Document scanner velocity command synthesis using time optimal command shaping

Vibration induced scan velocity fluctuation during high speed scanning can cause color mis-registration and Moire patterns which degrade the quality of the scanned image. To avoid this problem, scanner manufacturers often introduce additional buffer between velocity ramp-up and constant scan velocity regions in order to allow the initial velocity transient to settle down. This buffer region results in longer scanning time and larger scanner footprint. To address these issues, this paper proposes using a time optimal command shaping algorithm to synthesize the velocity ramp-up profile for a stepper motor belt drive system, resulting in reduced oscillations in the transient region. The benefit is twofold - the required platen length as well as the time for completing a scan are reduced. Experimental results demonstrate the effectiveness of the proposed approach in minimizing overshoots in ramp up velocity transient thereby shortening the initial velocity stabilization buffer by 8%. This also corresponds to 0.9 inch reduction in the length of the platen.