PC-Based Control Delivers for Manufacturing

Increasing numbers of manufacturing applications benefit from the flexibility, access to software tools, and lower system cost attributed to today’s PC-based controls. Ease of connectivity to business systems ‘sweetens the pot.’

Influences of personal computer (PC) technology are all around us. Penetration of PC control into industrial communication, operator interfaces, production monitoring, and so on is enormous. PCs also have spawned a host of application software and tools that help streamline diagnostics, data management, and other plant functions.

Yet, there is another level of PC-based technology that performs actual control of processing lines or products being manufactured. It exists with a lot less fanfare, and even with some reluctance to being labeled as “PC-based,” because of the technology’s earlier image and relative criticality of products or processes controlled. The extent of such “real” PC-based control is therefore less well documented. Several examples presented here form just the tip of a growing iceberg of such applications.

A changing image

Image of PC-based control is changing, albeit slowly as users’ trust builds. And no, the hardware typically used in PC-based control is not the same bargainpriced personal computer you buy for home or office use. Many industrial computers (IPCs) are designed specifically for their stated purpose. As a result, they have higher reliability by eliminating moving parts like hard drive and cooling fan—replaced by flash memory, solid-state devices, and plug-in boards for special tasks. For some applications an IPC may be a single-board computer. In use “testing” adds to the reliability of these board products.

On the software side, PC-based control fosters more high-level programming language development and the PC becomes the programming device.

PC technology also allows simulation and can simplify system startup.

Curing tires in high gear

Automotive tire manufacture consists of complex processes, made critical by safety and reliability issues added to the process mix. In 2004, Continental Tire (U.S. operations of Germany’s Continental AG) embarked on an upgrade of 34 curing presses for large tires to PC control at its Charlotte, NC, facility.

The line was previously run by PLCs of early 1990s vintage. Decision to move to a centralized PC-based control alternative was due mainly to limitations of the existing PLC system, higher cost of new PLC controls, and eliminating the need for extensive wiring with decentralized control architecture on so many machines.

The tire plant features new segmented mold machines designed by sister company Continental FMF. It selected CP7130 Panel PCs from Beckhoff Automation as the presses’ control core. Other control suppliers were considered, but Beckhoff was the leading candidate because of its long-standing relationship with Continental as a global standard supplier. The new presses were designed for three operating modes: manual, mold change, and automatic.

Manual mode allows manual actuation of machine components and processes so that changes and “tweaking” adjustments can be made safely.

Vacuum remains on the press bladders during this process-inactive phase and press segments cannot extend or retract, explains Jack Plyler, electrical engineer at Continental Tire.

If a press is idle for any length of time, the system switches to mold change mode where vacuum is turned off, allowing press segments to be moved. Tool change, maintenance, and machine cleaning are done in this mode. Automatic mode handles tire loading/unloading functions automatically, while curing and production data are monitored by Beckhoff TwinCat control system software and displayed on a Panel PC.

The upgrade added more system flexibility. For example, Plyler notes that prior PLC-controlled presses did not operate in a true manual mode. “Individual system sequences could be queued to operate, but not individual components. As a result, components could not be tested in a stand-alone fashion,” he says. Also, Continental’s plant imposed an operating temperature requirement of up to 150 °F on the motherboard, which was met by PC controls.

Flash memory, no hard drive

“A key feature of CP7130 was that we were able to spec 330 MB of compact flash memory running [Microsoft] Windows XPE operating system (OS) rather than a hard drive,” continues Plyler. “This removed last ditch arguments for keeping the PLC approach. Plus, the Panel PC has a heat sink instead of a fan.” Key to using Microsoft Windows in an industrial controller is Beckhoff’s TwinCat software, which runs in the Windows kernel, independent of other OS processes. “In the unlikely event of a Windows problem, TwinCAT has ‘fail-safes’ that allow real-time tasks such as PLC and NC to continue running and bring controlled processes into a safe state,” Plyler adds.

He reminds us that an industrial PC controller with Windows should not be likened to an office or home computer. Beckhoff has applied controllers with Windows OS for several years in various demanding industrial applications and seeks to continue the approach.

Cost savings with PCbased design were immediately apparent. According to Continental, 50% savings were realized for electrical and mechanical controls on the 34 upgraded tire-curing presses and electric installation time was 50% less (amounting to over 100 engineer hours)—compared to the older PLC-based system.

