Intelligent control of a three-DOF planar underactuated manipulator

Recently, computational intelligence has been applied extensively in control engineering, especially for systems that cannot easily be controlled by conventional means. In this article, attention is paid to the control of a three-DOF planar underactuated manipulator, also known as the three-link gymnastic robot, by utilizing a neural network (NN) and a genetic algorithm (GA). In an attempt to make the problem more analogous to human gymnastics, constraints are applied to the joint angles. With different swing-up timings, the performance of the proposed controller is investigated and control simulations are performed. Numerical simulations show that the neurocontroller is able to control the system effectively within the constraints and given timings.     

基于轨迹规划的平面三连杆欠驱动机械臂位置控制

针对中间关节为欠驱动的二阶非完整平面三连杆机械臂,提出一种基于轨迹规划的末端点位置控制策略.首先,建立系统的动力学模型,并根据几何关系利用差分进化算法求取所有连杆与目标位置相对应的目标角度;然后,根据驱动关节与欠驱动关节的耦合关系,采用时间缩放法和双向法分别规划两根驱动连杆的两条轨迹,并利用遗传算法优化合适的第1连杆中间位置,将两条轨迹拼接成一条完整可达轨迹;最后,设计滑模变结构控制器以跟踪完整可达轨迹,实现系统从初始位置到目标位置的控制目标.数值仿真结果表明了所提出控制策略的有效性.     

Modeling,tracking, vibration and balance control of an underactuated mobile manipulator (UMM)

This paper presents an underactuated mobile manipulator (UMM) and focuses on solving modeling, tracking, and vibration- and balance-control problems. Although the study has been directed at warehousing applications, the developed techniques are general and can be applied to other applications. The derivation of equations of motion of the UMM, disturbance analysis, and model validation are investigated to reveal the actual system dynamics. Additionally, a simple but effective strategy is also developed to solve the equilibrium point and balance problem. Based on the dynamic model, two control architectures are proposed: Model Predictive Control (MPC) and MPC+Proportional-Integral (PI) with integral actions, respectively, and they can also be applied to other robotic systems. Compared to other MPC-based control strategies, the proposed controllers require less effort to implement in practice. Finally, simulations, experiments, and robustness verification are conducted and discussed, and the results are satisfactory.     

On point-to-point motion planning for underactuated space manipulator systems

In free-floating mode, space manipulator systems have their actuators turned off, and exhibit nonholonomic behavior due to angular momentum conservation. The system is underactuated and a challenging problem is to control both the location of the end effector and the attitude of the base, using manipulator actuators only. Here a path planning methodology satisfying this requirement is developed. The method uses high order polynomials, as arguments in cosine functions, to specify the desired path directly in joint-space. In this way, the accessibility of final configurations is extended drastically, and the free parameters are determined by optimization techniques. It was found that this approach leads always to a path, provided that the desired change in configuration lies between physically permissible limits. Physical limitations, imposed by system’s dynamic parameters, are examined. Lower and upper bounds for base rotation, due to manipulator motions, are estimated and shown in the implementation section. The presented method avoids the need for many small cyclical motions, and uses smooth functions in the planning scheme, leading to smooth configuration changes in finite and prescribed time.     

欠驱动桥式吊车系统自适应控制

针对桥式吊车这类非线性欠驱动系统, 提出了一种基于耗散理论的自适应控制器. 它能够有效地抑制运输过程中负载的摆动, 并将其快速准确地运送到指定的位置. 相比其他吊车控制系统, 这种控制器无需准确测量台车和负载质量以及吊绳长度, 可以根据系统响应情况来对这些参数进行在线估计, 这将极大地方便控制器在实际吊车系统中的推广应用. 对于闭环系统的稳定性, 文中通过李雅普诺夫理论及拉塞尔不变性原理进行了证明, 仿真结果也证实了这种自适应控制器能够对吊车系统进行良好的控制.     

