July 2010 18 – 311
18.5 Position Measurement via Motor Encoder (Indirect Position Measurement)
Switching position measurement from the linear encoder to the motor encoder may be helpful
to ...
Facilitate dismounting of a defective position encoder
(e.g. if the axis is at a position in which you cannot dismount the scale)
Analyze errors in the control loop
(See “Error Localization by Switching from Direct to Indirect Position Measurement” on page
6 – 70)
Analyze the quality of the encoder signals from the position encoder with a PWT
(See “Further Examination of Position and Speed Encoders” on page 18 – 308)
Note! Read this information carefully before you switch to position capture via motor encoder!
Normally, this quickly results in error messages such as Excessive servo lag, etc. and the
control generates an EMERGENCY STOP.
Furthermore, an automatic plausibility test for the MP 1040.x (algebraic sign of the nominal
speed value) has been introduced with the NC software version 34049x-02 in combination with
a CC 424 (B). Error message Incorrect entry in MP 1040.x states that MP 1040 must now be
inverted.
For older software versions and the use of CC 422 it is recommended ...
to check the tolerance limits for the monitoring of following error, movement and standstill and
to reduce the set values, if necessary (See “Annex: Monitoring Functions” on page 3 – 661).
to reduce the kv factor for the position control loop (MP 1510.x, MP 1810.x).
to reduce the proportional factor (MP 2500.x) and the integral factor (MP 2510.x) of the speed
controller equally.
Contact your machine tool builder.
Traverse with indirect position measurement is described for servicing only!
You must not continue to work with the machine tool!
Reasons:
No reference point for the axis concerned is evaluated.
You could move to the limit switches or the mechanical stops.
An automatic tool change is usually not possible any longer.
The manufacturer has not prepared the machine for traverse with motor encoders
as position information systems.
When switching from the scale / scale tape / angle encoder to the motor encoder, the
counting direction of the position encoder signals (MP 210.x) or the sign of the
nominal speed value (MP 1040.x) may no longer be correct!
In this case the feedback for a control loop is transformed into positive feedback,
which in the worst case could cause the affected axis to race.
Always secure vertical axes to prevent them from falling down before you switch to position
capture via motor encoder!
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