4.Sensors Mecatrónica – [PDF Document]

  • 8/9/2019 4.Sensors Mecatrónica1/531540 Introduction To Mechatronics: Slide 1Stefan B. WilliamsIntroduction to MechatronicsMech-1540Sensors 1
  • 8/9/2019 4.Sensors Mecatrónica2/531540 Introduction To Mechatronics: Slide 2Stefan B. WilliamsSchedule of EventsQ 2 of Assign 2MID SEMESTER BREAK Spare19/614Due 13/6Major Assignment12/613Case Study : Unmanned Air/Land/Sea Vehicles5/612Case Study : Formula SAE29/511Active Sensor Systems (Graham Brooker)22/510Due 16/5Assignment 2 – Control and Modelling15/59Q 4 of Assign 2System Modelling and Control8/58Q 3 of Assign 2Computer – Software and Design Tools1/57654321Week 17/410/43/427/320/313/3DateComputer – HardwareAssignment 1 – Design ExerciseSensorsActuatorsDesign ProcessIntroductionContentQ 1 of Assign 2Due 11/4Q 3 of Assign 1Q 2 of Assign 1Q 1 of Assign. 1Assignment Notes
  • 8/9/2019 4.Sensors Mecatrónica3/531540 Introduction To Mechatronics: Slide 3Stefan B. WilliamsIndustrial Sensors• Proximity – Mechanical – Optical – Inductive/Capacitive• Position/Velocity – Potentiometer – LVDT – Encoders – Tachogenerator • Force/Pressure• Vibration/acceleration
  • 8/9/2019 4.Sensors Mecatrónica4/531540 Introduction To Mechatronics: Slide 4Stefan B. WilliamsDefinitions• Accuracy: The agreement between the actual value andthe measured value• Resolution: The change in measured variable to whichthe sensor will respond• Repeatability: Variation of sensormeasurements whenthe same quantity is measured several times• Range: Upper and lower limits of the variable that can bemeasured• Sensitivity and Linearity
  • 8/9/2019 4.Sensors Mecatrónica5/531540 Introduction To Mechatronics: Slide 5Stefan B. WilliamsProximity Sensors• Widely used in general industrial automation – Conveyor lines (counting,jam detection, etc) – Machine tools (safety interlock, sequencing)• Usually digital (on/off) sensors detecting thepresence orabsence of an object• Consist of: – Sensor head: optical, inductive, capacitive – Detector circuit – Amplifier – Output circuit: TTL, solid state relay
  • 8/9/2019 4.Sensors Mecatrónica6/531540 Introduction To Mechatronics: Slide 6Stefan B. WilliamsMechanical Proximity Switches• Essentially amechanical switch• On/off operation only• Two general modes – Normally Open (NO) – Normally Closed (NC)• Come in a wide varietyof mechanical forms• For a wide range of usesActuator Common NormallyClosed NormallyOpen
  • 8/9/2019 4.Sensors Mecatrónica7/531540 Introduction To Mechatronics: Slide 7Stefan B. WilliamsExample Mechanical ProximitySwitches
  • 8/9/2019 4.Sensors Mecatrónica8/531540 Introduction To Mechatronics: Slide 8Stefan B. WilliamsWhen to Use MechanicalProximity Switches• Where physical contact is possible• Where definitive position is required• In operation-criticalor safety-criticalsituations• Where environment conditions preclude theuse of optical or inductive sensors
  • 8/9/2019 4.Sensors Mecatrónica9/531540 Introduction To Mechatronics: Slide 9Stefan B. WilliamsApplications and Use ofMechanical Proximity Switches• Easy to integrate into machinery of all types• Requires contact (thus wear)• Range of voltages: DC 0-1000V, AC, etc.• Very robust(explosion proof if required)• Usually used as: – Limit switch – Presence/absence indicator – Door closed/open
  • 8/9/2019 4.Sensors Mecatrónica10/531540 Introduction To Mechatronics: Slide 10Stefan B.WilliamsPlaces You Find MechanicalProximity Switches !
