Design And Parameter Optimization Of Stalk Chopping,Leaf Stripping And Top Breaking Devices For Sugarcane Harvester

Sugarcane is an important economic crop and raw material for biofuels,which is widely planted in southern China,especially in the Guangxi Region and in Guangdong,Yunnan,and Hainan Provinces.Mechanical harvesting technologies of sugarcane can greatly improve production efficiency,reduce harvesting costs and labor intensity.Mechanical harvesting of sugarcane in China is performed using two general types of harvesters which are chopper harvester and whole-stalk harvester.The chopper harvesters have been widely used because of their suitability for high yielding sugarcane varieties.While the chopper harvesters could lead to serious sugar juice loss and billet damage during chopping process.The whole-stalk harvesters have low harvesting efficiency and poor adaptability,and the impurity content(including leaves,leaf sheaths and tops in this study)after harvesting is high.The harvesting quality of the two types of harvesters need to be improved.Based on the sugarcane planting pattern and production system in sugarcane planting area of southern China,the physical and chemical properties and cutting mechanical properties of sugarcane were explored in this study.Combining with virtual prototyping technology,theoretical analysis and experimental research were carried out on the chopping system of chopper harvester and the leaf stripping and top breaking devices of whole-stalk harvester.The main structure and operating parameters of the chopping system,leaf stripping and top breaking devices were determined,which provided key technical support for the design and improvement of sugarcane harvester and had important reference value.The main research contents and conclusions are as follows:(1)Research on the cutting characteristics of sugarcane in terms of physical and chemical properties.The morphological traits,physical properties,anatomical features,chemical compositions and cutting characteristics of two general kinds of sugarcanes(commercial cane and fruit cane)at nodes and internodes of six different sections along the stalk were detected and compared.Results showed that these properties were significantly different due to the difference in sampling sections and varieties,which led to different maximal cutting force along the stalk.(2)Optimization and finite element simulation of the chopping system for chopper harvester.Based on the cutting properties of the stalks,a chopping system used in a sugarcane chopper harvester was developed and utilized to evaluate the effect of rotational speed of chopping rollers,overlapping length of upper and lower chopping blades and bevel angle on chopping quality and power requirement.Box-Behnken design combining with response surface method was employed to conduct experiments and build regression models.The optimal operating parameters were determined to be overlapping length of chopping blades of 2 mm,bevel angle of 21.8?,and chopping roller speed of 200 to 250 r/min.A high-speed camera system was then applied to capture the stalk trajectory during chopping process,and motion analysis software was used to analysis the motion pattern of stalks.Results suggested that maintaining a stable and low conveying speed of sugarcanes during mechanical harvesting could reduce stalk damage and juice loss.A sugarcane-blade finite element model was finally established to simulate the chopping process by using three-dimensional design software and finite element analysis software.The chopping resistance of blades,stress distribution of sugarcane and blades in the chopping process were analysed.(3)Finite element simulation and experiments of the leaf stripping device for whole-stalk harvester.A sugarcane leaf stripping simulation model was established,and the stress and force changes of stalk and leaf stripping elements during leaf stripping process were analyzed.The results of virtual single factor experiments showed that the maximal stress of stalk decreased initially and then increased with the increase of feeding roller speed,and increased continuously with the increase of leaf stripping roller speed and overlapping length of stalk and leaf stripping element.A leaf stripping test rig was established based on the simulation analysis.Box-Behnken design was utilized to study the effects of feeding roller speed,leaf stripping roller speed,overlapping length and feeding rate on leafy trash content.The optimal operating parameters were computed as feeding roller speed of 250 r/min,leaf stripping roller speed of 540 r/min,overlapping length of stalk and leaf stripping element of 13.9 mm and feeding rate of 1.68.Under these conditions,the predicted value of leafy trash content was 2.2%.The leaf stripping process and movement state of stalks were analysed by conducting high-speed photography experiment.Results showed that if the rotational speed of rollers was high during leaf stripping process,the conveying speed of the stalks fluctuated drastically,which resulted in stalk fracture.(4)Optimization and simulation analysis of the top breaking device for whole-stalk sugarcane harvester.An anti-float top breaking device was developed based on the mechanical tests which showed that the bending resistance,deformation resistance and impact resistance of cane tops were significantly lower than those of the middle and bottom cane parts.The Central composite design combined with response surface method was used to explore the effects of key operating parameters on top breaking rate,non-fracture rate and power requirement.The optimal operating parameters were determined to be feeding roller speed of 305 r/min,top breaking roller speed of 520 r/min,stagger angle of upper and lower top breaking elements of 14°,and distance between upper and lower top breaking elements of 10 mm.The theoretical optimal values of the top breaking rate,non-fracture rate and power requirement were 85%,83% and 690 W,respectively.The results of high-speed photography experiment showed that the conveying speed of the stalks fluctuated in the range of 3.0 to 4.5 m/s under the optimal conditions.Finally,the rigid-flexible simulation model of sugarcane-top breaking device was established by using SolidWorks,ADAMS and ANSYS softwares,and the movement state of the stalk during top breaking process was analyzed.The displacement and speed of the mass center of the stalk in the vertical direction during top breaking process ranged from-85.28 to 87.38 mm and from-32821.16 to 18082.80 mm/s,respectively.The maximal resultant force of top breaking element on stalk was 807.68 N,and the maximal striking force in the vertical direction was 547.04 N.(5)Optimization of the rotational speeds of the whole-stalk operating system.A whole-stalk operating system with leaf shredding function was established.The orthogonal experiments combining with comprehensive evaluation method were carried out to optimize the rotational speeds of operating rollers.The optimal rotational speeds of feeding roller,leaf shredding roller,leaf stripping roller and top breaking roller were determined to be 200,500,600 and 500 r/min,respectively.The results of contrast experiments showed that the leaf shredding device could effectively reduce the leafy trash content,while this device also increased the abrasion rate of stalks.