US3736593A

US3736593A - Ink drop writing system with nozzle drive frequency control

Info

Publication number: US3736593A
Application number: US00187976A
Authority: US
Inventors: R Keur; H Dahl
Original assignee: AB Dick Co
Current assignee: AB Dick Co; Videojet Technologies Inc
Priority date: 1971-10-12
Filing date: 1971-10-12
Publication date: 1973-05-29
Anticipated expiration: 1990-05-29
Also published as: GB1412464A; JPS5430259B2; DE2250089B2; JPS4862344A; CA965065A; DE2250089A1

Abstract

In an apparatus of the type wherein ink under pressure is applied to a nozzle which is vibrated, and the ink emitted by the nozzle thereafter breaks down into ink drops which are charged in a charging tunnel in response to video signals, an arrangement for establishing the nozzle vibration frequency to be a function of the video signals'' frequency and the shape of the video signals.

Description

United States Patent 119 1111 3,736,593

Keur et al. [4 1 May 29, 1973 [54] INK DROP WRITING SYSTEM WITH [56] References Cited NOZZLE DRIVE FREQUENCY UNITED STATES PATENTS CONTROL 3,373,437 3/1968 Sweet et al. ..346/75 [75] Inventors: Robert I. Keur, Niles; Henry A.

Dahl, Mount Prospect, both of Ill. Primary Exammer JPseph i a Att0mey Samuel Lindenberg, Abraham Wasserman, [73] Ass1gnee: A. B. Dick Company, Ch1cago, Ill. Leon Rosen at F 2 [22] iled Oct 12, 1971 ABSTRACT [21] Appl' 187976 In an apparatus of the type wherein ink under pressure is applied to a nozzle which is vibrated, and the ink 52 US. Cl ..346/75 emitted y the nozzle thereafter breaks down into ink 51 Int. Cl. ..G0ld 15/18 l which are charged in a charging tunnel in [58] response to video signals, an arrangement for F l f Search 346/75 317/3 establishing the nozzle vibration frequency to be a function of the video signals frequency and the shape of the video signals.

8 Claims, 3 Drawing Figures DROP FQEQ. DEC FIELD 4o 516NAL S soulzce sougce 51A 32 L 2C0 50 IO d 24 25 NK 1 l2) 2o {22 g aeseavowz 8 17:;

TQANSDUCEQ CHAQQ-HNQI TUNNEL WAST 36 Qset2voil2 INK DROP WRITING SYSTEM WITH NOZZLE DRIVE FREQUENCY CONTROL 7 BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to apparatus for writing with ink drops which are charged by a video signal and directed through an electric field to be deflected in accordance with the charge, and more particularly to improvements therein.

2. Description of the Prior Art An ink drop writing apparatus has been developed wherein ink is applied under pressure to a nozzle. The

. nozzle is vibrated or driven in response to synchronizing signals, provided at a selected nozzle drive frequency. The vibrated nozzle causes an ink jet, which is emitted therefrom to break up into uniform drops at a distance away from the tip of the nozzle. The rate of such drop formation is determined by the vibration rate. A means for charging each drop is provided at the location at which the ink stream begins to break into drops. This means usually is a conductive tube or cylinder. Video signals are applied between the nozzle and the cylinder in response to which a drop assumes a charge determined by the amplitude of the'video signal at the time that the drop breaks away from the jet stream.

The drop thereafter passes through a fixed electric field, as a result of which it is deflected by an amount determined by the amplitude of the charge on the drop.

At the boundary of the electric field there is positioned a writing medium upon which the drop falls. Since the deflection of the drop is determined by the charge on the drop, the arrangement enables one to write information with the ink which is carried by the video signal.

As previously stated, at the time that a drop separates from the fluid stream, the drops are charged by electrostatic induction. If the field established by the video signal is maintained while the drop separates, the drop will carry a charge determined by this video signal. Obviously, if the video signal is in the process of rising or falling or is not present at the time the drops separate, the charge on the drop will not be that of the video signal. In order to place specific charges on given drops, one must known when drop separation is occurring or the phasing of the drop formation relative to the video signal. In the absence of control over drop separation time, because of unpredictable phase changes in the ink drop formation, the uniformity and the fidelity of the printing are affected adversely.

