Networking for modular manufacturing

InTech, Oct 2001 by Komarek, Larry

Open device-level networks add grist to latest trend

It's an age-old question in the business world: How do you get more for less? Now systems integrators, OEMs, and users are taking a look at modular manufacturing techniques to lower costs and provide customized solutions in less time. They are finding significant differences among device-level networks that have an impact on the cost and time required to implement a modular manufacturing solution.

Open device-level networks, standardized object-oriented software control languages, and new connector/ wiring approaches are fueling the rapidly growing use of modular manufacturing. These systems start with the combination of mechanical assemblies and the required sensors/actuators/ automation devices and control software blocks into subsystems. These preengineered and predocumented subsystems combined create a customized machine or manufacturing process. There are many advantages to this approach vs. a custom-engineered approach:

* Reduces engineering time while offering "customer customized" solutions

* Speeds time to market via reduced system delivery, installation, and start-up times

* Provides higher reliability via pretested assemblies based on standardized components and "debugged" control software routines

* Lowers cost and risk to expand or adapt the manufacturing line As a result, systems integrators and OEMs are looking to modular manufacturing and machine designs to increase profitability while offering customized solutions faster. Users win by lowering the cost of their systems and meeting new production start dates. In response to changing consumer needs, the ability to modify these systems quickly, affordably, and with low risk becomes a strategic manufacturing advantage.

The subsystems, or "modules," used to build the manufacturing system vary greatly in complexity. Material handling systems in warehouse distribution systems containing miles of conveyors consist of conveyor and sorting segments containing basic sensors, pneumatic/ solenoid driven actuators, soft starts, and motor starters. Other sections may also contain more intelligent devices such as bar-code readers, powered rollers, and variable frequency drives. These basic types of subsystems are also in automatic storage and retrieval systems and in small to medium-sized assembly machines. A growing number of OEMs are also creating small-, medium-, and large-capacity machine families based on a common scalable control architecture.

Intelligent subsystems contain networked distributed controllers such as PC-based control/operator stations, micro programmable logic controllers (PLCs), single-axis servo motion, coordinated drives, and multiaxis robot control systems. Each of these subsystems may contain a subnetwork of basic devices. This approach is similar to the use of office PCs with universal serial bus networked printers/scanners, etc. connected to a higher-level company intranet. Larger-scale automotive assembly lines, stamping lines, test stands, and paper machines may use more than 100 intelligent subsystems per system.

Open device-level networks are part of implementing a modular manufacturing system. The smaller the manufacturing subsystem, the more precisely the systems will match the user's price/ performance/capacity requirements. The greater the quantity of subsystems used, the more highly distributed the resulting system will be and the greater the demands on the network. Differences in network specifications can have a significant impact on the time and cost required to design, start up, and maintain the system. While the use of fiber optics is growing, copper cable is still the most popular and is the focus of this discussion. Before ramping up a system, users should consider these factors:

Layout/Performance trade-offs

The quantity of devices and maximum distance vary with transmission rate, and cable types determine the overall capacity of a single network. The greater the number of trade-offs, the more engineering effort is required when deciding whether a certain quantity and combination of subsystems will work at the desired rate. Transmission rate vs. layout factors include trunk length, trunk length vs. cable type, cumulative drop length, repeater segment length, and quantity of repeater segments vs. repeater timing characteristics. Summation frame networks, such as Interbus, have a signal boosting capability (repeater functionality) embedded into each device that allows for availability of the full rate at the maximum distance.

Design stage: Flexibility

Each of the major networks varies as to what layout constraints exist. Once again, the greater the constraints, the greater the engineering time when piecing together permutations and combinations of subsystems that fit the physical requirements of the customer's specific installation. On smaller modular machine applications, this is rarely a major factor. On larger-scale systems, however, the impact can be significant.

The use and cost of wire can vary 15% to more than 40% based on the topology. Many devices packed into a modest-sized machine can use significant "cable length budget" when routed back and forth across the machine. This is true when mounting networked devices directly on the machine vs. conventional junction boxes or panels.