CA1300974C - Hydraulically tuned channel architecture - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
The use of lumped resistive elements (22, 24, 32) in an ink feed channel (10) between an ink-propelling element, such as a resistor, (12) and an ink supply plenum (16) provide a means of achieving resistive decoupling and meniscus resonance control with a mini-mum of deleterious side effects and design compromises typical of prior art solutions.

Description

13t~(~9'~4 8YDRAULICALLY TUNED CHAN~EL ARCXIT~CTURE

1 TE OENICA~ F$ELD

The present invention relates to lnk-~et printers, and, more particularly, to a structure for controlling 5 fluld reflll of flrlng chacbers, ~in~nlzin~ nenlscus travel and mlnimlzln~ cross-talk betwcen adJacent noz-zles in the prlnthead u~ed to flre droplets of lnk toward a prlnt mediu~

BACXGROUND ART

When designlng printheads containing a plurallty of lnk-e~ectlng nozzle~ ln a denscly packed array, it i~ nece~sary to provlde so~e neans o~ l~olatlng the dyna~lc~ o2 any ~iven nozzle fro~ lts nel~hbor~, or else cro~s-talk wl~l occur between the nozzles a~ they fire droplets of ink fro~ clements a~sociated wlth the nozzles Thls cro~-talk ~erlou~ly degrados prlnt quallty and he~ce ny providently designed ink-~et prlnthe~d u~t lnclud~ ~one ~eatures to acconpllsh decouplln~ between the noz21e~ ~nd the coaaon lnk ~up-ply plenu~ ~o that the plenum doe~ not ~upply a cro~-talk path between nel~hborln~ nozzle~
Further, ~hen an lnk-~et prlnthead 1~ called upon to dl~char~e lnk droplets at a very hl~h rate, the ~otlon of the ~enlscu~ present in each nozzle nu~t be carefully controlled ~o as to prevent any o~cillatlon ~3~974 1 or ~ringlng" of the meniscus caused by reflll dynamics from lnterferlng wlth the e~ectlon of subse~uently fired droplets. Ordinarily, the ~settl ing time" re-quired between ~irina~ ot~ a l~lt on th- ~aximu~
repetitlon rate at which the nozzle can operate. If an lnk droplet 18 flred from a nozzle too 800n after the prevlous flring, the rlnging of the ~enlscus modulates the quantlty of lnk in the second droplet out. In the case where the menl~cus has "overshot" lts equillbrium posltlon, a flrlng superimposed on overshoot ylelds an unacceptably large e~ected droplet. The opposlte 1~
true lf the flrlng 18 superl~posed on an undershoot condltlon: the eJected droplet 18 too~ s~all. There-fore, ln order to enhance the aaxinu~ printlng rate of an lnk-~et prlnthead, it 18 necessary to lnclude ln lts desl~n sone neans for reduclng neniscus o~clllatlon 80 a8 to ~ininlze the ~ettling tl~e between sequentlal flrings of any one nozzle.
Previous approache~ to the probl~m of cro-s-talk, or minlnlzing inter-nozzle coupling, can be separated lnto three classe~: resi~tlve, ~nertlal, and capacl-tive. The followlng 18 a brlef dlscusslon of each uethod and a crltique of the typieal embodinents of these nethods.
Reslstive decoupling use~ the fluld friction pres-ent ln the ink feed channels as a neans of dissipating the en-r~y content of tho cro~-talk ~urge-, thoreby prev~ntlng the dynanics of any ~ingle neni~cu~ from belng ~trongly falt by its neare~t nelghbor~. In the prlor art, thi~ 1~ typlcally luple~ented by aaking the lnk ~eed channels longer or cnall~r in eross-~ection than the nain ~upply plenun. While these are ~inple ~olutlons, they have several drawbac~s. Flrst, ~uch ~olut~ons rely upon rluid notlon to generate the pres-130~974 1 sure drops as~ociated wlth the energy dissipation; a8 such, they can only attenuate the cross-tal~ ~urges, not completely block them. Thus, some cross-talk "leakages" wlll alway~ bo pr~ent. ~-cond, ~ny atte~pt to shut off cro~-talk co~pletely by these ~ethods will necessarily re~trlct the refill rate of the nozzles, thereby co~pronislng the naxi~u~ rate at which thc prlnthead can print. Third, the resi~tive decoupling technlques as practiced ln the prlor art add to the lnertia of the fluid reflll channcl, whlch has serlous lnpllcation~ for the printhead perfor~ance (a8 ~ill be explained at the end of the lnertial decoupllng exposi-tlon whlch follows shortly).
In capacitlve decoupllng, an extra hole ls put ln ~5 the nozzle plate above that polnt where the lnk feed channel neets the lnk supply plenum. Any pressure surges ln the lnk feed channel are transfor~ed lnto displace~ents of the nenlscus present in the extra hole (or du~my nozzle"). In thls way, the hole actJ as an lsolator for brlef pre~sure pulses but does not lnter-fere ~ith reflll flo~. The locatlon, slze and shape of the lsolator hole nust be carefully chosen to derive the required degree of decoupling wlthout allo~ing the hole to e~ect droplets of lnk as lf lt were a nozzle.
