Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1999-07-23
2001-09-11
Tran, Huan (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S011000, C347S014000, C347S019000
Reexamination Certificate
active
06286923
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink jet printer for ejecting ink to print images, such as characters and symbols.
2. Description of the Related Art
Ink jet printers can be divided roughly into two types depending on how they generate force for ejecting ink droplets. Electrothermal conversion types generate force by converting electric power into heat, and electromechanical conversion types generate force by converting electric power into mechanical force.
Electrothermal conversion types use a thermal resistor or other actuator to heat a portion of ink filling an ink chamber to boiling. The force of the resultant expanding vapor bubble ejects an ink droplet through a nozzle of the ink chamber.
Electromechanical conversion types use electric power to mechanically deform piezoelectric material in order to eject ink. That is, a voltage is applied either perpendicular to or parallel with the polarization direction of the piezoelectric material. As a result, the piezoelectric material deforms so as to apply pressure to ink in an ink channel. An ink droplet is ejected from a nozzle of the ink channel as a result.
Electromechanical converting type ink jet printers can be divided into two types. In the first type, a side of an ejection channel is covered by a vibration plate, or a diaphragm. A piezoelectric material is disposed on top of the vibration plate. In the second type, a plurality of ejection channels are cut directly into a plate of piezoelectric material. The ejection channels are partitioned by side walls formed from the piezoelectric material.
SUMMARY OF THE INVENTION
In both electrothermal and electromechanical converting type ink jet printers, ejection characteristics degrade after the actuators are driven a great number of times. When the ejection characteristics degrade, speed and volume of ejected ink droplets decrease. Recording quality degrades, especially when the print head is mounted on a carriage that scans in front of the recording medium. In this case, the position where droplets impinge on the recording medium can become shifted out of alignment with surrounding dots.
Recording quality degrades to a particularly high degree with piezoelectric ink jet printers, because the polarization of the piezoelectric can greatly degrade when the piezoelectric material is driven a great number of times. As the polarization of the piezoelectric material degrades, the piezoelectric material will deform less and less when applied with the same voltage. The problem of shift in dot location occurs as a result.
It is an objective of the present invention to overcome the above-described problems and to provide an ink jet printer that compensates for reduction in speed and volume of ejected ink droplets caused by the print head being driven a large number of times, so that good print quality can be maintained over a long period of time.
According to a first aspect of the present invention, an ink jet printer includes a counter that counts the number of times a drive circuit drives a print head. A memory stores the number of times counted by the counter. Based on the number of times stored in the memory, a waveform change unit changes waveform of the drive pulse applied by the drive circuit to the print head, in order to increase force at which the print head ejects ink. With this configuration, the waveform of the drive pulse can be changed based on the number of times the print head is driven, to take into account degradation of printing characteristics that occur when the print head is driven a large number of times.
The ink jet printer is desirably a piezoelectric type ink jet printer, wherein the print head includes an actuator formed from piezoelectric material. Force to eject ink from an ejection channel is generated by the drive circuit applying drive pulses to the piezoelectric material, so that the piezoelectric material deforms. In this case, even if the polarity of the piezoelectric material degrades after the piezoelectric material is driven for a great number of times, print quality can be maintained in a good condition by changing the waveform of the drive pulse based on the number of times the drive circuit drives the print head.
It is desirable that the piezoelectric type print head and the memory both be mounted on a head holder, which is detachably mounted on the carriage of the printer. With this configuration, both the print head and the memory are exchanged together with the head holder. In other words, when the print head is exchanged for a new one, the memory will be exchanged as well. As a result, the number of drive pulses applied to the new print head will be counted starting from zero. Also, print heads can be temporarily switched, for example, to change printing colors, without confusing the number of drive times for different print heads.
It is also desirable that the piezoelectric actuator include partition walls that define the ejection channels, and that the partition walls be at least partially polarized. With this configuration, the change in the waveform of the drive pulse is immediately reflected in ejection of ink.
According to a second aspect of the present invention the memory is connected to the print head, and the print head is detachably mounted on the printer body. The printer body includes a control circuit that includes the counter, and that updates the number of times in the memory each time a certain amount of printing is completed. With this configuration, the memory is replaced along with the print head, so that calculation of the number of drive times is started afresh with respect to the newly replaced print head. Also, because the number of drive times is counted on the printer body side and the counted number is stored in the memory on the print head, counting operations are easy to control and there is no need to frequently store the numbers in the memory.
According to a third aspect of the present invention, a print medium judgement unit is provided to judge timing of when printing is stopped on one print medium before starting on another print medium. A waveform change unit changes the waveform of the drive pulse only at timing judged by the print medium judgement unit.
If the waveform of the drive pulse is changed while printing on a particular recording medium, then the location where the change is made will be obvious to the user, because, for example, the portion of an image printed before changing the waveform may have a lighter tone than the portion printed after changing the waveform. However, when this change is made between separate recording media as per this aspect of the present invention, that is after printing on one printing medium has stopped but before printing on another printing medium has started, then the change will not be so obvious so that printing quality can be maintained at a high level.
It is desirable that the waveform be changed at timing based on either a new page signal or a new print command, but most desirably based on a new page signal, because the change can be made more quickly.
It is desirable that the waveform change unit control the drive circuit to change the width or height of the waveform of drive pulses applied to the print head. With this configuration, although printing characteristics of the print head will degrade when the print head is driven a great number of times, this degradation can be compensated for so a predetermined ejection speed and an ejection volume can be maintained. Ejection can be performed efficiently.
REFERENCES:
patent: 5475405 (1995-12-01), Widder et al.
patent: 5557304 (1996-09-01), Stortz
patent: 5764256 (1998-06-01), Zhang
patent: 5790139 (1998-08-01), Umeno et al.
patent: 6000773 (1999-12-01), Murray et al.
patent: 6116717 (2000-08-01), Anderson et al.
Brother Kogyo Kabushiki Kaisha
Dudding Alfred
Oliff & Berridg,e PLC
Tran Huan
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