PCs bring real time IT to cranes

Rubber tyred gantry cranes (RTGs) are hardly a regular feature of C&I. But a system of 52 crane-mounted, Windows Pentium PCs with STEbus I/O providing in-cab VGA touch screens and a real time database – all directing and tracking movements of 17,000 cont

The PCs are industrial devices installed right in the cranes’ ground level electrical rooms, which link to their lifting gear. Coupled with inputs from sensors which detect external reference position tags in the ground, the PCs sense which area of the park their RTGs are in and the individual container being handled.

A system-wide container `map’ is automatically updated by these remote systems – within five seconds of each movement. And the PCs also run the crane drivers’ interactive job allocation system.

The system was developed by the Port’s own IT team using Arcom’s Eurocard PCs with their DIN style interfaces to the STE backplane that accesses the I/O cards. It’s this level of ruggedness that allowed them to be installed on the 52 RTGs themselves.

Hosting all this is a pair of Pentium PCs linked to a radio modem comms system, providing access to the RTG PCs – and thus updating jobs and schedules for the RTG drivers on their screens.

Why PC technology? Well, according to Robin Pattinson, senior analyst at Felixstowe, it allowed the development team to use industry standard software, exploiting, for example, Microsoft Windows and Visual Basic (VB) to speed up the work.

Pattinson says: `Originally, a software house was used. But things change quite fast, and we wanted to control development ourselves. Earlier controls were written in C and Assembler; using Visual Basic was certainly an improvement. In fact, we had to take some of the functionality out.’

The system was put together using VB v3.0 and Windows 3.1. Today, Arcom would, of course, be offering the latest 32bit technology with Windows NT v4.0. Things do indeed change fast.

However, VB v3.0 meant no standard access for the application to the hardware resources. And, Windows 3.1’s co-operative multi-tasking was not ideal for the realities of real time.

Arcom handled this by providing its I/O SuperDrivers for Visual Basic. Essentially, these are VB extensions for the I/O boards which also integrate with Windows at a lower level to deliver the requisite determinism.

Arcom also used external hardware counters, for example, on the incremental encoder boards (from Andover Microsystems) which sense crane wheel movement pulses. Counting in software was not recommended!

But running PCs in this kind of environment meant solving other hardware problems too. For example, Windows provides a good GUI, but you need a disk drive – not clever. So Arcom used 8Mb Flash EPROM STEbus boards.

Then there was getting the displays to work 80 metres from the PCs! The touch sense link had to be changed from RS232 to 422.

As for the analogue VGA, although Arcom thought video boosters would be needed, simply using high quality screened cable did the trick!