Bolt assembly by robots is a vital and difficult task for replacing astronauts in extravehicular activities(EVA),but the trajectory efficiency still needs to be improved during the wrench insertion into hex hole of bo...Bolt assembly by robots is a vital and difficult task for replacing astronauts in extravehicular activities(EVA),but the trajectory efficiency still needs to be improved during the wrench insertion into hex hole of bolt.In this paper,a policy iteration method based on reinforcement learning(RL)is proposed,by which the problem of trajectory efficiency improvement is constructed as an issue of RL-based objective optimization.Firstly,the projection relation between raw data and state-action space is established,and then a policy iteration initialization method is designed based on the projection to provide the initialization policy for iteration.Policy iteration based on the protective policy is applied to continuously evaluating and optimizing the action-value function of all state-action pairs till the convergence is obtained.To verify the feasibility and effectiveness of the proposed method,a noncontact demonstration experiment with human supervision is performed.Experimental results show that the initialization policy and the generated policy can be obtained by the policy iteration method in a limited number of demonstrations.A comparison between the experiments with two different assembly tolerances shows that the convergent generated policy possesses higher trajectory efficiency than the conservative one.In addition,this method can ensure safety during the training process and improve utilization efficiency of demonstration data.展开更多
Seven-degree-of-freedom redundant manipulators with link offset have many advantages,including obvious geometric significance and suitability for configuration control.Their configuration is similar to that of the exp...Seven-degree-of-freedom redundant manipulators with link offset have many advantages,including obvious geometric significance and suitability for configuration control.Their configuration is similar to that of the experimental module manipulator(EMM)in the Chinese Space Station Remote Manipulator System.However,finding the analytical solution of an EMM on the basis of arm angle parameterization is difficult.This study proposes a high-precision,semi-analytical inverse method for EMMs.Firstly,the analytical inverse kinematic solution is established based on joint angle parameterization.Secondly,the analytical inverse kinematic solution for a non-offset spherical-roll-spherical(SRS)redundant manipulator is derived based on arm angle parameterization.The approximate solution of the EMM is calculated in accordance with the relationship between the joint angles of the EMM and the SRS manipulator.Thirdly,the error is corrected using a numerical method through the analytical inverse solution based on joint angle parameterization.After selecting the stride and termination condition,the precise inverse solution is computed for the EMM based on arm angle parameterization.Lastly,case solutions confirm that this method has high precision,and the arm angle parameterization method is superior to the joint angle parameterization method in terms of parameter selection.展开更多
Gecko has the ability to climb flexibly on various natural surfaces because of its fine layered adhesion system of foot,which has motivated researchers to carry out a lot of researches on it.Significant progresses hav...Gecko has the ability to climb flexibly on various natural surfaces because of its fine layered adhesion system of foot,which has motivated researchers to carry out a lot of researches on it.Significant progresses have been made in the gecko-like dry adhesive surfaces in the past 2 decades,such as the mechanical measurement of adhesive characteristics,the theoretical modeling of adhesive mechanism and the production of synthetic dry adhesive surfaces.Relevant application researches have been carried out as well.This paper focuses on the investigations made in recent years on the gecko-like dry adhesive surfaces,so as to lay the foundation for further research breakthroughs.First,the adhesion system of gecko’s foot and its excellent adhesive characteristics are reviewed,and the adhesive models describing the gecko adhesion are summarily reviewed according to the diff erent contact modes.Then,some gecko-like dry adhesive surfaces with outstanding adhesive characteristics are presented.Next,some application researches based on the gecko-like dry adhesive surfaces are introduced.Finally,the full text is summarized and the problems to be solved on the gecko-like dry adhesive surfaces are prospected.展开更多
Adapter ring is a commonly used component in non-cooperative satellites,which has high strength and is suitable to be recognized and grasped by the space manipulator.During proximity operations,this circle feature may...Adapter ring is a commonly used component in non-cooperative satellites,which has high strength and is suitable to be recognized and grasped by the space manipulator.During proximity operations,this circle feature may be occluded by the robot arm or limited field of view.Moreover,the captured images may be underexposed when there is not enough illumination.To address these problems,this paper presents a structured light vision system with three line lasers and a monocular camera.The lasers project lines onto the surface of the satellite,and six break points are formed along both sides of the adapter ring.A closed-form solution for real-time pose estimation is given using these break points.Then,a virtual structured light platform is constructed to simulate synthetic images of the target satellite.Compared with the predefined camera parameters and relative positions,the proposed method is demonstrated to be more effective,especially at a close distance.Besides,a physical space verification system is set up to prove the effectiveness and robustness of our method under different light conditions.Experimental results indicate that it is a practical and effective method for the pose measurement of on-orbit tasks.展开更多
