Introduction to Robotics

Prof A S Rao

Robotics & CAD/CAM Laboratory Mechanical Engineering Department

VEERMATA JIJABAI TECHNOLOGICAL INSTITUTE MUMBAI-400019

Outline• What 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

What is Robotics:• Robotics is an interdisciplinary subject that benefits

from mechanical engineering, electrical and electronic engineering, computer science, biology and many other disciplines.

• Robotics is defined as that branch of engineering which deals with the study of different types of robots, their simulations, their designs, their constructions, operations, performance etc.

• Robotics is a form of Industrial Automation and is a technology with a future and a technology for the future

What is a Robot :• When we compare a crane attached to a utility or towing vehicle and

robot manipulator which appears to be very similar because :– Both posses a number of links attached serially to each other with

joints– In both the systems, the hand of the manipulator can be moved in

space and be placed in any desired location with in the workspace of the system

– Each one is controlled by a central controller which controls the actuators

However one is called a robot and the other a manipulator (i.e. a crane)

– The fundamental difference between the two is that the crane is controlled by a human who operates and controls the actuators, whereas a robot manipulator is controlled by a computer that runs a program.

• 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 “a software 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 manipulate physical objects”

What is a Robot : Definition :

Classification of Robots:I. Drive Technology II. Work Envelope/Coordinate GeometryIII. Motion Control Methods

I. Drive Technology:

Motors are part of any robot system they produce spatial 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

1. Electrical drive technology:

Most Robotic manipulators today use electric drives in the 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

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

3. Pneumatic drive technology:

It is used as at the gripper for manipulating delicate objects, 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. Work Envelope/Coordinate 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)

III. Motion Control Methods :

1. Point to Point motion : The discrete points are specified, 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 3D space 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.

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

Degree of Freedom (DOF) :• The no. of independent movements a robot can

perform in 3D space. (or) Direction in which a robot moves when a particular joint is activated

• To fully place the object in space and also orientate it as desired we need to have six DOF.

• A system with seven DOF does not have unique solution i.e Robot mounted on conveyor belt or mobile platform

• In 3.5 DoF, 3 DoF are along X,Y,Z axes, and 1/2 DoF for not fully controlled movement like fully extended or retracted position of pneumatic cylinder

Robot Joints :

Robots may have types of joints like,

• Linear (Prismatic): Either hydraulic or pneumatic cylinder, used in Gantry, cylindrical or similar configurations

• Rotary (Revolute) : Most such joints electrically driven either by servomotors or stepper motors

• Spherical : They posses multiple DOF ,difficult to control they are not commonly used except in research work.

Robot Coordinates :

Robot configurations are specified by a succession of P’s, R’s or S’s like “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 revolute

joints, similar to a human’s arm, common for Industrial robots

• Selective Compliance Assembly Robot Arm (SCARA) : 2 revolute joints, 1 prismatic (vertical)

they are very common in assembly operations

Robot motions are accomplished in 3 coordinate frames like, • World Reference Frame : Defined by X,Y,Z Axes motions

simultaneously, this is universal coordinate frame.

• Joint Reference Frame : Only one joint moves at a time

• Tool Reference Frame : Defined by X’,Y’,Z’ Axes motions simultaneously attached to the hand defines the motions of the hand relative to this local frame. This is very useful in robotic programming.

Robot Reference Frames :

Programming Modes :

Commonly used Programming Modes :• Physical Setup: In this mode operator sets up switches

and hard stops along with devices like PLC’s

• Lead Through or Teach Mode : In this mode the robot joints are moved with a teach pendant, point to point mode

• Continuously Walk -Through Mode : In this mode the robot joints are moved simultaneously with a program, it’s a continuous mode, for example painting robots

Robot Characteristics :

• Payload : It is the weight a robot can carry with out losing accuracy, Typical values 6.6 lbs of 86 lbs Fanuc Robot LR mate.

• Reach : Reach is the a maximum distance a robot can reach with in its work envelope (reaching dexterous points)

• Precision (Validity) : It is defined as how accurately a specified point can be reached. Typical value 0.001 inch (resolution of robot)

• Repeatability (Variability) : It is defined as how accurately the same position can be reached. Typical value 0.001 inch range for 100 runs (say)

Robot WorkSpace :

• Depending on their configuration and size of their links and joints robot can reach a collection 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

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 VAL® and AML® , so debugging is easier

• Compiler based languages execute whole program at time such as AL® and so debugging is difficult

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

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 :