CNC System Becomes Easier to Maintain and Expand by Converting to the TenAsys INtime RTOS for Windows

The Burny Phantom, a PC-based numeric control system (CNC) developed by Cleveland Motion Controls (CMC) of Cleveland, OH, is a fully integrated package featuring real-time coordinated multi-axis motion control and a Windows-based operator’s console.

The Phantom CNC manages extremely precise and repeatable motion control and supports many features not found in other numeric control systems, without requiring expensive add-in cards or a secondary motion control platform. The entire system runs on a PC-compatible single-board computer designed for operation in extreme and harsh environments.

Two virtual machines

The single-board computer simultaneously supports Microsoft Windows XP Embedded and the INtime RTOS by TenAsys, on a Pentium M mobile processor. Using this arrangement, CMC is able to host two virtual computers on a single hardware platform, resulting in a very high level of integration for both software and hardware components.

The CNC is programmed by end-users with a built-in soft PLC using a touch-screen interface. The soft PLC is an IEC 61131-compatible Windows application of CMC’s own design that can be programmed with ladder logic and can interpret standard "M" and "G" code CNC programs. The soft PLC provides target position set points to the real-time motion software and manages non-real-time operations directly. A shared memory interface common to the Windows and INtime virtual machines is used to pass information and commands between the Soft PLC and the time-critical motion control software that runs simultaneously on the INtime RTOS.

Windows flexibility combined with hard real-time control

CNC machines are members of a class of sophisticated embedded systems that require a time-critical and reliable machine control component and a sophisticated human interface component – two competing requirements that drove CMC to find a means to combine Windows with a real-time operating system. The flexibility of the Windows platform combined with the determinism of the INtime RTOS equals a platform that CMC can use to build a CNC that can control any cutting machine, with interfaces for virtually all cutting processes including: oxyfuel, plasma, laser, waterjet, routers, punches, drills, knives, and markers.

CMC real-time software running on the INtime RTOS provides position control of the CNC drives and directly implements multi-axis motion coordination. Depending on the motion hardware employed by the CNC system, the INtime real-time system hosts one of two motion control loops. It can host a one-millisecond loop for conventional analog drives (where velocity is deduced from position feedback) or a two-millisecond loop that controls SERCOS drives (a high-level digital motion control interface). Auxiliary I/O, such as limit switches and general-purpose I/O points, is also managed by INtime real-time applications.

Moved from the old to the new in a day

The Phantom, in production for five years, was upgraded to the INtime RTOS from a competing real-time Windows system. The old system didn’t provide CMC with the level of sophistication in multi-process operation and debugging capabilities they required to move the product forward.

The conversion to the INtime platform went quickly and easily for CMC. "With direct help from TenAsys engineering, we had the conversion substantially complete in one day," said Dan Dailey, CMC lead engineer. "That gave us confidence that moving to INtime from the old platform would not be a problem."

Run-time security and development simplicity

INtime applications run in protection ring three (user mode) on Intel Architecture processors rather than ring zero (supervisor mode) as do other real-time operating systems. If one real-time process should fail it can be safely halted or aborted without stopping the rest of the system. This provides a high degree of safety to INtime-based systems and simplifies identifying faulty applications.

Another advantage of the INtime RTOS for CMC is that real-time applications are developed and debugged directly within the Microsoft Visual Studio development environment, just as they do for their Windows applications. Using a single development environment, including source code debugger, for real-time and non real-time portions of the Phantom system greatly shortened the time required to port the code from the old system to INtime. It also significantly reduced the time required to get both real-time and non-real-time portions of the Phantom machine working together smoothly.

Future platforms for enhanced performance

By having the real-time and Windows environments tightly linked, CMC has a growth path to add new features in future iterations of their CNC products. For example, CMC is considering porting the soft PLC run-time engine to execute on the INtime kernel in order to increase system throughput.

Currently, the Phantom's industrial PC uses a single-core Intel processor, but the company is looking forward to moving the system to a multi-core implementation. This would add further performance enhancements by taking advantage of TenAsys’ support for running the INtime real-time environment and Windows on separate processor cores.