DE2750303A1 - Ink jet speed control for printer - has two droplet detectors positioned along flight path and connected to oscillator generator control - Google Patents

Abstract

Ink jet printer has a control for regulating the speed of the ink jet within a predetermined speed range. Two ink droplet detectors (24, 25) are positioned at a predetermined distance from one another and the droplet selection unit (17) and are connected to a servo-control (23) to which an impulse generator (16, 16a) is also coupled. This generator is connected to an oscillator (15). In the direction of flight the distance of the first detector (24) from the droplet formation point and the distance of the second detector (25) from the selection unit (17) amount in each case to a certain number of droplet wave lengths. When the droplets are travelling at the desired speed, the spacing between the two detectors amounts to.

Description

Method and arrangement for regulating the speed of a

Inkjet in an Inkjet Printer The invention relates to a type of method for regulation specified in the preamble of claim 1 the speed of an ink jet in an ink jet printer.

In ink jet printers of known type, drops are of a controllable type Ink is formed and ejected from a nozzle against the paper to be printed. the Ink is supplied to the nozzle at a pressure sufficient to keep the ink in In the form of a continuous stream from the nozzle. A drop generator for example a piezoelectric or magnetostrictive vibrator, which is attached to the Nozzle or other components located close to the continuous flow, produces disturbances in the current, in order to break down the same into individual parts of essentially the same size and break up equally spaced droplets. In the neighborhood of the stream are field control devices arranged in accordance With the data signals controlled to produce individual droplets in the shape of the desired one Direct data pattern onto the paper to be printed. To get the correct position of the droplets It is important to ensure that the speed of the droplets is as constant as possible.

In the prior art, there is a need to keep it constant the speed of the ink droplets for the purpose of achieving good print quality recognized.

An arrangement for controlling the speed of ink droplets is disclosed in U.S. Patent 3,600,955.

In this control circuit, the phase difference between the through a droplet detector in the vicinity of the Inkjet generated Pulses and the electrical pulses used to charge the droplets. A time-varying impulse resulting therefrom sets the speed of the droplets and is fed to a measuring instrument that is calibrated to measure the degree and indicates the direction of the speed deviation. By observing this Measuring instrument, the pressure of the pump delivering the ink for a corresponding Regulation of the droplet speeds can be readjusted.

A speed correction can also be achieved by (IBM Technical Disclosure Bulletin, Vol. 16, No. 3, August 1973, page 984) that phase differences between the pulses applied to the ink jet to create droplets and the pulses derived from a droplet detector, which in a fixed Distance is attached in the direction of the path of the ink flow to be determined.

According to the prior art, the largest pulse phase shift is i.e., the largest speed deviation for the still precise speed correction is possible, 1800. Another way of looking at it is that the droplet is then accurate for the ideal speed with the detector aligned when the droplet generator or the charging electrode for the droplet is driven in a pulsed manner.

When the droplet frequency is the same, a change in velocity occurs on, then the droplet is not aligned with the detector. For example, if the speed decreases, then the one previously aligned with the detector !, Droplets have not flown that far and are still in front of the 1 detector, when the droplet generator is driven in a pulsed manner. In the same way will an increase in speed have the consequence that with a pulsed control of the droplet generator, the droplet is already behind the detector is located. If a speed correction is carried out, this is communicated to the detector closest droplets are aligned with the detector, i.e. that for example an ink flow that is flying too fast is slowed down in the vicinity of the detector flying droplets, when the generator is driven impulsively will move towards and align with the detector.

An accurate speed correction according to the state of the art can only be carried out if the distance between that of the nth wavelength associated droplet and the detector is smaller than half the droplet wavelength at the time when the droplet generator or the charging electrode are pulsed is controlled. The correction arrangements for the speed correction according to the prior art are not capable of larger speed deviations to correct, i.e., a speed deviation in which the displacement more than half the wavelength at the nth droplet location with respect to the detector.

