Experiment and simulation of rolling friction characteristic of corn seed based on high-speed photography

Abstract: The physical properties of corn seeds, including the dimension feature, density, Poisson's rate, shear modulus, coefficient of restitution, coefficient of static fraction, and coefficient of rolling fraction are vital to the design of the precision seed-metering device and the simulation of its working process. There have been many relative studies on them, but no mature theory and accurate method to measure the coefficient of rolling friction has been developed. Due to the shape and dimension character limitation, most methods for measuring the coefficient of rolling fraction are not applicable to corn seed. Only one method based on the principle of conservation of energy gave some enlightenment on the way to achieve it.The method and principle used to obtain the coefficient of rolling friction was: A static spherical corn seed rolls from the top of an inclined rail to the end. The gravitational potential energy (U) of the seed on the top is equal to the kinetic energy at the end (Ek) and the work done by the rolling friction within this distance (Wfr). And the ratio of Wfr and U () has a linear relation with cotθ (θ is the angle of the inclined rail). The equation of linear regression can be fitted by changing θ eight times from 15°to 50°, the slop of the straight line just is the coefficient of rolling friction. U can be calculated by the distance of the inclined rail and θ easily, but Ek needs the aid of high-speed photography technology to capture the velocity of the seed at the end.The experimental materials included several selected spherical corn seeds that were used as roll ball, an angle adjustable frame of rail, and three rails which were made of the PMMA (polymethyl methacrylate), galvanized steel, and corn seeds respectively. The main testing equipment was the Phantom v9.1 high-speed camera, which was produced by Vision Research. The frame rate used in the experiment was 1 000 fps.According to the results of the experiment, the coefficient of rolling friction of corn seeds against PMMA (polymethyl methacrylate), galvanized steel, and corn seeds are known as 0.0931, 0.0531 and 0.0782 respectively. Although there were some inevitable errors caused by the materials and image processing method for getting the velocity, the results were proved to be truthful by the contrast tests about the angle of repose for corn seeds both by laboratory tests and EDEM simulation. The data measured can be used for design calculation and simulation analysis.