  • 8/9/2019 4.Sensors Mecatrónica11/531540 Introduction To Mechatronics: Slide 11Stefan B.WilliamsOptical Proximity Sensors• Consist of a light source (LED) and lightdetector(phototransistor)• Modulation of signal to minimize ambientlightingconditions• Various models: 12-30V DC, 24-240V AC, power • Output: TTL 5V, Solid-state relay, etc.Demodulator Amplifier Modulator Power OutputMixer SignalPower SupplyLoad
  • 8/9/2019 4.Sensors Mecatrónica12/531540 Introduction To Mechatronics: Slide 12Stefan B.WilliamsOperational Modes• Through Beam: – Long range (20m) – Alignment is critical !• Retro-reflective – Range 1-3m – Popular and cheap• Diffuse-reflective – Range 12-300mm – Cheap and easyto use
  • 8/9/2019 4.Sensors Mecatrónica13/531540 Introduction To Mechatronics: Slide 13Stefan B.WilliamsExample Optical Proximity IOptical FibreDelivery System
  • 8/9/2019 4.Sensors Mecatrónica14/531540 Introduction To Mechatronics: Slide 14Stefan B.WilliamsExample Optical Proximity IISlot BeamSystems
  • 8/9/2019 4.Sensors Mecatrónica15/53
  • 8/9/2019 4.Sensors Mecatrónica16/53
  • 8/9/2019 4.Sensors Mecatrónica17/531540 Introduction To Mechatronics: Slide 17Stefan B.WilliamsOther Optical DevicesLightCurtainCollision Detection
  • 8/9/2019 4.Sensors Mecatrónica18/531540 Introduction To Mechatronics: Slide 18Stefan B.WilliamsUltrasonic Proximity Sensors• Use sound pulses• Measures amplitude and timeof flight• Range provides more thanon/off information• Frequencies 40KHz-2MHzPulseEchoVibrating Membrane(metal or ceramic)Sensor Object
  • 8/9/2019 4.Sensors Mecatrónica19/531540 Introduction To Mechatronics: Slide 19Stefan B.WilliamsWhen to use Ultrasonic Sensors• Provide range data directly:• Level monitoring of solid and liquids• Approach warning (collisions)• Can (usually) work in heavy dust and water • Ambient noise is potentially an issuehttp://www.automationsensors.com/
  • 8/9/2019 4.Sensors Mecatrónica20/531540 Introduction To Mechatronics: Slide 20Stefan B.WilliamsExample ApplicationsCar WashApplicationPaper rollThickness Monitor Waste waterflow volume
  • 8/9/2019 4.Sensors Mecatrónica21/531540 Introduction To Mechatronics: Slide 21Stefan B.WilliamsInductive and CapacitiveProximity Sensors• Inductive sensors use change in localmagnetic field to detect presence of metaltarget• Capacitive Sensors use change in localcapacitance caused by non-metallic objects• Generally short ranges only• Regarded as very robust and reliable
  • 8/9/2019 4.Sensors Mecatrónica22/531540 Introduction To Mechatronics: Slide 22Stefan B.WilliamsExample Inductive Sensors IDetection ofopen/close functionsDetection ofrotation
  • 8/9/2019 4.Sensors Mecatrónica23/531540 Introduction To Mechatronics: Slide 23Stefan B.WilliamsExample Inductive Sensors IIBulk mounted inductivesensors. Detect presence of object without contact.Range 3mm +/- 10%
  • 8/9/2019 4.Sensors Mecatrónica24/531540 Introduction To Mechatronics: Slide 24Stefan B.WilliamsExample Capacitive SensorsPanel Mounted CapacitiveSensor. Can detect wood, plastic and metal.Range 3mm-25mmFlat mounted CapacitiveSensor. Used for detecting panels of glass.Range=10mm +/- 10%
  • 8/9/2019 4.Sensors Mecatrónica25/531540 Introduction To Mechatronics: Slide 25Stefan B.WilliamsPosition and VelocityMeasurement• Position and velocity measurementis often required in feedbackloops• For positioning, and velocity control• Position measurement: – Potentiometers – LVDT – Encoders• Velocity Measurement:• Tachometer
  • 8/9/2019 4.Sensors Mecatrónica26/531540 Introduction To Mechatronics: Slide 26Stefan B.WilliamsPotentiometersR VinVoutAn analog sensor Works as a voltage divider
