FireWire sets a blistering pace for automation

The IEEE1394 standard has been slow to find industrial applications, despite its capabilities: Aerotech's Simon Smith explores its potential.

Aerotech may have raised a few eyebrows when it unveiled the world's first servo motion control system that was entirely software driven from a standard PC.

If software lay at the heart of the new Automation 3200 motion controller, it was the choice of FireWire for the networking that gave the arterial system its breathtaking performance.

There really should have been no surprise that FireWire should create such a revolution in motion control but, as this article explores, the IEEE1394 standard has been slow to find applications.

Automation, control and design engineers are spoilt for choice when it comes to the selection of high performance communications networks, control hardware and languages.

The sheer range of protocols - from device to enterprise levels - is overwhelming.

However, one clear leader, based on a proven architecture, is steadily emerging.

It does, without a doubt, have the potential to leave all others trailing in its wake.

IEEE1394 (FireWire) has been around for a lot longer than many people think.

First developed by the Apple Corp in the early 1990s, it was originally touted as "a USB bus on steroids".

In fact, its performance was so impressive that many industry insiders thought that it would be difficult for it to compete with slower, less capable protocols.

FireWire's first major leap into the consciousness of the public was when a tiny, relatively unknown connector appeared on Sony's DV Camcorders.

With the DV application, FireWire exploded onto the scene in a big way and, in 1995, it was accepted, by the IEEE as a bona fide communications standard.

The worlds of computers and audio visual hardware were quick to take up this exciting new "miracle" protocol as it promised performance figures far above what was currently available.

However, even with this type of take up in consumer- and office-based applications, the industrial world has been distinctly lax in its adoption - even though FireWire has the potential to rewrite the rulebooks.

This lack of take up is not indicative of the capabilities or, indeed, any shortcomings, if any, of the protocol.

The finger can, instead, be pointed at the powerful members of the industrial consortium backing USB - FireWire's biggest competitor.

One could argue that this situation is analogous to the early posturing between Betamax and VHS - like Betamax, FireWire is superior in many ways.

However, unlike Betamax, FireWire is growing in stature and is definitely here to stay.

(As an interesting aside, many of the world's leading professional camera systems still use Betamax).

When you consider the capabilities FireWire has to offer, it is difficult to fathom why it has not become the de-facto standard.

Not only does the latest wire based version (FireWire 800) offer an 800Mbit/s bandwidth (compared with 480Mbit/s for USB 2.0) but its next hardware layer is defined in a fibre version which will allow up to 3Gbit/s, allowing Aerotech to offer more complex functionality without future redesigns.

It also offers plug and play, determinism and, with its single-wire connectivity, it slashes both the volume and complexity of the wiring, compared to a traditional PC-based motion control platform.

It also reduces many of the analogue noise errors that can occur with analogue input signals.

Determinism, the ability to guarantee data across the network on a time critical basis, is of massive importance when considering advanced and high-speed motion profiles, especially when multiple axes need to operate concurrently.

FireWire has a determinism rate of 8kHz, which Aerotech uses to update target set point information.

Conventional PC-based motion controllers normally calculate trajectory positions at a rate of 1-4 kHz, and close the servo loop accordingly.

With modern processes, where speed or dynamic performance is of the essence, 1kHz is no longer fast enough - people are looking for higher speeds; and those dealing with servo loops, even higher servo closure rates.

As a comparison, Ethernet, a widely used communications standard, exhibits data packet collisions as part of its standard software layer.

If there is a collision, it will resend the data but cannot guarantee successful delivery.

FireWire, on the other hand, due to its high data rate can check each device in turn and guarantee data delivery.

Target position data needs to be guaranteed in servo loop applications otherwise motion would be interrupted.

Aerotech, a world leader in precision motion and automation devices and systems, has reinforced its ethic as a forward thinking company by recognising the potential FireWire has to offer and, more importantly, the capabilities it will offer its customers.

Addressing many a wish list, the company's A3200 motion, vision and I/O system not only takes the mantle as the World's first high performance software-only controller to offer 32 axes of synchronised motion, but it does so using the FireWire protocol.

With a variety of digital networks available, Aerotech developed a list of criteria that the Automation 3200 network interface had to possess.

A checklist that would be pertinent to any high end, high performance motion controller.

The following characteristics detail the criteria used to ultimately select FireWire and why those criteria were considered important.

Determinism - complex motion such as contouring requires that all axes receive their data at exactly the same point in time, each time.

Bandwidth greater than 100Mbit/s - the faster the network, the lower the latency between transmitting and receiving data.

This also allows the user to view real-time diagnostic and status data on the PC.

Standard on PCs - the Automation 3200 does not require a motion card.

Having FireWire as standard on PCs eliminates the cost of additional hardware.

Supported by the Windows operating systems - this ensures that the software will work on the PC with the network.

Continued R and D effort by the chip makers - a strong R and D effort by manufacturers allows the performance to increase and cost of the chips to decrease.

Tree topology - unlike a ring topology, a tree topology does not require a link back to the originating PC, which reduces the cabling effort.

Peer-to-peer transmissions - these allow the transfer of data between two drives without going through the root node.

This allows the transmission of encoder or I/O or any other type of information quickly between drives.

More and more devices are becoming available and support from Microsoft will ensure that integration with the majority of the world's computer systems will not be a problem.

The appearance of the new fibre version, with its massive datarates, will also allow users to future proof their designs, as new hardware will not have to wait for a new bus system to catch up.

FireWire has already demonstrated its capabilities in numerous applications; with its user base expanding and its support base strengthening it will remain one of the most powerful communication protocols for years to come.

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