Ink Analyzer And Compensator

Abstract

In an ink drop writing system a vibrating nozzle forms drops, which are thereafter deflected electrostatically, whereby characters or waveforms are written on paper by the deflected drops. The fluid resonance of the ink must be considered in the design of the nozzle if good drop formation and printing is to be obtained. This invention maintains a desired fluid resonance by compensating for the effects of evaporation on fluid resonance.

Description

BACKGROUND OF THE INVENTION

This invention relates to ink drop printing systems, and more particularly, to improvements therein.

In a U.S. Pat. No. 3,683,396, there is described a technique for designing a nozzle for ink drop writing apparatus in a manner to create fast satellite ink drops whereby better drop charging and thereby improved ink drop writing is made to occur, and also in a manner to improve the efficiency of operation of an ink drop writing system. As the ink stream emitted by a vibrating nozzle is broken up into drops, it is noted that each drop is accompanied by a small drop known as a satellite. Describing this separation in more detail, when a drop is formed there is a fine filament of the fluid that connects the drop to the stream just before separation. This filament forms a satellite. If the drop separates from the filament before the filament separates from the stream, the filament will form into a satellite whose speed will be less than that of the drop, which is known as a slow satellite condition. If the filament separates from the stream before it separates from the drop, the filament will form into a satellite whose speed is greater than that of the drop, resulting in a fast satellite condition. There is an intermediate satellite condition which occurs when the drop and filament separate simultaneously, resulting in the satellite speed being the same as that of the drop. In the fast satellite condition, the charge applied to the drop also charges the satellite, where as in the other satellite conditions, charge must be applied to both drop and satellite to insure that the satellite will not arrive at the paper at a location outside of the character or waveshape being formed, otherwise, the drop writing has a poor and sloppy appearance.

It should be appreciated that the synchronism of the drop charge inducing voltages is much less difficult with a fast satellite condition than with a slow satellite condition because the charging voltage need only be synchronous with one separation per drop period, instead of two separations per drop period, which is resorted to, if the satellite is to receive a charge which will direct it to the proper location. Operation in a fast satellite condition is facilitated by designing the nozzle for fluid resonance. In the design of the nozzle for fluid resonance, its internal length is determined by the formula F=N/4 .sup.. V.sub.f /L.sub.f is the internal length of the nozzle, and F is the desired frequency of resonance. The frequency of resonance is determined amongst other things, by the frequency in which the nozzle is vibrated.

From the foregoing formula, it is seen that once a nozzle is designed and built, the only variable which is left at a fixed F, is V.sub.f for the speed of sound through the fluid in the nozzle. Normally, the ink which is to be used is contained in a reservoir out of which it is pumped to thereafter pass through the vibrating nozzle. The ink contains a solvent. Evaporation of this solvent from the ink, alters the velocity of sound through the ink, thereby shifting the fluid resonance of the nozzle and thereby changing the drive requirement.

OBJECTS AND SUMMARY OF THE INVENTION

An object of this invention is to provide an arrangement for maintaining the velocity of sound through the ink, in an ink drop writing system substantially constant despite the presence of evaporation.

Another object of this invention is the provision of a novel and useful ink parameter monitoring and maintenance system.

This invention measures the velocity of sound periodically through the ink and, if it departs from the predetermined value, this invention adds solvent to the ink to compensate for the solvent which has been evaporated to restore the solution to a condition whereby the speed of sound again attains a desired value. Thie is accomplished by measuring the interval required for a sonic pulse to travel through the ink a predetermined distance. If the interval varies from a predetermined value, a value is operated to permit solvent from a source to flow into the ink reservoir.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an embodiment of the invention.

FIG. 2 is a series of waveform diagrams which are shown to assist in an understanding of the operation of the circuit arrangement, shown in FIG. 1 .

