Specifying the workpiece surface (SET_POS, surface)

Calculating deviation

The deviation of the real workpiece surface from the specified command position (SET_POS) is determined in each cycle by the electronic probe. Deviation results from:

Deviation = motor encoder + sensor encoder - set position (SET_POS)

                     = actual workpiece surface position - set position (SET_POS)

To compensate for the workpiece surface deviation, the drive position is additionally moved by the calculated offset of the distance control:

Drive setpoint = programmed setpoint (PCS) + distance control offset

Specifying the ideal workpiece surface for distance control
Specifying the ideal workpiece surface for distance control
Block diagram of distance control
Block diagram of distance control

Selecting and deselecting via the NC program

The NC program activates and deactivates distance control and also freezes the current correction value. Example:

N10 Z[DIST_CTRL SET_POS=30] Set the position

Nxx Z[DIST_CTRL ON] Select

…

Nxx Z[DIST_CTRL OFF] Deselect

N999 M30

The complete CNC syntax is described in the Programming chapter.

Typical sequence

Typical sequence for activating distance control:

  1. The tool is replaced.
  2. X and Y axes move to machining position.
  3. Distance control is activated and the workpiece set position is set. The Z axis must then be located within the detection range of the distance sensor.
  4. Sensor or probe ring signals distance; distance control corrects height errors.
  5. Z axis is lowered.
  6. Distance control is active; thickness tolerances or position differences are compensated.

Deactivating distance control:

  1. Distance control is deactivated via the NC program
  2. Distance control is inactive; thickness tolerances or position differences are no longer compensated; and the current offset remains active until the next position request.

Operating principle

With distance control, deviations in the position of the workpiece surface (actual position) can be corrected with respect to a specified set position:

Ideal workpiece
Ideal workpiece

Deviation

A deviation from the ideal workpiece surface (e.g. with a thinner workpiece) is detected by the sensor (encoder 2):

Real workpiece without distance control
Real workpiece without distance control

Offset compensation

After activation of distance control with SET_POS=20 mm (expected workpiece height), the offset is compensated by distance control. As a result, there is no need to adapt the NC program (PCS position). The NC program assumes a constant workpiece surface of Z=20 mm.

Real workpiece with distance control
Real workpiece with distance control

Notice

notice

Distance control is automatically deactivated if an axis error or a CNC reset occurs.

At program end, distance control remains active.

Constant workpiece surface with changed tool distance
Constant workpiece surface with changed tool distance

Height changes

Changes in the workpiece surface are compensated by distance control. The NC program therefore assumes a plane workpiece. Height changes in the workpiece surface can be defined by programming the axis. At Z=SET_POS the TCP tip touches the workpiece surface.