Controlling interest

When it comes to machine tool control, manufacturers are increasingly taking the soft option. Rob Coppinger finds out why

A machine tool is an expensive investment, but it is useless without the controller, the interface through which the operator tells the machine what to do.

For many years, the operation of machine tools has been dominated by the numerical control (NC) system, with its ‘g-code’ programming language. Too often, however, this system offered more capability than most users required, with little in the way of user-friendliness.

Now, after a long period in which there have been few developments, machine tool control is beginning to undergo changes as rapid as the fast- moving personal computer market, and the pre-eminence of NC programming is being challenged. It is being recognised that what machine tool users really want is a control system that is easy to use, reliable, and capable of continuous cutting operations, rather than waiting around while blocks of CAD/CAM data are processed.

Recent advances in electronics and display technology are making possible a new generation of easy-to-use interfaces which promise to bring machine tool programming within the grasp of setters and operators with little or no prior programming experience.

But the biggest developments are being driven by PC-based ‘soft logic’ controllers. Though these have been around for some time in other industries, in recent years PC-based control has emerged for machine tools as an add-on to the typical NC controller. The features on offer are expanding and it will not be long before the internet arrives on the shopfloor.

At its most basic, the advantage of PC-based systems is an improved graphical interface using an operating system such as Windows, with a colour display rather than the NC controller’s more usual green on black.

These Windows-based front-enddisplays offer icon-driven control,making use of symbols on a touch-sensitive screen to represent complex NC commands. In addition, graphical programming allows representations of a part’s geometry to be combined to model the shape to be machined.

The complicated process of entering part dimensions is greatly simplified, helping to limit data entry errors. Networking the machine to the design engineer’s PC allows CAD data to be downloaded directly. In addition, the control software allows simulated machining to ensure that the machine has the correct data.

The PC does not have to be theconventional box and screen sitting to one side of the milling or grinding machine. The software can be combined with a hard drive on a printed circuit board. As Patrick McNally, business development manager at Mitsubishi, says: ‘Often this is all built into a PC card. The card can be slotted in to replace an NC device’s graphics card, giving a customised PC display.’ In the US, where PC-based control has taken off in a big way due to the low cost of PC components, companies are not stopping at offering better interfaces. The latest idea is the ‘total soft solution’. Here, software directly operates the machine tool’s servo motors, which move the cutting head.

Beyond that, the next big development will be arrival of the internet on the shopfloor. Providers of PC controlsystems promise the development of remote monitoring, diagnostics, control and other internet-related features. A single machine or a complete local area network will be controlled from a single PC, providing the facility for up and downloading programmes between the remote PC and the machine tool. This development will be particularly useful if engineers want machine tool suppliers to assist in solving programming problems or to give advice on diagnostic interpretation.

The data from the machine tool could be monitored remotely using diagnostic software, eliminating the need for machine tool suppliers’ to send technicians to the site in the event of a breakdown. Servicing costs and wasted travel time will be reduced considerably.

Using a customisable front-end may not necessitate a great deal of new training either. PC systems can be used with an NC emulator, giving the user the ability to switch to a traditional NCdisplay and back, providing flexibility and reducing any period of changeover between the old and the new.A product with features such as these is supplied by GE Fanuc. Known as Open CNC, it features a touch-sensitive panel and a Windows 95 compatible keyboard, while the microprocessor at the heart of the system is an Intel Pentium – normally found in domestic PCs. A modem can also be attached for remote monitoring.

Martin Vaughan, application engineering manager at GE Fanuc, says: ‘The customer can use a customised front-end for certain specialist machines. With software tools supplied by us, the machine tool builder will be able to design and make thedisplay interface to the customer’s exact specifications.’ Despite all this, in the UK, PC-based control has not become as prevalent as in the US. NC control is still preferred by the UK machine tool industry,primarily because NC is seen as more stable and the manufacturers are cautious about how reliable software such as Windows is. Customers want a cast iron guarantee of surviving a Windows crash or a hard disk failure.

Another drawback of PC control, pointed to by controller manufacturers, is the susceptibility of PC cards with hard drives to vibration. Where PC cards are built into the existing machine tool control system, vibration can hinder the ability of the hard drive to read and write to itself.

Solutions are being developed. Crash-resistant Windows systems and PCs with NC built in are now on offer. Mitsubishi’s InTime system and itsMeldasmagic 64 are two examples.

InTime uses Windows NT, the software for PC networks, and has been designed to designate machine toolcontrol as the highest system priority to protect it from potential failures in other Windows NT-based applications.

Meldasmagic 64, which has an NC card built into a Windows 95 PC, uses CAD/CAM software and customised screens. The company claims it achieves the flexibility of a PC with the reliability and familiarity that engineers have with their NC systems.

As for machine vibration, this problem has been solved by manufacturers using solid-state hard drives. Other problems are more difficult to overcome. One is the nature of the PC industry, where technology moves on so quickly that parts for machines can become obsolete very quickly. While processors could become outdated within a year, the expense of machine tool upgrades means they can onlyhappen over periods of years.

Another drawback of PCs is that components can be stolen from them. Just as corporations have suffered computer chip theft from their offices, machine-based PC’s can also havecomponent parts removed. This has happened already. So NC control,perhaps unsurprisingly, remains a favourite for now. But despite the issues with PC-based control, advantages do exist for those who recognise the benefits for their machining operations.

The NC versus PC debate among machine tool builders and control system suppliers may not be over in the UK, but the increasing reliability of software, the speed and processing power of off-the-shelf computer chips and the new options of remote control and diagnostics are perhaps reasons for engineering managers everywhere to reconsider the soft control option