摘要
为了减少采摘机器人末端执行器在夹持过程中对果实造成的损伤,该文通过在末端执行器上设置柔顺机构,并对柔顺机构力学性能进行计算,求解果实无损采摘所需的柔顺恒力特性。首先,基于形状函数建立边界条件约束下的柔顺梁非线性常微分控制方程;然后,利用打靶法将上述边值问题重新描述为初值问题,并结合遗传算法进行初值优化求解,采用序列二次规划法优化梁的形状函数,使其在一定变形范围内实现恒力输出;最后,在给出求解所需参数和柔顺机构初始形状参数基础上,以苹果采摘为例,通过优化计算,使柔顺梁对果实的夹持力维持在7.9 N左右,非线性有限元计算和力-位移特性试验验证了计算结果的准确性,多次苹果夹持试验的抓取完好率为95%,验证了该柔顺机构无损夹持苹果的可行性。研究结果可为不同类型果实的恒力夹持提供参考。
In order to reduce the damage caused by end effector of picking robot during fruit clamping process,non-destructive fruit picking has gradually become a key technology of fruit harvesters.The application of compliant constant-force mechanism may enable a constant output force within a certain range of operating displacement.The existing compliant constant force mechanism has the defect that the constant force interval is small relative to the size of the mechanism,which makes it difficult to apply in the situations requiring compact structure design such as fruit picking.In this paper,a method to generate compliant constant-force mechanism is introduced.Firstly,based on the shape function,a set of nonlinear ordinary differential equations for buckling deformation of compliant beams under boundary conditions is established.Secondly,the boundary value problem is redescribed as the initial value problem by applying the shooting method combined with the Runge-kutta method,the 3D nonlinear equations are obtained according to three boundary conditions,two unknown variables and one unknown initial value.Thirdly,the nonlinear equations is solved as an optimization problem.To avoid the optimization problem falling into local convergence,the genetic algorithm is employed to globally find the appropriate initial values of the three unknowns in the nonlinear equations,the solution of the differential equations is obtained according to the principle of the shooting method.Finally,the sequential quadratic programming method is implemented to optimize the parameters of the shape function,the optimization objective is to achieve a constant output force within a certain range of displacement input,and the constraints are the design boundary and the maximum permissible stress of the beams.A two-finger apple picking end effector is taken as an example,the initial shape parameters of the compliant mechanism are set and the algorithm is realized in Matlab.After optimization,the constant clamping force of the compliant beam to the fru
作者
苗玉彬
郑家丰
Miao Yubin;Zheng Jiafeng(School of Mechanical Engineering,Shanghai Jiao Tong University,Shanghai 200240,China)
出处
《农业工程学报》
EI
CAS
CSCD
北大核心
2019年第10期19-25,共7页
Transactions of the Chinese Society of Agricultural Engineering
基金
上海市科研计划项目(16391901700)
沪农科推字(2018)第1-2号、(2015)第4-1号
上海市工程技术研究中心建设专项(17DZ2252300)
关键词
机器人
末端执行器
设计
恒力柔顺机构
打靶法
robots
end effectors
design
compliant constant force mechanism
shooting method
