Mechanical informatics refers to the information technologies to achieve efficiency, effectiveness, and reliability in the mechanical environment. The mechanical informatics researches in SS lab have been conducted focusing on the industrial automation systems. Major issues include:
- Delay-guaranteed EtherCAT servo drive
- Development and evaluation of open-source EtherCAT PLC
- PLCopen OPC UA
- Motionware: a motion control middleware
- OPC gateway
- “Development of general-purpose motion controller based on standardised KOSMOS (Korea Open Source MOtion System) for automated manufacturing”, Ministry of Industry, Trade and Energy, 2014.06 ~2017.05.
- “Modeling of logic circuit software to verify timing requirements in railway train control”, Korea Railway Research Institute, 2016.07 ~ 2018.02.
DELAY-GUARANTEED ETHERCAT SERVO DRIVE
In cooperation with Prof. T. Kim (U. of Seoul) and Prof. K. Kim (Soongsil U.), 2008.6 ~ 2012.1
For the development of a precision motor drive, we have to cope with challenges in software design: “how to bound the end-to-end delay from message release to motor actuation” and “how to integrate all the control loops so that responsiveness is maximized”. Our main contributions are (a) restructuring of drive software into a multi-task model, (b) period synthesis for minimized cycle time, and (c) stochastic analysis of end-to-end delay.
For flexibility and better analyzability, a proprietary real-time kernel has been developed to
realize a multi-tasked software in the resource-constrained drive hardware, i.e.,
with a DSP of 60 MIPS and 128 KB of memory. The kernel has only 7KB of memory footprint and 3 us of interrupt latency. Based on this, the legacy big-loop style drive software has been restructured into a multi-tasked one and EtherCAT slave function has been added. For minimized controller cycle, task periods have been synthesized. Using stochastic response time analysis, we could successfully find the task periods that maximize the processor utilisation while the deadline miss probabilities are less than the given thresholds. The developed software is currently in use in a commercial servo drive.
DEVELOPMENT AND EVALUATION OF OPEN-SOURCE ETHERCAT PLC
In cooperation with Prof. T. Kim (U. of Seoul)
EtherCAT, a real-time Ethernet for industrial communication is gaining attraction in various automation applications. For precision motion control, EtherCAT-based PLC offers tremendous advantages over traditional analog-link-based centralised systems.
For our study, a software-based EtherCAT PLC has been developed solely using open source software solutions: Xenomai-patched Linux, IgH EtherCAT protocol stack, and Beremiz. This facilitates a highly synchronized control process, whereby the Xenomai kernel significantly reduces the deviation of controller delay, while EtherCAT enhances the predictability of the message and clock events through its almost deterministic message relaying and precisely synchronized clock.
In Beremiz, we implemented the EtherCAT plugin and integrated the EtherCAT stack via the plugin interface. The plugin is mainly composed of two types of classes, each representing the profiles of the controller and slave devices. We also implemented a C wrapper API to the EtherCAT stack. The class definitions together with the EtherCAT API are used by the IEC compiler for the generation of runtime codes. When a new program has been configured to use EtherCAT, the plugin support module imports information on the slave profile and the EtherCAT API from the plugin definition. Using a realistic motion control workload, the performance of the developed system has been extensively evaluated. It was seen that the controller could successfully operate tens of drives in position or velocity mode with a cycle time of 0.5 ms. The supported hardware includes Freescale i.MX6 and Altera Cyclone V as well as industrial PC.
PLCOPEN OPC UA
OPC Unified Architecture (UA) is a communication technology for secure, reliable and interoperable transport of information in control and automation environment. PLCopen OPC UA maps the IEC 61131-3 software model to the OPC UA information model. Based on the Beremiz PLC framework, the PLCopen OPC UA functions are implemented and evaluated.
MOTIONWARE: A MOTION CONTROL MIDDLEWARE
Motionware is a middleware for precision motion control and monitoring. Using a high-level programming language, users can easily realize synchronized precision motion over up to 16 axes. Motionware support two kinds of command interfaces, i.e., online command and program command: an online command is executed instantly as users enter a command to the server while program commands are used in MOTION and PLC program which are executed by an interpreter.
Motionware runs as an add-on component in the Beremiz platform, enabling an easy-to-use script-based motion control interface. Motionware consists of a command server and a motion server, which are responsible for host command processing and real-time motion control, respectively. Using a built-in interpreter, the command server allows users to write and run motion scripts online without the needs of compilation or system reboot. Using Xenomai-patched Linux, Motionware successfully runs both the servo control tasks that are repeated at a very short cycle, e.g., 500 us and the non real-time user programs.
The motion server has been developed using Beremiz PLC. It is composed of a number of data structures and motion function blocks. The supported functions include LINEAR, RAPID, and JOG motion. Since the motion server runs in the Xenomai domain, the execution of real-time loop for sensing and actuation is guaranteed without interference from user PLC and motion programs.