5.14 Setting Unit Systems
5.14.1 Setting the Position Reference Unit
5-42
5.14
Setting Unit Systems
You can set the SERVOPACK reference units with EtherCAT (CoE) communications. You can
set the following four reference units with EtherCAT communications.
•
Position reference unit
•
Speed reference unit
•
Acceleration reference unit
•
Torque reference unit
The setting procedures are given below.
5.14.1
Setting the Position Reference Unit
Set the position reference unit in
position user unit
(2701 hex). The position reference unit set-
ting will be used for the electronic gear ratio setting.
Note: Refer to the following section for information on
position user unit
(2701 hex).
The minimum unit of the position data that is used to move a load is called the reference unit.
The reference unit is used to give travel amounts, not in pulses, but rather in distances or other
physical units (such as
μ
m or
°
) that are easier to understand.
The electronic gear is used to convert the travel distances that are specified in reference units
to pulses, which are required for actual movements.
With the electronic gear, one reference unit is equal to the workpiece travel distance per refer-
ence pulse input to the SERVOPACK. In other words, if you use the SERVOPACK’s electronic
gear, pulses can be read as reference units.
The difference between using and not using the electronic gear is shown below.
•
Rotary Servomotors
In this example, the following machine configuration is used to move the workpiece 10 mm.
•
For a Rotary Servomotor with an encoder resolution of 24 bits (16,777,216), Pn20E (Electronic
Gear Ratio (Numerator)) is automatically set to 16 and Pn210 (Electronic Gear Ratio (Denomi-
nator)) is automatically set to 1. Therefore, the encoder resolution will be equivalent to 20 bits
(1,048,576). Consider this when you set the position reference unit in
position user unit
(2701
hex).
•
Set the position reference unit within the following range.
1/4,096 < Numerator/Denominator < 65,536
If the setting range is exceeded, an A.A20 alarm (Parameter Setting Error) will occur.
Index
Subin-
dex
Name
Data
Type
Access
PDO
Mappings
Value
Saving to
EEPROM
2701
hex
0
Number of entries
USINT
RO
No
2
No
1
Numerator
UDINT
RW
No
1 to 1,073,741,823
(default: 1)
Yes
2
Denominator
UDINT
RW
No
1 to 1,073,741,823
(default: 1)
Yes
Important
Workpiece
Resolution:
16,777,216 (24 bits)
Ball screw lead: 6 mm
