Dual-arm Space Robot System Research Articles

Synthetic control with target sticking for on-orbit capturing using a dual-arm space robot

On-orbit capturing is a crucial step in the application of dual-arm space robots, aiming to accurately grasp a moving target and avoid damage to the arms terminal parts (i.e. the end effectors) due to contact force saturation. This paper presents a synthetic control method with target sticking for on-orbit capturing using a dual-arm space robot system from the approaching phase to pre-grasping phase. In the approaching phase, an online trajectory planning method based on visual servoing is proposed to obtain the desired trajectories for end effectors in work space. Then the joint torques are designed by the inverse kinematics and inverse dynamics to track the desired trajectories. Different from most of the current research, a new sticking phase is proposed after the approaching phase and before the pre-grasping phase. In the sticking phase, a force and motion control method is designed to maintain a close relative distance between end effectors and the target, which can avoid saturation of contact forces and avoid damage to the end effectors. In what follows, an impedance control method is proposed in the pre-grasping phase to absorb the impact energy and grasp the target accurately. The synthetic control strategy integrates the controllers of all the phases mentioned above. Automatic switching among the phases is realized by using logic judgment according to the system real states, which is more consistent with the real capturing environment. Finally, numerical simulation results demonstrate the effectiveness of the proposed synthetic control scheme. The results can be applied to the trajectory planning and control of on-orbit capturing, avoiding contact force saturation and ensuring the safety of the system.

Coordinated trajectory planning of a dual-arm space robot with multiple avoidance constraints

This paper presents a coordinated trajectory planning method for a free-floating dual-arm space robot system. The research purpose of this paper is to enable a space robot to complete the specified goals while avoiding collision with an obstacle by planning the motion of the joints. The coordinated trajectory planning problem for a space robot is transformed into an optimization problem to find the optimal trajectory of the base and manipulators by using particle swarm optimization (PSO). Since the optimization method is used to find an optimal trajectory, it is unnecessary to calculate the position of the base and the inverse kinematics of the joints. Therefore, the kinematic singular problem in seeking the inverse solution can be avoided. The joint trajectories are parametrized by a sine function with seventh-order polynomial parameters. Multiple constraints are added to the objective function as penalty items, and a new increasing strategy for a penalty factor is proposed to balance the penalty and search ability under multiple constraints. Finally, numerical simulations are carried out to verify the effectiveness of the proposed method.

Parameter Optimization of dsRNA Splicing Evolutionary Algorithm Based Fixed-Time Obstacle-Avoidance Trajectory Planning for Space Robot

This paper addresses a smoother fixed-time obstacle-avoidance trajectory planning based on double-stranded ribonucleic acid (dsRNA) splicing evolutionary algorithm for a dual-arm free-floating space robot, the smoothness of large joint angular velocity is improved by 15.61% on average compared with the current trajectory planning strategy based on pose feedback, and the convergence performance is improved by 76.44% compared with the existing optimal trajectory planning strategy without pose feedback. Firstly, according to the idea of pose feedback, a novel trajectory planning strategy with low joint angular velocity input is proposed to make the pose errors of the end-effector and base converge asymptotically within fixed time. Secondly, a novel evolutionary algorithm based on the gene splicing idea of dsRNA virus is proposed to optimize the parameter of the fixed-time error response function and obstacle-avoidance algorithm, which can make joint angular velocity trajectory is planned smooth. In the end, the optimized trajectory planning strategy is applied into the dual-arm space robot system so that the robotic arm can smoothly, fast and accurately complete the tracking task. The proposed novel algorithm achieved 7.56–30.40% comprehensive performance improvement over the benchmark methods, experiment and simulation verify the effectiveness of the proposed method.

Optimal grasping pose for dual-arm space robot cooperative manipulation based on global manipulability

This paper presents an approach to determine optimal grasping poses for dual-arm space robot cooperatively grasping an uncooperative satellite. Aiming at better manipulating the satellite after capture, it is necessary to plan properly grasping poses on the satellite for dual-arm end-effectors to maximize the manipulability of space robot. In this paper, global manipulability based on capability map is applied as the quality index to seek optimal grasping poses. First, the technique to generate cooperative workspace for a closed chain system is introduced fusing the workspace of each single-arm with self-collision avoidance. Second, several general manipulability indices, such as dexterity, manipulability measure and task compatibility, are extended to the entire cooperative workspace to construct capability maps. Next, global manipulability is evaluated for dual-arm space robot cooperative manipulation based on the capability maps. Following this, the optimal grasping poses among all feasible grasping poses on the satellite are obtained by the global manipulability. Finally, a simulation study is carried out to verify the feasibility of the proposed approach based on a redundant dual-arm space robotic system.

