Hybrid task priority-based motion control of a redundant free-floating space robot

This paper presents a novel hybrid task priority-based motion planning algorithm of a space robot. The satellite attitude control task is defined as the primary task, while the leastsquares-based non-strict task priority solution of the end-effector plus the multi-constraint task is viewed as the secondary task. Furthermore, a null-space task compensation strategy in the joint space is proposed to derive the combination of non-strict and strict task-priority motion planning,and this novel combination is termed hybrid task priority control. Thus, the secondary task is implemented in the primary task＇s null-space. Besides, the transition of the state of multiple constraints between activeness and inactiveness will only influence the end-effector task without any effect on the primary task. A set of numerical experiments made in a real-time simulation system under Linux/RTAI shows the validity and feasibility of the proposed methodology.

Spatial Operator Algebra for Free-floating Space Robot Modeling and Simulation

As the dynamic equations of space robots are highly nonlinear,strongly coupled and nonholonomic constrained,the efficiency of current dynamic modeling algorithms is difficult to meet the requirements of real-time simulation.This paper combines an efficient spatial operator algebra（SOA） algorithm for base fixed robots with the conservation of linear and angular momentum theory to establish dynamic equations for the free-floating space robot,and analyzes the influence to the base body＇s position and posture when the manipulator is capturing a target.The recursive Newton-Euler kinematic equations on screw form for the space robot are derived,and the techniques of the sequential filtering and smoothing methods in optimal estimation theory are used to derive an innovation factorization and inverse of the generalized mass matrix which immediately achieve high computational efficiency.The high efficient SOA algorithm is spatially recursive and has a simple math expression and a clear physical understanding,and its computational complexity grows only linearly with the number of degrees of freedom.Finally,a space robot with three degrees of freedom manipulator is simulated in Matematica 6.0.Compared with ADAMS,the simulation reveals that the SOA algorithm is much more efficient to solve the forward and inverse dynamic problems.As a result,the requirements of real-time simulation for dynamics of free-floating space robot are solved and a new analytic modeling system is established for free-floating space robot.

Motion planning for redundant prismatic-jointed manipulators in the free-floating mode

This paper investigates the motion planning of redundant free-floating manipulators with seven prismatic joints. On the earth, prismatic-jointed manipulators could only position their end-effectors in a desired way. However, in space, the end-effectors of free-floating manipulators can achieve both the desired orientation and desired position due to the dynamical coupling between manipulator and satellite movement, which is formally expressed by linear and angular momentum conservation laws. In this study, a tractable algorithm particle swarm optimization combined with differential evolution （PSODE） is provided to deal with the motion planning of redundant free-floating prismatic-jointed manipulators, which could avoid the pseudo inverse of the Jacobian matrix. The polynomial functions, as argument in sine functions are used to specify the joint paths. The co- efficients of the polynomials are optimized to achieve the desired end-effector orientation and position, and simulta- neously minimize the unit-mass-kinetic energy using the redundancy. Relevant simulations prove that this method pro- vides satisfactory smooth paths for redundant free-floating prismatic-jointed manipulators. This study could help to recognize the advantages of redundant prismatic-jointed space manipulators.

Singular perturbation composite control of a free-floating flexible dual-arm space robot

The Free-floating Flexible Dual-arm Space Robot is a highly nonlinear and coupled dynamics system. In this paper, the dynamic model is derived of a Free-floating Flexible Dual-arm Space Robot holding a rigid payload. Furthermore, according to the singular perturbation method, the system is separated into a slow subsystem representing rigid body motion of the robot and a fast subsystem representing the flexible link dynamics. For the slow subsystem, based on the second method of Lyapunov, using simple quantitative bounds on the model uncertainties, a robust tracking controller design is used during the trajectory tracking phase. The optimal control method is designed in the fast subsystem to guarantee the exponential stability. With the combination of the two above, the system can track the expected trajectory accurately, even though with uncertainty in model parameters, and its flexible vibration gets suppressed, too. Finally, some simulation tests have been conducted to verify the effectiveness of the proposed methods.

