Adaptive neural network control of tendon-driven mechanisms with elastic tendons

We propose an adaptive control and an adaptive neural network control (composed of two RBF neural components and one adaptive component) for tendon-driven robotic mechanisms with elastic tendons. These controllers can be applied to serial or parallel tendon-driven manipulators having linear or non-linear elastic tendons. We begin by proving the stability of the adaptive control system for our mechanism, and then we prove the stability of the adaptive neural network system and report on the results of numerical simulations and experimental results performed using a 2-DOF tendon-driven mechanism having six elastic tendons.     

Numerical analysis of feedforward position control for non-pulley musculoskeletal system: a case study of muscular arrangements of a two-link planar system with six muscles

In a musculoskeletal system like a tendon-driven robot, redundant actuation is necessary because muscles (or mechanical parts such as tendons) can transmit tension only unidirectionally. This redundancy yields internal force among muscles, which has a particular field of potential energy. Using internal force as a feedforward input, a musculoskeletal system can achieve feedforward position control with no sensory feedback. This paper studies the feedforward position control coming from the redundancy for a non-pulley musculoskeletal system. Targeting a planar two-link system with six muscles as a case study, the motion convergence depending on the muscular arrangement is examined quasi-statically. The results point out that the convergence is extremely sensitive to the muscular arrangement, and adding small offsets for the muscular connected points can remarkably improve the positioning performance.     

Force control of a two-linke planar manipulator with one flexible link

Force control of a two-link planar manipulator with one flexible link is considered in this study. The equations of motion are derived using the extended Hamilton's principle with only structural flexibility effects included in the dynamic model. The linear quadratic Gaussian/loop transfer recovery (LQG/LTR) design methodology is exploited to design a robust feedback control system that can handle modelling errors and sensor noise, and operate on Cartesian space trajectory errors. The LQG/LTR compensator together with a feedforward loop is used to simultaneously control the force exerted by the flexible manipulator normal to the environment and the position of the end-point in a direction tangent to the environment. Simulated results are presented for a numerical example.     

Fuzzy sliding mode control for a robot manipulator

This work presents the design of a robust control system using a sliding mode controller that incorporates a fuzzy control scheme. The presented control law superposes a sliding mode controller and a fuzzy logic controller. A fuzzy tuning scheme is employed to improve the performance of the control system. The proposed fuzzy sliding mode control (FSMC) scheme utilizes the complementary cooperation of the traditional sliding mode control (SMC) and the fuzzy logic control (FLC). In other words, the proposed control scheme has the advantages which it can guarantee the stability in the sense of Lyapunov function theory and can ameliorate the tracking errors, compared with the FLC and SMC, respectively. Simulation results for the trajectory tracking control of a two-link robot manipulator are presented to show the feasibility and robustness of the proposed control scheme. This work was presented in part at the 13th International Symposium on Artificial Life and Robotics, Oita, Japan, January 31–February 2, 2008     

PPR型平面欠驱动机械臂的点位控制

研究了PPR型平面欠驱动机械臂(第1个关节和第2个关节是移动关节且是受控的,第3个关节为被动的转动关节)在水平面运动的点位控制问题.首先,通过输入和坐标变换方法,系统的动力学方程被变换成二阶链式形式.其次,提出用反步法推导出保证系统指数渐近稳定的控制器.仿真结果表明,机械臂能够稳定地从任意初始位置运动到任意给定的位置,从而证明了控制器设计的有效性.     

GA-pattern matching-based manipulator control system for real-time visual servoing

_—In robotic applications, tasks of picking and placing are the most fundamental ones. Also, for a robot manipulator, the recognition of its working environment is one of the most important issues to do intelligent tasks, since this aptitude enables it to work in a variable environment. This paper presents a new control strategy for robot manipulators, which utilizes visual information to direct the manipulator in its working space, to pick up an object of known shape, but with arbitrary position and orientation. During the search for an object to be picked up, vision-based control by closed-loop feedback, referred to as visual servoing, is performed to obtain the motion control of the manipulator hand. The system employs a genetic algorithm (GA) and a pattern matching technique to explore the search space and exploit the best solutions by this search technique. The control strategy utilizes the found results of GA-pattern matching in every step of GA evolution to direct the manipulator towards the target object. We named this control strategy step-GA-evnlution. This control method can be applied for manipulator real-time visual servoing and solve its path planning problem in real-time, i.e. in order for the manipulator to adapt the execution of the task by visual information during the process execution. Simulations have been performed, using a two-link planar manipulator and three image models, in order to find which one is the best for real-time visual servoing and the results show the effectiveness of the control method.     

Boundary antisaturation vibration control design for a flexible Timoshenko robotic manipulator

This article focuses on the angle positioning and vibration isolation of flexible Timoshenko manipulators possessing extraneous disturbances and saturation nonlinearities. Boundary control strategies with auxiliary systems are presented to achieve the expected angle, suppress the shear deformation and elastic oscillation, and mitigate the saturation nonlinearities effect. With the constructed controllers, a controlled system is ensured and certified to be exponentially stable. The simulation and comparison results show the control performance of the suggested approach.     

