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Digitax HD M753 Control User Guide
Issue Number: 3
9.26
Advanced features
9.26.1
Distributed clocks
The EtherCAT interface supports Distributed clocks. This is the scheme
used by EtherCAT to accurately time synchronize slave devices.
Position, speed and current control loops can all be synchronized.
The EtherCAT Distributed Clocks facility can be used to provide a time
synchronization signal so the drive speed and current tasks are
synchronized to the network. The position controller, and appropriate
motion features will also be synchronized to the drive speed task.
In CoE interpolated position mode the position command provided by
the master every interpolation cycle time is used to generate a position
command for the drive every 250
μ
s.
9.26.2
Time synchronization support
The EtherCAT distributed clocks facility can be used to provide a time
synchronisation signal so that the drive tasks (including the motion,
speed and current tasks) are synchronised to the network. The option
synchronous task will also be synchronized to the drive OPT_SYNC
signal.
If possible, the Ethernet interface will provide a synchronization signal
suitable for the longest interval drive cyclic task (this will also, of course,
synchronize the higher rate tasks, if they are phase locked to the lowest
rate task).
The drive motion and speed loops are executed every 250
μ
s, which
coincides with OPT_SYNC edges. This will be referred to as the control
loop cycle. Synchronization must be enabled if the Cyclic Sync or
Interpolated Position modes are used; an error will be indicated if this is
not the case. These modes have an operating mode cycle time of the
interpolation cycle time; other modes will have an operating mode cycle
time matching the synchronous task (250
μ
s).
Any operating mode cycle will be restarted every operating mode cycle
time, in phase with the synchronisation events; if synchronization is
enabled, the operating mode will not start execution until the first
synchronization event occurs. If synchronization is lost, an error will be
indicated, and the standard EtherCAT action for this event will occur.
Command and feedback values which are handled cyclically will be read
at defined times in the cycle. Command values handled/used every
cycle (operating mode or control loop) will be cached from the object
dictionary in the task immediately before the drive critical update period.
Any feedback values read during a cycle will be scaled as appropriate in
that cycle, cached, and then written to the object dictionary in the task
occurring immediately after the drive critical update period. Feedback
values that change internally between control loop cycles (but whose
objects are only updated every profile cycle) will be read from the last
control loop cycle in the operating mode cycle. PDO data will be copied
to and from the object dictionary (from and to the sync manager memory
areas) in the drive critical update period at the beginning of every
operating mode cycle.
PDO data mapped to drive parameters (but not parameters accessed
using Inter-Option Communications, or eCMP), will be written to those
parameters in the critical update period at the beginning of every control
loop cycle. This behaviour can be modified by the advanced cyclic data
configuration objects.
Figure 9-17 Profile Cycle Timing
9.27
EtherCAT protocol support
The following are supported:
•
Four Sync Managers. Two are used for the Mailbox Protocol
(non-cyclic data) and two are used for process data (cyclic data)
•
Distributed Clocks
•
CANopen over EtherCAT (CoE)
NOTE
Drive Sync
Waveform
(OptSync)
Profile Cycles
Control Loop
Cycles (current
torque)
62.5µs*
This time can vary according to drive
frequency (which can change during
operation to reduce temperature in drive)
250µs OptSync Interrupt
time
Critical Task
(task length
varies with
amount of data
exchanged)
Pre-Critical Task
(task length
varies with
amount of data
exchanged)
Post-Critical
Task (task length
varies with
amount of data
exchanged).
After Drive
Critical update
period has
completed.
75µs*
75µs*
75µs*
70µs*
70µs*
70µs*
*
Summary of Contents for Digitax HD M753 EtherCAT
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