This paper presents a novel hybrid task priority-based motion planning algorithm of a space robot. The satellite attitude control task is defined as the primary task, while the leastsquares-based non-strict task prior...This paper presents a novel hybrid task priority-based motion planning algorithm of a space robot. The satellite attitude control task is defined as the primary task, while the leastsquares-based non-strict task priority solution of the end-effector plus the multi-constraint task is viewed as the secondary task. Furthermore, a null-space task compensation strategy in the joint space is proposed to derive the combination of non-strict and strict task-priority motion planning,and this novel combination is termed hybrid task priority control. Thus, the secondary task is implemented in the primary task＇s null-space. Besides, the transition of the state of multiple constraints between activeness and inactiveness will only influence the end-effector task without any effect on the primary task. A set of numerical experiments made in a real-time simulation system under Linux/RTAI shows the validity and feasibility of the proposed methodology.展开更多
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...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.展开更多
This study traces the development of dexterous hand research and proposes a novel antagonistic variable stiffness dexterous finger mechanism to improve the safety of dexterous hand in unpredictable environments,such a...This study traces the development of dexterous hand research and proposes a novel antagonistic variable stiffness dexterous finger mechanism to improve the safety of dexterous hand in unpredictable environments,such as unstructured or man-made operational errors through comprehensive consideration of cost,accuracy,manufacturing,and application.Based on the concept of mechanical passive compliance,which is widely implemented in robots for interactions,a finger is dedicated to improving mechanical robustness.The finger mechanism not only achieves passive compliance against physical impacts,but also implements the variable stiffness actuator principle in a compact finger without adding supererogatory actuators.It achieves finger stiffness adjustability according to the biologically inspired stiffness variation principle of discarding some mobilities to adjust stiffness.The mechanical design of the finger and its stiffness adjusting methods are elaborated.The stiffness characteristics of the finger joint and the actuation unit are analyzed.Experimental results of the finger joint stiffness identification and finger impact tests under different finger stiffness presets are provided to verify the validity of the model.Fingers have been experimentally proven to be robust against physical impacts.Moreover,the experimental part verifies that fingers have good power,grasping,and manipulation performance.展开更多
基金supported by the National Natural Science Foundation of China(No.91848202)the Special Foundation(Pre-Station)of China Postdoctoral Science(No.2021TQ0089)。
文摘Bolt assembly by robots is a vital and difficult task for replacing astronauts in extravehicular activities(EVA),but the trajectory efficiency still needs to be improved during the wrench insertion into hex hole of bolt.In this paper,a policy iteration method based on reinforcement learning(RL)is proposed,by which the problem of trajectory efficiency improvement is constructed as an issue of RL-based objective optimization.Firstly,the projection relation between raw data and state-action space is established,and then a policy iteration initialization method is designed based on the projection to provide the initialization policy for iteration.Policy iteration based on the protective policy is applied to continuously evaluating and optimizing the action-value function of all state-action pairs till the convergence is obtained.To verify the feasibility and effectiveness of the proposed method,a noncontact demonstration experiment with human supervision is performed.Experimental results show that the initialization policy and the generated policy can be obtained by the policy iteration method in a limited number of demonstrations.A comparison between the experiments with two different assembly tolerances shows that the convergent generated policy possesses higher trajectory efficiency than the conservative one.In addition,this method can ensure safety during the training process and improve utilization efficiency of demonstration data.
基金This work was supported by the Foundation for Innovative Research Groups of the National Natural Science Foundation of China(Grant No.51521003)the Major Research Plan of National Natural Science Foundation of China(Grant No.91848202).
文摘Seven-degree-of-freedom redundant manipulators with link offset have many advantages,including obvious geometric significance and suitability for configuration control.Their configuration is similar to that of the experimental module manipulator(EMM)in the Chinese Space Station Remote Manipulator System.However,finding the analytical solution of an EMM on the basis of arm angle parameterization is difficult.This study proposes a high-precision,semi-analytical inverse method for EMMs.Firstly,the analytical inverse kinematic solution is established based on joint angle parameterization.Secondly,the analytical inverse kinematic solution for a non-offset spherical-roll-spherical(SRS)redundant manipulator is derived based on arm angle parameterization.The approximate solution of the EMM is calculated in accordance with the relationship between the joint angles of the EMM and the SRS manipulator.Thirdly,the error is corrected using a numerical method through the analytical inverse solution based on joint angle parameterization.After selecting the stride and termination condition,the precise inverse solution is computed for the EMM based on arm angle parameterization.Lastly,case solutions confirm that this method has high precision,and the arm angle parameterization method is superior to the joint angle parameterization method in terms of parameter selection.
