Drive control and features
38
Position control
In position control, the load is positioned along a single axis from the start position to
the defined target position. A position reference is given to the drive to indicate the
target position. The path to the target position is calculated by the position profile
generator, controlled by position reference sets.
The position reference is taken from a moving target via an encoder, the master
drive, the PLC, or the virtual master function. If the drive falls behind the moving
target, the difference will be accumulated to the position reference generator as a
synchron error. (In section Position/synchron control features on page 59, the
moving target is referred to as the master position (reference) and the controlled
drive position is referred to as the follower position.)
Position feedback (encoder or resolver) must always be used in position control to
determine the actual position of the load. The same encoder can also be used to
provide speed feedback. It is also possible to have separate encoders for the load
(position feedback) and motor sides (speed feedback).
Note: It is emphasised that all position relevant parameters are load side related, eg,
the setting of parameter 70.04 POS SPEED LIM (dynamic limiter speed limitation) of
300 rpm denotes that, with a load gear ratio of 1:10, the motor can run at up to 3000
rpm.
Position control is available in both local and external control.
Synchron control
Synchron control is used to synchronise several mechanical systems (axes). The
control is similar to position control, but in synchron control the position reference is
taken from a moving target via an encoder, the master drive, the PLC, or from the
virtual master function.
Position feedback (encoder or resolver) must always be used in synchron control to
determine the actual position of the load.
Mechanical slippage etc. can be compensated using the cyclic correction functions.
Note: Synchron control is not available in local control mode.
For detailed examples of synchron control with lists of the related parameters, see
Appendix D – Application examples.
Virtual master function
With the virtual master function, a physical master drive or PLC is not needed in a
synchron-controlled follower. The follower will generate its own synchron reference
by converting the speed reference selected by parameter 67.02 VIRT MAS REF SEL
into a position reference by integration.
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