Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1998-06-15
2001-02-20
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
Reexamination Certificate
active
06189992
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The invention relates to the adjustment of ink ejection timing of an ink jet printer.
2. Description of Related Art
Known ink jet printers print on a recording sheet when the capacity of each ink reservoir chamber formed in an actuator of a print head is expanded and restored using piezoelectric elements, so that the ink in the reservoir chamber is pressurized and therefore ejected out of the ink ejecting pores formed in the ink reservoir chamber onto a recording sheet. A print head is normally mounted on a carriage for reciprocating movements in the direction along the width of a recording sheet. While being reciprocated, the print head ejects ink to form a print image on a recording sheet.
In an ink jet printer as described above, the ink ejecting pores are disposed at a predetermined distance apart from the plane of a recording sheet. Therefore, when an ink droplet is ejected out of an ink ejecting pore upon application of a drive voltage to the corresponding piezoelectric element, it takes a predetermined transit time for an ink droplet to land on a recording sheet. Consequently, in order to cause an ink droplet to land at a predetermined position on a recording sheet, it is necessary to apply the drive voltage to the corresponding piezoelectric element at a time that takes into account the transit time. The transit time of an ink droplet depends on the ejection speed of the ink droplet, the size of the gap between the ink ejecting pores and the plane of a recording sheet, and the like. Based on these factors and the moving speed of the print head mounted on the carriage, the time of ejecting an ink droplet can be determined. In other words, if the aforementioned quantities are estimated, the time for applying the drive voltage to an ink piezoelectric element can be determined so that an ejected ink droplet may land on a predetermined position on a recording sheet.
In the conventional ink jet printers, however, the displacement characteristic of the piezoelectric elements deteriorates over long periods of use so that the pressurization of the ink becomes insufficient, resulting in an undesirably reduced ejection speed of the ink droplets. The ink droplet ejection speed may also decrease due to deformation of component members of a print head, such as a diaphragm and the like, over long periods of use. Such a reduction in the ejection speed increases the ink droplet transit time so that the actual landing positions of ink droplets on a recording sheet deviate from the intended landing positions. Moreover, if a print head on the carriage reciprocates while ejecting ink droplets, a reduction in the ink droplet ejection speed results in deviations from the intended landing positions in opposite directions corresponding to the moving directions of the print head. In this case, a longitudinal line (in the paper-conveyance direction) printed on a recording sheet becomes rough or disturbed, thereby significantly degrading the print quality.
SUMMARY OF THE INVENTION
Accordingly, it is an aspect of the invention to provide an ink jet printer capable of correcting the application time of a drive voltage to piezoelectric elements on the basis of changes in the ink droplet ejection speed over time.
According to the invention, an ink jet printer is provided including a print head having an ink passage, a plurality of ink reservoir chambers branching from the ink passage and having ink ejecting holes, and a plurality of piezoelectric elements that change the capacity of the individual ink reservoir chambers. The print head ejects ink droplets from the ink ejecting holes to a recording medium that is conveyed in a conveyance direction. A mover unit moves the print head in a direction substantially orthogonal to the conveyance direction while the print head is ejecting an ink droplet to the recording medium. A drive voltage generator unit generates a drive voltage to deform at least one of the piezoelectric elements so that an ink droplet is ejected from at least one of the ink ejecting holes. On the basis of an ink droplet transit time between ejection of an ink droplet and the landing of the ink droplet on the recording medium, and a moving speed of the mover unit, an application timing control unit controls the application time of the drive voltage to a piezoelectric element so that an ink droplet ejected by the piezoelectric element lands at a predetermined ink droplet landing position on the recording medium. The application timing control unit corrects for a deviation in the ink droplet landing position caused by a change in the ink droplet transit time that is caused by a change in the ink droplet ejection speed over time. The correction is performed by changing the application time in accordance with the change in the ink droplet transit time.
In the ink jet printer of the invention, ink droplets are ejected from the ink ejecting holes of the print head by applying the drive voltage to the piezoelectric elements and thereby deforming the piezoelectric elements while the print head is being reciprocally moved in the directions orthogonal to the recording medium conveyance direction. The ink jet printer changes the application time of the drive voltage to eject an ink droplet, in accordance with the ink droplet transit time and the moving speed of the mover unit, so as to correct for a deviation in the ink droplet landing position caused by a change in the ink droplet transit time over time. Therefore, if the ink droplet ejection speed changes due to various factors and therefore changes the ink droplet transit time, the drive voltage application time is appropriately adjusted so as to offset the change in the ink droplet transit time. Consequently, the ink jet printer always prevents a deviation in the ink droplet landing position, and maintains good print quality without degradation.
The application timing control unit may determine an increase in the ink droplet transit time due to a decrease in the ink droplet ejection speed that is caused by a change in a deformation characteristic of the piezoelectric elements over time. A correction may be performed by advancing the application time by the increase in the ink droplet transit time.
With this structure, if the ink droplet ejection speed decreases due to a reduction in the amount of deformation of the piezoelectric elements that occurs over a long period of use, the application timing control unit advances the drive voltage application time by an increase in the ink droplet transit time. Therefore, if the ink droplet ejection speed decreases due to a long-time-use deterioration of the deformation characteristic of the piezoelectric element, the drive voltage application time will be adjusted to an optimal time. Consequently, the ink jet printer always prevents a deviation in the ink droplet landing position, and maintains good print quality without degradation.
The application timing control unit may determine the change in the ink droplet transit time based on a power-on time of the ink jet printer, and may perform the application time correction in accordance with the change in the ink droplet transit time.
With this structure, the drive voltage application time is determined on the basis of the power-on time of the ink jet printer. Therefore, if the characteristics of the piezoelectric elements or other component members change over a long period of use, the drive voltage application time will be adjusted to an optimal time. Consequently, the ink jet printer always prevents a deviation in the ink droplet landing position, and maintains good print quality without degradation.
The application timing control unit may determine the change in the ink droplet transit time based on an amount of ink used on the recording medium by the ink jet printer, and may perform the application time correction in accordance with the change in the ink droplet transit time.
With this structure, the drive voltage application time is determined on the basis of the amount of ink used by the ink jet pr
Barlow John
Brother Kogyo Kabushiki Kaisha
Oliff & Berridg,e PLC
Stewart Jr. Charles W.
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