For the first time, PC-based controls for manufacturing took the spotlight away from traditional programmable controllers (PLCs) at this year’s IPC show. The PC-based controls that were shown have not reached the ultimate goal of total openness, modularity, and flexibility — that’s a few years away. They have, however, made control selection easier. Rather than weigh the pros and cons of PC vs. PLC, or compare a long list of features, engineers can focus on whether the proposed control meets scan speed requirements and can run other software programs besides the program an engineer creates to control a process.
Real-time vs. real-time
The main drawbacks of earlier PCbased control, real-time deterministic operating system and orderly shutdown, have been addressed. Be aware, though, that some solutions address these issues by degrees.
Industrial PCs have a real-time operating system (OS). Presently, there are three popular versions: iRMX, the manufacturer’s proprietary OS used in their PLC products, or one of the Windows products such as Windows 95 and Windows NT.
The iRMX system is a real-time, deterministic operating system developed by Intel about 18 years ago. It is factory proven with close to 2 million installations. Depending on the number of I/O and the size of the control program, it can offer scan times to 1 msec. The engineer may never know that iRMX is the OS, because industrial PCs also offer a version of Windows as a front-end that runs on top of it. Any programming, display development, or monitoring is done on Windows, which translates these functions into the iRMX code that executes the functions and does the actual control.
The manufacturer’s proprietary operating system is also factory proven and provides real-time deterministic and millisecond scan response. No longer technologically behind the times, manufacturers have put their software code on the latest chips, including Pentium.
A few industrial PCs chose to use Windows 95, or increasingly Windows NT, as both the real-time operating system and program development, display, monitoring, and control system. However, several manufacturers caution against Windows 95 or NT for deterministic, real-time discrete control. “Windows NT is a solid platform for graphical, communication, and information technology, but it can not provide the level of fast, reliable, deterministic control that an industrial controller requires,” said Mike Klein, president of Steeplechase Software. According to some, Windows can provide scan times as fast as 100 milliseconds, depending on the number of I/O and control program. (Some PLCs provide scan times in the microsecond range).
Regardless of which operating system is used, engineers should ensure that the industrial PC, or any control, can execute an orderly shutdown should a failure occur. In over simplified terms, this means that incoming and shutdown signals follow a user-specified priority to protect critical functions in an application. All PLCs offer this feature. Many, but not all, industrial PCs do too. Not all industrial control manufacturers will volunteer whether their control has this feature, so if it’s important to your application, ask.
Unexpected shutdown is less likely with the new industrial controls, though. Most have taken the techniques used in PLCs, such as card slots with retaining catches on three sides, gold connectors, and even passive backplanes for improved reliability in harsh environments.
Opening the PLC
In addition to offering PC-based products, PLC manufacturers are continuing to upgrade their core product, altering it into a more flexible, open control — changing it so that the user sees more PC and less PLC.
An important part of the strategy of control manufacturers to make PLCs look and feel more like computers involves Windows. (Let no one doubt Microsoft’s ability to invade the factory market). Though Windows may not be the best system for real-time, millisecond control, it is everywhere, on every PLC, on every industrial PC, and in almost every third-party programming software.
Along with make-the-PLC-look-like-a- PC strategy, many PLCs now offer integrated peripherals and features available on plug-in cards that meet PC slot dimension requirements and that are compatible with PCs, such as ISA and PCMCIA compatible cards and SCSI interface ports.
Communication networks and software also received attention at the show.
Be it SDS, Interbus-S, Seriplex, or DeviceNet, many makers of peripheral control products are installing microprocessor interfaces to one or more of these device-level buses. TR Encoder Solutions, for example, offers a line of CANbus compatible absolute encoders and linear transducers. These products interface to a bus through a direct-bus node or through a multi-axis box. The engineer can program system parameters from a remote control and send them through the bus to the device.
New versions of control and programming software begin to address the problem of managing tag names among the various software databases. Past versions of software programs have methods of labeling inputs and outputs to and from various actuation and control devices that are unique to each program. Each of these programs does a good job of managing the tag names within its software database boundaries. But as more programs share data among each other, it’s come out that none of the programs follow the same naming format. There is no standard. An engineer designing a control system may have to track up to four, or more, tag-name databases while creating a control program.
Solutions are in their infancy. Several vendors offer software that will handle the database management among all your databases, but these solutions are often limited to specific operating systems, specific front-end software such as Windows, and specific manufacturers.
Aside from new products, a few companies announced unique alliances or agreements. One of the more interesting ones came from Chrysler Corp. and Rockwell Automation. The two companies announced a five-year agreement, effective through May 2001, where Rockwell Automation will be brought into the design phase of new products. “Automation controls typically are considered after automotive products are designed,” said Frank Ewasyshyn, vice president, Advance Manufacturing Engineering at Chrysler. “Sharing advanced technology much earlier in the process will reduce the time spent to design, debug, and start up an automation control system.” The goal is to reduce total manufacturing system costs and improve product time-to-market.
There has been sharing of such technology between supplier and customer before, but not to this magnitude. This is the first time that an automaker has brought an automation controls company into the process so early. According to officials at both companies, this agreement will take business relationships between automakers and controls suppliers to a new level.
Under the agreement, Rockwell Automation will develop software that helps Chrysler integrate the design of automation controls into Chrysler’s product design phase. This lets the automation controls meet manufacturing process needs immediately. The controls supplier will also be the automation controls supplier of choice for Chyrsler assembly plants, stamping and welding plants, and all powertrain facilities over the next five years.
In other announcement news, the Indramat Div. of Rexroth Corp. and Cutler- Hammer announced that they have formed a technical alliance to co-develop, market, and support open-architecture application solutions for automotive manufacturing. The alliance combines Indramat’s machine-motion control systems with Cutler-Hammer’s logic control, communication hardware, and software. The two companies plan to be a supplier to the automotive marketplace.
The first product will be a singlesource open-architecture solution that connects motion control with a device level network, providing data access and communication from the logic platform to the motor shaft for transfer line applications. It will link Indramat’s Trans-01D multi-axis digital CNC control to Cutler- Hammer’s PC-based logic control system using DeviceNet and Ethernet networks.
“The goal of this alliance is to offer best-in-class open-architecture solutions,” said Richard Huss, vice president of sales & marketing, Indramat.
Adds Dave Williams, marketing manager at Cutler-Hammer, “Transfer lines are a perfect application for DeviceNet. Operator interfaces, motor starters, variable- speed drives, servo systems, sensors, I/O, machine controls, motion and logic controllers, and hydraulic, pneumatic and linear mechanical equipment, can interoperate at a very high speed over this network.”
The system lets engineers configure a motion control from the network. It reduces system wiring, replaces a PLC with PC, and lets users run a three-axis machine tool in the drive.
Both companies’ distribution channels will be separate. There will be one program manager coordinating each automotive program; one phone number for users to call for help or information.
For more information on the following products.
For the Open Controller (1747-OC), from Allen-Bradley, Rockwell Automation.
For the Trans-01D from the Indramat Div. of Rexroth Corp.
For Visual Logic Controller/NT , from Steeplechase Software.
For the D700 Series industrial personal computers, from Cutler-Hammer.