Various systems have been proposed and designed to control drop phasing in order to improve the printing of such ink drop writing devices. Two such systems are described in U. S. Pat. Nos. 3,465,351 and 3,562,761. None of the prior art systems control drop phasing on the basis of the shape of the video signals on which the probability of proper drop charging greatly depends.

OBJECTS AND SUMMARY OF THE INVENTION in an ink drop writing system a novel arrangement for controlling the nozzle drive frequency so as to maximize the probability of proper drop charging.

These and other objects of the present invention are achieved by providing in an ink drop writing system an arrangement which establishes the nozzle drive at a frequency, i.e., the frequency at which the nozzle vibrates, to be a function of the frequency of the video signals, as well as the shape of such signals.

The novel features of the invention are set forth with particularlity in the appended claims. The invention will best be understood from the following description when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a typical prior art ink drop writing system;

FIG. 2 is a diagram of a single video signal; and

FIG. 3 is a block diagram of one embodiment of an ink drop writing system in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic drawing of thepresently known arrangement which is shown to afford a better understanding of the invention. An ink reservoir 10 provides ink under pressure'to tubing 12 which is flexible. An electromechanical transducer 14 is usually placed adjacent to or around the tubing. The transducer is driven in response to signals from a source 16. The transducer serves to vibrate and/or compress the tubing 12 in the region of the nozzle 18. This results in an ink jet 20 being emitted which at a short distance downstream breaks up into drops 22 which are formed at a rate determined by the frequency of the vibration. In the re- 'gion where the stream 20 breaks down into drops, a charging tunnel 24 is provided. This comprises a conductive cylinder to which video signals from a video signal source 26 are applied. The video signals establish a field within the charging tunnel so that the ink drops which are formed therein assume a charge determined by the amplitude of the video signal present at the time the drop separates from the ink jet 20.

Downstream of the charging tunnel there are usually placed a pair of electrodes 28 which are connected to a field bias source 30. As a result, there is established between the electrodes a constant electric field. The ink drops, which bear charges in accordance with the video signal, enter this field and are deflected by an amount which is proportional to the amplitude of the charge. This enables intelligent writing to occur on a writing medium 32, which is moved at some synchronous rate past the electrodes. Drops which do not bear a video charge are captured by a tube or trough 34 which is'judiciouslylplaced at one side so as to capture these drops. It leads to a waste reservoir 36. The paper 32 moves into the plane of the drawing whereby its motion, together with the deflection of the drops, may be used for forming intelligible characters.

As previously stated intelligible characters can only be formed if the drops are properly charged, which is achievable only with proper drop phasing. Alternately stated, proper drop charging can be achieved only when the frequencies of the video signals and the nozzle vibration or drive are in a proper relationship. In accordance with the present invention, unlike prior art systems, the nozzle drive frequency is chosen as a function of the video signals frequency, hereafter designated F,,, and the shape of such signals.

FIG. 2 to which reference is now made is a waveform diagram of a single video signal or pulse, the abscissa designating time and the ordinate amplitude or level in terms of volts. Each signal comprises an interval T during which the signal amplitude is at an established level, designated by line 40. The interval or time T is preceded and followed by a'signal rise time T, and a signal fall time T,, respectively. The video period equalling T,+T is defined as T, and the total signal time is defined as T The number of video periods T, per second is defined as the video frequency and is designated as F,.

In accordance with the present invention the nozzle is driven at a frequency, hereafter referred to as the drop frequency and designated F somewhat different than the video frequency F This frequency difference has been found to prevent the system from being set in an improper phase or bad phase condition for long periods of time, which if permitted to occur would result in unacceptable performance. It has been discovered that no more than one error on adjacent video pulses occurs if one of the following relationships is maintained:

F as expressed in equation (2), is higher than F,. It

represents a drop period equal to T If the following relationship is held:

there will be one or more drops that separate from the stream during T i.e., the interval of the flat top of the there will be fewer drops than video pulses.

One can think of the drop separations as sampling of the video condition. If there are fewer samples taken than there are pulses to detect, it is obvious that some pulses will not be displayed as deflected drops. Then there will be missing spots in the construction of a character. If there are more samples taken than there are video pulses, there will be extra drops in the construction ofa character but no needed drops will be missing. Based on these considerations it has been determined that near optimum results are achieved when F x T l and a ri/( r)- F 16,500/l 16,500 X 10 16,777 Hz.

