Robotics Basics

Robot

A robot is a machine designed to execute one or more tasks automatically with speed and precision. There are as many different types of robots as there are tasks for them to perform.

Robots that resemble humans are known as androids; however, many robots aren’t built on the human model. Industrial robots, for example, are often designed to perform repetitive tasks that aren’t facilitated by a human-like construction. A robot can be remotely controlled by a human operator, sometimes from a great distance. A telechir is a complex robot that is remotely controlled by a human operator for a telepresence system, which gives that individual the sense of being on location in a remote, dangerous or alien environment and the ability to interact with it. Telepresence robots, which simulate the experience and some of the capabilities of being physically present, can enable remote business consultations, healthcare, home monitoring and childcare, among many other possibilities.



An autonomous robot acts as a stand-alone system, complete with its own computer (called the controller). The most advanced example is the smart robot, which has a built-in artificial intelligence (AI) system that can learn from its environment and its experience and build on its capabilities based on that knowledge.

Swarm robots, sometimes referred to as insect robots, work in fleets ranging in number from a few to thousands, with all fleet members under the supervision of a single controller. The term arises from the similarity of the system to a colony of insects, where the individuals and behaviors are simple but the fleet as a whole can be sophisticated.

Robots are sometimes grouped according to the time frame in which they were first widely used. First-generation robots date from the 1970s and consist of stationary, nonprogrammable, electromechanical devices without sensors. Second-generation robots were developed in the 1980s and can contain sensors and programmable controllers. Third-generation robots were developed between approximately 1990 and the present. These machines can be stationary or mobile, autonomous or insect type, with sophisticated programming, speech recognition and/or synthesis, and other advanced features. Fourth-generation robots are in the research-and-development phase, and include features such as artificial intelligence, self-replication, self-assembly, and nanoscale size (physical dimensions on the order of nanometers, or units of 10-9meter).

History of robots

  • 1921 – Czech writer, Karel Capek, in his drama ( rossum’s univesal robot ) introduced the word robot to the world. It is derived from czech word “robota” meaning “forced labourer”.
  • 1942 – Isaac Asimov the well – known Russian science fiction writer, coined the word “robotics” in his story “Runaround”, to denote science devoted to study of robots and give three rules of robotics.
  • 1950 – Inspired by Asimov’s books on robots, Joseph F Engelberger tried to design a working robot
  • 1958 – Joseph F Engelberger and George C Devol started the “UNIMATION” Robotics company in the USA
  • 1961 – The first unimate robot , was installed in General Motor’s automobile factory in New Jersey , USA.

Laws of robotics

 

  • A robot should not injure a human being or, through inaction , allow a human to be harmed
  • A robot must obey orders given by humans except when that conflicts with the first law

A robot must protect its own existence unless that conflicts with the first or second law

  • When the robot is moving in our workspace we have to ensure that the robot can be halted in an emergency.
  • In the end part of robot have in-built dual safety chains or run-chains. These are two parallel circuits that when broken will prevent the robot from moving.
  • Externally, we can use emergency stop.
  • All robots have electrically operated disc brakes on each axis. These are on whenever power is not applied to release them.
  • Make emergency stop, interlock with peripheral equipment when either device threatens to damage the other.

Study of kinematics and dynamics of robot

  • Kinematics is the study of motion without regard for the forces that cause it.
  • It ignores concepts such as torque, force, mass, energy, and inertia.

                         Forward kinematics

                         Inverse kinematics

  • By knowing the position and orientation of joints, we are going to find the position and orientation of end – effecter is called forward kinematics.
  • By knowing the position and orientation of end – effecter , we are going to find the position and orientation of joints is called inverse kinematics.