This ~ethod 1~ extre~ely effectlve in preventlng cross-talk (but can lntroduce proble~s wlth nozzle nenlscus dyn ~lc~, a~ will be dl~cuss~d belo~).
In lnertlal decoupllng, the feed channels are ~ade ~8 long and ~lender aJ posslble, thereby a~xlnlzlng the lnertlal a~pect of the fluld entralned ~lthln then.
Thc lnertla of the fluld "claops" lts ablllty to re-cpond to cro~-talk ~urges ln proportlon to the ~udden-ness of the ~urgc and thereby lnhlblts the trans~lsslon of cross-talk pulses lnto or out of the ~nk feed chan-:13()C~9'74 1 nel. While thls decouplln~ sche2e 18 used in the priorart, it requlre~ considerable area ("real e~tate") withln the prlnt head to l~ple~ent, maklng ~ co~pact structure i~posslble. Furthcr~or~ nc- th- r--l~Slve co~ponent of a plpe havlng a rectangular cross-~ectlon ~cales dlrectly wlth len~th and lnversely with the third power of the s~ller of the two cross-section dinenslons, the flow reslstance can grow to an unac-ceptable level, co~pro~lsing reflll speed. More l~por-tantly, however, are the dyna~lc effects caused by thecoupling of thls inertance to the co~pllance of the nozzle nenlscus, a~ ~111 be discu~sed below.
Wlth regard to the proble~ of ~eniscus dyna~lcs, there are apparently no solutlons offered ln the prlor lS art. Apparently, thls 18 a proble~ that has only re-cently surSaced as prlnthead desl~ns have been pushed to accou~odate hlgher and hl~her repetitlon rates.
Clearly, any nethod u~ed to decouple the dyna~lc~ of nelghborlng nozzles wlll al~o ald ln da~plng out enls-CU8 oscillations, at least fron a superflcial conslder-ation. In practice, problens are experlenced when try~n~ to u~e the decoupling ~eans as the osclllatory da~plng neans. These problens can be traced to the ~yner~lstlc effect~ between the nozzle nenlscus and the fluld entralned wlth~n the lnk feed channel, as out-llned below.
If re~l~tive decouplln~ 1~ attenpted by reducing the wldth of the entlre lnk feed channel, the lnertla of the fluld entralned wlthln the foed channel in-crea~es. When thi~ lnertla 1~ coupled to the conpll-nce of the nenlscu~ ln the nozzle, lt result~ ln alower resonant frequency of osclllation of the nenls-cu~, whlch rc~uire~ a lon~er settllng tl~e between flrlng~ of the nozzle. The lnertlal effect and the 13~ 974 1 reslstive effect are hence deadlocked, wlth th~ net effect belng that settllng tlme cannot be reduced.
Capacltlve decoupling has been proven effectlve at droplet e~ectlon fre~uencle- b-low that eorre~pondln~
S to the resonant frequency of the nozzle ~enlscus eou-pled to the feed channel lnertla. However, lts l~ple-nentation at frequeneles near ~enlscus resonance 18 also co~pllcated by lnteract~ve effects. Speelflcally, the lsolator oriflce aets as a low l~pedance shunt path for hlgh frequency surges. Henee, the hlgh frequency lnpedance of an lnk feed channel ter~inated at lts plenun end wlth an lsolator orlflce wlll be lower than an equlvalent cha~nel wlthout an lsolator. Thls ~eans that durlng the bubble growth phase, blow-back flow away fron the nozzle 18 lnereased by the lsolator orl-flee. Thls robs klnetlc energy fron the droplet ener~-lng fron the nozzle, whleh results ln s~aller droplet slze and lower droplet veloeltles and thus lower e~ec-tlon efflelency. Durlng the bubble collapse phase, the lsolator orlflce uenl~eus puops fluld flow back lnto the reflll ehauber, whlch excltes a resonant node ln whlch the t~o aenlscl trade fluld between thenselYes vla the lnk feed cbannel. Slnce these two neniscl are for aost practlcal deslgns sl~llar ln sl2e, and slnce they are effectlvely ~ln serles", the equlvalent con-pllance o~ the coupled syste~ 1~ rou~hly half of that wlth only one orlflee ln lt. ~he two-orlflce ~ysten wl~l t~u~ r-Jonate at a hl~her frequency, whlch 1~ a ; benefit froa a settlln~ tlne polnt of vlew, but the ener~y ~tored ln the re~onatln~ ~yste~ stlll need~ to be dls~lpated and therefore eonstrlctlve danpln~ wlll be neeessary ln ~ueh an lnple~entatlon. Whlle the effeets of these resonances 18 poorly under~tood at 13~ 974 1 thls ti~e, the efficlency decrease may be severe enough to pre~ent the prlnthead from workin~
It 1~ clear that what is needed 1B a printhead structure that aeco~pll~h-~ both (~ ol~tlon of any ~lven nczzle fro~ lts neighbors and (2) redueed osell-latlon of the ~en1seus eaused by reflll dyna~lcs from interferlns wlth the e~ectlon of ~ubsequently fired droplets, whlle ll~ltlng the severlty of any ~lde ef-feets lneurred ln the l~ple~entatlon of the deslred structure DISCLOSUR~ OF INV~NTION

