Abstract
The diameter measurement of a moving and vibrating yarn with a photoelectric sensor device is difficult. Two main restrictions are concerned with the photoelectric measurement of yarn diameter and yarn evenness. One is the inhomogeneous radiant intensity of the emitted light on the sensor device, and the other is the irregular shape of the yarn cross-section. The improvement of the variation of radiant intensity in the horizontal light slot so as to obtain a homogeneous radiant flux in the test section by using the area-compensation method (ACM) is discussed in this study. The radiant-intensity distribution of an infra-red-emitting radiation was investigated by using the cubic-spline interpolation after the light had penetrated through a convex lens and a rectangular light slot. The ACM was then applied for obtaining a modified light slot, which was added to the convex lens. The ACM was developed according to the concept that the radiant flux is equal to the product of the radiant intensity and solid angle. Provided that the yarn diameter is constant, it is easy to determine the variance of an inhomogeneous radiant intensity. A steel bar of diameter 1 mm was applied for simulating the yarn diameter in this study. If the radiant intensity in this case is homogeneous, the projectile irradiance on the sensor would remain constant when the simulating yarn moved in the test section. The yarn diameter could be measured exactly in the homogeneous test section no matter how the yarn moved and vibrated. The coefficient of variation (CV%) of the radiant intensity decreased from 8.3% to 0.4% when the ACM was used. This sensor device was applied to measure the yarn-evenness variation of a 13.9-tex ring-spun yarn. The CV% decreased from 17.8% to 15.4%. Under the same testing conditions, the CV% was 14.3% with the Uster Evenness Tester. The variance of radiant intensity has accordingly been improved with the ACM.
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