Adaptive robust decoupling control of multi-arm space robots using time-delay estimation technique

The most distinctive difference between a space robot and a base-fixed robot is its free-flying/floating base, which results in the dynamic coupling effect. The mounted manipulator motion will disturb the position and attitude of the base, thereby deteriorating the operational accuracy of the end effector. This paper focuses on decoupling or counteracting the coupling between the manipulator and the base. The dynamics model of multi-arm space robots is established using the composite rigid dynamics modeling approach to analyze the dynamic coupling force/torque. An adaptive robust controller that is based on time-delay estimation (TDE) and sliding mode control (SMC) is designed to decouple the multi-arm space robot. In contrast to the online computation method, the proposed controller compensates for the dynamic coupling via the TDE technique and the SMC can complement and reinforce the robustness of the TDE. The global asymptotic stability of the proposed decoupling controller is mathematically proven. Several contrastive simulation studies on a dual-arm space robot system are conducted to evaluate the performance of the TDE-based SMC controller. The results of qualitative and quantitative analysis illustrate that the proposed controller is simpler and yet more effective.

Modeling and Analysis of the Multiple Dynamic Coupling Effects of a Dual-arm Space Robotic System

SUMMARYA dual-arm space robot has large potentials in on-orbit servicing. However, there exist multiple dynamic coupling effects between the two arms, each arm, and the base, bringing great challenges to the trajectory planning and dynamic control of the dual-arm space robotic system. In this paper, we propose a dynamic coupling modeling and analysis method for a dual-arm space robot. Firstly, according to the conservation principle of the linear and angular momentum, the dynamic coupling between the base and each manipulator is deduced. The dynamic coupling factor is then defined to evaluate the dynamic coupling degree. Secondly, the dynamic coupling equations between the two arms, each arm, and the base are deduced, respectively. The dynamic coupling factor is suitable not only for single-arm space robots but also for multi-arm space robot systems. Finally, the multiple coupling effects of the dual-arm space robotic system are analyzed in detail through typical cases. Simulation results verified the proposed method.

Virtual Stereovision Pose Measurement of Noncooperative Space Targets for a Dual-Arm Space Robot

Noncooperative target pose (position and attitude) measurement is very important for on-orbital servicing tasks, such as malfunctioned spacecraft capturing and repairing, space debris removal, and so on. Traditional stereovision-based methods require the two cameras to observe the same object and form a common observation area, limiting system flexibility, and measurement distance. In this paper, a virtual stereovision (VSV) modeling and pose measurement method are proposed for a dual-arm space robotic system. Each arm only carries one camera to observe different objects. The geometry features (i.e., the triangle, quadrilateral, or circular features) are independently extracted from the images of each camera. The two separate cameras are mapped to a stereo measurement range and the, respectively, identified features are converted into an equivalent “virtual common feature.” Then, a “VSV measurement system” is constructed. The rocket nozzle and the triangular support of the satellite are considered as different objects to be observed by the two cameras of a dual-arm space robot. The pose of the nozzles and the triangular brackets is further achieved based on the VSV information. Finally, we developed an experimental system, which is composed of a satellite mockup, two monocular cameras, and high precision laser tracker (used to evaluate the vision measure accuracy). The experimental results verified the proposed method. The average position error of the method is less than 6.1367 mm, and the average attitude error is less than 2.415°.