In aecordance wlth the lnventlon, a loealized eon~trlctlon (also referred to as a lunped reslstance ele~ent) 18 lntrodueed lnto the feed ehannel eonneetlng eaeh nozzle's flrlnq ehanber wlth the na~n lnk supply plenu~ The faet that the reslstlve aspeet of each nozzle 18 loeallzed per~lt~ the~e eon~trletlon~ to be u~eful ln cross-talk eontrol, slnce the quantlty of lnertia they lntroduce lnto the feed ehannels 18 nlnl-nal Thls overconeJ the arore~entloned problen of - para~ltle lnertanee pre~ent ln the prlor art ln whleh the re~lJtive aJpeet 18 dlstrlbuted alon~, and thereby ~eales dlreetly ~lth, the length of the feed ehannel The u~e of lu~ped resl~tanee elenents allows the prlnt-head de~lgner to vary the relatlve a-ounts of resl~-tanee and lnertanee pre~ent ~n the reed e~ nnel ~ub-~tantlally lndependently o~ eaeh other and thereby ~tune~ the ~eed ehannel for an optl~u~ eonblnatlon of lnertance and reslst~nee In one e-bodlnent, the lu~ped re~lstanee ele-ent conprlses a p$nch polnt between two oppoJed pro~ectlons ln the lnk feed slde walls Slnce these feed wall~ are i3~974 1 co~monly patterned ln photoreslst, the pinch po1nts are easlly l~ple~ented by lncluding the~ in the photo~a6k whlch defines the lnk feed channel geometrles. The de~ree of "plnch" poc-lble 1- -n-ltlv-ly d t-rnlned by the photoche~lcal characterlstlcs of the reslct flln.
In practlcal terns, when uslng co ~crclally col~on reslst fll~ and ll~ht sources, the ratlo o-f flln thlc~ness (l.e., wall helght) to pinch wldth ran~es up to about 1.2.
Shls anount of plnch aay not be sufflclent for all appllcatlons. Therefore, another enbodl~ent conprlses one or nore sharp bends ln the lnk feed channel. ~ach ~harp bend acts a8 a lunped reslstlve element to gener-ate a pressure drop equlvalent to that present ln an equlvalent len~th of lnk feed channel of from about 5D
to lOD, ~here D 1~ the cross-sectional dluenslon of the channel. Shl~ reslstlve enhancenent 18 acconpllshed wlthout a proportlonal Incrcase ln the lnertla of the feed channel, and wlthout vlolatlng the helght-to-wldth llnlts of the flln. Thl~ concatenatlon of serlal lu~ped re~l~tlve elenents 1~ appllcable ln prlnclple to the plnch polnt enbodlnent a~ well, although care ust be e~erclJed to avold lncludlng any features whlch nlght behave a~ bubble trap~ or lnterfere wlth photore-si~t developnent and subsequent washlng.
In another enbodlnent, the lnk-propelllng ele~ent (re~l~tlve heatlng elenent, plczoelectrlc elenent, ctc.) 1~ placed below the level of the f~ed channel, a~aln lntroduclng a charp bend ln the lnk feed channel.
In yet another enbodlnent, a plnch polnt 18 lntro-duced lnto the feed ch~nnel by partlally obstructlng the channel wlth a dlke or ~peed bu~p" lylng acro~s the ~ldth of the channel. ~hls feature can be photo-lltho~raphlcally deflned and deposlted upon the prlnt-~3~t~9~74 1 head substrate uslng a film thlnner than that used to for~ the side walls, or it may be affixed to the under-side of the oriflce plate which forms the "ceiling" of the lnk feed channel. ~n thl~ c~--, tho dlk~ c~n con-sist elther of photoreslst fll~ or of electro~eposltednetal. In the latter instance, the electrodeposltlon can be an operation separate from that used to create the oriflce plate, or, ln the case of electroforned orlfice plates, lt can be an lnte~ral part of the elec-trofor~ing process. It 18 also posslble ln prlnclpleto electrodeposlt a netalllc dlke onto the prlnthead - ~ubstrate, provlded that the substrate 18 conpatible wlth the electrodeposltlon baths.
It should be noted that none of the speed bunp lzplementatlons descrlbed above are requlred to com-pletely span the rull wldth of the lnk feed channel:
free standlng ~tructures are pernlsslble whlch act ~8 lu~ped re~lstlve ele~ents and are ll~lted ln thelr appllcatlon only by the practlcal conslderatlons out-llned ln the prevlous sectlons.
These lu~ped reslstlve ele~ents can be used slnglyor in conblnatlon wlth ele~ents Or the ~ane or of dif-ferent types, dependlng on the detall~ Or the applica-tlon and are not ~trlctly llnlted to the shapes, nate-2S rlals, and layout~ offered above as exaoples.
The novel prlnthead ~tructures of the lnventlonacco~plish both (1) i~olatlon Or any glven ~ozzle fron lts nel~hbor~, l.e., cross-talk reduction, and (2) reduced osclll~tlon Or thc neniscu~ caused by reflll dyna~lc~ ln any lndlvldual nozzle. T~ls prevents ne-nl~cus dlsplacezents fron ~nterferlng wlth the e~ectlon of ~ubsequently flred droplets, whlle llnltlng the ~cverity of any slde effects lncurred ln the lzplenen-tatlon of the deslred structure. She ncw prlnthead 13~V974 structure have the additional advantage of being easy to implement and easy to "tune" for maximum effectiveness.
These structures are directly applicable across the full range of ink-jet printheads.
Various aspects of the invention are as follows:
An improved ink-jet printhead including a plurality of ink-propelling elements, each ink-propelling element disposed in a separate firing chamber defined by three barrier walls and a fourth side open to a reservoir of ink common to at least some of said elements, and a plurality of nozzles comprising orifices disposed in a cover plate above said elements, each orifice associated with an element for firing a quantity of ink normal to the plane defined by each said element and through said orifices toward a print medium in defined patterns to form alpha-numeric characters and graphics thereon, wherein ink is supplied to said element from a plenum chamber by means of an ink feed channel, wherein the improvement comprises:
(a) a pair of opposed projections formed in walls in said ink feed channel and separated by a first width to cause a first constriction between said plenum and said channel;
and (b~ a second constriction along the length of said ink feed channel defined by a second width between said walls of said ink feed channel, said second width narrower than the width of said firing chamber and wider than said first width between said opposed projections and sufficient to physically support said projections without adversely J ~

