基于改进PSO的模糊PID高枝修剪机械臂末端抑振算法与试验

摘要

针对设计的高枝修剪机械臂定位过程易产生振动,难以快速、准确地将待修树枝对入锯切口的问题,分析大臂展、高负载自重比臂架系统的柔性特征,在此基础上研究末端修枝锯的抑振控制方法,实现末端修枝锯的快速精准定位.首先介绍了高枝修剪机械臂结构和工作原理,分析了臂架系统的柔性特征对末端修枝锯定位产生的影响;其次通过结构关系推导和有限元方法建立了机械臂的数学模型并进行动力学分析,并设计基于改进粒子群离线优化的模糊PID控制方法,实现了对末端修枝锯的主动抑振控制;最后分别在Simulink环境中和样机系统上进行了数值仿真和试验验证.综合仿真和试验结果表明:该文设计的控制方法可以实现末端修枝锯的主动抑振,定位过程中修枝锯能够在短时间内进入稳态,超调量不足开环状态下的50%,震荡调整时间小于1 s,经1 s后振幅衰减至峰值的5%以下,从而达到了较好的末端抑振效果,改善了修枝锯的定位性能,提高了高枝修剪机械臂的作业效率.相关研究可为其他具有一定相似柔性特征的机械提供末端抑振和精准定位的控制经验参考.%Pruning trees is an important work in forestry production, which plays an important role on the growth of trees and timber and the forest fire prevention. However, domestic and foreign high-altitude pruning machinery is still in its infancy, whose working height is generally less than 8 m and is not high flexible. It is difficult to effectively improve work efficiency in pruning high branches. In this paper, a simple, low-cost mobile tall tree pruning machine was designed, which could be easily towed to the forest area, and prune high branches within 15 m height. This machine had the working radius of 6 m and the maximum pruning diameter of 10 cm. However, in the process of sawing and positioning, due to the long arm span and high load weight ratio, there were obviously flexible features for its arms, and the end-effector (pruning saw) was easy to vibrate during its positioning. Thus, it was difficult to achieve fast and accurate positioning, as well as fix the branch to be cut. Aiming to the above problems, this paper analyzed the flexible characteristics of the boom system with the boom display and the high load weight ratio. On this basis, the vibration suppression control method of the end of pruning saws was investigated to achieve the rapid and accurate positioning of the end of pruning saws. In this paper, focusing the flexible characteristics of the manipulator and the vibration suppression of the end-point, based on the introduction of the boom structure and working principle, we analyzed the impact of flexible features on the positioning of the end of pruning saws by geometric derivation, and the FEM (finite element modeling) was used for the dynamics analysis of the boom system. And the fuzzy PID (proportion, integral, derivative) controller was designed based on an improved PSO (particle swarm optimization) algorithm, in order to realize the active vibration suppression control of the end of the actuator. In the designed fuzzy PID controller, the improved PSO algorithm was used on the numerical simulation model to optimize the fuzzy domain intelligently. The parameters of the PID controller were adjusted and the vibration of the pendulum saw was suppressed, and the simulation and experimental verification were performed in the SIMULINK environment and a prototype system, respectively. The experimental results showed that the design of the tall trees pruning manipulator control method could realize the end-point vibration suppression, and the pruning saw could be accurately positioned into the steady state during the localization process in a short period of time. The actual measured data showed that the overshoot was less than 50% under the open-loop state, the amplitude decay was less than 5% of the peak after 1 s, the vibration adjustment time was less than 1 s, and the system could achieve steady state, and achieve a more effective vibration suppression effect. Verification results showed that under the effect of the control algorithm and the controller designed in this paper, the end-effector could be stabilized in a short time after the positioning to achieve better active vibration suppression effect. The control algorithm improved the pruning saw's positioning accuracy and speed, and optimized the dynamic performance of the entire machinery to ensure the flexible control of high branch pruning machinery. Through the simulation analysis and prototype test using the proposed active control algorithm, the results verify the reliability of the algorithm and accumulate the valuable experience for the further development of the high branch pruning machinery.