FR2558076A1 - DROPLET EJECTOR - Google Patents

Abstract

THE DROPLET EJECTOR OF THE INVENTION INCLUDES A TANK 26 INCLUDING AN INLET ORIFICE 24 FOR INTRODUCING A LIQUID THEREIN AND AN OUTLET ORIFICE 18 FOR EJECTING DROPLET OF LIQUID THERE, A FIRST TRANSDUCER 20 TO EJECT A DROPLET OF LIQUID THROUGH THE OUTPUT ORIFICE IN RESPONSE TO ELECTRIC SIGNALS, A SECOND TRANSDUCER 22 TO ISOLATE THE TANK FROM A MAIN LIQUID SUPPLY 30,13 DURING A DROP EJECTION FROM THE TANK AND TO FILL THE TANK WITH LIQUID AFTER EJECTION 'A DROP IN RESPONSE TO ELECTRICAL SIGNALS. APPLICATION TO "DOT ON DEMAND" INKJET PRINTERS.

Description

DROPLET EJECTOR

  The invention relates to droplet ejectors

  and, more specifically, a droplet ejector-

  which is particularly useful as a driving force

  in a "point-by-point" ink jet printer.

  Inkjet printers combine a high quality

  reasonable print quality with print speeds

  rather high. Common types of drive heads

  generally available printers including

  are continuous jet devices and

  drops on demand. In continuous jet devices

  naked, a continuous stream of droplets is ejected from a head

  selected droplets are de-

  to a return bucket; the droplets

  aunties come into contact with a blank sheet of paper

  to form the desired image. In contrast, in the provisions

  droplets on demand, the droplets are not

  formed according to needs, and each droplet-

helps you to form the image.

  On-demand droplet devices have a number of

  number of inherent advantages over

  continuous feeding, including food

  In addition, there is no need for electrically charging the droplets for the purpose of flight control. However, they are really more

  slow than continuous feed devices, and this

has limited their utility.

  An object of the invention is to provide an ejector

of perfected droplets.

  Another object of the invention is to provide an ejection

  droplet unit which is particularly suitable for dot-matrix inkjet printing.

the demand.

  Yet another object of the invention is to provide an improved droplet ejector that functions

at increased speeds.

  According to the present invention, a drop ejector

  telescopes has a reservoir of limited capacity for storing a liquid therein, the reservoir comprising a

  fice exit to eject ink from it

  ci and an inlet through which it is filled with li-

  of food from a diet primarily

  pale in liquid. A driving transducer expels the droplets from the reservoir in response to signals

which are applied to it.

  Advantageously, the reservoir comprises a tube

  cylindrical and the transducer comprises a crystal piezo

  zoelectric that surrounds the tube and that tightens and expands

  alternatively the bore of the tube to expel the liquid

  of it. A useful device of this type is disclosed in U.S. No. 3,683,212 issued August 8, 1972 to S.I. Zoltan. According to the present invention, a second transducer adjusts communications between

  the outlet and a main supply of

  quide. The second transducer that serves as a transducer

  shut off the reservoir inlet port

  as a droplet of liquid is expelled from the

  fice exit, and he then opens the entrance port

  to fill the reservoir with the liquid of

  from the main supply.

  This configuration provides important advantages

  in point printers on demand. In particular, the blocking of the inlet orifice during droplet ejection prevents a dissipation of the droplet driving force which is otherwise

  caused by a backflow of liquid from the rear of the tank.

  see up to the main power supply. Consequently,

  it requires a smaller transducer and energy from

  lower drag to expel a droplet from the tank. Conversely, for a given drive energy input, a greater proportion of the energy is applied to expel a droplet, which is accelerated to higher speeds.

  and thus contributes to the achievement of

  bigger pressure. Thus, in the case of

  point pressure on demand currently available.

  about 10% of the applied drive energy is only transmitted to the expelled droplet; the rest is dissipated mainly in the liquid remaining behind in the print head. In contrast, in the present invention, almost all of the applied energy is transmitted to the ejected droplet, which significantly increases its momentum in response to a given input energy thereby increasing the printing speed and in that facilitating a set up order. In addition to the increase in yield and

  print speed, providing a barrier or ob-

  on the tank and the main feed

  pale in liquid, we effectively separate the food

  the main reservoir during a drop ejection

  lette, and it is thus possible to isolate the dynamic part

  of the reservoir and ejection head of the dynamic part

  the main supply. Consequently, the characteristics of each of them can be established to a large extent independently of the restrictions that would otherwise be imposed by the other. Furthermore,

  the shutter effectively damps the oscillations

  in the reservoir and thus allows the liquid to return to its rest state in a shorter period

  only in the case where this shutter is absent. In consequence

  quence, the time interval between ejection

  telettes can be reduced significantly, and

  the printing speed can thus be increased.