In other words, if there is a very large deviation in speed exists, then the number of between the droplet generator and the droplet detector flying droplets be wrong. One carried out according to the state of the art Speed correction could then achieve a correction for the number of Droplets that should be present in the stream of droplets. It is thus possible that previously known correction devices actually do not have any speed error can show when in reality the number of droplets in the droplet stream at the time the speed error correction is too small or too large.

The object of the invention specified in claim 1 is therefore to provide a method and an arrangement for correcting for deviations in the velocity of the ink droplets in an inkjet printer that also has very large speed errors can be corrected relatively easily, with a change in the drop generation frequency not is required.

Further features of the invention can be found in the subclaims.

Details of the invention are given below with reference to one shown in FIGS. illustrated embodiment described.

1 shows a block diagram of an inkjet printer a control circuit for keeping the drop speed constant, FIG. 2 diagrams to illustrate the speed correction and FIGS. 3 and 4 a block diagram the cruise control circuit.

The ink jet printer of Fig. 1 has the nozzle 10 through which a stream of field controllable ink 111, such as ferromagnetic ink, is ejected under pressure in that associated with the ink reservoir 12 Pump 13 is generated. The droplets 14 are in the ink stream by the exciter 15 generated, which represent a magnetostrictive element connected to the nozzle can, which oscillates at a frequency determined by the clock 16a, to in the ink stream Generate disturbances and thereby the droplets at a fixed point in the trajectory of the current against the paper 19 to be printed. Not for the pressure The droplets used are removed from their initial current trajectory through the magnetic Selector 17 in the ink collecting aperture 18 distracted that before to be printed paper 19 is arranged. The data pulse source 20 leads the magnetic Selector 17 to a pattern of electrical impulses, in time correspondence with the flight of the droplets 14. The scan generator 21 supplies the magnetic deflector 22 raster scanning signals, which deflect the droplets in a right-angled direction, so that they impinge on the paper 19 to be printed in the desired data pattern. To this extent, the described inkjet printer belongs to the state of the art (e.g. U.S. Patent 3,959,797). Magnetostrective devices and their uses in the generation of droplets are also known (e.g. IBM Technical Disclosure Bulletin September 1976, Vol. 19, No. 4, pages 1201 and 1202).

The speed of the ink droplets 14 as they move against the paper to be printed 19 is controlled by regulating the pump 13, wherein a Coarse / fine control 23 is used, which controls the clock pulses from the clock generators 16 and 16a and speed detection pulses from drop detectors 24 and 25 are supplied that are close to the trajectory of the droplets 14 in front of the drop selector 14 are firmly arranged.

Various types of drop detectors can be used.

A preferred embodiment of a drop generator is in the IBM Technical Disclosure Bulletin Vol. 16, No. 3, dated August 1973, at page 880. The drop detectors 24 and 25 represent such optical drop detectors, that for the emission of separate light beams, across the ink stream against on the light-sensitive semiconductor elements arranged on the other side of the flow of ink optical fibers.

use. The light rays of the drop detectors 24 and 25 are interrupted by an ink drop, causing an electrical signal through each of the semiconductor devices required for the coarse / fine control 23 is produced is.

In a preferred embodiment of the invention, the direction a velocity error by measuring the phase between adjacent droplets 14 determined. This is achieved by arranging the drop detectors 24 and 25 at a distance from one another which corresponds to a drop wavelength when the Ink flows through the drops at its ideal speed and print frequency the clock generator 16a is generated and by arranging the drop detectors 24 and 25 in a known distance between the drop formation point and the magnetic selector 17. For example, if the drop detector 24 is 10 drop wavelengths away from the drop formation point and the drop detector 25 is 10 drop wavelengths is away from the magnetic selector 17, the location of a droplet is relative known to the magnetic selector 17 within 1.0%. If the phase error is greater than 0.5% is found between detectors 24 and 25, the speed can be adjusted in the appropriate direction to adjust the distance between the droplets 14 to get the right value. For example, if a speed error of 10 % is present over a distance of 10 wavelengths would do the droplet count be larger or smaller than a full drop. An extra drop would be a full one 360 ° phase and was not detected and the system was at be locked to a drop level that has a 10% deviation. When the detectors 24 and 25 are spaced a wavelength apart and the speed drops by more than 50 *, there are three drops at a distance of one drop wavelength. The method of detecting a phase change or an error in speed this amount changes the ink flow rate in two sensing cycles. Of the first cycle includes making the change and making rough speed settings, to achieve a change of less than 10% of the desired value, whereupon one or several fine adjustments are made to achieve an accuracy of 1 8 to achieve. The method of the present invention includes executing a sequence from rough adjustment steps in a first direction until a change in direction the phase is determined, which is followed by one or more coarse adjustments Swing around zero speed before fine-tuning to do the final adjustment at the zero point.

