DE2346059A1 - LIQUID JET PRINTER - Google Patents

Description

Official file number: New registration

File d. Applicant:

Docket EN 971 050

Liquid jet printer

The invention is based on one specified in the preamble of claim 1 Kind of out.

However, the print quality poses difficulties in such print shops. because they fly through the electric field between "the baffles Due to their charge, drops influence the field in such a way that subsequent drops do not exactly at the desired point on the Recording media can be deposited. One tried this Difficulties to be overcome by means of a standardized, balanced network with an RC circuit (Technical Report No. 1722-1, page 64, Fig. 36c, from March 1964, Stanford Electronics Laboratories, Stanford University) and by compensating the

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harmful
/ Influence of the charge of an ink drop just formed on the charge of subsequent ink drops with the aid of an amplifier which amplifies a video signal and which comes into action as often as an earlier drop is charged (US Pat. No. 3,631,511).

The invention specified in claim 1 is based on the object the print quality of liquid jet printers with high printing speed effective to increase printer life while achieving a long service life.

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

Details of the invention are described below with reference to exemplary embodiments illustrated in the figures. Show it:

Fig. 1 nozzle and charging electrode of an inkjet

Printer,

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2 shows a first exemplary embodiment of a compensation

circuit,

3 shows a second exemplary embodiment of a compensation

circuit,

Fig. 4a to voltage ratio se at different points of the 4d circuit according to FIG. 3,

5 shows a third exemplary embodiment of a compensation

circuit,

6 shows a fourth exemplary embodiment of a compensation circuit

A09815 / Ü7A1

7a shows a compensation network,

FIGS. 7b and 7c input and Ausgongssignale of the compensation network of FIG. 7a '

^% Fig. 8 shows a compensation circuit with the network according to

Fig. 7a,

Figs. 9a to 9d at various points of the circuit gemSss Fig. 8! occurring waveforms,

Fig. 10 tabularly compensated values of the charging voltage,

11 shows an uncompensated staircase voltage,

FIG. 12 shows a suggested dimensioning for the voltage divider in FIG.

1 shows an ink jet 1 emerging from a nozzle N. A drop 2 constricts from the jet 1, while drops 3 and A are already independent of the jet. By means of a charging electrode 5, an electrical charge is applied to the droplets that are forming, so that the droplets appear on a surface according to a predetermined pattern.

en 9-71-050 4098154Q741

can be distracted. The charging electrode 5 is connected to a voltage source 6.

The following is a brief generalized derivation of the drop to be assigned modified voltage pulses are given, which ensure that the drops are accurately placed on the recording medium.

In the following analysis, φ.ίΟ denotes the potential and q. (T) denotes the Charge at time t with respect to the i-th conductor in Fig. 1. According to the theory In electrostatics, the charge and potential for an arrangement according to Fig. are linked by the relationship:

5
M = ΣΖ C. $ (t);

i = 1, 2 5 (1)

where C is the coefficient of capacity and C with i ^ j is the coefficient electrostatic induction. This relationship can also be written in the form:

where C * are direct capacities, in particular C * are self-capacities.

Furthermore, according to the theory of electrostatics, C ^ O, C. ^ O for i > £ J and C *> 0.

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Without loss of general validity, φ (L) and <$ ₂ ^ 9 can ^{easily be set to} zero or to ground potential, since equation (2) implies that the charges depend only on the relative potentials that the conductors have. With <$, (t) - ■■ = Φ ₂ (*) = ■ "0 simplified, equation (1) is as follows:

qw = Σ ° ϋ 4iW ^; * ^s1 · ^z >"' ^{5 (3)}

j = 3 ^{J J}

The conductor No. 5 in Fig. 1 means the charging electrode 5, therefore

! $ ₅ (t) = f (t) (4)

where f (t) ' denotes a voltage pulse which is proportional to the curve through the sequence of intended drop deflections. Combining equation (3) with equation (5) and explicitly resolving it according to $ ₃ (t) and $ ₄ (t) results in:

q ₃ (t) - C _3s i (t) (5)

q ₄ (t) - C _4S f (t) (6)

BAD *> fiK3HNAL 9-71-050

Now the words for φ «(0 and §At) are inserted into the expression for q _? (t) inserted in equation (3):

fr * ^C Z3 ^(C 34 ^C 45 ' ^C 44 ^C 3 5 » + ^C Z4 < ^C 43 ^C 35" ^C 33 ^C 4 5> \

^{1 25 C} 33 ^G 44 * ^C 43 ^C 34 J

. ^C 23 ^C 44 - ^C 24 ^C 43,. ₄ ^C 24 ° 33 " ^C 23 ^C 34

SÄTTc-G- ^ ₃ W ⁺ C ^ -Tc-C-

33 44 43 34 33 44 34 43

It follows that if f (t) is in any proportion to the intended. Deflection of the instantly formed drop, the r .- ;: ·· jli'.w-rende charge is not proportional to the intended deflection .

