CA2027161C - Method of multi-tone printing - Google Patents
Method of multi-tone printing Download PDFInfo
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- CA2027161C CA2027161C CA002027161A CA2027161A CA2027161C CA 2027161 C CA2027161 C CA 2027161C CA 002027161 A CA002027161 A CA 002027161A CA 2027161 A CA2027161 A CA 2027161A CA 2027161 C CA2027161 C CA 2027161C
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- channels
- channel
- printing
- medium
- droplets
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Classifications
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
- H04N1/40—Picture signal circuits
- H04N1/40025—Circuits exciting or modulating particular heads for reproducing continuous tone value scales
- H04N1/40031—Circuits exciting or modulating particular heads for reproducing continuous tone value scales for a plurality of reproducing elements simultaneously
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
- B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
- B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
- B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
- B41J2/01—Ink jet
- B41J2/135—Nozzles
- B41J2/14—Structure thereof only for on-demand ink jet heads
- B41J2/14201—Structure of print heads with piezoelectric elements
- B41J2/14209—Structure of print heads with piezoelectric elements of finger type, chamber walls consisting integrally of piezoelectric material
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
- B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
- B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
- B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
- B41J2/01—Ink jet
- B41J2/21—Ink jet for multi-colour printing
- B41J2/2121—Ink jet for multi-colour printing characterised by dot size, e.g. combinations of printed dots of different diameter
- B41J2/2128—Ink jet for multi-colour printing characterised by dot size, e.g. combinations of printed dots of different diameter by means of energy modulation
Abstract
A method of multi-tone printing employs a drop-on-demand printing apparatus for depositing ink droplets on printing element areas of a medium which is movable relatively to said apparatus. The droplets are deposited from an array of channels on a medium which is movable relatively to the channels. The channels length and nozzle location and dimensions afford each channel with a high longitudinal resonant frequency and electrically actuable means supply energy pulses to selected channels at or near the resonant frequency of the channels to deposit from each selected channel in the corresponding printing element area of the medium a number of drops equal to the number of pulses applied thereto, the number of pulses applied being dependent on the tone of printing required. Single channel and colour versions of the invention are also disclosed.
Description
Method of Multi-i~onc~= Pr_~ntin This invent:ioru ~el.ates to mult~i-tone printing employing drop-on-demand ~>r:int: ing apparatus . More particularly the invention relates to such apparatus for printing droplets on pr:__nting el.:4ment: areas on a medium which is movable relatively to saic-i apparatus and comprises an array of parallel., uniformly =>pac;c.~d channels provided with respective droplet ejection nozzles, a liquid supply means common to said channelvs an~_3 eLectr.ically operated means for applying pulses of energy to droplet liquid in said channels to effect droplet ejeca~icri the>refrom.
Aspects of such printi_ncl apparatus are described for example in Unites States Patent Specification 4,584,590 and our European Pat:ent Application Nos. 88300146.3 and 88300144.8.
The types of printing apparatus disclosed in the references quoted are of the kind in which energy pulses are imparted to dr_op_l_et liquid r»r displacement of wall portions of the respe:cti_ve droplet liquid channels. The present invention is, however, also applicable to drop-on-demand printing apparatus having an ar ay of channels such as is known .f=rom US-A 3, 1'79, 042, anc_I GB--A-2,. 007, 162 and GB-A-2, 106, 039 in which droplet= eject:ion :is effected from the channels by applying a pulse of thermal energy to droplet liquid therein.
_, <_ It is known that the human eye c:an sense sixty-four gradations of greyscale in multi-tone printing. It is even suggested t.h_rt- a:> many as 128 gradations can. be discriminated. Accordingly, it is one aim of high quality tone printing, including colon r printing, to produce a printer capab:l.e of print.i_ng a number of greyscale tone's as near as possible t.o the diac:~riminating capability of the eye of the viewer.
In the L)nited States specification 4,513,299 there is disclosed a single charvne_L, drop-on-demand ink jet printing device in wlic~u droplets of ink having different droplet volumes c:an be deposited on a print medium at a droplet repetition rate just. below the re~~onant frequency of the ink channel. The different droplet volumes are achieved by following a droplet. ejection pulse ,with additional droplet, ejection pulses of like magnitude to the initial droplet ejc~c:tion pul se at a frequency at or near the channel rescn~3nt ivrec~uency. The additional droplet ejection pulses cause ejection from the ink channel of further drop volumes of subatant:i.al.ly the same size as the drop volume emitted from the <_hannE>1 by t:he initial droplet ejection pulse. In t_ue series of drop volumes thus emiti~ed, the second and subsE:eduent drop volumes are each connected to the preceding drop volume en.itted and the drop volumes join together to form an enlarged droplet which is deposited on the ~m:int medium. However, in high density array drop-on--demand printer: s, ~. . a . an~rays of at least two parallel channels ~%er mm, the known method of droplet ejection severely limits, to only a few, the number of droplet volumes which can be added to the droplet volume initially ejected from any particular channel. This number diminishes rapidly with increase of channel density. It follows that the number of greyscale gradations which can be achieved by this known method is limited in the achievable number of different drop volumes which can be deposited at a pixel of the printed image.
It is, accordingly, an object of the present invention, to provide an improved method of greyscale printing which employs a drop-on-demand printer having an array of parallel channels which enables printing of a substantially greater number of greyscale gradations than has been achievable hitherto.
The present invention consists in the method of printing employing drop on demand ink jet apparatus comprising an array of parallel channels disposed side by side and having respective side walls which extend in the lengthwise direction of the channels and separate one from the next of the channels, a series of nozzles which communicate respectively with said channels for ejection of droplets of ink therefrom, connection means for connecting the channels with a source of ink and electrically actuable means for effecting upon selection of any of said channels transverse displacement of a portion at least of a channel separating side wall of said selected channel to apply a pulse of energy to ink contained in the selected channel to effect droplet ejection therefrom, characterised by the steps of choosing the length of said channels and the dimension and location of said nozzles to afford a longitudinal acoustic resonant frequency of 25 KHz or more, selecting a channel and a tone of printing for that channel, and actuating the electrically actuable means to apply a sequence of pulses of energy to cause droplet ejection from the selected channel at or near the longitudinal acoustic resonant frequency to eject a corresponding number of droplets, said number being determined by the selected tone of printing.
Alternatively, said electrically actuable means effect droplet ejection from said channels by causing thermal stress in the ink therein.
Preferably, where the medium is continuously moving during printing, droplet deposition from each channel takes place over a length of said medium which is within a printing element area traversed during printing by the channels.
Suitably, droplet deposition on said medium from each channel takes place over approximately two thirds of the pitch of the printing element areas in the direction of relative motion of the apparatus and medium and is symmetrically disposed with respect thereto. The pitch in the direction of relative motion between the medium and the printing apparatus of the printing element areas is suitable made equal to the ink channel pitch.
__ In one i:vorm, the method of the invention is practised wit:h a print head comprising a body of piezo-electric medium in which sai.cl channels ar_e formed and opposed channel dividing sid<> walls of each of said channels have respective piezo-F~lectric portions which are displaceable in shear mode by operation of said electrically actuable means to effect droplet ejection from said channel. When ::m.lch a printhead is employed, according to said form of the invention, the channels are divided into a plura:Lity of groups of= interleaved channels and droplet ejection is enabled. ire each group simultaneously from selected charnels, the charnels selected in such group being actuated in ~>uc cessive phases of the frequency of the applied enercxy pulses. In orie form the channels are arranged in t:wo groups and ,elect:ed channels of said two groups are enabled for drop_.et: ejection at interval's of half a cycle of them frequency of pulses applied by said electrically actuable mean:> to the channels selected for droplet ejection.
Where colour print:inc; i:~ reguired, the method of invention consists i.n arr_anging the array of channels in a set or sets of four xvowa of channels, the rows of each set being respectively suppl=ied with black .ink and ink of the t=hree primary col_ou:rs and disp:>sing the rows of each set for printing a row of pz:in~~i.rug element areas extending transversely to the di evect:i.on of relative me>tion of the array and the medium :~.o that each area printed can be printed in b:Lack i.nk or ink of one of the three primary colours.
