Dual-arm Space Robot Research Articles

Dynamic manipulability measure for on-orbit manipulation by frictional contacts

Due to unilateral constraints of frictional contacts and the dynamic coupling phenomenon, the study on the unfixed manipulation through frictional contacts for multi-arm space robots is few carried out. This paper proposes a new measure method to assess the dynamic manipulability of the unfixed manipulation through frictional contacts. In particular, the explicit map from the base actuation and joint torques to the object acceleration, the base acceleration, and the internal force is formulated under unilateral constraints of frictional contacts. Considering typical control scenarios of both free-floating and free-flying systems, dynamic manipulabilities are derived separately. As an illustrative example, the dynamic manipulability of a planar dual-arm space robot is computed and reported, which visualizes the influence of different system parameters.

Coordinated control of free-floating dual-arm space robots based on hybrid task-priority approach

This paper addresses the problem of the coordinated control of the free-floating dual-arm space robots, in the case of multiple conflict tasks. Taking the dynamic coupling effect into consideration, a relative Jacobian matrix is presented to establish the kinematic model of the free-floating dual-arm space robot. Then, an adaptive coordinated controller is elaborately developed for three conflict tasks, including position tracking of the master arm, relative motion of dual arms, and obstacle avoidance. Owing to the hybrid task-priority approach, the proposed controller can effectively ensure the execution of the obstacle avoidance task without sacrificing the performance of the first two tasks. In addition, the singularity problem is settled via introducing an adaptive damping factor based damped least-squares inverse. Meanwhile, a novel hyperbolic tangent function is designed to handle the discontinuity in performing the null space task. Finally, numerical simulations were constructed to compare the performance of the proposed coordinated controller based on hybrid task-priority approach with the controller based on task-priority approach. The simulation results show that the proposed controller has an improved tracking performance of the master arm and safety performance, compared with single task-priority approach.

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.

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.

Capture and detumble of a non-cooperative target without a specific gripping point by a dual-arm space robot

This paper focuses on the control strategy of a dual-arm space robot to capture and detumble a non-cooperative satellite without a specific gripping point. First, an elastic hemispherical claw was designed to reduce the collision impacts and adjust the capture position, and its contact dynamics and capture ability were verified by ground experiments. Analysis of the position constraints led to the proposal of a compliant control scheme to achieve stable capture without a contact-force sensor. Subsequently, a modified adaptive sliding mode based prescribed trajectory tracking control (PTTC) and null space intersection approach was proposed to achieve target detumbling under the actuator constraints. The control system stability was analyzed via the Lyapunov method. Finally, numerical simulations were employed to validate the effectiveness and correctness of the strategy. Results showed that, a large inertia target could be steadily captured and detumbled within 80 s.

Capture and detumbling control for active debris removal by a dual-arm space robot

Active debris removal (ADR) technology is an effective approach to remediate the proliferation of space debris, which seriously threatens the operational safety of orbital spacecraft. This study aims to design a controller for a dual-arm space robot to capture tumbling debris, including capture control and detumbling control. Typical space debris is considered as a non-cooperative target, which has no specific capture points and unknown dynamic parameters. Compliant clamping control and the adaptive backstepping-based prescribed trajectory tracking control (PTTC) method are proposed in this paper. First, the differential geometry theory is utilized to establish the constraint equations, the dynamic model of the chaser-target system is obtained by applying the Hamilton variational principle, and the compliance clamping controller is further designed to capture the non-cooperative target without contact force feedback. Next, in the post-capture phase, an adaptive backstepping-based PTTC is proposed to detumble the combined spacecraft in the presence of model uncertainties. Finally, numerical simulations are carried out to validate the feasibility of the proposed capture and detumbling control method. Simulation results indicate that the target detumbling achieved by the PTTC method can reduce propellant consumption by up to 24.11%.

OPTIMAL GRASPING STRATEGY OF SPACE TUMBLING TARGET BASED ON MANIPULABILITY

Due to the tumbling motion of the target, the dual-arm space robot to grasp a dynamic target is more challenging compared to a static target. Besides, optimization of the grasping strategy can improve the manipulability of the space robot to operate on the tumbling targets to ensure the success of the grasping mission. In this paper, a method for grasping strategy optimization is proposed based on the manipulability evaluation. When the dual-arm space robot cooperatively grasping a target, the dual-arm end-effectors contact the target simultaneously and a closed kinematics chain is formed. As a result, the formation of the closed-chain constraint complicates the evaluation of the manipulability of the space robot. First, the kinematics and dynamics of a dual-arm space robot manipulating a target are analyzed in this paper. Following this, a cooperative workspace considering the closed-chain constraint is established, and a task compatibility based detumbling manipulability metric is analyzed. The established cooperative workspace contains both the position and the attitude information of the manipulated target in the task space, which can be used for the calculation of dexterity. Then, the optimal grasping points of the end-effectors to grasping a target are determined based on the global dexterity metric, as well as the optimal grasping configuration of the space robot to grasp a tumbling target is found based on the force task compatibility metric considering the field-of-view constraint of the camera and the velocity tracking constraint of the end-effectors to the tumbling motion of the target. Using the manipulability metrics to determine the grasping strategy can make full use of the coordination of both arms to increase the manipulability of the space robot to manipulate dynamic targets, and simulations are conducted using a 7 degree of freedom dual-arm space robot to verify the feasibility and effectiveness of the proposed grasping strategy.