  By controlling the time during which the shutter is open, the tank can be filled from

2558076 -

  the main power supply so as to ensure that the

  filling is carried out with a disturbance of

  minimum In particular, according to this invention

  The filling of the reservoir takes place only after the ejection of a droplet. In addition, one can control. ler exactly the filling time and the shutter displacement so that the amount of liquid supplied to the tank is just equal to that which is removed from it

  by the ejected droplet. As a result, the droplets

  successive letters have a constant mass and density

  Constant printing is thus maintained. In addition, the print density can be easily varied in a manner controllable with the present invention.

  when you want it, for example, in

  phic, among other applications. -

  Other features and advantages of the pre-

  invention will be highlighted in the descrip-

  following, given by way of non-limiting example, with reference to the accompanying drawings in which:

  Figure 1 is a vertical sectional view of an ejection

  droplets in its rest state according to the pre-

this invention;

  Figures 2, 3 and 4 are vertical sectional views.

  the droplet ejector of Figure 1 in successive phases of operation; and Figure 5 is a diagram of theoretical drive signals applied to the transducers of the ejector, and

the resulting displacement.

  In Figure 1, a droplet ejector 10

  consists of a base 12 having a collar

  cylindrical link 14 from which a tube cy-

  16. A bore 18 at the upper end

  tube is used as an outlet port through which

  Liquid telescopes are ejected. A cymbal transducer

  lindrique 20 surrounds the tube 16 and provides the force

  quise to eject droplets from it. A

  second transducer 22 is located at the lower end

  re of the collar 14 and abuts against the base face

  14a of this necklace. The transducer 22, shown at

  For example, in the form of a flat rectangular plate, spans the input 24 of the collar 14 and blocks it as shown in FIG.

  inlet for the tube 16 which thus constitutes a reservoir

  see 26 for a liquid. Liquid is supplied at the base

  12, and thus to the tube 16, from a food source

  tation (not shown) by a tube 30 and

a room 13.

  The transducers 20 and 22 are preferably

  piezoelectric transducers that are ordered electrically

  trially by a pulse generator 32 having commands 34a, 34b, 36a, 36b, 38a and 38b for setting parameters such as amplitude, duration, and

  phase of the electrical impulses applied to transduc-

20 and 22, respectively.

  The transducer 20 serves as a training transducer.

  ment. When it is excited by a drive signal from the generator 32, it tightens and thus compresses the tube 16 so as to reduce the volume of the reservoir 26 and cause the ejection of a droplet therefrom. In contrast, the transducer 22 serves as

  shutter transducer. It regulates the flow of

  quide in tube 16 and thus allows to fill the

  26. Furthermore, it limits the transmission of

  these between the reservoir 26 and the main supply via the pipe 30 during the ejection

  of a droplet, and in this way not only does it increase

  the effectiveness of the ejection operation, but it

  also a communication of oscillations between

  the main supply and the reservoir 26 which delays

  otherwise the return of the tank to its state of rest.

  We can now understand in detail the function

  the droplet ejector.

  In the state of rest of the ejector, the transducers

  are de-excited, as shown in Figure 1, that is,

  that is, no control voltage is applied to them

  cated. In this state, the transducer 20 puts the input 24 out of communication with the conduit 30. A slight meniscus

  that negative is formed in the output bore 18.

  To begin the ejection operation, a drive signal such as a voltage pulse 40 is

  applied to the transducer 20 during a first interval

  the time, t1. The transducer shrinks in diameter upon receiving it and it in turn presses towards

  inside the tank 26 to reduce its diameter.

  be. The liquid in the reservoir thereby undergoes a displacement 42 that forces the meniscus from a negative state or displacement to a positive state, as shown in Figure 5 at 44. In its most extended extension state, outside, the liquid droplet 46 (Figure 3) forming the meniscus is detached from the rest of the liquid in the reservoir 26 and begins its

  path to the support (for example, a sheet of pa-

  pier) on which a point must be formed. The liquid

  in the reservoir 26, and thus the liquid forming

  the new meniscus, remains in a displaced state

  the rest of the training signal applied, as shown in Figure 5. When this signal ends, the reservoir 26 returns to its state of rest and the meniscus. As shown in Figure 5, the latter undergoes a damped oscillation for a period after

  the driving pulse is complete.

  After sending the drive pulse

  to the transducer 20 be completed, a training impulse

  50 is applied to the transducer 22. As an example, the pulse 50 follows the end of the pulse

  provided to the transducer 20 of less than a quarter cycle.

