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Grain sieve losses are important parameters to judge the performance of cleaning shoes in combine harvesters. To keep grain sieve loss within acceptable limits, an impact-type piezoelectric sensor was developed for real-time monitoring. Rice grain and short straw particle models were established according to their physical properties, and discrete element method (DEM) simulations were carried out to understand their collision behaviour with the sensor. The influence of grain shape, straw length and impact angle on variations of the maximum normal contact force and force rise-time were analysed in detail. Differences in normal collision force, and force rise-time occurred which lead to corresponding differences in signal frequency and voltage amplitude. A signal processing circuit, which mainly consisted of a band-pass filter circuit and a voltage comparator circuit, was designed to discriminate for full grains. Field tests results indicated that measurement errors recorded by the sensor and checked against manually measurements were <4.48%.Highlights· Collision behaviour of rice grain and straw with the sensor was studied utilizing DEM simulations. · A signal processing circuit was designed to discriminate for rice grains. · Field tests results indicated that measurement errors of the developed sensor were <4.48%. [ABSTRACT FROM AUTHOR]

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 η 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 η. t r was generally distributed between 12 and 54 μs. 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 μs. [Copyright &y& Elsevier]

Impact damage is the main form of rice threshing and it is also a significant cause of rice injury. Based on contact mechanics, models of the compressed displacement and the largest pressure distribution were established for the case when the threshing tooth obliquely impacts against the rice kernel. A critical velocity formula for impact damage was developed. A computer-aided design model of a rice kernel comprising of three layered ellipsoids was established. HyperMesh software was used to partition mesh elements and to set material and contact parameters for each element, constructing a finite element model for the analysis. Using LS-DYNA software, the impact between the threshing tooth and the rice kernel was simulated and analysed. The simulation showed that the rice husk was subjected to tensile stresses. Tensile stress was a maximum at the front of the contact zone and shifted continuously. The entire kernel rolled during impact. The critical damage velocity for the kernel, corresponding to the critical von Mises stress was 29.5 m s−1, which was in agreement with experimental results. [Copyright &y& Elsevier]

The performance of a vacuum-cylinder seeder for the precision sowing of rape seeds was investigated. For releasing seeds from nozzles smoothly, a positive differential pressure was applied to the seed. The forces acting on the seeds in free flight were calculated using the computational fluid dynamics (CFD) software Fluent. Using the differential equation for seed motion, seeds falling trajectories using different working parameters were numerically determined. A high-speed camera system mounted on a laboratory seeder test-rig was used to record the motion of seeds. A mean shift algorithm for tracking seeds was used. The horizontal displacement x and the fall time t f of seeds predicted by the numerical analysis and measured by the high-speed camera system were compared. The results indicated that the relative errors of x and t f were <5.5% and 6.5%, respectively, indicating good agreement. Based on the analysis of seeds falling trajectories, it was found that the variations of positive differential pressure Δp and release angle θ had significant effects on seeding uniformity. In order to analyse their effects on horizontal displacement, a coefficient of positive differential pressure variation χ p and coefficient of sowing angle variation χ θ were proposed and their values calculated. Calculations indicated that the optimum levels for Δp and θ for the precision seeding of rape seeds were in the range of 1–2kPa and from −10 to 0°, respectively. Experiments were carried out on the vacuum-cylinder precision seeder test-rig and the results showed that the average seed spacing interval error reached the minimum at Δp =1.5kPa and θ =−5° and that the error increased almost linearly with increasing of cylinder rotational speed. [Copyright &y& Elsevier]