CA1056439A - Method and apparatus for controlling satellites in an ink jet printing system - Google Patents

Abstract

METHOD AND APPARATUS FOR CONTROLLING SATELLITES
IN AN INK JET PRINTING SYSTEM
ABSTRACT OF THE DISCLOSURE

A continuous jet stream of a ferrofluid ink is broken into individual drops by an asymmetrical perturbation force applied to the stream. The ink, as it exits from an orifice under pressure, is excited by an electro-magnetic transducer energized with an asymmetrical excitation signal having a fundamental and higher harmonics. An asymmetrical excitation signal, such as a sawtooth, having a substantial second and/or third harmonics content which produce an excitation signal with different rise and fall times can form a stream of drops free of satellites. Asymmetry of magnetic field forces can be produced with single stage or multi-stage transducers located at spaced positions along the stream. Asymmetry can also be produced using an electromagnetic transducer having a non-uniform gap.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS
Application af George J. Fan and Richard A. Toupin entitled "Method and Apparatus for Forming Droplets from a Magnetic Liquid Stream", Canadian Serial No. 215,260, filed December 20, 1974, now C.P. 1,021,837, and Application of Edward F. Helinski and Jack L. Zable entitled "Method and Apparatus for Fast Merging Satellites in an Ink Jet Printing System", Canadian Serial No. 238,097 filed October 20, 1975.
BACKGROUND OF THE INVENTION
1. Field of the InYention , .
. .

iOS6439 1 Thi~ ~nvention relates to ink iet

2 recordin~ and particularly to a method and apparatus

3 for generating a stream of drops for use in an ink

4 jet printer.
2. Description of Prior Art 6 In ink jet recording it is well known 7 to produc~ a stream of li~uid ink under pressure and 8 to cause perturbations in the stream to make it break 9 up into individual drops which are then directed in a controlled manner onto a record medium to visually ll record the information. The perturbations can he 12 formed by electromechanical devices which vibrate the 13 jet-forming elements or by the application of external 14 fields to the unsupported jet stream which produce varicosities in the jet stream. U. S. Patent 3,596,275, 16 issued July 27, 1971 to ~ichard G. Sweet, shows using 17 either a magnétostrictive vibrator or an excitational 18 electrode for producing drops from a conductive ink 19 jet. In U. S. Patent 3,298,030, issued on July 12, 1965 to Arthur M. Lewis and Arling D. Brown, Jr., a 21 piezoelectric transducer is used as the perturbation-22 producing means. In the previously-mentioned applica-23 tion of George J. Fan and Richard A. Toupin, drops are 24 formed in a magnetic ink jet stream using externally-applied magnetic fields at plural uniformly-spaced 26 positions along the stream, the spacing of the field-27 producing elements being equ'al to the wavelength of 28 the varicosities produced in the stream or a multiple 29 thereof.
;i One of the problems associated with 31 previous drop generators has been the fact that a~

., ' ~

~0S6~39 the stream breaks up into indiv;dual drops there is a tendency for satel-lites to form. The precise explanation of why satellites form is not fully understood; however, it has been observed that satellite drops, when formed, will usually form from the ligament portions of the jet stream which connect the varicosities produced by the perturbations. It has also been observed that the satellites can have a velocity equal to or different from the adjacent large drops. Depending on the relative velocity of the satellite and large drops merging will take place if their relative velocities are different. The rate at which merging takes place, however, can affect the control of the droplets and the print quality or contamination of the ink jet apparatus.
U.S. Patent 3,683,396, issued August 8, 1972 to Robert I. Keur, Sandra Miller and Henry A. Dahl, attempts to solve the satellite prob-lem by designing the nozzle to have fluid resonance to obtain the forma-tion of fast satellites. The nozzle is designed so that its internal length is determined in relation to the speed of sound through the fluid in the nozzle and the desired frequency of resonance.
~ .S. Patent 3,334,351, issued August 1, 1967 to Norman L. Stauffer, shows a method of merging satellite drops by vibrating the stream to impart a rolling motion to ink drops through the use of dual vibration means operating transverse to and in the direction of flow of the jet stream.

