Webs are continuous strips of thin flexible materials--including paper, cloth, metals, and polymers--that are transported under tension at high speed during their manufacture and subsequent use. In paper production and sheet metal manufacturing, for instance, webs are guided through carefully designed transport paths as they are coated, laminated, slit, processed, and wound. Webs also constitute important elements of such common industrial and consumer products as printers, copiers, and magnetic and optical tape drives. Poor guiding in the manufacturing and processing of webs causes edge damage, wrinkling, and breakage. Positioning errors also lead to ineffective read/write operations in tape drives, and poor quality in printers and copiers. In short, the guiding and precise positioning of webs, both laterally (in-plane) and transversely (out-of-plane) are generic issues in web transport systems.;Through analytical, computational, and experimental means, this thesis investigates web transport from the standpoint of ensuring the stable and accurate positioning and guiding of webs. In this regard, natural frequencies and damping ratios are used as performance measures in optimizing design and operating parameters, as well as in predicting the onset of wrinkling or other instability. The specific issues that are addressed, and contributions of this work, include: (1) Wrinkling of webs during lateral position control. Offset guides are commonly used to steer webs laterally, but they induce in-plane forces that can cause wrinkling. Models of common transport components are developed to obtain relationships between the extent of misalignment, lateral web position, and the onset of wrinkling. Experimental and analytical techniques are developed to predict the web's proximity to wrinkling based on measurement of its natural frequencies. (2) Transverse positioning of webs using self-pressurized air bearings. The natural frequencies, damping ratios, and vibration modes of coupled web-bearing systems are effective monitors of their stability. The computational effort in predicting these measures is reduced by two new analytical developments: adaptive nodal point allocation and closed form expressions for transverse web deformation. The sensitivities of the system-level stiffness and damping to various web and air bearing parameters are predicted and compared with measurements. Applicability of the web-bearing model to predict the behavior of finite width webs is investigated.
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