i3(~9'7~

9a adding to resistance to ink refill of said channel.
An improved ink-jet printhead including a plurality of ink-propelling elements, each ink-propelling element disposed in a separate firing chamber defined by three barrier walls and a fourth side open to a reservoir of ink common to at least some of said elements, and a plurality of nozzles comprising orifices disposed in a cover plate above said elements, each orifice associated with an element for firing a quantity of ink normal to the plane defined by each said element and through said orifices toward a print medium in defined patterns to form alpha-numeric characters and graphics thereon, wherein ink is supplied to said element from a plenum chamber by means of an ink feed channel, wherein the improvement comprises: (a) a pair of opposed projections formed in walls in said ink feed channel and separated by a first width to cause a first constriction between said plenum and said channel;
(b) a second constriction along the length of said ink feed channel defined by a second width between said walls of said ink feed channel, said second width narrow than the width of said firing chamber and wider than said first width between said opposed projections and sufficient to physically support said projections without adversely adding to resistance to ink refill of said channel; and (c) means for assisting in purging any bubbles in said ink, said means comprising a pair of lead-in lobes disposed between said projections and said plenum chamber and ~3C~Q974 9b separating one ink feed channel from a neighboring ink feed channel.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a top plan view of a prior art resistor and ink feed channel configuration;
FIG. 2, on coordinates of distance in ~m and time in ,usec, is a plot of meniscus damping of an active nozzle and an adjacent nozzle for the prior art configuration of FIG.
l;
FIG. 3a is a top plan view of a resistor and ink feed channel configuration in accordance with one embodiment of the invention;
FIG. 3b is a side elevation view, depicting two alternate embodiments: a "speed bump" structure that can be used in conjunction with the structure depicted in FIG. 3a and a well structure, in which the resistor is placed below the level of the ink channel;
FIG. 3c is an enlarged view of a portion of FIG. 3a;
FIG. 4, on coordinates of volume in pl and time in ~sec, is a plot of meniscus damping of an active nozzle and an adjacent nozzle for the embodiment depicted in FIGS. 3a-b;
FIG. 5 is a top plan view of a resistor and ink feed channel configuration in accordance with an alternate embodiment of the invention;
FIG. 6 is a perspective view of the resistor, ink feed channel and orifice, depicting yet another embodiment of the invention; and i ~

