Do PC-based CNC controls keep their promises?

PC-based CNC controls are a new and fast-growing segment of today's CNC control market. These days, more and more PC based CNC controls are introduced, primarily by motion control companies and companies that were previously unknown. The "big players" in the CNC world have tried to stay with their proprietary hardware and software as long as possible. However, demand for PC-based controls has also forced them to enter into this expanding market segment. The control user's main attraction to these innovative PC-based CNC products is simple they are less expensive and easier to service than traditional CNC controls.

Primary advantages of PC-based CNC controls

Being able to use off-the-shelf PC hardware (including keyboard, power supply, monitor, etc.) allows CNC vendors to reach the low sales price ranges that were previously out of reach for complete control. Also, customers usually want to understand as much as possible about their control systems. A PC-based CNC system provides a more familiar environment for the control user, because most users have at least one person who can work with PC hardware and software. As a result, CNC controls are no longer mysterious "black boxes" that are made up of the CNC vendor's proprietary hardware and software.

Every machine tool builder asks a CNC vendor about worldwide service, and in the past this was the biggest drawback for small but innovative vendors. However, using off-the-shelf PC hardware allows those smaller vendors to provide their customers with basic spare parts which are available from any computer store in the world.

Since the CNC software is loaded via the floppy disk drive and the proprietary hardware is limited, service and troubleshooting typically can be done by the end user. In the past, customers bought the big and famous brands, just because of the service and technical support issues. Meanwhile, the CNC world changed to the point where the generic phrase "PC-based" collectively stands right next to the "big brands."

One of the biggest advantages of a PC-based control, no matter who is the actual vendor, is that they have the biggest development department in the world (figuratively speaking). Thousands and thousands of people are developing software for PCs, which can run directly on those types of controls. These software products include computer-aided manufacturing (CAM) systems, statistical process control systems, shop floor software, networks, etc. No proprietary hardware approach is able to keep up with this rate of innovation.

Product differences

In terms of hardware, PC-based controls are realized in different ways. As mentioned before, some of the bigger, old-fashioned CNC companies have introduced their "PC compatible" CNC controls, which still use proprietary hardware and not off-the-shelf PC hardware. Their customers are able to run certain PC software programs. However, the end users are not able to purchase basic spare parts from a computer store, because the spare parts are proprietary and only available from the CNC vendor.

The CNC companies with a motion control background use the DSP processor, which are capable of extremely high block cycle times. This seems to be a very good selling feature to uneducated users who do not understand that block cycle time alone is irrelevant in a CNC, as long as there are no advanced algorithms that take advantage of this extremely fast hardware.

Being Windows-based is another big selling feature. Basically, it is promoted most of the time to people that have a strong PC background but less of a CNC background. The advantage of Windows is that many people are familiar with it. However, typically people that run Windows, Windows NT or Windows for Work Groups, need an extra 486 processor just to run the Man-Machine-Interface (MMI). Some CNC vendors, for example, not only use a standard 486 or Pentium PC, but in addition, they have to mount a second PC motherboard into their control chassis. Otherwise, the operation of their machine is slowed down too much when running these Windows products.

Most PC-based CNC vendors offer a Windows platform, however, the ones with more CNC background offer alternative MMIs that are developed for real time CNC applications. Only the truly high-performance controls can run the MMI, multiple CNC tasks, multiple PLC tasks, and PC in real time on a standard486 or Pentium motherboard. These controls will set the standards for the future, because only they have the least expensive hardware concept possible. They do not need extra CPU boards, whether it is an additional PC motherboard or a DSP.

This extremely simple design has resulted in a strategic and conceptual advantage. They have "built-in" performance updates. For example, if Intel releases a new processor, these CNC vendors simply must get the newer and faster motherboards to make their CNC software run faster overnight. All the other vendors must redesign their hardware in order to upgrade their product's performance, and this takes at least five to six months to complete.

This concept has incredible upgrade possibilities in the field, because even an end user can put an axis board in a higher performance PC, load the software and double the performance of the original CNC control.

CNC kit or full featured CNC

More and more companies, especially the newer and smaller companies, offer their motion control boards as "open architecture" PC-based and/or Windows based CNC controls. They offer tools and libraries to write software. Their customers get excited because finally, they have their open architecture control, where they can do everything. However, sometimes, these customers get a rude awakening.

In addition to the ability to develop G-codes, look ahead functions, etc., it is actually a necessity to do this development work because many of these kits were never a complete, full featured, standard CNC control. Even the basic features need to be developed by the customer.

Theoretically, the most open architecture, PC-based CNC control would be a Pentium with a "C++" software complier. In this case, the user can change everything, but everything also must be created from scratch. Therefore, the customer should look at the CNC vendors very carefully to check their past experience with producing complete, full featured CNC controls.

Not every customer is able to develop a complete CNC control by using a CNC kit and starting from the drawing board. Even if users are able to develop two or three applications relatively easily and quickly, the decision to use the correct hardware/software platform is very critical for the long term usefulness of the CNC that they create.

If a user outgrows the capabilities of the CNC that he developed, he must throw it away and buy a new CNC, in order to add more advanced CNC features such as look ahead, advanced regulation algorithms, or real time transformations. Users must keep future requirements in mind when buying a PC-based CNC to satisfy today's needs.

Summary

"PC-based" is already another standard in CNC controls, in addition to the big and famous brands. It seems that there is a lot of advertising and talk about the capabilities of PC-based controls, although, I think that many of them are not yet as easy to implement as they claim. However, this is a young and growing market, and due to the demand for this type of product, it is guaranteed that by fall of 1996, every ChIC vendor will have at least some sort of PC-based CNC control available.

PC-based CNC controls can keep their promises, in terms of versatility, efficiency, serviceability and cost effectiveness. However, it is up to the CNC control user to discover what are the advantages and disadvantages of the various PC-based systems. Only then can a user discover what the advantages and disadvantages are of the various PC-based systems. Only then can a user select the best PC-based CNC for his needs.

Oliver Fuchs is an Application Engineer with IBH Automation Inc. of Illinois. He can be reached at [phone].