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Introduction to Robotics
Prof A S Rao
Robotics & CAD/CAM Laboratory
Mechanical Engineering Department
VEERMATA JIJABAI TECHNOLOGICAL INSTITUTE
MUMBAI-400019
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OutlineWhat is Robotics Robot Coordinates
Laws of Robotics Robot Reference Frames
What is a Robot Programming Modes
Classification Robot Characteristics
Robot Components Robot Workspace
Robot DOF Robot languages
Robot Joints Robot Applications
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What is Robotics:
Robotics is an interdisciplinary subject that benefitsfrom mechanical engineering, electrical andelectronic engineering, computer science, biologyand many other disciplines.
Robotics is defined as that branch of engineeringwhich deals with the study of different types ofrobots, their simulations, their designs, theirconstructions, operations, performance etc.
Robotics is a form of Industrial Automation and is atechnology with a future and a technology for thefuture
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What is a Robot :
When we compare a crane attached to a utility or towing vehicleand robot manipulator which appears to be very similar because :
Both posses a number of links attached serially to each otherwith joints
In both the systems, the hand of the manipulator can be movedin space and be placed in any desired location with in theworkspace of the system
Each one is controlled by a central controller which controls theactuators
However one is called a robot and the other a manipulator (i.e. acrane)
The fundamental difference between the two is that the crane iscontrolled by a human who operates and controls the actuators,whereas a robot manipulator is controlled by a computer thatruns a program.
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The Automatic progrmmable machines which does the required
job through various programmed motions
According to RIA: A robot is a reprogrammable multifunctional
manipulator designed to move various objects, tools, materials or
specialized devices through variable programmed motions for the
performance of variety of tasks
Law of Japan states that a robot is All purpose machine equipped
with a memory device (for handling) capable of replacing human
labour for the automatic performance of tasks
Robert Schilling defines a robot as asoftware controlled mechanical
device that uses sensors to guide one or more of its end effectors
through various programmed motions in a work space in order to
mani ulate h sical ob ects
What is a Robot : Definition :
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Classification of Robots:
I. Dr ive Techno logy
II. Work Envelope/Coord inate Geometry
III. Mot ion Con trol Methods
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I. Drive Techno logy:
Motors are part of any robot system they producespatial displacement and control axis motions of the
robot. Based on power used to drive the joints of
the robot the 3 drive technologies are :
1) Electrical drive technology
2) Hydraulic drive technology
3) Pneumatic drive technology
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1. Electrical drive technology:
Most Robotic manipulators today use electric drives inthe form of either D.C.Servomotors or D.C.Stepped
motors
D.C.Servomotors : More controllability for precision
work (neat/precise)
D.C.Stepped motors : Load carrying capacity is large
Applications :
- PCB Assembly
- IC manufacture, etc
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2. Hydraulic drive technology:
Robotic manipulator which uses oil/liquid/gel as a
drive technology. We use it for very heavy load
carrying capacity purpose.
Limitation : Cleanliness will not be maintained
Applications:
-In steel industry for carrying molten steel
-Automobile industry
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3. Pneumatic drive technology:
It is used as at the gripper for manipulating delicateobjects, e.g. used in glass industry.
The robot operates from compressed air and they are
activated tools.Limitation: Built in compliance of air, i.e. air can be
compressed, creates noise while operation.
Application:Used in pick and place operations in glass industry
II W k E l /C d i t
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II. Wo rk Envelope/Coo rd inate
Geometry :
Work Envelope is defined as locus of points in 3
Dimensional space that can be reached by the wrist of
robot.
It consists of Rotary/Revolute motion about an axis
and Translation motion along an axis (i.e.
linear/sliding/prismatic/translate)
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III. Motion Con tro l Methods :
1. Point to Point motion : The discrete points arespecified, the tool moves in a sequence of discrete
points in the workspace.
2. Continuous or Controlled path motion : The
end effector must follow a prescribed path in 3Dspace and speed of motion along the path may
vary
Examples : PTP : Spot welding, Loading &Unloading, Pick and Place, etc.
CP : Spray painting, Arc welding, Grinding, etc.
