【作者】 吴金波；

【导师】 熊有伦； 尹周平；

【作者基本信息】 华中科技大学 ， 机械电子工程， 2007， 博士

【摘要】 本文研究了由同步带驱动的两轴拱架机器人的建模与控制问题,该类机器人提供了两个相互垂直方向的运动,即沿梁运动的工作头(x方向)和沿基座运动的梁(y方向)。两运动轴由于工作头在x轴的位置影响y轴的动力学特性而相互耦合,这一耦合的产生是由于工作头在梁上的位置决定了y轴的质量分布,也即y轴运动的振动特性。同步带驱动系统将电机扭矩转换为两运动机构的线性驱动力,目的是使工作头尽可能快地移动到目标位置并达到微米级的定位精度,但摩擦力的干扰、柔性梁和同步带驱动系统的结构振动以及两运动机构之间的动力学耦合给这一控制目标的实现增加了难度。目前,对同时具有驱动柔性和结构柔性的拱架机器人的研究还非常少。首先,建立了拱架机器人x方向的动力学模型。为减小由同步带驱动的直线伺服定位系统的振动,构造了双闭环控制系统,基于对系统数学模型的频域分析,将系统振动分为低频振动和高频振动,这一区分对系统控制器的振动抑制策略非常重要。采用低陷滤波器抑制系统的高频振动,时滞滤波方法规划了合适的参考输入,并结合PID控制实现快速的点到点运动并保持较小的残余振动。作为一种离线规划措施,此控制器设计方法不需改变系统的任何硬件设施,能直接、有效地应用于现有的柔性驱动系统中。其次,对拱架机器人的y向动力学进行了建模,模型考虑了系统的结构柔性与驱动柔性以及两者之间的耦合作用。结构柔性具体体现为三种类型的振动:柔性梁在刚性模态下的扭转振动,一端支撑于扭簧上的柔性梁的弯曲振动和简化为一移动振荡子的贴装头的振动。基于系统的振动特性分析,提出了原型机的机械设计改进方法。另外,分别研究了当工作头静止和移动时,柔性梁的H_∞输出反馈控制器设计方法。当工作头在x方向固定时,应用线性矩阵不等式处理方法,给出了系统的输出反馈最优控制器。当工作头沿柔性梁移动时,拱架机器人的y向动力学模型可作为一线性变参数系统处理。采用严格的等价变换将一类通用的线性变参数系统描述模型变换为一简化模型,引入变H_∞性能将控制器的设计问题转换为满足线性矩阵不等式约束的参数矩阵的求解问题,并给出了无需变参数变化率反馈的变增益全阶输出反馈H∞控制器设计方法。接着基于“H_∞性能覆盖”的概念,给出了保H_∞性能的插值方法。仿真结果表明: H_∞鲁棒控制器具有较小的调节时间且有效抑制了系统的振动和外部干扰,且本文提出的变增益H_∞控制器设计方法能有效降低控制系统的保守性。然后,针对普通变增益H_∞控制器设计过程复杂及权函数选择困难等缺陷,采用回路成形方法设计线性变参数系统的H_∞控制器,并将其应用于拱架机器人上。为了得到线性变参数系统的连续控制器,通常对选定的变参数值设计线性控制器后,需要在变参数集合内对这些线性控制器进行插值。本文给出了输出反馈线性控制器进行保稳定性插补的充分条件,确保系统指数稳定的变参数变化率的上界也可在计算出控制器插值后得出。由于此方法得出的控制器通常具有较高的阶数,为方便工程应用,对控制器进行降阶处理,采用变增益PID控制器逼近高阶鲁棒控制器,从而将最终的H_∞控制结构转化为PID+滤波器的常见形式。仿真结果验证了所提控制方法的有效性。最后,介绍了拱架机器人在RFID封装设备中贴装模块的集成设计方法,并给出了本文理论研究成果在该机器人中的实现方法。更多还原