Rules to select robot usage

  • When our job is dull, dirty, difficult, dangerous then humans can not perform the task efficiently then we have to use robotics and automation.
  • Robots should not leave human jobless.
  • Ask if any humans willing to do the job otherwise we should go for robotic

General classification of robot

  • Industrial Robot à Robots used to do the job in factory environment

       Welding,    Cutting ,     Painting,      Loading and Unloading

  • Non – Industrial Robot or Special purpose robot à Robots used other than factory environment

      Medical field,      Space research,      Undersea exploration

Industrial robot

  • Resembles human arm movements, so we call industrial robot as robotic arm.
  • Robotic arm consist of body and arm movement, wrist movement.
  • Always body is mounted in floor, wall, ceiling, Automated Guided Vehicle.
  • Arm movements X Y        Z
  • Wrist movements yaw, pitch, roll

Industrial Robot

Definition of industrial robot

An industrial robot is a reprogrammable, multifunctional manipulator designed to move materials, parts, tools, or specialized devices through various programmed motions for the performance of a variety of tasks.

Manipulator

  • An manipulator is composed of a series of links connected to each other via joints. Each joint usually has an actuator (eg: a motor) connected to it.
  • These actuators are used to cause relative motion between successive links. One end of the manipulator is usually connected to a stable base and the other end is used to deploy a tool.

Types of joints

  • Prismatic joint (P)

                     Linear joint (L)

                     Orthogonal joint (O)

  • Revolute joint (R)

                     Rotational joint (R)

                     Twisted joint(T)

                     Revolving joint(V)

Joint notation scheme

  • Colon ( : ) used to differentiate the joints between arm and wrist movement

  Example:       TRT : R

                        TRV : L

                        LOO :

Robotic system

  • Motion subsystem
  • Recognition subsystem
  • Control system

Motion subsystem

Manipulator :

  • The physical structure consisting of links and joints.
  • Links made up of steel or aluminium.
  • Joints may be of rotary or translational.

End effector :

  • The part attached to the end of the manipulator is called as end effectors.
  • The end effectors may be of finger type gripper, paintbrush, welding electrodes, grinding wheel etc.

Actuator :

  • It provides motion to the manipulator and the end effectors.

They are classified to

  1. Pneumatic
  2. Hydraulic
  3. Electric

Transmission :

  • These elements are used to transmit, motion from the motors and actuators to the links of the manipulator.

They are classified to

  1. Belt and chain drives
  2. Gears
  3. Link mechanism

Recognition subsystem

Sensor :

  • Sensors are the transducers, which convert one form of signal to another.
  • In robotic system, based on senses the sensors are classified to
  • Proprioceptors – To measure internal parameters
  • Exteroceptors – To measure external parameters

ADC :

  • This is an electronic device that interfaces the sensors and the robot’s controller.

For eg: the ADC converts the voltages signal to digital signal.

Control subsystem

Digital controller :

  • It is an electronic device that has a cpu, memory and hard disk to store the data.
  • It is used to control the movement of manipulator and end effectors.
  • It is also used to as robot controller, which process the program and send the appropriate signals to actuators through DAC.

DAC :

  • It converts the digital signal from the robot controller to analog signal to activate the actuators.

Amplifier :

  • The control commands from the digital controller converted to analog signals by the ADC are very weak. Hence the amplifiers are used for the amplification of the signals.

Classification of industrial robot

  • by Application
  • by Coordinate system
  • by Actuation system
  • by Control method
  • Based on application

By application

Assembly Robot

Welding Robot

Heavy Duty Robot

Loading and Unloading Robot

Painting  Robot

Cutting Robot

Based on co-ordinate system

 based on joints used in arm movement

Cartesian/Rectangular Gantry(3P)

These Robots are made of 3 Linear joints that orient the end effector, which are usually followed by additional revolute joints.

Cylindrical (R2P):

Cylindrical coordinate Robots have 2 prismatic joints and one revolute joint.

Spherical joint (2RP):

They follow a spherical coordinate system, which has one

Articulated/anthropomorphic(3R) :

An articulated robot’s joints are all revolute, similar to a human’s arm.