~30~97~

1 FIG. ~ ls a view slmllar to a portion o~ FIG. 6, deplcting still another e~bodi~ent of the invention.

BEST MODES FOR CARRYINO OU~ E~Y~T~ON

Referrlng now to the drawings wherein like nu~er-als of reference designate llke ele~ents ehroughout, an lnk feed channel 10 18 shown, wlth a reslstor 12 sltu-ated at one end lOa thereof. Ink (not ~hown) ls lntro-duced at the oppo~ite end lOb thercof, ao lndlcated byarrow "A", fron a plenum, indlcated generally at 1~.
Assoclated wlth the resl~tor 1Q a nozzle 16 (~uch as seen in FIG. 3b), located above the resistor 12. Drop-let~ of lnk are eJected through the nozzle ~l.e., nor-nal to the plane of FIG. 1) upon heating of a quantltyof lnk by the reslstor 12.
Whlle the lnventlon 19 preferably dlrected to lnprovlng the operatlon o~ ther~al lnk-Jet pr~ntheads, ~hlch eaploy re~l~tors 12 a8 ele~ents used to propel droplets of lnk toward a print uedluo, such as paper, lt wlll be appreclated by the person skillcd in thls art that the teachings of the ~nventlon are suitably e~ployed to luprove the operatlon of lnk-Jet prlntheads in general. Exanple~ of othcr types of lnk-Jet prlnt-hcad~ benefited by the teachings of the lnventlonlnclude plezoelectrlc, whlch e~ploy a plezoelectrlc elesent to propel droplets of lnk to~ard the prlnt ~edlu~.
~tte~pt~ to ~lnl~lzc cross-talk betwcen ad~acent nozzles have lnc~uded lengthenlng the ch~nnel 10, as shown by the dot~ed llnes 10'.
Thc ~tralght channel 10 doc~ not pcr~it faclle da~ping of the lnk. A~ ceen ln ~IG. 2, danplng Or the neniscus of ink in the actlve nozzle take~ norc than 130~374 1 ~00 ~sec ICurve 161. Si~ultaneously, the meniscus of ink In a nelghborlng nozzle ~s adversely affected by the action of thc ~eniscus of lnk in the act~ve nozzle (Curve 20).
~n accordance ~lth the lnvention, a locallzed constrictlon 22 ~also referred to as a luoped resis-tance elenent) i8 lntroduced into the feed channel connecting each nozzle' 8 flring cha~ber ~ith the ~aln ink supply plenu~. The localized constriction 22 nay conprlse a sharp bend or a pair of opposed pro~ectlonç, and one or ~ore such constrictlons nay be present ln varlou~ conblnatlons.
~ or exanple, a pair of opposed proJectlons 2~, depicted ln FIG. 3a, 1~ enployed alone or ln conJunc-tion wlth locatlng the resistor 12 below the floor 26(lndlcated by the dash~d lines) of the channel ~0, as seen ln ~IG. 3b.
The use of one or nore sharp bends, or constrlc-tlon~, con~lderably l-prov-~ the da plng of the flu~d notions as seen ln FIG. ~. Danplng of the nenlscus of ink occurs ln about 2S0 p~ (Curve 28). Sinultaneously, the fl~ld nenl~cus ln a nelghboring nozzle 18 hardly affected by the actlon of the nenlscus the actlve noz-zle (Curve 30).
2S Preferably, the length of the channel 10 ran~es fron clo~e to the resistor to about 60 pn. She he~ght of thc channel 10 range- froa about 15 to 30 pn, ~hile the ~idth of thc channel ranges fron about 20 to ~0 pn.
The con~lderations that govern the channel dlnen-~lons relate to thc A-ount of lnk that has to be re-plac~d after each flrlng. Th~s aoount lc the sun of the quantlty of ink that i~ eJected out through the nozzle 16 plu~ the quantlty of lnk that uoves back through the feed channel. The latter quantlty 1~ re-13()~974 1 ferred to as the blow-back, and i8 de~irably as 8mall a~ pOS8 ~ ble.
