5.Robo Unit III

7/27/2019 5.Robo Unit III

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Subject: Mechanism &Robotics

Subject code: MSD Batch 5B

By

Haridasa Nayak


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Joints and Links in Robots

A joint of an industrial robot is similar to a joint in the humanbody: It provides relative motion between two parts of the body.

Each joint, or axis as it is sometimes called, provides the robotwith a so-called degree-of-freedom(D.O.F) of motion.

In nearly all cases, only one degree-of-freedom is associatedwith a joint.

Connected to each joint are twolinks, an input link and outputlink.

Linksare the rigid components ofthe robot manipulator.

The purpose of the joint is toprovide controlled relativemovement between the input linkand the output link.


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Most of robots are mounted on a stationary base on the floor.

The base and its connection to the first joint is Link 0.

Link 0 is the input link of joint 1, the first joint of a series of joints used

in the construction of the robot.

The output link of joint 1 is the link 1.

Link 1 is the input link to joint 2, whose output link is link 2, and soforth.


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Nearly all industrial robots have mechanical joints that can beclassified into one of the five types:

Two types that provide translational motion. Three types that provide rotary motion

1. Linear Joint (type L joint)

The relative movement between the input link and the output linkis a translational sliding motion, with the axes of the two linksbeing parallel.


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2. Orthogonal joint (type O joint)

This is also a translational sliding motion, but the input link andoutput links are perpendicular to each other during the move.


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3. Rotational Joint (type R joint)

This type provides rotational relative motion, with the axis ofrotation perpendicular to the axes of the input and output links.


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4. Twisting Joint (type T joint)

This joint also involves rotary motion, but the axis of rotation isparallel to the axes of the two links.


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5. Revolving Joint (type V joint, V from the v in revolving)

In this joint type, the axis of the input link is parallel to the axis

of rotation of the joint, and the axis of the output link isperpendicular to the axis of rotation


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A robot manipulator can be divided into two sections:

A Body-and-arm assembly.

Wrist assembly.

There are usually three degree-of-freedom associated with the body-and-arm , and either two or three degrees-of-freedom with the wrist.

At the end of the manipulators wrist is a device related to the task thatmust be accomplished by the robot. The device, called an end effector, isusually either:

1. A gripper for holding a workpart, or

2. A tool for performing some process.

The body-and-arm of the robot is used to position the end effector, andthe robots wrist is used to orient the end effector.


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There are five basic configurations commonly available incommercial industrial robots:

1. Spherical (Polar) Configuration

This configuration consists of a sliding arm (L joint) actuated relative tothe body, that can rotate about a vertical axis (T joint) and ahorizontal axis (R joint)


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2. Cylindrical Configuration

This robot configuration consists of a vertical column, relative towhich an arm assembly is moved up and down. The arm can bemoved in and out relative to the axis of the column.

A T joint to rotate the column about its axis. An L joint is used tomove the arm assembly vertically along the column. An O joint isused to achieve radial movement of the arm.


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3. Cartesian (Rectangular) Configuration

It is composed of three sliding joints, two of which are orthogonal.


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4. Jointed-arm robot (articulated) Configuration

This robot manipulator has the general configuration of a human

arm. The joined arm consists of a vertical column that swivels aboutthe base using a T joint.

At the top of the column is a shoulder joint (R joint), whose aboutlink connects to an elbow joint (R joint)


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5. SCARA (Selective Complains Assembly Robot Arm)

This configuration is similar to the jointed robot except that theshoulder and elbow rotational axes are vertical, which means thatthe arm is very rigid in the vertical direction, but complaint in thehorizontal direction.


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Wrist Configurations

The robots wrist is used to establish the orientation of the end

effector. Robot wrists usually consists of two or three degrees-of-freedom. The three joints are defined as:

1. Roll , using a T joint to accomplish rotation about the robots arm axis.

2. Pitch, which involves up-and-down rotation, typically a R joint.

3. Yaw , which involves right-and-left rotation, also accomplished bymeans of an R-Joint.

A two D-O-F wrist typically includes only roll and pitch joints (T andR joints)


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Joint Notation System

The letter symbols for the five joint types (L, O, R, T, and V) can be usedto define a joint notation system for the robot manipulator.

