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ROBOTICS
DEFINITION
A robot is a reprogrammable, multifunctional manipulator
designed to move material, parts, tools, or specialized devices
through programmed motions for the performance of a variety
of tasks.
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ROBOT MANIPULATOR
Manipulator: A manipulator is a collection of mechanical
linkages connected by joints to form an open loop kinematic
chain.

A robot manipulator can be divided into two sections: a
body-and-arm assembly and a wrist assembly.

There are usually three degrees-of-freedom associated with
the body-and-arm,

Two or three degrees-of-freedom associated with the wrist.

At the end of the wrist there is an end-effector, related to
the task that must be accomplished by the robot.
ROBOT MANIPULATOR

An end-effector is usually either (1) a gripper for holding a
Work-part or (2) a Tool for performing some process.

The body-and-arm of the robot is used to position the endeffector, and the robot's wrist is used to orient the endeffector.
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Wrist assembly
Body-and-arm assembly
Some possible wrist configurations
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EXAMPLES OF END-EFFECTORS
CLASSIFICATION OF ROBOTS
Classification will be performed in two different ways, based
on:

The particular coordinate system utilized in designing the
mechanical structure

The method of controlling the various robotic axis
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CLASSIFICATION BY COORDINATE SYSTEM
Cylindrical Coordinate Robots

When a horizontal arm is mounted on a vertical column
and this column is then mounted on a rotating base.
CYLINDRICAL COORDINATE ROBOTS

Has two linear motions and one rotary motion.

Robots can achieve variable motion.



The first coordinate describe the angle theta of base
rotation--- about the up-down axis.
The second coordinate correspond to a radical or y--- in out
motion at whatever angle the robot is positioned.
The final coordinate again corresponds to the up-down z
position.
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CYLINDRICAL COORDINATE ROBOTS




Rotational ability gives the advantage of moving rapidly to
the point in z plane of rotation.
Results in a larger work envelope than a rectangular robot
manipulator.
Suited for pick-and-place operations.
Because of the mechanical limitations, the overall volume
or work envelope is a portion of a cylinder.
CYLINDRICAL COORDINATE ROBOTS


ADVANTAGE:

Their vertical structure conserves floor space.

Their deep horizontal reach is useful for far-reaching
operations.

Their capacity is capable of carrying large payloads.
DISADVANTAGE:

Their overall mechanical rigidity is lower than that of
the rectilinear robots because their rotary axis must
overcome inertia.

Their repeatability and accuracy are also lower in the
direction of rotary motion.

Their configuration requires a more sophisticated
control system than the rectangular robots.
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APPLICATION

Assembly

Coating applications.

Conveyor pallet transfer.

Die casting.

Foundry and forging applications.

Inspection molding.

Investment casting.

Machine loading and unloading.
CLASSIFICATION BY COORDINATE SYSTEM
Spherical Coordinate Robots

Has one linear motion and two rotary motions.

The work volume is like a section of sphere.

The first motion corresponds to a base rotation about a
vertical axis.

The second motion corresponds to an elbow rotation.

The third motion corresponds to a radial, or in-out,
translation.

A spherical-coordinated robots provides a larger work
envelope than the rectilinear or cylindrical robot.
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SPHERICAL COORDINATE ROBOTS

Because
of
the
mechanical
and/or
actuator
connection
limitations, the work envelope is a portion of a sphere.

Advantages and disadvantages same as cylindrical-coordinated
design.
JOINTED ARM ROBOTS

A Jointed Arm robot has three rotational axes connecting three
rigid links and a base.

The first joint above the base is referred to as the shoulder. The
shoulder joint is connected to the upper arm, which is connected
at the elbow joint.

Jointed Arm robots are suitable for a wide variety of industrial
tasks, ranging from welding to assembly.
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CARTESIAN COORDINATE ROBOTS

A `Cartesian coordinate robot` (also called `linear robot`) is
an industrial robot whose three principal axes of control are
linear (i.e. they move in a straight line rather than rotate)
and are at right angles to each other.
1)
Cantilevered Cartesian
2)
Gantry-Style Cartesian
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SCARA

SCARA is an acronym for Selective Compliance Assembly
Robot Arm.

This configuration is similar to the jointed arm robot except
that the shoulder and elbow rotational axes are vertical,
which means that the arm is very rigid in the vertical
direction, but compliant in the horizontal direction.

This permits the robot to perform insertion tasks (for
assembly) in a vertical direction, where some side-to-side
alignment may be needed to mate the two parts properly.
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MAJOR COMPONENTS OF A ROBOT
There are four major components in common:
1. A manipulator or arm (the mechanical unit)
2. One or more sensors
3. A controller (the brain)
4. A power supply
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MANIPULATOR

This is the collection of mechanical linkages connected by
joints to form an open-loop kinematic chain.

