Base Attitude Disturbance Research Articles

Trajectory planning of a free-floating dual-arm space robot with minimal base disturbance in obstacle environments

This paper addresses the issue of trajectory planning for a free-floating dual-arm space robot, considering the constraints of collision avoidance while simultaneously minimizing the base position and attitude disturbance during on-orbit tasks. One arm is designated as the mission arm, tracking a prescribed path to complete specific goals, while the other serves as the balance arm, compensating for any base attitude disturbance. A collision-free path planning approach is presented for the mission arm, which utilizes a hybrid map, improved artificial potential field (IAPF) and adaptive coupling guidance method. The hybrid map in the mission arm joint space contains the coupling relationship between the deviation of the base position and the motion of the dual arms, along with obstacles transformed from Cartesian space. Then, to address the problem of the goals nonreachable with obstacles nearby (GNRON) of the artificial potential field (APF), a novel repulsive potential field is incorporated into the IAPF. To minimize the base position disturbance, a coupling guidance method is presented that enables the mission arm to move in areas with lower coupling factors on the hybrid map. Finally, simulations are conducted to demonstrate the effectiveness and superiority of the proposed hybrid map and coordinated trajectory planning approach.

Risk Assessment Model-Guided Configuration Optimization for Free-Floating Space Robot Performing Contact Task

The use of free-floating space robots for contact tasks is very promising in space exploration. However, severe damage or obvious disturbance may occur if inappropriate operation is implemented. In this paper, a novel risk assessment method is first proposed to give a clear description of the risk state before contact happens and provide guidance for configuration optimization to reduce risk on contact tasks. Firstly, the dynamics model of a free-floating space robot is given. On this basis, two important risk assessment indicators, the maximum contact force and the base attitude disturbance caused by contact, are derived. By integrating the risk assessment indicators, a novel risk assessment model is proposed for a free-floating space robot performing a contact task. It is a multidimensional and extensible risk assessment space which could give a clear description of the risk state before contact happens. Thereafter, considering the results given by the risk assessment model, the configuration optimization for a free-floating space robot is implemented based on the design of optimization factor in null space. Finally, numerical simulation for a 7-degree-of-freedom free-floating space robot performing a contact task is carried out, and the simulation results verify the effectiveness of the proposed method.

Non-inverse kinematics of free-floating space robot based on motion planning of sampling

Motion planning is one of the fundamental technologies for robots to achieve autonomy. Free-floating space robots composed manipulators and base satellite that do not actively control its position and attitude has nonholonomic characteristics, and there is a first-order differential relationship between its joint angle and the base attitude. In addition, the planning framework which first converts the goal end-effector pose to its corresponding target configuration, and then plan the trajectory from the initial configuration to the goal configuration still has the following problems: the goal configuration and the initial configuration may not be in the same connected domain. Based on the RRT framework, the motion planning of a free-floating space robot from the initial configuration to the goal end-effector pose is studied. In the algorithm design, in order to deal with the differential constraints of the free-floating space robot, and the requirement that the attitude disturbance of its base cannot exceed its limit, a control-based local planner for random configuration guiding growth of the tree and a control-based local planner for goal end-effector pose guiding growth of the tree that can adjust the attitude of the base when necessary are proposed. The former can ensure the effective exploration of the configuration space, and the latter can avoid the occurrence of singularity while ensuring that the algorithm converges quickly and the base attitude disturbance meets the constraints. The present algorithm does not need to solve the inverse kinematics, can successfully complete the planning task, and ensure that the base attitude disturbance meets the requirements. The simulation verifies the effectiveness of the algorithm.

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.

Multiobjective preimpact trajectory planning of space manipulator for self-assembling a heavy payload

To assemble a heavy payload to the spacecraft (free-floating base), the present study proposes a scheme of multiobjective trajectory planning for preimpact motion of redundant space manipulator (mounted on the base). Force impulse for self-assembly is derived as the function of joint angles/velocities, base pose, and impact direction. The trajectory planning problem is formulated as multiobjective optimization to minimize force impulse, base attitude disturbance, and energy consumption in the load-carrying process. A two-stage trajectory planning algorithm is proposed. To be specific, at the first stage, multiple desired configurations at the contact point are generated by position-level inverse kinematics with Newton–Raphson iterative method. At the second stage, joint trajectories satisfying joint angle limits and desired motion of the payload are parameterized by coefficients of sinusoidal polynomial functions. Multiobjective particle swarm optimization algorithm is adopted to solve the problem of multiobjective trajectory planning, and screening process is conducted to reserve nondominated solutions in limits of joint torques. The algorithm is implemented to a seven degrees of freedom space manipulator, and the effectiveness of the proposed method is verified by simulation results.