A preferred embodiment of a control system is shown in Fig. 3, in which the flip-flop circuit 26 is actuated by electrical pulses from the drop detectors 24 and 25 is operated. The drop detector 24 toggles the flip-flop circuit 26 in their plus state and the drop detector 25 in their negative state. That's why represent the output waveforms 70, 71 and 72 (Fig. 2) of the flip-flop circuit 26 shows the phase indication of the ink drops relative to the drop detectors 24 and 25 Waveforms 71 and 72 illustrate two types of phase errors that for speed errors of + 25% (1/4 A) could exist while the waveform 70 shows no speed error. To understand the phase error of waveforms 70, To be able to measure 71 and 72 with an accuracy of 0.5%, it is necessary that the phase error time interval (W) is divided into a part of 200, i.e., into 1/200 = 0.005 = 0.5%. For a typical drop generation rate of 25 KHz, equivalent to the Exciter 15 is supplied by the clock 16a, and by counting down of 5 MHz (clock 16) is obtained, a 5 MHz pulse rate is obtained by the clock 16 and the AND circuit 28 are supplied to the error counter 29. Pulses from the clock 16 are closed by the AND circuit 28 to the error counter 29 during of the time interval (W) of the output pulse of the flip-flop circuit 26 and during the time interval of every other output pulse of the flip-flop circuit 26 who divided the -two circuit 27 happens to drive. The latter is used to check the phase error, each other Drop pair. This is done by checking the counters for resetting them after each test Time is left. At a 5 MHz pulse rate, the clock counts 200 16 of a wavelength of time. Therefore +50 counts are 1/4 wavelength, which is the highest counter of the error counter 29. If therefore the phase counter a count less than 50 can be assigned (waveform 71 or 70b of Fig. 2), the droplet separation is less than a wavelength and must be the speed gain weight. If the count of the error counter 29 is SO (+ error in 70a or 72), the speed must be reduced because the separation between the drops, which is determined by the time pulse of the flip-flop circuit 26, greater than one Wavelength is. It should be noted that the error counter 29 indicates the direction into which the speed is to be changed. The size of the correction will not determined because the pump 13 is not linear. The pump 13 works only with fixed rough adjustment steps in the desired direction opposite to the direction of the error as it is determined by the counting status of the error counter 29.

When the error counter 29 reaches the nth count, it becomes the bistable Toggle switch 30 reset. The pulse of the delay circuit 31 can Output pulse of the bistable ripple circuit 30 through the AND circuits 32 and 33 through.

