7/1/2007 | 7 MINUTE READ

Factory Control Developments

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Nothing revolutionary per se, but just the sorts of “tweaks” that can help make factory operations all the more productive. Here are a few of the more recent developments.


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Small and Connected

For easier access to machine diagnostics and system data, there’s the new Allen-Bradley EWEB module for the CompactLogix programmable automation controller (PAC) from Rockwell Automation (Mayfield Heights, OH; www.ab.com/networks/compactlogixeweb.html). This module provides large-system network connectivity and Web capabilities to small control systems (less than 2,000 I/O nodes), and lets users receive alarm notifications through authenticated email and share system data with external applications using eXtensible Markup Language (XML). The module offers up to 2 MB of memory for storing web pages, documents, and data. It supports RS-232-C (serial) ports, EtherNet/IP or ControlNet channels, and modular and DeviceNet communications. While EtherNet/IP lets the CompactLogix PAC connect to any standard Ethernet device, such as radio frequency identification (RFID) scanners or printers, the module also lets CompactLogix communicate to any non-EtherNet/IP or non-CIP device. The local I/O capacity can range from 8 to 30 I/O modules.

What this means: Big-controller networking capabilities in a small, machine-level controller. Available for a year now, the CompactLogix L4x line, with its faster bus, can control up to four coordinated real, two feedback, and six virtual SERCOS axes. The L3x line controls stepper, servo via DeviceNet, and analog AC drives. While ControlLogix PACs can have multiple CPUs in a rack, CompactLogix PACs are aimed at stand-alone machines requiring a single CPU for control. The EWEB module adds networking to CompactLogix. Now, for instance, with the EWEB module’s interface to third-party robots, even CompactLogix can control multiple robots in a workcell.


Plug-n-Play Error Proofing

Rockwell Automation (Bloomington, MN; www.rockwellautomation.com/industries/automotive) began delivering error-proofing systems in 1987. This year, the company announced an error-proofing and Andon solution that’s built using preconfigured modular templates within FactoryTalk. (FactoryTalk is a suite of software modules that tie enterprise systems to plant-floor systems. In this instance, FactoryTalk integrates the error-proofing application with the assembly line and other enterprise systems.) The templates provide work instruction displays, part verification, and automatic tool control that prompt operators through production. In operation, the error-proofing process includes verifying that the proper parts and tools are used, and that procedures and specifications are followed. Other-wise work is stopped.

The Andon component works with Rockwell’s Logix Control Platform to capture real-time events, identify product problems, and adjust operations to minimize errors and reduce downtime. The Andon system works with any type of alert system, such as line side displays, stack lights, and pull chords. Out of the box, this application consists of programmable logic controller (PLC) code, FactoryTalk configuration, and extensions to FactoryTalk ProductCentre or Rockwell Software PlantMetrics. These two latter systems track WIP, institute dynamic workflow-based routings, enforce manufacturing processes, collect performance parameters, provide genealogy information, and perform other supervisory control and data acquisition tasks. Rockwell has already mapped things out so that users for the most part need only work in a Microsoft Excel spreadsheet to configure the work zones (identify the number of zones, then pick the type and number of tools used in each zone, such as pick bins, torque guns, barcodes, pull cords, and Andon displays). Users also need to enter routings in ProductionCentre and associate them with equipment centers. The error-proofing component will peel off relevant information from a bill of materials, manage work instructions, and push this information down to the PLCs, which typically act as line controllers. 

The error proofing and Andon solution comes configured for 10 work zones, with two operator stations per work zone. Tools are included to add work zones without writing any code. The solution can be applied to handle manual operations requiring bar code scanners, work instruction displays, and genealogy tracking, right on up to complex, multi-station assembly lines.

What this means: No rip-and-replace. No one-offs. By breaking factory automation into understandable, discrete chunks of information (and control) technology, manufacturing engineers can apply “plug-n-play” information technology concepts to factory control—with each chunk fitting a need, demonstrating value, and offering an attractive return on investment (ROI). This leads to faster, simpler, more reliable, and much more economical production/assembly line implementations. Error-proofing and Andon operation are such a chunk.