The invention is not however restricted to array apparatus. Thus the invention also consists in the method of multi-tone printing employing drop-on-demand printing apparatus foiv depositing liquid droplets on a printing element area of a medium, comprising a liquid channel provided with an e=jection nozzle, droplet liquid supply means connected with said channel and electrically actuable means for applyincx pulses of energy to liquid in said channel to effect drop7_et eje<Jti.on therefrom, characterised by choosing the charnel. dimensi ons and the dimensions and location of i.~he nozzle so tha' said channel has a high longitudinal acoust:i_c resonant frequency and applying to liquid in said channEe:L by said electrically actuable means, one or a sequence o' pulses of energy of amplitude and frequency to cause d~:~oplet ejection from the nozzle of said channel at or near t:he resonant frequency of said channel thereby to eject a number of droplets from said nozzle corresponding to the number of pulses applied to the liquid in said channel, sai~~ number of: pulses being determined by the tone of print.i:~g required to be effected in said printing element area. In this fornl Of the invention the medium would normally be held s!~ationary relatively to the apparatus during printing. P.Lso in this form of the invention colour pr:Lnting can be effected by providing four channels respectively supplied with black ink and ink of the three primary colours, the nc~zzles of said channels -7_ being arranged so that each printing element area can be printed with any one of said inks.
The invention further consists in a drop on demand ink jet apparatus comprising an array of parallel channels disposed side by side and having respective side walls which extend in the lengthwise direction of the channels and separate one from the next of channels, a series of nozzles which communicate respectively with said channels for ejection of droplets of ink therefrom, connection means for connecting the channels with a source of ink and electrically actuable means for effecting upon selection of any of said channels transverse displacement of a portion at least of a channel separating side wall of said selected channel to apply a pulse of energy to ink contained in the selected channel to effect droplet ejection therefrom, characterised in that the length of said channels and the dimension and length of said nozzles are such as to afford a longitudinal acoustic resonant frequency of 25 KHz or more and that upon se~.ection of a channel and upon selection of a tone of printing for that channel, the electrically actuable means serves to apply a sequence of pulses of energy to cause droplet ejection from the selected channel at or near the longitudinal acoustic resonant frequency to eject a corresponding number of droplets, said number being determined by the selected tone of printing.
-g_ Said channels are advantageously arranged in a plurality of groups of interleaved channels, the channels of the respective groups being disposed in repeated sequences and said electrically actuable means are adapted to cause selected channels of each group to be enabled for actuation simultaneously and to effect enabling of the groups of channels in successive intervals of duration to allow ejection of several drops from the enabled channels.
Advantageously, the channel length, channel nozzle diameter and channel density of the apparatus lie respectively in the range 10 to lmm, 20 to 10~m and 2 to 12 per mm. For any particular printhead apparatus, the said dimensions are chosen to provide channel resonant frequencies of above 25 KHz.
Preferably, the chosen resonant frequency is in the range 50 KHz to 250 KHz.
The invention further consists in an electrically pulsed droplet deposition apparatus, comprising a liquid channel having an ink ejection nozzle, droplet liquid supply means connected with said channel and electrically actuable means for supplying pulses of energy to liquid in said channel to effect droplet ejection therefrom, characterised in t=hat the dimensions of the channel and the dimensions and location of the nozzle are adapted to provide t=he channel with a high longitudinal acoustic resonant frequency so that. application to ink in the channel of one or a sequence of pulses of energy of amplitude and freque~rucy at o:r near_ the resonant frequency of the channel causes ejection of droplets corresponding in number t.o said applied pu:Lses whereby the number of droplets deposited from the nozzle can be selected to correspond with a desired tone of printing.
Suitably, translating means are provided for moving the channel or group of ch<~nnels relatively t:o a medium to be printed..
In this manifestation of the invention where colour printing i.s require~_i there are provided four channels respectively supplied with black ink and ink of the three pr:Lmary colours, the nozzles of the channels being arranged so t=hat any printing element area of a medium can be printed with any one of said inks.
In a fu~::ther_ form, the invention consists i.n a drop-on-demand pr~.nting apparatus for depositing ink droplets on a mecaium compris:i.ng an array of printing channels provided wit=h respective nozzles for deposit=ing ink droplets on resl:ective printing element areas of raid medium, ink supply means conne~~ted with said channels and electrically actuable means for applying pulses of energy to ink in said c~anr.els to eff=e~Jt droplet ejection therefrom, characterised in tha.r the length of the channels and the location anc't dimensions of the nozzles provide the channels with high lc>ngitu<iinal resonant frequency so that application to ink in. the channels for a pulse sequence or of pulses of enerc:Yyofv amplitudeand frequency to cause droplet ejection from the channels at or near resonant the frequency of the charv_nels causes ejection of droplets form the channels come: ponding in number to the number of energy pulses applied to the .ink therein whereby the number of droplets deposit=ed from each nc>zzle can be selected to correspond with a desired tone of printing and effect printing witYu the medium stationary relatively to the apparatus.
The invention will now be described, by way of example with refei:e;:zce to the accompanying drawings, in which:
FIGURE 1 i_':~lustrates the effect of depositing in successive printing .element areas, that is to say, pixels, as the print medium moves past a nozzle of a channel of a drop-on-demand ink jet printer, a variable number of ink drops between 1 and F>4;
FIGURE 2 illustrates diagrammatically one embodiment of the invent: ion; arid FIGURE 3 illustrates diagrammatically, in another embodiment of: the invention, the printing of a line of printing element <areas or pixels from a group of ten channels, the respective nozzlea of which eject bursts of varying numbers of drc>plets between l and 64.
-l~.-The method of the invention can be performed by a drop-on-demand i.nls jet printing apparatus comprising an array, preferably a high dF:ns_ity array, of parallel uniformly spaced channels provided with respective droplet ejection nozzles, an ink supply common to said channels and electrically aca uabl.e means for displacing respective piezo-electric side wall portions of said channe l; to effect droplet ejectior: form the channels. In the prior United States specif.i_cation No. 4,'i84,590 referred to the displaceable piezo-electric side wall portions are provided as the top or roof walls of t:he respective channels, the channel density bez.ng up to two pe:r mm, whereas in our co-pending European pate=nt: applic:at:ion No. 88300146.3 there is described e.g. witru reference to Figs, 2(a) - (d), a form of printhead in which said disp~.aceable piezo-electric wall portions comprise the channel dividing side walls. In this latter case each ~:W t=he channel dividing side walls is shared between the channels which it separates so that in a first of successive phases of operation it can be defle~~ted together with the taping wall oL one of the channels which it separates to eject. a droplet from said one of the channels whilst in a succeeding phase of the operation the said channel dividing wall together with the facing side wall of the other of t=he channels which it separates can be deflected to eject: a droplet: from said other of the channels. The chanr~.el densities of such printheads can be from 2 to 16 per mrn. Hitherto, the operation of this worm of printhead has been limited to the application of a voltage waveform pulse which acts :o eject a single drop of ink from the channel. to which the pulse is applied. The present invention calls for droplet ejection from the channels at high frequency at o:r near the longitudinal acoustic resonant frequency of the channels. Accordingly the channel length and nozzle dimensions have to be chosen to that end.
Printhead:~ of the kind described can also be employed according t:o this irmer_tion as greyscale and, therefore, colour printers. An acceptable range of resolution of print=ir~_g element areas or pixels on a paper medium for a prirut:head as described in our co-pending European patent appl..ication referred t:o would be 6 to 12 per mm. In the area corresponding to each pixel, a variable number of droplets in t:he range i t:o 64 is made available as hereinafter described.
Typical values of ink drop parameters at each channel nozzle and on the paper medium area are as follows:
Resolution Pitch Full 64 Single Single Droplet of of I%r~~plet Da_op Droplet Frequency Printhead Nozzles Volume Volume Diameter -/mm um ~~l ~>1 Ixm KHz 12 83 33 0.51 10 180 6 167 130 2.04 15.7 90 The full :=~.i.ze drop volume, which forms a pool of 64 single ejected smal_.1 droplets on the paper medium is chosen to forms cone iruaous dots at: fu_Ll tone.
-l Figures 1 shows the effect of depositing a variable number of ink droplets between 1 and 64 in successive pixels a:; the paper moves past the nozzle.
Typically, the maximum droplet production frequency is sufficient to genermt:e 100 droplets per pixel, so that if 64 droplets a.re generated, these are deposited in a line occupying approximat=ely 2/3 of: the pixel pitch "p" . When smaller numbers of droplets a.x:e generated as a sequence these are deposited along correspondingly shorter lines.
From the above table of typical values and assuming there are 100 droplets able to be generated per pixel, the spacing between droplets deposited longitudinally in each pixel, for_ Twelve pixels per mm, is 0.83 um and for six ~~ixels per mm is 1.67 um. Laterally the nozzle pitch is equal to the pixel pitch. The spacing in the lines in which they are deposited of the small droplets is small compared with the diameter of the small droplets, 0.83 um compared w:it:h 10 um for twelve pixels per mm and 1.67 um compared with L_'>.7 ~m for six pixels per mm. Also, the period during which a droplet; saquence is ejected, i.e.
