design and fabrication of a device for an estimation of the coefficient of friction of agricultural materials

agricultural crops and food materials exert frictional forces on agricultural machinery elements and on storage walls during their harvest, transportation, processing and storage. coefficient of friction is an important parameter to be predetermined in designing equipments and evaluating processes. an assessment of the coefficient of friction for agricultural materials is usually done through simple equipments of low accuracy in which many errors are introduced during the process. the device that was designed and fabricated in this work measures coefficients of static and dynamic frictions for agricultural crops on different surfaces with high accuracy. while a box filled with sample material is being pulled on the frictional surface, the tensile force is measured by use of a load cell with the data saved in the memory of the device. then a microcontroller estimates the static and dynamic coefficients of friction. to evaluate the performance of the device, some static and dynamic coefficients of friction were assessed for wheat and for peas on four different surfaces (glass, wood, galvanized as well as steel sheets) at three speed levels (0.05, 0.1 and 0.2 m/s). the results were then compared with the ones obtained from inclined plane method, under the same conditions. the data obtained from application of the designed device were close to those from the inclined plane, while the standard deviation of the results from inclined plane was up to 3.5 times that of the results obtained through the new device.