Sensors and detectors
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Sensors and detectors. How to use sensor and detectors (in robotics ) RACE PROJECT VIGO (SPAIN) September 26-29, 2012. Definitions (1). Sensor: a device for sensing a physical variable of a physical system or an environment

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Sensors and detectors

Sensors and detectors

Howtousesensor and detectors (in robotics)

RACE PROJECT

VIGO (SPAIN) September 26-29, 2012


Definitions 1

Definitions (1)

  • Sensor: a device for sensing a physical variable of a physical system or an environment

  • A sensor is in most cases associated with electronic circuits (converter) to generate a conditioned, normalized, amplified electric signal

  • A sensor plus a converter form a transducer, a device which transforms energy from one type to another (in this specific case electric energy)

  • Sometimes the sensor reacts by generating an electric signal itself, so it can be considered a transducer

  • Definitions of sensors and transducers do not always agree, so the word “sensor” alone might be enough to indicate these types of devices

  • Sensors are what the robotsneedtoknow the world …

    • fromhttp://www.robotshop.com/sensors.html


Classifications 1 physical characteristic

Classifications 1 (physicalcharacteristic)

  • Primary (sensors/transducers)

    • Temperature

    • Light (photoelettric)

    • Strain gauge / Mechanicaltension

    • Magneticfield

    • Displacement (potenziometers)

  • Secondary (sensors/transducers)

    • Force, acceleration, pressure (based on strain gauge)

    • Displacement (based on photoelettric, magneticfield, capacitance, …)

    • Speed (based on displacement and time)


Classifications 2 output electric signal

Classifications 2 (output electricsignal)

  • Analog

    • The output isanelectricsignalwhichvariescontinuouslyaccordingto the variationsof the physicalvariablesbeeingmeasured

  • Digital

    • The output isanelectricpulsesignalwhich can assume onlytwovalues: logical 0 and 1. The frequency or the code associatedwith the pulsesequencecarries the information about the physicalvariablesbeeingmeasured


Classifications 3 energetic behavior

Classifications 3 (energeticbehavior)

  • Active

    • Theyprovideanelectricsignalwhich can bedirectlyprocessedwithoutfurtherconsumptionofenergy: forexample the photovoltaiccells and termocouples

  • Passive

    • The requireanelectricalgenerator in ordertotransduce the physicalvariable in anelectricsignal: forexample the potentiometer


Specifications static and dynamic parameters

Specifications (static and dynamicparameters)

  • Transfer function (transcaratteristic)

  • Monotone function

  • Linearity

  • Offset

  • Operationrange

  • Hysteresis

  • Sensitivity

  • Resolution

  • Repeatibility

  • Stability

  • Responsetime (timecostant e bandwidth)

  • Input and output impedance


Specifications parametri caratteristici statici e dinamici

Specifications (parametri caratteristici statici e dinamici)

Monotone function

Linearity

Sensitivity


Sensors in this presentation

Sensors (in thispresentation)

  • Thermoresistance, thermistor, PN junction, integratedsensor (temperature)

  • Photoresistor, photodiode, phototransistor (light)

  • Tachometer (angolar speed)

  • Encoder (differenttipesfordisplacement and speed)


Temperature thermoresistance 1

Temperature - Thermoresistance (1)

Metallicconductorswith a known “resistance vs temperature caracteristic curve”.

The basicphysicalprincipleofthesedevicesisthat the electricconductivity (resistivity) decreases (increases) as the temperature increases. Thisholdstrueformaterialslikeplatinum, nickel, copper.

The valueof T is in 0C

If β and γ are smallcomparedto the valueofαthis relation can beconsideredlinear (forexampleplatinum)

Ifnotitmightbenecessarytoperform a linearization (forexamplefor nickel and copperfortemperaturesabove 1000C)

Thermoresistancehave a low sensitivity


Temperature thermoresistance 2

Temperature - Thermoresistance (2)

Exampleof a temperature monitoring system from 00C to 3000C, output tensionbetween 0V and 10 V, based on PT100.

VR

V1


Temperature thermistor ntc

Temperature - Thermistor NTC

Unipolar semiconductor material

The basicphysicalprincipleofthesedevicesisthat the electricconductivity (resistivity) of the pure semiconductor material increases (decreases) as the temperature increases.

NTC (Negative Temperature Coefficient); T is in 0K

Thermistors are very sensitive, but R isstrongly non linearwithrespectto T.

Withhighlydopedsemicobductor material itispossibletoobtain PTC type (Positive Temperature Coefficient) thermistors


Temperature pn junction

Temperature - PN junction

In a directbias PN junctionwithcostantcurrent the directdiodetensiondecreasesby 2,5 mVwith the increaseof 10C of the temperature.

The exactvalueof the tensionfor a given temperature dependsupon the valueof the costantcurrentof the diode.

A smallsignaljunctiondiodelike 1N914 or 1N4148 can beeasilyusedas a temperature sensor.

