2 robotic systems configurations

7/29/2019 2 Robotic Systems Configurations

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Robotic Systems(2)

Dr Richard Crowder

School of Electronics and Computer Science


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DefinitionsAn industrial robot is a reprogrammable device designed to both manipulate

and transport parts, tools, or specialised manufacturing implements throughprogrammed motions for the performance of specific manufacturing tasks.

but as we noted is far too specific

An intelligent robot is a machine able to extract information from itsenvironment and use knowledge about its world to move safely in a meaningfuland purposeful manner.

For convenience we can broadly class robotics into two:

Conventional robotics for static industrial and similar systems. Behaviour based, more biologically inspired and currently restricted to the

research field.


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Definitions

Configuration: a complete specification of the location of every pointon the manipulator

A configuration can be represented by a set of joint variables

Degrees of freedom (DOF): minimum number of parametersneeded to specify its configuration

# of DOF = the dimension of the configuration space

A rigid object in 3D has 6 DOF: 3 for positioning and three for

orientation. A manipulator having more than 6 DOF is referred to as a

kinematically redundant manipulator

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Basic Structure (Fixed Robot)

Network/

Program

Sensors

Processor

End of Arm

tooling

Mechanical

Arm

Power

Supply and

Drives

Input

Device

Environment


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Robot Structure

Depending on the type of robot and the application, the mechanicalstructure of a robot can normally be divided into two parts, the mainmanipulator andwrist assembly.

The manipulator will position the end effector while the wrist willcontrol its orientation.

A manipulator is a system with a number ofjoints and links that canbe controlled within three-dimensional space.

All interaction between the robot, and other machines, parts andprocesses must take place within theworkspace

Reachable: the entire set of points reachable by the manipulator Dexterous: the set of points reachable by the end effector with an

arbitrary orientation


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Robot Configurations

The structure of the robot consists of a number ofJointsand Links.

To achieve complete control of the end effectors position

and orientation a minimum ofsix joints are required.

Even though there are a large number of possible robotconfigurations, only five configurations are commonly usedin industrial robotics:


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Symbolic representation of robots

Robot manipulator: a kinematic chain formed by linksconnected by joints

Joints

Rotary: revolute joint (R)joint variable

Linear: prismatic joint (P) joint variable d

Revolute Prismatic


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Work volume or work space

All tasks must be undertaken in this volume, which isdefined by the robots configuration and size.

Formal mathematical definition will be discussed later, but

is limited by:

Joint type

Limits to motion of travel

Relative lengths of joints.


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Polar Arm Configuration

Joint 2

Joint 1

Joint 3

RRP configuration (RevoluteRevolutePrismatic config)

Consists of telescopic link (Prismatic joint), that can extend backwards and forwards,

about a horizontal revolute joint. These two links are mounted on a rotating base.

A linear extending arm is capable of being rotated around the horizontal and vertical

axes.

Used for spraying painting

Workspace


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Cylindrical Arm ConfigurationJoint 1

Joint 3

Joint 2

RPP Configuration

A linear extending arm (Prismatic Joint) can be moved vertically up and down

(Prismatic Joint) around a rotating column (Revolute Joint)


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Gantry

Joint 1

Joint 2

Joint 3

PPP Configuration

Comprises of three orthogonal (perpendicular) sliding or prismatic joints


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Jointed Arm

Joint 1

Joint 3

Joint 2

RRR Configuration

Three joints arranged in an anthropomorphic (ascribing human form or

attributes) configuration


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SCARA

Joint 1

Joint 2

Joint 3

RRP Configuration

Selective Compliance Assembly Robotic Arm


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Wrist

Joint 1

Joint 2

Joint 3

Tool

Interface

To orientate the tools, three additional joints are required, these are normally

mounted at the end of the arm as the wrist, it is conventional to define the joints

of a wrist ro l l , pi tch and yaw.


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Comments on configurations

A rotary motion is normally quicker that the equivalentlinear motion. However to achieve linear motion usingrotary joints, a co-ordinated move is required.


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continued

Not all robots require 6 axes, for example paint sprayingthat is symmetrical about the roll axis.


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Parallel Manipulators

AStewart platform is a parallel manipulator using anoctahedral assembly of struts. A Stewart platform has sixdegrees of freedom

Passive rotary joint

Linear ActuatorDevices placed on the top plate can be

moved in the six degrees of freedom.

These are the three linear movements

x, y, z (lateral, longitudinal and vertical),

and the three rotations pitch, roll, &

yaw
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Mobile Robots

Gives the robot the flexibility to move within the workspace an explorethe environment in detail or undertake specific tasks.

Automated Guided Vehicles

Typically used in factories for material handling Predetermined paths

Visible line

Inductive wires buried in the floor

Structured environment


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Mobility - Wheels

Four wheels at the corners:

Normally 2 or 4 wheel drive with 2 or 4 wheel steer, but skid steer ispossible

Cannot turn on the spot.

Suspension system and differential wheel speeds required. Three wheeled:

Suspension system not needed to keep all wheels on the ground.

Can have front steering and back 2 driving; or front steering and driving;or back 2 driving independently.

Problem with combining steer and drive in the front wheel is that it'scomplex and has been shown to lead to significant steering errors overshort distances.

Having the back wheels drive independently allows steering to becontrolled by changing the speed of the back wheels.


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Mobility - Wheels

Six wheeled

6 interpedently driven wheels, with the 2 front and 2 back wheelssteering. The 4 steering wheels allow it to turn on the spot. highdegree of redundancy


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Mobility - Legs

Advantages

Step over obstacles

Walk up and down steps

Walk on very uneven ground

Give a smooth ride over rough ground;

Are less likely to sink into soft ground.

Disadvantages

Mechanically complex with various joints; usually custom built

Are more difficult to control - have to be co-ordinated Relatively slow and energy inefficient.


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Mobility- Others

Tracks

Wheel based hence easy to control.

Difficult to control a turn - skids by slowing one track down, thetank then turns in that direction.

Can go fast and are relatively efficient (not as efficient as wheels)

Good at rough terrain.

Aircraft or balloons

True biological systems

Fish, snakes, cockroaches, ants..

2 robotic systems configurations

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