DEM simulation and physical testing of rice seed impact against a grain loss sensor

A triaxial ellipsoidal particle model was established according to the physical properties of rice seed, and its impact behaviour against a grain loss sensor was simulated using the discrete element method (DEM). The contact criterion was developed directly by solving the intersection equations, and the contact forces were calculated according to elastic-plastic and Mindlin models. It was shown that the seeds may perform translational and rotational motion in a 3D space after the impact. With the influences of particle shape, orientation and angle of incidence, three typical impact processes were found: single impact, multiple impacts in a short-time, and continuous impacts. Two important parameters for the design of loss sensors are the maximum normal impact force F-n max and the force rise-time t(r). Simulations showed that an increase in particle ellipticity strongly enlarged the differences in F-n max. As the ellipticities increased from unity to 2, the defined force ratio eta decreased from 100% to about 40%, and this value decreased to less than 20% when ellipticities continuously increased from 2 to 4. Tangential velocity led to an asymmetric variation of eta. t(r) was generally distributed between 12 and 54 mu s. In laboratory tests, rice seeds were allowed to free fall onto a loss sensor from a height of 320 mm. Results indicated that the peak output voltage was fluctuated in 1.5-4.5 V, and the rise-time was in 14-48 mu s. (C) 2013 IAgrE. Published by Elsevier Ltd. All rights reserved.