  • 8/9/2019 4.Sensors Mecatrónica27/531540 Introduction To Mechatronics: Slide 27Stefan B.WilliamsTypes of Potentiometer • Wirewound – Wiper slides along coil of Ni-chrome wire – Wire tends to fail, temperature variations• Cermet – Wiper slides on conductive ceramic track – Better than wire inmost respects• Plastic film – High resolution – Long life and good temperature stability
  • 8/9/2019 4.Sensors Mecatrónica28/53
  • 8/9/2019 4.Sensors Mecatrónica29/531540 Introduction To Mechatronics: Slide 29Stefan B.WilliamsWhen to use a Potentiometer • Require analog signal for control• Require absolute positional information• Low cost• Temperature and wear variations• Not in dusty or wet environments
  • 8/9/2019 4.Sensors Mecatrónica30/53
  • 8/9/2019 4.Sensors Mecatrónica31/531540 Introduction To Mechatronics: Slide 31Stefan B.WilliamsLVDT Signal Conditioning• Uses AC modulation,demodulation andphase comparison• Available in a singlemonolithic packagePower SupplyCarrier Oscillator AmplitudeControlLVDTCurrentAmplifier Demodulator PhaseShifter ZeroSetAC Power
  • 8/9/2019 4.Sensors Mecatrónica32/531540 Introduction To Mechatronics: Slide 32Stefan B.WilliamsExample LVDTsSpring-loadedStandard for useIn hydraulic cylindersFree core LVDTs foruse in hostile environmentsAnd total emersion
  • 8/9/2019 4.Sensors Mecatrónica33/531540 Introduction To Mechatronics: Slide 33Stefan B.WilliamsWhen to use an LVDT• High accuracy• Linear operation (synchro resolver isequivalent rotary LVDT)• Harsh environment• Analog position control• Embedding (in cylinder for example)
  • 8/9/2019 4.Sensors Mecatrónica34/531540 Introduction To Mechatronics: Slide 34Stefan B.WilliamsOptical Encoders• Encoders are digital Sensors commonly used toprovide positionfeedback for actuators• Consist of a glass or plastic disc that rotatesbetween a light source (LED) and a pair of photo-detectors• Disk is encoded with alternate light and darksectorsso pulses are produced as disk rotates
  • 8/9/2019 4.Sensors Mecatrónica35/531540 Introduction To Mechatronics: Slide 35Stefan B.WilliamsEncoder Internal Structure
  • 8/9/2019 4.Sensors Mecatrónica36/531540 Introduction To Mechatronics: Slide 36Stefan B.WilliamsIncremental Encoders• Pulses from leds arecounted to providerotary position• Two detectors are usedto determine direction(quadrature)• Index pulse used todenote start point• Otherwise pulses arenot unique
  • 8/9/2019 4.Sensors Mecatrónica37/531540 Introduction To Mechatronics: Slide 37Stefan B.WilliamsAbsolute Encoders• Absolute encoders havea unique code that canbe detected for everyangular position• Often in the form of a“grey code”; a binarycode of minimal change• Absolute encoders aremuch more complexand expensive thanincremental encoders
  • 8/9/2019 4.Sensors Mecatrónica38/531540 Introduction To Mechatronics: Slide 38Stefan B.WilliamsEncoder processing• Need a squaring circuitto digitise signal• A counter and indexmonitor • Generally available inmonolithic form• Often with algorithmsfor control externallyprogrammable
  • 8/9/2019 4.Sensors Mecatrónica39/531540 Introduction To Mechatronics: Slide 39Stefan B.WilliamsWhen to Use an Encoder • Require accurateposition information: – 10,000 line incremental – 360 line absolute• Digital feed-back loop• Compact andreasonably rugged (notas good as inductive)• Linear encoders alsoavailable
  • 8/9/2019 4.Sensors Mecatrónica40/531540 Introduction To Mechatronics: Slide 40Stefan B.WilliamsTachometers• Measurement of rotaryspeed using a DCgenerator • Essentially a motorrunning in reverse• Used to be common tohave these attached tomotors to enabledirectanalog feedback• Much less common nowwith digital control (useincrementalencoders)Tacho generator for largeindustrial plant (GE)
