mechanical

Classification of Robot

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Robots can be classified according to various criteria such as their degrees of freedom, kinematical structure, drive technology, work-shop geometry and motion characteristics.

[A] Classification by Degrees of Freedom: A manipulator should have 6 degrees of freedom to manipulate an object freely in three dimensional spaces. From this point of view a robot may be a

General purpose robot: if it possesses 6 degrees of freedom.
Redundant robot: if it possesses more than 6 degrees of freedom. It provides more freedom to move around obstacles and operate in a tightly confined work space.
Deficient robot: if it possesses less than 6 degrees of freedom.

[B] Classification by Kinematic Structure: according to kinematic structure robots can be classified as

Serial Robot or Open- loop Manipulator: A robot is said to be a serial robot or an open-loop manipulator if its kinematic structure takes the form of an open-loop chain. Example: Adept-One Robot.
Parallel Manipulator: if it is made up of a closed-loop chain. In general, a parallel manipulator has the advantages of higher stiffness, higher payload capacity, and lower inertia to the manipulation problem than a comparable serial manipulator, at the price of a smaller workspace and more complex mechanism
Hybrid Manipulator: if it consists of both open and closed loop chains. Example: Fanuc S-900 W. Many industrial robots employ this type of robot construction.

[C] Classification by Drive Technology: Manipulators can also be classified by their drive technology. The three popular drive technologies are

Electric: Most manipulators use either electric DC servomotor or stepper motors because they are clean and relatively easy to control.
Hydraulic: used for high speed and/or high-load-carrying capabilities. A major disadvantage associated with this is the possibility of leaking oils. A hydraulic drive is inherently flexible, due to bulk modulus of oil.
Pneumatic: Also used for high speed and/or high-load-carrying capabilities. A pneumatic drive is clean and fast but it is difficult to control because air is a compressible fluid.

[D] Classification by Workspace Geometry: the workspace of a manipulator can be defined as the volume of space the end of effecter can reach. The workspace can be of two types: A reachable workspace is the volume of space within which every point can be reached by the end effecter in at least one orientation. A dextrous workspace is the volume of space within which every point can be reached by the end effecter in all possible orientation.

Cartesian robot: In this the kinematic structure of a robot arm is made of three mutually perpendicular prismatic joints. The wrist center position of of a Cartesian robot can be conveniently described by three Cartesian co-ordinates associated with the three prismatic joints. The regional work-space of a Cartesian robot is a rectangular box.

When a Cartesian robot is mounted on rails above its workspace, it is called a

gantry robot.

Cylindrical Robot: A robot arm is called cylindrical robot if either the first or second joint of a Cartesian robot is replaced by a revolute join. The wrist center position of a cylindrical robot can be described by a set of cylindrical coordinate system associated with the three joint variables. The workspace of a cylindrical robot is confined by two concentric cylinders of finite length.

Spherical Robot: A robot arm is called a spherical robot if either the first or second joint of a Cartesian robot is replaced by a revolute joint. The wrist center position of a spherical robot can be described by a set of spherical coordinate system associated with the three joint variables. The workspace of cylindrical robot is confined by two concentric spheres.

Articulated Robot: A robot arm is said to be an articulated robot if all three joints are revolute. The workspace of an articulated robot is very complex, typically a crescent shaped cross section. Puma robot is an articulated robot.

The SCARA (selective compliance assembly robot arm) Robot: it is a special type of robot consisting of two revolute joints followed by a prismatic joint. All three joint axes are parallel to each other and usually point along the direction of gravity. The wrist has one degree of freedom and hence the entire robot has 4 degrees of freedom. This type of robot is useful for assembling parts on a plane.

[E] Classification by Motion Characteristics: robot manipulators can also be classified by according to their nature of motion.

Planar: A manipulator is called a planar manipulator if its mechanism is a planar mechanism. Planar manipulators are useful for manipulating an object on a plane.
Spherical: A rigid body is said to be under a spherical motion if all particles in the body describe curves that lie on concentric spheres. A mechanism is said to be a spherical mechanism if all the moving links perform spherical motion about a common stationary point. A manipulator is called a spherical manipulator if it is made up of a spherical mechanism.
Spatial Manipulator: A rigid body is said to perform a spatial motion if its motion cannot be characterized as planar or spherical motion. A manipulator is called a spatial manipulator if at least one of the moving links in the mechanism possesses a general spatial motion. Planar and spherical mechanisms can be considered as special cases of spatial mechanisms.

Links, Mechanism, Machine, Machine Tools, Equipments and Instruments

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Link: Part of a machine which moves relative to some other parts is known as link or element. Link may be rigid or flexible or it can be a fluid link.

