Space Robotic Arm Research Articles

参数突变自由漂浮空间机器人神经集成控制

This paper studies the free- oating space robot as a control object. In order to answer the question how control precisions are ensured after a great quality target is caught by a space robot arm, this paper brings forward a robust control method based on neural networks. Because of the in uence of such factors as measuring errors and outside disturbance, two kinds of uncertainties exist in the space robot system, namely, parameter uncertainties and the non- parameter uncertainties. The radial function neural network makes use of the study ability of itself. Parameter uncertainties are studied by the neural network, and the network weights between concealed layer and output layer are adjusted online real-time. Non-parameter uncertainties and approach errors are compensated by the robust controller, and two controllers are integrated by redundancy theory. Global asymptotic stability of the whole closed-loop system based on Lyapunov theory is demonstrated in the paper. This scheme does not need a precise space robot model. Simulation results show that the controller is valid. The space robot manipulators run at the low speed condition, which provides ample study time for the neural network, so engineering application real-time quality is guaranteed because of the above reasons. The control method brought forward by this paper has potential applications in defense, aerospace and other major security fields.

Design of a virtual foundation for impedance control in a dual arm cooperative space robot

This work presents the design of virtual foundation through which impedance control is achieved in a dual arm space robot for cooperative manipulation of arms. A docking operation by the two arms of the space robot has been carried out. During this docking operation, the space robot has a mechanical interaction with the compliant objects which encounter force and motion constraints. The docking operation requires that the object must be gripped and follows a specific path to dock the selected object. By use of the virtual foundation, impedance control is achieved to fulfill both objectives, i.e. force control during gripping and trajectory control during docking. The space robot base compensation is designed to achieve the desired trajectory to control the interaction forces. The methodology has been validated with simulated results.

Spacecraft Attitude Disturbance Optimization of Space Robot in Target Capturing Process

The free-floating space robot arm will bring attitude reactions to the spacecraft in target capturing process.For this problem,a new Cartesian trajectory optimization method is proposed.An objective function is established for measuring the variation of spacecraft attitude.This function constrains the angle of each joint within their ranges,and eliminates the influence of dynamics singularity.By the optimization of genetic algorithm,the influence on spacecraft attitude deduced by the Cartesian trajectory tracking motion of the space manipulator end effector is reduced.The simulation results verify the validity of the algorithm.

Improved Telemanipulator Navigation During Display-Control Misalignments Using Augmented Reality Cues

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> An augmented reality (AR) cueing method designed to improve teleoperator performance under conditions of display-control misalignment is investigated. The teleoperation task was designed to mimic the operation of space robot arms, which are manipulated using hand controllers (HCs) to orient and translate the body-fixed coordinates at the end effector (EE). Cameras provide visual feedback. However, the pose of the EE seen through the camera hinders operator performance due to misalignments between the displayed EE axes and the HC axes. In this paper, the coordinate system of the EE is graphically overlaid in three dimensions on the video views with uniquely colored axes using AR. The same color scheme is used to label the corresponding axes on the HCs. Operators use these color cues to map each axis on the HCs to the corresponding colored axis of the augmented coordinates at the EE to obtain EE movement in the desired direction. Between-groups and within-participant experiments comparing EE trajectory distance, deviation from path, navigation errors, and HC axis usage were used to determine the effectiveness of the augmented coordinates over conventional teleoperation without augmented coordinates. Significant reductions in EE trajectory distance, deviation from path, navigation errors, and single-axis HC usage were observed when participants manipulated the remote robot with augmented coordinates. The results demonstrate that the use of simple AR cues in remote robot arm teleoperation is beneficial to the operator. </para>

S1903-1-3 テンセグリティ構造を利用した宇宙用ロボットアームの伸展機構の提案(宇宙構造・材料)

S1903-1-3 テンセグリティ構造を利用した宇宙用ロボットアームの伸展機構の提案(宇宙構造・材料)

大型柔軟ロボットアームの操作時振動抑制実験

In flexible long arm operation, residual vibration due to excitation degrades working efficiency. Input Shaping method decreases residual vibration in flexible systems by filtering the reference command with sequence of impulses known as input shaper. The principle of Input Shaping is very simple, but it is necessary to consider implementation hardware, especially in the space system. In this paper, ground experimental setup of an 8m long space robotic arm is constructed, and the effect on vibration suppression using Input Shaping is considered. The results of the ground experiment are discussed.

