Whole-Body Kinematic Control of Nonholonomic Mobile Manipulators Using Linear Programming

This paper presents some improvements to the robot kinematic control strategy based on linear programming, as well as its application to a nonholonomic mobile manipulator. In addition to being computationally efficient, this approach enables the inclusion of inequality and equality constraints in the system control inputs and has formal guarantee of stability. We first propose a new positive definite function of the error variation to avoid joint movements when the robot end-effector stabilizes at a point different from the desired one. In addition, the nonholonomic constraint of the mobile base is imposed as an equality constraint, and inequality constraints are defined to avoid both violation of joint limits and collisions between the mobile base and obstacles in the plane. Last, a performance comparison between the linear programming strategy and an approach based on the pseudoinverse of the whole-body Jacobian matrix is presented. Experimental results show that the controller based on linear programming has low computational cost, and the robot is able to control its end-effector without colliding with obstacles in the plane and without violating its joints limits. However, it tends to generate more abrupt control signals than the continuous controller based on the pseudoinverse of the whole-body Jacobian matrix.     

轮式移动机械臂的建模与仿真研究

移动机械臂系统一般由移动平台和机器臂组成,它既具有机器臂的操作灵活性,又具有移动机器人的可移动性,因此其应用范围要比单个系统宽得多。这篇文章主要研究了由非完整移动平台和完整机械臂组成的轮式移动机械臂系统的建模、跟踪控制及仿真问题。首先。利用拉格朗日动力学方程和非完整动力学罗兹方程建立了移动机械臂系统的精确数学模型;然后。利用非线性反馈将系统解耦。采用类PD控制器进行控制。在考虑了非完整约束及移动平台和机械臂的动态交互影响情况下,该控制算法保证系统同时跟踪给定的终端执行器和平台轨迹;最后,使用Maflah6．5对系统进行了仿真研究,仿真结果表明了其数学模型及控制方法的正确有效性。     

Motion Control of a Nonholonomic Mobile Manipulator in Task Space

In this paper, the motion control of a mobile manipulator subjected to nonholonomic constraints is investigated. The control objective is to design a computed‐torque controller based on the coupled dynamics of the mobile manipulator. The proposed controller achieves the capability of simultaneous tracking of a reference velocity for the mobile base and a reference trajectory for the end‐effector. The aforementioned reference velocity and trajectory are defined in the task space, such task setting imitates the actual working conditions of a mobile manipulator and thus makes the control problem practical. To solve this tracking problem, a steering velocity is firstly designed based on the first‐order kinematic model of the nonholonomic mobile base via dynamic feedback linearization. The main merit of the proposed steering velocity design is that it directly utilizes the reference velocity set in the task space without requiring the knowledge of a reference orientation. A torque controller is subsequently developed based on a proposed Lyapunov function which explicitly considers the coupled dynamics of the mobile manipulator to ensure the mobile base and end‐effector track the reference velocity and trajectory respectively. This proposed computed‐torque controller is able to realize asymptotic stability of both the base velocity tracking error and the end‐effector motion tracking error. Simulations are conducted to demonstrate the effectiveness of the proposed controller.     

Dynamic Modeling and Tracking Control of a Nonholonomic Wheeled Mobile Manipulator with Dual Arms

This paper presents methodologies for dynamic modeling and trajectory tracking of a nonholonomic wheeled mobile manipulator (WMM) with dual arms. The complete dynamic model of such a manipulator is easily established using the Lagrange’s equation and MATHEMATICA. The structural properties of the overall system along with its subsystems are also well investigated and then exploited in further controller synthesis. The derived model is shown valid by reducing it to agree well with the mobile platform model. In order to solve the path tracking control problem of the wheeled mobile manipulator, a novel kinematic control scheme is proposed to deal with the nonholonomic constraints. With the backstepping technique and the filtered-error method, the nonlinear tracking control laws for the mobile manipulator system are constructed based on the Lyapunov stability theory. The proposed control scheme not only achieves simultaneous trajectory and velocity tracking, but also compensates for the dynamic interactions caused by the motions of the mobile platform and the two onboard manipulators. Simulation results are performed to illustrate the efficacy of the proposed control strategy.     

