Incremental printing of symbolic information – Ink jet – Ejector mechanism
Utility Patent
1997-06-27
2001-01-02
Brase, Sandra (Department: 2852)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Utility Patent
active
06169556
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink discharging method using an ink jet head for discharging ink toward a medium (sheet, cap, etc.) by an input of an electrical signal, and an ink jet recording apparatus for implementing the ink discharging method and an ink jet recording head to be mounted on the apparatus. More particularly, the present invention relates to the drive of a recording head having a plurality of heaters arranged in each nozzle.
2. Related Background Art
Most of the ink jet recording apparatus have been known as printing apparatus in such equipments as printers, facsimile machines, word processors and copying machines. Among others, the ink jet recording apparatus of a system using thermal energy as energy to be utilized for the ink discharge, that is, a system which generates bubbles in ink by the thermal energy and discharges the ink by using a pressure in generating the bubbles has recently been widely used.
As another application of the ink jet recording apparatus of this system, an ink jet dying apparatus which prints a predetermined pattern or picture or a synthesized image on cloth has recently been developed.
The ink jet recording head used in the above ink jet recording apparatus uses electro-thermal transducer elements (hereinafter also referred to as heaters) to generate the thermal energy. The heaters are normally arranged in an ink flow path (hereinafter also referred to as a nozzle) connected to an orifice. In many cases, such an ink jet recording head adopts an arrangement of providing one heater for one nozzle.
In such an ink jet recording head, a distance from a center of gravity of the heater to the orifice (hereinafter referred to as OH) is a significant factor which influences a discharge characteristic of the ink jet recording head such as a discharge rate of ink droplets and a refill frequency. Specifically, it has been known that for the discharge rate of the ink droplets, the discharge rate is higher as the OH is shorter, and for the refill frequency, the frequency is lower as the OH is shorter. It is thus apparent that in the prior art ink jet recording head structure, the discharge rate of the ink droplets and the refill frequency are involved in trade-off for the OH, and in the prior art, the OH is determined in a range in which both the discharge rate of the ink droplets and the refill frequency are at practical levels.
In the field of the ink jet, further improvement of the image quality has recently been demanded. As one of means for printing an image of high resolution, the construction to form the image by small ink droplets of 25 pl or less. In order to discharge the small ink droplets by the above ink jet recording head, the thermal energy generated by the heater is normally reduced. As a result, the discharge rate of the small ink droplets tends to be reduced. The reduction of the discharge rate leads to the deterioration of the precision of impact points of the small ink droplets, and it particularly leads to the deterioration of the image quality in the image of high resolution. Accordingly, in such a case, it is desirable to set the OH lower in the ink jet recording head in order to prevent the reduction of the discharge rate.
However, in the above method, the print dots must be increased because the one-dot area displayed by the small ink droplet is reduced, and a higher print speed than that in the prior art, particularly the improvement of the refill frequency is required. As described above, since the refill frequency is lowered as the OH is reduced, the print speed is lower than that of the prior art when the above method is used.
Further, a problem may be raised in the predischarge which is conducted as a part of the discharge recovery process. In the predischarge, the ink which does not serve to the recording is discharged from the ink jet recording head at a predetermined position in the apparatus. In this manner, the high viscosity ink in the ink jet recording head is removed to keep good ink discharge condition. Such predischarge is normally conducted immediately after the power-on of the apparatus and periodically during the printing. When the printing is conducted by the small ink droplets or in the low temperature/low humidity environment, it is necessary to reduce the interval between predischarges. Because the discharge power by the small ink droplets is low and the high viscosity ink may not be stably discharged depending on the condition of the viscosity of the ink due to the evaporation of water at the orifice.
Since the predischarge is conducted at the predetermined non-print unit, it takes a long time. Accordingly, even if the discharge frequency is raised, the substantial print time may be long. Further, the consumption of the ink by the frequently conducted predischarge is not negligible.
FIG. 8
shows a relation between the distance OH and the predischarge interval IPE together with the discharge characteristic described above. When the distance OH is short, the predischarge interval may be remarkably long. Thus, the pre-discharge interval and the refill frequency fr of the ink are of conflict relation.
On the other hand, an apparatus having a plurality of heaters for each orifice from the viewpoint described below has been known. It uses a plurality of heaters for the purpose of increasing a range in which the ink discharge amount is changed. In this case, the discharge amount is changed by selecting the heaters to be driven (that is, the heaters to generate heat) and the number thereof.
In a specific construction, a plurality of heaters are arranged along the direction of ink discharge in the liquid flow path connected to the orifice of the ink jet head, and the distance between the orifice and the center of the driven heater is changed by selecting the driven heaters and the number thereof so that the discharge amount is changed.
In another construction, a plurality of heaters having different surface areas from each other are arranged in the liquid flow path, and the driven heaters or the number thereof is changed to change the ink discharge amount.
However, several problems are involved in implementing the ink jet recording apparatus having variable discharge amount.
In one problem, when the ink of small discharge amount is discharged, bubbles are generated by heaters having a small discharge power, that is, having a small heater area. As a result, not only the discharge amount but also the discharge rate are reduced. As an important matter, a problem may occur in connection with the predischarge which is conducted as a part of the discharge recovery process. In the predischarge, the ink which does not serve to the printing is discharged from the ink jet head at a predetermined position in the apparatus. Thus, the high viscosity ink in the ink jet head is removed and a good ink discharge condition may be maintained. The predischarge is normally conducted immediately after the power-on of the apparatus and periodically during the printing.
However, when the printing is made at the small discharge amount getting, it is necessary to shorten the predischarge interval. If the interval is too long, the high viscosity ink may not be stably discharged depending on the condition of the viscosity of the ink due to the evaporation of the water at the orifice because the power of the small discharge ink droplets is low. As a result, it is necessary to shorten the predischarge interval periodically conducted during the printing and the throughput of the printing is lowered.
As another problem, when the printing is made at the small discharge amount setting, the resolution is raised, the amount of image data is increased and the print dots are increased so that the print speed cannot be increased unless the discharge repetition frequency is raised.
The problems described above significantly depending on the type of ink.
SUMMARY OF THE INVENTION
It is an object of the present invention to significantly improve the refill frequency over the prior art by re
Koitabashi Noribumi
Tsuboi Hitoshi
Brase Sandra
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
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