Development of CNC | CNC Technology

The PC's CNC transformation

Noaker, Paula M

Will a PC be the soul of your next machine tool? Control vendors can't seem to agree on the answer. Some believe its place is as a front-end interface for a conventional CNC. Others say the control of preference in coming years will be a PC with a CNC motion control board inside. Both groups, though, agree that most future controls will probably be one or the other.

Fueling the growth of PC-based control software is a recent, major initiative by the Big 3 automakers to develop an open, modular architecture controller. The automakers are working with control manufacturers to promote development of economical control technology that is:

* Open, integrating off-the-shelf hardware and software components into a de facto standard control environment.

* Modular, permitting plug-and-play of components to best meet a specific application's control needs.

* Scalable, allowing easy and efficient reconfiguration as control needs change.

* Maintainable, supporting maximum machine tool uptime, expeditious repair (minimum downtime), and easy maintenance.

"Various levels of openness can be achieved with machine tool controllers," says C. Jerry Yen, NAO-Machining Centers/Manufacturing Controls Dept., GM (Warren, MI). "The ultimate level is a software-based controller, with a variety of functional modules that can be easily added or interchanged. At this level of openness, the control will be hardware-platform independent. Along the way, though, we are targeting use of PC-based controls to provide a more open control environment--using the current PC platform and operating system standards and trying to integrate off-the-shelf components.

"We see the initial step in GM's efforts to use open-architecture controls as being the open-environment control. Controls will use PCs with the Microsoft Windows operating environment, which has become an off-the-shelf de facto standard. Moreover, a control will be open in the sense that you can pick and choose the application components that you need. The problem is that you need a lot of engineering time to integrate all these components, which aren't designed to come together easily. They may all run within the Windows environment, but that doesn't mean they will automatically interact as needed to control the process when I load the software into a system."

CNC Inside the PC

When control vendors say they have a PC-based control, they usually mean that the motion control board or complete CNC unit with integrated programmable logic control will fit into a standard slot of an IBM or compatible PC. Thomas Glynn, CFO, CNC Software & Systems Inc.(Wells, ME) reports that its multitasking CNC-PC software for Windows, which emulates GE Fanuc in both screen functionality and G code input style, uses a Galil motion control board to handle all machining movement. This frees the PC's CPU for other uses, such as tool management, programming, and statistical process control. Because of this, if the PC Windows environment were to lock up, the motion control board would shut the system down in an orderly fashion.

Henry Glick of Mitsubishi Electric Industrial Controls Inc. (Mount Prospect, IL) adds that PC-based CNC users no longer need worry about sacrificing servo update times for position feedback that could limit the speeds demanded by some precision machining applications. In Mitsubishi's MeldusMagic PC-based control, servo update times are comparable with conventional CNCs.

An obvious benefit of PC-based controls is their cost. Consider Wizdom Controls Inc.'s (Naperville, IL) Wizdom Paradym-31 Version 2.6 Windows-based industrial programming, simulation, and control software, which works with a Delta Tau PMAC (motion control) board. A ladder-logic-only version of the software costs about $695 for programming, monitoring, and execution. A complete control, simulation, monitoring, and execution package ranges from $2995 to $3995. (Prices don't include the controller board.)

Price/performance ratios for PCs continue to improve. Technology Automation Services (Englewood, co) notes in its recent "Technology Trends in CAD/CAM" report that $3000 worth of PC packs a lot more processing power than in 1992--one computer vendor now offers 16 MB of RAM instead of 8 MB, 1 GB of disk drive capacity vs. 200 MB, and 256 kB of cache memory vs. 64 kB. Controls also benefit from the rapid and inexpensive upgrading of today's PC technology.

Still, the key benefit of PC-based controls is their flexibility to run a variety of user-specified software programs, in addition to providing machine control. For example, with FlexMate Inc.'s (Fren Park, FL) PC-based control with Windows 3.1, an AcadView option allows viewing standard AutoCad drawings and control schematics directly from the control display. Minimum system requirements are 4 MB of memory, DOS 6.22, and a 486 DX33 PC with a mouse or trackball.

As another example, CNC Software & Systems's CNC-PC software operates concurrently with a range of shop-floor control software, such as solid modeling, SPC, tool crib inventory, and PLC graphical user interface. It also accommodates using touch probes for part inspection and location, automatic tool offsets, and SPC data collection; as well as toolchangers, video cameras, coolant control, and systems for part handling or inspection.

PC-based software's customizable interface also is more user-friendly than a standard CNC. Ease of networking PC-based controls via the Novell network, another de facto standard, is a further benefit.

