Four applications

Lets briefly take a look at four common motion applications to see how their controls might use, or not use, networks. While not an all-inclusive list, these applications are intended to represent a fairly broad spectrum of industries and products that use motion control. The four applications will be called conveyer belt, standalone, local controller, and synchronized multi-axis.

Conveyer-belt. Typical applications: packaging, factory floor automation, continuous flow processing, medical liquids analyzers.

This application involves motion that occurs over a relatively large distance. There tends to be a variety of actuators used including servo motors, cutters, valves, etc. In this application the primary motion elements tend to be standalone drives or intelligent amplifiers which control a single motor, and which are loosely linked to other sensors and actuators. Sub-millisecond synchronization is generally not required here, and the interactivity tends to be localized and autonomous. That is, “move when this local sensor goes active” etc. In this kind of application the network dramatically reduces the cost of wiring because of the large number of axes, and the relatively large distances involved. This application would be well served either by CANbus or one of the higher-level protocols CanOpen and DeviceNet. Ethernet is also an option here, and if Ethernet-based off-theshelf actuators can be purchased, this option may be an equal if not preferable approach.

Standalone machine. Typical applications: semiconductor and medical robotics, pointing systems, scientific instruments.

This application describes a machine that is relatively small (usually from a few cubic feet in size to no more than closet-sized.) In this application there is a serious question as to whether networking is even warranted, because distribution of electronics throughout the machine often causes more servicing problems than it solves, despite the total reduction in number of wires. If networking can be used to an advantage, then one of the device networks such as CANbus could be used. To communicate to the “outside” world, any number of networks can be used, but Ethernet would probably be the best choice.

Hybrid controller. Typical applications: Chemical Processing, Pharmaceuticals, Semiconductor Equipment, some general automation, some medical systems

These applications include both standalone and conveyor-belt type control elements, blending the need to communicate between intelligent modules and the need to provide direct control of device-level actuators and sensors. Ethernet, CANbus, or RS485 can work in this application, depending on the bandwidth requirement.

Synchronized multi-axis. Typical applications: Machine tools, plotters, measuring machines.

This application entails systems that perform highly synchronized multi-axis motion. For this application SERCOS may be a good choice, and for the more adventurous, FireWire. Be aware that you may find that a traditional multi-axis card-based centralized controller is every bit as cost effective and reliable as a distributed controller for this type of application.