Dynamics and control of space free-flyers with multiple manipulators

This paper studies the motion control of a multiple manipulator free-flying space robot chasing a passive object in near proximity. Free-flyer kinematics are developed using a minimum set of body-fixed barycentric vectors. Using a general and a quasi-coordinate Lagrangian formulation, equations of motion for model-based controllers are derived. Two model-based and one transposed Jacobian control algorithms are developed that allow coordinated tracking control of the manipulators and the spacecraft. In particular, an Euler parameter model-based control algorithm is presented that overcomes the non-physical singularities due to Euler angle representation of attitude. To ensure smooth operation, and reduce disturbances on the spacecraft and on the object just before grasping, appropriate trajectories for the motion of spacecraft/manipulators are planned. The performance of model-based algorithms is compared, by simulation, to that of a transposed Jacobian algorithm. Results show that due to the complexity of space robotic systems, a drastic deterioration in the performance of model-based algorithms in the presence of model uncertainties results. In such cases, a simple transposed Jacobian algorithm yields comparable results with much reduced computational burden, an issue which is very important in space.     

On the dynamics and control of flexible joint space manipulators

Space manipulator systems are designed to have lightweight structure and long arms in order to achieve reduction of fuel consumption and large reachable workspaces, respectively. Such systems are subject to link flexibilities. Moreover, space manipulator actuators are usually driven by harmonic gear mechanisms which lead to joint flexibility. These types of flexibility may cause vibrations both in the manipulator and the spacecraft making the positioning of the end-effector very difficult. Here, both types of flexibilities are lumped at the joints and the dynamic equations of a general flexible joint space manipulator are derived. Their internal structure is highlighted and similarities and differences with fixed-base robots are discussed. It is shown that one can exploit the derived dynamic structure in order to design a static feedback linearization control law and obtain an exact linearization and decoupling result. The application of such controllers is desired in space applications due to their small computational effort. In case of fixed-base manipulators, the effective use of a static feedback controller is feasible only if a simplified model is considered. Then, the proposed static feedback linearization control law is applied to achieve end-effector precise trajectory tracking in Cartesian space maintaining a desirable non-oscillatory motion of the spacecraft. The application of the proposed controller is illustrated by a planar seven degrees of freedom (dof) system.     

On adaptive inverse dynamics for free-floating space manipulators

This paper is devoted to the investigation of adaptive inverse dynamics for free-floating space manipulators (FFSMs) suffering from parameter uncertainties/variations. To overcome the nonlinear parametric problem of the dynamics of FFSMs, we introduce a new regressor matrix called the generalized dynamic regressor. Based on this regressor, and with Lyapunov stability analysis tools, we obtain a new parameter adaptation law and show that the closed-loop system is stable, and that the joint tracking errors converge asymptotically to zero. Simulation results are provided to illustrate the performance of the proposed adaptive algorithm. Furthermore, we conduct a comparative study between adaptive inverse dynamics, prediction error based adaptation, and passivity based adaptation.     

Adaptive synchronised tracking control for multiple robotic manipulators with uncertain kinematics and dynamics

In this study, a new adaptive synchronised tracking control approach is developed for the operation of multiple robotic manipulators in the presence of uncertain kinematics and dynamics. In terms of the system synchronisation and adaptive control, the proposed approach can stabilise position tracking of each robotic manipulator while coordinating its motion with the other robotic manipulators. On the other hand, the developed approach can cope with kinematic and dynamic uncertainties. The corresponding stability analysis is presented to lay a foundation for theoretical understanding of the underlying issues as well as an assurance for safely operating real systems. Illustrative examples are bench tested to validate the effectiveness of the proposed approach. In addition, to face the challenging issues, this study provides an exemplary showcase with effectively to integrate several cross boundary theoretical results to formulate an interdisciplinary solution.     

Synchronized adaptive control for coordinating manipulators with time‐varying actuator constraint and uncertain dynamics

This paper addresses the control issue for cooperative visual servoing manipulators on strongly connected graph with communication delays, in which case that the uncertain robot dynamics and kinematics, uncalibrated camera model, and actuator constraint are simultaneously considered. An adaptive cooperative image‐based approach is established to overcome the control difficulty arising from nonlinear coupling between visual model and robot agents. To estimate the coupled camera‐robot parameters, a novel adaptive strategy is developed and its superiority mainly lies in the containment of both individual image‐space errors and the synchronous errors among networked robots; thus, the cooperative performance is significantly strengthened. Moreover, the proposed cooperative controller with a Nussbaum‐type gain is implemented to both globally stabilize the closed‐loop systems and realize the synchronization control objective under the existence of unknown and time‐varying actuator constraint. Finally, simulations are carried out to validate the developed approach.     

