Robots

Industrial Robots
An industrial robot is a general-purpose,
programmable machine. It possesses some
anthropomorphic characteristics.

Applications
An automatically controlled, reprogrammable,
multipurpose, manipulator programmable in
three or more axes, which may be either fixed
in place or mobile for use
in industrial automation applications
• Machine loading
• Spot welding
• Spray painting
• Assembly

Advantages of Robots
• Robots are good substitutes to the human beings in
hazardous or uncomfortable work environments.
• A robot performs its work cycle with a consistency
and repeatability which is difficult for human beings
to attain over a long period of continuous working.

Advantages of Robots
• Robots can be reprogrammed. When the production run of the
current task is completed, a robot can be reprogrammed and
equipped with the necessary tooling to perform an altogether
different task.
• Robots can be connected to the computer systems and other
robotics systems. Nowadays robots can be controlled with
wire-less control technologies. This has enhanced the
productivity and efficiency of automation industry.

Joints
• Linear (L) Joint
• Orthogonal (O) Joint
• Rotational (R) Joint
• Twisting (T) Joint
• Revolving (V) Joint

Linear (L) Joint
The relative movement between the input link
and the output link is a translational sliding
motion, with the axes of the two links being
parallel.

Orthogonal (O) Joint
This is also a translational sliding motion, but
the input and output links are perpendicular
to each other during the move.

Rotational (R) Joint
This type provides rotational relative motion,
with the axis of rotation perpendicular to the
axes of the input and output links.

Twisting (T) Joint
This joint also involves rotary motion, but the
axis or rotation is parallel to the axes of the
two links.

Revolving (V) Joint
In this type, axis of input link is parallel to the
axis of rotation of the joint. However the axis
of the output link is perpendicular to the axis
of rotation.

Degrees of freedom (Robot Motions)
• Basically the robot manipulator has two
parts viz. a body-and-arm assembly with
three degrees-of-freedom
Vertical motion: Z-axis motion
Radial motion: In and out or Y-axis motion
Right to left motion: X-axis motion
.

A wrist assembly with two or three degrees-of-
freedom
Wrist Swivel: Rotation of the wrist
Wrist Yaw: Right or left swivel of the wrist
Wrist bend: Up or down movement of wrist

Robot Configurations
Five common body-and-arm configurations:
1.Polar configuration
2.Cylindrical configuration
3.Cartesian coordinate configuration
4.Jointed arm configuration
5.SCARA configuration

Polar configuration (L-T-R)
It consists of a sliding arm (L-joint), actuated
relative to the body, which rotates around
both a vertical axis (T-joint), and horizontal
axis (R-joint)

Cylindrical configuration(T-L-O)
It consists of a vertical column. An arm assembly is moved
up or down relative to the vertical column. The arm can be
moved in and out relative to the axis of the column.
Common configuration is to use a T-joint to rotate the
column about its axis. An L-joint is used to move the arm
assembly vertically along the column, while an O-joint is
used to achieve radial movement of the arm.

Cylindrical configuration(T-L-O)

Cartesian coordinate configuration(L-O-O)
It is also known as rectilinear robot and x-y-z
robot. It consists of three sliding joints, two of
which are orthogonal O-joints.

Jointed arm configuration(T-R-R)
It is similar to the configuration of a human arm. It consists of a
vertical column that swivels about the base using a T-joint.
Shoulder joint (R-joint) is located at the top of the column. The
output link is an elbow joint (another R joint).

SCARA configuration
Selective Compliance Assembly Robot Arm
It is similar in construction to the jointer-arm robot, except the
shoulder and elbow rotational axes are vertical. It means that the
arm is very rigid in the vertical direction, but compliant in the
horizontal direction. This permits robots to perform insertion
task for assembly.

Characteristics of an Industrial robot
• Work volume
• Speed of movement
• Spatial resolution
• Accuracy
• Repeatability
• Weight carrying capacity
• Stability

Work volume
It is the Space or envelope with in which the
robot arm can be rotated. Depending on robot
configuration and size of the links and wrist
joint the arm can reach a collection of points.

