Sang C. Park

Plant model generation for PLC simulation

This paper reports an automated procedure for constructing a plant model for PLC simulation. Since PLC programs contain only the control logic without information on the plant model, it is necessary to build the corresponding plant model to perform the simulation. Conventionally, a plant model for PLC simulation has been constructed manually, which requires much effort and in-depth knowledge of the simulation. As a remedy for this problem, we propose an automated procedure for generating a plant model from the symbol table of a PLC program. To do so, we propose a naming rule for PLC symbols so that the symbol names include sufficient information on the plant model. By analysing such symbol names, we extract a plant model automatically. The proposed methodology has been implemented and test runs performed.

Development of Virtual Simulator for Visual Validation of PLC Program

Agile and flexible manufacturing systems make it mandatory that control programs have features such as agility, flexibility and reusability to meet fast- changing customer demands. Visual validation of control logics is one of the most sought-after ways to make the control logic more feasible for rapid product prototyping, concurrent engineering and flexible and agile manufacturing. This paper presents the development of virtual simulator to validate control programs (PLC) visually. For simplification, virtual cell is separated into generic model that resembles the operations and events of real cell and graphic model - a visualization module - which gives easy understanding of dynamic behavior of cell. The generic model is formalized using timed Finite State Automata. ROBOWORKS and IGRIP are used for graphic model. We developed tools for easy integration of proposed simulators with 3D graphic simulators and soft PLCs. We applied our system to real PLC applications and found that PLC programs can be easily validated by this system.

Simulation framework for small scale engagement

Developing future weapons systems has become increasingly complicated and costly. The armed forces of major nations use modeling and simulation techniques for new weapons systems from the conceptual stage to design, production, deployment and training stages to shorten the development cycle and guarantee their effectiveness. Failure in the development cycle carries too much loss in time and money. Therefore, computer-based modeling and simulation techniques are applied from the conceptual stage to gauge the efficacy of new weapons systems. The objective of this study is to develop a modeling and simulation methodology for small scale engagement using the DEVS formalism. The entities required for modeling and simulation are divided into three categories: combat, logical, and environmental entities. Combat entities represent the military hardware or combatants; logical entities represent the judgment and decision entities for the interaction between various entities; and environmental entities emulate the constituents of real combat environment. The combat entities are further modeled into Shell and Core Parts to maximize their reusability under various combat scenarios. The proposed framework is verified using a one-on-one combat engagement simulation (written in C++) between two submarines.

A concurrent design methodology of a production system for virtual commissioning

In this article, a concurrent design procedure of a production system is presented, which supports the virtual commissioning between a real controller and a virtual plant consisting of virtual devices. To achieve the concurrency, we split a virtual device model into two parts, a physical device model (a geometric model with kinematics for the motion programming of tasks) and a logical device model (a behavioral model to interact with a real controller). The whole design procedure consists of four major steps: (1) process design, (2) physical device modeling, (3) logical device modeling, and (4) system control modeling. First, the process design step identifies effective manufacturing processes and produces the sequence of operations. Once the sequence of operations is obtained at Step 1, then the other three steps can be performed concurrently without interfering each other. All the three concurrent steps start from the sequence of operations, and a detailed procedure for each of the step has been developed. The concurrent attribute of the proposed design procedure significantly contributes to the saving of the delays in time to market. The proposed design procedure has been implemented and tested for various examples.

Generation of PLC Ladder Diagram Using Modular Structure

In this research work, auto-generation of PLC ladder diagram program is explained. This work is carried out in real time operation of PLCs in the plant and simulation of the models in the PlcStudioreg. Involved modelling and simulation tasks are performed in PlcStudioreg which is research product of digital manufacturing system (DMS) team in Ajou University, consists of input/output model and graphics tool for PLC based industries. Object-oriented approach DEVS (discrete event system) is employed in formalism of process structures, later, formalized model is simulated using plc-DEVS simulator, which is extended from conventional DEVS. Generated sequence of operation (SOP) from the simulation and mapping it into input/output table to generate executable ladder diagram is explained consecutively in the paper. The algorithm developed to connect plc-DEVS and graphics module of PlcStudioreg is elaborated. In the mean time, to show the applicability of methodology, pallet conveyor system is described.

