摘要
多自由度机械手运动系统在汽车风挡玻璃涂胶作业中应用广泛,其中机械手运动轨迹控制尤为关键。胶水的易燃性使得机械手气压驱动方式极具竞争力。本研究的主要目的就是使用气动位置伺服驱动方式组成多自由度机械手,结合气动系统的特点研究机械手空间运动轨迹控制,为其在汽车风挡玻璃涂胶等领域的工业应用打下坚实的基础。
本文根据涂胶要求结合现有条件研制了一种三自由度关节串联式气动机械手控制系统。单关节(腰部、大臂、小臂)动力机构采用气动比例流量阀控缸。首先介绍了机械手的基本组成和工作原理,建立了机械手运动学模型,进行了运动学正解和反解分析。结合气动机械手运动学模型,使用基于运动学模型的逆推关节的角度规划轨迹方法,完成了多种轨迹的仿真分析,提出了适合机械手单关节气动位置伺服系统特点的规划轨迹理论指导。
关节动力学特性是机械手关节控制的理论基础。本文推导了气动机械手关节动力学方程并进行了简化。通过动力学仿真得出机械手在低速运动时重力矩为关节驱动力矩主要部分,由此根据简化的动力学方程,提出了使用规划轨迹位置的重力矩补偿控制方法,得到了各关节实时简单的期望重力补偿力矩。给出了重力补偿力矩的基本变化规律,为轨迹规划提供了参考依据。通过空间直线轨迹运动实验证明了补偿方法的有效性。
建立了气动机械手单关节的线性化模型。通过机械手关节辨识实验,得到了关节辨识模型,经过对比,二者低频段特性相似,理论推导结果可信。针对气动系统特性复杂等特点,设计了基于关节线性化模型的机械手单关节气动位置伺服系统极点配置控制器,针对机械手运动中单关节不同负载、不同轨迹、不同工况以及不同控制模型条件下,分析了系统极点位置配置区域,得到了适应多任务情况的系统闭环主导极点的配置范围。针对机械手低速运动时气缸易出现爬行现象研究了气动系统的颤振补偿效应,通过叠加正弦颤振信号,使气缸产生交变的微小运动,减小了摩擦力引起的系统非线性影响,消减了低速运行时气缸的爬行,给出了颤振信号幅值与频率与系统性能的关系,提出了气动机械手关节颤振信号参数设计依据。建立了气动机械手Simulink/ADAMS联合仿真模型,对比了机械手单关节及三关节联动时各关节运动跟踪响应特性,发现联动时关节间的耦合明显,误差变大。最后完成了机械手单关节特性实验,结果表明系统具有较好的跟踪能力和鲁棒性。
气动机械手关节间联动时存在明显的耦合。根据单关节比例流量阀控直线气缸数学模型,结合关节动力学简化方程,建立了机械手大小臂双关节动力机构耦合动力学关系,研究了大小臂关节的耦合影响,分析了关节角加速度对关节耦合惯性力矩的关系。根据重力补偿和实际工况参数,设计了解耦补偿控制器了双关节解耦补偿控制器,该方法对消除机械手关节之间的交连耦合,提高系统单关节的动态特性效果明显。
最后,进行了机械手空间轨迹控制实验研究。介绍了气动机械手的组成及针对其多关节多任务特点所设计的实时控制系统。综合关节极点配置控制策略控制方法,辅以规划轨迹位置关节重力矩补偿、大小臂解耦补偿控制,进行了机械手三关节联动空间运动轨迹跟踪控制实验,分别跟踪了空间直线,空间圆周以及某车风挡玻璃1:2外形轮廓,结果表明机械手末端跟踪误差少,跟踪轨迹在笛卡尔空间各坐标轴分量平均相对偏差率保持在2%以内,机械手三关节动作同步性好,末端运动速度波动控制在2mm/s以内。综合以上性能气动机械手能够满足实际的工业涂胶应用的精度及均匀性要求,为进一步的工业实用化打下了基础。
The automatic gumming manipulator system has been widely used in the automobile windshield glass gumming. It is particularly critical to control the trajectory tracking of the manipulator. Furthermore, the glue flammability brings the pneumatic drive working mode a highly competitive position. Therefore, the main purpose of this research is to develop a multi-DOF manipulator by using a pneumatic position servo system, and to study the spatial trajectory control of this manipulator. This work will provide a solid foundation for the industrial application of the automobile windshield glass gumming.