Stabilization of second-order nonholonomic systems in canonical chained form

Stabilization of a class of second-order nonholonomic systems in canonical chained form is investigated in this paper. First, the models of two typical second-order nonholonomic systems, namely, a three-link planar manipulator with the third joint unactuated, and a kinematic redundant manipulator with all joints free and driven by forces/torques imposing on the end-effector, are presented and converted to second-order chained form by transformations of coordinate and input. A discontinuous control law is then proposed to stabilize all states of the system to the desired equilibrium point exponentially. Computer simulation is given to show the effectiveness of the proposed controller.     

Robust adaptive control for mobile manipulators

This paper addresses the trajectory tracking control of a nonholonomic wheeled mobile manipulator with parameter uncertainties and disturbances. The proposed algorithm adopts a robust adaptive control strategy where parametric uncertainties are compensated by adaptive update techniques and the disturbances are suppressed. A kinematic controller is first designed to make the robot follow a desired end-effector and platform trajectories in task space coordinates simultaneously. Then, an adaptive control scheme is proposed, which ensures that the trajectories are accurately tracked even in the presence of external disturbances and uncertainties. The system stability and the convergence of tracking errors to zero are rigorously proven using Lyapunov theory. Simulations results are given to illustrate the effectiveness of the proposed robust adaptive control law in comparison with a sliding mode controller.     

Intelligent compliant force/motion control of nonholonomic mobile manipulator working on the nonrigid surface

The task under consideration is to control a mobile manipulator for the class of nonrigid constrained motion. The working surface is deformable. The geometric and physical model of the surface is unknown and all contact force is nonlinear and difficult to model. To accomplish a task of this kind, we propose a force/motion fuzzy controller based on the philosophy of the parallel approach in two decoupled subspaces. In one subspace, we control the constant contact force normal to the surface and estimate the end-effector tool’s deformable depth of the surface; in the other, we keep the end-effector’s constant velocity parallel to the tangential plane of the surface and suppress the tangential force of the surface deformation. The nonholonomic mobile base is utilized to avoid the singularity. Stability is established and conditions for the control parameters are derived. Performance of the proposed controller is verified through computer simulations compared with the model-based control.     

非完整移动机械手鲁棒自适应模糊控制

考虑系统存在的参数、外界扰动和未建模动态等不确定性,研究非完整移动机械手的鲁棒自适应控制器设计方法.基于用旋量理论建立的非完整移动机械手的动力学模型,设计了移动平台子系统的运动控制器,然后应用非线性反步控制技术和模糊逻辑系统的通用逼近性,用参数化线性模糊逻辑系统逼近非完整移动机械手动力学模型中的不确定项,基于Lyapu...     

检测与修补移动机械手系统的协调控制技术研究

针对2自由度轮式移动载体与5自由度机械手组成的检测与修补移动机械手进行了运动分析及其控制技术的研究．首先分析了移动机械手的结构特点,描述了移动载体与机械手的动力耦合对机械手系统的性能影响．其次,根据移动机械手动力学的复杂性,提出了移动机械手的运动控制策略,建立了基于神经网络的移动机械手三层智能控制的体系结构,底层是执行层,中间层是处理层,顶层是决策层．处理层包括两个RBF神经网络子控制器,未知的移动载体和机械手的动力学参数分别由各自的RBF神经网络辨识和补偿,形成闭环逼近的控制．应用Matlab编程软件对所建立的RBF神经网络进行训练仿真,最后,在实验环境中对移动机械手的运动进行了相关的实验验证．实验结果验证了移动机械手完成相关任务的有效性和可靠性．     

移动机械手鲁棒自适应模糊控制

基于旋量理论建立了非完整移动机械手系统的动力学模型,通过反步控制技术,应用非线性参数化模糊逻辑系统设计了移动机械手的鲁棒自适应模糊控制器.该控制器放松了移动机械手控制器设计中斜对称性的要求,对移动机械手系统中存在的参数或外界扰动等不确定性具有较强的鲁棒性和自适应能力.理论证明和仿真结果表明,所设计的控制器是有效的.     

