1、Autonomous Mobile Robots CPE 470/670,Lecture 4 Instructor: Monica Nicolescu,CPE 470/670 - 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 DOF Locomotio
2、n: holonomicity, stability Manipulation: direct and inverse kinematics,CPE 470/670 - Lecture 4,3,Effectors,Effector: any robot device that has an effect on the environment Robot effectors Wheels, tracks, arms grippers The role of the controller get the effectors to produce the desired effect on the
3、environment, based on the robots task,CPE 470/670 - Lecture 4,4,Wheels,Wheels are the locomotion effector of choice in robotics Simplicity of control Stability If so, why dont animals have wheels? Some do! Certain bacteria have wheel-like structures However, legs are more prevalent in nature Most ro
4、bots have four wheels or two wheelsand a passive caster for balance Such models are non-holonomic,CPE 470/670 - Lecture 4,5,Differential Drive & Steering,Wheels can be controlled in different ways Differential drive Two or more wheels can be driven separately and differently Differential steeringTwo
5、 or more wheels can be steered separately and differently Why is this useful? Turning in place: drive wheels in different directions Following arbitrary trajectories,CPE 470/670 - Lecture 4,6,Getting There,Robot locomotion is necessary for Getting the robot to a particular location Having the robot
6、follow a particular path Path following is more difficult than getting to a destination Some paths are impossible to follow This is due to non-holonomicity Some paths can be followed, but only with discontinuous velocity (stop, turn, go) Parallel parking,CPE 470/670 - Lecture 4,7,Why Follow Trajecto
7、ries?,Autonomous car driving Surgery Trajectory (motion) planning Searching through all possible trajectories and evaluating them based on some criteria (shortest, safest, most efficient) Computationally complex process Robot shape (geometry) must be taken into account Practical robots may not be so
8、 concerned with following specific trajectories,CPE 470/670 - Lecture 4,8,Manipulation,Manipulation: moving a part of the robot (manipulator arm) to a desired location and orientation in 3D The end-effector is the extreme part of the manipulator that affects the world Manipulation has numerous chall
9、enges Getting there safely: should not hurt others or hurt yourself Getting there effectively Manipulation started with tele-operation,CPE 470/670 - Lecture 4,9,Teleoperation,Requires a great deal of skill from the human operator Manipulator complexity Interface constraints (joystick, exoskeleton) S
10、ensing limitations Applications in robot-assisted surgery,CPE 470/670 - Lecture 4,10,Kinematics,Kinematics: correspondence between what the actuator does and the resulting effector motion Manipulators are typically composed of several links connected by joints Position of each joint is given as angl
11、e w.r.t adjacent joints Kinematics encode the rules describing the structure of the manipulator Find where the end-point is, given the joint angles of a robot arm,CPE 470/670 - Lecture 4,11,Types of Joints,There are two main types of jointsRotary Rotational movement around a fixed axisPrismatic Line
12、ar movement,CPE 470/670 - Lecture 4,12,Inverse Kinematics,To get the end-effector to a desired point one needs to plan a path that moves the entire arm safely to the goal The end point is in Cartesian space (x, y, z) Joint positions are in joint space (angle ) Inverse Kinematics: converting from Car
13、tesian (x, y, z) position to joint angles of the arm (theta) Given the goal position, find the joint angles for the robot arm This is a computationally intensive process,CPE 470/670 - Lecture 4,13,Sensors,Physical devices that provide information about the world Based on the origin of the received s
14、timuli we have: Proprioception: sensing internal state - stimuli arising from within the 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 ro
15、bots perceptual system,CPE 470/670 - Lecture 4,14,Sensor Examples,Physical Property,Sensor,contact,switch,distance,ultrasound, radar, infrared,light level,photocells, cameras,sound level,microphone,rotation,encoders and potentiometers,acceleration,accelerometers gyroscopes,CPE 470/670 - Lecture 4,15
16、,More Sensor Examples,Physical Property,Sensor,magnetism,compass,smell,chemical,temperature,thermal, infra red,inclination,inclinometers, gyroscopes,pressure,pressure gauges,altitude,altimeters,strain,strain gauges,CPE 470/670 - Lecture 4,16,Knowing whats Going On,Perceiving environmental state is c
17、rucial for the survival or successful achievement of goals Why is this hard? Environment 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
18、 physical quantities,CPE 470/670 - Lecture 4,17,Types of Sensors,Sensors provide raw 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: 51
19、2x512 pixels Human retina: more than a hundred million photosensive elements,CPE 470/670 - Lecture 4,18,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 reco
20、nstruction of the world Simple sensors can answer the first question Their output can be used directly Complex sensors can answer both questions Their information needs to be processed,CPE 470/670 - Lecture 4,19,Signal to Symbol Problem,Sensors produce only signals, not symbolic descriptions of the
