Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
2003-01-16
2004-11-30
Pham, Hai (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S238000
Reexamination Certificate
active
06825865
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a printer used for forming images on a photosensitive recording medium by a photosensitive system.
2. Description of the Related Art
An image captured by a digital camera, for example, can be formed on an ordinary paper based on the digital data by an ink jet system or a thermal transfer system. It is also considered to record such an image on a photosensitive film based on the digital data by a photosensitive system. In the photosensitive system, an image is formed by exposing a photosensitive film to light followed by developing the film. Therefore, an image forming apparatus utilizing this system can be made compact relatively easily as compared with one utilizing the ink jet system or the thermal transfer system. For this reason, a digital camera has been commercially introduced which incorporates a print head of a photosensitive type for printing an image immediately after capturing the image. For easier carriage of the digital camera, it is necessary to reduce the size of the print head as well as other parts of the camera.
In forming an image on a photosensitive film by the photosensitive system, for example, the photosensitive film is irradiated with light in the form of a line extending in the primary scanning direction and the irradiation region is shifted in the secondary scanning direction for scanning the entirety of the photosensitive film. As the print head for emitting light in the form of a line, use may be made of one including a plurality of light emitting elements (point light sources) aligned in a row extending in the primary scanning direction. As the light emitting elements, light emitting diodes are typically used. However, organic EL light emitting elements may alternatively be used. An organic EL element means an element which emits light by electroluminescence when electric field is applied to a light emitting layer containing an organic material.
However, light emitting elements deteriorate with a lapse of time, reducing the amount of light emitted. Particularly, EL light emitting elements are likely to deteriorate due to the formation of impurities or entering of water in the light emitting layer. Further, the plurality of light emitting elements do not deteriorate to a same degree with a lapse of time and differ from each other in speed of deterioration. Therefore, when one light emitting element deteriorates to a considerably large degree (thereby emitting little amount of light) as compared with others, it is impossible to irradiate the photosensitive film properly with linear light. In such a case, when the print head is moved in the secondary scanning direction to irradiate the entire photosensitive film with light, a portion of the photosensitive film extending in the secondary scanning direction is left insufficiently irradiated with light. This portion appears as a line in the formed image. This also means that a print head has a short lifetime when a light emitting element such as an organic EL light emitting element which is likely to deteriorate is utilized.
Although, an LED is unlikely to deteriorate as compared with an organic EL light emitting element, its power consumption is disadvantageously higher than that of the organic EL element. Therefore, when a plurality of LEDs are used as a light source of a print head, its power consumption becomes high. Since the printer of a digital camera as a portable device typically uses a low-capacity dry cell or rechargeable battery as the light source, the power consumption need be decreased.
SUMMARY OF THE INVENTION
The present invention aims to provide a print head for irradiating a photosensitive recording medium with light, which is firstly capable of preventing deterioration of a formed image due to the degradation of the light source for forming a proper image, which secondly has a long lifetime, and which thirdly has a small size and low power consumption.
According to the present invention, there is provided a print head comprising an illuminator for emitting light in a line extending in a primary scanning direction, a liquid crystal shutter for selecting whether or not light traveling from the illuminator is allowed to pass and, and a light emitting portion for emitting light traveling from the liquid crystal shutter toward a photosensitive recording medium.
With such a structure, after light emitted from the illuminator becomes incident on the liquid crystal shutter, the light passing through the liquid crystal shutter is emitted from the light emitting portion. Thus, the liquid crystal shutter can define the state of light (amount, wavelength and the like) to be emitted from the light emitting portion. Therefore, even when the light source device includes a portion emitting a smaller amount of light, for example, and hence variation exists in the amount of light, the liquid crystal shutter can eliminate such variation.
For example, the liquid crystal shutter may include a plurality of individual shutter portions aligned in the primary scanning direction. In this case, each of the shutter portions is capable of individually selecting whether or not the light traveling from the illuminator is allowed to pass.
For example, the illuminator may emit light (e.g. white light) which includes red light, green light and blue light. Specifically, the illuminator may be provided with a light emitting portion in the form of a strip extending in the primary scanning direction or a plurality of point light emitting portions aligned in a row extending in the primary scanning direction. For performing color printing using such an illuminator, the plurality of shutter portions may include a plurality of first shutter portions aligned in a row extending in the primary scanning direction for selectively passing red light, a plurality of second shutter portions aligned in a row extending in the primary scanning direction for selectively passing green light, and a plurality of third shutter portions aligned in a row extending in the primary scanning direction for selectively passing blue light.
The liquid crystal shutter may include a plurality of first electrodes arranged adjacent to each other, a plurality of second electrodes arranged adjacent to each other and extending transversely to the first electrodes, and a liquid crystal layer provided between the first electrodes and the second electrodes. In this case, the transverse portions of the first and the second electrodes correspond to the first through the third shutter portions.
With such a structure, for irradiating the photosensitive recording medium with red light for example, a shutter portion through which red right is to pass is selected from the first shutter portions depending on the image to be formed, and light is allowed to pass through the selected first shutter portion. For the selected first shutter portion, a voltage is applied to the liquid crystal between the first electrode and the second electrode constituting the first shutter portion. At that time, when a non-selected first shutter portion through which red light should not pass exists adjacent to the selected first shutter portion, a potential difference is generated between the adjacent first electrodes or between the adjacent second electrodes constituting these shutter portions. Such a potential difference is more likely to be generated as the distance between the electrodes (between adjacent shutter portions) decreases. When the potential difference is generated between the adjacent electrodes, the alignment of liquid crystal nearby is disturbed. As a result, the light component of green light or blue light, for example, may unintentionally pass through the liquid crystal shutter.
For dissolving such a problem, it is preferable that the first shutter portions, the second shutter portions and the third shutter portions are respectively arranged in a plurality of rows, and that the shutter portions in each row are disposed in staggered relationship with the shutter portions in an adjacent
Fujimoto Hisayoshi
Koshio Minori
Onishi Hiroaki
Takakura Toshihiko
Pham Hai
Rohm & Co., Ltd.
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