EP0751873B1 - Verbesserungen an einer gepulsten tröpfchen-niederschlagsvorrichtung - Google Patents

Verbesserungen an einer gepulsten tröpfchen-niederschlagsvorrichtung Download PDF

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Publication number
EP0751873B1
EP0751873B1 EP95911395A EP95911395A EP0751873B1 EP 0751873 B1 EP0751873 B1 EP 0751873B1 EP 95911395 A EP95911395 A EP 95911395A EP 95911395 A EP95911395 A EP 95911395A EP 0751873 B1 EP0751873 B1 EP 0751873B1
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EP
European Patent Office
Prior art keywords
voltage
channels
channel
pressure
waveform
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Expired - Lifetime
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EP95911395A
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English (en)
French (fr)
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EP0751873A1 (de
Inventor
Stephen Temple
Michael George Arnott
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Xaar Technology Ltd
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Xaar Technology Ltd
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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
    • B41J2/015—Ink jet characterised by the jet generation process
    • B41J2/04—Ink jet characterised by the jet generation process generating single droplets or particles on demand
    • B41J2/045—Ink jet characterised by the jet generation process generating single droplets or particles on demand by pressure, e.g. electromechanical transducers
    • B41J2/04501—Control methods or devices therefor, e.g. driver circuits, control circuits
    • B41J2/04525—Control methods or devices therefor, e.g. driver circuits, control circuits reducing occurrence of cross talk
    • 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
    • B41J2/015—Ink jet characterised by the jet generation process
    • B41J2/04—Ink jet characterised by the jet generation process generating single droplets or particles on demand
    • B41J2/045—Ink jet characterised by the jet generation process generating single droplets or particles on demand by pressure, e.g. electromechanical transducers
    • B41J2/04501—Control methods or devices therefor, e.g. driver circuits, control circuits
    • B41J2/04581—Control methods or devices therefor, e.g. driver circuits, control circuits controlling heads based on piezoelectric elements
    • 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
    • B41J2/015—Ink jet characterised by the jet generation process
    • B41J2/04—Ink jet characterised by the jet generation process generating single droplets or particles on demand
    • B41J2/045—Ink jet characterised by the jet generation process generating single droplets or particles on demand by pressure, e.g. electromechanical transducers
    • B41J2/04501—Control methods or devices therefor, e.g. driver circuits, control circuits
    • B41J2/04588—Control methods or devices therefor, e.g. driver circuits, control circuits using a specific waveform
    • 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
    • B41J2/015—Ink jet characterised by the jet generation process
    • B41J2/04—Ink jet characterised by the jet generation process generating single droplets or particles on demand
    • B41J2/045—Ink jet characterised by the jet generation process generating single droplets or particles on demand by pressure, e.g. electromechanical transducers
    • B41J2/04501—Control methods or devices therefor, e.g. driver circuits, control circuits
    • B41J2/04596—Non-ejecting pulses
    • 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
    • B41J2/015—Ink jet characterised by the jet generation process
    • B41J2/04—Ink jet characterised by the jet generation process generating single droplets or particles on demand
    • B41J2/045—Ink jet characterised by the jet generation process generating single droplets or particles on demand by pressure, e.g. electromechanical transducers
    • B41J2/055—Devices for absorbing or preventing back-pressure
    • 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
    • B41J2202/00—Embodiments of or processes related to ink-jet or thermal heads
    • B41J2202/01—Embodiments of or processes related to ink-jet heads
    • B41J2202/10—Finger type piezoelectric elements

Definitions

  • the present invention relates to pulsed droplet deposition apparatus, for example drop-on-demand-ink jet printing apparatus and, in the most important example, provides voltage waveforms for the control of such apparatus.
  • Ink jet printing apparatus having a multiplicity of closely spaced parallel ink channels and channel separating piezo-electrically displaceable wall actuators have been disclosed for example in US-A-4879568 (EP-B-0277703) and in US-A-4887100 (EP-B-0278590).
  • each channel is actuable by one or both of the displaceable side-walls.
  • an external connection is provided which relates to each channel and when a voltage difference is applied between the electrode corresponding to one channel and the electrodes of the neighbouring channels, the walls adjacent to the channel are displaced causing the volume of the centre channel, depending on the voltage sign, to expand or to contract and an ink drop to be ejected from the nozzle communicating with the channel.
  • One feature of the above printing apparatus having displaceable side-walls is that operation of every channel at the same time is excluded. Operation takes place by dividing the printhead into two groups of odd and even channels, which are operated alternately. Alternatively the printhead is divided into groups of three, four or more channels which are operated in rotation (EP-A-0376532).
  • Such a waveform is implemented in the prior art by an oscillatory circuit, or if a pulsed waveform generator is employed pulses of both positive and negative polarity are required to generate it.
  • the drive circuit necessarily takes the form of an integrated circuit chip, and such devices have the disadvantage of being considerably more expensive if required to handle bipolar signals.
  • the present invention seeks to reduce or eliminate one or both of the foregoing disadvantages.
  • the present invention consists in one aspect in a method of operating multichannel pulsed droplet deposition apparatus having droplet liquid channels each with a nozzle having a negative pressure wave reflection coefficient r , where r is negative, and each channel having a negative pressure wave reflection coefficient at the termination connected to droplet liquid supply means, the method comprising ejecting a droplet from a selected channel by generating a defined pressure pulse therein and substantially cancelling residual pressure waves in said channel by generating a further pressure pulse of opposite sign to said defined pressure pulse after a delay of 2L/c where L is the length of the channel and c is the effective velocity of pressure waves therein.
  • the amplitude of said further pressure pulse being related to the amplitude of said defined pressure pulse by the factor r .
  • the method comprises ejecting a droplet from a selected channel by generating a negative pressure pulse of duration L / c followed by a positive pressure pulse of duration at least L / c with the duration of said positive pressure pulse preferably being 2L / c .
  • the selected channel is bounded by a displaceable wall actuator, displacement of which generates said first and further pressure pulses, said actuator also bounding an adjacent non-selected channel, the selected and non-selected channels being in respective groups of channels which are actuated sequentially, the displacement of the actuator also generating a complementary first pressure pulse in the adjacent channel and a complementary further pulse in said adjacent channel which cancels residual pressure waves therein arising from the complementary first pressure pulse.
  • the present invention consists in a method of operating multichannel pulsed droplet deposition apparatus having droplet liquid channels each with a nozzle having a pressure wave reflection coefficient r , where r is negative, the channels being separated by wall actuators displaceable on the application thereto of a voltage difference, each channel having electrode means associated with the wall actuators bounding that channel such that a voltage difference can be applied to a specified wall actuator by the application of different voltages to the respective electrode means of the two channels separated by the said wall actuator, the method comprising the actuation of a selected channel through the steps of applying in different time periods a first actuating voltage to the electrode means of the selected channel and a second actuating voltage of the same polarity to the electrode means of non-selected channels, thereby to cause an expansion and contraction of the droplet liquid volume of the selected channel to effect ejection of a droplet therefrom.
  • the channels are divided into at least two groups, the groups being sequentially enabled for actuation, adjacent channels being in different groups.
  • said voltages are applied in time periods spaced by the interval L / c or multiples thereof, where L is the length of the channel and c is the effective velocity of pressure waves therein and, suitably, the first voltage is applied for a first time period L / c and the second voltage is applied for the immediately following second time period L / c .
  • the present invention consists in a method of operating multichannel pulsed droplet deposition apparatus having droplet liquid channels, the channels being divided into at least two groups, the groups being sequentially enabled for actuation, adjacent channels being in different groups, comprising the steps of actuating selected channels by the application thereto of an actuating pressure variation to effect droplet ejection therefrom, and ensure no pressure wave contribution to the droplet liquid in the channels of sequentially enabled groups of channels by the application of a correcting pressure variation.
  • the correcting pressure variation is delayed in time with respect to the actuating pressure variation by the interval 2L / c .
  • the present invention consists in a method of operating multichannel pulsed droplet deposition apparatus having droplet liquid channels separated by wall actuators displaceable on the application thereto of a voltage difference, each channel having electrode means associated with the wall actuators bounding that channel such that a voltage difference can be applied to a specified wall actuator by the application of different voltages to the respective electrode means of the two channels separated by the said wall actuator, the method comprising the actuation of a selected channel through the steps of applying an actuating voltage to the electrode means of the selected channel thereby to effect ejection of a droplet therefrom and the at least partial cancellation of residual pressure waves by applying a correcting voltage of the same polarity to the electrode means of non-selected channels.
