CH1-Intro To Mobile Robot and Locomotion [PDF]

Zitiervorschau

PLT 424 AUTOMATED GUIDED VEHICLE Dr. Sukhairi bin Sudin Phone no: 019-4772556 Email: [email protected] Teaching Engineer: En Muhammad Abid Abdul Rahman

General Information ◼

Contributes 3 units: ◼ Lectures ◼ Tuesday (8.00 – 10.00) Online ◼

Labs/Tutorials ◼ Monday (12.30 - 15.30) ◼ Tuesday (14.00 – 17.00)

Schedule • • • • •

Lab 1 (Week 5) Lab 2 (Week 6) Lab 3 (Week 9) Lab 4 (Week 11) Lab 5 (Week 12)

• • • •

Tutorial 1 (Week 3) Tutorial 2 (Week 7) Tutorial 3 (Week 10) Tutorial 4 (Week 14)

• Assignment (Week 12)

• Test 1 (Week 7)

Evaluation Contribution Examination: Final Examination : 40% Course Work: Test Lab (5 labs) Assignment Project

: 20% : 25% : 10% : 5%

Project : Team (Three/Four)

Course Outcomes CO1 : Ability to demonstrate the moving mechanism of mobile robots such as wheeled, walking, swimming, flying and climbing robots. CO2: Ability to analyze the force-torque requirements of mobile robots and deciding the servo and stepper motor specifications. CO3: Ability to evaluate the requirement of sensors and control systems for wheeled robot mechanism.

Introduction : MOBILE ROBOTS

Autonomous Guided Vehicle • The dictionary of transport and logistic, David Lowe “Automatic Guided Vehicle(AGV) is a load/personnel carrying computercontrolled vehicle that follows an automatic guidance system (invariably laid in the floor) without manual steering or control – usually found in warehouses and large stores.”

• A Dictionary of Computing, Encyclopedia.com. , John Daintith “A form of mobile robot that can transport goods and materials from one place to another in a constrained environment, usually in manufacturing industries but also increasingly in service and health-care applications.”

Autonomous System Knowledge, Data Base

Mission Commands

Localization Map Building

“Position” Global Map

Environment Model Local Map

Cognition Path Planning Path

Information Extraction

Path Execution

Raw Data

Actuator Commands

Sensing

Acting Real World Environment

Mobile Robots • Definition: • A robot mounted on a moveable platform that transport it to the area where it carries out tasks.

• Mobile robots may be classified by: • The environment in which they travel: • Land or home robots. They are most commonly wheeled, but also include legged robots with two or more legs (humanoid, or resembling animals or insects.) • Aerial robots are usually referred to as unmanned aerial vehicles (UAVs). • Underwater robot are usually called autonomous underwater vehicles (AUVs). • Flying robots.

• The device the use to move, mainly: • Legged robot : human-like legs (i.e. an android) or animal-like legs. • Wheeled robot. • Tracks

Indoor Mobile Robots • Industrial AGVs • Service robots (mostly human guided) • Cleaning • Hospital • Hotels • Entertainment • Toy robots • Movies

• Research • Micro robot • Office buildings • Hostile environment • Tour guides • Surveillance • Fire fighting

Outdoor Mobile Robots • Man-made environment • Autonomous/semi-autonomous car or trucks • City guides • Handicapped aids • Autonomous trains • Sewage tube • ….etc

• Rough terrain • • • •

Agriculture Forestry Construction Fire fighting

• Military

• Air/Space • • • •

Airplanes Helicopter Space crafts Satellites

• Water/Underwater • Ships • Boats • Submarines

Mobile Robots • • • • •

• • • •

Wheeled Walking Climbing swimming flying

Differential Drive Synchro Drive Ackerman Steer Inverse Kinematics

• • • •

Obstacle detection Obstacle avoidance Path planning Navigation

KINEMATICS

LOCOMOTION

CONTROL & NAVIGATION

CONCEPT

MOBILE ROBOT PHYSICAL HARDWARE • • • •

Actuator Power supply Stability Design

DECISION MAKING & AUTONOMY

SENSOR • • • • •

Sonar Tactile Ultrasonic Infrared Camera

• • •

Encoder Compass GPS

• • • • •

AI Behavioral based Unmanned Autonomous Wireless

LOCOMOTION CONCEPTS (AUTONOMOUS GUIDED VEHICLE (AGV)

Overview Underwater Industrial AGVs

Service Robot

Entertainment

Military

MOBILE ROBOT

Domestic

Air/Space Medical

Rough Terrain

Multi Terrain

Locomotion How does this robot move?

Locomotion : movement or ability to move from one place to another [Oxford Dictionary]

Type of Locomotion Natured Inspired

• • • • • • • • •

Legged Swimming Running Walking Jumping Climbing Sliding Crawling …etc

Invention

• • • • • •

Wheeled Track Propeller Turbine Ballast tank ...etc

Locomotion Concept • Concepts found in nature are difficult to imitate • Most conventional robot technically use wheels or caterpillars • Rolling is most efficient, but not found in nature

Issues • Stability • • • •

Number and geometry of contact points Center of gravity Static/dynamic stability Inclination of terrain

• Characteristics of contact • Contact point/path size and shape • Angle of contact • friction

• Type of environment • Structure • Medium (e.g. water, air, soft or hard ground)

Non-holonomic constraint So what does that mean? Your robot can move in some directions (forwards and backwards), but not others (side to side). The robot can instantly move forward and back, but can not move to the right or left without the wheels slipping.