64 x 10' - 0.35 mse~;. For 12 pixels per mm and 64 x 10' - 0.7 rnsec for six pixels per mm is short compared with the time, of: a few milliser_onds, that ink takes to be absorbed into the p<~per rnediurn.
Thus t=he deposited line: of ink droplets in each pixel have time to coll_e;:t anat :,pread as dots on the paper surface. The line in which the droplets from any particular nozzle are deposited ha; litt:le effe<:a on the shape but only on the diameter of the dot forvmed at the pixel. Figure 1 shows that the relative timing of the deposition of the lines of droplets at the pixels is cho:~~en so that each drop sequence is deposited symmetrically with respect to the corresponding p:ixel.. 'this reduces any distortion in the image which could resu:Lt. in c:ont.ouring a:nd inhibits any tendency to merging of the droplets deposited at adjacent pixels.
Referring now to Figure 2, there is illustrated therein a printhead 100, which is ~xenerally similar to that described i.n relation to figures 2. (a) vo (d) of co--pending European application No. 88300146.3. The printhead 100 comprises a sheet of piezo-electric medium poled in a direction normal thereto and formed with parallel channels 104 at a density of two or more per millimetre having channel dividing side walls 7.06. The channels 104 are each lined with a metal electrode ~.ayer (not shown). The channels which are ,arranged in the three groups of interleaved channels with the channels of the groups disposed successively, are actuated in shear mode by applying an electric potential difference between the electrode layer of art actuated cl-.ianne L and the electrode layers of the channel, s on eit:he..r si~:le of the actuated channel. The potential difference applied is a signal of frequenr_y at or near the longituciir~al acoustic: resonant _1c;_ frequency of the channels and is applied for the duration of a number of pu_L _~es cf the sign<~l corresponding to the number of droplets which i.t iv; des;.ired t:o eject from the actuated channel... The channels are supplied with printing liquid form a common supply duct 10f3 connected with each channel at t:he end thereof opposite that at which is located a nozzle plate ~~07 formed with respective nozzles 109 which terminate the channels. The nozzles of each group are co-li.nearly disposed transversely to the direction of medium , e.g. paper movement and the groups of nozzles are spaced in the direc:tLOn of medium movement.
Figure ~ i1_Lustrates circuitry for operating channels of one of tie three channel groups. This comprises connections 110 to v he electrodes of the channels of the group, like conneca:i.ons (not shown) being made to the electrodes of each of the channels of the other two groups.
The connections 110 le<~d to the channels 104 from a processor 1'~2 which is supplied with clock pulses from a conductor 1L4, the pulse: on which in sequence enable the connect:i~~ns 110 to t:he respective groups of channels. A further c_:lock line con.ducaor 116 provides the processor witLu clockpulses a frequency at or near shat at of the longitudinal acousticresonant: frequency the of channels. Print dai=<:.s_n the form of multi-bit words(a) instructs the procc=:ssor as to which channels of the group of channels which arE~ enabled by the pulse on the conductor 114 are to bc; selE:ec;t:ed for act:uat;ion, (b) activates the selected channels eawlu with a number from 1 to 64 of pu-uses at the frequency su~~plied by way of the conductor 116, and (c) locates the pu.L.ses activating the selected channels centrally in the pc:~riod during which the connections 110 of the group are enabi.ed.
They frequency of pulses supplied by way of the conductor 114 is one-hundredth -shat of the pulse frequency supplied by way of conductor 1.16 and the period of the pulses at the frequeZCy suppl_iec3 via conductor 116 is equal to the time taken fc>r successive pixels on the medium to pass the charnel nozzles. It will. apparent that clock be line conductor 114 is not strictly necessary since the proc essor can be arranged to afford pulses, divided from the pulses supplie<:L by of: conductor 116, for enabling way the connections 110 to of_ each group at the channels a frequency of one-hun<xredth that of the frequency supplied by way of the conductor 116.
It will aLao be apprec_iat=ed that at any instant during operation, an <actuated channel is separated from the next nearest actuated channel. by at least two inactive channels. Because o=E this cro:sstalk between channels is reduced and risk of spurious droplet ejection form inactive channels adjacent actuated channels is avoided.
The spacing, referred to above of channel nozzles of each grc~ul; in the directic>n of printing medium movement compensatc~~~ f_or the i.ime interval between the actuation of the selected chanr~.els or the groups so that printed spots deposited at the pixels of each row thereof transverse to medium movement appear substantially collinear.
Figure 3 illustr<zte~; diagrammatically an alternative manner _iru which them droplets are ejected from the nozzles of ten channels ef a :>egment of a high density array printhead of t:he type described in our co-pending European patent application No. 88300146.3, for example, with respect to figure 2(a) to (c) hereof. The channel here are arranged in sow groups of interleaved odd and even numbered channels. To act=ivate a s~~t of adjacent channels, the selected channce:Ls of one group a:re activated by applying a resonant:. waveform in alternating phase with the channels of the othcer group. Thus drops are ejected from channels of the two groups in numbers depending on the number of waveforms applied in al.t~srnating phases of the resonant waveform as t:he dividing walls pressurise channels of the interleaved groups alternately.
In Figure 3 t:he densities at pixels opposite the ten channel nozzles are for_ channels 1 to 10 respecti~,rely 64, 64, 60, 55, 40 3?, 17, 8, 5 and 1 droplets. A single pixel in the direction of re=L.ative mo t:ion between the printhead and paper: medium is traversed in a period which is equal to the period of 100 ~~ycles of the resonant frequency of the channels, i.e. for the frequencies 180 KHz and 90KHz of the t:a.~le set. out: above of typical values, respectively, 0.55 and 1.11 msE~cs. These times are those which it would take tc> emit 100 droplets from each channel.
The dots in the drawing represent droplets a maximum of 64 -1_8-of which are dep<>sited from any particular channel per pixel and the actuation of t:he channe:Ls is preferably arranged so that tl~e~ droplets depo~~i.ted from any particular channel are symmetr:ic<~lly deposited with respect to the pixel being p inted, that. is to say the centre of the pixel is traversed after the elapse of fifty of the hundred cycles allocated t~~ that pixel. The lateral pitch of the channel nozzle>_s is made equal to the longitudinal pitch of the pixels traversed by each nozzle.
Thl.rs in E~~.uch pixel period, i.e. the period in which, if su~plie<i to the elect=rodes of any particular channel, the applied voltage pulses would generate 1.00 droplets, the number of droplets from each channel would be between one arnd sixty--four in the numbers stated earlier.
The droplets are ejected from the selected odd numbered channels as a :result of actuating of the channels during the positive parts of t~l~e cycles and the selected even numberee~ channels ar_e actuated one half cycle following, that is to say, out of phase with, activation of the selected odd nurnl~>ere~_i channels.
Printing :atarts wi.'h the pixels having the maximum number:, i.e.,. 64, of droplets which are the pixels traversed by t:he noz::l.es of channels 1 and 2 and the timing of droplet deposition pro~~eeds a:~ follows:
Cycles Channels Cycles fhannel.s Cycles Channels Depositing Dex:~ositing Depositing Drops L>rop.s Drops 0 to NIL 30'~ 2, 4 42~ 2, 4, 6 19 1 31 l, 3, 5 43 1, 3, 5, 19~ 2 31~ 2,4 43~ 2,4,6 20 1 32 l, _3, 5 44 l, 3, 5, 20~ 2 32~ 2,4 44~ 2,4,6 21 1, 3 33 1, 3, 5 45 l, 3, 5, 21~ 2 33'-~i 2, 4 95~ 2, 4, 6 22 L, 3 34 l , 3, 5 46 1v3, 5, 22~ '? ~~4=~ 2, ~I 46~ 2, 4, 6 23 l, 3 35 1., 3, 5 47 l, 3, 5, 23'-~ 2, 4 3 5~ 2, 4, 6 47~ 2, 4, 6, 24 1, 3 36 l, 3, 5 48 l, 3, 5, 24~ 2, 4 36~ 2, 4, 6 48~ 2, 4, 6, 25 1, 3 3~7 1, ~, 5 49 l, 3, 5, 7, 9 25~ 2 , 4 37~ 2, ::_, 6 49'-~ 2, 4, 6, 26 1, 3 3F3 1, ~;, .'~ 50 1, 3, 5, 7, 9 26~ 2, 4 38~ 2, ~~, 6 50~~ 2, 4, 6, 8, 10 27 1, 3 39 l, _3, 5 51 l, 3, 5, 7, 9 27~ 2, 4 39~ 2, 4, 6 51~ 2, 4, 6, 28 l, 3 40 1, _~, 5 52 l, 3, 5, 7, 9 28~ 2,4 40~ 2,4,6 29 1, 3 41 1, ;, 5 etc. etc.