  • the present invention consists in a driving circuit for activating a multi-channel pulsed droplet deposition apparatus.
  • waveforms are suitable for the operation of multi-channel ink jet printheads having channel dividing wall actuators in which the channels are operated in groups.
  • the waveforms are arranged for application by a unipolar drive circuit, but maintain the advantages of driving the ink channels to eject drops by causing both expansion and contraction of ink channels during operation.
  • the waveforms incorporate reflection suppressing pulses which are applied in the printhead after a period of 2 L / c following the application of the drop ejecting pulse.
  • One particular advantage of the waveforms in the type of printhead referred to is that suppression of the reflected pressure waves occurs in the neighbouring channels as opposed to the channels from which a drop has just been ejected. Since in a printhead in which channels are divided into groups actuated in rotation, it is the neighbouring channel that is next operated, this enables actuation to continue, by applying a waveform for drop ejection to the next channel without delay as soon as the waveform from a first channel is complete.
  • Another advantage is that the pressure generated in each channel for drop ejection is as much as three times the pressure that is generated by a simple unipolar pulse and that the drop ejection waveform for drop ejection including reflection wave suppression is completed within five or in one case within four channel acoustic periods 2 L / c .
  • the waveform applied to the wall actuators comprises step voltage changes at periodic intervals L / c of the channel.
  • the waveform is completed after five intervals L / c : in another embodiment the waveform is completed after four intervals.
  • a portion of the waveform in selected periodic intervals may be applied to the wall actuators adjacent to channels not selected for firing and the remaining portion may be applied to the wall actuators adjacent to channels selected for actuation in accordance with print data provided to the group designated for printing.
  • the waveform applied to the wall actuators, in causing the walls both to expand and contract the volume of said selected channels, generates both positive and negative acoustic pressure waves.
  • the positive wave in the second period may be selected in magnitude to control the ejection velocity of the drop.
  • the negative pressure wave in the third period may be selected in magnitude to control drop break-off.
  • voltage waveform is selected in the last two periods thereof to suppress residual acoustic pressure waves in the head, by generating voltage magnitudes which generate pressure waves to substantially cancel the residual acoustic energy after drop ejection in the said selected channel.
  • the voltage magnitudes are selected in relation to the nozzle reflection coefficient ( r ).
  • the voltage magnitudes for cancellation are applied two acoustic periods L / c (ie. one characteristic time Tc ) after the period of generation of acoustic pressure waves generated to effect drop ejection or drop break-up.
  • the voltage waveform may be selected to suppress residual acoustic waves in neighbouring channels adjacent the channel selected for drop ejection.
  • Figure 1 shows an exploded view in perspective of a typical ink jet printhead 8 incorporating piezo-electric wall actuators operating in shear mode. It comprises a base 10 of piezo electric material mounted on a base 12 of which only a section showing connection tracks 14 is illustrated. A cover 16, which is bonded during assembly to the base 10 is shown above its assembled location. A nozzle plate 17 is also shown adjacent the printhead base.
  • a multiplicity of parallel grooves 18 are formed in the base 10 extending into the layer of piezo-electric material.
  • the grooves are formed for example as described in US-A-5016028 (EP-A-364136) and comprise a forward part in which the grooves are comparatively deep to provide ink channels 20 separated by opposing actuator walls 22.
  • the grooves in the rearward part are comparatively shallow to provide locations for connection tracks.
  • metallized plating is deposited in the forward part providing electrodes 26 on the opposing faces of the ink channels 20 where it extends approximately one half of the channel height from the tops of the walls and in the rearward part is deposited providing connection tracks 24 connected to the electrodes in each channel 20.
  • the tops of the walls are kept free of plating metal so that the track 24 and the electrodes 26 form isolated actuating electrodes for each channel.
  • the base 10 After the deposition of metallized plating and coating of the base 10 with a passivant layer for electrical isolation of the electrode parts from the ink, the base 10 is mounted as shown in Figure 1 on the circuit board 12 and bonded wire connections are made connecting the connection tracks 24 on the base part 10 to the connection tracks 14 on the circuit board 12.
  • the ink jet printhead 8 is illustrated after assembly in Figure 2.
  • the cover 16 is secured by bonding to the tops of the actuator walls 22 thereby forming a multiplicity of closed channels 20 having access at one end to the window 27 in the cover 16 which provides a manifold 28 for the supply of replenishment ink.
  • the nozzle plate 17 is attached by bonding at the other end of the ink channels.
  • the nozzles 30 are shown in locations in the nozzle plate communicating to each channel formed by UV excimer laser ablation.
  • the printhead is operated by delivering ink from an ink cartridge via the ink manifold 28, from where it is drawn into the ink channels to the nozzles 30 by capillary suction.
  • the drive circuit 32 connected to the printhead is illustrated in Figure 3. In one form it is an external circuit connected to the connection tracks 14, but in an alternate form (not shown) an integrated circuit chip may be mounted on the printhead.
  • the drive circuit 32 is operated by applying by a data link 34 the print data 35 defining print locations in each print line as the printhead is scanned over a print surface 36 and at the same time applying an actuating voltage waveform 38 via the signal link 37.
  • the present invention relates particularly to printheads of the type described in US-A-4879568 (EP-B-0277703) and US-A-4887100 (EP-B-0278590) and related patent specifications. That is to say printheads of the type in which ink channels are divided by laterally displaceable wall actuators and in which each ink channels is actuable by displacing the two wall actuators which bound it on either side.
  • the laterally displaceable wall actuators are actuated by the application of a voltage difference between electrodes located on or adjacent to the walls, so that there may in some constructions be two external electrodes per wall, requiring two external connections for actuation.
  • connections it is usually convenient for connections to be made between the wail electrodes internally to provide one electrode per channel: when a voltage waveform is applied to the electrode corresponding to a channel and a datum voltage is applied to the electrodes of the neighbouring channel, the applied fields in the walls adjacent the channel then effect displacements of each wall causing the volume and pressure in the ink in each channel to be either increased or decreased.
  • the connections are made internally or externally of the printhead it is then convenient to describe the actuating signal as being applied in relation to a selected channel to effect drop ejection from that channel.
  • a second feature as indicated in the above patent specifications and related patent specifications is that only selected ink channels can be operated at one time and conveniently the channels may be operated in groups.
  • the printhead may be divided into two groups of odd and even channels which are actuated alternately.
  • the channels may be divided into three or four or more groups actuated in rotation.
  • the frequency at which drops may be ejected from one channel is determined by the replenishment time, that is the time following drop ejection that is required to restore the meniscus of ink in the nozzle. If a second waveform to effect drop ejection is applied to the channel following a first waveform before the ink meniscus has come to rest or is completely restored to the nozzle exit, so that replenishment of the channel following the first waveform is incomplete, then the drop generated via the second waveform is found to have a different volume and different velocity from the first drop.
  • printers having displaceable wall actuators by dividing the channels into groups actuated in rotation at first sight might appear to be at a disadvantage, because the speed of operation is reduced by two, three or four or more times depending on the number of groups.
  • ink replenishment time in each channel that controls print rate and there is usually time for drop ejection to take place before replenishment is complete in the first channel
  • this apparent disadvantage of operation in groups is found not to arise in practice: and therefore the advantages of printheads having displaceable wall actuators, which are high channel density, efficient and low voltage operation and low cost of manufacture are obtained with no serious cost in terms of performance or frequency of operation.
  • the present invention is described by reference to actuation of a printhead having displaceable wall actuators by applying voltage waveforms to the electrodes of channels divided into three groups. That is to say the printhead comprises ink channels divided into three groups a , b , and c . It is generally found with the waveforms described that after actuating selected channels of the group a , there is time to actuate channels with the same waveform from groups b and c before replenishment is complete in group a , when a further waveform may then be applied to a .
  • a typical ink channel 20 containing ink and terminated by a nozzle 30 has been recognised in the prior art (e.g. US-A-4743924 or US-A-4752790) as behaving as an acoustic wave guide in which longitudinal pressure waves are generated.