Selective Compliance Assembly Robot Arm (SCARA) (2R1P):

They have two revolute joints that are parallel and allow the Robot to move in a horizontal plane, plus an additional prismatic joint that moves vertically

Based on actuator

By power source

  • Electric
  • Hydraulic
  • Pneumatic

ELECTRIC

  • It provides less power and speed as compared with hydraulic systems.
  • Accuracy of electric drives are usually better.
  • Electric robots tend to be smaller, requiring less floor space, and their applications tend toward more precise work such as assembly.
  • The cost of electric actuator is much more proportional to its size
  • It can be well suited for rotational as well as linear movements.
  • The electric drive system will be perfect for small robots and precise applications.

PNEUMATIC

  • Working fluid is compressible.
  • Working fluid lack lubricating property
  • Operating pressure is lower
  • Output power is less
  • Accuracy of actuator is poor
  • External leakage is permissible but internal leakage must be avoided
  • No return pipes are required
  • Insensitive to temperature changes
  • Fire and explosion proof
  • Especially used for the small type robots, which have less than five degree of freedom
  • Cost is less compared with hydraulic system
  • Not suitable for the fast operation.

HYDRAULIC

  • Working fluid is incompressible
  • Working fluid acts as lubricant
  • Higher operating pressure
  • More output power
  • More accuracy may be made
  • Internal leakage is permissible and external leakage must be avoided
  • Return pipes are required
  • Sensitive to changes in temperature
  • Not afire and explosion proof
  • Completely meant for the large – sized robot.

Based on control method

By control method

  • Servo control and non – servo control
  • Path control
  • Limited Sequence robot
  • Playback with pt. to pt. control
  • Playback with continuous path control
  • Intelligent robot

Servo controlled :

  • It is a closed loop type.
  • In this method of control,
  1. Commands are sent to arm drives.
  2. Actual movements are monitored and compared with the command signal.
  3. The gap between command and actual is send as feedback to controller to enable further commands.
  • Servo controlled is used widely in the industrial robots

Non Servo Control

  • implemented by setting limits or mechanical stops for each joint and sequencing the actuation of each joint to accomplish the cycle
  • end point robot, limited sequence robot, bang-bang robot
  • No control over the motion at the intermediate points, only end points are known
  • Programming accomplished by
    • setting desired sequence of moves
    • adjusting end stops for each axis accordingly
    • the sequence of moves is controlled by a “squencer”, which uses feedback received from the end stops to index to next step in the program
  • Low cost and easy to maintain, reliable
  • relatively high speed
  • repeatability of up to 0.01 inch
  • limited flexibility
  • typically hydraulic, pneumatic drives

Limited sequence control :

  • Do not use servo-control to indicate relative positions of the joints.
  • They are controlled by setting limit switches and/or mechanical stops together with a sequencer to coordinate and time the actuation of the joints.
  • With this method of control, the individual joints can only be moved to their extreme limits of travel.
  • Pick-and-place operations using mechanical stops to set positions

POINT TO POINT CONTROL :

  • Only the end points are programmed, the path used to connect the end points are computed by the controller
  • Feedback control is used during motion to ascertain that individual joints have achieved desired location
  • Often used hydraulic drives, recent trend towards servomotors
  • loads up to 500lb and large reach

Applications

  • pick and place type operations
  • palletizing
  • machine loading

CONTINUOUS PATH CONTROL :

  • in addition to the control over the endpoints, the path taken by the end effector can be controlled
  • Path is controlled by manipulating the joints throughout the entire motion, via closed loop control

Applications:

  • spray painting, polishing, grinding, arc welding

 

INTELLIGENT ROBOT :

  • The intelligent control robot is capable of performing some of the functions and tasks carried out by human beings.
  • Much like humans, the robot observes and evaluates the immediate environment by perception and pattern recognition.
  • Artificial intelligence (AI) that will enable the robots to respond, adapt, reason, and make decisions to react to change is also an inherent capability of the intelligent robot.
  • It can detect changes in the work environment by means of sensory perception

 

Specification of industrial robots

  • Robot model
  • Structure
  • Number of axis
  • Drive system
  • Payload
  • Accuracy
  • H-reach
  • Repeatability
  • Robot mass
  • Mounting

Programming methods in industrial robots

  • Leadthrough methods
  • Textual robot languages

Leadthrough programming methods

  • The robot is moved through the desired motion path in order to record the path into the controller memory. There are two ways of accomplishing Leadthrough programming :
  • Powered leadthrough

using of a teach pendant to control the various joint motors, and each point is recorded into for later playback during workcycle.

