Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1999-01-22
2001-11-27
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
Reexamination Certificate
active
06322193
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority benefit of Taiwan application serial no. 87117559, filed Oct. 23, 1998, the full disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method and an apparatus for measuring the frequency response of, and more particularly, to a magnetoelectric method and apparatus for measuring the droplet frequency response of an ink jet printhead.
2. Description of Related Art
For most commercial inkjet printers, printing graphics and documents is normally carried out by the printhead. In principle, a printhead of an inkjet printer heats up the ink and vaporizes the ink to form ink bubbles by converting electric energy into heat. The printhead then jets the ink drops, which are developed from the ink bubbles, onto a destination surface through spouts. In order to speed up the printing efficiency of an inkjet printer, the manufacturers normally focus on increasing the droplet frequency response. That is, the droplet frequency response indicates the printing speed of an inkjet printer. Hence, how to measure the droplet frequency response of an inkjet printhead has become a very important technique in inkjet printer manufacture.
The droplet frequency response is obtained by comparing the detected actual jetting frequency of an inkjet printhead with the driving frequency actually applied to the inkjet printhead. The maximum droplet frequency response of the inkjet printhead can be measured by checking the matching between different driving frequencies applied on the inkjet printhead and the actual responding jetting frequencies of the inkjet printhead. Since the ink bubbles are generated at the printhead in a frequency varied from several kilo-Hertz (kHz) to several tens kHz, it is impossible to detect the actual droplet frequency response through a regular image mapping system. Even though utilizing a high-speed camera it is possible to catch the actual droplet frequency response of an inkjet printhead, and determine the droplet frequency response of the inkjet printhead, it is not cost effective. Hence, some apparatuses and methods have been developed for the purpose of measuring droplet frequency response of an inkjet printhead, such as those disclosed by U.S. Pat. Nos. 4,484,199 and 4,590,482.
The schematic cross-sectional diagram of a conventional measuring apparatus for determining the droplet frequency response is illustrated in FIG.
1
.
Referring to
FIG. 1
, a planar detecting electrode
106
is placed parallel to a metallic nozzle plate
100
, and a voltage difference exists between the detecting electrode
106
and the nozzle plate
100
. The detecting electrode
106
and the nozzle plate
100
are not electrically connected, though the distance between them is quite short, for example less than 100 &mgr;m. Once an ink drop
104
is jetted by the nozzle plate
100
through nozzle
102
, the ink drop forms an electric connection between the detecting electrode
106
and the nozzle plate
100
before the ink drop
14
totally leaves the nozzle plate
100
. The electric connections formed by continuously jetted ink drops out of the nozzle plate
100
can be detected by an attached electronic circuit (not shown in figure) for obtaining the forming frequency of the ink drops. However, ink drops are easily stuck within the narrow space between the detecting electrode
106
and the nozzle plate
100
, and that leads to an error reading on the forming frequency of ink drops while a detecting process is performed.
The schematic cross-sectional diagram of another conventional measuring apparatus for determining the droplet frequency response is illustrated in FIG.
2
.
Referring to
FIG. 2
, a pair of electrodes
208
is placed between the nozzle plate
200
and the detecting electrode
206
, wherein a high voltage is applied on the electrodes
208
to provide a high-voltage electric field. While an ink drop
204
jetted by the nozzle plate
100
passes through the electrodes
208
, the ink drop is charged. An electric signal can then be detected at the detecting electrode
206
after the charged ink drop hits the detecting electrode
206
. By counting the number of the electric signals within a period of time, the forming frequency of the ink drops is obtained. An ink drop, which is about 100 pico liters (pl) in volume, is possibly broken into several sub-drops while the ink drop
204
passes through the high-voltage electric field says, exceeding 1000 volts. Therefore, the detected forming frequency at the detecting electrode is interfered by the noise signals given by the sub-drops.
SUMMARY OF THE INVENTION
It is therefore an objective of the present invention to provide a method and apparatus that ensures a more precise measurement of the droplet frequency response which is not interfered with by the noise signal and error reading.
In accordance with the foregoing objective of the present invention, the magnetoelectric apparatus of the invention for measuring the forming frequency of ink drops at a printhead contains a metallic detecting plate and a magnetic ring. The method of the invention then determines the maximum droplet frequency response of the printhead by comparing the forming frequencies and the corresponding driving frequencies. When an ink drop jetted from the nozzle makes a contact with the detecting plate, which is perpendicular to the nozzle plate of the printhead, a current flows through the detecting plate immediately, and detected as a portion of the expected signal. As soon as the ink drop leaves the nozzle completely, the foregoing current no longer exists. However, the magnetic ring generates an induced current that flows in the same direction as that of the foregoing current to complement the absence thereof, wherein the induced current is also detected as another portion of the expected signal. The expected signal is then processed by a signal-processing routine for determining the maximum droplet frequency response of the inkjet printhead.
REFERENCES:
patent: 4484199 (1984-11-01), Watanabe
Hu Hung-Lieh
Lai Yi-Hsuan
Lee Ming-Ling
Lian Zhi-Ru
Wang Chieh-Wen
Barlow John
Huang Jiawei
Industrial Technology Research Institute
J. C. Patents
Stewart Jr. Charles W.
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