A kinematically compatible framework for cooperative payload transport by nonholonomic mobile manipulators

In this paper, we examine the development of a kinematically compatible control framework for a modular system of wheeled mobile manipulators that can team up to cooperatively transport a common payload. Each individually autonomous mobile manipulator consists of a differentially-driven Wheeled Mobile Robot (WMR) with a mounted two degree-of-freedom (d.o.f) revolute-jointed, planar and passive manipulator arm. The composite wheeled vehicle, formed by placing a payload at the end-effectors of two (or more) such mobile manipulators, has the capability to accommodate, detect and correct both instantaneous and finite relative configuration errors. The kinematically-compatible motion-planning/control framework developed here is intended to facilitate maintenance of all kinematic (holonomic and nonholonomic) constraints within such systems. Given an arbitrary end-effector trajectory, each individual mobile-manipulator's bi-level hierarchical controller first generates a kinematically-feasible desired trajectory for the WMR base, which is then tracked by a suitable lower-level posture stabilizing controller. Two variants of system-level cooperative control schemes—leader-follower and decentralized control—are then created based on the individual mobile-manipulator control scheme. Both methods are evaluated within an implementation framework that emphasizes both virtual prototyping (VP) and hardware-in-the-loop (HIL) experimentation. Simulation and experimental results of an example of a two-module system are used to highlight the capabilities of a real-time local sensor-based controller for accommodation, detection and corection of relative formation errors.     

Robust control of mobile manipulators

A mobile manipulator is basically a manipulator mounted on a mobile vehicle. This arrangement has some advantages over stationary robots and mobile robots, such as the infinite workspace and the ability to avoid singularities. However, the control problem becomes a sophisticated one. This is due to the nonlinear and nonholonomic constraints governing the motion of the vehicle. Moreover, the dynamics of the manipulator and the vehicle are highly coupled; ground-surface irregularities, for example, affect the motion of the end effector kinematically and dynamically. A mobile manipulator is expected to pass through different environmental conditions, a fact which calls for a robust control scheme. Unfortunately, the robust control problem for nonholonomic systems is not well defined yet. Since the ultimate goal of control is to control the motion of the manipulator's end effector, it is proposed in this article to tackle the robustness issue by designing a manipulator decoupling controller. This controller aims at rejecting disturbances arising from the motion of the vehicle. © 1996 John Wiley & Sons, Inc.     

控制受限的移动机器人鲁棒跟踪控制器设计

研究了非完整移动机器人动力学模型中带有参数不确定和控制受限的鲁棒轨迹跟踪控 制器的设计问题.在建立移动机器人的全动态误差模型的基础上,应用滚动时域控制(RHC)和线 性矩阵不等式(LMIs)方法,设计了鲁棒跟踪控制器,在满足非完整和控制约束的条件下,实现了 机器人位置,导向角以及速度的同时渐近跟踪.系统稳定性的充分条件以LMI的形式给出.仿真 结果验证了提出方法的可行性和有效性.     

Sliding Mode Adaptive Neural-Network Control for Nonholonomic Mobile Modular Manipulators

A general mobile modular manipulator can be defined as a m-wheeled holonomic/nonholonomic mobile platform combining with a n-degree of freedom modular manipulator. This paper presents a sliding mode adaptive neural-network controller for trajectory following of nonholonomic mobile modular manipulators in task space. Dynamic model for the entire mobile modular manipulator is established in consideration of nonholonomic constraints and the interactive motions between the mobile platform and the onboard modular manipulator. Multilayered perceptrons (MLP) are used as estimators to approximate the dynamic model of the mobile modular manipulator. Sliding mode control and direct adaptive technique are combined together to suppress bounded disturbances and modeling errors caused by parameter uncertainties. Simulations are performed to demonstrate that the dynamic modeling method is valid and the controller design algorithm is effective.     

