EP0568162A1 - Device for an electrothermal printhead drive - Google Patents

Abstract

Arrangement for actuating an electrothermal print head drive, having memory means (7) with a microprocessor control (5) for an electrothermal printing unit (3) and having a current collector electrode (6), energy for the electrodes of the electrothermal printing unit being provided from a controllable current source or voltage source, the number of electrodes which are temporarily connected to the controllable energy source (1) being predetermined by the microprocessor control (5) which outputs a control signal, which corresponds to the dependence on the number of driven electrodes, to the controllable energy source which feeds the electrodes which are temporarily connected to the latter via a switching unit (2) with a current or the voltage whose level has a dependence on the temporarily different number of actuated electrodes such that a larger number of electrodes are supplied with a higher current or voltage than a smaller number. <IMAGE>

Description

The invention relates to an arrangement for an ETR printhead control of the type specified in the preamble of claim 1. An ETR printer can be used, for example, in a franking machine for franking mail.

In addition to the mechanics, the ETR printer includes an electronic head control, an ETR print head with a large number of electrodes and a current collecting electrode which are connected to a power supply. The pressure energy is fed as a constant current in each current path associated with each electrode in order to ensure a uniform print quality.

The ETR printhead acts on the recording medium, preferably paper, via a resistance ink ribbon which is moved with the recording medium. The resistance ribbon has an upper one with the ETR printhead in contact resistance layer, a middle current return layer and a lower color layer in contact with the recording medium.

The ETR print head contains a multiplicity of electrodes which are arranged insulated from one another, each of which can generate a pixel of the printed image. The energy supplied via these electrodes is converted into current heat in the area of the resistance layer assigned to each pixel, which leads to the melting of the color of the color layer located in the area.

Such an ETR printer with back electrodes is known from EP 0 301 891 A1. The energy to be supplied depends on the resistance of each current path assigned to a pixel, on the melting temperature of the color, the intended contrast of the printed image and on the speed of the moving resistance ribbon and increases non-linearly with the roughness of the paper surface.

It is already known from DE 38 33 746 A1 a switching unit for a print head which is actuated via a control unit (ASE) and which, in contrast to the ETR print head, already contains the resistance elements themselves (thermal transfer printing method) and a selective control with preheating of the resistance elements to reduce the heating power when printing, known.

A series / parallel shift register loaded with the serial print data transfers the print data to the latches of an intermediate store in a first control phase. In a second control phase, each gate controlled by the associated outputs of the latches is switched to continuity during a strobe pulse and a control pulse to the respective one Resistor element delivered. The resistance heating elements are preheated directly by a clock frequency which is adapted to the required heating energy in terms of its pulse height and pulse width.

Such preheating via energy from a voltage source is in principle not possible with an ETR printer because the resistance elements are located in the resistance layer of the resistance ribbon.

Since the overall system consisting of the ETR head with the electrodes, the ETR ribbon and the back electrode has a large number of parasitic series resistances of variable value (contact resistance between electrode and band, sheet resistance of the aluminum layer in the band, contact resistance between band and back electrode) , which lead to a variation of the total resistance during operation, an energy supply by means of a voltage source is not suitable, since the varying partial voltage across the heating (= pressure) resistance would lead to different pressure energies. This would result in fluctuating print quality.

From a technical point of view, the energy supply to the individual electrodes of an ETR head is best provided by a constant current source, since the accuracy of the constant current and the specific tape resistance guarantee a very even printing performance.

However, a technically optimal solution with a current control for each electrode path is often not affordable due to the (possibly) very high number of electrodes of an ETR head.

Solutions are now known which attempt to implement a technically justifiable solution with reasonable effort. This includes the method of integrating a series resistor in each electrode path, the value of which is approx. 3-4 times higher than the effective heating (= pressure) resistance of the ETR tape.

This artificially increased total resistance of the system means that the now relatively small changes in the parasitic series resistances in the system cannot cause any significant change in the effective voltage across the heating resistor. In this way, the current of each electrode path has been "stabilized" and an improvement in print quality is achieved depending on the ratio of the series resistors to the effective heating resistor of the ETR band.

