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

Multibody System Dynamics - 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...     

深空探测柔性太阳帆航天器动力学建模与姿态控制

太阳帆利用太阳辐射压力提供太空航行的必要动力,由于具有理论上的无限速度和无需消耗任何燃料等优势,被认为是完成未来深空探测任务的有效技术途径之一.柔性太阳帆航天器的动力学模型包括多体动力学、刚柔耦合动力学和太阳辐射光压模型,复杂的动力学特性导致其姿态控制设计具有很强的挑战性.针对带有控制杆的柔性太阳帆航天器,本文采用拉格朗日方程和有限元法,给出了面向控制的解析式动力学模型.所推导的刚柔耦合动力学模型,刻画了太阳帆航天器的本质动力学特性,即双框架控制杆的短周期运动,姿态与柔性太阳帆的耦合效应,以及在太阳光压恢复力矩下的姿态静稳定性和长周期运动.基于带控制杆的太阳帆航天器的双时间尺度特性,提出了双回路控制结构,用于实现航天器俯仰轴和偏航轴的姿态控制.将内回路设计为PD控制器,用于实现质心位置的调整.将外回路设计为PID控制器,用于阻尼姿态运动,并实现在平衡太阳光压力矩下的姿态保持.从而将柔性太阳帆航天器的复杂姿态控制问题转化为两个低阶子问题,实现了在不同频带上的控制设计.仿真结果验证了动力学建模和姿态控制设计方法的有效性.     

Unified multi-domain modelling and simulation of space robot for capturing a moving target

Space robotic systems are expected to play an increasingly important role in the future on-orbit service. The applications include repairing, refueling or de-orbiting of a satellite, or removal of the space debris. The dynamical performances of space robotic system result from the multi-physics interactions between mechanical, electrical, electronic, control, etc. In this paper, we developed a unified multi-domain modelling and simulation system. The system is composed of the following modules: the path planner, joint controllers, motor and its driver, gearing mechanism of the space manipulators, the Guidance, Navigation, and Control (GNC) system, the actuators of the base, and the orbital environment, orbital dynamic and the multi-body dynamic of the whole system, etc. Based on this system, the operation during different stages, including far range rendezvous, close range rendezvous (is usually divided into two sub-phases: closing and final approach) and target capturing can be studied from the view of multi-physics domains. The key algorithms, such as pose (position and attitude) measurement, GNC of the base, path planning and control of the space manipulator, and so on, can be validated using the system. As examples, the capturing processes of a moving target under free-floating and attitude-controlled modes are simulated and the simulation results are given.     

Dynamic features of flexible spacecraft control in process of its transformation into a large space structure

Consideration was given to dynamics of angular motion control of the flexible spacecraft reconstructed into a large space structure. In formal terms, this transformation lies in gradual reduction of the constructive rigidity to small values giving rise to low-frequency ( $ \tilde f Consideration was given to dynamics of angular motion control of the flexible spacecraft reconstructed into a large space structure. In formal terms, this transformation lies in gradual reduction of the constructive rigidity to small values giving rise to low-frequency ( ≤ 0.05 Hz) oscillations which represent one of the attributes of the class of large space structures. The existing quantitative definition of the large space structure was specified. It was demonstrated that as the frequencies of structure’s elastic oscillations approach those of the control of object “rigid” motion, a new kind of interrelations between the motions of both types, the so-called “capture” of the controller frequency by that of the elastic oscillations, arises which impairs control efficiency to the point of losing system stability. Analytical (for the linear control systems) and computer-aided (for the discrete systems) methods for determination of the boundaries separating the two qualitatively different forms of existence of the transformed elastic object were proposed. Some results of computer simulation of the orientation control of variable objects such as flexible spacecraft and large space structure were presented. Original Russian Text ? I.N. Krutova, V.M. Sukhanov, 2008, published in Avtomatika i Telemekhanika, 2008, No. 5, pp. 41–56. This work was supported by the Russian Foundation for Basic Research, project no. 05-08-18175.     