It will be appreciated that the prior art solutions for eliminating or merging satellite drops require specialized complex structures. Fur-thermore, such structures lack versatility, since the mechanical devices once designed are strictly confined to specific operating conditions having a very narrow range. As the conditions of the ink and the operat-ing properties of the system vary, the effectiveness of prevention or merging of satellites degrades considerably and the means for controlling the variation in operating conditions becomes complex and costly.
SUMMARY OF THE I~VENTION
It is a general object of this invention to provide an improved method and apparatus for producing an ink jet stream comprised of suc-cessive ink drops.
It is a more specific object of this invention to provide an im-proved method and apparatus for controlling the formation of satellites in an ink jet stream.
It is a further object to provide an improved method and appara-tus for generating drops from a liquid jet stream in which drops can be generated which are free of satellites.
It is a still further object to provide a method and apparatus for forming drops in an ink jet is . ~,...
' ' ' .

1~56439 1 system which is relatively simple in structure, easy 2 to control, relatively easy to manufacture and operable 3 over a wider range for printing purposes.
4 The above, as well as other objects, are attained in the practice of this invention by disturb-ing an ink jet stream in such a way as to cause an 7 a~ymmetric momentum distribution or velocity variation 8 in the stream. Broadly, in accordance with the inven-g tion, the asymmetric momentum distribution or velocity variation in the stream is obtained by applying a 11 periodic force asymmetrical in space and/or time to the 12 fluid stream. In the preferred form in which this 13 invention is practiced, a transducer operated to cause 14 perturbations in a jet stream is energized with an excitation signal having an asymmetrical waveform, A
16 preferred excitation signal includes higher integral 17 harmonics in combination with the fundamental frequency 18 which corresponds with the desired drop rate~ Very 19 good control over satellite formation has been obtained using an excitation signal waveform which includes 21 second or second and third harmonics in phase or out of 22 phase with the fundamental frequency in such a manner 23 that the excitation signal has differential rise and 24 fall times.
The transducer can be either electro-26 mechanical, such as the piezoelectric crystal attached 27 to a fluid chamber, or a field exciter located adja-28 cent the field controllable jet stream in advance of 29 drop breakoff position. In a specific embodiment in which the invention is practiced, the field controllable 31 jet stream is formed using a magnetic ink such as a 1 ferro~luid. The magnetic ink jet stream is subjected 2 to an asymmetrical field force by exciting an electro-3 magnetic transducer located proximate the jet stream 4 with an excitation signal having an asymmetrical wave~
form as previously described. The magnetic exciter 6 can be sin,le stage or multiple stage. In the latter 7 case, the stages can be spaced differentially relative 8 to the wavelength of the varicosities in the stream, 9 i.e. the drop wavelength. The asymmetrical field force can also be obtained by structuring the trans-11 ducer to have a non-uniform,gap arrangement through 12 which the stream is projected in which case the exci-13 tation signal may have either a symmetrical waveform 14 or asymmetrical waveform depending on what type of satellite control is desired.
16 Thus, it will be appreciated that great 17 versatility has been provided by this invention.
18 Operation can occur over a wider range there,by greatly 19 facilitating ink jet recording. Using this invention drops can be generated free of satellites and under 21 certain conditions where satellites form, merging can 22 be obtained within the space of a single drop wave-23 length.
24 The foregoing and other objects, fea-tures and advantages of the invention will be apparent 26 from the following more particular description of pre-27 ferred embodiments of the invention, as illustrated in 28 the accompanying drawings.
29 BRIEF DES~RIPTION OF DRAWINGS
FIG. 1 is an isometric view of an ink 31 jet recorder incorporating the drop generator apparatus and method of this invention.
FIGS. 2 - 5 show the force and momentum distribution characteris-tics for certain waveshapes for explaining the principles of asymmetry as embodied in this invention.
FIGS. 6 - 13 show various waveforms for generating drops free of satellites and for merging in forward or rearward directions in accord-ance with this invention.
FIG. 14 is a schematic circuit diagram illustrating a drop fre-quency generator useful for producing the various illustrated waveforms.
DETAILED DESORIPTION OF THE INVENTION
Referring to the drawings, and particularly FIG. 1, there is shown an ink supply 10 of magnetic ink. The magnetic ink may be any suitable magnetic ink which is preferably isotropic and virtually free of reman-ence. One suitable example of a magnetic ink is a ferrofluid of the type described in co-pending application of George J. Fan and Richard A. Toupin, entitled "Recording System Utilizing Magnetic Deflection", Serial Number 215,260. Another example of the magnetic ink is a stable colloidal suspension in water of 100 angstrom-sized particles of mag-netite (FE304) with surfactant surrounding the particles.
The ink supply 10 supplies the magnetic ink to a nozzle 11 under a pressure such as 20-50 psi, for example, from which the ink issues as a stream 12 through an opening at the end of the nozzle 11. An ts ~
'~