Control of three degrees-of-freedom underactuated manipulator using fuzzy based switching

A novel concept for designing a fuzzy logic-based switching controller to control underactuated manipulators is presented. The proposed controller employs elemental controllers, which are designed in advance. Parameters of both antecedent and consequent parts of a fuzzy indexer are optimized by using evolutionary computation. Design parameters of the fuzzy indexer are encoded into chromosomes, i.e., the shapes of the Gaussian membership functions and corresponding switching laws of the consequent part are evolved to minimize the angular position errors. Then, these trained fuzzy rules can be brought into the online operation of underactuated manipulators. Simulation results show that the new methodology is effective in designing controllers for underactuated robot manipulators.This work was presented, in part, at the 8th International Symposium on Artificial Life and Robotics, Oita, Japan, January 24–26, 2003     

Application of SSTT control algorithm for underactuated: surface vessel,PPR manipulator and pneumatically actuated slider-inverted pendulum

The paper deals with verifications and validation of the control algorithm for simultaneous stabilization and trajectory tracking of underactuated nonlinear mechanical systems. A simplicity, universality, and effectiveness of the control law are shown on simulations to the both multibody second-order nonholonomic systems (a planar PPR manipulator and an inverted pendulum) and underactuated systems with forces/moments input coupling (a surface vessel). An experimental verification has been made on the novel pneumatically actuated slider-inverted pendulum with included friction effects. Also, an actuator compensator is constructed and implemented for this highly nonlinear experimental setup to avoid the increase of the system’s relative degree in the closed control loop, and to avoid the unnecessary time derivation of the system’s functions with non-differentiable Coulomb friction effects.     

Tracking and regulation control of an underactuated surface vesselwith nonintegrable dynamics

A continuous, time-varying tracking controller is designed that globally exponentially forces the position/orientation tracking error of an underactuated surface vessel to a neighborhood about zero that can be made arbitrarily small i.e. global uniformly ultimately boundedness (GUUB). The result is facilitated by fusing a filtered tracking error transformation with a dynamic oscillator design. We also illustrate that the proposed tracking controller yields a GUUB result for the regulation problem     

基于浸入和不变技术的非线性跟踪控制

为实现欠驱动四旋翼飞行器的位置及偏航渐近跟踪,本文基于浸入和不变技术(immersion and invariance,II)提出非线性跟踪控制方法.针对四旋翼飞行器的欠驱动特性,设计了内/外环分别为姿态和位置的双闭环结构,并采用浸入和不变技术构建内/外环的稳定跟踪控制器,利用李雅普诺夫定理保证闭环系统的渐近稳定性.最后,在MATLAB/Simulink环境下进行数值仿真,验证了II控制方案的有效性.     

Finite-time control of underactuated spacecraft hovering

Finite-time controllers are proposed in this paper for underactuated spacecraft hovering in the absence of the radial or in-track thrust. The indirect method, which is generally adopted to solve the singularity problem in the conventional terminal sliding mode, is modified to ensure the continuity of the high-order time derivative of the sliding surface at the switch points. Rigorous proofs via the Lyapunov-based approaches verify the finite-time stability of the closed-loop system. By comparisons with the asymptotic controllers, the advantages of the finite-time ones in faster convergence rate and enhanced control precision have also been substantiated.     

Robust adaptive tracking control of an underactuated ship with guaranteed transient performance

In this paper, a robust adaptive controller for a underactuated ship is proposed to make the ship follow a predefined path with guaranteed transient performance and arbitrarily small steady-state position error and orientation error, despite the presence of environmental disturbances induced by wave, wind and ocean current and unknown system parameters. We design a new adaptive state feedback controller and parameter estimators to guarantee converging exponentially by assuming all states are available. It is shown that the mean-square tracking errors are of order of an arbitrarily small design parameter, and the position error and the orientation error also decrease at a pre-specified exponential rate. Simulations with a commercial monohull ship using Matlab also demonstrate the effectiveness of the controllers.     

Line-of-sight based three-dimensional path following control for an underactuated robotic dolphin

This paper investigates the three-dimensional(3-D)path following control problem for an under-actuated robotic dolphin.With a comprehensive consideration of the...     

欠驱动TORA系统的自耦PID控制策略

针对欠驱动旋转激励平移振荡器(translational oscillations with a rotational actuator,TORA)系统的控制问题,使用一种自耦PID(self-coupling proportional-integral-differential,SCPID)控制方法.该方法首先利用坐标变换使TORA系统的质心映射为Huygens振动中心,以实现新系统控制输入解耦,避免零动态不稳定问题;然后对Huygens振动中心设计平移位置的SCPID控制器,同时获得小球偏转角度的虚拟指令,进而设计小球偏转角度的SCPID控制器,从而实现TORA系统的平衡点跟踪控制;最后在复频域对闭环控制系统的稳定性进行严格的数学分析和证明.仿真及与其他方法的结果对比表明,所设计的控制算法简单高效,在欠驱动控制系统领域具有实际的应用价值.     