In practice F, is a function of the character generation system and the desired character rate, and therefore is generally fixed. Based on the shape of the video pulses and F,,, F, is determined in accordance with equation (2) and (5).

FIG. 3 to which reference is now made is a diagram of an embodiment of an ink drop writing system which incorporates the teachings of the present invention. Therein elements like those in FIG. 1 are designated by like numerals. In accordance with the present invention a drop frequency source 40 which is connected to transducer 14 is incorporated. Source 40 activates the transducer with signals at the drop frequency F d which, once chosen as herebefore explained, remains constant and is not changed unless F or the video pulse shape is changed. I

There has accordingly been shown and described herein an improved ink drop writing system. The improvement over the prior art is realized by the means for and method of controlling the relative frequencies of the video signals and the nozzle vibration to minimize the likelihood of improper charging of successive drops. Basically in accordance with the present invention the nozzle drive frequency, referred to as the drop frequency, is made to be a function of the video signal frequency and video signal waveshape.

It should be appreciated that various modifications and/or equivalents may be substituted for the arrangements as shown without departing from the true spirit of the invention. For example, herebefore F d was described as being a function of T,. This is based on the assumption that the rise time T, is greater than the fall time T,, which is typical of most video pulses. If how ever one were to. use video pulses with a fall time greater than the rise time, T, should be substituted for T, in equation (2). Thus in general it may be stated that F,, is a function of F, and the rise or fall times, whichever is greater. Also herebefore it was indicated that it is preferable to chose F in accordance with equation (2). In such a case, though extra drops may occur,one insures against any voids in the generated character. Clearly if one or more voids can be tolerated in the'generated characters, F d can be chosen in accordance with equation l i.e., F =F l+F,,XT,). Therefore all such modifications and equivalents are deemed to fall within the scope of the invention as defined in the appended claims.

What is claimed is:

1. In an ink drop writing system of the type wherein ink under pressure is delivered to a nozzle, a transducer vibrates the nozzle as a function of drive signals supplied thereto, the nozzle emits an ink jet which breaks up into drops, a charging tunnel is positioned in the region at which the ink jet breaks up into the drops, the charging tunnel being adapted to respond to video signals to charge the drops passing therethrough as a function of said video signals, the improvement comprising: video pulse signal source means coupled to said charging tunnel for applying video signals thereto at a preselected first frequency; and nozzle drive means for applying drive signals to said transducer at a second frequency to vibrate said nozzle therewith, said second frequency being a function of said first frequency and the rise or fall time of said video pulse signals. 2. The arrangement as recited in claim 1 wherein said second frequency is higher than said first frequency.

3. In a ink drop writing system of the type wherein ink under pressure is delivered to a nozzle, a transducer vibrates the nozzle as a function of drive signals supplied thereto, the nozzle emits an ink jet which breaks up into drops, a charging tunnel is positioned in the region at which the ink jet breaks up into the drops, the charging tunnel being adapted to respond to video signals to charge the drops passing therethrough as a function of said video signals, the improvement comprising: video signal source means coupled to said charging tunnel for applying video signals thereto at a preselected first frequency; and nozzle drive means for applying drive signals to said transducer at a second frequency to vibrate said nozzle therewith, said second frequency being a function of said first frequency and the shape of said video signals, the duration of each video signal being characterized by a first time interval during which the level of the signal rises from a reference level to a selected level, a second time interval, following said first time interval, during which the signal level is at said selected level, and a third time interval, following said second time interval, during which said signal level falls from said selected level to said reference level,said first and third time intervals being definable as the rise and fall times of the signal, respectively, said second frequency being a function of at least said'first frequency and said rise time.

4. The arrangement as recited in claim 3 wherein F,, F,,/l F, T,, where F, and F d are the first and second frequencies respectively, and T is said rise time.

5. The arrangement as recited in claim 3 wherein the second frequency, definable as F is higher than said first frequency, and F -T is not less than 1, where T, represents said second time interval.

6. The arrangement as recited in claim 3 wherein F =F,,/( l F,,-T,,), where F and F are the first and second frequencies respectively, and T, is the greater of said rise time and fall time.

7. The arrangement as recited in claim 6 wherein the second frequency, F d is higher than said first frequency and F -T is not less than 1, where T is said second time interval.

8. The arrangement as recited in claim 3 wherein F =F,,(1F,,-T,) where F, and F d are the first and second frequencies respectively, and T, is the greater of said rise time and fall time.

