Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2000-05-31
2002-04-16
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S009000, C347S010000, C310S316020
Reexamination Certificate
active
06371587
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an ink jet recording apparatus comprising a recording head for jetting ink drops through nozzle orifices by selectively supplying a drive signal to each piezoelectric vibrator.
An ink jet recording apparatus such as an ink jet printer comprises a recording head having a large number of nozzle orifices formed as the nozzle orifices are arranged like rows. The recording head may comprise pressure generating chambers communicating with the nozzle orifices and piezoelectric vibrators for expanding and contacting the pressure generating chambers, thereby changing the ink pressure in each pressure generating chamber. In such a recording head, a drive signal is supplied to each piezoelectric vibrator, thereby changing ink pressure for jetting an ink drop through the nozzle orifice.
For an ink jet recording apparatus of this kind, an art for jetting different amounts of ink drops through one nozzle orifice is proposed to satisfy contradictory needs for improving the image quality and improving the record speed. For example, a necessary waveform element is selected appropriately from a drive signal sequence comprising a plurality of waveform elements connected and the selected waveform element is supplied to a piezoelectric vibrator, thereby jetting a plurality of types of ink drops different in amount.
Each piezoelectric vibrator used with the recording head is considered as an ideal condenser. That is, it is considered that the potential of the piezoelectric vibrator (segment potential) continues to hold the potential at the point in time at which the previous waveform element supply is stopped. Based on this consideration, the termination potential of the previously supplied waveform element and the initial potential of the later supplied waveform element are put into the same level.
However, it is found that the actual piezoelectric vibrator has insulating resistance and that if it is left standing without supplying a drive signal, the potential gradually drops because of natural discharge. The potential drop is caused by non uniformity of piezoelectric substance in piezoelectric layer, for example.
The longer the time between the supply end of the previous waveform element and the supply start of the subsequent waveform element, namely, the longer the supply period of no drive signal, the larger the potential drop amount.
The potential drop is noticeable as the film thickness is thinner (the field effect strength becomes stronger). Thus, with the recently required piezoelectric vibrator having a small volume (thin thickness), the difference between the potential and the initial potential of the subsequent waveform element becomes large if the supply period of no drive signal is extremely short.
If the subsequent waveform element is supplied to the piezoelectric element in a state in which the difference between the potential and the initial potential of the subsequent waveform element is large, the piezoelectric potential varies largely in a short time just after supply of the waveform element starts. Consequently, rapid deformation occurs in the piezoelectric vibrator and an ink drop is jetted in error; this is a problem. Since a large current exceeding the allowable range flows into the piezoelectric vibrator, the function of the piezoelectric vibrator can be degraded and the piezoelectric vibrator can be destroyed.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to prevent ink drops from being jetted in error and a piezoelectric vibrator from being destroyed for enhancing the reliability of a recording apparatus by easing a rapid rise in the potential in the piezoelectric vibrator.
In order to achive the above object, according to the present invention, there is provided an ink jet recording apparatus comprising:
a recording head including a piezoelectric vibrator to be deformed for varying the volume of a pressure generating chamber communicated with a nozzle orifice to eject an ink drop therefrom;
a drive signal generator for generating a drive signal in which a plurality of waveform elements are connected;
a waveform element supplier for selectively supplying at least two waveform elements from the drive signal to the piezoelectric vibrator; and
a potential difference compensator for compensating a potential difference between a termination potential of a previous waveform element and an initial potential of a subsequent waveform element respectively selected by the waveform element supplier.
According to the above configuration, the termination potential of the previous waveform element and the initial potential of the subsequent waveform element can be matched with each other by the potential difference compensator. Thus, a rapid rise in the potential of the piezoelectric vibrator when the subsequent waveform element is supplied can be eased. Therefore, the disadvantages involved in the rapid rise in the potential, such as erroneous jetting of an ink drop and destroying of the piezoelectric vibrator, can be prevented. Consequently, the reliability of the recording apparatus can be enhanced.
Prefereably, the potential difference compensator includes:
a first supply switch connected between the piezoelectric vibrator and a drive signal line for supplying the drive signal to the piezoelectric vibrator in order to control the waveform element supply;
a second supply switch connected between the drive signal line and the piezoelectric vibrator in parallel with the first supply switch;
a first switch controller for supplying a first switching signal to the first switch for controlling the same;
a second switch controller for supplying a second switching signal to the second switch for controlling the same; and
a rectifier connected in serial with the second supply switch such that a current flow direction from the drive signal line to the piezoelectric vibrator is defined as a forward direction.
Preferably, the drive signal includes a first waveform element for deforming the piezoelectric vibrator and, a second waveform element, one portion of which is convex to the lower potential side;
wherein the first switch controller generates the first switching signal in at least a part of a period while the first waveform element is generated; and
wherein the second switch controller generates the second switching signal at a predetermined timing in a period while the second waveform element is generated so as to turn on the second supply switch.
Preferably, the lowest potential of the second waveform element is lower than a potential of the piezoelectric vibrator at the time where the second switch is turned on.
Preferably, the second switch controller generates the second switching signal for turning on the second switch in a period while the potential of the second waveform element is rising.
According to the above configuration, an electric current flows into the piezoelectric vibrator through the second supply switch and the rectifier only when the waveform element potential becomes higher than the piezoelectric potential by previously turning on the second supply switch in a state in which the potential lowers. Consequently, a rapid rise in the potential can be eased.
Alternatively, the potential difference compensator includes an initial potential setter for lowering an initial potential of the subsequent waveform element than a termination potential of the previous waveform element in response to potential drop of the piezoelectric vibrator.
Preferably, the subsequent waveform element includes a compensation element for restoring the potential thereof from the initial potential to the termination potential of the previous waveform element.
Preferably, the waveform supplier includes a compensation element collective supplier for supplying the compensation element to every piezoelectric vibrator collectively.
Preferably, the waveform supplier includes a compensation element selectively supplier for supplying the compensation element to a predetermined piezoelectric vibrator selectively.
Preferably, the init
Barlow John
Dudding Alfred
Seiko Epson Corporation
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