February 2012 19 – 317
19.5 Position measurement via motor encoder (indirect position measurement)
Switching path measurement from the linear encoder to the motor encoder may be helpful to ...
facilitate the dismounting of a defective position encoder.
(E.g. if the axis is at a position at which you cannot dismount the scale)
analyze the quality of the encoder signals from the position encoder with a PWT.
(See ”Further examination of position and speed encoders” on page 19 – 314.)
analyze errors in the control loop.
(See ”Error localization by switching from direct to indirect position measurement” on page 6 – 69.)
Please 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.
Moreover, the iTNC 530 HSCI runs an automatic plausibility check for the MP1040.x (sign of nominal
speed value). The error message Incorrect entry in MP1040.x means that MP1040 must be inverted
now.
Traverse with indirect position measurement is described for servicing only!
You must not continue working with the machine tool!
Reasons:
No reference point is evaluated for the axis concerned; thus, you could traverse to the limit
switches or the mechanical stops. 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 (MP210.x) or the sign of the nominal speed value
(MP1040.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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