Page 50 - Robot Builder's Bonanza

THE BODY OF THE ROBOT 19

Arms and Grippers
The ability to manipulate objects is a trait that has enabled humans, as well as a few other
creatures in the animal kingdom, to take command of their environment. Without our arms
and hands we wouldn’t be able to use tools, and without tools we wouldn’t be able to build
houses, cars, and— hmmm— robots.
Arms and grippers are used by themselves in stationary robots, or they can be attached to
a mobile robot. An arm can be considered any appendage of the robot that can be individually
and specifically manipulated; grippers (also called end- effectors) are the hands and fingers and
can be attached either directly to the robot or to an arm.
The human arm has joints that provide various degrees of freedom (DOF) for orienting it
to most any direction. Likewise, robotic arms also have degrees of freedom. In most designs
the number of degrees of freedom is fairly limited, to between one and three DOF. In addition
to degrees of freedom, robot arms are further classified by the shape of the area that the end
of the arm (where the gripper is) can reach. This accessible area is called the work envelope.
Read more about these in Chapter 28, “Experimenting with Robotic Arms.”
You can duplicate human arms in a robot with just a couple of motors, some metal rods,
and a few other parts. Add a gripper to the end of the robot arm and you’ve created a
complete arm- hand module. Of course, not all robot arms are modeled after the human
appendage. Some look more like forklifts than arms, and a few use retractable push rods to
move a hand or gripper toward or away from
the robot.
Robot grippers come in a variety of styles;
few are designed to emulate the human counter-
part. A functional robot claw can be built that
has just two fingers. The fingers close like a vise
and can exert, if desired, a surprising amount of
pressure. See Chapter 29, “Experimenting with
Robotic Grippers,” for more information.

Android and Humanoid
Android and humanoid robots are specifically
modeled after the human form: a head, torso,
two legs, and possibly one or two arms. In cur-
rent usage, the terms android and humanoid
are not the same: an android is a robot designed
to look as much like a human being as possible,
including ears, hair, and even an articulated
mouth. A humanoid robot is one that shares the
basic architecture of a human— bipedal (two
legs), head at the top, two arms at the side— but
is not meant to be a physiological replica.
Figure 2-7 shows an example humanoid
Figure 2-7 Bipedal (two- legged) robots present bipedal robot that you can actually build; Figure
special challenges, not only in construction, but in
programming. Standardized metal brackets, like those 2-8 shows a make- believe android bot that for
used here, make building easier by not requiring you to most hobbyists is beyond the reach of pocket-
have a complete metalworking shop in your garage book and technology. Menacing grin optional.
(though if you do, by all means use it!). (Photo courtesy Whether a true android or a humanoid, this
Lynxmotion.) category of robots is something of the Holy Grail

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