Reference loss (reference monitoring)

Notice

notice

Reference monitoring is currently possible only for the SERCOS drive type (see P-AXIS-00020). For all other drive types, the error message P-ERR-110548 is output when reference monitoring is activated.

Motivation

In most cases it is desirable to check whether an axis that was 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 may happen after a few years that the backup battery is exhausted and the absolute encoder supplies an incorrect position.

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

In both cases, this leads to an unexpected shift in the position supplied by the drive relative to the mechanical position of the axis. This may result in damage to the machine.

To prevent this, an option was devised to check whether an axis has lost its reference.

Operating principle

In reference monitoring, a signal generated in the drive controller indicates whether the axis is referenced. The signal is transferred via the cyclic process data to the CNC. There a check is made whether the expected state 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.

For an axis without absolute value encoder, the axis is referenced as soon as drive-controlled homing is completed successfully.

The CNC controller has the possibility to compare the reference signal supplied by the drive with the internally calculated expected reference signal and to output an error message in the event of deviations.

Parameterisation

The parameterisation basically defines transfer of the reference signal from the drive to the CNC.

The name of the cyclic process data item that transfers the reference signal must then 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 always configured automatically.

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

Activation/effect

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

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

Example

example

Parameterisation example 1

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

Parameterisation in the drive:

The reference signal must be assigned to the real-time control bit 1 in the drive. This takes place by assigned the value S-0-403 (status of actual value position) to the drive parameter S-0-305 (assign real-time status bit 1).

Axis parameters:

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

The real-time status bit 1 in the status word 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

Example

example

Parameterisation example 2

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

Parameterisation in the drive:

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

Axis parameters:

Since the reference signal is read from P-0-4078, the value "P-0-4078" must be entered in P-AXIS-00426.

The reference signal in P-0-4078 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