1、Topics: Introduction to Robotics CS 491/691(X),Lecture 4 Instructor: Monica Nicolescu,CS 491/691(X) - Lecture 4,2,Review,DC motors inefficiencies, operating voltage and current, stall voltage and current and torquecurrent and work of a motor Gearing Up, down, combining gears Servo motors Effectors D
2、OF Locomotion: holonomicity, stability Manipulation: direct and inverse kinematics,CS 491/691(X) - Lecture 4,3,Sensors,Physical devices that provide information about the world Based on the origin of the received stimuli we have: Proprioception: sensing internal state - stimuli arising from within t
3、he agent (e.g., muscle tension, limb position) Exteroception: sensing external state external stimuli (e.g., vision, audition, smell, etc.) The ensemble of proprioceptive and exteroceptive sensors constitute the robots perceptual system,CS 491/691(X) - Lecture 4,4,Sensor Examples,Physical Property,S
4、ensor,contact,switch,distance,ultrasound, radar, infrared,light level,photocells, cameras,sound level,microphone,rotation,encoders and potentiometers,acceleration,accelerometers gyroscopes,CS 491/691(X) - Lecture 4,5,More Sensor Examples,Physical Property,Sensor,magnetism,compass,smell,chemical,temp
5、erature,thermal, infra red,inclination,inclinometers, gyroscopes,pressure,pressure gauges,altitude,altimeters,strain,strain gauges,CS 491/691(X) - Lecture 4,6,Knowing whats Going On,Perceiving environmental state is crucial for the survival or successful achievement of goals Why is this hard? Enviro
6、nment is dynamic Only partial information about the world is available Sensors are limited and noisy There is a lot of information to be perceived Sensors do not provide state Sensors are physical devices that measure physical quantities,CS 491/691(X) - Lecture 4,7,Types of Sensors,Sensors provide r
7、aw measurements that need to be processed Depending on how much information they provide, sensors can be simple or complex Simple sensors: A switch: provides 1 bit of information (on, off) Complex sensors: A camera: 512x512 pixels Human retina: more than a hundred million photosensive elements,CS 49
8、1/691(X) - Lecture 4,8,Getting Answers From Sensors,Given a sensory reading, what should I do? Deals with actions in the world Given a sensory reading, what was the world like when the reading was taken? Deals with reconstruction of the world Simple sensors can answer the first question Their output
9、 can be used directly Complex sensors can answer both questions Their information needs to be processed,CS 491/691(X) - Lecture 4,9,Signal to Symbol Problem,Sensors produce only signals, not symbolic descriptions of the world To extract the information necessary for making intelligent decisions a lo
10、t of sensor pre-processing is needed Symbols are abstract representations of the sensory data Sensor pre-processing Uses methods from electronics, signal processing and computation,CS 491/691(X) - Lecture 4,10,Levels of Processing,Finding out if a switch is open or closed Measure voltage going throu
11、gh the circuit electronicsUsing a microphone to recognize voice Separate signal from noise, compare with store voices for recognition signal processingUsing a surveillance camera Find people in the image and recognize intruders, comparing them to a large database computation,CS 491/691(X) - Lecture
12、4,11,Perception Requirements,Perception requires more than just sensors: Sensors Power and electronics Computation More power and electronics Connectors To connect it all,CS 491/691(X) - Lecture 4,12,Perception Designs,Historically perception has been treated in isolation perception in isolation per
13、ception as “king” perception as reconstruction Generally it is not a good idea to separate: What the robot senses How it senses it How it processes it How it uses it,CS 491/691(X) - Lecture 4,13,A Better Way,Instead it is good to think about it as a single complete design The task the robot has to p
14、erform The best suited sensors for the task The best suited mechanical design that would allow the robot to get the necessary sensory information for the task (e.g. body shape, placement of the sensors),CS 491/691(X) - Lecture 4,14,A New Perceptual Paradigm,Perception without the context of actions
15、is meaningless Action-oriented perception How can perception provide the information necessary for behavior? Perceptual processing is tuned to meet motor activity needs World is viewed differently based on the robots intentions Only the information necessary for the task is extracted Active percepti
16、on How can motor behaviors support perceptual activity? Motor control can enhance perceptual processing Intelligent data acquisition, guided by feedback and a priori knowledge,CS 491/691(X) - Lecture 4,15,Using A Priori Knowledge of the World,Perceptual processing can benefit if knowledge about the