PLCStudio: simulation based PLC code verification

Proposed in this paper is the architecture of a PLC programming environment that enables a visual verification of PLC programs. The proposed architecture integrates a PLC program with a corresponding plant model, so that users can intuitively verify the PLC program in a 3D graphic environment. The plant model includes all manufacturing devices of a production system as well as corresponding device programs to perform their tasks in the production system, and a PLC program contains the control logic for the plant model. For the implementation of the proposed PLC programming environment, it is essential to develop an efficient methodology to construct a virtual device model as well as a virtual plant model. The proposed PLC programming environment provides an efficient construction method for a plant model based on the DEVS (discrete event systems specifications) formalism, which supports the specification of discrete event models in a hierarchical, modular manner.

Hardware-in-the-loop simulation for a production system

This paper proposes a hardware-in-the-loop simulation (HILS) approach for the design and verification of a production system. The design of a production system involves two major activities: mechanical design (device specification and layouts) and electrical design (device behaviour and system control). Conventionally, the mechanical and electrical design activities have been performed sequentially, wasting time. We propose a concurrent procedure of mechanical and electrical design based on the HILS methodology to cope with this problem. The proposed HILS approach provides two major benefits: (1) the verified control program can be directly used for the real plant with minor adaptations; and (2) the verified 3D layout model can be used to generate the detailed drawings for the implementation of the plant. We can minimise the stabilisation time of a production system, since most mechanical and electrical errors can be found and fixed using HILS.

Fixture modelling for an automotive assembly line

This paper proposes an efficient fixture modelling procedure for automotive body assembly lines. A fixture model consists of two sub-models; a geometric model and a kinetic model that should be remodelled frequently whenever design changes occur. We develop an algorithm extracting the kinetic model from the geometric model of a fixture to reduce the fixture modelling time and effort. Although the geometric models of fixtures used in automotive assembly lines vary, most follow the same kinetic mechanism, the so-called slider-crank mechanism; this is a four-axis system of three revolute and one prismatic joint. The prismatic axis of a fixture represents a pneumatic actuator involving a piston and a cylinder. It is very important to identify the prismatic axis from a given geometric model to extract the kinetic model of a fixture. We use the concept of the ‘moment of inertia’, which is a measure of an objects resistance to changes in its rotation rate, to identify the prismatic axis. Since the exact computation of the moment of inertia for an arbitrary solid model requires complicated computations, we introduce an approximating method for the moment of inertia. The proposed procedure has been implemented and tested with various examples.

New modelling formalism for control programs of flexible manufacturing systems

Proposed in this paper is a modelling formalism, called the FMS control model, which is able to provide a detailed guideline for the implementation of the FMS control program (PLC program). Although, there are numerous simulation models for FMSs describing the system dynamics at the level of discrete event simulation, they cannot be fully utilised for the generation of a real control program involving sensors and actuators. Due to this, PLC programs for FMSs are usually done by the repetitive method of code writing, testing, and debugging until the control objectives are achieved. This is an error-prone and time-consuming task. The proposed FMS control model is described at the level of sensors and actuators. It can support the PLC program generation from the model. Since the FMS control model has been developed by expanding the DEVS formalism, it has a well-defined formalism. The proposed methodology has been implemented and test runs were made.

Short-Term Bottleneck Detection for Process Planning in a FAB

decided by a bottleneck. In this paper, we define the problem of a bottleneck process and propose a simulation based framework for short-term (3 shift) bottleneck detection. By the proposed framework of this paper, the performance of a wafer FAB is improved in on-time delivery and the mean of minimum of cycle time.