If the error counter 29 is less than the full N count less Missing: 1: less than the full bistable flip-flop circuit 30 not reset and the output signal at output Q remains and a phase error pulse becomes by 4-ßltzAzarren 34, which indicates an error in the elus direction will. This fault indication is stored in the comparator 36. When the error counter 29 has a full count for testness indicating an error in the Minus direction indicates, the bistable flip-flop 30 is flipped over, whereby the output signal at the output Q changes from its lower to its upper level and a phase error pulse passed through the AND circuit 32 by a pulse of the delay circuit 31 is and from there reaches the comparator 36 via the 4-bit counter 35 and there is saved. The output signals of the AND circuits 32, 33 are also via the OR circuit 37 is fed to the test counter 38 and at the end of a predetermined one Number of tests (e.g. 10), an error signal is delivered which has a significant Part of the test counter 38 provides an output pulse for the AND circuit 39 and the delay circuit 40 generated, the output of which is connected to the AND circuits 41, 42 and 43. Of the The pulse from the delay circuit 40 leaves the one stored in the comparator 36 Speed error direction information for coarse or fine correction control loops through. The coarse correction control loop contains the up / down counter 51 and the digital / analog converter 52. The fine correction control loop contains the up / down counter 57 and the digital / analog converter 58. The monostable multivibrator 54 connected to an external source becomes used for preloading a count state into the up / down counters 51 and 52. Of the If desired, the precharge count can be set to a level which corresponds to the Digital-to-analog converter 52 causes the pump driver 53 to operate so that the Pressure from pump 13 increases the speed of the pump flow to a higher speed error condition adjusts to ensure that there are no more than two droplets between the drop detectors 24 and 25 are located.

For every change in the count of the up / down counter 51, the works Digital-to-analog converter 52 to give the pump driver 53 a coarse voltage adjustment step to deliver. With every change in the count of the up / down counter 57, the digital / Analog converter 58 has a smaller voltage setting step Pump driver 53 to.

A first indicating a high speed condition (A> B) The output of the comparator 36 is passed through the AND circuit 41, the inverter circuit 45, the coarse rule AND circuit 47 and the OR circuit 50 of the lower side of the up / down counter 51 supplied. The first output of the comparator 36 is also via the AND / inverter circuit 55 fed to the lower side of the up / down counter 57. A second, a low speed state (A <B) representative output signal of the comparator 36 is via the AND circuit 42, the inverter circuit 46, the coarse rule AND circuit 48 and the OR circuit 49 on the side of the up / down counter 51 is supplied.

A second output signal of the comparator 36 is also via the AND inverter circuit 56 on the side of the up / down counter 57 is supplied.

A third output signal that does not indicate a speed error of the comparator 36 is via the AND circuit 43, the OR circuit 61 and the Inverter circuit 62 supplied to the IN terminal of the latch circuit 63, the Has outputs Hnach fine "and" nach coarse ", which provide feedback pulses, which the speed error detection means and the coarse control with each other connect as well as the fine control.

As described above, in the coarse control, an or several coarse tension adjustment steps are fed to the pump 13 by the pump driver 53, until a change of direction of the speed error by the error counter 29, the bistable multivibrator 30 and the comparator 36 is determined. A settling control, which causes the coarse control to settle into the zero speed state, contains the flip-flop 59, which is triggered by pulses from the AND circuits 47 and 48 is actuated, the Directional impulses from the comparator 36 feed the up / down counter 51. Whenever there is a reversal in the direction of the Speed error is detected by the comparator 36, and the up / down counter 51 is supplied with a corresponding signal, the bistable multivibrator 59 operated to store a count in the settling counter 60. If the latter has reached its highest count, indicating that the coarse cruise control has swung around the zero state several times, a signal is sent via the OR circuit 61 of the inverter circuit 62, which the latch circuit 63 in their ON state to change the output signal from "to coarse" to "to fine". A feedback pulse is via the delay circuit 65, the monostable Flip circuit 66 and the OR circuit 67 supplied to the settling counter 60 to reset the same.

The "after fine" signal of the latch circuit 63 becomes the fine control supplied through the AND / inverter circuits 55 and 56. If the "after fine" signal is generated, the drop detector 25 is no longer required for fine control, The drop detector 24, for example 10A of the fixed tear-off point of the drop is located remotely, now stores speed error correction signals in the Comparator 36, the AND circuits 41 and 42 by a pulse from the Delay circuit 40 passed through AND / inverter circuits 55 and 56 to advance the up / down counter 57 in one of the two counting directions, to operate the digibal / analog converter 58 which is a fine step of a voltage setting the pump driver 53 supplies. If the up / down counter 57 its range over a previously determined count after several repetitions of the test technique and settings of the pump 13, a Dcodier-O or a Decoder -63 signal is through the AND circuits 68 or 69 are generated to reset the latch 63 and change the speed control from fine back to srob. So should any change in the Speed of the droplet stream occur that exceed a predetermined gross error value, the Fine control fixes this change and shows the speed control that there is a gross error and sets the control to the coarse correction. At this point in time, a coarse correction takes place until the settling takes place and the control switches to fine control, as described above.