Also included are gears, couplings devices, and so on.

The manipulator is capable of movement in various
directions and is said to do the work of the robot.

The
terms
robot
and
manipulator
are
often
used
interchangeably, although, strictly speaking, this is not
correct.

Joints of a manipulator fall into one of two classes.
1 -Rotary joint (revolute)
2 -Linear joint (Prismatic)
MANIPULATOR

Each joint defines a joint axis about or along which the
particular link either rotate or slides (translates).

Every joint axis defines a degree of freedom (DOF), so that
the total number of DOFs is equal to the number of joints.

Many robots have six DOFs, three for positioning and three
for orientation.

It is possible to have as few as two and as many as eight
DOFs.

The manipulator structure generally contains three main
elements; the arm, the wrist, and the hand (end-effector).
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SENSORY DEVICES

These elements inform the robot about the status of the
manipulator. This can be done continuously or only at the
end of a desired motion.

In continuous monitoring the sensors provide instantaneous
position, velocity, and possibly acceleration information
about the individual links.

In simple situation, the controller can be informed only
when the individual links have reached their programmed
final position.

The information provided by the sensors can be either
analog, digital, or a combination.
SENSORY DEVICES

Sensors used in modern robots can be divided into two
general classes:
1. Non-visual: Limit switches (e.g., proximity, photoelectric,
or mechanical), position sensors (e.g., optical encoders,
potentiometers, or resolvers), velocity sensors (e.g.,
tachometer), or force and tactile sensors.
2. Visual: The second group consists of CCD or CID Tv
cameras
coupled
to
appropriate
image-detection
hardware. They are used for tracking, object recognition,
or object grasping.
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THE CONTROLLER
Robot controllers generally perform three functions:

1. They initiate and terminate the motion of the individual
components of the manipulator in a desired sequence and
at specified points.
2. They store position and sequence data in their memory.
3. They permit the robot to be interfaced to the outside world
via sensors mounted in the area where work is being
performed (workstation).
JOINT DRIVE SYSTEMS

Electric



Hydraulic



Uses electric motors to actuate individual joints
Preferred drive system in today's robots
Uses hydraulic pistons and rotary vane actuators
Noted for their high power and lift capacity
Pneumatic

Typically limited to smaller robots and simple material
transfer applications
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ROBOT CONTROL SYSTEMS




Limited sequence control – pick-and-place operations using
mechanical stops to set positions
Playback with point-to-point control – records work cycle
as a sequence of points, then plays back the sequence
during program execution
Playback with continuous path control – greater memory
capacity and/or interpolation capability to execute paths (in
addition to points)
Intelligent control – exhibits behavior that makes it seem
intelligent, e.g., responds to sensor inputs, makes
decisions, communicates with its environment.
THE POWER CONVERSION UNIT

The purpose of this part of the robot is to provide the
necessary energy to the manipulator’s actuators.

It can take the form of a power amplifier in the case of
servomotor-actuated
system,
or
it
can
be
a
remote
compressor when pneumatic or hydraulic devices are used.
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Robot manipulator - a series of joint-link combinations
CLASSIFICATION OF ROBOTS BY THE TYPE AND
ORDER OF JOINTS

Translational motion (Prismatic joint)



Linear joint (type L)
Orthogonal joint (type O)
Rotary motion (Revolute joint)



Rotational joint (type R)
Twisting joint (type T)
Revolving joint (type V)
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TRANSLATIONAL MOTION JOINTS
Linear joint
(type L)
Orthogonal joint
(type O)
ROTARY MOTION JOINTS
Rotational joint
(type R)
Twisting joint
(type T)
Revolving joint
(type V)
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JOINT NOTATION SCHEME
Use joint symbols (L, O, R, T, V) to designate joint types.
 Separates body-and-arm assembly from wrist assembly
using a colon (:)
 Example: TLR : TR

CURRENT ROBOT APPLICATIONS
1-Welding

Welding is one of the major uses for an industrial robot.

Two
types
of
welding
operations
are
readily
and
economically performed by robots: spot and arc welding.

In spot welding, the robot is taught a series of distinct
points.

Since the metal parts may be quit irregular, a wrist with
good dexterity is required so that it can be aligned properly
at the desired weld points without the gun coming in contact
with other portions of the part.


Typically, the welding tools are large and heavy
Also, it is usually necessary for the manipulator to have long
reach.
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CURRENT ROBOT APPLICATIONS
1-Welding

Therefore, large point-to-point servo controlled robots are
used for this purpose.

The automobile industry is a heavy user of this type of robot.

Since, the weld points are pre-taught, sensory information is
generally not required.
CURRENT ROBOT APPLICATIONS
1-Arc Welding

Arc welding is also utilized extensively by the auto industry.