Integrate and Save

The IndraDrive Mi from Bosch Rexroth Corporation (Hoffman Estates, IL; www.boschrexroth-us.com) is not just a servo motor, nor just a control system. It’s motion and control logic in a single unit that takes the heat generation portion (the electronics) out of the control cabinet. The drive unit is a thin block on the top of the motor housing, thus keeping the length of the motor itself at a minimum. Only one cable is needed for both power and communications; multiple drive units can be daisy-chained together. The distributed device has full IEC 61131-3 PLC capability at high speeds. As necessary, OEMs and plant engineers can run the PLC in one drive (master) and connect further drives and I/O using Ethernet SERCOS III. The master drive would communicate diagnostics, process-related information, and overall control signal information back to up the control hierarchy to a controller through fieldbus and to a human/machine interface (HMI) through Ethernet. This way, data exchange is deterministic down to 0.25 milliseconds.

The cost of the integrated drive is about the same as that for the drive and motor separately. One would think the integrated unit would be less expensive, however the electronics mounted on the motor need to be built for up to 155°C ambient, which is a more costly proposition than the 48°C found in a control cabinet.

IndraDrive Mi is especially suitable for applications with many moving axes (such as in gantry and other applications with cable tracks, and assembly systems). For the time being, the IndraDrive Mi has no input for external feedback, such as a scale, because there’s physically no space for a connector. (Currently, only local motor feedback is available.)

What this means: Excessive heat is always a problem, especially because air conditioning is generally a low-priority maintenance item. So moving control logic to the business end of a servo motor eliminates regular maintenance for a control cabinet. It also reduces part count and the requirements for cabinet cooling, plant floor space, and spare parts. Company officials estimate that the IndraDrive Mi can yield reductions of up to 85% in installation costs (direct cost of assembly and wiring), up to 70% in control cabinet volume, and up to 75% in cabling, as well as speed installation, simplify commissioning, and make troubleshooting easier.


Don’t Forget Memory

Schneider Electric North American Operating Division (Palatine, IL; www.us.schneider-electric.com) just added the Modicon M340 PAC to its Modicon line (joining Modicon Premium and the high-end Modicon Quantum). This PAC has 4 MB of internal memory (upgradable to 16 MB), and can manage applications with up to 70 KB instructions. This memory can be dynamically reallocated between function block programming and ladder programming.

Open networking is built into the M340. It comes with a high-speed USB port and can have two additional communi-cations ports (CANopen, Ethernet, or Modbus). The PAC can automatically back up data and applications in its internal flash memory and SD-based memory card, respectively. The memory card is “plug and load”—it can be updated or transferred to other machines with no disruption in the PAC’s operation. Data files, such as traceability and maintenance logs, can be stored and accessed from a PC or drag-and-dropped to an FTP (file transfer protocol) site. The M340 can accept from 4 to 12 modules with maximum density of 64 channels per module. Each module supports hot swapping, and is automatically reconfigured by the PAC’s CPU at replacement.

In October 2006, Schneider introduced its Magelis XBT-GT graphical touch screen terminals, which now comes in six sizes ranging from 3.8 in. to 15 in. These terminals are powered by 64-bit processors, yielding snappier and higher quality displays and videos. The terminals can have up to 1 GB of memory to, for example, collect more data and process more complex applications.

What this means: I/O communications and management have long been no-brainers. Providing development tools, such as Schneider’s Unity Pro, so that control engineers can easily pick and choose from various IEC 61131-3 languages in creating control programs is mostly standard. But with each advance in functionality and the more foreground control and background monitoring applications added to new entry-level PACs and HMIs, there comes the additional need for greater compute horsepower, increased memory space, faster response times, and built-in data communications of various flavors. The M340 PAC and the XBT-GT terminal are at the same time entry-level factory control devices and powerhouses—devices that not too long ago required serious ROI analysis, and now are just standard intelligent factory control devices.