Dynamics modeling and analysis of a biped walking robot actuated by a closed-chain mechanism

We developed a new type of human-sized biped walking robot (BWR) driven by the closed-chain type of joint actuator. Each leg of the robot is composed of three pitch joints and one roll joint. In all, a 15 degree-of-freedom robot including four arm joints and three joints for the head was developed. The BWR was developed to walk autonomously such that all leg joints are actuated by small 90 W dc motors/drivers and dc batteries and controllers which are boarded. The joint actuator for the BWR is composed of the four-bar-link mechanism driven by the ball screw which has high strength and high gear ratio. A dynamics modeling of the developed BWR for forward walking is presented in which the revolute joint dynamics are transformed into the prismatic joint dynamics of the ball screw. Also, an analysis on the four-bar-link mechanism applied to the joint actuator and on the structure of the BWR is shown. The design specification of the actuating motor for the BWR is analyzed through the torque analysis of the four-bar-link actuator. Through walking experiments of the BWR, the walking performance and trajectory tracking ability is shown. © 2004 Wiley Periodicals, Inc.     

Synthesis of a linearly interpolated gain scheduling controller for large flexible spacecraft ETS-VIII

This paper illustrates a design procedure for a linearly interpolated gain scheduling controller for Engineering Test Satellite VIII (ETS-VIII) using its linear parameter-varying (LPV) model. The LPV model here consists of piecewise-linear functions of the paddle rotation angle and a norm-bounded perturbation. The main purpose of this research is to derive a simple structured scheduling law that can be easily implemented in a satellite onboard computer. The derived gain has only two grid points and is scheduled simply by linear interpolation, which is desirable from the standpoint of implementability. Moreover, since the synthesis condition is based on parameter-dependent Lyapunov functions, it gives less conservative results than existing methods. Simulation results are presented to show the effectiveness of the proposed synthesis.     

带Stewart平台的航天器刚柔耦合动力学建模与仿真分析

本文采用柔性多体系统单向递推组集的建模方法,基于速度变分原理建立了带Stewart平台、柔性帆板和CMG组件的航天器刚柔耦合动力学模型.由于该模型自由度较大,无法满足实时控制的需求,因此建立了简化的Stewart平台等效模型,并通过与柔性Stewart平台完整模型对比,验证了所建立的动力学简化模型的正确性与高效性.分析了星体平台运动及柔性帆板的振动对有效载荷动力学响应的影响,指出了设计Stewart平台的微振动抑制方案时不能忽略下平台的运动及柔性附件的振动.本研究为带Stewart平台的航天器的微振动减振设计与高精度指向提供了有效的技术支撑.     

Synthesis and analysis of a flexible elephant trunk robot

This paper presents a novel synthesis and analysis of a flexible elephant trunk robot (biological continuum–style manipulator). The robot includes eight flexible segments, although it can be extended to more segments as necessary. In this study the gravity of the springs is neglected due to the fact that the manipulation force is much larger than these gravity forces. This mechanism exhibits a wide range of maneuverability and has a large number of degrees of freedom. Each segment is designed using a novel flexible mechanism based on the loading of a compression spring in both transverse and axial directions, and using cable–conduit systems. The rotational motion is transformed to tendon-like behavior, which enables the location of the actuators away from the trunk (e.g. at the end of the trunk). The forward kinematics of the mechanism is also presented and lends itself well to computer control. It is shown that the solution of the transverse deflection of each segment is obtained in a general form, while the stiffness coefficients are obtained in closed form from a two-dimensional model (small and large deflection angles) and from a three-dimensional model used in a finite element method to verify results. The friction in the analysis between the cable and the conduit is neglected in the analysis. A prototype trunk segment is experimentally tested, the results are verified and the elephant trunk robot is built. A bench-top actuation system has been developed and a control scheme used in prosthetic hand control has been implemented to control the mechanism.     