To ~et ~ax~um performance, fast refill ti~e in con~unctlon ~ith avoldlng havlng to overco~e blow-back S in the lnX Seed ehannel 10 i8 re~ulred. Whlle a re~ill tl~e Or 0 p~ec wlth very fast da~plng tno o~clllation) is ldeal, lt is not posslble. Ref~ll ti~es of about 250 psee and less are ~ound to provide adequate result~
at a frequeney of ~ ~z. ~or a pen operatlng at 6 ~z, the eorre~pondlng aec~ptable ref111 tl~e ~8 about 16 psee and less.
- - She tradeorf is that lncrea~ed damplng l~plles a slower reflll. Since lt i~ deslred to aaxlnlze both re~lll and danplng, optlnlzing t~en i8 the only po~sl-~5 bllity.
The shape of the pro~ectlon~ 2~ ln the area o~ the openlng lOa ean contrlbute to the optinlzatlon of re-flll and da~ping. Speclflcally, the pro~ectlons can be ~harp, ~8 ~ho~n in FI~. 3a, or round~d, as shown ln ~IG. 3e. The radlus ~ of t~e roundlng aay ran~e Sron about S to 10 pn.
The eonflguratlon Or the pro~ectlons 2~ afreets turbulent flow of the lnk ln the vlelnlty thereof. In partleular, sharper corners increase tho turbulence, 2S thus leadlng to hlgher re~lstanee, ln the lnk feed ehannel 10 durlng the bubble ~ro~th phase. ~hi~ re-duees blo~-bae~ and d~cre~s-~ roSll~ tlne.
~ harp eorner~ are dl~fieult to deflne lithographi-eally in ~one re~l~t~, ~ueh a~ DuPont's VACR~L. ~o~-ever, other re~l~t~, ~uch ac the polylnlde~, aay pernltb~tter de~lnltlon.
Thus, it ean be seen that blo~-back ean be ulni-~lzed by con~trleting the opening to the ehannel 10 ~ith thc oppo~ed proJectlon~ 2~, by constrlctlng the :13C~(~974 1 channel (such as provldlng a "speed bump" 32 across the ~unctlon of the channel and the firing cha~ber on the floor 26' thereof (FIG. 3b?, by placing the re~istor 12 $n a well below tho lovcl of th- r-flll channel (as alternately deplcted ln FIG. 3b), or by lntroduclng bends 22 ln ehe lnk feed channel. In the case of the speed bu~p 32, lt ~ay be placed on the floor or the celling, partially or fully extendlng across the width of the channel 10.
In lts broad aspect, the lnvention conte~plateQ
place~ent of one or nore constrictions 22, 24, whether enploying pro~ectlons or one or more sharp bends ln the lnk feed channel 10, between the plenuc 14 and the nozzle ~6. ~ach sharp bend 22 lntroduces a preQsure 1~ drop equlvalent to that generated by an equivalent len~th of ln~ feed channel 10 of fron about Sd to lOd, where d 18 the cross-~ectional dlmenslon of the chan-nel, wlthout lntroduclng the lnertla enhancement ef-fect. This 18 because the reslstance enhancenent swamp~ out and overwhel~s the lnertia change. Thus, the lengthenlng of the channel 10, deplcted ln FIG. 1, 1~ avoided by addlng one or nore constrictions 22, 2 therein.
A~ ~hown above, the sharp bends nay be lntroduced by ~etting the re~lstor 12 bclow the channel 10 or by adding a ~pced bump 32 across the floor 26' or celllng o~ the c~ann~l. In anot~er e~bodl~ent, deplcted in FIG. 5, one or aore charp b~nd~ 22 ay be lntroduced ln the channel 10. $n partlcular, FIG. 5 deplcts two con~trlctlon~, one at 22a and the other at 22b. FI~S.
6 and ~ deplct yet addltlonal embodlnents, ~uch a~
opposed pro~ectlons 2~ (FSG. 6) or a free-standlng plllar 22' ln lleu of a speed bump 32 ~FIG. 7).

