Speed Limit Detect, Look Ahead for velocity limit

General

This function generates a CNC status signal depending on the motion blocks and the current path velocity. It is mainly used for plasma cutting technology to deactivate distance control of the cutting head via the PLC if the speed drops below a certain limit. This occurs, for example

• when decelerating ahead of and
• accelerating after a corner.

Therefore, the critical positions in the motion segment (corner) are defined by a speed limit.

"Speed limit detect” status flag

The “speed limit detect” status flag to the PLC is set if the current path velocity is below the specified limit. The drop in path velocity results from:

• Reduction in velocity at block transition due to a kink in the path contour.
• Reduction of velocity due to override setting.
• Expected M function acknowledgement from PLC at block transition.
• Look-ahead reduces velocity because of inadequate block supply.

Zone

In addition the signal can be set in advance or cleared with a delay at a specified distance (time/distance).

• Advance: The expected velocity at block end undershoots the speed limit, for example due to a geometrical corner. The status flag is set in advance at the specified distance to the expected limit undershoot.
• Delay: The expected velocity at block start already undershoots the speed limit. The status flag is again cleared with a delay at the specified distance to the actual speed overshoot.

Clear

I.e. the status flag is reset when both of the following conditions are met:

• The current path velocity rises above the speed limit.
• The path position is outside the specified time and distance delay.