FEDERAL UNIVERSITY OF PETROLEUM RESOURCES
EFFURUN, DELTA STATE
INTRODUCTION TO INDUSTRIAL ROBOTS
WRITTEN BY
ENGR. OMAMERHI OTURUHOYI
SCHOOL OF POST GRADUATE STUDIES
(DEPARTMENT OF MECHANICAL ENGINEERING)
2022/2023 SESSION
COURSE: MANUFACTURING AUTOMATION (MEE 832)
LECTURER: DR. MODESTUS O. OKWU
INTRODUCTION TO INDUSTRIAL ROBOTS
Robot as a word was first mentioned through a Czechoslovakian play titled “Rossum’s Universal
Robot”, written by Karel Capek in 1920s. The word Robot emanated from the Czech word Robota,
which means “forced worker” and converted to robot according to English translation.
An industrial robot is a machine formed by a mechanism including several degree of freedom,
often having the appearance of one or several arms ending in a wrist capable of holding a tool, a
work piece or an inspection device.
An industrial robot is 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. The robot is a machine possessing different kinds of ability of
which one of them is its mechanical arm. The robot have the capability to respond to sensory
inputs, communicate with other machines and make decisions. This enables the robot perform
different industrial tasks.
Industrial tasks are commercially and technologically important because:
i.
They can be substituted for human in hazardous or uncomfortable work environment
ii.
They perform their work cycle with consistency repeatedly that cannot be attained by
humans
iii.
They can be reprogrammed to perform different jobs when you want them to do.
ROBOT COMPONENT
The components of industrial robot are the manipulator, end effector, mechanical grippers, power
supply and controller.
(i) Manipulator: Also known as arm and wrist. The manipulator is a mechanical unit that
provides motion (trajectories) similar to those of a human arm and hand. The end of the wrist can
reach a point in space orientation. Most industrial robots have six rotational joints and seven
degrees of freedom or redundant robots.
(ii) End Effector: The end of the wrist in a robot is equipped with an end effector, also called end
of arm tooling. Depending on the type of operation, conventional end effectors may be equipped
with any of the following devices, which are:
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-
Grippers, hooks, scoops, electromagnets, vacuum cups and adhesive fingers for material
handling.
-
Spray guns for painting
-
Attachments for spot and arc welding and for arc cutting
-
Power tools (such as drills, nut, drivers and burrs)
-
Measuring instrument
(iii)
Mechanical Grippers: Are used the most commonly and are equipped with two or
more fingers to hold material and equipment firmly for different industrial purpose.
Compliant end effectors are used to handle fragile materials or to facilitate assembly.
This end effectors uses elastic mechanism to limit the force that can be applied to the
work piece.
(iv)
Power Supply: Each motion of the manipulator (linear or rotational) is controlled and
regulated by independent actuators that use an electrical, a pneumatic or a hydraulic
power supply.
(v)
Controller: (Control System) This is the communication and information processing
system that gives command for the movement of the robot. It is the BRAIN of the robot
and stores data to initiate and terminate movements of the manipulator. The controller
is the nervous system of the robot. It interferes with computers and other equipment,
such as manufacturing cells or assembly system. Feedback such as transducers are an
important part of the control system. Robots with a fixed set of motions have open loop
control. In this system, commands are given and the robot arms goes through its
motions. Unlike feedback in close loop system, in loop systems the accuracy of the
movements is not monitored. An open loop system does not have a self-correcting
capability.
CLASSIFICATION OF INDUSTRIAL ROBOTS
Robots can be classified by basics of type like Cartesian or rectilinear, cylindrical, spherical or
polar and articulated, revolute, jointed or anthropomorphic.
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TYPES OF ROBOT
1. Fixed Sequence and Variable Sequence Robots
This is also called the pick-an-place robot. It is programmed for specific operations. Its
movement are from point to point and the cycle is repeated continuously. These robots are
simple and relatively inexpensive and can also be programmed for a different sequence of
operation.
2. Playback Robot: An operator leads or walks the playback robot and its end effector
through the desired path. The operator teaches the robot by showing it what to do. The
robot records the part and sequence of the motion and can repeat them continually without
any further action of guidance by the operator.
3. Numerically Controlled (NC) Robot: The NC robot is programmed and operated much
like a numerically controlled machine. The robot is servo-controlled by digital data and its
sequence of movement can be modified with relative ease.
4. Intelligent Robots: Intelligent robots also called Sensory robots is capable of performing
some of the functions and tasks carried out by humans. It is equipped with a variety of
sensors with visual (computer vision) and tactile capabilities. Much like human, the robot
observes and evaluates its immediate environment and its own proximity to other objects
(especially machinery) by perception and pattern recognition. It then makes appropriate
decisions for the next movement and proceeds accordingly. A complex and power
computer is required to control this type of robot.
APPLICATIONS AND SELECTION OF ROBOTS
Industrial robots applications and selections are based on their different types of operation
which are:
1.) Material Handling Operation: This operation can be performed reliably and repeatedly with
robots thereby improving quality and reducing scrap losses. Example is casting and
molding operations. To accomplish the relocation task, the robot is equipped with a
Gripper. The gripper must be custom designed to grasp the particular part in the
application.
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2.) Processing Operation: This requires the robot to manipulate a tool at its end effector. The
application includes spot welding, continuous arc welding, spray coating and certain metal
cutting and deburring operations in which the robot manipulates a special tool.
3.) Assembly Application: Assembly application often involves the stacking of one part onto
another part (basically a part handling task). In other assembly operations, a tool is
manipulated such as an automatic screw driver
4.) Material Transfer: The primary purpose is for the robots to move parts from one location
to another. This is called pick and place operations which the robot picks up a part and
place it at a new location, transferring part from one conveyor to another is an example.
ROBOTIC SENSORS
Sensors used in industrial robotics can be classified into two categories:
i)
Internal and
ii)
External
Internal sensors are components of the robot and are used to control the positions and velocities of
the robot joints. These sensors form a feedback control loop with the robot controller. Typical
sensors used to control the position of the robot arm includes potentiometers and optical encoders.
Tachometers of various types are used to control the speed of the robot arm. External sensors are
external to the robot and are used to co-ordinate the operation of the robot with other equipment
in the cell. Other situations require more advanced sensor technologies including:
a) Tactile Sensors: These are used to determine whether contact is made between the sensor
and another object. Tactile sensors is divided into two types, which are (1) Touch sensors
(2) Force sensors. Touch sensors indicate that contact has been made with the object. Force
sensor indicate the magnitude of the force with the object. This is useful in gripper to
measure and control the force being applied to grasp a delicate object.
b) Proximity Sensor: These indicate when an object is close to the sensor. When this sensor
is used to indicate the actual distance of the object, it is called a range sensor.
c) Optical Sensors; Photocells and other photometric devices can be used to detect the
presence and absence of objects and are used for proximity.
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d)
Machine Vision: Machine vision is used on robotics for inspection, parts identification,
guidance and other uses.
Industrial robots have a wide range of application in the manufacturing industry and its benefits
are: increase in quality of product, improved safety, reduced human error, reduced labour cost
and help to save money.
REFERENCES
Amic P.J., “Computer Numerical Control Programming”, Prentice Hall, 1996.
Asrahl C.R., “Robots and Manufacturing Automation” 2nd Edition, Wiley 1992.
Colestock A., “Industrial Robotic Selection, Design and Maintenance”, McGraw Hill, New York
2004.
Craine J.J., “Introduction to Robotics, Mechanics and Control, 3rd Edition, Pearson Eduction, NJ
2004.
Galbiati I.J., Machine Vision and Digital Image Processing Fundamentals.
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