Measurement run to fixed stop

Detection of fixed stop

When measuring by motion to a fixed stop, the measuring event used is the detection of a mechanical stop against which the measuring axis moves.

Several criteria, also combined, can be used to detect the fixed stop:

• Overshooting a predefined position lag during the measurement movement.
• Undershooting a minimum actual speed of the axis during the measurement movement.

Default setting

When a measurement run is executed with Move to a fixed stop, torque limitation must be activated in all drives involved and any drive-based position lag error monitor must be disabled.

Measurement on the path

The measurement run ends as soon as the fixed stop is detected in one of the axes involved in the measurement run.

Process

When measuring by Move to a fixed stop, an axis motion is automatically generated after the fixed stop is detected, during which the axes involved in the measurement run are moved to the latched measuring position in each case. This relieves mechanical stresses accumulated when the axis is pressed against the fixed stop.

Measurement with gantry axes

With gantry systems (soft and hard gantry), the master axis is always used for measuring. During the measurement run, the slave axes also move. For this reason, torque limitation must also be activated and position lag monitoring disabled for Move to a fixed stop in slave axis drives.

As of CNC Build V3.1.3121.0 a search can also be made for a fixed stop on gantry slave axes. This is dependent on whether P-AXIS-00835 is set in the master axis.

The parameters for detecting the fixed stop can be set separately for each axis. It is advisable to select the same parameters for detecting the fixed stop for the slave and master axes.

On TwinCAT systems, torque limitation or position lag monitoring disable in the drives can be alternatively enabled in the PLC (via ADS) instead of the NC program (#IDENT...).

Channel parameters

The following entries must be assigned in the channel parameter list:

Select measurement type in the NC program

Alternatively, the measurement type can be changed in the NC program by the command #MEAS MODE[7].

Parameterisation of fixed stop detection

Several criteria, also combined, can be used to detect the fixed stop:

• Overshooting a predefined position lag during the measurement movement.
• Undershooting a minimum actual speed of the axis during the measurement movement.

The active criteria in each case must be fulfilled for a certain period before the fixed stop is considered to be detected.

In addition, a minimum path distance can be specified until fixed stop detection is activated in the measurement motion block. This can be specified as an absolute value or as a percentage based on the length of the measurement motion block.

If the minimum path distance is specified both as an absolute value and as a percentage, the smaller of the two values is used to activate fixed stop detection.

The minimum value of all axes is used for activation in the case of a measurement run with several axes.

By default, fixed stop detection is activated immediately at the beginning of the block.

Axis parameter

The following entries must be assigned in the axis parameter lists:

Sequence of measurement run

Measurement by Move to a fixed stop can be illustrated by the example of SERCOS drives as shown in the sequence below.