Types of Robots

Introduction to a Robot

This article is dedicated to all the geeks as well as enthusiasts out there, who are keen to escalate their comprehension about types of automatic and intelligent machines. Well, that’s in short what we call – A Robot – An Intelligent Machine.

So how is it intelligent?

Well, the fact that a robot can determine its own movements to accomplish a task makes it an intelligent machine. This intelligence is actually given by different sensors which allow the robot to manipulate its work as per changes in the environment.

As per International Standard of Organisation (ISO), a Robot is a reprogrammable, multifunctional manipulator which is designed to move things with the help of variable programmed motions.

Reprogrammable means a Robot is controlled through a computer-based program which can be changed at any time. Multi-functional attribute signifies the multiple number of applications carried out by a robot.

How did Robots evolve – A quick recap

It all commenced in 1921, when the Czech writer Karel Capek used the term ‘Robot’ to denote a human replaced machine, by a fictional character, in his play – Rossum’s Universal Robots.

Though after effect of the play was, in fact, dreadful – Fear in the mind of people that Robots would eventually wipe out humans from the earth, it was Isaac Asimov, in 1940, who envisioned a robot as an asset to humans, by postulating the three basic laws:

1. No man should be harmed by a robot or its actions.
2. Human orders should always be obeyed unless it is contrary to the first law.
3. Robots should protect from harm

In 1958, Joseph F Engel Berger along with George C Devol founded the UNIMATION Robotics Company, which worked on designing the first ever working robot.

However, it was a General Motors automobile company in New Jersey, in 1961, which first used an automated die-casting mould which dropped red-hot car parts into pools of cooling liquid, which transported them to workers for trimming and buffing.

Classification of Robots

Here, we are going to talk about different types of Robots as per different criterion. First and foremost, let us investigate some of the internationally approved classifications:

Classification by Japanese Industrial Robot Association (JIRA)

1. Class 1 or Manual Handling Device: Device with multiple degrees of freedom (different directions in which a part can move) and actuated by an operator. An example is a Crane.
2. Class 2 or Fixed Sequence Robot: Device which performs successive stages of a task as per a fixed method.
3. Class 3 or Variable Sequence Robot: Device that performs same as Class 2 robots, but whose control can be modified.
4. Class 4 or Playback Robot: Device which repeats tasks performed by humans, by following the recorded version of manual work.
5. Class 5 or Numerical Control Robot: Device controlled by a computer through movement program.
6. Class 6 or Intelligent Robot: A device which has a good assessment of its environment and performs tasks by manipulating its movements as per changes in the surroundings.

However, note that as per the Robotics Institute of America (RIA), only the last 4 types are Robots and not the first two.

Classification by Association Francoise de Robotique (AFR):

1. Type A: Manually controlled handling devices.
2. Type B: Automatic handling devices with predetermined cycles.
3. Type C: Programmable, motor-controlled robots with the point to point or continuous path.
4. Type D: Same as Type C, but with environmental sensing capacity.

Classification as per Application

• Industrial: Industrial robots are generally fixed manipulators which perform in various working environments. They perform various general-purpose tasks like Welding, Painting, machining, etc.  In fact, the first robots were the industrial robots which were used for simple repetitive tasks.
• Non-Industrial or Special Purpose: These are robots which assist humans in their chores
  • Medical: There has been an increasing use of robots in the medical field for surgery, rehabilitation and training. Medical robots are not meant to replace the surgeons but serve as a surgical assistant to the surgeon.
  • Space: With the advent of robotic technologies, exploration of various celestial bodies has been a reality.  Tasks like space manipulation, surface mobility and scientific experiments are performed by space robots.
  • Defence Robots: These include bomb disposal robots, transportation robots and reconnaissance drones. Equipped with infrared sensors, these robots react more rapidly than humans in emergency and hazardous situations.
  • Security: These robots are used for surveillance and guarding large civilian facilities such as Power generating plants, oil refineries, etc which are under threat from terrorists. An example is DRDO’s NETRA (An Unmanned Aerial Vehicle)
  • Domestic: These robots are used to perform daily tasks at home, such as robotic vacuum cleaner, cleaning robots.
  • Entertainment: These robots are used in various entertainment places like amusement parks, joy rides, sports, etc. Examples include KUKA Robocoaster (amusement ride robot), Honda’s Asimo, Sony’s Aibo, etc.

Classification by Degrees of Freedom

Degrees of freedom refers to the different directions a robotic arm can move.  They represent the location as well as the orientation of an object. Basically, such type of robots is pick and place robots, which pick and place the objects on a location and with an orientation.

1. 3 Degrees of Freedom: A robot with 3 degrees of freedom can only pick up the object and place it anywhere in its workspace, using the 3 different coordinate axes.
2. 6 Degrees of Freedom: A robot with 6 degrees of freedom can pick the object and place it anywhere in its workspace, at any orientation.
3. Other Degrees of Freedom: A robot with degrees of freedom other than 3 or 6 has restricted movement in either linear or angular direction. In other words, it may orientate the object in any desired direction , but can place the object in only limited directions.  

However, a robot with higher degrees of freedom – say 7, can have infinite possible ways to place as well as orientate the object.

Classification by Kinematic Structure:

The word ‘Kinematic’ refers to a study of the motion of points, bodies and system of bodies, without taking into effect the mass of each of the bodies. Before going deep into the study of robotics, let us first understand the simple analogy –  Consider your arm. It has 3 joints.