29~ 2, 4 41.~ ~', 4, 6 30 l, 3 4~' 1, 3, 5. 8~ t NIL
It will be apparent jvrorrc inspection of the above table that the band of actua':.ed channels gr~idually widens and then narrows. Channel No. _ thus deposits drops every cycle :From cycle 19 to cycle 82, channel No. 2 every half cycle From cycle 19~~ to 82~, :hannel No. 3 every cycle from cycle 21 to cycle 80, channel No. 4 ever~n h~~l.f cycle from cycle 23=~
to cycle 79=~, channe:L _'~ every circled from cycle 31 to cycle 70, channel 6 every half r_ycle from cycle 35~ to 66~, channel '7 every cyclEe from c:yclE: 4% to cycle 58, channel 8 every half cycle f rora c:ycl.e 47'~ ~o ~4'-~, channel 9 every cycle from cycle 49 to cycle 53, and channel 10 at half cycle 50~.
By reducing the period in which a pixel_ is traversed and redu:vng the density of printing, it becomes possible to simulate t=he laying down of lines of varying linear density.
Although in cperati_on either of described of the embodiments cf the invention the frequency operation, of which may be .in the range 25 to KHz, and small size 250 the of nozzle employed trend to ensuret;h<~t the sequences drop emitted from the nozzles compri~~e separate drops, there may be an inclination for tine first= few drops of a sequence to merge. 'Ibis can be avoided by applying initial sub-threshold resonant waveforms or- by increasing the energy content of the first few pulses applied by the electrically operated means of printhead to the channel selected for droplet ejection.
It is to .:~e noted that 1=he embodiment of Figure 3 represents a higher: speed (x~,) embodiment of printhead.
However it i~> lim_i.ted in the range of patterns it will print, to a maximum spatial frequency. It will print "white, black, white"; but not "black, white, black" across the row of channel:>. Differenr_1.~,~ expressed, the embodiment of Figure 3 with a d~nsit:y of nozzles at I2 per mm. prints any pattern at: s~.>at.iml_ frequencies o:E and below 4 lines per mm: but is restrict=ed in the patterns that= can be printed at spatial frequent.°y of 6 lines per nun. The embodiment of Figure 2 does not h:~w<~ such a rE=_:;triction but operates more slowly.
In the embodiment=s of the invention described with reference to Figures 2 and 3 the pulses of energy applied to the printing liquid in the channels of the array are obta:i.nE=d by t=he use of electrically displaceable charonel :>ide ua.~ll,s . fluid resonance in the channels oa= the pr_inthead can however be accomplished irl >ther way:;. For example, as earlier referred to, thermal energy L~ulses can be imparted to liquid in the channels f~~r droplet ejection. To perform the present invention the pulses would app=Lied at or near the nat~_~r_a_L longitudinal resonant frequency of the channels, the length and channel dimension's of which would be made such as to provide the requisite high resonant fre:~quency above 2:~ KHz. At relatively low specific energy, t:he energy coupling to the liquid in the channel; involves thermal expansion and contract:.i_on of thE.~ =L.:iquid and, above a specific energy threshold, the energy input= to the channel liquid would cause ~>ubblanucl_eatic~n and collapse.
Alt ernat ive forms c:~f actuation which might possibly be c:onsic~erved invo Lv~; a fluid which swells in the presence of ~ f field or which becomes solid and thus _inhi.bit~:, dis~~l.acement in the presence of a filed, the resonant energy being applied externally.
Aspects of such printi_ncl apparatus are described for example in Unites States Patent Specification 4,584,590 and our European Pat:ent Application Nos. 88300146.3 and 88300144.8.
The types of printing apparatus disclosed in the references quoted are of the kind in which energy pulses are imparted to dr_op_l_et liquid r»r displacement of wall portions of the respe:cti_ve droplet liquid channels. The present invention is, however, also applicable to drop-on-demand printing apparatus having an ar ay of channels such as is known .f=rom US-A 3, 1'79, 042, anc_I GB--A-2,. 007, 162 and GB-A-2, 106, 039 in which droplet= eject:ion :is effected from the channels by applying a pulse of thermal energy to droplet liquid therein.
_, <_ It is known that the human eye c:an sense sixty-four gradations of greyscale in multi-tone printing. It is even suggested t.h_rt- a:> many as 128 gradations can. be discriminated. Accordingly, it is one aim of high quality tone printing, including colon r printing, to produce a printer capab:l.e of print.i_ng a number of greyscale tone's as near as possible t.o the diac:~riminating capability of the eye of the viewer.
In the L)nited States specification 4,513,299 there is disclosed a single charvne_L, drop-on-demand ink jet printing device in wlic~u droplets of ink having different droplet volumes c:an be deposited on a print medium at a droplet repetition rate just. below the re~~onant frequency of the ink channel. The different droplet volumes are achieved by following a droplet. ejection pulse ,with additional droplet, ejection pulses of like magnitude to the initial droplet ejc~c:tion pul se at a frequency at or near the channel rescn~3nt ivrec~uency. The additional droplet ejection pulses cause ejection from the ink channel of further drop volumes of subatant:i.al.ly the same size as the drop volume emitted from the <_hannE>1 by t:he initial droplet ejection pulse. In t_ue series of drop volumes thus emiti~ed, the second and subsE:eduent drop volumes are each connected to the preceding drop volume en.itted and the drop volumes join together to form an enlarged droplet which is deposited on the ~m:int medium. However, in high density array drop-on--demand printer: s, ~. . a . an~rays of at least two parallel channels ~%er mm, the known method of droplet ejection severely limits, to only a few, the number of droplet volumes which can be added to the droplet volume initially ejected from any particular channel. This number diminishes rapidly with increase of channel density. It follows that the number of greyscale gradations which can be achieved by this known method is limited in the achievable number of different drop volumes which can be deposited at a pixel of the printed image.
It is, accordingly, an object of the present invention, to provide an improved method of greyscale printing which employs a drop-on-demand printer having an array of parallel channels which enables printing of a substantially greater number of greyscale gradations than has been achievable hitherto.
The present invention consists in the method of printing employing drop on demand ink jet apparatus comprising an array of parallel channels disposed side by side and having respective side walls which extend in the lengthwise direction of the channels and separate one from the next of the channels, a series of nozzles which communicate respectively with said channels for ejection of droplets of ink therefrom, connection means for connecting the channels with a source of ink and electrically actuable means for effecting upon selection of any of said channels transverse displacement of a portion at least of a channel separating side wall of said selected channel to apply a pulse of energy to ink contained in the selected channel to effect droplet ejection therefrom, characterised by the steps of choosing the length of said channels and the dimension and location of said nozzles to afford a longitudinal acoustic resonant frequency of 25 KHz or more, selecting a channel and a tone of printing for that channel, and actuating the electrically actuable means to apply a sequence of pulses of energy to cause droplet ejection from the selected channel at or near the longitudinal acoustic resonant frequency to eject a corresponding number of droplets, said number being determined by the selected tone of printing.
Alternatively, said electrically actuable means effect droplet ejection from said channels by causing thermal stress in the ink therein.
Preferably, where the medium is continuously moving during printing, droplet deposition from each channel takes place over a length of said medium which is within a printing element area traversed during printing by the channels.
Suitably, droplet deposition on said medium from each channel takes place over approximately two thirds of the pitch of the printing element areas in the direction of relative motion of the apparatus and medium and is symmetrically disposed with respect thereto. The pitch in the direction of relative motion between the medium and the printing apparatus of the printing element areas is suitable made equal to the ink channel pitch.
__ In one i:vorm, the method of the invention is practised wit:h a print head comprising a body of piezo-electric medium in which sai.cl channels ar_e formed and opposed channel dividing sid<> walls of each of said channels have respective piezo-F~lectric portions which are displaceable in shear mode by operation of said electrically actuable means to effect droplet ejection from said channel. When ::m.lch a printhead is employed, according to said form of the invention, the channels are divided into a plura:Lity of groups of= interleaved channels and droplet ejection is enabled. ire each group simultaneously from selected charnels, the charnels selected in such group being actuated in ~>uc cessive phases of the frequency of the applied enercxy pulses. In orie form the channels are arranged in t:wo groups and ,elect:ed channels of said two groups are enabled for drop_.et: ejection at interval's of half a cycle of them frequency of pulses applied by said electrically actuable mean:> to the channels selected for droplet ejection.