Goodtimeresponse

Calibrationisrequired


Temperature ic ad590 1

Temperature - IC AD590 (1)

Integratedsensor:

Deviceswhichembed the sensor plus the circuitstonormalize, linearize, amplify the signal, in otherwords a “transducer”.

The integrated T sensors are based on the lineardipendencebetween VD e T of the directbiascostantcurrentdiode (seeprevouspage). The junctionis the BE junctionof a BJT transistor

AD590: high impedencecurrent generatori

T is in 0K; K isμA/0K

The generatedcurrentisdirectlyproportionalto the absolute T value

It can belocated far from the measurementinstrument (itworkswithcurrent) and itisnotverysensitivtonoise

It can show scale and offset errors

The output currentsignalisconvertedtotensiomthrough a resistance plus a I/V converter (forexamplebased on OpAmp)


Temperature ic ad590 2

Temperature - IC AD590 (2)


Light sensor photoresistor 1

Light sensor – Photoresistor (1)

  • Devices in which the information associatedto light isconverted in variationofresistance: resistivitydecreases (conductivityincreases) as the light increases

  • Madewith N typesemiconductore materiale (not a PN junction)

  • Thoughness, low priced, sensitivity

  • They can dissipatehighvaluesofpower (forexampletocontrolrelays)

  • Limitedbandwidth


Light sensor photoresistor 2

Light sensor – Photoresistor (2)


Light sensor photodiode 1

Light sensor – Photodiode (1)

  • When a reversedbiased PN junctionisilluminated the total reverse currentisgivenby the sum of the typical revers current plus a componentproportionalto the luminousflux

  • Thesedevices are very fast and are highlyusedasdetectors in telecommunicationsystemsbased on fiberoptics


Light sensor photodiode 2

Light sensor – Photodiode (2)


Speed tachometer generator 1

Speed-Tachometergenerator (1)

The tachometer generator (dynamo) is a small generator that produces an output voltage that is very accurately determined by its operating speed


Tachometer generator 2

Tachometergenerator (2)

  • Simulation file


Speed incremental encoder 1

Speed - Incremental encoder (1)

Devicewhichmeasures the angolar displacementof a shaft in ordertogetinformationsabout the angularspeed (forexampleof a motor)

Itismadeby a rotary disc and a Led/fototransistor system.

On the circumferenceof the disc a set ofholeshasbeen set all at the samedistance on from the other.

When the disc rotates the light beameitherisinterrupted (no hole and bjt in cut-off mode) or goesthroughfrom the led to the phototransistor (precenceof the hole and bjt in saturation mode).

The phototransistorgenerates a trainpulse, onepulseforeachholecrossedby the light beam.

From the numberofpulsesitispossibletodetermine the angulardisplacement and, in relation totime, the angularspeed

With the incremental encoder itispossibletomeasure the speed, butitisnotpossibletodetermine the rotational direction


Speed incremental encoder 2

Speed - Incremental encoder (2)


Speed incremental encoder 21

Speed - Incremental encoder (2)

INSERIRE LA FIGURA


Speed incremental encoder 3

Speed - Incremental encoder (3)

Two/threephasesincremental encoder todetermine the rotational direction


Speed incremental encoder 4

Speed - Incremental encoder (4)

Two/threephasesincremental encoder


Speed absolute encoder 1

Speed – Absolute encoder (1)

Usedtodetermine the shaftangular position.

Eachcombinationofholesiscoded so toprovide the angular position of the disc.

Normally the Gray code isused in ordertoprevent the transmissionoferrors

WithsimplecombinatoryExorcircuititispossibletoconvertGray code in natualbinary code


Motor control with encoder 1

Motor controlwith encoder (1)

Analogcontrol system


Motor control with encoder 2

Motor controlwith encoder (2)

Digitalcontrol system


Sensors society of robots

Sensors(Society ofrobots)

  • Sensorsspecificforrobotics: Society ofrobots

  • http://www.societyofrobots.com/sensors.shtml


Sensors in robotics applications

Sensors in robotics & applications

  • Accelerometer

  • Color Sensors

  • DigitalCompass

  • Encoder (Slot, Rotary, Linear)

  • InfraredEmitter/Detector

  • Load and TorqueSensors

  • Mercury Tilt Switch

  • Photoresistor

  • Robot Computer Vision

  • SharpIRRangefinder

  • Sonar

  • Tactile Bumper Switch


Sensors in robotics applications1

Sensors in robotics & applications

  • Accelerometer

  • Color Sensors

  • DigitalCompass

  • Encoder (Slot, Rotary, Linear)

  • InfraredEmitter/Detector

  • Load and TorqueSensors

  • Mercury Tilt Switch

  • Photoresistor

  • Robot Computer Vision

  • SharpIRRangefinder

  • Sonar

  • Tactile Bumper Switch


Robot for the contest

Robot for the contest

  • Ideasfor the final meeting


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