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HRTC Meeting12 September 2002, Vienna
Smart Sensors
Thomas Losert
12 Sept. 2002 / p.2Thomas Losert
Overview
• Smart Transducers(Definition, Observations, Interfaces)
• Principles of Operation• Architecture• Sensor Fusion (Definition, Concepts)• Case Study• Conclusion & Outlook
12 Sept. 2002 / p.3Thomas Losert
Overview
• Smart Transducers(Definition, Observations, Interfaces)
• Principles of Operation• Architecture• Sensor Fusion (Definition, Concepts)• Case Study• Conclusion & Outlook
12 Sept. 2002 / p.4Thomas Losert
Smart Transducer (ST)
Comprises the Integration of one or more Sensor/Actuator Elements with a Micro-controller and a Communication Network Interface that provides the following Services across standard Interfaces:
Diagnostic and Management Real-Time Communication Calibration of Sensor Signal Conditioning and Conversion to
standard Units
12 Sept. 2002 / p.5Thomas Losert
Advantages
No noise pickup from long external signal transmission lines.
Better Diagnostics – Simple external ST failure modes (e.g., fail-silent)
"Plug-and-play" capability if the ST contains its own documentation on silicon or in an external database.
Reduction of the complexity at the system hardware and software and the internal ST failure modes can be hidden from the user by a well-designed fully specified ST interface.
Cost reduction in installation and maintenance.
12 Sept. 2002 / p.6Thomas Losert
Overview
• Smart Transducers(Definition, Observations, Interfaces)
• Principles of Operation• Architecture• Sensor Fusion (Definition, Concepts)• Case Study• Conclusion & Outlook
12 Sept. 2002 / p.7Thomas Losert
Observations
An observation consists of an atomic tuple
< observed value, instant, RT-entity Name >
For Communication of Observations across an RS interface a common set of concepts is necessary:
Common representation of values in a Shared code-space Common notion of time and its representation Common meaning of the names of RT entities Access protocol to the information.
12 Sept. 2002 / p.8Thomas Losert
Observations
An observation consists of an atomic tuple
< observed value, instant, RT-entity Name >
For Communication of Observations across an RS interface a common set of concepts is necessary:
Common representation of values in a Shared code-space Common notion of time and its representation Common meaning of the names of RT entities Access protocol to the information.
12 Sept. 2002 / p.9Thomas Losert
State vs. Event Values
Characteristic State Observation
Event Observation
Value Full Value Value Difference
Frequency Periodic Sporadic
Loss of Observ. Period lost Loss of synch.
Semantics At-least-once Exactly-once
Error Detection At receiver At sender only
12 Sept. 2002 / p.10Thomas Losert
Observations
An observation consists of an atomic tuple
< observed value, instant, RT-entity Name >
For Communication of Observations across an RS interface a common set of concepts is necessary:
Common representation of values in a Shared code-space Common notion of time and its representation Common meaning of the names of RT entities Access protocol to the information.
12 Sept. 2002 / p.11Thomas Losert
GPS - Time
GPS weeks and GPS seconds since the GPS epoch
(6. Jan. 1980, 00:00:00 UTC)
Advantages:
• Continuous representation of Time(no leapseconds)
• High availability with low jitter
Disadvantages:
• Overflow every 19.6 years because GPS week is represented as a 10 bit value
12 Sept. 2002 / p.12Thomas Losert
Based on GPS; advantages of GPS are preserved
Additional advantages:• Enhanced granularity (about 60 ns)• Easy Access to the full second• No overflow during the lifetime of the product
(horizon of more than 10 000 years)• Easy manipulation of timestamps
Global Notion of Time
2-24 seconds
external time format (8 bytes)
1 sec (20 seconds)239 seconds
12 Sept. 2002 / p.13Thomas Losert
Observations
An observation consists of an atomic tuple
< observed value, instant, RT-entity Name >
For Communication of Observations across an RS interface a common set of concepts is necessary:
Common representation of values in a Shared code-space Common notion of time and its representation Common meaning of the names of RT entities Access protocol to the information.
12 Sept. 2002 / p.14Thomas Losert
Interface File System (IFS)
Hierarchical, distributed File-System that is the
Source and Sink of each communication
Map all relevant properties of a node into the IFS:
• Sensor and actuator data
• Calibration data, parameters, etc.
• Configuration Information
• Node identification (physical name, global name)
• Documentation and pointer to register service
12 Sept. 2002 / p.15Thomas Losert
Global Name
Transducer Node
CORBA-Gateway
Active Master
Active Master
Active Master
Cluster A Cluster B Cluster C
Is the concatenation of
Cluster Name,
Logical Name
File Name, and
Record Name
• Up to 250 Clusters
• Up to 250 Nodes
• Up to 64 Files
• Up to 256 Records
12 Sept. 2002 / p.16Thomas Losert
Observations
An observation consists of an atomic tuple
< observed value, instant, RT-entity Name >
For Communication of Observations across an RS interface a common set of concepts is necessary:
Common representation of values in a Shared code-space Common notion of time and its representation Common meaning of the names of RT entities Access protocol to the information (see TTP/A).
12 Sept. 2002 / p.17Thomas Losert
Overview
• Smart Transducers(Definition, Observations, Interfaces)
• Principles of Operation• Architecture• Sensor Fusion (Definition, Concepts)• Case Study• Conclusion & Outlook
12 Sept. 2002 / p.18Thomas Losert
Three Interfaces of a Node
12 Sept. 2002 / p.19Thomas Losert
Overview
• Smart Transducers(Definition, Observations, Interfaces)
• Principles of Operation• Architecture• Sensor Fusion (Definition, Concepts)• Case Study• Conclusion & Outlook
12 Sept. 2002 / p.20Thomas Losert
Why Time-Triggered?