Here, an often irregularly shaped seam or a wide joint must
be made, therefore, a continuous path servo controlled robot
is required.

If the parts can be accurately positioned and held in place,
the complex 3D path can be pre-taught and no external
sensors may be required.

A major advantage of a robotic welder is that the arc time
can be carefully controlled.
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CURRENT ROBOT APPLICATIONS
2-Spray Painting

Because of the potential fire hazard and the fact that a fine
mist of paint is toxic, spray painting should not be done by
human beings.

Another advantage is that the resulting coating will be far
more uniform than human being could produce.

This results in high quality products, less reworking, and
considerably less paint being used (40% saving).

For spray painting robots are capable of performing both
straight-line and continuous-path motions.
CURRENT ROBOT APPLICATIONS
3-Grinding

As a result of arc welding, a bead is formed at the seam.

This is also a natural task for a robot since the manipulator
can use the same program that was employed in the arc
welding.

All that must be done is to remove the welding tool and
replace it with a rotary grinder.

Another important grinding task is on metal casting.

The third application is deburring.
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CURRENT ROBOT APPLICATIONS
4-Other applications involving rotary tools

In addition to the rotary grinding or deburring applications,
robots are also currently used for drilling holes, polishing,
nut running, and driving of screws.

Preprogramming can be performed when extreme accuracy
is not required.

For accurate parts, it may be necessary to use template.

But the template or part may be damaged if the wrist does
not has some compliance.

This problem is overcome by using compliant wrist.

It permits the drill bit to be aligned in the template hole
even if there is a positional error.
CURRENT ROBOT APPLICATIONS
5-Parts handling and transfer

Palletization and depalletization

Acquiring of blank or unfinished parts and feeding them into
type of machine tools.
6-Assembly operations

Humans are capable of assembling a group of diverse parts
to produce a product because of their ability to utilize good
eye-hand coordination in conjunction with the important
sense of touch.

However, these jobs may be extremely tedious because of
their repetition nature

As such, assembly operations represent an attractive
application of robots.
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CURRENT ROBOT APPLICATIONS
5-Parts sorting
6-Parts inspection
PRECISION IN NC POSITIONING

For accurate positioning, the positioning system must possess a high
degree of precision.

Three measures of precision:
1.
Control resolution
2.
Accuracy
3.
Repeatability
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CONTROL RESOLUTION
Control resolution is defined as the distance separating two adjacent
addressable points in the axis movement.

Addressable points are locations along the axis to which the robotic
arm can be specifically directed to go.

It is desirable for control resolution to be as small as possible.
Control
resolution
Bit storage
capacity of the
controller
Electromechanical
components
·
·
·
·
Lead-screw pitch
Gear ratio
Step angle
Angle b/w encoder slots
CONTROL RESOLUTION
 Control
Resolution
Components

of
the
Electromechanical
A number of electromechanical factors affect control resolution,
including leadscrew pitch, gear ratio in the drive system, and
the step angle in a stepping motor for an open-loop system or
the angle between slots in an encoder disk for a closed-loop
system. For an open-loop positioning system driven by a
stepper motor, these factors can be combined into an expression
that defines control resolution as follows:
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CONTROL RESOLUTION
 Control
resolution of the computer system

The ability to divide the axis range into individual increments
depends on the bit storage capacity in the control memory

The number of increments = 2 n
n = number of bits in the control memory

Control resolution
CR2 

L
2 1
n
Control resolution of the overall positioning system
CR  Max CR1, CR2 
CONTROL RESOLUTION

A desirable criterion is for CR2 < CR1, meaning the electromechanical
system is the limiting factor.

The bit storage capacity of modern computer controller is sufficient
to satisfy the requirement.

Resolutions of 0.0025 mm is within the current state of NC
technology.
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ACCURACY
 The
accuracy of any given axis of a positioning system is
the maximum possible error that can occur between the
desired target point and the actual position taken by the
system.
ACCURACY IN IDEAL CASE
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MECHANICAL ERRORS
 The
capability of a positioning system to move the
worktable to the exact location is limited by the following
mechanical errors.
1.
Play between the lead-screw and the table
2.
Backlash in the gears
3.
Elastic deflection in the structural members
4.
Stretching of pulley cords
ACCURACY IN REAL CASE
 Assumptions
1.
Mechanical errors form an normal distribution about
the control point whose mean is 0
2.
Standard deviation is constant over the range of the
axis.
 Accuracy
is defined under worst case conditions in which
the desired target point lies in the middle between two
adjacent addressable points.
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ACCURACY IN REAL CASE
 This
is the maximum possible positioning error.
 Mathematically
Accuracy 
CR
 3
2
REPEATABILITY
 Repeatability
refers to the capability of the positioning
system to return to a given addressable point that has
been previously programmed
Re peatability  3
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