EP0011251B1 - Driving circuitry for the printing jets in mosaic colour printers - Google Patents

Description

The present invention relates to a circuit arrangement for actuating writing nozzles in ink mosaic writing devices according to the preamble of patent claim 1.

It is known (DE-OS 2144892) to use a pulsed device for ejecting ink drops for recording information on recording media, which device contains a tubular writing chamber surrounded by a piezoelectric transducer. In this writing chamber, the internal volume is changed in response to an electrical signal in such a way that, by contraction of the piezoelectric transducer, the displacement of the enclosed ink volume leads to the ejection of an ink droplet from a writing nozzle. To eject an ink droplet, the applied voltage is short-circuited via an electronic circuit arrangement, namely a switching transistor, to which the piezoelectric transducer reacts by sudden contraction and ejects an ink droplet. After ejecting a drop, the short circuit for the voltage applied to the piezoelectric transducer is canceled again via this electronic switch arrangement, so that this piezoelectric transducer is again subjected to the original voltage and returns to its expanded status.

In addition, a further circuit arrangement for controlling a piezoelectric transducer is known (DE-OS 2 548 691), in which an electronic switch, namely a transistor Darlington circuit, in connection with a transformer, controls the piezoelectric transducer. In order to initiate the ejection process of the ink droplets, the drive elements which are at rest are expanded by applying an appropriate control of the circuit arrangement by applying a corresponding voltage potential to the piezoelectric transducers. In order to eject the ink droplets, the drive elements are brought from the expanded into a narrowed state by means of a polarization change in the control voltage via this circuit arrangement. The ink droplets are ejected from the nozzles of the writing chambers.

When using the known circuit arrangements, it is necessary to use the entire circuit arrangement for each piezoelectric transducer to be loaded. Both voltage potentials for the piezoelectric transducer are switched by the same electronic switching element. The potential change that must be carried out for the contraction of the piezoelectric transducer is particularly noteworthy. As can be seen from the known state of the art, this potential change must take place significantly more quickly than the potential change which extends the piezoelectric transducer. In the case of a large number of piezoelectric transducers, the high voltages and currents that occur may have an influence on the adjacent lines.

It is an object of the present invention to provide a circuit arrangement for driving electromechanical transducers, in particular piezoelectric transducers, which are arranged in a plurality next to one another, on the one hand preventing the control circuits from influencing one another, but on the other hand also preventing the individual control conditions for the individual electromechanical ones Converters are to be retained.

A circuit arrangement that meets this task has the features specified in the characterizing part of claim 1.

This ensures that the two different voltage potentials can be switched independently of one another with different, clearly realizable switching characteristics. The circuit arrangement according to the invention is preferably characterized by a first voltage potential that widens the diameter of the electronic transducers and a second voltage potential that narrows the diameter of the electronic transducers.

The second voltage potential is preferably a zero potential and is connected to ground.

By means of the circuit arrangement according to the invention, ink liquid is individually sucked into the writing chambers, from which a droplet is to be ejected, by expanding the electromechanical transducers, while the electromechanical transducer does not expand into the writing chambers, from which no ink droplet ejection is directly intended and so that no suction of ink liquid is carried out. A disturbing interference of neighboring lines is not to be expected, but at least harmless. To eject the ink droplets from the individual writing chambers, the electromechanical transducers are all switched together to zero potential, ie short-circuited. If the electronic switch for short-circuiting the electrodes of the electromechanical transducers is arranged in the immediate vicinity of these transducers, only very short distances have to be covered for the short-circuit currents. It goes without saying that well-known circuit measures can be used to limit the current in the electrical engineering field. Since in this arrangement designed according to the invention only the electro Can contract mechanical transducers that had undergone an expansion in the first activation phase, ink droplets are ejected only from the writing chambers assigned to them, so that the desired writing can be achieved.

According to a preferred embodiment, the circuit arrangement according to the invention is characterized in that the current conducted via the electronic switch for supplying the first voltage potential to the electromechanical converter is controllably limited. According to another preferred embodiment, the circuit arrangement according to the invention is characterized in that a controllable resistor is connected in parallel with the electromechanical converter, which resistor forms a voltage divider together with a resistor that limits the current supply to the first voltage potential. Using one of these two measures, differences in the switching characteristic of the overall arrangement, but in particular differences in the switching characteristic of the electromechanical converter, can be compared.

