Research On Space Robot Teleoperation Based On Virtual Reality And Local Autonomy

Space robots are utilized to complete space tasks instead of astronauts, which will not only avoid potential injury of astronauts while carrying out space tasks, but also decrease the cost and improve the efficiency of space exploration activities. Space robots usually works in an changeable workspace, and due to the limit of computer, control, artificial intelligence and mechanism technology, it is difficult to develop an autonomous space robot which could work automatically in the space environment. Therefore, the feasible way to control the space robot is ground teleoperation, which uses the human intelligence to achieve the high task planning. In this dissertation, the ground demonstration platform of satellite self-serving teleoperation is built, and virtual reality and local autonomy based space robot teleoperation is investigated.The ground teleoperation demonstration system of satellite on-orbit self-serving is established in this dissertation. In order to simulate the large time delay of space teleoperation, the artificial time delay is added and the operator(in Wuhan, China) teleoperates the space robot(in Harbin, China) to complete the satelliate serving tasks through Internet. The three-dimensional graphic predictive display is realized by virtual reality and the influernce of large time delay to teleoperation is conquered. Furthermore, according to the limit communication bandwidth, a virtual model of the actual environment is created at the operator side by the feedback robot joint angles and target visual recognition result, which overcomes the lack of smooth video due to the limit bandwidth, and the operator can obtain the remote status intuitively.At the master side, the manipulative safety and performance are mutually exclusive. Freehand control can achieve low precision and good abnormity handling ability, and the off-line task planning can obtain good precision and worse abnormity handling ability. In this paper an flexible virtual fixture is proposed to assist teleoperation at the operator side. It utilizes a flexible coefficient to regulate the prefered degree for robot movement, then combines freehand control and off-line task planning effectively, and makes a tradeoff between the manipulative safety and performance. Furthermore, the virtual force feedback, color recognition and virtual thickness are added to the flexible virtual fixture to enhance the manipulative performance.At the slave robot side, the robot intelligence is improved by local autonomy based on multi-sensors, which includes the robot joint position sensors, joint torque sensors, wrist force/torque sensor and vision sensor. During free space operation, the robot is control though the optimal approaching velocity based on vision. While during constraint space operation, according to the usual high stiffness contact tasks, a force tracking method based on the explicit control strategy is proposed in this thesis, which uses the impedance controller instead of the conventional position controller as the inner loop. The comparative experimental results show better force tracking performance according to the conventional method.The virtual reality based teleoperation seriously relies on the consistency of virtual model and real scene. However, because of the varying space environment and error of sensors measuring, there is inevitable model errors between the virtual model and real scene. In this thesis the method of model calibration and slave robot control with robustness against model errors are combined together to eliminate these errors. On one hand, at the operator side the virtual robot is correted through feedback robot joint angles, and virtual manipulative object is correted through vision, which eliminates the model errors at the largest degree. On the other hand, according to the small remaining model errors, at the remote slave robot side the impedance control and hybrid impedance control are used to eliminate the model errors further.At the last part of this dissertation, according to the structure space environment, the virtual reality is used to overcome the large communication time delay(bout 14 seconds)influence, and the deploying the antenna teleoperation experiment is accomplished successfully. According to the space environment with model errors, two representative satelliate self-serving teleoperation experimnets of deploying solar panel and rubbing camera lens are carried out, which overcomes the influence of model errors during teleoperation. The experimental results show the validity of the proposed space robot teleoperation method.