Network-Oriented Real-Time Embedded System Considering Synchronous Joint Space Motion for an Omnidirectional Mobile Robot

Abstract

This paper proposes a real-time embedded system for joint space control of omnidirectional mobile robots. Actuators driving an omnidirectional mobile robot are connected in a line topology which requires synchronization to move simultaneously in translation and rotation. We employ EtherCAT, a real-time Ethernet network, to control servo controllers for the mobile robot. The first part of this study focuses on the design of a low-cost embedded system utilizing an open-source EtherCAT master. Although satisfying real-time constraints is critical, a desired trajectory on the center of the mobile robot should be decomposed into the joint space to drive the servo controllers. For the center of the robot, a convolution-based path planner and a corresponding joint space control algorithm are presented considering its physical limits. To avoid obstacles that introduce geometric constraints on the curved path, a trajectory generation algorithm considering high curvature turning points is adapted for an omnidirectional mobile robot. Tracking a high curvature path increases mathematical complexity, which requires precise synchronization between the actuators of the mobile robot. An improvement of the distributed clock—the synchronization mechanism of EtherCAT for slaves—is presented and applied to the joint controllers of the mobile robot. The local time of the EtherCAT master is dynamically adjusted according to the drift of the reference slave, which minimizes the synchronization error between each joint. Experiments are conducted on our own developed four-wheeled omnidirectional mobile robot. The experiment results confirm that the proposed system is very effective in real-time control applications for precise motion control of the robot even for tracking high curvature paths.

Safe and Policy Oriented Secure Android-Based Industrial Embedded Control System

“…As EtherCAT is becoming the standard network protocol in ICSs, an open source EtherCAT master, IgH Etherlab, was stacked on top of Xenomai to establish a connection with an actual industrial network. In the literature, numerous studies are present related to the implementation and performance of EtherCAT on different variations of real-time Linux [25,32,33]. To our knowledge, this work is the first attempt on implementing EtherCAT on an Android-based embedded system.…”

“…An important metric to evaluate the real-time performance of the system is the periodicity and response times of the RT task. Conducting the same experiment in the previous section, the periodicity and response times of the RT task were measured following the detailed evaluation procedures presented in our previous works [25,36]. The periodicity and response time of an RT task determines whether the task is schedulable or not.…”

“…In this sense, the three-sigma probabilistic limit of the jitter is considered exceptional with approximately 4 µs. Depending on the real-time application, developers can improve the response time by attaching an external network interface card with the necessary real-time driver [25,36], or by developing a real-time device driver for the on-board Ethernet controller, which is outside the scope of this paper. Considering the average response times, we can determine that the average CPU utilization of the EtherCAT control task is 0.09.…”

“…This interface ensures integration and smooth communication between Android applications and Xenomai real-time tasks. An open source EtherCAT master was implemented on top of Xenomai [25] to connect with actual ICS networks.…”

Design and Implementation Procedure for an Advanced Driver Assistance System Based on an Open Source AUTOSAR

“…T period represents the actual time that it takes for one cycle of the task. Its relationship with the jitter is defined by the following equation [32,33]: The results show that the task with the highest priority had the best performance with the lowest deviation to the statistical average of period and jitter. Therefore, it is confirmed that the AUTOSAR OS performed scheduling according to priority and satisfied periodicity.…”