| 摘要 |
A method is provided for controlling a water-ink equilibrium on a moving offset plate 2 in an offset copying machine wherein the offset plate is fixed to a rotating cylinder 1. The method includes the step of illuminating a predetermined area 35 of the moving offset plate 2, the density of which is known, with a coherent light source 30 under normal incidence. A portion of the light reflected around an axis perpendicular to the plane of the illuminated area 35 is collected in the focal plane of a convergent optical system 32. The intensity of the collected light is measured at at least one location in the focal plane of the convergent optical system. In another aspect of the invention there is provided a device for regulating a water-ink equilibrium on a movable offset plate fixed to a rotatable cylinder in an offset copying machine, the device including a coherent light source illuminating under a normal incidence a predetermined area of the offset plate, light-intensity measuring means including a sensor placed at an axis of and in a focal plane of a convergent optical system for collecting and measuring the intensity of a fraction of the light reflected from the predetermined area and for generating a corresponding signal, and a servo-control system disposed to receive and respond to the signal provided by the sensor to adjust wetting and/or inking of the moving offset plate.
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