Singularity robust path planning for real time base attitude adjustment of free-floating space robot

This paper presents a singularity robust path planning for space manipulator to achieve base (satellite) attitude adjustment and end-effector task. The base attitude adjustment by the movement of manipulator will save propellant compared with conventional attitude control system. A task-priority reaction null-space control method is applied to achieve the primary task of adjusting attitude and secondary task of accomplishing end-effector task. Furthermore, the algorithm singularity is eliminated in the proposed algorithm compared with conventional reaction null-space algorithm. And the singular value filtering decomposition is introduced to dispose the dynamic singularity, the unit quaternion is also introduced to overcome representation singularity. Hence, a singularity robust path planning algorithm of space robot for base attitude adjustment is derived. A real time simulation system of the space robot under Linux/RTAI (realtime application interface) is developed to verify and test the feasibility and reliability of the method. The experimental results demonstrate the feasibility of online base attitude adjustment of space robot by the proposed algorithm.     

移动机械手的跟踪控制

讨论一类不确定非完整移动机械手的跟踪控制问题。在系统惯性参数不精确知道的情况下,提出一种鲁棒控制器。为提高跟踪性能,进一步设计出使跟踪误差指数收敛的控制器。计算机仿真验证了所提出控制律的有效性。     

A fuzzy cerebellar model articulation controller based visual servo system for robot

This paper presents a novel online learning visual servo controller integrating the FCMAC with proportion controller for the control of position of manipulator end-effector. Since the FCMAC has good learning capability and fast learning speed, and can save much computer memory space by fuzzy processing of input space division and memory unit activation, it is used to develop an adaptive control law by learning the relationship between the image feature errors and manipulator input, and the aim of online learning of the FCMAC is to minimize the output of proportion controller. Furthermore, the FCMAC has no need for models of robot manipulator and image feature extraction, so that the capability of proposed controller for tasks under uncertain environment can be improved. Finally, the proposed controller is proved to be effective by the experiment, and compared with BP neural network.     

Adaptive motion/force control of uncertain nonholonomic mobile manipulator with estimation of unknown external force

This paper describes a stable adaptive motion/force control of uncertain nonholonomic mobile manipulator with the consideration of external force. As it is well known, unexpected external force makes the motion of the system unstable since there are no fixed points in the stationary coordinate. Here, a novel adaptive control scheme is utilized to estimate and compensate the unknown external force exerted to the end-effector even if the parameters of the system are uncertain. The important advantages of this approach are to achieve estimation without the requirement of force-sensing feedback and the knowledge of the system dynamic model. The update laws for the force and the parameters are derived from a Lyapunov function to guarantee the control system stability. Furthermore, a unified operational space dynamic formulation is presented to solve the problem of redundancy. As a result, the desired end-effector and platform trajectories are simultaneously tracked with a perfect coordination between the two subsystems. Therefore, the proposed controller proves that it can not only guarantee the stability, but also the tracking performance of the system in the task space. The effectiveness of the proposed algorithm is evaluated through extensive simulations and they demonstrate the stability, tracking trajectories and feasibility in estimating the external force and the dynamic uncertainties.     

自由飞行空间机器人系统的协调运动控制

考虑由载体和机械臂组成的空间机器人系统的协调控制问题,提出了一种新的协调 控制策略.该策略首先利用简单的变结构控制器粗略控制载体的运动,进而设计机械臂控制 器以保证手端精确跟踪其期望的运动轨迹.应用该策略分别对手端自由运动和受限运动设计 了相应的控制器,并对两杆平面空间机器人系统进行了仿真,证实了控制策略的有效性.     

Planning and control of under-actuated mobile manipulators using differential flatness

Mobile manipulators are intrinsically nonholonomic systems since the mobile base is subject to nonholonomic constraints that result from no-slip constraints on the wheels. The highly nonlinear dynamic coupling between the mobile base and the manipulator arm, in addition to the nonholonomic constraints at the base, makes these systems difficult to plan and control. If the system is under-actuated, the problem becomes even more difficult.