‘Concrete’ PC-based control

A leading U.S. building materials supplier and highway contractor, New Enterprise Stone & Lime Co. Inc. (NES&L) owns and operates numerous concrete plants, quarries, and related production facilities throughout Pennsylvania and Delaware. NES&L currently uses PC-based control and I/O systems from Opto 22 to control a variety of equipment for manufacturing concrete, blacktop, cement, asphalt, and other aggregates.

Concrete, in particular, is a non-uniform material. Ashley Fleck, automation programmer at NES&L, notes distinct differences between concrete used for sport stadium risers or prison walls and that used for parking lots and residential projects. “Each type of concrete requires a different mix of many different ingredients—sand, crushed stone, steel fibers, etc.,” he says. This is where modern controls enter the picture.

Opto 22 systems at work in NES&L’s concrete mixing operations include intelligent B3000 Ethernet I/O processor/controller, combined with analog and digital I/O modules that control movement of conveyors to haul stone into the mix and communicate to a PC over Ethernet. Control software (created by NES&L) runs on a PC rather than the controller. Opto’s system also controls opening and closing of hydraulic gates used to release appropriate amounts of ingredients into the mix.

These and other plant processes are defined and implemented via a custom, PC-based control application created by NES&L programmers using Visual Basic (VB). Numerous options built into the application program handle different control strategies needed for scores of concrete “recipes” created by NES&L. “These strategies often require modification depending on the individual plant’s needs,” says Fleck. “We knew it would be easier to make these types of changes with our own ‘home-grown’ application, rather than with vendor-supplied software tools.”

Fleck describes Opto 22’s approach as one that develops and provides the necessary hardware without forcing users into proprietary software. This often can eliminate a thousand dollars or more per seat, he explains. NES&L has cut such costs using its own software developers and Opto hardware, which offers a more open architecture. “[This also] allows interfaces from custom apps written in VB, C, and other common programming languages,” he adds.

Reasons for going with PC-based control at NES&L include less cost, software flexibility, and inherent “enterprise connectivity” of PCs. The latter simplifies data acquisition and communication to software databases, reportedly without the need for special software, proprietary servers, or other intermediary devices often needed when trying to do the same with a PLC or similar hardware.

PC-based control has proven extremely reliable and given NES&L a distinct advantage as it commissions new plants and production lines, according to Fleck. “Many NES&L subcompanies and subsidiaries have discovered this firsthand. We’ve installed the controls in many locations and literally have never had to go back [for rework],” he says.

Boosting driveshaft production

Spicer Driveshaft Manufacturing Inc. (part of Dana Automotive Systems Group) uses CNC Trunnion manufacturing systems designed and built by City Machine Tool & Die Co. Inc. (Muncie, IN) to increase production of end yokes and yoke shafts used in Spicer driveshaft assemblies. Trunnion machines represent a design challenge as they handle up to six operations, address singlecontrol programmability, and provide efficient tool changeovers, according to City Machine. These multi-station indexing machines—similar to dialindexers, except for a horizontally oriented axis of rotation—also satisfy a growing need for smaller machine footprint with dimensions of 150 x 189 x 121-in. (W x L x H). Trunnion machines feature a single Rexroth MTC200 CNC system with PC-based controls from Bosch Rexroth Electric Drives and Controls division.

Every station on Trunnion performs independent operations, ranging from drilling, tapping, and threading to full CNC turning and boring, explains Dennis Kelly, City Machine engineering manager. Efficient tool changeover is important. “If operators want to retool for a different part, they should be able to easily convert programs, offsets, and other partspecific information. That can only be done if many systems are integrated to behave like one system,” says Kelly.

As for Rexroth MTC200, one system is said to simultaneously control up to seven independent CNC processes and command multiple machining operations involving various spindles and slide groups while coordinating automated handling and measuring systems. As many as 32 axes can be assigned to the seven CNC processes. MTC200 performs all functions required for 3-D, circular, and helical interpolation; polar coordinate transformation; main spindle synchronization; and follower (synchronous) and gantry axes, explains Karl Rapp, Bosch Rexroth branch manager for automation and machine tools.

