06-Chapter+6-Sensors

1IntroductionIndustrial robot requires sensory feedback to:1. Locate randomly placed object;2. Allow for variations in sape of objects;!. "rotect a#ainst dan#erous and une$pected situations. %specially if te robot must work close to umans:&. Allow 'intelli#ent( recovery form error conditions;). "erform quality control.*e main objective of incorporatin# sensors in robotic system is to enable robots to work in nonstructural and random environments.+ensors will make robots more intelli#ent. ,ut te associated robotic software must ave te ability to receive data from te sensors and to process te necessary real time information and commands needed for te decision makin#.-at is +ensin# ./ollect information about te world+ensor 0 an electrical1mecanical1cemical device tat maps an environmental attribute to a quantitative measurement%ac sensor is based on a transduction principle - conversion of ener#y from one form to anoter*ransduction to electronics*ermistor: temperature0to0resistance%lectrocemical: cemistry0to0volta#e"otocurrent: li#t intensity0to0current"yroelectric: termal radiation0to0volta#e2umidity: umidity0to0capacitanceLen#t 3L45*: Linear variable differential transformers6 : position0to0inductance7icropone: sound pressure0to08anytin#92uman sensin# and or#ans4ision: eyes 3optics: li#t62earin#: ears 3acoustics: sound6*ouc: skin 3mecanics: eat6;dor: nose 3vapor0pase cemistry6*aste: ton#ue 3liquid0pase cemistry6/ounterpart.%$tended ran#es and modalities4ision outside te k2? ran#eAltrasonic ran#e measurement/emical analysis beyond taste and smell" This is important when mounting a camera near or on the end)e6ector of a root")O0" 1olume SensorH A sensor that pro'ide three)dimensional information" The sensor may otain the information y using the directional laser or acoustic range ;nders" )T+cematic representation of a trian#ulation ran#e finderI(A/E RE%RESENTATIONH Crom the diagram elow" C=7#y> is used to denote the two)dimensional image out of a tele'ision camera or other imaging de'ice"H ?7@ and ?y@ denote the spatial coordinates =image plane>H ?f@ at any point =7#y> is proportional to the rightness =intensity> of the image at that point"H In form suitale for computer processing# an image function f=7#y> must e digiti&ed oth spatially and in amplitude =intensity>" -igiti&ation of the spatial coordinates =7#y> will e $nown as image sampling# while amplitude digiti&ation is $nown as intensity or grey)le'el quanti&ation"H The array of =N# (> rows and columns# where each sample is sampled uniformly# and also quanti&ed in intensity is $nown as a digital image" Each element in the array is called image element# picture element =or pi7el>"P>E6ects of reducing sampling grid si&e"a> 4*,74*," > ,4D7,4D" c> *,E7*,E" d> D07D0" e> .,7.,"P1 %ffect produced by reducin# te number of intensity levels wile maintainin# te spatial resolution constant at )12$)12. *e 2)P0: 12O0 and P&0levels are of acceptable quality. a6 2)P: b6 12O: c6 P&: d6 !2: e6 1P: f6 O: #6 &: and 6 2 levelsP2ILL9(INATION TEC3NI89ESH Illumination of a scene is an important factor that often a6ects the comple7ity of 'ision algorithms"H A well designed lighting system illuminates a scene so that the comple7ity of the resulting image is minimised# while the information required for o!ect detection and e7traction is enhanced"H Aritrary lighting of the en'ironment is often not acceptale ecause it can result in low contras images# specular re:ections# shadows and e7traneous details"H There are 0 main illumination techniques for a root wor$ space 2P!ILL9(INATION TEC3NI89ES*"-ICC9SE)LI/3TIN/H This technique is for smooth# regular surface o!ect" It is used where surface characteristic are important"HE7ample2P&5iffuse0li#tin# tecniqueILL9(INATION TEC3NI89ES,"FACGLI/3TIN/H %roduce lac$ and white image" This technique suited for applications in which silhouettes of o!ect are suHcient for recognition or other measurement" H E7ample2P),ackli#tin# tecniqueILL9(INATION TEC3NI89ES ." STR9CT9RE- LI/3TIN/H Consist of pro!ecting points# stripes# grids onto wor$ surface"H This lighting technique has , important ad'antages2*" It estalishes a $nown light pattern on the wor$ space and disturances of this indicate the presence of an o!ect# thus simplifying the o!ect detection prolems"," Fy analysing the way which the light pattern