of the side wall 40c, thepartition 48, and theridges 51 of thelid 50. Thusthere is a space 50b between the porous member 61 andtheinner wall surface 50a of thetank lid 50, and thisspace 50b communicates with theair hole 42. Theporousmembers 61, 62 have different average hole sizes ordiameters. The porous member 61, which has a largeraverage hole diameter, is placed on top of the otherporous member 62. Thus theporous member 62 which iscloser to theink supply port 41, is made of a porousmaterial having a smaller average hole diameter thanthat of the porous member 61, while the porous member61, which is further from theink supply port 41 has agreater average hole diameter than that of theporousmember 62.

In the ink guide assembly and the ink tank thusconstructed, the capillary attraction is successivelygreater along the ink path, that is, successively fromthe porous member 61 having the larger average holediameter to theporous member 62 having the smalleraverage hole diameter and thence to the

ink guide slots

45a, 45b, 45c provided in the raisedsurface 44 of thebottom or inner wall surface 40a of theink tank body 40and so to the ink guide grooves 12b provided in the inksupply guide arm 12d and hence to gaps between theinksupply guide 12 and thewire guide 13, and finally tothe gap between theink supply guide 12 and the wire andthe gap between thewire guide 12 and the wire. Theabove capillary attraction setting can be achieved byproviding the following dimensions:

The average hole diameter of the porous member 61	0.4 mm.
The average hole diameter of theporous member 62	0.3 mm.
The width of each of theink guide slots 45a, 45b, 45c	0.12 mm.
The width of the ink guide grooves 12b	0.1 mm
The gaps between theink supply guide 12 and thewire guide 13	0.1 mm
The gap between the surface defining the wire guide hole 13a and the wire	0.01 mm

