Design and test of parallel multi-picking head safflower picking device

Safflower is one of Xinjiang's key specialty cash crops, offering multiple values including medicinal, edible, dye, oil, and feed uses. It serves as a vital pillar for increasing local farmers' income. The harvesting of its filaments has long relied on manual labor, which is labor-intensive, costly, and plagued by seasonal labor shortages. Furthermore, fresh safflower fruit balls are characterized by their scattered spatial distribution and varying heights. Existing harvesting equipment often struggles with low efficiency, a high fruit ball miss rate, or fruit damage, making it difficult to achieve both high throughput and a satisfactory picking rate. There is, therefore, an urgent need to develop efficient and well-adapted mechanical harvesters for safflower.This study proposes a core strategy of "gathering first, picking later" and designs a parallel multi-picking-head safflower harvesting device. It aims to enhance harvesting efficiency through continuous mechanical operation and to achieve efficient, low-damage, continuous blind harvesting of fresh safflower by coordinating a feeding/gathering mechanism with multiple picking units to form a continuous dynamic envelope around the plant canopy. First, based on an analysis of the physical properties of safflower plants and the mechanics of their branches, a feeding and gathering mechanism was designed. Its key parameters were determined as a channel width of 200 mm, a divider plate angle of 66°, and an installation height of 580 mm. This configuration significantly compressed the lateral distribution width of the fruit balls by 47.62%, creating an orderly picking interface. Subsequently, a parallel picking unit centered on three sets of counter-rotating rollers was designed. The roller parameters were set as follows: diameter 30 mm, gap 1.8 mm, length 300 mm, and center distance 85 mm. Mass property analysis and kinematic constraints determined the unit's minimum reciprocating cycle to be greater than 2.45 s. A spatial motion trajectory model was established, coupling the machine's forward speed, the reciprocating cycle of the picking units, and their phase difference. This model elucidates the mechanism by which multiple picking heads, through complementary phase differences, achieve full coverage of the harvesting area and form a continuous dynamic envelope. Using the filament net picking rate and the fruit ball miss rate as evaluation metrics, single-factor tests were conducted to determine the parameter ranges. Subsequently, Box-Behnken response surface methodology was employed for optimization, yielding the optimal operational parameters: a phase difference of 0.54π, a reciprocating cycle of 2.9 s, and a forward speed of 0.46 km/h. Field validation tests under these optimal parameters resulted in a filament net picking rate of 90.27% and a fruit ball miss rate of 10.93%. The relative error between the experimental results and the model predictions was less than 5%, meeting relevant industry standards for mechanized safflower harvesting. The device features a rational structure and simple operation. By effectively integrating the gathering and multi-head coordinated picking actions, it achieves efficient continuous blind harvesting of fresh safflower. It is well-suited for large-scale cultivation in arid regions like Xinjiang and can significantly reduce labor intensity and production costs. This study provides a practical technical solution for the mechanized harvesting of fresh safflower and offers a theoretical reference and technical basis for developing harvesting equipment for similar crops.