  • the channel in the above cited art is characterised by an open end at the termination connected to the ink supply and by an acoustically closed end at the nozzle.
  • a characteristic time which is the time taken by a wave to traverse to and fro along the channel is where L is the channel length and c is the effective velocity of longitudinal pressure waves.
  • the pressure waves traverse the channel by 2 L and return to the starting point, but have inverted sign after the characteristic time Tc.
  • a cancelling wave is generated which suppresses or completely cancels the initial drop ejecting pressure pulse by applying a voltage waveform of the same form, but opposite in sign to the original drop ejecting waveform after a time equal to an even multiple of the characteristic time Tc (i.e. 2Tc, 4Tc, 6Tc etc. which equals 4 L/c, 8 L/c, 12 L/c etc.).
  • Tc characteristic time
  • Such a voltage pulse is referred to as reflection suppressing or self canceling.
  • R N will vary depending upon the nozzle geometry and ink characteristics.
  • a pressure wave is generated by applying a pulsed voltage waveform of magnitudes proportional to 1, 0, r, 0 in successive periods.
  • This voltage waveform generates pressure pulses in response to step changes in the applied voltage.
  • the resulting applied pressure changes are of magnitudes proportional to +1, -1, +r, -r in successive periods of time interval L / c .
  • the applied voltage pulses and consequential pressure pulses are set in Table I below, with columns corresponding with successive time intervals L / c .
  • Applied voltage pulse 1 0 r 0 Applied pressure pulse +1 -1 +r -r Total right going pressure wave +1 -2 +1 0 Total left going pressure wave +1 (-1+r) -r 0
  • each period L / c generate right and left going waves which in turn reflect from the terminations, and add further pressure waves.
  • the magnitudes of the total right and left going waves may be obtained, and these are shown in the third and fourth rows of Table I.
  • the cancelling voltage pulse +r in the third period is then seen to cause complete cancellation of both the right going and left going pressure waves in the fourth period. Since r is negative, the cancelling pressure pulse is opposite in sign to the initial pulse.
  • FIG. 4(a) A typical voltage waveform for drop ejection is illustrated in Figure 4(a). This is a voltage waveform of the draw release type first described initially in US-A-4161670 in connection with tubular actuators, wherein a voltage pulse is applied in the channel to be actuated first to expand the ink tube and to draw back ink in the nozzle termination and then a voltage of opposite polarity is applied causing the ink tube to contract and a pressure pulse to be generated causing ink drop ejection.
  • the waveform includes both the draw - release waveform above and further incorporates reflected pressure wave suppression in accordance with one aspect of the present invention.
  • This waveform consists of voltage pulses applied in successive periods corresponding to one acoustic period L / c of the channel of magnitudes -1, 1+r, 1, r(1+r) and r (1+r) where r is negative.
  • the voltage waveform thus lasts five acoustic periods.
  • corresponding pressures in the neighbouring lines assuming that the actuator walls are comparatively rigid compared with the compliance of the ink in the channels are of opposite sign and of value approximately one half of these values. If the compliance of the actuated walls is significant compared with that of the ink then a corresponding pressure ratio between the pressure in the actuated and non-actuated channels may be calculated as a function of the compliance ratio between the actuator wall and the ink.
  • the waveform illustrated in Figure 4 is self cancelling. This may also be seen by resolving the wave into an actuating pulsed voltage waveform applied in successive periods L / c of magnitudes -1, 1+r, 1+r, 0,0 and a corresponding canceling waveform obtained by adding waveforms of the same magnitude multiplied by r and delayed by ie. of magnitudes 0, 0, -r (r+r 2 ), (r+r 2 ) . This is shown in Table IV below and in Figure 4(c), where the correcting waveform C is shown separately from the actuating waveform A .
  • Figure 5(a) illustrates the unipolar voltage waveforms applied to fired and unfired channels of groups a , b and c , these being shown in three periods a , b , c corresponding to the operation successively of channels in each group.
  • the voltage waveform to eject a drop and to cancel the residual acoustic waves lasts a period of 5 L / c in each group, so that for three groups a , b and c the frequency of printing each line of printed dots is ( 15L / c ).
  • This will be seen evidently to be the maximum print speed for operation, although blank periods may be inserted in a drop-on-demand printer to reduce the rate of output for variable speed applications.
  • the operating frequency may be 10 kHz .
  • this period is also usually dictated by replenishment time.
  • the normal operation of the printhead for a non-firing channel involves the application of no voltage in periods 1, 4 and 5 of the five periods of L / c when a voltage waveform is applied in each group.
  • a positive voltage pulse of (1+r) and 1 is applied in periods 2 and 3 of the voltage waveform for a non-firing channel.
  • voltage excursions are applied to all lines of a printhead even when no channels are activated.
  • no pressures are generated.
  • the voltage applied to fire a channel is illustrated in the period allocated for the operation of each group a , b c etc., by reference to the voltage waveform for firing channels in the corresponding period.
  • a positive voltage of magnitude 1 is applied in the first period and a voltage r(r + 1) is applied in periods 4 and 5, while the voltage magnitude in the fired lines is zero in periods 2 and 3.
  • the voltages in the other groups b and c in the period correspond to those of neighbouring non-firing lines.
  • the sign convention in this example is that the positive voltage applied to a channel relative to the voltage in the neighbouring lines causes the ink channel to expand.
  • FIG. 6(a) A further voltage waveform, which suppresses residual acoustic waves is illustrated in Figure 6(a).
  • This waveform also lasts a period of five acoustic periods 5L / c .
  • the waveform shown in Figure 6(a) similarly includes a waveform applied to non-firing lines and a second waveform which is applied to a fired channel in the time designated for the group corresponding to the fired channels.
  • the voltage waveform differs in that the voltage magnitude has values 1, 1 instead of (l + r), 1 in the non-fired lines.
  • the waveform in periods 4 and 5 is now r, r(1 + r) instead of r(1 + r), r(1 + r) in the fired lines.
  • the voltage difference waveform applied to the wall actuator of a selected channel again takes the form of an actuating voltage difference waveform followed after a delay 2L / c by a correcting voltage difference waveform reduced in amplitude by the factor -0.3 . This is shown in Figure 6(c).
  • FIG. 7 A further form of unipolar voltage waveform is illustrated in Figure 7.
  • This waveform lasts 4 periods of L / c in each group, so that the frequency of operation may be increased to c/12L , which is 20% faster.
  • it has pressure waves 3,-3 in periods 2 and 3, so that the pressure reversal in this case is now -6 instead of -4.4 in the waveform of Figure 5.
  • This waveform may be further understood by reference to the following table: Applied voltage pulse -1 1 -r r 0 Applied pressure pulse -1 2 -(1+r) 2r -r Total right going pressure wave -1 3 -3 1 0 Total left going pressure wave -1 2-r -(1-2r) -r 0
  • Figure 7(a) shows the unipolar voltages applied to the fired channel and adjacent non-fired channel whilst Figure 7(b) shows the right going pressure waves, that is to say the pressure waves incident upon the nozzle.
  • voltage pulses are presented which first develop energetic pressure waves to effect drop ejection and then cancel or suppress the residual pressure wave energy.
  • the voltages and corresponding right and left going magnitudes are presented in simplified form in terms of a constant nozzle reflection coefficient.
  • the nozzle reflection coefficient is not exactly constant. Although broadly constant when the ink meniscus is external to the nozzle it falls progressively in magnitude to more negative values when the ink meniscus retracts into the nozzle, and in particular takes lower values following drop ejection. Therefore although the above voltage waveforms provide clear guidance to the timing and magnitudes of voltage pulses to effect cancellation, and may in appropriate circumstances be usable directly. The values used may also be measured or verified experimentally.
  • a drop ejection signal in response to a subsequent waveform generally results in drop ejection at reduced velocity. This is more particularly the case for the four period waveform described by reference to Figure 7.
  • Drop ejection velocity from the succeeding group (such as group b) is then increased by application of either a + ve pressure applied to the next - to - last pulse or a - ve pressure pulse applied to the last pulse period.
  • a + ve pressure applied to the next - to - last pulse or a - ve pressure pulse applied to the last pulse period There are accordingly a range of pulse magnitudes of the combined pulses in the two periods that create a pressure signal of the phase appropriate to effect correction or cancellation of the drop velocity variation.
