30 Unit One Principles of Robotics
on a workpiece. The end effector is one of the most important components
of a robot system. The robot’s performance is a direct result of how well
the end effector meets the task requirements. The area within reach of the
robot’s end effector is called its work envelope.
Power Supply
The power supply provides the energy to drive the controller and actu-
ators. It may convert ac voltage to the dc voltage required by the robot’s
internal circuits, or it may be a pump or compressor providing hydraulic
or pneumatic power. The three basic types of power supplies are electrical,
hydraulic, and pneumatic.
The most common energy source available, where industrial robots are
used, is electricity. The second most common is compressed air, and the
least common is hydraulic power. These primary sources of energy must
be converted into the form and amount required by the type of robot being
used. The electronic part of the control unit, and any electric drive actuator,
requires electrical power. A robot containing hydraulic actuators requires
the conversion of electrical power into hydraulic energy through the use of
an electric, motor-driven, hydraulic pump. A robot with pneumatic actua-
tors requires compressed air, which is usually supplied by a compressor
driven by an electric motor.
Means for Programming
The means for programming is used to record movements into the
robot’s memory. A robot may be programmed using any of several
different methods. The teach pendant, also called a teach box or hand-
held programmer, Figure 2-8, teaches a robot the movements required to
perform a useful task. The operator uses a teach pendant to move the robot
through the series of points that describe its desired path. The points are
recorded by the controller for later use.
2.2 Degrees of Freedom
Although robots have a certain amount of dexterity, it does not compare
to human dexterity. The movements of the human hand are controlled by
35 muscles. Fifteen of these muscles are located in the forearm. The arrange-
ment of muscles in the hand provides great strength to the fingers and thumb
for grasping objects. Each finger can act alone or together with the thumb.
This enables the hand to do many intricate and delicate tasks. In addition, the
human hand has 27 bones. Figure 2-9 shows the bones found in the hand and
wrist. This bone, joint, and muscle arrangement gives the hand its dexterity.
Degrees of freedom (DOF) is a term used to describe a robot’s freedom
of motion in three dimensional space—specifically, the ability to move
forward and backward, up and down, and to the left and to the right. For
each degree of freedom, a joint is required. A robot requires six degrees of