Impulsive control for angular momentum management of tumbling spacecraft

We discuss an angular momentum control of a tumbling spacecraft. The proposed control method is to apply an impulse by a space robot arm, to measure and control the relative position and attitude between the target spacecraft, and then to apply another impulse until the rotational motion of the target spacecraft is well damped. A discrete controller is designed using the simplified equations of rotational motion through appropriate coordinate transformation. The stationary response under contact model uncertainty is investigated and stability condition is analytically derived. Numerical simulations are given to validate the proposed approach.

POSITION/TORQUE CONTROL OF A SPACE ROBOTICS ARM

Torque sensors are used in space robot joints to increase robot capabilities and operational flexibility. Cascaded to a load position loop, a torque loop increases the performance of a position servo facing large variations of load inertia, typical of space robot arms. The issue specifically addressed in this paper is to what extent non linear elements, like sensor resolutions and friction, affect performance of the cascaded position/torque control strategy for a joint of a space arm. The detrimental effects of the comparatively low resolution of the load position sensor are discussed. A solution to this problem is proposed based on the adaptation of a Kinematic Kalman Filter. Finally it is pointed out that the adoption of a PI torque controller, in addition to a PID position controller, easily induces limit cycles of the hunting type, thus supporting the adoption of a proportional torque controller.

COMPACT DIAGNOSES REPRESENTATION IN DIAGNOSTIC PROBLEM SOLVING

The paper addresses the problem of finding a compact representation of the diagnoses within a model-based approach to diagnosis. To this end, we introduce the notion of scenario, a special kind of CNF formula over the component variables, which can be used to encode a large number of diagnoses using the same amount of space needed for encoding just a single diagnosis. We show how the solutions to a diagnostic problem can be computed as sets of scenarios by presenting first an exhaustive algorithm and then an efficient algorithm, which exploits probabilistic information to restrict the result set to preferred scenarios. Finally, we discuss the issue of how to efficiently extract preferred diagnoses from sets of scenarios and characterize a class of system models for which our techniques perform particularly well. Concepts and algorithms introduced in the paper have been tested within the prototype of the diagnostic agent of a space robotic arm; resulting statistics are reported and critically discussed.

Micro-gravity experiment of a space robotic arm using parabolic flight

We conducted a micro-gravity flight experiment on a space robotic arm, which is a part of the Reconfigurable Brachiating space Robot (RBR) unit arm developed by the authors. We used a 4-d.o.f. arm and an end-effector in the experiment. The airplane (MU-300) generates the micro-gravity environment for approximately 20 s in parabolic flight operation. After the flight, we conducted the corresponding ground experiments, and obtained the data of the motor current, servo control characteristics and manipulation performances, which were compared with the flight experiment data. Then, we conducted the numerical analysis of the 4-d.o.f. RBR arm based on the experiment results. In the analysis, we investigated feasibility of simulation model and identified model parameters. In this paper, we report the results of the flight experiments and numerical analysis.

宇宙用アクティブリンプロボット関節の開発

The active limp joint was developed for the purpose of the joint for space robots from which good compliant nature is obtained to pulling in by the attaching mechanism in on-orbit assembly work. The contact work in on-orbit assembly work was analyzed, and joint active limp control was proposed as a force control system which realizes compliant action. Moreover, the small cable lap mechanism of the torque sensor of high stiffness and disturbance torque was developed. The space robot joint mechanism which these are built in was developed, and it verified that forcing for the object by application of fine joint torque sensor and joint compliance control could be performed by characteristic testing. Furthermore, it verified that good compliant action was realizable to pulling-in action by joint active limp control. Thus, the joint mechanism and control system suitable for the next-generation space robot arm which does on-orbit assembly work were developed.

インパルス外力の繰り返しによるタンブリング衛星の運動制御

An angular momentum control of a tumbling spacecraft by applying repetitive impulses from a space robot arm is discussed. By assuming inputs by the arm, the direction, size and timing of the input forces are relatively free to choose. At each control timing, however, torques parallel to the contact direction cannot be generated. Therefore, the design of controller is not straightforward. To solve this difficulty, the equations of rotational motion are rewritten into simpler forms by applying appropriate coordinates transformation. Then a discrete controller is designed so that the component of the angular momentum parallel to the contact direction is damped out by choosing the directions of input forces properly. The closed loop characteristics considering constant disturbance torques and contact model uncertainty are discussed. Numerical simulations are given to show that the angular momentum is efficiently damped.

