Reference loss (reference monitoring)

Reference loss (reference monitoring) 1:

Reference monitoring is currently possible only for the SERCOS drive type (see P-AXIS-00020removed link: P-AXIS-00020). In the case of all other drive types, the error message P-ERR-110458 is issued when reference monitoring is activated.

Motivation

In some cases it is desirable to check whether an axis that has been referenced once has lost its reference.

For example, when absolute encoders are used that store internal working data in a memory with battery backup, it can happen after a few years that the backup battery is exhausted, and the absolute encoder returns an incorrect position.

Equally, when drive amplifiers are parameterized and decisive parameters are altered, it can happen that an already referenced axis loses its reference again.

In both cases, this leads to an unexpected shifting of the position returned by the drive in comparison with the mechanical position of the axis, which may lead to damaging of the machine.

To prevent this, a possibility has been created of checking whether an axis has lost its reference.

Principle of operation

In the case of reference monitoring, a signal generated in the drive controller that indicates whether the respective axis is referenced is transferred via the cyclic process data to the CNC and a check is made there as to whether the expected status of this signal is correct. This 'axis is referenced' signal is referred to below as the reference signal.

For example, for an absolute value encoder the axis is referenced immediately after the start of cyclic data transfer.

In the case of an axis without an absolute value encoder, the axis is referenced as soon as a drive-controlled reference point travel operation has been completed successfully.

The CNC controller has a possibility of comparing the reference signal returned by the drive with the internally calculated, expected reference signal and of issuing an error message in the event of discrepancies.

Parameter definition

The parameterization essential defines transfer of the reference signal from the drive to the CNC.

To this end, the name of the cyclic process data item that transfers the reference signal must be specified in the axis parameter P-AXIS-00426.

If the reference signal is transferred in one of the real-time status bits of the SERCOS status word, the value "S-0-0135" must be entered in P-AXIS-00426. The signal status word need not be explicitly configured in the input process data because it is automatically always configured.

If the name configured in P-AXIS-00426has not been found in the cyclic input process data, the error message P-ERR-70401is issued and reference monitoring is deactivated.

Activation/ effect

Reference checking is activated as soon as valid values have been configured for the axis parameters P-AXIS-00425 and P-AXIS-00426.

When reference checking is active, the error message P-ERR-70400 is issued as soon as the CNC detects a discrepancy between the reference signal returned by the drive and the CNC's internal reference signal.

Parameter definition Example 1

A reference check is to be implemented for a SERCOS drive. The reference signal should be transferred via the real-time status bit 1.

Parameter definition in the drive:

In the drive, the reference signal must be assigned to the real-time status bit 1; this is done by assigning the value S-0-403 (actual position value status) to the drive parameter S-0-305 (assignment of real-time status bit 1).

Axis parameters:

As the reference signal is read out of the real-time status bit of the status word, the value "S-0-0135" must be entered in P-AXIS-00426.

In the status word, the real-time status bit 1 is the bit with the number 6 (counted from 0) and so the value 6 must be entered in P-AXIS-00425

antr.homing_check.element_name       S-0-0135
antr.homing_check.bit_nr             6

Parameter definition Example 2

A reference check is to be implemented for a SERCOS drive. The reference signal is to be transferred via bit 2 of the drive parameter P-0-4078.

Parameter definition in the drive:

The parameter P-0-4078 must be configured in the drive's cyclic process data.

Axis parameters:

As the reference signal is read out of P-0-4078, the value "P-0-4078" must be entered in P-AXIS-00426.

In P-0-4078, the reference signal is the bit with the number 2 (counted from 0) and so the value 2 must be entered in P-AXIS-00425

antr.sercos.at[1].ident_nr 36846 
antr.sercos.at[1].ident_len 2 
antr.sercos.at[1].nc_ref P-0-4078 
antr.homing_check.element_name P-0-4078 
antr.homing_check.bit_nr 2