Lenze E94P PositionServo with MVOB - Manual (Page 60)

58 L PM94H201B_13xxxxxx_EN
Programming
2.15 Homing
2.15.1 What is Homing?
Homing is the method by which a drive seeks the home position (also called the datum, reference point, or zero point).
There are various methods of achieving this using:
• limit switches at the ends of travel, or
• a dedicated home switch, or
• an Index Pulse or zero reference from the motor feedback device, or
• a combination of the above.
Predefined (firmware based) homing functionality is available on PositionServo drives with firmware 3.03 or later.
In addition custom homing functionality can be created by the programmer within the user program by utilizing the
programming command set available.
Examples of custom homing routine creation as well as user program code to replicate each of the predefined homing
routines is available from technical support.
2.15.2 The Homing Function
The homing function provides a set of trajectory parameters to the position loop, as shown in Figure 22. They are
calculated based on user supplied variable values as listed below:
VAR_HOME_OFFSET
VAR_HOME_METHOD
VAR_HOME_SWITCH_INPUT
VAR_HOME_FAST_VEL
VAR_HOME_SLOW_VEL
VAR_HOME_ACCEL
VAR_START_HOMING
Trajectory
Parameter Position
Demand
Homing
Function
Trajectory
Generator Position
Loop
Home Offset
Homing Method
Homing Speeds
Home Velocity Fast/Slow
Homing Acceleration
Figure: 22: Homing Function
Homing Function Monitoring:
The extended drive status variable (#83 EXSTATUS variable) contains bit values for monitoring the homing function
over a communications interface.
Bit 21 of EXSTATUS indicates homing procedure in progress and is set to logic 1 while homing is being executed.
Bit 22 of EXSTATUS indicates homing complete. It is set to 1 upon the successful completion of the homing routine.
2.15.3 Home Offset
The home offset is the difference between the zero position for the application and the machine home position (found
during homing). During homing the home position is found and once the homing is completed the zero position is offset
from the home position by adding the home offset to the home position. All subsequent absolute moves are made
relative to this new zero position. This is illustrated in Figure 23. Offset can either be set in User Units (UU) by writing
to variable #240, or in encoder counts by writing to variable #241. Setting a value for either variable #240 or #241 will
result in a value automatically being calculated and stored in the respective variable.
VAR_HOME_OFFSET (#240)
VAR_HOME_OFFSET_PULSES (#241) Home
Position
Zero
Position
home_offset
Figure 23: Home Offset