Space Robot Research Articles

A Virtual Linkage-Based Dual Event-Triggered Formation Control Strategy for Multiple Amphibious Spherical Robots in Constrained Space With Limited Communication

Aiming to deal with the formation maintaining in constrained space for a group of robots, this paper proposed a virtual linkage-based dual event-triggered formation control strategy. Based on the idea of virtual linkage and event-trigger, a dual event trigger is proposed to guarantees robot formation keeping and collision avoidance. Unlike classical event-triggered control, the control strategy triggered by the detection of the state of virtual linkage determine the motion mode of the robot, which can reduce the control updating and eliminate continuous communication between robots. Moreover, an adaptive control law inspired by the motion of a simple pendulum was developed to adjust the given angle of the virtual linkage in the case that the multi-robot system pass the restricted region. Finally, to validate the performance of the formation control strategy, simulations and a series of experiments in an indoor swimming pool are presented. The results demonstrate the robustness and feasibility of the proposed formation control strategy.

China's space robotics for on-orbit servicing: the state of the art.

China's space robotics for on-orbit servicing: the state of the art.

Progress, Challenges, and Prospects of Soft Robotics for Space Applications

The development of space robots is vital to broadening human cognitive boundaries. Space robots have been deployed in space science experiments, extravehicular operations, and deep space exploration. The application of space robots undoubtedly reduces the risk and cost of space activities. Traditional space robots primarily utilize rigid structures, resulting in limited degrees of freedom, which restricts their operational capabilities. In contrast, soft robots with greater flexibility and robustness may be used for future space exploration. Soft robots applied in space environments must overcome significant challenges associated with ultrahigh vacuum, microgravity, extreme temperatures, and high‐energy radiation. Herein, a comprehensive analysis of the key advantages of soft robots is presented based on the special requirements of the space environments for soft robots. Furthermore, brief insights into how soft robots must be changed in terms of their design, modeling, fabrication, sensing, and control to adapt to space environments are discussed. Specifically, soft robot scenarios with potential space application value are introduced. Finally, opinions regarding the potential directions of soft space robots are provided.

Development of a Virtual Bench for Modeling and Research of a Mobile Robot in Simintech

A virtual bench is designed for students studying simulation, model-oriented design of mechatronic systems and control devices. A review of existing virtual stands is performed. The training starts with simulation of a mobile robot (MR) with a single drive, for example, a transport robot moving along one coordinate, then simulation of MR with differential control moving on a plane, and then simulation of multicopters (quadcopter, hexacopter, octocopter). The virtual simulator consists of a model of MR with a single DC motor drive, MR controller, control panel. The drive model of the mobile robot in the state space is developed. Negative trends in the development of laboratory benches have been revealed: fast obsolescence of laboratory equipment; high cost; small range of equipment. Positive directions of their development have been identified: expansion of software capabilities (high-level languages) allowing to create any applications quickly and easily; appearance and improvement of special software used to create multimedia applications, as well as specialized software intended for design automation (AutoCAD, KOMPAS, Altium Designer, etc.) and mathematical calculations (Matlab, MathCAD, etc.). Software tools include SimInTech, MatLab/Simulink, LabVIEW, procedure-oriented languages VB, Delphi, Java, etc.; problem-oriented languages LISP, C++, C#, etc. In this connection, it is expedient to partially abandon traditional laboratory benches and switch to wider application of simulation modeling and computational experiment methods. Virtual laboratory benches should form the basis of such transition. As a result of simulation, the following parameters of MR model were obtained: MR displacement at 2.5 m, maximum gearbox angular speed 0.2 rad/s, maximum torque on gearbox output shaft 15 N∙m, maximum angular speed of DC motor 30 rad/s. Simulation of MR was performed in SimInTech program.

Determining the coordinates of a mobile robot in an industrial space using BLE technology based on RSSI data received from base stations

Existing global positioning technologies cannot be applied indoors, where the signal from satellites or communication towers is significantly reduced or completely absent due to signal weakening in the walls of the building. Wireless network technologies such as Bluetooth or Wi-Fi can also be used in the process of local determining the mobile platforms position in industrial premises. But such methods have a problem with providing the required accuracy. The relevance of these studies is associated with solving the problem of local positioning of mobile robots in a room with an accuracy of ten centimeters. The article presents a comparative analysis of determining coordinates’ principles by the AOA, TOA, TDOA and RSSI methods. It is proposed to use BLE technologies based on the RSSI data received from base stations. Using the triangulation method, formulas are obtained for solving the problem of determining the coordinates of an object moving in space. The software and hardware complex architecture has been developed. It is proposed to use ESP32 modules as base radio stations. The RSSI value is very unstable, so the positioning accuracy will depend on the number of base stations and the additional software tools used.

