Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
2003-07-18
2004-12-28
Pham, Hai (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S239000
Reexamination Certificate
active
06836284
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates in general to the non-destructive pulsed laser marking of objects in a pattern defined by a digital micro-mirror device. The laser energy induces a color change in a radiation sensitive material that is contained in the object without damaging the object.
2. Description of the Prior Art
It is well recognized that ultraviolet and visible light lasers are suited to marking objects by reason of causing color changing reactions in a radiation sensitive material that is included within an object. The radiation sensitive material strongly absorbs the laser energy and undergoes a color change. Except for the energy absorbing material the object preferably absorbs very little of the laser energy. Infrared lasers generally tend to damage the objects because the energy is adsorbed and heats the object. Generally, infrared lasers are not used for non-destructive marking purposes. See, for example, Mercx et al., U.S. Pat. No. 6,214,916, and Faber et al. U.S. Pat. No. 5,489,639.
It is well recognized that pulsed UV lasers find application in the marking of titanium dioxide containing substrates. See, for example, Murokh U.S. Pat. No. 6,429,889 (consumable articles). See also, U.S. Pat. Nos. 5,501,827, 5,091,284, 5,415,939, 5,697,390, 5,111,523, 4,595,647, 4,753,863, 4,769,310, 5,030,551, 5,206,280, 5,773,494, and 5,798,037. Laser marking in the ultraviolet region causes a color change, typically, by photochemical reaction. It is customary to use masks of one description or another between the laser and the substrate to be marked. The mask serves to define the pattern of the coherent UV light that impinges upon the substrate, and, thus, the image that is recorded on the substrate. Alternatively, controlled beam deflection produces images one dot at a time, roughly comparable to a conventional dot matrix printer. See, for example, Faber et al. U.S. Pat. No. 5,489,639. Typically, the titanium dioxide in the substrate is white, and it turns black when coherent UV energy of at least a minimum flux density impinges on it in the pattern defined by the mask.
The use of pulsed laser energy to mark ceramics and glasses that contain radiation sensitive inorganic pigments is known. See, for example, Gugger et al. U.S. Pat. No. 4,769,310.
Pulsed lasers deliver very short but powerful bursts of energy. The duration of a typical pulse is from approximately 5 to 100 nanoseconds at as much as several megawatts of power. Many substances degrade at high levels of coherent UV or visible flux density if they absorb any significant amount of the coherent energy. Typically, titanium dioxide is present in a substrate material that is substantially UV transparent and does not absorb any significant amount of the UV energy. Titanium dioxide absorbs UV energy and undergoes a photochemical reaction so that it changes color from white to black. It is thus possible to mark titanium dioxide containing substrates with coherent UV energy without degrading the substrate to any visible degree. Other substrates are designed to absorb UV energy so as to prevent its reflection from the absorbing substrate. The titanium dioxide in the UV transparent substrate changes color at a level of coherent UV flux density that is at or above the level at which the typical UV absorbing substrate degrades significantly. The use of pulsed coherent UV energy at a controlled flux density combined with titanium dioxide in a visible part of the object permits objects to be marked without causing visible physical degradation to the object. See particularly, Murokh U.S. Pat. No. 6,429,889. Where the marking is made visible by reason of the physical degradation of the object (as by ablation, melting or burning) high levels of flux density are employed, the coherent marking energy is generally supplied in the visible or infrared regions, and the substrate that suffers ablation absorbs the coherent energy.
The energy absorbing characteristics of natural and synthetic silicon and organic plastic materials are well known and need not be repeated here. Where coherent ultraviolet energy is employed to generate the desired marking, the substrate material from which the object to be marked is made should be selected so that does not absorb enough ultraviolet energy to cause ablation, thermochemical reaction, melting, vaporization, or other visible degradation.
Conventional laser marking systems generate the desired marking pattern using masks, linear marking, or dot matrix methods. The linear marking and dot matrix methods require careful coordination between the movement of the object to be marked and the laser beam. If the mask is moving so as to generate different patterns, the same careful coordination is required.
Digital micro-mirror devices (DMD) are well known. Typically, a digital micro-mirror device consists of an array of tiny mirrors (typically, several million per square inch), wherein the angular position of each mirror element is individually controllable between at least two positions that are angularly off from one another by approximately 10 to 20 degrees. A mirror base is located behind the mirror elements. The individually addressable mirror elements are tiltably mounted on mechanical hinges, and typically the array of mirror elements overlays a layer of controlling circuitry in the mirror base, all of which is mounted on a semiconductor chip. The mirror face of a DMD is composed of a generally rectangular grid array of the tiny rectangular mirror elements. A typical mirror element is about 16 micrometers square, and the individual elements are separated from one another by a distance of about 1 micron. Because of these separations, a portion of any energy that falls on the mirror face will bypass the mirror elements and fall on the mirror base. Individually controlled tilting of the mirror elements in the array around at least one axis allows energy that is reflected from the mirror face to be formed into a predetermined pattern. Further, the mirror face can be substantially instantaneously reconfigured responsive to digital signals to form a different pattern. Such reconfiguration generally requires approximately 25 microseconds. Digital micro-mirror devices have been proposed for use in high-resolution projectors. Proposals have been made to utilize these characteristics of a digital micro-mirror device in printing using generally continuous, visible, and non-coherent light. See, for example, Florence et al. U.S. Pat. No. 5,461,411, and Allen et al. U.S. Pat. No. 6,414,706. It has also been proposed to use a DMD to define a pattern of ultraviolet light on a substrate to catalyze a chemical reaction on the substrate in the pattern formed by the light. See Garner U.S. Pat. No. 6,295,153.
There are spaces between the adjacent edges of the individual mirror elements in the mirror array on the mirror face of a DMD so as to allow them the freedom to tilt independently responsive to commands by the control circuitry. Radiant energy that bypasses the individual mirror elements impinges on the base, including the controlling circuitry, hinges and supporting substrate below the mirror face. This bypass radiant energy should be absorbed, reflected away from the target substrate, or conducted elsewhere so that its random reflection does not blur the intended image that is reflected from the mirror face to the intended target. Absorption of the bypass energy causes an undesired build up of heat in the base. Also, particularly with coherent UV energy, the structure and circuitry below the mirror face tends to be damaged or disrupted by high levels of absorbed bypass radiant energy. There is a maximum acceptable level of absorbed bypass energy flux that can be tolerated by a DMD. Above this level, the DMD is at significant risk of failure.
The maximum level of coherent energy flux density that a DMD can tolerate is generally substantially below the minimum level of coherent energy flux density that is required to cause titanium dioxide or other radiation sensitive marking
Filatov Sergey
Kerner Alex
Murokh Igor
Jagger Bruce A.
Pham Hai
Tri-Star Technologies
LandOfFree
Laser marking using a digital micro-mirror device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Laser marking using a digital micro-mirror device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Laser marking using a digital micro-mirror device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3290617