基金supported by the Major Research Plan of the National Natural Science Foundation of China[Grant number 91848202]supported by the Self-Planned Task of State Key Laboratory of Robotics and System(HIT)[Grant number SKLRS202106B].
文摘Gecko has the ability to climb flexibly on various natural surfaces because of its fine layered adhesion system of foot,which has motivated researchers to carry out a lot of researches on it.Significant progresses have been made in the gecko-like dry adhesive surfaces in the past 2 decades,such as the mechanical measurement of adhesive characteristics,the theoretical modeling of adhesive mechanism and the production of synthetic dry adhesive surfaces.Relevant application researches have been carried out as well.This paper focuses on the investigations made in recent years on the gecko-like dry adhesive surfaces,so as to lay the foundation for further research breakthroughs.First,the adhesion system of gecko’s foot and its excellent adhesive characteristics are reviewed,and the adhesive models describing the gecko adhesion are summarily reviewed according to the diff erent contact modes.Then,some gecko-like dry adhesive surfaces with outstanding adhesive characteristics are presented.Next,some application researches based on the gecko-like dry adhesive surfaces are introduced.Finally,the full text is summarized and the problems to be solved on the gecko-like dry adhesive surfaces are prospected.
基金financial support provided by the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (Nos. 51521003 and 61690210)
文摘Adapter ring is a commonly used component in non-cooperative satellites,which has high strength and is suitable to be recognized and grasped by the space manipulator.During proximity operations,this circle feature may be occluded by the robot arm or limited field of view.Moreover,the captured images may be underexposed when there is not enough illumination.To address these problems,this paper presents a structured light vision system with three line lasers and a monocular camera.The lasers project lines onto the surface of the satellite,and six break points are formed along both sides of the adapter ring.A closed-form solution for real-time pose estimation is given using these break points.Then,a virtual structured light platform is constructed to simulate synthetic images of the target satellite.Compared with the predefined camera parameters and relative positions,the proposed method is demonstrated to be more effective,especially at a close distance.Besides,a physical space verification system is set up to prove the effectiveness and robustness of our method under different light conditions.Experimental results indicate that it is a practical and effective method for the pose measurement of on-orbit tasks.
基金supported in part by the National Program on Key Basic Research Project (No. 2013CB733103)the Program for New Century Excellent Talents in University (No. NCET-10-0058)
文摘This paper presents a novel hybrid task priority-based motion planning algorithm of a space robot. The satellite attitude control task is defined as the primary task, while the leastsquares-based non-strict task priority solution of the end-effector plus the multi-constraint task is viewed as the secondary task. Furthermore, a null-space task compensation strategy in the joint space is proposed to derive the combination of non-strict and strict task-priority motion planning,and this novel combination is termed hybrid task priority control. Thus, the secondary task is implemented in the primary task＇s null-space. Besides, the transition of the state of multiple constraints between activeness and inactiveness will only influence the end-effector task without any effect on the primary task. A set of numerical experiments made in a real-time simulation system under Linux/RTAI shows the validity and feasibility of the proposed methodology.
基金This study was funded by the Foundation for Innovative Research Groups of the National Natural Science Foundation of China(Grant No.91848202)the National Natural Science Foundation of China(Grant No.51875114).
文摘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.
基金This work was supported by the National Key R&D Program of China(Grant No.2017YFB1300400)the Major Research Plan of the National Natural Science Foundation of China(Grant No.91848202).
文摘This study traces the development of dexterous hand research and proposes a novel antagonistic variable stiffness dexterous finger mechanism to improve the safety of dexterous hand in unpredictable environments,such as unstructured or man-made operational errors through comprehensive consideration of cost,accuracy,manufacturing,and application.Based on the concept of mechanical passive compliance,which is widely implemented in robots for interactions,a finger is dedicated to improving mechanical robustness.The finger mechanism not only achieves passive compliance against physical impacts,but also implements the variable stiffness actuator principle in a compact finger without adding supererogatory actuators.It achieves finger stiffness adjustability according to the biologically inspired stiffness variation principle of discarding some mobilities to adjust stiffness.The mechanical design of the finger and its stiffness adjusting methods are elaborated.The stiffness characteristics of the finger joint and the actuation unit are analyzed.Experimental results of the finger joint stiffness identification and finger impact tests under different finger stiffness presets are provided to verify the validity of the model.Fingers have been experimentally proven to be robust against physical impacts.Moreover,the experimental part verifies that fingers have good power,grasping,and manipulation performance.