Sampling-Based Motion Planning for Free-Floating Space Robot without Inverse Kinematics

Motion planning is one of the most important technologies for free-floating space robots (FFSRs) to increase operation safety and autonomy in orbit. As a nonholonomic system, a first-order differential relationship exists between the joint angle and the base attitude of the space robot, which makes it pretty challenging to implement the relevant motion planning. Meanwhile, the existing planning framework must solve inverse kinematics for goal configuration and has the limitation that the goal configuration and the initial configuration may not be in the same connected domain. Thus, faced with these questions, this paper investigates a novel motion planning algorithm based on rapidly-exploring random trees (RRTs) for an FFSR from an initial configuration to a goal end-effector (EE) pose. In a motion planning algorithm designed to deal with differential constraints and restrict base attitude disturbance, two control-based local planners are proposed, respectively, for random configuration guiding growth and goal EE pose-guiding growth of the tree. The former can ensure the effective exploration of the configuration space, and the latter can reduce the possibility of occurrence of singularity while ensuring the fast convergence of the algorithm and no violation of the attitude constraints. Compared with the existing works, it does not require the inverse kinematics to be solved while the planning task is completed and the attitude constraint is preserved. The simulation results verify the effectiveness of the algorithm.

Cartesian trajectory planning of space robots using a multi-objective optimization

Cartesian trajectory planning of a free-floating space robot is impacted by dynamic singularities due to the inverse kinematics equations. Although various methods have been proposed to avoid the singularities, very few of them are suitable for the trajectory planning of a high degree-of-freedom (DOF) space robot in the Cartesian space. In this paper, a method of combining Damped Least Squares (DLS) and feedback compensation is developed to avoid such singularities. The trajectories of the end-effector are parametrized with Bézier curves, which are simple and make it easy to limit the joint velocities. Moreover, because of certain missions, such as communication and observation, base attitude disturbance and moving time are considered to establish a cost function and the trajectory planning is transformed into a multi-objective optimization. Chaotic particle swarm optimization (CPSO) is employed to solve the optimization, which can improve the premature phenomenon of particle swarm optimization (PSO). Simulation results are presented for the trajectory planning of a 6 DOF space robot and demonstrate the effectiveness of the proposed method.

Obstacle Avoidance Path Planning of Space Redundant Manipulator Based on a Collision Detection Algorithm

This paper focuses on the path planning of free-floating space redundant manipulator in an environment with obstacles. Firstly, based on the idea of spherical bounding volume and spatial superposition, the spatial occupying relationship between obstacles and manipulators is described in a simpler way. Then the relative position relationship between straight line segment and sphere is used to judge whether a collision between the manipulator and the obstacle. With the principle of forward kinematics, we use the joint parameterization method to transform the path planning problem into a parameter optimization problem with constraints. In this optimization problem, the objective function is a weighted optimization objective function, which includes two terms, the first term describes the base attitude disturbance and the second one is established according to the requirement of avoidance collision. The motion trajectories of the manipulator joints can be obtained by solving the optimization problem using the particle swarm optimization algorithm. We choose a 7-DOF space redundant manipulator for simulation study, and simulation results show the effectiveness of the proposed method, there is no collision between the manipulator and obstacles, and there is no disturbance on the base attitude. What's more, the trajectory of the joint is smooth, which can make the end-effector reach the desired pose with a high accuracy.

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.

Minimum Base Attitude Disturbance Planning for a Space Robot During Target Capture

This paper presents a method to minimize the base attitude disturbance of a space robot during target capture. First, a general dynamic model of a free-floating space robot capturing a target is established using spatial operator Algebra, and a simple analytical formula for the base angular velocity change during the impact phase is obtained. Compared with the former models proposed in the literature, this model has a simpler form, a wider range of applications, and O(n) computation complexity. Second, based on the orthogonal projection matrix lemma, we propose the generalized mass Jacobian matrix (GMJM) and find that the base angular velocity change is a constant multiple of the component which the impact impulse projects to the column space of the GMJM. Third, a new concept, the base attitude disturbance ellipsoid (BADE), is proposed to express the relationship between the base attitude disturbance and the impact direction. The impact direction satisfying the minimum base attitude disturbance can be straightforwardly obtained from the BADE. In particular, for a planar space robot, we draw the useful conclusion that the impact direction unchanged base attitude must exist. Furthermore, the average axial length of the BADE is used as a measurement to illustrate the average base attitude disturbance under impact impulses from different directions. With this measurement, the desired pre-impact configuration with minimum average base attitude disturbance can be easily determined. The validity and the efficiency of this method are verified using a three-link planar space robot and a 7DOF space robot.

