SERCOS axis

Homing for SERCOS

SERCOS axes can be reference with the following methods:

(The homing type executed is defined in the axis parameter P-AXIS-00299 (homing_type).)

• Drive-controlled (default)
  In this case, only P-AXIS-00014 (abs_pos_gueltig) and P-AXIS-00015 (achs_mode) need be parameterised as CNC parameters. The homing sequence must be set in the drive
• CNC-controlled with zero pulse latch.
• CNC-controlled with zero pulse latch via probing input
• CNC-controlled at encoder overflow.

Drive-controlled homing

Drive-controlled homing is the default setting for SERCOS axes.

In drive-controlled homing, the CNC starts the SERCOS command S-0-148 in the drive and waits for the drive to acknowledge it. After acknowledgement, the CNC adopts the drive command values as CNC-internal command values.

The homing sequence and the drive reference position are completely parameterised in the drive.

The reference cam must be connected to the drive.

This homing type is set by assigning the value ‘DRIVE_CONTROLLED’ to the axis parameter P-AXIS-00299 (homing_type).

No drive-controlled homing is possible for SERCOS axes whose position control is executed in the controller.

CNC-controlled with zero pulse latch via S-0-146

With CNC-controlled homing, all the sequence variants described in the section Sequence strategies for homing are available.

The zero pulse search is performed by executing the SERCOS command S-0-146 in the drive. After the zero pulse is detected in the drive, the actual position is switched over to the reference position in the drive and the CNC adopts this position.

The reference position is set by the axis parameter P-AXIS-00152 (pos_refpkt). This value is transferred to the drive at the start of homing

This homing type is set by assigning the value ‘CNC_CONTROLLED’ to the axis parameter P-AXIS-00299 (homing_type).

The value 0 must be assigned to the axis parameter P-AXIS-00299) (homing_without_zero_pulse); the parameter P-AXIS-00386 (drive_supports_cnc_homing) activates use of the drive-internal zero pulse latch.

For the zero pulse search sequence, the encoder used to perform homing must be entered in the parameter P-AXIS-00388 (cnc_homing_encoder).

In addition, control and status information must be transferred between the drive and the CNC to control the homing sequence. This can be performed either by using the real-time bits in the control or status word of the drive or by signal, control and status worlds. The axis parameter P-AXIS-00387 (cnc_homing_rt_bit_layout) sets how these bits are transferred. Control and status bits must also be assigned in the drive to match the set value of P-AXIS-00387. If the signal control and status words are used, they must be configured in the cyclic process data.

The reference cam is evaluated in the CNC. It can either be transferred to the CNC via the HLI or via the real-time status bit of the status word, see P-AXIS-00321 (reference_cam_signal).

The section SERCOS with zero pulse latch with S-0-146 contains a parameterisation example.

CNC-controlled with manufacturer-specific zero pulse latch AX5000

For AX5000 drives from Beckhoff, a zero pulse latch can be executed by using the drive-internal latch logic without using the command S-0-146. The latched zero pulse is then transferred as measured value to the CNC: The CNC must then be parameterised for measuring with a SERCOS drive (see function description [FCT-C4]); in addition the occurrence of the zero pulse must be configured in the drive latch event. The CNC must be notified of the real-time control and real-time status bit used in the parameter kenngr.echtzeit_bit_nr (P-AXIS-00060). Please refer to the manufacturer’s documentation for information on drive parameterisation.

With CNC-controlled homing, all the sequence variants described in the section Sequence strategies for homing are available.

The reference position is set by the axis parameter P-AXIS-00152 (pos_refpkt).

This homing type is set by assigning the value ‘CNC_CONTROLLED’ to the axis parameter P-AXIS-00299 (homing_type).

The value 0 must be assigned to the axis parameter P-AXIS-00299) (homing_without_zero_pulse).

CNC-controlled at encoder overflow

If the encoder used in the drive supplies an absolute position during a motor revolution (this means the encoder position does not change when the drive is switched off and back on), the encoder overflow can be used for referencing instead of the zero pulse

The encoder can then mask and check a settable number of position value bits when this position overflows. This encoder overflow uniquely marks a mechanical motor position during a motor revolution and can then be used for referencing.

With CNC-controlled homing, all the sequence variants described in the section Sequence strategies for homing are available.

This homing type is activated by setting the axis parameter P-AXIS-00294 (homing_overflow_evaluation) to 1. In addition set P-AXIS-00084 (homing_without_zero_pulse) to 0.

The number of bits of the actual value position transferred by the drive and used to calculate overflow must be entered in axis parameter P-AXIS-00355 (encoder_bit_range).

The axis parameter P-AXIS-00354 (encoder_overflow_offset) can shift the position of encoder overflow during a motor revolution.

The reference position is set by the axis parameter P-AXIS-00152 (pos_refpkt).

Notice

This referencing type only supplies reproducible results if the encoder used supplies an absolute position during a motor revolution. This means that, after the drive is switched off and on, the encoder position supplied by the drive must be identical if the mechanical motor position is identical. If in doubt, please refer to the drive documentation or contact the drive manufacturer.