CNC motion and PLC logic execution—inherent to all CNCs, according to Rapp—occur on PC plugin cards located in the PC. “Advantage of this solution is that machine performance does not depend on the PC and Windows operating system. Communication of all CNC information in such a high-axis-count machine is critical and can be accomplished well via the ISA/PCI bus,” he adds.

“Usability” was key to Trunnion’s design and it was the main reason for selecting Rexroth PC-based MTC200 CNC system for the machine’s control.

“We needed the ability to store and recall many programs for various parts,” says Kelly. “Our machine makes a variety of parts. A PLC-controlled machine would need to be re-programmed every time the operator wanted to make a new part number. With PC-based control we can select from a menu of programs depending on the part number and touch it in. It’s loaded up and the machine control is ready to go.

“We looked at PLCs, but our control requirements were too complex,” continues Kelly. “Out of the box, this controller on its own will do what a PLC and many third-party devices hooked together could accomplish. Our customers get a system that’s easier to use and debug with quick, simple part changeover.”

Software rejuvenates machines

Starting in 1993, Great Lakes Industries (GLI, Jackson, MI) retrofitted its first CNC lathe with OpenCNC software, realizing a dramatic, almost immediate drop in downtime and repair costs. Developed by Manufacturing Data Systems Inc. (MDSI), OpenCNC software works with commercially available PC technology and is said to be industry’s first production-proven, software-based CNC machine tool control.

GLI manufactures gears and sprockets for such companies as John Deere. Its shop floor is organized in several machining cells, each of which may see three to four setups per day. Production lot size averages 200 pieces, depending on machine capability, part size/weight, and operations required. The company specializes in employing retrofitted equipment, giving machines a “second life.” Rick Stafford, GLI automation engineer, says, “Before we installed MDSI’s OpenCNC, we had several machine tools that still made good parts, but they had obsolete controls. We couldn’t afford new machines. But downtime and control repair costs were major roadblocks to meeting our commitments.”

OpenCNC became available on PCs in 1995; it runs with current version Microsoft OS and a realtime extension from Ardence Inc. (formerly Venturcom). For added reliability, MDSI vice president of R&D, Bruce Nourse, suggests use of an Intel chip set and motherboard, and avoiding non-productive PC extensions that take over the memory bus system. “As nearly as possible this control is implemented entirely in PC-based software,”

says Nourse. Only two cards are needed, available from multiple sources. One card reads axis encoder counts for position and outputs a ±10-V signal for servo-velocity control for interfacing to the machine tool. Another card handles single-point digital inputs/outputs, which support soft logic, he explains.

“There is no motion card used in the control,” adds Nourse. “Trajectory planning and multi-axis feedback loops are all handled in software. This includes S-curve velocity control with software-settable limits on acceleration and jerk, and complete PID-loop control with velocity and acceleration feedforward.”

Traditional machine controls are proprietary computers, which pose costly downtime and repairs when they fail. A company has two options: buy an expensive new control or wait for the manufacturer’s service technician to repair the outdated one. Virtually all machines at GLI—turret lathes, vertical mills, 4-axis hobber, 6-axis welder, and induction heat treater—have been implemented with OpenCNC since the initial application, explains Stafford. “We have written the code to allow OpenCNC to do that.

Uptime is much higher now—up 20-50% or more, compared to the original CNC control—and we can troubleshoot ourselves rather than wait for an outside vendor.

“Where we had machines with a two-minute cycle time, after retrofitting with OpenCNC we have realized up to a 100% increase in productivity. OpenCNC enables us to buy machines with obsolete controls, retrofit them and make them operational for one tenth their original cost,” he says. OpenCNC’s operator-friendly interface also contributed to the control’s quick acceptance, plus a great reduction in training time, Stafford concludes.

In summary, PC-based control is here to stay. It offers growing benefits of open architectures, fast execution time for high-speed control needs, easier maintenance and upgrading of manufacturing systems—and not least, simpler interfacing to business systems. However, implementing PC controls requires careful planning.

Experts suggest that a single supplier of the total hardware-software system is best for successful PC-based control implementation.

For more information, visit:

www.ardence.com

www.beckhoffautomation.com

www.boschrexroth-us.com

www.controleng.com

www.gefanuc.com

www.mdsi2.com

www.microsoft.com

www.opto22.com