Chapter 2 Fundamentals of Robotics 39
• Simple to maintain.
• Capable of fairly high speeds of operation.
• Small in size.
• Limited to relatively simple programs.
Servo Robots
The servo robot is a closed-loop system because it allows for feedback.
In a closed-loop system, the feedback signal sent to the servo amplifier
affects the output of the system. A servo amplifier translates signals from
the controller into motor voltage and current signals. Servo amplifiers are
used in motion control systems where precise control of position or velocity
is necessary. In a sense, a servomechanism is a type of control system that
detects and corrects for errors. Figure 2-18 shows a block diagram of a
servo robot system.
The principle of servo control can be compared to many tasks performed
by human beings. One example is cutting a circle from a piece of stock on a
power bandsaw, shown in Figure 2-19. The machine operator’s eye studies
the position of the stock to be cut in relation to the cutting edge of the blade.
The eye transmits a signal to the brain. The brain compares the actual posi-
tion to the desired position. The brain then sends a signal to the arms to
move the stock beneath the cutting edge of the blade. The eyes are used as
a feedback sensing device, while the brain compares desired locations with
Peripheral
equipment
Input/output
Memory
System monitor
Teach pendant
Microprocessor
Robot’s power supply
Servo
controllers
Actuators Robot arm
Robot
hand/gripper
(Feedback)
Manipulator End effector
Servo
amplifiers
Sensors
internal/external
Controller
Figure 2-18. A servo robot system, such as the one depicted in this block diagram, might be classifi ed
as intelligent or highly intelligent, depending on the level of sensory data it can interpret. Components
in the shaded area are part of the control system.