Data sampling time scheduling based on maximum allowable loop delay for networked control system

Abstract

Networked Control System (NCS) has gained the popularity recently due to low installation and maintenance cost, high reliability, and less wiring. This control approach of NCS differs from traditional control system since controller and plant are physically separated and connected through a communication network. Despite these advantages that the system offers, the main challenge of NCS is networkedinduced delay that occurs while data is exchanged between components. Data Sampling Time scheduling with Offset (DSTOS) algorithm is an existing method and one of the effective approaches developed to handle time delays by allocating data according to priority for linear order system. In this work, the NCS of non-linear 2-link planar robot is developed based on Controller Area Network (CAN) where Proportional and Derivative (PD) controller is adapted to form a closed loop system. Based on this configuration, DSTOS algorithm is reconfigured for non-linear system and implemented such that the assignment of message priority is assigned according to the calculated Maximum Allowable Loop Delay (MALD) in every loop to reduce network delay. The NCS of 2-Link planar robot is formed based on two loops which consist of two sensor nodes, two actuator nodes and two controller nodes that perform data exchange in CAN 2.0A data frames under various CAN speeds. Simulations are performed by using MATLAB/SIMULINK with TrueTime Toolbox. Analysis of simulation results shows that the CAN-based non-linear system is able to accommodate this method and meets the real time and control requirements. By using DSTOS algorithm, the maximum data latency of control loops is reduced by almost 15% as compared to system without DSTOS. The reduction in link angle error is evident based on low value of IAE index. DSTOS also promotes lower energy consumption of DC servomotor which is important especially for industry.