Parallel parking, Series of maneuvers

Idealized Rolling Wheel • Assumptions:

Non-slipping and pure rolling

• No slip occurs in the orthogonal direction of rolling (non-slipping). • No translation slip occurs between the wheel and the floor (pure rolling). • At most one steering link per wheel with the steering axis perpendicular to the floor.

• Wheel parameters: • • • • Lateral slip

r = wheel radius v = wheel linear velocity w = wheel angular velocity t = steering velocity

Basic Wheel Types Fixed wheel

Off-centered orientable wheel

(Castor wheel)

Centered orientable wheel

Swedish wheel:omnidirectional

property

Examples of WMR • Smooth motion • Risk of slipping • Some times use roller-ball to make balance

Example

Bi-wheel type robot ▪ ▪ ▪

Exact straight motion Robust to slipping Inexact modeling of turning

▪ ▪ ▪

Free motion Complex structure Weakness of the frame

Caterpillar type robot

Omnidirectional robot

Mobile Robot Locomotion • Instantaneous center of rotation (ICR) • is the point fixed to a body undergoing planar movement

OR • Instantaneous center of curvature (ICC) • A cross point of all axes of the wheels

Mobile Robot Locomotion • Differential Drive • two driving wheels (plus roller-ball for balance) • simplest drive mechanism • sensitive to the relative velocity of the two wheels (small error result in different trajectories, not just speed)

• Tricycle • Steering wheel with two rear wheels • cannot turn 90º • limited radius of curvature

• Synchronous Drive • Omni-directional • Car Drive (Ackerman Steering)

Degree of Mobility • Degree of mobility The degree of freedom of the robot motion Cannot move anywhere (No ICR) • Degree of mobility : 0

Variable arc motion (line of ICRs)

• Degree of mobility : 2

Fixed arc motion (Only one ICR) • Degree of mobility : 1 Fully free motion ( ICR can be located at any position) • Degree of mobility : 3

Degree of Steerability • Degree of steerability The number of centered orientable wheels that can be steered independently in order to steer the robot No centered orientable wheels • Degree of steerability : 0

One centered orientable wheel Two mutually dependent centered orientable wheels • Degree of steerability : 1

Two mutually independent centered orientable wheels • Degree of steerability : 2

Degree of Maneuverability

28

M = m + s

Differential Drive VR (t )– linear velocity of right wheel VL (t ) – linear velocity of left wheel r – nominal radius of each wheel R – instantaneous curvature radius of the robot trajectory (distance from ICC to the midpoint between the two wheels).

Property: At each time instant, the left and right wheels must follow a trajectory that moves around the ICC at the same angular rate , i.e.,

L 2

 ( R + ) = VR

L 2

 ( R − ) = VL

Differential Drive Posture Kinematics Model (in world frame)

▪

Relation between the control input and speed of wheels

▪

Kinematic equation

▪

Nonholonomic constraint

H : A unit vector orthogonal to the plane of wheels

Differential Drive Configuration Kinematics Model (in robot frame)

Basic Motion Control • Instantaneous center of rotation

R : Radius of rotation

▪

Straight motion R = Infinity

▪

VR = VL

Rotational motion R= 0

VR = -VL

Tricycle • Three wheels: two rear wheels and one front wheel • Steering and power are provided through the front wheel • control variables: • steering direction α(t) • angular velocity of steering wheel ws(t) The ICC must lie on the line that passes through, and is perpendicular to, the fixed rear wheels

Tricycle • If the steering wheel is set to an angle α(t) from the straight-line direction, the tricycle will rotate with angular velocity w(t) about a point lying a distance R along the line perpendicular to and passing through the rear wheels.

Tricycle Kinematics model in the robot frame ---configuration kinematics model

With no slippage

Tricycle

Tricycle Kinematics model in the world frame ---Posture kinematics model

Synchronous Drive • In a synchronous drive robot, each wheel is capable of being driven and steered. • Typical configurations • Three steered wheels arranged as vertices of an equilateral • triangle often surmounted by a cylindrical platform • All the wheels turn and drive in unison

• This leads to a holonomic behavior

Synchronous Drive

Synchronous Drive • All the wheels turn in unison • All of the three wheels point in the same direction and turn at the same rate • This is typically achieved through the use of a complex collection of belts that physically link the wheels together

• The vehicle controls the direction in which the wheels point and the rate at which they roll • Because all the wheels remain parallel the synchro drive always rotate about the center of the robot • The synchro drive robot has the ability to control the orientation θ of their pose directly.

Synchronous Drive • Control variables (independent) • v(t), w(t)

Synchronous Drive • Particular cases: • v(t)=0, w(t)=w during a time interval ∆t, The robot rotates in place by an amount w ∆t . • v(t)=v, w(t)=0 during a time interval ∆t , the robot moves in the direction its pointing a distance v ∆t.

Omni-directional

Swedish Wheel

Car Drive (Ackerman Steering) • Used in motor vehicles, the inside front wheel is rotated slightly sharper than the outside wheel (reduces tire slippage). • Ackerman steering provides a fairly accurate dead-reckoning solution while supporting traction and ground clearance. • Generally the method of choice for outdoor autonomous vehicles.

Ackerman Steering

Ackerman Steering • The Ackerman Steering equation: • cot i- cot o=d/l

• where • • • •

d = lateral wheel separation l = longitudinal wheel separation i = relative angle of inside wheel o = relative angle of outside wheel

Ackerman Steering

Snake Robot

Grasshopper Robot • A tiny two-legged robot that stores elastic energy in springs has leaped 27 times its own height • The robot is only 5 centimeters tall, and weighs just 7 grams.

Omnidirectional

Mecanum Wheel

THE END