Optimal Path Planning for Minimizing Base Disturbance of Space Robot

The path planning of free-floating space robot in space on-orbit service has been paid more and more attention. The problem is more complicated because of the interaction between the space robot and base. Therefore, it is necessary to minimize the base position and attitude disturbance to improve the path planning of free-floating space robot, reducing the fuel consumption for the position and attitude maintenance. In this paper, a reasonable path planning method to solve the problem is presented, which is feasible and relatively simple. First, the kinematic model of 6 degrees of freedom free-floating space robot is established. And then the joint angles are parameterized using the 7th order polynomial sine functions. The fitness function is defined according to the position and attitude of minimizing base disturbance and constraints of space robot. Furthermore, an improved chaotic particle swarm optimization (ICPSO) is presented. The proposed algorithm is compared with the standard PSO and CPSO algorithm in the literature by the experimental simulation. The simulation results demonstrate that the proposed algorithm is more effective than the two other approaches, such as easy to find the optimal solution, and this method could provide a satisfactory path for the free-floating space robot.

Pre-impact trajectory planning for minimizing base attitude disturbance in space manipulator systems for a capture task

Aimed at capture task for a free-floating space manipulator, a scheme of pre-impact trajectory planning for minimizing base attitude disturbance caused by impact is proposed in this paper. Firstly, base attitude disturbance is established as a function of joint angles, collision direction and relative velocity between robotic hand and the target. Secondly, on the premise of keeping correct capture pose, a novel optimization factor in null space is designed to minimize base attitude disturbance and ensure that the joint angles do not exceed their limits simultaneously. After reaching the balance state, a desired configuration is achieved at the contact point. Thereafter, particle swarm optimization (PSO) algorithm is employed to solve the pre-impact trajectory planning from its initial configuration to the desired configuration to achieve the minimized base attitude disturbance caused by impact and the correct capture pose simultaneously. Finally, the proposed method is applied to a 7-dof free-floating space manipulator and the simulation results verify the effectiveness.

The Analysis of Free-Floating Space Manipulator when Tracking Desired Force/Position

For free-floating space manipulator, a double loop control law is applied to the manipulator to achieve the force/position tracking of the end-effector, and the influence to the manipulator system is analyzed in this paper. First, the dynamic model is established based on Lagrange's equations. On this basis, a double loop control law which is based on the idea of impedance control is applied to the manipulator. During the force/position tracking, the influence of each part of free-floating space manipulator is analyzed, especially the base attitude disturbance. Finally, a simulation is given to show the analyze results.

Optimal path planning of redundant free-floating revolute-jointed space manipulators with seven links

The path planning of free-floating manipulators is of great interest in space operations. The manipulators in the free-floating mode exhibit nonholonomic characteristics due to the nonintegrability of the angular momentum, which makes the problem complicated. This paper analyzes the path planning of redundant, free-floating space manipulators with revolute joints and 7 degrees of freedom. The primary task of manipulators is to move the manipulator arms so that the desired end-effector position and orientation can be achieved. The motion of the manipulators can produce an attitude disturbance of the base, which has an adverse impact on the spacecraft operation. Thus, it is necessary to minimize the base attitude disturbance in order to reduce the fuel consumption for attitude maintenance. Practically, the path planning of redundant free-floating manipulators with higher degrees of freedom (7 degrees of freedom in this paper) in three-dimensional space is more complicated than path planning with fewer degrees of freedom, including planar or fixed base cases. This paper provides a tractable planning method to solve this problem, which could avoid the pseudo inverse of the Jacobian matrix. The sine functions, whose arguments are the polynomial functions with unknown coefficients, are used to specify the joint paths. The PSODE algorithm (particle swarm optimization combined with differential evolution) is applied to optimize the unknown coefficients of the polynomials in order to achieve the desired end-effector position and orientation and simultaneously minimize the base attitude disturbance. The simulations demonstrate that this method could provide satisfactory smooth paths for redundant free-floating space manipulators.

Motion Control of a Three-Link Space Robot to Reduce the Base Attitude Disturbance (Experimental Verification by Using Two-Degree-of-Freedom Control)

In this paper, we deal with a three-link space robot moving in planar space without controls for the base attitude. Our experimental setup of the three-link space robot can levitate by use of compressed air. Using d'Alembert principle, it is shown that the state equation of the three-link space robot can be reconstructed as a first-order nonholonomic system with the constraint condition that the rotational velocity of the base is set to be zero. The suitable final postures corresponding to the desired position of the end effector can be determined using the concept of the enhanced disturbance map. Based on the state equation, the feedforward torque inputs can be obtained by the final-state control in order to bring the end effector from an initial position to the desired position. The torque inputs and trajectories obtained are smooth. We designed a two-degree-of-freedom control to follow the obtained trajectory. It is verified from simulation and experiment that the proposed method of motion control is useful.

201 本体姿勢変動を抑える3リンク宇宙ロボットの運動制御 : 実験的検証

201 本体姿勢変動を抑える3リンク宇宙ロボットの運動制御 : 実験的検証