Common Sensing Techniques for Reactive Robots

By Safa Hamdare

OutlineLogical sensorsDesigning a Sensor SuiteTypes of a sensorAttributes of a sensorProprioceptive SensorsGPSProximity SensorsSonar, Infrared, CCD Cameras, Stereo camera pairs, Light stripers, Laser

University Asked QuestionsList the sensors used for reactive robots and explain the GPS system. (Dec 2010, Dec 2012, June 2013)Write short note on Proximity Sensor and representing knowledge in an uncertain domain. (Dec 2010)What is proximity sensor? Explain Sonar Sensor? (Dec 2011)Explain steps in designing reactive behavioural system. (Dec 2010 Dec 2011)What are the attributes of Sensor? List different types of Sensors? (June 2011)Describe Infrared Sensor and Sonar Sensor? (June 2013)

Logical SensorsA unit of sensing or module (supplies a particular percept). It consists of the signal processing and the software processing. Can be easily implemented as a perceptual schema.Different sensors/perceptual schemas can produce the same percept - motor schema doesnt care!Behavior can pick whats availableExample: ring of IRs, ring of sonar'sIf sensor fails, then another can be substituted without deliberation or explicit modelingConflicts in allocation can be solved by using logical sensors (deliberation is required to assign)

Active vs. Passive (Example)

Active sensorsSensor emits some form of energy and then measures the impact as a way of understanding the environment- Ex. Ultrasonics, laser

Passive sensorsSensor receives energy already in the environment - Ex. CameraPassive consume less energy, but often signal-noise problemsActive often have restricted environmentsStereoCamera pairThermalsensorLaserrangerSonarsBumpsensor

Behavioral Sensor FusionSensor fusion is a broad term used for any process that combines information from multiple sensors into a single percept.In some cases multiple sensors are used when a particular sensor is too imprecise or noisy to give reliable data. Adding a second sensor can give another vote for the percept.

When a sensor leads the robot to believe that a percept is present, but it is not, the error is called a false positive.

The robot has made a positive identification of percept, but it was false. Likewise, an error where the robot misses a percept is known as a false negative.False positiveFalse negative

Sensing Model11Sensor/TransducerBehaviorAction

Sensing in Reactive ParadigmEach behavior has its own dedicated sensing. One behavior literally does not know what another behavior is doing or perceiving.BehaviorBehaviorBehavior

PerceptualSchemasMotor SchemasBehavioral Sensor Fusion: -1.sensor fissionThis sensor fission in part as a take off on the connotations of the word fusion in nuclear physics. In nuclear fusion- energy is created by forcing atoms and particles together, while in fission- energy is creating by separating atoms and particles.

PerceptualSchemaMotor SchemaBehavioral Sensor Fusion: -2. action-oriented sensor fusionThis type of sensor fusion is called action-oriented sensor fusion to emphasize that the sensor data is being transformed into a behavior-specific representation in order to support a particular action, not for constructing a world model.

PerceptualSchemaMotor SchemaBehavioral Sensor Fusion: -3. sensor fashionSensor fashion, an alterative name intended to imply the robot was changing sensors with changing circumstances just as people change styles of clothes with the seasons.

Designing a Sensor Suite -Types/ Categories of Sensors values internal to the system (robot), e.g. battery level, wheel position, joint angleused for observation of the environments, objects

Designing a Sensor Suite-Attributes of a sensor Field of view, range : does it cover the right area?Accuracy & repeatability : how well does it work?Responsiveness in target domain : how well does it work for this domain?Power consumption : may suck the batteries, dry too fastReliability : can be a bit flakey, vulnerableSize : always a concern!Computational Complexity : can you process it fast enough?Interpretation Reliability : do you believe what its saying?

Should be considered for the entire sensing suite :Simplicity- Simple sensors which have straightforward hardware and operating principles are more desirable than sensors which are complex and requires constant maintenance.Modularity- In order to reconfigure a sensor suite (add new sensors, remove ones that aren't appropriate for the task), designer could remove one sensor and/or its perceptual schema without impacting any other sensing capability.Redundancy In military application, it is imperative that the robot functions correctly, since it would put people at risk to try to retrieve the robot and fix it. Physical Redundancy(there are several instances of physically identical sensors on the robot) Logical Redundancy(another sensor using a different sensing modality can produce the same percept or releaser)

Designing a Sensor Suite -Attributes of a sensor suite

Sensor CategoriesProprioceptiveGlobal Positioning System(GPS)Inertial Navigation System (INS)CompassExteroceptiveProximity SensorSONAR SensorINFRA RED Sensor

A very precise positioning systemGPS systems work by receiving signals from satellites orbiting the Earth.GPS does not work indoors(environmental limit)Satellite Based 24 satellites 20,200 km high orbit

Proprioceptive Sensors(2)-Global Positioning System (GPS)

BUT!Although it is a very precise geographic positioning systemIt is very easy to get yourself into troubleWhy?Because you (probably) dont understand how it worksAnd that leads to garbage

Characteristics of GPSAlmost! Accurate (precise)Characteristics of GPS

Segments of GPS1. Space SegmentA constellation of 24 satellites2. Control SegmentA network of earth-based facilities3. Users SegmentSource:Trimble