Motion Control of Tumbling Spacecraft by Repetitive Impulse Inputs

An angular momentum control of a tumbling spacecraft by applying repetitive impulses from a space robot arm is discussed. By assuming inputs by the arm, the direction, size and timing of the input forces are relatively free to choose. At each control timing, however, torques parallel to the contact direction cannot be generated. Therefore, the design of controller is not straightforward. To solve this difficulty, the equations of rotational motion are rewritten into simpler forms by applying appropriate coordinates transformation. Then a discrete controller is designed so that the component of the angular momentum parallel to the contact direction is damped out by choosing the directions of input forces properly. The closed loop characteristics considering constant disturbance torques and contact model uncertainty are discussed. Numerical simulations are given to show that the angular momentum is efficiently damped.

ＥＴＳ‐ＶＩＩを用いた宇宙ロボット制御実験

This paper presents the flight experiments on the dynamics and control of a space robotic arm mounted on ETS-VII (Engineering Test Satellite VII). The experiments were successfully carried out to evaluate the performance of (1) reaction null-space based reactionless manipulation, (2) generalized Jacobian based inertial manipulation, (3) offset command based feedforward attitude control, and (4) bi-directional approach of non-holonomic path planning. Inertia parameters of ETS-VII is identified based on the momentum equation and the effect of gravity gradient torque is also evaluated.

Fast and accurate collision detection based on enclosed ellipsoid

A fast and accurate method for detecting the collisions of convex polyhedra in a graphical simulation environment based on a newly developed method of distance estimate is presented. By the simultaneous use of the enclosing and the enclosed ellipsoids of convex polyhedra, potential collisions can be detected more accurate than those methods using only bounding volume for object representation, and more efficient than the polyhedral methods. An approach for computing the enclosed ellipsoid of a convex polyhedron by compressing, stretching and scaling operations on its best-fit enclosing ellipsoid is introduced. Graphical simulations of two case studies (moving polyhedral objects in three-dimensional space and multiple robot arms undergoing straight line motions) are conducted to demonstrate the accuracy of the proposed algorithm for collision detection.

ターゲットヘの接触・押し動作時における宇宙ロボットアームの関節剛性の影響

This paper discusses the effects of the joint stiffness during the contact operation to the target by the space robotic arm. The contact dynamics in low frequency domain are focused rather than the impulse dynamics in high frequency domain. The authors proposed contact/pushing based control of the target satellite for damping its rotational motion. This method is conducted as follows: 1) a cushion type damper attached to the end-effector is approached to the selected points on the target, 2) the arm softly pushes the damper to the target, 3) the contact and/or pushing force between the damper and the target causes the angular momentum of the target to decrease. The effects of the arm vibration due to joint stiffness during such a contact operation are evaluated through numerical simulations.

Development of Space Operation Simulator.

In order to evaluate the space manufacturing process at a ground site, a space operation simulator has been developed. The simulator supports mission planning, robot task evaluation and process monitoring. This is accomplished by integrating a 3-dimensional zero-gravity simulator which can simulate relative 6DOF motion between a free-flying space robot and a work object under a zero-gravity environment, an image processing module, a space robot arm and an operation environment, on a computer network system. The capability of this simulator was verified through an ORU exchange experiment. For a 3-D zero-gravity simulator, simulator performance such as real- time-simulated relative motion accuracy and simulation system stability were also analyzed experimentally.

A note on avoiding obstacles

In this paper, a mathematical model for avoiding obstacles by the movement of a flexible robot arm with multiple joints and expandable or contractable links in Cartesian coordinates is developed. In the model, the only decision variables are the coordinates of each joint of the robot arm with respect to the base of the robot arm, and the only necessary information besides the geometric parameters of the robot arm are the coordinates of the origin and the destination points of the robot arm in space, and the corresponding linear inequalities used to characterize the feasible region polytope for the movement of the robot arm.

Toward the intelligent control of robots

A new adaptive control architecture for the intelligent control of robotic manipulators is developed. The design is capable of utilizing external sensory information for the robot control. To achieve this, first a model reference adaptive control (MRAC) is developed which can be applied to a robot arm in the task space. Then the concept of virtual adaptive model is defined, which is used to formulate a maneuvering strategy in response to the external information. Finally, the virtual model provides the modified reference signals to the MRAC system to control the corresponding modified motion of the robot in the environment. The design does not require any knowledge about the dynamic parameters of the robot or that of the environment.

Resolved motion rate control of space manipulators with generalized Jacobian matrix

The authors establish a control method for space manipulators taking dynamical interaction between the manipulator arm and the base satellite into account. The kinematics of free-flying multibody systems is investigated by introducing the momentum conservation law into the formulation and a novel Jacobian matrix in generalized form for space robotic arms is derived. The authors develop a control method for space manipulators based on the resolved motion control concept. The proposed method is widely applicable in solving not only free-flying manipulation problems but also attitude-control problems. The validity of the method is demonstrated by computer simulations with a realistic model of a robot satellite.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>