The upper or shoulder joint allows your arm to move in the angular direction and hence is a revolute joint. The middle or elbow joint allows arm movement in different angular directions and hence is a revolute joint. The lower or palm joint is also a revolute joint and thus allows rotary motion.

Similarly, Robots can be classified based on their coordinate systems, i.e. based on reachable coordinates of a point on the end-effector.

1. 1. Cartesian:  When arms of a robot move in the XYZ rectangular coordinate system, it is known as a Cartesian robot. It needs a large volume to operate and has a rigid structure. A set of rotary motors coupled with nut and ball screws make it possible to achieve the rectilinear motion. However, owing to frequent maintenance of these screws, the robots tend to more expensive.
   2. Cylindrical: When arms of a robot move in one angular and two linear directions, it is known as a Cylindrical robot. It has basic rotation, elevation and reach. Unlike Cartesian robots, these robots require less volume. These are used in applications where the requirement is to reach into small openings or working on cylindrical surfaces like welding pipes.
   3. Spherical: The arms of this robot move in two angular and one linear direction. It has a base rotation, angular elevation and reach. It works in a spherical work environment.
   4. SCARA: Selective Compliance Arm for Robotic Assembly or SCARA robots have two parallel revolute joints providing compliance in a selected plane. Compliance refers to the flexible behaviour of the robot in response to external forces. Applications include assembly, packaging, sorting, light-duty drilling.
   5. Articulated: Also known as the anthropomorphic robot, the robot arm has 3 revolute joints. As the actuators are directly coupled through a set of rotary gear or belt elements, these robots are easy to fabricate and maintain. However, since this robot is designed to achieve rotary motion, achieving linear motion requires complex mathematical calculations.-d

Classification by Movement

1. Fixed: Most of the fixed robots are industrial robots which work in well-defined environments. These robots are mounted on a stable base on the ground and based on their internal configuration, they can compute their positions.
2. Mobile: As the name suggests, mobile robots are not fixed to a surface, rather can achieve free movement over the surface. It can be a legged or a wheeled robot.  
   1. Terrestrial Robots:
      1. a. Wheeled: Similar to vehicles, the wheeled robots are guided by kinematic models which rely on motion rather than the cause of the motion. The most primitive version was the Automatic Guided Vehicle (AGV), a 4 wheeled electric power vehicle.
         1. . Single Wheeled: It consists of a single wheel to balance and navigate. The practical example is the Murato girl (Seiko).
         2. TwoWheeled: It consists of parallel wheels with the centre of gravity below the wheel axle. A tilt sensor is used to maintain the balance of wheels by detecting the tilt of the robot, and then guide the actuator to move the robot in that direction. The practical example is the 2 wheeled NBOT.
         3. Three Wheel: It has 3 wheels in the triangular shape and hence is balanced. Usually, the front wheel is the steering wheel, while the rear wheels provide the movement.
         4. Four Wheel: It is the most efficient robot on the list. While the first two provide steering, the other two provide the motion. An example is NASA’s rover – Scarab.
         5. Multi-wheel: Designing these robots is most complex, owing to the fact that each wheel needs to have the same speed when the robots move forward. The practical example includes Mars Rover with 6 wheels.
      2. b. Legged: These are generally the walking robots which use limbs for movement. These are mostly used to provide movement in highly unstructured environments. Though complex to design, these robots have a greater edge over wheeled robots in terms of navigation on any kind of path or terrain.
         1. Bipedal: A robot having 2 legs is a Bipedal robot. A classical example is a Humanoid robot. These robots work in the environment like that of humans and are designed to imitate human behaviour. Stability is maintained by calculating each step and moving the weight in a well-defined way. Practical examples include Sony’s QRIO and Honda’s ASIMO.
         2. Tripodal: These robots have 3 points of contact with the ground and are statically stable, i.e. they are well balanced and can stand without toppling over. The practical example includes STRIDER (Self Excited Tripodal Dynamic Experimental Robot) from RoMeLa.
         3. Quadrupedal: Also known as Tetrapod robots, these have 4 legs and their walking pattern similar to that of animals. Being statically stable, they are well balanced in posture. They can move either by moving one leg at a time or moving the alternate pair of legs.
         4. Hexapod: These robots have 6 legs and their walking pattern mimic that of a spider. They have higher stability while standing and moving. They can move either by moving each pair of leg in a consecutive manner or moving alternate legs of each pair. Practical examples include the Ohio State University (OSU) Hexapod, OSU Adaptive Suspension Vehicle (ASV) etc.
   2. Swimming Robots: These robots are the latest addition to the robot’s family, working underwater and used for navigation, assist in swimming, etc. The practical example includes the Autonomous Underwater Vehicle (AUV), PacX Wave Glider (which travelled a distance of approx. 17000 km over the Pacific Ocean to collect high-resolution ocean data) and Swumanoid robot (which is being built by Japanese researches, to help athletes swim faster)
   3. Flying Robots: These are mostly micro-sized robots which mimic an insect’s morphology. Some also are designed as the Unmanned Aerial Vehicle (UAV). There are two types of UAV –Drones and Quadrotors. Drones can range from a small radio-controlled toy helicopter to a 32000-pound Global Hawk. Initially used mostly for research applications, these robots are finding their use in commercial applications as well.

Robotics is a vast emerging field with advent of numerous types every year. Future of robotics lies not only in research, but in commercial applications as well. This is only a small introduction I have included, rest being out of scope of the article.

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