  • there is one that also effects cancellation in the alternate pressure wave phase it is generally not deleterious but is sometimes useful to leave some energy in the alternate phase to modify performance of the printhead in some other respect.
  • Figure 8 shows a firing waveform in firing lines, that may be compared to the voltage waveform in Figure 7(a).
  • Each waveform has a total period of 4L/c .
  • the firing line voltage has an initial pulse 81 that withdraws ink into the nozzle.
  • the following firing pulse 82 is then applied to the non-fired lines in the active group and to all the lines in the inactive group in period two.
  • the waveform of Figure 8 follows the waveform in 7(a).
  • a cancelling pulse 83 is also applied in period four of the fired lines, whose magnitude is derived experimentally (by normalising the velocity of drops in the succeeding group).
  • This pulse has a value somewhat greater than the corresponding pulse magnitude in Figure 7(a) due to the absence in Figures 8 of a canceling pulse in period three of the non-fired lines.
  • Such a pulse 83 may always be found to effect cancellation of the residual pressure wave contribution to drop velocity in the succeeding phase.
  • Figure 9 illustrates the other extreme where the cancellation pulse 93 in period three of the non-fired lines is present to a greater degree than employed in Figure 7(a). In the extreme its magnitude can be made so great that the pulse contribution 94 in period four, instead of compromising a positive pulse in the fired lines, becomes negative so that instead the pulse is applied to the non-fired lines.
  • a typical combination of pulses 93 and 94 in the third and fourth pulse periods in the non-fired lines is illustrated in Figure 9. The pulse magnitudes are determined experimentally by observing the drop velocity in the succeeding group and restoring its value to normal.
  • the waveform in Figure 9 illustrates the alternative extreme to that in Figure 8, since the latter has no cancellation pulse and the former maximum cancellation pulse in period three, while the cancellation pulse in period four in each case is chosen empirically to effect drop velocity control in the succeeding group.
  • the waveform in Figure 9 is particularly useful for printheads which develop drops of large volume and at high velocity (typically above 10m.sec -1 ), in which the tendency to eject accidental drops from non-fired lines is increased, and where the waveform of Figure 9 corrects such a tendency.
  • the dotted line in Figure 9 illustrates that a rectangular pulse for such cancellation pulses is not essential and that a sloped wave form 95 can sometimes be identified which effects cancellation.
  • a method of correction found to be effective to allow for velocity variation due to a print pattern or print density variation is to vary the pulse width of the initial withdrawal pulse in the fired lines as shown in Figure 11 by reference to 106.
  • Pulse width 106 is narrowed when a higher density of line neighbours are selected and is restored to its normalised width when a single line without near neighbours is fired.
  • the above voltage waveforms may readily be implemented in a unipolar electronic chip connected to each channel of the ink jet printhead.
  • the present invention relates to pulsed droplet deposition apparatus, for example drop-on-demand-ink jet printing apparatus and, in the most important example, provides voltage waveforms for the control of such apparatus.
  • Ink jet printing apparatus having a multiplicity of closely spaced parallel ink channels and channel separating piezo-electrically displaceable wall actuators have been disclosed for example in US-A-4879568 (EP-B-0277703) and in US-A-4887100 (EP-B-0278590).
  • each channel is actuable by one or both of the displaceable side-walls.
  • an external connection is provided which relates to each channel and when a voltage difference is applied between the electrode corresponding to one channel and the electrodes of the neighbouring channels, the walls adjacent to the channel are displaced causing the volume of the centre channel, depending on the voltage sign, to expand or to contract and an ink drop to be ejected from the nozzle communicating with the channel.
  • One feature of the above printing apparatus having displaceable side-walls is that operation of every channel at the same time is excluded. Operation takes place by dividing the printhead into two groups of odd and even channels, which are operated alternately. Alternatively the printhead is divided into groups of three, four or more channels which are operated in rotation (EP-A-0376532).
  • Such a waveform is implemented in the prior art by an oscillatory circuit, or if a pulsed waveform generator is employed pulses of both positive and negative polarity are required to generate it.
  • the drive circuit necessarily takes the form of an integrated circuit chip, and such devices have the disadvantage of being considerably more expensive if required to handle bipolar signals.
  • EP-A-0652106 discloses the use of a suppression pulse after a delay of two periods L/c. It is prior art only under Art 54(3) EPC.
  • the present invention seeks to reduce or eliminate one or both of the foregoing disadvantages.
  • the present invention consists in one aspect in a method of operating multichannel pulsed droplet deposition apparatus having droplet liquid channels each with a nozzle having a negative pressure wave reflection coefficient r where r is negative, and each channel having a negative pressure wave reflection coefficient at the termination connected to droplet liquid supply means, the method comprising ejecting a droplet from a selected channel by generating therein defined pressure changes comprising a negative pressure pulse of duration L/c followed by a positive pressure pulse of duration at least L/c and substantially cancelling residual pressure waves in said channel by generating further pressure changes of opposite sign to said defined pressure changes after a delay of 2L/c where L is the length of the channel and c is the effective velocity of pressure waves therein.
  • the amplitude of said further pressure pulse are related to the amplitude of said defined pressure pulse by the factor r.
  • the duration of said positive pressure pulse preferably is 2L/c.
  • the selected channel is bounded by a displaceable wall actuator, displacement of which generates said defined and further pressure changes, said actuator also bounding an adjacent non-selected channel, the selected and non-selected channels being in respective groups of channels which are actuated sequentially, the displacement of the actuator also generating a complementary defined pressure changes in the adjacent channel and complementary further pressure changes in said adjacent channel which cancels residual pressure waves therein arising from the complementary defined pressure changes.
  • the multichannel pulsed droplet deposition apparatus has droplet liquid channels separated by wall actuators displaceable on the application thereto of a voltage difference, each channel having electrode means associated with the wall actuators bounding that channel such that a voltage difference can be applied to a specified wall actuator by the application of different voltages to the respective electrode means of the two channels separated by the said wall actuator, the method comprising the actuation of a selected channel through the steps of applying in different time periods a first actuating voltage to the electrode means of the selected channel and a second actuating voltage of the same polarity to the electrode means of non-selected channels, thereby to cause an expansion and contraction of the droplet liquid volume of the selected channel to generate said defined pressure changes.
  • the channels are divided into at least two groups, the groups being sequentially enabled for actuation, adjacent channels being in different groups.
  • waveforms are suitable for the operation of multi-channel ink jet printheads having channel dividing wall actuators in which the channels are operated in groups.
  • the waveforms are arranged for application by a unipolar drive circuit, but maintain the advantages of driving the ink channels to eject drops by causing both expansion and contraction of ink channels during operation.
  • the waveforms incorporate reflection suppressing pulses which are applied in the printhead after a period of 2 L/c following the application of the drop ejecting pulse.
  • One particular advantage of the waveforms in the type of printhead referred to is that suppression of the reflected pressure waves occurs in the neighbouring channels as opposed to the channels from which a drop has just been ejected. Since in a printhead in which channels are divided into groups actuated in rotation, it is the neighbouring channel that is next operated, this enables actuation to continue, by applying a waveform for drop ejection to the next channel without delay as soon as the waveform from a first channel is complete.
  • Another advantage is that the pressure generated in each channel for drop ejection is as much as three times the pressure that is generated by a simple unipolar pulse and that the drop ejection waveform for drop ejection including reflection wave suppression is completed within five or in one case within four channel acoustic periods 2 L / c .
  • the waveform applied to the wall actuators comprises step voltage changes at periodic intervals L/c of the channel.
  • the waveform is completed after five intervals L / c : in another embodiment the waveform is completed after four intervals.
  • a portion of the waveform in selected periodic intervals may be applied to the wall actuators adjacent to channels not selected for firing and the remaining portion may be applied to the wall actuators adjacent to channels selected for actuation in accordance with print data provided to the group designated for printing.
  • the waveform applied to the wall actuators, in causing the walls both to expand and contract the volume of said selected channels, generates both positive and negative acoustic pressure waves.
  • the positive wave in the second period may be selected in magnitude to control the ejection velocity of the drop.
  • the negative pressure wave in the third period may be selected in magnitude to control drop break-off.