iOS6439 >
1exciter 14 is disposed in axial alignment with the 2path of the stream 12 as it exits from the nozzle 11.
3The exciter comprises a C-shaped magnetic core 15 4having upper pole 16 and a lower pole 17 in mutual Svertical alignment above and below the ink jet stream 612. A co~1 18 is wound on the arm portions of the 7C-shaped magnetic core 15 to obtain a maximum flux 8concentration in the ends of the magnetic poles. The 9coil 18 is connected to a drop frequency generator 19 10which in accordance with this invention applies a 11periodic current which produces a magnetic field which 12produces an asymmetrical field force to cause pertur-13 bations in stream 12. The width of each of the pole , ~-14 faces 16 and 17 in the direction of the stream is less , than the distance between droplets 22 which are formed 16 by the exciter 1~ from stream 12 and preferably is one-, .~ .
17 half of the wavelength of the perturbations produced 18 in the stream 12 by the exciter plus or minus up to 60~.
19 It is appreciated that this basic dimension may be increased by a length any integral number of wavelengths 21 without a significant deterioration of the operation.
22 While a single stage exciter is shown in 23 FIG. 1, the present invention includes the use of a 24 dual or multiple stage exciter of the type shown in the co-pending application of E. F. Helinski and J. L.
26 Zable previously mentioned and would in desired condi-27 tions utilize the differential spacing to produce out-28 o~-phase multiple perturbation field forces along witl 29 asymmetr~ disclosed herein.
The gap between the pole faces 16 and 31 17 must not be too wide. Otherwise, the magnetic field E~974030 -8-..

.

,, , ~ . .
, ~056439 1 produced by the current flowin~ through the coil 18 2 would not act on the stream 12 in the desired manner 3 to produce the desired perturbations in the stream 12.
4 This i8 due to the density of the magnetic field decreasing as the gap between the opposed pole faces 6 increases. Similarly, the intensity of the magnetic 7 field also decreases as the gap between the pole faces 8 increases. Thus, the distance across the gap between g the pole faces of each pole pair is about 2.5 - 4 times the diameter of the stream. Further details of the 11 relationship of the gaps and magnetic fields may be 12 obtained by reference to the aforementioned application 13 of George J. Fan and Richard A. Toupin. The energiza-14 tion of the coil 18 of magnetic core 15 by the signal generator 19 produces perturbations in the jet stream 16 12 to cause drops 20 to break off from the stream in a 17 succession of uniformly~spaced drops of substantially 18 uniform size. The stream of ink drops 20 then passes 19 through a magnetic selector 21 having coil 22 which is selectively pulsed by a data signal generator 23 in 21 accordance with a data input to de~lect predetermined 22 drops 20 from the original jet stream trajectory to be 23 ultimately caught by a gutter mec~anism 24 located 24 in front of the print medium 25. The drops 20 deflected by the selector magnet 21 and those drops 26 not deflected thereby continue to move as a stream 27 through a gap in deflection magnet 26 located in 28 advance of the gutter 24 and print medium 25. A saw-29 tooth signal from raster scan 28 applied to a coil 29 on deflection ~agnet 26 causes the selected and 31 unselected drops 20 to be deflected vertically.

.

