Ceng4480 a1

Sensors (v.1c) 1

JANGAM RAKESH KUMAR

SNIGDHA ROYSANJAY KALKAREPRIYA ANAMIKANEHA

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CENG4480_A1Sensors

Sensing the real world

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Sensors

Motion (Orientation/inclination )sensorsForce/pressure/strainPositionTemperature and humidityRotary positionLight and magnetic field sensors

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Motion (Orientation/inclination sensors

Acceleration GyroscopeCompassTilt Sensor

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Accelerometer

Functions: measure acceleration in one or more directions,

position can be deduced by integration. Orientation sensing : tilt sensor Vibration sensing

Methods: Mass spring method ADXL78 (from Analog Device )

Air pocket method (MX2125)

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ADXL78 (from Analog Device http://www.analog.com/UploadedFiles/Data_Sheets/ADXL78.pdf )Mass spring type (output acceleration in G)Measure the capacitance to create output

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ADXL330 accelerometer for three (X,Y,Z ) directions http://www.analog.com/UploadedFiles/Data_Sheets/ADXL330.pdf

3D

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2D translational accelerometerMX2125

Gas pocket typeWhen the sensor

moves, the temperatures of the 4 sensors are used to evaluate the 2D accelerations

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Accelerometer demo:orientation sensing

Self-balance RobotSensor demo

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Accelerometer demo :Tilt sensing demo

Tilt sensing demo

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Gyroscopes

Gyroscope Measure rotational angle

Rate Gyroscope measure the rate of rotation along 3-axes of X

(pitch), Y (roll), and Z (yaw). Modern implementations are using

Microelectromechanical systems (MEMS) technologies.

Gyroscope

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FEATURES Complete rate gyroscope on a single chip Microelectromechanical systems (MEMS) Z-axis (yaw-rate) response

APPLICATIONS GPS navigation systems Image stabilization Inertial measurement units Platform stabilization

Gyroscope to measure Rational acceleration ADXRS401

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Compass-- the Philips KMZ51 magnetic field sensor

50/60Hz (high) operation, a jitter of around 1.5°

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Rate gyroscope demo

Using Gyroscope compass for virtual reality application in an iphone

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Application of motion sensorsSelf balancing robot

by Kelvin Ko http://hk.youtube.com/watch?v=2u-EO2FDFG0

20cm

20cm

35cm35cm

Motion sensors: gyroscope and accelerometer

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Complementary filterComplementary filter

Since Since

Combine two sensors to find outputCombine two sensors to find output

1616

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Complementary filterComplementary filterθθ=rotation angle, =rotation angle, =filter time constant, s=laplace =filter time constant, s=laplace operator operator http://en.wikipedia.org/wiki/Low-pass_filter

1717

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Self Balanced robot using Self Balanced robot using complementary filtercomplementary filter

1818

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Tilt Sensor by OMRON

Detect tilting 35 ~ 65 degrees in right-and-left inclination

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Force/pressure/strain

Force-sensitive resistor (FSR)Strain gaugeFlexionAir pressure

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Force Sensing Resistors

FSR402

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Force Sensing Resistor Demo

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Application for a walking robot

Walking robot

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Application of force sensing resistance sensors to balance a walking robot

Balancing Floor tilled rightupper leg bend left

Floor tilled leftupper leg bend rightNeutral position

Four sensors under the foot

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Four Force sensors under the foot

D

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The Nao robot uses force feedback at its feet

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Strain Gauge : Force sensors

Piezoelectric crystal: produces a voltage that is proportional to force applied

Strain gauge: cemented on a rod. One end of the rod is fixed, force is applied to the other end. The resistance of the gauge will change with the force.

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Single element strain gauge

sensitive to temperature change.

resistance gauge unstrainedR

gauge theof length Lfactor, gauge strainG and G for

4424220

L

L

R

R

L

LGVb

R

RVb

RR

RV

RR

R

R

RVV bb

Vb

R

R R

Gauge=R+Rgauge

load

rodV0

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Four-element (Wheatstone bridge) strain gauge sensor,

Four times more sensitive than single gauge system; not sensitive to temperature change.

