Many steps in the electrophotographic process can contribute to density oscillations in the process direction. Line spacing variation has been discussed as a contributor to density variations in great detail in the past. This paper focuses on sources other than line spacing variations and describes techniques used for identification and analysis. The sensitivity of the process to the mechanical runout of the rollers involved was investigated as well as the sensitivity to speed variations in the drive systems. Mechanical vibration or oscillation as well as electrical oscillations were studied. It could be demonstrated how beats between frequencies outside the visible spectrum can cause visible density variations. Low frequency density oscillations with cycle periods of several centimeters might not be visible to the human observer as banding but can cause process control oscillations and color inconsistency. Analysis methods for improving the frequency resolution necessary to identify these oscillations are shown together with other evaluation techniques.
Ulrich von Huelsen, "Techniques for Identifying and Analyzing Banding Sources in the Electrophotographic Process" in Proc. IS&T Int'l Conf. on Digital Printing Technologies (NIP19), 2003, pp 49 - 52, https://doi.org/10.2352/ISSN.2169-4451.2003.19.1.art00014_1