Parameter optimization and experiment of dual roller harvesting device for safflower

Abstract: Because of the growth characteristics of safflower, it is very difficult to realize mechanized harvesting. At present, the mechanized harvesting technology of safflower in China is still in infancy. Most of the current harvesters are divided into 3 types according to their working principle, including the cutting type device, the pneumatic plucking type device and the cutting-pneumatic plucking combination type device. The current harvesting machines have some disadvantages. For example, safflower petals are easily broken and dropped, and safflower fruit balls are easily broken. Therefore, there is no application of 3 types of machines above in safflower harvesting. For the safflower has the characteristics that a single petal is small, light, slim, and easily interfered by air, the research presented a method for safflower harvesting which made use of the negative pressure generated from a pair of high-speed spinning rollers. It achieved the harvesting of safflower mainly by the modes of capture, friction and extrusion. Compared with 3 types of machines above, the plucking device with dual rollers had the advantages of high harvesting rate, and low petal dropping rate and broken rate, so it would be widely applied for harvesting safflower. In order to further study the safflower picking device and improve the work quality for the safflower harvesting device, the dual-roller harvesting testbed was designed. The safflower plucking testbed consisted of plucking unit, driving device, frame and collecting box. The experiment chose the safflower of "Yu Min stingless" as the object. In order to determine the operation parameters of the safflower plucking device, the response surface experiment with 3 factors and 5 levels was completed on the safflower plucking testbed with dual rollers. Three parameters, including roller diameter, dual-roller clearance and rotation speed, were selected as the input variables, and safflower removal rate, dropping rate and safflower broken rate were selected as the output parameters. Quadratic orthogonal rotary regressive experimental design was employed to develop the second order polynomial regression model, which explained the relationship between the input and output parameters. By the Design-Expert 6.0.10 software, the corresponding mathematical regression model was established, the influence of significant factors on the quality of operation was analyzed, and the experimental parameters were optimized. The optimal combination of parameters determined was as follows: roller diameter was 40 mm, dual-roller clearance was 0.5 mm and rotation speed was 1400 r/min. Based on the combination of optimization parameters, the roller clearance was revised as 0.5 mm, and safflower harvesting test was done 1-5 days after the flowering (moisture content ranged from 44.6% to 78.4%). The experimental results indicated that the removal rate was more than 90.02%, the dropping rate was less than 2.46%, and the safflower broken rate was less than 3.04%. However, when the moisture content was in the range of 22.9%-29.5%, the removal rate of the device was less than 19.37%. Therefore, the period within 1-5 days after the flowering was appropriate for the timely harvesting of safflower. Through the field testing of prototype in Xinjiang, the harvesting and laboratory results were basically consistent. This design provides a new reference for mechanical harvesting of safflower, and the study may also provide the basis for mechanism design and parameter optimization of harvesting machine with dual rollers.