As cheap and technically simple as this solution is on the one hand, it has the considerable disadvantage on the other hand that only a fraction of the energy fed into the overall system is required for the actual printing process. Most of the energy is converted into heat loss. In addition, a fluctuation in the voltage across the respective heating resistor is unavoidable, because in contrast to the thermal transfer printing principle, with the ETR printing principle, there are variable contact resistances during the movement of the ribbon at the contact points of the resistance layer of the resistance ribbon with the electrodes of the ETR print head and the current collecting electrode, and also variable resistance heating elements effective in the band.

The invention has for its object to find a technical control for any ETR print head that is simple and therefore inexpensive combines technical design with minimal power dissipation in the system and thus also causes only low operating costs, and at the same time maximum print quality.

The object is achieved with the characterizing features of claim 1.

The invention is based on the fact that the arrangement for an ETR print head control is equipped with storage means and with a control for the ETR print unit, the control of an ETR print head within a printing system being carried out consistently with the help of microprocessors, microcomputers or computers and The electrodes of an ETR printing unit are provided with energy from a voltage source for the individual pixels of the printed image, the number of electrodes temporarily connected to the controllable voltage source being predetermined by a microprocessor control, which generates a control signal corresponding to the dependence on the number of activated electrodes outputs to the controllable voltage source.

The invention is further based on the consideration that with a microprocessor control unit the relevant print information is loaded into the switching unit at the appropriate time, which in the active state ensures that the pixels to be printed are energized for a defined time, so that the necessary for the printing process Heat is generated in the ETR band.

Figur 1,

Blockschaltbild der erfindungsgemäßen Anordnung

Figur 2,

Schaltung der Schalteinheit

Figur 3a,

elektrisches Ersatzschaltbild für ETR-Drucker mit einer einzigen Konstantstromquelle I_s

Figur 3b,

elektrisches Ersatzschaltbild für ETR-Drucker mit einer einzigen Konstantspannungsquelle U_s

Figur 4,

Variante einer steuerbaren Spannungsquelle

Figur 5,

Variante für eine beliebige Druckgeschwindigkeit und für einstellbaren Kontrast

Figur 6,

Variante für eine zusätzliche Regelung der Druckqualität mit invertierenden Verstärker

Figur 7,

Variante für eine zusätzliche Regelung der Druckqualität mit Subtrahierverstärker

Die in der Figur 1 gezeigte Anordnung für eine ETR-Druckkopfansteuerung weist eine steuerbare Energiequelle 1, eine Schalteinheit 2, eine ETR-Druckeinheit 3, eine Mikroprozessoreinheit 5, eine Stromsammelelektrode 6 und ein Speichermittel 7 auf, das mit der Mikroprozessorsteuereinheit 5 für die Ansteuerung der ETR-Druckeinheit 3 verbunden ist. Das Speichermittel 7 enthält mindestens die Grafikdaten für ein Druckbild.Advantageous developments of the invention are characterized in the subclaims or are shown below together with the description of the preferred embodiment of the invention with reference to the figures. Show it:

Figure 1,

Block diagram of the arrangement according to the invention

Figure 2,

Switching the switching unit

Figure 3a,

electrical equivalent circuit for ETR printers with a single constant current source I _s

Figure 3b,

electrical equivalent circuit for ETR printers with a single constant voltage source U _s

Figure 4,

Variant of a controllable voltage source

Figure 5,

Variant for any printing speed and for adjustable contrast

Figure 6,

Variant for an additional control of the print quality with inverting amplifier

Figure 7,

Variant for an additional control of the print quality with subtraction amplifier

The arrangement shown in FIG. 1 for an ETR printhead control has a controllable energy source 1, a switching unit 2, an ETR printing unit 3, a microprocessor unit 5, a current collecting electrode 6 and a storage means 7 which is connected to the microprocessor control unit 5 for the control of the ETR printing unit 3 is connected. The storage means 7 contains at least the graphic data for a print image.

The energy for the electrodes of the ETR printing unit 3 is provided by a single controllable energy source 1, the number n of the electrodes 31, 32, 33, ... temporarily connected to the controllable energy source 1 being predetermined by the microprocessor control unit 5 which additionally outputs a control signal corresponding to the dependence on the number of activated electrodes to the controllable energy source 1.

