The latest release of NUM’s Flexium+ 3D simulation software includes algorithms for the RTCP function to support advanced 5-axis machining applications.

Two-Channel CNC Kernel for Cost-Effective Control

Sept. 18, 2014
Control flexibility lowers cost of complex synchronization for MTM systems U.S. debut for Flexium+ 8 Rotation Around Tool Center Point function Simulation with five-axes kinematic equations

Designed for developers of small to medium-sized machine tools with four or five axes, the Flexium+ 8 CNC provides machine operators with a cost-effective control solution that in many cases eliminates the need for a second CNC kernel. NUM introduced the technology to the U.S. market at IMTS, where it also launched a new version of its 3D simulation software -- now including kinematic equations to support advanced five-axis machining applications.

The Flexium+ 8 CNC kernel offers two CNC channels and accommodates up to five axes, four of which may be interpolated. At any time, either CNC channel may be used to control a spindle motor and four axes, instead of the full complement of five axes.

This control flexibility helps machine designers to lower the cost of machines with complex synchronization requirements. For example, on a grinding machine, one channel could control two X/Z axes and a spindle to perform the grinding functions while the other channel controls two rear mounted U/W dressing axes.

Each channel can run either its own part program asynchronously and operate autonomously (as if it had a dedicated CNC kernel), or the two channels can be synchronized. Control of one to five axes, or a spindle, can be passed on-the-fly from one channel to the other, to maximize use of available hardware resources.

Flexium+ 8 firmware (and all NUM CNC systems) includes “rotation around tool center point” (RTCP) and Inclined Plane functions. Pioneered by NUM, the RTCP function provides advantages for precision five-axes machining applications. By very accurately controlling the machine’s rotary axes, such as a dual rotary tool-head or a table and cradle holding the part, the function enables the tool to be held in contact with the part, and at a constant angle, throughout the machining process.

RTCP also is beneficial if the part is not flat; it automatically computes all the offsets due to factors such as tool head mechanics and tool length that are needed to maintain accurate tool contact.

As its name implies, the reference point for all RTCP calculations is the tool’s center, or contact point, not the tool-head position, which would require the contact point to be determined mechanically. The difference between these two methods has a major impact on machining.

For example, if the distance between the tool tip and the center of the rotary head is 600 mm, a head positioning error of just one-hundredth of a degree will cause a tool tip error of 0.1 mm. Without the RTCP function, this may result in tool or part damage.

Another advantage of the RTCP function is that the programmed coordinates are those of the part contour, not the machine, which makes the programs machine-independent, and means that tool offsets can be applied without program modification. The RTCP function is implemented as part of the Flexium+ CNC post-processor, which further helps to ensure part program portability.

NUM recently integrated the complex coordinate transformation algorithms of the RTCP function into its Flexium+ 3D simulation software. Users can now analyze and optimize the kinematic performance of part programs for four- and five-axis machines easily and accurately by employing advanced 3D visualization techniques. The software includes comprehensive collision monitoring and detection to guard against tool, part or machine damage.

Integrated or Standalone Simulation

For maximum flexibility, NUM offers two versions of Flexium+ 3D simulation software. One is designed for standalone use without a CNC system, as a production planning tool for verifying part programs. The other is fully integrated with the Flexium+ HMI (human machine interface) and is connected to the machine’s CNC system.

NUM’s Flexium+ 3D simulator visualizes the TCP path and simulates workpiece material removal, while checking constantly for collisions between the tool, workpiece, and machine.

Unlike many CAD/CAM visualization systems, this uses the NC code that is being processed by the CNC interpolator to create a true real-time representation of machine operation. Part programs can be simulated at the same time that other programs are being executed on the machine, and the same part program can be executed and simulated simultaneously. The simulator visualizes the tools, the machine’s kinematic properties and the workpiece blank as 3D volumes, and shows the TCP (tool center point) and material removal as the tool moves along the machining path defined by the part program.

The Flexium+ 8 CNC kernel can be used with various NUM drives. For optimal performance it is best teamed with the latest NUMDrive X digital servo drive modules. These are some of the smallest drives on the market and offer numerous configuration options to help designers minimize machine build costs through use of axis-appropriate technology. The drives use advanced DSP control techniques to maximize the CNC kernel-to-drive servo bus speed, and feature high loop bandwidths and special acceleration algorithms for uncompromised speed and positioning accuracy. A numerical processor in the CNC kernel, together with the precision number-handling capabilities of Flexium+ software, helps to ensure a high overall CNC resolution and facilitates ‘sub nano’ interpolation between axes.

Flexium+ 8 also features an inherently scalable safety architecture known as NUMSafe. A safety PLC built into the CNC system oversees all critical operations; in conjunction with NUM’s safe I/O modules and the safe motion monitoring circuits in NUMDrive X servo drives, this enables machine designers to implement high-integrity safety functions using minimal additional components. The safety architecture complies with the EN ISO 13849-1 machinery safety standard up to PL e, as well as the EN 61800-5-2 functional safety standard for variable speed drives, up to SIL 3.

NUM’s Flexium+ CNC platform now includes three CNC kernels that machine designers can use to configure cost- and performance-optimized control systems for automation:  Flexium+ 6, Flexium+ 8, and the Flexium+ 68. Flexium+ 6 has a single CNC channel, can control four interpolated axes and a spindle, and is designed for small to medium size machines. Flexium+ 68 is designed for larger and more complex machine control applications. Offering up to eight CNC channels, each accommodating up to nine interpolated axes and as many as 32 spindles, it provides a foundation for multi-spindle applications, such as transfer machines.

The Flexium+ platform is backed by custom software. All CNC, servo drive, I/O, automation PLC and safety PLC functions are programmed using a single unified toolset. A fully customizable HMI allows users to add value to their machines, through improved ergonomics and touch-sensitive controls. NUM’s application support software covers a broad range of machining functions such as grinding, tool grinding, turning, milling, gear hobbing, shaping and finishing, as well as water-jet, laser and plasma cutting.