• Taking into account the fact that the drops are formed around the time 6t after their predecessor, the phenomenon described in equation (9) can be written as a differential equation of the second order:

_q (") _{= D} >) _{+ D q} (nl) _{+ Oq} fr'Q

OX £ *

in which. . '. .

q ^Kn} = q (n-6t), i ^[n) = f (n-St) (11)

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and the coefficients D, D ₁ and D ,. the factors in equation (9)

Ol Z

correspond. Equation (10) gives:

_q (nD _{= D f} (nD ₊ (n-2) ₊ (n-3)

O 1 £

_q (n-2) _{= D f} (nZ) _{+ D} (n-3) _{+ D} (n-4)

Substituting equations (11) and (12) into equation (10), get

o {1 2JoI

+ D ₁ (D ₁ ² + 2D ₂ ) q ⁽ⁿ - ³⁾ + D ₂ (D ₁ ² + D ₂ ) q ⁽ⁿ - ⁴⁾ (14)

From physical considerations one can assume that 1>D.> D_. In fact, an experimentally confirmed estimate for a particular arrangement shows that D. = 0.15 and D.sub.n = 0.05. It follows that some terms in equation (14) have only a very small influence on the value of q.

From a technical point of view, it is desirable that q be proportional to f. One solution is to modify the charging voltage before it is applied to the electrode 5. From the charge distortion that results from equation (14), one can derive a Korrckturscheina that turns the generation of a new charging voltage pulse V (t)

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closes:

V (t) = f (t) - Df (t- Bt) - D ₉ ί (t - 2 8t)

(15)

To confirm, let V (t) be substituted for f (t) in equation (14): _v (n) _sf (n) _ ^ (n-1) _ _lv (n-2)

_v (nl) _{b £} (nl). _Dif (n-2) _ ^ (n-3) _v (n-2) _{= f} (n-2) _ _{D £} (n-3) _ _{ß f} (n-4)

1 ^VI = D

+ D ₂ )

(16)

The difference between q and D f is a measure of the charge distortion, which according to equation (16) has the value:

| q ⁽ⁿ - ⁴⁾ -D _o f «-«) j

Because of the smallness of the numerical values for D and D, the conclusion is allows q -Df to approach zero very quickly as η increases. This is the desired direct proportionality between the charge of the

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49

Drops and the intended deflection of the drops essentially given. In practice this is achieved by using the modified Charge voltage V (t) is applied instead of i (t).

A generalization of the above analysis gives the following: Let f (t) be a voltage pulse such that f (nSt) is proportional to the intended deflection of the η-th drop, the proportionality factor being the same for all integer η. So that the charge impressed on the n-tcn drop is proportional to f (nSt), a modified voltage pulse must be applied to the charging electrode 5

K
V (t) = OlYZßi (t.iit) (18)

i = 0 '

be applied, where oc is an amplitude factor, K is the number of previous drops with a capacity coupling that cannot be allocated to the drop just formed, and ß. mean constants dependent on the values of the coupling capacitance. The case with K = 2 and <xj3 ³ 1 is reduced to what has already been discussed in detail. The values of the parameters can be determined by adjusting the resistors in the circuit of FIG. 2 for optimal drop deflection.

In Fig. 2, a character generator 10 is shown, based on stored Character information outputs signals to the charging electrode 5. To the exact

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Positioning of the drops, a compensation circuit H is rearranged between dom Zoichengenerdtor 10 and electrode 5. The circuit 14 can have a resistor 16, which connects the character generator 10 directly to the electrode 5, so that a voltage can be supplied to the electrode 5 without a time delay in accordance with the respective signal from the generator 10. A memory, for example a shift register or a delay element 18, can be provided in parallel with the resistor 16. The delay element hot a delay 5t corresponding to the time interval between successive 'drops. With the delay element 18, a resistor 20 is connected in series, the value of which is R / O ₁ , with R equal to the value of the

ο '1 ο

Resistance 16. This series connection generates a compensation voltage which is impressed by that of the drop that preceded by St Charge depends.

