Figure 29: Synchronization Without Virtual Master - Danfoss VLT 5000 Operating Instructions Manual

Absolute value encoder - This is a special form of incremental encoder, as it indicates not only
Track error
Accuracy
PPR
Virtual master
MG.10.N4.02 - VLT is a registered Danfoss trademark
Synchronizing controller
the speed and direction of rotation but also the absolute physical position.
This is communicated via transfer of the position in parallel form or in the
form of a telegram in serial form. Absolute value encoders also come in two
versions: Single-Turn encoders supply an absolute position on a shaft
rotation; Multi-Turn encoders can report the absolute position via a specific
quantity, or via a freely-definable number of rotations.
- The synchronizing controller of the slave drive uses the master drive signal
and the gear ratio to calculate a reference position value for the slave drive.
The deviation of the feedback position from the calculated position is known
as the track error. This is specified in quad counts. The maximum track error
is also a threshold value that defines the permitted operating area of the
synchronizing controller.
- This value specifies the permitted deviation between the master and slave at
which synchronization is still present.
- Pulses per revolution
- If several axes are to travel in synchrony, or if the synchronization error is so
to be kept as small as possible, it is often more advantageous not to take the
reference position from a drive, but to have a master that simulates the
reference position. This has the advantage that the cycle times of the
individual drives are not added. These differences are illustrated below for
the synchronous control of three conveyor belts. First, we show the classic
synchronization procedure, where the reference value signal is taken from
the preceding drive in each case.

Figure 29: Synchronization without virtual master

81