Design and optimisation of bump-enhanced conditioning rollers for uniform alfalfa stem damage

Conditioning is a critical step in alfalfa hay harvesting, directly influencing its quality. A conditioning model was developed to identify the key factors affecting conditioning effectiveness. To address the issue of uneven stem damage caused by conventional conditioning rollers, a surface bump structure was designed. By arranging these bumps spatially, the rollers applied micro-rubbing actions to the alfalfa stems, thereby enhancing structural disruption. Parametric optimisation studies clarified how bump diameter, non-interference distance and helix angle influence stem disruption efficiency. The design was further refined using the finite element method. Subsequently, a Box–Behnken experimental design was employed to optimise three key operational parameters: feed rate, roller gap, and roller rotational speed. Drying tests were then conducted to compare the conditioning performance of different roller designs. Results showed that the minimum number of broken branches (0.67) and maximum number of non-fracture damage occurrences (7.67) were achieved with a bump diameter of 2.85 mm, a non-interference distance of 1.61 mm, and a helix angle of 23.85°. Aiming to maximise the conditioning while minimising the conditioning loss rate and energy consumption, the optimal parameters were determined to be a roller rotational speed of 683 r min⁻¹, a roller gap of 3.13 mm and a feed rate of 779 g s⁻¹. The moisture content of alfalfa conditioned using the roller with bumps dropped to around 40 % within the first 60 min. Compared with the other two conditioning rollers, this design demonstrated superior performance.