A three DOF serial joint pneumatic manipulator control system was developed based on the gumming requirements and the existing conditions. The pneumatic proportional flow valve controlled cylinder system was used in the power mechanism of the single joint (the waist, the main arm and the lower arm). Firstly, the basic elements and the operating principle of the pneumatic manipulator are introduced. Then, the kinematics model of the pneumatic manipulator was established. The forward and inverse kinematics analysis has been carried out. Several typical kinds of trajectory simulation results were obtained by using inverse angle angles planning trajectory method, based on the pneumatic manipulator kinematics model. Finally, a planning trajectory theoretical guidance which can be suitable for the characteristics of pneumatic position servo system was proposed.
The joint dynamic characteristics are the theoretical basis for the manipulator joint control. In this paper, the dynamic equations of the pneumatic manipulator were deduced and simplified reasonably. The dynamics simulation results show that the gravity torque is the major part of the driving torque when the end point of pneumatic manipulator is at a low speed. Thus, according to the above simplified joint dynamic equations, a control method on the gravity compensation torque with planning trajectory was presented. In addition, the gravity torque changing law with main arm and lower arm joints angles was obtained. It can provide a reference for the planning trajectory. The experiments verify the validity of this compensation method.
The computation linearized models of the pneumatic manipulator joints were built. Compared with the identified model in the pneumatic manipulator joints identification experiment, the characteristics in low frequency is as same as the computation models. This result shows that the theoretical model is correct. By considering the complex characteristics of the pneumatic system, the pole-placement controller was designed as the control strategy for the single joint pneumatic position servo system based on the computation linearized models. The system pole configuration region was analyzed, by taking the different loads, the different traces, the different conditions and the different control models into account. The system closed-loop dominant poles which can meet well with the multiple task conditions were obtained. A flutter compensation method was investigated, for describing the cylinder creeping phenomenon when the pneumatic position servo system was at a low speed. The superposition sine flutter signal was used to produce the alternate minimal motion in cylinder and decrease the system nonlinear effect caused by the friction. Thus it can diminish the cylinder creeping phenomenon. The relationship between the frequency and the amplitude of the sine flutter signal and the system characteristics was obtained. A model of co-simulation based on Simulink/ADAMS was built. The simulation results show that the coupling characteristics in the joints were obvious and the tracking error in the tri-joints moving together was bigger than the single joint moving. The characteristic experiments of the pneumatic manipulator single joint were performed. The results show that the system has a good tracking performance and robustness.
There is obvious coupling phenomenon in the joints of the serial pneumatic manipulator. According to the mathematic model of the electro-pneumatic proportional flow valve controlling a linear cylinder and the simplified equations of the joints, the decoupling dynamic equations of the dual-joint (the main arm and the lower arm) were obtained. And the relationship between the joint angular acceleration and the joint coupling inertial torque was analyzed. According to the gravity compensation and working condition parameters, the decoupling controller of the dual-joint was also designed. It is obvious that this method can eliminate the effect of joints coupling and can improve the system dynamic characteristics.
Finally, the spatial trajectory control experiments of the pneumatic manipulator were performed. The compositions of the manipulator and the real-time control system which can meet the multi-joint multi-task were introduced. In addition, the single-joint pole–placement controller, the gravity compensation torque with the planning trajectory control method and the decoupling compensation control method were used in the joint control in the pneumatic manipulator. The experiments of the manipulator spatial trajectory tracking with tri-joints combined moving were carried out. The spatial line, the spatial circular and the car windshield 1:2 glass shape were tracked, respectively. The experimental results show that the tracking error of the manipulator end point is small; the average relative tracking error of the trajectory in Cartesian coordinate axes is less than 2%; the tri-joints’moving is in a good synchronization; and the manipulator end point velocity fluctuation is maintained in 10%. The above performances show that the pneumatic manipulator meets well with the industrial gumming precision and the uniformity requirement. The present work provides a support for the industrial application of the pneumatic manipulator.
引文
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