robot definition and classification

1. INTRODUCTORY ROBOTICS
SYSTEMS
Robot Definition, Classification and
Terminologies.

2. ROBOTICS
 Robotics is a branch of technology that deals with the design, construction and operation of
robots.
What is a robot?
A robot is 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.
As stated by the Robotics Institute of America

3. INDUSTRIAL ROBOTS
 Industrial robot is a robot system used for manufacturing. They are automated,
programmable and capable of movement on three or more axis.
 A major reason for the growth in the use of industrial robots is their declining cost.
 They are not just getting cheaper; they are becoming more effective, faster, more
accurate and more flexible.
 As robots become more capable they are able to do more and more tasks that
might be dangerous or impossible for human workers to perform.

4. TERMINOLOGIES AND CONCEPTS
Frames - A frame is a reference system within which the position and orientation of a body can
be expressed.
Links - Links are individual bodies that make up a mechanism. They are mostly treated as rigid
bodies except for high speed or highly loaded mechanisms. They are connected in pairs.
Joints - the connection between two links is called a joint. It provides some physical constraints
on the relative motion between two links/members.
End-Effector - At the free end of the chain of links that make up the manipulator is the end-
effector. Depending on the intended application of the robot, the end-effector could be a
gripper, an electromagnet or any other device.
Kinematic Chain – is an assemblage of links that are connected by joints. It is called a
mechanism when one of its links is fixed to the ground.
Degrees of Freedom – is the number of independent position variables that would have to be
specified in order to locate all parts of a mechanism. It depends on the number of links, joints
and the types of joints used for construction of the mechanism. This is a general term used for
any mechanism.

5. TYPES OF JOINT
Name Description No of constraints Degrees of
freedom
revolute joint permits two paired elements to rotate with
respect to each other about an axis that is
defined by the geometry of the joint
5 1
prismatic joint allows two paired elements to slide with
respect to each other along an axis that is
defined by the geometry of the joint
5 1
cylindrical joint permits rotation about, and independent
translation along, an axis that is defined by the
geometry of the joint
4 2
helical joint allows two paired elements to rotate about,
and translate
along, an axis defined by the geometry of the
joint
5 1
spherical joint Allows one element to rotate freely with
respect to the
other about the center of the sphere in all
possible orientations.
3 3
plane pair Permits two translational degrees of freedom
along the plane of contact and a rotational
degree of freedom about an axis normal to
the plane of contact.
3 3

6. ROBOT CLASSIFICATION
Classification by degrees of freedom
 Ideally, a manipulator should possess 6 degrees of freedom in order to manipulate
an object freely in three-dimensional space.
 From this point of view, we call a robot a general-purpose robot if it possesses 6
degrees of freedom,
 a redundant robot if it possesses more than 6 degrees of freedom, and
 a deficient robot if it possesses less than 6 degrees of freedom.

7. ROBOT CLASSIFICATION
Classification by kinematic Structure
 A robot is said to be a serial robot or open-loop manipulator if its kinematic
structure takes the form of an open-loop chain,
 a parallel manipulator if it is made up of a closed-loop chain, and
 a hybrid manipulator if it consists of both open- and closed-loop chains.

8. ROBOT CLASSIFICATION
Classification by Drive Technology
 Manipulators can also be classified by their drive technology. The three popular drive
technologies are electric, hydraulic, and pneumatic.
 Most manipulators use either electric dc servomotors or stepper motors, because they are
clean and relatively easy to control.
 However, when high-speed or high-load-carrying capabilities are needed, hydraulic or
pneumatic drive is preferred.
 A major disadvantage associated with the use of hydraulic drive is the possibility of leaking
oils. Additionally, a hydraulic drive is inherently flexible due to the bulk modulus of oil.
Although a pneumatic drive is clean and fast, it is difficult to control because air is a
compressible fluid.

9. ROBOT CLASSIFICATION
Classification by Motion Characteristics
Planar - A mechanism is said to be a planar mechanism if all the moving links in the
mechanism perform planar motions that are parallel to one another. For a planar
mechanism, the loci of all points in all links can be drawn conveniently on a plane.
Spherical - A mechanism is said to be a spherical mechanism if all the moving links perform
spherical motions about a common stationary point. In a spherical mechanism, the motions
of all particles can be described by their radial projections on the surface of a unit sphere.
Spatial - A rigid body is said to perform a spatial motion if its motion cannot be
characterized as planar or spherical motion or if at least one of the moving links in the
mechanism possesses a general spatial motion

10. ROBOT CLASSIFICATION
Classification by Workspace Geometry….
The workspace of a manipulator is the volume of space the end effector can reach.
Reachable workspace – is the volume of space within which every point can be reached by
the end effector in at least one orientation.
Dextrous workspace – is the volume of space within which every point can be reached by
the end effector in all possible orientations. As a result, the dexterous workspace is a subset
of the reachable workspace.
Mostly, the first three (3) links of a robot are primarily used for manipulating position of a
robot. It is called the arm. The remaining links for controlling the orientation of the end
effector. It is called the wrist.
The arm can assume different kinematic structures and therefore generates different work
envelopes called regional workspaces.

11. ROBOT CLASSIFICATION
Classification by Workspace Geometry
Cartesian Robot – a robot arm with three (3) mutually perpendicular prismatic joints. When
mounted on rails above its workplace, it is called a gantry robot. The regional workspace is a
rectangular box.
Cylindrical Robot – this is a cartesian robot arm with either the first or second joint replaced
by a revolute joint. The prismatic joints usually have mechanical limits on both ends. Hence
the workspace is confined by two concentric cylinders of finite length.
Spherical Robot – is a robot arm with two intersecting revolute joints in the first two joints
and a third joint which is prismatic. the workspace is confined by two concentric spheres.
Articulated Robot – is a robot arm with all three joints revolute. The workspace is very
complex. Many industrial robots are of the articulated type.
The SCARA (Selective Compliance Assembly Robot) robot is a special type of robot. It
consists 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 the gravity.

12.  Thank You
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