  The transducer 22 extends out of the inlet 24 as shown at 52 in Figure 5 (in the drawings, the extension is in the downward direction as shown in Figures 2-4) and he puts the tank 26

  in communication with the main tank through

  30. A small amount of liquid 54 then enters the reservoir 26 from the reservoir.

  duit 30 and the chamber 13 to replace the droplet-

  you ejected. As shown in Figure 5, this occurs while oscillations of the meniscus of the reservoir 26 occur after the end of the application of the voltage.

  transducer drive 20. The drop ejector

  lettes is so ready to repeat the cycle for the

next drop.

  As noted previously, the generator 32 is provided with means for establishing the amplitude, the duration

  and the phase of each of the respective applied signals

  to the transducers 20,22. By a suitable adjustment of these quantities, the user can adjust the drive levels and the relationship between the opening and the closing of the inlet orifice 24 with respect to the ejection time of a droplet of the bore 18 so as to ensure the ejection of the droplets of uniform mass at a defined speed, whatever the variations

  density and other physical characteristics if

  of the liquid used. Obtaining a density

  Uniform drop tee is an important feature of viable inkjet printers. It's obvious that

  in some applications, it may be desirable to

  the mass of the droplets, and therefore the diameter of the points as applied to the support which receives the ink,

  in a controlled manner. For example, he is often

  It is easy to vary the resolution in many graphic applications. This is easily obtained

  in the present invention by varying amounts of

  such as the rise time and the time of

  training impulses, as well as their

of, their duration and their phase.

  From the foregoing, it is seen that an improved droplet ejector has been provided. The ejector is

  simple construction and lends itself to easy calibration

  for uniform droplet ejection and thus uniform print density when used in an ink jet printer. The ejector isolates the liquid that is ejected from a communication with the main power supply during the ejection phase; this increases the efficiency of the ejection operation and also facilitates the damping of oscillations which

  otherwise increase the recovery time

  after droplet ejection and decreases

  thus the permissible speed of ejection. The replacement

  Liquid creasing is performed at a defined time following the ejection of the drop so as to minimize disruption of the device. To separate the droplet ejection from the liquid fill, one

  can make the ejection mechanism and the dynamic part

  than the ejection operation of optimum efficiency, regardless of the physical restrictions of the cycle of

  filling. We can thus greatly improve the contro-

  the speed of the ejected droplet, and we can

  cilate achieve a variation of the diameters of points

  and thus a variation of image resolution.

Claims (10)

  Droplet ejector for controllably ejecting droplets of liquid on demand, characterized in that it comprises:   A. a reservoir (26) having an orifice   trea (24) for admitting a liquid and an outlet (18) for ejecting droplets therefrom,   B. a first transducer (20) associated with the reservoir   see and able to function in response to signals   electrical devices applied to it to eject a drop of through the exit port, and   C. a second transducer (22) associated with the reservoir   see and able to function in response to signals   electrical appliances applied to it to regulate a trans-   liquid flow through the inlet.   2. Droplet ejector according to the claim   1, characterized in that the second transducer (22) restricts flow through the inlet port during ejection of the droplet.   3. Droplet ejector according to the claim   2, characterized in that the second transducer (22) is operable to fill the first reservoir (26)   of liquid after ejection of a droplet thereof.   4. Droplet ejector according to the claim   3, characterized in that said transducer (22) is positioned to block the inlet (24) so that there is no liquid flow therefrom when it is de-energized, and what it can work to open the input port in response to signals which are applied to it.   5. Droplet ejector according to the claim   4, characterized in that said transducer (22)   consists of a piezoelectric crystal.   6. Droplet ejector according to the claim   1, characterized in that the second transducer (22) is connected to operate in synchronism with the   first transducer (20) for blocking the   (24) during the ejection of the liquid from the reservoir (26) and to open said orifice thereupon to fill the tank with liquid.   7. Droplet ejector according to the claim   6, characterized in that the first and second trans-   ductors (20,22) consist of piezoelectric crystals cudgels.   8. Droplet ejector according to the claim   1, characterized in that the second transducer (22)   is constituted by a piezoelectric transducer   as for the inlet port when it is in the state of rest   and who can be excited electrically to open the ori-   entry point (24) to put the liquid in communi- cation with the reservoir (26).   9. Droplet ejector according to the claim   8, characterized in that it comprises means (32) for selectively energizing the second transducer (22)   to block the inlet port (24) during ejection   reservoir (26) and to open the opening   fice to fill the liquid reservoir as a result of the ejection of liquid from it.   10. Device for ejecting in a controlled manner   lable droplets of liquid on demand, characterized   A means (16) defining a first reservoir (26) having an outlet port (18) for ejecting droplets therefrom; B. means (20) operable to eject a droplet of the tank,   C. means (22) for selectively combining   munication the tank with another source of liquid (30,13).