Segments of GPSSource:Trimble1. Space SegmentA constellation of 24 satellites

GPS Monitoring Station

How GPS Works Uses measurements from 4+ satellitesDistance = travel time x speed of lightSource:Trimble

Determining GPS Position Suppose the distance from Satellite A to our position is 11,000 miles At this point we could be located anywhere on the specified sphere Next, let us take another measurement from a second satellite, Satellite B Now our position is narrowed down to the intersection of theses two sphere

Determining GPS Position Taking another measurement from a 3rd satellite narrows our position down even further, to the two points So by ranging from 3 satellites we can narrow our position to just two points in space These points are located where the 3rd sphere cuts through the intersection of first two spheres

How do we decide which one is our true location? We could make a 4th measurement from another satellite to determine the true point However, GPS receivers use a 4th satellite to precisely locate our position We can eliminate one of the two points that gives a ridiculous answer The ridiculous point may be too far from the earthOR

Determining GPS Position

How accurate is GPS?Depends on some variables

Common use of GPSGIS data collection & mappingB. NavigationC. Recreation

GPS for Navigation

GPS for Navigation GPS in PDA Are getting popular in car Comes with voice guidance

GPS in recreation

GPS in Farmland

Proximity Sensors(1)-Sonar or ultrasonic

Sonar refers to any system for using sound to measure range. (use a sonar for underwater vehicles ).The process of finding your location based upon sonar is echolocation.

Ultrasonic sensors generate high frequency sound waves and evaluate the echo which is received back by the sensor. Sensors calculate the time interval between sending the signal and receiving the echo to determine the distance to an object.

Ultrasonic is possibly the most common sensor on commercial robots operating. Polaroid Ultrasonic Transducer

SONAR: RELIABILITY Blind zone is when an echo arrives before the transducer is ready to receive and objects are not detected reliably.

Sensor readings vary based upon:Distance to object(s).Angle that object makes with respect to sensor axis.Direction that objects enter sensing range.

Proximity Sensors(1) - Three problems with sonar range readings ForeshorteningCross-talkSpecular reflection

SONAR: 1. ForeshorteningSonar has a 30 degree field of view, this means that sound is being broadcast in a 30 degree wide cone.If the surface is not perpendicular to the transducer, one side of the cone will reach the object first and return a range first.Most software assumes the reading is along the axis of the sound wave.If it uses the reading(which is really the reading for 15 degree) the robot will respond to wrong data.

SONAR: 2. Specular Reflection Sensitivity to obstacle angle can result in improper range readings.When the beam angle of incidence falls below a certain critical angle specular reflection errors occur.

Sonar: 3. CrosstalkUsing multiple fixed sensors can lead to crosstalkCrosstalk is interference in which echoes emitted from one sensor are detected by others.

Sonar: 3. Crosstalk SolutionCrosstalk signals are impossible to detect unless signals are unique (coded)Crosstalk can be reduced by carefully timing the emitting of signalsEmit from one and wait for a time intervalEmit from a select few that may not have interferenceEmit adjacent sensors at different frequencies

Power consumptionHighReliabilityLots of problemsSizeSize of a Half dollar, board is similar size and can be creatively packagedComputational ComplexityLow; doesnt give much informationInterpretation Reliabilitypoor

Proximity Sensors(1)- Attributes of ultrasonic

They emit near-infrared energy and measure whether any significant amount of the IR light is returned. These often fail in practice because the light emitted is often washed out by bright ambient lighting or is absorbed by dark materials (i.e., the environment has too much noise).Proximity Sensors(2) - Infrared ray (IR) Sharp GP2Y0A21YK

Proximity Sensors(2):INFRARED RANGE SENSORSEmit light from Infrared LEDLight is reflected from objectReceiver measures strength of light returnedRange depends on object propertiesShiny objects (metal) are difficult to detectCannot detect glassWhite/black surfaces report different ranges

Proximity Sensors(2):INFRARED RANGE SENSORS

Thank you

*It consists of the signal processing from the physical sensor and the software processing needed to extract the percept. ***Sensing in the Reactive Paradigm is local to each behavior, or behavior- specific. Each behavior has its own dedicated sensing. In many cases, this isimplemented as one sensor and perceptual schema per behavior. But in other cases, more than one behavior can take the same output from a sensor andprocess it differently (via the behaviors perceptual schema). One behavior literally does not know what another behavior is doing or perceiving.******At the cost of 15 billion dollar of your tax money*****Speed of the light: 186,000 mile/sec300,000 km/sec3x10^8 meter/sec**********Farm equipment capable of producing yield map during harvesting shows how crop yield varies across the field. Allowing farmers to plan fertilizer application for future crops.**an angle of incidence is the angle between a beam incident on a surface and the line perpendicular to the surface at the point of incidence, called the normal. The beam can be formed by any wave: optical, acoustical, microwave, X-ray etc. The angle of incidence at which light is first totally internally reflected is known as the critical angle. The angle of reflection and angle of refraction are other angles related to beams. the critical angle is defined as the angle of incidence which provides an angle of refraction of 90-degrees. ***