轮腿混合四足机器人六自由度并联机械腿设计

为了设计一种可以同时实现迈步行走、有动力轮式机动、无动力轮旱冰式滑行3种运动方式的轮腿混合农业四足机器人,提出了一种基于3-UPS机构的六自由度并联机械腿,选取结构参数并给出设计方案。首先,通过矢量回路法推导出机构的位置反解方程,并建立机构的速度映射模型;采用搜索法对机构的工作空间进行分析,并绘制出工作空间三维分布图,揭示出机构结构参数和工作空间之间的关系;基于速度映射模型绘制出雅可比矩阵条件数在工作空间内的三维分布图。接着,定义了一组运动灵活性评价指标,对机械腿的机构进行运动灵活性分析,并绘制出结构参数与运动灵活性评价指标关系曲线,揭示出结构参数对机构运动灵活性的影响规律。然后,基于工作空间特性和运动灵活性评价指标,采用蒙特卡罗法进行结构参数设计,通过建立各结构参数的概率模型空间选取了一组综合性能较好的结构参数:机械腿固定平台万向副分布直角边长为230 mm,运动平台球面副分布直角边长为70 mm,支链最大直径为60 mm,各支链套筒和伸缩杆长度均为500 mm。最后,采用选取的结构参数设计出机械腿及轮腿混合四足机器人整体的虚拟样机,并对虚拟样机进行迈步运动仿真,结果表明:机械腿的各驱动参数变化非常平稳且峰值均在合理范围之内,证明机械腿的设计方案和结构参数较为合理。该研究为拓展轮腿混合四足机器人在农业工程领域的应用提供了参考。

Design of 6-DOF parallel mechanical leg of wheel-leg hybrid quadruped robot

Abstract: In the field of agricultural engineering, a lot of work is carried out on rough terrains, such as rugged mountains or hills. Mobile robots are very suitable to be used in these areas, and these kinds of robots can work in the rugged mountains or hills environment without caring about the safety of workers. The wheel-leg hybrid quadruped robot is very suitable to be used in agricultural engineering. It can move with the dynamic driving wheels in the road with high speed, and also can walk by stepping alternately in the ruins with its mechanical legs. The wheel-leg hybrid quadruped robot can also skate in a flat road by the wheels without dynamic driving, and in this state, the robot can obtain the maximum speed with the minimum energy consumption. In order to design a kind of wheel-leg hybrid agricultural quadruped robot, which can achieve walking, dynamic wheel moving, and roller-skating, a new mechanical leg based on the 3-UPS(U-universal joint, P-prismatic joint, S-spherical joint) parallel mechanism is proposed. The structure parameters of the mechanical leg are determined. The design schemes of the mechanical leg and the wheel-leg hybrid quadruped robot are given. First, using the vector chain method, the inverse position equation is presented, and the velocity transmission model is established. The workspace analysis of the leg mechanism is performed and the 3D (three-dimensional) map of the workspace is drawn by searching method. The relationship between the structural parameters of the mechanism and the workspace is revealed. The 3D map of condition number of Jacobian matrix is drawn in the workspace based on the velocity transmission model. Also, a set of kinematics performance evaluation indices are defined, and the kinematics dexterity of the leg mechanism is analyzed. And the relationship curves between structure parameters and the kinematics performance evaluation indices are drawn. These curves reveal the influence of structural parameters on the flexibility of the mechanism. Then, based on the indices of workspace and kinematics dexterity, the structure parameters are analyzed by Monte Carlo method. By establishing the probability space model of each structure parameter, an excellent set of structural parameters are found: The distance between two universal joint''s rotation center points of the fixed platform is 230 mm, the distance between two spherical joint''s rotation center points of the moving platform is 70 mm, the maximum diameter of the telescopic sleeve is 60 mm, and the lengths of each branch''s sleeve and the telescopic rod are both 500 mm. Finally, based on the excellent set of structural parameters, the virtual prototypes of wheel-leg hybrid quadruped robot and its parallel mechanical leg are designed. The motion simulation analysis of the virtual prototype is performed, and the driving speed curves of parallel mechanical leg''s driving joints are obtained. Simulation results show that: The driving parameters of the mechanical legs are very stable, and the peak values of the driving parameters are within the reasonable range. These prove that the design scheme and the structural parameters of the mechanical leg are very reasonable. The results provide the theoretical reference for further study of wheel-leg hybrid quadruped robot.