Error model-oriented vibration suppression control of free-floating space robot with flexible joints based on adaptive neural network

At the same time, considering the uncertain factors such as load variation, external interference and joint flexibility in engineering practice, a robust control method based on adaptive neural network is proposed. The dynamic model of free-floating space robot is established, and the error model caused by uncertain factors is deduced. Different from the traditional compensation algorithm that ignores the error model, a compensation controller based on Radial basis function neural network (RBFNN) is designed to approximate the error model. The approximation error is eliminated by robust controller to improve the control accuracy. In order to make full use of the nonlinear approximation ability of neural network, the error model is decomposed into four parts according to the input characteristics, and the neural network compensator is designed for separate and overall compensation, which further improves the control accuracy and robustness. The adaptive learning rates of network weights are designed to ensure online real-time adjustment without offline learning stage. A flexible compensator based on torque and a controller based on moment difference feedback controller (MDFC) are designed to suppress elastic vibration. Simulation and experimental studies show that the proposed strategy can have good compensation performance and robustness, and can better suppress elastic vibration, which proves the effectiveness and superiority of the proposed scheme.

A New Approach for Including Social Conventions into Social Robots Navigation by Using Polygonal Triangulation and Group Asymmetric Gaussian Functions.

Many authors have been working on approaches that can be applied to social robots to allow a more realistic/comfortable relationship between humans and robots in the same space. This paper proposes a new navigation strategy for social environments by recognizing and considering the social conventions of people and groups. To achieve that, we proposed the application of Delaunay triangulation for connecting people as vertices of a triangle network. Then, we defined a complete asymmetric Gaussian function (for individuals and groups) to decide zones where the robot must avoid passing. Furthermore, a feature generalization scheme called socialization feature was proposed to incorporate perception information that can be used to change the variance of the Gaussian function. Simulation results have been presented to demonstrate that the proposed approach can modify the path according to the perception of the robot compared to a standard A* algorithm.

Mobile Robot Control Based on 3D Visual Servoing: A New Approach Combining Pose Estimation by Neural Network and Differential Flatness

This paper deals with 3D visual servoing applied to mobile robots in the presence of measurement disturbances, caused in particular by target occlusion. We propose a new approach based on the flatness concept. In 3D visual servoing, the task is performed out of image coordinate space and targets may leave the camera field of view during navigation (servoing). Forced to navigate blindly during one or more periods of time, the robot will use our new open-loop control algorithm inspired by the flatness concept. The 3D visual servoing method is performed using robot pose estimation. This estimation generally contains some errors. The exact position of the robot is therefore not guaranteed, and robust feedback control is necessary to reject these errors in the input. To solve this problem, we propose a new pose estimation method that uses neural networks. We reduce the complexity of the architecture of the neural networks used (the number of variables to estimate) by proving that the location and the orientation of the robot can be ensured by using a single point in the image coordinate space for mobile robots with two degrees of freedom. To show the efficiency of the proposed algorithm, we use the RVCTOOLS MATLAB toolbox.

Loop Closure Detection Based on Differentiable Manifold

Loop closure detection is an important part of SLAM (simultaneous location and mapping), which can effectively reduce the cumulative error of the system after long period of exploration. The existing loop closure detection methods are mainly to evenly distribute the accumulated error in the robot trajectory, but the motion error of the actual robot is also related to its motion speed and rotation angle, while the corrected motion trajectory of the robot is difficult to match the real trajectory. Based on the analysis of the mechanism of robot motion error, this paper proposes a novel loop closure detection method based on differentiable manifold, which mainly includes real-time pose based on manifold tangent space and smooth motion trajectory model of robot based on differential geometry. Firstly, we introduce the Frenet framework structure and establish the corresponding manifold tangent space theory for the keyframe pose nodes. The real-time problem of robot motion is equivalent to the problem of finding the optimal angle tangent vector. Secondly, the motion speed between keyframes is used to determine the characteristics of the robot motion trajectory. We calculate the curvature and torsion of the curve composed of several nodes based on the manifold tangent space and then combine the curve interpolation and fitting of the keyframe nodes to achieve the approximation of the robot motion trajectory, and the smooth curve of the robot trajectory is obtained. Finally, the experiment verifies that the method in this paper can effectively ensure the continuity and smoothness of the robot’s trajectory, thereby reducing the cumulative error of the system and improving the accuracy of loop closure detection.