• Speed of movement: The speed with which the robot
can manipulate the end effector.
• Spatial resolution: smallest increment of motion at the
wrist end that can be controlled by the robot
• Accuracy: Capability of the robot to position its wrist
end at the given target point in its work volume.
• Repeatability: this is the ability of a robot to position its
wrist end back to a point that was previously taught.
• Weight carrying capacity: Weight of the gripper to
grasp the objects
• Stability: is the amount of oscillations occurs in the
robots motion at the end arm as it attempts to move to
the next programmed location

Robot Actuators/Drive systems
Actuators provides the mechanical power in
order to act the mechanical structures against
gravity, inertia and other external forces to
change the geometric location of the tool/end
effector.
Hydraulic Actuators/drivers
Electric Actuators/drivers
Pneumatic Actuators/drivers

Hydraulic Actuators:
• Large Robots
• More floor space
• Mechanical simplicity
• More strength
• More Speed
Electric Actuators:
Step/Servo Motors
• Compatibility to computing
systems
• Accuracy & repeatability is good
• Less floor space
• Less strength
• Less Speed/ Commercial
Applications
Pneumatic Actuators:
Linear Pistons /Rotary vane
actuators
•Smaller
•Used for high cycle speeds
•Less sophisticated
•Pick and place simple tasks

Robot Control systems
The joint movements an industrial robot must
accurately be controlled. Micro-processor-
based controllers are used to control the
robots.
• Limited sequence control
• Playback with point to point control
• Playback with continuous path control
• Intelligent control

Limited sequence control
• It is an elementary control type.
• It is used for simple motion cycles, such as pick-and-place
operations.
• It is implemented by fixing limits or mechanical stops for each joint
and sequencing the movement of joints to accomplish operation.
• Feedback loops may be used to inform the controller that the action
has been performed, so that the program can move to the next step.
• Precision of such control system is less. It is generally used in
pneumatically driven robots.

Playback with point to point control
• Playback control uses a controller with memory to record motion
sequences in a work cycle, as well as associated locations and other
parameters, and then plays back the work cycle during program
execution.
• Point-to-point control means individual robot positions are
recorded in the memory. These positions include both mechanical
stops for each joint, and the set of values that represent locations in
the range of each joint.
• Feedback control is used to confirm that the individual joints
achieve the specified locations in the program.

Playback with continuous path control
• Continuous path control refers to a control system
capable of continuous simultaneous control of two or
more axes.
• The following advantages are noted with this type
of playback control: greater storage capacity—the
number of locations that can be stored is greater than
in point-to-point;
• interpolation calculations may be used, especially
linear and circular interpolations.

Intelligent control
it may have capacity to interact with its ambient surroundings;
• decision-making capability;
• ability to communicate with humans;
• ability to carry out computational analysis during the work cycle;
• responsiveness to advanced sensor inputs.
• They may also possess the playback facilities.
• However it requires a high level of computer control, and an
advanced programming language to input the decision-making logic
and other ‘intelligence' into the memory.

Robot programming
• A robot program is a path in the space that to be followed by the
manipulator, combined with peripheral actions that support the
work cycle.
• To program a robot, specific commands are entered into the
robot's controller memory, and these actions may be performed in
a number of ways.
• Online programming
Teach pendant programming
Lead through programming
• Off-line programming

Teach pendant programming
A control box for programming the motions of a robot.
Also called a "teach box," the robot is set to "learning"
or "teach" mode, and the pendant is used to control
the robot step by step. Teach pendants are typically
handheld devices and may be wired or wireless. The
technician operates the teach box to control motion of
end effector of robot.

The technician has the ability to send the robot to
the desired position then record the point.
He may also change the speed since low speed is
always required for careful positioning.
Once the technician has recorded and test the
program then teach pendent is disconnected and
the robot can operated the stored program at
more speed.

Lead through programming
• Task is taught to the robot by manually moving the
manipulator through the required cycle, and
simultaneously entering the program in to the
controller memory for playback.

Computer-like Programming
These are computer-like languages which use on-line/off-line methods
of programming. The advantages of textual programming over its
lead-through counterpart include:
• The use of enhanced sensor capabilities, including the use of
analogue and digital inputs
• Improved output capabilities for controlling external equipment
• Extended program logic, beyond lead-through capabilities
• Advanced computation and data processing capabilities
• Communications with other computer systems

Industrial Robot Applications:
1.Material transfer
2.Machine loading
3.Welding
4.Spray coating
5.Processing operations
6.Assembly
7.Inspection

A-6
Q1.What are the basic configurations of an
industrial robot? Explain them schematically.
Q2.What are the basic actuator systems used in
industrial robots? Explain the applications of
industrial robots?
Q3.Classify robot control systems. Enumerate
their merits and demerits.

Robots

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