An additional compensation effect can be achieved by a further delay element 22 with a delay time of 2 hours, which is connected to the electrode 5 via a corresponding resistor 23 '- with a value of R / β *. This series connection provides a

Compensation voltage with respect to the penultimate drop. The resistance 16 and the the. Delay elements 18 and 22 having series circuits can be connected to a control member 24, which is via

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an operational amplifier 26 mil the Elektiudc 5 is connected. The operational amplifier 26 can have a feedback loop with a resistor 28, the value of which is OiR.

In Fig. 3 is another embodiment of a compensation circuit 30 shown. This has series-connected delay elements 32 and 34 whose delay time is δί. An adjustable one Resistor 36 is connected to the junction of delay elements 32 and 34 and connected to the electrode 5 via an amplifier and adder 38. A second resistor 40 connects the output <each delay element 34 with the amplifier and adder 38. One Line 42 forms a direct connection from the character generator 10 to Electrode 5 through amplifier and adder 38.

Accordingly, each time a signal is transmitted from the character generator 10 to the electrode S, time-delayed signals are supplied by the delay elements 32 and 34, which are representative of the charges of the drops leading by <5t or 2 ot. The curves in FIGS. 4a to 4d show the development of the resulting compensation signal (FIG. 4d) from the original charging signal (FIG. 4a).

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$ 4

Fig. 5 shows a nozzle 44 with an electromagnetic transducer 4G for vibrating the nozzle 44 in order to break up the ink jet 1 into individual drops, which are statically charged by means of the electrode 5 and deflected by deflection plates 48 either into a collecting device 50 or for printing onto a recording medium 52 will. Signals from a circuit 54 for controlling the amplitude of the charging voltage, together with signals from a character generator 56, can now be applied to the electrode 5. The signals of the circuit 54 can, for example, have the shape of a staircase; the character generator generates output pulses which are characteristic of certain characters. The amplitude control circuit 54 can also be connected to a driver 58 via an AND element 60 and an OR element. A voltage divider 64 with resistors 66 and 68 is arranged between point X of the output line of circuit 54 and ground. A tap 70 of the voltage divider 64 is connected to the OR element 62 via an AND element 72.

A two-position shift register 74 is connected to the character generator 56 and is advanced by a drop frequency generator 76, which is also connected to the converter 46 for generating drops. The stage A of the shift register 74 is connected to the AND elements 60 and 72, the stage "B" only to the AND element GO. The resistors 66 and

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of the voltage divider are dimensioned so that the output signal at point X the Torn ·! f (t) + / 3 f (t- St), the one at point Y the form f (t). The voltage at point Y thus corresponds to the uncompensated one Signal that is normally supplied to the electrode the voltage at point X is compensated according to the charge given to the previous drop, provided that the previous drops ever charged v / ar. Whether a drop is loaded is or not is determined by the shift register 74.

When the drop is charged, the shift register 74 passes the signal from point X through the AND gate 60 and the OR gate 62 to the electrode 5, where the compensated signal is thus available. When the preceding droplet is not charged, the Ausgongssignal Step B is the register 74 ¹ O *, and the signal from point X and therefore can not pass through the AND gate 60th The electrode 5 is therefore only supplied with the uncompensated signal from point Y via the AND element 72 and the OR element 62.

In Fig. 6, a three-digit shift register 80 is shown with AND gates 82, 84, 66 and 88 as well as to an OR gate 90 is connected to under the control of the character generator 56 by means of the driver 58 and the drop frequency generator 76 compensated signals to the electrode 5

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submit. The circuit 54 for controlling the amplitude of the charging voltage is connected directly to the AND gate 82 and to a voltage divider 92, the resistors 93, 94, 95 and 96. At the taps W, X, Y, and Z of the voltage divider 92 the following signals occur:

W = f (t) + fl ^ if - St) + / y (t - 2 Ot)
X

Y »f (t) + p ^ lKx - 2 6t)

The shift register 80 controls the state of the AND gates 82, 84, 86 and 88 depending on whether the immediately preceding or this previous drop was loaded or not. The Signals from the taps W, X, Y or Z on the electrode 5 are connected.

7a shows a compensation network 100 in the form of a T-G member, with a resistor Rl in the longitudinal branch and a series connection of one Resistance R2 and a capacitance C in the shunt arm. Modified this network a waveform fed to it according to FIG. 7b into a waveform according to FIG. 7c. The disadvantage of this network is that a

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exact compensation occurs only in a moment of a clock cycle, while a drop will separate at any time during a clock cycle can.

