Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2002-09-06
2004-03-09
Nguyen, Thinh (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S071000
Reexamination Certificate
active
06702430
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an actuating device for a multi-nozzle ink jet printhead comprising a linear array of electromechanical transducers some of which are configured as actuator fingers associated with the nozzles of the printhead while others are configured as support fingers intervening between the actuator fingers, wherein each transducer has a first and a second electrode and is adapted to expand and contract in accordance with a voltage applied between the first and second electrodes.
An actuating device of this type has been disclosed in EP-B-0 820 869. The electromechanical transducers are formed by piezoelectric elements and are disposed on one side of a channel plate in which a plurality of parallel ink channels are formed each of which lead to a nozzle of the printhead. Each of the transducers serving as an actuator is disposed adjacent to one of the ink channels so that, by contraction and expansion of the actuator finger, ink is drawn into the ink channel from an ink reservoir and is then expelled from the associated nozzle. The support fingers intervening between the actuator fingers are connected to dam portions separating the individual ink channels. The ends of the support fingers and actuator fingers opposite to the channel plate are interconnected by a backing plate which, together with the support fingers, has the purpose of absorbing the reaction forces of the contraction and expansion strokes of the actuator fingers.
While an alternating arrangement of actuator fingers and support fingers is possible, the cited document proposes an arrangement with one support finger for two actuator fingers. In a preferred embodiment disclosed in this publication, the support fingers are passive. However, it is mentioned that these support fingers may be formed also by piezoelectric transducers which could then be controlled actively in order to compensate for the reaction forces of the actuator fingers. However, an electronic control system permitting the control of each of the active support fingers individually would considerably add to the complexity of the system.
On the other hand, when passive support fingers are used, the backing plate is caused to vibrate, especially when a large number of nozzles of the printhead are activated simultaneously, and this leads to the production of noise, at a frequency in the order of 10 kHZ for example, to an increased power consumption and to the cross-talk phenomena causing the volumes and velocities of the ink droplets expelled from the various nozzles to become non-uniform,
It is generally known to actively compensate for the cross-talk phenomena by modifying the control signals applied to the actuator fingers in accordance with the activation or non-activation state of the neighboring actuators, for example by means of a resistor network, as described in U.S. Pat. No. 4,381,515.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an actuating device of the type indicated in the opening paragraph of the present description, in which active control of the support fingers can be achieved by simplified control means. According to the present invention, this object is achieved by the feature that the totality of the linear array of electromechanical transducers consists of at least one group which includes a plurality of actuator fingers and a plurality of support fingers, and control means that are associated with each group for applying a voltage, depending on the number of active actuator fingers in this group, to the first electrodes of all support fingers in the group.
It has been found that since the vibration of the backing plate caused by the reaction forces of the actuator fingers becomes significant only when a large number of actuator fingers is activated simultaneously, the disturbing effect of this vibration can largely be eliminated when the actuator and support fingers are grouped and all support fingers belonging to the same group are controlled by one and the same control signal, which depends on the number of active actuator fingers in this group. As a result, the number of control signals that have to be generated in real-time corresponds only to the comparatively small number of groups and not to the comparatively large number of individual support fingers, so that the control means can be considerably simplified.
In an extreme situation, the totality of the transducers may form only a single group, so that not more than one control signal is required for all actuator fingers.
In a particularly attractive embodiment, the first electrodes of all actuator fingers and all support fingers belonging to the same group are interconnected with each other and are held on a floating potential. Then, electrically, the actuator fingers and the support fingers form a network of impedance elements with the actuator fingers connected in parallel with each other and the support fingers also connected in parallel with each other but with the actuator fingers and the support fingers connected in series, with the floating potential between them. As a result, the support fingers are actively controlled by the voltage drop between the common potential and their respective second electrode, and the common potential will automatically depend on the number of active actuator fingers in the group.
The impedances (i.e. capacitances in case of piezoelectric elements) of the support fingers in relation to the impedances of the actuator fingers may be adjusted in order to achieve an optimal compensation of the reaction forces.
If Ohmic resistances are neglected, the first electrodes of all support fingers within a group are maintained at exactly the same voltage. However, if impedances in the lines interconnecting the first electrodes of the various support fingers are considered, the voltages applied to the individual support fingers may deviate from one another. If only a single actuator finger of the group is activated, then the voltages applied to the first electrodes of the support fingers will decay with increasing distance from the activated actuator finger. On the other hand, the deflection or bending stress of the backing plate caused by the reaction force of the active actuator finger will also decay with increasing distance from this actuator finger. As a result, it is possible to adjust the impedances between the adjacent first electrodes of the transducers so as to map the decay of the stresses in the backing plate. In this way, it is even possible to attenuate a local deflection of the backing plate, although the support fingers are not controlled individually.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
REFERENCES:
patent: 4381515 (1983-04-01), Bain
patent: 5818482 (1998-10-01), Ohta et al.
patent: 6161925 (2000-12-01), Reinten et al.
patent: 6513917 (2003-02-01), Matsuda et al.
patent: 0 820 869 (1998-01-01), None
patent: 03258550 (1991-11-01), None
Blom Franciscus Richard
Erren André Jozef Christiaan Gerardus
Reinten Hans
Nguyen Thinh
Oce--Technologies B.V.
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