1056~39 1 Selected, i.e. the unwanted, drops are caught by the 2 gutter 24 whereas the unselected, i.e. the print drops 3 pass to t~e right of knife edge 30 of gutter 24 to be 4 deposited on the prillt medium 25 in accordance with the rastex scan si~nal and the length of time that the 6 individual drops are in the magnetic field generated 7 by the deflection magnet 24. A relative lateral motion 8 is provided between the medium 25 and the jet stream to 9 thereby record information in the form of dot matrix characters or other symbols in a manner which is 11 well-known.
12 As previously discussed, this invention 13 deals with a method and apparatus for generating drops 14 in which a liquid stream is subjected to an asymmetri-cal perturbation force. To illustrate the phenomenon 16 reference is made to FIGS. 2A, 2B and 2C. As seen in 17 FIG. 2A, a perfectly symmetrical (or anti-symmetrical) 18 current waveform such as square wave 32 is applied by 19 the drop frequency generator 19 of FIG. 1 to exciter 14.
The spatial distribution of magnetic force (which is 21 approximately a linear function of current level) by a 2Z dual stage magnetic exciter, for example, having uniform 23 gaps and a distance between midpoints 33 and 34 equal to 24 a wavelength is shown in FIG. 2A. The spatial force distribution, curve 37, is antisymmetric about point 26 3I. This force distribution with waveform 32 results 27 in the velocity variation Gf the moving stream shown by 28 curves 38 in FIG. 2C and is perfectly antisymmetric 29 about the points where drops are formed. This results in satellites 39 and parent drops 40 which are perfectly 31 sl:able since the integrated momentum for the drops is z~ro.

lOS6~39 1 FIGS. 3A - 3C show the case in which 2 asymmetry i~ obtained. In FIG. 3A a distorted current 3 waveform 41 is applied to a dual stage exciter having 4 poles 35 and 36 which have a uniform gap and are spaced along the stream a distance equal to the wave-6 length of the drops to be formed. In this case the 7 spatial distribution of magnetic forces about point 31 B is still anti-symmetrical. However, the resultant 9 momentum distribution is skewed, as seen from exag-gerated curve 43 in FIG. 3C, due to the time dependent 11 asymmetric variation in force amplitude in accordance 12 with the energizing waveform 41 while the stream is 13 passed through the exciter. In this case the parent 14 drops 40 form in stable position, but the satellites 39 are unstable and accelerate toward the parent drops.
16 As seen in FIGS. 4A - 4C, the spatial 17 distxibution of the magnetic forces is skewed by alter-18 ing the exciter structure by the provision of non-19 uniform field gaps. In this case a symmetrical square wave 32 (FIG. 4A) is used to energize the dual pole 21 exciter. The poles 44 and 45 have non-uniform gaps 46 22 and 47 tapered in the upstream direction. The spatial 23 distribution of magnetic forces, as shown by curve 48 24 in FIG. 4B, is no longer anti-symmetrical but,has be-come asymmetrical. The result is to produce an asymme-26 trical momentum distribution in which the satellites 27 39 are unstable and accelérate toward the parent drops 28 40, as seen by the velocity curve 49 in FIG. 4C. In 2~ the case of FIGS. 4A - 4C, asymmetry is produced solely by the structure of non-uniform gaps while the energiz-31 ifl~ currerlc remains symmetricai.

l In FIGS. 5A - 5C the combined effects 2 of distorted waveform energization (curve 41 in FIG.
3 5A) and non-uniform air gaps (46 and 47 in FIG. 5B) for 4 the poles (44 and 45 in FIG. 5B) of a dual stage exciter, are shown. As illustrated by curve 50 in FIG. 5B, the 6 spatial di~tribution of magnetic forces have become 7 asymmetrical. In addition, the variation in the force 8 amplitude while the stream is passed through the exciter 9 results in a skewing of the momentum distribution, as shown by curve 51 in FIG. 5C, which causes the satellites ll 39 to be unstable and accelerate toward the parent drops 12 40.
13 While certain specific structural forms 14 are shown.in relation to a dual stage magnetic exciter, it is understood that the same structural forms are 16 applicable to the single stage magnetic exciter or other 17 types of multi-stage magnetic exciters. Also, single l~ stage or multi-stage exciters can be modified to have 19 other forms or excited by other waveforms to produce asymmetrical perturbation fleld forces which cause fast 21 satellite merging or satellite free drop formation.
22 For example, the dual stage exciter of FIGS. 2 - 5, as 23 well as other multi-stage exciters, might have succes-24 sively different non-uniform gaps to produce the Z5 force skewing and momentum skewing described above.
26 Various asymmetric waveforms can be used 27 which produce satellite-free drop formation or fast 28 merging of satellites. In FIG. 6 the current waveform 29 55 having a peak amplitude of 0.5 amperes and a fre-quency of 30.8 K~lz was applied to a single stage 31 exciter 14 having a uniform gap of 6 mils. The width . . .