A switching unit 2 acted upon by the microprocessor control unit 5 transmits the energy to an ETR printhead 30 of the ETR printing unit 3, which is in contact with an ETR resistance ink ribbon 10 via electrodes 31, 32, 33,.. Relevant print information at the correspondingly correct time t 1 are loaded into the switching unit 2, which in the activated state from t 2 ensures that the pixels to be printed are energized for a defined time t _j , so that the heat required for the printing process in the controlled, briefly contacted areas 101 , 102, ..., the resistance layer 100 of the resistance ribbon 10 is produced.

A circuit of the switching unit 2 is shown in FIG. A with the serial print data directly or via a decoder 20 not shown series / parallel shift register 21 of the switching unit 2 transfers the print data in a first control phase from t₁ to the latches of an intermediate memory 22. So the current print information is sufficiently long before actual printing process in the control unit 2 before.

In a second control phase from t₂, each of the associated outputs during a strobe pulse the latches controlled gate G₁, G₂, ..., an output-side driver 23 switched to continuity and a drive pulse to the respective current path with the associated resistor R _p . The control circuit SN 75518 with 32 bit shift register, 32 latches and 32 AND gates can advantageously be used as switching unit 2. After a defined time has elapsed, the new print data are provided by the microprocessor control unit 5 and stored in the latches of the buffer store 22.

In der Figur 3a ist ein elektrisches Ersatzschaltbild für ETR-Drucker mit einem eingeschalteten Strompfad mit dem zugehörigen Widerstand R_p und mit einer einzigen Konstantstromquelle I_s angegeben. Der Widerstand R_p ergibt sich als Widerstandssumme zu:

${\text{R}}_{\text{p}}{\text{= R}}_{\text{v}}{\text{+ R}}_{\text{k}}{\text{+ R}}_{\text{h}}{\text{+ R}}_{\text{r}}{\text{+ R}}_{\text{b}}{\text{+ R}}_{\text{ü}}{\text{+ R}}_{\text{l}}\text{ (2)}$

mit
R_v - Vorwiderstand
R_k - Kontaktwiderstand einer Elektrode
R_h - Widerstandsheizelement
R_r - Stromrückleitwiderstand
R_b - Bandwiderstand
R_ü - Übergangswiderstand Band/Rückelektrode
R_l - Leitungswiderstand
Der Kontaktwiderstand R_k einer Elektrode mit der oberen Widerstandsschicht 100 des Widerstandsfarbbandes 10 ist von der Größe der wirksamen Elektrodenfläche und vom Andruck an das Band abhängig. Der Stromrückleitwiderstand R_r der mittleren Schicht 8 des Widerstandsfarbbandes besteht vorzugsweise aus Aluminium und hängt vom Gesamtstrom ab, der Entfernung der Rückelektrode. Die Aluminiumschicht 8 ist ca. 0,8 µm dick. Gegenüber der Widerstandsschicht 100, die ca. 15 µm dick ist und gegenüber der Farbschicht 9, deren Dicke ca 6 µm beträgt. Bei naher Anordnung der Stromsammelelektrode 6 bezüglich der Elktorden des ETR-Drukkopfes 30 ist der Stromrückleitwiderstand R_r vernachlässigbar gering. Der Bandwiderstand R_b der Widerstandsschicht 100 des Widerstandsfarbbandes 10 ist vom Umschlingungswinkel β der Fläche der Rückelektrode 6 bestimmt. Der Übergangswiderstand R_ü zwischen Band 10 und Stromsammelelektrode 6 hängt vom Druck und der Rückelektrodenfläche ab.For a constant print quality, the printer drive is set so that for each belt speed V _bj with j = 1, 2, ..., m:

${\text{t}}_{\text{j}}{\text{* V}}_{\text{bj}}\text{= c with c = constant (1)}$

FIG. 3a shows an electrical equivalent circuit diagram for ETR printers with an activated current path with the associated resistor R _p and with a single constant current source I _s . The resistance R _p is the sum of the resistances:

${\text{R}}_{\text{p}}{\text{= R}}_{\text{v}}{\text{+ R}}_{\text{k}}{\text{+ R}}_{\text{H}}{\text{+ R}}_{\text{r}}{\text{+ R}}_{\text{b}}{\text{+ R}}_{\text{ü}}{\text{+ R}}_{\text{l}}\text{(2)}$