  • the voltage waveform is selected in the last two periods thereof to suppress residual acoustic pressure waves in the head, by generating voltage magnitudes which generate pressure waves to substantially cancel the residual acoustic energy after drop ejection in the said selected channel.
  • the voltage magnitudes are selected in relation to the nozzle reflection coefficient ( r ).
  • the voltage magnitudes for cancellation are applied two acoustic periods L / c (ie. one characteristic time Tc ) after the period of generation of acoustic pressure waves generated to effect drop ejection or drop break-up.
  • the voltage waveform may be selected to suppress residual acoustic waves in neighbouring channels adjacent the channel selected for drop ejection.
  • Figure 1 shows an exploded view in perspective of a typical ink jet printhead 8 incorporating piezo-electric wall actuators operating in shear mode. It comprises a base 10 of piezo electric material mounted on a base 12 of which only a section showing connection tracks 14 is illustrated. A cover 16, which is bonded during assembly to the base 10 is shown above its assembled location. A nozzle plate 17 is also shown adjacent the printhead base.
  • a multiplicity of parallel grooves 18 are formed in the base 10 extending into the layer of piezo-electric material.
  • the grooves are formed for example as described in US-A-5016028 (EP-A-364136) and comprise a forward part in which the grooves are comparatively deep to provide ink channels 20 separated by opposing actuator walls 22.
  • the grooves in the rearward part are comparatively shallow to provide locations for connection tracks.
  • metallized plating is deposited in the forward part providing electrodes 26 on the opposing faces of the ink channels 20 where it extends approximately one half of the channel height from the tops of the walls and in the rearward part is deposited providing connection tracks 24 connected to the electrodes in each channel 20.
  • the tops of the walls are kept free of plating metal so that the track 24 and the electrodes 26 form isolated actuating electrodes for each channel.
  • the base 10 After the deposition of metallized plating and coating of the base 10 with a passivant layer for electrical isolation of the electrode parts from the ink, the base 10 is mounted as shown in Figure 1 on the circuit board 12 and bonded wire connections are made connecting the connection tracks 24 on the base part 10 to the connection tracks 14 on the circuit board 12.
  • the ink jet printhead 8 is illustrated after assembly in Figure 2.
  • the cover 16 is secured by bonding to the tops of the actuator walls 22 thereby forming a multiplicity of closed channels 20 having access at one end to the window 27 in the cover 16 which provides a manifold 28 for the supply of replenishment ink.
  • the nozzle plate 17 is attached by bonding at the other end of the ink channels.
  • the nozzles 30 are shown in locations in the nozzle plate communicating to each channel formed by UV excimer laser ablation.
  • the printhead is operated by delivering ink from an ink cartridge via the ink manifold 28, from where it is drawn into the ink channels to the nozzles 30 by capillary suction.
  • the drive circuit 32 connected to the printhead is illustrated in Figure 3. In one form it is an external circuit connected to the connection tracks 14, but in an alternate form (not shown) an integrated circuit chip may be mounted on the printhead.
  • the drive circuit 32 is operated by applying by a data link 34 the print data 35 defining print locations in each print line as the printhead is scanned over a print surface 36 and at the same time applying an actuating voltage waveform 38 via the signal link 37.
  • the present invention relates particularly to printheads of the type described in US-A-4879568 (EP-B-0277703) and US-A-4887100 (EP-B-0278590) and related patent specifications. That is to say printheads of the type in which ink channels are divided by laterally displaceable wall actuators and in which each ink channels is actuable by displacing the two wall actuators which bound it on either side.
  • the laterally displaceable wall actuators are actuated by the application of a voltage difference between electrodes located on or adjacent to the walls, so that there may in some constructions be two external electrodes per wall, requiring two external connections for actuation.
  • the connections are made internally or externally of the printhead it is then convenient to describe the actuating signal as being applied in relation to a selected channel to effect drop ejection from that channel.
  • a second feature as indicated in the above patent specifications and related patent specifications is that only selected ink channels can be operated at one time and conveniently the channels may be operated in groups.
  • the printhead may be divided into two groups of odd and even channels which are actuated alternately.
  • the channels may be divided into three or four or more groups actuated in rotation.
  • the frequency at which drops may be ejected from one channel is determined by the replenishment time, that is the time following drop ejection that is required to restore the meniscus of ink in the nozzle. If a second waveform to effect drop ejection is applied to the channel following a first waveform before the ink meniscus has come to rest or is completely restored to the nozzle exit, so that replenishment of the channel following the first waveform is incomplete, then the drop generated via the second waveform is found to have a different volume and different velocity from the first drop.
  • printers having displaceable wall actuators by dividing the channels into groups actuated in rotation at first sight might appear to be at a disadvantage, because the speed of operation is reduced by two, three or four or more times depending on the number of groups.
  • ink replenishment time in each channel that controls print rate and there is usually time for drop ejection to take place before replenishment is complete in the first channel
  • this apparent disadvantage of operation in groups is found not to arise in practice: and therefore the advantages of printheads having displaceable wall actuators, which are high channel density, efficient and low voltage operation and low cost of manufacture are obtained with no serious cost in terms of performance or frequency of operation.
  • the present invention is described by reference to actuation of a printhead having displaceable wall actuators by applying voltage waveforms to the electrodes of channels divided into three groups. That is to say the printhead comprises ink channels divided into three groups a , b , and c . It is generally found with the waveforms described that after actuating selected channels of the group a , there is time to actuate channels with the same waveform from groups b and c before replenishment is complete in group a , when a further waveform may then be applied to a .
  • a typical ink channel 20 containing ink and terminated by a nozzle 30 has been recognised in the prior art (e.g. US-A-4743924 or US-A-4752790) as behaving as an acoustic wave guide in which longitudinal pressure waves are generated.
  • the channel in the above cited art is characterised by an open end at the termination connected to the ink supply and by an acoustically closed end at the nozzle.
  • a characteristic time which is the time taken by a wave to traverse to and fro along the channel is where L is the channel length and c is the effective velocity of longitudinal pressure waves.
  • the pressure waves traverse the channel by 2 L and return to the starting point, but have inverted sign after the characteristic time Tc.
  • a canceling wave is generated which suppresses or completely cancels the initial drop ejecting pressure pulse by applying a voltage waveform of the same form, but opposite in sign to the original drop ejecting waveform after a time equal to an even multiple of the characteristic time Tc (i.e. 2Tc, 4Tc, 6Tc etc. which equals 4 L/c, 8 L/c, 12 L/c etc.).
  • Tc characteristic time
  • Such a voltage pulse is referred to as reflection suppressing or self canceling.
  • R N will vary depending upon the nozzle geometry and ink characteristics.
  • a pressure wave is generated by applying a pulsed voltage waveform of magnitudes proportional to 1, 0, r, 0 in successive periods.
  • This voltage waveform generates pressure pulses in response to step changes in the applied voltage.
  • the resulting applied pressure changes are of magnitudes proportional to +1, -1, +r, -r in successive periods of time interval L / c .
  • the applied voltage pulses and consequential pressure pulses are set in Table I below, with columns corresponding with successive time intervals L / c .
  • Applied voltage pulse 1 0 r 0 Applied pressure pulse +1 -1 +r -r Total right going pressure wave +1 -2 +1 0 Total left going pressure wave +1 (-1+r) -r 0
  • each period L / c generate right and left going waves which in turn reflect from the terminations, and add further pressure waves.
  • the magnitudes of the total right and left going waves may be obtained, and these are shown in the third and fourth rows of Table I.
  • the cancelling voltage pulse +r in the third period is then seen to cause complete cancellation of both the right going and left going pressure waves in the fourth period. Since r is negative, the canceling pressure pulse is opposite in sign to the initial pulse.
  • FIG. 4(a) A typical voltage waveform for drop ejection is illustrated in Figure 4(a). This is a voltage waveform of the draw release type first described initially in US-A-4161670 in connection with tubular actuators, wherein a voltage pulse is applied in the channel to be actuated first to expand the ink tube and to draw back ink in the nozzle termination and then a voltage of opposite polarity is applied causing the ink tube to contract and a pressure pulse to be generated causing ink drop ejection.
  • the waveform includes both the draw - release waveform above and further incorporates reflected pressure wave suppression in accordance with one aspect of the present invention.