Fuzzy control of a manipulator using an actuator and multibrakes

This paper is concerned with the control of a manipulator with n-degrees of freedom by one actuator and n ? 1 brakes using fuzzy inference. All the links of the manipulator are excited by a motor placed on the base link, and the excitation torque is successively transmitted through each link from the base link until the final link. The brakes on the joints act at identical frequency with different phases, and the phases of timing on the brakes are controlled by fuzzy inference such that all the joint angles of links are followed to the desired trajectories. The effectiveness of the proposed method is illustrated by a simple example.     

A coordinated control of an underwater vehicle and robotic manipulator

Remotely operated underwater robotic vehicles (URVs) have been used for various tasks: inspection, recovery, construction, etc. With the increased utilization of remotely operated vehicles in subsea applications, the development of autonomous vehicles becomes highly desirable to enhance operator efficiency. However, engineering problems associated with the high density, nonuniform and unstructured seawater environment, and the nonlinear response of the vehicle make a high degree of autonomy difficult to achieve. The vehicles are usually equipped with mechanical manipulators that are utilized during the working mode. The accurate performance of the vehicle during the working mode can be achieved by controlling the vehicle and manipulator at the same time and compensating the end-effector error due to the vehicle motion. This article describes an adaptive control strategy for the coordinated control of an underwater vehicle and its robotic manipulator. The effectiveness of the control system is investigated by case study. The results show that the presented control system can provide the high performance of the vehicle and manipulator in the presence of unpredictable changes in the dynamics of the vehicle and its environment.     

Nonlinear model predictive control for hydrobatics: Experiments with an underactuated AUV

Hydrobatic autonomous underwater vehicles (AUVs) can be efficient in range and speed, as well as agile in maneuvering. They can be beneficial in scenarios such as obstacle avoidance, inspections, docking, and under-ice operations. However, such AUVs are underactuated systems—this means exploiting the system dynamics is key to achieving elegant hydrobatic maneuvers with minimum controls. This paper explores the use of model predictive control (MPC) techniques to control underactuated AUVs in hydrobatic maneuvers and presents new simulation and experimental results with the small and hydrobatic SAM AUV. Simulations are performed using nonlinear model predictive control (NMPC) on the full AUV system to provide optimal control policies for several hydrobatic maneuvers in Matlab/Simulink. For implementation on AUV hardware in robot operating system, a linear time varying MPC (LTV-MPC) is derived from the nonlinear model to enable real-time control. In simulations, NMPC and LTV-MPC shows promising results to offer much more efficient control strategies than what can be obtained with PID and linear quadratic regulator based controllers in terms of rise-time, overshoot, steady-state error, and robustness. The LTV-MPC shows satisfactory real-time performance in experimental validation. The paper further also demonstrates experimentally that LTV-MPC can be run real-time on the AUV in performing hydrobatic maneouvers.     

欠驱动两足步行机器人侧向稳定控制方法研究

以欠驱动两足步行机器人为对象研究其侧向运动稳定控制问题。首先分析引起机器人侧向运动不稳定的原因,然后提出步宽控制和侧向力矩补偿两种控制策略。步宽控制通过控制机器人侧向落脚位置,使其侧向运动周期与前向周期趋于一致实现侧向运动稳定。力矩补偿控制通过在踝关节引入侧向控制力矩,使侧向运动与前向运动协调一致实现侧向运动稳定。仿真实验表明,机器人实现了稳定的3D动态行走,达到了预期的控制效果。     

Time-scaling symmetry and Zeno solutions

Symmetries are often helpful in reducing the complexity of the analysis of dynamical systems. Here we discuss a symmetry that combines a transformation in space with a scaling of time. Examples are given of a number of nonsmooth dynamical systems in which a symmetry of this type occurs. The time-scaling symmetry can be combined with return mapping analysis to achieve a dimension reduction in addition to the one already obtained from considering the return map. The method is applied in a study of Zeno behavior in linear systems with relay feedback.     

Robot manipulator control system

The paper analyzes design concepts for up-to-date robot manipulator control systems. Approaches to building software and hardware architecture are described. The developed IntNCR control system is examined.