五自由度混联机器人优化设计与运动学分析

为提高农业自动化程度,拓宽并联机构在农业工程领域的应用,提出一种存在连续转轴、关节数目少、易于控制的两移一转运动冗余平面并联机构,该并联机构任意位置的转轴均为相互平行的连续转轴,使其具备良好的灵活性。基于此平面并联机构,构造出了多种五自由度混联机器人,首先建立了五自由度混联机器人的运动学模型,并对其进行了奇异分析,给出了减少机构奇异位型的条件;然后基于灵活性指标,对并联机构进行了尺寸优化,绘制了用于选取结构尺寸的性能图谱,且借助有限元软件对基于优化所得结构尺寸绘制的具有运动冗余特性的平面机构进行了结构拓扑优化,,完成了整体结构优化前后的静力学分析与对比,结果显示优化前后整体变形仅增大0.51%,优化前后机构优化部分的质量减少33.02%,满足机构变形要求。该混联机器人具有结构简单、运动学模型简单、结构刚度高和模块化程度高的特点,且其结构的变胞性有助于实现机构运动和驱动冗余模式的切换,增强了机器人的可研究性。该文可为混联机器人运动学分析及优化设计提供参考。

Optimal design and kinematics analysis of 5-DOF hybrid serial-parallel manipulator

Abstract: In recent years, with the development of various types of intelligent robots, new agricultural robots have become frontier technology in the field of international agricultural machinery. And as the complexity and diversity of the agricultural production and operation, the characteristics of advancement and practicability are needed to add to the agricultural robots. In this paper, in order to increase the automation level of agricultural operations and improve the ability of adapting to different working environments, a novel kinematically redundant planar parallel mechanism (PM) with continuous rotational axis and fewer joints is proposed, which has one rotational degree of freedom (DOF) and 2 translational DOFs (2T1R). For the rotational DOF, the rotational axes of the moving platform are mutually parallel at any position of the whole workspace; for the translational DOFs, the directions are simple horizontal and vertical. This robot has a quite simple structure. As we all know, simple structures of the robot can reduce the manufacturing cost to a great extent. This kinematically redundant planar PM is a metamorphic mechanism. For instant, when the moving platform and the intermediate link are locked, the PM becomes an actuation redundant PM. So this PM can be used to research not only the kinematically redundant property but also the actuation redundant property. Actually, this new type PM can be used in the field of food packaging, seed selection, fruit classification, transport, picking, and so on. For the purpose of improving the robot properties, 15 5-DOF hybrid serial-parallel manipulators are constructed on the basis of this type of planar PM. One of these manipulators is selected to do some analysis in this paper, which is more likely to be applied in agriculture. Firstly, the kinematic model of the 5-DOF hybrid manipulator is established. Especially, the forward and inverse kinematics models show the briefness of this robot. What is worth mentioning is that a simple kinematics model is conducive to realize the control of the robot. And this matches the strategy of robot intelligence. The velocity Jacobian matrix is deduced, the singularity analysis of the PM is done according to the Jacobian matrix, and the conditions for reducing singularity are listed. The concept of singularity degree is defined, which can be used to keep away from mechanism singularity. Then based on the flexibility performance index, the optimal design of the 2T1R planar PM is investigated and the performance atlas is drawn. From the performance atlas, we can choose the physical dimensions of the PM. The 3-dimentional model based on a set of optimal physical dimensions is established. After that, in order to reduce weight without the loss of stiffness, the structural topology optimization is accomplished by means of the finite element software. The analysis and comparison of the whole structure are also carried out. This novel hybrid manipulator has the characteristics of simple structure, simple kinematic model, high stiffness, and high degree of modularity, which provides a very variety of application prospects in the field of agricultural machinery.