软体机械臂的建模与神经网络控制

Modeling and neural network control of a soft manipulator

  • 摘要: 软体机械臂因其出色的环境适应能力以及安全的人机交互使其在医疗、航天航空等领域有着广阔的应用前景。但由于软体机械臂是一类连续体装置,不能采用传统的刚体机械臂的建模和控制方法,需要一种新的建模方法。针对一类线驱动软体机械臂,本文提出一种基于应变参数化方法的软体机械臂建模方法,能够描述软体机械臂在三维空间下在不同布线方式下的运动。首先把整个软体机械臂当作一个Cosserat梁,利用成熟的Cosserat梁理论进行建模,其核心思想是利用Ritz方法对软体机械臂应变场进行离散化,得到一组常微分方程组,其次利用反向传播(Back propagation,BP)神经网络完成形状空间与驱动器空间的驱动力转换。针对软体机械臂模型中存在的未知动态,利用径向基函数(Radial basis function,RBF)神经网络进行逼近和补偿。然后基于Lyapunov稳定理论证明了引入自适应神经网络控制器后闭环系统的稳定性。最后,针对模型与自适应神经网络控制器进行了一系列的仿真实验,验证了模型和控制算法的有效性。因此,可以实现对一类软体机械臂的建模控制。

     

    Abstract: With the vigorous development of material synthesis, mechanical manufacturing, and computer technology, as well as the in-depth study of control theory and bionics, robotics has undergone tremendous changes in recent decades. From rigid robots to discrete redundancy robots, from continuum robots to soft robots, the application of robots has long been beyond traditional industrial fields such as assembly, welding, and painting. It has expanded to medicine, education, agriculture, the military, etc., covering almost every aspect of people's lives. Soft manipulators have broad application prospects in medicine, aerospace engineering, and other fields due to their excellent environmental adaptability and safe human–machine interaction. However, soft robots comprise flexible materials and often have no internal support structure, so their ends have a very limited carrying capacity. To compensate for this inadequacy, soft robots usually use the bending of the entire body to grasp objects or operate underwater to partially counteract gravity. In addition, the deformation state of a soft robot is difficult to estimate when it is affected by external force or in contact with the environment, which also causes many difficulties in the modeling and control of soft robots. In the case of inaccurate modeling and poor controllability, the accessibility and accuracy of its end are bound to be greatly compromised. For a class of line-driven soft manipulators, a modeling method based on strain parameterization is proposed that can describe the motion of soft manipulators in three-dimensional space under different wiring methods. First, the entire soft manipulator is treated as a Cosserat beam and modeled by the mature Cosserat beam theory, wherein the strain field of the soft manipulator is discretized using the Ritz method to obtain a set of ordinary differential equations, and then a back propagation (BP) neural network is used to complete the drive force conversion between the shape and driver spaces. A radial basis function (RBF) neural network is used to approximate and compensate for the unknown dynamics present in the soft manipulator model. The stability of the closed-loop system after introducing the adaptive neural network controller is then demonstrated on the basis of Lyapunov's stability theory. Finally, a series of simulation experiments are performed for the model and the adaptive neural network controller to verify the effectiveness of the model and the control algorithm. Therefore, the modeling control of a type of soft manipulator is realized.

     

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