32 Unit One Principles of Robotics
freedom to be completely versatile. Its movements are clumsier than those
of a human hand, which has 22 degrees of freedom.
The number of degrees of freedom defines the robot’s configuration.
For example, many simple applications require movement along three
axes: X, Y, and Z. See Figure 2-10. These tasks require three joints, or three
degrees of freedom. The three degrees of freedom in the robot arm are
the rotational traverse, the radial traverse, and the vertical traverse. The
rotational traverse is movement on a vertical axis. This is the side-to-side
swivel of the robot’s arm on its base. The radial traverse is the extension
and retraction of the arm, creating in-and-out motion relative to the base.
The vertical traverse provides up-and-down motion.
For applications that require more freedom, additional degrees can be
obtained from the wrist, which gives the end effector its flexibility. The
three degrees of freedom in the wrist have aeronautical names: pitch, yaw,
and roll. See Figure 2-11. The pitch, or bend, is the up-and-down move-
ment of the wrist. The yaw is the side-to-side movement, and the roll, or
swivel, involves rotation.
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8 Carpals
14 Phalanges
5 Metacarpals
27 Bones
22 Degrees of freedom
Figure 2-9. The arrangement of bones and joints found in the human hand provides dexterity. Each joint
represents a degree of freedom; there are 22 joints, and thus, 22 degrees of freedom in the human hand.