Development of a suspended residual cotton picking device

Residual cotton left in fields after mechanical harvesting has caused significant resource waste in Xinjiang, China. Existing pickup machinery can also be confined to the low collection efficiency and high impurity content. In this study, a suspended pickup device was developed for residual cotton to integrate picking, cleaning, and conveying functions. The study material was utilized as the cotton variety, Guoxin AW04, at an experimental site in Xinjiang. The core components of the device included the pickup mechanism, the saw-tooth cleaning unit, and the screw conveyor. Kinematic analysis was conducted to determine the structural parameters. The design specifications were derived as follows: The pickup roller speed exceeded 37.4 r/min; the round steel bar diameter of the grate was 30 mm with a spacing of 40 mm; the clearance between the grate bars and the tooth tips was set at 20 mm; the saw-tooth roller speed was below 525 r/min; the doffing roller speed was greater than 350 r/min; and the screw conveyor auger speed was specified as 215 r/min. A prototype was fabricated after the theoretical design. A three-factor and three-level Box-Behnken experiment was implemented to evaluate the performance of the device. The independent variables were selected as the machine forward speed, pickup roller speed, and saw-tooth roller speed. The response variables were the residual cotton pickup rate and the impurity content rate. A regression function was used to evaluate the relationship between the variables and responses. Multiple objective optimization was subsequently performed using Design-Expert 10.0.4 software. The results showed that: 1) An optimal combination of parameters was determined as: a forward speed of 0.7 m/s, a pickup roller speed of 251.31 r/min, and a saw-tooth roller speed of 249.31 r/min. The pickup rate of residual cotton was predicted as 90.22% with an impurity content rate of 18.27%. 2) Factor significance analysis revealed that the influencing factors on the pickup rate were ranked in descending order of pickup roller speed, forward speed, and saw-tooth roller speed. Conversely, the influencing factors on the impurity content rate were ranked in descending order of forward speed, pickup roller speed, and saw-tooth roller speed. 3) Factor interaction effects revealed further insights. An excessively high forward speed led to missed pickup, thus reducing the collection rate. While an extremely low speed compromised operational efficiency, to accelerate component wear. The high pickup roller speed also promoted the detachment of seed cotton from the ground and stalks, thus facilitating conveyance. An overly high speed caused seed cotton to be flung away or torn, adversely affecting both the pickup rate and the quality of the recovered material. An insufficient pickup roller speed hindered effective collection and ejection. A higher forward speed increased the material throughput of the saw-tooth cleaner, leading to inadequate cleaning and thus higher impurity content. A lower speed reduced throughput for the high cleaning effectiveness, thus lowering impurity levels. Furthermore, an excessively high pickup roller speed subjected the cotton to greater impact during pickup, which reintroduced separated impurities back into the fiber mass. An inadequately low speed failed to effectively separate impurities, resulting in elevated impurity content in both scenarios. A final validation test was conducted using practical, rounded parameter values after optimization: a forward speed of 0.7 m/s, a pickup roller speed of 250 r/min, and a saw-tooth roller speed of 250 r/min. The average pickup rate was measured as 89.53% (a decrease of 0.69 percentage points from the predicted optimum), and the average impurity content rate was 18.91% (an increase of 0.64 percentage points). These deviations fell within an acceptable error range, thus confirming the reliability of the optimization. The performance of the device fully met the agronomic requirements. In conclusion, this research can provide a valuable reference to develop the mechanical equipment for residual cotton recovery. Moreover, theoretical and practical insights can also offer for the pickup of irregular, clumped, flexible materials in general.