Chapter 2 Fundamentals of Robotics 41
8. The servo control valves close when there are no more error signals,
shutting off the flow of fluid.
9. The manipulator comes to rest at the desired position.
10. The controller then addresses the next instruction in the program,
which may be to move to another location or operate some peripheral
equipment.
The process is repeated until all steps of the program are completed.
Characteristics of servo robots:
• Relatively expensive to purchase, operate, and maintain.
• Use a sophisticated, closed-loop controller.
• Wide range of capabilities.
• Can transfer objects from one point to another, as well as along a
controlled, continuous path.
• Respond to very sophisticated programming.
• Use a manipulator arm that can be programmed to avoid obstructions
within the work envelope.
Type of Actuator Drive
One common method of classifying robots is the type of drive required
by the actuators.
• Electrical actuators use electric power.
• Pneumatic actuators use pneumatic (air) power.
• Hydraulic actuators, Figure 2-21, use hydraulic (fluid) power.
Controller
Signal comparator
Signal
Resolver
Tachometer
Feedback
signals
Rotary
actuator
Servo valve
Supply
+ +
Servo amp.
Figure 2-20. Feedback signals from sensors allow the system to make corrections whenever the
actual speed or position of the robot does not agree with the values contained in the robot’s program.