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a circuit diagram of an ink parameter monitoring arrangement for sensing the velocity of sound in the ink, together with a container 10 for ink solvent, and a valve 12 which is operated when it is desired to permit ink solvent to be metered from the container 10 into an ink reservoir 14. The ink reservoir 14 is connected through a pipe 16, shown in fragmentary fashion to the ink nozzle, (not shown) which comprises the ink jet writing system. Ink jet writing systems of the type with which this invention is concerned, are briefly shown and described in the aforementioned U.S. Pat. No. 3,683,396, and U.S. Pat. No. 3,512,172, amongst others.

In accordance with this invention, a clock pulse generator 20, which may be the clock pulse generator for the ink jet writing system, applies a clock pulse to a transducer driver 22, and to an inverter amplifier 26. The transducer driver 22, applies a pulse to a sonic transmitting transducer 25, in response to the clock pulse.

FIG. 2 is a waveform diagram shown to assist in an understanding of the invention. Waveform A represents the clock output of inverter amplifier 26. Waveform B is a sound pulse or acoustic pulse output from transducer driver 22 which is applied to the transducer 25, upon the occurrence of each leading edge of a clock pulse.

The sonic transducer 25, transmit a pulse through the ink to a second sonic receiving transducer 28. The received pulse, shown in FIG. 2 as waveform C, is supplied to the receive amplifier 38 and is a positive going pulse to AND gate 30. A second input to the AND gate 30 is an output of the inverter amplifier 26. Accordingly, if the pulse received by the receiving transducer 28, as represented by waveform C, is received before the negative going trailing edge of the clock pulse A, has occurred then, gate 30, under these circumstances is enabled, that is, with the input from the receive amplifier 38 being positive, before the clock pulse positive going trailing edge occurs, and the gate then applies an output to the one-shot circuit 32. One-shot circuit 32 applies a pulse of a predetermined duration, exemplified by 150 microseconds, to a delay circuit 34. The output of the delay circuit is applied through an amplifier driver 36 to the valve 12, and maintains it open for the interval determined by the interval of the one-shot. Thereby, a predetermined amount of solvent is added to the ink in the ink reservoir 14.

If the receive pulse coming from transducer 28 occurs simultaneously with or after the occurrence of the trailing edge of the clock pulse A, then AND gate 30 is not enabled, and the valve will not be opened. If the receive pulse coming from transducer 28 occurs before the trailing edge of the clock pulse A, the valve will be opened. Accordingly, when the time required for the sonic pulse to travel between the two transducers through the ink is less than the interval of the clock pulse, it is known that enough solvent is evaporated so that the speed of sound through the ink is not proper for operation of the nozzle at the fluid resonance region desired. If the interval measured by the speed of the sonic pulse over the distance between the two transducers is greater than the interval of the clock pulse, then there is too much solvent in the ink and the system will not operate to add solvent until a sufficient amount is evaporated to bring the circuit that adds solvent into operation.

It should be appreciated from the foregoing that the width of the clock pulse or the interval over which it occurs is adjusted to be equal to the time required for sound to travel through the ink between transducers 25 and 28, when the ink has a consistency which provides a desired velocity of sound.

The reason for the use of the delay circuit 34 is to insure that the system does not operate to add solvent again, once solvent has been added until such time as the solvent which has just been added has had a chance to be mixed throughout the ink in the reservoir. A suitable delay interval is readily determined from this "mixing interval."

There has accordingly been described and shown herein, a novel and useful arrangement for maintaining a predetermined substantially constant velocity of sound for the ink.

Claims

What is claimed is:

1. A system for maintaining the velocity of sound through an ink contained in a reservoir, which is used in an ink jet writing system, substantially constant, said system comprising:

means for generating a sonic pulse,

transmitting transducer means for applying said sonic pulse to said ink,

receiving transducer means positioned a predetermined distance away from said transmitting transducer means for producing an output pulse responsive to receiving the pulse applied to said ink,

means for measuring the interval elapsed between the application of said sonic pulse by said transmitting transducer to said ink, and the time said receiving transducer provides an output pulse,

a source of solvent, and

means responsive to said interval differing from a predetermined time interval for adding a predetermined amount of solvent from said source to said ink.