Virtual-base modeling and coordinated control of a dual-arm space robot for target capturing and manipulation

A dual-arm space robotic system has large potential in on-orbit servicing missions, such as satellite repairing, large space structure construction and space debris removal. However, there exist multiple dynamic couplings between the base, the manipulators and the target, bringing large challenge to the motion planning and control. In this paper, a virtual-base modeling method (VBM) and coordinated control strategy are proposed for a dual-arm space robot. One of the arms’ end-effector is considered as the virtual base, and the other bodies, including each link of the arms and the center body of the spacecraft, form a combined manipulator. Correspondingly, we derive the kinematic and dynamic equations of the combined manipulator with the virtual base, taking it as a hyper-redundant space manipulator. Furthermore, the coordinated trajectory planning and control methods are presented for capturing and manipulating a space target. For the pre-contact stage, the virtual base and end-effector are controlled simultaneously to track the desired trajectory in the inertial space. During contact, the operational force is regulated using admittance control law, by simplifying the operational forces of the two arms as the equivalent operational force of the combined manipulator. After the target is captured and fixed to the two arms, its pose is adjusted by simultaneously controlling the trajectory and the operational force of the virtual base and the combined manipulator. Finally, a co-simulation system is created based on MATLAB/Simulink and MSC.ADAMS. Simulation results verify the effectiveness and robustness of the proposed methods.

A fast trajectory planning framework with task-priority for space robot

This paper addresses trajectory planning issue for free-floating space robotic system which is designed to track a prescribed path simultaneously fulfilling imposed constraints such as collision avoidance and minimizing base attitude disturbance. Collision avoidance can be treated as inequality constraints as part of the trajectory planning. To generate smooth trajectory for robot motion, a novel local collision avoidance method considering multiple velocity damper constraints is proposed for non-strictly convex polyhedra. Moreover, we propose a task-priority handling strategy incorporated with a full-fledged Quadratic Programming(QP) procedure to solve the planning problem with sequential tasks. The proposed task-priority handling strategy enables a rapid adaptation of the space manipulators motion, which makes this strategy feasible for real-time planning. The trajectory planning framework with collision avoidance method and task-priority handling strategy were implemented and demonstrated via a kinematically redundant dual-arm space robotic system.

Coordinated motion control of a dual-arm space robot with joint-limit avoidance and uncertain inertial parameters

In this article, a new adaptive coordinated motion control approach is introduced for a dual-arm free-floating space robot. This adaptive algorithm is used for the post-capture of a large noncooperative target with joint-limit avoidance and uncertain dynamic parameters. To overcome the problem of dynamics coupling between the space base, its manipulators, and the target, we develop a dual-arm space robotic system. One arm is used to complete the capture task and the other is used to counteract the disturbance to the space base. In this case, a new coordinated motion control law is derived based on reaction null space control. An improved joint-limit avoidance algorithm is implemented for large noncooperative target capture; otherwise, a significant base disturbance may result if the joint-limit constraints are not explicitly considered. Based on momentum conservation, the linear regression form of the estimation problem is obtained, and we further identify the unknown inertial parameters of the target. Finally, the simulation results demonstrate the effectiveness of the proposed algorithm.

Study on Trajectory Planning of Dual-arm Space Robot Keeping the Base Stabilized

Aiming at the case that the base is required to be stabilized by a balance arm when a dual-arm space robotic system is performing on-orbit missions, we propose coordinated trajectory planning methods of two typical applications — keeping the base centroid fixed (approximately; the same below), and keeping the base attitude and centroid position fixed synchronously. Firstly, the concept of “system centroid equivalent manipulator” is presented, and its kinematic model is derived. Based on the resolution of the position-level kinematic equation, the trajectory of the balance arm for stabilizing the base centroid is planned. Secondly, by combining with the control of a reaction flywheel, the base attitude and centroid can be kept fixed at the same time. The desired angular speed of the flywheel is determined according to the angular momentum conservation law. Finally, a multi-body dynamic model of a dual-arm space robotic system is developed and simulation study is carried out. The proposed methods can overcome the singularity problem which is un-avoidable for previous approaches based on differential kinematics. Furthermore, there are not special requirements on the mass properties and installation position of the balance arm. Simulation results have verified the proposed methods.

Robust Control Based on Velocity Filter of Free-floating Dual-arm Space Robot System in Inertial Space

针对末端所持载荷参数未知的自由漂浮双臂空间机器人系统, 提出了基于速度滤波器的鲁棒控制方法. 利用拉格朗日方法进行运动学及动力学分析, 建立了双臂空间机器人系统欠驱动形式的动力学模型. 借助于增广变量法, 证明了可将空间机器人系统的增广广义Jacobi矩阵及动力学方程表示为一组组合惯性参数的线性函数. 在此基础上引入速度滤波器, 设计了双臂空间机器人基于速度滤波器的惯性空间轨迹跟踪鲁棒控制方案. 该速度滤波器可利用实测位置误差生成末端爪手的伪速度信号, 有效避免了相关速度信号的实时测量与反馈. 该方案的显著优点在于, 不需要测量、反馈末端爪手的移动速度和加速度, 同时有效消除了控制过程中的抖振现象. 平面自由漂浮双臂空间机器人系统的数值仿真验证了算法的有效性.