Jerk Optimized Motion Planning of Redundant Space Robot Based on Grey-Wolf Optimization Approach

Jerk Optimized Motion Planning of Redundant Space Robot Based on Grey-Wolf Optimization Approach

Minimum disturbance control based on synchronous and adaptive acceleration planning of dual-arm space robot to capture a rotating target

PurposeThis study aims to design a controller which can improve the end-effector low-frequency chattering resulting from the measurement noise and the time delay in the on-orbit tasks. The rendezvous point will move along the rendezvous ring owing to the error of the camera, and the manipulators’ collision need be avoided. In addition, owing to the dynamics coupling, the manipulators’ motion will disturb the spacecraft, and the low tracking accuracy of the end-effector needs to be improved.Design/methodology/approachThis paper proposes a minimum disturbance controller based on the synchronous and adaptive acceleration planning to improve the tracking error and the disturbance energy. The synchronous and adaptive acceleration planning method plans the optimal rendezvous point and designs synchronous approaching method and provides an estimation method of the rendezvous point acceleration. A minimum disturbance controller is designed based on the energy conservation to optimize the disturbance resulting from the manipulator’s motion.FindingsThe acceleration planning method avoids the collision of two end-effectors and reduces the error caused by the low-frequency chattering. The minimum disturbance controller minimizes the disturbance energy of the manipulators’ motion transferred to the spacecraft. Experiment results show that the proposed method improves the low-frequency chattering, and the average position tracking error reduces by 30%, and disturbance energy reduces by 30% at least. In addition, it has good performances in the synchronous motion and adaptive tracking.Originality/valueGiven the immeasurability of the target satellite acceleration in space, this paper proposes an estimation method of the acceleration. This paper proposes a synchronous and adaptive acceleration planning method. In addition, the rendezvous points are optimized to avoid the two end-effectors collisions. By the energy conservation, the minimum disturbance controller is designed to ensure a satisfying tracking error and reduce the disturbance energy resulting from the manipulators’ motion.

Grasping force optimization for dual-arm space robot after capturing target based on task compatibility

Grasping force optimization (GFO) is a crucial step in multi-arm manipulation tasks, aiming to suitably distribute the external force applied on the target to manipulators. The problem has not been applied to the field of space robot, which is more complex than ground mechanisms due to the dynamic coupling effect and multiple constraints. This paper presents the GFO method for the dual-arm space robot after capturing target. The problem is formulated as a convex optimization problem, which considers the friction constraints and generalized input constraints synthetically. The input constraints are derived for the space robotic system which contain both kinematic and dynamic characteristics. In order to reduce the dimension of the problem, a convenient method based on the concept of task compatibility is proposed to obtain the initial value and decouple the input constraints from the optimization problem. Meanwhile, the line search method based on eigenvalue analysis is adopted to determine the step size. Finally, simulation results are presented to show the effectiveness of the proposed method for different target motion.

A Space Robot Control at Approaching and Inspecting a Geostationary Satellite State

The problems of approaching a space robot to a geostationary satellite and visual checking its technical state are considered. The robot’s control system uses both plasma and catalytic electric propulsion units as well as a cluster of four control moment gyros. The simulation results of the developed guidance and control algorithms are presented that demonstrate their effectiveness.

Attitude and Orbit Control of a Space Robot at Additional Launching and Approaching a Geostationary Satellite

Background: The problems of putting a space robot into a geostationary orbit using a combined scheme and its approach to a geostationary satellite are considered. The authors’ previous results on this topic are briefly analyzed. Objective: The paper deals with three problems: further development of a rational strategy for the robot’s add-launching on geostationary orbit and its approaching target using a plasma electric propulsion unit only; synthesis of the guidance and control laws; a nonlinear dynamical analysis of the robot’s attitude and orbit control system during these modes. Methods: The developed methods and algorithms are based on the local optimizing the fuel consumption of the plasma electric propulsion unit during each inter-orbital flight of a space robot. Results: Simulation results on the guidance and control algorithms are presented that demonstrate their effectiveness. Conclusion: The breakthroughs are as follows: original strategy of add-launching and forecasting the influence of gravitational disturbances as well as solar pressure forces when synthesizing a robot’s guidance law for its inter-orbital flights.

