9-8
Extended Drive Functions
MPH-02, MPB-02, MPD-02
DOK-INDRV*-MP*-02VRS**-FK01-EN-P
9.2 Measuring
Encoder
Brief Description
Measuring encoders are used for position evaluation of a rotary motion
that takes effect as a command variable for drive control. The actual
position value of the measuring encoder therefore is of command value
nature for drive control, the measuring encoder acts as a master axis
encoder, for example.
Depending on its design and the mechanical arrangement at the axis, the
measuring encoder can be evaluated as
•
relative encoder (incremental encoder)
- or -
•
absolute encoder (absolute value encoder)
In the case of relative position measurement, only position differences
can be evaluated by means of the measuring system. The actual position
values signaled by the measuring system refer to the (mostly undefined)
position at the time the drive is switched on. If the actual position value is
to refer to an axis or shaft, it is necessary to establish position data
reference ("homing").
In the case of absolute position measurement, the encoder signals actual
position values with a fixed encoder-dependent reference point to the
controller. After the drive is switched on the correct actual position value is
immediately available for each axis or shaft position. Due to the mostly
undefined mounting situation of the encoder, it is necessary during initial
commissioning to once adjust the actual position value to the axis or shaft
("set absolute measuring").
The precision of the position measurement depends on:
•
the resolution of the measuring system (division periods = DP)
•
the absolute encoder precision
•
the digitalization quality of the analog encoder signals
•
the size of the selected modulo range of the encoder
The correct position information of the measuring encoder is required for
correct detection of a command variable. The encoder signals are
therefore monitored for plausibility and compliance with the allowed
tolerances.
In addition, it is possible to monitor drives with an encoder that can be
evaluated in absolute form for compliance with the position when
switching on compared to the last time the drive was switched off.
See "Measuring Systems: Monitoring the Measuring Systems" in chapter
"Motor, Mechanical Axis System, Measuring Systems"
For connecting the measuring systems to the controller the control section
has to be equipped with the corresponding interfaces. Parameter
P-0-0079, Assignment measuring encoder ->optional slot
is used to
determine the interface to which the respective encoder is connected.
Position Measurement
Evaluating Position
Measurement
Relative Position Measurement
Absolute Position Measurement
Precision, Resolution
Monitoring Functions
Hardware Requirements
Expansion package
synchronization
(order code
SNC
) in all characteristics
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of
CMA/Flodyne/Hydradyne
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Control
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