Homing modes

Overview

Axes without an absolute encoder can use the homing function to restore the position to a previously defined location.

This can be done with a limit switch or at the current location.

CiA 402 profile specification: IEC61800-7-201 defines different homing methods, SOMANET supports methods 33, 34, 35 and 37.

Homing method 33/34

Methods 33 and 34 (move to next or previous single-turn position, or “index pulse”) can be used to center on the sensor’s reference position (in positive or negative direction).

The shaft will rotate less than one rotation.

Homing method 35/37

Methods 35 and 37 (zero the current position) are used to define the current position as home position.

Note

Homing method 35/37 can be performed in any operational state. All other homing methods require the drive to be in “operation enabled” state.

Use case: Homing on current position while operation is not enabled

If the axis is moved to a desired homing position by external force (for example manually), Homing Mode 35/37 can be used to determine the current position as home.

Use case: Relative position command

The current position can be taken as the reference point.

Use case: Homing on current position

When the motor is moved to the desired position in CSP the position can be taken as homing position.

Settings for homing mode

Homing method

You can select the desired homing method in object 0x6098: Homing Method.

Value Description Remark
0 No homing method assigned. This is the default value.
33 Homing on negative index pulse.  
34 Homing on positive index pulse.  
35 Homing on current position. Methods 35 and 37 are identical.
37 Homing on current position Methods 35 and 37 are identical.

Homing speeds

Two homing speeds must be selected in object 0x6099: Homing Speed: in a typical cycle, the faster speed is used to find the home switch and the slower speed is used to find the index pulse.

Note

Homing speeds are not required in method 35/37.

Homing acceleration

In object 0x609A: Homing Acceleration a value for acceleration during homing must be defined.

Note

An acceleration is not needed in method 35/37.

How to perform homing

The following diagram shows the steps that are necessary to perform the homing function.

../../../../../../_images/perform_homing.png

After the home position is found, the position controller stays active, holding the motor at that position (except for method 35/37).

Communications

Inputs

  • Object 0x60FD (Digital inputs) reports the state of the digital inputs which can be configured for limit switches, interlock, etc.

Status of the homing process

Bits 10, 12, 13 of the Statusword (0x6041) are used to indicate the current state of the homing process:

  • Bit 13: Homing error
  • Bit 12: Homing attained
  • Bit 10: Target reached

Objects used

Specifies the homing method that shall be used.

Offset from user’s zero position to the home position.

Speed with which to move during homing.

Acceleration used during homing.

Set bit 8 to 0 and bit 4 to 1 to start homing.

Indicates the current state of the homing process.

Array of supported homing methods.