Communications Design for Relay Elevators and Escalators in a Distributed Monitoring and Control System

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Communications Designfor Relay Elevators and
Escalatorsin a DistributedMonitoring and
Control System
Antti Orrainen S-72.158 Thesis Seminar on
Communications Technology 1.6.2004 Helsinki
University of Technology
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About the Thesis

• Thesis was written at KONE Corporation
  (Elevators Escalators) RD, which is located
  in Hyvinkää
• Supervisor Professor Timo Korhonen (HUT
  Communications Laboratory)
• Instructor Kari Suihkonen (KONE Corporation)

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Agenda

• Introduction (to monitoring and control systems
  for elevators and escalators)
• Goal of the Thesis
• The LonWorks Technology
• Fieldbus Simulations Results
• Communications Design
• Conclusions

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Introduction to Monitoring and Control Systems
for Elevators and Escalators

• Real-time monitoring (e.g. malfunctions,
  elevator position)
• Control commands (e.g. out of service, priority
  drive)
• Traffic statistics (e.g. capacity estimations)

• Connectivity to ordinary building automation

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Introduction to Monitoring and Control Systems
for Elevators and EscalatorsNew System
Architecture
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Introduction to Monitoring and Control Systems
for Elevators and EscalatorsNew System
Architecture

• Gateway provides real-time data
• Statistics server provides historical data
• OPC (Object Linking and Embedding for Process
  Control)
• De facto standard for open connectivity in
  automation applications
• Gateway implements the OPC Data Access
  specification
• Statistics server implements the OPC Historical
  Data Access specification

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Goal of the Thesis

• How to connect relay elevators and escalators to
  the new monitoring and control system? (only at
  the level of a design)
• Relay elevators do not support the system by
  nature
• relay interface units are needed
• A suitable relay interface unit hardware has
  already been designed for the purposes of
  another project (V2 analyser)

• How can this unit be used with the new
  monitoring and control system?

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Goal of the Thesis

Relay interface unit
Gateway
Field bus
Signalling cables
Relay elevators and escalators

• Relay interface units provide distributed I/O
• (16 inputs and 4 outputs per unit)
• Relay interface units communicate using the
  LonWorks technology (EIA-485 bus, 78 kb/s)

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The LonWorks Technology

• Developed by Echelon at the beginning of the
  1990s
• Packet based LonTalk protocol provides all the 7
  layers of the OSI (Open Systems Interconnection)
  reference model
• Predictive p-persistent MAC (Medium Access
  Control) algorithm

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The LonWorks Technology
Code violation
L2 header
L2 trailer
Beta 2 slots
Beta 1
Preamble
L3-L7 headers
Payload
P
1
1
R
...
...
Randomising slots
Priority slots

• Number of randomising slots increases as the
  network traffic increases (16-1008 slots in use)
• Collision probability decreases but medium
  access delay might increase

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Fieldbus Simulations
Hall calls (8 floors/unit) (1 packet/s)
Floor position (16 floors/unit) (0,5 packets/s)
Basic signals (4 packets/s)
Signalling cables for elevator
Total of 9 packets/s for one elevator

• 3 bytes of payload per packet
• Medium access delay comparison for the
  LonTalk acknowledged (predictive p-persistent)
  and the application level acknowledged service
  (normal 1/16-persistent)

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Fieldbus Simulation Results
  APP LON APP LON
Number of elevators 5 5 8 8 9 9 10 10
Average access delay (fastest value from different retransmission intervals below) 3,7 ms (64 ms interval) 4,8 ms (128 ms interval) 6,7 ms (64 ms interval) 9,9 ms (128 ms interval) 8,0 ms (64 ms interval) 13 ms (128 ms interval) 13 ms (96 ms interval) 23 ms (192 ms interval)
(64 ms interval) 3,7 ms 8,3 ms 6,7 ms 1800 ms 8,0 ms 9100 ms 11000 ms 7700 ms
(96 ms interval) 4,7 ms 9,1 ms 8,9 ms 71 ms 11 ms 1300 ms 13 ms 4800 ms
(128 interval) 5,9 ms 4,8 ms 11 ms 9,9 ms 14 ms 13 ms 17 ms 250 ms
(192 ms interval) 7,8 ms 6,6 ms 15 ms 14 ms 18 ms 18 ms 22 ms 23 ms
Maximum access delay 330 ms 390 ms 390 ms 400 ms 440 ms 520 ms 490 ms 1000 ms
Missed deadlines (500 ms) 0 0 0 0 0 8 0 129
Successful transactions 160819 162435 254423 259594 285911 291381 316389 323805
Average packet rate of a relay interface unit 1,3 packets/s 1,3 packets/s 1,4 packets/s 1,3 packets/s 1,4 packets/s 1,3 packets/s 1,4 packets/s 1,4 packets/s
Collided I/O packets 2,1 1,1 4,2 2,3 5,1 2,9 6,1 3,6
Average number of Beta 2 slots in use 16 26 16 40 16 46 16 56
Time the field bus was reserved 25 24 40 39 45 44 50 49

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Fieldbus Simulation Results

• With 10 elevators in the field bus (circa 50
  load), theoritically better average access delay
  performance when the predictive p-persistent
  mode is not used (13 ms vs. 23 ms)
• Though, predictive p-persistent mode can keep
  collision rate lower (6,1 vs. 3,6 )

• In practice, application level acknowledged
  service is not desirable in the non-real-time
  Linux operating system (generating
  acknowledgement packets manually burdens the
  processor of the gateway)
• When the predictive p-persistent mode is in use,
  a LonWorks network adapter can generate the
  acknowledgement packets automatically (i.e. no
  burden to the processor of the gateway)

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Fieldbus Simulation Results

• The priority service of the LonTalk protocol can
  be used to decrease the access delay
• If a deadline (500 ms) is about to be missed,
  send a priority packet missed
  deadlines decreased from 129 to 26

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Communications Design
V2 analyser (with a selectable node identifier)
Network adapter (e.g. USB connection)
Terminating resistors (at the both ends of the
bus)
EIA-485 bus (max. total length 500 m without
repeaters)
Gateway

• The LonTalk acknowledged service together with
  the priority service should be used
• Bus topology (simple cabling)
• Gateway should provide all the logic of the
  system

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Communications DesignNetwork Driver in the
Gateway
Data point
Data value Status flags (quality) Timestamp
Shared memory
Network driver
OPC DA server
Configuration database

• Communication with the OPC Data Access server
  via a block of shared memory (OPC data items)
• Configuration database provides configuration
  information about the field bus

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Conclusions

• This thesis presented a design for relay
  elevator and escalator support in the new
  monitoring and control system
• The predictive p-persistent LonTalk protocol is
  not the most optimal solution for the real-time
  system in question
• However, the LonTalk protocol can provide
  adequate performance if limitations (number of
  nodes, packet rate) to the utilisation of the
  field bus are set
• The design needs to be implemented to prove its
  applicability in practice

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Thank you!
Questions?