Sliding mode control of a large flexible space structure

This paper presents an experimental study on active vibration control of a flexible structure. The control uses constant force air-jet thrusters as actuators, and the switching logic is designed using the theory of sliding mode control. The design of the sliding surface for the system is based on a quadratic criterion involving the first six natural modes of the structure. It allows the system response to be shaped and the relative importance of the control of each mode to be defined with respect to the control power available. Experimental results were found to be very satisfactory when compared with those obtained in previous studies on the same structure. To face the same disturbance, the control time is shorter and the residual speed smaller.     

Dynamics of a rotating flexible and symmetric spacecraft using impedance matrix in terms of the flexible appendages cantilever modes

The subject of this work is the dynamics of a rotating spacecraft. The spacecraft is modeled as a main rigid body connected to two flexible solar panels. The orbital motion of the whole spacecraft with a constant angular velocity is considered, interacting with small rigid motions of the main body, and small elastic deformations and infinitesimal vibrations of the solar panels. A continuum approach based on the Rayleigh–Ritz discretization is used to describe the distributed flexibility in the spacecraft. Rayleigh–Ritz discretization functions used are the clamped modes of the solar panels. This method enables us to construct the impedance matrix of the whole system relating to the displacement of the main body and the external torque. A spectral expansion of this impedance matrix, in terms of these clamped modes is obtained in the frequency domain. The numerical results presented show that for small values of orbital angular velocity, the vibration motion frequencies of the flexible parts (solar panels) are not perturbed substantially. Moreover, when great values of orbital angular velocity are simulated, these frequencies change considerably. The present investigation based on the Rayleigh–Ritz discretization shows the effect of the interaction between the orbital motion of the whole spacecraft and the vibration motions of the flexible parts.     

含弹簧阻尼缓冲机构空间机器人捕获卫星操作的避撞柔顺强化学习控制

针对空间机器人捕获卫星操作过程中,关节因受冲击载荷而易造成冲击破坏的问题,在关节电机与机械臂之间设计了一种弹簧阻尼缓冲机构.缓冲机构不仅能利用弹簧实现捕获操作过程的柔顺化,利用阻尼器实现碰撞能量的吸收及柔性振动的抑制;还能通过合理设计与之配合的避撞柔顺策略使关节所受冲击力矩限定在安全范围内.首先,分别利用含耗散力Lagrange方程法与Newton-Euler法导出了碰撞前的空间机器人与被捕获卫星的分体系统动力学方程;然后,结合Newton第三定律、捕获点的速度约束、各分体的位置约束获得了捕获后的混合体系统动力学方程,且基于动量守恒关系计算了碰撞冲击效应与冲击力;最后,提出了一种结合缓冲机构的避撞柔顺强化学习控制方案,该方案通过实时与动态环境试错交互得到惩罚信号,并利用惩罚信号对控制器进行优化,实现对失稳混合体系统的镇定控制.利用Lyapunov定理证明了系统的稳定性;数值仿真验证了缓冲结构的抗冲击性能及所提策略的有效性.     

空间对接机构动力学仿真分析

以俄罗斯“异体同构”周边内翻式对接机构(APAS89)为研究对象,利用ADAMS建立对接机构的差动式机电缓冲阻尼系统的动力学模型。对差动式机构的动态特性进行仿真,得到系统的等效刚度和阻尼特性．对差动式机电缓冲阻尼系统及其主要部件的动态特性进行仿真研究。可以为对接机构设计提供仿真工具和设计依据。其仿真结果对空间对接机构的设计研究以及空间对接过程动力学建模具有参考作用．     

Attitude synchronization control for a group of flexible spacecraft

To solve the problem of attitude synchronization for a group of flexible spacecraft during formation maneuvers, a distributed attitude cooperative control strategy is investigated in this paper. Based on the backstepping design and the neighbor-based design rule, a distributed attitude control law is constructed step by step. Using cascaded systems’ theory and graph theory, it is shown that the attitude synchronization is achieved asymptotically and the induced vibrations by flexible appendages are simultaneously suppressed under the proposed control law.     