Kinematics of a Trinal-Branch Space Robotic Manipulator with Redundancy

This paper presents a trinal-branch space robotic manipulator with redundancy, due to hash application environments, such as in the station. One end-effector of the manipulator can be attached to the base, and other two be controlled to accomplish tasks. The manipulator permits operation of science payload, during periods when astronauts may not be present. In order to provide theoretic basis for kinematics optimization, dynamics optimization and fault-tolerant control, its inverse kinematics is analyzed by using screw theory, and its unified formulation is established. Base on closed-form resolution of spherical wrist, a simplified inverse kinematics is proposed. Computer simulation results demonstrate the validity of the proposed inverse kinematics.

Reorientation and obstacle avoidance control of free-floating modular robots using sinusoidal oscillator

This paper presents that a serpentine curve-based controller can solve locomotion control problems for articulated space robots with extensive flight phases,such as obstacle avoidance during free floating or attitude adjustment before landing.The proposed algorithm achieves articulated robots to use closed paths in the joint space to accomplish the above tasks.Flying snakes,which can shuttle through gaps and adjust their landing posture by swinging their body during gliding in jungle environments,inspired the design of two maneuvers.The first maneuver generates a rotation of the system by varying the moment of inertia between the joints of the robot,with the magnitude of the net rotation depending on the controller parameters.This maneuver can be repeated to allow the robot to reach arbitrary reorientation.The second maneuver involves periodic undulations,allowing the robot to avoid collisions when the trajectory of the global Center of Mass(CM)passes through the obstacle.Both maneuvers are based on the improved serpenoid curve,which can adapt to redundant systems consisting of different numbers of modules.Finally,the simulation illustrates that combining the two maneuvers can help a free-floating chain-type robot traverse complex environments.Our proposed algorithm can be used with similar articulated robot models.

Reaction Torque Control of Redundant Free-floating Space Robot

This paper presents the reaction torque based satellite base reactionless control or base disturbance minimization of a redundant free-floating space robot. This subject is of vital importance in the study of the free-floating space robot because the base disturbance minimization will result in less energy consumption and prolonged control application. The analytical formulation of the reaction torque is derived in this article, and the reaction torque control can achieve reactionless control and satellite base disturbance minimization. Furthermore, we derive the reaction torque based control of the space robot for base disturbance minimization from both the non-strict task priority and strict task priority control strategy. The dynamics singularity in the proposed algorithm is avoided in this paper. Besides, a real time simulation system of the space robot under Linux/real time application interface（RTAI） is developed to verify and test the feasibility and reliability of the method. The experimental results demonstrate the feasibility of online reaction torque control of the redundant free-floating space robot.

冗余漂浮空间机器人多任务轨迹规划

针对冗余漂浮空间机器人在单次行程中连续执行多项轨道任务的能耗最优轨迹规划问题,本文提出一种改进遗传算法,将同时优化3种类型基因引入,使得每条染色体包含3部分,即任务序列、与任务序列对应的关节构型序列和描述机器人关节轨迹的正弦多项式系数,对染色体的3部分进行独立编码,并在迭代寻优过程中对3个组成部分独立执行交叉和变异操作。仿真结果表明:与传统遗传算法相比,本文算法具有精度高、计算量少和CPU时间短的优点。

Comparison of internal force antagonism between redundant cable-driven parallel robots and redundant rigid parallel robots

The internal force antagonism(IFA)problem is one of the most important issues limiting the applications and popularization of redundant parallel robots in industry.Redundant cable-driven parallel robots(RCDPRs)and redundant rigid parallel robots(RRPRs)behave very differently in this problem.To clarify the essence of IFA,this study first analyzes the causes and influencing factors of IFA.Next,an evaluation index for IFA is proposed,and its calculating algorithm is developed.Then,three graphical analysis methods based on this index are proposed.Finally,the performance of RCDPRs and RRPRs in IFA under three configurations are analyzed.Results show that RRPRs produce IFA in nearly all the areas of the workspace,whereas RCDPRs produce IFA in only some areas of the workspace,and the IFA in RCDPRs is milder than that RRPRs.Thus,RCDPRs more fault-tolerant and easier to control and thus more conducive for industrial application and popularization than RRPRs.Furthermore,the proposed analysis methods can be used for the configuration optimization design of RCDPRs.