Robust nonlinear control of a planar 2-DOF parallel manipulator with redundant actuation

A new robust nonlinear controller is presented and applied to a planar 2-DOF parallel manipulator with redundant actuation. The robust nonlinear controller is designed by combining the nonlinear PD (NPD) control with the robust dynamics compensation. The NPD control is used to eliminate the trajectory disturbances, unmodeled dynamics and nonlinear friction, and the robust control is used to restrain the model uncertainties of the parallel manipulator. The proposed controller is proven to guarantee the uniform ultimate boundedness of the closed-loop system by the Lyapunov theory. The trajectory tracking experiment with the robust nonlinear controller is implemented on an actual planar 2-DOF parallel manipulator with redundant actuation. The experimental results are compared with the augmented PD (APD) controller, and the proposed controller shows much better trajectory tracking accuracy.     

A nonlinear robust HVDC control for a parallel AC/DC power system

In this paper, a parallel AC/DC power system is investigated, and a nonlinear robust controller is proposed to improve transient stability of the power system and to damp out any prolonged oscillation after a fault is cleared. Lyapunov's direct method is used to synthesize the control, and asymptotic stability of the closed loop system and improved dynamic performance are shown by both theoretical proof and simulation results.     

Dynamic formulation of a planar 3-DOF parallel manipulator with actuation redundancy

In this paper, based on the conventional Newton–Euler approach, a simplification method is proposed to derive the dynamic formulation of a planar 3-DOF parallel manipulator with actuation redundancy. Closed-form solutions are developed for the inverse kinematics. Based on the kinematics, the Newton–Euler approach in simplification form is used to derive the inverse dynamic model of the redundant parallel manipulator. Then, the driving force optimization is performed by minimizing an objective function which is the square of the sum of four driving forces. The dynamic simulations are done for the parallel manipulator with both the redundant and non-redundant actuations. The result shows that the dynamic characteristics of the manipulator in the redundant case are better than that in the non-redundancy. The redundantly actuated parallel manipulator was incorporated into a 4-DOF hybrid machine tool which includes a feed worktable.     

Indirect disturbance compensation control of a planar parallel (2-PRP and 1-PPR) robotic manipulator

This study addresses the dynamic modelling and indirect disturbance compensation control of planar parallel robotic motion platform with three degrees of freedom (3-DOF) in the presence of parameter uncertainties and external disturbances. The proposed planar parallel motion platform is a singularity free manipulator and has three manipulator legs located on the same plane linked with a moving platform. Of the three aforementioned manipulator legs, two legs have a prismatic–revolute–prismatic (PRP) joint configuration each with only one prismatic joint deliberated to be active, and the other leg consists of prismatic–revolute–prismatic (PPR) joint configuration with one active prismatic joint. The closed form kinematic solution (both forward and reverse kinematics) for the platform has been obtained in completion. In addition, the dynamic model for the platform has been communicated using the energy based Euler–Lagrangian formulation method. The proposed controller is based on a computer torque control with disturbance compensation integrated with it. Disturbance vectors comprising disturbances due to parameter variations, payload variations, frictional effects and other additional effects have been estimated using an extended Kalman filter (EKF). The EKF proposed for this specific platform uses only position and orientation measurements for estimation and noise mitigation. Simulations with a characteristic trajectory are presented and the results have been paralleled with traditional controllers such as the proportional integral derivative (PID) controller and computed torque controller (CTC). The results demonstrate satisfactory tracking performance for the proposed controller in the presence of parameter uncertainties and external disturbances.     

基于C/S结构的空间机械臂控制系统软件架构设计

为了获得性能优越、实用性强的空间机械臂控制软件,提出了一种C/S结构下基于多线程和循环队列的空间机械臂控制系统软件架构,并详细介绍了各线程及队列的实现过程。在分析空间机械臂控制软件的特点和功能需求的基础上,按照横向分块、纵向分层的原则,将机械臂控制软件的各项功能合理分配到四个并行线程中,借助两个循环队列构建缓存机制,以提高控制系统的数据处理能力并减少不必要的等待时间。四个线程及两个循环队列之间相互通信,协同工作。实验结果表明,该架构能够以较小的控制延迟实现机械臂的运动控制,架构性能满足实际控制需求,证明了方案的有效性和可行性。     

Stability of hybrid position and force control for robotic manipulator with kinematics and dynamics uncertainties

Most research so far on hybrid position and force control laws of robotic manipulator has assumed that knowledge of kinematics is known exactly. In the presence of modeling errors, it is unknown whether the stability of the constrained robot system can still be ensured. In this paper, stability and setpoint control problems of constrained robot with kinematics and dynamics uncertainties are formulated and solved. We shall show that the manipulator end-effector's motion is asymptotically stable even in the presence of such uncertainties.     