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.

Base attitude disturbance minimizing trajectory planning for a dual-arm space robot

Space robots are playing an increasingly important role in on-orbit services. Affected by the coupling of dynamics, the base attitude of a space robot will deflect with the motion of its manipulators, which leads to unfavorable effect to the success of the mission. The trajectory planning problem for base attitude disturbance minimization of a dual-arm space robot will be studied in this article. Along the planned trajectory, the attitude of the base will keep unchanged when the end effectors of the manipulators arrive at the desired position. First, the dynamic equation of the dual-arm space robot is given, and the direct-inverse mixed dynamic equation is also derived. Then, the rotation trajectory of the manipulator joints is parameterized, and the attitude deflection of the base with respect to the given parameters is calculated based on the direct-inverse mixed dynamic equation. The particle swarm optimization algorithm is utilized to obtain the optimal trajectory. Finally, numerical simulations are carried out to verify the effectiveness of the method proposed in this article. Four cases are included, considering symmetrical or asymmetrical initial configuration and synchronous or asynchronous start of the dual arms. The simulation results show that, in each case, the method proposed can effectively plan the trajectory along which the base attitude will keep nearly unchanged before and after the motion of the dual arms.

Hybrid rigid-continuum dual-arm space robots: Modeling, coupling analysis, and coordinated motion planning

Hybrid Rigid-Continuum Space Robots are “couple strength and gentleness” and therefore more adaptable to the environment and mission. However, compared to traditional discrete multi-jointed space robots, this multi-type manipulator coexistence system has a more complex system model. The coordination planning between different types of manipulators is challenging. This paper presents a novel Hybrid Rigid-Continuum Dual-Arm Space Robot (HRCDASR) that consists of a rigid manipulator and a continuum manipulator. First, we use the definition to establish momentum equations of the continuum manipulator. On this basis, a generalized Jacobi matrix (GJM) of HRCDASR in the free-floating mode is developed for the first time. Furthermore, the coupling between different types of manipulators is studied in depth. The influence laws of different kinds of manipulators on the motion of the base are also discussed. According to the dynamic coupling feature, a coordinated planning method for HRCDASR based on task priority is proposed to minimize the interfering effects of the system during target capturing. Finally, the coupling factors of HRCDASR are analyzed in detail, and the comparison motion planning simulations are performed to validate the proposed HRCDASR planning 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.

A strategy to decelerate and capture a spinning object by a dual-arm space robot

With the increasing requirement of grasping the non-cooperative objects in space by space robots, this paper introduces a new strategy operated by a dual-arm space robot. The strategy includes path planning to capture a spinning target, hybrid control of the motion and the contact force for the end-effectors, coordinated control of the base attitude, and parameter identification of the spinning target during the capture phase. Notably, a pair of proper contact forces can be applied to the two grasp points of the spinning target by the two manipulators, which can decelerate the spinning speed of the target and be utilized to identify the target's moment of inertia around its spinning axis. Considering the non-cooperative situation with the spinning target like a defunct satellite, the uncertainties of the space robot and the target, such as parameters of mass and moment of inertia, are concerned in the design of the Sliding Mode Controller (SMC) with good robustness. Moreover, due to the coupling movement of the base and arms of a dual-arm space robot, the base attitude will be simultaneously maintained by the mounted reaction wheels during the capture operation for good communications and effective solar energy collection. The post-capture process is also presented in the paper to bring the entire system of the space robot and the target into stationary status. To compare the system performance against the uncertainties by different controllers, PID-type Computed Torque Controller (CTC) and SMC are designed together for comparison. When the uncertainties of the mass and the moment of inertia are applied to the system, the simulation results show that SMC has better performance against the uncertainties by delivering higher accuracy of the tracking errors to the desired trajectories than CTC.

The fuzzy neural network control scheme with H tracking characteristic of space robot system with dual-arm after capturing a spin spacecraft

In this paper, the dynamic evolution for a dual-arm space robot capturing a spacecraft is studied, the impact effect and the coordinated stabilization control problem for post-impact closed chain system are discussed. At first, the pre-impact dynamic equations of open chain dual-arm space robot are established by Lagrangian approach, and the dynamic equations of a spacecraft are obtained by Newton-Euler method. Based on the results, with the process of integral and simplify, the response of the dual-arm space robot impacted by the spacecraft is analyzed by momentum conservation law and force transfer law. The closed chain system is formed in the post-impact phase. Closed chain constraint equations are obtained by the constraints of closed-loop geometry and kinematics. With the closed chain constraint equations, the composite system dynamic equations are derived. Secondly, the recurrent fuzzy neural network control scheme is designed for calm motion of unstable closed chain system with uncertain system parameter. In order to overcome the effects of uncertain system inertial parameters, the recurrent fuzzy neural network is used to approximate the unknown part, the control method with H&#x221E tracking characteristic. According to the Lyapunov theory, the global stability is demonstrated. Meanwhile, the weighted minimum-norm theory is introduced to distribute torques guarantee that cooperative operation between manipulators. At last, numerical examples simulate the response of the collision, and the efficiency of the control scheme is verified by the simulation results.