With
R _v - series resistor
R _k - contact resistance of an electrode
R _h - resistance heating element
R _r - current return resistance
R _b - band resistance
R _ü - contact resistance band / back electrode
R _l - line resistance
The contact resistance R _{k of} an electrode with the upper resistance layer 100 of the resistance ribbon 10 is depending on the size of the effective electrode area and the pressure on the tape. The current return resistance R _{r of} the middle layer 8 of the resistance ribbon is preferably made of aluminum and depends on the total current, the distance of the back electrode. The aluminum layer 8 is approximately 0.8 μm thick. Compared to the resistance layer 100, which is about 15 microns thick and against the color layer 9, the thickness of which is about 6 microns. When the current collecting electrode 6 is arranged closer to the electrode ends of the ETR printing head 30, the current return resistance R _{r is} negligible. The band resistance R _{b of} the resistance layer 100 of the resistance ink ribbon 10 is determined by the wrap angle β of the surface of the back electrode 6. The contact resistance R _ü between band 10 and current collecting electrode 6 depends on the pressure and the back electrode area.

Die erforderliche Impulshöhe wird von der angesteuerten Energiequelle 1 bereitgestellt, welche die mit dieser über die Schalteinheit 2 temporär in Verbindung stehenden Elektroden 31, 32, 33,..., mit einem Strom I_s oder mit einer Spannung U_s beaufschlagt, deren Höhe eine derartige Abhängigkeit von der temporär verschiedenen Anzahl n an angesteuerten Elektroden aufweist, daß eine größere Anzahl an Elektroden mit einem höheren Strom oder mit einer höheren Spannung versorgt werden, als eine geringere Anzahl.The resistance heating elements R _h are driven by a clock frequency which is matched to the required heating energy in terms of its pulse height and pulse width. This results in the energy W _p determining the print quality in each resistance heating element R _h :

${\text{W}}_{\text{p}}{\text{= (<figure-callout id="2" label="I p" filenames="imgf0001.png,imgf0002.png" state="{{state}}">I </figure-callout>}}_{\text{p}}{\text{² * R}}_{\text{H}}{\text{) * t}}_{\text{j}}{\text{= (<figure-callout id="2" label="U H" filenames="imgf0001.png,imgf0002.png" state="{{state}}">U </figure-callout>}}_{\text{H}}{\text{² / R}}_{\text{H}}{\text{) * t}}_{\text{j}}\text{(3)}$

The required pulse level is provided by the controlled energy source 1, which applies a current I _s or a voltage U _{s to} the electrodes 31, 32, 33, ..., which are temporarily connected to it via the switching unit 2, the level of which is one has such a dependency on the temporarily different number n of activated electrodes that a larger number of electrodes are supplied with a higher current or with a higher voltage than a smaller number.

In the first variant — shown in FIG. 1 — an energy source 1 that can be controlled in an analog manner is provided, which can be controlled by the analog output of a D / A converter 4 that is connected with its digital inputs to outputs of the microprocessor control unit 5.

For each current print column, before the print information is output to the switching unit 2 in accordance with the number n of print points to be activated, this number, in binary code, is output to the digital / analog converter 4 by the microprocessor control unit 5. With a simple 8-bit D / A converter, 256 different analog levels can be generated in this way, which correspond directly to the number of dots to be printed. These analog levels now serve to control a controllable and adjustable energy source 1. A defined energy corresponding to the number of dots to be printed in each printing column is therefore fed into the system.

Der Wert des Vorwiderstandes R_v beträgt 1/2 bis 1/8 vom Wert des effektiven Heizwiderstandes, vorzugsweise 1/3 bis 1/4, was gegenüber des o.g. Standes der Technik mit sehr viel größeren R_v die Verlustenergie des Systems minimiert. Für ${\text{R}}_{\text{h}}{\text{+ R}}_{\text{v}}{\text{» R}}_{\text{r}}{\text{+ R}}_{\text{b}}{\text{+ R}}_{\text{ü}}{\text{+ R}}_{\text{l}}$

sind die Verluste minimal.On the one hand, this has the advantage that, for example, a single controllable and adjustable constant current source I _{s is} sufficient for the entire system with any number of ETR electrodes and not one must be available for each current path, and on the other hand there is only a very small series resistor R _v in each current path I, II, III, ..., required to set the current distribution. At the same time, however, the controllable constant current source ensures for each printing column that the exact, predetermined printing energy is always available for melting the lower ink layer 9. The following applies approximately to the controllable constant current:

${\text{I.}}_{\text{s}}{\text{= (I}}_{\text{p1}}{\text{+ I}}_{\text{p2}}{\text{+ ... + I}}_{\text{pi}}\text{) (4)}$

The value of the series resistor R _v is 1/2 to 1/8 of the value of the effective heating resistor, preferably 1/3 to 1/4, which minimizes the energy loss of the system compared to the prior art mentioned above with much larger R _v . For ${\text{R}}_{\text{H}}{\text{+ R}}_{\text{v}}{\text{»R}}_{\text{r}}{\text{+ R}}_{\text{b}}{\text{+ R}}_{\text{ü}}{\text{+ R}}_{\text{l}}$

the losses are minimal.

Another advantage of this invention is based on the fact that the pressure intensity of the entire ETR head can be very easily changed by changing a single actuator S, namely by changing a factor y of the controllable constant current I _s or constant voltage U _{s of} the controllable energy source 1 If another factor z is changed with the same actuator S, the printing speed or belt speed V _{b can also be} taken into account.

mittels der Vorwiderstände R_v eingestellt ist, gilt:

${\text{I}}_{\text{s}}{\text{= y * z * n * I}}_{\text{p}}\text{ (5)}$

In der Figur 3b ist ein elektrisches Ersatzschaltbild für ETR-Drucker mit einer einzigen Konstantspannungsquelle U_s aufgezeigt. Beim Einsatz einer Spannungsquelle U_s als Energiequelle 1, wird durch Einschalten eines seriellen Meßwiderstandes R_m in den Stromkreis für eine Linearisierung des Spannungsabfalls über den Restwiderstand ${\text{R}}_{\text{rest}}{\text{= R}}_{\text{r}}{\text{+ R}}_{\text{b}}{\text{+ R}}_{\text{ü}}{\text{+ R}}_{\text{m}}$

gesorgt. Es gilt dann für ${\text{R}}_{\text{m}}{\text{» R}}_{\text{r}}{\text{+ R}}_{\text{b}}{\text{+ R}}_{\text{ü}}$

annähernd die Beziehung:

${\text{R}}_{\text{rest}}{\text{= R}}_{\text{m}}\text{ (6)}$

Weil der Strom I_p jedes Strompfades über den Meßwiderstand R_m (der den Leitungswiderstand R_l einschließt) fließt, kann der Gesamtstrom ${\text{I}}_{\text{g}}{\text{= n * I}}_{\text{p}}$

über U_m gemessen werden. Es gilt:

${\text{U}}_{\text{m}}{\text{= n * I}}_{\text{p}}{\text{* R}}_{\text{m}}\text{ (7)}$

Für nur einen eingeschalteten Strompfad, d.h. die kleinste Einheit, die dem Wert einer ETR-Elektrode entspricht, ist der Faktor n = 1.The factors y and z increase with higher printing speed V _b and printing intensity (contrast). Since the partial flows in the current paths are the same, the relationship ${\text{I.}}_{\text{p}}{\text{= I}}_{\text{p1}}{\text{= I}}_{\text{p2}}{\text{= ... = I}}_{\text{pi}}$

is set by means of the series resistors R _v :

${\text{I.}}_{\text{s}}{\text{= y * z * n * I}}_{\text{p}}\text{(5)}$

FIG. 3b shows an electrical equivalent circuit diagram for ETR printers with a single constant voltage source U _s . When using a voltage source U _s as energy source 1, by switching on a serial measuring resistor R _m in the circuit for a linearization of the voltage drop across the residual resistance ${\text{R}}_{\text{rest}}{\text{= R}}_{\text{r}}{\text{+ R}}_{\text{b}}{\text{+ R}}_{\text{ü}}{\text{+ R}}_{\text{m}}$

worried. It then applies to ${\text{R}}_{\text{m}}{\text{»R}}_{\text{r}}{\text{+ R}}_{\text{b}}{\text{+ R}}_{\text{ü}}$

roughly the relationship:

${\text{R}}_{\text{rest}}{\text{= R}}_{\text{m}}\text{(6)}$

Because the current I _{p of} each current path flows through the measuring resistor R _m (which includes the line resistance R _l ), the total current can ${\text{I.}}_{\text{G}}{\text{= n * I}}_{\text{p}}$

measured over U _m . The following applies:

${\text{U}}_{\text{m}}{\text{= n * I}}_{\text{p}}{\text{* R}}_{\text{m}}\text{(7)}$

For only one current path switched on, ie the smallest unit that corresponds to the value of an ETR electrode, the factor n = 1.