Where colour print:inc; i:~ reguired, the method of invention consists i.n arr_anging the array of channels in a set or sets of four xvowa of channels, the rows of each set being respectively suppl=ied with black .ink and ink of the t=hree primary col_ou:rs and disp:>sing the rows of each set for printing a row of pz:in~~i.rug element areas extending transversely to the di evect:i.on of relative me>tion of the array and the medium :~.o that each area printed can be printed in b:Lack i.nk or ink of one of the three primary colours.
The invention is not however restricted to array apparatus. Thus the invention also consists in the method of multi-tone printing employing drop-on-demand printing apparatus foiv depositing liquid droplets on a printing element area of a medium, comprising a liquid channel provided with an e=jection nozzle, droplet liquid supply means connected with said channel and electrically actuable means for applyincx pulses of energy to liquid in said channel to effect drop7_et eje<Jti.on therefrom, characterised by choosing the charnel. dimensi ons and the dimensions and location of i.~he nozzle so tha' said channel has a high longitudinal acoust:i_c resonant frequency and applying to liquid in said channEe:L by said electrically actuable means, one or a sequence o' pulses of energy of amplitude and frequency to cause d~:~oplet ejection from the nozzle of said channel at or near t:he resonant frequency of said channel thereby to eject a number of droplets from said nozzle corresponding to the number of pulses applied to the liquid in said channel, sai~~ number of: pulses being determined by the tone of print.i:~g required to be effected in said printing element area. In this fornl Of the invention the medium would normally be held s!~ationary relatively to the apparatus during printing. P.Lso in this form of the invention colour pr:Lnting can be effected by providing four channels respectively supplied with black ink and ink of the three primary colours, the nc~zzles of said channels -7_ being arranged so that each printing element area can be printed with any one of said inks.
The invention further consists in a drop on demand ink jet apparatus comprising an array of parallel channels disposed side by side and having respective side walls which extend in the lengthwise direction of the channels and separate one from the next of channels, a series of nozzles which communicate respectively with said channels for ejection of droplets of ink therefrom, connection means for connecting the channels with a source of ink and electrically actuable means for effecting upon selection of any of said channels transverse displacement of a portion at least of a channel separating side wall of said selected channel to apply a pulse of energy to ink contained in the selected channel to effect droplet ejection therefrom, characterised in that the length of said channels and the dimension and length of said nozzles are such as to afford a longitudinal acoustic resonant frequency of 25 KHz or more and that upon se~.ection of a channel and upon selection of a tone of printing for that channel, the electrically actuable means serves to apply a sequence of pulses of energy to cause droplet ejection from the selected channel at or near the longitudinal acoustic resonant frequency to eject a corresponding number of droplets, said number being determined by the selected tone of printing.
-g_ Said channels are advantageously arranged in a plurality of groups of interleaved channels, the channels of the respective groups being disposed in repeated sequences and said electrically actuable means are adapted to cause selected channels of each group to be enabled for actuation simultaneously and to effect enabling of the groups of channels in successive intervals of duration to allow ejection of several drops from the enabled channels.
Advantageously, the channel length, channel nozzle diameter and channel density of the apparatus lie respectively in the range 10 to lmm, 20 to 10~m and 2 to 12 per mm. For any particular printhead apparatus, the said dimensions are chosen to provide channel resonant frequencies of above 25 KHz.
Preferably, the chosen resonant frequency is in the range 50 KHz to 250 KHz.
The invention further consists in an electrically pulsed droplet deposition apparatus, comprising a liquid channel having an ink ejection nozzle, droplet liquid supply means connected with said channel and electrically actuable means for supplying pulses of energy to liquid in said channel to effect droplet ejection therefrom, characterised in t=hat the dimensions of the channel and the dimensions and location of the nozzle are adapted to provide t=he channel with a high longitudinal acoustic resonant frequency so that. application to ink in the channel of one or a sequence of pulses of energy of amplitude and freque~rucy at o:r near_ the resonant frequency of the channel causes ejection of droplets corresponding in number t.o said applied pu:Lses whereby the number of droplets deposited from the nozzle can be selected to correspond with a desired tone of printing.
Suitably, translating means are provided for moving the channel or group of ch<~nnels relatively t:o a medium to be printed..
In this manifestation of the invention where colour printing i.s require~_i there are provided four channels respectively supplied with black ink and ink of the three pr:Lmary colours, the nozzles of the channels being arranged so t=hat any printing element area of a medium can be printed with any one of said inks.
In a fu~::ther_ form, the invention consists i.n a drop-on-demand pr~.nting apparatus for depositing ink droplets on a mecaium compris:i.ng an array of printing channels provided wit=h respective nozzles for deposit=ing ink droplets on resl:ective printing element areas of raid medium, ink supply means conne~~ted with said channels and electrically actuable means for applying pulses of energy to ink in said c~anr.els to eff=e~Jt droplet ejection therefrom, characterised in tha.r the length of the channels and the location anc't dimensions of the nozzles provide the channels with high lc>ngitu<iinal resonant frequency so that application to ink in. the channels for a pulse sequence or of pulses of enerc:Yyofv amplitudeand frequency to cause droplet ejection from the channels at or near resonant the frequency of the charv_nels causes ejection of droplets form the channels come: ponding in number to the number of energy pulses applied to the .ink therein whereby the number of droplets deposit=ed from each nc>zzle can be selected to correspond with a desired tone of printing and effect printing witYu the medium stationary relatively to the apparatus.
The invention will now be described, by way of example with refei:e;:zce to the accompanying drawings, in which:
FIGURE 1 i_':~lustrates the effect of depositing in successive printing .element areas, that is to say, pixels, as the print medium moves past a nozzle of a channel of a drop-on-demand ink jet printer, a variable number of ink drops between 1 and F>4;
FIGURE 2 illustrates diagrammatically one embodiment of the invent: ion; arid FIGURE 3 illustrates diagrammatically, in another embodiment of: the invention, the printing of a line of printing element <areas or pixels from a group of ten channels, the respective nozzlea of which eject bursts of varying numbers of drc>plets between l and 64.
-l~.-The method of the invention can be performed by a drop-on-demand i.nls jet printing apparatus comprising an array, preferably a high dF:ns_ity array, of parallel uniformly spaced channels provided with respective droplet ejection nozzles, an ink supply common to said channels and electrically aca uabl.e means for displacing respective piezo-electric side wall portions of said channe l; to effect droplet ejectior: form the channels. In the prior United States specif.i_cation No. 4,'i84,590 referred to the displaceable piezo-electric side wall portions are provided as the top or roof walls of t:he respective channels, the channel density bez.ng up to two pe:r mm, whereas in our co-pending European pate=nt: applic:at:ion No. 88300146.3 there is described e.g. witru reference to Figs, 2(a) - (d), a form of printhead in which said disp~.aceable piezo-electric wall portions comprise the channel dividing side walls. In this latter case each ~:W t=he channel dividing side walls is shared between the channels which it separates so that in a first of successive phases of operation it can be defle~~ted together with the taping wall oL one of the channels which it separates to eject. a droplet from said one of the channels whilst in a succeeding phase of the operation the said channel dividing wall together with the facing side wall of the other of t=he channels which it separates can be deflected to eject: a droplet: from said other of the channels. The chanr~.el densities of such printheads can be from 2 to 16 per mrn. Hitherto, the operation of this worm of printhead has been limited to the application of a voltage waveform pulse which acts :o eject a single drop of ink from the channel. to which the pulse is applied. The present invention calls for droplet ejection from the channels at high frequency at o:r near the longitudinal acoustic resonant frequency of the channels. Accordingly the channel length and nozzle dimensions have to be chosen to that end.
Printhead:~ of the kind described can also be employed according t:o this irmer_tion as greyscale and, therefore, colour printers. An acceptable range of resolution of print=ir~_g element areas or pixels on a paper medium for a prirut:head as described in our co-pending European patent appl..ication referred t:o would be 6 to 12 per mm. In the area corresponding to each pixel, a variable number of droplets in t:he range i t:o 64 is made available as hereinafter described.
Typical values of ink drop parameters at each channel nozzle and on the paper medium area are as follows:
Resolution Pitch Full 64 Single Single Droplet of of I%r~~plet Da_op Droplet Frequency Printhead Nozzles Volume Volume Diameter -/mm um ~~l ~>1 Ixm KHz 12 83 33 0.51 10 180 6 167 130 2.04 15.7 90 The full :=~.i.ze drop volume, which forms a pool of 64 single ejected smal_.1 droplets on the paper medium is chosen to forms cone iruaous dots at: fu_Ll tone.
