Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1999-11-03
2002-03-19
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S014000
Reexamination Certificate
active
06357849
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a technique of ejecting ink droplets to implement printing.
2. Description of the Related Art
FIG. 33
shows a positional relationship between an ink ejection detector and a head in a prior art ink jet printer. In an ink jet printer with a head
801
that has a plurality of nozzle arrays
802
,
808
to eject ink droplets, an ink ejection detector (a light-emitter
803
and a light-receiver
804
). is generally used to detect failure of ink ejection from each nozzle, because of clogging of the nozzle or shortage of ink. In
FIG. 33
,
805
shows a light sensor sensitive area and the head
801
moves along an arrow
813
.
The prior art ink ejection detector carries out detection of ink ejection for each nozzle. Every time failure of ink ejection is detected, because of the clogging of the nozzle, the ink jet printer requires a specific operation to prepare for resumption of ink ejection with recovery means. While in the case of shortage of ink, a new supply of ink is required for resumption of ink ejection. Accordingly a fairly long time is required to implement detection of ink ejection with regard to all the nozzles or any arbitrary nozzle array. The one-by-one nozzle detection technique takes a long time to complete detection for a large number of nozzles, and requires higher sensitivity for the ink ejection detector as nozzle density increases.
SUMMARY OF THE INVENTION
The object of the present invention is thus to provide an ink jet printer that is able to detect ink ejection from nozzles with high-accuracy.
In order to attain the above object, an ink jet printer according to the present invention comprises a carriage configured to be able to reciprocate relative to a printing medium, and a plurality of nozzle arrays mounted on the carriage to eject ink droplets, wherein the ink jet printer further comprises light detection unit scans the plurality of nozzle arrays at a predetermined angle relative to a columnar direction of the nozzle arrays, wherein the angle is attained by a clockwise or a counterclockwise rotation about a center of each nozzle array.
The light detection unit may include a light sensor that is disposed at a specific position so that light is scattered by ink droplets ejected from each nozzle array.
The light detection unit may be disposed at the predetermined angle, so that a sensitive area of the light sensor is fully utilized with regard to each nozzle array.
The light detection unit may have an optical axis arranged at a preset angle relative to a head nozzle surface.
Since the arrangement of the present invention carries out detection of ink ejection on an array-by-array basis in the ink jet printer, even if there are a plurality of nozzles that do not eject ink in one nozzle array, because of the clogging, the present invention use recovery means once for each array but not once for each nozzle, thereby shortening a time period from detection of ink ejection failure to its recovery with the recovery means.
Further, the inclination of the optical axis of the light detection unit (ink ejection detector) at the predetermined angle relative to the nozzle arrays, increases the light-shielding area of the sensor of the light detection unit. This improves the sensitivity of the sensor and effects high accuracy detection of ink ejection without requiring any highly sensitive ink ejection detector, even if there exist a large number of nozzles.
The present invention is also directed to an ink jet printer comprising a print head having a plurality of nozzles in arrays for ejecting ink droplets, a carriage for reciprocating the print head relative to a printing medium, and a light detection unit for detecting an ejection state of each nozzle, wherein the light detection unit includes a light-emitting element and a light-receiving element, where an optical axis connecting the light-emitting element with the light-receiving element is arranged at a predetermined angle relative to a columnar direction of the nozzles.
It is preferable that the light detection unit has a sensitive area within a predetermined distance from the optical axis, in which ink droplets are detected, and that the light detection unit is arranged at the predetermined angle relative to the columnar direction of the nozzles in order to cause nozzles on both ends of each nozzle array, among the plurality of nozzles, to be within the sensitive area.
The ink light detection unit may be arranged at a home position of the print head, or may alternatively be disposed on either one of the print head and the carriage with the print head mounted thereon. In the former case, it is preferable that the home position is also a position of blind ejection for recovery of the nozzles.
In order to attain at least part of the above objects, the present invention carries out inspection of nozzles for ejection of ink droplets with regard to an ink jet printer (printing apparatus) as discussed below. In the description hereof, the inspection for ejection of ink droplets is referred to as the ‘dot dropout inspection’. The present invention is directed to an ink jet printer that ejects ink droplets and thereby implements printing. The ink jet printer includes a print head having a plurality of nozzles, from which ink droplets are ejected, a light detection unit (inspection unit) that has a light emitting element for emitting a light beam and a light receiving element for receiving the light beam emitted from the light emitting element and determines the active or inactive state of the nozzles based on whether or not the light beam is intercepted by ink droplets, and a carriage (feeding mechanism) that moves at least one of the print head and the light detection unit, so as to move the print head relative to the light detection unit. At least part of the plurality of nozzles are inspected while the print head moves relative to the light detection unit.
This arrangement ensures the higher-speed inspection of the plurality of nozzles for ejection, compared with the prior art structure that carries out the inspection for ejection while the light detection unit and the print head are at a stop. This accordingly shortens the time period required for the inspection for ejection. In the prior art structure that repeats the feed and the stop of the light detection unit or the print head for the inspection of the plurality of nozzles for ejection, the repeated feed and stop may increase the mechanical errors. The arrangement of the present invention, however, carries out the inspection of the plurality of nozzles for ejection of ink droplets while either the light detection unit or the print head is moved, thereby having no such problems.
It is preferable that the print head moves relative to the light detection unit at a fixed speed. In this arrangement, the timecan be readily estimated, when an ink droplet passes through the light beam in the process of inspection for ejection of ink droplets.
In one preferable application of the present invention, the plurality of nozzles constitute at least one nozzle array and arranged in the array at a fixed nozzle pitch in a predetermined alignment direction. In this application, the light beam is emitted in a specific direction having an angle &thgr; relative to the predetermined alignment direction (where &thgr; is greater than 0 and less than 180 degrees). It is further preferable that ink droplets are ejected towards the light beam while the print head is moving relative to the light detection unit at the fixed speed.
In this application, the movement of either the print head or the light detection unit causes the nozzle array to relatively pass through the light beam having the predetermined angle &thgr; relative to the nozzle array. In the case where the alignment direction of the nozzle array is coincident with the optical axis of the light beam, all the nozzles included in the nozzle array simultaneously intersect the optical path of the light beam. The preferable application of the present
Endo Hironori
Saruta Toshihisa
Takizawa Jinichi
Tojo Hiroaki
Barlow John
Beyer Weaver & Thomas LLP
Dudding A.
Seiko Epson Corporation
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