A construction for removably attaching the inktank 2 will be described with reference to Figures 1 and3.
The printer head body 1 has ahead frame 30including side walls extending from upper and backportions of the printer head body 1 and serving as aholder support 31. Each of the side walls of theholder support 31 has aholder support hole 32, aleafspring 36 which is defined by twovertical recesses 33a,33b in theholder support 31 and which has aholderattachment hole 34, and aguide slot 35. Aholder 70ahas on each of its opposite sides a cylindricalprojection 71a, which is rotatably mounted in aholdersupport hole 32 in thehead frame 30, and asemispherical projection 72a, which is engageable in aholder attachment hole 34. Each of the ink tanks 2a, 2bhas a side disposed closer to therespective holder support 31 and having acylindrical projection 49engageable with a lower edge of therespective guideslot 35.
The ink tank 2 can be attached to theholder 70aand detached therefrom in the following manner.
Theholder 70a is supported in the position shownin Figure 3, and the ink tank 2 is inserted into theholder 70a in the direction of the arrow C. At thistime, the ink tank 2 is not required to be accuratelypositioned in theholder 70a and hence can easily beinserted into theholder 70a. Then, the holder 70#a isturned in the direction of the arrow D to bring theprojection 49 on each of the sides of the ink tank 2 intocontact with an edge of therespective guide slot 35 in thehead frame 30, whereupon the ink tank 2 is positionedwith respect to thehead frame 30.
Theink supply port 41 is now positioned correctlyabove thearm 12d of theink supply guide 12 whichprojects upwardly from the printer head body 1.
Continued turning movement of theholder 70a causes thearm 12d to engage in theink support port 41 and beinserted into the ink tank 2. Thesemisphericalprojection 72a on each side of thetank holder 70aengages and spreads theleaf springs 36 apart from eachother. Thesemispherical projections 72a finally engagein the attachment holes 34 in theleaf springs 36,whereupon theleaf springs 36 return to the verticalpositions to retain theholder 70a securely in position.At this time, theink guide slots 45a, 45b, 45c in thebottom or inner wall surface 40a of the ink tank 2 aredisposed opposite to the ink guide grooves 12b in thearm 12d of theink supply guide 12, thus forming partof the ink path from the ink tank 2 to the printer headbody 1. The ink tank 2 can be removed in a procedure which is the reverse of the attachment process describedabove.
In operation, the distal end of the wire projectsthrough the ink meniscus, carries ink thereon, and hitsa sheet of print paper (not shown) to transfer the inkto the print paper. When the wire is in a standbyposition, the distal end thereof is located inwardly ofthedistal end surface 13c of thewire guide 13 so thatan ink meniscus is formed in front of the distal end ofthe wire. Accordingly, ink is attached successively tothe distal end of the wire as the latter is projectedand retracted. The transfer of ink to the distal end ofthe wire 11, and other details of an inked-wire dotmatrix printing process are described inEP-A-97,009 and will therefore not bedescribed here in greater detail.
Any excessive ink on thedistal end surface 13c ofthewire guide 13 is drawn under capillary attractioninto cross-sectionally V-shaped collection grooves 13b(Figure 4) provided in the front and side surfaces ofthewire guide 13 and is returned to theink supplyguide 12 without smearing the print paper. The grooves13b are thus provided in the distal end surface of thewire guide 13 and communicate with the wire guide hole13a. As shown in Figure 4, the grooves 13b extend to theouter periphery of thewire guide 13 so as to be open tothe atmosphere.
The operation of the ink supply mechanism of theinked wire dot matrix printer head referred to abovewill now be described.
In order to obtain a proper dot density, it isnecessary to apply an appropriate quantity of ink stablyto the distal end of the wire. Therefore, the wire guidehole 13a should have a proper dimension in the vicinity of the distal end of the wire and a proper amount ofink, without either an excess or a shortage of ink,should be supplied from the ink tank 2.
In the printer head construction described above,the ink guide path from the ink tank 2 to a position inthe vicinity of the distal end of the wire, is composedof slots, grooves, and gaps. By selecting suitabledimensions of the widths of the slots, grooves, andgaps, the amount of ink necessary for printing can beguided to the distal end of the wire under appropriatecapillary attraction without causing an overflow.
An appropriate quantity of ink can be suppliedeven when the ink supply from the ink supply grooves 12bis reduced due to increased use of ink.
The dimensions of the ink supply grooves and gaps,the hole diameters of theporous members 61, 62 and thewidths of theslots 45a, 45b, 45c are selected so thatthe capillary attraction is progressively greater alongthe ink path. Therefore, ink will not be interrupted inthe ink path as described below.
The ink is consumed from the ink tank 2 asprinting progresses, ink flows from theporous member 62through the ink guide grooves 12b, or through the inkguide grooves 12b and theslots 45a, 45b, 45c, into theprinter head body 1. Since the ink moves transverselyacross theporous member 62 at this time, the distancethat the ink moves through theporous member 62 is smalland no ink interruption occurs. When ink in theporousmember 62 is consumed, a pressure difference immediatelyoccurs between the ink in the porous member 61 and theink in theporous member 62 due to the differencebetween their average hole diameters, and the samequantity of ink as is consumed is supplied from theporous member 61 to theporous member 62. No ink interruption takes place at this time since the inkmoves transversely in and across the porous member 61.The amount of ink retained in theporous member 62 thusremains substantially the same as ink which has been fedout. Therefore, as the printing operation progresses,the ink in the porous member 61 is first used up, andthen the ink in theporous member 62 is used up.
The ink guide mechanism in the printer head bodyoperates to produce the same advantage. If the flow ofink is interrupted in the ink path by reason ofvibrations or the like, a mass of ink which has been sointerrupted is moved forward until it is joined to apreceding mass of ink since the capillary attraction isgreater in the ink path than in the ink tank. Since thecapillary attraction is greater in the vicinity of thedistal end of the wire than in the portion of the inkpath in which the flow of ink is interrupted, no ink isretracted from the distal end of the wire, and hencethe dot density will not be rendered unstable evenmomentarily, so that all ink on the distal end of thewire can be used up.
In the ink tank construction described above, theink-impregnatedmembers 61, 62 are supported on theridges 47, 51 in theink tank body 40. The ink-impregnatedmembers 61, 62 are therefore surrounded by alayer of air which communicates by way of theair hole42 with the ambient air. Since the ink is impregnatedunder a low pressure, there is substantially no airlayer or pocket enclosed by the ink in the ink-impregnatedmembers 61, 62. Therefore, any expansion ofthe air in the tank 2 caused by a temperature rise or bya reduction in atmospheric pressure is released throughtheair hole 42, so that the pressure in the tank 2 isequalized to atmospheric pressure and does not force the ink out of the ink tank 2.
The ink tank 2 is therefore protected from an inkoutflow due to variations in temperature and atmosphericpressure, and is capable of supplying ink stably.
The ink tank 2 and the ink guide path forsupplying ink to the wire have dimensions dependent onthe accuracy of the shapes of the components. Since thecomponents can be easily formed with high dimensionalaccuracy, as by moulding, the ink tank 2 and the inkguide path can be highly dimensionally accurate and havea stable ink supply capability. The ink tank 2 and theink guide path can easily be assembled as they arecomposed of a small number of parts. They may bemaintained free from wear and deformation for a longperiod of use and can keep their initial performancepartly because of the lubrication effected by the ink.
As shown in Figure 4, theink guide groove 12"b hasmounted therein an ink guideporous member 12"e whichserves as an extension of the ink-impregnated members inthe ink tank. The operation of theink guide member 12"is essentially the same as that of themember 12 ofFigure 2.
Figure 5 is an exploded perspective view of anink tank 2" as a further embodiment of the present invention.The parts of the ink tank of Figure 7 other than aporous member 60" are the same as those in theembodiment shown in Figure 2. Theporous member 60" hasdifferent front and rear thicknesses so that the thickerfront portion, which is disposed adjacent to theinksupply port 41, is compressed by thetank lid 50 whentheporous member 60" is introduced into thetank body40. Therefore, even if theporous member 60" has uniformhole diameters, the front portion thereof, which isadjacent to theink supply port 41, has a smaller average hole diameter, with the hole diameter becomingprogressively greater toward the rear portion, which isremote from theink supply port 41, at the time when theporous member 60" is placed in theink tank body 40. Theporous member 60" is structurally equivalent to aplurality of porous sheet layers of different averagehole diameters which are placed in theink tank body 40"with the average hole diameters becoming progressivelygreater from the front to rear portion of themember60". Therefore, the operation of theporous member 60"is basically the same as that of theporous members 61,62 shown in Figure 2.
Although in the embodiment of Figure 1, the inktank 2 is placed above the printer head 1, the ink tank2 may be located below the wires to achieve a stableprinting density through the ink guiding processdescribed above.
In the constructions described above, ink can bestably supplied through a simple construction from anink tank to the distal end of a wire, and ink is stablyattached to the distal end of the wire for producing astable and proper ink dot density. The ink will not beinterrupted in the ink guide path and the risk of asupply failure will be reduced. The quantity of inkabsorbed in the ink guide path is smaller than would bethe case with a known arrangement in which a porousmember is used to apply ink to the distal end of thewire. Therefore, any wasted ink which is not used forprinting is of a small quantity, and hence substantiallyall the ink in the ink t4ank can effectively be used forprinting.
If the ink tank runs short of ink, or if the inkin the ink tank is rendered highly viscous by beingdried at a high temperature, or if the supply of ink fails due to its solidification, a fresh cartridge inktank can be mounted in place so that fresh ink canimmediately be supplied to the distal end of the wirefor resuming the desired printing operation.
In the printer head described above, no ink flowoccurs due to variations in temperature and atmosphericpressure and a stable ink dot density is available.Unwanted ink flow out of the ink tank is prevented, thusavoiding smearing the print paper with undesired inkspots. No ink will enter the printer head mechanism,which is prevented from malfunctioning. The cartridgeink tank can easily be detached and attached for inkreplenishment.
Since the described ink supply system issimple in construction, it takes up only a small space.Where a multi-colour printer head employs ink supplysystems as described above, the ink supply systems fordifferent ink colours can be spaced widely so that anyunwanted colour mixing can be avoided.

