Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2002-05-29
2003-11-04
Nguyen, Judy (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S081000, C250S573000
Reexamination Certificate
active
06641246
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a technique for inspecting inkjet nozzles to detect a non-operating nozzle.
2. Description of the Related Art
In an ink-jet printer, ink droplets are ejected from a plurality of nozzles provided at a print head. Some of the nozzles occasionally get clogged and are rendered incapable of ejecting ink droplets because of an increase in ink viscosity, formation of gas bubbles in an ink passage, and other factors. Nozzle clogging produces images with missing dots and has an adverse effect on image quality. Nozzle inspection is therefore desired to detect a non-operating nozzle. Nozzle inspection will also be referred to herein as “dot loss inspection.”
Numerous methods are used to inspect the nozzles of ink-jet printers, and light-based inspection is one such method. In this method, light is emitted by a light-emitting element toward a light-receiving element, ink droplets are sequentially ejected from the nozzles of the print head in the direction of this light, and the operating state of each nozzle is determined based on whether the light is actually blocked by the ink droplets ejected from the nozzles. In this type of inspection, light is focused with a lens.
Because light is focused by a lens, the thickness of the light beam is at its minimum at a certain point on the optical path and increases in the direction away from this point. For this reason, inspecting conditions differ greatly for the inspected nozzles disposed in the vicinity of the location (beam waist) at which the light beam has minimal thickness and the inspected nozzles disposed farther away from the beam waist because of their position on the print head.
A technique featuring two parallel laser beams whose beam waists are shifted along the optical path is disclosed in JPA 10-119307 as a means of addressing these problems. According to this technique, each of the two laser beams is used in nozzle inspection, and the plurality of nozzles being examined is divided between the two beams of laser light. As a result, the nozzles are inspected under more-uniform conditions than that when a single beam of laser light is used. However, this technique still fails to adequately resolve the above-described variations in the inspecting conditions along the optical axis of laser light.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention, is to provide a technique whereby a non-operating nozzle can be detected with higher accuracy.
In order to attain at least part of the above and related objects of the present invention, there is provided a printer for printing images by ejecting ink droplets from a plurality of nozzles. The printer comprises a print head having a plurality of nozzles; and a sensor including a light-emitting element configured to emit detection light which has a substantially circular cross-section and a light-receiving element configured to receive the detection light, and configured to inspect operation of a nozzle by determining whether the detection light has been blocked by the ink droplets ejected by the nozzle. The sensor further comprises a first condensing element configured to condense the detection light, and an apertured element having a substantially circular aperture for the detection light. The aperture has a size of a same order as the cross-section of the detection light. The detection light intersects an ejecting path of the ink droplets at an exit side of the apertured element and the first condensing element.
In the printer in accordance with the present invention, a light-emitting element, a first condensing, an apertured element and a light-receiving element are provided. The light-emitting element is configured to emit detection light. The first condensing element is configured to condense the detection light. The apertured element having an aperture for the detection light. The light-receiving element is configured to receive the detection light after the detection light intersects a path of the ink droplets ejected by a nozzle. Then the detection light is emitted from the light-emitting element. Ink droplets are ejected from a nozzle. A non-operating nozzle is detected by determining whether the detection light received by the light-receiving element has been blocked by the ink droplets.
Adopting such an arrangement allows the light beam for detecting ink droplets to be constricted through the aperture. At the same time, the narrowest portion of the light beam can be expanded because of a reduction in the angle at which the light is focused. In other words, the thickness of the light beam can be made more uniform along the optical axis. It is therefore possible to reduce variations in the inspecting conditions along the optical axis of the light beam and to inspect the ejection of ink droplets with higher accuracy.
The apertured element may comprise a regular polygonal aperture having four or more angles. These apertures make the cross-section of the light substantially circular. It is more preferable that the apertured element comprises the regular polygonal aperture having six or more angles. Such aperture makes the cross-section of the light nearer circular.
The apertured element is preferably disposed at an exit side of the first condensing element. Minute ink droplets are scattered when an ink droplet is ejected in inspection. But adopting the above-described arrangement allows the scattered ink droplets to be blocked by the apertured element, and makes it less likely that the condensing element will be contaminated. The first condensing element may be disposed at an exit side of the aperture of the apertured element.
The sensor preferably further comprises an angle-adjusting element configured to adjust a direction of emission of the detection light. This allows the direction of the detection light to be adjusted for more-uniform conditions for inspecting the ejection of ink droplets by each nozzle.
The sensor preferably further comprises a position-adjusting element configured to adjust a position of the light-emitting element in a direction intersecting the direction of emission of the detection light. Such an arrangement allows the position of the light-receiving element to be adjusted such that the light-receiving element can accurately receive light when the position of the light emitting element has the deviation.
When the plurality of nozzles are disposed on a same nozzle plane of the print head, the angle-adjusting element is preferably configured to adjust the direction of emission of the detection light within a plane perpendicular to the nozzle plane. Adopting this arrangement allows the direction of emission of the detection light to be adjusted such that the optical axis remains parallel to the nozzle plane.
The angle-adjusting element preferably adjusts the direction of emission of the detection light about an axis intersecting an optical path of detection light within confines of the aperture. Adopting this arrangement allows the center position of the detection light in the aperture to remain constant when the direction of emission of the detection light is adjusted.
The sensor preferably further comprises a first ink mist screen having a first aperture for the detection light. The first ink mist screen is disposed at an exit side of the first condensing element and the apertured element, and divides a first area including the light-emitting element, the first condensing element, and the apertured element, and a second area in which the ink droplets are ejected in a direction of an optical path of the detection light.
Adopting this arrangement allows the first ink mist screen to prevent the light-emitting element or the condensing element from the deposition of the ink mist produced during the ejection of ink droplets by the nozzles. The light-emitting element and first ink mist screen are therefore less likely to suffer reduced performance, and the ejection of ink droplets can be inspected with consistent accuracy when the sensor is operated for a long t
Asawa Hiroshi
Endo Hironori
Matsumoto Hitoshi
Mouttet Blaise
Nguyen Judy
Seiko Epson Corporation
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