Rigid Link: Link or element which is capable of transmitting the motion with negligible deformation in it. In general we can say there is no link which is perfectly rigid. For example: crank, piston, cylinder, etc.

Flexible Link: this link is also capable of transmitting the power or motion with slight deformation in it. In practical machines we can say most of them links which are used are flexible links. For example,: spring, belt, etc.

Fluid Link: Fluid link is just of fluid element by which power or motion is transmitted from one element to another element.

The basic concept for transmitting motion with the help of fluid link will be the exerted pressure. With the help of the pressure the motion is transmitted from one point to another point. For example: hydraulic presses, hydraulic jacks, accumulators, etc.

Mechanism: When one link is fixed in a kinematic chain then it becomes a mechanism.

Machine: A mechanism which is basically used to convert available energy into useful work is known as machine.

Each machine is a machine but all mechanisms are not machines.

Machine tools: A machine tool is a powered mechanical device, used to fabricate metal components or machines by machining. Examples are: broaching machine, drill press, gear shaper, lathe, screw machines, milling machine, shaper, saws, planer, grinding machines, etc.

Equipment: The tools, machines, or the other things that we need for a particular job or activity. For example: safety equipments, electrical equipments, etc.

Instrument: A tool or implement, esp. one used for delicate work (or mild task) or for scientific or artistic purposes. For example: scientific instrument such as microscopes, artistic instruments such as guitar, violin, etc.
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Historical Development of Robot:

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The beginning of robot may traced to the great greek engineer Ctesibius (270B.C.) Ctesibius applied a knowledge of pneumatics and hydraulics to produce the first organ and water clock by moving figures. Ctesibius’s disciple Philo of Byzantium (200B.C.) wrote Mechanical Collection describing Ctesibius work. Building on Ctesibius’s work , Hero of Alexandria (85 A.D.) wrote On Automatic Theaters, On Pneumatics, and On Mechanics and is recognized as the greatest Greek engineer. Hero, famous for invention of steam engine, presented the first well documented, workable robot outside of mythology.

Leonardo da Vinci (1452-1519) followed in hero’s footsteps, studying everything he could obtain on his work. He was actively engaged in verifying Greek reconstructions, an actively that no doubt inspired him to devise water powered organs and clocks equipped with jacquemart for striking the hours. Another automation that Leonardo was surely was aware of was the famous Strasbourg cock which was in operation from 1352 to 1789.he also developed a leaf spring powered car as proper source of actuating wings, and probably as the propulsion system for an automation.

Nikola Tesla(1856-1943), drawing inspiration from Leonardo da Vinci, Tesla shared his hero’s ability at spetial visualization and demonstrated a precocious ability to build model turbines and motor powered by bugs. In 1898 Tesla demonstrated a remote controlled submersible boat. It was controlled by coded pulses via Hertzian waves (i.e. radio controlled).

The play RUR (Russums Universal Robots) was written by Carl Capek and made its 1921 premier in Prague, Czecoslovakia (Capek 1973). Starting as ideal workers, the robots, (the play introduced the word robot) have emotions added to them to increase their productivity. A variation on the theme put forth in Mary Shelley’s Frankenstien recurs when the robots turn on their creators and destroy them. The play ends with an interesting twist: a robot couple is presented as the successor of humans. The play present the duality of technology, the threat vs the promise, through the concept of the perfect worker – the robot. From this points on the robots have been perceived as both a savior and a potential enemy of mankind. Since the advent of this play , robots have achieved their own unique identity. This is reflected in the appearance of robots built for fairs, explosions and movies. No longer made to copy the outward appearance of man, they have become a hybrid- functioning as a human while appearing as a machine.

The word 'robotics' was first used in Runaround, a short story published in 1942, by Isaac Asimov (born Jan. 2, 1920, died Apr. 6, 1992). I, Robot, a collection of several of these stories, was published in 1950.

What is robot?

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There are some definitions given as bellow

The Robotics Institute of America defines a robot as a "re-programmable multi-functional manipulator designed to move materials, parts, tools, or specialized devices through variable programmed motions for the performance of a variety of tasks."
The International Organization for Standardization gives a definition of robot as "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."
A robot is "any automatically operated machine that replaces human effort, though it may not resemble human beings in appearance or perform functions in a humanlike manner".
It is an electric machine which has some ability to interact with physical objects and to be given electronic programming to do a specific task. It may also have some ability to perceive and absorb data on physical objects, or on its local physical environment, or to process data, or to respond to various stimuli.
A mechanical device that sometimes resembles a human and is capable of performing a variety of often complex human tasks on command or by being programmed in advance.