  • This waveform consists of voltage pulses applied in successive periods corresponding to one acoustic period L/c of the channel of magnitudes -1, 1+r, 1, r(1 +r) and r(1 +r) where r is negative.
  • the voltage waveform thus lasts five acoustic periods.
  • corresponding pressures in the neighbouring lines assuming that the actuator walls are comparatively rigid compared with the compliance of the ink in the channels are of opposite sign and of value approximately one half of these values. If the compliance of the actuated walls is significant compared with that of the ink then a corresponding pressure ratio between the pressure in the actuated and non-actuated channels may be calculated as a function of the compliance ratio between the actuator wall and the ink.
  • the waveform illustrated in Figure 4 is self cancelling. This may also be seen by resolving the wave into an actuating pulsed voltage waveform applied in successive periods L / c of magnitudes -1, 1+r, 1+r, 0,0 and a corresponding cancelling waveform obtained by adding waveforms of the same magnitude multiplied by r and delayed by ie. of magnitudes 0, 0, -r (r+r 2 ), (r+r 2 ) . This is shown in Table IV below and in Figure 4(c), where the correcting waveform C is shown separately from the actuating waveform A .
  • Figure 5(a) illustrates the unipolar voltage waveforms applied to fired and unfired channels of groups a , b and c , these being shown in three periods a , b , c corresponding to the operation successively of channels in each group.
  • the voltage waveform to eject a drop and to cancel the residual acoustic waves lasts a period of 5 L / c in each group, so that for three groups a , b and c the frequency of printing each line of printed dots is ( 15L / c ).
  • This will be seen evidently to be the maximum print speed for operation, although blank periods may be inserted in a drop-on-demand printer to reduce the rate of output for variable speed applications.
  • the operating frequency may be 10 kHz. As already stated, this period is also usually dictated by replenishment time.
  • the normal operation of the printhead for a non-firing channel involves the application of no voltage in periods 1, 4 and 5 of the five periods of L/c when a voltage waveform is applied in each group.
  • a positive voltage pulse of (1+r) and 1 is applied in periods 2 and 3 of the voltage waveform for a non-firing channel.
  • voltage excursions are applied to all lines of a printhead even when no channels are activated.
  • no pressures are generated.
  • the voltage applied to fire a channel is illustrated in the period allocated for the operation of each group a , b c etc., by reference to the voltage waveform for firing channels in the corresponding period.
  • a positive voltage of magnitude 1 is applied in the first period and a voltage r(r + 1) is applied in periods 4 and 5, while the voltage magnitude in the fired lines is zero in periods 2 and 3.
  • the voltages in the other groups b and c in the period correspond to those of neighbouring non-firing lines.
  • the sign convention in this example is that the positive voltage applied to a channel relative to the voltage in the neighbouring lines causes the ink channel to expand.
  • FIG. 6(a) A further voltage waveform, which suppresses residual acoustic waves is illustrated in Figure 6(a).
  • This waveform also lasts a period of five acoustic periods 5L / c .
  • the waveform shown in Figure 6(a) similarly includes a waveform applied to non-firing lines and a second waveform which is applied to a fired channel in the time designated for the group corresponding to the fired channels.
  • the voltage waveform differs in that the voltage magnitude has values 1, 1 instead of (l + r), 1 in the non-fired lines.
  • the waveform in periods 4 and 5 is now r, r(1 + r) instead of r(1 + r), r(1 + r) in the fired lines.
  • the voltage difference waveform applied to the wall actuator of a selected channel again takes the form of an actuating voltage difference waveform followed after a delay 2L/c by a correcting voltage difference waveform reduced in amplitude by the factor -0.3 . This is shown in Figure 6(c).
  • FIG. 7 A further form of unipolar voltage waveform is illustrated in Figure 7.
  • This waveform lasts 4 periods of L / c in each group, so that the frequency of operation may be increased to c/12L , which is 20% faster.
  • it has pressure waves 3,-3 in periods 2 and 3, so that the pressure reversal in this case is now -6 instead of -4.4 in the waveform of Figure 5.
  • This waveform may be further understood by reference to the following table: Applied voltage pulse -1 1 -r r 0 Applied pressure pulse -1 2 -(1+r) 2r -r Total right going pressure wave -1 3 -3 1 0 Total left going pressure wave -1 2-r -(1-2r) -r 0
  • Figure 7(a) shows the unipolar voltages applied to the fired channel and adjacent non-fired channel whilst Figure 7(b) shows the right going pressure waves, that is to say the pressure waves incident upon the nozzle.
  • voltage pulses are presented which first develop energetic pressure waves to effect drop ejection and then cancel or suppress the residual pressure wave energy.
  • the voltages and corresponding right and left going magnitudes are presented in simplified form in terms of a constant nozzle reflection coefficient.
  • the nozzle reflection coefficient is not exactly constant. Although broadly constant when the ink meniscus is external to the nozzle it falls progressively in magnitude to more negative values when the ink meniscus retracts into the nozzle, and in particular takes lower values following drop ejection. Therefore although the above voltage waveforms provide clear guidance to the timing and magnitudes of voltage pulses to effect cancellation, and may in appropriate circumstances be usable directly. The values used may also be measured or verified experimentally.
  • a drop ejection signal in response to a subsequent waveform generally results in drop ejection at reduced velocity. This is more particularly the case for the four period waveform described by reference to Figure 7.
  • Drop ejection velocity from the succeeding group (such as group b) is then increased by application of either a + ve pressure applied to the next - to - last pulse or a - ve pressure pulse applied to the last pulse period.
  • a + ve pressure applied to the next - to - last pulse or a - ve pressure pulse applied to the last pulse period There are accordingly a range of pulse magnitudes of the combined pulses in the two periods that create a pressure signal of the phase appropriate to effect correction or cancellation of the drop velocity variation.
  • there is one that also effects cancellation in the alternate pressure wave phase it is generally not deleterious but is sometimes useful to leave some energy in the alternate phase to modify performance of the printhead in some other respect.
  • Figure 8 shows a firing waveform in firing lines, that may be compared to the voltage waveform in Figure 7(a).
  • Each waveform has a total period of 4L / c .
  • the firing line voltage has an initial pulse 81 that withdraws ink into the nozzle.
  • the following firing pulse 82 is then applied to the non-fired lines in the active group and to all the lines in the inactive group in period two.
  • the waveform of Figure 8 follows the waveform in 7(a).
  • a cancelling pulse 83 is also applied in period four of the fired lines, whose magnitude is derived experimentally (by normalising the velocity of drops in the succeeding group).
  • This pulse has a value somewhat greater than the corresponding pulse magnitude in Figure 7(a) due to the absence in Figures 8 of a cancelling pulse in period three of the non-fired lines.
  • Such a pulse 83 may always be found to effect cancellation of the residual pressure wave contribution to drop velocity in the succeeding phase.
  • Figure 9 illustrates the other extreme where the cancellation pulse 93 in period three of the non-fired lines is present to a greater degree than employed in Figure 7(a). In the extreme its magnitude can be made so great that the pulse contribution 94 in period four, instead of compromising a positive pulse in the fired lines, becomes negative so that instead the pulse is applied to the non-fired lines.
  • a typical combination of pulses 93 and 94 in the third and fourth pulse periods in the non-fired lines is illustrated in Figure 9. The pulse magnitudes are determined experimentally by observing the drop velocity in the succeeding group and restoring its value to normal.
  • the waveform in Figure 9 illustrates the alternative extreme to that in Figure 8, since the latter has no cancellation pulse and the former maximum cancellation pulse in period three, while the cancellation pulse in period four in each case is chosen empirically to effect drop velocity control in the succeeding group.
  • the waveform in Figure 9 is particularly useful for printheads which develop drops of large volume and at high velocity (typically above 10m.sec -1 ), in which the tendency to eject accidental drops from non-fired lines is increased, and where the waveform of Figure 9 corrects such a tendency.
  • the dotted line in Figure 9 illustrates that a rectangular pulse for such cancellation pulses is not essential and that a sloped wave form 95 can sometimes be identified which effects cancellation.
  • a method of correction found to be effective to allow for velocity variation due to a print pattern or print density variation is to vary the pulse width of the initial withdrawal pulse in the fired lines as shown in Figure 11 by reference to 106.