• Requirement to record value and instant when measurement was performed
• Requirement to perform synchronous distributed measurements
• Requirement to gather multiple measurements with bounded delay
12 Sept. 2002 / p.21Thomas Losert
Principles of Operation: Temporal Firewall
• Best way of communication for Producer• Best way of communication for Consumer• Predictable time-triggered communication• Components have access to a global time• Communication and measurement synchronized• Temporal firewall in communication
12 Sept. 2002 / p.22Thomas Losert
Time-Triggered Protocol/Class A (TTP/A)
• Low-cost time-triggered sensor bus• Supports „Smart Transducers“• Currently subject of a standardization
process at Object Management Group
12 Sept. 2002 / p.23Thomas Losert
Principles of Operation: TTP/A (1)
• One active master• Up to 250 slaves• Communication organized in rounds• TDMA bus allocation
12 Sept. 2002 / p.24Thomas Losert
Principles of Operation: TTP/A (2)
• Time-Triggered Protocol for Fieldbus Applications
• TDMA Bus Access Scheme
• Communication Organized into Rounds
• Supports Various Physical Layers
Each round is initiated by the master by sending the
Fireworks-Byte
• Multipartner (MP): Real-Time Service Interface
• Master/Slave (MS): Monitoring and Configuration
12 Sept. 2002 / p.25Thomas Losert
TTP/A: Principles of Operation (2)
12 Sept. 2002 / p.26Thomas Losert
Overview
• Smart Transducers(Definition, Observations, Interfaces)
• Principles of Operation• Architecture• Sensor Fusion (Definition, Concepts)• Case Study• Conclusion & Outlook
12 Sept. 2002 / p.27Thomas Losert
Architecture
12 Sept. 2002 / p.28Thomas Losert
CORBA
CORBA Smart Transducers Interface (STI)• Allows (re)configuration of the Smart
Transducer cluster, e.g. over the internet• Allows monitoring of the ST cluster• Allows access to the real-time service
interface for cases, when a RT-CORBA supporting end-to-end predictability is used
12 Sept. 2002 / p.29Thomas Losert
Overview
• Smart Transducers(Definition, Observations, Interfaces)
• Principles of Operation• Architecture• Sensor Fusion (Definition, Concepts)• Case Study• Conclusion & Outlook
12 Sept. 2002 / p.30Thomas Losert
„Sensor Fusion is the combination of sensory data or data derived from sensory data such that the resulting information is in some sense better than would be possible when these sources were used individually.“
Definition of Sensor Fusion
12 Sept. 2002 / p.31Thomas Losert
„better“ can mean:• More robust (fault-tolerant sensor clusters)
• Extended spatial and temporal coverage
• Increased confidence
• Reduced ambiguity and uncertainty
• Robustness against interference
• Improved resolution
• Emerging services
Purposes of Sensor Fusion
12 Sept. 2002 / p.32Thomas Losert
Overview
• Smart Transducers(Definition, Observations, Interfaces)
• Principles of Operation• Architecture• Sensor Fusion (Definition, Concepts)• Case Study• Conclusion & Outlook
12 Sept. 2002 / p.33Thomas Losert
A Typical Sensor Fusion Control Loop
12 Sept. 2002 / p.34Thomas Losert
Introducing a Sensor Fusion Model
Three levels of computation:• Node level• Cluster level• Control application level
Well-defined interfaces between levels• Smart Transducer Interface• Environmental image
12 Sept. 2002 / p.35Thomas Losert
Control Loop in the Three-Level Model
12 Sept. 2002 / p.36Thomas Losert
Overview• Smart Transducers
(Definition, Observations, Interfaces)• Principles of Operation• Architecture• Sensor Fusion (Definition, Concepts)• Case Study• Conclusion & Outlook
12 Sept. 2002 / p.37Thomas Losert
Case Study:Autonomous Mobile Robot
• TTP/A fieldbus network with 1 master• 1 node for sensor fusion and navigation• 15 smart transducers (9 actuators/6 sensors)
12 Sept. 2002 / p.38Thomas Losert
ST-Types
• 2 Ultrasonic Far Distance Sensors• 3 Infrared Low Distance Sensors• 1 Luminance Sensor
• 1 Steering Control• 1 Speed Control• 3 Servos for Moving Infrared Sensors• 4 Lighting Control
12 Sept. 2002 / p.39Thomas Losert
Control Loop
12 Sept. 2002 / p.40Thomas Losert
The „Smart Car“
12 Sept. 2002 / p.41Thomas Losert
Overview
• Smart Transducers(Definition, Observations, Interfaces)
• Principles of Operation• Architecture• Sensor Fusion (Definition, Concepts)• Case Study• Conclusion & Outlook
12 Sept. 2002 / p.42Thomas Losert
Conclusion & Outlook
Case Study• Proof of concept for TTP/A• Testbed for Sensor Fusion• Demonstrator for CORBA-STI
The Standard Proposal has been adopted in Jan. 2002 by the Board of Directors and is called Smart Transducers Interface Standard now. The standardization process continues ...
12 Sept. 2002 / p.43Thomas Losert
Thank you for your attention!
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