UNITED STATES PATENT OFFICE 5 v CERTIFICATE OF C( )RREC"1I ON Patent No- 3,736,593 f Dated May 299 1973 lnventofls) ROBERT 1'. KEUR, ET; AL. V I I It is certi fied that' error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 5, '1ine 45 should read as follows Video pulse. However if; "'1 Column 4 line 11, lt he'denomlnator of the fraction" should be enclosed- .in parent'he sis and shou-ld appear as follows: 7 16,5'00/(1-16 ,S0O Column 6, line 12, thedenominator-10f ti 1e frac-t ion ehoul d be in" parenthesis and should appear as follows:

Signed and sealed this 22nd day: of Jan ua-ry 1-1974;

V SEAL] Att'est': I I

EDWARD M.FLETCHER,JR, "RENE D. TEGTMEYER v a a Att esting. Officer i I, A a tingConirnis eioner of Patents UNITED STATES PATENT OFFICE CETIFICATE OF CORRECTION Patent No. 5,736,593 Dated May 29, 1973 lnventofls) ROBERT I. KEUR, ET. AL.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column. 3, line 45 should read as follows: video pulse However if: k Column 4, line 11, the denominator of the fraction should be enclosed in parenthesis and shou-ld n appear as follows: l6,500/(ll6,500 x 10- j Column 6, line 12, the denominator of the fraction should be in parenthesis and should appear as follows F l-F T Signed and sealed this 22nd "day of January 1974.

(S A Attest:

EDWARD M.PL ETCHE R,JR. RENE D. TEGTMEYER Attesting Officer Acting Commissioner of Patents

Claims

1. In an ink drop writing system of the type wherein ink under pressure is delivered to a nozzle, a transducer vibrates the nozzle as a function of drive signals supplied thereto, the nozzle emits an ink jet which breaks up into drops, a charging tunnel is positioned in the region at which the ink jet breaks up into the drops, the charging tunnel being adapted to respond to video signals to charge the drops passing therethrough as a function of said video signals, the improvement comprising: video pulse signal source means coupled to said charging tunnel for applying video signals thereto at a preselected first frequency; and nozzle drive means for applying drive signals to said transducer at a second frequency to vibrate said nozzle therewith, said second frequency being a function of said first frequency and the rise or fall time of said video pulse signals.

2. The arrangement as recited in claim 1 wherein said second frequency is higher than said first frequency.

3. In a ink drop writing system of the type wherein ink under pressure is delivered to a nozzle, a transducer vibrates the nozzle as a function of drive signals supplied thereto, the nozzle emits an ink jet which breaks up into drops, a charging tunnel is positioned in the region at which the ink jet breaks up into the drops, the charging tunnel being adapted to respond to video signals to charge the drops passing therethrough as a function of said video signals, the improvement comprising: video signal source means coupled to said charging tunnel for applying video signals thereto at a preselected first frequency; and nozzle drive means for applying drive signals to said transducer at a second frequency to vibrate said nozzle therewith, said second frequency being a function of said first frequency and the shape of said video signals, the duration of each video signal being characterized by a first time interval during which the level of the signal rises from a reference level to a selected level, a second time interval, following said first time interval, during which the signal level is at said selected level, and a third time interval, following said second time interval, during which said signal level falls from said selected level to said reference level, said first and third time intervals being definable as the rise and fall times of the signal, respectivEly, said second frequency being a function of at least said first frequency and said rise time.

4. The arrangement as recited in claim 3 wherein Fd Fv/1 - Fv Tr, where Fv and Fd are the first and second frequencies respectively, and Tr is said rise time.

5. The arrangement as recited in claim 3 wherein the second frequency, definable as Fd is higher than said first frequency, and Fd.Te is not less than 1, where Te represents said second time interval.

6. The arrangement as recited in claim 3 wherein Fd Fv/(1-Fv.Tx), where Fv and Fd are the first and second frequencies respectively, and Tx is the greater of said rise time and fall time.

7. The arrangement as recited in claim 6 wherein the second frequency, Fd is higher than said first frequency and Fd.Te is not less than 1, where Te is said second time interval.

8. The arrangement as recited in claim 3 wherein Fd Fv(1-Fv.Tx) where Fv and Fd are the first and second frequencies respectively, and Tx is the greater of said rise time and fall time.