In particular, when using a writing head with a large number of individual writing chambers that moves along the writing line in front of the recording medium, the problem arises that a corresponding large number of control lines have to be routed from the stationary part of the writing unit to the moving writing head. Both the mechanical outlay and the fact that interference from adjacent power lines are to be feared have an unfavorable effect on the overall concept. For this reason, the circuit arrangement according to the invention is preferably further developed in such a way that a shift register acted upon by data pulses and by control clocks is arranged in the spatially immediately close region of the electronic switch supplying the first voltage potential, the individual stages of which are each assigned to an electronic switch, which is also close to the electromechanical one Transducers are arranged.

In this context, it is expedient under certain conditions to design the circuit arrangement according to the invention in such a way that a common electronic switch is connected in series with the electrical switches which supply the first voltage potential for the individual electromechanical converters. This can be used to transfer the contents of the shift register to control the individual electronic switches.

• Fig. 1 ein Prinzipschaltbild zur Ansteuerung von piezoelektrischen Wandlern,
• Fig. 2 ein Steuerdiagramm dieser Schaltungsanordnung,
• Fig. 3 ein Prinzipschaltbild einer weiteren Ansteuerschaltung für piezoelektrische Wandler,
• Fig. 4 ein Steuerdiagramm für diese Ansteuerschaltung,
• Fig. 5 ein Prinzipschaltbild einer Ansteuerschaltung für piezoelektrische Wandler unter Verwendung eines vorgeschalteten Schieberegisters,
• Fig. 6 eine davon abgewandelte Steuerschaltung für piezoelektrische Wandler und
• Fig. 7 ein Steuerdiagramm für diese Schaltungsanordnungen.

Exemplary embodiments designed according to the features are described in more detail below with reference to the drawing. It shows

• 1 is a basic circuit diagram for controlling piezoelectric transducers,
• 2 shows a control diagram of this circuit arrangement,
• 3 shows a basic circuit diagram of a further control circuit for piezoelectric transducers,
• 4 shows a control diagram for this control circuit,
• 5 shows a basic circuit diagram of a control circuit for piezoelectric transducers using an upstream shift register,
• Fig. 6 shows a modified control circuit for piezoelectric transducers and
• Fig. 7 is a control diagram for these circuit arrangements.

Piezoceramic transducers P1 to Pn used as electromechanical transducers are the drive elements of writing chambers of a mosaic ink writing head, by means of which characters are recorded on a recording medium through the targeted ejection of ink droplets.

In the case of a circuit arrangement according to FIG. 1, a control signal is supplied to the input SU1 in the event that droplet ejection is to take place through the piezoelectric transducer P1. The transistor T2 is controlled to be permeable via the transistor T1. Depending on the setting of a controllable resistor R2, the base of the transistor T2 is controlled in connection with a further resistor R1 by means of a bridge circuit, so that the transistor T2 becomes permeable in a current-limiting manner. The capacitance of the piezoelectric transducer P1 is thus set to a drive potential in accordance with the applied supply voltage + UB1, which is approximately 300 V, the resistance value of the resistor R3 and the transistor T2 and the opening time of the transistor T2. The piezoelectric transducer P1 expands, as a result of which ink liquid is sucked into the associated writing chamber. To eject the ink droplets from the chambers into which ink has been sucked in, a control pulse is applied to the input SUO, which switches the transistor TUO on. Thus, all charged piezoelectric transducers P1 to Pn are discharged by short-circuiting their two electrodes via the diodes D used for decoupling. The resulting contraction of the relevant piezoelectric transducers P1 to Pn causes the droplets to be ejected.

Fig. 3 shows a modified circuit arrangement compared to the arrangement according to Fig. 1 to the extent that the bridge resistor R2 at the base of the transistor T2 is now not adjustable, but that it is designed as a fixed resistor, so that the transistor T2 acts as a pure switch. The voltage potential to be set at the piezoelectric transducer P is regulated by an adjustable resistor R5 connected in parallel with this piezoelectric transducer in conjunction with the resistor R3. By comparing FIGS. 4 and 4, the charging characteristics Up, which are different for the piezo, due to the two circuit arrangements electrical converter P can be seen.