【Abstract】 This dissertation mainly studies the modeling and control of two-axis belt-driven gantry robots. Such robots provide two orthogonal motions, a head sliding along a beam (x-axis motion) and the beam sliding along a frame (y-axis motion). The two axes are coupled in the sense that the x-axis position influences the y-axis dynamics. This coupling arises because the location of the head on the beam determines the mass distribution and hence the vibration characteristics for y-axis motion. Belt-pulley transmissions convert rotary motor torque into linear forces that drive the two-axis mechanism. The control objective is to move the gantry head to the target position as fast as possible, yet also settle quickly withμm accuracy. But friction force disturbances, structural vibrations in the gantry beam, transmission resonance and the coupling effect of the two-axis mechanism add difficulties to achieve this objective. At present, the study about the gantry robots which inclue both drive elasticity and structure flexibility is very few.Firstly, the modeling for the x-axis dynamic of the gantry robot is deduced. To suppress the vibration of the linear belt-driven system and improve the transient response performance, a double closed-loop control system is constructed and the mechanical resonance of the belt-driven system is analyzed and classified into two categories: low frequency resonance and high frequency resonance, which is crucial for guiding the design of controller. A notch filter is adopted to attenuate the high-frequency vibration. A new kind of input pre-shaping method producing an appropriate reference profile accompanied with a PID controller is proposed for suppressing the low frequency vibration to ensure fast point-to-point motions with minimum residual vibration. As an off-line method, the proposed method can be easily and effectively adopted to the existing elastic-driven system without any modification of the hardware setup. Next, the y-axis dynamic of the gantry robot is modeled. The model considers the structure flexibility and drive elasticity in addition to their coupling effect. The structure flexibility is embodied through three types of vibration, namely, the torsional vibration of a flexible beam in rigid motion mode, the transverse vibration of the flexibility beam with supports on torsional spring at one end and the vibration of the head which is simplified as a moving oscillator. Based on analysis of the vibration characteristic in the system, the improvement measures of the mechanical design are proposed.In addition, the design method of the H_∞output feedback controller for the flexible beam in y-direction with stationary and moving head is studied respectively. When the head is stationary in x-direction, the optimum output feedback controller of the system is devised based on the linear matrix inequality (LMI) approach. When the bonding head moves along the flexible beam, the dynamic model of the gantry robot in y-direction can be considered as a linear parameter-varying (LPV) system. The general LPV system is transformed into a simplified model using strict equivalent transformation. Using parameter-varying H_∞performance, the controller design is translated into the solution of parameter matrices which satisfy the constraints of LMI. And the design method of the gain scheduling full order output feedback controller without parameter-rate feedback is also proposed. In succession, based on the concept of“H_∞performance covering”, the interpolation method which meets the demands of H_∞performance preserved is introduced. Simulation results indicate that the H_∞controller provides small settling times with reduced structural vibration and disturbance attenuation. In addition, the design method of the gain-scheduling H_∞controller proposed in this dissertation can reduce the conservation of the system effectively. Then, in order to overcome the deficiency of the ordinary H_∞controller design method, such as the complication of the design procedure and difficulities of the weight selection, a loop shaping design procedure using H_∞synthesis is introduced and applied to the gantry robot. To get the continuous gain-scheduling controller of LPV system, these designed linear controllers for the selections of scheduling variable shoule be interpolated in the scheduling variable set. This dissertation provides a sufficient condition on the selections of scheduling variable for which output feedback controllers are designed such that a stability preserving interpolation of the linear controllers can be calculated. Once the interpolation is computed, an upper bound on the rate of variation of the scheduling variable to assure exponentially stability can be calculated. Because the controller achieved from this design method generally has high orders, it is necessary to reduce the controller order for the convenience of engineering applications. A gain-scheduling PID controller is presented to approximate the high-order robust controller so that the last H_∞control structure is transformed into the form of“PID+filters”. Simulation results verify the effectiveness of the proposed control method.Lastly, the integration design methods of gantry robot which is used in RFID package equipment pre-bonding module are introduced. And the realization methods of the academic research achievements, which are proposed in this paper and will be used on the gantry robot, are also developed.更多还原