§ This session is focused at helping designers of EtherNet/IP based real-time
control systems (like motion) understand:
§ How real-time applications like motion control can be accomplished
over a non-deterministic network like Ethernet
§ How to design an automation network that provides a platform for high
performance control
§ Compliance and backlash
§ Mechanical system time constants
§ System Tuning
Fluctuations introduced by network
infrastructure are measured in nanoseconds
and microseconds, so they are usually
negligible compared to other boundaries in the
system:
§ But Ethernet is not deterministic!
§ How can time-sensitive applications like motion control and time-stamping
possibly be accomplished over Ethernet?
All members (devices) have clocks to compare
time to an absolute base and scale
§ A destination (position) is targeted for the event
§ A time (timestamp) is set for when the event
shall occur
§ A message is sent to each member (device) to
meet at the given place at the pre-determined
time
§ Not all messages might arrive at precisely
the same time!
§ CIP Motion coordinates devices in a manner
that’s similar to our own methods for
coordinating meetings and events
All members (devices) have clocks to compare
time to an absolute base and scale
§ A destination (position) is targeted for the event
§ A time (timestamp) is set for when the event
shall occur
§ A message is sent to each member (device) to
meet at the given place at the pre-determined
time
§ Not all messages might arrive at precisely
the same time!
§ But all members arrive in the proper
position at the proper time for the event to
take place!
§ CIP Motion coordinates devices in a manner
that’s similar to our own methods for
coordinating meetings and events
§ Master/slave hierarchy of clocks
§ Master is typically controller
§ Slave is typically a drive
§ Master clock broadcasts time
§ Once per second
§ Allows clocks to be tuned
§ Slave devices measure delays
§ Accounts for network latency
§ Provides accuracy ~ 100ns
How Precision Time Protocol (PTP) Synchronizes All Clocks
§ Ethernet can be deterministic!
§ CIP Sync per IEEE1588 keeps all the clocks synchronized, enabling realtime applications like motion control over Ethernet
§ What are you trying to do?
§ Choose a switch based on the application:
§ Real-time applications imply switches that support time
§ Motion control implies time accuracy near +/-1 microsecond
d
§ Will the system be connected to a larger infrastructure?
All members (devices) continue to
compare time to an absolute base and
time scale
§ A destination (position) is targeted for
the event
§ A time (timestamp) is set for when the
event shall occur
§ A message is sent to each member
(device) to meet at the given place at
the pre-determined time
§ If clocks are off, members don’t know
that their clocks are different from
others against which they are
coordinating
Members will arrive at the right
place….
But at the wrong time….
….this results in positioning error…
All members (devices) continue to
compare time to an absolute base and
time scale
§ A destination (position) is targeted for
the event
§ A time (timestamp) is set for when the
event shall occur
§ A message is sent to each member
(device) to meet at the given place at
the pre-determined time
§
§ If clocks are off, members don’t know
that their clocks are different from
others against which they are
coordinating
Look for IEEE158
IEEE1588
88888
8--2008
2008 and work with your
20
switch vendor to provide
provid
provid a QoS policy that
pro
prov
supports automation.
NOTE: These are NOT featu
features
ures excl
exclusive
lusive
to Rockwell Autom
Automation;
n; EtherNet
ett is an
et/IP
open standard.
§ Topological Arrangement
§
§ Device Clock Filtering
How do I protect time in the system?
Other Mechanisms
Typically Managed Switch
§ What are you trying to do?
§ There are many reasons to Connect the Enterprise:
§ Provide a common time across the Enterprise for alarm/event logs
§ Gain access to manufacturing data for analytics
§ Provide Smart Machines that enable proactive maintenance
§ (And EtherNet/IP is the only network that can connect IT to OT)
§ You must architect your infrastructure for the application:
§ Do not connect cells of motion without a CIP Sync-capable backbone
§ You will see ControlSync Faults/Alarms with these switches
§ We analyzed system time by observing device level jitter and registration:
§ Case 1: Steady-state cell-to-cell time coordination
§ Case 2: Effects of Grandmaster changes on time coordination
More…
§ System layout #1 using Stratix 8300 layer 3 switch:
§ Steady-state jitter <70ns, registration time around -2 to 1us
§ Grandmaster changes lead to jitter ~ 50us, registration ~ +/- 20us
GuardLogix controller acting as data concentrator,
line safety controller AND Grandmaster time clock
§ System layout #2 using ControlLogix gateway (as a data concentrator):
§ Steady-state jitter <70ns, registration time around -1 to 1us
§ Grandmaster changes lead to jitter ~ 12us, registration ~ +/- 10us
§ System layout #3 using Cisco Catalyst 3750-X layer 3 switch:
§ Steady-state jitter <80ns, registration time around -2 to 1us
§ Grandmaster changes lead to jitter ~ 170us, registration ~ +/- 20us
§ Discuss a plan with your customers early about network integration
§ IP Address scheme and PTP multicast groups
§ Data that would like produced on network
§ Secure, remote access options for you?
§ By default, NAT switches will block PTP traffic, isolating cells:
§ S5700 can be made to pass PTP, if layer 3 switch supports IEEE1588
§ Bonus: Machines can use identical IP addresses (code mgmt.)