Page 131 - Welding Robots Technology, System Issues, and Applications

118 Welding Robots
3. Data sharing: most of the services require data sharing, files and databases
between the client and the server. Consequently, the mechanism provided
by the RPC technology to implement data sharing must be used.

Another important thing to consider is the need to interface intelligent sensors with
the system. The most easy and portable way to do that is to build software
components that implement the methods, properties and data structures necessary
to configure and use the sensor. Consequently, a technology to implement software
components is also needed. The basic architecture presented in Figure 4.9 details
all these requirements.

4.5 Application to Robot Manipulators

Actual industrial robot manipulators are controlled by advanced multiprocessor
computer systems, based on standard parallel buses (VME, for example) or a serial
internal communication mechanism (CAN, DeviceNet, etc.). Generally these robot
control systems use a real-time operating system for low level interfaces, like
RTOS or WxWorks, and a more friendly operating system with the sub-systems
used for user interface (Win32 based OS, etc.). Robot controllers also provide local
programming environments based on structured Pascal-like languages, along with
a set of libraries that enable the user to build custom applications, interface with
other machines and with operators, etc., exploring fully the robot and controller
facilities.

Any software architecture designed to operate with this type of machine should
comply with current standards in terms of communication protocols, remote
interfaces and software components. The reason is to avoid incompatibilities and
excessive dependency with specific technologies that limit the users or force them
into certain directions not representative.

The software presented in this book was designed to be used with robot
manipulators (Figure 4.9) in distributed applications, and is divided into three main
parts:
1. A set of functions that implement the robot-PC communication operations,
including the access to the RPC services available in the robot controller.
Those services include: variable access services, file management services,
program management services, IO control, robot controller state services,
etc.
2. A set of functions based on TCP/IP sockets that implement the same robot
controller access described above. These functions were designed to
operate with a TCP/IP server running as a task on the robot controller.
3. An OPC (OLE for Process Control) client component that implements calls
to any OPC DA (Data Access) server [31]. The particular implementation
used in this book works with ABB IRC5 OPC DA servers [31] to
demonstrate the principle.