17、world is available Expectation-based perception (what to look for) Knowledge of the world constraints the interpretation of sensors Focus of attention methods (where to look for it) Knowledge can constrain where things may appear Perceptual classes (how to look for it) Partition the world into categ
18、ories of interaction,CS 491/691(X) - Lecture 4,16,Sensor Fusion,A man with a watch knows what time it is; a man with two watches isnt so sure Combining multiple sensors to get better information about the world Sensor fusion is a complex process Different sensor accuracy Different sensor complexity
19、Contradictory information Asynchronous perception Cleverness is needed to put this information together,CS 491/691(X) - Lecture 4,17,Neuroscientific Evidence,Our brain process information from multiple sensory modalities Vision, touch, smell, hearing, sound Individual sensory modalities use separate
20、 regions in the brain (sight, hearing, touch) Vision itself uses multiple regions Two main vision streams: the “what” (object recognition) and the “where” (position information) Pattern, color, movement, intensity, orientation,CS 491/691(X) - Lecture 4,18,What Can We Learn from Biology?,Sensor funct
21、ion should decide its form Evolved sensors have specific geometric and mechanical properties Examples Flies: complex facetted eyes Birds: polarized light sensors Bugs: horizon line sensors Humans: complicated auditory systems Biology uses clever designs to maximize the sensors perceptual properties,
22、 range and accuracy,CS 491/691(X) - Lecture 4,19,Psychological Insights: Affordances,Affordances: refer to the meaning of objects in relation to an organisms motor intents Perceptual entities are not semantic abstractions, but opportunities that the environment presents Perception is biased by the r
23、obots task A chair: Something to sit in Something blocking the way Something to throw if attacked,CS 491/691(X) - Lecture 4,20,How Would You Detect People?,Use the interaction with the world, keep in mind the task Camera: great deal of processing Movement: if everything else is static: movement mean
24、s people Color: If you know the particular color people wear Temperature: can use sensors that detect the range of human body heat Distance: If any open-range becomes blocked,CS 491/691(X) - Lecture 4,21,How Would You Measure Distance?,Ultrasound sensors (sonar) provide distance measurement directly
25、 (time of flight) Infra red sensors provide return signal intensity Two cameras (i.e., stereo) can be used to compute distance/depth A laser and a camera: triangulate distance Laser-based structured light: overly grid patterns on the world, use distortions to compute distance,CS 491/691(X) - Lecture
26、 4,22,Sensor Categories,Passive Sensors Measure a physical property from the environment Active Sensors Provide their own signal and use the interaction of the signal with the environment Consist of an emitter and a detector Sensor complexity Determined by the amount of processing required Active/pa
27、ssive Determined by the sensor mechanism,CS 491/691(X) - Lecture 4,23,Electronics for Simple Sensors,Ohms law Explains the relationship between voltage (V), current (I) and resistance (R)Series resistance Resistances in series add upVoltage divider Voltage can be divided by using two resistors in se
28、ries,V = IR,Vin = I(R1 + R2),Vout = Vin R2/(R1 + R2),CS 491/691(X) - Lecture 4,24,Switch Sensors,Among the simplest sensors of all Do not require processing, work at “circuit” level If the switch is open there is no current flowing If the switch is closed current will flow Can be Normally open (more
29、 common) Normally closed,CS 491/691(X) - Lecture 4,25,Uses of Switch Sensors,Contact sensors: detect contact with another object (e.g., triggers when a robot hits a wall or grabs an object, etc.) Limit sensors: detect when a mechanism has moved to the end of its range (e.g., triggers when a gripper
30、is wide open) Shaft encoder sensors: detect how many times a shaft turns (e.g., a switch clicks at every turn, clicks are counted),CS 491/691(X) - Lecture 4,26,Example of Switch Uses,In everyday life Light switches, computer mouse, keys on the keyboard, buttons on the phone In robotics Bump switch:
31、detect hitting an obstacle Whisker: Attach a long metal whisker to a switch; when the whisker has bent enough the switch will close Place a conductive wire (whisker) inside a metal tube; when the whisker bends it touches the tube and closes the circuit,CS 491/691(X) - Lecture 4,27,Light Sensors,Ligh
32、t sensors measure the amount of light impacting a photocell The sensitivity of the photocell to light is reflected in changes in resistance Low when illuminated Vsens High when in the dark: Vsens Light sensors are “dark” sensors Could invert the output so that low means dark and high means bright,=
