Electronic circuit for driving an array of inkjet print elements

Abstract

An electronic circuit for driving an inkjet print element in an array of print elements with an electric waveform is provided. The print element includes a piezo transducer for converting the electric waveform in a mechanical displacement. The electric waveform is tunable for an individual print element. The circuit includes a common waveform generator that is connected to the piezo transducer through a first print data dependent switch for providing an electric waveform independent of the print element. The circuit further includes a waveform tuning part, dependent on the print element and the print data, for controlling a second switch that adds electric energy from a voltage source to the electric waveform. The switches are operable in either a saturation state or a blocking state to limit an amount of dissipation in the switches.

Claims

1. An electronic circuit for driving an inkjet print element in an array of print elements with an electric waveform, the inkjet print element comprising a piezo transducer for converting the electric waveform in a mechanical displacement, the electric waveform being tunable for an individual print element, the electronic circuit comprising: a common waveform generator connected to the piezo transducer through a first print data dependent switch for providing a common electric waveform, independent of the inkjet print element; and a waveform tuning part, dependent on the print element and the print data, for controlling a second switch that adds electric energy from a fixed voltage source to the common electric waveform, wherein the first and second switches are operable in either a saturation state or a blocking state to limit an amount of dissipation in the first and second switches.

2. The electronic circuit according to claim 1, wherein the fixed voltage source has a lower voltage than a peak voltage from the common waveform generator.

3. The electronic circuit according to claim 1, wherein the waveform tuning part further depends on the print data of neighbouring print elements.

4. The electronic circuit according to claim 1, wherein the waveform tuning part further depends on the print data associated with previous waveforms.

5. The electronic circuit according to claim 1, wherein a third switch is provided to the inkjet print element for adding electric energy in a second part of the electric waveform.

6. The electronic circuit according to claim 1, wherein the waveform tuning part comprises timing parameters for controlling the second switch.

7. A print head module comprising: a print head chip: and a driver board, wherein the print head chip and the driver board are connected by a module comprising the electronic circuit according to claim 1, and wherein the print head chip comprises the array of print elements, the print head module comprises the first and second switches for applying the electric waveform to the print elements, and the driver board comprises the common waveform generator and the fixed voltage source.

8. The print head module according to claim 7, wherein the driver board further comprises a memory for saving waveform tuning parameters for a print element of the array of print elements.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will become more fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:

(2) FIG. 1 illustrates a tunable waveform as known in the prior art;

(3) FIG. 2 shows a tunable waveform according to the present invention;

(4) FIG. 3 shows a preferred shape of the tunable waveform, and

(5) FIG. 4 is an embodiment of an electronic circuit that provides the intended tunable waveform.

DETAILED DESCRIPTION OF EMBODIMENTS

(6) The present invention will now be described with reference to the accompanying drawings, wherein the same or similar elements are identified with the same reference numeral.

(7) FIG. 1 shows a waveform 1 comprising two parts, or two pulses, as is known in the prior art. The waveform takes a time in the order of 5 to 25 us (microseconds) and a maximum voltage is of the order of 30 to 80 V (Volts). A first pulse 2, the jet pulse, is applied to a piezo actuator of a print element for ejecting an ink drop from a nozzle in the print element. A second pulse 3, the brake pulse, is applied to reduce the residual vibrations of the ink inside the print element. Both pulses are tunable in respect to the maximum voltage to adjust the velocity and volume of the ejected droplet and to adjust the effectivity of the brake pulse respectively. It is noted that the waveform 1 may deform somewhat by the capacitive load of the piezo actuator.

(8) FIG. 2 shows a waveform as applied by the circuit according to the present invention. In this waveform the jet pulse 2 and brake pulse 3 are composed of a basic part that is independent of the print element. In addition to this basic part an extra voltage 4 and an extra voltage 5 are supplied to the capacitive load. Both extra voltages have a variable duration 6 and 7, thereby tuning the deformation of the piezo actuator and the energy supplied to the ink in the print element.

(9) FIG. 3 shows a preferred waveform wherein the extra voltage has a lower voltage than the peak voltage from the common waveform generator, both in the jet pulse 2 and in the brake pulse 3. Since there is only one alteration of the voltage at a variable timing 6 and 7, the power dissipated in the tuning part of the circuit is reduced by a factor of two relative to the waveform shown in FIG. 2.

(10) FIG. 4 is a print head module wherein print elements are actuated according to the waveform of FIG. 2 or FIG. 3. It comprises a print head driver board 10, a driver ASIC 11 and a print head chip 12 comprising print elements 23, each print element having a piezo electric actuator for transforming an electric voltage to an acoustic wave in the ink of the element. The piezo actuator is electrically a capacitive load for the electronic circuit.

(11) The driver board 10 comprises a common waveform generator 13 that generates a basic waveform independent of a specific print element. Two fixed voltage sources, 14 and 15, are on the board to be used for supplying the extra voltages 4 and 5 in the waveform. A print data memory 16 is available for the wave shape selection module 17 that specifies the timing 6 and 7 for tuning the waveform to the individual print elements 23. A driver ASIC 11 is positioned as close as possible to the print head 12 in order to reduce parasitic effects. The ASIC 11 comprises a main switch control 20 and a switch module 22 for each print element. Each switch module 22 comprises a tune switch control 21 and three transistor switches 31, 32 and 33. The main switch control 20 determines from the print data 16, the timing of the first switch 31 for connecting the basic part of the waveform generated by generator 13 to a print element. The wave shape selection module 17 supplies the parameters for the tune switch control 21 to determine the timing to bring the switches 32 and 33 from their open, blocking state into a closed, saturation state. These transistors are therefore not operated in a conducting state, which limits the dissipation that they provide. The resulting voltage supplied to the print element 23 is a summation of a number of fixed sources controlled by the various switches to obtain an actuation that is individually tunable for each print element.

(12) The skilled person will recognise that other embodiments are possible within the scope of the appended claims.

(13) The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.