Damping Selection for Cartesian Impedance Control With Dynamic Response Modulation

This article presents an analytical method to modulate the dynamic response of a robotic manipulator interacting with its environment when performing impedance-related robotic tasks, through the choice of stiffness and damping parameters. By joint space analysis of vibration and experiments, we prove that in order to preserve a desired dynamic behavior of the robot in the Cartesian space, neither a stiffness nor damping matrix can be arbitrarily chosen; this choice has to meet the desired dynamic criteria for any given configuration. After mapping the parameters (matrices) into the joint space, we analyze the vibratory dynamics of the robot and identify the proper way of suppressing of the vibration modes by specific elements in the Cartesian damping matrix without need of trial and error. Our method is especially useful for redundant robots. We show and compare experimental results from two different 7 degrees of freedom robotic manipulators.

Learning-Based Sliding-Mode Control for Underactuated Deployment of Tethered Space Robot With Limited Input

This article proposes a learning-based adaptive sliding-mode control for the underactuted deployment of tethered space robot with limited input. The reduced-order system on the sliding surface is optimized by the critic neural network-based nearly optimal approximation algorithm, and both the linear and nonlinear situations are taken into account. To remove the assumption that the state-dependent disturbance is vanishing, the behavior of state synchronization on the sliding surface is revealed for the first time, and the nearly optimal solution of limited input for generating stable trajectory can be approximated by the actor neural network-based adaptive dynamic programming. The hyperbolic tangent of desired input is synthesized into the optimal value function, and it can be obtained by the actor-critic neural network-based reinforcement learning algorithm solving the corresponding Hamilton–Jacobi–Bellman equation. The numerical simulation takes the numerical example of the deployment of tethered space robot to verify the effectiveness of the proposed method.

Nonholonomic Reorientation of Free-Flying Space Robots Using Parallelogram Actuation in Joint Space

A robot with large-degree-of-freedom joints is a promising future space robot capable of adapting to various environments and can perform dexterous tasks with multiple manipulators. The attitude dynamics of a free-flying robot shows nonholonomy, which enables the robot to reorient its attitude by moving its body. However, previous studies were not generally able to handle the nonholonomy, especially for robots with large degrees of freedom of joints. In the present study, we analytically investigate a maneuver in which joints are actuated along a parallelogram trajectory in joint angle space and propose an analytical path modification method in joint angle space in order to achieve the target attitude. Parallelogram actuation guarantees that the body configuration is returned to the initial state after one set of maneuvers, and thus the attitude of the robot is independently reoriented to the target maintaining the body configuration. The analytical solution is provided by applying Magnus expansion to the kinematics equation of rotational matrices, and its Lie group structure contributes to concise mathematical expressions. In addition, the analytical solution does not cause numerical difficulties, such as combinatorial explosion, and so can fully make use of the reorientation ability of a robot with large degrees of freedom.

Fixed-time anti-saturation compensators based impedance control with finite-time convergence for a free-flying flexible-joint space robot

Fixed-time anti-saturation compensators based impedance control with finite-time convergence for a free-flying flexible-joint space robot

Role of Robotics in Space

Role of Robotics in Space

Impedance Control of Space Robot On-Orbit Insertion and Extraction Based on Prescribed Performance Method

Aiming at the force position control problem of the on-orbit insertion and extraction operation of the free-floating space robot, the system dynamics model is established. According to the interaction between the end of manipulator and the environment, the second-order impedance model is established. In order to improves the calculation efficiency, the above models are reconstructed to avoid the use of acceleration signal by introducing filtering operation. This is also conducive to the application of robot actual control. Then, an estimator requiring only the system inertia matrix is designed to compensate the modeling uncertainty, external bounded disturbance and impact effect in the process of inserting and extracting. Its structure is simple and reliable. Only one control parameter needs to be adjusted, which greatly reduces the amount of calculation. Considering that the on-orbit operation of insertion and extraction is a kind of precision operation, its control system needs to have a high-quality control performance. By introducing the prescribed performance method, the tracking error is constrained within the given range and to ensure the transient performance and steady-state performance of the control system is ensured. Finally, three simulation conditions are designed, and the results are presented to verify that the proposed algorithm has a faster convergence speed compared with traditional sliding mode controller. It can achieve vertically inserting and accurate force tracking of the manipulator end.