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面向大工作空间高速拾放的驱动同轴并联机器人的研究
中文摘要

拾放操作是工业生产中的典型工艺,用以完成上下料、分拣、包装等任务。并联机器人因其高速、高加速度的性能优势,能够提高作业的效率,成为工业拾放操作的热门之选。然而传统的并联机器人具有一个根本性的缺陷:占地较大,而工作空间非常有限。这一缺陷大大限制了并联机器人,尤其是在拾放操作方面的应用。本文面向平面三、四自由度拾放操作,提出了一类主动关节同轴的并联机器人,不仅保留了并联机器人高动态性能的优势,并且其工作空间大大拓展,达到了接近串联机器人工作空间的水平。由此,本文就该驱动同轴式并联机器人展开构型设计、运动学与动力学分析、优化设计和运动控制等研究。论文的主要内容包括: 本文以一款驱动同轴三自由度平面运动并联机器人V3为主要研究对象。首先,对其进行了建模与分析,包括:从机器人闭链方程出发对机器人的运动学进行推导与分析,基于反向运动学进行灵巧工作空间分析,利用速度雅可比矩阵进行奇异性分析,以及利用虚功原理建立刚体动力学模型。接着,基于V3并联机器人的构型提出了一款新型的能够实现三平动一转动的四自由度驱动同轴并联机器人T4。该机器人为V3并联机器人的升级设计,保留了大工作空间和末端执行器能够不受限旋转的优点。通过改变原有支链构型,并增加新的提拉支链,使其克服了V3并联机器人末端执行器不能沿竖直方向平动和承重能力差的缺点。随后,本文从T4并联机器人闭链方程出发对机器人的运动学进行推导与分析,基于反向运动学得到了机器人灵巧工作空间的解析表达式,利用速度雅可比矩阵奇异性进行了分析。 针对高速拾放操作的工业应用需求提出了三种机器人机构的优化设计方法,并对V3并联机器人机构进行了优化设计,从而获得最优的杆件几何参数。这三种优化设计方法分别以灵巧性指标、速度指标、精度指标、加速度指标、电机输出功率指标和弯曲刚度指标中的若干项为约束条件,并均以最大化满足性能指标要求的工作空间为目标。通过仿真实验验证了优化设计的有效性,各最优设计的性能都得到了极大改善。 在考虑机器人杆件运动柔性时,本文对V3并联机器人系统进行了结构控制一体化设计的研究。效率是高速拾放操作的关键需求。为了达到高加速度通常都会减轻运动部件的质量,但是这会导致杆件的柔性效应增加。由于结构参数与控制参数对机器人系统整体性能有耦合影响,一体化设计的方法被用于改进V3并联机器人系统整体性能。有限元方法被用来推导动力学模型。机器人闭环系统采用比例微分控制策略。针对高速拾放操作的应用需求,本文提出了一种基于操作效率的一体化设计方法。该方法以精度作为性能约束,通过求解一体化设计问题同时优化结构和控制参数。仿真实验结果显示一体化设计方法在保证精度同时,使机器人系统的操作效率得到了提升。 结合机器人的结构特征和机构优化设计后奇异位形的分布情况,研究了无奇异的路径规划策略。该策略能够通过起始点与终止点的末端执行器的位置与姿态信息判断能否进行无奇异路径规划和选择路径的类型。 最后,本文研制了V3并联机器人系统的样机。制造该机器人系统样机采用了工业自动化设备中常用的零部件。以该机器人系统样机为基础进行了实验研究,实验结果表明该样机能够应用于高速拾放操作以及机构优化设计的有效性。 关键词:驱动同轴并联机器人;大工作空间;拾放操作;运动学;动力学;优化设计

英文摘要

Pick-and-place operation is a typical process in industrial production to be utilized for loading/unloading, sorting, packing and so on. Due to their high velocity and high acceleration, parallel robots have been widely recognized as prospective candidates for industrial high-speed pick-and-place operations to improve production efficiency. However, the traditional parallel robots exhibit fundamental drawbacks in large footprint and limited workspace, which greatly restrict their applications, particularly to pick-and-place operations. In this dissertation, for planar 3 degree-of-freedom and 4 degree-of-freedom pick-and-place operations, a family of parallel robots whose actuated joints have a common axis of rotation have been introduced. Not only do they retain the high dynamic performance of parallel robots, but also their workspaces are greatly expanded, which are similar to serial robots’. Thus, a series of researches about structure, kinematics, dynamics, optimal design, motion control, etc. of the co-axis actuated parallel robots have been carried out in this dissertation. The following contents are mainly investigated. In this dissertation, a 3 degree-of-freedom planar parallel robot with common axis actuated joints, named the V3 robot, is the main subject. Firstly, its geometric model, kinematics starting with the loop-closure equations, dextrous workspace based on the inverse kinematics, singularity from the velocity equations and rigid-body dynamic model based on the virtual work principle are derived and analyzed. Then, based on the structure of the V3 parallel robot, this dissertation presents a novel 4 degree-of-freedom parallel robot with common axis actuated joints, named the T4 robot, which is an upgraded design of the V3 parallel robot and capable of three translations and one rotation. It retains large workspace and unlimited rotation capability of the end-effector. Due to the modified type synthesis of the subchains and the introduction of a lifting subchain, this robot overcomes the disadvantages of the V3 parallel robot, which is short of a vertical translation and weak in load bearing capacity. The inverse and forward kinematics are derived and analyzed starting with the loop-closure equations. An algebraic derivation of the dextrous workspace is presented from the inverse kinematic equations. The singularity analysis is discussed based on the relationship between the velocities of the actuated joints and the end-effector. For high-speed pick-and-place operations, three new optimal design methods are proposed for the V3 robot mechanism to obtain optimal geometric parameters. Combining some of the alternative performance indices, which consist of dexterity, velocity, accuracy, acceleration, motor output power and bending stiffness, these optimal design problems are formulated to maximize the workspace having specified desired performances. Simulation results show these methods are effective and that the optimized structures’ performances are greatly improved. Considering the flexible-link robot system, the integrated structure and control design method for the V3 parallel robot system is studied. Efficiency is critical requirement for high-speed pick-and-place operations. In order to achieve high acceleration, low moving mass/inertia is inevitable, which leads to increasing flexible effects due to the applied thin and light links. In view of the coupled effects of structure and control parameters in the whole system performance, the integrated method is utilized to improve the performance of the V3 parallel robot system. The dynamic model is derived by the finite element method. The proportional-derivative control strategy is applied in the closed-loop system. Efficiency is critical requirement for high-speed pick-and-place operations. In this dissertation, an efficiency based the integrated structure and control design method is presented for high-speed pick-and-place operations. The structural and control parameters are optimized simultaneously by solving the integrated design problem with accuracy constraints. Simulation shows that the integrated design method presents improved system performance on efficiency, at the same time the accuracy is also guaranteed. Considering the optimized structures and the singularities, singularity-free path planning strategy is studied. This strategy can be used to decide whether the singularity-free path can be achieved and choose the path type by the positions and the orientations of the end-effector at the starting and ending points. At last, the prototype of the V3 parallel robot system is designed and established, which is made of common components and parts in industrial automation equipments. The results of the experiments based on this prototype confirm it can be applied to high-speed pick-and-place operations and the optimal design is effective. Keywords: co-axis actuated parallel robot, large workspace, pick-and-place operation, kinematics, dynamics, optimal design

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