All gauges have unstrained resistance R.

L

LGV

R

RV

RRRR

RR

RRRR

RRVV bbb 2

20

b1=R-Rt2=R+ R

b2=R-R t1=R+RVb

t1 t2

b1 b2

rod

load

V0

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Flexion (bend) sensors

resistance: 10 KΩ (0°); 30-40 KΩ (90°) /

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Felixon resistance Demo

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Air pressure sensor

Measure up to 150 psi (pressure per square inch ).

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Position sensors

Infra-red range sensorLinear and Rotary position sensors

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Infra-red Range detectors by SHARP (4 to 30cm)

An emitter sends out light pulses. A small linear CCD array receives reflected light.

The distance corresponds to the triangle formed.

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IR radar using the Sharp range detector

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Position sensors, from[1]

Rotary Linear

Optical shaft encoder

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Magnetic rotary encoder)

non touch sensing

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Optical rotary encoder)

The light received (on or off) will tell the rotation angle)

3 light emitters

3 light receivers

Rotation shaft

Light paths

http://www.youtube.com/watch?v=RuIislTGOwA

Crank shaft sensor

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Temperature and humidity

Temperaturehumidity

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Temperature sensorsLM135/235/335 features(from NS)

Directly calibrated in °Kelvin 1°C initial accuracy available Operates from 400 µA to 5 mA Less than 1 Ohm dynamic impedance Easily calibrated Wide operating temperature range 200°C over range Low cost

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Application note (connecting to an ADC e.g. ADC0820 or ADC0801)

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Capacitive Atmospheric Humidity Sensor

BCcomponents 2322 691 90001 10-90%RH Dc

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Leaf Sensor Alerts When Plants Are Thirsty

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TSL250, TSL251, TSL252LIGHT-TO-VOLTAGE OPTICAL SENSORS

Light-to-voltage optical sensors, each combining a photodiode and an amplifier (feedback resistor = 16 MW, 8 MW, and 2 MW respectively).

The output voltage is directly proportional to the light intensity on the photodiode.

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Cadmium Sulfoselenide (CdS) Photoconductive Photocells

Light sensing using CdS

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Hall effect Sensors for sensing magnetic flux“B field”, see:

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Application on Magnetic levitation 磁懸浮

Magnetic levitation Train Model 磁懸浮火車

frog levitation

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Hall effect sensors and brushless DC motors

Brushless DC motor

Is it using Hall effect sensor? Don't known.

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Novel sensors

Kinect /

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Many KINECT DIY projects

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Control systemsExample: A temperature control

system

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Control example: Temperature control system

Temp.Sensor A/D

CPU

D/APulse Width modulation

& solid state relay

Heater

Timer

Sample&

Hold

Digital controlcircuit

Instrum. amp.

Water tank

computer

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Temperature control method 1: ON-Off (bang-bang) control (poor)

Easy to implement, bad control result -- contains overshoot undershot. Algorithm for on-off-control:

Loop forever: If (Tfrom_sensor > Treq required temperature)

then (heater off ) else (heater on).

Treq

Undershoot

Overshoot

Time

TempOn-off control result

Steady state error

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Temperature control method 2 : Proportional-integral-differential (PID) temperature control (good)

Init. (set required temperature Treq)

Loop forever{ get temperature T from sensor, e=T - Treq

then Tw =e*G*{Kp+Kd*[d(e)/dt] +Ki*e dt } else

} //G,Kp,Kd,Ki can be adjusted by user

Tw

Tw

Proportional, differential, integral

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PID block diagram

Figure 1 - Parallel PID block diagram

Kd

Ki

Kp

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PID control using pulse width modulation PWM

Fixed period and fixed number of pulses

Tw (depends on e )

Treq

PID control resultof method 2

On-off control: oscillates and unstable

Time

Temperature

Time

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Summary

Studied the characteristics of various sensors

and their applications