~3(~974 1 The constrlcted feed channel or the labyrlnth feed channel can be 1ntrodaced lnto the printhead architec-ture wlthout leng~hening the feed channel structure and wlthout revlsln~ the orlflce pl~t- wlth th- additlon of S l~olator orifices.
The ~ass ~seen" by the nozzle men~scus as it 08-clllates 1~, for the labyrinth, predominantly the fluld nass ln the flring chamber. The resi~tance of the labyrlnth lnk feed channel decouples this ~ass from that entrained ln the labyrlnth.

INDUSTRIAL APP~ICABILITY

The use of lunped reslstlvc ele~ents ln the lnk feed channel to allow lndependent ad~ust~ent of the feed channel's re~lstive and lnertial paraneter~ 18 useful ln lnk-~et prlnter appllcatlons based on ther~al and non-ther~al lnk-~et technologles.

BAMPLES

~ conparison was ~ade between a stralght lnk feed channel of the type deplcted ln FIG. 1 (prlor art) and an ink feed channel of the lnventlon a~ deplcted in FIG. 3a. In each case, the reslstor was 50 pn x 50 p~
~quare. In the prlor art case (~stralghtn), the ink fced channel w~ 150 pa long and 70 ~n wide. In the confi~uratlon of the lnventlon (noppo~ed pro~ectionn), the re~l~tor wa~ placed 25 ~ below the bottoa of the 1nk feed channel; the lnk feed channel wa~ 50 pn long (~ron the edge of the resistor to the opening to the re~ervolr) and had protuberances affording an openlng o~ 35 p~ wlde.
, .

i3(~:}974 1 In the co~parlson, for a given drop 61ze (ln plco-llters, pl), the refill tl~e (in microseconds, ~sec) and the overshoot volume (in pl) and the blow-back volu~c (ln pl) were ~e~cured. Th~ ult- are hown ln Table I below.

Table I.

Barrler Drop Size, Reflll Overshoot Blow-back 10 TvDe Pl Tlme. usec Vol., ~l Vol., Dl Straight75 130 36 75 lSO 2~2 38 232 Opp. 75 135 16 ~0 ProJ. 100 150 16 ~

Table I shows that the opposed pro~ection configu-ration of the inventlon wor~s because the blow-back volu~e 18 held in check. The stral~ht barrier ~ith lSO
pl drop actually has to refill 382 pl because of the excessive anount of blow-back.
In nother exa ple, the W and L dl~ensions, de-picted ln FIG. 3c, were varled. The pro~ectlon~ all had 5 ~n radiu~ ~R) rounded corners. The drop volu~e ~as 150 pl in all ca~es. ~he re~ult~ ~re shown ln Table II.

~3~974 1 Table II.

L, ~ W, ~m Reflll Ti~e, Overshoot Blow-bac~
u~-c Volu~ 1 Vo~u~

22 1~ 11 71 26 1~2 16 8S
1~ 20 9 ~ 3~ 182 2 ~ 38 200 2~ ~2~
~ ~2 212 29 ~SO
.__________________________________________________________ 4 30 1~4 20 9 ~ 30 18~ 19 91 lS 12 30 19~ 18 8g 16 30 209 1~ 92 ~ rom the foregoing data, lt appears that the donl-nant contributor to fast reflll 1~ the ~idth W provided by the opposed proJections, or the aoount of constric-tion. She length ~ of the stralght sectlon ~hould be held to a nlnl~u~, since lncreased length does slow refill.
A ~tudy ~as also ~ade of opposed proJectlons ~lth 2S sharp corners and opp~sed pro~ection~ with ~ ~n radlus rounded corner~. The reflll tlne ~as found to be 20 ~cc ~horter for the ~har7 corner conflguratlon, but the blo~-back volu e was 3 pl le~. Of thc 20 ~-ec ~pe~d-up, 80ne ~ay be attributed to thc reductlon down to zero of the e~ulvalent straight plpe sectlon inher-ent in the rounded corners.

