Exposure control of energy sources.

摘要

In a printer using an array (10) of light-emitting diodes (LEDs) to expose a photo-sensitive material in accord with supplied image information (14), the LEDs in the array (10) are individually energised for exposure durations dependent on the image information. The LED array (10) is energised from a Power Supply Unit 40 whose bus voltage (VD) varies with the number of LEDs turned on at any time. Thus the exposure energisation from the LEDs is not that obtained from the diodes if the voltage (VD) were constant. The exposure durations are controlled from a clock provide by a voltage-controlled oscillator - VCO-(50). The VCO (50) is responsive to the bus supply voltage (VD) so that the exposure durations vary as an inverse function of this voltage. The VCO may also be used to control the drive rate of a stepper motor (20) which moves the photo-sensitive material past the LED array (10) in order to better maintain media registration as the exposure durations are varied. A specific embodiment of this is shown in Fig. 2. The above techniques may also be applied to printing with a thermal print-head array. <IMAGE>