DE2345748A1 - INKJET WRITING PROCEDURE AND DEVICE FOR CARRYING OUT THIS PROCESS - Google Patents

Description

DJPL-ING. DIETER JANDER '218 / 15.103 DE

DR.-ING. ■ · r ED BÖNING "" _A , _

: ■ .. : _N υ September 7, 1973

KURfü.WTL · töAiviM 66
TELEPHONE 883 50 71

Patent application

of the company

PAILLARD S.A.

Sainte-Croix (Vaud, Switzerland)

Ink jet writing method and apparatus for carrying out this method

A writing method is known in which an ink jet, consisting of a sequence of ink droplets, which are torn out of a nozzle under the influence of an electric field and strike a writing surface, whereby the ink jet passes between deflection electrodes, where by potential difference between two opposite electrodes a transverse field to the beam is generated, which these to the sign of a The writing trace on a writing pad deflects, this potential difference undergoing sudden changes

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BATH ORIGINAL

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not continuous writing and the transition from one character to the next, as well as when the ink jet passes from a collecting plate to the writing surface or vice versa, at the beginning or at the end of a write period that occurs before or after a standstill period.

This process can involve ejecting the ink droplets take place at a certain frequency, e.g. under the action of a vibrator acting on the discharge nozzle. In other devices, one simply lets the frequency for ejecting the droplets adjust itself. With erratic Change in the potential difference, e.g. if the character to be written does not run continuously or at the transition from one character to the next or at the beginning or at the end of a writing period, a droplet of ink just traveling between the deflection electrodes are located. In this case, the first section of its trajectory corresponds to a specific point on the one to be written Character, while the second section of its trajectory corresponds to another point. This results in a intermediate trajectory at which this droplet hits the writing surface at a point that is otherwise unwritten should be. As a result, the writing surface has numerous

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BAD ORfQJNAL

Blobs that, although very small, prevent the font from looking flawless.

It is an object of the present invention to avoid these lost droplets and the resulting blobs. To this end, the invention is characterized in that the passage of the individual droplets is determined and that the sudden changes in the potential difference with the times at which there are no droplets are located between the deflection electrodes to match to be brought.

The invention also relates to a device for carrying out said method. This device includes a nozzle for ejecting an ink jet consisting of successive droplets, electrodes for deflection this beam and a circuit that supplies deflection voltages to the electrodes. This device is characterized by that it includes a measuring circuit for determining the changes in the potential of the nozzle.

The single figure of the accompanying drawing shows schematically and by way of example an embodiment of a device for carrying out the method according to the invention.

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With reference to the drawing, the ink is supplied from an ink container (not shown) via a line 2 to a spray nozzle I ₁ , which ejects an ink jet consisting of a sequence of droplets ^ produced by an electrical current between this nozzle and a ring electrode ^ f Field to be accelerated. The droplets then come to impact on a writing surface, which is on a cylindrical support ^. is arranged, or on a collecting plate 1 ^ _- . At their plug track between the nozzle I ₁ and the carrier ^. the droplets ^ are passed between deflection electrodes 6a_ and 6b. The electric field for accelerating the droplets is generated by a generator 2, which is connected to the nozzle I ₁ via a resistor Rl.

To determine the passage of the individual droplets between the electrodes 6a_ and 6b, the take-off of each droplet from the nozzle 1 is recorded. The departure of each droplet corresponds to an electrical charge that _{leaves the nozzle I 1} and thus changes its potential very slightly. Actually, this change is in the order of magnitude of 1 / 100O of the DC voltage supplied by the generator "] _.

To detect these changes in potential, the voltage

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between the nozzle JL and the ground through a capacitor Cl and a resistor to be fed to the input of a differential amplifier Q. Due to the small value of these voltage changes, it is necessary to suppress any disturbing voltage changes that can occur at the nozzle JL. For this purpose, the second input of the amplifier Q is fed from a branch consisting of a resistor R3, a capacitor C2, and a resistor R #. The resistors R1 and RJj have the same value, as do the resistors R2. and R4 .. As a result, all voltage changes occurring at the terminals of the generator 2 are fed to the two inputs of the amplifier 8 with the same amplitude and therefore do not generate a differential output signal. In contrast, the voltage changes inherent in the nozzle JL deliver a signal exclusively to a single input of the amplifier 8 and generate a differential output signal.