Thu~, a feed channel archltecture for an lnk-~et pen i~ provided for use ln thernal lnk-Jet prlnter~.

13~)V9'74 1 It wlll be clear to one of ordinary sklll in the art that various changes and modifications of an obviouq nature ~ay be made without departing from the splrlt of the lnvention, and all uch c~an~ n~ modlflcat~on~
are deemed to fall wlthin the ~cope of the invention as defined by the appended clai~8 .

Claims (16)

1. An improved ink-jet printhead including a plurality of ink-propelling elements, each ink-propelling element disposed in a separate firing chamber defined by three barrier walls and a fourth side open to a reservoir of ink common to at least some of said elements, and a plurality of nozzles comprising orifices disposed in a cover plate above said elements, each orifice associated with an element for firing a quantity of ink normal to the plane defined by each said element and through said orifices toward a print medium in defined patterns to form alpha-numeric characters and graphics thereon, wherein ink is supplied to said element from a plenum chamber by means of an ink feed channel, wherein the improvement comprises:
(a) a pair of opposed projections formed in walls in said ink feed channel and separated by a first width to cause a first constriction between said plenum and said channel;
and (b) a second constriction along the length of said ink feed channel defined by a second width between said walls of said ink feed channel, said second width narrower than the width of said firing chamber and wider than said first width between said opposed projections and sufficient to physically support said projections without adversely adding to resistance to ink refill of said channel.

2. The printhead of claim 1 wherein said ink-propelling elements comprise resistive heating elements.

3. The printhead of claim 1 wherein said projections are sharp.

4. The printhead of claim 1 wherein said projections are round, with the radius of rounding ranging from about 5 to 10 µm.

5. The printhead of claim 1 wherein said second width of said secondary constriction is about 40 to 60% of the difference between said width of said firing chamber and said first width plus said first width.

6. The printhead of claim 1 wherein said first width is about 35 µm, said width of said firing chamber is about 70 µm, and said second width is about 40 to 60 µm and wherein the length of said secondary constriction is about 20 to 40 µm.

7. The printhead of claim 6 wherein said second width is about 50 µm and wherein the length of said secondary constriction is about 30 µm.

8. The printhead of claim 1 further comprising means for assisting in purging any bubbles in said ink, said means disposed between said projections and said plenum chamber and separating one ink feed channel from a neighboring ink feed channel.

9. The printhead of claim 8 wherein said means for purging bubbles comprises a pair of lead-in lobes, one lobe diposed on either side of said ink feed channel.

10. An improved ink-jet printhead including a plurality of ink-propelling elements, each ink-propelling element disposed in a separate firing chamber defined by three barrier walls and a fourth side open to a reservoir of ink common to at least some of said elements, and a plurality of nozzles comprising orifices disposed in a cover plate above said elements, each orifice associated with an element for firing a quantity of ink normal to the plane defined by each said element and through said orifices toward a print medium in defined patterns to form alpha-numeric characters and graphics thereon, wherein ink is supplied to said element from a plenum chamber by means of an ink feed channel, wherein the improvement comprises:

(a) a pair of opposed projections formed in walls in said ink feed channel and separated by a first width to cause a first constriction between said plenum and said channel;
(b) a second constriction along the length of said ink feed channel defined by a second width between said walls of said ink feed channel, said second width narrower than the width of said firing chamber and wider than said first width between said opposed projections and sufficient to physically support said projections without adversely adding to resistance to ink refill of said channel; and (c) means for assisting in purging any bubbles in said ink, said means comprising a pair of lead-in lobes disposed between said projections and said plenum chamber and separating one ink feed channel from a neighboring ink feed channel.

11. The printhead of claim 10 wherein said ink-propelling elements comprise resistive heating elements.

12. The printhead of claim 10 wherein said projections are sharp.

13. The printhead of claim 10 wherein said projections are round, with the radius of rounding ranging from about 5 to 10 µm.

14. The printhead of claim 10 wherein said second width of said secondary constriction is about 40 to 60% of the difference between said width of said firing chamber and said first width plus said first width.

15. The printhead of claim 10 wherein said first width is about 35 µm, said width of said firing chamber is about 70 µm, and said second width is about 40 to 60 µm and wherein the length of said secondary constriction is about 20 to 40 µm.

16. The printhead of claim 15 wherein said second width is about 50 µm and wherein the length of said secondary constriction is about 30 µm.