Banding Reduction in Electrophotographic Process Using Human Contrast Sensitivity Function Shaped Photoreceptor Velocity Control

Abstract

This article presents a process control strategy for reducing banding artifact in electrophotographic (EP) process. EP banding was shown to be closely related to the angular velocity fluctuation of the photoreceptor. Proper regulation of the photoreceptor rotational velocity under various process uncertainties and variations will improve EP process stability and reduce the occurrence of visual banding. The proposed closed-loop control strategy is to modulate the main drive motor speed based on the velocity measurement of the photoreceptor. The controller featured two levels of angular velocity regulation. The first level utilized the loop-shaping technique to incorporate the human visual system (HVS) model, i.e., an approximation of the human contrast sensitivity function (CSF), into the feedback loop to eliminate low frequency and non-periodic velocity fluctuations. The second level used an internal model based repetitive controller to reduce the effect of periodic velocity fluctuation. The HVS based loop shaping design is intended for addressing the subjective evaluation of the human visual perception. Experimental result from a low cost 600 dpi EP engine showed significant banding reduction from reflectance measurement as well as subjective evaluation of the printed image.