36 Unit One Principles of Robotics
Type of Control System
Robots may use one of two control systems—non-servo and servo. The
earliest type of robot was non-servo, which is considered a non-intelligent robot.
The second classification is the servo robot. These robots are classified as either
intelligent or highly intelligent. The primary difference between an intelligent
and highly intelligent robot is the level of awareness of its environment.
Non-Servo Robots
Non-servo robots are the simplest robots and are often referred to as
“limited sequence,” “pick-and-place,” or “fixed-stop robots.” The non-servo
robot is an open-loop system. In an open-loop system, no feedback mecha-
nism is used to compare programmed positions to actual positions.
A good example of an open-loop system is the operating cycle of a washing
machine, Figure 2-16. At the beginning of the operation, the dirty clothes and the
detergent are placed in the machine’s tub. The cycle selector is set for the proper
1. Rotational traverse
4. Yaw (top view) 5. Pitch (side view) 6. Roll (front view)
2. Radial traverse 3. Vertical traverse
Figure 2-15. The six degrees of freedom, demonstrated by a person using a spray gun. Illustrations 1,
2, and 3 are arm movements. Illustrations 4, 5, and 6 are wrist movements.