33、0v,= +5 v,CS 491/691(X) - Lecture 4,28,Uses of Light Sensors,Can measure the following properties Light intensity: how light/dark it is Differential intensity: difference between photocells Break-beams: changes in intensity Photocells can be shielded to improve accuracy and range,Rphoto2 = Rphoto1Vo
34、ut = 2.5 vRphoto2 Rphoto1Vout = gnd,CS 491/691(X) - Lecture 4,29,Polarized Light,Waves in normal light travel in all directions A polarizing filter will only let light in a specified direction polarized light Why is it useful? Distinguish between different light sources Can tell if the robot is poin
35、ted at a light beacon One photocell will receive only ambient light, while the other receives both ambient and source light In the absence of filters both photocells would receive the same amount of light,CS 491/691(X) - Lecture 4,30,Polarized Light Sensors,Filters can be combined to select various
36、directions and amounts of light Polarized light can be used by placing polarizing filters: at the output of a light source (emitter) at the input of a photocell (receiver)Depending on whether the filters add (pass through) or subtract (block) the light, various effects can be achieved,CS 491/691(X)
37、- Lecture 4,31,Resistive Position Sensors,Finger flexing in Nintendo PowerGlove In robotics: useful for contact sensing and wall-tracking Electrically, the bend sensor is a simple resistance The resistance of a material increases as it is bent The bend sensor is less robust than a light sensor, and
38、requires strong protection at its base, near the electrical contacts Unless the sensor is well-protected from direct forces, it will fail over time,CS 491/691(X) - Lecture 4,32,Potentiometers,Also known as “pots” Manually-controlled variable resistor, commonly used as volume/tone controls of stereos
39、 Designed from a movable tab along two ends Tuning the knob adjusts the resistance of the sensor,CS 491/691(X) - Lecture 4,33,Biological Analogs,All of the sensors we have seen so far exist in biological systems Touch/contact sensors with much more precision and complexity in all species Polarized l
40、ight sensors in insects and birds Bend/resistance receptors in muscles and many more.,CS 491/691(X) - Lecture 4,34,Active Sensors,Active sensors provide their own signal/stimulus (and thus the associated source of energy) reflectance break-beam infra red (IR) ultrasound (sonar) others,CS 491/691(X)
41、- Lecture 4,35,Reflective Optosensors,Include a source of light emitter (light emitting diodes LED) and a light detector (photodiode or phototransistor) Two arrangements, depending on the positions of the emitter and detector Reflectance sensors: Emitter and detector are side by side; Light reflects
42、 from the object back into the detector Break-beam sensors: The emitter and detector face each other; Object is detected if light between them is interrupted,CS 491/691(X) - Lecture 4,36,Photocells vs. Phototransistors,Photocells easy to work with, electrically they are just resistors their response
43、 time is slow suitable for low frequency applications (e.g., detecting when an object is between two fingers of a robot gripper) Reflective optosensors (photodiode or phototransistor) rapid response time more sensitive to small levels of light, which allows the illumination source to be a simple LED
44、 element,CS 491/691(X) - Lecture 4,37,Reflectance Sensing,Used in numerous applications Detect the presence of an object Detect the distance to an object Detect some surface feature (wall, line, for following) Bar code reading Rotational shaft encoding,CS 491/691(X) - Lecture 4,38,Properties of Refl
45、ectivity,Reflectivity is dependent on the color, texture of the surface Light colored surfaces reflect better A matte black surface may not reflect light at all Lighter objects farther away seem closer than darker objects close by Another factor that influences reflective light sensors Ambient light
46、: how can a robot tell the difference between a stronger reflection and simply an increase in light in the robots environment?,CS 491/691(X) - Lecture 4,39,Ambient light,Ambient / background light can interfere with the sensor measurement To correct it we need to subtract the ambient light level fro
47、m the sensor measurement This is how: take two (or more, for increased accuracy) readings of the detector, one with the emitter on, one with it off, then subtract themThe result is the ambient light level,CS 491/691(X) - Lecture 4,40,Calibration,The ambient light level should be subtracted to get on
48、ly the emitter light level Calibration: the process of adjusting a mechanism so as to maximize its performance Ambient light can change sensors need to be calibrated repeatedly Detecting ambient light is difficult if the emitter has the same wavelength Adjust the wavelength of the emitter,CS 491/691(X) - Lecture 4,41,Readings,F. Martin: Chapter 3, Section 6.1 M. Matari: Chapters 7, 8,
