基于碰撞变形能的机械采收蓝莓果实碰撞损伤评估

Collision injury assessment of mechanical harvesting blueberry fruit based on collision deformation energy

为解决机械采收蓝莓与接果设备碰撞导致果实内部损伤的问题,对果实变形能及其碰撞过程展开研究,以果实储存变形能大小评价其损伤程度。研究了果实下落过程的运动学和接触力学特性,果实损失的机械能转化为变形能,确定影响果实变形能因素,建立碰撞变形量方程。通过有限元仿真技术求解变形量及变形能的理论值。仿真结果表明,果实下落高度和接果板角度是影响变形能的主要因素。最后搭建物理样机进行果实下落碰撞试验,得到变形能试验值与理论值的误差为0.49×10^(-3) J。当蓝莓生长集中区域与蓝莓采收机接果板距离接近600 mm,接果板角度接近15°时,果实碰撞变形能小于0.68×10^(-3) J,果实损伤最少。该研究可以为蓝莓采收机作业参数及其他类似设备研究提供一定的理论依据。

The blueberry belongs to small berry.Mechanical harvesting is the most effective way,but the falling and collision of the blueberries cannot be avoided.As a result the quality of the blueberries cannot be guaranteed.Even though the appearance of the fruit has not any obvious change,the inner of the fruit may be injured.In order to reduce the collision injury degree of the fruit in the process of harvesting,the collision characteristics of the blueberry fruit are researched based on the principle of the fruit energy balance.The highbush blueberry fruit is seriously damaged during mechanical harvesting,so it is selected to be analyzed.The geometric and mechanical parameters are obtained by measurement.The quasi static compression test of the fruit is conducted,and the compression deformation energy is analyzed.The deformation energy makes the fruit injured.An evaluation method of blueberry injury degree is proposed,and the injury degree can be determined according to the quantity of the deformation energy.The mechanical injury evaluation criterion of the fruit is obtained.The kinematics analysis of the fruit in the process of falling and collision is conducted based on the principle of mechanical harvesting.The maximum mechanical energy loss happens in the process of the first collision,which is transformed into the deformation energy.The equation of mechanical energy loss is obtained.The influence factors on the mechanical energy loss are the tilt angle of collecting plate of the harvester,the falling height and the mass of the fruit.The contact and collision between the collecting plate and the fruit is analyzed based on the Hertz theory.The deformation calculation is carried out,and the deformation of the fruit at normal direction can be obtained.Once the deformation value of the fruit is determined,the deformation energy can be determined.An orthogonal test scheme of fruit collision is designed.Three test factors,i.e.the tilt angle of collecting plate,the falling height and the mass of the fruit,are selected.Each factor has 3 levels.The finite element model of the blueberry fruit is established.Through the collision simulation with the model,the stress and strain data of the contact area are obtained.According to the deformation calculation equation,the theoretical values of collision deformation are acquired.And the theoretical values of the deformation energy are obtained.The sequence of the influence factors from high to low is the falling height,the title angle of the collecting plate and the mass of the fruit.To verify the correctness of the analysis result,a falling and collision test-bed of the blueberry is established.The collision test parameters are designed,through which the deformation energy values are obtained.The deformation energy values are nearly consistent with the theoretical values.The error between them is 0.49×10^-3 J.The correctness and feasibility of the analysis of blueberry collision injury based on the energy method are verified.The installation and use parameters of the blueberry harvester are obtained.When the harvester satisfies the condition that the fruit concentration area of the blueberry tree is 600 mm from the collecting plate and the tilt angle of collecting plate is 15°,the deformation energy is less then 0.68×10^-3 J and the number of fruit injured is the least.The research results have certain guiding significance and reference value for the design and use of the harvesting device of the blueberry harvesters.