Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1999-04-05
2002-08-13
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S009000, C347S011000, C347S068000
Reexamination Certificate
active
06431675
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of driving an ink jet printhead in which a part of a pressure generating chamber, which communicates with a nozzle orifice for ejecting an ink drop, is formed with a vibration plate, a piezoelectric layer is formed on the surface of the vibration plate, and an ink drop is ejected from the nozzle orifice by a displacement of the piezoelectric layer.
2. Description of the Related Art
There is known an ink jet printhead in which a part of a pressure generating chamber, which communicates with a nozzle orifice for ejecting an ink drop, is formed with a vibration plate. The piezoelectric element deforms the vibration plate to pressurize ink within the pressure generating chamber, and to eject ink through in the form of an ink drop through the nozzle orifice. This printhead is classified into two printheads. A first printhead uses a piezoelectric actuator in which a piezoelectric element generates a longitudinal vibration mode in the axial direction of the actuator. A second printhead uses a piezoelectric actuator in which a piezoelectric element generates a flexural vibration around the axis.
In the first printhead, a volume of the pressure generating chamber may be varied by bringing the end face of the piezoelectric element into contact with the vibrating plate. An advantage of the first printhead is that it can be manufactured so as to be suitable for high density printing. This printhead suffers from the following disadvantage. It is necessary to form a piezoelectric green sheet into a comb-shape of piezoelectric elements by cutting in conformity with the pitches of the orifice array, and 2) to position the comb-shaped piezoelectric elements to the pressure generating chambers and fasten them thereonto. Therefore, the manufacturing process of the printhead is intricate.
The second printhead is manufactured by a relatively easy process of shaping a piezoelectric green sheet in conformity with the pressure generating chambers and pasting the thus shaped green sheet onto the chamber, and sintering the resultant.
The second printhead requires a larger displacement area than that of the first printhead, and hence a large volume of the pressure generating chamber. As a result, an ejected ink drop is large in volume. In this respect, where the second printhead is used, it is difficult to form dots of small size, which are essential to graphic printing. A possible approach to solve the problem is to reduce the amount of ejecting ink by lessening a displacement of the flexural type piezoelectric actuator. The approach is disadvantageous in that the ink ejecting pressure is low, the ink ejecting speed is low, the ejected ink drop lands at an incorrect position. Further, degradation of the print quality is noticeable particularly in the printing of the type in which an exact dot printing is required, for example, graphic printing.
To cope with this, there is proposed a drive method in JP-A-63-71355. In this method, the ink drop is ejected from the nozzle orifice by contracting the pressure generating chamber after the ink ejection, and then the pressure generating chamber is expanded again to absorb the tail of the ink drop, whereby the ink drops secondarily formed are removed. However, the ink drop per se is not reduced in this method.
There is another proposal (JP-A-7-76087) in which after expanded, the pressure generating chamber is contracted at a first contracting rate and then at a second contracting rate lower than the first one, to thereby reduce the length between the leading and trailing ends of the ink drop or a time difference therebetween as short as possible and to form spherical ink dots.
A recent marked trend of high definition printing needs ink drops of extremely small size, while high speed printing needs ink drops of large volume. Further, high speed and stable driving of the printhead is also desired.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a method of driving an ink jet printhead which reduces a volume of an ink drop without lowering traveling speed of the ink drop, and is suitable for graphic printing.
A first mode of the invention is a method of driving an ink jet printhead in which when one of piezoelectric vibrators each associated with a pressure generating chamber, which communicatively connects to an orifice and a reservoir, both being associated with the pressure generating chamber, is driven, the pressure generating chamber associated with the driven piezoelectric vibrator is expanded or contracted to eject an ink drop through the nozzle orifice associated with the driven pressure generating chamber. The method includes: a contracting step for ejecting an ink drop through the nozzle orifice by contracting the pressure generating chamber; and an expanding step for expanding the pressure generating chamber till a velocity of the trailing end of the ejected ink drop is substantially 0 at a position near the nozzle orifice.
In the first mode of the invention, the pressure generating chamber starts to expand before the ejection of an ink drop that is about to discharge as the result of its contraction in the contraction step is completed. Only the portion of ink having been about to discharge is ejected in the form of an ink drop. A volume of the ink drop can be controlled depending on an expansion start timing.
A second mode of the invention, based on the first mode, is a method of driving an ink jet printhead in which an expansion of the pressure generating chamber in the expanding step following the contracting step starts after a time point where the meniscus of ink in the nozzle orifice starts to be deformed to form the leading edge of an ink drop to be ejected through the nozzle orifice.
In the second mode, the leading end of an ink drop is ejected at an instant that the pressure generating chamber starts to expand in the expanding step.
A third mode of the invention, based on the mode
1
or
2
, is a method of driving an ink jet printhead in which an expansion period of the expanding step is no more than ¼ Tc, wherein Tc is the Helmholtz frequency of the pressure generating chamber.
The third mode can most effectively hold back the retraction of the meniscus, which follows the ink drop ejection.
A fourth mode of the invention is a method of driving an ink jet printhead in which when one of piezoelectric vibrators each associated with a pressure generating chamber, which communicatively connects to an orifice and a reservoir, both being associated with the pressure generating chamber, is driven, the pressure generating chamber associated with the driven piezoelectric vibrator is expanded or contracted to eject an ink drop through the nozzle orifice associated with the driven pressure generating chamber. The method includes: a contracting step for ejecting an ink drop through the nozzle orifice by contracting the pressure generating chamber; and an expanding step for expanding the pressure generating chamber at such a timing as to reduce a volume of an ink drop to be ejected for a period being no more than ¼ Tc, wherein Tc is the Helmholtz frequency.
The fourth mode can control a volume of an ink drop in a manner that the pressure generating chamber is expanded for a predetermined time period before the ejection of an ink drop that is about to discharge as the result of its contraction in the contraction step is completed.
A fifth mode of the invention, based on any of the first to fourth modes, is a method of driving an ink jet printhead which further includes a hold step, following the contracting step, for holding the contraction state of the pressure generating chamber for a period being no more than ⅓ Tc, wherein Tc is the Helmholtz frequency of the pressure generating chamber.
The fifth mode can reduces the amount of an ink drop ejected by reducing the contraction holding period.
A sixth mode of the invention is a method of driving an ink jet printhead in which when one of piezoelectric vi
Barlow John
Dudding Al
Seiko Epson Corporation
Sughrue & Mion, PLLC
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