Color Registration Error Reduction in Document Scanner Using Iterative Velocity Command Synthesis

Document scanners enjoy widespread use for converting hardcopy documents into digital images. Improving image quality is a key issue for scanner manufacturers. This paper proposes an ILC based step timing synthesis technique for reducing color registration error in stepper motor driven document scanners with no real-time feedback. To quantify color registration error, a line pattern image based technique is devised. Based on the measured color registration error signal, a single iteration convergent iterative learning control scheme is proposed to synthesize a stepper motor step timing command for the scan region. Reduction in color registration error is achieved by compensating for velocity fluctuations in the constant speed portion of the motion. Experimental results demonstrate the effectiveness of the proposed approach in reducing color registration error in scanned image.