In this notation system, the manipulator is described by the joints thatmake up the body-and-arm assembly, followed by the joint symbols thatmake up the wrist.

For example, the notation TLR:TR represents a five degree-of-freedommanipulator whose body-and-arm is made up of :

1. A twisting joint (Joint 1 = T)

2. A linear joint (joint 2 = L)

3. A rotational joint (joint 3 = R)

The wrist consists of two joints:

4. A twisting joint (joint 4 = T)

5. A rotational joint (joint 5 = R)

A colon separates the body-and-arm notation from the wrist notation.


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Joint Notation System - Example

Designate the robot configurations shown below, using the jointnotation scheme.

Solution

1. This configuration has two linear joints, Hence, it is designated LL.

2. This configuration has three rotational joints, Hence, it is designated RRR.

3. This configuration has one twsiting joint and one linear joint. This is

indicated by TL

J i t N t ti S t E l


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Joint Notation System - Example The robots shown below are equipped with a wrist that has twisting, rotary,

and twisting joints in sequence from the arm to the end-effector. Give thedesignation for the complete configuration of each robot

For the robots shown above, the complete designation is as follows:

(a) LRL:TRT (b) RRL:TRT (c) TRL:TRT (d) LVL:TRT

W k V l


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Work Volume

The work volume (work envelope) of the manipulator is defined as theenvelope or space within which the robot can manipulate the end of its

wrist.

Work volume is determined by:

1. the number and types of joints in the manipulator (body-and-arm

and wrist),2. the ranges of the various joints, and

3. the physical sizes of the links

The shape of the work volume depends largely on the robots

configuration

W k V l


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Work Volume

A Cartesian robot has a rectangular work volume

W k V l


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Work Volume A cylindrical robot has a cylindrical work volume

W k V l


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Work Volume A spherical robot tends to have a sphere as its work volume


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Motion Types PointtoPoint Motion:

All Axes start and end simultaneously All Geometry is computed for targets and relevant

Joint changes which are then forced to be followedduring program execution

Path or Trajectory Controller Motion Here the motion is performed through a time

sequence of intermediate configurations computedahead of time (like above but without stop-startoperation) or in real time

Paths are Space Curves for the n-Frame to follow

This motion is a continuous scheme to move theTCP from one location to the next along a desired(straight or curved) line under direct operationalcontrol


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Basically this was a technique whereby a skilled operator took a robotarm (for welding or painting) and used it like his/her weld tool or paintsprayer and performed the required process at reasonable speed

The robot is equipped with a position recording device and memorizes alarge number of points during the teaching session

These learned points then would be played back to replicate theskilled operators motions

Lead Through Path Creation


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Lead Through Path Creation

Advantages: Simple way to create complex paths

All points are sure to be physically attainable Playback speed can be controlled by an externaldevice

Disadvantages:

Precision placements are required (program must bereplayed at exactly the initial placement)

Major concern with operator safety: robot ispowered and operator is physically touching it(OSHA rules it unsafe practice!)


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PROGRAMMING

Three Programming Methods:

Manual teaching Lead through teaching

Programming languages


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1.Manual Teaching:

Point to Point applications

2.Lead Through Teaching:

Continuous Path Programming

Robot Simulator

Advantage is direct programming but also havedisadvantages


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Disadvantages:

Every motion is recorded and played back

in the same manner.So unintentionalmotions also be played.

Impossible to achieve exact requiredvelocity

Memory size is required to store the data.

Investment in a simulator is required.


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3.Programming Languages:

AL-Assembly language

VAL-Victors assembly languages

AML-Advanced machine language

MCL-Machine control language


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Classification of Robotics Languages:

First Generation Language

Second Generation Language

World modelling and task oriented object

level language


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First Generation Language:

Off-Line Programming used in combination

with teach pendant.

VAL is an example of this kind.


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Second Generation Language:

AML,VAL II etc

Structural Programming language performingcomplex tasks.

Apart from straight line interpolation performscomplex motions.