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.     

Dynamic modeling and control of hopping robot in planar space

The paper presents two-mass inverted pendulum (TMIP) model and its control scheme for hopping robot. Unlike the conventional spring-loaded inverted pendulum (SLIP) model, the proposed TMIP model is able to provide the functions of energy storing and releasing by using a linear actuator. Also it becomes more accurate comparing to the conventional SLIP model by taking the foot mass into consideration. Furthermore how to determine both takeoff angle and velocity for hopping is analytically suggested to accomplish the desired stride and height of hopping robot. The control method for the TMIP model is also presented in the paper. Finally, the effectiveness of the proposed model and control scheme is verified through the simulation.     

The decentralized control of large flexible space structures

The decentralized robust servomechanism problem with constant disturbances/set points is considered in this paper for large flexible space structures (LFSS). It is shown that for LFSS which have colocated, mutually dual sensors and actuators, the decentralized fixed modes [1] of the system are precisely equal to the centralized fixed modes [2] of the system. Simple necessary and sufficient conditions are then obtained for a solution to exist for the robust decentralized servomechanism problem [3] for the system. A controller is demonstrated which, for this class of LFSS systems, eliminates the "spillover problem." A two-hundreth-order numerical example of an LFSS control problem using the Purdue model [4] is included to illustrate the results.     

空间机器人捕获航天器操作的避撞柔顺复合自抗扰控制

讨论空间机器人在轨捕获非合作航天器过程避免关节受冲击力矩破坏的避撞柔顺控制问题.在机械臂与关节电机之间配置一种弹簧类柔顺装置—–旋转型串联弹性执行器(RSEA),其作用在于:1)在捕获碰撞阶段,可通过其内置弹簧的变形吸收碰撞产生的能量;2)在镇定运动阶段,结合避撞柔顺策略适时开、关电机,以保证关节所受冲击力矩受限在安全...     

Output attitude tracking for flexible spacecraft

In this work a class of nonlinear controllers has been derived for spacecraft with flexible appendages. The control aim is to track a given desired attitude. First, a static controller based on the measure of the whole state is determined. Then, a dynamic controller is designed; this controller does not use measures from the modal variables, and the variables measured are the parameters describing the attitude and the spacecraft angular velocity. Finally, it is shown that a relaxed version of the tracking problem can be solved when the only measured variable is the spacecraft angular velocity. Simulations show the performances of such control schemes.     

Attitude control of a spinning flexible spacecraft

The dynamics of rotational motion of a spinning orbiting spacecraft consisting of two rigid bodies connected by a flexible joint and arbitrary number of flexible appendages (two of which are flexible massless booms having masses on their tips) is analyzed. Active attitude control is provided by momentum exchange devices (e.g. control moment gyroscopes) or a mass expulsion system. The linearized equations of motion describing the vehicle are presented, and a large scale digital simulation that has been developed at the Marshall Space Flight Center is presented. A simplified model of the geometrically complex vehicle is selected to make it analytically tractable. The simplified model consists of a single rigid core body with two attached flexible massless booms having tip masses. The states of the vehicle are defined as small perturbations about its steady-state spin. An analysis is performed to determine the domain of stability.     

Dynamics and elasto-dynamics optimization of a 2-DOF planar parallel pick-and-place robot with flexible links

Dynamic modeling and analysis of a 2-DOF translational parallel robot with flexible links for high-speed pick-and-place operation is presented in this paper. Optimization is implemented with the goal to improve the dynamic accuracy of the end-effector at high speed. The governing equations of flexible links within the robot are formulated in the floating reference frame using Euler–Lagrange method, leading to a global FEM model being generated using the KED (Kineto-Elasto-Dynamics) technique. The dynamic characteristics of the robot are then investigated by model analysis. A numerical dynamic index is proposed to identity the range of natural frequency when the robot reaches different configurations. The comparisons are made between the optimized and original designs in terms of dynamic stress and response.