[PDF] - Effectors CSCI545 Introduction to Robotics Hadi Moradi Previous PDF Document

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Effectors

CSCI545 Introduction to Robotics Hadi Moradi

Previous Lecture

Introduction to Robots

Introduction to Robots Basics of Manipulators

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Effector vs. Actuator

Effector: Any device affecting Effector: Any device affecting

the environment.

Actuator: The actual

h i th t b i ti mechanism that brings action

Actuator

Degree Of Freedom (DOF)

The number of independent motions a

device can make

Examples: Examples:

Simple sliding

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Degree Of Freedom (DOF)

Examples:

Rotation + translation:

Degree Of Freedom (DOF)

Examples:

A free body in space: 6DOF

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Degree Of Freedom (DOF)

Q: How many DOF are Q: How many DOF are

needed to position parts

n a planar surface?

The Use of Effectors

Locomotion: Moving robot around

Locomotion: Moving robot around Manipulation: Moving other objects

Example: (courtesy of Martin Rohrmeier)

Puma 560 Puma 560 Kr6

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Locomotion

Types:

Legs Wheels Arms Flippers …

Actuators

Example:

Pneumatic (air pressure) Hydraulics (fluid pressure)

Give another example!

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Actuators

Example:

Motors (current)

DC Motors

The most used in mobile robots

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DC Motors DC Motor: Permanent Magnet

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DC Motors Different DC Motor Confs

Image: Courtesy of Paul Hill

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DC Motors

Efficiency: Loss on friction Efficiency: Loss on friction

90% high end models 50% low end models

Operating Voltage:

DC Motors

Current: proportional to the load Current: proportional to the load

Pushing toward a wall Free rotation:

T t ti l f

Torque = = rotational force More current = >

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Torque and Power

Stall torque: The amount Stall torque: The amount

f rotational force when

stalled.

Power= torque *

rotational velocity

Torque vs. Power

Image: Courtesy of Paul Hill

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DC Motor Specs: Iskra 6-pole Torque and Speed

How do you measure torque?

How do you measure torque? How do you measure speed?

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Stall Torque calculation Speed

3 000 to 9 000 RPM

3,000 to 9,000 RPM

Or 50 to 150 RPS

High speed = >

Example: fans

In robotics:

Load should be carried + not very high speed

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Gearing

Too much speed:

Too much speed: Cars:

1000 RPM standby

1000 RPM standby 3000-6000

Operational

Gearing

What is the idea?

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Gearing

Two gears meshed together

Gear Teeth

Backlash: moving back and forth Backlash: moving back and forth Reducing backlash = > tight meshing

Problem?

Designing a gear box:

3:1 speed reduction

Q: How much reduction can we get? Infinite?

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Gear Boxes

Multiple gears in series

8 24 40 8 24

Servo Motors

Goal:

Gear reduction Position sensor Position control

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Inside a Servo Motor

Top cover removed Gears are removed

Inside a servo motor

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Pulse Width Modulation

10% duty cycle 50% duty cycle 90% duty cycle

PWM

10% of 9 volts = > 0 9 v

10% of 9 volts = > 0.9 v 50% of 9 volts = > 4.5 v

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PWM

How frequently the pulses should be

repeated?

Working frequency: 1KHz – 200 KHz Note:

Stepper Motor vs. Servo Motor

Servo motor: DC motor with position

control (feedback/closed loop)

Stepper motor:

Open loop Many coils:

Many coils:

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Stepper vs. DC vs. AC

DC motor

Stepper motor AC motor

Continuous Rotation Motors

Use DC motors

Use DC motors Use servo motors:

Remove mechanical limits Remove position sensor Apply two resistors to fool the control Apply two resistors to fool the control