Uses force, torque and other sensors. Data processing, file management and keeping all

records is done.


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World modelling & task oriented object

level language:

More advanced language is WORLD

modelling.

TIGHTEN THE NUT.

Intelligence is required.


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In a robot, there are 3 basic modes of

operation:

Monitor mode

Edit mode

Run or Execute mode


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Monitor mode:

Programmer define locations, load a

particular information in a register, savetransfer programs from storage.

Move back and forth into edit or run mode


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Edit mode:

Programmer can edit or change set of instructions.

Run or Execute mode: Pre defined task can be executed in run mode.

Dry run can be tested.

Debugging.


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1. INTRODUCTION TO VAL:

Programming language and operating

system which controls a robotic system.

VAL programs also include

subroutines,which are separate programs.


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2.LOCATIONS:

Represents the position and orientation of robot

tool. Two ways of representing robot locations

* Precision point.

* Cartesian coordinates and orientation angles. These are called transformations.


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3.TRAJECTORY CONTROL:

Two methods to control the path of the robot.

Interpolate between initial and final

position, producing tool tip curve in space.

Move the robot tip in straight line path.


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3.TRAJECTORY CONTROL:

For the first case,called JOINT

INTERPOLATED MOTION, the totaltime required is that of the longest joint in

the robot.

In the second case, the motion speed ofthe robot tool tip can be accurately

controlled.


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4.MONITOR COMMANDS:

To enter and execute a program, we have to

use monitor commands.

Defining and Determining Locations.

Editing Programs.

Listing Program and Location Data.

Storing, Retrieving and Location Data. Program control


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Determining and Defining Locations:

HERE and POINT command.

WHERE command is used to display the

current location.

TEACH command is used for recording

locations when RECORD button is pressed.


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Editing Programs:

EDIT command.

Listing Program and Location Data: LISTL & LISTP commands.

Storing, Retrieving and Location Data:

LISTF command.

STOREP, STOREL and STORE commands.

LOADP, LOADL and LOAD commands.


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Storing, Retrieving and Location Data:

In VAL II, an additional command is

FLIST. Besides VAL and VAL II can accept

commands.

COPYRENAME

DELETE


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Program control:

SPEED command.

EXECUTE command.

ABORT command.

DRIVE command.

DO ALIGN command.


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PROGRAM INSTRUCTIONS:

Describes some important instructions

included in the program. Robot Configuration Control.

Motion Control.

Hand Control.

Location, Assignment and Modification.

Program Control.


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Robot Configuration Control:

Execution of next motion of instruction

other than a straight line.

RIGHTY or LEFTY command.

ABOVE or BELOW command.


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Motion Control:

MOVE command.

MOVES command. DRAW command.

APPRO command.

DEPART command.

APPROS or DEPARTS commands.

CIRCLE command.


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Hand Control:

OPEN and CLOSE commands.

OPENI and CLOSEI commands. CLOSEI 75 in VAL II, if a servo-controlled

gripper is used, then this command causes thegripper to close immediately to 75 mm.

A gripper closing command is also given byGRASP 20, 15


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Hand Control:

MOVEST PART, 30

Indicates the servo controlled end

effector causes a straight line motion to a

point defined by the PART and the

gripper opening is changed to 30 mm.


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Hand Control:

MOVET PART, 30

Causes the gripper to move to position, PART

with an opening of 30 mm by Joint

Interpolated Motion.


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Location, Assignment and Modification:

The instructions that do the same as

the corresponding monitor commands

SET and HERE commands.


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VAL SYSTEM AND

LANGUAGE contdProgram Control:

SETI command sets the value of an integervariable to the result of an expression

TYPEI displays the name and value of an integervariable.

GOTO20

GOSUB and RETURN PAUSE


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VAL SYSTEM AND

LANGUAGE contdProgram Control:

PROCEED

SIGNAL

IFSIG and WAIT

RESET


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ECONOMICS

A simple economic analysis assumes that the

payback period is given by

P = R / (L-M)Where P = payback period in years

R = investment in robot and accessories

L = labor saving per year

M = maintenance and programming cost per year

5.Robo Unit III

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