Task space control of free-floating space robots using constrained adaptive RBF-NTSM

Trajectory tracking control of space robots in task space is of great importance to space missions, which require on-orbit manipulations. This paper focuses on position and attitude tracking control of a tree-floating space robot in task space. Since nei- ther the nonlinear terms and parametric uncertainties of the dynamic model, nor the external disturbances are known, an adap- tive radial basis function network based nonsingular terminal sliding mode （RBF-NTSM） control method is presented. The proposed algorithm combines the nonlinear sliding manifold with the radial basis function to improve control performance. Moreover, in order to account for actuator physical constraints, a constrained adaptive RBF-NTSM, which employs a RBF network to compensate for the limited input is developed. The adaptive updating laws acquired by Lyapunov approach guar- antee the global stability of the control system and suppress chattering problems. Two examples are provided using a six-link free-floating space robot. Simulation results clearly demonstrate that the proposed constrained adaptive RBF-NTSM control method performs high precision task based on incomplete dynamic model of the space robots. In addition, the control errors converge faster and the chattering is eliminated comparing to traditional sliding mode control.

Path planning of a free-floating space robot based on the degree of controllability

An effective and more efficient path planning algorithm is developed for a kinematically non-redundant free-floating space robot(FFSR) system by proposing a concept of degree of controllability(DOC) for underactuated systems. The DOC concept is proposed for making full use of the internal couplings and then achieving a better control effect, followed by a certain definition of controllability measurement which measures the DOC, based on obtaining an explicit and finite equivalent affine system and singular value decomposition. A simple method for nilpotent approximation of the Lie algebra generated by the FFSR system is put forward by direct Taylor expansion when obtaining the equivalent system. Afterwards, a large-controlla- bility-measurement(LCM) nominal path is searched by a weighted A* algorithm, and an optimal self-correcting method is designed to track the nominal path approximately, yielding an efficient underactuated path. The proposed strategy successfully avoids the drawback of inefficiency inherent in previous path-planning schemes, which is due to the neglect of internal couplings, and illustrative numerical examples show its efficacy.

Trajectory planning and base attitude restoration of dual-arm free-floating space robot by enhanced bidirectional approach

When free-floating space robots perform space tasks,the satellite base attitude is disturbed by the dynamic coupling.The disturbance of the base orientation may affect the communication between the space robot and the control center on earth.In this paper,the enhanced bidirectional approach is proposed to plan the manipulator trajectory and eliminate the final base attitude variation.A novel acceleration level state equation for the nonholonomic problem is proposed,and a new intermediate variable-based Lyapunov function is derived and solved for smooth joint trajectory and restorable base trajectories.In the method,the state equation is first proposed for dual-arm robots with and without end constraints,and the system stability is analyzed to obtain the system input.The input modification further increases the system stability and simplifies the calculation complexity.Simulations are carried out in the end,and the proposed method is validated in minimizing final base attitude change and trajectory smoothness.Moreover,the minute internal force during the coordinated operation and the considerable computing efficiency increases the feasibility of the method during space tasks.

基于改进RRT^(*)算法的可重构机器人路径规划

针对可重构机器人在复杂环境中的路径规划问题,设计了一种基于改进RRT^(*)算法的可重构机器人路径规划方法。首先,针对RRT^(*)算法规划时间过长问题,提出缩小节点采样空间法,并在迭代过程中优化采样区域,避免了资源的浪费。此外,设计了路径点冗余裁剪法,使得可重构机器人路径点数减少,拐点消减,总体规划路径缩短。在此基础上,建立多足可重构机器人的基本运动状态库,能够根据不同的环境改变自身构型来完成路径规划。采用MATLAB软件在障碍物数目和环境不同的状况下进行路径规划仿真实验,实验结果表明改进后的RRT^(*)算法减少了规划时间,缩短了规划路径,验证了算法的有效性。

