Research And Implementation Of Network-based Remote Control For A Robot Arm System

Network-based remote control is a multidisciplinary filed which involves computing, communication and control. Although such a technology has been widely applied in various areas, the uncertain network-introduced delay remains as a nuisance, which can deteriorate the performance of control systems and even destabilize the systems. In this thesis, we studied the time delay and its compensation strategy from both aspects of theory and practice. Our main work is as following:Firstly, in the networked control system with a simple-packet and simple-loop transmission and without data packet dropout, the general formulas of system model are deduced for different cases, in which the sensor adopts time-driven mode, with the controller and the actuator using either time-driven or event-driven mode. The effects of different driven modes for network nodes on the system performance are analyzed and compared. The issue about how to select suitable driven modes for nodes is discussed with regard to different system requirements and delay ranges. The simulation experiments are carried out to confirm the theoretical analysis.Secondly, the deterministic control for networked control system is studied, in which a receiving buffer is introduced to change the time-varying delay into a fixed value. Three main methods of the deterministic control, including state predictive control, staged transformation control and Smith predictive control, are compared. The relationships among the three methods are discussed through state transition and a simulation example is presented to prove the theoretical results.Thirdly, a controlled object, namely a 2-dof serial robot arm system with the drawing capacity, is described, including its hardware environment, software structure and work principle. A local control scheme is proposed to improve precision and speed of actual motion. With a remote controller and a local computer connected with the robot arm system assigned to act as the client and the server, respectively, and using the C-S mode with Winsock API, software bottom control and UDP connection, a network-based robot arm remote control system platform is built to study the delay. Fourthly, a monitoring-software is developed to obtain the time delay in the remote control experiment. An offline and an online delay compensation strategy are designed respectively under the default point-to-point control mode in order to make up for the delay of task-finished time from the remote control. After comparing the experiment result between before and after the compensation, a continuous path control strategy on the joint-coordinate-space-based serial robot remote control system is introduced to overcome the limitations of the point-to-point control mode. The condition needed by system parameters is presented to guarantee the continuous motion of the robot arm. The remote control system based on continuous path control mode is implemented, and its experimental results are compared with that of remote control system with point-to-point control.