The example shown in FIG. 5 shows a shift register SR with n stages. The outputs Q1 to Qn of the stages are connected to the inputs of the control shades for the individual piezoelectric transducers P1 to Pn. After loading the shift register SR with data pulses SD corresponding to the piezoelectric transducers to be controlled by taking over the data pulses SD with the clocks SC, the first voltage potentials are switched on by applying the so-called enable signal SE via the outputs of the shift register and the relevant piezoelectric transducers reach the expanded state. The connection with the second voltage potential, in the example with ground potential, is made via the switch Th common to all control circuits, which is then switched by a control pulse SUO. This results in a low-resistance circuit to ground for all piezoelectric transducers P1 to Pn, which, when the other connection of the piezoelectric transducers is also grounded, acts almost as a short circuit.

Fig. Shows a detailed embodiment. The data pulses SD for the piezoelectric transducers P1 to Pn to be carried out are offered serially to the shift register SR via an optocoupler OK and taken over into the individual stages with the clock signals SC, which are fed to the clock input of the shift register SR via the transistor TC. After the shift register SR has been fully charged, the control criteria are transferred to the piezoelectric transducers P1 to Pn either by applying the enable signal SE to the input of the shift register SR or, as shown in FIG. 6, via a further switch which switches the transistor TE, contains a voltage divider R6, R7 and the switching transistor TUB1. In this case, with the signal UE corresponding to the enable signal, the operating voltage ₊ UB1 is connected to those piezoelectric transducers to which the signal U1 to Un is offered in accordance with the data signals transferred to the shift register SR. The driven piezoelectric transducers P1 to Pn thus assume their expanded state. The droplets are ejected in the manner described by activating the switch Th by means of the pulse SUO. FIG. 1 shows a compilation of the signals SC, SD, SE and SUO mentioned in the description of FIG. 6. The charging line Up for the piezoelectric transducers P1 to Pn is shown in the last line.

Claims (9)

1. A circuit arrangement for controlling printing nozzles in ink mosaic printing devices employing tubular drive elements which contain printing fluid and consist of electro-mechanical, in particular piezo-electric transducers, whose diameter adjusts itself to different values when different electric potentials are applied, comprising an electronic switch which is assigned to each electro-mechanical transducer and serves to apply a first potential, characterised in that all electro-mechanical transducers (P1 to Pn) are commonly assigned a further electronic switch (TUO or Th) by means of which the terminals of the electro-mechanical transducers (P1 to Pn) have a second potential applied.

2. A circuit arrangement as claimed in Claim 1, characterised in that the first potential enlarges the diameters of the electro-mechanical transducers (P1 to Pn) and the second potential reduces the diameters of the electro-mechanical transducers (P1 to Pn).

3. A circuit arrangement as claimed in one of Claims 1 or 2, characterised in that the second potential is a zero potential.

4. A circuit arrangement as claimed in one of Claims 1 to 3, characterised in that the second potential is an earth potential.

5. A circuit arrangement as claimed in one of Claims 1 to 4, characterised in that the current, which is directed to the electro-mechanical transducer (P1 to Pn) in each case by means of the electronic switch (T2) for applying the first voltage potential, is limited in an adjustable fashion.

6. A circuit arrangement as claimed in one of Claims 1 to 6, characterised in that an adjustable resistor (R5) is connected in parallel to the electro-mechanical transducer (P1 to Pn), which resistor forms a voltage divider together with a resistor (R3) which is currentlimiting in respect of the application of the first potential.

7. A circuit arrangement as claimed in one of Claims 1 to 6, characterised in that the electronic switches (T2, TUO, Th) are arranged spatially in the direct vicinity of the electro-mechanical transducers (P1 to Pn).

8. A circuit arrangement as claimed in one of Claims 1 to 7, in particular in the use of a printing head travelling in front of the data carrier along the printing line, characterised in that in the directly close region of the electronic switches (T2), which apply the first potential to the electro-mechanical transducers (P1 to Pn), there is arranged a shift register (SR) which can be controlled by data pulses (SD) and control clock pulses (SC) and whose individual stages have their outputs (Q1 to Qn) respectively connected to one of the switches (T2).

9. A circuit arrangement as claimed in one of Claims 1 to 8, characterised in that a common electronic switch (TUB1) is connected in series with the electronic switch (T2) which applies the first potential to the electro-mechanical transducers (P1 to Pn).

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