  • Pulse width 106 is narrowed when a higher density of line neighbours are selected and is restored to its normalised width when a single line without near neighbours is fired.
  • the above voltage waveforms may readily be implemented in a unipolar electronic chip connected to each channel of the ink jet printhead.

Landscapes

  • Particle Formation And Scattering Control In Inkjet Printers (AREA)

Claims (32)

  1. Verfahren zum Betrieb einer gepulsten Metukanal-Tröpfchenniederschlagseinrichtung mit Tröpfchenflüssigkeitskanälen, von denen jeder eine Düse mit einem Druckwellen-Reflektionskoeffizienten r aufweist, wobei r negativ ist, und wobei jeder Kanal mit einem negativen Druckwellenreflektionskoeffizienten am Abschluß mit Tröpfchenflüssigkeit-Zufuhreinrichtungen verbunden ist, wobei das Verfahren das Ausstoßen eines Tröpfchens aus einem gewählten Kanal durch Erzeugen eines definierten Druckimpulses darin und im wesentlichen das Unterbinden verbleibender Druckwellen im Kanal durch Erzeugen eines weiteren Druckimpulses mit entgegengesetzen Vorzeichen zum definierten Druckimpuls nach einer Verzögerung von 2L/c umfaßt, wobei L die Länge des Kanals und c die Effektivgeschwindigkeit der Druckwellen darin ist.
  2. Verfahren nach Anspruch 1, bei dem die Amplitude des weiteren Druckimpulses sich zur Amplitude des definierten Druckimpulses mit dem Faktor r verhält.
  3. Verfahren nach Anspruch 2, welches das Ausstoßen eines Tröpfchens aus einem gewählten Kanal durch das Erzeugen eines negativen Druckimpulses der Dauer L/c, gefolgt von einem positiven Druckimpuls einer Dauer von mindestens L/c umfaßt.
  4. Verfahren nach Anspruch 3, bei dem die Dauer des positiven Druckimpulses 2L/c ist.
  5. Verfahren nach Anspruch 3 oder Anspruch 4 welches das Erzeugen eines ersten weiteren Druckimpulses mit einer Verzögerung von 2L/c nach dem negativen Druckimpuls und das Erzeugen eines zweiten weiteren Druckimpulses mit einer Verzögerung von 2L/c nach dem positiven Druckimpuls umfaßt.
  6. Verfahren nach einem der Ansprüche 1 bis 5, bei dem der gewählte Kanal von einer ortsveränderlichen Wandbetätigungseinrichtung begrenzt wird, deren Ortsveränderung den ersten und weitere Druckimpulse erzeugt, wobei die Betätigungseinrichtung ebenfalls einen danebenliegenden nicht ausgewählten Kanal begrenzt, wobei der ausgewählte und nicht ausgewählte Kanal in jeweiligen Kanalgruppen liegen, die abfolgend betätigt werden, wobei die Ortsveränderung der Betätigungseinrichtung ebenfalls einen ersten komplementären Druckimpuls in dem danebenliegenden Kanal und einen weiteren komplementären Impuls in dem danebenliegenden Kanal erzeugt, welcher verbleibende Druckwellen darin unterbindet, die vom ersten komplementären Druckimpuls herstammen.
  7. Verfahren nach Anspruch 1, welches die Schritte des Betätigens gewählter Kanäle durch die Aufbringung einer Betätigungs-Druckänderung darauf, um Tröpfchenausstoße daraus zu bewirken, und des Unterbindens verbleibender Wellen durch die Aufbringung einer korrigierenden Druckänderung, die um das Intervall 2L/c verzögert ist, umfaßt, wobei die korrigierende Druckänderung in derselben Weise wie die Betätigungsdruckänderung zeitlich variiert und bezüglich der Amplitude zur Betätigungs-Druckänderung über einen Faktor mit negativen Vorzeichen und einer Höhe, die geringer als 1 ist, in Relation steht.
  8. Verfahren nach Anspruch 7, bei dem die Druckänderungen durch Spannungssignale mit einer Stufen-Wellenform mit Stufen der Dauer L/c aufgebracht werden.
  9. Verfahren nach Anspruch 8, bei dem die Spannungssignale jeweils eine Periode von vier solchen Schritten haben.
  10. Verfahren nach Anspruch 8, bei dem die Spannungssignale jeweils eine Periode von fünf solchen Schritten haben.
  11. Verfahren nach einem der Ansprüche 7 bis 10, bei in jedem Schritt ein Spannungssignal nur dann einen Wert hat, der nicht Null ist, wenn das andere Spannungssignal Null ist.
  12. Verfahren nach einem der Ansprüche 7 bis 11, bei dem der Faktor r ist.
  13. Verfahren zum Betrieb einer gepulsten Mehrkanal-Tröpfchenniederschlagseinrichtung mit Tröpfchenflüssigkeitskanälen, von denen jeder eine Düse mit einem Druckwellenreflektionskoeffizienten r hat, wobei r negativ ist, wobei die Kanäle durch Wandbetätigungseinrichtungen getrennt sind, die bei der Aufbringung einer Spannungsdifferenz ortsveränderlich sind, wobei jeder Kanal Elekrodeneinrichtungen hat, die den Wandbetätigungseinrichtungen zugeordnet sind, welche den Kanal begrenzen, so daß eine Spannungsdifferenz an eine bestimmte Wandbetätigungseinrichtung durch das Anlegen verschiedener Spannungen an die jeweiligen Elektrodeneinrichtungen der beiden Kanäle angelegt werden kann, die durch die Wandbetätigungseinrichtung getrennt sind, wobei das Verfahren die Betätigung eines ausgewählten Kanals durch die Schritte des Anlegens einer ersten Betätigungsspannung an die Elektrodeneinrichtung des ausgewählten Kanals und einer zweiten Betätigungsspannung derselben Polarität an die Elektrodeneinrichtung der nicht gewählten Kanäle in unterschiedlichen Zeitperioden umfaßt, wodurch eine Expansion und Kontraktion des Tröpfchenflüssigkeitsvolumens des ausgewählten Kanals bewirkt wird, um das Ausstoßen eines Tröpfchens daraus zu bewirken.
  14. Verfahren gemäß Anspruch 13, bei dem die Kanäle in mindestens zwei Gruppen unterteilt sind, wobei die Gruppen abfolgend zur Betätigung freigegeben werden und benachbarte Kanäle in verschiedenen Gruppen sind.
  15. Verfahren nach Anspruch 13 oder 14, bei dem die Spannungen in Zeitperioden angelegt werden, die durch das Intervall L/c oder dessen Vielfache beabstandet sind, wobei L die Länge des Kanals und c die effektive Geschwindigkeit der Druckwellen darin ist.
  16. Verfahren nach Anspruch 15, bei dem die erste Spannung für eine erste Zeitperiode L/c und die zweite Spannung für die unmittelbar folgende zweite Zeitperiode L/c angelegt werden.
  17. Verfahren nach Anspruch 16, bei dem die zweite Spannung über die unmittelbar folgenden zweiten und dritten Zeitperioden L/c angelegt wird.
  18. Verfahren nach Anspruch 16, bei dem eine dritte Spannung derselben Polarität auf die Elektrodeneinrichtung nicht ausgewählter Kanäle über eine dritte unmittelbar folgende Zeitperiode L/c angelegt wird.
  19. Verfahren nach einem der Ansprüche 13 bis 18, bei dem eine korrigierende Spannung an eine oder mehrere Elektrodeneinrichtungen angelegt wird, um die verbleibenden Druckwellen zu unterbinden.
  20. Verfahren nach einem der Ansprüche 13 bis 18, bei dem eine korrigierende Spannung an eine oder mehrere Elektrodeneinrichtungen angelegt wird, um einen Ruhemeniskus in der Tröpfchenflüssigkeit der nicht ausgewählten Kanäle zu erzeugen.
  21. Verfahren nach einem der Ansprüche 13 bis 19, bei dem eine korrigierende Spannung an eine oder mehrere Elektrodeneinrichtungen angelegt wird, um sicherzustellen, daß keine Druckwelleneinwirkung auf die Tröpfchenflüssigkeit in den Kanälen abfolgend freigegebener Kanalgruppen stattfindet.
