lec 5 sensors for mobile robots - national chiao tung ...isci.cn.nctu.edu.tw/courses/95_course_1/lec...
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Lec 5 Sensors for Mobile Robots
Importance of sensorsMost used sensors for mobile robotsInterfacing electronics
An autonomous mobile robot moving around in an unstructured and dynamically changing environment must use various sensors to obtain information about its surroundings to determine its action and accomplish assigned task .
Importance of sensors
From the viewpoint of control, sensor data are required to feedback the actual state of the plant or process, such that the desired state can be achieved. Depending on how the feedback loop is closed, the behavior of robot needs various types of sensor information.
C P
S
Camera
IVaVd△F
Fi
Fa
+
_
Ts = 0.01sec
Ts = 0.5sec
Encoder
Types of robotic sensors
Internal sensors: sensors used for robots to understand the state of itself.e.g. sensors for self-localization (pose estimation),
sensors for motor servo control (shaft encoders), gyros, limit switches, etc
External sensors: sensors used for robots to understand the external world.e.g. ultrasonic range sensors, infrared sensors, laser scanner (range finder), image sensor, microphone, touch sensor, gas sensor, etcOn-board sensors: sensors that are installed on board the robot.
Types of robotic sensors (Cont.)
Intelligent environment: intelligent devices that are installed (deployed) in the environment. These devices can measure the changes of environment as well as robot pose and provide the information to the robot.e.g. Ultrasonic sensor network
Wi-Fi, ZigBee sensor networkRFID systemnetworked cameras
Human friendly room of KAIST, Korea
Elderly-care robot of KAIST
A general connection for sensor inputs
Digital inputs
Switch is released (open)+5v logic1
switch is pressed (closed)0v logic 0
+5v+5v
GND
Sensor signal
+5v
Vsens: connects to either digital input circuitry or analog input circuitry.
Nc No C Touch sensor:Logic high = not pressedLogic low = pressed
Using touch sensors to turn around a corner
Light sensor (Analog inputs)
R2
R1
Vout
Vin
inout VRR
RV21
2+
=
Connecting a resistive sensor
47k
Vsens
Rphoto
+5v
Single photocell circuit1. Brightly illuminated
Rphoto : smallVsens : close to 0
2.DarkRphoto : largeVsens : close to 5V
Connecting a photocell,Analog input, need an A/D converter
Use of light sensors
• Light seeking experiment
Differential photocell sensor
Vsens
Rphoto1
Rphoto2
+5v
12
15
photophoto
photo
RR
RVsens
+=
choose photocell that haves a relatively small dark resistance (i.e. about 10k)
Ω≈+ kkk
25.847
110
1
Wire a pair of photocells to produce a voltage that represents the difference in value between the two.
Resistive position sensors
VL
A
B
d
VsdT
Eth=Vs x
Rth=Rp x(1-x)
RL
xdd
T=
LthL
sL RRRxVV+
=
RLRP
Photo diodes
Photo diode/ photo transistors vs. photocells(CdS) photo resistors
- rapid response time- more sensitive to small level of
light (e.g. from LED element)
Near-infrared proximity sensor
• ~880nm from LED element (Emitter)These sensors typically do not return actual distance to an object, they signify whether or not something is present within the cone of detection.These types of sensors usually have much narrower beam width than sonar range finders.
IR photo diode
Sonar
Laser range finder
Reflective optosensors (active sensors)
Light is reflective off a surface into a detector element, consisting of an emitter LED and a detector photo diode
emitter detectorTransmitter LED and Receiver photo diode
Ambient light is a problem
+5v
i
330Ω47k
Vsens
The more light received by the phototransistor, the more current flows. This creates a voltage drop in the 47K pull-up resistor. This voltage drop is reflected in a smaller voltage on the Vsenssignal line. i =0.01mAV= i R = 0.01*10-3*47*103= 0.47VVsens= 5 - 0.47 = 4.53V
Measurement of light intensity
Imax=100mA
50Ω
+5v
2k
50k
Vcc
2N2222
100Ω
Vo
Vcc
Light sensor interface circuitry
Light emitting LEDReceiving photo transistor
Break-beam sensors
Vsens
+5v
47k
330Ω
GND
+5v
The break-beam device consists of a light-emitting component aimed at a light-detecting component. When an opaque object comes between the emitter and detector, the beam of light is occluded, and the output of the detector changes
Modulated IR signal
IR detectors respond to a modulated carrier sent by the near-infrared LED. The programmer is responsible for blinking the LED in certain pattern such that the detector will respond.
LM538Gndsignal+5v
Stabilized voltage
Modulated signal
40k carrier
Sharp GP1U 52X near-infrared proximity detector
Light is modulated so that intensity of ambient light will not affect the sensitivity of module.Liteon IR330, 38KHz 940nm
Single Infrared SignalTransmit single infrared signal
Receive single infrared signal660μs
26μs
660μs
Continuous Infrared Signal
Transmitted signal660μs continuous pulse
and 1800 μs logic low.
