Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reissue Patent
2000-07-14
2001-09-18
Le, N. (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S255000
Reissue Patent
active
RE037376
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to laser scanning and in particular, to scanning of thermal materials, also known as thermographic materials, with high power lasers.
BACKGROUND OF THE INVENTION
With the increased speed of laser scanning systems the exposure time of a single pixel is exceedingly short. This time is sometimes too short for the desired chemical reaction to take place in the material being exposed. Increasing the power does not solve the problem, as it causes the top layer of the material to become too hot and ablate or decompose, while the material below the surface remains cold.
For example, in a modern laser scanner of the internal drum type used to expose thermal printing plates, dwell times as short as 10 nS are used. This exposure time is much shorter than the thermal time constant of the plate active polymer layer, being about 1 &mgr;S for a typical plate. As the exposure time is about 100 times shorter than the thermal time constant, the surface of the polymer has to be heated up to thousands of degrees centigrade to allow the average temperature to be about a hundred degrees (after the heat distributed itself throughout the polymer layer). Such a high peak temperature causes the polymer to decompose or ablate instead of undergoing the desired transformation.
The common solution is to use a multibeam system, as the exposure time of each spot goes up in proportion to the number of beams for a given data rate. Multibeam systems increase the cost of a laser scanner, therefore it is desirable to increase the exposure time of a single beam system. Increasing the exposure time by simply increasing the spot size is not practical due to loss of resolution.
Another object of the invention is to achieve higher utilization of the laser. Thermal imaging systems use high power and expensive IR lasers, typically multiwatt diode-pumped YAG lasers. The present invention enables the use of lasers which are allowed to have poor beam quality in one of the spot dimensions, such as wide area laser diode emitters, which are significantly cheaper than YAG lasers. When multiple light sources are used according to the invention, no intensity matching between the sources is required. This is an advantage over systems using multiple spots in parallel, where intensity match is critical.
SUMMARY OF THE INVENTION
The invention uses a scanning beam imaging a linear array of light sources to form each spot on the material being exposed. The data is shifted serially through this linear array while the array is imaged onto the material in a mode known as Time Domain Integration (TDI). In this mode the total exposure time of each spot on the material is multiplied by the number of light sources (e.g. if the internal drum scanner used in the previous example had ten light sources, the exposure time will go from 10 nS to 100 nS while the system will stay a single beam system). In order to achieve TDI imaging, the rate of shifting the data serially through the array of light spots needs to be matched to the scanning velocity in order to achieve a stationary image of the shifting data on the material being exposed. The TDI mode of imaging is well known in imaging sensors, such as Charge Coupled Devices (CCD), where it is used to increase sensitivity by integrating the light into a longer exposure without the loss of resolution. The same light integrating property of TDI scanning is used by the present invention, in a single scan line configuration, to increase the exposure time without loss of resolution. The invention and multiple ways of using it will become apparent after considering the preferred embodiment in conjunction with the drawings.
REFERENCES:
patent: 3750189 (1973-07-01), Fleischer
patent: 4206482 (1980-06-01), De Lavalette et al.
patent: 4348593 (1982-09-01), Seachman
patent: 4357627 (1982-11-01), Johnson
patent: 4595957 (1986-06-01), Holthusen
patent: 4639073 (1987-01-01), Yip et al.
patent: 5049901 (1991-09-01), Gelbart
patent: 5132723 (1992-07-01), Gelbart
patent: 6025864 (2000-02-01), Nashimoto
Creo Products Inc.
Le N.
Oyen Wiggs Green & Mutala
Vo Anh T. N.
LandOfFree
Method for rapid imaging of thermographic materials by... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for rapid imaging of thermographic materials by..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for rapid imaging of thermographic materials by... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2441661