Communication parameters for transmitting data to follower drives
The communication on the master/follower link is based on the DDCS protocol,
which employs data sets. Position control uses one data set containing three 16-bit
words. The content of the data set is configurable by selection parameters
61.1…61.3. The data is broadcast by the master and it typically consists of a 32-bit
position value (88.53) and a 16-bit velocity value (88.54). As data words only have
16 bits, the position value will be transmitted in two consecutive data words. In
effect, selecting the 32-bit value D2D position for data word 1 in parameter 61.1
also reserves data word 2. In this case, D2D velocity can only be selected for data
word 3 in 61.3. Similarly, choosing D2D position for data word 2 in 61.2 also reserves
data word 3, leaving only data word 1 available for the velocity value. D2D position
cannot be selected for data word 3.
The three data words sent onto the master/follower link are displayed by
parameters 61.25…61.27.
It is possible to send only the position data to follower drives without sending the
velocity value. However, it is then not possible to adjust follower velocity during
synchronized operation.
Communication parameters for receiving data from the master drive
In the follower drive, parameters 62.1…62.3 must be configured according to the
settings of master drive parameters 61.1…61.3. This means that M/F position
should be selected for the same data word in the follower as D2D position is
selected in the master. Similarly, M/F velocity should be selected in the follower
for the same data word as D2D velocity is selected in the master.
The three data words received through the master/follower link are displayed by
parameters 62.25…62.27. The two 16-bit words containing the position are merged
back into a 32-bit value, and displayed in 62.241. The received velocity value is
displayed in 62.242.
Example
The XD2D connectors of the master and follower drives are connected by electrical
cable. The actual position of the master axis is used as a master reference for the
followers, and the master axis is synchronized to a virtual master.
The following table shows the main parameter settings. The settings labeled
“Check” mean application-specific values, to be set according to the actual system
and its limitations.
In case there are several followers operating in the same manner, the settings for
each follower are the same except for the node address (60.2).
54 Position control program features
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