摘要
气动机械手广泛应用于汽车、医药、食品等工业生产线、特别适用于高温、易燃、易爆、多尘、强磁、辐射等恶劣环境；在上述某些场合下,要求机械手能抓取易碎、易变形的物体,这对机械手夹持力的控制性能提出了很高的要求。因此,对气动机械手的力控制研究,已经成为气动机械手研究领域的一个重要方面具有较好的理论研究和实际工程价值。本文在查阅国内外文献的基础上,总结归纳了气动比例伺服力控制系统以及气动机械手的研究现状。介绍了气动机械手夹持力控制系统的结构组成及其工作原理,对其进行了分析研究,提出了本文研究的系统的性能指标。
本文提出了影响夹持力控制精度的因素,并对该因素进行了理论分析研究,得出了其产生的原因和改善措施,建立了气动机械手夹持力控制系统的数学模型,分析得出包括系统的高频未建模特性、比例阀的死区特性以及气动系统的非线性等影响建模准确性的因素。主要从气动系统的动态特性、气缸的摩擦力以及爬行现象等方面对气动系统的非线性进行了相关分析,并运用MATLAB软件对气动机械手夹持力控制系统传递函数的频域特性进行了分析研究。
由于滑模变结构控制具有良好的抗干扰能力和抗模型参数摄动能力,针对气动系统存在的压缩性、摩擦力、气源压力和负载的变化等一系列非线性因素,确定采用上述控制策略来解决气动系统中未建模部分的动态特性和有界干扰问题,以提高气动力伺服系统的控制精度和稳定性。为克服滑模变结构控制系统存在的抖振现象,通过对控制器设计方法的分析研究,选用准滑动模态控制设计,采用基于饱和函数的趋近律方法设计了滑模变结构控制器,从根本上避免或减弱了抖振。
采用Matlab软件,对加入控制器后的气动控制系统进行了仿真研究。与未加入控制器以及加入PID控制的气动机械手夹持力控制系统的仿真结果进行分析比较。仿真结果表明,加入变结构智能控制器后系统具有较好的鲁棒性,提高了系统的响应速度和稳定性,频宽由0.53Hz提高到了5.54Hz；控制精度由2.6%提高到了0.8%；得到了较好的控制效果。
Pneumatic manipulators are widely used in industrial production lines such as automobile industry, pharmaceuticals industry, food processing industry and so on, especially in the harsh circumstances like high temperature, flammable, explosive, dust, magnetic, radiation. In some of these situations robots are required to crawl the fragile, yielding object, which need a high requirement on clamping force control the of robots. Therefore, it has become an important aspect in the force control of the pneumatic manipulator, which has better theoretical research and practical engineering value. Based on the domestic and international documents, this dissertation summarizes the current research status of pneumatic proportional servo force control system and pneumatic manipulator. The structure components and working principle of clamping force control system are introduced and analyzed in this dissertation. System performance indicators are proposed based on these analyses.
The factors which affect accuracy of the clamping force control are proposed, and the theory of the factors is studied. Then we obtained its causes and improvement measures. Reasonable assumptions and approximations in the linear process based on the established pneumatic manipulator clamping force control system mathematical model to analyze the frequency is undesirable, including system modeling features, dead zone characteristics of proportional valve and the nonlinear characteristic of pneumatic system and other factors will affect the modeling accuracy. This dissertation is mainly from points of the dynamic characteristic of pneumatic system, cylinder friction and creep phenomena of nonlinear pneumatic system for correlation analysis. Pneumatic manipulator clamping force control system transfer function of the frequency domain characteristics were analyzed by MATLAB software.
As the sliding mode control has a good anti-interference ability and capacity of the model parameter perturbation, for a series of non-linear factors of compression, friction, air pressure and load changing in the pneumatic system, the above control strategy is adopted to solve the unmodeled part of the pneumatic system dynamics and bounded disturbances, so it can improve accuracy and stability of the aerodynamic servo system. To overcome the chattering phenomenon of sliding mode control system, through the analysis of controller designing, selection of quasi-sliding mode control designing and design a sliding mode controller based on saturation function of reaching law to avoid or reduce the chattering.
Pneumatic control system combined with controller is simulated in the Matlab software. Simulation result is compared with no controller or the control system with PID controller. Simulation result shows that the system combined with intelligent variable structure controller has better robustness. The system response speed and stability are improved. The control accuracy is improved from2.6%to0.8%. And the Bandwidth is improved from0.53Hz to5.54Hz, which gets a better comprehensive control effect.
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