偏置式冗余空间机械臂逆运动学求解的参数化方法

针对肩、肘、腕均有偏置的空间站遥操作机械臂(SSRMS)型7DOF冗余机械臂,提出了逆运动学求解的关节角参数化及臂型角参数化两种方法。前者根据机械臂的臂型特征,推导以θ1、θ2、θ6、θ7中的一个作为给定参数时其他关节角的表达式,得出8种可能解;后者首先构造与SSRMS型机械臂相对应的零偏置球关节—旋转关节—球关节(SRS)机械臂,然后以臂型角为参数求解SRS机械臂的逆运动学,再根据SSRMS与SRS机械臂的关系,得到SSRMS的8组逆解。仿真算例校验了所提方法的有效性。

冗余自由度机器人的运动学优化研究

冗余自由度机器人的引入主要是为了利用其冗余特性解决象避障、避奇异位形等运动学控制问题．解决这些问题的途径是在机器人雅可比矩阵的零空间上进行运动学规划，其中最主要的是优化目标函数和放大系数的选取．文中着重讨论和确定了优化目标函数和放大系数的选取方法，并通过计算机仿真证明了所给出的方法是有效的．

冗余度机器人扩展作业空间方法算法奇异的研究

本文对冗余度操作机最为常用的求逆解方法——扩展作业空间方法的算法奇异问题进行了深入的研究．Ｋｌｅｉｎ［２，４］及Ｃｈｏ［３，５］提出冗余度机器人采用扩展作业空间方法必须首先确定由于性能指标函数及扩展Ｊａｃｏｂｉａｎ矩阵所引起的算法奇异在关节空间中的分布区域，只有这样才能避免方法引起的算法奇异．通过本文对扩展作业空间方法的优化性能指标函数的必要条件及算法奇异产生的条件的比较及研究，得出了在应用扩展作业空间方法时，不可能出现算法奇异的情况．因此在应用扩展作业空间方法时无需考虑算法奇异问题．

控制力矩陀螺驱动空间机器人的角动量平衡控制

针对V构型控制力矩陀螺(CMGs)驱动的冗余空间机器人的CMGs角动量饱和问题,提出一种角动量平衡控制方法。该方法从平衡使用机械臂各臂杆CMGs角动量的思想出发,定义了角动量平衡指标,并使用加速度分解技术和逆动力学方法设计了角动量平衡控制器。该控制器可在保证机械臂跟踪工作空间轨迹的同时,利用机械臂的空转运动使得角动量平衡指标尽量减小,即各臂CMGs的角动量使用趋于平均,从而降低某些臂杆的CMGs先行饱和的可能性,充分利用CMGs的控制能力。基于平面三自由度冗余机械臂的数值仿真结果验证了所设计的控制器的有效性。

被动冗余度空间机器人运动学综合

分析了“被动冗余度”空间机器人主 ,被动关节之间的运动学耦合 ,得到了可用于运动学规划的耦合指标 ;分析了“被动冗余度”空间机器人的运动学奇异问题 ,以及与对应全主动关节冗余度空间机器人的运动学奇异的区别 ,得到的新的可操作性指标同样可用于机器人的运动规划 ;推导出了“被动冗余度”空间机器人的最佳最小二乘运动学优化方程 ,通过“准自运动”实现被动冗余度空间机器人优化控制 ;通过对平面

构形平面方法求解冗余机械臂逆运动学

由于冗余机械臂存在冗余自由度,导致其逆运动学求解方法复杂。本文依据构形平面的基本理论,提出了一种快速、简洁的冗余机械臂逆运动学求解方法。首先对冗余机械臂的结构进行分析,将冗余机械臂分解成若干个构形平面。然后,采用构形平面匹配方法,将该机械臂工作构形进行位置和姿态匹配,同时采用半解析的方式求得逆运动学解。最后,对7自由度冗余机械臂进行仿真计算,实验结果验证了该方法求解精度高、求解速度快,而且避免产生奇异值。

串并混联空间机械臂全自由度轨迹规划算法

目前,国内外对串并混联空间机械臂的研究较少;而且大多在舍弃冗余自由度的情况下进行轨迹规划.针对7自由度串并混联空间机械臂,提出了一种基于解析解、并且充分放开全部7个自由度的机械臂轨迹规划算法.该规划算法既扩大了串并混联空间机械臂的规划可达空间,又保证了规划的实时性,同时还保留了结构承载能力强的优点,可以充分发挥其作为空间抓捕用臂的优势.通过仿真和地面空间操作抓捕试验,验证了算法的有效性.