Explicit synchronisation of heterogeneous dynamics networks via three-layer communication framework

This paper addresses the explicit synchronisation of heterogeneous dynamics networks via three-layer communication framework. The main contribution is to propose an explicit synchronisation algorithm, in which the synchronisation errors of all the agents are decoupled. By constructing a three-layer node model, the proposed algorithm removes the assumptions that the topology is fixed and the synchronisation process is coupled. By introducing appropriate assumptions, the algorithm leads to a class of explicit synchronisation protocols based on the states of agents in different layers. It is proved in the sense of Lyapunov that, if the dwell time is larger than a threshold, the explicit synchronisation can be achieved for closed-loop heterogeneous dynamics networks under switching topologies. The results are further extended to the cases in which the switching topologies are only frequently but not always connected. Simulation results are presented with four single-link manipulators to verify the theoretical analysis.     

Robust computationally efficient control of cooperative closed-chain manipulators with uncertain dynamics

This article presents a decentralized control scheme for the complex problem of simultaneous position and internal force control in cooperative multiple manipulator systems. The proposed controller is composed of a sliding mode control term and a force robustifying term to simultaneously control the payload's position/orientation as well as the internal forces induced in the system. This is accomplished independently of the manipulators dynamics. Unlike most controllers that do not require prior knowledge of the manipulators dynamics, the suggested controller does not use fuzzy logic inferencing and is computationally inexpensive. Using a Lyapunov stability approach, the controller is proven to be robust in the face of varying system's dynamics. The payload's position/orientation and the internal force errors are also shown to asymptotically converge to zero under such conditions.     

柔性航天器拖拽空间碎片动力学与控制仿真研究

针对地球静止轨道空间碎片清除需求,开展了服务星通过绳索拖拽空间碎片离轨多体动力学与控制仿真研究.分析了在轨拖拽期间系统拓扑构型,采用递推方法推导了考虑地球J2摄动的服务星和空间碎片柔性多体动力学方程组,建立了基于集中参数法的绳索动力学模型,通过约束方程将绳索与服务星和空间碎片相连接,建立了服务星姿态控制力矩方程,最后形成了服务星在轨拖拽空间碎片期间柔性多体系统多体动力学方程.通过悬链线模型与本文采用的集中参数模型的比较验证了本文采用的柔性绳索模型的正确性,然后通过数值仿真分析了与服务星质量接近的空间碎片被拖动期间动力学特性,为这类航天器总体设计及空间碎片清除策略制定提供了参考依据.     

Tracking control via switched Integral Sliding Mode with application to robot manipulators

This paper presents a switching structure scheme for motion control of industrial robot manipulators. To overcome the issues deriving from choosing a priori a specific control scheme, which can result in limited performances when the operating condition of the system varies, the scheme implements both a decentralized approach, suited for lower performance requirements and high transmission ratios, and the inverse dynamics based centralized approach, suited for higher performances in terms of velocity and acceleration. In both cases, the Integral Sliding Mode algorithm is used to compensate matched disturbances and to estimate the unmodeled dynamics used for the switching decision mechanism.     

Adaptive containment control of second-order multi-agent systems with nonlinear dynamics and multiple input-bounded leaders

This paper considers the adaptive containment control problem of second-order multi-agent systems with inherent nonlinear dynamics. In particular, the leaders’ control inputs are nonzero, bounded, and not available to any follower. Based on the relative states among neighbouring agents, a discontinuous adaptive protocol is first proposed to ensure that the containment errors of each follower converge to zero asymptotically, i.e. the states of the followers asymptotically converge to the convex hull spanned by those of the leaders. To eliminate the chattering effect caused by the discontinuous protocol, a continuous adaptive protocol is further designed based on the boundary layer technique and the σ-modification technique. Numerical examples are provided to demonstrate the effectiveness of our theoretical results.     

Position synchronised control of multiple robotic manipulators based on integral sliding mode

In this study, a new position synchronised control algorithm is developed for multiple robotic manipulator systems. In the merit of system synchronisation and integral sliding mode control, the proposed approach can stabilise position tracking of each robotic manipulator while coordinating its motion with the other manipulators. With the integral sliding mode, the proposed approach has insensitiveness against the lumped system uncertainty within the entire process of operation. Further, a perturbation estimator is proposed to reduce chattering effect. The corresponding stability analysis is presented to lay a foundation for theoretical understanding to the underlying issues as well as safely operating real systems. An illustrative example is bench tested to validate the effectiveness of the proposed approach.     