${\text{Dabei gilt U₁ = U}}_{\text{v}}{\text{+ U}}_{\text{k}}{\text{+ U}}_{\text{h}}{\text{und U₂ = R}}_{\text{rest}}{\text{* I}}_{\text{p}}\text{ (9)}$

Die Einstellzeiten der steuerbaren Energiequelle 1 sind im Hinblick auf die mit der ETR-Technologie erreichbaren maximalen Druckgeschwindigkeiten im Bereich von ca. 500 mm/s unkritisch. Der technische und preisliche Aufwand ist bei optimalen Druckergebnissen vergleichsweise gering.The controllable constant voltage then results in consideration of n current paths:

${\text{U}}_{\text{s}}\text{= y * z * (U₁ + [n * U₂]) (8)}$

${\text{U₁ = U}}_{\text{v}}{\text{+ U}}_{\text{k}}{\text{+ U}}_{\text{H}}{\text{and U₂ = R}}_{\text{rest}}{\text{* I}}_{\text{p}}\text{(9)}$

The setting times of the controllable energy source 1 are not critical with regard to the maximum printing speeds in the range of approximately 500 mm / s that can be achieved with the ETR technology. The technical and price expenditure is comparatively low with optimal printing results.

Das Widerstandsverhältnis R_s/R_e des Stellgliedes S₁ gestattet das Einstellen der Grundverstärkung und/oder eine von der Mikroprozessorsteuereinheit 5 gesteuerte - in der Figur 5 gezeigte - Umschaltung einer Widerstandskette entsprechend den erforderlichen Faktoren y und z.A variant of a controllable voltage source is presented in FIG. 4, with a linear regulator 11 to which the unregulated input voltage U _g and a setpoint value amplified via a non-inverting operational amplifier 12 are supplied and which outputs a voltage U _{s on the} output side. The setpoint voltage results from the analog control voltage:

${\text{U}}_{\text{should}}{\text{= (1 + R}}_{\text{s}}{\text{/ R}}_{\text{e}}{\text{) * U}}_{\text{stell}}\text{(10)}$

The resistance ratio R _s / R _{e of} the actuator S₁ allows the basic gain to be set and / or a switching of a resistor chain controlled by the microprocessor control unit 5 - shown in FIG. 5 - according to the required factors y and z.

FIG. 6 shows a further variant for a controllable voltage source, which is equipped with a connection for additional regulation of the print quality by means of the measuring voltage U _m . The measuring voltage drops across the measuring resistor R _m , which is orders of magnitude smaller than the series resistors R _v or the heating resistors R _h and smaller than the current return resistor R _r . The measuring voltage U _m is connected through a resistor R _d and the inverted control voltage -U _alternate via a resistance R _t at the node of inverting amplifier 13. With increasing total resistance decreases, the total current and thus _m U, which _{is intended} to increase the nominal voltage U leads .

FIG. 7 shows a further variant for a controllable voltage source with additional regulation. The amplifier 12 is designed as a subtracting amplifier. In contrast to the variant according to FIG. 6, positive voltages U _stell and U _m can be applied on the input side, with otherwise the same mode of operation.

In einer - in der Figur 1 nicht gezeigten - weiteren Variante ist eine digital ansteuerbare Energiequelle 1 (Stromquelle I_s oder Spannungsquelle U_s) direkt mit den Ausgängen der Mikroprozessorsteuereinheit 5 verbunden.A further variant for a controllable voltage source with digital control inputs, for setting according to the selected printing speed, for setting the contrast per se and with additional regulation of the print quality by means of the measuring voltage U _m results from FIG. 5 in connection with one not shown in FIG Extension of the block diagram which will be discussed below becomes. The microprocessor unit 5 is additionally equipped on the input side with an analog / digital converter 14, at the input of which the measuring voltage U _m is present. The digital data corresponding to the measuring voltage U _m are entered into the microprocessor unit 5 and form a correction quantity U 3, which is also included in the above-mentioned equation (8). This results in the control voltage:

${\text{U}}_{\text{stell}}\text{= (U₁ - U₃ + [n * U₂]) (11)}$

In a further variant - not shown in FIG. 1 - a digitally controllable energy source 1 (current source I _s or voltage source U _s ) is connected directly to the outputs of the microprocessor control unit 5.

