The beard method is used for sampling cotton fibers to generate fibrograms from which length parameters can be obtained. It is the sampling method used by the Uster High Volume Instrument (HVI TM ). A fundamental issue of this sampling method is its bias since the mathematical computation to obtain length parameters is quite different. There have been different assumptions regarding the bias of the beard sampling method. In our experiments, we have seen discrepancies in measurements that cannot be explained as length-biased or unbiased, especially in the short fiber region. We report a fundamental research, including experimental and theoretical analysis, and computer simulations, that reveals the bias due to this sampling method. We find that the beard sampling method as used in HVI is not completely length-biased; fibers sampled by using this method are similar to the original fibers except in the short fiber region. Short fiber content (SFC) of the sampled fiber is lower than that of the original fiber, and this difference is inherently introduced by the sampling method.
IntroductionThe beard method was developed to test cotton fiber length parameters rapidly. Cotton fibers are selected by the needles of the fiber comb and formed into a gradually tapered fiber beard. Then a measurement device utilizes optical or pneumatic method to scan the fiber beard to generate length fibrograms by measuring the light attenuation or airflow rate along the tapered beard. Various length parameters can be obtained from the fibrogram. Woo (1967) provided a comprehensive appraisal and developed a series of equations for computing different fiber length parameters from fibrograms. Beard method is used by Uster HVI for length measurement. HVI has brought significant impacts on cotton industry (Suh & Sasser, 1996). Because of its speed and consistency, HVI is now extensively used to measure cotton properties, including fiber length parameters and strength, color, trash, and Micronaire (an indicator of cotton maturity and fineness). HVI uses a fiber comb to pick up fibers from the Fibrosampler TM to form a tapered beard. During the sampling process, the fiber comb makes circular movements around the Fibrosampler cylinder in which cotton fibers are held; needles of the comb pick up fibers protruding through the holes on the Fibrosampler cylinder surface. Figure 1(a) and (b) show the comb as used in Uster HVI 900 model and the fiber beard formed by using such a comb, respectively.