Received signal660μs logic Low and
1800 μs logic High.
660μs
26μs
0V
5V
1800 μs 1800 μs
660 μs
1800 μs
0V 1800 μs 1800 μs
660 μs
1800 μs
5V
Actual
time
600μs 600μs
ideal
(strong)
(weak)
Transmitted signal
Module output
Delay 3 blinks
Delay 8-9 blinks
Pulse width different, depending on the strength of signal don’tknow when to read state of signal Received signal is integrated weak
signal takes longer to integrate to comparator’s trip point
Actual received signal
Start 1 1 1 0 1 0 0 0 stopBit form
Start 0 1
Bit interval
2200μs1560μs1120μs
.. .. .. ..
550μs 550μs 550μs 550μs
How to read a digital code?
Coded Infrared SignalLow interval of transmitted signal
Start bit :1120 μs Logic 1 :1560 μs Logic 0 :2200 μs
Received signal code
550 μs
1120 μs 1560 μs 2200 μs
Start 1 0
26μs
550μs
550 μs
1120 μs 1560 μs 2200 μs
Start 1 0
Decoding of infrared signal
Look at elapsed time between falling edges to determine if a bit is “1” or “0”.
Ex: 1.67ms --> start2.11ms --> 12.75ms --> 0
Sony unit: 1.2ms = 0
1.8ms = 1
Shield of light
IR modules receive light(signals) from wide angles need to narrow angle of received signal to leave it on it.
Window tube (shield )
(Side view)(Front view)
Check point #3Homing: need to recognize a digital code for distinguish robot’s home.Basic Stamp: can use COUNT command to count pulses (1-0-1)COUNT Pin, Period, VariablePeriod: time period that cycles are counted for
variable:where count is stored
During contest, goal will be randomly assigned needto be able to quickly change robot’s goal
Ultrasonic ranging system
SONAR (Polaroid 6500)Measures the time of flight for a sonar “chirp” to bounce off a target and return to the sonar (Echo). More accurate than IR, giving a distance to a direction, possible to make a scanning of the environment.
Echoreceived
Generatechirp
transmitter
receiver
speaker
microphone
countduration
Processed echo
Transmission .. ..
INIT(trigger)
Echo
60ms 40ms
Polaroid 6500 sonar ranging system
Characteristics of Sonar system
A transducer which acts as both the speaker and microphoneA circuit boardchirp frequency 50kHz (49.4kHz), 16 cyclesBlanking of signal in the beginning for 2.38ms (40cm)
d(cm)40
Characteristics of ultrasonic ranging system
22.5°
45°
S0S1
S2
S3
S4
S5
S6
S7
S8
S9
S10
S11
Limitations
Specular reflection
beam angle = 22.5°
Bean angle of the ultrasonic transducer causes measurement error
Beam angle of ultrasonic transducers
Optical distance sensing detector with Sharp GP2D02
PSD(1-D)Position sensitive detector (photo diode plus ckt)Infrared emitter (laser diode)
An IR emitter LED projects a spot of modulated light onto the target surface.
The light is focused on a 1D PSD element.
The angle of the incoming light will change depending on the distance between the target surface and the sensor.
The spot of light will project to different point along the PSD.
The location of the light spot on PSD is a function of distance.
Other types of sensors for environment detection
Pyroelectric sensor can detect the existence of heat generated by human body (1~2 μm
infrared)Cameraa. CCDb. CMOSc. PTZImage frames contain much information of the immediate environment. It’s therefore required to segment useful features and extract information need for task execution.
image acquisition + image processing + recognition algorithm ( visual servoing ,visual tracking )
Laser Sensor for Navigation
Laser scanner Can get accurate environment distance, fast scanning, powerful, but expensive. 75Hz, 81m (10mm resolution), 0~ 180Deg (0.25/0.5/1 Deg resolution)RS 232,RS 422.
Hardware
Laser scanner
IPC
Motion control card
Laser scanner
Laser scanner data
Experimental result
Blue: Robot trajectory recorded by the proposed methodRed: Robot trajectory recorded by odometer only
-300 -200 -100 0 100 200 3000
100
200
300
400
500
600
X(cm)
Y(c
m)
Localization System
Odometer
Experimental result
-500 -400 -300 -200 -100 0 100 200 300 400 5000
100
200
300
400
500
600
700
800
900
1000
X(cm)
Y(c
m)
Robot trajectory recorded by the proposed method
Real-Time Imaging System
TI TMS320C6416 DSK
CMOS Sensor ICM205B Frame Buffer
AL422B
FLEX10K70RC240
Eye-in-Hand ConfigurationThe robot is equipped a 3 degree-of-freedom manipulator to grasp objects.Eye-in-hand configuration for camera mounting.Real-time robotic vision system for image processing.Foot and gripper motion control cards to activate motors.
Foot and gripperMotion control card
IPC
BatteryBattery
CMOS sensor board
Real-time robotic vision system
Power supply (DC-DC converter)