Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Patent
1996-05-28
1999-03-02
Yockey, David F.
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
347258, B41J 247
Patent
active
058778004
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to apparatus and methods for optical data recording, and relates particularly, though not exclusively, to dye thermal transfer printing.
BACKGROUND OF THE INVENTION
In dye thermal transfer printing, heat is applied to selected pixel areas of a dyesheet to cause dye to transfer from the heated areas to form printed pixels on an adjacent dye receiver sheet and thereby form a printed image.
Laser diodes are often chosen as the heat source, as they are inexpensive, reliable and compact. In typical printing apparatus, the output beam from a single laser diode is intensity modulated as it is scanned across the dyesheet, and each scan prints a line of pixels to the receiver sheet. The beam may be modulated merely on or off, so that a pixel is either printed or not, or the beam intensity may be varied over a range of values to vary the amount of dye transferred from a pixel area and provide pixels of varying tones to allow for continuous tone printing.
Laser diodes, however, typically emit light from an elongate stripe area, and so the beam quality is asymmetric, the output beam having a high divergence in the axis of the stripe's width and a low divergence in the axis of the stripe's length. A problem with laser diodes then is that, although the beam may be focused quite readily to a relatively high resolution in its high divergence axis, it is more difficult to do this in the low divergence axis, and so high overall resolution is difficult to achieve.
A further problem of the above apparatus is that the print speed is low, because each pixel must be individually printed in turn. Also, the beam-scanning optical assembly is complex and increases the costs and size of the apparatus, whilst reducing reliability.
One way of increasing print speed, and of simplifying the scanning assembly, is to arrange a plurality of laser diodes into an array, and to intensity modulate each laser diode individually while scanning the output beams together across the dyesheet. This then allows a plurality of pixel lines to be printed simultaneously. The use of a plurality of laser diodes, however, itself, adds to the expense and complexity of the apparatus.
SUMMARY OF THE INVENTION
From a first aspect, the present invention provides data recording apparatus comprising a laser diode which, in use, emits a light beam from an elongate stripe area, modulator means arranged in one dimension only parallel to the low divergence axis of the beam and operable to individually modulate different regions of the beam cross-section along said axis to produce a plurality of individually modulated beam portions, and means for focusing the beam portions onto a recording medium to effect data recording.
From a further aspect the invention provides a data recording method which comprises modulating in one dimension the light beam from a laser diode, which dimension is parallel to the low divergence axis of the beam, such that different cross-sectional regions of the beam along said axis are individually modulated to provide respective beam portions which are focused onto a recording medium.
The invention is preferably for use in dye thermal transfer printing, in which case the recording medium may be a pair of adjacent dye donor and receiver elements. Other applications, however, may be envisaged, such as the etching of pits or the reorientation of regions of a magnetic material, as data, in suitable recording media.
By spatially splitting the main beam into an array of separate beam portions along the low divergence axis (i.e. the axis which is parallel to the long dimension of the laser diode emitting stripe), the problems of resolution in that axis are reduced, as each separate beam portion can be focused to a separate pixel area. Better resolution can therefore be achieved in the low divergence axis, which, if desired, can be set to match the resolution in the high divergence axis, along which the beam is not divided.
Further, the separate beam portions can print a plurality of pixels simultaneou
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Pettigrew Robert Martin
Robinson Laurence John
Imperial Chemical Industries plc
Yockey David F.
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