| Tobacco is a kind of crop which has high economic added value and tobacco production has become an important part of agricultural economy in China.Topping of tobacco is one of the key processes in field production,which is of great significance to high quality and suitable yield to tobacco.At present,tobacco is topped by artificial as the main method in China.The topping equipments which under research are all large and medium-sized machines being suitable for plain areas.The southwest tobacco growing area is the largest tobacco growing area in China,in which the terrain is mostly hilly that is difficult to operate and use large equipment.In view of the mountainous and hilly terrain in southwest China,there is no relevant machinery,so it is necessary to study a small size,light weight,flexible operation of tobacco topping equipment.In view of the above problems,this paper puts forward a research project on the design of tobacco topping machine with UAV as carrier,which is of great practical significance to the tobacco topping work in mountainous and hilly areas.The main research work of this paper is as follows:Firstly,according to the research status and development trend of tobacco topping equipment at home and abroad,combining with the agronomic requirements of topping operation,the overall design scheme of tobacco topping equipment based on multi-rotor UAV is proposed.The structure and design principle of the UAV are introduced,so the work flow of the UAV is determined,which provides the basis for the design and analysis of the following parts.Secondly,the mechanical properties of tobacco stem at full flowering stage were studied.Through the test,the unit cutting force and the Bending Shear modulus of the stem are calculated.According to the mechanical characteristics and topping characteristics of tobacco stem,the material of cutting system was selected,and the blade and cutter shaft of tobacco cutting system are designed.The static analysis is carried out and the corresponding parameters such as stress and displacement are obtained.The finite element modal analysis of the whole blade is carried out,so the natural frequency,vibration characteristics and critical speed of the cutting system are obtained.Then,the downwash flow field of rotorcraft topping equipment is simulated and analyzed by CFD software,and the downwash flow field velocity streamline diagram,pressure nephogram and velocity nephogram are obtained.By the method of intercepting velocity,finding that the maximum position of downwash velocity of X-Z plane is 0.2 m below the underside of the machine,and the maximum position of downwash velocity of Y-Z plane is directly below the propeller.Next,the three-dimensional model of retractable and retractable mechanism and rhomboid mechanism arm in SW are introduced into the dynamic simulation software,and the corresponding displacement,velocity and stress of key nodes are obtained,so the correlation analysis is carried out,the displacement and strain nephogram are obtained and analyzed by using the stress simulation software,and the modal analysis of the lower platform provides the basis for the optimal design of the mechanism.Next,through the analysis of downwash flow field after installing the anti-disturbance device,the position of 0.2 m below the underside of the machine is chosen as the installation height for the anti-disturbance plate.besides,the size of the anti-disturbance plate should cover the propeller motor.After the anti-disturbance plate was installed,the air velocity was reduced obviously,which proved that the anti-disturbance plate could reduce the plant sloshing at the top.Finally,trial production and testing of the prototype.On the basis of theoretical analysis and simulation,the structure design of the topping equipment is completed,and the prototype is debugged and tested.The results showed that the accurate topping rate was94.4% and the leaf injury rate was 3.6%,which could meet the demand of tobacco topping in southwest China. |
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