  • 8/9/2019 4.Sensors Mecatrónica41/531540 Introduction To Mechatronics: Slide 41Stefan B.WilliamsForce and Pressure• Force and Pressure generally measuredindirectly throughdeflection of an alternatesurface• Mechanism include: – Physical motion and measurementusing (eg) anLVDT – Strain gauges (metal that changes resistance whenstressed) – Piezo electric materials that generate acurrentwhen deformed
  • 8/9/2019 4.Sensors Mecatrónica42/531540 Introduction To Mechatronics: Slide 42Stefan B.WilliamsLVDT Load CellTable ForceSpring or PistonLVDTOuter Platform
  • 8/9/2019 4.Sensors Mecatrónica43/531540 Introduction To Mechatronics: Slide 43Stefan B.WilliamsStrain Gauge Bridge R R R RGF L L R R GF εε∆ ∆= =∆∆ = ⋅ ⋅TensionStrain Gauges( )3 23 4 1 21 2 43, ,42measexcGGmeasmeas excV R RV R R R Rassume R R R R R R RV thenGF V V ε= − + += == + ∆−=−
  • 8/9/2019 4.Sensors Mecatrónica44/531540 Introduction To Mechatronics: Slide 44Stefan B.WilliamsExample Load CellsReaction torqueload cellAxial load cellhttp://www.entran.com/ltoc.htmSubminatureLoad cells
  • 8/9/2019 4.Sensors Mecatrónica45/531540 Introduction To Mechatronics: Slide 45Stefan B.WilliamsSub-miniature Load cellsAll signal conditioningand amplification integratedwith the sensor Load cell bridge structure
  • 8/9/2019 4.Sensors Mecatrónica46/531540 Introduction To Mechatronics: Slide 46Stefan B.WilliamsPiezo Load Cells• Distortion of crystal,either quartz or BaTiO3• Used for accuratemeasurement of smallloads• Come in the form of:• single axis load washers• or multiple axis loadwashers and tables
  • 8/9/2019 4.Sensors Mecatrónica47/531540 Introduction To Mechatronics: Slide 47Stefan B.WilliamsPressure• Pressure measured by: – Pitot tube and – Deformation of fixedmembrane• Deformation measuredusing same methods asfor force:• Spring (manometer)• Piezo distortion• Strain gaugesMiniatureIndustry IP69High Temperature
  • 8/9/2019 4.Sensors Mecatrónica48/531540 Introduction To Mechatronics: Slide 48Stefan B.WilliamsAcceleration• Acceleration is alsomeasured via the forceexerted by anaccelerating mass• Distortion of a piezo• Motion of a cantilever • Strain on massrestraints• Accelerometers mainlyused to measurevibrationSingle Axis,10,000gShielded forSevereenvironmentEMIshielded
  • 8/9/2019 4.Sensors Mecatrónica49/531540 Introduction To Mechatronics: Slide 49Stefan B.WilliamsTri-axial Accelerometers• Triaxial accelerometersused in mobile systems – In high-performance cars – Inside rotating elementsof turbines – In aircraft elements• Provide vibrationinformation• Provide short-termposition dataTriple axisAccelerometerFor racing cars
  • 8/9/2019 4.Sensors Mecatrónica50/531540 Introduction To Mechatronics: Slide 50Stefan B.WilliamsSilicon MachinedAccelerometersCantilever beamsUsed in eg air-bags
  • 8/9/2019 4.Sensors Mecatrónica51/531540 Introduction To Mechatronics: Slide 51Stefan B.WilliamsSilicon Gyroscopes• Structural arrangementof silicon which recordscentrifugal accelerationand thus angular speed• Use strain-gaugebridges and/or piezostructure to recorddeformations• Multiple componentelements to calibrateother accelrations
  • 8/9/2019 4.Sensors Mecatrónica52/531540 Introduction To Mechatronics: Slide 52Stefan B.WilliamsInertial Systems• Many different types of accelerometer andgyroscope systems• Mechanical bodies, fibre optic, etc• Together in an orthogonal arrangement ofaccelerometers andgyroscopes, thesecomprise an inertial measurement unit (IMU)• An IMU that is used for navigation is called aninertialnavigation system (INS)• These are widely used in aircraft and missilenavigation andguidance
  • 8/9/2019 4.Sensors Mecatrónica53/53Aerospace INShttp://www.littongcs.com/products/2guidance/space/overview.htmlAircraftBallisticMissile

    • Publicaciones Similares