AUTOMATION TECHNOLOGY:INTEGRATION TECHNOLOGY

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INTEGRATION TECHNOLOGY

Recent communication technologies have enabled another revolution in automation technologies. Stand-alone automated systems are integrated via communication technologies. Integration can be identified into three categories:

1. Networking: Ability to communicate.

2. Coordinating: Ability to synchronize the processes of distributed automated systems. The coordination is realized by either a controller or an arbitrary rule (protocol).

3. Integration: Distributed automated systems are able to cooperate or collaborate with other automated systems to fulfill a global goal while satisfying their individual goals. The cooperation / collaboration is normally realized via a protocol that is agreed upon by distributed automated systems. However, the agreement is formed through the intelligence of the auto- mated systems in protocol selection and adjustment.

In this section, automated technologies are introduced based on the above categories. However, truly integrated systems (technologies) are still under development and are mostly designed as agent-based systems, described in Section 6. Only technologies from the first two categories are introduced in this section.

Networking Technologies

To connect automated systems, the simplest and the most economic method is to wire the switches on the automated systems to the I / O modules of the programmable logic controller (PLC). Ladder diagrams that represent the control logic on the automated systems are popularly applied in PLCs. However, as the automated systems are remotely distributed, automated systems become more intel- ligent and diversified in the communication standards that they are built in, and the coordination decisions become more complex, the simple messages handled by the PLC-based network are ob- viously not enough for the control of the automated systems. Hence, some fundamental technologies, such as field bus (Mahalik and Moore 1997) and local area networks (LANs), and some advanced communication standards, such as LonWorks, Profibus, Manufacturing Automation Protocol (MAP), Communications Network for Manufacturing Applications (CNMA), and SEMI* Equipment Com- munication Standard (SECS) are developed.

In a field bus, automated devices are interconnected. Usually the amount of data transmitted in the bus is not large. In order to deliver message among equipment’s timely in a field bus, the seven layers of the open system interconnection (OSI) are simplified into three layers: physical layer, data link layer, and application layer. Unlike a field bus, which usually handles the connections among devices, office activities are automated and connected by a LAN. Usually more than one file server is connected in a LAN for data storage, retrieval, and sharing among the connected personal com- puters. Three technological issues have to be designed / defined in a LAN topology, media, and access methods (Cohen and Apte 1997).

For the advanced communication standard, MAP and CNMA are two technologies that are well known and widely applied. Both technologies are based on the Manufacturing Message Specification (MMS) (SISCO 1995), which was developed by the ISO Industrial Automation Technical Committee Number 184. MMS provides a definition to specify automated equipment’s external behaviors (Shan- mugham et al. 1995). Through the specification, users can control the automated equipment with little knowledge about the internal message conversion within MMS and the equipment.

SECS is currently a popular communication standard in semiconductor industries (SEMI 1997). The standard was developed by SEMI based on two standards, SECS-I (SEMI Equipment Commu- nications Standard Part 1 Message Transfer) and SECS-II (SEMI Equipment Communication Stan- dard 2 Message Content). The relationship between SECS-I and SECS-II, as shown in Figure 7, shows that SECS-I transmits the message that is defined by SECS-II to RS-232. SECS-II’s message

Automation Technology-0011

Automation Technology-0012

is added as control information by the SECS-I so the transmission message can conform the format of RS-232 for message delivery. For SECS-II, it provides a set of interequipment communication standards under various situations. Hence, engineers only need to know and follow the SECS-II to control the connected automated equipment, rather than taking time to define the detailed message conversion.

Object Orientation and Petri Net Techniques

Object orientation and Petri net are automation techniques in modeling and analysis levels. Automated systems and their associated information and resources can be modeled by object models. The co- ordination and communication among the automated systems can then be unified with the message passing among the objects. However, the complex message passing that is used to coordinate behav- iors of the automated systems relies on the technique of Petri net. The graphical and mathematically analyzable characteristics make Petri net a very suitable tool for synchronizing the behaviors and preventing deadlocks among automated systems. Combinations of both techniques have been devel- oped and applied in the controllers of flexible manufacturing systems (Wang 1996; Wang and Wu 1998).

Distributed Control vs. Central Control

The rapid development of microprocessor technology has made distributed control possible and at- tractive. The use of reliable communication between a large number of individual controllers, each responsible for its own tasks rather than for the complete operation, improves the response of the total system. We can take PLC-based control as a typical example of central control system and LonWorks, developed by Echelon, as an example of distributed control system. In LonWorks, each automated device is controlled by a control module—LTM-10 (Figure 8). The control modules are connected on a LonTalk network that provides an ISO / OSI compatible protocol for communication.

Virtual Machines

Figure 8 Applying LonWorks to Develop Virtual Machines.

Automation Technology-0013

Usually the control modules are loaded with Neuron C programs from a host computer that has a PCNSS network card for network management and Neuron C programming. Hence, under running mode the host computer is not necessary and the control modules can work under a purely distributed environment.

Distributed automated systems have the following advantages over centralized automated systems:

• Higher system reliability

• Better response to local demands

• Lower cost in revising the system control programs when automated equipment is added or deleted from the system

Robot Simulator / Emulator

In recent years, powerful robot simulators / emulators have been developed by several companies (Nof 1999). Examples include ROBCAD by Tecnomatix and RAPID by Adept Technologies. With these highly interactive, graphic software, one can program, model, and analyze both the robots and their integration into a production facility. Furthermore, with the geometric robot models, the emulation can also check for physical reachability and identify potential collisions. Another important feature of the robot simulators / emulators is off-line programming of robotic equipment, which allows de- signers to compare alternative virtual design before the program is transferred to actual robots (see Figure 9).

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