Measuring Deformations of Limp Fabrics for Material Handling

Abstract

There is an increasing focus on automating the textile industry, particularly labor- intensive tasks such as fabric manipulation and assembly. The highly flexible nature of these materials makes automation very challenging. Not only are fabrics difficult to manipulate, but their geometric characteristics are difficult to measure with conventional instruments. Accurate ways of measuring the state of the workpiece are needed to provide feedback for system control. This paper proposes a system for measuring the shape and range of locations for a wrinkle along the length of a fabric strip, based on a measurement of the difference between its total unwrinkled length and total wrinkled length Δ Ltotal. A relationship can be established between ΔLtotal and the forces necessary to sustain the wrinkle that corresponds to Δ Ltotal using Clapp's model for the fabric elastica and a model of the flat fabric lying on the table. Force balances that include the frictional force required to support the wrinkle provide the basis for locating it along a spatial length. A nondi mensional variation of Clapp's model shows many possible solutions or modes for a wrinkle shape corresponding to one value of Δ Ltotal, although the boundary forces will be different for each mode. Each wrinkle shape is unique in the number of "humps" it contains. This variation of the model also shows that as the wrinkle gets taller, an effect similar to an inverted pendulum occurs when the simulated wrinkle tends to lean to one side or the other. These results can be observed experimentally with actual fabrics, although heavier weight fabrics have poorer comparisons to their modeled simulations. One explanation is that heavier fabrics are prone to interfiber friction that creates material memory, which was not included in the mathematical model analysis. This system provides a useful measuring tool for industry. The general solution provided by the nondimensional model defines important relationships between the wrinkle's boundary forces and Δ Ltotal. Finding the material parameters of a fabric, which costs only a small initial time investment, provides information the general model needs to predict a shape and range of locations for a wrinkle in a high-speed industrial environment.