Sensors human sensing 5+N senses <link> basic sensory tactile touchless (distant) virtual advanced sensory e.g. camera, radar / lidar, MS Kinect
Human senses Traditional sight smell taste touch hearing Other senses balance acceleration pain pressure/tension time temperature kinesthetic sense internal body senses
Sensors local x remote detection (contact x contactless) detection x measurement Is there an obstacle? How far is the obstacle? active x passive
Favourite sensors in (mobile) robotics tactile micro switches, end switches, bumpers electrical motor current consumption measurement, induced current sensing/measurement etc. directional acoustic, optical point measurement using detection of reflected beam obstacle detection, environment mapping line sensors directional measurement multiplexed in time cameras image processing MEMS use of microscopic phenomena to replace big mechanical sensors various sensor types (accelerometers / gyros, pressure, temperature, ) also as actuators (pumps, motors ) virtual indirect measurement, using action consequences to detect the action
Measurement using signal reflection TOF measuring time needed for the signal to return precise measurement needed phase-shift sending modulated signal, measuring phase shift of reflected signal 2 * π * f * TOF
Measurement using signal reflection ultrasonic, infrared, laser, radar intensity measurement possible in addition the signal must get reflected the measurement is active environment vulnerability interferences detectable signal
Measurement using signal interruption gate detection of signal reflection (or lack of) reflected signal intensity thresholding
Ultrasonic direct TOF measurement is possible measurement range ~ 1 cm 10m multiple reflection detection is possible
Ultrasonic Reality:
Infrared PSD beam spread exploitation up to single meters distance measurement illumination problems Example: Sharp GP2D12, GP2Y0A21
Infrared single narrow beam reflexive short range CNY-70, QRD1113/4, GP2S60
Laser 1D, 2D, 3D rangefinder, scanner 20 km possible
Some popular laser rangefinders SICK Hokuyo LMS 100 TIM 310 LMS 400 NAV
MEMS components in scale 1-100 µm accelerometers gyros pressure sensors displays, pumps, engines
MEMS components in scale 1-100 µm accelerometers gyros pressure sensors displays, pumps, engines
MEMS
Odometry measurement of distance travelled wheel revolution measurement motor revolutions measurement gearbox! sensing mechanical inductive, capacitive resolver, synchro optical Hall effect sensor
Hall effect V H = k I B
encoders absolute x relative rate quadrature binary Gray single-track Gray
Rate sensor detects change between black/white (or between nothing/reflection, nothing/signal) number of changes indicates rotation angle frequency of changes indicates speed
Rate
PostSript the Mighty /grc 0.5 def /noofarc 4 def /frc 360 noofarc div def /radius 30 def 0 2 noofarc { /pos exch def black 0 0 moveto 0 0 radius pos grc sub frc mul pos 1 grc sub add frc mul arc fill white 0 0 moveto 0 0 radius pos 1 grc sub add frc mul pos 2 add grc sub frc mul arc fill } for
Quadrature two sensors two tracks displaced by ½ step, sensors on a cord single track, two sensors displaced by ½ step angle
Quadrature clockwise counterclockwise phase A B phase A B 1 0 0 4 1 0 2 0 1 3 1 1 3 1 1 2 0 1 4 1 0 1 0 0
How to interpret the signal?
Binary more sensors in different tracks problem edges & sensor placement & noise
Gray code single change in each step recursive construction 0 + level n-1 1 + reversed level n-1 0 1 00 01 11 10 000 001 011 010 110 111 101 100 0000 0001 0011 0010 0110 0111 0101 0100 1100 1101 1111 1110 1010 1011 1001 1000
Binary vs Gray code
Single-track Gray code Precision problem 01111 At least 9 tracks needed for 1 Gray code precision 1994 N.B.Spedding 2001 Hiltgen, Paterson single-track for 9 sensors, 360 positions 10000 10100 11100 11110 11010 11000 01000 01010 01110 01101 01100 00100 00101 00111 10111 10110 00110 00010 10010 10011 11011 01011 00011 00001 01001 11001 11101 10101 10001
Some real encoders Old style computer mouse
Some real encoders US Digital E4 E4 Miniature Optical Kit Encoder 100-360 CPR (400-1440 PPR) 2 channel quadrature TTL squarewave out
Some real encoders Austria Microsystems AS5035 AS5035 Magnetic Rotary Position Sensor 2 quadrature A/B outputs 64 pulses per channel / 256 edges per rev. / 1.4 per step Index output (one pulse per revolution) user-programmable zero position 3.3V / 5V power
DIY Encoder sensors CNY70, QRD1114 + encoder wheel