1 of the pole was 5 mils. A ferrofluid ink was applied 2 at the pressure of 36 psi to a nozzle with a 2.5 mil 3 diameter, resulting in a drop distance of 17.5 mils.
4 Arrow 56 indicates the direction of flow of the jet stream. As seen, drop 57 has detached from the liga-6 ment portion 58 of the continuous jet stream 12 with a 7 forward ligament 59 attached thereto. Within the dis-8 tance of one drop wavelength the ligament portion has 9 substantially disappeared into the main drop portion.
As seen in FIG. 7, satellite 60 will 11 form ahead of drop 61 and then merges with drop 61 12 within a single drop wavelength. The exciter of FIG.
13 7 was the same as for FIG. 6 except that the amplitude 14 of the current waveform 62 was approximately 0.25 amperes.
Thus, in an actual machine environment when a fluctua-16 tion or temporary change in the power supply condition 17 causes the power applied to the exciter to become 18 reduced, the print quality of the ink jet printer will 19 not be significantly degraded, since while satellites might form, merging occurs in a very short space so 21 that substantially the same drop dynamics are encountered 22 and satellites present do not affect print quality.
23 In FIG. 8 the waveform 63 is a fast rise, 24 slow fall current waveform, with an amplitude of 0.5 amperes. The single stage exciter of FIGS. 6 and 7 was 26 used with substantially the same operating conditions.
27 As seen in FIG. 8, the ligament portion 64 does not 28 break off separately, but remains attached to the rear 29 of drop 65 at breakoff and almost disappears within one drop wavelength.
~1 In FIG. 9, the fast rise, slow fall 1 wav~form 66 had an amplitude of 0~4 amperes. Other-2 wise, the conditions and structure remain the same as 3 for FIG. 8. In this case, the drop formation is also 4 satellite free. However, it is to be observed that the connection of the ligament portion 64 to drop por-6 tion 65 is less secure and it is expected that with a 7 lower amplitude current satellites would probably form.
8 However, due to the asymmetrical force caused by the 9 asymmetry of the waveform 66 fast merging within one drop wavelength can be expected.
11 It is also to be noted from the above 12 specific examples that by changing the waveform from 13 slow rise to fast rise the direction of merging of 14 attached ligament or satellite is changed.
In FIGS. 10 and 11 the same waveforms 16 55 and 62, as used in FIGS. 6 and 7, are used at an 17 applied frequency of 32.2 KHz with a dual stage mag-18 netic exciter. The width of the poles was 9 mils and 19 the pole gap was approximately 6 mils and the separa-tion from the poles was 15 mils. Ferrofluid ink was 21 supplied at a pressure of 36 psi to a 2.5 mil diameter 22 nozzle, resulting in drop distance of 15 mils. As 23 seen in FIG. 10, the ligament portion 64 remains 24 attached to the rear of the drop portion 65 to provide a satellite-free drop formation. In FIG. 11, the 26 ligamen~ portion breaks off to the rear of the drop 27 portion to form satellites 68 which are merged with 28 drops 69 within three drop wavelengths. It is apparent 29 from FIGS. 10 and 11 that an increase in amplitude cur-rent from 0.2 amperes or waveform 62 would reduce the 31 merge distance or eliminate satellite formation.
~N974030 -14-1 In FIGS. 12 and 13 substantially the 2 same fast rise, slow fall waveforms 63 and 66 of FIGS.
3 8 and 9 were used with a dual staye exciter of FIGS.
4 10 and 11 operated with substantially the same condi-tions. As seen in FIG. 11, the ligament portion 70 6 forms ahead of the drop portions 71 upon breakoff from 7 the stream 12. In FIG. 13 the ligament portion forms 8 a satellite 72 which merges with drop 73 within three 9 drop wavelengths. As in previous case with a single stage exciter, changlng the current waveform from the 11 slow rise to fast rise produced a change in direction 12 of ligament formation for satellite merging.
13 Various other asymmetrical waveforms 14 can be used to produce satellite-free drop formation or fast merging. From the above examples it can be seen 16 that the preferred asymmetrical waveform takes the form 17 of sawtooth with essentially a linear ramp. Such a 18 signal essentially has a waveform comprising a funda-19 mental frequency and higher harmonics. The specific waveform 55 has a harmonic content in which the approxi-21 mate ratio of the second harmonic to the fundamental 22 a2/al = 0.5 and the ratio of the third harmonic 23 a3/al - 0.33, where the equation of the idealized saw-24 tooth waveform is expressed as follows:

