Drying and gas or vapor contact with solids
Reexamination Certificate
2000-04-19
2001-12-04
Tran, Huan (Department: 2861)
Drying and gas or vapor contact with solids
C347S187000
Reexamination Certificate
active
06325474
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device for writing on thermographic material. This device includes a heater for pre-heating the thermographic material to a temperature below a writing temperature required for writing on the thermographic material, and a writing instrument for writing on the thermographic material according to a predefined information signal s(t), wherein the writing instrument is spaced apart from the thermographic material.
2. Description of the Related Art
A device of this type is described in EP 0 734 870 A2. This known device preheats a thermographic material using a heater in form of a rotatably supported heater drum to a temperature below a writing temperature of the thermographic material. The pre-heating step, however, is designed to not induce writing on the thermographic material. The light beam of a single laser is projected on the thermographic material using an optical device. The laser is modulated with an information signal. The thermographic material includes a layer for converting radiation energy into thermal energy. When the modulated laser beam impinges on this layer, thermal energy corresponding to the information signal is produced in the thermographic material. The thermal energy is superimposed on the thermal energy produced by the pre-heating step, thereby exceeding the writing temperature of the thermographic material. The thermographic material is thereby blackened with a density variation corresponding to the information signal modulating the laser. The blackening of the thermographic material occurs row-by-row, with the pixels of the row being blackened consecutively. The optical device projecting the laser beam on the thermographic material has a polygon mirror which rotates at a very high rotation speed. The laser beam is reflected by the polygon mirror, so that the entire row of the thermographic material can be blackened by the laser beam. The laser beam is aimed from one end of the row of the thermographic material to the other end. To blacken the next row of the thermographic material, the heater drum and thus also the thermographic material are rotated by another row width.
The known device requires a complex mirror and lens arrangement for focusing and steering the laser beam to write the entire row. Since the required optical path is quite long, it may not be possible to accurately steer the laser beam. Moreover, the polygon mirror must be adjusted and supported very precisely and also has to rotate at an extremely high rotation speed so that the material can be blackened in a sufficiently short time.
EP 0 424 175 A2 describes a device for exposing photosensitive material.
This device has a plurality of individually addressable light emitting diodes (LED) arranged side-by-side, so that the light sensitive material can be exposed pixel-by-pixel. A lens arrangement is placed between the LED's and the photosensitive material to focus the light beams emitted by the LED's. The known exposure device can eliminate intensity variations between adjacent pixels by transmitting an identical light energy to the pixels in a region of the light sensitive material. LED's emit light at very low energy and can therefore not be used to write on thermographic material.
It is therefore the object of the present invention to provide a compact device based on conventional devices, which makes it possible to write on thermographic material in a simple manner.
SUMMARY OF THE INVENTION
The device according to the invention for writing on thermographic material includes a writing device having a plurality of individually addressable point sources, wherein the point sources can be used to write on the thermographic material pixel-by-pixel based on a specified information signal.
The invention advantageously obviates the need for a polygon mirror. Since the writing instrument is spaced apart from the thermographic material, the writing instrument does not directly contact the material, thereby preventing damage and abrasion of the writing instrument as well as of the thermographic material.
At least a portion of the individually addressable point sources can be addressed at the same time, so that writing on the thermographic material is very fast, since the points of the thermographic material associated with the simultaneously addressed point sources can be written almost simultaneously. The pixel may also be written over a longer time period, thereby increasing the response time for each individual point source for writing the pixel associated with the point source. As a result, the power to be produced by each point source for writing the pixel associated with the point source can advantageously be kept small, because the respective point source has more time to write the pixel. Moreover, the required response time required by the respective point source to react to a change in the signal setting can be relatively long. Consequently, a less complex technology can be used for implementing the point sources.
In an advantageous embodiment of the invention, each of the individually addressable point sources includes a laser. During operation of the device of the invention, the laser emits a laser beam which impinges on the layer of the thermographic material which converts the radiation energy of the laser beam to thermal energy. Advantageous, lasers provide sufficiently high power and can be easily modulated with a signal source.
Advantageously, several point sources can be connected in parallel so as to commonly write a single pixel of the thermographic material. The power to be produced by each of the point sources connected in parallel for writing the associated pixel on the thermographic material can thereby be reduced according to the number of point sources connected in parallel.
According to another advantageous embodiment of the invention, means for controlling the radiation energy emitted by the point sources are disposed between the writing instrument and the thermographic material. In the case where each of the point sources includes a single laser, the means for controlling the radiation energy is simply an optical lens. In this way, the beam path of the emitted radiation energy of the individual point sources can be corrected so that the radiated energy, in particular when the point sources are connected in parallel, is concentrated in the associated pixel of the thermographic material.
In a particularly advantageous embodiment of the invention, where each of the point sources includes one respective laser, the lasers are arranged in two rows on a semiconductor material, wherein the lasers of one row are offset relative to the lasers in the other row. In this way, the lasers are sufficiently spaced apart during manufacture so that the semiconductor material can be separated between two lasers. This approach considerably simplifies the fabrication of the writing instrument for a suitable number of lasers.
Advantageously, heating is provided in the form of a rotatably supported, inductively heated drum. A first and second pressure roller can be employed to press the thermographic material against the drum. The writing instrument is arranged so that the emitted radiation of the individual point sources of the writing instrument impinges on the thermographic material between the two pressure rollers. By pressing the thermographic material against the drum, the thermographic material is heated during the writing step which significantly simplifies the writing process of the thermographic material. The lasers need only supply a low power. In addition, the two pressure rollers can also be used to guide and advance the thermographic material.
At least one additional pressure roller may advantageously be placed before the first pressure roller. In this way, the thermographic material is pre-heated for a longer time before being written by the laser, so that even a relatively low heating temperature of the drum produces a sufficiently high pre-heating temperature in the therm
Betzold Wolfram
Gebele Herbert
Hoogmartens Ivan
Kappeler Franz
Leenders Luc
AGFA Gevaert AG
Darby & Darby
Tran Huan
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