Parameter groups: 74 Position status & control words (page 440) and 86.2 Actual
position (page 463).
Position controller
The position controller calculates a velocity reference (88.3) that is used as the
feed forward term (88.4) to minimize the difference between position reference
and actual values. The position controller is a P-type controller. The user can set
the controller gain (88.10 Position control gain), the feed forward value gain (88.11),
and a cycle delay (88.12) between the reference and actual value. The delay can be
used to minimize system position error especially in master-follower setups.
The output of the position controller has a gear function (86.21 and 86.22) for
transferring position and speed data from the load side to the motor side.
The position controller also supervises the error (88.6) between the reference
position (88.1) and actual position (86.2). The maximum positive and negative
error values are stored into resettable parameters 88.33 and 88.32 for fine-tuning
purposes. If the position error exceeds the limit set by 88.30, the action selected
by 88.31 is taken.
Settings and diagnostics
Parameter groups: 86.2 Actual position (page 463) and 88 Position control (page 478).
Master reference
Parameter group 87 Master position contains several settings to define the
reference source and operation in synchronized mode. The master reference source
is selected by parameter 87.11 and provides various selections:
• analog input (AI1/AI2)
• fieldbus reference
• master encoder (encoder 1/2)
• master/follower link
• virtual master.
The follower axis is synchronized with master reference by the “Gear in” command,
whose source is defined by 74.32 (See also section Gear in (page 36).) The gear-in
ratio (87.35/87.36) defines the fixed velocity ratio between the follower and master
axes. These parameters cannot be changed during operation, but 87.31 can be
used to adjust the velocity ratio on the fly. A new gear-in ratio can be activated by
a new gear-in command during operation when 74.15 is set to Edge and 74.16 is
set to True.
In addition to the synchronization ratio, PI control (see page 56) or an external
source (87.30) can be used to adjust the follower’s velocity in synchronized mode.
Parameter 87.25 and 87.26 can be used for master reference filtering. Any undesired
Position control program features 51
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