偏移剪叉式油茶果收集装置设计与试验

Design and test of the fruit collecting device of camellia oleifera with angular scissor mechanism

为改进林果收获机收集装置的折展性能和环境适应性,该研究采用变比例剪叉机构,设计偏移剪叉式林果收集机械装置。首先,针对偏移剪叉式林果收集机构进行运动学分析,确定收集装置铰接点的运动轨迹和侧翼剪叉机构的完全展开倾角。以国内特有木本油料作物油茶为应用实例,通过测量油茶树冠幅大小及油茶果与收集布的静摩擦力系数,设计收集装置的机构尺寸参数,并利用MATLAB计算收集装置的理论运动曲线。创建偏移剪叉式林果收集装置ADAMS仿真模型,比较收集装置剪叉机构关键点位置和完全展开倾角的仿真与理论计算结果,验证偏移剪叉式林果收集装置设计方案的可行性与准确性。最后搭建偏移剪叉式林果收集装置1:3缩比模型,实现收集装置倒圆台型环形展收运动,侧翼剪叉机构完全展开时测得倾角约为25.67°,与理论设计倾角一致;缩比样机完全展开与收拢状态体积比约为59.7,可实现高折展比林果收集工作。

Forest fruit collecting machinery is very necessary to balance the bulky machine size,the limited applicable environment,and the high spacing requirement in practical operation.The unsolved deflections have also started to hinder the full mechanization of the forest fruit industry.The angular scissor mechanism can be expected to improve the folding/deploying performance and environment adaptability of a mechanical automation system in the field of forest fruit harvesting.In this study,a new type of forest fruit-collecting device was proposed with a series of angular scissor elements in the variant arrangement.Firstly,the comprehensive description of the device was defined by the Cartesian and polar coordinate systems.All intermediate hinge points were not set along the same straight line.Among them,the intermediate hinge points of the horizontal circular scissor mechanism were located on the same arc.The intermediate hinge points of the side scissor mechanism were connected in a Z-shaped arrangement,leading to an angle of declination from the Z-axis in the global coordinate system.Both circular and side scissor elements were deployed with the angular scissor elements.Then,the kinematics analysis was also conducted for the forest fruit collecting mechanism,according to the sines and cosines.The theoretical expression was derived subsequently for the movement trajectories of hinge points on the collecting device.Moreover,the mathematical formula was deduced for the complete deployment angle of the side scissor mechanism,according to the sines.Next,an application example was taken as the camellia oleifera tree,a unique and well-known woody oil tree in China.The dimensional parameters of the camellia fruit collecting device were calculated to measure the canopy size of camellia oleifera trees,and the static friction coefficient between camellia oleifera fruits and collecting fabric.The average value of the static friction coefficient was obtained using friction angle testing with five groups of camellia oleifera fruit samples.The obtained structural parameters were selected to calculate the theoretical motion trajectories of several hinge points for the fruit-collecting device in MATLAB software.Furthermore,a simulation model of the forest fruit-collecting mechanism was established to verify the angular scissor elements using ADAMS software.The simulated position coordinates of each key hinge point were selected to compare the complete deployment angle from the theoretical analysis.The relatively low position errors of hinge points demonstrated the feasibility and accuracy of the theoretical design for the forest fruit-collecting device with the angular scissor.Finally,the physical prototype of the angular scissor fruit-collecting device was manufactured at the scale of 1:3 and then assembled.Collecting fabric was also covered over the angular scissor mechanism.The stored/deployed movement of the forest fruit collecting device was implemented at the site via the simultaneous control of the actuation displacement using two electric cylinders.Consequently,the complete deployment angle of the side scissor mechanism was measured to be about 25.67º,which was in better agreement with the previous theoretical parameter.More importantly,the ratio of the volume in the completely deployed state to that in the stored state for the forest fruit collecting device was estimated to be about 59.7,indicating the practical benefit of realizing collecting work of camellia oleifera fruits with the high stored/deployed ratio.