-l Figures 1 shows the effect of depositing a variable number of ink droplets between 1 and 64 in successive pixels a:; the paper moves past the nozzle.
Typically, the maximum droplet production frequency is sufficient to genermt:e 100 droplets per pixel, so that if 64 droplets a.re generated, these are deposited in a line occupying approximat=ely 2/3 of: the pixel pitch "p" . When smaller numbers of droplets a.x:e generated as a sequence these are deposited along correspondingly shorter lines.
From the above table of typical values and assuming there are 100 droplets able to be generated per pixel, the spacing between droplets deposited longitudinally in each pixel, for_ Twelve pixels per mm, is 0.83 um and for six ~~ixels per mm is 1.67 um. Laterally the nozzle pitch is equal to the pixel pitch. The spacing in the lines in which they are deposited of the small droplets is small compared with the diameter of the small droplets, 0.83 um compared w:it:h 10 um for twelve pixels per mm and 1.67 um compared with L_'>.7 ~m for six pixels per mm. Also, the period during which a droplet; saquence is ejected, i.e.
64 x 10' - 0.35 mse~;. For 12 pixels per mm and 64 x 10' - 0.7 rnsec for six pixels per mm is short compared with the time, of: a few milliser_onds, that ink takes to be absorbed into the p<~per rnediurn.
Thus t=he deposited line: of ink droplets in each pixel have time to coll_e;:t anat :,pread as dots on the paper surface. The line in which the droplets from any particular nozzle are deposited ha; litt:le effe<:a on the shape but only on the diameter of the dot forvmed at the pixel. Figure 1 shows that the relative timing of the deposition of the lines of droplets at the pixels is cho:~~en so that each drop sequence is deposited symmetrically with respect to the corresponding p:ixel.. 'this reduces any distortion in the image which could resu:Lt. in c:ont.ouring a:nd inhibits any tendency to merging of the droplets deposited at adjacent pixels.
Referring now to Figure 2, there is illustrated therein a printhead 100, which is ~xenerally similar to that described i.n relation to figures 2. (a) vo (d) of co--pending European application No. 88300146.3. The printhead 100 comprises a sheet of piezo-electric medium poled in a direction normal thereto and formed with parallel channels 104 at a density of two or more per millimetre having channel dividing side walls 7.06. The channels 104 are each lined with a metal electrode ~.ayer (not shown). The channels which are ,arranged in the three groups of interleaved channels with the channels of the groups disposed successively, are actuated in shear mode by applying an electric potential difference between the electrode layer of art actuated cl-.ianne L and the electrode layers of the channel, s on eit:he..r si~:le of the actuated channel. The potential difference applied is a signal of frequenr_y at or near the longituciir~al acoustic: resonant _1c;_ frequency of the channels and is applied for the duration of a number of pu_L _~es cf the sign<~l corresponding to the number of droplets which i.t iv; des;.ired t:o eject from the actuated channel... The channels are supplied with printing liquid form a common supply duct 10f3 connected with each channel at t:he end thereof opposite that at which is located a nozzle plate ~~07 formed with respective nozzles 109 which terminate the channels. The nozzles of each group are co-li.nearly disposed transversely to the direction of medium , e.g. paper movement and the groups of nozzles are spaced in the direc:tLOn of medium movement.
Figure ~ i1_Lustrates circuitry for operating channels of one of tie three channel groups. This comprises connections 110 to v he electrodes of the channels of the group, like conneca:i.ons (not shown) being made to the electrodes of each of the channels of the other two groups.
The connections 110 le<~d to the channels 104 from a processor 1'~2 which is supplied with clock pulses from a conductor 1L4, the pulse: on which in sequence enable the connect:i~~ns 110 to t:he respective groups of channels. A further c_:lock line con.ducaor 116 provides the processor witLu clockpulses a frequency at or near shat at of the longitudinal acousticresonant: frequency the of channels. Print dai=<:.s_n the form of multi-bit words(a) instructs the procc=:ssor as to which channels of the group of channels which arE~ enabled by the pulse on the conductor 114 are to bc; selE:ec;t:ed for act:uat;ion, (b) activates the selected channels eawlu with a number from 1 to 64 of pu-uses at the frequency su~~plied by way of the conductor 116, and (c) locates the pu.L.ses activating the selected channels centrally in the pc:~riod during which the connections 110 of the group are enabi.ed.
They frequency of pulses supplied by way of the conductor 114 is one-hundredth -shat of the pulse frequency supplied by way of conductor 1.16 and the period of the pulses at the frequeZCy suppl_iec3 via conductor 116 is equal to the time taken fc>r successive pixels on the medium to pass the charnel nozzles. It will. apparent that clock be line conductor 114 is not strictly necessary since the proc essor can be arranged to afford pulses, divided from the pulses supplie<:L by of: conductor 116, for enabling way the connections 110 to of_ each group at the channels a frequency of one-hun<xredth that of the frequency supplied by way of the conductor 116.
It will aLao be apprec_iat=ed that at any instant during operation, an <actuated channel is separated from the next nearest actuated channel. by at least two inactive channels. Because o=E this cro:sstalk between channels is reduced and risk of spurious droplet ejection form inactive channels adjacent actuated channels is avoided.
The spacing, referred to above of channel nozzles of each grc~ul; in the directic>n of printing medium movement compensatc~~~ f_or the i.ime interval between the actuation of the selected chanr~.els or the groups so that printed spots deposited at the pixels of each row thereof transverse to medium movement appear substantially collinear.
Figure 3 illustr<zte~; diagrammatically an alternative manner _iru which them droplets are ejected from the nozzles of ten channels ef a :>egment of a high density array printhead of t:he type described in our co-pending European patent application No. 88300146.3, for example, with respect to figure 2(a) to (c) hereof. The channel here are arranged in sow groups of interleaved odd and even numbered channels. To act=ivate a s~~t of adjacent channels, the selected channce:Ls of one group a:re activated by applying a resonant:. waveform in alternating phase with the channels of the othcer group. Thus drops are ejected from channels of the two groups in numbers depending on the number of waveforms applied in al.t~srnating phases of the resonant waveform as t:he dividing walls pressurise channels of the interleaved groups alternately.
In Figure 3 t:he densities at pixels opposite the ten channel nozzles are for_ channels 1 to 10 respecti~,rely 64, 64, 60, 55, 40 3?, 17, 8, 5 and 1 droplets. A single pixel in the direction of re=L.ative mo t:ion between the printhead and paper: medium is traversed in a period which is equal to the period of 100 ~~ycles of the resonant frequency of the channels, i.e. for the frequencies 180 KHz and 90KHz of the t:a.~le set. out: above of typical values, respectively, 0.55 and 1.11 msE~cs. These times are those which it would take tc> emit 100 droplets from each channel.
The dots in the drawing represent droplets a maximum of 64 -1_8-of which are dep<>sited from any particular channel per pixel and the actuation of t:he channe:Ls is preferably arranged so that tl~e~ droplets depo~~i.ted from any particular channel are symmetr:ic<~lly deposited with respect to the pixel being p inted, that. is to say the centre of the pixel is traversed after the elapse of fifty of the hundred cycles allocated t~~ that pixel. The lateral pitch of the channel nozzle>_s is made equal to the longitudinal pitch of the pixels traversed by each nozzle.
Thl.rs in E~~.uch pixel period, i.e. the period in which, if su~plie<i to the elect=rodes of any particular channel, the applied voltage pulses would generate 1.00 droplets, the number of droplets from each channel would be between one arnd sixty--four in the numbers stated earlier.
The droplets are ejected from the selected odd numbered channels as a :result of actuating of the channels during the positive parts of t~l~e cycles and the selected even numberee~ channels ar_e actuated one half cycle following, that is to say, out of phase with, activation of the selected odd nurnl~>ere~_i channels.