PC-based controls also can eliminate G-code programming, adds Bill Gibbs, president of shop-floor programming software manufacturer Gibbs Q Associates (Moorpark, CA). Programs can be built graphically, reducing the programming learning curve dramatically.

Pros and Cons

Don't expect all control vendors to replace their conventional CNC technology soon, though. PC-based controls still face hurdles. For instance, while some reportedly can control up to 10 axes, applications requiring complex five-axis machining still will demand some conventional CNC technology. Moreover, most end users will probably not be running heavy-duty CAM work with the PC-based control while the machine tool is cutting metal. In addition, retrofitting the PC-based controls can take time. One retrofit of a PC-based control required four to six weeks. The end user reports three weeks of this required machine tool downtime.

For companies that want PC processing flexibility, but don't want to or can't give up conventional CNC technology, several control manufacturers offer a PC front end. John Turner at GE Fanuc Automation North America (Charlottesville, VA) reports that the control vendor provides several variations. One is its Machine Management Control-IV PC-compatible computer embedded in a common backplane bus with a GE Fanuc Series 15B, 16B, or 18B CNC. Users can easily replace their control's CRT with another option, the Intelligent Terminal. Turner says this combines the functionality of the first option with a high-speed serial bus for high-speed data transfer. GE Fanuc also makes it easy to link any PC in the shop with their CNCs through the Open System CNC option. This contains the serial cable, and two interface cards, as well as all interface libraries and screen generation software needed.

The PC interface is only one option in Siemens's (Elk Grove Village, IL) modular approach to CNC. Its Sinumerik 840D machine tool control allows you to plug-in power as needed. For example, if you need a fifth axis, you simply add a feed module and motor to the system. Users can decide between the MMC 101 interface with an integral Windows-based PC, the MMC 100 standard operator interface, and the MMC 102 interface, which can be used for 2-D and 3-D simulation. NC control units include the following: The NCU 571, with a 960 RISC processor, 128-kB CNC, and 64-kB PLC user memory for up to five axes and two spindles; the NCU 572 with its 486/DX33 processor, 256-kB CNC, and 96-kB PLC user memory for up to eight axes and five spindles; and the NCU 573, which builds on the NC 572 model by adding a high-speed 100-MHz Pentium processor.

As another example, the PCNC from NUM Corp. (Naperville, IL) merges an IBM PC with a multitasking OS/2 2.1 operating system with the model 1060 23-bit CNC. The PC is compatible with Microsoft Windows and OS/2 Presentation Manager and handles user and manufacturer-specific applications, including programming and machine supervision.

Future Facts

Least you attempt to downplay the impact PCs will have on machine tool control in the future, consider this. Cincinnati Milacron's (Cincinnati) control of the future, its Acramatic 2100 (A2100), is PC-based and runs on the Microsoft Windows NT operating system. According to Ron Pieper at the Electronic Systems Div., the CNC will eventually supersede both the 850SX and 950 series controls. At present, though, those wanting complex five-axis control will still see an advantage in using the 950 control.

Pieper reports the Acramatic 2100 control differs from other PC-based units because it is a dual-PC platform. One PC motherboard controls workstation functions such as shop-floor programming and database work. The other handles real-time servo control. Upgrading will be easier and less costly than with a specialized motion control board, says Pieper. The user also pays for no more capability than needed. For example, the two PC buses are linked- via a proprietary bridge board, which holds I/O cards, and servo control cards, and leaves slots available for options such as an Ethernet adapter, as your needs grow.

Pieper sees an advantage to using Microsoft Windows NT for control. Unlike Microsoft Windows, which resides above the DOS operating system, Windows NT is its own operating system. Pieper reports this operating environment offers more protection against crashes. It also assigns different priority levels to various tasks, which ensures that CNC software has priority over other application software. Windows NT also is platform independent, allowing a company to move to other hardware as needs dictate.

The 2100's three basic components include an operator CRT, the control box, and a hand-held pendant that provides all CNC push buttons and controls required for standard operation. The pendant eliminates the need for the operator to stretch and strain to keep one hand on the feed hold button and one eye on the machine, notes Pieper. Also gone are the constant back and forth motions between part and CNC during setup and programming of a job. Moreover, the pendant's LCD readout allows the operator to observe the machining cycle from almost any angle without losing access to major CNC functions.

Programming also is simplified using a resident assistant programmer. This allows programming a variety of cycles without G codes. Instead, operators touch an on screen icon of the desired machining function, then enter information when prompted by the system. The control's Gibbs shop-floor programming system, for example, has an option that allows the user to verify the part during programming.