| Compared with a single robot with complex structure and function,a multi-robot system composed of multiple robots with simple structure has advantages such as lower cost,greater redundancy and better robustness.Therefore,the multi-robot system is more promissing in applications such as large-scale surveillance,safety inspection,and cooperative transportation missions.However,with limitation to the current technology of mechanical design,sensing,controlling and artificial intelligence,it is still difficult to develop fully autonomous intelligent robots in unknown and unstructured environments.Therefore,it is a feasible and effective solution to design a teleoperation system based on shared control scheme.The system combines the advantages of high accuracy and efficiency of the robots and high-level cognitive and decision-making capabilities of the human operator.In the system,the robots complete tasks with the help of the supervision and assistance of human operator.If the operator in the master side can receive the force/haptic information from the slave side,the telepresence and responsiveness of the operator will be improved significantly.The bilateral teleoperation system has better performances than the system without force/haptic feedback.This paper focuses on the bilateral teleoperation system of multiple mobile robots,and mainly studies the formation control algorithms,the control of bilateral teleoperation systems,the design of feedback force and the cooperative transportation method.Firstly,the formation control algorithms are researched.In the process of completing formation,each robot should be assigned to a target position.A role assignment scheme is designed for the two situations with uncertain and certain target formation positions to improve the efficiency of the whole system.Formation can simplify the control of multi-robot system,and there are many methods for different application requirements.The formation method based on the relative distance and relative angle transforms the problem into the follower robot tracking the trajectory of the leader robot,and this method is applied to the task of light intensity monitoring.A consensus formation algorithm based on relative displacements is proposed for the situation with known target positions.The artificial potential field and force among the robots are designed,and the calculation method of angle between the robot and obstacles in traditional artificial potential field is modified.In addition,an intelligent emergency service system based on a wireless sensor and actuator network is realized in this paper.The formation control of the multi-robot system is realized by the proposed consensus formation protocol.Secondly,a bilateral teleoperation system for the multiple robots is proposed and designed.A robot with force feedback is selected as the human-machine interaction device in the master side.Multiple differential drive mobile robots are used in the slave side to execute tasks.There exist mismatches of the model,the number of degree of freedoms and workspace between the master and slave robots.For these mismatches,the reference average velocities and the target formation of the slave robots are related to the position of haptic interface point(HIP)of the master robot.The stability of the bilateral teleoperation system is verified on basis of the passivity theory.A semi-physical experiment platform for the bilateral teleoperation system of the multiple robots is designed through Simulink and SimMechanics.In the bilateral teleoperation system,feedback force is the main way for the operator to understand the state of the slave side.Therefore,the design of the feedback force is very important.The influences of feedback force are researched in different simulation scenarios.The results show that feedback force can improve the performances.Two kinds of feedback force are designed for the operator,i.e.force based on the mismatch between the desired and actual velocities,and the repulsive force from the obstacles.The former force is more suitable for the bilateral teleoperation system of multiple robots than the latter one.The multi-robot system has to change its formation to adapt to different scenarios and tasks.A smooth transition method is proposed to avoid damage to the robot due to the mutations of the target formation.The method can ensure that the trajectories of the slave robots have C2 Continuity.Lastly,a bilateral teleoperation system based on force and vision feedbacks is proposed for the task of cooperation transportation.An overhead camera is employed in the slave side to localize the positions of the robots and other targets,as well as provide visual feedback for the operator in the master side.In the real applications,the communication delay between the master side and the slave side is unavoidable,and the delay will cause the system instable.The wave variable method is applied to the bilateral teleoperation system of multiple robots to ensure the stability.A force is designed to make the robots reach the box with low velocities,to avoid damaging the robots and box.In the process of cooperative transportation,Support Vector Machine(SVM)is used to identify the different states to provide the operator with more accurate information.Free motion experiments and cooperation transportation experiments are carried out to verify the effectiveness of the bilateral teleoperation system.The multi-robot system in the slave side can respond to the command from the operator in the master side,and converge to the target values.Meanwhile,with the help of the designed feedback force,the operator can understand the state of the multiple robots and the interaction with the environments. |