Printing :atarts wi.'h the pixels having the maximum number:, i.e.,. 64, of droplets which are the pixels traversed by t:he noz::l.es of channels 1 and 2 and the timing of droplet deposition pro~~eeds a:~ follows:
Cycles Channels Cycles fhannel.s Cycles Channels Depositing Dex:~ositing Depositing Drops L>rop.s Drops 0 to NIL 30'~ 2, 4 42~ 2, 4, 6 19 1 31 l, 3, 5 43 1, 3, 5, 19~ 2 31~ 2,4 43~ 2,4,6 20 1 32 l, _3, 5 44 l, 3, 5, 20~ 2 32~ 2,4 44~ 2,4,6 21 1, 3 33 1, 3, 5 45 l, 3, 5, 21~ 2 33'-~i 2, 4 95~ 2, 4, 6 22 L, 3 34 l , 3, 5 46 1v3, 5, 22~ '? ~~4=~ 2, ~I 46~ 2, 4, 6 23 l, 3 35 1., 3, 5 47 l, 3, 5, 23'-~ 2, 4 3 5~ 2, 4, 6 47~ 2, 4, 6, 24 1, 3 36 l, 3, 5 48 l, 3, 5, 24~ 2, 4 36~ 2, 4, 6 48~ 2, 4, 6, 25 1, 3 3~7 1, ~, 5 49 l, 3, 5, 7, 9 25~ 2 , 4 37~ 2, ::_, 6 49'-~ 2, 4, 6, 26 1, 3 3F3 1, ~;, .'~ 50 1, 3, 5, 7, 9 26~ 2, 4 38~ 2, ~~, 6 50~~ 2, 4, 6, 8, 10 27 1, 3 39 l, _3, 5 51 l, 3, 5, 7, 9 27~ 2, 4 39~ 2, 4, 6 51~ 2, 4, 6, 28 l, 3 40 1, _~, 5 52 l, 3, 5, 7, 9 28~ 2,4 40~ 2,4,6 29 1, 3 41 1, ;, 5 etc. etc.
29~ 2, 4 41.~ ~', 4, 6 30 l, 3 4~' 1, 3, 5. 8~ t NIL
It will be apparent jvrorrc inspection of the above table that the band of actua':.ed channels gr~idually widens and then narrows. Channel No. _ thus deposits drops every cycle :From cycle 19 to cycle 82, channel No. 2 every half cycle From cycle 19~~ to 82~, :hannel No. 3 every cycle from cycle 21 to cycle 80, channel No. 4 ever~n h~~l.f cycle from cycle 23=~
to cycle 79=~, channe:L _'~ every circled from cycle 31 to cycle 70, channel 6 every half r_ycle from cycle 35~ to 66~, channel '7 every cyclEe from c:yclE: 4% to cycle 58, channel 8 every half cycle f rora c:ycl.e 47'~ ~o ~4'-~, channel 9 every cycle from cycle 49 to cycle 53, and channel 10 at half cycle 50~.
By reducing the period in which a pixel_ is traversed and redu:vng the density of printing, it becomes possible to simulate t=he laying down of lines of varying linear density.
Although in cperati_on either of described of the embodiments cf the invention the frequency operation, of which may be .in the range 25 to KHz, and small size 250 the of nozzle employed trend to ensuret;h<~t the sequences drop emitted from the nozzles compri~~e separate drops, there may be an inclination for tine first= few drops of a sequence to merge. 'Ibis can be avoided by applying initial sub-threshold resonant waveforms or- by increasing the energy content of the first few pulses applied by the electrically operated means of printhead to the channel selected for droplet ejection.
It is to .:~e noted that 1=he embodiment of Figure 3 represents a higher: speed (x~,) embodiment of printhead.
However it i~> lim_i.ted in the range of patterns it will print, to a maximum spatial frequency. It will print "white, black, white"; but not "black, white, black" across the row of channel:>. Differenr_1.~,~ expressed, the embodiment of Figure 3 with a d~nsit:y of nozzles at I2 per mm. prints any pattern at: s~.>at.iml_ frequencies o:E and below 4 lines per mm: but is restrict=ed in the patterns that= can be printed at spatial frequent.°y of 6 lines per nun. The embodiment of Figure 2 does not h:~w<~ such a rE=_:;triction but operates more slowly.
In the embodiment=s of the invention described with reference to Figures 2 and 3 the pulses of energy applied to the printing liquid in the channels of the array are obta:i.nE=d by t=he use of electrically displaceable charonel :>ide ua.~ll,s . fluid resonance in the channels oa= the pr_inthead can however be accomplished irl >ther way:;. For example, as earlier referred to, thermal energy L~ulses can be imparted to liquid in the channels f~~r droplet ejection. To perform the present invention the pulses would app=Lied at or near the nat~_~r_a_L longitudinal resonant frequency of the channels, the length and channel dimension's of which would be made such as to provide the requisite high resonant fre:~quency above 2:~ KHz. At relatively low specific energy, t:he energy coupling to the liquid in the channel; involves thermal expansion and contract:.i_on of thE.~ =L.:iquid and, above a specific energy threshold, the energy input= to the channel liquid would cause ~>ubblanucl_eatic~n and collapse.
Alt ernat ive forms c:~f actuation which might possibly be c:onsic~erved invo Lv~; a fluid which swells in the presence of ~ f field or which becomes solid and thus _inhi.bit~:, dis~~l.acement in the presence of a filed, the resonant energy being applied externally.
Claims (31)
1. The method of printing employing drop on demand ink jet apparatus comprising an array of parallel channels disposed side by side and having respective side walls which extend in the lengthwise direction of the channels and separate one from the next of the channels; a series of nozzles which communicate respectively with said channels for ejection of droplets of ink therefrom; connection means for connecting the channels with a source of ink and electrically actuable means for effecting upon selection of any of said channels transverse displacement of a portion at least of a channel separating side wall of said selected channel to apply a pulse of energy to ink contained in the selected channel to effect droplet ejection therefrom; characterised by the steps of choosing the length of said channels and the dimension and location of said nozzles to afford a longitudinal acoustic resonant frequency of 25 KHz or more; selecting a channel and a tone of printing for that channel, and actuating the electrically actuable means to apply a sequence of pulses of energy to cause droplet ejection from the selected channel at or near the longitudinal acoustic resonant frequency to eject a corresponding number of droplets, said number being determined by the selected tone of printing.
2. The method as claimed in Claim 1, wherein said electrically actuable means effecting droplet ejection from said channels by displacement of respective, piezo-electric side wall portions of said channels.
3. The method claimed in Claim 1 or Claim 2, and in which the medium being printed on is moving continuously relatively to the printing apparatus, characterised by effecting droplet deposition from each channel over a length of said medium within a printing element area traversed by said channel.
4. The method claimed in Claim 3, characterised by effecting droplet deposition on said medium from each channel in approximately two thirds of the pitch of said printing element areas.
5. The method claimed in Claim 3 or Claim 4, characterised by enabling deposition on each printing element area from the corresponding channel of any number, up to sixty-four of droplets.
6. The method claimed in Claim 3, Claim 4 or Claim 5, comprising the step of effecting droplet deposition on said medium symmetrically with respect to the center of said length of the medium within the printing element area printed by said channel.
7. The method claimed in any one of Claims 3 to 6, comprising the step of effecting substantial equality between the pitch of the printing element areas on the medium in said direction of relative movement and the pitch of said nozzles.
8. The method claimed in any one of claims 1 to 7, in which said apparatus is a printhead comprising a body of piezo-electric medium in which said channels are formed and opposed channel dividing side walls of each of said channels have respective piezo-electric portions which are displaceable in shear mode by operation of said electrically actuable means to effect droplet ejection from said channel, comprising arranging the channels in a plurality of groups of interleaved channels, enabling simultaneously in each group for droplet ejection selected channels thereof and actuating the selected channels of each group in successive phases of the frequency of said energy pulses.
9. The method claimed in Claim 8, and in which the channels are arranged in two groups, comprising the step of enabling for droplet ejection selected channels of one of said groups at an interval following enabling of selected channels of the other of said groups of a half cycle of the frequency of pulses applied by said electrically operated means to the channels selected for droplet ejection.
10. The method according to any one of Claims 1 to 8, wherein the channels are arranged in two interleaved groups of odd and even channels respectively, comprising the steps of selecting a band of adjacent channels for droplet ejection and actuating the electrically actuable means to apply sequences of pulses of energy to the odd channels of the band in anti-phase with sequences of pulses of energy applied to the even channels of the band to eject corresponding numbers of droplets from the odd channels in the band in anti-phase with the ejection of droplets from the even channels in the band.
11. The method according to Claim 10, comprising the further step of varying the width of the band of selected channels in successive cycles of the resonant frequency to vary the print density.
12. The method claimed in any one of Claims 1 to 7 in which said apparatus is a printhead comprising a body of piezo-electric medium in which said channels are formed and opposed channel dividing side walls of each of said channels have respective piezo-electric portions which are displaceable by said electrically actuable means to effect droplet ejection from said channels, characterised by arranging said channels in at least three groups of interleaved channels, each group having between successive channels a channel of each of the other groups and simultaneously enabling for droplet ejection therefrom, droplet ejection of droplets from selected channels of each group being effected in successive intervals.
13. The method claimed in any one of claims 1 to 12, wherein the channel length, channel nozzle diameter and channel density respectively lie in the ranges of 10 to 1mm, 20 to 10 µm and 2 to 12 per mm.
