15.04.2011 | Autor / Editor: P.J. O’Brien / Marcel Dröttboom
Belt scale accuracy is important to the efficiency and quality of processes dependent on mass flow. Non-contact, Ethernet camera technology can be used to produce an integrated volume measurement of product on a conveyor which optimise accuracy and reliability of the mass flow measurement.
Measuring the volume of material being transported by a conveying system is a difficult task for traditional weight scales. Problems associated with installation, vibration and maintenance can all affect the accuracy of a belt scale system. In addition, calibration must be checked frequently and the re-calibration process is not an insignificant undertaking usually requiring the belt to be off line.
Scales are important elements in many processing applications. Manufacturers use scales to monitor such things as the total weight for custody transfer of product or the weight of product feeding a continuous process, or even the weight of multiple product streams feeding a blending process. Whatever the use, the accuracy of the scale is important to the efficiency of the overall process as well as the quality of the end product. Inaccuracy due to calibration drift, and the associated down time for maintenance and repair, negatively impacts cost and quality.
Vision technology provides a method for analysis of belt flow that avoids these costly problems of traditional belt scales. The concept employed is based on a mathematical integration of the flow profile as it falls off a pulley or belt terminus, see Fig. 2.
Referencing back to the calculus text books at school one will remember the integral is defined as a summation of thin chunks of area under the function curve (Fig. 3). As the thickness of these chunks tends toward 0 the true value of the function is determined.
If we think of point ‘a’ as the belt pulley, where the profile of the product is measured, and the boxes to the right of point ‘a’ as sections of product on the belt moving up to the pulley it becomes apparent that totalling a series of profiles taken in rapid succession fits the definition of the integral well.
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