Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1998-03-09
2001-03-27
Nguyen, Thinh (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S065000, C347S071000
Reexamination Certificate
active
06206501
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an ink jet recording head having a plurality of nozzle openings disposed in a sheet forwarding direction, with each nozzle opening jetting an ink droplet due to pressure provided by a pressure producing chamber. More particularly, the invention is directed to a nozzle opening arrangement on the ink jet recording head.
2. Description of the Related Art
Ink jet recording heads are widely used throughout the printing industry. Such ink jet recording heads exhibit high recording density, are capable of printing dots of various sizes, and are relatively quiet during operation.
Two basic types of ink jet recording heads exist. A bubble jet type recording head uses thermal energy provided by a heater to effect printing. On the other hand, in a piezoelectric vibration element driven recording head, the displacement of piezoelectric vibration elements causes ink to be emitted to effect printing.
Two general types of piezoelectric vibration element driven recording heads exist. In the first type, vertical vibration of the piezoelectric vibration elements causes ink to be emitted. In the second type, flexural vibration of the piezoelectric vibration elements causes ink to be emitted.
In the first type of piezoelectric vibration element driven recording heads, the area in which a piezoelectric vibration element abuts against the vibration plate can be reduced. Hence, the interval between the nozzle opening arrays can easily be made small. However, the process for assembling such a recording head is complicated because each piezoelectric vibration element is extremely small.
The second type of piezoelectric vibration element driven recording heads employs a laminated structure, such as described in Japanese Unexamined Patent Publication No. 4-366643. That is, a common ink supply section, and pressure producing chambers or ink flow paths, are first formed in each of a plurality of thin plate members. These thin plate members are then sequentially laminated on the back of a nozzle plate. Accordingly, the assembly process is simple.
However, in this arrangement, each flow path extending from the pressure producing chamber to the nozzle openings is formed by making communicating holes in each thin plate member, and arranging these communicating holes proximate to one another. Hence, it is difficult to discharge the tiny air bubbles in the ink from the corners of the flow paths formed in each thin plate member.
In addition, in this arrangement, the size of the piezoelectric vibration plate mounted on the pressure producing chamber is larger than that of the piezoelectric vibration plate used as the piezoelectric vibration element in the first type of piezoelectric vibration element driven recording head. Hence, the distance between the nozzle opening arrays is increased.
If the distance between the nozzle opening arrays is increased, error between dots printed on a recording sheet in the auxiliary scanning direction tends to increase if three or more nozzle opening arrays are formed in an attempt to improve printing quality. In this case, however, printing quality is actually reduced.
That is, a recording head having a plurality of nozzle opening arrays is designed so that each nozzle opening array enables a dot to be printed at a predetermined position in the auxiliary scanning direction. As a result, this type of recording head has the uppermost nozzle opening and the lowermost nozzle opening arranged at opposite ends in the main scanning direction. This causes an error of G×sin&thgr; between lines in the auxiliary scanning direction before and after sheet forwarding, assuming that the distance between the nozzle opening array at one end and the nozzle opening array at the other end in the main scanning direction is G, and the angle of inclination between the direction in which the nozzle opening arrays of the recording head extend and the sheet forwarding direction is &thgr;. This error, G×sin&thgr;, causes white lines and black lines to be intermingled during printing, thereby impairing painting quality.
An ink jet recording head designed to eliminate this problem is described in European Laid-Open Patent Publication No. 554907. In this ink jet recording head, four nozzle opening arrays, each having a plurality of nozzle openings linearly pitched in the sheet forwarding direction at an interval corresponding to the number of nozzle opening arrays, have their positions in the main scanning direction staggered by a predetermined interval so as to be different from the physically arranged sequence thereof. This arrangement, which reduces the distance in the auxiliary scanning direction between the uppermost nozzle opening and the lowermost nozzle opening of the recording head, can prevent printing of white lines and black lines due to displacement in the angle &thgr; between the nozzle opening array and the sheet forwarding direction.
However, this advantage is realized only when the number of nozzle opening arrays is four. Hence, such a design is applicable to a limited number of recording heads.
SUMMARY OF THE INVENTION
In view of the above problems associated with conventional ink jet recording heads, an object of the present invention is to provide a laminated type ink jet recording head which minimizes stagnation of air bubbles in its ink flow paths.
To achieve this object, the present invention provides an ink jet recording head that is formed by laminating a plurality of thin plate members having a plurality of ink flow paths partially formed therein. Each ink flow path extends continuously so as to reach a nozzle opening from an ink supply section via a pressure producing chamber. In such an ink jet recording head, communicating holes formed in the respective thin plate members to enable the pressure producing chamber to communicate with the nozzle opening are linearly arranged. As a result of this construction, the ink from the pressure producing chamber can flow without stagnating in the communicating holes in the thin plate members, so that the air bubbles in the ink can be discharged from the nozzle openings effectively.
A second object of the invention is to provide an ink jet recording head which can be employed in a recording head having three or more nozzle opening arrays and which can minimize inter-line distance error to ensure high-quality printing.
To achieve the above objects, the invention provides an ink jet recording head having a plurality of nozzle openings arrays, arranged in an auxiliary scanning direction, which is substantially perpendicular to the main scanning direction. The nozzle opening arrays are divided into three groups and spaced at predetermined intervals in the main scanning direction.
In such an ink jet recording head, nozzle openings of the groups arranged on both sides of a group arranged in the middle of the recording head supplement spaces between these nozzle openings of the middle array. Furthermore, a nozzle opening of the group arranged in the middle is positioned uppermost or lowermost on the face of the print head, so that lines printed by the nozzle openings of the groups arranged on both sides interpose the lines printed by the nozzle openings of the middle group. As a result, the maximum distance between nozzle openings printing adjacent lines in the main scanning direction can be equal or substantially equal to half the maximum distance between the nozzle opening arrays at both sides of the print head. Therefore, inter-line positional error is reduced.
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patent: 5087930 (1
Ishii Takayuki
Kitahara Kohei
Nguyen Thinh
Seiko Epson Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
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