In keeping with the trend toward PCs, the MTC200 control from Indramat can be tailored to milling, turning, grinding, or other machining functions by plugging in cards for CNC, PLC, human-machine interface, and input and output modules. It can handle up to 32 machine axes with up to seven independent processors.

A device that is still operating after ten years used to be something to brag about. This is no longer true for the industrial control. Be it a PC, PLC, or CNC, a control that old most likely can't communicate to a high-level manufacturing network. It certainly can't use the latest Windows-based software. It requires a specialist to upgrade. And it's still using old computing architectures and motion algorithms.

More controls are in this aged state then you might think; research firms put the number at about 60% of the world's CNCs. Until recently, the incentive to move to newer controls was small. But the influences of the Open Modular Architecture Control (OMAC) concept demanded by General Motors, the explosion of the Internet and intranets, and the requirement to access production and performance data from every device on the factory floor have given OEMs and end users reason to change.

From isolated island to on-line peripheral

Every controller has data on the operation of the device it directs. Because more than 95% of all CNCs are proprietary, however, engineers could not access the data without the control manufacturer's help. Obtaining different data meant returning to the control manufacturer to gain access.

To reduce this dependence on the manufacturer, one solution is to replace the old controls with something a bit more open. There are three options, each offering different degrees of openness. The two PC-based solutions have little effect on how motion is controlled. The software solution brings changes.

Engineers can keep the traditional CNC and add a PC to it to function as the front-end device. The CNC continues to run the machine and handle all motion control without any change. The personal computer, however, gives engineers access to Windows-based applications and third-party software for such functions as statistical process control, tool management, and interaction with manufacturing execution systems. Another advantage is that all such controls have common screen displays.

Using large scale integration and surface mount technology, GE Fanuc eliminated the entire control logic rack and created CNCs that fit on a printed circuit board. The board can be installed on the back of a flat panel LCD display, making the entire control smaller than a laptop PC.

Access to machine data, however, is still limited unless efforts are taken to integrate the two controls. In addition, upgrades will be restricted to those doable on the personal computer. The machine tool supplier must handle CNC upgrades.

The next option is to replace the CNC with a PC and a motion card. Here, the motion card is really the machine control reduced to the size of a board. It either fits inside a personal computer or is placed near the drive component and connected to the personal computer through cables. The motion card uses fast, powerful 32-bit microprocessors, typically has one or more DSP chips on board, and a lot more memory. Motion control is relatively unchanged. The motion program is written on the PC, but the machine control handles all the number crunching and closes the servo loop.

Access to machine data is better because processors on the motion card are compatible with the personal computer's operating system. Also, the two controls share the same backplane or, in the case of the separate motion card, use standard interface drivers. Through the PC, the machine tool can connect to manufacturing networks to send data to corporate measurement and analysis systems.

Depending on the control manufacturer, initial investment with this configuration is less than traditional machine controls. Life cycle costs are also low and reconfiguration is easier because you don't need to purchase a new control every time an application needs different or additional features. In most PC-based systems, such features are often available as software or plug-in boards.

A disadvantage, however, is that some installations may require special skills available only from that manufacturer. Also, you may be limited to the manufacturer's stock for replacement or upgrades of the motion card.

Rethinking control

The most recent option is to use a PC and eliminate the motion card as well as its cost. Using a software operating system that duplicates the functions of a CNC, the personal computer handles the motion calculations, sends signals to the drives, receives data from the various interface cards and input and output modules, sends data back, and performs the other usual control functions.

However several manufacturers dispute the potential savings from eliminating the motion card. As they point out, the cost of one or more motion processors is small compared to the cost of the interface devices on the machine tool.

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