Claims

An ink tank for supplying a proper amount of ink needed toa dot matrix printer head,
the ink tank comprising a top wall (50), a bottom wall(40a) and walls (40b, 40c) extending therebetween,
an ink supply port (41) which is arranged in the bottomwall (40a) to receive ink from at least one porous member(60", 61, 62), which is impregnated with ink undersubatmospheric pressure and has substantially no air layeror pocket enclosed by the ink,
the at least one porous member (60"; 61, 62) being arrangedin the ink tank such that only a projecting portion (44),ridges (47, 51) or a partition wall (48) of at least onewall (40a, 40b, 40c, 50) contacts the at least one porousmember (60"; 61, 62) so that the remaining portion of theat least one wall (40a, 40b, 40c, 50) is spaced at adistance from the at least one porous member (60"; 61, 62)and that an air hole (42) in one of the ink tank wallscommunicates air in the space with the ambient air, and
the at least one porous member (60"; 61, 62) having poreswhich progressively reduce in size.
Ink tank according to claim 1 characterized in that saidink tank (2") is formed as a detachably mounted unit, witha plurality of ink-supply sections, each of said ink-supplysections having an ink-supply delivery port, each of said ink-supply sections containing an ink absorbing member(60"; 61, 62) formed by said porous member and impregnatedwith ink, and at least two of said ink-supply sectionscarrying ink of different colors.
Ink tank according to claim 1 characterized in that saidunitary ink supply tank is formed with a plurality of ink-supplysections, each of said ink-supply sections having anink supply port, said unitary ink supply tank containing anink absorbing member in each of said ink-supply sectionsformed by the porous member and impregnated with ink, atleast two of said ink-supply sections carrying ink ofdifferent colors, said ink in said ink-supply sectionsbeing of a color other than black; and
a further separate ink-supply tank formed with an inksupply port, a separate ink absorbing member formed of aporous material contained within said separate ink-supplytank and impregnated with ink, and the ink contained insaid separate ink supply tank being black.
Ink tank as claimed in claim 2 or 3, characterized in thatthe ink absorbing member (60") is compressed by the topwall (50) of the ink supply tank (2").
Ink tank as claimed in any one of the preceding claims 2 to4, characterized in that the ink absorbing member (60") hasa tapered portion (60"').
Ink tank as claimed in claims 1 to 5, characterized in thatthe ink absorbing member (60") has a thicker portion in thevicinity of the ink supply port (41).