COMPLEX CAPABILITIES

Advanced programming functions allow the use of elements from high-level languages, such as loops, conditional statements, and branches. Other capabilities include, for example, tangential transition arcs, acceleration/deceleration ramps, and automatic tangential-axis functions. Data from PLC application programs are exchanged over a powerful interface, so users can even control program execution in real time. Thus, settings such as tool radius and end points of path sections can be changed while the program is being executed, because data are available synchronous to the path. Additional features include:

Dynamic functions. Influencing dynamic characteristics such as path speed, acceleration, and jerk is especially critical when using path control in certain cases. The Soft CNC's ability to change these characteristics during runtime or automatically adjust them according to the path curvature is essential for some applications.

The controls also include cutterdiameter compensation. Invalid intersections, notches, and peaks do not necessarily require a stop along the path. In fact, on a plasmacutting machine stops could heavily damage the workpiece. Instead, the Soft CNC automatically makes needed corrections according to user specifications.

Also, an integrated look-ahead ensures a consistently optimized path speed. This is especially important when a particular path would tend to have frequent acceleration changes and cause machine vibration.

Error compensation. Sometimes it is necessary to cheat physics a little in order to improve the process. Thus, it can be helpful to intentionally overshoot dynamic-axis limits. For example, cutting machines automatically align the cutting tool tangentially to the path. When a transition between two path elements creates too large an angle and the tool is moving too fast, the tool might not align quickly enough. To stay within preset limits, the path speed would have to be reduced but this would reduce the quality of the cut. Thus, it is better to overshoot the limit values for the tangential axis. The temporary position error has much less of an influence on cut quality than a speed reduction.

Correction functions. Typical examples include free rotation of a working plane in 3D space and skew correction for machine axes. The latter helps when it is mechanically impossible or considerably difficult to square the coordinate axes. The Soft CNC distorts the part program so the actual path matches the path in an ideally squared system.

The control also handles axiscorrection functions such as spindle pitch error and backlash compensation. These result in excellent path precision, even on machines that are mechanically less precise.

MORE THAN A CNC

All these functions are useful beyond the traditional CNC area because, in general, a CNC system offers advantages of better path precision and potentially higher path speeds due to built-in lookahead functions. Another advantage could be the programming interface. CNC programs that use ISO Standard G codes are rather simple, letting operators familiar with CNC terminology program robots without special training in vendorspecific programming languages.

The Soft CNC also has interfaces that let it identify the kinematic description of a mechanical structure: reverse and forward transformations. Forward transformation calculates position and orientation in space using the robot's joint angles; reverse transformation is the opposite, calculating joint angles based on position in space.

This lets engineers use the CNC system's advantages to control robots. For example, it can replace a simple series of straight lines with free-form curves, and the integrated look-ahead function ensures an optimal path speed. This architecture is especially suited for applications that need path precision as well as simple pointto-point movements.

The Soft CNC supports transformation functions for six-axis articulated-arm robots and Scara systems. Programming is the same as with CNCs; however, there are now six significant axes. X, Y, and Z define position in space, and A, B, and C define orientation (for example, as an Eularian angle). In the future, other languages should also be available for programming robot movements.

MAKE CONTACT:
B&R Industrial Automation Corp., br‑automation.com

The Soft CNC is embedded in the PLC's realtime operating system, meeting demands for complex machining and robotic handling tasks. This concept opens the door to innovative machine designs.

Using CNC systems to control robots offers advantages such as better path precision and higher speeds, due to built-in look-ahead functions. It can also simplify programming.