Chapter 2 Fundamentals of Robotics 47
gripper or the end of the tool bit. Therefore, the work envelope is slightly
larger when the tip of the tool is considered.
Work envelopes vary from one manufacturer to another, depending on
the exact design of the manipulator arm. Combining different configura-
tions in a single robot can result in another set of possible work envelopes.
Before choosing a particular robot configuration, the application must be
studied carefully to determine the precise work envelope requirements.
Some work envelopes have a geometric shape; others are irregular. One
method of classifying a robot is by the configuration of its work envelope.
Some robots may be equipped for more than one configuration. The four
major configurations are: revolute, Cartesian, cylindrical, and spherical.
Each configuration is used for specific applications.
Revolute Configuration (Articulated)
The revolute configuration, or jointed-arm, is the most common. These
robots are often referred to as anthropomorphic because their movements
closely resemble those of the human body. Rigid segments resemble the
human forearm and upper arm. Various joints mimic the action of the
wrist, elbow, and shoulder. A joint called the sweep represents the waist.
A revolute coordinate robot performs in an irregularly shaped work
envelope. There are two basic revolute configurations: vertically articu-
lated and horizontally articulated.
The vertically articulated configuration, shown in Figure 2-27, has
five revolute (rotary) joints. A vertically articulated robot is depicted in
Figure 2-28. The jointed-arm, vertically articulated robot is useful for
painting applications because of the long reach this configuration allows.
The horizontally articulated configuration generally has one vertical
(linear) and two revolute joints. Also called the SCARA (selective compli-
ance assembly robot arm) configuration, it was designed by Professor
Makino of Yamanashi University, Japan. The primary objective was a
configuration that would be fairly yielding in horizontal motions and rather
rigid in vertical motions. The basic SCARA configuration, Figure 2-29, is
an adaptation of the cylindrical configuration. The SCARA robot shown in
Figure 2-30 is designed for clean-room applications, such as wafer and disk
handling in the electronics industry.
SCARA robots are ideally suited for operations in which the vertical motion
requirements are small compared to the horizontal motion requirements. Such
an application would be assembly work where parts are picked up from a parts
holder and moved along a nearly horizontal path to the unit being assembled.
The revolute configuration has several advantages. It is, by far, the most
versatile configuration and provides a larger work envelope than the Carte-
sian, cylindrical, or spherical configurations. It also offers a more flexible
reach than the other configurations, making it ideally suited to welding
and spray painting operations.
However, there are also disadvantages to the revolute configuration. It
requires a very sophisticated controller, and programming is more complex
than for the other three configurations. Different locations in the work envelope