Although the control circuit in conjunction with special percentages the error correction and special error settings and special spacing of the Drop detectors from each other and the drop point in the selector has been described, The invention is of course also with other parameters depending on the ton desired correction range and the nature of the components used can be used.

L e r s e i t e

Claims (7)

PATENT CLAIMS Method for controlling the speed of a Inkjet in an inkjet printer within a given speed range, in which a continuous jet of ink droplets thereby along a Web is directed to a recording medium that ink under pressure from a nozzle and the ink stream by introducing disturbances in ink droplets with uniform frequency is resolved, characterized in that the phase position two neighboring ink droplets are measured and the pressure of the ink opposite to the direction of the measured phase deviation changed in coarse steps until a change in the direction of the phase deviation is measured, whereupon a or several rough steps are carried out around the zero position before the Final adjustment of the pressure of the ink takes place in fine steps. 2. Arrangement for performing a method according to claim 1 with a servo control for monitoring and maintaining a substantially constant Speed of the nozzle emerging from a nozzle under the pressure of a pump, according to a recording medium directed ink jet generated by a vibrator is broken up into individual droplets, characterized in that in the vicinity of the jet of ink droplets, two droplet detectors (24, 25) in a given Distance both from each other and on the one hand from the droplet formation point and on the other hand, arranged by a per se known droplet selection device (17) are connected to the servo control (23), with which also a to the Vibration generator (15) connected clock (16a, 16) is connected. 3. Arrangement according to claim 2, characterized in that the distance of the first droplet detector (24) seen in the direction of flight of the ink droplets (14) from the droplet formation point and the distance of the second droplet detector (25) of the selection device (17) is in each case 10 droplet wavelengths and that at the target speed of the ink droplets, the pitch of the two droplet detectors (24, 25) is a droplet wavelength. 4. Arrangement according to claim 2, characterized in that the servo control (23) contains a flip-flop circuit (26), each with its two inputs one of the two droplet detectors (24, 25) is connected and its output is connected to an AND circuit (28), the other input of which is connected to the clock generator (16) and whose output is connected to an error counter (29) whose output signal a bistable multivibrator (30) controls the two error signals of which each have one direction leading outputs are each connected to a counter (34 or 35), which a Comparator (36) is connected downstream, which depends on the comparison result either a coarse correction counter (52) or a fine correction counter (57) or a latch circuit (63) actuated, which in turn by further logical Links either the output of the coarse correction counter (51) or the output of the fine correction counter (57) to the pump driver (53) that actuates the pump (13) connects. 5. Arrangement according to claim 4, characterized in that both the Coarse correction counter (51) and the fine correction counter (57) have a common monostable Toggle circuit (54) is connected upstream for precharging the two counters (51, 57) on Beginning of the correction to a previously determined high count, the one Ink speed Si-manufactures with no more than two droplets (14) between the two droplets detectors (24, 25) are located. 6. Arrangement according to claim 4, characterized in that a settling circuit is provided, which has a bistable multivibrator (59), the two inputs of which are connected in parallel to the two inputs of the coarse correction counter (51) and its output via a counter (60) to the ON input of the interlock circuit (63) is connected, the IN output of which is connected to the fine correction counter (57) is. 7. Arrangement according to claim 4 and 6, characterized in that the Fine correction counter (57) has two outputs that connect to the OFF input of the interlocking circuit (63) are connected, the OFF output of which is connected to the coarse correction counter (51) is.