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Robot Components :
Main components are :
- Manipulator : Main body (Links, Joints etc)
- End effector : Welding Torch, Paint spray gun etc
- Actuators : servo motors,stepper motors,cylinders etc- Sensors : Vision, Touch, Speech synthesizers etc
- Controller : receives data from PC and controls the
actuators- Processor: calculates motions of joints@speeds
- Software : OS, Appliaction s/w
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Degree of Freedom (DOF) : The no. of independent movements a robot can
perform in 3D space. (or) Direction in which a robotmoves when a particular joint is activated
To fully place the object in space and alsoorientate it as desired we need to have six DOF.
A system with seven DOF does not have uniquesolution i.e Robot mounted on conveyor belt ormobile platform
In 3.5 DoF, 3 DoF are along X,Y,Z axes, and 1/2DoF for not fully controlled movement like fullyextended or retracted position of pneumaticcylinder
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Robot Joints :
Robots may have types of joints like,
Linear (Prismatic): Either hydraulic or pneumaticcylinder, used in Gantry, cylindrical or similar configurations
Rotary (Revolute) : Most such joints electrically driveneither by servomotors or stepper motors
Spherical :They posses multiple DOF ,difficult to controlthey are not commonly used except in research work.
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Robot Coordinates :
Robot configurations are specified by a succession of
Ps,Rsor Sslike 3P3R
Cartesian/Rectangular/Gantry (3P) : 3 linear joints
Cylindrical (R2P) : 2 prismatic and 1 revolute joints
Spherical (2RP) :1 prismatic and 2 revolute joints
Articulated/anthropomorphic (3R) :All revolutejoints, similar to a humansarm, common for Industrial robots
Selective Compliance Assembly RobotArm (SCARA) :2 revolute joints, 1 prismatic (vertical)they are very common in assembly operations
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Robot motions are accomplished in 3 coordinate frames like,
World Reference Frame : Defined by X,Y,Z Axes motionssimultaneously, this is universal coordinate frame.
Joint Reference Frame : Only one joint moves at a time
Tool Reference Frame : Defined by X,Y,Z Axes motionssimultaneously attached to the hand defines the motions of thehand relative to this local frame. This is very useful in robotic
programming.
Robot Reference Frames :
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Programming Modes
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Programming Modes :
Commonly used Programming Modes : Physical Setup: In this mode operator sets up switches
and hard stops along with devices like PLCs
Lead Through or Teach Mode : In this mode therobot joints are moved with a teach pendant, point to point mode
Continuously Walk -Through Mode :In this modethe robot joints are moved simultaneously with a program, itsa
continuousmode, for example painting robots
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Robot Characteristics :
Payload : It is the weight a robot can carry with out losingaccuracy, Typical values 6.6 lbs of 86 lbs Fanuc Robot LR mate.
Reach : Reach is the a maximum distance a robot can reachwith in its work envelope (reaching dexterous points)
Precision (Validity) : It is defined as how accurately aspecified point can be reached. Typical value 0.001 inch
(resolution of robot)
Repeatability (Variability) : It is defined as howaccurately the same position can be reached. Typical value
0.001 inch range for 100 runs (say)
Robot WorkSpace :
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Robot WorkSpace :
Depending on their configuration and size of
their links and joints robot can reach acollection of points called a WorkSpace
Shape of WS depends on each robot
characteristics WS may be found by moving each joint
through its range of motions
Typical WS are Cartesian,Cylindrical,
Spherical,Articulated etc
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Robot Languages :
Many robot languages are based on Cobol, Basic, C
and Fortran etc Other languages are unique and at different level
from machine level to high level languages.
High level languages are either interpreter based or
compiler based
Interpreter based languages execute one line of the
program at time such as VALand AML, so
debugging is easier
Compiler based languages execute whole program
at time such as AL and so debugging is difficult
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Robot Applications :
Machine Loading
Pick and Place operations
Welding
Painting
Inspection and testing Assembly operations
Manufacturing like drilling, deburring, cutting etc.
Surveillance
Medical applications
Hazardous environments
Underwater,space, and remote locations
T t B k
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Text Books :
Fundamentals of Robotics - T.C. Manjunath
Robotics and Control - R.K.Mittal/I J Nagrath
Introduction to Robotics - Saeed B. Niku
Introduction to Robotics - John J CRAIG
Robotics - Ashitava Ghosal
Reference Books :
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