By Steve Gahbauer

Until now, critical control functions in factory automation projects were not performed by personal computers, but this is changing. According to Ron Sieck, vice-president and general manager, sales and marketing, of Honeywell's Micro Switch Division: "Collapsing PLC control functionality into PC functionality is a natural, and once you've had a PC you never go back

A trend toward open, modular architectures is putting pressure on programmable logic controllers (PLCs) and proprietary automation systems. Many users are looking to leverage multi-vendor control solutions, simplify integration, and ease their maintenance problems with the ubiquitous and powerful PC.

Honeywell manufactures a network of binary devices with embedded computer chips and a digital bus, offered as a total solution in distributed machine control system technology. Called SDS (Smart Distributed System), it makes use of CPUs originally designed by Robert Bosch GmbH in the 1980s for Control Area Networks (CAN).

In the SDS scheme, sensors and actuators aren't just dumb slave devices. They become intelligent communication and control units through a robust, open network, with the help of the CAN chip.

The system brings the power of communication to the device level on the factory floor, reducing downtime and operating costs. The embedded chips can talk to each other or to a central controller. The open architecture of SDS offers flexibility in selecting the devices that are best for a given application. The system can interface with any PC or PLC.

The system enables PCs, PLCs, sensors, actuators and other control devices to communicate via a single, four-wire cable or a two-wire digital bus. It provides system and device diagnostics and status. Potential bus growth includes peer-to-peer communication, where empowered devices take action on information without going through any dedicated control device.

The system capitalizes on common perceptions that PCs, as opposed to proprietary control hardware, will come to play an increasingly dominant part on the factory floor. Microswitch Div. planners say that PC-based factory control systems will almost totally displace conventional, proprietary programmable controller-based technology within a short time, and that PCs will be the controllers of choice in tomorrow's systems.

The benefits of open systems can be very attractive. You pay market price for the module you want; you choose standard, upgradable hardware and software interfaces; integration is simplified because of the modularity and scalability of computers; and open systems are easier to maintain, change and upgrade.

Honeywell introduced the initial digital bus network for SDS in January, 1994. The following year, it added a PC interface card-paving the way for the use of industrial computers in real-time control applications, by combining PCs with intelligent I/O.

Last November, Honeywell rolled out Phase III-a completely integrated, totally open and modular PC control solution which eliminates the need for programmable controllers. It makes the acquisition and use of information-not just data-a reality for the factory floor.

More than just another PC integrator, Honeywell brings considerable expertise in manufacturing systems to the table. "Honeywell will be there to ensure that customers have someone to call," says Sieck.

Despite its relatively recent introduction, SDS is already proving itself around the globe.

Installations at General Motors in Michigan and Australia provide diagnostics. Motorola is using it to automate its PCB manufacturing and lists plug-and-play assembly flexibility as a primary benefit. Crown Cork & Seal is applying SDS to its container manufacturing line, and reports cost savings and increased system functionality as a result. And diagnostics are given as major benefit of the SDS systems implemented by AT&T and Coca Cola. Reader Service Number 312.

Analysis breaks speed barriers

By Tom Kelly

Pioneering mathematics research at the University of Minsk in Russia has permitted significant advances in structural analysis with computers. Procision software lets a designer analyze models on a CAD workstation without the storage (typically up to a gigabyte) required for conventional methods

Analysis time is dramatically improved, as well: an analysis taking two hours by conventional methods would take only 15 minutes with Procision, says Dan Smith, vice-president, engineering, of Rand Technologies, Mississauga, Ont. Rand is the Canadian reseller of CAD software and systems which has brought the product to the worldwide market.

Precision is another benefit. Stress is shown as continuous contours over the model's surface and stress concentrations around holes and similar features are displayed. As well, flexion and displacements due to loads or vibration are clearly visible and parts containing both solid and thin-wall sections can be analyzed.

Procision runs on Silicon Graphics and Hewlett-Packard workstations. It will be ported to other Unix platforms and to Windows NT soon. The software runs under PRO/Engineer, the parametric solid-modelling software developed by Parametric Technology Corp.

The user clicks on a single prompt in a PRO/Engineer menu, selects the type of analysis to be done from a second menu, and enters some data to specify the properties of the material, such as elasticity. The calculations are automatic.

The resulting color image shows the degrees of stress across the surface. A graph of stress also can be plotted along any rubber-band line across the surface. The program will display the displacement of the model under load conditions and compare it to a wire drawing of the model under no load. Color is used to indicate the degree of displacement at different locations. The degree and direction of displacement under vibration at different frequencies also can be displayed.

Since Procision runs under PRO/Engineer, a designer can analyze a model, switch back to the modelling software to make improvements, and then repeat the analysis. "As the designer is thinking about some geometry and making design decisions, he can do a quick analysis on the spot to take the design in the right direction," says Smith.

In traditional analysis methods, a model is segmented into a mesh of tens of thousands of elements. This requires the calculation of large numbers of simultaneous equations and time-consuming reads and writes to disk.

"Because other systems use a mesh, they only calculate the results for the predetermined elements and average from one element to another," says Smith. "The precision is driven by the number of elements used, and the higher number of elements drives up the solution time.

Procision calculates a set of functions and produces results for any X-Y-Z coordinate on the model. The results are continuous over the surface, rather than at predetermined locations. Although each equation is much more complex than the simultaneous equations of traditional element analysis, there are far fewer of them, so there is no need to store intermediate results on disk.

Another benefit is that there is no need to de-feature, and no danger that removing a feature to simplify the analysis will alter the stress reactions. Deciding which features to remove and how many elements to divide the model into usually demands the skills of an analyst.

One unique characteristic of the Procision mathematics is that the equations do not need to be identical in form. This, as well as the absence of a mesh, enables the software to analyze areas of particular interest, such as stress concentrations around a hole or slot. Another advantage is the ability to analyze parts with solid and thin-wall sections.

The system automatically performs convergence calculations to ensure it obtains reliable results in the shortest possible time. The calculations are repeated several times, each time using a higher-order and lengthier calculation. Each result is compared with the previous one until there is a negligible difference. The curve showing the convergence of the calculations is displayed on the screen to demonstrate that the most accurate results have been obtained.

The analyses are presented in a manner familiar to design engineers. Procision has been put through its paces at a number of beta sites in the automotive, automotive-parts and aerospace industries. Its results have been verified with traditional analyses and measured against strain-gauge tests of actual parts. Reader Service Number 313.

Tom Kelly is Electronics Field Editor for Design Engineering