基于系统动力学的对虾养殖品质风险应用

针对目前南美白对虾养殖环节存在的溯源点不清晰、养殖过程监管薄弱、品质评价不健全等品质风险问题,以 HACCP 为基准,结合国内外在养殖环节关键影响要素研究现状,对养殖环节建模,利用判断树的方法初选品质风险控制的关键控制点,然后结合 Vensim 软件建立南美白对虾养殖品质风险动力学模型,从而确定关键控制点的核心影响因素。仿真结果表明：南美白对虾养殖品质风险动力学模型能动态仿真五类影响要素对于幼虾品质和成活率的变化关系,从而反映品质风险动态变化情况。由此为南美白对虾溯源管理信息系统中溯源点的选取和养殖过程的实时监控和过程品质动态评价提供理论参考。     

Development of wheel-less snake robot with two distinct gaits and gait transition capability

Snake robots are mostly designed based on single mode locomotion. However, single mode gait most likely could not work effectively when the robot is subject to an unstructured working environment with different measures of terrain complexity. As a solution, mixed mode locomotion is proposed in this paper by synchronizing two types of gaits known as serpentine and wriggler gaits used for non-constricted and narrow space environments, respectively, but for straight line locomotion only. A gait transition algorithm is developed to efficiently change the gait from one to another. This study includes the investigation on kinematics analysis followed by dynamics analysis while considering related structural constraints for both gaits. The approach utilizes the speed of the serpentine gait for open area locomotion and exploits the narrow space access capability of the wriggler gait. Hence, it can increase motion flexibility in view of the fact that the robot is able to change its mode of locomotion according to the working environment.     

Control of nonholonomic systems with extended base space dynamics

This paper extends certain results in Reference 1 to a more general class of nonholonomic systems with extended base space dynamics. This extension is important in applications for which control actuator dynamics are significant. These nonlinear control systems are referred to as nonholonomic control systems owing to certain nonintegrability assumptions which are made. The class of systems considered in this paper are characterized by general nonlinear base space dynamics that are input-output decouplable. Controllability results for this class of nonholonomic control systems are presented.     

Digital control of space robot manipulators with velocity type joint controller using transpose of generalized Jacobian matrix

For free floating space robots having manipulators, we have proposed a discrete-time tracking control method using the transpose of Generalized Jacobian Matrix (GJM). Control inputs of the control method are joint torques of the manipulator. In this paper, the control method is augmented for angular velocity inputs of the joints. Computer simulations have shown the effectiveness of the augmented method. This work was presented in part and awarded as Best Paper Award at the 13th International Symposium on Artificial Life and Robotics, Oita, Japan, January 31–February 2, 2008     

刚柔耦合系统动力学研究进展

首先简要回顾了柔性多体系统动力学前期研究的3个阶段．针对传统零次近似模型的缺陷提出了新的建模理论,并在新的一次近似耦合模型的基础上,就“动力刚化”问题和刚柔耦合动力学问题中的离散化方法与实验等方面进行研究;研制了供理论研究和动力学现象揭示的实验平台．文中对所取得的研究成果进行介绍．文末对今后的研究方向进行了展望．     

Adaptive finite-time stabilizing control of fractional-order nonlinear systems with unmodeled dynamics via sampled-data output-feedback

This article realizes an adaptive finite-time sampled-data output-feedback stabilization for a class of fractional-order nonlinear systems with unmodeled dynamics and unavailable states. K-filters are constructed to estimate unavailable states, a dynamic signal is introduced to handle unmodeled dynamics and neural networks were used to approximate uncertain nonlinearities existed in stabilizer construction. With the help of backstepping technique, an adaptive sampled-data output-feedback stabilizer is exported, and such stabilizer with allowable design parameters and sampling period can render the corresponding closed-loop system reaches practically finite-time stable, which can be demonstrated by means of selected Lyapunov function candidates. In the end, two simulations with a numerical and an engineering examples are presented to verify the effectiveness of the proposed scheme.     

JSAE-SICE benchmark problem for vehicle dynamics control

Recently many new types of small vehicles for future urban societies have been proposed and developed. Such small vehicles tends to have reduced stability and handling ability than conventional vehicles because of their lighter weight and reduced tire performance. To cope with this problem by active collaboration of Japanese academia and industries, a benchmark problem of designing vehicle control logic for an articulated In-Wheel-Motor vehicle was settled by Japanese society of automotive industries and academia. For this purpose, simulation models of the new vehicle using multi-physics acausal modeling language Modelica were provided from the industry side. Challengers were requested to design controllers of tire steering angle, tire camber angle and tire driving force to satisfy requested vehicle dynamic characteristics. There also were some restrictions about the range of actuators. Four test scenarios were given to evaluate the control performance. Many challengers from Japanese Universities have tackled with this benchmark problem. Some results of their researches are also introduced in this paper.     

Neural-network-based two-loop control of robotic manipulators including actuator dynamics in task space

A neural-network-based motion controller in task space is presented in this paper. The proposed controller is addressed as a two-loop cascade control scheme. The outer loop is given by kinematic control in the task space. It provides a joint velocity reference signal to the inner one. The inner loop implements a velocity servo loop at the robot joint level. A radial basis function network （RBFN） is integrated with proportional-integral （PI） control to construct a velocity tracking control scheme for the inner loop. Finally, a prototype technology based control system is designed for a robotic manipulator. The proposed control scheme is applied to the robotic manipulator. Experimental results confirm the validity of the proposed control scheme by comparing it with other control strategies.