User`s manual

Configuration
GFK-1742A Chapter 4 Configuration 4-27
4
6.02 Analog Servo Command.
The Analog Servo Command determines whether the analog
command issued by the DSM300 series module is a velocity or torque command. The torque
command selection is not supported in the present DSM314 firmware. Default: Velocity
6.03 Position Error Limit.
Position Error Limit (User Units). The Position Error Limit is the
maximum
Position Error (Commanded Position - Actual Position
) allowed when the DSM314 is
controlling a servo. Position Error Limit should normally be set to a value 10% to 20% higher than
the highest
Position Error
encountered under normal servo operation. Default: 60000.
The Position Error Limit range formula is:
256
x
(user units/counts)
≤
Position Error Limit
≤
60,000
x
(user units/counts)
If Velocity Feedforward is not used, Position Error Limit can be set to a value approximately 20%
higher than the
Position Error
required to produce a 4000-rpm command.
The Position Error
(User Units) required to produce a 4000 rpm command with 0% Velocity Feed forward is:
Position Error (user units) = Position Loop Time Constant (ms) x Servo Velocity @ 4000 rpm (user units/sec)
1000
Example
The user units:counts ratio is 2:1 and the Position Loop Time Constant is 50 ms.
Step 1:
Calculate servo velocity at 4000 rpm = (2 user units/count) x (8192 counts/rev) x (4000 revs/minute)
(60 seconds/minute)
= 1,092,266 user units/second
Step 2:
Calculate
Position Error
at 4000 rpm =
(50 milliseconds) x (1,092,266 user units/second)
1000 milliseconds/second
= 54613 user units
If Velocity Feedforward is used to reduce the following error, a smaller error limit value can be
used, but in general, the error limit value should be 10% - 20% higher than the largest expected
following error.
Note
An
Out of Sync
error will occur and cause a fast stop if the
Position Error Limit
Va lu e i s
exceeded by more than 1000 counts. The DSM314 attempts to prevent an
Out of Sync
error by temporarily halting the internal command generator whenever position error
exceeds the
Position Error Limit
. Halting the command generator allows the position
feedback to catch up and reduce position error below the error limit value.
If the feedback does not catch up and the position error continues to grow, the
Out of Sync
condition will occur. Possible causes are:
1. Erroneous feedback wiring
2. Feedback device coupling slippage