  • Manual leadthrough

The programmer physically grasps the robot arm and manually moves it through the desired motion cycle.

  • Textual robot languages

Writing a software program in a problem-oriented language.

First generation languages :

  • AL – Assembly Language
  • VAL –Versatile Algorithmic Language

Second generation languages :

  • RAIL –Robotic Automatix Incorp. Language
  • AML –A Manufacturing Language
  • MCL –Manufacturing Control Language
  • APT –Automatically Programmed Tooling

Reference frames

  • Robot Reference Frame which is a universal coordinate frame, as defined by the x-y-z axes. In this case the joints of the robot move simultaneously so as to create motions along the three major axes.
  • Joint Reference Frame which is used to specify movements of each individual joint of the Robot. In this case each joint may be accessed individually and thus only one joint moves at a time.
  • Tool Reference Frame which specifies the movements of the Robots hand relative to the frame attached to the hand. The x, y and z axes attached to the hand define the motions of the hand relative to this local frame. All joints of the Robot move simultaneously to create coordinated motions about the Tool frame.

Construction of controller

  • Multi power supply unit
  • Raiser board
  • Cpu board
  • System c/f
  • Sequence board
  • Power unit
  • IPM drive unit
  • Teach pendant

(1)Multi power supply unit

     – DC+5V power supply

     – DC+12V power supply

     – DC+24V power supply

     – Primary power supply monitoring circuit

(2) Raiser board

     – Bus connection between each board, electric supply

(3) CPU board

     – Microprocessor and its peripheral circuit

     – LCD I/F

     – RS232C

     – Ethernet

     (For servo, teach pendant and user)

     – PCI bus I/F

     – Compact flash card I/F (for system)

     – USB memory I/F (for backing up the user data)

(4) Sequence board

– I/O circuit for inside of robot controller

– Sequence circuit for inside of robot controller

– Emergency stop safety circuit

          – Arc I/F extend function

(5) Power unit

     – Motor power supply electromagnetic contactor control

     – Primary side power supply branch

(6) IPM drive unit

     – Servo control CPU

     – Encoder I/F

     – Power supply for driving motor

     – Motor power control circuit

     – Power supply for brake control

     – Brake control circuit

(7) Teach pendant

     – Operation switch circuit

     (emergency stop, enable switch and TP selector switch)

– Keyboard, jog dial, liquid-crystal display and touch panel circuit for teaching, various settings

     – USB memory connector

ADVANTAGES OF ROBOT

  • Quality:
    Industrial automated robots have the capacity to dramatically improve product quality. Applications are performed with precision and high repeatability every time.
  • Production:
    With robots, throughput speeds increase, which directly impacts production. Because an automated robot has the ability to work at a constant speed without pausing for breaks, sleep, vacations, it has the potential to produce more than a human worker.
  • Safety:
    Robots increase workplace safety. Workers are moved to supervisory roles where they no longer have to perform dangerous applications in hazardous settings.
  • Savings:
    Improved worker safety leads to financial savings. Automated robots also offer untiring performance which saves valuable time. Their movements are always exact, minimizing material waste.

 

DISADVANTAGES OF ROBOT 

 

  • Robots are an expensive initial cost.
  • Employees will require additional training and experience before working with the robots.
  • Creates a very dangerous environment if humans are present.

Can only do what it is instructed to do; nothing more, nothing less

ROBOT APPLICATION

  • Machine loading
  • Pick and place operations
  • Welding
  • Painting
  • Sampling
  • Assembly operation
  • Manufacturing
  • Surveillance
  • Medical applications
  • Assisting disabled individuals
  • Hazardous environments
  • Underwater, space, and remote locations