An improved compensation circuit is shown in FIG. A Network 100 is arranged between a clock generator 102 and a character generator 104 and the driver 58, which supplies the charging voltage delivers to the electrode 5. Sampling and storage element 106 is connected between the network 100 and the driver. This is done by a control circuit 108 connected to a delay element 110, so that the output signal of compensation network 100 In each case the electrode 5 is transferred laterally. This will always gives the drop the correct charge, regardless of that The moment it actually separates from the inkjet. The delay element 110 guarantees the synchronization between the output signal of the control circuit 108 and the character generator 104. The Time relationships are shown in FIGS. 9a to 9c.

Fig. 10 shows in a table the at the taps W, X, Y and Z of Fig. occurring voltages when using an uncompensated step curve signal according to Fig. 11. The values of the resistors 93 to 90, with which the voltages of Fig. 10 can be obtained are shown in Fig.

EN 9-71-050

specified. A typical value for K is £ 1000 7 ..

With the circuit described it is possible to continuously and automatically adjust the voltage for the charging electrode of an ink jet printer, taking into account the capacitive influence of the radiation field by charged drops. By using a memory, such as a delay element for deriving the compensated charging voltage, the print quality can be considerably improved. Delay elements can be used with uniform as well as non-uniform signals. Using a voltage divider gives very good results with uniform signals, such as staircase voltages, where the differences between the charges for successive drops can be determined in a simple manner .

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Claims (9)

PATENT CLAIMS 2 3 4 6 OS . l.) y liquid jet printer with a nozzle dispensed and a sequence of ink drops directed onto a recording medium, as well as having an electrode for electrostatic charging of the individual drops in order to deflect them according to the signals of a character generator and on the recording medium to be able to position in predetermined patterns, and with circuit means that connect the character generator to the electrode, characterized by a compensation circuit (14, 30, Fig. 5, 6 and 8) with storage means (18, 22, 32, 34, 74, 80), which Compensation circuit between the circuit means (58, 60, 62, 82 ... 88, 90) and the electrode (5) are arranged to the To determine the charge of at least one drop preceding the respective drop to be charged and the signal of the character generator (10, 56, 104) to automatically modify depending on the determined charge in such a way that the charge caused by the charge at least one of the preceding drops caused influence on the respective drop to be charged is compensated. 2.) Liquid jet printer according to claim 1, characterized in that the compensation circuit (14, 30, Fig. 5, 6, 8) is designed so that it receives the signal f (t) of the character generator (10, 56, 104) corresponding to the Equation v (t) = * c {f (t) + / 3 jf (t - S t) + / 3 ₂ f (t - 2 S t) ... j modified, where V (t) is the compensated charging voltage, f (t) the output voltage of the character generator (10, 56, 104), oC is an amplitude factor, / 3 and β from the coupling capacitance - * ■ Ci dependent constants, and (ft mean the drop period. Docket EN 971 050 409815/0741 3.) Liquid jet printer according to claim 1, characterized in that that the storage means comprise at least one delay element (18, 22), 4.) Liquid jet printer according to claim 3, characterized in that that the storage means have several delay elements (18, 22), the delay times of which are in integer ratios and those in parallel between the character generator (10) and the electrode (5) are arranged. 5.) Liquid jet printer according to claim 3, characterized in that that the storage means comprise a plurality of delay elements (32, 34), the delay times of which are in integer ratios stand to each other and which are arranged in a cascade connection between the character generator (10) and the electrode (5), 6.) liquid jet printer according to claim 2, characterized in that that the! compensation circuit (Fig. 6) has a voltage divider (92), its individual resistors (93 to 96) accordingly the terms of the equation v (t) = f (t) + ß ^ t- St) + / 3 ₂ f (t- are dimensioned and that logic circuits (82, 84, 86, 88) are provided, their switching states depending on Charge state of the drops are controllable and which ones accordingly Connect taps (W, X, Y, Z) of the voltage divider (92) assigned to their switching state to the electrode (5). Docket EN 971 050 A 0 8 8 1 5/0 7 Λ 1 ίο 7.) Liquid jet printer according to claim 6, characterized in that that to control the stop states of the linkage « schäl lines (82, 84, 86, 88) a shift register connected to these (80) is provided, 8,) Liquid jet printer according to claim 6, characterized in that that the logic circuits (82, 84, 86, 88) are connected to an OR gate (90), which is that of his Inputs through which the maximum input large e is applied. 9.) Liquid jet printer according to claim 1, characterized in that that the compensation circuit (Fig, 8) has an RC network (100) and a sampling and storage element (106), which with a switch delay circuit (108, 110) connected is. Cover EN 971 050 - 3 - 4098 15/0741 Blank page