14 . The method claimed in any one of claims 1 to 13, wherein said frequency of pulses applied by the electrically actuated means is in the range 50 KHz to 250 KHz.
15 . The method claimed in any one of claims 1 to 14, comprising the step of controlling the energy content of initial pulses of each of said sequences of pulses to ensure that the droplets emitted by said initial pulses are discrete.
16. The method claimed in Claim 1, in which the channels are arranged in a plurality of rows extending transversely to the direction of relative motion of the medium and the apparatus and the nozzle pitch in each row is a multiple equal to the number of said rows of the pitch of said printing element areas in the direction transverse to said direction of relative motion, comprising the step of disposing the rows of channel and their nozzles so that the nozzles of one row serve to print picture element areas of a row of such areas on the medium which are being printed which extends normal to said direction of relative motion which are interleaved with those which the nozzles of the other rows serve to print.
17.The method claimed in Claim 1, comprising the step of effecting each printing operation within a printing element area with the medium and apparatus stationary and causing relative motion between the medium and the apparatus between successive printing operations to move the medium relatively to the apparatus by the pitch in said direction of relative motion of the printing element areas.
18.The method claimed in Claim 17, comprising the step of printing by depositing droplets from the channel nozzles in the centre of each printing element area printed.
19.The method claimed in any one of claims 1 to 18, comprising the step of arranging arrays of channels in a set or sets of four rows of channels, the rows of each set being respectively supplied with black ink and ink of the three primary colours and disposing the rows of each set for printing a row of printing element areas extending transversely to the direction of relative motion of the array and the medium so that each area printed can be printed in black ink or ink of any of the three primary colours.
20. Drop on demand ink jet apparatus comprising an array of parallel channels disposed side by side and having respective side walls which extend in the lengthwise direction of the channels and separate one from the next of the channels; a series of nozzles which communicate respectively with said channels for ejection of droplets of ink therefrom; connection means for connecting the channels with a source of ink and electrically actuable means for effecting upon selection of any of said channels transverse displacement of a portion at least of a channel separating side wall of said selected channel to apply a pulse of energy to ink contained in the selected channel to effect droplet ejection therefrom; characterised in that the length of said channels and the dimension and length of said nozzles are such as to afford a longitudinal acoustic resonant frequency of 25 KHz or more and that upon selection of a channel and upon selection of a tone of printing for that channel, the electrically actuable means serves to apply a sequence of pulses of energy to cause droplet ejection from the selected channel at or near the longitudinal acoustic resonant frequency to eject a corresponding number of droplets, said number being determined by the selected tone of printing.
21. Apparatus as claimed in Claim 20, wherein said channels are formed in a body of piezo-electric medium and have side wall portions poled so as to be displaceable by operation of said electrically actuable means.
22 Apparatus as claimed in Claim 21, wherein said side wall portions are poled so as to be displaced in shear mode by said electrically actuable means.
23.Apparatus as claimed in any one of claims 20 to 22 wherein said channels are arranged in a plurality of groups of interleaved channels, the channels of the respective groups being disposed in repeated sequences and said electrically actuable means are adapted to cause selected channels of each group to be enabled for actuation simultaneously and to effect enabling of the groups of channels in successive intervals of duration to allow ejection of several drops from the enabled channels.
24. Apparatus as claimed in Claim 23 in which all channel dividing side walls are actuable and facing channel side walls are displaced by said electrically actuable means to effect droplet ejection from a channel therebetween, wherein the channels are arranged in at least three groups of interleaved channels.
25.Apparatus according to any one of Claims 20 to 23 wherein the channels are arranged in two interleaved groups of odd and even channels respectively and wherein the electrically actuable means serves upon selection of a band of adjacent channels to apply sequences of pulses of energy to the odd channels of the band in anti-phase with sequences of pulses of energy applied to the even channels of the band to eject corresponding numbers of droplets from the odd channels in the band in anti-phase with the ejection of droplets from the even channels of the band.
26. Apparatus as claimed in Claim 20, in which all channel dividing side walls are displaceable and facing channel side walls are displaced by said electrically actuable means to effect droplet ejection from a channel therebetween, wherein the channels are arranged in two groups of interleaved channels and said electrically actuable means are adapted to enable simultaneously selected channels of the respective groups and to enable the groups of channels in sequence, the period that channels of the groups are enabled being adequate to allow ejection of several droplets therefrom.
27. Apparatus as claimed in Claim 26, wherein said electrically actuable means are adapted to enable droplet ejection from adjacent channels at successive half cycles of the frequency of actuation pulses applied to the channels.
28.Apparatus as claimed in any one of Claims 20 to 27, wherein said electrically actuable means are adapted to enable each channel for a period sufficient for ejection therefrom of up to sixty-four droplets .
29. Apparatus as claimed in any one of Claims 20 to 28, where in the channel length, channel nozzle diameter and channel density respectively lie in the range 10 to 1mm, 20 to 10µm and 2 to 12 per mm.
30. Apparatus as claimed in any one of Claims 20 to 29, wherein the channels are arranged in a plurality of rows extending in operation when said apparatus is printing on printing element areas of a medium transversely to the direction of relative motion between the apparatus and the medium and the nozzle pitch in each row is a multiple equal to the number of said rows of the pitch said printing element areas in the direction transverse to said direction of relative motion and said channels and their nozzles are disposed so that the nozzles of each row serve to print picture element areas of a row of such areas on the medium which are being printed which extends normal to said direction of relative motion and which are interleaved with those which the nozzles of the other rows serve to print.
31. Apparatus as claimed in any one of Claims 20 to 30, wherein the array of channels is arranged in a set or sets of four rows of channels, the rows of each set being adapted for the supply thereto respectively of black ink and ink of one of the three primary colours, and the nozzles of the rows of each set are disposed to enable printing of printing elements areas by any channel of said set in black ink or ink of any one of the three primary colours.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB898922821A GB8922821D0 (en) | 1989-10-10 | 1989-10-10 | Method of multi-tone printing |
| GB8922821.7 | 1989-10-10 | ||
| GB909001493A GB9001493D0 (en) | 1990-01-23 | 1990-01-23 | Method of multi-tone printing |
| GB9001493.7 | 1990-01-23 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2027161A1 CA2027161A1 (en) | 1991-04-11 |
| CA2027161C true CA2027161C (en) | 2004-02-24 |
Family
ID=26296027
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002027161A Expired - Lifetime CA2027161C (en) | 1989-10-10 | 1990-10-09 | Method of multi-tone printing |
Country Status (8)
| Country | Link |
|---|---|
| US (1) | US5361084A (en) |
| EP (1) | EP0422870B1 (en) |
| JP (2) | JP2800065B2 (en) |
| AT (1) | ATE116908T1 (en) |
| CA (1) | CA2027161C (en) |
| DE (1) | DE69015953T2 (en) |
| DK (1) | DK0422870T3 (en) |
| ES (1) | ES2066149T3 (en) |
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-
1990
- 1990-10-08 ES ES90311001T patent/ES2066149T3/en not_active Expired - Lifetime
- 1990-10-08 DK DK90311001.3T patent/DK0422870T3/en active
- 1990-10-08 EP EP90311001A patent/EP0422870B1/en not_active Expired - Lifetime
- 1990-10-08 AT AT90311001T patent/ATE116908T1/en not_active IP Right Cessation
- 1990-10-08 DE DE69015953T patent/DE69015953T2/en not_active Expired - Lifetime
- 1990-10-09 US US07/594,772 patent/US5361084A/en not_active Expired - Lifetime
- 1990-10-09 CA CA002027161A patent/CA2027161C/en not_active Expired - Lifetime
- 1990-10-11 JP JP2270645A patent/JP2800065B2/en not_active Expired - Lifetime
-
1995
- 1995-10-25 JP JP7277381A patent/JP2881566B2/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| DK0422870T3 (en) | 1995-03-27 |
| CA2027161A1 (en) | 1991-04-11 |
| JP2800065B2 (en) | 1998-09-21 |
| US5361084A (en) | 1994-11-01 |
| EP0422870B1 (en) | 1995-01-11 |
| JP2881566B2 (en) | 1999-04-12 |
| EP0422870A3 (en) | 1991-07-03 |
| ES2066149T3 (en) | 1995-03-01 |
| DE69015953T2 (en) | 1995-05-11 |
| EP0422870A2 (en) | 1991-04-17 |
| JPH08207319A (en) | 1996-08-13 |
| ATE116908T1 (en) | 1995-01-15 |
| JPH03173655A (en) | 1991-07-26 |
| DE69015953D1 (en) | 1995-02-23 |
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