21、world To extract the information necessary for making intelligent decisions a lot 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,CPE 470/670 - Lecture 4,20,Levels of Pr
22、ocessing,Finding out if a switch is open or closed Measure voltage going through 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 intr
23、uders, comparing them to a large database computation,CPE 470/670 - Lecture 4,21,Perception Requirements,Perception requires more than just sensors: Sensors Power and electronics Computation More power and electronics Connectors To connect it all,CPE 470/670 - Lecture 4,22,Perception Designs,Histori
24、cally perception has been treated in isolation perception in isolation perception 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,CPE 470/670 - Lecture 4,23,A Better Way,Instead it is good t
25、o think about it as a single complete design The task the robot has to perform 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),CPE 470/670 - Lecture 4,2
26、4,A New Perceptual Paradigm,Perception without the context of actions 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 On
27、ly the information necessary for the task is extracted Active perception How can motor behaviors support perceptual activity? Motor control can enhance perceptual processing Intelligent data acquisition, guided by feedback and a priori knowledge,CPE 470/670 - Lecture 4,25,Using A Priori Knowledge of
28、 the World,Perceptual processing can benefit if knowledge about the 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 Pe
29、rceptual classes (how to look for it) Partition the world into categories of interaction,CPE 470/670 - Lecture 4,26,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 comp
30、lex process Different sensor accuracy Different sensor complexity Contradictory information Asynchronous perception Cleverness is needed to put this information together,CPE 470/670 - Lecture 4,27,Neuroscientific Evidence,Our brain process information from multiple sensory modalities Vision, touch,
31、smell, hearing, sound Individual sensory modalities use separate 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,CPE 470/6
32、70 - Lecture 4,28,What Can We Learn from Biology?,Sensor function 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
33、 clever designs to maximize the sensors perceptual properties, range and accuracy,CPE 470/670 - Lecture 4,29,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
34、 that the environment presents Perception is biased by the robots task A chair: Something to sit in Something blocking the way Something to throw if attacked,CPE 470/670 - Lecture 4,30,How Would You Detect People?,Use the interaction with the world, keep in mind the task Camera: great deal of proces
35、sing Movement: if everything else is static: movement means 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,CPE 470/670 - Lecture 4,31,How Would You Measure Distance?,Ultrasou
36、nd sensors (sonar) provide distance measurement directly (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
37、 distortions to compute distance,CPE 470/670 - Lecture 4,32,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 Det
38、ermined by the amount of processing required Active/passive Determined by the sensor mechanism,CPE 470/670 - Lecture 4,33,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
39、 Voltage can be divided by using two resistors in series,V = IR,Vin = I(R1 + R2),Vout = Vin R2/(R1 + R2),CPE 470/670 - Lecture 4,34,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 c
40、losed current will flow Can be Normally open (more common) Normally closed,CPE 470/670 - Lecture 4,35,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
41、end of its range (e.g., triggers when a gripper is wide open) Shaft encoder sensors: detect how many times a shaft turns (e.g., a switch clicks at every turn, clicks are counted),CPE 470/670 - Lecture 4,36,Example of Switch Uses,In everyday life Light switches, computer mouse, keys on the keyboard,
42、buttons on the phone In robotics Bump switch: 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,C
43、PE 470/670 - Lecture 4,37,Light Sensors,Light 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
44、that low means dark and high means bright,= 0v,= +5 v,CPE 470/670 - Lecture 4,38,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 impr
45、ove accuracy and range,Rphoto2 = Rphoto1Vout = 2.5 vRphoto2 Rphoto1Vout = gnd,CPE 470/670 - Lecture 4,39,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 lig
46、ht sources Can tell if the robot is pointed 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,CPE 470/670 - Lecture 4,40,Polarized Light Sensors,Filt
47、ers can be combined to select various 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
48、effects can be achieved,CPE 470/670 - Lecture 4,41,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 l
49、ess robust than a light sensor, and requires strong protection at its base, near the electrical contacts Unless the sensor is well-protected from direct forces, it will fail over time,CPE 470/670 - Lecture 4,42,Potentiometers,Also known as “pots” Manually-controlled variable resistor, commonly used
50、as volume/tone controls of stereos Designed from a movable tab along two ends Tuning the knob adjusts the resistance of the sensor,CPE 470/670 - Lecture 4,43,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 light sensors in insects and birds Bend/resistance receptors in muscles and many more.,