Design for Fuzzy Variable Structure Controller of Hybrid Position and Force Control for Dual-arm Coordinated Space Robot Systems

讨论了载体位置、姿态均不受控制的漂浮基双臂空间机器人抓物系统的动力学建模和控制问题. 利用拉格朗日方法和牛顿欧拉法分别建立了双臂空间机器人及负载的非线性动力学模型, 结合空间机器人固有的特性及闭合链约束关系, 得到抓持系统合成动力学方程. 以此为基础, 考虑到空间机器人系统结构的复杂性及某些参数的变动性, 根据具有较强鲁棒性的变结构控制理论, 针对该抓持系统惯性空间轨迹跟踪设计了全局滑模控制方案及相应的PI内力控制方案, 从而达到位置、力的混合控制. 为克服滑模控制器抖振的缺点, 附加设计了模糊控制器, 根据系统的输出来动态调节滑模控制器的参数, 从而既可确保系统的快速响应又可降底原有的抖振. 系统数值仿真证明了上述控制方案的有效性与准确性.

Adaptive neural network control for coordinated motion of a dual-arm space robot system with uncertain parameters

Control of coordinated motion between the base attitude and the arm joints of a free-floating dual-arm space robot with uncertain parameters is discussed. By combining the relation of system linear momentum conversation with the Lagrangian approach, the dynamic equation of a robot is established. Based on the above results, the free-floating dual-arm space robot system is modeled with RBF neural networks, the GL matrix and its product operator. With all uncertain inertial system parameters, an adaptive RBF neural network control scheme is developed for coordinated motion between the base attitude and the arm joints. The proposed scheme does not need linear parameterization of the dynamic equation of the system and any accurate prior-knowledge of the actual inertial parameters. Also it does not need to train the neural network offline so that it would present real-time and online applications. A planar free-floating dual-arm space robot is simulated to show feasibility of the proposed scheme.

Adaptive Control for Free-Floating Dual-Arm Space Robot System in Joint Space

讨论了载体位置、姿态均不受控制情况下,具有未知参数的自由漂浮双臂空间机器人系统的自适应控制问题.由于此类机器人系统具有结合系统动量及动量矩守恒关系得到完全能控形式的系统动力学方程,以及系统惯性参数不符合惯常的线性函数关系的特点,因而地面机器人的控制方法在此难以直接推广应用.为了克服上述难点,仅将系统动量守恒关系耦合到系统动力学方程当中,而不耦合系统动量矩守恒关系,结果得到一组欠驱动形式的系统动力学方程.该系统动力学方程的优点是关于一组组合惯性参数能保持惯常的线性函数关系.以此为基础,并借助增广变量法,针对双臂空间机器人末端爪手所持载荷参数未知的情况,设计了关节空间轨迹跟踪的自适应控制方案.该控制方案的显著优点为,不需要测量、反馈双臂空间机器人漂浮基的位置、移动速度和移动加速度.系统的数值仿真,证实了方法的有效性.

Dynamic control of a free-floating flexible dual-arm space robotic system

Based on the assumed modes method,deformation for the flexible link is approximately described.Dynamics of the flexible arm with ignoring high-order elastic modes is analyzed using Lagrange principle.In terms of dynamics of the flexible dual-arm and the object,the constraint relationship between end of the flexible arm and the object as well as the momentum conservation,the dynamic model of the closed chain system for a free-floating flexible dual-arm space robot holding a rigid payload is derived.Aiming at a high frequency characteristic of the flexible state,a slow subsystem and a fast subsystem have been separated based on the singular perturbation method in which the sliding-mode control method and the nonlinear PD control method are adopted in each subsystem respectively to have state outputs of stiffness and flexibility reach desired outputs.Using this combined control method,the payload can track the expected trajectory preferably and the elastic vibration is suppressed.At the same time,there are few effects to the motion of the spacecraft,and internal force and internal torque can smoothly track the given values. Finally,some simulation tests have conducted to verify the effectiveness of the proposed methods.