Coordinated motion control of a dual-arm space robot for assembling modular parts

This paper aims to develop a coordinated control strategy for assembling two modular parts carried by a free-floating dual-arm space robot. The assembly task is divided into pre-assembly and final assembly phases. During the pre-assembly phase, in order to drive the modular parts to desired relative positions and attitudes, the coordinated motion between two arms are planned by formulating a special optimization objective function based on the generalized relative Jacobian matrix (GRJM). Notably, the coordinated motion control law is formulated in terms of relative position and pose errors whereby more degrees of freedom of manipulators are released for disturbance minimization and collision avoidance. In the final assembly phase, trajectory tracking problem of one arm is addressed while the other arm is kept rest. More specially, the translational velocity of the moving arm is involved in the objective function and its angular velocity in the constraint equations, which ensures the attitude coordination between two modular parts during position tracking. Finally, the proposed control strategy is demonstrated through numerical simulations and experiment tests using an air bearing simulator floating on a granite testbed.

Space robot motion planning in the presence of nonconserved linear and angular momenta

On-orbit servicing, active debris removal or assembling large structures on orbit are only some of the tasks that could be accomplished by space robots. In all these cases, a contact between a space robot and the satellite being serviced, deorbited, or assembled will occur. This contact results in a contact force exerted on the space robot, and therefore momenta of the space robot system are no longer conserved. Most of the papers that are concerned with motion planning problems of a space robot manipulator either consider that no external forces or moments are acting on the space robot system or use additional controllers when the space robot is subjected to external forces and moments. Such a controller minimizes end-effector position and orientation errors caused by the changes in system momenta due to external forces and moments acting on this system. The novelty of this work is that it proposes a new method for planning the motion of dual-arm space robot manipulators when linear and angular momenta of the space robot system are not conserved due to external forces and moments acting on the space robot base or/and manipulators’ end-effectors. In the proposed method the changes in system momenta are considered, but no additional controllers are needed. In this paper, we derive the motion planning equations for dual-arm space robot manipulators, where external forces and moments are acting on both satellite and manipulator end-effectors. The proposed method has been verified by numerical simulations, and the results are presented and discussed.

A trajectory optimization method with frictional contacts for on-orbit capture

Using space robots to perform capture missions are challenging problems due to potential contacts. Most state-of-the-art techniques sidestep contacts by separating a capture mission into pre- and post-capture phases, and assuming the end-effector fixes to the target instantaneously. In this paper, frictional contacts have been taken into consideration, and a corresponding trajectory optimization method is developed. The frictional contact is formulated as two sets of complementarity constraints for the compression phase and the decompression phase. The direct method for trajectory optimization with complementarity constraints is established. The combination mechanism based on the sequential quadratic programming is proposed to solve resultant highly complex optimization problems, which can provide local optimal trajectories for space robots. The method is verified via numerical simulations of a planar dual-arm space robot capturing a spinning target, and results illustrate its great performance and potential usability on other scenarios.

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.

Coordinated control of a dual-arm space robot to approach and synchronise with the motion of a spinning target in 3D space

The non-cooperative objects in space such as space debris and spinning defunct satellites have attracted significant attention because of the rapid development of space exploration. To approach and capture the spinning targets in 3D space, the dual-arm space robot could be more efficient and safer than single-arm space robot to carry out the complicated tasks for spinning targets. The paper extends the model of a dual-arm space robot with Reaction Wheels into 3D space, which is more realistic in practice. The desired trajectories for end-effectors of the space robot are designed to securely approach and prepare to capture the spinning object through synchronising with the grasp points, while at the same time the desired attitude of the base could be maintained. Then coordinated control of the base and end-effectors could be carried out by Nonlinear Model Predictive Controller (NMPC) with the consideration of the uncertainties of the space robot system. NMPC has performed with a high accuracy without the uncertainties of the space robot system. Considering the imperfect knowledge of the mass and inertia as the uncertainties, NMPC could hold the accuracy of tracking error at the same level of accuracy in the presence of the uncertainties.

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.

Spline-RRT⁎: Coordinated Motion Planning of Dual-Arm Space Robot

Abstract This paper addresses the coordinated motion planning issue for a dual-arm free-floating space robot. Based on the sampling-based planning method, a novel coordinated RRT⁎-based path planning framework is proposed for a dual-arm manipulation. First, an asymptotically optimal sampling-based method, RRT⁎, is employed to generate the initial rough path for each end-effector in the task-space. To avoid self-collision, we present a coordinated strategy which samples from separated inertial spaces when performing RRT⁎ algorithm. Second quartic, splines are used to smooth the generated RRT⁎ path so that the robot can execute smoothly. Physical constraints including the end-effectors’ limit, joint limit and boundary conditions are all controlled within the design of the quartic splines. The effectiveness of the proposed path planning framework is illustrated and demonstrated via a kinematically redundant dual-arm space robot.