This gives 8 pulses at the output of the amplifier which each correspond to the exit of a droplet from the nozzle JL. These impulses are triggered by a Schmitt trigger £ shaped to be fed to a delay circuit JLO which gives a delay time which is approximately the time

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corresponds to the span between the time at which a droplet leaves the nozzle 1. and the time at which two successive droplets are in the positions ^ L and ~ £ _ with respect to the electrodes 6a and 6b, i.e. at the time at there are no droplets between these electrodes.

The signal emerging from this delay circuit .10 is passed through a circuit IJL, which consists of a monostable multivibrator, which imposes a certain duration on each pulse, this duration being considerably shorter than the transit time of a droplet from one to the other symmetrical positions ^ L ^and 3 " « The signal emerging from the flip-flop 1I _- is, after inversion, fed to the input CP. is generated and the output f £ of this signal via an amplifier 14 to the electrodes 6a and 6_b must pass.

As a result, once the circuit JJ. ^A deflection signal, which corresponds to a voltage jump between the electrodes 6a_ and 6_b, generates this deflection signal in the shift register

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12 and only passed on to the deflection electrodes when a pulse arrives at the input CP, which indicates that no droplet passes between the electrodes 6a and 6jb.

Of course, various modifications to the above can be made Device can be provided and in particular one can detect the presence of a droplet between the electrodes determine by other means. In particular, one could evaluate the interruption of a light beam by these droplets, which is picked up by a photoconductor. However, such a design would be expensive the extremely small dimensions of the droplets,

If the droplets are ejected by a vibrator, then by observing the oscillation phase of the Vibrator are indicated at which point in time there is no droplet between the electrodes 6a and 6b.

- patent claims -

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Claims (1)

218 / 15.103 DE 7th September 1973 Patent application of the company PAILLARD S.A. Sainte-Croix (Vaud, Switzerland) Claims [1.JWriting method in which an ink jet, consisting from an order of ink droplets falling under are torn out of a nozzle by the influence of an electric field and hit a writing surface, whereby the ink jet passes between deflection electrodes, where by potential difference between two opposite electrodes a field running transversely to the beam is generated, which is used for drawing 409812/0967 / ~ distracts a trace of writing on a writing pad, this potential difference undergoes abrupt changes when writing is not carried out continuously and at the transition from one character to the next, as well as at the transition of the ink jet from a collecting plate to the writing surface or vice versa, at the beginning or at the end of a write period that occurs before or after a standstill period, characterized in that, that the passage of the individual droplets (3) is determined and that the erratic ones Changes in the potential difference with the times at which there are no droplets (jj) between the deflection electrodes (6a and 6b) are to be brought into agreement. 2. The method according to claim 1, characterized in that the ejection of each droplet (3) through the measurement of the change in potential at the nozzle (l) is recorded. 3. Device for performing the method according to claim 1, consisting of a nozzle for ejecting an ink jet formed from successive droplets and electrodes to deflect this beam 409012/0967 and a circuit which supplies deflection voltages to the electrodes, characterized in that that it comprises a circuit (Rl, R2, R3, R4, Cl, C2) for measuring the changes in potential at the nozzle (l), 4. Apparatus according to claim 3, characterized in that it is a differential amplifier (8) includes, from which both inputs are fed by signals, respectively from the nozzle (l) and one Generator (7) originate, which applies a voltage to this nozzle (1), which accelerates the droplets (3), so that only signals resulting from the changes in potential at the nozzle (l) are at the output of this amplifier (8) can be obtained. 5. Device according to claims 3 and 4, characterized in that it comprises a delay circuit (10) which is excited by said amplifier (8) , the delay time of this circuit being approximately the same as the time between the point in time at a droplet (3) leaves the nozzle (1) and the point in time at which there is no droplet (3) between the deflection electrodes (6a, 6b). 409812/0967 6. Device according to claims; 5 to 5, characterized by a monostable circuit (ll) which is controlled by a delay circuit (10) and delivers pulses whose duration is considerably shorter than the transit time of a droplet (3) between the electrodes ( 6a, 6b). 7. Device according to claims 3 to 6, characterized in that it comprises a delay memory (12), which the command signals of the erratic Changes in deflection voltage receives these command signals through pulses sent by the monostable Circuit (ll) are generated, can be read out of the memory, whereby it is achieved that the sudden changes in voltage between the electrodes (6a, 6b) only take place if there is no droplet (3) between said deflection electrodes (6a, 6b) is located. 409812/0967 Blank page