Mechanism study of the effect of a surface liquid film on the collision adhesion behaviour of rice stalks

Abstract

Cleaning is a critical procedure in rice combine harvesting. Liquid films on rice stalks significantly enhance adhesion, causing sieve hole blockages in vibrating screens and production issues, reducing cleaning efficiency and increasing grain loss. In this study, a wet sticky rice stalk collision adhesion sensor was designed using polyvinylidene difluoride piezoelectric film (PVDF) as the sensitive element. A drop collision test device, combined with high-speed cameras, recorded and analysed motion patterns of rice stalks undergoing adhesion/detachment. It was shown that the liquid film produced capillary liquid bridges during collisions, and the adhesive effect of these capillary liquid bridges regulated the adhesion/detachment condition of the rice stalks. The adhesion vibration of rice stalk-PVDF piezoelectric film was modelled. The results indicated that when the drop height was 100 mm and the liquid film volume increased from 0 μL to 2.0 μL, the maximum impact voltage decreased from 1.80 V to 1.28 V, and the decay time reduced from 18.01 μs to 7.08 μs. Both the maximum impact voltage and the decay time were critical characteristic values for evaluating the collision adhesion state. The additional m₂-k₂-c₂ vibration system acted as a power absorber, showing a significant difference in the impact voltage signal of the adhesion sensor caused by the presence or absence of a liquid film on the surface of the rice stalk. This disparity provides a basis for determining the presence of the liquid film on the rice stalk surface, helping to solve adhesion and blockage issues in rice harvesting and cleaning operations.