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Rockwell Automation Publication 2080-UM002L-EN-E - November 2021
Chapter 7 Motion Control
Scenario 4: Moving part at left (negative) side of Lower Limit switch before homing starts
In this case, the homing motion fails and moves continuously to the left until
drive or moving part fails to move. User needs to make sure the moving part at
the proper location before homing starts.
MC_HOME_LIMIT_SWITCH
For Homing against Lower Limit switch, one positive home offset can be
configured; for Homing against Upper Limit switch, one negative home offset
can be configured.
MC_HOME_LIMIT_SWITCH (1) homing procedure performs a homing
operation against Limit switch. The actual motion sequence is dependent on
the limit switch configuration and the actual status for the switch before
homing starts—that is, when the MC_Home function block is issued.
Scenario 1: Moving part at right (positive) side of Lower Limit switch before homing starts
The homing motion sequence for this scenario is as follows:
1. Moving part moves to its left side (in negative direction);
2. When Lower Limit switch is detected, the moving part decelerates to
stop, or stops immediately, according to Limit Switch Hard Stop
configuration;
3. Moving part moves back (in positive direction) in creep velocity to detect
Lower Limit switch On
→
Off edge;
4. Once Lower Limit switch On
→
Off edge is detected, record the position as
mechanical home position, and decelerate to stop;
5. Move to the configured home position. The mechanical home position
recorded during moving back sequence, plus the home offset configured
for the axis through the Connected Components Workbench software.
Scenario 2: Moving part on Lower Limit switch before homing starts
The homing motion sequence for this scenario is as follows:
1. Moving part moves to its right side (in positive direction) in creep
velocity to detect Lower Limit switch On
→
Off edge;
2. Once Lower Limit switch On
→
Off edge is detected, record the position as
mechanical home position, and decelerate to stop;
3. Move to the configured home position. The mechanical home position
recorded during moving right sequence, plus the home offset configured
for the axis through the software.
Scenario 3: Moving part at left (negative) side of Lower Limit switch before homing starts
In this case, the homing motion fails and moves continuously to the left until
drive or moving part fails to move. User needs to make sure the moving part is
at the proper location before homing starts.
IMPORTANT
If Lower Limit switch is not configured as Enabled, MC_HOME_LIMIT_SWITCH
(1) homing will fail (Error ID: MC_FB_ERR_PARAM).