26 f (t) = aO+~ lansin T
27 In the case of waveform 66 (see FIG. 9) the approxi-28 mate ratio a2/al was 0O24 and the ratio a3/al was equal to 0.11. Harmonics higher than the third may also be present in the sawtooth waveforms illustrated. Their 31 effect on asymmetry is considered to be generally ~N974030 -15-~ ~', ' . ., :

1 negligible. Other combination of harmonics and funda-2 mentals may ~e used. Howe~er, the best results are 3 obtained if the composite asymmetrical waveform pro-4 duced has a rise time substantially different from the fall time. By controlling these differences and with 6 proper construction of exciters, it is possible to con-7 trol the direction of ligament breakoff and merging 8 when satellites form as previously illustrated.
9 Various drop generator circuit devices might be used for generating the waveforms practiced 11 with this invention.
12 In FIG. 14, a periodic signal from a 13 pulse generator 80 passes through a pulse width con-14 trol circuit 81 to operate a switch 82 for controlling the charge and discharge of capacitor 83. The fre-16 quency of the signal from pulse generator 80 corre-17 ~ponds with the desired perturbation and drop rate in 18 stream 12. The pulse width is regulated by pulse width 19 control circuit 81 and controls the duty cycle of the coil 18. Positive and negative current sources 84 and 21 85, respectively, the magnitudes of which Io and Ii, 22 are controlled by variable resistors 86 and 87 in such 23 a way that current Io never exceeds current Ii. Diodes 24 88 and 89 maintain the input voltage VIN within a pre-determined upper and lower voltage values. During an 26 on portion of switch 82, the current difference (Ii-Io) 27 determines the charging rate of capacitor 83 and controls 28 the slope of the rising voltage (i.e. the rise time) of 29 signal 90 while in the off portion of switch 82 the current Io controls the discharge rate and, thus, the 31 slope of the falling voltage ti.e. the fall time) of lOS6439 1 the input signal 90. A tran~conductance amplifier 91 2 converts the voltage in signal 90 into an output cur-3 rent signal 92 of the same form as signal 90. The coil 4 18 of exciter 14 is connected to a supply voltage Eo S which is set to exceed the maximum inductive potential 6 of the exciter 14. The amplitude of the current waveform 7 92 can be controlled by altering the gain of the trans-8 conductance amplifier 91 or by varying the level of the 9 input voltage VIN. The rise and fall time of the volt-iO age signal 90 and the current signal 92 is controlled by 11 controlling the on-off times of switch 82 through the 12 regulation of the pulse width control circuit 81.
13 Thus, it will be seen that an improved 14 method and apparatus have been provided for generating drops from a liquid stream in which the individual drops 16 can be readily formed free of satellites or satellites, 17 if formed, can be fast merged. A wide range of choices 18 for operation is also provided in accordance,with this ' invention and can be operated under a wide range of con-ditions in an actual jet printing apparatus. By pro-21 viding satellite-free drop formation and fast merging 22 of satellites improved drop dynamics is obtained and 23 the control of the drops for deflection to trajectories 24 to form characters is greatly simplified for improving print quality in an ink jet recorder.
26 While the invention has been particularly 27 shown and described with reference to preferred embodi-28 ments thereof, it will be understood by those skilled in 29 the art that the foregoing and other changes in form and details may be made therein without departing from the 31 spirit and scope of the invention.

Claims (20)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In an ink drop forming system of the type having means for supplying magnetic ink under pressure to a nozzle or the like to cause a continuous jet stream of magnetic ink to flow from said nozzle and magnetic transducer means for forming periodic perturbations in said stream, the improvement comprising:
said transducer having means for generating an asymmetrical force field at a predetermined frequency in the vicinity of a segment of said jet stream for controlling the formation of satel-lites produced by said periodic perturbations.

