Drives and Controls Magazine

Hardware motion controller gains a soft sibling

01 August, 2003

Hardware motion controller gains a soft sibling

Rockwell has developed a PC-based version of its Kinetix motion control technology, which uses Sercos to link a PC to up to 64 servo axes. The SoftLogix 5800 package uses the same program code as its ControlLogix hardware counterpart, allowing users to migrate easily from one technology to the other.

Rockwell expects the software version to be particularly attractive for applications which need to be integrated with other Windows packages, or PC peripherals such as Webcams. It will also be useful when large amounts of data need to be gathered and stored, or where the PC display can be used as an HMI, avoiding the need for a separate dedicated display. The PC screen could also be used to display video feeds, animations and manuals.

John Pritchard, Rockwell`s marketing manager for motion products, says that one of the attractions of the PC-based approach is that "you can now implement a control system in one box".

He emphasises that the software motion controller is not aimed at low-cost applications, where PLCs would be better, or at applications that might suffer losses of power. Also ruled out, are applications needing a speedy boot-up.

Pritchard also points out that there is no great saving in opting for the software version of the controller — typically costing £1,000-2,500 — instead of the hardware version.

He expects the software-based motion controller to appeal, in particular, to designers of applications requiring fast execution times, coupled with high-speed servo control. Examples could come from the printing, packaging and materials-handling industries.

One advantage of using the same code both for the hardware and software versions of the controller, Pritchard adds, is that "we are not forcing customers to choose PLCs or PCs at the time they are writing their programs".

Unlike some other PC-based controllers which rely on separate processors or third-party, real-time extensions to Windows, to maintain determinism, Rockwell uses the PC`s processor to execute the motion commands and to generate the motion profiles. Pritchard maintains that this approach is preferable because it keeps the "openness" of Windows, allowing other Windows software to run at the same time.

The fibre-optic Sercos cables used to link the PCI motion cards to the servo motors, replace up to 20 wires per axis, making it easier and quicker to commission installations. Each motion card supports 12 axes.

Another attraction of the PC-based motion controller is that it supports the use of a "virtual backplane" via which devices and applications can communicate in real-time. "The virtual backplane becomes the preferred method for achieving faster data transfer rates between SoftLogix 5800 and a variety of partner applications and devices," says Pritchard. "This can include any combination of networking, integrated motion control and vision-control systems."