Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Patent
1998-10-13
2000-12-12
Sikes, William L.
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
349 2, 349 22, 345103, 347224, G02F 11343, G02F 113, G02F 1133, G09G 336, B41J 2435
Patent
active
061606030
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a liquid crystal laser marker using a liquid crystal mask and a marking method using the same.
BACKGROUND ART
One of the widely used laser markers that provide a laser beam for marking characters or figures on workpieces, such as semiconductor packages, is a so-called liquid crystal laser marker using a liquid crystal mask. In the liquid crystal laser marker, a design of the characters or figures to be marked is converted to dot information, e.g., where "0" indicates an unmarking portion and "1" indicates a marking portion, and is displayed on the liquid crystal mask having a given number of pixels in accordance with the dot information. Then a laser beam is directed to be incident on the liquid crystal mask and is transmitted through the pixels, corresponding to the characters or figures, to the surface of a workpiece so that the workpiece will be marked with the transmitted laser beam. Therefore, the more the number of pixels of the liquid crystal mask increases per unit area of the workpiece, the more the characters or figures can be marked smoothly with high resolution.
A conventional marking method for such a liquid crystal laser marker will be described with respect to FIGS. 14 to 17.
FIG. 14 is a schematic diagram showing an exemplary structure of the liquid crystal laser marker. In FIG. 14, the laser oscillator 21 can be a YAG laser oscillator, the output of which is a pulse train driven by a Q switch. A first deflector 23X, 23Y conducts the laser beam from the laser oscillator 21 to a liquid crystal mask 2 while deflecting it in given X and Y directions so that the liquid crystal mask 2 will be raster scanned. The first deflector comprises of an X-directional deflector or polygonal mirror 23X and a Y-directional deflector or galvanometer scanner 23Y, provided separately from each other. Such scanning directions, i.e., the X-axis scanned by rotating the polygonal mirror 23X and the Y-axis scanned by moving the galvanometer scanner 23Y, intersect at right angles. The polygonal mirror 23X is rotatable in several constant speed rotation modes, and the rotation mode is selected for each workpiece to be marked. Each plane of the polygonal mirror 23X corresponds to one line in the X-direction on the liquid crystal mask 2. On the other hand, the galvanometer scanner 23Y is operable with given steps of minute, equiangular deflections, and moves only by a minute deflection angle and stops there as the light-receiving point of the laser beam from the galvanometer scanner 23Y is changed from one plane to another by the rotation of the polygonal mirror 23X. Each of the minute deflection angles corresponds to one line feed in the Y-direction on the liquid crystal mask 2.
As shown in FIG. 15, the liquid crystal mask 2, called a transmission dispersion type liquid crystal mask, can be a liquid crystal device in which a given number of liquid crystal elements are arranged in a dot matrix. The liquid crystal elements constituting the liquid crystal mask 2 have the same size. Further, electrode lines, not shown, are arranged on both sides of the liquid crystal elements so as to be parallel on each side and to perpendicularly intersect between both sides. The electrode lines apply a given voltage to certain or specific liquid crystal elements to place them in a laser-beam transmission state. The other liquid crystal elements to which no voltage is applied are in a laser-beam scattered state. The liquid crystal elements arranged in the dot matrix are used as the pixels 3 of a design to be marked. Each of the pixels 3 is converted to dot information "0" or "1", where "0" indicates an unmarking portion and "1" indicates a marking portion. The given voltage is applied to the pixels 3 corresponding to the portions to be marked such dot information is displayed on the liquid crystal mask 2, so that the laser beam will be transmitted therethrough, thus marking a workpiece with the transmitted laser beam. As discussed above, the liquid crystal mask 2 serves as a light shutter for
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Ohkubo Tsuyoshi
Tanaka Hirokazu
Yamazaki Taku
Chowdhury Tarifur R.
Komatsu Ltd.
Sikes William L.
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