2. In an ink drop forming system of the type in accordance with claim 1 in which said transducer means comprises a magnetic core device disposed proximate at least one segment of said stream, said core device being structured to produce an asymmetrical force field on said segment of said stream, and means for periodically energizing said magnetic core device at said predetermined frequency in timed relation with the flow of said stream relative to said magnetic core device.

-CLAIMS 1 and 2-

3. In an ink drop forming system of the type in accordance with claim 2 in which said magnetic core device includes pole portions disposed proximate said segment of said stream, and said pole portions forming a non-uniform gap along said segment of said stream.

4. In an ink drop forming system of the type in accordance with claim 3 in which said pole portions are tapered in the direction of said stream flow to form said non-uniform gaps.

5. An ink drop system of the type in accordance with claim 1 in which said magnetic transducer means comprises a magnetic core device disclosed to produce a magnetic field proximate at least one segment of said stream, and means for periodically applying an ener-gizing signal at said predetermined frequency to said magnetic core device, said energizing signal having an asym-metrical waveform.

6. In an ink drop forming system of the type in accordance with claim 5 in which said energizing signal contains harmonics higher than one for producing said asym-metrical waveform.

-CLAIMS 3, 4, 5 and 6-

7. In an ink drop system of the type in accordance with claim 5 in which said higher harmonics includes a second harmonic.

8. In an ink drop system in accordance with claim 6 in which said higher harmonics are out of phase with the fundamental frequency of said signal.

9. In an ink drop system in accordance with claim 5 in which said signal has a long rise time relative to its fall time.

10. In an ink drop system of the type in accordance with claim 5 in which said signal has a short rise time rela-tive to its fall time.

-Claims 7, 8, 9 and 10-

11. In an ink drop forming system of the type having means for supplying field controllable ink under pressure to a nozzle or the like to cause a continuous jet stream of magnetic ink to flow from said nozzle, and transducer means for forming periodic perturbations in said stream, the improvement comprising:
said transducer means having means for generating an asymmetrical force field at a predetermined frequency in the vicinity of a segment of said jet stream for controlling the formation of satellites produced by said periodic perturbations.

12. In an ink drop forming system of the type having means for supplying magnetic ink under pressure to a nozzle or the like to cause a continuous jet stream of ink to flow from said nozzle, and transducer means for forming periodic perturbations in said stream, the improvement comprising:
said transducer means having means for applying an asymmetrical force at a predetermined frequency to said jet stream for controlling the formation of satellites produced by said periodic perturbations.

-CLAIMS 11 and 12-

13. In an ink drop forming system of the type having means for supplying magnetic ink under pressure to a nozzle or the like to cause a continuous jet stream of ink to flow from said nozzle, and a transducer for causing periodic perturbations in said stream at a pre-determined frequency whereby drops are formed in said jet stream, the improvement comprising, a method of controlling the forma-tion of satellites by energizing said transducer with a signal having an asymmetrical waveform.

14. In an ink drop forming system of the type in accordance with claim 13, the improvement further comprising energizing said transducer with an asymmetrical waveform having a fundamental frequency and higher harmonics.

15. In an ink drop forming system of the type in accordance with claim 14, the improvement further comprising energizing said transducer with an asymmetrical waveform in which the higher harmonics includes at least the second harmonic.

16. In an ink drop forming system of the type in accordance with claim 15 in which the ratio of the amplitude of the second harmonic to the fundamental frequency is at least equal to 0.5.

-CLAIMS 13, 14, 15 and 16-

17. In an ink drop forming system of the type having means for supplying magnetic ink under pressure to a nozzle or the like to cause a continuous jet stream of ink to flow from said nozzle means for forming drops in said stream comprising in combination, a transducer for causing periodic perturbations in said stream at a predetermined fre-quency, and means for energizing said transducer with a signal having an asymmetrical waveform.

18. In an ink drop forming apparatus in accordance with claim 17 in which said signal has a sawtooth waveform.

19. In an ink drop forming apparatus in accordance with claim 18 in which said sawtooth waveform has a slow rise time and a fast drop time.

20. In an ink drop forming apparatus in accordance with claim 18 in which said sawtooth waveform has a fast rise time and a slow drop time.

-CLAIMS 17, 18, 19 and 20