采用预测控制的龙门架式冗余自由度机械臂轨迹规划算法

为解决近年来工业常用的复杂结构大型机械臂的运动控制问题,本文以龙门架式机械臂为研究对象,首先结合材料力学分析,对在双臂荷载下的横梁挠度公式进行推导,进而对机械臂系统建立精确的运动学模型.为了便于后期算法设计,又在此基础上进行了降阶、线性化等模型简化工作.针对这一具有关节限位等约束条件和冗余自由度的多输入多输出高维复杂系统,提出了一种基于预测控制的轨迹规划算法.该算法根据模型中不同关节的运动范围以及定位精度等特性,划定其不同的运动优先级,通过在优化问题中对各个关节控制量设置不同的权重,来解决冗余问题.同时通过实时更新与滚动优化,很好的保证了控制的及时陛.仿真结果表明了本文所推导的挠度公式的准确性和所提出算法的有效性,不仅很好地解决了冗余问题,而且充分利用不同关节的运动特性,针对不同类型的跟踪目标值给出相适应的轨迹规划方案.     

足尺人造板力学性能自动检测样机控制系统研究

为了快速检测足尺人造板的力学性能,自行研制了检测样机,该样机的控制系统采用PC＋NI运动控制卡的结构。硬件主要由PC机、NI运动控制卡、电机、接近开关、传感器等组成,系统软件使用图形化编程语言Labview为开发平台,对多轴运动控制系统进行开发。重点阐述了控制原理、如何提高系统的稳定性及抗干扰性。结果表明,该系统人机界面友好,开发周期短,易于操作,具有很好的稳定性和抗干扰性。     

Robust robot manipulator control with autonomous consideration algorithm of torque saturation

As each joint actuator of a robot manipulator has a limit value of torque, the motion control system should consider the torque saturation. Conventional motion control based on robust acceleration controller cannot consider the torque saturation and it often causes an oscillated or wrong response. This paper proposes a new autonomous consideration method of joint torque saturation for robust manipulator motion control. The proposed method consists of three on-line autonomous algorithms. These algorithms are the torque limitation algorithm in joint space, the adjustment algorithm of motion control in Cartesian space, and the adjustment algorithm of motion reference in Cartesian space. The robot motion control using the proposed algorithms realizes smooth and robust robot motion response.     

A stabilizing model predictive control for networked control system with data packet dropout

A constrained model predictive control （MPC） algorithm for networked control system with data packet dropout is proposed in this paper. A buffer is designed to store the predicted control sequence between controller and actuator. It is shown that if the control horizon of MPC is not less than the number of data packets lost continuously, feasibility of MPC at initial time implies asymptotical stability of the closed-loop system. A simulation example illustrates the effectiveness of the proposed approach.     

一类时延网络控制系统的骱容错保成本控制

针对具有时延和参数不确定性的网络控制系统的研究。考虑系统的时延小于一个采样周期,传感器是时钟驱动,控制器和执行器是事件驱动。当执行器发生故障时,研究网络控制系统的Hoo容错保成本控制。依据所描述情况建立系统模型,基于Lyapunov稳定性理论、容错控制理论和线性矩阵不等式（LMIs）处理方法,推导出网络控制系统是渐近稳定的,并且得出系统的Hoo容错保成本控制的充分条件和系统的保成本上界。实例仿真证明结论的有效性。     

学习增强型PID控制系统的收敛性分析

针对具有可重复性的一般离散时间非线性系统, 在已存在的PID控制系统的基础上, 利用重复性的特点, 给出了一种学习增强型PID控制方法, 严格证明了收敛性, 并通过快速路交通系统的仿真验证了该方法的有效性和优越性. 该种方法的主要特点是, 不需要对已有的PID控制装置和系统做任何改动, 只需在PID控制器的外环加上迭代学习控制器即可, 是一种模块化的设计. 该方法实现了PID与迭代学习控制的优势互补.     

Flexibility analysis of a tracking control method for air-breathing hypersonic vehicles

This paper studies the flexibility of a tracking control method originally proposed by the authors for air-breathing hypersonic vehicles （AHVs）. The main feature of this method is to design the tracking controller without canceling but using aero-propulsive, as well as elevator-to-lift couplings. By introducing a virtual input, the tracking controller and external reference trajectories are simultaneously obtained by solving a system of linear algebraic equations. This system of linear algebraic equations is always solvable and the solution space of the corresponding homogeneous system is of dimension 3, which leads to much freedom in choosing or defining the free variables. The flexibility is reflected by the fact that the flight requirements of AHVs are involved in the definition of the free variables. Three case studies on different maneuvers, i.e., flight at constant dynamic pressure, flight at variant dynamic pressure and flight with fast climb rate are considered to verify the flexibility of this method. Simulation results show its effectiveness and flexibility.