  22. Verfahren nach einem der Ansprüche 19 bis 21, bei dem die korrigierende Spannung eine erste korrigierende Spannung umfaßt, die um zwei L/c hinsichtlich der ersten Betätigungsspannung verzögert ist, welche an die Elektrodeneinrichtung nicht ausgewählter Kanäle angelegt wird, und eine zweite korrigierende Spannung, die um 2 L/c hinsichtlich der zweiten Betätigungsspannung verzögert ist, welche an die Elektrodeneinrichtungen der ausgewählten Kanäle angelegt wird.
  23. Verfahren nach Anspruch 23, bei dem die erste korrigierende Spannung bezüglich ihrer Stärke zur ersten Betätigungsspannung mit einem Faktor, der kleiner ist als 1, in Relation steht und die zweite korrigierende Spannung bezüglich ihrer Stärke zur zweiten Betätigungsspannung mit einem Faktor in Relation steht der kleiner als 1 ist.
  24. Verfahren nach Anspruch 23, bei dem die Faktoren gleich sind.
  25. Verfahren nach einem der Ansprüche 13 bis 24, welches die Schritte des Anlegens einer ersten Spannung einer relativen Höhe 1 an die Elektrodeneinrichtungen des gewählten Kanals in einer ersten Zeitperiode L/c, einer zweiten Spannung der relativen Höhe 1 auf die Elektrodeneinrichtungen der nicht ausgewählten Kanäle in einer zweiten Zeitperiode L/c, einer dritten Spannung der relativen Höhe zwischen 0 und 1+r auf die Elektrodeneinrichtungen nicht ausgewählter Kanäle in einer dritten Zeitperiode L/c und einer vierten Spannung der relativen Höhe zwischen 0 und 1+r auf die Elektrodeneinrichtungen entweder des ausgewählten Kanals oder der nicht ausgewählten Kanäle in einer vierten Zeitperiode L/c aufweist, wobei die vierte Spannung nicht Null ist, wenn die dritte Spannung Null ist.
  26. Verfahren nach Anspruch 25, bei dem die relative Höhe der dritten Spannung gleich r ist und wobei die vierte Spannung eine relative Höhe r hat und an die Elektrodeneinrichtungen des ausgewählten Kanals angelegt wird.
  27. Verfahren zum Betreiben einer gepulsten Mehrkanal-Tröpfchenniederschlagsein richtung mit Tröpfchenflüssigkeitskanälen, wobei die Kanäle in mindestens drei Gruppen unterteilt sind, die Gruppen abfolgend zur Betätigung freigegeben werden, benachbarte Kanäle sich in verschiedenen Gruppen befinden, mit den Schritten des Betätigens ausgewählter Kanäle durch die Aufbringung einer Betätigungs-Druckänderung, um Tröpfchenausstoß daraus zu bewirken und sicherzustellen, daß keine Druckwelleneinwirkung auf die Tröpfchenflüssigkeit in den Kanälen abfolgend freigegebener Gruppen von Kanälen stattfindet und zwar durch die Aufbringung einer korrigierenden Druckänderung.
  28. Verfahren nach Anspruch 27, bei dem die korrigierende Druckänderung zeitlich hinsichtlich der Betätigungs-Druckänderung durch das Intervall 2L/c verzögert ist.
  29. Verfahren nach Anspruch 27 oder 28, bei dem die korrigierende Druckänderung in derselben Weise zeitlich variiert, wie die Betätigungs-Druckänderung und hinsichtlich der Amplitude zur Betätigungs-Druckänderung mit einem Faktor in Relation steht, der kleiner ist als 1.
  30. Verfahren zum Betreiben einer gepulsten Mehrkanal-Tröpfchenniederschlagseinrichtung mit Tröpfchenflüssigkeitskanälen, die durch Wandbetätigungseinrichtungen getrennt sind, welche beim Anlegen einer Spannungsdifferenz ortsveränderlich sind, wobei jeder Kanal Elektrodeneinrichtungen aufweist, die den Wandbetätigungseinrichtungen zugeordnet sind, welche den Kanal begrenzen, so daß eine Spannungsdifferenz an eine bestimmte Wand-Betätigungseinrichtung durch das Anlegen verschiedener Spannungen an die jeweiligen Elektrodeneinrichtungen der beiden Kanäle angelegt werden kann, die durch die Wand-Betätigungseinrichtung getrennt sind, wobei das Verfahren die Betätigung eines ausgewählten Kanals umfaßt, und zwar durch die Schritte des Anlegens einer Betätigungsspannung an die Elektrodeneinrichtungen des ausgewählten Kanals, wodurch das Ausstoßen eines Tröpfchens aus diesem bewirkt wird, und die zumindest teilweise Unterbindung von verbleibenden Druckwellen durch das Anlegen einer korrigierenden Spannung derselben Polarität an die Elektrodeneinrichtungen nicht ausgewählter Kanäle.
  31. Betriebsschaltung für eine gepulste Mehrkanal-Tröpfchenniederschlagseinrichtung mit Tröpfchenflüssigkeitskanälen der Länge L, die eine effektive Geschwindigkeit c der Druckwellen darin aufweisen, mit einer Tröpfchen-Ausstoßdüse mit einem Druckwellenreflektionskoeffizienten r, wobei die Betriebsschaltung angepaßt ist, um die Einrichtung gemäß einem hervorgehenden Anspruch zu betreiben.
  32. Gepulste Mehrkanal-Tröpfchenniederschlagseinrichtung mit einer Tröpfchen-Niederschlagseinrichtung mit kanaltrennenden, ortsveränderlichen Wandbetätigungsvorrichtungen und einer Betriebsschaltung, die im Anspruch 31 beansprucht wird.
EP95911395A 1994-03-16 1995-03-16 Verbesserungen an einer gepulsten tröpfchen-niederschlagsvorrichtung Expired - Lifetime EP0751873B1 (de)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
GB9405137 1994-03-16
GB9405137A GB9405137D0 (en) 1994-03-16 1994-03-16 Improvements relating to pulsed droplet deposition apparatus
SG9608012A SG93789A1 (en) 1994-03-16 1994-03-16 Improvements relating to pulsed droplet deposition apparatus
PCT/GB1995/000562 WO1995025011A1 (en) 1994-03-16 1995-03-16 Improvements relating to pulsed droplet deposition apparatus

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EP0751873A1 EP0751873A1 (de) 1997-01-08
EP0751873B1 true EP0751873B1 (de) 1998-11-11

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EP (1) EP0751873B1 (de)
JP (1) JP2969570B2 (de)
CA (1) CA2184076C (de)
DE (1) DE69505960T2 (de)
GB (1) GB9405137D0 (de)
HK (1) HK1013639A1 (de)
SG (1) SG93789A1 (de)
WO (1) WO1995025011A1 (de)

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CH691049A5 (de) * 1996-10-08 2001-04-12 Pelikan Produktions Ag Verfahren zum Ansteuern von Piezoelementen in einem Druckkopf eines Tropfenerzeugers.
EP0983145B1 (de) 1997-05-15 2002-09-18 Xaar Technology Limited Betrieb einer tröpfchen-niederschlag-vorrichtung
GB9802871D0 (en) 1998-02-12 1998-04-08 Xaar Technology Ltd Operation of droplet deposition apparatus
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PT1648421T (pt) 2003-07-24 2017-12-22 Glaxosmithkline Llc Películas de dissolução oral
EP2184168B1 (de) * 2008-11-07 2012-02-15 Konica Minolta IJ Technologies, Inc. Tintenstrahlaufzeichnungsvorrichtung
JP5440412B2 (ja) 2009-06-29 2014-03-12 コニカミノルタ株式会社 インクジェット記録装置及び記録ヘッドの駆動方法
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Also Published As

Publication number Publication date
SG93789A1 (en) 2003-01-21
WO1995025011A1 (en) 1995-09-21
HK1013639A1 (en) 1999-09-03
GB9405137D0 (en) 1994-04-27
CA2184076C (en) 2005-08-09
DE69505960D1 (de) 1998-12-17
JP2969570B2 (ja) 1999-11-02
DE69505960T2 (de) 1999-04-08
CA2184076A1 (en) 1995-09-21
JPH09505532A (ja) 1997-06-03
EP0751873A1 (de) 1997-01-08

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