28 Unit One Principles of Robotics
of the robot (see Figures 2-2 and 2-3) which must move materials, parts,
tools, or special devices through various motions to provide useful work.
A manipulator can be identified by method of control, power source, actua-
tion of the joints, and other factors. These factors help identify the best type
of robot for the task at hand. For example, you would not use an electric
robot in an environment where combustible fumes exist and a spark could
cause an explosion.
The manipulator is made up of a series of segments and joints much
like those found in the human arm. Joints connect two segments together
and allow them to move relative to one another. The joints provide either
linear (straight line) or rotary (circular) movement, Figure 2-6.
The muscles of the human body supply the driving force that moves the
various body joints. Similarly, a robot uses actuators to move its arm along
programmed paths and then to hold its joints rigid once the correct position
is reached. There are two basic types of motion provided by actuators: linear
and rotary, Figure 2-7. Linear actuators provide motion along a straight line;
they extend or retract their attached loads. Rotary actuators provide rota-
tion, moving their loads in an arc or circle. Rotary motion can be converted
into linear motion using a lead screw or other mechanical means of conver-
sion. These types of actuators are also used outside the robot to move work-
pieces and provide other kinds of motion within the work envelope.
Segments
Joint
Linear Joint Rotary Joint
Segments
Joint
Figure 2-6. Both linear and rotary joints are commonly found in robots.