Classification of Robot

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 

1. General purpose robot: if it possesses 6 degrees of freedom.
2. 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.
3. 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 

1. 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.
2. 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
3. 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 

1. Electric: Most manipulators use either electric DC servomotor or stepper motors because they are clean and relatively easy to control.
2. 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.
3. 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.

1. 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.

2. 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.

3. 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.

4. 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.

5. 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. 

1. 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.
2. 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.
3. 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.