Laws of Robotics

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Asimov proposed the three "Laws of Robotics", and he later added a 'zeroth law' which are given as under below:

Law Zero: A robot may not injure humanity, or, through inaction, allow humanity to come to harm.
Law One: A robot may not injure a human being, or, through inaction, allow a human being to come to harm, unless this would violate a higher order law.
Law Two: A robot must obey orders given it by human beings, except where such orders would conflict with a higher order law.
Law Three: A robot must protect its own existence as long as such protection does not conflict with a higher order law.

Comments:

♦ The MAARS (Modular Advanced Armed Robotic System) provide machine gun

to robots which cause humans to kill. This opposes the laws given by Asimov.

♦ The point here is that much of the funding for robotic research, now a days,

comes from the military, which is paying for robots that follow the very opposite

of Asimov's laws. It wants robots that can kill, won't take orders from

just any human, and don't care about their own existences.

♦ Law number two is appropriate for robots but they are required to have as much

judgment as an adult human to evaluate the fitness of a human who gives them

orders. They should obey only privileged humans.

♦ We see our automobiles kill a number of people in road accidents. If we provide

AI (Artificial Intelligence) to our automobile, it can save lives.

♦ The third law says a robot MUST be capable of self protection but not so

protective as to disobey their key holders or to corrupt their own operating system

parameters that make them meet the “highest legal and professional standards of

safety and ethics”. They ignore Asimov’s first law, which was the point of the

whole thing after all.

Basic Elements of Robotics System

2010-05-31T19:19:00.000+05:30

The basic element of a robot is given as under below:

Mechanical platform- the hardware base
Sensors
Motors
Driving mechanisms
Power supplies
Electronic controls
Microcontroller systems
Languages
R/C Servos
Pneumatics
Driving high-current loads from logic controllers

Mechanical platform- the hardware base: such as a wheeled platform, arm, or other construction, capable of interacting with its environment.

Sensors: Sensors are the parts that sense and can detect objects or things like heat and light and convert the object information into symbols or in analog or digital form and then robot reacts according to the information provided by the sensory system. The sensors used in robotics are

Vision Sensors: Camera, Frame Grabber, Image processing unit
Proximity Sensors: distance is estimated between the robot and the object.
Proprioceptive Sensors: are responsible for monitoring self maintenance and controlling internal status. This includes battery monitoring, current sensing, and heat monitoring.
Logical Sensors

Motors: A variety of electric motors provide power to robots, making them move with various programmed motions. AC /DC motors can be used.

Driving Mechanisms: Gears and Chains, Pulleys and Belts, Gearboxes are used to transmit rotational motion from one place to another

Servomotors: They adjust themselves until they match the signal. A very common use of servos is in Radio Controlled models (R/C Servos).

Power Supply: Power supply is provided by two types of sources:

Batteries that are used once only and then discarded; and
Rechargeable batteries: that operate from a reversible chemical reaction and can be recharged thousand times.

Electronic controls: This uses a digital logic control circuit which controls the mechanical system. This circuit is connected to the mechanical system through a bridge-relay. A control signal generates a magnetic field in the relay's coil that mechanically closes a switch.

Microcontroller systems: Microcontrollers are intelligent electronic devices that are used inside robots. They deliver functions similar to those performed by a microprocessor (CPU) inside a personal computer. It comprises

Speed: is designated in clock cycles, and is usually measured in millions of cycles per second (Megahertz, MHz).
Size: specifies the number of bits of information the Microcontroller can process in one step (for example, 4-, 8-, 16-, and 32-bits).
Memory: Microcontrollers count most of their read-only memory (ROM) in thousands of bytes (kB) and random access memory (RAM) in single bytes.

Languages: the following programming languages are used:

VAL (Variable Assembly Language):it is the first language used in programming.
Robo ML (Robotic Mark-up Language)
ROBOFORTH
ROSSUM
XRCL (Extensible Robot Control Language)
Scripting language such as RoboLogics
Visual Programming Languages is written by Labview

Pneumatics: Pneumatic system is used for actuating purposes.Pneumatics are useful for generating linear motion.

Driving high-current loads from logic controllers: One of the most common tasks in designing and building robots is the interfacing of logic circuitry to high current loads such as motors, solenoids, or Nitinol wire. Logic circuitry can sink and source loads in the range of 1 to 20 mA. The logic circuitry are

Switch basics: interface for high-current loads can be though of as a switch.
Relays: One of the simplest ways to accomplish high-current.
Transistors: an semiconductor version of a relay.
H-Bridges: Most loads such as motors need to be operated in both forward and reverse. This requirement often leads to a circuit layout known as an H-Bridge.