Plessey Overseas Limited

The Plessey Company Plc

George A Chilton

Peter B Hart

Richard A Kirk

Peter R Lee

Alan J Cobb

In order to reduce thermal coupling between diodes in a light emitting diode array for a printing or imaging system which has the undesirable effect of wavelength shift and output reductions, rows (12, 14) of diodes are provided which are separated and inclined to the direction (Y) of scanning movement during a print operation, wherein current pulses applied to the diodes of each row for energization are delayed with respect to one another such that energization and printing occurs in a line perpendicular to the direction of scanning movement.

Light emitting diode array

A method of alignment of monolithic chips of arrays of light emitting diodes to form part of a print head, the method comprising placing microscopically visible alignment marks on each chip in predetermined positions relative to the diode array carried on the chip, positioning two chips adjacent to one another in desired relative positions, and viewing the two chips through a microscope having a graticule, whereby the alignment marks of the two chips are positioned on the cross wires of the graticule whereby the chips are aligned with their respective diode arrays in a correct spacing and orientation relative to one another.

Method of alignment of LED chips

A simple and reliable method of recalibrating a LED print head comprises providing a photodetector array for detecting the intensity of illumination of each LED, comparing the actual intensity with a desired value and adjusting the level of current applied to the LED array until the actual and desired values correspond, at which time a memory storing the current levels to be applied to the diode array is updated. One or more reference diodes are provided and employed in an initial step in which the current applied to the reference diodes is adjusted until actual and desired current levels correspond, at which time all stored current values for all LED are updated.

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Buckinghamshire, United Kingdom

George A Chilton