distorted# it is possile to gain insight into three)dimensional characteristics of the o!ect"PP+tructured li#tin# tecniqueH The following ;gure illustrates the structured lighting technique using two light planes pro!ected from di6erent directions# ut con'erging on a single stripe on the surface" The two light sources guarantee that the o!ect will rea$ the light stripe only when it is directly elow the camera"H This technique is suitale for mo'ing o!ect"H Note2 ?The line scan camera sees only the line on which the two light planes con'erge# ut two)dimension information can e accumulated as the o!ect mo'e past the camera@PJ!. +* Corce 5 Torque Sensors"J&20SI)I0(4 VE+0CI)56 ,CCE+E7,)I0( SE(S07S%otentiometerH %otentiometer transducers can e used to measure oth linear and angular displacementJ)3a6 "otentiometer 3b6 3b6 +cematic dia#ram of te potentiometerLinear 1ariale -i6erential Transformer =L1-T>H L-1T is a roust and precise de'ice which produce a 'oltage output proportional to the displacement of a ferrous armature for measurement of root !oints or end)e6ectors" It is much e7pensi'e ut outperforms the potentiometer transducer"JPLinear 4ariable 5ifferential *ransformer 3L45*6Corce 5 Torque SensorsH Corce transducers are often ased on displacement principles" There 'arious type force and torque transducer a'ailale commerciallyJJA force0measurin# device based on a compression sprin# and L54*.JO*is fi#ure illustrate a tension load cell. It can be used to measure te force required to pick up eavy load in industryCorce 5 Torque SensorsH Corce can e measured using pie&oelectric principle" H Cigure shows a load washer type pie&oelectric force transducer" It is designed to measure a7ial forces" It is preloaded when manufactured and can measure oth tensile and compressi'e forces"JTCorce 5 Torque SensorsH (easured using pie&oelectric principle" H Cigure shows a three)component dynamometer type pie&oelectric force transducer that measures three orthogonal components of force"O>(otor EncoderIncremental Optical Encoders) direction ) resolution gratinglight emitterlight sensordecode circuitryABA leads F Incremental %ncoder: It #enerates pulses proportional to te rotation speed of te saft.H $irection can also be indicated wit a two pase encoder:Absolute Optical Encoders=ray /odeAsed wen loss of reference is not possible. =ray codes: only one bit can#es at a time 3 less uncertainty6.H *e information is transferred in parallel form 3many wires are necessary6.000001011010110111101100000001010011100101110111BinaryOther Odometry Sensors Resolver Potentiometer = varying resistanceIt as two stator windin#s positioned at T> de#rees. *e output volta#e is proportional to te sine or cosine function of te rotorUs an#le. *e rotor is made up of a tird windin#: windin# /Inertial SensorsH*yroscopes @(easure the rate of rotation independent of the coordinate frame @Common applications2 H3eading sensors#Cull Inertial Na'igation systems =INS>HAccelerometers @(easure accelerations with respect to an inertial frame @Common applications2 HTilt sensor in static applications# 1iration Analysis# Cull INS SystemsAccelerometers HThey measure the inertia force generated when a mass is a6ected y a change in 'elocity" HThis force may change @ The tension of a string @ The de:ection of a eam @ The 'irating frequency of a massAccelerometerH(ain elements of an accelerometer2 *" (ass ," Suspension mechanism ." Sensing elementHigh quality acceleroeter! i"clu#e a !er$o loo% to i%ro$e the li"earity o& the !e"!or'kxdtdxct d x dm F + + =22/yroscopes HThese de'ices return a signal proportional to the rotational 'elocity" HThere is a large 'ariety of gyroscopes that are ased on di6erent principles/loal %ositioning System =/%S>Space Segmentttp:11www.cnde.iastate.edu1staff1swormley1#ps1#ps.tml2& satellites 3Lseveral spares6 broadcast time: identity: orbital parameters 3latitude: lon#itude: altitude6/loal %ositioning System =/%S>Space Segmentttp:11www.cnde.iastate.edu1staff1swormley1#ps1#ps.tml2& satellites 3Lseveral spares6 broadcast time: identity: orbital parameters 3latitude: lon#itude: altitude6Noise IssuesHReal sensors are noisyHOrigins2 natural phenomena M less)than)ideal engineeringHConsequences2 limited accuracy and precision of measurementsHCiltering2 @software2 a'eraging# signal processing algorithm@hardware tric$y2 capacitorThan$ youN