International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395 -0056
Volume: 04 Issue: 02 | Feb -2017
p-ISSN: 2395-0072
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A Distributed Time Triggered Control for a Feedback Control System Hoang Dung Bui Faculty of International Training, Thai Nguyen University of Technology, 666, 3-2 stress, Thai Nguyen City, 251182, Vietnam ---------------------------------------------------------------------***---------------------------------------------------------------------
Abstract - The paper presents a distributed time triggered
must be implemented inside predefined intervals. The second one is the communication has to perform deterministically with little latency. Moreover, the distributed control can handle the events such as adjusting the input from the operator, or displaying the IRP’s states.
control using time triggered CAN (TTCAN) for a closed-loop control system. The balance of computing load is the rule to separate the control system into functional parts for controllers. The controllers are operated by time triggered control with TTCAN communication. The challenge is minimizing the response time to regulate the controlled system. It is done by adjusting the processing cycle that depends on the tasks’ processing time, data transmission time and the clock synchronizing drift. The system operation is managed by the communication and operation schedules which are also able to deal with several aperiodic events. The designs are experimented on an inverted rotary pendulum with the processing period of three milliseconds. The tasks and communication activities are triggered at the predefined time points and processed within the designed intervals. That makes the pendulum working stably at upright position. Key Words: distributed control, time triggered, feedback control system, Inverted rotary pendulum, TTCAN
The distributed control is performed on a set of controllers which cannot individually process all the tasks. The tasks are assigned to controllers based on the balance of computation load. To manage the system operation, communication and operation schedules are built. And the controllers’ clocks are synchronized. FreeRTOS is deployed for the controllers as operation system. It gives the priority for the task which should perform ahead if two tasks perform at the same time [5]. Therefore, ensuring the critical tasks are implemented at predefined time points. The paper’s content is as follow: section 2 discusses about distributed control, section 3 mentions about Time Triggered Control. Section 4 describes the experiment and results, and the conclusion is discussed in section 5.
1. INTRODUCTION Distributed control is applied for a distributed network system which consists of multiple subsystems [1]. The subsystems called nodes receive data and transmit the output via communication network to implement the tasks. To regulate a closed-loop control system, real time control is required. It means the tasks in the system must be completed before the deadlines [2].
2. DISTRIBUTED CONTROL To design a distributed control, the controlled system is analyzed the functionality then separated into tasks. Based on the rule of balance of computing load, the tasks are grouped and assigned to the controllers.
2.1 Inverted Rotary Pendulum
Time triggered CAN has wide application in industrial application with advantages such as high dependability, deterministic communication and low latency jitters of transmitting messages [3-4]. In the protocol, all events such as transmitting or receiving in the system are activated by time segment elapsing [3]. Despite of drawbacks such as lack on flexibility and the restrictive design process, it is significantly suitable for a closed-loop control system that works autonomously and has little interaction with human [3].
IRP is a two links system with two rotational joints as shown on Fig -1. It consists of an arm and a bar that rotate around the Z- and Y-axis with two angles α and , respectively. In steady state, mass M stands at the upright position and the arm stays at a desired position. The variations of α and (the IRP’s outputs) are detected by two optical encoders. From the errors between the angles and desired inputs, the controllers calculate amount of energy used and direction for the DC motor. In a limited time interval the data’s processing and communication must be completed to response to the angles’ variations, thus keep the mass M at the upright position. Moreover, a Human – Machine Interface (HMI) is required to interact with operator.
In the paper, a distributed time triggered control is designed for an inverted rotary pendulum (IRP) using TTCAN as communication mean. The challenge is minimizing the response time to make the calculated value from the control program still valuable to regulate the IRP. To shorten the response time, there are two problems to solve. The first one is all critical tasks that directly affect to the control process such as data collection, data processing and actuator control
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