Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1999-04-23
2001-10-02
Nguyen, Thinh (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S011000, C347S012000, C347S014000, C347S015000, C347S049000, C347S023000
Reexamination Certificate
active
06296341
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an ink jet print head provided in an ink jet type recording device, and more particularly, to a method for improving the reliability and accuracy of ink droplet ejection from an ink jet print head by regulating the drive signals that effect ink droplet ejection.
Some conventional ink ejection devices employ a piezoelectric ceramic element to alter the capacity of an ink chamber containing ink. An ink droplet is expressed from the ink chamber through an associated nozzle when the capacity of the ink chamber is decreased, and ink is introduced into the ink chamber through an ink inlet when the capacity of the ink chamber is increased. This type of ink jet print head is formed with a plurality of ink chambers. The ink chambers are separated by partitions formed of a piezoelectric ceramic material. An ink supply device, such as an ink cartridge, is connected in fluid communication on one end of the plurality of ink chambers, while ink ejection nozzles (hereinafter abbreviated to nozzles) are provided on the other end of the plurality of ink chambers. When drive signals are applied to the partition walls, the partition walls are deformed. This deformation decreases the capacity of the interposed ink chamber and generates a pressure wave in the ink that forces an ink droplet to be ejected through the associated nozzle onto a recording medium, forming characters, patterns, and the like.
If variations exist in the dimensions of the ink chambers or nozzles, however, the ink droplets cannot be reliably ejected from the nozzles in an accurate direction, even when the ink jet print head is driven by a regulated drive waveform. This is evident when unevenness appears in dot arrays recorded on the recording medium and when the recording device cannot achieve a prescribed recording quality.
The consistency of this ink droplet ejection is dependent on both the time required for the pressure wave generated in the ink to propagate once across the length of the ink chamber and the pressure wave generated by the drive waveform. These two factors cannot be coordinated if variation exists in the dimensions of the ink chambers. As a result, the ink droplets cannot be reliably ejected with an accurate aim. Due to this problem, it is necessary to require extremely strict tolerances for the dimensions of the ink chambers and nozzles during the production process in order to maintain a uniform printing quality for each ink jet print head.
According to the method proposed in Japanese Laid-Open Patent Application (Kokai) No. HEI-7-32651, a plurality of test images is recorded on a recording medium, and the density of these test images is measured using an optical scanner. Next, a characteristic curve is graphed using the measured density and drive control values. The characteristics of each ink jet print head are optimized by calculating the optimal value of the derived control values for each ink jet print head based on the characteristic curvature, test results, test control values, and desired density. However, this method of calculating the optimal drive control value is not efficient because it requires a large number of processes. In addition, the above process does not consider the consistency of the ink droplet ejection direction, which has a major effect on the recording quality. Accordingly, this process is not sufficient for reliably achieving and maintaining a prescribed printing quality.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention to provide a drive regulation method for an ink jet print head capable of maintaining a uniform recording quality for each ink jet print head without requiring a strict tolerance in the production process.
These and other objects of the present invention will be attained by a method for regulating ink droplet drive control in an ink jet print head, wherein an ejection signal is applied to an actuator provided in the ink jet print head to eject ink stored in an ink chamber through an associated nozzle. In this method, a plurality of signal types are preselected for driving the ink jet print head under a variety of conditions. From these preselected ejection signals, the ejection signal most capable of stabilizing the directions in which the ink ejects from the nozzles is employed as the ink jet ejection signal to drive the ink jet print head. The type of ejection signal selected from the plurality of preselected types is determined based on experience and testing taking variations in the dimensions of the ink chambers and nozzles into consideration. With this method, a plurality of ejection signals are preselected for driving each of the ink jet print heads under various conditions, and the ink jet print head is driven based on the selected ejection signal. Subsequently, the ink ejection signal most capable of stabilizing the direction in which ink droplets are ejected from the nozzle is used as the ink jet print head ejection signal. Therefore, each ink jet print head can be driven with a different ejection signal. As a result the direction in which ink droplets are ejected from the nozzle is stabilized for each ink jet print head even when inconsistencies exist from the manufacturing process, making it possible to achieve a uniform printing quality. Further, this method is beneficial for mass production, as the process requires only selected an ejection signal for each ink jet print head from a plurality of preselected signals.
Preferably, an ejection signal is selected by examining the unevenness or distortion in the dot array recorded on the recording medium to determine whether the direction of ink ejection has been stabilized or not. That is, the direction in which ink is ejected from the ink jet print head is determined to be more consistent when less distortion is found in the dot array recorded on the recording medium. Therefore, the invention provides an easy method for determining whether the aim of each nozzle has been optimized.
Preferably, the actuator is provided on one side of the ink chamber for generating a pressure wave in the ink based on the ejection signal. Further, the plurality of ejection signals are configured of pulse signals that differ in pulse width. With this construction, ink ejection is stabilized when the pulse width of the ejection signal has a prescribed relationship with the time required for the pulse width to propagate one way in the lengthwise direction of the ink chamber. In this way, an ejection signal having an optimal pulse width can be selected from the plurality of ejection signals.
Preferably, each of the ejection signals is a combination of a primary pulse having pulse widths different from each other and an auxiliary pulse having a timing and a pulse width capable of substantially dampening or offsetting meniscus vibrations caused by the primary pulse. With this construction, ink is ejected according to the primary pulse, after which the auxiliary pulse is used to substantially cancel the meniscus vibrations resulting from the primary pulse. If meniscus vibrations are appropriately dampened at this time, then the direction in which the next ink droplet is ejected will be stabilized. Accordingly, an ejection signal having an optimal primary pulse and auxiliary pulse is selected from the plurality of ejection signals for stabilizing the direction in which ink droplets are ejected from the ink jet print head.
Preferably, the plurality of preset ejection signals are configured by varying the primary pulse width, the auxiliary pulse width, and the interval between the two pulse widths at a uniform proportion. Accordingly, this method enables or simplify selection of the plurality of ejection signals.
Preferably, a memory device is integrally provided on the ink jet print head for storing data corresponding to the selected ejection signal. With this construction, during the actual recording operations, the ink jet print heads can be controlled to eject ink droplets based on the data stored in this memory device, ther
Brother Kogyo Kabushiki Kaisha
Nguyen Thinh
Oliff & Berridg,e PLC
Stewart Jr. Charles W.
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