4.5 Absolute Position Detection
4-21
Feed Axis
Operation
4.5.6
Origin Offset
If you use an absolute encoder, you can set an offset for the encoder position and the machine coordinate sys-
tem position. You can use the offset to set the mechanical origin in the absolute value coordinate system. The
origin offset can be stored in the host controller or in the SERVOPACK.
(1) Storing the Origin Offset in the Host Controller
Allocate memory (registers) to store the origin offset in the host controller.
The memory used to store the origin offset must meet the following specifications.
• To save the origin permanently, use non-volatile memory or memory with a battery backup for storage.
• Use a 32-bit register to store the origin.
• The origin offset can be in the forward or reverse direction, so it can be set in a range from -(2
31
- 1) to (2
31
- 1).
To set the encoder coordinate position (x) as the machine coordinate origin (0), set the origin offset memory to
-x.
CPOS: Command position
APOS: Coordinate system position (feedback position)
X =
χ
+ Origin offset memory value
Use the following procedure to set the origin offset.
1.
After the power supply is turned ON, use the Turn Sensor ON command (SENS_ON: 23 hex) to
turn ON the encoder.
2.
Set up the coordinate system for the host controller by using the reference position (CPOS) and
align the coordinates for the SERVOPACK and host controller.
3.
Turn ON the main circuit power supply for the SERVOPACK and use the SV_ON (31 hex)
command to turn ON the servo.
4.
Use manual operation to move the machine axis to the machine reference point.
Now, set the origin in the host controller. With the current machine coordinate system position as APOS
and the reference point machine coordinate system position as APOS
new
, we get the following formula.
New origin offset = Previous origin offset - (APOS - APOS
new
)
Write the new origin offset value to the host controller’s internal non-volatile memory or memory with a
battery backup.
5.
Use this newly set origin offset value to reset the coordinate system.
Origin offset completes when the coordinate system reset completes.
Machine coordinates
(CPOS and APOS)
Machine
coordinate origin
Current
position X
Common parameter 23
(Pn808)
Encoder coordinate
Encoder origin
