Study On Resource Scheduling Of Networked Motion Control Systems

As the foundation of modern equipment manufacturing, networked is an important means to realize high-speed and high-precision motion control systems. Networked Motion Control Systems (NMCS), a special kind of Networked Control Systems (NCS), have such advantages as reduced line-connecting, high reliability, easy to expand and realize information sharing, but the network intervene gives rise to some new problems such as network-induced delay, multi-packet transmission and packet loss, network communication constraints, network scheduling and so on. To address these problems, needing effective control methods, more importantly, is to take the appropriate resource scheduling strategy to compensate or improve network adverse effects on system performance.In this paper, from the view of resource scheduling, some key technologies are studied, such as the structure of Networked Motion Control Systems, modeling and delay analysis methods, scheduling methods and typical system design and so on. Two kinds of NMCS discrete-time model based on typical node trigger mode combination are derived. Based on the study of CPU task scheduling, the feasibility, performance and scheduling optimization of classic real-time scheduling algorithm RM and EDF for NMCS, are studied by simulation. Starting from the system performance evaluation indexes, the scheduling methods based on bandwidth allocation, considering QoS (Quality of Service) and QoC (Quality of Control), are studied, and two kinds of dynamic bandwidth allocation algorithms are proposed. By introducing CPU task response time analysis method into CAN network schedulability analysis, based on Stateflow toolbox of Matalb/Simulink, the performance of CAN is studied. A kind of NMCS implementation structure of CAN-based master-slave mode is proposed, and a typical CAN-based NMCS experimental platform is built. Hardware and software design process, including electronic component selecting, PCB (Printed Circuit Board) design, software porting, etc, are summarized. For the real-time scheduling algorithms of RM and EDF, dynamic bandwidth allocation algorithm 1 and 2, the performance testing and analysis are carried out on the experimental platform. Details are as follows:1. On the analysis of NMCS structure characteristics and the key problems to be solved, from the general study approach of Networked Control Systems, the problems such as NMCS structure, modeling and delay analysis methods, etc, are discussed. Based on the NMCS structure research, two kinds of NMCS discrete-time model based on typical node trigger mode combination, S(T)+C(T)+A(E) and (S(T)+C(E)+A(E)), are derived. Such problems as the cause of delay and delay type, the impact of delay on system performance, are studied. Based on the summary of current research methods of delay problems, for network delay impact on system performance in the three typical cases (zero, constant and variable), and random delay distribution under different load conditions, the related simulations are completed. Simulation conclusions are as follows: reducing forward channel delayτca portion in the total delay can improve system performance, random delay on NMCS impact more seriously than the fixed delay.2. Based on the simulation research on single processor task scheduling theory, the feasibility of single processor task scheduling algorithm expanded to network scheduling is studied. Through constructing simulation model, the performance of using the single processor task scheduling methods of RM and EDF for network scheduling, are studied, and the simulation for scheduling optimization problem is given. Simulation results show that:for the lack of monitoring network state effectively, RM and EDF can not adapt to the dynamic changing of system performance, the feedback scheduling method is necessary to NMCS scheduling.3. Because NMCS is a synthesis of control and communication, the performance of each control loop is limited by network bandwidth. Starting from the evaluation indexes of QoC and QoS, the scheduling method based on bandwidth allocation, considering QoS and QoC, is studied. Two kinds of dynamic bandwidth allocation algorithm based on feedback control theory are designed, and are validated by simulation. Bandwidth allocation algorithm one allocate bandwidth on demand, according to the network and system requirements, with the flexibility of real-time adjusting, but easily resul in existing unstable factors for the sampling period frequently regulated. To address the problems, by using default three typical sampling period, bandwidth allocation algorithm two avoid instability caused by the sampling period switching frequently and the excessive consumption of resources.4. For the control network of CAN, its real-time is studied. Based on the summary of CAN characteristics, the problems of CAN real-time aspects and research progress on CAN real-time improvement are pointed out. By using the task response time analysis method for single processor, schedulability of CAN is analyzed. With the Matalb/Simulink and Stateflow toolbox, the relationships between CAN data transmission of real-time and network bandwidth utilization are studied. Under the conditions of network load and transmission rate changing, network delay and throughput changing trend curve are got.5. A kind of CAN-based NMCS realizing structure based on master-slave mode is proposed, which can effectively reduce the calculating complexity of the slave node and communication conflicts, facilitating the implementation of scheduling and complex control algorithms. Based on the master-slave structure, a typical CAN-based and ARM +U-boot+Linux-based NMCS experimental platform is built, and the hardware/software design procedure are summarized. For real-time scheduling algorithm RM and EDF, dynamic bandwidth allocation algorithm 1 and 2, the actual performance testing are carried out on the experimental platform, and the effectiveness of the scheduling algorithms are further illustrated.In this paper, focusing on some problems of NMCS such as system modeling, network scheduling, bus real-time analysis, system hardware/software design, etc, from the resource scheduling perspective, the key implementation technologies of NMCS are studied. It has important practical significance and reference value to realize motion control systems networked and improve performance.