2. A system as recited in claim 1 wherein said means for generating a sonic pulse includes means for generating a clock pulse having a duration equal to said predetermined interval, and

said means for measuring the interval elapsed between the application of said sonic pulse by said transmitting transducer to said ink and the time said receiving transducer provides an output pulse comprises,

gate means to which said clock pulse and output pulse of said receiving transducer are applied for producing a gate output pulse when said output pulse of said receiving transducer occurs prior to the termination of said clock pulse, and

means for applying said gate output pulse to said means for adding a predetermined amount of solvent to enable it to add solvent from said source to said ink for a predetermined interval.

3. In an ink drop writing system wherein it is desired to maintain the speed of sound through the mixture of ink-solvent which is used, substantially constant, a system comprising:

a sonic transmitting transducer positioned within said ink-solvent mixture,

a sonic receiving transducer positioned a predetermined distance from said transmitting transducer within said ink solvent,

a source of solvent,

normally closed valve means for permitting, when opened, a predetermined amount of solvent from said source, to be added to said ink and solvent mixture,

means for applying a pulse signal to said transmitting transducer to be transmitted through said ink-solvent mixture and received by said receiving transducer, which produces a transducer signal responsive thereto,

means for measuring the interval required for said pulse signal to travel between said transmitting transducer and said receiving transducer, and producing an output signal when said interval is less than a predetermined value, and

means responsive to said output signal for opening said valve means for a predetermined interval, whereby a predetermined amount of solvent is added to said ink and solvent mixture.

4. A system as recited in claim 3 wherein said means for measuring the interval required for said pulse to travel between said transmitting transducer and said receiving transducer comprises:

an AND gate comparator,

means to apply said pulse signal which drives said transmitting transducer also to said AND gate comparator, and

means for applying said transducer signal receiving transducer to said AND gate comparator whereby the output of the AND gate comparator is indicative that the interval required for said pulse signal to travel from said transmitting to said receiving transducer through said ink-solvent mixture is less than a predetermined interval.

5. Apparatus as recited in claim 3 wherein said means for opening said valve means over a predetermined interval when the interval for a pulse to travel between said transmitting and receiving transducer is less than a predetermined interval includes:

a two input AND gate,

means for applying a clock signal to one input of said AND gate simultaneously with the application of a pulse signal to said transmitting transducer, and

means to apply the transducer signal of said receiving transducer to the other input of said AND gate to enable said AND gate when it occurs in the presence of said clock signal,

a one-shot circuit providing an output for a predetermined interval in response to an input pulse,

means to apply the output of said AND gate to said one-shot circuit, and

means to apply the output of said one-shot circuit to said valve means.

6. Apparatus as recited in claim 5 wherein said means to apply the output of said one-shot circuit to said valve means includes:

a delay circuit, for delaying the application of the output of said one-shot circuit to said valve means for a predetermined interval.

7. In an ink drop writing system wherein it is desired to maintain the velocity of sound through an ink-solvent mixture contained in a reservoir substantially constant, apparatus comprising:

a sonic transmitting transducer positioned within said ink-solvent mixture,

a sonic receiving transducer positioned within said ink-solvent mixture at a predetermined distance from said transmitting transducer,

normally closed valve means for enabling solvent to be added from said source to said ink solvent mixture when open,

a source of clock pulses having a predetermined width,

means responsive to the leading edge of a pulse from said source to apply a pulse to said transmitting transducer, whereby said receiving transducer will provide a transducer pulse at an interval thereafter determined by the time required for the pulse from said transmitter transducer to travel through said ink-solvent mixture to said receiving transducer,

And gate means,

means for applying a clock pulse from said source to said AND gate means,

means for applying said transducer pulse to said AND gate means whereby said AND gate means provides an output when said pulse from said receiving transducer for providing a transducer pulse occurs during the interval of said clock pulse, and

means responsive to said AND gate means output for enabling said valve means to be opened for a predetermined interval.

8. Apparatus as recited in claim 7 wherein said means for applying said AND gate means output to said valve means includes:

a delay circuit for delaying application of subsequent pulses to said valve means until the solvent which has been added by the last operation of said valve means has been dispersed through said solvent ink mixture.