Adjusting the rate of application of printing energy in response to change of resolution of a thermal stencil cutter.

摘要

A thermal imaging arrangement of the kind in which a line-print-head spans the width of a sheet or web to be imaged so as to record a whole line of image points at a time, and in which the sheet or web is indexed past the print head so that the pitch from line to line is determined by the substrate movement between successive point imaging operations, characterised in that:- (1) the arrangement is adapted to print with at least two different selectable line pitch resolutions by use of respective different substrate feeding rates, (2) the heating elements, as measured in the direction of indexing of the substrate, are shorter than the minimum selectable line pitch (greatest selectable resolution), (3) the rate of application of printing energy (controlled either by reducing the printing energy per point imaged, or by increasing the interval between successive point imaging operations) is reduced in response to an increase in line pitch resolution (reduction of interline spacing). The pitch of image points along a line is dependent upon the print head construction, and remains unchanged. The smallness of the printing elements w.r.t the line pitch ensures that discrete ink conducting holes are formed in a mimeograph stencil. The variation of print energy application rate with resolution tailors the size of the holes to ensure high print density printing under all available resolutions (e.g. from 300 to 400 dpi in the stencil transporting direction as shown in Figs 18A and 18B) without the ink conducting holes coalescing together when the highest resolution is selected. The printing energy may also be adjusted in response to accumulated heat in the print head (as measured by a sensor associated with the head); the nature (e.g. fluidity) of the ink, and the temperature of the ink (as measured by a sensor in the ink reservoir). The heating energy per point imaged may be adjusted by altering the current, or the width of the printing pulses, or by the incorporation (or elimination) of subsidiary pulses subsequent to each main pulse. IMAGE