For example, the number n of electrodes temporarily connected to the controllable current source I _{s is} specified directly by the microprocessor control unit 5, which outputs a control signal corresponding to the number n of the controlled electrodes to the controllable energy source 1, so that each resistance heating element R _p provides the required uniform heating power when printing.

If the ETR printer is used for a franking machine, its memory and microprocessor control unit can also be used for control. Such a franking machine consists of a storage means and a receiving means connected thereto for data that can be transmitted via a transmission means, an input means, a control module and the ETR printer.

The embodiment of the invention is not limited to the preferred exemplary embodiment specified above. Rather, a number of variants are conceivable who make use of the solution shown, even with fundamentally different types.

Claims (11)

Arrangement for an ETR print head control with storage means and with a control for the ETR print unit, the electrodes of an ETR print unit providing energy from an energy source for the individual pixels of the print image,
characterized in that
the energy source is a controllable energy source (1) which applies a voltage or a constant current to the electrodes (31, 32, 33, ...) which are temporarily connected to it via a switching unit (2), the amount of which is such a dependence of the temporarily different number n of electrodes, that a larger number of electrodes are supplied with a higher voltage or a higher constant current than a smaller number,
that the number of electrodes temporarily connected to the controllable energy source is predetermined by a microprocessor control unit (5) which emits a control signal corresponding to the dependence on the number of activated electrodes to the controllable energy source. Arrangement according to Claim 1, characterized in that a digitally controllable voltage source U _{s is} connected directly to control outputs of the microprocessor control unit (5), the voltage emitted by the voltage source ${\text{U}}_{\text{s}}\text{= y * z * (U₁ + [n U₂]}$

is and the total current I _{g flows} through a measuring resistor R _m . Arrangement according to claims 1 and 2, characterized in that the controllable voltage source can be controlled analogously via a D / A converter (4) which is connected with its digital inputs to outputs of the microprocessor control unit (5), and an actuator (S) is provided for setting the basic gain and / or for adapting the pressure intensity to the set printing speed V _b . Arrangement according to claims 1 to 3, characterized in that each output of the switching unit (2) has a current source character for the electrodes of the ETR printing unit (3) or has series resistors R _v for the electrodes. Arrangement according to claim 4, characterized in that each current source or current distribution can be set by a resistor R _v in each current path. Arrangement according to claim 5, characterized in that the ETR electrodes are assigned a series resistor R _v <R _h in each current path, preferably with half the value up to one eighth of the value of the effective resistance heating element R _h . Arrangement according to one of the preceding claims 1 to 6, characterized in that the controllable voltage source U _s next to the control input for the control voltage U _alternate with a connection for the additional control of the print quality by means of the measuring voltage U _m equipped with the measuring voltage U _m over a resistor R _d and the inverted control voltage -U _alternate via a resistance R _t at the node of an inverting amplifier 13 or the non-inverted control voltage U _alternate directly or through the resistance R _t at the noninverting input of a subtracting amplifier 12 and the measuring voltage at its inverting input via resistor R _d is present. Arrangement according to one of the preceding claims 1 to 7, characterized in that the relevant print information is loaded into the switching unit (2) at a correspondingly correct point in time t₁ in a first control phase, which is controlled by the microprocessor control unit (5) so that the activated State of the output gates of a driver (23) during a second activation phase, the resistance heating elements R _h assigned to the pixels to be printed are energized in the ETR band for a defined time t _{j in} accordance with the selected printing speed, so that the heat required for the printing process is generated in the ETR band becomes. Arrangement according to claim 8, characterized in that the switching unit (2) has a decoder (20) on the input side of the microprocessor control unit (5) with data, commands and / or signals. Arrangement according to one of the preceding claims 1 to 9, characterized in that the control of an ETR print head (30) within a printing system is carried out consistently with the aid of microprocessors with memories, microcomputers or computers, these being used as part of another system . Arrangement according to claim 10, characterized in that the arrangement is used for an ETR print head control in a franking machine.

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