Robotics/Machine Vision

Robert Love, Venkat Jayaraman

July 17, 2008SSTP Seminar – Lecture 7

Overview• Presentation

– Parts of a Robot– Robotics Components

• Joints and Linkages• Actuators• Sensors• Controller

– Machine Vision• Basic Theory, Application: Harvesters

– Image processing• Aircraft Control, Bonding• Visual Image Correlation, Photogrammetry

• Discussion• Activity

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Parts of a Robot

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• Body • Effectors• Actuators• Sensors• Controller

Sensors Controller Actuator

End Effector

Body

• Robot Body is typically defined by links and joints

• A link is a part, a shape with physical properties.

• A joint is a constraint on the spatial relations of two or more links.

Robot Body

Types of Joints• Revolute, Cylindric, Prismatic, Screw, Spherical

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a12 S2

S1, a23

S3

S4

a34, a45

S5

a56

a3

4

a45

, a56

Mitsubishi PA10-6C

• End Effectors – The Component usually attached at the end of the robotic arm to accomplish the desired task

• Examples : Hand, torch, wheels, weld gun

Robot End Effectors

End Effector

• Actuators: ‘Muscles’ of the robot• These can be electric motors, hydraulic

systems, pneumatic systems, or any other system that can apply forces to the system.

Robot Actuators

• Allow for perception.• Sensors can be active or passive:• Active – derive information from

environment’s reaction to robot’s actions, e.g. range sensors.

• Passive – observers only, e.g. temperature sensors, strain gauge .

Robot Sensors

Range Sensor

Oxygen Sensor

Robot Controller

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• Controllers direct a robot how to move.• There are two controller paradigms

– Open-loop controllers execute robot movement without feedback.

– Closed-loop controllers execute robot movement and judge progress withsensors. They can thus compensate for errors.

• Kinematics is the study of motion without regard for the forces that cause it.

– Refers to all time-based and geometrical properties of motion.

– Ignores concepts such as torque, force, mass, energy, and inertia.

• Forward Kinematics – Determination of the configuration, given the starting configuration of the mechanism and joint angles.

• Inverse Kinematics - Determination of the joint angles, given the desired position of the end effector.

Robot Kinematics

Machine Vision Basic Theory

• Vision – A powerful sense– Models the human eye

• Applications – Autonomous vehicles, face recognition, industrial inspection, safety systems, Visual stock control etc

• No ‘universal’ solution

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A Typical machine vision system

Basic Concepts

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• Characteristics of an image– Composed of pixels– Primary colors – red, green and blue

• Segmentation – Partitioning of the digital image into two or more regions

• Edge Detection• Corner Detection

– Corners can be used as Feature points

Robotic Harvesting

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Robot Harvesting Video

Basic Theory Image Processing

• Basic Image information– focal length, line of sight, field of view, intensity of pixel

• Projection of point in 3D space onto 2D image plane

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Basic Image Processing• Goal: Define Coordinates in 3D Space• Methods:

– Motion Capture– Photogrammetry: Your digital camera– Stereophotogrammetry/Videogrammetry– Digital Image Correlation– Projector + IR sensor

• Some analysis tools:– Photoshop (Better, not free), Gimp (open source)– Matlab Image Processing Toolbox (Digitize07-open source)– Microsoft Photosynth Live Labs– Johnny Chung’s Wii Remote Project (open source)

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Flight Control• Basic Process

– Extract Feature Points (from intensity spikes in image)– Estimate optic flow vectors– Create estimates of roll, pitch, yaw from average optic flow

vectors , use to formulate control model

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Digital Image Correlation

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Power SupplyCalibrated Voltageto Flapping Frequency

High Speed DIC CamerasPhantom v7 CMOS0-1000 fps3 halogen lightsVICSNAP, VIC3D Software

Electromagnetic ShakerUsed for excitation whileperforming DIC

Wings and MechanismStinger extends fromshaker through load cell to 18 g mechanismMechanism: 1-20 Hz

Spray Paint Speckle PatternDIC uses temporal tracking of unique regions of speckles

Vibration isolationOptical lab table and foamunder shaker

Activity

• Think of an application where a robot could help• Make a “design sketch” including:

– Task Description (think basic task!)– Basic Actuation Method– Sensors required

• Share with neighbor and get feedback on how might improve design

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