Spreading out system smarts

Distributed versus centralized control is defined by the location of processing power for the motion control. With a centralized architecture, a fixed amount of PLC processing power is divided among all the axes. As axes are added, available processing power is reduced. Distributed intelligence (DI) solves the problem by moving the burden of controlling an individual axis out to the drive. Due to advances in microelectronics, intelligence can be distributed throughout a machine — to sensors, motors, drives, and other components.

In a DI system, each drive is capable of closing the feedback loop and can handle advanced functions such as cam tables, absolute feedback, electronic line shafting (ELS), diagnostics, and high-speed registration. It's even possible to add safety on board and predictive maintenance functionality at the drive level.

The processing power that can be built into the drive with low-cost processors and memory allows the drive to be quite intelligent. Most important, when you add a drive, you add more intelligence to the system.

Distributed intelligence not only reduces the processing load on the controller, it changes the controller's role in motion control to a supervisory status. Some of today's decentralized controls can handle up to 64 axes — with no degradation in system performance.

Super scalability

Distributed intelligence is a modular, responsive architecture. It supports the scalability that is an absolute requirement in many operating environments. Adding an axis is greatly simplified: just add a new servo axis. Additional expansion cards or controller functionality are unnecessary because the intelligence is in the drive itself.

Adding intelligence in a drive-bydrive distributed fashion frees design engineers to create machines that better serve end user demands for convenience and flexibility.

Because processing power has ceased to be a limitation, more servo-controlled axes are practical, along with the advantages of faster setup, greater precision, and higher reliability.

Why DI

Implementing a DI system requires several components engineered to work in a decentralized architecture, including intelligent drives and a DI-ready controller. Some may think an intelligent drive is one that can simply handle the position loop and receive inputs. However, this type of drive still places a heavy burden on the processor. For true distributed intelligence, a drive should be able to handle tasks such as closing the position loop, absolute positioning, high-speed registration, cam tables, ELS, and diagnostics.

As more remedial tasks are handled by the drive, the controller's workload is reduced. A good example is to specify safety and predictive maintenance tasks at the drive level. By making them drive-specific, problems can be quickly isolated, downtime reduced, and machine throughput optimized.

The motion controller is the next component in this architecture. A DI-ready controller must take full advantage of intelligent drives. Its key tasks will include running logic, overseeing drive communications, I/O peripherals, HMIs, and system networks. Involvement in the motion will exist primarily at a supervisory level.

Logic on sale

OEMs and end users can achieve dramatic hardware and software savings using distributed intelligence, while still assuring improved machine performance. First and foremost, PLC and motion control hardware can be eliminated and integrated into the servodrive. Eliminating the PLC also leads to reduced wiring requirements, installation costs, and a smaller electrical cabinet.

Industry analysts indicate that this can reduce hardware costs from $7,000 to $1,000 in a typical application. Plus, eliminating the interface card and wiring between the PLC and servodrive can provide an additional $2,000 savings. Low axes count machines such as infeeds, wrappers, cartoners, casepackers, and palletizers will be able to derive the greatest benefit.