CNC fundamentals

As its name suggests, the NC interpreter interprets the NC program, analyzing its syntax and converting the information into an internal format. For each positioning block, it forwards the position of the contour corners, the required type of movement (linear or circular), and the associated feed rate to the geometry data processor. The interpreter forwards other switching functions, tool calls, etc. directly to the PLC. The control synchronizes the resulting commands with the geometry data. For example, a tool change will only take place after the control has completed the previous geometry block.

• Functions:
• Velocity feedforward control
• Geometric transformations
• Compensation calculations

The velocity feedforward control makes adjustments to speed and acceleration, taking the geometry and dynamics of the axis drives into account.

Geometric transformations include datum shifts, rotations, and mirroring. The geometry data processor calculates the positions to be approached, taking these transformations into account.

In addition, the geometry data processor accounts for any compensations, such as tool length compensation or tool radius compensation. If you programmed a tool radius compensation (RL or RR), the current tool data is used to calculate offsets to the programmed contour.

The interpolator calculates so-called intermediate points for a contour section specified in the NC program. Thus, the contour movement, resulting from the simultaneous movement of multiple axes, is subdivided into sections for each individual axis. This means that each axis can change its position independently of the other axes.

• Interpolation types:
• Straight interpolation
• Circular interpolation
• Spline interpolation

• In order to avoid geometric deviations at the workpiece, the interpolator compensates external effects as well as static and dynamic shifts.
• Temperature compensation
• Compensation of geometry errors

• The geometry data processor sends the following values to the feed drive units:
• Nominal position values
• Nominal velocity values
• Nominal current values

These nominal values are adopted as command variables in the corresponding control loops.